Four convictions motivate this paper.1 First, nuclear power could make a significant contribution to climate change mitigation. To do so, however, nuclear power would have to be deployed extensively, including in the developing world. A “one-tier” world will be required – that is, a world with an agreed set of rules to govern nuclear power that are the same in all countries.
Second, the world is not now safe for a rapid global expansion of nuclear energy. Nuclear-energy use today relies on technologies and a system of national governance of the nuclear fuel cycle that carry substantial risks of nuclear weapons proliferation. There are still more than 20,000 nuclear weapons in the world, and in the current international system, nations see these weapons as instruments of power and sources of prestige. These nations have competing interests and long-standing conflicts. There are also subnational groups that resort to force. The risks that a global expansion of nuclear power will facilitate nuclear proliferation and incidents of nuclear terrorism, or even lead to regional nuclear war, are significant. Nuclear war is a terrible trade for slowing the pace of climate change.
Third, a world considerably safer for nuclear power could emerge as a co-benefit of the nuclear disarmament process. The national-security community is currently engaged, to an unprecedented degree, in seeking progress toward nuclear disarmament. A by-product of this process could be different technology choices and innovations in the governance of nuclear power – notably, a halt to spent-fuel reprocessing to separate plutonium as well as multinational ownership and control of uranium enrichment facilities. These developments could begin to decouple nuclear power from nuclear weapons.
Finally, the next decade is critical. While several approaches to climate change mitigation are available for immediate, rapid scale-up, nuclear power could be so in maybe 10 years, provided the coming decade is used to establish adequate technologies and new norms of governance. Nuclear power ought to be deployed seriously as a mitigation strategy only when and if it can provide a sustainable contribution. The world will not benefit if nuclear power’s contribution is withdrawn a decade or two after global scale-up begins, as a result of flaws related to its coupling to nuclear weapons.
There are 3,000 billion tons of carbon dioxide (CO2) in the atmosphere today, about 800 billion tons more than there were 200 years ago. For centuries further back, the amount of CO2 in the atmosphere was about constant: the forests and oceans and atmosphere were in approximate equilibrium. Disequilibrium is increasing with every passing year, as human beings bring carbon from deep underground to the surface (in fossil fuel) and burn it.
The climate science and policy communities have positioned warning lights between 3,500 and 4,000 billion tons of CO2, levels that would be reached in 30 and 60 years, respectively, at today’s rate of growth. For such CO2 levels, although the most favorable outcomes could be benign, the worst outcomes could be catastrophic for human civilization, which has built many of its cities on coasts and has matched its choices of crops to relatively predictable snowmelt, rainfall, and temperature patterns. We are confronted with a risk-management problem of unprecedented complexity.
Everything about climate change is global. The global atmosphere is well stirred and scarcely registers where CO2 is emitted. Demand for electricity and fuels is driven by middle-class consumption, which takes similar forms in countries with a wide range of per capita CO2 emissions.2 Electricity serving air conditioner compressors, computer circuits, incandescent lights, and appliances arrives along wires that, worldwide, run from power plants of only a few kinds. To be sure, nations differ in their endowments of resources; but, even so, a good strategy for mitigating climate change in one country will be a good strategy in many other countries.
A “wedge model,” published in 2004, quantifies the task of global climate change mitigation.3 We human beings today emit 30 billion tons of CO2 per year by burning fossil fuels. We would emit 60 billion tons per year in 2050 if we were oblivious to climate change (the so-called business-as-usual world), and we can congratulate ourselves if we cut the anticipated 2050 emissions rate in half, emitting CO2 at the same rate in 2050 as today. A stabilization wedge is a campaign or strategy motivated by climate change (that is, not happening for other reasons) that results in 4 billion tons of CO2 per year not emitted in 2050.
Available options for wedges include energy efficiency wedges, wind wedges, nuclear wedges, and wedges from CO2 capture and storage (CCS)– capturing the CO2 produced at coal plants and burying it deep below ground. About eight wedges are needed to pat ourselves on the back, and we can choose a portfolio of them in many ways. A portfolio of wedges is needed because solving climate change with only one or two kinds of wedges is close to impossible. Moreover, there are enough options for the portfolio that none is indispensable. Thus, climate change mitigation can succeed without nuclear power, or any other single option, at some increased overall cost for mitigation.4
A nuclear wedge is equivalent to 700 large base load nuclear power plants on the scene in 2050 and 700 equally large base load coal plants not built.5 The world has the equivalent of about 350 large nuclear plants today, so phasing out nuclear power in favor of coal power is minus half a wedge.
Arguments for giving priority to climate change mitigation are uncomfortable bedfellows with arguments for nuclear power. The dissonance arises among a political constituency, particularly powerful in Europe, for which mitigating climate change is seen as an opportunity for pursuing deep changes in social and economic structures and in values – away from consumerism and centralized authority. To meet this aspiration, climate policy often promotes wind power, solar thermal and solar photoelectric power, and other forms of renewables, relative to nuclear energy. This perspective also underpins the climate-policy focus on energy efficiency as a way to reduce global energy demand.
On the other hand, putting a price on CO2 emissions as a way to mitigate climate change helps nuclear power. Roughly, an emissions price of $20 per ton of CO2 gives nuclear power a 2¢/ kWh boost relative to power from coal and a 1¢/kWh boost relative to power from natural gas – in both cases assuming that these fossil fuel plants vent rather than capture and store CO2.6 Moreover, serious CO2 management may be accompanied by support for accelerated electrification of the economy to reduce dispersed emissions from transportation and space heating, which would increase overall demand for electric power.
In this paper we consider a nuclear future where 1,500 GW of base load nuclear power is deployed in 2050. A nuclear fleet of this size would contribute about one wedge, if the power plant that would have been built instead of the nuclear plant has the average CO2 emissions per kilowatt hour of all operating plants, which might be half of the value for a coal plant.7 Base load power of 1,500 GW would contribute one fourth of total electric power in a business-as-usual world that produced 50,000 terawatt-hours (TWh) of electricity per year, two-and-a-half times the global power consumption today.8 However, in a world focused on climate change mitigation, one would expect massive global investments in energy efficiency – more efficient motors, compressors, lighting, and circuit boards – that by 2050 could cut total electricity demand in half, relative to business as usual. In such a world, 1,500 GW of nuclear power would provide half of the power.
We can get a feel for the geopolitical dimension of climate change mitigation from the widely cited scenarios by the International Energy Agency (IEA) presented annually in its World Energy Outlook (WEO),9 even though these now go only to 2030. The WEO 2008 estimates energy, electricity, and CO2 emissions by region. Its 2030 world emits 40.5 billion tons of CO2, 45 percent from electric power plants. The countries of the Organisation for Economic Co-operation and Development (OECD) emit less than one third of total global fossil fuel emissions and less than one third of global emissions from electric power production. By extrapolation, at midcentury the OECD could contribute only one quarter of the world’s greenhouse gas emissions.
It is hard for Western analysts to grasp the importance of these numbers. The focus of climate change mitigation today is on leadership from the OECD countries, which are wealthier and more risk averse. But within a decade, the targets under discussion today can be within reach only if mitigation is in full gear in those parts of the developing world that share production and consumption patterns with the industrialized world.
The map (see Figure 1) shows a hypothetical global distribution of nuclear power in the year 2050 based on a high-nuclear scenario proposed in a widely cited MIT report published in 2003.10 Three-fifths of the nuclear capacity in 2050 as stated in the MIT report is located in the OECD, and more nuclear power is deployed in the United States in 2050 than in the whole world today. The worldview underlying these results is pessimistic about electricity growth rates for key developing countries, relative to many other sources. Notably, per capita electricity consumption in almost every developing country remains below 4,000 kWh per year in 2050, which is one-fifth of the assumed U.S. value for the same year. Such a ratio would startle many analysts today – certainly many in China.
The Geography of a Hypothetical Nuclear Expansion to 1,500 GWe
In this scenario, 58 countries would be using nuclear energy, but only about 40 percent of the capacity would be in non-OECD countries. Source: Based on information from The Future of Nuclear Power (MIT, 2003).
It is well within limits of credulity that nuclear power in 2050 could be nearly absent from the United States and the European Union and at the same time widely deployed in several of the countries rapidly industrializing today. Such a bifurcation could emerge, for example, if public opposition to nuclear power in the United States and Europe remains powerful enough to prevent nuclear expansion, while elsewhere, perhaps where modernization and geopolitical considerations trump other concerns, nuclear power proceeds vigorously. It may be that the United States and other countries of the OECD will have substantial leverage over the development of nuclear power for only a decade or so.
Change will not happen overnight. Since 2006, almost 50 countries that today have no nuclear power plants have approached the International Atomic Energy Agency (IAEA) for assistance, and many of them have announced plans to build one or more reactors by 2020. Most of these countries, however, are not currently in a good position to do so. Many face important technical and economic constraints, such as grid capacity, electricity demand, or GDP. Many have too few trained nuclear scientists and engineers, or lack an adequate regulatory framework and related legislation, or have not yet had a public debate about the rationale for the project. Overall, the iaea has estimated that “for a State with little developed technical base the implementation of the first [nuclear power plant] would, on average, take about 15 years.”11 This lead time constrains rapid expansion of nuclear energy today.
A wedge of nuclear power is, necessarily, nuclear power deployed widely – including in regions that are politically unstable today. If nuclear power is sufficiently unattractive in such a deployment scenario, nuclear power is not on the list of solutions to climate change.
Nuclear power is not just another wedge. Briefly, here are some of the many distinctive attributes of nuclear power:
- Time-tested. Relative to competing wedges like renewable energy and CCS, nuclear power has been in place longer. Commercial nuclear power has been deployed for about 50 years and today is found in 30 countries. Deployment is highly concentrated, however; 10 countries operate more than 80 percent of all power reactors.
- Small physical flows. The thermal energy required to produce 1,000 MW of power for a year is released from the fission of only 1 ton of uranium in fuel produced from 200 tons of uranium, but from the burning of 3 million tons of coal. The flip side of compactness, of course, is that danger comes in very small packages: it takes only a few kilograms of fissile material to make a nuclear weapon.
- Minimal CO2 emissions. About 90 percent of the CO2 is expected to be excluded from the atmosphere if coal power and gas power are combined with CO2 capture and storage. (The economic optimum percent, to be sure, depends on the CO2 emissions price.) In that case, the CO2 emissions from CCS power, nuclear power, and most forms of renewable energy are likely to be comparably small – all emitting less than 100 grams of CO2/kWh, one-tenth of the value for today’s coal plants.
- Large, centralized plants with fixed output. To be economic, nuclear plants are large and connected to extensive electricity grids that distribute power over long distances. The power output of nuclear power plants is not easily ramped up and down, rendering it an inflexible component of an electric power system. The inflexibility of base load nuclear power and the intermittency of wind and solar energy share the feature that neither of these low-CO2 emitters can meet a time-varying demand for electric power without assistance from complementary systems: load-following and peaking plants and storage.
- Safety makes all plants mutual hostages. The Three Mile Island and Chernobyl accidents of 1979 and 1986, respectively, taught the world that a nuclear power accident anywhere in the world affects the prospects for nuclear power everywhere. Nuclear energy is more “brittle” than other strategies to mitigate climate change, as one major future accident could overnight nullify the resources and time invested in nuclear power made up to that point.
- Nuclear power plants are potential military targets. It is all too likely that a commercial nuclear power plant in a country at war would be attacked, with horrendous consequences. No taboo on such attacks exists today.12
- Storage of spent fuel remains a problem. At the advent of nuclear power, its advocates promised that no future generation would need to attend to our wastes. That goal of early final disposal has proven to be overly ambitious. Today, the second best approach to the waste problem is interim dry-cask storage of nuclear spent fuel, now widely deployed, which provides a century-scale solution while the search for solutions that isolate nuclear wastes for millennia continues.
- Coupling to nuclear weapons. With a nuclear power plant comes a fuel cycle, with a front-end that can require uranium isotope enrichment and a back-end that can entail the separation of plutonium and its insertion into commerce. Both the front- and back-end present significant and enduring challenges.
For the rest of this paper, we focus only on the last of these aspects of nuclear power. In our view, the fact that nuclear power is coupled to nuclear weapons is the most disabling attribute of global nuclear power at the present time.
Separated plutonium and highly enriched uranium are the key ingredients for making nuclear weapons. It is widely accepted that the production or acquisition of these fissile materials is the most difficult, visible, and time-consuming step in the proliferation process. Reprocessing and enrichment under national control essentially removes this obstacle and offers – intended or not – important latent proliferation capabilities.
Regarding reprocessing and plutonium recycle, the world is now divided. Six countries reprocess their commercial spent fuel today. France, India, Japan, and Russia are deeply committed to reprocessing; China operates a pilot reprocessing plant and is contemplating commercial reprocessing today; and the United Kingdom is on the verge of abandoning reprocessing. The United States does not reprocess civilian spent fuel nor does it introduce plutonium into its power plants, policies established under Presidents Ford and Carter.
The principal arguments against plutonium recycling are that separation, stockpiling, transport, and use of plutonium create risks of diversion to military purposes and risks of theft, the latter being of particular concern in the context of efforts to prevent nuclear terrorism. Compared to other types of nuclear facilities, reprocessing plants are extremely difficult and costly to safeguard.
The bar graph (see Figure 2) shows the quantities of separated plutonium in the world today. Civilian-separated plutonium and military-separated plutonium are both roughly equal at about 250 tons.13 Military plutonium is in two categories: material in the weapons complex and material declared “excess” as a result of reductions from previous warhead levels. The bar graph also shows the substantial further reductions in military plutonium associated with nuclear weapons if the world’s weapons stockpile is reduced first to 15,000 and then 4,000 warheads.14 In this process, additional military stocks would become excess and would need to be disposed of. Over time, unless reprocessing of civilian spent fuel swiftly draws to a close, the world can expect to become increasingly preoccupied with latent proliferation and “breakout” 15 associated with civilian-separated plutonium – even if nuclear power does not expand significantly. A global nuclear power expansion with reprocessing makes matters much worse.
Military- and Civilian-Separated Plutonium Today, and Military Plutonium in Weapons in a Disarming World
We assume an average of 4 kg of plutonium per warhead and a working stock of 20 percent. Civilian stockpiles are based on the latest declarations for the beginning of 2008. The current military stockpile carries an error bar of plus or minus 25 tons, largely because of the uncertainties in the estimate of Russia’s inventory. Source: Based on information from International Panel on Fissile Materials, Global Fissile Material Report 2009 (Princeton, N.J.:I PFM, forthcoming).
So far, no country that decided to pursue commercial reprocessing has managed to balance the rates of separation and use of plutonium, which has led to a continuous increase of civilian plutonium inventories over the past decades – hypothetically enough for more than 30,000 weapons.16 The flow of plutonium could be enormous in a world with much more nuclear energy. The 2003 MIT report works out the plutonium flows for a scenario with 1,500 GW of nuclear power where 40 percent of total capacity is from breeder reactors.17 About 1,000 tons of plutonium would be separated from the spent fuel each year to fabricate new fuel for these reactors. The IAEA cannot reduce the overall uncertainty of measurements for the annual material balance in reprocessing plants much below 1 percent.18 Assuming that 20 large-scale reprocessing plants existed in this world, the uncertainty would be equivalent to 500 kg of plutonium every year for every plant – enough for 60 bombs per year from each of these plants. Within these margins, the IAEA would be unable to confirm with high confidence that all material is accounted for. It is hard to see how these flows and levels of uncertainty could ever be acceptable, in particular with fuel cycles under national control.
Many discussions of a potential global nuclear expansion posit that uranium resources will run short unless the world moves to the “closed” fuel cycle. In the case of the once-through fuel cycle, as noted above, about 200 tons of uranium are mined and purified for every ton of material fissioned each year in a 1GW reactor. This “inefficiency” has plagued nuclear engineers and reactor designers from the very beginning of the nuclear era. Already in 1944, a group of eminent scientists of the U.S. Manhattan Project devised the concept of the breeder reactor, which would produce more fuel than it consumes, because they were concerned that uranium might be too scarce to build even a small number of bombs.19 And since the 1950s, several countries have launched plutonium breeder reactor programs, motivated in part by concern that deposits of high-grade natural uranium ore might become scarce as nuclear power expanded.20
The argument for reprocessing based on the scarcity of uranium, however, is a weak one. Plutonium fuels will remain non-competitive compared to uranium fuels until the price of uranium increases to more than $500/kg of uranium, about four times its price today.21 The estimated global reserve is sufficient to fuel thousands of reactors. Even with a major expansion of nuclear power, availability and price of uranium will not significantly affect the viability or competitiveness of the once-through fuel cycle through 2050 and probably even beyond.
Unlike reprocessing, uranium enrichment is an essential part of the nuclear fuel cycle today.22 As with reprocessing, however, even a relatively small enrichment plant is sufficiently large to support a significant military program. A standard 1 GW reactor requires about 20 tons per year of low-enriched uranium (LEU), which in turn requires 200 tons of natural uranium input to an enrichment plant. The same enrichment plant (the size that Brazil and Iran are currently building) with the same natural uranium input can be used to produce about 600 kg per year of weapons-grade highly enriched uranium (HEU), enough for 25 to 50 weapons per year.
Centrifuge enrichment plants now dominate the modern nuclear fuel cycle, even though it was always understood that the technology is highly proliferation prone.23 They can be converted quickly from production of LEU to production of HEU.24 And they can be built clandestinely, a primary concern with Iran’s program today.
Even if we assume that the accumulation of separated plutonium can be stopped in a world with a greater role for nuclear power, we are left with the problem of the spread of other sensitive nuclear-fuel-cycle technology (notably, centrifuge enrichment) to non-weapons states. Multinational ownership and control of sensitive fuel-cycle facilities would therefore seem to be a necessary element of a world where nuclear power is deployed widely but risks of nuclear war and nuclear terrorism are smaller than today.
Can nuclear power be decoupled from nuclear weapons? From the very beginning of the nuclear age, it was understood that allowing nuclear facilities to operate under national control, even under international monitoring, carried serious risks. Nonetheless, civilian nuclear energy use and related proliferation risks received little attention for the first 25 years, while the nuclear arms race of the two superpowers was unfolding and the weapons programs in other countries were largely unconstrained.
The debate over alternative, multilateral approaches to the nuclear fuel cycle first engaged the world in the mid-1970s, and is now with us again.25 The nuclear industry, however, has traditionally been reluctant to acknowledge the connection between civilian and military use of nuclear energy. The Director General of the World Nuclear Association, an industry lobby group, recently said, “[T]he global non-proliferation and safeguards system effectively curtails any link between civil and military programs.”26 He added, “[W]hatever proliferation risk we face would be unaffected even by a 20-fold increase in the global use of safeguarded nuclear reactors.”
What degree of decoupling of nuclear power from nuclear weapons could be accomplished with multilateral approaches? To answer this question, one must consider the points of view of both providers and recipients of nuclear technology.27
Nuclear-supplier states and today’s nuclear-weapons states emphasize the objectives of preventing the further spread of sensitive nuclear technologies and of ensuring that they are used only for peaceful purposes where they remain. Many states, however – in particular, recipient and non-weapons states – have different priorities. For them to support and participate in multilateral approaches and to forgo research and development of certain elements of the fuel cycle, they require specific incentives. Increased energy security through fuel assurances is often not one of them, because most states are already satisfied with the current market structure characterized by several independent and reliable fuel suppliers. The interests of many recipient states lie elsewhere.
Among many non-weapons states, there is broad dissatisfaction with the status and prospects of the Non-Proliferation Treaty (NPT). Their priority is limiting any differential nuclear weapons capability in their region, but they are also unhappy about the implementation of Articles IV and VI, which define rights and obligations with respect to peaceful use and disarmament.28 The current system of supplier states, which is based in the nuclear-weapons states and a few closely allied countries, is seen as a major expression of a distorted implementation of Article IV.
Some proposals for multilateral approaches to the nuclear fuel cycle tend to increase this tension further by creating a two-tier world of “suppliers” and “users.” But other approaches recognize this dilemma. They envision a more active role for non-weapons states in the supplier market, for example, featuring participation in multinational enrichment plants.
Fuel-cycle facilities under multinational ownership and control are not a silver bullet, but they offer several important advantages vis-à-vis plants under national control. At a minimum, multinational plants can serve as a confidence-building measure through regional cooperation and make breakout politically more costly. Moreover, if sensitive technologies are used on a “black-box” basis, as they often are today in the case of centrifuge enrichment plants even in weapons states, participants would not unnecessarily acquire latent proliferation capabilities. Over time, multinational ownership and control could therefore alleviate concerns about parallel clandestine programs.
In support of sustainable one-tier arrangements, multinational ownership of fuel-cycle facilities in the nuclear weapons states and supplier states will be a necessary complement to similar arrangements in non-weapons states and recipient states. Eventually, conversion of all existing national enrichment plants to multinational ownership and control will be required. Enrichment providers will not easily cede control of their existing facilities and place them in a new, and initially uncertain, institutional framework. However, if nuclear disarmament proceeds and deeper cuts in nuclear arsenals are agreed upon, the weapons states – all of which have built or are building large-scale uranium enrichment plants – would themselves have strong incentives to embrace multinational controls as a way to constrain national breakout capabilities and reduce the risk of clandestine enrichment plants.
Nuclear power will confront two major tests in the coming decade. First, issues related to coupling to weapons must be resolved. Second, the cost of nuclear electricity must be demonstrated to be competitive. How should this next decade be used? We identify four priorities.
First, to address the coupling to weapons, the once-through fuel cycle must become the norm. The trend of accumulating stockpiles of civilian plutonium must be stopped and reversed. Current reprocessing must be phased out so that there are no additions to the massive overhangs of separated plutonium now in place in countries that have been reprocessing, and work toward the safe disposal of existing separated plutonium stocks must begin. Moreover, all enrichment plants must be brought under effective multinational ownership and control.
Second, to improve the competitiveness of nuclear power relative to other sources of energy supply, reductions in construction and operating costs will be required. Broadly based sharing of information about the construction of new nuclear power plants is in the interest of the industry; such sharing should result in a firm understanding of the costs when best practices are pursued.29 Similarly, plant operation procedures for both new and existing plants (including operator training) could be coordinated internationally beyond the levels today.
Not much new capacity is likely to be added to the grid in this decade,30 but the bottlenecks that today thwart expansion must be addressed. These include production of pressure vessels and other distinctive high-technology components, trained people, and regulatory and legal frameworks. To promote innovation and reduce concerns about the safety of older plants worldwide, incentives that today strongly favor plant-life extension should be revised in favor of retirement and new construction.
Third, during the coming decade, the social contract between the nuclear industry and the public regarding burdening future generations with the management of nuclear waste must be renegotiated, so that interim storage of nuclear waste can become the option of choice for at least several decades. Drycask storage can be widely implemented. Development and exploration of potential sites for long-term geologic disposal of nuclear wastes can continue, but with reduced pressure to authorize long-term repositories.31
Finally, research and development undertaken in the next one or two decades must support the transition to a nuclear fuel cycle compatible with nuclear energy on a larger scale and in more countries.32 Some of this activity must explore advanced safeguards techniques and further expand the idea of safeguards-by-design, which recognizes that plant design can “facilitate or frustrate” IAEA safeguards efforts.33
We end with four questions that we believe deserve much more discussion, and we provide tentative answers.
Will nuclear energy fare better in a world where climate change is a priority? Not necessarily. Climate change policy could handicap fossil fuels but forcefully promote renewable energy and efficiency. Nuclear power’s short-term fate depends more on other factors, notably capital and operating costs, safety record, coupling to nuclear militarization, and the overall sense of competence and responsibility that the industry projects.
Can we have much more nuclear energy without nuclear disarmament? Only with great difficulty. A multilateral nuclear disarmament process might be the most effective way – perhaps the only way – for states to move away from enrichment and reprocessing plants under national control. Proposals for multilateral approaches to the nuclear fuel cycle need to take the nuclear disarmament process, rather than traditional nuclear nonproliferation efforts, as their main frame of reference.
Can we have nuclear energy in a nuclear-weapons-free world? A nuclear-weapons-free world would be more stable and more secure without nuclear energy. But a new framework for the nuclear fuel cycle could make nuclear energy compatible with a nuclear-weapons-free world.
Will the nuclear power cure for climate change be worse than the disease? Every “solution” to climate change can be done badly or well. Done badly, it can be worse than the disease. Making climate change the world’s exclusive priority is therefore dangerous. It results in an overemphasis on speed of transformation of the current energy system and a dismissal of the very large risks of going too fast. Looming over energy efficiency is the shadow of excessive regimentation; over renewables, land-use conflicts (with food, biodiversity, and wilderness values); over carbon dioxide capture and storage, the environmental abuses that continue to characterize the fossil fuel industries; and over geoengineering, granting excessive authority to a technocracy. Looming over nuclear power is nuclear war.
The upper limits of climate change are terrifying, amounting to a loss of control of the climate system as positive feedbacks of various kinds set in. Nonetheless, at this moment, and conceding that such calculations can only embody the most subjective of considerations, we judge the hazard of aggressively pursuing a global expansion of nuclear power today to be worse than the hazard of slowing the attack on climate change by whatever increment such caution entails.
If over the next decade the world demonstrates that it can do nuclear power well, a global expansion of nuclear power would have to be – indeed, should be – seriously reexamined.
1 The authors have benefited from numerous suggestions from Zia Mian. We are also indebted to Jan Beyea, Harold Feiveson, Steven Fetter, José Goldemberg, Robert Goldston, Robert Keohane, Scott Sagan, Sharon Squassoni, and Frank von Hippel for close readings of an earlier draft.
2 Shoibal Chakravarty, Ananth Chikkatur, Heleen de Coninck, Stephen Pacala, Robert Socolow, and Massimo Tavoni, “Sharing Global CO2 Emission Reductions among One Billion High Emitters,” Proceedings of the National Academy of Sciences 106 (29) (2009): 11884–11888; www.pnas.org/content/106/29/11884.
3 Stephen Pacala and Robert Socolow, “Stabilization Wedges: Solving the Climate Problem for the Next 50 Years with Current Technologies,” Science 305 (2004): 968–972. Here, we slightly redefine a wedge to refer to 4 billion tons of CO2 per year not emitted in 2050, versus 1 billion tons of carbon not emitted in 50 years in the 2004 paper.
4 For the purposes of this paper it is a detail that the center of gravity of discussions since wedges were introduced in 2004 has moved toward tougher targets. The “two-degrees” target widely discussed today – an average surface temperature rise limited to 2°C greater than its pre-industrial value – requires that global CO2 emissions fall to half of today’s value by 2050. For such a tough target, less than 10 percent of the job is done by one wedge.
5 We define a large plant to be one with a capacity of 1,000 MW, that is, 1 GWe, and base load to mean operating 8,000 hours per year. Our reference base load coal plant, somewhat more efficient than the coal plant one can build today, emits 800 grams of CO2 for every kilowatt-hour of electricity, or 6.4 million tons of CO2 per year. The nuclear plant displacing the coal plant has life cycle emissions of about 50 grams of CO2/kWh; its carbon intensity is 16 times less than a coal plant. Rounding off, 700 nuclear plants emit 4 billion tons less a year than 700 coal plants.
7 Think of a nuclear plant displacing a coal plant half the time and a carbon-free renewable power plant the other half of the time, or, equivalently, a nuclear plant displacing a natural gas plant. Confirming this view, in 2006 the carbon intensity of average power was 56 percent of the carbon intensity of coal power; International Energy Agency, World Energy Outlook 2008 (Paris: OECD/IEA, 2008), www.worldenergyoutlook.org.
10 The Future of Nuclear Power (MIT, 2003), web.mit.edu/nuclearpower. In MIT’s high-nuclear scenario, 14,100 TWh of nuclear power are produced in 2050, which corresponds to 1,760 GW of base load power running 8,000 hours per year. The MIT report calculates 1,609 GW of “equivalent capacity” by assuming constant output throughout the 8,760 hours of the year. The map rescales the mit totals to 1,500 GW of base load power to match the deployment scale chosen here.
12 Several nuclear reactors were attacked and destroyed while under construction (that is, without risking radiological contamination): Iraq attacked Iran’s Busher reactors during the Iraq-Iran War; Israel destroyed Iraq’s Osirak research reactor in 1981 and perhaps another reactor in Syria in August 2007. Attacks on operational reactors were also considered. In 1991, Iraq fired a Scud missile with a cement warhead at Israel, apparently in an attempt to damage the Dimona reactor. The United States considered destruction of North Korea’s Yongbyon reactor in the early 1990s to prevent plutonium recovery from the irradiated fuel in the core. India and Pakistan are a notable exception: they have signed an agreement not to attack each other’s nuclear installations in the case of war.
13 Separated means unaccompanied by large amounts of radioactivity, and therefore relatively easily accessed. Today, more than 1,500 tons of civilian plutonium have not been separated and are still in spent fuel.
14 Under the planned START Follow-on Treaty, the United States and Russia have agreed to reduce their strategic nuclear warheads to 1,500–1,675 by 2016. According to estimates by the Federation of American Scientists, however, each country is expected to retain a total of about 7,000 warheads since they will continue to have non-strategic warheads, weapons in reserve, and weapons awaiting dismantlement. The global stockpile of nuclear weapons could therefore be on the order of 15,000 warheads. In a subsequent reduction, the United States and Russia might reduce to 1,000–1,500 total warheads on each side, which could correspond to 4,000 nuclear weapons worldwide.
15 Breakout describes a scenario in which a host state begins production of fissile materials for weapons purposes (without concealing this effort) at a facility that was previously used for peaceful purposes.
16 International Panel on Fissile Materials, Global Fissile Material Report 2008 (Princeton, N.J.: IPFM, October 2008), Appendix 1A; www.ipfmlibrary.org/gfmr08.pdf. Germany is the only country that managed to stabilize and gradually draw down its plutonium stockpile after having stopped shipping spent fuel for reprocessing (in France and the United Kingdom) in 2005.
17 This is a balanced thermal and fast reactor system in which the plutonium generated in the spent fuel from the fleet of light water reactors is used to fuel a fleet of fast reactors operated in a burner mode. The Future of Nuclear Power, Appendix Chapter 4, 124–126.
18 Shirley Johnson, The Safeguards at Reprocessing Plants under a Fissile Material (Cutoff) Treaty, IPFM Research Report 6 (IPFM, February 2009), www.ipfmlibrary.org/rr06.pdf.
20 Thomas B. Cochran, Harold A. Feiveson, Frank von Hippel, Walt Patterson, Gennadi Pshakin, M. V. Ramana, Mycle Schneider, and Tatsujiro Suzuki, Fast Breeder Programs: History and Status, IPFM Research Report 8 (IPFM, forthcoming).
21 For this estimate, we assume typical transaction costs for the various steps of the fuel fabrication process, in particular $1,000/kg and $1,500/kg for reprocessing and MOX fuel fabrication. For the methodology, see The Future of Nuclear Power, Appendix Chapter 5.D. Our value for reprocessing is conservative. For example, the levelized cost of reprocessing at Japan’s new reprocessing plant is about $3,750/kg. In general, fuel costs of nuclear energy are small compared to capital costs. Costs of standard LEU fuel add up to about 0.9¢/kWh, which is on the order of 10 to 20 percent of the levelized cost of electricity from nuclear energy.
22 The most common reactor type requires LEU (3 to 5 percent uranium-235, as compared to 0.7 percent of this isotope in naturally occurring uranium). LEU is not usable for weapons, but the same enrichment facility can in principle produce weapons-grade HEU(for instance, 90 percent uranium-235). In principle, nuclear energy can be deployed and used without relying on enrichment or reprocessing. For example, Canada’s original CANDU reactor design, which is natural-uranium fueled and heavy-water moderated and cooled, requires about 25 percent less uranium than a typical light water reactor.
23 More than 25 years ago, Allan S. Krass and coauthors recommended a shift toward proliferation- resistant enrichment technology, with plants operated under the authority of an International Nuclear Fuel Agency (INFA). With regard to centrifuge technology, they concluded: “Unfortunately . . . a number of operating facilities already exist. Preferably, these facilities should be shut down and dismantled”; Allan Krass, Peter Boskma, Boelie Elzen, and Wim A. Smit, Uranium Enrichment and Nuclear Weapon Proliferation (London and New York: Taylor & Francis/Stockholm International Peace Research Institute, 1983); free electronic access at books.sipri.org. Besides centrifuge enrichment technology, there is now also renewed interest in laser isotope separation (LIS), a technology that has been explored off and on since the 1970s as a “next-generation” process for uranium enrichment. In July 2009, Global Laser Enrichment, a joint venture, submitted a license application for a large laser-enrichment plant in the United States; if it decides to move forward, it wishes to begin commercial operation in 2012. Little is known about the details of the LIS process, and no dedicated IAEA safeguards approach now exists. It is likely that the technology will raise proliferation concerns similar to those of centrifuges.
25 The current debate gained momentum in October 2003 when The Economist published an article by IAEA Director General Mohamed ElBaradei, in which he acknowledged the shortcomings of the current nonproliferation regime; “Towards a Safer World,” The Economist, October 16, 2003.
26 John Ritch, The Necessity of Nuclear Power: A Global Human and Environmental Imperative, World Nuclear University, “Key Issues in Today’s World Nuclear Industry,” Balseiro Institute, San Carlos de Bariloche, Argentina, March 10, 2008, www.world-nuclear.org.
27 For detailed discussion, see: Multilateral Approaches to the Nuclear Fuel Cycle: Expert Group Report Submitted to the Director General of the International Atomic Energy Agency, INFCIRC/ 640 (Vienna, Austria: International Atomic Energy Agency, February 22, 2005); Alexander Glaser, Internationalization of the Nuclear Fuel Cycle, International Commission on Nuclear Non-proliferation and Disarmament, ICNND Research Paper No. 9, February 2009; and Y. Yudin, Multilateralization of the Nuclear Fuel Cycle: Assessing the Existing Proposals (New York and Geneva: United Nations Institute for Disarmament Research, 2009).
28 From this perspective, Article IV is particularly unbalanced. Besides guaranteeing the “inalienable right . . . to develop research, production and use of nuclear energy for peaceful purposes without discrimination,” Article Ⅳ also specifies that states with advanced nuclear technologies should cooperate in contributing to “the further development of the applications of nuclear energy for peaceful purposes, especially in the territories of nonnuclear-weapon States Party to the Treaty.”
30 A new study by the U.S. National Academy of Sciences estimates that “as many as five to nine new nuclear plants could be built in the United States by 2020.” The National Academy of Sciences and the National Academy of Engineering, America’s Energy Future: Technology and Transformation, Summary Edition (Washington, D.C.: The National Academies Press, 2009), 112; http://www.nap.edu/catalog.php?record_id=12710.
32 For example, increasing the burn-up of standard LEU fuel could improve overall economics of the once-through fuel cycle and also reduce uranium requirements to some degree. Using thorium fuel in new light water reactor types as a partial substitute for standard LEU fuel could be another productive field of mid-term research. If implemented sensibly, thorium use would also reduce the total amount of plutonium embedded in spent fuel from light water reactors and perhaps reduce some proliferation concerns of the once-through fuel cycle.


The Crystallisation Crucible is a crafting machine added by GregTech 6. It creates Silicon and Redstone Alloy Boules from molten Silicon or Redstone Alloy, Silicon or Redstone Alloy Dust, and a noble gas. It is required for creating circuits.
The Crystallisation Crucible is powered by heat or HU provided by a burning box or electric heater.
Recipe[edit | edit source]
Usage[edit | edit source]
The Crystallization Crucible crafts a single Boule from four units of Silicon or Redstone Alloy, plus 1000L of a noble gas (one of Helium, Neon, Argon, Krypton, Xenon, or Radon, obtained by centrifuging compressed air cells). The four units of material are provided as one tiny dust plus the remainder (560L) as molten material. The Crucible may also craft nine Boules in one extended operation, if provided with one normal dust, 35 units (5040L) of molten material, and 9000L of noble gas.


BRUSSELS, Belgium_The European Commission urged EU nations Tuesday to force airlines to cut carbon dioxide emissions to help bring down greenhouse gases in line with the 1997 Kyoto treaty.
EU Environment Commissioner Stavros Dimas said EU nations may miss the 2012 emission targets unless further measures are taken to bring down greenhouse gases.
"I therefore urge them to do this swiftly," he told a news conference.
Dimas said emissions from the EU's 15 most industrialized nations - including Germany, Britain, France, Italy, Spain and the Netherlands - in 2005 were 2 percent below those of 1990.
He estimated this will rise to 7.4 percent below by 2010, just shy of the Kyoto treaty's ultimate target of an 8 percent cut by 2012.
To make that happen, Dimas has proposed forcing airlines to contribute to the lowering of greenhouse gas emissions. Currently exempted, the airline industry opposes his suggestion, now being debated by EU governments.
EU officials say the 15 most industrialized EU nations can cut greenhouse gases by 11.4 percent by 2012 if the airlines participate in meeting Kyoto targets, and if tax breaks and incentives such as traffic congestion charges for cars are implemented.
At a Dec. 3-14 climate conference in Bali, the EU will push for a 'roadmap' for a new UN climate change agreement to succeed the Kyoto treaty that expires in 2012.
EU officials said the ambition must be to halve global greenhouse gases emissions by 2050 from the 1990 level.
In a series of reports leading up to the Bali conference, a U.N. panel of scientists has called global warming "unequivocal," forcing sea levels up and threatening water and food supplies.
On Tuesday, EU officials welcomed the plan of Australia's incoming government to ratify the Kyoto agreement after a decade on the sidelines with the United States.
EU officials, speaking privately, said they see a growing awareness in the United States and China to be more active in reigning in global warming.
Last March, EU leaders pledged the EU would cut its greenhouse gas emissions by 30 percent below 1990 levels by 2020 if other developed countries do likewise. If not, the EU will cut its emissions by at least 20 percent by 2020.
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Guest post by Francois Galgani, IFREMER
Because of its energy independence, its long-duration persistence and its cost-effective operation, the Wave Glider platform is able to collect and transmit data over distances of thousands of miles across wide geographic areas and specific areas of interest and operation. Many applications have been described but to date, the use of video has not been tested for regular and long distance surveys. A first application of video camera to monitor surface/subsurface marine litter at sea was tested in 2013 (Galgani et al., 2013), using a a HD GoPro HERO2 Long-Play camera in resistant tube fixed on ballast, sea surface oriented to enable observation in the 0-4.5 meters subsurface layer. A speed never above 1.5 knots and the immersion of the camera provided consistent and stable images along straights routes.
During an additional experiment performed recently by IFREMER and Lamma using a Wave Glider (SV3 066, Lamma/IFREMER), the video system was replaced by a camera in order to facilitate the management and storage of data (images) and to support the future development of a data screening system using an image analysis software.
The robustness of the system was tested in July 2018 during a 4.5 day survey, and retested in 2019 in a large pelagic protected area (Pelagos Sanctuary, North Western Mediterranean Sea; analysis of 2019 data in progress).
In order to save space and autonomy, the prototype camera was supplied on board through a solar panel, allowing continuous use. The choice was made to shoot in “Photo” mode using a GoPro HERO3, with an acquisition every 7 seconds to limit the number of images, enabling full coverage of the track without overlapping images. The camera (256 GB memory card) was mounted on the sub ballast, oriented at 45° for a surface coverage of 12.4 meters in width.
Good quality images were obtained enabling observations of both litter and large planktonic organisms or fish. Approximately 45,000 images were obtained over a period of 4.5 days (images taken between 07:00 and 21:00).
In July 2018, a survey was performed to test the possible long range survey of subsurface marine litter. The survey was possible with consistent data and 45,000 stable images recorded, enabling an assessment of marine debris in the sub surface layer (0-4.5m). 6 debris per km2 were counted, in the range of visual observations (Suaria et al., 2017).
Results showed the possible long-term and large scale utilization of the Wave Glider as a tool for monitoring marine litter. It is well adapted to cover large coastal or oceanic zones, including large MPAs, to monitor surface (0-4.5m) debris, and demonstrates strong potential for remote areas.
Learn more about the work IFREMER does to understand our oceans.
Photos: S.D’entrecolas and F. Galgani/IFREMER


I don't entirely understand the why, but here is what I do know. The main reason for this convention is that F2-F1 gives a plot where the X axis better matches tongue position in back round vowels. The problem with bare F2 is that it makes vowels positions slope to the right as you go up (with [u o ɔ] not matching [ɯ ɤ ʌ]), but F2-F1 makes the back round vowels track actual tongue position, so that they slope to the left. The exact reason for this is somewhat mysterious to me.
Part of the mysterious nature of the relationship between formants, tongue position and vowel charts comes from the traditional habit of thinking of vowel articulations as being a governed by two independent factors. However, a lifetime of work by Fant and others has demonstrated that a better model is a tube with a constriction, so there is as a first approximation only one factor (the second approximation adds differences in tube length, as a function of lip protrusion).
Rounding lengthens the tube, which lowers all formants. The effect of rounding is greatest on F2, and it is greatest in back vowels. This bit of subtractive magic has the effect of "figuring out" what the lowering contribution of rounding is, and mostly removing it from the vowel plot. What is left, then, is an X value more based on tongue position, rather than the total length of the front tube.


Rainbows always capture our imaginations, and we've started a story about one on this worksheet - the kids just need to carry it on...
Rainbow Story Starter
Trace the outlines of the rainbow on this tracing page – fun for a weather-themed pencil control activity. Kids can colour in the rainbow after tracing the outline!
Here's a fun printable about a rather interesting puddle, to encourage some creative writing. We've started the story - all the children have to do is write down what happens next!


Exploring Lake Superior: Researching the water and waves
True to Gitche Gumee’s character, a day spent on the UMD research vessel Blue Heron required preparation for all weather conditions.
“We’re just headed up kind of near Stoney Point today,” Craig Hill said.
Hill is an assistant professor of mechanical and industrial engineering at the University of Minnesota-Duluth.
“I’m from Minnesota,” he said. “I spent my summers in northern Minnesota, and being able to come here to Duluth and have some of my research and some of the teaching I do centered around Lake Superior and the Great Lakes is really something that I love to do.”
One of his research goals is to see how new, lower-cost systems work collecting data on the Great Lakes.
“We’ve completely designed and built in-house a small observation buoy,” Hill explained. “It measures air temperature, water temperature, wave heights and directions, GPS coordinates.”
Hill called the Acoustic Doppler Current Profiler that was being dropped into Lake Superior the “underwater workhorse” of the project. It will record 20 minutes of data every hour for the next couple of months.
Cheaper devices might help researchers like Hill fill a data gap.
“I think over the last 40 years, about 98% of the measurements we have on the surface of the water come during a six- or seven-month period,” he said. “So we really have a big data gap in the wintertime.”
Jonathan Book, a senior mechanical engineering student at UMD, helped build the device.
“This is designed to be a low-cost buoy that you can put out there as long as you need to. If the ice wrecks it or you lose it in a storm, it’s not that big of a deal,” Book said.
The whole project has been student-led and went through several semesters of design. So Book was excited to be there when it went in the water.
“This was one of the first things I really got to start working on in a formal manner, not just a little project at home,” he said. “And seeing it on the CAD model and seeing it in real life all put together out in the water, I mean, that’s pretty cool.”
It’s the kind of experience that can mold a career.
“I used to be steering towards aerospace, but now I think I’m steering more towards marine,” Book said.
The Big Lake’s unpredictability presents a fun challenge too.
“We’re completely at the mercy of Lake Superior,” Hill said. “You come out here hoping everything’s going to go smoothly, and really it’s like a small ocean when you’re out here. The waves got maybe 4 or 5 feet tall when we were out there, but that’s nothing compared to the storms we’ll get this fall.”
Whether it’s foggy and choppy, as it was when the Blue Heron left the dock, or sunny and smooth like when it returned, Lake Superior influences many lives.
“The more data we have, whether it’s about water quality or what the surface conditions are like, that data helps us make informed decisions,” Hill said. “You have to have a lot of respect for Lake Superior.”


A sample of an essay on to kill a mockingbird about symbolism story, but for the messages concerning education, racism, and other problems of her time. The next time someone doesn't understand systemic prejudice, send them running processes and executing rule-based symbolic manipulation,” from stop & frisk to unarmed black men getting killed on a regular basis. Keywords: racism, comfort zone, symbolic/realistic threats breed, a (2014, december 7) police killing data filled with many unknowns retrieved from.
Free essay: analyse how symbolism was used to convey an interesting idea in an extended written text prejudice, in the 1930s, was an. Bias: an inclination of temperament or outlook prejudice is, in a sense, a form of bias and to a police officer being put on the case of their spouse's murder bias has a far more nuanced meaning and expresses a more nuanced feeling,.
Prejudice is an idea or opinion that is not based on fact, logic or actual experience in to kill a mockingbird by harper lee, some citizens look down on the. To kill someone without hesitation, mercy, or discernment the general warned the rebels that they must either surrender or be killed with extreme prejudice. A secondary school revision resource for gcse english literature about the themes in harper lee's to kill a mockingbird.
Prejudice is an affective feeling towards a person or group member based solely on that person's group membership the word is often used to refer to. Play on the term “terminate with prejudice” when an employee's employment is terminated, meaning “will not rehire employee to same position in future” (ie, prejudiced against rehiring), hence “terminate definitively, ie, kill. Harper lee effectively uses symbolism throughout her novel, to kill a mockingbird tim johnson is another symbol of prejudice and his shooting by atticus is. Symbolism of the mockingbird in to kill a mockingbird by harper lee boo radley represents a mockingbird slain by society's prejudice. Poll: majority sees confederate flag as southern pride symbol, not racist the confederate flag as a symbol of racism, just 25% of whites agree since nine african-american churchgoers were killed by a white man who.
After the bubonic plague broke out in 1348 and eventually killed more than termed laissez-faire, symbolic, or modern racism, that amounts to a “kinder, gentler. The rabid dog is a symbol of the racism that is in the town racism, like the disease of rabies, will continue to spread unless it is shot down in its path the rabid. Accordingly, most prejudices have some functional significance for the ninety-two percent of black murder victims and 666 percent of white murder victims.
This article begins with the link of culture to prejudice, noting specific tutsis ( and many hutus) by hutus in rwanda to the mass killing of 70 people, mostly youths, this definition of culture, like most definitions that take a symbolic, process,. Get everything you need to know about prejudice in to kill a mockingbird analysis, related quotes, theme tracking. The title of harper lee's 1960 classic to kill a mockingbird is like that for me, to the plot, but it carries a great deal of symbolic weight in the book of democracy when prejudice, myth, and misinformation go unchecked.
A social media post claims that levi's two horse logo is a racist symbol that represents a slave's being killed. Here, the analysis of religion as a meaning system illuminates how traditional psychological perspectives on religion and prejudice are.
Stereotyping often results from, and leads to, prejudice and bigotry 2 of receiving a death penalty than whites convicted of first degree murder, for example what was the significance of the us supreme court decision in brown vs. Prejudice definition is - injury or damage resulting from some judgment or action of the stun belt and leg braces that arias wore during trial (as do most murder . They enforced prejudices and social hierarchies, but they also inspired unlikely of monsters reflect the ambiguities in the meaning of the word itself images like these—no less than those of dragons or child-killing. Free essay: “to kill a mocking bird” is a novel which was written by harper lee in my essay i will discuss how harper lee explores the theme of prejudice by.


One of the main challenges of urban wind energy harvesting is the understanding of the flow characteristics where urban wind turbines are to be installed. Among viable locations within the urban environment, high-rise buildings are particularly promising due to the elevated height and relatively undisturbed wind conditions. Most research studies on high-rise buildings deal with the calculation of the wind loads in terms of surface pressure. In the present paper, flow pattern characteristics are investigated for a typical high-rise building in a variety of configurations and wind directions in wind tunnel tests. The aim is to improve the understanding of the wind energy resource in the built environment and give designers meaningful data on the positioning strategy of wind turbines to improve performance. In addition, the study provides suitable and realistic turbulence characteristics to be reproduced in physical or numerical simulations of urban wind turbines for several locations above the roof region of the building. The study showed that at a height of 10 m from the roof surface, the flow resembles atmospheric turbulence with an enhanced turbulence intensity above 10% combined with large length scales of about 200 m. Results also showed that high-rise buildings in clusters might provide a very suitable configuration for the installation of urban wind turbines, although there is a strong difference between the performance of a wind turbine installed at the centre of the roof and one installed on the leeward and windward corners or edges, depending on the wind direction.
On the Wind Energy Resource Above High-Rise Buildings / Vita, Giulio; ( (S))arki('(c))-Glumac, Anina; Hemida, Hassan; Salvadori, Simone; Baniotopoulos, Charalampos. - In: ENERGIES. - ISSN 1996-1073. - ELETTRONICO. - 13:14(2020), p. 3641. [10.3390/en13143641]
|Titolo:||On the Wind Energy Resource Above High-Rise Buildings|
|Data di pubblicazione:||2020|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.3390/en13143641|
|Appare nelle tipologie:||1.1 Articolo in rivista|


This is an introduction to the key abstractions used in the Pyro Robotics system. This module provides an exploration of the objects and their attributes, properties, and methods. When completed, the reader should be able to discuss the design of robotics controllers.
Overview of Pyro Objects
Pyro is written using object oriented programming (OOP) in Python. There are four main classes in Pyro: robot, brain, gui, and engine. This module will explore these objects and how they interact to form the core of Pyro.
In order to do anything in Pyro, you will need a Pyro robot instance. All robot types are extensions of pyrobot.robot. The following table shows the names of robots and their corresponding simulator or hardware.
|Pyro Robot Name||Pyro Simulator Name||Robot Hardware|
|Player6665, Player6666||StageSimulator, GazeboSimulator||Pioneer family, ER1, Khepera, B21R, etc.|
|Khepera, Hemisson||N/A||Khepera 1 and 2, Hemisson|
|Robocup, RobocupTeamA, RobocupTeamB||RobocupSimulator||N/A|
Each simulator is actually a different process, and each one has its own method of talking to Pyro. For example, the simulator for the Pyrobot robots uses ports, while KheperaSimulated uses shared memory.
It is generally a requirement to start up any simulator before attempting to load the corresponding Pyro robot instance. On the other hand, you should stop Pyro before stopping a simulator. Consider a simulator to be the server, and Pyro the client. A server will stop when Pyro is stopped.
Robot objects are responsible for the details of interfacing with the simulators and real hardware. All robots are defined in the pyrobot/robot/ directory. For example, the following files have the details of connecting onto the symbolic Pyrobot simulator, Player, and Khepera robots, respectively:
pyrobot/robot/symbolic.py pyrobot/robot/player.py pyrobot/robot/khepera.py
For some robots, this involves many details. You may find that some of the lowest-level details are in a lower-level directory of pyrobot/robot/. But all robots get their core definition from:
Robot instances are passive objects: they only do things when a brain or gui object tells them to. They command the motors of real and simulated robots, but only as directed by a brain.
Each robot has exactly one brain. All brains are extensions of:
Brains are themselves extensions of threads. Thus, brains are capable of running on their own, in their own process. Sometimes a brain may have multiple behaviors, but they all run in a single thread.
Brains may operate continuously, but they do so one step at a time. Most brain threads call their step() methods about 10 times per second. But you can implement your own brain that steps many thousands of times a second.
If you have loops (for or while loops, for example) in your step function, you may experience erratic behavior, either in the robot or in the gui. Remember that step() is already in a loop, and runs many times a second.
Each brain/robot pair has an associated graphical user interface, or gui. The basic gui is defined in:
The gui is responsible for drawing things, if necessary. There are two main gui's, and they must be indicated on the command line:
pyrobot -g tty # A basic TTY console non-gui pyrobot -g tk # A Tk-based graphical interface
The tty gui is a bare interface to provide interaction and control over a slow connection, such as wireless. The tk gui will ask the robot (and its devices) for data so that it can render visual representations. Note that the tty GUI does not update devices' displays. If you run with the tty gui and wish to have graphical windows (for example, on a camera) then you will need an camera.updateWindow() call in your brain.
Finally, the engine is the last main object. The engine is designed as a container for the brain/robot/gui trio (and some other overhead objects). The engine is the place where the above objects can find each other. You can find the engine definition in:
You can ignore engines, as they are not seen unless you want to write raw Python code to control multiple robots.


or call us at: (832) 699-9265
Sinus infections are common problems for toddlers and children. A sinus infection, also known as sinusitis, is the inflammation of a toddler’s nose and sinuses. Sinus infections, especially in children, should be treated as soon as possible. This is because children’s immune system is weak and might not be able to deal with such infections.
In addition to understanding the basics of treating sinus infections in toddlers, a parent must also understand the common causes of sinus infections in toddlers.
If the sinus infection occurs while a toddler is suffering from a common cold, it usually is a viral sinus infection. If it occurs following a common cold, then it’s a bacterial sinus infection.
Because of the possibility of a toddler experiencing a sinus infection associated with or following a common cold, great care should be taken to treat the symptoms of that common cold when they first appear.
A toddler that experiences or suffers from seasonal allergies is quite likely to be afflicted with a sinus infection as well. As is the case with a common cold and an associated sinus infection, a parent is wise to take a proactive course in addressing the prospect of an allergy related sinus infection. If a parent detects that a child is suffering from the early symptoms of seasonal allergies, he or she should take immediate steps to address the allergies.
By taking a proactive stance, a parent is best able to prevent a toddler from experiencing a sinus infection associated with seasonal allergies. Because of the young age of a toddler, a doctor should be consulted to determine the most appropriate course of treatment for seasonal allergies.
As is the case with the common cold and seasonal allergies, the flu is another cause of a sinus infection in toddlers. Indeed, the flu is a serious condition for a toddler. A parent with a child who appears to have the symptoms of the flu should seek prompt medical attention not only to control the symptoms of that illness but to prevent or address the onset of a sinus infection as well.
Colds and flus can be passed from one child to another when they are in close proximity. Indeed, perhaps the most common cause of a sinus infection in toddlers is exposure of these young children to peers suffering from the cold or the flu.
A toddler runs the risk of a sinus infection through his or her own unclean hands. A child can catch a cold or the flu in this manner, which can lead to a sinus infection. A parent needs to be diligent in keeping his or her child’s hands as clean as possible.
Similarly, unclean toys can be the source of a cold or the flu, which can lead to a sinus infection. For this reason, a parent need to be diligent in keeping a toddler’s toys as clean as possible.
Finally, toddlers fairly regularly catch “bugs,” including a cold or the flu from a parent. Again, this can lead to a sinus infection. A parent needs to avoid contacting the child if or she is suffering from a cold or a flu.
If you suspect that your child little one has a sinus infection, you should seek help as soon as possible. Contact us today to book an appointment.


National Naval Responsibility Initiative
The Navy and Marine Corps operate on—and above, under and from—the sea. The maritime environment extends from the sea floor to space and includes the land battlespace that is reached from the sea. It is complex and challenging, and it makes Naval operations inherently difficult and dangerous even under the best conditions. The Department of Navy (DoN) has therefore historically placed great emphasis on maintaining a vigorous science and technology program in those areas where research is critically important to maintaining naval superiority.
Many of those areas, uniquely important to the Navy and Marine Corps, are simply not addressed by research investments from the other Services, or for that matter from the National Science Foundation, the National Institutes of Health, other federal research establishments or even private industry. This means that the health, strength and growth of our scientific and technical capabilities in those fields depend upon the DoN.
On behalf of the DoN, the Office of Naval Research (ONR) must ensure continuing U.S. leadership in these vitally important scientific and technical disciplines. It does so through research, recruitment and education, all done with a view to sustaining an adequate base of talent and the critical infrastructure necessary to carry out research and experimentation.
How does DoN determine its National Responsibilities?
In consultation with experts drawn from the National Academies and elsewhere, ONR identifies National Naval Responsibilities. ONR looks at various scientific fields and assesses:
- The scope of naval responsibility
- Funding and funding trends
- The scope, degree, stability and trend of non-Naval funding
- The scientific and technological performer base—in academia, government and industry
- The scientific and technological infrastructure
- The scientific and technological knowledge-base—including graduate and post-doctoral programs in the area
- The prospects of integration with and transition to engineering development and acquisition programs.
What does DoN do to meet its National Responsibilities?
Above all, it seeks to keep the field healthy by giving it stability. ONR finds relevant programs and allocates resources to them. It keeps key areas of basic and applied research strong, and it balances theoretical, empirical and field work to sustain a research infrastructure. It actively seeks to attract talented investigators to the field through civilian and military fellowships, and by supporting entry-level faculty. And finally the ONR establishes centers, real and virtual, of integrated research when appropriate.
What are the National Naval Responsibility Programs?
ONR-approved National Naval Responsibility initiatives include:


1. Like any art, poetry is defined by Aristotle as what?
2. In what three ways does Aristotle differentiate various art forms from one another?
3. Aristotle explains that the medium specific to poetry is one that uses what?
4. How does Aristotle differentiate poetry from prose?
5. The object poetry portrays is what, according to Aristotle?
This section contains 6,101 words
(approx. 21 pages at 300 words per page)


What are some of the challenges with local anesthetic?
One of the parts of most visits to the dentist is local anesthetic or getting frozen as people often say. It is interesting to note that the first local anesthetic was actually cocaine. Cocaine was first isolated in the 1860’s and first used clinically in 1884. While the local anesthetic effect was a good thing, the addiction it produced, of course, was not. In 1905, chemists managed to change the cocaine molecule in such a way that the addictive effects were eliminated and much of the local anesthetic effect was retained creating procaine (Novocaine). The disadvantages of this new local anesthetic included a high allergic potential, it took a long time to produce numbness, and it wore off very quickly. The first modern local anesthetic was lidocaine which was invented in the 1940’s. Lidocaine produced much deeper local anesthesia, had a much shorter onset, and with the addition of epinephrine, lasted several hours. Lidocaine was the first of the broad category of the local anesthetics used today (called amide type anesthetics). The latest addition to the local anesthetic lineup is Articaine and represents a major advancement in anesthetic technology. It diffuses through bone much more effectively than previous types of anesthetic thus nearly eliminating the need for difficult and less reliable block type anesthesia on all but the lower molars. Articaine has been used in Europe since 1976, Canada since 1983, and was only approved for use in the USA in 2000. There are other kinds of anesthetic in this amide type group. Each has its own advantages and disadvantages.
For all but the lower molars, infiltration (placing the anesthetic right next to the tooth needing to be numb) is the method of choice. Infiltration is reliable, usually gets only a small area numb, and takes effect within only a few minutes. This type of anesthesia presents little challenge most of the time. However, for the lower molars, the situation is quite different. The bone in the lower molar region is too dense for infiltration to be effective. This area requires another anesthetic technique called block anesthesia. In block anesthesia, the anesthetic is placed near the entrance into the lower jaw of the nerve supplying the lower molars (the inferior alveolar nerve) quite far behind where the teeth are located. Individual anatomy presents a unique challenge to anesthetizing (freezing) the lower molars. The opening for the inferior alveolar nerve can be located in a spot that is not the most common spot. As well, there can be several openings for the nerve, all of which would have to be anesthetized in order to achieve numbness of the lower molars. There is little chance the dentist will have access to the kind of imaging required to know of these significant anatomic irregularities in his individual patient. Block anesthesia typically anesthetizes a much larger area than infiltration and takes quite a bit longer to take effect and to leave the area after the work is done. Success rates for profound anesthesia to the desired teeth approach 100% when infiltration can be used, but when block anesthesia has to be used (for lower molars), success rates for the first cartridge of anesthetic deposited in the area range between 21% and 67%. Another cartridge is often required, and sometimes a supplemental technique is also required in order to achieve the required amount of numbness in the tooth to be treated.
Other challenges to anesthetizing patients include substance abuse. Patients who abuse alcohol regularly or are recreational drug users present unique problems to effective anesthesia for dental procedures. Often, these patients require more anesthetic and more time for the anesthetic to begin to be effective. Active glue sniffing presents significant anesthesia problems that often cannot be overcome with regular techniques. As well, the mind is a powerful force. People who are very afraid or who are certain they cannot become numb will have difficulty being anesthetized. Medications to alleviate anxiety can be considered for this kind of person.
There is ongoing research on alternate anesthesia techniques including electrical devices as well as acupuncture. Continued advancement in the chemistry of injection type anesthetics is probable. Make sure you communicate any fears you might have or other concerns about local anesthesia to your dentist. Ask your dentist if you would like more information about local anesthesia.
- This article was written by Dr. Mike Christensen and published in the Daily Miner and News, and Enterprise. Local Kenora News Publicatons (1998-2006)


PITTSBURGH (KDKA) – Identical twins Jocelyn and Haley Lehotsky have the same embarrassing problem — they sweat too much.
“We would sweat through anything. Couldn’t wear, like, light clothing. You’d have sweat marks really bad,” says Jocelyn.
“Presentations, too. When you get the anxiety and just make it even worse, then, and think, oh, am I sweating?” says Haley.
They have a condition called hyperhidrosis, or excessive sweating. It usually happens under the arms or on the palms of the hands or soles of the feet. It affects three out of every 100 people.
“It can be made worse by things like feeling stressed or maybe feeling embarrassed, but even in moments when you’re not under stress, it will just sort of occur,” says Dr. Brian Horvath of Hovath Dermatology.
It can be hereditary. Less commonly, it can be from a medicine or a tumor, but the sweating tends to be all over in those cases.
The twins have tried special antiperspirants.
“You’d put it on before bed, and it would burn your armpits, or you’d get cuts from it, because it was so strong,” Jocelyn said.
They also tried pills.
“With the pills, you get the dry mouth, and it’s just hard to like, talk to people for extended amount of time,” says Haley.
They even tried Botox.
“Botox is a very effective treatment, that stops sweating for about six months,” says Dr. Horvath.
So, the need for something better and less painful led to a new option that has just come on the market — a wipe called Qbrexa.
“That medicine actually stops the sweat glands from getting the signal to start sweating. They never sweat in the first place,” says Dr. Horvath.
You would still be able to sweat in other places, so you don’t overheat.
Some people still have dry eyes, even with wiping just the armpits.
In studies, it was only used under the arms.
“We have great hopes it might help with other areas, like the hands and the bottom of the feet, which are the two other most worrisome spots for sweating,” says Dr. Horvath, “A lot of people have sweating at the top of their forehead. We’ll have to see if we can use it in that area without having the dry eyes.”
It takes three to four days of once-a-day use to become effective.
And as a new product, it is likely to be expensive.
“We don’t know yet what the price is going to be of the medication, we don’t know yet what the insurance coverage is going to be,” Dr. Horvath says.
Even so, the twins would like to try them.
“I would definitely try it. I mean, we’ve tried three other things, might as well try one more. But, if it works, I mean I’d try it. It probably would be the easiest, too, to apply,” says Haley.


Sightline Maps is changing the way we view topographical mapping data with the help of 3D printing, and on the 8th of September they are launching a Kickstarter. The Californian based company created a web based platform that enables users to create custom 3D models of any area in the world.
Sightline Maps has many uses; construction, mining, city planning and even extreme sports like mountain climbing, but the most notable is education, and this is the focus of their Kickstarter. Two-dimensional images can explain only so much about the world we live in, so by easily creating 3D printed models students can have a much better learning experience. The aim of the Kickstarter is to get the platform into as many schools as possible. It works with any printer, and any operating system.
“We initially created this software to improve the military’s mission planning capabilities – being Navy veterans – but quickly realized we could have an awesome impact in the classroom when we saw children work with our maps.” said Jason Ray, Operations Manager at Sightline Maps.
“After giving the software to several schools, we realized a few things – 1) They all had great ideas for features that would make the tool better, all of which would cost money to implement, 2) selling to schools is a very challenging sales cycle, 3) we would have to figure out a way to raise money for the features so we can give the software to the schools,” added Ray. “So we came to the Kickstarter platform with the idea that not only will our backers get a really cool color 3D print of a topographical map for supporting us, but every penny they provide will go to sponsoring schools for subscriptions to our software and improving the site.”
For every $100 the Kickstarter raises, one school will receive a year long subscription to Sightline Maps. This includes:
- Immediate access to existing and future features
- Unlimited file downloads for every student and teacher
- Lesson plans designed to support integration of Sightline Maps into existing curriculums
- Direct influence on new feature development
The goal is to bring the platform to 400 schools, the Kickstarter preview page can be viewed here before it goes live on the 8th.
Featured image: Kim Rodriguez and her 5th grade class at Woodin Elementary with the Sightline Maps team. Image: Sightline Maps


Ivy, the eternal green mystery
A touch mysterious and quietly ever-present: ivy (Hedera) is the big provider of greenery which represents a stable element in the garden through all four seasons. This ground-covering or climbing foliage shrub is hardy and evergreen. There’s a wide range of leaf colours, whilst all ivy species grow quickly and are easily trained and can therefore cover fences, wire fencing, summerhouses or walls. As groundcover ivy gives weeds no chance, which makes it the most decorative garden helper ever.
Various ivy species are suitable for the garden. Green-leafed Hedera hibernica has large leaves and is very suitable as groundcover or to create partitions. H. colchica has more leathery leaves, whilst Hedera helix is the most common species and is available with various leaf shapes and colours such as green and variegated white or gold. Hedera helix ‘Arborescens’ is a more bushy plant which produces attractive black berries after flowering. A classic ivy is H. canariensis ‘Gloire de Marengo’, an impressive presence with its larger leaves and creamy white leaf edges, but not entirely hardy.
- The name Hedera is derived from an ancient Indo-European sound which represents ‘seizing’ or ‘gripping’, which refers to the clinging roots.
- Because the plant is evergreen, ivy symbolises eternal life.
- Ivy also plays an important role in the garden’s ecology: birds like to nest amongst the greenery, and insects often drop by. Ivy therefore enriches the entire circle of life in its environment.
- Ivy appears in ancient Celtic and Germanic legends as a protector (it provides excellent insulation against heat and cold when grown against a house), bringer of luck and provider of hope. Particularly when Nature is hibernating, ivy’s greenery reminds us that spring will come again.
Ivy is native to Asia, Europe and North Africa. In the wild the plant grows on trees and rocks and can climb to a height of 25-30 metres. It particularly thrives in cooler regions.
What to look for when buying
- The pot size and the number of stems or thickness of the plant must be in proportion.
- With Hedera ‘Arborescens’ check the distribution of buds or berries.
- Damaged or marked leaves are usually caused by the wrong storage or incorrect shipping.
- Ivy is prone to red spider mite, which is shown by a faint grey discolouration of the leaf.
Sales and display tips for ivy
Display ivy on a table in blocks or stripes by colour in order to draw more attention. Another way to bring this garden plant to life for consumers is to display it alongside other climbing plants such as clematis, passion flower or climbing roses for an inspiring effect. If you have the space, grow a green wall or hut using chicken-wire which can be re-styled appealingly every season.
Care tips for consumers
- Ivy thrives in both shady and light positions, but not in full sunlight.
- The soil may not dry out, but excess water is also not good for ivy.
- If the plant is in a sheltered spot, such as on a veranda or balcony, regular spraying helps to prevent red spider mite.
- Give some plant food once a month, particularly if the ivy in is in a container or pot.
- Good to know: the clinging roots can leave marks on walls.
- Prune in late spring after the biggest growth spurt and in the autumn before winter arrives.


Intro to cron and editing your crontab schedule
When managing data across different environments, there are a number of recurring processes that are essential to maintaining data integrity. For example, taking regular database backups, sending out data health reports, and monitoring systems for slow queries. Writing scripts to schedule these operations helps relieve the pressure of remembering to perform these tasks and ensures critical operations are happening consistently.
One of the most popular ways to schedule tasks is by using a crontab file. For example, you can set up a cron job to run your backup every day at 6:00 p.m., which ensures that your data will always be recoverable.
In this article we'll walk through how to schedule recurring tasks using cron jobs. We'll discuss crontab’s structure and syntax, real-life use cases, and some limitations. We'll also touch on some alternatives to cron.
Introduction to cron and crontab
Cron is a time-based job scheduler used on Unix-like operating systems. It executes recurring tasks at specified intervals (e.g., hourly, daily, weekly, yearly, and so on) using the cron daemon. A daemon is a program used to run background processes that perform system tasks; the cron daemon uses a crontab file to specify what tasks to run and when to run them on the system.
A cron job is a command run by the cron daemon at scheduled intervals.
A crontab, short for "cron table", is a file that contains a list of commands that get run using a cron command to schedule tasks.
Here’s a code snippet that shows a sample crontab task when you run
crontab -l in your terminal:
# Begin Whenever generated tasks for: /Users/florencenjeri/projects/slackbot/config/schedule.rb at: 2022-03-24 13:14:20 +0300 0 * * * * /bin/bash -l -c 'cd /Users/florencenjeri/projects/slackbot && RAILS_ENV=production bundle exec rake notifications_schedule:create --silent >> log/cron.log 2>&1' # End Whenever generated tasks for: /Users/florencenjeri/projects/slackbot/config/schedule.rb at: 2022-03-24 13:14:20 +0300
As you can imagine, crontab files can be used for a variety of practical purposes. Here are a few common use cases:
A company might schedule weekly database backups of the data they have collected during the week. Since running a full database backup can utilize a large amount of system resources—thus impacting performance—many organizations perform backups at night, when fewer people are using the system.
Batch operations occur when a computer performs batches of jobs in sequential order. They’re typically used for very large tasks that get broken down into a group of processes to maximize efficiency. Consider an online e-commerce store, which might have thousands of customers subscribed to get email notifications when certain items are back in stock. Using a cron job, you could schedule a batch update that sends 100 emails out to users on 10-minute intervals until every subscribed customer receives an in-stock update.
Regular system updates ensure that your system is up-to-date with the latest security patches. Most of these security patches are done monthly—you may have noticed monthly update prompts on your phone, tablet, or laptop. These monthly updates can be scheduled using cron.
Task scheduling with crontab files
Recurring tasks are scheduled to run at a specified time by adding them to a crontab file. In this section, we'll walk through how to implement cron jobs using crontab files.
Crontab syntax and structure
The commands in a crontab file are written using a specific structure, as shown in the following code snippet:
# * * * * * command to be executed # | | | | | # | | | | | # | | | | | # | | | | |_______________ Day of the Week (0 - 6)(Sunday to Saturday) # | | | | # | | | |_______________ Month of the Year (1 - 12) # | | | # | | |_______________ Day of the Month (1 - 31) # | | # | |_______________ Hour (0 - 23) # | # |_______________ Minute (0 - 59)
Here’s a breakdown of the cron command structure as displayed above:
- Minute: The value expected is between 0–59 minutes.
- Hour: The value expected is between 0–23, representing the 24 hours in a day.
- Day of the Month: The value expected is between 1–31, representing the 31 possible days a month.
- Month of the Year: The value expected is between 1–12, representing the 12 months of the year. This value can also be defined using the first three letters of the month, like JAN, FEB, NOV, etc.
- Day of the Week: The value expected is between 0–6, from Sunday (0) to Saturday (6). You can also use the first three letters of the day, like SUN, WED, etc.
Putting this all together, a cron command that says
0 5 6 2 * would run every year on February 6 at 5:00 a.m. UTC, regardless of the day of the week. Similarly, the cron command
0 0-7 * 1 0 would run every hour at minute 0 from midnight to 7 a.m. UTC on Sundays in January, regardless of the day of the month.
Additional cron components
There are a variety of symbols that can be used within cron commands that help to better define time-related details. Here’s are some additional specifications that can be included:
- Any value (*): Asterisks are used as wildcards, which match all possible characters (e.g., every minute, every hour, every day, etc.). For example,
0 5 * * *runs the task every day at 5:00 UTC and
* * * * *would run every minute all of the time.
- Multiple values (,): Commas are used to separate multiple items in a list. For example,
2,4,8 * * * * commandwill run the task on the second, fourth, and eighth minute. For example, 1:02 and 2:08 would match.
- Multiple ranges (-): Dashes are used to define a range of values. For example,
* * 2-5 * * commandruns the task between February and May.
- Interval repetition (/): Slashes are used to signify frequencies within a given time period. For example,
*/4in the month field (
* * * */4 * command) will run the task every four months. (Note: This would be virtually the same as writing
4,8,12on the month field.)
Crontab commands are used to list, edit, or remove cron jobs from a crontab file. Here's how you can use them:
List cron jobs
To view all the tasks scheduled on your local machine, run the command
crontab -l in your terminal. You should see output similar to the screenshot below, showing a list of all your scheduled tasks:
Edit crontab file
To edit a crontab file or create a new one, run the command
crontab -e. You will be redirected to an editor similar to the one shown in the screenshot below. You can then add your tasks (one per line), save, and then exit from the editor.
Remove crontab file
To remove the current crontab file, run the command
Edit another user’s crontab file
To edit other users’ crontab files, run the command
crontab -u <username>. (Note: running this command requires that you have system administrator privileges.)
Examples of cron jobs
Below are a few examples of schedules you can use for your cron tasks.
Scheduling tasks every minute
The following command allows you to schedule tasks to run every minute:
* * * * * /bin/bash -l -c 'cd /Users/florencenjeri/projects/slackbot && RAILS_ENV=production bundle exec rake notifications_schedule:create --silent >> log/cron.log 2>&1
The command in the example above runs a task in a Ruby on Rails rake file. It has three parts:
/bin/bash -l -c: the shell used to run the cron commands
cd /Users/florencenjeri/projects/slackbot && RAILS_ENV=production bundle exec rake notifications_schedule:create --silent: the path to the task, as well as the name of task,
notifications_schedule:create, to be scheduled
>> log/cron.log 2>&1: specifies where to log the output of your scheduled tasks
Scheduling tasks every 15 minutes
The following command allows you to schedule tasks to run every 15 minutes:
*/15 * * * * command
Scheduling tasks every two hours
The following command allows you to schedule a task to run every two hours:
0 */2 * * * command
Scheduling daily tasks
The following command allows you to schedule a task to run every day at midnight:
0 0 * * * command
Scheduling weekly tasks
The following command allows you to schedule a task to run every week on Sunday at midnight:
0 0 * * 0 command
Scheduling yearly tasks
The following command allows you to schedule a task to run at midnight on the first of January every year:
0 0 1 1 * command
Scheduling tasks between specific hours
Finally, the following command allows you to schedule a task to run once an hour (at minute 0) every day from midnight to 7:00 a.m.
0 0-7 * * * command
The limitations of cron
Despite cron being the most widely used job-scheduling command, it has some limitations that derail its efficiency as a job-scheduling mechanism. Some of these limitations include the following:
Difficult to maintain
When using cron, you have to build your own monitoring and alerting systems to make cron jobs usable. Most tasks scheduled using cron are crucial, such as performing database backups. If a server goes down, for example, you'll need to be able to quickly identify which of your jobs are no longer running. With cron, these checks need to be manually added as there's no support for failure handling or alerts when jobs have failed.
Lack of security
As an organization scales, hundreds of cron jobs created by several different people can proliferate across several servers. Not only is this tough to maintain, but it's also problematic from a security perspective. It's a good security practice to limit access to production servers as a company scales, but if several people need to maintain cron jobs they've written in the past, it may be harder to lock down prod access.
Cron doesn't provide a central place to see, update, and manage all the cron jobs you have running. Especially as your organization grows, it becomes very difficult to have visibility into how many and which jobs are running on which machines since cron doesn't easily surface that information.
Cron doesn't log by default so you have to explicitly add in logic to capture logs for every cron jobs that you have running. Doing this for every script can be time-consuming and makes it challenging to monitor and remediate failed jobs.
Using Airplane to schedule tasks
Airplane is a developer platform for building internal tools. Airplane has first-class support for features like permissions and audit logs that make it an easier-to-use and safer alternative to cron. Scheduling tasks using Airplane can help you overcome some of the limitations described above.
Some of the advantages of replacing cron jobs with scheduled tasks in Airplane include the following:
Audit logging: Airplane automatically logs all tasks. The Activity page shows a log of all events with event details, actors, and timestamps.
Failure handling: On the Activity page you'll also see the task's status which will show if tasks have succeeded or failed. You'll automatically receive notifications via Slack and email when tasks fail for increased security and easier system maintenance. This should also make debugging easier.
Security and access controls: Using Airplane, you can set granular permissions for who can view, request, execute, and be an admin on a task-by-task basis. You'll be able to create group-based access controls which are not supported with crontabs.
Easy-to-use UI: You can view, create, and edit tasks all in one place from the Schedules page. This will provide a quick view of the schedule, when it's expected to run, and who has scheduled it. Cron jobs only show the tasks themselves (not who scheduled them). Editing a scheduled task is also simple with Airplane. You can do this directly from the UI.
Airplane provides a number of benefits that make it a simpler and safer alternative to cron. Airplane tasks are serverless, come with audit logs, permissions, and notifications, and can be used for scheduled tasks or for one-off operations that need to be run on-demand rather than on a schedule (such as testing your REST API).
Author: Florence Njeri
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7cad 3D Unfold
This programming project began when I tried to make a pottery model in paper, as a toy. Then I found making a 3D Unfold app is great not only for CAD users, but also for myself to perfect my geometry and polyline programming system.
Click the Add-in ribbon tab and you can see the 7cad 3D Unfold ribbon.
7cad_Unfold command's window has 2 tabs. The first tab is to unfold a general 3D model shape. It is recommended the 3D model is a decimated 3D mesh.
The second tab is for the case of unfolding an octagon revolve shape. No need a 3D model here. You only need to specify the rotating curve polyline and the axis.
After unfold command has done the job, you can run 7cad_FoldUp command to see how the flatten unfold faces can be fold up and get back to the original. This command will create a block names "Fold Up Animation". Within the block, all animation items are put into layers name "Fold Up Animation 1", "Fold Up Animation 2", ... Click the "Forward" and "Back" arrow to see the animation. This command is for demonstration purpose only.
Finally, it is 7cad_Cutout command. This command joins unfold pieces together in union polylines. Print the unfold layouts to papers, cut the union polylines out, fold up and stick them together, then you can have your favourite real world paper model!
A web version of the app is available here, powered by Autodesk Forge Design Automation:


Conceptual Building Blocks of Geometry 3-1-17 and 3-2-17: No Fee for CKEC Member Districts, Closed to Non-Member Districts
peaker: Mark Helton
Target Audience: Middle School General Education and Special Education teachers, Elementary Gifted/Talented teachers, Algebra 1 teachers, High School Special Education teachers, Middle School and High School Interventionists and Instructional Coaches
The Conceptual Building Blocks is a series of three modules designed to build a teacher’s capacity to work with students in various settings. The approach is rooted in a conceptual understanding of key concepts in middle school mathematics. The objectives are:
- 1. To build teacher knowledge around the foundational concepts in middle school mathematics
- 2. To provide strategies for teaching content and differentiating instruction
- 3. To develop a conceptual understanding of the core components of proportional reasoning, algebraic thinking, and geometry
- 4. To catalyze change within the school through coaching sessions
This module uses the middle school Kentucky Academic Standards around geometry to focus our work. We will explore the big ideas of geometric thinking, including the van Heile levels of geometric thought, discover how to use the concreteàsemi-concreteàabstract sequence of instruction, explore misconceptions, and much more!
Note: This is a two-day module. Attendance at both days is expected.
PGES Connections: 1a, 1b, 2b, 3c, 4e
Location: CKEC Training Center