bluuebunny/crossref_metadata_2025 huggingface dataset:
Does Rent‐sharing Profit Female and Male Workers? Evidence from Israeli Matched Employer–Employee Data
Authors: Navon Guy , Tojerow Ilan
Published: July 2013

This paper analyses the impact of workplace characteristics on individual wages based on a unique cross‐section matched employer–employee data set for the Israeli private manufacturing sector in 1995. Specifically, we examine the effects of the interaction between profit‐sharing and wages on the gender wage gap. The empirical findings show that individual compensation is significantly and positively correlated with firms’ profits‐per‐employee, even when controlling for all of the following: group effects in the residuals, individual and firms’ characteristics, industry wage differentials and endogeneity of profits. Wage–profit elasticity is found to be 11 per cent and it does not significantly differ between genders. With respect to the overall gender wage gap (on average women earn 28 per cent less than men), the results show that within firms there is no gender discrimination and that 12 per cent of this gap can be explained by the wage–profits profile and by the fact that women are more likely to be employed in less profitable firms than men.
Elementary School ELLs' Reading Skill Profiles Using Cognitive Diagnosis Modeling: Roles of Length of Residence and Home Language Environment
Authors: Jang Eunice Eunhee , Dunlop Maggie , Wagner Maryam , Kim Youn‐Hee , Gu Zhimei
Published: July 2013

The study examined differences in reading achievement and mastery skill development among Grade‐6 students with different language background profiles, using cognitive diagnosis modeling applied to large‐scale provincial reading test performance data. Our analyses revealed that students residing in various home language environments show different reading achievement growth patterns. Earlier gaps in their reading achievement disappear the longer they reside in the target language community. Additionally, students who come from home environments where they use English and another language equally demonstrate higher skill mastery achievement levels, indicating that immigrant students' diverse home language environments do not adversely affect their reading achievement in the longer term. The study results support the evidence that multilingual home language environments are not a cause of low achievement; however, the achievement patterns of Canadian‐born English language learners (ELLs) do differ from their immigrant counterparts, revealing that time alone is not a sufficient condition of reading skill achievement. ELLs' outperformance of monolinguals after 5 years of residence is a result of ongoing instructional support and a rich linguistic environment. The study results hold important policy implications: The evaluation of ELLs' academic achievement and school effectiveness for accountability purposes should be based on longitudinal data that track their developmental growths.
Burkholderia BcpA mediates biofilm formation independently of interbacterial contact‐dependent growth inhibition
Authors: Garcia Erin C. , Anderson Melissa S. , Hagar Jon A. , Cotter Peggy A.
Published: July 2013

Contact‐dependent growth inhibition (CDI) is a phenomenon in which Gram‐negative bacteria use the toxic C‐terminus of a large surface‐exposed exoprotein to inhibit the growth of susceptible bacteria upon cell–cell contact. Little is known about when and where bacteria express the genes encoding CDI system proteins and how these systems contribute to the survival of bacteria in their natural niche. Here we establish that, in addition to mediating interbacterial competition, the Burkholderia thailandensis CDI system exoprotein BcpA is required for biofilm development. We also provide evidence that the catalytic activity of BcpA and extracellular DNA are required for the characteristic biofilm pillars to form. We show using a bcpA–gfp fusion that within the biofilm, expression of the CDI system‐encoding genes is below the limit of detection for the majority of bacteria and only a subset of cells express the genes strongly at any given time. Analysis of a strain constitutively expressing the genes indicates that native expression is critical for biofilm architecture. Although CDI systems have so far only been demonstrated to be involved in interbacterial competition, constitutive production of the system's immunity protein in the entire bacterial population did not alter biofilm formation, indicating a CDI‐independent role for BcpA in this process. We propose, therefore, that bacteria may use CDI proteins in cooperative behaviours, like building biofilm communities, and in competitive behaviours that prevent non‐self bacteria from entering the community.
Workplace Mediation: An Underdeveloped Research Area
Authors: Bollen Katalien , Euwema Martin
Published: July 2013

In this article, we review the literature on workplace mediation. To organize the literature in a logical way, we have relied primarily on the model of Margaret Herrman and her colleagues and examine the important influence of culture and feedback loops on the practice of workplace mediation. Workplace mediation has become a frequent practice in the United States, Europe, much of Asia, and Australia. In the literature, we have found various descriptions of this practice as well as long lists of its assumed benefits, but empirical studies examining the effectiveness of workplace mediation have been few; a limited number of studies have investigated which conditions ensure the effectiveness of workplace mediation, and few studies have relied on observations. As such, workplace mediation represents an underdeveloped research area. In this article, we describe the findings from the existing literature and offer suggestions for future research.
Belief Revision II: Ranking Theory
Authors: Huber Franz
Published: July 2013

Belief revision theory studies how an ideal doxastic agent should revise her beliefs when she receives new information. In part I, I have first presented the AGM theory of belief revision. Then I have focused on the problem of iterated belief revisions. In part II, I will first present ranking theory (Spohn 1988). Then I will show how it solves the problem of iterated belief revisions. I will conclude by sketching two areas of future research.
Quantitative Properties
Authors: Eddon M.
Published: July 2013

Two grams mass, three coulombs charge, five inches long – these are examples of quantitative properties. Quantitative properties have certain structural features that other sorts of properties lack. What are the metaphysical underpinnings of quantitative structure? This paper considers several accounts of quantity and assesses the merits of each.
Cloning and characterisation of a putative pollen‐specific polygalacturonase gene (CpPG1) differentially regulated during pollen development in zucchini (Cucurbita pepo L.)
Authors: Carvajal F. , Garrido D. , Jamilena M. , Rosales R.
Published: July 2013

Studies in zucchini (Cucurbita pepo L. spp. pepo) pollen have been limited to the viability and morphology of the mature pollen grain. The enzyme polygalacturonase (PG) is involved in pollen development and pollination in many species. In this work, we study anther and pollen development of C. pepo and present the cloning and characterisation of a putative PG CpPG1 (Accession no. HQ232488) from pollen cDNA in C. pepo. The predicted protein for CpPG1 has 416 amino acids, with a high homology to other pollen PGs, such as P22 from Oenothera organensis (76%) and PGA3 from Arabidopsis thaliana (73%). CpPG1 belongs to clade C, which comprises PGs expressed in pollen, and presents a 34 amino acid signal peptide for secretion towards the cell wall. DNA‐blot analysis revealed that there are at least another two genes that code for PGs in C. pepo. The spatial and temporal accumulation of CpPG1 was studied by semi‐quantitative‐ and qRT‐PCR. In addition, mRNA was detected only in anthers, pollen and the rudimentary anthers of bisexual flowers (only present in some zucchini cultivars under certain environmental conditions that trigger anther development in the third whorl of female flowers). However, no expression was detected in cotyledons, stem or fruit. Furthermore, CpPG1 mRNA was accumulated throughout anther development, with the highest expression found in mature pollen. Similarly, exo‐PG activity increased from immature anther stages to mature anthers and mature pollen. Overall, these data support the pollen specificity of this gene and suggest an involvement of CpPG1 in pollen development in C. pepo.
The Contextual Presidency: The Negative Shift in Presidential Immigration Rhetoric
Authors: Arthur Damien , Woods Joshua
Published: July 2013

Party platforms from 1993 through 2008 show a positive approach to immigration policy. Presidential rhetoric, however, does not match the tone of the platforms. There are negative frames (illegality, criminality, terrorism, and economic threats) in nearly 50% of immigration speeches. We argue that social context motivates presidents to talk about immigration negatively. This analysis provides insight into rhetoric as responsive to context rather than a mechanism of power. We coded each speech on immigration from Presidents Bill Clinton, George W. Bush, and Barack Obama, and found statistically significant results that show that immigration rhetoric is more negative when certain social conditions are present.
Congressional Power over Executive Branch Policy Making: Limitations on Bureaucratic Regulations, 1989‐2009
Authors: Macdonald Jason A.
Published: July 2013

Research on American political institutions correctly emphasizes the ascendency of presidential power over the last century. Nevertheless, Congress possesses tools to influence how the executive branch shapes public policy. I examine how the use of limitation riders in appropriations laws allows Congress to affect the substance of bureaucratic decisions when Congress otherwise would not have much traction with the bureaucracy: under divided government. In examining the history of limitation riders that forbade the issuance of bureaucratic regulations from 1989 to 2009, I find support for this perspective. The findings suggest that, although Congress may be at a disadvantage in shaping law and policy relative to the president in many cases, its constitutionally protected spending authority continues to promote its ability to influence the executive branch.
The Law: In Service to Power: Legal Scholars as Executive Branch Lawyers in the Obama Administration
Authors: Edelson Chris
Published: July 2013

Harold Koh, David Barron, and Martin Lederman, all legal scholars with a record of emphasizing limits on presidential power, changed their views when they became executive branch lawyers in the Obama administration. Koh found a way to justify President Barack Obama's unilateral use of force in Libya, while Barron and Lederman provided justification for the targeted killing, without judicial hearing, of U.S. citizens identified by the executive branch as senior operational terrorist leaders. This article considers whether these changed approaches can be justified by the scholars' changed roles.
Intelligible Realism about Consciousness: A Response to Nagel's Paradox
Authors: Eilan Naomi
Published: July 2013

Is the location of consciousness in the objectively represented world intelligible? The paper examines the grounds for Nagel's negative answer, which can be presented as a response to the following paradox. (1) We are realists about consciousness. (2) Realism about a domain of reference requires commitment to the possibility of an objective, perspective‐free conception of it. (3) The phenomenal character of an experience can only be captured by means of perspectival concepts. According to Nagel, we can have either realism about consciousness or the link between realism and objectivity. He opts for the former, where this leads to the postulation of an essentially perspectivally reality inhabited by consciousness. I argue, contra Nagel, that questions about the intelligibility of locating consciousness in the objectively representable world should be asked relative the kinds of objectivity provided for by our spatial thought. Not only does this formally dissolve the paradox, as such thought allows for essential reliance on perspectival concepts; but it also shows how we do in fact make sense of the objective location of consciousness, in virtue of the link between spatial thought and something Strawson calls our ‘commonsense realism’ about physical objects, which ascribes ‘phenomenally‐laden’ properties to such objects.
Effect of cutting frequency on above‐ and belowground biomass production of Rumex alpinus, R. crispus, R. obtusifolius and the Rumex hybrid (R. patienta × R. tianschanicus) in the seeding year
Authors: Hujerová R , Pavlů V , Hejcman M , Pavlů L , Gaisler J
Published: July 2013

Rumex species are important weeds in grasslands and on arable land. The Rumex hybrid (R. patienta × R. tianschanicus; cv. OK‐2, Uteusha) has been planted as a forage and energy crop since 2001 in the Czech Republic, but its ecological requirements and its potential to become a new weedy species have never been investigated. In 2010 and 2011, we performed a pot experiment to investigate the effect of none, one and two cuts per year on biomass production of Rumex OK‐2 and common broad‐leaved Rumex species (Rumex obtusifolius, R. crispus and R. alpinus). The higher cutting frequency can reduce the belowground biomass, but no effect on the aboveground biomass was detected. Flowering in the seeding year was recorded in only 50% of R. obtusifolius plants. Non‐flowering R. obtusifolius plants produced significantly more belowground biomass than flowering plants under no cutting or one cut treatments. The growth response of Rumex OK‐2 to different cutting treatments was very similar to R. crispus. These similarities indicate the weed potential of the hybrid to become a troublesome weedy species, similar to R. crispus.
Pore Network Modelling of Surface Heterogeneity in Brine-Filled Porous Media for Carbon Sequestration
Authors: Ellis J. S. , Bazylak A.
Published: July 2013

Trapping of carbon in deep underground brine-filled reservoirs is a promising approach for the reduction of atmospheric greenhouse gas emissions. However, estimation of the amount of carbon dioxide (CO2) that can be captured in a reservoir remains a challenge. One difficulty lies in the estimation of local capillary pressure effects that arise from mineral surface heterogeneity inherent in underground geological formations. As a preliminary step to address this issue, we present a series of pore network modeling (PNM) simulations of two-phase immiscible flow in 3D structured porous media with contact angle heterogeneity. We present saturation patterns for networks with homogeneous and heterogeneous wettability under typical reservoir conditions, taking into account varying contact angles for CO2 on mica and quartz at supercritical conditions. At lower flow rates, our preliminary results showed higher saturations for the heterogeneous networks than for the homogeneous ones. To characterize the fingering patterns, we have introduced R as the ratio of filled throats to the total network saturation. Based on this measure, the heterogeneous networks demonstrated thicker fingering patterns than the homogeneous networks. These preliminary results highlight the importance of micro-scale surface heterogeneity for the modeling of carbon storage processes.
Uncertainty Analysis for Dimensioning Solar Photovoltaic Arrays
Authors: Cho Heejin , Fumo Nelson
Published: July 2013

As the world population increases, so does their demand for energy. The demand of energy is mainly in the form of electricity with an origin primarily from fossil fuels. Since solar photovoltaic technology has the ability to convert solar energy directly into electricity, this technology has become one of the most popular alternatives at all scales for substitution of technology that uses fossil fuels. However, a limiting factor for the massive use solar photovoltaic technology is economics. A key component in the overall strategy to overcome the economic limitation of solar photovoltaic technology is the system size optimization at the design stage. At the design stage, data related to the solar energy availability, energy demand, and equipment performance is used to determine the size of the equipment while being able to satisfy the targeted peak energy demand. In general, a common engineering safety factor is used to ensure the system to meet the energy demand during its life cycle operation. The sizing procedure of solar photovoltaic systems can be further improved to be more reliable and economical when the uncertainty in the design process is considered. This paper presents a framework to perform an uncertainty analysis that can lead to improve sizing process for solar photovoltaic arrays. Through results from the application of the proposed approach, a reliable interval for the size of the photovoltaic array is found that can lead to more accurate and economic design compared to the use of common engineering safety factors.
MicroCT Investigations and Pore Network Reconstructions of Limestone and Carbonate-Based Rocks for Deep Geologic Carbon Sequestration
Authors: Freire-Gormaly M. , MacLean H. , Bazylak A.
Published: July 2013

In this paper, we characterized the microstructure of Indiana Limestone rock samples using X-ray micro-computed tomography (microCT) measurements. Our preliminary results include the porosity, and three-dimensional pore reconstructions for each sample. The resulting porosity values are consistent with experimental permeability tests.
Predicting Hydrodynamic and Heat Transfer Effects of Sparger Geometry and Placement Within a Column Photobioreactor Using Computational Fluid Dynamics
Authors: Bari Ghazi S. , Gent Stephen P. , Suess Taylor N. , Anderson Gary A.
Published: July 2013

This project investigates the effects of sparger geometry and placement on bubble and fluid flow patterns and convective heat transfer within a column photobioreactor (PBR) using Computational Fluid Dynamics (CFD). Experimental and computational studies have been completed that focused on the hydrodynamics and heat transfer within a rectangular column photobioreactor (34.29 cm long × 15.25 cm wide × 34.29 cm tall) with a single sparger located at the center of its base (33.02 cm × 1.27 cm) running lengthwise. This study extends previous work by investigating the flow patterns and heat transfer effects due to full bottom sparger or porous sparger. The gas bubbles and the water-based media within the photobioreactor are modeled using the Lagrangian-Eulerian approach. A low Reynolds k-Epsilon turbulence model is used to predict near-wall flow patterns. A flat surface photobioreactor is used to achieve sufficient light penetration into the system. The main interaction forces between the bubbles and the media, including drag forces, added mass forces, and lift forces are considered. The overarching goal of this research is to produce biofuels and bioproducts through the improved design of column PBRs used for microalgae production. An important factor in designing photobioreactors is the appropriate selection of sparger geometry and placement. The sparger governs the bubble size distribution and gas holdup. These factors in turn influence flow pattern, effective interfacial area, rates of mass transfer, heat transfer, and mixing. It is hypothesized that increasing the sparger width will improve uniformity of bubble distribution as well as mixing. Despite its importance, optimizing the sparger geometry and placement in PBRs for microalgae production is still largely not understood. In this study, the simulation’s results are presented for various spargers, which can be helpful in designing appropriate sparger geometry and proper placement for increased microalgae production.
Impact of Thermal Storage Option for CHP Systems on the Optimal Prime Mover Size and the Need for Additional Heat Production
Authors: Smith Amanda D. , Mago Pedro J.
Published: July 2013

Combined heat and power (CHP) or cogeneration systems provide both electricity and useful heat to a building. CHP systems can result in lower operational cost, primary energy consumption (PEC), and carbon dioxide emissions when compared to the standard alternative of purchasing electricity from the grid and supplying heat from a boiler. However, the potential for these benefits is closely linked to the relationship between the ratio of power to heat supplied by the CHP system and the ratio of power to heat demanded by the building. Therefore, the benefits of the CHP system also vary with the size of the prime mover.

In the model presented in this paper, the CHP system is base-loaded, providing a constant power-to-heat ratio. The power-to-heat ratio demanded by the building depends on the location and the needs of the building, which vary throughout the day and throughout the year. At times when the CHP system does not provide the electricity needed by the building, electricity is purchased from the grid, and when the CHP system does not provide the heat needed by the building, heat is generated with a supplemental boiler. Thermal storage is an option to address the building’s load variation by storing excess heat when the building needs less heat than the heat produced by the CHP system, which can then be used later when the building needs more heat than the heat produced by the CHP system.

The potential for a CHP system with thermal storage to reduce cost, PEC, and emissions is investigated, and compared with both a CHP system without thermal storage and with the standard reference case. This proposed model is evaluated for three different commercial building types in three different U.S. climate zones. The size of the power generation unit (PGU) is varied and the effect of the correspondingly smaller or larger base load on the cost, PEC, and emissions savings is analyzed. The most beneficial PGU size for a CHP system with the thermal storage option is compared with the most beneficial PGU size without the thermal storage option. The need for a supplemental boiler to provide additional heat is also examined in each case with the thermal storage option.
Design, Construction, and Testing of a Small Scale Solar Chimney for Nomadic Herdsmen
Authors: Chappell Ryan D. , Congdon Michael J. , French Jesse J.
Published: July 2013

The basic solar chimney concept remains largely unchanged since being proposed nearly a century ago. The air inside a collector heats up, and becomes less dense and begins rising toward the center of the collector as the covering is sloped upward towards a centrally located chimney. Heat and air flow increases as it moves toward the chimney. When a turbine is placed in this chimney, electricity can be generated from the air flow.

Using previously published research [1] on small scale solar chimneys, the authors designed and fabricated a small scale solar chimney. Performance variables were optimized to achieve peak performance and theoretical electrical output. The solar chimney was designed to achieve low material cost, and minimal maintenance effort without the use of heavy machinery.

The solar chimney designed by the authors was constructed and tested for implementation in remote regions where land space is practically unrestricted and electrical power is desired for lighting and communication. The project team conducted an assessment of one likely location for this solar chimney in Northern Mongolia during the summer of 2011. There are nomadic people groups who do not have electrical power but have vast amounts of land at their disposal. The solar chimney is a potential source of electricity for these people groups, as it was also designed to be transportable, lightweight, and inexpensive.
An Unexpected Sustainable Energy Solution
Authors: Keller Michael F.
Published: July 2013

A recently patented hybrid technology may prove to be an energy game-changer. This innovative integrated combined cycle uses two fuels and a large gas (combustion) turbine in tandem with a small, efficient helium nuclear reactor to cleanly produce electrical power.

The hybrid approach to energy sustainability combines the strengths of individual energy assets to yield an optimal solution to meet the planet’s needs. This integration is more effective than the sum of the individual technologies by themselves. The hybrid is able to efficiently use all of fuel resources available in the US in a single power plant.

The hybrid-nuclear family of technologies is a fail-safe, environmentally friendly and evolutionary new direction for nuclear power and energy production.
Enhanced Gas-Side Heat Transfer in Rectangular Micro-Honeycombs
Authors: Krishnan Shankar , Leith Steve , Hendricks Terry
Published: July 2013

Gas and air-side heat transfer is ubiquitous throughout many technological sectors, including HVAC (heating, ventilating, and air conditioning) systems, thermo-electric power generators and coolers, renewable energy, electronics and vehicle cooling, and forced-draft cooling in the petrochemical and power industries. The poor thermal conductivity and low heat capacity of air causes air-side heat transfer to typically dominate heat transfer resistance even with the use of extended area structures. In this paper, we report design, analysis, cost modeling, fabrication, and performance characterization of micro-honeycombs for gas-side heat transfer augmentation in thermoelectric (TE) cooling and power systems. Semi-empirical model aided by experimental validation was undertaken to characterize fluid flow and heat transfer parameters. We explored a variety of polygonal shapes to optimize the duct shape for air-side heat transfer enhancement. Predictions using rectangular micro-honeycomb heat exchangers, among other polygonal shapes, suggest that these classes of geometries are able to provide augmented heat transfer performance in high-temperature energy recovery streams and low-temperature cooling streams. Based on insight gained from theoretical models, rectangular micro-honeycomb heat exchangers that can deliver high performance were fabricated and tested. High- and low-cost manufacturing prototype designs with different thermal performance expectations were fabricated to explore the cost-performance design domain. Simple metrics were developed to correlate heat transfer performance with heat exchanger cost and weight and define optimum design points. The merits of the proposed air-side heat transfer augmentation approach are also discussed within the context of relevant thermoelectric power and cooling systems.
Modeling of a High-Temperature Latent Heat Thermal Storage Module for Brayton Cycle Applications
Authors: Gehring Brian , Miller Fletcher
Published: July 2013

Concentrating solar power (CSP) plants with thermal energy storage offer several advantages to plants without storage. Thermal energy storage (TES) allows CSP plants to produce power for longer periods of time each day, making them produce energy more like traditional, fossil fuel power plants. TES also gives the ability to time shift production of energy to times of peak demand, allowing the plant to sell the energy when prices are highest. A CSP plant with storage can increase turbine performance and reach higher levels of efficiency by load leveling production and can remain productive through cloud transients.

Power tower CSP plants are capable of producing extremely high temperatures, as they have the ability to oversize their solar field and achieve a greater concentration ratio. Studies have been conducted on variable working fluids, leading to higher working temperatures. This theoretically allows power towers to use more efficient, higher temperature cycles including the recuperated air Brayton cycle, although none currently exist on a commercial scale. This research focuses on developing a model of a high temperature TES system for use with an air Brayton cycle for a power tower CSP plant.

In this research we model one module of a latent heat TES system designed to meet the thermal needs of a recuperated Brayton engine of 4.6 MWe capacity for six hours. A metal alloy, aluminum-silicide (AlSi), is considered as the phase change medium. The storage tank is approximately 161 m3, or a cylinder with a 5 m diameter that is 8 m tall filled with AlSi with several air pipes throughout the volume. We model the volume around a single pipe in a 2-D cylindrical coordinate system, for a module size of 0.2 m in diameter and 8 m long. The advantages of using AlSi alloys is that they have variable melting temperatures depending on the relative concentration of the two metals, from 577 C for the eutectic composition of 12.6% silicon to 1411 C for 100% silicon. This attribute is taken advantage of by the TES model as the composition of the AlSi alloy will vary axially. This will allow a cascaded type storage system within one tank and with one material. The use of FLUENT to model this problem is first validated by several analytical solutions including Neumann’s exact solution for a one-dimensional Cartesian geometry and the Quasi-Steady Approximation in a 1-D cylindrical geometry. The model developed will establish charge/discharge times for the storage system, round-trip efficiency of the system, ability of the system to meet the demand of the Brayton cycle, and the validity of using off-eutectic metal alloys in a cascade as a latent heat TES medium.
Energy Demand Projections in the 21st Century for Coastal California
Authors: Sequera Pedro , Molina Yanelly , Gonzalez Jorge E. , Bornstein Robert
Published: July 2013

Previous studies conducted by Lebassi et al. (2010) and Sequera et al. (2011) have showed a strong correlation between summer temperature and electricity demand per capita trends for the past four decades for California. Decreasing summer temperature trends in low elevation coastal California sites between 1970–2010 resulted in decreasing electricity demand for the same locations. On the other hand, increasing temperature trends in high-elevation and inland California sites for the same period showed increasing electricity demand during summers. As a consequence of an increased gradient of the concurrent sea breeze potential for the same period, the authors suggested that this increased in sea breeze was responsible for the observed coastal cooling, attributing the seabreeze increase to a counter effect of global warming. The authors also reported increasing temperatures during winter throughout California for the same period, resulting in decreasing natural gas consumption. This work extends this analysis by determining spatial and temporal trends in residential electricity and natural gas consumption using 1990 to 2009 data from the California Energy Commission. Results show yearly electricity consumption per person is lower for coastal counties than inland counties. In contrast, yearly natural gas consumption per capita is decreasing for both coastal and inland counties. Additional work includes the examination of future summer axysymmetric warming and winter homogenous warming as well as their implications on energy demands into the 21st century. Results from 16 downscaled Global Circulation Models for 2 green-house gas emissions scenarios are used to forecast future average temperatures. These projections are correlated with electricity consumption during the summer and natural gas consumption during the winter. Statistical analysis of these results is provided in order to quantify uncertainty on these forecasts.
Design and Development of a Hybrid Photovoltaic-Thermal/PVT System
Authors: Tabatabaian Mehrzad , Tivy Wolf , Bibby Chris
Published: July 2013

A Photovoltaic/PV cell converts solar radiation to electrical power. In order to have practical power output from these cells they are framed into modules. A typical module provides about 160–200 Wp. The electrical efficiency of the module decreases from its typical value of 19% by about 0.4–0.5% per degree K/°C. In order to increase the electrical efficiency of a PV system it is possible to cool the modules down by augmenting compact heat exchangers with a working fluid (e.g., air). The extracted heat can have several applications and through cooling the PV modules we can increase the efficiency of the system by about 30–40%, combined (i.e., heat and power). Two design concepts are presented and supported by CFD models. Prototypes of these systems are fabricated and installed and experimental investigations of their performances are currently in progress.
Shaping Our Future With Sustainable Energy: A Direction From Young Engineers
Authors: Feldhoff Jan Fabian , Hofmann Carina , Hübner Stefan , Kammesheidt Jan Oliver , Kilbane Martin , Bachmann Kulik Julie , Pilli Siva , Schubert Franco , Tsutsui Waterloo , Tung Charlene
Published: July 2013

It is broadly accepted that current energy systems should become more sustainable in both a global and local context. However, setting common goals and shared objectives and determining the appropriate means by which to get there is the subject of heavy debate. Therefore, the American Society of Mechanical Engineers (ASME) and the German Association of Engineers (VDI) initiated a joint project aimed at providing a young engineers’ perspective to the global energy conversation. The young engineer project teams set a common goal of assembling a completely sustainable energy system for the U.S. and Germany by 2050. This includes not only the electricity market, but the overall energy system. Based on the current global energy paradigm, a completely sustainable energy system seems very ambitious. However, multiple analyses show that this path is possible and would in the medium to long run not only be desirable, but also competitive in the market. This future ‘energy puzzle’ consists of many important pieces, and the overall picture must be shaped by an overarching strategy of sustainability. Besides the many detailed pieces, four main critical issues must be addressed by engineers, politicians and everybody else alike. These challenges are:

i) Rational use of energy:

This uncomfortable topic is rather unappealing to communicate, but is a key issue to reduce energy demand and to meet the potentials of renewable energy carriers.

ii) Balancing of electricity demand and generation:

This is a challenge to the electricity markets and infrastructures that are currently designed for base-load, mainly fossil power plants. The overall mix of renewable energy generation, storage technologies, grid infrastructure, and power electronics will decide how efficient and reliable a future energy system will be.

iii) Cost efficiency and competitiveness:

It is a prerequisite for industrialized countries to stay competitive and to establish RE in the market. Developing economic technologies while at the same time establishing a strong RE market is the secret of success.

iv) Acceptance of the system and its consequences:

The best energy strategy cannot be realized without broad public acceptance for it. Therefore, the understanding of the energy technologies and an objective discussion must be promoted — without old fashioned emotionalizing of certain risks.

The paper will present details on the four mentioned aspects, compare the situations between the U.S. and Germany, and propose solutions for appropriate political frame conditions to achieve a sustainable energy system.
Variable Speed Direct Drive Wind Controller for a Rim Driven Wind Turbine
Authors: Hubbard Chase , Hovsapian Rob , Kosaraju Srinivas
Published: July 2013

Multi-blade shaft driven wind turbines depend greatly on the angle of attack as an important factor that the control system monitors such that a maximum amount of aerodynamic force is seen by the rotor blades. This is one significant difference when controlling a Rim Driven Wind Turbine (RDWT). The controller for a RDWT is required to simply point the tower such that it is facing the wind for maximum power generation. This is achieved by incorporating a Variable Speed Direct Drive (VSDD) wind operation control system to control the power production and safe operation of the RDWT. Another consideration for the control system is its integration with the generator. Since the power generation is rim driven, thus operating at a higher variable speed.

With information related to the wind turbine’s diameter and the wind speed at any given time it can be calculated how much power can be potentially generated. This can then be in turn relayed to the generator from the wind turbine controller. This information can be relayed using controller-controller communication (such as an analog voltage signal or protocol based communication such as MODBUS RTU or TCP/IP) representing the power coefficient from Betz’ Law.

A feasibly controllable system implements a signal from the overall wind turbine controller that in turn supplies the generator with how much power is available in the system to maximize power generation for a broad range of traditionally unrealizable wind conditions (3 m/s to 30 m/s). Rim Driven Wind Turbines represent an evolution in fundamental design of how the wind can be harnessed for power.

This paper will discuss the VSDD’s unique design and aspects of maintaining controllability thorough out the overall system operation.
A New Heat Engine and its Applications in Concentrating Solar Power (CSP)
Authors: Cao Yiding
Published: July 2013

This paper introduces a new heat engine using a gas, such as air or nitrogen, as the working fluid that extracts thermal energy from a heat source as the energy input. The heat engine is to mimic the performance of an air-standard Otto cycle. This is achieved by drastically increasing the time duration of heat acquisition from the heat source in conjunction with the timing of the heat acquisition and a large heat transfer surface area. Performance simulations show that the new heat engine can potentially attain a thermal efficiency above 50% and a power output above 100 kW under open-cycle operation. Additionally, it could drastically reduce engine costs and operate in open cycles, effectively removing the difficulties of dry cooling requirement. The new heat engine may find extensive applications in renewable energy industries, such as concentrating solar power and geothermal energy power. Furthermore, the heat engine may be employed to recover energy from exhaust streams of internal combustion engines, gas turbine engines, and various industrial processes. It may also work as a thermal-to-mechanical conversion system in a nuclear power plant, and function as an external combustion engine in which the heat source is the combustion gas from an external combustion chamber.
Solar Panel Orientation and Modeling Based on Hourly Clearness Index
Authors: Naraghi Mohammad H. , Etienne Gregory
Published: July 2013

Published hourly solar irradiance data are used to calculate the hourly clearness indices for three municipalities (Los Angles, Orlando and New York City). The clearness index method is then used to model the hourly total solar irradiance (summation of beam, diffuse and ground reflected) on an arbitrarily oriented surface. The orientations of solar panel for maximum annual solar irradiance for these locations are determined. It is shown that in some cases the southward solar panels do not yield maximum annual solar irradiance. Further, it is shown that using the hourly clearness index results in solar irradiance distribution that is not symmetric with respect to the solar noon.
An Open Source Licensed Vertical Axis Wind Turbine for Rural Electrification and Sustainability
Authors: Bassett Kyle , Fleischmann Ino
Published: July 2013

This paper documents the iterative design and development of six operational vertical axis wind turbine prototypes tailor built for rural electrification projects in Central America. All prototypes have been based on the unique lift type blade system consisting of sailcloth material which allows for the turbine to operate with variable blade pitch and profile camber. The latest prototype is presented along with a detailed discussion of fundamental design aspects such as the sail blades, frame tower, alternator, and transmission systems. The VosREC headquarters for research, development and testing is located in a remote, rural, and non-electrified village in Nicaragua. This location provides researchers with the unique opportunity to experience and observe first-hand how renewable energy technologies can be applied to improve quality of life for people living without connection to national electricity grids. Aspects and benefits of the “open source hardware” approach are presented along with a discussion on implementation models, “bottom-up”, empowerment and self-organization.
Analysis of a Latent Thermocline Energy Storage System for Concentrating Solar Power Plants
Authors: Nithyanandam Karthik , Pitchumani Ranga , Mathur Anoop
Published: July 2013

The primary purpose of a thermal energy storage system in a concentrating solar power (CSP) plant is to extend the operation of plant at times when energy from the sun is not adequate by dispatching its stored energy. Storing sun’s energy in the form of latent thermal energy of a phase change material (PCM) is desirable due to its high energy storage density which translates to less amount of salt required for a given storage capacity. The objective of this paper is to analyze the dynamic behavior of a packed bed encapsulated PCM energy storage subjected to partial charging and discharging cycles, and constraints on charge and discharge temperatures as encountered in a CSP plant operation. A transient, numerical analysis of a molten salt, single tank latent thermocline energy storage system (LTES) is performed for repeated charging and discharging cycles to investigate its dynamic response. The influence of the design configuration and operating parameters on the dynamic storage and delivery performance of the system is analyzed to identify configurations that lead to higher utilization. This study provides important guidelines for designing a storage tank with encapsulated PCM for a CSP plant operation.
Optimization Under Uncertainty: A Case Study of a Solar Absorption Cooling and Heating System for a Medium-Sized Office Building in Atlanta
Authors: Hang Yin , Qu Ming , Zhao Fu
Published: July 2013

Solar absorption cooling and heating (SACH) systems currently still stay at development and demonstration stage due to the nature of the complex system. It is critical for practitioners and engineers to have a correct and complete performance analyses and evaluation for SACH systems with respects of energy, economics, and environment. Optimization is necessarily involved to find the optimal system design by considering these three aspects. However, many assumptions made in the optimization are sensitive to the energy, economic, and environmental variations, and thus the optimization results will be affected. Therefore, the sensitivity and uncertainty analysis is important and necessary to make optimization robust.

This paper uses a case study to explore the influence of the uncertainties on the SACH system optimization results. The case is a SACH system for a medium size office building in Atlanta. The one parameter at a time (OAT) sensitivity analysis method was applied firstly to determine the most sensitive inputs. Monte Carlo statistical method was utilized to generate the data sets for uncertainty analysis. The optimization problem under uncertainty was then formulated and solved. Due to the uncertainty associated with system inputs, the optimization solutions were found with certain types of the distributions. In addition, the scenario analysis on electricity price does not show large sensitivity to the objectives.
Promoting the Development of Concentrating Solar Power in the Middle East and North Africa Regions: Policy and Regulatory Implications
Authors: Gboney William K.
Published: July 2013

It is estimated that within the next 40 years, solar thermal power plants would be capable of supplying more than half of the electricity needs of EUMENA. While solar irradiance differs widely in Europe due to seasonal variations, in the MENA region, there is abundant and continuous solar irradiance. This make the MENA region suitable for establishing CSP plants and exporting the electricity generated to Europe. This has driven many institutions and agencies, including the World Bank and the Desertec Foundation, to propose various schemes to promote the use of CSP systems in the MENA region.

The objective of this paper is to examine the existing policy and regulatory frameworks in the MENA countries, identify any barriers and make recommendations on how to surmount these barriers, to increase the scale and scope of utilizing CSPs and other renewable energy technologies (RETs) in the region. The paper concludes by making a number of policy and regulatory recommendations to support utilization of solar thermal energy resource within the MENA region.
Parametric Investigation of the Melting and Solidification Process in an Encapsulated Spherical Container
Authors: Ramos Archibold Antonio , Rahman Muhammad M. , Goswami D. Yogi , Stefanakos Elias L.
Published: July 2013

A comprehensive parametric investigation on the fluid flow and heat transfer in a Latent-heat based energy storage/release system is explored for the axisymmetric melting and solidification process inside an encapsulated spherical container of 10, 20, 30 and 40mm in diameter. A numerical solution is developed using the finite-volume method and the enthalpy-porosity technique to solve Navier–Stokes and energy equations for natural convection coupled to a solid-liquid phase change. The study focused on Phase Change Materials (PCMs) with a melting temperature lying in the practical range of operation of concentrated solar thermal power generation (573.15K to 673.15K). Numerical calculations are performed in order to compute the evolution of the melting front and the velocity and temperature fields for different Grashof, Stefan and Fourier numbers. Also the effect of different metal coating materials subjected to a uniform wall temperature from 5K to 11K above the mean melting temperature of the PCM is presented. Simulation results show that a recirculating vortex is formed between the top region of the solid phase and the inner wall of the capsule that causes a more intense melting process in the upper part of the solid phase compared to the bottom region. The location of the eye of the recirculation pattern is observed to be dependent on the Grashof number and moves toward the unmelted portion of the PCM as natural convection is intensified.