# Presentation: 534410

## EMERGY & ENERGY SYSTEMS

**Session 1 **
**Short Course for ECO Interns, EPA and Partners**

**Notes:**
This tutorial provides an overview of concepts and methods important for understanding and completing several kinds of emergy evaluations, and is specifically focused on completing regional evaluations of both natural and human systems.  It is impossible to teach all the concepts of emergy, energy and systems ecology in ten short lessons.  Some of this material you already know, although you may not have considered it in the context we will be using.  In fact, this course will present only a small subset of these theoretical principles and applications, focusing on those points we feel are essential to understanding and completing state evaluations for use by EPA in quantifying the connection between society, economics and the environment.
These sessions follow a short course outline provided by Dr. H.T. Odum ,t he father of emergy.  I was a student of Odum’s and am currently a research scientistat USEPA/ORD/NHEERL/AED.  This work has been peer reviewed.

## Topics Introduced

- Energy/ecology/systems
- Energy language systems diagrams
- Fundamental emergy concepts
- Emergy evaluations
- Emergy and economics
- Evaluating tangibles
- Evaluating information

- Ratios and interpretations
- Scale and boundary definition
- Spatial emergy concepts
- Emergy as decision tool
- Comprehensive state and regional evaluations
- State and regional case studies

**Notes:**
These are the topics that will be presented in these 10 units.  In addition, there is a list of suggested outside reading and some practice examples in almost every unit.
Case studies are presented as Adobe PDF files, and templates for completing the data gathering and conversion are provided as EXCEL spreadsheets.  After the first two units, you might want to stop and read a paper by H.T. Odum provided in PDF format at the bottom of the main web page.  Also, a book written by Dr. Odum is available that introduces emergy and provides a deeper understanding of the principles along with more case studies and applications – Environmental Accounting (Odum 1996).

## GOALS

- Diagram a complex system network using energy systems language symbols
- Aggregate diagram to answer a question
- Identify data required for evaluation
- Understand conversion of raw data into kinetic or potential energy amounts
- Understand theory of emergy ratios and how to choose the right one

**Notes:**
When you are through with these 10 units you should be familiar with the set of symbols important to conveying the mathematics and kinds of interactions that exist in both natural and developed systems.  You will be able to use those symbols and at least hand sketch a diagram portraying almost any system you may encounter, whether it is a simple suburban lawn with low diversity or a large city with high occupational diversity and lots of inflowing money and information.
You will understand what we really mean when we aggregate a complex “spaghetti” diagram into one with just a few components and pathways.  You will be able to apply this to your own “kitchen sink” diagrams to answer a relevant question.
You will see that, once you have put a lot of thought into a system diagram and its appropriate boundaries, the data you need to evaluate the energy inherent in that system will fall right out of the process.  Of course, finding that data may not be that easy, but we will point you in some good directions there as well.
You will begin to understand the theory and assumptions behind converting raw data into data useful for an emergy evaluation, relying on the laws of physics, chemistry and thermodynamics.  And knowing all of this, you will have developed a little sophistication in selecting the right emergy ratio, both to convert energy data into a common numeric value, but also to compare results from different parts of your own work and the work of others throughout the world.

## Energy and Ecology

- Hierarchy and concentration
- Natural patterns
- Thermodynamic Laws
- Measurement: heat, work
- Flows and forces
- Available, free, dispersed energy
- Limiting factors and interactions
- Maximum power principle

**Goals for this unit**

**Notes:**
In this first lesson, we will be reviewing some basic terms and principles associated with energy use, flow and storage, and its part in systems ecology – things like the Laws of Thermodynamics and basic physics.  Because this is an environmental organization, we assume a certain level of ecological background information as we quickly work through this lesson.  However, we want to make sure we are all using the same definitions before we move into the harder material, beginning with the hierarchy of energy concentration evident in all systems, both natural and societal. 

## HierarchyFood Chains and Pyramid Charts 

**Hierarchy****Food Chains and Pyramid Charts**** **

**Notes:**
As ecology has become entrenched in American grade school curriculums, almost everyone is now familiar and comfortable with the idea of food chains and  food webs and to a lesser degree, pyramid charts.  We  have at least a qualitative understanding that a whole lot of plants are necessary to support a smaller population of animals and that lots of small animals are needed to feed a few larger animals, creating a process of concentration based on food energy.  Only about 10% of all incoming food is translated into food for the next organism on the chain to use, and so on up to the top.  
 That food is energy is another lesson the current culture knows well.  If you eat more than ~1800 calories a day you will increase your body mass.  If you eat 3500 calories less a week you will lose a pound. If you walk vigorously for an hour you will burn about 250 calories.  These messages bring home the fact that food is energy and that exercise is work that uses energy.
What is a little less ubiquitous is where all the “lost” energy goes to or what purpose it may serve in understanding the networks that surround us.  And although most people understand that the sun is necessary for plants to grow, not everyone has the entrenched understanding that without the sun and two other forms of primary earth energy, nothing on this planet would work.  Oil appears to be the driving force for modern culture, but it too is derived from a process of concentration that began with the sun, some plants and animals and a lot of deep earth heat and work.

## HierarchyFood Chains and Pyramid Charts 

- Carnivores
- Grazers
- Plants
- Sun

- More quantitative perspective

**Notes:**
Translating these food chains into pyramid charts, while removing the flexibility of showing complete networks,  allows a more visually quantitative comparison of the actual amount of energy concentration that is going on as we step up the chain. The sun is not usually shown in pyramid charts, but because it is the largest energy source for all earth processes, and because it is the only energy source which is added to an otherwise closed global system, it is important to account for this energy whenever a hierarchy is proposed.   Each one of these yellow boxes is the amount of energy inherent in the mass or heat flowing from one level in the hierarchy to the next.  The blue boxes represent the amount of energy that is lost in the concentrating process. 
Lost is actually not the best word to describe this energy.  If you didn’t already know this, you will reminded again and again throughout this course, that energy is never lost.  It is lost only to the system being evaluated, moving into another system lower in the hierarchy where it is still capable of doing work or where it will build in storage and be reordered when a pulse of energy arrives from somewhere else.  This is an important concept that we will discuss in more detail later.
These blue boxes also help us keep in mind the total energy that was required to get to the endpoint.  In its simplest of all definitions, the sum of the yellow and blue boxes is the emergy of each component in the pyramid, with the lion having the same total emergy as all of the plants combined.  The important point though is that if you compare the ratio of this blue box energy to the yellow box, you will see that the lion has a much higher ratio. 
Keep this in mind.  It is the basic foundation for beginning to value the work that the environment does in delivering food to our plate or gas to our car.

## HierarchyFood Chains and Pyramid Charts 

- Think left to right

**Notes:**
At this point it might be useful to start combining the concepts of left to right food chains with quantitative pyramids.  Turning the pyramid on its side does not change the  meaning but allows us to transition into viewing a hierarchy of concentration from left to right, similar to conventional x-y axes.

## Hierarchy

**Hierarchy**

- Heat Sink
- Entropy
- Dissipated Energy

- Less available energy
- Concentrated and able to do more work

**Notes:**
I have rearranged this pyramid for a purpose which you will see shortly, and it is not just to keep you on your toes.  Let’s also move away from the food chain example and start talking about other energy hierarchies, using the process that built coal deposits and now allows us to have electricity for our computers and air conditioners for instance. 
At the lower end of the pyramid, or the far left now that we have turned things over, the sun contributed to plant material that died and started decomposing.  With the addition of other energy and time, this peat became different forms of coal, each one successfully harder and providing more concentrated heating or electrical power per gram.
You will see that now each yellow box has a small blue box just underneath it with an arrow and some lines pointing downwards.  All of the energy or material in the box to the left is necessary for transformation into the smaller storage of useful material or energy.  However, this blue box represents how much was lost in heat to the surrounding environment while this transformation happened.  We call this a heat sink and the arrow with lines is a symbol that indicates the second law of thermodynamics.  
We will talk about this more in a few slides, but just think of your refrigerator to get a clearer picture.  Some amount of energy is input to your refrigerator to in effect reduce the temperature of the contents, but not without throwing off heat from the coils below or behind.   This heat is dissipated energy useful for heating the air immediately surrounding the fridge, but not to do much else without adding more energy in the way of heat exchangers or whatnot.  This is the heat sink for the process of refrigeration.
Each of these individual boxes represents the energy lost at each transformation step (you will hear some people call this exergy), but the larger box reminds us of the total amount of energy that was required to get to that point.

## Concentration

- Fertilizer

**Concentration**

- O2,
- H2O

- O2,
- H2O

**Notes:**
We return to the potentially more familiar food chain to make the next points.  One thing that pyramids and food chains do not permit us to see is the other sources of energy and materials that are necessary to keep transforming and concentrating from a form low in the hierarchy to one at the top of the list.  For example, nutrients and carbon are used in reactions fueled by solar energy to build plant structure.  Animals require water and oxygen as fuel to transform the plant carbohydrates, fat and proteins into more complete proteins and fats.
The heat sink from the plant box indicates that for all of the production of leaves and trunks, there is ongoing respiration necessary to keep the system running.  This dissipates energy in the form of heat and gas, not all of which is useful within the system.  Heat sinks from animals are also due to metabolic functions that keep storages from building.
Heat sinks do not include the energy required to capture food or to reproduce since these are expenditures that do work within the system.  These are self- or species- reinforcing pathways used to increase the total amount of energy available for use.  This concept will be talked about in greater depth over the next few sessions, but the fact that these interactions cannot be shown in pyramids and chains is another reason we need to move beyond these methods and towards some that allow evaluation of complex system dynamics.

## Concentration

**Concentration**

- 1000

- 100

- 10

- 1

- 100

- 10

- 1110 (1109)

- Producer

- Consumer

- Force

- Force

- Force

- Consumer

**Notes:**
In almost every figure shown so far, these symbols have been behind the components we have been considering.  In the next session we will talk about these and a few others and the meaning each one of them has, but for now these three major symbols are all you need to remember.  The circle at the left represents a form of energy coming from outside the system boundary.  In our plant to lion example the boundary would be the top of the trees down to the ground surface or the edible portion of the understory and perhaps an area equivalent to the average territory of a small lion.  We obviously have not included everything in this diagram that might be in that territory, but it is obvious that solar power for photosynthesis is outside the boundary, and is a driving force for the system.
The next symbol, bullet shaped, represents producers/autotrophs/photosynthesizers, while the hexagon is used to represent consumers/heterotrophs.   There is a heat sink associated with each component and the numbers on each pathway detail the amount of energy that is passed from each level to the next, as well as the amount dissipated.

## Patterns

**Notes:**
It should be clear by now that natural systems have a hierarchy of concentration as materials and energy are transformed into new materials or energies. This diagram is actually a better representation of the interactions in most systems, with a lot of diffuse energy at the left or lower end of the system, concentrating to the right, but with some feedback control from the larger consumers to the smaller and to the producers.  
Think of each plant or animal as a little processing plant churning out proteins or oxygen.  Now think about how much territory each of these items require to get enough raw materials for the processing.
Territory is a familiar concept to most of us – the amount of space a tomato plant needs in order to produce a large crop or the amount of territory a lion must roam to get enough protein to eat.  It should come as no surprise then that the hierarchy of energy convergence creates a characteristic pattern in nature.  Things low in the hierarchy require less room per individual than items at the top of the chain.
We present this concept of patterns created in the landscape because of energy flows so that you can connect the intangible concept of energy with some tangible phenomena you have seen in your everyday life.  This spatial perspective will help later as we make decisions about how to determine certain renewable energy sources that vary geographically.

## Patterns - point source

**Wells**
**Springs**

**Notes:**
There are other patterns beside population density that are familiar from nature even if you do not know the energy form or process that helped to create that pattern.
Within each hierarchical level, there are adaptive spatial patterns that result from energy delivered to the landscape in different forms. The three energy “shapes” are point sources, line sources, and planar sources.  Most landscapes receive energy from several different sources, but the highest, most concentrated energy will determine the spatial shape taken.  
Point sources, such as desert springs or high concentrations of rare elements or information, create spatial patterns reflecting the energy driving the system. Nearly circular growth of lush vegetative communities occurs in decreasing concentric density around the spring, while clearings and settlements surround the immediate location of extractable resources, with no other settlements or patches in the region. 

## Patterns - line source

- Coast
- Highway
- River

**Notes:**
Line sources, highways and coastlines for instance, create linear patterns of both vegetative zones and development. These energy sources often intersect, creating the light pattern recognizable from space. Extractable resources often occur as line sources, or “seams”, and patterns at the human hierarchy level reflect the linearity of the trade good. 

## Patterns - Planar

- Sun
- Rain

**Notes:**
Planar sources create less distinct landscape features, because by definition these sources are distributed more evenly over large regions. Solar energy and its carrying media, rain and wind, are examples of planar energies. Expanses of grassy plains and deserts are spatial examples of planar energy shapes.

## Patterns – combined sources

- Point and line

**Notes:**
There are, of course, landscapes where no adaptive pattern or hierarchy is discernible. Several properties likely contribute to this. The area may lie somewhere between the distinct hierarchical levels evident at differing scales.  However, receiving equal energy from different source “shapes” also leads to overlapping landscape patterns.  As spatial hierarchies become more complex, with energy convergence at the ecosystem and economic levels creating overlapping hierarchical levels, “noise” might obscure the signatures evident at lower levels of energy or higher scale (lower resolution) of reference, just as highly differing temporal scales create noise in the graphing of pulsing cycles.

## Thermodynamic Laws

- First law of thermodynamics
- Law of Conservation
- The total energy of any system and its surroundings is conserved.
- i.e.Energy is neither created nor destroyed, it changes from one form to another.
- dU = Q - W

**Notes:**
While space and the rest of the universe may operate on a different set of laws, things here on earth appear to follow, at a minimum, two simple rules.  Knowing these rules helps establish a set of conceptual equations which in turn can be used to define more detailed equations that can be used to calculate, or estimate, the energy in any storage or action. 
First and foremost, making accounting infinitely easier, energy is either here or it is there.  It does not go away. Because material is just a form of potential energy, it too is conserved.  It may leave one ecosystem and go to another, but the material that was here when the earth started is still here.  It is true that every day we gain energy from the sun, but everyday energy is reflected back out of the atmosphere, too.

## Thermodynamic Laws

- The Second Law of Thermodynamics
- The entropy change of any system and its surroundings, considered together, resulting from any real process, is positive and approaches a limiting value of zero for any process that approaches irreversibility.
- dS = dQrev/T; S = K*log(N)
- dS = dSsystem + dSsurroundings

**Notes:**
The second law is a little less tangible, but we have tackled it already through our discussion of heat sinks.  Basically for every transformation of energy or material into another kind, some energy is lost from the system.  A system that is 100% efficient will move so slowly as to appear to produce no work at all.  Every system requires this kind of “payment” in order to be productive. 

In classic thermodynamics, entropy is related to changes in temperature (dS = dQrev/T), or energy as heat in other words.  In information theory, entropy is often defined as a function of connections or pathways (S = K*log(N)) – the more the number of possible interactions, the higher the complexity, the higher the entropy.

## Forms of Energy

- light
- chemical
- mechanical
- heat
- electric
- atomic
- sound

**Notes:**
There are many different kinds of energy.

## Theoretical Energy

- _Potential_

- _stored energy of position_
- Gravitational
- PEgrav = m*g*h
- Elastic
- 	PEspring = 1⁄2*k*x2

**Notes:**
Mechanical energy can be broken into two forms: potential and kinetic.
Potential energy is the work that is waiting to happen as soon as motion begins.  A rock on a ledge is filled with potential energy to smash a passing toe if a small amount of energy comes into the system to overcome its inertia.  A spring that is compressed has the energy to open a box or door, once the force  holding it is removed. 
A mountain has a great deal of potential energy and the geologic forces that built this slope differential determine the force with which rivers flow down into valleys.  These basic physical equations relating energy to mass and gravity can be used to determine the potential energy in many different naturally occuring phenomena.

## Theoretical Energy

- _Kinetic_

- KE = 1⁄2*m*v2
- _energy of motion_
- vibrational
- rotational
- translational

**Notes:**
Kinetic energy is the energy being used to keep something in motion.  A river has kinetic energy associated with the volume of water and the velocity at which it is moving.  Waves deliver kinetic energy to beaches and estuaries.  Both these energies do work on moving sediment and nutrient around, mechanically breaking down rocks and plants, and so on.

## Theoretical Energy

- _Gibbs Free_

- dG = dH –d(TS)
- G – G0 = RT ln _f__i_
-                                       f0
- fi,0 = f(molarity of solutions)

**Notes:**
You will often hear the terms free energy and available energy used to evaluate the amount of work a system can do.  With  potential energy, there  is the energy available to do work in a resting object.  In chemical reactions, there is often enough heat generated beyond the combining of atoms to do work in another system.  This is another form of available energy, referred to as free energy and given a mathematical definition by Dr. Gibbs.
In simplest terms this means that the change in free energy is equal to the change in enthalpy minus the changes in temperature and entropy.  Enthalpy is directly related to the amount of heat in a system – you may be familiar with heat capacity values, water having a high heat capacity.  This should feel familiar: from the first law, the change in energy in a system is equal to the change in heat minus the work done.  In this relationship, the available energy left is equal to the total heat less the entropy, or energy no longer useful to the system.
There are hundreds of derivations from this equation depending upon the chemical system being evaluated – ideal gases, pure liquids, ideal solutions, temperature constant, pressure constant (the original definition) and so on.  In the environment, we rarely work with ideal gases or measurements of enthalpy. It turns out that for a changing mixture, such as fresh water flowing into salt, using a version of the relationship that uses the ideal gas equation and fugacity is of greatest use, and you will see a version of this in many emergy evaluations. Don’t dwell on the concept of fugacity.  This can be converted to more easily measured concentration values, and this is the form you will see later as we begin talking about emergy.

## Energy Terms

- Heat
- Temperature
- Work
- W = F(orce) x D(istance) x cos 
- How far does it move
- How hard to get it there

**Notes:**
There are several ways that energy is measured, but heat and work are two classics.  Temperature change is a measure of the amount of energy added or removed from a system, or the amount of energy generated by a chemical reaction.  The amount of force that is required to move something a measurable distance is a measure of mechanical work.

## Energy Terms

- _Power_

- _Rate at which work is done_
- Power = _work_

- time

**Notes:**
Power can be thought of as the intensity of work done.  If a mountain is moved in a few weeks using dynamite or in a few millenia using acid rain and tectonic plate movement, the total amount of work is the same, but because the amount of time required to reach the final reorganization is different, the amount of power is different.

## Energy Terms

- _Units of measure_

- _Joule (J)_ – kg*m2/s2
- _Newton (N) _– kg*m/s2
- _Kilowatt (kW)_ – 1000J/s

**Notes:**
Work – joule
Energy required to move a mass of 1 kg accelerating at a rate of 1 m/s2 a distance of 1 meter

Force - newton Standard International (SI) unit
force required to accelerate a mass of one kilogram at a rate of one meter per second squared - other force-producing effects absent.

Power – remember work/time so J/s

## Energy and Ecology Terms

- Limiting factors
- Interactions
- Stress reactions

**Notes:**
A plant can only produce a finite amount of carbohydrates or protein, regardless of how much sun is available, and that is because other elements or energy are necessary for the photosynthetic and respiratory processes.  These limiting factors can be external – nitrogen or phosphorus, for instance - or internal -  bound in organic storage such as leaves, for example.  The same is true for human systems – all production in our economic systems is tied to the energy from natural resources.  Regardless of how much money is available, only a finite amount of goods can be created.
Limiting factors is one kind of interaction between energies of different kinds.  Other familiar interactions are competition and mutualism.  When resources are scarce, energy is expended on outcompeting other organisms.  When limiting factors have high thresholds, energy is reallocated to specialization, more niches and mutualism.
Stress is an energy effect, and usually a high quality energy.    Some are occasional pulses such as the huge energy from a tornado, while others are more cyclical such as complete water drawdown alternating with two-foot inundation  Stress reactions cause diversion of energy to either reduce or compensate for an environment that is less than ideal.  Using energy to flee rather than to mate is one example.  Plants and animals have numerous physiological reactions to stress that divert energy from one process to another. Those who adapt to maximum use of the energy provided, using it to pull in more sources of energy, are the survivors.. 

## Maximum Power Principle

- Systems prevail that develop designs that maximize the flow of useful energy.
- 	Lotka, 1922

- Autocatalytic feedback

**Notes:**
That brings us to Maximum Power Principle.  An organism that diverts excess energy into building storage that can bring in more energy will outcompete other organisms that do not.  Using this self-generated storage to interact with other limiting agents is called autocatalytic feedback.  This system diagram and process is common to most unit operations in the real world.  Villages that build in areas of high natural energy, at the junction of two rivers or near a naturally deep bay, and that convert this incoming energy into high quality structure such as commercial buildings will begin to attract more investment and soon become a thriving city.  Communities that use excess energy to build diversity can use these different abilities to pull in more energy or to keep energy incoming in times of resource fluctuation, just as you hopefully diversify your portfolios.  This is a common unit model because it is the system that prevails most often.

## Maximum Power Principle

- When energy inputs are low, no feedback or storage develops and energy is dispersed.

- No feedback or storage

**Notes:**
Systems that do not have enough energy available to build storage, or that do not divert energy, are unable to take advantage of additional energy that might be available.  One example of this might be the wealthy heir who spends all of his trust finds on depreciating commodities – cars, entertainment, or clothing.  Without diverting funds to investments or savings, he has no ability to pull more energy in when his original resource dwindles.

## Energy Conversion

- Dimensional analysis

- 1bbl oil x 42 gal x 1.26E5 BTU x 1055 J = 5.6E9 J
-                        bbl            gal                BTU

**Notes:**
Switching gears a little, in order to complete an analysis of energy or emergy we need to be comfortable with the mechanics of conversion calculations.  Raw energy and material data comes in many different units and forms.  Regardless of how the data is presented, there is a way to convert this to Joules or grams.  Methods for converting physical and potential energy will be discussed in a later section when we present some assumptions useful for emergy evaluations of important but elusive energies such as mountains.  A lot of data, however, requires simple conversion using equivalent factors.  To make sure that you are ending up with the appropriate amounts and units, it is useful to set up a dimensional analysis equation and make sure all the right units cancel out.
Here is an equation converting barrels of oil to joules.  To make sure we have correctly converted, we will check that all the units of measure cancel out.  This is called dimensional analysis.

## Dimensional analysis

- 1bbl oil x 42 gal x 1.26E5 BTU x 1055 J = 5.6E9 J
-                        bbl            gal                BTU

- x

- x

**Notes:**
Barrel conversion complete, and so the units are crossed out.  The numbers remain however, in order to complete the calculation..

## Dimensional analysis

- 1bbl oil x 42 gal x 1.26E5 BTU x 1055 J = 5.6E9 J
-                        bbl            gal                BTU

- x

- x

- x

- x

**Notes:**
Liquid quantity converted to potential energy (BTU/gal factor) through use of previously generated heating values.  These exist for most petroleum products.

## Dimensional analysis

- 1bbl oil x 42 gal x 1.26E5 BTU x 1055 J = 5.6E9 J
-                        bbl            gal                BTU

- x

- x

- x

- x

- x

- x

**Notes:**
BTUs converted to joules, and that is where we wanted to end up.

## Energy Conversion

- Practice conversions using dimensional analysis

- 1.2E6 gal water to grams
- Average of 56 KW electricity every hour for one week to J
- 1.3 short ton bituminous coal to J
- 112 bushels cucumbers to J
- 100 lb 10-9-11-5 fertilizer to grams P, grams N and grams K

**Notes:**
Set these conversions up to practice finding conversion factors and getting an accurate end number.

## Check Your Conversions Check mine, too

- 1.20E6 gal H2O x 3785.4 cm3 x 1.00 gram H2O =                        4.54E9 grams H2O
-                           U.S. gal           cm3 H2O
- 56.0 KW x  1 week x 168.0 hours x 3.6E6 J =                                            3.4E10 J
-        hr                         week             KWH
- 1.3 tons x  2000 lb x  13,500 BTU x 1055 J =                                             3.7E10 J
-              short ton    lb bituminous     BTU
- 112 bushels X 55 lb x 454 g x (1-0.964) x (0.24*24 KJ + 0.04*39 KJ + 0.72*17KJ) x 1000J = 1.97E9 J
-                       bushel      lb                                         g                   g                   g             KJ
- 100 lb fertilizer x  454 grams x 0.09g P2O5 x     62 gmoles P            =                    1784 gP
-                                   lb                  g fert.        142 gmoles P2O5
- 100 lb fertilizer x  454 grams x 0.1g N x     =                                                        4540 gN
-                                      lb           g fert.
- 100 lb fertilizer x 454 grams x 0.11g K2O x    78.2 gmoles K            =                  2750 gK
-                                    lb               g fert.        142 gmoles K2O

**Notes:**
Are there any mistakes in these answers?

Did you use different conversion factors anywhere?