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Energy Exchange (energy + exchange)

Distribution by Scientific Domains

Earth and Environmental Science	41%
Chemistry	16%

Selected Abstracts

The pricing of electricity futures: Evidence from the European energy exchange

THE JOURNAL OF FUTURES MARKETS, Issue 4 2007
Sascha Wilkens
This study investigates the pricing of electricity futures at the European Energy Exchange (EEX) over the period 2002 through 2004. To calculate theoretical contract values, the reduced-form models of J. J. Lucia and E. S. Schwartz (2002) are used, and a thorough empirical analysis by means of an out-of-sample test is conducted for both one- and two-factor models, incorporating a constant non-zero price of risk. Although the models are proven to capture all basic spot market characteristics and provide an accurate in-the-sample fit to observed futures prices, the forecasting performance is subject to biases. For instance, it was found that the relative mispricing depends on both the spot price level and the remaining time-to-maturity of the futures contracts. © 2007 Wiley Periodicals, Inc. Jrl Fut Mark 27:387,410, 2007 [source]

Effects of environmental perturbations on abundance of subarctic plants after three, seven and ten years of treatments

ECOGRAPHY, Issue 1 2001
Enrico Graglia
Analyses of changes in vegetation were carried out after three, seven and ten years of fertilizer addition, warming and light attenuation in two subarctic, alpine dwarf shrub heaths. One site was just above the tree line, at ca 450 m a.s.l., and the other at a much colder fell-field at ca 1150 m altitude. The aim was to investigate how the treatments affected the abundance of different species and growth forms over time, including examinations of transient changes. Grasses, which increased in abundance by fertilizer addition, and cryptogams, which, by contrast, decreased by fertilizer addition and warming, were the most sensitive functional groups to the treatments at both sites. Nutrient addition exerted a stronger and more consistent effect than both shading and warming. Warming at the fell-field had slightly greater effect than at the warmer tree line with an increase in deciduous shrubs. The decreased abundance of mosses and lichens to fertilizer addition and/or warming was most likely an indirect treatment effect, caused by competition through increased abundance and overgrowth of grasses. Such changes in species composition are likely to alter decomposition rates and the water and energy exchange at the soil surface. We observed few, if any, transient effects of declining responses during the 10 yr of treatments. Instead, there were many cumulative effects of the treatments for all functional groups and many interactions between time and treatment, suggesting that once a change in community composition is triggered, it will continue with unchanged or accelerated rate for a long period of time. [source]

Brane-bulk energy exchange and cosmological acceleration

FORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 6-7 2004
E. Kiritsis
The consequences for the brane cosmological evolution of energy exchange between the brane and the bulk are analyzed. A rich variety of brane cosmologies is obtained, depending on the precise mechanism of energy transfer, the equation of state of brane-matter and the spatial topology. An accelerating era is generically a feature of the solutions. [source]

A regional climate study of Central America using the MM5 modeling system: results and comparison to observations

INTERNATIONAL JOURNAL OF CLIMATOLOGY, Issue 15 2006
Jose L. Hernandez
Abstract The Mesoscale Modeling system, version 3.6 (MM5) regional modeling system has been applied to Central America and has been evaluated against National Oceanic and Atmospheric Administration/National Climatic Data Center (NOAA/NCDC) daily observations and the Global Precipitation Climatology Project (GPCP) precipitation data. We compare model results and observations for 1997 and evaluate various climate parameters (temperature, wind speed, precipitation and water vapor mixing ratio), emphasizing the differences within the context of the station dependent geographical features and the land use (LU) categories. At 9 of the 16 analyzed stations the modeled temperature, wind speed and vapor mixing ratio are in agreement with observations with average model-observation differences consistently lower than 25%. MM5 has better performance at stations strongly impacted by monsoon systems, regions typified by low topography in coastal areas and areas characterized by evergreen, broad-leaf and shrub land vegetation types. At four stations the model precipitation is about a factor of 3,5 higher than the observations, while the simulated wind is roughly twice what is observed. These stations include two inland stations characterized by croplands close to water bodies; one coastal station in El Salvador adjacent to a mountain-based cropland area and one station at sea-level. This suggests that the model does not adequately represent the influence of topographic features and water bodies close to these stations. In general, the model agrees reasonably well with measurements and therefore provides an acceptable description of regional climate. The simulations in this study use only two seasonal maps of land cover. The main model discrepancies are likely attributable to the actual annual cycle of land,atmosphere vapor and energy exchange that has a temporal scale of days to weeks. These fluxes are impacted by surface moisture availability, albedo and thermal inertia parameters. Copyright © 2006 Royal Meteorological Society. [source]

Adiabatic decoupling of the reaction coordinate

INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 10 2008
J. C. Lorquet
Abstract When the dynamics is constrained by adiabatic invariance, a reactive process can be described as a one-dimensional motion along the reaction coordinate in an effective potential. This simplification is often valid for central potentials and for the curved harmonic valley studied in the reaction path Hamiltonian model. For an ion,molecule reaction, the action integral ,P,, = (1/2,),P,d, is an adiabatic invariant. The Poisson bracket of ,P,,2 with Hamiltonians corresponding to a great variety of long-range electrostatic interactions is found to decrease with the separation coordinate r, faster than the corresponding potential. This indicates that the validity of the adiabatic approximation is not directly related to the shape of the potential energy surface. The leading role played by the translational momentum is accounted for by Jacobi's form of the least action principle. However, although the identification of adiabatic regions by this procedure is limited to a specific range of coordinate configurations, equivalent constraints must persist all along the reaction coordinate and must operate during the entire reaction, as a result of entropy conservation. The study of the translational kinetic energy released on the fragments is particularly appropriate to detect restrictions on energy exchange between the reaction coordinate and the bath of internal degrees of freedom. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source]

Structural complexity and land-surface energy exchange along a gradient from arctic tundra to boreal forest

JOURNAL OF VEGETATION SCIENCE, Issue 3 2004
C. Thompson
Abstract: Question: Current climate changes in the Alaskan Arctic, which are characterized by increases in temperature and length of growing season, could alter vegetation structure, especially through increases in shrub cover or the movement of treeline. These changes in vegetation structure have consequences for the climate system. What is the relationship between structural complexity and partitioning of surface energy along a gradient from tundra through shrub tundra to closed canopy forest? Location: Arctic tundra-boreal forest transition in the Alaskan Arctic. Methods: Along this gradient of increasing canopy complexity, we measured key vegetation characteristics, including community composition, biomass, cover, height, leaf area index and stem area index. We relate these vegetation characteristics to albedo and the partitioning of net radiation into ground, latent, and sensible heating fluxes. Results: Canopy complexity increased along the sequence from tundra to forest due to the addition of new plant functional types. This led to non-linear changes in biomass, cover, and height in the understory. The increased canopy complexity resulted in reduced ground heat fluxes, relatively conserved latent heat fluxes and increased sensible heat fluxes. The localized warming associated with increased sensible heating over more complex canopies may amplify regional warming, causing further vegetation change in the Alaskan Arctic. [source]

Environmental variation, vegetation distribution, carbon dynamics and water/energy exchange at high latitudes

JOURNAL OF VEGETATION SCIENCE, Issue 3 2002
A.D. McGuire
Abstract. The responses of high latitude ecosystems to global change involve complex interactions among environmental variables, vegetation distribution, carbon dynamics, and water and energy exchange. These responses may have important consequences for the earth system. In this study, we evaluated how vegetation distribution, carbon stocks and turnover, and water and energy exchange are related to environmental variation spanned by the network of the IGBP high latitude transects. While the most notable feature of the high latitude transects is that they generally span temperature gradients from southern to northern latitudes, there are substantial differences in temperature among the transects. Also, along each transect temperature co-varies with precipitation and photosynthetically active radiation, which are also variable among the transects. Both climate and disturbance interact to influence latitudinal patterns of vegetation and soil carbon storage among the transects, and vegetation distribution appears to interact with climate to determine exchanges of heat and moisture in high latitudes. Despite limitations imposed by the data we assembled, the analyses in this study have taken an important step toward clarifying the complexity of interactions among environmental variables, vegetation distribution, carbon stocks and turnover, and water and energy exchange in high latitude regions. This study reveals the need to conduct coordinated global change studies in high latitudes to further elucidate how interactions among climate, disturbance, and vegetation distribution influence carbon dynamics and water and energy exchange in high latitudes. [source]

The pricing of electricity futures: Evidence from the European energy exchange

Extension of potential predictability of Indian summer monsoon dry and wet spells in recent decades

THE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 648 2010
J. M. Neena
Abstract An understanding of the limit on potential predictability is crucial for developing appropriate tools for extended-range prediction of active/break spells of the Indian summer monsoon (ISM). The global low-frequency changes in climate modulate the annual cycle of the ISM and can influence the intrinsic predictability limit of the ISM intraseasonal oscillations (ISOs). Using 104-year (1901,2004) long daily rainfall data, the change in potential predictability of active and break spells are estimated by an empirical method. It is found that the potential predictability of both active and break spells have undergone a rapid increase during the recent three decades. The potential predictability of active spells has shown an increase from one week to two weeks while that for break spells increased from two weeks to three weeks. This result is interesting and intriguing in the backdrop of recent finding that the potential predictability of monsoon weather has decreased substantially over the same period compared to earlier decades due to increased potential instability of the atmosphere. The possible role of internal dynamics and external forcing in producing this change has been explored. The changes in energy exchange between the synoptic and ISO scale and the different ISO modes as evidenced by energetics computations in frequency domain also support the increased potential predictability of ISO. Our finding provides optimism for improved and useful extended-range prediction of monsoon active and break spells. Copyright © 2010 Royal Meteorological Society [source]

Gaseous Ion Activation Dynamics: The Role of the Bulk Gas in the Racemization of Chiral Oxonium Ions

CHEMPHYSCHEM, Issue 10 2004
Antonello Filippi Dr.
Abstract The kinetics of the inversion of configuration of a family of chiral oxonium ions, that is, O-protonated 1-aryl-1-methoxyethanes [YMe+], were investigated in two different gaseous media (in CH3X with X=F and X=Cl) at 720 torr of pressure and in the temperature range: 25,140,°C. The activation parameters of the [YMe+] inversion reaction were found to obey two different isokinetic relationships (IKR), depending on the nature and the position of the substituents in the oxonium ions and on the nature of the bulk gas employed. The observation of two IKR for the same family of reactions was related to a switchover in the resonant vibrational energy exchange between the reactants' critical mode, active in the transition state (,), and the discrete vibrational levels , of the bulk gas. In CH3F, this vibrational,vibrational coupling switchover concerns the out-of-plane CF,,,HO bending (the , family) and the H3CF stretching (the , family) modes in the proton-bound [CH3F,YMe+] complex. In CH3Cl, the coupling switchover concerns the out-of-plane CCl,,,HO bending (the , family) and the H3CCl methyl group rocking (the , family) modes in the proton-bound [CH3Cl,YMe+] complex. The [YMe+] activation dynamics also determine the inversion dynamics. The [YMe+]ret,[YMe+]invisomerization for the , family involves the same "thermodynamically most favorable" transition state in both the CH3F and the CH3Cl media, whereas the same process for the , family proceeds through different, dynamically favored transition states. [source]