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Open System (open + system)
Selected AbstractsGeothermal energy systems for major projects , design and construction / . Geothermieanlagen bei Großprojekten , Planung und UmsetzungGEOMECHANICS AND TUNNELLING, Issue 5 2010Dipl.-Ing. Geothermal energy - Geothermie Abstract The application of geothermal energy has increased in the last couple of years in order to provide the heating or cooling demands of major projects. Open systems using groundwater directly can be used for geothermal energy extraction as well as closed systems with absorber pipes installed in underground structures. An accurate design, which considers the requirements of the energy consumer in particular but also the subsoiland groundwater conditions, the foundation concept and the building structure, as well as project-specific technical, legal and economic conditions, is required for economically efficient application. Diligent supervision is necessary during the construction stage to avoid any damage to absorber pipes, which could result in loss of performance. Zur Deckung des Heiz- oder Kühlbedarfs bei Großprojekten wird in den letzten Jahren vermehrt auf eine Erdwärmenutzung gesetzt. Dabei kommen sowohl offene Systeme wie eine direkte Grundwassernutzung als auch geschlossene Systeme mit Absorberleitungen in erdberührten Bauteilen zur Anwendung. Für eine wirtschaftliche Umsetzung bedarf es zunächst einer sorgfältigen Planung, wobei insbesondere die Anforderungen des Nutzers, die Untergrund- und Grundwasserverhältnisse, das Gründungskonzept einschließlich der Gebäudestruktur sowie projektspezifische technische, rechtliche und wirtschaftliche Randbedingungen zu berücksichtigen sind. In der Bauphase ist für eine plangemäße Umsetzung mit besonderer Sorgfalt vorzugehen, um Beschädigungen der Absorberleitungen und somit Leistungsminderungen zu vermeiden. [source] Creep of saturated materials as a chemically enhanced rate-dependent damage processINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 14 2007Liang Bo Hu Abstract Material behaviour that exhibits characteristics of creep induced by a spontaneous mineral dissolution enhanced by material damage is studied. It is believed that the characteristic rates of the chemical processes involved determine the time-rate dependence of the resulting strain. A basic model of a combined chemo-plastic softening and chemically enhanced deviatoric strain hardening for saturated geomaterials is presented. Chemical softening is postulated to occur as a consequence of the net mass removal resulting from dissolution and precipitation of specific minerals occurring at the damage-generated inter-phase interfaces. Closed and open systems are discussed. In the former case, deformation at constant stress results entirely from a local compensation mechanism between the chemical softening and strain hardening. The classical three stages of creep are interpreted in terms of mechanisms of dissolution and precipitation, as well as the variation in the reaction surface areas involved in the mass exchange. In an open system, the above local mechanism is enhanced by the removal of mass via diffusion of species affecting the mass balance. Such a system is addressed via a boundary value problem as shown in an example. Copyright © 2007 John Wiley & Sons, Ltd. [source] Discrete thermodynamics of chemical equilibria and classical limit in thermodynamic simulationISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2007Boris Zilbergleyt This article sets forth comprehensive basic concepts of the discrete thermodynamics of chemical equilibrium as balance between internal and external thermodynamic forces. Conditions of chemical equilibrium in the open chemical system are obtained in the form of a logistic map, containing only one new parameter that defines the chemical system's resistance to external impact and its deviation from thermodynamic equilibrium. Solutions to the basic map are bifurcation diagrams that have quite traditional shape but the diagram areas feature specific meanings for chemical systems and constitute the system's domain of states. The article is focused on two such areas: the area of "true" thermodynamic equilibrium and the area of open chemical equilibrium. The border between them represents the classical limit, a transition point between the classical and newly formulated equilibrium conditions. This limit also separates regions of the system ideality, typical for isolated classical systems, and non-ideality due to the limitations imposed on the open system from outside. Numerical examples illustrating the difference between results of classical and discrete thermodynamic simulation methods are presented. The article offers an analytical formula to find the classical limit, compares analytical results with these obtained by simulation, and shows the classical limit dependence upon the chemical reaction stoichiometry and robustness. [source] Reaction localization and softening of texturally hardened mylonites in a reactivated fault zone, central ArgentinaJOURNAL OF METAMORPHIC GEOLOGY, Issue 6 2005S. J. WHITMEYER Abstract The Tres Arboles ductile fault zone in the Eastern Sierras Pampeanas, central Argentina, experienced multiple ductile deformation and faulting events that involved a variety of textural and reaction hardening and softening processes. Much of the fault zone is characterized by a (D2) ultramylonite, composed of fine-grained biotite + plagioclase, that lacks a well-defined preferred orientation. The D2 fabric consists of a strong network of intergrown and interlocking grains that show little textural evidence for dislocation or dissolution creep. These ultramylonites contain gneissic rock fragments and porphyroclasts of plagioclase, sillimanite and garnet inherited from the gneissic and migmatitic protolith (D1) of the hangingwall. The assemblage of garnet + sillimanite + biotite suggests that D1-related fabrics developed under upper amphibolite facies conditions, and the persistence of biotite + garnet + sillimanite + plagioclase suggests that the ultramylonite of D2 developed under middle amphibolite facies conditions. Greenschist facies, mylonitic shear bands (D3) locally overprint D2 ultramylonites. Fine-grained folia of muscovite + chlorite ± biotite truncate earlier biotite + plagioclase textures, and coarser-grained muscovite partially replaces relic sillimanite grains. Anorthite content of shear band (D3) plagioclase is c. An30, distinct from D1 and D2 plagioclase (c. An35). The anorthite content of D3 plagioclase is consistent with a pervasive grain boundary fluid that facilitated partial replacement of plagioclase by muscovite. Biotite is partially replaced by muscovite and/or chlorite, particularly in areas of inferred high strain. Quartz precipitated in porphyroclast pressure shadows and ribbons that help define the mylonitic fabric. All D3 reactions require the introduction of H+ and/or H2O, indicating an open system, and typically result in a volume decrease. Syntectonic D3 muscovite + quartz + chlorite preferentially grew in an orientation favourable for strain localization, which produced a strong textural softening. Strain localization occurred only where reactions progressed with the infiltration of aqueous fluids, on a scale of hundreds of micrometre. Local fracturing and microseismicity may have induced reactivation of the fault zone and the initial introduction of fluids. However, the predominant greenschist facies deformation (D3) along discrete shear bands was primarily a consequence of the localization of replacement reactions in a partially open system. [source] Optimization of a gastrointestinal model applicable to the evaluation of bioaccessibility in fish feedsJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 7 2009Mariam Hamdan Abstract BACKGROUND: Although several types of in vitro digestibility assays have been applied to nutritional evaluation of feeds for aquatic organisms, all of them are based on the use of closed reactors and do not simulate the gastric phase of the digestion. Our objective was to evaluate the suitability of a gastrointestinal model based on the use of a digestion cell provided by a semi-permeable reaction chamber, which allows continuous removal of digestion products as they are produced. We tested the effects of some factors, like the inclusion of a gastric phase, reaction temperature or bile salts on the hydrolysis of feed proteins by fish enzymes. RESULTS: We found that the most suitable operational conditions to simulate the digestion process must include a short acid pre-digestion as well as the use of bile salts in the reaction mixture. Acid pre-digestion resulted in a significant increase in the liberation of amino acids which represented more than twice that measured when using a single phase. The addition of two bile salts (45 µmol L,1 sodium taurocholate + chenodesoxycolate) resulted in almost a threefold increase in the hydrolysis of feed protein. The use of the described open system also allows the evaluation of carbohydrate hydrolysis as well as determination of residual undigested matter, in a similar manner to that carried out in ruminants with the DAISY system. CONCLUSION: Results suggest the system can be a very suitable model for evaluation of bioaccessibility in fish feeds. Copyright © 2009 Society of Chemical Industry [source] Learning and organizational effectiveness: A systems perspectivePERFORMANCE IMPROVEMENT, Issue 1 2009Nicholas Andreadis The challenge for leaders today is to create and develop the capability of their organization. Leaders must perceive and manage their organization as a dynamic, open system where learning is the core competence underlying innovation, growth, and sustainability. Creating a culture of learning is the first work of leadership. This article presents a practical framework in which to consider organizational effectiveness, emphasizing the critical role of systems thinking and learning theory in organizational development. [source] The potential efficiency of irrigation management and propargyl bromide in controlling three soil pests: Tylenchulus semipenetrans, Fusarium oxysporum and Echinochloa crus-galliPEST MANAGEMENT SCIENCE (FORMERLY: PESTICIDE SCIENCE), Issue 8 2005Suzanne E Allaire Abstract Propargyl bromide (3-bromopropyne, 3BP) is a potential alternative for methyl bromide. Little information is available about its efficiency in controlling pests. The purpose of this paper is to estimate the 3BP dose required for killing three pests and to compare the efficiency of water management approaches to that of fumigation. The pests, Fusarium oxysporum Schlecht (fungus), Echinochloa crus-galli (L) Beauv (grass) and Tylenchulus semipenetrans Cobb (nematode) were exposed to different 3BP concentrations in a sandy loam at 30 °C in a closed system. The lethal dose for killing 90% of the population (LD90) was calculated from the total applied mass, and varied from 0.3 µg g,1 soil for the nematode, 3 µg g,1 for the grass, and 9 µg g,1 for the fungus. The concentration,time index for killing 90% of the population (CT90) was 11 µg g,1 h for the nematode, 112 µg g,1 h for the grass and 345 µg g,1 h for the fungus. 3BP seems as efficient as other fumigant alternatives in controlling these pests. Using an open system, it was shown that the volume of soil in which the pests were controlled varied for different irrigation managements. Even 96 h after fumigation (with a concentration 10 times higher than would potentially be applied in the field), more than 20% of the soil volume had not reached the fungus and grass CT90 of the non-irrigated soil. The soil underneath the furrow and the bed reached CT90 only slowly in all irrigated treatments even though techniques for increasing efficiency were used (tarping, surface sealing with water and high application rate). Copyright © 2005 Society of Chemical Industry [source] Influence of nitrogen source and concentration on nitrogen isotopic discrimination in two barley genotypes (Hordeum vulgare L.)PLANT CELL & ENVIRONMENT, Issue 9 2003K. J. KOLB ABSTRACT The occurrence of nitrogen isotope discrimination with absorption and assimilation of nitrate (NO3,) and ammonium (NH4+) was investigated using two genotypes of barley, Hordeum vulgare L. cv. Steptoe and Az12 : Az70, the latter of which lacks the characterized nitrate reductase isozymes. Plants were grown under two situations: a closed system with limited nitrogen or an open system with unlimited nitrogen, to elucidate the conditions and processes that influence discrimination. There was no discrimination observed for Az12 : Az70 when supplied with limited nitrogen. Discrimination was observed for Steptoe seedlings at high external NO3, concentrations, but not with low NO3, when assimilation is probably rapid and complete. The same pattern was observed for Steptoe when NH4+ was supplied; indicating that for both nitrogen forms discrimination is dependent upon the presence of the assimilatory enzyme and the external concentration. The implications of this study are that both internal (assimilatory enzyme distribution) and external (source concentration) factors may have a larger impact on tissue , 15N than the form of nitrogen utilized. This suggests that tissue , 15N may not always be a reliable indicator of a plant's integrated nitrogen nutrition. [source] Atmospheric CO2 concentration does not directly affect leaf respiration in bean or poplarPLANT CELL & ENVIRONMENT, Issue 11 2001S. Jahnke Abstract It is a matter of debate if there is a direct (short-term) effect of elevated atmospheric CO2 concentration (Ca) on plant respiration in the dark. When Ca doubles, some authors found no (or only minor) changes in dark respiration, whereas most studies suggest a respiratory inhibition of 15,20%. The present study shows that the measurement artefacts , particularly leaks between leaf chamber gaskets and leaf surface, CO2 memory and leakage effects of gas exchange systems as well as the water vapour (,water dilution') effect on DCO2 measurement caused by transpiration , may result in larger errors than generally discussed. A gas exchange system that was used in three different ways , as a closed system in which Ca increased continuously from 200 to 4200 mmol (CO2) mol -1 (air) due to respiration of the enclosed leaf; as an intermittently closed system that was repeatedly closed and opened during Ca periods of either 350 or 2000 mmol mol -1, and as an open system in which Ca varied between 350 and 2000 mmol mol -1, is described. In control experiments (with an empty leaf chamber), the respective system characteristics were evaluated carefully. When all relevant system parameters were taken into account, no effects of short-term changes in CO2 on dark CO2 efflux of bean and poplar leaves were found, even when Ca increased to 4200 mmol mol -1. It is concluded that the leaf respiration of bean and poplar is not directly inhibited by elevated atmospheric CO2. [source] A comprehensive kinetic model of laccase-catalyzed oxidation of aqueous phenolBIOTECHNOLOGY PROGRESS, Issue 3 2009Selvia Kurniawati Abstract A comprehensive model was developed to describe the kinetics of the laccase-catalyzed oxidation of phenol that incorporates enzyme kinetics, enzyme inactivation, variable reaction stoichiometry between substrate and oxygen, and oxygen mass-transfer. The model was calibrated and validated against data obtained from experiments conducted in an open system, which allowed oxygen to transfer from air to the reacting mixture and phenol conversion to approach completion. Inactivation of laccase was observed over the course of the reaction and was found to be dependent on the rate of substrate transformation. A single kinetic expression was sufficient to describe laccase inactivation arising from interaction with reacting species over time. Excellent agreement was found between model predictions of phenol and oxygen concentrations and experimental data over time for a wide range of initial substrate concentrations and enzyme activities. © 2009 American Institute of Chemical Engineers Biotechnol. Prog., 2009 [source] ChemInform Abstract: A Simplified and Efficient Bromine-Facilitated SF4 -Preparation Method.CHEMINFORM, Issue 35 2010Rolf Winter Abstract SF4 is synthesized with 70,96% yield by reaction of elemental S, KF, and Br2 either under autogeneous pressure at ambient temperature (steel bomb, several days) or by heating at 70,86 °C (open system, 8 h). [source] Dispersal frequency affects local biomass production by controlling local diversityECOLOGY LETTERS, Issue 6 2006Birte Matthiessen Abstract Dispersal is a major factor regulating the number of coexisting species, but the relationship between species diversity and ecosystem processes has mainly been analysed for communities closed to dispersal. We experimentally investigated how initial local diversity and dispersal frequency affect local diversity and biomass production in open benthic microalgal metacommunities. Final local species richness and local biomass production were strongly influenced by dispersal frequency but not by initial local diversity. Both final local richness and final local biomass showed a hump-shaped pattern with increasing dispersal frequency, with a maximum at intermediate dispersal frequencies. Consequently, final local biomass increased linearly with increasing final richness. We conclude that the general relationship between richness and ecosystem functioning remains valid in open systems, but the maintenance of ecosystem processes significantly depends on the effects of dispersal on species richness and local interactions. [source] Transepidermal water loss reflects permeability barrier status: validation in human and rodent in vivo and ex vivo modelsEXPERIMENTAL DERMATOLOGY, Issue 7 2006Joachim W. Fluhr Abstract:, Permeability barrier function is measured with instruments that assess transepidermal water loss (TEWL), either with closed- or open-loop systems. Yet, the validity of TEWL as a measure of barrier status has been questioned recently. Hence, we tested the validity of this measure by comparing TEWL across a wide range of perturbations, with a variety of methods, and in a variety of models. TEWL rates with two closed-chamber systems (VapoMeter and H4300) and one closed-loop system (MEECO) under different experimental in vivo conditions were compared with data from four open-loop instruments, i.e. TM 210, TM 300, DermaLab and EP 1. The instruments were compared in vivo both in humans and hairless mice skin subjected to different degrees of acute barrier disruption. The values obtained with bioengineering systems were correlated with absolute water loss rates, determined gravimetrically. Measurements with both closed and open systems correlated not only with each other, but each method detected different degrees of barrier dysfunction. Although all instruments differentiated among gradations in TEWL in the mid-range of barrier disruption in vivo, differences in very low and very high levels of disruption were less accurately measured with the H4300 and DermaLab systems. Nevertheless, a high Pearson correlation coefficient (r) was calculated for data from all instruments vs. gravimetrically assessed TEWL. Together, these results verify the utility of TEWL as a measure of permeability barrier status. Moreover, all tested instruments are reliable tools for the assessment of variations in permeability barrier function. [source] Theory and numerics of geometrically non-linear open system mechanicsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 11 2003E. Kuhl Abstract The present contribution aims at deriving a general theoretical and numerical framework for open system thermodynamics. The balance equations for open systems differ from the classical balance equations by additional terms arising from possible local changes in mass. In contrast to existing formulations, these changes not only originate from additional mass sources or sinks but also from a possible in- or outflux of matter. Constitutive equations for the mass source and the mass flux are discussed for the particular model problem of bone remodelling in hard tissue mechanics. Particular emphasis is dedicated to the spatial discretization of the coupled system of the balance of mass and momentum. To this end we suggest a geometrically non-linear monolithic finite element based solution technique introducing the density and the deformation map as primary unknowns. It is supplemented by the consistent linearization of the governing equations. The resulting algorithm is validated qualitatively for classical examples from structural mechanics as well as for biomechanical applications with particular focus on the functional adaption of bones. It turns out that, owing to the additional incorporation of the mass flux, the proposed model is able to simulate size effects typically encountered in microstructural materials such as open-pored cellular solids, e.g. bones. Copyright © 2003 John Wiley & Sons, Ltd. [source] Fundamentals of exergy analysis, entropy generation minimization, and the generation of flow architectureINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 7 2002Adrian Bejan Abstract This paper outlines the fundamentals of the methods of exergy analysis and entropy generation minimization (or thermodynamic optimization,the minimization of exergy destruction). The paper begins with a review of the concept of irreversibility, entropy generation, or exergy destruction. Examples illustrate the accounting for exergy flows and accumulation in closed systems, open systems, heat transfer processes, and power and refrigeration plants. The proportionality between exergy destruction and entropy generation sends the designer in search of improved thermodynamic performance subject to finite-size constraints and specified environmental conditions. Examples are drawn from energy storage systems for sensible heat and latent heat, solar energy, and the generation of maximum power in a power plant model with finite heat transfer surface inventory. It is shown that the physical structure (geometric configuration, topology) of the system springs out of the process of global thermodynamic optimization subject to global constraints. This principle generates structure not only in engineering but also in physics and biology (constructal theory). Copyright © 2002 John Wiley & Sons, Ltd. [source] Sexual reproduction of scleractinian corals in public aquariums: current status and future perspectivesINTERNATIONAL ZOO YEARBOOK, Issue 1 2007D. PETERSEN A multiple-choice questionnaire was distributed, mainly via the list servers of the EUAC (European Union of Aquarium Curators) Coral ASP (Animal Sustainability Program) and AquaticInfo, to evaluate the potential of today's aquariums for the captive breeding of scleractinian corals. Sixteen (including the temperate coral Astroides calycularis) of, in total, 24 species (nine families) were recorded as showing reproductive behaviour that could establish an F1 generation. Broadcast spawners (13 species) reproduced mainly in open systems under natural light conditions (in all cases natural moonlight exposure), whereas brooders (11 species) showed less sensitivity towards certain environmental factors known to trigger reproduction in field populations (here moonlight and temperature fluctuations). Except for a few recruits of Galaxea fascicularis and Echinopora lamellosa maintained in a 750 000 litre system, recruits of broadcast spawners could be exclusively obtained by manipulating fertilization and settlement. Brooding corals established generally less than 100 recruits if settlement was not enhanced experimentally. When reproduction was manipulated, it enhanced reproductive success, in most cases to above 100 recruits. We assume that more species, especially brooders, might reproduce in public aquariums without being noticed by the staff owing to the lack of recruitment and of experimental design (larval collection). This study illustrates the great potential for public aquariums to reproduce corals sexually. However, more investigation is necessary to optimize reproductive success and possibly to broaden the spectrum of species reproduced in public aquariums. [source] TV-Anytime Phase 1 and MPEG-7JOURNAL OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE AND TECHNOLOGY, Issue 9 2007Jean-Pierre Evain Personal video recorders have the capability to change the media delivery industry fundamentally, and in this context, many believe the real international age of personal digital recorders (PDRs) will arrive with the use of "open" systems. The world reached an important milestone with the publication of the TV-Anytime Phase 1 specifications for unidirectional broadcast and metadata services over bidirectional networks. TV-Anytime is a worldwide prestandardization body; this article gives an overview of the main features of TV-Anytime's metadata specification and its relationship to MPEG-7 and provides insight into ways two organizations concerned with standards work together. Phase 2 has since been completed and TV-Anytime has been adopted by various international standards organizations dealing with telecommunications and is now in the implementation phase. [source] Critical Evaluation of How the Rosgen Classification and Associated "Natural Channel Design" Methods Fail to Integrate and Quantify Fluvial Processes and Channel Response,JOURNAL OF THE AMERICAN WATER RESOURCES ASSOCIATION, Issue 5 2007A. Simon Abstract:, Over the past 10 years the Rosgen classification system and its associated methods of "natural channel design" have become synonymous to some with the term "stream restoration" and the science of fluvial geomorphology. Since the mid 1990s, this classification approach has become widely adopted by governmental agencies, particularly those funding restoration projects. The purposes of this article are to present a critical review, highlight inconsistencies and identify technical problems of Rosgen's "natural channel design" approach to stream restoration. This paper's primary thesis is that alluvial streams are open systems that adjust to altered inputs of energy and materials, and that a form-based system largely ignores this critical component. Problems with the use of the classification are encountered with identifying bankfull dimensions, particularly in incising channels and with the mixing of bed and bank sediment into a single population. Its use for engineering design and restoration may be flawed by ignoring some processes governed by force and resistance, and the imbalance between sediment supply and transporting power in unstable systems. An example of how C5 channels composed of different bank sediments adjust differently and to different equilibrium morphologies in response to an identical disturbance is shown. This contradicts the fundamental underpinning of "natural channel design" and the "reference-reach approach." The Rosgen classification is probably best applied as a communication tool to describe channel form but, in combination with "natural channel design" techniques, are not diagnostic of how to mitigate channel instability or predict equilibrium morphologies. For this, physically based, mechanistic approaches that rely on quantifying the driving and resisting forces that control active processes and ultimate channel morphology are better suited as the physics of erosion, transport, and deposition are the same regardless of the hydro-physiographic province or stream type because of the uniformity of physical laws. [source] Entanglement and parametric dynamics in quantum optics with interacting polaritonsPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2008S. Portolan Abstract We report on a microscopic investigation of the polariton parametric emission in the presence of coherent and incoherent interaction processes by means of a full quantum description based on a nonequilibrium quantum Langevin approach for open systems applied to interacting-electron complexes described within the dynamics controlled truncation scheme. It provides an easy recipe to calculate multi-time correlation functions which are key-quantities in quantum optics. In particular we report on calculations of polariton intensities (i.e. single time correlators) and spectra (i.e. two times correlators). We apply our scheme to a two-pumps set-up in microcavity recently proposed showing a quantitative analysis of the quantum correlation properties of the emitted photons. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Democratisation and corruption in MongoliaPUBLIC ADMINISTRATION & DEVELOPMENT, Issue 3 2007Verena Fritz Abstract More democratic and open systems of government are generally assumed to contain corruption. Subsequent to the end of the communist system in 1990, Mongolia has established a democratic regime, and has been assessed as being relatively well governed. However, more recently, corruption has been worsening, despite the continuation of a democratic regime. This article inquires into the drivers of corruption and into the reasons for why accountability has not been more effective despite a democratic form of government. The availability of three major forms of rents,foreign aid, privatisation and natural resource extraction,is discussed as important drivers. The recent mining boom appears to have reinforced weaknesses in Mongolia's system of accountability. Underlying weaknesses include certain communist legacies, especially of intransparent government and of a ,dependent' judicial system, and substantially increased inequality as a result of transition. Copyright © 2007 John Wiley & Sons, Ltd. [source] Combination theory and equilibrium evaporationTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 574 2001M. R. Raupach Abstract This paper is an analysis of equilibrium evaporation and its role in the energy balance of a terrestrial surface, as described by combination theory. Three themes are covered: first, a brief historical review identifies multiple definitions of the concept of equilibrium evaporation. Second, these are formalized by developing the basic principles of combination theory with minimum approximation. Several measures are utilized to do this: linearization is avoided, radiative and storage coupling are incorporated systematically, and actual and linearized saturation deficits are distinguished. The formalism is used to analyse several algebraically defined states and limits for the surface energy balance. Third, the thermodynamic foundation of equilibrium evaporation is analysed by studying surface-atmosphere feedbacks in arbitrary closed and open evaporating systems. It is shown that under steady energy supply any closed evaporating system evolves towards a quasi-steady state in which the Bowen ratio takes the equilibrium value 1/,v, where ,v is the ratio of the latent- and sensible-heat contents of saturated air with temperature, evaluated at the volume-averaged temperature in the closed system. This applies whether the system is well-mixed or imperfectly mixed, and whatever the internal distribution of surface fluxes and surface and aerodynamic resistances. In contrast, open systems cannot reach such an equilibrium. This evolutionary definition of equilibrium evaporation differs from an alternative algebraic definition, the fully decoupled limit. The differences between the two definitions are identified, and the evolutionary definition is shown to be more fundamental. Thus, the correct temperature for evaluating , in determining equilibrium evaporation is the volume-averaged temperature in a closed region, which in the case of a convective boundary layer is well approximated by the mixed-layer temperature. [source] | ||||||||||||||||||||||