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Equilibrium Conditions (equilibrium + condition)
Selected AbstractsParticle clusters in gravel-bed rivers: an experimental morphological approach to bed material transport and stability conceptsEARTH SURFACE PROCESSES AND LANDFORMS, Issue 11 2005Lea Wittenberg Abstract Structured gravel river beds clearly exert a major influence on bed stability. Indexing structural stability by field measurements of bed strength neglects the processes operating to entrain and transport bed material in different parts of each structure. This study takes a morphological approach to interpreting the critical processes, using particle tracing to determine the movement of individual cluster particles over a range of flood event magnitudes and durations. The experiment was carried out on the River South Tyne, UK; it uses flow hydrographs measured nearby and also benefits from previous studies of historical development, channel morphology and sediment transport at the same site. More than 30 clusters were monitored over a seven-month period during which clusters occupied 7,16 per cent of the bed. Threshold flows delimiting three apparently contrasting bed sediment process regimes for cluster particles are tentatively set at 100 m3 s,1 and 183 m3 s,1; durations of flow at these levels are critical for cluster development, rather than flow peak values. Wake particles are transported most easily. Flow straightening in the wandering channel planform reduces the stability of clusters, since mechanical strength is markedly reduced by this change of direction. The overall area covered by clusters between significant transport events varies little, implying a dynamic equilibrium condition. Copyright © 2005 John Wiley & Sons, Ltd. [source] Adapting the logical basis of tests for Hardy-Weinberg Equilibrium to the real needs of association studies in human and medical geneticsGENETIC EPIDEMIOLOGY, Issue 7 2009Katrina A. B. Goddard Abstract The standard procedure to assess genetic equilibrium is a ,2 test of goodness-of-fit. As is the case with any statistical procedure of that type, the null hypothesis is that the distribution underlying the data is in agreement with the model. Thus, a significant result indicates incompatibility of the observed data with the model, which is clearly at variance with the aim in the majority of applications: to exclude the existence of gross violations of the equilibrium condition. In current practice, we try to avoid this basic logical difficulty by increasing the significance bound to the P -value (e.g. from 5 to 10%) and inferring compatibility of the data with Hardy Weinberg Equilibrium (HWE) from an insignificant result. Unfortunately, such direct inversion of a statistical testing procedure fails to produce a valid test of the hypothesis of interest, namely, that the data are in sufficiently good agreement with the model under which the P -value is calculated. We present a logically unflawed solution to the problem of establishing (approximate) compatibility of an observed genotype distribution with HWE. The test is available in one- and two-sided versions. For both versions, we provide tools for exact power calculation. We demonstrate the merits of the new approach through comparison with the traditional ,2 goodness-of-fit test in 2×60 genotype distributions from 43 published genetic studies of complex diseases where departure from HWE was noted in either the case or control sample. In addition, we show that the new test is useful for the analysis of genome-wide association studies. Genet. Epidemiol. 33:569,580, 2009. © 2009 Wiley-Liss, Inc. [source] Equal strain consolidation for stone columns reinforced foundationINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 15 2009Kang-He Xie Abstract Column consolidation and deformation are considered by assuming that the quantity of water flowing through the disturbed soil zone into the column is not equal to that flowing out from the column and the difference between them is equal to the volume change of the column. In addition, three patterns of distribution of the horizontal permeability of soil in the disturbed zone are also considered to account for the disturbance effect of columns construction on the surrounding soil. These three patterns include the constant distribution pattern (Pattern I), the linear distribution pattern (Pattern II) and the parabolic distribution pattern (Pattern III). By incorporating the aforementioned characteristics into the analyses, the governing equations containing two variables (i.e. the average excess pore-water pressures within the column and within the entire foundation at any depth) for the consolidation of a composite foundation are derived. The solutions of the governing equations are then obtained using a new initial condition derived from the assumption of equal strain and the equilibrium condition. On the basis of the solutions for excess pore-water pressures, the average degree of consolidation of a composite foundation is obtained and discussed. Finally, a comparison is made of some available solutions. Copyright © 2009 John Wiley & Sons, Ltd. [source] A geometrically and materially non-linear piezoelectric three-dimensional-beam finite element formulation including warping effectsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 5 2008A. Butz Abstract This paper is concerned with a three-dimensional piezoelectric beam formulation and its finite element implementation. The developed model considers geometrically and materially non-linear effects. An eccentric beam formulation is derived based on the Timoshenko kinematics. The kinematic assumptions are extended by three additional warping functions of the cross section. These functions follow from torsion and piezoelectrically induced shear deformations. The presented beam formulation incorporates large displacements and finite rotations and allows the investigation of stability problems. The finite element model has two nodes with nine mechanical and five electrical degrees of freedom. It provides an accurate approximation of the electric potential, which is assumed to be linear in the direction of the beam axis and quadratic within the cross section. The mechanical degrees of freedom are three displacements, three rotations and three scaling factors for the warping functions. The latter are computed in a preprocess by solving a two-dimensional in-plane equilibrium condition with the finite element method. The gained warping patterns are considered within the integration through the cross section of the beam formulation. With respect to material non-linearities, which arise in ferroelectric materials, the scalar Preisach model is embedded in the formulation. This model is a mathematical model for the general description of hysteresis phenomena. Its application to piezoelectric materials leads to a phenomenological model for ferroelectric hysteresis effects. Here, the polarization direction is assumed to be constant, which leads to unidirectional constitutive equations. Some examples demonstrate the capability of the proposed model. Copyright © 2008 John Wiley & Sons, Ltd. [source] Elastoplastic dynamic analysis with hybrid stress elementsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 3 2002J. A. Teixeira de Freitas Abstract The stress model of the hybrid finite element formulation is applied to the solution of dynamic elastoplastic structural problems. The stress field is approximated in the domain of the elements and the displacements on its boundary. The displacement, velocity and acceleration approximations in the domain of the element are implicit, in the sense that they result from a combination of the stress estimate with the time integration procedure that ensures that the equilibrium condition is locally satisfied. The finite elements are subdivided in plastic cells where a gradient dependent model is implemented using a hybrid formulation based on the approximation of the plastic parameter and the plastic radiation fields in the domain and on the boundary of the plastic cells, respectively. Generalized variables associated with orthogonal and naturally hierarchical bases are used. The resulting solving systems are symmetric, sparse, p -adaptive and well suited to parallel processing. The performance of the element is assessed using a representative set of testing problems. Copyright © 2001 John Wiley & Sons, Ltd. [source] An analysis of uncertainty in non-equilibrium and equilibrium geothermobarometryJOURNAL OF METAMORPHIC GEOLOGY, Issue 9 2004J. R. ASHWORTH Abstract In statistically optimised P,T estimation, the contributions to overall uncertainty from different sources are represented by ellipses. One source, for a diffusion-controlled reaction at non-equilibrium, is diffusion modelling of the reaction texture. This modelling is used to estimate ratios, Q, between free-energy differences, ,G, of reactions among mineral end-members, to replace the equilibrium condition ,G = 0. The associated uncertainty is compared with those already inherent in the equilibrium case (from end-member data, activity models and mineral compositions). A compact matrix formulation is introduced for activity coefficients, and their partial derivatives governing error propagation. The non-equilibrium example studied is a corona reaction with the assemblage Grt,Opx,Cpx,Pl,Qtz. Two garnet compositions are used, from opposite sides of the corona. In one of them, affected by post-reaction Fe, Mg exchange with pyroxene, the problem of reconstructing the original composition is overcome by direct use of ratios between chemical-potential differences, given by the diffusion modelling. The number of geothermobarometers in the optimisation is limited by near-degeneracies. Their weightings are affected by strong correlations among Q ratios. Uncertainty from diffusion modelling is not large in comparison with other sources. Overall precision is limited mainly by uncertainties in activity models. Hypothetical equilibrium P,T are also estimated for both garnet compositions. By this approach, departure from equilibrium can be measured, with statistical uncertainties. For the example, the result for difference from equilibrium pressure is 1.2 ± 0.7 kbar. [source] Electrostatic Charge Measurement and Charge Neutralization of Fine Aerosol Particles during the Generation ProcessPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 5 2005Chuen-Jinn Tsai Abstract An aerosol charge analyzer has been constructed to measure the charge distribution of NaCl particles generated in the laboratory. A radioactive electrostatic charge neutralizer utilizing Po-210 was used to neutralize the electrostatic charge of the particles. The atomization technique was used to generate NaCl particles with diameters of 0.2 to 0.8 ,m, while the evaporation and condensation method was adopted to generate particles of 0.01 to 0.2 ,m in diameter. The experimental data demonstrates that the absolute average particle charge depends on the particle diameter, and is higher than that calculated by the Boltzmann charge equilibrium for particles within the range of 0.2 to 0.8 ,m. The charge increases with decreasing NaCl concentration. When these particles are neutralized using the Po-210 neutralizer, it is found that the electrostatic charge reaches the Boltzmann charge equilibrium. For 0.01 to 0.2 ,m NaCl particles generated using the evaporation and condensation method, test results show that the absolute average particle charge is higher than that calculated by the Boltzmann charge equilibrium for particles larger than 0.03 to 0.05 ,m in diameter, while it is lower than that predicted by the Fuchs theory [1], for particles smaller than 0.03 to 0.05 ,m. However, after charge neutralization, particles with diameter above 0.05 ,m reach the Boltzmann charge equilibrium condition, and the charges for particles with diameters of 0.010 to 0.05 ,m, agree well with Fuchs' theory. [source] The effect of transient conditions on an equilibrium permafrost-climate modelPERMAFROST AND PERIGLACIAL PROCESSES, Issue 1 2007Dan Riseborough Abstract Equilibrium permafrost models assume a stationary temperature and snow-cover climate. With a variable or changing climate, short-term energy imbalances between the active layer and permafrost result in transient departures from the equilibrium condition. This study examines the effects of such variability on an equilibrium permafrost-climate model, the temperature at the top of permafrost (TTOP) model. Comparisons between numerical results and temperatures predicted by the TTOP-model suggest that stationary inter-annual variability introduces an error in the top-of-permafrost temperature obtained with the equilibrium model that is higher where permafrost temperature is close to 0°C, although multi-year averaging reduces the error to 0.1°C or less. In the presence of a warming trend, the equilibrium model prediction tracked the changing top-of-permafrost temperature until permafrost temperatures reached 0°C, after which the equilibrium model produced significant errors. Errors up to 1°C were due to the temperature gradient through the developing talik, and depended on the warming rate, and the thickness of the talik. For all warming rates, the error was largest when the permafrost table was about 4,m below the surface, with the error declining as the permafrost table fell. Copyright © 2007 John Wiley & Sons, Ltd. [source] Time-Evolving Self-Organization and Autonomous Structural Adaptation of Cobalt(II),Organic Framework Materials with scu and pts NetsCHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2008Jing-Yun Wu Dr. Going where? The spontaneous, dynamic adjustment of equilibrium condition (KI/CoII ratio) is found to be a key factor in switching the assembly direction of CoII and K4btec (btec=benzene-1,2,4,5-tetracarboxylate). Compound 1 with a rare scu net was generated within the first three days. A few days later a new product,compound 2 with a pts net,autonomously formed. [source] Charge-Shift Bonding,A Class of Electron-Pair Bonds That Emerges from Valence Bond Theory and Is Supported by the Electron Localization Function ApproachCHEMISTRY - A EUROPEAN JOURNAL, Issue 21 2005Sason Shaik Prof. Abstract This paper deals with a central paradigm of chemistry, the electron-pair bond. Valence bond (VB) theory and electron-localization function (ELF) calculations of 21 single bonds demonstrate that along the two classical bond families of covalent and ionic bonds, there exists a class of charge-shift bonds (CS bonds) in which the fluctuation of the electron pair density plays a dominant role. In VB theory, CS bonding manifests by way of a large covalent-ionic resonance energy, RECS, and in ELF by a depleted basin population with large variances (fluctuations). CS bonding is shown to be a fundamental mechanism that is necessary to satisfy the equilibrium condition, namely the virial ratio of the kinetic and potential energy contributions to the bond energy. The paper defines the atomic propensity and territory for CS bonding: Atoms (fragments) that are prone to CS bonding are compact electronegative and/or lone-pair-rich species. As such, the territory of CS bonding transcends considerations of static charge distribution, and involves: a) homopolar bonds of heteroatoms with zero static ionicity, b) heteropolar , and , bonds of the electronegative and/or electron-pair-rich elements among themselves and to other atoms (e.g., the higher metalloids, Si, Ge, Sn, etc), c) all hypercoordinate molecules. Several experimental manifestations of charge-shift bonding are discussed, such as depleted bonding density, the rarity of ionic chemistry of silicon in condensed phases, and the high barriers of halogen-transfer reactions as compared to hydrogen-transfers. [source] Analysis of effects of contracts on the stability of dynamic power marketsEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 1 2009Jia Yan-Bing Abstract Experiences with operations of power markets show that contracts may affect stability of markets. Therefore, it is necessary to consider whether the market with bilateral contracts will lead to a stable equilibrium conditions after the market is exposed to certain kinds of disturbances. In this paper, the dynamic behaviour of power markets is expressed by differential/algebraic equations, and eigenvalue analysis is used to study effects of contracts on stability of the model. Results of the analysis show that suitable relative ratio of contracts can improve the stability of power markets and even make the unstable markets stable. On the other hand, unsuitable relative ratio of contracts may deteriorate the stability of markets. Copyright © 2007 John Wiley & Sons, Ltd. [source] Analytic Determination of Hydrocarbon Transmissivity from Baildown TestsGROUND WATER, Issue 1 2000David Huntley Hydrocarbon baildown tests involve the rapid removal of floating hydrocarbon from an observation or production well, followed by monitoring the rate of recovery of both the oil/air and oil/water interfaces. This test has been used erroneously for several years to calculate the "true thickness" of hydrocarbon in the adjacent formation. More recent analysis of hydrocarbon distribution by Farr et al. (1990), Lenhard and Parker (1990), Huntley et al. (1994), and others have shown that, under vertical equilibrium conditions, there is no thickness exaggeration of hydrocarbon in a monitoring well, though there is a significant volume exaggeration. This body of work can be used to demonstrate that the calculation of a "true hydrocarbon thickness" using a baildown test has no basis in theory. The same body of work, however, also demonstrates that hydrocarbon saturations are typically much less than one, and are often below 0.5. Because the relative permeability decreases as hydrocarbon saturation decreases, the effective conductivity and mobility of the hydrocarbon is much less than that of water, even ignoring the effects of increased viscosity and decreased density. It is important to evaluate this decreased mobility of hydrocarbon due to partial pore saturation, as it has substantial impacts on both risk and remediation. This paper presents two analytic approaches to the analysis of hydrocarbon baildown test results to determine hydrocarbon transmissivity. The first approach is based on a modification of the Bouwer and Rice (1976) analysis of slug withdrawal test data. The second approach is based on a modification of Jacob and Lohman's (1952) constant drawdown,variable discharge aquifer test approach. The first approach can be applied only when the effective water transmissivity across the screened interval to water is much greater than the effective hydrocarbon transmissivity. When this condition is met, the two approaches give effectively identical results. [source] Analytical Model for Removal of a Uniformly Distributed Single-Component NAPL Under Nonequilibrium ConditionsGROUND WATER MONITORING & REMEDIATION, Issue 3 2001H.J.H. Brouwers In this paper a simple analytical model is presented for the one-dimensional transport equation describing the removal of a uniformly distributed, single-component NAPL under nonequilibrium conditions. Both advective and dispersive transport are included in the model. The model describes two distinct stages: a solution for the time the amount of NAPL declines but the length of the NAPL-containing region remains constant, and a solution from the moment the front, behind which all NAPL is depleted, starts to move. The model is valid for both dissolution (i.e., by water) or volatilization (i.e., by air). Dissolution (or volatilization) is considered a firstorder rate process with a constant mass-transfer rate coefficient. As expected, the model approaches the solution for equilibrium conditions if the mass-transfer coefficient tends to infinity. Even though the model is based on some rigorous assumptions, the simplicity of the model makes it useful for obtaining an initial mass-transfer rate coefficient from experimental data, which can be used to estimate the time required to dissolve all NAPL, as shown for two data sets taken from the literature. [source] Mechanical response of a jointed rock beam,numerical study of centrifuge modelsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 8 2007Michael Tsesarsky Abstract In this paper we present a comparison between a set of benchmark centrifuge models of a jointed beam and the predictions of two numerical models: fast Lagrangian analysis of continua (FLAC) and discontinuous deformation analysis (DDA). The primary objective of this paper is a comparison between the measured deformation profiles and thrust evolution to predictions of the numerical methods employed. A secondary objective is an attempt to clarify the issue of compressive arch geometry which is still in controversy among researchers. It is found that both FLAC and DDA result in insufficiently accurate predictions to the measured displacements. The mode of deformation is only partially captured and is dependent on the aspect ratio of the individual blocks which made up the beam. It is shown that the accuracy of the predicted displacements is a function of the assigned interface stiffness. The thrust predicted by both methods is found to be considerably lower than that measured in the model; however, the linear evolution of thrust and equilibrium conditions are correctly captured. The geometry of the compressive arch as predicted by FLAC compares extremely well with the data measured in the physical model. Based on the FLAC analysis it is found that for a beam composed of equidimensional blocks the thickness of the compressive arch varies from 0.8t at the abutment interface to the entire beam thickness (1t) at a distance of a half block width from the abutment face, extending across the interface separating the block and its neighbour, and attains a value of 0.5t at the beam mid span. Copyright © 2006 John Wiley & Sons, Ltd. [source] Evaporation of a model skin lotion with beta-hydroxy acidsINTERNATIONAL JOURNAL OF COSMETIC SCIENCE, Issue 6 2004A. Al Bawab Synopsis Two , -hydroxy acids, malic and salicylic acids were combined with a non-ionic surfactant, a commercial pentaoxyethylene sorbitan mono-oleate and water to form a simple model of a skin lotion and the phase diagrams were determined. One emulsion formulation with relative amounts of the three components similar to those in commercial lotions was used to observe microscopically the changes in the emulsion structure during evaporation. The microscope images were subsequently compared to the information from the phase diagram under equilibrium conditions. The results showed the behavior of the systems of the two acids to be distinctly different; as exemplified by that of a typical formulation with 3% by weight of acid and 5% of surfactant. The malic acid system consisted of vesicles, exclusively formed by the surfactant and water, in an aqueous molecular solution of the acid and the initial evaporation resulted in an increase of the acid concentration in the aqueous solution to reach 35.5%, before solid crystals of the acid solid solution appeared. The salicylic acid formulation, on the other hand, already at the beginning of the determination consisted of water, particles of the acid solid solution and surfactant vesicles. In both cases the remaining deposit after total evaporation was particles of a solid acid solution and liquid surfactant. Résumé Deux acides , -hydroxy malique et salicylique ont été combinés avec un surfactant non ionique, un pentaoxyethylene sorbitan mono-oleate commercial et de l'eau pour former un model simple de lotion pour la peau. Leurs diagrammes de phase ont été déterminés. Une formule d'émulsion avec une quantité relative des trois composantes similaire a celles des lotions commerciales a été utilisée pour observer les changements microscopiques dans la structure de l'émulsion au cours de l,évaporation. Les images du microscope ont été ensuite comparées aux informations des diagrammes de phase dans les conditions d'équilibre. Les résultats ont montré que le comportement des systémes des deux acides est clairement différent, comme le montre l'exemple d'une formulation typique à 3% du poids d'acide et 5% du surfactant. Le système d'acide malique est constitué de vésicules exclusivement formées du surfactant et d'eau, dans une solution aqueuse moléculaire de l'acide, et l'évaporation initiale a eu comme consèquence l'augmentation de la concentration de l'acide en solution aqueuse qui a atteint 35.5% avant l'apparition des cristaux de la solution de l'acide solide. D'autre part la formulation de l'acide salicylique des le début de la détermination fut constituée d'eau, de particules de solution de l'acide solide et des vésicules du surfactant. Dans les deux cas les restes déposés après l'évaporation totale ètaient constitués des particules de la solution solide d'acide et du liquide surfactant. [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] Investigation of Pluronic© F127,Water solutions phase transitions by DSC and dielectric spectroscopyJOURNAL OF APPLIED POLYMER SCIENCE, Issue 2 2009Anna Angela Barba Abstract The water solutions of the block copolymers PEOn -PPOm -PEOn, known as pluronics, show a complex thermal behavior, since they are liquid at low temperature (5°C), and they can give soft gel when heated at body temperature (37°C). These properties are of great interest in biomedical applications. To properly design these applications, a prerequisite is the knowledge of the thermodynamics,how much,and of the kinetics,how fast,with which these transformations take place. In this work, solutions of F127 (the copolymer for which n = 100 and m = 65) were studied by varying the concentration and the temperature and analyzing their behavior when heated under several heating rates. The studies were performed by differential scanning calorimetry (DCS) and dielectric spectroscopy. The investigations carried out under equilibrium conditions allowed us to determine the thermodynamics of the phase transitions, whereas the investigations carried out under varying conditions allowed us to quantify the kinetics of the phase transitions. Empirical models were also proposed to describe both the thermodynamics and the kinetics observed. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 [source] pH, TEMPERATURE AND HYDRATION KINETICS OF FABA BEANS (VICIA FABA L.)JOURNAL OF FOOD PROCESSING AND PRESERVATION, Issue 1 2003NANOR HALADJIAN Soaking kinetics of dry faba beans was studied in the temperature range 20,65C, and at pH 3, 6, 9 and 12 by the method of weight gain until equilibrium conditions were attained. Increasing the soaking temperature from 20 to 35C resulted in a small increase in hydration rate constants as compared to that realized with further increase to 50 and 65C in the investigated range of pH. Soaking at 65C decreased the amount of water absorbed by the beans and the time at which equilibrium was attained. Beans soaked at alkaline pH exhibited higher hydration rates especially when hydration was carried out at , 50C [source] Isotopic climate record in a Holocene stalagmite from Ursilor Cave (Romania)JOURNAL OF QUATERNARY SCIENCE, Issue 4 2002Bogdan Petroniu Onac Abstract The PU-2 stalagmite from Ursilor Cave provides the first dated Romanian isotope record for the Holocene. The overall growth rate of the speleothem was 3.5 cm kyr,1, corresponding to a temporal resolution of 142 y between each isotope analysis. The ,Hendy' tests indicate that isotopic equilibrium conditions occurred during the formation of PU-2, and hence that it is suitable for palaeoclimatic studies. The relationship between ,18O and temperature was found to be positive. This can be interpreted either as rain-out with distance from the west-northwest ocean source of evaporation or shifts in air mass source with changing North Atlantic Oscillation indices. Applying five U,Th thermal ionisation mass spectrometric (TIMS) dates to a 17.5 cm isotope profile (,18O and ,13C) along the stalagmite growth axis enabled a tentative interpretation of the palaeoclimate signal over the past 7.1 kyr. Spikes of depleted isotopic ,18O values are centred near ca. 7, ca. 5.2 and ca. 4 ka, reflecting cool conditions. The record shows two warm intervals between ca. 3.8 and ca. 3.2 ka (the maximum warmth) and from ca. 2 to ca. 1.4 ka, when the ,18O values were less negative than present. The ,Holocene Climate Optimum' spanning the time interval from ca. 6.8 to ca. 4.4 ka is not well expressed in the PU-2 stalagmite. Individual spikes of lighter ,13C are interpreted as indicative of periods of heavy rainfall, at ca. 7, ca. 5.5, and ca. 3.5 ka. The overall trend to lighter ,13C in the PU-2 stalagmite may reflect a gradual decrease in water,rock interaction. The results demonstrate that the effect of North Atlantic oceanic changes extended to the investigated area. Nevertheless, some differences in temporal correlation and intensity of stable isotopic response to these climatic events have been found, but the exact nature of these differences and the underlying mechanism is yet to be determined. Copyright © 2002 John Wiley & Sons, Ltd. [source] Comprehensive Linkage of Defect and Phase Equilibria through Ferroelectric Transition Behavior in BaTiO3 -Based Dielectrics: Part 1.JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2008Defect Energies Under Ambient Air Conditions Defect and phase equilibria have been investigated via the ferroelectric phase transition behavior of pure and equilibrated nonstoichiometric BaTiO3 powder samples. Through fabricating the BaTiO3 materials under highly controlled conditions to preserve the equilibrium conditions with respect to Ba/Ti ratio, annealing temperature (T), and oxygen partial pressure (PO2), systematic variations in the phase transition temperature can be noted with respect to Ba/Ti ratio and T. From the data extracted, we can then determine solubility limits. Equilibrating the defect reactions at the solubility limits provides a direct approach to identify and calculate the defect energetics. The phase transition temperature decreased with increasing concentration of the TiO2 partial-Schottky defects (BaTi1,,O3,2,) and the BaO partial-Schottky defects (Ba1,,TiO3,,), and showed discontinuous changes in the two-phase region. The formation enthalpy and entropy for the partial-Schottky defect reactions was evaluated to be 2.32±0.1 eV and 10.15±0.7 kB for the BaO partial-Schottky defect, and 2.89±0.1 eV and 8.0±1.5 kB for the TiO2 partial-Schottky defects equilibrated under air annealing conditions. [source] Influence of composition and structure of oil-in-water emulsions on retention of aroma compoundsJOURNAL OF THE SCIENCE OF FOOD AND AGRICULTURE, Issue 9 2002Dr Saskia M van Ruth Abstract The influence of the composition and structure of oil-in-water emulsions on aroma retention was examined for 20 volatile compounds. Compositional and structural parameters included the fraction of emulsifier phase, the fraction of lipid phase and the particle size distribution of the dispersed lipid phase in the emulsion. Air/liquid partition coefficients of dimethyl sulphide, 1-propanol, diacetyl, 2-butanone, ethyl acetate, 1-butanol, 2-pentanol, propyl acetate, 3-methyl-1-butanol, ethyl butyrate, hexanal, butyl acetate, 1-hexanol, 2-heptanone, heptanal, ,-pinene, 2-octanone, octanal, 2-nonanol and 2-decanone were determined by static headspace gas chromatography. The hydrophobicity of the compounds determined the influence of the compositional and structural parameters of the emulsions on air/liquid partitioning. Increase of the emulsifier fraction increased the retention of mainly hydrophilic aroma compounds and decreased the retention of hydrophobic compounds. Higher lipid levels led to increased retention of hydrophobic compounds and release of hydrophilic compounds. Emulsions with larger particles showed increased aroma retention, which was independent of the lipid fraction and the polarity of the aroma compounds. The data demonstrated a profound effect of both composition and structure of oil-in-water emulsions on the air/liquid partitioning of the 20 aroma compounds under equilibrium conditions. © 2002 Society of Chemical Industry [source] Sediment dynamics and pollutant mobility in rivers: An interdisciplinary approachLAKES & RESERVOIRS: RESEARCH AND MANAGEMENT, Issue 1 2004Ulrich Förstner Abstract Characteristic dynamic features of sediment-related processes in rivers include dramatic effects of stormwater events on particle transport, rapid and far-reaching effects of sulphide oxidation during resuspension, and biological accumulation and potential release of toxic chemicals. Pollutant mobility is the net result of the stabilizing and mobilizing effects in both hydraulic and chemical fields. In practice, emphasis has to be given to fine-grained sediments and suspended matter as these materials exhibit large surface areas and high sorption capacities. Organic materials are highly reactive. Degradation of organic matter will induce oxygen depletion and might enhance formation of flocs and biofilms. Study of variations of sediment and water chemistry should predominantly include changes of pH and redox conditions, competition of dissolved ions and processes such as complexation by organic substances. Major questions relate to the potential reduction of sorption sites on minerals and degradation of organic carrier materials. All these processes will influence solution/solid equilibrium conditions and have to be studied prior to modelling the overall effects of pollutants on the water body and aquatic ecosystems. With respect to handling and remediation of contaminated river sediments, either in-place or excavated, a chemical and biological characterization of the material, of the (disposal) site and of the long-term processes is crucial. Passive techniques (e.g. in situ stabilization, subaqueous capping) provide economic advantages as there are no operation costs following their installation. However, the success of these ecological and geochemical engineering approaches is mainly based on an in-depth knowledge of the underlying processes. [source] FTIR Microanalysis and Phase Behaviour of Ethylene/1-Hexene Random CopolymersMACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 14 2007Mariano Pracella Abstract Ethylene/1-hexene random copolymers with 1-hexene content in the range of 1,5 mol-%, synthesised in the presence of new heterogeneous catalyst systems based on bis-carboxylato and -bis-chloro-carboxylato titanium chelate complexes, have been characterised by FTIR microspectroscopy (FTIR-M), DSC calorimetry and X-ray scattering. The co-monomer content and sequence distribution in the various samples were determined by means of both FTIR-M and 13C NMR spectroscopy. The deformation bands of methyl groups in the region of 1,400,1,330 cm,1 were used for the structural analysis of these copolymers. The effect of composition on the crystallinity and phase transitions of copolymers was analysed both in 1,500,1,300 and 760,690 cm,1 frequency ranges as a function of the annealing temperature. A neat variation of the absorbance ratio of methyl band at 1,378 cm,1 was recorded between 110 and 130,°C corresponding to the melting range of the copolymer crystals. The crystallisation behaviour of the copolymers was examined by DSC in dynamic and isothermal conditions; the isothermal kinetics were analysed according to the Avrami model. A marked decrease in the bulk crystallisation rate, accompanied by changes in the nucleation and growth of crystals, was found with an increase in the co-monomer content. The melting behaviour of isothermally crystallised samples was also investigated and the melting temperatures of the copolymers at equilibrium conditions were related to the composition; the experimental data were consistent with the Flory exclusion model of side branches from the crystalline phase. The lowering of crystal growth rate in the copolymers has been accounted for by an increase in the free energy of formation of critical size nuclei due to the effect of the side branches. [source] Capability of thermodynamic calculation in the development of alloys for deposition of corrosion-protection coatings via thermal sprayingMATERIALS AND CORROSION/WERKSTOFFE UND KORROSION, Issue 9 2007M. Born The capability of thermodynamic calculations for the development of materials for corrosion protection of steels via thermal spraying is illustrated in several practical examples. Although the thermodynamic calculations are usually performed for the equilibrium state, they can yield important information even about fast chemical reactions that are far from the equilibrium conditions. The relevance and reliability of thermodynamic calculations can be improved significantly if their results are complemented by chemical and microstructural analyses. In this contribution, details on the melting and alloying processes in technically relevant nickel-based alloys were obtained from the combination of the thermodynamic calculations, differential thermal analysis, local chemical analysis using scanning electron microscopy with energy dispersive spectroscopy of characteristic X-rays and X-ray diffraction analysis. Furthermore, the results of the thermodynamic calculations performed on nickel-based alloys clarified the role of individual chemical elements dissolved in the alloys for the corrosion resistance of the alloys and thus they contributed to the improvement of the chemical stability of these alloys during the chemical reaction with gaseous substances containing chlorine. [source] Polymorphic tetranucleotide microsatellite markers in the Caribbean spiny lobster, Panulirus argusMOLECULAR ECOLOGY RESOURCES, Issue 3 2004F. M. DINIZ Abstract Ten tetranucleotide microsatellite loci are described for the Caribbean spiny lobster Panulirus argus. Loci were polymorphic (4,15 alleles per locus) and exhibited high levels of expected (0.553,0.921) and observed heterozygosity (0.469,0.906) from samples caught off Belize and Puerto Rico coasts. No significant departure from Hardy,Weinberg equilibrium conditions were observed for any locus. All microsatellite loci should be useful for assessing population discrimination for this valuable marine animal currently subjected to excessive fishing efforts. [source] HARVESTING AN AGE-STRUCTURED POPULATION AS BIOMASS: DOES IT WORK?NATURAL RESOURCE MODELING, Issue 4 2008OLLI TAHVONEN Abstract The economics of fisheries is based heavily on describing fish populations by the surplus production model. Both economists and ecologists have different opinions on whether this approach provides an adequate biological basis for economic analysis. This study takes an age-structured population model and shows how, under equilibrium conditions, it determines the surplus production model. The surplus production model is then used to solve an optimal feedback policy for a generic optimal harvesting problem. Next, it is assumed that the fishery manager applies this feedback policy even though the fish population actually evolves according to the age-structured model. This framework is applied to the widow rockfish, Atlantic menhaden, and Pacific halibut fisheries. Population age-structure contains information on future harvest possibilities. The surplus production model neglects this information and may lead to major deviations between the expected and actual outcomes especially under multiple steady states and nonlinearities. [source] THE FISCAL THEORY OF THE PRICE LEVEL: A CRITIQUE*THE ECONOMIC JOURNAL, Issue 481 2002Willem H. Buiter This paper argues that the `fiscal theory of the price level' (FTPL) has feet of clay. The source of the problem is a fundamental economic misspecification. The FTPL confuses two key building blocks of a model of a market economy: budget constraints, which must be satisfied identically, and market clearing or equilibrium conditions. The FTPL asssumes that the government's intertemporal budget constraint needs to be satisfied only in equilibrium. This economic misspecification has far-reaching implications for the mathematical properties of the equilibria supported by models that impose the structure of the FTPL. It produces a rash of contradictions and anomalies. [source] Mesoscale simulations of organized convection: Importance of convective equilibriumTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 616 2006J. M. Done Abstract The validity of convective parametrization breaks down at the resolution of mesoscale models, and the success of parametrized versus explicit treatments of convection is likely to depend on the large-scale environment. In this paper we examine the hypothesis that a key feature determining the sensitivity to the environment is whether the forcing of convection is sufficiently homogeneous and slowly varying that the convection can be considered to be in equilibrium. Two case studies of mesoscale convective systems over the UK, one where equilibrium conditions are expected and one where equilibrium is unlikely, are simulated using a mesoscale forecasting model. The time evolution of area-average convective available potential energy and the time evolution and magnitude of the timescale of convective adjustment are consistent with the hypothesis of equilibrium for case 1 and non-equilibrium for case 2. For each case, three experiments are performed with different partitionings between parametrized and explicit convection: fully parametrized convection, fully explicit convection and a simulation with significant amounts of both. In the equilibrium case, bulk properties of the convection such as area-integrated rain rates are insensitive to the treatment of convection. However, the detailed structure of the precipitation field changes; the simulation with parametrized convection behaves well and produces a smooth field that follows the forcing region, and the simulation with explicit convection has a small number of localized intense regions of precipitation that track with the mid-levelflow. For the non-equilibrium case, bulk properties of the convection such as area-integrated rain rates are sensitive to the treatment of convection. The simulation with explicit convection behaves similarly to the equilibrium case with a few localized precipitation regions. In contrast, the cumulus parametrization fails dramatically and develops intense propagating bows of precipitation that were not observed. The simulations with both parametrized and explicit convection follow the pattern seen in the other experiments, with a transition over the duration of the run from parametrized to explicit precipitation. The impact of convection on the large-scaleflow, as measured by upper-level wind and potential-vorticity perturbations, is very sensitive to the partitioning of convection for both cases. © Royal Meteorological Society, 2006. Contributions by P. A. Clark and M. E. B. Gray are Crown Copyright. [source] Stochastic Modeling of Affinity AdsorptionBIOTECHNOLOGY PROGRESS, Issue 3 2001John Hubble A stochastic model is described that allows surface proximity and packing effects to be incorporated into predictions of adsorption kinetics and equilibrium of affinity adsorption. Equilibrium predictions show that, depending on conditions chosen, the results obtained for equilibrium conditions can exhibit either a Freundlich- or a Langmuir-type relationship. Under conditions of surface density imposed adsorption constraints, the time taken for equilibrium to be reached increases as the "off" constant is decreased. This suggests that for resins having a high immobilized ligand density binding kinetics may be more highly limited by the "off" constant than by mass transfer limitations. [source] Functional Characterization of the Recombinant N -Methyltransferase Domain from the Multienzyme Enniatin SynthetaseCHEMBIOCHEM, Issue 9 2007Till Hornbogen Dr. Abstract A 51 kDa fusion protein incorporating the N -methyltransferase domain of the multienzyme enniatin synthetase from Fusarium scirpi was expressed in Saccharomyces cerevisiae. The protein was purified and found to bind S -adenosyl methionine (AdoMet) as demonstrated by cross-linking experiments with 14C-methyl-AdoMet under UV irradiation. Cofactor binding at equilibrium conditions was followed by saturation transfer difference (STD) NMR spectroscopy, and the native conformation of the methyltransferase was assigned. STD NMR spectroscopy yielded significant signals for H2 and H8 of the adenine moiety, H1' of D -ribose, and SCH3 group of AdoMet. Methyl group transfer catalyzed by the enzyme was demonstrated by using aminoacyl- N -acetylcysteamine thioesters (aminoacyl-SNACs) of L -Val, L -Ile, and L -Leu, which mimic the natural substrate amino acids of enniatin synthetase presented by the enzyme bound 4,-phosphopantetheine arm. In these experiments the enzyme was incubated in the presence of the corresponding aminoacyl-SNAC and 14C-methyl-AdoMet for various lengths of time, for up to 30 min. N -[14C-Methyl]-aminoacyl-SNAC products were extracted with EtOAc and separated by TLC. Acid hydrolysis of the isolated labeled compounds yielded the corresponding N -[14C-methyl] amino acids. Further proof for the formation of N - 14C-methyl-aminoacyl-SNACs came from MALDI-TOF mass spectrometry which yielded 23,212 Da for N -methyl-valyl-SNAC, accompanied by the expected postsource decay (PSD) pattern. Interestingly, L -Phe, which is not a substrate amino acid of enniatin synthetase, also proved to be a methyl group acceptor. D -Val was not accepted as a substrate; this indicates selectivity for the L isomer. [source] | ||||||||||||||||||||||||||||||||||||||||