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Thermal Equilibrium (thermal + equilibrium)
Kinds of Thermal Equilibrium Selected AbstractsSpins as probes of different electronic statesCONCEPTS IN MAGNETIC RESONANCE, Issue 2 2007Dieter Suter Abstract Nuclear spins are efficient probes of electronic states. Because most NMR experiments are performed in thermal equilibrium, they probe the electronic ground state,the only state that is significantly populated under ambient conditions. Probing electronically excited states becomes possible, if magnetic resonance techniques are combined with optical (laser) excitation. Depending on the nature of the electronic state, drastic changes of the magnetic resonance parameters may be observed. We discuss the basic principles of this type of investigation. Depending on the lifetime of the electronically excited state, it is possible to measure separate spectra of ground and excited state if the lifetime is long on the NMR timescale, or an averaged spectrum if the lifetime is short. We present examples for both limiting cases using rare earth ions and semiconductor heterostructures. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 116,126, 2007. [source] Interaction of exchange and differential relaxation in the saturation recovery behavior of the binary spin-bath model for magnetization transferCONCEPTS IN MAGNETIC RESONANCE, Issue 4 2006Gunther Helms Abstract Most closed-form analytical solutions of the binary spin-bath are difficult to interpret in terms of underlying physics. The key notions are the presence of a kinetic and a thermal equilibrium and that the time course of saturation recovery under conditions of fast exchange can be understood as conjoint relaxation and lossless transfer. By introducing a suitable parameter, it is shown how exchange and differential relaxation counteract each other: the amount of transferred saturation (transfer term) is altered and the kinetic equilibrium appears slightly disturbed (difference term). Although the factorization formally represents the general solution of saturation recovery in the binary spin-bath, this interpretation applies only to the case of fast exchange and slow relaxation. By calculating the set of parameters for a wide range of hypothetical relaxation rates, it was shown that the difference term is crucial to describe the transition to the slow-exchange limit. The transfer term vanishes as the two pools appear decoupled in this approximation. © 2006 Wiley Periodicals, Inc. Concepts Magn Reson Part A 28A: 291,298, 2006. [source] Composition of Partially Ionized Systems Using the PlanckLarkin Partition Function of Mid-Z ionsCONTRIBUTIONS TO PLASMA PHYSICS, Issue 10 2009A. Sengebusch Abstract We report on the composition of warm, dense plasmas of M-shell ions. Assuming local thermal equilibrium, the abundance of different ionization stages is given by a set of coupled Saha-equations. In order to avoid discontinuities at the Mott density, the partition functions have to account for pressure ionization due to continuum lowering consistently. The Planck-Larkin renormalization of bound and scattering states is well elaborated for hydrogenic systems. This paper shows the consistent extension to moderately ionized Mid-Z elements. We present results for solid-density polymere and titanium plasmas (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Combustion of a substitution fuel made of cardboard and polyethylene: influence of the mix characteristics,modelingFIRE AND MATERIALS, Issue 7 2008S. Salvador Abstract The model proposed in this paper describes the combustion of a porous medium subjected to a radiative heat flux at its surface. There is no forced convection of air through the medium; hence this situation corresponds to the one encountered at the surface of fuel elements such as pellets, bricks or ballots, inside a furnace or kiln. Ash is not removed from the surface. No assumption is made a priori in terms of the limiting phenomena. The medium is composed of cardboard and polyethylene (PE). Based on previous experimental work (Fuel 2004; 83:451,462), the material is assumed to be a macroscopically homogeneous porous medium. Local thermal equilibrium is also assumed. Most of the parameters required for the modeling were determined from specific experiments. Good predictions of the sample mass evolution and of the temperature levels inside the sample body were obtained for a large range of densities and PE content. A devolatilization front of about 20,mm first propagates inside the medium. The volatile matter flux is advected to the surface, which leads to the formation of the flame above the surface. Then a second char oxidation front propagates, starting from the surface. The front thickness is approximately 25,mm under the experimental conditions. Copyright © 2008 John Wiley & Sons, Ltd. [source] Theoretical performance analysis of the multi-stage gas,solid fluidized bed air preheaterINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2001Sang Il Park Abstract The multi-stage fluidized bed can be used to preheat the combustion air by recovering the waste heat from the exhaust gas from industrial furnaces. The dilute-phase fluidized bed may be formed to exclude the excessive pressure drop across the multi-stage fluidized bed. But, in this case, the solid particles do not reach to the thermal equilibrium due to relatively short residence time in each layer of fluidized bed. In this study, a theoretical analysis on the dilute phase multistage fluidized bed heat exchanger was performed. A parameter related to the degree of thermal equilibrium between gas and solid particles at the dilute-phase fluidized beds was derived. Using this parameter, a relatively simple expression was obtained for the thermal efficiencies of the multi-stage fluidized bed heat exchanger and air preheater. Copyright © 2001 John Wiley & Sons, Ltd. [source] Monte Carlo modelling of abrupt InP/InGaAs HBTsINTERNATIONAL JOURNAL OF NUMERICAL MODELLING: ELECTRONIC NETWORKS, DEVICES AND FIELDS, Issue 4 2003Pau Garcias-Salvá Abstract In this paper a Monte Carlo simulator which is focused on the modelling of abrupt heterojunction bipolar transistors (HBTs) is described. In addition, simulation results of an abrupt InP/InGaAs HBT are analysed in order to describe the behaviour of this kind of device, and are compared with experimental data. A distinctive feature of InP/InGaAs HBTs is their spike-like discontinuity in the Ec level at the emitter,base heterojunction interface. The transport of electrons through this potential barrier can be described by the Schrödinger's equation. Therefore, in our simulator we have consistently included the numerical solution of this equation in the iterative Monte Carlo procedure. The simulation results of the transistor include the density of electrons along the device and their velocity, kinetic energy and occupation of the upper conduction sub-bands. It is shown that the electrons in the base region and in the base,collector depletion region are far from thermal equilibrium, and therefore the drift,diffusion transport model is no longer applicable. Finally, the experimental and simulated Gummel plots JC(VBE) and JB(VBE) are compared in the bias range of common operation of these transistors, showing a good data agreement. Copyright © 2003 John Wiley & Sons, Ltd. [source] The role of inequalities in the analysis of many-body systems,INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2010J. K. PercusArticle first published online: 8 SEP 2010 Abstract We discuss the strategy of determining properties of many-body systems by applying successively more stringent limitations on the domain on which solutions can lie, i.e., sharpening the degree of resolution of the results obtained. A rough division is made into universal, or system-independent inequalities and system-dependent ones, which are joined by equalities or sum rules. General examples include Fermion ground states and classical fluids in thermal equilibrium, and for the latter, the effect of estimation by saturating inequalities. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] Magnetic Resonance Temperature Mapping of Microwave-Fried Chicken FingersJOURNAL OF FOOD SCIENCE, Issue 5 2009Isil Barutcu ABSTRACT:, The main objective of this study was to compare the heating patterns of chicken fingers deep-fried conventionally and using a microwave. Two dimensional internal temperature maps of fried chicken fingers with rectangular geometry were measured post frying using magnetic resonance imaging (MRI). Frying was performed in a microwave oven at 365 W power level for 0.5 and 1.5 min after bringing the oil temperature to 180 ± 1 °C. Samples were also fried in a conventional fryer at 180 °C for 2 and 5 min for comparison. Variations in internal temperature distribution increased proportionally to frying time in both microwave and conventional frying. Internal thermal equilibrium is reached in all samples after 13 min of holding time. Internal structural changes, void formation, were also visualized in the images. Void formation did not significantly impact cooling rates. [source] Molecular dynamics simulations of MALDI: laser fluence and pulse width dependence of plume characteristics and consequences for matrix and analyte ionizationJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 4 2010Richard Knochenmuss Abstract Molecular dynamics simulations of matrix-assisted laser desorption/ionization were carried out to investigate laser pulse width and fluence effects on primary and secondary ionization process. At the same fluence, short (35 or 350 ps) pulses lead to much higher initial pressures and ion concentrations than longer ones (3 ns), but these differences do not persist because the system relaxes toward local thermal equilibrium on a nanosecond timescale. Higher fluences accentuate the initial disparities, but downstream differences are not substantial. Axial velocities of ions and neutrals are found to span a wide range, and be fluence dependent. Total ion yield is only weakly dependent on pulse width, and consistent with experimental estimates. Secondary reactions of matrix cations with analyte neutrals are efficient even though analyte ions are ablated in clusters of matrix. Copyright © 2010 John Wiley & Sons, Ltd. [source] ZnCdO/ZnO , a new heterosystem for green-wavelength semiconductor lasingLASER & PHOTONICS REVIEWS, Issue 3 2009S. Kalusniak Abstract We report on our efforts to cultivate the ternary compound ZnCdO as a semiconductor laser material. Molecular beam epitaxy far from thermal equilibrium allows us to overcome the standard solubility limit and to fabricate alloys with band gaps ranging from 3.4 down to 2.1 eV. Optimized structures containing well-defined quantum wells as active zones are capable of low-threshold lasing under optical pumping up to room temperature. The longest lasing wavelength achieved so far is 510 nm. [source] The oxygen vacancy in Ga2O3: a double resonance investigation,MAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2005H. J. Kümmerer Abstract When produced under reducing conditions, ,-Ga2O3 is transformed into an n -type semiconductor with delocalized conduction electrons that exhibit a very strong electron spin resonance (ESR) and a strong hyperfine coupling to the gallium nuclei of the host lattice. We apply the Overhauser-shift technique to investigate single crystals of this compound. With extension to the high magnetic field of a W-band spectrometer, we were able to resolve all spectral lines that were recorded and to assign them to their corresponding electronic and nuclear states. This separate analysis was the basis to access additional sample characteristics: the hyperfine coupling that is actually averaged out in the ESR signal, as well as the nuclear relaxation rates could be analyzed. Systematic measurements by varying the microwave power revealed the Overhauser shift in thermal equilibrium. The signal could be tracked to very small microwave saturation parameters, at which the deviation from the usual linear relation between power and shift becomes evident and the shift clearly approaches a constant value. This value in equilibrium was determined directly from a fit to a sequence of measurements, whereas standard X-band experiments only provided indirect conclusions. The probability densities of the electrons at the nuclei in the two nonequivalent crystallographic positions,the lattice sites with octahedral and tetrahedral coordination,could also be determined directly. The enhanced resolution revealed an otherwise hidden substructure in the nuclear resonance signals. On the basis of a microscopic model, this structure could be used to probe the environment of the oxygen vacancy more precisely and to determine the extension of the electronic wave function of the donor electrons. Copyright © 2005 John Wiley & Sons, Ltd. [source] On the evolution of the nova-like variable AE AquariiMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 1 2002P. J. Meintjes Abstract A possible evolution for the enigmatic cataclysmic variable AE Aquarii is considered that may put into context the long orbital period and short white dwarf rotation period compared with other DQ Her systems. It has been shown that mass transfer could have been initiated when the secondary KIV,V star was already somewhat evolved when it established Roche lobe contact. In this initial phase the orbital period of the system was probably Porb,i, 8.5 h, and the white dwarf rotation period P*,i > 1 h. Mass transfer in the form of diamagnetic gas blobs will result in an initial discless accretion process, resulting in an efficient drain of the binary orbital angular momentum. Since the initial mass ratio of the binary was probably qi, 0.8, a high mass transfer rate and a slow expansion of the Roche lobe of the secondary star followed, accompanied by a fast expanding secondary following the mass loss. This could have resulted in the KIV,V secondary flooding its Roche surface, causing a run-away mass transfer of that lasted for approximately , during which time the binary expanded to an orbital period of approximately Porb, 11 h. During this phase the mass accretion rate on to the surface of the white dwarf most probably exceeded the critical value for stable nuclear burning , which could have resulted in AE Aqr turning into an ultrasoft X-ray source. The high mass transfer terminated when a critical mass ratio of qcrit= 0.73 was reached. Disc torques spun-up the white dwarf to a period close to 33 s within the time-scale before the high mass transfer shut down when qcrit was reached. The decrease in the mass loss of the secondary allowed it to re-establish hydrostatic equilibrium on the dynamical time-scale (fraction of a day). From this point when qcrit is reached the mass transfer and binary evolution proceed at a slower rate since mass transfer from the secondary star is driven by magnetic braking of the secondary on a time-scale , which is the same as the thermal time-scale tth, 6.3 × 107 yr, i.e. the time-scale on which the secondary shrinks to restore its perturbed thermal equilibrium after the high mass loss. The significantly lower mass transfer in this phase will result in mass ejection from the system. This propeller,ejector action erodes the rotational kinetic energy of the white dwarf, channelling it into mass ejection and non-thermal activity, which explains the non-thermal outbursts that are observed at radio wavelengths and occasionally also at TeV energies. [source] Mirror eclipses in the cataclysmic variable IP PegMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2001S.P. Littlefair We present time resolved K -band infrared spectra of the dwarf nova (DN) IP Peg in early quiescence. The Brackett , and He i (,2.0581) lines in our data show hitherto unseen behaviour, which we term a mirror eclipse, and interpret as an eclipse of the secondary star by an optically thin accretion disc. Mirror eclipses are a direct probe of the structure and physical conditions of accretion discs. For example, on assuming the relevant level populations to be in local thermal equilibrium, we constrain the temperature and density of the optically thin material, causing the mirror eclipse in IP Peg to be and respectively. In order to match our data, we find that at least the outermost 20 per cent of the disc (in radius) must be entirely optically thin. Implications for time-dependent disc models are examined. [source] Variations in Photosystem I Properties in the Primordial Cyanobacterium Gloeobacter violaceus PCC 7421PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2010Mamoru Mimuro We compared the optical properties of the trimeric photosystem (PS) I complexes of the primordial cyanobacterium Gloeobacter violaceus PCC 7421 with those of Synechocystis sp. PCC 6803. Gloeobacter violaceus PS I showed (1) a shorter difference maximum of P700 by approximately 2 nm, (2) a smaller antenna size by approximately 10 chlorophyll (Chl) a molecules and (3) an absence of Red Chls. The energy transfer kinetics in the antennae at physiological temperatures were very similar between the two species due to the thermal equilibrium within the antenna; however, they differed at 77 K where energy transfer to Red Chls was clearly observed in Synechocystis sp. PCC 6803. Taken together with the lower P700 redox potential in G. violaceus by approximately 60 mV, we discuss differences in the optical properties of the PS I complexes with respect to the amino acid sequences of core proteins and further to evolution of cyanobacteria. [source] The long-wavelength limit of the structure factor of amorphous silicon and vitreous silicaACTA CRYSTALLOGRAPHICA SECTION A, Issue 1 2010Adam M. R. De Graff Liquids are in thermal equilibrium and have a non-zero structure factor = = in the long-wavelength limit where is the number density, is the temperature, is the scattering vector and is the isothermal compressibility. The first part of this result involving the number (or density) fluctuations is a purely geometrical result and does not involve any assumptions about thermal equilibrium or ergodicity, so is obeyed by all materials. From a large computer model of amorphous silicon, local number fluctuations extrapolate to give = 0.035 0.001. The same computation on a large model of vitreous silica using only the silicon atoms and rescaling the distances gives = , which suggests that this numerical result is robust and perhaps similar for all amorphous tetrahedral networks. For vitreous silica, it is found that = , close to the experimental value of = obtained recently by small-angle neutron scattering. Further experimental and modeling studies are needed to determine the relationship between the fictive temperature and structure. [source] Nonequilibrium quantum anharmonic oscillator and scalar field: high temperature approximationsANNALEN DER PHYSIK, Issue 6 2009R.F. Alvarez-Estrada Abstract We treat a relativistic quantum boson gas, described by a scalar quantum field, with quartic self-interaction (,4) in three spatial dimensions: we review the known equilibrium case and present new proposals off-equilibrium. For high temperature and large spatial scales, the behaviour of the gas at equilibrium simplifies nonperturbatively (equilibrium dimensional reduction or EDR): its thermodynamics is described by classical statistical mechanics with some quantum field effects. By assumption, the initial state of the gas off-equilibrium includes interactions and inhomogeneities and is not far from thermal equilibrium. We employ real-time generating functionals and obtain the free nonequilibrium correlators at non-zero temperature. The nonequilibrium quantum gas appears to simplify nonperturbatively in the regime of high temperature and large temporal and spatial scales (nonequilibrium dimensional reduction or NEDR), its dynamics being described by classical statistical mechanics with some quantum field effects. We outline the renormalization of the ,4 theory, the nonequilibrium statistical mechanics of a quantum anharmonic oscillator and the high temperature simplifications, all of which provide very useful hints for NEDR in the field case. Our main proposals are NEDR and the associated new (renormalized) real-time nonequilibrium generating functionals for the ,4 theory. [source] Liouville and Fokker,Planck dynamics for classical plasmas and radiationANNALEN DER PHYSIK, Issue 6 2006R.F. Alvarez-Estrada Abstract We consider a nonequilibrium statistical system formed by many classical non-relativistic particles of opposite electric charges (plasma) and by the classical dynamical electromagnetic (EM) field. The charges interact with one another directly through instantaneous Coulomb potentials and with the dynamical degrees of freedom of the transverse EM field. The system may also be subject to external influences of: i) either static, but spatially inhomogeneous, electric and magnetic fields (case 1)), or ii) weak distributions of electric charges and currents (case 2)). The particles and the dynamical EM field are described, for any time t > 0, by the classical phase-space probability distribution functional (CPSPDF) f and, at the initial time (t = 0), by the initial CPSPDF fin. The CPSPDF f and fin, multiplied by suitable Hermite polynomials (for particles and field) and integrated over all canonical momenta, yield new moments. The Liouville equation and fin imply a new nonequilibrium linear infinite hierarchy for the moments. In case 1), fin describes local equilibrium but global nonequilibrium, and we propose a long-time approximation in the hierarchy, which introduces irreversibility and relaxation towards global thermal equilibrium. In case 2), the statistical system, having been at global thermal equilibrium, without external influences, for t , 0, is subject to weak external charge-current distributions: then, new hierarchies for moments and their long-time behaviours are discussed in outline. As examples, approximate mean-field (Vlasov) approximations are treated for both cases 1) and 2). [source] | ||||||||||||||||