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Pressure Dependence (pressure + dependence)
Selected AbstractsPressure Dependence of Exchange Parameters and Neel Temperature in La2CuO4ISRAEL JOURNAL OF CHEMISTRY, Issue 3-4 2007Anatolii Ya. Microscopic mechanisms responsible for the observed pressure dependencies of the Neel temperature TN and parameters of isotropic and anisotropic exchange interaction in the orthorhombic antiferromagnet La2CuO4 are investigated. Within the framework of the Anderson microscopic theory of superexchange interaction, the expressions establishing interrelation between parameters of isotropic and anisotropic (both symmetric and antisymmetric) exchange interactions and by the structural parameters describing the Cu-O-Cu bonding angle and the Cu-O bond length in La2CuO4 are obtained. Experimentally determined pressure dependencies of structural parameters by H. Takahashi et al., allow one to present pressure dependencies of exchange parameters and TN in an apparent form. [source] ChemInform Abstract: Pressure Dependence of the Superconducting Transition Temperature of Magnesium Diboride.CHEMINFORM, Issue 30 2001M. Monteverde Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Pressure dependence of photoluminescence of InAs/InP self-assembled quantum wiresPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007M. Ruiz-Castillo Abstract This paper investigates the electronic structure of self-assembled InAs quantum wires (QWrs), grown under different conditions by molecular beam epitaxy on InP, by means of photoluminescence measurements under pressure. In samples with regularly distributed QWrs, room pressure photoluminescence spectra consist of a broad band centred at about 0.85 eV, which can be easily de-convoluted in a few Gaussian peaks. In samples with isolated QWrs, photoluminescence spectra exhibit up to four clearly resolved bands. Applying hydrostatic pressure, the whole emission band monotonously shifts towards higher photon energies with pressure coefficients ranging from 72 to 98 meV/GPa. In contrast to InAs quantum dots on GaAs, quantum wires photoluminescence is observed up to 10 GPa, indicating that InAs QWrs are metastable well above pressure at which bulk InAs undergoes a phase transition to the rock-salt phase (7 GPa). (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pressure dependence of the optical properties of wurtzite and rock-salt Zn1,xCoxO thin filmsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007J. A. Sans Abstract In this paper we investigate the electronic structure of Zn1,xCoxO by means of optical absorption measurements under pressure. Thin films of Zn1,xCoxO with different Co content (from 1 to 30%) were prepared by pulsed laser deposition on mica substrates. Absorption spectra exhibit three main features that are clearly correlated to the Co content in the films: (i) absorption peaks in the infrared associated to crystal-field-split internal transitions in the Co 3d shell, with very small pressure coefficients due to their atomic character; (ii) a broad absorption band below the fundamental edge associated to charge transfer transitions, that exhibit relatively large pressure coefficients, indicating that the Co 3d final states must be strongly hybridized to the conduction band; and (iii) a blue-shifted fundamental absorption edge associated to band to band transitions with a pressure coefficient close to that of pure ZnO. In the up-stroke the transition pressure from wurtzite to rock-salt phase decrease almost linearly as the Co increases, from 9.5 GPa in pure ZnO to about 6.5 GPa for x = 30%. In the down-stroke pressure we observe a similar behavior, yielding a metastable rock-salt phase at room pressure, after a pressure cycle up to 15 GPa. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Pressure dependence of photoluminescence spectra of self-assembled InAs/GaAs quantum dotsPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003F.J. Manjón Abstract Photoluminescence (PL) measurements have been performed in InAs/GaAs self-assembled quantum dots (QDs) under high excitation conditions at low temperatures and under high hydrostatic pressures up to 10 GPa. Mechanically polished samples for high pressure experiments exhibited PL emission from the QD ground state but not from the excited states. Instead, a new broad band is observed in the energy range of the first excited state, which is tentatively attributed to emission from smaller dots formed during the mechanical thinning of the sample. With increasing pressure we found a similar blue shift for the PL maxima of the QD ground state (65 meV/GPa) and of the new broad band (69 meV/GPa). These pressure coefficients are 20% and 40% lower than those reported for dots of less than half the height as in our case and for the wetting layer, respectively. Our results point to a systematic reduction of the pressure coefficient of the InAs QDs with the increase of the dot height. [source] Electrical properties of bulk n-ZnO single crystals under hydrostatic pressurePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2009I. K. Kamilov Abstract Pressure dependences of Hall coefficient RH(P) and resistivity , (P) have been measured for n-ZnO bulk crystals with impurity concentration Ni = 1017,1018 cm,3 and concentration of free electrons ,1017 cm,3 at T = 300 K at hydrostatic pressures up to P = 25 GPa. It has been found that the exponential increase of RH(P) and , (P), observed in the vicinity of the polymorphous transition PPH = 9 GPa, is caused by the increase of ionization energy of shallow donors. At P > PPH, a step-like decrease of the resistivity has been observed, indicating a phase transition from diamond structure to NaCl-type structure. In accordance with formulas derived from the ,heterophase structure , effective medium' model, phase volume fractions in the critical region of the polymorphous transformation have been calculated and the threshold values of normalized effective resistivity have been determined. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Rotational and Vibrational Temperature Measurements in a High-Pressure Cylindrical Dielectric Barrier Discharge (C-DBD)CONTRIBUTIONS TO PLASMA PHYSICS, Issue 1 2005N. Masoud Abstract The rotational (TR) and vibrational (Tv) temperatures of N2 molecules were measured in a high-pressure cylindrical dielectric barrier discharge (C-DBD) source in Ne with trace amounts (0.02 %) of N2 and dry air excited by radio-frequency (rf) power. Both TR and Tv of the N2 molecules in the C 3,u state were determined from an emission spectroscopic analysis the 2nd positive system (C 3,u , B3,g). Gas temperatures were inferred from the measured rotational temperatures. As a function of pressure, the rotational temperature is essentially constant at about 360 K in the range from 200 Torr to 600 Torr (at 30W rf power) and increases slightly with increasing rf power at constant pressure. As one would expect, vibrational temperature measurements revealed significantly higher temperatures. The vibrational temperature decreases with pressure from 3030 K at 200 Torr to 2270 K at 600 Torr (at 30 W rf power). As a function of rf power, the vibrational temperature increases from 2520 K at 20 W to 2940 K at 60 W (at 400 Torr). Both TR and Tv also show a dependence on the excitation frequency at the two frequencies that we studied, 400 kHz and 13.56 MHz. Adding trace amounts of air instead of N2 to the Ne in the discharge resulted in higher TR and Tv values and in a different pressure dependence of the rotational and vibrational temperatures. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Inelastic constitutive properties and shear localization in Tennessee marbleINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 2 2001D. J. Holcomb Abstract The inelastic response of Tennessee marble is modelled by an elastic plastic constitutive relation that includes pressure dependence of yield, strain-softening and inelastic volume strain (dilatancy). Data from 12 axisymmetric compression tests at confining pressures from 0 to 100 MPa are used to determine the dependence of the yield function and plastic potential, which are different, on the first and second stress invariants and the accumulated inelastic shear strain. Because the data requires that the strain at peak stress depends on the mean stress, the locus of peak stresses is neither a yield surface nor a failure envelope, as is often assumed. Based on the constitutive model and Rudnicki and Rice criterion, localization is not predicted to occur in axisymmetric compression although faulting is observed in the tests. The discrepancy is likely due to the overly stiff response of a smooth yield surface model to abrupt changes in the pattern of straining. The constitutive model determined from the axisymmetric compression data describes well the variation of the in-plane stress observed in a plane strain experiment. The out-of-plane stress is not modelled well, apparently because the inelastic normal strain in this direction is overpredicted. In plane strain, localization is predicted to occur close to peak stress, in good agreement with the experiment. Observation of localization on the rising portion of the stress,strain curve in plane strain does not, however, indicate prepeak localization. Because of the rapid increase of mean stress in plane strain, the stress,strain curve can be rising while the shear stress versus shear strain curve at constant mean stress is falling (negative hardening modulus). Copyright © 2001 John Wiley & Sons, Ltd. [source] Shock tube study of 1,3,5-triazine dissociation and relaxation and relaxation of pyrazineINTERNATIONAL JOURNAL OF CHEMICAL KINETICS, Issue 4 2010Hui Xu The three-body dissociation of 1,3,5-triazine (s-triazine, s-C3H3N3 , 3HCN) has been observed in incident shock waves with the laser-schlieren technique. The experiments use 5% triazine/Kr and cover 1630,2350 K for 100,600 Torr. These experiments show dissociation rates with strong falloff and a slight but fully expected pressure dependence. The dissociation is without secondary reaction save for a possible, but rather unlikely, contribution from the isomerization HCN , HNC. Electronic structure calculations of the transition-state properties (G3B3, HL1, Eo = 84.6 kcal/mol) are used to construct a Rice,Ramsperger,Kassel,Marcus (RRKM) model whose fit to the rate measurements suggests a ,,E,down of 1200 cm,1. However, a seemingly better fit is achieved using the barrier of 81 kcal/mol proposed by Dyakov et al. (J. Phys. Chem. A 2007, 111, 9591,9599). With this barrier k, (s,1) = 5.3 × 1016 exp(,86.6(kcal/mol)/RT), and the fit now accepts the more routine ,,E,down = 126(T/298)0.9. It seems the dissociation most likely occurs by a direct, one-step, "triple" dissociation to 3HCN, although the present experiments cannot rule out a multistep process. Vibrational relaxation of the triazine was also examined in 5% and 20% mixtures with Kr over 770,1500 K for pressures between 6 and 14 Torr. Relaxation is very fast, with a slight inverse temperature dependence, P, rising from 100 to 200 ns-atm over the full temperature range. Integrated gradients are in good accord with calculated total changes in density, indicating a single exponential relaxation. A separate investigation of relaxation in the related molecule pyrazine (500,1300 K, in 1% and 5% in Kr, between 13 and 66 Torr) is included. Again relaxation is rapid, but here the temperature dependence seems more normal, the relaxation times decreasing slightly with temperature. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 211,220, 2010 [source] Temperature and pressure effects on structural formations in a ternary microemulsionJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 3-1 2000M. Nagao Small angle neutron scattering experiments were conducted on a temperature-induced phase transition in a ternary microemulsion composed of AOT (dioctyl sulfosuccinate sodium salt), D2 O and n -decane and the results were compared with those of pressure-induced one. Although the static features of both the temperature- and the pressure-induced phase behaviour were similar, a temperature dependence of its characteristic repeat distance at high temperature was quite different from a pressure dependence of that at high pressure. Neutron spin echo experiments were also performed on both the phase transitions. The dynamics of the high temperature phase was different from that of the high pressure phase. These results indicated that the effect of pressure on the structural formation was different from that of temperature. [source] Theoretical approach to the mechanism of reactions between halogen atoms and unsaturated hydrocarbons: The Cl + propene reactionJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 16 2003Pedro Braña Abstract The potential energy surface for the Cl + propene reaction was analyzed at the MP2 level using Pople's 6-31G(d,p) and 6-311+G(d,p), and Dunning's cc-pVDZ and aug-cc-pVDZ basis sets. Two different channels for the addition reaction leading to chloroalkyl radicals and five alternative channels for the abstraction reaction leading to C3H + HCl were explored. The corresponding energy profiles were computed at the QCISD(T)/aug-cc-pVDZ//MP2/aug-cc-pVDZ level of theory. Theoretical results suggest that the previously established mechanism consisting of (1) direct abstraction and (2) addition,elimination steps is instead made up of (1) addition through an intermediate and (2) two-step abstraction processes. No direct abstraction mechanism exists on the potential energy surface. The kinetic equations derived for the new mechanism are consistent with the pressure dependence experimentally observed for this reaction. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 2044,2062, 2003 [source] Combined Pressure,temperature Inactivation of Alkaline Phosphatase in Bovine Milk: A Kinetic StudyJOURNAL OF FOOD SCIENCE, Issue 1 2000L. Ludikhuyze ABSTRACT: A detailed kinetic study on pressure-temperature inactivation of alkaline phosphatase has been performed in the pressure range 0.1 to 725 MPa at temperatures between 25 and 63 °C. Inactivation could be accurately described by a first order kinetic model, allowing D-values to be calculated. According to the thermal death time terminology, zr - and zp -values were calculated, expressing temperature and pressure dependence respectively. However, at high temperature, pressure dependence could not be calculated unambiguously. D-values firstly increased with increasing pressure up to 300 MPa and then decreased with further pressure increase, showing thermal inactivation to be counteracted by low pressure. Finally, a global model describing the D-value as a function of pressure and temperature has been formulated. [source] Fountain flow revisited: The effect of various fluid mechanics parametersAICHE JOURNAL, Issue 5 2010Evan Mitsoulis Abstract Numerical simulations have been undertaken for the benchmark problem of fountain flow present in injection-mold filling. The finite element method (FEM) is used to provide numerical results for both cases of planar and axisymmetric domains under laminar, isothermal, steady-state conditions for Newtonian fluids. The effects of inertia, gravity, surface tension, compressibility, slip at the wall, and pressure dependence of the viscosity are all considered individually in parametric studies covering a wide range of the relevant parameters. These results extend previous ones regarding the shape of the front, and in particular the centerline front position, as a function of the dimensionless parameters. The pressures from the simulations have been used to compute the excess pressure losses in the system (front pressure correction or exit correction). Inertia leads to highly extended front positions relative to the inertialess Newtonian values, which are 0.895 for the planar case and 0.835 for the axisymmetric one. Gravity acting in the direction of flow shows the same effect, while gravity opposing the flow gives a reduced bulge of the fountain. Surface tension, slip at the wall, and compressibility, all decrease the shape of the front. Pressure-dependence of the viscosity leads to increased front position as a corresponding dimensionless parameter goes from zero (no effect) to higher values of the pressure-shift factor. The exit correction increases monotonically with inertia, compressibility, and gravity, while it decreases monotonically with slip and pressure-dependence of the viscosity. Contour plots of the primary variables (velocity-pressure) show interesting trends compared with the base case (zero values of the dimensionless parameters and of surface tension). © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Ethylene Polymerization Kinetics with a Heterogeneous Metallocene Catalyst , Comparison of Gas and Slurry PhasesMACROMOLECULAR MATERIALS & ENGINEERING, Issue 6 2005Michiel F. Bergstra Abstract Summary: Ethylene homopolymerizations were executed with a supported Ind2ZrCl2/MAO catalyst using the so-called Reactive Bed Preparation method. This RBP method combined a slurry polymerization with a gas phase polymerization with the same polymerizing particles, i.e., a reactive bed. Polymerization kinetics were measured with high accuracy and reproducibility. Slurry and gas phase polymerization rates showed the same dependency on monomer bulk concentration. A complexation model has been proposed to describe the non-first order polymerization rate-monomer concentration dependence observed. This model also explains the non-Arrhenius temperature dependence and the observed pressure dependence of the activation energy of the commonly used polymerization rate model: Rp,=,kp,·,C*,·,M. [source] Solubility islands for polymer blends , a new option to homogenize incompatible polymers?MACROMOLECULAR SYMPOSIA, Issue 1 2003Attila R. Imre Abstract Experimental results of liquid-liquid phase equilibrium in a polydisperse blend of two polyalkylsiloxane are presented here. The UCST has an unusual pressure dependence: pressure induced miscibility at moderate pressures and pressure induced immiscibility at higher pressures, above a double critical point. The cloud point curve has two maxima in (concentration, temperature) as well as in (concentration, pressure) space. Approaching the double critical point, the high and low pressure branches of the cloud point curve merge and in a certain stage of this merging, they form a miscibility island located inside the two-phase region. Islands of this kind can give us a new tool to mix virtually immiscible blends. [source] Effect of Pressure on the Miscibility of Polyethylene/Poly(ethylene- alt -propylene) BlendsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 7 2006Phillip Choi Abstract Summary: Effect of density, and hence pressure, on the miscibility of a 50:50 mol/mol PE/PEP blend was studied using a coarse-grained MC simulation approach on a high-coordination lattice, with the conformations of the coarse-grained chains constrained by the RIS model. Interchain pair correlation functions are used to assess the miscibility of the mixtures. Miscibility increases with increasing temperature over the range ,50,150,°C. It is rather insensitive to pressure at high temperatures, but at ,50,°C, the blend miscibility increases with decreasing pressure. The findings are consistent with the fact that the blend is an UCST blend and that the simulation temperatures used, except ,50,°C, were considerably higher than the UCST of the blend. The pressure dependence of the blend miscibility observed near ,50,°C is also in agreement with the experimental observation that the blend exhibits a negative volume change of mixing. The present work demonstrates that the coarse-grained MC approach, when it is used with periodic boundary cells of different sizes filled with the same number of chains, is capable of capturing the pressure dependence of UCST blends. In addition, such a simulation also provides us with insights about the molecular origin of the observed pressure dependence of miscibility. In the present case, the segregation of PE and PEP chains at low temperatures and high pressure simply originates from the fact that fully extended segments of PE chains tend to cluster so that their intermolecular interactions can be maximized. As the temperature increases, there is a decrease in the probability of a trans state at a CC bond in PE, and therefore the attraction between the PE chains is reduced at higher temperatures, promoting miscibility and the UCST behavior. Density (pressure) dependence of the 2nd shell pair correlation function values for a 50/50 PE/PEP blend at ,50,°C. [source] Temperature and Pressure Effects on Local Structure and Chain Packing in cis -1,4-Polybutadiene from Detailed Molecular Dynamics SimulationsMACROMOLECULAR THEORY AND SIMULATIONS, Issue 5 2006Georgia Tsolou Abstract Summary: We present results for the temperature and pressure dependence of local structure and chain packing in cis -1,4-polybutadiene (cis -1,4-PB) from detailed molecular dynamics (MD) simulations with a united-atom model. The simulations have been executed in the NPT statistical ensemble with a parallel, multiple time step MD algorithm, which allowed us to access simulation times up to 1 µs. Because of this, a 32 chain C128cis -1,4-PB system was successfully simulated over a wide range of temperature (from 430 to 195 K) and pressure (from 1 atm to 3 kbar) conditions. Simulation predictions are reported for the temperature and pressure dependence of the: (a) density; (b) chain characteristic ratio, Cn; (c) intermolecular pair distribution function, g(r), static structure factor, S(q), and first peak position, Qmax, in the S(q) pattern; (d) free volume around each monomer unit along a chain for the simulated polymer system. These were thoroughly compared against available experimental data. One of the most important findings of this work is that the component of the S(q) vs. q plot representing intramolecular contributions in a fully deuterated cis -1,4-PB sample exhibits a monotonic decrease with q which remains completely unaffected by the pressure. In contrast, the intermolecular contribution exhibits a distinct peak (at around 1.4 Å,1) whose position shifts towards higher q values as the pressure is raised, accompanied by a decrease in its intensity. 3D view of the simulation box containing 32 chains of C128cis -1,4-polybutadiene at density ,,=,0.849 g,·,cm,3 and the conformation of a single C128cis -1,4-PB chain fully unwrapped in space. [source] Semiempirical LUC-INDO calculations on the effect of pressure on the electronic structure of diamondPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2007Ibtesam O. Radi Abstract A self-consistent LUC (large unit cell) formalism on the basis of semiempirical INDO (intermediate neglect of differential overlap) Hamiltonians has been used to study the electronic properties of diamond and to investigate the pressure dependence of these properties. The calculated properties are in good agreement with the experiments except the conduction-band width. The increase of pressure on diamond is predicted to cause the following effects; an increase of the valence and conduction-band widths with a decrease of the direct bandgap, an increase of the electronic occupation probability for the p-orbital with a decrease of this probability for the s-orbital, and a decrease of the X-ray scattering factor. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Temperature and pressure dependence of carrier recombination processes in GaAsSb/GaAs quantum well lasersPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2007Konstanze Hild Abstract We investigated the temperature and pressure dependence of carrier recombination processes occurring in GaAsSb edge-emitting lasers operating near 1.3 ,m. Below ,100 K, the threshold current, Ith, is dominated by the radiative current, Irad, and is proportional to temperature, T. However, above 100 K, non-radiative recombination increases abruptly such that by 125 K it accounts for 40% of Ith. From high pressure measurements at this temperature, we find that the non-radiative current decreases with increasing pressure, consistent with the presence of Auger recombination. At room temperature, non-radiative recombination accounts for ,90% Ith and gives rise to a super-linear temperature dependence of Ith, in spite of the fact that Irad , T. At room temperature the non-radiative current increases with increasing pressure, indicating that under ambient operating conditions, the devices are also limited by carrier leakage into the ,-minimum of the GaAs barriers and possibly also into the X-minima of the GaAsP confining layers. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Carrier recombination processes in 1.3 ,m and 1.5 ,m InGaAs(P)-based lasers at cryogenic temperatures and high pressuresPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 14 2004S. J. Sweeney Abstract We describe measurements of the threshold current of 1.3 ,m and 1.5 ,m InGaAs(P)-based quantum-well lasers measured at cryogenic temperatures and at high pressures. At low temperatures (,100 K), we find that the threshold current of the devices increases with increasing pressure consistent with the calculated pressure variation of the radiative current. This is in sharp contrast with their pressure dependence at room temperature (RT), where the threshold current decreases with increasing pressure due to the decrease in importance of Auger recombination. These low-temperature, high-pressure results agree well with previous temperature dependence measurements on the same devices, which show a transition from radiative to non-radiative Auger recombination dominated behaviour as the laser temperature is increased from ,100 K to room temperature. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Conduction band filling in In-rich InGaN and InN under hydrostatic pressurePHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2008G. Franssen Abstract We demonstrate the effect of conduction band shape evolution of InGaN with increasing In content and applying hydrostatic pressure. The influence of conduction band filling on the hydrostatic pressure dependence of photoluminescence in In0.7Ga0.3N and InN is investigated. It is found that the PL pressure coefficient dEPL/dp of InN changes from ,27 meV/GPa to ,21 meV/GPa when the electron concentration increases from 3.6×1017 cm,3 to 1.1×1019 cm,3. In contrast, no significant change of dEPL/dp with electron concentration was observed for In0.7Ga0.3N. We conclude that the pressure sensitivity of the Fermi level, which is responsible for the lowering of dEPL/dp with respect to dEG/dp in InN, is much less prominent in In0.7Ga0.3N than in InN. We attribute this difference to the larger band gap of In0.7Ga0.3N, which lowers the pressure sensitivity of m*. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] True and Apparent Temperature Dependence of Protein Adsorption Equilibrium in Reversed-Phase HPLCBIOTECHNOLOGY PROGRESS, Issue 6 2002Szabelski The adsorption behavior of bovine insulin on a C8 -bonded silica stationary phase was investigated at different column pressures and temperatures in isocratic reversed-phase HPLC. Changes in the molar volume of insulin (, Vm) upon adsorption were derived from the pressure dependence of the isothermal retention factor ( k,). The values of , Vm were found to be practically independent of the temperature between 25 and 50 °C at ,96 mL/mol and to increase with increasing temperature, up to ,108 mL/mol reached at 50 °C. This trend was confirmed by two separate series of measurements of the thermal dependence of ln( k,). In the first series the average column pressure was kept constant. The second series involved measurements of ln( k,) under constant mobile-phase flow rate, the average column pressure varying with the temperature. In both cases, a parabolic shape relationship was observed between ln( k,) and the temperature, but the values obtained for ln k, were higher in the first than in the second case. The relative difference in ln( k,), caused by the change in pressure drop induced by the temperature, is equivalent to a systematic error in the estimate of the Gibbs free energy of 12%. Thus, a substantial error is made in the estimates of the enthalpy and entropy of adsorption when neglecting the pressure effects associated with the change in the molar volume of insulin. This work proves that the average column pressure must be kept constant during thermodynamic measurements of protein adsorption constants, especially in RPLC and HIC. Our results show also that there is a critical temperature, Tc , 53 °C, at which ln( k,) is maximum and the insulin adsorption process changes from an exothermic to an endothermic one. This temperature determines also the transition point in the molecular mechanism of insulin adsorption that involves successive unfolding of the protein chain. [source] Phase transition and elasticity of CdO under pressurePHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 1 2009Feng Peng Abstract First-principles calculations of the crystal structures, and phase transition, and elastic properties of cadmium oxide (CdO) have been carried out with the plane-wave pseudopotential within the generalized gradient approximation in the frame of density functional theory method. The calculated values (for crystal structures) are in good agreement with experimental data as well as with some of the existing model calculations. For CsCl-type CdO, the dependence of the elastic constants cij, the aggregate elastic modulus (B, G, E), and the elastic anisotropy on the pressure have been investigated. Moreover, the pressure dependences of the Poisson ratio, Debye temperature, and the compressional and shear elastic wave velocities have been investigated for the first time. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Conductivity of graphite and fullerene under pressures up to 50 GPaPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 2 2003G. V. Tikhomirova Abstract The DC resistance of polycrystalline fullerene C60 and graphite in the temperature range 77,450 K were studied at pressures up to 50 GPa. The AC measurements were performed at room temperature. The temperature and pressure dependences of resistance for both materials are of a similar character. However, the resistance of both materials is different by many orders of magnitude. It is shown that both fullerene and graphite keep some features of their original microscopic structure even at high pressures. [source] Aplanarity of CO3 groups: a theoretical investigationACTA CRYSTALLOGRAPHICA SECTION B, Issue 4 2000Björn Winkler Density functional theory-based calculations have been used to demonstrate that the aplanarity of CO groups in some carbonates such as dolomite, CaMg(CO), aragonite, CaCO, and norsethite, BaMg(CO), is a ground-state property. This distortion stabilizes dolomite by ,500,J,mol. Up to at least 6,GPa, the aplanarity of CO groups in dolomite is independent of pressure. In aragonite the aplanarity increases slightly on increasing pressure, while a significant tilting of the CO groups occurs. The calculations do not support previous findings of anomalously low values for the pressure derivative of the bulk moduli, , of aragonite and dolomite. Instead, the computed pressure dependences of the unit-cell volumes correspond to = 5.0,(5) for aragonite and = 4,(1) for dolomite, when fitted with a third-order Birch,Murnaghan equation-of-state. [source] | |||||||||||||||||||