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Temperature Dependency (temperature + dependency)

Distribution by Scientific Domains

Chemistry	55%
Polymers and Materials Science	14%
Physics and Astronomy	14%
Life Sciences	11%

Selected Abstracts

Extent and mechanism of solvation and partitioning of isomers of substituted benzoic acids: A thermodynamic study in the solid state and in solution

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2008
German L. Perlovich
Abstract Temperature dependency of saturated vapour pressure and thermochemical characteristics of fusion processes for 2-, 3- and 4-methoxybenzoic acids (anisic acids) were measured and thermodynamic functions of sublimation, fusion, and evaporation calculated. A new approach to split specific and nonspecific energetic terms in the crystal lattice was developed. For methoxybenzoic acid isomers as well as for a number of analogous molecules, a parameter describing molecular packing density by the ratio of free volume of the molecules in the crystal lattice and van der Waals molecular volume is defined. Its relationship to Gibbs energy of sublimation and to the respective melting points was analysed. Temperature dependencies of solubility in buffers with pH 2.0 and 7.4, n -octanol and n -hexane were measured. The thermodynamic functions of solubility, solvation and transfer processes were deduced. Concentration dependence of partition coefficients for the outlined isomers was measured. Specific and nonspecific solvation terms were distinguished using the transfer from the ,inert' n -hexane to the other solvents. Comparison analysis of specific and nonspecific interactions in the solid state and in solution was carried out. A diagram enabling analysis of the mechanism of the partitioning process was applied. It was found that position of substituents essentially affects the mechanism of partitioning in buffer pH 2.0, however, at pH 7.4, the mechanism is independent of the position of the substituent. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 97:3883,3896, 2008 [source]

Energetic aspects of diclofenac acid in crystal modifications and in solutions,mechanism of solvation, partitioning and distribution

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 5 2007
German L. Perlovich
Abstract Temperature dependency of saturated vapor pressure and heat capacity for the diclofenac acid (Form II) were measured and thermodynamic functions of sublimation calculated (,,=,49.3 kJ,·,mol,1; ,,=,115.6,±,1.3 kJ,·,mol,1; ,,=,222,±,4 J,·,mol,1,·,K,1). Crystal polymorphic Forms I (P21/c) and II (C2/c) of diclofenac acid have been prepared and characterized by X-ray diffraction experiments. The difference between crystal lattice energies of the two forms were obtained by solution calorimetry: ,,Hsol(I,,,II),=,1.6,±,0.4 kJ,·,mol,1. Temperature dependencies of the solubility in buffers with pH 2.0 and 7.4, n-octanol and n-hexane were measured. The thermodynamic functions of solubility, solvation, and transfer processes were deduced. Specific and non-specific solvation terms were distinguished using the transfer from the "inert" n-hexane to the other solvents. The transfer of diclofenac acid molecules from the buffers to n-octanol (partitioning and distribution) is an entropy driven process. © 2007 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 1031,1042, 2007 [source]

Structure and Phase Transitions of Poly(heptamethylene p,p,-bibenzoate): Time-Resolved Synchrotron WAXS and DSC Studies

MACROMOLECULAR CHEMISTRY AND PHYSICS, Issue 14 2003
Ernesto Pérez
Abstract Time-resolved wide-angle X-ray scattering (WAXS), as well as differential scanning calorimetry (DSC) and polarisation microscopy studies, were applied to investigate the structure and phase transitions of poly(heptamethylene p,p,-bibenzoate). Temperature dependencies of several structural parameters were determined. Complete transformation from an isotropic melt to a smectic phase was suggested whereas the transition from a smectic to crystalline phase is only partial (around 30%), although it takes place from the ordered SCA phase. Crystals are formed within the SCA domains with nearly the same coherent length. On the basis of the analysis of the position and the profile of the diffuse wide-angle X-ray scattering and mesogenic layer spacing, it was assumed that either crystallisation modifies the smectic structure, or mesophase losses its positional order because of the lack of mobility of the spacers at low temperatures. WAXS scattering profiles corresponding to P7MB: a) cooling from the isotropic melt at 2,°C,·,min,1; b) subsequent melting at 12,°C,·,min,1. [source]

Temperature dependencies of amide 1H- and 15N-chemical shifts in hyaluronan oligosaccharides

MAGNETIC RESONANCE IN CHEMISTRY, Issue 5 2007
Charles D. Blundell
Abstract Temperature coefficients (,,/,T) of amide chemical shifts of N -acetylglucosamine residues have been measured in a range of oligosaccharides of the important vertebrate polysaccharide hyaluronan. Odd- and even-numbered oligosaccharides with glucuronic acid, ,-4,5-unsaturated glucuronic acid and N -acetylglucosamine at the termini were investigated. All amide proton temperature coefficients were only slightly less negative (,6.9 to , 9.1 ppb/ °C) than those of amide protons in free exchange with water (,, 11 ppb/ °C), indicating an absence of persistent intramolecular hydrogen bonds. With the exception of amide groups in reducing-terminal N -acetylglucosamine rings, all amide proton environments have the same temperature coefficient (,6.9 ppb/ °C), irrespective of differences in amide group chemical shifts and 3JHH coupling constants, i.e. they do not sense subtle differences in orientation of the amide group. Amide nitrogen temperature coefficients report the same phenomena but with greater sensitivity. These data provide a set of reference values for temperature coefficients measured in other carbohydrates with acetamido sugars. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Temperature dependency of granule characteristics and kinetic behavior in UASB reactors

JOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 8 2004
Hsin-Hsien Chou
Abstract When an inhibitory substrate, phenol, was treated under mesophilic conditions (25, 30, 35, and 40 °C), the upflow anaerobic sludge bed (UASB) reactors at 30 °C resulted in the greatest amount of biomass and the largest granule size, while the UASB reactors at 25 °C resulted in the smallest granule size and the greatest amount of wash-out of sludge. The granule size tended to be negatively correlated with the amount of wash-out of sludge. With an increase in temperature, the kinetic constant k for anaerobic phenol degradation increased and the half saturation constant (Ks) decreased. The mass fraction of methanogens (f) increased with increasing operational temperature in the UASB reactors and the activation energy (Ea) for acetate methanogenesis was larger than that for phenol acidogenesis in the batch reactors, indicating that the operational temperature imposes a more influential effect on methanogens than on acidogens. From the results of the activity of acidogens and methanogens (expressed in specific COD utilization rate), the rate-limiting step is phenol acidogenesis. Copyright © 2004 Society of Chemical Industry [source]

Extent and mechanism of solvation and partitioning of isomers of substituted benzoic acids: A thermodynamic study in the solid state and in solution

Energetic aspects of diclofenac acid in crystal modifications and in solutions,mechanism of solvation, partitioning and distribution

Novel Fabrication of Ca-Doped LaNbO4 Thin-Film Proton-Conducting Fuel Cells by Pulsed Laser Deposition

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2010
Anna Magrasó
Thin films of 0.5% Ca-doped La0.995Ca0.005NbO4,, (LCNO) proton-conducting electrolytes of ,2 ,m thickness were obtained by pulsed laser deposition on NiO,LaNbO4 composite substrates. The morphology of the films was granular after annealing at T,1000°C and evolved to spherical-like grains at 1100°C and above. The structure and composition of the films were characterized by X-ray diffraction and X-ray photoelectron spectrocopy. LCNO films showed the monoclinic fergusonite-type structure at room temperature. The area-specific resistance for a ,2-,m-thick electrolyte was in the order of 0.4 ,·cm2 at 600°C based on estimates of the electrode area. Temperature dependency of the electrical conductivity at 600°,700°C was comparable with that of bulk disks of the material. [source]

Kinetic and thermodynamic characterization of HIV-1 protease inhibitors

JOURNAL OF MOLECULAR RECOGNITION, Issue 2 2004
Cynthia F. Shuman
Abstract Interaction kinetic and thermodynamic analyses provide information beyond that obtained in general inhibition studies, and may contribute to the design of improved inhibitors and increased understanding of molecular interactions. Thus, a biosensor-based method was used to characterize the interactions between HIV-1 protease and seven inhibitors, revealing distinguishing kinetic and thermodynamic characteristics for the inhibitors. Lopinavir had fast association and the highest affinity of the tested compounds, and the interaction kinetics were less temperature-dependent as compared with the other inhibitors. Amprenavir, indinavir and ritonavir showed non-linear temperature dependencies of the kinetics. The free energy, enthalpy and entropy (,G, ,H, ,S) were determined, and the energetics of complex association (,Gon, ,Hon, ,Son) and dissociation (,Goff, ,Hoff, ,Soff) were resolved. In general, the energetics for the studied inhibitors was in the same range, with the negative free energy change (,G,<,0) due primarily to increased entropy (,S,>,0). Thus, the driving force of the interaction was increased degrees of freedom in the system (entropy) rather than the formation of bonds between the enzyme and inhibitor (enthalpy). Although the ,Gon and ,Goff were in the same range for all inhibitors, the enthalpy and entropy terms contributed differently to association and dissociation, distinguishing these phases energetically. Dissociation was accompanied by positive enthalpy (,Hoff,>,0) and negative entropy (,Soff,<,0) changes, whereas association for all inhibitors except lopinavir had positive entropy changes (,Son,>,0), demonstrating unique energetic characteristics for lopinavir. This study indicates that this type of data will be useful for the characterization of target,ligand interactions and the development of new inhibitors of HIV-1 protease. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Synthesis, pharmacology, crystal properties, and quantitative solvation studies from a drug transport perspective for three new 1,2,4-thiadiazoles

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 9 2010
German L. Perlovich
Abstract A novel 1,2,4-thiadiazoles were synthesized. Crystal structures of these compounds were solved by X-ray diffraction experiments and comparative analysis of molecular conformational states, packing architecture, and hydrogen bonds networks were carried out. Thermodynamic aspects of sublimation processes of studied compounds were determined using temperature dependencies of vapor pressure. Thermophysical characteristics of the molecular crystals were obtained and compared with the sublimation and structural parameters. Solubility and solvation processes of 1,2,4-thiadiazoles in buffer, n -hexane and n -octanol were studied within the wide range of temperature intervals and thermodynamic functions were calculated. Specific and nonspecific interactions of molecules resolved in crystals and solvents were estimated and compared. Distribution processes of compounds in buffer/n -octanol and buffer/n -hexane systems (describing different types of membranes) were investigated. Analysis of transfer processes of studied molecules from the buffer to n -octanol/n -hexane phases was carried out by the diagram method with evaluation of the enthalpic and entropic terms. This approach allows us to design drug molecules with optimal passive transport properties. Calcium-blocking properties of the substances were evaluated. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:3754,3768, 2010 [source]

Coexistence of Domains with Distinct Order and Polarity in Fluid Bacterial Membranes,

PHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 1 2002
Sharon Vanounou
ABSTRACT In this study we sought the detection and characterization of bacterial membrane domains. Fluorescence generalized polarization (GP) spectra of laurdan-labeled Escherichia coli and temperature dependencies of both laurdan's GP and fluorescence anisotropy of 1,3-diphenyl-1,3,5-hexatriene (DPH) (rDPH) affirmed that at physiological temperatures, the E. coli membrane is in a liquid-crystalline phase. However, the strong excitation wavelength dependence of rlaurdan at 37°C reflects membrane heterogeneity. Time-resolved fluorescence emission spectra, which display distinct biphasic redshift kinetics, verified the coexistence of two subpopulations of laurdan. In the initial phase, <50 ps, the redshift in the spectral mass center is much faster for laurdan excited at the blue edge (350 nm), whereas at longer time intervals, similar kinetics is observed upon excitation at either blue or red edge (400 nm). Excitation in the blue region selects laurdan molecules presumably located in a lipid domain in which fast intramolecular relaxation and low anisotropy characterize laurdan's emission. In the proteo-lipid domain, laurdan motion and conformation are restricted as exhibited by a slower relaxation rate, higher anisotropy and a lower GP value. Triple-Gaussian decomposition of laurdan emission spectra showed a sharp phase transition in the temperature dependence of individual components when excited in the blue but not in the red region. At least two kinds of domains of distinct polarity and order are suggested to coexist in the liquid-crystalline bacterial membrane: a lipid-enriched and a proteo-lipid domain. In bacteria with chloramphenicol (Cam),inhibited protein synthesis, laurdan showed reduced polarity and restoration of an isoemissive point in the temperature-dependent spectra. These results suggest a decrease in membrane heterogeneity caused by Cam-induced domain dissipation. [source]

Phase transitions and transport phenomena in Li0.25Cu1.75Se superionic compound

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 15 2004
M. Kh.
Abstract Phase transformation points in Li0.25Cu1.75Se mixed electronic,ionic conductor have been determined by calorimetric, conductometric and thermoelectric measurements. The phase transformation (PT) from triclinic to monoclinic occurs at 403,413 K. At 503,515 K the monoclinic phase is followed by a rhombohedral modification. Both of these PTs are accompanied by drops on the calorimetric curve. At about 653 K observed anomalies in the temperature dependencies of the ionic conductivity, of the chemical diffusion coefficient and the jump of the ionic Seebeck coefficient have been induced by the PT to hexagonal phase. Neutron diffraction studies reveal the cubic structure of Li0.25Cu1.75Se compound (with space group Fm3m) at 773 K. The corresponding PT causes anomalies in the electrical and diffusion properties at 703,713 K. Cu ions are statistically distributed over tetrahedral and trigonal voids in an Fm3m cage; lithium ions randomly occupy 32(f) positions. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Temperature-induced changes of domain structures in ultrathin magnetic films

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 5 2006
T. Polyakova
Abstract We describe the thermal-driven evolution of stripe domain structures in ultrathin magnetic films with perpendicular anisotropy. Taking into account temperature dependencies of the film magnetic parameters we analyze possible temperature dependencies of the domain period. It is shown that the film heating leads to a decrease in the domain period. In soft films thermally assisted domain nucleation could provide a continuous decrease of the domain period while the domain structure passes through equilibrium states. On increasing the temperature of a hard film, the domain structure exists as metastable one adjusting its period by a sequence of jumps towards to equilibrium. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Predominant point defects in tellurium saturated CdTe

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2006
P. Fochuk
Abstract High temperature Hall effect measurements at 570,1070 K under well defined Te vapor pressure in CdTe single crystals grown by THM and Bridgman techniques were made. Both the free carrier density versus Te vapour pressure value and temperature dependencies were studied. At heating up till ,870 K the hole density was Te vapor pressure independent, but it varied in different samples from 1 × 1016 to 1 × 1017 cm,3. At higher temperatures the conductivity becomes of intrinsic type, turning then into n-type one. A theoretical analysis of native point defects contents at different conditions in the framework of Krögers quasichemical formalism was performed. It resulted in the impossibility of mutual compensation of native donors and acceptors proposed by different authors. The results were explained assuming the presence of an electrically active foreign point defect , the oxygen interstitial acceptor. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Temperature acclimation of photosynthesis in spinach leaves: analyses of photosynthetic components and temperature dependencies of photosynthetic partial reactions

PLANT CELL & ENVIRONMENT, Issue 4 2005
WATARU YAMORI
ABSTRACT Spinach (Spinacia oleracea) plants were grown under the day/night temperature regime of 15/10 °C (LT) or 30/25 °C (HT). The plants were also transferred from HT to LT when the sample leaves were at particular developmental stages (HL-transfer). With fully mature leaves, the light-saturated photosynthetic rate (A) at the ambient CO2 concentration (Ca) of 1500 µL L,1 (A1500) and the initial slope of A versus intercellular CO2 concentration (Ci) at low Ci region (IS) were obtained to assess capacities of RuBP regeneration and carboxylation. Photosynthetic components including Rubisco and cytochrome f (Cyt f) were also determined. The optimum temperatures for A at Ca of 360 µL L,1 (A360), A1500 and IS in HT leaves were 27, 36 and 24 °C, whereas those in LT leaves were 18, 30 and 18 °C. The optimum temperatures in HL-transfer leaves approached those of LT leaves with the increase in the duration at LT. The shift in the optimum temperature was greater and quicker for IS than A1500. By the HL-transfer, the maximum values of A1500 and IS also increased. The maximum A1500 and Cyt f content increased more promptly than IS and Rubisco content. Changes in the Cyt f/Rubisco ratio were reflected to those in the A1500/IS ratio. Taken together, photosynthetic acclimation to low temperature in spinach leaves was due not only to the change in the balance of the absolute rates of RuBP regeneration and carboxylation but also to the large change in the optimum temperature of RuBP carboxylation. [source]

Dielectric properties of an epoxy-amine system at a high microwave frequency

POLYMER ENGINEERING & SCIENCE, Issue 12 2005
Liming Zong
The dielectric properties of a curing diglycidyl ether of bisphenol A (DGEBA)/Jeffamine D-230 system have been studied over the temperature range of 20,90°C at 2.45 GHz. It was found that, generally, both the dielectric constant and the dielectric loss factor of the system increased with temperature and decreased as the reaction proceeded. The epoxy resins at different extents of cure exhibited the , relaxation, which can be described by the Arrhenius Rate Law. The relaxation is attributed to the motions of the dipolar groups associated with the reactants. The Davidson-Cole model can represent the temperature dependencies of the dielectric properties. The nature of the information yielded by dielectrometry on the dynamics of the system is discussed. The evolution of the parameters of the models during the polymerization was mainly affected by the decreasing number of the dipolar groups involved in the reaction and increasing medium viscosity. POLYM. ENG. SCI. 45:1576,1580, 2005. © 2005 Society of Plastics Engineers [source]

Binding specificity and the ligand dissociation process in the E. coli biotin holoenzyme synthetase

PROTEIN SCIENCE, Issue 3 2002
Keehwan Kwon
Abstract The binding of the Escherichia coli biotin holoenzyme synthetase to the two ligands, biotin and bio-5,-AMP, is coupled to disorder-to-order transitions in the protein. In the structure of the biotin complex, a "glycine-rich" loop that is disordered in the apo-enzyme is folded over the ligand. Mutations in three residues in this loop result in significant changes in the affinity of the enzyme for both biotin and bio-5,-AMP. The kinetic basis of these losses in the affinity resides primarily in changes in the unimolecular rates of dissociation of the complexes. In this work, isothermal titration calorimetry has been employed to examine the detailed thermodynamics of binding of three loop mutants to biotin and bio-5,-AMP. The energetic features of dissociation of the protein,ligand complexes also have been probed by measuring the temperature dependencies of the unimolecular dissociation rates. Analysis of the data using the Eyring formalism yielded entropic and enthalpic contributions to the energetic barrier to dissociation. The thermodynamic results coupled with the known structures of the apo-enzyme and biotin complex have been used to formulate a model for progression from the ground-state complex to the transition state in biotin dissociation. In this model, the transition-state is characterized by both partial disruption of noncovalent bonds and acquisition of some of the disorder that characterizes the glycine-rich loop in the absence of ligand. [source]

The Dual Mode Microwave Afterglow Apparatus for Measuring the Electron Temperature Dependence of the Electron-Ion Recombination

CONTRIBUTIONS TO PLASMA PHYSICS, Issue 4 2008
O. Miku
Abstract Three dual mode microwave apparatus (one using S -band and two using X -band) have been developed to determine ambipolar diffusion and electron-ion recombination rates under conditions such that Tgas = 300K and Te is varied from 300 K to 6300 K, in the afterglow period of the dc glow discharge. TheTM010 cylindrical cavity (in S -band) and TM011 open cylindrical cavity (X -band) are used to determine the electron density during the afterglow period and a non-resonant waveguide mode is used to apply a constant microwave heating field to the electrons. To test the properties of the apparatus the neon afterglow plasma has been investigated. At Te = 300 K a value of , (Ne+2) = (1.7± 0.2) × 10,7cm3/s is obtained which is in good agreement with values of other investigators. Also similar variations of , as T,0.4e (S -band) and as T,0.42e (X -band) obeyed over the range 300 , Te , 6300K are in good agreement with some other previous measurements. The simplicity of the X-band microwave apparatus also allows the measurements of the gas temperature dependency and the study of electron attachment and may be used simultaneously with optical or mass spectrometry investigations. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Assembly of Dinuclear CuII Rigid Blocks by Bridging Azido or Poly(thiocyanato)chromates: Synthesis, Structures and Magnetic Properties of Coordination Polymers and Polynuclear Complexes

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2010
Sergey V. Kolotilov
Abstract Reaction of a dinuclear cationic copper(II) complex of 4,4,-[2-(3-hydroxyiminobutyl)imino]biphenyl [CuII2(LH)2]2+ with N3, resulted in the formation of a dinuclear azido [CuII2(LH)2(N3)2(H2O)2] complex or a 2D coordination polymer [CuII2(LH)2(N3)2]n. Reaction of the dinuclear complex with [CrIII(NCS)6]3, or [CrIII(NCS)4(NH3)2], produced a 2D polymer {[CuII2(LH)2(CH3CN)2]3[CrIII(NCS)6]2}n or a 1D chain, constructed from tetranuclear units {[CuII2(LH)2][CrIII(NCS)4(NH3)2]2}n. Structures of the compounds were determined by X-ray crystallography and complexes were characterised by the temperature dependency of the magnetic susceptibility and by ESR spectroscopy. Magnetic properties of homometallic compounds were fit with the model of a dimer with the Hamiltonian , = ,J,1·,2. For heterometallic complexes ,MT curves were fit as the superposition of magnetism resulting from both [CuII2(LH)2]2+ and the adjacent CrIII -containing anion. J values for the complexes lie in the range from ,12.74(4) to ,17.77(8) cm,1. It was shown that the 4,4,-biphenyl bridge efficiently mediates exchange interactions. [source]

Strain-life approach in thermo-mechanical fatigue evaluation of complex structures

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 9 2007

ABSTRACT This paper is a contribution to strain-life approach evaluation of thermo-mechanically loaded structures. It takes into consideration the uncoupling of stress and damage evaluation and has the option of importing non-linear or linear stress results from finite element analysis (FEA). The multiaxiality is considered with the signed von Mises method. In the developed Damage Calculation Program (DCP) local temperature-stress-strain behaviour is modelled with an operator of the Prandtl type and damage is estimated by use of the strain-life approach and Skelton's energy criterion. Material data were obtained from standard isothermal strain-controlled low cycle fatigue (LCF) tests, with linear parameter interpolation or piecewise cubic Hermite interpolation being used to estimate values at unmeasured temperature points. The model is shown with examples of constant temperature loading and random force-temperature history. Additional research was done regarding the temperature dependency of the Kp used in the Neuber approximate formula for stress-strain estimation from linear FEA results. The proposed model enables computationally fast thermo-mechanical fatigue (TMF) damage estimations for random load and temperature histories. [source]

Adaptation of soil microbial communities to temperature: comparison of fungi and bacteria in a laboratory experiment

GLOBAL CHANGE BIOLOGY, Issue 12 2009
GEMA BÁRCENAS-MORENO
Abstract Temperature not only has direct effects on microbial activity, but can also affect activity indirectly by changing the temperature dependency of the community. This would result in communities performing better over time in response to increased temperatures. We have for the first time studied the effect of soil temperature (5,50 °C) on the community adaptation of both bacterial (leucine incorporation) and fungal growth (acetate-in-ergosterol incorporation). Growth at different temperatures was estimated after about a month using a short-term assay to avoid confounding the effects of temperature on substrate availability. Before the experiment started, fungal and bacterial growth was optimal around 30 °C. Increasing soil temperature above this resulted in an increase in the optimum for bacterial growth, correlated to soil temperature, with parallel shifts in the total response curve. Below the optimum, soil temperature had only minor effects, although lower temperatures selected for communities growing better at the lowest temperature. Fungi were affected in the same way as bacteria, with large shifts in temperature tolerance at soil temperatures above that of optimum for growth. A simplified technique, only comparing growth at two contrasting temperatures, gave similar results as using a complete temperature curve, allowing for large scale measurements also in field situations with small differences in temperature. [source]

Numerical study on flame structure in H2,O2/CO2 laminar flames

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 7 2003
Jeong Park
Abstract Numerical study, aimed at the understanding of the flame structure in O2/CO2 recycling combustion system, has been conducted with detailed chemistry. Special concern is focused on addition effect of carbon dioxide on flame structure in H2,O2 counterflow diffusion flame as a simulating configuration. To clarify chemical and thermal effects on flame structure, the comparison between predicted results with a virtual species X to displace the real carbon dioxide and with added carbon dioxide in oxidizer stream is made according to strain rate and the concentration of added CO2. From the systematical comparison of a dominant radical producing reaction with a chain termination reaction the effects of strain rate and composition control of oxidizer stream on flame structure are estimated. It is found that the behaviours of C1 - and C2 -branch species are a direct outcome of that of produced CO due to the breakdown of added CO2. There exists a temperature dependency in the behaviour of produced CO and this competes for the behaviour of the produced CO with chemical effects due to the backward reaction of CO+OH=CO2+H. Copyright © 2003 John Wiley & Sons, Ltd. [source]

A comparative in situ Rietveld refinement study: thermal decomposition and transformation of CoAl and CoZnAl layered double hydroxides

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2008
Rune E. Johnsen
Rietveld refinement based on in situ X-ray powder diffraction (XRPD) data was combined with thermogravimetric analysis (TGA) and mass spectrometry (MS) to study and compare the phase transformations, thermal stability, microstructural and structural changes of two cobalt-containing nitrate-based layered double hydroxides (LDHs) upon heating in a controlled inert atmosphere of nitrogen. The XRPD data were collected, using synchrotron X-ray radiation, with a time resolution of 107,s, which made it possible to carry out detailed structural studies of the initial layered double hydroxides as well as their decomposition products: spinel for a CoAl,NO3 LDH and spinel/zincite for a CoZnAl,NO3 LDH. Correlating these data with those from the TGA,MS analyses gives us information about the transformation mechanisms. Rietveld refinements of the two spinel phases reveal remarkable differences. The a axis of the spinel formed by decomposition of the CoAl,NO3 LDH increases almost linearly from approximately 598 to 1163,K, mainly due to the dominating thermal expansion, whereas the a axis of the spinel formed by decomposition of the CoZnAl,NO3 shows a more complex temperature dependency. Between approximately 698 and 1073,K, the a axis is almost constant due to pronounced chemical interaction with an additional amorphous phase and the zincite phase, whereas from 1073 up to 1163,K it increases linearly. Calculations, based on the results of the Rietveld refinements, of the size of the octahedral and tetrahedral coordination polyhedra in the spinel show that the octahedra shrink and the tetrahedra expand with increasing temperature. The unusual thermal behaviour of the octahedra is discussed and attributed to the low formation temperature of the cobalt aluminium spinel phase. Finally, the intensity of a low-angle scattering (LAS) signal observed in the XRPD patterns was correlated with the decomposition of the LDH, and determination of the specific surface areas gave the temperature-dependent BET surface areas. [source]

Thermal Inactivation Kinetics of Salmonella and Listeria in Ground Chicken Breast Meat and Liquid Medium

JOURNAL OF FOOD SCIENCE, Issue 4 2000
R.Y. Murphy
ABSTRACT: Thermal inactivation of Listeria innocua and 6 Salmonella serotypes in ground chicken breast meat was compared to that in peptone (0.1%) - agar (0.1%) solution. Inoculated samples were packed in a thin-wall metal tube and submerged in a water bath at temperatures ranging from 55.0 to 70.0 °C. For Salmonella and Listeria, the D values in ground chicken breast meat at 55 to 70 °C were higher (p < 0.0001) than those in peptone-agar solution; however, the z values were not significantly different. Complete first-order inactivation models, with Arrhenius temperature dependency, were developed for each inoculum and medium. [source]

Reverse osmosis of nonaqueous solutions through porous silica-zirconia membranes

AICHE JOURNAL, Issue 2 2006
Toshinori Tsuru
Abstract Porous silica-zirconia membranes with pore diameters from 0.8 to 2 nm were prepared by a sol-gel process, and applied to the separation of alcohols (hexanol, octanol, decanol) and alkanes (hexane, decane, tetradecane) in ethanol solutions by reverse osmosis over the temperature range from 25 to 60° C. A silica-zirconia membrane with a pore diameter of 1 nm showed a molecular weight-cut-off (MWCO) of 200 in ethanol solutions. Rejection increased with the applied pressure, for both alcohol and alkane solutes. However, the rejection of alcohols was found to decrease with temperature, while that for alkanes remained nearly constant. The separation characteristics were examined for the following membrane parameters: solvent permeability, Lp, reflection coefficient, ,, and solute permeability, P, based on the Spiegler-Kedem equation. The viscosity of solutions and the diffusivity of alkanes and alcohol solutes in nano-sized pores were found to show a larger temperature dependency than in bulk. The diffusivity of alkane solutes showed the same temperature dependency as the viscosity of ethanol in nano-sized pores, while the diffusivity of alcohol solutes showed a larger temperature dependency than the viscosity of ethanol, probably because of a larger interaction between alcohol solutes and the hydrophilic surface of silica-zirconia membranes. Diffusion experiments were carried out to confirm the temperature dependency of the diffusivities in nano-sized pores. A bilayer model verified that solute permeabilities by reverse osmosis and diffusion experiments were consistent with each other. © 2005 American Institute of Chemical Engineers AIChE J, 2006 [source]

A chemical understanding for the enhanced hydrogen tunnelling in hydroperoxidation of linoleic acid catalysed by soybean lipoxygenase-1

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 7-8 2008
Monica Barroso
Abstract The reaction path of the Interacting-State Model (ISM) is used with the Transition-State Theory (TST) and the semiclassical correction for tunnelling (ISM/scTST) to calculate the rates of H-atom abstraction from C(11) of linoleic acid catalysed by soybean lipoxygenase-1 (SLO), as well as of an analogous uncatalysed reaction in solution. The calculated hydrogen-atom transfer rates, their temperature dependency and kinetic isotope effect (KIE) are in good agreement with the experimental data. ISM/scTST calculations reveal the hypersensitivity of the rate to protein dynamics when the hydrogen bonding to a carbon atom is present in the reaction coordinate. Copyright © 2008 John Wiley & Sons, Ltd. [source]