bluuebunny/crossref_metadata_2025_split huggingface dataset:
Excess Properties of Liquid Cyclohexane/Hydrocarbon Mixtures I. Experimental Results of the Excess Enthalpy
Authors: Wagner H. , Lichtenthaler R. N. 
Published: July 2012

AbstractExperimental results of the composition dependence of the molar excess enthalpy HE of ten mixtures of cyclohexane with saturated and unsaturated hydrocarbons at 298.15 K and 1 bar are reported. The results of the mixtures With the saturated hydrocarbons confirm the systematic behaviour of HE with respect to the chain length and the degree of branching deduced from already existing data. The results of the mixtures with unsaturated components allow to extend the systematics taking into account the number and the location of multiple bonds within the molecules.
Thermodynamics of S.˙.S 2σ/1σ* Three‐electron Bonds and Deprotonation Kinetics of Thioether Radical Cations in Aqueous Solution
Authors: Mönig J. , Goslich R. , Asmus K.‐D. 
Published: July 2012

AbstractTime‐resolved pulse radiolysis studies have been carried out on the R2S+· R2S ⇆ (R2S.˙.SR2)+ equilibrium and associated decay kinetics of sulfur centered radical cations. ‐ Equilibrium constants of K = 2.0 · 105 and 5.4 · 102 mol−1 dm3 at 20°C have been determined for the species with R = CH3 and (CH3)2CH, respectively. Absolute rate constants have been measured for the back reaction of the above equilibrium: k‐1 = 1.5 · 104 s−1 and 5.6 · 106 s−1, respectively, at 20°C. Further rate constants refer to the deprotonation of R2S+ by various proton acceptors (phosphate, acetate and water). ‐ ΔH≠ = 57 kJ mol−1 and 17 kJ mol−1 were determined for the dissociation of the sulfur‐sulfur 3‐electron bond in (Me2S.˙.SMe2)± and (i‐Pr2S.˙.S i‐Pr2)+, respectively. On this basis the S.˙.S bond energies were estimated to ≲80 kJ mol−1 and ≲40 kJ mol−1 for these two species. The kinetic and thermodynamic results substantiate previous conclusions on the electronic structure and relative stability of S.˙.S bonded radicals and corroborate some theoretical calculations.
Nuclear Spin‐lattice Relaxation and Self‐diffusion Coefficient for Toluene around Supercritical Region
Authors: Shimokawa Shigezo 
Published: July 2012

AbstractThe molecular motion of toluene has been studied through measurements of the nuclear spin‐lattice relaxation time (T1), the self‐diffusion coefficient (D), and the mass density (ϱ) up to the supercritical region. 1H NMR measurements were made at 38.2 MHz, in the range 294 ≤. T/K 761, 0.1 ≤ P/MPa ≤ 15 under toluene vapour pressure. T1 for ring protons has a maximum (95 sec) near the critical temperature (Tc = 591.4 K) and decreases above Tc. The value of D, on the other hand, changes abruptly near Tc. T1 for methyl protons are nearly constant between 380–580 K. The value of ϱ for the toluene‐d3 was measured in the same temperature and pressure range in situ by the one‐dimensional projection method. The various contributions to the relaxation rate are separated and the molecular motions of toluene molecules in the liquid and supercritical regions are discussed.
Studies on the n‐GaAs Photoanode in Aqueous Electrolytes. 3. Recombination Resistance
Authors: Vaiunaekelbergh D. , Gomes W. P. , Cardon F. 
Published: July 2012

AbstractThe resistive part of the additional impedance, caused by illumination of the n‐GaAs/electrolyte interface, has been studied both experimentally and theoretically. The dependence of this resistive part on the electrode potential, the light intensity and the measuring frequency is interpreted on the basis of a model in which it is assumed that surface recombination is involved. A quantitative expression for the recently introduced concept of recombination resistance is derived.
Strukturuntersuchung konzentrierter wäßriger Caesiumhydroxid‐Lösungen mit Röntgen‐ und Neutronenstreuung
Authors: Bertagnolli H. , Ehrig R. , Weidner J. U. , Zimmermann H. W. 
Published: July 2012

AbstractX‐ray and neutron diffraction measurements each on three differently concentrated aqueous solutions of Cesiumhydroxid are reported. After the correction for background, self‐absorption, multiple scattering, inelastic effects and in case of X‐rays for the wavelength distribution of the incident beam the structure of the water molecule was deduced from the coherent neutron scattering cross section. The Cs+–Cs+–and Cs+–H2O/OH−pair correlation functions could be determined from these three X‐ray measurements. A quantitative analysis was performed by use of a geometrical model, which reproduces very well all measurements as well as the individual atom pair correlation functions. It turns out that the local order in aqueous CsOH‐solutions is very similar to the structure of solid CsOH · H2O. The Cs+‐ions are located between layers consisting of slightly puckered hexagon rings of H2O and OH−, which are connected by H‐bonds.
Thermal Decomposition of Cyanogen Measured in C2N2/O2 and C2N2/H2 Reaction Systems by Atomic Resonance Absorption
Authors: Natarajan K. , Thielen K. , Hermanns H. D. , Roth P. 
Published: July 2012

AbstractThe thermal decomposition of cyanogen has been measured behind reflected shock waves in the temperature range 1900–2650 K at pressures of about 1.8–2.0 bar using Atomic Resonance Absorption Spectroscopy (ARAS). C2N2/O2 and C2N2/H2 mixtures highly diluted in argon were shock heated and O and H atom concentrations were monitored in the post shock reaction zone. Because of the fast secondary reactions of the dissociation product CN, the measured concentrations of O or H were strongly dependent on the rate of dissociation of cyanogen. The experimentally determined rate coefficient data for the dissociation of cyanogen are closely fit by the Arrhenius expression: k = · 2.97 10−7 exp(−53665 K/T)cm3/s. The present rate coefficient data is compared with the results of previous investigators and also with the estimates obtained from the weak collision unimolecular reaction rate theory.
Some New Details in the Kinetic Considerations of the Oscillatory Decomposition of Hydrogen Peroxide
Authors: Anić S. , Kolar‐Anić L. J. 
Published: July 2012

AbstractIt is found that decomposition of hydrogen peroxide in the presence of constant amount of potassium iodate and sulphuric acid ([KIO3] = 7.35 · 10−2 mol/dm3, [H2SO4] = 2.45 · 10−2 mol/dm3) exhibits an oscillatory behaviour with only one induction period if the initial concentration of hydrogen peroxide ranges from 3.5 · 10−4 to 7.9 · 10−3 mol/dm3. If this concentration is larger than 7.9 · 10−3 mol/dm3, but less than the concentration of KIO3, two induction periods separated by one oscillation are observed. For the highest concentrations of [H2O2]0 taken into account, the one oscillation between the two induction periods disappears, and they are both fused together, without losing their own kinetic characteristics. For all the examined initial concentrations [H2O2]0 above 7.9 · 10−3 mol/dm3, the overall decomposition of hydrogen peroxide is found to follow the first order kinetics, with the rate constant found to be equal to 1.88 · 10−2 min−1, at T = 335.2 ± 0.2 K. The dependence of the number of oscillations on [H2O2]0 is examined. It is found that, under the conditions of our experiments, 2.6 · 10−4 mol/dm3 of hydrogen peroxide is necessary for the onset of one oscillation.
Thermodynamics of Ionic Solid Solutions and Its Application to the Formation and Stability of Biominerals
Authors: Driessens F. C. M. 
Published: July 2012

AbstractThe classification of equilibrium between ionic solid solutions and aqueous solutions by Roozeboom is interpreted as being a result of the ideal or regular behaviour of the ionic solid solutions. Due to the fact that the solubility products of isomorphous compounds which form ionic solid solutions differs in general by several orders of magnitude, it is very unlikely that precipitates differ much from the stoichiometry of one of these compounds. This principle is applied to the problem of biominerals, especially bone mineral. As a result it appears that the first mineral deposited in bone is octocalcium phosphate. Under in vivo conditions this phase is transformed into a mixture of three other calcium phosphates having a much lower solubility. The solubility controlling phase in living bone appears to be octocalcium phosphate which is continuously formed during the turn‐over of bone. This model for bone mineral has lead to the explanation of the formation of renal stones, pathological calcifications and osteoporosis as a consequence of slight chronic magnesium deficiency. The action of magnesium is mediated by the osteocytes.
Modelling of Polymerization Phenomena
Authors: Ray W. H. 
Published: July 2012

AbstractPolymerization phenomena provide interesting subjects for modelling at several levels. At the microscopic level, the kinetics of chain growth are most complex, with branching reactions, end group formation, multifunctional growth, etc. These kinetics are largely responsible for the final polymer properties. However, the kinetics are also influenced by mesoscale consideration of simultaneous phase changes, heat and mass transfer and equilibria between phases, and polymer morphology during polymerization. Often these considerations also have a major influence on the polymer properties. Finally, at the macroscale, we have the polymerization reactor which must be well designed and controlled in order for the smaller scale processes to proceed as planned. Each of these levels of scale will be discussed and specified examples of the practical application of modelling will be presented.
Kinetics of Proton‐Transport‐Coupled ATP Synthesis Catalyzed by the Chloroplast ATP Synthase
Authors: Gräber P. , Fromme P. , Junesch U. , Schmidt G. , Thulke G. 
Published: July 2012

AbstractThe kinetics of proton‐transport‐coupled ATP synthesis catalyzed by the chloroplast ATPase (ATP synthase) was investigated after energization of the membrane by an artificially generated ΔpH and an electric potential difference, Δψ. With a rapid mixing system, ATP synthesis was studied at short reaction times (<200 ms) where all relevant parameters (pHout, pHin, Δψ, substrate and product concentrations) remain practically constant at their initial values. The reaction is investigated at three levels of complexity. (1) The ATPase is embedded in the natural membrane. (2) The ATPase is isolated, purified and reconstituted into asolectin liposomes. (3) The reconstituted ATPase is investigated under single site, single turnover conditions. The following results were obtained:

The dependence of the activation and of the catalytic reaction on pHin is measured.
The dependence of the rate of ATP synthesis on the ADP concentration at ΔpH = 3.2 is, at low ADP concentration, diffusion controlled with a rate constant of 6·106 M−1s−1 . At high ADP concentration, the maximal enzyme turnover is 700 s−1.
When the ATPase is reconstituted into asolectin liposomes practically the same rate is obtained as in the natural membrane, demonstrating that for optimal activity only one protein with an inert membrane is necessary.
Under single site conditions the equilibrium constant at the enzyme between bound P1 and bound ATP is K ≈ 0.13.
Calculation of Nematic‐Isotropic Phase Equilibria in Solutions of Polymers in Nematic Liquid Crystals Using the Flory Lattice Model
Authors: Ballauff M. 
Published: July 2012

AbstractA treatment of phase equilibria occuring in mixtures of polymers in nematic liquid crystals is presented. The steric pan of the mixing partition function is evaluated using the Flory lattice model, the soft anisotropic forces between the rods enter as an additional factor in the partition function. Isotropic interaction between the nematic solvent and the polymeric solute is introduced in terms of a single interaction parameter. It is shown that the marked incompatibility observed in nematic solutions of high polymers is due to the entropic part of the resulting free energy of mixing. Unfavorite isotropic interactions between solvent and solute leads to the occurence of a reentrant isotropic phase rich in polymer. If the solvent power of the nematic fluid is low enough, liquid‐liquid demixing will take place in the isotropic phase followed by a triple point at lower temperature where a nematic phase is coexisting with two isotropic phases. Below the triple point a nematic phase containing only minute amounts of polymer is in equilibrium with an isotropic phase exhibiting a high concentration of the macromolecular solute.
Modellierung des Kohlenstoffaustauschs zwischen Atmosphäre und Landvegetation unter Berücksichtigung von Landnutzungsänderungen und CO2‐Düngungseffekt
Authors: Kohlmaier G. H. , Bröhl H. , Janecek A. , Benderoth G. 
Published: July 2012

AbstractThe role of the terrestrial biota within the global carbon cycle is analysed with respect to human impacts causing releases of CO2 into the atmosphere and to a CO2 fertilization effect caused by enhanced atmospheric CO2 concentrations. Two different model structures representing different plant responses on enhanced CO2 are suggested, and the related global net fluxes of carbon are estimated. It is shown that, while clearings of forests and use of biomass as fuel nowadays may cause a net carbon release from the biota between 0.6 and 1.8 Gt C/a, a CO2 fertilization effect may compensate at least part of this release (0.25 to 1.5 Gt C/a), such that the role of the terrestrial biota as source or sink of atmospheric CO2 is unclear on the present database.
On Topological‐Dynamical Equivalent Representations of Reaction Networks: The Omega‐Equation and a Canonical Class of Mass Action Kinetics
Authors: Siré Ernst‐Olof 
Published: July 2012

AbstractAn unifying concept ‐ the Omega‐equation ‐ is introduced to describe analogies of dynamical systems such as for chemical reaction systems, transport and metabolism of coupled compartments, cell populations, population genetics and animal behavior in ecology. The phenomenology of rate‐laws of such systems are frequently described, perhaps after an equivalent transformation, in terms of ordinary polynomial differential equations, which can be incorporated in the strong formalism of mass action reaction networks. Furthermore, we show that the set of all mass action kinetics can be reduced to the smaller class of so‐called μ‐molar mass action networks, which generate homogeneous polynomial Ω‐equations of order μ.
Thermodynamic and Dielectric Properties of Binary Polar + Non‐Polar Mixtures I. Static Dielectric Constants and Excess Molar Enthalpies of n‐Alkylamine + n‐Dodecane Systems
Authors: Otín Santos , Fernández Javier , Embid José Muñoz , Velasco Inmaculada , Losa Celso Gutiérrez 
Published: July 2012

AbstractExcess molar enthalpies HE at atmospheric pressure and 303.15 K, and static dielectric constants, ϵs, at 2 MHz and temperature ranging from 293.05 to 323.25 K, have been determined for n‐dodecane + n‐propylamine, + n‐butylamine, + n‐hexylamine, + n‐octylamine, + n‐decylamine, + n‐dodecylamine and + pentadecylamine. From the experimental results, the variation of HE and ϵEs with the chain length of the amine is shown.
Retardation of the Cd2+ and In3+ Reduction Processes at DME in Chloride Medium in Relation to Adsorption of Coumarin
Authors: Mazhar A. A. , Heakal F. El‐Taib 
Published: July 2012

AbstractThe adsorption of coumarin on mercury in MKC1 has been determined from electrocapillary and capacitance measurements. At relatively high coumarin concentrations (≥ 10−3 M), the molecules reorient from the parallel to the vertical form at the more negative potentials. The results were found to fit the isotherm having a configurational term θ/ex‐1(1‐θ)x. From the values calculated for the standard free energy of adsorption and its variation with potential, it may be inferred that coumarin is not strongly adsorbed. In presence of coumarin, the Cd2+/Cd(Hg) and ln3+/ln(Hg) exchange reactions occur through the free surface, and the decrease in the rate constant is exponentially related to the surface coverage.
Kinetic Study of Chemically Activated Fluorocyclopropane
Authors: Dall'O L. , Heydtmann H. 
Published: July 2012

AbstractThe photolysis of ketene at 313 nm was studied in the presence of fluoroethene and oxygen. The product formation was observed as a function of total pressure between 12 and 1080 mbar. Chemically activated fluorocyclopropane was formed by addition of singlet methylene to the double bond, and subsequent isomerization to the fluoropropenes as well as decomposition of these primary products to allene, propyne and HF was observed. The product yield was described by RRKM calculations; a stepladder deactivation model was used.
Diffusion of Fluorine in Silica
Authors: Hermann Wilhelm , Raith Angelika , Rau Hans 
Published: July 2012

AbstractDiffusion constants of fluorine in silica were determined at temperatures between 1385 K and 1873 K. Samples were prepared by the PCVD (Plasma activated Chemical Vapor Deposition) method and diffusion profiles measured by SEM investigations. The resulting least squares fit is log(D(cm2 s−1)) = ‐0.920 ‐ 18337 K/T.
Thermodynamic excess functions for quasiternary solid solutions of type (MkN(1‐k)) (XlY(1‐l))
Authors: Leute Volkmar 
Published: July 2012

AbstractThe excess enthalpy for a quasiternary system of type MkN(1‐k)XlY(1‐l) is derived by use of a model, which considers the interaction of clusters composed of four particles. The distribution of the lattice constituents is assumed to be random. Based on this model the excess enthalpy can be described by a cubic function of the mole fractions k and l with the standard reaction enthalpy and 8 interaction parameters as constants. It is shown, that the ternary interaction parameters can be calculated from the interaction parameters of the subregular quasibinary subsystems, whereas the reaction enthalpy for the double conversion between the binary components can be derived from their standard enthalpies. Thus the phase diagrams of quasiternary systems with two mixed sublattices can be derived from the quasibinary data without introducing any special ternary interaction parameter. ‐ The influence of the interaction parameters on the shape of the phase diagram and especially the influence of the standard reaction enthalpy on the tie line field is demonstrated by some calculated phase diagrams.
Temperature dependence studies of NQR frequencies of halogens and also of quadrupolar relaxation times of chlorine nuclei in ammonium hexahalotellurates(IV)
Authors: Furukawa Yoshihiro , Nakamura Daiyu 
Published: July 2012

AbstractThe temperature dependence of NQR frequencies of halogens in ammonium hexahalotellurates(IV) has been reinvestigated in a wide range of temperature. A second‐order phase transition was definitely located at 89 K for (NH4)2TeCl6, below which temperature the existence of multiplet structure was suggested The temperature of a first‐order phase transition was determined for (NH4)2TeBr6 at 194 K in addition to the phase transition previously reported, which was located accurately at 212 K. The lowest‐frequency line among the three 81Br resonance lines observed below 194 K exhibited a positive temperature coefficient whereas the remaining two lines showed normal negative temperature coefficients. Except for the highest‐frequency v1 and v2 lines, the all four 127I lines observed for (NH4)2TeI6 showed anomalous temperature dependences. These temperature dependences could be interpreted by considering that the Te‐I…H type hydrogen bonds partially break due to the thermal activation of the motion of ammonium ions in crystals. A phase transition was located at 449 K by means of differential thermal analysis.
Electrochemical and solid state reactions of copper with n‐SnS2
Authors: Jaegermann W. , Ohuchi F. S. , Parkinson B. A. 
Published: July 2012

AbstractThe intercalation reaction of Cu with n‐SnS2 has been studied with a variety of techniques. Electrochemical and photoelectrochemical methods provided information about the energetics of the intercalation reaction and the band gap and carrier type of the new phase (p‐CuSnS2). X‐ray photoelectron spectroscopy (XPS) was used to characterize the stoichiometry of the new phase as prepared both electrochemically and in UHV. The thermal stability of CuSnS2 was studied with XPS and transmission electron microscopy (TEM) and the diffusion of copper through the van der Waals planes of SnS2 was demonstrated. A structure for the new phase is proposed which is consistent with the measured physical properties. The intercalation reaction is discussed with respect to its differences from the rigid band model of intercalation.
Deviations from equilibrium at the interface of a charged membrane
Authors: Manzanares J. A. , Mafé S. , Pellicer J. 
Published: July 2012

AbstractThe local equilibrium assumption commonly employed for the transport through the interface of a charged membrane has been analysed from a simplified electric double layer model. This layer is characterized on the basis of a surface potential arising from a non‐zero surface charge density placed on the membrane surface. The dependence of deviations from local equilibrium on the characteristic parameters of the problem is shown. Connection with the classical treatment by Donnan is discussed. Although the complexity of the problem calls for a number of simplifications, the results obtained appears to be significative. Thus, the analysis carried out displays not only that deviations from equilibrium are small, but also that in the limit of small fluxes, omission of a detailed study of the electric double layer is probably justified when characterizing ionic transport through common synthetic membranes
Composition dependent electronic conductivities and hall coefficients of mixed ionic‐electronic conductors. Part III: Beta silver sulfide revisited
Authors: Sohège J. , Funke K. 
Published: July 2012

AbstractIn a previous paper (I) we presented the composition dependent electronic conductivity and Hall coefficient of β‐Ag2+δS at different temperatures. The mobility of conduction‐band electrons was found to vary with temperature as T−3/2. In this paper we point out that, due to a temperature dependent effective electron mass, the relaxation time of conduction‐band electrons varies as T−1 and not as T−3/2.
NMR studies of molecular motion in various defect pyrochlores containing ammonium
Authors: Möller H. , Möller‐Warmuth W. , Kuntz M. , Tomandl G. 
Published: July 2012

AbstractNH4TaWO6, ND4TaWO6, and NH4NbWO6 have been studied by NMR at various frequencies and over a large range of temperatures. At low temperatures, ammonium ions exist as an entity tunnelling in the center of the cavities of the pyrochlore framework. From relaxation data an activation energy of this process of about 6.5 kJ/mol is obtained for all three materials. At temperatures above about 250 K translational motion narrows the spectra and produces relaxation. The experiments suggest a Grotthus type of proton transfer, where both local back ‐ and forth‐hopping (13–20 kJ/mol) and long range migration (31–39 kJ/mol) plays a role. At higher temperatures NH4+ and NH3 may diffuse as a whole. This is shown in particular for NH4NbWO6 which served as diaphragm in a water vapour electrolysis cell, and where ammonia becomes exchanged by water.
Elementary reactions of N2(A3Σ+u) with H2, F2 and H2C2O in the gas phase
Authors: Böhmer E. , Hack W. 
Published: July 2012

AbstractOverall rate constants for the removal of N2(A, v') by H2(X), F2(X) and H2C2O(X̄) were measured at T = 298 K in a fast flow reactor at constant injector position. N2(A) molecules in the vibrational states v' = 0, 1, 2, 3 were produced in the reaction of Ar(3P0,2) with N2(X) and detected by laser induced fluorescence (LIF) using the excitation of the first positive system of N2, B(3Πg)σ A(3Σ+u). The measured rate constants are: magnified imageThe rates of reactions (1), (2) and (3) and the reaction mechanisms are discussed.