bluuebunny/crossref_metadata_2025_split huggingface dataset:
Der Einfluß von Temperatur und Zusammensetzung auf die Art von Phasenübergängen cholesterischer Flüssigkristalle bis zu Drücken von 2,5 kbar
Authors: Pollmann P. , Scherer G. 
Published: July 2012

AbstractSeit 1973 ist bekannt (Keyes et al.), daß ein Wechsel der Art eines Phasenübergangs nicht nur durch Variation des Mischungsverhältnisses von Zwei‐Komponenten‐Systemen bei Normaldruck erreicht werden kann, sondern im Fall reiner Stoffe auch durch Anwendung von Druck. — Eigene Untersuchungen an Cholesterylmyristat (CM) und Cholesterylnonanoat (CN) haben jetzt gezeigt, daß der trikritische Punkt der reinen Stoffe bei hohen Drücken für den Phasenübergang smektisch‐A/cholesterisch kontinuierlich gegen die Normaldruckebene durch Zumischen einer geeigneten zweiten Komponente verschoben wird. Auf diese Weise wird eine trikritische Linie gebildet. — Bei der Prüfung der McMillan‐Theorie aufgrund der experimentell erhaltenen reduzierten Temperaturen der trikritischen Punkte — diese haben Werte zwischen 0,83 und 0,96 — ergab sich, daß die Vereinfachung, den Modellparameter δ = 0 (bzw. δ = const.) zu setzen. aufgegeben werden muß. Dazu mußten die Modellgleichungen der McMillan‐Theorie vollständig gelöst werden. — Die Veränderungen der McMillan‐Parameter entlang der trikritischen Linie werden diskutiert. — Die Phasenübergänge smektisch‐A/cholesterisch und cholesterisch isotrop von CM und CN sowie ihrer Mischungen mit p‐Pentylphenyl‐2‐chlor‐4‐(p‐pentylbenzoyloxy)benzoat wurden bis 2,5 kbar bestimmt.
Combined Ruthenium Lead Surface Treatment of Gallium Arsenide Photoanodes
Authors: Heller A. , Lewerenz H. J. , Miller B. 
Published: July 2012

AbstractAn increase in the solar‐to‐electrical conversion efficiency beyond that due to chemisorption of ruthenium results from subsequent adsorption of lead from alkaline solutions on both single crystal and polycrystalline n‐GaAs photoanodes. An efficiency of 7.8% is reached with thin film, chemically vapor deposited polycrystalline GaAs in the cell n‐GaAs/0.8 M K2Se0.1 M K2Se21 M KOH/C.
Electron Transfer through the Space Charge Barrier on TiO2 (Rutile) Electrodes via Interstitial Protons
Authors: Schumacher Rolf 
Published: July 2012

AbstractIt is reported on charge transfer reactions on n‐TiO2 electrodes in electrochemical experiments. The electrodes used were cleaned prior to treatment in oxygen and/or air at room temperature by a standardized procedure with H2SO4. The experiments showed that hydrogen interstitials located close to the electrode surface influence the charge transfer reaction. These states were introduced by the surface reaction with the acid. As the experiments showed the typical feature of the oxidation current peak changed dramatically to an unpronounced shape when using samples loaded with very little unbound hydrogen. Investigations on the influence of electrolyte‐pH on the charge transfer reaction revealed that a potential drop in the depletion region of around 2.1 V is needed to initiate this anodic process. The existence of the anodic peak is discussed in terms of resonance tunneling via states created by the pre‐treatment procedures in the charge barrier and at the surface.
Dielectric Measurements at High Pressures and Low Temperatures. II. The Dielectric Constant of Acetonitrile
Authors: Würflinger A. 
Published: July 2012

AbstractThe dielectric constant of acetonitrile is studied at temperatures between −60°C and +30°C up to pressures of 3 kbar. The electrode set developed is described. The dielectric constant of liquid acetonitrile together with recently determined PVT‐ data allow the calculation of the Kirkwood correlation factor g. This g‐factor decreases on approaching the melting curve to a constant value of approximately 0.7, independent of the pressure. On freezing the dielectric constant falls off from 49 to about 4 at atmospheric pressure and from 45.5 to about 4 at 3 kbar. In the solid state the dielectric constant is fairly independent of temperature and pressure, however, a small change is observed at a lower solid‐solid transition.
Study of a Fluid/Solid Interface over a Wide Density Range Including the Critical Region. I. Surface Excess of Ethylene/Graphite
Authors: Specovius J. , Findenegg G. H. 
Published: July 2012

AbstractThe surface excess amount of ethylene adsorbed on graphitised carbon black has been measured over a pressure range from 1 to 120 bar using a high pressure microbalance technique. The data span a range of temperatures from 263 to 323 K (0.93 ≤ T/Tc ≤ 1.14) and a range of bulk densities up to ρ/ρc=1.7. The results show the transition from the low‐temperature behavior (T < Tc) with multilayer adsorption on approaching the saturation pressure, to the situation above the critical temperature Tc when the surface excess isotherms Γσ(P) exhibit a pronounced maximum at a pressure Pmax > Pc. The dependence of Pmax on temperature, and the variation of Γσ with temperature along the critical isochore, is determined quantitatively. The surface excess is discussed in terms of an operationally defined exponential density profile of the fluid at the interface. The dependence of the decay length of this profile on the bulk density and on temperature is shown.
Der Isotopieeffekt bei der Verdampfung von Ammoniumchlorid
Authors: Virnich H.‐H. , Höpfner A. 
Published: July 2012

AbstractNormales und deuteriertes Ammoniumchlorid zeigt bei seiner irreversiblen Verdampfung recht unterschiedliche Verdampfungsgeschwindigkeiten. Je nach Verdampfungstemperatur wurde im Verhältnis der Sublimationsraten eine bis zu 10fach gesteigerte Verdampfung des normalen Salzes gegenüber der deuterierten Substanz beobachtet. — Eine theoretische Deutung dieses Phänomens kann im Rahmen eines Modells gefunden werden, in welchem der geschwindigkeitsbestimmende Schritt in der an die Kristalloberfläche gebundenen Dissoziation von Ammoniumchlorid zu Ammoniak und Chlorwasserstoff gesehen wird. Dies befindet sich im Einklang mit der seit längerem bekannten Tatsache, daß der Dampf von Salmiak aus den genannten Komponenten besteht. — Die am Modell in harmonischer Oszillator‐Approximation entwickelten Rechnungen liefern für beide Substanzen mit den Experimenten übereinstimmende Aktivierungsenergien.
Rotational Diffusion Tensor of Cyclohexene Molecule Determined from Selective Measurements of T1
Authors: Pajak Z. , Latanowicz L. , Jurga K. 
Published: July 2012

AbstractPerformed analysis of the experimental data obtained from selectively measured proton spin‐lattice relaxation times T1 for cyclohexene solutions in carbon tetrachloride at various temperatures is shown to be a method for determining the rotational diffusion coefficients of the molecule, treated as a symmetrical top since Ix ≅ Iy ≠ Iz. The evidenced anisotropy of the rotational motion is of a gas‐like nature — the reorientation about the axis of the greatest moment of inertia i. e. the symmetry axis of the diffusion tensor is the slowest and has the largest activation energy. The rotational diffusion model with small‐angle reorientations describes adequately the motional behaviour. The values of the rotational diffusion coefficients obtained for the neat liquid at room temperature D‖ = 8.3 · 1010 s−1 and D⟂ = 13.9 · 1010 s−1 are in agreement with calculations based on the modified Nora Hill model.
On the Approach to Steady States of Reacting Systems in the Continuous Stirred Tank Reactor
Authors: Heinrichs M. , Schneider F. W. 
Published: July 2012

AbstractA theoretical investigation is presented of the approach of chemical reactions to their steady states in a continuous stirred tank reactor (CSTR). We define a approach time tϵ which is a measure of the time required for any perturbation to decrease below a certain value where ϵ = 1/e is a convenient choice for linear networks. We shown analytically for any first order network that the approach time is less than or equal to the average residence time but never longer regardless whether „overshoot”︁ or „false start”︁ occurs if the sum of the initial CSTR concentrations does not exceed the sum of the input concentrations. For higher order single step CSTR reactions we present analytical solutions for small perturbations from their steady states. We show that the longest relaxation time is equal to the average residence time for all non‐autocatalytic higher order reactions in the CSTR. For autocatalytic reactions, however, the relaxation time constant in the CSTR may become infinite at critical flow rates. This interesting phenomenon is called critical slowing down and it has an analogy in second order equilibrium phase transitions. We show that critical slowing down may occur also in higher order autocatalysis. It may act as a tunable low pass filter i.e. the open autocatalytic reaction may resemble a kinetic buffer system that absorbs even large perturbations. As illustrations a number of examples of reaction types are presented.
Crystal Structure and Phase Transformation of Trichloroethylidene Trichlorolactic Ester (Chloralide), Cl3CCHOCOCHOCCl3. An X‐Ray and NQR Study
Authors: Hashimoto M. , Paulus H. , Weiss Alarich 
Published: July 2012

AbstractTrichloroethylidene trichlorolactic ester (Chloralide), Cl3CCHOCOCHOCCl3, crystallizes at room temperature (T ≈︁ 298 K) monoclinic, space group C52h — P21/c, with 4 molecules in the unit cell. The lattice constants are a = (619.94 ± 0.20) pm, b = (1716.3 ± 0.6) pm, c = (1037.0 ± 0.3) pm, β = 95.083° ± 0.010°. The crystal structure was determined with a reliability factor R = 0.044 (1638 symmetry independent reflexes with I > σ(I)). At 343 ≦ T/K ≦ 344 a phase transformation occurs, which shows super heating phenomena. — In the 35Cl‐NQR the 6 line low temperature spectrum 38.178 ≦ v/MHz ≦ 40.178 at T = 77 K is in accordance with the crystal structure. By intensity considerations an assignment of the spectrum of the two different CCl3 groups in the molecule was possible. The high temperature phase of Chloralide shows the fade out phenomenon in the NQR‐spectrum due to hindered rotations of one of the two CCl3 groups. The kinetics of the transformation phase II → phase I is of first order.
Analytische Diskussion des Austauschs von Kohlendioxid zwischen Atmosphäre und Ozean an Hand eines Advektions‐Diffusions‐Modells
Authors: Kohlmaier G. H. , Siré E. O. , Kratz G. , Fischbach U. , Bröhl H. 
Published: July 2012

AbstractEine analytische Behandlung des Kohlenstoffaustauschs zwischen der Atmosphäre und der Oberflächenschicht des Meeres sowie zwischen dieser und der Tiefsee wird vorgestellt. Anhand der daraus gewonnenen Ergebnisse wird diskutiert, inwieweit die Festlandbiota (im Rahmen der bisher konstruierten Ozeanmodelle) als Quelle oder als Senke für zusätzliches atmosphärisches CO2 in Frage kommen. Außerdem werden die Auswirkungen verschiedener Szenarien des fossilen Kohlenstoffinputs auf den CO2‐Gehalt der Atmosphäre für die nächsten Jahrzehnte abgeschätzt.
Thermodynamic investigations of Ag2Se
Authors: Oehsen U. V. , Schmalzried H. 
Published: July 2012

AbstractWith the help of coulometric titrations, using the solid state galvanic cell Ag/Ag4RbI5/Ag2+δSe/C between 75°C and 190°C, the following parameters have been determined in addition to the phase diagram: Point defect concentrations, Fermi‐level and width of band gap, effective mass of electrons and holes, partial molar enthalpies and entropies of electrons.
Density, viscosity, and electrical conductivity of acidic AICI3 ‐ LiCl ‐ NaCl melts
Authors: Carpio Ronald A. , Kibler Fred C. , King Lowell A. , Brockner W. , Tørklep Knut , Øye Harald A. 
Published: July 2012

AbstractDensities, viscosities, and specific conductivities were measured for ternary AlCl3‐LiCl‐NaCl melts in the range 0.5 ≤ XAlCl3 ≤ 0.8, 0 < XLiCl/(XLiCl + XNaCl) < 1. In addition, specific conductivities were measured for AlCl3 ‐ NaCl binary melts. The behavior of molar volume, viscosity, and equivalent conductivity of the ternary melts was rationalized in terms of a shift in the equilibrium 2Al2Cl−7 ⇄ 2AlCl−4 + Al2Cl6 as the composition of the ternary is changed, as well as a stronger interaction between Li+ and AlCl4− than between Na+ and AlCl−4.
Desaktivierungsverhalten von Arenen und Heteroarenen XIX. Die Temperatur‐ und Lösungsmittelabhängigkeit der Desaktivierung des Benzo[g]chinolins
Authors: Bendig J. , Henkel B. , Kreysig D. 
Published: July 2012

AbstractThe energetic lowest excited singlet and triplet states, the quantum yields of fluorescence, intersystem crossing, and internal conversion, the singlet life times, the fluorescence anisotropy and the dipol moments of the ground and the excited states of benzo[g]quinoline are determined. The dependence of the fluorescence quantum yield on temperature is attributed to a thermal activated deactivation process of the first excited singlet state by intersystem crossing. Considering a contribution of temperature independent radiationless deactivation this temperature dependence obeys the Arrhenius equation. ‐ At increasing acceptor behaviour and ET‐values of the solvent the activation energy of temperature dependent intersystem crossing is increasing too. A linear relationship between the experimental determined activation energies and the solvent parameter (ET + b · NA), (NA = Acceptor number, b = 8.3 J · mol−1), is obtained. The rate constants of the temperature dependent intersystem crossing process are different in the cases of investigated solvents and correlate with the above‐mentioned solvent parameter, provided heavy atomes are absent. These results are explained by the different solvation of S1 (π π*‐character) and T3 (π π*‐with partial nπ*‐character). — At 77 K no phosphorescence can be observed (øp ≤ 0.01). It follows that the temperature independent intersystem crossing process is negligible. — The quantum yields of internal conversion decrease at increasing solvent parameter. This fact is attributed to the weaker coupling of the S1 (π π*) and S2 (n π*) states in the case of increasing energy distance and, connected with this, smaller Franck‐Condon‐factors of the internal conversion.
Electrolytic separation of ions of different valency by ion‐exchange membranes
Authors: Chakravarti A. , Langer P. , Wiedner G. , Bojadzijev Z. 
Published: July 2012

AbstractThe transport properties through a cation‐exchange membrane were investigated for ions of different valency, using an electric field as driving force. In agreement with theoretical considerations a distinct preference of the higher valent ions was found.
Solid‐liquid equilibria in n‐alkylbenzene + n‐alkane mixtures. A group contribution study of phase diagrams
Authors: Kehiaian Henry V. , Guieu Raymond , Faradjzadeh Abolhassan , Carbonnel Luce 
Published: July 2012

AbstractThe solid‐liquid equilibrium diagrams of following 11 binary systems were determined: benzene, toluene, ethylbenzene, n‐propylbenzene, and n‐butylbenzene + n‐heptane or n‐tetradecane and benzene + n‐dodecane. All these diagrams could be calculated accurately (maximum deviation ca. 1 K) in terms of the group‐contribution theory (in the random mixing approximation) developed by Kehiaian et al. [7], which is essentially the surface version of the Guggenheim‐Barker lattice theory. Most interchange parameters were identical to those derived previously [7, 31, 33] from experimental data (liquid‐vapor equilibria, excess enthalpies, excess heat capacities). Where experimental data were lacking, the parameters were estimated and finely adjusted to the observed equilibrium diagrams.
Termination rates by time‐resolved ESR. The N‐hydro‐4‐acetylpyridinyl radical in solution
Authors: Krohn Holger , Leuschner Rainer , Dohrmann Jürgen K. 
Published: July 2012

AbstractThe second‐order rate constants for the self‐termination reaction of the N‐hydro‐4‐acetylpyridinyl radical in propanol(‐2) and propanol(‐2) acetone have been measured by time‐resolved ESR during intermittent photolysis. The radical was generated from 4‐acetylpyridine via different photochemical reactions. The rate constants were measured in the temperature range ‐10 to 26°C. The frequency factor and the activation energy from the Arrhenius plot are (1.1 ± 0.4) · 1010M−1· s−1and 16.6 ± 0.6 kJ · mol−1, respectively. The Arrhenius parameters were independent of the solvent composition and the method of radical generation. The termination reaction is attributed to the formation of the respective pinacol by the combination of two radicals. The reaction rate is not diffusion‐controlled. Possible mechanisms are proposed and discussed.
Mechanism of the reaction of H atoms with methanol
Authors: Hoyermann K. , Sievert R. , Wagner H. Gg. 
Published: July 2012

AbstractThe reactions of normal and deuterated methanols with H/D atoms have been studied in an isothermal discharge flow reactor (500 ≤ T(K) ≤ 680) at low pressures (2–8 mbar). Samples were withdrawn by a molecular beam sampling system directly into the ion source of a mass spectrometer. Concentration measurements with calibration procedures and the knowledge of secondary radical + atom reactions establish the reaction route

The reaction route

was found to be negligible (ratio of efficiencies (I)/(II) > 10). ‐ The rate constants for the reactions H + CH3OH, H + CD3OH, and H + CD3OD were measured in the temperature range 500‐680 K, leading to

.
Pressure induced reorientation and aggregation of pheophytin in monomolecular layers
Authors: Fischer A. , Heithier H. , Knoll W. , Möhwald H. 
Published: July 2012

AbstractMonomolecular layers of pheophytin were investigated by absorption spectroscopy, by thermodynamic, and by light‐ and electron microscopical measurements. — It is shown, that a pressure increase induces reorientations of the porphyrin rings. At pressures above a critical value pk pheophytin aggregates in an arrangement with coplanar stacking of the porphyrin rings. Size and shape of the aggregates are determined microscopically. The diameters amount to 2 μm, the thickness to 500 Å. — The results prove the stability of the monolayers for pressures below pk = 15 dyn/cm and the existence of instable phases at higher pressures.
Component self‐diffusion in liquid binary solutions
Authors: Hawlicka E. , Reimschüssel W. 
Published: July 2012

AbstractComponent self‐diffusion coefficients in solutions: n‐hexane‐cyclohexane, n‐hexane‐benzene, benzene‐nitrobenzene, and n‐hexane‐nitrobenzene have been determined as a temperature function over the entire composition range. The activation energies of component self‐diffusion have been calculated. The excess self‐diffusion coefficients as a useful way to determine a solution structure have been discussed.
Cyclische Voltammetrie an dünnen Elektrolyt‐ und Chemisorptionsschichten beim Vorliegen eines reversiblen Semichinon‐ und Dimerenbildungsgleichgewichts
Authors: Huck H. 
Published: July 2012

AbstractThe paper presents the derivation of equations for the determination of semiquinone formation and dimerization constants from the half peak width and the peak distance of a double peak by means of thin layer and adsorbat voltammetry. As an experimental example flavin adenine dinucleotide adsorbed on a roughened glassy carbon electrode was chosen, for which a semiquinone formation constant of 2.6 (0.77 in solution) was found at pH 7.
Zum Mechanismus der Induktionsperioden bei der Oxidation N‐substituierter p‐Phenylendiamine
Authors: Nickel Ulrich 
Published: July 2012

AbstractThe appearance of induction periods when oxidizing p‐phenylene diamines may be due to different reasons. In acidified aqueous solution distinct induction periods are observed for the formation of semiquinonediimine as well as quinonediimine with nearly all oxidizing agents employed. In this case primary oxidation is very slow because of the low concentration of oxidizable unprotonated p‐phenylenediamine. After the formation of some semiquinonediimine which is unprotonated, however, its subsequent oxidation accelerates the reaction in an autocatalytic way. Under different conditions of reaction either formation of quinonediimine or semiquinonediimine is retarded. Certain foreign substances give rise to a significant shortening or prolongation of the induction period, although the actual oxidation reaction is not noticeably. The different mechanisms are discussed and the reaction rates for the autocatalytic reaction are presented for some redox systems.
Thermodynamics of Al — Si and Al — Ge — Si liquid alloys: Enthalpies of formation by high temperature calorimetry
Authors: Bros J. P. , Eslami H. , Gaune P. 
Published: July 2012

AbstractThe enthalpies of formation of Al — Si and Al — Ge — Si liquid alloys were investigated by high temperature calorimetry. A new mixing and stirring device was designed in order to take into account the physicochemical properties of the metals involved. — The enthalpy of formation of the ternary alloys were found satisfactory using the Kohler's equation; the quasi‐ideality assumption for the binary Ge — Si revealed verified within the experimental accuracy.
Evidence of Hydrophobic Effects from Critical Phenomena
Authors: Pelger M. , Klein H. , Woermann D. 
Published: July 2012

AbstractData of the temperature dependence of partial molar quantities (heat capacity and temperature derivative of partial molar volume) of perfluoromethylcyclohexane and carbon tetrachloride in a mixture of critical composition are reported. It is found that for both components the signs of the critical amplitudes of the partial molar quantities are positive. Using these data a thermodynamic relation between the critical amplitudes of specific head capacity, partial molar heat capacity, temperature derivative of specific volume and temperature derivative of partial molar volume is tested. — Analogous experiments on the system isobutyric acid/water give results which are characteristically different: (1) the sign of the critical amplitude of the partial molar heat capacity of isobutyric acid is positive whereas that of water is negative, (2) the opposite is true for the sign of the critical amplitude of the temperature derivative of the partial molar volume of the two components. The characteristics of the system isobutyric acid/water are interpreted by assuming that in a critical mixture, approaching the critical point from the one fluid phase region, the extent of hydrogen bonding between water molecules in the vicinity of the hydrophobic part of isobutyric acid molecules increases with decreasing temperature difference from the critical temperature.
Unusual Thermodynamic and Electrical Properties of Metallic Solutions Near the Critical Point of the Almost Pure Solvent
Authors: Schönherr G. , Hensel F. 
Published: July 2012

AbstractThe paper presents experimental results of the electrical conductivity σ, the equation of state data and different related properties such as excess volumes of mixingVExand partial molar volumes V̄Infor dilute amalgams of In as a function of pressurep. temperatureTand compositionXInto 2700 bar, 1900 K and 2.85 at‐% In, respectively. Particular attention is given to the behaviour of these properties in the metal‐nonmetal transition range and close to the critical point of pure Hg. It is found that the divergence of the compressibility χTof pure Hg at the critical point is reflected in the behaviour ofVEx, V̄Inand in the concentration dependenceof the conductivity. The limiting values of the negative partial molar volume V̄Inand offor infinitely dilute solutions become extremely large as the critical point of pure Hg is approached. — An attempt is made to separate the different effects of temperature, volume and concentration and to analyze the data in terms of existing models for the electrical transport in expanded Hg and the critical behaviour of fluid dilute solutions.