bluuebunny/crossref_metadata_2025_split huggingface dataset:
Calculation of High Pressure Counterflow Diffusion Flames up to 3000 bar
Authors: Saur A. M. , Behrendt F. , Franck E. U. 
Published: July 2012

AbstractThe combustion of methane, hydrogen and carbon monoxide at atmospheric pressure in one‐dimensional diffusion flames was quantitatively described with computer simulations by Warnatz et al. and others. The present paper extends the one‐dimensional flame description from dilute gas regions to pressures of 3000 bar, where particles are mostly in contact with each other. A realistic equation of state with repulsion and attraction terms is used. Transport phenomena are modelled with a modified Enskog equation. A special problem arises from the stiffness of the systems of differential equations. Integration uses methods developed by Deuflhard et al.Flames of methane and hydrogen burning in mixtures with argon or supercritical water with injected oxygen are simulated and discussed. Profiles of temperature and other functions at high pressures through the reaction coordinate are shown. The width of the reaction zone is narrowed to less than 5% if pressure is increased from 1 to 1000 bar. Maximum temperatures of 3500 K are attained with CH4/Ar‐O2‐flames. Maximum flame temperatures decrease with pressure above about 500 bar. Several concentration profiles including those of H‐ and O‐radicals and H2O2 are presented. Comparison with recently measured high pressure flame temperatures is made.
Solid State Reactions in the Quasiternary System (ZnkCd1−k)(SelTe1−l
Authors: Leute Volkmar , Wulff Birgit 
Published: July 2012

AbstractIn this study solid state reactions between the binary components of the quasiternary system (ZnkCd1‐k)(SelTe1‐l) are investigated for chalcogen saturated and for metal saturated samples at different temperatures. The X‐ray intensity profiles, taken with an electron microprobe, are transformed to reaction paths, which are projected onto isothermal sections of the phase diagram. From these representations and from diffusion data of the quasibinary subsystems conclusions can be drawn concerning the defect mechanism of the diffusion processes of the solid state reaction.
On the Composition of Higher Solid Nickel Oxocompounds
Authors: Balej Jan , Divisek Jiri 
Published: July 2012

AbstractCritically selected equilibrium or rest potentials of solid nickel oxocompounds with 2<zNi≦3.6 measured at ambient temperatures by various authors were reevaluated. Comparing the measured data converted to uniform conditions (25 °C, aKOH = aH2O = 1.0 Evr vs. RHE) with the theoretical course of Er vs. zNi, derived for the case that the NiOx system can be formed either by Ni(II)+Ni(III)+Ni(IV) or by Ni(II)+Ni(IV) components, it was found that the so called “βNi(OH)2/β‐NiOOH” systems with zNi<3.0 can be regarded as thermodynamically unstable or metastable, as they exhibit an unusual decrease of EvT with increasing zNi in the range of 2.6<zNi<3.0. Experimental results corresponding to a sequence of stable valence stages Ni(II) → Ni(III) → Ni(IV) were not observed. In contrary, the so called “α‐Ni(OH)2/γ‐NiOOH” systems exhibit a monotonous S‐shaped course of Evr vs. zNi in the whole investigated range of 2.0<zNi≦3.6, with the lowest Evr values at the given zNi, so that they can be regarded as thermodynamically stable systems representing solid solutions of Ni(II)+Ni(IV) components only.
On the Photoionization Mechanism of Liquid Water
Authors: Sander Martin U. , Luther Klaus , Troe JüRgen 
Published: July 2012

AbstractExperimental data on the photoionization of liquid water are reviewed and reanalyzed. It is suggested that, near to the ionization threshold at 6.5 eV and up to about 8 eV, an optical Charge Transfer (CT) mechanism leads to the formation of hydrated electrons with a low quantum yield. The absorption band of liquid water at the longest UV wavelengths is assigned to this CT transition superimposed on an intramolecular transition into the R3s state. At excitation energies where the R3p states become attainable, i.e. somewhere between 6.5 and 8 eV, a photo‐induced electron transfer mechanism sets in which is characterized by high quantum yields of hydrated electrons and by average electron‐ion separations below those expected for intermediately “quasi‐free” electrons. This mechanism is dominant up to at least 10 eV, i.e. up to the highest excitation energies for which subpicosecond studies are currently available. In this energy range, autoionization generates only a minor part of all hydrated electrons produced. Only at excitation energies approaching the gas‐phase ionization potential, autoionization and direct photoionization are supposed to become dominant. If any autoionization channels are open below excitation energies of 10 eV, then the band gap energy of water, which is currently believed to be about 8.9 eV, has to be located as high as 10–12 eV.
The Effect of Short‐Range Hydrogen‐Bonded Interactions on the Nature of the Critical Point of Ionic Fluids. Part II: Static and Dynamic Light Scattering on Solutions of Ethylammonium Nitrate in n‐Octanol
Authors: Schröer W. , Wiegand S. , Weingärtner H. 
Published: July 2012

AbstractWe report on static and dynamic light scattering measurements of near‐critical fluctuations of an ionic liquid. The system is ethylammonium nitrate (EAN) dissolved in n‐octanol which exhibits a liquid‐liquid phase transition in the salt rich regime with an upper critical point near 315 K at a mole fraction of the salt x1 = 0.773. The correlation lengths and scattering intensities scale with temperature corresponding to an Ising‐like critical point. This contrasts with previous observations of mean‐field behaviour in electrolyte systems with liquid‐liquid phase transitions driven by long‐range Coulombic interactions. Rationalizations of this discrepancy are offered taking into account a) the competition of intermolecular interactions with long‐range and short‐range character and b) the possibility of crossover from mean‐field to Ising behaviour as predicted by the Landau‐Ginzburg theory.
Modelling the H3O+‐Ion: A Simulation Study of an Aqueous HCl Solution
Authors: Laurs Norbert , Bopp Philippe 
Published: July 2012

AbstractA molecular dynamics (MD) simulation study of structural and dynamical properties of a dilute solution of HCl in water is presented. We assume that the acid is completely dissociated at the low concentration which is investigated, and that H3O+ and Cl− are the ionic species. A new model interaction potential is constructed on the basis of available experimental and theoretical information for this cation. In keeping with the flexible model employed for the water, it is also modelled as a flexible entity. The intermolecular H3O+‐water potential is constructed on the basis of an ab‐initio charge distribution and the short‐range parts from the water‐water potential. The other potentials are taken from the literature. Simulations of 1.1 m HCl solutions are performed at several temperatures. The structure of the liquid, and specially the hydration of H3O+, are discussed in terms of radial and many‐body distribution functions. Dynamical properties are calculated from velocity‐ and other autocorrelation functions. A stabilization of the pyramidal structure of H3O+ is observed in the solutions.
A Study of the Equitransference Level of Concentrated Aqueous RbBr, RbI and NH4I, and their Characterization as Ultra‐Concentrated Salt Bridges for the Minimization of Liquid Junction Potentials
Authors: Mussini P. R. , Rondinini S. , Cipolii A. , Manenti R. , Mauretti M. 
Published: July 2012

AbstractIon and solvent transference numbers for aqueous RbBr, RbI and NH4I solutions have been determined at molalities up to 5.5, 6.5 and 7.5mol·kg−1, respectively, from e.m,f. measurements on appropriate transference cells. The results demonstrate that, for the minimization of liquid junction potentials, all the three salts above are better “salt bridges” than the popular saturated‐KCl one, both because they are more nearly equitransferent (over the whole molality range) and because they can reach saturation molalities (7.01, 7.38 and 12.69 mol·kg−1, respectively, at 25°C) much higher than that of KCl (4.804 mol·kg−1). Therefore, concentrated RbBr, RbI and NH4I solutions can be recommended as advantageous salt bridges for replacement of the KCl one.
Planar Membrane‐Cable: Voltage‐Profile Recorded by Fluorescent Dye
Authors: Fromherz Peter , Müller Jörg Uwe 
Published: July 2012

AbstractA black lipid membrane of glycerolmonooleate was spanned over a shallow groove in silica. Gramicidin was incorporated into the bilayer. The electrical properties of the cable were characterized by admittance measurements. The membrane was stained with the voltage‐sensitive dye di4ANEPPS. A voltage was applied to one end of the cable. The change of fluorescence was recorded along the cable. The profile of the relative change of fluorescence corresponds closely to the profile of voltage for a linear core‐coat conductor computed from the Kelvin‐equation.
Oxidation and Hydrothermolysis of Hydrocarbons in Supercritical Water at High Pressures
Authors: Hirth Th. , Franck E. U. 
Published: July 2012

AbstractOxidation, pyrolysis and hydrolysis of methane, ethane, methanol and to some extent heptane and toluene, in supercritical water or nitrogen, at temperatures to 600°C and pressures to 1000 bar were studied. Temperatures of the reactive mixtures were always above the respective critical curves. Oxidation was performed with oxygen or air injection, flameless or with diffusion flames. High pressure, non‐corrosive reaction vessels of different types and the complementary apparatus for high pressure injection and analysis are described.Flameless oxidation of methane in homogeneous supercritical aqueous mixtures produces CO, CO2, H2and CH3OH. Methanol formation can reach 30% of reacted methane, “selectivity”, at 600 bar. High pressure increases the methanol selectivity, flame reaction decreases it. Overall rate constants are given. Similar studies were made with supercritical aqueous ethane mixtures. Hydrothermal pyrolysis, “hydrothermolysis”, was investigated. Even at 600°C and 600 bar less than 3% methane decomposed after 120 minutes. Pyrolysis of methanol at 500°C and 600 bar is much slower in an aqueous environment than in nitrogen. Hydrothermal soot formation was studied with several hydrocarbons in supercritical fluids. Water, as compared with argon, as a mixture component appears to suppress soot formation. CO conversion with supercritical water was also quantitatively pursued.
Ab initio Monte Carlo‐Studies of Concentrated Aqueous Cesium Hydroxide‐Solutions
Authors: Bertagnolli H. , Zweier H. , David A. 
Published: July 2012

AbstractAb initio Monte Carlo simulations of concentrated aqueous cesium hydroxide solutions are reported. This method of structure modelling that requires no intermolecular interaction potential as input was applied to ionic solutions for the first time. The comparison of the resulting atom pair correlation functions with those of pure liquid water indicated a disordered arrangement of the water molecules. The influence of the structure breaking cesium ions seems to prevent an orientation of the water molecules according to the pure water structure even in the dilutest solution.
Structure Modelling of Fluid Carbon Dioxide Using ab initio Monte Carlo‐Simulation
Authors: Bertagnolli H. , Glania C. , Zweier H. , David A. 
Published: July 2012

AbstractAb initio Monte Carlo simulations of fluid carbon dioxide are reported. The technique, which does not require intermolecular potential as input, was used to investigate the effects of density variation on the short range order. Experimental data could be reproduced to perfection; the resulting atom‐atom pair correlation functions and angular distribution functions revealed no preferred conformation at lower densities, whereas parallel conformations were more likely at higher densities.
2H, 14N, and 35Cl Nuclear Magnetic Resonance in Crystalline Deuterated Guanidinium Perchlorate [C(ND2)3]ClO4
Authors: Furukawa Yoshihiro , Ikeda Ryuichi 
Published: July 2012

AbstractThe temperature dependences of 2H, 14N, and 35Cl NMR spin‐lattice relaxation times (T1) were measured for deuterated guanidinium perchlorate [C(ND2)3]ClO4. The 2H T1 (41.6 MHz) minimum of 2.2 ms observed in the room‐temperature phase obtainable below 451 K was assigned to the three‐fold reorientation of the planar cation. The ionic‐plastic phase obtained above 452 K forms a cubic CsCl‐type crystal with a = 5.56 Å and Z = 1 as determined for the protonated sample at 360 K. In this phase, 2H and 14N T1 values are mainly governed by the overall reorientation of the cations although slow self‐diffusion also takes place. The quadrupole coupling constant (e2Qq/h) and asymmetry parameter η were determined as a function of temperature for 2H and 35Cl nuclei.
Effects of Bismuth(III)‐Oxide on the Structural and Electrochemical Properties of Pyrolusite (β‐MnO2)
Authors: Axmann P. , Glemser O. 
Published: July 2012

AbstractCycle‐life and charge/discharge curves of pure and physically Bi2O3‐doped pyrolusite (β‐MnO2) were studied. Crystalline intermediate products of the first three semi‐cycles give information about the effects of Bi2O3. A mechanism is postulated. In the first two semi cycles pyrolusite (β‐MnO2) is converted to the layered δ‐MnO2 with β&hyphen;Mn(OH)2 in the fully discharged state. In the course of the following discharge hausmannite Mn3O4, which is electrochemically inert, is formed. No hausmannite is found in presence of Bi2O3.Pieces of information on mechanistical aspects can be gathered from the initial discharge process. During the initial discharge of β‐MnO2, δ‐MnO2 is formed as an intermediate product. In the undoped case this species can be found around MnO1.75. In presence of Bi2O3, however, δ‐MnO2 is existent nearly down to MnO1.25 over the whole discharge region.The reaction path diverges at the [MnIII(OH)4(H2O)2]− ion, dissoluted during the cycling process: in presence of Bi2O3 the reaction is controlled kinetically by a quick disproportionation of the [MnIII(OH)4(H2O)2]− ions resulting in δ‐MnO2 and β‐Mn(OH)2. In absence of Bi2O3, thermodynamical control occurs, and [MnIII(OH)4(H2O)2]− reacts with [MnII(OH)4(H2O)2]2‐ forming the electrochemical non‐reactive hausmannite Mn3O4.
Orientational Order in Liquid Crystals: Experiment and Theory
Authors: Luckhurst G. R. 
Published: July 2012

AbstractThe long range orientational order of a liquid crystal is one of its prime characteristics. Before the extent of this order can be measured, however, it is necessary to define what is meant by the orientational order. This can be achieved in a variety of ways the most pragmatic of which is via the order parameters; these vanish in the isotropic phase and are one for systems with complete order. The techniques available for the determination of the order parameters are described, with particular attention paid to deuterium NMR spectroscopy. The results obtained for rod‐like mesogenic molecules are considered and the use of model systems, as studied by computer simulation, to understand them is discussed. Of particular significance is the relative role of anisotropic attractive and repulsive forces in determining liquid crystal behaviour. In recent years chemists have developed a new generation of liquid‐crystalline materials in which the fundamental building blocks of rods, discs and chains are linked together in many ways. As an example the transitional behaviour of liquid crystal dimers is considered in detail. The orientational order for dimers with both odd and even spacers has been studied using NMR. The results of such investigations have prompted the development of a novel model for the molecular organisation in the nematic phase. Finally, the synergy of order and conformation for mesogens composed of the simplest flexible liquid crystal dimers is explored using computer simulation techniques.
Molecular Dynamics Simulation Study of Isotropic and Nematic PCH‐5
Authors: Krümer G. , Paschek D. , Geiger A. 
Published: July 2012

Abstract4‐(trans‐4‐Pentyl‐cyclohexyl)‐benzonitril (PCH‐5) has been studied by molecular dynamics simulations of the isotropic liquid as well as the nematic mesophase. The intra‐ and intermolecular interaction are described in pseudoatom approach. Besides the nematic order parameters S we calculate various distributions functions to characterize and compare the microscopic structure. In both phases we find a distinct antiparallel arrangement of neighbouring molecules, in accord with the known crystal structure of homologous substances. The molecular dynamics shows strong anisotropic behaviour in both phases. The corresponding diffusion coefficients are determined and compared with an experimental value.
Druckabhängigkeit der optischen Aktivität in der isotropen Phase eines chiralen Flüssigkristalls
Authors: Voß E. , Pollmann P. , Hollmann J. 
Published: July 2012

AbstractOptical activity measurements in the isotropic liquid phase of cholesteryl oleyl carbonate just above the liquid‐crystal transition pressure were performed for various temperatures up to 200 MPa. The observed optical activity exceeds the molecular activity and can be explained as a pretransitional phenomenon.The maximum value, which the optical activity reaches as the transition to the liquid‐crystal phase is approached, first decreases then increases when clearing temperature and pressure are raised. A theoretical relationship between the pretransitional optical activity and two structural modes is used to interpret this unusual behaviour.
An Extended Microscopic Model of the Spontaneous Polarization in Ferroelectric Liquid Crystals
Authors: Meister R. , Stegemeyer H. 
Published: July 2012

AbstractThe well‐known microscopic model from Žekš et al. for the spontaneous polarization of smectic C* phases has been extended by taking into account different orientations of the considered molecular transverse axes. A stronger temperature dependence of the tilt angle reduced polarization P0 = PS/θ results. The extended model explains differences between the quadrupolar order parameters calculated from P0(T) and from 14N‐NQR measurements. Additionally, temperature induced sign inversions of PS, described in the literature, can be explained by considering a possible competition between polar and quadrupolar ordering.
The Domain Mode in a Single Component Ferroelectric Liquid Crystal — Dielectrical and Electrooptical Investigations
Authors: Hiller S. , Beresnev L. A. , Wrobel S. , Haase W. 
Published: July 2012

AbstractIn this paper we present the dielectric and electrooptic investigations on the single component ferroelectric liquid crystal 3‐Octyloxy‐6‐[2‐fluoro‐4‐(2‐fluoro‐octyloxy)phenyl]‐pyridine (FFP), synthesized by E. Merck Company. The investigations were performed in an ITO‐cell with the thickness of 900 nm. The sample was aligned planarly.Under the polarization microscope a Domain structure was observed. The threshold voltage for the helix unwinding in the SmC* phase was determined.The complex dielectric permittivity component ε* was measured in the frequency range from 10 Hz up to 10 MHz. Beside the Goldstone mode, a Domain mode relaxation was found in the dielectric spectra of this substance. Due to the small cell thickness only one Domain process, namely the surface Domain mode could be detected. BIAS field and temperature dependent measurements of this Domain mode process were performed. In order to obtain the characteristic relaxation strengths and dispersion frequencies of the observed processes the Havriliak‐Negami equation was fitted to the data obtained.
Optische Eigenschaften von Flüssigkristall‐Mikrolinsen und Adaptierungslinsen, Vergleich von numerischen Simulationen und Messungen
Authors: Schwabe F. , Knoll P. M. , Nerding R. , Dickmann S. , Eschler J. , Miyuski D. A. 
Published: July 2012

AbstractLiquid Crystal (LC) cells with a suitable electrode structure can be used as electrically controlled lenses. Two types of LC‐lenses are known: LC‐adaptive lenses [1] (LCAL) and LC‐microlenses [2, 3] (LCML). LC‐microlenses have a simple electrode structure, but offer only slow response times up to several seconds and apertures up to 1 mm.A LCML works as follows: The front electrode is divided by a gap, which can be up to 10 times larger than the cell gap. The inhomogeneous electrical field within the gap produces an inhomogeneous director distribution. This distribution allows to focus monochrome light from the infinity down to about 1 mm.With a 2‐D numerical simulation [4–6] it is possible to describe the behaviour of the director in an inhomogeneous electrical field. It can be seen, that there are some configurations, which cause distortions between the electrodes. These make the optical properties worse. From the director configuration the optical properties of the LC‐lens can be calculated.The influence of inhomogenities can be improved with LC‐adaptive lenses. Here we use several parallel electrodes to produce directly the director distribution to focus monochrome light. The advantages of adaptive lenses are: the switching times are shorter. There are less inhomogenities. But the minimum focal distance is about some cm.
Photoinduced Reorientation of Cholesteric Liquid Crystalline Polysiloxanes and Applications in Optical Information Storage and Second Harmonic Generation
Authors: Petri A. , Kummer S. , Anneser H. , Feiner F. , Bräuchles Ch. 
Published: July 2012

AbstractWhen liquid crystalline polymers, which contain an azo dye as a side chain, are irradiated with light which is absorbed by the azo dye, both the index of refraction and the absorbance are changed. It was proven that the modulation of the optical properties mainly rests upon a reorientation of the long molecular axis of the chromophores and of the mesogenic units. This change of the alignment of the side chains occurs after numerous trans‐cis‐isomerization cycles of the azo dye. Spectroscopic investigations show that by irradiating the samples completely new and well ordered textures appear. The characteristic features of the new textures depend on the structure of the liquid‐crystalline polymer before irradiation and on the polarization state of the actinic light.We investigated cholesteric polysiloxanes which were either irradiated with linearly or with circularly polarized light (unpolarized light respectively). The characterization of the new textures was done with different spectroscopic methods. The photochemically induced changes of the texture are usable in applications like optical information storage, e.g. for the generation of holograms or for the production of displays. We further investigated samples with dipolar azo dyes which were reoriented with light under the influence of an electrical field. The cooperative effect of light and field results in a polar alignment of the azo dye which was proven by second harmonic generation (SHG). We compare material properties like longterm stability and efficiency of the SHG in samples which were prepared by this new procedure, by contact poling and by corona poling.
Structure and Dynamics of Liquid‐Crystalline Polymers with Different Molecular Architectures from Multidimensional NMR Plenary Lecture
Authors: Spiess H. W. 
Published: July 2012

AbstractA survey is given on the structure and dynamics of liquid‐crystalline polymers with different molecular architectures as revealed by multidimensional NMR. Specific examples discussed include semiflexible systems, rigid‐rod systems, calamitic, and discotic liquid crystals. Structural aspects include the determination of high rank order parameters, the micro‐order in frozen liquid crystals and the packing of flexible side chains. Dynamic processes discussed are local dynamics in the glassy state, conformational dynamics and collective phenomena such as the development of convective director structures and dynamic density modulations along columnar structures. It is demonstrated that advanced NMR spectroscopy yields highly specific information not available from conventional scattering, microscopic and relaxation techniques.