bluuebunny/crossref_metadata_2025_split huggingface dataset:
Phyllotactic Iterations
Authors: Scholz H. J. 
Published: July 2012

AbstractThe origin of the golden angle γ = 137.5° found in most leaf arrangements is investigated by an inhibitor diffusion model. A recursive iteration scheme is set up generating inhibitor concentrations on the meristematic ring and angles xn between succeeding leaves. The universality of γ is reflected by existence of a broad parameter range with lim xn ≈ γ. Likewise, the golden angle is shown to occur in a modified Gierer‐Meinhardt model of nonlinear activator and inhibitor reactions.
Catalytic Dehydrochlorination of t‐Butyl Chloride on Alkali Halides
Authors: Yoshida N. , Akebe O. , Kishimoto S. 
Published: July 2012

AbstractPotassium bromide treated with bromine and chlorine vapor respectively, was used as catalyst for the dehydrochlorination of t‐butyl chloride. The results indicated a clear correlation between the presence of color centers (V‐centers) in the halides and their catalytic activity. The activation energies of the catalytic dehydrochlorination were measured.
Hydration Dependence of the Head Group Mobility in Phospholipid (DMPC) Membranes
Authors: Nimtz G. , Enders A. , Binggeli B. 
Published: July 2012

AbstractThe dielectric dispersion in the frequency range 2–800 MHz of the zwitterionic dipolar phosphocholine head group has been measured from −20 to +60°C for DMPC depending on the amount of bound water. It is found that the head group rotation shows a sudden change at the gel‐fluid phase transition, 1. the rotation frequency becomes much higher and 2. the related dielectric response becomes much more pronounced in the fluid phase. Below 15 H2O molecules bound per lipid molecule the head group rotation frequency decreases with decreasing number of bound water. This observation reveals for the first time that there is a correlation between hydration dependence of the chain melting temperature and head group rotation. The thermal activation of the head group rotation in the fluid phase made us conclude that three hydrogen bonds have to be broken in order to rotate the head group.
Estimation of Structural Heterogeneity in Radical Copolymerized Polymer Networks by Comparison with Structural Homogeneous Model Networks
Authors: Fuhrmann J. , Leicht R. , Karim N. 
Published: July 2012

AbstractA retrospective recalculation of the parameters of four known swelling equations has been performed so as to give the best correspondence to the swelling data points reported in the literature for homogeneous model polystyrene networks in benzene. A one parameter modification of the relation which fits the reported data best is used to describe the structural network heterogeneity according to a two phase model. This modified relation has been applied to study the increasing structural heterogeneity with increasing monomer conversion during the radical network formation of styrenedivinylbenzene networks with different initial divinyl composition as parameter.
Zum Einfluß der Zwischenphase und spezifischer Lösungsmittelwechselwirkungen auf Morphologie und Domänengrößen bei Blockcopolymeren
Authors: Bühler F. , Annighöfer F. , Gronski W. 
Published: July 2012

AbstractFor styrene‐isoprene blockcopolymers of lamellar morphology obtained by casting from solution the influence of various modifications of thermodynamic interactions on lamellar dimensions and longperiods is studied by electron microscopy. The thermodynamic interactions are modified by the generation of a broad interphase caused by the insertion of a poly(isoprene‐co‐styrene)copolymer block of random structure between the pure blocks and by use of a preferential solvent of the diene component in blockcopolymers containing 20 wt‐% isoprene leading to a highly ordered asymmetrical lamellar morphology. Both modifications lead to a compression of the lamellar domains and longperiods relative to the dimensions of symmetrical unmodified systems. The influence of the interblock content is described by the same functional dependence for both symmetrical and asymmetrical systems.
2H NMR Studies of Liquid Crystal Main Chain Polymers
Authors: Müller Klaus , Kothe Gerd 
Published: July 2012

AbstractSemiflexible thermotropic polyesters, specifically deuterated at different positions of the polymer chain, are studied by multipulse dynamic NMR techniques. Analysis of the various 2H NMR experiments is achieved, employing a comprehensive theory, based on the stochastic Liouville equation. Computer simulations provide the orientational distributions and conformations of the polymer chains and the correlation times of the various motions. In the anisotropic melt the correlation times for chain rotation and chain fluctuation are of the order of 10−8s, while trans‐gauche isomerization occurs even faster. Below the melting point two components are observed in the NMR experiments. The dynamics of the liquid crystalline component (40%) continues into the biphasic region. In contrast, the crystalline component (60%) shows a drastic motional decrease at the melting point. The chain order parameters Szz increase with decreasing temperature to limiting values, which depend upon the number n of flexible spacer segments. Polymers with n = even exhibit limiting order parameters of Szz = 0.9, a value considerably higher than those observed in low molecular weight nematogens. In addition, the chains adopt highly extended conformations, evidenced by trans populations of nt= 0.76, exhibited throughout the spacer. The liquid crystalline order is quantitatively retained, when the polymers are cooled below the melting point and glass transition, respectively.
Dielectric Measurements at High Pressures and Low Temperatures VIII: Dielectric and Thermodynamic Properties of Cycloheptanol
Authors: Poser U. , Schulte L. , Würflinger A. 
Published: July 2012

AbstractThe thermodynamic and dielectric behaviours of liquid and solid cycloheptanol have been investigated using differential thermal analysis and capacitance measurements up to 10 MHz. The phase behaviour has been studied between 80 and 340 K and pressures up to 300 MPa. The well‐known phase transformations at 1 atm have also been observed at elevated pressures that enables to calculate the associated volume changes. The static and complex permittivities have been determined in the temperature range 240–310 K and pressures up to 300 MPa. Activation parameters derived from the dielectric relaxation occurring in the two plastic phases are similar to previously reported data for cyclopentanol and cyclohexanol.
The Influence of Surface Oxygen on the Auger Signal Intensities of Ti, Mn, Ni, Zr, La and Fe
Authors: Sicking G. , Eisenhuth A. 
Published: July 2012

AbstractThe Auger electron intensities of some metals are measured as a function of the oxygen content of the metallic surface. A strong correlation between the Auger signal strength of the metal and that of oxygen is discovered. Thus correlation is discussed as a weakening process of Auger electrons by surface oxygen. The relationships allow to calculate elemental sensitivity factors for the metal Auger signals from oxygen containing surfaces. It is also possible to determine relative weakening coefficients by oxygen for different elements or for the same element but different Auger energies. It is found that the weakening coefficient of low energy Auger electrons is about twice that of high energy Auger electrons. The 92 eV Auger electrons of Zr show up an anomaly since they are roughly not weakened by oxygen. —It is pointed out that the different contributions responsible for a weakening of the peak‐to‐peak amplitudes of differentiated Auger spectra sum up and can be described by a single weakening coefficient.
Temperature Dependence of the Inhibition and Enhancement of Positronium Formation by Pyridine in Decane and Toluene Solutions
Authors: Alfassi Zeev B. , Ache Hans J. 
Published: July 2012

AbstractThe effect of temperature (‐20°C‐+25°C) on positronium formation in decane and toluene solutions of pyridine was studied. At low concentration of pyridine an enhancement was found in decane solution at ‐20°C and toluene solution at +25°C. Decane solutions at 25°C and toluene solutions at ‐20°C show constant yield of o‐Ps, independent of pyridine concentration, at low concentration. At high pyridine concentration there is an inhibition in all cases. The rate constants for inhibition decreases with temperature for both toluene and decane solutions.
Oxide Formation during the Reaction of Carbon Monoxide and Oxygen on Polycrystalline Platinum
Authors: Häfele E. , Lintz H.‐G. 
Published: July 2012

AbstractThe oxidation of carbon monoxide by air is studied on polycrystalline platinum at normal pressure in the temperature range 350 < ϑ/°C < 600. Simultaneously the oxygen activity on the surface is measured under reaction conditions by solid electrolyte potentiometry. The results show that the formation of PtO2 is thermodynamically possible in a certain temperature range but oxide formation is only observed in the case of preoxidized samples.
Catalytic Activity of Colored Sodium Chloride for the Dehydrochlorination of t‐Butyl Chloride
Authors: Ueda W. , Hiraiwa J. , Yoshida N. , Kishimoto S. 
Published: July 2012

AbstractWhen NaCl was colored with Na vapor, X‐rays and Cl2 vapor, respectively, the surface became highly active catalytically. Almost without exception, the decrease in the enhanced activity upon heating occurs in the range of the annihilation temperature of the color centers. This result indicates that both F‐ and V‐centers in NaCl may contribute to the reaction as active sites.
A Further 1H NMR Study on Cubic HxWO3: Reasons for the Apparent “Prefactor Anomaly”
Authors: Ritter Cl. , Müller‐Warmuth W. , Schöllhorn R. 
Published: July 2012

AbstractNMR studies of the cubic hydrogen bronze Hx WO3 have confirmed the hydrogen location proposed by Dickens et al. The diffusion of protons is limited by the availability of a framework of suitable oxygen sites and was found to contain elements of reduced dimensionality. The activation energy is of the order of magnitude of 40–50 kJ/mol, and the preexponential factor amounts to about 10‐13 s as usual. A “prefactor anomaly” observed in several other studies may arise if the dimensionality of the motion is not considered. Comparison with hydrogen bronzes HxMoO3 is discussed.
Self‐Diffusion, Overall Rotation of Molecules, and Ring Motions in the Three Solid Phases of Formylferrocene, Fe(C5H5) (C5H4CHO), as Studied by 1H NMR and Differential Thermal Analysis
Authors: Kubo Atsushi , Ikeda Ryuichi , Nakamura Daiyu 
Published: July 2012

AbstractThe temperature dependences of static and rotating frame 1H spin‐lattice relaxation times, T1 and T1ϱ, respectively, and also of 1H spin‐spin relaxation time, T*2 were studied for formylferrocene Fe(C5H5)(C5H4CHO). Broadline 1H NMR was investigated over a wide range of temperature. Differential thermal analysis revealed a new second‐order phase transition at 294 K. At 77 K, formylferrocene was found to form a rigid lattice. Above 130 K, the onset of the Cs reorientation of the cyclopentadienyl ring in the molecule about its C5 axis was observed to take place with the average activation energy of 14.5 kJ mol−1. In the plastic phase above 317 K, the uniaxial as well as overall rotations and self‐diffusion of the molecule as a whole were detected to occur. Other motional parameters of the unsubstituted cyclopentadienyl rings and the molecules in each phase were evaluated.
Study of Dipolar Interaction in Liquid Pyridine by X‐Ray and Neutron Diffraction
Authors: Bertagnolli H. , Engelhardt T. , Chieux P. 
Published: July 2012

AbstractX‐ray and neutron diffraction experiments on liquid pyridine are reported. After data reduction and evaluation the intramolecular contribution was separated from the total intensity and the intramolecular geometry in the liquid phase was determined. The combination of X‐ray and neutron intermolecular differential cross sections permits an assignment of intermolecular distances to specific atom pairs. Based on these identifications a two‐dimensional model of the local order existing in liquid pyridine is deduced. A quantitative calculation leads to a refined model, reproducing simultaneously the X‐ray and neutron data. Most probable is an antiparallel “side‐side” for the nearest and a “head‐on‐tail” configuration for the next molecule respectively. This means, that the dipolar interaction is the structure determining factor.
Optical Absorbance and Photoelectrochemical Quantum Efficiency of Titanium Oxide Modified by Ion Implantation and Reductive/Oxidative Annealing
Authors: Teschner D. M. , Schumacher R. , Stritzker B. 
Published: July 2012

AbstractWe report on the optical absorbance A and the photoelectrochemical quantum efficiency η of Titanium oxide samples modified by ion implantation and reductive/oxidative annealing. Rutherford‐Backscattering spectra were taken to probe the depth profile of implanted Kr+. It is shown that A varies drastically upon modification. Generally, with increasing Ti/O ratios the absorbance decreases. The observed decrease in A upon implantation of stoichiometric TiO2 is attributed to an increase of the Ti/O ratio. The suggested explanation takes into account the formation of Ti3+ ‐ O vacancy complexes which influence the electronic structure of TiO2. Furthermore it is shown that changes of A give rise to conductivity changes. This reflects changes in ND, the doping density, εr, the relative dielectric constant, and lp, the mean free diffusion length of minority carriers. The observed photoelectrochemical quantum efficiency η of modified samples is discussed in terms of model calculations which take into account changes of ND, εr, lp and the absorption coefficient α. Recombination losses of photo‐produced electron‐hole‐pairs via band gap states introduced by the implanted ions are also discussed.
Bulk Counterion Diffusion in Rod‐Like Polyelectrolyte Solutions
Authors: Cametti C. , Biasio A. Di 
Published: July 2012

AbstractThe bulk counterion diffusion along a charged rod‐like polyion is considered in the light of the linearized Poisson‐Boltzmann equation of the Gouy‐Chapman double layer theory to estimate the contribution of this process on the high‐frequency dielectric dispersions of dilute polyelectrolyte solutions. This model, which has been previously applied to colloidal suspensions of charged spherical particles, allows to predict the functional form of the dependence of the dielectric and conductometric parameters on the bulk counterion concentration and on the dielectric constants of the polyion domain and electrolyte solution, in the limit of very small polyion content. The derived expressions for the dielectric and conductivity increments show that the influence of the bulk counterion diffusion is generally very small and in particular conditions negligible. Nevertheless these effects may be important correcting factors to take into account in the accurate interpretation of dielectric measurements.
Interstitial Site Occupancy of Hydrogen Atoms in Laves Phases and Structurally Related Compounds
Authors: Hauck J. 
Published: July 2012

AbstractThe Laves phases with MgCu2 or MgZn2 structure and structurally related phases with CeNi3, PuNi3, Ce2Ni7, or CaCu5 structure were compared for site preference of hydrogen atoms in different octahedral and tetrahedral sites. The site preference energies of different transition metals are similar to crystal field stabilization energies of transition metal atoms in oxides. The structural data and some thermodynamic properties as solubility of hydrogen in alloys and instability of ternary phases are correlated to the site preference energies.
An Experiment for Determining the Kinetics of Heterogeneously Catalysed Gas Reactions
Authors: Schneider U. , Alavi M. , Duschner H. 
Published: July 2012

AbstractAn experiment for determining the kinetics of heterogeneously catalysed gas reactions is presented. In a closed glas tube system, a gas flow is induced by a temperature gradient between the heated catalyst and a jacket cooler. Partial pressures of all gaseous components are monitored by a quadrupole mass‐spectrometer, directly connected to the reaction chamber via a special mica filter. Using this apparatus, the catalytic hydrogen reduction of sulfur dioxide over 0.5% Ru/Al2O3 was investigated.
A X‐Ray Study of Specific Bromine Interaction in Liquid Ethylbromine and its Interpretation by Geometrical and Potential Models
Authors: Bertagnolli H. , Schulz G. 
Published: July 2012

AbstractA X‐ray experiment on liquid ethylbromine at 25°C is reported. After the usually applied data reduction and evaluation the intramolecular contribution was separated and the intra‐ and intermolecular geometry in the liquid phase was determined. A well defined Br ‐ Br distance of 3.9 Å exists indicating a strongly attractive interaction between the highly polarizable Br‐atoms. Quantitative calculations based on geometrical models lead to a more antiparallel orientation of the ethylbromine molecules with close Br‐contact. Comparison with potential calculations without and with electrostatic interactions confirms that dispersion forces outweigh the dipole effect on the orientation of neighbouring molecules.
Melt Grown Layered Crystals: Comparison of Optoelectronic Properties
Authors: Hofmann W. K. , Könenkamp R. , Schwarzlose Th. , Kunst M. , Tributsch H. , Lewerenz H. J. 
Published: July 2012

AbstractSingle crystals of the layer type compounds MoSe2 and WSe2 have been grown from various high temperature solutions. The fluxes used for crystal growth were either metals (Sb, Bi, Te), semiconductors (Se) or saltlike melts (PbCl2). The photoactivity of these materials was investigated by photoelectrochemical methods, time resolved microwave conductivity (TRMC) and temperature dependent DC conductivity. The comparison of crystals grown from different melts and from chemical vapor transport (CVT) indicates that foreign phase melts are deleterious for the optoelectronic properties. Melt grown crystals are less photoactive than selected CVT material. Possible origins of the observed differences are discussed.
On Some Aspects of the Modelling of the Crystal Growth
Authors: Beckmann Wolfgang , Lacmann Rolf 
Published: July 2012

AbstractThe growth of crystals is a complex process where several steps can be rate determining. For the deduction of growth mechanisms from experimental data, it is essential, that the models yield realistic parameters. For the growth of stearic acid from solutions, the sensitivity of parameters of the growth models was analyzed by simulating rate data and evaluating then by different techniques. The influence of different growth limiting steps and errors in the measurements was analyzed. For the electrochemical deposition of an alloy, the influence of several parameters on the composition of the alloy was studied.
Infrared Laser Induced Ignition of Gas Mixtures
Authors: Raffel B. , Wolfrum J. 
Published: July 2012

AbstractO2/O3 mixtures are ignited by absorption of laser pulses of a TEA CO2 laser along the axis of a cylindrical vessel. For mixtures of 0.35 bar total pressure and 20% O3 the laser excitation as well as the molecular relaxation of O3 and the flame propagation is observed by UV‐light absorption of O3 perpendicular to the cell axis. Temperatures reached in the irradiated volume by absorption of the laser pulses are deduced from the alteration of the UV intensity and from absorbed laser energy below and above the ignition limit. The results are compared with corresponding numerical simulations. Minor differences can be attributed to the simplifications of the simulations being performed in one spatial dimension with the uniform pressure assumption and a solely thermal source term.
Parameter Optimization in Detailed Chemical Kinetics Modeling
Authors: Gardiner William 
Published: July 2012

AbstractComputer models describing complex chemical kinetics are often based on the assumption that each reaction included is a true elementary process in the physical‐chemical sense. If the elementary reaction rate coefficients are to be determined as part of the modeling study, then one has to solve a parameter optimization problem that differs in two respects from a textbook response‐function analysis: use of numerical integration of kinetic equations for computing parameter sensitivities and dominance of systematic over random errors in the data base. While modern computing technology offers efficient solutions to the sensitivity computation problem, dealing with systematic errors requires reformulation and simplification of the mathematical structure so that it interacts efficiently with chemical understanding derived from experimental investigations. A systematic procedure for extending a proposed mathematical structure to the entire literature data base of hydrocarbon combustion is presented and discussed.
Ein diskretes mathematisches Modell für die Dynamik der Methanoloxidation an einem Palladium‐Trägerkatalysator
Authors: Gerhardt M. , Schuster H. , Plath P. J. 
Published: July 2012

AbstractThe dynamics of the methanol oxidation on a Pd‐supported catalyst is described by a discrete mathematical model including a phase transition of the catalytic system. A possible synchronisation of the not uniformly acting catalyst by an heat transfer between neighboured Pd‐crystallites is studied by coupling several dynamical systems.
Transport Properties of Liquids VI. Viscosity, Excess Volumes, and Self‐Diffusion of Nearly Athermal Mixtures
Authors: Fischer Jens , Weiss Alarich 
Published: July 2012

AbstractSelf‐diffusion D, dynamic viscosity ζ, mass density η, and excess volume VE were measured for twelve binary liquid systems CCl4‐compound 2 in the temperature range 285 ≤ T/K. ≤ 345 at p = 1 bar. In average for each system, seven different compositions were studied within the range 0 < x2 ≤ 1. Compounds 2 were: cyclopentane, cyclohexane, cycloheptane, cyclooctane, cyclodecane, cyclo‐dodecane, hexamethylcyclotrisiloxane, octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, cis‐decaline, trans‐decaline, and bicyclohexane.—The self‐diffusion coefficients found are discussed within the frame of the extended free volume model of liquids. η=f(x2, T) can be explained by the Arrhenius relation for the viscosity of liquids, including a modified Grunberg‐Nissan parameter. The excess viscosities and the molar excess volumes observed are rather small, in correspondence with the fact that the twelve systems investigated are nearly athermal. This fact reproduces itself in the excess activation energies of the viscous flow and mass transport.
The Volume of Liquid HgIn and HgSn Alloys
Authors: Morikawa Y. , Itami T. , Shimoji M. 
Published: July 2012

AbstractPrecise measurements were made to determine the concentration dependence of the volume and the thermal expansion coefficient of liquid HgIn and HgSn alloys. The molar volume of both systems shows slightly negative deviations from the linear law. For liquid HgIn alloys, a small hump was found in the curve of the thermal expansion coefficient in the dilute In range, but not for liquid HgSn.—The molar volumes of these alloys have been calculated by modifying a simple pseudopotential approach, and results obtained in this way are found to be in qualitative agreement with experimental values.