bluuebunny/crossref_metadata_2025 huggingface dataset:
Sensitivity of basal conditions in an inverse model: Vestfonna ice cap, Nordaustlandet/Svalbard
Authors: Schäfer M. , Zwinger T. , Christoffersen P. , Gillet-Chaulet F. , Laakso K. , Pettersson R. , Pohjola V. A. , Strozzi T. , Moore J. C.
Published: July 2012

Abstract. The dynamics of Vestfonna ice cap (Svalbard) are dominated by fast-flowing outlet glaciers. Its mass balance is poorly known and affected dynamically by these fast-flowing outlet glaciers. Hence, it is a challenging target for ice flow modeling. Precise knowledge of the basal conditions and implementation of a good sliding law are crucial for the modeling of this ice cap. Here we use the full-Stokes finite element code Elmer/Ice to model the 3-D flow over the whole ice cap. We use a Robin inverse method to infer the basal friction from the surface velocities observed in 1995. Our results illustrate the importance of the basal friction parameter in reproducing observed velocity fields. We also show the importance of having variable basal friction as given by the inverse method to reproduce the velocity fields of each outlet glacier – a simple parametrization of basal friction cannot give realistic velocities in a forward model. We study the robustness and sensitivity of this method with respect to different parameters (mesh characteristics, ice temperature, errors in topographic and velocity data). The uncertainty in the observational parameters and input data proved to be sufficiently small as not to adversely affect the fidelity of the model.
ARAMID–NYLON 6.6 HYBRID CORDS AND INVESTIGATION OF THEIR PROPERTIES
Authors: Yilmaz Berrin
Published: July 2012

Hybrid cords of two different polyamide yarns, poly(p-phenylene terephthalamide; aramid) and poly(hexamethylene adipamide; nylon 6.6) have been investigated. Aramid is a high-tenacity, high-modulus, low-elongation, and thermally stable yarn material. Nylon 6.6 is a high-elongation, low-modulus, high-fatigue-resistant, and good adhering synthetic yarn. The combination of these two different synthetic yarns enables hybrid cords with a diversified range of mechanical properties. The hybrid cord product property diversification is achieved by proper combination of different cord-forming properties of individual plies, such as linear densities, twist levels, ply numbers, treating conditions, and so forth. The effect of linear densities, twist level of plies, and twist level of cabled cord and ply number on the cord properties and also cord performance have been summarized. Aramid yarn having an 1100 linear density has been combined with nylon 6.6 yarn with a different linear density, ranging from 940 to 2100, to form hybrid cord structures. Twisting of aramid and nylon 6.6 yarns has been kept between 150 and 450 twists per meter, while the ply number of aramid and nylon 6.6 yarns has been varied as one and two plies by keeping the total ply number of the cord as three.
Polymorphism‐Dependent Emission for Di(p‐methoxylphenyl)dibenzofulvene and Analogues: Optical Waveguide/Amplified Spontaneous Emission Behaviors
Authors: Gu Xinggui , Yao Jingjing , Zhang Guanxin , Yan Yongli , Zhang Chuang , Peng Qian , Liao Qing , Wu Yishi , Xu Zhenzhen , Zhao Yongsheng , Fu Hongbing , Zhang Deqing
Published: July 2012

The synthesis and optical investigations of di(p‐methoxylphenyl)dibenzofulvene (1) and its analogues 2, 3, 4, 5, 6, and 7 with different lengths of alkoxyl chains are presented. All of these molecules exhibit emission in the solid state. The following interesting properties are reported for compound 1: 1) the solid‐state fluorescence of 1 is dependent on the polymorphism forms; the two crystalline forms 1a and 1b are strongly blue‐ and yellow‐green‐emissive, whereas the amorphous solid is weakly fluorescent with orange emission; 2) on the basis of crystal‐structural analysis, the intermolecular interactions will restrict the internal rotations, leading to fluorescence enhancement for the two crystalline forms 1a and 1b; however, the difference in emission color between 1a and 1b is ascribed to the molecular conformational alteration; 3) the solid‐state fluorescence of 1 can be tuned by heating and cooling as well as grinding. Importantly, microrods of 1a and 1b exhibit outstanding optical waveguide behaviors. Moreover, amplified spontaneous emission for 1b and multimode‐lasing behavior for 1a are presented. Besides the studies of compound 1, the crystal structures and solid‐state fluorescence behaviors of 2, 3, 4, 5, 6, and 7 are also described.
Medium chain acyl‐CoA dehydrogenase deficiency detected among Hispanics by New Jersey newborn screening
Authors: Anderson Sharon , Botti Christina , Li Bo , Millonig James H. , Lyon Elaine , Millson Alison , Karabin Suzanne S.M. , Brooks Susan Sklower
Published: July 2012

In the follow‐up of New Jersey newborn screens suggestive of medium chain acyl‐CoA dehydrogenase deficiency (MCADD) during a 30‐month period, we identified five patients of Hispanic American ethnicity. With information provided by the New Jersey Department of Health and Human Services Newborn Screening program we calculated an overall cumulative incidence of approximately 7.20/100,000 for MCADD; 7.58/100,000 among Hispanic Americans and 7.08/100,000 among non‐Hispanic Americans. Among the five Hispanic American infants who screened positive, a common variant (c.443G>A [p.R148K]) was identified which accounted for 30% of the alleles; c.799G>A (p.G267R) and c.985A>G (p.K329E) each accounted for an additional 20%; and a novel variant c.302G>A (p.G101E) was identified in one patient. Although treated prospectively during interim illnesses to prevent unwanted sequelae; till date, none of the patients carrying the c.443G>A variant have been symptomatic. © 2012 Wiley Periodicals, Inc.
Infants' MTHFR polymorphisms and nonsyndromic orofacial clefts susceptibility: A meta‐analysis based on 17 case–control studies
Authors: Pan Yongchu , Zhang Weibing , Ma Junqing , Du Yifei , Li Dandan , Cai Qi , Jiang Hongbing , Wang Meilin , Zhang Zhengdong , Wang Lin
Published: July 2012

Methylenetetrahydrofolate reductase (MTHFR), an important enzyme in folate metabolism, is thought to be involved in the development of nonsyndromic orofacial clefts (NSOC). However, conflicting results have been achieved when evaluating the associations between infants' MTHFR C677T and A1298C polymorphisms and the risk of NSOC. To obtain more precise estimations of these associations, a meta‐analysis recruiting 17 case–control studies was performed. Among Asians we found that CT heterozygote, TT homozygote, and CT/TT of infants' MTHFR C677T variant could contribute to elevated risks of NSOC, compared with CC wild‐type homozygote (OR = 1.741, 95% CI = 1.043–2.907 for CT vs. CC, OR = 2.311, 95% CI = 1.313–4.041 for TT vs. CC, and OR = 1.740, 95% CI = 1.051–2.882 for CT/TT vs. CC, respectively). Similar effect was also observed on MTHFR 677T T allele, when using C allele as a reference in Asians (OR = 1.420, 95% CI = 1.191–1.693, for T allele vs. C allele). Furthermore, in stratified analysis by types of disease, CT/CC was suggested to confer decreased susceptibility to CL/P under recessive genetic model (OR = 0.854, 95% CI = 0.730–1.000). For MTHFR A1298C, the MTHFR 1298C allele in the case group of Caucasians was significantly lower than that in the control group, suggesting a protective effect against NSOC in Caucasian populations (OR = 0.711, 95% CI = 0.641–0.790, for C allele vs. A allele). In conclusion, the meta‐analysis provided confirmative evidences that infants' MTHFR C677T and A1298C polymorphisms were involved in the development of NSOC. © 2012 Wiley Periodicals, Inc.
Electron Transfer Reactions Between Iron (III) and Substituted Ferrocenes in Cationic and Non‐Ionic Micellar Systems
Authors: Carbone Antonio I. , Paolo Cavasino F. , Sbriziolo Carmelo , Pelizzetti Ezio
Published: July 2012

The kinetics of the electron transfer reactions of aquoiron(III) with ferrocene (Fer) and its n‐butyl (BFer), 1,1′‐dimethyl (DMFer) and 1,1′‐di‐n‐butyl (DBFer) derivatives have been studied in the presence of cationic (CTAN) and non‐ionic (Triton X‐100) micelles at 20.0°C and ionic strength 0.02 mol dm−3. Both surfactants inhibit nearly at the same extent the reaction involving a given ferrocene derivative. The rate inhibition depends strongly on the alkyl groups present in the molecule of ferrocene, following the order DBFer > BFer > DMFer > Fer. The binding constants and the contribution of a methylene (or methyl) group of the alkyl substituents to the transfer free energy from water to micelle have been estimated and discussed, suggesting that ferrocenes are located inside the micelle.
Solubility of Hydrogen in Titanium Alloys. I. The Solubility of Hydrogen in the System Ti1‐xGax, 0 ≦ x ≦ 0.25
Authors: Mrowietz Michael , Weiss Alarich
Published: July 2012

Applying the manometric method, the solubility of hydrogen in alloys Ti1‐xGax was studied in the range 0 ≦ x ≦ 25; 5 · 10−5 ≦ pH2/bar ≦ 1; 773 ≦ T/K ≦ 1298. Within the given range of p and T the phase diagram of Ti1‐xGaxHr was investigated for 9 compositions x. In the range of solid solutions, 0 ≦ x ≦ 0.11, with increasing x the range Δr of the hcp phase α‐Ti1‐xGaxHr increases slightly, whereas the range of the bcc phase β‐Ti1‐xGaxHr, narrows strongly with increasing x. The width Δr of the two phase region α + β is nearly independent of x and the phase boundary between β‐phase and (β + γ) region shifts with decreasing Δr of the β‐phase to smaller r. In α‐T1‐xGaxHr the enthalpy of hydrogen solution ΔHH is practically independent of r but depends slightly on x, decreasing from ‐46.0 kJ mol−1 (x = 0) to ‐46.5 kJ mol−1 (x = 0.10). In the bcc phase β‐Ti1‐xGaxHr, ΔHH decreases markedly from ‐57 kJ mol−1 (r → 0) to ‐70 kJ mol−1 (r ⇌ 1). ΔHH is independent of the gallium content x within the limits of error. — Assuming a plausible blocking model for the occupancy of interstitial sites in the metal matrix by hydrogen, the excess entropies of dissolved hydrogen were evaluated. In α‐Ti1‐xGaxHr an increase of ΔSEH is found with increasing r from ‐55 JK−1 mol−1 (r→0) to ‐53 JK−1 mol−1 (r = 0.1). ΔSEH depends much stronger on r in β‐Ti1‐xGaxHr: ΔSEH = ‐70 JK−1 mol−1 (r→0); ΔSEH = ‐66.5 JK−1 mol−1 (r = 0.8). There is negligible influence of x on ΔSEH in both phases. — In the ordered hcp phase α2‐Ti3GaHr there is an increase of exothermicity compared to α‐Ti1‐xGaxHr. ΔHH (r → 0) is ‐51.3 kJ mol−1 for the ordered phase and it depends on r, increasing to ‐50 kJ mol−1 at r ⇌ 0.1. ΔSEH for this phase is independent of r, ΔSEH = ‐53 JK−1 mol−1. — Additional data on the hydrogen solubility in α‐Ti3Sb are given, resulting on more accurate thermodynamic data ΔHH, ΔSH, and ΔSEH.
Dynamics of Trans‐Cis Photoisomerization of Stilbene in Hydrocarbon Solutions
Authors: Sundström Villy , Gillbro Tomas
Published: July 2012

We have determined the intramolecular potential barrier as well as total activation energies of trans‐cis isomerization in the excited state of stilbene in hydrocarbons, using UV picosecond transient‐absorption Spectroscopy. The dynamics of the isomerization is compared with theoretical predictions offered by the activated barrier crossing models of Kramers, and Grote and Hynes.
Tunable VUV Laser Excitation of H2
Authors: Meier W. , Rottke H. , Zacharias H. , Welge K. H.
Published: July 2012

Rotational state selective single photon excitation of H2 in the (0 — 0) and (3 — 0) bands of the B 1Σ+u ← X1Σ+g transition around λ = 111.0 nm and λ = 106.3 nm has been performed in a molecular beam. VUV laser induced fluorescene detection will be compared with resonantly enhanced two photon ionization where a second UV laser for ionization of the excited B state was employed.
Dynamics and Absolute Cross Sections of Some Hot Hydrogen Atom Reactions
Authors: Kleinermanns K. , Wolfrum J.
Published: July 2012

The dynamics of chemical reactions with high threshold energies is studied by combining hot atom production by laser photolysis and fast and state selective product detection by laser induced fluorescence. — The nascent OH rotational, vibrational and fine structure (λ‐doublet and spin‐doublet) state distributions produced in the reactions

have been measured at collision energies up to 240 kJ/mol (C.M.‐system) with hot H atoms from the Excimer laser photolysis of HJ, and HBr at 193 nm and 248 nm. Absolute reaction cross sections have been obtained by measuring reactant and product densities at short times. Polarization experiments with photolysis‐ and probelaser polarized parallel and perpendicular to each other are performed. — For the reaction H + O2, the experimental results are compared with extensive trajectory calculations on an ab initio potential surface (Melius, Blint 1979).
Rotational Polarization of Product Molecules: Crossed Laser‐Molecular Beam Studies of Ca* + HF and Ca + F2
Authors: Engelke F. , Meiwes‐Broer K. H.
Published: July 2012

Quantitative results have been obtained for the alignment, due to chemical reactions under single collision conditions, in CaF(X) product molecules using the technique of laser‐induced fluorescence (LIF). We find that the anisotropic distribution of angular momenta is of the form 1 + A2P2(cosv), where the alignment appears to be large (A2 = ‐ 1.82 ± 0.06) for Ca* + HF → CaF + H, while for Ca + F2 → CaF + F a considerably smaller alignment (A2 = ‐0.14 ± 0.09) is measured and discussed.
Reactions of CHF (X̃ 1A') and NCO (X̃ 2Π) Radicals
Authors: Cookson J. L. , Hancock G. , Mckendrick K. G.
Published: July 2012

Infrared multiple photon dissociation has been used to produce ground state radicals CHF(X̃ 1A') and NCO (X̃ 2Π), and their kinetic behaviour in the presence of added gases studied by time resolved laser induced fluorescence. Both kinetics and the products of reactions of CHF with NO, NO2, O and N atoms, and of NCO with NO will be discussed.
Solubility of Hydrogen in Titanium Alloys. II. Blocking Models and Hole Size Considerations
Authors: Mrowietz Michael , Weiss Alarich
Published: July 2012

Assuming a geometrical model with mutual (H‐H) blocking, for hydrogen dissolved in titanium and titanium alloys experimental data are compared. It is found that interstitial sites with pure titanium coordination only host hydrogen atoms. In alloys with bcc crystal lattices only tetrahedral interstitial sites are occupied, whereas in hep alloys both tetrahedral and octahedral interstitials host hydrogen. A linear relation is found which connects the partial molar absorption enthalpy ΔHOHand the partial molar excess absorption entropy ΔSE, OHat infinite dilution of dissolved hydrogen. The enthalpy of absorption ΔHOHcan be rationalized as a function of interstitial hole size and an optimum hole radius of 47 pm is found for titanium and titanium alloys.
Analysis of Trapping and Recombination Effects in Photoelectrochemical Processes at Semiconductor Electrodes: Investigations at n‐GaAs
Authors: Schröder K. , Memming R.
Published: July 2012

Fast impedance measurements have shown that reliable flatband potentials of GaAs can only be obtained using high scan rates. Illumination leads to a shift of energy bands at the interface which is interpreted by hole trapping in surface states. A recombination conductance determined by impedance measurements is used to characterize the recombination of minority carriers injected by light or a redox system. A semiquantitative model is discussed according to which the recombination occurs mainly in the space charge region of the semiconductor.
Potential Distribution and Interaction between two Parallel Dielectric Cylinders in a Static Transverse Field. I
Authors: Schlögl Reinhard W.
Published: July 2012

At first the following potential problem is solved: Two infinitely long cylinders with radii R1, R2 and dielectric constants ϵ1, ϵ2 are placed in a static transverse homogeneous field with an otherwise arbitrary orientation. The interaction between the cylinders is then evaluated. By suitable transformations, solutions are found in closed form in terms of rapidly convergent series. R1 = R2, ϵ1 = ϵ2 is treated as a special case. In very “unsymmetrical” cases (R1 > R2, ϵ1 ϵ2 < 0), unexpected changes of sign of the forces are found, which are due to “image forces”. The results for a static field carry over for alternating fields, provided that dielectric losses do not contribute significantly.
Solubility and Diffusion of Chlorine in Silica Glass
Authors: Hermann Wilhelm , Rau Hans , Ungelenk Joachim
Published: July 2012

Chlorine diffusion profiles in silica glass have been studied by SEM techniques. From the results the diffusion coefficient D (log10(D·cm−2 s) = −11080 K/T −3.498), the equilibrium solubility of Cl in silica glass (0.25 or 0.32 weight per cent at 1 bar Cl2 pressure and 1438 K or 1970 K), and the pressure dependence of the solubility were derived. The latter is proportional to the fourth root of the CI2 pressure. There are no detectable differences in the behaviour of chlorine in silica made by the PCVD method (plasma activated chemical vapour deposition) or in commercially produced silica (HERALUX, wave guide quality), but the chlorine concentration is much higher in PCVD silica than expected from the small chlorine pressures present during deposition.
Periodic Operation of a Stirred Flow Reactor with Limit Cycle Oscillations
Authors: Taylor T. W. , Geiseler W.
Published: July 2012

The oscillating flow reaction of bromate, bromide, and cerous ions was investigated computationally in a continuously stirred tank reactor (CSTR) where periodic perturbations were imposed on either the input rate or one of the inflow concentrations. The model computations predict a variety of interesting phenomena such as harmonic and subharmonic entrainment, chaos, transient behavior, and low amplitude harmonics. Under certain conditions the natural oscillations of the system can be considerably damped or enhanced by perturbation inputs of the proper frequency. The theoretical behavior of the system, studied under various experimental conditions, suggests many feasible experiments which are interesting in themselves, but may also serve as an additional probe of the complex mechanism used.
Fluid Phase Equilibria of Binary Mixtures of SF6 with Octane, Nonane, Hendecane, and Decahydronaphthalene,cis at Temperatures between 280 K and 440 K and at Pressures up to 140 MPa in Comparison to Mixtures of Hydrocarbons with CO2, CF4, and CHF3
Authors: Matzik I. , Schneider G. M.
Published: July 2012

Binary mixtures of SF6 + octane, + nonane, + hendecane, and + decahydronaphthalene,cis were investigated up to 140 MPa. Measurements were performed according to the synthetic method using an optical high pressure cell. ‐ Going from SF6 + octane to SF6 + nonane the critical p(T)‐curves show a continuous transition between the type of liquid‐liquid (ll) phase equilibrium with upper critical solution temperatures (UCST) and the gas‐gas (gg) equilibrium of the 2nd kind. For the SF6 + n‐alkane systems there is a systematical shift of the high‐pressure branches of the critical curves of about 20 K to higher temperatures per CH2‐unit. The experimental results are discussed in comparison to computer calculations with two semiempirical equations of state. Solvent properties of SF6 are compared to those of CO2, CF4, and CHF3.
Observation of Entrainment, Quasiperiodicity and Chaos in Glycolyzing Yeast Extracts under Periodic Glucose Input
Authors: Markus Mario , Müller Stefan C. , Hess Benno
Published: July 2012

Entrained, quasiperiodic and chaotic oscillations are observed by monitoring the fluorescence of NADH in glycolyzing baker's yeast under sinusoidal glucose input flux. These dynamic processes occur in the ranges of input amplitude and frequency predicted by numerical analysis of a two‐enzyme glycolytic model. Entrained responses having periods equal to 1, 2, 3, 4, 5, 7 and 9 times the input period were measured. Stroboscopic transfer plots obtained from the measured quasiperiodic and chaotic oscillations match well with the numerical calculations.
Macromolecular Evolution: Dynamical Ordering in Sequence Space
Authors: Eigen Manfred
Published: July 2012

Evolution of self‐replicating macromolecules through natural selection is a dynamically ordered process. Two concepts are introduced to describe the physical regularity of macromolecular evolution: sequence space and quasi‐species. Natural selection means localization of a mutant distribution in sequence space. This localized distribution, called the quasi‐species, is centered around a master sequence (or a degenerate set), that the biologist would call the wild‐type. The self‐ordering of such a system is an essential consequence of its formation through self‐reproduction of its macromolecular constituents, a process that in the dynamical equations expresses itself by positive diagonal coefficients called selective values. The theory describes how population numbers of wild type and mutants are related to the distribution of selective values, that is to say, how value topology maps into population topology. For selectively (nearly) neutral mutants appearing in the quasi‐species distribution, population numbers are greatly enhanced as compared to those of disadvantageous mutants, even more so in continuous domains of such selectively valuable mutants. As a consequence mutants far‐distant from the wild‐type may occur because they are produced with the help of highly populated less‐distant precursors. Since values are cohesively distributed, like mountains on earth, and since their positions are multiply connected in the high‐dimensional sequence space, the overpopulation of (nearly) neutral mutants provides guidance for the evolutionary process. Localization in sequence space, subject to a threshold in the fidelity of reproduction, is steadily challenged until an optimal state is reached. The model has been designed according to experimentally determined properties of self‐replicating molecules. The conclusions reached from the theoretical models can in turn be used to construct machines that provide optimal conditions for the evolution of functional macromolecules.
Noise Induced Limit Cycles of the Bonhoeffer‐Van der Pol Model of Neural Pulses
Authors: Treutlein Herbert , Schulten Klaus
Published: July 2012

The effect of additive noise on the Bonhoeffer‐van der Pol (BvP) model is studied. For this purpose we developed a numerical algorithm to solve the pertinent 2‐dim. Fokker‐Planck equation. The results demonstrate that the global behaviour of the system is determined by certain lines toward which the distribution function is attracted. These lines are also the seeds for the limit cycle in the deterministic system. The noisy BvP model exhibits a limit cycle (oscillations) even when the deterministic system does not. This behaviour may explain the firing pattern of neurons.
A Low‐Pressure Extension of the Stokes‐Einstein Relationship
Authors: Hippler H. , Schubert V. , Troe J.
Published: July 2012

An empirical relation between diffusion coefficients and viscosities is proposed which interpolates between the kinetic theory of dilute gases and the Stokes‐Einstein equation of liquids. This extended Stokes‐Einstein‐relationship is tested with experimental examples. It is useful for studies of reaction processes over large density ranges.
Laser Flash Induced Charge Carrier Transfer in Polycrystalline n‐TiO2 Semiconductors
Authors: Hartig K. J. , Grabner G. , Getoff N. , Popkirov G. , Kanev St.
Published: July 2012

Photocurrent and photovoltage transients have been measured at n‐TiO2 electrolyte junctions by means of ns‐laser pulse excitation. Two different kinds of build‐up, independent of excitation intensity and external resistance have been observed. It is concluded that the charge carrier transit through the depletion layer is the rate determining step if traps or grain boundaries of the microcrystals acting as such, play a significant role. The result is a longer rise time of either photocurrent or ‐voltage, which exceeds the laser pulse width by orders of magnitude.
Electrochemical Study of the Mechanism of Photoreduction of Silver Ions at a Zinc Oxide Surface
Authors: Tanemura H. , Yonezawa Y. , Hada H.
Published: July 2012

The electrochemical behavior of ZnO sinter electrode has been investigated in order to clarify the mechanism of photoreduction of Ag+ on a ZnO surface in aqueous solutions. The flat‐band potential of ZnO electrode depends on the Ag+ concentration. From the stationary polarization curves of the electrode in the dark and under irradiation, we have determined the zero‐current potential, Ezcp, at which total current under irradiation is zero, and the cathodic current at this potential, idzcp. It has been shown that the greater part of idzcp contributes to the photoreduction of Ag+. We could obtain the general expressions for the dependences of Ezcp, idzcp, and the quantum efficiency of idzcp, Φhv, on the Ag+ concentration, which are able to explain the essential features of our experimental findings.
Inelastic Neutron Scattering and Far IR Spectroscopy of Acetonitrile in Solid Ar and CCl4 Matrices
Authors: Langel Walter , Kollhoff Helmut , Knözinger Erich
Published: July 2012

Inelastic neutron scattering has been applied for the first time to the study of matrix isolated species whose thermodynamically stable phase under normal conditions is the liquid. The aims of these investigations, which are complemented by far infrared studies, are to explore the aggregational behaviour of acetonitrile and the intermolecular dynamics of the respective aggregates in low temperature matrices of solid Ar and CCl4. The only aggregate observed, using a variety of different spectroscopic techniques and diverse experimental conditions, is an antiparallel dimer. In contrast to the external intermolecular modes of this aggregate, which were not accessible by vibrational spectroscopy, the internal modes could be described and assigned.
Charge Transfer from the n‐Hexadecane Radical Cation to Cycloalkanes, Alkenes and Aromatics
Authors: Mehnert R. , Brede O. , Naumann W.
Published: July 2012

Charge transfer from n‐hexadecane radical cations C16H+34 to solutes as cycloalkanes, alkenes and aromatics was studied by pulse radiolysis. Using ion‐pair kinetics the rate constants ks of the electron transfer reactions

equation image

were determined. The electron transfer rate constants ks increase from low values for slightly exothermic reactions to a limiting value of 9 · 109 dm3 mol−1 s−1 when the electron transfer reaction is more exothermic than −0.4 eV.
Small Angle Neutron Scattering on Nematic Lyotropic Liquid Crystals
Authors: Herbst L. , Hoffmann H. , Kalus J. , Reizlein K. , Schmelzer U. , Ibel K.
Published: July 2012

A solution of 30% by weight of the tetramethylammonium salt of the perfluorononanoic acid (TMPFN = C8F17COON(CH3)4) in D2O forms a nematic phase in the temperature range between 32 and 37°C. The nematic phase was aligned and cooled down to 25°C in a magnetic field of 1.63 and 1.26 T. The structure of the aligned sample was studied with small angle neutron scattering (SANS) at different temperatures. In the liquid crystalline phase first and second order Bragg‐peaks were observed. This phase consists mainly of liquid crystals build by sheets of disk‐like TMPFN micelles alternating with layers of D2O. The lattice parameter is around 75 Å at 25°C. An order parameter S near 1 was determined by a thorough analysis of a rocking experiment. Besides the Bragg‐peaks further scattering features were observed: A Debye‐Scherrer like ring probably related to disclike micelles and a ridge related to a unknown aligned structure. The SANS‐pattern was examined in an temperature range between 25 and 45°C.
Information Theoretical Approach to the Excess Entropy of Liquid Mixtures
Authors: Bär Hans‐Jürgen , Brickmann Jürgen
Published: July 2012

A new approach to treat the problem of excess entropies of liquid mixtures on the basis of probability measure functions (PMF) is introduced. In this the excess entropy is proportional to the entropy deficiency where the molar fractions are interpreted as probabilities. It turns out that the PMF's can be easily linked to macroscopic activity coefficients of the constituents in the mixture. On the other hand, first ideas on the microscopic structure can be directly obtained from these new quantities.
Kinetics of the Reactions between CH2(X̃3B1)‐Radicals and Saturated Hydrocarbons in the Temperature Range 296 K ≤ T ≤ 707 K
Authors: Böhland T. , Dõbẽ S. , Temps F. , Wagner H. Gg.
Published: July 2012

The reaction between CH2‐radicals in their ground electronic state (X̃3B1) and n‐hexane

equation image

was studied in a discharge flow system with LMR detection of CH2. In the temperature regime 413 K ≤ T ≤ 707 K the experimental rate constant was found to be

equation image

The reaction proceeds both via direct H‐atom abstraction by CH2(X̃) and via thermal excitation of CH2(X̃) to the low‐lying singlet state (ã1A1) followed by fast consecutive reactions of CH2(ã). The contributions due to thermal excitation and singlet reaction were evaluated for the present work as well as for a recent study of the reactions of CH2(X̃) with a series of other hydrocarbons. Corrected rate constants kT for the direct reactions of CH2(X̃) with the reactants HR = CH4 (1), C2H6 (2), C3H8 (3), n‐C6H14 (4), i‐C4H10 (5), and CH3CHO (6) in the temperature range 296 K ≤ T ≤ 707 K were found to be

equation image

The activation energies for the reactions studied are described by an Evans Polanyi type relation. Arrhenius expressions are proposed for the rate constants of H‐atom abstraction by CH2(X̃3B1) from primary, secondary, tertiary, and aldehydic C ‐H bonds. The results are compared to the isoelectronic reactions of O(3P).
On the Physical Crosslinking of Amine‐Extended Polyurethane Urea Elastomers: A Crystallographic Analysis of Bis‐Urea from Diphenyl Methane‐4‐Isocyanate and 1,4‐Butane Diamine
Authors: Born L. , Hespe H.
Published: July 2012

The substance under investigation is taken as a model for hard segments consisting of diphenylmethane‐4,4′‐di‐isocyanate (MDI) and 1,4‐butane diamine. It crystallizes in the triclinic space group P1 with a = 4.6297; b = 5.8259; c = 25.286 A; α = 90.721; β = 91.580; γ = 102.90 degrees and Z = 1. Bond distances and angles are given, together with some data on the conformation. — The most significant finding is that neighbouring molecules in one and the same plane are linked to one another by means of bifurcated hydrogen bonds. — A comparison with the corresponding data for an analogous bis‐urethane provides a plausible explanation of the main differences between diamine and glycol extension in polyurethane elastomers.
Structural Models for Some Liquid Crystalline Cellulose Derivatives
Authors: Vogt U. , Zugenmaier P.
Published: July 2012

Models for helicoidal cholesteric structures are proposed for some cellulose derivative/solvent systems. The pitch of these structures is determined by independent methods as a function of temperature, concentration, solvent, degree of polymerization. The results are discussed on the basis of available theoretical considerations.
Effect of Interfacial Polarization on the Critical Behaviour of Electrical Resistivity and Dielectric Constant in Polar + Nonpolar Binary Liquid Mixtures
Authors: Gunasekharan M. K. , Guha S. , Vani V. , Gopal E. S. R.
Published: July 2012

The dielectric constant ϵ and the resistance R have been measured as a function of frequency in the region 1 kHz to 1 MHz. The measurements have been performed on two critical binary liquid mixtures cyclohexane + methanol and carbondisulphide + acetonitrile in the one phase region. The measurements are carried out using a double ratio transformer bridge, in a bath with millidegree temperature control. At low frequencies ϵ and R increase with T → Tc+. Above 100 kHz the resistance reaches a maximum and begins to decrease as T → Tc+. The observed behaviour is explained qualitatively on the basis of interfacial polarization mechanisms (IPM) using the ideas of the droplet model theory of binary Liquid mixtures. The analysis of the low frequency data using the functional form R or ϵ ˜ tθ shows a value of θ near 0.9. The high frequency data have been analysed with a new functional form, but the quantitative discussions of the IPM are hampered by the lack of information of its dependence upon t.
Structural Phase Transition in Orthorhombic and Monoclinic Fe3+ Doped K3Co(CN)6 Crystals as Studied by the Temperature Variation of 14N NQR Frequencies
Authors: Fukada Shin‐Ichi , Horiuchi Keizo , Asaji Tetsuo , Nakamura Daiyu
Published: July 2012

The temperature dependence of 14N NQR frequencies was observed for Orthorhombic crystals of K3[Co(1‐x)Fex(CN)6] (x ∼ 0.02) and monoclinic crystals of K3[Co(1‐x)Fex(CN)6] (x · 0.005). The former crystals yielded two pairs of vI and vII frequencies above 84 K indicating the existence of at least two crystallographically nonequivalent nitrogens. Below 84 K, each line split into two, the average frequency of which increases smoothly with decreasing temperature without showing discontinuity in frequency itself and also its temperature derivative at 84 K. This can be regarded as that the crystal undergoes a structural phase transition of second order at 84 K which agrees fairly well with the previously reported temperature. The mechanism of the phase transition is interpreted in terms of softening of a translational mode of the anions and/or cations. For the monoclinic crystals, a structural phase transition was located at 65 K in agreement with the reported value.
Electronic and Thermodynamic Properties of the Liquid TIAgTe System
Authors: Uemura O. , Sekiya T. , Ishikawa H. , Satow T.
Published: July 2012

The electrical conductivity, the magnetic susceptibility, and the thermoelectric power of the liquid TI‐AgTe system have been obtained as functions of temperature and composition. The thermodynamic properties of the system have also been determined by means of the EMF method. The system shows a sharp minimum in electrical conductivity and a marked maximum in diamagnetic susceptibility at the stoichiometric composition of AgTlTe, where the change in sign of thermoelectric power also appears. These electronic properties are discussed in the light of current transport theories employed in the amorphous and liquid semiconductors. Further, the presence of the local order around the stoichiometric composition in the system is discussed by the support of the results of thermodynamic properties.
Modification of the Electric Double Layer Properties of the Interface Mica/Aqueous Solution by Adsorption of Polyelectrolytes
Authors: Wehn R. , Woermann D.
Published: July 2012

Measurements of streaming potentials with an rectangular channel formed by two mica plates and spacers are used to study (a) the properties of the electric double layer at the interface mica/aqueous alkali chloride solution and (b) modifications of these properties by adsorption of polyelectrolytes (poly‐4‐vinyl‐pyridinium bromide, heparine, poly‐vinyl sulfate). The results obtained for the unmodified
Relaxation and Reconstruction of Solid Surfaces
Authors: Müller K.
Published: July 2012

It has long been known from LEED (low energy electron diffraction) experiments that semiconductor surface structures differ from those of simple truncations of the bulk solid. Unexpected and sometimes complicated diffraction patterns of a growing number of semiconductor as well as metal surfaces indicate a selvedge region of altered structure. This is uow recognized as a common phenomenon.—The selvedge consists of several atomic layers with modified two‐dimensional periodicity in the outermost layer(s), reconstruction, and with interlayer distances altered with respect to the bulk, relaxation. Structure determinations reveal for monoatomic surfaces a damped oscillatory multilayer relaxation, alloys may even show a rippled relaxation of their surfaces. The kind of reconstruction can be merely displacive where bond lengths are slightly changed. The more dramatic form of reconstruction involves considerable mass transport, broken bonds, formation of steps and domains, etc. In every case the static order and (as a consequence) electronic and dynamic properties as well as the reactivity of the surface are changed.—Structure determinations by LEED and other methods are all but easy. Recent experimental improvements and developments in computational schemes led to rather sophisticated methods which revealed surface models with detailed structural parameters. The reliability and accuracy of different methods are still being discussed. Some results, however, seem to be widely accepted by now.—Adsorption generally affects reconstruction and relaxation. Therefore adsorption sites can no longer be assumed as fixed positions. Phase transitions between ordered phases can be studied as a function of independent parameters such as coverage or temperature. Relaxation and reconstruction trends as well as stability considerations for different model surfaces are now being developed from theoretical studies of the surface energy.
On the Kinetics and Mechanism of the Oxygen Induced (2 × 1) Reconstruction of Ni(HO)
Authors: Behm R. J. , Ertl G. , Wintterlin J.
Published: July 2012

The kinetics for the formation of the reconstructed (2 × 1) structure of O/Ni(110) from a nonreconstructed phase were investigated by LEED and work function measurements. The rates fit well to an “Avrami” type kinetics, which can be interpreted in terms of a nucleation and growth process. An activation barrier of 24 kj/mole is derived, the mechanism and energetic driving force are discussed in this picture and compared to other adsorbate induced surface phase transformations.
Photoelectrochemical Properties of Polycrystalline Mg‐Doped p‐Type Iron (III) Oxide
Authors: Tinnemans Oxide A. H. A. , Koster T. P. M. , Thewissen D. H. M. W. , Mackor A. , Schoonman J.
Published: July 2012

Polycrystalline Mg‐doped (0.1–5 at. %) Fe2O3 photoelectrodes have been prepared by annealing at 1573 K followed by slow cooling in air to ambient temperature. These materials are essentially single‐phase at Mg concentrations not exceeding 0.5 at. %. Disk‐shaped (photo)‐electrodes were prepared, and their electric and photoelectrochemical (PEC) properties were measured. The positive sign of the photovoltage and of the thermoelectric power θ, confirmed the materials to be p‐type semiconducting.—Carrier concentrations calculated from θ, revealed each Mg2+ to introduce one electron‐hole up to about 0.1 at. % Mg. The a.c. conductivities, showing conductivity activation enthalpies of about 0.5 eV in the temperature region 300–800 K, are affected by grain growth and porosity.—The current‐voltage characteristics in the dark and under illumination, the spectral response, and the flatband potential (Vfb = +2.2 V vs. SCE pH = 10) have also been determined.—PEC photocurrents in the visible region correspond to very low (∼0.1%) monochromatic quantum efficiency which is due to the low electron‐hole mobility. The electronic transition in the visible region is indirect, and evidence has been found for this transition to be Fe‐Fe charge transfer. Surface pretreatment is found to have a major effect on the photoelectrochemical properties as deduced from current‐voltage curves. The stability of the α‐Fe2O3 electrode in alkaline solution is discussed.
An Improved Quartz Microbalance. Applications to the Electrocrystallization and ‐dissolution of Nickel
Authors: Benje Michael , Eiermann Matthias , Pittermann Udo , Weil Konrad G.
Published: July 2012

A transistorized Pierce‐Miller‐oscillator is described which can be used to excite a quartz vibrator in contact with a solution. Changes of the resonance frequency of the quartz induced by deposition or dissolution of substances on one of its surfaces can be measured. We also describe a simple teflon holder which allows fixation of the crystal in a position in which only one of its faces is in contact with the solution.—The influence of simultaneous gas evolution on the performance of the balance is discussed. Preliminary results on the role of hydrides during nickel deposition and dissolution are presented and compared with literature data.
Dielectric Properties of Polyelectrolyte Solutions II. Behaviour of Aqueous Solutions of Carboxymethylcellulose with Divalent Counterions
Authors: Bordi F. , Cametti C.
Published: July 2012

The dielectric properties of well‐characterized Carboxymethylcellulose samples of different molecular weights in aqueous solutions of 2:1 valent electrolytes (BaCl2 and CaCl2) have been measured in the frequency range from 1 KHz to 10 MHz at the temperature of 20.0°C.—The results are discussed in comparison with those reported in a previous paper for univalent counterions on the basis of rod‐like Polyelectrolyte dielectric models and the effects of Ba++ and Ca++ counterions on the conformation of the polyion in aqueous solution have been investigated.
The Goldman Constant Field Assumption: Significance and Applicability Conditions
Authors: Mafé S. , Pellicer J. , Aguilella V. M.
Published: July 2012

Ionic transport phenomena in simple, porous membranes can be approximately represented by the Nernst‐Planck flux equations and Poisson's equation. In order to solve this set of equations for each particular case, the Goldman constant field assumption is one of the most widely used. In the present paper the significance and the applicability conditions of the above hypothesis is critically examined. and the particular situations where it is exact are shown. These conditions are later verified by solving numerically the electrodiffusion equations. The analysis carried out shows that some of the earlier studies based on asymptotic expansions and numerical solutions should be partially revised.
Excess Enthalpies of Binary Liquid Mixtures Containing Oxiranes Part 1: HE (298.15 K, 101.3 kPa) of the Four Systems Chloromethyl‐ and Bromomethyl‐Oxirane + n‐Hexane and n‐Heptane
Authors: Kramer U. , Koçak M. , Steiger A. , Becker F.
Published: July 2012

The excess enthalpies of the four systems chloromethyl‐ and bromomethyl‐oxirane + n‐hexane and + n‐heptane at 298.15 K and 101.3 kPa have been determined by continuous isothermal mixing calorimetry at constant volume using the overflow method. The HE data were evaluated with equilibrium models assuming that the strong endothermic heat effect on mixing is governed by two types of intermolecular interactions, (1) the unspecific mutual solvation of the components, (2) the self‐association of the oxiranes via CH…O interactions. The latter interactions, for which an energy parameter of ‐10 kJ mol−1 is calculated, are enhanced by the electron‐attracting substituents at the oxirane ring.
The Optical Properties of Liquid Se and Se1‐xTex Alloys
Authors: Seyer H.‐P. , Tamura K. , Hoshino H. , Endo H. , Hensel F.
Published: July 2012

The temperature and pressure dependence of the optical properties of liquid Se and Se1‐xTex alloys have been determined by means of normal incident reflectivity measurements between 0.5 and 5.0 eV. The optical conductivity σ(ω) and the real part of the dielectric function ε1(ω) have been derived by means of a modified Kramers‐Kronig analysis. The reported results give useful information about the electronic structure of liquid Se and Se1‐xTex alloys. In particular, the results provide the first direct experimental evidence for coordination driven changes in the electronic structure of these liquids in course of the transition from a nonmetallic to a metal‐like state.
Interstitial Transition Metal Impurities as a Possible Cause of Enhanced Reactivities
Authors: Behner T. , Elbers G. , Remme S. , Prissok F. , Stegger P. , Lehmann G.
Published: July 2012

Trivalent ions of Fe, Cr and Mo are easily incorporated into CsCl‐type lattices. Evidently their geometries partly derive from those for divalent ions by exchange of a neutral molecule by hydroxyl or halide. In the ammonium halides hydrogen bonding manifests itself in predominance of low site symmetries and dynamic effects. Evidence for interstitial incorporation of di‐ and trivalent ions in quartz and isomorphous ABO4 compounds is also presented. EPR data for Fe3+ indicate simultaneous incorporation of O2− or OH− in the c‐axis channels. A kinetic reason for preferred interstitial incorporation is proposed. Enhanced mobilities of these as well as certain main constituents may also enhance the reactivities.
Order‐Disorder in Solid 1,2,3‐Trichlorobenzene. A Single Crystal 35CI NQR Study
Authors: Sharma Surendra , Weiden Norbert , Weiss Alarich
Published: July 2012

By single crystal Zeeman split NQR spectroscopy the nuclear quadrupole coupling tensors, NQCT, of 35CI in magnitude, orientation, and symmetry were studied in the range 140 ≦ T/K ≦ 250. Neither the asymmetry parameters nor the orientations of the NQCTs depend significantly on temperature. The disappearance of the 35CI NQR signal well below the melting point was investigated by studying the line width Δv and the spin lattice relaxation time T1 as a function of temperature. From Δv = f(T) an activation energy of 31 kj mol−1 and 36 kJ mol−1, respectively, was found for the two crystallographically inequivalent molecules in the unit cell. The onset of static order‐disorder or the creation of lattice vacancies may be responsible for the line broadening and the change in T1.
Densitometric Characterization of the Main Phase Transition of Dimyristoyl‐Phosphatidylcholine between 0.1 and 40 MPa
Authors: Vennemann Norbert , Lechner M. Dieter , Henkel Thomas , Knoll Wolfgang
Published: July 2012

Densitometric measurements employing the mechanical oscillator technique have been performed with dilute aqueous dispersions of dimyristoyllecithin at different temperatures and pressures up to 400 · 105 Pa. Isothermal compressibilities of xLα = 4.5 · 10−10 Pa−1 for the fluid phase and xPβ' = 2.9 · 10−10 Pa−1 for the ordered phase, respectively, are obtained. It is demonstrated that the first order main phase transition from the fluid to the condensed phase can be induced isothermally by increasing the hydrostatic pressure in the measuring cell. The coexistence of the two phases is limited to a narrow pressure range of about 10 · 105 Pa which corresponds to the intrinsic width of the transition. The volume change associated with the phase transition decreases with increasing pressure. The slope of the transition pressure‐temperature relationship increases with increasing pressure. From the limiting slope for p → 105 Pa a transition enthalpy of ΔH = 24.6 kJ·mol−1 is derived.
A Kinetic Study of the Diazotization of Substituted 1‐Naphthylamines
Authors: Castro Albino , Iglesias Emilia , Ram Leis J. ÓN , Peña M. Elena
Published: July 2012

The diazotization of various substituted naphthylamines has been found to be catalysed by the nucleophiles Cl−, Br−, SCN− and thiourea due to the formation of the corresponding nitrosyl salts. The rate controlling steps depend on the concentration of catalyst, with respect to which the order of the reaction varies between 1 and 0. The theoretical rate constants deduced from the proposed reaction mechanism are discussed in terms of the basicity of the amines and the nucleophilicity of the catalysts. The reaction rate's dependence on ionic strength and acidity in the absence of catalysts is also reported and discussed.