bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polyion Selfdiffusion in Salt‐Free Solutions of Sodium Poly(Styrene Sulfonate)
Authors: Oostwal M. G. , Blees M. H. , De Bleijser J. , Leyte J. C. 
Published: July 2012

AbstractThe selfdiffusion of polyions in semidilute aqueous salt‐free solutions of the linear polyelectrolyte Sodium Poly(Styrene sulfonate) has been studied by use of Pulsed Field Gradient NMR as a function of concentration and degree of polymerization. The diffusion of the polyions was found to be only moderately dependent on polymer concentration over a large concentration range. A possible transition in diffusional behaviour, apparently independent of molecular weight, has been found to occur at a polymer concentration of about 0.05 monomolal. The molecular weight dependence of the diffusion exhibited almost Rouse‐like behaviour over the concentration range under consideration for degrees of polymerization between 87 (Mw = 16000) and 1066 (Mw = 195000) which indicates that entanglements are probably only of minor importance. Both the concentration and molecular weight dependencies are in contrast to the behaviour of neutral polymers in the semidilute regime.
Determination of Binary Diffusion Coefficients in Supercritical Carbon Dioxide with Supercritical Fluid Chromatography (SFC)
Authors: Dahmen Nicolaus , Dülberg Andreas , Schneider Gerhard M. 
Published: July 2012

AbstractBinary diffusion coefficients D12 in supercritical carbon dioxide were determined in a Supercritical Fluid Chromatography (SFC) apparatus by the peak broadening method (PBM). Some cyclic and linear ketones were investigated as a function of pressure between 9.5 and 18 MPa at about 314 K corresponding to densities from 513 to 820 kg m−3. The resulting D12 values are of the order of 10−8 m2 s−1 and In D12 decreases about linearly with increasing density ϱ of the CO2.
Pressure‐Jump Experiments for the Study of the Kinetics of Phase Separation in the Binary System Ethene/Hexane. II. Measurements of Pressure‐Induced Temperature Changes
Authors: Metz U. , Schneider G. M. 
Published: July 2012

AbstractIn order to study the process of demixing of the binary gas/liquid system ethene/hexane we used a pressure‐jump technique that makes possible to generate differential pressure jumps from 0.05 up to 1 MPa into the miscibility gap. For relating the time‐dependent appearance of a new phase by means of light scattering to the respective maximum supersaturation of the system under test (see Part I), the knowledge of the corresponding adiabatic temperature changes induced by the pressure jumps was necessary. In this paper we report transient temperature measurements at pressures up to 8 MPa and temperatures from 293 to 323 K that were made with a thermocouple in contact with the binary liquid phase. An empirical formula is presented and discussed which relates the adiabatic thermal pressure coefficient to the critical temperatures and the critical pressures of the binary system over pressures and temperatures ranging from 2 MPa and 20 K respectively away from the vicinity of the critical line.
Elementary Processes of CF2(Ā1B1) and CF2(X̄1A1) with Reactive Gases
Authors: Dornhöfer G. , Hack W. , Hoyermann K. , Rohde G. 
Published: July 2012

AbstractElementary reactions of CF2(Ā1B1) and CF2(X̄1A1) were studied in the gas phase at low pressures and room temperature. Microwave discharges, IR‐ and UV‐Laser photolysis were used to produce CF2(X̄) radicals. Single vibronic level (SVL) excitation into the Ā1B1(0, 6, 0) state was performed with a KrF laser, and the fluorescence of that state was used to monitor their decay. Different experimental arrangements have been used. ‐ The rates of collisional removal of CF2(Ā) radicals were directly measured by the time resolved fluorescence in a quasistatic laser photolysis cell. The rates at room temperature were found to be: (CH3)2 C2(CH3)2 (39 ± 5), CH3 OCHCH2 (27 ± 5), CH2O (13 ± 2), SO2 (30 ± 1), NH3 (14 ± 2) H2O (3.5 ± 0.5), CO2 (0.39 ± 0.1) and H2 (0.82 ± 0.1) (in 1013 cm3/mol s units). The contribution of chemical product formation in the reaction CF2(Ā) + H2 CHF(X̄) + HF was deduced from the CHF(X̄) concentration as measured via LIF. ‐ By mass spectrometric studies of the reactions of CF2(Ā) radicals with (CH3)2C2(CH3)2 and (CH3)2C2H2, the removal rates of CF2(Ā) were assigned to physical quenching (> 99%). The rate constants for the reactions of CF2(X̄) with (CH3)2C2(CH3)2 and (CH3)2C2H2 were determined as (3.6 ± 1.5) · 109 and (6.67 ± 3) · 108 cm3/mol s respectively.
The Static Dielectric Constant of Methyl Cyanide to 350°C and 2000 bar
Authors: Hill W. W. , Rosenzweig S. , Franck E. U. 
Published: July 2012

AbstractThe relative static dielectric constant	ε of methyl cyanide was measured from 20 to 350°C, from 50 to 2250 bar and for the liquid along the saturation line to 270°C (Tc = 274.7°C). — Equipment and experimental procedure are described. At 20°C and pressures of 50 and 2000 bar ε changes from 37.7 to 42.9. At 100°C the change over the same pressure range is from 26.6 to 32.4 and at 300°C from 2.50 to 18.5. The accuracy of the data is ±0.4% up to 100°C and ±0.6% up to 300°C. Above 300°C and below 200 bar the data may be uncertain within ±1 or ±2%. Diagrams with ε‐values in dependence of density and temperature are given. The Kirkwood correlation factor below a density of 0.4 g cm−3 is slightly above unity. At densities higher than 0.4 g cm−3 ε declines at all temperatures to about 0.8 at 0.8 g cm−3. This may indicate a certain degree of dimerization, which is discussed.
Importance of Metastable RNA Folding in Template‐Replicase Interactions
Authors: Fernández Ariel 
Published: July 2012

AbstractWe consider the autocatalytic synthesis of MDV‐1 RNA by Q beta replicase, which proceeds by template‐instructed replication. We predict the effect of a particular point mutation in the sequence on the overall doubling time and conjecture its role on the recognition step. The mutation considered destabilizes the folding of the internal recognition site. The theoretical analysis is based on the calculation of nonequilibrium re‐folding events which occur in the RNA chains as they are being synthesized. Free‐energy minima are irrelevant. In order to test the theoretical findings, we incubate both the natural template and the mutant simultaneously, in the presence of the replicase. The experiment reveals that the mutation facilitates the enzyme‐template interaction, thus enhancing recognition. However, examining the exponential phase of the replication kinetics, where the enzyme is in large excess with respect to the RNA species, we can conclude that the mutant presents a larger overall doubling time, in good agreement with our theoretical findings.
Structural Study of Liquid Ethylbromide Using Differential Anomalous X‐ray Scattering
Authors: Mager T. , Schultz E. , Bertagnolli H. , Frahm R. 
Published: July 2012

AbstractSynchrotron radiation was used for a differential anomalous X‐ray scattering (DAS) study of liquid ethylbromide (C2H5Br). Two diffraction experiments were carried out at photon energies of 12500 and 13464 eV. The dispersion corrections were determined from photoabsorption coefficients obtained from an absorption experiment. After an elaborate and involved data evaluation and correction procedure a differential structure factor was obtained. The peak assignation in the differential atom pair correlation function (DAPCF) was verified by comparison with a theoretical intramolecular distribution function calculated from well known data of the intramolecular geometry of ethylbromide. In addition, a peak at 4.1 Å is found in the DAPCF, which may be assigned to an intermolecular Br—Br atom pair suggesting a strong dispersion interaction.
TiO2 and Bi2O3 Thin Film Oxygen Sensor Materials
Authors: Nicoloso N. 
Published: July 2012

AbstractThe electrical conductivity of polycrystalline TiO2 and Bi2O3, deposited on sapphire substrate by various methods, has been determined as a function of the film thickness, the oxygen partial pressure and the temperature. As a rule, TiO2 films with d ≲ 30 nm are incoherent after heat treatment, thereby restricting the miniaturization of the planar sensor device. Larger films essentially behave like bulk material with fully ionized oxygen defects V2•o (or Ti4•i interstitials) as major intrinsic defects. In case of extrinsic p‐type films, the conductivity contribution of the TiO2/sapphire substrate and TiO2/gas phase interfaces is clearly enhanced with respect to the bulk contribution, mainly due to segregation effects. Doubly ionized oxygen vacancies V2•o and M'Ti defects (trivalent acceptor atoms at Ti‐sites) appear to be the main intrinsic and extrinsic defects involved in the segregation process and in the oxygen exchange reaction. In contrast to TiO2, thin films of Bi2O3 react strongly with the substrate ultimately forming a new stable phase, Al4Bi2O9. Along with this structural change, the conductivity decreases by several orders of magnitude, classifying Bi2O3 as an unsuitable material for such thin film sensor devices.
In Situ Measurements of Tropospheric OH Radicals — A Challenge for the Experimentalist
Authors: Armerding W. , Herbert A. , Schindler T. , Spiekermann M. , Comes F. J. 
Published: July 2012

AbstractA method for monitoring tropospheric OH and other tropospheric trace gases is discribed which makes use of differential absorption spectroscopy and is based on the fast scanning of a narrowband, frequency‐doubled, and power‐stabilized dye laser. Due to the fast scanning and the power stabilization the fluctuations of the atmosphere and the light source are minimized thus a detection limit better than 10−5 can be achieved for atmospheric long‐path absorption measurements. In a first test in the near of Frankfurt/Main tropospheric OH was observed with an averaged concentration of 1 · 106 OH cm−3. The absorption path‐length was 800 m and the acquisition time 5 min.
Temperature Dependence of Molecular Motions in Polymethylmethacrylate Studied by Positron Annihilation Techniques
Authors: Millán S. , Geckle U. , Lévay B. , Ache H. J. 
Published: July 2012

AbstractUntreated polymethylmethacrylate (PMMA) as well as PMMA into which charges were injected (PMMA‐electret) were studied by positron annihilation techniques (PAT). A comparison of the PAT data with previously reported results obtained via different techniques including thermally stimulated discharge (TSD) shows good agreement and suggests that the observed effects can be explained by the onset of different types of molecular motions in the polymer. It appears that in the case of the PMMA‐electret an additional transition at 130 K can be identified which may be correlated with a different type of molecular motion, presumably with the rotation of the methyl group of the ester side chain.
Photochemistry in Porous Materials I: Fluorescence Quenching of Anthracene Adsorbed on Different Silicagel Preparations
Authors: Wolff Thomas , Akbarian Fatemeh , Von Bünau Günther 
Published: July 2012

AbstractFluorescence excitation spectra of anthracene adsorbed on the internal surface of two silicagel preparations (pore diameters of 3.7 and 8.6 nm respectively) were recorded in the wavelength interval 290 to 390 nm in the absence and presence of oxygen and argon. Areas under these curves were taken as relative measures of fluorescence quantum yields. Fluorescence is quenched strongly by oxygen, following Langmuir‐Hinshelwood‐kinetics with respect to oxygen partial pressures. Very little quenching occurs in the presence of argon. Oxygen quenching rates do not depend on pore size.
Subbandgap Photocurrent of a Ru‐Covered n‐GaAs|Acidic‐Electrolyte Junction
Authors: Jung Ch. , Kolb D. M. 
Published: July 2012

AbstractThe subbandgap photocurrent dependence on electrode potential and light energy has been investigated for the n‐GaAs(100) | 1 M HCl junction after surface modification by electroless deposition of ruthenium. A pronounced peak in the photocurrent‐potential curve was found for Ru‐treated electrodes between −0.6 and −0.1 V/SCE. This behaviour is explained in a model simulation for the photocurrent which takes into account the hole generation in a Ru‐induced surface state by absorption of subbandgap light.
KrF Laser Induced Telomerization of Bromides with Olefins. Part 1: Self‐Inhibition and Kinetic Analysis
Authors: Linyang Zhang , Fuß W. , Kompa K. L. 
Published: July 2012

AbstractThe chain reaction of several organic bromides with olefins was induced by a KrF laser. In all cases we found a self‐inhibition, leading to a termination of first order in the radical concentration. There is indirect evidence that it is due to molecular bromine, accumulated during the reaction in spite of the presence of olefins. It has not been noticed previously. We show that kinetic analysis is easy also for pulsed excitation, and the example CF3Br + C2H4 is studied in detail. We found rate constants for CF3 + C2H4 → CF2C2H4 (7.2 · 109 cm3 mol−1 s−1; this is in between two previous values) and for CF3C2H4 + CF3Br → CF3C2H4Br + CF3 (1.2 · 109 cm3 mol−1 s−1) as well as preliminary values for some other reactions.
Solid State Electrochemical Chlorine Gas Sensor
Authors: Schlechtriemen Gerd‐Ludwig , Sohège Jürgen 
Published: July 2012

AbstractA solid state sensor for monitoring chlorine is presented. The applied method is the potentiometric partial pressure measurement via heterogeneous secondary equilibria using an appropriate solid state galvanic cell. The sensor is a planar double cell mounted on a supporting ceramic carrier. A high impedance converting circuit and a thick film heating structure are integrated. The various fabrication steps are reported. The sensor is working between 430 and 490 K. The sensitivity to chlorine ranges down to the sub‐ppm region. The response behaviour as well as interferences of water vapour and hydrogen sulfide are discussed.
Electrochemical Detection of Organic Gases: The Development of a Formaldehyde Sensor
Authors: Baltruschat H. , Anastasijevic N. A. , Beltowska‐Brzezinska M. , Hambitzer G. , Heitbaum J. 
Published: July 2012

AbstractUsing differential electrochemical mass spectrometry, we determined the amount of H2‐evolution occuring during formaldehyde oxidation as a function in the potential region of the first oxidation wave. In the second wave, the oxidation product is CO2 in pH 8 solution, as opposed to more alcaline solutions where only formiate is formed. Formaldehyde is reduced to methanol at potentials negative of the RHE.—An electrochemical formaldehyde sensor was built with a sensitivity below 1 ppm. Cross sensitivities towards alcohols can be lowered by UPD of Ag or Hg.
Polymer Membranes for Fuel Cells
Authors: Scherer Günther G. 
Published: July 2012

AbstractA brief description of the ion exchange membrane fuel cell, of important membrane properties and of some earlier membrane development work is given. We describe some results of membrane stability tests in electrolysis cells, which are important for fuel cell application, in context with fluorination degree and morphology of the membrane. These results demonstrate, that fluorinated membranes with “defined” morphology can be applied in these cells. Finally, we give evidence for asymmetric degradation of membranes at the H2‐side.
An FTIR Study of the Catalytic Activity of a 85:15 Pt:Ru Alloy for Methanol Oxidation
Authors: Iwasita T. , Nart F. C. , Vielstich W. 
Published: July 2012

AbstractIn situ Fourier Transform Infrared Spectroscopy is used to study the catalytic properties of a Pt/Ru alloy as compared to pure platinum. Spectra taken at different potentials show the different behaviour of both metals with respect to methanol adsorption and oxidation. In the potential region below 700 mV the presence of Ru atoms increases the electrocatalytic activity of platinum. In the case of the alloy the poisoning adsorbate COad is adsorbed to a less extent and its seems to be weaker bonded to the Pt/Ru than to the Pt surface.
Tungsten Carbide Catalyzed Hydrogen Anodes for Electrochemical Processes
Authors: Möbius A. , Wiesener K. 
Published: July 2012

AbstractThe application of hydrogen diffusion anodes for the substitution of oxygen developing anodes in technical electrolyses for metal winning also in connection with recycling processes as well as the use of hydrogen diffusion anodes in electroplating technology is to be discussed under following aspects:
more effective energy use,
electrolytic generation of metals of higher purity,
generation of alloyed layers in electroplating and electroforming technology with improved properties and
recycling of pickling and etching bathes.
79Br and 127I Nuclear Quadrupole Resonance Study of Para‐Substituted Anilinium Halides, 4‐RC6H4NH⊕3X⊖ with X = Br, I and R = Cl, Br, SCN, and OCH3. Crystal Structure of 4‐Chloro‐ and 4‐Bromoanilinium Bromide Hemihydrate
Authors: Hartmann Jutta , Dou Shi‐Qi , Weiss Alarich 
Published: July 2012

AbstractThe 79Br and 127I nuclear quadrupole resonance spectra of para‐substituted anilinium bromides and iodides 4‐RC6H4NH⊕3X⊖ with X = Br, I and R = Cl, Br, SCN, OCH3 were studied in the temperature range 77 ≤ T/K ≤ 420. 4‐ClC6H4NH⊕3Br⊖ shows a phase transition at Tc = 132 ± 1 K. 4‐ClC6H4NH⊕3Br⊖ as well as 4‐BrC6H4NH⊕3Br⊖ exist as hemihydrates, too. The two hemihydrates are isomorphous, crystallizing monoclinic, C52h ‐ P21/c, Z = 8. 4‐ClC6H4NH⊕3Br⊖·1/2 H2O: a = 1370.9(5) pm, b = 789.1(3) pm, c = 1940.1(7) pm, β = 125.38(1)°; 4‐BrC6H4NH⊕3Br⊖ · 1/2 H2O: a = 1380.1(7) pm, b = 794.8(5) pm, c = 1934.2(9) pm, β = 125.11(1)°. The influence of hydrogen bonds on 79Br NQR is investigated. NQR results and the structures of the studied compounds are discussed in comparison with known bond properties of anilinium halides.
The Membrane Properties of the Electro‐Polymerized Conducting Pyrrole/N‐Sulfopropyl‐Pyrrole Copolymer
Authors: Zhong Chuanjian , Storck Winfried , Doblhofer Karl 
Published: July 2012

AbstractElectronically conducting polymer films were prepared electrochemically from aqueous electrolytes containing mixtures of pyrrole and N‐(3‐sulfopropyl)pyrrole. The reversible electrochemical oxidation and reduction (redox‐switching) of these coatings have been studied, mainly with the method of cyclic voltammetry. At various electrode potentials the coated electrodes were withdrawn from the solutions to determine the composition of the films gravimetrically and by energy‐dispersive analysis of X‐rays (EDAX). Volta‐potential measurements were conducted to obtain information on the Donnan‐potentials. Thus the membrane properties of the coatings were characterized as a function of the electrode potential and the mole fraction of sulfonate groups fixed in the copolymer matrix. While conventional polypyrrole films constitute anion exchangers in the oxidized state, the copolymers can be either anion‐ or cation‐exchangers, depending on the concentration of the fixed anions. When the polymer matrix contains about one sulfonate group per 10 pyrrole units, the film undergoes, during redox‐switching, a reversible and complete transition between anion‐ and cation‐exchange character.
Current Oscillations in the Anodic Dissolution of Silicon in Fluoride Electrolytes
Authors: Ozanam F. , Chazalviel J.‐N. , Radi A. , Etman M. 
Published: July 2012

AbstractThe oscillations of the current which take place during the anodic dissolution of silicon in fluoride electrolytes have been investigated. These oscillations occur only upon a perturbation in the electrode potential, and are associated with a fluctuation of the thickness of an oxide layer on the electrode surface. In the corresponding potential range, the experimental data strongly support the picture of a surface consisting of a juxtaposition of small self‐oscillating areas. These areas are decorrelated from each other in the steady state, but are synchronized by a potential perturbation, giving rise to macroscopic oscillations.
Boltzmann Transformation of Taylor Dispersion Profiles to Determine Concentration‐Dependent Diffusion Coefficients. Aqueous Cetylpyridinium Chloride near the Critical Micelle Concentration
Authors: Leaist Derek G. 
Published: July 2012

AbstractThe Taylor dispersion technique is modified to measure the concentration‐dependent mutual diffusion coefficient D of cetylpyridinium chloride (CPC) + water at 25°C near the critical micelle concentration. The solution flowing into the dispersion tube is changed from a solution of CPC concentration C− to a solution of concentration C− + ΔC, forming an initially‐sharp moving boundary at the tube inlet. The broadened concentration profile across the eluted boundary is followed by using a flow‐through differential refractometer at the tube outlet. A numerical procedure similar to the Boltzmann‐Matano procedure for the analysis of free diffusion profiles yields the values of D at the concentrations between C− and C− + ΔC, from a single dispersion run. D for aqueous CPC is found to drop very sharply as the concentration is raised through the critical micelle concentration.
Measurements and Analysis of Excess Enthalpies of Ester + n‐Alkane Using the UNIFAC Model
Authors: Ortega J. , Legido J. L. , Fernández J. , Pías L. , Paz Andrade M. I. 
Published: July 2012

AbstractWe present new experimental data of the excess molar enthalpies at 298.15 K for eighteen different binary mixtures of nine methyl alkanoates (ethanoate to decanoate) with n‐heptane and n‐undecane. The results show that all the systems are endothermic, hE values increase with the length of the n‐alkane and decrease with the length of the methyl ester. The data have been analysed with a version of the UNIFAC model, and the parameters corresponding to the CH2/COOC interaction have been recalculated using a larger base of experimental data. New values for the CH2/COO interaction parameters have been obtained.
Solvent Polarity Dependent Formation Dynamics of TICT States. I. Differential Solvatokinetics
Authors: Rettig Wolfgang 
Published: July 2012

AbstractComparison of the fluorescence kinetics of two dialkylaminobenzonitriles with different hindrance to planarity is used to extract information on the polar‐solvent induced shape changes of the excited‐state potential surface for TICT formation. The conical intersection between B* and A* states is shown to move to smaller twist angles as solvent polarity increases.
Rate Processes in Proteins
Authors: Frauenfelder Hans , Ulrich Nienhaus G. , Bruce Johnson J. 
Published: July 2012

AbstractFlash photolysis experiments on carbonmonoxymyoglobin over wide ranges in time and temperature provide information about the rate processes involved in the rebinding reaction. The non‐exponential rebinding at low temperatures shows that the myoglobin molecules are frozen into a large number of conformational substates with different enthalpic barriers. Above 160 K we observe a relaxation process that shifts the peak of the barrier distribution from ∼ 10 kJ/mol to ∼ 21 kJ/mol. This process is non‐exponential in time and does not obey the Arrhenius law. Above 220 K equilibrium fluctuations between the conformational substates lead to an averaging of the binding rate distribution and to the opening of pathways for the ligands to escape from the protein molecules.
Stiffness Effects in Multidimensional Diffusive Barrier Crossing
Authors: Agmon Noam , Rabinovich Savely 
Published: July 2012

AbstractThe model of Agmon and Kosloff for two‐dimensional diffusive barrier crossing is extended. We demonstrate how an increase in stiffness of the potential perpendicular to the reaction coordinate leads to viscosity dependent rates which are closer to the one‐dimensional Kramers result. The range over which the dynamics are truly two dimensional is characterized by a fractional viscosity dependence of reaction rates and viscosity dependent activation energies. It is a transition region between Kramers behaviors observed in the two extreme limits. A simple kinetic approximation rationalizes these observations as arising from two competing pathways. It shows surprisingly good agreement with the full calculation.