bluuebunny/crossref_metadata_2025_split huggingface dataset:
Generalized Stokes‐Einstein Relation
Authors: Balucani U. , Vallauri R. , Gaskell T. 
Published: July 2012

AbstractA means of deriving a generalization of the Stokes‐Einstein relation, when the “Brownian” particle has a size comparable with that of the atoms of the surrounding medium, is discussed. Through the introduction of a velocity field concept, a physical meaning can be inferred for the “effective” particle radius. As a result of such a generalization, we discuss the relevance of the coupling with collective variables for the description of single particle motion. Computer simulation results for the involved quantities are also presented.
Dynamics and Orientation of Molecules Adsorbed on Graphite Studied by Deuteron NMR Spectroscopy
Authors: Boddenberg B. , Grundke V. , Auer G. 
Published: July 2012

AbstractDeuteron magnetic resonance spectra and spin‐lattice relaxation times of deuterated molecules (fluorobenzene (C6D5F) and neopentane (C5D12)) adsorbed on the graphitized carbon black Graphon were measured as function of temperature (75 — 288 K) and resonance frequency (13.68 and 52.72 MHz). These data reveal a strong influence of the extramolecular magnetic shielding coupling on the spectra and relaxation times. Information is obtained about the orientation and the anisotropic rotational dynamics of the adsorbed molecules as well as about the translational dynamics across the surface of the microcrystalline graphite particles. Surface diffusion coefficients are evaluated which indicate a very high translational mobility of adsorbed molecules on graphite.
Vibrational Dephasing of Simple Liquids Investigated by Picosecond and Femtosecond CARS
Authors: Aechtner P. , Fickenscher M. , Laubereau A. 
Published: July 2012

AbstractUsing picosecond CARS the dephasing rate of the ν1‐mode of CS2 is investigated in several solvents and in the neat liquid. A large pressure effect (factor of ≤3) is reported for the range 0 to 4 kbar similar to spontaneous Raman results. For an extended interval of 160 to 450 K, a non‐monotonic temperature dependence is reported for the first time and compared with theoretical models. — A novel non‐degenerate CARS spectrometer is described with 80 fs time resolution and improved measuring accuracy. A dephasing time of T2 = 608 ± 6 fs is reported for the ν1 mode of neat acetone of 293 K; negligible inhomogeneous broadening (< 1%) is indicated by the scattering data for this vibration.
OH Radicals Generated by NO Photolysis in Aqueous Solution: Competition Kinetics and a Study of the Reaction OH + CH2(OH)SO
Authors: Deister Ursula , Warneck Peter , Wurzinger Christa 
Published: July 2012

AbstractNitrate ion photodecomposition is explored as a source of OH radicals for the determination of rate coefficients associated with OH reactions in aerated aqueous solutions. The oxidation of benzene to phenol serves as a standard reaction phenol provides an indicator for the extent of competition by other reactants. Rate coefficients for ten organic compounds, determined relative to that for benzene, are in good agreement with literature values over a range of 3 orders of magnitude. By comparison with the yield of acetone from the reaction of OH with 2‐propanol the yield of phenol from the reaction with benzene is found to be ∼0.95. The reaction of OH with hydroxymethane sulfonate generates sulfate as a major product. It was not possible to determine the associated rate coefficient with the competition technique because the data for sulfate and phenol show the reaction to be a chain process in which SO−4 radicals appear to be the main chain carrier. Steady state calculations based on a postulated reaction mechanism indicate for the reaction OH + HMS a rate coefficient exceeding 1 · 109 M−1 s−1.
Remarks on the Electrochemical Potential of Small Silver Clusters in Aqueous Solution
Authors: Henglein Arnim 
Published: July 2012

AbstractSilver clusters in aqueous solutions containing excess Ag+ ions may be regarded as tiny metal‐electrodes. The electrochemical standard potentials of metal electrode equilibria Agn⇆Agn‐1 + Ag+ + e− are much more negative than that of the compact silver‐metal electrode. The potential generally strives toward the value of the compact electrode with increasing agglomeration n of the particles, although a strong oscillation occurs in the n = 1 to 3 range. The trend is opposite to the size dependence of the ionization potential in vacuo. The main factor determining the redox potential in solution is not the hydration of the clusters {as one may suppose at first sight} but the binding energy of a silver atom in a cluster. — The electrochemical potentials of equilibria of the type Agn⇆Agn + e− and Agn−⇆Agn + e− are also discussed. — It is pointed out that results from photoionization experiments on clusters in vacuo would importantly improve our present knowledge of the electrochemistry of clusters.
The Atmospheric Corrosion of Iron — A Discussion of the Physico‐Chemical Fundamentals of this Omnipresent Corrosion Process Invited Review
Authors: Stratmann M. 
Published: July 2012

AbstractIn this review the physico‐chemical fundamentals of the atmospheric corrosion of iron are discussed, as they result from a number of electrochemical and spectroscopic techniques, which have been applied in order to analyze the corrosion mechanism of the atmospheric corrosion during wet‐dry‐wet transitions. — After wetting a dry corroded metal surface the cathodic partial reaction of the corrosion process is given by the reduction of Fe3+‐ to Fe2+‐states within the lattice of γ‐FeOOH. If the corrosion potential is rather negative, then also magnetite is formed. As a consequence of the formation of Fe2+ states the electronic conductivity of oxide crystals close to the metal/oxide interface is increased. This results in an acceleration of the kinetics of the oxygen reduction. It could be shown, that oxygen is reduced predominantly at the oxide/electrolyte and not at the metal/electrolyte interface and therefore the rate of the oxygen reduction is determined by the electronic properties of the oxide crystals, the kinetics of the electron‐transfer reaction being very fast at oxides, which are highly doped with Fe2+ states. If the metal surface is covered with a thick electrolyte layer, then the charge transfer reaction is so fast within the reduced oxide scale, that the overall rate of the oxygen reduction is given by the diffusion of oxygen through the water filled pore system of the scale and by the surface area of the highly doped oxide scale, which allows an electron transfer to occur at the oxide/electrolyte interface. The size of this effective surface area is determined by the amount of the reduction of the oxide scale immediately after wetting the dry metal surface. During drying, oxygen diffuses rapidely into the pore system of the oxide scale by gas diffusion. Then the corrosion rate is increased dramatically due to the fast oxygen reduction at the electron‐conducting large surface area oxide cathode. Due to the fast corrosion a dense oxide layer is formed on top of the metal surface and the surface is passivated. The corrosion stage of drying is terminated by a reoxidation of the oxide scale by oxygen, which causes the rate of the oxygen reduction to decrease as the electronic conductivity of the oxide scale is reduced.
A New Process for Optical Data Recording by Photoelectrochemical Etching
Authors: Ryan M. A. , Levy‐Clement C. , Mahalu D. , Tenne R. 
Published: July 2012

AbstractPhotoetching of holographic gratings was performed on materials belonging to two families of compounds, exhibiting bidimensional and tridimensional structures. Fringes of poor quality only could be obtained on the Van der Waals face of quasi‐two dimensional (layered) semiconductors due to their high resistance to photocorrosion (WSe2), or large diffusion length of minority carriers along this face (InSe), while good morphological and optical contrasts were obtained on the surface of II — VI semiconductors. — Using a laser scanning setup, the photoresponse of Schottky diodes which were made from these semiconductors was used to convert optical information into electrical signal. The photoetched part exhibits an improved photoresponse, which produces electrical contrast between the two parts. This observation is used to transform optical information into an electrical signal. The diffusion length of minority carriers was determined from this photocurrent profile. Some applications for this method for holography and for optical data recording and its retrieval are discussed. Guidelines for materials' selection for this kind of application are proposed.
Untersuchungen zur Kinetik der Anatas‐Rutil‐Umwandlung an DeNOx‐Katalysatoren für V2O5—WO3—TiO2 (Anatas) und V2O5—MoO3—TiO2 (Anatas)
Authors: Hums Erich , Range Klaus‐Jürgen 
Published: July 2012

AbstractThe effect of preparation — specific parameters such as energy input, thermal treatment, V2O5‐content — on the kinetics of the anatase‐rutile transformation, were investigated and their relative contributions analysed. The various degrees of transformation were determined by quantitative X‐ray diffraction measurements and checked for various rate laws. The rate constants evaluated according to Avrami for the V2O5—WO3—TiO2 (anatase)‐system were extrapolated from Arrhenius plots for temperature values corresponding to conditions in power plants. The experimental results yield information on the stabilities (exposition periods) of the anatase‐modification which react sensitively towards changes in phase composition at the anatase phase boundary, thus reflecting activation and deactivation processes which have an effect on the kinetics of the anatase‐rutile phase transformation. The kinetic behaviour determined according to Avrami for the V2O5—WO3—TiO2 (anatase)‐system has not been found for the V2O5—MoO3—TiO2 (anatase)‐system. A unique feature of MoO3‐systems consists in the following: after passing through a kinetically controlled region they form stable phases which can no longer be influenced kinetically. The anatase content of such phases can be adjusted by maintaining specific preparation parameters.
Transition from Oscillatory to Chaotic Behaviour in the Belousov‐Zhabotinskii Reaction of Oxaloacetic Acid
Authors: Koo J.‐B. , Krüger A. , Richter P. , Steiger A. , Becker F. 
Published: July 2012

AbstractThe Belousov‐Zhabotinskii (BZ) reaction of oxaloacetic acid (OAA) = oxobutanedioic acid is investigated spectrophotometrically both in the closed system and in the continuous‐flow stirred tank reactor (CSTR). Using ferroin as catalyst, the reaction in the closed system exhibits a very complicated oscillatory pattern with three different types of oscillations being separated by induction periods. “Chemical chaos” = deterministic aperiodicity of the type 2 oscillations is observed in a very small range of the ferroin concentrations in the closed system. In the CSTR, change from sustained limit‐cycle oscillations to aperiodicity is produced by small variations of the temperature, or of the ferroin concentration. A qualitative discussion of these results is given in terms of coupled oscillators resulting from the simultaneous BZ reactions of the three equilibrium species of OAA in aqueous solution: the hydrate, the keto and the enol forms. The influence of the stirring rate on the oscillatory pattern in the CSTR is discussed.
The Advancement of Fuel Cell Systems and Spin‐off Battery Technology
Authors: Kordesch Karl 
Published: July 2012

AbstractThe possibly large influence of fuel cell technology on several energy conversion and environmental aspects of the future is discussed. Solar energy and other renewable energy sources must have electrochemical storage facilities. Nuclear power can be used efficiently to electrolize water. The replacement of combustion engines in vehicles by fuel cell systems operating on hydrogen is the only way of reducing the increase of CO2 in the atmosphere if the greenhouse effect is becoming a threat. The fuel cell projects related to the manned space vehicles can provide many important spin‐off's for accumulator designs and battery technology.
Impedance Measurements on Oxygen Reduction Reaction in Molten Carbonate
Authors: Makkus R. C. , Hemmes K. , De Witt J. H. W. 
Published: July 2012

AbstractTo elucidate the oxygen reduction in molten carbonate the process is studied by means of impedance measurements. On the basis of the super oxide mechanism a theoretical impedance model has been developed. It consists of a charge transfer resistance, a Warburg impedance and a Gerischer or homogeneous reaction impedance. The latter is due to the recombination reaction of oxide with carbon dioxide forming carbonate. This model also holds for the peroxide mechanism apart from a different dependency on the oxygen and carbon dioxide partial pressure. The impedance data measured on a flat electrode in a half cell for several gas mixtures were fitted according to this model under the assumption that only one mechanism, the peroxide or super oxide mechanism, dominates the reaction. The measured dependency of the various elements in the model on oxygen and carbon dioxide partial pressure do not fully agree with the theoretical expected dependency. This might be due to the fact that neither one of the mechanism predominates in the melt, but both occur simultaneously.
Wetting Behaviour of Candidate Molten Carbonate Fuel Cell Anode Materials and Electrolytes
Authors: Weewer R. , Vente J. F. , Hemmes K. , De Wit J. H. W. , Fisher J. M. 
Published: July 2012

AbstractContact angles of various electrolyte compositions were determined on some candidate molten carbonate fuel cell anode materials in a typical anode gas atmosphere using the sessile drop method. The contact angles showed to increase with the nobility of the substrate composition in the order: Cr—Ni/Al—Ni/Cr—Ni/Cu—Cu—Ni and to decrease with carbonate composition in the order: Li/Na—Li K—Li/K/Ba.
Electrode Kinetics and Interface Analysis of Solid Electrolytes for Fuel Cells and Sensors
Authors: Göpel Wolfgang , Wiemhöfer Hans‐Dieter 
Published: July 2012

AbstractTypical experimental techniques and results are presented to characterize properties of solid electrolytes with particular emphasis on their different surfaces and interfaces which determine electrode processes in sensor and fuel cell applications. Experimental results are discussed of electronic structures and chemical compositions at reversible electrode/electrolyte interfaces of the “prototype material” yttria‐stabilized zirconia.
Bioelectrochemical Fuel Cells
Authors: Kreysa G. , Sell D. , Krämer P. 
Published: July 2012

AbstractIn a biochemical fuel cell different microorganisms were employed as biocatalysts and 2‐hydroxy‐1,4‐naphthoquinone as a redox mediator. An oxygen gas diffusion electrode was used successfully; by means of a packed bed electrode as an anode the electricity output of the fuel cell could be raised considerably. Even a mixed population from a plant for the biological treatment of industrial waste gas was successfully utilized as a biocatalyst.—Experiments were carried out using the biofuel cell for bioanalytical and biosensor purposes.—Microbial mediator reduction, which is the key reaction of such a fuel cell, was examined separately for different microorganisms.
Theoretical Study of the Pressure Dependence of the Knight Shift in Alkali Metals
Authors: Leiberich R. , Philipp S. , Schmidt P. C. 
Published: July 2012

AbstractFor Li and Na metals we investigated theoretically the pressure dependence of the atomic spin susceptibility χA, the probability density PF and the Knight shift Ks = (8π/3)χAPF by the spin polarized version of the scalar relativistic augmented plane wave method. The calculations were performed within the volume range V0 ≥ V ≥ 0.5 V0, where V0 is the volume at 1 bar. Recently it was found experimentally by Bertani et al. that a) the slopes of the curves Ks = Ks(V) have different signs for lithium and sodium metals and b) for high pressures Ks(V) goes through a minimum for Na metal. We found in the present investigation that this behavior can be understood in terms of a competition between the pressure dependence of χA and PF for these metals.
Ternary Systems Water‐Alkane‐Sodium Chloride and Methanol‐Methane‐Sodium Bromide to High Pressures and Temperatures
Authors: Michelberger Th. , Franck E. U. 
Published: July 2012

AbstractExperimental results are reported for the fluid phase equilibria of the ternary system H2O—C2H6—NaCl, H2O—n‐hexane—NaCl and CH3OH—CH4—NaBr. Measurements were extended to 800 K and 250 MPa and to 450 K and 200 MPa with the methanol system. A “synthetic” method, described earlier, was used with a high pressure autoclave with improved sapphire window arrangement. Pressure‐temperature curves on the three‐dimensional pTx‐phase boundary surfaces at constant compositions, x, were obtained (“isopleths”). Temperatures, pressures and molar densities along 14, 5 and 7 isopleths for the systems with ethane, n‐hexane and methanol‐methane, respectively, are reported. Salt concentrations between 0.1 and 8 weight percent, relative to water or methanol, are applied. The addition of salt shifts the fluid‐fluid two‐phase region to higher temperatures and pressures in all three systems. The isobaric and isothermal shifts in certain regions can reach 100 K and more and 500 bar and more with 8 weight percent of salt. Even with only 0.1 weight percent 15 K shifts are observed near the respective critical curves. For the H2O—C2H6—NaCl and the H2O‐hexane‐NaCl systems computational descriptions of the isopleths, based on a “quasi‐binary” approach and a recently derived rational equation of state are given.
Effect of the Adsorption of Monovalent Intermediate on the Kinetics of Two‐Step Charge Transfer of Metal/Metal Ion Electrode
Authors: Plonski I. H. 
Published: July 2012

AbstractTheoretical relationships for the kinetics of two‐step charge transfer of bivalent metal were derived taking into account the adsorption of the intermediate according to the Langmuir isotherm. The polarization transients can exhibit inductive behaviour in two anodic and two cathodic particular cases. Inductive transients in the range of low Tafel slope are excluded.
Cation‐Cation Association of Tetramethylammonium Ions in Aqueous Mixed Electrolyte Solutions
Authors: Holz M. , Patil K. J. 
Published: July 2012

AbstractWe have measured the1H nuclear magnetic relaxation rates and the self‐diffusion coefficients of (CH3)4N+ions in aqueous solution of (CH3)4NBr as a function of salt concentration and in aqueous mixed electrolyte solution ofx4m (CH3)4NBr + (1 ‐x) 4mMBr, (M = Li, K, Cs) as a function of the mole fractionxof (CH3)4N+. By measuring also the2H relaxation rate of the solvent D2O, we could separate the (CH3)4N+proton relaxation rates into the intra‐ and intermolecular contribution. This allowed the determination of the so‐called association parameterA, which is connected with the integral over the pair correlation function. The results for the cation‐cationA‐parameter show that in the pure (CH3)4NBr solution no or only weak (CH3)4N+‐(CH3)4N+attraction is present, whereas in the mixed electrolyte solutions containing KBr or CsBr a strong association of the hydrophobic cations occurs. With M = Li, this attractive interaction is also present, however less pronounced. The sequence of the effectiveness of the alkali ions is the same as in the so‐called Hofmeister series for salting‐out effects on biological macromolecules.
Determination of Lennard‐Jones Potential Parameters of Liquid Ethyliodide by Analysis of the X‐ray Scattering Intensity using Structure Modelling and RISM Calculations
Authors: Bertagnolli H. , Schulz G. 
Published: July 2012

AbstractLiquid ethyliodide was studied by means of X‐ray diffraction experiments in order to investigate which type of intermolecular interaction determines the structure of the liquid state. The X‐ray diffraction studies of liquid ethyliodide were carried out at a wavelength of 1.54 Å. The data were corrected for polarization, absorption. Compton scattering and multiple scattering. The structure of the molecule was determined from the coherent distinct differential cross section. After subtraction of the intramolecular contribution a structure modelling technique was used to generate a model system which reproduces the Intermolecular cross section. The computed pair correlation functions of the model system were simulated by RISM calculations based on Lennard‐Jones interactions. The parameter values obtained by comparing the simulated atom pair correlation function with the model functions suggest the existence of strongly attractive interactions between the highly polarizable iodine atoms.
Steric Considerations in the Plastic Phase of Cyclohexane
Authors: Würflinger Albert 
Published: July 2012

AbstractPossible orientations of the molecules in the plastic phase of cyclohexane are discussed by using different models, which are characterized by a certain coincidence of the symmetry elements of the molecular point group and of the fcc‐lattice site. For each model all possible combinations of orientations for nearest‐neighbour pairs are considered with respect to the occurrence of overlaps. For each combination also different rotational states about the molecular triad axis as well as varying intermolecular distances are accounted for. The least number of overlaps was found for model A, when the molecular triad axis is aligned parallel to [111] or equivalent directions of the lattice. This model represents the maximum number of common symmetry elements. In this case the four distinguishable orientations for the C3‐axis: [111], [&1macr;11], [1&1macr;1], [11&1macr;] can be equally distributed over the lattice sites such that all interactions between nearest neighbours are of the same kind. There are 8 solutions for such a distribution of orientations. Orientational disorder can be explained by switching from one solution to another, although this requires temporary closer contacts and more unfavourable overlaps of neighbouring molecules.
First Passage Times and Transport in Systems with Disorder
Authors: van Den Broeck C. , Balakrishnan V. 
Published: July 2012

AbstractWe illustrate how first passage times can be calculated in systems with disorder. We use a renormalization approach to discuss first passage times in one‐dimensional continuous time random walks and on deterministic fractals. We discuss the phenomenon of field‐induced trapping on a random comb. Finally, we calculate mean first‐passage times for one‐dimensional random random walks, and discuss, in particular, the case of Sinai disorder. In a short Appendix, we show how mean first‐passage times can be calculated for an arbitrary inhomogeneous continuous time random walk in one dimension, using a recursion relation similar in spirit to the renormalization approach.
Quantum Coherence in Rate Processes
Authors: Weiss Ulrich , Sassetti Maura 
Published: July 2012

AbstractThe quantum dissipative dynamics of a particle which tunnels through the barrier of a double well potential and is coupled to an Ohmic heat bath is studied. Exact formal expressions for correlation functions are presented and examined. Attention is focused on the region in which coherence effects are important, and on the algebraic long‐time tails at zero temperature. Coherence effects in the dissipative quantum transport of a particle in a tight‐binding lattice are also investigated.
In‐Situ Observation of the Ortho‐Para‐Hydrogen Conversion in Chabazite by Neutron Scattering
Authors: Stockmeyer Rolf 
Published: July 2012

AbstractThe ortho‐para conversion of hydrogen adsorbed in chabazite has been observed by recording the neutron transmission of the sample after gradual adsorption of hydrogen in steps of one molecule per unit cell at temperatures between 40 and 70 K. The neutron data were fitted by a model assuming that the o‐H2 (s = 1) state decays exponentially with a time constant K = 0.5% per minute at a porefilling of n = 1 (molecule/unitcell). With increasing adsorption the value found for the o‐p‐H2 conversion rate is smaller: K = 0.2% per minute at n = 9.