bluuebunny/crossref_metadata_2025_split huggingface dataset:
Water Dissociation Effects in Ion Transport Through Anion Exchange Membranes with Thin Cation Exchange Surface Films
Authors: Ramírez P. , Manzanares J. A. , Mafé S. 
Published: July 2012

AbstractWater dissociation effects in ion transport through anion exchange membranes with adhered cation exchange surface films are studied on the basis of a theory previously proposed for bipolar membranes. The effects that the adhered surface film exerts on the limiting current and on the electric current carried by the ions coming from water dissociation are found to be of particular relevance for the fouling phenomena observed in ion exchange membranes. Finally, some limitations of the theory concerning the use of the Onsager's theory of the second Wien effect to describe the electric‐field‐enhanced water dissociation are discussed.
Gas‐Liquid Critical Temperatures of Binary Mixtures of Polar Compounds + Hydrocarbons or + other Polar Compounds
Authors: Christou G. , Young C. L. , Svejda P. 
Published: July 2012

AbstractGas‐liquid critical temperatures have been measured for binary mixtures of the polar compounds acetonitrile, 2‐butanone and monochlorobenzene + 2,2,4‐trimethylpentane or + n‐alkanes as well as + some other polar compounds. The data were analysed in terms of a parameter of interaction between unlike molecules using conformal solution theory. It was shown that the shape of the molecules did not play an important role at the critical state. The strength of intermolecular interaction could be quantified and corresponded to the excess properties of the same mixtures in the liquid state.
The Dissociation Constant of Pyruvic Acid: Determination by Spectrophotometric Measurements
Authors: Fischer Michael , Warneck Peter 
Published: July 2012

AbstractAqueous solutions of sodium pyruvate/hydrochloric acid mixtures were studied with regard to changes in the intensity of optical absorption at 317 nm wavelength, caused by varying pH and temperature. The data were evaluated to determine the pyruvic acid apparent dissociation constant at infinite dilution. Its temperature dependence followed the relation ln Kod = −(0.55 ± 0.47) − (1538 ± 135)/T or, if previous results of Pedersen at two temperatures are included, In Kod = −(0.97 ± 0.35) − (1418 ± 102)T. The effective absorption coefficient for pyruvic acid and its anion differ because the former species is largely hydrated, whereas the latter is not. The known hydration constant and its temperature dependence were used to derive the dissociation constant K1b for unhydrated pyruvic acid at infinite dilution. Its pK is 1.88 at 25°C with In K1d = −(8.67 ± 0.35) + (1296 ± 102)/T. The absorption coefficients for unhydrated pyruvic acid and its anion are essentially the same.
Site Specific Surface Interaction of Electron Donors and Acceptors on FeS2(100) Cleavage Planes
Authors: Pettenkofer C. , Jaegermann W. , Bronold M. 
Published: July 2012

AbstractThe interaction of UHV cleaved FeS2(100) surfaces with adsorbed H2O as an electron donor and adsorbed Br2 as an electron acceptor has been studied with LEED, LEISS, UPS, and XPS to simulate semiconductor/electrolyte interfaces in UHV. The (100) cleavage plane is characterized by a c(2 × 2) or p(√2 × 2)R 45° LEED pattern which is interpreted in terms of the unreconstructed FeS2 surface. H2O is molecularly adsorbed at low temperatures (100 K) and desorbs completely at room temperature (RT). LEIS‐spectra taken at low coverages (<0.5 ML) suggest a preferential interaction with the Fe sites. Br2 is ionosorbed at low coverages (<0.5 ML) as well interacting specifically with Fe‐sites. It is molecularly adsorbed at higher coverages. The ionosorbed part does not desorb at RT. The behavior of specific adsorption is related to the electronic nature of the band edges which are derived from Fe d‐states.
Electrostatic Interactions of Bodies Bearing Thin Double‐Layers III. Dissimilar Double‐Layers
Authors: Adamczyk Z. , Belouschek P. , Lorenz D. 
Published: July 2012

AbstractA new numerical algorythm was used to calculate the electrostatic interaction forces between regularly shaped particles bearing thin double‐layers immersed in an arbitrary electrolyte. Our numerical procedure enabled the solution of the nonlinear one‐dimensional Poisson‐Boltzmann (PB) equation in which the excluded volume effect is quantitatively considered for an arbitrary surface charge. Using these onedimensional solutions (parallel‐plate system) the electrostatic force of interaction between regularly shaped particles was calculated according to the modified Derjaguin summation method. Calculations were performed for plates and particles bearing dissimilar surface charge (heterointeractions) for simple electrolytes and electrolyte mixtures with constant charge and constant potential boundary conditions. From these solutions the range of validity of previously derived limiting analytical expressions was estimated. A significant role of trace amounts of higher valency electrolytes decreasing considerably the interaction force was confirmed.
Integration of Stiff Differential Equations Including Sensitivity Analysis by Laplace‐Transformation
Authors: Berndt T. , Picht R. , Scherzer K. 
Published: July 2012

AbstractA new method has been developed to calculate analytical functions for the time‐dependence of concentration and sensitivity coefficients based on a system of ODE by LAPLACE‐transforms. The procedure is suitable for a special class of models containing first and second order steps. The usefulness of the method is demonstrated for the case of zinc dimethyl decomposition in toluene. Comparison with a conventional integration routine is made.
An in situ FTIR Study of the behavior of Phosphate Species at Platinum. Bulk Effects and their Influence on the Spectra for Adsorbed Ions
Authors: Iwasita T. , Nart F. C. , Polligkeit H. 
Published: July 2012

AbstractPotential dependent pH changes in the microcavity of the thin layer cause the appearance of absorption bands for phosphate ions in the solution. This disturbs the measurement of spectra for adsorbed phosphate species, and has to be accounted for in the analysis of spectral data. Literature data are analyzed in the light of the results presented here.
The Mutual Influence of Ligands in Sb(III) Complex Salts. An X‐Ray Diffraction and NQR Study
Authors: Ishihara Hideta , Dou Shi‐Qi , Weiss Alarich 
Published: July 2012

AbstractThe crystal structure of 2,2'‐bipyridinium pentabromoantimonate (III), (2,2'‐C10H8N2H2)SbBr5, was determined (T = 297 K): C2h5‐P21/c, Z = 8, a = 1457.5 pm, b = 1472.6 pm, c = 1677.5 pm, β = 110.34°, Rw(F) = 0.057. Characteristic for the structure is the tetrameric anion {[SbBr5]2⊖}4. No 79,81Br NQR could be observed in this compound. The crystal structure of 4,4'‐bipyridinium pentabromoantimonate (III), (4,4'‐C10H8N2H2)SbBr5, was also studied (T = 300 K): Ci1‐P1, Z = 2, a = 1128.7 pm, b = 1012.1 pm, c = 854.8 pm, α = 98.94°, β = 101.06°, γ = 113.57°, Rw(F) = 0.052. Characteristic for the structure of this compound is the dimeric anion {[SbBr5]2⊖}2. The 81Br NQR spectrum of 4,4'‐bipyridinium pentabromoantimonate (III) was studied in the temperature range 77 ≤ T/K ≤ 300. A five line spectrum is present over the whole temperature range covered. The 81Br NQR frequencies are spread out over a wide range; at 77 K: 34 ≤ v(81Br)/MHz ≤ 113. 81Br NQR spectrum and crystal structure of 4,4'‐bipyridinium pentabromoantimonate (III) are discussed and a model for both, the temperature dependence of the NQR frequencies and of their spread is given as is an assignment: Position of the Br atom in the complex anion ↔ 81Br NQR frequency.
Etching of CdS in Aqueous Halogen Solutions
Authors: De Wit A. R. , Kelly J. J. 
Published: July 2012

AbstractDissolution of CdS in aqueous solutions of Br2 and I2 has been studied by ring‐disc voltammetry and flow‐cell measurements. The semiconductor is etched chemically at a considerable rate by Br2. CdS is dissolved in I2 solutions only when a high concentration of chloride ions is present. It is suggested that inter‐halogen species play a role. A novel chemical etching reaction was observed in the iodine case: cathodic reduction of iodine produces an intermediate capable of oxidizing the semiconductor.
Cobalt(II) — Cyanometallates as New Inorganic Polymeric Materials for Surface‐Modification of Some Conducting Substrates
Authors: Jiang Mian , Zhou Xingyao , Zhao Zaofan 
Published: July 2012

AbstractCobalt cyanometallate thin film modified electrodes have been prepared and also electrochemically and spectroscopically characterized. Results showed that these films can be considered as novel Prussian Blue analogues. The selective cation transport into or out of these films has been explained in terms of the effective ionic radii and the channel size in the film lattice whereas other factors can not be negligible. On the other hand, the high redox‐reversibility and high stability of the modified electrodes make them potentially attractive in application of catalysis and electrochromism.
Behaviour of the Electroclinic Effect in a Homologous Series of Ferroelectric Liquid Crystals
Authors: Bahr Ch. , Heppke G. , Klemke U. 
Published: July 2012

AbstractThe electroclinic effect, a kind of inverse piezoelectric effect, is studied in the smectic A phase of several homologous liquid crystal compounds. The induced tilt/applied field ratio θ/E is found to increase with increasing length of the alkyl chain whereas the coupling constant k = Pθ/θ between induced tilt and induced polarization decreases with increasing chain length. The measurements allow the determination of the tilt controlling susceptibility coefficient of the smectic A phase, which is found to decrease considerably with increasing alkyl chain length.
Towards a Theoretical Description of UV‐VIS Absorption Bands of Organic Molecules
Authors: Menzel Ralf , Naumann Karl‐Heinz 
Published: July 2012

AbstractThe UV‐Vis absorption spectra of organic molecules are calculated with a new ansatz based on the simultaneous coupling of several vibrations during the electronic transition. Even with the simplest assumption of a Boltzmann weighted statistical mixing of the vibrational modes it is possible to reproduce the experimental absorption spectra, e.g. of naphthalene, surprisingly well. Using this method the homogeneous line width can be determined with an error of less than 30% from the common absorption spectra.
Determination of the Bending Modulus in Microemulsions by Using the Dynamic Kerr Effect
Authors: Linden E. V. D. , Bedeaux D. , Hilfiker R. , Eicke H.‐F. 
Published: July 2012

AbstractWe have determined the value of the bending modulus k in w/o (decaline)‐microemulsions using the dynamic Kerr effect. The relaxation of the electrically induced birefringence in a dilute w/o‐microemulsion corresponds to the relaxation of the individual nanodroplets towards their spherical form. The experimental results were described by using a theory for the dynamics of a microemulsion droplet; two cases are discussed: (i) a model in which a constant mean excess surface area during relaxation has been assumed and (ii) where a variable surface area has been considered. For a polydispersity in droplet size of 30%, we find k = 0.4 kBT (± 20%). This is in accordance with findings using the static Kerr effect.
Studies on the Interactions of Co2+ and Zn2+ with the Polynucleotides Poly(A) and Poly(C)
Authors: Dhathathreyan K. S. , Diebler H. 
Published: July 2012

AbstractUV‐Spectrophotometric techniques have been used to study the binding of Co2+ and Zn2+ to the single‐stranded polynucleotides poly(A) and poly(C). The spectrophotometric data can be described by a simple binding equilibrium, i.e. by a 2‐state model. The apparent binding constants which have been evaluated with poly(A), KCo‐poly(A) = 4.5 · 103 M−1 and KZn‐poly(A) = 2.9 · 103 M−1 (25°C, ionic strength I = 0.1 M, pH 6.5–7.0), are compared to those for Ni2+ and Mg2+ with poly(A), determined earlier. It is concluded that Co2+, Zn2+ and Ni2+ form inner‐sphere complexes with poly(A), in contrast to Mg2+. Kinetic studies confirmed the inner‐sphere binding mode for Co2+ (and Ni2+). In the case of Zn2+, however, the inner‐sphere substitution reactions are apparently too fast to be distinguished from the helix‐coil transitions of the poly‐nucleotide. A second method for equilibrium measurements, based on using murexide as an indicator of the concentration of free Co2+, gave for KCo‐poly(A) a value of 5.5 · 103 M−1 at I = 0.1 M. At I = 0.01 M, the binding constants KNi‐poly(A) and KCo‐poly(A) are about 30‐fold higher than at 0.1 M, according to the uv‐data. With poly(C), the stability constants of all 4 metal ions are nearly the same, about 650 (±100) M−1 at I = 0.1 M. The available evidence suggests that these metal ions are bound to poly(C) mainly by electrostatic interactions, with little or no inner‐sphere coordination.
Decay Dynamics of H2O(Ã 1B1): Excitation by two Photon Absorption at 354.6 nm
Authors: Mikulecky K. , Gericke K.‐H. , Comes F. J. 
Published: July 2012

AbstractWater was photolyzed at 177.3 nm via a two‐photon excitation by a frequency‐tripled Nd:YAG laser (354.6 nm). The complete product state distribution of the ejected OH product was determined by LIF. The OH is produced in the vibrational ground state exclusively. OH shows a Boltzmann‐type rotational distribution with a temperature parameter of about 350 K. No preferred population of Λ‐ or spin‐orbit states was observed.
Ionic Transport in Oxide Glasses and Frequency Dependence of Conductivity
Authors: Kahnt H. 
Published: July 2012

AbstractCurrent models attribute the power law frequency dependence of ionic conductivity in oxide glasses alternatively to structural disorder or to interactions between moving ions. To distinguish between the influence of disorder and of interaction the frequency dependence of conductivity was investigated for three different series of glasses that have been selected according to special considerations on network structure and bonding of alkali ions. It was shown that the frequency response is independent of alkali concentration and structure. This result is discussed in terms of Coulomb interactions between mobile charged point defects and favours the jump relaxation model of Funke.
Segmental Dynamics in a Glassy Polyelectrolyte: Solid‐State 2H‐NMR
Authors: Schaefer D. , Rietz R. R. , Meyer W. H. , Spiess H. W. 
Published: July 2012

AbstractThe segmental dynamics of a special “ionene” polyelectrolyte, poly[(dimethylimino)decamethylene‐tetra‐fluoroborate]‐[–(CH2)10–N+(CH3)2–]n*BF4−, has been investigated by applying one‐and two‐dimensional deuteron NMR techniques. Selective deuteration in the methyl groups and in the α‐, β‐ and γ‐positions of the methylene chain allow for investigation of the molecular mobility of each site. Below the glass transition the ammonium groups are essentially static, due to strong Coulombic interactions between the cationic centres, whereas the methylene chains undergo trans‐gauche isomerizations. At Tg the ammonium groups become mobile, and we discuss the coupling of this glass transition process to the local methylene dynamics.
Ultraslow Relaxation Phenomena in Gels
Authors: Dorfmüller Thomas , Stellbrink Jörg 
Published: July 2012

AbstractThe dynamics of a polyacrylamide gel was studied by means of photon correlation spectroscopy. The gels display, in addition to the relatively fast modes observed with the correlator, very slow intensity fluctuations which appear to be constitutive of the equilibrium dynamics of these systems. The relation between the gel mode as described in the Tanaka theory, the mode ascribed to the diffusion of latex particles introduced into the gel and the ultraslow modes is discussed.
Scaling Behaviour of Structural Relaxation near the Glass Transition: A Critical Analysis
Authors: Mezei F. 
Published: July 2012

AbstractInelastic neutron scattering has proved to be a powerful tool for exploring the characteristic dynamics in glassy systems on the time and length scale of atomic motions. Results obtained in a number of chemically very different sample systems of the fragile glass category reveal a catalogue of common features including a complex structural relaxation pattern. This relaxation pattern displays a two step nature, tentatively identified with the “α” and “β” relaxation processes, as predicted by recent mode coupling theories. The data also show a remarkable compatibility with the theoretically predicted scaling features, which partially corresponds to the so‐called time‐temperature superposition property. In this respect there is a contradiction between the neutron scattering results and macroscopic type relaxation experiments. A critical analysis of new, extended neutron data in an archetypical ionic glassy system reveals that in a broader temperature range deviations from the time‐temperature superposition scaling become evident and, in addition, considering worst case errors, there remains no hard evidence for the asymptotic validity of scaling near a critical temperature. Thus, even if the compatibility of neutron scattering and mode coupling results is impressively broad, in the light of an advocatus diaboli approach the remarkable two step character of the structural relaxation and the roughly wavenumber independent dynamics only remain as real and arguably decisive evidence in favour of mode coupling theories.
A Redetermination of the Rate Constant of the Reaction F + HNO3 → HF + NO3
Authors: Becker E. , Benter Th. , Kampf R. , Schindler R. N. , Wille U. 
Published: July 2012

AbstractThe rate constant k(1) of the reaction F + HNO3 → HF ± NO3 at 298 K has been redetermined using two fast flow systems employing different detectors. In the first, growth of NO3 was measured by mass‐spectrometric detection of the ion signal at m/e 62. In the other, the decay of F‐atoms was measured by following their ESR signal. Uncoated quartz flow tubes were used in both cases. The reactants were kept in the range 12 < [HNO3]/[F] < 140 in all experiments such that pseudo‐first‐order evaluation of the data was possible and secondary reactions were suppressed. A total of 52 experiments with [HNO3] in the range (2.5–8.2) · 1013 cm−3 yielded k(1) = (2.2 ± 0.2) · 10−11 cm3 molecule−1 s−1, where the error stated is the random error 2σ for 96% confidence limit. Model calculations have shown that the systematic error in k(1) due to secondary reactions is less than 2%. The total systematic error in k(1) is estimated to be 10%. The effect of poisoning the flow tube with halocarbon wax was studied in a few experiments and an interpretation for the observation is suggested.
Lower Critical Solution Point in Aqueous Mixtures: Enhanced Water Activity
Authors: Balevicius Vytautas 
Published: July 2012

AbstractSome aspects of the lower critical solution point (LCSP) of binary aqueous mixtures have been studied by means of renormalization‐group (RG) and decorated lattice (DL) methods. The fitting of symmetrized experimental and calculated coexistence curves has revealed the advantage of the DL method. A new theoretical approach‐enhanced water activity, i.e. the activity of water being much higher than that of the second component, has been developed yielding satisfactory agreement with unsymmetrized experimental composition (in mole fractions)‐vs.‐temperature curves in the vicinity of LCSP. It has been shown that the lower critical concentration is determined by the coordination number of the primary lattice. Thus, the information about the structure of the solution is being lost by the symmetrization. It follows that the second component containing oxygen, i.e. atom with two lone‐pairs of electrons, stabilizes the ice‐like structure of the solution. In the case of components with nitrogen atoms (one lone‐pair) the structures with the higher coordination numbers are realized.
Order Parameters of Guest/Host Systems from UV Spectra – A Test of a New Method and its Application to Rigid Guest Molecules –
Authors: Kuball H.‐G. , Junge M. , Schultheis B. , Schönhofer A. 
Published: July 2012

AbstractFor a determination of the order parametersS*,D* of nematic guest/host phases from polarized UV and sometimes IR spectroscopy, the experimental information is often not sufficient because of overlapping absorption bands. For molecules with only one purely polarized band, the temperature dependence of the degree of anisotropy and a theoretical relationD* =f(S*) can be used to overcome this lack of information. A method introduced earlier [7] is examined with respect to its range of applicability. It can be shown that in the region of overlapping bands an amount of about 30% of the band with the proper polarization direction is sufficient to determineS* andD* with an error of at most 2 to 5% and 5 to 10%, respectively. The temperature dependence ofS*,D* for the rigid molecules azulene, phenanthrene, anthracene, 9,10‐dichloro‐, 9,10‐dibromo‐, 9,10‐dimethylanthracene, phenazine, and acridine in ZLI 1695 has been determined. Three different types of structural dependence can be derived from the experimental data.
Berechnung des zweiten Virialkoeffizienten B(T) für gasförmigen molekularen Wasserstoff im Temperaturintervall von 1 K bis 3000 K
Authors: Artym R. , Kliem M. 
Published: July 2012

AbstractThe second virial coefficient B(T) of hydrogen (H2) has been calculated at temperatures over the range 1 K to 3000 K using the Woolley potential function. The potential constants ε/k = 28,79 K, rm = 0,34473 nm, e1 = 0,01 have been determined from the B(T)‐data of Michels et al. (1959). The calculated second virial coefficients B(T) agree very well with the available experimental data over the whole temperature range from 13 K to 3000 K. A new method of calculating second virial coefficients has been suggested for low temperatures based on the representation of (y–y0)/(x–x0) vs x by a straight line (x = T1/2, y = T5/4 B).
Ultrathin Metal Films: From One to Three Dimensions Plenary Lecture
Authors: Bauer E. 
Published: July 2012

AbstractThe growth, structure, thermodynamic and electronic properties of ultrathin metal films is discussed, starting from the submonolayer range up to thicknesses at which bulk properties are reached. The following topics are selected from the wide field of phenomena: one‐dimensional crystals, shape and stability of twodimensional crystals, film‐substrate and lateral interactions, electronic structure and bonding, structural transitions and quantum size effects. The substrates used are mainly W(110), Mo(110) and Si(111) surfaces, the film materials several fcc metals.
Interface Properties of Thin YBa2Cu3O7–x Films
Authors: Ziegler Ch. , Frank G. , Göpel W. 
Published: July 2012

AbstractStructures and stability ranges of the YBa2Cu3O7–x interface were studied with AES, SIMS, XPS, and TEM. For silicon substrates, the formation of Ba silicates can be detected which even at T = 550 K leads to reduced Tc values and non‐epitaxial growth of YBa2Cu3O7–x (YBCO). Yttria stabilized zirconia (YSZ) buffer layers between Si substrates and YBCO lead to epitaxial overlayer growth and improved superconducting properties whereas CaF2 is not suitable for this purpose.—Furthermore, SiO2, YSZ, and CaF2 were tested for their suitability as passivation layers against the influence of humidity. As‐passivated superconducting films are stable up to 500 K in 100% humid air. Above this temperature the superconductor is reduced chemically. Non‐passivated films, however, are stable only at temperatures below 450 K and are destroyed totally in humid air at higher temperatures.