bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and characterization of nanosilica/waterborne polyurethane end‐capped by alkoxysilane via a sol‐gel process
Authors: Zhai Lanlan , Liu Ruowang , Peng Feng , Zhang Yunhao , Zhong Kai , Yuan Jixin , Lan Yunjun
Published: July 2012

A novel method was used to synthesis nanosilica/waterborne polyurethane (WPU) hybrids by in situ hydrolysis and condensation of tetraethyl orthosilicate (TEOS) and/or 3‐aminopropyltriethoxylsilane bonding at the end of the WPU molecular chain. The hybrid was characterized by scanning electron microscopy, energy dispersive spectroscopy (EDS), transmission electron microscopy, Fourier transform infrared spectroscopy (FTIR), and X‐ray photoelectron spectroscopy (XPS). The results showed that the nanosilica/WPU hybrids with well‐dispersed nanosilica particles were synthesized, in which the particles had typical diameters of about 50 nm. In addition, XPS and FTIR analyses demonstrated that chemical interaction occurred between WPU and silica. The effects of TEOS on surface wettability, water resistance, mechanical strength, and thermal properties of the hybrid were also evaluated by contact angle measurements, water absorption tests, mechanical tests, and differential scanning calorimetry, respectively. An increase in advancing contact angles, water resistance, and tensile strength, as well as decrease in elongation at break and glass transition temperature, were obtained with the addition of TEOS. Water absorption decreased from 17.3 to 5.5%. The tensile strength increased to a maximum of 29.7 MPa, an increase of about 34%. Elongations at break of the hybrids decreased 191%. These results were attributed to the effects of the nanosilica and the chemical interaction between WPU and silica. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
Cationic polymerization of 1,3‐pentadiene coinitiated by zinc halides
Authors: Rozentsvet Victor A. , Kozlov Valery G. , Korovina Nelly A. , Ivanova Valentina P. , Kostjuk Sergei V.
Published: July 2012

Technology of industrial production of liquid rubber under trademark “SKOP” is based on the cationic polymerization of 1,3‐penadiene (piperylene) in the presence of TiCl4 or AlCl3‐based catalytic systems. The disadvantage of these catalytic systems is the high probability of formation of branched and insoluble fractions due to the chain transfer to polymer. This deteriorates the useful qualities of SKOP. Here we propose the new initiating systems for the cationic polymerization of 1,3‐pentadiene based on the homogeneous (dissolved in a minimal amount of diethyl ether) zinc halides (ZnCl2 and ZnBr2) as coinitiators and hydrochloric acid, tert‐butyl chloride or trichloroacetic acid as initiators. These initiating systems allow to synthesize fully soluble low molecular weight (Mn = 1000–3000 g mol−1) poly(1,3‐pentadiene)s with relatively narrow molecular weight distribution (Mw/Mn < 2.0), which do not contain any high molecular weight and insoluble fractions in the whole range of monomer conversion. The polymers synthesized in the presence of zinc halides possess the same microstructure that those prepared with TiCl4 as coinitiator. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
New Upper and Lower Eigenvalue Bounds for the Solution of the Continuous AlgebraicRiccati Equation
Authors: Liu Jianzhou , Zhang Juan
Published: August 2012

In this paper, applying majorization inequalities, new upper and lower bounds for summation of eigenvalues (including the trace) of the solution of the continuous algebraicRiccati equation are presented. Corresponding numerical examples illustrate that our new bounds extend some of the recent results.
Methanspeicherung in Kristallen
Authors: Stockmeyer R. , Monkenbusch M.
Published: August 2012

Untersuchungen der Physisorption von Methan in verschiedenen Adsorbentien lassen Zeolith‐Mikrokristalle als Speichermaterial besonders geeignet erscheinen. Die statistische Interpretation von Adsorptionsisothermen liefert Hinweise auf die Bewegung von CH4‐Molekülen in den Gitterkäfigen der Kristallstruktur. Die zum Teil widersprüchlichen Schlußfolgerungen aus makroskopischen Daten werden durch direkte Messungen der Molekülbewegung auf mikroskopischer Ebene geklärt.
Density Studies in N‐(p‐n‐Butoxybenzylidene)‐p‐n‐Butylaniline
Authors: Rao J. V. , Rao N. V. S. , Pisipati V. G. K. M. , Murty C. R. K.
Published: August 2012

The density ρ of N‐(p‐n‐butoxybenzylidene) p‐n‐butylaniline (BBBA) has been measured as a function of temperature from SH to isotropic liquid phase. The compound exhibits three smectic and two nematic phases. The phases assigned are SH ↔ SB ↔ SA ↔ NC ↔ NO ↔ I. The change of ρ across the transition SH‐SB is more predominant than the other transitions. The SH‐SB, SA‐NC, and NC‐NO transitions have been observed for the first time from density studies. The variation of ρ with temperature and the calculated thermal expansion coefficients in liquid crystalline region suggest that all the transitions are of first order. It is suggested that the transition of NC‐NO at 59.4°C is cybotactic nematic to ordinary nematic phase.
Static Permittivity and Dielectric Relaxation of Solutions of Ions in Methanol
Authors: Kaatze U. , Adolph D. , Gottlob D. , Pottel R.
Published: August 2012

The frequency spectrum of the complex permittivity of methanolic salt solutions has been measured between 0.6 and 38 GHz. Two distinct relaxations arise in this frequency range. The relaxation time of the dominant process is 50 ps or even longer while that of the second process is smaller than 10 ps at 25°C. — The extrapolated static permittivity of the solutions is discussed with respect to the effects of kinetic polarization deficiency and dielectric saturation. Comparison with corresponding data for aqueous solutions shows, that solvation seems to be stronger in methanol than in water. This result is confirmed by the values obtained for the ion‐induced shift in the dielectric relaxation time of the dominant low‐frequency relaxation process.
A High‐Temperature, High‐Pressure Oscillating‐Disk Viscometer for Concentrated Ionic Solutions
Authors: Kestin J. , Paul R. , Shankland I. R. , Khalifa H. E.
Published: August 2012

In this paper we describe a new, high‐precision oscillating‐disk viscometer which has been designed specifically to measure the viscosity of concentrated ionic solutions at temperatures extending to 300°C and to pressures of 35 MPa, simultaneously. The viscometer is intended to provide reliable values of the viscosity of a wide spectrum of aqueous salt solutions under conditions similar to those prevailing in hydrothermal geothermal reservoirs. Results of preliminary calibration runs are included. They indicate that the behavior of the viscometer is reliable and satisfactory. This is further confirmed by new measurements of the viscosity of liquid water up to 200°C and 30 MPa.
An Indirect Method for Measuring Iodine Quenching Rate Constants Through a Chemical Laser
Authors: Arguello G. A. , Staricco E. H.
Published: July 2012

Marked differences in laser action (1.315 μm) following flash photolysis of CF3I‐inert gas mixtures were observed. Through the measurement of optical gain and considering the contribution to line broadening, collisional relaxation rate constants were obtained. Using another iodine source, i.e. C2F5I experimental results showed no significant differences.
Preferential Removal of Co from CoPd‐Alloys in HCl/H2‐Gas Mixtures
Authors: Singheiser L. , Auer W. , Kaesche H.
Published: July 2012

The chlorination behaviour of Co and CoPd‐alloys with up to 90 weight‐% palladium was investigated in the temperature range from 1023 K to 1265 K with HCl‐pressures between 0.3 and 0.9 bar. For Co‐rich CoPd‐alloys a constant rate of weight loss was observed due to the formation of gaseous CoCl2 according to the reaction Co(CoPd) + 2HCl(g) → CoCl2(g) + H2(g).

The results can be well understood by assuming that transport of gaseous CoCl2 through the gas boundary layer adjacent to the sample surface is the rate determining step of chlorination kinetics. These results are in good agreement with theoretical calculations of CoCl2‐vapor pressures and transport properties away from a flat plate. — Dissolution of Co from the alloy results in the formation of a very porous Pd‐rich layer. — At intermediate Pd‐contents, and during long times of chlorination, a linear‐parabolic chlorination behaviour was observed due to the rate determining CoCl2‐diffusion in pores. — At high Pd‐contents the chlorination behaviour is described by a parabolic rate law. Diffusion of Co in the alloy is then rate determining.
Differential Scanning Calorimetry (DSC) at Pressures up to 5 kbar Configurational Contributions of Transition Entropies in the Plastic Crystals Cyclohexane and Diamantane
Authors: Sandrock R. , Schneider G. M.
Published: July 2012

A method of extrapolating configurational entropies from high pressure DSC data will be described. The method allows the separation of configurational entropies from entropy changes due to the volume changes of the transitions. The results on the solid‐solid transitions in the plastic crystals cyclohexane (with the use of literature data) and diamantane (using own experimental DSC measurements up to 5 kbar) are discussed with respect to the number of possible molecular orientations. Contrary to literature data rather small numbers are found that can be more easily discussed with consideration of the geometrical parameters of the molecule and the crystal lattice.
Energy Transfer from the Cyclohexane Singlet – A Pulse Radiolysis Study
Authors: Mehnert R. , Brede O. , Naumann W. , Hermann R.
Published: July 2012

After irradiation of liquid cyclohexane with 0.5 ns electron pulses time resolved emission from the cyclohexane singlet state (RH(S1)) was observed. From the decrease of the cyclohexane fluorescence lifetime by adding solutes (S) as alkanes, alkenes and aromatics rate constants of the energy transfer reaction
\documentclass{article}\pagestyle{empty}\begin{document}$ \begin{array}{*{20}c} {{\rm RH}({\rm S}^1) + {\rm S} \to {\rm S}({\rm S}^1) + {\rm RH}} & {(1)} \\ \end{array} $\end{document} were determined. The rate constants of reaction (1) showed a pronounced dependence on the zero‐zero singlet energy difference ΔE of the donor acceptor pair. This k1 vs. ΔE dependence is explained in terms of changes in the Franck‐Condon vibrational overlap factors as well as by a classical model according to Rehm and Weller [1].
Effect of Surface Hydrolysis at Tin Dioxide Polycrystalline Thin Film Electrodes on Dye Sensitization Quantum Efficiency
Authors: Bressel Burkhard , Gerischer Heinz
Published: July 2012

The quantum efficiency of dye sensitization at polycrystalline SnO2 thin films can reach a high value close to ϕ = 1 if determined immediately after preparation, however it slowly drops down to low values (ϕ ∼ 0.01) after inserting the electrode into aqueous electrolyte solutions. The quantum efficiency decay rate depends on the electrolyte composition. Capacitance and cyclic voltammetry measurements indicate the formation of an insulating layer. Auger‐ and IR‐reflection spectra have been used to identify this layer as a mixed oxide/hydroxide formed by hydrolysis of the surface oxide. This layer acts as an energy barrier for the injection current from the excited dye molecule thus decreasing the sensitization quantum efficiency.
Ultrasonic Absorption Measurements Near the Critical Point of a Reactive Binary Mixture
Authors: Dunker H. , Woermann D. , Bhattacharjee Jayanta K.
Published: July 2012

Measurements of sound attenuation and velocity in the homogeneous phase near the critical mixing point of isobutyric acid and water have been carried out. The data are obtained by a pulse transmission technique at seven frequencies between 9 and 45 MHz in a temperature range between 26.29°C and 40 °C. The experimental results are analysed in terms of a theory of critical ultrasonic absorption proposed by Bhattacharjee and Ferrell which contains no adjustable parameters. All the values of these parameters are known for the investigated system from independent experiments. The frequency dependence of the absorption coefficient of ultrasound at the critical temperature is in good agreement with this theory which takes into account only sound absorption by local concentration fluctuations. The absorption data obtained at temperatures away from the critical temperature do not scale when plotted as function of a reduced frequency given by the theory. This clearly indicates an additional mechanism causing absorption of ultrasound. This additional sound absorption can be represented by a single temperature dependent relaxation process. It is assumed that this process is due to an unspecified chemical reaction. The temperature dependence of the relaxation time follows a power law of the form τr ∝︁ (T‐Tc)−a with 1 ≤ a ≤ 1.25. This result seems to support the idea of Gitterman. Procaccia and Hentschel that chemical reactions slow down near the critical point.
The Viscosity of Carbon‐Monoxide Mixtures with Four Gases in the Temperature Range 25–200°C. Supplement
Authors: Kestin J. , Ro S. T.
Published: July 2012

The paper reports new, absolute measurements of the viscosity of carbon monoxide (CO) with krypton (Kr), carbon dioxide (CO2), methane (CH4) and carbon tetra‐fluoride (CF4). The measurements have been carried out in an oscillating‐disk viscometer at a pressure of 0.1 MPa in the temperature range 25–200 °C. The accuracy is estimated to lie between ± 0.1 % and ± 0.2%. The data have been correlated by means of the two‐parameter extended law of corresponding states. They have been utilized to derive binary diffusion coefficients. This paper is a supplement to an earlier publication on mixtures with He, Ne, Ar, and N2. The great similarity between the viscosity of binary mixtures with N2 and CO, respectively, is confirmed to a high degree of accuracy.
Current‐Voltage Relationship for a Fixed Charge Membrane
Authors: Seshadri M. S.
Published: July 2012

The range of validity of the electroneutrality assumption is examined in the context of a membrane model, a fixed charge membrane permeable only to the counter ions. Following the treatment of MacGillivray, the perturbation approach employed invokes asymptotic matching procedures to match the solutions in the two boundary layers with those in the membrane core. The perturbation parameter is the ratio of the Debye length to the membrane thickness. It turns out that in the membrane core, electroneutrality and constant field obtain to all orders in the perturbation parameter. It is pointed out that these features are peculiar to the model considered. A current‐voltage relationship is also derived.
Dimerisierung einiger organischer Säuren in der Gasphase
Authors: Büttner R. , Maurer G.
Published: July 2012

Experimental results for the compressibility factor of formic acid, acetic acid, and acrylic acid in the low pressure region at temperatures between 45 and 120 °C were used to determine the dimerization constant (2 A ⇌ AA) of these carboxylic acids in the vapour phase. The direct experimental results were evaluated applying three different models for the composition of the gas phase: besides monomers and dimers also the presence of trimers or tetramers was assumed. All three evaluations resulted only in small differences in the entropy and enthalpy of dimerization (maximum differences 6.3 and 5.7 per cent respectively for acetic acid). Assuming the existence of trimers or tetramers resulted in an essentially better agreement between calculated and measured compressibility factors only for formic and acetic acid, but not for acrylic acid. When only the formation of dimers is considered the following dimerization constants were obtained:

Formic acid: ln KAA = −18.0763 + 7130.9/(T/K)

Acetic acid: ln KAA = −19.1001 + 7928.7/(T/K)

Acrylic acid: ln KAA = −22.2774 + 9308.1/(T/K)
Kinetic Modeling of CO Production from the Reaction of CH3with O2in Shock Waves
Authors: Hsu D. S. Y. , Shaub W. M. , Creamer T. , Gutman D. , Lin M. C.
Published: July 2012

CO concentration‐time profiles have been measured by using CO laser resonance absorption in shock tube experiments on the reaction of CH3with O2in the temperature range from 1150 to 1560 K. Computer kinetic modeling of our profile data yieldedk2= 1.0 x 1014e−(15,500 ± 1,100)/Tcm3mol sec for the CH3+ O2→ CH3O + O reaction. An RRKM calculation, which took into consideration branching of the CH3+ O2reaction into different product channels, revealed that by assuming a loose transition state (allowing two free internal rotations) leading to the CH3O + O product channel, we could account very satisfactorily for our results as well as those reported previously for the reaction. A three‐parameter leastsquares fit of a smooth curve covering data from three independent studies gave rise to the expression:k2= 2.20 x 1034(T/K)−5.94exp (–21,300 K/T) cm3mol sec for the temperature range 1150‐2300 K.
Atomic and Molecular Orbital Electronegativity Models Based on the Transition State and Transition Operator Approaches
Authors: Schmidt Peter C. , Böhm Michael C.
Published: July 2012

Orbital electronegativities χi of atoms A, χi(A), and organic molecular radicals G, χi(G), have been determined by means of transition state (TS) calculations for atomic systems as well as by means of the transition operator (TO) method in the molecular domain. The theoretically determined χi(A) values are compared with “experimentally” deduced electronegativities and the correlation between χi(A) and χi(G) and measured nuclear quadrupole coupling constants C = e2qQ/h in ACl and GCl systems have been studied. In all examples an increase of the electronegativity is accompanied by an increase of the absolute value to C(35Cl). It is found that a linear relation C ∼ χi holds for a series of similar compounds in those cases, for which one active orbital i describes the bonding mechanism between G and Cl satisfactorily. In these systems the calculation of χi based on the TS and TO methods is a helpful tool to analyze coupling constants, and thus to rationalize the nature of the chemical bonds. ‐ On the other hand for systems where the bonding mechanism is of larger complexity, and where one specific active orbital is not a suitable model for the representation of the heterobonds AX or GX, the interplay of different one‐electron states has to be taken into consideration. For atomic systems an additional problem occurs, e.g. an appropriate active valence state has to be defined, which describes the bonding mechanism in AX compounds quantitatively.
The Bond Indium‐Halogen in Isomorphous Complexes A2InX5 · H2O (A = K, NH4, Rb, Cs; X = Cl, Br). A 35Cl, 79,81Br, and 115In NQR study
Authors: Yamada Koji , Weiss Alarich
Published: July 2012

The isomorphous series of complexes A2InX5 · H2O (A = K, NH4, Rb, Cs; X = Cl, Br) was investigated by 35Cl, 79,81Br, and 115In nuclear quadrupole resonance spectroscopy. For the bromine compounds the temperature dependence of the NQR spectra was studied in the range 77 ≦ T/K ≦ 380. Solid state phase transitions are found for K2InBr5 · H2O at T = 145.5 K and for (NH4)2InBr5 · H2O at T = 82 K. The 81Br NQR frequencies are observed between 65 and 80 MHz. At room temperature the 35CI NQR frequencies are found in the range 9.8 ≦ ν (35Cl)/MHz ≦ 11.6. The nuclear quadrupole coupling constants /e2 ϕzzQh−1 (115In)/in the compounds vary between 60 MHz and 115 MHz. There is a marked dependence of /e2 ϕzzQh−1 (115In)/on cation radius rA and temperature. /e2 ϕzzQh−1 (115In) /(increases with increasing rA, and such a dependence is observed for ν(81Br), too. As a function of temperature, n(115In) goes through 1. On the basis of the semiempirical MO model of Townes and Dailey the covalent character of the bond In‐Halogen is estimated. From this the increase of /e2 ϕzzQh−1 (115In)/and of ν(81Br) is understood to be due to small changes in the bond character with rA and with temperature.
Kohärente Kurzzeit‐Strukturen und momentane Brechzahl‐, Dichte‐ und Temperaturprofile in einer n‐Hexan‐Tankflamme
Authors: Brötz W. , Schönbucher A. , Lucas R. , Schieß N.
Published: July 2012

Coherent short‐time structures of a n‐hexan pool flame were shown as a 1000 exposures/sec picture‐sequence using a holographic real‐time synchronous interferometer. These coherent structures have eddies, thermal boundary layers as well as luminous flame fronts. Also gaschromatographically measured concentration profiles of 18 stable molecules of the flame gas mixture were considered. ‐ As a result, the refraction index profiles and also the density and temperature profiles were determined up to 60% by the chemical composition of the pool flame. In the upper flame plume as well as mainly within the thermal boundary layer the density profiles are solely determined by the temperature field. ‐ The quasi‐instantaneous density and temperature profiles are NON‐Gaußian distributed. Within the visible flame field quasi‐instantaneous temperature maxima reach values up to about 2000°C, whereas maximal temperatures within the instantaneous flame neck come up to about 900°C. – This big difference between the maximal flame temperatures can be explained by the momentary number of eddies responsible for the heat and matter exchange. The maximal flame temperatures in the plume are much higher in case of less eddies being in this range than in the neck.
Unstetigkeiten im Abbrandverhalten angeströmter Kohlenstoffoberflächen
Authors: Adomeit G. , Hocks W. , Henriksen K.
Published: July 2012

In the present work the ignition and quench phenomena of the combustion of a carbon surface in oxidizing cross flow is investigated theoretically. For certain values of moisture content and of heterogeneous reaction rates, multiple ignition and quench phenomena are observed together with non‐monotonous dependence of the burning rate upon the surface temperature. These phenomena occur in the region of transition from the reaction controlled to the transport controlled regime. In dependence upon reaction rates this regime extends from 1300 K to about 2000 K.
The Photochemistry of 1,3‐Diphenyltriazene in Various Media. II: Solid State Photolysis
Authors: Baro J. , Dudek D. , Luther K. , Troe J.
Published: July 2012

Solid 1,3‐diphenyltriazene (DPT) has been photolyzed at 290 nm and 360 nm. The distribution of the photoproducts showed that recombination of the radicals produced after photochemical excitation was governed by a “cage effect” favouring a minimum of motion of the recombining radicals. In many details the results differ from observations on the photochemistry of DPT in liquid solutions. The photolysis of DPT in polymethylmethacrylate films, however, resembles the photochemistry of DPT in liquid solutions.
Molecular Dynamics Calculations of a Second Order Kinetic Phase Transition in an Open System (CSTR)
Authors: Heinrichs M. , Schneider F. W.
Published: July 2012

We performed Molecular Dynamics calculations (MD) for a few hundred reacting molecules in a continuous flow stirred tank reactor (CSTR), in order to assess the significance of fluctuations in particle numbers at the point of a second order kinetic phase transition. The latter occurs in the following mechanism A + B → C; C + B → D + B, D → 2B (net: A + 2B → 3 B) under given conditions of in‐flow of A and B into the reactor at the critical flow rate. All molecules are represented by hard spheres and periodic boundary conditions are assumed. The MD calculations for ∼500 particles show deviations from the deterministic steady states particularly at the critical flow rate where the distribution function of B particles is found to display about two maxima (MD) instead of one (Poisson distribution for the deterministic case). The magnitude of the concentration fluctuations is enhanced at low frequencies at or near the critical flow rate as exemplified by a Fourier transformation from the time to frequency domain for the MD results in analogy to the phenomenon of critical slowing down in the deterministic CSTR calculations. We conclude that the macroscopic rate laws for first and second order reactions may be applied with confidence to only a few hundred reacting molecules if one is willing to accept some scatter in the rate constants. This conclusion does not apply to the point of a kinetic phase transition in the CSTR which shows a qualitatively different behavior in the low number limit, because of the large and “slow” fluctuations at that point. We present a new approach to the MD treatment of second order rate constants. Kinetic processes in biological cells or on biological membranes may be realistically simulated by MD calculations.
Die photochemische Valenzisomerisierung 9‐alkylsubstituierter Anthrazene zu 9,10‐Dewarisomeren
Authors: Jahn B. , Dreeskamp H.
Published: July 2012

On light absorption in the long wavelength 1La‐band 9‐alkyl‐substituted anthracenes in fluid solutions isomerise with low quantum yield (about 0.016 at 300 K) to the 9,10‐Dewarisomer, provided the substituent is sufficiently spacefilling (t‐butyl or t‐pentyl). On increasing the viscosity and/or reducing the temperature the quantum yield of this valence isomerisation decreases while the quantum yield of fluorescence and the vibrational structure of the fluorescence emission increases. From spectroscopic, caloric and kinetic data an energy diagram of the ground and first excited states is constructed for this photo‐ and thermoreversible reaction in which the folding along the 9,10‐axis of the anthracene sceleton serves as the main reaction coordinate. Steric interaction of the bulky substituent effects a folding of the anthracene sceleton along the 9,10‐axis already in the ground state, which was confirmed by an X‐ray analysis. Thereby a transition from the excited state to a hypersurface is facilitated on which a transformation in low yield to the Dewarisomer and mainly to the starting compound occurs.
Interfacial Phenomena of Some Titanate Photoanodes
Authors: Lam R. U. E. 'T , Janssen L. H. J. M. , Schoonman J.
Published: July 2012

Two types of titanate photoanodes are discussed, viz. mechanically polished n‐TiO2: Nb and hydrogen‐reduced n‐SrTiO3: Nb surface‐doped with LaCrO3. The anodes are investigated in acidic as well as in basic solutions. In addition the influence of ultraviolet irradiation is examined. Detailed equivalent circuits are proposed for both types of cells. Mott‐Schottky plots indicate the presence of a severely disturbed space‐charge region for both photoelectrodes. In the case of the mechanically polished n‐TiO2: Nb anode, the disturbance is attributed to surface roughness effects, whereas for the hydrogen‐reduced n‐SrTiO3: Nb, LaCrO3 anode, the existence of a nonuniform donor level is suggested.
Clustering in Free Jets — Aggregation by Dispersion
Authors: Ryali S. B. , Fenn J. B.
Published: July 2012

The nature of free jet expansion is reviewed with emphasis on those features that are important in the clustering process. Thermodynamic and kinetic aspects are examined. The importance of nozzle geometry is discussed along with some of the implications of the newly developing pulsed flow technique. Some problems relating to free jet sampling into vacuum from high pressure are identified.
Electron Localization and Electron Induced Cluster Formation in Dense Polar Vapors
Authors: Krebs Peter
Published: July 2012

We discuss the mobilities of electrons photoinjected in dense sub‐ and supercritical polar vapors (NH3, H2O) as a function of vapor density and temperature. With increasing density they show a transition from the quasi‐free to the localized electron state. The density range where the onset of this transition is observed obeys the Ioffe‐Regel principle. At this density large radius orientational fluctuations of the dipole molecules as precursors of dense clusters are important for electron localization. Electron cluster formation is strongly supported by the observed temperature dependence of the electron mobility in low density H2O vapor. These results are discussed in context with optical absorption measurements on excess electrons in sub‐ and supercritical D2O and ND3. In NH3 gas around the critical density the electron mobility shows an anomalous density dependence. It is concluded that there occurs a further transition: the electron localized in a dense orientational cluster obviously turns over to an electron localized in a cavity (solvated electron).
Para‐ and Diamagnetic Polyhalide Anions in Liquid CsI – I2
Authors: Nakowsky B. , Nicoloso N. , Freyland W.
Published: July 2012

We have measured the concentration and temperature dependence of the magnetic susceptibility in liquid CsI–I2 mixtures. At low iodine concentrations we have also investigated the EPR and optical absorption spectra. From these results we deduce that localized paramagnetic states similar to V centers exist in CsI rich solutions. With increasing I2 concentration these transform in equilibrium with diamagnetic polyiodide anions like I2n+1− A conduction mechanism via bond fluctuations within iodine clusters is suggested which accounts for the unusual transport properties of these solutions.
Fast Photocurrent Transients in Photoelectrochemical Cells with Semiconductor and Insulator Electrodes
Authors: Willig F. , Bitterling K. , Charlé K.‐P. , Decker F.
Published: July 2012

Photocurrent transients have been measured with better than 1 nanosecond time resolution in photoelectrochemical cells with insulator and semiconductor electrodes. The shape of the transients observed with semiconductor electrodes in the time window of several nanoseconds can be deduced from a simple equivalent circuit. The transient observed in the external circuit consists of two contributions, the first is the time integral and the second is directly proportional to the actual photoresponse. At low light intensity good semiconductor electrodes show only the first contribution. There is no direct influence of charge carrier discharge or of the Helmholtz‐layer as such on the fast transient in the nano‐second range.
Kinetics of the Reactions of HCO with HCO and O2
Authors: Temps F. , Wagner H. Gg.
Published: July 2012

The reactions

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and

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have been studied at room temperature in an isothermal flow reactor using helium in the pressure range 1 mbar ≤ p ≤ 5 mbar as carrier gas. The concentrations of HCO‐, HO2‐ and OH‐radicals were measured by laser magnetic resonance. The reaction F + H2CO → HF + HCO served as radical source. The experiments yielded the results

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For the conditions used here HO2 + CO are found to be the only products formed in the reaction of HCO‐radicals with O2.
Rate Constants for the Reactions of OH‐Radicals with CH2O and HCO
Authors: Temps F. , Wagner H. Gg.
Published: July 2012

The rate constants for the reactions

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and

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have been determined at room temperature in an isothermal discharge flow reactor using laser magnetic resonance to monitor OH‐ and HCO‐radicals. For the study of reaction (1) low initial OH concentrations were used, so that stoichiometry corrections were negligible. By varying the surface to volume ratio of the flow reactors employed, wall effects were carefully controlled. From pseudo first order analysis of the OH‐decay a rate constant of k1(296K) = (4.9 ± 1.0) · 1012cm3/mol · s was obtained. The rate constant for reaction (2) was determined relative to k1 yielding k2(296K) = (1.1 ± 0.4) · 1014 cm3/mol·s.
Termination Rates by Time‐Resolved ESR. The N‐Hydropyridinyl Radical in Solution and the Influence of Non‐Uniform Radical Concentration on the Apparent Rate Constant
Authors: Leuschner Rainer , Krohn Holger , Dohrmann Jürgen K.
Published: July 2012

The rate constants (2 k) for the second‐order self‐termination reaction of the N‐hydropyridinyl radical have been measured by time‐resolved ESR during intermittent UV photolysis of pyridine in various solvents containing propanol(‐2). The frequency factor and the activation energy are (1.8 ± 0.4) · 1010 M−1 s−1 and (10.7 ± 0.4) kJ · mol−1, respectively, in propanol(‐2)/acetone (1:1 by volume) as obtained from the Arrhenius plot of 2 A: in the temperature range between 293 and 230 K. The rate constants at 285 K are (7 ± 1) · 108 M−1 s−1 in H2O/propanol(‐2)/acetone (2:1:1 by volume), independent of the pH value (7.5 – 13.7), and (6 ± 1) · 108 M−1 s−1 in neat propanol(‐2), the latter value being essentially diffusion controlled. The rate constants measured in propanol(‐2)/acetone (1:1) containing various amounts of water correlate with Kosower's solvent polarity parameter. The self‐termination reaction ultimately leads to the destruction of the pyridine ring. Finally, a model is presented for the correction of the influence of non‐uniform radical concentration on apparent values of second‐order rate constants as determined by time‐resolved ESR during intermittent photolysis.
Rate Constant of the Reaction HO + CO in the Presence of N2 and O2
Authors: Hofzumahaus A. , Stuhl F.
Published: July 2012

The kinetics of the reaction HO + CO was studied in the presence and in the absence of O2 using VUV flash photolysis of H2O and kinetic absorption spectroscopy of HO. In the absence of O2, the value of the rate constant was found to vary from 1.4 · 10−13 cm3 s−1 at low total pressures to (2.30 ± 0.16) · 10−13 cm3 s−1 at atmospheric pressure of N2. In the presence of traces of O2, a complex reaction mechanism is necessary to explain the HO decays. With recent rate data, the mechanism allows us to reinterpret the experimental data of Biermann et al. [9] which were significantly influenced by secondary reactions thus simulating the previously reported O2‐effect.
Photochemistry of Colloidal Metal Sulfides. 7. Absorption and Fluorescence of Extremely Small ZnS Particles (The World of the Neglected Dimensions)
Authors: Weller H. , Koch U. , Gutiérrez M. , Henglein A.
Published: July 2012

Extremely small colloidal ZnS particles (diameter ∼ 1.7 nm) were made by either photo‐degradation of 3 nm particles or rapid precipitation in phosphate containing solution at pH = 7‐−8. The absorption spectra of these particles are different from that of macrocrystalline ZnS, and the changes are regarded as an indication for the transition from semiconductor ZnS to polymolecular ZnS with decreasing particle size. – The dependence of the intensity of the fluorescence on particle size, temperature, photoanodic corrosion and the quenching of fluorescence were investigated for colloids on a silicon dioxide carrier, in phosphate solution, and without a stabilizer. Photo‐anodic corrosion strongly improves the fluorescence properties. – One adsorbed Cd2+ ion per colloidal particle is sufficient for efficient quenching of the fluorescence. However, a new fluorescence band appears which is explained by the formation of a layer of 1:1 co‐colloid at the surface of the ZnS particles. – Methylviologen was also found to be a very efficient quencher. The decay of the fluorescence is wavelength dependent, i.e. the fraction of long‐lived fluorescence is greater at longer wavelengths. – A mechanism is discussed, where the fluorescence centers are anion vacancies, and fluorescence is emitted when electrons trapped in states of different energies and exhibiting different life‐times tunnel to the localized positive holes.
Negative Ions in the Gas Phase Observed in Electron Transmission and Electron Attachment Spectroscopy
Authors: Heni Martin , Kwiatkowski Georg , Illenberger Eugen
Published: July 2012

A new electron transmission spectrometer is applied to study the formation of negative ions in ethylene and the fluoroethylenes. It is found that the electron attachment energy in the fluoroethylenes observed in electron transmission completely coincides with the energy of the resonances associated with the formation of F− (and various other stable negative fragments) observed in dissociative electron attachment. This demonstrates that the combination of electron transmission and dissociative electron attachment spectroscopy yields information on the formation and decomposition of molecular negative ions in the gas phase.
On the Determination of the Fractionation Factors of Aqueous Bromide and Iodide Ions by Proton NMR
Authors: El Seoud Monica I. , El Seoud Omar A.
Published: July 2012

The deuterium‐protium fractionation in aqueous solutions of KBr, NaBr, KI, and NaI was studied by 1H NMR. The fractionation factor of the bromide ion (ϕBr‐), and that of the iodide ion (π1‐) were determined from the dependence of the chemical shift of the water protons on the concentration of the solubilized salts, and on the deuterium content of the solvent. The values of the fractionation factors were: ϕBr‐ = 0.96 ± 0.05 and ϕ1‐ = 0.97 ± 0.04. These are practically the same as the one recently determined for the aqueous chloride ion. The present work is in good agreement with the results of other studies which demonstrated that the structure of the water in the solvation shells of these halide ions is only slightly disturbed.
New Developments in the Field of High‐Pressure Extraction of Natural Products with Dense Gases (Invited Lecture)
Authors: Stahl Egon , Quirin K. W. , Glatz A. , Gerard D. , Rau G.
Published: July 2012

A short historical review is followed by a survey of more recent work, some of it still unpublished. Solubility determinations in the pressure range up to 3000 bar and at temperatures up to 80°C yielded new surprising results for the substance classes of the triglycerides, wax esters and sterols. The difficult problem of the high pressure extraction of flexible viscous masses, such as crude lecithin and similar pastes and slimes, could be elegantly solved by the continuous high pressure jet procedure. In the field of separation of substances of high vapour pressure, e.g. essential oils, new paths were opened up. We succeeded in separating selectively undesirable fatty oils, waxes and colouring matter. The procedure for the continuous deterpenation for the recovery of high quality concentrated flavours is also new. We could further show the possibility of removing lipophilic pesticides from plant material, e.g. DDT, γ‐HCH from sennae leaves and ‐pods.
Thermal Conductivity in Supercritical Fluids
Authors: Le Neindre B. , Garrabos Y. , Tufeu R.
Published: July 2012

Now it is well established that the thermal conductivity of a fluid shows a strong enhancement in its critical region. Several experimental results are reported on the thermal conductivity of various fluids in their critical region. A tentative method is given to predict the thermal conductivity excess of any kind of pure fluid in its supercritical region. Results of the calculation are compared with experimental data of some fluid solvents.
1H NMR Studies on the Dynamics of Planar [C(NH2)3]+ Cations in the Crystal of Various Guanidinium Salts
Authors: Gima Shin‐Ei , Furukawa Yoshihiro , Nakamura Daiyu
Published: July 2012

The temperature dependences of 1H NMR spin‐lattice relaxation times and 1H NMR second moments were observed for guanidinium chloride, bromide, iodide, thiocyanate, nitrate, and perchlorate. The results of the NMR experiments carried out with the crystals of these compounds except the last one can be interpreted in terms of the C3 reorientation of the cation about its symmetry axis. The solid‐solid phase transition at 454 K reported for guanidinium perchlorate could be resolved into two phase transitions taking place successively at 450 and 452 K. In the low temperature phase of this salt, the C3 reorientation of the cation is activated. The occurrence of cationic self‐diffusion in the high temperature phase was confirmed by the measurements of 1H NMR relaxation times. The NMR motional parameters are evaluated for these cationic motions in the present salts. The phase transition temperature of guanidinium iodide was strongly depended on the grain size of the sample employed. Guanidinium bromide yielded a single 81Br NQR line at room temperature indicating that all bromide ions in the crystal are crystallographically equivalent in agreement with the results of X‐ray analysis.
Measurements of the Volumetric Properties for Perfluoro−2‐methylpentane in the Range of Temperatures 333 to 473 K up to 5.7 MPa
Authors: Momoda K. , Uematsu M. , Watanabe K.
Published: July 2012

The PVT properties and vapor‐pressures for 2‐CF3C5F11 have been measured in the range of temperatures 333 to 473 K and of pressures 0.1 to 5.7 MPa, which corresponds to density variation from 115 to 1368 kg/m3, by using a constant‐volume spherical piezometer. The experimental uncertainty of the temperature, pressure and density measurements were estimated to be less than 10 mK, 1.5 kPa and 0.12%, respectively. The temperatures of orthobaric densities were determined graphically based on the present measurements. The critical parameters were proposed to be ρc = 635 ± 6 kg/m3, Tc = 455.3 ± 0.3 K and Pc = 1.923 ± 0.012 MPa.
Cardiac Involvement in Adult Polymyositis or Dermatomyositis: A Systematic Review
Authors: Lu Zhang , Guo‐chun Wang , Li Ma , Ning Zu
Published: July 2012

Background:

To investigate the clinical features of cardiac involvement in polymyositis (PM) or dermatomyositis (DM).

Hypothesis:

More attention will be focused on the heart in PM/DM as we would have wished, which contribute to improve the prognosis.

Methods:

All articles published in English were retrieved by searching MEDLINE via PubMed (1975–2011). After selecting eligible articles according to the predefined inclusion and exclusion criteria, a systemic review was carried out.

Results:

A total of 26 articles were included in this study, which included 1530 patients. The incidence of cardiac involvement was 9% to 72%. Heart failure was the most frequent (32% to 77%) clinical symptom. Among the abnormal electrocardiogram and ultrasonic cardiogram, the incidence of conduction abnormalities, left ventricular diastolic dysfunction, and hyperkinetic left ventricular contraction were 25% to 38.5%, 42%, and 6% to 12%, respectively. The pathologic findings revealed myocardial inflammation, degenerative changes and necrosis similar to that in skeletal muscles. Cardiac manifestations of some patients improved after glucocorticoid and immunosuppressant treatment. Thirty‐seven patients (46.3%) died as a direct result of heart disease.

Conclusions:

Heart abnormalities are frequent in patients with PM/DM, most of which were subclinical. The efficacy of glucocorticoids and immunosuppressants is uncertain. Cardiac involvement is a common cause of death. Clin. Cardiol. 2012 doi: 10.1002/clc.22026

The authors have no funding, financial relationships, or conflicts of interest to disclose.
Lithium–Sulfur Batteries Based on Nitrogen‐Doped Carbon and an Ionic‐Liquid Electrolyte
Authors: Sun Xiao‐Guang , Wang Xiqing , Mayes Richard T. , Dai Sheng
Published: July 2012

Nitrogen‐doped mesoporous carbon (NC) and sulfur were used to prepare an NC/S composite cathode, which was evaluated in an ionic‐liquid electrolyte of 0.5 M lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) in methylpropylpyrrolidinium bis(trifluoromethane sulfonyl)imide ([MPPY][TFSI]) by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and cycle testing. To facilitate the comparison, a C/S composite based on activated carbon (AC) without nitrogen doping was also fabricated under the same conditions. Compared with the AC/S composite, the NC/S composite showed enhanced activity toward sulfur reduction, as evidenced by the lower onset sulfur reduction potential, higher redox current density in the CV test, and faster charge‐transfer kinetics, as indicated by EIS measurements. At room temperature under a current density of 84 mA g−1 (C/20), the battery based on the NC/S composite exhibited a higher discharge potential and an initial capacity of 1420 mAh g−1, whereas the battery based on the AC/S composite showed a lower discharge potential and an initial capacity of 1120 mAh g−1. Both batteries showed similar capacity fading with cycling due to the intrinsic polysulfide solubility and the polysulfide shuttle mechanism; capacity fading can be improved by further cathode modification.
A process‐based hypothesis for the barchan–parabolic transformation and implications for dune activity modelling
Authors: Barchyn Thomas E. , Hugenholtz Chris H.
Published: July 2012

The introduction of vegetation to bare barchan dunes can result in a morphological transformation to vegetated parabolic dunes. Models can mimic this planform inversion, but little is known about the specific processes and mechanisms responsible. Here we outline a minimalist, quantitative, and process‐based hypothesis to explain the barchan–parabolic transformation. The process is described in terms of variations in the stabilization of wind‐parallel cross‐sectional dune slices. We hypothesize that stabilization of individual ‘dune slices’ is the predictable result of feedbacks initiated from colonization of vegetation on the slipface, which can only occur when slipface deposition rates are less than the deposition tolerance of vegetation. Under a constant vegetation growth regime the transformation of a barchan dune into a parabolic dune is a geometric response to spanwise gradients in deposition rates. Initial vegetation colonization of barchan horns causes shear between the anchored sides and the advancing centre of the dune, which rotates the planform brinkline angle from concave‐ to convex‐downwind. This reduces slipface deposition rate and allows vegetation to expand inward from the arms to the dune centre. The planform inversion of bare barchans dunes into vegetated parabolic dunes ultimately leads to complete stabilization. Our hypothesis raises several important questions for future study: (i) are parabolic dunes transitional landforms between active and vegetation‐stabilized dune states? (ii) should stabilization modelling of parabolic dune fields be treated differently than linear dunes? and (iii) are stabilized parabolic dune fields ‘armoured’ against re‐activation? Copyright © 2012 John Wiley & Sons, Ltd.
Chitosan dressing promotes healing in third degree burns in mice: Gene expression analysis shows biphasic effects for rapid tissue regeneration and decreased fibrotic signaling
Authors: Baxter Ruth M. , Dai Tianhong , Kimball Jess , Wang Eugenia , Hamblin Michael R. , Wiesmann William P. , McCarthy Simon J. , Baker Shenda M.
Published: July 2012

Burns are a significant health challenge and healing can result in scar formation. Chitosan, a derivative of chitin, has been used to promote wound healing. In this study we used gene expression profiling in a mouse model of full thickness cutaneous burn to assess the benefits of treating with a chitosan lactate dressing. Three days after wounding mice treated with chitosan showed increased expression of genes associated with formation of granulation tissue. At a later time point, seven days after wounding, genes that initially showed increased expression were now down‐regulated, and there was increased expression of genes involved in remodeling suggesting that the chitosan treatment results in accelerated healing. Quantitative RT‐PCR showed modulated mRNA levels for TGFβ1 by the chitosan dressing. TGFβ1 initially promotes healing but extended activity can result in scarring. Importantly we found that expression was elevated at day three, but decreased at day seven suggesting that chitosan treatment will not result in scar formation, and may even be beneficial in preventing scar formation. Additionally, the biphasic regulation of expression of TGFβ1 could be a powerful biomarker for future studies of the wound‐healing potential of chitosan based and other treatments for burn wounds. © 2012 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2013.