bluuebunny/crossref_metadata_2025_split huggingface dataset:
Correlation of Viscometric and Molecular Dynamics Behaviour for the Model Lubricant, 2‐Ethylhexyl Benzoate (EHB)
Authors: Whitley A. , Yarwood J. , Gardiner D. J. 
Published: July 2012

AbstractVariations in shear viscosity and reorientational correlation times with temperature for EHB have been interpreted according to the hydrodynamic model of Kivelson et al. in order to extract effective molecular volumes or “torque” parameters. The data fall into high and low temperature regimes characterised by different (Arrhenius) activation energies for reorientation. The hydrodynamic model appears to point to a correlation between rotational times and the internal motions which lead to relatively low effective volumes and which reflect molecular flexibility. Evidence for a “transition” temperature for molecular flexibility is presented and discussed.
Influence of Electric Fields on the Heat Conductivity of Liquids Investigated by the Thermal Lensing Effect
Authors: Eden G. , Schröer W. 
Published: July 2012

AbstractThe energy absorbed in a liquid sample from a laser beam causes an inhomogenity in the temperature and in the refractive index. This makes the sample to behave as a concave lens. In an electric field this effect, which is known as the thermal lensing effect, is reduced. For various compounds (Benzene, Toluene, Trifluorotoluene, o‐Dichloro‐benzene, Nitrobenzene) the time dependence of the intensity at the centre of the laser beam is investigated as function of the applied field. The experiments are analysed assuming an anisotropic contribution to the heat conductivity tensor, determined by the electric field. The averaged heat conductivity is found to depend linearly on the voltage, which suggests to explain the enhancement of the heat transfer from the laser beam by a micro convection connected to the small ionic current.
Anomalous Thermal Conductivity in the Close Neighbourhood of a UCST
Authors: Maczek A. O. S. , Davies M. K. 
Published: July 2012

AbstractResults of measurements of the temperature dependence of the thermal conductivity of the binary system perfluoromethylcyclohexane + methylcyclohexane are reported. These were obtained using a modified hot‐wire transient technique which allowed measurements to be made using very small temperature rises (<100 mK), with a precision of better than ± 0.5%. The results show a small but unmistakable anomalous rise in thermal conductivity on very close approach to the critical point. Analysis shows that this rise is compatible with a value for the critical exponent χλ= 0.572, in agreement with the theoretical predictions of dynamic renormalisation group theory. The anomaly is very small‐some five hundred times smaller in magnitude than the corresponding anomaly in thermal conductivity for a one component fluid near its gas‐liquid critical point.
Evidence for a Change in the Fluidity of DDAB Vesicular Membranes following γ‐Irradiation by Use of Lucigenin Chemiluminescent Reaction
Authors: Domazou A. S. , Mantaka‐Marketou A. E. 
Published: July 2012

AbstractThe fluidity changes of the Didodecyldimethylammonium Bromide (DDAB) vesicular bilayer, mimetic agent of biological membranes, following γ‐irradiation were investigated under conditions where mainly OH radicals existed. The chemiluminescence (CL) quantum yields of Lucigenin light reaction were found to be strongly depended upon the irradiation dose above 0.65 kGy. Quenching of N‐Methylacridone fluorescence, the primary emitter of the light reaction, after irradiation was not observed. Thus, the increase in fluidity of the vesicular bilayer structure seems to be the principal cause of the CL decrease.
Increasing the Replicative Capacity of a Naturally‐Occurring RNA Template
Authors: Fernändez Ariel 
Published: July 2012

AbstractWe consider the template‐directed autocatalytic synthesis of RNA strands by Qβ‐replicase. We introduce a mutation on a naturally‐occurring template, MDV‐1RNA, for the replicase. The autocatalytic activity is improved over that of the original system. We demonstrate that this enhancement is not the result of an acceleration of the replica assembling process itself. Instead, the initiation step is enhanced as a consequence of the mutation which has the effect of destabilizing the folding structure of the internal recognition site.
Crystal Structure and Nuclear Quadrupole Resonance. The Bond Length C — Cl and 35Cl NQR
Authors: Brummer Stefanie , Weiss Alarich 
Published: July 2012

AbstractThe intramolecular distances dC—Cl for chlorine bound to sp2 carbon and to sp3 carbon, respectively, and the 35Cl NQR frequencies assigned to the corresponding Cl atoms correlate quite well according to the theory: v(35Cl) ∼ (dC—Cl)−3. The relation is v(35Cl) = (4 ± 6) MHz + (166 ± 31) · 106 · (dC—Cl)−3 · MHz · pm3 for {sp2‐C}‐Cl and v(35Cl) = (21 ± 5) MHz + (101 ± 25) · 106 · (dC—Cl)−3 · MHz · pm3 for {sp3‐C}‐Cl. — The crystal structures and chemical bonds of 1 (4‐methyl‐4‐trichloromethyl‐2,5‐cyclohexadiene‐1‐one), 2 (2‐chloro‐4,5‐dimethyl‐4‐trichloromethyl‐2,5‐cyclohexadiene‐1‐one), 3 (4,5‐dichloro‐1‐phenyl‐pyridazine‐6‐one), and 4 (2,2,4,5‐tetrachloro‐cyclo‐pentene‐1,3‐dione) were studied by single crystal X‐ray diffraction and 35Cl nuclear quadrupole resonance (NQR). 1 crystallizes with the space group D152h‐Pbca, Z = 8. The lattice constants are a = 1206.0(3) pm, b = 1341.3(3) pm, and c = 1178.8(3) pm. 2 crystallizes monoclinic, space group C52h‐P21/c, Z = 4, a = 696.3(3) pm, b = 1404.0(5) pm, c = 1151.4(5) pm, and β = 100.23(1)°. 3 crystallizes in the orthorhombic space group D4h‐P212121, Z = 4, a = 4303(1) pm, b = 586.8(2) pm, and c = 390.5(1) pm. 4 crystallizes cubic, space group T4h‐Fd3, with 48 molecules in the unit cell, a = 2181.5(5) pm. The 35Cl NQR spectra were observed for the two 2,5‐cyclohexadiene‐1‐ones, 1 and 2 in the temperature range 77 < T/K < melting point. For 3, the 35Cl NQR spectra was determined at T = 77 K and T = 295 K. No phase transition has been found for the three compounds in the temperature range in which the 35Cl NQR spectroscopy was performed.
Elementary Reactions of Ketene with Fluorine and Chlorine Atoms in the Gas Phase
Authors: Ebrecht J. , Hack W. , Gg. Wagner H. 
Published: July 2012

AbstractThe elementary reactions of F and Cl atoms with CH2CO were studied in an isothermal flow reactor with a mass spectrometric detection device. The atoms were produced in a microwave discharge of F2/He and Cl2/Ar mixtures respectively. — For the reactions of F and Cl atoms with CH2CO, applying pseudo first order conditions ([F]0 → [CH2CO]0 and [Cl]0 → [CH2CO]0 respectively, the second order rate constants magnified image were found. — The following mechanism was obtained for the F atom reaction: magnified image The abstraction channel to form HF and CHCO was calibrated to contribute 20% to the overall reaction. — For the Cl reaction the two main reaction pathways magnified image were determined.
Solution of Hydrogen in Cold‐Worked and Annealed Pd95Ag5 Alloys
Authors: Kishimoto Shozo , Yoshida Noritetsu , Arita Yoshitaka , Flanagan Ted B. 
Published: July 2012

AbstractThe effect of cold‐working and subsequent annealing on the hydrogen solubility of a Pd95Ag5 random substitutional alloy has been examined. For the first time a correlation of physical properties such as electrical resistance and hardness with hydrogen solubility has been made.
Form and Structure Factors of Water/AOT/Oil Microemulsions from Synchrotron SAXS
Authors: Hilfiker Rolf , Eicke Hans‐Friedrich , Sager Wiebke , Steeb Christian , Hofmeier Urs , Gehrke Rainer 
Published: July 2012

AbstractSynchrotron small angle X‐ray scattering (SAXS) measurements were performed on water/AOT/n‐hexane w/o microemulsions with w0 ( = [H2O]/[AOT]) values ranging from about 0 to 100. The volume fraction of solute and the temperature were varied in a wide range. The scattering behaviour (form and structure factor) could be explained on the basis of a pseudo hard sphere model, where the spheres were allowed to be spheroidally deformed to a certain extent. We have shown that these deformations become larger as the lower consolute point of the mixture is approached. Furthermore, we have demonstrated that the radius of gyration is temperature independent, and that it depends linearly on w0. The w0‐dependence of the scattering intensity could be explained on the basis of the droplet model.
Magnetite (Fe3O4) in an Oxygen Potential Gradient: Chemical Diffusion, Tracer Diffusion, and Phase Boundary Reaction
Authors: Dorris S. , Martin M. 
Published: July 2012

AbstractAn analysis is given for chemical and tracer diffusion in magnetite exposed to an oxygen potential gradient. From a single experiment, the correlation factor and the self‐diffusion coefficient of the dominant defect can be determined. Results are provided for both the provided for both the vacancy and interstitial regimes. In addition, the rate constant is determined for the exchange of oxygen between magnetite and CO/CO2 mixtures.
A Thermodynamic Study of Adsorption of Cationic Surfactants from their Aqueous Solutions onto Oxide Surfaces: Theoretical Description of Adsorption Isotherms and Heats of Adsorption
Authors: Narkiewicz‐Michalek J. 
Published: July 2012

AbstractExcept for the region of very low surface coverages, the adsorption of cationic surfactants from their aqueous solutions onto negatively charged oxide surfaces is governed by the competition between monolayer‐like and bilayer‐like surfactant aggregates formed on the solid surface. That adsorption mechanism combines, thus, the features of both ion and polymer adsorption, and yet is influenced strongly by the energetic heterogeneity of the surfaces of the real oxides. — Starting from that adsorption model a theoretical approach is developed, making a quantitative description of experimental adsorption isotherms and heats of adsorption possible. Illustrative calculations are presented for DTAB adsorption on silica gel.
The Dynamical Structure Factor of Particles Diffusing in a Closed Volume
Authors: Stockmeyer Rolf 
Published: July 2012

AbstractThe dynamical structure factor of incoherently scattering nuclei, diffusing in a restricted volume of rectangular shape, is calculated and the result is compared with the corresponding curves for particles enclosed in a spherical shell. A program is written, running on a popular minicomputer with industry‐standard‐architecture, which quickly yields the parameters of the diffusion model to fit a given set of neutron scattering data.
Electrochemical Properties of a Molten Carbonate Fuel Cell
Authors: Landes H. , Luft G. , Mund K. , Rummel W. 
Published: July 2012

AbstractThe characteristics of electrodes of a fuel cell containing molten carbonate electrolyte were investigated in a small laboratory scale cell. The cell can be operated at 650°C and a current density of 150 mA/cm2 be derived at a voltage of 0.76 V. The analysis of impedance measurements revealed for both electrodes that the voltage drop in the electrolyte of the working layer determines the loading capacity. In addition to the charge transfer reaction, also the adsorption is rate determining for the anode. The diffusion of oxygen in the electrolyte of the working layer increases the polarization resistance of the cathode.
PEM‐Fuel Cells: State of the Art and Development Possibilities
Authors: Straßer K. 
Published: July 2012

AbstractAfter conducting an analysis of fuel cell systems for comparison, the basic know how of the PEM‐fuel cell was transferred from GE to Siemens 1983/84 and in the following Siemens has started the development of FC‐modules as power source of an air‐independent propulsion system. The PEM‐FC‐system, which is characterized by its simple design, high power density and favourable longlife behaviour, is superior to other FC‐systems by the versatility of service. At a current density of 0.5 A/cm2 cells were operated during more than 20000 hours. A current density of 5 A/cm2 is possible. Cells with an active area of more than 1000 cm2 and 10 kW‐stacks, which contains 20 cells, were constructed. Test results and possibilities of improvements will be reported.
Ion Exchange Membranes as Electrolyte for Electrochemical Energy Conversion
Authors: Ledjeff K. , Ahn J. , Zylka D. , Heinzel A. 
Published: July 2012

AbstractFor solar energy systems long term energy storage with a high efficiency is required. Hydrogen is a suitable energy carrier, its generation by water electrolysis, the conversion into heat by (catalytic) combustion and into electrical energy by fuel cells is the present state of the art. Electrolyzer and fuel cell with a solid polymer electrolyte show several advantages compared to cells with liquid electrolyte. In compact modules high energy densities and high efficiencies are realized without a costly and complicated peripheral gas and electrolyte management system. The current work is concerned with the construction of a pressure electrolyzer, a hydrogen/oxygen fuel cell and the development of a “reversible” system which works as electrolyzer and fuel cell as well. The modification of the fuel cell for the use of methanol as a fuel is a promising goal. Methanol is an attractive fuel for a back up system in the case of exhausted hydrogen reverse. The electrochemical reactions of hydrogen, oxygen and methanol at membrane/electrode composites are investigated.
Long‐Term Poisoning of Methanol Anodes
Authors: Hamnett A. , Weeks S. A. , Kennedy B. J. , Troughton G. , Christensen P. A. 
Published: July 2012

AbstractThe evidence for oxide formation on dispersed platinum particles being the main cause for long‐term poisoning of methanol anodes in direct methanol fuel cells is reviewed. On the basis of in situ FTIR, XPS and current interrupt data, it is shown that poisoning by organic oxidation fragments is far less significant on such particles than on planar platinum. In addition, the mode of long‐term poisoning on Pt/Ru electrodes is also investigated; quite different behaviour from pure platinum is found, with conversion of an active hydrous oxide to the inactive rutile form of RuO2 being primarily responsible for the decline in activity with time.
Ions and Charged Soot Particles in Hydrocarbon Flames III. Negative Ions in Fuel‐rich Acetylene/Oxygen Flames
Authors: Gerhardt Ph. , Homann K. H. 
Published: July 2012

AbstractNegative ions up to masses > 3 · 103 u in fuel‐rich and sooting premixed low‐pressure acetylene/oxygen flames have been analyzed by means of a time‐of‐flight mass spectrometer. This work deals with the quantitative analysis of ions up to masses of 200 u, but the larger polyhedral carbon ions, which were negative charge carriers in the soot forming zone, are not considered here. Concentration profiles of ca. 50 different ions and the dependence of maximum ion concentrations on the C/O ratio are reported. ‐ Ions in the preheating zone were anions of carbonic acids and diacids which contained oxo, keto and peroxy groups. With increasing height in the flame these anions decomposed by decarboxylation and dissociative electron detachment. At higher temperature in the oxidation zone, polyynides (C2nH−), linear polycarbon ions and higher ketenides (CmHO−) prevailed. The polyynides were in chemical equilibrium with acetylene and higher neutral polyynes. Enthalpies of formation (referenced to that of C2H−, 274 kJ/mol) were determined for C4H− (414), C6H− (603), C8H− (810) and C10H− (1025 kJ/mol). Possible reaction mechanisms for the formation of the acid anions and the ketenides are discussed. Negative polycyclic aromatic hydrocarbon ions were completely missing in acetylene flames, in contrast to their occurrence in benzene flames.
Pressure Effect on the Radiationless Deactivation of Singlet Oxygen in Solution
Authors: Schmidt R. , Seikel K. , Brauer H. D. 
Published: July 2012

AbstractLifetimes of 1Δg singlet oxygen (1O2) have been determined in 12 solvents in dependence of pressure and in part of temperature using time resolved phosphorescence techniques. Experimental activation volumes for the deactivation of 1O2 by solvent molecules vary between ‐11.9 (pentane) ≤ ΔV#obs ≤ ‐4.1 ml mol−1 (formamide) at 298 K. The increase of ΔV#obs with temperature was measured in toluene and CH3CN. The data are analyzed by means of a kinetic scheme assuming a preequilibrium of 1O2 and solvent molecule to form a singlet contact complex 1C. Deactivation of 1O2 occurs by energy transfer between the collision partners of C converting 1C to 3C, which subsequently splits into the deactivation products. A statistical model developed by Yoshimura and Nakahara is used to calculate the reaction volume ΔVc of the preequilibrium. It is revealed that the major part of ΔV#obs, consists of ΔVc. Activation volumes ΔV#E of the actual deactivation of 1O2 by oscillators X–Y of the solvent molecule depend neither on the polarities of solvent nor of X–Y. Independent of oscillator they are estimated to be ΔV#E ≈ −2 ml mol−1 if X–Y is C–H, C–CI, C–F, N–H or C=S.
Viscosity of the n‐Decane—Methane System in the Liquid Phase
Authors: Knapstad B. , Skjølsvik P. A. , Øye H. A. 
Published: July 2012

AbstractThe viscosity of liquid n‐decane and liquid mixtures of n‐decane—methane containing 31.2, 55.7, 69 and 84.7 mol% methane has been measured using an absolute oscillation vessel viscometer. The measurements have been performed in the temperature range 20–150°C, and at pressures up to 40 MPa.—The viscosities of the n‐decane and the liquid mixtures are described separately by an empirical correlation in terms of temperature and pressure. The standard deviation in fit are 0.14–0.2%. The estimated accuracy is ± 1% for n‐decane at 20°C deteriorating to ±4% at 150°C for the mixtures containing 84.7 mol% methane.—Applying a generalization of the Grundberg and Nissan equation, the experimental viscosities are expressed as a function of temperature, pressure and composition with an overall standard deviation in the fit of 0.6%.—Literature data deviate 0‐ +4% from the correlated n‐decane viscosities, and +10 to +40% from the mixture viscosities of the present investigation.
Study of Non‐Equilibrium States of a Homogeneous 2‐Butoxyethanol/Water Mixture of Critical Composition in the Vicinity of Its Lower Critical Point Using Fast Pressure Jumps
Authors: Sieber M. , Woermann D. 
Published: July 2012

AbstractThe pressure dependence of the critical temperature is used to bring a homogeneous 2‐butoxyethanol/ water mixture of critical composition (xc = 0.0598; mole fraction of 2‐butoxyethanol; critical temperature Tc (P = 1 bar) = 49.39°C) from a state away from its critical temperature to a state close to the critical temperature. This is accomplished by fast pressure jumps (expansions) with an amplitude in the range of −50 bar < ΔP < −5 bar (ΔP = (Pf‐Pi); Pf, hydrostatic pressure in the final state (Pf = 1 bar); Pi, hydrostatic pressure in the initial state) and a characteristic time constant of τp ≃ 0.3 ms. The coefficient characterizing the pressure dependence of the critical temperature has a value of (dTc/dP)c.l. = 43 mK bar−1. The delayed increase of the intensity of scattered light (“critical opalescence”) is measured as function of time at different scattering angles (10° ≤ θ ≤ 60°) and different temperature differences (Tc ‐ Tf) (Tc. critical temperature; Tf, final temperature after the pressure jump). The fast pressure jump leads to a small decrease of the temperature of the sample ((∂T/∂P)s = 6 mK bar−1). The measured relaxation curves are found to be single exponentials for times short compared with the relaxation time τT of the heat conduction process bringing the system back to its initial temperature Tf (τT is in the order of seconds). – For small values of the scaling variable (qζf) < 0.7 (q, absolute value of scattering wave vector; q = (4μñ/λ0) sin (0/2); 0, scattering angle; ñ, index of refraction; λ0, wavelength of incident light in vacuum; ζ, correlation length of local concentration fluctuations) the structure factor relaxes as expected on the basis of linear response (τhyd/τexp = 1; τhyd, hydrodynamic relaxation time calculated from independent dynamic and static light scattering experiments; τexp, experimental relaxation time). At larger values of (qζf) ((qζf) > 0.7) the structure factor relaxes more slowly than theoretically expected (i.e. τhyd/τexp < 1). This behaviour is similar to that of the systems 3‐methyl‐pentane/nitroethane and 2, 6‐dimethylpyridine/water.
The Debye‐Hückel Theory for Hydrated Ions III. The Square‐Cross Rule for the Gibbs Energy of Aqueous Solutions of Some 1:1 Electrolytes at 25°C
Authors: Schönert Hansjürgen 
Published: July 2012

AbstractA recently formulated Debye‐Hückel theory for aqueous solutions of hydrated, singly charged ions is extended to solutions with reciprocal electrolyte pairs: MX, MY, NX and NY. The results are analyzed with respect to the square‐cross rule for the excess Gibbs energy of hydrogen and alkali halogenides. The parameters for the model are taken from a fit to the activity coefficients of the respective binary solutions. The DH 2 variation of the new model theory is in good agreement with the square‐cross rule.
The Role of Some Solvent Binaries in the Alkaline Decomposition of Tetraphenylphosphonium Bromide
Authors: Hanna M. T. , Khalil Fayez Y. , El‐Batouti M. 
Published: July 2012

AbstractComparative study of the role of solvent effects of aqueous methyl cellosolve and tetrahydrofuran solvent systems on the alkaline decomposition of tetraphenylphosphonium bromide was carried out. The reaction rate increases remarkably as the medium changes from purely aqueous to a water‐organic cosolvent reaction mixture. The relative changes in the solvation states of both reactants and transition state as the structural properties of the two solvent binaries change were shown to be the direct reasons for the difference in the effects on rate and activation energies.
Negative Thermal Expansion in One‐Dimensional Fluids
Authors: Yoshimura Y. 
Published: July 2012

AbstractThe molecular origin of the negative thermal expansion of fluids has been studied for the one‐dimensional system with nearest‐neighbor interactions. The PLT behavior accompanying the negative thermal expansion is demonstrated for two model potential functions: Added to the hard core repulsive force, Model I has a truncated power potential function and Model II has a step potential function. In Model II, the negative thermal expansion is accompanied by the positive thermal expansion in the lower temperature region, i. e. the length of the system has the maximum and the minimum with increasing the temperature at constant pressure in Model II. Peculiar thermodynamical behavior of Model II is ascribed to the thermal transition between two molecular states, which is simulated by the mixture model of fluids. – The negative thermal expansion is analyzed on the basis of the theory of thermal fluctuation: The thermal expansion of length is composed of two terms due to the correlation between the internal energy and the length and the autocorrelation of the length, respectively. The negative thermal expansion is brought about by the negative correlation between the internal energy and the length, and the system shows a large fluctuation within and around the region of the negative thermal expansion. Since the attractive interaction reduces the fluctuation of the length, the attractive interaction enlarges the region of the negative thermal expansion in cooperation with soft‐repulsive interactions. Present results on the one‐dimensional system reproduce the essential feature of the negative thermal expansion in the real systems such as water or liquid tellurium.