bluuebunny/crossref_metadata_2025_split huggingface dataset:
Translational diffusion in C60 and C70 fullerene solutions
Authors: Haselmeier R. , Holz M. , Kappes M. M. , Michel R. H. , Fuchs D. 
Published: July 2012

AbstractSelf‐diffusion coefficients D of C60 and C70 and of the solvent molecules C6H6 and CS2 have been investigated in liquid fullerene solutions by the 13C and 1H NMR pulsed field gradient techniques. The C60/benzene measurement is in good agreement with a recent report, while data obtained for C60/CS2 and C70/CS2 are first measurements. The C70 number reflects the only diffusion measurement yet carried out on this molecule. Data were obtained with 5% 13C enriched fullerenes at 298 K. The sample preparation and the separation of 13C enriched C60 and C70 is described. The fullerene diffusion data are in excellent agreement with values predicted by the Stokes‐Einstein equation, however, under slip boundary conditions. In CS2 solution we find D(C60) = (1.85±0.18) × 10−9 m2s−1 and D(C70) = (1.56±0.16) × 10−9m2s−1 at 298 K, thus showing that fullerenes differing slightly in shape can be discriminated via their diffusivity. C70 may be regarded as an ideal ellipsoidal particle for the test of theories of diffusion. Our experimental result for C70 indicates that the long semi‐axis of the ellipsoid determines the diffusion behavior. Preliminary temperature dependent diffusion measurements of C60 in CS2 do not reveal a difference in the activation energy of solute and solvent. We could not detect that the diffusion coefficients of the solvent molecules are influenced by the presence of the fullerenes in the solutions under investigation.
Disquac application to SLE of binary mixtures containing long chain 1‐alkanols (1‐tetradecanol, 1‐hexadecanol, 1‐octadecanol, or 1‐eicosanol) and N‐alkanes (C8–C16)
Authors: González J. A. , Garc de la Fuente I. Ía , Cobos J. C. , Casanova C. , Domańska U. 
Published: July 2012

AbstractThirty‐four sets of data on solid‐liquid equilibria for the entitled mixtures are examined in terms of DISQUAC. On the basis of data for systems containing n‐octane, new first dispersive interchange coefficients are given for the hydroxyl/aliphatic contacts involved. They are constant from 1‐hexadecanol. The remainder interchange coefficients are kept the same as in our previous works. The relative standard deviations for the equilibrium temperatures are less than 0.025 for all the mixtures investigated. Results depend on the difference in size of the mixture compounds.
Prediction of surface tension of liquids
Authors: Rubio José E. F. , Baonza Valentín G. , Cáceres Mercedes , Núñez Javier 
Published: July 2012

AbstractMost of useful estimation techniques for surface tension of liquids are based on empirical correlations and general methods with molecular basis are rare in the literature. In this paper we show how combining an expression derived from the hole theory of Fürth with an statistical‐mechanical based equation of state, an estimation of surface tension and its behavior with temperature is easily obtained.
Hydrogen absorption and thermodynamic properties of hydrogen in low rh content Pd‐Rh alloys
Authors: Sakamoto Y. , Haraguchi Y. , Ura M. , Chen F. L. 
Published: July 2012

AbstractThe hydrogen absorption characteristics of fully annealed Pd‐Rh alloys containing up to 10.0 at.% Rh have been investigated at temperatures between 273 K and 433 K and hydrogen pressures up to 1000 Torr by means of pressure‐composition isotherm measurements. For the p‐c isotherms of Pd‐7.5 at.% Rh alloy, in addition to the normal (α+β) two‐phase plateaus, “anomalous plateaus” are observed near the normal βmin phase boundaries. The formation of this anomalous plateau implies that in the fully annealed alloys some precursory phase separation exists, together with the metastable, homogeneous solid solution phase. The low pressure hydrogen solubilities decrease with an increase of Rh content and the main plateau pressures increase with the solute metal content. The hydrogen solubilities exhibit a maximum at about 7.5 at.% Rh at 1000 Torr. The derived relative partial molar thermodynamic quantities at infinite dilution, and also the plateau thermodynamic parameters are in agreement with the previously reported results. These thermodynamic quantities are not affected by the formation of the anomalous hydride phase, because the hydride does not form in the dilute phase region, and because the amount of hydrogen involved in the anomalous hydride phase is small compared to the main hydride phase.
The rotational spectrum of the benzonitrile‐argon van der Waals complex
Authors: Dahmen U. , Stahl W. , Dreizler H. 
Published: July 2012

AbstractThe microwave spectra of 14N‐ and 15N‐benzonitrile‐argon have been recorded using a pulsed molecular beam Fourier transform microwave spectrometer. In the case of 14N‐benzonitrile‐argon, the rotational constants were determined to be A = 1347.7899(12) MHz, B = 1006.02030(94) MHz, C = 719.81749(24) MHz. The quartic centrifugal distortion constants (van Eijck) are D'J = 3.9982(14) kHz, D'JK = −15.3062(79) kHz, D'K = 21.8510(92) kHz, d'J = 1.65065(83) kHz, R'6 = 0.03043(38) kHz, and the 14N‐nuclear quadrupole coupling constants are χaa = −0.4479(17) MHz, χbb‐χcc = −4.1255(17) MHz. For 15N‐benzonitrile‐argon the rotational constants were found to be A = 1335.09150(30) MHz, B = 989.86421(15) MHz, and C = 707.91548(07) MHz. The centrifugal distortion constants are of the same magnitude as for the 14N‐isotopomer. The argon atom is placed 3.545 Å above the center of the ring plane. In addition, the spectra of benzonitrile and six isotopic species have been reinvestigated; the derived constants and the resulting structure are of higher accuracy than in earlier work.
Laser photolysis of naphthoquinone diazide in cyclohexane – two‐laser chemistry
Authors: Bendig J. , Mitzner R. 
Published: July 2012

AbstractThe laser photochemistry of 1,2‐naphthoquinone‐diazide‐(2)‐5‐sulfonic acid phenylester in cyclohexane has been investigated. The photolysis experiments have been done using a KrF laser pulse (generation pulse) and a nitrogen laser pulse (transformation pulse) with various time delay from 40 ns up to 1 s. At a time delay between the two laser pulses in the μs‐region, the formation of indene and cyclohexyl‐indene derivatives has been observed, additional to the corresponding indenecarboxylic acid. The laserspecific formation of these compounds is the result of the electronic excitation of the intermediately formed ketene and its reaction by decarbonylation. The time delay for getting a high yield of the indene and the cyclohexyl‐indene derivatives correlates closely with the rise time and the life time of the ketene.
Characterisation of CN in the photodissociation of cyanogen azide at 193 nm
Authors: Baumgärtel S. , Gericke K.‐H. , Comes F. J. 
Published: July 2012

AbstractThe photodissociation dynamics of NCN3 has been investigated by observation of the CN(X2Σ) product molecule. The CN fragment is formed in vibrational states ν = 0,1,2 with a population ratio of P(ν = 0):P(ν = 1):P(ν = 2) = 0.42:0.33:0.25. The rotational state distribution is broad, a Boltzmann plot shows a nonlinear behavior. The rotational excitation carries 9% of the available energy. The CN recoil velocity distribution is also broad and indicates a significant internal excitation of the N3 product molecule. The spin is distributed statistically. The fragmentation does not proceed in the Franck‐Condon limit but strong forces act on the upper potential energy surface.
On the dependence of the photoluminescence decay on the externally applied potential at the junction n‐GaAs/1 M HCl
Authors: Krüger O. , Jung Ch. 
Published: July 2012

AbstractThe decay of the integral band‐to‐band photoluminescence (PL) at (100) orientated n‐doped GaAs (Te; n0 = 5×1017 … 1×1018cm3) in contact with aqueous 1 M HCl was investigated with the time‐correlated single photon counting technique. The PL‐decay was measured at various externally applied potentials, at constant and low density of injected carriers (pi≪n0), and at an excitation wavelength of λexc = 647.1 nm. The studies included electrodes modified by dipping in a solution of 5×10−3 M RuCl3 in 1 M HCl for 20 minutes. It was observed that the PL‐decay measured at low injection level shows a reproducible and characteristic dependence on the externally applied potential. Within the accuracy of our time‐correlated single photon counting equipment, the PL‐decay time remains nearly constant and short in the range of potential U = (−0.3 … −0.9) V(Ag/AgCl). For the nonmodified electrodes the PL‐decay time increases with increasing cathodic polarization in the range of potential U = (‐0.9 … −1.1) V(Ag/AgCl) up to a maximum at U ≈ −1.1 V(Ag/AgCl), which corresponds to the (Mott‐Schottky) flatband potential in the dark. At further cathodic polarization the cathodic current (due to the evolution of hydrogen) during the measurements becomes significant and it was observed that the PL‐decay time decreases. After a treatment with Ru3+, the behaviour in the range of potential on the cathodic side of U = −0.9 V(Ag/AgCl) is different. The experimental observations could be confirmed qualitatively by results of computer simulations based on the Two‐dimensional Semi‐Conductor Analysis Package (TOSCA). At potentials on the anodic side of the flatband potential (depletion range) the decay times are short as well as independent of the degree of the band bending, of the surface recombination velocity, and of the photocurrent, respectively. This observation will be interpreted qualitatively by including the diffusion of the minority carriers toward the (dark) depletion layer as a competitive process for the radiative recombination in the bulk. Near the flatband potential the decay time of PL increases within a potential range of ΔU ≈ 200 mV depending on the density of injected carriers as well as on the rates of the surface recombination and of the minority carrier transfer (photocurrent). Based on a qualitative explanation for this characteristic dependence of the PL‐decay time on the potential, the values of the surface recombination velocity and of the exchange photocurrent density are estimated to be S0<106 cm/s and jph,0<10−8 A/cm2, respectively, for nonmodified electrodes and S0≥106 cm/s and/or jph,0≥10−8 A/cm2, respectively, for electrodes treated with Ru3+ ions.
Temperature polarization in membrane distillation of water using a porous hydrophobic membrane
Authors: Dittscher U. , Woermann D. , Wiedner G. 
Published: July 2012

AbstractThe rate of water transport across porous membranes with a hydrophobic matrix (porosity ϵ ≈ 0.5; characteristic length of voids ξ ≈ 150 nm; thickness δ ≈ 30 μm) caused by a temperature difference between the bulk phases is studied. The voids of the membrane are filled with water vapour. The effective temperature difference (T′–T″) across the membrane is smaller than the temperature difference (T′–T″) between the bulk phases (“temperature polarization”) caused by heat conduction and by heat flow associated with the water transport. An experimental method is described and tested to determine the temperature polarization coefficient τ ( = (T′–T″)/(T′–T″) for a given experimental situation. The phenomenological transport coefficient of the membrane for water vapour has to be known from independent experiments. This method is a simple alternative to the method developed by Schofield et al. (J. Membrane Sci. 33, 299 (1987)). The dominating factor determining the temperature polarization coefficient is the value of the thickness of the two boundary layer of heat conduction at the interfaces of the membrane.
An investigation about the NH(X3Σ−) formation in the thermal decomposition of HN3
Authors: Röhrig Michael , Wagner Heinz Georg 
Published: July 2012

AbstractThe thermal decomposition of HN3 was investigated behind incident shock waves in the temperature range of 1400–1800 K at densities around 2.6·10−6 mol/cm3. The rate constant of HN3 decomposition was determined by the evaluation of NH(X3Σ−) concentration profiles to be k1 = (7±4)·1014 exp (‐(150±10) kJmol−1/RT) cm3/mol s. The pyrolysis of hydrazoic acid leads almost exclusively to NH in its electronic ground state and can therefore be used as a NH(X3Σ−) source in the temperature range of 1000–1800 K.
Spectra and temperatures of diffusion flames at high pressures to 1000 bar
Authors: Pohsner G. M. , Franck E. U. 
Published: July 2012

AbstractDiffusion flames have been produced by injection of oxygen into homogeneous dense mixtures of methane or hydrogen with supercritical water or argon. The mixture temperatures were around 500°C, pressures were varied between 50 and 1000 bar. The fuel concentrations were 30 mole percent or lower. Flames appeared spontaneously. Apparatus and procedure are described. Diffusion flame photographs to 1000 bar are shown. Emission spectra from 275 to 600 nm were recorded with a grating spectrometer and 1024 channel diode array. Emission in the visible is not of black body character and does not permit pyrometric temperature measurement. Flame temperature determination was based on the intense rotational emission of OH‐radicals in the near UV, produced by vibrational 0–0 and 1–0 transitions of the electronic A2Σ–X2∏ transition. The 0–0 band is near 306 nm. A fit program to determine rotational temperatures is developed which includes the influence of pressure broadening. The temperatures obtained for CH4 and H2 in supercritical water increase with pressure and reach 4000 to 4500 K at 1000 bar. Rotational temperatures obtained for dense argon environment are lower: 3000–3200 K. Adiabatic temperatures and calculated values for one‐dimensional diffusion flames are given for comparison.
On the potential role of DNA in an RNA world: Pattern generation and information accumulation in replicator systems
Authors: Hogeweg P. 
Published: July 2012

AbstractApparently at some stage in early evolution DNA evolved to complement RNA for information storage. In this paper we investigate under which circumstances the amount of accessible information is enhanced by using long‐lived molecules for information storage.We show that pattern formation is essential for the exploitation of information stored in long‐lived molecules.
The role of feedback circuits: Positive feedback circuits are a necessary condition for positive real eigenvalues of the Jacobian matrix
Authors: Thomas R. 
Published: July 2012

AbstractThis talk deals with the biological roles of feedback loops and their combinations. It has progressively become clear that a negative loop is a necessary (not sufficient) condition for a stable periodic behaviour and that a positive loop is a necessary (not sufficient) condition for multistationarity. Of these old conjectures (e.g. Stud. phys. theor. Chem. 28, 307 (1983)), the second has now two formal demonstrations by others (Plahte et al., Snoussi). Here, we remark that this statement can be generalised as follows. The presence of a positive loop (in the Jacobian matrix of the system) is a necessary condition for having at least one real positive root in the characteristic equation (this can be shown to directly derive from the Descartes rule) and at least one real positive root in turn is a necessary condition for multistationarity.
Enzymatic RNA synthesis in self‐reproducing vesicles: An approach to the construction of a minimal synthetic cell
Authors: Luisi Pier Luigi , Walde Peter , Oberholzer Thomas 
Published: July 2012

AbstractOur approach towards “core‐and‐shell self‐reproduction” is reviewed here. With this term, we indicate a process by which the shell‐reproduction of a spherically bounded system (micelles or vesicles) proceeds simultaneously with the replication of nucleic acid which is hosted inside the micelles or vesicles. The realization of such a process is seen as a step towards the construction of a synthetic cell model. Two chemical systems are examined here, one based on the polynucleotide phosphorylase‐catalyzed synthesis of poly(A) starting from ADP; and the other based on the enzyme Qβ replicase, which is able to catalyze the synthesis of a RNA template. In both cases, production of RNA macromolecules proceeds simultaneously with self‐reproduction of the oleic acid/oleate vesicles. One still open question is the determination of the redistribution of the guest macromolecular components during the reproduction of the shell. Within these limits, it is argued that this work offers a system which goes beyond the two approaches to self‐replication presented until now in the literature, namely the template self‐reproduction of linear sequences of oligonucleotides and the autopoietic shell reproduction of micelles and vesicles.
Coupling between ionic and electronic fluxes in mixed ionic/electronic conductors: Experiments on Co1‐δO
Authors: Janek J. 
Published: July 2012

AbstractIn investigations of the isothermal transport properties of mixed conductors the dynamical coupling between ionic and electronic partial fluxes is usually neglected. Within the formalism of (linear) irreversible thermodynamics this assumption is expressed by a vanishing cross coefficient L12 in the matrix of the phenomenological transport coefficients. By analysing the phenomenological flux equations for cation vacancies and electron holes, experiments for the determination of the cross coefficient are defined. Experimental results for the coupling effect in Co1‐δO are presented, which have been obtained from three independent techniques. The results are discussed in the light of previous theoretical considerations. It is shown that a strong coupling between cation vacancies and electron holes exists in the case of Co1‐δO. To account for this coupling, an effective charge number of ions has to be introduced for use in the formulation of ionic fluxes.
Stationary state and dynamics of birefringence and nonlinear optical properties induced by electric field poling in polymeric films
Authors: Sekkat Z. , Knoll W. 
Published: July 2012

AbstractWe present a theoretical study concerning the effect of the electric field poling process on the molecular angular distribution of polar nonlinear‐optical molecules in a polymeric environment. This is required for investigating the contribution of the molecular order to the anisotropy and nonlinear‐optical processes (second‐harmonic generation (SHG), electro‐optic Pockels (EOPE) and Kerr (EOKE) effects). We demonstrate mathematically that the order parameters at thermodynamical equilibrium are defined exactly by the spherical modified Bessel functions (An(μE/kT) = in(μE/kT)/io(μE/kT)). They can be related to Langevin functions but with complicated relations for high orders of n. Their evolution with μE/kT confirms that the second order nonlinear‐optical processes (SHG and EOPE) are more sensitive to the strength of the poling field than are the linear (birefringence) and third‐order nonlinear‐optical effects (EOKE). We show that it is possible to measure the molecular anisotropy of nonlinear‐optical molecules by quadratic electro‐optic experiments. The transients of the poling are studied with the rotational diffusion equation, characterized by a rotational diffusion constant D. This is solved using important recurrence relations of Legendre polynomials. An almost exact analytical solution is found for the physical and practical case where μE/kT is close to 1, and the nonvanishing order parameters are almost equal to the rigourous expressions given by the spherical modified Bessel functions. It is shown that the onset of birefringence and nonlinear‐optical processes (SHG, EOPE and EOKE) involves two time constants τ1,2 = [2D(2 ± √1–(μE/kT)2/5)]−1 which depend on D and μE/kT. After the removal of the poling field, the relaxation of the linear and nonlinear‐optical properties is also discussed.
The relationship between the Raoultian and Henrian activity of a solute
Authors: Näfe H. 
Published: July 2012

AbstractA relationship between the Raoultian and Henrian activity of any component in any given mixture is derived which proves to be a real alternative to the relationships known so far. The derivation reveals that the Henrian saturation activity of the respective component represents the link between the two reference systems which has to date been overlooked in the literature.
Observation of mixing‐induced twist grain boundary phases in liquid crystals
Authors: Kuczynski W. , Stegemeyer H. 
Published: July 2012

AbstractTwo twist grain boundary phases (TGB) have been observed in binary liquid crystalline mixtures exhibiting a nematic – smectic A – smectic C triple point. The observed TGB phases are very stable – for some concentrations the temperature ranges exceeded 20 K for each of them. Optical properties and textures have been investigated. Phase transitions between the phases under discussion have been determined by measurements of the dielectric permittivity and the optical rotation. A distinct influence of surface interactions on the stability of the twisted smectic A phase was observed.
Sublimation of pure C60fullerene and of C60adsorbed on MgO or graphite powders
Authors: Richter H. , Dereux A. , Gilles J. M. , Guillaume C. , Thiry P. A. , Lucas A. A. , Rozenberg R. , Spǒte A. , De Hoffmann E. , Girard Ch. 
Published: July 2012

AbstractThe sublimation of pure C60and the thermal desorption of C60fullerene deposited on MgO and graphite samples have been analyzed by mass spectrometry. The experiments have been performed in the Desorption Electron Impact mode (DEI) using a heating current between 40 and 1200 mA. The desorption from a substrate as well as the C60sublimation is a first order process with an activation energy of about 200 kJ mole−1. This value confirms the computational results obtained for van der Waals interaction. The peak broadening in the case of C60/graphite can be explained by a strong interaction between C60and the graphite substrate which is also predicted theoretically.
Spectroscopy: Past and present
Authors: Schlag E. W. 
Published: July 2012

AbstractWe present a review of historical methods in spectroscopy culminating in modern techniques made available by the advent of laser technology. Spectroscopy is undergoing a worldwide renaissance as a result of these methods which point to entire new fields of application. Special examples are given, such as mass spectrometry, very high resolution methods, photoelectron spectroscopy and ZEKE spectroscopy as well as modern ultrafast techniques.
From molecular processes to global mechanisms of chemical transformations
Authors: Troe J. 
Published: July 2012

AbstractMany of the founders of modern gas phase reaction kinetics were members of the Deutsche Bunsengesellschaft für Physikalische Chemie (the former Deutsche Elektrochemische Gesellschaft). The evolution of this field from its beginnings around 1894 towards today, from qualitative understanding to quantitative modelling is reviewed. The connection between global mechanisms and elementary reaction steps is exemplified by sensitivity tests. Elementary reaction rates then are related to potential energy surfaces showing intermediate energy maxima, i.e. single activated complexes, or intermediate energy minima, i.e. involving several activated complexes.