bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nonlinear Behavior in the Optical Spectra of Solid Fullerene C60
Authors: Diehl M. , Degen J. , Schmidtke H.‐H. 
Published: July 2012

AbstractOptical emission spectra of solid C60 have been recorded at 1.9 K. Several vibronic transitions are observed. In particular the dependence of the emission spectrum with respect to the excitation intensity has been studied at room temperature and at 12 K under excitation with 514.5 nm and 488.0 nm laser radiation. The emission intensity increases with excitation intensity stronger than linear. At higher excitation powers an additional optical transition centered at 16500 cm−1 becomes dominant. In an absorption experiment in solution (1.4‐10−5 mol/l), the absorbed power of light is also nonlinear with respect to the excitation power.
Sorption and Diffusivity Measurements of Cyclohexane+Benzene and Cyclohexene+Toluene Mixtures in Polyurethane Membranes. Model Calculations of the Pervaporation Process
Authors: Enneking L. , Stephan W. , Heintz A. 
Published: July 2012

AbstractData of vapor sorption measurements of the solvents cyclohexane, benzene and toluene in polyurethane (PU) membranes are presented. Vapour sorption isotherms have been obtained from equilibrium data. Kinetic sorption data have been used for determining diffusion coefficients of the solvents in the membrane material. Further measurements of the individual solubilities of liquid cyclohexane+benzene and cyclohexane+toluene mixture components in PU‐membrane material have been carried out using the so‐called swelling density method and a gaschromatographic analytical method. Vapor sorption isotherms as well as solubility data of the liquid mixtures can be described with the UNIQUAC‐model in good agreement with experiments. All results obtained for solubilities and diffusion coefficients are used for predictive calculations of fluxes and separation diagrams in the pervaporation process of cyclohexane+benzene and cyclohexane+toluene mixtures through PU‐membranes. The basis of these model calculations is the solution‐diffusion model. Predicted results of pervaporation agree well with experimental data taken from literature provided diffusion coupling of the components permeating the membrane is taken into account.
Dilute Near‐Critical Solutions of Iodine in Xenon: Determination of V, S and (δp/δx) from Solubility Data
Authors: Fernández Diego P. , Fernández‐Prini Roberto 
Published: July 2012

AbstractUsing recently determined solubility data for solid iodine dissolved in near‐critical xenon, we have calculated the partial molar entropy and volume of the solute. These quantities show a strong density dependence in the vicinity of the solvent critical point. The quantity (δp/δx)V,T' which does not show a strong divergence in the critical region, was also determined from experimental data. Two procedures have been employed to describe the latter quantity and the solubility itself. It is shown that a first order perturbation method may be employed to describe the observed behaviour with a cross intermolecular energy parameter, ε12, which, for low densities becomes dependent on the fluid density, but not on the temperature. The PYLJ integral theory is shown to account very well for the data with the value of ε12 obtained employing the Lorentz‐Berthelot combining rule.
Self‐Diffusion of 18F‐Ions in a PPS‐Cation‐Exchange Membrane
Authors: Daniel T. , Seidel W. , Sattler E. L. , Seibold G. 
Published: July 2012

AbstractSelf‐diffusion of 18F ions in a poly‐phenol‐sulphonate (PPS) membrane was investigated by counting continuously the γ,γ‐coincidence emitted from positron annihilation processes. The apparent coefficient of self‐diffusion was determined for different concentrations.
Vapour‐Liquid Equilibria of Square‐Well Fluids of Variable Width by Barker‐Henderson Perturbation Theory I
Authors: Szalai I. , Liszi J. 
Published: July 2012

AbstractVapour‐liquid equilibria of square‐well fluids of variable width (λ = 1.375, 1.5, 1.75 and 2.0) were studied based on the Barker‐Henderson perturbation theory. Orthobaric densities, vapour pressures and heats of vaporization were calculated with local and macroscopic compressibility approximation. Comparison of the results with those of McLure and et al. [J. Chem. Phys. 96, 2296 (1992)] obtained with Monte Carlo simulation on Gibbs ensemble showed good agreement, except for results obtained close to the critical temperatures.
Properties and Design Criteria of Second‐order Nonlinear Optical Materials Based on Side Chain Polyesters with an Aromatic Main Chain
Authors: Servay Th. K. , Winkelhahn H.‐J. , Schulze M. , Boeffel C. , Neher D. , Wegner G. , Kalvoda L. 
Published: July 2012

AbstractPolymers composed of an aromatic polyester backbone to which NLO‐active chromophores and flexible alkyl side chains are attached have been developed as a class of second order nonlinear optical materials.Thin films suitable to be used as waveguides could be produced by spin coating technique and were investigated for their NLO‐properties. The polymers were investigated by optical microscopy, DSC, X‐ray diffraction, 2H‐NMR, dielectric relaxation spectroscopy and — for their optical properties — by the method of attenuated total reflection of visible light.The solid state structure is best described by an arrangement of alternating layers of polyester backbones and flexible side chains with good layer correlation, especially for derivatives with long side chains. The low nonlinear optical response of these derivatives seems to be due to dipole pair formation of the chromophores. Polyesters with short side chains show a similar main chain packing but substantially different optical properties. In addition, they could be macroscopically aligned in strong magnetic fields. Anisotropic samples prepared in this way indicated a restricted orientational freedom of the chromophores in the space available between the backbone layers. Consequently the ratio of the second order susceptibilities χ versus χ deviated significantly from the expected isotropic value of three.
Molecular Weight Dependence of the Rotational Diffusion Constant and the Rotational Viscosity of Nematic Side‐Group Polymers
Authors: Götz S. , Stille W. , Strobl G. , Scheuermann H. 
Published: July 2012

AbstractA combination of dielectric relaxation spectroscopy and measurements of the rotational viscosity by director reorientation experiments was used to study nematic side‐group polymethacrylates with different molecular weight. The contribution γ of the mesogenic groups to the total rotational viscosity γ is estimated on the base of Marrucci's theory from the rotational diffusion constant Dr obtained by relaxation frequency determinations. γ then is used to separate the contribution Δγ1 of the friction due to rearrangements of anisotropic ordered polymer backbones to γ. The molecular weight dependence of Δγ1 can be described by a power law, as predicted by Brochard's theory. The resulting exponent gives evidence for the presence of nonentangled random coil conformations.
Freely‐Suspended and Transferred Freely‐Suspended Films of Polymeric Liquid Crystals
Authors: Decher G. , Reibel J. , Honig M. , Voigt‐Martin I. G. , Dittrich A. , Ringsdorf H. , Poths H. , Zentel R. 
Published: July 2012

AbstractFreely‐suspended (FS) liquid‐crystal (LC) films of a polymethylsiloxane homo‐ and a copolymer with different mesogenic side groups have been prepared and investigated. For both substances the preparation of the films succeeded only in the isotropic phase but the higher ordered phases were reached after cooling. The films of the homopolymer have only been obtained with thicknesses estimated to be in the pm‐range and with an unusual “Book‐Shelf” orientation of the smectic layers. In contrast, the films of the copolymer were thinner and showed a homeotropic orientation of the mesogens in the smectic A phase. Interestingly, this material exhibited a different layer spacing in film and bulk, although no differences in the phase transition temperatures could be detected within experimental error. FS‐films of the homopolymer have been transferred to solid supports. Both the FS and the transferred freely‐suspended (TFS) films of this material were particularly stable as compared to films of low molecular weight compounds.
Isothermal Switching of Phases in Lyotropic Liquid Crystalline Surfactant Systems via Photoreactions of Solubilized Molecules
Authors: Wolff Thomas , Klaußner Bernhard , Nees Dieter 
Published: July 2012

AbstractLight induced phase transitions were found in lyotropic liquid crystalline systems of aqueous cetyltrimethyl‐ammonium bromide (CTAB) and of Aerosol‐OT(AOT)/decane/water: the isothermal transitions isotropic → nematic and isotropic → hexagonal in CTAB systems were triggered by the photocyclization of a solubilized naphthyl vinyl ether, the transition isotropic → inverse‐hexagonal in the ternary AOT system was induced by the trans‐cis photoisomerization of a solubilized stilbazolium salt. The transition time (between starting irradiations and detecting anisotropic phases) was found to increase with the difference between irradiation temperature and transition temperature in the non irradiated case; transition times were shorter by two orders of magnitude in the AOT‐system as compared to CTAB. The position of isotropic/liquid crystalline phase borders produced by partial irradiation of layers of aqueous CTAB were more stable in hexagonal as compared to nematic systems.
Chemistry of Colloidal Silver: Reactions of Lead Atoms and Small Lead Aggregates with Agn
Authors: Henglein Arnim , Holzwarth Arnold , Janata Eberhard 
Published: July 2012

AbstractThe reactions of lead atoms with 70 Å colloidal silver particles in aqueous solution are investigated. The lead atoms are generated by a short pulse of high energy radiation. The formation of a lead mantle around the silver particles is recognized by the changes in the shape of the surface plasmon absorption band of the silver particles. At low intensities (low lead atom concentration of 5·10−8 M) almost all the lead atoms generated reach the silver particles before they form larger aggregates by coalescence reactions in the bulk of the solution. The specific rate of the reaction of lead atoms with silver particles is about 5 times smaller than expected from a diffusion controlled rate. The plasmon absorption band is blue‐shifted when the lead atoms react with the silver particles. It is concluded from the details of this shift that the first Pb atoms reaching the silver particles transfer an electron to them, and that the atoms, which arrive later, are just deposited. Time resolved measurements show that small aggregates of lead, which are formed at higher intensities, can still contribute to mantle formation around the silver particles. Lead particles with agglomeration numbers larger than 10 to 20 do no longer contribute to lead deposition; they form colloidal lead.
Information of the Nature of the Transition State of the Addition of Pyrazole to an α,β‐unsaturated Fischer Carbene Complex from a Combined Solvent, Temperature and Pressure Dependence Study
Authors: Pipoh Rolf , Martinez Pablo , Eldik Rudi Van 
Published: July 2012

AbstractThe temperature and pressure dependence of the addition of pyrazole to the carbene complex (CO)5WC[(OC2H5)(C2C6H5)] in a series of solvent mixtures (acetonitrile/toluene) were studied, and the corresponding activation parameters are reported. The solvent dependence data enables the estimation of the radius and dipole moment of the transition state, following different theoretical treatments. The results are in good agreement and demonstrate that the transition state is significantly more polar than the reactant state, and leads to the formation of a zwitter‐ionic intermediate.
Semi‐Empirical Calculations on the Optical Absorption of Methylviologen and p‐Cyanophenylviologen in Different Oxidation States
Authors: Mizuguchi Jin , Karfunkel Heinrich 
Published: July 2012

AbstractViologen compounds are known as materials suitable for electrochromic displays based on the electrochemical color change. INDO /S, PM3 and MNDOC calculations have been carried out on methylviologen and p ‐cyanophenylviologen in order to interpret the spectral changes in the visible region upon electrochemical reduction. The viologens investigated are colorless in the dication state, but they exhibit an intense optical absorption band in the visible region due to the formation of monocation radicals upon reduction. Molecular geometries are optimized by the AM1 and PM3 methods for the initial dication state, monocation radical state and fully‐reduced neutral state. Bipyridyl rings in both methylviologen and p ‐cyanophenylviologen are considerably twisted by about 40–50° in the initial state, but these become almost planar in the first‐reduced state and completely planar in the second‐reduced stat e. Optical absorptions are calculated on the basis of the optimized geometry. The results show a satisfactory agreement with experimental values, although the calculated longest‐wavelength absorption in the visible region is overestimated towards longer wavelength s. The planarity of the bipyridyl rings as well as the resulting delocalization of the unpaired electron of the free monocation radical is found to be important to cause the appearance of the optical absorption band in the visible region.
Treatment of Ionic Transport Processes in Electrolytic Conductivity by the Dynamic Frictional Formalism of Nonequilibrium Thermodynamics
Authors: Vink Hans 
Published: July 2012

AbstractIonic transport in electrolytic conductivity has been considered in terms of the dynamic frictional formalism of nonequilibrium thermodynamics. The treatment includes multicomponent electrolyte mixtures and solutions containing polyelectrolytes and colloids. It is shown that the dissipation function for the process can be split into two terms characterising interionic friction and ion‐solvent friction, respectively. The corresponding friction coefficients are well‐defined and experimentally determinable. They have been evaluated for a number of binary electrolytes from electrolytic conductivity data found in the literature. For 1:1 electrolytes the reduced interionic friction coefficients vary slightly and in a regular fashion with concentration. For higher valency type electrolytes deviations from this behaviour occur, which in general can be explained by ionic association.
Formation of Nanometer‐Size Silicon Particles in a Laser Induced Plasma in SiH4
Authors: Fojtik A. , Giersig M. , Henglein A. 
Published: July 2012

AbstractCrystalline silicon particles of cubic structure are formed in the plasma which is initiated in an argon‐silane mixture by a focussed 694 nm Ruby laser flash. Part of the particles can be dissolved as colloid in organic solvents. The solubilization is increased by small amounts of 1,3‐propane‐dithiol. The raw material has a broad size distribution. Centrifugation and filtration methods are applied to obtain samples with narrow size distribution. Small silicon particles have structured absorption spectra. The particles luminesce after etching with HF under air. The larger particles have a red luminescence (peaking at 720 nm) and the smaller particles emit a blue luminesce. The luminescence effects are explained by size quantization of the electronic energy levels in the particles.
Flow Characterization in Particle‐Loaden Coal Burner Systems
Authors: Schnell Uwe 
Published: July 2012

AbstractIn pulverized coal combustion, one of the most important parameters for pollutant formation in the near‐burner zone is the flow and mixing process of fuel and oxygen. To study the near‐field aerodynamics of pulverized coal burners, non‐intrusive optical measurements with Laser Doppler Velocimetry (LDV) were performed. In order to provide a better understanding of the mixing process of the small coal particles with the surrounding combustion air, the unavoidable formation of ropes and the dispersion of the particles was first investigated in an idealized two‐phase flow with glass beads under isothermal conditions.Furthermore, non‐intrusive measurements of velocity and turbulence intensities in the complex flow situation of radiating pulverized coal flames have been performed using a two component LDV system with a 15 W Argon‐ion laser, operating in backscatter mode. It has been used for flow characterization in a semi‐industrial pulverized coal combustion facility with a maximal thermal load of 500 kW. LDV is an indispensable research instrument to study the interdependencies between fluid flow, combustion reactions and pollutant formation processes in reactive flows. Additionally, results of numerical simulation obtained with a pulverized coal combustion code are validated with the LDV measurements and the experimentally observed phenomena are further explained. The influence of the flow pattern in the near‐burner region on pollutant emission will be discussed.
In Situ Measurements of Concentration and Temperatures. Laser Raman Diagnostics for Propulsion Systems Development
Authors: Eckbreth Alan C , Anderson Torger J. , Shirley John A. 
Published: July 2012

AbstractRaman‐based laser diagnostics for combustion temperature and major species measurements in propulsion development test facilities are discussed. Focus is primarily directed toward multi‐color, coherent anti‐Stokes Raman spectroscopy (CARS) techniques for simultaneous multiple species capability and ultraviolet spontaneous Raman scattering vis‐a‐vis its utility for hydrocarbon‐fueled combustor testing. Field instruments employed for feasibility demonstrations and measurement programs are described.
Surface Analysis by Laser Ionization
Authors: Schröder H. , Wagner M. , Kaesdorf S. , Kompa K. L. 
Published: July 2012

AbstractA new reflecting time of flight mass spectrometer is described which allows to display absolute saturation of laser ionization. For each specific chargeq/mthe new TOF instrument creates two ion bunches containing the ions originating respectively inside and outside a sharply‐limited acceptance volume of the spectrometer. Thus quantification of laser ionization is possible. This method has been applied to non‐resonant KrF excimer laser post‐ionization of sputtered metal atoms. It may be developed into a very sensitive tool for quantitative surface analysis.
On‐Line Diagnostics for Industrial Laser Surface Treatments
Authors: Bergmann H. W. 
Published: July 2012

AbstractThe paper presents some recent developments in sensor technology for on‐line diagnostics and control of laser materials processing. The results focus on three topics e.g.

—pyrometric temperature measurements and on‐line output power control of cw‐lasers
— quality control using differential reflectometry
— short time detection techniques for process monitoring of laser beam interaction with materials during short (50 ns) and intense (MW/cm2 to GW/cm2) laser pulses.
Investigations on a Spark‐Ignited Engine Using Two‐Dimensional Laser‐Induced Fluorescence
Authors: Bäuerle B. , Hoffmann F. , Behrendt F. , Warnatz J. 
Published: July 2012

AbstractThe method of laser‐induced fluorescence (LIF) was applied to a modified industrial two‐stroke engine with a single cylinder and spark ignition. Together, the disc‐shaped combustion chamber and the low clearance height of the piston ensure mainly two‐dimensional flame propagation. Formaldehyde is used as a natural tracer species for detecting and studying exothermic centres (so‐called “hot spots”) in the end gas. The latter contain a larger amount of formaldehyde than the enclosing end gas due to the slightly higher temperatures. To obtain two‐dimensional excitation of the formaldehyde a laser light sheet enters from sideways through a ring‐shaped quartz window. The fluorescence is detected via a full‐size top window by means of an ultrashort‐exposure ICCD‐camera, and the frames are stored in a PC. Here, frames are presented which show 2D‐LIF of formaldehyde in non‐knocking as well as in knocking cycles.
An ab initio investigation of structure and energetics of clusters KnCln and LinFn
Authors: Ochsenfeld Christian , Ahlrichs Reinhart 
Published: July 2012

AbstractResults of a systematic study of clusters KnCln and LinFn up to n = 32 are reported within self‐consistent‐field (SCF), second‐order Møller‐Plesset perturbation theory (MP2), and the single‐ and double‐excitation coupled cluster method with a perturbational estimate of triple excitations CCSD(T). Stationary geometries are characterized as local minima by SCF force field calculations up to K9Cl9 and Li8F8, respectively.The clusters KnCln show great similarities with previously studied NanCln. The energetically most stable isomers of even the smaller potassium chloride clusters show a clear preference for geometries which are fragments of the solid state lattice. This effect is enhanced by electron correlation.Lithium fluoride clusters, LinFn, show a different behaviour: hexagonal structures (stacked six‐rings) are prefered to lattice fragments (cubic) on the SCF level at least up to Li18F18. This preference is only slightly reduced by electron correlation.The present results for KnCln and LinFn allow for an estimate of lattice energies by extrapolation n → ∞, which is in good agreement with, experiment. The structure constants found for K32Cl32 approach that of the solid. This is different for Li32F32: clusters of LiF show a slower convergence towards bulk properties on increasing cluster size.
Oxidative decarboxylation of cyclohexane monocarboxylic acid as a degenerate branching chain reaction. I. kinetics
Authors: Nemes I. , Héberger K. , Keszler Á. , Vasvári G. , Gál D. , Cotarca Livius , Delogu Pietro 
Published: July 2012

AbstractKinetics of product accumulation during the oxidative decarboxylation of cyclohexane monocarboxylic acid has been followed by GCMS, inhibitor and chemiluminescence methods. Results indicate that in the degenerate branching chain process selective (peroxy) radicals abstract predominantly tertiary hydrogen atoms from the substrate while non‐selective (e.g. hydroxyl, alkoxy) radicals attack also secondary hydrogen atoms. The rate constant of the chain propagation was found to be kp = 7.5×106exp(‐57.6kJmol−1/RT) 1mol−1 s−1. Furthermore it has been established, that the oxidative decarboxylation proceeds via two parallel pathways: one resulting in cyclohexanone, while the other avoiding the formation of the latter.
Substituent effects on the intramolecular electron exchange reaction in 5‐substituted 1,3‐dinitrobenzene radical anions
Authors: Telo João P. , Shohoji M. Cândida B. L. 
Published: July 2012

AbstractNine new radical anions of 1,3‐dinitrobenzenes with various substituents on position 5 (2, 3, 5–7, 9–11 and 13) were prepared by electrochemical reduction in acetonitrile and studied by EPR at temperatures between 240 K and 320 K. Another eight known radicals of the same type were reexamined in the same conditions in order to complete the set of data. Their EPR spectra showed alternating linebroadening effects due to intramolecular electron exchange induced by asymmetric solvation of the two nitro groups. Rate constants at 293 K range from 1.4×109s−1 (3,5‐dinitrophenolate) to 1.2×1010s−1 (3,5‐dinitrobenzonitrile). Good Hammett correlations between the rate constants of intramolecular electron exchange and the parameter σm of the substituent on position 5 were obtained. The reaction is accelerated by electron withdrawing groups. ρ values range from 0.95 at 240 K to 0.74 at 320 K. Activation parameters were estimated by using the Rips and Jortner equation for the rate constant of a uniform adiabatic reaction. ΔG* was found to increase with the electron donating ability of the substituent, mainly due to an increase of the interaction between the reactants and the solvent. The pre‐exponential factor A is constant within the experimental error, as predicted by theory.