bluuebunny/crossref_metadata_2025_split huggingface dataset:
Migration of Air Bubbles in Silicone Oil under the Action of Buoyancy and Thermocapillarity
Authors: Morick F. , Woermann D. 
Published: July 2012

AbstractThe buoyancy driven migration of air bubbles in dimethyl‐polysiloxane and phenylmethyl‐polysiloxane under isothermal conditions is studied. The radius of the migrating bubbles increases or decreases with time The changes of the radii are attributed to an exchange of gas between the bubbles and polysiloxane. The direction of the gas transport depends of the state of saturation of the liquid with air. The velocity of migrating air bubbles as function of time in dimethyl‐polysiloxane can be described by the Rybczynski‐Hadamard relation using the instantaneous values of the velocity of migration and the instantaneous value of the radius of the bubbles. The analysis of corresponding the data obtained with air bubbles migrating in phenylmethyl‐polysiloxane reveal that in that liquid the velocity of migration is described by the Stokes relation using the instantaneous values of the velocity and the radius of the bubbles. The bubbles behave like “hard spheres with a time dependent radius”. The different behavior of air bubbles in the two types of polysiloxane is attributed to structural differences between macromolecules forming them. The observed thermocapillary motion of air bubbles in dimethyl‐polysiloxane in the presence of buoyancy forces is described by the theory of Young, Goldstein, Block (J. Fluid. Mech. 6, 350 (1959)). No thermocapillary motion of air bubbles is found in phenylmethyl‐polysiloxane. This is expected from the behaviour of air bubbles in phenylmethyl‐polysiloxane under isothermal conditions.
ARAS Measurements on the S(1D) Formation in Shock Heated COS/Ar mixtures
Authors: Woiki D. , Roth P. 
Published: July 2012

AbstractThe formation of electronically excited S(1D) atoms was studied during the thermal decomposition of carbonyl sulfide behind reflected shock waves by using atomic resonance absorption spectroscopy (ARAS). The experiments were performed in highly diluted mixtures of Ar with relative concentrations of COS between 8 to 100 ppm in the temperature range 2130 K≤T≤3020 K at pressures of about 1.2 bar. The measured rate of the linear S(1D) increases divided by the initial reactants was found to obey the Arrhenius law: magnified image.Assuming a fast thermalisation between the (3P) and (1D) states of S atoms this result is in agreement with previous measurements of the S(3P) formation during the thermal decomposition of COS reported recently [1].
Morphology Dependent Resonances in Raman Spectra of Optically Levitated Microparticles: Determination of Radius and Evaporation Rate of Single Glycerol/Water Droplets by means of Internal Mode Assignment
Authors: Schaschek K. , Popp J. , Kiefer W. 
Published: July 2012

AbstractAn experimental setup for studies of morphology dependent resonances (MDRs) in Raman spectra of optically levitated microdroplets is described. This instrumentation is used for the study of MDRs in the Raman spectra of glycerol/water (3:1) droplets. Furthermore we show how the MDRs observed in the Raman spectra and their change with time can be used to determine the radius and the index of refraction of single optically levitated droplets with very high accuracy. We further show how the results of this study can be used to calculate the efficiency factor of the radiation pressure and compare it with the experimental monitored laser power.
Effect of the Kinks Blockage by Adsorbed Hydrogen on the Kinetics of Iron Electrode
Authors: Plonski I. H. 
Published: July 2012

AbstractTheoretical relationships for the kinetics of iron corrosion in acid media were derived taking into account the preferential adsorption of the intermediate atomic and molecular hydrogen on the kinks, assumed as main dissolution sites. Anodic initial and steady state Tafel slopes of 59 and 25 … 45 mV, respectively, anodic reaction order with respect to OH− between 1 and 2, inductive transients, as well as open circuit values dEcor/dpH = ‐59 …‐47 mV and d log icor/dpH = 0.0…‐1.0 were found, in agreement with the experimental data reported in the literature.
Raman‐Spectroscopic Evidence for Four‐Fold Coordinated Titanium in Silicalite I
Authors: Pilz W. , Peuker Ch. , Tuan V. A. , Fricke R. , Kosslick H. 
Published: July 2012

AbstractRaman spectroscopic investigations reveal the synthesis of Ti‐Silicalite I with four‐fold coordinated titanium. A new Raman band at 960 cm−1 assigned to tetrahedrally coordinated titanium in the SiO2 matrix is found. Non‐framework TiO2 species containing octahedrally coordinated titanium could be also distinguished.
Dielectric Relaxation Spectroscopy of Electrolyte Solutions: LiClO4 in Tetraethyleneglycol Dimethylether
Authors: Schütz G. , Stockhausen M. 
Published: July 2012

AbstractThe frequency dependent complex permittivity of LiClO4 solutions in tetraethyleneglycol dimethylether (tetraglyme) with concentrations up to 1.5 mol/1 is measured at 20 °C over a broad frequency range (5 MHz to 72 GHz). Apart from the conductivity contribution, there are two distinguishable absorption regions. The relaxation at higher frequencies is due to the solvent. The lower frequency feature is due to ionic processes. It comprises two spectral components, which both are unlikely to be caused by rotational tumbling motion of well‐defined ionic species (e.g. ion pairs) but rather seem to involve some other processes such as confined translational modes of ionic motion.
Catalytic Oxidation of Sulfurous Acid by Molecular Oxygen. Investigations on the Electrochemical Estimation of the Catalytic Activity
Authors: Timpe O. , Schlögl R. 
Published: July 2012

AbstractThe catalytic oxidation of sulfurous acid S(IV) to sulfuric acid S(VI) can be monitored by measuring the increasing conductivity of the solution while the reaction proceeds. The turnover‐frequency and thereby the activity of the catalyst sample examined is calculated from the conductivity derivative by multiplying it with a factor (f); this factor is based on the difference between the molar conductivities of the reaction product S(VI) and the educt S(IV). The factor was found to depend on both the temperature and slightly on the starting concentration [SIV]0. An empirical interpolation formula for calculation of the factor was derived from the calibration experiments. The molar conductivities (λ) of S(IV) and S(VI) were determined at 6 different temperatures from 228 to 313 K in the concentration range from 0.1 to 2.0 mM. To illustrate the method some applications are presented. These include measurements with Fe‐graphite and NH3 treated carbon black samples as catalysts. For the latter the catalytic activity is discussed in relation to XPS surface characterisation and elemental chemical analysis. The exemplary experimental runs prove the method's plausibility but indicate that such reactions are very complex in their kinetics: when estimating catalytic activities reaction parameters like especially the temperature and the S(IV)‐concentration should be adjusted carefully, to warrant reproducible results.
On the Kinetics of Hydrogen Bonded Association of Pyri(mi)dines with Hexanolactam in Cyclohexane
Authors: Hopmann Rudolf F. W. 
Published: July 2012

AbstractThe kinetics of the formation of bivalently hydrogen bonded complexes of hexanolactam with 2‐amino‐pyri(mi)dines in cyclohexane is diffusion controlled with association rate constants of 3.2·1010 (2‐aminopyrimidine, 2AP), 1.65·1010 (2‐amino‐pyridine, APA) and 0.9·1010 M−1·s−1 (2‐amino‐6‐methyl‐pyridine, AMP), respectively. In reference to APA, 2AP is faster, because there is a second nuclear nitrogen atom in α‐position to the amino group capable of accepting a hydrogen bond, whereas the association kinetics of AMP is slower, because the methyl group in α‐position to the ring nitrogen exerts an steric effect. The evaluation of the kinetic amplitudes supports simplexation over duplexation.
Continuous Coupling of Chaotic and Periodic States of Chemical Oscillators With and Without Time Delay
Authors: Zeyer K.‐P. , Holz R. , Schneider F. W. 
Published: July 2012

AbstractWe present continuous coupling experiments and calculations of two mutually flow‐rate‐coupled Belousov‐Zhabotinsky (BZ) oscillators. The Ce4+‐concentration of one BZ‐reactor controls the flow rate into the other BZ‐reactor and vice versa. Flow‐rate control is proportional to the difference between the (time delayed) Ce4+‐and an average Ce4+‐concentration. When both period one (P1) BZ oscillators are weakly coupled, the P1 oscillations are retained in both oscillators whose periods increase with increasing coupling strength. At high coupling strengths statistically aperiodic oscillations are produced. The introduction of time delayed coupling does not reduce the noise in the strongly coupled system. We distinguish between statistical aperiodicity due to experimental noise and deterministic chaos due to the system's nonlinear dynamics. At constant coupling strength a rising delay time produces a “sawtooth” like behaviour of the P1 periods. Mutual flow‐rate‐coupling of two chaotic states without time delay retains chaos in both reactors at low coupling strengths. When the coupling strength increases the Hausdorff dimension passes through a maximum (≈︁ 2.5). At very high coupling strengths, a transition from chaos to periodic states takes place.
Magnetic Relaxation under Fast Internal Rotation in Liquid Part II). A Variable Temperature NMR Study Using 13C Spin‐Lattice Relaxation Time Measurements in Liquid Mesitylene
Authors: Suchanski W. 
Published: July 2012

AbstractThe 13C nuclear spin‐lattice relaxation times of ring and methyl carbons in liquid mesitylene (1,3,5‐trimethyl‐benzene, 1,3,5‐TMB) have been measured as a function of temperature. The results have been analyzed in terms of two relaxation mechanisms: intramolecular dipole‐dipole coupling and spin‐rotation interaction. In order to separate these contributions, also the nuclear Overhauser enhancement factors have been studied. The results have been analyzed in terms of the theory of Gordon and Langevin models for internal motion of methyl groups with a low barrier to internal rotation and are in good agreement with predictions of both theories.
Computer Simulation of Chiral Liquid Crystal Phases II. The Use of Twisted Boundary Conditions
Authors: Memmer R. , Kuball H.‐G. , Schönhofer A. 
Published: July 2012

AbstractUsing the Monte Carlo technique, we study an ensemble of N = 256 particles interacting via a chiral modified Gay‐Berne potential introduced in part I. We introduce twisted boundary conditions which allow the formation of helical phases with lower potential energy and a larger pitch in comparison with the results of simulations using cubic periodic boundary conditions. The amount of chiral and achiral energy contributions to the total potential energy are discussed for the obtained cholesteric, helical smectic and blue phases.
Dielectric Studies on Liquid Crystals under High Pressure: V. Static Permittivity and Low Frequency Relaxation Process in 4‐n‐Heptyl‐4'‐Cyanobiphenyl (7CB)
Authors: Brückert T. , Würflinger A. , Urban S. 
Published: July 2012

AbstractDielectric studies have been performed on 4‐n‐heptyl‐4'‐cyanobiphenyl, 7CB, between 305 and 341 K and at elevated pressures up to 150MPa. From measurements of the dielectric relaxation (up to 13 MHz) we calculate the activation enthalpy (decreasing with increasing pressure) and the activation volume (decreasing with increasing temperature) in the nematic state. The low‐frequency process connected with molecular rotations about the short molecular axis was analysed in terms of the Martin‐Meier‐Saupe theory, yielding q ≈︁ 5 kJ/mol for the nematic potential. The dielectric behaviour is similar to previous results for 5CB and 6CB.
Liquid Crystals in Information Technology
Authors: Schadt Martin 
Published: July 2012

AbstractTo establish and to improve the increasingly complex interaction between man and machine requires sophisticated, versatile and compact displays. The liquid crystal display (LCD)‐technology is the only technology which is capable to display equally well the simple time information of digital wrist watches as well as the complex color images of future high definition television sets; it is a key technology in the years to come.There have been three major prerequisites for the establishment and the success of the LCD technology since the early 1970s. Namely, the discovery of potent electro‐optical field effects on which LCDs are based, the successful search for liquid crystal (LC) materials with effect‐specific properties, and last but not least, the development of the technological tools required for manufacturing LCDs.Virtually all of today's commercial LCDs are based on the twisted nematic (TN)‐ or on various supertwisted nematic (STN)‐effects. Those LC‐material properties and electro‐optical effects that essentially determine the operability of LCDs are reviewed. The performance of TN‐LCDs, STN‐LCDs and optical mode interference (OMI)‐LCDs in modern, high information content applications is shown. Included are recent developments such as TV compatible, time multiplexed OMI‐LCDs and operation of TN‐LCDs in bright LCD‐color projectors whose functional parts, such as polarizers, optical filters and modulators consist entirely of liquid crystal devices. Moreover, it is shown that planar, uniaxial alignment of liquid crystals cannot only be achieved by conventional, mechanically treated substrates, but also by a novel, photo‐induced alignment concept. Photo‐induced alignment opens up the possibility to realize azimuthal variations of the liquid crystal director on LCD‐substrates and the possibility to achieve high resolution director pattern. Thus, among many other possibilities, LCD‐stereo projection, in‐situ interference filters for STN‐LCDs and new optical storage applications become feasible.
The β‐Relaxation in Ferroelectric Liquid Crystals
Authors: Schönfeld A. , Kremer F. 
Published: July 2012

AbstractBroadband dielectric measurements (102 Hz to 109 Hz) on ferroelectric liquid crystals (FLC) beeing oriented in the bookshelf geometry were performed. In the frequency regime between 106 Hz and 109 Hz one dielectric relaxation process — the β‐relaxation — is observed and it is shown — for the first time — that this process has a DC‐bias field dependence similar to the (low frequency) Goldstone‐mode. The β‐relaxation is assigned to the hindered rotation (libration) of the mesogene around its long molecular axis. It has an Arrhenius‐type temperature dependence. A critical behaviour at the phase transition SA/S (nonferroelectric/ferroelectric) is not observable. These experimental findings lead to a modified picture for the molecular origin of ferroelectricity in FLC.
Electrooptical Properties of Liquid‐Crystalline Rigid Rod‐Like Polymers with NLO‐Active Sidegroups
Authors: Winkelhahn H.‐J. , Servay Th. K. , Kalvoda L. , Schulze M. , Neher D. , Wegner G. 
Published: July 2012

AbstractThe second order nonlinear susceptibility χ(2) of a novel class of poled polymer films was investigated by means of the attenuated total reflection (ATR) method. The polymers are composed of an aromatic polyester backbone to which NLO active stilbene chromophores and flexible alkyl side chains are alternately attached. The optical properties and the dynamics of relaxation of the poled state were strongly depending on the length of the aliphatic side chains. The relaxation determined at different temperatures above and below Tg showed a temperature dependence that differs from an Arrhenius type behaviour. An empirical equation which relates the temperature dependence of the relaxation times to the glass transition temperature is presented.The polyester main chains could be macroscopically aligned in strong magnetic fields. Electric poling of the samples with aligned main chains results in ratios of χ χ which deviate significantly from the ratio of 3 one obtains for samples with isotropically distributed main chains. This behaviour is explained by the solid state structure of this kind of polymer, which is best described by a sequence of alternating layers of polyester backbones and flexible side chains.
Collective Motions and Viscoelastic Properties in Main Chain Liquid Crystal Polymers. A Deuteron Spin Relaxation Study
Authors: Heaton N. , Reimer D. , Kothe G. 
Published: July 2012

AbstractMultipulse dynamic NMR techniques have been employed to investigate collective motions and viscoelastic properties in a main chain liquid crystal polymer and low molar mass analogues in the nematic phase. Transverse deuteron spin relaxation times measured as a function of pulse spacing using a modified Carr‐Purcell‐Meiboom‐Gill pulse sequence are analysed in terms of a simple hydrodynamic model for nematic director fluctuations. Combining these results with those of NMR slow sample spinning experiments allows determination of the effective viscosity and the average elastic constant of the material. Results are compared for compounds with different molecular weights and with the results of analogous proton field‐cycling experiments. The viscosity is found to increase approximately as the square of the molecular weight, Mn, whilst the elastic constant shows a much shallower Mn dependence apparently tending to a plateau value at moderate molecular weights.
Flüssigkristalle mit fluorhaltigen Alkylgruppen
Authors: Bartmann Ekkehard 
Published: July 2012

AbstractA series of compounds with the basic structures typical for liquid crystals (cyclohexyl benzenes, biphenyles, bicyclohexylbenzenes and cyclohexylbiphenyls) and alkyl groups containing fluorine (methyl to pentyl, mono‐ to perfluorinated, attached to the benzene end of the core) was investigated. Their physical properties relevant for application in LC displays such as phase ranges, dielectric anisotropies and viscosities are discussed as functions of the structural parameters of the fluorinated alkyl chains such as chain length, content of fluorine and position of the fluorine atoms in the chain.
Characterization of Mesoscopic Structures from Polymerizable Amphiphiles: The Water‐SSPOM System
Authors: Von Berlepsch H. , Strey R. 
Published: July 2012

AbstractSolutions of sodiumsulfopropyloctadecylmaleate (SSPOM) and water form ordered lamellar structures. Remarkable is that the structures form below the Krafft discontinuity indicating a frozen state of the hydrocarbon chains. Phase behaviour and microstructure were characterized using optical microscopy, differential scanning calorimetry (DSC), electrical conductivity, backscattering of light, small‐angle X‐ray scattering (SAXS) and freeze fracture electron microscopy (FFEM). We find a highly swollen lamellar structure displaying iridescent colours when illuminated with white light. The repeat distance of the bilayer membranes is estimated by light and X‐ray scattering and shows a non‐linear dependence on inverse surfactant concentration. Above the chain melting temperature near 37°C the liquid crystalline hexagonal phase (Ha) is observed.
Local Monitoring of Absolute NO2 Concentrations in Ambient Air by Multipass Absorption Spectroscopy
Authors: Armerding W. , Walter J. , Rüger Chr. , Spiekermann M. , Comes F. J. 
Published: July 2012

AbstractA method for monitoring tropospheric NO2 is described which makes use of differential absorption spectroscopy in the red at 600–620 nm. The absorption path‐length of up to 2.7 km is folded inside a 6 m White cell type multiple reflection system. The detectable fractional absorbance of 1 × 10−5 corresponds to a sensitivity of 50 pptv and 200 pptv NO2 for measurements performed at 612.7 nm or 616.0 nm, respectively. The averaging time is at maximum one minute. Since the system can be operated simultaneously in the VIS and the UV (second harmonic) it is capable to measure NO2 as well as OH, SO2, CH2O and C10H8 at the same time. The MOAS (Multipass Optical Absorption Spectroscopy) instrument is interesting for in situ measurements of atmospheric NO2 with high spatial and temporal resolution and sensitivity. It can be used as an external standard to calibrate other NO2 devices under field conditions. Its capability to measure OH and NO2 simultaneously within the same compartment offers a unique possibility to perform field tests of model calculations of fast tropospheric photochemistry.
Solid State NMR Relaxation and Hindered Rotations in Fully Asymmetric Local Environments
Authors: Knop E. , Latanowicz L. , Reynhardt E. C. 
Published: July 2012

AbstractThe temperature dependences of spin‐lattice relaxation rates in the laboratory and rotating frames and the second moment of an NMR line with I = 1/2 have been determined for molecular motions in fully asymmetric triple and double potential wells. With a view to emphasising some of the important features of the results, a number of examples are given.
In‐Situ Gas Analysis with Infrared Lasers
Authors: Ebert V. , Hemberger R. , Meienburg W. , Wolfrum J. 
Published: July 2012

AbstractIn the first part of the paper we present the experimental validation of models describing the NOx removal from flue gases through the SNCR process. The Selective Non‐Catalytic NOx Reduction process was realized in a high temperature flow reactor. A lead salt diode laser system combined with second derivative spectroscopy monitored the concentration of NO, NH3, N2O, NO2, HCN behind the reactor. After the injection of ethane at concentrations of up to 1000 ppm the shift (up to 220 K) of the temperature window of the SNCR process was measured.In the second part a Laser In‐Situ Ammonia‐monitor (LISA) based on a 13CO2‐wave guide laser is used to establish an on‐line control of the SNCR in an industrial environment by measuring in‐situ the excess ammonia behind the reduction zone. With differential absorption spectroscopy and a special referencing scheme sensitivities in the order of several ppm·m of NH3 at atmospheric pressure have been achieved even in heavily dust laden flue gases. With a multi‐channel LISA system the 2‐dimensional NH3 distribution in the flue gas channel of an experimental coal burner system could be measured and the persistence of spatial inhomogeneities, caused by incomplete mixing of NH3 and the flue gas could be shown.In the third part we present first results aimed at the measurement of the local O2‐concentration in combustion systems. With a thermally stabilized 5 mW NIR diode laser at 760 nm we detected oxygen at atmospheric pressure with a sensitivity of less than 500 ppm·m using two beam absorption spectroscopy.