bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser Photooxidation of n‐Butane and Carbon Monoxide
Authors: Lalo C. , Masanet J. , Lempereur F. , Tardieu De Maleissye J.
Published: July 2012

The vibrational photoexcitation by laser of one component in a binary gaseous reactant mixture, gives the possibility to initiate bimolecular reactions under walless conditions. The present work concerns the initiation by laser of two reactions of oxidation.

magnified image

n‐C4H10 and SO2 are activated by absorption of the C. W. radiation of a tunable CO2 laser. The results concerning the formation of products as a function of the irradiation time and the role of the initial pressure of reactants is discussed.
Direct Observations of Energy Transfer of Vibrationally Highly Excited Triatomic and Large Polyatomic Molecules
Authors: Hippler H.
Published: July 2012

Average energies 〈ΔE〉 transferred per collision between vibrationally highly excited molecules and surrounding bath gases have been measured directly by using time resolved UV absorption spectroscopy after laser excitation. The experiments have been performed with highly excited CS2, SO2, toluene, azulene, ethyl‐, and isopropyl‐cycloheptatriene respectively. A great variety of up to 60 different bath gas molecules has been investigated. The temperature has been varied from 300 K to 1000 K. For the same bath gas molecule, the effect of the molecular size of the excited molecule on the 〈ΔE〉 values has been shown to be large at low degrees of excitation while it becomes almost negligible at high excitation energies. In contrast to that the molecular size of the deactivating molecule shows always a large effect on the 〈ΔE〉 values independent from the internal energy of the “hot” molecule. The reported temperature coefficients on the 〈ΔE〉 values are small in all cases. They vary from 〈ΔE〉αT−0.5 for n‐heptane deactivating “hot” toluene or “hot” CS2 molecules, to 〈ΔE〉αT0.0 for collisions of the noble gases with “hot” toluene, and to 〈ΔE〉αT1.0 for Ne deactivating “hot,” CS2.
Determination of Rate Constants for Vibration‐to‐Vibration Energy Transfer
Authors: Teitelbaum Heshel
Published: July 2012

The rate equation lor vibrational relaxation of diatomic molecules is generalized by considering microscopic rate coefficients of the form kα(v + 1)e−C|ΔE|. It is shown that for most molecules of interest the rate equation reduces analytically to the form previously obtained. The consequences of its use and misuse are discussed. A prescription is given for extracting V V rate constants from rate data.
Direct Detection of Hydroxy‐Cyclohexadienyl in the Gas Phase by cw‐UV‐Laser Absorption
Authors: Fritz B. , Handwerk V. , Preidel M. , Zellner R.
Published: July 2012

Formation of hydroxy‐cyclohexadienyl (HCHD), the product of the OH + benzene reaction, has been observed directly in the gas phase at 298 K using long‐path cw‐UV‐laser absorption at 308 nm. The absorption cross section at this wavelength is found to be (9.2 ± 2) · 10−18 cm2. The use of this technique to study directly the subsequent oxidation of HCHD by O2 is emphasized.
Nonlinear Optics at Solid State Surfaces
Authors: Dick Bernhard , Gierulski Alfred , Marowsky Gerd
Published: July 2012

We have studied the process of optical second harmonic generation in thin surface layers between centrosymmetric materials. The surface susceptibilities are dominated by the electronic properties of adsorbed monolayers of dye molecules. Through the appropriate choice of dye one or two electronic resonances can be employed in the process leading to dramatic enhancement of the generated signal.
Photodissociation of Negative Ions and their Clusters: CO−3 and its Hydrates
Authors: Castleman A. W. , Hunton D. E. , Albertoni C. R. , Hofmann M. , Lindeman T. G.
Published: July 2012

Photodissociation of the ion CO−3(H2O)n (0 ≤ n ≤ 3) is accomplished in a mass selected ion beam using an intracavity dye laser pumped with an argon ion laser. The unhydrated parent ion is observed to have a bound electronic excited state, through which absorption of a second photon proceeds to a repulsive state leading to the ejection of O− with about 20% of the available energy being partitioned into relative translation. Cluster dissociation is initiated by the same 2A1←2B1 transition from the ground to a weakly bound excited state of the core ion, leading to the loss of all water molecules within the time of observation. This is in direct contrast to collisional dissociation processes which lead largely to the loss of a single water molecule per collision. Analysis of the kinetic energy distribution of the photofragment CO−3 ions has established that an upper limit to the lifetime of the excited clusters is 20 μsec; most of the available energy is partitioned into internal motion of the CO−3 fragment rather than into relative translation of the photofragments or internal excitation of the ejected water molecules.
Thermodynamic Properties of Liquid Non‐Metallic NaNaBr Solutions
Authors: Egan J. J. , Freyland W.
Published: July 2012

The thermodynamic properties of molten NaNaBr mixtures were determined at 800°C for concentrations of Na up to 5 atom‐% using an emf technique with CaF2 solid electrolyte. Concentrations were controlled by the method of coulometric titration. The activity coefficient is found to pass through a maximum at 0.5 atom‐% Na. An atomic model is presented to explain the thermodynamic results of these solutions. It predicts the concentration dependence of the number of F‐centers as well as the number of F‐center associates, e. g., dimers. Calculations using the model also explain results from spectroscopic, magnetic, and electrical conductivity measurements quantitatively.
The Growth and Reduction of Duplex Oxide Films on Copper
Authors: Speckmann H.‐D. , Lohrengel M. M. , Schultze J. W. , Strehblow H.‐H.
Published: July 2012

The formation and reduction of anodic oxides on copper was studied by potentiodynamic polarization curves, fast potentiostatic pulse experiments and capacity measurements in alkaline solutions. Four different oxide species could be distinguished by their kinetic and capacitive behaviour: the oxide CuOx, which represents few monomolecular layers of copper oxide, formed in short periods or at low potentials, the oxides Cu2O and CuO at intermediate potentials and for longer polarization times, and a non‐defined oxidation product CuOy·zH2O at high potentials. The first 3 oxides form semiconducting films, which grow according to a high field mechanism. At intermediate potentials and at longer polarization times, the passive film consists of an inner Cu2O‐ and an outer CuO‐film, the properties of which are limited by the electronic properties. The common analysis for a high field mechanism of oxide growth can be applied to both stable oxides, taking into account the local potential difference Δϕi < Δε. The potential drop Δϕi in each of these oxides does not exceed 0.5 V. The potential drop ΔϕH in the Helmholtz layer is constant at potentials up to 1.2 V, but it increases with ε at higher potentials. The capacitive behaviour cannot be explained only by capacitors in series but parallel with diodes short circuiting the layers at an upper value of Δϕi. The oxide formation of CuOx, Cu2O and CuO takes place homogeneously all over the surface with almost constant thickness. The reduction occurs by an island mechanism for the duplex film as well as for the CuOx, film. The results are explained on the basis of a tentatively band structure model of the passive film.
Radiale Verteilung von Emissionskoeffizienten im sichtbaren und infraroten Spektralbereich in n‐Hexan‐ und Methanol‐Tankflammen
Authors: Schönbucher A. , Brötz W. , Kettler A.
Published: July 2012

Volumetric emission coefficients of pool fires are determined from photograms and infrared radiance distributions of fires. The volumetric emission coefficients have maximum values of 0.12W/(cm3 sr) for an n‐hexane pool fire. A simplified model, based on the assumptions of the optically thin limit and non‐uniformities in temperature and species concentrations is used to compute the axisymmetric distribution of the volumetric emission coefficients from sampling probe measurements of stable species and temperatures.
Some Basic Concepts of Synergetics with Respect to Pattern Formation. Morphogenesis of Behavior
Authors: Haken H.
Published: July 2012

Many systems in chemistry, physics, and biology can be described at different levels, in particular at a microscopic level and a macroscopic level. In synergetics an attempt is made to relate these two levels in order to understand and describe the formation of macroscopic structures (patterns) through selforganisation of interacting microscopic elements. The concept of order parameters allows us to describe patterns at a macroscopic level. The slaving principle relates the macroscopic to the microscopic level. ‐ We first present theoretic results on pattern formation of fluids and flames, and on morphogenesis. We then study a second class of phenomena which at the present level of our knowledge can be represented at the macroscopic level by means of suitable order parameters. We devise a mathematical model which will present the transition of a specific behavioral pattern of hand movement to another one. It is believed the such kind of modelling applies also to more complicated transitions between behavioral patterns, for instance when horses change the gaits. In the sense of synergetics a behavioral pattern is an outcome of a highly correlated function of microscopic elements. Though their behavior is not known explicitly the slaving principle shows us that such a high correlation is taking place and allows us to formulate equations in terms of order parameters.
Static Dielectric Permittivity and Density of Liquid Dichloromethane to 200 MPa
Authors: Diguet R. , Deul R. , Franck E. U.
Published: July 2012

The static dielectric permittivity, ϵ, and density, ϱ, of dichloromethane was measured from 303 to 423 K and from 10 to 200 MPa. Both quantities were determined simultaneously with the same samples in one autoclave which served as dilatometer and capacitor. The high pressure cell and auxiliary equipment are described. The ϵ‐values vary between 5.36 at 423 K and 20 MPa and 10.01 at 303 K and 200 MPa. The new ϵ‐results agree with existing literature data at 303 K but are about 2% higher than those for 323 K. Isotherms of ϵ increase almost linearly with ϱ. The density data are fitted with a modified Hayward equation. The recent Vedam‐Limsuwan‐Chen‐equation correlates ϵ and ϱ and permits to calculate ϵ or ϱ with an uncertainty lower than the experimental error. With the Onsager‐Kirkwood‐Fröhlich equation a correlation factorgclose the unity (1.1 to 1.2) is obtained.
Electrochemical Behaviour of 2,3′‐Dinitrobenzidine in N,N‐Dimethylformamide
Authors: Aravamuthan S. , Kalidas C. , Venkatachalam C. S.
Published: July 2012

The electrochemical reduction of 2,3′‐dinitrobenzidine (I) has been investigated in N,N‐dimethylformamide solutions. Three diffusion‐controlled polarographic waves were obtained. The first wave is due to a reversible single electron‐transfer while the second and third waves result from irreversible processes involving one and two electron‐transfers, respectively. The radical anion formed in the first step of reduction was confirmed by ESR technique. The red colour compound formed due to “ion association” after the second electron‐transfer step gives rise to a polarographic “minimum” and a “dip” in the chronopotentiogram in addition to the new “peak clusters” seen in cyclic voltammograms. A mechanism is suggested for the reduction of I leading to the formation of 2,3′‐dinitrosobenzidine.
Excess Molar Gibbs Free Energy of Solid {xKCl + (1 ‐ x)KBr} at 820 K and Partial Pressures of Its Components Determined by Knudsen Effusion‐Mass Spectrometry
Authors: Miller M. , Skudlarski K.
Published: July 2012

Excess molar Gibbs free energy and partial pressures of the solid {xKCl + (1 ‐ x)KBr} at 820 K have been determined by Knudsen effusion‐mass Spectrometry. The parameter of the Redlich‐Kister equation for GEm has been calculated as B1 = (1944 ± 123) J mol−1. A good agreement has been found between thermodynamic data obtained from the molecular ion intensities of KCl+ and KBr+ and those obtained from dimeric ion intensities K2Cl+ (from K2Cl2) and K2Br+ (from K2Br2) assigned according to AMS/IEM method. — The results have been compared with the respective data published by other authors.
Coupled Catalytic and Autocatalytic Oxidation Reactions Linked by a Feedback Reaction Part 1. The Mechanism of the Superadditive Oxidation of p‐Phenylenediamines by Iron(III)aq and Hexacyanoferrate
Authors: Nickel Ulrich , Mao Zhou B. , Gulden G.
Published: July 2012

The 2‐step oxidation of some organic compounds in homogeneous aqueous solution often occurs according to an autocatalytic mechanism, because by a feedback reaction the semi oxidized form is autocatalytically increased. In presence of two different oxidants additional homogeneous catalysis can sometimes be observed, yielding a complex redox system which often causes curious experimental curves. For example p‐phenylenediamines are oxidized by iron(III)aq irreversibly, but slowly, whereas hexacyanoferrate(III) oxidizes rapidly, but reversibly. A mixture of both oxidants, however, oxidizes rapidly and irreversibly, even if the concentration of hexacyanoferrate is less than 10−8 M.
The Contributions of Intersystem Crossing and Reaction in the Removal of CH2(ã1A1) by Hydrocarbons Studied with the LMR
Authors: Böhland T. , Temps F. , Wagner H. Gg.
Published: July 2012

The formation of ground state CH2(X̃ 3B1)‐radicals in the collisional removal of CH2(ã1 A1) by selected hydrocarbons

with RH = CH4 (1), C2H6 (2), C3H8 (3), i‐C4H10 (4) and C2H4 (5 ) was studied in the gas phase at room temperature using Laser Magnetic Resonance (LMR). CH2(ã1A1)‐radicals wer_e generated by excimer laser photolysis of CH2CO at λ = 308 nm in the presence of varying concentrations of RH. The yields of CH2(X̃3B1) produced by intersystem crossing (1a)–(5a) were measured with the LMR. Presuming the primary quantum yield for CH2(X̃3B1) formation in the CH2CO photodissociation to be ϕ3 = 0 the branching ratios for intersystem crossing were found to be k1a/k1 = 0.17 ± 0.05, k2a/k2 = 0.19 ± 0.05, k3a/k3 = 0.24 ± 0.07, k4a/k4 = 0.28 ± 0.08, and k5a/k5 = 0.12 ± 0.06. For ϕ > 0 these values would have to be regarded as upper limits. Hence, for all hydrocarbons studied reactive quenching (1b)‐(5b) is the dominating CH2(ã1A1) removal pathway.
An Efficient Continuous Flow Technique for Investigating the Magnetic Field Dependence of Photochemical Quantum Yields
Authors: Schlenker Wolfgang , Steiner Ulrich E.
Published: July 2012

A continuous‐flow technique has been applied to study the magnetic field effect on the photobleaching quantum yield of thionine in the reaction with aniline in reversed micellar solution and with p‐iodoaniline in methanol. The principle of the experimental technique is to irradiate the solution in a flow‐through cuvette within a magnetic field which is varied in steps and to observe optical density changes in a second cuvette connected to the first one in a flow system. Although the absolute quantum yields of the two photoreactions are below 1%, relative changes due to the magnetic field effect could be resolved with an accuracy of 1%. The observed effects on the permanent photobleaching yield closely follow the effects on the radical yield previously observed in time‐resolved experiments and are explained by the radical pair mechanism and the triplet mechanism, respectively.
Theory of Block Copolymer‐Homopolymer Blends
Authors: Noolandi Jaan
Published: July 2012

The theory of phase separation and microdomain formation in block copolymer‐homopolymer blends is reviewed. The calculations involve the solution of modified mean field diffusion equations for the polymer distribution functions, which are used to construct a general free energy expression, taking into account the connectedness of the blocks of the copolymer, and including changes in the conformational entropy in interphase regions, stretching of the polymer chains, enthalpic interaction terms between different chemical species, and configurational entropy terms. The effect of solid surfaces on grafted polymers is also included in the theory. As examples we discuss pure block copolymers, the use of block copolymers as surfactants in mixtures of incompatible homopolymers, and the structure of block copolymer micelles in a homopolymer matrix. A few interesting features of the equilibrium phase diagrams of blends are pointed out, and we give a preview of current theoretical work on crystalline‐amorphous block copolymers.
Electrochemical Studies on the Formation and Properties of Conducting Polymers
Authors: Heinze Jürgen , Hinkelmann Klaus , Dietrich Michael , Mortensen John
Published: July 2012

PA can be reversibly oxidized in SO2 up to 8 mol‐% of charging, while in propylenecarbonate(PC) the discharging process becomes partly irreversible at an oxidation level of 4 mol‐% or higher. The experimental results obtained in both solvents reveal that the degradation of “p‐doped” PA in the range of its first oxidation wave is caused mainly by nucleophilic attack of the solvent. Degradation of the “n‐doped” species in a THF/Na+‐electrolyte is probably due to the attack of Na on the polymer or on the solvent. Cyclic voltammetric measurements on N‐phenyl‐carbazol show that the anodic formation of conducting polymers is due to a radical‐radical ion dimerisation (R‐R route).
Preparation and Characterization of Platinized‐Carbon Hydrogen Anodes for Alkali and Acid Fuel Cells
Authors: Shukla A. K. , Ramesh K. V. , Manoharan R. , Sarode P. R. , Vasudevan S.
Published: July 2012

Highly dispersed platinized‐carbon hydrogen anodes are developed for utilization in alkali and acidic media power sources viz., hydrogen/air fuel cells and nickel/hydrogen batteries, by tailor making both the macro as well as micro structures of these electrodes. The optimized hydrogen anodes can withstand load currents upto 350, 800 and 500 mA/cm2 for extended periods in 6N KOH, 5N H2SO4 and 2ON H3PO4 electrolytes respectively. Characterization techniques such as photoelectron Spectroscopy, X‐ray absorption Spectroscopy, chemisorption, X‐ray diffraction, electron microscopy, electron spin resonance etc., are found to be useful in developing such electrodes. The study clearly demonstrates the significance of physico‐chemical characterization techniques in developing fuel cell electrodes.
Excess Properties of Liquid Cyclohexane/Hydrocarbon Mixtures I. Experimental Results of the Excess Enthalpy
Authors: Wagner H. , Lichtenthaler R. N.
Published: July 2012

Experimental results of the composition dependence of the molar excess enthalpy HE of ten mixtures of cyclohexane with saturated and unsaturated hydrocarbons at 298.15 K and 1 bar are reported. The results of the mixtures With the saturated hydrocarbons confirm the systematic behaviour of HE with respect to the chain length and the degree of branching deduced from already existing data. The results of the mixtures with unsaturated components allow to extend the systematics taking into account the number and the location of multiple bonds within the molecules.
Thermodynamics of S.˙.S 2σ/1σ* Three‐electron Bonds and Deprotonation Kinetics of Thioether Radical Cations in Aqueous Solution
Authors: Mönig J. , Goslich R. , Asmus K.‐D.
Published: July 2012

Time‐resolved pulse radiolysis studies have been carried out on the R2S+· R2S ⇆ (R2S.˙.SR2)+ equilibrium and associated decay kinetics of sulfur centered radical cations. ‐ Equilibrium constants of K = 2.0 · 105 and 5.4 · 102 mol−1 dm3 at 20°C have been determined for the species with R = CH3 and (CH3)2CH, respectively. Absolute rate constants have been measured for the back reaction of the above equilibrium: k‐1 = 1.5 · 104 s−1 and 5.6 · 106 s−1, respectively, at 20°C. Further rate constants refer to the deprotonation of R2S+ by various proton acceptors (phosphate, acetate and water). ‐ ΔH≠ = 57 kJ mol−1 and 17 kJ mol−1 were determined for the dissociation of the sulfur‐sulfur 3‐electron bond in (Me2S.˙.SMe2)± and (i‐Pr2S.˙.S i‐Pr2)+, respectively. On this basis the S.˙.S bond energies were estimated to ≲80 kJ mol−1 and ≲40 kJ mol−1 for these two species. The kinetic and thermodynamic results substantiate previous conclusions on the electronic structure and relative stability of S.˙.S bonded radicals and corroborate some theoretical calculations.
Nuclear Spin‐lattice Relaxation and Self‐diffusion Coefficient for Toluene around Supercritical Region
Authors: Shimokawa Shigezo
Published: July 2012

The molecular motion of toluene has been studied through measurements of the nuclear spin‐lattice relaxation time (T1), the self‐diffusion coefficient (D), and the mass density (ϱ) up to the supercritical region. 1H NMR measurements were made at 38.2 MHz, in the range 294 ≤. T/K 761, 0.1 ≤ P/MPa ≤ 15 under toluene vapour pressure. T1 for ring protons has a maximum (95 sec) near the critical temperature (Tc = 591.4 K) and decreases above Tc. The value of D, on the other hand, changes abruptly near Tc. T1 for methyl protons are nearly constant between 380–580 K. The value of ϱ for the toluene‐d3 was measured in the same temperature and pressure range in situ by the one‐dimensional projection method. The various contributions to the relaxation rate are separated and the molecular motions of toluene molecules in the liquid and supercritical regions are discussed.
Studies on the n‐GaAs Photoanode in Aqueous Electrolytes. 3. Recombination Resistance
Authors: Vaiunaekelbergh D. , Gomes W. P. , Cardon F.
Published: July 2012

The resistive part of the additional impedance, caused by illumination of the n‐GaAs/electrolyte interface, has been studied both experimentally and theoretically. The dependence of this resistive part on the electrode potential, the light intensity and the measuring frequency is interpreted on the basis of a model in which it is assumed that surface recombination is involved. A quantitative expression for the recently introduced concept of recombination resistance is derived.
Strukturuntersuchung konzentrierter wäßriger Caesiumhydroxid‐Lösungen mit Röntgen‐ und Neutronenstreuung
Authors: Bertagnolli H. , Ehrig R. , Weidner J. U. , Zimmermann H. W.
Published: July 2012

X‐ray and neutron diffraction measurements each on three differently concentrated aqueous solutions of Cesiumhydroxid are reported. After the correction for background, self‐absorption, multiple scattering, inelastic effects and in case of X‐rays for the wavelength distribution of the incident beam the structure of the water molecule was deduced from the coherent neutron scattering cross section. The Cs+–Cs+–and Cs+–H2O/OH−pair correlation functions could be determined from these three X‐ray measurements. A quantitative analysis was performed by use of a geometrical model, which reproduces very well all measurements as well as the individual atom pair correlation functions. It turns out that the local order in aqueous CsOH‐solutions is very similar to the structure of solid CsOH · H2O. The Cs+‐ions are located between layers consisting of slightly puckered hexagon rings of H2O and OH−, which are connected by H‐bonds.
Thermal Decomposition of Cyanogen Measured in C2N2/O2 and C2N2/H2 Reaction Systems by Atomic Resonance Absorption
Authors: Natarajan K. , Thielen K. , Hermanns H. D. , Roth P.
Published: July 2012

The thermal decomposition of cyanogen has been measured behind reflected shock waves in the temperature range 1900–2650 K at pressures of about 1.8–2.0 bar using Atomic Resonance Absorption Spectroscopy (ARAS). C2N2/O2 and C2N2/H2 mixtures highly diluted in argon were shock heated and O and H atom concentrations were monitored in the post shock reaction zone. Because of the fast secondary reactions of the dissociation product CN, the measured concentrations of O or H were strongly dependent on the rate of dissociation of cyanogen. The experimentally determined rate coefficient data for the dissociation of cyanogen are closely fit by the Arrhenius expression: k = · 2.97 10−7 exp(−53665 K/T)cm3/s. The present rate coefficient data is compared with the results of previous investigators and also with the estimates obtained from the weak collision unimolecular reaction rate theory.
Some New Details in the Kinetic Considerations of the Oscillatory Decomposition of Hydrogen Peroxide
Authors: Anić S. , Kolar‐Anić L. J.
Published: July 2012

It is found that decomposition of hydrogen peroxide in the presence of constant amount of potassium iodate and sulphuric acid ([KIO3] = 7.35 · 10−2 mol/dm3, [H2SO4] = 2.45 · 10−2 mol/dm3) exhibits an oscillatory behaviour with only one induction period if the initial concentration of hydrogen peroxide ranges from 3.5 · 10−4 to 7.9 · 10−3 mol/dm3. If this concentration is larger than 7.9 · 10−3 mol/dm3, but less than the concentration of KIO3, two induction periods separated by one oscillation are observed. For the highest concentrations of [H2O2]0 taken into account, the one oscillation between the two induction periods disappears, and they are both fused together, without losing their own kinetic characteristics. For all the examined initial concentrations [H2O2]0 above 7.9 · 10−3 mol/dm3, the overall decomposition of hydrogen peroxide is found to follow the first order kinetics, with the rate constant found to be equal to 1.88 · 10−2 min−1, at T = 335.2 ± 0.2 K. The dependence of the number of oscillations on [H2O2]0 is examined. It is found that, under the conditions of our experiments, 2.6 · 10−4 mol/dm3 of hydrogen peroxide is necessary for the onset of one oscillation.
Thermodynamics of Ionic Solid Solutions and Its Application to the Formation and Stability of Biominerals
Authors: Driessens F. C. M.
Published: July 2012

The classification of equilibrium between ionic solid solutions and aqueous solutions by Roozeboom is interpreted as being a result of the ideal or regular behaviour of the ionic solid solutions. Due to the fact that the solubility products of isomorphous compounds which form ionic solid solutions differs in general by several orders of magnitude, it is very unlikely that precipitates differ much from the stoichiometry of one of these compounds. This principle is applied to the problem of biominerals, especially bone mineral. As a result it appears that the first mineral deposited in bone is octocalcium phosphate. Under in vivo conditions this phase is transformed into a mixture of three other calcium phosphates having a much lower solubility. The solubility controlling phase in living bone appears to be octocalcium phosphate which is continuously formed during the turn‐over of bone. This model for bone mineral has lead to the explanation of the formation of renal stones, pathological calcifications and osteoporosis as a consequence of slight chronic magnesium deficiency. The action of magnesium is mediated by the osteocytes.
Modelling of Polymerization Phenomena
Authors: Ray W. H.
Published: July 2012

Polymerization phenomena provide interesting subjects for modelling at several levels. At the microscopic level, the kinetics of chain growth are most complex, with branching reactions, end group formation, multifunctional growth, etc. These kinetics are largely responsible for the final polymer properties. However, the kinetics are also influenced by mesoscale consideration of simultaneous phase changes, heat and mass transfer and equilibria between phases, and polymer morphology during polymerization. Often these considerations also have a major influence on the polymer properties. Finally, at the macroscale, we have the polymerization reactor which must be well designed and controlled in order for the smaller scale processes to proceed as planned. Each of these levels of scale will be discussed and specified examples of the practical application of modelling will be presented.
Kinetics of Proton‐Transport‐Coupled ATP Synthesis Catalyzed by the Chloroplast ATP Synthase
Authors: Gräber P. , Fromme P. , Junesch U. , Schmidt G. , Thulke G.
Published: July 2012

The kinetics of proton‐transport‐coupled ATP synthesis catalyzed by the chloroplast ATPase (ATP synthase) was investigated after energization of the membrane by an artificially generated ΔpH and an electric potential difference, Δψ. With a rapid mixing system, ATP synthesis was studied at short reaction times (<200 ms) where all relevant parameters (pHout, pHin, Δψ, substrate and product concentrations) remain practically constant at their initial values. The reaction is investigated at three levels of complexity. (1) The ATPase is embedded in the natural membrane. (2) The ATPase is isolated, purified and reconstituted into asolectin liposomes. (3) The reconstituted ATPase is investigated under single site, single turnover conditions. The following results were obtained:

The dependence of the activation and of the catalytic reaction on pHin is measured.

The dependence of the rate of ATP synthesis on the ADP concentration at ΔpH = 3.2 is, at low ADP concentration, diffusion controlled with a rate constant of 6·106 M−1s−1 . At high ADP concentration, the maximal enzyme turnover is 700 s−1.

When the ATPase is reconstituted into asolectin liposomes practically the same rate is obtained as in the natural membrane, demonstrating that for optimal activity only one protein with an inert membrane is necessary.

Under single site conditions the equilibrium constant at the enzyme between bound P1 and bound ATP is K ≈ 0.13.
Calculation of Nematic‐Isotropic Phase Equilibria in Solutions of Polymers in Nematic Liquid Crystals Using the Flory Lattice Model
Authors: Ballauff M.
Published: July 2012

A treatment of phase equilibria occuring in mixtures of polymers in nematic liquid crystals is presented. The steric pan of the mixing partition function is evaluated using the Flory lattice model, the soft anisotropic forces between the rods enter as an additional factor in the partition function. Isotropic interaction between the nematic solvent and the polymeric solute is introduced in terms of a single interaction parameter. It is shown that the marked incompatibility observed in nematic solutions of high polymers is due to the entropic part of the resulting free energy of mixing. Unfavorite isotropic interactions between solvent and solute leads to the occurence of a reentrant isotropic phase rich in polymer. If the solvent power of the nematic fluid is low enough, liquid‐liquid demixing will take place in the isotropic phase followed by a triple point at lower temperature where a nematic phase is coexisting with two isotropic phases. Below the triple point a nematic phase containing only minute amounts of polymer is in equilibrium with an isotropic phase exhibiting a high concentration of the macromolecular solute.
Modellierung des Kohlenstoffaustauschs zwischen Atmosphäre und Landvegetation unter Berücksichtigung von Landnutzungsänderungen und CO2‐Düngungseffekt
Authors: Kohlmaier G. H. , Bröhl H. , Janecek A. , Benderoth G.
Published: July 2012

The role of the terrestrial biota within the global carbon cycle is analysed with respect to human impacts causing releases of CO2 into the atmosphere and to a CO2 fertilization effect caused by enhanced atmospheric CO2 concentrations. Two different model structures representing different plant responses on enhanced CO2 are suggested, and the related global net fluxes of carbon are estimated. It is shown that, while clearings of forests and use of biomass as fuel nowadays may cause a net carbon release from the biota between 0.6 and 1.8 Gt C/a, a CO2 fertilization effect may compensate at least part of this release (0.25 to 1.5 Gt C/a), such that the role of the terrestrial biota as source or sink of atmospheric CO2 is unclear on the present database.
On Topological‐Dynamical Equivalent Representations of Reaction Networks: The Omega‐Equation and a Canonical Class of Mass Action Kinetics
Authors: Siré Ernst‐Olof
Published: July 2012

An unifying concept ‐ the Omega‐equation ‐ is introduced to describe analogies of dynamical systems such as for chemical reaction systems, transport and metabolism of coupled compartments, cell populations, population genetics and animal behavior in ecology. The phenomenology of rate‐laws of such systems are frequently described, perhaps after an equivalent transformation, in terms of ordinary polynomial differential equations, which can be incorporated in the strong formalism of mass action reaction networks. Furthermore, we show that the set of all mass action kinetics can be reduced to the smaller class of so‐called μ‐molar mass action networks, which generate homogeneous polynomial Ω‐equations of order μ.
Thermodynamic and Dielectric Properties of Binary Polar + Non‐Polar Mixtures I. Static Dielectric Constants and Excess Molar Enthalpies of n‐Alkylamine + n‐Dodecane Systems
Authors: Otín Santos , Fernández Javier , Embid José Muñoz , Velasco Inmaculada , Losa Celso Gutiérrez
Published: July 2012

Excess molar enthalpies HE at atmospheric pressure and 303.15 K, and static dielectric constants, ϵs, at 2 MHz and temperature ranging from 293.05 to 323.25 K, have been determined for n‐dodecane + n‐propylamine, + n‐butylamine, + n‐hexylamine, + n‐octylamine, + n‐decylamine, + n‐dodecylamine and + pentadecylamine. From the experimental results, the variation of HE and ϵEs with the chain length of the amine is shown.
Retardation of the Cd2+ and In3+ Reduction Processes at DME in Chloride Medium in Relation to Adsorption of Coumarin
Authors: Mazhar A. A. , Heakal F. El‐Taib
Published: July 2012

The adsorption of coumarin on mercury in MKC1 has been determined from electrocapillary and capacitance measurements. At relatively high coumarin concentrations (≥ 10−3 M), the molecules reorient from the parallel to the vertical form at the more negative potentials. The results were found to fit the isotherm having a configurational term θ/ex‐1(1‐θ)x. From the values calculated for the standard free energy of adsorption and its variation with potential, it may be inferred that coumarin is not strongly adsorbed. In presence of coumarin, the Cd2+/Cd(Hg) and ln3+/ln(Hg) exchange reactions occur through the free surface, and the decrease in the rate constant is exponentially related to the surface coverage.
Kinetic Study of Chemically Activated Fluorocyclopropane
Authors: Dall'O L. , Heydtmann H.
Published: July 2012

The photolysis of ketene at 313 nm was studied in the presence of fluoroethene and oxygen. The product formation was observed as a function of total pressure between 12 and 1080 mbar. Chemically activated fluorocyclopropane was formed by addition of singlet methylene to the double bond, and subsequent isomerization to the fluoropropenes as well as decomposition of these primary products to allene, propyne and HF was observed. The product yield was described by RRKM calculations; a stepladder deactivation model was used.
Diffusion of Fluorine in Silica
Authors: Hermann Wilhelm , Raith Angelika , Rau Hans
Published: July 2012

Diffusion constants of fluorine in silica were determined at temperatures between 1385 K and 1873 K. Samples were prepared by the PCVD (Plasma activated Chemical Vapor Deposition) method and diffusion profiles measured by SEM investigations. The resulting least squares fit is log(D(cm2 s−1)) = ‐0.920 ‐ 18337 K/T.
Thermodynamic excess functions for quasiternary solid solutions of type (MkN(1‐k)) (XlY(1‐l))
Authors: Leute Volkmar
Published: July 2012

The excess enthalpy for a quasiternary system of type MkN(1‐k)XlY(1‐l) is derived by use of a model, which considers the interaction of clusters composed of four particles. The distribution of the lattice constituents is assumed to be random. Based on this model the excess enthalpy can be described by a cubic function of the mole fractions k and l with the standard reaction enthalpy and 8 interaction parameters as constants. It is shown, that the ternary interaction parameters can be calculated from the interaction parameters of the subregular quasibinary subsystems, whereas the reaction enthalpy for the double conversion between the binary components can be derived from their standard enthalpies. Thus the phase diagrams of quasiternary systems with two mixed sublattices can be derived from the quasibinary data without introducing any special ternary interaction parameter. ‐ The influence of the interaction parameters on the shape of the phase diagram and especially the influence of the standard reaction enthalpy on the tie line field is demonstrated by some calculated phase diagrams.
Temperature dependence studies of NQR frequencies of halogens and also of quadrupolar relaxation times of chlorine nuclei in ammonium hexahalotellurates(IV)
Authors: Furukawa Yoshihiro , Nakamura Daiyu
Published: July 2012

The temperature dependence of NQR frequencies of halogens in ammonium hexahalotellurates(IV) has been reinvestigated in a wide range of temperature. A second‐order phase transition was definitely located at 89 K for (NH4)2TeCl6, below which temperature the existence of multiplet structure was suggested The temperature of a first‐order phase transition was determined for (NH4)2TeBr6 at 194 K in addition to the phase transition previously reported, which was located accurately at 212 K. The lowest‐frequency line among the three 81Br resonance lines observed below 194 K exhibited a positive temperature coefficient whereas the remaining two lines showed normal negative temperature coefficients. Except for the highest‐frequency v1 and v2 lines, the all four 127I lines observed for (NH4)2TeI6 showed anomalous temperature dependences. These temperature dependences could be interpreted by considering that the Te‐I…H type hydrogen bonds partially break due to the thermal activation of the motion of ammonium ions in crystals. A phase transition was located at 449 K by means of differential thermal analysis.
Electrochemical and solid state reactions of copper with n‐SnS2
Authors: Jaegermann W. , Ohuchi F. S. , Parkinson B. A.
Published: July 2012

The intercalation reaction of Cu with n‐SnS2 has been studied with a variety of techniques. Electrochemical and photoelectrochemical methods provided information about the energetics of the intercalation reaction and the band gap and carrier type of the new phase (p‐CuSnS2). X‐ray photoelectron spectroscopy (XPS) was used to characterize the stoichiometry of the new phase as prepared both electrochemically and in UHV. The thermal stability of CuSnS2 was studied with XPS and transmission electron microscopy (TEM) and the diffusion of copper through the van der Waals planes of SnS2 was demonstrated. A structure for the new phase is proposed which is consistent with the measured physical properties. The intercalation reaction is discussed with respect to its differences from the rigid band model of intercalation.
Deviations from equilibrium at the interface of a charged membrane
Authors: Manzanares J. A. , Mafé S. , Pellicer J.
Published: July 2012

The local equilibrium assumption commonly employed for the transport through the interface of a charged membrane has been analysed from a simplified electric double layer model. This layer is characterized on the basis of a surface potential arising from a non‐zero surface charge density placed on the membrane surface. The dependence of deviations from local equilibrium on the characteristic parameters of the problem is shown. Connection with the classical treatment by Donnan is discussed. Although the complexity of the problem calls for a number of simplifications, the results obtained appears to be significative. Thus, the analysis carried out displays not only that deviations from equilibrium are small, but also that in the limit of small fluxes, omission of a detailed study of the electric double layer is probably justified when characterizing ionic transport through common synthetic membranes
Composition dependent electronic conductivities and hall coefficients of mixed ionic‐electronic conductors. Part III: Beta silver sulfide revisited
Authors: Sohège J. , Funke K.
Published: July 2012

In a previous paper (I) we presented the composition dependent electronic conductivity and Hall coefficient of β‐Ag2+δS at different temperatures. The mobility of conduction‐band electrons was found to vary with temperature as T−3/2. In this paper we point out that, due to a temperature dependent effective electron mass, the relaxation time of conduction‐band electrons varies as T−1 and not as T−3/2.
NMR studies of molecular motion in various defect pyrochlores containing ammonium
Authors: Möller H. , Möller‐Warmuth W. , Kuntz M. , Tomandl G.
Published: July 2012

NH4TaWO6, ND4TaWO6, and NH4NbWO6 have been studied by NMR at various frequencies and over a large range of temperatures. At low temperatures, ammonium ions exist as an entity tunnelling in the center of the cavities of the pyrochlore framework. From relaxation data an activation energy of this process of about 6.5 kJ/mol is obtained for all three materials. At temperatures above about 250 K translational motion narrows the spectra and produces relaxation. The experiments suggest a Grotthus type of proton transfer, where both local back ‐ and forth‐hopping (13–20 kJ/mol) and long range migration (31–39 kJ/mol) plays a role. At higher temperatures NH4+ and NH3 may diffuse as a whole. This is shown in particular for NH4NbWO6 which served as diaphragm in a water vapour electrolysis cell, and where ammonia becomes exchanged by water.
Elementary reactions of N2(A3Σ+u) with H2, F2 and H2C2O in the gas phase
Authors: Böhmer E. , Hack W.
Published: July 2012

Overall rate constants for the removal of N2(A, v') by H2(X), F2(X) and H2C2O(X̄) were measured at T = 298 K in a fast flow reactor at constant injector position. N2(A) molecules in the vibrational states v' = 0, 1, 2, 3 were produced in the reaction of Ar(3P0,2) with N2(X) and detected by laser induced fluorescence (LIF) using the excitation of the first positive system of N2, B(3Πg)σ A(3Σ+u). The measured rate constants are: magnified imageThe rates of reactions (1), (2) and (3) and the reaction mechanisms are discussed.
The electric birefringence anomaly in colloidal and micellar systems
Authors: Angel M. , Hoffmann H. , Krämer U. , Thurn H.
Published: July 2012

Rod‐like micelles of perfluorosurfactants in aqueous solution were examined by using the transient and dynamic electric birefringence method. Tetraethylammoniumperfluoroctanesulfonat shows in the overlap region of the rods between 5 mM and 15 mM up to three different relaxation times τ1, τ2 and τ3 between a few μs and several ms. A forth very long relaxation time τ4 (seconds) appears at higher concentrations. The relaxation processes with the time constants τ1, τ3 and τ4 have a negative birefringence, while τ2 has a positive sign. In the anomaly region the total birefringence can change sign as a function of the total surfactant concentration and of the field strength. The anomalous behaviour of the time and frequence dependence of the electric birefringence is explained on the basis of intermicellar interaction. It is assumed, that the external electric field induces an additional anisotropic Lorentz‐field, which changes dramatically the local Lorentz‐field around the micelles. As a result both the correlation of the center of masses and the correlation of the rodlike micelles changes. This gives rise to the processes τ1, τ2 and τ3. The largest relaxation time τ4 seems to be due to a deformation and relaxation of a temporary network, which is built by the rodlike micelles.
IR spectroscopic investigations during oscillations of the CO/NO and the CO/O2reaction on Pt and Pd catalysts I: Platinum
Authors: Schüth F. , Wicke E.
Published: July 2012

The CO/NO reaction on Platinum supported catalysts exhibits oscillatory behaviour at temperatures between 650 and 750 K and NO/CO ratios between 0.8 and 4. The oscillations are accompanied with large temperature variations which seem to be necessary to synchronize the instabilities at different crystallites. IR spectroscopic investigations reveal appreciable shifts of the position of the L —CO band on Pt. This leads to a model involving the hex ⇄ 1 × 1 surface transformation of the Pt(100) plane as the crucial step during an oscillation cycle. A comparison with results of other groups confirms this proposition. —Concerning the CO/O2reaction, however, no indication for the applicability of the hex ⇄ 1 × 1 model for oscillations at atmospheric pressures could be found by means of IR spectroscopy. Also oxidation‐reduction models could be excluded. The only mechanism discussed in the literature which is in agreement with our findings explains the oscillations by reversible microfacetting of the Pt(110) plane.
Laser induced shock wave lithotripsy
Authors: Thomas S. , Engelhardt R. , Meyer W. , Brinkmann R. , Hofstetter A. G.
Published: July 2012

Laser induced shock wave lithotripsy has the potential to become a standard procedure in the endourologic management of urinary stone disease. To date, there are two fairly well established laser systems for laser induced shock wave lithotripsy in clinical practice, the Q‐switched Nd: YAG and the flashlamp pumped dye laser. —The Q‐switched Nd: YAG Laser (20 ns pulses) is distinguished by the high stone selectivity of its coupler systems, but the necessity of a coupler and its fairly small rate of conversion of light into mechanical energy present a grievous draw back. Furthermore, the minimal outer diameter of the transmission system is 1.8 mm, limiting its range of application. —By using longer pulses in the range of 1–2 μs that can be produced with both a flashlamp pumped dye or a low‐gain solid state laser with the same pulse energies (∽ 50 mJ) these disadvantages can be overcome. —Pulses of the dye laser can be passed through a highly flexible and uncomplicated 200 μm quarz fiber. Laser lithotripsy is performed with the bare fiber tip placed directly in contact with the stone at repetition rates of up to 10 Hz. The quality of the fiber tip in contact with the stone is uncritical. —Biological evaluation of damage caused by direct irradiation shows that both laser systems cause minor damage of different degree. —Our newest development is a optical feedback regulation system to avoid damage to adjacent tissue even under direct contact, enabling intracorporeal lithotripsy without endoscopic control.
On the way to the ideal lithotripsy laser
Authors: Brinkmann R. , Meyer W. , Oehlert P. , Thomas S. , Engelhardt R.
Published: July 2012

The poster describes a possible way to the ideal lithotripsy laser including the problem of an ideal application system to minimize secondary effects to the patient. It summarizes the advantages and disadvantages of already established laser systems in term sof physical and clinical aspects. Furthermore it presents an optical feedback regulation system to avoid adverse tissue effects. Finally, an active Q‐switched Alexandrite laser is presented as an ideal LISL‐system.
Thermal origin during excimer laser interaction with tissue
Authors: Steinmetz M.
Published: July 2012

It is discussed controversly whether the interaction of excimer laserlight (wavelengths in the UV‐region with short pulses and high fluence) with tissue is predominantly a photochemical or photothermal reaction. The results of current histological investigations suggest that the kind of reaction depends on the wavelengths, maintaining constant fluence and pulse length. In order to get more information on that point we measured pressure and temperature profiles during laser interaction in single laser pulse mode. For temperature measurements we developed a microthermocouple device with high spatial (μm) and temporal (μs) resolution based on thin film technique. —First results indicate that laser interaction even at a wavelength of 351 nm are predominantly photothermal processes: 1) the higher the heat capacity of the sample the higher the removal threshold, 2) once the removal threshold is exceeded, the temperature increases with increasing irradiance, 3) pressure waves can be generated in a light absorbing fluid without target, 4) characteristic thermal effects like tissue discoloration and smoke generation can be observed.