bluuebunny/crossref_metadata_2025 huggingface dataset:
A powder diffraction study of the phase transition in LaAlO3
Authors: Lehnert H. , Boysen Hans , Schneider J. , Frey Friedrich , Hohlwein D. , Radaelli P. , Ehrenberg H.
Published: August 2006

The structure of LaAlO3 has been investigated around the phase transition at Tc ≈ 800 K by neutron powder diffraction in vacuum and by X-ray powder diffraction under nitrogen atmosphere as well as by a very high resolution synchrotron experiment in air. The results were analysed in frame of the Landau theory using the fluctuation-dissipation theorem to relate the susceptibility to the atomic displacement parameters. The room temperature structure is a rhombohedrally distorted perovskite structure, space group R-3c , which undergoes a transition to the ideal perovskite structure, space group Pm-3m , at high temperatures. The order parameter is a rotation of the O6-octahedron described by one x(O)-parameter. This parameter and the spontaneous strain (c/a-√6), as well as the relevant atomic displacement parameter Uop
11(O) in the order parameter system, show a critical behaviour in agreement with a second order phase transition. Although the critical exponents of the order parameter and strain show the expected coupling behaviour, there is a striking difference of the transition temperature: the metric becomes cubic roughly 30 K below the proper Tc. This is related to spontaneous formation of domains imposing the average cubic symmetry via internal stresses.
Pyrolysis Nozzles Coupled to a Microwave Spectrometer with Stark Modulation for the Detection of Transients Species in a Supersonic Expansion
Authors: McNaughton D. , Evans C.J.
Published: August 2006

Two types of pyrolysis nozzles have been constructed and coupled to a new Stark modulated microwave spectrometer. The nozzles were tested on their ability to generate rotationally cooled transient species through a supersonic expansion. The transients species vinylamine, thioketene and ketene were generated and detected using nozzle temperatures ranging from 400-800°C. Pyrolysis temperatures were generally lower than those used in normal flow pyrolysis experiments and rotational temperatures of ca. 10 K were achieved. A preliminary investigation of the jet nozzle pyrolysis of 3-methyl-4-hydroxy-iminoisoxaline-5-one was carried out and showed a different distribution of CHNO pyrolysis products to that observed in previous low pressure studies.
Approximate Factorization of Molecular Potential Surfaces II. Internal Rotors
Authors: Pearman R. , Gruebele M.
Published: August 2006

Scaling models for the polyatomic potential energy surface occupy a ground intermediate between ab initio surfaces and random matrix models. They are useful for the study of vibrational energy redistribution (IVR) in large molecules, and have been shown to reproduce many features of more accurate spectroscopically fitted or
Chemical Reactions in Ionic Molecular Aggregates. An ab initio and R2PI-Study of the Halogenbenzene/Ammonia System
Authors: Günther P.A. , Oppel M. , Baumgärtel Helmut
Published: August 2006

The structure, charge distribution and intermolecular binding energy of stable neutral and ionic aggregates of m-difluorobenzene and m-fluorochlorobenzene with one and two ammonia molecules are calculated on the MP2/6-31 G** level. The R2PI spectra of m-difluorobenzene/ammonia aggregates are reported. The origin of the size dependence of chemical reactions observed in the ionic aggregates is discussed.
The Concentration and Temperature Dependence of the Deuterium Quadrupole Coupling Parameter and Rotational Correlation Time of Ethanol-Carbon Tetrachloride Binary Mixtures
Authors: Ferris Th.D. , Farrar Th.C.
Published: August 2006

Concentration and temperature dependent measurements of the hydroxyl proton chemical shift and deuterium longitudinal relaxation time of binary mixtures of ethanol and carbon tetrachloride were made over a 60 degree temperature range. Concentrations ranged from 1.02 mole percent to neat ethanol.
Conformational Preference of Acetyl-Azaalanine-N-Methyl Amide
Authors: Ro S. , Yoon C.-J.
Published: August 2006

Conformational preference of Ac-AzAla-NHMe has been investigated using ab initio calculations. Azaalanine in peptides prefer to adopt two conformational families including four conformations in which (φ,ψ) are (-90°, -13°), (90°, 13°), (-70°, 164°) and (70°, -164°). The stability at φ = ±90° is explained by repulsion of lone pairs on the nitrogens and hydrogen bonding between Ac-N and terminal N(Me)H. On the other hand, the angle ψ adopts only ~0° or 180° since the N(Me)-C(O) bond has double bond character. One conformational family in which the (φ,ψ) torsion angles are (-90°, -13°) or (90°, 13°), is similar to the i+2 position of typical β-I or β-II turns. The other conformation in which the (φ,ψ) torsion angles are (-70°, 164°) or (70°, -164°), is similar to the polyproline II structure appearing in collagen. We believe that these results are useful in designing constrained peptidomimetics for drug discovery and peptide engineering.
Reaction Rate Enhancement in Nanoporous Materials with Single-File Behaviour
Authors: Kärger J. , Bräuer P. , Pfeifer H.
Published: August 2006

In the concept of ´´molecular traffic control´´, Derouane and Gabelica postulated an enhancement of the effective conversion rate in catalytic reactions if the reactant and product molecules avoid each other by preferentially choosing different channel systems on their diffusion path into and out of the catalyst particles. After two decades of controversial discussions, the feasibility of this concept has recently been demonstrated by considering a network of intersecting single-file channels, whose accessibility by the reactant and product molecules was mutually excluded. The present communication analyses the dependence of molecular distribution over the different elements of the channel system on the intrinsic reactivity and the pore filling factor. The obtained patterns are compared with those of a reference system where all channels are equally accessible by the reactant and product molecules. Special attention is given to the effect of particle self-blockages under molecular traffic control, which occurs for large intrinsic reactivities and pore filling factors. It is demonstrated that under these conditions the simulations end up in an immobilised state which is a function of the particular simulation run. Such a behaviour is not observable in the reference system.
Reaction between 8-Hydroxyquinoline and Salicylic Acid in Solid State and Solution
Authors: Singh N.B. , Singh R. , Singh K.
Published: August 2006

8-Hydroxyquinoline reacts with salicylic acid both in solid state and solution forming a yellow coloured compound. Phase diagram studies have shown the formation of a 1:1 addition compound stable in solid state and dissociated in solution. Differential thermal studies have shown that the reaction products obtained from solution and solid state reaction are almost identical except that there is a possibility of entrapped solvent molecules when the product was prepared from benzene. Also the reaction product shows a thermochromic effect. X-ray diffraction studies have revealed some structural difference between the reaction product obtained from solution and solid state reaction. Spectroscopic studies show the possibility of hydrogen bonding in the reaction product.

The reaction in the solid state is slow and once a thin layer of reaction product is formed at the surface of salicylic acid crystals, the reaction rate becomes practically negligible. This may be due to the compactness of the product layer and unfavourable crystal packing in to the crystal lattice of salicylic acid. Microstructural studies have shown that there are structural changes during solid state reaction.
Particle Entropies and Entropy Quanta. I. The Ideal Gas
Authors: Zimmermann Helmuth W.
Published: August 2006

We consider an ideal gas of monatomic independent particles, which is enclosed in a cubic box. At temperature T the particles are in thermal equilibrium. All relevant properties of the gas can be deduced from the particle statistics on the assumption that each particle of the ensemble has the particle entropy σ = ε/T = ka. ε is the translational energy of the particle. The non-dimensional number a measures the particle entropy σ in multiples of the Boltzmann constant k, which acts as an atomic entropy unit. a obeies an eigenvalue equation and satisfies boundary conditions. Eigenvalues and eigenfunctions are determined by the translational quantum numbers. Using particle entropies it is easy to calculate the Bose-Einstein and the Boltzmann distribution; and in combination with the density function we immediately get the internal energy E and the Helmholtz free energy F, the total entropy S, the chemical potential μ, the equation of state of the ideal gas at ordinary temperatures and at low temperatures near absolute zero, inclusively Bose-Einstein condensation. Entropy quanta are used to introduce the temperature into the equations of statistical thermodynamics and to calculate the thermal and the actual de Broglie wavelength at temperature T.
T,p-Dependence of Self-Diffusion in the Lower N-methylsubstituted Amides
Authors: Chen Liuping , Groß T. , Lüdemann H.-D.
Published: August 2006

Self-diffusion coefficients
Time Necessary for Reaching Chemical Equilibrium: First Passage Time Approach
Authors: Solc M.
Published: August 2006

The time necessary for reaching the macroscopic chemical equilibrium is defined as the time of first passage of system composition into the state of exact chemical equilibrium. The exact and approximate formulas for the first passage time in the case of reversible first order reaction with an arbitrary value of equilibrium constant are derived.
Solubilities of Amino Acids in Dioxane + Water Mixtures and the Determination of Transfer Free Energies of Interaction of Amino Acid from Water to Aquo-Organic Mixtures
Authors: Majumder K. , Majumder K. Mrs. , Lahiri Sujit Chandra
Published: August 2006

The solubilities of amino acids (Glycine, α-alanine, L-asparagine, L-methionine, L-proline, L-valine, L-leucine, L-phenylalanine, L-glutamine) in dioxane-water mixtures (0-100%) have been determined colorimetrically as well as pH metrically using acid-free formaldehyde solution. The solubility decreases enormously with increase in percentage of dioxane. The results have been interpreted in terms of specific solvation and hydrophobic effects.

In order to comprehend the results better, the scaled particle theory has been applied to determine the transfer free energy changes for interaction from water to aquo-organic solvent mixtures and the results are qualitatively in agreement. An estimate of the hydrophobic interactions due to constituent groups in different aquo-organic mixtures has been attempted.
Influencing the Solid-Solid Phase Transition in Phenanthrene by Suitable Doping
Authors: Gloistein U. , Epple M. , Cammenga H.K.
Published: August 2006

The order-disorder phase transition in solid phenanthrene was studied with differential scanning calorimetry and X-ray powder diffraction. This fully reversible transformation can be influenced by doping phenanthrene with structurally similar polycyclic aromatic hydrocarbons or heterocyclic aromatics. So far, four dopants have been used: benzo[c]cinnoline, phenanthridine, anthracene and carbazole. It was found that the transformation is not influenced by dopants that form eutectic phase diagrams with phenanthrene (benzo[c]cinnoline, phenanthridine). However, if the dopant is incorporated into the phenanthrene lattice to form a mixed crystal, the transition is inhibited above 3.7 mol% anthracene and 6.1 mol% carbazole, respectively. By X-ray diffraction, it is shown that these dopants induce the formation of the high-temperature phase already at room temperature.
The Structure of Laminar Premixed H2-Air Flames at Elevated Pressures
Authors: El-Gamal M. , Gutheil E. , Warnatz J.
Published: August 2006

In high-pressure flames that occur in many practical combustion devices such as industrial furnaces, rocket propulsion and internal engine combustion, the assumption of an ideal gas is not appropriate. The present paper presents a model that includes modifications of the equation of state, transport and thermodynamic properties. The model is implemented into a Fortran program that was developed to simulate numerically one-dimensional planar premixed flames. The influence of the modifications for the real gas behavior on the laminar flame speed and on flame structure is illustrated for stoichiometric H
A Combined Experimental and Theoretical Investigation of the Reactions of 3-Pentoxy Radicals: Reaction with O2 and Unimolecular Decomposition
Authors: Hein H. , Somnitz H. , Hoffmann A. , Zellner R.
Published: August 2006

The reactions of 3-pentoxy radicals with O

In addition to the experimental investigation, the unimolecular reaction channels of 3-pentoxy radicals were also analyzed by a combined
Modeling Study on Initial Soot Formation at High Pressures
Authors: Hu D. , Braun-Unkhoff M. , Frank P.
Published: August 2006

Detailed modeling of soot formation was carried out using different complex models. Main effort was put on modeling particle inception. The experimental data base consisted of soot volume fraction measurements observed in laminar premixed ethene flames for pressures between 5 and 20 bar and behind reflected shock waves for the pressure range of 4.5 to 55 bar with the fuel ethene and benzene, respectively. Due to the observation time scale in the shock wave experiments (a few milliseconds) induction period and initial soot formation zone are temporally well resolved. The present study investigates the formation and growth of the polycyclic aromatic hydrocarbon (PAH) and the adjacent section of particle formation by PAH coagulation. For the models the same relatively large reaction gas phase mechanism up to the first aromatic ring structure was used. PAH formation was described either by applying linear lumping of the well known HACA sequence (model I) or by using a detailed chemical kinetic model for species ranging from benzene to coronene (model II). Particle inception and growth was described by applying a standard mechanistic model which comprises coagulation and surface growth. The modeling study showed that growth of soot precursors and particle inception predicted by the PAH reaction mechanism (model II) gives better agreement with measured soot volume fration profiles than the HACA mechanism alone (model I). From the study it was also deduced that a simplified PAH growth model based on reactive coagulation of a relevant growth species (model III) gives similar results. From the comparison with the high pressure flame experiments it was also shown that the modified soot model is able to predict soot formation and oxidation in the post flame zone.
Kinetics of the C2(a3Πu) Radical Reacting with Selected Molecules and Atoms
Authors: Becker K.H. , Donner B. , Freitas Dinis C.M. , Geiger H. , Schmidt F. , Wiesen P.
Published: August 2006

Rate coefficients for reactions of the C

This work represents the first study of reactions of C

For the reaction C

The reaction C
Influence of Vibrational Resonances and Coriolis Coupling on Dissociation Rates in the Near-threshold Unimolecular Fragmentation of HOCl
Authors: Hauschildt J. , Weiß J. , Schinke R.
Published: August 2006

The unimolecular dissociation of HOCl in the ground electronic state near the HO+Cl fragmentation threshold is investigated employing an ab initio potential energy surface. The dynamics calculations are performed by using an imaginary absorbing potential and filter diagonalization. The computational study is mainly focused on the influence of accidental or systematic vibrational resonances on the total angular momentum dependence of dissociation rates and the importance of Coriolis interaction.
How do Parity Violating Weak Nuclear Interactions Influence Rovibrational Frequencies in Chiral Molecules?
Authors: Quack M. , Stohner J.
Published: August 2006

We outline the general theory as well as various approximations to the accurate calculation of vibrational and rotational transition frequency shifts between enantiomers of chiral molecules due to the parity violating weak nuclear interaction. The calculation of the effective parity violating potentials as a function of molecular geometry is mainly based on our recent, accurate Multiconfiguration-Linear Response approach (MC-LR, RPA and CASSCF, Berger and Quack, J. Chem. Phys.
Second Virial Coefficients of the CH4/CF4 System and Intermolecular Potentials
Authors: Schramm B. , Saad A.L.G. , El-Geubeily S.A. , Lamp J.A. , Kanan K.
Published: August 2006

This work presents a careful consideration of the second virial coefficients for methane, tetrafluoromethane, and their binary mixtures. This system is characterized by the abnormal property that the virial coefficients of the mixture are not in between the virial coefficients of the pure components. In searching for an explanation for this phenomenon, the potential parameters of the Lennard-Jones (n-6) and (n-7) families were determined from the temperature dependence of the second virial coefficients of the pure gases and their mixture. The study is based upon published data for the system as well as our own new measurements. It was concluded that the reason for this unusual behaviour is simply that the pure gases and their mixture do not follow the same intermolecular potential model. This was confirmed by two facts: first, they do not follow the law of corresponding states; and, second, the depth of the potential for the mixture and its zero are almost the geometric and arithmetic means of the corresponding parameters of the pure components, all obtained according to their respective best potential model. An application of the obtained parameters to calculate the viscosity coefficients indicated, however, that they can not describe both properties simultaneously.
The Elementary Reaction of CHF(X˜1A´) with Ozone
Authors: Hack Walter , Wagner B. , Hoyermann Karlheinz
Published: August 2006

The reaction CHF(X

k

was obtained. No change in the rate constant was observed, substituting He by the quenchers N
A theoretical investigation of the silicon-carbon chain molecule SiC8
Authors: Botschwina Peter , Schulz B. , Oswald Rainer , Stoll H.
Published: August 2006

Large-scale coupled cluster calculations have been carried out for linear SiC
A Saturated LIF Study on the High Pressure Limiting Rate Constant of the Reaction CN + NO + M → NCNO + M between 200 and 600 K
Authors: Reznickova J.G. , Hippler H. , Striebel F. , Tevzadze L.
Published: August 2006

The reaction CN + NO + M ↔ NCNO + M was studied in the bath gas helium at temperatures between 200 and 600 K and in the pressure range between 1 and 100 bar. CN radicals were generated by laser flash photolysis of BrCN at 193 nm in the presence of NO and high helium pressures. The concentration of CN radicals was detected by recording their non-resonant fluorescence yield at 420 nm after delayed excitation in the (0, 1)-band of the X
One- and Two-Dimensional Variable-Temperature 13C MAS NMR Studies on the Adsorption of Methane on Zeolite HY
Authors: Seidel U. , Brunner E. , Kärger J. , Pfeifer H.
Published: August 2006

We present a 13C MAS NMR study on the adsorption of methane on HY zeolite. These investigations were carried out at temperatures ranging from 295 K to 135 K and at loadings up to 105 methane molecules per unit cell. Up to three signals appear in the 13C MAS NMR spectra. From the dependence of their intensities and chemical shifts and results of 1H PFG NMR measurements of diffusion it could be concluded that they are due to gaseous methane in the void space above the zeolite powder, to methane adsorbed in the large cavities of the HY zeolite and to methane in the pores formed by neighbouring crystallites.
Speeds of Sound and Isentropic Compressibilities of Diethylene Glycol Dimethyl Ether - n-Alcohol Mixtures at 298.15 K
Authors: Pal A. , Dass G.
Published: August 2006

The speeds of sound has been obtained at a frequency of 4 MHz in diethylene glycol dimethyl ether + methanol, + ethanol, + 1-butanol, and + 1-pentanol across the entire composition range, at the temperature 298.15 K and atmospheric pressure using a NUSONIC velocimeter based on the sing-around technique. The ultrasonic speed values have been combined with those of the excess molar volumes converted to densities to obtain estimates of the product KS,m of the molar volumes and isentropic compressibility κS, and excess quantity KE
S,m. The KE
S,m values are negative over the entire range of composition for all mixtures with the exception of 1-pentanol, which changes sign from positive to negative. The magnitude of KE
S,m increase with the number of carbon atoms in the n-alcohol. The deviations of the speeds of sound uD from their ideal values uid in an ideal mixture were also calculated for all measured mole fractions. The behaviour of u, uD, and KE
S,m with composition and the number of carbon atoms in the alcohol molecule is discussed.
Adsorption and Desorption of Ions at the Surface of Liquid
Authors: Bunkin N.F. , Bunkin F.V.
Published: August 2006

A theoretic model of adsorption and desorption of ions at the interface liquid ionic solution - neutral gas is developed. The mechanism and quantitative criterion for the dissolved ions selection with respect to their ability or disability to adsorb is suggested. An essential attention is focused on the analysis of adsorption and desorption processes at the surface of bubbles in an aqueous electrolyte solution. The Debye-Hückel problem for the case of eφ/kT > 1 (φ is the electric potential and T is the temperature) is solved for the bubbles which are in the diffusion equilibrium with an ambient liquid. The general problem of existence of the so-called bubston microphase in molecular liquid is formulated in the Conclusion.
Phase Space, Density Matrices, Energy Densities, and Exchange Holes
Authors: Springborg M. , Perdew J. P. , Schmidt K.
Published: August 2006

In the general case, quantum-mechanical quantities are represented by operators in position- or momentum-space representations, but in phase space they are represented by functions. The correspondence between classical mechanics and quantum mechanics is non-unique as a consequence of [
Photodissociation of the Ethyl Bromide Cation at 355 nm by Means of TOF-MS and Ion Velocity Imaging Techniques
Authors: Xu D. , Price R.J. , Huang J. , Jackson W.M.
Published: August 2006

Photodissociation of ethyl bromide cation, C
Linear Triplet SiC3 and SiC5: Results of Coupled Cluster Calculations
Authors: Botschwina Peter , Oswald Rainer
Published: August 2006

Partially restricted coupled cluster calculations involving connected triple substitutions have been carried out for linear SiC
A Vibrational Spectroscopic Study of Ion Solvation and Association in Lithium Perchlorate/γ-Butyrolactone Electrolyte
Authors: Wang Jianji , Xuan X. , Lu J. , Pei N. , Mo Y.
Published: August 2006

The Raman and infrared (IR) spectra of γ-butyrolactone (BL) containing various concentrations of LiClO
Determination of Stoichiometric Dissociation Constants of Glycolic Acid in Dilute Aqueous Sodium or Potassium Chloride Solutions at 298.15 K
Authors: Partanen Jaakko I. , Juusola P.M. , Minkkinen P.O.
Published: August 2006

Equations were determined for the calculation of the stoichiometric (molality scale) dissociation constant, K
Dissociation Constants of Substituted Aryl Azo Barbituric and Thiobarbituric Acids
Authors: Masoud M.S. , Ghonaim A.K. , Ahmed R.H. , Mahmoud A.A. , Ali A.
Published: August 2006

The acid dissociation constants of 5-(substituted phenylazo) barbituric and thiobarbituric acids were determined in aqueous media and in 25–75% (v/v) ethanol–water and dioxane–water mixtures potentiometrically in the temperature range 25–40 °C, in presence of 0.5 M KCl. The values of the enthalpy change ΔH (kJ mol
Thermodynamic of Transfer and Preferential Solvation of Antibiotic Cephradine in 1,4-Dioxane-Water Mixtures
Authors: Shehatta I.
Published: August 2006

The ionization constants of cephradine in 0, 10, 20, 30, 40, 50, 60, 70, 80 and 90% ( v/v ) 1,4-dioxane-water mixed solvents were determined using a potentiometric technique and an automatic titrator. The measurements were performed at four different temperatures and 0.1 M KCl, and thus the thermodynamic parameters of ionization and transfer were evaluated. The ionization of cephradine has been found to be endothermic and entropically unfavourable. A non-linear dependence of the ionization Gibbs energies (Δ
Ion–Molecule Reactions of State Selected HCl+ Ions with Carbon Dioxide and Ethene
Authors: Malow M. , Brembs K. , Weitzel Karl-Michael
Published: August 2006

The ion–molecule reactions of state selected HCl
Crossed Beam Scattering Studies of the Dynamics of the Reaction NH+(D2; H,D) NHD+, ND2+
Authors: Wittemann A. , Sadílek M. , Polách J. , Teloy E. , Schlier Ch. , Herman Z.
Published: August 2006

The dynamics of formation of NHD
Blue-Shift in the Frequencies of the CH Stretches of Chloro- and Fluoroform Induced by C–H...π Hydrogen Bonding with Benzene Derivatives: the Influence of Electron Donating and Withdrawing Substituents
Authors: Reimann B. , Buchhold K. , Vaupel S. , Brutschy B.
Published: August 2006

Mixed clusters of benzene derivatives and trihalogenmethanes have been prepared in a supersonic beam and studied with infrared vibrational predissociation spectroscopy detected by resonant two photon ionization (IR/R2PI). We report the spectra of chloroform and fluoroform attached to the chromophores fluorobenzene, benzene, toluene,
Singlet Methylene Removal Rate Constants from the (0,1,0) Vibrational Level: Enhancement via Complex-Mediated Vibrational Relaxation
Authors: Buntine M.A. , Gutsche G.J. , Staker W.S. , Heaven M.W. , King K.D. , Lawrance W.D.
Published: August 2006

The technique of laser flash photolysis/laser absorption has been used to obtain absolute removal rate constants for singlet methylene,
Electronic Spectral Properties of Substituted Arylazothiobarbiturate Compounds in the Presence of Different Solvents
Authors: Masoud M.S. , El-Enein S.A. , Obeid N.A.
Published: August 2006

The electronic absorption spectra of 5-(substituted phenylazo) thiobarbituric acid compounds in the presence of different solvents are analyzed by the multiple regression technique using the equation:
Charge-Transfer Interactions between Quinones and Drugs (Papaverine, Pentazocine, Amodiaquin, Barbitone and Phenobarbitone)
Authors: Gangopadhyay J. , Lahiri Sujit Chandra
Published: August 2006

Charge-transfer complex formation of drugs like papaverine, pentazocine, amodiaquin, barbitone and phenobarbitone with acceptors like
Dynamic Properties of Entangled Wormlike Micelles: Sodium Laurylethersulfate at High Ionic Strength-(II)
Authors: Clancy S.F. , Fuller J.G. , Scheidt T. , Paradies H.H.
Published: August 2006

We report on the viscous behaviour of long and flexible wormlike micelles at volume fractions between Ø = 0.05–0.14 comprised of sodium laurylethersulfate (SLES) in 0.15–0.5 M NaCl equivalent of SLES concentrations between 20–50 mM at temperatures ranging from 25 °C to 45 °C by means of static and dynamic light scattering and rheology, which is an extension of previous experiments on dilute/semi-dilute solutions of SLES micelles at much lower surfactant concentrations in the presence of low salt concentrations (Clancy and Paradies, Z. Phys. Chem.
The Rate constant of the Reaction of OH(A2Σ+) with H2O2(X˜1A)
Authors: Hack Walter , Jordan R.
Published: August 2006

The rate constant of the depletion of OH radicals in the first electronically excited state with hydrogenperoxid:

OH(

was determined at room temperature under pseudo first-order conditions [OH(

The rate constant is:

similar to the quenching rate constant of OH(
An Experimental and Modelling Study of Ignition Delays in Shock-Heated Ethane-Oxygen-Argon Mixtures Inhibited by 2H-Heptafluoropropane
Authors: Ikeda K. , Mackie J.C.
Published: August 2006

Ignition delay times have been measured behind reflected shock waves in ethane-oxygen-argon mixtures at temperatures between 1150 and 1500 K and pre-ignition pressures between 10 and 14 atm. Delay times have been measured both by pressure rise and OH absorption at 307 nm. Kinetic modelling of the ignition delays has been made using the GRIMech 3.0 mechanism which with addition of several reactions involving HO
Thermodynamics of Homogeneous Nucleation under Different Constraints
Authors: Vogelsberger W.
Published: August 2006

The thermodynamics of nucleation of a pure vapour is investigated under different constraints. The well-known cases isothermal-isobaric, isothermal-isochoric and isolated are considered. The systems are composed of a number of clusters having identical size. The appropriate thermodynamic potentials are calculated from a common point of view. The actual state of the system, clusters and vapour, is compared to the initial supersaturated state. A very large number of such actual states exist if the amount of molecules in the system is large. They form a surface of the potential function. It is looked for relatively stable states of the system compared to neighbouring states of the system. These states are determined by partial derivation of the potential functions or the determination of gradient curves on the surfaces. In all three cases investigated critical states can be found. They belong to maxima of the potential function in the isothermal-isobaric and the isothermal-isochoric cases and to minima in the isolated case. No stable state can be found in the isothermal-isobaric system. On the contrary in the remaining two cases the stable equilibrium of the bulk condensed phase at saturation pressure can be reached by the system. In the isothermal-isobaric and in the isothermal-isochoric system there exists a bottom line of the potential function surface and in the isolated case a crest line can be found. Both these curves belong to relatively stable states of the system. Nucleation and ripening phases of the system may be attributed to these graphs. It is shown that the Kelvin equation gives a proper description of critical or stable states only in special regions of cluster size and cluster concentrations. It is furthermore demonstrated that the constraint of constant pressure is responsible for the significant differences between the isothermal-isobaric case and the remaining two cases in a one component system. If the presence of an inert substance is allowed the stable equilibrium of the condensed phase at saturation vapour pressure may also be attainable under constant pressure. The considerations presented for the transition vapour condensed phase can easily be applied to phase transitions in condensed phases, respectively.
The Gas-Phase Pyrolysis of Nitrocyclobutanes: a Shock-Tube Investigation Supplemented with DFT Calculations of their Thermochemical and Structural Parameters
Authors: Zhang Y.-X. , Wilcox C.F. , Bauer S.H.
Published: August 2006

Mono- and 1,1-dinitrocyclobutanes (highly diluted in Ar) were pyrolyzed at temperatures 860–1300 K in reflected shocks. Activation energies for their initial fragmentations were derived from measurements of relative rates of species loss, compared to cyclobutyl chloride and isopropyl bromide:
From Quasispecies to Universal Grammar
Authors: Nowak Martin A.
Published: August 2006

The perspective of this paper is to compare mathematical models for the evolutionary dynamics of genomes and languages. The quasispecies equation describes the evolution of genetic sequences under the influence of mutation and selection. A central result is an error threshold which specifies the minimum replication accuracy required for maintaining genetic information of a certain length. The language equation describes the evolution of communication, including the cultural evolution of grammar and the biological evolution of universal grammar. A central result is a coherence threshold which specifies certain conditions that universal grammar has to fulfill in order to induce coherent communication in a population.
Simulation of a Chemical Autonomous Agent
Authors: Daley Andrew J. , Girvin Andrew , Kauffman Stuart A. , Wills Peter R. , Yamins Daniel
Published: August 2006

A chemical autonomous agent is defined as a reproducing molecular system that carries out a thermodynamic work cycle, reminiscent of the earliest prebiotic replicators that harnessed free energy. The efficiency with which free energy is utilized to promote replication is a measure of the selective fitness of such a system. Simulations of the operation of a typical autonomous agent over a wide range of possible parameter settings reveals a fitness landscape with a well-defined maximum and a variety of features that are amenable to interpretation in terms of evolutionary concepts.
Evolutionary Consequences of Tradeoffs between Yield and Rate of ATP Production
Authors: Pfeiffer Thomas , Bonhoeffer Sebastian
Published: August 2006

Adenosine triphosphate (ATP) is a key compound in the energy metabolism of cells and is required to drive vital biochemical reactions. In heterotrophic organisms ATP production is coupled to the degradation of energy-rich organic material taken up from the environment. In the transfer of the environmental energy to cellular processes heterotrophs face a tradeoff, since the conversion of the environmental energy into ATP cannot be both maximally fast and efficient. Here we show how tradeoffs between rate and yield of ATP production arise firstly from thermodynamical principles, and secondly for the ATP production by respiration and fermentation. Using methods derived from game theory and population dynamics we investigate the evolutionary consequences for both tradeoffs. We show that spatially structured environments enable the evolution of efficient pathways with high yield. The strategies of ATP production realized in a population, however, depend on the quantitative properties of the tradeoffs.
Empirical Interatomic Potential from Polarized and Depolarized Interaction-Induced Light Scattering Spectra for Gaseous Helium
Authors: El-Kader Mohamed Sayed Abdel
Published: August 2006

Polarized and depolarized interaction-induced light scattering spectra at room temperature (294.5±1) K have been used for deriving the empirical multiparameter Morse–Morse–Morse–spline–van der Waals interatomic potential. These new data of scattering are accurate enough to permit for the first time a reliable determination of the interatomic potential of the gaseous helium as a function of the interatomic separation. The potential parameters describing the location and depth of the attractive well are given by ε = 11.2±0.015 K,
Two- and Three-Dimensional Surfaces
Authors: Hauck J. , Mika K.
Published: August 2006

The periodic zero-potential surfaces were calculated for 17 two- and 84 three-dimensional structures A
Recombination Spaces, Metrics, and Pretopologies
Authors: Stadler Bärbel M. R. , Stadler Peter F. , Shpak Max , Wagner Günther .P.
Published: August 2006

The topological features of genotype spaces given a genetic operator have a substantial impact on the course of evolution. We explore the structure of the recombination spaces arising from five different unequal crossover models in the context of pretopological spaces. We show that four of the models are incompatible with metric distance measures due to a lack of symmetry.
Kinetics and Mechanism of the Heterogeneous Oxidation of N-Substituted-p-Phenylenediamines over Supported Zinc Oxide
Authors: Salem Ibrahim A.
Published: August 2006

The kinetics and mechanism of the oxidation of some N-substituted-p-phenylenediamines over ZnO supported with some transition metal sulfates were investigated at 25 °C. The rate of reaction decreased in the following order; N,N,N´,N´-tetramethyl-p-phenylenediamine, TMPPD > N,N-diethyl-p-phenylenediamine, DEPPD > N,N-di-methyl-p-phenylenediamine, DMPPD, due to the positive inductive effect of alkyl groups. For the oxidation of DEPPD, the rate of reaction was observed to have the order: Cu(II) > Fe(III) > Ni(II) > Cr(III) > Mn(II) > Co(II). The initial rate of reaction was decreased with decreasing pH as a result of the protonation of the diamine nitrogen atoms. Also, it follows a first order dependence of the initial concentration of the diamine and attained a maximum at higher concentrations. Moreover, it increased with increasing amount of the oxidant. Greater amounts, however, reduced the rate of reaction as a result of the adsorption of the formed p-semiquinonediimine, S
Extending the Tuning Range of Short-Pulse Lasers by Transient Stimulated Raman Scattering in Gases
Authors: Fischer Ingo , Krylov V. , Bespalov V. , Staselko D.
Published: August 2006

Transient stimulated Raman scattering (SRS) is a convenient method to extend the tuning range of short-pulse lasers. In this paper we present results obtained by using 400 nm pump pulses of 2.5 ps duration. After briefly reviewing earlier work on transient SRS in pure hydrogen and in H
Periodic and Bursting pH Oscillations in an Enzyme Model Reaction
Authors: Hauser Marcus J. B. , Fricke N. , Storb U. , Müller S.C.
Published: August 2006

Oscillatory behaviour in the pH value was observed during the oxidation of sulfite by hydrogen peroxide mediated by hemin in a continuous-flow stirred tank reactor. The dynamics of this reaction was studied for a variety of flow rates of the reactants. As the flow rates increase, the oscillations evolve from relaxation oscillations to more complex shapes, displaying, among others, bursting behaviour. A reaction mechanism is proposed that involves the autocatalytic oxidation of HSO
Predicting Gas Chromatographic Retention Time of Polychlorinated Dibenzo-p-Dioxins from Molecular Structure
Authors: Delgado Eduardo J. , Matamala Adelio , Alderete Joel B.
Published: August 2006

A quantitative structure-property relationship (QSPR) model is developed to correlate the gas chromatographic retention time of polychlorinated dibenzo-
Spatiotemporal Mixed-Mode Oscillations on a Ring Electrode
Authors: Lee Jaeyoung , Christoph Johannes , Eiswirth Markus , Ertl Gerhard
Published: August 2006

We present spatiotemporal mixed-mode oscillations in the electrocatalytic oxidation of formic acid on a platinum ring electrode modified by bismuth deposition. On the anodic scan, we observed spontaneous reversal of direction of a rotating activation pulse occurring repeatedly at the same location of the ring. In the constant potential method, spatiotemporal mixed-mode oscillations of pulse reversal were shown to constitute a fraction of an ordered Farey sequence.
Detection of Short Term Correlated Events Hidden within Noise
Authors: Parmananda P. , Sahle Sven , Baier Gerold
Published: August 2006

A method for detecting transient correlated activity shrouded by high levels of noise is presented. An artificially constructed data set that is a composite of white noise and short periodic modulations is used as a probing perturbation for a spatially extended system exhibiting excitable spatiotemporal chaos. The periodic events are detected "on-line" by means of transiently induced coherence.
Spiral Waves and Euclidean Symmetries
Authors: Wulff Claudia
Published: August 2006

Spiral waves can be found in various chemical systems, for example in the Belousov–Zhabotinsky-reaction and in the catalysis on platinum surfaces. Such systems can be modelled by reaction-diffusion equations on the plane and have the symmetry of the Euclidean group of the plane. We present a center-manifold reduction ("slaving principle") near spiral waves which enables us to reduce the spiral wave dynamics to a small system of ordinary differential equations. Then we discuss the structure of the ordinary differential equations in detail. Our approach holds for any symmetry group
Femtosecond Fluorescence Anisotropy Kinetics as a Signature of Ultrafast Electronic Energy Transfer in Bichromophoric Molecules
Authors: Fidler V. , Kapusta P. , Nepras M. , Schroeder J. , Rubtsov I.V. , Yoshihara K.
Published: August 2006

Ultrafast time resolved fluorescence anisotropy decay measurements were performed to gain insight into the energy gap dependence of donor-acceptor inter-chromophoric coupling within one supra-molecule. Three new compounds, each consisting of two semi-rigidly linked and strongly coupled chromophores, were designed and synthesized for this study. Their general structure is donor-spacer-acceptor, where "donor" is phenylamino, pyrenylamino, or benzanthronylamino moiety, and acceptor is aminobenzanthrone. While being similar structurally, the compounds differ significantly in the excitation energy difference of the two chromophores in a supra-molecule. Experimental data show an ultrafast initial fluorescence emission anisotropy decrease (within less then 1 ps) when the excited state energies of the interacting chromophores are close to each other or equal. No such fast fluorescence anisotropy dynamics is observed for a compound with a large energy gap.
NMR Study of Hydrogen Bonding Association of some Sterically Hindered Alcohols in Carbon Tetrachloride, Chloroform and Cyclohexane
Authors: Luo W.-C. , Lay J.-L. , Chen Jenn-Shing
Published: August 2006

The self-association (dimerization) due to hydrogen bonding for some alcohols with bulky side chains was investigated by nuclear magnetic resonance spectroscopy. The systems studied include 2,4-dimethyl-3-pentanol or 3-methyl-3-pentanol in [
Temperature Dependence of Silicon Cluster Isomerization
Authors: Rosemeyer M. , Becker J. A. , Schäfer Rolf
Published: August 2006

The thermally induced isomerization of neutral silicon clusters has been studied by a molecular beam experiment, investigating velocity slip distributions with a time-of-flight method. The clusters dispersed in helium flow through a heated tube and, at its end, expand into vacuum. The observed velocity distributions can be explained by the existence of a cylindrical and a spherical class of isomers, whose relative intensities can be examined in dependence of the tube temperature. Assuming that the isomerization can be described by a unimolecular gas-phase reaction, one is able to derive a rate constant for the isomerization. The results are analyzed within the activated complex theory and give evidence, that entropic effects play a crucial role for the cluster isomerization reaction.
Stochastic Model of the n-Stage Reversible First-Order Reaction: Relation between the Time of First Passage to the Most Probable Microstate and the Mean Equilibrium Fluctuations Lifetime
Authors: Solc M.
Published: August 2006

Using the stochastic model of
Studies on the Solubility and Dissociation Constants of Oxalic Acid in Aquo + Ethanolic Mixtures and Determination of Single-Ion Gibbs Energy of Transfer from Aqueous to Aquo + Ethanolic Mixtures
Authors: Gumtya S. K. , Lahiri Sujit Chandra , Aditya S.
Published: August 2006

The dissociation constants of the simplest dibasic organic acid, oxalic acid were determined conductometrically and pH metrically in ethanol + water mixtures (0–87 wt% of ethanol). These data were coupled with solubility values of oxalic acid and potassium hydrogen oxalate to calculate the Gibbs energies of transfer of oxalic acid, bioxalate(HOX

The p

[H
Kinetics and Mechanisms of the Non-Catalyzed and Manganese(II) Catalyzed Oxidation of Neutral Red with Potassium Periodate in Aqueous Solution
Authors: Salem Ibrahim A.
Published: August 2006

A detailed kinetic and spectrophotometric investigation has been made for the oxidation of neutral red, a cationic phenazine dye, using potassium periodate in aqueous media. The rate of the oxidation reaction attained a first order dependence on the dye and the oxidant only at lower concentrations of the latter. The rate of reaction increases with increasing pH of the medium due to the deprotonation of the substrate nitrogen atoms. Moreover, the rate of reaction decreases with increasing ionic strength of the medium, suggesting an interaction between two singly oppositely charged ions in the activated complex. However, addition of trace amounts of manganese(II) ions sharply increases the oxidation rate. Mechanisms are proposed for both the non-catalyzed and manganese(II) catalyzed reactions which are in agreement with the experimental data.
Ultrasonic Speeds and Volumetric Properties of Dipropylene Glycol Monomethyl Ether–n-Alkylamine Mixtures at 298.15 K
Authors: Pal A. , Bhardwaj R. K.
Published: August 2006

The excess molar volume and ultrasonic speed have been measured in dipropylene glycol monomethyl ether + butylamine, dibutylamine, and tributylamine across the entire composition range, at the temperature 298.15 K and atmospheric pressure. The ultrasonic speed values have been combined with those of the excess molar volumes converted to densities to give estimates of the product
Thermodynamic and UV Studies of Association Reaction between Phenols and Benzil Mono Benzylidene Aniline
Authors: Azzouz A.S.P.
Published: August 2006

The study includes two complementary topics. Firstly, the influence of various concentrations of phenols on the UV absorption spectrum of benzil mono benzylidene aniline (BMBA) in different solvents. Experiments show a bathochromic shift in the UV spectrum of BMBA obtained after addition of phenol. When phenol is replaced by 2,4-dimethylphenol, rather similar results are observed. The results are interpreted interms of hydrogen bond formation between BMBA and phenol. Secondly, it is decided to confirm the hydrogen-bond formation stated above by thermodynamic method. Accordingly, the effect of temperature on the equilibrium constant value of the interaction between BMBA and phenol is considered. Evaluated thermodynamic parameters Δ
Developmental expression and cellular distribution of Müllerian inhibiting substance in the primate ovary
Authors: Modi Deepak , Bhartiya Deepa , Puri Chander
Published: August 2006

Ovarian follicle formation during development and follicle maturation in adulthood are crucial determinants of female fertility and disruptions in these processes may result in subfertility or infertility. Among the several factors that are involved in ovarian physiology, Müllerian inhibiting substance (MIS) also known as anti-Müllerian hormone has emerged as an important marker to predict the follicle reserve. However, the roles of MIS in human ovarian physiology are unknown. To gain an insight into the potential roles of MIS in human ovarian differentiation during development and its regulation in adulthood, the expression profiles of MIS mRNA in the developing and adult human and monkey ovaries was examined by in situ hybridization. The results revealed that in the fetal human ovaries, MIS is specifically expressed at low levels in the granulosa cells of the developing primordial follicles; a small subset (~2–3%) of oocytes express high amounts of MIS. In the adult human and monkey ovary, MIS mRNA is expressed at low levels in the primordial follicles, maximally in the primary and secondary follicles, and the expression is downregulated in the antral and atetric follicles. MIS expression is extinguished in the granulosa cells only after ovulation. These observations strongly favor the regulatory roles of MIS in folliculogenesis. MIS in the primate ovary may exert its effect during the primordial follicle formation to the terminal granulosa cell differentiation. The presence of MIS in a small subset of oocytes in the fetal ovary further points towards its additional role during fetal oocyte development.