bluuebunny/crossref_metadata_2025_split huggingface dataset:
Long-time Dynamics of Spontaneous Parametric Down-conversion and Quantum Limitations of Conversion Efficiency
Authors: Fleischhauer Michael , Veits Oliver 
Published: February 2015

Abstract
We analyze the long-time quantum dynamics of degenerate parametric down-conversion from an initial sub-harmonic vacuum (spontaenous down-conversion). Standard linearization of the Heisenberg equations of motion fails in this case, since it is based on an expansion around an unstable classical solution and neglects pump depletion. Introducing a mean-field approximation we find a periodic exchange of energy between the pump and subharmonic mode goverened by an anharmonic pendulum equation. From this equation the optimum interaction time or crystal length for maximum conversion can be determined. A numerical integration of the 2-mode Schrödinger equation using a dynamically optimized basis of displaced and squeezed number states verifies the characteristic times predicted by the mean-field approximation. In contrast to semiclassical and mean-field predictions it is found that quantum fluctuations of the pump mode lead to a substantial limitation of the efficiency of parametric down-conversion.
Symmetrie and Asymmetrie Nuclear Matter in the Thomas-Fermi Model at Finite Temperatures
Authors: Strobel K. , Weber F. , Weigel M. K. 
Published: February 2015

Abstract
The properties of warm symmetric and asymmetric nuclear matter are investigated in the frame of the Thomas-Fermi approximation using a recent modern parameterization of the effective nucleon-nucleon interaction of Myers and Świątecki. Special attention is paid to the liquid-gas phase transition, which is of special interest in modern nuclear physics. We have determined the critical temperature, critical density and the so-called flash temperature. Furthermore, the equation of state for cold neutron star matter is calculated.
A Simplified Approach to the Density Functional Theory of Molecules
Authors: Kollmar Christian 
Published: February 2015

Abstract
A simplified molecular orbital (MO) formalism based on density functional theory is developed. Starting from the same energy expression as Kohn-Sham theory the electronic density is expanded in terms of atomic mono-center densities. Application of the variational principle leads to a secular matrix with a particularly transparent structure which allows the definition of a resonance integral taking into account the effect of interference in a natural way. The construction of the secular matrix scales formally as N2 instead of N3 in the Kohn-Sham formalism with N being the dimension of the atomic orbital (AO) basis set.
Study of Water and Dimethylformamide Interaction by Computer Simulation
Authors: Cordeiro João Manuel Marques , Gomide Freitas Luiz Carlos 
Published: February 2015

Abstract
Monte Carlo simulations of water-dimethylformamide (DMF) mixtures were performed in the isothermal and isobaric ensemble at 298.15 K and 1 atm. The intermolecular interaction energy was calculated using the classical 6-12 Lennard-Jones pairwise potential plus a Coulomb term. The TIP4P model was used for simulating water molecules, and a six-site model previously optimised by us was used to represent DMF. The potential energy for the water-DMF interaction was obtained via standard geometric combining rules using the original potential parameters for the pure liquids. The radial distribution functions calculated for water-DMF mixtures show well characterised hydrogen bonds between the oxygen site of DMF and hydrogen of water. A structureless correlation curve was observed for the interaction between the hydrogen site of the carbonyl group and the oxygen site of water. Hydration effects on the stabilisation of the DMF molecule in aqueous solution have been investigated using statistical perturbation theory. The results show that energetic changes involved in the hydration process are not strong enough to stabilise another configuration of DMF than the planar one.
The Oxidation Kinetics of Thin Copper Films Studied by Resistivity Measurements
Authors: Rauh M. , Finzel H.-U. , Wißmann P. 
Published: February 2015

Abstract
Resistivity measurements on thin metal films allow to study the kinetics of oxidation. The method is applied to 50 - 60 nm thick copper films deposited on glass substrates under UHV conditions. After annealing at 150°C, the films are exposed to pure oxygen at various temperatures in the range 85 -135°C, and the electrical resistivity is recorded in situ. At these temperatures, the oxygen begins to penetrate into the interior of the films, which results in a relatively steep increase in the film resistivity. A linear time law is valid to good approximation, which can be attributed to the influence of the dissociation of an adsorbed molecular species of oxygen on the reaction velocity. A potential diffusion of oxygen in the grain boundaries is also discussed.
Pure Rotational Spectra of CS
Authors: Ahrens V. , Winnewisser G. 
Published: February 2015

Abstract
The pure rotational spectra of CS and its isotopomers 12C 33S, 12C 34S, 13C 32S, 13C 33S, 13C 34S including the very rare isotopomer 12C 36S were observed. The rotational spectra include ground and vibrationally excited transitions up to v = 16. The new measurements have been performed with the Cologne terahertz spectrometer covering the frequency region from 259 to 1075 GHz. These newly observed rotational transitions together with earlier data were fitted to a Dunham-type Hamiltonian. The obtained isotopically invariant parameters include vibrational and rotational expansion coefficients.
An EPR Study of Mo5+ Introduced into NaY Zeolites by Solid-State Reactions
Authors: Ucun F. , Sağlam A. , Köksal F. , Bahçeli S. 
Published: February 2015

Abstract
By means of an EPR investigation of Mo5+ ions introduced into NaY zeolites by solid-state reactions, the location and coordination of Mo5+ in zeolites were investigated. Two different locations, free and distorted tetrahedral, were found. The molecular orbital coefficient, ß2 , and the effective charge, Q, for the MO5+ ions in a distorted tetrahedral structure were calculated and interpreted.
Structural and Dynamic Approaches of Molten Salts by High Temperature Spectroscopies
Authors: Bessada C. , Lacassagne V. , Massiot D. , Florian P. , Coutures J.-P. , Robert E. , Gilbert B. 
Published: February 2015

Abstract
The combination of 27AI NMR expriments and Molecular Dynamics simulation confirms the exis-tence of penta-coordinated Aluminium in several molten aluminium oxides. In the case of fluoroalumi-nate molten salts, NMR and Raman spectroscopies provide complementary approaches leading to a structural description in term of AIF−
4, AlF5
2-and AlF6
3−species.
Differential Scanning Calorimetry (DSC) under High Pressure on 10-TPEB
Authors: Masberg S. , Ernst C. , Schneider G. M. , Würflinger A. , Dąbrowski R. 
Published: February 2015

Abstract
The phase behaviour of a new liquid crystal, belonging to the series l-[4-n-alkyl-biphenyl]-2-[4-isothio-cyanato-phenyl]ethane (nTPEB), n = 10, has been investigated with differential scanning calorimetry at ambient and high pressure. The phase behaviour depends on the thermal treatment. Phase transition temperatures have been determined as a function of pressure up to 300 MPa. No pressure-induced or pressure-limited phases are observed in this pressure range. Enthalpy-and volume-changes accompanying the phase transitions have been calculated using the Clausius-Clapeyron equation.
Dromion Interactions of a (2+1)-Dimensional sine-Gordon Equation
Authors: Ruan Hang-yu , Chen Yi-xin 
Published: February 2015

Abstract
Starting from two line solitons, the solution of an integrable (2 + 1)-dimensional sine-Gordon equation in bilinear form yields a dromion solution that is localized in all directions for a suitable potential. The interaction between two dromions is studied in detail through the method of figure analysis. For different selections of parameters, the interactions between two dromions may be elastic, not completely elastic, or completely inelastic.
J-Modulation in ID NMR 1H Spectrum of Taurine and Aspartate Using Spin-Echo Technique
Authors: Oturak Halil , Sağlam Adnan , Bahçeli Semiha 
Published: February 2015

Abstract
This study reports on a theoretical calculation of Hahn's spin-echo experiment in case of a model A2B2 spin system with a strongly coupling character and gives the experimental results of one-dimension 1H high-resolution NMR spectra of taurine and aspartate. The calculated amplitudes of the spin-echoes for two different proton groups of taurine are given. Using results of our calculations for taurine, the computer simulations of J-modulation are implemented. It is shown that the agreement be-tween the experimental and simulated spectra is good.
Effective Pair Potentials and Structure of Water
Authors: Cordeiro J. M. M. 
Published: February 2015

Abstract
Classical Monte Carlo calculations have been performed in order to investigate the ability of the TIP4P, SPC, and SPCE water models to reproduce the structural features of liquid water. The simulations were carried out in the NPT ensemble at 4 thermodynamic conditions. The results are compared with recent neutron diffraction data. Essentially, the three models capture equally well the thermodynamic and structural features of water. Although they were parametrized to reproduce the water properties at ambient conditions, the agreement with the experimental pair correlation functions was even better at super-critical conditions. This is because the effective pair potentials have some difficulty to re-produce cooperative interactions, like hydrogen bonds. These interactions are less effective at super-critical conditions, where the liquid behaves roughly like a gas
Nonlinear Analysis of Individual Quantum Events in a Model with Bohm Trajectories
Authors: Bräuer Kurt 
Published: February 2015

Abstract
The quantum mechanical model under consideration describes a particle beam under the influence of an oscillator. Bohm’s causal interpretation of quantum mechanics is used to calculate trajectories of the particles. Individual quantum events are defined by the intersection of the beam particle trajectories and the particle detector. The time sequence of individual quantum events is interpreted as a time series and is analyzed by linear and nonlinear methods, which involves reconstruction and investigation of the system in an embedding space. The Fourier amplitudes and the fill factors show white noise, however the Karhunen-Loeve components indicate the influence of the oscillator on the beam particles. In this model individual quantum events carry information which can be detected by the Karhunen-Loeve ex-pansion.
Medium Range Structure of Hydrogenated Amorphous Ti84Si16
Authors: Pojtinger A. , Lamparter P. , Steeb S. 
Published: February 2015

Abstract
Amorphous melt-spun Ti84Si16 was investigated by small angle neutron scattering (SANS) in the blank state as well as after loading with hydrogen or deuterium. The integrated intensity and the fractal dimension of the SANS signal change strongly with increasing H, D content. A model is proposed which explains the changes of the scattering signal. By means of this model it is concluded that melt-spun amorphous Ti84Si16 consists of two types of regions. The first type contains pure Ti and the composition of the second type is Ti80Si20-The inner surfaces between these types of regions have fractal features.
Correlated Atomic Pair Functions by the e-ϱ-Method. I. Ground State 11S and Lowest Excited States n1S (n > 1) and n3S of Helium
Authors: Seelig F. F. , Becker G. A. 
Published: February 2015

Abstract
Some low n1S and n3S states of the helium atom are computed with the aid of the e-e method which formulates the electronic wave function of the 2 electrons ψ = e-e F, where ϱ=Z(r1+r2)–½r12 and here Z = 2. Both the differential and the integral equation for F contain a pseudopotential Ṽ instead of the true potential V that contrary to V is finite. For the ground state, F = 1 yields nearly the Hartree-Fock SCF accuracy, whereas a multinomial expansion in r1, r2 , r2 yields a relative error of about 10-7 . All integrals can be computed analytically and are derived from one single “parent” integral.
Computer Simulation of Chiral Liquid Crystal Phases IX. Chiral Induction in Guest-host Systems - Calculation of the Helical Twisting Power
Authors: Memmer Reiner , Janssen Folkert 
Published: February 2015

Abstract
The chiral induction in liquid crystalline phases was studied by Monte Carlo simulation of the chiral Lebwohl-Lasher model. Binary guest-host systems composed of achiral and chiral molecules as well as of different chiral molecules were investigated in dependence on the composition. A cholesteric phase was induced by dissolving a small fraction of chiral molecules in a nematic phase. For dilute solutions the equilibrium pitch was found to be a linear function of the chiral dopant concentration. Independent of system size effects the application of self-determined boundary conditions enabled the determination of the symmetry adapted quantities for the chiral induction, the helical twisting power (HTP) and the achiral helical twisting power (AHTP). Additionally, a different orientational behaviour of enantiomeric dopants in the chiral surroundings of a cholesteric host phase has been determined.
Dynamics of Two-Dimensionally Arranged n-Octylammonium Ions Intercalated into Tetrasilicicfluormica
Authors: Yamauchi Miho , Ishimaru Shin’ichi , Ikeda Ryuichi 
Published: February 2015

Abstract
The dynamic behaviour of n-octylammonium ions intercalated into tetrasilicicfluormica was investigated by measuring 1H and 2H solid state NMR spectra and 1H spin-lattice relaxation times. X-Ray diffraction measurements revealed that the cations are arranged with the long axis parallel to the clay sheet. Uniaxial rotation of cations was found to take place above ca. 200 K among non-equivalent potential wells made by clay sheets. As a new type of 2-D motion mode, whole cationic in-plane tumbling in the 2-D layer seems to be excited above ca. 450 K. The obtained results are compared with those previously reported on saponite of an analogous structure.
Monte Carlo Calculation of the Correlation Functions for Molecular Rotation-Application to NMR
Authors: Goc Roman 
Published: February 2015

Abstract
The Monte Carlo method for calculating correlation functions for the rotational motion of atoms is presented. This method applies to crystalline solids and allows the determination of the correlation functions for any model of rotating atoms, molecules or ions constituting the material of interest, if only its crystal structure is known. The presented method permits the calculation of the correlation functions for a whole block of unit cells, not only for a single group of particles. The described method can be employed to calculate correlation functions used in the theoretical description of NMR, dielectric or neutron diffraction experiments. As an example the correlation functions and NMR relaxation time T1 of solid benzene are calculated by the Monte Carlo method for the.
Dielectric Studies of 4-w-Hexyloxy-4’-Cyanobiphenyl (60CB) at Elevated Pressure
Authors: Urban S. , Smoluchowski M. 
Published: February 2015

Abstract
The principal dielectric permittivity components in the nematic phase of 4-rc-hexyloxy-4’-cyanobiph-enyl (60CB) were measured as functions of temperature at ambient pressure and as functions of pres-sure up to 100 MPa at several constant temperatures. The dielectric anisotropy is analized in the frame of the Maier-Meier equations. The pressure dependence of the order parameter is deduced. Preliminary results for the activation volume and activation enthalpy from the pressure and temperature dependenc-es of the longitudinal relaxation times are obtained.
EPR Spectra of VO2+ Doped Ammonium Oxalate Monohydrate Single Crystals
Authors: Karabulut B. , Tapramaz R. 
Published: February 2015

Abstract
The EPR spectra of VO2+ ions in ammonium oxalate monohydrate, [(NH 4)2C2O4-H2O], single crystals have been studied at room temperature and at 113 K in mutually three perpendicular planes. The spin Hamiltonian parameters are determined using a numerical technique together with a trial and error procedure to resolve the single crystal spectra. The parallel and perpendicular components of axially symmetric g and hyperfine tensors for VO2+ ion in ammonium oxalate monohydrate single crystal are determined, and the results are discussed.
New Non-traveling Solitary Wave Solutions for a Second-order Korteweg-de Vries Equation
Authors: Hong Woo-Pyo , Jung Young-Dae 
Published: February 2015

Abstract
Modeling the propagation of two different wave modes simultaneously, the second-order KdV equation is of current interest. Applying a tanh-typed method with symbolic computation, we have found certain new analytic soliton-typed solutions which go beyond the the previously obtained traveling wave solutions.
Ground-and Excited-State Dipole Moments of 6-Propionyl-2-(dimethylamino)naphthalene Determined from Solvatochromic Shifts
Authors: Kawski A. 
Published: February 2015

Abstract
The dipole moments in the ground-and excited-state of the fluorescence probe 6-propionyl-2-(dim-ethylamino)naphthalene (PRODAN) are determined from solvatochromic shifts to μe = 2.1 D and μg = 6.4 D. These values concern the free molecule. In the first excited singlet state the dipole moment is only 3 times greater than in the ground state.
Dielectric Relaxation Study of Some Solutions Containing β-Cyclodextrin and Dimethylsulfoxide
Authors: Betting H. , Stockhausen M. 
Published: February 2015

Abstract
Dielectric spectra have been measured up to 72 GHz at 20°C for solutions of β-cyclodextrin (CD) in the following solvents over the whole solubility range of CD: dimethylsulfoxide (DMSO), DMSO/ 1,4-dioxane mixture (2:1 molar ratio), DMSO/water mixtures (2:1 and 1:2). The spectra are analyzed into a sum of Debye type spectral components. These are likely to be caused by different physical pro-cesses. The discussion shows (i) that there is a preferential CD-DMSO interaction, by far exceeding the CD-water interaction, and (») that, concerning CD-DMSO, a loose interaction can be distinguished from the formation of an inclusion complex.
Heat Capacity of the Rb3LnCl6 Compounds with Ln = La, Ce, Pr, Nd
Authors: Rycerz L. , Gaune-Escard M. 
Published: February 2015

Abstract
The heat capacities of the solid and liquid Rb3LnCl6 compounds, where Ln = La, Ce, Pr, Nd, have been determined by differential scanning calorimetry (DSC) in the temperature range 300 -1100 K. The heat capacity shows a small decrease with increasing temperature from the temperature of phase transition up to 150 -200 K above this transition for the Rb3CeCl6, Rb3PrCl6 and Rb3NdCl6 compounds. The measured heat capacities were used to calculate the formation enthalpy of the liquid phase. The results obtained compare satisfactorily with the known experimental data.
The Effects of Collisions with Neutral Particles on the Instability of Two Superposed Composite Plasmas Streaming Through Porous Medium
Authors: El-Sayed Mohamed Fahmy 
Published: February 2015

Abstract
The effects of collisions with neutral atoms on the hydromagnetic stability of the plane interface separating two streaming superposed composite plasmas of uniform densities in a porous medium are investigated. In the absence of fluid velocities, it is found, for a potentially stable configuration, that the system remains stable, while for a potentially unstable configuraion, the unstable system becomes stable under a certain condition of the wavenumber depending on the values of the fluid densities, Alfvén velocities, and the orientation of the magnetic field. The porosity of the porous medium does not have any significant effect on the stability criterion. In the presence of fluid velocities, it is found that, the instability criterion is independent of the permeability of the medium and the collision effects with neutral particles. The criterion determing the stability does not depend on the permeability of the medium but depends on the density of neutral particles. The porosity of the medium is found to have a significant effect on both the stability and instability criteria in this case. The role of the permeability of the medium, the collisional frequency, and the porosity of the porous medium on the growth rate of the unstable mode is examined analitically. Routh’s test of stability is applied to confirm the above results.
Dynamic Solvent Effects in the Degenerate Isomerization of a Hexafluoroacetone Anil Studied by High-Pressure 19 F NMR
Authors: Ohga Yasushi , Asano Tsutomu , Karger Norbert , Gross Thomas , Lüdemann Hans-Dietrich 
Published: February 2015

Abstract
The rate of the degenerate isomerization of N-hexafluoroisopropylidene-N’,N’-dimethyl-ρ-phe-nylenediamine was measured by high-pressure 19F NMR spectroscopy in a viscous hydrocar-bon, 2,4-dicyclohexyl-2-methylpentane. Pressure-induced retardations that cannot be rationalized within the framework of the transition state theory (TST) were observed, and it was concluded that the reaction was cast into the TST-invalid nonequilibrium conditions by high pressure.
NMR Studies on Dynamics of Water Intercalated in Clay Minerals
Authors: Ishimaru Shin’ichi , Ikeda Ryuichi 
Published: February 2015

Abstract
The dynamics of water molecules intercalated in D2O saturated synthetic and natural smectites, and a synthetic Na-fluormica were studied by measurements of solid state 2H NMR spectra and spin-lattice relaxation times at 150 - 370 K. The obtained results could be explained by the 2-site flip, the C2 rotation and the isotropic rotation of the D2O molecules in smectites. In fluormica, the isotropic motion was undetectable, but the axial rotation of the hydration sphere as a whole was observed. The activation energies and correlation times of the C2 rotation were almost independent of the interlayer cations but depended on the character of clay-layers.
Hydrogen Bonds in Crystalline Imidazoles Studied by 15N NMR and ab initio MO Calculations
Authors: Ueda Takahiro , Nagatomo Shigenori , Masui Hirotsugu , Nakamura Nobuo , Hayashi Shigenobu 
Published: February 2015

Abstract
Intermolecular hydrogen bonds of the type N-H...N in crystals of imidazole and its 4-substituted and 4,5-disubstituted derivatives were studied by 15N CP/MAS NMR and an ab initio molecular orbital (MO) calculation. In the 15N CP/MAS NMR spectrum of each of the imidazole derivatives, two peaks due to the two different functional groups, >NH and =N-, were observed. The value of the 15N isotropic chemical shift for each nitrogen atom depends on both the length of the intermolecular hydrogen bond and the kind of the substituent or substituents. It was found that the difference between the experimen-tal chemical shifts of >NH and =N-varies predominantly with the hydrogen bond length but does not show any systematic dependence on the kind of substituent. The ab initio MO calculations suggest that the hydrogen bond formation influences the 15N isotropic chemical shift predominantly, and that the difference between the 15N isotropic chemical shift of >NH and =N-varies linearly with the hydrogen bond length.