bluuebunny/crossref_metadata_2025_split huggingface dataset:
Polymer Crystallization as the Self-Organization of Chain Macromolecules
Authors: Melker A. I. , Vorobyeva T. V. 
Published: February 2015

Abstract
MD simulation is used to investigate ther self-organization exhibited by a chain o f atom s with strong interaction between nearest neighbours and weak interaction between more distant atoms. It is shown that the supermolecular structure is formed in several steps: at first, an initially straight chain becom es zigzag-shaped, then the zigzag ribbon folds, producing regions of crystalline and amorphous structure; after that the system contracts into a globe, the amorphous-structure regions transforming into crystalline ones by a reptile like motion. A simple analytical description of such polymer structuring is also given.
The 33S Nuclear Hyperfine Structure in the Rotational Spectrum of Isothiazole
Authors: Gripp J. , Kretschmer U. , Dreizler H. 
Published: February 2015

Abstract
We investigated the 33S nuclear quadrupole coupling in the rotational spectrum of isothiazole in natural abundance by molecular beam Fourier transform microwave spectroscopy. In addition the 14N nuclear quadrupole coupling could be analyzed with high precision. We derived the rotational constants A = 8275.51880(80) MHz, B = 5767.06181 (40) MHz, and C = 3396.85702(36) MHz, quartic centrifugal distortion constants, and the quadrupole coupling constants χaa (33S) = 8.7015 (57) MHz, χbb(33S) = -32.9696(60) MHz, χaa(14N) = 1.0732(47) MHz and χbb(14N) = -2.4753(46) MHz.
The Origin of the Helical Twist Inversion in Single Component Cholesteric Liquid Crystals
Authors: Dierking I. , Gießelmann F. , Zugenmaier P. , Mohr K. , Zaschke H. , Kuczynski W. 
Published: February 2015

Abstract
The cholesteric twist inversion by temperature variation o f a single component thermotropic liquid crystalline system was experimentally investigated and is explained by the partial twisting power model, evaluating the temperature dependent pitch o f five different configurations of a benzoic acid biphenyl ester with two chiral centers. The temperature dependence o f the twisting power and the cholesteric pitch for several stereoisomeric compounds can in first approximation be predicted by the partial twisting powers of the individual chiral centers determined from the partially racemic configurations.
Fluorescence of 8-(Phenylamino)-1-naphthalene-ammonium- sulfonate in Solvents of Different Polarity
Authors: Hüttenhain S. H. , Balzer W. , Feldmann R. 
Published: February 2015

Abstract
The solvatochromic fluorescence properties of 8-(phenylamino)-1-naphthalene-ammoniumsulfonate (1) were investigated in 22 pure solvents of rising polarity. The measurements of both Stokes' shifts and intensities discriminated between protic and aprotic solvents. Fairly good linear correlation plots of the dependence could be obtained on neglection of the values of tert.-butanol, DMF and DMSO.
Hydromagnetic Kelvin-Heimholtz Instability in the Presence of Suspended Particles and Finite Larmor Radius Effect
Authors: Sanghvi R. K. , Chhajlani R. K. 
Published: February 2015

Abstract
A linear analysis of the combined influence of a finite ion Larmor radius and suspended particles on Kelvin-Helmholtz instability in the presence of a uniform magnetic field is carried out. The magnetic field is assumed to be uniform and transverse to the direction of streaming. The medium is assumed to be incompressible. Certain simplifying assumptions are made for the motion of the suspended particles. A dispersion relation for such a medium has been obtained using appropriate boundary conditions. The stabilizing effect of a finite Larmor radius has been reasserted in the absence of the suspended particles. A stability criterion for the medium is derived, which is found to be independent of the presence of the suspended particles. Similarly a condition of instability of the system is also derived. Numerical analysis is presented in a few limiting cases of interest. Furthermore, growth rates of unstable modes of the configuration with increasing relaxation fre­quency of the particles and finite Larmor radius have been evaluated analytically. It is shown that the finite Larmor radius in the presence of the suspended particles destabilizes a certain wave number band which is stable otherwise. Implications of the suspended particles on the growth rate of unstable modes are discussed in the limit of vanishing ion Larmor radius.
Hierarchic Analysis of Chaotic Scattering in Reactive Collisions
Authors: Kovács Zoltán , Wiesenfeld Laurent 
Published: February 2015

Abstract
The method of classical trajectories is applied for a double Morse potential modeling indirect reactive collisions of three collinear atoms. The system shows chaotic scattering, which is studied in details through a hierarchic analysis of the singularities of the time delay function. Tools of the thermodynamic formalism are used to extract global quantities characterizing the scattering process.
Comments on H/D Isotope Effects on Polarizabilities of Small Molecules. Correlation with Virial Coefficient, Molar Volume, and Electronic Second Moment Isotope Effects
Authors: Van Hook W. Alexander , Wolfsberg Max 
Published: February 2015

Abstract
Literature data on H/D isotope effects on polarizability are reviewed. An argument based on perturbation theory correlates the isotopic differences with electronic transition moments via vibrational averaging. The contribution of the second moment isotope effect is especially important. The approach is first illustrated with a calculation on H2/D2 and then employed to correlate differential refractive index data on about twenty other H/D isotopic pairs. A table of bond polarizability isotope effects is presented which permits the estimation of polarizability isotope effects for various kinds of H/D substituted compounds. Coupling these results with known isotope effects on vibrational amplitude permits calculation of vapor phase virial coefficient isotope effects, while combina­tion with refractive index data on liquids yields reasonable values for the sum of the isotope effects on molar volume and electronic second moment. However the quantitative correlation of the polarizability isotope effect with isotope effects on vapor pressure or thermodynamic activity is less direct.
Pair Formation of Free Nucleobases and Mononucleosides in the Gas Phase
Authors: Dey Michael , Grotemeyer Jürgen , Schlag Edward W. 
Published: February 2015

Abstract
The formation of neutral bimolecular clusters of unsubstituted nucleobases and mononucleosides in the gas phase has been studied by IR laser desorption of the neutral molecules into a supersonic beam expansion. The complementary nucleobase pairs adenine-thymine and cytosine-guanine of D N A have been found to be formed in preference to non complementary base pairs. Association constants for the formation of the dimers of free nucleobases and nucleosides in the gas phase are calculated from the experimental results. A strong influence due to side groups affecting the dimer formation of the nucleobases is shown.
Fluorescence Anisotropy Decays of 4-Cyano-N,N-dimethylaniline in Propylene Glycol Studied by Frequency-Domain Fluorometry
Authors: Kawski A. , Piszczek G. , Gryczyńskia I. , Gryczyńskia Z. 
Published: February 2015

Abstract
The fluorescence lifetimes of 4-cyano-N,N-dimethylaniline (CDMA), measured in propylene glycol at 293 K using frequency-domain fluorometry, in the short emission (SE) and long emission (LE) bands are 20 ps and 1.65 ns, respectively. The higher emission anisotropies in the SE band compared to that in the LE band are due to weaker rotational depolarization of fluorescence. Emission anisotropy decays imply that the initial limiting emission anisotropy, r (0), is the same in the SE and LE bands and amounts to 0.28. This reflects the fact that the directions of transition moments in these bands are parallel. In the case of CDMA in propylene and ethylene glycol at temperatures from 293 to 343 K, viscosity more strongly affects the relaxation to the TICT state than does the change in polarity of the solvents used.
Isolated versus Condensed Anion Structure IV: An NQR Study and X-ray Structure Analysis of [H3N(CH2)3NH3]CdI4 * 2H2O, [H3CNH2(CH2)3NH3]CdBr4, [(CH3)4N]2CdBr 4, and [(CH3)3S]2CdBr4*
Authors: Ishiharaa Hideta , Horiuchib Keizo , Douc Shi-qi , Gesingc Thorsten M. , Buhlc J.-Christian , Paulus Helmut , Fuessd Hartmut 
Published: February 2015

Abstract
The phase I of [H3N(CH2)3NH3]CdI4 • 2H2O (1) crystallizes with isolated [CdI4]2-tetrahedra; monoclinic, C2/c, Z = 8, a = 1702.6(3), b= 1459.3(3), c= 1555.5(3) pm, and ß= 120.32(3)° at 299 K. (1) shows a first-order phase transition at T1↔II = 245 K. The eight 127I(v1) NQR lines in phase II change discontinuously into four lines in phase I. The transition entropy from DSC measurements, ∆S = 5.0 J K1- mol-1 , shows that this transition is probably due to order-disorder of cations. [H3CNH2(CH2)3NH3]CdBr4 (2) crystallizes with isolated [CdBr4]2- tetrahedra; orthorhombic P212121, Z = 4,a= 1447.8(5), b = 1280.3 (4), c = 709.7(3) pm at 299 K. (2) shows four 81Br NQR lines between II and around 325 K, above which temperature the lines disappear. [(CH3)4N]2CdBr4 (3) shows a second-order phase transition at T1↔II = 271 K. Three of four 81Br NQR lines in phase II disappear below this transition point, the other line can be observed up to 315 K. The transition entropy, ∆S = 9.01 J KT-1 mol-1 , indicates that the transition is an order-disorder type of the cations. [(CH3)3S]2CdBr4 (4) shows a first-order type phase transition at T1↔II = 304 K. The four lines spectrum of 81Br NQR is observed in phase II and disappears above the transition point. The transition entropy, ∆S = 46.8 J K- 1 mol-1 is abnormally large. The role of the hydrogen bond and the bridging power between the halogen and cadmium atoms upon the formation of the condensed anion structure is discussed.
Structural Investigation of Amorphous Europium Metaphosphate by X-ray Diffraction
Authors: Cannas Mario , Manca Enrico , Pinna Gabriella , Bettinelli Marco , Speghini Adolfo 
Published: February 2015

Abstract
The local coordination of europium in vitreous Eu metaphosphate has been investigated, using information obtainable from crystalline EuP3O9. One glassy sample and one crystalline sample of nominal EuP3O9 composition were examined by X-ray diffraction. The description of the close coordination of Eu, deduced from the orthorhombic structure of the crystalline sample, was used as a model for the amorphous situation. Besides, as a monoclinic form of Eu metaphosphate is also reported to exist, a second model was deduced from this structure, starting from the isomorphous monoclinic Yb metaphosphate. Best fitting calculations indicated that orthorhombic coordination is the better model for the short range order of europium in the vitreous metaphosphate.
Ionic Conduction and Molecular Structure of Molten FeCl3
Authors: Akdeniz Z. , Tosia M. P. 
Published: February 2015

Abstract
Former experiments on molten FeCl3 have shown that, as for AlCl3 , melting is accompanied by a transition from sixfold to essentially fourfold coordination. However, in contrast to AICI3, the FeCl3 melt near freezing has an appreciable ionic conductivity. We propose a model for the structure of FeCl3 melt as consisting of closely packed Fe2Cl6 bitetrahedral molecules in equilibrium with (Fe2Cl5) + and (Fe2Cl7)- ionised species.
The Absolute Configuration of Isoancistrocladine and 'Isohamatine' by Quantumchemical CD-Calculations
Authors: Fleischhauer J. , Koslowski A. , Repges Ch. , Gulden K.-R , Bringmann G. 
Published: February 2015

Abstract
The absolute configuration of the naphthylisoquinolines isoancistrocladine and isohamatine at the biaryl axis was determined by comparing the measured and the calculated CD spectra.
In order to calculate these spectra we used the CNDO/S method in combination with a Boltzmann weighting of conformers with different dihedral angles at the biaryl axis. The Boltzmann factors were obtained with the AM 1 method.
Unravelling the Internal Complexities of Molten Salts
Authors: Adya Ashok K. , Takagi Ryuzo , Gaune-Escard Marcelle 
Published: February 2015

Abstract
Much experimental and theoretical effort has gone into revealing the internal complexities of molten salts for the past two decades. In this paper we shall show how neutron diffraction and computer simulation techniques have helped in gaining a better understanding of these systems at the microscopic level. Firstly, a short review on the structure of molten halide systems as revealed by these techniques will be presented. Complementarity of using X-rays with neutrons and, some recent results on the structure of molten DyCl3 obtained by combining neutron and X-ray diffraction with molecular dynamic simulations will be discussed. Neutron diffraction isotopic substitution techniques have played an important role in elucidating the interatomic structure of a diversity of molten salts. Pair distribution functions (PDFs), determined for a number of 1:1 and 2 :1 halide melts, provided theorists with a critical test of their model potentials. It is now clear that for 1:1 molten systems theoretical models based on Fumi-Tosi potentials can adequately describe many of the structural features. Nevertheless, the chal-lenge is two fold: (i) to determine real interatomic potentials for 2:1 and 3 :1 molten systems capable of reproducing not only the microscopic structural details obtained at the partial PDF, gαβ (r) level, but also their macroscopic behaviour and, (ii) to characterise the structure in binary molten salt mixtures.
Development of a Field Cycling NMR System for PQR Detection in Biopolymers
Authors: Ivanov Dmitri , Redfield Alfred 
Published: February 2015

Abstract
Our goal is to extend the sensitivity of field cycling pure quadrupole resonance (PQR) methods to be of use in biological systems. The nuclei of interest are 25Mg, 67Zn, 43Ca, 11B and 17O. The experiment is based on a field cycling double resonance technique, in which the quadrupole resonance of a rare nucleus is found through its effect on the magnetic order of the abundant nucleus to which the rare nucleus is coupled through dipole-dipole interaction. A field-cycling NMR spectrometer has been developed, based on our existing 500 MHz high resolution spectrometer. The sample can be shuttled pneumatically from the high field of a commercial 500 MHz magnet to the magnet's top, where the residual field and its gradient is canceled out by a pair of Helmholtz coils. Low field homogeneity is within 0.5 gauss. The X H signal is observed at high field as a free induction decay (FID) after a 90° pulse. At low field the sample can be irradiated by a digitally tuned RF coil in the 300 kHz-7 MHz range. The sample has to be maintained at low temperature (~30 K) to avoid relaxation via thermal motion of methyl groups in biomolecules. For this purpose field cycling equipment is placed in a variable temperature dewar (4 - 300 K). We plan to use solutions of biomolecules in standard cryoprotective buffer, containing ~ 30% glycerol. Preliminary results on the quadrupole resonance of natural abundance 17O in the cryoprotective buffer and of natural abundance 11B in a protease inhibitor at 50 mM are presented.
2D Off-Resonance Nutation NQR Spectroscopy of Spin 3/2 Nuclei
Authors: Maćkowiak Mariusz , Kątowski Piotr 
Published: February 2015

Abstract
The effects of off-resonance irradiation in nutation NQR experiments are demonstrated both experimentally and theoretically. The theoretical description of the off-resonance effects in 2D nutation NQR spectroscopy is given, and general exact formulas for the asymmetry parameter are obtained. It is shown that the outcome of the off-resonance nutation experiments depends on the data acquisition procedure, leading to one- or three-line nutation spectra. To explain this fact and to describe the off-resonance nutation experiment properly, the transient response theory of a quadrupolar spin system to an RF pulse was modified using the wave-function approach. The 2D separation of interactions technique has been applied to separate a static and a randomly time-fluctuating dynamic part of the quadrupole interaction in the antiferroelectric phase of poly-crystalline ammonium dihydrogen arsenate.
Two-dimensional off-resonance nutation NQR spectroscopy has been used to determine the full quadrupolar tensor of spin-3/2 nuclei in several molecular crystals containing the 35Cl and 75As nuclei. The off-resonance phenomena in 2D NQR are very important from the practical point of view (determination of ƞ in multiple or broad-line spectrum) and also provide interesting information on the dynamic properties of a quadrupolar spin system.
Halogen Nuclear Quadrupole Coupling Constants: Comparison of ab initio Calculations which include Correlation, with Experiment
Authors: Palmer Michael H. , Blair-Fish John A. , Sherwood Paul , Guest Martyn F. 
Published: February 2015

Abstract
Ab initio determination of the electric field gradient (EFG) tensors at halogen and other centres ena-bled determination of the nuclear quadrupole coupling constants (NQCC) for a diverse set of axially symmetric (C3v , C∞v, D∞h and other symmetries) inorganic and organic molecules, where the heavy ele-ments are Cl, Br, and I with C, Si, Ge, and Sn hydrides. The latter elements are in an approximately tetrahedral environment. The study presents results at a standardised level of calculation, triple-zeta in the valence space (TZV) plus polarisation functions (TZVP) for the equilibrium geometry stage; all-electron MP2 correlation is included in all these studies. f-Orbital exponents were optimised for both Br and I centres in the methanes; the atomic populations of the f-orbital components are very small for the Br-and I-atoms, confirming their role as polarisation functions rather than having any bonding character. The EFG are determined at equilibrium with the TZVP basis set, except Sn and I centres where the basis set is TZV + MP2. For the bromo and iodo compounds, especially the latter, it is essential to allow for core polarisation, by decontraction of the p,d-functions. This is conveniently done by initial optimization of the structure with a partly contracted basis, followed by reestablishment of the equilibrium structure with the decontracted basis. A close correlation of the observed (microwave spectral) data with the calculations was observed, using the 'best' values for the atomic quadrupole moments for Cl, Br, and I; thus there seems no need to postulate that the value of QBr for 79Br and 81Br are in error. The SCF and MP2 wave-functions were converted into localised molecular orbitals by the Boys Method. This allowed a study of the differing s/p/d-hybridisation ratios, and the centroid positions, to be compared with the quadrupole coupling constants. The charge distributions for the atoms were converted into local bond dipoles, which in turn are correlated with the electronegativity differences of the bonded atoms.
Dynamic Properties and Phase Transitions in A2ZnBr4(A= (CH3)4 N and (CH3)4P) as Studied by 79Br NQR and Multinuclear NMR
Authors: Tada Hironobu , Nakayama Hirokazu , Nakamura Nobuo 
Published: February 2015

Abstract
In order to understand the mechanism of ferroelastic phase transitions in A2ZnBr4 (A = (CH3)4 N and (CH3)4 P), the temperature dependences of 79Br NQR frequencies and the spin-lattice relaxation times were measured. The temperature dependences of the 1H and 31P spin-lattice relaxation times were measured as well for a possible correlation between the cation dynamics and the phase transition. Although the phase transition temperatures of these two compounds differ much (~ 100 K), the correlation times for the cation reorientation at the individual transition temperatures amount to some 10-11 s for both compounds.
Structure and Dynamics of Li3InBr6 and NaInBr4 by Means of Nuclear Magnetic Resonance
Authors: Tomita Yasumasa , Yamada Koji , Ohki Hiroshi , Okuda Tsutomu 
Published: February 2015

Abstract
Li3InBr6 and NaInBr4 have been synthesized and characterized by means of DTA, 81Br NQR, 6Li, 7Li, 23Na, and 115In NMR, and AC conductivity. These measurements revealed the presence of phase transitions and cationic diffusion in both compounds. From the spin-lattice relaxation times of 81Br NQR and the peak widths of 7Li and 23Na NMR spectra, it is deduced that the conduction is due to cationic diffusion. The activity energy for the Li+ diffusion was found to be 24 kJ/mol for Li3InBr6 .
Pressure Dependence of the EFG in Semimetallic Arsenic and Antimony
Authors: Hill G. J. , Keartland J. M. , Hoch M. J. R. 
Published: February 2015

Abstract
The pressure variation of the axial EFG at the ion sites in semimetallic arsenic and antimony, at am-bient temperature, has been investigated using pulsed NQR. A weakly nonlinear decrease of the EFG is observed in both systems. The data are analyzed in terms of the lattice contribution to the EFG, which involves a lattice of point monopoles immersed in a uniform, compensating, background charge. The pressure dependence of the EFG obtained from the present measurements is far weaker than the pres-sure dependence of the calculated lattice contribution. Our results support previous suggestions that va-lence effects are important in determining the EFG in these semimetals.
NQR Studies of Halogen Treated 1-2-3 System
Authors: Ossipyan Ya. A. , Sidorov N. S. , Kulakov V. I. , Matukhin V. L. , Pogoreltsev A. I. , Anashkin V. N. , Safin I. A. , Matukhin L. E. 
Published: February 2015

Abstract
NQR spectra of copper in polycrystalline samples of iodine treated RBa2Cu3Oy (R = Y, Gd) were studied. The results of all the experiments show evidence for the modifications occurring in the oxygen sublattice in treated compounds.
Comparison of 35Cl NQR Spectra between the Mixed Crystals K2Sn1-xRexCl6 and the Al3+ Doped Crystals K2SnCl6:Al3+
Authors: Seo Y. M. , Pelzl J. , Dimitropoulus C. 
Published: February 2015

Abstract

35Cl Nuclear Quadrupole Resonance (NQR) has provided a valuable tool for investigating the local structure in mixed crystals K2S1-xRexCl6 and Al3+ doped crystals K2SnCl6:Al3+ . The measured NQR line shapes and relaxation times of both kinds of impurity containing crystals in the cubic phase of the host K2SnCl6 show markedly different impurity effects; static impurity effects in K2Sn1-x RexCl6 and dynamic effects in K2SnCl6 :Al3+ . The 35Cl NQR spectra of K2SnCl6:Al3+ near the transition temperature (Tc) indicate the presence of pretransition of the local structure in the high temperature cubic phase.
Nuclear Quadrupole Interactions of 27Al in Alexandrite Single Crystal
Authors: Yeom T. H. , Choh S. H. , Hong K. S. , Yeom H. Y. , Park Y. H. , Yu Y. M. 
Published: February 2015

Abstract
In an alexandrite single crystal four sets of NMR spectra for 27Al (I=5/2) were observed in the crystallographic ab, be, and ca planes. The AI (I) center has four magnetically inequivalent Al sites, whereas the AI (II) center has two. The nuclear quadrupole coupling constant and asymmetry parameter of Al(I) and AI(II) in an alexandrite crystal were determined. Within the experimental accuracy, our parameters turned out to have the same values as those of a chrysoberyl crystal.