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1999[X]
101Author    DanielA. Blank, Ruedi StoopRequires cookie*
 Title      
 Abstract    We describe a novel type of bursting that we observe in simulations of large recurrent networks of biophysically plausible, intrinsically non-bursting neurons. The mechanism responsible for the bursting is a combination of excitatory feedback received from neighbouring neurons, together with an activity-dependent adaptation mechanism that slows down spiking. During the bursting phases, the firing patterns are not repeated and the lengths of the interburst intervals are varying. We develop a simple phenomenological model that captures most qualitative aspects of the observed collective bursting. We compare the parameter range leading to bursting in the phenomenological model, with parameter estimates from cortical anatomy and physiology, and conjecture that the discovered new type of bursting should also be observable in biological neocortical networks. 
  Reference    Z. Naturforsch. 54a, 617—627 (1999); received September 17 1999 
  Published    1999 
  Keywords    Bursting, Recurrent Excitation, Network Dynamics 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0617.pdf 
 Identifier    ZNA-1999-54a-0617 
 Volume    54 
102Author    Hideta Ishihara, Keizo Horiuchi, Shi-Qi Dou, ThorstenM. Gesing, J.-Christian Buhl, Helmut Paulus, Ingrid Svoboda, Hartmut FuessRequires cookie*
 Title    Isolated versus Condensed Anion Structure V: X-ray Structure Analysis and 81 Br NQR of f-butylammonium tribromocadmate(II)-l/2 water, /-propylammonium tribromocadmate(II), and fra-trimethylammonium heptabromodicadmate(II)  
 Abstract    The crystal structures of the condensed bromocadmate anions with chains built of [CdBr 3 ] were de-termined by X-ray structure analysis at 300 K. In addition, the temperature dependence of the Br NQR frequencies was observed. [O-CjHyNHOCdBr^-^O (1) crystallizes with a double Br bridged chain (monoclinic, P2/c, Z = 4, a = 1963.4(8), 6 = 887.7(4), c= 1432.1(6) pm, and ß= 110.66(2)°). Six ' 'Br NQR lines are observed at temperatures between 77 and 330 K. (j'-C 3 H 7 NH 3)CdBr 3 (2) crystalliz-es with a triple Br bridged chain (orthrhombic, Pbca, Z= 8, a = 1975.4(6), b = 1415.8(4), c = 690.1(2) pm). (2) shows three x Br NQR lines at temperatures between 77 and 193 K. A phase transition occurs at 224 K. The structure of [(CH 3) 3 NH] 3 Cd 2 Br 7 ] (3) was redetermined. (3) consists of a triple Br bridged chain and a discrete [CdBr 4 ] tetrahedron (hexagonal, P6 3 mc, Z= 8, a = 1483.5(2), c = 685.7(5) pm). The structure of (3) is identical to the one reported by Daoud, Perret, and Dusausoy, Acta Crystallogr., B35, 2718 (1979). Three 81 Br NQR lines are observed at temperatures between 77 and 243 K. 
  Reference    Z. Naturforsch. 54a, 628—636 (1999); received September 6 1999 
  Published    1999 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0628.pdf 
 Identifier    ZNA-1999-54a-0628 
 Volume    54 
103Author    OlegD. JefimenkoRequires cookie*
 Title    On the Relativistic Invariance of Maxwell's Equation  
 Abstract    It is common knowledge that Maxwell's electromagnetic equations are invariant under relativistic transformations. However the relativistic invariance of Maxwell's equations has certain heretofore over-looked peculiarities. These peculiarities point out to the need of reexamining the physical significance of some basic electromagnetic formulas and equations. 
  Reference    Z. Naturforsch. 54a, 637—644 (1999); received September 25 1999 
  Published    1999 
  Keywords    Maxwell's Equation, Special Relativity, Lorentz Contraction 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0637.pdf 
 Identifier    ZNA-1999-54a-0637 
 Volume    54 
104Author    Rui-Hua Xie, Qin RaoRequires cookie*
 Title    Third-order Optical Nonlinearities of Higher Fullerene and Carbon Nanotube  
 Abstract    Recent theoretical and experimental studies on the third-order optical nonlinearities of higher fullerenes including C 7 o, C76, Cs4, Cs6, C90, C94 and C% are briefly reviewed. The extended Su-Schrieffer-Heeger model is introduced and applied to study the third-order optical nonlinearity of chiral carbon nanotubes (CCN), where the average contribution r of one carbon atom to the third-order optical nonlinearity of each CCN is calculated and compared with that of a well characterized polyenic polymer. It is found that (i) the smaller the diameter of a CCN, the larger the average contribution T; (ii) the metallic CCN favors larger third-order optical nonlinearity than the semiconducting one; (iii) CCN can compete with the conducting polymer achieving a large third-order optical susceptibility. Also the doping effect on the second-order hyperpolarizability of a tubular fullerene is investigated. It is found that the doping effect increases greatly the magnitude of the second-order hyperpolarizability of tubular fullerene. 
  Reference    Z. Naturforsch. 54a, 645—658 (1999); received July 23 1999 
  Published    1999 
  Keywords    Optical Susceptibility, Hyperpolarizability, Sum-over-state Approach, Resonance En-hancement, CM, Higher Fullerene, Tubular Fullerene, Carbon Nanotube, Chiral Effect, Doping Effect 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0645.pdf 
 Identifier    ZNA-1999-54a-0645 
 Volume    54 
105Author    E. J. BaranRequires cookie*
 Title    Mean Amplitudes of Vibration of the Novel BiFy -and Dianions  
  Reference    Z. Naturforsch. 54a, 659 (1999) 
  Published    1999 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0659_n.pdf 
 Identifier    ZNA-1999-54a-0659_n 
 Volume    54 
106Author    H. Betting, M. StockhausenRequires cookie*
 Title    Dielectric Relaxation of Hexadeutero Dimethylsulfoxide  
 Abstract    The dielectric relaxation parameters of the title substance (DMSO-d fi) in its pure liquid state are determined from meas-urements up to 72 GHz at 20°C in comparison to protonated DMSO. While the relaxation strengths do not differ, the relax-ation time of DMSO-d 6 is significantly longer (21.3 ps) than that of DMSO (19.5 ps). 
  Reference    Z. Naturforsch. 54a, 661 (1999); received September 7 1999 
  Published    1999 
  Keywords    Dielectries, Isotopic Substitution, Liquids, Rela-xation 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0661_n.pdf 
 Identifier    ZNA-1999-54a-0661_n 
 Volume    54 
107Author    Kurt BräuerRequires cookie*
 Title    Nonlinear Analysis of Individual Quantum Events in a Model with Böhm Trajectories  
 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. 
  Reference    Z. Naturforsch. 54a, 663—674 (1999); received September 27 1999 
  Published    1999 
  Keywords    Individual Quantum Events, Nonlocality, Böhm Trajectories, Time Series, Reconstruction of Trajectories 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0663.pdf 
 Identifier    ZNA-1999-54a-0663 
 Volume    54 
108Author    M. Massalska-Arodź, A. Würflinger, D. BüsingRequires cookie*
 Title    High-pressure DTA Studies of the Phase Behaviors of 4-n -butyl-thiocyanobiphenyl (4TCB) and 4-w-pentyl-4'-n-phenyl-cyanocyclohexane (5HCP)  
 Abstract    DTA measurements of 4-/i-butyl-thiocyanobiphenyl (4TCB) and/?-cyano-/?'-pentylphenyl-cyclohex-ane (5HCP) have been performed in the temperature range 220 K-390 K and pressures up to 400 MPa. For 4TCP a transition from a crystalline to a liquid crystal phase (probably smectic E) could be detect-ed at higher pressures > 90 MPa. The pressure dependence of the transition temperature has been estab-lished. At pressures lower than 88.7 MPa no transition of SmE into a crystal or into a glass has been found. For 5HCP only the melting curve was observed, in contrast to 5PCH, which displays a liquid crystalline nematic phase. 
  Reference    Z. Naturforsch. 54a, 675—678 (1999); received November 5 1999 
  Published    1999 
  Keywords    DTA, High Pressures, Phase Transitions, Liquid Crystals 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0675.pdf 
 Identifier    ZNA-1999-54a-0675 
 Volume    54 
109Author    B.Thimme Gowda, D.Krishna Bhat, H. Fuess, Al WeissRequires cookie*
 Title    C1 NQR Spectra of Substituted N-(phenyl)-2-chloroacetamides  
 Abstract    Fifteen methyl-, nitro-, or mixed substituted N-(phenyl)-2-chloroacetamides were investigated by 35 C1 NQR. The temperature dependence of the frequencies of the 3-methylphenyl and 2,6-dimethylphe-nyl derivatives were studied for the range 77 K<T<300 K. Only one co C-Cl frequency was observed for the compound with the two exceptions. For N-(2-nitro,4-chlorophenyl)-2-chloroacetamide the ob-served values of 35.623 and 35.350 MHz were assigned to ft) C-C 1 and ring C-Cl, whereas the corre-sponding values are 36.254 and 34.815 MHz for N-(2-methyl, 3-chlorophenyl)-2-chloroacetamide. The experimental frequencies of all compounds have been compared with values estimated from NQR sub-stituent parameters and the frequency of N-(phenyl)-2-chloroacetamide. The agreement is remark-ably good with a maximum deviation of 1.64 MHz. Furthermore y(35 Cl) of all compounds has been correlated with X k, and with the Hammett constants. 
  Reference    Z. Naturforsch. 54a, 679—684 (1999); received September 7 1999 
  Published    1999 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0679.pdf 
 Identifier    ZNA-1999-54a-0679 
 Volume    54 
110Author    T. A. Mirnaya, V. S. Dradrah, G. G. YaremchukRequires cookie*
 Title    Mesophase and Glass Formation in Binary Systems of Caesium and Alkali-Earth Metal Butyrates  
 Abstract    The phase diagrams of the binary systems of non-mesomorphic components such as caesium-mag-nesium, caesium-calcium and caesium-barium butyrates have been studied by differential thermal analysis and hot stage polarization microscopy. Smectic liquid crystals are found in some composition ranges of the binaries with calcium and barium butyrates. The liquid crystal appearance in these systems is explained by the exhibition of latent mesomorphism of caesium butyrate. Glasses are obtained in all systems studied, the formation of vitreous optical anisotropic mesophase being revealed only for binary from caesium and barium butyrates. 
  Reference    Z. Naturforsch. 54a, 685—688 (1999); received October 19 1999 
  Published    1999 
  Keywords    Phase Diagram, Mesophase, Glass, Metal Alkanoate 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0685.pdf 
 Identifier    ZNA-1999-54a-0685 
 Volume    54 
111Author    R. Goc, J. Wąsicki, S. LewickiRequires cookie*
 Title    Ammonium Ions Dynamics in NH 4 Br -Proton NMR T 1 Measurements and Simulations  
 Abstract    Monte Carlo simulation of correlation functions for ammonium bromide have been carried out and the NMR relaxation times T { resulting from these functions were calculated. Results of simulations are compared to experimental values of T x measured in the temperature range 92 K to 292 K. 
  Reference    Z. Naturforsch. 54a, 689—694 (1999); received October 29 1999 
  Published    1999 
  Keywords    NMR, NH 4 Br, Relaxation, Monte Carlo, Simulation 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0689.pdf 
 Identifier    ZNA-1999-54a-0689 
 Volume    54 
112Author    Tie-Jun Zhou, Z. Yu, Y. W. DuRequires cookie*
 Title    T\inneling Magnetoresistance in a Two-Layered La^^Ca^^MnjO Polycrystal  
 Abstract    By the sol-gel method, a polycrystal bulk of two-layered La2-2xCai+2 X Mn207 with x = 0.2 was successfully synthesized. A high sensitive low-field TMR was found at low temperature. PACS numbers: 75.30.Kz, 72.15.Gd 
  Reference    Z. Naturforsch. 54a, 695—698 (1999); received August 20 1999 
  Published    1999 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0695.pdf 
 Identifier    ZNA-1999-54a-0695 
 Volume    54 
113Author    A. Pojtinger, P. Lamparter, S. SteebRequires cookie*
 Title    Structure of Sputtered Amorphous Zr-Hf-Si Alloys  
 Abstract    Amorphous (Zr,Hf)37Si 63 alloys were produced by sputtering. Their total structure factors were determined by X-ray diffraction. Using the methods of isomorphous substitution and Reverse Monte Carlo simulation, the partial pair correlation functions were obtained. The results were compared with the partial functions of amorphous Ti^Si^. In the amorphous alloys under inves-tigation the transition metal -metalloid correlation dominates the short range order. 
  Reference    Z. Naturforsch. 54a, 699—703 (1999); received November 2 1999 
  Published    1999 
  Keywords    Amorphous Zr-Hf-Si, X-ray Diffraction, RMC Model 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0699.pdf 
 Identifier    ZNA-1999-54a-0699 
 Volume    54 
114Author    A. Pojtinger, P. Lamparter, S. SteebRequires cookie*
 Title    Medium Range Structure of Hydrogenated Amorphous Ti 84 Si 16  
 Abstract    Amorphous melt-spun Ti 84 Si 16 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 Ti 84 Si 16 consists of two types of regions. The first type contains pure Ti and the composition of the second type is Ti 80 Si 2 o-The inner surfaces between these types of regions have fractal features. 
  Reference    Z. Naturforsch. 54a, 704—710 (1999); received November 2 1999 
  Published    1999 
  Keywords    Amorphous Ti 84 Si 16, Small Angle Neutron Scattering, Hydrogen Loading 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0704.pdf 
 Identifier    ZNA-1999-54a-0704 
 Volume    54 
115Author    F. F. Seelig, G. A. BeckerRequires cookie*
 Title    Correlated Atomic Pair Functions by the -Method. I. Ground State 1 J S and Lowest Excited States « J S (n > 1) and TI 3 S of Helium  
 Abstract    Some low n 1 S and n 3 S 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 as = e~ e F, where q = Z(r\ + r 2) -\r\ 2 and here Z = 2. Both the differential and the integral equation for F contain a pseudopotential V 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 n, r 2 , r\ 2 yields a relative error of about 10 -7 . All integrals can be computed analytically and are derived from one single "parent" integral. 
  Reference    Z. Naturforsch. 54a, 711—717 (1999); received October 29 1999 
  Published    1999 
  Keywords    Electron Correlation, Pair Function, 5-states of Helium 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0711.pdf 
 Identifier    ZNA-1999-54a-0711 
 Volume    54 
116Author    MichaelC. Böhm, Christoph SaalRequires cookie*
 Title    On a Direct Superconducting Pairing Mechanism  
 Abstract    We suggest that superconductivity can be traced back to a first-order interaction between the charge carriers which does not necessarily involve second-order electron-phonon coupling. For small molecular model systems it is demonstrated that the formation of Cooper pairs can lead to an attenuation of the destabilizing influence of the Pauli antisymmetry principle (PAP). We suggest that this attenuation of a fermionic quantum constraint is the driving force for the superconducting transition. Whenever the PAP is activated in single-particle hoppings of electrons, the corresponding moves reduce the electronic derealization; they raise the ensemble energy. The stability of a fermionic system is enhanced with decreasing influence of the PAP. Moves of Cooper pairs are not influenced by any quantum constraint of the intersite type. This behaviour differs from the well-known fermionic constraints. The quantum statistics of Cooper pairs is of a mixed type combining a fermionic on-site and a bosonic intersite behaviour. It coincides with the quantum statistics of so-called hard core bosonic ensembles. In the present work Cooper pair formation has been studied for smaller molecular models. The electronic Hamiltonian employed is of the two-parameter Hubbard-type. The solid state phenomenon superconductivity is correlated with the molecular concepts of "antiaromaticity" and "aromaticity". Arguments are given which support the present interpretation. 
  Reference    Z. Naturforsch. 54a, 718—738 (1999); received May 26 1999 
  Published    1999 
  Keywords    Superconductivity, Possible First-Order Pairing Interaction, Quantum Statistics, Pauli Antisymmetry Principle, Superconductivity vs Antiaromaticity and Aromaticity 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0718.pdf 
 Identifier    ZNA-1999-54a-0718 
 Volume    54 
117Author    Masahiko Matsumiya, Masatoshi Takano, Ryuzo Takagi, Reiko FujitaRequires cookie*
 Title    Electrochemical Behavior of Ba 2+ at Liquid Metal Cathodes in Molten Chlorides  
 Abstract    The electrochemcal behavior of Ba 2+ on several liquid metal electrodes (AI, Bi, Cd, Pb, Sn and Zn) in a NaCl-KCl equimolar solvent at 1000 K has been investigated by means of cyclic voltammetry and chronopotentiometry. The kinetic parameters and the diffusion coefficient for Ba 2+ were determined by cyclic voltammetry with conventional, semi-integral, semi-differential methods and chronopotentiometry. It was revealed that on a liquid Pb electrode in the NaCl-KC1 system at 1000 K the quasi-reversible cathodic reaction Ba 2+ + 2e~ + Pb —> BaPb takes place. In addition, the kinetic parameters and the diffusion coefficient agree well with the values determined by various electroanalyses. The possibility of alloy formation between Ba and Sn was also demonstrated in this paper. 
  Reference    Z. Naturforsch. 54a, 739—746 (1999); received September 13 1999 
  Published    1999 
  Keywords    Alloy Formation Reaction, Barium, Liquid Metal Cathodes, Molten Salts 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0739.pdf 
 Identifier    ZNA-1999-54a-0739 
 Volume    54 
118Author    Reiner Memmer, Folkert JanssenRequires cookie*
 Title    Computer Simulation of Chiral Liquid Crystal Phases IX. Chiral Induction in Guest-host Systems - Calculation of the Helical Twisting Power  
 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 enantiomer-ic dopants in the chiral surroundings of a cholesteric host phase has been determined. 
  Reference    Z. Naturforsch. 54a, 747—754 (1999); received October 29 1999 
  Published    1999 
  Keywords    Chirality, Liquid Crystals, Computer Simulation, Induced Cholesteric Phases, Helical Twisting Power 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0747.pdf 
 Identifier    ZNA-1999-54a-0747 
 Volume    54 
119Author    Miho Yamauchi, Shin'. Ichi, Ishimaru, Ryuichi IkedaRequires cookie*
 Title    Dynamics of Two-Dimensionally Arranged n-Octylammonium Ions Intercalated into Tetrasilicicfluormica  
 Abstract    The dynamic behaviour of rc-octylammonium ions intercalated into tetrasilicicfluormica was inve-stigated by measuring 'H and 2 H solid state NMR spectra and 'H 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 poten-tial 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 pre-viously reported on saponite of an analogous structure. 
  Reference    Z. Naturforsch. 54a, 755—760 (1999); received November 15 1999 
  Published    1999 
  Keywords    Tetrasilicicfluormica, n-Octylammonium Ion, *H and 2 H NMR, Intercalation Compound, Spin-Lattice Relaxation 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0755.pdf 
 Identifier    ZNA-1999-54a-0755 
 Volume    54 
120Author    Yi-Tian Gao, Bo TianRequires cookie*
 Title    On the Variable-coefficient Burgers-Hlavaty Equation  
 Abstract    We study Hlavaty's generalization of the Burgers equation containing certain coefficient functions. We obtain a new auto-Bäcklund transformation and a family of exact analytical solu-tions along with the constraints on those coefficients. 
  Reference    Z. Naturforsch. 54a, 761—762 (1999); received April 27 1999 
  Published    1999 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0761_n.pdf 
 Identifier    ZNA-1999-54a-0761_n 
 Volume    54 
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