bluuebunny/crossref_metadata_2025 huggingface dataset:
Interactions in undersaturated and supersaturated lysozyme solutions: Static and dynamic light scattering results
Authors: Muschol Martin , Rosenberger Franz
Published: July 2002

We have performed multiangle static and dynamic light scattering studies of lysozyme solutions at pH=4.7. The Rayleigh ratio Rθ and the collective diffusion coefficient Dc were determined as function of both protein concentration cp and salt concentration cs with two different salts. At low salt concentrations, the scattering ratio Kcp/Rθ and diffusivity increased with protein concentration above the values for a monomeric, ideal solution. With increasing salt concentration this trend was eventually reversed. The hydrodynamic interactions of lysozyme in solution, extracted from the combination of static and dynamic scattering data, decreased significantly with increasing salt concentration. These observations reflect changes in protein interactions, in response to increased salt screening, from net repulsion to net attraction. Both salts had the same qualitative effect, but the quantitative behavior did not scale with the ionic strength of the solution. This indicates the presence of salt specific effects. At low protein concentrations, the slopes of Kcp/Rθ and Dc vs cp were obtained. The dependence of the slopes on ionic strength was modeled using a DLVO potential for colloidal interactions of two spheres, with the net protein charge Ze and Hamaker constant AH as fitting parameters. The model reproduces the observed variations with ionic strength quite well. Independent fits to the static and dynamic data, however, led to different values of the fitting parameters. These and other shortcomings suggest that colloidal interaction models alone are insufficient to explain protein interactions in solutions.
Nature of optical transitions in conjugated oligomers. I. Theoretical characterization of neutral and doped oligo(phenylenevinylene)s
Authors: Cornil J. , Beljonne D. , Brédas J. L.
Published: July 2002

The nature of the main optical transitions taking place in oligo(phenylenevinylene)s is analyzed in both the neutral and oxidized states. Geometry optimizations are first carried out with the Hartree–Fock semiempirical Austin Model 1(AM1) method; on the basis of the resulting geometries, the transition energies and their intensities are determined by means of the Hartree–Fock semiempirical intermediate neglect of differential overlap (INDO) method combined with a single configuration-interaction (SCI) technique. The major aspect of the results is to show that two subgap absorption peaks are induced by the generation of polarons (radical cations), while a single absorption feature is expected when bipolarons (dications) are formed, in agreement with the experimental absorption spectra of the oligomers; this situation is, however, in marked contrast with that in the polymer. The possible formation of diamagnetic π dimers is also discussed.
The distribution function of internal distances of a single polymer chain with excluded volume in two and three dimensions: A Monte Carlo study
Authors: Wittkop M. , Kreitmeier S. , Göritz D.
Published: July 2002

The probability distribution functions Ps(r) of the distance r between the end points of subchains of a single excluded volume chain in two and three dimensions were studied using the bond-fluctuation model. The index s refers to three principle cases. Case s=0: the subchain is identical to the whole chain. Case s=1: the subchain constitutes one extremity of the whole chain. Case s=2: the subchain belongs to the central part of the whole chain. It is shown that the data can be described by the functions fs(x)∼xθs for small x and fs(x)∼xκs exp(−Dsxδs) for large x, x being the scaled distance. All exponents θs, κs, and δs were calculated and compared with existing values in the literature. In two dimensions a crossover between θs and κs was detected whereas in three dimensions θs≂κs within statistical errors.
A model of attractive interactions to account for fluid–fluid phase separation of protein solutions
Authors: Malfois Marc , Bonneté Françoise , Belloni Luc , Tardieu Annette
Published: July 2002

Concentrated γ-crystallin and lysozyme solutions have been reported to undergo a fluid–fluid phase separation when cooled below a critical temperature. This behavior is under control of the weak forces acting in solution between macromolecules. We have used small angle x-ray scattering at the synchrotron radiation facility LURE (Orsay, France) to analyze the interaction potentials. A model of attractive interactions which depends upon three parameters, protein diameter, potential depth, and range, is able to account for both the x-ray structure factors measured at high temperature and for the low temperature phase separation. Although van der Waals forces could be at the origin of the attractive interaction potentials, other more specific effects also contribute to the protein phase diagrams.
Brownian motion through a two-dimensional glass: Trapping, hopping, and diffusion
Authors: Luo Li-Shi , Phillies George D. J.
Published: July 2002

Computer simulations and computational diagnostics are used to study a Monte Carlo Brownian walker moving through a glass of immobile force centers. Clear evidence for distinct trapping, hopping, and hindered-diffusive regimes is seen in the mean-square displacement and the probability distribution P(r,t) for a step r during delay t. In the hopping regime distinct time scales for intratrap and intertrap motion are apparent; probe localization and time scale separation depend inversely on temperature T. In the hindered-diffusion regime, the effective diffusion coefficient D̄ follows an Arrhenius temperature dependence. In this regime, 〈r2(t)〉 is very nearly linear in t, even for walkers that have only diffused a small fraction of the matrix particle nearest-neighbor distance. We infer that analytic calculations using relatively low-order time expansions should give reasonable values for D̄ of probe particles in our glass.
Brownian dynamics simulation of needle chains
Authors: Nyland Gunnar H. , Skjetne Paal , Mikkelsen Arne , Elgsaeter Arnljot
Published: July 2002

Polymers consisting of rigid segments connected by flexible joints (needle chains) constitute an important class of biopolymers. Using kinetic theory as a starting point, we first derive the generalized coordinate–space diffusion (Fokker–Planck) equation for the needle chain polymer model. Next, the equivalent generalized coordinate Itô stochastic differential equation is established. Nonlinear transformations of variables finally yield a stochastic differential equation for the needle chain spatial coordinates in the laboratory coordinate system where the coefficients are expressed in terms of the chain constraint conditions. This latter equation constitutes the basis for our needle chain Brownian dynamics (BD) algorithm. The used needle chain model includes needle translation–translation and rotation–rotation hydrodynamic interactions, a homogeneous solvent flow field, external forces, excluded volume effects, and bending and twisting stiffness between nearest neighbor segments. For this chain model we find that by proper generalization of the involved parameters the mathematical analysis of the polymer dynamics, in great detail, maps onto the analysis of the bead–rod–spring polymer chain model with constraints presented by Öttinger in Phys. Rev. E 50, 2696 (1994). Preliminary numerical simulation data show that for a three segment needle chain, with needle axial ratio equal to five, our new needle chain BD algorithm is, in general, more than about 103 times more efficient than the bead–spring polymer chain BD algorithm commonly used as an approximation for studies of such polymer chains. This efficiency ratio increases asymptotically proportional to approximately the fourth power of the needle axial ratio. In addition to this major gain in efficiency, the needle chain model for segmented polymers, in general, incorporates a more realistic hydrodynamic description of the individual segments and, in particular, the joints between the segments than the bead–rod–spring models.
Diffusion limited first contact of the ends of a polymer: Comparison of theory with simulation
Authors: Pastor Richard W. , Zwanzig Robert , Szabo Attila
Published: July 2002

The mean first passage time for the close approach of the ends of a polymer is investigated by computer simulation of the Brownian dynamics of a Rouse model. There are N bonds, of length b, and the contact distance is a. The results for N=50, 75, and 100 are compared with theoretical predictions by Wilemski and Fixman (WF), and by Szabo, Schulten, and Schulten (SSS). Theory differs from simulation by a factor of 1.3 to 3 when a is comparable to b but improves considerably when a is reduced. Closest agreement is obtained at a/b=0.1 for WF with a δ function sink, where theory is within the statistical error (≊5%) of the simulation for each case.
Raman light scattering from supracritical binary fluid mixtures: CH4/CF4
Authors: Baglin F. G. , Sweitzer S. , Stanbery W.
Published: July 2002

A supracritical fluid mixture of CH4/CF4 (1:9 mole ratio) has been studied at 323 K at densities between 3.0 and 19.1 mol -ℓ (m/ℓ) by inelastic (Raman) light scattering originating from the ν1 totally symmetric stretching mode of methane. Furthermore, a Raman depolarization ratio study of the integrated intensities of the ν1 mode was also carried out as a function of density. A model is proposed to aid in the understanding of the intensity-density behavior in terms of both allowed and interaction-induced (ii) contributions to the overall observed signal. The model makes use of one, two, and three body light scattering via both the dipole polarizability, the dipole–quadrupole polarizability, and also takes into account various partner combinations in the multibody light scattering. Whereas, the model generally predicts correct Iνh behavior, (here I is the Raman intensity and the subscripts refer to the vertical polarization direction of the laser (ν) and the direction of the analyzer either ν or h (horizontal)), it is shown that the standard assumption of the no V–R coupling is violated, leading to a different mechanism for Iiso Raman light scattering. This leads to extensive three-body ii Iiso signal cancellation, but none from the Iνh spectrum. The model adequately explains these concepts through the usual interaction induced processes as well as a unique cross term.
The topology of multidimensional potential energy surfaces: Theory and application to peptide structure and kinetics
Authors: Becker Oren M. , Karplus Martin
Published: July 2002

Topological characteristics of multidimensional potential energy surfaces are explored and the full conformation space is mapped on the set of local minima. This map partitions conformation space into energy-dependent or temperature-dependent “attraction basins’’ and generates a “disconnectivity’’ graph that reflects the basin connectivity and characterizes the shape of the multidimensional surface. The partitioning of the conformation space is used to express the temporal behavior of the system in terms of basin-to-basin kinetics instead of the usual state-to-state transitions. For this purpose the transition matrix of the system is expressed in terms of basin-to-basin transitions and the corresponding master equation is solved. As an example, the approach is applied to the tetrapeptide, isobutyryl-(ala)3-NH-methyl (IAN), which is the shortest peptide that can form a full helical turn. A nearly complete list of minima and barriers is available for this system from the work of Czerminiski and Elber. The multidimensional potential energy surface of the peptide is shown to exhibit an overall “funnel’’ shape. The relation between connectivity and spatial proximity in dihedral angle space is examined. It is found that, although the two are similar, closeness in one does not always imply closeness in the other. The basin to basin kinetics is examined using a master equation and the results are interpreted in terms of kinetic connectivity. The conformation space of the peptide is divided up in terms of the surface topography to model its “folding’’ behavior. Even in this very simple system, the kinetics exhibit a “trapping’’ state which appears as a “kinetic intermediate,’’ as in the folding of proteins. The approach described here can be used more generally to classify multidimensional potential energy surfaces and the time development of complex systems.
Modified nonequilibrium molecular dynamics for fluid flows with energy conservation
Authors: Tuckerman Mark E. , Mundy Christopher J. , Balasubramanian Sundaram , Klein Michael L.
Published: July 2002

The nonequilibrium molecular dynamics generated by the SLLOD algorithm [so called due to its association with the DOLLS tensor algorithm (D. J. Evans and G. P. Morriss, Statistical Mechanics of Nonequilibrium Liquids (Academic, New York, 1990)] for fluid flow is considered. It is shown that, in the absence of time-dependent boundary conditions (e.g., shearing boundary conditions via explicit cell dynamics or Lees–Edwards boundary conditions), a conserved energy, H exists for the equations of motion. The phase space distribution generated by SLLOD dynamics can be explicitly derived from H. In the case of a fluid confined between two immobile boundaries undergoing planar Couette flow, the phase space distribution predicts a linear velocity profile, a fact which suggests the flow is field driven rather than boundary driven. For a general flow in the absence of time-dependent boundaries, it is shown that the SLLOD equations are no longer canonical in the laboratory momenta, and a modified form of the SLLOD dynamics is presented which is valid arbitrarily far from equilibrium for boundary conditions appropriate to the flow. From an analysis of the conserved energy for the new SLLOD equations in the absence of time-dependent boundary conditions, it is shown that the correct local thermodynamics is obtained. In addition, the idea of coupling each degree of freedom in the system to a Nosé–Hoover chain thermostat is presented as a means of efficiently generating the phase space distribution.
Theory of double quantum two-dimensional electron spin resonance with application to distance measurements
Authors: Saxena Sunil , Freed Jack H.
Published: July 2002

A formulation is presented for calculating double quantum two dimensional electron spin resonance (DQ-2D ESR) spectra in the rigid limit that correspond to recent experimental DQ-2D ESR spectra obtained from a nitroxide biradical. The theory includes the dipolar interaction between the nitroxide moieties as well as the fully asymmetric g and hyperfine tensors and the angular geometry of the biradical. The effects of arbitrary pulses (strong but not truly nonselective pulses) are included by adapting the recently introduced split Hamiltonian theory for numerical simulations. It is shown how arbitrary pulses in magnetic resonance create “forbidden” coherence pathways, and their role in DQ-2D ESR is delineated. The high sensitivity of these DQ-2D ESR signals to the strength of the dipolar interaction is demonstrated and rationalized in terms of the orientational selectivity of the “forbidden” pathways. It is further shown that this selectivity also provides constraints on the structural geometry (i.e., the orientations of the nitroxide moieties) of the biradicals. The theory is applied to the recent double quantum modulation (DQM) experiment on an end-labeled poly-proline peptide biradical. A distance of 18.5 Å between the ends is found for this biradical. A new two pulse double quantum experiment is proposed (by analogy to recent NMR experiments), and its feasibility for the ESR case is theoretically explored.
A three-dimensional quantum mechanical study of the H+H2+→H2+H+ system: Competition between chemical exchange and inelastic processes
Authors: Last Isidore , Gilibert Miquel , Baer Michael
Published: July 2002

In this publication is presented a three-dimensional quantum mechanical study, within the coupled states approximation, of the process H+H2+(v1=0,j1)→H++H2. Both reactive (exchange) and inelastic processes were considered. The main findings are: (a) The charge transfer process takes place at large distances (∼3.5 Å) and so the reagents are essentially on the lower potential energy surface when they approach the close interaction region; (b) The main contributions to the reaction (exchange) are from large impact parameters; (c) The initial rotational states have at most a minor effect on the results (whether being charge transfer or chemical exchange); (d) The deep potential well in the interaction region of the lower surface has only a secondary effect on the results.
Photoelectron spectroscopy of Cn− produced from laser ablated dehydroannulene derivatives having carbon ring size of n=12, 16, 18, 20, and 24
Authors: Wakabayashi Tomonari , Kohno Masamichi , Achiba Yohji , Shiromaru Haruo , Momose Takamasa , Shida Tadamasa , Naemura Koichiro , Tobe Yoshito
Published: July 2002

n -Dehydroannulenes with the ring size of n=12, 16, 18, 20, and 24 and with three to five indanyl substituents are laser ablated by 355 nm photons. The indanyl unit is lost stepwise up to the complete deletion to leave the bare annulenyl skeleton. The monoanions of these products are mass analyzed first, and then subjected to a second laser pulse of 266 nm to obtain photoelectron spectra for Cn− with n=12, 16, 18, 20, and 24. The spectra are compared with those obtained by using graphite as a target of the laser ablation. The comparison of the two spectra provides useful information on the structure of neutral carbon clusters.
Density functional calculations of molecular hyperfine interactions in the zero order regular approximation for relativistic effects
Authors: van Lenthe Erik , van der Avoird Ad , Wormer Paul E. S.
Published: July 2002

Expressions are derived within the relativistic regular approximation (ZORA) for the evaluation of the magnetic hyperfine interactions in paramagnetic molecules. For hydrogen-like atoms exact first order relations between the ZORA and Dirac formalism are given for the calculation of g- and A-tensors. Density functional calculations are performed on the neutral atoms Cu, Ag and Au, on some small test molecules NO2, HCO, and TiF3, and on some paramagnetic clusters consisting of 5 or 7 atoms of the group IB metals: Cu7, Cu2Ag5, CuAg6, Ag5, Ag7, and Au7. It is shown that the calculated ESR parameters of the heptamers are in good agreement with results of experiments, which originally were assigned to pentamers.
A femtosecond snapshot of crystalline order in molecular liquids
Authors: Ratajska-Gadomska B. , Gadomski W. , Wiewior P. , Radzewicz C.
Published: July 2002

A theoretical model of ultrafast dynamics in the optical Kerr effect in molecular liquids is developed. It assumes that for short times there exist dynamic quasicrystalline structures including a central molecule and its nearest neighbors. The interaction of such structures with a femtosecond laser pulse leads to excitation of vibrational modes (local phonons) which are responsible for subpicosecond nonlinear polarizability of the liquid. The results of numerical calculations performed for benzene show a very good agreement with the experimental data. The lifetime of the dynamic quasicrystalline structures in benzene, at room temperature, is estimated to be about 200 fs.
Spin contamination in quantum Monte Carlo wave functions
Authors: Huang Chien-Jung , Filippi Claudia , Umrigar C. J.
Published: July 2002

The wave function usually employed in quantum Monte Carlo (QMC) electronic structure calculations is the product of a Jastrow factor and a sum of products of up-spin and down-spin determinants. Typically, a different Jastrow factor is used for parallel- and antiparallel-spin electrons in order to satisfy the cusp conditions and thereby ensure that the local energy at electron–electron coincidence points is finite. However, when the Jastrow factor is not completely symmetric under interchange of the spatial coordinates of the electrons, the resulting wave function may not be an eigenstate of the spin operator Ŝ2. For the Li and Be atoms, we evaluate the spin contamination in a variety of wave functions with progressively higher body-order correlations in the Jastrow factor. The spin contamination is found to be small for all the wave functions (10−3–10−5), the smaller values being obtained for the more accurate wave functions. On the other hand, if we eliminate the spin contamination by employing a symmetric Jastrow (and sacrificing the parallel-spin cusp condition), the resulting wave functions typically have about 20%–40% larger root mean square fluctuations in the local energy. A wave function which both satisfies the cusp conditions and has definite spin can be constructed, but for systems with many electrons, its computational cost is higher than for the commonly used QMC wave functions.
Vibronic structure of the valence π-photoelectron bands in furan, pyrrole, and thiophene
Authors: Trofimov A. B. , Köppel H. , Schirmer J.
Published: July 2002

The A22 and B12 states formed in the ionization of the outermost π orbitals in furan, pyrrole and thiophene are shown to interact vibronically via nontotally symmetric b2 vibrational modes. The interaction is strongest in pyrrole and thiophene, where the conical intersection between the two adiabatic surfaces occurs near the minimum of the upper (B12) state. The resulting nonadiabatic effects manifest themselves in the B12 bands by a lack of resolved structure in case of pyrrole and thiophene, and by a line broadening in case of furan. The spectra are investigated using a linear vibronic coupling model. All totally symmetric a1 (tuning) modes and nontotally symmetric b2 (coupling) modes describing the ring motion are taken into account. The parameters of the model are obtained with the aid of ab initio calculations. The ground state optimized geometries and vibrational frequencies are computed at the level of the second-order Mo/ller–Plesset perturbation theory, while the dependence of the ionization energies on the nuclear configuration is evaluated using the outer valence Green’s function method. Where appropriate, assignments of the observed structure are given.
On the physical interpretation of torsion-rotation parameters in methanol and acetaldehyde: Comparison of global fit and ab initio results
Authors: Xu Li-Hong , Lees Ronald M. , Hougen Jon T.
Published: July 2002

Equilibrium structural constants and certain torsion–rotation interaction parameters have been determined for methanol and acetaldehyde from ab initio calculations using GAUSSIAN 94. The substantial molecular flexing which occurs in going from the bottom to the top of the torsional potential barrier can be quantitatively related to coefficients of torsion–rotation terms having a (1−cos 3γ) dependence on torsional angle γ. The barrier height, six equilibrium structural constants characterizing the bottom of the potential well, and six torsion–rotation constants are all compared to experimental parameters obtained from global fits to large microwave and far-infrared data sets for methanol and acetaldehyde. The rather encouraging agreement between the Gaussian and global fit results for methanol seems both to validate the accuracy of ab initio calculations of these parameters, and to demonstrate that the physical origin of these torsion–rotation interaction terms in methanol lies primarily in structural relaxation with torsion. The less satisfactory agreement between theory and experiment for acetaldehyde requires further study.
Properties of the constant loss in ionically conducting glasses, melts, and crystals
Authors: Ngai K. L.
Published: July 2002

A frequency independent or nearly frequency independent contribution to the dielectric loss is present in all ionic conductors independent of the chemical and physical structures. An exhaustive collection of dielectric relaxation data of glassy, crystalline, and molten ionic conductors are analyzed to obtain the magnitudes of their constant losses and the dependencies on temperature, ion density, ion mass, dc conductivity activation energy, dc conductivity level, the nonexponential conductivity relaxation parameter β, the mixed alkali effect, and the decoupling index Rτ. Trends of changes in the constant loss when modifying the structure of the glassy matrix or mixing two different alkali ions are also found. In a glass-forming molten salt, 0.4Ca(NO3)2⋅0.6KNO3, the constant loss turns out to have approximately the same temperature dependence as the mean square displacement of the ions obtained by elastic neutron scattering measurement. All dependencies and properties found indicate that the physical origin of the constant loss may be traced to the displacement of the ions in their local librational or vibrational motion, but anharmonicity is not a necessary ingredient.
Torsional motion and vibrational overtone spectroscopy of methanol
Authors: Hänninen V. , Horn M. , Halonen L.
Published: July 2002

An internal coordinate Hamiltonian model has been constructed to model torsional motion in the OH stretching vibrational overtone region of methanol, CH3OH. The model includes harmonic couplings between OH and CH stretching vibrations and Fermi resonance interactions between OH stretches and COH bends and between CH stretches and CH2 bends. A symmetrized basis set has been used to form block diagonal Hamiltonian matrices with strong resonance couplings off-diagonal. Observed torsional levels of the excited vibrational states have been used as data in a least squares optimization of the model parameters, some of which have been estimated by ab initio calculations. The experimentally observed increase in the effective torsional barrier in moving to highly excited OH stretching states has been explained by the model.
Ultrafast structural deformation of NO2 in intense laser fields studied by mass-resolved momentum imaging
Authors: Hishikawa Akiyoshi , Iwamae Atsushi , Yamanouchi Kaoru
Published: July 2002

The ultrafast structural deformation of NO2 in an intense laser field (1.0 PW/cm2) is studied by mass-resolved momentum imaging (MRMI) of the Op+ and Nq+ (p,q=1–3) fragment ions produced from NO2z+ through the Coulomb explosion processes, NO2z+→Op++Nq++Or+ (z=p+q+r). The N–O distance just before the Coulomb explosion is elongated significantly from that in the electronic ground state, and it monotonically increases from 1.7 to 2.1 Å as z increases from 4 to 9. The ∠O–N–O bond angle increases toward a linear configuration as a function of z, which is interpreted in terms of the formation of the light-dressed potential energy surfaces. The two-body fragmentation pathways to produce NO+ and NO2+ are also investigated by the MRMI measurements to derive the extent of the asymmetrical bond elongation of one of the two N–O bonds.
Monte Carlo simulation of a grafted polymer chain confined in a tube
Authors: Sotta P. , Lesne A. , Victor J. M.
Published: July 2002

We study a grafted polymer chain confined in a tube by Monte Carlo simulations of a self-avoiding walk on a cubic lattice. We measure the probability distribution of the one-dimensional gyration radius r∥ and of the length of tube z occupied by the chain. We use a biased Monte Carlo algorithm in order to sample a large interval of r∥ or z. A simple scaling law is proposed for the length of tube z occupied by the chain, in the regime where the chain behaves as a linear, one-dimensional packing of units submitted to excluded-volume (blobs). A simple scaling law is also proposed for the number of contacts as a function of z. A model expression for the free energy of the confined chain is then deduced. It has a scaling structure similar to that of a free self-avoiding walk, with a different exponent of z in the small z regime.
A study of the BrO and BrO2 radicals with vacuum ultraviolet photoelectron spectroscopy
Authors: Dyke J. M. , Gamblin S. D. , Hooper N. , Lee E. P. F. , Morris A. , Mok D. K. W. , Chau F. T.
Published: July 2002

The BrO radical, prepared by the Br+O3 reaction, has been investigated by ultraviolet photoelectron spectroscopy. Two vibrationally resolved bands were observed corresponding to the ionizations BrO+(X 3Σ−)←BrO(X 2Π) and BrO+(a 1Δ)←BrO(X 2Π). These assignments are supported by the results of complete active space self-consistent field/multireference configuration interaction (CASSCF/MRCI) calculations performed as part of this work. The adiabatic ionization energies of these bands were measured as (10.46±0.02) and (11.21±0.02)eV, respectively. Measurement of the vibrational separations in these bands led to estimates of the vibrational constants in the ionic states of (840±30) cm−1 and (880±30) cm−1, and Franck–Condon simulations of the vibrational envelopes gave values of the ionic state bond lengths of (1.635±0.005) and (1.641±0.005) Å for the X 3Σ− and a 1Δ states of BrO+, respectively. The O+Br2 reaction was found to give a band at (10.26±0.02) eV associated with a reaction product. Comparison of the results obtained for the Br+O3 reaction showed that it could not be assigned to ionization of BrO. Calculations of the first adiabatic ionization energies and Franck–Condon simulations of the vibrational envelopes of the first photoelectron bands of BrO2 and Br2O and their isomers demonstrated that this band corresponds to the first ionization of OBrO, the BrO2+(X 1A1)←BrO2(X 2B1) ionization. Franck–Condon simulations were performed with the experimental geometry of BrO2(X̃ 2B1) but with different cationic state geometries. The simulated envelope which most closely matched the experimental envelope gave geometrical parameters of re=1.6135 Å and ∠OBrO=117.5° for the ionic state.
Orientational and collision-induced contribution to third-order nonlinear optical response of liquid CS2
Authors: Kiyohara Kenji , Kamada Kenji , Ohta Koji
Published: July 2002

We investigated the mechanism of the third-order nonlinear optical (NLO) response of liquid CS2 by molecular dynamics simulation from both qualitative and quantitative aspects. The time-dependent relative importance of the orientational and collision-induced dynamics of the molecules to the fluctuation of polarizability was analyzed in order to understand the relation between the dynamics of the molecules and the third-order NLO response. Our analysis shows that the fluctuation of polarizability associated with the orientational dynamics of the molecules is responsible for 81% of the total NLO response. We calculated the values of the third-order NLO coefficients and they were found to be in semiquantitative agreement with the experimental values. We discuss the validity of fitting semiempirical theoretical models to the experimental signals as a means to analyze the mechanism of the NLO response.
Computation of elliptic functions
Authors: Critchfield Charles L.
Published: July 2002

The duplication formula for Weierstrass’ elliptic function is the basis for a simple algorithm by which one can calculate values of that function. As in the case for sin θ, this method is more efficient when the argument is reduced to a value near the origin by addition or subtraction of a suitable number of full periods of the function. When the invariants g2 and g3 are real numbers, (z;g2,g3) is periodic on both the real and imaginary axes of z, although these periods are not necessarily the basic ones. Convenient formulas for determining the relevant periods are given. They include an expression for q(k2) in terms of Gauss’ arithmetico-geometrical sequence. The method is applied to Jacobian functions by finding the invariants that represent a given k2. When this parameter is real the periods are well known and the Jacobian functions are calculated directly without transforming to those for which the parameter lies between zero and unity.
Nonperturbative approximate solution for Lane–Emden equation
Authors: Shawagfeh N. T.
Published: July 2002

A nonperturbative approximate analytical solution is derived for the Lane–Emden equation using the Adomian decomposition method. The solution is in the form of a power series with easily computable coefficients. The Padé approximants method is used to accelerate the convergence of the power series. Comparison with some known exact and numerical solutions shows that the present solution is highly accurate.
Localized solutions of the Dirac–Maxwell equations
Authors: Radford C. J.
Published: July 2002

The full classical Dirac–Maxwell equations are considered in a somewhat novel form and under various simplifying assumptions. A reduction of the equations is performed in the case when the Dirac field is static. A further reduction of the equations is made under the assumption of spherical symmetry. These static spherically symmetric equations are examined in some detail and a numerical solution presented. Some surprising results emerge from this investigation: (i) Spherical symmetry necessitates the existence of a magnetic monopole. (ii) There exists a uniquely defined solution, determined only by the demand that the solution be analytic at infinity. (iii) The equations describe highly compact objects with an inner onion like shell structure.
On the thermodynamical interpretation of perfect fluid solutions of the Einstein equations with no symmetry
Authors: Krasiński Andrzej , Quevedo Hernando , Sussman Roberto A.
Published: July 2002

The Gibbs–Duhem equation dU+pdV=TdS imposes restrictions on the perfect fluid solutions of Einstein equations that have a one-dimensional symmetry group or no symmetry at all. In this paper, we investigate the restrictions imposed on the Stephani Universe and on the two classes of models found by Szafron. Upon the Stephani Universe and the β≠0 class of Szafron symmetries are forced. We find the most general subcases of the β=0 model of Szafron that are consistent with the Gibbs–Duhem equation and have no symmetry.
Mechanical systems with nonholonomic constraints
Authors: Krupková Olga
Published: July 2002

A geometric setting for the theory of first-order mechanical systems subject to general nonholonomic constraints is presented. Mechanical systems under consideration are not supposed to be Lagrangian systems, and the constraints are not supposed to be of a special form in the velocities (as, e.g., affine or linear). A mechanical system is characterized by a certain equivalence class of 2-forms on the first jet prolongation of a fibered manifold. The nonholonomic constraints are defined to be a submanifold of the first jet prolongation. It is shown that this submanifold is canonically endowed with a distribution—this distribution (resp., its vertical subdistribution) has the meaning of generalized possible (resp., virtual) displacements. The concept of a constraint force is defined, and a geometric version of the principle of virtual work is proposed. From the principle of virtual work a formula for a workless constraint force is obtained. A mechanical system subject nonholonomic constraints is modeled as a deformation of the original (unconstrained) system. A direct characterization of a constrained system by means of a class of 2-forms along the canonical distribution is given, and “constrained equations of motion” in an intrinsic form are found. A geometric definition of regularity for systems under nonholonomic constraints is provided. In particular, the case of Lagrangian systems is discussed. Also systems subject to holonomic constraints and nonholonomic constraints affine in the velocities are investigated within the range of the general scheme.
On the theory of skin effect: inclusion of arriving term in collision integral
Authors: Kaganov M. I. , Lyubarskiı̆ G. Ya. , Mitina A. G.
Published: July 2002

An algorithm for calculating the surface impedance of a normal isotropic metal is constructed by taking into account the arriving term in the collision integral (in the case of specular reflection). Analytic expressions are obtained for scattering probability describing the s-, p-, and d-scattering.
Effect of magnetic flux trapped in intergranular space on magnetic field dependences of rf absorption in HTS materials
Authors: Golubnichaya G. V. , Kirichenko A. Ya. , Maksimchuk I. G. , Cherpak N. T.
Published: July 2002

Dependences of rf absorption in HTS ceramic samples on a magnetic field H<Hc1g (Hc1g is the lower critical field for granules) have been investigated. Some features of these dependences cannot be described by the standard model of critical states, taking into account magnetic flux trapping only in granules. A new electrodynamic model, taking into account qualitatively the magnetic flux trapping both in granules and in the intergranular space is proposed. The modified model makes it possible to explain all the currently observed peculiarities in the magnetic-field dependences of rf absorption both for H>Hc1g and for H<Hc1g.
Acoustic transparency of layered conductors
Authors: Galbova O. , Ivanovski G. , Kirichenko O. V. , Peschansky V. G.
Published: July 2002

The method for investigating the electron properties of metals, which was developed by I. M. Lifshits under the assumption that the form of the energy–momentum relation for charge carriers is known a priori, and for reconstructing the electron energy spectrum from experimental data is applied for studying acoustoelectronic effects in layered conductors with a strongly anisotropic conductivity of the metallic type. It is shown that the attenuation of acoustic waves propagating along the layers can become much weaker in strong magnetic fields. The conditions for acoustic transparency of layered conductors with a quasi-two-dimensional electron spectrum are obtained, and the oscillatory dependence of acoustic damping decrement on the magnetic field is analyzed for various orientations of the acoustic wave vector and the magnetic field.
A new type of spin density waves in quasi-one-dimensional antiferromagnetic metals
Authors: Petrova T. G. , Rozhavskii A. S.
Published: July 2002

The model of a quasi-one-dimensional metal having antiferromagnetic order is considered. It is shown that the electron spectrum undergoes dielectrization in the ground state, accompanied by the emergence of a magnetic superstructure, i.e., spin density waves (SDW). In contrast to the triplet SDW observed in paramagnetic metals, the order parameter of SDW in this case is singlet-type. The dependence of the dielectric gap in the one-electron spectrum and the shape of the magnetic spiral on the commensurability parameter in a SDW is obtained. It is shown that, upon a transition to the SDW state, the rearrangement of the system occurs in such a way that its total magnetic moment remains equal to zero.
Persistent current in a ballistic ring with a quantum dot
Authors: Moskalets M. V.
Published: July 2002

The influence of temperature and chemical potential on the persistent resonant current in a ballistic ring with a quantum dot connected to an electron reservoir is considered.
Superconductivity effects in hopping conductivity of La2CuO4 single crystal with excess oxygen
Authors: Belevtsev B. I. , Dalakova N. V. , Panfilov A. C.
Published: July 2002

The hopping conductivity of La2CuO4+δ single crystal with excess oxygen has been studied. It is found that the transition from variable-range hopping (with the temperature dependence of resistance R∝exp(T0/T)1/4) to simple activation conductivity (R∝exp(Δ/kT)) occurs at a temperature lower than 20 K. This transition is accompanied with significant changes in the behavior of magnetoresistance and current–voltage characteristics. It is shown that such a behavior of hopping conductivity below 20 K is due to the presence of superconducting inclusions in insulating sample due to phase separation of La2CuO4+δ. The observed peculiarities in the conducting properties are in good agreement with the known effects of competition between electron localization and superconductivity in homogeneous systems.
Quantum nucleation of cavities in a liquid helium at low temperatures
Authors: Burmistrov S. N. , Dubovskii L. B.
Published: July 2002

The rate of the quantum cavitation in normal fluid He3 and superfluid He4 at temperatures down to absolute zero has been studied. The effect of energy dissipation due to viscosity and the effect of the finite compressibility of a fluid are incorporated into the calculation of the quantum cavitation rate. Because of the dissipative processes, the kinetics of the quantum cavitation in He3 and He4 proves to be qualitatively different. In normal He3 it corresponds to the dissipative tunneling through a potential barrier. In contrast, in superfluid He4 the effect of dissipation is of minor importance. In both liquids the role of the compressibility of a fluid enhances significantly for the small critical nuclei, which have several interatomic distances and can provide us the nucleation rates sufficient for the experimental observation of the homogeneous cavitation in the quantum regime.
Ultralow temperatures in a transport vessel: A dilution refrigerator to achieve 30 mK by continuous adsorption pumping
Authors: Batey G. J. , White J. P. , Duncan W. D. , Simpson A. F. , Mikheev V. A.
Published: July 2002

A novel design of dilution refrigerator (DR) is described for continuous operation inside a transport dewar with a neck diameter more than 51 mm. The time required for cooling the mixing chamber from room temperature to 30 mK is 3.5–4.5 h. Warming up to 300 K requires 0.5–1.0 h. The cooling power achieved is 40 at 100 mK. The DR is fitted with 6-mm line-of-sight access down to the mixing chamber. A distinguishing feature of this refrigerator is the absence of a conventional gas-handling system, which makes it easy to transport in a small car and quickly commission in a new laboratory within a few hours.
Weakly damping waves in quasi-two-dimensional conductors
Authors: Peschansky V. G. , Torjanik D. A. , Lopez J. A. Roldan
Published: July 2002

The transfer of electromagnetic field to the bulk of a layered conductor by charge carriers with a quasi-2D energy spectrum is most effective when the electric field of the wave is polarized along the normal to the layers.
On peculiarities of superconducting state formation in 2D metallic systems
Authors: Gusynin V. P. , Loktev V. M. , Sharapov S. G.
Published: July 2002

It is shown that the phase diagram of a 2D metal with a varying charge carrier density consists of normal phase regions in which the modulus of the order parameter is zero, the so-called anomalously normal phase in which it differs from zero but has a random phase, and the Berezinskii–Kosterlitz–Thouless phase. The characteristic temperatures of transitions between these phases are determined as well as the behavior of the chemical potential as a function of the fermion density and temperature. An attempt is made to compare qualitatively the obtained phase diagram with the observed peculiarities in the behavior of underdoped high-Tc superconducting compounds above their critical temperature.
Magnetic field induced phase transition in A1−xCaxMnO3 (A=Nd, Bi, Sm, Eu, Tb)
Authors: Troyanchuk I. O. , Samsonenko N. V. , Solovykh T. K. , Sirenko V. A. , Szymczak H. , Nabialek A.
Published: July 2002

A study of Nd0.6Ca0.4MnO3 shows that the application of a magnetic field at 4.2 K induces a transition from the insulating antiferromagnetic state to the conducting ferromagnetic state, which is accompanied by a decrease in the sample volume by 0.1%. The replacement of Nd ions by Bi ions leads to stabilization of the antiferromagnetic state, while the substitution of Sm and Eu ions results in manifestation of properties typical of spin glasses.
Zero-temperature relaxation in spin-polarized Fermi systems
Authors: Meyerovich A. E. , Naish J. H. , Owers-Bradley J. R. , Stepaniants A.
Published: July 2002

The effect of zero-temperature attenuation, which has been recently observed in spin dynamics of Fermi liquids, on various processes in helium and ferromagnetic systems is described. A brief review of theoretical and experimental data on zero-temperature attenuation in transverse spin dynamics of helium systems is followed by a discussion of coupling between longitudinal and transverse processes, the Castaing instability in He3 and He3−4Hemixtures, and applications to pure ferromagnetic metals.
Hamiltonian formalism in the theory of quadruple magnet
Authors: Isayev A. A.
Published: July 2002

Poisson brackets are obtained for dynamic variables of a quadrupole magnet, i.e., the spin density and the matrix of the quadruple moments. The starting point for the analysis is the derivation of the kinematic component of the Lagrangean of the system. Equations of motion are derived, and the number of Goldstone and activation modes is determined for the case when the energy functional is invariant to spin rotations.
On paired nature of superfluid condensate in helium-II
Authors: Vil’chinsky S. I. , Pashitsky E. A. , Fomin P. I.
Published: July 2002

A hypothesis on pairing of helium atoms below the λ-point is put forth on the basis of empirical data on the dynamics of He3 impurity atoms in superfluid He4, that suggest an abnormally large effective mass of He3. The role of paired condensate in superfluidity of He4 is considered as well as the possibility of additional experimental proofs of the pairing of He4 atoms, including the observation of vortices with a half-integral velocity circulation quantum.
Dynamical behavior of He I–He II interface layer caused by forced heat flow
Authors: Murakami M. , Kamiya K. , Sato T.
Published: July 2002

The appearance and dynamical behavior of a He I–He II phase interface is investigated experimentally. The experimental mode in which nearly saturated He I initially at a little bit higher temperature than the lambda temperature is cooled by sudden evaporative cooling is primarily employed in the present experiment among several possibilities. In this mode where an interface appears and propagates downward, some dynamical aspects of an interface layer can be preferably investigated. The phenomenon is investigated by the application of the schlieren visualization method, and by measuring the temperature variation by superconductive temperature sensors and the pressure variation as well as the evaporating vapor flow rate which can be converted into the cooling rate.
Testing critical point universality along the λ-line
Authors: Nissen J. A. , Swanson D. R. , Geng Z. K. , Dohm V. , Israelsson U. E. , DiPirro M. J. , Lipa J. A.
Published: July 2002

We are currently building a prototype for a new test of critical-point universality at the lambda transition in He4, which is to be performed in microgravity conditions. The flight experiment will measure the second-sound velocity as a function of temperature at pressures from 1 to 30 bars in the region close to the lambda line. The critical exponents and other parameters characterizing the behavior of the superfluid density will be determined from the measurements. The microgravity measurements will be quite extensive, probably taking 30 days to complete. In addition to the superfluid density, some measurements of the specific heat will be made using the low-g simulator at the Jet Propulsion Laboratory. The results of the superfluid density and specific heat measurements will be used to compare the asymptotic exponents and other universal aspects of the superfluid density with the theoretical predictions currently established by renormalization group techniques.