bluuebunny/crossref_metadata_2025 huggingface dataset:
Toward the understanding of ethylene photodissociation: Theoretical study of energy partition in products and rate constants
Authors: Chang A. H. H. , Hwang D. W. , Yang X.-M. , Mebel A. M. , Lin S. H. , Lee Y. T.
Published: July 2002

The energy partition in the products of ethylene photodissociation (including C2H4, C2D4, D2CCH2, cis- and trans-HDCCDH) at 193 and 157 nm and the rate constants of H loss channels were computed based on ab initio ethylene ground-state surfaces of which most were reported earlier. In the calculations of the energy partitions, a simple model was used in which the excess energy above the transition state is distributed statistically and the energy released by the exit barrier is described by the modified impulsive model. The rate constants of the ethylene H(D) elimination were calculated according to the variational RRKM (Rice–Ramsperger–Kassel–Marcus) theory, and the RRKM rate constants with tunneling corrections were obtained for vinyl decomposition at 193 nm. In contrast with previous conclusions drawn by LIF (laser induced fluorescence) studies, the rate constant calculations suggest that the H loss may be a nonstatistical process. However, the computed variational transition states for H loss appear reasonable as indicated by the translational energy. That with present investigation indicates that the atomic elimination proceeds via the predicted transition states though the process is nonstatistical. Analysis of the H2 translational energy measured at 193 and 157 nm by molecular beam experiments gives evidence that the overall mechanisms of the molecular elimination are different at the two wavelengths, which is also in disagreement with previous belief. At 193 nm, both H2 elimination channels may occur through the predicted transition states. On the other hand, further comparison of the theoretical and experimental translational energy of hydrogen molecule at 157 nm suggests that the observed (1,1E) reaction path is most likely of much higher “exit barrier” than the one computed. For the (1,2E) channel, the calculations are still in support of the computed transition state being the one along the experimentally observed pathway at 157 nm.
Deuterium isotope effect on the solvation dynamics of a dye molecule in methanol and acetonitrile
Authors: Lee Sang-Hoon , Lee Jin-Ho , Joo Taiha
Published: July 2002

Solvation dynamics of a dye molecule in methanol, acetonitrile, and their deuterated analogs has been measured by the three-pulse stimulated photon echo peak shift. The effects of deuterium substitution on the stationary fluorescence spectra and the time domain data are found to be significant in both solvents. Moreover, the deuterium isotope effects are contrasted in methanol and acetonitrile. The ultrafast component, found to be 200–260 fs, is not slowed down by the deuterium substitution of the hydroxyl group in methanol, and it is even slightly shortened by deuteration in acetonitrile. The isotope dependence and the time scales suggest that the ultrafast component is not originated from the inertial free rotation of the solvent molecules but from collective dispersive solvent motion, at least for the present system. In addition to the ultrafast and ps solvation time scales usually observed in methanol and acetonitrile, a large amplitude ns component is observed in all solvents. The amplitudes of the ns component are substantially different in isotopomers, showing the opposite trend in methanol and acetonitrile.
Equation of state of hard and Weeks–Chandler–Anderson hyperspheres in four and five dimensions
Authors: Bishop Marvin , Masters Andrew , Clarke Julian H. R.
Published: July 2002

The fifth and sixth virial coefficient for hard hyperspheres in four and five dimensions has been computed using Monte Carlo techniques. It is found that B5/B24 has values 0.035 63±0.000 07 and 0.012 87±0.000 06 and that B6/B25 has values 0.007 691±0.000 028 and 0.000 942±0.000 027 in four and five dimensions, respectively. These values are used to investigate the equation of state of hard and Weeks–Chandler–Anderson (WCA) hyperspheres in four and five dimensions. Molecular dynamics simulations are performed for WCA hyperspheres. When compared to the molecular dynamics calculations, it is found that both the hard hypersphere and WCA equations of state are well described by a variety of theoretical approaches as long as the density is in the low-to-moderate regime. At the highest fluid densities studied, the Luban–Michels procedure provides the best accuracy for hard hyperspheres. The WCA prescription for the scaling of the reference system to a hard hypersphere one is a very good approximation in the fluid region.
Ultrafast intermolecular electron transfer from orthomethoxyaniline to excited coumarin dyes
Authors: Pal Haridas , Shirota Hideaki , Tominaga Keisuke , Yoshihara Keitaro
Published: July 2002

Ultrafast intermolecular electron transfer (ET) from orthomethoxyaniline (orthoanisidine, ANS) to a number of excited (S1) 4-trifluoromethyl-1,2-benzopyrones (coumarins) having differently substituted 7-amino group has been investigated by femtosecond fluorescence up-conversion technique. The ET dynamics in the present systems are nonsingle-exponential and occur faster than the diffusive solvation dynamics. The ET rates are largely dependent on the nature of the substituents at the 7-amino group of the coumarins. This dependence is well correlated with the free energy changes (ΔG0) for the ET reactions. The ET dynamics become slower on using deuterated ANS as the donor, where the amino group hydrogens of ANS are substituted by deuterium. The deuterium isotope effect, however, gradually reduces as the ET dynamics becomes faster. Conventional ET theories can not explain all the observations. The results are explained on the basis of the two-dimensional ET model, which considers the solvent coordinate and the intramolecular coordinate separately to depict the ET process. It is seen that in coumarin-ANS systems the ET occurs much faster than the coumarin-aniline systems. It is indicated that the electronic coupling matrix element, a parameter which determines the extent of interaction between the reactant and the product states in the ET process, is much larger in the present systems than for the coumarin-aniline systems. The deuterium isotope effect on the ET dynamics is explained in terms of the changes in the ΔG0 values on isotopic substitution of the solvent donors.
Femtosecond time-resolved photoelectron–photoion coincidence imaging studies of dissociation dynamics
Authors: Davies J. A. , LeClaire J. E. , Continetti R. E. , Hayden C. C.
Published: July 2002

We present the first results using a new technique that combines femtosecond pump–probe methods with energy- and angle-resolved photoelectron–photoion coincidence imaging. The dominant dissociative multiphoton ionization (DMI) pathway for NO2 at 375.3 nm is identified as three-photon excitation to a repulsive potential surface correlating to NO(C 2Π)+O(3P) followed by one-photon ionization to NO+(X 1Σ+). Dissociation along this surface is followed on a femtosecond timescale.
Time-resolved infrared diode laser spectroscopy of the ν3 band of the jet-cooled Fe(CO)2 radical produced by ultraviolet photolysis of Fe(CO)5
Authors: Tanaka Keiichi , Tachikawa Yasuhisa , Sakaguchi Kouichi , Hikida Toshihide , Tanaka Takehiko
Published: July 2002

The infrared spectrum of the iron dicarbonyl radical Fe(CO)2 produced in a supersonic jet expansion by the excimer laser photolysis of iron pentacarbonyl Fe(CO)5 was observed by time-resolved infrared diode laser spectroscopy. About 170 transitions, each split into one or two fine structure components, were assigned to the ν3 (CO antisymmetric stretch) band of Fe(CO)2. The assignment was greatly facilitated by spectral simplification caused by rotational as well as vibrational cooling in the supersonic jet. It was observed that lines are missing at alternate J quantum numbers in each spin component, which confirmed that Fe(CO)2 is a linear molecule with D∞h symmetry and that the electronic ground state is of 3Σg− symmetry. The rotational and centrifugal distortion constants in the ground state were determined to be B0=1414.675(46) MHz and D0=0.3077(74) kHz, respectively. The spin–spin interaction constants obtained, λ0=655.3(42) GHz, is comparable with that of the FeCO radical, λ0=684.470(51) GHz. The ν3 band origin was determined to be 1928.184335 (82) cm−1. The figures in parentheses are uncertainties (1σ) in units of the last digit.
Thermodynamic limit of the excess internal energy of the fluid phase of a one-component plasma: A Monte Carlo study
Authors: Caillol J. M.
Published: July 2002

The thermodynamic limit of the excess internal energy per particle u of the fluid phase of the three-dimensional one-component plasma is investigated by means of Monte Carlo simulations. The simulations are performed in the canonical ensemble within hyperspherical boundary conditions. u is computed for 31 values of the coupling parameter Γ in the range 1⩽Γ⩽190. For each value of Γ the thermodynamic limit of u is obtained by studying the scaling law which governs the behavior of u with the number N of particles.
Spectroscopic studies of mass selected clusters of Sr+ solvated by H2O and D2O
Authors: Sperry David C. , Midey Anthony J. , Lee James I. , Qian Jun , Farrar James M.
Published: July 2002

In this paper we present the results of spectroscopic studies on mass selected Sr+(H2O)n, n=1–4 and Sr+(D2O)n, n=1–6 clusters. Mass spectra of nascent clusters formed in our laser vaporization source show that hydrated metal ion species are predominant for n⩽4. Clusters larger than this size are more abundant in the hydrogen loss form SrOH+(H2O)n−1. The cluster size at which the product switching occurs is slightly larger (n=5) in the deuterated species. Photodissociation of all clusters results in both ligand loss and H/D atom loss occurring via an intracluster reaction. The monomer and dimer cluster species exhibit distinct absorption bands attributable to electronic excitation of the 5s valence electron of Sr+. Metal–ligand stretching frequencies are extracted from Franck–Condon progressions in the excited state. Spectroscopic parameters agree well with ab initio calculations [Bauschlicher et al., J. Chem. Phys. 96, 4453 (1992), and Sodupe et al., Chem. Phys. Lett. 212, 624 (1993)]. Analysis of the product branching ratios allows us to conclude that, when below the threshold for excited state dissociation, rapid internal conversion followed by an intracluster reaction preferentially occurs on the ground state surface, while evaporation occurs primarily in the excited state. We find evidence in the spectral profiles of clusters with n⩾3 for a consistent “substructure” characterized by a pπ state lacking σ-type interactions with the ligand molecules.
Theoretical description of the vibrational echo spectroscopy by time-resolved infrared–infrared–visible difference-frequency generation
Authors: Cho Minhaeng
Published: July 2002

Theoretical descriptions of the time-resolved infrared–infrared visible (IIV) sum and difference frequency generation are presented. The IIV sum-frequency generation (SFG) method is shown to be useful in selectively studying the vibrational relaxation of the overtone mode. The IIV difference-frequency generation (DFG), which is a specific case of the doubly resonant four-wave mixing spectroscopies, involves a rephasing period so that the elimination of the vibrational inhomogeneous broadening can be achieved by using this method. The decay of the diagonal IIV-DFG signal is proven to be independent on the inhomogeneous distribution of the vibrational frequency. Furthermore, it is shown that the two-dimensional time-resolved IIV-DFG signal along the antidiagonal provides a direct information on the vibrational inhomogeneous distribution function.
The electronic spectrum of silicon methylidyne (SiCH), a molecule with a silicon–carbon triple bond in the excited state
Authors: Smith Tony C. , Li Haiyang , Clouthier Dennis J. , Kingston Christopher T. , Merer Anthony J.
Published: July 2002

The Ã 2Σ+–X̃ 2Πi transition of jet-cooled silicon methylidyne, SiCH, has been recorded by laser-induced fluorescence in the 850–600 nm region. The radical was produced in an electric discharge using tetramethylsilane as the precursor. Fifteen cold bands of SiCH and 16 bands of SiCD have been assigned vibrationally, giving the upper state frequencies as v2′=715/558 cm−1 and v3′=1168/1127 cm−1 for SiCH/SiCD. Rotational analysis of the 000 and 303 bands for each isotopomer has given the following molecular structures: r0″(Si–C)=1.692 52(8), r0″(C–H)=1.0677(4), r0′(Si–C)=1.6118(1), and r0′(C–H)=1.0625(5) Å. The silicon–carbon bond length in the X̃ 2Π ground state of SiCH (electron configuration …σ2π3) is typical for a Si=C double bond; in the Ã 2Σ+ excited state (…σ1π4) it corresponds to a triple bond. This work provides the first experimental measurement of the length of the carbon–silicon triple bond.
Laser ablation at solid–liquid interfaces: An approach from optical emission spectra
Authors: Sakka Tetsuo , Iwanaga Shuji , Ogata Yukio H. , Matsunawa Akira , Takemoto Tadashi
Published: July 2002

The emission spectra from the solid–liquid interface irradiated by a pulsed laser were studied. The solid target used in this study was graphite and boron nitride, and the liquid in which the target was immersed was water, benzene, n-hexane, and carbon tetrachloride. The results showed strong continuous spectrum immediately after a pulse shot, whereas after ≈100 ns later from the irradiation it was greatly reduced, and instead, the emission from small molecules dominated the spectra. The line spectra of small molecules observed in the later time range indicate the chemical reaction between the ablated species and the species originated from the liquid molecules. The intensity of the continuous spectrum was very prominent compared to what has been observed for solid–gas interfaces. This is due to rapid electron ion recombination or bremsstrahlung due to highly confined interface plasma.
Spectroscopic constants of the X̃(1A1), ã(3B1), and Ã(1B1) states of CF2, CCl2, and CBr2 and heats of formation of selected halocarbenes: An ab initio quantum chemical study
Authors: Sendt Karina , Bacskay George B.
Published: July 2002

The geometries, rotational constants, harmonic force constants and frequencies, dissociation and term energies of CF2, CCl2, and CBr2 in their respective X̃(1A1), ã(3B1) and Ã(1B1) states, computed by complete active space self-consistent field (CASSCF), complete active space second-order purturbation (CASPT2), and coupled-cluster with single, double and perturbative triple excitations [CCSD(T)] methods and cc-pVTZ basis sets, are reported. For CCl2 and CBr2 the barriers to linearity are also characterized. The computed spectroscopic constants are in good agreement with the available experimental data. The atomization energies and hence heats of formation at 0 and 298 K of these molecules as well as of CHF, CHCl, and CFCl, all in their lowest singlet ground states were also computed by the CCSD(T) method utilizing basis sets ranging from cc-pVDZ to aug-cc-pVQZ, cc-pCVQZ and G3large, enabling the extrapolation of the energies to a complete basis set (CBS) limit and the inclusion of core–valence correlation (with the exception of CBr2). Scalar relativistic corrections, computed by CASPT2, were also taken into account. The final CBS results are ΔfH2980(CHF)=147±4 kJ mol−1, ΔfH2980(CHCl)=320±4 kJ mol−1, ΔfH2980(CFCl)=29±4 kJ mol−1, ΔfH2980(CCl2)=229±4 kJ mol−1, and ΔfH2980(CBr2)=337±8 kJ mol−1. The GAUSSIAN-3 (G3) heats of formation of these molecules are within 2 kJ mol−1 of the CBS values, representing significant improvement over the GAUSSIAN-2 predictions which differ from the CBS results by up to ∼10 kJ mol−1. Similarly, the G3 triplet/singlet energy separations are found to be in good agreement with those obtained at the CCSD(T)/cc-pVQZ level of theory including core–valence correlation corrections, as well as experiment.
Anharmonic force field, vibrational energies, and barrier to inversion of SiH3−
Authors: Aarset Kirsten , Császár Attila G. , Sibert Edwin L. , Allen Wesley D. , Schaefer Henry F. , Klopper Wim , Noga Jozef
Published: July 2002

The full quartic force field of the ground electronic state of the silyl anion (SiH3−) has been determined at the CCSD(T)-R12 level employing a [Si/H]=[16s11p6d5f/7s5p4d] basis set. The vibrational energy levels, using the quartic force field as a representation of the potential energy hypersurface around equilibrium, have been determined by vibrational perturbation theory carried out to second, fourth, and sixth order. The undetected vibrational fundamental for the umbrella mode, ν2, is predicted to be 844 cm−1. High-quality ab initio quantum chemical methods, including higher-order coupled cluster (CC) and many-body perturbation (MP) theory with basis sets ranging from [Si/H] [5s4p2d/3s2p] to [8s7p6d5f4g3h/7s6p5d4f3g] have been employed to obtain the best possible value for the inversion barrier of the silyl anion. The rarely quantified effects of one- and two-particle relativistic terms, core correlation, and the diagonal Born–Oppenheimer correction (DBOC) have been included in the determination of the barrier for this model system. The final electronic (vibrationless) extrapolated barrier height of this study is 8351±100 cm−1.
The gas phase L2,3VV Auger electron spectra of chlorine in XCl (X=H, D, Li, Na, K) molecules
Authors: Kivilompolo Mika , Kivimäki Antti , Aksela Helena , Huttula Marko , Aksela Seppo , Fink Reinhold F.
Published: July 2002

The Auger electron spectra (AES) following the chlorine 2p ionization in the gas phase alkali-chlorides as well as in the HCl and DCl molecules were studied theoretically and experimentally. Nonrelativistic ab initio calculations based on quantum chemical methods and the one-center approximation were used to compute the Cl L2,3VV AES. The vibrational band structure in the AES was simulated by full life time vibrational interference (LVI) theory and a more approximate moment method. Calculations were compared with the corresponding experimental electron or photon impact excited spectra. Overall features and changes in the series of the experimental AES are correctly predicted by the theory. For the most intense transitions in these spectra a qualitative explanation of the energies is given on the basis of a model that includes electrostatic interactions, Pauli repulsion, and polarization. This explains that the substantial changes of the spectra with X are due to a R−3 dependence of the electrostatic interaction on the X–Cl bond length. A comparison of the two theoretical methods shows that the LVI vibrational band breadths are well reproduced by the moment method in the AES of HCl, DCl, and LiCl, whereas the moment breadths are underestimated in the AES of NaCl and KCl. The LVI band breadths for HCl, DCl, and KCl are in good agreement with experimental data. In contrast, the experimental spectra for LiCl and NaCl show almost two times broader vibrational bands than predicted by the LVI theory. This contradiction indicates that the LiCl and NaCl vapors are contaminated by the dimer form of these substances. A large contribution of Li2Cl2 (74%) and Na2Cl2 (29%) was measured in the LiCl and NaCl vapors by time-of-flight mass spectroscopy. The Auger peaks in the spectra of the dimers lie very close to the monomer peaks, and thus make it very difficult to distinguish dimer and monomer contributions.
Density functional theory of simple polymers in a slit pore. III. Surface tension
Authors: Hooper Justin B. , McCoy John D. , Curro John G. , van Swol Frank
Published: July 2002

In a previous study of tangent hard-site chains near a surface, the inhomogeneous density profiles were found through density functional theory. In the current study, the surface tensions of these systems are found from the results of the previous study through a thermodynamic integration. The calculated surface tensions are then compared to those found directly through computer simulation. Both the surface tension and surface excess for polymeric systems are shown to differ qualitatively from those of atomic systems, although certain similarities are seen at high densities.
The energy levels and the corresponding normalized wave functions for a model of a compressed atom
Authors: Fröman Per Olof , Yngve Staffan , Fröman Nanny
Published: July 2002

In the model of a compressed atom (or ion) considered in the present paper the boundary condition associated with the corresponding uncompressed atom, i.e., the condition that the radial wave function must vanish at r=∞, is replaced by the boundary condition that the radial wave function must have a node at the finite distance r=a. The treatment of the problem of obtaining the energy shift due to the compression is based on the phase-integral method developed by Fröman and Fröman, an essential feature of which is that one can use exact formulas in the calculations and make all approximations in the final stage. The treatment of the problem of obtaining the relative change of the wave function due to the compression is based on the rigorous evaluation of the normalization integral developed by Furry [Phys. Rev. 71, 360 (1947)] and Yngve [J. Math. Phys. 13, 324 (1972)], in which one also uses exact formulas in the calculations and makes all approximations in the final stage. Since compression of an atom gives rise to very subtle effects, rigorous methods are indispensible for obtaining accurate and reliable analytical final formulas. As an application, the resulting general formulas are particularized to the case of a hydrogenic atom, and a numerical illustration of the accuracy of the formulas is given.
Canonical formalism of dissipative fields in thermo field dynamics
Authors: Arimitsu T. , Umezawa H. , Yamanaka Y.
Published: July 2002

For the stationary case the canonical formalism of thermally dissipative fields with both positive- and negative-frequency parts is constructed. This formulation enables one to follow the self-consistent renormalization scheme which creates the dissipation spontaneously. The self-interacting φ3 model is examined as an example of the spontaneous creation of dissipation. The parameter α appearing in the thermal state conditions as well as observables independent of the choice of α are discussed.
An analogy of the charge distribution on Julia sets with the Brownian motion
Authors: Lopes Artur O.
Published: July 2002

A way to compute the entropy of an invariant measure of a hyperbolic rational map from the information given by a Ruelle–Perron–Frobenius operator of a generic Holder-continuous function will be shown. This result was motivated by an analogy of the Brownian motion with the dynamical system given by a rational map and the maximal measure. In the case the rational map is a polynomial, then the maximal measure is the charge distribution in the Julia set. The main theorem of this paper can be seen as a large deviation result. It is a kind of Donsker–Varadhan formula for dynamical systems.
Equivalence of generic equation method and the phenomenological model for linear transport problems in a two-state random scattering medium
Authors: Sahni D. C.
Published: July 2002

Linear particle transport problems in a two-state random Markov medium are considered. Explicit equations are constructed that determine the expected particle density in a scattering medium. It is shown that the generic equation method is equivalent to the phenomenological model if the free flights of the particle are uncorrelated.
Conditions for runaway phenomena in the kinetic theory of particle swarms
Authors: Frosali Giovanni , van der Mee Cornelis V. M. , Paveri-Fontana Stefano L.
Published: July 2002

The velocity distribution of a spatially uniform diluted guest population of charged particles moving within a host medium under the influence of a D. C. electric field is studied. A simplified one-dimensional Boltzmann model of the Kač type is adopted. Necessary conditions and sufficient conditions are established for the existence, uniqueness, and attractivity of a stationary non-negative distribution corresponding to a specified concentration level. Conditions for the onset of the runaway process are established.
Vertex operator construction of nonassociative algebras and their affinizations
Authors: Günaydin M.
Published: July 2002

A general method for the vertex operator construction of nonassociative algebras and triple systems and their super analogs is given. Using this method the natural affine extensions of these algebraic structures can be defined and constructed. Essentially all the algebraic structures of physical theories based on ‘‘point particles’’ can be constructed this way. Conversely, these methods can be used to define the ‘‘stringy’’ analogs of these algebraic structures.
The discrete Boltzmann equation with multiple collisions: Global existence and stability for the initial value problem
Authors: Bellomo N. , Kawashima S.
Published: July 2002

This paper deals with the analysis of the initial value problem in all space Rd, d≥2, for the discrete Boltzmann equation with multiple collisions. After a preliminary analysis of the mathematical modeling of the evolution equations, global existence and asymptotic behavior are proven using suitable stability criteria. Some applications verify the analysis for specific models.
Exact plane-wave solutions of the coupled Maxwell–Klein–Gordon equations
Authors: Das A. , Biech T. , Kay D.
Published: July 2002

Solutions of the classical Maxwell–Klein–Gordon equations are investigated for which the Klein–Gordon field is assumed to be ψ(x)=αeipμxμ. It is shown that for this class the exponential factor can be ‘‘gauged away’’ and the resulting system of equations can be reduced to a single (complicated) nonlinear equation. Furthermore, the electromagnetic four-potential field becomes massive ‘‘absorbing scalar particles.’’ The steady-state (or stationary) subclass of the resulting system of equations is examined. It is proved that in absence of any magnetic field, the steady-state system does not have a solution. In the simple case for which four-potential components Aμ depend on one spatial coordinate, the equations are completely solved and explicitly analyzed.
Curvature collineations in general relativity. II
Authors: Hall G. S. , da Costa J.
Published: July 2002

This paper is the second of a set of two papers on curvature collineations in general relativity. The first paper presented the mathematical basis of curvature collineations and a possible approach to their study. This paper continues from the first one by investigating in detail many of the cases where curvature collineations can occur in space-time. It is based on a classification of the curvature tensor which is discussed in the first paper and reviewed briefly here. This, together with the geometrical approach favored in this paper, leads to a rather general discussion of the problem which, it is hoped, does not obscure those physical aspects of the situation that are important in Einstein’s theory.
Negative powers of Olver recursion operators
Authors: Verosky John M.
Published: July 2002

Olver’s concept of a recursion operator for symmetries of an evolution equation is extended to include negative powers of the operator. Some negative order KdV equations are derived in this way. In particular, the inverse image of the trivial zero symmetry generator has an elegant formulation in terms of an eigenfunction of the associated Schrödinger equation used in the inverse scattering solution of the KdV equation and this formulation is used to show that this new equation is the Miura transform of a sinh-Gordon equation.
Soliton solutions to coupled higher-order nonlinear Schrödinger equations
Authors: Tasgal R. S. , Potasek M. J.
Published: July 2002

A set of coupled higher-order nonlinear Schrödinger equations, which describe electromagnetic pulse propagation in coupled optical waveguides, is formulated in terms of an eigenvalue problem. Using that result, the inverse scattering problem is solved and explicit soliton solutions are found. Additionally, linear coupling terms are studied systematically.
Modeling charged particle loss in a fuel/shell mixture
Authors: Levermore C. D. , Zimmerman G. B.
Published: July 2002

The hydrodynamic mixing of shell material into the fuel region of an inertial confinement fusion (ICF) target during compression will suppress the thermonuclear yield due to the loss of charged fusion reaction products to the entrained shell material. Adopting a binary Markovian model for this mixture an exact formula for the fraction of particles lost is derived.
Some integrable hierarchies in (2+1) dimensions and their twistor description
Authors: Strachan I. A. B.
Published: July 2002

The twistor space construction, due to Mason and Sparling, for solutions of the nonlinear Schrödinger and Korteweg–deVries hierarchies is generalized, resulting in families of integrable models in (2+1) dimensions. Soliton solutions to one such hierarchy [associated with the gauge group SU(2)] are constructed by adapting the methods used to construct instanton and monopole solutions. These integrable models have the feature that their solutions depend on a number of arbitrary functions as well as arbitrary constants, in contrast to the closely related Davey–Stewartson hierachy.
Algebraic q-integration and Fourier theory on quantum and braided spaces
Authors: Kempf Achim , Majid Shahn
Published: July 2002

An algebraic theory of integration on quantum planes and other braided spaces is introduced. In the one-dimensional case a novel picture of the Jackson q- integral as indefinite integration on the braided group of functions in one variable x is obtained. Here x is treated with braid statistics q rather than the usual bosonic or Grassmann ones. It is shown that the definite integral ∫x∞−x∞ can also be evaluated algebraically as multiples of the integral of a q-Gaussian, with x remaining as a bosonic scaling variable associated with the q-deformation. Further composing the algebraic integration with a representation then leads to ordinary numbers for the integral. Integration is also used to develop a full theory of q-Fourier transformation ℱ The braided addition Δx=x⊗1+1⊗x and braided-antipode S is used to define a convolution product, and prove a convolution theorem. It is also proven that ℱ2=S. The analogous results are proven on any braided group, including integration and Fourier transformation on quantum planes associated to general R matrices, including q-Euclidean and q-Minkowski spaces.
Strong asymptotics of Laguerre polynomials and information entropies of two-dimensional harmonic oscillator and one-dimensional Coulomb potentials
Authors: Dehesa J. S. , Yáñez R. J. , Aptekarev A. I. , Buyarov V.
Published: July 2002

The information entropies of the two-dimensional harmonic oscillator, V(x,y)=1/2λ(x2+y2), and the one-dimensional hydrogen atom, V(x)=−1/|x|, can be expressed by means of some entropy integrals of Laguerre polynomials whose values have not yet been analytically determined. Here, we first study the asymptotical behavior of these integrals in detail by extensive use of strong asymptotics of Laguerre polynomials. Then, this result (which is also important by itself in a context of both approximation theory and potential theory) is employed to analyze the information entropies of the aforementioned quantum-mechanical potentials for the very excited states in both position and momentum spaces. It is observed, in particular, that the sum of position and momentum entropies has a logarithmic growth with respect to the main quantum number which characterizes the corresponding physical state. Finally, the rate of convergence of the entropies is numerically examined.
Classification of curvature collineations of plane symmetric static spacetimes
Authors: Bokhari Ashfaque H. , Kashif Abdul R. , Qadir Asghar
Published: July 2002

A complete classification of curvature collineations of static plane symmetric spacetimes is obtained and then a comparison between isometries and Ricci Collineations of the corresponding metrics is given.
On a multidimensional Schrödinger–Poisson scattering model for semiconductors
Authors: Abdallah Naoufel Ben
Published: July 2002

We consider a stationary Schrödinger–Poisson problem modeling a self-consistent transport in a quantum coupler. The Schrödinger equation is set on a bounded domain with transparent boundary conditions describing incoming scattering states of the Schrödinger operator. The coupling with the Poisson equation is done thanks to a nonlinear limiting absorption procedure. The charge density of the limit potential is shown to be equal to the sum of the scattering state and bound state densities.
Acoustic emission of the HTS ceramic YBa2Cu3O7−δ in the vicinity of the superconducting transition
Authors: Stoev P. I. , Papirov I. I. , Finkel’ V. A.
Published: July 2002

Acoustic emission (AE) of the HTS ceramic YBa2Cu3O7−δ is studied under heating from liquid nitrogen temperature. For heating at a high rate, a peak in the AE activity is observed in the temperature interval 100–115 K. The parameters of the peak depend on the oxygen content in the HTS ceramic, heating rate, initial temperature to which the ceramic was cooled, and the sample thickness. The observed AE is associated with the relaxation of microscopic thermal stresses generated at the grain boundaries due to anisotropy of the thermal expansion coefficients and their anomalous behavior at these temperatures. Possible relaxation mechanisms of such stresses are the movement of dislocation groups and the formation of microcracks along the least favorably oriented grain boundaries.
Pinning and dynamics of magnetic flux in YBaCuO single crystals for vortex motion along twin boundaries
Authors: Bondarenko A. V. , Shklovskij V. A. , Vovk R. V. , Obolenskii M. A. , Prodan A. A.
Published: July 2002

Current-voltage characteristics of YBaCuO single crystals are studied for a Lorentz force aligned along the twin planes. The temperature dependences of the depinning critical currents are determined in magnetic fields that are parallel or tilted with respect to the twin planes for magnetic field vectors oriented almost along axis c. A nearly 50% decrease in the critical current in parallel magnetic fields is attributed to the plastic flow of vortices along channels formed by twin boundaries. It is shown that the resistance to the viscous flux flow is described quite correctly by the Bardeen–Stephen model. The peculiarities in the current and temperature dependences of the differential resistivity at temperatures higher than the melting point but lower than the temperature of onset of vortex pinning by twin boundaries are attributed to the coexistence of solid and liquid vortex phases in this temperature region. A large number of peaks observed in the current dependences of the differential resistivity in a parallel field at temperatures below the melting point of the vortex lattice is associated with nonuniform indirect vortex pinning caused by the fluctuations of the separation between twins.
A vortex-dipole sheet model for a wake
Authors: Krasny Robert
Published: July 2002

A vortex model for a free shear layer with a wake component is proposed. The layer is represented by a curve which supports both a vortex sheet and a vortex-dipole sheet. The vortex sheet yields a monotonic velocity profile that connects the outer flows on either side of the shear layer. The vortex-dipole sheet captures the effect of oppositely signed vorticity that is present in the wake due to boundary layers upstream from the separation point. The equations governing a vortex-dipole sheet are given and a temporal instability calculation for a free sinusoidal wake shows the development of a vortex street.
Disintegration of liquid sheets
Authors: Mansour Adel , Chigier Norman
Published: July 2002

The development, stability, and disintegration of liquid sheets issuing from a two-dimensional air-assisted nozzle have been studied. Detailed measurements of mean drop size (SMD) and velocity have been made using a phase Doppler particle analyzer. Without air flow the liquid sheet converges toward the axis as a result of surface tension forces. There is a linear increase in convergence length with increases in liquid flow rate. With air flow a quasi-two-dimensional expanding spray is formed. It is shown that the air flow is responsible for the formation of large, ordered, and small, chaotic ‘‘cell’’ structures. These structures are bounded by large diameter ligaments containing thin membranes inside. The ligaments are the origin of the large droplets in the spray and the membranes contribute to the formation of the smaller droplets. The air flow causes small variations in sheet thickness to develop into major disturbances with the result that disruption starts before the formation of the main breakup region. The phase Doppler measurements show that the spray two-dimensionality breaks down at a short distance from the nozzle in the downstream region. Boundary layer growth and turbulent mixing result in the redistribution of droplets according to their size class. The droplets detached from the central part of the sheet are subject to further breakup because of high local relative velocities. Droplets detached from the rims are outside the main air flow field and have diameters close to that of the rims. The spray acquires a Gaussian velocity profile in both the Y and Z directions.
On the motion of small particles in a homogeneous isotropic turbulent flow
Authors: Yeh Fungee , Lei U.
Published: July 2002

The motion of small spherical solid particles are simulated numerically in a decaying homogeneous isotropic turbulent gas flow field generated by the large eddy simulation. By comparing with the previous experimental and theoretical studies, the present method is found to be a successful tool to generate the properties of the particle motion involving the second-order statistics, such as the mean-square displacement, the dispersion coefficient, and the root-mean-square velocity fluctuation. The present results are complementary to the experimental data and include a detailed study of the effects of the flow turbulence, the particle’s inertia, and the particle’s free-fall velocity in a still fluid on the particle dispersion and turbulence intensity. By performing particle simulation in the flow fields generated with different values of the coefficient in the subgrid model and with different sizes of the calculation domain, it is found that the particle motion is indeed controlled mainly by the large eddies, and there are only minor contributions of the high wave number components of the flow field to the particle motion. Also included in the results is the effect of the turbulence decay on the long time particle dispersion. It is found that the peak value of the dispersion coefficient during the turbulence decay can be correlated with the large-scale Reynolds number and the velocity ratio between the particle’s free-fall velocity and the root-mean-square velocity fluctuation of the fluid. Simulation also shows that the particle’s settling velocity in turbulence is greater than that in a still fluid.
An application of the stochastic estimation to the jet mixing layer
Authors: Cole Daniel R. , Glauser Mark N. , Guezennec Yann G.
Published: July 2002

The linear stochastic estimation is a powerful technique that provides a means of estimating conditional eddies given unconditional two-point correlation data. This procedure was used to reconstruct estimates of multipoint conditional averages of the dominant structures in the jet mixing layer of Glauser and George (Proceedings of the Sixth Symposium on Turbulent Shear Flows, Toulouse, France, 1987). The pseudodynamic evolution of these conditional eddies was systematically compared to the instantaneous velocity fields and the results were quantified in terms of the percentage of the energy captured by the multipoint stochastic estimates. It was found that the single-point estimates do not yield adequate representations of the instantaneous velocity field, but that two reference points located on opposite sides of the shear layer yield realistic estimates, with little gained by adding more reference points.
Linear instability characteristics of wake-shear layers
Authors: Wallace D. , Redekopp L. G.
Published: July 2002

Stability characteristics are presented for a family of plane wake-shear layer velocity profiles. The presence of shear across the wake, or any other distortion which breaks the profile symmetry, forces the neutrally stable modes to be singular. The neutral modes, the domains of absolute and convective instability, and the parameter conditions for which the von Kármán mode of vortex roll-up for a wake changes to a shear layer mode of roll-up as the velocity ratio increases have been computed.
The dynamics of long frontal waves in the shallow-water equations
Authors: Nycander J. , Dritschel D. G. , Sutyrin G. G.
Published: July 2002

A simple equation is derived for the nonlinear evolution of a front (a potential-vorticity discontinuity) in the rotating shallow-water equations, assuming weak along-front variations relative to the internal radius of deformation. This equation can be transformed into the modified Korteweg–de Vries equation, which is integrable and possesses exact, time-dependent solutions.
Nearly incompressible fluids. II: Magnetohydrodynamics, turbulence, and waves
Authors: Zank G. P. , Matthaeus W. H.
Published: July 2002

The theory of nearly incompressible (NI) fluid dynamics developed previously for hydrodynamics is extended to magnetohydrodynamics (MHD). On the basis of a singular expansion technique, modified systems of fluid equations are derived for which the effects of compressibility are admitted only weakly in terms of the different possible incompressible solutions (thus ‘‘nearly incompressible MHD’’). NI MHD represents the interface between the compressible and incompressible magnetofluid descriptions in the subsonic regime. The theory developed here does not hold in the presence of very large thermal, gravitational, or field gradients. It is found that there exist three distinct NI descriptions corresponding to each of the three possible plasma beta (β ≡ the ratio of thermal to magnetic pressure) regimes (β≪1, β∼1, β≫1). In the β≫1 regime, the compressible MHD description converges in the low Mach number limit to the equations of classical incompressible three-dimensional (3-D) MHD. However, for the remaining plasma beta regimes, the imposition of a large dc magnetic field forces the equations of fully compressible 3-D MHD to converge to the equations of 2-D incompressible MHD in the low Mach number limit. The ‘‘collapse in dimensionality’’ corresponding to the different plasma beta regimes clarifies the distinction between the 3-D and 2-D incompressible MHD descriptions (and also that of 21/2-D incompressible MHD). The collapse in dimensionality that occurs as a result of a decreased plasma beta can carry over to the weakly compressible corrections. For a β∼1 plasma, Alfvén waves propagate parallel to the applied magnetic field (reminiscent of reduced MHD), while for a β≪1 magnetofluid, quasi-1-D long-wavelength acoustic modes propagate parallel to the applied magnetic field. The detailed theory of weakly compressible corrections to the various incompressible MHD descriptions is presented and the implications for the solar wind emphasized.
Comments on ‘‘Rigorous link between fluid permeability, electrical conductivity, and relaxation times for transport in porous media’’
Authors: Lafarge Denis
Published: July 2002

Recently, Avellaneda and Torquato [Phys. Fluids A 3, 2529 (1991)] derived several expressions for both the static and dynamic permeability for flow through porous media, in terms of the characteristic viscous relaxation times. In this Brief Communication the focus is on the physical interpretation, Darcy’s law is explicitly obtained, and a slightly misleading statement (which has no effect on the mathematics but may induce erroneous interpretations) is corrected.
The self-trapping of light waves by beat-wave excitation.
Authors: Gibbon Paul
Published: July 2002

Self-fosusing thresholds are derived for multiple laser beams in the presence of a beat-excited plasma wave. The effects of relativistic electron ‘‘quiver’’ motion and the interaction of the beams with the plasma wave are included self-consistently. When the plasma wave is driven resonantly to large amplitude, transfer of the pump energy into sidebands causes the beams to defocus more rapidly. Consequently, relativistic focusing occurs above an irradiance threshold of Iλ2≊2×1017 W cm−2 μm2, instead of the usual power threshold for double-frequency illumination P≊4√2×109(ω0/ωp)2 W. Numerical solusions show that self-trapping of the laser energy is possible only for relatively small amplitude plasma waves. Comparisons are made with ‘‘cascade focusing,’’ which occurs when the plasma wave is driven below the plasma frequency. The threshold for the latter is up to ten times lower than for relativistic focusing. Numerical studies in this case indicate that self-trapped solutions do not exist, but the rate of beam collapse can be controlled by choosing an appropriate density mismatch.
Convective growth of parametrically unstable modes in inhomogeneous media
Authors: Williams Edward A.
Published: July 2002

By a suitable definition of an amplification coefficient, a convenient analytic criterion for convective instability of damped parametrically coupled unstable modes in an inhomogeneous medium is obtained. The net growth factor F3 on propagation through the resonant interaction region is found to be given by F3 = exp[(πγ20/κ′v1v2)F(√ν1ν2/γ0)], where the reduction factor F(x) = (2/π)[acos(x) − x√1−x2]. This can readily be seen to reduce to the usual inhomogeneous gain formula when damping is negligible and F=1, and to manifest the homogeneous convective threshold, γ20 ≳ ν1ν2. This result should find useful application in laser fusion plasmas, where damping and spatial inhomogeneity are frequently suppression mechanisms of comparable importance for laser-driven parametric instabilities.
Fragmentation and stopping of heavy cluster ions in a lithium target−Application to target implosion
Authors: Deutsch C. , Tahir N. A.
Published: July 2002

Heavy-ion clusters are considered for driving directly a pellet for inertial confinement fusion. They are shown to be effective at much lower energy than requested for heavy atomic ions. Multifragmentation, arising from a Coulomb explosion, in the target, is discussed with a maximum entropy hypothesis. Direct driving pressure imparted to a deuterium–tritium (DT) pellet is estimated through the ion debris range in the target. The correlated stopping of N ions flowing close to the initial projectile trajectory is seen to be much larger than the uncorrelated one. Specific attention is paid to a few regular geometrics of cluster ion debris stopped in a lithium pusher. The calculations elaborate on the very high driving pressure obtained, for the case of a solid-state density of cluster ion projectiles around the pellet (moving tamper). A target containing 4 mg of deuterium and tritium fuel is demonstrated to be thus imploded in 5 nsec. A driving pressure of 500 Mbars yields an energy output of 630 MJ. This result can be obtained with an initial cluster kinetic energy smaller than 20 keV/amu.