bluuebunny/crossref_metadata_2025 huggingface dataset:
A new class of strongly bound, doubly excited valence states of neutral van der Waals molecules: Mg(3pπ,3pπ 3P
J)⋅Ar(3Σ)
Authors: Massick Steven , Breckenridge W. H.
Published: July 2002

The first of a new class of strongly bound, double excited valence states of neutral van der Waals molecules, Mg(3pπ,3pπ 3PJ)⋅Ar(3Σ−), has been characterized by R2PI (resonance two-photon ionization) spectroscopy via excitation of metastable Mg(3s3pπ 3PJ)⋅Ar(3Π0+,0−) states in a supersonic jet. The MgAr(3Σ−) state has a bond energy of ∼2900 cm−1, more than twice that of the MgAr+ ion.
The generalized discrete variable representation. An optimal design
Authors: Szalay Viktor
Published: July 2002

The generalized discrete variable representation, as opposed to the discrete variable representation, of a Hamiltonian is such that it can give accurate eigenvalues of the Hamiltonian even if non-Gaussian quadrature points and weights are used in its construction. A new method of building up the generalized discrete variable representation of a Hamiltonian has been described and its properties have been analyzed. This new method appears to be optimal, meaning that no other design based on the same points, weights, and basis functions can be conceived which would give more accurate eigenvalues. Numerical calculations have revealed that, remarkable accuracy can be achieved even with general, non-Gaussian quadrature points and weights.
The interacting B 4Σ− and d 2Π states of CrN: A laser induced and dispersed fluorescence study
Authors: Zhou Chi , Balfour Walter J. , Qian Charles X. W.
Published: July 2002

Chromium mononitride molecules have been produced in a laser vaporization molecular beam source using Cr metal and ammonia. The complex CrN LIF spectra between 430 and 490 nm have been examined in detail and representative bands in three new electronic subsystems, labeled B 4Σ−←X 4Σ−, d 2Π3/2←X 4Σ−, and d 2Π1/2←X 4Σ−, have been rotationally analyzed. Perturbations between the B 4Σ− and d 2Π states and their dependence on vibrational quantum numbers have been examined. Dispersed fluorescence (DF) spectra have been recorded which provided a measure of the state mixing. The DF spectra also reveal the presence of an electronic state of CrN with T∼6000 cm−1, identified as the a 2Σ− state. Molecular parameters in the B 4Σ−, d 2Π, and a 2Σ− states have been established.
Theoretical study of the Coulombic explosion in doubly charged Xe clusters
Authors: Athanasopoulos Demosthenes C. , Schmidt Kevin E.
Published: July 2002

In this work we introduce a theoretical model for the description of doubly charged xenon clusters. It is based on the assumption that the charges migrate inside the cluster by isotropic hopping through a Hubbard Hamiltonian. The Xe atoms are considered classical polarizable particles. For their interaction we use a 2-body potential to which we add charge–charge, charge–dipole, and dipole–dipole interactions. The calculations are carried out within the ground state approximation. We perform molecular-dynamics calculations on doubly charged clusters of up to 55 atoms. We investigate the role that the quantum degree of freedom plays on the critical size for the appearance of the doubly charged clusters. The incorporation of the quantum hopping results in a fragmentation energy barrier for clusters larger than the experimentally observed critical size, so that the calculated critical appearance size is in agreement with experiment.
Angular geometries of complexes containing the O⋯Cl–F linkage: Rotational spectrum of formaldehyde⋯chlorine monofluoride
Authors: Cooke S. A. , Corlett G. K. , Evans C. M. , Legon A. C. , Holloway J. H.
Published: July 2002

Ground-state rotational spectra of the three isotopomers H2CO⋯35ClF, H2CO⋯37ClF and D2CO⋯35ClF of a complex formed by formaldehyde and chlorine monofluoride were observed with a Balle–Flygare, Fourier-transform microwave spectrometer. A fast-mixing nozzle, specially modified to generate a continuous supply of H2CO from paraformaldehyde in situ close to the nozzle exit, was used to preclude the chemical reaction of H2CO and ClF. The rotational constants A0, B0, and C0, centrifugal distortion constants ΔJ, ΔJK, and δJ, components χaa, χbb−χcc, χab of the Cl-nuclear quadrupole tensor, and the spin–rotation coupling constant 1/2(Mbb+Mcc) were determined. Interpretation of the spectroscopic constants led to the conclusion that H2CO⋯ClF is a planar complex of Cs symmetry with r(O⋯Cl)=2.523(7) Å, with an angle 180−φ=69.1(7)° between the C2 axis of H2CO and the O⋯Cl internuclear line, but with a deviation θ of the O⋯Cl–F nuclei from collinearity of only 3.2(7)°. A family relationship between the angular geometries of several complexes B⋯XY, where B is 2,5-dihydrofuran, oxirane, or formaldehyde, and XY is ClF or HCl, is discussed. It is shown that for a given B the angle 180-φ is the same for XY=HCl or ClF, while the nonlinearity θ of the O⋯X–Y system is almost negligible for XY is ClF but significant when XY is HCl. Reasons for this family relationship and the nonlinear O⋯H–Cl hydrogen bonds are discussed.
Theory for chain conformations and static structure of dilute and semidilute polyelectrolyte solutions
Authors: Yethiraj Arun
Published: July 2002

A theory is presented for the conformational properties and static structure of polyelectrolyte solutions. The theory combines field theoretic methods with liquid-state theory, and incorporates screening from counterions and polyions through a self-consistently determined solvation potential. Predictions for the size of the polymer molecules and the static structure factor are in good agreement with molecular dynamics simulations over the entire concentration regime, with no adjustable parameters.
Mass-resolved VUV laser spectroscopy of XeAr: Two competing predissociation pathways in the C1 state
Authors: Liu Shilin , Hishikawa Akiyoshi , Yamanouchi Kaoru
Published: July 2002

Mass-resolved excitation spectra of the C1–X0+ band of XeAr were measured under jet-cooled conditions using a tunable coherent vacuum ultraviolet (VUV) light (λ∼130 nm) as an excitation light source and a high-resolution (m/Δm∼1100) reflectron time-of-flight mass spectrometer. The rotational structure of the C1–X0+ (v′,0) (v′=2–6) vibronic bands were recorded by monitoring the parent Xe40132Ar+ ions and the fragment Xe+132 ions. From the analysis of the rotational structures, the existence of the two dissociation pathways from the C1 state was identified for the first time; i.e., (i) the rotationally dependent predissociation caused by an electron-rotation interaction (L- and/or S-uncoupling) with the dissociative state with 0− symmetry correlating with the Xe 6s′(1/2)0 level, and (ii) the rotationally independent predissociation caused by the electrostatic interaction with a repulsive state with Ω=1 symmetry correlated either with the Xe 6s(3/2)1 level or the Xe 6s(3/2)2 level. From the least-squares fit to the partially resolved rotational structures, the dissociation rates for these two pathways as well as the band origins and the rotational constants, were derived for the v′=2–6 levels in the C1 state.
Surface femtochemistry of CO/O2/Pt(111): The importance of nonthermalized substrate electrons
Authors: Her Tsing-Hua , Finlay Richard J. , Wu Claudia , Mazur Eric
Published: July 2002

We studied the surface femtochemistry of CO/O2/Pt(111) induced with 0.3 ps laser pulses over a wide range of wavelength and fluence. Below 10 μJ/mm2, the yields depend linearly on fluence. Above 10 μJ/mm2, the yields scale nonlinearly in the fluence. From the dependence of the yields on wavelength, we determine that the nonlinear surface femtochemistry is influenced by nonthermal substrate electrons.
New Ã–X̃ vibronic bands of laser-vaporized C3
Authors: Izuha Mitsuaki , Yamanouchi Kaoru
Published: July 2002

The laser-induced fluorescence (LIF) spectrum for the Ã 1Πu–X̃ 1Σg+ band of C3 was observed under jet-cooled conditions. On the basis of our previous report [Chem. Phys. Lett. 242, 435 (1995)], in which the ν3 fundamental in the Ã 1Πu state was determined to be 541.7(1) cm−1 through the first identification of the Ã(0,0,1)–X̃(0,0,1) hot-band transition, we extended the measurements of the ν3 related key bands; the high-resolution spectra (Δν∼0.08 cm−1) of eight vibronically allowed Σu+–Σg+-type transitions and two Πg–Σu+ hot-band transitions were measured, and their rotational structures were analyzed. The determined band-origin wave numbers and the symmetries of the rotational structures led to firm assignments of the vibrational levels in the Ã 1Πu state. Using the vibrational level energies of the Ã(0,0,v3)(v3=1–3) levels, the anharmonic potential along the ν3 mode in the Ã 1Πu state was estimated to have double minima with a barrier height of 284.3 cm−1 at the linear configuration.
Size-dependent electronic level structure of InAs nanocrystal quantum dots: Test of multiband effective mass theory
Authors: Banin U. , Lee C. J. , Guzelian A. A. , Kadavanich A. V. , Alivisatos A. P. , Jaskolski W. , Bryant G. W. , Efros Al. L. , Rosen M.
Published: July 2002

The size dependence of the electronic spectrum of InAs nanocrystals ranging in radius from 10–35 Å has been studied by size-selective spectroscopy. An eight-band effective mass theory of the quantum size levels has been developed which describes the observed absorption level structure and transition intensities very well down to smallest crystal size using bulk band parameters. This model generalizes the six-band model which works well in CdSe nanocrystals and should adequately describe most direct semiconductor nanocrystals with band edge at the Γ-point of the Brillouin zone.
Effect of counterion species on the dynamics of polystyrenesulfonate in aqueous solution as studied by dynamic light scattering
Authors: Matsuoka Hideki , Ogura Yoshito , Yamaoka Hitoshi
Published: July 2002

The diffusion behavior of macroions in aqueous solutions especially at low salt concentrations has been interesting and also mysterious problem since Schurr et al. found slow mode in 1978. By the systematic investigations on the structure and dynamics of charged particles and macromolecules in solution, it has been suggested that some novel factor(s) should be taken into account for understanding of interesting phenomena in these systems. In this study, the dynamic character, i.e., diffusion behavior of polystyrenesulfonate (PSS) in aqueous solution has been studied by dynamic light scattering (DLS) as a function of salt concentration in various salt forms. Both fast and slow modes were clearly detected. With increasing salt concentration, the fast mode became dominant and its decay rate became slower. On the other hand, the slow mode was not so sensitive to salt concentration but its contribution markedly decreased with increasing salt concentration and then became almost negligible at higher salt concentrations. The fast mode of LiPSS, NaPSS, and CsPSS was in the order of LiPSS≦NaPSS<CsPSS, although the difference was small, and was consistent with the order of diffusion coefficients of counterions. The fast mode of HPSS was much faster than that of other PSS salts. The same tendency was also observed for HPES and NaPES, salts of polyethylenesulfonate. The slow mode also depended on the counterion species, which may predict the important role of counterion dynamics in electric interaction between macroions.
Solvation dynamics of an excess electron in methanol and water
Authors: Mosyak Alexander A. , Prezhdo Oleg V. , Rossky Peter J.
Published: July 2002

Molecular dynamics simulation has been used to explore the nature of solvation dynamics for an excess electron in methanol and in water. We perform the analysis within the linear response theory and show that nonlinear corrections are small in both cases. The response function characterizing solvent relaxation after electron photoexcitation and that following the subsequent nonradiative transition are modeled and found to behave very similarly in methanol, in contrast to water. For methanol, each is comprised of an extremely short Gaussian inertial component of small amplitude and a bi-exponential diffusive decay. A relatively fast ∼1 ps exponential accounts for approximately half of the solvent relaxation and is followed by a slower ∼7 ps relaxation of comparable magnitude, a solvation response that is rather similar to that reported previously for relatively large molecules in methanol. Spectral densities of energy gap fluctuations for the equilibrium ground and excited state trajectories show that translational motion dominates solvation. Relaxational processes in methanol have been compared with the results for water. In contrast to methanol, librational motions of solvent molecules significantly influence aqueous solvation dynamics, especially following excited state decay. This difference is reflected in the relaxational processes, which are an order of magnitude slower in methanol than in water.
Image charge effects on colloidal crystal ordering
Authors: Tandon Shalabh , Kesavamoorthy R. , Asher Sanford A.
Published: July 2002

We theoretically investigated the effect of the container wall on the structural ordering of aqueous dispersions of negatively charged electrostatically stabilized colloidal spherical particles. The colloidal crystal contained between two quartz plates is modeled as a set of crystal planes oriented parallel to the quartz walls. We consider the electrostatic interactions between the particles and the container wall, and the particles and their induced image charges. The position-dependent interaction energies of a plane with its neighbors and the induced image charges are calculated under the Debye–Hückel approximation. We also theoretically investigate the effect of charged container walls on the ordering of the colloidal particle dispersion. For zero wall surface charge, the colloidal sphere plane nearest to the container wall is held in a deeper potential well than are interior colloidal planes. A negative wall surface charge creates a shallower well for the nearest colloidal sphere plane, which is still deeper than that of the interior planes. A positive wall surface charge creates the deepest potential well. These results rationalize our recent observations of the initial nucleation of crystalline colloidal array by formation of 2D hexagonal colloidal layers near the container wall. We calculate the root-mean-square displacement of the planes at various distances from the wall and use the Lindermann-type melting criteria to examine ordering.
Cooperative diffusion in colloidal mixtures
Authors: Nägele G. , Bergenholtz J. , Dhont J. K. G.
Published: July 2002

In this work we develop a general method to examine cooperative diffusion, i.e., the partial dynamic structure factors, in multicomponent colloidal mixtures of spherical particles. Using a multivariable projection operator formalism based on the many-body Smoluchowski diffusion equation, we derive an exact microscopic expression for the matrix of irreducible memory functions associated with the partial dynamic structure factors and the long-time cooperative diffusion coefficients of the system. Starting from this microscopic expression, we present a derivation of a self-consistent mode coupling scheme (MCS) for cooperative diffusion in colloidal mixtures. This scheme accounts not only for the direct particle interactions, but also for the far-field part of the solvent mediated hydrodynamic interactions. Combined with our recent work on the mode coupling theory of tracer–diffusion and linear viscoelasticity of colloidal suspensions, this MCS provides a unified method for calculating dynamic and low-shear rheological properties of multicomponent colloidal dispersions. The MCS can be used to study polydispersity and mixing effects in concentrated colloidal systems. Some applications related to cooperative diffusion, interdiffusion, and glass transition in binary mixtures are discussed to illustrate the method.
Photodissociation spectroscopy of the Mg+-Ne complex
Authors: Reddic J. E. , Duncan M. A.
Published: July 2002

The weakly bound complex Mg+-Ne is prepared in a pulsed nozzle/laser vaporization cluster source and the low-lying electronic states are studied with mass-selected photodissociation spectroscopy. The chromophore giving rise to the electronic spectrum is the P←22S atomic transition of Mg+. A Σ+2 ground state with Σ+2 and Π2 excited states is derived from this atomic transition. An unresolved continuum is observed to the blue of the atomic transition and is assigned to the B 2Σ+←X 2Σ+ transition. Sharp structure to the red of the atomic transition is assigned to the vibrationally resolved A 2Π←X 2Σ+ band system. Extrapolation of the Mg+-Ne stretch progression in this system determines the excited-state dissociation energy to be D0′=1696±50 cm−1, and an energetic cycle determines the ground-state value to be D0″=96±50 cm−1. The Πr2←2Σ+(9,0) vibronic transition is rotationally resolved for both spin-orbit components, definitively assigning the two Π2 electronic states and yielding bond lengths of r0″=3.17±0.05 Å in the ground state and r9′=2.59±0.05 Å in the excited state.
Direct measurement of the electric polarizability of isolated C60 molecules
Authors: Antoine R. , Dugourd Ph. , Rayane D. , Benichou E. , Broyer M. , Chandezon F. , Guet C.
Published: July 2002

We present the first direct measurement of the electric polarizability of isolated C60 molecules by molecular beam deflection technique. We have obtained a value of 76.5±8.0 Å3 which is consistent with most of the recent calculations and slightly lower than the value of the polarizability of C60 measured in fullerite crystals.
A derivation of centroid molecular dynamics and other approximate time evolution methods for path integral centroid variables
Authors: Jang Seogjoo , Voth Gregory A.
Published: July 2002

Several methods to approximately evolve path integral centroid variables in real time are presented in this paper, the first of which, the centroid molecular dynamics (CMD) method, is recast into the new formalism of the preceding paper and thereby derived. The approximations involved in the CMD method are thus fully characterized by mathematical derivations. Additional new approaches are also presented: centroid Hamiltonian dynamics (CHD), linearized quantum dynamics (LQD), and a perturbative correction of the LQD method (PT-LQD). The CHD method is shown to be a variation of the CMD method which conserves the approximate time dependent centroid Hamiltonian. The LQD method amounts to a linear approximation for the quantum Liouville equation, while the PT-LQD method includes a perturbative correction to the LQD method. All of these approaches are then tested for the equilibrium position correlation functions of three different one-dimensional nondissipative model systems, and it is shown that certain quantum effects are accounted for by all of them, while others, such as the long time coherence characteristic of low-dimensional nondissipative systems, are not. The CMD method is found to be consistently better than the LQD method, while the PT-LQD method improves the latter and is better than the CMD method in most cases. The CHD method gives results complementary to those of the CMD method.
A single-bond approach to orientation-dependent interactions and its implications for liquid water
Authors: Truskett Thomas M. , Debenedetti Pablo G. , Sastry Srikanth , Torquato Salvatore
Published: July 2002

A simple model of an associating fluid is proposed that accounts for the fact that hydrogen bonds are highly directional and favor the formation of locally open structures. The resulting analytical equation of state reproduces the distinguishing thermodynamic features of liquid water. In contrast to previous models in which the relationship between bonding and bulk density is assumed a priori, the extent of hydrogen bonding is derived in the present work from a simple microscopic model. Furthermore, by altering the parameters which control the geometric constraints on bonding, the model is able to exhibit the two thermodynamically consistent scenarios that can explain the observed behavior of supercooled liquid water, namely the two-critical-point and singularity-free scenarios. This suggests that the two scenarios are closely related through subtle features of the hydrogen-bond geometry.
Heteronuclear rare-gas dimer bonding: Understanding the nature of the Rydberg states that dissociate to the highest energy level of the Xe*(5d) manifold
Authors: Mao D. M. , Hu X. K. , Shi Y. J. , Lipson R. H.
Published: July 2002

(1+1 ′ ) resonance enhanced multiphoton ionization (REMPI) spectra of jet-cooled KrXe and ArXe in the vicinity of the high energy Xe*5d[3/2]10←Xe(1S0) atomic line at 83889.99 cm−1 were obtained by exciting the neutral dimers with tunable coherent vacuum ultraviolet (VUV) radiation generated by four-wave sum mixing in mercury vapor, and then detecting the resultant ions in a time-of-flight (TOF) mass spectrometer. Precise excited state constants were derived from analyses of the resultant vibrational fine structure, while equilibrium bond lengths were estimated from Franck–Condon factor intensity simulations. Excited state symmetries were deduced from separate ultraviolet (UV) (2+1) REMPI spectra recorded with linearly and circularly polarized light. The results of this work confirm a recent model proposed by Lipson and Field, where the RgXe*(5d) states are predicted to be strongly destabilized relative to RgXe*(6p) due to strong 5d-6p Xe* l-mixing induced by the ground state Rg atom partner making up the dimer. Orbital mixing is also responsible for the observation of appreciably strong RgXe*(5d) spectra in both one- and two-photon excitation.
From Rouse dynamics to local relaxation: A neutron spin echo study on polyisobutylene melts
Authors: Richter D. , Monkenbusch M. , Allgeier J. , Arbe A. , Colmenero J. , Farago B. , Cheol Bae Y. , Faust R.
Published: July 2002

We investigated the single chain motions of monodisperse polyisobutylene chains in the melt by neutron spin echo spectroscopy. Thereby a wide range in momentum space over a large dynamic range was covered. Motional processes from the center of mass diffusion, the Rouse dynamics to the more local relaxation processes which limit the validity of the standard Rouse model, were elucidated. The observed dynamic structure factors were analyzed in terms of relevant theoretical approaches addressing the limiting factors of the Rouse model. We found that other than claimed in the literature effects of local chain stiffness—they were treated in terms of the all rotational states model and a bending force model—cannot account for the experimental observations. It appears that additional damping effects related to an internal viscosity of the chain have to be involved, in order to explain the experimental results.
Fine and hyperfine interactions in CrN and MoN
Authors: Namiki Kei-ichi C. , Steimle Timothy C.
Published: July 2002

Pure rotational transitions of 52Cr14N and 98Mo14N radicals in their X 4Σ− state were recorded using a pump/probe microwave-optical double resonance (PPMODR) technique from which the hyperfine parameters of 14N (I=1) were precisely determined. In addition, the (0,0) A 4Π–X 4Σ band system of 53CrN was recorded from which the hyperfine parameters of 53Cr (I=32) were determined. The newly determined hyperfine interactions for 53Cr and 14N in CrN and 14N in MoN and the previously determined hyperfine interactions for other early transition metal mononitrides were analyzed using a simple, single configurational, model. The improved set of fine structure parameters for the CrN and MoN are discussed in terms of possible electronic state distributions.
Pseudorotation pathway and equilibrium structure from the rotational spectrum of jet-cooled tetrahydrofuran
Authors: Meyer Rolf , López Juan Carlos , Alonso José L. , Melandri Sonia , Favero Paolo G. , Caminati Walther
Published: July 2002

The rotational spectrum of jet-cooled tetrahydrofuran has been investigated in the 8–18 and 60–78 GHz frequency ranges. Only the four lowest vibrational levels remain populated in the jet conditions. Two pseudorotation vibrational spacings have been measured directly to be ΔE01=21 307.71(3) MHz and ΔE23=61 205.69(3) MHz. They have been used, together with the lowest 10 measured far infrared transition frequencies and with the effective moments of inertia of the ground state and their shifts upon excitation observed in this work, to determine the potential energy function for pseudorotation and the associated structural relaxations. The potential energy barriers are 45 cm−1 at the envelope conformation of the oxygen and 16 cm−1 at the twisted conformation of the Cβ–Cβ′ bond relative to the CαOCα′ plane. The four symmetrically equivalent equilibrium structures are close to the envelope conformations of the CH2 groups next to the oxygen atom. While the C–O bond lengths and the local CH2 angles appeared to remain unaffected by pseudorotation, significant changes found for the diagonal O⋯C distances as well as for the C–C and C–H bond lengths are of interest as possible effects of hyperconjugation.
Molecular simulation and theory of the isotropic–nematic interface
Authors: Allen Michael P.
Published: July 2002

Computer simulations of a simple model of liquid crystals confined between parallel walls have been used to investigate the properties of nematic wetting films and the planar nematic–isotropic interface. Comparison is made with the theoretical predictions of Onsager’s density-functional theory, obtained by numerical minimization of the appropriate free energy. Several different anchoring conditions at the wall–nematic interface are investigated. The theory is known to overestimate the bulk coexistence densities, but with this proviso, the agreement between simulation and theory is excellent. For the model studied, simulation and theory give density profiles which vary monotonically through the interface; the simulations also confirm the theoretical prediction that the density profile is shifted towards the nematic phase relative to the order parameter profile. The width of the interface, as measured by the order parameter profile, varies as expected with director tilt angle; the angle-dependence of the density profile width is smaller, and seems to be somewhat overestimated by the theory.
Cavity ringdown spectroscopy of the linear carbon chains HC7H, HC9H, HC11H, and HC13H
Authors: Ball C. D. , McCarthy M. C. , Thaddeus P.
Published: July 2002

Optical bands from the Σu−3←X Σg−3 transition of the linear carbon chains HC7H, HC9H, HC11H, and HC13H have been measured in the gas phase by cavity ringdown spectroscopy. The bands exhibit well resolved P and R branches, which for HC7H are partially rotationally resolved. Comparisons between observed and simulated spectra indicate broadening in excess of that expected from the laser linewidth and Doppler width, suggesting rapid radiationless transitions in roughly 0.1–0.01 ns, a time scale consistent with the absence of observed fluorescence from these molecules. The HC7H and HC9H bands are of nearly equal strength, but those of the shorter chain HC5H are too weak to detect at the 1 ppm level. None of the bands observed here lies sufficiently close to any of the optical diffuse interstellar bands to provide positive identification.
Relationship between specific surface area and spatial correlation functions for anisotropic porous media
Authors: Berryman James G.
Published: July 2002

A result of Debye, Anderson, and Brumberger [P. Debye, H. R. Anderson, Jr., and H. Brumberger, J. Appl. Phys. 28, 679 (1957)] for isotropic porous media states that the derivative of the two-point spatial correlation at the origin is equal to minus one-quarter of the specific surface area. This result is generalized for nonisotropic media by noting that the angular average of the anisotropic two-point spatial correlation function has the same relationship to the specific surface area.
The scalar product in two-particle relativistic quantum mechanics
Authors: Sazdjian H.
Published: July 2002

In the framework of two-particle relativistic quantum mechanics, a Poincaré-invariant scalar product and the corresponding physical Hilbert space of states are constructed. This is achieved by finding a tensor current of rank 2, jμν(x1,x2), satisfying two independent conservation laws, relative to particles 1 and 2, respectively. Then the scalar product is obtained by integrating the current jμν over two three-dimensional spacelike hypersurfaces. The Hermiticity of the Poincaré group generators is ensured by the fact that the kernel of the current jμν is translation invariant and covariant. A simple expression of the scalar product is obtained when one chooses for the two spacelike hypersurfaces two constant parallel hyperplanes. The positivity of the norm is, in general, ensured if the spectrum of the eigenvalues of the total mass squared operator comes out to be positive.
Solutions of certain integrable nonlinear PDE’s describing nonresonant N-wave interactions
Authors: Calogero F.
Published: July 2002

The evolution equations that describe, in appropriately ‘‘coarse-grained’’ and ‘‘slow’’ variables, the evolution of the envelopes of N nonresonant dispersive waves, can be reduced to the ‘‘universal’’ form (∂/∂t+vn ∂/∂x) un(x,t) =un(x,t) ∑Nm=1βnmum(x,t). In this paper the special case with βnm=(vm−vn) βm, which is integrable by quadratures, is investigated. The subclass of localized solutions (i.e., vanishing as x→±∞) gives rise to a novel solitonic phenomenology. The class of solutions that are asymptotically finite contains a richer solitonic phenomenology, including those of novel type (which move with the speeds vn, and can have any shape) and more standard kinks (which can move with any speed, and have standard shapes). The class of rational solutions, and the integrable dynamical systems naturally associated with these solutions, are also investigated; these dynamical systems include, and extend, known integrable systems. In this paper the treatment is confined to 1+1 dimensions; at the end, together with some other generalizations, a partially solvable multidimensional extension is reported.
Approximate representations of the scattering amplitude
Authors: Dashen Roger , Wurmser Daniel
Published: July 2002

This is the second in a series of articles about the theory of scattering from a rough surface. A symmetric representation of the scattering amplitude and a formal statement of the composite model, both derived in the previous article, are used to approximate the scattering amplitude in terms of the known results for a reference surface. When the reference surface is a plane, the small slope approximation follows, while the traditional composite model is obtained if the curvature of the reference surface is neglected. The medium is assumed to be homogeneous, and the calculation is performed for scalar waves obeying Dirichlet or Neumann boundary conditions, electromagnetic waves obeying perfect conductor boundary conditions and the interface between two media for both types of waves. Finally, the requirement that the formal composite model must reproduce the traditional composite model in the appropriate limit is used to obtain a new approximation to the scattering amplitude. This is done for the Dirichlet, Neumann, and perfect conductor problems. The error goes as the square of the curvature.
Bianchi type-I cosmological models in Lyra’s geometry
Authors: Singh T. , Singh G. P.
Published: July 2002

Exact solutions are obtained for the anisotropic Bianchi type-I model in normal gauge for Lyra’s geometry. The physical behavior of the models is examined in vacuum and in the presence of perfect fluids.
Uniqueness of the scalar product in the tensor product of quaternion Hilbert modules
Authors: Razon A. , Horwitz L. P.
Published: July 2002

In the construction of a tensor product of quaternion Hilbert modules, given in a previous work (real, complex, and quaternionic), inner products were defined in the vector spaces formed from the tensor product of quaternion algebras H modulo an appropriate left ideal in each case. Under conditions that are necessary for the definition of a scalar product in the quaternionic Hilbert modules and a natural condition on the algebraic structure, it is proven that the scalar products which are defined are unique.
The finite-band solution of the Jaulent–Miodek equation
Authors: Zhou Ruguang
Published: July 2002

A method to construct the finite-band solution to the soliton equation is presented. We take the Jaulent–Miodek equation as an example. With the use of the nonlinearization of Lax pair, the Jaulent–Miodek equation is decomposed into two finite-dimensional integrable systems, whose properties are studied from the view of an r-matrix. Then through solving these finite-dimensional integrable systems, the finite-band solution of the Jaulent–Miodek equation is obtained.
Transformation of general curve evolution to a modified Belavin–Polyakov equation
Authors: Balakrishnan Radha , Blumenfeld Raphael
Published: July 2002

We show that the general evolution of the tangent to a curve in three-dimensional space can be transformed to a modified form of the Belavin–Polyakov equation. Using this, we find a rich variety of exact instanton and twist solutions for several classes of evolution. Certain physical applications are also discussed.
Towards a theory of negative dependence
Authors: Pemantle Robin
Published: July 2002

The FKG theorem says that the positive lattice condition, an easily checkable hypothesis which holds for many natural families of events, implies positive association, a very useful property. Thus there is a natural and useful theory of positively dependent events. There is, as yet, no corresponding theory of negatively dependent events. There is, however, a need for such a theory. This paper, unfortunately, contains no substantial theorems. Its purpose is to present examples that motivate a need for such a theory, give plausibility arguments for the existence of such a theory, outline a few possible directions such a theory might take, and state a number of specific conjectures which pertain to the examples and to a wish list of theorems.
Linear instabilities in two-dimensional compressible mixing layers
Authors: Ragab Saad A. , Wu J. L.
Published: July 2002

Linear instability waves in supersonic shear layers are analyzed. Both viscous and inviscid disturbances are considered. The basic state is obtained by solving the compressible laminar boundary-layer equations or is specified by the hyperbolic tangent profile. The effects of the velocity ratio and temperature ratio are determined. The numerical results show that the maximum growth rate depends nonlinearly on the velocity ratio. The results also substantiate the convective Mach number as a compressibility parameter for mixing layers.
Turbulent thermal convection in a finite domain: Part II. Numerical results
Authors: Park H. , Sirovich L.
Published: July 2002

A pseudospectral method is used to solve the Boussinesq equations for a fully inhomogeneous turbulent flow. The numerical data are analyzed using the empirical eigenfunction technique. As a result of the underlying inhomogeneity of the flow, the eigenfunctions (structures) are inhomogeneous in all three directions. This is the first instance in which fully three-dimensional empirical eigenfunctions have been calculated. The generated basis set is extremely efficient at depicting the flow. The first eigenfunction captures almost 60% of the average energy. The eigenfunctions are an optimal basis for capturing the energy of the flow and more than 95% of the energy is captured by the first 100 eigenfunctions. Ten classes of eigenfunctions are present and examples of each are shown. The average Nusselt number for the bounded geometry is found to be lower than that for a correspondong homogeneous case and the physics causing this decrease is analyzed and discussed.
The manipulation of capillary stream breakup using amplitude-modulated disturbances: A pictorial and quantitative representation
Authors: Orme M. , Muntz E. P.
Published: July 2002

Droplet formation from capillary streams of viscous low vapor pressure fluids in a vacuum has been studied. A new form of capillary stream breakup, which entails the use of an amplitude-modulated sinusoidal disturbance, has been employed extensively in this work. The genesis of droplets formed due to an amplitude-modulated disturbance on a stream is reviewed in some detail and illustrated pictorially. Because capillary stream breakup and subsequent droplet propagation took place in a vacuum there were no significant interactions with the surrounding atmosphere. Sensitive measurements of the relative speeds of each drop have been made by allowing them to travel 6 m in a vertical vacuum chamber, and measuring the time between drops using an optical method. Speed differences as low as 3.5×10−7 times the average stream speed have been measured. New information about capillary stream breakup is inferred by comparing the speed variations for droplet streams generated with both amplitude-modulated disturbances and single-frequency disturbances. An autoregressive model is developed and found to represent the deviations in time between droplets with consistency and reproducibility.
Numerical analysis of gas flows condensing on its plane condensed phase on the basis of kinetic theory
Authors: Aoki Kazuo , Sone Yoshio , Yamada Tatsuo
Published: July 2002

Gas flows condensing on its plane condensed phase are considered on the basis of the Boltzmann–Krook–Welander equation. First, the formation and propagation of disturbances in an initially uniform gas blowing against its plane condensed phase are investigated under the conventional boundary condition on the condensed phase to supplement the authors’ previous work, where some solutions require more detailed computation. Then, with the aid of time-dependent analysis, the behavior of steady condensation is clarified: The range of the variables at infinity and on the condensed phase that allows a steady solution is determined; the profiles of typical steady solutions are presented.
Kinetic study of evaporation flows from cylindrical jets
Authors: Sibold D. , Urbassek H. M.
Published: July 2002

The steady flow of particles evaporated from a cylindrical jet into vacuum is studied on the basis of a Monte Carlo simulation of the Boltzmann equation. The cases of very small and very large Knudsen numbers Kn can be treated analytically using ideal gas dynamics and collision-free flow, respectively. Here the simulation yields very good agreement with theory, indicating that the code can be used on a wide range of Knudsen numbers. For the gas-dynamical case a Knudsen layer is formed by the equilibration of the flow in the vicinity of the jet; it is studied in some detail. Simulation of a flow at Kn≂1 shows that the radial velocity component attains equilibrium nowhere. This example models a recent experiment on the evaporation from liquid water jets, and gives good agreement with the measured speed ratio.
An experimental study of oscillatory thermocapillary convection in cylindrical containers
Authors: Kamotani Y. , Lee J. H. , Ostrach S. , Pline A.
Published: July 2002

An experimental study of oscillatory thermocapillary convection in small cylindrical containers with a heating wire placed along the center axis is performed by investigating the flow structures and temperature distributions under various conditions. To supplement the flow visualization the surface is scanned using an infrared imager. Here 2 cS viscosity (Pr=27) silicone oil is used as the test fluid. It is observed that beyond a certain temperature difference between the container wall and the heating wire, a distinctive unsteady flow pattern appears. This unsteady phenomenon is identified as oscillatory thermocapillary. After the onset of oscillations the flow structure becomes nonaxisymmetric and wave motion is observed at the free surface. It is shown that the critical temperature difference is independent of container dimensions if the aspect ratio is fixed.
Corewise cross-flow transport in hairpin vortices—The ‘‘tornado effect’’
Authors: Hagen J. P. , Kurosaka M.
Published: July 2002

There is increasing awareness that even in fully turbulent boundary layers, large-scale structures in the form of hairpin vortices abound. Although their implications are not all that clear at the present time, they seem to play an important role in turbulent flows. Due to the inherent unpredictability of hairpin vortices in their natural state, in the past effort has been made to generate synthetic hairpin vortices in a laminar boundary layer; from their study considerable insight into the processes underlying various features of turbulent flows has been gained. Contrary to those preceding studies where attention has been directed to the flows external to hairpin vortices, interest here is focused solely upon their interiors: the possible existence of cross-flow transport inside the cores of the hairpin legs. In synthetic hairpin vortices, the presence of such a corewise transport away from a wall surface, or the ‘‘tornado effect,’’ is substantiated in a water tunnel with flow visualization techniques. The effect is also verified using heated fluid injected near the wall surface by measuring the temperature at various points along the hairpin vortex core.
Proton ring formation and trapping in a gated magnetic mirror
Authors: Pedrow P. D. , Greenly J. B. , Hammer D. A. , Sudan R. N.
Published: July 2002

A detailed study of the trapping of proton rings in a magnetic mirror both in uniform gas fillings and in localized puffed-gas fillings is presented. The trapping of about 3×1014, 400 keV protons in a 1.5 m long, 0.8 T magnetic mirror was accomplished with a static 1.23:1 downstream mirror and a fast ‘‘gate’’ upstream mirror with mirror ratio <1.3:1. Protons were trapped for 4 μs (>50 cyclotron periods) or longer. The proton ring mean radius, length, and annular thickness in the trap were 10 cm, 1.5 m, and 5–8 cm, respectively. Detailed study of the dynamics of the injected and trapped protons with a variety of diagnostic techniques showed that the bulk of the protons followed trajectories that could be fully explained using the ion diode voltage and the details of the applied magnetic field configuration. However, a small fraction of the injected protons had axial energy much higher than was possible from single-particle trajectories; incomplete electrostatic neutralization of the proton ring by the beam-generated plasma in the injection region is postulated to explain this observation. Ring proton lifetime in the mirror trap appeared to be determined by mirror losses upon initially encountering the downstream and then the upstream mirrors, followed by a gradual radial loss due to charge-exchange collisions with the neutral gas contained in the experiment chamber.
Collisionless electron temperature gradient-driven instability in field-reversed configurations
Authors: Farengo R. , Guzdar P. N. , Lee Y. C.
Published: July 2002

The collisionless electron temperature gradient-driven instability is studied in the parameter regime relevant for field-reversed configurations. Perturbations in the electrostatic potential and all three components of the vector potential are considered and fully magnetized models, which include finite beta orbit modifications, are used for electrons and ions. It is shown that the electron temperature gradient can drive unstable modes over a wide range of values of β and ηe. These modes require a finite (but small) kz and propagate in the direction opposite to the lower hybrid drift.
Analytic, two fluid, field reversed configuration equilibrium with sheared rotation
Authors: Soběhart J. R.
Published: July 2002

A two fluid model is used to derive an analytical equilibrium for elongated field reversed configurations containing shear in both the electron and ion velocity profiles. Like some semiempirical models used previously, the analytical expressions obtained provide a satisfactory fit to the experimental results for all radii with a few key parameters. The present results reduce to the rigid rotor model and the infinite conductivity case for a specific choice of the parameters.
A numerical solution of the Boltzmann equation for high-powered short pulse microwave breakdown in nitrogen
Authors: Mulbrandon M. J. , Chen J. , Palmadesso P. J. , Sullivan C. A. , Ali A. W.
Published: July 2002

A theoretical formulation that provides a basis for generating approximate solutions of the Boltzmann equation for the study of high-powered microwave pulses interacting with a background atmosphere is given. A numerical scheme is implemented using realistic cross sections for electron–nitrogen collisions, including excitation and ionization. It is found that the numerical results agree well with previous experimental and theoretical values when α is less than about 0.1 kV/cm Torr, where α is the effective electric field divided by the pressure (α=Ee/P). Results are presented providing a simple fit for the time averaged momentum transfer rate and the ionization rate as a function of the microwave electric field E, wavelength λ, and gas pressure P, for 0.1≤α≤1.0 kV/cm Torr. This fit is compared with recent experimental data for breakdown times.
Low-frequency drift dissipative modes in field-reversed configurations
Authors: Soběhart J. R. , Farengo R.
Published: July 2002

Low-frequency drift dissipative modes are studied in the parameter regime relevant to field-reversed configurations. It is shown that previous theories [Phys. Fluids 30, 878 (1987)] are not accurate in that the effect of collisions was not properly included. Analytic and numerical studies with a dispersion relation that correctly includes the effect of collisions and uses the same approximations as in the above-mentioned reference have yielded no unstable modes.
Flux trapping efficiency during the early formation phase of a field reversed configuration
Authors: Soběhart Jorge R.
Published: July 2002

The observed discrepancy between the recently reported trapped flux efficiency during the field reversal phase of field reversed configurations in a fast theta pinch and previous scaling laws has been further analyzed and attributed to a change in the trapped flux loss mechanism consistent with a modified inertial loss.
Compton harmonic resonances, stochastic instabilities, quasilinear diffusion, and collisionless damping with ultra-high-intensity laser waves
Authors: Rax J. M.
Published: July 2002

The dynamics of an electron in a finite set of linearly or circularly polarized ultra-high-intensity (above 1018 W/cm2) laser waves is investigated within the framework of a Hamiltonian analysis. The Compton harmonic resonances are identified as the source of various stochastic instabilities. The stochasticity threshold due to resonance overlap is calculated and the structure of the resonances is analyzed. The quasilinear kinetic equation describing the evolution of the electron distribution function is derived, and the associated collisionless damping coefficient is calculated. The implications of these new processes are considered and discussed.