bluuebunny/crossref_metadata_2025 huggingface dataset:
Time-domain chirp electron nuclear double resonance spectroscopy in one and two dimensions
Authors: Jeschke G. , Schweiger A.
Published: July 2002

It is demonstrated by theory and experiment that time-domain broadband electron nuclear double resonance (ENDOR) spectroscopy can be performed by using radio frequency chirp pulses. The chirp ENDOR experiment is shown to have a sensitivity comparable to that of established pulsed ENDOR experiments while featuring at the same time a higher resolution. Two pulsed schemes are proposed for chirp ENDOR that are related to the Davies- and Mims-ENDOR experiments. A simple two-step phase cycle can remove the contributions from unwanted coherence transfer pathways and, unlike in time-domain ENDOR with pulses of fixed radio frequency, no quadrature readout is needed. The basic chirp ENDOR experiment can easily be extended by applying concepts from electron spin echo envelope modulation and nuclear magnetic resonance spectroscopy. A novel hyperfine sublevel correlation (HYSCORE) experiment based on chirp ENDOR is proposed.
Electronic properties of polymers based on thienothiadiazole and thiophene
Authors: Bakhshi A. K. , Ago Hiroki , Yoshizawa Kazunari , Tanaka Kazuyoshi , Yamabe Tokio
Published: July 2002

Ab initio crystal orbital (CO) studies on the geometric and the electronic structures of poly(thienothiadiazole) (Poly-1a) and periodic copolymers of thienothiadiazole and thiophene with the ratio of 1:1 (Poly-2b) and 1:2 (Poly-3b) are presented. In Poly-1a and Poly-2b, considerable change in the geometries is found to occur as one moves from their oligomers to the polymers. Although thienothiadiazole oligomers have a very small highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) separation, the corresponding polymer (Poly-1a) has a considerably large band gap. On the contrary, the geometric and electronic structures of Poly-3b are almost identical to those of the oligomer, and Poly-3b possesses a direct band gap of 1.3 eV estimated by simple scaling. The reasons for these differences are discussed in terms of orbital interactions and nonbonding molecular orbitals in the oligomers, and the reduced π-conjugation and enhanced intercell interaction in the polymers.
A high level ab initio map and direct statistical treatment of the fragmentation of singlet ketene
Authors: Klippenstein Stephen J. , East Allan L. L. , Allen Wesley D.
Published: July 2002

State-of-the-art ab initio quantum chemical techniques have been employed to ascertain the reaction path and associated energetics for the dissociation of CH2CO into 1CH2+CO and thereby to investigate the kinetics of this dissociation via variational Rice–Ramsperger–Kassel–Marcus (RRKM) theory. The quantum chemical computations focused on the determination of geometric structures, energies, and force fields for four constrained C–C distances (2.2, 2.5, 2.8, and 3.1 Å) spanning the inner transition-state region. Optimized structures were obtained with the coupled-cluster singles and doubles method including a perturbative triples term [CCSD(T)], as implemented with a contracted [C/O, H] basis set of [5s4p2d1f, 4s2p1d] quality. The resulting energetics were corrected for basis set incompleteness and higher-order electron correlation with the aid of second-order Mo/ller–Plesset perturbation theory (MP2) predictions given by an immense [13s8p6d4f, 8s6p4d] basis combined with 6–31G* Brueckner doubles results augmented with perturbative contributions from both connected triple and quadruple excitations. Quadratic force fields along the reaction path were determined at the CCSD/[5s4p2d, 4s2p] level of theory. Anharmonic effects in the enumeration of accessible states for the transition state were accounted for by a direct statistics approach involving repeated MP2/6-31G* energy evaluations. Two separate reaction coordinates defined by the C–C bond length or alternatively the center-of-mass separation between the 1CH2 and CO fragments were explicitly considered in these direct statistical analyses. A spectroscopic quality quartic force field for ketene derived in a companion ab initio study was employed in the evaluation of the anharmonic reactant density of states. The final statistical predictions for the energy dependence of the dissociation rate constant are found to be in quantitative agreement with experiment (i.e., generally within 30%), thereby providing strong evidence for the quantitative validity of variational RRKM theory.
Alkyl chain dynamics in perovskite bilayers and their variation with structural phase as studied by powder and single crystal NMR
Authors: Zhang H. , Kulshrestha N. P. , Woehler S. E. , Wittebort R. J.
Published: July 2002

A single crystal magnetic resonance study of C4Cd, [(C4H9NH3)2Cd]Cl4, specifically deuterated at a variety of positions is reported. This class of compound forms bilayered structures and C4Cd itself undergoes at least three phase transitions over the temperature range studied, 120 to 350 K. The experimental results yield a detailed picture of the variation of molecular ordering in the butyl chain with temperature and structural phase and bear substantial resemblance to 2H NMR results reported for lipid membranes. In the high and intermediate phases, complete order tensors are determined in the bilayer frame which are compared (unsuccessfully) with the disordered high temperature x-ray structure of the isomorphous manganese analog, C4Mn. On the time scale of 10−5 s, the butyl chain is nearly stationary at 120 K where it is found to occupy the expected all-trans configuration which runs parallel to the bilayer normal. At temperatures between the intermediate phase and 120 K, a mosaic structure is observed in which the C–D bonds occupy for long times (≳10−3 s) a distribution of orientations. A qualitative model for the high and intermediate phases based on gauche–trans isomerization is presented. To explain the measured order tensors, we assume that (a) gauche–trans isomerization is coupled to molecular reorientation and (b) the configurations are distorted from ideal diamond lattice configurations so as to make molecular packing more compact. It is suggested that in the mosaic structure, configurations containing gauche sequences remain populated but the isomerization rate is dramatically slowed.
Response of a single grafted polyethylene chain to simple shear flow: A Brownian dynamics simulation study
Authors: Haliloglu Turkan , Bahar Ivet , Erman Burak
Published: July 2002

The behavior of a single polyethylene chain grafted to an impenetrable surface, under shear flow, is investigated using Brownian dynamics simulations. Both short-range conformational energies and excluded volume effects are included in the model. Simulations are performed in good and poor solvent conditions in order to explore the effect of solvent quality. The shear flow is represented by the superposition of a force profile increasing linearly with the distance from the surface. Distribution of rotational angles, chain dimensions, components of the radius of gyration, segment density distribution, average layer thickness, and average orientation of bond vectors with respect to flow direction are determined and compared with other studies. Above a certain value of the shear rate, a significant increase in chain dimensions is observed for both good and poor solvents, the transition from coiled to stretched state being sharper in poor solvent. In good solvent, chain dimensions along the two perpendicular directions to the flow direction diminish with increasing shear rate. On the other hand, in poor solvent, there is an overall expansion in chain dimensions in all directions at low shear rates, which is subsequently followed by the orientation and alignment of the chain along the direction of flow. The experimentally observed increase in chain dimensions normal to the flow field at low shear rates is evidenced for the first time by simulations.
Molecular beam optical Zeeman spectroscopy of iridium mononitride
Authors: Steimle T. C. , Marr A. J. , Beaton S. A. , Brown J. M.
Published: July 2002

The Zeeman effect on the F-1/2←3/2 hyperfine component of the R(0) line in the (0,0) band of the A1Π–X1Σ+ transition of iridium mononitride, IrN, was investigated using a supersonic molecular beam optical spectrometer. The magnetic gJ-factor for IrN in the A1Π state was determined to be 0.96±0.05. The general applicability of Zeeman measurements is described and the gJ-factor which is determined is related to plausible molecular orbital descriptions for IrN in the A1Π state.
The influence of image interactions on the structure of water and electrolytes in front of a metal surface
Authors: Krämer A. , Vossen M. , Forstmann F.
Published: July 2002

The structure of liquid water in contact with a metallic planar wall is calculated for the central force water model which is a stoichiometric mixture of partially charged hydrogen and oxygen atoms interacting via effective spherical pair potentials. The density profiles near the wall are obtained from the Wertheim–Lovett–Mou–Buff equation where the bulk information enters through the direct correlation functions. In this approach image interactions which are characteristic for a metallic boundary, and which cannot be treated as a simple particle–wall interaction are considered within a mean-field ansatz. We discuss the structural properties of the interface layer for both cases, the charged and the uncharged wall, and compare the results to those for an unpolarizable boundary where the image forces have been switched off. The differential capacitance as function of the wall charge is seen to show a characteristic “hump” which can be related to the transition between two possible icelike water structures in front of the wall.
Effect of symmetry breaking on vibrational coherence transfer in impulsive photolysis of trihalide ions
Authors: Gershgoren E. , Gordon E. , Ruhman S.
Published: July 2002

Initial breaking of centrosymmetry is demonstrated to enhance transfer of vibrational coherence to products in impulsive photodissociation of trihalide ions in solution.
A coarse-grained, “realistic” model for protein folding
Authors: Bruscolini Pierpaolo
Published: July 2002

A phenomenological model Hamiltonian to describe the folding of a protein with any given sequence is proposed. The protein is thought of as a collection of pieces of helices; as a consequence its configuration space increases with the number of secondary structure elements rather than with the number of residues. The Hamiltonian presents both local (i.e., single helix, accounting for the stiffness of the chain) and non-local (interactions between hydrophobically–charged helices) terms, and is expected to provide a first tool for studying the folding of real proteins. The partition function for a simplified, but by no means trivial, version of the model is calculated almost completely in an analytical way. The latter simplified model is also applied to the study of a synthetic protein, and some preliminary results are shown.
Improved method for calculating projected frequencies along a reaction path
Authors: Baboul Anwar G. , Schlegel H. Bernhard
Published: July 2002

Some of the factors affecting the accuracy of following reaction paths and calculating projected frequencies perpendicular to the reaction path have been examined. The SN2 reaction of Cl− with CH3Cl computed at the HF/6-31G* level of theory has been used as a test case. The symmetric C–H stretching mode couples strongly to the reaction path, and the projected frequency of this mode is very sensitive to the numerical accuracy of the path following and frequency projection methods. The transition state geometry must be converged very tightly so that the path steps in the correct direction. For second order implicit algorithms, improved accuracy can be obtained by computing the tangent used for path following and frequency projection from the displacement along the path rather than from the gradient. An even greater increase in accuracy can be achieved by employing the Hessian, used to compute the frequencies, to take a Newton–Raphson step to improve the convergence of the reaction path following. Taken together, these techniques yield a one to three order of magnitude decrease in the errors in the projected frequencies along the reaction path.
Solvation free energies of methane and alkali halide ion pairs: An expanded ensemble molecular dynamics simulation study
Authors: Lyubartsev A. P. , Fo/rrisdahl O. K. , Laaksonen A.
Published: July 2002

Solvation free energy for methane, dissolved both in pure water, water/methane mixture (14 mol % methane) and in aqueous NaCl solution, is calculated using the expanded ensemble molecular dynamics method. Dependencies due to system size and potential model are investigated. Results, using a simple one-site methane model, together with large enough system size, are found in very good agreement with experimental data, while calculations using a flexible five-site methane model give too high free energies. Also, the solvation energy for 20 different ion pairs of alkali halides is calculated in a systematic study. Very good overall agreement is found for the solvation energies of all the ion pairs. Calculations of solvation free energies provide a sensitive test of the used potential models.
Spin uncoupling in surface chemisorption of unsaturated hydrocarbons
Authors: Triguero Luciano , Pettersson Lars G. M. , Minaev Boris , Ågren Hans
Published: July 2002

Unsaturated hydrocarbons, such as acetylene and ethylene, show strong geometrical distortions when coordinated to transition metals or to surfaces; the bonding is normally analysed in terms of a π-donation—π*-backdonation process. In the present work we use chemisorption of the unsaturated hydrocarbons (ethylene, acetylene, and benzene) on cluster models of the copper (100), (110), and (111) surfaces to demonstrate the importance of considering the available excited states of the free molecule in analyzing the bonding scheme of the adsorbate at the surface. By comparison to the structures of the triplet excited states in the gas phase we demonstrate that these must be considered as the states actually involved in the bonding. This implies a spin-uncoupling in both adsorbate and substrate as part of the chemisorption process or bond formation. In particular, for benzene we identify the quinoid gas phase triplet state as the specific state that is most strongly bound to the Cu(110) substrate; the structure is an inverted boat form. The gas phase antiquinoid triplet state leads to a planar, less strongly bound, chemisorbed state. By explicitly considering the excited state of the adsorbate that corresponds to the bonding state—the ground state for the chemisorbed system—barriers in the chemisorption path are analyzed in terms of avoided crossings between the initial closed-shell singlet state and the bond-prepared excited triplet state, which, together with the substrate, forms an overall singlet. It is argued that this picture with bond-preparation through spin-uncoupling can be very useful to understand and predict reaction paths in heterogeneous catalysis.
Local interactions and protein folding: A model study on the square and triangular lattices
Authors: Irbäck Anders , Sandelin Erik
Published: July 2002

We study a simple heteropolymer model containing sequence-independent local interactions on both square and triangular lattices. Sticking to a two-letter code, we investigate the model for varying strength κ of the local interactions; κ=0 corresponds to the well-known HP model [K. F. Lau and K. A. Dill, Macromolecules 22, 3986 (1989)]. By exhaustive enumerations for short chains, we obtain all structures which act as a unique and pronounced energy minimum for at least one sequence. We find that the number of such designable structures depends strongly on κ. Also, we find that the number of designable structures can differ widely for the two lattices at a given κ. This is the case, for example, at κ=0, which implies that the HP model exhibits different behavior on the two lattices. Our findings clearly show that sequence-independent local properties of the chains can play an important role in the formation of unique minimum energy structures.
Is F3+ viable? A high-level ab initio comparison of F3+ and Cl3+
Authors: Valeev Edward F. , Botee Hozefa M. , Schaefer Henry F.
Published: July 2002

High-level coupled-cluster computations of the two lightest trihalogen cations (F3+ and Cl3+) predict the ground electronic state to be X̃ 1A1. As expected, the trifluorine cation is even less stable than the trichlorine cation, which has been detected and studied experimentally. The Brueckner-reference coupled-cluster doubles and perturbatively connected triples method with a basis set of beyond triple-ζ quality predicts the classical X̃ 1A1 F3+→2P F+2Π F2+ dissociation energy to be 15 kcal/mol. We expect that more complete basis sets and higher levels of theoretical treatment will not qualitatively change this dissociation barrier, and thus the trifluorine cation should be a viable species. The lowest linear triplet states of both F3+ and Cl3+ at the correlated levels of theory are bound by only 2–3 kcal/mol. The electronic wave function for the X̃ 1A1 state of F3+ exhibits substantial multireference character and, similar to X̃ 1A1 O3, proves to be a difficult case for single-reference ab initio methods based on a spin-restricted Hartree–Fock (RHF) determinant. More specifically, RHF-based coupled-cluster singles and doubles method and its extension with connected triple excitations predict different orderings of the X̃ 1A1 F3+ stretching frequencies (ω1 and ω3). Reliable predictions for the harmonic vibrational frequencies of this system are obtained through the use of two Brueckner-reference coupled-cluster methods and a large basis set of beyond triple-ζ quality [our best predictions are ω1(A1)=825 cm−1, ω2(A1)=376 cm−1, ω3(B2) =752 cm−1]. Comparison with the previous ab initio analyses of F3+ stresses the need for a very high level of treatment of dynamic electron correlation to obtain chemically accurate results. The issue of inversion symmetry breaking in a possible dissociation product of the trifluorine molecular cation, F2+, is also addressed and it is shown that a “symmetry dilemma” in the region near the equilibrium F–F distance (∼1.3 Å) can be resolved through the use of coupled-cluster methods based on a Brueckner-reference determinant, which has a reference instability shifted away from its position in spin-restricted open-shell and spin-unrestricted Hartree–Fock determinants.
Vibrational and electronic second hyperpolarizabilities of all-trans polysilane chains
Authors: Perpète Eric A. , André Jean-Marie , Champagne Benoı̂t
Published: July 2002

The vibrational (γLv) and electronic (γLe) longitudinal second hyperpolarizabilities of increasingly large polysilane chains are determined at the Hartree–Fock 6-31G level by adopting both the double harmonic oscillator approximation and the infinite optical frequency finite field relaxation procedure. The relative importance of the electronic, Raman, infrared/hyperRaman and lowest-order anharmonicity contributions to the second hyperpolarizability is evaluated for the most common nonlinear optical (NLO) processes. At the double harmonic oscillator level of approximation the most contributing vibrational normal modes to γLv are characterized as a function of the polysilane chain length. Comparisons with experimental and other theoretical studies are carried out in what concerns the infrared and Raman vibrational spectra as well as the NLO properties of various oligosilanes and polysilanes.
Non-Cartesian coordinates for instantaneous normal mode theory of atomic liquids
Authors: Li Wu-Xiong , Keyes T. , Murry Robert L. , Fourkas John T.
Published: July 2002

A hybrid coordinate system of spherical polar coordinates for the mutual nearest-neighbor pairs and Cartesian coordinates for the unpaired atoms is introduced for instantaneous normal mode (INM) analysis of atomic liquids. Densities of states (dos) calculated with the hybrid coordinates in a unit-density, supercooled Lennard-Jones liquid differ from those obtained with Cartesian coordinates, primarily at imaginary frequency. A brief discussion of coordinate dependence is presented, with an analytic treatment of the frequency moments, and it is argued that the hybrid dos are more physically meaningful. INM theory strives to relate Im ω modes to diffusion and barrier crossing, but spurious nondiffusive contributions must be removed. Hybrid coordinates yield substantially fewer Im ω indicating that some nondiffusive modes are simply Cartesian artifacts. Normalized hybrid and Cartesian Re ω dos are nearly identical, as are velocity correlation functions C(t) obtained by treating the Re ω INM as a complete set of harmonic modes. These C(t) are in fair agreement with simulation, but, notably, reach an insufficiently deep negative minimum value at too short a time. A harmonic approximation using the hybrid-translational Re ω dos, in which the hybrid modes are projected onto the center-of-mass translations of the mutual neighbor pairs plus the unpaired atoms, yields much better agreement.
Phase-sensitive observables as a route to understanding molecular continua
Authors: Seideman Tamar
Published: July 2002

We consider the origin and implications of the phase lag, an observable in two-pathway excitation schemes whose recent measurement raised both interest and controversy. A closed-form expression is derived which illustrates the various sources of a nonvanishing phase lag, distinguishes their roles and exposes their unifying feature. Several formally interesting and experimentally relevant limits of the general form are considered and the potential application of phase-sensitive measurements as a route to understanding molecular coupling mechanisms is illustrated.
Examination of the structural properties of the H3O+(H2O)n clusters in the (μPT) Grand Canonical ensemble, by employing a new many-body potential-energy function
Authors: Shevkunov Sergey V. , Vegiri Alice
Published: July 2002

In the current work we examine the structural properties of water clusters that result from the hydration of a rigid H3O+ ion, under thermal conditions at T=250 K and for four different vapor pressures at 0.0156, 0.0625, 0.25, and 1 mbar. For this purpose we have constructed a model potential function that accounts explicitly not only for the three-body but for all orders of many-body interactions between the ion and the water molecules and for charge transfer effects as well. The adjustable parameters of the potential have been derived within ∼0.1kBT accuracy through a concurrent fit to experimental enthalpy and entropy values from the corresponding cluster growth reactions. Many-body interactions have been found to comprise ∼10% the three-body interactions, a fact that can not be ignored. The calculations have been carried out in the Grand Canonical ensemble (μPT) where cluster sizes with a mean number of 6.69, 9.67, 29.17, and 44.37 water molecules for the four respective vapor pressures, have been generated. We have found a steady population transfer from the contact to the ion region to the second hydration shell as the vapor pressure increases. Typical equilibrium molecular configurations consist predominantly of pentagonal and hexagonal rings, that at p=1 mbar completely encircle the ion, forming in this way pronounced spherical cages. Radial distribution functions, polarization, and cluster density profiles have also been calculated.
The CO product of the reaction of O(3P) with CH3 radicals
Authors: Min Zhiyuan , Quandt Robert W. , Wong Teh-Hwa , Bersohn Richard
Published: July 2002

The reaction of O(3P) atoms with CH3 radicals is shown to produce CO (in addition to the major product CH2O) which is detected by laser induced fluorescence. The rotational and vibrational temperatures of the CO product are about 2000 K. The results are explained by the assumption that the reaction takes place mainly by an indirect mechanism in which a methoxyl radical is formed and then dissociates unimolecularly.
Comment on “Molecular simulation and continuum mechanics study of simple fluids in nonisothermal planar Couette flows” [J. Chem. Phys. 107, 2589 (1997)]
Authors: Todd B. D. , Evans Denis J. , Travis Karl P. , Daivis Peter J.
Published: July 2002

We comment on the paper by Khare et al. [J. Chem. Phys. 107, 2589 (1997)], which considers simulations of confined fluids under planar shear with and without the application of a thermostat. We suggest an alternative interpretation of some of their results, which leads to the same conclusion that applying a thermostat directly to a confined shearing fluid is not the preferred simulation procedure to follow.
A fast ab initio model for the calculation of excited electronic states of atoms and molecules in a weakly polarizable environment. II. Application to the spectrum of cesium in liquid helium
Authors: Kunz Christian F. , Hess Bernd A.
Published: July 2002

We report the first application of a recently developed ab initio scheme for the calculation of electronic spectra of atoms and molecules in an environment of discrete, unpolarizable particles acting as a solvent. We simulate the P2←S2 excitation spectrum of atomic cesium in a solution of liquid helium and compare the results with experimental data taken from the literature.
Microscopic density fluctuations and solvation in polymeric fluids
Authors: Garde Shekhar , Khare Rajesh , Hummer Gerhard
Published: July 2002

The information theory approach is used to study molecular-scale density fluctuations and solvation of hard-core molecules in a condensed polymeric system, supported by extensive computer simulations. In contrast to simple liquids, it is found that the bond connectivity in polymers leads to non-Gaussian density fluctuations in molecular volumes. We define “renormalized” polymers with a reduced number of monomers of increased effective size. This reduces correlations between monomers and simplifies the effective density fluctuations. Chemical potentials of hard-core solutes in polyethylene can then be calculated accurately using information theory.
Interaction second virial coefficients from a recent H2–CO potential energy surface
Authors: Gottfried J. , McBane George C.
Published: July 2002

Interaction second virial coefficients for mixtures of hydrogen and CO are computed from a recent rigid rotor potential energy surface [J. Chem. Phys. 108, 3554 (1998)]. The calculations include the most important quantum corrections. A comparison with experimental data indicates that the attractive well of the ab initio surface is too deep by 4%–9%.
Many-body Green’s-function calculations on the electronic excited states of extended systems
Authors: Hirata So , Bartlett Rodney J.
Published: July 2002

Electron correlation corrections to the excitation energy of the lowest-lying singlet exciton state of polyethylene are evaluated with the aid of the quasiparticle energies obtained from second-order many-body perturbation theory and from the second-order inverse Dyson equation. A simple approximation is proposed to avoid the evaluation of the quasiparticle energies for high- and low-lying energy bands, which is particularly problematic in extended-system calculations. The inclusion of both the electron correlation effects and diffuse basis functions is important for the proper description of the exciton state. The electron correlation corrections calculated by this method appear to be too large, probably due to the neglect of the screening effects of the quasiparticle interactions.
Gauge theory of a group of diffeomorphisms. I. General principles
Authors: Lord Eric A. , Goswami P.
Published: July 2002

Any (N+M)-parameter Lie group G with an N-parameter subgroup H can be realized as a global group of diffeomorphisms on an M-dimensional base space B, with representations in terms of transformation laws of fields on B belonging to linear representations of H. The gauged generalization of the global diffeomorphisms consists of general diffeomorphisms (or coordinate transformations) on a base space together with a local action of H on the fields. The particular applications of the scheme to space-time symmetries is discussed in terms of Lagrangians, field equations, currents, and source identities.
Spectra of supersymmetric O(N) sigma models in 0+1 dimension
Authors: Sathiapalan B.
Published: July 2002

The spectra of the supersymmetric O(N) nonlinear sigma models in 0+1 space-time dimension are computed exactly for any N, using group theoretical methods. The allowed representations are O(N) analogs of the Wigner d functions.
Linearization and Painlevé property of Liouville and Cheng equations
Authors: Tamizhmani K. M. , Lakshmanan M.
Published: July 2002

It is demonstrated that the Liouville equation and the Cheng equation (describing a chemical reaction) are free from movable critical manifolds and possess the Painlevé property. The associated linearizing transformations and general solutions follow naturally from the Painlevé analysis.
An exactly soluble relativistic quantum two-fermion problem
Authors: Barut A. O. , Ünal N.
Published: July 2002

The two-fermion problem of quantum electrodynamics in which both particles are treated relativistically and full spin degrees of freedom are taken into account is shown to be exactly soluble when potentials up to order α4 are kept. It is therefore a good starting point for radiative corrections of higher order for the precision tests of QED in bound-state problems. Recoil corrections are included to all orders.
Representations of E8 and other algebras
Authors: Capps Richard H.
Published: July 2002

A simple procedure is given for determining whether or not an arbitrary weight of a simple Lie algebra is contained in an arbitrary irreducible representation. The procedure involves two steps, determining the Weyl class of the weight and determining the classes contained in the representation. The second step applies without alteration to all simple algebras, while the first step is given here only for E8. The weights of the shortest 31 Weyl classes of E8 are listed in a convenient, orthogonal basis.
Decomposition of the SO*(8) enveloping algebra under U(4)⊇U(3)
Authors: Le Blanc R. , Rowe D. J.
Published: July 2002

The existence of a complete set of SU(3) tensor operators in the enveloping algebra of SO*(8) is demonstrated. The analysis recasts a parallel analysis by Biedenharn and Flath [Commun. Math. Phys. 93, 143 (1984)] concerning an SO(6,2) model for SU(3) in the isomorphic but simpler framework of an SO*(8) model.
Existence and observability of spinor structure
Authors: Magnon Anne M. R.
Published: July 2002

A mechanism by which space-time topological modifications could have been controlled, in the early universe or at the Planck length, to enable onset of spinor structure is investigated. This mechanism (based on a reshuffling of topological charges and related modification of characteristic classes) could provide a gravitational analog of the Aharonov–Susskind Gedankenexperiment proposed to detect relative rotation in the universe, spinor behavior, or to keep track of the two homotopy classes of the Lorentz Lie group. The space-time topology [and in particular the trivial (nontrivial) bundle structure at conformal null infinity] provide a labeling of the asymptotic Lorentz homotopy classes which originates in the first Chern class (enclosed magnetic mass) or in the parametrization of the second homology group, and gives rise to a necessary (and sufficient) condition for the existence of spinor structure. This underlines the intertwined roles of topology and curvature. The mechanism could also be viewed as an ‘‘unwinding’’ of gravitational magnetic monopoles with one asymptotic region into electric mass (black-hole) solutions with two asymptotic regions. In such situations a discrete PT symmetry could emerge from a continous transformation. Possible implications on the CPT theorem are mentioned.
Comment on the paper ‘‘Theta series and magic numbers for diamond and certain ionic crystal structures’’ [J. Math. Phys. 2
8, 1653 (1987)]
Authors: Hall George L.
Published: July 2002

Sloane’s work [J. Math. Phys. 28, 1653 (1987)] is supplemented by published theorems that have been applied to the NaCl, CsCl, ZnS, and CaF2 structures to give formulas for the radii of all occupied shells (i.e., all radii for which Sn=0 are identified) and to give the species of atoms in each shell. In this paper the sort of information these theorems can provide is briefly reviewed and some predictions based on them are checked with the tabulated results of Sloane and others.
SU(2) classification of N=2 complex supersymmetric representations
Authors: Saidi E. H.
Published: July 2002

The N=2 extended complex supersymmetry representations are constructed. The classification of N=2 multiplets in SU(2) representations is obtained. The relation with N=2 harmonic superspace is also discussed.
The quadratic-Hamiltonian theorem in infinite dimensions
Authors: Schmid Rudolf
Published: July 2002

It is shown that a smooth diffeomorphism on a symplectic Banach space is canonical if it is canonoid with respect to all dynamical systems whose Hamiltonian functions are quadratic.
A 29-root soluble model for the nonlinear calculation of a four-body propagator
Authors: Giraud B. G. , Kessal S. , Weiguny A.
Published: July 2002

The time-independent mean-field theory of collisions is applied to the collision of four one-dimensional particles. Their two-body interactions are taken as separable, with Lorentzian form factors. This allows completely analytical solutions. A unique and satisfactory physical branch emerges out of 29 candidate solutions. It is very stable when the strength of the interaction is modified.
A novel class of G function integrals
Authors: Wille L. T.
Published: July 2002

A number of Euler integrals involving Meijer’s G function with arguments [α2(1−x)−1+β2x−1]−1, λx(1−x), and [α2x+β2(1−x)]2/[x(1−x)] are evaluated in closed form. These results generalize and extend recent work on Bessel-function integrals. As a by-product some new closed form expressions for Meijer’s G function are obtained.
Grassmannian σ models and strings
Authors: Arik M. , Neyzi F.
Published: July 2002

The relation between the Nambu–Goto string in D dimensions and the two-dimensional σ model defined on the Grassmannian manifold SO(D−1,1)/SO(D−2)×SO(1,1) is investigated. For D=3 and D=4 the Nambu–Goto string is identified with a definite sector of the Grassmannian σ model. For D=3 the remaining sector is again a string model with an additional term in the Nambu–Goto action.
Some new stationary axisymmetric asymptotically flat space-times obtained from Painlevé transcendents
Authors: Persides Sotirios , Xanthopoulos Basilis C.
Published: July 2002

For the stationary axisymmetric Einstein vacuum equations in cylindrical coordinates we find that both the Ernst equation and the two real equations which alternatively describe the stationary axisymmetric problem separate, leading to Painlevé transcendents. The boundary and asymptotic behaviors of the resulting space-times are investigated in both cases. Two families of solutions are determined which, away from the symmetry axis, become asymptotically flat. The analysis provides an example to the conjecture that the Painlevé property implies integrability.
The vacuum Einstein equations as closed ideals of matrix-valued differential forms
Authors: Bonanos S.
Published: July 2002

The vacuum Einstein equations are written as a closed differential ideal of three-dimensional matrices of differential forms, allowing the Weyl tensor to appear explicitly in the equations. Possible uses of this formulation are indicated.
Spatial structure of anomalously localized states in disordered conductors
Authors: Mirlin Alexander D.
Published: July 2002

The spatial structure of wave functions of anomalously localized states (ALS) in disordered conductors is studied in the framework of the σ–model approach. These states are responsible for slowly decaying tails of various distribution functions. In the quasi-one-dimensional case, properties of ALS governing the asymptotic form of the distribution of eigenfunction amplitudes are investigated with the use of the transfer matrix method, which yields an exact solution to the problem. Comparison of the results with those obtained in the saddle-point approximation to the problem shows that the saddle-point configuration correctly describes the smoothed intensity of an ALS. On this basis, the properties of ALS in higher spatial dimensions are considered. We also study the ALS responsible for the asymptotic behavior of distribution functions of other quantities, such as relaxation time, local and global density of state. It is found that the structure of an ALS may be different, depending on the specific quantity, for which it constitutes an optimal fluctuation. Relations between various procedures of selection of ALS, and between asymptotics of corresponding distribution functions, are discussed.
Schrödinger operators with Rudin-Shapiro potentials are not palindromic
Authors: Allouche J.-P.
Published: July 2002

We prove a conjecture of A. Hof, O. Knill and B. Simon [Commun. Math. Phys. 174, 149–159 (1995)] by showing that the Rudin-Shapiro sequence is not palindromic, i.e., does not contain arbitrarily long palindromes. We prove actually this property for all paperfolding sequences and all Rudin-Shapiro sequences deduced from paperfolding sequences. As a consequence and as guessed by the above authors, their method cannot be used for establishing that discrete Schrödinger operators with Rudin-Shapiro potentials have a purely singular continuous spectrum.
Density matrices for itinerant and localized electrons with and without external fields
Authors: March N. H.
Published: July 2002

Forms of canonical (Bloch) and Dirac density matrices for free electrons with and without external applied fields are first considered. The basic tool employed is the Bloch equation with a one-electron Hamiltonian. Such an approach is used to obtain a perturbation theory to all orders for the idempotent Dirac density matrix when a common potential energy V(r) is switched on to originally free electrons. The relation to density functional theory is then considered and the exchange–correlation contribution Vxc(r) to V(r) is expressed in terms of first- and second-order density matrices following Holas and March. These latter density matrices are now for the fully interacting system and, in particular, the first-order density matrix is no longer idempotent, though it must still satisfy generalized Pauli Principle conditions. Reference is also made to a localized Wigner electron in a strong magnetic field.
Bounded Bose fields in 1+1 dimensions commuting for space- and timelike distances
Authors: Baumann Klaus
Published: July 2002

We consider scalar Bose fields Φ in 1+1 dimensions which are bounded [i.e., Φ(F) is a bounded operator], commute for space- and timelike distances, and are dilation covariant with scaling dimension d=1,3,5,… . We show that their truncated n-point-functions WnT are related to the truncated functions VnT of φ(x)=ψd/2(x+)⊗ψd/2(x−) via WnT=cnVnT with cn>0. ψd/2(x±) is a free chiral real Fermi field of dimension d/2 depending on the light cone coordinates x±=t±x. This comes close to the conjecture that under the above assumptions Φ is nothing but a weighted s-product of φ=ψd/2⊗ψd/2.
Generalization of the Birman–Schwinger method for the number of bound states
Authors: Chadan Khosrow , Kobayashi Reido , Lassaut Monique
Published: July 2002

We generalize the Birman–Schwinger method, and derive a general upper bound on the number of bound states in the S wave for a spherically symmetric potential. This general bound includes, of course, the Bargmann bound, but also leads, for increasing (negative) potentials, to a Calogero–Cohn-type bound. Finally, we show that for a large class among these potentials, one can obtain further improvements.
Poisson brackets of normal-ordered Wilson loops
Authors: Lee C.-W. H. , Rajeev S. G.
Published: July 2002

We formulate Yang–Mills theory in terms of the large-N limit, viewed as a classical limit, of gauge-invariant dynamical variables, which are closely related to Wilson loops, via deformation quantization. We obtain a Poisson algebra of these dynamical variables corresponding to normal-ordered quantum (at a finite value of ℏ) operators. Comparing with a Poisson algebra one of us introduced in the past for Weyl-ordered quantum operators, we find, using ideas closely related to topological graph theory, that these two Poisson algebras are, roughly speaking, the same. More precisely speaking, there exists an invertible Poisson morphism between them.
The effect of polymer additives on laminar separation
Authors: Kim B. K. , Telionis D. P.
Published: July 2002

Tests were conducted with dilute polymer solutions in a water tunnel. Subcritical flows over a circular cylinder were tested. The effects of free-stream turbulence and polymer additives on the development of laminar boundary layers and separation were examined.
The baroeffect and an appropriate momentum boundary condition
Authors: Noever David A.
Published: July 2002

As disparate molecular weight gases isothermally diffuse between two ends of a capillary tube, they can support a pressure gradient. The magnitude of this pressure gradient depends critically on viscous wall stress and becomes a measure of the boundary condition. This baroeffect has been used to test the state of a gas surface layer. Specifically, it allows one to quantify whether a binary gas has a finite wall velocity (diffusive slip). Here, a one-dimensional analytical model is proposed that allows for specular gas reflection from the wall. It explains anomalous (4/3) correction factors required previously to match experiment to baroeffect models. It predicts a new physical phenomenon, a surface-driven baroeffect for equal molecular weight gases. Diffusive slip contributions exceed the order of convective diffusion for Peclet number Pe<1 and approximately equal convective diffusion for 1<Pe<4. For binary gases, this model further extends the baroeffect experiment as a means to find momentum accommodation coefficients (MAC), slip lengths, and external friction coefficients. A corrected binary diffusion coefficient is defined. Analogous arguments can be made to explain corrections to thermal and viscous slip.
Weak shock structure on the basis of modified hydrodynamical equations
Authors: Khonkin A. D. , Orlov A. V.
Published: July 2002

The structure of a normal shock wave is calculated on the basis of the hydrodynamics of fast processes [A. D. Khonkin, Fluid Mech. Sov. Res. 9, 93 (1980)] to investigate the validity of the theory for this classical problem. The analysis shows that the theory predicts the continuous shock profile to exist only for M≤1.27. The shock thicknesses and the asymmetry factors resulting from the Mott-Smith method, the Navier–Stokes and the Burnett equations, and also from the experiments and simulations are compared to the present results for a gas of Maxwell molecules.
The effect of charge exchange on plasma flows
Authors: Valanju P. M. , Calvin M. D. , Hazeltine R. D. , Solano E. R.
Published: July 2002

A simple drift-kinetic derivation of the expressions for the poloidal ion and impurity flows in the presence of charge-exchange drag and ion-impurity collisions is presented.
Investigations of attractors arising from the interaction of drift waves and potential relaxation instabilities
Authors: Klinger T. , Piel A.
Published: July 2002

The nonlinear interaction between ion-drift waves and electrostatic potential relaxation instabilities (PRI) is studied in a magnetized double plasma with externally induced axial electron drift. The PRI is identified as unstable weak double layer which is determined by additional electron beam injection. The axial drift current Id is used as control parameter for the dynamical state of the plasma and shows a critical transition to anomalous resistivity. For various drift current values, time series of probe signal fluctuations have been recorded. The wave number and bispectral analysis is used to establish the interaction as nonresonant modulation of drift waves by PRI’s. The complexity of strongly nonlinear and fully turbulent regimes is investigated by statistical analysis of the reconstructed phase space. The nonlinear interaction is characterized by low correlation dimension values between 3≤D2≤5 and positive largest Lyapunov exponents. The results confirm earlier findings, which were obtained in a different device.
A model for the conversion of ion-beam energy into thermal radiation
Authors: Basko M. M.
Published: July 2002

A model is proposed for calculating the efficiency of conversion of the energy of charged-particle beams into thermal radiation. The model is based on a simplified system of radiation hydrodynamics equations and applies to optically thick converters with high conversion efficiencies ηc≥0.5. In the case of planar geometry, a self-similar solution of the model equations is obtained. This solution is used to derive a scaling law for the beam parameters required for efficient performance of planar radiative converters. A comparison of converter materials with different Z reveals that preference should be given to low-Z elements.
Nonlocal analysis of finite-beam-driven instabilities
Authors: Serizawa Y. , Dum C. T.
Published: July 2002

Electrostatic waves in an electron–beam–plasma system are studied in the low-temperature-beam regime and the warm-beam regime. The field-aligned electron beam is assumed to have a Gaussian density profile. The fully kinetic integral eigenmode equation in wave-number space is used to describe the nonlocal behavior of these waves. The case of strongly magnetized electrons and unmagnetized ions, which corresponds to the waves in a frequency range from the lower-hybrid to the electron plasma frequency, is examined in detail. Three groups of wave modes are found. The first group consists of modes that have dispersive properties similar to the uniform, infinite beam–plasma system. Depending on the beam width, the growth rates are, however, strongly reduced. The modes are localized, with the maximum amplitudes at the center of the beam. The behavior of the wave modes is interpreted as an emission of perturbations from the unstable region toward the surrounding medium which is stable to these perturbations. The second group, surface modes, are localized at the periphery of the beam region and are less unstable than the unstable modes of the first group. The third group represents natural oscillations of the background plasma. These modes are nearly unaffected by the beam. Their frequencies are very close to those expected in the uniform thermal plasma and all the modes are damped. The main effect of the beam appears as an exclusion of the modes from the beam region.
A numerical study of vortex merging in mixing layers
Authors: Davis R. W. , Moore E. F.
Published: July 2002

Numerical solutions are presented for forced spatially developing axisymmetric and two-dimensional mixing layers. The numerical scheme employs quadratic upwind differencing for convection and a Leith type of temporal differencing in order to solve the incompressible Navier–Stokes and continuity equations. The applied forcing function is derived from linear inviscid stability theory. The resulting large-scale vortex dynamics is visualized by means of streakline and isovorticity contour plots. It is seen that the vortex merging behavior in both types of mixing layers is determined by the subharmonics present in the forcing function. Manipulation of the vortex dynamics in a predictable fashion is possible through alterations in the frequency content of this applied forcing. Reynolds number is shown to be of only minor importance.