bluuebunny/crossref_metadata_2025 huggingface dataset:
Dissociative electron attachment in cyclopentanone, γ-butyrolactone, ethylene carbonate, and ethylene carbonate-d4: Role of dipole-bound resonances
Authors: Stepanović Momir , Pariat Yvan , Allan Michael
Published: July 2002

The title compounds allow the study of the effect of the dipole moment and the energy of the lowest shape resonance on dissociative electron attachment, since both the dipole moments (2.9, 4.5, and 5.3 Debye) and the π* attachment energies (1.15, 1.98, and 2.94 eV) increase progressively along the series. An unexpected observation was made in ethylene carbonate, the molecule with the largest dipole moment, where two fragments (CO3− and C2H3O−) are formed at low energies (1–1.5 eV), well below the first π* attachment energy. We assign these bands to dissociation of a vibrationally excited dipole bound anion formed upon electron attachment. Furthermore, the number of fragments at low energies (below 5 eV) was generally found to increase with the number of oxygen atoms in the molecules, presumably because of the larger number of possible fragments with large electron affinity. Finally, “scrambling” of atoms was found in the fragmentation of ethylene carbonate even at low energies, indicating that the initially formed autodetaching anion rapidly stabilizes by sliding to sections of the potential surface where autodetachment is slow or not possible, allowing more time for chemical rearrangement. Even more “scrambling” and more fragments are found at higher energies, 6–9 eV, for all three compounds, where dissociative attachment is assigned to doubly excited Feshbach resonances.
Vector parametrization of the N-atom problem in quantum mechanics. III. Separation into two subsystems: Application to NH3
Authors: Gatti Fabien
Published: July 2002

In this work, the vectorial formalism previously developed [Gatti et al., J. Chem. Phys. 108, 8804 (1998); 108, 8821 (1998)] is extended to radial coordinates and to the general study of dimers. This method is general and avoids the direct use of differential calculus in the derivation of the kinetic operator. Moreover, to study the spectrum of NH3, an exact and simple kinetic energy operator is proposed. The new system of coordinates (a combination of Jacobi and hyperspherical coordinates) fully displays the permutation symmetry of the three hydrogen atoms. It is adapted to study the umbrella motion and furthermore minimizes the Coriolis terms.
Gaussian-3 theory using scaled energies
Authors: Curtiss Larry A. , Raghavachari Krishnan , Redfern Paul C. , Pople John A.
Published: July 2002

A modification of Guassian-3 (G3) theory using multiplicative scale factors, instead of the additive higher level correction, is presented. In this method, referred to as G3S, the correlation energy is scaled by five parameters and the Hartree–Fock energy by one parameter. The six parameters are fitted to the G2/97 test set of 299 energies and the resulting mean absolute deviation from experiment is 0.99 kcal/mol compared to 1.01 kcal/mol for G3 theory. The G3S method has the advantage compared to G3 theory in that it can be used for studying potential energy surfaces where the products and reactants have a different number of paired electrons. In addition, versions of the computationally less intensive G3(MP3) and G3(MP2) methods that use scaled energies are also presented. These methods, referred to as G3S(MP3) and G3S(MP2), have mean absolute deviations of 1.16 and 1.35 kcal/mol, respectively.
The vibrational distribution of O2(X 3Σg−) produced in the photodissociation of ozone between 226 and 240 and at 266 nm
Authors: Geiser Joseph D. , Dylewski Scott M. , Mueller Julie A. , Wilson Ruth J. , Toumi Ralf , Houston Paul L.
Published: July 2002

Resonance-enhanced multiphoton ionization coupled with time-of-flight product imaging has been used to study the O3(X 1A1)+hν→O(2p 3PJ)+O2(X 3Σg−) product channel in the UV (ultraviolet) photodissociation of ozone at photolysis wavelengths of 226, 230, 233, 234, 240, and 266 nm. These imaging experiments, together with a measurement of the branching ratio into the different spin orbit states of the O atom, allowed the determination of the yields of the O2 product in vibrational states greater than or equal to 26 as a function of wavelength. It was found that at 226, 230, 233, 234, and 240 nm, the yield was 11.8±1.9%, 11.5±1.2%, 8.2±2.0%, 4.7±1.8%, and 0.6±0.1%, respectively.
The phase behavior of a hard sphere chain model of a binary n-alkane mixture
Authors: Malanoski A. P. , Monson P. A.
Published: July 2002

Monte Carlo computer simulations have been used to study the solid and fluid phase properties as well as phase equilibrium in a flexible, united atom, hard sphere chain model of n-heptane/n-octane mixtures. We describe a methodology for calculating the chemical potentials for the components in the mixture based on a technique used previously for atomic mixtures. The mixture was found to conform accurately to ideal solution behavior in the fluid phase. However, much greater nonidealities were seen in the solid phase. Phase equilibrium calculations indicate a phase diagram with solid–fluid phase equilibrium and a eutectic point. The components are only miscible in the solid phase for dilute solutions of the shorter chains in the longer chains.
Demonstration of quantum logic gates in liquid crystal nuclear magnetic resonance
Authors: Marjanska Malgorzata , Chuang Isaac L. , Kubinec Mark G.
Published: July 2002

H– 13 1 C heteronuclear dipolar couplings are used to produce the NMR (nuclear magnetic resonance) version of a two bit controlled-NOT quantum logic gate. This gate is coupled with the Hadamard gate to complete a circuit which generates the Einstein–Podolsky–Rosen (EPR) state which is the maximally entangled state of a pair of spins. The EPR state is crucial for the potential exponential speed advantage of quantum computers over their classical counterparts. We sample the deviation density matrix of the two spin system to verify the presence of the EPR state. EPR state lifetimes are also measured with this technique, thereby demonstrating the viability of liquid crystals as a platform for quantum computing.
Femtosecond energy- and angle-resolved photoelectron spectroscopy
Authors: Arasaki Yasuki , Takatsuka Kazuo , Wang Kwanghsi , McKoy Vincent
Published: July 2002

We present a formulation of energy- and angle-resolved photoelectron spectra for femtosecond pump–probe ionization of wave packets and results of its application to the Σu+1 double-minimum state of aligned Na2. The formulation is well-suited for inclusion of the underlying dynamics of molecular photoionization and its dependence on molecular geometry. Results are presented for three typical pump laser energies selected so as to investigate qualitatively different patterns of the spatio-temporal propagation of wave packets on the double-minimum potential curve and of their associated photoelectron spectra. Photoelectron angular distributions are also reported for different orientations of linearly polarized pump and probe pulses. The resulting photoelectron spectra illustrate the importance of a proper description of the underlying photoionization amplitudes and their dependence on geometry for unraveling wave packet dynamics from pump–probe photoelectron signals in nonadiabatic regions where the electronic structure evolves rapidly with geometry. The dependence of these photoelectron angular distributions on relative orientation of the molecule and polarization of the probe pulse are also seen to be potentially useful for real-time monitoring of molecular rotation.
Shear effects on phase separating polymer solutions: A molecular dynamics study
Authors: Liu Hong , Chakrabarti Amitabha
Published: July 2002

We study phase separation of quenched polymer solutions under an external shear flow by using a stochastic molecular dynamics method. We observe the formation of a stringlike pattern of polymer domains normal to the direction of the shear flow. The characteristic size of the layered domains has a power law relation with the shear rate. Shear-induced rheological behavior of the mixture is also examined in terms of the excess viscosity. We find that the maximum excess viscosity scales as the shear rate, and that the numerical value of the power-law exponent agrees well with theoretical scaling predictions.
Folding path in a semiflexible homopolymer chain: A Brownian dynamics simulation
Authors: Noguchi Hiroshi , Yoshikawa Kenichi
Published: July 2002

We studied the kinetics of the folding transition of a semiflexible homopolymer chain, such as DNA, using a Brownian dynamics simulation. The folding product of a semiflexible chain exhibits a toroidal morphology. We show that semiflexible chains fold through various paths from coiled states to toroidal states stochastically. Some chains fold directly by winding around a ring along a chain. Others fold through rod states, which are kinetically trapped metastable states. Both in toroids and rods, sliding motions are noticeable. Large toroids are generated as the intermediate conformation first, and then they become smaller through the sliding motion.
Spectral properties of the Dirac equation with anomalous magnetic moment
Authors: Behncke Horst
Published: July 2002

Though the electron possesses an anomalous magnetic moment, this term has so far been treated by perturbation methods only. Here this rather singular term is treated nonperturbatively. For a general and large class of spherical potentials it is shown that the Hamiltonian is essentially self-adjoint. If the potentials vanish at infinity the essential spectrum is R\(−m,m). These results hold for all, also strong, Coulomb-type potentials. We further establish that the eigenvalues for such Hamiltonians are stable and can be computed by a low-order perturbation theory, if l≥3. The above results can also be extended to multicenter potentials.
Reduction of quantum systems on Riemannian manifolds with symmetry and application to molecular mechanics
Authors: Tanimura Shogo , Iwai Toshihiro
Published: July 2002

This paper deals with a general method for the reduction of quantum systems with symmetry. For a Riemannian manifold M admitting a compact Lie group G as an isometry group, the quotient space Q=M/G is not a smooth manifold in general but stratified into a collection of smooth manifolds of various dimensions. If the action of the compact group G is free, M is made into a principal fiber bundle with structure group G. In this case, reduced quantum systems are set up as quantum systems on the associated vector bundles over Q=M/G. This idea of reduction fails, if the action of G on M is not free. However, the Peter–Weyl theorem works well for reducing quantum systems on M. When applied to the space of wave functions on M, the Peter–Weyl theorem provides the decomposition of the space of wave functions into spaces of equivariant functions on M, which are interpreted as Hilbert spaces for reduced quantum systems on Q. The concept of connection on a principal fiber bundle is generalized to be defined well on the stratified manifold M. Then the reduced Laplacian is well defined as a self-adjoint operator with the boundary conditions on singular sets of lower dimensions. Application to quantum molecular mechanics is also discussed in detail. In fact, the reduction of quantum systems studied in this paper stems from molecular mechanics. If one wishes to consider the molecule which is allowed to lie in a line when it is in motion, the reduction method presented in this paper works well.
Non-existence of time-periodic solutions of the Dirac equation in a Reissner-Nordström black hole background
Authors: Finster Felix , Smoller Joel , Yau Shing-Tung
Published: July 2002

It is shown analytically that the Dirac equation has no normalizable, time-periodic solutions in a Reissner–Nordström black hole background; in particular, there are no static solutions of the Dirac equation in such a background metric. The physical interpretation is that Dirac particles can either disappear into the black hole or escape to infinity, but they cannot stay on a periodic orbit around the black hole.
Higher-order corrections to the axisymmetric interactions of nearly touching spheres
Authors: Jeffrey D. J.
Published: July 2002

Two unequal spheres are immersed in an axisymmetric low-Reynolds-number flow and are separated by a small nondimensional distance ε. The forces and stresslets exerted by the spheres on the fluid are calculated asymptotically to O(ε ln ε), in order to improve the convergence of numerical calculations of the same quantities. The main obstacle to the extension to O(ε ln ε) was the breakdown of the usual lubrication approach at higher orders in ε. The method adopted here obtains expressions for the functions of immediate interest, but does so by postponing the resolution of the fundamental difficulties until a higher order in ε.
A note on memory-integral contributions to the force on an accelerating spherical drop at low Reynolds number
Authors: Yang Seung-Man , Leal L. G.
Published: July 2002

The hydrodynamic force on a spherical drop that undergoes a translational acceleration in an unbounded fluid at low Reynolds number is considered. The force involves a memory-integral contribution that is not of the familiar form for a solid sphere. This result, in conjunction with the prior results of Lawrence and Weinbaum [J. Fluid Mech. 171, 208 (1986)] for a nonspherical particle, suggest that the form of the force law for a solid sphere is a very special case that is invalidated if there are any departures in either rigidity or shape from a solid sphere. In this Brief Communication the force on a spherical drop is evaluated for a number of limiting cases, after transforming the result from the Fourier-transform domain in which it is derived to the time domain.
The force on a bubble, drop, or particle in arbitrary time-dependent motion at small Reynolds number
Authors: Lovalenti Phillip M. , Brady John F.
Published: July 2002

The hydrodynamic force on a body that undergoes translational acceleration in an unbounded fluid at low Reynolds number is considered. The results extend the prior analysis of Lovalenti and Brady [to appear in J. Fluid Mech. (1993)] for rigid particles to drops and bubbles. Similar behavior is shown in that, with the inclusion of convective inertia, the long-time temporal decay of the force (or the approach to steady state) at finite Reynolds number is faster than the t−1/2 predicted by the unsteady Stokes equations.
Lightning channel decay
Authors: Hill R. D.
Published: July 2002

The radius of a lightning channel dissipating 1.5×104 J/m is estimated as approximately 9 cm when its temperature has fallen to 3000 K.
Transverse wake fields due to nonaxisymmetric drive beams in the dielectric wake-field accelerator
Authors: Garate Eusebio
Published: July 2002

The transverse wake fields in a dielectric wake-field accelerator are calculated for the case of an off-axis drive beam. The calculation is done taking into account the transverse dimensions of the wake-field structure including the ratio of inner to outer radii of the dielectric liner S. The results indicate that the m=1 radial transverse wake-field component is much smaller than the m=0 axial wake field for liners with small hole size (S≤0.2). Therefore, beam breakup instabilities can be avoided, even for large drive beam currents, in dielectric wake-field accelerators where S is small.
Effects of current profile on the ideal ballooning mode
Authors: Lao L. L. , Taylor T. S. , Chu M. S. , Chan V. S. , Ferron J. R. , Strait E. J.
Published: July 2002

The effects of current profile on the ideal ballooning mode for circular and shaped poloidal cross-section plasmas in tokamaks are studied analytically and numerically. The results show that for moderately shaped plasmas the critical normalized beta, βNC, against the ballooning mode increases approximately linearly with the plasma internal inductance li. As the plasma becomes more strongly shaped, this dependence on li becomes weaker, and for a divertor plasma βNC shows a very weak dependence on li for the range of moderate li values considered.
Locked modes and magnetic field errors in the Madison Symmetric Torus
Authors: Almagri A. F. , Assadi S. , Prager S. C. , Sarff J. S. , Kerst D. W.
Published: July 2002

In the Madison Symmetric Torus (MST) reversed-field pinch [Fusion Technol. 19, 131 (1991)] magnetic oscillations become stationary (locked) in the lab frame as a result of a process involving interactions between the modes, sawteeth, and field errors. Several helical modes become phase locked to each other to form a rotating localized disturbance, the disturbance locks to an impulsive field error generated at a sawtooth crash, the error fields grow monotonically after locking (perhaps due to an unstable interaction between the modes and field error), and over tens of milliseconds of growth confinement degrades and the discharge eventually terminates. Field error control has been partially successful in eliminating locking.
Simulation study of a magnetohydrodynamic dynamo: Convection in a rotating spherical shell
Authors: Kageyama A. , Watanabe K. , Sato T.
Published: July 2002

Numerical simulations on the thermal convection of a neutral fluid (without a magnetic field) in a rotating spherical shell have been carried out. The results indicate that sufficiently rapid rotation results in strong differential rotation, with a pronounced equatorial acceleration. The formation dynamics of convection columns aligned to the rotation axis is studied extensively. A new generation mechanism of differential rotation is then proposed which concludes that the fluid motion generates an equatorial acceleration by selectively exciting the cyclonic columns in the spherical shell.
Statistical theory of cubic Langmuir turbulence
Authors: Sun Guo-Zheng , Nicholson D. R. , Rose Harvey A.
Published: July 2002

The cubic direct interaction approximation is applied to a truncated (in Fourier space) version of the cubically nonlinear Schrödinger equation model of Langmuir physics. The results are compared (in the three-mode case) to those for an ensemble of numerical solutions of the dynamical equations with 10 000 different sets of Gaussianly distributed initial conditions. In the undriven, undamped case, the statistical theory (but not the ensemble) evolves to a state of thermal equilibrium. In the driven, damped case, the statistical theory appears to evolve to a state close to that corresponding to one of the limit cycles of the dynamical equations.
Filamental quenching of the current-driven ion-cyclotron instability
Authors: Cartier Steven L. , D’Angelo Nicola , Krumm Peter H. , Merlino Robert L.
Published: July 2002

Experimental evidence is presented on the effect of the finite width of the current channel for the excitation of the current-driven ion-cyclotron instability. The results are in agreement with the nonlocal theory of Bakshi, Ganguli, and Palmadesso.
Convective instability of a spherical fluid inclusion
Authors: Yih Chia-Shun
Published: July 2002

When a vertical temperature gradient is applied to a large solid containing a spherical fluid inclusion, the temperature in the fluid is a function only of height. The stability of this fluid against convection is investigated and it is found that the principle of exchange of stabilities applies. The linear differential system governing stability is then solved; the results show that the thermal conductivity of the surrounding solid is always stabilizing and that the most unstable mode is the first asymmetric mode, for which the critical Rayleigh number is given. The energy method can be applied, with due modifications to account for heat conduction in the surrounding solid. The same mathematical governing differential system would then be obtained, giving the same number for the upper bound of the Rayleigh numbers below which the fluid is stable. This number is then truly critical: The fluid is stable or unstable according to whether the Rayleigh number is below or above it, whatever the magnitude of the disturbance. The results are discussed in the context of the movement of the spherical inclusion in a soluble solid. The greater instability of the asymmetric mode indicates that when instability occurs, the fluid inclusion will have a sidewise component, which is greater for a greater supercritical Rayleigh number. The effect of double diffusion is also discussed.
On the nonlinear stability of thermally driven shear flow heated from below
Authors: Kaloni P. N. , Qiao Zongchun
Published: July 2002

The energy method, which gives the sufficient condition for the stability, is developed for the convection problem induced by an applied inclined temperature gradient in a shallow horizontal layer. A nonlinear stability analysis, which is valid for any Prandtl number, is carried out for the case of rigid conducting horizontal boundaries. The eigenvalue problem is solved by compound matrix method and the nonlinear stability results are compared with the results of the linear stability method.
Combined thermocapillary-buoyancy convection in a cavity: An experimental study
Authors: Gillon Pascale , Homsy G. M.
Published: July 2002

Convection in a cavity with a free surface and heated from the side is studied by a combination of flow visualization and particle image velocimetry. In these experiments, buoyancy and thermocapillarity are of comparable importance in driving the convection. The Prandtl number of the working fluid, the cavity aspect ratio, and the ratio of Rayleigh to Marangoni numbers are all held fixed; the primary experimentally varied parameter is the imposed temperature difference, which varied from 0.3 to 20 °C, resulting in a range of Marangoni numbers between 6×103 and 4.2×105. For low Marangoni numbers, the flow is steady and two dimensional, as expected. The global nature of the flow is in good agreement with available numerical simulations of combined thermocapillary-buoyancy driven convection. At higher Marangoni number, Ma>1.5×105, we observe a transition to steady three-dimensional convection. The nature of this transition is typical of an imperfect bifurcation, and the flow structure is investigated both qualitatively and quantitatively. It is concluded that for the parameter values studied the first unstable mode consists of steady three-dimensional, approximately cubical, vortical structures that are periodic along the axis of the cavity. The three-dimensional flows observed by visualizations are in remarkable agreement with the recent numerical computations of Mundrane and Zebib [Phys. Fluids A 5, 810 (1993)].
Measurements of surface-wave damping in a container
Authors: Howell David R. , Buhrow Ben , Heath Ted , McKenna Conor , Hwang Wook , Schatz Michael F.
Published: July 2002

For surface waves in brimful right circular cylinders with clean interfaces and pinned contact lines, damping rates and frequencies are measured for the six lowest frequency surface-wave modes over a two-decade range of the inverse Reynolds number C. Asymptotic calculations that include viscous dissipation in both Stokes boundary layers and the bulk show good agreement with measurements for small C; the theory typically overpredicts the measured damping rates for C large. Our measurements suggest interfacial contamination may account for a previously reported discrepancy between theory and experiment.
The potential around a test charge in magnetized dusty plasmas
Authors: Shukla P. K. , Salimullah M.
Published: July 2002

The potential of a test dust particle in a magnetized dusty plasma is calculated, taking into account the dielectric constant associated with electrostatic ion-cyclotron waves. Besides the well-known Debye-Hückel screening potential, an oscillatory potential distribution around a test dust particle is found, which strongly depends on the strength of the external magnetic field.
Microturbulence reduction during negative central shear tokamak discharges
Authors: Rettig C. L. , Peebles W. A. , Doyle E. J. , Burrell K. H. , Greenfield C. , Staebler G. M. , Rice B. W.
Published: July 2002

Increased temperature, confinement, and fusion reactivity recently achieved during discharges in the DIII-D Tokamak [J. Luxon et al., Plasma Physics and Controlled Nuclear Fusion Research, 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. 1, p. 159] with negative central magnetic shear (NCS) are accompanied by reduced core electrostatic microturbulence. Comparison of fluctuation characteristics between discharges with and without NCS reveals significant differences in the level and location of microturbulence. While the cause, or instability, for the microturbulence is not known, the reduction of the saturated level is consistent with models incorporating negative shear stabilization and turbulence stabilization by sheared E×B flow.
Experimental scaling of fluctuations and confinement with Lundquist number in the reversed-field pinch
Authors: Stoneking M. R. , Chapman J. T. , Den Hartog D. J. , Prager S. C. , Sarff J. S.
Published: July 2002

The scaling of the magnetic and velocity fluctuations with Lundquist number (S) is examined experimentally over a range of values from 7×104 to 106 in a reversed-field pinch (RFP) plasma. Magnetic fluctuations do not scale uniquely with the Lundquist number. At high (relative) density, fluctuations scale as b̃∝S−0.18, in agreement with recent numerical results. Fluctuations are almost independent of S at low (relative) density, b̃∝S−0.07. The range of measured exponents is narrow and is in clear disagreement with theories predicting b̃∝S−1/2. At high relative density, the scaling of the energy confinement time follows expectations for transport in a stochastic magnetic field. A confinement scaling law (nτE∝β4/5⋅T−7/10⋅a−3/5⋅Iφ2) is derived, assuming the persistent dominance of stochastic magnetic diffusion in the RFP and employing the measured scaling of magnetic fluctuations. The peak velocity fluctuations during a sawtooth cycle scale marginally stronger than magnetic fluctuations but weaker than a simple Ohm’s law prediction. The sawtooth period is determined by a resistive-Alfvénic hybrid time (Tsaw∝τRτA) rather than a purely resistive time.
Formation and locking of the “slinky mode” in reversed-field pinches
Authors: Fitzpatrick Richard
Published: July 2002

The formation and breakup of the “slinky mode” in a Reversed-Field Pinch (RFP) is investigated analytically. The slinky mode is a toroidally localized, coherent interference pattern in the magnetic field, which corotates with the plasma at the reversal surface. This mode forms, via a series of bifurcations, as a result of the nonlinear coupling of multiple m=1 core tearing modes. The slinky mode breaks up via a second series of bifurcations. However, the typical mode amplitude below which slinky breakup is triggered is much smaller than that above which slinky formation occurs. Analytic expressions for the slinky formation and breakup thresholds are obtained in all regimes of physical interest. The locking of the slinky mode to a static error field is also investigated analytically. Either the error field arrests the rotation of the plasma at the reversal surface before the formation of the slinky mode, so that the mode subsequently forms as a nonrotating mode, or the slinky mode forms as a rotating mode and subsequently locks to the error field. Analytic expressions for the locking and unlocking thresholds are obtained in all regimes of physical interest.
Simulation of charging and shielding of dust particles in drifting plasmas
Authors: Lapenta Giovanni
Published: July 2002

To understand the process of dust charging and shielding, self-consistent kinetic simulations are conducted using the Particle-In-Cell method to describe the plasma species, and the immersed boundary method to describe the plasma–dust interactions. The effect of a relative flow between the ions and the dust particles is considered in conditions similar to the real configuration of plasma reactors used in semiconductor manufacturing and in dusty plasma crystal experiments. The ion flow is found to induce changes in the equilibrium dust charge and in the shielding cloud. The ion flow causes a downstream potential wake. For dielectric dust particles, the ion flow has the additional effect of producing nonuniform charge distributions on the dust surface and multipolar components in the shielding potential. Comparisons with existing theories show sufficient accuracy of the orbit motion limited theory to determine the equilibrium charge. Instead, the linear theories for the Debye shielding are insufficient in some respects. Comparisons with experimental observations confirm the conclusions of the simulations.
Oblique collision of modified Korteweg–de Vries ion-acoustic solitons
Authors: Nakamura Y. , Bailung H. , Lonngren K. E.
Published: July 2002

Two-dimensional propagation and oblique collision of modified Korteweg–de Vries (mKdV) ion-acoustic solitons in a plasma with negative ions have been investigated experimentally. At a critical concentration of negative ions, both compressive and rarefractive mKdV solitons exhibit a resonance interaction at a particular amplitude when the colliding angle is fixed. The amplitude is found to be equal for both compressive and rarefractive solitons. The collided solitons suffer a positive phase shift during the interaction. The new solitons formed during the resonant interaction are found to obey the energy and momentum conservation laws of the mKdV solitons for three-wave interaction.
Theory of filamentation instability and stimulated Brillouin scattering with nonlocal hydrodynamics
Authors: Bychenkov V. Yu. , Rozmus W. , Brantov A. V. , Tikhonchuk V. T.
Published: July 2002

A linear theory of stimulated Brillouin scattering and filamentation instabilities has been formulated using nonlocal transport equations for a laser heated plasma, resulting in a model which is fully equivalent to a linearized kinetic description. The inverse-Bremsstrahlung heating, nonlocal energy redistribution, and ponderomotive laser–plasma interactions are correctly taken into account contributing to a new generalized driving force for these instabilities. Temporal and spatial growth rates, thresholds and dominant perturbation wavelengths are obtained. This theory predicts substantial modifications of the ponderomotive results for conditions relevant to many laser plasma interaction experiments. A new nonlocal and nonlinear model of laser propagation in weakly collisional plasmas has been derived.
Two-dimensional wake potentials in sub- and supersonic dusty plasmas
Authors: Lemons D. S. , Murillo M. S. , Daughton W. , Winske D.
Published: July 2002

Hot electrons and sub- and supersonic flows of cold ions around a charged dust particle create steady state wake and Debye screening fields. These linear, electrostatic fields are studied in two-dimensional planar or cylindrical geometry. An asymptotic analysis in the limit of large (compared to Debye length) downstream coordinate z yields analytic wakefields that are in good agreement with numerical integrations of the linear, steady state response function.
Spectral windowing of frequency-modulated optical pulses in a grating compressor
Authors: Heritage J. P. , Thurston R. N. , Tomlinson W. J. , Weiner A. M. , Stolen R. H.
Published: July 2002

Spectral windowing or apodization of the spatially dispersed frequency components within a grating compressor has been used to control the temporal shape of compressed optical pulses. Windowing of undesirable high and low-frequency components, which are not linearly chirped, results in nearly complete elimination of the energy in the wings of the compressed pulse. We have applied this technique to improve the quality of pulses from a mode-locked neodymium: yttrium aluminum garnet laser compressed to less than 2 ps using a fiber and double-pass grating pair with an internal aperture.
Electron spectroscopy study of the Si–O bonding and the polarization screening near the Si-SiO2 interface
Authors: Iqbal A. , Bates C. W. , Allen J. W.
Published: July 2002

Electron spectroscopy studies of thermally grown SiO2 on Si, α-quartz, α-cristobalite, and fused silica show that the variation in the Si–O–Si bond angle in SiO2 does not cause significant change in the charge transfer in the Si–O bond. The relative core level shifts are sensitive to etching and to variations in the oxidation process. Measurements of the Auger parameter for Si show no difference in polarization screening between the Si-SiO2 interface and the bulk SiO2 and that the nearest neighbors of Si in the SiO4 tetrahedron contribute predominantly to the polarization screening.
Quantum mechanical theory of linewidths of localized radiative transitions in semiconductor alloys
Authors: Singh Jasprit , Bajaj K. K.
Published: July 2002

A quantum mechanical formalism to calculate the effect of compositional disorder on the linewidth of localized radiative transitions in semiconducting alloys is developed. A variational-statistical approach is used to calculate the line broadening. The general theory is applied to the specific case of excitonic transitions in which the exciton is in the ground state. The linewidth as a function of alloy composition is derived and the results thus obtained are compared with those of previous theories. For illustration, the calculations are done for GaAlAs and the results are compared with the available low-temperature photoluminescence data.
Microstructure, domain walls, and magnetization reversal in hot-pressed Nd-Fe-B magnets
Authors: Mishra Raja K. , Lee Robert W.
Published: July 2002

Transmission electron microscopy study of hot-pressed and hot-deformed Nd0.14(Fe0.94B0.06)0.86 magnets shows that the magnetic alignment is achieved by the formation of a microstructure consisting of platelets of Nd2Fe14B grains with the c axis normal to the platelet surface and parallel to the press direction. Magnetic domain walls, lying parallel to the c axis, run through many grains and are pinned at the intergranular phases that are produced during processing. Magnetization reversal occurs by domain wall motion.
Effect of thermodynamics on ion mixing
Authors: Workman T. W. , Cheng Y. T. , Johnson W. L. , Nicolet M-A.
Published: July 2002

Ion mixing of elemental 4d-5d metallic bilayers at 77 K by 600 keV Xe++ ions has been studied to test the validity of the phenomenological model of ion mixing that predicts a dependence on the chemical heats of mixing, ΔHmix, and on the cohesive energies, ΔHcoh, of the bilayer elements. A series of samples was chosen to minimize the variation in kinematical properties between samples while maximizing the variation in heats of mixing. The experimental results agree well with the model’s predictions, and the experimentally determined constants K1=0.034 Å and K2=27 agree with those of previous work.
Superconducting Y-Ba-Cu-O oxide films by sputtering
Authors: Hong M. , Liou S. H. , Kwo J. , Davidson B. A.
Published: July 2002

We have prepared superconducting thin films of Y-Ba-Cu-O with Tc onsets above 95 K by both diode and magnetron sputtering. Films with full superconductivity (R=0) at 85 K have been produced by dc magnetron sputtering. The compositions of the films are fairly uniform across an area 50 mm in diameter and through the film thickness. Structural properties of the films were studied by x-ray diffraction. Critical current densities in the range of 3000 to 104 A/cm2 have been measured at 4.2 K.
GHz bandwidth magneto-optic interaction in yttrium iron garnet-gadolinium gallium garnet waveguide using magnetostatic forward volume waves
Authors: Young D. , Tsai C. S.
Published: July 2002

Very large bandwidth noncollinear coplanar magneto-optic interaction with magnetostatic forward volume waves in an yttrium iron garnet-gadolinium gallium garnet (YIG-GGG) waveguide is reported for the first time. Bandwidths of 0.78 and 1.03 GHz centered, respectively, at the carrier frequencies of 2.5 and 6.0 GHz, and TM0 -TE0 mode-conversion efficiencies of 0.54 and 0.50% have been achieved at the optical wavelength of 1.317 μm using a single microstrip transducer and homogeneous dc magnetic fields of 2200 and 3500 Oe. A summary of related coupled-mode analysis is also presented.
The human DnaJ protein, hTid-1, enhances binding of a multimer of the herpes simplex virus type 1 UL9 protein to ori
s
, an origin of viral DNA replication
Authors: Eom Chi-Yong , Lehman I. Robert
Published: July 2002

We have identified cellular proteins that interact with the herpes simplex virus type 1 (HSV-1) origin-binding protein (UL9 protein) by screening a HeLa cell complementary DNA library by using the yeast two-hybrid system. Approximately 7 × 10
5
colonies were screened. Five of the 48 positive clones contained cDNAs that encoded the p150
Glued
component of the dynactin complex, three contained cDNAs for the neural F Box 42-kDa protein (NFB42), which is highly enriched in neural tissue, and three contained hTid-1, a human homologue of the bacterial DnaJ protein. We have focused in this report on the interaction of the viral UL9 protein with the cellular hTid-1.
In vitro
immunoprecipitation experiments confirmed that hTid-1 interacts with the UL9 protein. Electrophoretic mobility-shift assays indicated that the hTid-1 enhances the binding of UL9 protein to an HSV-1 origin, ori
s
, and facilitates formation of the multimer from the dimeric UL9 protein. hTid-1 had no effect on the DNA-dependent ATPase or helicase activities associated with the UL9 protein. These findings implicate hTid-1 in HSV-1 DNA replication, and suggest that this cellular protein may provide a chaperone function analogous to the DnaJ protein in
Escherichia coli
DNA replication.
Experimentally based model of a complex between a snake toxin and the α7 nicotinic receptor
Authors: Fruchart-Gaillard Carole , Gilquin Bernard , Antil-Delbeke Stéphanie , Le Novère Nicolas , Tamiya Toru , Corringer Pierre-Jean , Changeux Jean-Pierre , Ménez André , Servent Denis
Published: July 2002

To understand how snake neurotoxins interact with nicotinic acetylcholine receptors, we have elaborated an experimentally based model of the α–cobratoxin–α7 receptor complex. This model was achieved by using (
i
) a three-dimensional model of the α7 extracellular domain derived from the crystallographic structure of the homologous acetylcholine-binding protein, (
ii
) the previously solved x-ray structure of the toxin, and (
iii
) nine pairs of residues identified by cycle-mutant experiments to make contacts between the α-cobratoxin and α7 receptor. Because the receptor loop F occludes entrance of the toxin binding pocket, we submitted this loop to a dynamics simulation and selected a conformation that allowed the toxin to reach its binding site. The three-dimensional structure of the toxin–receptor complex model was validated
a posteriori
by an additional double-mutant experiment. The model shows that the toxin interacts perpendicularly to the receptor axis, in an equatorial position of the extracellular domain. The tip of the toxin central loop plugs into the receptor between two subunits, just below the functional receptor loop C, the C-terminal tail of the toxin making adjacent additional interactions at the receptor surface. The receptor establishes major contacts with the toxin by its loop C, which is assisted by principal (loops A and B) and complementary (loops D, F, and 1) functional regions. This model explains the antagonistic properties of the toxin toward the neuronal receptor and opens the way to the design of new antagonists.
Müllerian Inhibiting Substance lowers testosterone in luteinizing hormone-stimulated rodents
Authors: Trbovich Alexander M. , Sluss Patrick M. , Laurich V. Matt , O'Neill Francis H. , MacLaughlin David T. , Donahoe Patricia K. , Teixeira Jose
Published: July 2002

Müllerian Inhibiting Substance (MIS) expression is inversely proportional to the serum concentration of testosterone in males after birth andin vitrostudies have shown that MIS can lower testosterone production by Leydig cells. Also, mice overexpressing MIS exhibited Leydig cell hypoplasia and lower levels of serum testosterone, but it is not clear whether this is a result of MIS affecting the development of Leydig cells or their capacity to produce testosterone. To examine the hypothesis that MIS treatment will result in decreased testosterone production by mature Leydig cellsin vivo, we treated luteinizing hormone (LH)-stimulated adult male rats and mice with MIS and demonstrated that it can lead to a several-fold reduction in testosterone in serum and in testicular extracts. There was also a slight decrease in 17-OH-progesterone compared to the more significant decrease in testosterone, suggesting that MIS might be regulating the lyase activity of cytochrome P450c17 hydroxylase/lyase (Cyp17), but not its hydroxylase activity. Northern analysis showed that, in both MIS-treated rats and mice, the mRNA for Cyp17, which catalyzes the committed step in androgen synthesis, was down-regulated. In rats, the mRNA for cytochrome P450 side-chain cleavage (P450scc) was also down-regulated by MIS. This was not observed in mice, indicating that there might be species-specific regulation by MIS of the enzymes involved in the testosterone biosynthetic pathway. Our results show that MIS can be usedin vivoto lower testosterone production by mature rodent Leydig cells and suggest that MIS-mediated down-regulation of the expression of Cyp17, and perhaps P450scc, contributes to that effect.
An initial ATP-independent step in the unwinding of a herpes simplex virus type I origin of replication by a complex of the viral origin-binding protein and single-strand DNA-binding protein
Authors: He Xiaodun , Lehman I. R.
Published: July 2002

Using a spectrophotometric assay that measures the hyperchromicity
that accompanies the unwinding of a DNA duplex, we have identified an
ATP-independent step in the unwinding of a herpes simplex virus type 1
(HSV-1) origin of replication, Ori
s
, by a complex of the
HSV-1 origin binding protein (UL9 protein) and the HSV-1 single-strand
DNA binding protein (ICP8). The sequence unwound is the 18-bp A +
T-rich segment that links the two high-affinity UL9 protein binding
sites, boxes I and II of Ori
s
. P1 nuclease sensitivity of
Ori
s
and single-strand DNA-dependent ATPase measurements of
the UL9 protein indicate that, at 37°C, the A + T-rich segment is
sufficiently single stranded to permit the binding of ICP8. Binding of
the UL9 protein to boxes I and II then results in the formation of the
UL9 protein–ICP8 complex, that can, in the absence of ATP, promote
unwinding of the A + T-rich segment. On addition of ATP, the helicase
activity of the UL9 protein–ICP8 complex can unwind boxes I and II,
permitting access of the replication machinery to the Ori
s
sequences.
Genes directly controlled by CtrA, a master regulator of the
Caulobacter
cell cycle
Authors: Laub Michael T. , Chen Swaine L. , Shapiro Lucy , McAdams Harley H.
Published: July 2002

Studies of the genetic network that controls the
Caulobacter
cell cycle have identified a response regulator, CtrA, that controls, directly or indirectly, one-quarter of the 553 cell cycle-regulated genes. We have performed
in vivo
genomic binding site analysis of the CtrA protein to identify which of these genes have regulatory regions bound directly by CtrA. By combining these data with previous global analysis of cell cycle transcription patterns and gene expression profiles of mutant
ctrA
strains, we have determined that CtrA directly regulates at least 95 genes. The total group of CtrA-regulated genes includes those involved in polar morphogenesis, DNA replication initiation, DNA methylation, cell division, and cell wall metabolism. Also among the genes in this notably large regulon are 14 that encode regulatory proteins, including 10 two-component signal transduction regulatory proteins. Identification of additional regulatory genes activated by CtrA will serve to directly connect new regulatory modules to the network controlling cell cycle progression.
Substituent effects on cation–π interactions: A quantitative study
Authors: Hunter Christopher A. , Low Caroline M. R. , Rotger Carmen , Vinter Jeremy G. , Zonta Cristiano
Published: July 2002

A synthetic supramolecular complex has been adapted to quantify cation–π interactions in chloroform by using chemical double-mutant cycles. The interaction of a pyridinium cation with the π-face of an aromatic ring is found to be very sensitive to the π-electron density. Electron-donating substituents lead to a strong attractive interaction (−8 kJ/mol
−1
), but electron-withdrawing groups lead to a repulsive interaction (+2 kJ/mol
−1
).
Global changes in gene expression by human polymorphonuclear leukocytes during receptor-mediated phagocytosis: Cell fate is regulated at the level of gene expression
Authors: Kobayashi Scott D. , Voyich Jovanka M. , Buhl Cassandra L. , Stahl Robert M. , DeLeo Frank R.
Published: July 2002

Phagocytes are a critical component of the innate immune response in humans and eliminate invading microorganisms through a process known as phagocytosis. Two distinct receptor-linked phagocytic pathways, one with Ab receptors (FcRs; FcR, Fc receptor) and the other complement receptors (CRs), mediate binding and ingestion of pathogens by human polymorphonuclear leukocytes (PMNs). Although progress has been made toward defining complex signal transduction processes that underlie phagocytosis in each pathway, very little is known about gene regulation during or after phagocytosis. Therefore, we used human oligonucleotide microarrays to identify changes in expression of 12,561 genes accompanying FcR- and CR-mediated phagocytosis. Eighty-four percent of 279 differentially expressed genes were induced or repressed 90 min after ingestion of Ab- and/or complement-opsonized particles. Unexpectedly, more than 30 of these genes encoded proteins involved in at least three distinct apoptotic pathways. Ninety-four differentially expressed cell fate-related genes were identified between 180 and 360 min after phagocytosis and most were induced or repressed by PMNs activated through both receptors simultaneously. By using flow cytometry, we found that FcR- and CR-mediated phagocytosis each promoted programmed cell death in human PMNs; however, phagocytosis mediated by the combination of FcRs and CRs induced apoptosis earlier than that by either receptor alone. Our results reveal distinct patterns of receptor-mediated gene expression that define complex inducible apoptotic pathways in activated PMNs. Most significantly, we discovered that programmed cell death is regulated at the level of gene expression. Thus, we hypothesize that gene regulation in PMNs facilitates resolution of inflammatory responses.
Phosphoinositide-3 kinase binds to a proline-rich motif in the Na
+
,K
+
-ATPase α subunit and regulates its trafficking
Authors: Yudowski Guillermo A. , Efendiev Riad , Pedemonte Carlos H. , Katz Adrian I. , Berggren Per-Olof , Bertorello Alejandro M.
Published: July 2002

Endocytosis of Na
+
,K
+
-ATPase molecules in response to G protein-coupled receptor stimulation requires activation of class I
A
phosphoinositide-3 kinase (PI3K-I
A
) in a protein kinase C-dependent manner. In this paper, we report that PI3K-I
A
, through its p85α subunit-SH3 domain, binds to a proline-rich region in the Na
+
,K
+
-ATPase catalytic α subunit. This interaction is enhanced by protein kinase C-dependent phosphorylation of a serine residue that flanks the proline-rich motif in the Na
+
,K
+
-ATPase α subunit and results in increased PI3K-I
A
activity, an effect necessary for adaptor protein 2 binding and clathrin recruitment. Thus, Ser-phosphorylation of the Na
+
,K
+
-ATPase catalytic subunit serves as an anchor signal for regulating the location of PI3K-I
A
and its activation during Na
+
,K
+
-ATPase endocytosis in response to G protein-coupled receptor signals.