bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of biospheric feedbacks in the simulation of the impact of historical land cover change on the Australian January climate
Authors: Narisma G. T. , Pitman A. J. , Eastman J. , Watterson I. G. , Pielke R. , Beltrán‐Przekurat A.
Published: November 2003

Increasing carbon dioxide (CO2) concentrations affect vegetation physiologically (through stomatal conductance) and structurally (through changes in leaf area index). It may be important to include these biospheric feedbacks in experiments that explore atmosphere‐surface interactions including the impact of historical land cover change (LCC) within the climate system. In this paper, we show that the biospheric feedback affects the simulation of historical human‐induced LCC over Australia for January. The biospheric feedbacks reduce the simulated impact of LCC on latent heat flux and temperature. Further, we show that the magnitude of these feedbacks is non‐negligible and can be comparable, at regional scales, to changes caused by increases in radiative forcing simulated by a climate model over the same time period. We suggest that exploring the impact of historical LCC, for example on 20th Century climate, without including the biospheric feedbacks may incorrectly assess the impact of LCC.
Binding at molecule/gold transport interfaces. I. Geometry and bonding
Authors: Basch Harold , Ratner Mark A.
Published: November 2003

Density functional methods on cluster models are used to examine the nature of the geometry, bonding, and energetics involved in the formation of molecular thiol junctions at gold electrode interfaces. The two gold electrodes are modeled as four atom clusters, without geometric constraint. We observe that the geometry nearly always favors twofold coordination of the thiol to a nearly planar array of four gold atoms. There are four essential structural motifs, that seem to characterize these interactions for alkyne, alkane, xylyl, and benzene dithiols. Bonding interactions are relatively strong, and correspond to a polarized covalent interaction. Results are given for different charge and spin components on the molecular bridge.
Binding at molecule/gold transport interfaces. II. Orbitals and density of states
Authors: Basch Harold , Ratner Mark A.
Published: November 2003

The density of states diagrams, and the associated orbital populations and structure, are analyzed for the discrete models for dithiol bridged molecular junctions discussed in the previous paper. The orbitals closest to the Fermi surface are generally dominated by the high s and d densities of metal atoms. Some orbitals are mixed metal/sulfur/hydrocarbon, and a few (generally lower-lying occupied) are dominantly within the hydrocarbon itself. These orbital populations suggest that the frontier orbitals are, in themselves, not adequate for quantitative description of transport, essentially because the Green’s functions of slightly lower-lying orbitals give large contributions to the mixing between electrodes that dominates the transport. Effects of different spin multiplicities and charges, as well as different choices of density functional, are also presented: the major conclusions seem robust, and are not strongly effected by these modifications.
Stochastic Wess–Zumino–Novikov–Witten model on the torus
Authors: Léandre Rémi
Published: November 2003

We define the Brownian motion on a torus group. We define the stochastic integral of a one-form over each canonical cycle of the torus and the stochastic integral on a two-form over the torus. We cannot apply martingale theory in order to define these stochastic integrals. We define a stochastic cohomology in the Chen–Souriau sense of the torus group, which allows us to define the stochastic Wess–Zumino term on the torus group. We show that it is related to the stochastic holonomy over a stochastic line bundle on the loop group.
Microbeam of 100 keV x ray with a sputtered-sliced Fresnel zone plate
Authors: Kamijo Nagao , Suzuki Yoshio , Takano Hidekazu , Tamura Shigeharu , Yasumoto Masato , Takeuchi Akihisa , Awaji Mitsuhiro
Published: November 2003

Microfocusing of 100 keV x ray with a sputtered-sliced Fresnel zone plate (ss-FZP) has been performed at the 250-m-long beamline (20XU) of SPring-8. The ss-FZP with an outermost zone width 0.16 μm which is composed of 70 layers of alternating Cu and Al layers and having thickness ∼180 μm was fabricated and characterized. The minimum focal spot size attained for the first order focal beam was 0.5 μm with a focal distance 900 mm at a photon energy 100 keV. The total flux of the microprobe was ∼2×106 photons s−1 μm−2.
On the generalized Borel transform and its application to the statistical mechanics of macromolecules
Authors: Marucho Marcelo , Carri Gustavo A.
Published: November 2003

We present a new integral transform called the generalized Borel transform (GBT) and show how to use it to compute distribution functions used to describe the statistical mechanics of macromolecules. For this purpose, we choose the random flight model (RFM) of macromolecules and show that the application of the GBT to this model leads to the exact expression of the polymer propagator (two-point correlation function) from which all the statistical properties of the model can be obtained. We also discuss the mathematical simplicity of the GBT and its applicability to macromolecules with other topologies.
An efficient method for simultaneous measurement of the integrated reflectivity of crystals in multiple orders of reflection using the bremsstrahlung continuum from an x-ray tube and comparison of experimental results for mica with theoretical calculations
Authors: Lee S. G. , Bak J. G. , Jung Y. S. , Bitter M. , Hill K. W. , Hölzer G. , Wehrhan O. , Förster E.
Published: November 2003

This article describes an efficient method for the simultaneous measurement of the integrated reflectivity of a crystal in multiple orders of reflection at a predefined Bragg angle by using the bremsstrahlung continuum from an x-ray tube in combination with an energy-sensitive detector. The technique is demonstrated with a mica crystal for Bragg angles of 43°, 47°, and 50°. The measured integrated reflectivity for Bragg reflections up to the 24th order is compared with theoretical predictions, which are also presented in this article.
Plasma heating via parametric beating of Alfvén waves, with heliospheric applications
Authors: Bekhor Steven H. , Drake R. Paul
Published: November 2003

This paper advances a novel mechanism to explain the dissipation of the Alfvén waves that carry much of the energy in heliospheric and astrophysical turbulence, with specific applications to solar wind heating. The essential point is that the nonlinear beating of relatively low-frequency Alfvén waves, which are abundant in the heliosphere, drives a compressible magnetosonic response whose damping can dissipate significant energy. This mechanism involves both kinetic and magnetohydrodynamic (MHD) processes. The damping of the magnetosonic waves is a kinetic process. The nonlinear beating of Alfvén waves, which produces the magnetosonic waves, is best described by MHD theory. This mechanism complements and may compete with the well-known alternative mechanism in which the cascade of turbulent energy to small-scale, high-frequency Alfvén waves dissipates by ion-cyclotron damping. The MHD analysis in this paper reveals that the fast magnetosonic mode dominates the dissipation when the plasma beta is near unity, and that the timescale of dissipation in the heliosphere can vary from hours to a year depending upon the direction of the driven wave and the plasma parameters where it is driven. The damping of the driven magnetosonic waves may also contribute to the observed high-energy particle distributions.
Electrostatic instabilities and nonlinear structures of low-frequency waves in nonuniform electron–positron–ion plasmas with shear flow
Authors: Mirza Arshad M. , Hasan Asma , Azeem M. , Saleem H.
Published: November 2003

It is found that the low-frequency ion acoustic and electrostatic drift waves can become unstable in uniform electron–ion and electron–positron–ion plasmas due to the ion shear flow. In a collisional plasma a drift-dissipative instability can also take place. In the presence of collisions the temporal behavior of nonlinear drift-dissipative mode can be represented in the form of well-known Lorenz and Stenflo type equations that admit chaotic trajectories. On the other hand, a quasi-stationary solution of the mode coupling equations can be represented in the form of monopolar vortex. The results of the present investigation can be helpful in understanding electrostatic turbulence and wave phenomena in laboratory and astrophysical plasmas.
General solutions of Einstein’s spherically symmetric gravitational equations with junction conditions
Authors: Das A. , DeBenedictis A. , Tariq N.
Published: November 2003

Einstein’s spherically symmetric interior gravitational equations are investigated. Following Synge’s procedure, the most general solution of the equations is furnished in case T11 and T44 are prescribed. The existence of a total mass function, M(r,t), is rigorously proved. Under suitable restrictions on the total mass function, the Schwarzschild mass M(r,t)=m, implicitly defines the boundary of the spherical body as r=B(t). Both Synge’s junction conditions as well as the continuity of the second fundamental form are examined and solved in a general manner. The weak energy conditions for an arbitrary boost are also considered. The most general solution of the spherically symmetric anisotropic fluid model satisfying both junction conditions is furnished. In the final section, various exotic solutions are explored using the developed scheme including gravitational instantons, interior T-domains, and D-dimensional generalizations.
K-shell transition absorption measurement of radiatively heated Al plasma
Authors: Yang Jiamin , Zhang Jiyang , Ding Yaonan , Peng Yonglun , Li Jiaming , Zheng Zhijian , Yang Guohong , Zhang Wenhai , Li Jun
Published: November 2003

High temperature aluminum plasmas have been produced by irradiating the layered Au–Al foils with the smoothed high power laser at the Xingguang II laser facility. High-resolution transmission spectrum of the Al plasma has been measured by using penta-erythritol tetrakis (hydroxymethy) methane C(CH2OH)4 crystal spectrometer. Absorption lines of the aluminum ion transition 1s−np(n=3,4,5) in the region of 0.61–0.70 nm, have been observed and identified. The unresolved transition array model has been introduced to calculate the transmission spectra of aluminum plasma. The measured transmission spectrum has been compared with those calculated.
Invariant integration over the unitary group
Authors: Aubert S. , Lam C. S.
Published: November 2003

Integrals for the product of unitary-matrix elements over the U(n) group will be discussed. A group-theoretical formula is available to convert them into a multiple sum, but unfortunately the sums are often tedious to compute. In this article, we develop an alternative method in which these sums are avoided, and group theory is rendered unnecessary. Only unitarity and the invariance of the Haar measure are required for the computation. The method can also be used to get a closed expression for the simpler integral of monomials over a hypersphere.
Electron bunch acceleration and trapping by the ponderomotive force of an intense short-pulse laser
Authors: Kong Q. , Miyazaki S. , Kawata S. , Miyauchi K. , Nakajima K. , Masuda S. , Miyanaga N. , Ho Y. K.
Published: November 2003

By utilizing a pulsed laser beam of TEM(1,0)+TEM(0,1) mode, it was found numerically for the first time that an electron bunch can be effectively trapped by the transverse ponderomotive force in the transverse direction and at the same time accelerated by the longitudinal ponderomotive force to about 378 MeV at the laser peak intensity of I∼5.48×1018 W/cm2. In addition, the electron bunch size is preferably small: at this laser intensity the electron bunch thickness is ∼10λ in the longitudinal direction and the bunch radius is about 625λ in the transverse direction.
A dynamic infrared source
Authors: Persky M. J.
Published: November 2003

A system is described that can be used for testing infrared focal plane cameras in situations where conventional blackbody sources are deficient. The system uses readily available components, electronics, and software. It can provide either a wide area or a point source of infrared flux that can be programmed to follow a prescribed temporal profile at higher rates than available from commercial blackbody sources and with excellent repeatability. Additionally, the system provides flux without suffering from the temporal noise characteristic of commercial, wide area, flat sheet sources that results from turbulence in front of the blackbody. The system consists of commercially available, rapid rise time infrared radiators, either coupled to an integrating sphere for broad area flux, or used individually with a pinhole and collimator as a point source. A programmable voltage supply provides the power versus time profile at frequencies to several Hertz. Transfer from a standard blackbody calibrates the flux levels. This article provides a description, testing results, and application examples.
Tapered microstrip balun for integrating a low noise amplifier with a nonplanar log periodic antenna
Authors: Engargiola G.
Published: November 2003

This article describes design parameters and test results for a 1–10 GHz microstrip balun with a 240 Ω balanced port and a 50 Ω unbalanced port. The tapered geometry and rf performance are favorable for integrating a low noise amplifier with a nonplanar log periodic antenna developed at the University of California’s radio astronomy lab. The design can be modified for use in cryogenic low noise applications. When the balun is placed in a conducting enclosure, excitation of unwanted transmission modes can be minimized by careful field and impedance matching of balun ports and by inclusion of a resistive vane in proximity to the balun.
Kinetic gravimetric sorption of low volatility gases and vapors in polymers
Authors: Dhoot Sushil N. , Freeman Benny D.
Published: November 2003

A kinetic gravimetric sorption apparatus for measuring solubility and diffusivity of low vapor pressure gases and vapors in polymers and other sorbents is described. Sorption and transport data for toluene vapor in poly(dimethyl siloxane) at 25 °C are provided to illustrate the method. These data were obtained by measuring the kinetic uptake of a mixture of carrier gas and toluene vapor and, for comparison, pure toluene vapor at the same thermodynamic activity. Excellent agreement was observed between toluene solubility and diffusivity values obtained from these two different experiments. In the mixture sorption experiments, the type of carrier gas (helium or nitrogen) had no effect on measured toluene solubility and diffusion coefficients.
Stereo camera system for three-dimensional reconstruction of a flyer plate in flight
Authors: Rupp Ted D. , Gehr Russell J. , Bucholtz Scott , Robbins David L. , Stahl David B. , Sheffield Stephen A.
Published: November 2003

A stereo camera system has been developed for use with the laser-driven MiniFlyer apparatus. The objective of the stereo camera is to determine the three-dimensional reconstruction of the surface of a flyer plate in flight. The resolution of the system is designed to be 10 μm, based on the maximum blur expected due to the flyer plate motion during the exposure. Illumination of the flyer plate in flight is accomplished with a Q-switched Nd:YAG laser. A grid is projected onto the flyer plate surface to provide reference points for the reconstruction. The software algorithm used for the reconstruction utilizes a bilinear interpolation to fill in the data between the grid lines. Data for copper and titanium flyer plates are discussed.
Low-impedance time-domain reflectometry for measuring the impedance characteristics of low-impedance transmission lines
Authors: Paulter N. G. , Palm R. H. , Hefner A. R. , Berning D. W.
Published: November 2003

An experimental examination of a 10 Ω and a 2 Ω time-domain reflectometer (TDR) technique for measuring low-impedance transmission line characteristics is presented. TDR measurements using these systems are compared to those using a 50 Ω TDR system. The results show that the uncertainties in the characteristic impedance, ZC, of a low-ZC transmission line are a significant fraction of ZC for 50 Ω TDR measurements, whereas the fractional uncertainties are much less when using a low-impedance TDR. The fractional ZC uncertainties for the 50 Ω TDR increase as ZC decreases.
High frequency ac bias for direct-coupled dc superconducting quantum interference device readout electronics
Authors: Oukhanski N. , Schultze V. , IJsselsteijn R. P. J. , Meyer H.-G.
Published: November 2003

A high frequency ac-bias technique for direct-coupled readout electronics, for high temperature dc superconducting quantum interference devices (HTc dc SQUIDs), is presented. The method was tested for ac-bias frequencies between 2 and 10 MHz on different HTc dc SQUIDs. The minimum white flux-noise level of 9.5 μΦ0/Hz1/2, corresponding to a noise limited magnetic field resolution of 24 fT/Hz1/2, was achieved with a HTc dc SQUID with a maximum voltage swing of 64 μVpp and an ac-bias frequency of about 7.7 MHz. A maximum system dynamic range of 156 dB (±600 Φ0) in the white noise frequency region was achieved for this sensor. For various HTc dc SQUID magnetometers a bandwidth of between 1.6 and 4 MHz was measured. The slew rates were in the range of 1–2 MΦ0/s for several HTc dc SQUIDs.
Lüders theorem for coherent-state POVMs
Authors: Weigert Stefan , Busch Paul
Published: November 2003

Lüders’ theorem states that two observables commute if measuring one of them does not disturb the measurement outcomes of the other. We study measurements which are described by continuous positive operator-valued measurements (or POVMs) associated with coherent states on Lie groups. In general, operators turn out to be invariant under the Lüders map if their P- and Q-symbols coincide. For a spin corresponding to SU(2), the identity is shown to be the only operator with this property. For a particle, a countable family of linearly independent operators is identified which are invariant under the Lüders map generated by the coherent states of the Heisenberg–Weyl group, H3. The Lüders map is also shown to implement the anti-normal ordering of creation and annihilation operators of a particle.
Role of the m=0 modes in the edge region of a reversed-field pinch during pulsed poloidal current drive
Authors: Cravotta A. , Spizzo G. , Zanca P. , Martin P.
Published: November 2003

Changes in the edge profile of soft x-ray emission during pulsed poloidal current drive (PPCD) experiments are in agreement with the modifications of the plasma surface, as seen from magnetic measurements. In particular, the m=0 modes resonant at the reversal radius have been analyzed. A comparison with an m=0 island reconstruction model shows that PPCD reduces the bulging associated with the m=0 modes by shifting inward the reversal surface, where the m=0 island is located. Regarding the total m=0 amplitude, there are evidences that during PPCD, on average, it does not change significantly. Additional data coming from standard discharges support the idea that two competing phenomena act during PPCD: one is the inward shift of the reversal, which destabilizes the m=0 modes; the other one is the decrease of the m=1 fluctuations, which acts in the opposite direction.
Cross-helicity and magnetized Trkal flows
Authors: Tasso H. , Throumoulopoulos G. N.
Published: November 2003

In a previous note [Tasso, Phys. Plasmas 2, 1789 (1995)], dissipative magnetized Trkal flows were proved to be Lyapunov stable nonlinearly under the conditions of sufficiently small Reynolds number and of an upper bound of the “force-free” current. An alternative Lyapunov functional containing the cross helicity and introduced recently for conservative magnetized Beltrami flows [Yoshida et al., J. Math. Phys. 44, 2168 (2003)] is extended here to the Trkal flows mentioned above. Stability is now proven under limitations on maximal velocity and current without introducing an upper bound on the Reynolds number.
Amalgamations of the Painlevé equations
Authors: Kudryashov Nikolai A.
Published: November 2003

New hierarchies of nonlinear ordinary differential equations that are generalizations of the Painlevé equations are presented. These hierarchies are shown to contain the Painlevé equations as special cases. Emphasis is on the sixth order ordinary differential equations. Special solutions for one of them are expressed via the general solutions of the P1,  P2 equations and special cases of the P3 and P5 equations. Special solutions of another sixth order ODE are determined by the general solutions of the P2,  P4,  P3, and P5 equations. Five of six Painlevé equations can be considered as special cases of these sixth order ODEs. Isomonodromic linear problems to solve the Cauchy problems of hierarchies by the inverse monodromy transform are given.
Hilbert space structure in classical mechanics. II
Authors: Deotto E. , Gozzi E. , Mauro D.
Published: November 2003

In this paper we analyze two different functional formulations of classical mechanics. In the first one the Jacobi fields are represented by bosonic variables and belong to the vector (or its dual) representation of the symplectic group. In the second formulation the Jacobi fields are given as condensates of Grassmannian variables belonging to the spinor representation of the metaplectic group. For both formulations we shall show that, differently from what happens in the case presented in paper I, it is possible to endow the associated Hilbert space with a positive definite scalar product and to describe the dynamics via a Hermitian Hamiltonian. The drawback of this formulation is that higher forms do not appear automatically and that the description of chaotic systems may need a further extension of the Hilbert space.
Representation of the exact relativistic electronic Hamiltonian within the regular approximation
Authors: Filatov Michael , Cremer Dieter
Published: November 2003

The exact relativistic Hamiltonian for electronic states is expanded in terms of energy-independent linear operators within the regular approximation. An effective relativistic Hamiltonian has been obtained, which yields in lowest order directly the infinite-order regular approximation (IORA) rather than the zeroth-order regular approximation method. Further perturbational expansion of the exact relativistic electronic energy utilizing the effective Hamiltonian leads to new methods based on ordinary (IORAn) or double [IORAn(2)] perturbation theory (n: order of expansion), which provide improved energies in atomic calculations. Energies calculated with IORA4 and IORA3(2) are accurate up to c−20. Furthermore, IORA is improved by using the IORA wave function to calculate the Rayleigh quotient, which, if minimized, leads to the exact relativistic energy. The outstanding performance of this new IORA method coined scaled IORA is documented in atomic and molecular calculations.
Conical intersections of three states: Energies, derivative couplings, and the geometric phase effect in the neighborhood of degeneracy subspaces. Application to the allyl radical
Authors: Han Seungsuk , Yarkony David R.
Published: November 2003

The properties of the five-dimensional branching space of conical intersections of three states of the same symmetry (denoted i,j,k) are considered. The results of a perturbative model are compared with multireference configuration interaction calculations for three spectroscopically observed states of the allyl radical. Of particular interest is the three-dimensional subspace of the branching space where two states remain degenerate. The energies, derivative couplings and geometric phase effect are studied in the neighborhood of this degeneracy subspace. The degeneracy subspace includes two kinds of conical intersections, i,j and j,k. The existence of a three-state intersection impacts the phase of the wave functions (and the derivative coupling) traversing a closed loop. For example, in the branching space, the number and kind of conical intersections in a surface bounding the closed loop is constrained if the closed loop contains the three-state intersection.
Sharp reconstruction of unsharp quantum observables
Authors: Beneduci Roberto , Nisticò Giuseppe
Published: November 2003

A well defined procedure exists which allows us to “reconstruct” a sharp, i.e., standard, quantum observable A starting from a given commutative unsharp observable F. In this work we prove that the outcomes of measurements of F can be consistently interpreted as the result of a stochastic diffusion of outcomes of its sharp reconstruction A. Furthermore, for every sharp observable B, such that F is unsharp realization of B, we explicitly construct a real mapping g such that A=g(B).
A combined source of electron bunches and microwave power
Authors: Xie J. L. , Wang F. Y. , Yang X. P. , Shen B. , Gu W. , Zhang L. W.
Published: November 2003

In this article, the possibility of using a high power klystron amplifier simultaneously as a microwave power source as usual and an electron bunches source by extracting the spent beam with a magnet and also as an oscillator by feedback is investigated. The purpose of this study is to demonstrate the feasibility of constructing a very compact electron linear accelerator or for other applications of electron bunches. The feasibility of the idea was first examined by computer simulation of the electron motion in a 5 MW klystron and the characteristics of the klystron spent beam. Experimental study was then carried out by installing a radio frequency cavity and a Faraday cage in sequence at the exit end of a bending magnet located at the top of the klystron collector. The energy and current of the chopped spent electron beam can then be measured. By properly choosing the feedback circuit elements, the frequency stability of the klystron in oscillator mode was proved to be good enough for linac operation. According to the results presented in this article, it is evident that an extremely compact linac for research and education with better affordability can be constructed to promote the applications of linacs.
Soft x-ray emission from postpulse expanding laser-produced plasmas
Authors: Weaver J. L. , Feldman U. , Mostovych A. N. , Seely J. F. , Colombant D. , Holland G.
Published: November 2003

A diagnostic spectrometer has been developed at the Naval Research Laboratory to measure the time resolved absolute intensity of radiation emitted from targets irradiated by the Nike laser. The spectrometer consists of a dispersive transmission grating of 2500 lines/mm or 5000 lines/mm and a detection system consisting of an absolutely calibrated Si photodiode array and a charge coupled device camera. In this article, this spectrometer was used to study the spatial distribution of soft x-ray radiation from low Z elements (primarily carbon) that lasted tens of nanoseconds after the main laser illumination was over. We recorded soft x-ray emission as a function of the target material and target orientation with respect to the incoming laser beam and the spectrometer line of sight. While a number of spectral features have been identified in the data, the instrument’s combined temporal and spatial resolution allowed observation of the plasma expansion from CH targets for up to ∼25 ns after the cessation of the main laser pulse. The inferred plasma expansion velocities are slightly higher than those previously reported.
An oscillating bubble device for direct measurement of molecular exchange processes at the air–liquid interface in the medium frequency range
Authors: Örtegren J. , Wantke K.-D. , Motschmann H.
Published: November 2003

An experiment for the investigation of the exchange dynamics of adsorbed and dissolved surfactants at the air–water interface is described. The experiment combines two established techniques: the method of the oscillating bubble generates in a well-defined fashion a nonequilibrium state by a periodic compression and expansion of the surface layer. The state of the adsorption layer is then investigated by surface second harmonic generation (SHG). SHG is a second order nonlinear optical technique, which probes only the adsorbed molecules. Contribution of the bulk is widely suppressed and information on the orientational order of the surfactant and the corresponding number density of the adsorbed species are gained. These data are of utmost importance to assess the established models of Gibbs adsorption layer. The combination of the nonlinear optical technique with a rapidly oscillating bubble imposes severe experimental hurdles such as the synchronization of the laser pulses with the state of the bubble or problems arising from a bad signal to noise ratio. The experimental setup discussed in this article overcomes these problems and outlines all relevant design parameters.
Large-grazing-angle, multi-image Kirkpatrick–Baez microscope as the front end to a high-resolution streak camera for OMEGA
Authors: Gotchev O. V. , Hayes L. J. , Jaanimagi P. A. , Knauer J. P. , Marshall F. J. , Meyerhofer D. D.
Published: November 2003

A high-resolution x-ray microscope with a large grazing angle has been developed, characterized, and fielded at the Laboratory for Laser Energetics. It increases the sensitivity and spatial resolution in planar direct-drive hydrodynamic stability experiments, relevant to inertial confinement fusion research. It has been designed to work as the optical front end of the PJX—a high-current, high-dynamic-range x-ray streak camera. Optical design optimization, results from numerical ray tracing, mirror-coating choice, and characterization have been described previously [O. V. Gotchev, et al., Rev. Sci. Instrum. 74, 2178 (2003)]. This work highlights the optics’ unique mechanical design and flexibility and considers certain applications that benefit from it. Characterization of the microscope’s resolution in terms of its modulation transfer function over the field of view is shown. Recent results from hydrodynamic stability experiments, diagnosed with the optic and the PJX, are provided to confirm the microscope’s advantages as a high-resolution, high-throughput x-ray optical front end for streaked imaging.
Characteristics of doped optical fiber for fluorescence-based fiber optic temperature systems
Authors: Forsyth D. I. , Sun T. , Grattan K. T. V. , Wade S. A. , Collins S. F.
Published: November 2003

A series of investigations has been carried out into the performance characteristics of Er3+-doped fibers for their application in optical probes designed to incorporate fluorescence-based optical fiber sensors. Issues, such as probe length and annealing characteristics, are investigated and results reported on a series of fibers which are well suited to be used in probe construction.
Excitation of nonreciprocal electromagnetic surface waves in semibounded magnetized plasmas by an electron beam
Authors: Shokri B. , Jazi B.
Published: November 2003

The dispersion relation of nonreciprocal electromagnetic surface waves propagating on the magnetized plasma–vacuum interface is obtained. Furthermore, the dependency of penetration depth on the magnetic field strength and its directivity is investigated. Finally, it will be shown that by an electron beam flowing on the plasma surface, aforementioned waves can be excited.
Quantum and tensorial modeling of multipolar nonlinear optical chromophores by a generalized equivalent internal potential
Authors: Weibel Jason D. , Yaron David , Zyss Joseph
Published: November 2003

The equivalent internal field model, originally developed for linear one-dimensional chromophores, is extended to three-dimensional multipolar chromophores. The extension requires two generalizations to the model. First, the equivalent internal field must be generalized to an equivalent internal potential. Second, all tensor components of the hyperpolarizability must be taken into account. A general formalism is developed for analyzing the hyperpolarizabilities induced by application of various internal potentials to a molecular skeleton, assuming the hyperpolarizabilities are linearly related to the internal potential. This formalism utilizes a symmetry analysis, along with quantum chemical calculations done here with the Hückel, Pariser–Parr–Pople and intermediate neglect of differential overlap (INDO) Hamiltonians and using single-configuration interaction theory. The formalism is applied to and tested on the benzene molecular skeleton. The hyperpolarizability is found to be linearly related to the internal potential provided the potential difference between carbon atoms is below a threshold of the order of 2 eV. Various predictions of the model are tested against explicit INDO and ab initio calculations on mono-substituted, ortho-disubstituted, meta-disubstituted, and tri-substituted benzenes. For the substituents F, CH3, OCH3, OH, and NH2, many of the predictions of the equivalent internal potential model apply, indicating that the internal potentials arising from these substituents are in the linear regime. For the NO2 and CN substituents, strong effects from nonlinear coupling are observed. The disagreements between the various quantum chemical treatments (INDO and various ab initio approaches) are largest for molecules exhibiting nonlinear coupling effects, indicating that the nonlinear effects are more difficult to calculate than linear effects.
Extended Hellmann–Feynman forces, canonical representations, and exponential propagators in the mixed quantum-classical molecular dynamics
Authors: Grochowski P. , Lesyng B.
Published: November 2003

Analytical expressions of the Hellmann–Feynman (HF) forces in the quantum-classical molecular dynamics (QCMD) are evaluated and analyzed. The conventional expression of the HF forces is valid in the differential form of the QCMD evolution equations, but the extended formula appears in the context of approximate, time-step propagators. The canonical Hamilton representation of QCMD, and its symplectic and nonsymplectic exponential propagators, are reviewed. Tests for a model proton transfer system are performed in order to compare efficiency of the proposed integration schemes. The most efficient scheme results from separation of either different time scales or different approximation orders for the quantum and classical parts, and also from correct accumulation of the HF forces, corresponding to an improved extended HF formula. We derive the canonical representation and propagators of QCMD in the adiabatic basis set. If the classical and quantum parts of the propagator are separated in that representation, the extended HF forces appear, and are related to transitions between the adiabatic states. Applications to the quantum-classical molecular dynamics are proposed, using multiple protonic and/or electronic adiabatic states.
On the nonrelativistic Lee model
Authors: Ayan Ali , Turgut O. Teoman
Published: November 2003

In this work we present two rigorous results on the nonrelativistic Lee model following a method proposed by Rajeev in an unpublished article (S. G. Rajeev, hep-th 9902025). Thus this short paper should be considered as a commentary on Rajeev. In the unpublished paper of Rajeev, the renormalization of the Hamiltonian is accomplished at the level of resolvents. We first establish that the renormalized resolvent of the interacting Hamiltonian indeed defines a unique closed densely defined operator acting on the free Fock space of bosons. Next we give a justification in the mean field approximation that the ground state energy is bounded from below and the system has a good thermodynamic limit by elaborating along the original arguments of Rajeev. Our arguments in two dimensions do not yield better bounds, but this could be due to the inadequacy of the method used. In both cases though the ground state energy is not significantly altered to give a nontrivial ground state energy per particle.
Density functional theory based molecular-dynamics study of aqueous chloride solvation
Authors: Heuft J. M. , Meijer E. J.
Published: November 2003

The aqueous solvation shell of chloride is studied using density functional theory based molecular-dynamics simulations. This method enables us to obtain a detailed understanding of the structural, dynamic and electronic properties of the system. Special attention is paid to the dynamic properties of the first solvation shell. The results obtained here are in good agreement both with experiments and other simulations. Our results suggest that the surrounding shell of water molecules is quite rigid. We observe no influence of the chloride ion on the electronic and structural properties of the coordinating water molecules.
Hydrogen bonding and molecular mobility in liquid water in external electromagnetic fields
Authors: English Niall J. , MacElroy J. M. D.
Published: November 2003

Nonequilibrium molecular dynamics simulations of water have been performed in the isothermal–isobaric ensemble in the presence of external electromagnetic fields of varying intensity in the microwave to far-infrared frequency range, using a rigid/polarizable and a flexible/nonpolarizable potential model, from 260 to 400 K. Significant alterations in molecular mobility and hydrogen bonding patterns were found vis-à-vis zero-field conditions. In addition, the influence of the isothermal–isobaric ensemble on these observations was gauged by means of comparison with pure Newtonian simulation findings in the presence of external fields, and the former results were in reasonable accord with the latter.
An efficient method for computation of long-ranged Coulomb forces in computer simulation of ionic fluids
Authors: Yakub Eugene , Ronchi Claudio
Published: November 2003

Angular averaging of Ewald sums eliminating the nonphysical cubic symmetry of electrostatic field in the uniform ionic system under conditions of computer simulation with periodic boundaries is proposed. The resulting effective potential is central, has simple analytical form and its range is correspondent to the main box size. The approach provides a fast method for computation of electrostatic contribution to the energy of ionic fluids and other dense, uniform Coulomb systems in Monte Carlo or molecular dynamics computer simulation.
Theoretical study of microscopic solvation of HCl in ammonia: HCl(NH3)n, n=1–4
Authors: Bacelo Daniel E. , Fioressi Silvina E.
Published: November 2003

The global minimum-energy and other significant structures of HCl(NH3)n (n=1–4) clusters have been identified by ab initio Monte Carlo simulated annealing. Geometries of the isomers were refined in density functional theoretical and Hartree–Fock plus second-order Møller–Plesset perturbation theoretical calculations. The energy orderings were confirmed in single-point higher-level calculations. While for HCl(NH3) only one hydrogen-bonded structure was found, for the larger clusters both ionic and molecular structures exist. Stabilization by hydrogen bonding is found to be less important in the ammonia clusters than in water clusters of similar size.
Resonance enhanced multiphoton ionization and zero electron kinetic energy spectroscopy of the DABCO–N2 van der Waals complex: Divergent energy level spacings as evidence for an offset parallel structure
Authors: Watkins Mark J. , Cockett Martin C. R.
Published: November 2003

The DABCO–N2 van der Waals complex has been investigated using a combination of (1+1′) resonance enhanced multiphoton ionization and zero electron kinetic energy spectroscopy, supported by ab initio molecular orbital calculations. The observation of extended vibrational progressions of low wave number with diverging vibrational spacings supports an assignment to an offset parallel structure analogous to the 45° canted parallel structures proposed for the nitrogen dimer. The active vibrational mode is assigned to a mixed van der Waals stretch/rocking mode in which the nitrogen solvent undergoes a hindered rotational motion against the DABCO framework in the plane containing the C3 axis in DABCO and the intermolecular axis in N2. The results of counterpoise corrected ab initio calculations support this assignment to the extent that they suggest that a parallel structure is the most stable with a cross structure identified as a transition state. No experimental evidence is found for the existence of other stable structures.
Spectroscopic study of N2O+(A 2Σ+) by photofragment excitation spectrum
Authors: Xu Haifeng , Guo Ying , Li Qifeng , Liu Shilin , Ma Xingxiao , Liang Jun , Li Haiyang
Published: November 2003

Photofragment NO+ excitation spectrum of N2O+ ions has been studied in the wavelength range of 278–328 nm, where the parent N2O+ ions were state-selectively prepared at the X 2Π1/2,3/2(000) levels by [3+1] multi-photon ionization of jet-cooled N2O molecules at 360.55 nm. The spectrum was attributed completely to the A 2Σ+←X 2Π3/2,1/2(000) electronic transition of N2O+. Totally 47 vibronic bands associated to 24 vibrational levels of the A 2Σ+ state were identified in the present work, most of which were observed for the first time. The sufficient spectroscopic data made it possible to investigate the Fermi-resonance between the ν1 and ν2 vibrational modes at the A 2Σ+ state. Based on the assignment, the spectral constants of the A 2Σ+ state, such as vibrational frequencies, anharmonic constants, and Fermi interaction constant, were determined with relatively high reliability and precision.
Reactive vibrational excitation spectroscopy of formic acid in solid argon: Quantum yield for infrared induced trans→cis isomerization and solid state effects on the vibrational spectrum
Authors: Maçôas E. M. S. , Khriachtchev L. , Pettersson M. , Juselius J. , Fausto R. , Räsänen M.
Published: November 2003

Formic acid molecules are trapped in two predominant local environments (sites) when isolated in an argon matrix at 8 K. Using narrowband tunable infrared (IR) radiation, we performed site-selective excitation of various vibrational modes of the lower-energy trans conformer. For all excited modes, ranging from 7000 to 2950 cm−1, we detected site-selective isomerization to the higher-energy cis form. By measuring the IR absorption of a selected band of the cis conformer as a function of the excitation frequency, the reactive vibrational excitation (RVE) spectra were obtained. The trans→cis isomerization quantum yields for the excited modes were determined. Remarkably, very high absolute values were obtained for the quantum yield (up to 40%) at excitation energies above the reaction barrier. The efficiency of the photoinduced isomerization is essentially independent of the excited vibrational mode in a broad energy interval. Even when the excitation energy was below the reaction barrier, IR-induced rotational isomerization was observed, which indicates tunneling from the vibrationally excited trans conformer to the cis form. Using the RVE spectra, phonon sidebands were detected on the high-frequency side of the zero-phonon-line of the OH stretching mode of trans-formic acid. These weak and broad bands were not observed in the absorption spectra. Additionally, a relatively narrow band blueshifted by 6 cm−1 from the OH stretching fundamental mode was assigned to a librational satellite based on simulations using the hindered rotation model for an asymmetric top trapped in an octahedral crystal field.
Kinetics of H atom adsorption on Si(100) at 500–650 K
Authors: Kutana A. , Makarenko B. , Rabalais J. W.
Published: November 2003

The kinetics of isothermal adsorption and migration of atomic hydrogen on a Si(100) surface has been investigated by the time-of-flight scattering and recoiling spectrometry technique. A continuous decrease in saturation coverage with temperature under constant atomic hydrogen exposure has been observed for temperatures in the range 325–750 K. This observation is in contrast with a widely accepted view of the Si(100)/H surface as having three fixed coverage states within certain temperature windows. For TS=500–650 K, the decrease is described by a kinetic model in which the surface concentration of physisorbed hydrogen atoms is depleted due to the increased rate of migration from precursor sites to primary monohydride sites. The model suggests a mechanism to explain the dependence of the saturation value on temperature in this range. The migration constant obeys an Arrhenius expression with an activation energy of 0.71 eV. A significant concentration of hydrogen atoms occupying precursor states acts as a reservoir, saturating the monohydride dangling bonds after the hydrogen source is shut off and discontinuation of Eley–Rideal abstraction.
Destabilization of fast magnetoacoustic waves by circulating energetic ions in toroidal plasmas
Authors: Belikov V. S. , Kolesnichenko Ya. I. , White R. B.
Published: November 2003

An instability of fast magnetoacoustic waves driven by circulating energetic ions in axisymmetric toroidal plasmas and characterized by frequencies below the ion gyrofrequency is considered. An important role of the l=0 resonance (l is the number of a cyclotron harmonic) in the wave–particle interaction is revealed: It is shown that this resonance considerably extends an unstable region in the space of the pitch-angles of the energetic ions and the wave frequencies. The analysis is carried out for a “slow” instability, which has the growth rate less than the bounce frequency of the energetic ions. Specific examples relevant to the National Spherical Torus Experiment [Spitzer et al., Fusion Technol. 30, 1337 (1996)], where instabilities of this kind were observed, are considered.
Formation and dynamics of water clusters on Ru(001)
Authors: Lilach Y. , Buch V. , Asscher M.
Published: November 2003

The adsorption kinetics of water on Ru(001) was simulated using molecular dynamics (MD) and equilibrium-model approach. The results nicely reproduce observations from STM imaging, work function change, and IR measurements. The agreement with experimental results is based on the formation of stable clusters already at very low surface coverage and temperature. Tetramers are predicted to be relatively stable compared to smaller and larger clusters. The dipole moment per water molecule continuously decreases from 2.2D for the monomer down to 1.1D for pentamer and larger clusters. Dimers are found to diffuse faster than monomers or larger clusters, with activation energy for diffusion of 2.9 kcal/mol, in agreement with recent STM measurements. A unique mechanism for dimers diffusion is proposed. Temperature programmed desorption (TPD) spectra from a metal surface were calculated by employing the MD scheme. These spectra were found identical to the standard Redhead line-shape analysis of the experimental TPD spectra of water from Pt(111) and Ru(001), an observation that was used to verify the consistency of the MD procedure. Finally, a kinetic model, fed by the MD calculated decreasing dipole moments per water molecule at larger clusters, explains well the highly nonlinear initial stages (up to 0.35BL) of the work function change data determined experimentally.