bluuebunny/crossref_metadata_2025 huggingface dataset:
Visible and near-infrared alternating-current electroluminescence from sputter-grown GaN thin films doped with Er
Authors: Kim Joo Han , Shepherd N. , Davidson M. R. , Holloway Paul H.
Published: November 2003

A demonstration of visible and near-infrared (NIR) alternating-current electroluminescence from sputter-grown GaN thin films doped with Er is reported. The alternating-current thin-film electroluminescent (ACTFEL) devices were constructed using a standard single-insulating structure, Al/GaN:Er/aluminum–titanium–oxide/indium–tin–oxide/Corning 7059 glass. Visible emissions peaked at 550 and 665 nm as well as NIR emissions centered at 1000 and 1550 nm were observed from the fabricated ACTFEL devices operating at room temperature. The visible and NIR emissions at 550, 665, 1000, and 1550 nm were attributed to the Er3+ 4f–4f intrashell transitions from the 4S3/2, 4F9/2, 4I11/2, and 4I13/2 excited-state levels to the 4I15/2 ground state, respectively. The green 550 nm emission had a larger dI/dV and a higher threshold voltage, Vth than the NIR 1550 nm emission, which could result from the need for higher electron impact energy to impact-excite the Er ion into the higher-energy excited-states for emission of green light.
Properties of chord length distributions of nonconvex bodies
Authors: Mazzolo Alain , Roesslinger Benoı̂t , Gille Wilfried
Published: November 2003

Cauchy’s formula which relates the mean chord length (isotropic uniform random chords) of a convex body in Rn with its volume and surface is extended to the case of nonconvex bodies in the framework of integral geometry. This allows us to generalize the extended Cauchy’s formula recently discovered by Blanco and Fournier [Europhys. Lett. 61 (2), 168 (2003)], in the field of diffusive random walks, to nonconvex bodies. Monte Carlo simulations illustrate these points in R2 and in R3.
Gauge symmetry of the N-body problem in the Hamilton–Jacobi approach
Authors: Efroimsky Michael , Goldreich Peter
Published: November 2003

In most books the Delaunay and Lagrange equations for the orbital elements are derived by the Hamilton–Jacobi method: one begins with the two-body Hamilton equations in spherical coordinates, performs a canonical transformation to the orbital elements, and obtains the Delaunay system. A standard trick is then used to generalize the approach to the N-body case. We reexamine this step and demonstrate that it contains an implicit condition which restricts the dynamics to a 9(N−1)-dimensional submanifold of the 12(N−1)-dimensional space spanned by the elements and their time derivatives. The tacit condition is equivalent to the constraint that Lagrange imposed “by hand” to remove the excessive freedom, when he was deriving his system of equations by variation of parameters. It is the condition of the orbital elements being osculating, i.e., of the instantaneous ellipse (or hyperbola) being always tangential to the physical velocity. Imposure of any supplementary condition different from the Lagrange constraint (but compatible with the equations of motion) is legitimate and will not alter the physical trajectory or velocity (though will alter the mathematical form of the planetary equations). This freedom of nomination of the supplementary constraint reveals a gauge-type internal symmetry instilled into the equations of celestial mechanics. Existence of this internal symmetry has consequences for the stability of numerical integrators. Another important aspect of this freedom is that any gauge different from that of Lagrange makes the Delaunay system noncanonical. In a more general setting, when the disturbance depends not only upon positions but also upon velocities, there is a “generalized Lagrange gauge” wherein the Delaunay system is symplectic. This special gauge renders orbital elements that are osculating in the phase space. It coincides with the regular Lagrange gauge when the perturbation is velocity independent.
Electron impact ionization of CHF2Cl: Unusual ordering of ionization energies for parent and fragment ions
Authors: Cicman P. , Gluch K. , Pelc A. , Sailer W. , Matt-Leubner S. , Scheier P. , Matejcik S. , Lukac P. , Robertson W. D. , Compton R. N. , Märk T. D.
Published: November 2003

Electron impact ionization of the chlorodifluoromethane molecule is studied using crossed beams of high-resolution electrons and an effusive molecular beam of CHF2Cl. Ionization energies (IEs) for many positive ions from CHF2Cl (CHF2Cl+,CF2Cl+,CHFCl+,CFCl+,CHF2+,CF2+,HCl+,Cl+,CF+,CH+,F+ C+) are determined from a careful examination of the threshold behavior of the ionization cross sections. Reaction pathways for the dissociative ionization products are suggested using known thermodynamic quantities. Surprisingly, it is observed that the ionization threshold for the parent positive ion IE(CHF2Cl+/CHF2Cl)=12.50(±0.05) eV lies above that for the fragment ions CHF2+, CHFCl+, and CF+ [IE(CHF2+/CHF2Cl)=12.24(±0.03) eV, IE(CHFCl+/CHF2Cl)=12.3(±0.05) eV, and IE(CF+/CHF2Cl)=11.5(±0.1) eV]. Experiments using a three sector field BEE mass spectrometer provide evidence for the existence of two states of the parent CHF2Cl+ ion, one exhibiting a short lifetime of about 2 μs and another parent ion state which appears to be stable on the time scale of the experiment (>20 μs) with an IE of 12.50 eV.
Marginal stability boundaries for infinite-n ballooning modes in a quasiaxisymmetric stellarator
Authors: Hudson S. R. , Hegna C. C.
Published: November 2003

A method for computing the ideal magnetohydrodynamic (MHD) stability boundaries in three-dimensional equilibria is employed. Following Hegna and Nakajima [Phys. Plasmas 5, 1336 (1998)], a two-dimensional family of equilibria is constructed by perturbing the pressure and rotational-transform profiles in the vicinity of a flux surface for a given stellarator equilibrium. The perturbations are constrained to preserve the MHD equilibrium condition. For each perturbed equilibrium, the infinite-n ballooning stability is calculated. Marginal stability diagrams are thus constructed that are analogous to (s,α) diagrams for axisymmetric configurations. A quasiaxisymmetric stellarator is considered. Calculations of stability boundaries generally show regions of instability can occur for either sign of the average magnetic shear. Additionally, regions of second-stability are present.
Model study of the influence of the magnetic field configuration on the performance and lifetime of a Hall thruster
Authors: Garrigues L. , Hagelaar G. J. M. , Bareilles J. , Boniface C. , Boeuf J. P.
Published: November 2003

A two-dimensional hybrid model of the discharge in Hall thrusters including the near outside region between cathode and exhaust plane has been developed. The topology of the applied magnetic field is calculated with a finite element software and used as input for the discharge code. In this paper, we examine the influence of the magnetic field topology on the thruster operation and properties, with emphasis on the thruster lifetime. Results show that a configuration with a zero magnetic field and a smaller region with large magnetic field tends to decrease wall erosion and low frequency current oscillations keeping a high level of performance.
First observation of density profile in directly laser-driven polystyrene targets for ablative Rayleigh–Taylor instability research
Authors: Fujioka Shinsuke , Shiraga Hiroyuki , Nishikino Masaharu , Shigemori Keisuke , Sunahara Atsushi , Nakai Mitsuo , Azechi Hiroshi , Nishihara Katsunobu , Yamanaka Tatsuhiko
Published: November 2003

The temporal evolution of the density profile of a directly laser-driven polystyrene target was observed for the first time using an x-ray penumbral imaging technique coupled with side-on x-ray backlighting at the GEKKO XII [C. Yamanaka et al., IEEE J. Quantum Electron. QE-17, 1639 (1981)]–High Intensity Plasma Experimental Research laser facility (IL=0.7×1014 W/cm2, λL=0.35 μm). This density measurement makes it possible to experimentally confirm all physical parameters [γ(k),k,g,ṁ,ρa,Lm] appearing in the modified Takabe formula for the growth rate of the ablative Rayleigh–Taylor instability. The measured density profiles were well reproduced by a one-dimensional hydrodynamic simulation code. The density measurement contributes toward fully understanding the ablative Rayleigh–Taylor instability.
Nonlinear slow shear Alfvén wave in electron–positron–ion plasmas
Authors: Mahmood S. , Saleem H.
Published: November 2003

Nonlinear solitary structures of an arbitrary amplitude slow shear Alfvén wave (SSAW) in ideal electron–positron–ion (e–p–i) plasmas are studied. It is found that the electron density dips of SSAW are formed in the super Alfvénic region. The amplitude and the width of the nonlinear shear Alfvén wave reduces with the increase in the concentration of positrons in electron–ion (e–i) plasmas. The width of the soliton also depends upon the direction of propagation of the perturbation in both e–i and e–p–i plasmas. The numerical results for several different cases have also been presented for illustrative purposes.
Cylindrical and spherical dust–ion acoustic shock waves
Authors: Xue Ju-Kui
Published: November 2003

The effect of the bounded nonplanar geometry on dust–ion acoustic shock wave (DIASW) in unmagnetized dusty plasmas is investigated for the first time. By using the standard reductive perturbation method, a cylindrical/spherical Korteweg–de Vries–Burgers (KdV–Burgers) equation is obtained. The change of the DIASW structure due to the effect of the geometry, dust density, and ion temperature is studied by numerical calculation of the cylindrical/spherical KdV–Burgers equation.
Inductive electronic load for testing of magnet power supplies in particle accelerators
Authors: Borage M. B. , Tiwari S. R. , Kotaiah S.
Published: November 2003

This article describes a simple and effective technique for adding inductive characteristics in a dissipative electronic load. Load resistance and inductance can be adjusted to desired value over a wide range. The additional feature offers flexible operation and eliminates the bulky and costly inductance for testing of power supplies as a dummy load. The proposed technique simulates the exponential current response to applied voltage step and attenuation of ripple in the load current. The energy storage and back electromotive force property of a physical inductor cannot be simulated. Experimental results confirm the inductive behavior of load.
Compensation of cross talk in the optical lever deflection method used in atomic force microscopy
Authors: Fujisawa Satoru , Ogiso Hisato
Published: November 2003

Most atomic force microscopes employ the optical lever deflection method using a quadrant photodetector as the displacement sensor of the cantilever, which enables it to detect lateral force (or friction force) as well as normal force. Misalignment between the cantilever direction and the photodetector direction causes cross talk between the lateral force signal and normal force signal. We analyze systematically the type of cross talk, and then propose a compensation method by using a two-dimensional rotary stage.
Superconductor and magnet levitation devices
Authors: Ma K. B. , Postrekhin Y. V. , Chu W. K.
Published: November 2003

This article reviews levitation devices using superconductors and magnets. Device concepts and their applications such as noncontact bearings, flywheels, and momentum wheels are discussed, following an exposition of the principles behind these devices. The basic magneto–mechanical phenomenon responsible for levitation in these devices is a result of flux pinning inherent in the interaction between a magnet and a type II superconductor, described and explained in this article by comparison with behavior expected of a perfect conductor or a nearly perfect conductor. The perfect conductor model is used to illustrate why there is a difference between the forces observed when the superconductor is cooled after or before the magnet is brought into position. The same model also establishes the principle that a resisting force or torque arises only in response to those motions of the magnet that changes the magnet field at the superconductor. A corollary of the converse, that no drag torque appears when an axisymmetric magnet levitated above a superconductor rotates, is the guiding concept in the design of superconductor magnet levitation bearings, which is the common component in a majority of levitation devices. The perfect conductor model is extended to a nearly perfect conductor to provide a qualitative understanding of the dissipative aspects such as creep and hysteresis in the interaction between magnets and superconductors. What all these entail in terms of forces, torques, and power loss is expounded further in the context of generic cases of a cylindrical permanent magnet levitated above a superconductor and a superconductor rotating in a transverse magnetic field. Then we proceed to compare the pros and cons of levitation bearings based on the first arrangement with conventional mechanical bearings and active magnetic bearings, and discuss how the weak points of the levitation bearing may be partially overcome. In the latter half, we examine designs of devices using superconductor magnet levitation, focusing more on issues specific to the application. We note that applications of superconductor magnet levitation devices tend to be most attractive in situations where energy conservation is critical. The most advanced in development are flywheel kinetic energy storage systems incorporating superconductor magnet bearings. Variations in the designs to enhance the performance in some specific regards are examined case by case. Next we present a reaction wheel for attitude control on small satellites, similar in overall design to the flywheel kinetic energy storage systems, but with subtle differences in details of emphasis, due to the difference in purpose and environment. Finally, we take a brief look at the case of vibration isolation devices as an example of a rectilinear modification of the more familiar rotational bearing applications.
Original superconducting quantum interference device (SQUID) design and measurement technique for flux noise source localization in SQUID systems
Authors: Sing M. Lam Chok , Flament S. , Ridereau X. , Gunther C. , Méchin L. , Bloyet D.
Published: November 2003

We present an original method for studying the low frequency flux noise due to vortices in superconducting quantum interference device (SQUID) systems. We use two SQUIDs connected to the same washer in order to study the correlation of their outputs. A dedicated electronic system has been built so as to operate both SQUIDs at the same time. It was thus possible to distinguish fluctuations due to vortices located in the film far from the SQUID from fluctuations originating from vortices located close to the SQUID itself. In this article, the experimental setup is described and some preliminary noise measurements are presented.
Yang–Mills connections over manifolds with Grassmann structure
Authors: Alekseevsky Dmitri V. , Cortés Vicente , Devchand Chandrashekar
Published: November 2003

Let M be a manifold with Grassmann structure, i.e., with an isomorphism of the cotangent bundle T*M≅E⊗H with the tensor product of two vector bundles E and H. We define the notion of a half-flat connection ∇W in a vector bundle W→M as a connection whose curvature F∈S2E⊗Λ2H⊗End W ⊂ Λ2T*M⊗End W. Under appropriate assumptions, for example, when the Grassmann structure is associated with a quaternionic Kähler structure on M, half-flatness implies the Yang–Mills equations. Inspired by the harmonic space approach, we develop a local construction of (holomorphic) half-flat connections ∇W over a complex manifold with (holomorphic) Grassmann structure equipped with a suitable linear connection. Any such connection ∇W can be obtained from a prepotential by solving a system of linear first order ODEs. The construction can be applied, for instance, to the complexification of hyper-Kähler manifolds or more generally to hyper-Kähler manifolds with admissible torsion and to their higher-spin analogs. It yields solutions of the Yang–Mills equations.
A new loop algebra and a corresponding integrable hierarchy, as well as its integrable coupling
Authors: Guo Fukui , Zhang Yufeng
Published: November 2003

A type of new interesting loop algebra G̃M (M=1,2,…) with a simple commutation operation just like that in the loop algebra Ã1 is constructed. With the help of the loop algebra G̃M, a new multicomponent integrable system, M-AKNS-KN hierarchy, is worked out. As reduction cases, the M-AKNS hierarchy and M-KN hierarchy are engendered, respectively. In addition, the system 1-AKNS-KN, which is a reduced case of the M-AKNS-KN hierarchy above, is a unified expressing integrable model of the AKNS hierarchy and the KN hierarchy. Obviously, the M-AKNS-KN hierarchy is again a united expressing integrable model of the multicomponent AKNS hierarchy (M-AKNS) and the multicomponent KN hierarchy(M-KN). This article provides a simple method for obtaining multicomponent integrable hierarchies of soliton equations. Finally, we work out an integrable coupling of the M-AKNS-KN hierarchy.
Investigation of the projectile ion velocity inside the interaction media by the x-ray spectromicroscopy method
Authors: Rosmej O. N. , Pikuz S. A. , Wieser J. , Blazevic A. , Brambrink E. , Roth M. , Efremov V. P. , Faenov A. Ya. , Pikuz T. A. , Skobelev I. Yu. , Hoffmann D. H. H.
Published: November 2003

A method for space resolved measurements of the fast heavy ion velocity during the interaction with matter are presented. The main idea is based upon the fact that the characteristic radiation from ions traveling in the stopping media undergoes the Doppler shift, which varies along the ion beam trajectory due to the ion deceleration. High spectrally (λ/Δλ=1000–3000) and spatially (up to 30–100 μm) resolved x-ray K-shell spectra of Ca projectile ions as well as of the ionized stopping media have been obtained using focusing spectrometers with spatial resolution (FSSR). Spherically bent crystals of quartz and mica with small curvature radii R=150 mm and large apertures (15×50 mm) have been used as dispersive elements. Fast Ca+6 ions with energies of 5.9 and 11.4 MeV/u were stopped in quartz, SiO2 aerogels and CaF2 targets. High spectral and spatial resolution of the spectra allowed measuring the velocity of heavy projectile ions at different points along the beam trajectory. A method based on the utilization of two equal spectrometers at different angles of observation (along and downstream the ion beam propagation direction) is proposed to measure the absolute values of ion velocity inside the stopping media. The use of aerogel targets with extremely low volume density (0.15 g/cc) increases the ion stopping range up to 50 times in comparison to solid quartz. This provides the resolution of the stopping process dynamics. Experimentally it was found that Ca+6 ions with the initial energies of 5.9 or 11.4 MeV/u propagate in solid dense matter as Ca+17–Ca+19 down to the energies of 2.0–2.2 MeV/u.
Scanning vector Hall probe microscope
Authors: Fedor J. , Cambel V. , Gregušová D. , Hanzelka P. , Dérer J. , Volko J.
Published: November 2003

We present a scanning vector Hall probe microscope for imaging the entire magnetic field vector in close proximity to magnetic and superconducting samples. The microscope combines a large scanned area and a high space resolution of the magnetic field vector measured. A special feature of the equipment is a vacuum-tight sample space connected with a moving system via a flexible metal bellows. The microscope is based on a vector Hall sensor that consists of three separate Hall probes of an active area 5×5 μm2, patterned on three sides of a GaAs pyramid. The top of the pyramid serves as a tunneling contact and helps to control the sensor–sample separation. The sensor and the sample are placed in a helium cryostat with a temperature control in the range 10–300 K. The sensor scans an area up to 5×5 mm2 in the whole temperature interval with a spatial resolution ∼5 μm.
Luminescence spectroscopy of P13 and P3 state atomic mercury isolated in solid Ar, Kr, and Xe
Authors: Collier Martin A. , McCaffrey John G.
Published: November 2003

Multicomponent emission bands are recorded for the P13→S01 transition of atomic mercury isolated at single sites in solid Ar, Kr, and Xe matrices. A blueshift observed at elevated temperatures on the 273 nm emission of Hg/Xe is identified in line shape analysis as arising from decreasing intensity of the central component in the band profile. The origin of the multiple components in the emission bands is ascribed to the existence of several vibronic modes which lead to excited state stabilization in the Hg(3P1)/RG matrix systems. A detailed description of these modes and their energetics is presented in the paper directly following. Photoexcitation of the P13 state also yields small amounts of P03 state emission. Hg atom P13 to P03 state intramultiplet relaxation (IMR) is most efficient in Hg/Xe where the ratio of this relaxation channel to P13 state radiative decay is 1/200 as established in time-integrated emission spectra. Despite the weakness of IMR, pulsed laser excitation combined with photon counting detection provide time-gated P03 state emission spectra largely free of the more intense P13 state emission. Such emission spectra recorded under high resolution for the P03→S01 transition of atomic mercury isolated in solid Xe provide the first example of the occurrence of a zero-phonon lines for a metal atom isolated in a rare gas matrix. Wp line shape analysis conducted on the emission bands recorded at specific temperatures, confirm this assignment. The electron–phonon coupling strength (Huang-Rhys, S factor) extracted in the line shape fits for the Hg/Xe transition is 1.3. Slightly stronger coupling is identified in Kr (S=2.2) and stronger still in Ar (S=3.3). Analysis of the diatomic Hg⋅RG potential energy curves reveal that the origin of the weak electron–phonon coupling lies primarily in the similarity in the ground and excited states, but also indicates the site size offered by the host solid plays a role.
A pair-potentials analysis of the emission spectroscopy of P13 state atomic mercury isolated in solid Ar, Kr, and Xe
Authors: Collier Martin A. , McCaffrey John G.
Published: November 2003

Pair-potentials calculations of the P13↔S01 absorption and emission energies of atomic mercury isolated in solid Ar, Kr, and Xe are conducted and compared with the spectral bands recorded in Hg/RG matrices. The Hg⋅RG pair potentials used are derived from spectroscopic studies of the mercury atom–rare gas atom diatomics and are implemented in a localized Hg⋅RG18 cluster model to simulate the spectroscopy of Hg atoms isolated in substitutional sites of the solid rare gases. The calculated absorptions are all on the red wing of the observed matrix bands and from these favorable comparisons, substitutional site occupancy is identified for ground state atomic mercury. A pairwise sum of the Hg(3P1)⋅RG [A 30+(3Π)] and [B 31] state potentials is used to examine the vibronic modes of the excited P13 state Hg⋅RG18 clusters which lead to stabilization. The energetics of waist and body vibronic modes, involving motion of the lattice atoms with respect to the excited state mercury atom and motion of this atom in the solid, respectively, were calculated for the three symmetry poles of the cubo-octahedral substitutional sites. Excited state stabilization was found for the waist mode of all the Hg/RG systems in the three possible coordinate systems, i.e., based on the fourfold, threefold, and twofold symmetry systems. In contrast, the body modes were stabilized only in Hg/Xe. The difference between Hg/Xe and the other Hg/RG systems is related to the larger substitutional site size presented by the former system. The three components identified in the recorded emission bands are correlated with the existence of several vibronic modes leading to stabilization. Emission energies calculated for the three stabilized vibronic modes in Ar are centered on the observed emission but exhibit a larger splitting. In Kr they are red of the observed band maximum but occur within the observed band. A curve crossing mechanism is identified which can explain the lack of emission for the strongly stabilized, fourfold symmetry modes in Hg/Xe.
Theory of electron transfer in the presence of dissipation
Authors: Zhang Ming-Liang , Zhang Shesheng , Pollak Eli
Published: November 2003

An analytic study of the density matrix and Wigner representation equations for dissipative electron transfer is presented. An explicit expression is derived for the off-diagonal Green’s function, which shows a very fast relaxation in time if the barrier to reaction is greater than the thermal energy. This fast relaxation invalidates previous attempts to derive coupled equations for the density in the large friction limit. The fast off-diagonal relaxation disallows an adiabatic elimination of the momentum even in the large friction limit. We then show, with the aid of the boundary layer method, how one can use the same analysis to derive a set of two coupled equations for the diagonal densities. These equations are a generalization to phase space of the large friction Zusman equations [Chem. Phys. 49, 295 (1980)]. Adiabatic elimination of the momentum from these generalized Zusman equations is correct in the large friction limit and naturally leads back to the Zusman equations. Numerical solution of the generalized Zusman equations is presented for symmetric electron transfer for weak and strong electronic coupling, moderate and high barriers, and a large range of damping. The numerical results provide new insight into the friction dependence of the rate in the weak damping regime and show that previous analytic expressions for the rate are only qualitative in nature.
Plasma flow and confinement in the vicinity of a rotating island in tokamaks
Authors: Shaing K. C.
Published: November 2003

The theory for the electric field and the plasma confinement in the vicinity of a magnetic island in tokamaks [Phys. Plasmas 9, 3470 (2002)] is extended to the situation where the magnetic island is rotating. The electric field that is parallel to the magnetic field, E∥, is assumed to vanish. With this assumption, the theory for a nonrotating island is applicable to a rotating island if the radial electric field in the nonrotating theory is replaced by the radial gradient of ℱ. Here, ℱ is the part of the electrostatic potential that is constant on the rotating island magnetic surface. As an application of the theory, the radial electric field, toroidal flow speed, ambipolar particle flux, heat flux, and island rotation frequency in the collisionless regime are also presented.
Enhancement of room-temperature photoluminescence in InAs quantum dots
Authors: Lu W. , Ji Y. L. , Chen G. B. , Tang N. Y. , Chen X. S. , Shen S. C. , Zhao Q. X. , Willander M.
Published: November 2003

We report pronounced enhancement of room-temperature photoluminescence up to 80-fold induced by proton implantation and the rapid thermal annealing process in a multilayer InAs/GaAs quantum-dot structure. This effect is studied by a combination of material methods and resulted from both proton passivation and carrier capture enhancement effects. The maximum photoluminescence peak shift is about 23 meV, resulting from the intermixing of quantum dots. Linear dependence behavior as observed for both the nonradiative recombination time and carrier relaxation time on the ion-implantation dose. Maximum enhancement of the photoluminescence is observed for a proton implantation dose of 1.0×1014 cm−2 followed by rapid thermal annealing at 700 °C. These effects will be useful for quantum dot optoelectronic devices.
Hilbert space structure in classical mechanics. I
Authors: Deotto E. , Gozzi E. , Mauro D.
Published: November 2003

In this paper we study the Hilbert space structure underlying the Koopman–von Neumann (KvN) operatorial formulation of classical mechanics. KvN limited themselves to study the Hilbert space of zero-forms that are the square integrable functions on phase space. They proved that in this Hilbert space the evolution is unitary for every system. In this paper we extend the KvN Hilbert space to higher forms which are basically functions of the phase space points and the differentials on phase space. We prove that if we equip this space with a positive definite scalar product the evolution can turn out to be nonunitary for some systems. Vice versa, if we insist in having a unitary evolution for every system then the scalar product cannot be positive definite. Identifying the one-forms with the Jacobi fields we provide a physical explanation of these phenomena. We also prove that the unitary/nonunitary character of the evolution is invariant under canonical transformations.
Elusive electron affinity of ClF
Authors: Horný Ľuboš , Sattelmeyer Kurt W. , Schaefer Henry F.
Published: November 2003

Highly correlated methods were used to obtain the optimized bond lengths and vibrational frequencies of ClF and ClF−. With convergent quantum mechanical methods, the anion is much more difficult to treat than neutral ClF. Adiabatic electron affinities (EAad), vertical electron affinities, and vertical detachment energies have been evaluated and compared to the controversial experimental values reported in the literature. Our best prediction for the zero-point vibrationally corrected EAad is 2.25±0.1 eV.
On the feasibility of chemi-ion formation in the system CH2CH(ã 4A″)+O(3P)
Authors: Metropoulos Aristophanes
Published: November 2003

We have investigated theoretically the possibility that the CH2CH(ã 4A″) radical can generate the CH2CHO+(X 1A′) ion upon collisions with O(3P). We have concluded that this is very unlikely because the minimum of the ground-state potential-energy surface of the ion is at about the same level as the potential energy of the asymptotic CH2CH(ã 4A″)+O(3P) fragments. In addition the Franck–Condon factors should not be favorable because of a drastic change in the geometry of the ion.
Electron spin relaxation due to small-angle motion: Theory for the canonical orientations and application to hierarchic cage dynamics in ionomers
Authors: Leporini D. , Schädler V. , Wiesner U. , Spiess H. W. , Jeschke G.
Published: November 2003

Analytical expressions for transverse electron spin relaxation induced by small angle motion were derived for the first time within an anisotropic model for rotational diffusion by using an approximation of the spin Hamiltonian and its variation during reorientation that is valid close to the canonical orientations. The dependence of the decay of the stimulated echo on such motion was studied by extensive Monte Carlo simulations and regimes were identified in which the time constant of this decay is related to parameters of the anisotropic diffusion model by simple equations. For testing these theoretical findings and obtaining insight into hierarchical cage dynamics in soft matter, high-field electron paramagnetic resonance (EPR) measurements were performed at a frequency of 94 GHz where the canonical orientations for nitroxide spin labels are well resolved. A combination of continuous wave EPR, saturation recovery measurements, and measurements of the decay of primary and stimulated electron spin echoes was employed to cover time scales from a few picoseconds up to several microseconds. Ionic spin probes attached by electrostatic interactions to the surface of ionic clusters in ionomers were used as a model system in which slow cage reorientation can be studied in the glass transition region of the polymer (0.64<T/Tg<1.05). Three hierarchical reorientation processes of the spin probe were observed on different time scales. The spin probe undergoes fast intramolecular libration on the time scale of a few picoseconds, it experiences a local rearrangement of the cage on the time scale of hundreds of nanoseconds and it performs cooperative reorientation coupled to the structural relaxation of the glassy matrix over time scales comparable to or longer than several microseconds in the glass transition region.
Absolute yields of CO(a′ 3Σ+, d 3Δi,e 3Σ−)+O from the dissociative recombination of CO2+ ions with electrons
Authors: Rosati Richard E. , Johnsen Rainer , Golde Michael F.
Published: November 2003

The flowing afterglow technique has been applied to the dissociative recombination CO2++e−→CO*+O, in order to determine the radiative cascade contribution from high-energy triplet states of CO, (a′ 3Σ+), (d 3Δi), and (e 3Σ−), to the total yield of the long-lived (a 3Π) state. The yields of the a′, d, e states were found to be approximately 18%, 20%, and 0.3%, respectively, of the total CO(a) yield, which leads us to conclude that (38±8)% of the total CO(a) yield is due to radiative cascading, rather than direct formation. When combined with our previously reported total CO(a) yield of 0.29±0.10, the absolute yields of the triplet states become f(a′)=0.053±0.024, f(d)=0.057±0.022, and f(e)∼9×10−4.
Stimulated Raman adiabatic passage in the presence of dephasing
Authors: Shi Qiang , Geva Eitan
Published: November 2003

The prospect of employing the stimulated Raman adiabatic Passage (STIRAP) technique under the influence of pure dephasing is explored. A general analysis of how decoherence influences the performance of STIRAP is provided. Starting from a general and fully quantum-mechanical system–bath Hamiltonian, we derive a quantum master equation (QME) that describes the reduced dynamics of a dissipative STIRAP system. The derivation is based on the standard assumptions of (1) weak system–bath coupling; (2) Markovity, in the sense that the relaxation times are long in comparison to the bath correlation time, τc; and (3) weak field–matter interaction, in the sense that the Rabi period of the driving laser fields, Ω−1, is longer than τc. The dissipative term in this QME is the same as it would have been in the absence of the driving fields, because of the assumption of weak field–matter interaction. This type of uncontrollable dephasing is seen to diminish the efficiency of STIRAP, although the actual loss strongly depends on the specific dephasing mechanism. We also derive a more general QME, which is applicable to driving fields of arbitrary intensity. The dissipative term in the new QME is explicitly dependent on the driving fields, and therefore controllable. Intense fields are shown to effectively slow down the dephasing when Ωτc>1, which suggests that it may be possible to use STIRAP in order to transfer population between the quantum states of a solute molecule embedded in a solvent.
Photon emission from driven single molecules
Authors: Zheng Yujun , Brown Frank L. H.
Published: November 2003

The detection of photons emitted from a single molecule under the influence of electromagnetic radiation is considered. Utilizing a generating function formalism, we derive several exact results for the statistics of such emitted photons within the framework of the temporally modulated optical Bloch equations. Additionally, it is shown how these results reduce to previously obtained limiting behaviors. An appealing feature of this formulation is the inclusion of both photon bunching and anti-bunching effects within a single theoretical framework that is well suited for numerical analysis. Several examples are considered to demonstrate the feasibility of the approach in calculations. In most cases, these results verify known phenomena. In one case, we report a result that was missed by prior approximate treatments. This new effect centers around the fact that a chromophore will display anti-bunching behavior in the limit of fast modulation of the resonant absorption frequency.
On intervector angle descriptions and their numerical implementation for solving molecular problems
Authors: Mladenović Mirjana
Published: November 2003

The angular parametrization comprising only bending angles is considered in detail. For tetratomic and pentatomic molecules, we first study the volume element, coordinate ranges, and parity-adapted basis functions. In contrast to the common belief, we show that the intervector angle description allows to uniquely specify the internal molecular geometry and to model tunneling through planarity. The redundant intervector angle and coordinate interdependences are explained by simple geometrical means. Principal difficulties arising from the interdependent coordinate ranges obstruct the numerical implementation of the description studied, since the angular basis functions are nonorthogonal and the overlap matrix may easily become ill-conditioned. For the symmetry-adapted representation, the origin of multiple solutions for the redundant coordinate is discussed. We additionally show that the redundant coordinate plays an important role by the characterization of the internal molecular geometry of pentatomic molecules described in terms of the cosines of the intervector angles.
Drift-ordered fluid equations for field-aligned modes in low-β collisional plasma with equilibrium pressure pedestals
Authors: Simakov Andrei N. , Catto Peter J.
Published: November 2003

Starting from the complete short mean-free path fluid equations describing magnetized plasmas, assuming that plasma pressure is small compared to magnetic pressure, considering field-aligned plasma fluctuations, and adopting an ordering in which the plasma species flow velocities are much smaller than the ion thermal speed, a system of nonlinear equations for plasma density, electron and ion temperatures, parallel ion flow velocity, parallel current, electrostatic potential, perturbed parallel electromagnetic potential, and a perturbed magnetic field is derived. The equations obtained allow sharp equilibrium radial gradients of plasma quantities, and are shown to contain the neoclassical (Pfirsch–Schlüter) results for plasma current, parallel ion flow velocity (with the correct temperature gradient terms), and parallel gradients of equilibrium electron and ion temperatures. Special care is taken to ensure the divergence-free character of perturbed magnetic field and total plasma current, as well as local particle number and total energy conservation.
Optimal lookup table construction for charge division with respect to efficiency flatness
Authors: Van Esch P. , Millier F.
Published: November 2003

Static lookup tables, as often used in the position calculation electronics in position sensitive detectors, suffer from the well-known problem that the propagation of digitization errors in the division leads to unequal efficiencies for the different output channels. In this article, we present a solution to the construction of such a lookup table which is optimal in the sense that the least possible efficiency errors are committed in the class of monotone lookup tables. The obtained resolution is comparable to what is obtained using the standard implementation of the fixed point division. After a theoretical explanation, we present some experimental results confirming our claim.
Entropy growth of shift-invariant states on a quantum spin chain
Authors: Fannes M. , Haegeman B. , Mosonyi M.
Published: November 2003

We study the entropy of pure shift-invariant states on a quantum spin chain. Unlike the classical case, the local restrictions to intervals of length N are typically mixed and have therefore a nonzero entropy SN which is, moreover, monotonically increasing in N. We are interested in the asymptotics of the total entropy. We investigate in detail a class of states derived from quasi-free states on a CAR algebra. These are characterized by a measurable subset of the unit interval. As the entropy density is known to vanish, SN is sublinear in N. For states corresponding to unions of finitely many intervals, SN is shown to grow slower than log2 N. Numerical calculations suggest a log N behavior. For the case with infinitely many intervals, we present a class of states for which the entropy SN increases as Nα where α can take any value in (0,1).
Universes encircling five-dimensional black holes
Authors: Seahra Sanjeev S. , Wesson Paul S.
Published: November 2003

We clarify the status of two known solutions to the five-dimensional vacuum Einstein field equations derived by Liu, Mashhoon, and Wesson (LMW) and Fukui, Seahra, and Wesson (FSW), respectively. Both 5-metrics explicitly embed four-dimensional Friedman–Lemaı̂tre–Robertson–Walker cosmologies with a wide range of characteristics. We show that both metrics are also equivalent to five-dimensional topological black hole (TBH) solutions, which is demonstrated by finding explicit coordinate transformations from the TBH to LMW and FSW line elements. We argue that the equivalence is a direct consequence of Birkhoff’s theorem generalized to five dimensions. Finally, for a special choice of parameters we plot constant coordinate surfaces of the LMW patch in a Penrose–Carter diagram. This shows that the LMW coordinates are regular across the black and/or white hole horizons.
Cross-calibrating spatial positions of light-viewing diagnostics using plasma edge sweeps in DIII-D
Authors: Solomon W. M. , Burrell K. H. , Gohil P. , Groebner R. , Kaplan D.
Published: November 2003

An experimental technique is presented that permits diagnostics viewing light from the plasma edge to be spatially calibrated relative to one another. By sweeping the plasma edge, each chord of each diagnostic sweeps out a portion of the light emission profile. A nonlinear least-squares fit to such data provides superior cross-calibration of diagnostics located at different toroidal locations compared with simple surveying. Another advantage of the technique is that it can be used to monitor the position of viewing chords during an experimental campaign to ensure that alignment does not change over time. Moverover, should such a change occur, the data can still be cross-calibrated and its usefulness retained.
Fabrication of quasi-two-dimensional, heterogeneously curved Belousov–Zhabotinsky systems
Authors: Manz N. , Müller S. C.
Published: November 2003

For many years the Belousov–Zhabotinsky reaction has been used to explore the large variety of dynamical behavior of excitation waves. The understanding of chemical waves can be applied to other physical and biological systems. Most theoretical and experimental work has been done in planar media, whereas for nonplanar systems there exist many theoretical but only very few experimental studies. In this article we present a methodology to develop quasi-two-dimensional, nonhomogeneously curved reaction media. These systems can be used to perform experiments on chemical reaction-diffusion processes which occur, for instance, in the Belousov–Zhabotinsky reaction placed in nonplanar geometries.
Infrared camera diagnostic for heat flux measurements on the National Spherical Torus Experiment
Authors: Mastrovito D. , Maingi R. , Kugel H. W. , Roquemore A. L.
Published: November 2003

An infrared imaging system has been installed on the National Spherical Torus Experiment at Princeton Plasma Physics Laboratory to measure the surface temperatures on the lower divertor and center stack. The imaging system is based on an Indigo Alpha 160×128 microbolometer camera with 12 bits/pixel operating in the 7–13 μm range with a 30 Hz frame rate and a dynamic temperature range of 0–700 °C. From these data and knowledge of graphite thermal properties, the heat flux is derived with a classic one-dimensional conduction model. Preliminary results of heat flux scaling are reported.
Self-normalized photothermal technique for accurate thermal diffusivity measurements in thin metal layers
Authors: Balderas-López J. A. , Mandelis A.
Published: November 2003

A self-normalized photothermal method for measuring thermal diffusivity of thin metal layers has been implemented using two experimental configurations based on photothermal radiometry and gas-cell photoacoustic detection. The corresponding measurement procedures involve linear fits in the photothermally thin and/or thick limits. As part of this method, simple experimental criteria have been developed to ascertain that a purely thermal-diffusion-wave mechanism is dominant throughout the selected frequency range, thus validating the accuracy of the thermal diffusivity measurements. Thermal-diffusivity values measured using the intrinsic reliability of this self-normalized photothermal measurement scheme are reported for two commercial samples of aluminum and steel thin layers.
Magnetic force and optical force sensing with ultrathin silicon resonator
Authors: Ono Takahito , Esashi Masayoshi
Published: November 2003

In this article, we demonstrated magnetic and optical force measurements using an ultrathin silicon cantilever down to 20 nm or 50 nm in thickness. The cantilever was heated in an ultrahigh vacuum for enhancing the Q factor and a magnetic particle was mounted at the end of the cantilever using a manipulator. The vibration was measured by a laser Doppler vibrometer and its signal was fed to an opposed metal electrode for electrostatic self-oscillation. An application of a magnetic field with a coil exerted a force to the magnetic material, which results in the change of the resonant frequency. However, the change in the mechanical properties of the cantilever, due to mechanical instability and temperature variation, drifts the resonance peak. Force balancing between the magnetic force and an electrostatic force in the opposite phase can minimize the vibration amplitude. From the electrostatic force at the minimum point, the exerted force can be estimated. A magnetic moment of 4×10−20 J/T was measured by this method. The same technique was also applied to measure the optical force of ∼10−17 N, impinging on the cantilever by a laser diode.
Comparison of force balance calibration techniques for the nano-Newton range
Authors: Selden Nathaniel P. , Ketsdever Andrew D.
Published: November 2003

With the rapid progress of micro- and nanoscale fabrication technology, devices are continually being created which produce extremely small forces. This creates a distinct need for a measurement instrument and adequate calibration techniques which can resolve forces below 1 μN. Two calibration methods for force balance measurements in the nano-Newton range are presented. These methods are based on a free molecule gas dynamic expansion through a thin-walled orifice and the electrostatic actuation of a miniature comb drive. Due to the advantages and disadvantages of every calibration technique, multiple techniques are often required to validate performance results for microscale devices. Because these calibration techniques typically rely on completely different physical processes and can be described by different sets of analytical equations, the comparison of one technique to another is necessary when high accuracy is required. The gas dynamic and electrostatic force calibration techniques have been compared and were found to agree to within 8% for force levels between 35 nano-Newtons and 1 μN.
Unique approach to measuring temperature variation of surface tension in smectic liquid crystals
Authors: Veum M. , Messman P. , Liu Z. Q. , Huang C. C. , Janarthanan N. , Hsu C. S.
Published: November 2003

We have measured the temperature variation of surface tension, σ, in freestanding films of three liquid-crystal compounds. To do so, we have constructed a curvature-pressure tensiometer that uses a feedback loop to hold constant the curvature of a film while the temperature of the system is smoothly ramped. The apparatus enables us to obtain the temperature variation of σ in a continuous manner with resolution in σ of ∼0.2%. We interpret reproducible features of our data in terms of phase transitions.