bluuebunny/crossref_metadata_2025 huggingface dataset:
Physical modeling of filament light sources
Authors: Fu Ling , Leutz Ralf , Ries Harald
Published: November 2006

Virtual prototyping of illumination optical systems based on ray tracing needs accurate and detailed models of utilized light sources. We present a physical model based on Planck’s radiation law and Kirchhoff’s law of thermal radiation and apply it to filament lamps. The advantage of our approach is that it generally needs a few parameters and, in addition, is capable of correctly modeling light recycling. The model based on thermodynamics, geometry, material, and electrical properties is widely applicable for any kind of filament lamp. In particular, emission, absorption, and light recycling properties are taken into consideration. The model starts by calculating the one-dimensional temperature distribution in the filament by solving the time dependent heat transfer equation. From this it creates the five-dimensional radiance distribution based on Planck’s law and the emissivity of the filament. Light recycling due to the coiled filament is a significant effect in this type of lamp. The model is validated with high resolution absolute radiance measurements. The model can easily be integrated into a ray-tracing software.
A rigorous full-dimensional quantum dynamics calculation of the vibrational energies of H3O2−
Authors: Yu Hua-Gen
Published: November 2006

The vibrational energy levels of the H3O2− anion have been calculated using a rigorous quantum dynamics method based on an accurate ab initio potential energy surface. The eigenvalue problem is solved using the two-layer Lanczos iterative diagonalization algorithm in a mixed grid/nondirect product basis set, where the system Hamiltonian is expressed in a set of orthogonal polyspherical coordinates. The lowest 312 vibrational energy levels in each inversion symmetry, together with a comparison of fundamental frequencies with previous quantum dynamics calculations, are reported. Finally, a statistical analysis of nearest level spacing distribution is carried out, revealing a strongly chaotic nature.
Scanning tunneling microscopy study of Pd growth on Ge(001)
Authors: Wang J. , Li M. , Altman E. I.
Published: December 2006

The interaction of Pd with the Ge(001) surface was studied as a function of Pd coverage and temperature using scanning tunneling microscopy. At 300K, initial Pd adsorption displaces Ge from the surface which then combines with additional Pd to form tetramers. At least some of the Pd moves subsurface inducing dimer vacancy complexes. As the temperature was increased, Pd–Ge alloy phases were observed on the surface. At 475K, these formed small three-dimensional clusters that were seen together with two-dimensional Ge islands created from Ge ejected from the surrounding vacancy rich terraces. When several Pd monolayers were deposited at 675K, larger faceted clusters were observed on the surface. High-resolution images revealed a hexagonal structure on the facets with the periodicity of a (3×3)R30° reconstruction of Pd2Ge(0001). This reconstruction was assigned to Pd adtrimers that make the Pd2Ge(0001) surface stoichiometric. At higher temperatures most of the Pd tended to move subsurface. After depositing 100 ML Pd at 300K and annealing to 1030K, however, very large three-dimensional clusters were observed. Atomic resolution images of the surfaces of these clusters revealed a nearly rectangular surface unit cell consistent with a (121−2) reconstruction of the PdGe(110) surface. Unlike recent results for Au and Pt on Ge(001), under no conditions were ordered metallic chains observed. The results were more similar to Ag on Ge(001) where three-dimensional cluster formation was also favored. The results reinforce recent suggestions that relativistic effects in the electronic structure of the 5d metals make them behave more like each other in low coordination than the corresponding 4d metals.
Plasma filling in reduced-scale hohlraums irradiated with multiple beam cones
Authors: Schneider M. B. , Hinkel D. E. , Landen O. L. , Froula D. H. , Heeter R. F. , Langdon A. B. , May M. J. , McDonald J. , Ross J. S. , Singh M. S. , Suter L. J. , Widmann K. , Young B. K. , Baldis H. A. , Constantin C. , Bahr R. , Glebov V. Yu. , Seka W. , Stoeckl C.
Published: November 2006

The radiation temperature achieved inside a hohlraum, a high-Z cylindrical cavity heated by high-power lasers, is limited by plasma filling of ablated wall material. Recent work [Dewald et al., Phys. Rev. Lett. 95, 215004 (2005)] tested radiation temperature limits in a simple on-axis laser-hohlraum geometry and validated an analytic plasma-fill model. The experiments reported here use several cones of beams to heat a 600μm diameter hohlraum. Thin-walled images show the time evolution: plasma stagnation followed by plasma filling of the hohlraum cavity. Features in the Raman backscatter spectra are correlated to the thin-walled images to measure a fill time. The quantity of hard x rays produced by hot electrons is proportional to the time left in the laser pulse after the fill time. Simulations using the radiation-hydrodynamic code LASNEX and the analytic plasma-fill model predict plasma filling consistent with the data. LASNEX predicts a much higher electron temperature than the analytic model.
Dielectric water sorption analysis
Authors: Giacomelli Penon M. , Picken S. J. , Wübbenhorst M. , de Vos G. , van Turnhout J.
Published: November 2006

The sorption of water vapor in Kapton® (polyimide) films has been investigated with a new method, dielectric sorption analysis (DSA). The technique is based on high-resolution time-resolved capacitance measurements performed during exposure of an organic coating to humidified nitrogen. The basis of the method is described together with experimental details related to the capacitance measurement, long-term stability, reproducibility, and other characteristics of the setup. The technique allows the determination of the sorption/desorption and diffusion characteristics of a coating on a time scale varying from seconds to days. Mass transport properties derived from complementary weight measurements are in good agreement with the DSA results. Real-time monitoring of the moisture sorption in organic coatings demonstrates the potential of the technique in the field of nondestructive coating inspection and testing.
Joint experimental and theoretical investigations of the reactivity of Au2On− and Au3On− (n=1–5) with carbon monoxide
Authors: Kimble Michele L. , Moore Nelly A. , Johnson Grant E. , Castleman A. W. , Bürgel Christian , Mitrić Roland , Bonačić-Koutecký Vlasta
Published: November 2006

The interactions between small gold oxide cluster anions, Au2,3On− (n=1–5), and CO were investigated in a fast-flow reactor mass spectrometer, and experimental results were verified with a guided ion beam mass spectrometer. Density functional calculations along with molecular dynamics simulations were also utilized to explain the experimental findings. From these studies, we show that, for the interactions between AumOn− and CO, each atom counts. With the addition of a single gold atom, it is observed that association of CO and replacement of O2 by CO become the dominant reaction channels as opposed to CO oxidation. We also present results that show that the oxidation of CO takes place only in the presence of a peripheral oxygen atom. However, this condition is not always sufficient. Furthermore, the association of CO onto AumOn− follows a general qualitative rule based on the relationship between the energy of the cluster lowest unoccupied molecular orbital and the binding energy of CO.
Submicrosecond dynamics of water explosive boiling and lift-off from laser-heated silicon surfaces
Authors: Kudryashov S. I. , Allen S. D.
Published: November 2006

Explosive boiling and lift-off of a thin layer of micron-sized transparent water droplets from an absorbing Si substrate heated by a nanosecond KrF laser were studied using a contact photoacoustic technique. The compressive photoacoustic response increases steeply to an asymptotic value on the order of the water critical pressure starting at a threshold laser fluence of 0.20J∕cm2, where lift-off of the water layer also occurs. Above this threshold, several reproducible discrete multimegahertz components are revealed in Fourier spectra of the acoustic transients, corresponding to nanosecond oscillations of steam bubbles inside the water droplets on the microsecond time scale of the lift-off process. The acoustic pressure buildup, bubble dynamics, and the subsequent lift-off of the thin water layer are interpreted as relaxation stages after near-spinodal explosive boiling of the superheated interfacial water.
Short-pulse laser absorption via J×B heating in ultrahigh intensity laser plasma interaction
Authors: Cai Hong-bo , Yu Wei , Zhu Shao-ping , Zheng Chun-yang
Published: December 2006

An analytical fluid model for J×B heating during the normal incidence by a short ultraintense linearly polarized laser on a solid-density plasma is proposed. The steepening of an originally smooth electron density profile as the electrons are pushed inward by the laser is included self-consistently. It is shown that the J×B heating includes two distinct coupling processes depending on the initial laser and plasma conditions: for a moderate intensity (a⩽1), the ponderomotive force of the laser light can drive a large plasma wave at the point ne=4γ0nc resonantly. When this plasma wave is damped, the energy is transferred to the plasma. At higher intensity, the electron density is steepened to a high level by the time-independent ponderomotive force, ne>4γ0nc, so that no 2ω resonance will occur, but the longitudinal component of the oscillating ponderomotive field can lead to an absorption mechanism similar to “vacuum heating.”
Gate leakage mechanisms in strained Si devices
Authors: Yan L. , Olsen S. H. , Kanoun M. , Agaiby R. , O’Neill A. G.
Published: December 2006

This work investigates gate leakage mechanisms in advanced strained Si∕SiGe metal-oxide-semiconductor field-effect transistor (MOSFET) devices. The impact of virtual substrate Ge content, epitaxial material quality, epitaxial layer structure, and device processing on gate oxide leakage characteristics are analyzed in detail. In state of the art MOSFETs, gate oxides are only a few nanometers thick. In order to minimize power consumption, leakage currents through the gate must be controlled. However, modifications to the energy band structure, Ge diffusion due to high temperature processing, and Si∕SiGe material quality may all affect gate oxide leakage in strained Si devices. We show that at high oxide electric fields where gate leakage is dominated by Fowler-Nordheim tunneling, tensile strained Si MOSFETs exhibit lower leakage levels compared with bulk Si devices. This is a direct result of strain-induced splitting of the conduction band states. However, for device operating regimes at lower oxide electric fields Poole-Frenkel emissions contribute to strained Si gate leakage and increase with increasing virtual substrate Ge content. The emissions are shown to predominantly originate from surface roughness generating bulk oxide traps, opposed to Ge diffusion, and can be improved by introducing a high temperature anneal. Gate oxide interface trap density exhibits a dissimilar behavior and is highly sensitive to Ge atoms at the oxidizing surface, degrading with increasing thermal budget. Consequently advanced strained Si∕SiGe devices are inadvertently subject to a potential tradeoff between power consumption (gate leakage current) and device reliability (gate oxide interface quality).
Magnetic and electrical transport properties of Ge1−xMnx thin films
Authors: Li Hongliang , Wu Yihong , Guo Zaibing , Luo Ping , Wang Shijie
Published: November 2006

We report on preparation and systematic study of the structural, magnetic, and electrical transport properties of Ge1−xMnx (x=25%–42%) alloy thin films grown on GaAs (001) substrates by molecular beam epitaxy. Amorphous Ge1−xMnx, and coexistence of amorphous Ge1−xMnx, Ge crystallites, and high TC secondary phases (Mn11Ge8 and Mn5Ge3) are obtained at substrate temperatures of 160 and 200–300°C, respectively. The amorphous samples are found to consist of a low-temperature highly ordered spin-glass-like phase with an ordering temperature of TC∼20K (x∼0.39), increasing with the Mn composition, and a high-temperature “clustered dopant” phase with an ordering temperature of TC*∼104K (x∼0.39), increasing with both the Mn composition and applied external field. The magnetization of the low-temperature phase is found to be coupled antiferromagnetically with that of the high-temperature phase, leading to the appearance of a negative thermal remanent magnetization. Detailed magnetic and electrical measurement revealed that the low-temperature highly ordered spin-glass-like phase consists of both spin-glass-like phase and ferromagnetically ordered region. The amorphous samples also exhibit a negative magnetoresistance and an anomalous Hall effect at low temperature. The good agreement between the values of TC and TC* for amorphous samples and those of the two characteristic temperatures reported in literature for epitaxially grown samples suggests that the ferromagnetic phase of the latter observed in the temperature range of 110–120K by some reports may not be of intrinsic origin. On the other hand, the samples grown at 300°C are ferromagnetic up to room temperature and exhibit a positive magnetoresistance.
Efficient electron injection into plasma waves using higher-order laser modes
Authors: Michel P. , Esarey E. , Schroeder C. B. , Shadwick B. A. , Leemans W. P.
Published: November 2006

Using higher-order transverse laser modes as drivers for plasma wave excitation, and, in particular, using ring laser beams with maximum intensities off-axis, results in reversal of the focusing and defocusing phase regions in a laser wakefield accelerator. This results in improved performance of self-trapping and laser injection schemes. Specifically, the trapping threshold required for optical injection is decreased and the maximum energy gain of the trapped electrons is increased. This method could also be of interest for the generation of ring electron beams or for beam conditioning.
Magnetic booster fast ignition macron accelerator
Authors: Winterberg F.
Published: November 2006

A new fast ignition scheme was recently proposed where the ignition is done by the impact of a small solid projectile accelerated to velocities in excess of 108cm∕s, with the acceleration done in two steps: first, by laser ablation of a flyer plate, and second by injecting the flyer plate into a conical duct. The two principal difficulties of this scheme are as follows: first, the required large mass ratio for the laser ablation rocket propelled flyer plate, and second, the Rayleigh-Taylor instability of the flyer plate during its implosive compression in the conical duct. To overcome these difficulties, it is suggested to accelerate a projectile by a magnetic fusion booster stage, made up of a dense, wall-confined magnetized plasma brought to thermonuclear temperatures. After ignition, this plasma undergoes a thermonuclear excursion greatly increasing its pressure, resulting in the explosion of a weakened segment of the wall, with the segment becoming a fast moving projectile. The maximum velocity this projectile can reach is the velocity of sound of the booster stage plasma, which at a temperature of 108K is of the order 108cm∕s.
CVRQD ab initio ground-state adiabatic potential energy surfaces for the water molecule
Authors: Barletta Paolo , Shirin Sergei V. , Zobov Nikolai F. , Polyansky Oleg L. , Tennyson Jonathan , Valeev Edward F. , Császár Attila G.
Published: November 2006

The high accuracy ab initio adiabatic potential energy surfaces (PESs) of the ground electronic state of the water molecule, determined originally by Polyansky et al. [Science 299, 539 (2003)] and called CVRQD, are extended and carefully characterized and analyzed. The CVRQD potential energy surfaces are obtained from extrapolation to the complete basis set of nearly full configuration interaction valence-only electronic structure computations, augmented by core, relativistic, quantum electrodynamics, and diagonal Born-Oppenheimer corrections. We also report ab initio calculations of several quantities characterizing the CVRQD PESs, including equilibrium and vibrationally averaged (0K) structures, harmonic and anharmonic force fields, harmonic vibrational frequencies, vibrational fundamentals, and zero-point energies. They can be considered as the best ab initio estimates of these quantities available today. Results of first-principles computations on the rovibrational energy levels of several isotopologues of the water molecule are also presented, based on the CVRQD PESs and the use of variational nuclear motion calculations employing an exact kinetic energy operator given in orthogonal internal coordinates. The variational nuclear motion calculations also include a simplified treatment of nonadiabatic effects. This sophisticated procedure to compute rovibrational energy levels reproduces all the known rovibrational levels of the water isotopologues considered, H2O16, H2O17, H2O18, and D2O16, to better than 1cm−1 on average. Finally, prospects for further improvement of the ground-state adiabatic ab initio PESs of water are discussed.
Thermodynamic and structural properties of confined discrete-potential fluids
Authors: Benavides A. L. , del Pino L. A. , Gil-Villegas A. , Sastre F.
Published: November 2006

The thermodynamic and structural behaviors of confined discrete-potential fluids are analyzed by computer simulations, studying in a systematic way the effects observed by varying the density, temperature, and parameters of the potentials that characterize the molecule-molecule interactions. The Gibbs ensemble simulation technique for confined fluids [A. Z. Panagiotopoulos, Mol. Phys. 62, 701 (1987)] is applied to a fluid confined between two parallel hard walls. Two different systems have been considered, both formed by spherical particles that differ by the interparticle pair potential: a square well plus square shoulder or a square shoulder plus square well interaction. These model interactions can describe in an effective way pair potentials of real molecular and colloidal systems. Results are compared with the simpler reference systems of square-shoulder and square-well fluids, both under confinement. From the adsorption characterization through the use of density profiles, it is possible to obtain specific values of the interparticle potential parameters that result in a positive to negative adsorption transition.
Effect of entropy production on microstructure change in eutectic SnPb flip chip solder joints by thermomigration
Authors: Ouyang Fan-Yi , Tu K. N. , Lai Yi-Shao , Gusak Andriy M.
Published: November 2006

Thermomigration in flip chip solder joints of eutectic SnPb has been studied at an ambient temperature of 100°C. Redistribution of Sn and Pb occurs with Pb moving to the cold end. A stepwise concentration profile is observed. Significantly, the lamellar microstructure becomes much finer after thermomigration. Since the lamellar interface is disordered and is a fast path of diffusion, it indicates a high rate of entropy production in the thermomigration, in agreement with Onsager’s principle of irreversible processes. The effect of entropy production on microstructure change is shown here. The molar heat of transport of Pb has been calculated to be −25.3kJ∕mole.
Local crystal structure and local electronic structure around Cr in low-temperature-grown GaCrN layers
Authors: Hashimoto M. , Emura S. , Tanaka H. , Honma T. , Umesaki N. , Hasegawa S. , Asahi H.
Published: November 2006

The local crystal structure and local electronic structure of low-temperature-grown Ga1−xCrxN (0.01<x<0.092) have been studied by x-ray absorption spectroscopy. We found that the majority of Cr atoms are substitutionally incorporated into the GaN matrix, and the solubility limit of Cr in Ga1−xCrxN is around x=0.04 for the layers grown at 600°C. Above the solubility limit, the onset of the formation of the CrN-like local structure occurs. The effective valency of Cr in GaCrN was found to be Cr(III) from the x-ray absorption near-edge structure (XANES). The results of XANES also revealed a drastic change in the local electronic structure of Ga1−xCrxN with x between 0.04 and 0.047. This is most likely due to the transformation of the Cr–N atomic configuration from that of substitutionally incorporated GaCrN into a CrN-like local structure. The presence of p-d hybridization between d orbitals of Cr and p orbitals of N has been confirmed in its preedge structure, which could play a role in its ferromagnetism.
Does nitrogen transport in vitreous silica only take place in molecular form?
Authors: Dong Q. , Hultquist G.
Published: November 2006

It is generally believed that nitrogen transport in vitreous silica exclusively takes place in molecular form, although no evidence for this is found in the literature. Actually, an analysis of literature data of transport of nitrogen and noble gases in vitreous silica at 900°C suggests it may not be the case. In order to clarify the operative species of nitrogen transport in this material, experiments of permeation and uptake/release have been performed with the use of gas phase analysis and isotopic labeling of nitrogen. By comparing the relative distributions of N214,14, N214,15, and N215,15 in exposure gas, permeated gas and released gas with distribution of equilibrated nitrogen molecules, the percentage of dissociated nitrogen in the transport has been evaluated at different temperatures. It has then been found that nitrogen undergoes dissociation not only on the surface of vitreous silica but also in its bulk and that the overall dissociation of nitrogen increases with temperature. It is concluded that nitrogen diffuses both in molecular and atomic forms with approximately 15% atomic nitrogen transport at 900°C. The observed transport rates are explained by diffusion of molecular nitrogen combined with a retardation of dissociated nitrogen in reversible traps.
Effects of the substitution of Al for Fe on phase transition, crystal structures, and magnetic properties of Nd3(Fe,Ti)29-type intermetallics
Authors: Liu X. F. , Lv J. Y. , Hu Z. B. , Han S. B. , Chen D. F. , Xue Y. J. , Li J. H. , Kiyanagi R. , Fieramosca J. S. , Short S. , Jorgensen J.
Published: November 2006

Effects of the substitution of nontransition metal Al on phase transition, crystal structures, and magnetic properties of Nd3(Fe,Ti)29-type intermetallics have been systematically investigated by means of x-ray diffractions, time-of-flight powder neutron diffraction, and magnetic measurements. Rietveld analyses of x-ray diffraction patterns indicate that Nd3Fe27.5−xTi1.5Alx compounds mainly crystallize in Nd3(Fe,Ti)29-type structure (A2∕m space group) when x⩽1.5, but the main phase was replaced by Th2Zn17-type structure (R3¯m space group) when x>1.5. The lattice parameters a, b, c, and unit cell volume V of 3:29 phase in Nd3Fe27.5−xTi1.5Alx increase linearly with the substitution of Al. The site distributions of Ti and Al atoms were determined by refining the powder neutron diffraction data and it was found that Ti atoms prefer to occupy 4i1, 4i2, and 4g sites with the largest number of Fe neighbors while Al atoms prefer to take 4i4 and 8j4 sites with the largest number of rare earth neighbors. The Curie temperature of Nd3Fe27.5−xTi1.5Alx increases monotonously while the saturated magnetization decreases almost linearly with increasing Al content (x⩽1.5).
Physical properties of equilibrium and nonequilibrium liquid osmium measured by levitation techniques
Authors: Paradis P.-F. , Ishikawa T. , Koike N.
Published: November 2006

To initiate a comprehensive study of the macroscopic and microscopic properties and structure of osmium, solid samples were levitated, melted, deeply undercooled, and resolidified under vacuum. Using noncontact diagnostic methods, several properties of equilibrium and nonequilibrium liquid osmium were measured. Over the 2670–3380K temperature range, the density could be expressed as ρ(T)=1.91×104−1.16(T−Tm)kgm−3, where Tm is the melting temperature (Tm=3306K). Similarly, the surface tension and the viscosity measurement data could be fitted, respectively, as σ(T)=2.48×103−0.34(T−Tm)mNm−1 and η(T)=0.00167exp[2.2×105∕(RT)]mPas over the 3230–3605K temperature interval.
Electrical transport properties and magnetic cluster glass behavior of Nd0.7Sr0.3MnO3 nanoparticles
Authors: Roy B. , Poddar A. , Das S.
Published: November 2006

The transport and magnetic properties have been investigated in Nd0.7Sr0.3MnO3 nanoparticles prepared by the sol-gel method. The resistivity (ρ) increases with the decrease of the particle size due to the enhancement of the grain boundary effect. ρ(T) shows two distinct transitions for all the samples such as metal-insulator transition and transition due to the barrier caused by the grain boundary effect. The thermopower (S) is found to be negative and at high temperature S follows the adiabatic small polaron hopping theory. In the metallic region the spin wave contribution is found to be dominant in the temperature dependence of the thermopower. The magnetoresistance (MR) of the ultrafine particles increases with the decrease of particle size indicating substantial contribution from the grain boundaries. Spin polarized intergrain tunneling effect plays an important role in the MR of a smaller size particle, whereas in the case of samples of higher dimension spin fluctuation contributes predominantly. The field cooled (FC) and zero field cooled (ZFC) magnetizations display a paramagnetic-ferromagnetic transition at TC with a large magnetic irreversibility. The ZFC peak temperature TB and the irreversibility temperature (Tirr) are field dependent and decrease with the decrease of the particle dimension. Magnetic measurement indicates that particles are single domain with the particles of highest dimension lying in the multidomain region. A cluster glasslike behavior of the particles is revealed from the analysis of the dc and ac magnetization data.
Accurate and unbiased estimation of power-law exponents from single-emitter blinking data
Authors: Hoogenboom Jacob P. , den Otter Wouter K. , Offerhaus Herman L.
Published: November 2006

Single emitter blinking with a power-law distribution for the on and off times has been observed on a variety of systems including semiconductor nanocrystals, conjugated polymers, fluorescent proteins, and organic fluorophores. The origin of this behavior is still under debate. Reliable estimation of power exponents from experimental data is crucial in validating the various models under consideration. We derive a maximum likelihood estimator for power-law distributed data and analyze its accuracy as a function of data set size and power exponent both analytically and numerically. Results are compared to least-squares fitting of the double logarithmically transformed probability density. We demonstrate that least-squares fitting introduces a severe bias in the estimation result and that the maximum likelihood procedure is superior in retrieving the correct exponent and reducing the statistical error. For a data set as small as 50 data points, the error margins of the maximum likelihood estimator are already below 7%, giving the possibility to quantify blinking behavior when data set size is limited, e.g., due to photobleaching.
Feasibility of fabricating microwave waveguide using friction stir welding
Authors: Goldberg Ira B. , Mahoney Murray W. , Bingel William H. , Hollingsworth Charles S.
Published: November 2006

Friction stir welding (FSW) as an alternative to brazing can be used for fabricating microwave waveguide structures. The FSW fabrication process is described, and the transmission and reflection of the straight sections of aluminum K-band waveguide made by FSW and brazing are compared. The section made by FSW exhibits 0.04dB lower transmission and slightly greater reflection than the brazed waveguide. In this preliminary evaluation, the welding process was not fully optimized. With optimization, FSW can provide a faster, more reliable fabrication process, but is limited to similar metals and cannot be used for fabricating window assemblies.
Addition by subtraction in coupled-cluster theory: A reconsideration of the CC and CI interface and the nCC hierarchy
Authors: Bartlett Rodney J. , Musiał Monika
Published: November 2006

The nCC hierarchy of coupled-cluster approximations, where n guarantees exactness for n electrons and all products of n electrons are derived and applied to several illustrative problems. The condition of exactness for n=2 defines nCCSD=2CC, with nCCSDT=3CC and nCCSDTQ=4CC being exact for three and four electrons. To achieve this, the minimum number of diagrams is evaluated, which is less than in the corresponding CC model. For all practical purposes, nCC is also the proper definition of a size-extensive CI. 2CC is also an orbitally invariant coupled electron pair approximation. The numerical results of nCC are close to those for the full CC variant, and in some cases are closer to the full CI reference result. As 2CC is exact for separated electron pairs, it is the natural zeroth-order approximation for the correlation problem in molecules with other effects introduced as these units start to interact. The nCC hierarchy of approximations has all the attractive features of CC including its size extensivity, orbital invariance, and orbital insensitivity, but in a conceptually appealing form suited to bond breaking, while being computationally less demanding. Excited states from the equation of motion (EOM-2CC) are also reported, which show results frequently approaching those of EOM-CCSDT.
Theoretical model of the intrinsic emittance of a photocathode
Authors: Jensen Kevin L. , O’Shea P. G. , Feldman D. W. , Moody N. A.
Published: November 2006

A theoretical expression for the intrinsic emittance of a photocathode is developed based on a method of evaluating moments of the emission distribution function. The method is first used to reevaluate the well-known rms emittance of a thermionic source, and then, using analogous approximations but with an updated theoretical model of photoemission, an equation for the intrinsic emittance and brightness of a photocathode of comparable simplicity to the thermionic case is obtained in the limit of weak field and low temperature.
Integratable 40dB optical waveguide isolators using a resonant-layer effect with mode coupling
Authors: Hammer Jacob M. , Ozgur Gokhan , Evans Gary A. , Butler Jerome K.
Published: November 2006

Resonant-layer effect (RLE) optical isolators can be integrated with a wide variety of optical waveguide devices and systems and theoretically provide a high degree of isolation with low insertion loss. The effect of mode coupling within the isolator and the losses due to coupling between the isolator and the input and output waveguides on the performance of RLE isolators is calculated. The results predict that isolators integrated with semiconductor waveguides similar to those used for efficient lasers and amplifiers and isolators integrated with quartzlike waveguides can give 40dB of isolation with insertion losses below 3dB. The calculations also show relaxed dimensional tolerance and lengths in the 1–2mm range, which makes commercial production of such isolators attractive.
Influence of bimolecular recombination on xerographic discharge process
Authors: Jung Jaroslaw
Published: November 2006

The photoinduced decay of surface potential, known as xerographic discharge, is analyzed as a method of determination of photogeneration quantum yield taking into account the recombination processes. The effects of slowing down the surface potential decay with time of illumination and nonzero residual potential are usually explained by trapping of the charge carriers in the bulk of the photoconductor. However, these effects can be explained also by bimolecular recombination in the illuminated thin surface layer occurring simultaneously with the photogeneration. In this work it is assumed that as a result of the illumination the mobile positive charge carriers and immobile negative recombination centers are generated. The critical value of the recombination cross section is determined for which the nonzero residual surface potential appears. This analysis allows also to determine an influence of the accumulated recombination centers on the photocurrent decay and build up of the residual potential in a series of subsequent xerographic discharge experiments.
Steering of a grain boundary with strain, electromagnetic field, and stochastic boundary excitation
Authors: Lusk Mark T. , Vincent Tyrone , Upmanyu Moneesh
Published: November 2006

In a previous work [Lusk et al., J. Appl. Phys. 99, 023505 (2006)], grain boundary and triple junction motion control using a laser spot was simulated within a noninertial, two-dimensional setting. That work focused on the physical process by which these defect structures could be induced to move. The present work seeks to begin the development of a control theory for such steering operations. To this end, a model system is introduced wherein the control of grain boundaries is abstracted into a piecewise homogeneous chain of harmonic oscillators. The interface demarcates regions of differing elastic stiffness and accretes via isothermal fluctuation theory. Energy is controlled via Langevin excitation and viscous damping applied to a single boundary mass. Steering of the grain boundary is achieved via applied strain and body forces. A closed-form relationship is established which allows the time-dependent probability distribution of the interface position to be expressed in terms of temperature, strain, body force, number of masses, and one dimensionless ratio. This analytical result is used to validate the predictions of molecular dynamics and dissipative particle dynamics (DPD) simulations. The DPD simulator is then treated as a physical experiment, and interface control via both constant and time-varying actuation is explored, with time-varying trajectories calculated using the analytic expression for interface position distribution.
Second-order Møller-Plesset perturbation energy obtained from divide-and-conquer Hartree-Fock density matrix
Authors: Kobayashi Masato , Akama Tomoko , Nakai Hiromi
Published: November 2006

The density matrix (DM) obtained from Yang’s [Phys. Rev. Lett. 66, 1438 (1991)] divide-and-conquer (DC) Hartree-Fock (HF) calculation is applied to the explicit second-order Møller-Plesset perturbation (MP2) energy functional of the HF DM, which was firstly mentioned by Ayala and Scuseria [J. Chem. Phys. 110, 3660 (1999)] and was improved by Surján [Chem. Phys. Lett. 406, 318 (2005)] as DM-Laplace MP2. This procedure, termed DC-DM MP2, requires the HF DM of holes, for which we propose two evaluation schemes in DC manner. Numerical studies reveal that the DC-DM MP2 energy deviation from canonical MP2 is the same order of magnitude as DC-HF energy deviation from conventional HF whichever type of hole DM is adopted. It is also confirmed that the central processing unit time of DC-DM MP2 is less than that of DM-Laplace MP2 because the DC-HF DM is sparser than conventional DM.
Optogalvanic spectroscopy of the C″Πui5−A′Σg+5 electronic system of N2
Authors: Pirali O. , Tokaryk D. W.
Published: November 2006

We have recorded spectra involving the 3-1, 4-2, 2-0, and 2-2 bands of the C″Πui5−A′Σg+5 electronic system of N2 using optogalvanic detection in a discharge through a supersonic jet expansion of argon mixed with a trace of nitrogen gas. The spectra have an effective rotational temperature of about 45K. They involve all five spin-orbit components of the C″Πui5 state, which has allowed for precise determination of the spin-orbit coupling in this state. Analysis of the C″Πui5 state Λ-doubling shows that it is caused primarily by a first-order spin-spin effect rather than by interaction with Σu± states. Our results allow us to assign lines in the 4-2 and 2-0 bands observed in a fluorescence depletion experiment conducted over ten years ago [Ch. Ottinger and A. F. Vilesov, J. Chem. Phys. 103, 9929 (1995)], and to comment on the suggestion that perturbations to the CΠu3 v=1 level of N2 arise from interactions with the C″Πui5 state.
Effect of ionization on femtosecond laser pulse interaction with silicon
Authors: Li Huayu , Ki Hyungson
Published: November 2006

Femtosecond laser pulse interaction with silicon is studied numerically considering the ionization process induced by the intense electromagnetic field of the laser pulse. The electromagnetic field is calculated by solving Maxwell’s equations using the finite-difference time-domain method, and the two-temperature model is employed for the electron-lattice energy coupling. The electron number density is computed by an ionization model based on the energy balance of laser energy; the electrical conductivity of the dense plasma is predicted accounting for the number density and temperature of electrons. This article presents some interesting results on electromagnetic field in the silicon substrate, electron and lattice temperatures, electrical conductivity, and electron number density depending on laser pulse energy and pulse width. In particular, this study explains some physical phenomena pertaining only to femtosecond laser pulses, such as existence of threshold intensity.
Positioning cavity solitons with a phase mask
Authors: Pedaci F. , Genevet P. , Barland S. , Giudici M. , Tredicce J. R.
Published: November 2006

Nonlinear interaction between a coherent electric field and a semiconductor medium inside a high Fresnel number cavity may give rise to the formation of cavity solitons. It is theoretically predicted that the position of these structures, mutually independent and bistable, can be controlled by gradients in the injection beam. Using a liquid crystal light valve to spatially modulate the phase of a coherent beam injected into a broad area vertical cavity semiconductor laser, the authors create reconfigurable arrays of cavity solitons. Fast time scales associated with semiconductor lasers and plasticity of localized structures suggest their potential for optical data processing.
Partial amorphization of a Cu–Zr–Ti alloy by high pressure torsion
Authors: Révész Ádám , Hóbor Sándor , Lábár János L. , Zhilyaev Alex P. , Kovács Zsolt
Published: November 2006

High pressure torsion was applied to produce disk-shape specimen of Cu60Zr20Ti20 composition. Radial dependence of the microstructure was monitored by x-ray diffraction, scanning, and transmission electron microscopies. The disk consists of a top surface layer, homogeneous on a micrometer scale with an average thickness of 10–20μm, and an inhomogeneous bulk region of 200μm thickness. Calorimetric studies revealed that the disk contains detectable amount of amorphous phase. Characteristics of this amorphous content were compared to a fully amorphous melt-quenched Cu60Zr20Ti20 ribbon.
Organic CuTCNQ integrated in complementary metal oxide semiconductor copper back end-of-line for nonvolatile memories
Authors: Müller R. , De Jonge S. , Myny K. , Wouters D. J. , Genoe J. , Heremans P.
Published: November 2006

Nanowires of the organometallic semiconductor CuTCNQ were grown from TCNQ vapor in 250nm diameter vias of a Cu back end-of-line process. Corresponding prototypes of cross-point Cu∕CuTCNQ nanowire/Al memories exhibited nonvolatile bistable conductive switching for several ten write-erase cycles with switching currents below 10μA and current densities 1000 times higher than for large-area devices. Scaling of memory elements was also investigated.
Swelling of cross-linked polystyrene spheres in toluene vapor
Authors: Zhang R. , Graf K. , Berger R.
Published: November 2006

The swelling behavior of individual micron-sized polystyrene (PS) spheres in toluene vapor was studied via mass loading by means of micromechanical cantilever sensors. For 4%–8% cross-linked PS a mass increase of 180% in saturated toluene vapor was measured. The mass of the swollen PS sphere decreases with increasing exposure time to ultraviolet light. In addition, the swelling response is significantly different between the first and the second exposure to toluene vapor. This is attributed to the formation of a cross-linked shell at the surface of the PS spheres. Shape persistent parts were observed for locally irradiated PS spheres.
Curvature and torsion effects in electric current-carrying twisted solar loops
Authors: Garcia de Andrade L. C.
Published: December 2006

Riemannian geometry of the electric current-carrying solar loops is obtained from a thin tube approximation of twisted magnetic flux tubes. The Frenet torsion and curvature affect the electron drift speed of the electrons of the current along the toroidal direction of the tube. The twist of the tube is computed and it is shown that twist is maximum at the surface of the tube and minimum at the tube axis. This acts as inertia effects to the electron drift. The higher the torsion of the tube axis the smaller is the velocity along the direction of the tube. This effect is similar to the one obtained by Tyspin et al. [Physics of Plasmas, 5, 3385 (1998)] in the case of toroidal devices with curvature and torsion. Here the simple geometrical effects are enough to slow down the currents and no viscosity in the fluid is taken into account. A slight compressibility of the plasma flow is due to the twist of the tube. As applications of these ideas, it is shown that torsion effects are not enough to accelerate electrons up to relativistic energies, and the torsion is computed in the case of the force-free loop. The value of torsion is used to compute the electron acceleration in two distinct cases. The first is the case when the Riemann loop suffers the action of a dc electric sub-Dreicer field, where the magnetic field is direct along the magnetic loop, and the loop moves along the orthogonal direction to the loop as in vortex filaments. In this case, the acceleration is shown to be of the order of 10−17cms−2 for a solar torsion of the order of 10−4cm−1. The second case is for the curvature drift contribution, where torsion is also present. In this case we show that torsion is not present in the velocity drift but just in the electron acceleration. Though these values are extremely low, they can be improved by considering small loops lowering the radius of the loop which, here, was taken as 600km. Curvature drift acceleration is also estimated as 100cms−2.
Aspects of hole burning and spectro-temporal holography in molecular doped solids (Review)
Authors: Galaup Jean-Pierre
Published: December 2006

The persistent spectral hole-burning (PSHB) phenomenon has been known since 1974. It is still an important research area for the study of the intimacy of complex molecular systems in the solid state, revealing high-resolution spectra, photophysics, photochemistry, and dynamics of molecular doped amorphous media, organic as well as inorganic. From another point of view, PSHB allows the engraving of any spectral structures in the inhomogeneous absorption band profile of molecular doped amorphous hosts or ion doped crystals cooled down to liquid helium temperatures. Therefore, a PSHB material is programmable in the spectral domain and consequently it can be transformed in an optical processor capable of achieving user-defined optical functions. Some aspects of both fields are illustrated in the present paper. Concerning the search for efficient PSHB materials, the hole-burning performances and the photophysics of polymer and xerogel based systems are compared. The problem of high-temperature persistent spectral hole-burning materials and the search for new frequency selective photosensitive systems for fast optical pulse processing at 800nm are considered. Regarding the points treated, inorganic hosts based on silicate xerogels or porous glasses have shown the best results. Moreover, by combining inorganic and organic capabilities or by grafting organic species to the host, hybrid xerogels have not yet revealed all possibilities. Also, the interest of two-photon materials for engraving spectral features with near-infrared or infrared light is developed. As an introduction to possible applications of PSHB material, the basics of spectro-temporal holography are remembered and a demonstrative experiment using a naphthalocyanine-doped polymer film is described, proving that the temporal aberration free recompression of ultrashort light pulses is feasible, therefore opening a way for applications in ultrashort light pulse shaping. Aspects for a comparison between cw hole-burning and femtosecond spectro-temporal experiments are considered, and prospects for coherent control of light fields or photochemical processes are also evoked.
Photoluminescence of ortho-bromobenzophenone
Authors: Avdeenko A. A. , Pyshkin O. S. , Eremenko V. V. , Strzhemechny M. A. , Buravtseva L. M. , Romashkin R. V.
Published: December 2006

Phosphorescence spectra of crystalline ortho-bromobenzophenone (2-bromobenzophenone, 2BrBP) were measured from 1.6K to room temperature. A cardinal emission mechanism crossover occurs within this temperature range. At low temperature the phosphorescence spectrum is a superposition of two similar sets of equidistant bands spaced by the CO stretch frequency. We ascribe these two sets to the emission of two different conformers, one of which is metastable and does not manifest itself above approximately 70K. The presence of two conformers is explained by the fact that the 2BrBP molecule deforms considerably upon excitation. The emission from the stable conformer survives up to approximately 140K or even higher. At roughly 60K and higher, another type of emission reveals itself in the shape of two very broad, partly overlapping bands, which gains in intensity with increasing temperature. Above 150K only this two-hump feature is observed in phosphorescence spectra. Additional phosphorescence experiments were carried out to elucidate the nature of this spectrum, including phosphorescence measurements of 2BrBP in ethanol solutions as well as time-resolved and varying-excitation-intensity measurements from crystals. Based on results of all the experiments reported here and on our own single-crystal x-ray structure data we conclude that the above two-band spectrum recorded near room temperature is due to the emission of single-photon bimolecular triplet excimer formed by the carbonyl groups of two neighboring 2-bromobenzophenone molecules. This is the first time that a bimolecular excimer has been observed and reliably identified in a benzophenone derivative solid.
Lattice distortion of quantum cryocrystals under pressure
Authors: Tretyak S. M. , Antsygina T. N. , Freiman Yu. A.
Published: December 2006

The hcp lattice distortion parameter δ, the deviation of the ratio c∕a from the ideal hcp value 8∕3, is calculated for solid He under pressure, taking into account two- and three-body interatomic forces. The resulting lattice distortion parameter is small and negative, i.e., the lattice is slightly flattened compared with the ideal hcp lattice. It increases monotonically in absolute value with pressure and reaches 10−3 for a molar volume of ∼2.5cm3∕mol. Such small distortions are most likely beyond the capabilities of x-ray or neutron experiments but can be detected by optical methods based on measurements of the birefringence. The data on δ can be used as a probe of the many-body forces.
Oxygen-driven relaxation processes in pre-irradiated Ar cryocrystals
Authors: Savchenko E. V. , Belov A. G. , Gumenchuk G. B. , Ponomaryov A. N. , Bondybey V. E.
Published: December 2006

Relaxation processes in oxygen-containing Ar cryocrystals pre-irradiated by low-energy electrons are studied with the focus on the role of the diffusion-controlled atom-atom recombination reaction of oxygen in the relaxation cascades. The results of real-time-correlated measurements of thermally stimulated phenomena are presented. The experiments have been performed using activation spectroscopy methods—thermally stimulated exoelectron emission and spectrally resolved thermally stimulated luminescence. Solid evidence for the radiative mechanism of electron detrapping triggering the relaxation cascades is obtained.