bluuebunny/crossref_metadata_2025 huggingface dataset:
Analytical instrumentation infrastructure for combinatorial and high-throughput development of formulated discrete and gradient polymeric sensor materials arrays
Authors: Potyrailo Radislav A. , Hassib Lamyaa
Published: June 2005

Multicomponent polymer-based formulations of optical sensor materials are difficult and time consuming to optimize using conventional approaches. To address these challenges, our long-term goal is to determine relationships between sensor formulation and sensor response parameters using new scientific methodologies. As the first step, we have designed and implemented an automated analytical instrumentation infrastructure for combinatorial and high-throughput development of polymeric sensor materials for optical sensors. Our approach is based on the fabrication and performance screening of discrete and gradient sensor arrays. Simultaneous formation of multiple sensor coatings into discrete 4×6, 6×8, and 8×12 element arrays (3–15μL volume per element) and their screening provides not only a well-recognized acceleration in the screening rate, but also considerably reduces or even eliminates sources of variability, which are randomly affecting sensors response during a conventional one-at-a-time sensor coating evaluation. The application of gradient sensor arrays provides additional capabilities for rapid finding of the optimal formulation parameters.
Time-dependent density-functional theory calculations of triplet-triplet absorption
Authors: Cronstrand Peter , Rinkevicius Zilvinas , Luo Yi , Ågren Hans
Published: June 2005

We present density-functional theory calculations of triplet-triplet absorption by three different approaches based on time-dependent density-functional theory (DFT): unrestricted DFT linear response, open-shell restricted DFT linear response applied to the triplet state, and quadratic response with triplet excitations applied to the ground state. Comparison is also made with corresponding results obtained by Hartree–Fock and multiconfiguration self-consistent-field response theory. Two main conclusions concerning triplet-triplet transitions are drawn in this study: First, the very good agreement between unrestricted and restricted DFT results indicates that spin contamination of the triplet state is not a serious problem when computing triplet-triplet spectra of common organic molecules. Second, DFT response calculations of triplet-triplet transitions can be affected by triplet instability problems, especially for the combination of DFT quadratic response with functionals containing fractional exact Hartree–Fock exchange.
Melting of icosahedral gold nanoclusters from molecular dynamics simulations
Authors: Wang Yanting , Teitel S. , Dellago Christoph
Published: June 2005

Molecular dynamics simulations show that gold clusters with about 600–3000 atoms crystallize into a Mackay icosahedron upon cooling from the liquid. A detailed surface analysis shows that the facets on the surface of the Mackay icosahedral gold clusters soften but do not premelt below the bulk melting temperature. This softening is found to be due to the increasing mobility of vertex and edge atoms with temperature, which leads to inter-layer and intra-layer diffusion, and a shrinkage of the average facet size, so that the average shape of the cluster is nearly spherical at melting.
Single photon locking of an all-fiber interferometer
Authors: Pulford David , Robillard Craig , Huntington Elanor
Published: June 2005

We describe locking of a fiber-based Mach–Zehnder interferometer. This work used a coherent state as input with a mean of 0.1 photons per gating period of an avalanche photodiode operated in geiger mode. Feedback from the avalanche photodiode loop was used to lock the intensity of the interferometer such that the output was balanced. Details of the technique are discussed as well as locking fiber-based interferometers to arbitrary output states and using number states as input. Applications in quantum computing, quantum communications, and quantum key distribution are discussed.
Two-particle friction in a mesoscopic solvent
Authors: Lee Song Hi , Kapral Raymond
Published: June 2005

The effects of hydrodynamic interactions on the friction tensors for two particles in solution are studied. The particles have linear dimensions on nanometer scales and are either simple spherical particles interacting with the solvent through repulsive Lennard-Jones forces or are composite cluster particles whose atomic components interact with the solvent through repulsive Lennard-Jones forces. The solvent dynamics is modeled at a mesoscopic level through multiparticle collisions that conserve mass, momentum, and energy. The dependence of the two-particle relative friction tensors on the interparticle separation indicates the importance of hydrodynamic interactions for these nanoparticles.
Electronic structure of a vapor-deposited metal-free phthalocyanine thin film
Authors: Alfredsson Y. , Brena B. , Nilson K. , Åhlund J. , Kjeldgaard L. , Nyberg M. , Luo Y. , Mårtensson N. , Sandell A. , Puglia C. , Siegbahn H.
Published: June 2005

The electronic structure of a vapor-sublimated thin film of metal-free phthalocyanine (H2Pc) is studied experimentally and theoretically. An atom-specific picture of the occupied and unoccupied electronic states is obtained using x-ray-absorption spectroscopy (XAS), core- and valence-level x-ray photoelectron spectroscopy (XPS), and density-functional theory (DFT) calculations. The DFT calculations allow for an identification of the contributions from individual nitrogen atoms to the experimental N1s XAS and valence XPS spectra. This comprehensive study of metal-free phthalocyanine is relevant for the application of such molecules in molecular electronics and provides a solid foundation for identifying modifications in the electronic structure induced by various substituent groups.
Ab initio computational investigation of physisorption of molecular hydrogen on achiral single-walled carbon nanotubes
Authors: Ferre-Vilaplana A.
Published: June 2005

Using relatively approximated methods, physisorption of molecular hydrogen on single-walled carbon nanotubes (SWCNTs) as a mechanism to develop hydrogen storage systems has been only partially investigated in literature. Here, we use ab initio molecular-orbital theory, at benchmark quality level, to provide a more complete description about the mentioned mechanism. Physisorption inside and outside achiral—armchair and zigzag—SWCNTs, in the range of diameters from about 6Å—chiral vectors (5,5) and (8,0)—to more than 30Å—chiral vectors (30,30) and (40,0)—was examined. Perpendicular, longitudinal, and transversal configurations, with the hydrogen molecule centered on an aromatic ring, were taken into account. SWCNTs were modeled as curved coronenelike (C24H12) graphene sheets. Local modeling strategies, using more complete basis sets for the adsorbate and for the nearest atoms to the adsorbate than for the lion’s share of the substrate, at the Møller–Plesset second-order correlation level, were selected for numerical treatment. Basis-set superposition errors were corrected by means of the counterpoise method of Bois and Bernardi. It was found that physisorption of molecular hydrogen on SWCNTs would depend mainly on the diameter being virtually independent of the chirality. Lowest physisorption energies, up to 20% less than that on planar graphene, would be reached outside nanotubes in the range of diameters of 6–10Å. For hydrogen storage purposes, highest physisorption energies, up to 40% greater than that on planar graphene, but not more, would be reached inside nanotubes in the relatively narrow range of diameters of 10–20Å. Finally, for diameters from 20Å onwards physisorption of molecular hydrogen on SWCNTs would be in the range of ±10% of that on planar graphene. To our knowledge, this would be the most complete and realistic theoretical investigation of the target physisorption mechanism to date.
Symmetry-adapted perturbation-theory calculations of intermolecular forces employing density-functional description of monomers
Authors: Misquitta Alston J. , Szalewicz Krzysztof
Published: June 2005

A symmetry-adapted perturbation theory based on Kohn–Sham determinants [SAPT(KS)] and utilizing asymptotically corrected exchange-correlation potentials has been applied to the He2, Ne2, (H2O)2, and (CO2)2 dimers. It is shown that SAPT(KS) is able to recover the electrostatic, first-order exchange, second-order induction, and exchange-induction energies with an accuracy approaching and occasionally surpassing that of regular SAPT at the currently programmed theory level. The use of the asymptotic corrections is critical to achieve this accuracy. The SAPT(KS) results can be obtained at a small fraction of the time needed for regular SAPT calculations. The robustness of the SAPT(KS) method with respect to the basis set size is also demonstrated. A theoretical justification for high accuracy of SAPT(KS) predictions for the electrostatic, first-order exchange, and second-order induction energies has been provided.
A practical treatment for the three-body interactions in the transcorrelated variational Monte Carlo method: Application to atoms from lithium to neon
Authors: Umezawa Naoto , Tsuneyuki Shinji , Ohno Takahisa , Shiraishi Kenji , Chikyow Toyohiro
Published: June 2005

We suggest a practical solution to dealing with the three-body interactions in the transcorrelated variational Monte Carlo method (TC-VMC). In the TC-VMC method, which was suggested in our previous paper [N. Umezawa and S. Tsuneyuki, J. Chem. Phys. 119, 10015 (2003)], the Jastrow–Slater-type wave function is efficiently optimized through a self-consistent procedure by minimizing the variance of the local energy. The three-body terms in the transcorrelated self-consistent-field equation, which have been simply ignored in our previous works, are efficiently calculated by the Monte Carlo numerical integration. We found that our treatment for the three-body interactions is successful for atoms from Li to Ne.
Layering, condensation, and evaporation of short chains in narrow slit pores
Authors: Li Zhidong , Cao Dapeng , Wu Jianzhong
Published: June 2005

The phase behavior of short-chain fluids in slit pores is investigated by using a nonlocal-density-functional theory that takes into account the effects of segment size, chain connectivity, and van der Waals attractions explicitly. The layering and capillary condensation/evaporation transitions are examined at different chain length, temperature, pore width, and surface energy. It is found that longer chains are more likely to show hysteresis loops and multilayer adsorptions along with the capillary condensation and evaporation. Decreasing temperature favors the inclusion of layering transitions into the condensation/evaporation hysteresis loops. For large pores, the surface energy has relatively small effect on the pressures of the capillary condensation and evaporation but affects significantly on the layering pressures. It is also observed that all phase transitions within the pore take place at pressures lower than the corresponding bulk saturation pressure. The critical temperature of condensation/evaporation is always smaller than that of the bulk fluid. All coexistence curves for confined phase transitions are contained within the corresponding bulk vapor-liquid coexistence curve. As in the bulk phase, the longer the chain length, the higher are the critical temperatures of phase transitions in the pore.
Multifractal analysis of dynamic potential surface of ion-conducting materials
Authors: Habasaki Junko , Ngai K. L.
Published: June 2005

A multifractal analysis using singularity spectra [T.C. Halsey et al., Phys. Rev. A 33, 1141 (1986)] provides a general tool to study the temporal-spatial properties of particles in complex disordered materials such as ions in ionically conducting glasses and melts. Obtained by molecular-dynamics simulations, the accumulated positions of the particles dynamically form a structural pattern called the dynamical potential surface. In this work, the complex dynamical potential surfaces of Li ions in the lithium silicates were visualized and characterized by the multifractal analysis. The fractal dimensions and strength of the singularity related to the spatial intermittency of the dynamics are examined, and the relationship between dynamics and the singularity spectra is discussed.
Nonequilibrium effects in diffusion of interacting particles on vicinal surfaces
Authors: Mašín M. , Vattulainen I. , Ala-Nissila T. , Chvoj Z.
Published: June 2005

We study the influence of nonequilibrium conditions on the collective diffusion of interacting particles on vicinal surfaces. To this end, we perform Monte Carlo simulations of a lattice-gas model of an ideal stepped surface, where adatoms have nearest-neighbor attractive or repulsive interactions. Applying the Boltzmann–Matano method to spreading density profiles of the adatoms allows the definition of an effective, time-dependent collective diffusion coefficient DCt(θ) for all coverages θ. In the case of diffusion across the steps and strong binding at lower step edges we observe three stages in the behavior of the corresponding Dxx,Ct(θ). At early times when the adatoms have not yet crossed the steps, Dxx,Ct(θ) is influenced by the presence of steps only weakly. At intermediate times, where the adatoms have crossed several steps, there are sharp peaks at coverages θ<1∕L and θ>1−1∕L, where L is the terrace width. These peaks are due to different rates of relaxation of the density at successive terraces. At late stages of spreading, these peaks vanish and Dxx,Ct(θ) crosses over to its equilibrium value, where for strong step edge binding there is a maximum at θ=1∕L. In the case of diffusion in direction along the steps the nonequilibrium effects in Dyy,Ct(θ) are much weaker, and are apparent only when diffusion along ledges is strongly suppressed or enhanced.
Density-functional study of model bidisperse ferrocolloids in an external magnetic field
Authors: Range Gabriel M. , Klapp Sabine H. L.
Published: June 2005

We present phase diagrams of a model bidisperse ferrocolloid consisting of a binary mixture of dipolar hard spheres (DHSs) under the influence of an external magnetic field. The dipole moments of the particles are chosen proportional to the particle volume to mimic real ferrocolloids, and we focus on dipole-dominated systems where isotropic attractive interactions are absent. Our results are based on density-functional theory in the modified mean-field (MMF) approximation. For one-component DHS fluids in external fields, and for corresponding mixtures dominated by one of the components, MMF theory predicts the tricritical point of the transition between an isotropic gas and a ferromagnetic liquid occurring at zero field to be changed into a critical point separating two magnetically ordered phases of different density. The corresponding critical temperature displays a nonmonotonic dependence on the field strength. Completely different behavior is found for the critical temperature related to the demixing phase transitions appearing in strongly asymmetric mixtures [G. M. Range and S. H. L. Klapp, Phys. Rev. E 70, 061407 (2004)]. For such systems, we find a monotonic decrease of the demixing critical temperature with increasing field. The field strength dependence of the critical temperature can therefore be tuned between nonmonotonic and monotonic behaviors just by changing the composition of the mixture—e.g., by adjusting the chemical potentials. This allows us to efficiently control the influence of external magnetic fields on the phase behavior over a large temperature interval.
Pulsed-field ionization electron spectroscopy and conformation of copper-diammonia
Authors: Li Shenggang , Sohnlein Bradford R. , Yang Dong-Sheng , Miyawaki Jun , Sugawara Ko-Ichi
Published: June 2005

Copper-diammonia, Cu(NH3)2, and its deuterated species, Cu(ND3)2, are produced in supersonic molecular beams and studied by pulsed-field ionization zero electron kinetic energy photoelectron spectroscopy and ab initio calculations. Structural isomers with a copper atom binding to an ammonia dimer or two ammonia molecules are obtained by the calculations. By comparing the experimental measurements to the theoretical calculations, the neutral and ionic forms of copper-diammonia are determined to be in a doubly bound linear conformation in their ground electronic states. The adiabatic ionization potentials of Cu(NH3)2 and Cu(ND3)2 are measured as 29 532 (5) and 29313(5)cm−1, respectively. The metal-ligand symmetric stretching frequencies are measured to be 436cm−1 for Cu+–(NH3)2 and 398cm−1 for Cu+–(ND3)2, and the metal-ligand bending frequencies 75∕139cm−1 for Cu∕Cu+–(NH3)2 and 70∕125cm−1 for Cu∕Cu+–(ND3)2. Moreover, the dissociation energy of Cu(NH3)2→CuNH3+NH3 is determined to be 11(3)kcalmol−1 through a thermodynamic relationship.
Absolute electronic excitation cross sections for low-energy electron (5–12eV) scattering from condensed thymine
Authors: Levesque P. L. , Michaud M. , Cho W. , Sanche L.
Published: June 2005

The absolute cross sections for electronic excitations of thymine by electron impact between 5 and 12eV are determined by means of electron-energy loss (EEL) spectroscopy for the molecule deposited at submonolayer coverage on an inert Ar substrate. The lowest EEL features at 3.7 and 4.0eV are attributed to the excitation of the triplet 1A′3(π→π*) and 1A″3(n→π*) valence states of the molecule. The higher EEL features located at 4.9, 6.3, 7.3, and 9eV with a weak shoulder around 6eV are ascribed mostly to triplet valence (π→π*) excitation manifold of the molecule. The energy dependence of the cross section for both the lowest triplet valence excitations shows essentially a peak at about 5eV reaching a value of 2.9×10−17cm2. The cross sections for the higher EEL features are generally characterized by a common broad maximum around 8eV. The latter reaches a value of 1.36×10−16cm2 for the combined 6 and 6.3eV excitation region. The maxima in the present cross sections are found to correspond to the resonances that have been reported at about the same energies in the O− yield from electron impact on thymine in the gas phase.
Electronic energy levels with the help of trajectory-guided random grid of coupled wave packets. I. Six-dimensional simulation of H2
Authors: Shalashilin Dmitrii V. , Child Mark S.
Published: June 2005

As a preliminary to future work on the behavior of atoms and molecules in strong time-dependent fields, we apply the coupled coherent-states (CCS) technique of multidimensional phase-space quantum dynamics to obtain Born–Oppenheimer energy levels of electrons in molecules. Unlike traditional approaches based on atomic and molecular-orbital basis sets and time-independent Schrödinger equation the CCS method exploits the solution of the time-dependent Schrödinger equation in the basis of Monte Carlo-selected trajectory-guided coherent states, which treat classical electron correlations exactly. In addition the CCS trajectories move over averaged potentials, which remove the Coulombic singularities.
Quantifying the effects of the self-interaction error in DFT: When do the delocalized states appear?
Authors: Lundberg Marcus , Siegbahn Per E. M.
Published: June 2005

The self-interaction error in density-functional theory leads to artificial stabilization of delocalized states, most evident in systems with an odd number of electrons. Clear examples are dissociations of carbocation radicals that often give delocalized states at long distances and large errors in computed binding energies. On the other hand, many mixed-valence transition-metal dimers known to exhibit valence trapping are correctly predicted to be localized. To understand the effects of the self-interaction error on these different systems, energy differences between delocalized and localized states are calculated with B3LYP. In the dissociation of radicals into symmetric fragments at infinite distance, this energy difference equals the error of the density-functional treatment. The energy difference decreases with increasing size of the system, from 55kcal∕mol in H2+ to 15kcal∕mol for C12H26+. Solvent corrections stabilize the localized state and result in smaller errors. Most reactions are asymmetric and this decreases the effect of the self-interaction error. In many systems, delocalization will not occur if the cost to move the electron from one fragment to the other is 70–80kcal∕mol (3.0–3.5eV). This estimate refers to a situation where the distance between the fragments is infinite. The limit decreases with decreasing fragment distance. B3LYP calculations on the ferromagnetic state of a Mn(III,IV) dimer predict that the correct localized state is 22kcal∕mol more stable than the incorrect delocalized state. At short metal–metal distances the effect of the self-interaction error is predicted to be small. However, as the distance between the two manganese centers is increased to 7Å, the dimer starts to delocalize and the energy artificially decreases. In the dissociation limit, the error is 10kcal∕mol. This is interpreted as an artifact originating from the self-interaction error. Delocalization is not encountered in many systems due to relatively short metal–metal distances and asymmetric ligand environments. However, some charge-transfer complexes cannot be properly calculated and delocalized states may become a problem in large models of enzyme systems with multiple transition-metal complexes.
Compact multipolar representation of the electrostatic potential for flexible molecules
Authors: Chodkiewicz Michal Leszek
Published: June 2005

A new method for generating a compact multipolar representation of the electrostatic potential (EP) for flexible molecules is presented. The method is based on a constrained minimization of the difference between the quantum mechanical and the classical EP. The fitting procedure used adopts the least absolute shrinkage and selection operator technique [R. Tibshirani, J. Roy. Stat. Soc. B 58, 267 (1996)] which can be seen as penalized ordinary least squares. The penalty function optimized for the particular molecule of interest effectively removes redundant multipoles. It is shown that the use of multiple conformations is crucial for the predictive ability of the EP model for flexible molecules. The multipole local coordinate systems are chosen in a way that best reflects the key conformational changes. It was demonstrated that such an approach improves the predictive ability of EP models. It also allows to exploit equivalence of atoms in the calculation of multipoles components. In the case of polar flexible molecules, the augmentation of the EP model based on charges by higher multipoles decreases the relative root mean square error by a factor of 1.5–5. The corresponding effect of enlargement of the set of multipoles was significantly reduced.
Investigation of valence orbitals of propene by electron momentum spectroscopy
Authors: Ning C. G. , Ren X. G. , Deng J. K. , Zhang S. F. , Su G. L. , Huang F. , Li G. Q.
Published: June 2005

The binding energy spectra and momentum distributions of all valence orbitals of propene were studied by electron momentum spectroscopy (EMS) as well as Hartree–Fock and density functional theoretical calculations. The experiment was carried out at impact energies of 1200eV and 600eV on the state-of-the-art EMS spectrometer developed at Tsinghua University recently. The experimental momentum profiles of the valence orbitals were obtained and compared with the various theoretical calculations. Moreover, the experiment with a new analysis method presents a strong support for the correct ordering of the orbital 8a′ and 1a″, i.e., 9a′<8a′<1a″<7a′.
Combinatorial electrochemical synthesis and screening of Pt-WO3 catalysts for electro-oxidation of methanol
Authors: Jayaraman Shrisudersan , Baeck Sung-Hyeon , Jaramillo Thomas F. , Kleiman-Shwarsctein Alan , McFarland Eric W.
Published: June 2005

An automated system for high-throughput electrochemical synthesis and screening of fuel cell electro-oxidation catalysts is described. This system consists of an electrode probe that contains counter and reference electrodes that can be positioned inside an array of electrochemical cells created within a polypropylene block. The electrode probe is attached to an automated of X-Y-Z motion system. An externally controlled potentiostat is used to apply the electrochemical potential to the catalyst substrate. The motion and electrochemical control are integrated using a user-friendly software interface. During automated synthesis the deposition potential and/or current may be controlled by a pulse program triggered by the software using a data acquisition board. The screening includes automated experiments to obtain cyclic voltammograms. As an example, a platinum-tungsten oxide (Pt-WO3) library was synthesized and characterized for reactivity towards methanol electro-oxidation.
Water adsorption on a p(2×2)-Ni(111)–O surface studied by surface x-ray diffraction and infrared reflection absorption spectroscopy at 25 and 140K
Authors: Nakamura M. , Tanaka M. , Ito M. , Sakata O.
Published: June 2005

The adsorption of water molecules on an oxygen-predosed p(2×2)-Ni(111)–O surface was studied by surface x-ray diffraction and infrared reflection absorption spectroscopy (IRAS) at temperature of 25 and 140K. Precise structures including adsorbed water, predosed oxygen, and substrate nickel atoms at these two temperatures were determined by x-ray structural analysis. It was found that water molecules adsorb on oxygen additive sites, forming a hydrogen bond at 25K. A predosed 2×2 oxygen atom appears to accommodate one, two, or three water molecules at positions relating to threefold rotation symmetry. When the surface temperature was raised to 140K, water molecules appear at an atop site of Ni. The distance between Ni and the oxygen atoms of a monomer water molecule was found to be 0.2241(22)nm. The adsorbed water molecule induces buckling and a lateral shift of the substrate nickel. The IRAS results provided evidence regarding the existence of two distinct adsorption sites. Water molecules in the low-temperature phase exhibit bands from both hydrogen-bonded νOD and free OD stretchings, while those in the high-temperature phase lie flat with a molecular plane parallel to the surface.
Ab initio global potential-energy surface for H5+→H3++H2
Authors: Xie Zhen , Braams Bastiaan J. , Bowman Joel M.
Published: June 2005

An accurate global potential-energy surface (PES) is reported for H5+ based on more than 100 000 CCSD(T)/aug-cc-pVTZ ab initio energies. This PES has full permutational symmetry with respect to interchange of H atoms and dissociates to H3+ and H2. Ten known stationary points of H5+ are characterized and compared to previous ab initio calculations. Quantum diffusion Monte Carlo calculations are performed on the PES to obtain the zero-point energy of H5+ and the anharmonic dissociation energy (D0) of H5+→H3++H2. The rigorous zero-point state of H4D+ is also calculated and discussed within the context of a strictly classical approach to obtain the branching ratio of the reaction H4D+→H3++HD and H2D++H2. Such an approach is taken using the PES and critiqued based on the properties of the quantum zero-point state. Finally, a simple procedure for adding the long range-interaction energy is described.
Electron-impact excitation of D1Δ←X1Σ+ in carbon monoxide
Authors: Zhu Lin-Fan , Ren Heng-Feng , Liu Xiao-Jing , Yuan Zhen-Sheng , Wu Yi , Xu Ke-Zun
Published: June 2005

The dipole-forbidden transition of D1Δ←X1Σ+ of CO has been observed by a fast electron-energy-loss spectrometer at a large scattering angle of 7° and with an energy resolution of 60meV. The energy levels and the relative intensity distribution of D1Δ, v′=9–25 have been determined, most of the results are reported for the first time.
Statistical approach of weakly nonlinear ablative Rayleigh–Taylor instability
Authors: Garnier J. , Masse L.
Published: June 2005

A weakly nonlinear model is proposed for the Rayleigh–Taylor instability in presence of ablation and thermal transport. The nonlinear effects for a single-mode disturbance are computed, included the nonlinear correction to the exponential growth of the fundamental modulation. Mode coupling in the spectrum of a multimode disturbance is thoroughly analyzed by a statistical approach. The exponential growth of the linear regime is shown to be reduced by the nonlinear mode coupling. The saturation amplitude is around 0.1λ for long wavelengths, but higher for short instable wavelengths in the ablative regime.
Efficient sub 100nm focusing of hard x rays
Authors: Hignette O. , Cloetens P. , Rostaing G. , Bernard P. , Morawe C.
Published: June 2005

An x-ray beam with energy of 20.5keV has been efficiently focused down to a spot size as small as 90nm×90nm by a Kirkpatrick–Baez reflecting mirrors device. The first mirror, coated with a graded multilayer, plays both the role of vertical focusing device and monochromator, resulting in a very high flux (2×1011photons∕s) and medium monochromaticity (ΔE∕E∼10−2). Evaluation of the error contributions shows that the vertical focus is presently limited by the mirror figure errors, while the horizontal focus is limited by the horizontal extension of the x-ray source. With a gain in excess of a few million, this device opens up new possibilities in trace element nanoanalysis and fast projection microscopy.
Noncurvature-driven modes in a transport barrier
Authors: Rogers B. N. , Dorland W.
Published: June 2005

Transport barriers that form in both the edge and interior regions of high temperature magnetically confined discharges are characterized by steep plasma gradients, strong E×B and diamagnetic flows, and varying levels of magnetic shear. This study addresses the linear stability of such configurations in the context of a simple slab model using both analytic calculations as well as numerical simulations from the gyrokinetic GS2 code. Three linear modes of potential importance are found: the Kelvin–Helmholtz instability, the tertiary mode, and a nonlocal drift wave instability. Each mode is unstable only in the presence of nontrivial spatial variations in either the E×B flow and∕or the plasma gradients. The strongest conclusion of this study is that the drift wave mode may be an important driver of anomalous transport in the edge region of magnetic confinement devices. Two other weaker conclusions that warrant further study are as follows: (1) the Kelvin–Helmholtz instability may be associated with edge-localized modes or edge transport and (2) the tertiary mode can potentially limit the radial growth of a transport barrier.
Numerical studies of driven, chirped Bernstein, Greene, and Kruskal modes
Authors: Peinetti F. , Bertsche W. , Fajans J. , Wurtele J. , Friedland L.
Published: June 2005

Recent experiments showed the possibility of creating long-lived, nonlinear kinetic structures in a pure-electron plasma. These structures, responsible for large-amplitude periodic density fluctuations, were induced by driving the plasma with a weak oscillating drive, whose frequency was adiabatically decreased in time [W. Bertsche, J. Fajans, and L. Friedland, Phys. Rev. Lett. 91, 265003 (2003)]. A one-dimensional analytical model of the system was developed [L. Friedland, F. Peinetti, W. Bertsche, J. Fajans, and J. Wurtele, Phys. Plasmas 11, 4305 (2004)], which pointed out the phenomenon responsible for the modifications induced by the weak drive in the phase-space distribution of the plasma (initially Maxwellian). In order to validate the theory and to perform quantitative comparisons with the experiments, a more accurate description of the system is developed and presented here. The new detailed analysis of the geometry under consideration allows for more precise simulations of the excitation process, in which important physical and geometrical parameters (such as the length of the plasma column) are evaluated accurately. The numerical investigations probe properties and features of the modes not accessible to direct measurement. Due to the presence of two distinct time scales (because of the adiabatic chirp of the drive frequency), a fully two-dimensional numerical study of the system is expected to be rather time consuming. This becomes particularly important when, as here, a large number of comparisons (covering a wide range of drive parameters) are performed. For this reason, a coupled one-dimensional, radially averaged model is derived and implemented in a particle-in-cell code.
Stable five axes cryogenic photoemission manipulator without a differentially pumped rotary feedthrough
Authors: Kim Bum Joon , Kim Hyeong-Do , Cho Deok-Yong , Kim Myongjin , Oh S.-J. , Kim Changyoung
Published: June 2005

We report on the design and construction of an ultrahigh vacuum compatible cryogenic manipulator for angle resolved photoemission spectroscopy. Unlike designs that have been used so far, our design allows five motions (three translational and two angular) without a differentially pumped rotary feedthrough. The design greatly reduces the sample motion upon rotation, which is crucial in automatic data acquisition over a large area in the momentum space. The constructed manipulator shows smooth motions in vacuum and the lowest temperature it could reach is about 8K at the sample position. Angular reproducibilities are found to be about 0.02° for both of the angular motions. The wobbling motion from the rotation around the vertical rotation axis is found to be virtually nonexistent (less than 0.1mm).
Development and applications of an epifluorescence module for synchrotron x-ray fluorescence microprobe imaging
Authors: Miller Lisa M. , Smith Randy J. , Ruppel Meghan E. , Ott Cassandra H. , Lanzirotti Antonio
Published: June 2005

Synchrotron x-ray fluorescence (XRF) microprobe is a valuable analysis tool for imaging trace element composition in situ at a resolution of a few microns. Frequently, epifluorescence microscopy is beneficial for identifying the region of interest. To date, combining epifluorescence microscopy with x-ray microprobe has involved analyses with two different microscopes. We report the development of an epifluorescence module that is integrated into a synchrotron XRF microprobe beamline, such that visible fluorescence from a sample can be viewed while collecting x-ray microprobe images simultaneously. This unique combination has been used to identify metal accumulation in Alzheimer’s disease plaques and the mineral distribution in geological samples. The flexibility of this accessory permits its use on almost any synchrotron x-ray fluorescence microprobe beamline and applications in many fields of science can benefit from this technology.
Lifting Bell inequalities
Authors: Pironio Stefano
Published: June 2005

A Bell inequality defined for a specific experimental configuration can always be extended to a situation involving more observers, measurement settings, or measurement outcomes. In this article, such “liftings” of Bell inequalities are studied. It is shown that if the original inequality defines a facet of the polytope of local joint outcome probabilities then the lifted one also defines a facet of the more complex polytope.
Equation-of-motion coupled-cluster study on exciton states of polyethylene with periodic boundary condition
Authors: Katagiri Hideki
Published: June 2005

Equation-of-motion coupled cluster with singles and doubles (EOM-CCSD) method has been applied to exciton states of polyethylene using ab initio crystal Hartree–Fock method with one-dimensional periodic boundary condition. Full transformation of two-electron integrals from atomic-orbital basis to crystal-orbital basis has been performed for EOM-CCSD calculations. In order to make transformed integrals to have correct properties of translational symmetry, a lattice summation scheme has been proposed. The EOM-CCSD excitation energies have been obtained for the lowest singlet and triplet exciton states of polyethylene. The excitation energies converge with system size much faster than oligomer calculations using n-alkanes. Quasiparticle energy-level calculations by second-order many-body perturbation theory and by solving the inverse Dyson equation have also been performed to obtain exciton binding energies. Basis set dependencies on excitation energy, quasiparticle band gap, and exciton binding energy have been investigated. At the 6-31+G level, the excitation energy of the lowest singlet-exciton state and its binding energy are calculated to be 8.1 and 3.2eV, respectively. The calculated excitation energy is well comparable with the corresponding experimental value, 7.6eV.
Sawtooth stabilization by barely trapped energetic electrons
Authors: Zhou Deng , Wang Shaojie , Zhang Cheng
Published: June 2005

The barely trapped energetic electrons produced by the electron cyclotron resonance heating can interact efficiently with the internal kink mode and stabilize sawtooth oscillations. The effects of the spatial distribution and the pitch angle distribution of the energetic electrons are considered. The most effective stabilization is obtained when the peak of the spatial distribution locates on the q=1 rational surface. This machanism gives a reasonable explanation of the difference between the high-field-side heating and the low-field-side heating on tokamaks.
Upconversion luminescence from CdSe nanoparticles
Authors: Chen Wei , Joly Alan G. , McCready David E.
Published: June 2005

Efficient upconversion luminescence has been observed from CdSe nanoparticles ranging in size from 2.5 to 6 nm. The upconversion luminescence exhibits a near-quadratic laser power dependence. Emissions from both excitons and trap states are observed in the upconversion and photoluminescence spectra, and in the upconversion luminescence the emission from the trap states is enhanced relative to the trap-state emission in the photoluminescence. The upconversion decay lifetimes are slightly longer than the photoluminescence decay lifetimes. Time-resolved spectral measurements indicate that this is due to the involvement of long decay components from surface or trap states. Both the photoluminescence and upconversion luminescence decrease in intensity with increasing temperature due mainly to thermal quenching. All the observations indicate that trap states work as emitters rather than as intermediate states for upconversion luminescence and that two-photon absorption is the likely excitation mechanism.
Effective superconfiguration temperature and the radiative properties of nonlocal thermodynamical equilibrium hot dense plasma
Authors: Peyrusse O. , Bauche-Arnoult C. , Bauche J.
Published: June 2005

The model of superconfiguration (SC) temperatures has been used extensively for computing the population dynamics of very large systems in hot dense plasmas. Plasmas of Ge, Xe, and Au have been studied for a wide range of values of Te and Ne. For plasmas containing a distribution of a dozen of ionization states, two systems of a few hundreds of linear equations are solved, with one equation per SC. The power of the method lies in the possibility of determining the populations of all the electronic configurations belonging to those SCs. This opens the way to detailed modeling of complex spectra and to calculations of emissivities and opacities in laser-plasma simulations and experiments.
Magnetohydrodynamic flow of RedOx electrolyte
Authors: Qian Shizhi , Bau Haim H.
Published: June 2005

Magnetohydrodynamic (MHD) flow of a RedOx electrolyte in a straight conduit is investigated theoretically. Inert electrodes are deposited along segments of the opposing walls of a straight conduit that is filled with a RedOx electrolyte solution. The conduit is positioned in a uniform magnetic field. When a potential difference is applied across the opposing electrodes, the resulting current interacts with the magnetic field to induce Lorentz forces. The species’ mass transport and the momentum equation are coupled and must be solved simultaneously. We compute the various species’ concentration distributions, the current flux distribution, and the liquid’s motion in the absence and presence of pressure gradients. The pressure gradients may either assist or oppose the MHD flow. At low potential differences, the current and the induced MHD flow increase nearly linearly as the potential difference increases. When the potential difference exceeds a certain critical value, the current and the flow rate saturate. We demonstrate that it is advantageous to use multiple electrode pairs with dielectric gaps between adjacent electrodes rather than a single electrode pair with an equivalent length. Finally, MHD flow with RedOx solution in the presence of abundant supporting electrolyte under limiting current conditions is analyzed using boundary layer theory. The approximate analytical solutions for the ions’ concentrations and the current agree well with the numerical solutions.
Waves and instabilities in weak inhomogeneous ideal Hall-magnetohydrodynamic plasmas
Authors: Kolberg Zohar , Liverts Edward , Mond Michael
Published: June 2005

The two-fluid magnetohydrodynamic equations in which the Hall term is taken into account in Faraday’s law (Hall magnetohydrodynamic) for low-density magnetized inhomogeneous plasmas with finite pressure, and accounting for the inertial electron and ion dynamics responses are considered for slab geometry. Waves that propagate in the direction perpendicular to the density gradient and close to the direction of the background magnetic field are considered and linear analysis is employed in order to derive a local dispersion relation. It is shown that both the ion-cyclotron acoustic mode as well as the magnetosound mode are susceptible to an instability that is driven by the spatial inhomogeneity of the plasma density. The condition under which unstable waves appear and the growth rate of the unstable modes are obtained for collisionless plasmas. The results of this theoretical investigation can be relevant to instabilities in low-beta fusion plasma devices as well as in various space applications.
Anomalous diffusion, clustering, and pinch of impurities in plasma edge turbulence
Authors: Priego M. , Garcia O. E. , Naulin V. , Rasmussen J. Juul
Published: June 2005

The turbulent transport of impurity particles in plasma edge turbulence is investigated. The impurities are modeled as a passive fluid advected by the electric and polarization drifts, while the ambient plasma turbulence is modeled using the two-dimensional Hasegawa–Wakatani paradigm for resistive drift-wave turbulence. The features of the turbulent transport of impurities are investigated by numerical simulations using a novel code that applies semi-Lagrangian pseudospectral schemes. The diffusive character of the turbulent transport of ideal impurities is demonstrated by relative-diffusion analysis of the evolution of impurity puffs. Additional effects appear for inertial impurities as a consequence of compressibility. First, the density of inertial impurities is found to correlate with the vorticity of the electric drift velocity, that is, impurities cluster in vortices of a precise orientation determined by the charge of the impurity particles. Second, a radial pinch scaling linearly with the mass–charge ratio of the impurities is discovered. Theoretical explanation for these observations is obtained by analysis of the model equations.
Broadband complex permeability characterization of magnetic thin films using shorted microstrip transmission-line perturbation
Authors: Liu Yan , Chen Linfeng , Tan C. Y. , Liu H. J. , Ong C. K.
Published: June 2005

A brief review of the methods used for broadband complex permeability measurement of magnetic thin films up to microwave frequencies is given. In particular, the working principles of the transmission-line perturbation methods for the characterization of magnetic thin films are discussed, with emphasis on short-circuited planar transmission-line perturbation methods. The algorithms for calculating the complex permeability of magnetic thin films for short-circuited planar transmission-line perturbation methods are analyzed. A shorted microstrip line is designed and fabricated as a prototype measurement fixture. The structure of the microstrip fixture and the corresponding measurement procedure are discussed in detail. A piece of 340 nm thick FeTaN thin film deposited on Si substrate using sputtering method is characterized using the microstrip fixture. An improved technique for obtaining permeability by using a saturation magnetization field is demonstrated here, and the results fit well with the Landau–Lifchitz–Gilbert theory. Approaches to extending this method to other aspects in the investigation of magnetic thin film are also discussed.
Microforce materials tester
Authors: Fujii Yusaku
Published: June 2005

A material tester for evaluating the mechanical response of general objects against micro-Newton level impact forces has been proposed. In the tester, an inertial mass is made to collide with the material under test. The impact force acting on the material is measured as the inertial force of the mass. A pneumatic linear bearing is used to realize linear motion with small friction acting on the mass that is the moving part of the bearing. The velocity of the mass is measured highly accurately by means of an optical interferometer. The acceleration, the inertial force, and the position of the mass is numerically calculated from the velocity after the collision measurement. The other force, which is mainly consisted of the friction acting inside the bearing, is determined using the same instrumentations. Using the estimated friction inside the bearing, the measured force is corrected. The force acting on the mass from the material under test of approximately 0.1 mN is measured with the standard uncertainty of approximately 1.4μN.
Comment on “Computation of the pseudorotation matrix to satisfy the Eckart axis conditions” [J. Chem. Phys. 122, 124103 (2005)]
Authors: Dierksen Marc
Published: June 2005

It is shown that the general solution for the computation of the pseudorotation matrix for satisfying the Eckart axis conditions recently proposed by Dymarsky and Kudin [J. Chem. Phys. 122, 124103 (2005)] is mathematically equivalent to a solution described in the Appendix of the paper of Pickett and Strauss [J. Am. Chem. Soc. 92, 7281 (1970)].
Elliptical-inertial instability of rotating Karman vortex streets
Authors: Stegner A. , Pichon T. , Beunier M.
Published: June 2005

Clouds often reveal a small-scale vortex shedding in the wake of mountainous islands. Unlike the classical bidimensional Karman street, these observed vortex streets are affected by the earth’s rotation and vertical stratification of the atmosphere. These effects induce a selective destabilization of anticyclonic vorticity regions. It is well known that inertial instability, also called centrifugal instability, induces a three-dimensional destabilization of anticyclonic vortices when the absolute vorticity is larger than the local Coriolis parameter. However, we have shown by means of laboratory experiments, that it is a different type of instability which is mainly responsible for the secondary destabilization of rotating Karman streets. A series of experiments were performed to study the wake of a cylinder in a rotating deep water layer, at a medium Reynolds number and an order one Rossby number. We have shown that the unstable mode is a core-centered perturbation and its vertical wavelength strongly depends on the Rossby number. These dynamical characteristics are the signature of an elliptical instability in rotating flows. We have also checked that an asymptotic instability criterion, valid around an elliptical stagnation point, was satisfied in the early stage of shedding when the anticyclonic boundary layer detaches and rolls up in elliptical structures. Similar asymmetric Karman streets were also found in the shallow-water configuration when the vertical to horizontal aspect ratio is close to unity.