bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis by ball milling and characterization of nanocrystalline Fe3O4 and Fe/Fe3O4 composite system
Authors: Bonetti E. , Del Bianco L. , Signoretti S. , Tiberto P.
Published: July 2002

Nanocrystalline Fe3O4 and a composite system constituted by nanocrystalline Fe and Fe3O4 have been synthesized by ball-milling commercial magnetite and an equimolar mixture of iron and magnetite powders. The physical parameters governing the milling process have been strictly controlled so as to achieve the nanocrystalline state of the precursor material and to avoid chemical reactions. X-ray diffraction and Mössbauer spectroscopy measurements have been carried out both on as-milled powders and on samples previously subjected to annealing treatments in the 100–600 °C temperature range. The results, providing information on the structural and compositional features of the produced samples, are discussed in terms of structural disorder which is healed by subsequent annealing. In the case of the composite system, this analysis indicates that a high mixing degree between the constituent phases has been reached. In particular, the presence of a sextet with anomalous hyperfine parameters in the Mössbauer spectrum of as-milled Fe+Fe3O4 has been associated with an alteration of the magnetite structure at the interface with bcc Fe. For both sets of samples, the influence of the structural features on the macroscopic magnetic behavior has been investigated by performing magnetic hysteresis loop measurements at room temperature.
Dielectric transition of nanostructured diamond films
Authors: Ye Haitao , Sun Chang Q. , Huang Haitao , Hing Peter
Published: July 2002

The dielectric behavior of nanostructured diamond films has been investigated by using an impedance analyzer up to 500 °C. Impedance data are presented in the form of the Cole–Cole plot. It is found that: (i) the resistivity contributed both from bulk grain interior and grain boundary decreases with increasing temperature; (ii) above 250 °C, the impurities at grain boundaries are thermally activated, and thus contribute to the dielectric relaxation; and (iii) the electrical conductivity of diamond films follows an Arrhenius law with an activation energy transition from 0.13 to 0.67 eV at 250 °C. Similar activation energy is found for the Arrhenius plot of relaxation frequencies from 0.14 to 0.73 eV. The dielectric transition is explained as the change of crystal field caused by the thermal expansion or by surface bond contraction of nanosized particles.
Carrier transport and localization in a one-dimensional electronic system over liquid helium
Authors: Gladchenko S. P. , Nikolaenko V. A. , Kovdrya Yu. Z. , Sokolov S. S.
Published: July 2002

The carrier mobility in a nearly one-dimensional electronic system over liquid helium is measured. One-dimensional conducting channels are created by using the curvature of the surface of liquid helium covering a profiled dielectric substrate and applying a clamping electric field, which holds the electrons on the bottom of the liquid troughs. Measurements are made in a temperature interval of 0.5–1.6 K at linear densities in the range (0.5–2.5)×104 cm−1 at a generator voltage of 2–200 mV. It is shown that for a clean substrate the mobility of the electrons is governed by their interaction with helium atoms in the vapor and with ripplons; the results of the measurements are in satisfactory agreement with a theoretical calculation that assumes no localization. It is found that for substrates carrying a charge or having defects on the surface, the electron mobility decreases in comparison with the value for a clean substrate, and at temperatures T<1 K is either practically independent of temperature or decreases slightly as the temperature is lowered. It is observed that the frequency of the plasma waves propagating in the system of conducting channels decreases as the electron mobility decreases. The observed effects can be explained by localization in the one-dimensional electronic system in a random potential and the diffusive motion of the carriers in hops from one localized state to another.
Enhanced electric polarizability in metal C60 compounds: Formation of a sodium droplet on C60
Authors: Dugourd Ph. , Antoine R. , Rayane D. , Compagnon I. , Broyer M.
Published: July 2002

We measured the electric polarizability of NaNC60 (N=1–34) molecules. The experimental values can be interpreted by the existence of a permanent electric dipole for every size. This cannot be explained by a metal shell around the C60, but this is in agreement with a sodium cluster bound to the C60.
The second-order Møller–Plesset limit for the barrier to linearity of water
Authors: Valeev Edward F. , Allen Wesley D. , Schaefer Henry F. , Császár Attila G.
Published: July 2002

A series of high-quality conventional and explicitly correlated second-order Møller–Plesset energies, denoted as MP2 and MP2-R12/A, respectively, was computed in a state-of-the-art attempt to arrive at the ab initio limit for the barrier to linearity of water. [O/H]-centered Gaussian basis sets as large as [19s13p11d9f7g5h3i/13s11p9d7f5g3h] were employed in the study. We find that basis functions with high orbital angular momentum quantum number (h and i) are important for highly accurate predictions of the electronic energy, even when explicitly correlated approaches are utilized. This observation is at variance with previous claims that explicitly correlated methods require basis sets saturated only to the level of f functions for spectroscopic accuracy. Our best explicitly computed value for the MP2 contribution to the barrier is −357 cm−1. The resulting final ab initio estimate for the classical barrier to linearity of water is 11 119±15 cm−1, in good agreement with the most recently obtained empirical value of 11 105±5 cm−1.
White-noise magnetization fluctuations in magnetoresistive heads
Authors: Smith Neil , Arnett Patrick
Published: July 2002

Thermal magnetization fluctuations in magnetoresistive (MR) heads for magnetic hard-disk storage are a fundamental limit on their signal-to-noise ratio. The resultant noise is essentially frequency flat (white), scales with head sensitivity as signal does, but increases inversely with sensor volume. It will impact the present course of industrial R&D efforts toward geometric scaling and increasing raw head sensitivity to achieve increased areal storage densities and data rates. Magnetization noise is shown to exceed Johnson noise in 0.4 μm sensor size, giant-MR spin-valve heads designed for ∼20 Gbit/in.2 areal storage density. The basic physics underlying the experimental results is shown to be consistent with predictions from the fluctuation–dissipation theorem.
Role of charge-density fluctuations and many-particle Coulomb correlations in the mechanism of high-temperature superconductivity of cuprate metal-oxide compounds
Authors: Pashitskiı̆ É. A. , Pentegov V. I.
Published: July 2002

The charge-fluctuation (plasmon) mechanism of d-wave Cooper pairing in high-Tc superconductors (HTSCs) is considered. This mechanism arises from the interaction of current carriers with collective low-frequency electron-density excitations. It is shown that for layered crystals of cuprate metal-oxide compounds the existence of a one-electron spectrum of anisotropic extended saddles (flat bands) with an anomalously high density of states can give rise to damped long-wavelength charge-density fluctuations that lead to suppression of the static screened Coulomb repulsion in the region of small momentum transfers. As a result, an effective attraction between electrons arises in the d-wave Cooper channel; this attraction is substantially enhanced by many-particle Coulomb correlations of the local-field-effects type, described by a Coulomb vertex Γc. It leads to Cooper pairing with dx2−y2 symmetry of the superconducting order parameter and can make for rather high maximum values of the critical temperature, Tc∼100 K, at the optimum doping level for cuprate metal-oxide compounds. Taking the anisotropy of the electron–phonon interaction into account makes it possible to describe the weak oxygen isotope effect in HTSC compounds.
Morphology and photonic band structure modification of polystyrene particle layers by reactive ion etching
Authors: Fujimura Toru , Tamura Tsuyoshi , Itoh Tadashi , Haginoya Chiseki , Komori Yuri , Koda Takao
Published: July 2002

Morphology of self-assembled polystyrene particle layers has been modified by reactive ion etching. The etched layers have two-dimensional periodic structures in submicron scale, the period of which is determined by the initial size of the particles, and the shape of the etched particles has been gradually changed to a thinner ellipsoid depending on the etching time. Resonant phenomenon between incident light and electromagnetic eigenmodes of the photonic band of the etched layers has been observed in transmission measurement. The resonant frequencies have gradually shifted according to the etching time, i.e., the photonic band structure of the layers has been successfully modified. Various kinds of applications can be expected due to the electromagnetic resonant phenomenon and the characteristic surface structure of the layers.
Array of nickel nanowires enveloped in polyaniline nanotubules and its magnetic behavior
Authors: Cao Huaqiang , Tie Chenyang , Xu Zheng , Hong Jianming , Sang Hai
Published: July 2002

An array of nickel nanowires enveloped in polyaniline nanotubules was prepared by the “second-order-template” method. As the first step, an array of the polyaniline nanotubules was synthesized in the pores of an alumina membrane, then nickel nanowires were fabricated by electrochemical deposition of the nickel into the polyaniline nanotubules. The composite nanostructure was characterized by x-ray powder diffraction, and scanning electron micrography. Its magnetic properties were measured by a vibrating sample magnetometer. The coercivity and remanence are of high anisotropy with a maximum at θ=90° (parallel to the nanowires).
Shallow thermal donors in nitrogen-doped silicon
Authors: Voronkov V. V. , Porrini M. , Collareta P. , Pretto M. G. , Scala R. , Falster R. , Voronkova G. I. , Batunina A. V. , Golovina V. N. , Arapkina L. V. , Guliaeva A. S. , Milvidski M. G.
Published: July 2002

Silicon crystals doped with nitrogen from the melt contain shallow thermal donors (STDs) detected both optically and electrically. Annealing samples at 600 and 650 °C results in a saturated STD concentration that depends on the nitrogen concentration approximately by a square-root law. This indicates the involvement of only one nitrogen atom in every STD species. The model of STDs consistent with the present data is the NOm complex of a nitrogen interstitial and m oxygen atoms; the concentration of every STD species reaches the equilibrium value during annealing. The temperature dependence of the equilibrium reaction constant allows us to estimate the average number of oxygen atoms m of the STD complexes as 3.
Magnetotransport properties of single crystal Co2MnGe/NM/Co2MnGe trilayers epitaxially grown on GaAs (001)
Authors: Ambrose T. , Krebs J. J. , Prinz G. A.
Published: July 2002

The magnetotransport properties of single crystal trilayers 60 Å Co2MnGe/NM/30 Å Co2MnGe where NM is a nonmagnetic spacer material has been studied. The samples were grown by molecular beam epitaxy on GaAs (001) substrates. The 2 to 1 ratios in thickness of the Co2MnGe layers allows for the easy determination of which ferromagnetic layers have switched during magnetometry measurements. A weak 90° coupling has been observed in trilayers with either a Mn or a V spacer layer. In these coupled films a giant magnetoresistance type magnetoresistance of less than 1% has been measured at room temperature.
Magnetostriction in the mixed state of superconducting 2H-NbSe2 single crystals
Authors: Eremenko V. V. , Sirenko V. A. , Schleser R. , Gammel P. L.
Published: July 2002

Magnetostriction measurements on 2H-NbSe2 single crystals in the temperature range 1.5–8 K in a magnetic field up to 14 T are reported. A peak and oscillations in the measured field dependences of magnetostriction are observed near Hc2. The reversible and irreversible components are separated and analyzed in the region of peak. The scaling parameters are defined, and the contribution of the elastic constants dependence on magnetic field is demonstrated. The oscillatory component is discussed in connection with Landau quantization of electronic spectrum.
Terahertz detection by high-electron-mobility transistor: Enhancement by drain bias
Authors: Lü Jian-Qiang , Shur Michael S.
Published: July 2002

We report on a regime of operation of high-electron-mobility-transistor (HEMT) terahertz detectors, in which we apply a constant drain bias. The drain bias dependence of the gate-to-source and gate-to-drain capacitances results in a much greater asymmetry in the boundary conditions for plasma waves and greatly enhances the HEMT detector responsivity. The measured responsivity increases with the drain current by more than an order of magnitude and saturates at a saturation drain current for a given gate bias. These results confirm our model linking the responsivity increase to the drain bias dependence of the HEMT capacitances.
Rationale for reagent reorientation in the activated bimolecular reaction N(2D)+H2: Beyond the angular dependent line of center model
Authors: Larrégaray P. , Bonnet L. , Rayez J. C.
Published: July 2002

The reaction N(2D)+H2(X 1Σg+)→NH(X 3Σg−)+H(2S) involves an early barrier of ∼2 kcal/mol and a significant exoergicity of ∼30 kcal/mol. Thus, for collision energies of several kcal/mol, barrier crossing leads to reaction with nearly unit probability. To our knowledge, the angular dependent line of center (ADLOC) model is to date the only one which allows the analytical formulation of the barrier overcoming cross section, identifiable here with the reaction cross section. This model, however, neglects the interaction between reagents up to the barrier top. As a consequence, it ignores the reorientation of H2 with respect to N which enhances, on average, the reactivity with respect to its predictions. The linear transformation model (LTM), recently derived in order to describe product separation in unimolecular fragmentations, is now applied to the study of reagent approach in the title reaction. The main interest of LTM is to take into account reorientation while leading to an expression of the reaction cross section as simple as the ADLOC one, but in much better agreement with dynamical calculations.
Measurement of molecular motion in solids by nuclear magnetic resonance spectroscopy of half-integer quadrupole nuclei
Authors: Kristensen J. H. , Farnan I.
Published: July 2002

An accurate and efficient formalism is presented for simulating the effects of molecular motion on satellite and central transition nuclear magnetic resonance (NMR) spectra of half-integer quadrupole nuclei. The approach is based on the principles of the density operator and the stochastic Liouville–von Neumann equation and may be applied for both rotating and nonrotating samples. The symmetry properties of nuclear spin ensembles have been used to rewrite the stochastic Liouville–von Neumann equation in the form of a linear homogeneous system of coupled first-order differential equations among the alignments and coherences. This system is highly stiff and can only be solved by methods that are sufficiently accurate and stable. The properties of Cartan–Weyl operators have been used to obtain the most efficient solution for secular interactions. The methodology has been incorporated into computer programs to simulate the effects of motion for any half-integer quadrupole nucleus. These programs include the first- and second-order quadrupole and first-order shielding interactions. The formalism has been used to calculate central transition O17 NMR spectra of representative model systems. The calculations have revealed several interesting and important properties of central transition NMR spectra that have been discussed in terms of the functional form of the line shape. The validity of the methodology has been demonstrated experimentally by simulating variable temperature central transition O17 NMR spectra of the silicate (SiO2) mineral cristobalite for both rotating and nonrotating samples. The simulations have allowed the structural and dynamical details of the α–β phase transition in cristobalite to be separated. The line shapes can only be simulated if the effects of motion are included and are consistent with a model where the oxygen atoms reorient between six different orientations. It is found that the oxygen motion is present both before and after the α–β phase transition and does not change significantly at the transition temperature. The observed changes in the quadrupole and shielding parameters are shown not to be the results of motional averaging but derive from an abrupt structural change associated with the first-order character of the α–β phase transition. The structural changes may be interpreted in terms of a model where the Si–O–Si bond angle increases slightly.
Influence of electrical stress voltage on cathode degradation of organic light-emitting devices
Authors: Lin Karen Ke , Chua Soo Jin , Wei-Wang  , Lim Shuang Fang
Published: July 2002

Our in situ experimental observations of the influence of electrical stress voltage on organic light-emitting device growth in dark spot areas are presented. We demonstrate the use of microsized silica particles to create uniformly sized defects on the protective layer. This is an efficient way to control the location and the number of dark spots. The growth in dark spot area was studied at different driving voltages from 0 up to 11 V. Dark field microscopy was used to monitor the dark spot size below the turn-on voltage. The bright field was used at or above the turn-on voltage. Our observations indicate that dark spot growth was strongly affected by the electrical stress voltage. A linear growth rate with respect to the voltage was observed with a fitting parameter better than 99.7% when the device is driven above the turn-on voltage. We interpret the dark spot growth in terms of the diffusion of moisture and oxygen accompanied by cathode layer chemical and physical changes.
Effective mass of two-dimensional electron gas in an Al0.2Ga0.8N/GaN heterojunction
Authors: Hang D. R. , Liang C.-T. , Huang C. F. , Chang Y. H. , Chen Y. F. , Jiang H. X. , Lin J. Y.
Published: July 2002

We have performed a magnetotransport study on an AlGaN/GaN heterostructure at low temperatures. The effective-mass values have been evaluated by analyzing the exact form of the temperature-dependent Shubnikov–de Haas oscillation function. The values obtained increase with the magnetic field. This mass enhancement is attributed to conduction-band nonparabolicity. The effective-mass variation with the magnetic field was extrapolated to zero field, together with further correction due to the triangular confinement of the carriers, yielding an effective mass of 0.185±0.005 of the free-electron mass. Our result is in excellent agreement with the results obtained by first-principle calculations and the tight-binding method, and suggest the significance of magnetic-field-induced nonparabolicity in transport measurements.
Unique morphologies of boron nitride nanotubes
Authors: Golberg D. , Bando Y.
Published: July 2002

Unusual morphological features of boron nitride nanotubes produced via metal–oxide-promoted high-temperature syntheses from carbon nanotubes, boron oxide, and nitrogen were observed using high-resolution transmission electron microscopy. The tubes normally displayed open ends and preferentially two or four tubular layers as revealed by statistical analysis of 600 nanotubes. In addition, the total amount of tubes with even number of shells (61% occurrence) markedly prevailed over that with odd number of shells (39%). All three characteristics are exceptional for BN compared to other layered materials which may be assembled in tubules.
Effect of palladium cap layer thickness on desorption of hydrogen from PrHx films: A spectroscopic ellipsometry study
Authors: Mor G. K. , Malhotra L. K. , Bhattacharyya D.
Published: July 2002

Optical characterization of palladium (Pd) capped PrHx films has been performed using phase modulated spectroscopic ellipsometry to study the effect of thickness of a cap layer on the deloading of hydrogen from the capped hydride films. Experimental Ψ and Δ spectra have been fitted to an optical model consisting of an air/Pd/PrHx/glass substrate. The direct band gap of the PrHx films, calculated from the Tauc plots of these films, has been found to decrease with an increase in the thickness of the Pd overlayer, which in fact is due to enhanced deloading of hydrogen. The removal of hydrogen from PrHx films leads to the formation of localized states, whose signature is clearly observed in the Tauc plots. The energy corresponding to a transition involving these states and the conduction band has been found to increase with increasing Pd overlayer thickness.
Measurement of the excited-state position of bound-to-bound quantum-well infrared detectors
Authors: Zhou L. , Chee Y. H. , Karunasiri G.
Published: July 2002

The energy of the first excited state of quantum-well infrared detectors plays an important role in determining performance. The uncertainties in material and growth parameters make it difficult to design quantum-well detectors with a precise control of the location of energy states. Such uncertainties will cause detectors to be either bound to continuum or bound to bound. In this article, we present a technique to locate the excited-state position in bound-to-bound quantum-well infrared detectors by measuring the bias dependence of the photoresponse. We have employed an InGaAs/AlGaAs quantum-well detector operating near 5 μm for this study. The photocurrent was found to have a strong bias dependence indicating the infrared transition in the quantum well is bound to bound in nature. The bias dependence of the photoresponse was compared with theoretical estimates including the tunneling of photoexcited electrons through the barrier. The results showed a good agreement and this allowed us to determine the location of the excited state from the barrier edge.
Evidence of eutectic crystallization and transient nucleation in Al89La6Ni5 amorphous alloy
Authors: Zhuang Y. X. , Jiang J. Z. , Lin Z. G. , Mezouar M. , Crichton W. , Inoue A.
Published: July 2002

The phase evolution with the temperature and time in the process of crystallization of Al89La6Ni5 amorphous alloy has been investigated by in situ high-temperature and high-pressure x-ray powder diffraction using synchrotron radiation. Two crystalline phases, fcc-Al and a metastable bcc-(AlNi)11La3-like phase, were identified after the first crystallization reaction, revealing a eutectic reaction instead of a primary reaction suggested in the literature. Time-dependent nucleation in the amorphous alloy is detected and the experimental data can be fitted by both the Zeldovich’s and Kashchiev’s transient nucleation models with transient nucleation times of 220 and 120 min, respectively.
Compressibility of nanostructured alumina phases determined from synchrotron x-ray diffraction studies at high pressure
Authors: Zhao J. , Hearne G. R. , Maaza M. , Laher-Lacour F. , Witcomb M. J. , Le Bihan T. , Mezouar M.
Published: July 2002

Synchrotron x-ray diffraction studies up to pressures of 30 GPa have been performed on both nanostructured γ-Al2O3 and α-Al2O3. The P-V equation of state has been calculated from a fit to the diffraction data to obtain the compressibility for each of the compounds. The bulk modulus B0 of nanostructured γ-Al2O3 having grain-size diameters in the range 4 – 8 nm is B0 =152(8) GPa, appreciably lower than the value B0≈250 GPa of its bulk structural analog. The bulk-modulus of nanophase α-Al2O3 of 25 nm average crystallite diameter, which is difficult to stabilize at smaller dimensions because of thermodynamic considerations, is 252(9) GPa and therefore similar to that of bulk α-Al2O3. These studies suggest that only if the grain-size of alumina is below a critical value of several nanometers can substantial changes be expected in the isothermal bulk modulus compared to that of the isostructural bulk compound.
High resolution femtosecond coherent anti-Stokes Raman scattering: Determination of rotational constants, molecular anharmonicity, collisional line shifts, and temperature
Authors: Lang T. , Motzkus M. , Frey H. M. , Beaud P.
Published: July 2002

In this paper we present high resolution spectroscopy performed with femtosecond coherent anti-Stokes Raman scattering (CARS). After a theoretical treatment of the issue, specific experimental configurations will be introduced. Transients from nonresonant rotational and vibrational CARS on di- and polyatomics in the gas phase were analyzed. Rotational and vibrational constants and pressure-dependent line shifts are determined with high accuracy. The method is suitable for precise measurement of temperatures. We present thermometry on combustion relevant species like H2 and N2 and discuss the reliability and accuracy of the data.
Development of high-performance blue–violet-emitting organic electroluminescent devices
Authors: Okumoto Kenji , Shirota Yasuhiko
Published: July 2002

Two high-performance blue-violet-emitting organic electroluminescent devices with electroluminescence peaking at 404 and 415 nm were developed using a hole-blocking amorphous molecular material, 1,3,5-tris(4-fluorobiphenyl-4′-yl)benzene, and emitting amorphous molecular materials, N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine and N,N′-di(4-biphenylyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine. The devices show maximum luminaces of 3960 cd m−2 at 15 V and 2550 cd m−2 at 12.0 V, having turn-on voltages of 4.0 V and external quantum efficiencies of 1.40% and 1.25%.
Large scale and mesoscopic hydrodynamics for dissipative particle dynamics
Authors: Ripoll M. , Ernst M. H. , Español P.
Published: July 2002

Decay rates and related transport coefficients of hydrodynamic disturbances in the isothermal dissipative particle dynamics (DPD) fluid depend strongly on how the probing wave length (in simulations: sizes of colloidal particles, polymers, pores, etc.) compares to the dynamic correlation length and to the range of the DPD forces. In this article the wave number dependent transport properties (dispersion relations) of the DPD fluid are calculated analytically using methods of kinetic theory, as a natural generalization of the work by Marsh et al. [Phys. Rev. E 56, 1976 (1997)]. The Navier–Stokes transport coefficients are recovered in the hydrodynamic limit of long wavelength disturbances.
Development of a high power microwave plasma beam applicator
Authors: Gower S. A.
Published: July 2002

An efficient plasma beam applicator has been developed that utilizes countercurrent cooling techniques to operate at atmospheric pressure and at microwave powers in excess of 5 kW. The device has been operated continuously for tens of hours and shows no signs of degradation. Argon is used as the discharge gas and once initiated, the plasma is self-sustaining. The beam or jet of plasma is highly collimated with a beam diameter of 3 mm, is in excess of 250 mm in length, and has high heat capacity. It could potentially be used to melt industrial ceramics such as silica and alumina, but the immediate intended use is for sheet steel welding applications.
Dispersion fitted finite difference method with applications to molecular quantum mechanics
Authors: Gray Stephen K. , Goldfield Evelyn M.
Published: July 2002

An approach to finite difference approximation is presented based on the idea of fitting the dispersion relation up to a limiting accuracy. The resulting approximations to the second derivative can be more accurate than the standard, Lagrangian finite difference approximations by an order of magnitude or more. The locality of the methods makes them well suited to parallel computation, in contrast with pseudospectral methods. The approach is illustrated with application to a simple bound state problem and to a more challenging three dimensional reactive scattering problem.
Energy disposal in CN(X 2Σ+) produced in the 157 nm photodissociation of acrylonitrile
Authors: Guo Jingzhong , Carrington Tucker , Filseth S. V.
Published: July 2002

Photodissociation of acrylonitrile has been studied at 157.6 nm through analysis of laser-induced fluorescence experiments. The CN(X 2Σ+) radicals formed in this dissociation are detected in vibrational levels up to v=6 and rotational population distributions are measured for vibrational levels v=0–3. The average energies found in vibration and rotation of CN are approximately equal and represent about 5% of the available energy if the vinyl radical is the co-fragment. This is close to the 7% expected on the basis of the equipartition theorem which suggests that energy disposal is largely statistical. The vibrational and rotational distributions however are not in good agreement with an energy-conserving prior distribution suggesting that dynamical factors play a significant role in energy disposal.
Microsolvation and vibrational shifts of OCS in helium clusters
Authors: Paesani F. , Gianturco F. A. , Whaley K. B.
Published: July 2002

We present a theoretical study of the solvation structure around an OCS molecule embedded in helium clusters containing 1–100 He4 atoms, obtained from diffusion Monte Carlo calculations employing an ab initio, vibrational-state dependent internuclear potential and incorporating the molecular rotational degrees of freedom. The effect of the molecular rotation is to make the local helium density around the molecule considerably more delocalized in the ellipsoidal coordinates than that seen around a nonrotating OCS molecule. We find an unexpectedly sharp energy signature associated with completion of the first solvation shell at N∼20, suggesting that strongly bound molecules like OCS could have a “magic” quantum solvation number which is not apparent from the structural quantifiers of the solvating adatoms of that shell. The frequency shifts of the asymmetric stretch transition of the OCS molecule are computed as a function of cluster size via a dynamically adiabatic decoupling scheme. The vibrational frequency shows a monotonically increasing red shift with cluster size up to the completed first solvation shell at N∼20, where it saturates to a value in good agreement with experimental measurements made for OCS in much larger clusters.
Thermoelectric effects in a Luttinger liquid
Authors: Krive I. V. , Romanovsky I. A. , Bogachek E. N. , Scherbakov A. G. , Landman Uzi
Published: July 2002

Thermoelectric effects in a Luttinger liquid (LL) wire adiabatically connected to the leads of noninteracting electrons are considered. For a multichannel LL a staircase-like behavior of the thermal conductance as a function of chemical potential is found. The thermopower for a LL wire with an impurity is evaluated for two cases: (i) LL constriction, and (ii) infinite LL wire. We show that the thermopower is described a Mott-like formula renormalized by an interaction-dependent factor. For an infinite LL the renormalization factor decreases with increase of the interaction. However, for a realistic situation, when a LL wire is connected to the leads of noninteracting electrons (LL constriction), the repulsive electron-electron interaction enhances the thermopower. A nonlinear Peltier effect in a LL is briefly discussed.
Metric-tensor flexible-cell algorithm for isothermal–isobaric molecular dynamics simulations
Authors: Hernández E.
Published: July 2002

An extended Hamiltonian approach to conduct isothermal–isobaric molecular dynamics simulations with full cell flexibility is proposed. The components of the metric tensor are used as the fictitious degrees of freedom for the cell, thus avoiding the problem of spurious cell rotations and artificial symmetry breaking effects present in the original Parrinello–Rahman scheme. This is complemented by the Nosé–Poincaré approach for isothermal sampling. The combination of these two approaches leads to equations of motion that are Hamiltonian in structure, and which can therefore be solved numerically using recently developed powerful symplectic integrators. One such integrator, the generalized leapfrog, is employed to provide a numerical algorithm for integrating the isothermal–isobaric equations of motion obtained.
Equilibrium of a non-neutral plasma in a toroidal magnetic shear configuration
Authors: Saitoh Haruhiko , Yoshida Zensho , Nakashima Chihiro
Published: July 2002

The conventional rigid rotation model of thermal equilibrium does not apply to a toroidal non-neutral plasma trap; the nonuniformity of the magnetic field produces an inhomogeneous flow. For sufficiently large ωc/ωp (ωc: cyclotron frequency; ωp: plasma frequency), the flow can be approximated by the E×B drift velocity. The toroidal equilibrium of an electron plasma has been analyzed for a rather complex geometry of magnetic shear configuration.
A two-dimensional model of water: Solvation of nonpolar solutes
Authors: Urbič T. , Vlachy V. , Kalyuzhnyi Yu. V. , Southall N. T. , Dill K. A.
Published: July 2002

We recently applied a Wertheim integral equation theory (IET) and a thermodynamic perturbation theory (TPT) to the Mercedes–Benz (MB) model of pure water. These analytical theories offer the advantage of being computationally less intensive than the Monte Carlo simulations by orders of magnitudes. The long-term goal of this work is to develop analytical theories of water that can handle orientation-dependent interactions and the MB model serves as a simple workbench for this development. Here we apply the IET and TPT to the hydrophobic effect, the transfer of a nonpopular solute into MB water. As before, we find that the theories reproduce the Monte Carlo results quite accurately at higher temperatures, while they predict the qualitative trends in cold water.
Femtosecond intraband modulation spectroscopy
Authors: Mikhailovsky Alexander A. , Xu Su , Klimov Victor I.
Published: July 2002

We demonstrate several femtosecond spectroscopic techniques utilizing intraband carrier reexcitation for studies of relaxation processes in semiconductor materials. By introducing an additional infrared post-pump pulse into a conventional transient absorption experiment, we are able to visualize carrier intraband dynamics and to detect weak conduction-to-valence band transitions unresolved in the traditional transient absorption configuration. Intraband reexcitation spectroscopy also allows us to study dynamics of radiative transitions by monitoring a post-pump-induced modulation of time-integrated photoluminescence.
Thomson scattering system at the Tokyo electron beam ion trap
Authors: Kuramoto Hideharu , Kinugawa Tohru , Watanabe Hirofumi , Yamada Chikashi , Ohtani Shunsuke , Yamada Ichihiro , Currell Frederick John
Published: July 2002

A Thomson scattering system has been installed at the Tokyo electron beam ion trap for probing characteristics of the electron beam. A YVO4 green laser beam was injected antiparallel to the electron beam. The image of the Thomson scattering light from the electron beam has been observed using a charged-coupled device camera. By using a combination of interference filters, the spectral distribution of the Thomson scattering light has been measured. The Doppler shift observed for the scattered light is consistent with the beam energy. The beam radius dependence was investigated as a function of the beam energy, the beam current, and the magnetic field at the trap region. The variation of the measured beam radius against the beam current and the magnetic field were similar to those in Herrmann’s prediction. The beam radius as a function of the beam energy was also similar to Herrmann’s prediction but seemed to become larger at low energy.
Influence of temperature, magnetic field, and high hydrostatic pressure on the resistivity and magnetoresistance in La0.9Mn1.1O3±δ ceramics and laser-deposited films
Authors: Pashchenko V. P. , Kucherenko S. S. , Polyakov P. I. , Shemyakov A. A. , Dyakonov V. P.
Published: July 2002

The influence of the magnetic field strength (H=0, 2, 4, 6, 8 kOe), high hydrostatic pressures (P=0−1.8 GPa), and temperature (T=77−300 K) on the resistivity ρ, magnetoresistance (ΔR/R0), and phase transition temperatures in ceramic and thin-film samples of the lanthanum manganite La0.9Mn1.1O3±δ is investigated by x-ray-diffraction, magnetic, and resistive methods. It is found that with increasing H and P the resistivity decreases and the temperatures Tms of the metal-semiconductor phase transition and Tp of the magnetoresistance peak increase. The differences in the resistivities, magnetoresistances, and phase transition temperatures in the ceramics and laser-deposited films are explained by their different nonstoichiometry and defect density. The observed linear dependence of ρ and Tms on P suggests that lanthanum manganite ceramics and films could be used as pressure and temperature sensors.
Terahertz photomixing in quantum well structures using resonant excitation of plasma oscillations
Authors: Ryzhii V. , Khmyrova I. , Shur M.
Published: July 2002

We demonstrated that modulated infrared radiation can cause the resonant excitation of plasma oscillations in quantum well diode and transistor structures with high electron mobility. This effect provides a new mechanism for the generation of tunable terahertz radiation using photomixing of infrared signals. We developed a device model for a quantum well photomixer and calculated its high-frequency performance. It was shown that the proposed device can significantly surpass photomixers utilizing standard quantum well infrared photodetectors.
Transient airflow structures and particle transport in a sequentially branching lung airway model
Authors: Zhang Z. , Kleinstreuer C.
Published: July 2002

Considering oscillatory laminar incompressible three-dimensional flow in triple planar and nonplanar bifurcations representing generations three to six of the human respiratory system, air flow fields and micron-particle transport have been simulated under normal breathing and high-frequency ventilation (HFV) conditions. A finite-volume code (CFX4.3 from AEA Technology, Pittsburgh, PA) and its user-enhanced FORTRAN programs were validated with experimental velocity data points for a single bifurcation. The airflow structures and micron-particle motion in the triple bifurcations were analyzed for a representative normal breathing cycle as well as HFV condition. While both the peak inspiratory and expiratory velocity profiles for the low Womersley case (α=0.93) agree well with those of instantaneously equivalent steady-state cases, some differences can be observed between flow acceleration and deceleration at off-peak periods or near flow reversal, especially during inspiratory flow. Similarly, the basic features of instantaneous particle motion closely resemble the steady-state case at equivalent inlet Reynolds numbers. The preferential concentration of particles caused by the coherent vortical structures was found in both inhalation and exhalation; however, it is more complicated during expiration. The effects of Womersley number and non-planar geometries as well as the variations in secondary flow intensity plus pressure drops across various bifurcations under normal breathing and HFV conditions were analyzed as well. This work may elucidate basic physical insight of aerosol transport relevant in dosimetry-and-health-effect studies as well as for drug aerosol delivery analyses.
Study on the preparation techniques and properties of bonded magnetostrictive materials
Authors: Liu H. Y. , Li Y. X. , Qu J. P. , Liu B. D. , Guo H. Y. , Meng F. B. , Hu L. , Li S. Y. , Zhang Z. X. , Qin H. , Chen J. L. , Zhao H. W. , Wu G. H.
Published: July 2002

The preparation and measurement of the magnetoelastic properties of bonded Terfenol-D and Pr0.15Tb0.3Dy0.55Fe2 composites are reported. The experiments were carried out in various conditions, including compaction pressure and binder proportion in order to optimize the preparation method. The typical conditions are with the compaction pressure between 48 and 80 MPa and a weight ratio of binder to powder of 4:100. Large magnetostrictions of 1186×10−6 at 450 KA/m for the Terfenol-D composite with an applied compressive stress of 10 MPa and 900×10−6 at 900 KA/m for the Pr0.15Tb0.3Dy0.55Fe2 composite have been obtained with the following conditions: particle size of 165 μm, weight ratio of binder to powder of 4:100, and a compaction pressure of 80 MPa.
(Meta-)stability domain of ice XII revealed between ≈158–212 K and ≈0.7–1.5 GPa on isobaric heating of high-density amorphous ice
Authors: Loerting Thomas , Kohl Ingrid , Salzmann Christoph , Mayer Erwin , Hallbrucker Andreas
Published: July 2002

High-density amorphous ice was heated at constant pressures of between 0.52 to 1.9 GPa from 77 K up to 240 K. The formed phases were characterized by x-ray diffractograms of samples recovered under liquid N2 at 1 bar. The (meta)stability domain of ice XII thus revealed extends between ≈158–212 K from ≈0.7 to ≈1.5 GPa. We further discuss whether ice XII has a low-temperature region of stability within the ice VI domain. Our (meta)stability domain of ice XII is in a different region of water’s phase diagram than that shown by Koza et al. [Phys. Rev. Lett. 84, 4112 (2000)].
Modeling argon inductively coupled plasmas: The electron energy distribution function and metastable kinetics
Authors: Kiehlbauch Mark W. , Graves David B.
Published: July 2002

This article reports a simulation of argon inductively coupled plasma. Experimental measurements of the electron energy distribution function (EEDF) are fit to a power-law model and used to calculate electron impact rate coefficients in the simulation. Simulation results are compared to experimental measurements of electron density and temperature with good agreement, especially at the lower pressures investigated. At higher pressures, the disagreement between experiment and model is analyzed in terms of the nonlocality of the EEDF. Diffusive transport, neutral heating, gas phase electron impact reactions, and surface quenching all contribute to the predicted metastable profiles. Predicted metastable densities and neutral gas temperatures are compared to experimental results from the literature with reasonable agreement.
Direct observation of mass oscillations due to ablative Richtmyer–Meshkov instability and feedout in planar plastic targets
Authors: Aglitskiy Y. , Velikovich A. L. , Karasik M. , Serlin V. , Pawley C. J. , Schmitt A. J. , Obenschain S. P. , Mostovych A. N. , Gardner J. H. , Metzler N.
Published: July 2002

Perturbations that seed Rayleigh–Taylor (RT) instability in laser-driven targets form during the early-time period. This time includes a shock wave transit from the front to the rear surface of the target, and a rarefaction wave transit in the opposite direction. During this time interval, areal mass perturbations caused by all sources of nonuniformity (laser imprint, surface ripple) are expected to oscillate. The first direct experimental observations of the areal mass oscillations due to ablative Richtmyer–Meshkov (RM) instability and feedout followed by the RT growth of areal mass modulation are discussed. The experiments were made with 40–99 μm thick planar plastic targets rippled either on the front or on the rear with a sine wave ripple with either 30 or 45 μm wavelength and with 0.5, 1, or 1.5 μm amplitude. Targets were irradiated with 4 ns long Nike KrF laser pulses at ∼50 TW/cm2. The oscillations were observed with our novel diagnostic technique, a monochromatic x-ray imager coupled to a streak camera. For the ablative RM instability (front side ripple), the mass modulation amplitude was typically observed to grow, reach a peak, and then decrease, after which the exponential RT growth started. In some cases, one phase reversal due to the ablative RM instability was observed. For the feedout geometry (rear side ripple), in all cases two phase reversals were observed: a distinct half-oscillation was followed by the onset of the RT growth, resulting in a second phase reversal.
On the effective thermal diffusivity of fiber-reinforced composites
Authors: Salazar A. , Terrón J. M. , Sánchez-Lavega A. , Celorrio R.
Published: July 2002

Modulated photothermal techniques provide useful methods based on linear relations between measurable quantities to obtain the thermal diffusivity of homogeneous materials. In this letter the applicability of such linear relations in the case of unidirectional fiber-reinforced composites (UFRC) is analyzed. Based on the solution of the propagation of plane thermal waves in a material with aligned buried cylinders, we found that the linear relation valid for homogeneous materials still holds for UFRC. However, its slope does not give the effective thermal diffusivity as derived from the effective thermal conductivity measured by steady-state experiments. Anyway, as the number of cylinder rows increases the thermal diffusivity measured by modulated methods approaches the steady value asymptotically. The model is validated by photothermal measurements performed on calibrated samples.
Rotational dynamics of nondipolar probes in electrolyte solutions: Can specific interactions be modeled as dielectric friction?
Authors: Dutt G. B. , Ghanty T. K.
Published: July 2002

In a bid to explore how the presence of electrolyte ions influence the friction experienced by hydrogen bonding and nonhydrogen bonding solute molecules, rotational dynamics of two structurally similar nondipolar probes, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP), has been investigated in dimethylsulfoxide (DMSO) at several concentrations of LiNO3. The reorientation times of DMDPP, which does not strongly interact with the solvent, follow solution viscosity and dielectric parameters as the electrolyte concentration is increased. However, for DPP, which forms hydrogen bonds with DMSO, there is a 30% decrease in the viscosity-normalized reorientation times upon the addition of 2M LiNO3 due to the presence of electrolyte ions that shield the hydrogen-bonding interactions between the solute and the solvent. However, the reorientation times correlate well with the solution dielectric parameters with an increase in the electrolyte concentration as in the case of DMDPP. An attempt has been made to model the specific interactions between DPP and DMSO as dielectric friction using the extended charge distribution model of Alavi and Waldeck since both are electrostatic in nature.
Infrared emission spectroscopy of the [10.5]5Δ–X5Δ system of VF
Authors: Ram R. S. , Bernath P. F. , Davis S. P.
Published: July 2002

The emission spectrum of VF has been investigated in the 3400–17 000 cm−1 region using a Fourier transform spectrometer. The bands were excited in a high temperature carbon tube furnace from the reaction of vanadium metal vapor with CF4, as well as in a microwave discharge through a flowing mixture of VF4 vapor and helium. Several bands observed in the 9000–12 000 cm−1 region have been attributed to VF. The bands with high wave number R heads near 9156.8, 9816.4, 10 481.4, 11 035.8, and 11 587.2 cm−1 have been assigned as the 0-2, 0-1, 0-0, 1-0, and 2-0 bands, respectively, of the new [10.5]5Δ–X5Δ system of VF. A rotational analysis of the Δ15–Δ15, Δ25–Δ25, Δ35–Δ35, and Δ45–Δ45 subbands of the 0-1, 0-0, 1-0, and 2-0 bands has been carried out and spectroscopic parameters for VF have been obtained for the first time. The following equilibrium constants have been determined for the ground state of VF by averaging the constants of the different spin components: ΔG(1/2)=665.10 cm−1, Be=0.3863 cm−1, αe=0.0028 cm−1, and re=1.7758 Å.