bluuebunny/crossref_metadata_2025 huggingface dataset:
Nonlinear dielectric and magnetic relaxation after a sudden change of applied field
Authors: Felderhof B. U. , Jones R. B.
Published: July 2002

A dilute suspension of particles with permanent electric or magnetic dipole moment is subjected to an applied electric or magnetic field which suddenly changes its value. The relaxation of polarization or magnetization to the new equilibrium value is calculated from the solution of the Smoluchowski equation for the orientational distribution function. It is assumed that the new field has the same or opposite direction as the old one. For reversal of a strong field, comparison is made with an asymptotic calculation of van Kampen and with the solution of an approximate relaxation equation proposed by Martsenyuk et al.
Infrared spectroscopy and structures of Arn–HF in liquid helium nanodroplets
Authors: Nauta K. , Miller R. E.
Published: July 2002

Infrared spectra are reported for Arn–HF complexes up to the closing of the first solvent shell. These complexes were grown in superfluid helium droplets, leading to the formation of multiple isomers for n>3. The vibrational frequency shifts associated with the HF stretch are in excellent agreement with previous theoretical calculations. The relative abundances of the various isomers is found to be dependent upon the order of pick-up of the HF and argon. When HF is added to the droplets first the isomers corresponding to the solvated HF are produced in high abundance. Growth of the argon cluster prior to addition of the HF leads to the latter being on the “surface” of the argon cluster.
Deformation behavior of coherently strained InAs/GaAs(111)A heteroepitaxial systems: Theoretical calculations and experimental measurements
Authors: Zepeda-Ruiz Luis A. , Pelzel Rodney I. , Nosho Brett Z. , Weinberg W. Henry , Maroudas Dimitrios
Published: July 2002

A comprehensive, quantitative analysis is presented of the deformation behavior of coherently strained InAs/GaAs(111)A heteroepitaxial systems. The analysis combines a hierarchical theoretical approach with experimental measurements. Continuum linear elasticity theory is linked with atomic-scale calculations of structural relaxation for detailed theoretical studies of deformation in systems consisting of InAs thin films on thin GaAs(111)A substrates that are mechanically unconstrained at their bases. Molecular-beam epitaxy is used to grow very thin InAs films on both thick and thin GaAs buffer layers on epi-ready GaAs(111)A substrates. The deformation state of these samples is characterized by x-ray diffraction (XRD). The interplanar distances of thin GaAs buffer layers along the [220] and [111] crystallographic directions obtained from the corresponding XRD spectra indicate clearly that thin buffer layers deform parallel to the InAs/GaAs(111)A interfacial plane, thus aiding in the accommodation of the strain induced by lattice mismatch. The experimental measurements are in excellent agreement with the calculated lattice interplanar distances and the corresponding strain fields in the thin mechanically unconstrained substrates considered in the theoretical analysis. Therefore, this work contributes direct evidence in support of our earlier proposal that thin buffer layers in layer-by-layer semiconductor heteroepitaxy exhibit mechanical behavior similar to that of compliant substrates [see, e.g., B. Z. Nosho, L. A. Zepeda-Ruiz, R. I. Pelzel, W. H. Weinberg, and D. Maroudas, Appl. Phys. Lett. 75, 829 (1999)].
Compact bath cryostat filled with liquid helium inside an ordinary storage Dewar
Authors: Klimov A. E.
Published: July 2002

An economical bath cryostat for optical and galvano-magnetic measurements is described. The small overall diameter of the cryostat allows filling with liquid helium directly upon immersion into an ordinary storage Dewar vessel. As a result, it needs no more than 0.2 l of liquid helium for a single cycle of low-temperature measurements outside the storage Dewar lasting 1.5–4 h. Simplicity and low cost are other advantages of the cryostat. The basic ideas used in this device are the mobility of a helium can relative to the external body of the cryostat and the essential increase of the helium boiling point if pressure increases up to 0.5–1.5 atm over atmospheric pressure.
Reduction of nitrogen oxide in N2 by NH3 using intermittent dielectric barrier discharge
Authors: Nishida Mitsunori , Yukimura Ken , Kambara Shinji , Maruyama Toshiro
Published: July 2002

NO in N2 gas was removed by injecting ammonia radicals, which were externally generated by flowing the NH3 gas diluted with Ar gas through dielectric barrier discharge with a one-cycle sinusoidal-wave power source. The NO reduction for changes in both the applied voltage and the repetition rate was well correlated with the discharge power, which was proportional to the total discharge time per unit time. There was an optimum NH3 concentration in the narrow concentration window for the energy efficiency of NO reduction at a fixed discharge power. The maximum energy efficiency was obtained at small values of the NH3 concentration and the discharge power. The low NH3 concentration effectively increased the energy efficiency by drastically decreasing the discharge-firing voltage.
Quantum screening effects on nonrelativistic electron–ion bremsstrahlung process in two-component plasmas
Authors: Jung Young-Dae
Published: July 2002

Quantum screening effects on the nonrelativistic electron–ion bremsstrahlung process in two-component plasmas are investigated using the corrected Kelbg potential taking into account the classical effect as well as the quantum-mechanical effect. The Born approximation is assumed for the initial and final states of the projectile electron. The results show that the electron–ion bremsstrahlung radiation cross section decreases with increasing the de Broglie wavelength (λ). The quantum screening effect on the bremsstrahlung cross section increases with increasing the charge (Z) of the target ion. It is also found that the quantum screening effect on the bremsstrahlung cross section increases with increasing the radiation photon energy (ε).
Hydrogen elimination as a key step for the formation of polymerlike hydrocarbon films
Authors: Meier Matthias , Keudell Achim von
Published: July 2002

Recent experiments using H and CH3 radical beams as a model system for plasma deposition of C:H films revealed that CH3 adsorption at dangling bonds at the film surface is an important step for film formation. CH3 adsorption onto dangling bonds, which are created by hydrogen abstraction from incoming H, implies a net incorporation of two hydrogen atoms per carbon atom during steady state growth, although the H/C ratio of the deposited layers is only ∼1. Therefore, a reaction step of hydrogen elimination is essential to describe C:H film formation consistently. This hydrogen elimination is investigated by exposing polymerlike C:H films to quantified radical beams of CH3 and H. The resulting C:H film formation is monitored by in situ ellipsometry and infrared reflection spectroscopy. Based on experimental data, a model is developed to describe hydrogen elimination via a two step process: (i) first abstraction of surface bonded hydrogen from incoming H, followed by (ii) the recombination of dangling bonds via a local rearrangement of the C:H network. The latter process is self-limiting leading to a characteristic H/C ratio of 1 as a stoichiometric limit. Therefore, hydrogen elimination by atomic hydrogen corresponds to a key step for C:H film growth.
Decay instability and Kolmogorov spectra of ion-drift waves in low-β dusty plasmas
Authors: Onishchenko Oleg G. , Pokhotelov Oleg A. , Sagdeev Roald Z. , Pavlenko Vladimir P. , Stenflo Lennart , Shukla Padma K.
Published: July 2002

The interaction of nonlinear ion-drift waves in a low β, that is me/mi≪β≪1, dusty plasma is investigated. The matrix elements of the three-wave interactions in an inhomogeneous plasma with uniform ion temperature are derived. The decay instability growth rates and weakly turbulent plasma wave spectra of the ion-drift waves are evaluated and analyzed.
Enhanced-scattering experiments on a helicon discharge
Authors: Kaganskaya N. M. , Krämer M. , Selenin V. L.
Published: July 2002

The correlation enhanced-scattering diagnostic is applied for the first time to diagnose the low-frequency fluctuations in a helicon discharge for conditions where the electron plasma frequency is much higher than the cyclotron frequency. The dispersion relation deduced from the measured spectra can be attributed to turbulent ion-acoustic fluctuations.
Stochastic resonance with explicit internal signal
Authors: Li Qian Shu , Zhu Rui
Published: July 2002

A new type of internal signal stochastic resonance (ISSR) is found and investigated numerically by simulating a chemical model, which is proposed to account for chaos in the Belousov–Zhabotinsky reaction. When the system is in the dynamical region of period-1 oscillation, Gaussian white noise perturbation of the control parameter causes maxima to appear on the curve of signal-to-noise ratio versus noise intensity, showing the characteristic of stochastic resonance. The differences between this new type ISSR and the previous one studied by Hu et al. [Phys. Rev. Lett. 71, 807 (1993)] and Xin et al. [J. Chem. Phys. 111, 721 (1999)] are discussed.
Scanning tunneling nanolithography of amorphous GeSb2Te4 films
Authors: Sugawara Kentaro , Gotoh Tamihiro , Tanaka Keiji
Published: July 2002

Nanoscale surface modifications have been induced using a scanning tunneling microscope in a chalcogenide film GeSb2Te4, which is employed for optical phase change memories. Depressions and expansions appear when the surface is scanned with positive and negative tip voltages under relative humidity higher than ∼50%. It is plausible that the depression and the expansion are produced through electrochemical reactions and anodic oxidation processes.
Boundary conditions for a Gaussian wave beam
Authors: Poli E. , Peeters A. G. , Pereverzev G. V.
Published: July 2002

The beam tracing technique allows the description of short-wavelength wave beams by means of a set of ordinary differential equations, in which the effects of diffraction (neglected by the standard geometrical-optics procedure) are taken into account. The propagation of the beam is expressed in terms of a central ray and a set of parameters connected with the curvature of the wave front and the amplitude profile. Two crucial issues for the applicability of this technique to situations of experimental interest are the beam reflection from a mirror and the possibility of following the beam in its vacuum–plasma crossing. These problems are investigated in the paper. The parameters of the incident beam are regarded as known quantities and their values after reflection or inside the plasma are obtained.
The impact of molecular shape and polarity on chiral discrimination
Authors: Paci I. , Cann N. M.
Published: July 2002

The structure in eighteen racemates is explored at three temperatures and three densities. The enantiomers vary in shape from elongated, to nearly spherical, to flattened. Discrimination, as measured by the difference between like–like (LL) and like–unlike (LU) radial distributions, is assessed for these racemates. Elongated molecules show discrimination most readily with differences of up to 25% between the LL and LU distributions. However, the magnitude depends strongly on the orientation of the molecular dipole. Flattened molecules also show some discrimination but the magnitude is always quite small. The fluid structure is obtained from the molecule-based hypernetted chain theory (HNC) which has been applied, for the first time, to racemates. The incorporation of chirality into HNC theory is nontrivial. Specifically, for racemates, the number of nonzero coefficients in the rotational invariant expansions is very large, each coefficient is complex, and careful treatment of molecular shape into the closure relation is required. Our numerical procedures are discussed in detail. Bridge diagrams have also been evaluated for a reference system of hard ellipsoids. The impact of inclusion of these bridge diagrams has been considered for one racemate and found to be small.
On ion flow caused by the inductive electric field in a tokamak
Authors: Helander P.
Published: July 2002

It was recently pointed out that the inductive electric field in a tokamak can give rise to toroidal and poloidal plasma rotation comparable to that sometimes observed in experiments. Here it is shown that the flow velocity of heavy impurity ions, which is normally what is measured, is lower than that of the bulk plasma for rotation produced in this way. If the bulk ions and electrons are in the banana regime, the impurity rotation is at most about two thirds of the bulk plasma rotation and decreases with increasing effective ion charge (Zeff) and distance from the magnetic axis.
Predissociation dynamics of formyloxyl radical studied by the dissociative photodetachment of HCO2−/DCO2−+hν→H/D+CO2+e−
Authors: Clements Todd G. , Continetti Robert E.
Published: July 2002

The dissociative photodetachment (DPD) of HCO2− and DCO2− was studied at 258 nm. State-resolved translational energy distributions were observed correlated to bending excitation in the CO2 product for the channel producing H/D+CO2, indicating very low rotational excitation in the products consistent with predissociation of a C2ν HCO2 molecule. No evidence was found for dissociation into OH+CO. All three low-lying electronic states (2A1, B22, and A22) were found to dissociate, but resolved progressions were only observed from photodetachment to the A12 and B22 states. Photoelectron-photofragment coincidence spectra for DCO2− show resolved vertical bands and indicate that multiple CO2 vibrational states are accessible from each vibrational level in the predissociating DCO2 molecule. The resolved structure is assigned to vibrational predissociation sequence bands, observable in this DPD process owing to the dissociation dynamics and the near degeneracy of the vibrational levels in the A12 and B22 states of HCO2 and the bending mode of the CO2 products.
Dynamics of vibrationally mediated photodissociation of CH3CFCl2
Authors: Einfeld Tina , Maul Christof , Gericke Karl-Heinz , Marom Ran , Rosenwaks Salman , Bar Ilana
Published: July 2002

The ∼235 nm photodissociation of CH3CFCl2 pre-excited to three, four, and five quanta of C–H methyl stretches was studied to investigate the effect of internal parent excitation on the dynamics of two- and three-body photofragmentation. The ∼235 nm photons also tagged spin-orbit ground Cl 2P3/2 [Cl] and excited Cl 2P1/2 [Cl*] state photofragments, via (2+1) resonantly enhanced multiphoton ionization in a time-of-flight mass spectrometer. Monitoring the shapes of Cl35 and Cl*35 time-of-arrival profiles revealed their energies and angular distributions and showed broad and unstructured fragment kinetic energy distributions. Although a significant amount (∼50%) of the available energy is transferred into internal energy of the CH3CFCl fragment, the spatial Cl distribution is characterized by a nonvanishing anisotropy parameter, β, which indicates at a fast dissociation of the parent molecule along the C–Cl dissociation coordinate. Moreover, β for Cl changes from a slightly positive value to a negative value, while that for Cl* increases when the pre-excitation is increased from three to five quanta of C–H methyl stretches. This is attributed to the promotion of one of the nonbonding electrons located on the Cl atoms to the σ* antibonding C–Cl orbital and involvement of several upper states with different symmetry properties.
High order nonadiabatic perturbation theory on different adiabatic bases
Authors: Dufey Florian
Published: July 2002

A new partitioning of the nonadiabatic terms of a Hamiltonian consisting of a “slow” and a “fast” subsystem is introduced for high order numerical calculations of perturbation series. The Hamiltonian H(ν,λ) depends on two parameters, λ and ν. While the momentum dependent part of the perturbation is taken to be a linear function of the perturbation parameter λ, the other nonadiabatic terms are either assumed to be independent of λ, or depend quadratically on it. Especially the diagonal correction is partitioned into a constant and a quadratic function of λ. This partitioning will be controlled by the parameter ν. In zeroth order, the Hamiltonian will therefore be either the Born–Oppenheimer Hamiltonian, when ν=1, or the Born–Huang Hamiltonian, when ν=0. For other values of ν, more general adiabatic bases result. The new partitioning, in combination with the Hutson and Howard approach, forms a new method for the calculation of nonadiabatic perturbation series which is tested on a set of four model Hamiltonians. These have been studied already by Špirko et al. in a similar context. It is shown that the new method, as compared to traditional approaches, strongly enhances the rate of convergence and the accuracy of summability of the perturbation series, especially in the case of nearly avoided intersections or of near degeneracies.
Study of direct-drive, deuterium–tritium gas-filled plastic capsule implosions using nuclear diagnostics at OMEGA
Authors: Li C. K. , Séguin F. H. , Hicks D. G. , Frenje J. A. , Green K. M. , Kurebayashi S. , Petrasso R. D. , Meyerhofer D. D. , Soures J. M. , Glebov V. Yu. , Keck R. L. , Radha P. B. , Roberts S. , Seka W. , Skupsky S. , Stoeckl C. , Sangster T. C.
Published: July 2002

Implosions of direct-drive, deuterium–tritium (DT) gas-filled plastic capsules are studied using nuclear diagnostics at the OMEGA laser facility [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)]. In addition to traditional neutron measurements, comprehensive sets of spectra of deuterons, tritons, and protons elastically scattered from the fuel and shell by primary DT neutrons (“knock-on” particles) are, for the first time, obtained and used for characterizing target performance. It is shown with these measurements that, for 15-atm DT capsules with 20-μm CH shells, improvement of target performance is achieved when on-target irradiation nonuniformity is reduced. Specifically, with a two-dimensional (2D) single-color-cycle, 1-THz-bandwidth smoothing by spectral dispersion (SSD), plus polarization smoothing (PS), a primary neutron yield of ∼1×1013, a fuel areal density of ∼15 mg/cm2, and a shell areal density of ∼60 mg/cm2 are obtained; these are, respectively, ∼80%, ∼60%, and ∼35% higher than those achieved using 0.35-THz, 3-color-cycle, 2D SSD without PS. (In determining fuel areal density we assume the fuel to have equal numbers of D and T.) With full beam smoothing, implosions with moderate radial convergence (∼10–15) are shown to have ρR performance close to one-dimensional-code predictions, but a ratio of measured-to-predicted primary neutron yield of ∼0.3. Other capsules that are predicted to have much higher radial convergence (3.8-atm DT gas with 20-μm CH shell) are shown to have ρRfuel∼3 mg/cm2, falling short of prediction by about a factor of 5. The corresponding convergence ratios are similar to the values for 15-atm capsules. This indicates, not surprisingly, that the effects of mix are more deleterious for high-convergence implosions. A brief comparison of these moderate- and high-convergence implosions to those of similar deuterium–deuterium (D2) gas-filled capsules shows comparable hydrodynamic performance.
(
Ta
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Nb
x
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2
O
5
films produced by atomic layer deposition: Temperature dependent dielectric spectroscopy and room-temperature I–V characteristics
Authors: Strømme M. , Niklasson G. A. , Ritala M. , Leskelä M. , Kukli K.
Published: July 2002

Temperature dependent ac dielectric spectroscopy and room-temperature I–V characterization were performed on atomic layer deposited (Ta1−xNbx)2O5 films. The high frequency permittivity, as well as the dc conductivity of the films, were found to increase with increasing Nb content. The conduction mechanism in the mixed Ta–Nb oxide films was of the Poole–Frenkel type, while the high field conduction in pure Ta2O5 was space-charge limited. The activation energy for dc conduction was higher in mixed Ta–Nb oxides compared to pure Ta2O5 and Nb2O5 films. Irreversible changes in the conduction mechanism took place upon heat treatment above a certain irreversibility temperature. This temperature was higher for the mixed oxides than for the binary ones.
The role of energetic electrons in self-oscillations of a discharge plasma
Authors: Ping Y. , Yu C. X. , Xie J. L. , Ke J. , Hu X. W. , Li H. , Ding W. X.
Published: July 2002

The role of energetic electrons in periodic self-oscillations of a discharge plasma has been studied by measuring the spatiotemporal evolution of plasma potential, electron density, and electron velocity distribution function. It is found that the self-oscillation involves the instabilities of sheaths, propagation of a double layer and competition between the ionization, thermalization, and diffusion. The energetic electrons are the key factor which links these processes to form the oscillation cycle. The time interval of each phase in the cycle is estimated according to the physical process and the calculations are in agreement with experimental measurements. The study of the probe perturbation effect on the oscillations indicates that the length of the oscillation period is related to the amount of energetic electrons; the more energetic electrons, the shorter the period.
In situ observation of ferroelectric 90°-domain switching in epitaxial Pb(Zr, Ti)O3 thin films by synchrotron x-ray diffraction
Authors: Lee Kyeong Seok , Kim Yong Kwan , Baik Sunggi , Kim Jung , Jung II Sub
Published: July 2002

Switching behavior of 90° domains in epitaxial Pb(Zr0.32Ti0.68)O3 thin films under applied bias voltage was investigated in situ using synchrotron x-ray diffraction, and contribution of the switching to ferroelectric P–E hysteresis curve could be estimated. The electric field in the region illuminated by x ray was made confined exactly normal to the film/substrate interface by patterning an isolated capacitor (1×1 mm2) and etching off the remainder in order to eliminate mechanical constraint from nonswitching region. The portion of polarization taken up by 90° domain reversal was separated from 180° domain switching after measuring the changes in relative intensity ratio of PZT (001) and (100) reflections, which exhibited hysteresis behavior depending on applied voltage. Within the experimental region of electric field up to 24 kV/mm, maximum 27.8% of 90° domains were reoriented, which corresponds to ∼2% contribution to total polarization.
Transport implications of current drive by magnetic helicity injection
Authors: Moses Ronald W. , Gerwin Richard A. , Schoenberg Kurt F.
Published: July 2002

It is shown that in fusion plasma configurations sustained by electrode helicity injection, the core electron temperature (in electron volts) can, at most, be 25% to 40% of the electrode voltage (in volts). This result is obtained by assessing magnetic helicity injection as a driver of macroscopic steady-state plasma currents in magnetic confinement devices. Coaxial helicity injection using electrodes (CHI) and oscillating-field current drive (OFCD) are compared to inductive current drive. Magnetic helicity, K, is uniquely defined as the time-dependent volume integral of A⋅B when the surface components of A are purely solenoidal. Using an Ohm’s law including Hall terms, magnetic helicity transport modeling shows that no closed magnetic surfaces with time and volume averaged parallel currents can exist continuously within a plasma sustained only by CHI or OFCD. The 25% to 40% limitations are obtained by considering long and short electron mean-free-path models of parallel energy transport.
Gamma ray flashes by plasma effects in the middle atmosphere
Authors: Kaw P. K. , Milikh G. M. , Sharma A. S. , Guzdar P. N. , Papadopoulos K.
Published: July 2002

In this paper a novel mechanism is identified for the generation of gamma ray flashes observed on the Compton Gamma Ray Observatory satellite. During typical cloud to ground lightning flashes, the electromagnetic pulse can create a self-focused whistler wave channel or duct to guide 10–102/cm−3 of ∼1 MeV electrons (formed by static stratified electric field in clouds at 20 km), to a height of about 30 km where these electrons can create the gamma ray flash by bremsstrahlung. This scenario combines the various observational features of lightning-generated electromagnetic pulses and low altitude energetic electrons to provide a viable nonlinear transport mechanism of energetic electrons to the desired altitude of 30 km for conversion into gamma ray flashes.
Comment on “Electron vortices in magnetized plasmas” [Phys. Plasmas 8, 3232 (2001)]
Authors: Shukla P. K. , Stenflo L.
Published: July 2002

A compact set of three-dimensional electron magnetohydrodynamic (EMHD) equations for a nonuniform compressible magnetoplasma is presented. It is shown that the EMHD equations of Kuvshinov et al. [Phys. Plasmas 8, 3232 (2001)] must be improved.
Parametric dependence of density limits in the Tokamak Experiment for Technology Oriented Research (TEXTOR): Comparison of thermal instability theory with experiment
Authors: Kelly F. A. , Stacey W. M. , Rapp J.
Published: July 2002

The observed dependence of the TEXTOR [Tokamak Experiment for Technology Oriented Research: E. Hintz, P. Bogen, H. A. Claassen et al., Contributions to High Temperature Plasma Physics, edited by K. H. Spatschek and J. Uhlenbusch (Akademie Verlag, Berlin, 1994), p. 373] density limit on global parameters (I, B, P, etc.) and wall conditioning is compared with the predicted density limit parametric scaling of thermal instability theory. It is necessary first to relate the edge parameters of the thermal instability theory to n̄ and the other global parameters. The observed parametric dependence of the density limit in TEXTOR is generally consistent with the predicted density limit scaling of thermal instability theory. The observed wall conditioning dependence of the density limit can be reconciled with the theory in terms of the radiative emissivity temperature dependence of different impurities in the plasma edge. The thermal instability theory also provides an explanation of why symmetric detachment precedes radiative collapse for most low power shots, while a multifaceted asymmetric radiation from the edge MARFE precedes detachment for most high power shots.
High-n ballooning instabilities in toroidally rotating tokamaks
Authors: Furukawa M. , Nakamura Yuji , Hamaguchi S. , Wakatani M.
Published: July 2002

High-n ballooning instabilities are studied with an initial-value code for toroidally rotating tokamaks, where n is a toroidal mode number. The effects of toroidal rotation are classified into two parts: (i) increase of effective pressure gradient due to the centrifugal force of the toroidal flow, and (ii) averaging of local magnetic equilibrium configuration over a period of poloidal angle in the case of finite flow-velocity shear. With the increase of effective pressure gradient in the rigid-rotation case, the growth rate of ballooning mode increases in the low-pressure regime as the toroidal flow velocity is increased, whereas it decreases in the high-pressure regime. The flow-velocity shear generally reduces the growth rate of the high-n ballooning mode by the averaging of the local equilibrium magnetic configuration. However, it is found that the ballooning mode becomes unstable by increasing the flow-velocity shear in a low-aspect-ratio tokamak. This is understood by the change of the local magnetic configuration, and by the changes of both the mode structure and the potential function in the ballooning space.
Wetting transitions at the air–liquid interface of water+tetradecane+C6E2 mixtures
Authors: Yeh Ming-Chih , Chen Li-Jen
Published: July 2002

In this study, the interfacial phenomena and the wetting behaviors of the ternary system water+tetradecane+diethylene glycol monohexyl ether (C6E2) were carefully examined at 20 °C. There is one three-liquid-phase-coexisting tie triangle and three two-liquid-phase-coexisting envelopes in the triangle phase diagram of the system water+tetradecane+C6E2 at 20 °C. In the two-liquid-phase-coexisting region on the water/C6E2 side, the upper C6E2-rich liquid phase exhibits a sequence of transition: nonwetting→partial wetting→complete wetting at the lower aqueous phase/air interface by simply varying the system composition. Similarly, in another two-liquid-phase-coexisting region on the tetradecane/C6E2 side, the upper tetradecane-rich liquid phase also demonstrates a sequence of transition at the lower C6E2-rich phase/air interface. Some of these wetting transitions can be deduced by the critical wetting theory of Cahn, while the other transitions seem to have no obvious relevance to a critical end point.
Observation of the cyclic water hexamer in solid parahydrogen
Authors: Fajardo Mario E. , Tam Simon
Published: July 2002

We present infrared (IR) absorption spectra of cryogenic parahydrogen solids doped with small water clusters. We observe a sequence of peaks shifted to the red by ≈15 cm−1 from the absorptions of cyclic water clusters in liquid helium droplets [K. Nauta and R. E. Miller, Science 287, 293 (2000)]; this sequence includes the peak due to the cyclic isomer of the water hexamer: cyc-(H2O)6. We believe this is only the second spectroscopic observation of isolated cyc-(H2O)6, and the first report of the IR spectrum of the isolated cluster in the solid phase.
Radiative condensation modes in dense dusty plasmas
Authors: Birk Guido T. , Wiechen H.
Published: July 2002

Thermal condensation modes in static partially ionized dense dusty plasmas are investigated by linear mode analysis. A necessary and sufficient onset criterion for a coupled dust-neutral gas condensation mode is found with the help of the Hurwitz theorem. In the long wavelength limit one finds a coupled condensation mode and a new dust mode in the short wavelength limit. The growth rates of the modes are limited by elastic collisions between the different plasma components.
Convection in an asymmetrically sourced Z pinch
Authors: Rey A. M. , Hassam A. B.
Published: July 2002

The convection of a magnetically confined plasma resulting from heat and particle sources is studied. It is assumed that the convection is low-level in that the system stays stable to ideal interchange instabilities. A Z-pinch plasma with asymmetric particle and heat sources is considered. It is found that there is no convection if there are no particle sources, independent of the distribution of the heat sources. Particle sources result in convection which in turn influences heat transport. The central temperature, however, may go up or down in response to this convection, depending on the distribution of the source function.
Segregation in bimetallic alloys and its influence on wetting on a positive temperature coefficient resistor BaTiO3 ceramic
Authors: Cann David P. , Randall Clive A.
Published: July 2002

Bimetallic alloys have been considered in terms of their wetting behavior on semiconducting BaTiO3. In an earlier study, wetting behavior was strongly linked to ohmic contact behavior. However, the wetting behavior does not always correlate in the form of high work of adhesion-low contact resistance. The departure from this trend is associated with the nature of the segregation of the solute. Two extreme cases are considered in this study: no driving force for segregation and a strong driving force. These cases are characterized with sessile drop experiments and qualitatively analyzed in terms of thermodynamic analysis, both a surface enrichment model is considered together with an energy diagram approach. Both models give excellent qualitative agreement to the observed wetting behavior of the bimetallic alloy-BaTiO3 system.
Efficient energy upconversion emission in Tm3+/Yb3+-codoped TeO2-based optical glasses excited at 1.064 μm
Authors: dos Santos P. V. , Vermelho M. V. D. , Gouveia E. A. , de Araújo M. T. , Gouveia-Neto A. S. , Cassanjes F. C. , Ribeiro S. J. L. , Messaddeq Y.
Published: July 2002

Efficient energy upconversion of cw radiation at 1.064 μm into blue, red, and near infrared emission in Tm3+-doped Yb3+-sensitized 60TeO2-10GeO2-10K2O-10Li2O-10Nb2O5 glasses is reported. Intense blue upconversion luminescence at 485 nm corresponding to the Tm3+ G41→3H6 transition with a measured absolute power of 0.1 μW for 800 mW excitation power at room temperature is observed. The experimental results also revealed a sevenfold enhancement in the upconversion efficiency when the sample was heated from room temperature to 235 °C yielding 0.7 μW of blue absolute fluorescence power for 800 mW pump power. High brightness emission around 800 nm (3F4→3H6) in addition to a less intense 655 nm (1G4→3H4 and F2,33→3H6) fluorescence is also recorded. The energy upconversion excitation mechanism for thulium emitting levels is assigned to multiphonon-assisted anti-Stokes excitation of the ytterbium-sensitizer followed by multiphonon-assisted sequential energy-transfer processes.
Effect of polymeric coatings on the static fatigue of double-coated optical fibers
Authors: Shiue Sham-Tsong , Ouyang Hao
Published: July 2002

The effect of polymeric coatings on the static fatigue of double-coated optical fibers is investigated. A closed form solution of the tensile stress in the glass fiber under the action of a constant tensile force in the fiber’s axial direction is obtained using viscoelastic theory. The tensile force is applied to the glass fiber and polymeric coatings. The applied tensile fore is gradually transferred from the polymeric coating to the glass fiber due to the viscoelastic behavior of the former, and the tensile stress in the glass fiber increases with time. This increase accelerates the failure of the glass fiber. The thickness and Young’s modulus of the secondary coating should be increased to ensure the long-term reliability of optical fibers, and the relaxation time of the secondary coating should be significantly larger than the expected lifetime of the optical fiber. However, the ratio of the proof-test load to the allowable external load should be increased if the secondary coating of the optical fiber has a high axial rigidity and low relaxation time.
Self-trapped excitons in silicon nanocrystals with sizes below 1.5 nm in Si/SiO2 multilayers
Authors: Kamenev B. V. , Nassiopoulou A. G.
Published: July 2002

Photoluminescence from silicon nanocrystals in nc-Si/SiO2 multilayers has been investigated by time-resolved measurements. The photoluminescence (PL) decay is fitted by two exponentials with relaxation times of the order of ∼25–30 and ∼80–100 μm at room temperature which are independent of the emission wavelength. The experimental data are interpreted by considering two light emission mechanisms with closely similar wavelengths, both involving localized states and corresponding to two coupled subsystems. One involves localized states related to Si=O bonds, and the other self-trapped excitons. In the case of light emission from self-trapped exciton annihilation, PL was not limited by Auger recombination in the regime of multiple excitation of silicon nanocrystals.
Reaction of SO2 with pure and metal-doped MgO: Basic principles for the cleavage of S–O bonds
Authors: Rodriguez J. A. , Jirsak T. , González L. , Evans J. , Pérez M. , Maiti A.
Published: July 2002

Synchrotron-based high-resolution photoemission, x-ray absorption near-edge spectroscopy, and first-principles density-functional calculations are used to examine the interaction of SO2 with pure and modified surfaces of magnesium oxide. On a MgO(100) single crystal, SO2 reacts with O centers to form SO3 and SO4 species. The bonding interactions with the Mg cations are weak and do not lead to cleavage of S–O bonds. An identical result is found after adsorbing SO2 on pure stoichiometric powders of MgO and other oxides (TiO2, Cr2O3, Fe2O3, NiO, CuO, ZnO, V2O5, CeO2, BaO). In these systems, the occupied cations bands are too stable for effective bonding interactions with the LUMO of SO2. To activate an oxide for S–O bond cleavage, one has to create occupied metal states above the valence band of the oxide. DF calculations predict that in the presence of these “extra” electronic states the adsorption energy of SO2 should increase, and there should be a significant oxide→SO2(LUMO) charge transfer that facilitates the cleavage of the S–O bonds. In this article, we explore three different approaches (formation of O vacancies, promotion with alkali metals, and doping with transition metals) that lead to the activation of SO2 and S–O bond breaking on MgO and oxides in general. Basic principles for a rational design of catalysts with a high efficiency for the destruction of SO2 are presented.
Internal rotation in high-resolution ultraviolet spectra. I. Semirigid model of a C2v top–Cs frame internal motion
Authors: Schäfer Martin
Published: July 2002

An internal rotor model to fit and simulate rotationally resolved electronic spectra of molecules or complexes with an internal top of C2v symmetry and a frame of symmetry Cs or C2v in the semirigid approximation is described. The rotation–internal rotation problem is solved independently for both electronic states by numerical diagonalization of the energy matrices, which are factored according to the symmetry properties of the Hamiltonian. Finally, selection rules and line strength expressions for the simulation of electronic spectra are given.
Energy transfer to porphyrin derivative dopants in polymer light-emitting diodes
Authors: Higgins R. W. T. , Monkman A. P. , Nothofer H.-G. , Scherf U.
Published: July 2002

The device physics of bilayer polymer light-emitting diodes that utilize energy transfer to various porphyrin derivatives were investigated. The emissive host, α,ω-bis[N,N-di(4-methylphenyl) aminophenyl]-poly(9,9-bis(2-ethylhexyl)fluoren-2,7-diyl) (PF2/6am4), was doped to a variety of concentrations between 0.5 and 4 wt. % with 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin zinc(II) (ZnOEP), 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin palladium(II) (PdOEP), and 2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrin platinum(II) (PtOEP). The electroluminescent devices showed a maximum external quantum efficiency (EQE) of 1.19%, 0.22%, 1.08%, and 2.75% for undoped APFO, PF2/6am4:ZnOEP, PF2/6am4:PdOEP, and PF2/6am4:PtOEP blends, respectively. We attribute this variation in performance of the blends to be a product of both the luminescence quantum yield of the dopant molecules, which we take from the literature as 0.065, 0.2, and 0.5 for ZnOEP, PdOEP, and PtOEP, respectively, and the dopant excited state lifetime. We observe that at high brightness the EQE of the doped devices falls below that of the undoped device and we attribute this high-end falloff in performance to the excited state lifetimes of the dopant molecules, which determine at which current density devices exhibit peak efficiency. Past this peak in efficiency, we propose that saturation of the dopant sites is the major factor in detrimental device performance, which has wide reaching consequences for any future design that utilizes energy transfer of dopant molecules.
Mean-field Gaussian chain theory for semidilute theta chains in a slit
Authors: Teraoka Iwao , Cifra Peter
Published: July 2002

Mean-field Gaussian chain theory for nondilute polymer solutions is being applied to polymer chains in the theta condition confined to a slit in a wide range of concentrations. Various existing lattice chain theories were used to obtain the effective potential for the Gaussian chain. Calculation results for the monomer density profile, the partition coefficient, and the chain dimension across the slit at various concentrations were computed and compared with the results obtained in the lattice Monte Carlo simulations. The need for a higher concentration to flatten the density profile and to cause the weak-to-strong penetration transition, compared with athermal chains, was confirmed. At the monomer–monomer interaction widely used as the theta condition on the cubic lattice, the chain cluster theory by Freed and the random mixing approximation by Huggins provide a better agreement with the simulation results than the Flory model and the Guggenheim model do. The agreement is, however, not as good as the one for athermal chains.
Theoretical studies of the spin dynamics of quadrupolar nuclei at rotational resonance conditions
Authors: Walls Jamie D. , Lim Kwang Hun , Pines Alexander
Published: July 2002

A theory of the spin dynamics of I=3/2 quadrupolar nuclei in the sudden-passage limit is discussed in relation to the recently observed rotational resonance (RR) effects on the excitation and conversion of triple-quantum coherence in the FASTER multiple-quantum magic-angle spinning (MQMAS) experiments [T. Vosegaard, P. Florian, D. Massiot, and P. J. Grandinetti, J. Chem. Phys. 114, 4618 (2001)]. A novel interaction frame, which combines the quadrupolar interaction with the central transition radio frequency irradiation, is shown to be useful in understanding the complex spin dynamics at and away from RR conditions. Analytical expressions for the Hamiltonian obtained from bimodal Floquet theory are included in order to provide insight into the spin dynamics observed in the FASTER MQMAS experiments. Numerical simulations have been performed and were found to support the theoretical formalism.
Temperature dependent barrier characteristics of CrNiCo alloy Schottky contacts on n-type molecular-beam epitaxy GaAs
Authors: Gümüş A. , Türüt A. , Yalçin N.
Published: July 2002

The current–voltage (I–V) characteristics of CrNiCo alloy Schottky contacts on a molecular-beam epitaxy n-GaAs substrate have been measured over the temperature range of 130–330 K and have been interpreted based on the assumption of a Gaussian distribution of barrier heights due to barrier height inhomogeneities that prevail at the interface. It is shown that the occurrence of Gaussian distribution of then barrier heights is responsible for the decrease of the apparent barrier height Φb0, increase of the ideality factor n and nonlinearity in the activation energy plot at low temperatures. A Φb0 vs 1/T plot was drawn to obtain evidence of a Gaussian distribution of the barrier heights, and values of Φ̄b0(T=0)=1.02 eV and σ0=0.105 V for the mean barrier height and zero-bias standard deviation, respectively, have been obtained from this plot. Thus, a modified ln(I0/T2)−q2σ02/2k2T2 vs 1/T plot gives Φ̄b0(T=0) and A* as 1.02 eV and 5.13 A/cm2 K2, respectively, without using the temperature coefficient of the barrier height. It has been concluded that the temperature dependent I–V characteristics of the device can be successfully explained on the basis of a thermionic emission mechanism with Gaussian distribution of the barrier heights. Furthermore, a value of −0.305 meV/K for the temperature coefficient of the flat band barrier height has been obtained; this value for n-GaAs is in very close agreement with values in the literature.
Metallic ion beam production at HIMAC
Authors: Sasaki M. , Kitagawa A. , Muramatsu M. , Jincho K. , Sasaki N. , Sakuma T. , Takasugi W. , Yamamoto M.
Published: July 2002

In order to realize new investigations on physics, biology, and other fields, a metallic ion beam is quite effective and essential. To produce the metallic ion beam in an electron cyclotron resonance (ECR) ion source, how to supply the metallic gas into the ECR plasma is most important. At present, the NIRS-HEC, which is an 18 GHz ECR ion source installed for the Heavy Ion Medical Accelerator in Chiba at the National Institute of Radiological Sciences (NIRS), enables us to produce a stable Fe9+ beam of 180 eμA by the metal ions from volatile compounds technique. In addition, the development of a new gas supply method, using the electron-bombardment technique, is in progress. In this method, the tip of a metal target rod (2–6 mm diameter) at a high positive potential is melted by bombarding the thermoelectrons emitted from a surrounding hot filament and the evaporated gas is supplied into the ECR plasma.
Effect of a biased electrode on operation of electron cyclotron resonance ion source using liquid He free superconduction solenoid coils
Authors: Imanaka M. , Kurita T. , Tsukada M. , Arai I. , Lee S. M. , Nakagawa T.
Published: July 2002

We have constructed a liquid He free SC-ECRIS and successfully extracted intense beams of various heavy ions. To improve its performance, we installed a negatively biased electrode in the plasma chamber and observed its effect on the beam intensity systematically. We measured the beam intensity and the current of biased electrode as a function of both the applied bias voltage and the electrode position. Using the negatively biased electrode, the beam intensity of highly charged Xe ions was strongly enhanced. Furthermore, both the beam intensity and the current of biased electrode oscillated strongly. The frequency became higher when increasing the magnitude of bias voltage. This result shows that the biased electrode causes a certain instability in the electron cyclotron resonance plasma, so that the beam intensity is enhanced. In this contribution, we present the results of our experiment and the discussions about possible mechanisms of such instability.
Cesiated hollow cathodes in the multicusp ion source
Authors: Belchenko Yu. I. , Oka Y. , Hamabe M. , Kaneko O. , Krivenko A. , Takeiri Y. , Tsumori K. , Osakabe M. , Ikeda K. , Asano E. , Kawamoto T.
Published: July 2002

A cesiated hydrogen hollow cathode (CHC) was tested for plasma injection in the multicusp negative ion source (MS). The CHC arc with hydrogen feed and cesium seeding through the CHC volume was explored. One cathode unit (40 mm length, 19 mm in diameter, emission opening area 1–3 mm2) with no special cooling provided the MS discharge operation with direct current up to 30 A, and up to 60 A in the long-pulse mode. High efficiency of negative ion production in the MS discharge, driven by a CHC plasma injection was recorded.
A local interpolation method for direct classical dynamics calculations
Authors: Christoffel Kurt M. , Bowman Joel M. , Braams Bastiaan J.
Published: July 2002

We present a piecewise interpolation method for use in direct molecular dynamics calculations. The method smoothly and exactly reproduces function and gradient data on a multidimensional rectangular grid. It can be applied to significantly increase the efficiency of direct classical dynamics calculations. To illustrate its efficiency and accuracy, the method is applied to the classical dynamics of a strongly coupled two-dimensional model.
LIMBE: A new facility for low energy beams
Authors: Maunoury L. , Leroy R. , Been T. , Gaubert G. , Guillaume L. , Leclerc D. , Lepoutre A. , Mouton V. , Pacquet J. Y. , Ramillon J. M. , Vicquelin R. , Group The GANIL Ion Production
Published: July 2002

The goal of this article is to present the new facility LIMBE built at GANIL. This facility is dedicated to the ion–surface, ion–atom, and ion–molecule research. It is made of an ECR ion source called SUPERSHYPIE and two beam lines. We will describe the ECRIS, the beam properties, and the performances of LIMBE facility.
Diagnostic research of plasmas generated by a 14.5 GHz ECR ion source using Langmuir-probe
Authors: Kenéz L. , Biri S. , Karácsony J. , Valek A. , Nakagawa T. , Stiebing K. E. , Mironov V.
Published: July 2002

Electron cyclotron resonance (ECR) plasmas have already been studied in many ways, mainly by x-ray and UV measurements. Langmuir-probes, however, have proven useful for other kind of plasmas, and have rarely been used to explore the ECR plasma. A diagnostics setup has been built at the 14.5 GHz ATOMKI-ECRIS. Results of the cold plasma region measurements are shown. A modified version of the original methods for characteristics analysis is reported. This includes the complex nature of the plasma ion component. Calculated electron densities yielded by the two compared theoretical models up to a factor of 3 were observed. This obviously shows the necessary consideration of this effect. Studies of two-faced external effects, e.g., biased-disk on/off, beam extraction on/off, have also started; first results are reported.