bluuebunny/crossref_metadata_2025 huggingface dataset:
Sample mounting and transfer mechanism for in situ IR-visible sum frequency generation vibrational spectroscopy in high-pressure ultrahigh vacuum system
Authors: Yang Minchul , Tang David C. , Somorjai Gabor A.
Published: September 2003

We developed a sample mounting and transfer mechanism for studying heterogeneous catalytic reactions in a high-pressure ultrahigh vacuum system. The system is optimized for the use of sum frequency generation vibrational spectroscopy to probe surface species in situ during the reactions. The system allows wide-ranging working conditions: a pressure range between 4×10−10 and 760 Torr and a temperature range between 200 and 1200 K. Rigid and reproducible sample positioning as well as precise temperature control can be achieved by compact designs of a sample holder and a sample mount incorporating ultrahigh vacuum compatible plugs. The performance of the system is demonstrated here by monitoring surface intermediates over time during cyclohexene catalytic reactions using a Pt(111) single crystal and sum frequency generation vibrational spectroscopy.
Study on microstrip position sensitive detector with meandering resistive structure for the charge division method
Authors: Radhakrishna V. , Rajanna K. , Desai S. S. , Shaikh A. M.
Published: September 2003

Microstrip position sensitive detectors based on “charge division method” have been developed. In order to increase the resistance between two successive anodes, a meandering resistive strip structure is adopted. This provides greater control over the resistance between successive anodes. Measured position nonlinearity with this structure is very low and is less than 0.29%. Position resolution up to 0.48 mm has been obtained for x rays with Xe+CH4 mixture at 2.1 bar.
Fabrication of elliptical mirror at nanometer-level accuracy for hard x-ray focusing by numerically controlled plasma chemical vaporization machining
Authors: Yamamura Kazuya , Yamauchi Kazuto , Mimura Hidekazu , Sano Yasuhisa , Saito Akira , Endo Katsuyoshi , Souvorov Alexei , Yabashi Makina , Tamasaku Kenji , Ishikawa Tetsuya , Mori Yuzo
Published: September 2003

We established an efficient ultraprecise figuring process in which numerically controlled plasma chemical vaporization machining (NC-PCVM) and numerically controlled elastic emission machining (NC-EEM) are utilized serially. Intensity images of the x rays reflected by total reflection mirrors greatly fluctuate with respect to the figure error of spatial wavelength ranging from submillimeter to 10 mm. In NC-PCVM, figure errors for spatial wavelength range longer than 10 mm are removed efficiently by using the rotary electrode, and the spatial wavelength close to 1 mm can be corrected by using the pipe electrode. The residual figure error for the spatial wavelength close to 0.1 mm is finally removed by EEM. In this article, we describe the ultraprecise figuring process utilizing the NC-PCVM. Two elliptical mirrors for a Kirkpatrick–Baez (KB) microfocusing unit were manufactured by NC-PCVM using the rotary electrode and the pipe electrode in combination, and a figure accuracy higher than 3 nm (p–v) was achieved for the spatial wavelength range longer than 1 mm. The focusing properties of the two mirrors were evaluated at BL29XUL of SPring-8, and line focusing widths of 0.12 and 0.2 μm (full width at half maximum) were achieved at 15 keV.
Ultrasonic levitation for the examination of gas/solid reactions
Authors: Kavouras A. , Krammer G.
Published: September 2003

An experimental setup based on acoustic levitation for the examination of gas/solid reactions is presented. In this setup single particles in the diameter range 1 mm–30 μm can be held against gravity for any wanted time in a defined gas atmosphere at elevated temperatures. The change of particle size, shape, and position can be measured and recorded using an optical device, consisting of a camera and a long range microscope. Basic experiments with inert particles of different shape and solid density have shown that the axial position of a reacting particle can be employed to derive its weight change. A method to evaluate this change of the recorded position for the according weight change is proposed. Exemplary results in the context of dry flue gas cleaning using Ca(OH)2 powder are presented. Single Ca(OH)2 particles are exposed to a well defined gas atmosphere and after some time these particles are retrieved from the ultrasonic field for further analyses. Only an in situ measurement of the particle weight change (i.e., without removing the particle from the well defined reactive atmosphere) brings information regarding the uptake of water by the sorbent, which accompanies SO2 and HCl absorption.
Sawyer–Tower hysteresis measurements on micron sized Pb(Zr,Ti)O3 capacitors
Authors: Bouregba R. , Vilquin B. , Le Rhun G. , Poullain G. , Domenges B.
Published: September 2003

We have performed Sawyer–Tower hysteresis measurements on micron sized Pb(Zr,Ti)O3 (PZT) capacitors prepared on Pt/Ti/SiO2/Si substrates and patterned with a focused ion beam. Owing to a numerical compensating technique, we show that the increase of both linear dielectric constant εr and maximum polarization Pmax, when decreasing the size of the capacitors, is artificial and mainly due to the parasitic effect of the probing setup. Moreover, a suitable method is proposed to accurately determine and correct for the additional parasitic capacitance in parallel with the standard capacitor. Under these conditions, the dielectric and ferroelectric properties of micron sized PZT capacitors are found to be quite similar to those measured on a large contact, i.e., the device properties are area independent.
FRX-L: A field-reversed configuration plasma injector for magnetized target fusion
Authors: Taccetti J. M. , Intrator T. P. , Wurden G. A. , Zhang S. Y. , Aragonez R. , Assmus P. N. , Bass C. M. , Carey C. , deVries S. A. , Fienup W. J. , Furno I. , Hsu S. C. , Kozar M. P. , Langner M. C. , Liang J. , Maqueda R. J. , Martinez R. A. , Sanchez P. G. , Schoenberg K. F. , Scott K. J. , Siemon R. E. , Tejero E. M. , Trask E. H. , Tuszewski M. , Waganaar W. J. , Grabowski C. , Ruden E. L. , Degnan J. H. , Cavazos T. , Gale D. G. , Sommars W.
Published: September 2003

We describe the experiment and technology leading to a target plasma for the magnetized target fusion research effort, an approach to fusion wherein a plasma with embedded magnetic fields is formed and subsequently adiabatically compressed to fusion conditions. The target plasmas under consideration, field-reversed configurations (FRCs), have the required closed-field-line topology and are translatable and compressible. Our goal is to form high-density (1017 cm−3) FRCs on the field-reversed experiment-liner (FRX-L) device, inside a 36 cm long, 6.2 cm radius theta coil, with 5 T peak magnetic field and an azimuthal electric field as high as 1 kV/cm. FRCs have been formed with an equilibrium density ne≈(1 to 2)×1016 cm−3, Te+Ti≈250 eV, and excluded flux ≈2 to 3 mWb.
Hybrid evaporation: Glow discharge source for plasma immersion ion implantation
Authors: Li L. H. , Poon R. W. Y. , Kwok S. C. H. , Chu P. K. , Wu Y. Q. , Zhang Y. H.
Published: September 2003

In order to achieve stable operation for elements with a low melting point or high vapor pressure, a quasiequilibrium evaporation–glow discharge evaporation source has been designed and investigated for plasma immersion ion implantation. The important relationship between the pressure in the evaporation chamber and the implantation chamber is studied for optimal performance. Our experimental results show that the hybrid evaporation–glow discharge source is an effective method to produce ions from materials with low melting point and high vapor pressure.
Detection of high-Z objects using multiple scattering of cosmic ray muons
Authors: Priedhorsky William C. , Borozdin Konstantin N. , Hogan Gary E. , Morris Christopher , Saunders Alexander , Schultz Larry J. , Teasdale Margaret E.
Published: September 2003

We demonstrate that high-Z material can be detected and located in three dimensions using radiographs formed by cosmic-ray muons. Detection of high-Z material hidden inside large volume of ordinary cargo is an important and timely task given the danger associated with illegal transport of uranium and heavier elements. Existing radiography techniques are inefficient for shielded material, often expensive and involve radiation hazards, real and perceived. We recently demonstrated that radiographs can be formed using cosmic-ray muons [K. N. Borozdin et al., Nature (London) 422, 277 (2003)]. Here, we show that compact, high-Z objects can be detected and located in three dimensions with muon radiography. The natural flux of cosmic-ray muons [P. K. F. Grieder, Cosmic Rays at Earth (Elsevier, New York, 2001)], approximately 10 000 m−2 min−1, can form useful images in ∼1 min, using large-area muon detectors like those used in high-energy physics.
Thermal effusivity measurements of insulating liquids using microsized hot strip probes
Authors: Gustavsson M. , Nagai H. , Okutani T.
Published: September 2003

A method based on the pulse transient hot strip (PTHS) technique is developed for studies of thermal effusivity of insulating liquids only requiring a drop-size sample. The original technique is here extended to single-sided measurements of liquids with a known solid background, using a probe calibrated against a liquid reference medium. Tests were made on water and silicone oils of varying viscosity (5–3000 CS). The microsized probes produce results in agreement with macroscopic bulk data, without any influence from natural convection. It is proposed that relative errors from both radiation and convection are significantly reduced when shortening the experimental time scale by several orders of magnitude. An error analysis is included, presenting design criteria to optimize measurement sensitivity and accuracy.
Radio frequency characterization of a split-ringed, electrically small electro-optical bulk modulator
Authors: Young Jeffrey L. , Nelson Ronald O. , Kelly James F.
Published: September 2003

A radio frequency characterization of a split-ringed, electro-optical modulator (EOM) is provided herein. This characterization is given in terms of electromagnetic simulation data, as obtained from a finite-difference, time-domain code, and a lumped element circuit model. The simulation data provides insight into the field structure within the cavity; the circuit model provides a simple, yet accurate set of design and analysis formulas that relate resonant frequency, voltage levels and power levels to the geometrical and material parameters of the cavity. To validate the claims made from the simulation data and circuit model, experimental data is also provided and a favorable comparison among all data sets is shown. It is concluded that the cavity under consideration can be made to resonate at low frequencies, without increasing the overall size of the cavity. Even though the price in doing so is a reduction in cavity Q and electro-optical crystal voltage, this split-ringed EOM is well suited to an efficient thermal management scheme. Guidance is given on how to optimize the cavity in terms of voltage, Q, power levels, and voltage levels.
An instrument for low- and variable-temperature millimeter-wave surface impedance measurements under magnetic fields
Authors: Hanaguri Tetsuo , Takaki Keishi , Tsuchiya Yoshishige , Maeda Atsutaka
Published: September 2003

We describe a low-temperature millimeter-wave (44 GHz) surface impedance measurement instrument based on the cavity perturbation method. In this instrument, all millimeter-wave paths at low temperatures (including the cavity resonator), are located inside a high vacuum tube, which can be inserted into a 7 T superconducting magnet. This design, which is free of exchange gas, enables measurements over a wide temperature range as well as providing stable and reproducible operation. By pumping a He3 pot attached to a cavity, a sample can be cooled well below 1 K. We present experimental results which demonstrate the performance of the instrument.
Characterization of ZYX exfoliated graphite for studies of monolayer He3 below 1 mK
Authors: Niimi Y. , Murakawa S. , Matsumoto Y. , Kambara H. , Fukuyama Hiroshi
Published: September 2003

We have characterized ZYX exfoliated graphite (ZYX) by measuring the surface area and electrical resistivity perpendicular (ρ⊥) to the basal plane as a function of density. The purpose of the characterization is to seek possibilities to use this material as an adsorption substrate for studies of two dimensional (2D) He3 at ultralow temperatures (ULT) below 1 mK. A potential advantage of ZYX is its much larger single crystalline size (100–200 nm) than that of Grafoil (≈10 nm) which is an exfoliated graphite commonly used at ULT. Present results show that ZYX has sufficiently large surface area to be used in heat capacity or nuclear magnetic resonance experiments on 2D He3 samples and good thermal conductance to cool them well below 1 mK. We have demonstrated this by measuring nuclear magnetic susceptibility of monolayer solid He3 adsorbed on ZYX with a density of 1.1 g/cm3 down to 100 μK. Measured temperature dependencies of ρ⊥ and ρ∥ (resistivity parallel to the basal plane) below 70 K are discussed within the variable range hopping model plus a metallic component of carriers.
Hyperbolic field electron energy analyzer with second order focusing
Authors: Jacka M. , Kale A. , Traitler N.
Published: September 2003

Second order focusing is a desirable property of dispersion type electron energy analyzers because it allows a greater angular acceptance or, alternatively, higher energy resolution. We derive the second order focusing conditions for the hyperbolic field analyzer, which also allows a large range of energies to be collected in parallel, making it suitable for surface analysis techniques such as Auger spectroscopy.
Explosive and oscillatory tearing-mode instability in gyrotropic plasmas
Authors: Chiou S.-W. , Hau L.-N.
Published: September 2003

Linear theory of resistive tearing-mode instability in gyrotropic plasmas has predicted that for large pressure anisotropy of p⊥>p∥ the eigenmode is not purely exponential but contains oscillation with the overall growth rate much larger than the isotropic case. This paper shows that such solutions may develop in the nonlinear anisotropic magnetohydrodynamic model; in particular, the X-line and O-line take place alternatively with magnetic islands growing and saturated with oscillation period of about ten Alfvén transit times. The growth rate is on the order of the Alfvén time scale and the plasma flow velocity may reach the Alfvén speed. The presence of the mirror-mode wave may result in magnetic bottle structure on top of the X- and O-lines that is responsible for the enhanced growth rate and oscillation of magnetic reconnection.
Impedance up to 6 GHz in La0.67Sr0.33MnO3 thin films
Authors: Reversat L. , Crozat P. , Lyonnet R. , Dupas C. , Contour J.-P.
Published: September 2003

The ac electrical impedance of a 400-nm-thick La0.67Sr0.33MnO3 thin film (on MgO) has been measured in the frequency range from 30 MHz up to 6 GHz using etched strips. The impedance is found to be nearly a constant resistance that is equal to the dc resistance. The only deviations, in the order of their magnitude, are: (i) the contact pad impedance at low frequency, (ii) a small inductive part in the impedance of the material, and (iii) a low decrease of the resistance above 3 GHz.
Comment on “Charging of dust grains in a plasma with negative ions” [Phys. Plasmas 10, 1518 (2003)]
Authors: Islam M. K. , Nakashima Y.
Published: September 2003

The shortcoming in the expression of approximated negative ions current to negatively charged dust grains in the case of streaming negative ions distribution by Mamun and Shukla [Phys. Plasmas 10, 1518 (2003)] is pointed out. Improved estimation in dust grain charging current in the retarding field is presented in the case of streaming dusty plasmas, where the particles streaming velocity is much larger than their thermal velocity.
Response to “Comment on ‘Charging of dust grains in a plasma with negative ions’ ” [Phys. Plasmas 10, 4185 (2003)]
Authors: Mamun A. A. , Shukla P. K.
Published: September 2003

The Comment by Islam and Nakashima has been critically evaluated. The basis [viz. Eqs. (5) and (7)] of their comments is found to be incorrect and inconsistent from both mathematical and physical points of view. The work of Mamun and Shukla remains intact.
Shielding of resonant magnetic perturbations in the long mean-free path regime
Authors: Waelbroeck F. L.
Published: September 2003

The effect of diamagnetic drifts and of long electron mean free path on the shielding of resonant magnetic perturbations by plasma rotation is investigated. The nature of the force exerted on a moving plasma by a resonant perturbation is qualitatively altered by both drift and long mean-free-path effects. The force is found to have three minima, each of which is a possible locus for discontinuous transitions in plasma velocity. Between these minima are two points where the force exerted by the perturbation is resonant. These points describe locked states where shielding is ineffective and a magnetic island will grow. They correspond to rotation velocities such that either the electrons or the ions are at rest in the frame of the perturbation. The ion root, however, is unstable.
On the variational cohomology of g-invariant foliations
Authors: Almeida R. , Kumpera A. , Rubin J. L.
Published: September 2003

Let S be an integrable Pfaffian system. If it is invariant under a transversally free infinitesimal action of a finite dimensional real Lie algebra g, we show that the “vertical” variational cohomology of S is equal to the Lie algebra cohomology of g with values in the space of the “horizontal” cohomology in a maximum dimension. This result, besides giving an effective algorithm for the computation of the variational cohomology of an invariant Pfaffian system, provides a method for detecting obstructions to the existence of infinitesimal actions leaving a given system invariant.
Dirac operators on coset spaces
Authors: Balachandran A. P. , Immirzi Giorgio , Lee Joohan , Prešnajder Peter
Published: September 2003

The Dirac operator for a manifold Q, and its chirality operator when Q is even dimensional, have a central role in noncommutative geometry. We systematically develop the theory of this operator when Q=G/H, where G and H are compact connected Lie groups and G is simple. An elementary discussion of the differential geometric and bundle theoretic aspects of G/H, including its projective modules and complex, Kähler and Riemannian structures, is presented for this purpose. An attractive feature of our approach is that it transparently shows obstructions to spin- and spinc-structures. When a manifold is spinc and not spin, U(1) gauge fields have to be introduced in a particular way to define spinors, as shown by Avis, Isham, Cahen, and Gutt. Likewise, for manifolds like SU(3)/SO(3), which are not even spinc, we show that SU(2) and higher rank gauge fields have to be introduced to define spinors. This result has potential consequences for string theories if such manifolds occur as D-branes. The spectra and eigenstates of the Dirac operator on spheres Sn=SO(n+1)/SO(n), invariant under SO(n+1), are explicitly found. Aspects of our work overlap with the earlier research of Cahen et al.
The first law of thermodynamics and Dyson–Lieb’s perpetuum mobile
Authors: Borchers H. J. , Borchers Ch.
Published: September 2003

Some consequences of Dyson–Lieb’s N(7/5) law for the condensation of Bose particles are discussed.
Ion Coulomb explosion of clusters by a Gaussian laser beam
Authors: Liu C. S. , Tripathi V. K.
Published: September 2003

A collisionless model of ion Coulomb explosion of clusters, due to an intense short pulse laser with Gaussian radial intensity distribution, is developed. The laser quickly converts the clusters into plasma balls via tunnel ionization. The free electrons of a cluster execute oscillatory motion with large excursion Δ and partially move out of the cluster. The unbalanced positive charge within the cluster leads to ion Coulomb explosion. The ion energy distribution function due to a single cluster rises monotonically with energy ε up to a cutoff energy εm and vanishes beyond it. εm depends on electron excursion, hence decreases with r. The cumulative ion energy distribution due to all the clusters of the laser channel turns out to be a decreasing function of energy as observed in recent experiments. The ions so produced can generate neutrons with reasonably high yields. The scheme may also find application in tokamak fusion.
Dominance of deep over shallow donors in ZnO-based varistors
Authors: Fernández-Hevia D. , de Frutos J. , Caballero A. C. , Fernández J. F.
Published: September 2003

Broadband admittance spectroscopy measurements of ZnO-based varistors are analyzed in terms of charge transport theory through double Schottky barriers, hence obtaining empirical evidence about the nonmajority of the shallow donor in n-type ZnO. The dominant defect species is found to be a deep donor, which agrees with recent first-principles calculations. This result consistently explains the observed frequency-domain non-Debye and time-domain nonexponential electrical response, and invalidates a key assumption underlying various electrical characterization studies of this material. We find two deep levels with fine structures. These fine structures are attributable to fluctuating chemical environments around the defects.
Identification of Te alloys with suitable phase change characteristics
Authors: Detemple Ralf , Wamwangi Daniel , Wuttig Matthias , Bihlmayer Gustav
Published: September 2003

At present, the discovery and development of phase change materials is mainly based upon empirical strategies and trial and error approaches. Here, we present a structural criterion that needs to be met to enable the mandatory fast recrystallization with sufficient optical contrast that characterizes suitable phase change materials. Comparing the behavior of AgInTe2 and AgSbTe2 films it is demonstrated that only the AgSbTe2 films, which show a cubic coordination, have sufficient density contrast, and hence, also optical contrast to allow phase change recording.
Interfacial growth in HfOxNy gate dielectrics deposited using [(C2H5)2N]4Hf with O2 and NO
Authors: Lee M. , Lu Z.-H. , Ng W.-T. , Landheer D. , Wu X. , Moisa S.
Published: September 2003

The interface growth by oxygen diffusion has been investigated for 5 nm thick HfOxNy gate-quality dielectric films deposited on Si(100) by low-pressure pulsed metalorganic chemical vapor deposition. Analysis by x-ray photoelectron spectroscopy of the films deposited using the precursor tetrakis (diethylamido) hafnium with O2 showed that the films contained 4 at. % nitrogen. This increased to 11 at. % N when NO was used as the oxidant. Significant growth of the interface layer was observed for films exposed to air at ambient temperature and lower rates of growth were observed for vacuum annealed films and those with the higher N content. For films annealed in O2 at temperatures in the range 600–900 °C, the activation energies of the interfacial growth were 0.36 and 0.25 eV for N concentrations of 11 and 4 at. %, respectively. The results were interpreted in terms of atomic oxygen formation in the bulk and reaction at the interface. The increase in N incorporation from 4 to 11 at. % increases the crystallization temperature from between 500 and 600 °C to between 600 and 700 °C.
Low- to high-confinement mode transitions in the National Spherical Torus Experiment
Authors: Kaye S. M. , Bush C. E. , Fredrickson E. , LeBlanc B. , Maingi R. , Sabbagh S. A.
Published: September 2003

Edge data from plasmas in the National Spherical Torus Experiment (NSTX) [S. Kaye et al., Fusion Technol. 36, 16 (1999)] have been compared to theories of transport suppression that have been used to develop a physics framework for low-confinement (L) to high-confinement (H) mode transitions. The NSTX data were obtained in low aspect ratio (R/a≃1.3) discharges taken from a variety of discharge phases, including L-modes, L-H transitions and H-modes with and without edge localized modes. The comparisons show that the group of points taken just before the L-H mode transition are well mixed with the purely L-mode group to within the measurement uncertainties, indicating that changes in these parameters leading up to the transition are subtle. One of the theory parameters, αMHD=−Rq2 dβt/dr, does show a clear threshold (αMHD=1 to 2) between the H-mode grouping of points and those remaining in the L-mode or taken just prior to the transition. Additionally, there is no evidence for an edge temperature threshold necessary for transitioning into the H-mode. NSTX data indicate further a possible connection between L-H transitions and nonambipolar beam ion losses.
Non-existence of normal tokamak equilibria with negative central current
Authors: Hammett G. W. , Jardin S. C. , Stratton B. C.
Published: September 2003

Recent tokamak experiments employing off-axis, non-inductive current drive have found that a large central current hole can be produced. The current density is measured to be approximately zero in this region, though in principle there was sufficient current drive power for the central current density to have gone significantly negative. Recent papers have used a large aspect-ratio expansion to show that normal magnetohydrodynamic equilibria (with axisymmetric nested flux surfaces, non-singular fields, and monotonic peaked pressure profiles) cannot exist with negative central current. That proof is extended here to arbitrary aspect ratio, using a variant of the virial theorem to derive a relatively simple integral constraint on the equilibrium. However, this constraint does not, by itself, exclude equilibria with non-nested flux surfaces, or equilibria with singular fields and/or hollow pressure profiles that may be spontaneously generated.
A theoretical model for a spontaneous magnetic field in intense laser plasma interaction
Authors: Zhu Shao-ping , Zheng C. Y. , He X. T.
Published: September 2003

The experiment results on spontaneous magnetic fields given by Najmudin et al. [Phys. Rev. Lett. 87, 215004 (2001)] can be explained by the kinetic model proposed by the present authors [Phys. Plasmas 8, 312 (2001)]. The dependence of the peak spontaneous magnetic field on the laser intensity is discussed. It is found the ratio of the number of thermal electrons to the total number of electrons is an important parameter.
On the pseudo-Hermitian nondiagonalizable Hamiltonians
Authors: Scolarici G. , Solombrino L.
Published: September 2003

We consider a class of (possibly nondiagonalizable) pseudo-Hermitian operators with discrete spectrum, and we establish for such a class the equivalence between the pseudo-Hermiticity property and the existence of an antilinear involutory symmetry. Moreover, we prove that this class actually coincides with the one of (possibly nondiagonalizable) weak pseudo-Hermitian operators, and that in no case (unless they are diagonalizable and have a real spectrum) they are Hermitian with respect to a definite inner product. Finally, we show that a typical degeneracy of the real eigenvalues (which reduces to the well-known Kramers degeneracy in the Hermitian case) occurs whenever a fermionic (possibly nondiagonalizable) pseudo-Hermitian Hamiltonian admits an antilinear symmetry like the time-reversal operator T. Some consequences and applications are briefly discussed.
Dense Dirac combs in Euclidean space with pure point diffraction
Authors: Richard Christoph
Published: September 2003

Regular model sets, describing the point positions of ideal quasicrystallographic tilings, are mathematical models of quasicrystals. An important result in mathematical diffraction theory of regular model sets, which are defined on locally compact Abelian groups, is the pure pointedness of the diffraction spectrum. We derive an extension of this result, valid for dense point sets in Euclidean space, which is motivated by the study of quasicrystallographic random tilings.
Multi-Lagrangians, hereditary operators and Lax pairs for the Korteweg–de Vries positive and negative hierarchies
Authors: Bustamante Miguel D. , Hojman Sergio A.
Published: September 2003

We present an approach to the construction of action principles (the inverse problem of the calculus of variations), for first order (in time derivatives) differential equations, and generalize it to field theory in order to construct systematically, for integrable equations which are based on the existence of a Nijenhuis (or hereditary) operator, a (multi-Lagrangian) ladder of action principles which is complementary to the well-known multi-Hamiltonian formulation. We work out results for the Korteweg–de Vries (KdV) equation, which is a member of the positive hierarchy related to a hereditary operator. Three negative hierarchies of (negative) evolution equations are defined naturally from the hereditary operator as well, in a concise way, suitable for field theory. The Euler–Lagrange equations arising from the action principles are equivalent to deformations of the original evolution equation, and the deformations are obtained explicitly in terms of the positive and negative evolution vectors. We recognize, after appropriate coordinate transformations, the Liouville, Sinh–Gordon, Hunter–Zheng, and Camassa–Holm equations as negative evolution equations. The multi-Lagrangian ladder for KdV is directly mappable to a ladder for any of these negative equations and other positive evolution equations (e.g., the Harry–Dym and a special case of the Krichever–Novikov equations). For example, several nonequivalent, nonlocal time-reparametrization invariant action principles for KdV are constructed, and a new nonlocal action principle for the deformed system Sinh–Gordon+spatial translation vector is presented. Local and nonlocal Hamiltonian operators are obtained in factorized form as the inverses of all the nonequivalent symplectic two-forms in the ladder. Alternative Lax pairs for all negative evolution vectors are constructed, using the negative vectors and the hereditary operator as only input. This result leads us to conclude that, basically, all positive and negative evolution equations in the hierarchies share the same infinite-dimensional sets of local and nonlocal constants of the motion for KdV, which are explicitly obtained using symmetries and the local and nonlocal action principles for KdV.
High-filling-fraction inverted ZnS opals fabricated by atomic layer deposition
Authors: King J. S. , Neff C. W. , Summers C. J. , Park W. , Blomquist S. , Forsythe E. , Morton D.
Published: September 2003

The infiltration of three-dimensional opal structures has been investigated by atomic layer deposition. Demonstrations using ZnS:Mn show that filling fractions >95% can be achieved and that the infiltrated material is of high-quality crystalline material as assessed by photoluminescence measurements. These results demonstrate a flexible and practical pathway to attaining high-performance photonic crystal structures and optical microcavities.
Observation of domain walls in PbZr0.2Ti0.8O3 thin film using scanning nonlinear dielectric microscopy
Authors: Matsuura K. , Cho Y. , Ramesh R.
Published: September 2003

Using scanning nonlinear dielectric microscopy (SNDM), we measured the linear dielectric constant of a domains (c axis in the plane of the film) and c domains (c axis perpendicular to the film surface) in PbZr0.2Ti0.8O3 (PZT) thin film to confirm that the dielectric constant of the a domain is higher than that of the c domain. We observed 90° a–c domain walls and 180° c–c domain walls and found that, experimentally, the 180° c–c domain wall was smaller than the 90° a–c domain wall.
Collimation of PetaWatt laser-generated relativistic electron beams propagating through solid matter
Authors: Campbell R. B. , DeGroot J. S. , Mehlhorn T. A. , Welch D. R. , Oliver B. V.
Published: September 2003

Particle-in-cell simulations aimed at developing methods to control the relativistic electron beam blowup observed in recent laser-plasma experiments are described. By radially layering vacuum gaps and/or dissimilar materials with varying ionizability, a negative radial gradient in plasma density would be formed. This gradient results in confining fields that can, in principle, confine the hot electron column to nearly the laser injection spot size. Fully kinetic ion dynamics are included, to account for heavy particle transport effects across interfaces. Potential applications include radiography, electron beam focusing, and perhaps beam collimation for fast ignition. Experiments are presently being planned to test this concept.
Quantum ion-acoustic waves
Authors: Haas F. , Garcia L. G. , Goedert J. , Manfredi G.
Published: September 2003

The one-dimensional two-species quantum hydrodynamic model is considered in the limit of small mass ratio of the charge carriers. Closure is obtained by adopting an equation of state pertaining to a zero-temperature Fermi gas for the electrons and by disregarding pressure effects for the ions. By an appropriate rescaling of the variables, a nondimensional parameter H, proportional to quantum diffraction effects, is identified. The system is then shown to support linear waves, which in the limit of small H resemble the classical ion-acoustic waves. In the weakly nonlinear limit, the quantum plasma is shown to support waves described by a deformed Korteweg–de Vries equation which depends in a nontrivial way on the quantum parameter H. In the fully nonlinear regime, the system also admits traveling waves which can exhibit periodic patterns. The quasineutral limit of the system is also discussed.
Metal-doped magic clusters of Si, Ge, and Sn: The finding of a magnetic superatom
Authors: Kumar Vijay , Kawazoe Yoshiyuki
Published: September 2003

Studies on divalent-metal (M)-atom-doped XNM (X=Si, Ge, and Sn, N=8–12 and 14) clusters, using ab initio pseudopotential plane wave method, show that the well known nine- and ten-atom capped prism units as well as 12- and 14-atom clusters of these elements can transform to magic clusters with higher symmetries and larger highest occupied–lowest unoccupied molecular orbital gaps. Most strikingly doping of X12 with Mn leads to an icosahedral superatom, Mn@X12, X=Ge and Sn with a high magnetic moment of 5 μB, enriching the family of M-doped clusters of semiconductors for possible nanodevice applications.
Gyrokinetic simulations of microinstabilities in stellarator geometry
Authors: Lewandowski J. L. V.
Published: September 2003

A computational study of microinstabilities in general geometry is presented. The ion gyrokinetic is solved as an initial value problem. The advantage of this approach is the accurate treatment of some important kinetic effects. The magnetohydrodynamic equilibrium is obtained from a three-dimensional local equilibrium model. The use of a local magnetohydrodynamic equilibrium model allows for a computationally efficient systematic study of the impact of the magnetic structure on microinstabilities.
Molecular dynamics simulation of plasma flow around two stationary dust grains
Authors: Vladimirov S. V. , Maiorov S. A. , Ishihara O.
Published: September 2003

Plasma kinetics in the presence of ions flowing around two stationary dust grains aligned perpendicularly to the direction of the flow is studied by a three-dimensional molecular dynamics simulation code. The dynamics of plasma electrons and ions as well as the dust particle charging are simulated self-consistently. Distributions of electron and ion number densities and the electrostatic plasma potential are obtained for various intergrain distances, including those much less, of the order of, and more than the plasma electron Debye length.
Multiwave model for plasma–wave interaction
Authors: Evstatiev E. G. , Horton W. , Morrison P. J.
Published: September 2003

A model is presented that describes the interaction of electrons with both longitudinal and transverse waves in a cold plasma. Starting from the Lagrangian for the system of fields, background plasma, and particles, a finite dimensional self-consistent model is derived using the envelope approximation for the waves. The (squared) wave amplitudes and phases form action-angle variables in the closed system of waves and particles. The system conserves energy and momentum, and thus is natural for solving the beam-loading problem. Numerical simulations are performed to compare with earlier electrostatic problems.
Discharge plasma instabilities in the presence of an external constant electric field
Authors: Shokri B. , Niknam A. R.
Published: September 2003

The instabilities of a weakly ionized quasineutral plasma embedded in an external constant electric field are investigated. Special attention is paid to the dispersion equation with taking into account the interparticle collisions, the ionization and the recombinations. Dependency of the electron-neutral collision frequency, the electron-ion recombination coefficient and the ionization frequency on the electron temperature are considered. Most of the instabilities investigated are stipulated by the sign change of derivative of kinetic coefficients with respect to temperature. A new instability in which the plasma is assumed to be near the equilibrium state is found although an electric drift and heating of light particles (electrons) exists.
Comment on “Time-dependent solution for a star immersed in a background radiation” [H. Liu and Q. Zhang, J. Math. Phys. 43, 4904 (2002)]
Authors: Govinder K. S. , Govender M.
Published: September 2003

In a recent paper [J. Math. Phys. 43, 4904 (2002)] Liu and Zhang present a time-dependent solution for a star which is immersed in a background radiation. This solution was obtained by analyzing equations arising from the analysis of a five-dimensional solution that contained their solution. We show that, while their analysis and conclusions are valid, their equations are unnecessarily restrictive when applied to the four-dimensional case.
How to generate families of spinors
Authors: Mankoč Borštnik N. , Nielsen H. B.
Published: September 2003

Using a technique [Mankoč Borštnik et al., J. Math. Phys. 43, 5782 (2002)] to construct a basis for spinors and “families” of spinors in terms of Clifford algebra objects, we define other Clifford algebra objects, which transform the state of one “family” of spinors into the state of another “family” of spinors, changing nothing but the “family” number. The proposed transformation works—as does the technique—for all dimensions and any signature and might open a path to understanding families of quarks and leptons [Mankoč Borštnik, Phys. Lett. B 292, 25 (1992); J. Math. Phys. 34, 3731 (1993); Int. J. Theor. Phys. 40, 315 (2001); Borštnik Bračič and Mankoč Borštnik, hep-ph/0301029].
Electron cyclotron current drive efficiency in general tokamak geometry
Authors: Lin-Liu Y. R. , Chan V. S. , Prater R.
Published: September 2003

Green’s-function techniques are used to calculate electron cyclotron current drive (ECCD) efficiency in general tokamak geometry in the low-collisionality regime. Fully relativistic electron dynamics is employed in the theoretical formulation. The high-velocity collision model is used to model Coulomb collisions and a simplified quasilinear rf diffusion operator describes wave–particle interactions. The approximate analytic solutions which are benchmarked with a widely used ECCD model, facilitate time-dependent simulations of tokamak operational scenarios using the noninductive current drive of electron cyclotron waves.
The Green–Kubo formula and power spectrum of reversible Markov processes
Authors: Jiang Da-Quan , Zhang Fu-Xi
Published: September 2003

As is known, the entropy production rate of a stationary Markov process vanishes if and only if the process is reversible. In this paper, we discuss the reversibility of a stationary Markov process from a functional analysis point of view. It is shown that the process is reversible if and only if it has a symmetric Markov semigroup, equivalently, a self-adjoint infinitesimal generator. Applying this fact, we prove that the Green–Kubo formula holds for reversible Markov processes. By demonstrating that the power spectrum of each reversible Markov process is Lorentz-typed, we show that it is impossible for stochastic resonance to occur in systems with zero entropy production.
Recent advancements in microwave imaging plasma diagnostics
Authors: Park H. , Chang C. C. , Deng B. H. , Domier C. W. , Donné A. J. H. , Kawahata K. , Liang C. , Liang X. P. , Lu H. J. , Luhmann N. C. , Mase A. , Matsuura H. , Mazzucato E. , Miura A. , Mizuno K. , Munsat T. , Nagayama Y. , van de Pol M. J. , Wang J. , Xia Z. G. , Zhang W-K.
Published: September 2003

Significant advances in microwave and millimeter wave technology over the past decade have enabled the development of a new generation of imaging diagnostics for current and envisioned magnetic fusion devices. Prominent among these are microwave electron cyclotron emission imaging, microwave phase imaging interferometers, imaging microwave scattering, and microwave imaging reflectometer systems for imaging Te and ne fluctuations (both turbulent and coherent) and profiles (including transport barriers) on toroidal devices such as tokamaks, spherical tori, and stellarators. The diagnostic technology is reviewed, and typical diagnostic systems are analyzed. Representative experimental results obtained with these novel diagnostic systems are also presented.
Atomic force microscope with improved scan accuracy, scan speed, and optical vision
Authors: Kwon Joonhyung , Hong Jaewan , Kim Yong-Seok , Lee Dong-Youn , Lee Kyumin , Lee Sang-min , Park Sang-il
Published: September 2003

We have developed a new atomic force microscope (AFM), with a z scanner independent of the xy scanner. Unlike conventional AFM systems, our xy scanner moves only the sample in the xy plane, while the z scanner controls the AFM probe along the z axis. The xy scanner is a single module parallel-kinematics flexure stage that guarantees high orthogonality and minimum out-of-plane motion. The z scanner is a one-dimensional flexure stage with negligible out-of-axis motion. Separating the z scanner from the xy scanner practically eliminates the x–z cross coupling problem inherent in conventional AFMs. Furthermore, the z servo response is no longer limited by the xy scanner characteristics, allowing us to make full use of our high performance z scanner. Our system uses the laser beam bounce detection method, and only the cantilever and the photodetector are mounted on the z scanner to realize a lightweight probing unit. We have devised a unique design such that the photodetector signal measures only the cantilever deflection and not the z-scanner motion. Our new AFM provides fast z servo response and high scan accuracy.
In situ plasma diagnostics study by means of optical emission spectroscopy for diamond chemical vapor deposition under high gravity conditions
Authors: Tappero Fabrizio , Abe Yoshiyuki , Maizza Giovanni
Published: September 2003

A complete optical spectroscopy apparatus has been developed on board of a high gravity chemical vapor deposition facility. The article describes in detail the experimental apparatus and its main features. Preliminary results concern in situ plasma diagnostics under various gravity conditions up to 75g. The developed diagnostic apparatus is found to be a convenient tool for systematic in situ investigation of the influence of high gravity on the plasma composition. Thus, it is an effective means to clarify the most relevant active species playing a role during diamond film growth under high gravity conditions.
A hybrid scanning tunneling–atomic force microscope operable in air
Authors: Suganuma Yoshinori , Dhirani Al-Amin
Published: September 2003

We describe a hybrid scanning tunneling–atomic force microscope (STM–AFM) capable of measuring current and force simultaneously under ambient conditions. In order to reduce meniscus forces, the microscope uses a sharp STM tip as a probe and an AFM cantilever as a sample substrate. This improvement allows use of correspondingly flexible cantilevers enhancing force detection sensitivity. Using the STM–AFM, we have been able to explore a number of phenomena that can occur in nanometer scale tunnel junctions in air, including a correlation between hysteretic changes in contact potential and rapid increases in current at large bias voltages.
New isolated gate bipolar transistor two-quadrant chopper power supply for a fast field cycling nuclear magnetic resonance spectrometer
Authors: Sousa D. M. , Marques G. D. , Sebastião P. J. , Ribeiro A. C.
Published: September 2003

This work, presents, for the first time, an Isolated Gate Bipolar Transistor (IGBT) two-quadrant chopper power supply for a fast field cycling (FFC) nuclear magnetic resonance spectrometer. This power supply was designed to achieve a maximum current of 200 A with good efficiency, low semiconductor losses, low cost, and easy maintenance. Both energy storage circuits and dumping circuits are used to obtain switching times less than 2 ms between field levels in agreement with the FFC technique specifications. The current ripple at high currents is better than 1×10−4 and presents a specific shape which can be used for additional compensation using auxiliary circuits. The implemented power supply was tested and been continuously operating with a home-built FFC solenoidal magnet, associated cooling system, and rf units for fields between 0 and 0.2 T.
Inductance deep-level transient spectroscopy for determining temperature-dependent resistance and capacitance of Schottky diodes
Authors: Rangel-Kuoppa V. T. , Pessa M.
Published: September 2003

We present a modification of the deep-level transient spectroscopy (DLTS) to accurately determine the series resistance and capacitance of a semiconductor Schottky diode. In a DLTS sample, the resistance and capacitance are in series, but when measured by a capacitance meter they appear to be parallel, which causes a significant error in all DLTS parameters. We show theoretically and experimentally that the correct resistance and capacitance can simply be obtained if an inductor is placed in series with the sample.
Plasma-sheath transition and ion sound speed in weakly collisional plasmas
Authors: Kono Akihiro
Published: September 2003

The plasma-sheath transition in weakly collisional plasma is discussed in terms of a simple fluid model. The plasma-sheath transition region is characterized as a region where the ion flow speed is close to (N+/Ne)1/2c0 (N+ is the positive ion density, Ne the electron density, and c0 the usual Bohm speed), which can be interpreted as a local ion sound speed with non-neutrality taken into account. However, at low collisionality where one can clearly distinguish a plasma and a collisionless sheath joined by a transition region, numerical results show that (N+/Ne)1/2c0 at the point where the ion flow reaches this speed is practically identical with c0.
Merger and binary structure formation of two discrete vortices in a background vorticity distribution of a pure electron plasma
Authors: Soga Y. , Kiwamoto Y. , Sanpei A. , Aoki J.
Published: September 2003

Observations have shown that two discrete vortices (clumps) immersed in a broad profile of background vorticity merge quickly or form a binary state that lasts for a long period. The different paths of the vortical evolution critically depend on slight differences in the initial background vorticity distribution (BGVD). By a fine control of the BGVD the asymptotic inter-clump distance is found to be a two-valued function of ∇ζb/ζb2, where ζb is the BGV at the initial location of the clumps, corresponding to the merger and the binary state. The multiplicity is removed by considering the degree of depletion of BGVD between two clumps at the time of their proximity in the initial phase.