bluuebunny/crossref_metadata_2025 huggingface dataset:
Methylmercury distribution in the pregnant rat and embryo during early midbrain organogenesis
Authors: Lewandowski T.A. , Pierce C.H. , Pingree S.D. , Hong S. , Faustman E.M.
Published: October 2002

Background

The period of neurogenesis represents a window of susceptibility for in utero methylmercury (MeHg) exposure. This study examined the toxicokinetics of potentially neurotoxic doses of MeHg during neurogenesis in the developing rat to provide additional information in the areas of mercury speciation and inter‐study variability.

Methods

Pregnant Sprague‐Dawley rats were dosed s.c. with 5–22 mg/kg MeHg on Day 11 of gestation to target rapidly dividing cells of the developing midbrain. Maternal liver, kidney, skin, blood, placenta, and the embryonic body and brain were evaluated for total and inorganic mercury content at 24, 48, and 72 hr after dosing. Tissue Hg partitioning ratios derived from our data were then compared to those derived from previous studies.

Results

Mercury was present in all tissues examined by 24 hr after dosing, and levels remained relatively stable over the subsequent 2 days in most tissues. The exceptions were the maternal blood and kidney, in which total mercury decreased significantly over the three days after dosing. Inorganic mercury concentrations were similarly stable over time. At maternal MeHg doses above 12 mg/kg, non‐linearities were observed in mercury accumulation in the embryo, placenta and maternal liver. The mercury tissue partitioning coefficients ranged from 0.09 for maternal blood:embryo to 1.97 for maternal blood:kidney.

Conclusions

Our observations at the 5 mg/kg dose were consistent with those of previous studies that involved evaluations at slightly later gestational times. The estimates of tissue partitioning coefficients we derived using multiple studies provide valuable insight into the effects of inter‐study variability. Teratology 66:235–241, 2002. © 2002 Wiley‐Liss, Inc.
Risk factors for heart disease associated with abnormal sidedness
Authors: Kuehl Karen S. , Loffredo Christopher
Published: October 2002

Background

The purpose of this study is to obtain information on potential familial and environmental risk factors for liveborn cases of heart disease associated with abnormal visceral and vascular sidedness, heterotaxy heart disease, so that hypotheses about this congenital cardiovascular malformation (CCVM) and its risk factors can be generated. We describe the characteristics of infants with heterotaxy heart malformations and case‐control comparisons of interview data obtained on parental socio‐demographic characteristics, occupational and household environmental exposures.

Methods

Cases and controls are drawn from the Baltimore Washington Infant Study (BWIS) a population based case control study of CCVM diagnosed in the region from 1981–89.

Results

Maternal diabetes (OR = 5.5, 95% CI = 1.6–19.1) and family history of malformations (OR = 5.1, 95% CI = 2.0–12.9) are strongly associated with cardiac disorders of sidedness. Cocaine use by mothers during the first trimester is associated with heterotaxy heart disease with odds of 3.7 (95% CI = 1.3–10.7). Cases of isolated dextrocardia shared risk factors with other heterotaxy malformations. The odds of a twin proband having heterotaxy heart disease is 4.8 (95% CI = 1.9–11.8) compared to singleton births. Twin probands are predominantly monozygotic twins in contrast to twin probands in other congenital cardiovascular malformations.

Conclusions

Our findings are consistent with a role for multiple genetic factors in the development of left‐right axis formation and with variable cardiac phenotypes according to gene expression and possible gene‐environment interactions. Association with monozygotic twinning and with parental cocaine use may point to additional mechanistic clues for future research. Teratology 66:242–248, 2002. © 2002 Wiley‐Liss, Inc.
13C‐NMR study of hypoglycemia‐induced glycolytic changes in embryonic mouse heart
Authors: Ghatnekar Gautam S. , Gracz Hanna S. , Smoak Ida W.
Published: October 2002

Background

Glucose metabolites can be detected in embryonic mouse tissues using 13C‐NMR spectroscopy. The advantage of this method is in its chemical specificity and the ability to follow metabolic changes.

Methods

In this study, CD‐1 mice were mated and embryos excised on gestational day (GD) 10.5 (plug = GD 0.5). Hearts were isolated and cultured in 150 mg/dl glucose (normoglycemic medium) or 40 mg/dl glucose (hypoglycemic medium) for 6 hr. 13C‐labeled glucose comprised 62%–64% of total glucose in the culture medium. Pre‐ and postculture media were treated with deuterated water (D2O), and 13C spectra were obtained using a Bruker Avance 500 MHz spectrometer operating at 11.744 tesla (125.7 MHz for 13C). NMR spectra demonstrated resonances for 13C‐glucose in preculture normoglycemic and hypoglycemic media. Postculture spectra for normoglycemic and hypoglycemic media demonstrated 13C‐glucose signals as well as a signal for 13C‐lactate. Area under the curve (AUC) was measured for the [1‐13C‐glucose] resonance from preculture media and the [3‐13C‐lactate] resonance from postculture media. The ratios of AUC for postculture [3‐13C‐lactate] to preculture [1‐13C‐glucose] were calculated and found to be higher in hypoglycemic than in normoglycemic media.

Results

Our results confirm earlier findings using radiolabeled substrates and suggest that 13C‐NMR spectroscopy can be used to study glucose metabolism in isolated embryonic hearts exposed to hypoglycemia.

Conclusions

NMR effectively measures glucose and its metabolite, lactate, in the same spectrum and thus determines metabolic flux in the isolated embryonic heart after exposure to hypoglycemia and normoglycemia. This method could evaluate glucose metabolism in embryonic tissues following other teratogenic exposures. Teratology 66:267–272, 2002. © 2002 Wiley‐Liss, Inc.
Effect of (Mn, F) and (Mg, F) co-doping on dielectric and piezoelectric properties of lead zirconate titanate ceramics
Authors: Boucher E. , Guyomar D. , Lebrun L. , Guiffard B. , Grange G.
Published: October 2002

The influence of (Mn, F) and (Mg, F) dopants on the piezoelectric properties of lead zirconate titanate (PZT) ceramic compositions close to the morphotropic phase boundary is investigated. PZT ceramics are prepared by a chemical route based on co-precipitation of oxalates and hydroxides. The acceptor is incorporated into the B site of the materials and the fluorine ion is introduced into anionic sites. The d33 coefficient, the mechanical quality factor Qm and other properties are measured. Scanning electron microscopy is used to determine the grain size of the materials. Electron spin resonance is used to determine the valency state of Mn in fluorinated PZT ceramics. In Mn doped PZT, the introduction of a fluorine ion makes the poling process easier and increases the piezoelectric coefficients whereas the fluorination of Mg doped PZT constantly leads to hard materials with a lower piezoelectric response. This study shows that (Mn, F) co-doping produces semihard materials with high piezoelectric coefficients.
Submicron metal–semiconductor–metal ultraviolet detectors based on AlGaN grown on silicon: Results and simulation
Authors: Duboz J. Y. , Reverchon J. L. , Adam D. , Damilano B. , Grandjean N. , Semond F. , Massies J.
Published: October 2002

Solar blind metal–semiconductor–metal detectors have been fabricated based on AlGaN grown on Si by molecular-beam epitaxy. Submicron finger spacings were obtained by electron-beam lithography, and allowed us to demonstrate a significant improvement of the responsivity and the spectral selectivity. These results were explained by numerical two-dimensional calculations of the electric-field distribution. The simulation also explained the dependence of the response on applied bias.
Bethe ansatz for the Gaudin model and its relation with Knizhnik–Zamolodchikov equations
Authors: Garajeu Daniela
Published: October 2002

We recall the construction of the common eigenvectors of Gaudin Hamiltonians based on the Bethe ansatz. In the case of an arbitrary Lie algebra, this construction can be done either recursively or explicitly and we prove the equivalence of the two methods. We also prove that Bethe vectors are singular only if the Bethe equations are satisfied. In each eigenspace of the spin operator we construct additional common eigenvectors, having the same eigenvalue as the vacuum vector and which can not be obtained by the Bethe ansatz. These eigenvectors are not singular. We also recall the connection between Bethe vectors and integral solutions of the KZ equation. In an analogous way, the additional vectors lead to solutions of KZ equation which are not singular vectors and do not have an integral representation.
Characterization of fine particle trapping in a plasma-enhanced chemical vapor deposition reactor
Authors: Setyawan Heru , Shimada Manabu , Okuyama Kikuo
Published: October 2002

The distribution and transport of fine particles trapped in a radio-frequency (rf) plasma-enhanced chemical vapor deposition reactor was investigated using a laser light scattering technique. Structured clouds of particles were observed at localized regions between the holes below the showerhead. Typically, at a high rate of gas flow, particles emerging from the showerhead holes overshoot the equilibrium position of the particle trap, and the particle clouds in the trap were small and thin (winding mode). At a low rate of gas flow, the particles are directly attracted to the trap locations, and large particle clouds (lumping mode) were observed. The particle number concentration of trapped particles tends to increase with increasing rf power and decrease with increasing particle size. When the gas flow rate is increased, a sharp decrease occurs at a certain flow rate.
Studies of photoreflectance spectra in Cd1−xMnxTe/CdTe superlattices with high compositions
Authors: Chen Chenjia , Wang Xuezhong , Liang Xiaogan , Tavazzi S. , Borghesi A. , Sassella A. , Bellani V. , Geddo M. , Stella A.
Published: October 2002

Cd 1−x Mn x Te/CdTe superlattices were grown by molecular beam epitaxy with a CdTe buffer layer on GaAs(001) substrate. Photoreflectance spectra were performed on Cd1−xMnxTe/CdTe superlattices with high compositions of x=0.4, 0.8 at room temperature and liquid nitrogen temperature. The exciton transitions related to the heavy (H) and light (L) holes of 11H, 11L, 22H, and 33H are observed. After taking into account the strain-induced and quantum confinement effects, the theoretical calculations are in good agreement with the photoreflectance measurement results except x=0.8 of 33H. Photoluminescence measurements were also performed at room temperature and low temperature in order to compare with our photoreflectance results. Our results show that the photoreflectance spectroscopy technique is a powerful probe for the study of quantized state structures in superlattices systems.
Removal versus ablation in KrF dry laser cleaning of polystyrene particles from silicon
Authors: Kudryashov Sergey I. , Allen Susan D.
Published: October 2002

Direct absorption and melting of 0.2, 0.5 and 1.1 μm polystyrene particles on a Si substrate irradiated by 248 nm excimer laser radiation was found to contribute to their dry laser removal via a “hopping” mechanism at cleaning thresholds of 0.05, 0.1, and 0.16 J/cm2, respectively. Ablation of these particles, which starts near the beginning of substrate deceleration at fluences above 0.4–0.5 J/cm2, suppresses particle removal due to ablative recoil momentum. At fluences above a second cleaning threshold of 0.7 J/cm2 particles are completely evaporated without any visible surface damage of the Si substrate.
A fully state- and angle-resolved study of the H+HD→D+H2 reaction: Comparison of a molecular beam experiment to ab initio quantum reaction dynamics
Authors: Chao Sheng Der , Harich Steven A. , Xu Dai Dong , Wang Chia C. , Yang Xueming , Skodje Rex T.
Published: October 2002

We present the results of a joint experimental and theoretical investigation of the reaction dynamics of the H+HD→D+H2 chemical reaction. The experiment was performed using a crossed molecular beam apparatus that employed the Rydberg-atom time-of-flight detection scheme for the product D atom. The photolysis of a HI precursor molecule produced a beam source of hot H atoms, which, when crossed with a cold HD beam, yielded two well-defined center-of-mass collision energies, EC=0.498 and 1.200 eV. The resolution of the experiment was sufficient to allow the measurement of the rovibrationally state-resolved differential cross section from the ground state of the HD reagent. The reaction was modeled theoretically using a converged coupled channel scattering calculation employing the BKMP2 potential energy surface: The S matrix was computed on a grid of 56 energies in the range EC=0.245–1.551 eV. It is found that the experimental and theoretical state-to-state differential cross sections are in quantitative agreement at the two experimental energies. The geometric phase, which was not included in the calculation, is apparently not required at the energies considered. The spin statistics for the two identical protons is observed to have a dramatic effect on the rotational distribution of H2 products, giving rise to a saw-toothed distribution with odd-j′>even-j′. The differential cross section for several of the product states exhibited a dramatic forward peak that may be the signature of trapped quantum states near the saddle point. A detailed analysis of the reaction attributes is presented based on the energy dependence of the computed S matrix.
Weak pseudo-Hermiticity and antilinear commutant
Authors: Solombrino L.
Published: October 2002

We inquire into some properties of diagonalizable pseudo-Hermitian operators, showing that their definition can be relaxed and that the pseudo-Hermiticity property is strictly connected with the existence of an antilinear symmetry. This result is then illustrated by considering the particular case of the complex Morse potential.
Scattering into cones and flux across surfaces in quantum mechanics: A pathwise probabilistic approach
Authors: Posilicano Andrea , Ugolini Stefania
Published: October 2002

We show how the scattering-into-cones and flux-across-surfaces theorems in quantum mechanics have very intuitive pathwise probabilistic versions based on some results by Carlen about large time behavior of paths of Nelson’s diffusions. The quantum mechanical results can then be recovered by taking expectations in our pathwise statements.
How to generate spinor representations in any dimension in terms of projection and nilpotent operators
Authors: Borštnik N. Mankoč , Nielsen H. B.
Published: October 2002

We present a technique to construct a spinor space basis as products of certain nilpotents and projections formed from γa for which we only need to know that they obey the Clifford algebra. The technique works for all dimensions and signatures. We use this technique to deliver a concrete choice of γ-matrices and Lorentz group generators for (fundamental representations of) spinors in a rather systematic and transparent way. We further develop the formalism by proposing the corresponding graphic presentation of basic states, which offers an easy way to see all the quantum numbers of states with respect to the generators of the Lorentz group, as well as transformation properties of the states under any element of the Clifford algebra.
Quantum optical versus quantum Brownian motion master equation in terms of covariance and equilibrium properties
Authors: Vacchini Bassano
Published: October 2002

Structures of quantum Fokker–Planck equations are characterized with respect to the properties of complete positivity, covariance under symmetry transformations and satisfaction of equipartition, referring to recent mathematical work on structures of unbounded generators of covariant quantum dynamical semigroups. In particular the quantum optical master equation and the quantum Brownian motion master equation are shown to be associated to U(1) and R symmetry, respectively. Considering the motion of a Brownian particle, where the expression of the quantum Fokker–Planck equation is not completely fixed by the aforementioned requirements, a recently introduced microphysical kinetic model is briefly recalled, where a quantum generalization of the linear Boltzmann equation in the small energy and momentum transfer limit straightforwardly leads to quantum Brownian motion.
Low threshold distributed feedback lasers fabricated from blends of conjugated polymers: Reduced losses through Förster transfer
Authors: Gupta R. , Stevenson M. , Heeger A. J.
Published: October 2002

We report on low threshold photopumped amplified spontaneous emission (ASE) in blends of derivatives of poly (p-phenylene vinylene) and distributed feedback (DFB) lasers fabricated from the same materials. Förster energy transfer is used to spectrally shift the emission away from the absorption band, thereby reducing the optical losses. The concentration of the guest polymer in the blend determines the rate of energy transfer and, thereby, has a strong effect on the observed emission spectrum. The photoluminescence quantum efficiencies (ηPL) of the blends are higher than the ηPL of the pure emissive species (ηPL decreases with increasing amount of the guest polymer in the blends). The blends exhibit optical losses ∼3 cm−1 compared to ∼85 cm−1 in pure host. As a result, the ASE thresholds are reduced from 5000 W/cm2 in the host to 200 W/cm2 in the blends. The corresponding lasing threshold in the DFB structures is 100 W/cm2.
Spectral features of a pulsed CO2 laser
Authors: Witkowski Jerzy S. , Plinski Edward F. , Kalicinski Tomasz , Majewski Bartosz W. , Plawecki Tomasz , Abramski Krzysztof M.
Published: October 2002

The qualitative and quantitative description of the laser tuning effect during a pulse forming has been described in this article. A Mach–Zender interferometer to measure changes of the optical length of the laser resonator during pulse operation has been used. It has been proven that the reason for the line hopping during the pulse is because of the change in the refractive index.
Remarks on the connection between the additive separation of the Hamilton–Jacobi equation and the multiplicative separation of the Schrödinger equation. I. The completeness and Robertson conditions
Authors: Benenti S. , Chanu C. , Rastelli G.
Published: October 2002

The fundamental elements of the variable separation theory are revisited, including the Eisenhart and Robertson theorems, Kalnins–Miller theory, and the intrinsic characterization of the separation of the Hamilton–Jacobi equation, in a unitary and geometrical perspective. The general notion of complete integrability of first-order normal systems of PDEs leads in a natural way to completeness conditions for separated solutions of the Schrödinger equation and to the Robertson condition. Two general types of multiplicative separation for the Schrödinger equation are defined and analyzed: they are called “free” and “reduced” separation, respectively. In the free separation the coordinates are necessarily orthogonal, while the reduced separation may occur in nonorthogonal coordinates, but only in the presence of symmetries (Killing vectors).
Remarks on the connection between the additive separation of the Hamilton–Jacobi equation and the multiplicative separation of the Schrödinger equation. II. First integrals and symmetry operators
Authors: Benenti S. , Chanu C. , Rastelli G.
Published: October 2002

The commutation relations of the first-order and second-order operators associated with the first integrals in involution of a Hamiltonian separable system are examined. It is shown that these operators commute if and only if a “pre-Robertson condition” is satisfied. This condition involves the Ricci tensor of the configuration manifold and it is implied by the Robertson condition, which is necessary and sufficient for the separability of the Schrödinger equation.
Thermal conductivity of AlAs0.07Sb0.93 and Al0.9Ga0.1As0.07Sb0.93 alloys and (AlAs)1/(AlSb)11 digital-alloy superlattices
Authors: Borca-Tasciuc T. , Song D. W. , Meyer J. R. , Vurgaftman I. , Yang M.-J. , Nosho B. Z. , Whitman L. J. , Lee H. , Martinelli R. U. , Turner G. W. , Manfra M. J. , Chen G.
Published: October 2002

A differential 3ω technique is employed to determine the thermal conductivity of the AlAs0.07Sb0.93 ternary alloy, the Al0.9Ga0.1As0.07Sb0.93 quaternary alloy, and an (AlAs)1/(AlSb)11 digital-alloy superlattice. Between 80 and 300 K, the thermal conductivities for all three samples are relatively insensitive to temperature. The thermal conductivity of the (AlAs)1/(AlSb)11 superlattice is smaller than that of the AlAs0.07Sb0.93 ternary alloy, but much larger than the predictions of a model for phonon transport across the superlattice interfaces.
Raman characterization and stress analysis of AlN grown on SiC by sublimation
Authors: Liu L. , Liu B. , Edgar J. H. , Rajasingam S. , Kuball M.
Published: October 2002

The stress distribution in bulk AlN crystals seeded on 6H–SiC was theoretically modeled and also determined experimentally from Raman peak positions. The full width at half maximum of the AlN Raman peaks showed the crystal quality improved as its thickness increased. The theoretical frequency shifts of the E1 (transverse optical) mode calculated from model-predicted stress were in good agreement with experimental values taken along the edges of crystal samples. The stress was linearly distributed along the depth of the samples, and changed from compressive at the growing surface to tensile at the interface between AlN and SiC for thickness range of several hundred micrometers. Large tensile stresses, up to 0.6 GPa, were detected in the AlN at the interface. The effects of growth temperature and sample thickness were investigated. It is predicted that the AlN on 6H–SiC must be at least 2 mm thick to prevent it from cracking while cooling down the sample from a growth temperature of 2000 °C.
Experimental study and simulation of space charge stimulated discharge
Authors: Noskov M. D. , Malinovski A. S. , Cooke C. M. , Wright K. A. , Schwab A. J.
Published: October 2002

The electrical discharge of volume distributed space charge in poly(methylmethacrylate) (PMMA) has been investigated both experimentally and by computer simulation. The experimental space charge was implanted in dielectric samples by exposure to a monoenergetic electron beam of 3 MeV. Electrical breakdown through the implanted space charge region within the sample was initiated by a local electric field enhancement applied to the sample surface. A stochastic-deterministic dynamic model for electrical discharge was developed and used in a computer simulation of these breakdowns. The model employs stochastic rules to describe the physical growth of the discharge channels, and deterministic laws to describe the electric field, the charge, and energy dynamics within the discharge channels and the dielectric. Simulated spatial–temporal and current characteristics of the expanding discharge structure during physical growth are quantitatively compared with the experimental data to confirm the discharge model. It was found that a single fixed set of physically based dielectric parameter values was adequate to simulate the complete family of experimental space charge discharges in PMMA. It is proposed that such a set of parameters also provides a useful means to quantify the breakdown properties of other dielectrics.
Elliptic Ruijsenaars operators and functional equations
Authors: Komori Yasushi
Published: October 2002

We study mutually commutative difference operators introduced by Ruijsenaars, which are regarded as elliptic analogs of Macdonald operators and consist of the Jacobi theta functions and shift operators. These operators are constructed in terms of R-operators due to Shibukawa and Ueno or root algebras introduced by Cherednik, which give rise to a set of functional equations. We investigate solutions of these functional equations for generalizations of elliptic Ruijsenaars operators.
The foliation operator in history quantum field theory
Authors: Isham C. J. , Savvidou K.
Published: October 2002

As a preliminary to discussing the quantization of the foliation in a history form of general relativity, we show how the discussion in an earlier work [J. Math. Phys. 43, 3053 (2002)] of a history version of free, scalar quantum field theory can be augmented in such a way as to include the quantization of the unit-length, timelike vector that determines a Lorentzian foliation of Minkowski space–time. We employ a Hilbert bundle construction that is motivated by (i) discussing the role of the external Lorentz group in the existing history quantum field theory [J. Math. Phys. 43, 3053 (2002)] and (ii) considering a specific representation of the extended history algebra obtained from the multi-symplectic representation of scalar field theory.
The global existence in the Cauchy problem of the Maxwell–Chern–Simons–Higgs system
Authors: Chae Dongho , Chae Myeongju
Published: October 2002

In this article we prove the global existence of solution of the classical Maxwell–Chern–Simons–Higgs equations in (2+1)-dimensional Minkowski space–time in the Lorentz gauge. We also prove that the topological solution of the Maxwell–Chern–Simons–Higgs system converges to that of Maxwell–Higgs system as the Chern–Simons constant κ goes to zero, reproducing the classical result by Moncrief [J. Math. Phys. 21, 2291 (1980)] on the global existence of the Maxwell–Klein–Gordon system in (2+1)-dimension.
Controlled fabrication of silver or gold nanoparticle near-field optical atomic force probes: Enhancement of second-harmonic generation
Authors: Barsegova Inna , Lewis Aaron , Khatchatouriants Artium , Manevitch Alexandra , Ignatov Andrei , Axelrod Noel , Sukenik Chaim
Published: October 2002

A simple method is described for producing silver and gold nanoparticles at the tip of an atomic force microscope sensor. It is shown that these nanoparticles can enhance the nonlinear optical phenomenon of second-harmonic generation of a molecular system such as a styryl dye.
Density and current of a dissipative Schrödinger operator
Authors: Kaiser Hans-Christoph , Neidhardt Hagen , Rehberg Joachim
Published: October 2002

We regard a current flow through an open one-dimensional quantum system which is determined by a dissipative Schrödinger operator. The imaginary part of the corresponding form originates from Robin boundary conditions with certain complex valued coefficients imposed on Schrödinger’s equation. This dissipative Schrödinger operator can be regarded as a pseudo-Hamiltonian of the corresponding open quantum system. The dilation of the dissipative operator provides a (self-adjoint) quasi-Hamiltonian of the system, more precisely, the Hamiltonian of the minimal closed system which contains the open one is used to define physical quantities such as density and current for the open quantum system. The carrier density turns out to be an expression in the generalized eigenstates of the dilation while the current density is related to the characteristic function of the dissipative operator. Finally a rigorous setup of a dissipative Schrödinger–Poisson system is outlined.
Relativistic plasma maser interaction in the presence of ion acoustic turbulence
Authors: Deka N. K. , Saikia B. J. , Goswami K. S.
Published: October 2002

The plasma maser interaction between the high frequency nonresonant ordinary mode and low frequency resonant ion acoustic mode in a relativistic plasma has been studied for the first time. It has been shown that the growth rate of the high frequency wave occurs through the plasma maser interaction between relativistic electrons and the ion acoustic wave turbulence.
Structural and optical properties of rare-earth-doped Y2O3 waveguides grown by pulsed-laser deposition
Authors: Pons-Y-Moll Olivier , Perriere Jacques , Millon Eric , Defourneau Reine Marie , Defourneau Daniel , Vincent Brice , Essahlaoui Abdel , Boudrioua Azzedine , Seiler Wilfrid
Published: October 2002

Crystalline rare-earth-doped yttrium oxide thin films were grown by pulsed-laser deposition (PLD) on SiO2/Si substrates. The structural and morphological features of these films were studied, as a function of the growth conditions (temperature from 200 to 800 °C and oxygen pressure from 10−6 to 0.5 mbar), by using Rutherford backscattering spectroscopy, x-ray diffraction, and atomic force microscopy. The related optical properties were investigated by m-lines spectroscopy at 633 nm and 1.3 μm. The optimal conditions were found to be a temperature and a pressure of 700 °C and 10−6 mbar, respectively. In that case, the Y2O3 films are stoichiometric with controlled erbium and europium rates, and present a well-crystallized, (111) textured cubic phase and a low surface roughness of about 10 Å. Moreover, the PLD films show good waveguiding properties with a high refractive index (1.92 at 633 nm), a step-index structure, and low optical losses around 1 dB/cm in the near infrared region, promising for a planar amplifier function.
Observation and modeling of the initial fast interdiffusion regime in Si/SiGe multilayers
Authors: Aubertine D. B. , Mander M. A. , Ozguven N. , Marshall A. F. , McIntyre P. C. , Chu J. O. , Mooney P. M.
Published: October 2002

X-ray diffraction is used to probe interdiffusion in asymmetrically strained, low concentration Si/SiGe superlattices. The results are shown to be in good agreement with a model developed from literature data for Ge diffusion in SiGe alloys. Using this model, it is shown that the initial fast interdiffusion frequently observed in Si/SiGe superlattices results primarily from the concentration dependence of the activation enthalpy for SiGe interdiffusion. Time dependent strain relaxation is shown to play a discernible, but secondary role in the transition from fast to slow interdiffusion. The linear proportionality constant relating the activation enthalpy of SiGe interdiffusion to biaxial strain is found to be ∼19 eV/unit strain.
Influence of ordering on the magnetostriction of Fe–27.5 at. % Ga alloys
Authors: Srisukhumbowornchai N. , Guruswamy S.
Published: October 2002

Fe–Ga alloys with compositions near 27.5 at. % Ga (26–29 at. %) can be heat treated to obtain ordered phases based on α″ (ordered bcc), D019 (ordered hexagonal), and L12 (ordered fcc) structures. This work presents an evaluation of how the different ordering treatments influence the magnetostriction in cast polycrystalline Fe–27.5 at. % Ga alloy. Alloy samples were annealed first in the disordered bcc (A2) phase region to obtain a disordered bcc solid solution, followed by ordering-heat treatment in the appropriate temperature region of stability of each of the ordered phases. X-ray diffraction was used to characterize the phases present prior to and after heat treatments. Magnetostriction measurements were carried out at different prestress levels in the range of 0–50 MPa. Magnetic properties were measured using a vibrating sample magnetometer. Annealed Fe–27.5 at. % Ga sample with a disordered bcc (A2) structure and a weak [110] texture showed a magnetostriction value of 115×10−6. The α″ ordering treatment resulted in a small decrease of saturation magnetostriction. Magnetostriction decreased to negligible or small negative levels after D019 and L12 ordering treatments.
Properties of polymorphous silicon–germanium alloys deposited under high hydrogen dilution and at high pressure
Authors: Gueunier M. E. , Kleider J. P. , Brüggemann R. , Lebib S. , Roca i Cabarrocas P. , Meaudre R. , Canut B.
Published: October 2002

Hydrogenated polymorphous silicon–germanium samples with Ge content x up to 0.35 have been deposited in a plasma-enhanced chemical vapor deposition system from silane and germane precursors highly diluted in hydrogen and in a high pressure range. The optical, defect-related, and transport properties of both types of carriers have been studied using a set of complementary techniques before light soaking, after light soaking, and after subsequent annealing. Before light soaking, we observe a small deterioration of the electron transport properties with increasing Ge content. This is related to the widening of the conduction band tail and to the increase of a deep defect band with emission energies at about 0.4 eV below the conduction transport path, which is attributed to Ge dangling bonds. The hole transport properties are much less sensitive to the incorporation of Ge, which we attribute to the unchanged Urbach tail parameter. Light soaking results in a deterioration of the transport properties due to an increase of the density of states, the relative effect being less pronounced for the highest Ge contents due to the higher native defect concentrations. Again, the electron transport properties are more affected than the hole transport properties, which appear quite stable against light soaking. Annealing at 460 K following light soaking is found to restore the initial state more easily in the low Ge content samples. Compared to samples deposited under more conventional conditions (no or less hydrogen dilution and low pressure) the striking features of our alloys are that (i) they exhibit an enhanced stability of the transport properties against light soaking and (ii) the characteristic time of the light-soaking kinetics is shorter. These features reveal the polymorphous character of our alloys, related to a specific hydrogen microstructure observed by infrared spectroscopy and hydrogen effusion, which indicate that the amorphous matrix exhibits an improved order like in hydrogenated polymorphous silicon.
Role of electron-inertia-linked current source terms in the physics of cylindrically symmetric imploding snowplow shocks
Authors: Auluck S. K. H.
Published: October 2002

Snowplow shocks are supersonic flows in plasmas driven by a magnetic piston, in which the material impacted by the piston “sticks” to it, resulting in accretion of the plasma near the piston. The density front and the magnetic piston move together as a single structure. A typical example of a snowplow shock is the plasma focus sheath. When normally neglected electron-inertia (EI) terms in the fluid model of the plasma are taken into account, a time scale ωp−1 and a space scale cωp−1 are introduced which are negligible in the bulk of the plasma but are non-negligible in a transition region between the no-plasma region and the dense plasma. As a result “no-plasma” initial conditions are not valid for the fluid equations obtained by neglecting EI. A resonant coupling between two electron plasma modes via the Hall term is shown to result in spontaneous generation of axial magnetic field and rotation even in the presence of perfect azimuthal symmetry in the low density precursor plasma formed before the ideal plasma phase. Related physics issues such as spontaneous symmetry breaking mechanism are discussed.
The Schwinger SU(3) construction. I. Multiplicity problem and relation to induced representations
Authors: Chaturvedi S. , Mukunda N.
Published: October 2002

The Schwinger oscillator operator representation of SU(3) is analyzed with particular reference to the problem of multiplicity of irreducible representations. It is shown that with the use of an Sp(2,R) unitary representation commuting with the SU(3) representation, the infinity of occurrences of each SU(3) irreducible representation can be handled in complete detail. A natural “generating representation” for SU(3), containing each irreducible representation exactly once, is identified within a subspace of the Schwinger construction, and this is shown to be equivalent to an induced representation of SU(3).
The Schwinger SU(3) construction. II. Relations between Heisenberg–Weyl and SU(3) coherent states
Authors: Chaturvedi S. , Mukunda N.
Published: October 2002

The Schwinger oscillator operator representation of SU(3), studied in a previous paper from the representation theory point of view, is analyzed to discuss the intimate relationships between standard oscillator coherent state systems and systems of SU(3) coherent states. Both SU(3) standard coherent states, based on choice of highest weight vector as fiducial vector, and certain other specific systems of generalized coherent states, are found to be relevant. A complete analysis is presented, covering all the oscillator coherent states without exception, and amounting to SU(3) harmonic analysis of these states.
Image system for Stokes-flow singularity between two parallel planar walls
Authors: Bhattacharya S. , Bławzdziewicz J.
Published: October 2002

Using a recently developed image representation for Stokes flow in a half-space bounded by a planar wall [Cichocki and Jones, Physica A 258, 273 (1998)], the image system is constructed for the flow field produced by a force multipole in the space bounded by two parallel walls. The image singularities are expressed in terms of products of double-reflection matrices, and the expansion is simplified using symmetries of the double-reflection operation. Our analysis yields recurrence relations for the strengths of the image multipoles. The relations are solved explicitly, and a complete image system is obtained for an arbitrary source-force multipole. Applications of our image representation for evaluating the hydrodynamic friction and mobility matrices of particles interacting with two parallel planar walls are indicated.
Monopoles and dyons in SO(3) gauged Skyrme models: Corrigendum
Authors: Brihaye Y. , Hartmann B. , Tchrakian D. H.
Published: October 2002

The axially symmetric solutions of a gauged Skyrme model previously studied in an earlier work [J. Math. Phys. 42, 3270 (2001)] are reconsidered.
Drift-diffusion equation for ballistic transport in nanoscale metal-oxide-semiconductor field effect transistors
Authors: Rhew Jung-Hoon , Lundstrom Mark S.
Published: October 2002

We develop a drift-diffusion equation that describes ballistic transport in a nanoscale metal-oxide-semiconductor field effect transistor (MOSFET). We treat injection from different contacts separately, and describe each injection with a set of extended McKelvey one-flux equations [Phys. Rev. 123, 51 (1961); 125, 1570 (1962)] that include hierarchy closure approximations appropriate for high-field ballistic transport and degenerate carrier statistics. We then reexpress the extended one-flux equations in a drift-diffusion form with a properly defined Einstein relationship. The results obtained for a nanoscale MOSFET show excellent agreement with the solution of the ballistic Boltzmann transport equation with no fitting parameters. These results show that a macroscopic transport model based on the moments of the Boltzmann transport equation can describe ballistic transport.
Transient creep in free-standing thin polycrystalline aluminum films
Authors: Kalkman A. J. , Verbruggen A. H. , Janssen G. C. A. M. , Radelaar S.
Published: October 2002

We studied room-temperature transient creep in polycrystalline, free-standing Al films with a thickness between 220 and 550 nm using a high-resolution bulge test technique. A transient logarithmic creep strain is observed. The time and stress dependence of the creep strongly support the idea that dislocation glide, limited by forest dislocation cutting, is the prevailing rate limiting mechanism. This is in contradiction with the misfit dislocation model for thin-film strengthening but in agreement with recent work on plasticity in thin Ag and Cu films on a substrate. A comparison is made with data on bulk Al. Both the transient creep strain and the initial fast strain are at least three orders of magnitude smaller for the thin-film samples. We argue that the strain hardening coefficient is the key parameter distinguishing thin film from bulk creep.
Ultrathin oxide interfaces on 6H–SiC formed by plasma hydrogenation: Ultra shallow depth profile study
Authors: Xie Xianning , Loh Kian Ping
Published: October 2002

Silicon oxide ultrathin films grown on silicon carbide (6H–SiC) by plasma hydrogenation have been studied using ultrashallow depth profiling with time–of–flight secondary ion mass spectrometry. Plasma hydrogenation gives rise to an epitaxial 3×3R30° silicate structure on 6H–SiC(0001) and 6H–SiC(0001̄). By selecting appropriate sputtering conditions, an ultrathin and atomically abrupt interface delineating the boundary between the silicate epilayer (SiO+,Si2O+, and SiO3−,SiO2−) and bulk silicon carbide (SiC+) was observed on both C(0001̄) and Si(0001) faces. Differences in the sputtering profile between the C and Si faces suggest an enrichment of the interface stoichiometry by Si and O on the Si face. Our results support the structural models of the silicate on the C and Si-face 6H–SiC(0001) proposed by Starke [Appl. Phys. Lett. 74, 1084 (1999); J. Vac. Sci. Technol. A 17, 688 (1999)].
Failure mechanism of a multilayer (TiN/Al/TiN) diffusion barrier between copper and silicon
Authors: Kim Soo-Hyun , Nam Ki Tae , Datta Arindom , Kim Ki-Bum
Published: October 2002

The improvement of the diffusion barrier performance for Cu metallization, by inserting a thin Al layer between two TiN layers, has been clearly demonstrated and reported by us. The key idea behind our scheme is “stuffing” of grain boundaries of columnar TiN films by Al2O3. It has been also found that the barrier property is at its best when the Al thickness is 1 nm, but above this value, the barrier performance degrades drastically when the upper TiN film is not preannealed. In this study, why the barrier breaks down at above 1 nm of Al interlayer thickness is investigated. High-resolution transmission electron microscopy, scanning transmission electron microscopy, and energy dispersive spectroscopy analyses revealed that the fast diffusion of Cu in the presence of the free Al is the main reason for the failure of the present diffusion barrier scheme. These results are discussed on the basis of the differences between the movements of Al and Cu through TiN film, and the differences between the solid solubilities of Al in Cu and in Si. Our results show that both Al interlayer thickness and the oxygen content in TiN film should be properly controlled to take full advantage of the present multilayer diffusion barrier scheme.
Parameter analysis and optimization for the radiative cooling effect due to negative luminescence
Authors: Pipa V. I. , Liptuga A. I.
Published: October 2002

We present the results of theoretical and experimental investigation on the effect of radiative cooling (heating) of a thin layer with the pulsed semiconductor source of galvanomagnetic negative (positive) interband luminescence. The kinetics of layer cooling (heating), as well as subsequent layer temperature relaxation, is studied. Allowance is made for the attendant radiative heating of the layer related to Joule heating of the source. We analyze how the magnitude and rate of layer cooling depend on the parameters of the semiconductor source, cooled layer, and optical filter. The effect dependence on controlling electric and magnetic fields is investigated. It is shown that, having chosen the optimal parameter values, one can exert efficient radiative control over the passive object temperature by decreasing or increasing it relative to the ambient.
Insulator–metal transition and magnetoresistance of La0.5Ca0.5MnOy induced by tuning the oxygen content
Authors: Zhao Y. G. , Cai W. , Zhao J. , Zhang X. P. , Fan R. , Cao B. S. , Zhu M. H. , Wu Tom , Ogale S. B. , Shinde S. R. , Venkatesan T. , Tu Q. Y. , Mandal T. K. , Gopalakrishnan J.
Published: October 2002

The oxygen content of La0.5Ca0.5MnOy was tuned by annealing the samples at high temperatures in flowing nitrogen with graphite powder nearby. The reduction of oxygen content has dramatic effect on the electrical transport and magnetic properties. The samples with y=2.983, 2.83, and 2.803 show an insulator–metal transition, and an unusual temperature and magnetic-field dependence of the magnetoresistance. The paramagnetic-ferromagnetic transition also shifts to lower temperatures and the antiferromagnetic transition at lower temperature is suppressed. The results are discussed in terms of the effect of oxygen vacancies on the various properties of La0.5Ca0.5MnOy.
Propagation of sound and thermal waves in an ionizing-recombining hydrogen plasma: Revision of results
Authors: Sigalotti Leonardo Di G. , Sira Eloy , Tremola Ciro
Published: October 2002

The propagation of acoustic and thermal waves in a heat conducting, hydrogen plasma, in which photoionization and photorecombination [H++e−⇌H+hν(χ)] processes are progressing, is re-examined here using linear analysis. The resulting dispersion equation is solved analytically and the results are compared with previous solutions for the same plasma model. In particular, it is found that wave propagation in a slightly and highly ionized hydrogen plasma is affected by crossing between acoustic and thermal modes. At temperatures where the plasma is partially ionized, waves of all frequencies propagate without the occurrence of mode crossing. These results disagree with those reported in previous work, thereby leading to a different physical interpretation of the propagation of small linear disturbances in a conducting, ionizing-recombining, hydrogen plasma.
Late-stage kinetics of laser-induced photochemical deposition in liquid solutions
Authors: Hugonnot Emmanuel , Müller Xavier , Delville Jean-Pierre
Published: October 2002

Using a reaction-diffusion equation involving the one-photon excitation of a two-level system, we propose a rate equation that describes the late-stage growth of laser-induced photochemical deposits. With appropriate scaling, we show that the kinetics can be reduced to a single master curve for large beam radii. To experimentally illustrate the model, we investigate the coarsening of the deposit induced by a reaction with chromates photoactivated by a continuous Ar+ laser wave. Predicted growth laws are confirmed and the universal single-scaled dynamics is experimentally demonstrated.
Dynamics of a twisted nematic cell using a convergent beam system
Authors: Ruan L. Z. , Sambles J. R.
Published: October 2002

Using a convergent beam system and the full-leaky guided-mode technique, the dynamic relaxation in a twist nematic cell is explored on removal of an ac electrical field. From the dynamical guided-mode data, the director structure in the cell at different times during relaxation is obtained. Substantial backflow is observed during the first few milliseconds after the removal of the voltage. Detailed comparison of the experimental results with the model theory verifies the validity of the Ericksen–Leslie theory. Further, by carefully fitting the time dependent guided-mode data taken over the whole relaxation of the cell, the viscosity coefficients of the liquid crystal have been determined.
Coherent state triplets and their inner products
Authors: Rowe D. J. , Repka J.
Published: October 2002

It is shown that if ℍ is a Hilbert space for a representation of a group G, then there are triplets of spaces (FH,H,FH), in which FH is a space of coherent state or vector coherent state wave functions and FH is its dual relative to a conveniently defined measure. It is shown also that there is a sequence of maps FH→H→FH which facilitates the construction of the corresponding inner products. After completion if necessary, the spaces (FH,H,FH) become isomorphic Hilbert spaces. It is shown that the inner product for ℍ is often easier to evaluate in FH than in FH. Thus, we obtain integral expressions for the inner products of coherent state and vector coherent state representations. These expressions are equivalent to the algebraic expressions of K-matrix theory, but they are frequently more efficient to apply. The construction is illustrated by many examples.
New classes of quasi-solvable potentials, their exactly solvable limit, and related orthogonal polynomials
Authors: Ganguly Asish
Published: October 2002

We have generated, using an sl(2,R) Lie-algebraic formalism, several new classes of quasi-solvable elliptic potentials, which in the appropriate limit go over to the exactly solvable forms. We have obtained exact solutions of the corresponding spectral problem for some real values of the potential parameters. We have also given explicit expressions of the families of associated orthogonal polynomials in the energy variable.