bluuebunny/crossref_metadata_2025 huggingface dataset:
Persistent endothelial dysfunction is related to elevated C-reactive protein (CRP) levels in Type II diabetic patients after acute myocardial infarction
Authors: NYSTRÖM Thomas , NYGREN Arne , SJÖHOLM Åke
Published: January 2005

The atherosclerotic process is an ongoing dynamic and progressive state arising from endothelial dysfunction and inflammation. Although suffering from an acute coronary artery disease, patients with Type II diabetes have a poor outcome compared with non-diabetic patients, which may only partly be explained by traditional risk factors. Our purpose was to compare non-traditional risk factors, such as endothelial function, C-reactive protein (CRP) and adiponectin, in Type II diabetic and non-diabetic patients following AMI (acute myocardial infarction). Twenty Type II diabetic patients were compared with 25 non-diabetic patients at baseline (1–3 days from the onset of chest pain) and at 60 days follow-up after an AMI. Using high-resolution ultrasound, brachial artery responses to FMD (flow-mediated vasodilatation; endothelium-dependent vasodilatation) and NTG (nitroglycerine-induced vasodilatation; endothelium-independent vasodilatation) were measured. Plasma levels of CRP and adiponectin were measured by ELISA. At baseline, FMD (1.9 compared with 3.2%; P=0.22) and CRP levels (6.95 compared with. 5.51 mg/l; P=0.40) did not differ between Type II diabetic and non-diabetic patients, whereas adiponectin levels were lower in Type II diabetic patients (2.8 compared with 5.0 ng/ml; P<0.05). At 60 days follow-up, there were significant differences in FMD (1.5 compared with 4.1%; P<0.02), CRP (4.23 compared with 1.46 mg/ml; P<0.01) and adiponectin (3.3 compared with 5.3 ng/ml; P<0.05) levels between Type II diabetic and non-diabetic patients. In contrast, NTG responses improved in both groups between baseline and follow-up (Type II diabetic patients, 9.7 compared with 13.2% respectively, P<0.05; non-diabetic patients, 7.9 compared with 12.4% respectively, P<0.01). These results show a persistent endothelium-dependent dysfunction and inflammatory activity in patients with Type II diabetes, but not in non-diabetic patients, after AMI. These findings may, in part explain, the poor outcome in coronary artery disease seen in Type II diabetes.
Determination ofin vivoprotein synthesis in human palatine tonsil
Authors: JANUSZKIEWICZ Anna , KLAUDE Maria , LORÉ Karin , ANDERSSON Jan , RINGDÉN Olle , ROOYACKERS Olav , WERNERMAN Jan
Published: January 2005

The palatine tonsils are constantly exposed to ingested or inhaled antigens which, in turn, lead to a permanent activation of tonsillar immune cells, even in a basic physiological state. The aim of the present study was to investigate if the immunological activation of the human palatine tonsil is reflected by a high metabolic activity, as determined by in vivo measurement of protein synthesis. The protein synthesis rate of the tonsil was also compared with that of the circulating T-lymphocytes, the total blood mononuclear cells and the whole population of blood leucocytes. Phenotypic characterization of immune-competent cells in tonsil tissue and blood was performed by flow cytometry. Pinch tonsil biopsies were taken after induction of anaesthesia in healthy adult patients (n=12) scheduled for ear surgery, uvulopalatopharyngoplasty or nose surgery. Protein synthesis was quantitatively determined during a 90-min period by a flooding-dose technique. The in vivo protein synthesis rate in the palatine tonsils was 22.8±5.7%/24 h (mean±S.D.), whereas protein synthesis in the circulating T-lymphocytes was 10.7±3.4%/24 h, in mononuclear cells was 10.8±2.8%/24 h and in leucocytes was 3.2±1.2%/24 h. CD3+ lymphocytes were the most abundant cell population in the tonsil. The in vivo protein synthesis rate in human tonsils was higher compared with the circulating immune cells. This high metabolic rate may reflect the permanent immunological activity present in human tonsils, although cell phenotypes and activity markers do not explain the differences.
Transport characteristics of peptides and peptidomimetics: I. N‐methylated peptides as substrates for the oligopeptide transporter and P‐glycoprotein in the intestinal mucosa
Authors: Gao J. , Sudoh M. , Borchardt R.T. , Aubé J.
Published: January 2005

Abstract: Peptides and peptidomimetics often exhibit poor oral bioavailability due to their metabolic instability and low permeation across the intestinal mucosa. N‐Methylation has been used successfully in peptide‐based drug design in an attempt to improve the metabolic stability of a peptide‐based lead compound. However, the effect of N‐methylation on the absorption of peptides through the intestinal mucosa is not well understood, particularly when transporters, i.e. the oligopeptide transporter (OPT) and P‐glycoprotein (P‐gp), modulate the passive diffusion of these types of molecules. To examine this, terminally free and terminally modified (N‐acetylated and C‐amidated) analogs of H‐Ala‐Phe‐Ala‐OH with N‐methyl groups on either the Ala‐Phe or Phe‐Ala peptide bond were synthesized. Transport studies using Caco‐2 cell monolayers, an in vitro model of the intestinal mucosa, showed that N‐methylation of the Ala‐Phe peptide bond of H‐Ala‐Phe‐Ala‐OH stabilized the molecule to protease degradation, and the resulting analog exhibited significant substrate activity for OPT. However, N‐methylation of the Phe‐Ala peptide bond of H‐Ala‐Phe‐Ala‐OH did not stabilize the molecule to protease degradation, and the substrate activity of the resulting molecule for OPT could not be determined. Interestingly, N‐methylation of the Phe‐Ala peptide bond of the terminally modified tripeptide Ac‐Ala‐Phe‐Ala‐NH2 decreased the substrate activity of the molecule for the efflux transporter P‐gp. In contrast, N‐methylation of the Ala‐Phe peptide bond of the terminally modified tripeptide Ac‐Ala‐Phe‐Ala‐NH2 increased the substrate activity of the molecule for P‐gp.
Cecal Duplication Cyst: A Cause of Intestinal Obstruction in a Newborn Infant
Authors: Tawil Khalil Al , Crankson Stanley , Emam Saeed , Eldemerdash Alaa , Sabbagh Fauzia , Laimoun Bdeir Abu
Published: January 2005

Intestinal obstruction is the most common surgical emergency in newborn infants. We report a case of cecal duplication cyst (CDC) as a cause of intestinal obstruction in a newborn infant. Prenatal ultrasonography (US) had shown an intra-abdominal cyst that was confirmed by the first postnatal US. Water-soluble contrast enema and a repeat US showed an intracecal cyst, however, the diagnosis of CDC was only established at laparotomy. CDC should be considered in the differential diagnosis of intestinal obstruction in an infant with an intra-abdominal cyst on US and a palpable right iliac fossa mass.
Growth of CoSi2 on Si(001) by reactive deposition epitaxy
Authors: Lim C. W. , Shin C.-S. , Gall D. , Zuo J. M. , Petrov I. , Greene J. E.
Published: January 2005

Ca F 2 -structure CoSi2 layers were formed on Si(001) by reactive deposition epitaxy (RDE) and compared with CoSi2 layers obtained by conventional solid phase growth (SPG). In both sets of experiments, Co was deposited by ultrahigh-vacuum magnetron sputtering and CoSi2 formed at 600°C. However, in the case of RDE, CoSi2 formation occurred during Co deposition while for SPG, Co was deposited at 25°C and silicidation took place during subsequent annealing. X-ray diffraction pole figures and transmission electron microscopy results demonstrate that RDE CoSi2 layers are epitaxial with a cube-on-cube relationship, (001)CoSi2‖(001)Si and [100]CoSi2‖[100]Si. In contrast, SPG films are polycrystalline with an average grain size of ≃1000Å and a mixed 111∕002∕022∕112 orientation. We attribute the striking difference to rapid Co diffusion into the Si(001) substrate during RDE for which the high Co∕Si reactivity gives rise to a flux-limited reaction resulting in the direct formation of the disilicide phase. In contrast, sequential nucleation and transformation among increasingly Si-rich phases—from orthorhombic Co2Si to cubic CoSi to CoSi2—during SPG results in polycrystalline layers with a complex texture.
Composition of Ge(Si) islands in the growth of Ge on Si(111) by x-ray spectromicroscopy
Authors: Ratto Fulvio , Rosei Federico , Locatelli Andrea , Cherifi Salia , Fontana Stefano , Heun Stefan , Szkutnik Pierre-David , Sgarlata Anna , De Crescenzi Maurizio , Motta Nunzio
Published: January 2005

The stoichiometry of Ge∕Si islands grown on Si(111) substrates at temperatures ranging from 460to560°C was investigated by x-ray photoemission electron microscopy (XPEEM). By developing a specific analytical framework, quantitative information on the surface Ge∕Si stoichiometry was extracted from laterally resolved XPEEM Si 2p and Ge 3d spectra, exploiting the chemical sensitivity of the technique. Our data show the existence of a correlation between the base area of the self-assembled islands and their average surface Si content: the larger the lateral dimensions of the 3D structures, the higher their relative Si concentration. The deposition temperature determines the characteristics of this relation, pointing to the thermal activation of kinetic diffusion processes.
Dressed ion theory of size-asymmetric electrolytes: Effective ionic charges and the decay length of screened Coulomb potential and pair correlations
Authors: Forsberg Björn , Ulander Johan , Kjellander Roland
Published: January 2005

The effects of ionic size asymmetry on long-range electrostatic interactions in electrolyte solutions are investigated within the primitive model. Using the formalism of dressed ion theory we analyze correlation functions from Monte Carlo simulations and the hypernetted chain approximation for size asymmetric 1:1 electrolytes. We obtain decay lengths of the screened Coulomb potential, effective charges of ions, and effective permittivity of the solution. It is found that the variation of these quantities with the degree of size asymmetry depends in a quite intricate manner on the interplay between the electrostatic coupling and excluded volume effects. In most cases the magnitude of the effective charge of the small ion species is larger than that of the large species; the difference increases with increasing size asymmetry. The effective charges of both species are larger (in absolute value) than the bare ionic charge, except for high asymmetry where the effective charge of the large ions can become smaller than the bare charge.
Analysis of the validity of perturbation density functional theory: Based on extensive simulation for simple fluid at supercritical and subcritical temperature under various external potentials
Authors: Zhou Shiqi , Jamnik Andrej
Published: January 2005

Because of the scarcity of available simulation data for confined hard-core attractive Yukawa model fluid, extensive Monte Carlo (MC) simulation research for this fluid under the influence of various external potentials were carried out. The present MC simulation results were employed to test a performance of the third-order perturbation density functional theory (DFT) based on a high order direct correlation function (DCF) [S. Zhou and E. Ruckenstein, Phys. Rev. E. 61, 2704 (2000)]. It was found that the present perturbation DFT formalism is soundly structured only if the imported second-order DCF is reliable. In this case, the accuracy of the results can be satisfactory or even very high for various types of external potentials. Further, the associated adjustable parameter can be universal, i.e., independent of the particular external field responsible for the generation of a nonuniform density profile. Dependence of both the maintenance of the reliability of the formalism and holding of the universality of the adjustable parameter on the accuracy of the imported bulk second-order DCF can be strengthened by the large difference between the external field investigated and that caused by a single hard wall used for specification of the adjustable parameter. In case the gaseous density in the subcritical region is below the coexistence density, an excellent performance of the present formalism is observed even for the mean spherical approximation’s second-order DCF as an input. This advantageous property, combined with the fact that the present formalism needs only the second-order DCF of fluid at the coexistence state as an input, enables the present formalism to be a very good theoretical tool for the investigations of wetting and prewetting transitions.
Magnetohydrodynamic two-temperature equations for multicomponent plasma
Authors: Bobrova N. A. , Lazzaro E. , Sasorov P. V.
Published: January 2005

The physics of plasmas of mixed composition is of increasing importance both in laboratory experiments and in space plasmas. This work is devoted to constructing from first principles a set of magnetohydrodynamic equations for a multicomponent plasma of arbitrary concentrations, overcoming some limitations of the classical system by S. I. Braginskii [Sov. Phys. JETP 6, 358 (1958)]. A procedure applicable when the ion species have very different atomic masses is developed and applied to produce a full set of transport coefficients. Our approach permits us to explain the discrepancy between Braginskii results and results obtained by direct numerical solution of the electron kinetic equation by E. M. Epperlein and M. G. Haines [Phys. Fluids. 29, 1029 (1986)].
Radical-molecule reaction C3H+H2O: A mechanistic study
Authors: Dong Hao , Ding Yi-hong , Sun Chia-chung
Published: January 2005

Despite the importance of the C3H radical in both combustion and interstellar space, the reactions of C3H toward stable molecules have never been studied. In this paper, we report our detailed mechanistic study on the radical-molecule reaction C3H+H2O at the Becke's three parameter Lee–Yang–Parr–B3LYP∕6-311G(d,p) and coupled cluster with single, double, and triple excitations-CCSD(T)∕6-311G(2d,p) (single-point) levels. It is shown that the C3H+H2O reaction initially favors formation of the carbene-insertion intermediates HCCCHOH (1a,1b) rather than the direct H- or OH-abstraction process. Subsequently, the isomers (1a,1b) can undergo a direct H- extrusion to form the well-known product propynal HCCCHO (P5). Highly competitively, (1a,1b) can take the successive 1,4- and 1,2-H-shift interconversion to isomer H2CCCHO(2a,2b) and then to isomer H2CCHCO(3a,3b), which can finally take a direct C–C bond cleavage to give product C2H3 and CO (P1). The other products are kinetically much less feasible. With the overall entrance barrier 10.6kcal∕mol, the title reaction can be important in postburning processes. Particularly, our calculations suggest that the title reaction may play a role in the formation of the intriguing interstellar molecule, propynal HCCCHO. The calculated results will also be useful for the analogous C3H reactions such as with ammonia and alkanes.
Distribution kinetics of polymer crystallization and the Avrami equation
Authors: Yang Jiao , McCoy Benjamin J. , Madras Giridhar
Published: January 2005

Cluster distribution kinetics is adopted to explore the kinetics of polymer crystallization. Population balance equations based on crystal size distribution and concentration of amorphous polymer segments are solved numerically and the related dynamic moment equations are also solved. The model accounts for heterogeneous or homogeneous nucleation and crystal growth. Homogeneous nucleation rates follow the classical surface-energy nucleation theory. Different mass dependences of growth and dissociation rate coefficients are proposed to investigate the fundamental features of nucleation and crystal growth. A comparison of moment solutions with numerical solutions examines the validity of the model. The proposed distribution kinetics model provides a different interpretation of the familiar Avrami equation.
Energy levels in self-assembled quantum arbitrarily shaped dots
Authors: Tablero C.
Published: January 2005

A model to determine the electronic structure of self-assembled quantum arbitrarily shaped dots is applied. This model is based principally on constant effective mass and constant potentials of the barrier and quantum dot material. An analysis of the different parameters of this model is done and compared with those which take into account the variation of confining potentials, bands, and effective masses due to strain. The results are compared with several spectra reported in literature. By considering the symmetry, the computational cost is reduced with respect to other methods in literature. In addition, this model is not limited by the geometry of the quantum dot.
Investigations of short-scale fluctuations in a helicon plasma by cross-correlation enhanced scattering
Authors: Altukhov A. B. , Gusakov E. Z. , Irzak M. A. , Krämer M. , Lorenz B. , Selenin V. L.
Published: January 2005

Correlation enhanced scattering (CES) near the upper hybrid resonance has been applied for studying small-scale plasma density fluctuations excited by the rf fields in a helicon discharge. The turbulent fluctuations are diagnosed for conditions where the electron plasma frequency exceeds the electron cyclotron frequency considerably. The frequency and wave number spectra of the fluctuations are measured both in the plasma core as well as in outer region of the helicon discharge. The spectral measurements evidence the short-scale fluctuations to originate from a parametric decay instability. The low-frequency fluctuations obey the ion-sound dispersion relation while the lower sideband of the helicon wave frequency satisfies the Trivelpiece–Gould wave dispersion relation. In order to gain more insight in the experimental results and, in particular, to estimate the fluctuation level the backscattering process is analyzed both numerically and analytically for high-density plasma conditions. A fully electromagnetic model was developed that takes into account the radial density distribution of the plasma column as well as the antenna diagram of the rectangular emitting/receiving horn. Using this model the relative amplitude of ion-sound density fluctuations in the core of the helicon discharge is estimated as 11%. The role of nonlinear effects on formation of the scattering spectra due to the high fluctuation level in the plasma center is discussed. The findings also demonstrate that the CES diagnostic can be applied to diagnose fluctuations in spherical tokamak plasmas where the probing conditions resemble those of high-density helicon discharges.
Combined isothermal and nonisothermal dc measurements to analyze space-charge behavior in dielectric materials
Authors: Neagu Eugen R.
Published: January 2005

A combined isothermal and nonisothermal measurements technique is used to analyze charge injection, trapping/detrapping, and conduction in polyethylene terephthalate. By corroborating the results obtained during the four measurement steps a better understanding of the involved processes is achieved. An apparent peak was observed at 8–12 °C above the charging temperature. The maximum current scales linearly with the applied field but the peak position and the apparent activation energy are field independent. By using various heating rates the glass transition temperature was clearly identified at 124 °C. At high temperatures (up to 190 °C) the current increases nonlinearly with the charging field and no peak was observed above the glass transition temperature. Using various charging/discharging times a continuous distribution of the traps was explored in the range from 0.53 to 2.97 eV. The shape of the isothermal charging current changes with temperature and field, suggesting that at low fields and/or low temperatures the charge moves and is trapped mainly in the amorphous fraction but at higher fields and/or higher temperatures the charge penetrates and is trapped into the crystalline fraction as well. The isothermal discharging current is described by a power-law equation for charging temperatures between 40 and 105 °C, suggesting that the charge is released from thermally connected traps in the amorphous domains. A detailed analysis of the charge involved into the charging process and the total charge released from the sample shows that the two amounts of charge are almost equal, suggesting that the injected charge is trapped close to the metal-dielectric interface. A higher limit of the trap-modulated mobility was estimated at 1.6×10−17m2V−1s−1. The results are explained, assuming that the effective temperature in the crystalline domains is lower than in the amorphous volume.
Circular domain wall motion driven by spin-polarized currents in confined square nanomagnets
Authors: Xi Haiwen , Gao Kai-Zhong , Shi Yiming
Published: January 2005

The spin-transfer torque effect on the magnetization in a pillar structure has been investigated using micromagnetic simulation. The study shows that a spin-polarized dc current induces a domain wall formation from the initial inhomogeneous magnetization configuration of the square magnet and drives it to rotate in the constrained structure. Based on the result, the structure has potential use in magnetoelectronics as a rotor with no moving parts in the nanometer scale.
Theoretical study of increased electron temperature in mirror machines by tuned ion cyclotron resonance heating cycles
Authors: Ågren O. , Savenko N.
Published: January 2005

The end loss is a serious problem for a mirror fusion device. The purpose of this paper is to study an idea for improvement of end confinement of electrons and ions for a conventional singe mirror machine with a marginal minimum B stable confining magnetic field. By creating an electrostatic electron barrier that confines electrons sufficiently well, an electron temperature of the order of the ion temperature may be reached. This electrostatic electron barrier may be obtained by decreasing the fuel ion density at the mirror plug sufficiently much compared to the central cell density. Microinstabilities may be suppressed or even stabilized by tuned ICRH (ion cyclotron resonance heating) cycles with resonant absorption of the wave just outside one of the mirrors, since a distribution of sloshing ions would be created. Qualitative arguments indicate the possibility with tuned ICRH to reach an energy gain factor well above unity.
Fabrication and morphology of porous p-type SiC
Authors: Shishkin Y. , Ke Y. , Devaty R. P. , Choyke W. J.
Published: January 2005

Porous silicon carbide fabricated from p-type 4H and 6H SiC wafers by electrochemical etching in hydrofluoric electrolyte is studied. An investigation of the dependence on wafer polarity reveals that pore formation is favored on the C face while complete dissolution occurs on the Si face. When the etching is done on the C face, the pore wall thickness decreases with increasing current density. The morphology of the front surface of the sample depends on the prior treatment of the workpiece surface. The porosity is estimated based on the analysis of scanning electron microscope images, charge-transfer calculations, and gravimetric analysis.
Measurement of the shock-heated melt curve of lead using pyrometry and reflectometry
Authors: Partouche-Sebban D. , Pélissier J. L. , Abeyta F. G. , Anderson W. W. , Byers M. E. , Dennis-Koller D. , Esparza J. S. , Hixson R. S. , Holtkamp D. B. , Jensen B. J. , King J. C. , Rigg P. A. , Rodriguez P. , Shampine D. L. , Stone J. B. , Westley D. T. , Borror S. D. , Kruschwitz C. A.
Published: January 2005

Data on the high-pressure melting temperatures of metals is of great interest in several fields of physics including geophysics. Measuring melt curves is difficult but can be performed in static experiments (with laser-heated diamond-anvil cells, for instance) or dynamically (i.e., using shock experiments). However, at the present time, both experimental and theoretical results for the melt curve of lead are at too much variance to be considered definitive. As a result, we decided to perform a series of shock experiments designed to provide a measurement of the melt curve of lead up to about 50GPa in pressure. At the same time, we developed and fielded a reflectivity diagnostic, and conducted measurements on tin as well. The results show that the melt curve of lead is somewhat higher than the one previously obtained with static compression and heating techniques.
Electric-field-induced orthorhombic phase in Pb[(Zn1∕3Nb2∕3)0.955Ti0.045]O3 single crystals
Authors: Renault Alexandra-Evelyne , Dammak Hichem , Calvarin Gilbert , Gaucher Philippe , Pham Thi Mai
Published: January 2005

The ferroelectric phase transitions of [1¯01]-, [001]-, and [111]-oriented Pb[Zn1∕3Nb2∕3]O3–4.5%PbTiO3 (PZN–4.5%PT) single crystals were investigated as a function of temperature (T between 300 and 450K), and electric field (E field between 0 and 300kV∕m) by dielectric and x-ray diffraction combined measurements. Under null E field, PZN–4.5%PT exhibits the following phase transitions: cubic (C)→tetragonal (T)→rhombohedral (R), during cooling. Under E field applied on a [1¯01]-oriented single crystal, an intermediate orthorhombic (O) ferroelectric phase is induced at temperatures intermediate between that of the T and R phases. The temperature range of existence of this O phase depends both on the crystal orientation and on the measurement conditions: field cooling (FC), zero-field heating after field cooling (ZFHAFC), or field heating (FH). When E field is applied along [1¯01], the stability range is within 40K in FC and only 15K in ZFHAFC; when E field is applied along [001] or [111], this range is still narrower. The O phase is not even observed in FH for [001] orientation and in FC for [111] orientation. These observations show that the application of an E field favors the transition to an O phase, leading to a single-domain structure, when the direction of the field is parallel to the spontaneous polarization [1¯01] direction.
Nonlinear evolution of the modulational instability and chaos using one-dimensional Zakharov equations and a simplified model
Authors: Sharma R. P. , Batra K. , Verga A. D.
Published: January 2005

Nonlinear evolution of modulational instability by using the nonlinear Schrödinger equation in one dimension reveals a periodic reoccurrence of initial conditions. The nonlinear Schrödinger equation is the adiabatic limit of Zakharov equations, which couples the electrostatic electron plasma wave and ion-acoustic wave propagation. In the present paper nonlinear evolution of modulational instability is investigated by using one-dimensional Zakharov equations numerically. A simplified model is predicted that establishes the fact that the effect of relaxing the condition of adiabaticity is drastic on the nonlinear evolution patterns of modulational instability. These evolutions are quite sensitive to initial conditions, Fermi–Pasta–Ulam recurrence is broken up and a chaotic state develops. Next, quantitative methods like calculation of Lyapunov exponents and their variation with wave number is used to study spatial and temporally chaotic behavior. It is shown that regular patterns with a periodic sequence in space and time and spatiotemporal chaos with irregular localized patterns are formed in different regions of unstable wave numbers.
Evidence and mechanisms of axial-radiation asymmetry in dynamic hohlraums driven by wire-array Z pinches
Authors: Sanford T. W. L. , Nash T. J. , Mock R. C. , Peterson D. L. , Watt R. G. , Chrien R. E. , Apruzese J. P. , Clark R. W. , Roderick N. F. , Sarkisov G. S. , Haines M. G.
Published: January 2005

Dynamic hohlraums driven by arrays consisting of large numbers of tungsten wires in Z pinches exhibit differences in radiation emitted from REHs (radiation exit holes) symmetrically located at either end of the hohlraum [Sanford et al., Phys. Plasmas 10, 1187 (2003)]. Significantly greater peak power is radiated from the top (anode) REH relative to the bottom (cathode) REH. Spectral measurements of tungsten M-shell emission (2–2.4 keV) indicate the peak radiated power from either REH anticorrelates with the fraction of wire-array tungsten plasma inferred to sweep across (or into the field of view of) the REH near the time of peak axial emission. In all cases, greater M-shell emission relative to the total emission in the band 1.4–4 keV is measured at the bottom REH in comparison to the top REH. The decrease in peak power radiated from the bottom REH relative to the top appears to be due, in part, to an increase in localized opacity arising from the presence of increased wire-array tungsten plasma near the bottom REH. The asymmetry in both peak axial power and pulse shape is largely removed by adding two thin annular pedestals extending 3 mm into the anode-cathode gap from either electrode, just radially outboard of the REHs. The pedestals are designed to prevent the radial flow of tungsten plasma from prematurely crossing the REHs. A polarity effect [Sarkisov et al., Phys. Rev. E 66, 046413–6 (2002)] during wire initiation may offer one possible explanation for the underlying cause of such a tungsten-related axial power asymmetry.
Effect of electron-nuclear spin interactions for electron-spin qubits localized in InGaAs self-assembled quantum dots
Authors: Lee Seungwon , von Allmen Paul , Oyafuso Fabiano , Klimeck Gerhard , Whaley K. Birgitta
Published: January 2005

The effect of electron-nuclear spin interactions on qubit operations is investigated for a qubit represented by the spin of an electron localized in an InGaAs self-assembled quantum dot. The localized electron wave function is evaluated within the atomistic tight-binding model. The electron Zeeman splitting induced by the electron-nuclear spin interaction is estimated in the presence of an inhomogeneous environment characterized by a random nuclear spin configuration, by the dot-size distribution, alloy disorder, and interface disorder. Due to these inhomogeneities, the electron Zeeman splitting varies from one qubit to another by the order of 10−6, 10−6, 10−7, and 10−9eV, respectively. Such fluctuations cause errors in exchange operations due to the inequality of the Zeeman splitting between two qubits. However, the error can be made lower than the quantum error threshold if an exchange energy larger than 10−4eV is used for the operation. This result shows that the electron-nuclear spin interaction does not hinder quantum-dot based quantum computer architectures from being scalable even in the presence of inhomogeneous environments.
Liquid crystal–carbon nanotube dispersions
Authors: Dierking I. , Scalia G. , Morales P.
Published: January 2005

Parallel alignment of nanotubes can be obtained by dispersion in a self-organizing anisotropic fluid such as a nematic liquid crystal. Exploiting the cooperative reorientation of liquid crystals, the overall direction of the nanotube alignment can be controlled both statically and dynamically by the application of external fields. These can be electric, magnetic, mechanic, or even optic in nature. Employing multiwall as well as single-wall carbon nanotubes, we show their parallel alignment along a uniform liquid crystal director field and electrically verify their reorientation behavior for two complementary geometries. These demonstrate electrically controlled carbon nanotube OFF–ON and ON–OFF switches. Further applicational potential will be outlined.
Radiation resistance of GaAs–GaAlAs vertical cavity surface emitting lasers
Authors: Jabbour J. , Zazoui M. , Sun G. C. , Bourgoin J. C. , Gilard O.
Published: January 2005

The variations of the optical and electrical characteristics of a vertical cavity surface emitting laser based on GaAs quantum wells have been monitored versus irradiation with 1 MeV electrons. The results are understood by the introduction of nonradiative recombination centers in the wells whose characteristics, capture cross section for minority carriers times their introduction rate, can be determined. A similar study performed for proton irradiation shows that the results can be explained in the same way when the introduction rate of the defects is replaced by the proton energy loss into atomic collisions. These results allow us to deduce the equivalence between electron and proton irradiations: A flux of 1protoncm−2 which loses an energy Enℓ (eV) into atomic collisions is equivalent to a fluence of about 9×10−2Enℓcm−2, 1 MeV electrons.
Wave packet in a two-dimensional hexagonal crystal
Authors: Duan Wen-shan , Parkes John , Lin Mai-mai
Published: January 2005

The propagation of a nonlinear wave packet of dust lattice waves (DLW) in a two-dimensional hexagonal crystal is investigated. The dispersion relation and the group velocity for DLW are found for longitudinal m and transverse n propagation directions. The reductive perturbation method is used to derive a (2+1)-dimensional nonlinear Schrödinger equation (NLSE) that governs the weakly nonlinear propagation of the wave packet. This NLSE is used to investigate the modulational instability of the packet of DLW. It is found that the instability region is different for different propagation directions.
Low radiation temperature thermal photovoltaic cells
Authors: Liu Fei , Wang Kang L.
Published: January 2005

In order to improve thermal photovoltaic (TPV) cell efficiency for low radiation temperature applications, the limit efficiency of TPV cells is calculated using the detailed balance approach for different TPV configurations, including TPV cells with a single band, one and multiple numbers of intermediate levels. Furthermore, the improvement of cell efficiency by using filtering emitters is discussed. The numerical results show that the limit efficiency at low radiation temperatures can be largely improved by introducing intermediate levels. The optimum material bandgap for achieving maximum limit efficiency for each configuration is obtained. The figure of merit is considered to give guidance for TPV material selection. In the end, quantum dot interband–intersubband and quantum cascade intersubband TPV cells are proposed as possible structures to improve TPV efficiency.
First-principles study of ferromagnetic coupling in Zn1−xCrxTe thin film
Authors: Wang Q. , Sun Q. , Jena P. , Kawazoe Y.
Published: January 2005

Using gradient-corrected density functional theory and supercell technique, we have calculated total energies, electronic structure, and magnetic properties of Cr-doped ZnTe in both bulk and thin-film configurations. Calculations with full geometry optimization for a Zn1−xCrxTe supercell were carried out for different Cr concentrations (x=0.095, 0.143, and 0.19) and by varying the sites Cr atoms occupy. We show that the ferromagnetic phase of Zn1−xCrxTe in both bulk and thin film is energetically the most preferable state irrespective of the concentration and∕or site occupation of the Cr atom. The strong hybridization between Cr3d and Te5p states is found to be responsible for the ferromagnetic coupling, in agreement with recent experiments.
Eulerian calculations of wave breaking and multivalued solutions in a traveling wave tube
Authors: Wöhlbier J. G. , Jin S. , Sengele S.
Published: January 2005

The traveling wave tube is an electron beam device that works on a similar principle to the beam-plasma instability, where the background plasma is replaced by an electromagnetic waveguiding structure. The nonlinear evolution of the instability includes wave breaking and the formation of multivalued solutions, and conventionally these solutions have been computed using Lagrangian techniques. Recently, an Eulerian method for computing multivalued solutions was developed in the context of geometrical optics and has been applied to the klystron, a relative of the traveling wave tube. In this paper we apply the Eulerian technique to solve a traveling wave tube model and compare the results to a Lagrangian technique. The results are found to be in good qualitative agreement with small quantitative differences that are attributed to the numerical methods.
Transport and magnetic properties of metallic La1−xPbxNiO3−δ (0.0⩽x⩽0.1)
Authors: Pal Sudipta , Chaudhuri B. K. , Neeleshwar S. , Chen Y. Y. , Yang H. D.
Published: January 2005

Transport properties (resistivity and thermoelectric power) of Pb doped LaNiO3 viz. La1−xPbxNiO3−δ (0.0⩽x⩽0.1) show metallic behavior over a wide range of temperature (10–550K). Pb doping (up to 10%) at the La site does not destroy the metallic behavior of LaNiO3. The paramagnetic susceptibility χ decreases with Pb doping. Above 50K, χ is almost temperature independent and exhibits Pauli like features with a small additional Curie law contribution. The resistivity ρ increases with Pb doping though the thermoelectric power does not change proportionately, indicating that Pb doping does not introduce much disorder in the system. A linear T dependence of ρ observed above 150K suggests the importance of electron–phonon (el–ph) interactions but at temperature below 150K, ρ follows a T1.5 dependence. The estimated el–ph interaction constant λ increases (0.80–2.53) with Pb doping (x=0.0–0.1). No saturation of resistivity has been observed even up to 550K with x⩽0.1. The phonon frequency νph∼3444cm−1 of the undoped sample calculated from the absorption peak of the Fourier transform infrared spectra agrees well with that at ∼3025cm−1 estimated from the reported heat capacity data.
Fast ion beam chopping system for neutron generators
Authors: Hahto S. K. , Hahto S. T. , Leung K. N. , Reijonen J. , Miller T. G. , Van Staagen P. K.
Published: January 2005

Fast deuterium (D+) and tritium (T+) ion beam pulses are needed in some neutron-based imaging systems. A compact, integrated fast ion beam extraction and chopping system has been developed and tested at the Lawrence Berkeley National Laboratory for these applications, and beam pulses with 15ns full width at half maximum have been achieved. Computer simulations together with experimental tests indicate that even faster pulses are achievable by shortening the chopper voltage rise time. This chopper arrangement will be implemented in a coaxial neutron generator, in which a small point-like neutron source is created by multiple 120keV D+ ion beams hitting a titanium target at the center of the source.
Heterodyne laser Doppler vibrometer using a Zeeman-stabilized He–Ne laser with a one-shot frequency to voltage converter
Authors: La Jongpil , Choi Hyunseung , Park Kyihwan
Published: January 2005

The vibration measurement technique using a heterodyne laser interferometer is addressed in this article. A Zeeman-stabilized He–Ne laser is used as the light source. The frequency stabilization of the laser is performed by controlling the length of the laser tube via thermal control. The stability of the laser is measured by comparing it with an iodine-stabilized He–Ne laser. The root Allan variance of the laser is measured as below 5.5×10−9. The frequency modulation demodulation to convert the frequency of the interferent signal to the voltage signal using a one-shot frequency to voltage (F∕V) converter is also addressed. Simplicity and robustness of the measurement can be achieved by using the one-shot F∕V converter. Since the Doppler frequency is shifted by the heterodyne beat frequency, the compensation algorithm is added to remove the shifted frequency of the interferent signal in the signal processing circuit. The bandwidth of the signal processing circuit using the one-shot F∕V converter is 20kHz, and the maximum detectable velocity of the target is ±0.13m∕s. The proposed vibration measurement technique proved to be very fast and robust to external disturbances by experimental results.
Critical thickness enhancement of epitaxial SiGe films grown on small structures
Authors: Liang Yue , Nix William D. , Griffin Peter B. , Plummer James D.
Published: January 2005

This paper explores stress management in SiGe with two kinds of structures, namely, epitaxial SiGe films on small pillars and fins. In addition to the compliant substrate effect in the film/fin structures, the geometric effect in the film/pillar structures plays another important role in critical thickness enhancement. The stress-strain states of these two systems are calculated and the equilibrium critical thicknesses are predicted, using the work method, for different fin thicknesses, pillar radii, and Ge concentrations. Compared to conventional films grown on planar bulk substrates, the critical thicknesses for fin and pillar structures are increased significantly. SiGe films with various thicknesses and compositions were epitaxially grown around vertical fins and horizontal membranes with thicknesses as thin as 12nm to demonstrate the concepts. Cross-sectional transmission electron microscopy analysis showed that dislocation densities are much smaller than for films grown on bulk Si substrates. The dislocation density versus fin thickness also illustrated the expected trend.
PROTEX: A proton-recoil detector for inertial confinement fusion neutrons
Authors: Moran Michael J. , Glebov Vladimir Yu. , Stoeckl Christian , Rygg Ryan , Schwartz Brook-Eden
Published: January 2005

Fusion neutron diagnostics are important to inertial confinement fusion (ICF) because they characterize fusion performance and help to provide the understanding that is needed to develop higher-yield sources. Present yields in excess of 1012 deuterium–tritium (DT) neutrons now can be measured with a proton-recoil detector. This technique, which has not been practical with lower yields, is desirable because it provides prompt, accurate, and unambiguous results. The PROTEX is a proton-recoil detector which features a compact coaxial cylindrical geometry for maximum sensitivity, in situ simultaneous measurement of background signals, and an ab initio calculated absolute sensitivity. The calculated sensitivity has an estimated absolute accuracy of 6%. With simple adjustments, PROTEX can provide absolute measurement of yield for the National Ignition Facility, the Laser Megajoule Facility, or for any ICF source having a yield greater than 1012 DT neutrons.
An atom-transparent photon block for metal-atom deposition from high-temperature ovens
Authors: Murdey Richard , Liang S. J. S. , Stuckless J. Todd
Published: January 2005

We describe, in the context of polymer metallization calorimetry, the design and operation of a dual-chopper velocity selector to filter out the radiation background from high-temperature metal-atom oven sources. Particular attention is given to the resultant nonuniform atom flux profile.
Robust Point-Pattern Inference from Spatially Censored Data
Authors: Sweeney Stuart H , Konty Kevin J
Published: January 2005

Administrative data sources are increasingly being used for spatial analysis and policy formation. For example, ‘welfare to work’ programs have stimulated demand for spatial mismatch studies in which ES-202 employment files are used. The increased resolution gained by geocoding the address records in administrative files can be of enormous research value when the process under study resolves over small distances. Yet the resulting point-referenced data are problematic for inferential analysis. In particular, administrative data typically represent a sample of convenience, thus posing serious validity problems for statistical inference. The authors propose a robust estimation method for spatial pattern inference based on spatially censored data. The performance of the estimator is explored with the aid of simulated data and is also demonstrated with ES-202 data from North Carolina.
Street-Weighted Interpolation Techniques for Demographic Count Estimation in Incompatible Zone Systems
Authors: Reibel Michael , Bufalino Michael E
Published: January 2005

Data processing for the spatial analysis of small-area social, demographic, and economic data often requires the combination of data spatially aggregated to two or more incompatible zone systems in a region, such as a set of enumeration districts that changes over time. Such situations can be addressed by areal interpolation—the transfer of data between zonal systems according to spatial algorithms. The authors test a technique of areal interpolation using geographic information systems (GIS) that employs a digital map layer representing streets and roads to derive varying density weights for small areas within aggregation zones. The technique reduces errors in estimation compared with estimates derived using the commonly applied area-weighting technique, with its assumption of uniform density. The street-weighting technique is much easier to use than other interpolation techniques that have also been shown to reduce error compared with area-based weighting.
A Utility-Based Analysis of Activity Time Allocation Decisions Underlying Segmented Daily Activity–Travel Patterns
Authors: Joh Chang-Hyeon , Arentze Theo A , Timmermans Harry J P
Published: January 2005

This paper reports the results of an application of the Aurora model to estimate the utility functions underlying activity–duration decisions in daily activity–travel patterns. Multidimensional sequence alignment is used to derive segments for activity–travel diary data, collected in the Amsterdam–Utrecht corridor in the Netherlands. The profiles of the resulting segments are derived from a descriptive analysis of sociodemographic variables. A tailored genetic algorithm is then used to estimate the parameter of an asymmetrical utility function for each of the resulting segments. The results suggest that the utility of activity duration varies between activities and between segments, and hence sociodemographics.
Cities in Shade: Urban Geography and the Uses of Noir
Authors: Farish Matthew
Published: January 2005

This paper historicizes American cities after the Second World War through the rich motif of noir literature and film. But, in doing so, the paper is also a critical consideration of noir's work in urban studies. Noir has been drawn, often usefully but also unfortunately, away from its referents, from the terrain that it most directly summons but also from the spaces in which its contradictions are most apparent. Moving from a discussion of the distractions of Chinatown to contextual themes such as mobility and ruin, the paper links noir criticism and noir texts with broader debates in postwar urbanism and modernism. As just part of these discourses, noir not only is irreducible to certain essences, but can potentially perform the opposite role, challenging conventions of urban understanding and practice. The result would be a more detailed and subtle account of modernism's American geographies.
Anti-Nomadism, Institutions, and the Geographies of Childhood
Authors: Vanderbeck Robert M
Published: January 2005

Despite an increasing interest in the geographies of childhood, geographical research has given little attention to issues concerning young people from traditionally semi-nomadic groups, such as Gypsies and other Travellers. In this paper I explore the discursive construction of Traveller childhood within contemporary Britain, with an emphasis on the ways in which state educational discourse constructs young Travellers as needing greater involvement with the ‘mainstream’ education system. I draw on a range of sources, including documents, participant observation, and interviews with practitioners in Traveller education conducted between 1998 and 2001. I argue that contemporary discourse often continues to reflect long-standing notions of cultural disadvantage and deficit which have often been applied to Travellers, although more subtly expressed than in the past. I also argue that children's rights discourses are often employed to construct Traveller parents as obstacles to their children's development and well-being, and that these discourses can be used to legitimise various exertions of power (such as legal measures to prosecute parents). The evidence of the research highlights the need for more nuanced, empirically informed theorisations of the interface between Traveller children and state institutions than has generally been the case to date.