bluuebunny/crossref_metadata_2025 huggingface dataset:
N‐Acetylcysteine suppresses TNF‐induced NF‐κB activation through inhibition of IκB kinases
Authors: Oka Shin-ichi , Kamata Hideaki , Kamata Keiko , Yagisawa Hitoshi , Hirata Hajime
Published: July 2002

Here, we used a reductant, N‐acetyl‐L‐cysteine (NAC), to investigate the redox‐sensitive step(s) in the signalling pathway from the tumor necrosis factor (TNF) receptor to nuclear factor κB (NF‐κB). We found that NAC suppressed NF‐κB activation triggered by TNF or by overexpression of either the TNF receptor‐associated death domain protein, TNF receptor‐associated factor 2, NF‐κB‐inducing kinase (NIK), or IκB kinases (IKKα and IKKβ). NAC also suppressed the TNF‐induced activation of IKKα and IKKβ, phosphorylation and degradation of IκB, and nuclear translocation of NF‐κB. Furthermore, NAC suppressed the activation of IKKα and IKKβ triggered by the overexpression of NIK. These results indicate that IKKα and IKKβ are subject to redox regulation in the cells, and that NAC inhibits NF‐κB activation through the suppression of these kinases.
Cytoplasmic localization of the interferon‐inducible protein that is encoded by the AIM2 (absent in melanoma) gene from the 200‐gene family
Authors: Choubey Divaker , Walter Scott , Geng Yanbiao , Xin Hong
Published: July 2002

While interferons (IFNs) (α, β and γ), a family of cytokines, have the ability to exert the growth‐inhibitory effect on target cells, the molecular mechanism(s) by which IFNs inhibit cell growth remains to be identified. Because IFN‐inducible ‘effector’ proteins mediate the biological activities of IFNs, characterization of IFN‐inducible proteins is critical to identify their functional role in IFN action. One family (the 200‐family) of IFN‐inducible proteins is encoded by structurally related murine (Ifi202a, Ifi202b, Ifi203, Ifi204 and D3) and human (IFI16, MNDA and AIM2) genes. The proteins encoded by genes in the family share a unique repeat of 200‐amino acids and are primarily nuclear. The AIM2 gene is a newly identified gene that is not expressed in a human melanoma cell line. Here we report that AIM2 is estimated to be a 39 kDa protein and, unlike other proteins in the family, is localized primarily in the cytoplasm. Interestingly, overexpression of AIM2 in transfected cells retards proliferation and, under reduced serum conditions, increases the susceptibility to cell death. Moreover, AIM2 can heterodimerize with p202 in vitro. Together, these observations provide support to the idea that AIM2 may be an important mediator of IFN action.
Estimation of H2O2 gradients across biomembranes
Authors: Antunes Fernando , Cadenas Enrique
Published: July 2002

When cells are exposed to an external source of H2O2, the rapid enzymatic consumption of H2O2 inside the cell provides the driving force for the formation of the gradient across the plasma and other subcellular membranes. By using the concepts of enzyme latency, the following gradients – formed after a few seconds following the exposure to H2O2 – were estimated in Jurkat T‐cells: [H2O2]cytosol/[H2O2]peroxisomes=3; [H2O2]extracellular/[H2O2]cytosol=7. The procedure presented in this work can easily be applied to other cell lines and provides a quantitative framework to interpret the data obtained when cells are exposed to an external source of H2O2.
Service recovery: a framework and empirical investigation
Authors: Miller Janis L , Craighead Christopher W , Karwan Kirk R
Published: July 2002

Although recovery activities are primarily managed by the operations function, service recovery has received little attention in the operations management literature. This paper outlines a framework for examining the service recovery process and then reports on an empirical study to test this framework. The results not only validate much of what is anecdotally claimed by researchers and casual observers of service industries, but also highlight the role of operational activities in service recovery. The paper then points to the need for an array of operations‐based research efforts that will lead to better understanding of the recovery process and to more empirically based descriptive and prescriptive models.
REMOVING SERVICE BARRIERS FOR WOMEN WITH PHYSICAL DISABILITIES: PROMOTING ACCESSIBILITY IN THE GYNECOLOGIC CARE SETTING
Authors: Schopp Laura H. , Sanford Tiffany C. , Hagglund Kristofer J. , Gay John W. , Coatney Mary Ann
Published: July 2002

Although women with disabilities constitute a substantial segment of the population, their gynecologic health care needs often go unrecognized or untreated. Women with disabilities encounter a variety of obstacles to receiving health services including attitudinal, environmental, economic, and informational barriers. Standard screening and preventive services, such as pelvic examinations and mammograms, can be especially difficult to obtain, potentially placing women with disabilities at greater risk for diseases such as breast cancer and cervical cancer. This article reviews the current status of gynecologic care for women with disabilities and provides strategies for women's health care providers seeking to increase the accessibility of their practice settings.
Subcutaneous pseudomembranous fat necrosis: new observations/linkr>
Authors: Diaz‐Cascajo Carlos , Borghi Susanna
Published: July 2002

Background: Pseudomembranous fat necrosis is a peculiar manifestation of necrosis of adipose tissue characterized by formation of pseudocystic cavities lined by crenulated membranes. The underlying mechanism for the formation of pseudomembranes is unknown and numerous hypotheses have been proposed. Despite divergent interpretations, most authors consider necrotic fat cells to be the anatomic substrate for the formation of pseudomembranes.

Methods: A total of 341 panniculitides were reviewed for the presence of pseudomembranous fat necrosis. The specific diagnoses were established after correlation of all available clinical and laboratory data with the histopathology. Special attention was given to the time in the evolution of the disease when the biopsy was taken. Additional immunohistochemical studies were performed in 12 cases.

Results: Thirty of 341 cases of different types of panniculitides were found to show pseudomembranous fat necrosis, namely: 10 of 15 cases of sclerosing panniculitis (lipodermatosclerosis), 6 of 95 cases of erythema nodosum, 7 of 34 cases of traumatic panniculitis, 1 of 7 cases of lupus panniculitis, 1 of 20 cases of erythema induratum Bazin (nodular vasculitis), 1 of 9 cases of necrobiosis lipoidica, 1 of 4 cases of sclerotic lipogranuloma, 1 of 9 cases of infectious panniculitis (erysipelas), 1 of 2 cases of pancreatic panniculitis, and 1 of 4 cases of subcutaneous sarcoidosis. Pseudomembranous fat necrosis labelled strongly for the histiocytic markers CD68 and lysozyme.

Conclusions: Our series provides data suggesting that pseudomembranous fat necrosis represents a dynamic process that varies according to the evolution of the lesion at the time of the biopsy. In biopsies taken from early foci of panniculitides pseudomembranes show vescicular or picnotic nuclei. Later, pseudomembranes retain their crenulated appearance but lack nuclear elements. Furthermore, we present histopathologic, histochemical, and immunohistochemical evidence that pseudomembranous fat necrosis results from the interaction of residual products of disintegrated fat cells and macrophages. Histiocytic markers such as CD68 and lysozyme may be used as reliable tools in order to detect pseudomembranes in panniculitides.
Oral manifestations in 101 Cambodian patients with HIV infection and AIDS
Authors: Bendick C. , Scheifele C. , Reichart P. A.
Published: July 2002

Background: The HIV/AIDS epidemic in Cambodia has become a major problem in the last 7–8 years, mainly because in this formerly war‐stricken country the socioeconomic situation is only slowly improving. Since only very few studies have been published to date on the oral health status of Cambodian HIV/AIDS patients, it was the purpose of the present investigation to study oral manifestations in Cambodian patients with HIV disease.

Methods: One hundred one Cambodian patients with HIV infection or AIDS were examined for the presence of oral manifestations in one medical center in Phomh Penh, Cambodia.

Results: Sixty‐three men and 38 women with a median age of 32 years were examined (age range 7.5–63.5 years). Of these patients, 42.6% were smokers, 46.5% of men were heavy drinkers and 90.5% of men were promiscuous compared with 5.3% of women. The most frequent AIDS‐defining diseases were wasting syndrome (54.5%),Pneumocystis carinii pneumonia(PcP) (19.8%) and tuberculosis (18.8%). Puritic papular eruption, a common cutaneous manifestation in HIV‐infected patients, was seen in 17.8% of patients. Candida‐associated infections of the oral cavity were most common. Among the patients, 52.5% revealed pseudomembranous candidiasis and 35.6% had bilateral hairy leukoplakia. Only 10% of patients had no oral lesions. Also common were necrotising ulcerative gingivo‐periodontal diseases (27.7%).

Conclusion: The general health status of 101 Cambodian patients with HIV infection and AIDS was poor, and they demonstrated a large number of oral manifestations. Antiretroviral therapy is presently not available and only a fraction of patients receives antimycotic treatment (25.7%). HIV infection and the AIDS epidemic in Cambodia have become a serious problem and patients urgently need adequate diagnosis and antiretroviral therapies.
Role of oxidative stress in germ cell apoptosis induced by di(2-ethylhexyl)phthalate
Authors: KASAHARA Emiko , SATO Eisuke F. , MIYOSHI Mami , KONAKA Ryusei , HIRAMOTO Keiichi , SASAKI Junzo , TOKUDA Masaaki , NAKANO Yoshihisa , INOUE Masayasu
Published: July 2002

Phthalate esters have been used extensively as plasticizers of synthetic polymers. Recent studies have revealed that these esters induce atrophy of the testis, although its pathogenesis remains unknown. The present study describes the possible involvement of oxidative stress in the pathogenesis of atrophy of the rat testis induced by di(2-ethylhexyl)phthalate (DEHP). Biochemical and immunohistochemical analysis revealed that oral administration of DEHP increased the generation of reactive oxygen species, with concomitant decrease in the concentration of glutathione and ascorbic acid in the testis, and selectively induced apoptosis of spermatocytes, thereby causing atrophy of this organ. Oxidative stress was selectively induced in germ cells, but not in Sertoli cells, treated with mono(2-ethylhexyl)phthalate (MEHP), a hydrolysed metabolite of DEHP. Furthermore, MEHP selectively induced the release of cytochrome c from mitochondria of the testis. These results indicate that oxidative stress elicited by MEHP principally injured mitochondrial function and induced the release of cytochrome c, thereby inducing apoptosis of spermatocytes and causing atrophy of the testis.
Oxide formation during plasma etching of silicon-containing resists
Authors: Hartney M. A. , Chiang J. N. , Hess D. W. , Soane D. S.
Published: July 2002

Surface modification during oxygen plasma etching of polysilylmethylstyrene resists has been monitored using x-ray photoelectron spectroscopy. Plasma exposure converted the silicon present in the polymers to an oxidized surface region which prevented further chemical etching. Conversion was more rapid and more complete when etching under conditions where higher energy ion bombardment occurred. Polysilylmethylstyrene reached a steady-state oxide thickness between 3.4 and 5.8 nm, depending on etching conditions. A copolymer of this material with chloromethylstyrene showed a comparable thickness when etched at high ion energies, but did not reach a steady state when etched at conditions where the average ion energy was below 110 eV.
Passivation and depassivation of silicon dangling bonds at the Si/SiO2 interface by atomic hydrogen
Authors: Cartier E. , Stathis J. H. , Buchanan D. A.
Published: July 2002

Atomic hydrogen is found to simultaneously passivate and depassivate silicon dangling bonds at the Si(111)/SiO2 interface at room temperature via the reactions Pb+H0→PbH and PbH+H0→Pb+H2. The passivation reaction occurs more efficiently keeping the steady-state Pb density at a low value of only 3–6×1011 cm−2 during atomic hydrogen exposure. This low Pb density can only account for a small fraction of the total number of interface states produced by atomic hydrogen.
Advanced plasma fluctuation analysis techniques and their impact on fusion research (invited)
Authors: Ritz Ch. P. , Powers E. J. , Rhodes T. L. , Bengtson R. D. , Gentle K. W. , Lin Hong , Phillips P. E. , Wootton A. J. , Brower D. L. , Luhmann N. C. , Peebles W. A. , Schoch P. M. , Hickok R. L.
Published: July 2002

This article reviews digital spectral analysis techniques that yield experimental insight into plasma turbulence. Methods to quantify the statistical properties of the fluctuations and to measure the particle and heat flux caused by electrostatic fluctuations are presented. Furthermore, analysis techniques to study the nonlinear coupling process of turbulence and the redistribution of energy among the different modes are discussed. The impact of the analysis techniques on fusion research is demonstrated with experimental results collected with Langmuir probes, heavy-ion beam probes, and laser scattering in the tokamak TEXT. Special emphasis is given to the characterization of the wavenumber distribution and the correlation lengths in all toroidal directions, including a first measurement of k∥ in a tokamak.
Plasma-density measurements by microwave interferometry and Langmuir probes in an rf discharge
Authors: Neumann G. , Bänziger U. , Kammeyer M. , Lange M.
Published: July 2002

Improvements for two established methods for plasma-density measurements have been developed: (a) microwave interferometry and (b) single Langmuir-probe technique. The new microwave interferometer design allows us to avoid a rigid waveguide as the reference line and therefore results in a high flexibility for the use at plasma chambers with different geometries. The system is operated at 35 GHz and has a bandwidth of 10 MHz. The cylindrical single Langmuir-probe system has been equipped with a new rf-suppression circuit. This allows the application of probes of nearly arbitrary geometrical dimensions in rf-driven plasmas. The circuit is simply mounted outside the vacuum chamber between the probe feedthrough and the dc circuit. The performance of these two developments has been demonstrated and comparative measurements of charge carrier densities in a conventional rf-driven plasma show good agreement between the two methods.
Large area magneto-optical investigations of YBCO thin films
Authors: Kuhn M. , Schey B. , Biegel W. , Stritzker B. , Eisenmenger J. , Leiderer P.
Published: July 2002

A new apparatus for magneto-optical investigations of high temperature superconducting (HTS) films as large as 20×20 cm2 is presented. With this equipment flux penetration of an external magnetic field into YBCO thin films has been studied by scanning the samples through an inhomogeneous magnetic field (magneto-optical scanning technique, MOST). The normal penetration of magnetic flux into a superconductor will be changed drastically in the presence of defects. The apparatus was constructed to realize an effective quality control of large area HTS thin films used for device fabrication. With this technique, a visualization of flux pattern in superconducting films larger than 1×1 cm2 is presented for the first time. The results are compared to inductive jc measurements as well as to micrographs [optical microscope (OM), scanning electron microscopy (SEM)] and show that also in the large area characterization the magneto-optical method is very sensitive to microstructural defects impairing the critical current density, which is the relevant parameter for an application of the superconducting thin films. Moreover, it could be shown that MOST has appreciable advantages compared to inductive jc scans and microscopy (OM, SEM). In particular it is possible to observe defects, which are below the optical resolution of the MOST setup.
An inverted pendulum preisolator stage for the VIRGO suspension system
Authors: Losurdo G. , Bernardini M. , Braccini S. , Bradaschia C. , Casciano C. , Dattilo V. , De Salvo R. , Di Virgilio A. , Frasconi F. , Gaddi A. , Gennai A. , Giazotto A. , Pan H. B. , Paoletti F. , Pasqualetti A. , Passaquieti R. , Passuello D. , Taddei R. , Zhang Z. , Cella G. , Cuoco E. , D’Ambrosio E. , Fidecaro F. , Gaggero S. , La Penna P. , Mancini S. , Poggiani R. , Vicerè A. , Mazzoni M. , Stanga R. , Holloway L. , Winterflood J.
Published: July 2002

The design of a new preisolator stage for the VIRGO superattenuator is presented. The device is essentially a 6 m high inverted pendulum with horizontal resonant frequency of 30 mHz. An isolation of 65 dB at 1 Hz has been achieved. Very low forces are needed to move the whole superattenuator acting on the inverted pendulum. For this reason, the system is a suitable platform for the active control of the mirror suspension.
Raman scattering from nanometer-sized diamond
Authors: Yoshikawa M. , Mori Y. , Obata H. , Maegawa M. , Katagiri G. , Ishida H. , Ishitani A.
Published: July 2002

We have measured Raman spectra of diamond with nanometer size, called cluster diamond. The Raman bands assigned to sp2 and sp3 clusters have been observed at around 1600 and 1322 cm−1, respectively. This result suggests that the cluster diamond slightly contains the sp2 cluster. The Raman band assigned to sp3 cluster is found to shift by −10 cm−1, compared with that of bulk crystal and to be asymmetric with some tailing toward lower Raman frequency. The observed Raman spectrum agrees well with that calculated by a phonon confinement model. The crystallite size of the cluster diamond estimated from the phonon confinement model agrees approximately with that estimated from x-ray measurement. Raman spectroscopy gives some information about the crystallite size of diamond particles with nanometer size.
The effect of dislocation contrast on x-ray line broadening: A new approach to line profile analysis
Authors: Ungár T. , Borbély A.
Published: July 2002

The x-ray line profiles of an ultrafine grained copper crystal, produced by equal-channel angular pressing, were measured by a special high resolution diffractometer with negligible instrumental line broadening. The analysis of the line breadths and the Fourier coefficients have shown that taking into account the contrast caused by dislocations on line profiles gives new scaling factors in the Williamson–Hall plot and in the Warren–Averbach analysis, respectively. When strain is caused by dislocations the new procedure proposed here enables a straightforward determination of particle size and strain, the latter in terms of the dislocation density.
Photoconductivity nonlinearity at high excitation power in quantum well infrared photodetectors
Authors: Ershov M. , Liu H. C. , Buchanan M. , Wasilewski Z. R. , Ryzhii V.
Published: July 2002

Nonlinear photoconductivity effects at high excitation power in quantum well infrared photodetectors (QWIPs) are studied both experimentally and theoretically. The photoconductivity nonlinearity is mainly caused by a redistribution of the electric potential at high power, which leads to a decrease of electric field in the bulk of the QWIP. As a result of the decreased field, the photoexcited electron escape probability and drift velocity decrease resulting in a decrease of responsivity.
Magnetic properties of nanostructured Mn oxide particles
Authors: Li J. , Wang Y. J. , Zou B. S. , Wu X. C. , Lin J. G. , Guo L. , Li Q. S.
Published: July 2002

Nanostructured Mn oxide particles with an average size of about 7 nm have been prepared by a microemulsion method. X-ray diffraction analysis indicates that the particles possess orthorhombic structure of MnO(OH). The particles are ferromagnetic at low temperature. The Curie temperature is about 35 K and each MnO(OH) molecule generates a magnetic moment of about 0.7 μB. The appearance of the ferromagnetism at low temperature may result from size effect.
Effect of strain and temperature on anomalously large interdiffusion in InAsP/InP heterostructures
Authors: Tweet D. J. , Matsuhata H. , Fons P. , Oyanagi H. , Kamei H.
Published: July 2002

We present evidence for anomalously large, strain-dependent interdiffusion in InAs1−xPx layers grown on InP(001) substrates by organometallic vapor phase epitaxy at 620 °C. Specifically, there are strong indications for the existence of a “critical strain:” if the strain is ∼1.9% or more, much P–As mixing occurs, but for smaller strain the mixing is greatly decreased. The interdiffusion is also highly sensitive to temperature. A set of samples grown at 580 °C exhibits a factor of ∼2 decrease in P–As mixing compared to a set grown at 620 °C.
Hall-effect analysis of GaN films grown by hydride vapor phase epitaxy
Authors: Götz W. , Romano L. T. , Walker J. , Johnson N. M. , Molnar R. J.
Published: July 2002

Hall-effect measurements were conducted on unintentionally doped n-type GaN films grown on sapphire substrates by hydride vapor phase epitaxy. Film nucleation involved either a GaCl or ZnO pretreatment. Variable temperature Hall-effect measurements reveal a dependence of both the electron concentration and the Hall mobility on film thickness. We demonstrate that this dependence is indicative of a nonuniform distribution of electrically active defects. For GaCl-pretreated sapphire the presence of a highly conductive, 200-nm-thick near-interface layer is likely to account for the observed phenomena. For ZnO-pretreated sapphire the Hall-effect data clearly indicate a continuous reduction of the defect density with increasing film thickness.
Tunable magnetocaloric effect in ceramic perovskites
Authors: Bohigas X. , Tejada J. , del Barco E. , Zhang X. X. , Sales M.
Published: July 2002

A large entropy variation (magnetocaloric effect) has been discovered in ceramic perovskites with the formulas La0.65Ca0.35Ti1−xMnxO3−z and La0.5+x+yLi0.5−3yTi1−3xMn3xO3−z. Both Curie temperature and entropy change were studied from 4.2 to 400 K for different stoichiometric compositions and applied magnetic fields. Our conclusion is that these materials are excellent candidates for working materials in magnetic refrigeration and liquefaction devices in a wide temperature range.
The role of dislocation scattering in n-type GaN films
Authors: Ng H. M. , Doppalapudi D. , Moustakas T. D. , Weimann N. G. , Eastman L. F.
Published: July 2002

The lateral transport in GaN films produced by electron cyclotron resonance plasma-assisted molecular beam epitaxy doped n type with Si to the levels of 1015–1020 cm−3 was investigated. The room temperature electron mobility versus carrier concentration was found to follow a family of bell-shaped curves consistent with a recently proposed model of scattering by charged dislocations. The mechanism of this scattering was investigated by studying the temperature dependence of the carrier concentration and electron mobility. It was found that in the low carrier concentration region (<1017 cm−3), the electron mobility is thermally activated with an activation energy half of that of carrier concentration. This is in agreement with the prediction of the dislocation model.
The electronic conduction mechanism in barium strontium titanate thin films
Authors: Zafar Sufi , Jones Robert E. , Jiang Bo , White Bruce , Kaushik V. , Gillespie S.
Published: July 2002

In the literature, the Schottky emission equation is widely used to describe the conduction mechanism in perovskite-type titanate thin films. Though the equation provides a good fit to the leakage current data, the extracted values of the Richardson and dielectric constants are inconsistent with their experimental values. In this work, a modified Schottky equation is applied. This equation resolves the difficulties associated with the standard Schottky equation. Also, the electronic mobility in thin films of barium strontium titanate is reported.
Influence of strain on the magnetic properties of epitaxial (100) chromium dioxide (CrO2) films
Authors: Li X. W. , Gupta A. , Xiao Giang
Published: July 2002

Chromium dioxide (CrO2) films have been grown epitaxially on (100) TiO2 substrates using chemical vapor deposition and their magnetic properties were studied as a function of film thickness (500 Å–1.2 μm). Because of the lattice mismatch with the substrate, the films are strained as evidenced by x-ray diffraction measurements. The amount of strain depends on the thickness and also on the substrate cleaning conditions used prior to growth. Independent of their thickness, the films exhibit a sharp ferromagnetic transition with a Curie temperature in the range of 390–395 K. In-plane magnetic anisotropy is observed for the films, with [001] and [010] being the easy axis and hard axis directions, respectively, for the thicker films. The anisotropy field decreases with decreasing thickness, with the easy and hard axes switching directions for the thinnest films. The results are explained in terms of the competition between magnetocrystalline and strain anisotropies that favor the [001] and [010] magnetization directions, respectively.
Nonlinear changes in plasma and crater properties during laser ablation of Si
Authors: Liu H. C. , Mao X. L. , Yoo J. H. , Russo R. E.
Published: July 2002

A dramatic change in plasma characteristics, as well as a significant increase in the quantity of ablated mass were observed at a laser power density threshold of 20 GW/cm2. The electron number density and temperature of the laser-induced plasma show dramatic changes in their nonlinear behavior in the range of 2–80 GW/cm2. The crater volume undergoes some type of phase explosion at the threshold. Mechanisms such as inverse bremsstrahlung and self-regulation were used to describe the behavior below threshold. Self-focusing and critical temperature are discussed to explain the dramatic changes at the threshold.
Reduction of molecular aggregation and its application to the high-performance blue perylene-doped organic electroluminescent device
Authors: Mi B. X. , Gao Z. Q. , Lee C. S. , Lee S. T. , Kwong H. L. , Wong N. B.
Published: July 2002

A nonplanar derivative of perylene, 2,5,8,11-tetra-tertbutylperylene (TBPe), was synthesized via the Friedel–Crafts alkylation reaction. Electroluminescent (EL) devices were made using TBPe or perylene as a dopant in bis(2-methyl-8-quinolinolato)(para-phenylphenolato)aluminum(III) and their EL performance was compared. Similar to the device doped with the parent perylene molecule, the device doped with TBPe also emitted strongly in the blue. As the concentration of TBPe increased from 1% to 5%, the color coordinates in CIE 1931 chromaticity of the TBPe-doped device changed only slightly from (0.168,0.273) to (0.175,0.273), whereas the perylene-doped device exhibited a much larger shift from (0.165,0.196) to (0.178,0.252). The constancy of EL color and efficiency with respect to TBPe dopant concentration is attributable to diminishing molecular aggregation in the nonplanar perylene derivative, TBPe, due to the steric hindrance of the tert-butyl groups.
Characteristics of the surface layer of barium strontium titanate thin films deposited by laser ablation
Authors: Craciun V. , Singh R. K.
Published: July 2002

Ba 0.5 Sr 0.5 TiO 3 (BST) thin films grown on Si by an in situ ultraviolet-assisted pulsed laser deposition (UVPLD) technique exhibited significantly higher dielectric constant and refractive index values and lower leakage current densities than films grown by conventional PLD under similar conditions. X-ray photoelectron spectroscopy (XPS) investigations have shown that the surface layer of the grown films contained, besides the usual BST perovskite phase, an additional phase with Ba atoms in a different chemical state. PLD grown films always exhibited larger amounts of this phase, which was homogeneously mixed with the BST phase up to several nm depth, while UVPLD grown films exhibited a much thinner (∼1 nm) and continuous layer. The relative fraction of this phase was not correlated with the amount of C atoms present on the surface. Fourier transform infrared spectroscopy did not find any BaCO3 contamination layer, which was believed to be related to this new phase. X-ray diffraction measurement showed that although PLD grown films contained less oxygen atoms, the lattice parameter was closer to the bulk value than that of UVPLD grown films. After 4 keV Ar ion sputtering for 6 min, XPS analysis revealed a small suboxide Ba peak for the PLD grown films. This finding indicates that the average Ba–O bonds are weaker in these films, likely due to the presence of oxygen vacancies. It is suggested here that this new Ba phase corresponds to a relaxed BST surface layer.
Cluster Monte Carlo simulations of phase transitions and critical phenomena in zeolites
Authors: Dukovski Ilija , Machta Jonathan , Saravanan Chandra , Auerbach Scott M.
Published: July 2002

We simulated benzene adsorption in Na–X and Na–Y zeolites on a lattice of binding sites using a two-replica cluster Monte Carlo algorithm. Evidence for a vapor–liquid phase transition is explored for a range of guest–guest and host–guest energy and entropy parameters. The critical temperature is found to vanish precipitously with increasing energy difference between sites. For Na–X, critical temperatures as high as 300–400 K are found for reasonable values of the parameters, while for Na–Y no phase transition is predicted.
Interactions between dust grains in a dusty plasma
Authors: Lampe Martin , Joyce Glenn , Ganguli Gurudas , Gavrishchaka Valeriy
Published: July 2002

Dust grains in plasma acquire a large negative charge, and can constitute a strongly coupled system. If the plasma is stationary, the plasma-mediated electrostatic potential around a single grain can be calculated by orbital-motion-limited (OML) theory, including ion absorption at the grain surface. This potential is repulsive at all ranges, and falls off as r−2 at long range. Nonlinear modifications occur when there are several grains, but the interaction is still repulsive. If the plasma is streaming by the grains, each grain generates a wake field potential which can be calculated via linear response theory, and which attracts other grains to stationary points behind the grain. There is in addition an attractive force between grains, due to ion-impact momentum deposition. In certain parameter regimes, this “shadowing” force can yield a weak net attraction at long range. Trapped-ion effects are significant at high plasma density, but have not yet been calculated.
Contact resistivity and transport mechanisms in W contacts to p- and n-GaN
Authors: Zeitouny A. , Eizenberg M. , Pearton S. J. , Ren F.
Published: July 2002

The electrical properties of W contacts to both n- and p-GaN were investigated. W contacts to p-type GaN doped with Mg to a level of 1018 cm−3 were annealed for 1 min at temperatures from 350 to 900 °C. The contact resistivity was found to decrease with increasing annealing temperature parallel to an increase in the GaN sheet resistance. The contacts were rectifying after all of the heat treatments. Measurements at higher temperatures (up to 400 °C) resulted in I–V characteristics becoming almost linear and a decrease in contact resistivity with temperature down to 10−2 Ω cm2. These results are attributed to the ionization of more Mg acceptors as the temperature increases. In this system thermionic emission combined with tunneling through deep energy levels was found to be the transport mechanism. W contacts to heavily Si implanted (Nd∼1020 cm−3) n-GaN annealed at 750–1050 °C for 10 s produced ohmic behavior with no significant dependence of the contact resistivity on the annealing temperature. The observed weak dependence of the contact resistivity on the measurement temperature is attributed to the dominance of the field emission mechanism.
Hadamard regularization
Authors: Blanchet Luc , Faye Guillaume
Published: July 2002

Motivated by the problem of the dynamics of point-particles in high post-Newtonian (e.g., 3PN) approximations of general relativity, we consider a certain class of functions which are smooth except at some isolated points around which they admit a power-like singular expansion. We review the concepts of (i) Hadamard “partie finie” of such functions at the location of singular points, (ii) the partie finie of their divergent integral. We present and investigate different expressions, useful in applications, for the latter partie finie. To each singular function, we associate a partie-finie (Pf) pseudo-function. The multiplication of pseudo-functions is defined by the ordinary (pointwise) product. We construct a delta-pseudo-function on the class of singular functions, which reduces to the usual notion of Dirac distribution when applied on smooth functions with compact support. We introduce and analyze a new derivative operator acting on pseudo-functions, and generalizing, in this context, the Schwartz distributional derivative. This operator is uniquely defined up to an arbitrary numerical constant. Time derivatives and partial derivatives with respect to the singular points are also investigated. In the course of the paper, all the formulas needed in the application to the physical problem are derived.
Coarse graining of nonbonded inter-particle potentials using automatic simplex optimization to fit structural properties
Authors: Meyer Hendrik , Biermann Oliver , Faller Roland , Reith Dirk , Müller-Plathe Florian
Published: July 2002

We implemented a coarse-graining procedure to construct mesoscopic models of complex molecules. The final aim is to obtain better results on properties depending on slow modes of the molecules. Therefore the number of particles considered in molecular dynamics simulations is reduced while conserving as many properties of the original substance as possible. We address the problem of finding nonbonded interaction parameters which reproduce structural properties from experiment or atomistic simulations. The approach consists of optimizing automatically nonbonded parameters using the simplex algorithm to fit structural properties like the radial distribution function as target functions. Moreover, any mix of structural and thermodynamic properties can be included in the target function. Different spherically symmetric inter-particle potentials are discussed. Besides demonstrating the method for Lennard-Jones liquids, it is applied to several more complex molecular liquids such as diphenyl carbonate, tetrahydrofurane, and monomers of poly(isoprene).
Protein–membrane electrostatic interactions: Application of the Lekner summation technique
Authors: Juffer André H. , Shepherd Craig M. , Vogel Hans J.
Published: July 2002

A model has been developed to calculate the electrostatic interaction between biomolecules and lipid bilayers. The effect of ionic strength is included by means of explicit ions, while water is described as a background continuum. The bilayer is considered at the atomic level. The Lekner summation technique is employed to calculate the long-range electrostatic interactions. The new method is employed to estimate the electrostatic contribution to the free energy of binding of sandostatin, a cyclic eight-residue analogue of the peptide hormone somatostatin, to lipid bilayers with thermodynamic integration. Monte Carlo simulation techniques were employed to determine ion distributions and peptide orientations. Both neutral as well as negatively charged lipid bilayers were used. An error analysis to judge the quality of the computation is also presented. The applicability of the Lekner summation technique to combine it with computer simulation models that simulate the adsorption of peptides (and proteins) into the interfacial region of lipid bilayers is discussed.
Precise determination of the critical percolation threshold for the three-dimensional “Swiss cheese” model using a growth algorithm
Authors: Lorenz Christian D. , Ziff Robert M.
Published: July 2002

Precise values for the critical threshold for the three-dimensional “Swiss cheese” continuum percolation model have been calculated using extensive Monte Carlo simulations. These simulations used a growth algorithm and memory blocking scheme similar to what we used previously in three-dimensional lattice percolation. The simulations yield a value for the critical number density nc=0.652 960±0.000 005, which confirms recent work but extends the precision by two significant figures.
Computer simulation study of the velocity cross correlations between neighboring atoms in simple liquid binary mixtures
Authors: Verdaguer A. , Padró J. A.
Published: July 2002

The dynamic behavior of atoms in simple liquid binary mixtures is analyzed by molecular dynamic simulation. Time correlation functions between the initial velocity of a tagged particle and latter velocities of neighboring particles are calculated for soft-sphere liquid mixtures of species with different mass and/or size. The transfer of momentum from a tagged particle to its neighbors as well as the differences between the velocity cross correlation between particles of the same or different species is discussed.
Density functional theory for pair correlation functions in polymeric liquids
Authors: Yethiraj Arun , Fynewever Herb , Shew Chwen-Yang
Published: July 2002

A density functional theory is presented for the pair correlation functions in polymeric liquids. The theory uses the Yethiraj–Woodward free-energy functional for the polymeric liquid, where the ideal gas free-energy functional is treated exactly and the excess free-energy functional is obtained using a weighted density approximation with the simplest choice of the weighting function. Pair correlation functions are obtained using the Percus trick, where the external field is taken to be a single polymer molecule. The minimization of the free energy in the theory requires a two molecule simulation at each iteration. The theory is very accurate for the pair correlation functions in freely jointed tangent-hard-sphere chains and freely rotating fused-hard-sphere chains, especially at low densities and for long chains. In addition, the theory allows the calculation of the virial pressure in these systems and shows a remarkable degree of consistency between the virial and compressibility pressure.
Electrophoresis deposition of carbon nanotubes for triode-type field emission display
Authors: Choi W. B. , Jin Y. W. , Kim H. Y. , Lee S. J. , Yun M. J. , Kang J. H. , Choi Y. S. , Park N. S. , Lee N. S. , Kim J. M.
Published: July 2002

A triode-type field emission display has been fabricated using carbon nanotube emitters. Purified single walled carbon nanotubes were selectively deposited onto a cathode electrode in a triode-type structure by an electrophoresis. Emission current was modulated with gate potentials of 100–300 V. A high brightness of 1000 cd/m2 with uniform emission was obtained at 900 V at the anode and 200 V at the gate. The fluctuation of emission current was found to be less than 5% in a fully sealed field emission display. Selective deposition of carbon nanotubes by electrophoresis shows high feasibility for triode-type field emission displays.
Breakdown of continuity in large-eddy simulation
Authors: Langford Jacob A. , Moser Robert D.
Published: July 2002

In numerical simulations of incompressible flows—both direct and large-eddy simulations (LES)—the pressure is determined to enforce the continuity constraint. In this paper it is shown that for many common LES representations, there is no exact continuity constraint on the LES field, and thus a straightforward application of the continuity equation introduces errors. It is suggested that these errors can be reduced by optimizing the approximate continuity equation used to determine the pressure in an LES. Various strategies for constructing these approximate constraints are explored. The techniques are demonstrated on forced isotropic turbulence with a coarse finite-volume representation, and the a priori errors of several approximate continuity constraints are presented.
High-κ gate dielectrics: Current status and materials properties considerations
Authors: Wilk G. D. , Wallace R. M. , Anthony J. M.
Published: July 2002

Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal–oxide–semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward successful integration into the expected processing conditions for future CMOS technologies, especially due to their tendency to form at interfaces with Si (e.g. silicates). These pseudobinary systems also thereby enable the use of other high-κ materials by serving as an interfacial high-κ layer. While work is ongoing, much research is still required, as it is clear that any material which is to replace SiO2 as the gate dielectric faces a formidable challenge. The requirements for process integration compatibility are remarkably demanding, and any serious candidates will emerge only through continued, intensive investigation.
The effects of particle size on reversible shear thickening of concentrated colloidal dispersions
Authors: Maranzano Brent J. , Wagner Norman J.
Published: July 2002

The particle size dependence of the reversible shear thickening transition in dense colloidal suspensions is explored. Five suspensions of monodisperse silica are synthesized via the Stöber synthesis. The physicochemical properties of the dispersions are quantified using transmission electron microscopy, dynamic light scattering, small angle light scattering, electrophoresis, and viscometry. Rheology measurements indicate a critical stress marking the onset of reversible shear thickening that depends on the dispersion’s particle size, concentration, polydispersity, and interparticle interactions. A simplified two particle force balance between the interparticle repulsive forces and the hydrodynamic compressive forces is used to derive a scaling relationship between this critical shear stress and the suspension properties. The scaling is tested against the fully characterized silica dispersions, which span nearly a decade in particle size. Furthermore, bimodal mixtures of the dispersions are employed to evaluate the accuracy of the scaling to predict the critical shear stress for dispersions with varying degrees of polydispersity. The success of the scaling supports the hydrocluster mechanism for shear thickening and suggests methods for controlling shear thickening by tailoring particle properties.
Simultaneous particle image velocimetry and infrared imagery of microscale breaking waves
Authors: Siddiqui M. H. Kamran , Loewen Mark R. , Richardson Christine , Asher William E. , Jessup Andrew T.
Published: July 2002

We report the results from a laboratory investigation in which microscale breaking waves were detected using an infrared (IR) imager and two-dimensional (2-D) velocity fields were simultaneously measured using particle image velocimetry (PIV). In addition, the local heat transfer velocity was measured using the controlled flux technique. To the best of our knowledge these are the first measurements of the instantaneous 2-D velocity fields generated beneath microscale breaking waves. Careful measurements of the water surface profile enabled us to make accurate estimates of the near-surface velocities using PIV. Previous experiments have shown that behind the leading edge of a microscale breaker the cool skin layer is disrupted creating a thermal signature in the IR image [Jessup et al., J. Geophys. Res. 102, 23145 (1997)]. The simultaneously sampled IR images and PIV data enabled us to show that these disruptions or wakes are typically produced by a series of vortices that form behind the leading edge of the breaker. When the vortices are first formed they are very strong and coherent but as time passes, and they move from the crest region to the back face of the wave, they become weaker and less coherent. The near-surface vorticity was correlated with both the fractional area coverage of microscale breaking waves and the local heat transfer velocity. The strong correlations provide convincing evidence that the wakes produced by microscale breaking waves are regions of high near-surface vorticity that are in turn responsible for enhancing air–water heat transfer rates.
Influence of negative lattice expansion and metamagnetic transition on magnetic entropy change in the compound LaFe11.4Si1.6
Authors: Hu Feng-xia , Shen Bao-gen , Sun Ji-rong , Cheng Zhao-hua , Rao Guang-hui , Zhang Xi-xiang
Published: July 2002

Magnetization of the compound LaFe11.4Si1.6 with the cubic NaZn13-type structure was measured as functions of temperature and magnetic field around its Curie temperature TC of ∼208 K. It is found that the magnetic phase transition at TC is completely reversible. Magnetic entropy change ΔS, allowing one to estimate the magnetocaloric effect, was determined based on the thermodynamic Maxwell relation. The achieved magnitude of |ΔS| reaches 19.4 J/kg K under a field of 5 T, which exceeds that of most other materials involving a reversible magnetic transition in the corresponding temperature range. The large entropy change is ascribed to the sharp change of magnetization, which is caused by a large negative lattice expansion at the TC. An asymmetrical broadening of |ΔS| peak with increasing field was observed, which is resulted from the field-induced itinerant-electron metamagnetic transition from the paramagnetic to ferromagnetic state above the TC.
Demonstrating the achievement of lower temperatures with two-stage vortex tubes
Authors: Guillaume D. W. , Jolly J. L.
Published: July 2002

Vortex tubes separate single inlet streams of compressed air into two discharge streams. One stream exits at a lower temperature than the inlet stream, and the other exits at a higher temperature. The difference between the lower outlet temperature and the inlet temperature is ΔT. This study demonstrates that with equal inlet temperatures, a two-stage vortex tube (i.e., two vortex tubes operating simultaneously in series) can produce a greater ΔT than the ΔT produced by either one of the vortex tubes operating independently. Specifically, results demonstrate that two single-stage tubes that have ΔT values, which are, respectively, −17.37 and −16.17 °C, can be combined into a two-staged vortex tube that has a ΔT of −19.33 °C. Thus, the cooling capability of a vortex tube can be increased by staging.
Temperature dependence of the charge injection in poly-dialkoxy-p-phenylene vinylene
Authors: van Woudenbergh T. , Blom P. W. M. , Vissenberg M. C. J. M. , Huiberts J. N.
Published: July 2002

The injection of holes from a Ag electrode into poly-dialkoxy-p-phenylene vinylene is investigated by measuring the current–voltage characteristics as a function of temperature. For this model system, the hole injection is hindered by a contact energy barrier of about 1.0 eV. The observed temperature dependence of the injection-limited current does not agree with the predictions of classical injection models. A recent model, in which the spread in the charge transporting site energy due to disorder is taken into account, consistently describes the measured field and temperature dependence of the injection process.