bluuebunny/crossref_metadata_2025 huggingface dataset:
Fractal properties of seismicity in regions affected by large, shallow earthquakes in western Japan: Implications for fault formation processes based on a binary fractal fracture network model
Authors: Nakaya Shinji
Published: January 2005

The temporal variation in the b value (which is defined as the slope of the Gutenberg‐Richter frequency N–magnitude M relationship), log N = a − bM, and the multifractal dimension of the spatial distribution Dq of seismic activity are analyzed using earthquake catalog data for regions affected by two recent large earthquakes in Japan. An anomalous decrease in Dq and an increase in b value appear as a common seismic rupture response during the period of decreasing seismic energy release in the lead up to these large, shallow earthquakes. The change in fractal dimensions of faults inferred from sequential seismic events reflects the transition of fracture from a dispersive rupture process to an anomalous rupture process and shows that the growth of the fault network through fault linkage is abruptly restrained in the fault formation process leading up to the main shock. The anomalies in the fractal and multifractal dimensions prior to large earthquakes indicate that the anomalous activation and clustering of smaller earthquakes represents criticality of the state around asperities along a fault.
A high‐pressure X‐ray diffraction study of iron nitrides: Implications for Earth's core
Authors: Adler Jennifer F. , Williams Quentin
Published: January 2005

High‐pressure X‐ray diffraction studies of cubic close‐packed γ′‐Fe4N and hexagonal close‐packed ‐Fe7N3 have been performed to pressures of 51 GPa in order to constrain the elastic properties and phase transitions of these materials under the pressures of the Earth's interior. The ɛ‐Fe7N3 phase remains stable to the highest pressures of these measurements, with a bulk modulus (K) of 168(10) GPa and a (K′) of 5.7(1.5). Fe4N appears to undergo a phase transition to either a hexagonal crystalline structure similar to that of Fe7N3 or may disorder by 32.4 GPa. The bulk modulus of γ′‐Fe4N up to this pressure is 155(3) GPa, with K′ assumed to be 4. Both volume and Gibbs free energy calculations indicate that between these two nitride phases, the hexagonal close‐packed phase is more stable under deep Earth conditions. The amount of nitrogen in iron meteorites indicates that significant quantities of nitrogen (of order 0.5 wt %) could have been incorporated in Earth's core during accretion. Since iron meteorites are derived from the core material of differentiated bodies in the early solar system, nitrogen is likely a component of the light alloying elements in the Earth's core. If nitrogen partitions preferentially into interstitial sites within ɛ‐Fe relative to liquid, than the abundance of nitrogen in meteorites implies that N could be the primary light alloying component in Earth's inner core. The elastic properties of ɛ‐Fe7N3 extrapolated to inner core conditions are found to meet the primary criteria for a light alloying component of the inner core: It is both less dense than, and approximately as compressible as, ɛ‐Fe. Indeed, we document that the elasticity of nitrogen‐bearing iron compounds is quite similar to that of end‐member iron. However, the anisotropy of Fe7N3 on compression is substantially greater than that of ɛ‐Fe, with its a axis being substantially more compressible than its c axis. Thus a mixture of iron and iron nitride (or a solid solution between the two) in the inner core could easily generate the observed anisotropy of this body.
Generation of electric and magnetic field during detonation of high explosive charges in boreholes
Authors: Soloviev S. P. , Sweeney J. J.
Published: January 2005

We present experimental results of a study of electromagnetic field generation during underground detonation of high explosive charges in holes bored in sandy loam and granite. Three components of electric field (vertical component in air and two horizontal components in the soil) and three components of the magnetic induction were recorded during the field experiments. Test conditions and physicomechanical properties of the soil exert significant influence on the parameters of electromagnetic signals generated by underground explosions with masses of 2–200 kg. The electric and magnetic field experimental data are satisfactorily described by an electric dipole model with the source embedded in layered media. We used the solution for a field produced by stationary vertical and horizontal electric dipoles placed near the interface between two layers with different conductivity. The magnitude of the field source was estimated on the basis of the records of electromagnetic signals obtained at different distances from the borehole. For an underground explosion of a TNT charge with a mass of 2 kg carried out in granite the maximum estimated value of the electric dipole component is about 10−7 C m. This estimate is more than an order of magnitude greater than that obtained for an explosion of the same mass carried out in sandy loam.
Measuring and modeling thermal conductivity of gas hydrate‐bearing sand
Authors: Huang Duzi , Fan Shuanshi
Published: January 2005

Effective thermal conductivity (ETC) of both tetrahydrofuran (THF) and methane hydrate‐bearing sandy porous media was measured by the Hot Disk Thermal Constant Analyser. Thermal conductivity of methane hydrate is 0.575 W m−1K−1at 0°C and 6.6 MPa (methane gas pressure), which is close to THF hydrate's 0.51 W m−1K−1at 0°C and 0.1 MPa (atmosphere pressure). However, the measured 1 W m−1K−1ETC of methane hydrate‐bearing sand is significantly lower than that of THF hydrate‐bearing sand at ∼2 W m−1K−1. This is because the methane hydrate formed with a sodium dodecyl sulfate (SDS) solution in sand at our laboratory has a “wall creeping” growth characteristic and consequently a large part of the pores were filled with methane free gas. ETCs of sand containing gas hydrates were also calculated using a renormalization method. The process involves sample partitioning, labeling, initial value assignments, and renormalization calculations. A Monte Carlo analysis was applied to sample laboratory‐scale gas hydrate‐bearing sand assemblies. We found that the renormalization modeling results agreed well with measured ETCs when each photo of a 1.3 mm × 1.3 mm subsample was divided into 16 or more blocks.
Optical properties of urban aerosol from airborne and ground‐based in situ measurements performed during the Etude et Simulation de la Qualité de l'air en Ile de France (ESQUIF) program
Authors: Chazette Patrick , Randriamiarisoa Hariliva , Sanak Joseph , Couvert Pierre , Flamant Cyrille
Published: January 2005

Urban aerosol microphysical and optical properties were investigated over the Paris area coupling, for the first time, with dedicated airborne in situ instruments (nephelometer and particle sizers) and active remote sensor (lidar) as well as ground‐based in situ instrumentation. The experiment, covering two representative pollution events, was conducted in the framework of the Etude et Simulation de la Qualité de l'air en Ile de France (ESQUIF) program. Pollution plumes were observed under local northerly and southerly synoptic wind conditions on 19 and 31 July 2000, respectively. The 19 July (31 July) event was characterized by north‐northwesterly (westerly) advection of polluted (clean) air masses originating from Great Britain (the Atlantic Ocean). The aerosol number size distribution appeared to be composed mainly of two modes in the planetary boundary layer (accumulation and nucleation) and three modes in the surface layer (accumulation, nucleation, and coarse). The characteristics of the size distribution (modal radii and geometric dispersion) were remarkably similar on both days and very coherent with the aerosol optical parameters retrieved from lidar and nephelometer measurements. The city of Paris mainly produces aerosols in the nucleation mode (modal radius of ∼0.03 μm) that have little influence on the aerosol optical properties in the visible spectral range. The latter are largely dominated by the scattering properties of aerosols in the accumulation mode (modal radius of ∼0.12 μm). When the incoming air mass is already polluted (clear), the aerosol in the accumulation mode is shown to be essentially hydrophobic (hydrophilic) in the outgoing air mass.
A possible mechanism of solar modulation of the spatial structure of the North Atlantic Oscillation
Authors: Kodera Kunihiko , Kuroda Yuhji
Published: January 2005

The spatial structure of the North Atlantic Oscillation (NAO) in winter differs significantly according to the solar cycle. The NAO is confined to the Atlantic sector during low solar activity (LS), whereas it has a hemispherical structure during high solar activity (HS). The present study focuses on identifying the involved processes. The results of analyses suggest that the solar activity influence originates in the stratopause region, where the mode of interannual variation in the zonal‐mean zonal winds changes according to solar activity. In the early winter of HS, the leading zonal wind mode has a meridional dipole‐type structure that extends downward from the stratosphere to the troposphere through interaction with planetary waves. The dipole‐type anomaly in the zonal winds produces a hemispherical scale seesaw pattern in the surface pressure between the polar region and surrounding regions. Thus the NAO during HS has a hemispherical pattern. During LS, the downward extension of zonal‐mean zonal wind anomalies is weak, so the regional‐scale variation becomes dominant in the troposphere.
A volcanic interpretation of Gusev Crater surface materials from thermophysical, spectral, and morphological evidence
Authors: Martínez‐Alonso Sara , Jakosky Bruce M. , Mellon Michael T. , Putzig Nathaniel E.
Published: January 2005

Gusev Crater, the Mars Exploration Rover Spirit landing site (160 km diameter; 14.5°S, 184.5°W), has been identified in previous studies as a prime site of geological and exobiological interest on the basis of its potential for having hosted a fluviolacustrine environment; such environment may have been favorable for the development of biological activity. The origin and nature of the materials present at the surface of Gusev Crater are still being debated. In previous studies based on geomorphological and thermophysical data, surface materials in the crater have been interpreted as originating from fluviolacustrine, volcanic, or aeolian processes, or combinations thereof. We present results from the analysis of newly compiled thermophysical (Thermal Emission Spectrometer (TES) and Thermal Emission Imaging System (THEMIS)), spectroscopic (TES), and visible (THEMIS and Mars Observer Camera) data for the Gusev region. These data were analyzed using a new mosaicking technique developed to match the values of contiguous scenes and to produce seamless mosaics apt for geological interpretation. Thermophysical, spectroscopic, and morphological evidence point to the presence of local outcrops of lava flows of basaltic composition, materials consistent with a regolith developed from basaltic materials, fine‐grained deposits of basaltic composition strongly modified by wind erosion, and wind deposits. According to these findings, we conclude that most of the materials occupying the present surface of Gusev have characteristics consistent with those of volcanic and aeolian deposits. Fluviolacustrine deposits proposed by other authors may exist under the volcanic materials and may be exposed in impact craters.
Hydrological modeling of the Martian crust with application to the pressurization of aquifers
Authors: Hanna Jeffrey C. , Phillips Roger J.
Published: January 2005

We develop a hydrological model of the Martian crust, including both ancient heavily cratered terrains and younger basaltic and sedimentary terrains. The porosity, permeability, and compressibility are represented as interdependent functions of the effective stress state of the aquifer, as determined by the combination of the lithostatic pressure and the fluid pore pressure. In the megaregolith aquifer model, the crust is modeled as a 2 km thick megaregolith, composed of lithified and fractured impact ejecta, overlying the impact‐fractured and partially brecciated basement rock. The hydraulic properties depend primarily upon the abundance of breccia and the compressional state of the fractures. The porosity ranges from approximately 0.16 at the surface to 0.04 at a depth of 10 km, with a sharp discontinuity at the base of the regolith. The permeability varies from approximately 10−11 m2 at the surface to 10−15 m2 at depths of 5 km or more and is strongly dependent upon the fluid pore pressure. The hydrologic properties of basaltic and sedimentary aquifers are also considered. These parameters are used to model the fluid pressures generated beneath a thickening cryosphere during a postulated dramatic cooling of the climate at the end of the Noachian. As a result of a negative feedback between the fluid pore pressure and the permeability, it is more difficult than previously thought to generate pore pressures in excess of the lithostatic pressure by this mechanism. The production of the outflow channels as the result of such a climatic change is deemed unlikely.
Recognition and processing of a nuclear-encoded polyprotein precursor by mitochondrial processing peptidase
Authors: OSHIMA Tsutomu , YAMASAKI Eiki , OGISHIMA Tadashi , KADOWAKI Koh-ichi , ITO Akio , KITADA Sakae
Published: January 2005

The nuclear-encoded protein RPS14 (ribosomal protein S14) of rice mitochondria is synthesized in the cytosol as a polyprotein consisting of a large N-terminal domain comprising preSDHB (succinate dehydrogenase B precursor) and the C-terminal RPS14. After the preSDHB–RPS14 polyprotein is transported into the mitochondrial matrix, the protein is processed into three peptides: the N-terminal prepeptide, the SDHB domain and the C-terminal mature RPS14. Here we report that the general MPP (mitochondrial processing peptidase) plays an essential role in processing of the polyprotein. Purified yeast MPP cleaved both the N-terminal presequence and the connector region between SDHB and RPS14. Moreover, the connector region was processed more rapidly than the presequence. When the site of cleavage between SDHB and RPS14 was determined, it was located in an MPP processing motif that has also been shown to be present in the N-terminal presequence. Mutational analyses around the cleavage site in the connector region suggested that MPP interacts with multiple sites in the region, possibly in a similar manner to the interaction with the N-terminal presequence. In addition, MPP preferentially recognized the unfolded structure of preSDHB–RPS14. In mitochondria, MPP may recognize the stretched polyprotein during passage of the precursor through the translocational apparatus in the inner membrane, and cleave the connecting region between the SDHB and RPS14 domains even before processing of the presequence.
Independent roles of eIF5A and polyamines in cell proliferation
Authors: NISHIMURA Kazuhiro , MUROZUMI Kaori , SHIRAHATA Akira , PARK Myung Hee , KASHIWAGI Keiko , IGARASHI Kazuei
Published: January 2005

To examine the roles of active hypusinated eIF5A (eukaryotic translation initiation factor 5A) and polyamines in cell proliferation, mouse mammary carcinoma FM3A cells were treated with an inhibitor of deoxyhypusine synthase, GC7 (N1-guanyl-1, 7-diaminoheptane), or with an inhibitor of ornithine decarboxylase, DFMO (α-difluoromethylornithine), or with DFMO plus an inhibitor of spermine synthase, APCHA [N1-(3-aminopropyl)-cyclohexylamine]. Treatment with GC7 decreased the level of active eIF5A on day 1 without affecting cellular polyamine content, and inhibition of cell growth occurred from day 2. This delay reflects the fact that eIF5A was present in excess and was very stable in these cells. Treatment with DFMO or with DFMO plus APCHA inhibited cell growth on day 1. DFMO considerably decreased the levels of putrescine and spermidine, and the formation of active eIF5A began to decrease when the level of spermidine fell below 8 nmol/mg of protein after 12 h of incubation with DFMO. The combination of DFMO and APCHA markedly decreased the levels of putrescine and spermine and significantly decreased the level of spermidine, but did not affect the level of active eIF5A until day 3 when spermidine level decreased to 7 nmol/mg of protein. The results show that a decrease in either active eIF5A or polyamines inhibits cell growth, indicating that eIF5A and polyamines are independently involved in cell growth.
Expression and regulation of sterol 27-hydroxylase (CYP27A1) in human macrophages: a role for RXR and PPARγ ligands
Authors: QUINN Carmel M. , JESSUP Wendy , WONG Jenny , KRITHARIDES Leonard , BROWN Andrew J.
Published: January 2005

CYP27A1 (sterol 27-hydroxylase) catalyses an important sterol elimination pathway in the human macrophage, and consequently may protect against atherosclerosis. We studied the expression and regulation of CYP27A1 in a human macrophage-like cell-line, THP-1, and primary HMDMs (human monocyte-derived macrophages). In both macrophage cell types, we found that CYP27A1 expression is independent of cellular cholesterol levels and of LXR (liver X receptor)-dependent control of transcription. However, the RXR (retinoid X receptor) ligand, 9-cis-retinoic acid, upregulates CYP27A1 expression. Of the RXR heterodimeric partners tested, PPAR (peroxisome-proliferator-activated receptor) γ ligands significantly increased CYP27A1 mRNA levels. Its reversal by a PPARγ antagonist demonstrated the specificity of this effect. Interestingly, HMDMs express markedly higher levels of CYP27A1 than THP-1 macrophages, and this difference was reflected in both protein levels and enzyme activities between the two cell types. In conclusion, stimulation of CYP27A1 by PPARγ may represent a key previously unrecognized mechanism by which PPARγ protects against atherosclerosis.
Hypogin, a novel antifungal peptide from peanuts with sequence similarity to peanut allergen
Authors: Ye X. , Ng T.B.
Published: January 2005

Abstract: A protein designated hypogin, with a prominent suppressive action on the growth of the fungi Mycosphaerella arachidicola, Fusarium oxysporum and Coprinus comatus, was isolated from seeds of the peanut Arachis hypogaea. The protein inhibited human immunodeficiency virus (HIV) reverse transcriptase and enzymes associated with HIV infection including α‐glucosidase and β‐glucosidase. The proliferative response of mouse splenocytes was attenuated in the presence of the protein. The protein exhibited a molecular mass of 7.2 kDa in tricine gel electrophoresis and gel filtration on Superdex 75 and an N‐terminal sequence resembling peanut allergen Ara H1. The isolation procedure involved affinity chromatography on Affi‐gel blue gel and ion‐exchange chromatography on CM−Sepharose. The protein was adsorbed in both chromatographic media.
Universal collective rotation channels and quantum error correction
Authors: Junge Marius , Kim Peter T. , Kribs David W.
Published: January 2005

We present and investigate a new class of quantum channels, what we call “universal collective rotation channels,” that includes the class of collective rotation channels as a special case. The fixed point set and noise commutant coincide for a channel in this class. Computing the precise structure of this C*-algebra is a core problem in a particular noiseless subsystem method of quantum error correction. We prove that there is an abundance of noiseless subsystems for every channel in this class and that the Young tableaux combinatorial machine may be used to explicitly compute these subsystems.
Asymptotic flatness and Bondi energy in higher dimensional gravity
Authors: Hollands Stefan , Ishibashi Akihiro
Published: January 2005

We give a general geometric definition of asymptotic flatness at null infinity in d-dimensional general relativity (d even) within the framework of conformal infinity. Our definition is arrived at via an analysis of linear perturbations near null infinity and shown to be stable under such perturbations. The detailed falloff properties of the perturbations, as well as the gauge conditions that need to be imposed to make the perturbations regular at infinity, are qualitatively different in higher dimensions; in particular, the decay rate of a radiating solution at null infinity differs from that of a static solution in higher dimensions. The definition of asymptotic flatness in higher dimensions consequently also differs qualitatively from that in d=4. We then derive an expression for the generator conjugate to an asymptotic time translation symmetry for asymptotically flat space–times in d-dimensional general relativity (d even) within the Hamiltonian framework, making use especially of a formalism developed by Wald and Zoupas. This generator is given by an integral over a cross section at null infinity of a certain local expression and is taken to be the definition of the Bondi energy in d dimensions. Our definition yields a manifestly positive flux of radiated energy. Our definitions and constructions fail in odd space–time dimensions, essentially because the regularity properties of the metric at null infinity seem to be insufficient in that case. We also find that there is no direct analog of the well-known infinite set of angle dependent translational symmetries in more than four dimensions.
Effects of buffer layers on the structural and electronic properties of InSb films
Authors: Weng X. , Rudawski N. G. , Wang P. T. , Goldman R. S. , Partin D. L. , Heremans J.
Published: January 2005

We have investigated the effects of various buffer layers on the structural and electronic properties of n-doped InSb films. We find a significant decrease in room-temperature electron mobility of InSb films grown on low-misfit GaSb buffers, and a significant increase in room-temperature electron mobility of InSb films grown on high-misfit InAlSb or step-graded GaSb+InAlSb buffers, in comparison with those grown directly on GaAs. Plan-view transmission electron microscopy (TEM) indicates a significant increase in threading dislocation density for InSb films grown on the low-misfit buffers, and a significant decrease in threading dislocation density for InSb films grown on high-misfit or step-graded buffers, in comparison with those grown directly on GaAs. Cross-sectional TEM reveals the role of the film/buffer interfaces in the nucleation (filtering) of threading dislocations for the low-misfit (high-misfit and step-graded) buffers. A quantitative analysis of electron mobility and carrier-concentration dependence on threading dislocation density suggests that electron scattering from the lattice dilation associated with threading dislocations has a stronger effect on electron mobility than electron scattering from the depletion potential surrounding the dislocations. Furthermore, while lattice dilation is the predominant mobility-limiting factor in these n-doped InSb films, ionized impurity scattering associated with dopants also plays a role in limiting the electron mobility.
Demixing in athermal mixtures of colloids and excluded-volume polymers from density functional theory
Authors: Bryk Paweł
Published: January 2005

We study the structure and interfacial properties of model athermal mixtures of colloids and excluded volume polymers. The colloid particles are modeled as hard spheres whereas the polymer coils are modeled as chains formed from tangentially bonded hard spheres. Within the framework of the nonlocal density functional theory we study the influence of the chain length on the surface tension and the interfacial width. We find that the interfacial tension of the colloid-interacting polymer mixtures increases with the chain length and is significantly smaller than that of the ideal polymers. For certain parameters we find oscillations on the colloid-rich parts of the density profiles of both colloids and polymers with the oscillation period of the order of the colloid diameter. The interfacial width is few colloid diameters wide and also increases with the chain length. We find the interfacial width for the end segments to be larger than that for the middle segments and this effect is more pronounced for longer chains.
Effect of the excitation pulse frequency on the ultrafast photoinduced electron transfer dynamics
Authors: Fedunov Roman G. , Ivanov Anatoly I.
Published: January 2005

The dependence of the ultrafast photoinduced electron transfer dynamics in donor-acceptor complexes on the excitation pulse carrier frequency (spectral effect) has been investigated in the framework of a model involving three electronic state. The spectral effect has been shown to strongly depend on the angle θ between the reaction coordinate directions corresponding to optical and charge transfer transitions. Describing the solvent as a linear homogenous polar medium and accounting for Coulombic interaction of the transferred charge with the medium polarization fluctuations, the angle θ has been found out to be typically in the area 40°–85°. Exactly in this area of θ the spectral effect is predicted to be most pronounced.
Amorphous-amorphous transition in glassy polymers subjected to cold rolling studied by means of positron annihilation lifetime spectroscopy
Authors: Cangialosi D. , Wübbenhorst M. , Schut H. , van Veen A. , Picken S. J.
Published: January 2005

In this study, polycarbonate (PC) and polystyrene (PS) are subjected to plastic deformation by means of cold rolling and the resulting variation of the free volume and its subsequent time evolution after rolling is investigated by means of positron annihilation lifetime spectroscopy (PALS). The value of the long lifetime component that is attributed to the decay of ortho-positronium (τo-Ps) and its intensity (Io-Ps) are used to characterize, respectively, the size and the concentration of the free-volume holes. In addition to the PALS experiments, the effect of plastic deformation on the dynamic tensile modulus is investigated. The PALS results show that both for well-aged PC and PS an increase of τo-Ps and a decrease of Io-Ps occur upon plastic deformation. During the subsequent aging, τo-Ps tends to return to the value assumed before plastic deformation, while Io-Ps remains constant with time. These results corroborate the idea of an amorphous-amorphous transition, rather than that of a “mechanical rejuvenation” as proposed in the past to explain the ability of plastic deformation to reinitiate physical aging. Finally, a linear relation between the size of the free-volume holes and the dynamic tensile modulus is found, which suggests that the stiffness of amorphous glassy polymers is fully determined by their nanoscopic structure.
4
d
→
4
f
dipole resonance of the metal atom encapsulated in a fullerene cage: Ce@C82
Authors: Mitsuke Koichiro , Mori Takanori , Kou Junkei , Haruyama Yusuke , Kubozono Yoshihiro
Published: January 2005

The yield curves for photoions from Ce@C82 are measured by using synchrotron radiation in the photon energy range from 90to160eV. Parent Ce@C82z+ and fragment ions C60z+ and C70z+ are observed in a mass spectrum (z=1 and 2). The yield curves for doubly charged ionic species exhibit broad resonance in the photon energy region of from 120to140eV which is ascribed to the 4d→4f giant dipole resonance of the encapsulated Ce atom. The total photoabsorption cross section of Ce@C82 was determined from partial photoionization cross sections for formation of the parent and fragment ions to be 5.3−1.1+1.8 and 19.6−3.9+6.5Mb at photon energies of 110 and 130eV, respectively.
Dislocation reduction in sulfur- and germanium-doped indium phosphide single crystals grown by the vertical gradient freeze process: A transient finite-element study
Authors: Zhu X. A. , Tsai C. T.
Published: January 2005

During the growth of indium phosphide (InP) crystals, dislocations are mostly generated in a plastically deformed crystal due to crystallographic glide caused by excessive thermal stresses. High dislocation density presented in the InP crystal can reduce the performance, lifetime, and reliability of the InP-based microelectronic and optoelectronic devices/circuits. The generation of dislocations in InP single crystals grown from the melt can be predicted by using a transient finite-element model. This model couples microscopic dislocation motion and multiplication to macroscopic plastic deformation during the crystal growth process. The temperature fields in the crystal are determined by solving the partial differential equations of heat transfer for the vertical gradient freeze (VGF) process. These temperature fields are then employed to the transient finite-element model to study the effects of doping impurities and growth parameters (i.e., imposed temperature gradient, crystal radius, and growth rate) on dislocation reduction in InP crystals grown by different VGF processes.
Transport mechanism in lightly doped hydrogenated microcrystalline silicon thin films
Authors: Dussan A. , Buitrago R. H.
Published: January 2005

Boron-doped microcrystalline silicon films have been deposited in a plasma-enhanced chemical vapor deposition system using silane diluted in hydrogen, and diborane (B2H6) as a dopant gas. The temperature dependence of the dark conductivity has been measured from 120to420K in all samples. In the high-temperature range above room temperature, the carrier transport is found to be thermally activated, with a single activation energy that changes with the B2H6 compensation degree. In the low-temperature range (300–120K), variable range hopping (VRH) was established as a predominant electronic transport mechanism for all samples, with the exception of the sample with a diborane concentration of 12.5ppm. A model for Mott’s VRH, referred to as the “diffusional model,” which yields a relation between the conductivity and the localized density of gap states, is presented. Using classical equations from the percolation theory and the diffusional model, the density of states near the Fermi level, as well as the hopping parameters, are calculated. A correlation between the hopping parameters for both models is deduced. A numerical factor that improves the value of each parameter is calculated.
Coupled optical and electronic simulations of electrically pumped photonic-crystal-based light-emitting diodes
Authors: Veronis Georgios , Suh Wonjoo , Liu Yang , Han Minghui , Wang Zheng , Dutton Robert W. , Fan Shanhui
Published: January 2005

We use coupled optical and electronic simulations to investigate design trade-offs in electrically pumped photonic-crystal-based light-emitting diodes. A finite-difference frequency-domain electromagnetic solver is used to calculate the spontaneous emission enhancement factor and the extraction efficiency as a function of frequency and of position of the emitting source. The calculated enhancement factor is fed into an electronic simulator, which solves the coupled continuity equations for electrons and holes and Poisson’s equation. We simulate a two-dimensional structure consisting of a photonic-crystal slab with a single-defect cavity and investigate different electrical pumping geometries for such a cavity.
Nonpolar a-plane GaN film on Si(100) produced using a specially designed lattice-matched buffer: A fresh approach to eliminate the polarization effect
Authors: Song J. H. , Yoo Y. Z. , Nakajima Kiyomi , Chikyow Toyohiro , Sekiguchi Takashi , Koinuma Hideomi
Published: January 2005

Using pulsed laser deposition, nonpolar a-plane GaN thin films were grown on Si(100) substrates coated with a nonpolar MnS(100) plane buffer layer. The film showed an epitaxial relationship of GaN(112¯0)∥MnS(100)∥Si(100) with an in-plane alignment of GaN[1¯100]∥MnS[010]∥Si[010]. The high-resolution cross-sectional transmission electron microscopy image of the GaN∕MnS interface showed an abrupt atomic interface. A strong band-edge emission from the GaN film was observed at 364.3nm (=3.4eV) in cathodoluminescence measurements at 30K. This result in controlling the growth plane provides GaN films free of polarization effects in the direction of film growth, which favor the integration of optoelectronic devices combined with silicon.
The response of soda-lime glass-hydroxyterminated polybutadiene composites to shock loading
Authors: Millett J. C. F. , Bourne N. K. , Akhavan J. , Milne A. M.
Published: January 2005

The effect of particle size on the shock response of three soda-lime glass-hydroxyterminated polybutadiene composites has been investigated. While the shock velocity–particle velocity relationship has been shown to be nearly identical in all three materials, thus indicating that the hydrodynamic response is particle size independent, the shock stresses have been shown to be strongly dependent upon particle size. It has been proposed that this be due to the nature of the microstructure, with the larger particles restricting flow, and thus increasing shear strength, while the finer microstructure can flow as a whole.
Determination of band-offset enhanced in InGaAsP–InGaAsP strained multiquantum wells by photocurrent measurements
Authors: Tari Davide , De Giorgi Milena , Cingolani Roberto , Foti Ermanno , Coriasso Claudio
Published: January 2005

We experimentally determine the band offset of strain-compensated InGaAsP–InGaAsP multiquantum-well (MQW) heterostructures, emitting at 1.55μm, that were grown by metal-organic chemical vapor deposition. A band offset value of about 56% is found for the conduction band, which is higher than the value reported for the unstrained structure. The temperature dependence of the photoluminescence intensity shows that the unipolar detrapping of carriers in such MQWs is more efficient than the thermal activation of excitons.
Structural and magnetic properties of cobalt-doped rutile thin films deposited on TiN–Si
Authors: Yang Hyuck Soo , Singh Rajiv K.
Published: January 2005

Highly oriented Co-doped rutile TiO2 thin film on silicon has been achieved by using a TiN buffer layer. The direct deposition of TiO2:Co film on TiN–Si yields (110)-oriented film structure having two equivalent structural domains which are perpendicular to each other. Interestingly, no ferromagnetism is observed in this film structure down to 10K, the reason for which is attributed to the formation of cobalt silicide in the silicon. On the other hand, when the TiO2:Co film is deposited on TiO2, formed by in situ oxidation of TiN–Si, cobalt appears highly mobile leading to segregation at the TiO2–Si interface along with the formation of cobalt clusters in the TiO2:Co film region. This is responsible for the ferromagnetism in this case.
Facing-target sputtered Fe–C granular films: Structural and magnetic properties
Authors: Mi W. B. , Li Z. Q. , Wu P. , Jiang E. Y. , Bai H. L. , Hou D. L. , Li X. L.
Published: January 2005

Structural and magnetic properties of as-deposited and 550°C annealed Fe–C granular films have been investigated. It is found that the as-deposited samples are composed of amorphous Fe granules dispersed in an amorphous C matrix, and transformed to α(bcc)∕γ(fcc)-Fe and graphitelike C after being annealed at 550°C for one hour. The morphologies of the as-deposited samples are composition dependent, and the phase segregation between Fe and C phases can be seen by high-resolution transmission electron microscopy. Magnetic measurements reveal that the as-deposited samples are superparamagnetic at Fe composition of xv=49,58,65, and soft ferromagnetic at xv=77,84. The in-plane coercivity of the annealed specimens decreases with increasing xv, which is attributed to the enhanced intra-particle interaction, as evidenced by the long-range domain structures observed using magnetic force microscope images. The magnetic reversal mechanism deviates from ideal domain wall motion mode and approaches Stoner–Wohlfarth rotational mode with the decrease of Fe volume fraction.
Fabrication of high-density ordered nanoarrays in silicon dioxide by MeV ion track lithography
Authors: Razpet Alenka , Johansson Anders , Possnert Göran , Skupiński Marek , Hjort Klas , Hallén Anders
Published: January 2005

Self-assembled nanoporous alumina films were employed as masks for MeV ion track lithography. Films with thickness of 2 μm and pore diameters of 30 and 70 nm were attached to thermally grown SiO2 covered with a thin gold layer. The samples were aligned with respect to the beam by detecting backscattered He+ ions with the initial energy of 2 MeV. The ordered pattern of the porous alumina films was successfully transferred into SiO2 after irradiation with a 4 MeV Cl2+ beam at fluence of 1014ions∕cm2, followed by chemical etching in a 5% HF solution.
Data acquisition system for high speed atomic force microscopy
Authors: Fantner Georg E. , Hegarty Paul , Kindt Johannes H. , Schitter Georg , Cidade Geraldo A. G. , Hansma Paul K.
Published: January 2005

With the development of atomic force microscopes that allow higher scan speeds, the need for data acquisition systems (DAQ) that are capable of handling the increased amounts of data in real time arises. We have developed a low cost data acquisition and scan control system around a commercially available DAQ board in a WINDOWS environment. By minimizing the involvement of the processor in the data transfer using direct memory access, and generation of the scan signals synchronously with the data acquisition, we were able to record 30 frames per second with a pixel resolution of 150×150pixels and 14bit per channel.
Atomic force microscopy-based experimental setup for studying domain switching dynamics in ferroelectric capacitors
Authors: Dehoff C. , Rodriguez B. J. , Kingon A. I. , Nemanich R. J. , Gruverman A. , Cross J. S.
Published: January 2005

This article describes an experimental setup for combined measurements of domain switching dynamics and switching currents in micrometer scale ferroelectric capacitors. The setup is based on a commercial atomic force microscope (AFM) that is equipped with a piezoresponse mode for domain imaging and with a wide bandwidth current amplifier for switching current recording. The setup allows combined domain/current measurements in capacitors as small as 1μm2 with switching times resolved down to 10ns. The incorporation of switching current measurement capability into piezoresponse AFM makes detailed analysis of switching behavior in ferroelectric memory devices possible.
Intermediate crystalline states produced by isothermal annealing of sputter-deposited a-Si films
Authors: Akazawa Housei
Published: January 2005

The crystalline states produced by isothermally annealing sputter-deposited hydrogen-free amorphous-Si (a-Si) films greatly differ from those of a-Si:H films. Strained network and numerous vacancies in the a-Si film are indicated by the ⟨ε2⟩ spectrum. Annealing the sample at temperatures between 300 and 550°C relaxes the strained network due to local exchanges of Si–Si bond while maintaining the amorphous state. Self-assembly of hemispherical grains of microcrystalline Si on the film surface occurs during the onset of crystallization (600°C). At a slightly elevated temperature of 690°C, the cohesion of Si atoms in the film creates nanocrystalline Si (2-nm diameter), which directly corresponds to the emergence of the absorption peak feature below 3eV in the ⟨ε2⟩ spectrum. Dense voids at the interfacial region severely limit the range of solid phase epitaxy, thus facilitating preferential nucleation in the film.
Simulation of adsorption-induced stress of a microcantilever sensor
Authors: Dareing Don W. , Thundat Thomas
Published: January 2005

Molecular adsorption on a microcantilever surface causes the cantilever to bend as a result of adsorption-induced stresses. A model for adsorption-induced surface stress based on atomic or molecular interaction is proposed. The model was tested with mercury adsorption on gold-coated cantilevers. Calculated deflections based on the proposed simulation model agree well with measured deflection data. This model gives insight into the interatomic forces that play a significant role in creating adsorption-induced surface stresses and resultant mechanical bending of microcantilevers.
Microstructural and optical properties of self-organized GaN quantum-dot assemblies
Authors: Panin G. N. , Park Y. S. , Kang T. W. , Kim T. W. , Wang K. L. , Bao M.
Published: January 2005

The microstructural and optical properties of GaN quantum-dot (QD) assemblies self-organized in two-dimensional GaN epilayers grown on AlxGa1−xN layers by using plasma-assisted molecular beam epitaxy were investigated with high-resolution scanning electron microscopy (HRSEM) and cathodoluminescence (CL) measurements. The HRSEM images showed that QD assemblies were formed in separate regions of the slightly stressed GaN epilayer on the Al0.4Ga0.6N surface and that the size and the density of the self-organized QD assemblies were affected significantly by the thickness and the surface polarity of the GaN layer. The CL spectra of the GaN QD assemblies showed a blue shift of the near band gap emission, and the position of the emission peak depended on the polarity and the thickness of the GaN epilayer. Deep level luminescence spectra indicated the existence of impurity-assisted QD assembly formation.
A densely distributed high-sensitivity seismograph network in Japan:Hi-net by National Research Institute for Earth Science and DisasterPrevention
Authors: Obara Kazushige , Kasahara Keiji , Hori Sadaki , Okada Yoshimitsu
Published: January 2005

Seismic observations to retrieve various information from the Earth are the basis of seismology. A seismic observation system requires various technologies for vibration sensors, analog-and-digital measurement, data transmission, and computing for mass data analysis, for example. New developments in technology are adopted whenever possible in the construction of seismic observation systems. In Japan, after the disastrous Kobe Earthquake in 1995, a high-density and high-sensitivity seismograph network was constructed. The seismic network, called the National Research Institute for Earth Science and Disaster Prevention (NIED) Hi-net, uniformly covers the Japanese Islands with a spacing of 20–30km. As a result, the detection capability for microearthquakes has been greatly improved, and various research using Hi-net data has indicated that this seismic network has a great potential to resolve the underground structure and various geophysical phenomena as a radar-array oriented toward the Earth. Equipped with modern standard techniques, the Hi-net system is designed to be able to be smoothly upgradeable in the future.
Correlation between macroscopic transport parameters and microscopic electrical properties in GaN
Authors: Witte H. , Krtschil A. , Schrenk E. , Fluegge K. , Dadgar A. , Krost A.
Published: January 2005

In GaN layers grown by metal-organic vapor phase epitaxy on sapphire substrates the temperature-dependent Hall (TDH) and photo-Hall-effect (PHE) measurements show essential differences between undoped and Si-doped GaN. In undoped GaN the maximum of the Hall mobility occurs at temperatures near 300K with a low value. In PHE, an illumination introduces an enhancement of the mobility and a decrease of the electron density. In contrast, in Si-doped GaN the maximum Hall mobility is higher by a factor of 10 and is observed at temperatures between 100 and 180K. The photoinduced changes in the mobility and electron density are only marginal. Intensity dependent PHE measurements suggest the existence of internal potential barriers caused by inhomogeneities in the undoped samples. These results are combined with the surface-potential roughness on a microscale, as determined by scanning surface-potential microscopy (SSPM). In SSPM the undoped layers show strong potential fluctuations while they are lower for the Si-doped GaN samples. A correlation among the rms roughness of the surface potential, the maximum Hall mobility in TDH, and the maximum changes of the photo-Hall mobility is observed. In undoped GaN the mobility seems to be determined by the scattering at inner potential barriers stemming from structural inhomogeneities.
Room-temperature electroluminescence of a Si-based p-i-n diode with β-FeSi2 particles embedded in the intrinsic silicon
Authors: Li Cheng , Suemasu T. , Hasegawa F.
Published: January 2005

A Si-based p-i-n light emitting diode for 1.6μm operation at room temperature has been realized, with β-FeSi2 particles embedded in the unintentionally doped Si prepared by reactive deposition epitaxy. Room-temperature electroluminescence (EL) at 1.6μm was observed with the diode under a forward bias current density of about 2.0A∕cm2 and its intensity increased linearly with the current density. The temperature dependence of EL showed that luminescence was due to interband transitions in the β-FeSi2 particles and the loss of electron confinement at p-p β-FeSi2∕Si heterojunctions follows a thermally activated process with activation energy of about 0.198eV, the conduction band offset at β-FeSi2∕Si heterojunction.
Silicon diffusion in sol–gel derived isotopically enriched silica glasses
Authors: Bracht H. , Staskunaite R. , Haller E. E. , Fielitz P. , Borchardt G. , Grambole D.
Published: January 2005

We performed silicon diffusion experiments with sol–gel derived isotopically enriched silica glasses at temperatures between 1050 °C and 1300 °C. The diffusion profiles were measured by means of time-of-flight secondary ion mass spectrometry. Samples annealed in closed silica ampoules under argon or dry air reveal enhanced Si diffusion compared to Si diffusion in fused silica. On the other hand, annealing in a large alumina tube under O218 ambient yields Si and O diffusion coefficients which approach the results for thermally grown SiO2. The enhanced Si diffusion in sol–gel derived glass is proposed to be due to water residues which lead to the formation of silanol SiOH groups.
Full-dimensional vibrational calculations for H5O2+ using an ab initio potential energy surface
Authors: McCoy Anne B. , Huang Xinchuan , Carter Stuart , Landeweer Marc Y. , Bowman Joel M.
Published: January 2005

We report quantum diffusion Monte Carlo (DMC) and variational calculations in full dimensionality for selected vibrational states of H5O2+ using a new ab initio potential energy surface [X. Huang, B. Braams, and J. M. Bowman, J. Chem. Phys. 122, 044308 (2005)]. The energy and properties of the zero-point state are focused on in the rigorous DMC calculations. OH-stretch fundamentals are also calculated using “fixed-node” DMC calculations and variationally using two versions of the code MULTIMODE. These results are compared with infrared multiphoton dissociation measurements of Yeh et al. [L. I. Yeh, M. Okumura, J. D. Myers, J. M. Price, and Y. T. Lee, J. Chem. Phys. 91, 7319 (1989)]. Some preliminary results for the energies of several modes of the shared hydrogen are also reported.