bluuebunny/crossref_metadata_2025 huggingface dataset:
Block kinematics of the Pacific–North America plate boundary in the southwestern United States from inversion of GPS, seismological, and geologic data
Authors: McCaffrey Robert
Published: July 2005

The active deformation of the southwestern United States (30°–41°N) is represented by a finite number of rotating, elastic‐plastic spherical caps. GPS‐derived horizontal velocities, geologic fault slip rates, transform fault azimuths, and earthquake‐derived fault slip vector azimuths are inverted for block angular velocities, creep on block‐bounding faults, permanent strain rates within the blocks, and the rotations of 11 published GPS velocity fields into to a common North American reference frame. GPS velocities are considered to be a combination of rigid block rotations, recoverable elastic strain rates resulting from friction on block‐bounding faults, and nonrecoverable strain rates resulting from slip on faults within the blocks. The resulting Pacific–North America angular velocity is similar to some published estimates and satisfies transform azimuths and one spreading rate in the Gulf of California, earthquake slip vectors in the Gulf of California and Alaska, and GPS velocities along coastal California and within the Pacific Basin. Published fault slip rates are satisfied except in the southern Mojave Desert where the motion of the Mohave block relative to North America is faster than can be explained by mapped faults. The largest blocks, the Sierra Nevada–Great Valley and the eastern Basin and Range, show permanent strain rates, after removing elastic strain, of only a few nanostrain per year, demonstrating approximately rigid behavior. Observed horizontal strain rates correlate strongly with predicted strain rates from known faults suggesting that the short‐term strains evident in GPS velocities are largely elastic. In only about 20% of the region is distributed deformation needed to match the data, indicating that a plate tectonic style description of the deformation of the western United States is plausible. Most blocks rotate about vertical axes at approximately the same rate as the Pacific (relative to North America), suggesting that locally, spin rates are communicated from block to block, arguing against both floating block and ball‐bearing mechanisms of block rotation. The similarities of the blocks' spin rates to that of the Pacific suggests that the Pacific strongly influences their motions through edge tractions. However, it is shown that the blocks cannot rotate about the Pacific–North America pole without spinning counter to the sense of Pacific–North America shear. Unlike some other broad plate boundaries, in the western United States, vertical axis rotations take up very little of the slip rate budget across the region.
Compressibility of hydrated and anhydrous Na2O‐2SiO2 liquid and also glass to 8 GPa using Brillouin scattering
Authors: Tkachev Sergey N. , Manghnani Murli H. , Williams Quentin , Ming Li Chung
Published: July 2005

Brillouin scattering measurements have been carried out on an aqueous solution of Na2O‐2SiO2 and anhydrous Na2O‐2SiO2 glass and liquid under in situ pressures to 8 GPa in the temperature range from 300 to 850 K. This temperature range spans through the glass transition of both the hydrous and anhydrous forms of Na2O‐2SiO2. The “modified” platelet scattering geometry has allowed us for the first time to determine VP independently from refractive index and hence the adiabatic compressibility and density of liquids as a function of pressure and temperature. The observed increase in density of the melt and glass phases formed at high‐pressure‐temperature conditions is likely associated with structural effects. There is a marked change in pressure derivative of adiabatic bulk modulus (K′S = dKS/dP) between the two phases. The large values of K′S of the liquid phase illustrate that the means of compaction of the liquid differ substantially from those of the glass and that the liquid is able to access a wider range of compaction mechanisms. The measured bulk modulus of the aqueous sodium silicate solution is highly temperature‐dependent but is much more similar to values of silicate melts than to that of end‐member water, particularly at high pressures. Thus water‐rich silica‐bearing solutions present at depth are likely to be difficult to seismically distinguish from anhydrous silicate melts solely on the basis of their sound velocities. The data on water‐bearing compounds allow the pressure dependence of the partial molar volume of water to be assessed to upper mantle depths. These results are in excellent agreement with prior determinations and illustrate the utility of Brillouin experiments coupled with the externally heated diamond anvil cell in determining partial molar properties of liquids at high pressures.
Source mechanism of Vulcanian degassing at Popocatépetl Volcano, Mexico, determined from waveform inversions of very long period signals
Authors: Chouet Bernard , Dawson Phillip , Arciniega‐Ceballos Alejandra
Published: July 2005

The source mechanism of very long period (VLP) signals accompanying volcanic degassing bursts at Popocatépetl is analyzed in the 15–70 s band by minimizing the residual error between data and synthetics calculated for a point source embedded in a homogeneous medium. The waveforms of two eruptions (23 April and 23 May 2000) representative of mild Vulcanian activity are well reproduced by our inversion, which takes into account volcano topography. The source centroid is positioned 1500 m below the western perimeter of the summit crater, and the modeled source is composed of a shallow dipping crack (sill with easterly dip of 10°) intersecting a steeply dipping crack (northeast striking dike dipping 83° northwest), whose surface extension bisects the vent. Both cracks undergo a similar sequence of inflation, deflation, and reinflation, reflecting a cycle of pressurization, depressurization, and repressurization within a time interval of 3–5 min. The largest moment release occurs in the sill, showing a maximum volume change of 500–1000 m3, pressure drop of 3–5 MPa, and amplitude of recovered pressure equal to 1.2 times the amplitude of the pressure drop. In contrast, the maximum volume change in the dike is less (200–300 m3), with a corresponding pressure drop of 1–2 MPa and pressure recovery equal to the pressure drop. Accompanying these volumetric sources are single‐force components with magnitudes of 108 N, consistent with melt advection in response to pressure transients. The source time histories of the volumetric components of the source indicate that significant mass movement starts within the sill and triggers a mass movement response in the dike within a few seconds. Such source behavior is consistent with the opening of a pathway for escape of pent‐up gases from slow pressurization of the sill driven by magma crystallization. The opening of this pathway and associated rapid evacuation of volcanic gases induces the pressure drop. Pressure recovery in the magma filling the sill is driven by diffusion of gases from the resulting supersaturated melt into bubbles. Assuming a penny‐shaped crack at ambient pressure of 40 MPa, the observed pressure and volume variations can be modeled with the following attributes: crack radius (100 m), crack aperture (5 m), bubble number density (1010–1012 m−3), initial bubble radius (10−6 m), final bubble radius (∼10−5 m), and net decrease of gas concentration in the melt (0.01 wt %).
Overview of technical approaches to radio frequency interference mitigation
Authors: Briggs F. H. , Kocz J.
Published: July 2005

This overview provides an interface between lines of thought on radio frequency interference (RFI) mitigation in the fields of radio astronomy and signal processing. The goal is to explore the commonality of different approaches to help researchers in both fields interpret each other's concepts and jargon. The paper elaborates on the astronomers' concept of gain closure relations and how they may be used in a “self‐calibrating” system of RFI cancellation. Further discussion of the eigen‐decomposition method in terms of RFI power and antenna gains introduces adaptive nulling and RFI cancellation through matrix partitioning. While multipath scattering appears at first glance to be fatal to methods of RFI cancellation, its effect is easily incorporated in frequency‐dependent gain coefficients under many circumstances.
Bed and bank evolution of bifurcating channels
Authors: Bertoldi W. , Tubino M.
Published: July 2005

The evolution of natural river channels is strongly affected by the interplay between the altimetric pattern and the planimetric configuration acting contemporary in branches of braided rivers. Very few quantitative observations are presently available to characterize such interactions. In the present contribution we discuss the results of experimental runs performed with both uniform and graded sediments. The experiments were aimed at describing quantitatively the evolution of a single laterally unconstrained channel until the occurrence of the first bifurcation. An objective criterion for the occurrence of the bifurcation has been established using the data provided by the Fourier analysis of the evolving bank profiles; the procedure enabled us to characterize the morphodynamic sequence leading to flow and channel bifurcation. The sought outcome of the investigation is to derive a suitable description of the bifurcation process to be implemented in predictive models for braiding evolution, for which physically based nodal point conditions would be highly desirable.
Estimating contaminant loads in rivers: An application of adjusted maximum likelihood to type 1 censored data
Authors: Cohn Timothy A.
Published: July 2005

This paper presents an adjusted maximum likelihood estimator (AMLE) that can be used to estimate fluvial transport of contaminants, like phosphorus, that are subject to censoring because of analytical detection limits. The AMLE is a generalization of the widely accepted minimum variance unbiased estimator (MVUE), and Monte Carlo experiments confirm that it shares essentially all of the MVUE's desirable properties, including high efficiency and negligible bias. In particular, the AMLE exhibits substantially less bias than alternative censored‐data estimators such as the MLE (Tobit) or the MLE followed by a jackknife. As with the MLE and the MVUE the AMLE comes close to achieving the theoretical Frechet‐Cramér‐Rao bounds on its variance. This paper also presents a statistical framework, applicable to both censored and complete data, for understanding and estimating the components of uncertainty associated with load estimates. This can serve to lower the cost and improve the efficiency of both traditional and real‐time water quality monitoring.
Case study of inhomogeneous cloud parameter retrieval from MODIS data
Authors: Cornet Céline , Buriez Jean‐Claude , Riédi Jérôme , Isaka Harumi , Guillemet Bernard
Published: July 2005

Cloud parameter retrieval of inhomogeneous and fractional clouds is performed for a stratocumulus scene observed by MODIS at a solar zenith angle near 60°. The method is based on the use of neural network technique with multispectral and multiscale information. It allows to retrieve six cloud parameters, i.e. pixel means and standard deviations of optical thickness and effective radius, fractional cloud cover, and cloud top temperature. Retrieved cloud optical thickness and effective radius are compared to those retrieved with a classical method based on the homogeneous cloud assumption. Subpixel fractional cloud cover and optical thickness inhomogeneity are compared with their estimates obtained from 250m pixel observations; this comparison shows a fairly good agreement. The cloud top temperature appears also retrieved quite suitably.
Interannual variability of diurnal tide in the tropical mesopause region: A signature of the El Nino‐Southern Oscillation (ENSO)
Authors: Gurubaran S. , Rajaram R. , Nakamura T. , Tsuda T.
Published: July 2005

Long‐term MLT radar observations of the diurnal tide at 86 km over Jakarta (6.4°S, 106.7°E) and Tirunelveli (8.7°N, 77.8°E) during the years 1993–1999 are examined in this work. Monthly estimates of tidal amplitudes in the meridional direction over these sites reveal a pronounced interannual variability. The satellite derived Outgoing Longwave Radiation (OLR) is used as a proxy for deep tropical convection in this study. Removal of composite seasonal cycle yields ‘anomalies’ in the diurnal tide over Jakarta and Tirunelveli that are correlated with the OLR anomalies over the western Pacific region (∼120°E). It is suggested that the lower atmospheric large‐scale convective systems originating over the western Pacific region in response to the El Nino Southern Oscillation (ENSO) facilitate excitation of nonmigrating tides through latent heat release or large‐scale redistribution of water vapor that compete with the dominant migrating tide and possibly induce the observed interannual variability in the diurnal tide.
Detection of thirteen resonances of radio waves from particularly intense lightning discharges
Authors: Füllekrug Martin
Published: July 2005

Thirteen resonances of radio waves from particularly intense lightning discharges in the Earth's atmosphere are detected in the frequency range from 5–90 Hz. The inferred frequency dependent relative wave propagation velocities are in excellent agreement with theoretical predictions. The full sequence of the resonance frequencies may be used to monitor the global ionospheric D‐layer height variability resulting from space weather phenomena.
Antarctic mesospheric clouds formed from space shuttle exhaust
Authors: Stevens Michael H. , Meier R. R. , Chu Xinzhao , DeLand Matthew T. , Plane John M. C.
Published: July 2005

New satellite observations reveal lower thermospheric transport of a space shuttle exhaust plume into the southern hemisphere two days after a January, 2003 launch. A day later, ground‐based lidar observations in Antarctica identify iron ablated from the shuttle's main engines. Additional satellite observations of polar mesospheric clouds (PMCs) show a burst that constitutes 10–20% of the PMC mass between 65–79°S during the 2002–2003 season, comparable to previous results for an Arctic shuttle plume. This shows that shuttle exhaust can be an important global source of both PMC formation and variability.
Aerosols over Delhi during pre‐monsoon months: Characteristics and effects on surface radiation forcing
Authors: Singh Sachchidanand , Nath Shambhu , Kohli Ramesh , Singh Risal
Published: July 2005

The surface fluxes in the wavelength range 280–2800 nm were measured during the pre‐monsoon period, April–June 2003 along with the spectral distribution of aerosol optical depth (AOD) in the visible and near infrared wavelengths. The Ångström exponent alpha retrieved from the data showed abundance of desert aerosols over Delhi during this period. The aerosol composition constructed using the OPAC model indicated a typical mixture of two aerosol types: urban and desert. Due to this the aerosol mixture had a very low value of single scattering albedo ∼0.67. The average total radiative forcing efficiency observed at the surface in the broad wavelength band (280–2800 nm) was estimated and compared with the SBDART model calculated values.
GPS radio occultation with GRACE: Atmospheric profiling utilizing the zero difference technique
Authors: Beyerle G. , Schmidt T. , Michalak G. , Heise S. , Wickert J. , Reigber C.
Published: July 2005

Radio occultation events recorded on 28–29 July 2004 by a GPS receiver aboard the GRACE‐B satellite are analyzed. The stability of the receiver clock allows for the derivation of excess phase profiles using a zero difference technique, rendering the calibration procedure with concurrent observations of a reference GPS satellite obsolete. 101 refractivity profiles obtained by zero differencing and 96 profiles calculated with an improved single difference method are compared with co‐located ECMWF meteorological analyses. Good agreement is found at altitudes between 5 and 30 km with an average fractional refractivity deviation below 1% and a standard deviation of 2–3%. Results from end‐to‐end simulations are consistent with these observations.
Elastic waves push organic fluids from reservoir rock
Authors: Beresnev Igor A. , Vigil R. Dennis , Li Wenqing , Pennington Wayne D. , Turpening Roger M. , Iassonov Pavel P. , Ewing Robert P.
Published: July 2005

Elastic waves have been observed to increase productivity of oil wells, although the reason for the vibratory mobilization of the residual organic fluids has remained unclear. Residual oil is entrapped as ganglia in pore constrictions because of resisting capillary forces. An external pressure gradient exceeding an “unplugging” threshold is needed to carry the ganglia through. The vibrations help overcome this resistance by adding an oscillatory inertial forcing to the external gradient; when the vibratory forcing acts along the gradient and the threshold is exceeded, instant “unplugging” occurs. The mobilization effect is proportional to the amplitude and inversely proportional to the frequency of vibrations. We observe this dependence in a laboratory experiment, in which residual saturation is created in a glass micromodel, and mobilization of the dyed organic ganglia is monitored using digital photography. We also directly demonstrate the release of an entrapped ganglion by vibrations in a computational fluid‐dynamics simulation.
High‐resolution analysis of the gravest seismic normal modes after the 2004 Mw = 9 Sumatra earthquake using superconducting gravimeter data
Authors: Rosat S. , Sato T. , Imanishi Y. , Hinderer J. , Tamura Y. , McQueen H. , Ohashi M.
Published: July 2005

The Mw > 9 Sumatra‐Andaman earthquake on December 26, 2004 has strongly excited the low‐frequency seismic modes and is a unique opportunity to improve the frequency and damping measurements of the gravest seismic modes. The precise estimation of the frequency splitting of the seismic modes below 1 mHz is needed to improve 1D‐density models of the Earth. From this event, 2S1 is observed for the first time without any stacking on both SG (Superconducting Gravimeter) and seismic records. We report here analyses of SG data obtained from 11 sites. The spectra of SG records clearly show the splitting of 0S2 into 5 completely resolved singlets and the splitting of 0S3 into 7 singlets at individual stations. The present results demonstrate that SGs provide high quality data for a precise analysis of the low‐frequency seismic modes.
High temperature elastic anisotropy of the perovskite and post‐perovskite polymorphs of Al2O3
Authors: Stackhouse Stephen , Brodholt John P. , Price G. David
Published: July 2005

Finite temperature ab initio molecular dynamics calculations were performed to determine the high temperature elastic and seismic properties of the perovskite and post‐perovskite phases of pure end‐member Al2O3. The post‐perovskite phase exhibits very large degrees of shear‐wave splitting. The incorporation of a few mole percent of Al2O3 into MgSiO3 is predicted to have little effect on the perovskite to post‐perovskite phase transition pressure and seismic properties of the post‐perovskite phase; although a small difference in shear‐wave splitting may be observable.
Tracking painted pebbles: Short‐term rates of sediment movement on four Mojave Desert piedmont surfaces
Authors: Persico Lyman P. , Nichols Kyle K. , Bierman Paul R.
Published: July 2005

To quantify short‐term sediment movement rates across Mojave Desert piedmonts, 1600 painted and numbered pebbles were laid out in paired, orthogonal, 20 m lines at 4 sites and resurveyed five times over 2 years and revisited 2 years later. Pebble lines cross shallow (5–15 cm), ephemeral channels and adjacent unconsolidated interfluves, the latter being the dominant landform at all sites. Two sites are located on surfaces that have been or are impacted by military training activities, including the use of tracked vehicles. The two other sites have not been disturbed by human impact. Three different processes transport pebbles. Episodic streamflow in ephemeral channels transports a few pebbles long distances (decimeters to meters) down gradient. Bioturbation moves many pebbles small distances (centimeters) in any direction, and vehicular disturbance transports pebbles varying distances (centimeters to meters) in any direction. Significant down‐gradient sediment movement occurred dominantly in channels where flowing water was concentrated. Interfluves were stable surfaces where little transport occurred. Off‐road vehicle use is coincident with accelerated pebble movement. Pebbles moved further and faster down gradient at the disturbed Iron Mountain and East Range Road sites (mean speeds of 0.18 and 0.34 m yr−1, respectively) than at the undisturbed Chemehuevi and Goldstone sites, (mean speeds of 0.17 and 0.02 m yr−1, respectively). Mean pebble movement is highly and negatively correlated with vegetation density. Short‐term pebble movement rates are several times lower than long‐term (103 to 104 year) rates, suggesting the importance of rare, extreme precipitation events for sediment transport such as those of fall and winter 2004.
Collision-induced conformational changes in glycine
Authors: Miller Thomas F. , Clary David C. , Meijer Anthony J. H. M.
Published: July 2005

We present quantum dynamical calculations on the conformational changes of glycine in collisions with the He, Ne, and Ar rare-gas atoms. For two conformer interconversion processes (III→I and IV→I), we find that the probability of interconversion is dependent on several factors, including the energy of the collision, the angle at which the colliding atom approaches the glycine molecule, and the strength of the glycine-atom interaction. Furthermore, we show that attractive interactions between the colliding atom and the glycine molecule catalyze conformer interconversion at low collision energies. In previous infrared spectroscopy studies of glycine trapped in rare-gas matrices and helium clusters, conformer III has been consistently observed, but conformer IV has yet to be conclusively detected. Because of the calculated thermodynamic stability of conformer IV, its elusiveness has been attributed to the IV→I conformer interconversion process. However, our calculations present little indication that IV→I interconversion occurs more readily than III→I interconversion. Although we cannot determine whether conformer IV interconverts during experimental Ne- and Ar-matrix depositions, our evidence suggests that the conformer should be present in helium droplets. Anharmonic vibrational frequency calculations illustrate that previous efforts to detect conformer IV may have been hindered by the overlap of its IR-absorption bands with those of other conformers. We propose that the redshifted symmetric −CH2 stretch of conformer IV provides a means for its conclusive experimental detection.
Density functional energy decomposition into one- and two-atom contributions
Authors: Vyboishchikov Sergei F. , Salvador Pedro , Duran Miquel
Published: July 2005

The present work provides a generalization of Mayer’s energy decomposition for the density-functional theory (DFT) case. It is shown that one- and two-atom Hartree–Fock energy components in Mayer’s approach can be represented as an action of a one-atom potential VA on a one-atom density ρA or ρB. To treat the exchange-correlation term in the DFT energy expression in a similar way, the exchange-correlation energy density per electron is expanded into a linear combination of basis functions. Calculations carried out for a number of density functionals demonstrate that the DFT and Hartree–Fock two-atom energies agree to a reasonable extent with each other. The two-atom energies for strong covalent bonds are within the range of typical bond dissociation energies and are therefore a convenient computational tool for assessment of individual bond strength in polyatomic molecules. For nonspecific nonbonding interactions, the two-atom energies are low. They can be either repulsive or slightly attractive, but the DFT results more frequently yield small attractive values compared to the Hartree–Fock case. The hydrogen bond in the water dimer is calculated to be between the strong covalent and nonbonding interactions on the energy scale.
Different chemical dynamics for different conformers of biological molecules: Photoionization of glycine
Authors: Shemesh D. , Gerber R. B.
Published: July 2005

Single-photon ionization dynamics of two conformers of glycine is studied by classical trajectory simulations using the semiempirical PM3 potential surface in “on the fly” calculations. Initial conditions for the trajectories are weighted according to the Wigner distribution function computed for the initial vibrational ground state. Vertical ionization in the spirit of the classical Franck–Condon principle is assumed. The dynamics of the two conformers are compared during the first 10ps. The comparison shows very different dynamical behavior for the two conformers. In particular, the chemical fragmentation pathways differ in part. Also, one of the conformers gives much higher rates of conformational transitions, while the other conformer gives larger chemical fragmentation yields. The example shows significantly different chemical dynamics for two conformers close in energy and separated by a low barrier.
From dimer to condensed phases at extreme conditions: Accurate predictions of the properties of water by a Gaussian charge polarizable model
Authors: Paricaud Patrice , Předota Milan , Chialvo Ariel A. , Cummings Peter T.
Published: July 2005

Water exhibits many unusual properties that are essential for the existence of life. Water completely changes its character from ambient to supercritical conditions in a way that makes it possible to sustain life at extreme conditions, leading to conjectures that life may have originated in deep-sea vents. Molecular simulation can be very useful in exploring biological and chemical systems, particularly at extreme conditions for which experiments are either difficult or impossible; however this scenario entails an accurate molecular model for water applicable over a wide range of state conditions. Here, we present a Gaussian charge polarizable model (GCPM) based on the model developed earlier by Chialvo and Cummings [Fluid Phase Equilib. 150, 73 (1998)] which is, to our knowledge, the first that satisfies the water monomer and dimer properties, and simultaneously yields very accurate predictions of dielectric, structural, vapor-liquid equilibria, and transport properties, over the entire fluid range. This model would be appropriate for simulating biological and chemical systems at both ambient and extreme conditions. The particularity of the GCPM model is the use of Gaussian distributions instead of points to represent the partial charges on the water molecules. These charge distributions combined with a dipole polarizability and a Buckingham exp-6 potential are found to play a crucial role for the successful and simultaneous predictions of a variety of water properties. This work not only aims at presenting an accurate model for water, but also at proposing strategies to develop classical accurate models for the predictions of structural, dynamic, and thermodynamic properties.
Mechanics of hydrogenated amorphous carbon deposits from electron-beam-induced deposition of a paraffin precursor
Authors: Ding W. , Dikin D. A. , Chen X. , Piner R. D. , Ruoff R. S. , Zussman E. , Wang X. , Li X.
Published: July 2005

Many experiments on the mechanics of nanostructures require the creation of rigid clamps at specific locations. In this work, electron-beam-induced deposition (EBID) has been used to deposit carbon films that are similar to those that have recently been used for clamping nanostructures. The film deposition rate was accelerated by placing a paraffin source of hydrocarbon near the area where the EBID deposits were made. High-resolution transmission electron microscopy, electron-energy-loss spectroscopy, Raman spectroscopy, secondary-ion-mass spectrometry, and nanoindentation were used to characterize the chemical composition and the mechanics of the carbonaceous deposits. The typical EBID deposit was found to be hydrogenated amorphous carbon (a-C:H) having more sp2- than sp3-bonded carbon. Nanoindentation tests revealed a hardness of ∼4GPa and an elastic modulus of 30–60GPa, depending on the accelerating voltage. This reflects a relatively soft film, which is built out of precursor molecular ions impacting the growing surface layer with low energies. The use of such deposits as clamps for tensile tests of poly(acrylonitrile)-based carbon nanofibers loaded between opposing atomic force microscope cantilevers is presented as an example application
Polar anchoring energy measurement of vertically aligned liquid-crystal cells
Authors: Nie Xiangyi , Lin Yi-Hsin , Wu Thomas X. , Wang Haiying , Ge Zhibing , Wu Shin-Tson
Published: July 2005

An electric-field method is developed for measuring the polar anchoring energy of vertically aligned nematic liquid-crystal cells. Both theoretical analyses and confirming experimental results are presented. Vertically aligned liquid-crystal cells with buffed polyimide alignment layers are used to investigate the measurement techniques. Based on the voltage-dependent transmittance of the liquid-crystal cells, a linear fitting can be obtained, leading to a precise determination of the anchoring energy. If some specific liquid-crystal material parameters are known, measuring of the cell capacitance is not necessary.
Numerical description of discharge characteristics of the plasma needle
Authors: Brok W. J. M. , Bowden M. D. , van Dijk J. , van der Mullen J. J. A. M. , Kroesen G. M. W.
Published: July 2005

The plasma needle is a small atmospheric, nonthermal, radio-frequency discharge, generated at the tip of a needle, which can be used for localized disinfection of biological tissues. Although several experiments have characterized various qualities of the plasma needle, discharge characteristics and electrical properties are still not well known. In order to provide initial estimates on electrical properties and quantities such as particle densities, we employed a two-dimensional, time-dependent fluid model to describe the plasma needle. In this model the balance equation is solved in the drift-diffusion approach for various species and the electron energy, as well as Poisson’s equation. We found that the plasma production occurs in the sheath region and results in a steady flux of reactive species outwards. Even at small (<0.1%) admixtures of N2 to the He background, N2+ is the dominant ion. The electron density is typically 1011cm−3 and the dissipated power is in the order of 10mW. These results are consistent with the experimental data available and can give direction to the practical development of the plasma needle.
Epitaxial growth on silicon and characterization of MnF2 and ZnF2 layers with metastable orthorhombic structure
Authors: Kaveev A. K. , Anisimov O. V. , Banshchikov A. G. , Kartenko N. F. , Ulin V. P. , Sokolov N. S.
Published: July 2005

The growth of MnF2 and ZnF2 layers on Si(001) and Si(111) substrates was studied by molecular-beam epitaxy. Calcium fluoride buffer layers with (001), (110), and (111) orientations were used to prevent chemical interaction of MnF2 and ZnF2 molecules with the Si substrate. The analysis of x-ray and reflection high-energy electron-diffraction (RHEED) patterns showed that MnF2 layers grow on all of these planes in the orthorhombic α-PbO2-type crystal phase observed earlier only at high pressures and temperatures. Atomic force microscopy revealed a strong dependence of the surface morphology on the buffer orientation and growth temperature. The best-ordered MnF2 growth occurred at 500 °C on a CaF2 (110) buffer layer. The diffraction analysis enabled us to find the epitaxial relations at the MnF2∕CaF2 interface. A careful analysis of the RHEED patterns of the films grown on CaF2(001) showed a similarity in the structure and growth modes between MnF2 and ZnF2 layers, with ZnF2 tending to form multiphase layers. These findings are in agreement with the x-ray diffraction measurements.
Impact of dislocation densities on n+∕p and p+∕n junction GaAs diodes and solar cells on SiGe virtual substrates
Authors: Andre C. L. , Wilt D. M. , Pitera A. J. , Lee M. L. , Fitzgerald E. A. , Ringel S. A.
Published: July 2005

Recent experimental measurements have shown that in GaAs with elevated threading dislocation densities (TDDs) the electron lifetime is much lower than the hole lifetime [C. L. Andre, J. J. Boeckl, D. M. Wilt, A. J. Pitera, M. L. Lee, E. A. Fitzgerald, B. M. Keyes, and S. A. Ringel, Appl. Phys. Lett. 84, 3884 (2004)]. This lower electron lifetime suggests an increase in depletion region recombination and thus in the reverse saturation current (J0 for an n+∕p diode compared with a p+∕n diode at a given TDD. To confirm this, GaAs diodes of both polarities were grown on compositionally graded Ge∕Si1−xGex∕Si (SiGe) substrates with a TDD of 1×106cm−2. It is shown that the ratio of measured J0 values is consistent with the inverse ratio of the expected lifetimes. Using a TDD-dependent lifetime in solar cell current–voltage models we found that the Voc, for a given short-circuit current, also exhibits a poorer TDD tolerance for GaAs n+∕p solar cells compared with GaAs p+∕n solar cells. Experimentally, the open-circuit voltage (Voc) for the n+∕p GaAs solar cell grown on a SiGe substrate with a TDD of ∼1×106cm−2 was ∼880mV which was significantly lower than the ∼980mV measured for a p+∕n GaAs solar cell grown on SiGe at the same TDD and was consistent with the solar cell modeling results reported in this paper. We conclude that p+∕n polarity GaAs junctions demonstrate superior dislocation tolerance than n+∕p configured GaAs junctions, which is important for optimization of lattice-mismatched III–V devices.
Structural transformation of SbxSe100−x thin films for phase change nonvolatile memory applications
Authors: Kang M. J. , Choi S. Y. , Wamwangi D. , Wang K. , Steimer C. , Wuttig M.
Published: July 2005

The structural transformation and transformation kinetics of SbxSe100−x films (60⩽x⩽70) were studied to investigate the feasibility of applying SbxSe100−x alloys in phase change nonvolatile memories. Temperature-dependent van der Pauw measurements, x-ray diffraction, x-ray reflectometry, and a static tester were used to determine the structure and transformation kinetics of the SbxSe100−x films. The sheet resistance difference between the amorphous and crystalline states was higher than 104Ω∕◻. The crystalline structure of the metastable phase of SbxSe100−x alloys, which plays a major role in fast crystallization, is similar to that of Sb2Te (rhombohedral structure). The transition temperature, sheet resistance, and activation energy for transformation decrease as the amount of Sb increases in the SbxSe100−x film. The density and thickness variation of the Sb65Se35 thin film were 5.9% and 5.4%, respectively. Applying the Kissinger method, the activation energies for crystallization were in the range from 1.90±0.15to4.16±0.28eV. The desired crystallization speed can be obtained by a systematic change of the composition owing to the variation of the activation barrier with stoichiometry.
Scattering of edge currents through quantum point contacts
Authors: Cresti Alessandro
Published: July 2005

The distribution of currents through a narrow quantum point-contact device in a two-dimensional electron gas threaded by a perpendicular magnetic field is obtained by means of the Keldysh Green’s function formalism in the tight-binding one-electron framework. I show that chiral transport occurs in the regions far from the quantum point-contact scattering zone and I verify the exact quantization of the impinging current and of the transmitted plus backscattered current. An analysis of the density of occupied states in different regions of the system is also carried out.
Magnetic and transport properties of Mo substituted La0.67Ba0.33Mn1−xMoxO3 perovskite system
Authors: Kundaliya Darshan C. , Vij Reeta , Kulkarni R. G. , Varughese B. , Nigam A. K. , Malik S. K.
Published: July 2005

The effect of doping Mo for Mn on the magnetic and transport properties of the colossal magnetoresistance material La0.67Ba0.33MnO3 has been studied. Compounds of the series La0.67Ba0.33Mn1−xMoxO3(x=0.0–0.1) have been prepared and found to crystallize in the orthorhombic structure (space group Pbnm). Energy dispersive x-ray analysis measurements confirm the stoichiometry of all the samples. Magnetotransport and magnetization measurements reveal that the metal-insulator transition temperature (Tp) decreases from 330 K for x=0 to 255 K for x=0.1. The change in Tp on Mo substitution is relatively much smaller than the corresponding change observed on substitution by other transition elements, such as Ti, Fe, Co, Ni, etc. Further, the ferromagnetic transition temperature (TC) is nearly unchanged by Mo substitution. This is in striking contrast to the large decrease in TC observed with substitution of the above-mentioned 3d elements. These unusual magnetic and transport properties of La0.67Ba0.33Mn1−xMoxO3 may be either due to the formation of a magnetic pair between Mn and Mo or due to strong Mo(4d)–O(2p) overlap, which in turn, may affect the Mn–Mn interaction via the oxygen atoms.
Coarse graining using pretabulated potentials: Liquid benzene
Authors: Zacharopoulos Nikolas , Vergadou Niki , Theodorou Doros N.
Published: July 2005

The large length and time scales involved in polymer simulation render the atomistic representation of polymer systems a computationally expensive and unnecessarily detailed procedure. We present a novel coarse-graining method for the description of nonbonded interactions between moieties composing the monomeric units of polymers, phenyl rings in particular. The method is based on the determination of the interactions between pairs of moieties from precalculated and tabulated values of the energy between the moieties in their atomistic representation. Validation of the method is performed by carrying out coarse-grained and fully atomistic simulations of a benzene liquid, where structural and thermodynamic properties at various state points are compared. The effects of the coarse grained model assumptions and of the energy table dimension and discretization are investigated. Results are also presented for the reverse mapping from the coarse grained to the fully atomistic representation.
Fabrication of efficient microaxicon by direct electron-beam lithography for long nondiffracting distance of Bessel beams for optical manipulation
Authors: Cheong W. C. , Ahluwalia B. P. S. , Yuan X.-C. , Zhang L.-S. , Wang H. , Niu H. B. , Peng X.
Published: July 2005

We demonstrate a fabrication technique in the realization of microaxicon by single-step processing via electron-beam lithography. Microaxicon is used for the generation of propagation-invariant Bessel beams which find tremendous applications in optical trapping. The proposed technique is a simple, reliable, and reproducible method for the production of high-quality Bessel beams with long propagation-invariant distances, in our configuration, in excess of 20cm. Such Bessel beams with long nondiffracting distances are essential for optical tweezers systems in many cases.
Steady flows in pipes with finite curvature
Authors: Siggers J. H. , Waters S. L.
Published: July 2005

Motivated by blood flow in a curved artery, we consider fluid flow through a uniformly curved pipe, driven by a steady pressure gradient. Previous studies have typically considered pipes with asymptotically small curvature in which only the centrifugal effect is retained in the governing equations. Here we consider flows in pipes of finite curvature, and determine the effects of both the centrifugal and Coriolis forces on the flow. The flow behavior is governed by two dimensionless parameters: the curvature, δ, and the Dean number, D. Asymptotic solutions are developed for D⪡1 (using regular perturbation expansions) and D⪢1 (using matched asymptotic expansions and the Pohlhausen method). For intermediate values of D we use a pseudospectral code to obtain solutions. For values of D greater than a critical value, Dc, multiple steady solutions to the governing equations exist; we determine how Dc and the form of the solutions depends on δ. The results indicate that while many of the qualitative features of steady curved-pipe flows are captured by the asymptotic results, the effects of finite curvature can lead to substantial quantitative differences, e.g., in the wall shear stress distribution. The physiological implications of the results for blood flow in arteries are discussed.
Coupled hydrodynamic and diffusional-thermal instabilities in flame propagation at subunity Lewis numbers
Authors: Yuan Jiao , Ju Yiguang , Law Chung K.
Published: July 2005

The dynamics of flame cell evolution due to the coupling between hydrodynamic and diffusional-thermal instabilities in subunity Lewis number flames was simulated using a sixth-order central difference scheme and newly developed nonreflective boundary conditions. Results show that the interaction between these two modes of instabilities yields distinct evolutions of cell splitting, merging, growth, local extinction, and lateral motion, leading to fluctuations of the flow and species concentrations as well as substantial increase in the flame speed. The study also demonstrates that small computational domains cannot correctly predict cell merging and transverse motion.
Titanium-added praseodymium silicate high-k layers on Si(001)
Authors: Schroeder T. , Lupina G. , Dabrowski J. , Mane A. , Wenger Ch. , Lippert G. , Müssig H.-J.
Published: July 2005

Titanium-added praseodymium silicate layers on Si(001) are promising high-k insulators for silicon-based nanoelectronic devices. Synchrotron radiation x-ray photoelectron spectroscopy was applied to study the effect of titanium additives on the praseodymium silicate/Si system. Nondestructive depth profiling by variation of the photon energy shows that thermal annealing activates the diffusion of deposited titanium into the praseodymium silicate. A homogeneous praseodymium titanium silicate layer is formed that shows high-quality electrical properties.
Velocity measurement in turbulent boundary layer of drag-reducing surfactant solution
Authors: Itoh Motoyuki , Tamano Shinji , Yokota Kazuhiko , Ninagawa Masato
Published: July 2005

The influence of a drag-reducing surfactant on a zero-pressure gradient turbulent boundary layer was investigated using a two-component laser-Doppler velocimetry system. It was discovered that the streamwise turbulence intensity has a maximum near the center of the boundary layer in addition to the near-wall maximum which appears in canonical wall-bounded turbulent flow. At the location of the additional maximum, the Reynolds shear stress has a slight maximum, the skewness factor of streamwise turbulent fluctuation is zero, and the flatness factor has a minimum.
Control of drop positioning using chemical patterning
Authors: Dupuis A. , Léopoldès J. , Bucknall D. G. , Yeomans J. M.
Published: July 2005

We explore how chemical patterning on surfaces can be used to control drop wetting. Both numerical and experimental results are presented to show how the dynamic pathway and equilibrium shape of the drops are altered by a hydrophobic grid. The grid proves a successful way of confining drops and we show that it can be used to alleviate mottle, a degradation in image quality which results from uneven drop coalescence due to randomness in the positions of the drops within the jetted array.
GaAs on Si(111)—crystal shape and strain relaxation in nanoscale patterned growth
Authors: Lee S. C. , Dawson L. R. , Brueck S. R. J. , Jiang Y.-B.
Published: July 2005

Nanoscale patterned growth of GaAs on Si(111) by molecular beam epitaxy is examined. A 355 nm period two-dimensional array of circular holes (diameter ∼200–250nm) is fabricated into a 45-nm-thick SiO2 film on a Si(111) substrate by large-area interferometric lithography and dry etching. For 300 nm deposition, the GaAs epilayer selectively deposited within each hole on the patterned substrate is surrounded by {11¯0}-type sidewalls perpendicular to Si(111), resulting in a hexagon-based prismatic pillar, without significant lateral overgrowth. At the initial stage of growth, twins parallel to Si(111) and an aperiodic mixture of cubic and hexagonal phases are observed but most of the GaAs pillars are terminated with a cubic phase region. Raman scattering reveals that the individual nanoscale GaAs pillars are completely strain relaxed.
Three-dimensional confocal thermal imaging using anti-Stokes luminescence
Authors: Kachynski A. V. , Kuzmin A. N. , Pudavar H. E. , Prasad P. N.
Published: July 2005

High-resolution thermal images of dye-stained live cells are obtained using confocal anti-Stokes luminescence on a confocal laser scanning microscope. Stokes and anti-Stokes fluorescence signal ratio imaging, using dual laser excitation with a fast alternate line scan, is used to monitor dynamical temperature changes at submicrometer resolution. Temperature mapping of a dye-doped polymer film with local heating is shown as an example. Three-dimensional mapping of local temperature changes in living cells induced by an external laser as the heating source, is obtained with temperature resolution better than 0.5 K.
Electrical initialization and manipulation of electron spins in an L-shaped strained n-InGaAs channel
Authors: Kato Y. K. , Myers R. C. , Gossard A. C. , Awschalom D. D.
Published: July 2005

An L-shaped strained n-InGaAs channel is used to polarize and subsequently rotate electron spins solely by means of electric fields. Precession of electrically excited spins in the absence of applied magnetic fields is directly observed by Kerr rotation microscopy. In addition, in-plane and out-of-plane components of the spin polarization in the channel are simultaneously imaged.
Time-resolved chirp in an InAs∕InP quantum-dash optical amplifier operating with 10Gbit∕s data
Authors: Hadass D. , Mikhelashvili V. , Eisenstein G. , Somers A. , Deubert S. , Kaiser W. , Reithmaier J. P. , Forchel A. , Finzi D. , Maimon Y.
Published: July 2005

We describe time-resolved chirp measurements in InAs∕InP quantum-dash optical amplifiers operating at 1550 nm. We highlight the roles of gain saturation and of the saturating pulse duration relative to the gain recovery time. Using 10Gbit∕s data, we demonstrate a low transient α parameter of less than one which causes negative chirp at the leading edge and positive chirp during the trailing edge of the input pulse.
Approach to nonphotoperturbed differential capacitance measurements: A front-wing cantilever
Authors: Chang M. N. , Chen C. Y. , Huang W. J. , Cheng T. C.
Published: July 2005

We have developed a front-wing (FW) cantilever structure that can significantly suppress photoperturbation effects during scanning capacitance microscopy (SCM) and scanning capacitance spectroscopy (SCS) measurements. The FW cantilever provides an effective shadow area that fully covers the scan region, allowing us to synchronously obtain SCM images and the corresponding topographic images without photoperturbation problems. Nonphotoperturbed differential capacitance characteristics versus tip biases were also obtained for SCS by the use of these FW cantilevers. This means that nonphotoperturbed SCM and SCS measurements can be carried out during the typical SCM operations.