bluuebunny/crossref_metadata_2025 huggingface dataset:
Prise en charge de la phlegmasia cerulea dolens
Authors: Marty  , Depairon
Published: May 2006

La phlegmasia cerulea dolens (PCD) résulte d'une thrombose aiguë et massive du réseau veineux profond du membre inférieur envahissant souvent les veines iliaques. Elle se caractérise par une extrémité oedématiée fortement cyanosée intense et s'accompagnant de fortes douleurs. Le but thérapeutique est de sauver l'extrémité, d'éviter l'embolie pulmonaire et de prévenir le syndrome post-thrombotique. En cas d'échec thérapeutique conservateur, le traitement de choix se compose d'une thrombectomie iliaque à l'aide d'un ballon et d'une fibrinolyse périphérique simultanée avec expulsion des thrombi fémoro-poplités. La thrombectomie n'est possible qu'au niveau de l'axe iliaque avalvulé. La thrombolyse reste le moyen idéal pour une ablation efficace des thromboses des systèmes veineux superficiel et profond puisque ces derniers sont valvulés sur la plus grande partie de leur trajet. Cet article a essentiellement pour objet le traitement de la phlegmasia. Toutefois, la plupart des études citées concerne le traitement d'une thrombose veineuse profonde importante (TVP) touchant l'axe iliaque et souligne de ce fait que les thromboses ilio-fémorales massives peuvent également êtres considérées comme des indications au traitement invasif.
Junge Patientin mit Pfortader- und Mesenterialvenenthrombose sowie Proteus-Syndrom
Authors: Staub  , Schmid  , Huber
Published: May 2006

Eine junge Patientin mit bekanntem Proteus-Syndrom erlitt im 26. Lebensjahr eine Pfortader- und Mesenterialvenenthrombose. Aufgrund dieser thrombotischen Gefässobstruktion entwickelten sich im weiteren Verlauf im Rahmen einer portalen Hypertension eine Splenomegalie, Ösophagusvarizen mit Blutungen und eine Panzytopenie bei Hypersplenismus. Nach Splenektomie und splenorenaler Shuntoperation normalisierten sich die Blutwerte wieder. Aufgrund dieser untypisch lokalisierten Thrombose, den wiederholten Thrombophlebitiden und dem Proteus-Syndrom wurden umfassende Gerinnungsabklärungen durchgeführt. Diese ergaben ein Antiphospholipid-Syndrom mit einer leichten Hyperhomocysteinämie, welche mit dem gleichzeitigen Vorkommen eines Proteus-Syndroms zu einer hohen Rezidivwahrscheinlichkeit für weitere unter Umständen letale Thrombosen behaftet ist. Aufgrund der kombinierten Risikofaktoren für weitere thrombembolische Ereignisse steht die Patientin unter einer Dauerantikoagulation mit Phenprocoumon und regelmässigen Quickkontrollen.
Locally weighted polynomial regression: Parameter choice and application to forecasts of the Great Salt Lake
Authors: Lall Upmanu , Moon Young‐Il , Kwon Hyun‐Han , Bosworth Ken
Published: May 2006

Relationships between hydrologic variables are often nonlinear. Usually, the functional form of such a relationship is not known a priori. A multivariate, nonparametric regression methodology is provided here for approximating the underlying regression function using locally weighted polynomials. Locally weighted polynomials consider the approximation of the target function through a Taylor series expansion of the function in the neighborhood of the point of estimate. Cross‐validatory procedures for the selection of the size of the neighborhood over which this approximation should take place and for the order of the local polynomial to use are provided and shown for some simple situations. The utility of this nonparametric regression approach is demonstrated through an application to nonparametric short‐term forecasts of the biweekly Great Salt Lake volume. Blind forecasts up to 1 year in the future using the 1847–2004 time series of the Great Salt Lake are presented.
Strategies for successful U‐Th dating of paleolake carbonates: An example from the Bolivian Altiplano
Authors: Placzek Christa , Patchett P. Jonathan , Quade Jay , Wagner Jennifer D. M.
Published: May 2006

We report over 90 U‐Th dates from carbonates deposited around paleolakes on the Bolivian Altiplano. Petrographic and chemical data for tufas and the siliciclastic detritus contained within them allow (1) assessment of possible diagenetic effects, (2) a development of a strategy for selection of carbonate samples with low initial Th contents, and (3) assessment of the uncertainty due to initial Th. This strategy allows us to produce precise U‐Th dates from lacustrine carbonates. The principal consideration in dating such carbonates is the composition and quantity of initial Th incorporated into the carbonate, and additional uncertainty is introduced because this initial Th may have two sources in lacustrine deposits. Isochron plots, measured (230Th/232Th), and X‐ray diffraction and trace element chemistry of silicic residues all favor regional soil and dust as the sole source of initial Th in carbonates from the Bolivian Altiplano, a situation that simplifies single‐sample dating of Altiplano carbonates.
In situ Raman analyses of deep‐sea hydrothermal and cold seep systems (Gorda Ridge and Hydrate Ridge)
Authors: White S. N. , Dunk R. M. , Peltzer E. T. , Freeman J. J. , Brewer P. G.
Published: May 2006

The Deep Ocean Raman In Situ Spectrometer (DORISS) instrument was deployed at the Sea Cliff Hydrothermal Field and Hydrate Ridge in July 2004. The first in situ Raman spectra of hydrothermal minerals, fluids, and bacterial mats were obtained. These spectra were analyzed and compared to laboratory Raman measurements of standards and samples collected from the site. Spectra of vent fluid (∼294°C at the orifice) at ∼2700 m depth were collected with noncontact and immersion sampling optics. Compared to spectra of ambient (∼2°C) seawater, the vent fluid spectra show changes in the intensity and positions of the water O‐H stretch bands due to the elevated temperature. The sulfate band observed in seawater spectra is reduced in vent fluid spectra as sulfate is removed from vent fluid in the subseafloor. Additional components of hydrothermal fluid are present in concentrations too low to be detected with the current Raman system. A precision underwater positioner (PUP) was used to focus the laser spot on opaque samples such as minerals and bacterial mats. Spectra were obtained of anhydrite from actively venting chimneys, and of barite deposits in hydrothermal crusts. Laboratory analysis of rock samples collected in the vent field also detected the presence of gypsum. Spectra of bacterial mats revealed the presence of elemental sulfur (S8) and the carotenoid beta‐carotene. Challenges encountered include strong fluorescence from minerals and organics and insufficient sensitivity of the instrument. The next generation DORISS instrument addresses some of these challenges and holds great potential for use in deep‐sea vent environments.
What can we learn from Global Altimetry/Hydrography comparisons?
Authors: Guinehut Stephanie , Le Traon Pierre‐Yves , Larnicol Gilles
Published: May 2006

Differences and complementarities between altimeter and hydrographic data are studied to describe the sea level and ocean circulation variations in terms of steric and non‐steric contributions. Altimeter sea level anomalies (SLA) and hydrographic dynamic height anomalies (DHA) agree remarkably well. They also reveal, however, systematic large‐scale differences in several areas of the Pacific and Indian oceans that are related to a barotropic, Sverdrup‐like, response of the ocean to wind forcing. In addition, the use of the two data sets provides a good estimation of the partition between barotropic and baroclinic modes needed for data synthesis or assimilation studies.
Observations of nightside magnetic reconnection during substorm growth and expansion phases
Authors: Lam M. M. , Pinnock M. , Donovan E. F.
Published: May 2006

The temporal and spatial variability of nightside magnetic reconnection is described using two‐dimensional ionospheric measurements during the growth phase and early expansion phase of a single substorm. Two techniques (A and B) are used to address both the localized (across ∼15° longitude at ∼2300 magnetic local time (MLT)) and the large‐scale reconnection rate, using ionospheric data that provides the component of the electric field tangential to the polar cap boundary (PCB) in the stationary boundary frame. Technique A uses localized high‐resolution measurements derived from 630 nm all‐sky imager data at Rankin Inlet and ionospheric convection vectors obtained from line‐of‐sight velocity data from the Kapuskasing and Saskatoon Super Dual Auroral Radar Network (SuperDARN) HF radars. Technique B uses lower resolution global measurements, obtained by combining Polar VIS imager data and a velocity field derived using SuperDARN global convection mapping. A third technique (C) estimates the nightside reconnection potential from the dayside reconnection potential and the variation in the polar cap area. Technique A reveals standing wave‐like variation of period ∼16 min in the reconnection rate in the late growth phase (spatial noncontinuity in the x‐line). The localized measurements of the reconnection rate vary between 0 and 50 mV/m during both the growth and expansion phases. Technique B shows the expansion of the x‐line toward the duskside during the first 15 min of the expansion phase, from a width of ∼4 hours of MLT to ∼7 hours MLT.
Coronal mass ejection geoeffectiveness depending on field orientation and interplanetary coronal mass ejection classification
Authors: Kang Seung‐Mi , Moon Y.‐J. , Cho K.‐S. , Kim Yeon‐Han , Park Y. D. , Baek Ji‐Hye , Chang Heon‐Young
Published: May 2006

In this study, we have examined the coronal mass ejection (CME) geoeffectiveness characterized by Dst ≤ −50 nT according to the field orientation (N or S) in a CME source region and its dependence on interplanetary CME (ICME) classification (magnetic clouds or ejecta). We first considered 133 CME‐ICME pairs (1996 to 2001) whose CME source locations are identified by SOHO Large‐Angle Spectrometric Coronograph (SOHO/LASCO) and extreme ultraviolet imaging telescope (SOHO/EIT) data. Then we identified the shapes (S or Inverse‐S) of the X‐ray sigmoids associated with 63 of these CMEs using Yohkoh/Soft X‐Ray Telescope (SXT) data. To determine the field orientation in the sigmoids, we applied the coronal flux rope (CFR) model and the force‐free field (FFF) model to these 63 sigmoids using SOHO/Michelson Doppler Imager (MDI) images. We present the results in contingency tables, classified according to solar field orientation and geomagnetic storm strength/occurrence. We found that (1) the prediction of geomagnetic storms (Dst ≤ −50 nT) based on the CFR model is much better than that on the FFF model, (2) the prediction for magnetic clouds (MCs) is much better than that for ejecta (EJ), which implies that the field orientation of the MCs is well conserved through the heliosphere, and (3) for about 86% of the magnetic clouds, the directions of their leading fields are consistent with those in the CME source regions. Our results support the findings that the southward orientations of the magnetic field in the CME source regions plays an important role in the production of geomagnetic storms.
Lattice Boltzmann pore‐scale model for multicomponent reactive transport in porous media
Authors: Kang Qinjun , Lichtner Peter C. , Zhang Dongxiao
Published: May 2006

In this work, a multicomponent lattice Boltzmann (LB) model is presented for simulating reactive transport in porous media at the pore scale. In the model, a set of distribution functions is introduced to simulate fluid flow and solute transport. The model takes into account advection, diffusion, homogeneous reactions among multiple aqueous species, and heterogeneous reactions between the aqueous solution and minerals, as well as changes in solid and pore geometry. Homogeneous reactions are described through local equilibrium mass action relations. Mineral reactions are treated kinetically through boundary conditions at the mineral surface. The LB equation for flow recovers the correct pore‐scale continuity and Navier‐Stokes equations. The LB equations for solute transport are modified to recover advection‐diffusion equations for total concentrations at the pore scale. The model is applied to a hypothetical three‐component system with two aqueous complexes and two mineral reactions in a simple pore geometry. The effects of advection, diffusion, reaction rate constants, equilibrium constants of both homogeneous and heterogeneous reactions, and chemical compositions on mineral alteration of the porous medium and solute concentration are analyzed.
A survey of 71 earthquake bursts across southern California: Exploring the role of pore fluid pressure fluctuations and aseismic slip as drivers
Authors: Vidale John E. , Shearer Peter M.
Published: May 2006

We investigate the cause of seismicity bursts by examining a waveform‐relocated catalog for southern California between 1984 and 2002 and systematically identifying 71 isolated sequences of 40 or more earthquakes occurring within a 2‐km‐radius volume and a 4‐week interval. Fifty‐seven of the 71 bursts are difficult to interpret as primarily a main shock and its Omori‐law‐abiding foreshocks and aftershocks because they exhibit a more complicated evolution in space, time, and magnitude; we identify 18 of these sequences as particularly swarm‐like. Evidence against a simple cascade of elastic stress triggering includes the presence of an interval of steady seismicity rate, the tendency of the largest event to strike later in the sequence, the large spatial extent of some of the swarms compared to their cumulative moment, and the weak correlation between the number of events in each burst and the magnitude of the largest event in each burst. Shallow sequences and normal faulting mechanism sequences are most likely to be swarm‐like. The tendencies of the hypocenters in the swarm‐like sequences to occur on vertical planes and expand over time suggest pore fluid pressure fluctuations as the most likely mechanism driving the swarm‐like seismicity bursts. However, episodic aseismic slip could also be at least partly responsible and might provide a more compelling explanation for the steady rate of seismicity during swarms, whereas fluid pressure perturbations might be expected to diminish more rapidly with time. Both aftershock‐like and swarm‐like seismicity bursts are distributed across the entire study region, indicating that they are a general feature of tectonic faulting, rather than limited to a few geological conditions such as volcanic or geothermal areas.
Performance evaluation of the self‐organizing map for feature extraction
Authors: Liu Yonggang , Weisberg Robert H. , Mooers Christopher N. K.
Published: May 2006

Despite its wide applications as a tool for feature extraction, the Self‐Organizing Map (SOM) remains a black box to most meteorologists and oceanographers. This paper evaluates the feature extraction performance of the SOM by using artificial data representative of known patterns. The SOM is shown to extract the patterns of a linear progressive sine wave. Sensitivity studies are performed to ascertain the effects of the SOM tunable parameters. By adding random noise to the linear progressive wave data, it is demonstrated that the SOM extracts essential patterns from noisy data. Moreover, the SOM technique successfully chooses among multiple sets of patterns in contrast with an Empirical Orthogonal Function method that fails to do this. A practical way to apply the SOM is proposed and demonstrated using several examples, including long time series of coastal ocean currents from the West Florida Shelf. With improved SOM parameter choices, strong current patterns associated with severe weather forcing are extracted separate from previously identified asymmetric upwelling/downwelling and transitional patterns associated with more typical weather forcing.
A two‐step explicit solution of the Boussinesq equation for efficient simulation of unconfined aquifers in conjunctive‐use models
Authors: Pulido‐Velazquez David , Sahuquillo Andrés , Andreu Joaquín
Published: May 2006

Mathematical models that simultaneously simulate surface and groundwater components and their interaction are required to evaluate management alternatives in conjunctive‐use systems. Complex systems and scenarios defined over long time periods often force the use of computationally efficient aquifer models. Thus the groundwater flow equation needs to be solved using explicit techniques such as influence functions or the eigenvalue technique. The eigenvalue technique provides a continuous‐in‐time solution using a state equation with important computational advantages. These methods are strictly applicable only to confined aquifers, which are modeled with a linear groundwater flow equation. However, many commonly exploited aquifers connected with the surface system are unconfined and should be simulated using the nonlinear Boussinesq equation. A two‐step explicit solution of the unconfined groundwater flow problem is presented for aquifers with nearly horizontal bottom. It is based on a new approach to linearize the Boussinesq equation. Using a change of variable, it is possible to define an equation with a structure similar to the linear groundwater flow equation. The only difference is found in a term that depends on the solution. Approaching this term by means of a fictitious stress, we obtain a linear equation analogous to the confined groundwater flow equation. The boundary conditions can also be formulated as a function of this new variable with linear expressions. Therefore the unconfined groundwater flow problem can be solved by applying the superposition principle, and the solution can be obtained with a reduced computational cost using the eigenvalue technique.
Trends in 20th century drought over the continental United States
Authors: Andreadis Konstantinos M. , Lettenmaier Dennis P.
Published: May 2006

We used a simulated data set of hydro‐climatological variables to examine for 20th century trends in soil moisture, runoff, and drought characteristics over the conterminous United States (U.S.). An increasing trend is apparent in both model soil moisture and runoff over much of the U.S., with a few decreasing trends in parts of the Southwest. The trend patterns were qualitatively similar to those found in streamflow records observed at a station network minimally affected by anthropogenic activities. This wetting trend is consistent with the general increase in precipitation in the latter half of the 20th century. Droughts have, for the most part, become shorter, less frequent, and cover a smaller portion of the country over the last century. The main exception is the Southwest and parts of the interior of the West, where, notwithstanding increased precipitation (and in some cases increased soil moisture and runoff), increased temperature has led to trends in drought characteristics that are mostly opposite to those for the rest of the country especially in the case of drought duration and severity, which have increased.
Flow speed inside the brightness boundary of coronal streamers
Authors: Suess S. T. , Nerney S.
Published: May 2006

Density measurements in the legs of coronal streamers, where there might be outflow, are reproduced here using a magnetohydrodynamic model of the flow inside the brightness boundary of streamers. The model returns values for the flow speed and stream tube geometry (spreading) between the base and a few solar radii. The flow speed is consistent with there being no measurable outflow below 2.5 R⊙ and an outflow of ∼100 km/s at 5 R⊙. We briefly describe the model, observations, and physical interpretation.
New multi‐fluid MHD model of comet 26P/Grigg‐Skjellerup: Extrapolation to comet 67P/Churyumov‐Gerasimenko
Authors: Benna M. , Mahaffy P. R.
Published: May 2006

The Multi‐fluid MHD simulator CASIM3D models the atmosphere of comet 26P/Grigg‐Skjellerup as it was seen by the Giotto spacecraft during its flyby of the comet in July 1992. CASIM3D integrates the major chemical reactions and physical interactions to compute self‐consistently over an adaptive Cartesian mesh the dynamics of ions, electrons, and neutrals within the coma. Using this model, we derived water ion velocity and density profiles and magnetic field strength along the Giotto path that are in good agreement with the recorded observations. This model is also extrapolated to the case of 67P/Churyumov‐Gerasimenko for its perihelion passage of 2015 to provide a preliminary assessment of the structure of the coma of this comet. We show that the inner boundary layers are just few dozen kilometers large. This could provide an additional constraint to the orbit of the spacecraft Rosetta to maximize the science return of the mission.
Particle tracking from image sequences of complex plasma crystals
Authors: Hadziavdic Vedad , Melandsø Frank , Hanssen Alfred
Published: May 2006

In order to gather information about the physics of the complex plasma crystals from the experimental data, particles have to be tracked through a sequence of images. An application of the Kalman filter for that purpose is presented, using a one-dimensional approximation of the particle dynamics as a model for the filter. It is shown that Kalman filter is capable of tracking dust particles even with high levels of measurement noise. An inherent part of the Kalman filter, the innovation process, can be used to estimate values of the physical system parameters from the experimental data. The method is shown to be able to estimate the characteristic oscillation frequency from noisy data.
Modeling of resistive wall mode and its control in experiments and ITER
Authors: Liu Yueqiang , Chu M. S. , Garofalo A. M. , La Haye R. J. , Gribov Y. , Gryaznevich M. , Hender T. C. , Howell D. F. , de Vries P. , Okabayashi M. , Pinches S. D. , Reimerdes H. , contributors EFDA-JET
Published: May 2006

Active control of the resistive wall mode (RWM) for DIII-D [Luxon and Davis, Fusion Technol. 8, 441 (1985)] plasmas is studied using the MARS-F code [Y. Q. Liu, et al., Phys. Plasmas 7, 3681 (2000)]. Control optimization shows that the mode can be stabilized up to the ideal wall beta limit, using the internal control coils (I-coils) and poloidal sensors located at the outboard midplane, in combination with an ideal amplifier. With the present DIII-D power supply model, the stabilization is achieved up to 70% of the range between no-wall and ideal-wall limits. Reasonably good quantitative agreement is achieved between MARS-F simulations and experiments on DIII-D and JET (Joint European Torus) [P. H. Rebut et al., Nucl. Fusion 25, 1011 (1985)] on critical rotation for the mode stabilization. Dynamics of rotationally stabilized plasmas is well described by a single mode approximation; whilst a strongly unstable plasma requires a multiple mode description. For ITER [R. Aymar, P. Barabaschi, and Y. Shimomura, Plasma Phys. Controlled Fusion 44, 519 (2002)], the MARS-F simulations show the plasma rotation may not provide a robust mechanism for the RWM stabilization in the advanced scenario. With the assumption of ideal amplifiers, and using optimally tuned controllers and sensor signals, the present feedback coil design in ITER allows stabilization of the n=1 RWM for plasma pressures up to 80% of the range between the no-wall and ideal-wall limits.
First principles study on the interface of CrSb∕GaSb heterojunction
Authors: Wu R. Q. , Liu L. , Peng G. W. , Feng Y. P.
Published: May 2006

First principles calculations based on spin density functional theory are performed to study the energy alignment and magnetic properties of zinc-blende CrSb∕GaSb heterojunction. Our results suggest that at the interface CrSb remains half metallic. The Schottky barrier height of n-type GaSb is estimated to be 0.89eV with the Fermi level lying below the conduction band minimum (CBM) of GaSb. The CBM of the minority spin lies just above that of GaSb, suggesting that the majority spin can be injected into GaSb without being flipped to the conduction bands of the minority spin. Thus the CrSb∕GaSb heterojunction can be potentially useful in the field of spintronics.
Annealing behavior of atomic layer deposited hafnium oxide on silicon: Changes at the interface
Authors: Deshpande Anand , Inman Ronald , Jursich Gregory , Takoudis Christos G.
Published: May 2006

Thin films of hafnium oxide are deposited on Si(100) substrates by means of atomic layer deposition using tetrakis(diethylamino)hafnium and water on Si(100) at 300°C. Detailed studies of temperature induced annealing effects on the HfO2∕Si interface are done using angle resolved x-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, and time of flight secondary ion mass spectroscopy (ToF-SIMS). As-deposited films show mostly native silicon oxide at the interface. Crystallization of HfO2 film initiates at about 600°C. As the annealing temperature is increased, the hafnium silicate content in the film is found to increase and the mostly silicon oxide interlayer is found to grow thicker under Ar atmosphere. Also, the formation of hafnium silicide is found to take place at temperatures ⩾800°C. The XPS data shows decomposition of the interfacial hafnium silicate layer into hafnium oxide and silicon oxide at 1000°C along with increasing formation of hafnium silicide. The ToF-SIMS data suggest interdiffusion of the hafnium oxide film and the interfacial silicon oxide during the annealing process.
SiC-based optical interferometry at high pressures and temperatures for pressure and chemical sensing
Authors: Dakshinamurthy Surendramohan , Quick Nathaniel R. , Kar Aravinda
Published: May 2006

Crystalline silicon carbide is a chemically inert wide band gap semiconductor with good mechanical strength and oxidation-resistant properties at elevated temperatures, which make it a good sensor material for harsh environments such as combustion chambers and turbine systems. For such cases, optical sensors are generally superior to electrical sensors in many aspects such as responsivity, detectivity, and sensitivity. This paper presents a wireless technique for pressure and chemical sensing based on the pressure-and temperature-dependent refractive indices of silicon carbide. A helium-neon laser with a wavelength of 632.8nm was used as a probe laser to obtain the complementary Airy pattern of the laser power reflected off a silicon carbide wafer segment at high temperatures (up to 300°C) and pressures (up to 400psi). The interference patterns revealed unique characteristics for nitrogen and argon test gases. This pattern is different at the same pressure and temperature for the two gases, indicating the chemical sensing selectivity capability of silicon carbide. Also the pattern changes with pressures for the same gas, indicating the pressure sensing capability. The refractive index of silicon carbide has been obtained for different pressures and temperatures using the interference pattern. A three-layer model has been employed to determine the refractive indices of the gases using the reflected power data.
Interface effect on emission properties of Er-doped Si nanoclusters embedded in SiO2 prepared by magnetron sputtering
Authors: Bian L. F. , Zhang C. G. , Chen W. D. , Hsu C. C. , Qu Y. H. , Jiang D. S.
Published: May 2006

Er-doped Si nanoclusters embedded in SiO2 (NCSO) films were prepared by radio frequency magnetron sputtering on either silicon or quartz substrates. A 1.16μm (1.08eV) photoluminescence (PL) peak was observed from an Er-doped NCSO film deposited on a Si substrate. This 1.16μm peak is attributed to misfit dislocations at the NCSO/Si interface. The emission properties of the 1.16μm peak and its correlation with the Er3+ emission (1.54μm) have been studied in detail. The observed behavior suggests that the excitation mechanism of the 1.16μm PL is in a fashion similar to that shown for Er-doped Si nanoclusters embedded in a SiO2 matrix.
Charge exchange collisions and ion velocity distribution at the electrode of low pressure capacitive rf discharges
Authors: Israel D. , Riemann K.-U. , Tsendin L.
Published: May 2006

An analytic theory of the time-averaged ion distribution function (IDF) in the self-consistent sheath field of a low pressure capacitively coupled rf discharge is developed. A reliable simple quantitative description of the ion energy spectra formation is obtained and test calculations of charge exchange cross section reconstructions from IDFs are presented.
On the heat capacities of M2AlC (M=Ti,V,Cr) ternary carbides
Authors: Drulis Monika K. , Drulis H. , Gupta S. , Barsoum M. W. , El-Raghy T.
Published: May 2006

In this paper, we report on the heat capacities cp of bulk polycrystalline samples of Ti2AlC, V2AlC, and Cr2AlC in the 3–260K temperature range. Given the structural and chemical similarities of these compounds it is not surprising that the cp’s and their temperature dependencies were quite similar. Nevertheless, at all temperatures the heat capacity of Cr2AlC was higher than the other two. The density of states at the Fermi level were 3.9, 7.5, and 14.6(eVunitcell)−1 for Ti2AlC, V2AlC, and Cr2AlC, respectively. The results obtained are analyzed using the Debye and Einstein model approximations for cp. Good description of cp is obtained if one assumes that nine phonon modes vibrate according to the Debye model approximation whereas the remaining 3 of 12 modes expected for M2AlC formula unit fulfill an Einstein-like phonon vibration pattern. Debye temperatures θD describing acoustic phonon and Einstein temperature θE describing optical phonon contributions have been estimated for the studied compounds. The Debye temperatures are reasonably high and fall in the range of 600–700K. A linear dependence was found between the number of d electrons along the row Ti, V, and Cr and the density of states at the Fermi level.
Field emission from amorphous carbon films grown by electrochemical deposition using methanol liquid
Authors: Kiyota H. , Higashi M. , Kurosu T. , Iida M.
Published: May 2006

The field emission from an amorphous carbon (a-C) film grown by electrochemical deposition has been studied. The deposition of the a-C film was accomplished by applying a direct-current potential to a substrate that was immersed in methanol. Both scanning electron microscopy and Raman results indicate that smooth and homogeneous a-C films are grown on specific substrates such as Ti and Al. Field emission measurements demonstrate excellent emission properties such as threshold fields as low as 5V∕μm. Enhancement factors are estimated to be in the range of 1300-1500; these are attributed to local field enhancements around sp2 carbon clusters that are embedded in the a-C films. Emission properties of a-C films grown on Si exhibit a current saturation under higher applied fields. These saturation characteristics are explained by effects of a potential barrier at the interface between the a-C film and the substrate. The interface barrier is reduced by formation of the Ti interfacial layer, suggesting that the formation of TiC decreases the contact resistance between the substrate and the a-C film. Therefore, an approach to use carbide formation at the interface is verified as useful to improve the emission properties of a-C films.
Formation of an anisotropy lattice in Co∕Pt multilayers by direct laser interference patterning
Authors: Aktag Aliekber , Michalski Steven , Yue Lanping , Kirby Roger D. , Liou Sy-Hwang
Published: May 2006

We report on the use of direct laser interference patterning to form an “anisotropy” lattice in Co∕Pt thin film multilayers. Co∕Pt multilayers have been extensively studied and, for the compositions studied here, are characterized by strong perpendicular magnetic anisotropy in which the magnetic moment is perpendicular to the film plane. In direct laser interference patterning, two-to-four coherent laser beams from a pulsed Nd:YAG laser strike the sample surface simultaneously, and for sufficiently intense beams the sample properties are modified locally where interference maxima occur. Kerr rotation, magnetic force microscopy, and atomic force microscopy measurements after patterning by one pulse from the laser show that the films have a regular array of “dots” with in-plane magnetization in a background matrix of perpendicular magnetization. Such patterning holds promise for the study of model nanoscale magnetic systems.
Optical and structural characteristics of Nd:YVO4 film on SiO2∕Si substrate fabricated by pulsed laser deposition
Authors: Wang F. , Zhu S. N. , Cheah K. W.
Published: May 2006

The Nd:YVO4 thin films with a-axis preferred orientation have been grown on SiO2∕Si substrates using pulsed laser deposition. Their structural, spectroscopic ellipsometric, and emission characteristics have been systematically studied. The lower ambient oxygen pressure during deposition would lead to better crystallinity in the films. The fluorescence at 1064.8 and 1342nm in the Nd:YVO4 films was excited with an 808nm diode laser as pump. The results show that the highly a-axis oriented Nd:YVO4 films grown on Si substrates may have potential applications in actively integrated circuits.
Nanowire based quantum interference sensors for electromagnetic radiation
Authors: Lui G. P. , Qiao Bi , Ruda H. E.
Published: May 2006

We present a proposal for the use of a nanostructure for electromagnetic radiation sensing, which is based on quantum interference. One sensor format that is discussed is comprised of symmetric hexagonal nanowire loops or parallel nanowires. The relevant quantum interference properties are analyzed, showing that the influence phase functional for the current density depends on the final relative velocity of electrons in these nanostructures.
Tuning of a phase shift to reduce the polarization-dependent loss in an interferometer-type variable optical attenuator built in lithium niobate
Authors: Terashima Akira , Tamagawa Naomi , Mori Hiroshi
Published: May 2006

A method to adjust the phase mismatch between two paths of a Mach-Zehnder interferometer built in lithium niobate is presented. The importance of phase adjustment is that, in reducing polarization-dependent loss (PDL) in an optical attenuator based on lithium niobate z-propagation geometry, the phase shifts of two polarizations must be minimized or equalized. The method employs partially covering a waveguide arm with resin droplets using a microdispenser. In interferometer-type variable optical attenuators built in lithium niobate in x-cut/z-propagation geometry, the phase mismatch contribution to the PDL of less than 0.7dB was shown to be achievable by the present phase tuning method.
Analytic transmission for field emission from coated cold cathodes
Authors: Dragoman D. , Filip L. D.
Published: May 2006

We provide a simple analytical formula for the transmission coefficient of electrons emitted into vacuum from a coated tip, which is valid both at resonance and far from resonance. This formula assumes emission through two triangular-shaped potential barriers and allows the calculation of the tunneling time of electrons, parameter of crucial importance for high-frequency devices. It is shown that the current density calculated with the simple analytical formula for the transmission coefficient successfully explains the previously obtained experimental results.
Effect of contact metallization on electromigration reliability of Pb-free solder joints
Authors: Ding Min , Wang Guotao , Chao Brook , Ho Paul S. , Su Peng , Uehling Trent
Published: May 2006

The effect of underbump metallization (UBM) on electromigration (EM) lifetime and failure mechanism has been investigated for Pb-free solder bumps of 97Sn3Ag composition in the temperature range of 110–155°C. The EM lifetime of the SnAg Pb-free solders with either Cu or Ni UBM was found to be better than the eutectic SnPb (63Sn37Pb) solders but worse than high-Pb (95Pb5Sn) solders. In the test temperature range, the EM lifetimes were found to be comparable for Cu and Ni UBMs but with different activation energies: 0.64–0.72eV for Cu UBM and 1.03–1.11eV for Ni UBM. EM failure was observed only in solder bumps with electron current flow from UBM to the substrate. Failure analysis revealed that EM damage was initiated by the formation of intermetallic compounds (IMC) at the UBM∕solder interface which was found to be significantly enhanced by mass transport driven by the electron current. Under EM, the continued growth of IMC with the dissolution of the UBM and the accumulation of Kirkendall voids resulted in the formation of interfacial cracks and eventual EM failure of the solder bump. For Ni UBM, the IMC formation was dominated by the Ni3Sn4 phase while for Cu UBM, a bilayer of Cu3Sn∕Cu6Sn5 was found. Void formation at the Cu6Sn5∕solder interface was found to be important in controlling the EM lifetime of the Cu UBM solder.
Application of a combined system of polycapillary x-ray lens and toroidal mirror in micro-x-ray-absorption fine-structure facility
Authors: Sun Tianxi , Xie Yaning , Liu Zhiguo , Liu Tao , Hu Tiandou , Ding Xunliang
Published: May 2006

A micro-x-ray-absorption fine-structure facility based on a monolithic half focusing polycapillary x-ray lens (MHFPXRL), a toroidal mirror, and synchrotron radiation is proposed. The synchrotron radiation is focused by using a combined system of a MHFPXRL and a toroidal mirror. At 8.0keV, the synchrotron radiation beam with a 2.3×26-mm2 area is first focused into a beam spot with a 0.9×0.3-mm2 area by a toroidal mirror. This focused beam is then focused into a focal spot with a 21.4-μm diameter by using a MHFPXRL. The gain of power flux density in the focal spot of the combined system is 47 473. The focal distance of the MHFPXRL is 13.3mm. The transmitting extended x-ray-absorption fine-structure (EXAFS) spectrum of Ni foil and the fluorescent EXAFS spectrum of zinc in the zinc hyperaccumulator are measured.
Correlations between elastic moduli and properties in bulk metallic glasses
Authors: Wang Wei Hua
Published: May 2006

A survey of the elastic, mechanical, fragility, and thermodynamic properties of bulk metallic glasses (BMGs) and glass-forming liquids is presented. It is found that the elastic moduli of BMGs have correlations with the glass transition temperature, melting temperature, mechanical properties, and even liquid fragility. On the other hand, the elastic constants of available BMGs show a rough correlation with a weighted average of the elastic constants for the constituent elements. Although the theoretical and physical reasons for the correlations are to be clarified, these correlations could assist in understanding the long-standing issues of glass formation and the nature of glass and simulate the work of theorists. Based on the correlation, we show that the elastic moduli can assist in selecting alloying components for controlling the elastic properties and glass-forming ability of the BMGs and thus can guide BMG design. As case study, we report the formation of the families of rare-earth-based BMGs with controllable properties.
Improvements in quantum efficiency of excitonic emissions in ZnO epilayers by the elimination of point defects
Authors: Chichibu S. F. , Onuma T. , Kubota M. , Uedono A. , Sota T. , Tsukazaki A. , Ohtomo A. , Kawasaki M.
Published: May 2006

The internal quantum efficiency (ηint) of the near-band-edge (NBE) excitonic photoluminescence (PL) in ZnO epilayers was significantly improved by eliminating point defects, as well as by the use of ZnO high-temperature-annealed self-buffer layer (HITAB) on a ScAlMgO4 substrate as epitaxial templates. Negatively charged Zn vacancy (VZn) concentration was greatly reduced by high-temperature growth, and slower postgrowth cooling (annealing) under minimum oxygen pressure further reduced the gross concentration of positively and negatively charged and neutral point defects, according to the suppression of nonequilibrium defect quenching. The nonradiative PL lifetime (τnr) at room temperature was increased by decreasing the gross concentration of point defects, as well as by decreasing the concentration of VZn. Accordingly, certain point defect complexes incorporated with VZn (VZn-X complexes) are assigned to the dominant nonradiative recombination centers. As a result of the elimination of point defects, a record long τnr (3.8ns) at 300K was demonstrated. Because the radiative lifetime (τr) is in principle constant in bulk and epitaxial ZnO, the increase in τnr gave rise to the increase in ηint. Rich structures originating from exciton-polaritons and excited states of excitons were eventually observed in the low-temperature PL spectrum of the improved ZnO epilayer on HITAB, of which ηint of the NBE emission was 6.3% at 300K.
Influence of the oxygen concentration of atomic-layer-deposited HfO2 gate dielectric films on the electron mobility of polycrystalline-Si gate transistors
Authors: Park Jaehoo , Park Tae Joo , Cho Moonju , Kim Seong Keun , Hong Sug Hun , Kim Jeong Hwan , Seo Minha , Hwang Cheol Seong , Won Jeong Yeon , Jeong Ranju , Choi Jung-Hae
Published: May 2006

The influence of the ozone concentration (150–370g∕m3) during the atomic layer deposition of HfO2 gate dielectrics on the dielectric performance of the films and the device performance of metal-oxide-semiconductor field effect transistor (MOSFET) grown on Si was studied. The use of a lower ozone concentration (150g∕m3) produced a HfO2 film with a stoichiometric oxygen concentration, whereas a higher ozone concentration (390g∕m3) produced an oxygen excess HfO2 film. An almost identical Dit to that of the SiO2 gate dielectric film was obtained from the stoichiometric HfO2, whereas the oxygen excess HfO2 gate dielectric produced a much higher Dit with the polycrystalline-Si electrode. The investigation of the interface states using x-ray photoelectron spectroscopy revealed that the excessive oxygen incorporated during the film growth made the interfacial reaction and oxidation serious. This increased the interface trap density and degraded the interface properties. Accordingly, an electron effective mobility of ∼65% of the MOSFET with SiO2 as a gate dielectric was obtained from the stoichiometric HfO2 gate dielectric film. The effective mobility from the MOSFET with the oxygen excess HfO2 film was only ∼45%. The 35% loss of the effective mobility for the stoichiometric HfO2 MOSFET appeared to be due to factors such as carrier scattering by fixed charges and long range optical phonons.
Modeling the chemical kinetics of high-pressure glow discharges in mixtures of helium with real air
Authors: Stalder K. R. , Vidmar R. J. , Nersisyan G. , Graham W. G.
Published: May 2006

Atmospheric and near-atmospheric pressure glow discharges generated in both pure helium and helium-air mixtures have been studied using a plasma chemistry code originally developed for simulations of electron-beam-produced air plasmas. Comparisons are made with experimental data obtained from high-pressure glow discharges in helium-air mixtures developed by applying sinusoidal voltage wave forms between two parallel planar metallic electrodes covered by glass plates, with frequencies ranging from 10to50kHz and electric field strengths up to 5kV∕cm. The code simulates the plasma chemistry following periodic pulsations of ionization in prescribed E∕N environments. Many of the rate constants depend on gas temperature, electron temperature, and E∕N. In helium plasmas with small amounts (∼850ppm) of air added, rapid conversion of atomic helium ions to molecular helium ions dominate the positive ion kinetics and these species are strongly modulated while the radical species are not. The charged and neutral species concentrations at atmospheric pressure with air impurity levels up to 10000ppm are predicted. The negative ion densities are very small but increase as the air impurity level is raised, which indicates that in helium-based systems operated in open air the concentration of negative ions would be significant. If water vapor at typical humidity levels is present as one of the impurities, hydrated cluster ions eventually comprise a significant fraction of the charged species.
Bending energy level structure and quasilinearity of the X̃+B13 ground electronic state of NH2+
Authors: Willitsch S. , Jungen Ch. , Merkt F.
Published: May 2006

The bending level structure of the quasilinear X̃+B13 ground electronic state of the amidogen cation NH2+ was studied by pulsed-field-ionization zero-kinetic-energy photoelectron spectroscopy using a near-infrared vacuum-ultraviolet two-photon ionization sequence via selected rovibronic levels of the ÃA12 state of NH2. The careful selection of the intermediate levels permitted to optimize the transition intensities to the lowest vibrational levels of the cation in the photoionization step and to overcome the low sensitivity of previously employed single-photon ionization schemes. For the first time, all bending levels of the cationic ground state with quantum numbers υ2,lin+⩽4, N+⩽4, and ∣K+∣⩽2 could be observed, enabling a detailed characterization of the large-amplitude bending vibration. The rotational structure corresponds to that of an effectively linear molecule in all observed vibrational levels. The bending vibrational structure which shows marked deviations from a harmonic behavior was analyzed in terms of a semirigid bender model. The bending potential function was obtained from a fit to the experimental data. The height of the barrier at the linear geometry and the bond angle at the potential minimum were determined to be 231.8(22)cm−1 and 152.54(4)°, respectively, and all bending levels are located above the maximum of the barrier.
Solvation in supercritical water
Authors: Duan Jinsong , Shim Youngseon , Kim Hyung J.
Published: May 2006

Solvation in supercritical water under equilibrium and nonequilibrium conditions is studied via molecular dynamics simulations. The influence of solute charge distributions and solvent density on the solvation structures and dynamics is examined with a diatomic probe solute molecule. It is found that the solvation structure varies dramatically with the solute dipole moment, especially in low-density water, in accord with many previous studies on ion solvation. This electrostrictive effect has important consequences for solvation dynamics. In the case of a nonequilibrium solvent relaxation, if there are sufficiently many water molecules close to the solute at the outset of the relaxation, the solvent response measured as a dynamic Stokes shift is almost completely governed by inertial rotations of these water molecules. By contrast, in the opposite case of a low local solvent density near the solute, not only rotations but also translations of water molecules play an important role in solvent relaxation dynamics. The applicability of a linear response is found to be significantly restricted at low water densities.
Annealing process of ion-implantation-induced defects in ZnO: Chemical effect of the ion species
Authors: Chen Z. Q. , Maekawa M. , Kawasuso A. , Sakai S. , Naramoto H.
Published: May 2006

ZnO single crystals implanted with O+ and B+ ions were studied by positron annihilation and Raman scattering measurements. Positron annihilation results show that vacancy clusters are generated by implantation. For the B+-implanted sample, the vacancy clusters have a sufficient increase in size and evolve into microvoids after annealing up to 500°C. These microvoids need a high temperature of 900–1000°C to be annealed out. However, for the O+-implanted sample, the size of the vacancy clusters shows only a slight increase during annealing process, and they are removed at much lower temperature of 700–800°C. The different annealing process is supposed to be due to the chemical effect of boron impurities. Raman measurements reveal the production of oxygen vacancies by implantation. In the B+-implanted sample they have high thermal stability up to 700°C, while in the O+-implanted sample they are annealed out early at 400°C. It is thus suggested that the boron impurities might form complexes with oxygen interstitials and stabilize oxygen vacancies, which favors the vacancy agglomeration process.