bluuebunny/crossref_metadata_2025 huggingface dataset:
Erosion by rivers and transport pathways in the ocean: A provenance tool using40Ar‐39Ar incremental heating on fine‐grained sediment
Authors: VanLaningham Sam , Duncan Robert A. , Pisias Nicklas G.
Published: December 2006

We use40Ar‐39Ar incremental heating to fingerprint bulk fluvial sediment entering the northeast Pacific Ocean, with the long‐term intent of tracking sediment source and transport changes from the terrestrial system to the marine environment through time. We show reproducible age spectra from individual rivers accounting for the majority of sediment delivered to the Pacific margin. Two tests are performed to confirm the validity of the bulk sediment40Ar‐39Ar incremental heating measurements and to address why polymineralic sediment might yield concordant age steps. The first model tests, in light of bulk mineralogy and diffusion of Ar from silicates, whether measured K/Ca spectra (measured from39Ar and37Ar, respectively) are consistent with typical values for K‐ and Ca‐bearing minerals. Calculations show that the bulk mineralogy is reflected in the outgassing K/Ca spectra and identify plagioclase as the dominant mineral contributing to the plateau‐defining portion of the age spectra. A second model predicts bulk sediment ages from integrated bedrock cooling age‐area estimates in order to examine whether bulk sediment plateau ages are representative of the average cooling age of rocks from a given river basin. Calculated and observed ages are notably similar in three river basins when topographic and lithologic effects are accounted for. Overall, this technique shows considerable promise, not only in tracking individual terrigenous sources in the marine realm but also for understanding processes such as erosion and sediment transport in terrestrial systems.
Global vegetation phenology from Moderate Resolution Imaging Spectroradiometer (MODIS): Evaluation of global patterns and comparison with in situ measurements
Authors: Zhang Xiaoyang , Friedl Mark A. , Schaaf Crystal B.
Published: December 2006

In the last two decades the availability of global remote sensing data sets has provided a new means of studying global patterns and dynamics in vegetation. The vast majority of previous work in this domain has used data from the Advanced Very High Resolution Radiometer, which until recently was the primary source of global land remote sensing data. In recent years, however, a number of new remote sensing data sources have become available that have significantly improved the capability of remote sensing to monitor global ecosystem dynamics. In this paper, we describe recent results using data from NASA's Moderate Resolution Imaging Spectroradiometer to study global vegetation phenology. Using a novel new method based on fitting piecewise logistic models to time series data from MODIS, key transition dates in the annual cycle(s) of vegetation growth can be estimated in an ecologically realistic fashion. Using this method we have produced global maps of seven phenological metrics at 1‐km spatial resolution for all ecosystems exhibiting identifiable annual phenologies. These metrics include the date of year for (1) the onset of greenness increase (greenup), (2) the onset of greenness maximum (maturity), (3) the onset of greenness decrease (senescence), and (4) the onset of greenness minimum (dormancy). The three remaining metrics are the growing season minimum, maximum, and summation of the enhanced vegetation index derived from MODIS. Comparison of vegetation phenology retrieved from MODIS with in situ measurements shows that these metrics provide realistic estimates of the four transition dates identified above. More generally, the spatial distribution of phenological metrics estimated from MODIS data is qualitatively realistic, and exhibits strong correspondence with temperature patterns in mid‐ and high‐latitude climates, with rainfall seasonality in seasonally dry climates, and with cropping patterns in agricultural areas.
Numerical implementation of the mixed potential integral equation for planar structures with ferrite layers arbitrarily magnetized
Authors: Mesa F. , Medina F.
Published: December 2006

This work presents a new implementation of the mixed potential integral equation (MPIE) for planar structures that can include ferrite layers arbitrarily magnetized. The implementation of the MPIE here reported is carried out in the space domain. Thus it will combine the well‐known numerical advantages of working with potentials as well as the flexibility for analyzing nonrectangular shape conductors with the additional ability of including anisotropic layers of arbitrarily magnetized ferrites. In this way, our approach widens the scope of the space domain MPIE and sets this method as a very efficient and versatile numerical tool to deal with a wide class of planar microwave circuits and antennas.
Microscopic reactive diffusion of uranium in the contaminated sediments at Hanford, United States
Authors: Liu Chongxuan , Zachara John M. , Yantasee Wassana , Majors Paul D. , McKinley James P.
Published: December 2006

Microscopic and spectroscopic analyses of uranium‐contaminated sediments from select locations at the U.S. Department of Energy (DOE) Hanford site have revealed that sorbed uranium (U) often exists as uranyl precipitates associated with intragrain fractures of granitic clasts. The release of U to contacting fluids appears to be controlled by intragrain ion diffusion coupled with the dissolution kinetics of the precipitates that exist in the form of Na‐boltwoodite. Here we present a coupled microscopic reactive diffusion model for the contaminated sediment on the basis of experimental measurements of intragrain diffusivity in the granitic lithic fragments and the dissolution kinetics of synthetic Na‐boltwoodite. Nuclear magnetic resonance, pulse gradient spin echo measurements showed that the intragrain fractures of the granitic clasts isolated from the sediment contained two domains with distinct diffusivities. The fast diffusion domain had an apparent tortuosity of 1.5, while that of the slow region was two orders of magnitude larger. A two‐domain diffusion model was assembled and used to infer the geochemical conditions that led to intragrain uranyl precipitation during waste‐sediment interaction. Rapid precipitation of Na‐boltwoodite was simulated with an alkaline U‐containing, high‐carbonate tank waste solution that diffused into intragrain fractures, which originally contained Si‐rich pore water in equilibrium with feldspar grains in the lithic fragments. The model was also used to simulate uranyl dissolution and release from contaminated sediment to recharge waters. With independently characterized parameters for Na‐boltwoodite dissolution, the model simulations demonstrated that diffusion could significantly decrease the rates of intragrain uranyl mineral dissolution due to diffusion‐induced local solubility limitation with respect to Na‐boltwoodite.
Dihydropyridine Calcium Antagonists Increase Fibrinolytic Activity: A Systematic Review
Authors: Di Vergouwen Mervyn , Vermeulen Marinus , de Haan Rob J , Levi Marcel , Roos Yvo BWEM
Published: December 2006

Calcium antagonists have been shown to be superior over other antihypertensive drugs to prevent stroke. Because this cannot be fully attributed to blood pressure lowering effects, other mechanisms seem to play a role. Previously we found in patients with subarachnoid hemorrhage that nimodipine enhances fibrinolytic activity. The purpose of this systematic review was to investigate the fibrinolytic effect of calcium antagonists in general, especially in patients with hypertension. We systematically studied the entire PUBMED and EMBASE database with the search terms ‘calcium antagonist’ combined with ‘fibrinolysis’, ‘(euglobulin) clot lysis time’ (ECLT), ‘tissue plasminogen activator’ (tPA), or ‘plasminogen activator inhibitor’ (PAI). Twenty-six prospective studies were identified and 22 manuscripts were included (802 investigated individuals). The results show that calcium antagonists significantly increase fibrinolysis as shown by a reduction of the ECLT standardized mean differences (SMD) −0.58 (95% confidence interval (CI) −1.05 to −0.11)) and an increase of tPA activity (SMD 0.73 (95% CI 0.25 to 1.21)). This increase of fibrinolysis is apparently caused by an increase of the tPA antigen level (SMD 0.16 (95% CI −0.05 to 0.37)) and a decrease of the plasminogen activator inhibitor-1 antigen antigen (SMD −0.36 (95% CI −0.74 to 0.02)). A sensitivity analysis showed that dihydropyridines, but not phenylalkylamines, exert a fibrinolytic effect. This fibrinolytic effect is not only seen in patients with subarachnoid hemorrhage but also in hypertensive patients. In conclusions, calcium antagonists increase fibrinolytic activity. This may add to the beneficial pharmacological effect of calcium antagonists to prevent ischemic events in patients with hypertension and subarachnoid hemorrhage.
Monocyte Chemoattractant Protein-1 Plays a Critical Role in Neuroblast Migration after Focal Cerebral Ischemia
Authors: Yan Yi-Ping , Sailor Kurt A , Lang Bradley T , Park Seung-Won , Vemuganti Raghu , Dempsey Robert J
Published: December 2006

Transient focal ischemia is known to induce proliferation of neural progenitors in adult rodent brain. We presently report that doublecortin positive neuroblasts formed in the subventricular zone (SVZ) and the posterior peri-ventricle region migrate towards the cortical and striatal penumbra after transient middle cerebral artery occlusion (MCAO) in adult rodents. Cultured neural progenitor cells grafted into the non-infarcted area of the ipsilateral cortex migrated preferentially towards the infarct. As chemokines are known to induce cell migration, we investigated if monocyte chemoattractant protein-1 (MCP-1) has a role in post-ischemic neuroblast migration. Transient MCAO induced an increased expression of MCP-1 mRNA in the ipsilateral cortex and striatum. Immunostaining showed that the expression of MCP-1 was localized in the activated microglia and astrocytes present in the ischemic areas between days 1 and 3 of reperfusion. Furthermore, infusion of MCP-1 into the normal striatum induced neuroblast migration to the infusion site. The migrating neuroblasts expressed the MCP-1 receptor CCR2. In knockout mice that lacked either MCP-1 or its receptor CCR2, there was a significant decrease in the number of migrating neuroblasts from the ipsilateral SVZ to the ischemic striatum. These results show that MCP-1 is one of the factors that attract the migration of newly formed neuroblasts from neurogenic regions to the damaged regions of brain after focal ischemia.
Spin filter based tunnel junctions
Authors: Chapline Michael G. , Wang Shan X.
Published: December 2006

A theoretical estimate is given for the magnetoresistance ratio in ferromagnetic metal /nonmagnetic insulator/magnetic insulator/metallic junctions. Such a device has the potential to exhibit a room temperature magnetoresistive effect much larger than conventional magnetic tunnel devices. A half metallic electrode is desired but not required for achieving a sizable magnetoresistance in such devices. Some possible materials that could be used to fabricate such a device include ferrite based spin filters and CoFe∕MgO based electrodes. Such devices are predicted to give a magnetoresistance ratio >1000%.
Fluids in porous media. I. A hard sponge model
Authors: Zhao S. L. , Dong W. , Liu Q. H.
Published: December 2006

The morphology of many porous materials is spongelike. Despite the abundance of such materials, simple models which allow for a theoretical description of these materials are still lacking. Here, we propose a hard sponge model which is made by digging spherical cavities in a solid continuum. We found an analytical expression for describing the interaction potential between fluid particles and the spongelike porous matrix. The diagrammatic expansions of different correlation functions are derived as well as that of grand potential. We derived also the Ornstein-Zernike (OZ) equations for this model. In contrast to Madden-Glandt model of random porous media [W. G. Madden and E. D. Glandt, J. Stat. Phys. 51, 537 (1988)], the OZ equations for a fluid confined in our hard sponge model have some similarity to the OZ equations of a three-component fluid mixture. We show also how the replica method can be extended to study our sponge model and that the same OZ equations can be derived also from the extended replica method.
Universal T-matrix, representations of OSpq(1∕2) and little Q-Jacobi polynomials
Authors: Aizawa N. , Chakrabarti R. , Mohammed S. S. Naina , Segar J.
Published: December 2006

We obtain a closed form expression of the universal T-matrix encapsulating the duality between the quantum superalgebra Uq[osp(1∕2)] and the corresponding supergroup OSpq(1∕2). The classical q→1 limit of this universal T-matrix yields the group element of the undeformed OSpq(1∕2) supergroup. The finite dimensional representations of the quantum supergroup OSpq(1∕2) are readily constructed employing the above-mentioned universal T-matrix and the known finite dimensional representations of the dually related deformed Uq[osp(1∕2)] superalgebra. Proceeding further, we derive the product law, the recurrence relations, and the orthogonality of the representations of the quantum supergroup OSpq(1∕2). It is shown that the entries of these representation matrices are expressed in terms of the little Q-Jacobi polynomials with Q=−q. Two mutually complementary singular maps of the universal T-matrix on the universal R-matrix are also presented.
Topographically-induced enstrophy production/dissipation in coastal models
Authors: Terrile E. , Briganti R. , Brocchini M. , Kirby J. T.
Published: December 2006

Vorticity and enstrophy production and dissipation are studied for both wave-averaged and wave-resolving (Boussinesq-type) models of wave-induced near shore circulation. Quadratic flow properties of fundamental importance for shallow-water turbulence, i.e., energy and enstrophy, whose sources/sinks are clearly identifiable by positive/negative-definite contributions in the appropriate transport equations, are taken as the most suitable indicators for assessing model performance in describing flows characterized by large-scale vortices. Two state-of-the-art models, SHORECIRC and FUNWAVE2D, have been evaluated in detail. Suitable transport equations for enstrophy are derived and analyzed to get a clear insight into the mechanisms of generation/dissipation of this quantity in both models. Analytical results show that steep gradients of the total flow depth act as sinks as well as sources for vorticity and entrophy, similar to the results of Brocchini and Colombini [M. Brocchini and M. Colombini, Phys. Fluids 16, 2469 (2004)]. Predictive estimates have been given for the rate of change of circulation for waves breaking over a bar or breakwater and the vorticity source and sink terms have been numerically analyzed. The comparison between numerical results obtained using the two different circulation models reveals that while wave-resolving computations give well-structured rip currents, the wave-averaged model predicts less organized flows, given the different structure of the circulation forcing terms. The analysis of equivalent enstrophy-forcing terms characterizing the two models shows that they are all proportional to depth gradients in the case of wave-resolving models while their intensity is mainly due to the gradients of the wave-induced velocity for wave-averaged models. Energetic considerations are also given in support of the proposed vorticity/enstrophy generation mechanisms. Wave-averaged computations clearly show that, apart from bottom friction, the most intense dissipation mechanism is due to classic viscous effects [−νT(∇ω̃)2] while depth gradients weakly contribute. Rather surprisingly this also occurs for the wave-resolving model.
Measurements of relative x-ray line intensities and their application to a single standard procedure for quantitative x-ray microanalysis
Authors: Hatzistergos M. S. , Lifshin E.
Published: December 2006

X-ray spectra collected by an energy dispersive spectrometer on an electron microprobe analyzer were deconvoluted to determine relative line intensities between elements for a wide range of atomic numbers. The relative line intensities within spectral series for K, L, and M lines were also obtained. In the case of Kα lines an empirical formula is proposed for the prediction of generated line intensities of pure element standards relative to that of CuKα at 20keV used as a reference standard, although other line references can be used for lower beam energies. The generated ratios can be predicted with accuracy generally better than 2% relative to the actual measured values. The relationship covers elements with atomic numbers in the range of 12 (Mg) to 32 (Ge) and incident beam energies between 5 and 20keV. Unfortunately, L and M line data could not be fitted with the same level of accuracy to a single expression due to the inherent scatter in the data as a function of atomic number. These data are therefore presented in tabular form. The availability of relative line intensity measurements as a function of atomic number makes it possible to perform accurate quantitative x-ray microanalysis with the measurement of a single standard rather than a separate measurement of each element standard. As a result not only are measurement times shorter, but it is also possible to estimate values for elements for which pure standards may not be available. Furthermore, the method has been extended to quantitative analysis based only on the measurement of the sample spectrum.
Symmetric pairs of point vortices interacting with a neutrally buoyant two-dimensional circular cylinder
Authors: Shashikanth Banavara N.
Published: December 2006

The dynamic interaction of N symmetric pairs of point vortices with a neutrally buoyant two-dimensional rigid circular cylinder in the inviscid Hamiltonian model of Shashikanth et al. [Phys. Fluids 14, 1214 (2002)] and Shashikanth [Reg. Chaotic Dyn. 10, 1 (2005)] is examined. The model may be thought of as a section of an inviscid axisymmetric model of a neutrally buoyant sphere interacting with N coaxial circular vortex rings and has possible applications to problems such as fish swimming. The Hamiltonian structure of this half-space model is first presented. The cases N=1 and N=2 are then examined in detail. Equilibria and bifurcations are studied, and for both these cases an important bifurcation parameter involving the total linear “momentum” of the system, the strength of the vortex pairs, and the radius of the cylinder emerges. For N=1, it is shown that there exist the moving Föppl equilibrium and the moving normal line equilibrium (in which the vortices in the pair are located on the top and bottom of the moving cylinder). For N=2, when Γ1=Γ2 and when Γ1=−Γ2, there exists another set of equilibrium configurations. Linear stability analysis of all these equilibria, within the symmetric class of solutions, is carried out and phase portraits presented. In addition, for N=1, the velocity and acceleration surfaces for the cylinder are presented.
Unified model of association-induced lower critical solution temperature phase separation and its application to solutions of telechelic poly(ethylene oxide) and of telechelic poly(N-isopropylacrylamide) in water
Authors: Okada Yukinori , Tanaka Fumihiko , Kujawa Piotr , Winnik Françoise M.
Published: December 2006

The authors present a model describing the coexistence of hydrophobic association and phase separation with lower critical solution temperature (LCST) in aqueous solutions of polymers carrying short hydrophobic chains at both chain ends (telechelic associating polymers). The LCST of these solutions is found to decrease along the sol/gel transition curve as a result of both end-chain association (association-induced phase separation) and direct hydrophobic interaction of the end chains with water. The authors relate the magnitude of the LCST decrease to a hydration cooperativity parameter σ. The LCST decreases substantially (∼100K) in the case of random hydration (σ=1), whereas only a small shift (∼5–10K) occurs in the case of cooperative hydration (σ=0.3). The molecular weight dependence of the LCST drop is studied in detail in each case. The results are compared with experimental observations of the cloud points of telechelic poly(ethylene oxide) solutions, in which random hydration predominates, and of telechelic poly(N-isopropylacrylamide) solutions, in which cooperative hydration prevails.
Multiferroic properties of Pb(Zr,Ti)O3∕CoFe2O4 composite thin films
Authors: Ortega N. , Bhattacharya P. , Katiyar R. S. , Dutta P. , Manivannan A. , Seehra M. S. , Takeuchi I. , Majumder S. B.
Published: December 2006

In the present work we report multiferroic behavior in lead zirconate titanate (PZT)–cobalt iron oxide (CFO) composite thin films. It is found that upon annealing, the multilayered structures are intermixed at least partially, and CFO is phase separated into PZT matrix to form a composite film. The phase separation behavior has been characterized by x-ray photoelectron spectroscopy depth profiling of the constituent elements in conjunction with dielectric spectroscopy measurements. The composite films exhibited ferroelectric as well as ferromagnetic characteristics at room temperature. The coupling between the ferroelectric and the ferromagnetic order parameters has been demonstrated through the reduction of ferroelectric polarization when measured under an applied magnetic field.
Temperature dependence of the specific resistance in Ti∕Al∕Ni∕Au contacts on n-type GaN
Authors: Iucolano F. , Roccaforte F. , Alberti A. , Bongiorno C. , Di Franco S. , Raineri V.
Published: December 2006

The temperature dependence of the specific resistance ρc in annealed Ti∕Al∕Ni∕Au contacts on n-type GaN was monitored, obtaining information on the current transport mechanisms. After annealing at 600°C, the contacts exhibited a rectifying behavior and became Ohmic only after high temperature processes (>700°C), with ρc in the low 10−5Ωcm2 range. The results demonstrated that the current transport is ruled by two different mechanisms: thermoionic field emission occurs in the contacts annealed at 600°C, whereas field emission dominates after higher temperature annealing. The significant physical parameters related to the current transport, i.e., the Schottky barrier height and the carrier concentration under the contact, could be determined. In particular, a reduction of the Schottky barrier from 1.21eV after annealing at 600°Cto0.81eV at 800°C was determined, accompanied by a strong increase of the carrier concentration, i.e., from 2×1018cm−3 in the as-prepared sample to 4.6×1019cm−3 in the annealed contacts. The electrical properties were correlated to the microstructure of the interfacial region, providing a scenario to explain the transition from Schottky to Ohmic behavior in annealed Ti∕Al∕Ni∕Au contacts.
A dynamic subgrid-scale eddy viscosity model with a global model coefficient
Authors: Park Noma , Lee Sungwon , Lee Jungil , Choi Haecheon
Published: December 2006

In the present study, a dynamic subgrid-scale eddy viscosity model is proposed for large eddy simulation of turbulent flows in complex geometry. A subgrid-scale eddy viscosity model recently proposed by Vreman [Phys. Fluids 16, 3670 (2004)] which guarantees theoretically zero subgrid-scale dissipation for various laminar shear flows, is considered as a base model. A priori tests with the original Vreman model show that it predicts the correct profile of subgrid-scale dissipation in turbulent channel flow but the optimal model coefficient is far from universal. A dynamic procedure of determining the model coefficient is proposed based on the “global equilibrium” between the subgrid-scale dissipation and the viscous dissipation. An important feature of the proposed procedure is that the model coefficient determined is globally constant in space but varies only in time. A posteriori tests of the proposed dynamic model are conducted through large eddy simulations of forced isotropic turbulence at Reλ=103, turbulent channel flows at Reτ=180 and 590, flow over a circular cylinder at Red=3900, and flows over a sphere at Red=3700 and 104. The proposed dynamic model produces excellent performance for all flows considered. As shown in the present paper, the proposed model is robust and it can be readily applied to complex flows without homogeneous direction.
Writing and erasing data in magnetic domain wall logic systems
Authors: Allwood D. A. , Xiong Gang , Cowburn R. P.
Published: December 2006

We have developed magnetic elements for field-writable data input to magnetic domain wall logic circuits. The data input elements allow domain walls to be selectively nucleated while maintaining operation of other types of logic element. Here we show for two data input element designs how their performance is optimized and how each element design requires different operating conditions. Each element design is integrated with a shift register made up of a chain of logical NOT gates. A bitwise delete operation is demonstrated with one of these shift registers by controlling domain wall propagation to bring about selective domain wall pair annihilation.
Near-field thermal radiative transfer and thermoacoustic effects from vapor plumes produced by pulsed CO2 laser ablation of bulk water
Authors: Kudryashov S. I. , Lyon Kevin , Allen S. D.
Published: December 2006

Submillimeter deep heating of bulk water by thermal radiation from ablative water plumes produced by a 10.6μm transversely excited atmospheric CO2 laser and the related acoustic generation has been studied using a contact time-resolved photoacoustic technique. Effective penetration depths of thermal radiation in water were measured as a function of incident laser fluence and the corresponding plume temperatures were estimated. The near-field thermal and thermoacoustic effects of thermal radiation in laser-ablated bulk water and their potential near-field implications are discussed.
Electromigration in flip chip solder joints having a thick Cu column bump and a shallow solder interconnect
Authors: Nah Jae-Woong , Suh J. O. , Tu K. N. , Yoon Seung Wook , Rao Vempati Srinivasa , Kripesh Vaidyanathan , Hua Fay
Published: December 2006

In advanced electronic products, current crowding induced electromigration failure is one of the serious problems in fine pitch flip chip solder joints. To explore a strong resistance against current crowding induced electromigration failure, a very thick Cu column bump combined with a shallow solder interconnect at 100μm pitch for flip chip applications has been studied in this paper. Results revealed that these interconnects do not fail after 720h of current stressing at 100°C with a current density of 1×104A∕cm2 based on the area of interface between Cu column bump and solder. The reduction of current crowding in the solder region by using thick Cu column bumps increased the reliability against electromigration induced failure. The current distribution in a flip chip joint of a Cu column bump combined with a shallow solder has been confirmed by simulation. However, Kirkendall void formation was found to be much serious and enhanced by electromigration at the Cu∕Cu3Sn interface due to the large Cu∕Sn ratio. Since this is a system of a limited amount of Sn and an infinite supply of Cu, the Cu6Sn5 transforms to the Cu3Sn after all the Sn content in the solder bump is consumed and the Cu3Sn can grow very thick; the vacancy flux that opposes the Cu flux will condense to form Kirkendall voids. The mechanism of electromigration induced Kirkendall void formation in the Cu column with the shallow solder joint is discussed. Furthermore, a very large temperature gradient exists across the shallow solder interconnects, leading to thermomigration. Electromigration accompanied by thermomigration could replace current crowding as a serious reliability issue in using Cu column based interconnects.
Precise measurement of the differential cross section from the O16(α,α)O16 elastic reaction at 165° and 170° between 2.4 and 6.0MeV
Authors: Demarche Julien , Terwagne Guy
Published: December 2006

Non-Rutherford cross section for elastic scattering of α particles from oxygen has been measured for energies between 2.4 and 6.0MeV at commonly used backscattering angles of 165° and 170°. High precision in energy has been obtained with a 2MV Tandetron accelerator, with precise and stable energy calibration. The choice of a thin Ta2O5∕Ta∕C standard increased the sensitivity and reduced systematic errors due to the geometry. Precise data for energy, width, and ratio to Rutherford of the resonances have been extracted from nuclear shell models, and excitation levels of Ne20 have been deduced. The well-known resonance ER=3031.7±0.5keV and the narrow and intense resonance ER=5375.5±0.5keV, not included in cross-section libraries, have been applied for surface oxygen analysis in thin WCN∕SiO2∕Si multilayer samples, with improved depth resolution by optimizing the measuring geometry.
Resonant power absorption in helicon plasma sources
Authors: Chen Guangye , Arefiev Alexey V. , Bengtson Roger D. , Breizman Boris N. , Lee Charles A. , Raja Laxminarayan L.
Published: December 2006

Helicon discharges produce plasmas with a density gradient across the confining magnetic field. Such plasmas can create a radial potential well for nonaxisymmetric whistlers, allowing radially localized helicon (RLH) waves. This work presents new evidence that RLH waves play a significant role in helicon plasma sources. An experimentally measured plasma density profile in an argon helicon discharge is used to calculate the rf field structure. The calculations are performed using a two–dimensional field solver under the assumption that the density profile is axisymmetric. It is found that RLH waves with an azimuthal wave number m=1 form a standing wave structure in the axial direction and that the frequency of the RLH eigenmode is close to the driving frequency of the rf antenna. The calculated resonant power absorption, associated with the RLH eigenmode, accounts for most of the rf power deposited into the plasma in the experiment.
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-dimensional generalized Johnson model for cosmic dust-ion-acoustic nebulons with symbolic computation
Authors: Gao Yi-Tian , Tian Bo
Published: December 2006

In a cosmic dusty plasma, both azimuthal and height perturbations of a nonplanar cylindrical geometry are considered. For dust-ion-acoustic waves and with symbolic computation, (3+1)-dimensional generalized Johnson [(3+1)DGJ] model is derived and analytic solutions are constructed. Supernova-shell-typed expanding bright (3+1)DGJ nebulons and Saturn-F-ring-type expanding dark (3+1)DGJ nebulons are both pictured and discussed. Essential difference of this letter from the existing literature is pointed out, with the relevant, possibly observable (3+1)DGJ-nebulonic structures for the future cosmic experiments proposed.
Determination of rotary diffusivity of poly(n-propyl isocyanate) by molecular dynamics
Authors: Laso M. , Jimeno N. , Muneta L. M. , Müller M.
Published: December 2006

The rotational dynamics of a nondilute solution of the rodlike polymer poly(n-propyl isocyanate) (PPIC) has been studied on an atomistic model by means of a large-scale classical molecular dynamics investigation. The rotary diffusivity of PPIC in toluene solution has been determined from the Einsteinian diffusion regime of the end-to-end vector on the surface of the unit sphere and has been found to be Dr=10.5×105(±2.7)s−1, which falls in the range of the experimental data available. A comparison of molecular dynamics predictions with theoretical and perturbation expansion predictions has also been performed.
Loss and retardation effect on subwavelength imaging by compensated bilayer of anisotropic metamaterials
Authors: Chen Yan , Teng Xiaohua , Huang Ying , Feng Yijun
Published: December 2006

We analyze the subwavelength imaging using compensated bilayer of anisotropic metamaterials and study the material loss and retardation effect on the image properties. Through rigorous analysis of the electromagnetic wave transmission and numerical calculations of the electromagnetic field distribution, we demonstrate that the anisotropic bilayer lens exhibits a decreased sensitivity to material loss and retardation, therefore has a better image with subwavelength resolution than that of the isotropic perfect lens configuration. We find that this is due to the fact that the inhomogeneous evanescent waves that are responsible for image resolution beyond the diffraction limit have been converted to propagating waves in the anisotropic bilayer, resulting in less sensitive to material loss and retardation.
A quasi(unidirectional) Tellegen gyrator
Authors: Zhai Junyi , Li Jiefang , Dong Shuxiang , Viehland D. , Bichurin M. I.
Published: December 2006

We show that magnetoelectric (ME) laminate composites have characteristics of a previously conjectured, but unfound, fifth network circuit element—the Tellegen gyrator. Our findings establish that ME laminate composites (i) are nonreciprocal electrical elements, (ii) have significant nondissipative I-V conversion near a resonance frequency, and (iii) act like a unidirectional gyrator, i.e., an ideal Tellegen gyrator connected with a capacitor on one side and an inductor on the other.
Enhanced magnetoelectric effect in three-phase MnZnFe2O4∕Tb1−xDyxFe2−y∕Pb(Zr,Ti)O3 composites
Authors: Dong Shuxiang , Zhai Junyi , Li JieFang , Viehland D.
Published: December 2006

Three-phase magnetoelectric (ME) laminate composites made of high-permeability (μ) MnZnFe2O4, magnetostrictive Tb1−xDyxFe2−y, and piezoelectric Pb(Zr,Ti)O3 layers and operated in longitudinal magnetization and transverse polarization (L-T) bending modes have been studied. High-μ MnZnFe2O4 layers act as flux concentrators. This results in increased apparent piezomagnetic coefficients in the magnetostrictive Tb1−xDyxFe2−y layer and consequently larger induced voltages across the piezoelectric Pb(Zr,Ti)O3 layers. We find the enhanced ME field coefficients of up to 8 times for longitudinal magnetization mode, and up to 28 times for transverse magnetization mode, under small dc magnetic field bias.
Optical absorption intensity analysis and emission cross sections for the intermanifold and the inter-Stark transitions of Nd3+(4f3) in polycrystalline ceramic Y2O3
Authors: Sardar Dhiraj K. , Dee Douglas M. , Nash Kelly L. , Yow Raylon M. , Gruber John B.
Published: December 2006

Spectroscopic properties have been characterized for trivalent neodymium doped polycrystalline ceramic ytttria, Nd3+:Y2O3. The Judd-Ofelt [Phys. Rev. 127, 750 (1962); J. Chem. Phys. 37, 511 (1962)] analysis has been applied to the room temperature absorption spectrum to determine the radiative decay rates and branching ratios of Nd3+ transitions from the F3∕24 metastable manifold to the IJ4 lower-lying multiplet manifolds. The quantum efficiency is determined from the measured fluorescence lifetime and the radiative lifetime of the F3∕24 manifold state. In addition, a detailed characterization of the Stark energy levels of the I9∕24 and I11∕24 manifolds has been performed using the room temperature fluorescence spectra for the F3∕24→I9∕24 and F3∕24→I11∕24 transitions of Nd3+(4f3) in ceramic Y2O3. The emission cross sections of the F3∕24→I9∕24 and F3∕24→I11∕24 intermanifold transitions have been determined. Also, the peak emission cross sections of the principal inter-Stark peak transitions R1→X5 and R1→Y2 have been determined. Finally, the spectroscopic properties of ceramic Nd3+:Y2O3 are compared with those of ceramic Nd3+:YAG as well as single crystals of Nd3+:Y2O3 and Nd3+:YAG.
Epitaxial growth and orientation of AlN thin films on Si(001) substrates deposited by reactive magnetron sputtering
Authors: Valcheva E. , Birch J. , Persson P. O. Å. , Tungasmita S. , Hultman L.
Published: December 2006

Epitaxial domain formation and textured growth in AlN thin films deposited on Si(001) substrates by reactive magnetron sputtering was studied by transmission electron microscopy and x-ray diffraction. The films have a wurtzite type structure with a crystallographic orientation relationship to the silicon substrate of AlN(0001)‖Si(001). The AlN film is observed to nucleate randomly on the Si surface and grows three dimensionally, forming columnar domains. The in-plane orientation reveals four domains with their a axes rotated by 15° with respect to each other: AlN⟨112¯0⟩‖Si[110], AlN⟨011¯0⟩‖Si[110], AlN⟨112¯0⟩‖Si[100], and AlN⟨011¯0⟩‖Si[100] An explanation of the growth mode based on the large lattice mismatch and the topology of the substrate surface is proposed.
KrF excimer laser-assisted combustion-flame deposition of diamond films
Authors: Han Y. X. , Ling H. , Lu Y. F.
Published: December 2006

Cobalt (Co) composition has detrimental effects on the deposition of diamond films on cemented tungsten carbide (WC-Co) substrates. It decreases adhesion of the deposited films to the substrates and causes a transformation of sp3-bonded diamond to sp2-bonded graphite. In this study, a KrF excimer laser with a wavelength of 248nm, a pulse width of 23ns, and a pulse energy range of 84–450mJ was used in the combustion-flame method to improve the quality of the deposited diamond films. Scanning electron microscopy, energy dispersive x-ray analysis, and Raman spectroscopy of the deposited films showed that a laser irradiation during combustion-flame deposition of diamond decreased the cobalt composition drastically. Based on the experimental results, the influence of the laser irradiation on the deposition process was analyzed.
Synchrotron radiation x-ray beam profile monitor using chemical vapor deposition diamond film
Authors: Kudo Togo , Takahashi Sunao , Nariyama Nobuteru , Hirono Toko , Tachibana Takeshi , Kitamura Hideo
Published: December 2006

Photoluminescence (PL) of a Si-doped polycrystalline diamond film fabricated using the chemical vapor deposition technique was employed to measure the profile of a synchrotron radiation pink x-ray beam emitted from an in-vacuum hybrid undulator at the SPring-8 facility. The spectrum of the section of the diamond film penetrated by the emitted visible red light exhibited a peak at 739nm and a wideband structure extending from 550to700nm. The PL intensity increased with the absorbed dose of the incident beam in the diamond within a dynamic range of 103. A two-dimensional distribution of the PL intensity revealed the undulator beam profile.
Combining explicitly correlated R12 and Gaussian geminal electronic structure theories
Authors: Valeev Edward F.
Published: December 2006

Explicitly correlated R12 methods using a single short-range correlation factor (also known as F12 methods) have dramatically smaller basis set errors compared to the standard wave function counterparts, even when used with small basis sets. Correlations on several length scales, however, may not be described efficiently with one correlation factor. Here the authors explore a more general MP2-R12 method in which each electron pair uses a set of (contracted) Gaussian-type geminals (GTGs) with fixed exponents, whose coefficients are optimized linearly. The following features distinguish the current method from related explicitly correlated approaches published in the literature: (1) only two-electron integrals are needed, (2) the only approximations are the resolution of the identity and the generalized Brillouin condition, (3) only linear parameters are optimized, and (4) an arbitrary number of (non-)contracted GTGs can appear. The present method using only three GTGs and a double-zeta quality basis computed valence correlation energies for a set of 20 small molecules only 2.2% removed from the basis set limit. The average basis set error reduces to 1.2% using a near-complete set of seven GTGs with the double-zeta basis set. The conventional MP2 energies computed with much larger quadruple, quintuple, and sextuple basis sets all had larger average errors: 4.6%, 2.4%, and 1.5%, respectively. The new method compares well to the published MP2-R12 method using a single Slater-type geminal (STG) correlation factor. For example, the average basis set error in the absolute MP2-R12 energy obtained with the exp(−r12) correlation factor is 1.7%. Correlation contribution to atomization energies evaluated with the present method and with the STG-based method only required a double-zeta basis set to exceed the precision of the conventional sextuple-zeta result. The new method is shown to always be numerically stable if linear dependencies are removed from the two-particle basis and the zeroth-order Hamiltonian matrix is made positive definite.
Quantum mechanical polarizable force field (QMPFF3): Refinement and validation of the dispersion interaction for aromatic carbon
Authors: Donchev A. G. , Galkin N. G. , Pereyaslavets L. B. , Tarasov V. I.
Published: December 2006

The authors have recently introduced a general, polarizable force field QMPFF fitted solely to high-level quantum mechanical data for simulations of biomolecular systems. Here the authors demonstrate using an advanced version QMPFF3 how the problem of insufficient accuracy of the MP2-based training set for the aromatic carbon atom type can be effectively solved by a simple model correction using state-of-the-art CCSD(T) data. The approach demonstrates excellent transferability, which is confirmed for three phases of matter by accurate calculations of the second virial coefficient for benzene vapor and various properties of liquid benzene and polyaromatic hydrocarbon crystals.
H
∕
D
isotope effect on porphine and porphycene molecules with multicomponent hybrid density functional theory
Authors: Udagawa Taro , Tachikawa Masanori
Published: December 2006

To analyze the H∕D isotope effect on porphine and porphycene molecules including the protonic/deuteronic quantum nature and electron correlation efficiently, the authors have developed the new scheme of the multicomponent hybrid density functional theory [MC̱(HF+DFT)]. The optimized geometries of porphine, porphycene, and these deuterated isotopomers by our MC̱(HF+DFT) method are in good agreement with the experimental “high-symmetric” structures, contrary to the “low-symmetric” geometries optimized by pure multicomponent Hartree-Fock method. The optimized geometries for HD-porphine and HD-porphycene molecules, in which an inner hydrogen is replaced to a deuterium, are found to be low symmetric. Such drastic geometrical change induces the electronic polarization, and gives rise to the slight dipole moment values in these HD species. Their results clearly indicate that the difference of the nuclear quantum nature between inner proton and inner deuteron directly influences the molecular geometry and electronic structure.
Elastic deformation of nanometer-sized metal crystals in graphitic shells
Authors: Sun L. , Rodríguez-Manzo J. A. , Banhart F.
Published: December 2006

The elastic deformation of nanometer-sized metal crystals is achieved by encapsulating them in carbon nanotubes or carbon onions. Electron irradiation of these core-shell particles leads to high pressure in their center due to a shrinkage of the graphitic shells. Pressures in the range of 10–30GPa are found by measuring the decrease in lattice spacings in the encapsulated metal crystals. Hence, it is quantitatively shown how closed graphitic shells can be applied as compression cells on the nanoscale.
Quasi-mono-energetic ion acceleration from a homogeneous composite target by an intense laser pulse
Authors: Brantov A. V. , Tikhonchuk V. T. , Klimo O. , Romanov D. V. , Ter-Avetisyan S. , Schnürer M. , Sokollik T. , Nickles P. V.
Published: December 2006

The paper presents an analytical model and particle-in-cell simulations of the quasi-mono-energetic ion acceleration by an intense laser pulse in a multispecies target and the corresponding experimental observations. Homogeneous and heterogeneous targets are considered, and it is shown that the formation of the energy spectrum proceeds in three stages: (1) the initial light ion acceleration in the sheath electric field, (2) the ion species separation followed by the electrostatic shock formation, and (3) the interaction of spatially separated ion bunches accompanied by electron cooling. The field ionization of heavy ions and interaction between the heavy and light species play an important role in the formation and preservation of the energy spectrum of light ions. The simulation results are compared with the theoretical predictions and the experiments.
Coupled fluid-flow and magnetic-field simulation of the Riga dynamo experiment
Authors: Kenjereš S. , Hanjalić K. , Renaudier S. , Stefani F. , Gerbeth G. , Gailitis A.
Published: December 2006

Magnetic fields of planets, stars, and galaxies result from self-excitation in moving electroconducting fluids, also known as the dynamo effect. This phenomenon was recently experimentally confirmed in the Riga dynamo experiment [A. Gailitis et al., Phys. Rev. Lett. 84, 4365 (2000); A. Gailitis et al., Physics of Plasmas 11, 2838 (2004)], consisting of a helical motion of sodium in a long pipe followed by a straight backflow in a surrounding annular passage, which provided adequate conditions for magnetic-field self-excitation. In this paper, a first attempt to simulate computationally the Riga experiment is reported. The velocity and turbulence fields are modeled by a finite-volume Navier-Stokes solver using a Reynolds-averaged-Navier-Stokes turbulence model. The magnetic field is computed by an Adams-Bashforth finite-difference solver. The coupling of the two computational codes, although performed sequentially, provides an improved understanding of the interaction between the fluid velocity and magnetic fields in the saturation regime of the Riga dynamo experiment under realistic working conditions.
A double gate metal-oxide-semiconductor structure for modulation of the hyperfine interaction in phosphorous-doped Si device
Authors: Tehranchi Farzad , Leburton J.-P. , Thean Aaron
Published: December 2006

In this paper, we investigate a scheme for the control of the hyperfine interaction between a conduction electron and a P impurity nuclear spin in a symmetric metal-oxide-semiconductor structure with face-to-face gate oxide layers. We solve Poisson’s equation for the device electronics and Schrödinger’s equation for the quantum states in the silicon layer by taking into account the effective mass anisotropy around each of the six degenerate minima in the silicon conduction band. We show that the double gate device provides better performances, in terms of better wave function amplitude modulation and consequently higher nuclear magnetic resonance frequency than in single gate devices for relatively short impurity distances from the oxide layers.
Application of differential phase method to interferometry
Authors: Yamada Takuma , Ejiri Akira , Shiraiwa Syun'ichi , Takase Yuichi
Published: December 2006

The differential phase (DP) method was applied to microwave interferometry for the first time. Its advantage over standard interferometry is that the greatly reduced phase shift enables the unique determination of phase. Such a system was implemented on the Tokyo Spherical Tokamak-2 (TST-2), and demonstrated that the correct phase shift can be obtained even when the probing frequency is close to the cutoff density, and that very fast time evolutions of the line-integrated density can be measured.