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Distribution by Scientific Domains

Physics and Astronomy	27%
Medical Sciences	27%
Engineering	18%

Selected Abstracts

Primary particle size distribution of eroded material affected by degree of aggregate slaking and seal development

EUROPEAN JOURNAL OF SOIL SCIENCE, Issue 1 2009
D. N. Warrington
Summary Primary particle size distribution (PSD) of eroded sediment can be used to estimate potential nutrient losses from soil and pollution hazards to the environment. We studied eroded sediment PSDs from three saturated soils, packed in trays (20 × 40 × 4 cm), that had undergone either minimal aggregate slaking (MAS) or severe aggregate slaking (SAS) prior to a 60 mm simulated rainstorm (kinetic energy, 15.9 kJ m,3; droplet diameter, 2.97 mm) and collected runoff at regular intervals. The degree of aggregate slaking was controlled by the rate at which soils were wetted to saturation. The PSDs of eroded materials and of parent soils were determined using a laser particle size analyser. For each soil, PSD frequency curves of eroded sediments and parent soils were generally of a similar shape but most eroded sediments had larger clay contents than their parent soils. In the SAS treatment, cumulative clay enrichment in the eroded materials was inversely related to the parent soil clay content, these being 28.5, 26.6 and 22.8% richer in clay than their parent soils for the loam, sandy clay and clay, respectively. Generally, total clay loss was greater from soils with SAS than from those with MAS because of erosion rates; however, clay enrichment of sediments, compared with parent soil clay contents, was mostly greater in samples with MAS. Greater clay enrichment took place during the early seal development stage in the loam, but could not readily be associated with specific stages of seal development for the clay. In the sandy clay, the relation between seal development and clay enrichment in the eroded material depended on the initial degree of aggregate slaking. The observed large preferential loss of clay by erosion in cultivated soils re-emphasizes the need to employ erosion control measures. [source]

Empirical slip and viscosity model performance for microscale gas flow

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 11 2005
Matthew J. McNenly
Abstract For the simple geometries of Couette and Poiseuille flows, the velocity profile maintains a similar shape from continuum to free molecular flow. Therefore, modifications to the fluid viscosity and slip boundary conditions can improve the continuum based Navier,Stokes solution in the non-continuum non-equilibrium regime. In this investigation, the optimal modifications are found by a linear least-squares fit of the Navier,Stokes solution to the non-equilibrium solution obtained using the direct simulation Monte Carlo (DSMC) method. Models are then constructed for the Knudsen number dependence of the viscosity correction and the slip model from a database of DSMC solutions for Couette and Poiseuille flows of argon and nitrogen gas, with Knudsen numbers ranging from 0.01 to 10. Finally, the accuracy of the models is measured for non-equilibrium cases both in and outside the DSMC database. Flows outside the database include: combined Couette and Poiseuille flow, partial wall accommodation, helium gas, and non-zero convective acceleration. The models reproduce the velocity profiles in the DSMC database within an L2 error norm of 3% for Couette flows and 7% for Poiseuille flows. However, the errors in the model predictions outside the database are up to five times larger. Copyright © 2005 John Wiley & Sons, Ltd. [source]

Effects of Tooth Preparation Burs and Luting Cement Types on the Marginal Fit of Extracoronal Restorations

JOURNAL OF PROSTHODONTICS, Issue 2 2009
Mohamed F. Ayad BDS
Abstract Purpose: Although surface roughness of axial walls could contribute to precision of a cast restoration, it is unclear how the roughness of tooth preparation affects marginal fit of the restoration in clinical practice. The purpose of this study was to describe the morphologic features of dentin surfaces prepared by common rotary instruments of similar shapes and to determine their effects on the marginal fit for complete cast crowns. Materials and Methods: Ninety crowns were cast for standardized complete crown tooth preparations. Diamond, tungsten carbide finishing, and crosscut carbide burs of similar shape were used (N = 30). The crowns in each group were subdivided into three groups (n = 10) for use with different luting cements: zinc phosphate cement (Fleck's), glass ionomer cement (Ketac-Cem), and adhesive resin cement (Panavia 21). Marginal fit was measured with a light microscope in a plane parallel to the tooth surface before and after cementation between four pairs of index indentations placed at equal distances around the circumference of each specimen. Difference among groups was tested for statistical significance with analysis of variance (ANOVA) followed by Ryan-Einot-Gabriel-Welsch Multiple Range Test (,= 0.05). Results: Analysis of measurements disclosed a statistically significant difference for burs used to finish tooth preparations (p < 0.001); however, luting cement measurements were not significantly different (p= 0.152). Also, the interaction effect was not significantly different (p= 0.685). For zinc phosphate cement, the highest marginal discrepancy value (100 ± 106 ,m) was for tooth preparations refined with carbide burs, and the lowest discrepancy value (36 ± 30 ,m) was for tooth preparations refined with finishing burs. For glass ionomer cement, the highest marginal discrepancy value (61 ± 47 ,m) was for tooth preparations refined with carbide burs, and the lowest discrepancy value (33 ± 40 ,m) was for tooth preparations refined with finishing burs. For adhesive resin cement, the highest marginal discrepancy value (88 ± 81 ,m) was for tooth preparations refined with carbide burs, and the lowest discrepancy value (19 ± 17 ,m) was for tooth preparations refined with finishing burs. Conclusions: Marginal fit of complete cast crowns is influenced by tooth preparation surface characteristics, regardless of the type of luting agent used for cementation. Tooth preparations refined with finishing burs may favor the placement of restorations with the smallest marginal discrepancies, regardless of the type of cement used. [source]

A QSO host galaxy and its Ly, emission at z= 6.43,

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2009
Tomotsugu Goto
ABSTRACT Host galaxies of highest redshift quasi-stellar objects (QSOs) are of interest; they provide us with a valuable opportunity to investigate physics relevant to the starburst,active galactic nuclei (AGN) connection at the earliest epoch of the Universe, with the most luminous black holes. Here, we report an optical detection of an extended structure around a QSO at z= 6.43 in deep z,- and zr -band images of the Subaru/Suprime-Cam. Our target is CFHQS J2329-0301 (z= 6.43), the highest redshift QSO currently known. We have carefully subtracted a point spread function (PSF) constructed using nearby stars from the images. After the PSF (QSO) subtraction, a structure in the z, band extends more than 4 arcsec on the sky (Re= 11 kpc), and, thus, is well resolved (16, detection). The PSF-subtracted zr -band structure is in a similar shape to that in the z, band, but less significant with a 3, detection. In the z, band, a radial profile of the QSO+host shows a clear excess over that of the averaged PSF in 0.8,3 arcsec radius. Since the z, band includes a Ly, emission at z= 6.43, we suggest the z, flux is a mixture of the host (continuum light) and its Ly, emission, whereas the zr -band flux is from the host. Through a SED modelling, we estimate 40 per cent of the PSF-subtracted z,-band light is from the host (continuum) and 60 per cent is from Ly, emission. The absolute magnitude of the host is M1450=,23.9 (cf. M1450=,26.4 for the QSO). A lower limit of the SFR(Ly,) is 1.6 M, yr,1 with stellar mass ranging from 6.2 × 108 to 1.1 × 1010 M, when 100 Myr of age is assumed. The detection shows that a luminous QSO is already harboured by a large, star-forming galaxy in the early Universe only after ,840 Myr after the big bang. The host may be a forming giant galaxy, co-evolving with a super-massive black hole. [source]

Photoluminescence properties of erbium-doped amorphous gallium-germanium-selenium films fabricated by RF sputtering

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue S1 2009
Takahiko Imai
Abstract Chalcogenide glasses have various useful features for optical devices such as a high refractive index, low-loss transmission in the mid-IR, and low phonon energies. The fabrication of thin films is important for use in waveguide applications and integrated photonics. In this work, we report the properties of vacuum deposited films of gallium-germanium-selenium glasses onto fused silica substrates by an RF magnetron sputtering technique (RF electric power of 40-250 W and growth rate of 0.01-2.1 ,m/min). The concentration of Er3+ ions is controlled by the number of sintered Er2S3 small plates on a target. Samples are shown to be in an amorphous-like state as measured by X-ray diffraction experiments. Film thicknesses are proportional to the RF sputtering power and sputtering time. The compositions of films obtained from energy dispersive X-ray (EDX) analysis. There are much dependent on the condition of the sputtering target, for example whether the target is in the bulk or powder-state. Photoluminescence (PL) spectrum, intensity, and lifetime at 1550 nm band are measured by excitation from a 973 nm laser. The PL band of the films has a similar shape to those of bulk glasses. The PL intensity increased with the RF electric power. The PL lifetime at the 1550 nm band of the film is about 1.8-2.6 ms; the latter values are similar to those of bulk samples. The results show that the RF sputtering is a potential method of fabrication for Er-doped GeGaSe thin films. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Early neural activity in Necker-cube reversal: Evidence for low-level processing of a gestalt phenomenon

PSYCHOPHYSIOLOGY, Issue 1 2004
Jürgen Kornmeier
Abstract Normally we experience the visual world as stable. Ambiguous figures provide a fascinating exception: On prolonged inspection, the "Necker cube" undergoes a sudden, unavoidable reversal of its perceived front-back orientation. What happens in the brain when spontaneously switching between these equally likely interpretations? Does neural processing differ between an endogenously perceived reversal of a physically unchanged ambiguous stimulus and an exogenously caused reversal of an unambiguous stimulus? A refined EEG paradigm to measure such endogenous events uncovered an early electrophysiological correlate of this spontaneous reversal, a negativity beginning at 160 ms. Comparing across nine electrode locations suggests that this component originates in early visual areas. An EEG component of similar shape and scalp distribution, but 50 ms earlier, was evoked by an external reversal of unambiguous figures. Perceptual disambiguation seems to be accomplished by the same structures that represent objects per se, and to occur early in the visual stream. This suggests that low-level mechanisms play a crucial role in resolving perceptual ambiguity. [source]

Dimensional response analysis of yielding structures with first-mode dominated response

EARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 10 2006
Nicos Makris
Abstract This paper introduces a new way of estimating the inelastic response of first-mode dominated structures with behaviour that can be approximated with the elastoplastic idealization. The proposed approach emerges from formal dimensional analysis and is liberated from the response of the elastic system. The application of the proposed method hinges upon the existence of a distinct time scale and a length scale that characterize the most energetic component of the ground shaking. Such time and length scales emerge naturally from the distinguishable pulses which dominate a wide class of strong earthquake records; they are directly related with the rise time and slip velocity of faulting, and can be formally extracted with validated mathematical models published in the literature. The most decisive feature of this work is that the inelastic response curves that result with the proposed approach assume similar shapes for different values of the normalized yield displacement. Because of this similarity the paper proposes a single inelastic response curve which offers directly the maximum inelastic displacement of the structure given the energetic pulse period and pulse amplitude of the ground shaking. When the proposed method is applied to MDOF structures it is not capable to estimate interstorey drifts nor is capable to capture the effects of negative stiffness which may result due to P-delta effect. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Fuzzy information granules in time series data

INTERNATIONAL JOURNAL OF INTELLIGENT SYSTEMS, Issue 7 2004
Michael R. Berthold
Often, it is desirable to represent a set of time series through typical shapes in order to detect common patterns. The algorithm presented here compares pieces of a different time series in order to find such similar shapes. The use of a fuzzy clustering technique based on fuzzy c-means allows us to detect shapes that belong to a certain group of typical shapes with a degree of membership. Modifications to the original algorithm also allow this matching to be invariant with respect to a scaling of the time series. The algorithm is demonstrated on a widely known set of data taken from the electrocardiogram (ECG) rhythm analysis experiments performed at the Massachusetts Institute of Technology (MIT) laboratories and on data from protein mass spectrography. © 2004 Wiley Periodicals, Inc. [source]

Analysis of the Defibrillation Efficacy for 5-ms Waveforms

JOURNAL OF CARDIOVASCULAR ELECTROPHYSIOLOGY, Issue 4 2004
DONGXU GUAN Ph.D.
Introduction: Empirical studies have shown that biphasic defibrillation waveforms are more efficacious than monophasic waveforms. However, a more systematic approach to waveform development might be more productive. This study tested 147 multiphasic waveforms uniformly sampled from all possible 5-ms waveforms. Methods and Results: One hundred ninety-eight guinea pigs (850,1,050 g) received 30 episodes of ventricular fibrillation followed by transthoracic defibrillation. The first 10 shocks were used to determine the ED50 for a biphasic control. Then, 20 waveforms including 2 controls were tested once at the ED50. Of the 147 waveforms tested here, 21 waveforms showed equivalent or greater efficacies than the biphasic control, with one being statistically more efficacious (P < 0.05). Two fundamental assumptions were addressed: (1) similarly efficacious waveforms are analytically similar, and (2) a single optimal waveform can be described. The mean percentage of similarly efficacious waveforms with similar shapes was greater than zero in the most efficacious 21 waveforms (P = 0.023), but less efficacious waveforms showed randomly distributed shapes. Cluster analysis revealed that the best waveforms share a major phase containing most of the defibrillation energy. The optimal waveform shape extrapolated from the sample waveforms was a 2.5/1-ms biphasic-type waveform (highest correlation r = 0.701, P < 0.001). Conclusion: This work supports the assumption that efficacious waveforms are similarly shaped and the notion that one single optimum exists. (J Cardiovasc Electrophysiol, Vol. 15, pp. 447-454, April 2004) [source]

Effects of Tooth Preparation Burs and Luting Cement Types on the Marginal Fit of Extracoronal Restorations

Shape transition of medium-sized neutral silicon clusters

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 3 2003
A. Sieck
Abstract Addressing the shape transition of silicon clusters, indicated by mobility experiments on silicon cluster cations with 24 to 30 atoms, we investigate the structure of low energy neutral silicon clusters with 25, 29, and 35 atoms within a density-functional based tight-binding approach. Since there is strong evidence for several nearly degenerate low-energy isomers for clusters of this size, we perform an extensive, but limited global search with Simulated Annealing and statistically analyze for each cluster size the 100 clusters with the lowest energy. We find different dominant shapes in the set of low energy clusters for each size. For neutral silicon clusters with 25 atoms, both prolate and spherical structures with low cohesive energies exist. For clusters containing 29 or 35 atoms, the low-energy isomers exhibit a spherical shape. For each cluster size several stable isomers with similar shapes, and hence similar mobilities, but different bonding patterns exist. The most stable 25 atom cluster resulting from our global search has the lowest energy within DFT-GGA known so far. Finally, we investigate the transition to diamond-like bonding patterns expected for larger silicon clusters. Clusters with up to 239 atoms resemble amorphous silicon rather than the diamond structure and contain several highly coordinated atoms. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]