443 research outputs found
Parameterization of intrawave ripple-averaged sediment pickup above steep ripples
Near-bed sediment pickup is critical for predictions of intrawave suspension and in turn net sediment transport in coastal models. In the present study, numerical results from a two-dimensional Reynolds-averaged Navier-Stokes model are used to assess the functional relationship of intrawave ripple-averaged sediment pickup above steep ripples. The numerical model provides intrawave time histories of ripple-averaged near-bed velocities and turbulence, which are qualitatively interrogated to determine pickup functional relationships. Several specific sediment pickup formulations are implemented within the numerical model: expressions relating pickup to near-bed velocity or near-bed turbulent kinetic energy via the bed shear stress; and expressions relating pickup to near-bed shear production of turbulent kinetic energy. These are then tested via model-data comparisons of near-bed suspended sediment concentration. The results show that the traditional functions relating sediment pickup to near-bed velocity cannot lead to reasonable intrawave suspension predictions above vortex ripples under a ripple-averaged framework. Instead, relating sediment pickup to near-bed turbulence quantities, such as turbulent kinetic energy or shear production of turbulent kinetic energy, significantly improves the numerical predictions for these conditions. This article is protected by copyright. All rights reserved
Maximally-localized Wannier functions for entangled energy bands
We present a method for obtaining well-localized Wannier-like functions (WFs)
for energy bands that are attached to or mixed with other bands. The present
scheme removes the limitation of the usual maximally-localized WFs method (N.
Marzari and D. Vanderbilt, Phys. Rev. B 56, 12847 (1997)) that the bands of
interest should form an isolated group, separated by gaps from higher and lower
bands everywhere in the Brillouin zone. An energy window encompassing N bands
of interest is specified by the user, and the algorithm then proceeds to
disentangle these from the remaining bands inside the window by filtering out
an optimally connected N-dimensional subspace. This is achieved by minimizing a
functional that measures the subspace dispersion across the Brillouin zone. The
maximally-localized WFs for the optimal subspace are then obtained via the
algorithm of Marzari and Vanderbilt. The method, which functions as a
postprocessing step using the output of conventional electronic-structure
codes, is applied to the s and d bands of copper, and to the valence and
low-lying conduction bands of silicon. For the low-lying nearly-free-electron
bands of copper we find WFs which are centered at the tetrahedral interstitial
sites, suggesting an alternative tight-binding parametrization.Comment: 13 pages, with 9 postscript figures embedded. Uses REVTEX and epsf
macro
Multiple-photon Peak Generation Near The 10 M Range In Quantum Dot Infrared Photodetectors
We present results from simulations of the photocurrent observed in recently fabricated InAs quantum dot infrared photodetectors that respond with strong resonance peaks in the ∼ 10 m wavelength range. The results are in good agreement with experimental data generated earlier. Multiphoton scattering of electrons localized in the quantum dots are not only in accordance with the observed patterns, but are also necessary to explain the photocurrent spectrum obtained in the calculations. © 2011 American Institute of Physics.1096Martyniuk, P., Rogalski, A., (2008) Prog. Quantum Electron., 32, p. 89. , For a recent review, see, 10.1016/j.pquantelec.2008.07.001Chakrabarti, S., Stiff-Roberts, A.D., Su, X.H., Bhattacharya, P., Ariyawansa, G., Perera, A.G.U., High-performance mid-infrared quantum dot infrared photodetectors (2005) Journal of Physics D: Applied Physics, 38 (13), pp. 2135-2141. , DOI 10.1088/0022-3727/38/13/009, PII S002237270592069XLim, H., Zhang, W., Tsao, S., Sills, T., Szafraniec, J., Mi, K., Movaghar, B., Razeghi, M., Quantum dot infrared photodetectors: Comparison of experiment and theory (2005) Physical Review B - Condensed Matter and Materials Physics, 72 (8), p. 085332. , http://oai.aps.org/oai/?verb=ListRecords&metadataPrefix= oai_apsmeta_2&set=journal:PRB:72, DOI 10.1103/PhysRevB.72.085332Razeghi, M., Lim, H., Tsao, S., Szafraniec, J., Zhang, W., Mi, K., Movaghar, B., Transport and photodetection in self-assembled semiconductor quantum dots (2005) Nanotechnology, 16 (2), pp. 219-229. , DOI 10.1088/0957-4484/16/2/007Pal, D., Towe, E., (2006) Appl. Phys. Lett., 88, p. 153109. , 10.1063/1.2193466Bhattacharya, P., Su, X.H., Chakrabarti, S., Ariyawansa, G., Perera, A.G.U., Characteristics of a tunneling quantum-dot infrared photodetector operating at room temperature (2005) Applied Physics Letters, 86 (19), pp. 1-3. , DOI 10.1063/1.1923766, 191106Dupont, E., Corkum, P., Liu, H.C., Wilson, P.H., Buchanan, M., Wasilewski, Z.R., (1994) Appl. Phys. Lett., 65, p. 1560. , 10.1063/1.113004Maier, T., Schneider, H., Walther, M., Koidl, P., Liu, H.C., (2004) Appl. Phys. Lett., 84, p. 5162. , 10.1063/1.1763978Jiang, J., Fu, Y., Li, N., Chen, X.S., Zhen, H.L., Lu, W., Wang, M.K., Li, Y.G., (2004) Appl. Phys. Lett., 85, p. 3614. , 10.1063/1.1781732Aivaliotis, P., Zibik, E.A., Wilson, L.R., Cockburn, J.W., Hopkinson, M., Vinh, N.Q., (2008) Appl. Phys. Lett., 92, p. 023501. , 10.1063/1.2833691Sirtori, C., Capasso, F., Sivco, D.L., Cho, A.Y., (1992) Appl. Phys. Lett., 60, p. 2678. , 10.1063/1.106893Souza, P.L., Lopes, A.J., Gebhard, T., Unterrainer, K., Pires, M.P., Villas-Boas, J.M., Vieira, G.S., Studart, N., Quantum dot structures grown on Al containing quaternary material for infrared photodetection beyond 10 μm (2007) Applied Physics Letters, 90 (17), p. 173510. , DOI 10.1063/1.2733603Gebhard, T., Alvarenga, D., Souza, P.L., Guimares, P.S.S., Unterrainer, K., Pires, M.P., Vieira, G.S., Villas-Boas, J.M., (2008) Applied Phys. Lett., 93, p. 052103. , 10.1063/1.2965804Pryor, C.E., Pistol, M.-E., Band-edge diagrams for strained III-V semiconductor quantum wells, wires, and dots (2005) Physical Review B - Condensed Matter and Materials Physics, 72 (20), pp. 1-11. , http://oai.aps.org/oai/?verb=ListRecords&metadataPrefix= oai_apsmeta_2&set=journal:PRB:72, DOI 10.1103/PhysRevB.72.205311, 205311Degani, M.H., Maialle, M.Z., (2010) J. Comput. Theor. Nanosci., 7, p. 454. , 10.1166/jctn.2010.1380Feit, M.D., Fleck Jr., J.A., Steiger, A., (1982) J. Comput. Phys., 47, p. 412. , 10.1016/0021-9991(82)90091-2Degani, M.H., (1991) Appl. Phys. Lett., 59, p. 57(2002) Phys. Rev. B, 66, p. 23306. , 10.1063/1.105521Maialle, M.Z., Degani, M.H., Madureira, J.R., Farinas, P.F., (2009) J. Appl. Phys., 106, p. 123703. , 10.1063/1.3270263Fano, U., Cooper, J.W., (1968) Rev. Mod. Phys., 40, p. 441. , 10.1103/RevModPhys.40.441Tsolakidis, A., Snchez-Portal, D., Martin, R.M., (2002) Phys. Rev. B, 66, p. 235416. , 10.1103/PhysRevB.66.23541
Current-Density Functional Theory of the Response of Solids
The response of an extended periodic system to a homogeneous field (of
wave-vector ) cannot be obtained from a time-dependent density
functional theory (TDDFT) calculation, because the
Runge-Gross theorem does not apply. Time-dependent {\em current}-density
functional theory is needed and demonstrates that one key ingredient missing
from TDDFT is the macroscopic current. In the low-frequency limit, in certain
cases, density polarization functional theory is recovered and a formally exact
expression for the polarization functional is given.Comment: 5 pages, accepted in PR
Indicadores De Desempenho Motor Como Preditores De Fragilidade Em Idosos Cadastrados Em Uma Unidade De Saúde Da Família
This study aimed to identify the motor performance tests more strongly associated with frailty and respective cut-off points and verify the best motor performance indicator as screening tool to discriminate frailty in elderly registered in Family Health Unit Participated in the study 139 elderly aged ≥60 years 105 women and 34 men The frailty was identified by the criteria of Fried et al (2001) The motor performance tests realized were: Handgrip strength (HS) sit-to-stand test walk test (WT) and pick up a pen test Logistic regression analysis was used to associate the motor performance tests and frailty The cutoff points were evaluated by parameters provided by Receiver Operating Characteristic curve (ROC) with significance level of 5% Data were analyzed using SPSS 210 and MedCalc The mean age was 7232 ± 84 The walk test was positively associated with frailty (OR 130; p <001) and handgrip strength in elderly women was inversely associated with frailty on feminine sex (OR 074; p <0001) The WT presented a cutoff 5s (sensitivity 889 and specificity 745%) and the handgrip in the women obtained a cutoff point 146 kgf (sensitivity 833 and specificity 790%) It was concluded that the walk test was the best screening indicator to discriminate the frailty in elderly both sexes registered in a Family Health Unit. © Edições Desafio Singular.122889
Homogenized dynamics of stochastic partial differential equations with dynamical boundary conditions
A microscopic heterogeneous system under random influence is considered. The
randomness enters the system at physical boundary of small scale obstacles as
well as at the interior of the physical medium. This system is modeled by a
stochastic partial differential equation defined on a domain perforated with
small holes (obstacles or heterogeneities), together with random dynamical
boundary conditions on the boundaries of these small holes.
A homogenized macroscopic model for this microscopic heterogeneous stochastic
system is derived. This homogenized effective model is a new stochastic partial
differential equation defined on a unified domain without small holes, with
static boundary condition only. In fact, the random dynamical boundary
conditions are homogenized out, but the impact of random forces on the small
holes' boundaries is quantified as an extra stochastic term in the homogenized
stochastic partial differential equation. Moreover, the validity of the
homogenized model is justified by showing that the solutions of the microscopic
model converge to those of the effective macroscopic model in probability
distribution, as the size of small holes diminishes to zero.Comment: Communications in Mathematical Physics, to appear, 200
Evaluation of effectiveness of 45S5 bioglass doped with niobium for repairing critical-sized bone defect in in vitro and in vivo models
Here, we investigated the biocompatibility of a bioactive sodium calcium silicate glass containing 2.6 mol% Nb2O5 (denoted BGPN2.6) and compare the results with the archetypal 45S5 bioglass. The glass bioactivity was tested using a range of in vitro and in vivo experiments to assess its suitability for bone regeneration applications. in vitro studies consisted of assessing the cytocompatibility of the BGPN2.6 glass with bone-marrow-derived mesenchymal stem cells (BM-MSCs). Systemic biocompatibility was verified by means of the quantification of biochemical markers and histopathology of liver, kidneys, and muscles. The glass genotoxicity was assessed using the micronucleus test. The regeneration of a calvarial defect was assessed using both qualitative and quantitative analysis of three-dimensional microcomputed tomography images. The BGPN2.6 glass was not cytotoxic to BM-MSCs. It is systemically biocompatible causing no signs of damage to high metabolic and excretory organs such as the liver and kidneys. No mutagenic potential was observed in the micronucleus test. MicroCT images showed that BGPN2.6 was able to nearly fully regenerate a critical-sized calvarial defect and was far superior to standard 45S5 Bioglass. Defects filled with BGPN2.6 glass showed over 90% coverage compare to just 66% for 45S5 Bioglass. For one animal the defect was completely filled in 8 weeks. These results clearly show that Nb-containing bioactive glasses are a safe and effective biomaterial for bone replacement
Air Shower Measurements with the LOPES Radio Antenna Array
LOPES is set up at the location of the KASCADE-Grande extensive air shower
experiment in Karlsruhe, Germany and aims to measure and investigate radio
pulses from Extensive Air Showers. Since radio waves suffer very little
attenuation, radio measurements allow the detection of very distant or highly
inclined showers. These waves can be recorded day and night, and provide a
bolometric measure of the leptonic shower component. LOPES is designed as a
digital radio interferometer using high bandwidths and fast data processing and
profits from the reconstructed air shower observables of KASCADE-Grande. The
LOPES antennas are absolutely amplitude calibrated allowing to reconstruct the
electric field strength which can be compared with predictions from detailed
Monte Carlo simulations. We report about the analysis of correlations present
in the radio signals measured by the LOPES 30 antenna array. Additionally,
LOPES operates antennas of a different type (LOPES-STAR) which are optimized
for an application at the Pierre Auger Observatory. Status, recent results of
the data analysis and further perspectives of LOPES and the possible large
scale application of this new detection technique are discussed.Comment: 8 pages, 10 figures, Contribution to the Arena 2008 conference, Rome,
June 200
On noise treatment in radio measurements of cosmic ray air showers
Precise measurements of the radio emission by cosmic ray air showers require
an adequate treatment of noise. Unlike to usual experiments in particle
physics, where noise always adds to the signal, radio noise can in principle
decrease or increase the signal if it interferes by chance destructively or
constructively. Consequently, noise cannot simply be subtracted from the
signal, and its influence on amplitude and time measurement of radio pulses
must be studied with care. First, noise has to be determined consistently with
the definition of the radio signal which typically is the maximum field
strength of the radio pulse. Second, the average impact of noise on radio pulse
measurements at individual antennas is studied for LOPES. It is shown that a
correct treatment of noise is especially important at low signal-to-noise
ratios: noise can be the dominant source of uncertainty for pulse height and
time measurements, and it can systematically flatten the slope of lateral
distributions. The presented method can also be transfered to other experiments
in radio and acoustic detection of cosmic rays and neutrinos.Comment: 4 pages, 6 figures, submitted to NIM A, Proceedings of ARENA 2010,
Nantes, Franc
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