The Experts below are selected from a list of 135 Experts worldwide ranked by ideXlab platform
G Cescutti - One of the best experts on this subject based on the ideXlab platform.
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an Inhomogeneous Model for the galactic halo a possible explanation for the spread observed in s and r process elements
Astronomy and Astrophysics, 2008Co-Authors: G CescuttiAbstract:Aims. We propose an explanation for the considerable scatter of the abundances of neutron capture elements observed in lowmetallicity stars in the solar vicinity, compared to the small star-to-star scatter observed for the α-elements. Methods. We have developed a stochastic chemical evolution Model in which the main assumption is a random formation of new stars subject to the condition that the cumulative mass distribution follows a given initial mass function. Results. With our Model, we are able to reproduce the different spreads of neutron capture elements and α-elements in low-metallicity stars. Conclusions. The reason for different observed spreads in neutron capture elements and α-elements resides in the random birth of stars, coupled with different stellar mass ranges, from which α-elements and neutron capture elements originate. In particular, the site
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an Inhomogeneous Model for the galactic halo a possible explanation for the spread observed in s and r process elements
arXiv: Astrophysics, 2008Co-Authors: G CescuttiAbstract:We propose an explanation for the considerable scatter of the abundances of neutron capture elements observed in low-metallicity stars in the solar vicinity, compared to the small star-to-star scatter observed for the alpha-elements. We have developed a stochastic chemical evolution Model in which the main assumption is a random formation of new stars subject to the condition that the cumulative mass distribution follows a given initial mass function. With our Model, we are able to reproduce the different spreads of neutron capture elements and alpha-elements in low-metallicity stars. The reason for different observed spread in neutron capture elements and alpha-elements resides in the random birth of stars, coupled with different stellar mass ranges, from which alpha-elements and neutron capture elements originate. In particular, the site of production of alpha-elements is the whole range of massive stars, from 10 to 80 Msun whereas the mass range of production for neutron capture elements lies between 12 and 30 Msun.
Hengjing Tang - One of the best experts on this subject based on the ideXlab platform.
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current voltage temperature and capacitance voltage temperature characteristics of tiw alloy p inp schottky barrier diode
Journal of Alloys and Compounds, 2015Co-Authors: Jun Chen, Qingsong Wang, Hengjing TangAbstract:Abstract We systematically characterize TiW alloy/p-InP Schottky barrier diode using current–voltage (I–V) and capacitance–voltage (C–V) measurements for different temperatures from 300 K to 400 K. The electrical parameters such as barrier height (Φb0) and ideality factor (n) have been obtained from the thermal emission (TE) theory. Φb0 increases and n decreases with the increasing of temperature. The temperature dependency of barrier characteristics is interpreted by TE theory assuming a Gaussian distribution of the barrier heights according to the Inhomogeneous Model. The mean barrier height Φ ¯ b 0 ( T = 0 K ) = 1.09 V and standard deviation σ0 = 135 mV are obtained by plotting Φb0 versus 1/2kT, indicating the Gaussian distribution of the barrier heights. The value of extracted Richardson constant A* is 56.2504 Acm−2 K−2, which is in good agreement with the theoretical value. All these obtained results show that the carrier transport process can be Modeled by the TE theory. In addition, the C–V characteristics are analyzed by taking into account series resistance (Rs). The extracted interface states distribution shows the increase of the interface state density from midgap towards the top of the valence band.
Delmar S Larsen - One of the best experts on this subject based on the ideXlab platform.
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contrasting the excited state dynamics of the photoactive yellow protein chromophore protein versus solvent environments
Biophysical Journal, 2004Co-Authors: Mikas Vengris, Michael A Van Der Horst, Goran Zgrablic, Ivo H M Van Stokkum, Stefan Haacke, Majed Chergui, Klaas J Hellingwerf, Rienk Van Grondelle, Delmar S LarsenAbstract:Wavelength- and time-resolved fluorescence experiments have been performed on the photoactive yellow protein, the E46Q mutant, the hybrids of these proteins containing a nonisomerizing ''locked'' chromophore, and the native and locked chromophores in aqueous solution. The ultrafast dynamics of these six systems is compared and spectral signatures of isomerization and solvation are discussed. We find that the ultrafast red-shifting of fluorescence is associated mostly with solvation dynamics, whereas isomerization manifests itself as quenching of fluorescence. The observed multiexponential quenching of the protein samples differs from the single-exponential lifetimes of the chromophores in solution. The locked chromophore in the protein environment decays faster than in solution. This is due to additional channels of excited-state energy dissipation via the covalent and hydrogen bonds with the protein environment. The observed large dispersion of quenching timescales observed in the protein samples that contain the native pigment favors both an Inhomogeneous Model and an excited-state barrier for isomerization.
Robert L Sah - One of the best experts on this subject based on the ideXlab platform.
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depth and strain dependent mechanical and electromechanical properties of full thickness bovine articular cartilage in confined compression
Journal of Biomechanics, 2001Co-Authors: Albert C Chen, Won C Bae, Robert M Schinagl, Robert L SahAbstract:Compression tests have often been performed to assess the biomechanical properties of full-thickness articular cartilage. We tested whether the apparent homogeneous strain-dependent properties, deduced from such tests, reflect both strain- and depth-dependent material properties. Full-thickness bovine articular cartilage was tested by oscillatory confined compression superimposed on a static offset up to 45%. and the data fit to estimate modulus, permeability, and electrokinetic coefficient assuming homogeneity. Additional tests on partial-thickness cartilage were then performed to assess depth- and strain-dependent properties in an Inhomogeneous Model, assuming three discrete layers (i = 1 starting from the articular surface, to i = 3 up to the subchondral bone). Estimates of the zero-strain equilibrium confined compression modulus (H(A0)), the zero-strain permeability (kp0) and deformation dependence constant (M), and the deformation-dependent electrokinetic coefficient (ke) differed among individual layers of cartilage and full-thickness cartilage. HiA0 increased from layer 1 to 3 (0.27 to 0.71 MPa), and bracketed the apparent homogeneous value (0.47 MPa). ki(p0) decreased from layer 1 to 3 (4.6 x 10(-15) to 0.50 x 10(-15) m2/Pa s) and was less than the homogeneous value (7.3 x 10(-15) m2/Pa s), while Mi increased from layer 1 to 3 (5.5 to 7.4) and became similar to the homogeneous value (8.4). The amplitude of ki(e) increased markedly with compressive strain, as did the homogeneous value: at low strain, it was lowest near the articular surface and increased to a peak in the middle-deep region. These results help to interpret the biomechanical assessment of full-thickness articular cartilage.
Stratis V Sotirchos - One of the best experts on this subject based on the ideXlab platform.
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steady state versus transient measurement of effective diffusivities in porous media using the diffusion cell method
Chemical Engineering Science, 1992Co-Authors: Stratis V SotirchosAbstract:Abstract The relation between the effective diffusivities of gases obtained from transient and steady-state mass transport experiments using the diffusion-cell method is investigated in this study. A simple structure of parallel pores, of some pore-size distribution, is used to represent the porous medium, and, in order to investigate the effects of pore interaction on the problem, the pores are assumed to communicate with each other at a number of equidistant points between the two ends of the porous slab. It is shown that matching the zero and first moments of the experimental (Inhomogeneous Model) response of the diffusion cell with the corresponding moments of the response of the homogeneous Model yields the same effective diffusion coefficient as steady-state diffusion-cell experiments. Time-domain parameter estimation schemes tend to produce larger, in general, effective diffusivities, but the difference between the time-domain responses of the homogeneous and Inhomogeneous Model, with the same first two moments, decreases sharply if the pores are allowed to interact in the interior of the porous pellet.