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Search Results: 1 - 10 of 221842 matches for " L. Xue "
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Molecular Rotors as Switches
Mei Xue,Kang L. Wang
Sensors , 2012, DOI: 10.3390/s120911612
Abstract: The use of a functional molecular unit acting as a state variable provides an attractive alternative for the next generations of nanoscale electronics. It may help overcome the limits of conventional MOSFETd due to their potential scalability, low-cost, low variability, and highly integratable characteristics as well as the capability to exploit bottom-up self-assembly processes. This bottom-up construction and the operation of nanoscale machines/devices, in which the molecular motion can be controlled to perform functions, have been studied for their functionalities. Being triggered by external stimuli such as light, electricity or chemical reagents, these devices have shown various functions including those of diodes, rectifiers, memories, resonant tunnel junctions and single settable molecular switches that can be electronically configured for logic gates. Molecule-specific electronic switching has also been reported for several of these device structures, including nanopores containing oligo(phenylene ethynylene) monolayers, and planar junctions incorporating rotaxane and catenane monolayers for the construction and operation of complex molecular machines. A specific electrically driven surface mounted molecular rotor is described in detail in this review. The rotor is comprised of a monolayer of redox-active ligated copper compounds sandwiched between a gold electrode and a highly-doped P+ Si. This electrically driven sandwich-type monolayer molecular rotor device showed an on/off ratio of approximately 104, a read window of about 2.5 V, and a retention time of greater than 104 s. The rotation speed of this type of molecular rotor has been reported to be in the picosecond timescale, which provides a potential of high switching speed applications. Current-voltage spectroscopy (I-V) revealed a temperature-dependent negative differential resistance (NDR) associated with the device. The analysis of the device I–V characteristics suggests the source of the observed switching effects to be the result of the redox-induced ligand rotation around the copper metal center and this attribution of switching is consistent with the observed temperature dependence of the switching behavior as well as the proposed energy diagram of the device. The observed resistance switching shows the potential for future non-volatile memories and logic devices applications. This review will discuss the progress and provide a perspective of molecular motion for nanoelectronics and other applications.
The effects of mineral dust particles, aerosol regeneration and ice nucleation parameterizations on clouds and precipitation
A. Teller,L. Xue,Z. Levin
Atmospheric Chemistry and Physics (ACP) & Discussions (ACPD) , 2012, DOI: 10.5194/acp-12-9303-2012
Abstract: This study focuses on the effects of aerosol particles on the formation of convective clouds and precipitation in the Eastern Mediterranean Sea, with a special emphasis on the role of mineral dust particles in these processes. We used a new detailed numerical cloud microphysics scheme that has been implemented in the Weather Research and Forecast (WRF) model in order to study aerosol–cloud interaction in 3-D configuration based on 1° × 1° resolution reanalysis meteorological data. Using a number of sensitivity studies, we tested the contribution of mineral dust particles and different ice nucleation parameterizations to precipitation development. In this study we also investigated the importance of recycled (regenerated) aerosols that had been released to the atmosphere following the evaporation of cloud droplets. The results showed that increased aerosol concentration due to the presence of mineral dust enhanced the formation of ice crystals. The dynamic evolution of the cloud system sets the time periods and regions in which heavy or light precipitation occurred in the domain. The precipitation rate, the time and duration of precipitation were affected by the aerosol properties only at small spatial scales (with areas of about 20 km2). Changes of the ice nucleation scheme from ice supersaturation-dependent parameterization to a recent approach of aerosol concentration and temperature-dependent parameterization modified the ice crystals concentrations but did not affect the total precipitation in the domain. Aerosol regeneration modified the concentration of cloud droplets at cloud base by dynamic recirculation of the aerosols but also had only a minor effect on precipitation. The major conclusion from this study is that the effect of mineral dust particles on clouds and total precipitation is limited by the properties of the atmospheric dynamics and the only effect of aerosol on precipitation may come from significant increase in the concentration of accumulation mode aerosols. In addition, the presence of mineral dust had a much smaller effect on the total precipitation than on its spatial distribution.
electron-positron-photon plasma around a collapsing star
R. Ruffini,L. Vitagliano,S. -S. Xue
Physics , 2003,
Abstract: We describe electron-positron pairs creation around an electrically charged star core collapsing to an electromagnetic black hole (EMBH), as well as pairs annihilation into photons. We use the kinetic Vlasov equation formalism for the pairs and photons and show that a regime of plasma oscillations is established around the core. As a byproduct of our analysis we can provide an estimate for the thermalization time scale.
Plasma expansion in the geometry of a collapsing star
R. Ruffini,L. Vitagliano,S. -S. Xue
Physics , 2003,
Abstract: We describe the evolution of an electron-positron-photon plasma created by Sauter--Heisenberg--Euler--Schwinger mechanism around a collapsing charged star core in the Reissner-Nordstr\"{o}m geometry external to the core, in view of the application in the framework of the EMBH theory for gamma ray bursts.
On Plasma Oscillations in Strong Electric Fields
R. Ruffini,L. Vitagliano,S. -S. Xue
Physics , 2003, DOI: 10.1016/S0370-2693(03)00299-5
Abstract: We describe the creation and evolution of electron-positron pairs in a strong electric field as well as the pairs annihilation into photons. The formalism is based on generalized Vlasov equations, which are numerically integrated. We recover previous results about the oscillations of the charges, discuss the electric field screening and the relaxation of the system to a thermal equilibrium configuration. The timescale of the thermalization is estimated to be $\sim 10^{3}-10^{4} \hbar /m_{e}c^{2}$.
On a Separatrix in the Gravitational Collapse to an Overcritical Electromagnetic Black Hole
R. Ruffini,L. Vitagliano,S. -S. Xue
Physics , 2003, DOI: 10.1016/j.physletb.2003.08.051
Abstract: The dynamical properties of an electron--positron--photon plasma created by the vacuum polarization process occurring around a charged gravitationally collapsing core of an initially neutral star are examined within the framework of General Relativity and Quantum Field Theory. The Reissner--Nordstr\"{o}m geometry is assumed to apply between the collapsing core and the oppositely charged remnant of the star. The appearance of a separatrix at radius $\bar{R}$, well outside the asymptotic approach to the horizon, is evidenced. The neutral electron--positron--photon plasma created at radii $r>\bar{R}$ self-propels outwards to infinity, following the classical PEM--pulse analysis. The plasma created at $r<\bar{R}$ remains trapped and follows the gravitational collapse of the core only contributing to the reduction of the electromagnetic energy of the black hole and to the increase of its irreducible mass. This phenomenon has consequences for the observational properties of gamma--ray bursts and is especially relevant for the theoretical prediction of the temporal and spectral structure of the short bursts.
On black hole masses, radio-loudness and bulge luminosities of Seyfert galaxies
Xue-Bing Wu,J. L. Han
Physics , 2001, DOI: 10.1051/0004-6361:20011429
Abstract: We estimated black hole masses for 9 Seyfert 1 and 13 Seyfert 2 galaxies in the Palomar and CfA bright Seyfert samples using the tight correlation between black hole mass and bulge velocity dispersion. Combining other 13 Seyfert 1s and 2 Seyfert 2s in these samples but with black hole masses measured recently by reverberation mapping and stellar/gas dynamics, we studied the correlations of black hole masses with radio loudness and bulge luminosities for a sample of 37 Seyfert galaxies. We found that if radio-loudness is measured using the optical and radio luminosities of the nuclear components, the black hole masses of radio-loud Seyfert 1s tend to increase with the radio-loudness. The black hole masses of all Seyfert galaxies increase with the radio power, but Seyfert galaxies have larger radio powers than nearby galaxies with the same black hole masses. In addition, the correlation between black hole masses and bulge V-band luminosities for Seyfert galaxies is consistent with that found for quasars and normal galaxies. The combined sample of 37 Seyfert galaxies, 15 quasars and 30 normal galaxies suggests a possible universal nonlinear relation between black hole and bulge masses, $M(BH) \propto M(bulge)^{1.74\pm0.14}$, which is slightly steeper than that found recently by Laor (2001) for a smaller sample. This nonlinear relation is supported by a larger sample including 65 Seyfert galaxies. The different M(BH)/M(bulge) ratio for galaxies with different bulge luminosities or different black hole masses may be explained by this relation. These results are consistent with some theoretical implications and are important for understanding the nature of radio emissions and the formation and evolution of supermassive black holes and galaxies.
Inclinations and black hole masses of Seyfert 1 galaxies
Xue-Bing Wu,J. L. Han
Physics , 2001, DOI: 10.1086/324408
Abstract: A tight correlation of black hole mass and central velocity dispersion has been found recently for both active and quiescent galaxies. By applying this correlation, we develop a simple method to derive the inclination angles for a sample of 11 Seyfert 1 galaxies that have both measured central velocity dispersions and black hole masses estimated by reverberation mapping. These angles, with a mean value of 36 degree that agrees well with the result obtained by fitting the iron K$\alpha$ lines of Seyfert 1s observed with ASCA, provide further support to the orientation-dependent unification scheme of AGN. A positive correlation of the inclinations with observed FWHMs of H$\beta$ line and a possible anti-correlation with the nuclear radio-loudness have been found. We conclude that more accurate knowledge on inclinations and broad line region dynamics is needed to improve the black hole mass determination of AGN with the reverberation mapping technique.
Global regularity for the supercritical dissipative quasi-geostrophic equation with large dispersive forcing
M. Cannone,C. Miao,L. Xue
Mathematics , 2011, DOI: 10.1112/plms/pds046
Abstract: We consider the 2D quasi-geostrophic equation with supercritical dissipation and dispersive forcing in the whole space. When the dispersive amplitude parameter is large enough, we prove the global well-posedness of strong solution to the equation with large initial data. We also show the strong convergence result as the amplitude parameter goes to $\infty$. Both results rely on the Strichartz-type estimates for the corresponding linear equation.
Regeneration of green plants from seed-derived callus cultures of Poa
L Zong, L-M Ding, X Xue, T Wang
African Journal of Biotechnology , 2010,
Abstract: Plants were regenerated from callus derived from entire mature seeds of three Poa pratensis cultivars (Kentucky bluegrass, Fylking and Baron) and one Chinese native species, Poa sphendyLodes L. Kentucky bluegrass showed the highest regenerating capacity of the four cultivars. Addition of low concentration (0.2 mg/l) of (6-benzyladenine) 6-BA to Murashige and Skoog (MS) callus induction medium containing 2 mg/l 2,4-dichlorophenoxyacetic acid (2,4-D) strongly stimulated seeds inducing shoot-forming callus cultures in Kentucky bluegrass. High percentage of shoots was induced in Shenh and Hilde-brandi (SH) medium containing low concentration (0.1 mg/l) of 2,4-D. Roots were obtained in SH medium with 0.1 mg/l NAA (naphthalene-acetic acid).
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