611 research outputs found
Nonlinear transport theory for hybrid normal-superconducting devices
We report a theory for analyzing nonlinear DC transport properties of
mesoscopic or nanoscopic normal-superconducting (N-S) systems. Special
attention was paid such that our theory satisfies gauge invariance. At the
linear transport regime and the sub-gap region where the familiar scattering
matrix theory has been developed, we provide confirmation that our theory and
the scattering matrix theory are equivalent. At the nonlinear regime, however,
our theory allows the investigation of a number of important problems: for N-S
hybrid systems we have derived the general nonlinear current-voltage
characteristics in terms of the scattering Green's function, the second order
nonlinear conductance at the weakly nonlinear regime, and nonequilibrium charge
pile-up in the device which defines the electrochemical capacitance
coefficients
Shot noise of spin current and spin transfer torque
We report the theoretical investigation of noise spectrum of spin current and
spin transfer torque for non-colinear spin polarized transport in a spin-valve
device which consists of normal scattering region connected by two
ferromagnetic electrodes. Our theory was developed using non-equilibrium
Green's function method and general non-linear and
relations were derived as a function of angle between magnetization of
two leads. We have applied our theory to a quantum dot system with a resonant
level coupled with two ferromagnetic electrodes. It was found that for the MNM
system, the auto-correlation of spin current is enough to characterize the
fluctuation of spin current. For a system with three ferromagnetic layers,
however, both auto-correlation and cross-correlation of spin current are needed
to characterize the noise spectrum of spin current. Furthermore, the spin
transfer torque and the torque noise were studied for the MNM system. For a
quantum dot with a resonant level, the derivative of spin torque with respect
to bias voltage is proportional to when the system is far away
from the resonance. When the system is near the resonance, the spin transfer
torque becomes non-sinusoidal function of . The derivative of noise
spectrum of spin transfer torque with respect to the bias voltage
behaves differently when the system is near or far away from the resonance.
Specifically, the differential shot noise of spin transfer torque is a
concave function of near the resonance while it becomes convex
function of far away from resonance. For certain bias voltages, the
period becomes instead of . For small , it
was found that the differential shot noise of spin transfer torque is very
sensitive to the bias voltage and the other system parameters.Comment: 15pages, 6figure
The effect of the gravitational constant variation on the propagation of gravitational waves
Since the first detection of gravitational waves, they have been used to
investigate various fundamental problems, including the variation of physical
constants. Regarding the gravitational constant, previous works focused on the
effect of the gravitational constant variation on the gravitational wave
generation. In this paper, we investigate the effect of the gravitational
constant variation on the gravitational wave propagation. The Maxwell-like
equation that describes the propagation of gravitational waves is extended in
this paper to account for situations where the gravitational constant varies.
Based on this equation, we find that the amplitude of gravitational waves will
be corrected. Consequently the estimated distance to the gravitational wave
source without considering such a correction may be biased. Applying our
correction result to the well known binary neutron star coalescence event
GW170817, we get a constraint on the variation of the gravitational constant.
Relating our result to the Yukawa deviation of gravity, we for the first time
get the constraint of the Yukawa parameters in 10Mpc scale. This scale
corresponds to a graviton mass eV
Palaeomagnetic re-investigation of early permian rift basalts from the Baoshan block, SW China: Constraints on the site-of-origin of the gondwana-derived eastern cimmerian terranes
A palaeomagnetic investigation was carried out on a series of rift basalts (Woniusi Formation) that accumulated on the Baoshan block (SW China) in the Early Permian, the aim being to provide quantitative palaeogeographical information on the eastern Cimmerian terrane as it detached from eastern Gondwana. Reliable data were obtained from four locations/28 individual cooling units, and when combined with the findings of an earlier study (three locations/19 sites) indicate that breakup occurred at 41.9°S (with errors, 34.2-51.2°S). Using this information, we fit Baoshan against Gondwana within a narrow longitudinal belt close to where northeast Greater India and northwest Australia were once in close proximity. Furthermore, we suggest that Sibumasu (Simao-Burma-Malyasia-Sumatra; the largest of the eastern Cimmerian blocks) lay directly to the east, offshore of Australia; Qiangtang and Lhasa almost certainly sat to the west (off northern Greater India-SE Arabia), but we are uncertain as to their exact configuration. Our findings are compared with several rather different models that have been published in recent years. The new palaeomagnetic constraint highlights the flexibility authors currently have in reconstructing the region, principally because of the overall lack of similar high-quality data from the various blocks. We explain how new data could resolve these ambiguities, thereby offering more robust explanations for eastern Gondwana's late Palaeozoic development
Thermal Behaviour of Corn/Cotton Stalk Blends during Co-pyrolysis
AbstractThe pyrolysis behaviors and pyrolysis kinetics of corn straw (YM), cotton stalk(MG) and blends at different proportion were studied by TG-DSC technique. The results indicate that two kinds of biomass straw can be mixed fully. The pyrolysis process with its blend ratio is not a linear relationship and solid product reduced compared with single-stalk. In addition, the major pyrolysis process of mixture within the main range can be well described by a two-dimensional diffusion model with Malek method. Among the tested samples, the 40:60 MG/ YM blend shows the lowest activation energy of 51.7 KJ/mol. Besides corn straw plays a dominant role on the course of the thermal conversion. The experimental results may provide useful data to promote the application of biomass thermochemical conversion technology of biomass mixture
An abrupt extinction in the Middle Permian (Capitanian) of the Boreal Realm (Spitsbergen) and its link to anoxia and acidification
The controversial Capitanian (Middle Permian, 262 Ma) extinction event is only known from equatorial latitudes, and consequently its global extent is poorly resolved. We demonstrate that there were two, severe extinctions amongst brachiopods in northern Boreal latitudes (Spitsbergen) in the Middle to Late Permian, separated by a recovery phase. New age dating of the Spitsbergen strata (belonging to the Kapp Starostin Formation), using strontium isotopes and d13C trends and comparison with better-dated sections in Greenland, suggests that the first crisis occurred in the Capitanian. This age assignment indicates that this Middle Permian extinction is manifested at higher latitudes. Redox proxies (pyrite framboids and trace metals) show that the Boreal crisis coincided with an intensification of oxygen depletion, implicating anoxia in the extinction scenario. The widespread and near-total loss of carbonates across the Boreal Realm also suggests a role for acidification in the crisis. The recovery interval saw the appearance of new brachiopod and bivalve taxa alongside survivors, and an increased mollusk dominance, resulting in an assemblage reminiscent of younger Mesozoic assemblages. The subsequent end-Permian mass extinction terminated this Late Permian radiation
Revisiting the annihilation decay
It is very important to know the strength of annihilation contribution in B
charmless nonleptonic decays. process could
serve a good probe of the strength. We have studied the process in QCD
factorization framework. Using a gluon mass scale indicted by the studies of
infrared behavior of gluon propagators to avoid enhancements in the soft end
point regions, we find that the CP averaged branching ratio is about
, the direct CP asymmetry is about -0.05,
while the mixing-induced CP asymmetry quite large with the value
=0.18. The process could be measured at LHC-b experiments in the
near future and would deepen our understanding of dynamics of B charmless
decays.Comment: 9 pages, 3 eps figures. To appear in EPJ
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