46,017 research outputs found
Resonant Tunneling through S- and U-shaped Graphene Nanoribbons
We theoretically investigate resonant tunneling through S- and U-shaped
nanostructured graphene nanoribbons. A rich structure of resonant tunneling
peaks are found eminating from different quasi-bound states in the middle
region. The tunneling current can be turned on and off by varying the Fermi
energy. Tunability of resonant tunneling is realized by changing the width of
the left and/or right leads and without the use of any external gates.Comment: 6 pages, 7 figure
Vacuum Energy Density and Cosmological Constant in dS Brane World
We discuss the vacuum energy density and the cosmological constant of dS
brane world with a dilaton field. It is shown that a stable AdS brane can
be constructed and gravity localization can be realized. An explicit relation
between the dS bulk cosmological constant and the brane cosmological constant
is obtained. The discrete mass spectrum of the massive scalar field in the
AdS brane is used to acquire the relationship between the brane
cosmological constant and the vacuum energy density. The vacuum energy density
in the brane gotten by this method is in agreement with astronomical
observations.Comment: 16 pages,4 figure
Mediating exchange bias by Verwey transition in CoO/Fe3O4 thin film
We report the tunability of the exchange bias effect by the first-order
metal-insulator transition (known as the Verwey transition) of Fe3O4 in CoO (5
nm)/Fe3O4 (40 nm)/MgO (001) thin film. In the vicinity of the Verwey
transition, the exchange bias field is substantially enhanced because of a
sharp increase in magnetocrystalline anisotropy constant from high-temperature
cubic to lowtemperature monoclinic structure. Moreover, with respect to the
Fe3O4 (40 nm)/MgO (001) thin film, the coercivity field of the CoO (5 nm)/Fe3O4
(40 nm)/MgO (001) bilayer is greatly increased for all the temperature range,
which would be due to the coupling between Co spins and Fe spins across the
interface
Estimating Form Factors of and their Applications to Semi-leptonic and Non-leptonic Decays
and weak transition
form factors are estimated for the whole physical region with a method based on
an instantaneous approximated Mandelstam formulation of transition matrix
elements and the instantaneous Bethe-Salpeter equation. We apply the estimated
form factors to branching ratios, CP asymmetries and polarization fractions of
non-leptonic decays within the factorization approximation. And we study the
non-factorizable effects and annihilation contributions with the perturbative
QCD approach. The branching ratios of semi-leptonic decays are also evaluated. We show that the calculated
decay rates agree well with the available experimental data. The longitudinal
polarization fraction of decays are when
denotes a light meson, and are when denotes a
() meson.Comment: Final version published in J Phys. G 39 (2012) 045002 (Title also
changed
The NLO QCD Corrections to Meson Production in Decays
The decay width of to meson is evaluated at the next-to-leading
order(NLO) accuracy in strong interaction. Numerical calculation shows that the
NLO correction to this process is remarkable. The quantum
chromodynamics(QCD)renormalization scale dependence of the results is obviously
depressed, and hence the uncertainties lying in the leading order calculation
are reduced.Comment: 14 pages, 7 figures; references added; expressions and typos ammende
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