49,846 research outputs found
Resonant Tunneling through double-bended Graphene Nanoribbons
We investigate theoretically resonant tunneling through double-bended
graphene nanoribbon structures, i.e., armchair-edged graphene nanoribbons
(AGNRs) in between two semi-infinite zigzag graphene nanoribbon (ZGNR) leads.
Our numerical results demonstrate that the resonant tunneling can be tuned
dramatically by the Fermi energy and the length and/or widths of the AGNR for
both the metallic and semiconductor-like AGNRs. The structure can also be use
to control the valley polarization of the tunneling currents and could be
useful for potential application in valleytronics devices.Comment: 4 pages, 4 figure
OPERA superluminal neutrinos and Kinematics in Finsler spacetime
The OPERA collaboration recently reported that muon neutrinos could be
superluminal. More recently, Cohen and Glashow pointed that such superluminal
neutrinos would be suppressed since they lose their energies rapidly via
bremsstrahlung. In this Letter, we propose that Finslerian nature of spacetime
could account for the superluminal phenomena of particles. The Finsler
spacetime permits the existence of superluminal behavior of particles while the
casuality still holds. A new dispersion relation is obtained in a class of
Finsler spacetime. It is shown that the superluminal speed is linearly
dependent on the energy per unit mass of the particle. We find that such a
superluminal speed formula is consistent with data of OPERA, MINOS and
Fermilab-1979 neutrino experiments as well as observations on neutrinos from
SN1987a.Comment: 10 pages, 2 figures. Viewpoints of Finslerian special relativity on
OPERA superluminal neutrino
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
Quantum pumping in graphene nanoribbons at resonant transmission
Adiabatic quantum charge pumping in graphene nanoribbon double barrier
structures with armchair and zigzag edges in the resonant transmission regime
is analyzed. Using recursive Green's function method we numerically calculate
the pumped charge for pumping contours encircling a resonance. We find that for
armchair ribbons the whole resonance line contributes to the pumping of a
single electron (ignoring double spin degeneracy) per cycle through the device.
The case of zigzag ribbons is more interesting due to zero-conductance
resonances. These resonances separate the whole resonance line into several
parts, each of which corresponds to the pumping of a single electron through
the device. Moreover, in contrast to armchair ribbons, one electron can be
pumped from the left lead to the right one or backwards. The current direction
depends on the particular part of the resonance line encircled by the pumping
contour.Comment: 6 pages, 5 figures. This is an author-created, un-copyedited version
of an article accepted for publication in EPL. IOP Publishing Ltd is not
responsible for any errors or omissions in this version of the manuscript or
any version derived from it. The definitive publisher authenticated version
is available online at 10.1209/0295-5075/92/4701
Structure of the Partition Function and Transfer Matrices for the Potts Model in a Magnetic Field on Lattice Strips
We determine the general structure of the partition function of the -state
Potts model in an external magnetic field, for arbitrary ,
temperature variable , and magnetic field variable , on cyclic, M\"obius,
and free strip graphs of the square (sq), triangular (tri), and honeycomb
(hc) lattices with width and arbitrarily great length . For the
cyclic case we prove that the partition function has the form ,
where denotes the lattice type, are specified
polynomials of degree in , is the corresponding
transfer matrix, and () for ,
respectively. An analogous formula is given for M\"obius strips, while only
appears for free strips. We exhibit a method for
calculating for arbitrary and give illustrative
examples. Explicit results for arbitrary are presented for
with and . We find very simple formulas
for the determinant . We also give results for
self-dual cyclic strips of the square lattice.Comment: Reference added to a relevant paper by F. Y. W
Investigation of the energy dependence of the orbital light curve in LS 5039
LS 5039 is so far the best studied -ray binary system at
multi-wavelength energies. A time resolved study of its spectral energy
distribution (SED) shows that above 1 keV its power output is changing along
its binary orbit as well as being a function of energy. To disentangle the
energy dependence of the power output as a function of orbital phase, we
investigated in detail the orbital light curves as derived with different
telescopes at different energy bands. We analysed the data from all existing
\textit{INTEGRAL}/IBIS/ISGRI observations of the source and generated the most
up-to-date orbital light curves at hard X-ray energies. In the -ray
band, we carried out orbital phase-resolved analysis of \textit{Fermi}-LAT data
between 30 MeV and 10 GeV in 5 different energy bands. We found that, at
100 MeV and 1 TeV the peak of the -ray emission is
near orbital phase 0.7, while between 100 MeV and 1 GeV it moves
close to orbital phase 1.0 in an orbital anti-clockwise manner. This result
suggests that the transition region in the SED at soft -rays (below a
hundred MeV) is related to the orbital phase interval of 0.5--1.0 but not to
the one of 0.0--0.5, when the compact object is "behind" its companion. Another
interesting result is that between 3 and 20 GeV no orbital modulation is found,
although \textit{Fermi}-LAT significantly (18) detects LS 5039.
This is consistent with the fact that at these energies, the contributions to
the overall emission from the inferior conjunction phase region (INFC, orbital
phase 0.45 to 0.9) and from the superior conjunction phase region (SUPC,
orbital phase 0.9 to 0.45) are equal in strength. At TeV energies the power
output is again dominant in the INFC region and the flux peak occurs at phase
0.7.Comment: 7 pages, 6 figures, accepted for publication in MNRA
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