18,932 research outputs found
Thermal Logic Gates: Computation with phonons
Logic gates are basic digital elements for computers. We build up thermal
logic gates that can perform similar operations as their electronic
counterparts. The thermal logic gates are based on the nonlinear lattices,
which exhibit very intriguing phenomena due to their temperature dependent
power spectra. We demonstrate that phonons, the heat carriers, can be also used
to carry information and processed accordingly. The possibility of nanoscale
experiment is discussed.Comment: 5 pages, 5 figures. To appear in Phys. Rev. Let
A Herschel Study of 24 micron-Selected AGNs and Their Host Galaxies
We present a sample of 290 24-micron-selected active galactic nuclei (AGNs)
mostly at z ~ 0.3 -- 2.5, within 5.2 square degrees distributed as 25' X 25'
fields around each of 30 galaxy clusters in the Local Cluster Substructure
Survey (LoCuSS). The sample is nearly complete to 1 mJy at 24 microns, and has
a rich multi-wavelength set of ancillary data; 162 are detected by Herschel. We
use spectral templates for AGNs, stellar populations, and infrared emission by
star forming galaxies to decompose the spectral energy distributions (SEDs) of
these AGNs and their host galaxies, and estimate their star formation rates
(SFRs), AGN luminosities, and host galaxy stellar masses. The set of templates
is relatively simple: a standard Type-1 quasar template; another for the
photospheric output of the stellar population; and a far infrared star-forming
template. For the Type-2 AGN SEDs, we substitute templates including internal
obscuration, and some Type-1 objects require a warm component (T > 50 K). The
individually Herschel- detected Type-1 AGNs and a subset of 17 Type-2 ones
typically have luminosities > 10^{45} ergs/s, and supermassive black holes of ~
3 X 10^8 Msun emitting at ~ 10% of the Eddington rate. We find them in about
twice the numbers of AGN identified in SDSS data in the same fields, i.e., they
represent typical high luminosity AGN, not an infrared-selected minority. These
AGNs and their host galaxies are studied further in an accompanying paper
Radiation-induced magnetoresistance oscillations in two-dimensional electron systems under bichromatic irradiation
We analyze the magnetoresistance oscillations in high-mobility
two-dimensional electron systems induced by the combined driving of two
radiation fields of frequency and , based on the
balance-equation approach to magnetotransport for high-carrier-density systems
in Faraday geometry. It is shown that under bichromatic irradiation of
, most of the characterstic peak-valley pairs in the
curve of versus magnetic field in the case of monochromatic
irradiation of either or disappear, except the one around
or . oscillations
show up mainly as new peak-valley structures around other positions related to
multiple photon processes of mixing frequencies ,
, etc. Many minima of these resistance peak-valley pairs can
descend down to negative with enhancing radiation strength, indicating the
possible bichromaticzero-resistance states.Comment: 5 pages, 3 figures. Accepted for publication in Phys. Rev.
Average Density of States in Disordered Graphene systems
In this paper, the average density of states (ADOS) with a binary alloy
disorder in disordered graphene systems are calculated based on the recursion
method. We observe an obvious resonant peak caused by interactions with
surrounding impurities and an anti-resonance dip in ADOS curves near the Dirac
point. We also find that the resonance energy (Er) and the dip position are
sensitive to the concentration of disorders (x) and their on-site potentials
(v). An linear relation, not only holds when the impurity concentration is low
but this relation can be further extended to high impurity concentration regime
with certain constraints. We also calculate the ADOS with a finite density of
vacancies and compare our results with the previous theoretical results.Comment: 10 pages, 8 figure
Quantum transport of two-dimensional Dirac fermions in SrMnBi2
We report two-dimensional quantum transport in SrMnBi single crystals.
The linear energy dispersion leads to the unusual nonsaturated linear
magnetoresistance since all Dirac fermions occupy the lowest Landau level in
the quantum limit. The transverse magnetoresistance exhibits a crossover at a
critical field from semiclassical weak-field dependence to the
high-field linear-field dependence. With increase in the temperature, the
critical field increases and the temperature dependence of
satisfies quadratic behavior which is attributed to the Landau level splitting
of the linear energy dispersion. The effective magnetoresistant mobility
cm/Vs is derived. Angular dependent magnetoresistance
and quantum oscillations suggest dominant two-dimensional (2D) Fermi surfaces.
Our results illustrate the dominant 2D Dirac fermion states in SrMnBi and
imply that bulk crystals with Bi square nets can be used to study low
dimensional electronic transport commonly found in 2D materials like graphene.Comment: 5 papges, 4 figure
Effect of the Kondo correlation on thermopower in a Quantum Dot
In this paper we study the thermopower of a quantum dot connected to two
leads in the presence of Kondo correlation by employing a modified second-order
perturbation scheme at nonequilibrium. A simple scheme, Ng's ansatz [Phys. Rev.
Lett. {\bf 76}, 487 (1996)], is adopted to calculate nonequilibrium
distribution Green's function and its validity is further checked with regard
to the Onsager relation. Numerical results demonstrate that the sign of the
thermopower can be changed by tuning the energy level of the quantum dot,
leading to a oscillatory behavior with a suppressed magnitude due to the Kondo
effect. We also calculate the thermal conductance of the system, and find that
the Wiedemann-Franz law is obeyed at low temperature but violated with
increasing temperature, corresponding to emerging and quenching of the Kondo
effect.Comment: 6 pages, 4 figures; accepted for publication in J Phys.: Condensed
Matte
Elastic energy of proteins and the stages of protein folding
We propose a universal elastic energy for proteins, which depends only on the
radius of gyration and the residue number . It is constructed using
physical arguments based on the hydrophobic effect and hydrogen bonding.
Adjustable parameters are fitted to data from the computer simulation of the
folding of a set of proteins using the CSAW (conditioned self-avoiding walk)
model. The elastic energy gives rise to scaling relations of the form
in different regions. It shows three folding stages
characterized by the progression with exponents , which we
identify as the unfolded stage, pre-globule, and molten globule, respectively.
The pre-globule goes over to the molten globule via a break in behavior akin to
a first-order phase transition, which is initiated by a sudden acceleration of
hydrogen bonding
Effects of R-parity violating supersymmetry in top pair production at linear colliders with polarized beams
In the minimal supersymmetric standard model with R-parity violation, the
lepton number violating top quark interactions can contribute to the top pair
production at a linear collider via tree-level u-channel squark exchange
diagrams. We calculate such contributions and find that in the allowed range of
these R-violating couplings, the top pair production rate as well as the top
quark polarization and the forward-backward asymmetry can be significantly
altered. By comparing the unpolarized beams with the polarized beams, we find
that the polarized beams are more powerful in probing such new physics.Comment: 10 pages, 6 fig
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