5,388 research outputs found
Photoproduction of dileptons and photons in p-p collisions at Large Hadron Collider energies
The production of large dileptons and photons originating from
photoproduction processes in p-p collisions at Large Hadron Collider energies
is calculated. The comparisons between the exact treatment results and the ones
of the equivalent photon approximation approach are expressed as the
(the virtuality of photon) and distributions. The method developed by
Martin and Ryskin is used for avoiding double counting when the coherent and
incoherent contributions are considered simultaneously. The numerical results
indicate that, the equivalent photon approximation is only effective in small
region and can be used for coherent photoproduction processes with
proper choice of ( the choices or will cause obvious errors), but can not be used for
incoherent photoproduction processes. The exact treatment is needed to deal
accurately with the photoproduction of large dileptons and photons.Comment: 13 pages, 24 figure
T-Carbon: A Novel Carbon Allotrope
A structurally stable crystalline carbon allotrope is predicted by means of
the first-principles calculations. This allotrope can be derived by
substituting each atom in diamond with a carbon tetrahedron, and possesses the
same space group Fd^1 3m as diamond, which is thus coined as T- carbon. The
calculations on geometrical, vibrational and electronic properties reveal that
T-carbon, with a considerable structural stability and a much lower density
1.50 g/cm3, is a semiconductor with a direct band gap about 3.0 eV, and has a
Vickers hardness 61.1 GPa lower than diamond but comparable with cubic boron
nitride. Such a form of carbon, once obtained, would have wide applications in
photocatalysis, adsoption, hydrogen storage and aerospace materials
Search for the Gamma-ray Emission from M33 with Fermi LAT
In the work we search for the -ray signal from M33, one of the
biggest galaxies in the Local Group, by using the Pass 8 data of Fermi Large
Area Telescope (LAT). No statistically significant gamma-ray emission has been
detected in the direction of M33 and we report a new upper limit of high energy
() photon flux of ,
which is more strict than previous constrains and implies a cosmic ray density
of M33 lower than that speculated previously. Nevertheless the current limit is
still in agreement with the correlation of star formation rate and -ray
luminosity inferred from the Local group galaxies and a few nearby starburst
galaxies.Comment: 11 pages, 4 figure
Entanglement dynamics of a moving multi-photon Jaynes-Cummings model in mixed states
Using the algebraic dynamical method, the dynamics of entanglement in an
atom-field bipartite system in a mixed state is investigated. The atomic
center-ofmass motion and the field-mode structure are also included in this
system. We find that the larger values of the detuning and the average photon
number, the smaller fluctuation of the entanglement, but the period for the
evolution of the entanglement doesn't increase accordingly; It is also found
that the fluctuation of the entanglement varies slightly with the atomic motion
and oscillates fast with the value of the fieldmode structure and the
transition photon number increasing. Moreover, a damping evolution of the
entanglement appears when considering detuning and the atomic motion
simultaneously.Comment: 11 pages, 5 figure
Quantum phase transitions for two coupled sites with dipole-coupled effective Jaynes-Cummings model
The nature of the ground states for a system composed of two coupled cavities
with each containing a pair of dipole-coupled two-level atoms are studied over
a wide range of detunings and dipole coupling strengths. The cases for three
limits of exact resonance, large positive and negative detunings are discussed,
and four types of the ground states are revealed. Then the phase diagrams of
the ground state are plotted by choosing three different "order parameters". We
find that the phase space, determined by the combinative action of detuning and
the dipole coupling strength, is divided into four regions. This is different
from the general Bose-Hubbard model and more richer physics are presented in
the two-site coupled cavities system. That is, the insulator region may be
polaritonic or atomic and the superfluid region may be polaritonic or photonic
in nature.Comment: 7 pages, 11 figure
Saturation of ion irradiation effects in Cr2AlC
Cr2AlC materials were irradiated with 7 MeV Xe26+ ions and 500 keV He2+ ions
at room temperature. A structural transition with an increased c lattice
parameter and a decreased a lattice parameter occurs after irradiation to doses
above 1 dpa. Nevertheless, the modified structure is stable up to the dose of
5.2 dpa without obvious lattice disorder. The three samples irradiated to doses
above 1 dpa have comparable lattice parameters and hardness values, suggesting
a saturation of irradiation effects in Cr2AlC. The structural transition and
irradiation effects saturation are ascribed to irradiation-induced antisite
defects (CrAl and AlCr) and C interstitials, which is supported by the
calculations of the formation energies of various defects in Cr2AlC. The
irradiation-induced antisite defects and C interstitials may be critical to
understand the excellent resistance to irradiation-induced amorphization of MAX
phases.Comment: 14 pages, 8 figure
Strain-induced Dirac cone-like electronic structures and semiconductor-semimetal transition in graphdiyne
By means of the first-principles calculations combined with the tight-binding
approximation, the strain-induced semiconductor-semimetal transition in
graphdiyne is discovered. It is shown that the band gap of graphdiyne increases
from 0.47 eV to 1.39 eV with increasing the biaxial tensile strain, while the
band gap decreases from 0.47 eV to nearly zero with increasing the uniaxial
tensile strain, and Dirac cone-like electronic structures are observed. The
uniaxial strain-induced changes of the electronic structures of graphdiyne come
from the breaking of geometrical symmetry that lifts the degeneracy of energy
bands. The properties of graphdiyne under strains are disclosed different
remarkably from that of graphene.Comment: 7 pages, 7 figure
Conclusive quantum-state transfer with a single randomly coupled spin chain
We studied the quantum state transfer in randomly coupled spin chains. By
using local memories storing the information and dividing the task into
transfer portion and decoding portion, conclusive transfer was ingeniously
achieved with just one single spin chain. In our scheme, the probability of
successful transfer can be made arbitrary close to unity. Especially, our
scheme is a good protocol to decode information from memories without adding
another spin chain. Compared with Time-reversed protocol, the average decoding
time is much less in our scheme.Comment: 13 pages, 3 figure
Octagraphene as a Versatile Carbon Atomic Sheet for Novel Nanotubes, Unconventional Fullerenes and Hydrogen Storage
We study a versatile structurally favorable periodic -bonded carbon
atomic planar sheet with symmetry by means of the first-principles
calculations. This carbon allotrope is composed of carbon octagons and squares
with two bond lengths and is thus dubbed as octagraphene. It is a semimetal
with the Fermi surface consisting of one hole and one electron pocket, whose
low-energy physics can be well described by a tight-binding model of
-electrons. Its Young's modulus, breaking strength and Poisson's ratio are
obtained to be 306 , 34.4 and 0.13, respectively, which are close to
those of graphene. The novel sawtooth and armchair carbon nanotubes as well as
unconventional fullerenes can also be constructed from octagraphene. It is
found that the Ti-absorbed octagraphene can be allowed for hydrogen storage
with capacity around 7.76 wt%
Derivation of the Gasser-Leutwyler Lagrangian from QCD
The normal part of the Gasser-Leutwyler formulation of the chiral Lagrangian
is formally derived from the first principles of QCD without taking
approximations. All the coefficients are expressed in terms of certain Green's
functions in QCD, which can be regarded as the general QCD definitions of the
normal part of the coefficients. The approximate values of the coefficients are
also presented.Comment: 4 pages in RevTe
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