87,457 research outputs found
Acyclic orientations on the Sierpinski gasket
We study the number of acyclic orientations on the generalized
two-dimensional Sierpinski gasket at stage with equal to
two and three, and determine the asymptotic behaviors. We also derive upper
bounds for the asymptotic growth constants for and -dimensional
Sierpinski gasket .Comment: 20 pages, 8 figures and 6 table
Unitary Fermi Gas in a Harmonic Trap
We present an {\it ab initio} calculation of small numbers of trapped,
strongly interacting fermions using the Green's Function Monte Carlo method
(GFMC). The ground state energy, density profile and pairing gap are calculated
for particle numbers using the parameter-free "unitary"
interaction. Trial wave functions are taken of the form of correlated pairs in
a harmonic oscillator basis. We find that the lowest energies are obtained with
a minimum explicit pair correlation beyond that needed to exploit the
degeneracy of oscillator states. We find that energies can be well fitted by
the expression where is the
Thomas-Fermi energy of a noninteracting gas in the trap and is a
pairing gap. There is no evidence of a shell correction energy in the
systematics, but the density distributions show pronounced shell effects. We
find the value for the pairing gap. This is smaller
than the value found for the uniform gas at a density corresponding to the
central density of the trapped gas.Comment: 2 figures, 2 table
Ab initio study of a mechanically gated molecule: From weak to strong correlation
The electronic spectrum of a chemically contacted molecule in the junction of
a scanning tunneling microscope can be modified by tip retraction. We analyze
this effect by a combination of density functional, many-body perturbation and
numerical renormalization group theory, taking into account both the
non-locality and the dynamics of electronic correlation. Our findings, in
particular the evolution from a broad quasiparticle resonance below to a narrow
Kondo resonance at the Fermi energy, correspond to the experimental
observations.Comment: 4 pages, 3 figure
New constraints on a light CP-odd Higgs boson and related NMSSM Ideal Higgs Scenarios
Recent BaBar limits on \br(\Upsilon(3S)\to \gam a\to \gam \tau^+\tau^-) and
\br(\Upsilon(3S)\to \gam a\to \gam \mu^+\mu^-) provide increased constraints
on the a b\anti b coupling of a CP-odd Higgs boson, , with
. We extract these limits from the BaBar data and compare
to the limits previously obtained using other data sets, especially the
CLEO-III \br(\Upsilon(1S)\to \gam\to\tau^+\tau^-) limits. Comparisons are
made to predictions in the context of "ideal"-Higgs NMSSM scenarios, in which
the lightest CP-even Higgs boson, , can have mass below 105\gev (as
preferred by precision electroweak data) and yet can escape old LEP limits by
virtue of decays to a pair of the lightest CP-odd Higgs bosons, , with . Most such scenarios with are
eliminated, but the bulk of the m_{a_1}>7.5\gev scenarios, which are
theoretically the most favored, survive. We also outline the impact of the new
ALEPH LEP results in the \epem\to Z+4\tau channel. For ,
only NMSSM ideal Higgs scenarios with m_{h_1}\gsim 98\gev and close
to satisfy the ALEPH limits. For \tan\beta\lsim 2, the ALEPH limits
are easily satisfied for the most theoretically preferred NMSSM scenarios,
which are those with close to and m_{h_1}\sim
90\gev-100\gev.Comment: 24 pages, 25 figures, paper updated to incorporate final ALEPH limits
in Z+4\tau channel
A systematic study of Rayleigh-Brillouin scattering in air, N2 and O2 gases
Spontaneous Rayleigh-Brillouin scattering experiments in air, N2 and O2 have
been performed for a wide range of temperatures and pressures at a wavelength
of 403 nm and at a 90 degrees scattering angle. Measurements of the
Rayleigh-Brillouin spectral scattering profile were conducted at high
signal-to-noise ratio for all three species, yielding high-quality spectra
unambiguously showing the small differences between scattering in air, and its
constituents N2 and O2. Comparison of the experimental spectra with
calculations using the Tenti S6 model, developed in 1970s based on linearized
kinetic equations for molecular gases, demonstrates that this model is valid to
high accuracy. After previous measurements performed at 366 nm, the Tenti S6
model is here verified for a second wavelength of 403 nm. Values for the bulk
viscosity for the gases are derived by optimizing the model to the
measurements. It is verified that the bulk viscosity parameters obtained from
previous experiments at 366 nm, are valid for wavelengths of 403 nm. Also for
air, which is treated as a single-component gas with effective gas transport
coefficients, the Tenti S6 treatment is validated for 403 nm as for the
previously used wavelength of 366 nm, yielding an accurate model description of
the scattering profiles for a range of temperatures and pressures, including
those of relevance for atmospheric studies. It is concluded that the Tenti S6
model, further verified in the present study, is applicable to LIDAR
applications for exploring the wind velocity and the temperature profile
distributions of the Earth's atmosphere. Based on the present findings,
predictions can be made on the spectral profiles for a typical LIDAR
backscatter geometry, which deviate by some 7 percent from purely Gaussian
profiles at realistic sub-atmospheric pressures occurring at 3-5 km altitude in
the Earth's atmosphere
Exact Potts Model Partition Functions for Strips of the Honeycomb Lattice
We present exact calculations of the Potts model partition function
for arbitrary and temperature-like variable on -vertex
strip graphs of the honeycomb lattice for a variety of transverse widths
equal to vertices and for arbitrarily great length, with free
longitudinal boundary conditions and free and periodic transverse boundary
conditions. These partition functions have the form
, where
denotes the number of repeated subgraphs in the longitudinal direction. We give
general formulas for for arbitrary . We also present plots of
zeros of the partition function in the plane for various values of and
in the plane for various values of . Explicit results for partition
functions are given in the text for (free) and (cylindrical),
and plots of partition function zeros are given for up to 5 (free) and
(cylindrical). Plots of the internal energy and specific heat per site
for infinite-length strips are also presented.Comment: 39 pages, 34 eps figures, 3 sty file
Isolated Galaxies versus Interacting Pairs with MaNGA
We present preliminary results of the spectral analysis on the radial
distributions of the star formation history in both, a galaxy merger and a
spiral isolated galaxy observed with MaNGA. We find that the central part of
the isolated galaxy is composed by older stellar population (2 Gyr) than
in the outskirts (7 Gyr). Also, the time-scale is gradually larger from 1
Gyr in the inner part to 3 Gyr in the outer regions of the galaxy. In the case
of the merger, the stellar population in the central region is older than in
the tails, presenting a longer time-scale in comparison to central part in the
isolated galaxy. Our results are in agreement with a scenario where spiral
galaxies are built from inside-out. In the case of the merger, we find evidence
that interactions enhance star formation in the central part of the galaxy.Comment: 7 pages, 2 figures. Proceedings of the EWASS-2015 special session
Sp3, accepted for publication in Special Issue "3D View on Interacting and
Post-Interacting Galaxies from Clusters to Voids" of open access journal
"Galaxies
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