2,165 research outputs found
Quantum interference structures in trapped ion dynamics beyond the Lamb-Dicke and rotating wave approximations
We apply wave packet methods to study an ion-trap system in the strong
excitation regime imposing neither the rotating wave nor the Lamb-Dicke
approximations. By this approach we show the existence of states with
restricted phase space evolution, as a genuine consequence of quantum
interference between wave packet fractions. A particular instance of such a
state oscillates between maximal entanglement and pure disentanglement between
the constitute subsystems. The characteristic crossover time is very rapid
making them suitable for state preparations of EPR or Schrodinger cat states.
Over longer time periods the dynamics of these states exhibits collapse-revival
patterns with well resolved fractional revivals in autocorrelation, inversion
and entanglement.Comment: 11 pages, 5 figures. Replaced with revised version. Phys. Rev. A 77,
053808 (2008
A tachyonic scalar field with mutually interacting components
We investigate the tachyonic cosmological potential in two
different cases of the quasi-exponential expansion of universe and discuss
various forms of interaction between the two components---matter and the
cosmological constant--- of the tachyonic scalar field, which leads to the
viable solutions of their respective energy densities. The distinction among
the interaction forms is shown to appear in the diagnostic. Further,
the role of the high- and low-redshift observations of the Hubble parameter is
discussed to determine the proportionality constants and hence the correct form
of matter--cosmological constant interaction.Comment: 14 page
High temperature superconductivity (Tc onset at 34K) in the high pressure orthorhombic phase of FeSe
We have studied the structural and superconducting properties of tetragonal
FeSe under pressures up to 26GPa using synchrotron radiation and diamond anvil
cells. The bulk modulus of the tetragonal phase is 28.5(3)GPa, much smaller
than the rest of Fe based superconductors. At 12GPa we observe a phase
transition from the tetragonal to an orthorhombic symmetry. The high pressure
orthorhombic phase has a higher Tc reaching 34K at 22GPa.Comment: 15 pages, 4 figure
Dilatonic global strings
We examine the field equations of a self-gravitating global string in low
energy superstring gravity, allowing for an arbitrary coupling of the global
string to the dilaton. Massive and massless dilatons are considered. For the
massive dilaton the spacetime is similar to the recently discovered
non-singular time-dependent Einstein self-gravitating global string, but the
massless dilaton generically gives a singular spacetime, even allowing for
time-dependence. We also demonstrate a time-dependent non-singular
string/anti-string configuration, in which the string pair causes a
compactification of two of the spatial dimensions, albeit on a very large
scale.Comment: 18 pages RevTeX, 3 figures, references amende
Self-Similar Shocks and Winds in Galaxy Clusters
A theoretical model framework of spherical symmetry is presented for a
composite astrophysical system of two polytropic fluids coupled together by
gravity to explore large-scale shocks and flow dynamics in clusters of galaxies
or in globular clusters. The existence of such large-scale shocks in clusters
of galaxies as inferred by high-resolution X-ray and radio imaging observations
implies large-scale systematic flows that are beyond usual static models for
clusters of galaxies. Here, we explore self-similar two-fluid flow solutions
with shocks for a hot polytropic gas flow in a cluster of galaxies in the
presence of a massive dark matter (DM) flow after the initiation of a
gravitational core collapse or a central AGN activity or a large-scale merging
process. In particular, the possibility of DM shocks or sharp jumps of mass
density and of velocity dispersion in dark matter halo is discussed and such DM
shocks might be detectable through gravitational lensing effects. To examine
various plausible scenarios for clusters of galaxies, we describe three
possible classes of shock flows within our model framework for different types
of temperature, density and flow speed profiles. Depending upon sensible model
parameters and shock locations, the hot ICM and DM halo may have various
combinations of asymptotic behaviours of outflow, breeze, inflow, contraction
or static envelopes at large radii at a given time. We refer to asymptotic
outflows of hot ICM at large radii as the galaxy cluster wind. As a result of
such galaxy cluster winds and simultaneous contractions of DM halo during the
course of galaxy cluster evolution, there would be less hot ICM within clusters
of galaxies as compared to the average baryon fraction in the Universe.Comment: 26 pages, 20 figure
Dynamic Evolution of a Quasi-Spherical General Polytropic Magnetofluid with Self-Gravity
In various astrophysical contexts, we analyze self-similar behaviours of
magnetohydrodynamic (MHD) evolution of a quasi-spherical polytropic magnetized
gas under self-gravity with the specific entropy conserved along streamlines.
In particular, this MHD model analysis frees the scaling parameter in the
conventional polytropic self-similar transformation from the constraint of
with being the polytropic index and therefore
substantially generalizes earlier analysis results on polytropic gas dynamics
that has a constant specific entropy everywhere in space at all time. On the
basis of the self-similar nonlinear MHD ordinary differential equations, we
examine behaviours of the magnetosonic critical curves, the MHD shock
conditions, and various asymptotic solutions. We then construct global
semi-complete self-similar MHD solutions using a combination of analytical and
numerical means and indicate plausible astrophysical applications of these
magnetized flow solutions with or without MHD shocks.Comment: 21 pages, 7 figures, accepted for publication in APS
Galaxy Clusters Selected with the Sunyaev-Zel'dovich Effect from 2008 South Pole Telescope Observations
We present a detection-significance-limited catalog of 21 Sunyaev-Zel'dovich
selected galaxy clusters. These clusters, along with 1 unconfirmed candidate,
were identified in 178 deg^2 of sky surveyed in 2008 by the South Pole
Telescope to a depth of 18 uK-arcmin at 150 GHz. Optical imaging from the
Blanco Cosmology Survey (BCS) and Magellan telescopes provided photometric (and
in some cases spectroscopic) redshift estimates, with catalog redshifts ranging
from z=0.15 to z>1, with a median z = 0.74. Of the 21 confirmed galaxy
clusters, three were previously identified as Abell clusters, three were
presented as SPT discoveries in Staniszewski et al, 2009, and three were first
identified in a recent analysis of BCS data by Menanteau et al, 2010; the
remaining 12 clusters are presented for the first time in this work. Simulated
observations of the SPT fields predict the sample to be nearly 100% complete
above a mass threshold of M_200 ~ 5x10^14 M_sun/h at z = 0.6. This completeness
threshold pushes to lower mass with increasing redshift, dropping to ~4x10^14
M_sun/h at z=1. The size and redshift distribution of this catalog are in good
agreement with expectations based on our current understanding of galaxy
clusters and cosmology. In combination with other cosmological probes, we use
the cluster catalog to improve estimates of cosmological parameters. Assuming a
standard spatially flat wCDM cosmological model, the addition of our catalog to
the WMAP 7-year analysis yields sigma_8 = 0.81 +- 0.09 and w = -1.07 +- 0.29, a
~50% improvement in precision on both parameters over WMAP7 alone.Comment: 19 pages, 9 figures, 4 appendice
Properties of Binary Transition-Metal Arsenides (TAs)
We present thermodynamic and transport properties of transition-metal (T)
arsenides, TAs with T = Sc to Ni (3d), Zr, Nb, Ru (4d), Hf and Ta (5d).
Characterization of these binaries is made with powder X-ray diffraction,
temperature and field-dependent magnetization and resistivity,
temperature-dependent heat capacity, Seebeck coefficient, and thermal
conductivity. All binaries show metallic behavior except TaAs and RuAs. TaAs,
NbAs, ScAs and ZrAs are diamagnetic, while CoAs, VAs, TiAs, NiAs and RuAs show
approximately Pauli paramagnetic behavior. FeAs and CrAs undergo
antiferromagnetic order below TN = 71 K and TN \approx 260 K, respectively.
MnAs is a ferromagnet below TC = 317 K and undergoes
hexagonal-orthorhombic-hexagonal transitions at TS = 317 K and 384 K,
respectively. For TAs, Seebeck coefficients vary between + 40 uV/K and - 40
uV/K in the 2 K to 300 K range, whereas thermal conductivity values stay below
18 W/(m K). The Sommerfeld-coefficient {\gamma} are less than 10 mJ/(K2mol). At
room temperature with application of 8 Tesla magnetic field, large positive
magnetoresistance is found for TaAs (~25%), MnAs (~90%) and for NbAs (~75%).Comment: 7 figures; Will be published in the upcoming focus issue in
Superconductor Science and Technolog
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