5,185 research outputs found
Universality and Critical Behavior at the Mott transition
We report conductivity measurements of Cr-doped V2O3 using a variable
pressure technique. The critical behavior of the conductivity near the
Mott-insulator to metal critical endpoint is investigated in detail as a
function of pressure and temperature. The critical exponents are determined, as
well as the scaling function associated with the equation of state. The
universal properties of a liquid-gas transition are found. This is potentially
a generic description of the Mott critical endpoint in correlated electron
materials.Comment: 3 figure
Laser cooling of new atomic and molecular species with ultrafast pulses
We propose a new laser cooling method for atomic species whose level
structure makes traditional laser cooling difficult. For instance, laser
cooling of hydrogen requires single-frequency vacuum-ultraviolet light, while
multielectron atoms need single-frequency light at many widely separated
frequencies. These restrictions can be eased by laser cooling on two-photon
transitions with ultrafast pulse trains. Laser cooling of hydrogen,
antihydrogen, and many other species appears feasible, and extension of the
technique to molecules may be possible.Comment: revision of quant-ph/0306099, submitted to PR
Coulomb crystallization in expanding laser-cooled neutral plasmas
We present long-time simulations of expanding ultracold neutral plasmas,
including a full treatment of the strongly coupled ion dynamics. Thereby, the
relaxation dynamics of the expanding laser-cooled plasma is studied, taking
into account elastic as well as inelastic collisions. It is demonstrated that,
depending on the initial conditions, the ionic component of the plasma may
exhibit short-range order or even a superimposed long-range order resulting in
concentric ion shells. In contrast to ionic plasmas confined in traps, the
shell structures are built up from the center of the plasma cloud rather than
from the periphery
Imaging the Cosmic Matter Distribution using Gravitational Lensing of Pregalactic HI
21-cm emission from neutral hydrogen during and before the epoch of cosmic
reionisation is gravitationally lensed by material at all lower redshifts.
Low-frequency radio observations of this emission can be used to reconstruct
the projected mass distribution of foreground material, both light and dark. We
compare the potential imaging capabilities of such 21-cm lensing with those of
future galaxy lensing surveys. We use the Millennium Simulation to simulate
large-area maps of the lensing convergence with the noise, resolution and
redshift-weighting achievable with a variety of idealised observation
programmes. We find that the signal-to-noise of 21-cm lens maps can far exceed
that of any map made using galaxy lensing. If the irreducible noise limit can
be reached with a sufficiently large radio telescope, the projected convergence
map provides a high-fidelity image of the true matter distribution, allowing
the dark matter halos of individual galaxies to be viewed directly, and giving
a wealth of statistical and morphological information about the relative
distributions of mass and light. For instrumental designs like that planned for
the Square Kilometer Array (SKA), high-fidelity mass imaging may be possible
near the resolution limit of the core array of the telescope.Comment: version accepted for publication in MNRAS (reduced-resolution
figures
AUTORADIOGRAPHIC ANALYSIS OF LYMPHOPOIESIS AND LYMPHOCYTE MIGRATION IN MICE BEARING MULTIPLE THYMUS GRAFTS
Lymphopoiesis was studied in 3-month-old normal C57Bl mice and in 3-month-old C57Bl mice carrying from 12 to 48 C57Bl thymus grafts using tritiated thymidine labeling. Thymus graft lymphopoiesis was found to be identical with that of normal thymus tissue and the presence of thymus grafts was found to have no influence on host thymus lymphopoiesis. No evidence was found that the massive amounts of thymus graft tissue in the mice affected any parameter of host lymph node lymphopoiesis nor was any evidence detected for the migration of thymic lymphocytes from these massive deposits of thymus graft tissue either to host lymph nodes and blood or to other organs in the host animal. It is concluded that the majority of small lymphocytes produced in the thymus and thymus graft tissue do not migrate from these tissues but die locally at the end of their intrathymic life span of 3 to 4 days
Cosmological Information in the Gravitational Lensing of Pregalactic HI
We study the constraints which the next generation of radio telescopes could
place on the nature of dark energy, dark matter and inflation by studying the
gravitational lensing of high redshift 21 cm emission, and we compare with the
constraints obtainable from wide-angle surveys of galaxy lensing. If the
reionization epoch is effectively at z ~ 8 or later, very large amounts of
cosmological information will be accessible to telescopes like SKA and LOFAR.
We use simple characterizations of reionization history and of proposed
telescope designs to investigate how well the two-dimensional convergence power
spectrum, the three-dimensional matter power spectrum, the evolution of the
linear growth function, and the standard cosmological parameters can be
measured from radio data. The power spectra can be measured accurately over a
wide range of wavenumbers at z ~ 2, and the evolution in the cosmic energy
density can be probed from z ~ 0.5 to z ~ 7. This results in a characterization
of the shape of the power spectra (i.e. of the nature of dark matter and of
inflationary structure generation) which is potentially more precise than that
obtained from galaxy lensing surveys. On the other hand, the dark energy
parameters in their conventional parametrization (Omega_Lambda, w_o, w_a) are
somewhat less well constrained by feasible 21 cm lensing surveys than by an
all-sky galaxy lensing survey although a 21 cm surveys might be more powerful
than galaxy surveys for constraining models with "early" dark energy. Overall,
the best constraints come from combining surveys of the two types. This results
in extremely tight constraints on dark matter and inflation, and improves
constraints on dark energy, as judged by the standard figure of merit, by more
than an order of magnitude over either survey alone.Comment: submitted to MNRAS, 12 pages, error in computer code corrected which
changed constraints on some cosmological parameters, change to lensing
estimator to improve performanc
Radical political unionism reassessed
Defections from European social-democratic parties and a resurgence of union militancy have prompted some to diagnose a new left-wing trade unionism across Europe. This comment on the article by Connolly and Darlington scrutinizes trends in France and Germany but primarily analyses recent developments in Britain. While there are some instances of disaffiliation from the Labour Party, support for electoral alternatives, growth in political militancy and emphasis on new forms of internationalism, these have been limited. There is insufficient evidence to suggest that we are witnessing the making of a new radical collectivism
Spectral Dependence of Coherent Backscattering of Light in a Narrow-Resonance Atomic System
We report a combined theoretical and experimental study of the spectral and
polarization dependence of near resonant radiation coherently backscattered
from an ultracold gas of 85Rb atoms. Measurements in an approximately 6 MHz
range about the 5s^{2}S_{1/2}- 5p^{2}P_{3/2}, F=3 - F'=4 hyperfine transition
are compared with simulations based on a realistic model of the experimental
atomic density distribution. In the simulations, the influence of heating of
the atoms in the vapor, magnetization of the vapor, finite spectral bandwidth,
and other nonresonant hyperfine transitions are considered. Good agreement is
found between the simulations and measurements.Comment: 10 pages, 12 figur
Critical behavior of repulsive linear -mers on triangular lattices
Monte Carlo (MC) simulations and finite-size scaling analysis have been
carried out to study the critical behavior in a submonolayer two-dimensional
gas of repulsive linear -mers on a triangular lattice at coverage
. A low-temperature ordered phase, characterized by a repetition of
alternating files of adsorbed -mers separated by adjacent empty sites,
is separated from the disordered state by a order-disorder phase transition
occurring at a finite critical temperature, . The MC technique was
combined with the recently reported Free Energy Minimization Criterion Approach
(FEMCA), [F. Rom\'a et al., Phys. Rev. B, 68, 205407, (2003)], to predict the
dependence of the critical temperature of the order-disorder transformation.
The dependence on of the transition temperature, , observed in MC
is in qualitative agreement with FEMCA. In addition, an accurate determination
of the critical exponents has been obtained for adsorbate sizes ranging between
and . For , the results reveal that the system does not belong
to the universality class of the two-dimensional Potts model with (,
monomers). Based on symmetry concepts, we suggested that the behavior observed
for and 3 could be generalized to include larger particle sizes ().Comment: 17 pages, 13 figure
Australian Eclecticism and Theorizing in Information Systems Research
explains a variety of IS research approaches found in Australia, and relates them the the history of IS research and teaching in Australia, and to Australian culture in genera
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