30,269 research outputs found
Scarring Effects on Tunneling in Chaotic Double-Well Potentials
The connection between scarring and tunneling in chaotic double-well
potentials is studied in detail through the distribution of level splittings.
The mean level splitting is found to have oscillations as a function of energy,
as expected if scarring plays a role in determining the size of the splittings,
and the spacing between peaks is observed to be periodic of period
{} in action. Moreover, the size of the oscillations is directly
correlated with the strength of scarring. These results are interpreted within
the theoretical framework of Creagh and Whelan. The semiclassical limit and
finite-{} effects are discussed, and connections are made with reaction
rates and resonance widths in metastable wells.Comment: 22 pages, including 11 figure
The development of absorptive capacity-based innovation in a construction SME
Traditionally, construction has been a transaction-oriented industry. However, it is changing from the design-bid-build process into a business based on innovation capability and performance management, in which contracts are awarded on the basis of factors such as knowledge, intellectual capital and skills. This change presents a challenge to construction-sector SMEs with scarce resources, which must find ways to innovate based on those attributes to ensure their future competitiveness. This paper explores how dynamic capability, using an absorptive capacity framework in response to these challenges, has been developed in a construction-based SME. The paper also contributes to the literature on absorptive capacity and innovation by showing how the construct can be operationalized within an organization. The company studied formed a Knowledge Transfer Partnership using action research over a two-year period with a local university. The aim was to increase its absorptive capacity and hence its ability to meet the changing market challenges. The findings show that absorptive capacity can be operationalized into a change management approach for improving capability-based competitiveness. Moreover, it is important for absorptive capacity constructs and language to be contextualized within a given organizational setting (as in the case of the construction-based SME in the present study)
A New Experiment to Study Hyperon CP Violation and the Charmonium System
Fermilab operates the world's most intense antiproton source, now exclusively
dedicated to serving the needs of the Tevatron Collider. The anticipated 2009
shutdown of the Tevatron presents the opportunity for a world-leading low- and
medium-energy antiproton program. We summarize the status of the Fermilab
antiproton facility and review physics topics for which a future experiment
could make the world's best measurements.Comment: 16 pages, 3 figures, to appear in Proceedings of CTP symposium on
Supersymmetry at LHC: Theoretical and Experimental Perspectives, The British
University in Egypt, Cairo, Egypt, 11-14 March 200
The Influence of Thermal Pressure on Equilibrium Models of Hypermassive Neutron Star Merger Remnants
The merger of two neutron stars leaves behind a rapidly spinning hypermassive
object whose survival is believed to depend on the maximum mass supported by
the nuclear equation of state, angular momentum redistribution by
(magneto-)rotational instabilities, and spindown by gravitational waves. The
high temperatures (~5-40 MeV) prevailing in the merger remnant may provide
thermal pressure support that could increase its maximum mass and, thus, its
life on a neutrino-cooling timescale. We investigate the role of thermal
pressure support in hypermassive merger remnants by computing sequences of
spherically-symmetric and axisymmetric uniformly and differentially rotating
equilibrium solutions to the general-relativistic stellar structure equations.
Using a set of finite-temperature nuclear equations of state, we find that hot
maximum-mass critically spinning configurations generally do not support larger
baryonic masses than their cold counterparts. However, subcritically spinning
configurations with mean density of less than a few times nuclear saturation
density yield a significantly thermally enhanced mass. Even without decreasing
the maximum mass, cooling and other forms of energy loss can drive the remnant
to an unstable state. We infer secular instability by identifying approximate
energy turning points in equilibrium sequences of constant baryonic mass
parametrized by maximum density. Energy loss carries the remnant along the
direction of decreasing gravitational mass and higher density until instability
triggers collapse. Since configurations with more thermal pressure support are
less compact and thus begin their evolution at a lower maximum density, they
remain stable for longer periods after merger.Comment: 20 pages, 12 figures. Accepted for publication in Ap
The continued spectral and temporal evolution of RX J0720.4-3125
RX J0720.4-3125 is the most peculiar object among a group of seven isolated
X-ray pulsars (the so-called "Magnificent Seven"), since it shows long-term
variations of its spectral and temporal properties on time scales of years.
This behaviour was explained by different authors either by free precession
(with a seven or fourteen years period) or possibly a glitch that occurred
around .
We analysed our most recent XMM-Newton and Chandra observations in order to
further monitor the behaviour of this neutron star. With the new data sets, the
timing behaviour of RX J0720.4-3125 suggests a single (sudden) event (e.g. a
glitch) rather than a cyclic pattern as expected by free precession. The
spectral parameters changed significantly around the proposed glitch time, but
more gradual variations occurred already before the (putative) event. Since
the spectra indicate a very slow cooling by
2 eV over 7 years.Comment: seven pages, three figures, three tables; accepted by MNRA
Non-thermalization in trapped atomic ion spin chains
Linear arrays of trapped and laser cooled atomic ions are a versatile
platform for studying emergent phenomena in strongly-interacting many-body
systems. Effective spins are encoded in long-lived electronic levels of each
ion and made to interact through laser mediated optical dipole forces. The
advantages of experiments with cold trapped ions, including high spatiotemporal
resolution, decoupling from the external environment, and control over the
system Hamiltonian, are used to measure quantum effects not always accessible
in natural condensed matter samples. In this review we highlight recent work
using trapped ions to explore a variety of non-ergodic phenomena in long-range
interacting spin-models which are heralded by memory of out-of-equilibrium
initial conditions. We observe long-lived memory in static magnetizations for
quenched many-body localization and prethermalization, while memory is
preserved in the periodic oscillations of a driven discrete time crystal state.Comment: 14 pages, 5 figures, submitted for edition of Phil. Trans. R. Soc. A
on "Breakdown of ergodicity in quantum systems
The Long and Short of Nuclear Effective Field Theory Expansions
Nonperturbative effective field theory calculations for NN scattering seem to
break down at rather low momenta. By examining several toy models, we clarify
how effective field theory expansions can in general be used to properly
separate long- and short-range effects. We find that one-pion exchange has a
large effect on the scattering phase shift near poles in the amplitude, but
otherwise can be treated perturbatively. Analysis of a toy model that
reproduces 1S0 NN scattering data rather well suggests that failures of
effective field theories for momenta above the pion mass can be due to
short-range physics rather than the treatment of pion exchange. We discuss the
implications this has for extending the applicability of effective field
theories.Comment: 22 pages, 9 figures, references corrected, minor modification
Magnetic Hydrogen Atmosphere Models and the Neutron Star RX J1856.5-3754
RX J1856.5-3754 is one of the brightest nearby isolated neutron stars, and
considerable observational resources have been devoted to it. However, current
models are unable to satisfactorily explain the data. We show that our latest
models of a thin, magnetic, partially ionized hydrogen atmosphere on top of a
condensed surface can fit the entire spectrum, from X-rays to optical, of RX
J1856.5-3754, within the uncertainties. In our simplest model, the best-fit
parameters are an interstellar column density N_H \approx 1x10^20 cm^-2 and an
emitting area with R^infty \approx 17 km (assuming a distance to RX
J1856.5-3754 of 140 pc), temperature T^infty \approx 4.3x10^5 K, gravitational
redshift z_g \sim 0.22, atmospheric hydrogen column y_H \approx 1 g cm^-2, and
magnetic field B \approx (3-4)x10^12 G; the values for the temperature and
magnetic field indicate an effective average over the surface. We also
calculate a more realistic model, which accounts for magnetic field and
temperature variations over the neutron star surface as well as general
relativistic effects, to determine pulsations; we find there exist viewing
geometries that produce pulsations near the currently observed limits. The
origin of the thin atmospheres required to fit the data is an important
question, and we briefly discuss mechanisms for producing these atmospheres.
Our model thus represents the most self-consistent picture to date for
explaining all the observations of RX J1856.5-3754.Comment: 11 pages, 8 figures; MNRAS, accepte
Quenched QCD with domain wall fermions
We report on simulations of quenched QCD using domain wall fermions, where we
focus on basic questions about the formalism and its ability to produce
expected low energy hadronic physics for light quarks. The work reported here
is on quenched lattices at and 5.85, using values
for the length of the fifth dimension between 10 and 48. We report results for
parameter choices which lead to the desired number of flavors, a study of
undamped modes in the extra dimension and hadron masses.Comment: Contribution to Lattice '98. Presented by R. Mawhinney. 3 pages, 3
figure
Dynamical QCD thermodynamics with domain wall fermions
We present results from numerical simulations of full, two flavor QCD
thermodynamics at N_t=4 with domain wall fermions. For the first time a
numerical simulation of the full QCD phase transition displays a low
temperature phase with spontaneous chiral symmetry breaking but intact flavor
symmetry and a high temperature phase with the full SU(2) x SU(2) chiral flavor
symmetry.Comment: LATTICE98(hightemp
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