3,178 research outputs found
Loss of molecules in magneto-electrostatic traps due to nonadiabatic transitions
We analyze the dynamics of a paramagnetic, dipolar molecule in a generic
"magneto-electrostatic'' trap where both magnetic and electric fields may be
present. The potential energy that governs the dynamics of the molecules is
found using a reduced molecular model that incorporates the main features of
the system. We discuss the shape of the trapping potentials for different field
geometries, as well as the possibility of nonadiabatic transitions to untrapped
states, i.e., the analog of Majorana transitions in a quadrupole magnetic
atomic trap. Maximizing the lifetime of molecules in a trap is of great concern
in current experiments, and we assess the effect of nonadiabatic transitions on
obtainable trap lifetimes.Comment: 13 pages, 6 figure
One-dimensional magnetic order in the metalâorganic framework
Variable-temperature neutron scattering measurements, reverse Monte Carlo analysis and direct Monte Carlo simulation are used to characterise magnetic order in the metalâorganic framework (MOF) over the temperature range 100K to 1.6K = T. The magnetic transition at T is shown to involve one-dimensional ferromagnetic ordering to a partially-ordered state related to the triangular Ising antiferromagnet and distinct from the canonical âpartially-disordered antiferromagnetâ model. In this phase, the direction of magnetisation of ferromagnetic chains tends to alternate between neighbouring chains but this alternation is frustrated and is not itself ordered. We suggest the existence of low-dimensional magnetic order in is stabilised by the contrasting strength of inter- and intra-chain magnetic coupling, itself a consequence of the underlying MOF architecture. Our results demonstrate how MOFs may provide an attractive if as yet under-explored platform for the realisation and investigation of low-dimensional physics
Numerical simulations with a first order BSSN formulation of Einstein's field equations
We present a new fully first order strongly hyperbolic representation of the
BSSN formulation of Einstein's equations with optional constraint damping
terms. We describe the characteristic fields of the system, discuss its
hyperbolicity properties, and present two numerical implementations and
simulations: one using finite differences, adaptive mesh refinement and in
particular binary black holes, and another one using the discontinuous Galerkin
method in spherical symmetry. The results of this paper constitute a first step
in an effort to combine the robustness of BSSN evolutions with very high
accuracy numerical techniques, such as spectral collocation multi-domain or
discontinuous Galerkin methods.Comment: To appear in Physical Review
Operational Radiology Recovery in Academic Radiology Departments After the COVID-19 Pandemic: Moving Toward Normalcy
This article presents a current snapshot in time, describing how radiology departments around the country are planning recovery from the baseline of the coronavirus disease 2019 pandemic, with a focus on different domains of recovery such as managing appointment availability, patient safety and workflow changes, and operational data and analytics. An e-mail survey was sent through the Society of Chairs of Academic Radiology Departments list server to 114 academic radiology departments. On the basis of data reported by the 38 survey respondents, best practices and shared experience are described for three key areas: (1) planning for recovery, (2) creating a new normal, and (3) measuring and forecasting. Radiology practices should be aware of the common approaches and preparations academic radiology departments have taken to reopening imaging in the post-coronavirus disease 2019 world. This should all be done when maintaining a safe and patient-centric environment and preparing to minimize the impact of future outbreaks or pandemics
Taking Blockchain Seriously
In the present techno-political moment it is clear that ignoring or dismissing the hype surrounding blockchain is unwise, and certainly for regulatory authorities and governments who must keep a grip on the technology and those promoting it, in order to ensure democratic accountability and regulatory legitimacy within the blockchain ecosystem and beyond. Blockchain is telling (and showing) us something very important about the evolution of capital and neoliberal economic reason, and the likely impact in the near future on forms and patterns of work, social organization, and, crucially, on communities and individuals who lack influence over the technologies and data that increasingly shape and control their lives. In this short essay I introduce some of the problems in the regulation of blockchain and offer counter-narratives aimed at cutting through the hype fuelling the ascendency of this most contemporary of technologies
Unilateral thoracoscopic surgical approach for diffuse emphysema
AbstractWe evaluated the use of a lateral thoracoscopic approach for lung reduction surgery in patients with diffuse emphysema. Sixty-seven patients with a mean age of 61.9 years underwent operation. Operative side was determined by preoperative imaging. The procedures were laser ablation in 10 patients and stapler resection in 57 patients. Ten patients, including six of the 10 patients in the laser-only group had poor outcome (death or hospitalization longer than 30 days), leading us to abandon the laser technique. Of the remaining 57 patients undergoing primary stapled resection, duration of chest tube placement averaged 13 days (range 3 to 53 days) with a mean hospital stay of 17 days (range 6 to 99 days). Seven patients required ventilation for longer than 72 hours, six patients underwent conversion of the procedure to open thoracotomy, four patients acquired arrhythmias, and three patients were treated for empyema. There was one early death (1.7%), from cardiopulmonary failure. Forty patients returned for 3-month evaluation. Significant ( p < 0.0001) improvements were seen in forced vital capacity (2.69 L after vs 2.26 L before) and forced expiration volume in 1 second (1.04 L after vs 0.82 L before), with 25 of 40 patients (63%) showing an improvement of more than 20%. Lung volume measures, in particular residual volume, fell significantly. Arterial blood gas analysis revealed that carbon dioxide tension fell significantly in patients with preoperative hypercapnia (carbon dioxide tension >45 mm Hg, p = 0.018). Six-minute walk test results improved (894 feet after vs 784 feet before, p = 0.002), and symptomatic benefit was confirmed by significant improvement in the dyspnea index. The combination of both hypercapnia and reduced single-breath diffusing capacity for carbon monoxide was significantly more frequent ( p = 0.0026) and was 86% specific (5 of 6 patients) in predicting serious postoperative risk. We conclude that the lateral thoracoscopic surgical approach to diffuse emphysema offers significant improvement in pulmonary mechanics and functional impairment. Patients with a combination of hypercapnia and reduced single-breath diffusing capacity for carbon monoxide should not be considered for this procedure because of significant perioperative risk. (J THORAC CARDIOVASC SURG 1996;111:308-16
Meson Exchange Effect on Color Superconductivity
We investigate the effects of pion and gluon exchanges on the formation of
two-flavor color superconductivity at moderate density, . The
chiral quark model proposed by Manohar and Georgi containing pions as well as
gluons is employed to show that the pion exchange reduces substantially the
value of the superconducting gap gotten with the gluon exchange only. It turns
out that the pion exchanges produce a repulsion between quark-quark pair in a
spin and isospin singlet state.
We suggest that the phase consisiting of pions, gluons and quarks is one of
the candidates of in-medium QCD phase at moderate density.Comment: 8 pages, 1 figure, minor correction
The Specific Heat of Normal, Degenerate Quark Matter: Non-Fermi Liquid Corrections
In normal degenerate quark matter, the exchange of dynamically screened
transverse gluons introduces infrared divergences in the quark self-energies
that lead to the breakdown of the Fermi liquid description. If the core of
neutron stars are composed of quark matter with a normal component, cooling by
direct quark Urca processes may be modified by non-Fermi liquid corrections. We
find that while the quasiparticle density of states is finite and non-zero at
the Fermi surface, its frequency derivative diverges and results in non-Fermi
liquid corrections to the specific heat of the normal, degenerate component of
quark matter. We study these non-perturbative non-Fermi liquid corrections to
the specific heat and the temperature dependence of the chemical potential and
show that these lead to a reduction of the specific heat.Comment: new discussion, updated references, accepted in PR
Bethe-Salpeter equation for diquarks in color-flavor locked phase of cold dense QCD
The Bethe-Salpeter equations for diquarks with the quantum numbers of the
Nambu-Goldstone bosons are analyzed in the color-flavor locked phase of cold
dense QCD with three quark flavors. The decay constants and the velocities of
the Nambu-Goldstone bosons are calculated in the Pagels-Stokar approximation.
It is also shown that, in contrast to the case of dense QCD with two flavors,
there are no massive radial excitations with quantum numbers of the
Nambu-Goldstone bosons in the color-flavor locked phase. The role of the
Meissner effect in the pairing dynamics of diquarks is explained.Comment: 14 pages, no figures, REVTeX. An appendix is added. References are
slightly rearranged. Typos and an error in Eq.(80) are corrected. To appear
in Phys. Rev.
Less than 50% sublattice polarization in an insulating S=3/2 kagome' antiferromagnet at low T
We have found weak long range antiferromagnetic order in the
quasi-two-dimensional insulating oxide which contains
Cr S=3/2 ions on a kagom\'{e} lattice. In a sample with 76%
occupancy of the chromium sites the ordered moment is 1.1(3) per
chromium ion which is only one third of the N\'{e}el value .
The magnetic unit cell equals the chemical unit cell, a situation which is
favored by inter-plane interactions. Gapless quantum spin-fluctuations
(T_NS(Q,\omega)$ in the ordered
phase.Comment: 18 pages, RevTex/Latex, with 6 figure
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