3,336 research outputs found
Quantum Phase Transitions in Bosonic Heteronuclear Pairing Hamiltonians
We explore the phase diagram of two-component bosons with Feshbach resonant
pairing interactions in an optical lattice. It has been shown in previous work
to exhibit a rich variety of phases and phase transitions, including a
paradigmatic Ising quantum phase transition within the second Mott lobe. We
discuss the evolution of the phase diagram with system parameters and relate
this to the predictions of Landau theory. We extend our exact diagonalization
studies of the one-dimensional bosonic Hamiltonian and confirm additional Ising
critical exponents for the longitudinal and transverse magnetic
susceptibilities within the second Mott lobe. The numerical results for the
ground state energy and transverse magnetization are in good agreement with
exact solutions of the Ising model in the thermodynamic limit. We also provide
details of the low-energy spectrum, as well as density fluctuations and
superfluid fractions in the grand canonical ensemble.Comment: 11 pages, 14 figures. To appear in Phys. Rev.
Polaritons and Pairing Phenomena in Bose--Hubbard Mixtures
Motivated by recent experiments on cold atomic gases in ultra high finesse
optical cavities, we consider the problem of a two-band Bose--Hubbard model
coupled to quantum light. Photoexcitation promotes carriers between the bands
and we study the non-trivial interplay between Mott insulating behavior and
superfluidity. The model displays a global U(1) X U(1) symmetry which supports
the coexistence of Mott insulating and superfluid phases, and yields a rich
phase diagram with multicritical points. This symmetry property is shared by
several other problems of current experimental interest, including
two-component Bose gases in optical lattices, and the bosonic BEC-BCS crossover
problem for atom-molecule mixtures induced by a Feshbach resonance. We
corroborate our findings by numerical simulations.Comment: 4 pages, 3 figure
Smoking and COVID Living Review (v11): a bayesian analysis
Aims: To estimate the association of smoking status with rates of i) infection, ii) hospitalisation, iii) disease severity, and iv) mortality from SARS-CoV-2/COVID-19 disease.
Design: Living rapid review of observational and experimental studies with random-effects hierarchical Bayesian meta-analyses. Published articles and pre-prints were identified via MEDLINE and medRxiv.
Setting: Community or hospital. No restrictions on location.
Participants: Adults who received a SARS-CoV-2 test or a COVID-19 diagnosis.
Measurements: Outcomes were SARS-CoV-2 infection, hospitalisation, disease severity and mortality stratified by smoking status. Study quality was assessed (i.e. ‘good’, ‘fair’ and ‘poor’).
Findings: v11 (searches up to 2021-02-16) included 405 studies with 62 ‘good’ and ‘fair’ quality studies included in unadjusted meta-analyses. 121 studies (29.9%) reported current, former and never smoking status with the remainder using broader categories. Recorded smoking prevalence among people with COVID-19 was generally lower than national prevalence. Current compared with never smokers were at reduced risk of SARS-CoV-2 infection (RR = 0.71, 95% Credible Interval (CrI) = 0.61-0.82, τ = 0.34). Data for former smokers were inconclusive (RR = 1.03, 95% CrI = 0.95-1.11, τ = 0.17) but favoured there being no important association (4% probability of RR ≥1.1). Former compared with never smokers were at increased risk of hospitalisation (RR = 1.19, CrI = 1.1-1.29, τ = 0.13), greater disease severity (RR = 1.8, CrI = 1.27-2.55, τ = 0.46) and mortality (RR = 1.56, CrI = 1.23-2, τ = 0.43). Data for current smokers on hospitalisation, disease severity and mortality were inconclusive (RR = 1.1, 95% CrI = 0.99-1.21, τ = 0.15; RR 1.26, 95% CrI = 0.92-1.73, τ = 0.32; RR = 1.12, 95% CrI = 0.84-1.47, τ = 0.42, respectively) but favoured there being no important associations with hospitalisation and mortality (49% and 56% probability of RR ≥1.1, respectively) and a small but important association with disease severity (83% probability of RR ≥1.1).
Conclusions: Compared with never smokers, current smokers appear to be at reduced risk of SARS-CoV-2 infection while former smokers appear to be at increased risk of hospitalisation, greater disease severity and mortality from COVID-19. However, it is uncertain whether these associations are causal
Magnetic Properties of the Second Mott Lobe in Pairing Hamiltonians
We explore the Mott insulating state of single-band bosonic pairing
Hamiltonians using analytical approaches and large scale density matrix
renormalization group calculations. We focus on the second Mott lobe which
exhibits a magnetic quantum phase transition in the Ising universality class.
We use this feature to discuss the behavior of a range of physical observables
within the framework of the 1D quantum Ising model and the strongly anisotropic
Heisenberg model. This includes the properties of local expectation values and
correlation functions both at and away from criticality. Depending on the
microscopic interactions it is possible to achieve either antiferromagnetic or
ferromagnetic exchange interactions and we highlight the possibility of
observing the E8 mass spectrum for the critical Ising model in a longitudinal
magnetic field.Comment: 14 pages, 15 figure
A characterization of quadric constant mean curvature hypersurfaces of spheres
Let be an immersion of a
complete -dimensional oriented manifold. For any , let
us denote by the function given by
and by , the function given by
, where is a Gauss map. We will prove
that if has constant mean curvature, and, for some and some
real number , we have that , then, is
either a totally umbilical sphere or a Clifford hypersurface. As an
application, we will use this result to prove that the weak stability index of
any compact constant mean curvature hypersurface in
which is neither totally umbilical nor a Clifford hypersurface and has constant
scalar curvature is greater than or equal to .Comment: Final version (February 2008). To appear in the Journal of Geometric
Analysi
PTSD Symptoms and Alcohol-Related Problems among Veterans: Temporal Associations and Vulnerability
Posttraumatic stress disorder (PTSD) is associated with elevated risk of both alcohol use disorder (AUD) and related conduct problems, which are associated with behavioral and emotional dysregulation. We conducted an intensive longitudinal burst design study with 10 weeks of experience sampling over the course of 1.5 years with 250 veterans of recent conflicts. We tested time-series models of daily associations between posttraumatic stress symptoms (PTSS), alcohol dependence syndrome, and conduct problems. Exacerbations of PTSS predicted higher dependence syndrome and conduct problems the next day. This effect was significant after controlling for both concurrent (i.e., same-day) associations between drinking and the outcomes as well as the strength of associations between the outcomes from one day to the next (i.e., autoregression). Affect lability and disinhibition were hypothesized vulnerability factors increasing the strength of within-person predictors of dependence syndrome and conduct problems. Lability and disinhibition were associated with greater dependence syndrome symptoms and conduct problems over the follow-up period. Consistent with expectation, lability rather than disinhibition increased the association between drinking and dependence syndrome as well as the strength of association between dependence syndrome symptoms from one day to the next. Moderating effects of disinhibition in the conduct problems model were not significant. Importantly, results indicated reciprocal associations over time. Lability potentiated the association between dependence syndrome symptoms and next-day PTSS, whereas disinhibition potentiated the association between conduct problems and next-day PTSS. Results demonstrate complex dynamic associations between PTSS, AUD symptoms, and conduct problems over time indicative of broad regulatory impairments
Highly charged ion X-rays from Electron-Cyclotron Resonance Ion Sources
Radiation from the highly-charged ions contained in the plasma of
Electron-Cyclotron Resonance Ion Sources constitutes a very bright source of
X-rays. Because the ions have a relatively low kinetic energy ( eV)
transitions can be very narrow, containing only small Doppler broadening. We
describe preliminary accurate measurements of two and three-electron ions with
Z=16--18. We show how these measurement can test sensitively many-body
relativistic calculations or can be used as X-ray standards for precise
measurements of X-ray transitions in exotic atoms
Manifestation of Quantum Chaos in Electronic Band Structures
We use semiconductors as an example to show that quantum chaos manifests
itself in the energy spectrum of crystals. We analyze the {\it ab initio} band
structure of silicon and the tight-binding spectrum of the alloy
, and show that some of their statistical properties obey the
universal predictions of quantum chaos derived from the theory of random
matrices. Also, the Bloch momenta are interpreted as external, tunable,
parameters, acting on the reduced (unit cell) Hamiltonian, in close analogy to
Aharonov-Bohm fluxes threading a torus. They are used in the investigation of
the parametric autocorrelator of crystal velocities. We find that our results
are in good agreement with the universal curves recently proposed by Simons and
coworkers.Comment: 15 pages with 6 Postscript figures included, RevTex-3, CMT-ERM/940
Variational formulas of higher order mean curvatures
In this paper, we establish the first variational formula and its
Euler-Lagrange equation for the total -th mean curvature functional
of a submanifold in a general Riemannian manifold
for . As an example, we prove that closed
complex submanifolds in complex projective spaces are critical points of the
functional , called relatively -minimal submanifolds,
for all . At last, we discuss the relations between relatively -minimal
submanifolds and austere submanifolds in real space forms, as well as a special
variational problem.Comment: 13 pages, to appear in SCIENCE CHINA Mathematics 201
A Brownian Motion Model of Parametric Correlations in Ballistic Cavities
A Brownian motion model is proposed to study parametric correlations in the
transmission eigenvalues of open ballistic cavities. We find interesting
universal properties when the eigenvalues are rescaled at the hard edge of the
spectrum. We derive a formula for the power spectrum of the fluctuations of
transport observables as a response to an external adiabatic perturbation. Our
formula correctly recovers the Lorentzian-squared behaviour obtained by
semiclassical approaches for the correlation function of conductance
fluctuations.Comment: 19 pages, written in RevTe
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