498 research outputs found
Regularized Hamiltonians and Spinfoams
We review a recent proposal for the regularization of the scalar constraint
of General Relativity in the context of LQG. The resulting constraint presents
strengths and weaknesses compared to Thiemann's prescription. The main
improvement is that it can generate the 1-4 Pachner moves and its matrix
elements contain 15j Wigner symbols, it is therefore compatible with the
spinfoam formalism: the drawback is that Thiemann anomaly free proof is spoiled
because the nodes that the constraint creates have volume.Comment: 4 pages, based on a talk given at Loops '11 in Madrid, to appear in
Journal of Physics: Conference Series (JPCS
Financial Analysis of Dalbavancin for Acute Bacterial Skin and Skin Structure Infections for Self-Pay Patients
© 2020, The Author(s). Introduction: Acute bacterial skin and skin structure infections (ABSSSI) are an increasing cause of admission in the self-pay population. We previously reported that patients with ABSSSI discharged to receive dalbavancin showed a decreased length of stay (LOS) and total direct costs without increasing 30-day readmission rate. For patients who are financially eligible, a dalbavancin vial replacement program can offset costs. The objective of this study was to determine cost differences in treating ABSSSI in self-pay inpatients discharged to receive dalbavancin compared to standard of care (SOC). Methods: This retrospective cohort within a community health system compared self-pay adult inpatients with ABSSSI from February 3, 2016 to August 5, 2019 discharged to receive dalbavancin at an outpatient infusion center with SOC intravenous antibiotics. Patients were included with cellulitis, abscess, or postoperative wound infections diagnoses on the basis of International Classification of Disease, Tenth Revision (ICD-10) codes. Excluded populations were patients without dalbavancin vial replacement performed, pregnant, infections caused exclusively by gram-negative bacteria or fungi, or ICD-10 codes not consistent with ABSSSI. The primary outcome was direct cost of hospital stay. Secondary outcomes included length of stay (LOS), 30-day readmission rates, adverse events (AE), and indirect hospital costs. On the basis of previous studies, a one-sided Student’s t test was performed on financial data. Results: Twelve dalbavancin and 263 SOC patients met inclusion criteria. Direct cost (4010, p = 0.105) and indirect hospital cost (3646 , p = 0.162) per patient were less in the dalbavancin group. There was no significant difference between median LOS (4 vs 4, p = 0.888), AE (0% vs 14.8%), and 30-day readmission rates for dalbavancin vs SOC group (8.3% vs 7.2%, p = 0.604). Conclusion: Self-pay patients with ABSSSI discharged to receive dalbavancin with vial replacement resulted in decreased direct and indirect costs per patient with similar 30-day readmission rates, AE, and LOS. More studies targeted toward this population are warranted to determine ultimate benefit
Three dimensional loop quantum gravity: coupling to point particles
We consider the coupling between three dimensional gravity with zero
cosmological constant and massive spinning point particles. First, we study the
classical canonical analysis of the coupled system. Then, we go to the
Hamiltonian quantization generalizing loop quantum gravity techniques. We give
a complete description of the kinematical Hilbert space of the coupled system.
Finally, we define the physical Hilbert space of the system of self-gravitating
massive spinning point particles using Rovelli's generalized projection
operator which can be represented as a sum over spin foam amplitudes. In
addition we provide an explicit expression of the (physical) distance operator
between two particles which is defined as a Dirac observable.Comment: Typos corrected and references adde
Bogoliubov Excitations of Disordered Bose-Einstein Condensates
We describe repulsively interacting Bose-Einstein condensates in spatially
correlated disorder potentials of arbitrary dimension. The first effect of
disorder is to deform the mean-field condensate. Secondly, the quantum
excitation spectrum and condensate population are affected. By a saddle-point
expansion of the many-body Hamiltonian around the deformed mean-field ground
state, we derive the fundamental quadratic Hamiltonian of quantum fluctuations.
Importantly, a basis is used such that excitations are orthogonal to the
deformed condensate. Via Bogoliubov-Nambu perturbation theory, we compute the
effective excitation dispersion, including mean free paths and localization
lengths. Corrections to the speed of sound and average density of states are
calculated, due to correlated disorder in arbitrary dimensions, extending to
the case of weak lattice potentials.Comment: 23 pages, 11 figure
Timelike surfaces in Lorentz covariant loop gravity and spin foam models
We construct a canonical formulation of general relativity for the case of a
timelike foliation of spacetime. The formulation possesses explicit covariance
with respect to Lorentz transformations in the tangent space. Applying the loop
approach to quantize the theory we derive the spectrum of the area operator of
a two-dimensional surface. Its different branches are naturally associated to
spacelike and timelike surfaces. The results are compared with the predictions
of Lorentzian spin foam models. A restriction of the representations labeling
spin networks leads to perfect agreement between the states as well as the area
spectra in the two approaches.Comment: a wrong sign corrected in equation (65
Localization of solitons: linear response of the mean-field ground state to weak external potentials
Two aspects of bright matter-wave solitons in weak external potentials are
discussed. First, we briefly review recent results on the Anderson localization
of an entire soliton in disordered potentials [Sacha et al. PRL 103, 210402
(2009)], as a paradigmatic showcase of genuine quantum dynamics beyond simple
perturbation theory. Second, we calculate the linear response of the mean-field
soliton shape to a weak, but otherwise arbitrary external potential, with a
detailed application to lattice potentials.Comment: Selected paper presented at the 2010 Spring Meeting of the Quantum
Optics and Photonics Section of the German Physical Society. V2: minor
changes, published versio
A Guide to Localized Frames and Applications to Galerkin-like Representations of Operators
This chapter offers a detailed survey on intrinsically localized frames and
the corresponding matrix representation of operators. We re-investigate the
properties of localized frames and the associated Banach spaces in full detail.
We investigate the representation of operators using localized frames in a
Galerkin-type scheme. We show how the boundedness and the invertibility of
matrices and operators are linked and give some sufficient and necessary
conditions for the boundedness of operators between the associated Banach
spaces.Comment: 32 page
Early Universe Dynamics in Semi-Classical Loop Quantum Cosmology
Within the framework of loop quantum cosmology, there exists a semi-classical
regime where spacetime may be approximated in terms of a continuous manifold,
but where the standard Friedmann equations of classical Einstein gravity
receive non-perturbative quantum corrections. An approximate, analytical
approach to studying cosmic dynamics in this regime is developed for both
spatially flat and positively-curved isotropic universes sourced by a
self-interacting scalar field. In the former case, a direct correspondence
between the classical and semi-classical field equations can be established
together with a scale factor duality that directly relates different expanding
and contracting universes. Some examples of non-singular, bouncing cosmologies
are presented together with a scaling, power-law solution.Comment: 14 pages, In Press, JCA
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