1,526 research outputs found
Thermal entanglement in fully connected spin systems and its RPA description
We examine the thermal pairwise entanglement in a symmetric system of
spins fully connected through anisotropic -type couplings embedded in a
transverse magnetic field. We consider both the exact evaluation together with
that obtained with the static path + random phase approximation (RPA) and the
ensuing mean field + RPA. The latter is shown to provide an accurate analytic
description of both the parallel and antiparallel thermal concurrence in large
systems. We also analyze the limit temperature for pairwise entanglement, which
is shown to increase for large fields and to decrease logarithmically with
increasing . Special finite size effects are as well discussed.Comment: 9 pages, 5 figure
Description of thermal entanglement with the static path plus random-phase approximation
We discuss the application of the static path plus random phase approximation
(SPA+RPA) and the ensuing mean field+RPA treatment to the evaluation of
entanglement in composite quantum systems at finite temperature. These methods
involve just local diagonalizations and the determination of the generalized
collective vibrational frequencies. As illustration, we evaluate the pairwise
entanglement in a fully connected XXZ chain of spins at finite temperature
in a transverse magnetic field . It is shown that already the mean field+RPA
provides an accurate analytic description of the concurrence below the mean
field critical region (), exact for large , whereas the full
SPA+RPA is able to improve results for finite systems in the critical region.
It is proved as well that for weak entanglement also arises when the
ground state is separable (), with the limit temperature for pairwise
entanglement exhibiting quite distinct regimes for .Comment: 20 pages, 5 figure
Plant Essential Oils as Healthy Functional Ingredients of Nutraceuticals and Diet Supplements: A Review
Essential oils (EOs) are mixtures of volatile molecules endowed with health-promoting biological activities that go beyond their role as aromas and natural preservatives and can be exploited to develop functional foods and diet supplements. Their composition is briefly addressed along with regulatory aspects. The potential health benefit of human diet supplementation with EOs is outlined through a review of the recent literature on available clinical trials and preclinical research concerning EOs activity towards: (1) irritable bowel syndrome; (2) inflammatory bowel disease; (3) regulation of microbiota; (4) gastroprotection; (5) hepatoprotection; (6) protection of the urinary tract and diuresis; (7) management of metabolic disorders including hyperglycemia and hyperlipidemia; (8) anti-inflammatory and pain control; (9) immunomodulation and protection from influenza; and (10) neuroprotection and modulation of mood and cognitive performance. The emerging potential in such activities of selected EOs is given focus, particularly green and black cumin, bergamot, orange, myrtle, peppermint, sage, eucalyptus, lavender, thyme, lemon balm, ginger, and garlic
Quiz Games as a model for Information Hiding
We present a general computation model inspired in the notion of information
hiding in software engineering. This model has the form of a game which we call
quiz game. It allows in a uniform way to prove exponential lower bounds for
several complexity problems of elimination theory.Comment: 46 pages, to appear in Journal of Complexit
Relativistic Approach to Superfluidity in Nuclear Matter
Pairing correlations in symmetric nuclear matter are studied within a
relativistic mean-field approximation based on a field theory of nucleons
coupled to neutral ( and ) and to charged () mesons.
The Hartree-Fock and the pairing fields are calculated in a self-consistent
way. The energy gap is the result of a strong cancellation between the scalar
and vector components of the pairing field. We find that the pair amplitude
vanishes beyond a certain value of momentum of the paired nucleons. This fact
determines an effective cutoff in the gap equation. The value of this cutoff
gives an energy gap in agreement with the estimates of non relativistic
calculations.Comment: 21 pages, REVTEX, 8 ps-figures, to appear in Phys.Rev.C. e-mail:
[email protected]
Spacetime quantum and classical mechanics with dynamical foliation
The conventional phase space of classical physics treats space and time
differently, and this difference carries over to field theories and quantum
mechanics (QM). In this paper, the phase space is enhanced through two main
extensions. Firstly, we promote the time choice of the Legendre transform to a
dynamical variable. Secondly, we extend the Poisson brackets of matter fields
to a spacetime symmetric form. The ensuing "spacetime phase space" is employed
to obtain an explicitly covariant version of Hamilton equations for
relativistic field theories. A canonical-like quantization of the formalism is
then presented in which the fields satisfy spacetime commutation relations and
the foliation is quantum. In this approach, the classical action is also
promoted to an operator and retains explicit covariance through its
non-separability in the matter-foliation partition. The problem of establishing
a correspondence between the new noncausal framework (where fields at different
times are independent) and conventional QM is solved through a generalization
of spacelike correlators to spacetime. In this generalization, the Hamiltonian
is replaced by the action, and conventional particles by off-shell particles.
When the foliation is quantized, the previous map is recovered by conditioning
on foliation eigenstates, in analogy with the Page and Wootters mechanism. We
also provide an interpretation of the correspondence in which the causal
structure of a given theory emerges from the quantum correlations between the
system and an environment. This idea holds for general quantum systems and
allows one to generalize the density matrix to an operator containing the
information of correlators both in space and time.Comment: 25 pages, 4 figure
Path Integrals from Spacetime Quantum Actions
We present a spacetime Hilbert space formulation of Feynman path integrals
(PIs). It relies on a tensor product structure in time which provides extended
representations of dynamical quantum observables through a spacetime quantum
action operator. As a consequence, the ``sum over paths'' of the different PI
formulations naturally arise within the same Hilbert space, with each one
associated with a different quantum trajectory basis. New insights on PI-based
results naturally follow, including exact discretizations and a non-trivial
approach to the continuum limit.Comment: 8 pages, 1 figur
Spacetime Quantum Actions
We propose a formulation of quantum mechanics in an extended Fock space in
which a tensor product structure is applied to time. Subspaces of histories
consistent with the dynamics of a particular theory are defined by a direct
quantum generalization of the corresponding classical action. The
diagonalization of such quantum actions enables us to recover the predictions
of conventional quantum mechanics and reveals an extended unitary equivalence
between all physical theories. Quantum correlations and coherent effects across
time and between distinct theories acquire a rigorous meaning, which is encoded
in the rich temporal structure of physical states. Connections with modern
relativistic schemes and the path integral formulation also emerge.Comment: 16 pages, 3 figures, accepted for publication in Phys. Rev.
Pharmacological management of COVID-19 patients with ARDS (CARDS): A narrative review
Coronavirus disease 2019 (COVID-19) is highly infectious. It has been highlighted that if not expertly and individually managed with consideration of the vasocentric features, a COVID-19 patient with an acute respiratory distress syndrome (CARDS) may eventually develop multiorgan failure. Unfortunately, there is still no definite drug for CARDS that is capable of reducing either short-term or long-term mortality and no specific treatments for COVID-19 exist right now. In this narrative review, based on a selective literature search in EMBASE, MEDLINE, Scopus, The Cochrane Library, Web of Science, and Google Scholar and ClinicalTrials.gov, we have examined the emerging evidence on the possible treatment of CARDS. Although numerous pharmacologic therapies to improve clinical outcomes in CARDS have been studied also in clinical trials, none have shown efficacy and there is great uncertainty about their effectiveness. There is still no recommendation for the therapeutic use of any specific agent to treat CARDS because no drugs are validated to have significant efficacy in clinical treatment of COVID-19 patients in large-scale trials. However, there exist a number of drugs that may be useful at least in some patients. The real challenge now is to link the right patient to the right treatment
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