244 research outputs found
Thermodynamics and Phase Structure of the Two-Flavor Nambu--Jona-Lasinio Model Beyond Large-N_c
The optimized perturbation theory (OPT) method is applied to the
version of the Nambu--Jona-Lasinio (NJL) model both at zero and at finite
temperature and/or density. At the first nontrivial order the OPT exhibits a
class of 1/N_c corrections which produce nonperturbative results that go beyond
the standard large-N_c, or mean-field approximation. The consistency of the OPT
method with the Goldstone theorem at this order is established, and appropriate
OPT values of the basic NJL (vacuum) parameters are obtained by matching the
pion mass and decay constant consistently. Deviations from standard large-N_c
relations induced by OPT at this order are derived, for example, for the
Gell--Mann-Oakes-Renner relation. Next, the results for the critical quantities
and the phase diagram of the model, as well as a number of other
thermodynamical quantities of interest, are obtained with OPT and then
contrasted with the corresponding results at large N_c.Comment: 29 pages, 20 figures, revtex. Minor corrections. In press Phys. Rev.
Exact 1/N and Optimized Perturbative Evaluation of mu_c for Homogeneous Interacting Bose Gases
In the framework of the O(N) three-dimensional effective scalar field model
for homogeneous dilute weakly interacting Bose gases we use the 1/N expansion
to evaluate, within the large N limit, the parameter r_c which is directly
related to the critical chemical potential mu_c. This quantity enters the
order-a^2 n^{2/3} coefficient contributing to the critical temperature shift
Delta T_c where a represents the s-wave scattering length and n represents the
density. Compared to the recent precise numerical lattice simulation results,
our calculation suggests that the large N approximation performs rather well
even for the physical case N=2. We then calculate the same quantity but using
different forms of the optimized perturbative (variational) method, showing
that these produce excellent results both for the finite N and large-N cases.Comment: 12 pages, 2 figures. We have performed a refined and extended
numerical analysis to take into account the very recent results of Ref. [15
Critical and Tricritical Points for the Massless 2d Gross-Neveu Model Beyond Large N
Using optimized perturbation theory, we evaluate the effective potential for
the massless two dimensional Gross-Neveu model at finite temperature and
density containing corrections beyond the leading large-N contribution. For
large-N, our results exactly reproduce the well known 1/N leading order results
for the critical temperature, chemical potential and tricritical points. For
finite N, our critical values are smaller than the ones predicted by the
large-N approximation and seem to observe Landau's theorem for phase
transitions in one space dimension. New analytical results are presented for
the tricritical points that include 1/N corrections. The easiness with which
the calculations and renormalization are carried out allied to the seemingly
convergent optimized results displayed, in this particular application, show
the robustness of this method and allows us to obtain neat analytical
expressions for the critical as well as tricritical values beyond the results
currently known.Comment: 29 pages, 14 figure
A new improved optimization of perturbation theory: applications to the oscillator energy levels and Bose-Einstein critical temperature
Improving perturbation theory via a variational optimization has generally
produced in higher orders an embarrassingly large set of solutions, most of
them unphysical (complex). We introduce an extension of the optimized
perturbation method which leads to a drastic reduction of the number of
acceptable solutions. The properties of this new method are studied and it is
then applied to the calculation of relevant quantities in different
models, such as the anharmonic oscillator energy levels and the critical
Bose-Einstein Condensation temperature shift recently investigated
by various authors. Our present estimates of , incorporating the
most recently available six and seven loop perturbative information, are in
excellent agreement with all the available lattice numerical simulations. This
represents a very substantial improvement over previous treatments.Comment: 9 pages, no figures. v2: minor wording changes in title/abstract, to
appear in Phys.Rev.
Crystal structures, Hirshfeld surface analysis and a computational study of four ethyl 2-oxo-2H-chromene-3-carboxylate derivatives : a survey of organyl 2-oxo-2H-chromene-3-carboxylate structures
LRG thanks the Portuguese Foundation for Science and Technology (FCT) UID/Multi/04546/2013.for support. TvM is grateful to EaStCHEM for computational support via the EaStCHEM Research Computing Facility. JLW thanks CNPq, Brazil for support.Crystal structures, Hirshfeld surface analysis and a computational study have been carried out on 2-oxo-2H-chromene-3-carboxylates. Crystal structures are reported for ethyl R-2-oxo-2H-chromene-3-carboxylate derivatives, 2a: R=6-Me, 2b: 7-Me, 2c: 7-Me, 2d: R=7-MeO. In contrast to 2-oxo-2H-chromene-3-carboxamides, 1, in which classical intramolecular N–H···O hydrogen bonds stabilize planar structures and hinder rotation of the amido group out of the coumarin plane in 2, without an equivalent hydrogen bond, there is a greater rotational freedom of the carboxylate group. The interplanar angles between the coumarin core and its attached –C(O)–R substituent in crystalline 2a, 2b, 2c and 2d are 10.41(6), 36.65(6), 10.4(2) and 5.64(6)°, respectively, with distances between the carbonyl oxygen atoms of 2.8255(16), 2.9278(16), 4.226(2) and 2.8328(14) Å, respectively. A theoretical study of molecular conformations was carried out at the M06-2X density level with the 6-31+G(d) and aug-cc-pVTZ basis sets, in methanol solution modeled by PCM, indicated that the most stable conformations had the carbonyl group of the ester in the plane of the coumarin core: the s-cis arrangement of the ester carbonyl and the 2-oxo moieties being the slightly more stable than the s-trans form by less than 0.5 kcal/mol. The experimental conformations of 2a and 2d match well the low energy s-cis arrangement, and 2c matches the slightly lesser stable s-trans arrangement found in the theoretical study. A survey of the molecular conformations of more than 50 2H-chromene-3-carboxylates derivatives in the CCDC data base indicated two distinct groupings of conformations, s-cis and s-trans, each with interplanar angles <30°.Publisher PDFPeer reviewe
Nonperturbative Yukawa theory at finite density and temperature
In-medium Yukawa theory is part of the thermodynamics of the Standard Model
of particle physics and is one of the main building blocks of most effective
field theories of fermionic systems. By computing its pressure we investigate
the nonperturbative thermodynamics at finite temperature and density using the
optimized perturbation theory (OPT) framework. Our calculations are valid for
arbitrary fermion and scalar masses, temperature, chemical potential, and not
restricted to weak coupling. The model is considered in the presence as well as
in the absence of condensates. Comparison with nonperturbative results shows
that second order perturbation theory (PT) fails in the first case but performs
rather well when condensates are absent, even at high-temperature regimes.Comment: 18 pages, 15 figures; v2: references added, improved discussion in
the Conclusions, matches published versio
A Nonperturbative Study of Inverse Symmetry Breaking at High Temperatures
The optimized linear -expansion is applied to multi-field scalar theories at high temperatures. Using the imaginary time
formalism the thermal masses are evaluated perturbatively up to order
which considers consistently all two-loop contributions. A
variational procedure associated with the method generates nonperturbative
results which are used to search for parameters values for inverse symmetry
breaking (or symmetry nonrestoration) at high temperatures. Our results are
compared with the ones obtained by the one-loop perturbative approximation, the
gap equation solutions and the renormalization group approach, showing good
agreement with the latter method. Apart from strongly supporting inverse
symmetry breaking (or symmetry nonrestoration), our results reveal the
possibility of other high temperature symmetry breaking patterns for which the
last term in the breaking sequence is .Comment: 28 pages,5 eps figures (uses epsf), RevTeX. Only a small misprint in
Eq. (2.10) and a couple of typos fixe
Convergent resummed linear delta expansion in the critical O(N) (\phi_i^2)^2_{3d} model
The nonperturbative linear delta expansion (LDE) method is applied to the
critical O(N) phi^4 three-dimensional field theory which has been widely used
to study the critical temperature of condensation of dilute weakly interacting
homogeneous Bose gases. We study the higher order convergence of the LDE as it
is usually applied to this problem. We show how to improve both, the large-N
and finite N=2, LDE results with an efficient resummation technique which
accelerates convergence. In the large N limit, it reproduces the known exact
result within numerical integration accuracy. In the finite N=2 case, our
improved results support the recent numerical Monte Carlo estimates for the
critical transition temperature of Bose-Einstein condensation.Comment: 4 pages, Revtex 4. A misprint in Eq. (3) was corrected and ref. 17
(cond-mat/0207295) update
Validation of the surgical fear questionnaire in adult patients waiting for elective surgery
Objectives: Because existing instruments for assessing surgical fear seem either too general or too limited, the Surgical Fear Questionnaire (SFQ) was developed. The aim of this study is to assess the validity and reliability of the SFQ.
Methods: Based on existing literature and expert consultation the ten-item SFQ was composed. Data on the SFQ were obtained from 5 prospective studies (N = 3233) in inpatient or day surgery patients. These data were used for exploratory factor analysis (EFA), confirmatory factor analysis (CFA), reliability analysis and validity analysis.
Results: EFA in Study 1 and 2 revealed a two-factor structure with one factor associated with fear of the short-term consequences of surgery (SFQ-s, item 1-4) and the other factor with fear of the long-term consequences of surgery (SFQ-l, item 5-10). However, in both studies two items of the SFQ-l had low factor loadings. Therefore in Study 3 and 4 the 2-factor structure was tested and confirmed by CFA in an eight-item version of the SFQ. Across all studies significant correlations of the SFQ with pain catastrophizing, state anxiety, and preoperative pain intensity indicated good convergent validity. Internal consistency (Cronbach's alpha) was between 0.765-0.920 (SFQ-total), 0.766-0.877 (SFQ-s), and 0.628-0.899 (SFQ-l). The SFQ proved to be sensitive to detect differences based on age, sex, education level, employment status and preoperative pain intensity.
Discussion: The SFQ is a valid and reliable eight-item index of surgical fear consisting of two subscales: fear of the short-term consequences of surgery and fear of the long-term consequences.This study was conducted with departmental funding and supported by a grant from The Netherlands Organisation for Scientific Research (Zon-MW, http://www.zonmw.nl/en/), grant no. 110000007. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
Effect of High vs Low Doses of Chloroquine Diphosphate as Adjunctive Therapy for Patients Hospitalized With Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infection: A Randomized Clinical Trial.
There is no specific antiviral therapy recommended for coronavirus disease 2019 (COVID-19). In vitro studies indicate that the antiviral effect of chloroquine diphosphate (CQ) requires a high concentration of the drug.To evaluate the safety and efficacy of 2 CQ dosages in patients with severe COVID-19. This parallel, double-masked, randomized, phase IIb clinical trial with 81 adult patients who were hospitalized with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection was conducted from March 23 to April 5, 2020, at a tertiary care facility in Manaus, Brazilian Amazon. - Patients were allocated to receive high-dosage CQ (ie, 600 mg CQ twice daily for 10 days) or low-dosage CQ (ie, 450 mg twice daily on day 1 and once daily for 4 days). - Label: Main Outcomes and Measures
Primary outcome was reduction in lethality by at least 50% in the high-dosage group compared with the low-dosage group. Data presented here refer primarily to safety and lethality outcomes during treatment on day 13. Secondary end
points included participant clinical status, laboratory examinations, and electrocardiogram results. Outcomes will be presented to day 28. Viral respiratory secretion RNA detection was performed on days 0 and 4. Out of a predefined sample size of 440 patients, 81 were enrolled (41 [50.6%] to high-dosage group and 40 [49.4%] to low-dosage group). Enrolled patients had a mean (SD) age of 51.1 (13.9) years, and most (60 [75.3%]) were men.
Older age (mean [SD] age, 54.7 [13.7] years vs 47.4 [13.3] years) and more heart disease (5 of 28 [17.9%] vs 0) were seen in the high-dose group. Viral RNA was detected in 31 of 40 (77.5%) and 31 of 41 (75.6%) patients in the low-dosage and high-dosage groups, respectively. Lethality until day 13 was 39.0% in the high-dosage group (16 of 41) and 15.0% in the low-dosage group (6 of 40). The high-dosage group presented more instance of QTc interval greater than 500 milliseconds (7 of 37 [18.9%]) compared with the low-dosage group (4 of 36 [11.1%]).
Respiratory secretion at day 4 was negative in only 6 of 27 patients (22.2%). - Label: Conclusions and Relevance
The preliminary findings of this study suggest that the higher CQ dosage should not be recommended for critically ill patients with COVID-19 because of its potential safety hazards, especially when taken concurrently with azithromycin and oseltamivir. These findings cannot be extrapolated to patients with nonsevere COVID-19
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