Ultracold neutral plasma expansion in a strong uniform magnetic field.

In strongly magnetized neutral plasmas, electron motion is reduced perpendicular to the magnetic field direction. This changes dynamical plasma properties such as temperature equilibration, spatial density evolution, electron pressure, and thermal and electrical conductivity. In this paper we report measurements of free plasma expansion in the presence of a strong magnetic field. We image laser-induced fluorescence from an ultracold neutral Ca^{+} plasma to map the plasma size as a function of time for a range of magnetic field strengths. The asymptotic expansion velocity perpendicular to the magnetic field direction falls rapidly with increasing magnetic field strength. We observe that the initially Gaussian spatial distribution remains Gaussian throughout the expansion in both the parallel and perpendicular directions. We compare these observations with a diffusion model and with a self-similar expansion model and show that neither of these models reproduces the observed behavior over the entire range of magnetic fields used in this study. Modeling the expansion of a magnetized ultracold plasma poses a nontrivial theoretical challenge.

Regional Differences in Mortality Rates During the COVID-19 Epidemic in Italy.

OBJECTIVE: The coronavirus disease 2019 (COVID-19) outbreak started in Italy on February 20, 2020, and has resulted in many deaths and intensive care unit (ICU) admissions. This study aimed to illustrate the epidemic COVID-19 growth pattern in Italy by considering the regional differences in disease diffusion during the first 3 mo of the epidemic. METHODS: Official COVID-19 data were obtained from the Italian Civil Protection Department of the Council of Ministers Presidency. The mortality and ICU admission rates per 100,000 inhabitants were calculated at the regional level and summarized by means of a Bayesian multilevel meta-analysis. Data were retrieved until April 21, 2020. RESULTS: The highest cumulative mortality rates per 100 000 inhabitants were observed in northern Italy, particularly in Lombardia (85.3; 95% credibility intervals [CI], 75.7-94.7). The difference in the mortality rates between northern and southern Italy increased over time, reaching a difference of 67.72 (95% CI, 66-67) cases on April 2, 2020. CONCLUSIONS: Northern Italy showed higher and increasing mortality rates during the first 3 mo of the epidemic. The uncontrolled virus circulation preceding the infection spreading in southern Italy had a considerable impact on system burnout. This experience demonstrates that preparedness against the pandemic is of crucial importance to contain its disruptive effects.

Understanding the Factors Affecting COVID-19 Mortality in Italy: Does a Relationship Exist With a Sharp Increase in Intensive Care Unit Admissions?

OBJECTIVE: The present study aims to explore whether a relationship exists between the immediate sharp increase in intensive care unit (ICU) admissions and the mortality rates in Italy. METHODS: Official epidemiological data on coronavirus disease (COVID-19) were employed. The forward lagged (0, 3, 7, 14 days) daily variations in the number of deaths according to the number of days after the outbreak started and the daily increases in ICU admissions were estimated. RESULTS: A direct relationship between the sharp increase of ICU admissions and mortality rates has been shown. Furthermore, the analysis of the forward lagged daily variations in the number of deaths showed that an increase in the daily number of ICU admissions resulted in significantly higher mortality after 3, 7, and 14 days. The most pronounced effect was detected after 7 days, with 250 deaths (95% CI: 108.1-392.8) for the highest increase in the ICU admissions, from 100 to 200. CONCLUSIONS: These results would serve as a warning for the scientific community and the health care decision-makers to prevent a quick and out-of-control saturation of the ICU beds in case of a relapse of the COVID-19 outbreak.

Sound speed in Yukawa one-component plasmas across coupling regimes.

A many-body system of charged particles interacting via a pairwise Yukawa potential, the so-called Yukawa one-component plasma (YOCP), is a good approximation for a variety of physical systems. Such systems are completely characterized by two parameters: the screening parameter, κ, and the nominal coupling strength, Γ. It is well known that the collective spectrum of the YOCP is governed by a longitudinal acoustic mode, both in the weakly and strongly coupled regimes. In the long-wavelength limit, the linear term in the dispersion (i.e., ω=sk) defines the sound speed s. We study the evolution of this latter quantity from the weak- through the strong-coupling regimes by analyzing the dynamic structure function S(k,ω) in the low-frequency domain. Depending on the values of Γ and κ and w=s/v_{th} (i.e., the ratio between the phase velocity of the wave and the thermal speed of the particles), we identify five domains in the (κ,Γ) parameter space in which the physical behavior of the YOCP exhibits different features. The competing physical processes are the collective Coulomb-like versus binary-collision-dominated behavior and the individual particle motion versus quasilocalization. Our principal tool of investigation is molecular dynamics (MD) computer simulation from which we obtain S(k,ω). Recent improvements in the simulation technique have allowed us to obtain a large body of high-quality data in the range Γ={0.1-10000} and κ={0.5-5}. The theoretical results based on various models are compared in order to see which one provides the most cogent physical description and the best agreement with MD data in the different domains.

Digestive decontamination in burn patients: A systematic review of randomized clinical trials and observational studies.

OBJECTIVE: The objective of this systematic review is to assess the effect of selective digestive decontamination (SDD) or non-absorbable enteral antibiotics (EA) on mortality, the incidence of infection and its adverse effects in burn patients. MATERIAL AND METHODS: Systematic review of randomized clinical trials (RCT) or observational studies enrolling burn patients, and comparing SDD or EA prophylaxis with placebo or no treatment. The search includes Pubmed/Medline, EMBASE, WOS, Cochrane Library (1970-2015). Bibliographic references were also reviewed, as well as communications presented at conferences (2012-2015), without language restrictions. Two reviewers inspected each reference identified by the search independently; the risk of bias was assessed with the Cochrane Collaboration method for RCT and the Newcastle Ottawa Scale for observational studies. RESULTS: Five RCT and 5 observational studies were identified enrolling a total of 1680 patients. The overall methodological quality of the studies was poor. The pooled effect of RCT using EA was OR: 0.62 (95% CI: 0.20-1.94). The only RCT using SDD reported OR 0.20 (95% CI: 0.09-0.81). The incidence of Enterobacteriaceae bloodstream was lower in cases treated with SDD or EA. The incidence of pneumonia was only reduced in the studies using SDD. None of the studies reported an increase in antibiotic resistance but in one RCT SDD was associated to an increase in methicillin-resistant Staphylococcus aureus infections, that was controlled with enteral vancomycin. CONCLUSIONS: SDD and EA have shown a beneficial effect in burn patients. Both practices are safe. Higher quality RCTs should be conducted to properly assess the efficacy and safety of SDD in this population.

Impact of Oral Chlorhexidine on Bloodstream Infection in Critically Ill Patients: Systematic Review and Meta-Analysis of Randomized Controlled Trials.

OBJECTIVES: Oropharyngeal overgrowth of microorganisms in the critically ill is a risk factor for lower respiratory tract infection and subsequent invasion of the bloodstream. Oral chlorhexidine has been used to prevent pneumonia, but its effect on bloodstream infection never has been assessed in meta-analyses. The authors explored the effect of oral chlorhexidine on the incidence of bloodstream infection, the causative microorganism, and on all-cause mortality in critically ill patients. DESIGN: Systematic review and meta-analysis of published studies. SETTING: Intensive care unit. PARTICIPANTS: The study comprised critically ill patients receiving oral chlorhexidine (test group) and placebo or standard oral care (control group). INTERVENTIONS: PubMed and the Cochrane Register of Controlled Trials were searched. Odds ratios (ORs) were pooled using the random-effects model. MEASUREMENTS AND MAIN RESULTS: Five studies including 1,655 patients (832 chlorhexidine and 823 control patients) were identified. The majority of information was from studies at low or unclear risk bias; 1 study was at high risk of bias. Bloodstream infection and mortality were not reduced significantly by chlorhexidine (OR 0.74; 95% confidence interval [CI] 0.37-1.50 and OR 0.69; 95% CI 0.31-1.53, respectively). In the subgroup of surgical, mainly cardiac, patients, chlorhexidine reduced bloodstream infection (OR 0.47; 95% CI 0.22-0.97). Chlorhexidine did not affect any microorganism significantly. CONCLUSION: In critically ill patients, oropharyngeal chlorhexidine did not reduce bloodstream infection and mortality significantly and did not affect any microorganism involved. The presence of a high risk of bias in 1 study and unclear risk of bias in others may have affected the robustness of these findings.

Typical, finite baths as a means of exact simulation of open quantum systems.

There is presently considerable interest in accurately simulating the evolution of open systems for which Markovian master equations fail. Examples are systems that are time dependent and/or strongly damped. A number of elegant methods have now been devised to do this, but all use a bath consisting of a continuum of harmonic oscillators. While this bath is clearly appropriate for, e.g., systems coupled to the electromagnetic field, it is not so clear that it is a good model for generic many-body systems. Here we explore a different approach to exactly simulating open systems: using a finite bath chosen to have certain key properties of thermalizing many-body systems. To explore the numerical resources required by this method to approximate an open system coupled to an infinite bath, we simulate a weakly damped system and compare to the evolution given by the relevant Markovian master equation. We obtain the Markovian evolution with reasonable accuracy by using an additional averaging procedure, and elucidate how the typicality of the bath generates the correct thermal steady state via the process of "eigenstate thermalization."