The nonlinear semiclassical dynamics of the unbalanced, open Dicke model

In recent years there have been significant advances in the study of many-body interactions between atoms and light confined to optical cavities. One model which has received widespread attention of late is the Dicke model, which under certain conditions exhibits a quantum phase transition to a state in which the atoms collectively emit light into the cavity mode, known as superradiance. We consider a generalization of this model that features independently controllable strengths of the co- and counter-rotating terms of the interaction Hamiltonian. We study this system in the semiclassical (mean field) limit, i.e., neglecting the role of quantum fluctuations. Under this approximation, the model is described by a set of nonlinear differential equations, which determine the system's semiclassical evolution. By taking a dynamical systems approach, we perform a comprehensive analysis of these equations to reveal an abundance of novel and complex dynamics. Examples of the novel phenomena that we observe are the emergence of superradiant oscillations arising due to Hopf bifurcations, and the appearance of a pair of chaotic attractors arising from period-doubling cascades, followed by their collision to form a single, larger chaotic attractor via a sequence of infinitely many homoclinic bifurcations. Moreover, we find that a flip of the collective spin can result in the sudden emergence of chaotic dynamics. Overall, we provide a comprehensive roadmap of the possible dynamics that arise in the unbalanced, open Dicke model in the form of a phase diagram in the plane of the two interaction strengths. Hence, we lay out the foundations to make further advances in the study of the fingerprint of semiclassical chaos when considering the master equation of the unbalanced Dicke model, that is, the possibility of studying a manifestation of quantum chaos in a specific, experimentally realizable system.Comment: 19 pages, 18 figures, 1 appendi

Beyond cerebration : the Cambodian struggle for representation in Lowell, Massachusetts

Thesis (M.C.P.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 2008.Includes bibliographical references (p. 148-152).Since the early 1980s, an estimated 30,000 Cambodians have found their way to Lowell, Massachusetts. Constituting nearly 25% of the total population, they are now the city's dominant minority group. This thesis began as a study of the Cambodian community in Lowell and their rise to civic participation thirty years since their first arriving. By researching the evolution of one refugee community in one post-industrial mill town, I sought to answer two questions: 1) How do new immigrants to America's smaller cities progress from being "outsiders" to engaged community members? and 2) What can be done to facilitate this movement? This thesis shows that the path from "outsider" to "insider" is not easily described. There are multiple ways for immigrants to enter the civic structure of a city, and the routes chosen by a particular ethnic group in a particular city depend on a number of factors including, but not limited to: 1) the ethnic group's cultural predisposition toward politics, education, work, and enterprise, 2) the speed at which city institutions reform to meet demographic change, 3) the level of financial and institutional support that is available for different types of organizing activities, 4) the presence of a vocal, educated class, and 5) the city's overall tolerance for "otherness."In conversations with Lowell's Cambodian community leaders, I found that broadly supported art and cultural programs have given Cambodians a way in to civic life. These programs not only help them preserve their heritage and culture, they also act as community development tools. In addition, the existence of such programs helps reinforce Lowell's image as a progressive, cosmopolitan, and multi-cultural "Immigrant City."(cont) However, Cambodians and other non-whites have thus far had little success garnering positions on the school board, city council, city agencies, and police force. Given such exclusions, this thesis assesses the authenticity of Lowell's reputation as a good "Immigrant City" and gives voice to Cambodian community advocates who live and work within this construct.by Amy Stitely.M.C.P

Quantum Fluctuation Dynamics of Dispersive Superradiant Pulses in a Hybrid Light-Matter System

We consider theoretically a driven-dissipative quantum many-body system consisting of an atomic ensemble in a single-mode optical cavity as described by the open Tavis-Cummings model. In this hybrid light-matter system the interplay between coherent and dissipative processes leads to superradiant pulses with a build-up of strong correlations, even for systems comprising hundreds to thousands of particles. A central feature of the mean-field dynamics is a self-reversal of two spin degrees of freedom due to an underlying time-reversal symmetry, which is broken by quantum fluctuations. We demonstrate a quench protocol that can maintain highly non-Gaussian states over long time scales. This general mechanism offers interesting possibilities for the generation and control of complex fluctuation patterns, as suggested for the improvement of quantum sensing protocols for dissipative spin-amplification.Comment: 7 pages, 5 figures, 4 pages supplementa

Prophylactic Cefazolin Dosing and Surgical Site Infections: Does the Dose Matter in Obese Patients?

Background Most surgical prophylaxis guidelines recommend a 3-g cefazolin intravenous dose in patients weighing ≥ 120 kg. However, this recommendation is primarily based on pharmacokinetic studies rather than robust clinical evidence. This study aimed to compare the prevalence of surgical site infections (SSIs) in obese and non-obese patients (body mass index ≥ 30 kg/m2 and < 30 kg/m2), and those weighing ≥ 120 kg and < 120 kg, who received 2- g cefazolin preoperatively. Methods A retrospective case-control study was conducted in adult elective surgical patients. Patients receiving 2- g cefazolin were grouped as obese and non-obese, and by weight (≥ 120 kg or < 120 kg). The 90-day prevalence of SSI and potential contributing factors were investigated. Results We identified 152 obese (median 134 kg) and 152 non-obese control (median 73 kg) patients. Baseline characteristics were similar between groups, except for an increased prevalence in the obese group of diabetes (35.5% vs 13.2%; p < 0.001) and an American Society of Anaesthesiologists Score of 3 (61.8% vs 17.1%; p < 0.001). While not statistically significant, the prevalence of SSI in the obese group was almost double that in the non-obese group (8.6% vs 4.6%; p = 0.25) and in patients weighing ≥ 120 kg (n = 102) compared to those weighing < 120 kg (n = 202) (9.8% vs 5.0%; p = 0.17). Conclusion The prevalence of SSI was not significantly increased in obese patients, or those weighing ≥ 120 kg, who received cefazolin 2- g prophylactically; however, trends toward an increase were evident. Large-scale randomised trials are needed to examine whether a 2-g or 3-g cefazolin is adequate to prevent SSI in obese (and ≥ 120 kg) individuals

Which method is best for the induction of labour?: A systematic review, network meta-analysis and cost-effectiveness analysis

Background: More than 150,000 pregnant women in England and Wales have their labour induced each year. Multiple pharmacological, mechanical and complementary methods are available to induce labour. Objective: To assess the relative effectiveness, safety and cost-effectiveness of labour induction methods and, data permitting, effects in different clinical subgroups. Methods: We carried out a systematic review using Cochrane methods. The Cochrane Pregnancy and Childbirth Group’s Trials Register was searched (March 2014). This contains over 22,000 reports of controlled trials (published from 1923 onwards) retrieved from weekly searches of OVID MEDLINE (1966 to current); Cochrane Central Register of Controlled Trials (The Cochrane Library); EMBASE (1982 to current); Cumulative Index to Nursing and Allied Health Literature (1984 to current); ClinicalTrials.gov; the World Health Organization International Clinical Trials Registry Portal; and hand-searching of relevant conference proceedings and journals. We included randomised controlled trials examining interventions to induce labour compared with placebo, no treatment or other interventions in women eligible for third-trimester induction. We included outcomes relating to efficacy, safety and acceptability to women. In addition, for the economic analysis we searched the Database of Abstracts of Reviews of Effects, and Economic Evaluations Databases, NHS Economic Evaluation Database and the Health Technology Assessment database. We carried out a network meta-analysis (NMA) using all of the available evidence, both direct and indirect, to produce estimates of the relative effects of each treatment compared with others in a network. We developed a de novo decision tree model to estimate the cost-effectiveness of various methods. The costs included were the intervention and other hospital costs incurred (price year 2012–13). We reviewed the literature to identify preference-based utilities for the health-related outcomes in the model. We calculated incremental cost-effectiveness ratios, expected costs, utilities and net benefit. We represent uncertainty in the optimal intervention using cost-effectiveness acceptability curves. Results: We identified 1190 studies; 611 were eligible for inclusion. The interventions most likely to achieve vaginal delivery (VD) within 24 hours were intravenous oxytocin with amniotomy [posterior rank 2; 95% credible intervals (CrIs) 1 to 9] and higher-dose (≥ 50 μg) vaginal misoprostol (rank 3; 95% CrI 1 to 6). Compared with placebo, several treatments reduced the odds of caesarean section, but we observed considerable uncertainty in treatment rankings. For uterine hyperstimulation, double-balloon catheter had the highest probability of being among the best three treatments, whereas vaginal misoprostol (≥ 50 μg) was most likely to increase the odds of excessive uterine activity. For other safety outcomes there were insufficient data or there was too much uncertainty to identify which treatments performed ‘best’. Few studies collected information on women’s views. Owing to incomplete reporting of the VD within 24 hours outcome, the cost-effectiveness analysis could compare only 20 interventions. The analysis suggested that most interventions have similar utility and differ mainly in cost. With a caveat of considerable uncertainty, titrated (low-dose) misoprostol solution and buccal/sublingual misoprostol had the highest likelihood of being cost-effective. Limitations: There was considerable uncertainty in findings and there were insufficient data for some planned subgroup analyses. Conclusions: Overall, misoprostol and oxytocin with amniotomy (for women with favourable cervix) is more successful than other agents in achieving VD within 24 hours. The ranking according to safety of different methods was less clear. The cost-effectiveness analysis suggested that titrated (low-dose) oral misoprostol solution resulted in the highest utility, whereas buccal/sublingual misoprostol had the lowest cost. There was a high degree of uncertainty as to the most cost-effective intervention

Oral riboflavin to assess ureteral patency during cystoscopy: A randomized controlled clinical trial

Deidentified subject data for the study: Oral riboflavin to assess ureteral patency during cystoscopy: A randomized controlled clinical trial