Development and application of pulse echo techniques to the study of charge density waves and superconductivity in pressurized U₆Fe

Ultrasound measurement techniques have proven useful as a directional probe that is sensitive to both the atomic and electronic structure of materials. As such, they are a powerful tool for studying phase transitions, and were, for example, one of the first techniques to provide strong experimental evidence for the validity of the BCS theory of superconductivity. In this PhD project an ultrasound setup capable of generating longitudinal sound pulses with frequencies of hundreds of MHz was developed to study the heavy fermion superconductor U₆Fe under pressure and magnetic field at low temperatures. The practical challenges of implementing and interpreting pulse echo measurements at these frequencies is described. Measurements on the element niobium at room pressure are presented to establish trust in the set up. It was found that niobium in fact shows some interesting sample quality dependent features in the ultrasound attenuation just below its superconducting transition temperature. The results from the novel ultrasound study on U₆Fe corroborate the evidence given by prior X-ray diffraction measurements for the appearance of charge density wave (CDW) order below about 10 K. It is seen how the CDW state is gradually suppressed with increasing pressure, and that this is accompanied by an increase in the superconducting transition temperature (Tc). The features of an observed attenuation peak just below Tc, typically absent in BCS superconductors, are discussed and found to be explainable in terms of Landau- Khalatnikov (LK) damping. Several alternatives of varying plausibility as to the underlying cause of the LK damping are presented, along with ways in which further investigations might rule out some of these alternatives

New sustainable ternary copper phosphide thermoelectrics

Funding: R. J. Q. and J.-W. G. B. acknowledge the Leverhulme Trust (RPG-2020-177). A. D. H. acknowledges the EPSRC (EP/ R013004/1).The thermoelectric performance of ACuP (A = Mg and Ca) with abundant elements and low gravimetric density is reported. Both systems are p-type doped by intrinsic Cu vacancy defects, have large power factors and promising figures of merit, reaching zT = 0.5 at 800 K. This demonstrates that copper phosphides are a potential new class of thermoelectric materials for waste heat harvesting.Publisher PDFPeer reviewe

Coherent Quantum Transport in Photonic Lattices

Transferring quantum states efficiently between distant nodes of an information processing circuit is of paramount importance for scalable quantum computing. We report on the first observation of a perfect state transfer protocol on a lattice, thereby demonstrating the general concept of trans- porting arbitrary quantum information with high fidelity. Coherent transfer over 19 sites is realized by utilizing judiciously designed optical structures consisting of evanescently coupled waveguide ele- ments. We provide unequivocal evidence that such an approach is applicable in the quantum regime, for both bosons and fermions, as well as in the classical limit. Our results illustrate the potential of the perfect state transfer protocol as a promising route towards integrated quantum computing on a chip

The Sloan Digital Sky Survey Reverberation Mapping Project: Key Results

We present the final data from the Sloan Digital Sky Survey Reverberation Mapping (SDSS-RM) project, a precursor to the SDSS-V Black Hole Mapper Reverberation Mapping program. This data set includes 11-year photometric and 7-year spectroscopic light curves for 849 broad-line quasars over a redshift range of 0.1<z<4.5 and a luminosity range of Lbol=1E44-47.5 erg/s, along with spectral and variability measurements. We report 23, 81, 125, and 110 reverberation mapping lags (relative to optical continuum variability) for broad Halpha, Hbeta, MgII and CIV using the SDSS-RM sample, spanning much of the luminosity and redshift ranges of the sample. Using 30 low-redshift RM AGNs with dynamical-modeling black hole masses, we derive a new estimate of the average virial factor of =0.62+-0.07 for the line dispersion measured from the RMS spectrum. The intrinsic scatter of individual virial factors is 0.31+-0.07 dex, indicating a factor of two systematic uncertainty in RM black hole masses. Our lag measurements reveal significant R-L relations for Hbeta and MgII at high redshift, consistent with the latest measurements based on heterogeneous samples. While we are unable to robustly constrain the slope of the R-L relation for CIV given the limited dynamical range in luminosity, we found substantially larger scatter in CIV lags at fixed L1350. Using the SDSS-RM lag sample, we derive improved single-epoch (SE) mass recipes for Hbeta, MgII and CIV, which are consistent with their respective RM masses as well as between the SE recipes from two different lines, over the luminosity range probed by our sample. The new Hbeta and MgII recipes are approximately unbiased estimators at given RM masses, but there are systematic biases in the CIV recipe. The intrinsic scatter of SE masses around RM masses is ~0.45 dex for Hbeta and MgII, increasing to ~0.58 dex for CIV.Comment: 33 pages. Data products available at ftp://quasar.astro.illinois.edu/public/sdssrm/final_result

Surgical site infection after gastrointestinal surgery in high-income, middle-income, and low-income countries: a prospective, international, multicentre cohort study

Background: Surgical site infection (SSI) is one of the most common infections associated with health care, but its importance as a global health priority is not fully understood. We quantified the burden of SSI after gastrointestinal surgery in countries in all parts of the world. Methods: This international, prospective, multicentre cohort study included consecutive patients undergoing elective or emergency gastrointestinal resection within 2-week time periods at any health-care facility in any country. Countries with participating centres were stratified into high-income, middle-income, and low-income groups according to the UN's Human Development Index (HDI). Data variables from the GlobalSurg 1 study and other studies that have been found to affect the likelihood of SSI were entered into risk adjustment models. The primary outcome measure was the 30-day SSI incidence (defined by US Centers for Disease Control and Prevention criteria for superficial and deep incisional SSI). Relationships with explanatory variables were examined using Bayesian multilevel logistic regression models. This trial is registered with ClinicalTrials.gov, number NCT02662231. Findings: Between Jan 4, 2016, and July 31, 2016, 13 265 records were submitted for analysis. 12 539 patients from 343 hospitals in 66 countries were included. 7339 (58·5%) patient were from high-HDI countries (193 hospitals in 30 countries), 3918 (31·2%) patients were from middle-HDI countries (82 hospitals in 18 countries), and 1282 (10·2%) patients were from low-HDI countries (68 hospitals in 18 countries). In total, 1538 (12·3%) patients had SSI within 30 days of surgery. The incidence of SSI varied between countries with high (691 [9·4%] of 7339 patients), middle (549 [14·0%] of 3918 patients), and low (298 [23·2%] of 1282) HDI (p < 0·001). The highest SSI incidence in each HDI group was after dirty surgery (102 [17·8%] of 574 patients in high-HDI countries; 74 [31·4%] of 236 patients in middle-HDI countries; 72 [39·8%] of 181 patients in low-HDI countries). Following risk factor adjustment, patients in low-HDI countries were at greatest risk of SSI (adjusted odds ratio 1·60, 95% credible interval 1·05–2·37; p=0·030). 132 (21·6%) of 610 patients with an SSI and a microbiology culture result had an infection that was resistant to the prophylactic antibiotic used. Resistant infections were detected in 49 (16·6%) of 295 patients in high-HDI countries, in 37 (19·8%) of 187 patients in middle-HDI countries, and in 46 (35·9%) of 128 patients in low-HDI countries (p < 0·001). Interpretation: Countries with a low HDI carry a disproportionately greater burden of SSI than countries with a middle or high HDI and might have higher rates of antibiotic resistance. In view of WHO recommendations on SSI prevention that highlight the absence of high-quality interventional research, urgent, pragmatic, randomised trials based in LMICs are needed to assess measures aiming to reduce this preventable complication

Research Article: Antidepressant use among Asians in the United States

Objectives : We examined the prevalence and predictors of past-year antidepressant use in a nationally representative sample of Asian Americans and non-Latino Whites. Methods : Analyses of 12-month antidepressant medication use were based on data from the Collaborative Psychiatric Epidemiology Surveys that surveyed Asian (Chinese, Filipino, Vietnamese, and others; N=2,284) and non-Latino White (N=6,696) household residents ages 18 years and older in the 48 contiguous United States and Hawaii. Results : Prevalence rates for 12-month antidepressant use for Asians with major depression ranged from 8.7% among Vietnamese to 17% among Chinese respondents. Compared to non-Latino Whites (32.4%), all Asians (10.9%) meeting criteria for 12-month depressive and anxiety disorders, but especially Filipinos (8.8%) were less likely to report past-year antidepressant use. Conclusions : We found disparities in past-year antidepressant use among all the examined major Asian groups meeting criteria for 12-month depressive and anxiety disorders. These disparities were not explained by mental health need or socioeconomic factors that enable access to care. Depression and Anxiety, 2010. © 2009 Wiley-Liss, Inc.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/64896/1/20636_ftp.pd