The repulsive lattice gas, the independent-set polynomial, and the Lov\'asz local lemma

We elucidate the close connection between the repulsive lattice gas in equilibrium statistical mechanics and the Lovasz local lemma in probabilistic combinatorics. We show that the conclusion of the Lovasz local lemma holds for dependency graph G and probabilities {p_x} if and only if the independent-set polynomial for G is nonvanishing in the polydisc of radii {p_x}. Furthermore, we show that the usual proof of the Lovasz local lemma -- which provides a sufficient condition for this to occur -- corresponds to a simple inductive argument for the nonvanishing of the independent-set polynomial in a polydisc, which was discovered implicitly by Shearer and explicitly by Dobrushin. We also present some refinements and extensions of both arguments, including a generalization of the Lovasz local lemma that allows for "soft" dependencies. In addition, we prove some general properties of the partition function of a repulsive lattice gas, most of which are consequences of the alternating-sign property for the Mayer coefficients. We conclude with a brief discussion of the repulsive lattice gas on countably infinite graphs.Comment: LaTex2e, 97 pages. Version 2 makes slight changes to improve clarity. To be published in J. Stat. Phy

Risk factors for Coronavirus disease 2019 (Covid-19) death in a population cohort study from the Western Cape province, South Africa

Risk factors for coronavirus disease 2019 (COVID-19) death in sub-Saharan Africa and the effects of human immunodeficiency virus (HIV) and tuberculosis on COVID-19 outcomes are unknown. We conducted a population cohort study using linked data from adults attending public-sector health facilities in the Western Cape, South Africa. We used Cox proportional hazards models, adjusted for age, sex, location, and comorbidities, to examine the associations between HIV, tuberculosis, and COVID-19 death from 1 March to 9 June 2020 among (1) public-sector “active patients” (≥1 visit in the 3 years before March 2020); (2) laboratory-diagnosed COVID-19 cases; and (3) hospitalized COVID-19 cases. We calculated the standardized mortality ratio (SMR) for COVID-19, comparing adults living with and without HIV using modeled population estimates.Among 3 460 932 patients (16% living with HIV), 22 308 were diagnosed with COVID-19, of whom 625 died. COVID19 death was associated with male sex, increasing age, diabetes, hypertension, and chronic kidney disease. HIV was associated with COVID-19 mortality (adjusted hazard ratio [aHR], 2.14; 95% confidence interval [CI], 1.70–2.70), with similar risks across strata of viral loads and immunosuppression. Current and previous diagnoses of tuberculosis were associated with COVID-19 death (aHR, 2.70 [95% CI, 1.81–4.04] and 1.51 [95% CI, 1.18–1.93], respectively). The SMR for COVID-19 death associated with HIV was 2.39 (95% CI, 1.96–2.86); population attributable fraction 8.5% (95% CI, 6.1–11.1)

Key factors in work engagement and job motivation of teaching faculty at a university medical center

This study reports about teacher motivation and work engagement in a Dutch University Medical Centre (UMC). We examined factors affecting the motivation for teaching in a UMC, the engagement of UMC Utrecht teaching faculty in their work, and their engagement in teaching compared with engagement in patient care and research. Based on a pilot study within various departments at the UMCU, a survey on teaching motivation and work engagement was developed and sent to over 600 UMCU teachers. About 50 % responded. Work engagement was measured by the Utrecht Work Engagement Scale, included in this survey. From a list of 22 pre-defined items, 5 were marked as most motivating: teaching about my own speciality, noticeable appreciation for teaching by my direct superior, teaching small groups, feedback on my teaching performance, and freedom to determine what I teach. Feedback on my teaching performance showed the strongest predictive value for teaching engagement. Engagement scores were relatively favourable, but engagement with patient care was higher than with research and teaching. Task combinations appear to decrease teaching engagement. Our results match with self-determination theory and the job demands–resources model, and challenge the policy to combine teaching with research and patient care

Measurement and microscopic analysis of the B-11((p)over-right-arrow,(p)over-right-arrow) reaction at E-p=150 MeV. I. Inelastic scattering

Cross sections and analyzing powers for the B-11((p) over right arrow ,p(')) reaction have been measured using a 150-MeV polarized proton beam from the AGOR cyclotron at KVI. For the stronger inelastic transitions, also spin-flip probabilities have been extracted. To predict cross sections and spin observables a microscopic (coordinate space) model of elastic scattering has been used, whereas for inelastic scattering calculations were performed in the distorted-wave approximation. In the model calculations a medium-modified two-nucleon effective interaction was used and nuclear structure information was obtained from shell-model calculations in a complete (0+2)(h) over bar omega model space for parity-conserving transitions and a 1 (h) over bar omega shell-model description in the case of parity-changing transitions. With the help of these model calculations, spin-isovector parts of the M1 strengths for the negative-parity states at excitation energies of 2.125 MeV (J(pi)=1/2(-)), 4.445 MeV (J(pi)=5/2(-)), 5.020 MeV (J(pi)=3/2(-)), and 8.920 MeV (J(pi)=5/2(-)) have been extracted and compared to known Gamow-Teller strengths for the analog transitions to C-11

Measurement and microscopic analysis of the B-11((p)over-right-arrow,(p)over-right-arrow) reaction at E-p=150 MeV. II. Depolarization in elastic scattering from odd-A nuclei

The polarization-transfer coefficient D-nn(') in the elastic scattering of 150-MeV protons from B-11 has been measured in the angular range 5degree

Performance of an ASD-8 based wire chamber readout system.

For the medium-energy proton polarimeter mounted at the focal-plane of the Big-Bite Spectrometer at Kernfysisch Versneller Instituut Groningen, a new wire-chamber readout has been developed. The charge-sensitive preamplifier is based on the ASD-8 B chip which has an input impedance of 115 Omega. This low impedance and the short integration time of 6 ns at a usable sensitivity of 5 fC allow high readout rates and low gas amplifications. This front-end circuit is mounted on all four multi-wire proportional chambers and on two vertical-drift chambers with 3872 wires in total. Measurements have been made using sources and intermediate energy protons. Special attention was given to determine the time-over-threshold properties of the circuit, The time-over-threshold capabilities of the readout system extend future applications to particle discrimination, or, in connection with other detector types, to energy-resolving readout, The operational performance of the readout system is presented