Vibrational and rotational state dependence of dissociative attachment in e-H2 collisions

Resonant scattering theory is applied to the calculation of e-H2 dissociative attachment cross sections near threshold for several vibrational and rotational states of the H2 molecule. Typical values just above threshold are, in cm2, 2.8×10−21 for the ground state (v=0, J=0), 8.3×10−20 for (1, 0), 1.0×10−18 for (2, 0), and 3.5×10−20 for (0, 10). The effect of rotational excitation is found to be significant, although it is not as large as suggested by Chen and Peacher

Calculations of ion‐ion recombination rates at high pressures

The classical theory of ion‐ion recombination in gases of high density is extended to allow for arbitrary ratios of the masses of the three species involved. Calculations are performed for the recombination of Ar+, Ar+ 2, Kr+, and Kr+ 2 ions with F− and of Hg+ and Ar+ with Cl− in an argon gas. The effective two‐body rates peak between 2×10−6 and 3×10−6 cm3 sec−1 at pressures above 1 atm

Dissociative attachment and vibrational excitation in low-energy collisions of electrons with H2 and D2

A semiempirical analysis is made of the contributions of the two lowest resonant states to dissociative attachment and vibrational excitation in low-energy collisions of electrons with H2 and D2. The resonance models are based both on ab initio calculations and on fits to experimental data. The dissociative-attachment cross section near threshold is enhanced significantly by vibrational or rotational excitation of the initial molecule. Near 10 eV, contributions from both resonances are required to explain the observed cross sections for vibrational excitation

Factors associated with variation in hospital use at the end of life in England

Objective: To identify the relative importance of factors influencing hospital use at the end of life. Design: Retrospective cohort study of person and health system effects on hospital use in the past 12 months modelling differences in admissions, bed days and whether a person died in hospital. Setting: Residents in England for the period 2009/2010 to 2011/2012 using Hospital Episodes Statistics (HES) data from all acute care hospitals in England funded by the National Health Service (NHS). Participants: 1 223 859 people registered with a GP in England who died (decedents) in England (April 2009–March 2012) with a record of NHS hospital care. Main outcome measures: Hospital admissions, and hospital bed days and place of death (in or out of hospital) in the past 12 months of life. Results: The mean number of admissions in the past 12 months of life averaged 2.28 occupying 30.05 bed days—excluding 9.8% of patients with no hospital history. A total of 50.8% of people died in hospital. Difference in hospital use was associated with a range of patient descriptors (age, gender and ethnicity). The variables with the greatest ‘explanatory power’ were those that described the diagnoses and causes of death. So, for example, 65% of the variability in the model of hospital admissions was explained by diagnoses. Only moderate levels of variation were explained by the hospital provider variables for admissions and deaths in hospital, though the impacts on total bed days was large. Conclusions: Comparative analyses of hospital utilisation should standardise for a range of patient specific variables. Though the models indicated some degree of variability associated with individual providers, the scale of this was not great for admissions and death in hospital but the variability associated with length of stay differences suggests that attempts to optimise hospital use should look at differences in lengths of stay and bed use. This study adds important new information about variability in admissions by diagnostic group, and variability in bed days by diagnostic group and eventual cause of death

Teaching and Research within Further Education Colleges: chalk and cheese?

The expansion of Higher Education (HE) into Further Education (FE) Colleges has resulted in college lecturers with responsibility for teaching HE courses experiencing considerable changes in their working practices. College lecturers have worked collaboratively with universities to develop HE courses and been presented with opportunities to engage in scholarly activity and research. This paper draws on the experience of a group of college lecturers who undertook research into aspects of their teaching practice through an initiative introduced by the Higher Education Learning Partnerships (HELP) Centre for Excellence in Teaching and Learning (CETL). Through a series of semi-structured interviews, this paper examines the impact of their projects and experiences as researchers on their practice, and on the learning experiences they provided for their students. The paper explores the context of delivering HE within FE, and the lessons that can be learned from undertaking practitioner-led research in this environment. As the college lecturers demonstrate, their research was found to enhance their practice, and was highlighted as validating their profession identities as HE in FE professionals. They also considered the tensions and challenges present within an FE college where research activities are not necessarily seen a part of the teaching role. Based on the experiences of these college lecturers this paper argues for a more pro-active approach to scholarly activity in an HE in FE context

Resonant contributions to single charge transfer between He++ and He

Energy levels and lifetimes are calculated for the resonant states that are important in radiative single charge transfer in He2+-He collisions at thermal energies. The resonant contribution to the charge-transfer rate decreases with increasing temperature and is approximately 12% of the total rate at 300 K

Mobility of α particles in helium

The mobility of α particles in helium gas is calculated using the zeroth-order Viehland-Mason theory with interaction potentials recently computed by Cohen and Bardsley. The results show a dependence on field strength similar to the measurements of Johnsen and Biondi but are lower in magnitude by about 5%

Dissociative attachment in HCl, DCl, and F2

Resonant scattering models, using nonlocal decay widths, are developed for dissociative attachment of slow electrons to diatomic molecules. Cross sections are obtained for HCl and DCl in several initial rotational and vibrational states, and the dependence of the average attachment cross section upon the rotational and vibrational temperature is examined. For F_2 the cross section for ground state molecules agrees well with experiment above 0.2 eV but shows no zero energy peak. The attachment cross section is higher for vibrationally excited molecules, but the enhancement is much less than that found in H_2 and HCl

An approximate empirical Bayesian method for large-scale linear-Gaussian inverse problems

We study Bayesian inference methods for solving linear inverse problems, focusing on hierarchical formulations where the prior or the likelihood function depend on unspecified hyperparameters. In practice, these hyperparameters are often determined via an empirical Bayesian method that maximizes the marginal likelihood function, i.e., the probability density of the data conditional on the hyperparameters. Evaluating the marginal likelihood, however, is computationally challenging for large-scale problems. In this work, we present a method to approximately evaluate marginal likelihood functions, based on a low-rank approximation of the update from the prior covariance to the posterior covariance. We show that this approximation is optimal in a minimax sense. Moreover, we provide an efficient algorithm to implement the proposed method, based on a combination of the randomized SVD and a spectral approximation method to compute square roots of the prior covariance matrix. Several numerical examples demonstrate good performance of the proposed method

Exposing errors related to weak memory in GPU applications

© 2016 ACM.We present the systematic design of a testing environment that uses stressing and fuzzing to reveal errors in GPU applications that arise due to weak memory effects. We evaluate our approach on seven GPUS spanning three NVIDIA architectures, across ten CUDA applications that use fine-grained concurrency. Our results show that applications that rarely or never exhibit errors related to weak memory when executed natively can readily exhibit these errors when executed in our testing environment. Our testing environment also provides a means to help identify the root causes of such errors, and automatically suggests how to insert fences that harden an application against weak memory bugs. To understand the cost of GPU fences, we benchmark applications with fences provided by the hardening strategy as well as a more conservative, sound fencing strategy