Discovering Quantum Phase Transitions with Fermionic Neural Networks.

Deep neural networks have been very successful as highly accurate wave function Ansätze for variational Monte Carlo calculations of molecular ground states. We present an extension of one such Ansatz, FermiNet, to calculations of the ground states of periodic Hamiltonians, and study the homogeneous electron gas. FermiNet calculations of the ground-state energies of small electron gas systems are in excellent agreement with previous initiator full configuration interaction quantum Monte Carlo and diffusion Monte Carlo calculations. We investigate the spin-polarized homogeneous electron gas and demonstrate that the same neural network architecture is capable of accurately representing both the delocalized Fermi liquid state and the localized Wigner crystal state. The network converges on the translationally invariant ground state at high density and spontaneously breaks the symmetry to produce the crystalline ground state at low density, despite being given no a priori knowledge that a phase transition exists.

Quantum Monte Carlo Study of Positron Lifetimes in Solids.

We present an analysis of positron lifetimes in solids with unprecedented depth. Instead of modeling correlation effects with density functionals, we study positron-electron wave functions with long-range correlations included. This gives new insight in understanding positron annihilation in metals, insulators, and semiconductors. By using a new quantum Monte Carlo approach for computation of positron lifetimes, an improved accuracy compared to previous computations is obtained for a representative set of materials when compared with experiment. Thus, we present a method without free parameters as a useful alternative to the already existing methods for modeling positrons in solids.

Quasiparticle Effective Mass of the Three-Dimensional Fermi Liquid by Quantum Monte Carlo.

According to Landau's Fermi liquid theory, the main properties of the quasiparticle excitations of an electron gas are embodied in the effective mass m^{*}, which determines the energy of a single quasiparticle, and the Landau interaction function, which indicates how the energy of a quasiparticle is modified by the presence of other quasiparticles. This simple paradigm underlies most of our current understanding of the physical and chemical behavior of metallic systems. The quasiparticle effective mass of the three-dimensional homogeneous electron gas has been the subject of theoretical controversy, and there is a lack of experimental data. In this Letter, we deploy diffusion Monte Carlo (DMC) methods to calculate m^{*} as a function of density for paramagnetic and ferromagnetic three-dimensional homogeneous electron gases. The DMC results indicate that m^{*} decreases when the density is reduced, especially in the ferromagnetic case. The DMC quasiparticle energy bands exclude the possibility of a reduction in the occupied bandwidth relative to that of the free-electron model at density parameter r_{s}=4, which corresponds to Na metal.

Variational and diffusion quantum Monte Carlo calculations with the CASINO code.

We present an overview of the variational and diffusion quantum Monte Carlo methods as implemented in the casino program. We particularly focus on developments made in the last decade, describing state-of-the-art quantum Monte Carlo algorithms and software and discussing their strengths and weaknesses. We review a range of recent applications of casino.

Quasiparticle and excitonic gaps of one-dimensional carbon chains.

We report diffusion quantum Monte Carlo (DMC) calculations of the quasiparticle and excitonic gaps of hydrogen-terminated oligoynes and extended polyyne. The electronic gaps are found to be very sensitive to the atomic structure in these systems. We have therefore optimised the geometry of polyyne by directly minimising the DMC energy with respect to the lattice constant and the Peierls-induced carbon-carbon bond-length alternation. We find the bond-length alternation of polyyne to be 0.136(2) Å and the excitonic and quasiparticle gaps to be 3.30(7) and 3.4(1) eV, respectively. The DMC zone-centre longitudinal optical phonon frequency of polyyne is 2084(5) cm(-1), which is consistent with Raman spectroscopic measurements for large oligoynes.

Quantum Monte Carlo calculation of the binding energy of bilayer graphene.

We report diffusion quantum Monte Carlo calculations of the interlayer binding energy of bilayer graphene. We find the binding energies of the AA-and AB-stacked structures at the equilibrium separation to be 11.5(9) and 17.7(9) meV/atom, respectively. The out-of-plane zone-center optical phonon frequency predicted by our binding-energy curve is consistent with available experimental results. As well as assisting the modeling of interactions between graphene layers, our results will facilitate the development of van der Waals exchange-correlation functionals for density functional theory calculations.

Electron-phonon coupling and the metallization of solid helium at terapascal pressures.

Solid He is studied in the pressure and temperature ranges 1-40 TPa and 0-10 000 K using first-principles methods. Anharmonic vibrational properties are calculated within a self-consistent field framework, including the internal and free energies, density-pressure relation, stress tensor, thermal expansion, and the electron-phonon coupling renormalization of the electronic band gap. We find that an accurate description of electron-phonon coupling requires us to use a nonperturbative approach. The metallization pressure of 32.9 TPa at 0 K is larger than found previously. The vibrational effects are large; for example, at P=30 TPa the band gap is increased by 2.8 eV by electron-phonon coupling and a further 0.1 eV by thermal expansion compared to the static value. The implications of the calculated metallization pressure for the cooling of white dwarfs are discussed.

Current evidence for human yersiniosis in Ireland.

Yersiniosis associated with abdominal pain was commonly reported in Ireland in the 1980s. However, the Health Protection Surveillance Centre (HPSC) currently records only three to seven notified cases of yersiniosis per year. The most common cause of yersiniosis worldwide is Yersinia enterocolitica, and the leading source for this organism is consumption of pork-based food products. In contrast to the apparent current scarcity of yersiniosis cases in humans in Ireland, pathogenic Y. enterocolitica are detectable in a high percentages of pigs. To establish whether the small number of notifications of human disease was an underestimate due to lack of specific selective culture for Yersinia, we carried out a prospective culture study of faecal samples from outpatients with diarrhoea, with additional culture of throat swabs, appendix swabs and screening of human sewage. Pathogenic Yersinia strains were not isolated from 1,189 faeces samples, nor from 297 throat swabs, or 23 appendix swabs. This suggested that current low notification rates in Ireland are not due to the lack of specific Yersinia culture procedures. Molecular screening detected a wider variety of Y. enterocolitica-specific targets in pig slurry than in human sewage. A serological survey for antibodies against Yersinia YOP (Yersinia Outer Proteins) proteins in Irish blood donors found antibodies in 25 %, with an age-related trend to increased seropositivity, compatible with the hypothesis that yersiniosis may have been more prevalent in Ireland in the recent past.

Quantum Monte Carlo study of a positron in an electron gas.

Quantum Monte Carlo calculations of the relaxation energy, pair-correlation function, and annihilating-pair momentum density are presented for a positron immersed in a homogeneous electron gas. We find smaller relaxation energies and contact pair-correlation functions in the important low-density regime than predicted by earlier studies. Our annihilating-pair momentum densities have almost zero weight above the Fermi momentum due to the cancellation of electron-electron and electron-positron correlation effects.

Achieving quality primary care data: a description of the Canadian Primary Care Sentinel Surveillance Network data capture, extraction, and processing in Alberta.

INTRODUCTION: Electronic medical record (EMR) databases have become increasingly popular for secondary purposes, such as health research. The Canadian Primary Care Sentinel Surveillance Network (CPCSSN) is the first and only pan-Canadian primary care EMR data repository, with de-identified health information for almost two million Canadians. Comprehensive and freely available documentation describing the data 'lifecycle' is important for assessing potential data quality issues and appropriate interpretation of research findings. Here, we describe the flow and transformation of CPCSSN data in the province of Alberta. APPROACH: In Alberta, the data originate from 54 publicly-funded primary care settings, including one community pediatric clinic, with 318 providers contributing de-identified EMR data for 410,951 patients (as of December 2018). Data extraction methods have been developed for five different EMR systems, and include both backend and automated frontend extractions. The raw EMR data are transformed according to specific rules, including trimming implausible values, converting values and free text to standard terminologies or classification systems, and structuring the data into a common CPCSSN format. Following local data extraction and processing, the data are transferred to a central repository and made available for research and disease surveillance. CONCLUSION: This paper aims to provide important contextual information to future CPCSSN data users.

Inhomogeneous backflow transformations in quantum Monte Carlo calculations.

An inhomogeneous backflow transformation for many-particle wave functions is presented and applied to electrons in atoms, molecules, and solids. We report variational and diffusion quantum Monte Carlo (VMC and DMC) energies for various systems and study the computational cost of using backflow wave functions. We find that inhomogeneous backflow transformations can provide a substantial increase in the amount of correlation energy retrieved within VMC and DMC calculations. The backflow transformations significantly improve the wave functions and their nodal surfaces.

All-electron quantum Monte Carlo calculations for the noble gas atoms He to Xe.

We report all-electron variational and diffusion quantum Monte Carlo (VMC and DMC) calculations for the noble gas atoms He, Ne, Ar, Kr, and Xe. The calculations were performed using Slater-Jastrow wave functions with Hartree-Fock single-particle orbitals. The quality of both the optimized Jastrow factors and the nodal surfaces of the wave functions declines with increasing atomic number Z, but the DMC calculations are tractable and well behaved in all cases. We discuss the scaling of the computational cost of DMC calculations with Z.

Quantum Monte Carlo study of the phase diagram of solid molecular hydrogen at extreme pressures.

Establishing the phase diagram of hydrogen is a major challenge for experimental and theoretical physics. Experiment alone cannot establish the atomic structure of solid hydrogen at high pressure, because hydrogen scatters X-rays only weakly. Instead, our understanding of the atomic structure is largely based on density functional theory (DFT). By comparing Raman spectra for low-energy structures found in DFT searches with experimental spectra, candidate atomic structures have been identified for each experimentally observed phase. Unfortunately, DFT predicts a metallic structure to be energetically favoured at a broad range of pressures up to 400 GPa, where it is known experimentally that hydrogen is non-metallic. Here we show that more advanced theoretical methods (diffusion quantum Monte Carlo calculations) find the metallic structure to be uncompetitive, and predict a phase diagram in reasonable agreement with experiment. This greatly strengthens the claim that the candidate atomic structures accurately model the experimentally observed phases.

Functional inactivation of the oestrogen receptor by the antioestrogen, ZM 182780, sensitises tumour cells to reactive oxygen species.

Reactive oxygen species (ROS) play a fundamental role in both apoptotic and necrotic cell death. Their importance is highlighted by studies showing that they mediate cell death in response to radiotherapy and to some forms of chemotherapy. Here we provide the first evidence for a role of ROS in response to an antiendocrine agent currently undergoing clinical trials. Using the oestrogen receptor (ER) containing rat pituitary GH3 cell line, we show that cell death is induced by the pure steroidal antioestrogen, ZM 182780, and that this is blocked by the antioxidant, N-acetyl cysteine (NAC). By flow cytometry, we show that, prior to the onset of DNA breakdown measured by ELISA, ZM 182780 exposure has no significant effect on intracellular oxidant concentrations. In contrast, ZM 182780 exposure greatly increases sensitivity to oxidants generated by blocking cellular antioxidant pathways and from exogenous administration of hydrogen peroxide (H2O2). As both necrosis and apoptosis are controlled by mitochondrial function, further experiments conducted to determine mitochondrial membrane potential (Delta|gWm) have indicated that the ZM 182780-induced loss of ER function increases the ease with which oxidants collapse mitochondrial activity and, as a consequence, cell death.

Integrated care for patients with asthma: views of general practitioners.

BACKGROUND: In 1989, a shared or integrated care scheme was developed for hospital outpatients with asthma, using the computerized patient record system of Grampian Health Board, Scotland. Patients with asthma attending hospital clinics were entered into this scheme and were invited to attend their general practitioner instead of an outpatient clinic for review of their asthma. Three-monthly questionnaires covering clinical aspects of asthma were sent to these patients and their general practitioners; the latter then returned them to the specialist. Patients could be recalled to the hospital clinic if either the general practitioner or consultant felt this was necessary and all patients were reviewed after one year by the specialist. The success of integrated care for patients with asthma relies on the cooperation of general practitioners. AIM: The aim of this study was to investigate how this scheme worked in general practice, and general practitioners' perceptions of it, in order to identify factors that enhance or inhibit integrated care for patients with asthma in general practice. METHOD: A qualitative survey was carried out with a random, stratified sample of 38 of the 317 general practitioners in the region. Semi-structured interviews were designed to elicit general practitioners' accounts of their operation of integrated care and their attitudes towards the scheme. RESULTS: General practitioners perceived the scheme to have several advantages: the continuity and quality of care provided was improved; and the transmission of information between general practitioner and specialist was enhanced. Regular general practitioner reviews, instigated by standard letters generated by computer, were favoured as being clearly structured. Concerns were raised about the processing of paperwork, and the possibility that unnecessary reviews might be generated. CONCLUSION: Integrated care for asthma patients is an acceptable management option among general practitioners.

Locality commissioning: how much influence have general practitioners really had?

This paper investigates the various models of locality commissioning in relation to the participation of general practitioners (GPs), and explores the perceived successes of locality commissioning in the 15 health boards in Scotland and 13 health authorities in the Northern and Yorkshire Region of England. A postal questionnaire was sent to 190 individuals involved in commissioning, and semi-structured interviews with GPs (n = 31) and health authority managers (n = 41) were undertaken in each of the 28 health authorities. Seventy-five per cent of the health authorities had introduced some form of locality commissioning. Five types of locality commissioning organization were identified on the basis of the level of GP influence over decisions. All GP responders identified benefits resulting from their involvement in the process but only 27% of health authority responders did so. Most benefits related to improved professional relationships, not to service changes. On the whole, locality commissioning does not appear to have resulted in major changes to contracts or services.

Identifying asthmatic patients in the community: a new method.

Identifying a random sample of patients in the community has long proved problematic. In 1989 changes were made in the management of adult asthmatic patients referred to specialist clinics in the Grampian Health Board area. In order to estimate the effect of these changes on the management of patients not referred, it was necessary to identify two random samples of adult asthmatic patients treated solely in general practice. As it was felt that existing methods were open to bias and other errors, a method using National Health Service drug prescription forms was devised. Following the computerization of the Pharmacy Practice Division in Aberdeen, a similar method for the identification of a follow-up sample had to be devised. Nearly 400 general practitioners (86% of those eligible) took part in the first sampling in 1989; 96% of those contacted participated in the second sampling in 1991. Both methods were effective in identifying asthmatic patients in the community. Computerization has made the task simpler, less time consuming and, as a consequence, most cost effective.

Social variation in reasons for contacting general practice out-of-hours: implications for daytime service provision?

BACKGROUND: Contact with general practice out-of-hours services increases with socioeconomic deprivation. The reasons for this association are unclear but may include variations in access to daytime services or differences in morbidity. AIM: To identify the reasons for contact with the Glasgow Emergency Medical Service (GEMS) in relation to patient sociodemographic characteristics and the nature of the presenting problem. METHOD: All contacts with GEMS over a one-week period (n = 3193) in October 1996 were identified and a random 1:2 sample were sent a postal questionnaire investigating their reasons for contacting the service. Sociodemographic data and presenting problems were extracted from the service contact sheet. Data were analysed using correspondence analysis. RESULTS: Correspondence analysis identified two factors characterised as 'perceived problems with daytime services' and 'perceived urgency'. Scores on the former dimension were significantly associated with age (P < 0.0001), gender (P < 0.0001), socioeconomic category (P < 0.0001), and presenting problem (P = 0.015) and scores were higher in adults, in males, among the non-affluent (particularly those resident in deprived areas), and in those presenting with a musculoskeletal problem. Scores on the latter dimension were significantly associated with age (P < 0.0001) and presenting problem (P < 0.0001). Scores tended to increase after childhood and for each of the five most frequent categories of presenting problem relative to other symptoms. CONCLUSIONS: Compared to those from affluent areas, patients from non-affluent areas appear to perceive difficulties accessing their general practitioner during surgery hours and may contact out-of-hours services as an alternative.

What does GP out of hours care cost? An analysis of different models of out of hours care in Scotland.

BACKGROUND: The changes to out of hours care provided by General Practitioners have led to wide variation in the types and costs of out of hours care across the country. AIM: To examine the costs of different models of service delivery for GP out of hours organisations. METHODS: This was a prospective cross-sectional survey of eight GP out of hours organisations and samples of their patients. A deputising service, rotas, and various types of GP co-operative across Scotland were surveyed. Information on the quantities of resources used by each organisation was combined with unit costs. Costs incurred by patients and other NHS costs subsequent to the out of hours contact were also calculated. RESULTS: Annual costs incurred by the GP out of hours organisation per 1,000 population ranged from pounds sterling 2,916 to pounds sterling 12,120. There was no relationship between costs and type and size of organisation. There was a three-fold variation in total costs per out of hours contact (pounds sterling 15 to pounds sterling 51). Costs per phone contact were lowest (pounds sterling 6 to pounds sterling 11), followed by cost per centre contact (pounds sterling 10 to pounds sterling 16) and cost per home contact (pounds sterling 21 to pounds sterling 60). Total costs per episode ranged from pounds sterling 78 to pounds sterling 136 for centre contacts, from pounds sterling 130 to pounds sterling 303 for home contacts, and from pounds sterling 70 to pounds sterling 553 for telephone contacts. Home contacts had the highest average cost per episode (pounds sterling 212), followed by telephone contacts (pounds sterling 117) and centre contacts (pounds sterling 85). CONCLUSIONS: There are wide variations in the costs of operating GP out of hours services, It is likely that the context in which organisations were set up and local geography infuence variations in costs, as well as the level of GP cover.

The RCP's 'Three Key Questions' for asthma: review of practical use.

Assessment tools are a vital component of chronic disease management. The Royal College of Physicians has developed a patient-focused outcome measure for the treatment of asthma, the 'Three Key Questions'. However, in a study investigating the goals of people with asthma, several issues related to the tool emerged. Forty-seven adults of a range of ages and asthma severity but with no significant co-morbidity were interviewed. It emerged that the outcome measure may be subject to recall bias. Also, symptom reports may be conflated if daytime symptoms also occur with activity. 'Interference with activity' is a subjective term the interpretation of which varies considerably. Changes in the level of activity undertaken may be reported rather than changes in symptom severity. The 'Three Key Questions' are not fully patient-centred because they assess the presence of symptoms rather than their importance to the individual. The use of the 'Three Key Questions' as an outcome measure may not allow valid comparisons to be made between settings.