Polarized electron beam production via laser wakefield acceleration in pre-polarized plasma is investigated by particle-in-cell simulations. The evolution of the electron beam polarization is studied based on the Thomas–Bargmann–Michel–Telegdi equation for the transverse and longitudinal self-injection, and the depolarization process is found to be influenced by the injection schemes. In the case of transverse self-injection, as found typically in the bubble regime, the spin precession of the accelerated electrons is mainly influenced by the wakefield. However, in the case of longitudinal injection in the quasi-1D regime (for example, F. Y. Li et al., Phys. Rev. Lett. 110, 135002 (2013)), the direction of electron spin oscillates in the laser field. Since the electrons move around the laser axis, the net influence of the laser field is nearly zero and the contribution of the wakefield can be ignored. Finally, an ultra-short electron beam with polarization of $99\%$ can be obtained using longitudinal self-injection.

As a typical plasma-based optical element that can sustain ultra-high light intensity, plasma density gratings driven by intense laser pulses have been extensively studied for wide applications. Here, we show that the plasma density grating driven by two intersecting driver laser pulses is not only nonuniform in space but also varies over time. Consequently, the probe laser pulse that passes through such a dynamic plasma density grating will be depolarized, that is, its polarization becomes spatially and temporally variable. More importantly, the laser depolarization may spontaneously take place for crossed laser beams if their polarization angles are arranged properly. The laser depolarization by a dynamic plasma density grating may find application in mitigating parametric instabilities in laser-driven inertial confinement fusion.

Chlamydia trachomatis (CT) infection has been a major public health threat globally. Monitoring and prediction of CT epidemic status and trends are important for programme planning, allocating resources and assessing impact; however, such activities are limited in China. In this study, we aimed to apply a seasonal autoregressive integrated moving average (SARIMA) model to predict the incidence of CT infection in Shenzhen city, China. The monthly incidence of CT between January 2008 and June 2019 in Shenzhen was used to fit and validate the SARIMA model. A seasonal fluctuation and a slightly increasing pattern of a long-term trend were revealed in the time series of CT incidence. The monthly CT incidence ranged from 4.80/100 000 to 21.56/100 000. The mean absolute percentage error value of the optimal model was 8.08%. The SARIMA model could be applied to effectively predict the short-term CT incidence in Shenzhen and provide support for the development of interventions for disease control and prevention.

The majority of paediatric Clostridioides difficile infections (CDI) are community-associated (CA), but few data exist regarding associated risk factors. We conducted a case–control study to evaluate CA-CDI risk factors in young children. Participants were enrolled from eight US sites during October 2014–February 2016. Case-patients were defined as children aged 1–5 years with a positive C. difficile specimen collected as an outpatient or ⩽3 days of hospital admission, who had no healthcare facility admission in the prior 12 weeks and no history of CDI. Each case-patient was matched to one control. Caregivers were interviewed regarding relevant exposures. Multivariable conditional logistic regression was performed. Of 68 pairs, 44.1% were female. More case-patients than controls had a comorbidity (33.3% vs. 12.1%; P = 0.01); recent higher-risk outpatient exposures (34.9% vs. 17.7%; P = 0.03); recent antibiotic use (54.4% vs. 19.4%; P < 0.0001); or recent exposure to a household member with diarrhoea (41.3% vs. 21.5%; P = 0.04). In multivariable analysis, antibiotic exposure in the preceding 12 weeks was significantly associated with CA-CDI (adjusted matched odds ratio, 6.25; 95% CI 2.18–17.96). Improved antibiotic prescribing might reduce CA-CDI in this population. Further evaluation of the potential role of outpatient healthcare and household exposures in C. difficile transmission is needed.

Nutritional strategies to mitigate the negative effects of heat stress on animal welfare and productivity often involve changes in ration formulation. However, cattle commonly sort their ration in favour of certain components, and it is not clear how feed sorting responds to heat stress. This study investigated the association between heat stress and feed sorting behaviour. Lactating Holstein dairy cows (n = 32; parity = 2.8±1.2; mean±SD) were housed in a free stall barn and milked 3×/day. Cows were fed individually using the Calan Broadbent Feeding System and offered ad libitum access to a total mixed ration (containing on a dry matter basis: 3.3% ryegrass hay, 16.5% ryegrass baleage, 24.7% corn silage, 11.1% brewers grains, 19.7% ground corn, 19.8% concentrate and 4.9% protein/mineral supplement), provided 1×/day. Beginning at 186±60 days in milk, cows were exposed to either: heat stress conditions (HT; n = 15) (average temperature–humidity index: 77.6), or evaporative cooling (CL; n = 17), consisting of misters and fans over the freestall and feed bunks. Data were collected during a 4-day baseline period, and two 4-day experimental periods: starting at 10 days after implementing treatments (defined as acute heat stress for HT cows), and at 62 days after implementing treatments (defined as chronic heat stress for HT cows). Daily feed intake and physiological responses to heat stress (body temperature, respiration rate) were recorded. Samples of fresh and refused feed were collected daily from individual cows for particle size analysis. The particle size separator had three screens (19, 8 and 1.18 mm) and a bottom pan, resulting in 4 fractions (long, medium, short and fine particles). Feed sorting was calculated as the actual intake of each particle size fraction expressed as a percentage of the predicted intake of that fraction. During both heat stress periods, HT cows sorted for long particles more than CL cows (105.0% v. 100.6%; SE = 1.1). During acute heat stress, HT cows sorted to a greater extent than CL cows against medium and short particles, whereas sorting of these fractions did not differ during chronic heat stress. Body temperature and respiration rate were associated across treatments with the extent of sorting for long particles and against short particles during acute heat stress. These results suggest that feed sorting is particularly influenced during acute heat stress, and that sorting for longer particles may increase in heat stress.

Electronic health records (EHRs) provide great promise for identifying cohorts and enhancing research recruitment. Such approaches are sorely needed, but there are few descriptions in the literature of prevailing practices to guide their use. A multidisciplinary workgroup was formed to examine current practices in the use of EHRs in recruitment and to propose future directions. The group surveyed consortium members regarding current practices. Over 98% of the Clinical and Translational Science Award Consortium responded to the survey. Brokered and self-service data warehouse access are in early or full operation at 94% and 92% of institutions, respectively, whereas, EHR alerts to providers and to research teams are at 45% and 48%, respectively, and use of patient portals for research is at 20%. However, these percentages increase significantly to 88% and above if planning and exploratory work were considered cumulatively. For most approaches, implementation reflected perceived demand. Regulatory and workflow processes were similarly varied, and many respondents described substantive restrictions arising from logistical constraints and limitations on collaboration and data sharing. Survey results reflect wide variation in implementation and approach, and point to strong need for comparative research and development of best practices to protect patients and facilitate interinstitutional collaboration and multisite research.

In rock engineering, evaluating the post-peak strength and deformation of rock is necessary. To explore the elasto-plastic behavior of sandstone in the post-peak stage, a series of strain-controlled triaxial tests were conducted under different confining pressures. According to the post-peak characteristics, a constitutive model based on nonlinear elasticity and generalized plasticity is proposed. This proposed model is characterized by the following features: (1) Nonlinear elasticity is observed under hydrostatic and shear loading; (2) the associated flow rule is followed; (3) substantial plastic deformation occurs during shear loading; and (4) post-peak softening behavior is accurately predicted. This model requires twelve material parameters, three for elasticity and nine for plasticity. The proposed model was validated by comparing the triaxial test results of Mushan sandstone at different hydrostatic pressures under dry and saturated conditions. In addition, the model is versatile; it can simulate the deformational behavior of two other sandstones. In summary, the proposed model can reasonably predict the complete stress–strain curve of sandstone.

A stochastic risk model was developed to estimate the time elapsed before overcrowding (TOC) or feed interruption (TFI) emerged on the swine premises under movement restrictions during a classical swine fever (CSF) outbreak in Indiana, USA. Nursery (19 to 65 days of age) and grow-to-finish (40 to 165 days of age) pork production operations were modelled separately. Overcrowding was defined as the total weight of pigs on premises exceeding 100% to 115% of the maximum capacity of the premises, which was computed as the total weight of the pigs at harvest/transition age. Algorithms were developed to estimate age-specific weight of the pigs on premises and to compare the daily total weight of the pigs with the threshold weight defining overcrowding to flag the time when the total weight exceeded the threshold (i.e. when overcrowding occurred). To estimate TFI, an algorithm was constructed to model a swine producer’s decision to discontinue feed supply by incorporating the assumptions that a longer estimated epidemic duration, a longer time interval between the age of pigs at the onset of the outbreak and the harvest/transition age, or a longer progression of an ongoing outbreak would increase the probability of a producer’s decision to discontinue the feed supply. Adverse animal welfare conditions were modelled to emerge shortly after an interruption of feed supply. Simulations were run with 100 000 iterations each for a 365-day period. Overcrowding occurred in all simulated iterations, and feed interruption occurred in 30% of the iterations. The median (5th and 95th percentiles) TOC was 24 days (10, 43) in nursery operations and 78 days (26, 134) in grow-to-finish operations. Most feed interruptions, if they emerged, occurred within 15 days of an outbreak. The median (5th and 95th percentiles) time at which either overcrowding or feed interruption emerged was 19 days (4, 42) in nursery and 57 days (4, 130) in grow-to-finish operations. The study findings suggest that overcrowding and feed interruption could emerge early during a CSF outbreak among swine premises under movement restrictions. The outputs derived from the risk model could be used to estimate and evaluate associated mitigation strategies for alleviating adverse animal welfare conditions resulting from movement restrictions.

The generation of fast ion beams in the hole-boring radiation pressure acceleration by intense laser pulses has been studied for targets with different ion components. We find that the oscillation of the longitudinal electric field for accelerating ions can be effectively suppressed by using a two-ion-species target, because fast ions from a two-ion-species target are distributed into more bunches and each bunch bears less charge. Consequently, the energy spread of ion beams generated in the hole-boring radiation pressure acceleration can be greatly reduced down to 3.7% according to our numerical simulation.

This study adopted the distinct element method (DEM) to explore the key influencing factors on the variations of lateral earth pressure, including packing type, interior friction angle, particle stiffness and particle size. The reference parameters for the DEM model were retrieved from direct shear tests of a rod assembly. Based on the reference parameters, the evolution of lateral earth pressure is further simulated, and a parametric study was conducted. The results showed that: (1) the analysis model could effectively capture the variation of lateral earth pressure under both active and passive conditions, and the simulated failure patterns were consistent with those from the sandbox tests; (2) the greater interior friction angle ϕinterior decreased the active coefficient Ka and increased the passive coefficient Kp; (3) increasing particle stiffness decreased the active coefficient Ka and increased the passive coefficient Kp; (4) larger particle sizes led to a larger active coefficient Ka and a smaller passive coefficient Kp; and (5) when the particle assembly was arranged in order, its lateral pressure was much larger than that of the randomly packed assembly.

Extended abstract of a paper presented at Microscopy and Microanalysis 2011 in Nashville, Tennessee, USA, August 7–August 11, 2011.

Positron lifetime spectroscopy has been used to study the vacancy type defects in undoped gallium antimonide. Temperature dependent positron trapping into the VGa-related defect having a characteristic lifetime of 310ps was observed in the as-grown sample. The lifetime data were well described by a model involving the thermal ionization (0/-) of the VGa-related defect and its ionization energy was found to be E(0/-)=83meV. For the electron irradiated sample, the VGa-related defect with lifetime of 310ps that was found in the non-irradiated samples was also identified. Moreover, another lifetime component (280ps) was only observed in the electron irradiated sample but not in the non-irradiated sample. It was also attributed to the VGa-related defect. The two identified VGa-related defects should have different microstructures because of their difference in characteristic lifetimes. The 280ps component remains thermally stable after the 500°C annealing while the 310ps component anneals at 300°C.

Positron lifetime spectroscopy was employed to study the as-electron-irradiated (10 MeV, 1×1018 cm-2) n-type 6H silicon carbide sample in the measuring temperature range of 15 K to 294 K. Isochronal annealing studies were also performed up to the temperature of 1373 K by carrying out the room temperature positron lifetime measurement. Negatively charged carbon vacancies and VCVSi divacancy were identified as the major vacancy type defects induced by the electron irradiation process. The concentration of the VCVSi divacancy was found to decrease dramatically after the 1973 K annealing.

We show how positron annihilation can distinguish vacancies in undoped hydrogenated amorphous silicon by performing Variable Energy Positron Annihilation Spectroscopy experiments before and after light soaking. We find that vacancy clusters, di-vacancies and a new type of single vacancies are created in undoped as-grown a-Si:H thin film by light illumination. The fact that the vacancy clusters are eliminated by the thermal annealing suggests that the Staebler-Wronski effect is closely related to vacancy clusters in a-Si:H material. The creation of vacancy clusters and redistribution of di-vacancies and even single vacancies probably result in photo-induced structural changes in this material.