Multi-species ion acceleration from sub-ps, PW interactions with ultra-thin foils

Multi-species ion acceleration from ultra-thin foils was studied experimentally, employing the Vulcan Petawatt laser at the Central Laser Facility, UK. Plastic (CH) foils with thicknesses in the range 10–340 nm were irradiated with intense, short (750 fs) laser pulses producing maximum energies of ∼65 MeV and 25 MeV/nucleon obtained for H+ and C6+ ions, respectively. Ion spectra obtained from high resolution spectrometers suggest differences in the acceleration dynamics for the two species. Comparisons are made with two-dimensional Particle in Cell simulations, which identify, for an optimal thickness, two main mechanisms contributing to the ion acceleration process, namely multi-species target normal sheath acceleration (TNSA) and radiation pressure acceleration (RPA). Ion energies are further enhanced by the onset of relativistically induced transparency. A final stage in the acceleration is caused by the formation of electron jets (as the target undergoes transparency), which accelerate the ions off-axis. By analysing the spatial and temporal evolution of the accelerating fields, we are able to infer the effect of the different mechanisms on each species and how this translates to the experimental observations. The two main mechanisms, TNSA and RPA, are seen to each produce a distinct population of high energy protons whereas a single population of carbon is accelerated by a summation of these effects. This species-specific analysis sheds new light on the complex dynamics in a multi-species target expansion and on the contribution of different acceleration processes to the acceleration of the most energetic ions in the spectrum

Under- treatment and under diagnosis of hypertension: a serious problem in the United Arab Emirates

BACKGROUND: Hypertension, notably untreated or uncontrolled, is a major risk factor for cardiovascular diseases (CVD) morbidity and mortality. In countries in transition, little is known about the epidemiology of hypertension, and its biochemical correlates. This study was carried out in Al Ain, United Arab Emirates, to characterize self-reported (SR) normotensives and hypertensives in terms of actual hypertension status, demographic variables, CVD risk factors, treatment, and sequalae. METHODS: A sample, stratified by SR hypertensive status, of 349 SR hypertensives (Mean age ± SD; 50.8 ± 9.2 yrs; Male: 226) and 640 SR normotensives (42.9 ± 9.3 yrs, Male: 444) among nationals and expatriates was used. Hypertensives and normotensive subjects were recruited from various outpatient clinics and government organizations in Al-Ain city, United Arab Emirates (UAE) respectively. Anthropometric and demographic variables were measured by conventional methods. RESULTS: Both under-diagnosis of hypertension (33%) and under-treatment (76%) were common. Characteristics of undiagnosed hypertensives were intermediate between normotensives and SR hypertensives. Under-diagnosis of hypertension was more common among foreigners than among nationals. Risk factors for CVD were more prevalent among SR hypertensives. Obesity, lack of exercise and smoking were found as major risk factors for CVD among hypertensives in this population. CONCLUSION: Hypertension, even severe, is commonly under-diagnosed and under-treated in the UAE. Preventive strategies, better diagnosis and proper treatment compliance should be emphasized to reduce incidence of CVD in this population

Atypical interaction: Conversation analysis and communicative impairments

In this article I review conversation analytic work on “atypical interaction”—social interactions where a participant has a communicative impairment. Drawing together some of the main themes and findings in the field, I highlight three forms of atypicality in these interactions, with each linked to more than one type of communicative impairment: (a) atypical forms of delay in TCU progressivity; (b) atypical problems of understandability, intelligibility, and hearing; and (c) atypical actions. I also discuss forms of atypicality that appear to arise from one or more participants adapting their talk or conduct to deal with the impact of the impairment within interaction. The article concludes with some considerations of directions that future work in this field might take. Data are in British and Australian English

Absolute calibration of Fujifilm BAS-TR image plate response to laser driven protons up to 40 MeV

Image plates (IPs) are a popular detector in the field of laser driven ion acceleration, owing to their high dynamic range and reusability. An absolute calibration of these detectors to laser-driven protons in the routinely produced tens of MeV energy range is, therefore, essential. In this paper, the response of Fujifilm BAS-TR IPs to 1–40 MeV protons is calibrated by employing the detectors in high resolution Thomson parabola spectrometers in conjunction with a CR-39 nuclear track detector to determine absolute proton numbers. While CR-39 was placed in front of the image plate for lower energy protons, it was placed behind the image plate for energies above 10 MeV using suitable metal filters sandwiched between the image plate and CR-39 to select specific energies. The measured response agrees well with previously reported calibrations as well as standard models of IP response, providing, for the first time, an absolute calibration over a large range of proton energies of relevance to current experiments

Numerical Simulations of the Effects of a Tidal Turbine Array on Near-Bed Velocity and Local Bed Shear Stress

We apply a three-dimensional hydrodynamic model to consider the potential effects of energy extraction by an array of tidal turbines on the ambient near-bed velocity field and local bed shear stress in a coastal channel with strong tidal currents. Local bed shear stress plays a key role in local sediment dynamics. The model solves the Reynold-averaged Navier-Stokes (RANS) equations on an unstructured mesh using mixed finite element and finite volume techniques. Tidal turbines are represented through an additional form drag in the momentum balance equation, with the thrust imparted and power generated by the turbines being velocity dependent with appropriate cut-in and cut-out velocities. Arrays of 1, 4 and 57 tidal turbines, each of 1.5 MW capacity, were simulated. Effects due to a single turbine and an array of four turbines were negligible. The main effect of the array of 57 turbines was to cause a shift in position of the jet through the tidal channel, as the flow was diverted around the tidal array. The net effect of this shift was to increase near-bed velocities and bed shear stress along the northern perimeter of the array by up to 0.8 m·s−1 and 5 Pa respectively. Within the array and directly downstream, near-bed velocities and bed shear stress were reduced by similar amounts. Changes of this magnitude have the potential to modify the known sand and shell banks in the region. Continued monitoring of the sediment distributions in the region will provide a valuable dataset on the impacts of tidal energy extraction on local sediment dynamics. Finally, the mean power generated per turbine is shown to decrease as the turbine array increased in size