Optimization of double drive pulse pumping in Ne-like Ge x-ray lasers

Pumping of the Ne-like Ge x-ray laser with two 100 ps duration pulses (a prepulse and main pulse) is investigated using a fluid and atomic physics code coupled to a 3D ray tracing postprocessor code. The modeling predicts the optimum ratio of the irradiance of the two pulses for the maximum x-ray laser output resulting from the balance between the relative lower electron density gradients and wider gain region which is produced with a larger prepulse and the higher peak gain coefficients produced with a small prepulse. With a longer pulse interval between prepulse and main pulse, a relatively lower optimum pulse ratio is found. The threshold irradiance of the main driving pulse with a prepulse required to make an order of magnitude enhancement of laser output compared to irradiation without a prepulse is also found at 3-4x10(13) W/cm(2) for Ne-like Ge. (C) 1998 American Institute of Physics

A single-blind, pilot randomised trial of a weight management intervention for adults with intellectual disabilities and obesity: study protocol

Background: The prevalence of obesity in adults with intellectual disabilities has consistently been reported to be higher than the general population. Despite the negative impact of obesity on health, there is little evidence of the effectiveness of weight management interventions for adults with intellectual disabilities and obesity. Preliminary results from a single-stranded feasibility study of a multi-component weight management intervention specifically designed for adults with intellectual disabilities and obesity (TAKE 5) and that satisfied clinical recommendations reported that it was acceptable to adults with intellectual disabilities and their carers. This study aims to determine the feasibility of a full-scale clinical trial of TAKE 5.<p></p> Methods: This study will follow a pilot randomised trial design. Sixty-six obese participants (body mass index (BMI) ≥30 kg/m2) will be randomly allocated to the TAKE 5 multi-component weight management intervention or a health education ‘active’ control intervention (Waist Winners Too (WWToo)). Both interventions will be delivered over a 12-month period. Participants’ anthropometric measures (body weight, BMI, waist circumference, percentage body fat); indicators of activity (levels of physical activity and sedentary behaviour) and well-being will be measured at three time points: baseline, 6 and 12 months. The researcher collecting outcome measures will be blind to study group allocation.<p></p> Conclusions: The data from this study will generate pilot data on the acceptability of randomisation, attrition rates and the estimates of patient-centred outcomes of TAKE 5, which will help inform future research and the development of a full-scale randomised clinical trial

Experiments and Simulations of short-pulse laser-pumped extreme ultraviolet lasers

Recent experimental work on the development of extreme ultraviolet lasers undertaken using as the pumping source the VULCAN laser at the Rutherford Appleton Laboratory is compared to detailed simulations. It is shown that short duration (similar topicosecond) pumping can produce X-ray laser pulses of a few picosecond duration and that measurement of the emission from the plasma can give an estimate of the duration of the gain coefficient. The Ehybrid fluid and atomic physics code developed at the University of York is used to simulate X-ray laser gain and plasma emission. Two postprocessors to the Ehybrid code are utilized: 1) to raytrace the X-ray laser beam amplification and refraction and 2) to calculate the radiation emission in the kiloelectronvolt photon energy range. The raytracing and spectral simulations are compared, respectively, to measured X-ray laser output and the output of two diagnostics recording transverse X-ray emission. The pumping laser energy absorbed in the plasma is examined by comparing the simulations to experimental results. It is shown that at high pumping irradiance (>10(15) Wcm(-2)), fast electrons are produced by parametric processes in the preformed long scale-length plasmas. These fast electrons do not pump the population inversion and so pumping efficiency is reduced at high irradiance

A feasibility study of behavioural activation for depressive symptoms in adults with intellectual disabilities

Background: Important work has been carried out adapting cognitive behavioural therapy for people with intellectual disabilities. However, there is a lack of alternative psychological therapies available for people with intellectual disabilities and emotional difficulties. Behavioural activation for depression is less reliant on verbal communication and focuses on increasing purposeful activity and reducing avoidance. Method: This feasibility study involved the development and piloting of an adapted manual of behavioural activation for people with intellectual disabilities. The intervention consisted of 10–12 sessions and a key adaptation was that the therapist worked with the clients alongside a significant other in their life, either a paid carer or family member. Baseline, post-intervention (3 months after entering the study) and 6-month quantitative follow-up data were obtained. Primary outcome data were gathered, concerning depressive symptoms, participants' levels of activity and general well-being. Results: Twenty-three adults with intellectual disabilities with symptoms of depression were recruited from specialist health services. In terms of acceptability, the behavioural activation intervention was well received and only two individuals dropped out, with a further two lost to follow-up. The main measures of depression appeared to be sensitive to change. Pre- to post-intervention data showed a significant reduction in self-report of depressive symptoms with a strong effect size (r = 0.78), that was maintained at follow-up (r = 0.86). Positive change was also obtained for informant reports of depressive symptoms from pre- to post-intervention, with a strong effect size (r = 0.7). Once again, this positive change was maintained at follow-up (r = 0.72). Conclusions: The study suggested that behavioural activation may be a feasible and worthwhile approach to tackling depression in people with intellectual disabilities. However, a randomised controlled trial would be required to establish its effectiveness, with more sensitive measurement of change in activity

A review of X-ray laser development at Rutherford Appleton Laboratory

Recent experiments undertaken at the Rutherford Appleton Laboratory to produce X-ray lasing over the 5-30 nm wavelength range are reviewed. The efficiency of lasing is optimized when the main pumping pulse interacts with a preformed plasma. Experiments using double 75-ps pulses and picosecond pulses superimposed on 300-ps background pulses are described. The use of travelling wave pumping with the approximately picosecond pulse experiments is necessary as the gain duration becomes comparable to the time for the X-ray laser pulse to propagate along the target length. Results from a model taking account of laser saturation and deviations from the speed of light c of the travelling wave and X-ray laser group velocity are presented. We show that X-ray laser pulses as short as 2-3 ps can be produced with optical pumping pulses of approximate to1-ps

Optimization of double pulse pumping for Ni-like Sm x-ray lasers

We report a systematic study of double pulse pumping of the Ni-like Sm x-ray laser at 73 Angstrom, currently the shortest wavelength saturated x-ray laser. It is found that the Sm x-ray laser output can change by orders of magnitude when the intensity ratio of the pumping pulses and their relative delay are varied. Optimum pumping conditions are found and interpreted in terms of a simple model. (C) 1999 American Institute of Physics. [S0021-8979(99)07102-9]

Enhanced inverse bremsstrahlung heating rates in a strong laser field

Test particle studies of electron scattering on ions, in an oscillatory electromagnetic field have shown that standard theoretical assumptions of small angle collisions and phase independent orbits are incorrect for electron trajectories with drift velocities smaller than quiver velocity amplitude. This leads to significant enhancement of the electron energy gain and the inverse bremsstrahlung heating rate in strong laser fields. Nonlinear processes such as Coulomb focusing and correlated collisions of electrons being brought back to the same ion by the oscillatory field are responsible for large angle, head-on scattering processes. The statistical importance of these trajectories has been examined for mono-energetic beam-like, Maxwellian and highly anisotropic electron distribution functions. A new scaling of the inverse bremsstrahlung heating rate with drift velocity and laser intensity is discussed.Comment: 12 pages, 12 figure

Teenagers' experiences of life in lockdown: Implications for college and university support

We have all experienced significant change and disruption during the pandemic. Young people have been particularly impacted at a time when they are negotiating their transition through school to college or university. Dr Ola Demkowicz and her team reflect on their TELL research (Teenagers’ Experiences of Life in Lockdown