Plasma density measurements using chirped pulse broad-band Raman amplification

Stimulated Raman backscattering is used as a non-destructive method to determine the density of plasma media at localized positions in space and time. By colliding two counter-propagating, ultra-short laser pulses with a spectral bandwidth larger than twice the plasma frequency, amplification occurs at the Stokes wavelengths, which results in regions of gain and loss separated by twice the plasma frequency, from which the plasma density can be deduced. By varying the relative delay between the laser pulses, and therefore the position and timing of the interaction, the spatio-temporal distribution of the plasma density can be mapped out

Manoeuvring Experiments Using the MUN Explorer AUV

Autonomous Underwater Vehicles (AUVs) are self-propelled robotic platforms that can perform a predetermined mission completely unmanned. A series of manoeuvring experiments were performed using the MUN Explorer AUV during the summer of 2006 and a selection of these experimental results are presented in this paper. The purpose of these experiments was to collect a set of useful data for validating a hydrodynamic model of the dynamic performance of the vehicle. This paper aims at explaining the methods and measures adopted in accomplishing this task. Apart from providing a data set for validation of the hydrodynamic model, the data record also shows the ability of the AUV to perform extreme manoeuvres and the accuracy with which it can follow a pre-planned mission

Manoeuvring Trials with the MUN Explorer AUV: Data Analysis and Observations

Manoeuvring trials are usually performed to determine the manoeuvring characteristics of a marine vehicle. It is through certain standard manoeuvres we evaluate the robustness, performance and limitations of the vehicle control system. A series of open-water manoeuvring trials were performed using the MUN Explorer AUV in the summer of 2006. The actual purpose of these experiments was to collect a set of experimental data in order to validate a hydrodynamic model of the dynamic performance of the vehicle. This paper presents the results and observations from the analysis of a set of manoeuvring trials data: in particular the results from straightline (acceleration – deceleration) tests and turning circles. It outlines briefly the method by which these tests were conducted and discusses the results and observations made. Apart from providing a data set for validation purposes, the results also indicate the ability of the vehicle to follow a pre-planned mission with precision

Pepper-pot emittance measurement of laser-plasma wakefield accelerated electrons

The transverse emittance is an important parameter governing the brightness of an electron beam. Here we present the first pepper-pot measurement of the transverse emittance for a mono-energetic electron beam from a laser-plasma wakefield accelerator, carried out on the Advanced Laser-Plasma High Energy Accelerators towards X-Rays (ALPHA-X) beam line. Mono-energetic electrons are passed through an array of 52 mu m diameter holes in a tungsten mask. The pepper-pot results set an upper limit for the normalised emittance at 5.5 +/- 1 pi mm mrad for an 82 MeV beam

Chirped pulse Raman amplification in plasma

Raman amplification in plasma has been proposed to be a promising method of amplifying short radiation pulses. Here, we investigate chirped pulse Raman amplification (CPRA) where the pump pulse is chirped and leads to spatiotemporal distributed gain, which exhibits superradiant scaling in the linear regime, usually associated with the nonlinear pump depletion and Compton amplification regimes. CPRA has the potential to serve as a high-efficiency high-fidelity amplifier/compressor stage

Development of StressCheck: A telehealth motivational enhancement therapy to improve voluntary engagement for PTSD treatment among active-duty service members

Background: Rates of PTSD in active-duty military are high relative to the general population. Although efficacious treatments exist, they are underutilized. Many service members with PTSD do not present for treatment and, of those who do, many do not receive sufficient doses of the interventions to receive full benefits. Motivational Enhancement Therapy (MET) “check-ups”, are brief interventions designed to elicit treatment engagement for those who are not treatment-seeking. Methods: StressCheck is an MET for nontreatment seeking Army and Air Force personnel. StressCheck aims to improve PTSD and increase treatment engagement, especially around evidence-based interventions, as well as to decrease stigma about seeking mental health services and improve knowledge about treatment options. This paper describes the intervention components and process of treatment development. The paper also describes next steps in testing the effectiveness of the intervention. Conclusion: PTSD is associated with deleterious health, occupational, and psychological effects. If effective, this innovative intervention will bridge the gap between those who are not treatment seeking and existing services, thereby enhancing reach and impact of existing services

Gene dose influences cellular and calcium channel dysregulation in heterozygous and homozygous T4826I-RYR1 malignant hyperthermia-susceptible muscle

Malignant hyperthermia susceptibility (MHS) is primarily conferred by mutations within ryanodine receptor type 1 (RYR1). Here we address how the MHS mutation T4826I within the S4-S5 linker influences excitation-contraction coupling and resting myoplasmi

An ultrashort pulse ultra-violet radiation undulator source driven by a laser plasma wakefield accelerator

Narrow band undulator radiation tuneable over the wavelength range of 150–260 nm has been produced by short electron bunches from a 2 mm long laser plasma wakefield accelerator based on a 20 TW femtosecond laser system. The number of photons measured is up to 9 × 106 per shot for a 100 period undulator, with a mean peak brilliance of 1 × 1018 photons/s/mrad2/mm2/0.1% bandwidth. Simulations estimate that the driving electron bunch r.m.s. duration is as short as 3 fs when the electron beam has energy of 120–130 MeV with the radiation pulse duration in the range of 50–100 fs

Role of surface roughness in hard x-ray emission from femtosecond laser produced copper plasmas

The hard x-ray emission in the energy range of 30-300 keV from copper plasmas produced by 100 fs, 806 nm laser pulses at intensities in the range of 10$^{15}-10^{16}$ W cm$^{-2}$ is investigated. We demonstrate that surface roughness of the targets overrides the role of polarization state in the coupling of light to the plasma. We further show that surface roughness has a significant role in enhancing the x-ray emission in the above mentioned energy range.Comment: 5 pages, 4 figures, to appear in Phys. Rev.