Influence of spatial-intensity contrast in ultraintense laser-plasma interactions.

Increasing the intensity to which high power laser pulses are focused has opened up new research possibilities, including promising new approaches to particle acceleration and phenomena such as high field quantum electrodynamics. Whilst the intensity achievable with a laser pulse of a given power can be increased via tighter focusing, the focal spot profile also plays an important role in the interaction physics. Here we show that the spatial-intensity distribution, and specifically the ratio of the intensity in the peak of the laser focal spot to the halo surrounding it, is important in the interaction of ultraintense laser pulses with solid targets. By comparing proton acceleration measurements from foil targets irradiated with by a near-diffraction-limited wavelength scale focal spot and larger F-number focusing, we find that this spatial-intensity contrast parameter strongly influences laser energy coupling to fast electrons. We find that for multi-petawatt pulses, spatial-intensity contrast is potentially as important as temporal-intensity contrast.

Political feasibility of scaling-up five evidence-informed HIV interventions in Pakistan: a policy analysis.

BACKGROUND: Drawing on policy theories, an assessment was made of the perceived political feasibility of scaling-up five evidence-based interventions to curb Pakistan's HIV epidemic: needle and syringe exchange programmes; targeted behaviour change communication; sexual health care for male and transgender sex workers; sexual and reproductive health care for female sex workers; and promoting and protecting the rights of those at greatest risk. METHOD: A questionnaire was emailed to 40 stakeholders and completed by 22. They expressed their level of agreement with 15 statements for each intervention (related to variables associated with policy success). Semi-structured interviews were conducted with 12 respondents. RESULTS: The interventions represent considerable change from the status quo, but are perceived to respond to widely acknowledged problems. These perceptions, held by the HIV policy elite, need to be set in the context of the prevailing view that the AIDS response is not warranted given the small and concentrated nature of the epidemic and that the interventions do not resonate closely with values held by society. The interventions were perceived to be evidence-based, supported by at least one donor and subject to little resistance from frontline staff as they will be implemented by contracted non-government organisations. The results were mixed in terms of other factors determining political feasibility, including the extent to which interventions are easy to explain, exhibit simple technical features, require few additional funds, are supported and not opposed by powerful stakeholders. CONCLUSION: The interventions stand a good chance of being implemented although they depend on donor support. The prospects for scaling them would be improved by ongoing policy analysis and strengthening of domestic constituencies among the target groups.

Herpes simplex virus type 2: epidemiology and management options in developing countries.

Genital herpes simplex virus type 2 (HSV2) is highly prevalent worldwide and an increasingly important cause of genital ulcer disease (GUD). Continued HSV2 transmission is facilitated by the large number of undiagnosed cases, the frequency of atypical disease and the occurrence of asymptomatic shedding. The lack of easy, affordable diagnostic methods and specific antiviral treatment in countries with low and middle income is of great concern, given the ability of GUD to enhance HIV transmission and acquisition. With rising HSV2 prevalence contributing to an increase in the proportion of GUD attributed to genital herpes in high-HIV prevalence settings, a safe and effective HSV vaccine is urgently needed. Meanwhile, multifaceted interventions are required to improve recognition of genital herpes, to prevent its spread and also to prevent its potential to promote HIV transmission in developing countries.

Near-100 MeV protons via a laser-driven transparency-enhanced hybrid acceleration scheme.

The range of potential applications of compact laser-plasma ion sources motivates the development of new acceleration schemes to increase achievable ion energies and conversion efficiencies. Whilst the evolving nature of laser-plasma interactions can limit the effectiveness of individual acceleration mechanisms, it can also enable the development of hybrid schemes, allowing additional degrees of control on the properties of the resulting ion beam. Here we report on an experimental demonstration of efficient proton acceleration to energies exceeding 94 MeV via a hybrid scheme of radiation pressure-sheath acceleration in an ultrathin foil irradiated by a linearly polarised laser pulse. This occurs via a double-peaked electrostatic field structure, which, at an optimum foil thickness, is significantly enhanced by relativistic transparency and an associated jet of super-thermal electrons. The range of parameters over which this hybrid scenario occurs is discussed and implications for ion acceleration driven by next-generation, multi-petawatt laser facilities are explored.

Variation of retention volume with molecular weight of polyethylene glycol and with carbon number of n-alkanols.

Analysis of McReynolds' data for n-alkanols on polyethylene glycols of various molecular weights shows a continuous variation in retention properties up to molecular weights greater than 6000 and probably greater than 20,000. It is concluded that polyethylene glycol used as a "standard" stationary phase should have either very high or closely controlled molecular weight. The relation between log Vg and carbon number of the alkanol is nonlinear at C4 and below with negative deviations around 10% for C2 and C3 and a positive deviation of 25% for C1.

Compact laser accelerators for X-ray phase-contrast imaging.

Advances in X-ray imaging techniques have been driven by advances in novel X-ray sources. The latest fourth-generation X-ray sources can boast large photon fluxes at unprecedented brightness. However, the large size of these facilities means that these sources are not available for everyday applications. With advances in laser plasma acceleration, electron beams can now be generated at energies comparable to those used in light sources, but in university-sized laboratories. By making use of the strong transverse focusing of plasma accelerators, bright sources of betatron radiation have been produced. Here, we demonstrate phase-contrast imaging of a biological sample for the first time by radiation generated by GeV electron beams produced by a laser accelerator. The work was performed using a greater than 300 TW laser, which allowed the energy of the synchrotron source to be extended to the 10-100 keV range.

Near-GeV acceleration of electrons by a nonlinear plasma wave driven by a self-guided laser pulse.

The acceleration of electrons to approximately 0.8 GeV has been observed in a self-injecting laser wakefield accelerator driven at a plasma density of 5.5x10(18) cm(-3) by a 10 J, 55 fs, 800 nm laser pulse in the blowout regime. The laser pulse is found to be self-guided for 1 cm (>10zR), by measurement of a single filament containing >30% of the initial laser energy at this distance. Three-dimensional particle in cell simulations show that the intensity within the guided filament is amplified beyond its initial focused value to a normalized vector potential of a0>6, thus driving a highly nonlinear plasma wave.

Herpes simplex virus type 2: epidemiology and management options in developing countries.

Genital herpes simplex virus type 2 (HSV2) is highly prevalent worldwide and an increasingly important cause of genital ulcer disease (GUD). Continued HSV2 transmission is facilitated by the large number of undiagnosed cases, the frequency of atypical disease and the occurrence of asymptomatic shedding. The lack of easy, affordable diagnostic methods and specific antiviral treatment in countries with low and middle income is of great concern, given the ability of GUD to enhance HIV transmission and acquisition. With rising HSV2 prevalence contributing to an increase in the proportion of GUD attributed to genital herpes in high-HIV prevalence settings, a safe and effective HSV vaccine is urgently needed. Meanwhile, multifaceted interventions are required to improve recognition of genital herpes, to prevent its spread and also to prevent its potential to promote HIV transmission in developing countries.

Radiological characterisation of photon radiation from ultra-high-intensity laser-plasma and nuclear interactions.

With the increasing number of multi-terawatt (10(12) W) and petawatt (10(15) W) laser interaction facilities being built, the need for a detailed understanding of the potential radiological hazards is required and their impact on personnel is of major concern. Experiments at a number of facilities are being undertaken to achieve this aim. This paper describes the recent work completed on the Vulcan petawatt laser system at the CCLRC Rutherford Appleton Laboratory, where photon doses of up to 43 mSv at 1 m per shot have been measured during commissioning studies. It also overviews the shielding in place on the facility in order to comply with the Ionising Radiation Regulations 1999 (IRR99), maintaining a dose to personnel of less than 1 mSv yr(-1) and as low as reasonably practicable (ALARP).

Travel, migration and HIV.

This is a review of recent publications on the subject of travel (taken in its widest sense) and HIV/AIDS. As with all epidemics caused by transmissible pathogens, AIDS has been seen in many countries as an imported problem. What this perspective fails to recognize is that with the explosion of international travel in the past thirty years it is virtually impossible to prevent the spread of infectious disease across international frontiers. Here we highlight the relative paucity of studies that describe or investigate the context in which sexual risk behaviour of travellers takes place, and suggest areas of further research which could increase understanding of the nature of sexual risk taking, and help in the design of health education programmes.

PIP: In this review of the current literature on the relationship between travelers and transmission or infection from the HIV virus, it is apparent that the emphasis is on the risk to travelers for contracting the infection from host countries in the developing world. This review of European, American, British, and developing country studies is reported to add to the review reported at the VIII International Conference on AIDS in 1992. Recommendations are made for future research. More research is needed on the role that travelers play in increasing the spread of HIV infection. Specifically, the sex behavior of ordinary travelers, rather than longterm travelers or expatriates, needs to be carefully examined. In order to more appropriately target health education, a greater understanding is needed of e.g, social inhibitory norms and the role played by alcohol and drug consumption. Benefits will be reaped by both the host population and tourists. Some of the early studies focused on the ethical implications of restricting an individual's travel; travel was identified as a risk factor without explaining why. Many governments were quick to blame others for the source of the infection, without considering the scapegoating and the impossibility of closing borders to international travel. Europe was quick to connect the first AIDS cases to travelers, expatriates, and returning workers. Belgian studies found that the prevalence rates among Belgian advisors and European expatriates was 1.1% and 1.9% , respectively. Dutch studies recorded slightly lower rates among expatriates returning from sub-Saharan Africa after a visit of at least 6 months. Neither study included travelers for pleasure or study, or controlled for the number of new sexual partners abroad vs. at home, or reported whether the partners were African or non-African. US studies were of similar character and included a case study of a man returning from Rwanda after an automobile accident and a prospective survey of 282 Peace Corp volunteers serving in Zaire between 1985 and 1988. British and developing country studies also found links between travelers and being HIV positive.

Liver glycogenolysis during exercise in adrenodemedullated male and female rats.

Previous studies have shown that adrenodemedullation has no effect on the rate of liver glycogenolysis during exercise in male rats. Mature female rats have been reported to have a higher hepatic beta-adrenergic receptor activity than do male rats of the same age. The present study was undertaken to determine the role of plasma epinephrine in stimulating liver glycogenolysis during exercise in female rats. Both male and female rats were adrenodemedullated or sham operated. Three weeks later rats were run for 60 min at 21 m/min up a 15% grade. The rate of liver glycogenolysis during exercise was not affected by adrenodemedullation in either female rats or male rats. Hepatic adenosine 3',5'-cyclic monophosphate increased to approximately the same extent in sham operated as in adrenodemedullated female rats during exercise. Adrenodemedullation caused a significant reduction in the amount of glycogen utilized by the soleus muscle and in the degree of hyperglycemia during exercise. We conclude that epinephrine is unessential for stimulation of liver glycogenolysis during exercise in either male or female rats.

Wave-front control of a large-aperture laser system by use of a static phase corrector.

In large-aperture, ultrahigh-intensity laser systems, such as Vulcan at the Rutherford Appleton Laboratory, one of the most important factors that determines the ultimate on-target focused intensity is the wave-front quality of the laser pulse. We report on a wave-front analysis carried out on Vulcan to determine the nature and contribution of the aberrations present in the laser pulse that effectively limited the available on-target intensity. We also report on a significant improvement to the wave-front quality that was achieved by static correction of the main aberration, resulting in an increase of focused intensities by a factor of 4.