Biomedical subjects

R Allott

Publications and source records attributed to R Allott.

8 recordsLinked to original sources

PubMed2002

Measurements of relativistic self-phase-modulation in plasma.

We report the first systematic observations of relativistic self-phase-modulation (RSPM) due to the interaction of a high intensity laser pulse with plasma. The plasma was produced in front of a solid target by the prepulse of a 100 TW laser beam. RSPM was observed by monitoring the spectrum of the harmonics generated by the intense laser pulse during the interaction. The multipeaked broadened spectral structure produced by RSPM was studied in plasmas with different density scale lengths for laser interactions at intensities up to 3.0 x 10(19) W cm(-2) (a=p(osc)/m(e)c=4.7). The results are compared with calculated spectra and agreement is obtained.

Journal Article↗

PubMed2001

Observation of a hot high-current electron beam from a self-modulated laser wakefield accelerator.

A highly relativistic electron beam produced by a 50 TW laser-plasma accelerator has been characterized by photonuclear techniques. The beam has large divergence that increases with plasma density. The electron yield also increases with plasma density and reaches up to 4x10(11) electrons ( >10 MeV), with beam current approaching the Alfvén limit. Effective electron temperatures exceeding 8 MeV are found, leading to an order of magnitude higher photonuclear activation yield than in solid target experiments with the same laser system.

Journal Article↗

PubMed2001

Improving general practitioners' assessment and management of suicide risk.

Standards for assessing and managing suicide risk were developed and incorporated into a guidance manual for general practitioners. The effects of the manual on opinions and practice were evaluated using a quasi-experimental controlled before/after design, comparing participating general practitioners with others who did not use the manual. Thirty four general practitioners participated over a six-month period. The intervention group showed changes in perceptions, with increased satisfaction with their own methods and in their recognition and assessment of suicide risk. Their practice changed, with increased recording of relevant factors in notes. The comparison group did not change in these ways. It is concluded that general practitioners' practice and opinions in assessing and managing suicide risk were significantly improved using a minimal intervention. Given the importance of the topic and the small size of this study, further research is needed, examining changes in professional practice, knowledge and attitudes.

Affective Symptoms↗

PubMed2000

Effect of the plasma density scale length on the direction of fast electrons in relativistic laser-solid interactions

The angular distribution of bremsstrahlung gamma rays produced by fast electrons accelerated in relativistic laser-solid interaction has been studied by photoneutron activation in copper. We show that the gamma-ray beam moves from the target normal to the direction of the k(laser) vector as the scale length is increased. Similar behavior is found also in 2D particle-in-cell simulations.

Journal Article↗

PubMed2000

Photonuclear physics when a multiterawatt laser pulse interacts with solid targets

When a laser pulse of intensity 10(19) W cm(-2) interacts with solid targets, electrons of energies of some tens of MeV are produced. In a tantalum target, the electrons generate an intense highly directional gamma-ray beam that can be used to carry out photonuclear reactions. The isotopes 11C, 38K, (62,64)Cu, 63Zn, 106Ag, 140Pr, and 180Ta have been produced by (gamma,n) reactions using the VULCAN laser beam. In addition, laser-induced nuclear fission in 238U has been demonstrated, a process which was theoretically predicted at such laser intensities more than ten years ago. The ratio of the 11C and the 62Cu beta(+) activities yields shot-by-shot temperatures of the suprathermal electrons at laser intensities of approximately 10(19) W cm(-2).

Journal Article↗

PubMed1999

The development and evaluation of a brief risk screening instrument for the psychiatric inpatient setting.

This paper reports on the development and evaluation of a risk screening instrument (RSI) intended for use by nursing staff on general acute psychiatric admission wards. The RSI comprised six questions concerning patient status on admission (e.g. sex, legal status, employment) and 11 items of judgement concerning the presentation of the patient (e.g. threatening behaviour, suicidality, family and social support). The interrater reliability of the RSI was calculated to be 85% overall. The predictive value of the RSI was not confirmed when tested against harmful incidents subsequent to admission. However, the mean RSI score of that group of patients involved in harmful incidents tended to be higher than that group of patients not involved in such incidents, and all such incidents were found to occur within eight days of admission. Analysis of other data collected in the course of the study revealed discrete patient groups and provided systematic insights into their characteristics, which are potentially valuable when considering the nursing skills required on acute psychiatric inpatient units. It is concluded that the RSI tested has the potential to contribute to the assessment and management of risk within the acute psychiatric inpatient setting, by augmenting and guiding clinical judgement.

Adolescent↗

PubMed1999

Drug education: a review of British Government policy and evidence on effectiveness.

British Government policy on drugs primary prevention is outlined and principal recommendations are identified. The review is organized under the four main providers: police, teachers, peers and parents. Current methods are reviewed within a British policy framework with a focus on British programmes which have been evaluated. Most programmes use a combination of information, resistance or life skills training and normative education. Evaluative research suggests these methods are generally most effective. The police have achieved a community-wide approach, teachers have managed to integrate drug education into the National Curriculum, peer approaches have considered the needs of their target audience and parent approaches have recruited influential educators. However, more evaluative research is required before we can identify which particular programmes are most effective in reducing drug use.

Adolescent↗

PubMed1994

Lymphocyte microsomal epoxide hydrolase in patients on carbamazepine therapy.

1. In order to determine whether carbamazepine is an inducer of lymphocyte microsomal epoxide hydrolase, the activity of the enzyme has been measured in the lymphocytes of 40 patients on continuous drug therapy using [3H]-cis stilbene oxide as a substrate. 2. Induction of the cytochrome P450 isoform, CYP3A, has been assessed in the same patients by measurement of the 24 h urinary excretion of 6 beta-hydroxycortisol by radioimmunoassay. The urinary concentrations of carbamazepine and its two metabolites, the 10,11-epoxide and trans-dihydrodiol, have also been measured by h.p.l.c. 3. The 24 h urinary 6 beta-hydroxycortisol excretion in the patients increased with the dose of carbamazepine (r = 0.57, P < 0.001) indicating induction of CYP3A. 4. The total amount of trans-dihydrodiol excreted in the urine increased with the dose of carbamazepine, and it was the most abundant urinary metabolite in all patients and at all dose-levels. There was no relationship between the dose of carbamazepine and the diol to epoxide ratio (r = 0.01, NS). 5. Lymphocyte microsomal epoxide hydrolase activity was marginally, but significantly (P = 0.02) higher in the patients (28.4 pmol diol min-1 mg-1 protein) than in drug-free controls (23.4 pmol diol min-1 mg-1 protein (95% CI for difference -9 to -0.8)). 6. The results indicate that at concentrations of carbamazepine which produce marked induction of hepatic CYP3A, an enzyme involved in the metabolism and bioactivation of carbamazepine, there is only a slight increase in lymphocyte microsomal epoxide hydrolase.

Adolescent↗