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A Parsons

Publications and source records attributed to A Parsons.

At least 19 recordsLinked to original sources
PubMed2005

A link between prompt optical and prompt gamma-ray emission in gamma-ray bursts.

The prompt optical emission that arrives with the gamma-rays from a cosmic gamma-ray burst (GRB) is a signature of the engine powering the burst, the properties of the ultra-relativistic ejecta of the explosion, and the ejecta's interactions with the surroundings. Until now, only GRB 990123 had been detected at optical wavelengths during the burst phase. Its prompt optical emission was variable and uncorrelated with the prompt gamma-ray emission, suggesting that the optical emission was generated by a reverse shock arising from the ejecta's collision with surrounding material. Here we report prompt optical emission from GRB 041219a. It is variable and correlated with the prompt gamma-rays, indicating a common origin for the optical light and the gamma-rays. Within the context of the standard fireball model of GRBs, we attribute this new optical component to internal shocks driven into the burst ejecta by variations of the inner engine. The correlated optical emission is a direct probe of the jet isolated from the medium. The timing of the uncorrelated optical emission is strongly dependent on the nature of the medium.

Journal Article↗
PubMed2005

An infrared flash contemporaneous with the gamma-rays of GRB 041219a.

The explosion that results in a cosmic gamma-ray burst (GRB) is thought to produce emission from two physical processes: the central engine gives rise to the high-energy emission of the burst through internal shocking, and the subsequent interaction of the flow with the external environment produces long-wavelength afterglows. Although observations of afterglows continue to refine our understanding of GRB progenitors and relativistic shocks, gamma-ray observations alone have not yielded a clear picture of the origin of the prompt emission nor details of the central engine. Only one concurrent visible-light transient has been found and it was associated with emission from an external shock. Here we report the discovery of infrared emission contemporaneous with a GRB, beginning 7.2 minutes after the onset of GRB 041219a (ref. 8). We acquired 21 images during the active phase of the burst, yielding early multi-colour observations. Our analysis of the initial infrared pulse suggests an origin consistent with internal shocks.

Journal Article↗
PubMed2005

A giant gamma-ray flare from the magnetar SGR 1806-20.

Two classes of rotating neutron stars-soft gamma-ray repeaters (SGRs) and anomalous X-ray pulsars-are magnetars, whose X-ray emission is powered by a very strong magnetic field (B approximately 10(15) G). SGRs occasionally become 'active', producing many short X-ray bursts. Extremely rarely, an SGR emits a giant flare with a total energy about a thousand times higher than in a typical burst. Here we report that SGR 1806-20 emitted a giant flare on 27 December 2004. The total (isotropic) flare energy is 2 x 10(46) erg, which is about a hundred times higher than the other two previously observed giant flares. The energy release probably occurred during a catastrophic reconfiguration of the neutron star's magnetic field. If the event had occurred at a larger distance, but within 40 megaparsecs, it would have resembled a short, hard gamma-ray burst, suggesting that flares from extragalactic SGRs may form a subclass of such bursts.

Journal Article↗
PubMed2005

Ultrasound biomicroscopy in the management of melanocytoma of the ciliary body with extrascleral extension.

AIM: To demonstrate the ultrasound biomicroscopic features of a ciliary body melanocytoma with extrascleral extension, and a conservative approach in its management. METHOD: Observational case reports. Two cases of ciliary body melanocytoma were suspected at presentation, confirmed histologically by biopsy, and subsequently monitored for change by serial ultrasound biomicroscopic imaging. The main outcome measures were anatomical and functional preservation of the eye, with avoidance of formal surgical excision. RESULTS: Ultrasound biomicroscopy allows clear visualisation of the tumours, and the ultrasound characteristic is of low homogeneous internal reflectivity. 5 year follow up with observation only demonstrates success with this conservative management approach. Histopathological evaluation confirmed melanocytoma. CONCLUSIONS: Melanocytoma is a rare tumour. However if considered in the differential diagnosis at presentation and confirmed histologically, further management with use of the ultrasound biomicroscope as an accurate mode of imaging is an acceptable technique for preservation of the eye and avoids surgical excision.

Aged↗
PubMed2005

Factors related to the process of seeking and completing treatment for drug abuse (qualitative methods in drug abuse research).

Numerous studies have demonstrated the effectiveness of drug abuse treatment. Yet many drug abusers do not enter treatment, many who do enter leave prematurely, and relapse following treatment is common. Understanding motivation for change and treatment readiness is key to understanding how to induct and engage drug users in treatment. To the extent that treatment programs focus initially on reducing drug use, rather than psychosocial problems that motivate individuals to seek treatment, treatment programs may fail to meet the primary needs of users and thus fail to attract or engage them. Outcomes of substance abuse treatment programs historically have been measured by successful program completion, reduced drug use and illegal activity, and improved social functioning (employment, education etc). There is minimal reference to client expectations of treatment and factors that influenced treatment-seeking behavior. Studies that have assessed client dropout from substance abuse treatment have generally focused upon quantitative measures that attempt to determine what types of clients drop out or stay, or what types of characteristics best predict client dropout. Qualitative methods are the most appropriate to fill these gaps in substance abuse treatment research.

Humans↗
PubMed2003

Effect of raloxifene on sexual function in postmenopausal women.

OBJECTIVE: To determine the effects of raloxifene on sexual function in postmenopausal women with pre-existing vaginal atrophy treated with vaginal estrogen cream. METHODS: A total of 187 naturally postmenopausal women, 42-80 years of age, with signs of genitourinary atrophy were enrolled in this 6-month, multicenter, parallel-group study. Subjects were randomized to oral raloxifene HCl 60 mg daily or matching placebo; the same subjects were also randomized to receive one application of either vaginal conjugated estrogen cream 0.5 g twice weekly for 6 months or non-hormonal vaginal moisturizer twice weekly for 3 months, followed by conjugated estrogen cream for 3 months. Both investigators and subjects were masked to the identity of the oral medication. The vaginal preparations were administered in an open-label fashion. The Sexual Activity Questionnaire (SAQ) was administered at baseline and at 3 and 6 months. Safety was assessed throughout the study. RESULTS: A total of 102 women were sexually active at baseline and, of these, 82 were also sexually active at the 6-month end-point. At 6 months, raloxifene and placebo, in the presence of vaginal conjugated estrogen cream, were both associated with improvement from baseline in vaginal dryness and reduced discomfort during sexual activity. There were no significant differences between raloxifene and placebo groups in any SAQ item. Enjoyment of sexual activity significantly increased from baseline with raloxifene but not with placebo. No difference in adverse events was observed between groups. CONCLUSION: Raloxifene had no negative effects on sexual function in postmenopausal women with vaginal atrophy who were treated concomitantly with vaginal estrogen cream.

Administration, Intravaginal↗
PubMed2002

Quantitative neuropathological analysis of sudden infant death syndrome.

Detailed stereological analyses of specific regions of brains of children who had died from Sudden Infant Death Syndrome (SIDS) was undertaken to determine whether global evidence of an underlying pathology exists, contributing to an increased susceptibility to SIDS. A significant reduction in the total number of neocortical neurones and neurone volume was observed in SIDS normal birth weight (NBW) infants in comparison to controls. A significant reduction in both volume and total neurone number were also noted in the dorsal motor nucleus of the vagus in SIDS NBW group when compared with controls. Anomalies in regions of the brain involved with cardiorespiratory control (brainstem) and arousal (brainstem and neocortex) may play a crucial role in the chain of events resulting in a SIDS event.

Brain Stem↗
PubMed2001

Intracellular drug delivery using low-frequency ultrasound: quantification of molecular uptake and cell viability.

PURPOSE: To determine the dependence on acoustic parameters of molecular uptake and viability of cells exposed to low-frequency ultrasound. METHODS: DU145 prostate cancer cells bathed in a solution of calcein were exposed to ultrasound at 24 kHz over a range of different acoustic pressures. exposure times, pulse lengths, and duty cycles. Flow cytometry was employed to quantify the number of calcein molecules delivered into each cell and levels of cell viability. RESULTS: Both molecular uptake and cell viability showed a strong dependence on acoustic pressure and exposure time, weak dependence on pulse length, and no significant dependence on duty cycle. When all of the data were pooled together, they exhibited good correlation with acoustic energy exposure. Although molecular uptake showed large cell-to-cell heterogeneity, up to approximately 15% of cells achieved an intracellular calcein concentration approximately equal to its extracellular concentration. CONCLUSIONS: Large numbers of molecules can be delivered intracellularly using low-frequency ultrasound. Both uptake and viability correlate with acoustic energy, which is useful for design and control of ultrasound protocols.

Cell Membrane↗
PubMed2001

Nitric oxide potentiates response of trigeminal neurones to dural or facial stimulation in the rat.

Infusing glyceryl trinitrate as a donor molecule, we have used electrophysiological and c-fos immunostaining techniques to study the effects of nitric oxide on neurones in the nucleus trigeminalis caudalis. Following infusion of glyceryl trinitrate, responses of neurones to electrical stimulation of periorbital cutaneous afferents were potentiated and threshold for activation of neurones by stimulation of dural afferents was reduced. Expression of c-fos was unchanged by glyceryl trinitrate compared to saline controls. Intradermal injection of capsaicin in the periorbital area increased c-fos expression in nucleus trigeminalis caudalis; this was significantly potentiated by glyceryl trinitrate. These results suggest that, in the anaesthetized rat, glyceryl trinitrate alone may not acutely activate the trigeminovascular system to a significant degree at doses that cause headache and later trigger migraine headache in migraineurs. Nevertheless, it is susceptible to exogenous nitric oxide in that activation of trigeminal neurones through cutaneous or dural pathways is potentiated. This may in some measure underlie the pathogenesis of migraine headache.

Afferent Pathways↗
PubMed1999

A common variant of the endothelial nitric oxide synthase (Glu298-->Asp) is a major risk factor for coronary artery disease in the UK.

BACKGROUND: Endothelium-derived nitric oxide (NO) is synthesised from L-arginine by endothelial nitric oxide synthase (eNOS) encoded by the NOS 3 gene on chromosome 7. Because reduced NO synthesis has been implicated in the development of coronary atherosclerosis, which has a heritable component, we hypothesised that polymorphisms of NOS 3 might be associated with increased susceptibility to this disorder. METHODS AND RESULTS: Single-strand conformation polymorphism analysis of NOS 3 identified a G-->T polymorphism in exon 7 of the gene which encodes a Glu-->Asp amino acid substitution at residue 298 of eNOS. We investigated the relationship between this Glu(298)-->Asp variant and atherosclerotic coronary artery disease (CAD) using 2 independent case-controlled studies. In the first study (CHAOS), cases consisted of 298 unrelated patients with positive coronary angiograms and controls were 138 unrelated healthy individuals ascertained through a population health screen. In the second study (CHAOS II), the cases were 249 patients with recent myocardial infarction (MI), and a further 183 unrelated controls. There was an excess of homozygotes for the Asp298 variant among patients with angiographic CAD, and among patients with recent MI when compared with their respective controls (35.9% versus 10.2%, P<0.0001 in CHAOS, and 18.1% versus 8.7%, P<0.02 in CHAOS II). In comparison to Glu(298) homozygotes, homozygosity for Asp(298) was associated with an odds ratio of 4.2 (95% CI, 2.3 to 7.9) for angiographic CAD and 2.5 (95% CI, 1.3 to 4.2) for MI. CONCLUSIONS: Homozygosity for a common NOS 3 polymorphism (894 G-->T) which encodes a Glu298-->Asp amino acid substitution in eNOS is a risk factor for angiographic CAD and recent MI in this population.

Aged↗
PubMed1996

Randomised controlled trial of vitamin E in patients with coronary disease: Cambridge Heart Antioxidant Study (CHAOS)

BACKGROUND: Vitamin E (alpha-tocopherol) is thought to have a role in prevention of atherosclerosis, through inhibition of oxidation of low-density lipoprotein. Some epidemiological studies have shown an association between high dietary intake or high serum concentrations of alpha-tocopherol and lower rates of ischaemic heart disease. We tested the hypothesis that treatment with a high dose of alpha-tocopherol would reduce subsequent risk of myocardial infarction (MI) and cardiovascular death in patients with established ischaemic heart disease. METHODS: In this double-blind, placebo-controlled study with stratified randomisation, 2002 patients with angiographically proven coronary atherosclerosis were enrolled and followed up for a median of 510 days (range 3-981). 1035 patients were assigned alpha-tocopherol (capsules containing 800 IU daily for first 546 patients; 400 IU daily for remainder); 967 received identical placebo capsules. The primary endpoints were a combination of cardiovascular death and non-fatal MI as well as non-fatal MI alone. FINDINGS: Plasma alpha-tocopherol concentrations (measured in subsets of patients) rose in the actively treated group (from baseline mean 34.2 micromol/L to 51.1 micromol/L with 400 IU daily and 64.5 micromol/L with 800 IU daily) but did not change in the placebo group. Alpha-tocopherol treatment significantly reduced the risk of the primary trial endpoint of cardiovascular death and non-fatal MI (41 vs 64 events; relative risk 0.53 [95% Cl 0.34-0.83; p=0.005). The beneficial effects on this composite endpoint were due to a significant reduction in the risk of non-fatal MI (14 vs 41; 0.23 [0.11-0.47]; p=0.005); however, there was a non-significant excess of cardiovascular deaths in the alpha-tocopherol group (27 vs 23; 1.18 [0.62-2.27]; p=0.61). All-cause mortality was 36 of 1035 alpha-tocopherol-treated patients and 27 of 967 placebo recipients. INTERPRETATION: We conclude that in patients with angiographically proven symptomatic coronary atherosclerosis, alpha-tocopherol treatment substantially reduces the rate of non-fatal MI, with beneficial effects apparent after 1 year of treatment. The effect of alpha-tocopherol treatment on cardiovascular deaths requires further study.

Coronary Artery Disease↗
PubMed1996

Sonohysterographic imaging of the endometrial cavity.

Vaginal ultrasound is the most effective method of imaging the contents of the true pelvis in the female. Saline influsion sonohysterography (SIS) is a simple refinement of the standard vaginal sonographic exam. Here, we briefly describe and demonstrate our use of this latter technique.

Endometrial Neoplasms↗