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Biomedical subjects

P Woodruff

Publications and source records attributed to P Woodruff.

At least 19 recordsLinked to original sources
PubMed2005

Dopant radiative cooling effects in indirect-drive Ar-doped capsule implosion experiments.

We present results from simulations performed to investigate the effects of dopant radiative cooling in inertial confinement fusion indirect-drive capsule implosion experiments. Using a one-dimensional radiation-hydrodynamics code that includes inline collisional-radiative modeling, we compute in detail the non-local thermodynamic equilibrium atomic kinetics and spectral characteristics for Ar-doped DD fuel. Specifically, we present results from a series of calculations in which the concentration of the Ar is varied, and examine the sensitivity of the fuel conditions (e.g., electron temperature) and neutron yield to the Ar dopant concentration. Simulation results are compared with data obtained in OMEGA indirect-drive experiments in which monochromatic imaging and spectral measurements of Ar Hebeta and Lybeta line emission were recorded. The incident radiation drive on the capsule is computed with a three-dimensional view factor code using the laser beam pointings and powers from the OMEGA experiments. We also examine the sensitivity of the calculated compressed core electron temperatures and neutron yields to the radiation drive on the capsule and to the radiation and atomic modeling in the simulations.

Journal Article↗
PubMed2003

Cerebral tissue alterations and daily life stress experience in psychosis.

OBJECTIVE: To examine whether the total volumes of cerebrospinal fluid (CSF), cerebral grey matter and white matter were correlated with the experience of environmental stress in daily life situations. METHOD: Twenty-seven patients with psychosis underwent magnetic resonance imaging scanning and a random time-sampling self-assessment technique (Experience Sampling Method) to determine subjective daily life stress experiences. Total cerebral tissue volumes were derived from an automated segmentation procedure. RESULTS: CSF volume was positively associated with daily life event-related stress (beta=0.016, P=0.002), while the association with total white matter was negative (beta=-0.013, P=0.005). The effects were independent of each other and of total cerebral volume and other confounders. No large or significant association was found with grey matter volume. CONCLUSION: Subjective stress experience in daily life is associated with increased CSF and reduced white matter volumes in patients with psychosis, suggesting functional significance of these cerebral measures.

Adolescent↗
PubMed2002

X-ray absorption spectroscopy measurements of thin foil heating by Z-pinch radiation.

Absorption spectroscopy measurements of the time-dependent heating of thin foils exposed to intense z-pinch radiation sources are presented. These measurements and their analysis provide valuable benchmarks for, and insights into, the radiative heating of matter by x-ray sources. Z-pinch radiation sources with peak powers of up to 160 TW radiatively heated thin plastic-tamped aluminum foils to temperatures approximately 60 eV. The foils were located in open slots at the boundary of z-pinch hohlraums surrounding the pinch. Time-resolved Kalpha satellite absorption spectroscopy was used to measure the evolution of the Al ionization distribution, using a geometry in which the pinch served as the backlighter. The time-dependent pinch radius and x-ray power were monitored using framing camera, x-ray diode array, and bolometer measurements. A three-dimensional view factor code, within which one-dimensional (1D) radiation-hydrodynamics calculations were performed for each surface element in the view factor grid, was used to compute the incident and reemitted radiation flux distribution throughout the hohlraum and across the foil surface. Simulated absorption spectra were then generated by postprocessing radiation-hydrodynamics results for the foil heating using a 1D collisional-radiative code. Our simulated results were found to be in good general agreement with experimental x-ray spectra, indicating that the spectral measurements are consistent with independent measurements of the pinch power. We also discuss the sensitivity of our results to the spectrum of the radiation field incident on the foil, and the role of nonlocal thermodynamic equilibrium atomic kinetics in affecting the spectra.

Journal Article↗
PubMed2001

Deep venous thrombosis in postoperative vascular surgical patients: a frequent finding without prophylaxis.

PURPOSE: The place of routine perioperative thromboprophylaxis for vascular surgical patients remains controversial, because the incidence of postoperative deep venous thrombosis (DVT) is said to be quite low. This study was designed to measure the incidence of lower limb DVT after vascular surgical procedures. METHODS: All consenting, consecutive patients who came to a metropolitan veterans hospital for abdominal or lower-limb arterial surgery were studied. Clinical and operative data were recorded. Lower-limb color flow duplex scans were performed before and after surgery. RESULTS: Fifty patients, age 75 +/- 1 (mean +/- SEM) years, were studied. Abdominal procedures were performed on 22 patients, and lower-limb procedures were performed on 28 patients. A postoperative DVT was noted in 14 patients (32%), 9 patients (41%) in the abdominal surgical group and 5 patients (18%) in the lower-limb group. Calf DVTs were four times more common than femoropopliteal DVTs. CONCLUSION: The incidence of postoperative lower-limb DVTs in this cohort of vascular surgical patients was high. The small size of the study population precludes generalized recommendations, but the results indicate an urgent need for definitive investigation.

Abdomen↗
PubMed2000

Cortical activity during rotational and linear transformations.

Neuroimaging studies of cortical activation during image transformation tasks have shown that mental rotation may rely on similar brain regions as those underlying visual perceptual mechanisms. The V5 complex, which is specialised for visual motion, is one region that has been implicated. We used functional magnetic resonance imaging (fMRI) to investigate rotational and linear transformation of stimuli. Areas of significant brain activation were identified for each of the primary mental transformation tasks in contrast to its own perceptual reference task which was cognitively matched in all respects except for the variable of interest. Analysis of group data for perception of rotational and linear motion showed activation in areas corresponding to V5 as defined in earlier studies. Both rotational and linear mental transformations activated Brodman Area (BA) 19 but did not activate V5. An area within the inferior temporal gyrus, representing an inferior satellite area of V5, was activated by both the rotational perception and rotational transformation tasks, but showed no activation in response to linear motion perception or transformation. The findings demonstrate the extent to which neural substrates for image transformation and perception overlap and are distinct as well as revealing functional specialisation within perception and transformation processing systems.

Adult↗
PubMed2000

Early experience with clinical indicators in surgery.

BACKGROUND: In 1997 a set of 53 clinical indicators developed by the Royal Australasian College of Surgeons (RACS) and the Australian Council on Healthcare Standards (ACHS) Care Evaluation Programme (CEP), was introduced into the ACHS Evaluation and Quality Improvement Programme (EQuIP). The clinical indicators covered 20 different conditions or procedures for eight specialty groups and were designed to act as flags to possible problems in surgical care. METHODS: The development process took several years and included a literature review, field testing, and revision of the indicators prior to approval by the College council. In their first year 155 health-care organizations (HCO) addressed the indicators and this rose to 210 in 1998. Data were received from all states and both public and private facilities. RESULTS: The collected data for 1997 and 1998 for some of the indicators revealed rates which were comparable with those reported in the international literature. For example, the rates of bile duct injury in laparoscopic cholecystectomy were 0.7 and 0.53%, respectively; the mortality rates for coronary artery graft surgery were 2.5 and 2.1%, respectively; the mortality rates after elective abdominal aortic aneurysm repair were 2.5 and 3.7%, respectively; and the post-tonsillectomy reactionary haemorrhage rates were 0.9 and 1.3%, respectively. Results for some indicators differed appreciably from other reports, flagging the need for further investigation; for example, the negative histology rates for appendectomy in children were 18.6 and 21.2%, respectively, and the rates for completeness of excision of malignant skin tumours were 90.7 and 90%, respectively. The significance of these figures, however, depends upon validation of the data and their reliability and reproducibility. Because reliability can be finally determined only at the hospital level they are of limited value for broader comparison. CONCLUSION: The process of review established for the indicator set has led to refinement of some indicators through improvement of definitions, and to a considerable reduction in the number of indicators to 29 (covering 18 procedures), for the second version of the indicators (which was introduced for use from January 1999). The clinical indicator programme, as it has with other disciplines, hopefully will provide a stimulus to the modification and improvement of surgical practice. Clinician ownership should enhance the collection of reliable data and hence their usefulness.

Biomarkers↗
PubMed1999

Lap belt abdominal aortic trauma.

A case of vehicle accident trauma to the abdominal aorta in a patient wearing a lap-type seat belt is presented, together with its diagnosis and management. The role of the radiologist is emphasized.

Abdominal Injuries↗
PubMed1998

The anatomy of conscious vision: an fMRI study of visual hallucinations.

Despite recent advances in functional neuroimaging, the apparently simple question of how and where we see--the neurobiology of visual consciousness--continues to challenge neuroscientists. Without a method to differentiate neural processing specific to consciousness from unconscious afferent sensory signals, the issue has been difficult to resolve experimentally. Here we use functional magnetic resonance imaging (fMRI) to study patients with the Charles Bonnet syndrome, for whom visual perception and sensory input have become dissociated. We found that hallucinations of color, faces, textures and objects correlate with cerebral activity in ventral extrastriate visual cortex, that the content of the hallucinations reflects the functional specializations of the region and that patients who hallucinate have increased ventral extrastriate activity, which persists between hallucinations.

Brain Mapping↗
PubMed1998

First episodes of psychosis in Afro-Caribbean and White people. An 18-year follow-up population-based study.

BACKGROUND: There have been few prospective studies of the long-term outcome of psychosis in people of Afro-Caribbean origin in the UK. METHOD: We followed-up a population-based, consecutive series of 34 Afro-Caribbean and 54 White people with psychosis who had been extensively investigated during their first admission in 1973/74. Diagnoses were made by direct interview using the Present State Examination at both first admission and follow-up. RESULTS: Ninety-seven percent of the original sample were traced. A slightly greater proportion of the Afro-Caribbean people were assigned to the S+ Catego class (schizophrenia), both on first assessment and at follow-up. No difference was found between the two groups in the consistency of diagnosis over the 18 years or in the proportion of patients considered psychotic but Afro-Caribbean people tended to have fewer negative symptoms at follow-up. There were striking differences between the two groups in their experience of psychiatric care; Afro-Caribbean people were more likely to have been readmitted, to have experienced longer hospitalisations, and to have undergone more involuntary admissions than their White counterparts. CONCLUSIONS: Afro-Caribbean people who met clinical and research criteria for schizophrenia had a less satisfactory experience of, and response to, psychiatric care over 18 years than their White counterparts.

Adolescent↗
PubMed1995

Neural correlates of working memory in a visual letter monitoring task: an fMRI study.

Complex mental operations rely on the coordinated activity of widely distributed brain regions constituting neurocognitive networks. Using multislice echoplanar functional magnetic resonance imaging (fMRI) we have contrasted regional brain activity during a control and an experimental condition which differed with respect to the demands placed on verbal working memory. Subjects were seven right-handed healthy male volunteers. Analysis of group and individual data revealed activation in the anterior and posterior parasagittal cortex in all subjects, left parietal cortex (six subjects) and left dorsolateral prefontal cortex (five subjects). These results suggest that verbal working memory is subserved by a neurocognitive network comprising cortical regions involved in attention, executive function and short term mnemonic processes.

Adult↗
PubMed1995

Activation of area V5 by visual perception of motion demonstrated with echoplanar MR imaging.

Cortical activation in visual association areas known to be responsible for the perception of motion was investigated in two volunteers who viewed a projected animated cartoon periodically "run" and "frozen" during collection of echoplanar MR images. Ten axial, contiguous, 5 mm thick, T2-weighted, gradient-echo images (TE 40 ms, TR 3000 ms) depicting BOLD contrast were acquired through the occipital lobe using a GE Signa 1.5 T system with an advanced NMR operating console. Images were analysed by time series regression modelling estimating power in the MR signal at the ON-OFF frequency of motion. Highly significant activation in response to motion perception was identified in both subjects bilaterally in area V5.

Echo-Planar Imaging↗
PubMed1990

Selective expression of Purkinje-cell antigens in tumor tissue from patients with paraneoplastic cerebellar degeneration.

Paraneoplastic cerebellar degeneration is a rare syndrome that occurs in patients with gynecologic cancer and is characterized by widespread loss of Purkinje cells. To determine whether Purkinje-cell antigens are selectively expressed in the tumors of patients with the syndrome, we examined tumor tissue from 10 patients whose serum contained anti-Purkinje-cell (anti-Yo) antibodies. The origins of the cancers were the breast (five patients), ovary (three), endometrium (one), and fallopian tube (one). We used as controls tumor tissue from 11 patients with ovarian cancer and 10 patients with breast cancer who were neurologically normal. Using immunohistochemical and Western blot analysis, we found that Purkinje-cell antigens were expressed in all the tumors from the 10 patients with paraneoplastic cerebellar degeneration but in none of the tumors from the 21 neurologically normal patients. When IgG from patients with paraneoplastic cerebellar degeneration was affinity-purified to cerebellar Purkinje-cell antigen, immunohistochemical analysis showed that it reacted specifically with the tumor tissue from those patients. We conclude that in patients with paraneoplastic cerebellar degeneration, the anti-Yo antibody results from an immune response to neural antigens expressed by the gynecologic tumors in the patients.

Antigens, Neoplasm↗
PubMed1984

Tear and rupture of elastomeric dental impression materials.

The curing time dependence of the tear energy, tensile strength and ultimate extension ratio of a range of characterized elastomeric impression materials was investigated. This variation of tensile strength and ultimate extension ratio was correlated with the development of the network structure. The tear energy showed only minor changes as the curing proceeded.

Dental Impression Materials↗