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Biomedical subjects

D Whittaker

Publications and source records attributed to D Whittaker.

At least 19 recordsLinked to original sources
PubMed2006

Opacity measurements of a hot iron plasma using an x-ray laser.

The temporal evolution of the opacity of an iron plasma at high temperature (30-350 eV) and high density (0.001-0.2 g cm-3) has been measured using a nickel-like silver x-ray laser at 13.9 nm. The hot dense iron plasma was created in a thin (50 nm) iron layer buried 80 nm below the surface in a plastic target that was heated using a separate 80 ps pulse of 6-9 J, focused to a 100 microm diameter spot. The experimental opacities are compared with opacities evaluated from plasma conditions predicted using a fluid and atomic physics code.

Journal Article↗
PubMed2006

Dissecting the regulation of fructan metabolism in perennial ryegrass (Lolium perenne) with quantitative trait locus mapping.

Quantitative trait locus (QTL) mapping, which can be a useful tool for dissecting complex traits, has been used here to study the regulation of fructan metabolism in temperate forage grasses. An F2 mapping family, derived from a high water-soluble carbohydrate (WSC) x low WSC cross, was used to map fructans and the other components of WSC (sucrose, glucose and fructose) in leaves and tiller bases of perennial ryegrass (Lolium perenne) in spring and autumn. To characterize regions of the genome that control basic carbohydrate metabolism, a strategy to minimize the impact of genotype (G) x environment (E), and E-effects on the characterization of G-effects, was adopted. Most traits were highly variable within the family. There was also considerable year-to-year environmental variation. However, significant genetic effects were detected, and several traits had high broad-sense heritability. QTL were identified on chromosomes 1, 2, 5 and 6. Leaf and tiller base QTL did not coincide. Individual QTL explained between 8 and 59% of the total phenotypic variation in the traits. Fructan turnover, metabolism and their genetic control, and the effect of environment, are discussed in the context of the results.

Biomarkers↗
PubMed2003

Sexual behaviour of lesbians and bisexual women.

OBJECTIVES: To provide data about the sexual histories of a large sample of lesbians and bisexual women, to inform those who provide health care or carry out research with women who may be sexually active with other women. DESIGN: Cross sectional survey. SETTING/SUBJECTS: 803 lesbians and bisexual women attending, as new patients, lesbian sexual health clinics, and 415 lesbians and bisexual women from a community sample. MAIN OUTCOME MEASURES: Self reported sexual history and sexual practice with both male and female partners. RESULTS: 98% of the whole sample gave a history of sexual activity with women, 83% within the past year, with a median of one female partner in that year. 85% of the sample reported sexual activity with men; for most (70%) this was 4 or more years ago. First sexual experience tended to be with a man (median 18 years old), with first sexual experience with a woman a few years later (median 21 years). Oral sex, vaginal penetration with fingers, and mutual masturbation were the most commonly reported sexual practices between women. Vaginal penetration with penis or fingers and mutual masturbation were the most commonly reported sexual activities with men. CONCLUSIONS: These data from the largest UK survey of sexual behaviour between women to date demonstrate that lesbians and bisexual women may have varied sexual histories with both male and female partners. A non-judgmental manner and careful sexual history taking without making assumptions should help clinicians to avoid misunderstandings, and to offer appropriate sexual health advice to lesbians and bisexual women.

Adolescent↗
PubMed2000

Toward an Understanding of Norm Prevalence: A Comparative Analysis of 20 Years of Research.

/ Norms are defined as evaluative standards regarding individual behavior or conditions in a given context. They define what behavior should be, rather than actual behavior. Norm prevalence refers to the proportion of individuals in a population who can articulate a norm in a given evaluation context. This paper empirically examines the prevalence of encounter norms in 56 evaluation contexts. Data for this comparative analysis were obtained from 30 studies that used a single-item question asking recreationists to indicate the highest number of encounters they would tolerate before the experience changed. Four predictor variables were examined: (1) type of resource, (2) type of activity, (3) type of encounter, and (4) question response format. As anticipated, norm prevalence varied by type of resource (backcountry or frontcountry), type of encounter (no conflict versus conflict), and question response format (two-category implicit, two-category explicit, and three-category). These three independent variables explained 64% of the variance in norm prevalence. Also as hypothesized, there was no relationship between type of activity (consumptive or nonconsumptive) and norm prevalence. Implications for future research and management are discussed; it is argued that prevalence is an important characteristic of social norms.

Journal Article↗
PubMed1995

Cross-resistance studies on two K562 sublines resistant to diaziridinylbenzoquinones.

Two resistant K562 sublines have been developed by treatment with AZQ (2,5-bis(carboethoxyamino)-3,6-diaziridinyl-1,4-benzoquinone) and BZQ (2,5-bis(2-hydroxyethylamino)-3,6-diaziridinyl-1,4-benzoquinone). The ID50 values of for AZQ on K562, the AZQ-resistant sublines (AZQR) and the BZQ-resistant sublines (BZQR) were 0.063, 1.47 and 0.244 microM, respectively. The relative ID50 values for BZQ on the same cell lines were 0.2, 0.67 and 0.83 microM, respectively. Although it is generally believed that these two quinones function by different mechanisms, the two sublines have similar decreased levels of cytochrome P-450 reductase and DT-diaphorase and increased levels of glutathione and superoxide dismutase, compared to the parent cell line. The sublines are also cross-resistant to adriamycin, mitozolamide, N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and mitomycin C. This work indicates the potential multifactorial mechanisms by which drug resistance can be induced in cell lines in the absence of conventional 'P'-glycoprotein multidrug resistance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1985

A Yaba-like condition in a young baboon (Papio anubis).

A rapidly developing proliferation of subcutaneous nodules on the leg of a young baboon is described. Histologically the nodules consisted of plump round cells, many of which contained intracytoplasmic eosinophilic viral-like inclusions.

Animals↗
PubMed1984

Tumour-associated isoenzymes of gamma-glutamyl transferase in the serum of patients with hepatocellular carcinoma.

Sera from 391 southern African Blacks with hepatocellular carcinoma, matched controls, patients with other malignant tumours, and with various forms of hepatobiliary disease were fractionated by polyacrylamide gradient gel electrophoresis to determine the prevalence of tumour-associated gamma-glutamyl transferase isoenzymes in Black patients with hepatocellular carcinoma. One or more tumour-associated isoenzymes (I', I'' or II') were present in 58.6% of the patients with hepatocellular carcinoma: I' in 54.5%, I'' in 27.1%, and II' in 34%. These isoenzymes were detected in one patient with prostatic cancer, occasionally in patients with acute viral hepatitis, but in no normal individuals. The presence of tumour-associated isoenzymes was not related to patient age, sex or hepatitis-B virus status or to the tumour burden. Isoenzymes were present in 42 percent of hepatocellular carcinoma patients with a normal serum alpha-foetoprotein concentration and in 50% of those with a non-diagnostic value. gamma-glutamyl transferase isoenzymes may be supplementary to alpha-foetoprotein in the diagnosis of hepatocellular carcinoma.

Adolescent↗
PubMed1984

Isolation of ferritin from human hepatocellular carcinoma.

Ferritin was extracted from human hepatocellular carcinoma tissue and purified using column chromatography, gradient gel electrophoresis and cadmium sulphate crystallization. DEAE cellulose chromatography showed a difference between hepatoma and normal liver ferritin, indicative of a more acidic isoferritin profile in the tumour. Column-purified and crystalline ferritin and that remaining in the mother-liquor after crystallization was subjected to isoelectric focusing. Hepatoma ferritin showed higher concentrations of acidic isoferritins than liver ferritin. This was most obvious with mother-liquor ferritin, as crystallization tended to select out more basic isoferritins. Subunit analysis of hepatoma and liver ferritin showed a higher proportion of heavy subunits in the tumour ferritin, in keeping with the presence of acidic isoferritins. An antibody against hepatoma mother-liquor ferritin was raised in rabbits. However, hepatoma ferritin proved to be antigenically identical with normal liver ferritin, and we were thus unable to develop a specific radioimmunoassay for hepatoma ferritin.

Carcinoma, Hepatocellular↗
PubMed1983

High efficiency membrane oxygenator.

An adult membrane oxygenator of new design has been described which possesses excellent operating characteristics. The preliminary safety and efficacy of the device was demonstrated by in vitro performance testing and by the minimal blood trauma and absence of significant time dependent change during 6 hr ex vivo perfusions. These encouraging results are the basis for proceeding with clinical studies.

Animals↗