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Biomedical subjects

J H Dunn

Publications and source records attributed to J H Dunn.

At least 19 recordsLinked to original sources
PubMed2001

Quantitative analysis of L-edge white line intensities: the influence of saturation and transverse coherence.

We have performed x-ray absorption spectroscopy at the Fe, Ni, and Co L2,3 edges of in situ grown thin magnetic films. We compare electron yield measurements performed at SSRL and BESSY-I. Differences in the L2,3 white line intensities are found for all three elements, comparing data from the two facilities. We propose a correlation between spectral intensities and the degree of spatial coherence of the exciting radiation. The electron yield saturation effects are stronger for light with a higher degree of spatial coherence. Therefore the observed, coherence related, intensity variations are due to an increase in the absorption coefficient, and not to secondary channel related effects.

Journal Article↗
PubMed2001

Magnetisation reorientation in ultra-thin Fe films on Cu(100) upon deposition of Co.

Ultra thin films of Fe deposited on the (100) surface of a Cu single crystal exhibit a net perpendicular magnetic anisotropy. The addition of very low coverages of Co results in the easy magnetic direction reorienting into the film plane. This behavior is in contrast to the addition of similar amounts of Fe, whereupon the ferromagnetic response vanishes. This result is discussed in terms of the anisotropy energies derived from the spectroscopic data.

Journal Article↗
PubMed2001

Magnetic X-ray circular dichroism on in situ grown 3d magnetic thin films on surfaces.

Epitaxic thin and ultrathin films on surfaces allow crystallographic phases that do not occur naturally in the bulk to be stabilized. They also offer new possibilities for an improved understanding of soft X-ray photoabsorption in magnetic systems. Data collected using the Elliptically Polarizing Undulator at BL 5.2 of the Stanford Synchrotron Radiation Laboratory are presented herein. Fe, Co and Ni films were prepared on Cu(100) surfaces. L2,3-edge spectra were recorded with circular and linear light. Fresnel diffractometry was used to quantify the degree of transverse beam coherence. A quantitative analysis of the spectral features indicates a correlation of the spectral intensities and the transverse beam coherence. Resonant reflectivity spectra for Co ultrathin films that exhibit strong dichroism are presented. The reflectivity data indicate that interference effects of the reflected beams at the two interfaces are of importance, even for ultrathin films.

Journal Article↗
PubMed2000

Influence of source coherence on x-ray absorption spectroscopy.

Core-level x-ray absorption spectroscopy measurements have been performed at the L3,2 edges of Fe and Co thin films. The degree of source coherence was varied using soft x rays from five different beam lines. We observe an increase of the L edge resonance intensities relative to the continuum states which we propose is due to the presence of transverse coherence in the exciting radiation.

Journal Article↗
PubMed1997

A 'kickout' double salto backward tucked dismount from the horizontal bar performed by elite gymnasts.

The aim of this study was to identify the differences in the tucked and extended body positions, and in the spatiotemporal characteristics of the motion of the centre of mass, during the performance of kickout and non-kickout double salto backward tucked dismounts. A 16-mm camera, operating at 100 Hz, was used to record double salto backward tucked dismounts during the 1990 national championships in Japan and the USA. A high-scoring kickout group (n = 24) had a significantly (P < 0.005) higher body centre of mass at the tightest tuck position in the first salto, and shorter time to achieve maximum body extension during the second salto, than did a low-scoring non-kickout group (n = 24). Furthermore, the kickout group showed greater height of body centre of mass, larger normalized moment of inertia, and smaller body angle from the vertical at maximum body extension. Consequently, they had longer duration and larger distances of flight than the non-kickout group in which to display the maximum body extension before landing on the mat. It was concluded that the kickout double salto backward tucked dismount is indeed more effective than the non-kickout dismount because it involves (a) greater body extension in an inverted position before passing through the vertical and (b) greater heights of centre of mass at the peak of flight, at the tightest tuck and at maximum body extension. Furthermore, this dismount enhances the display of virtuosity for which bonus points are awarded. The results suggest that this kickout dismount may be helpful in developing the mechanical foundation necessary for learning more advanced dismounts, such as the triple salto backward tucked and double salto backward stretched, with increased effectiveness and safety.

Biomechanical Phenomena↗
PubMed1996

A comparison of techniques used by elite gymnasts in performing the basket-to-handstand mount.

Twenty-six subjects were selected from 25 American and 28 Japanese gymnasts filmed during their respective 1990 national championships. The 13 highest (Group 1) and 13 lowest (Group 2) scored basket-to-handstand mounts on the parallel bars were compared. It was hypothesized that there would be significant differences between the kinematics demonstrated by the gymnasts from the two groups and that differences in the early preparatory phases would account for most of the differences in the resulting movements. The results revealed significant differences (P < 0.005) between the two groups, with Group 1 achieving greater vertical displacement of the centre of mass during the upward inverted swing and larger vertical velocity at bar release; greater backward horizontal motion of the centre of mass and forward body rotation in the flight phase; and a higher body centre of mass at bar regrasp with greater fluency of upward body motion into the handstand position. There were no significant differences between the two groups in the performance of the jump to end of backward swing and forward swing to maximum body pike that could be attributed to the differences in the last three phases. Based on the findings of this study, successful performance is likely when the arm pull is sustained with maximum effort until the body centre of mass and the trunk are well above the bars to enable the bar release with high body centre of mass, high body angle, large vertical velocity, backward horizontal velocity and forward angular momentum. This brings about (1) the desired direction of linear motion of centre of mass and (2) high body centre of mass and high body angle close to the handstand position at bar regrasp, which together ensure the fluency of upward body motion into the final position.

Biomechanical Phenomena↗
PubMed1988

Imidazole therapy of coccidioidal meningitis in children.

The mortality related to coccidioidal meningitis (CM) has been reduced since the introduction of amphotericin B therapy, but children with CM continue to suffer significant morbidity. Some of this is related to the toxicity of the drug. We report nine children with CM treated with orally administered ketoconazole and intraventricularly administered miconazole. Four of them had been treated initially with amphotericin B with resultant failure in one and severe toxicity in all four. The other five children were treated only with imidazoles. All nine children had evidence of ventriculitis at the time of diagnosis and had ventriculoperitoneal shunts inserted for control of increased intracranial pressure. There was no relapse or recrudescence of CM in a follow-up period of 32 to 90 months on imidazole therapy. The coccidioidal complement-fixation antibody titers in the cerebrospinal fluid of the lateral ventricle became negative in all children 3 to 51 months after diagnosis (mean, 17 months). The serum antibody titers demonstrated a 16- to 256-fold decrease from their maximal levels. Four children are still receiving intraventricular miconazole whereas the others have not received miconazole for an average of 51 months. Therapy with the imidazoles was well-tolerated. The main morbidity was related to the shunts required for control of increased intracranial pressure. There was no evidence of hepatic toxicity and no clinical evidence of adrenal insufficiency although transient adrenal suppression was demonstrated at 4 but not at 24 hours after ketoconazole administration.

Administration, Oral↗
PubMed1982

Immunological analysis of a chromosomal antigen specific to human granulocytes.

A chromosomal protein antigen specific for human granulocytes is described. The antigen is present in large amounts in granulocytes and in granulocytic leukaemia. It is absent from HeLa cells, human fibrosarcoma cells and human lymphocytes. It is, however, present in small amounts in other human haemopoietic cell lines. The antigen binds tightly to DNA and requires the presence of DNA to react with the antibody.

Antibody Specificity↗
PubMed1982

Solid-phase radioimmunoassay of cell specific chromosomal proteins.

A solid-phase radioimmunoassay has been developed for the detection of cell specific chromosomal proteins which require the presence of DNA for their immunoreactivity. The assay involves the binding of chromatin particles sonicated under highly controlled conditions to PVC plates followed by first and second antibody with extensive detergent washing. The sensitivity and specificity of the assay system compares favourably with the complement fixation technique.

Binding Sites, Antibody↗
PubMed1980

DNA-binding specificity of a chromatin non-histone protein fraction of HeLa cells.

The DNA-binding site of a previously characterized non-histone chromosomal protein antigen(s) from HeLa cells was investigated for its species specificity. Treatment with large amounts of micrococcal nuclease abolishes immunoactivity, which can then be recovered by the subsequent addition of human or HeLa DNA to reconstitute the immune complex. Neither rat nor calif DNA exhibits this property, but DNA from monkey cells gives considerable activity. The antigen is not, however, detectable in monkey chromatin.

Animals↗
PubMed1977

Coordinate and non-coordinate accululation of aspartate transcarbamylase and dihydroorotase in synchronous Chlorella cells growing on different nitrogen sources.

Regulation of the levels of aspartate transcarbamylase (carbamoylphosphate:L-aspartate carbamoyltransferase, EC 2.1.3.2) and dihydroorotase (L-5,6-dihydro-orotate amidohydrolase, EC 3.5.2.3) was studied in synchronous cultures of the eucaryotic microorganism Chlorella. Analytical polyacrylamide gel electrophoresis and sucrose density-gradient centrifugation studies revealed that these cells contain a single aspartate transcarbamylase and a dihydroorotase with apparent molecular weights of 160 000 and 80 000, respectively. In synchronous cells cultured in nitrate medium, these two enzymes accumulated in single step-patterns over different periods of the cell cycle. In contrast, these enzymes accumulated in a coordinate manner throughout the cell cycle in ammonium medium. Experiments with inhibitors of protein and RNA synthesis indicated that dihydroorotase is stable in vivo and suggested that cell cycle changes in the turnover rate of aspartate transcarbamylase might determine whether or not these enzymes accumulate in a coordinate manner. Although uracil and uridine could be absorbed and metabolized by the cells, synthesis of these two enzymes could not be repressed by culturing synchronous cells in medium, containing high concentrations (29-40 mM) of uracil or uridine, for an entire cell cycle.

Amidohydrolases↗
PubMed1970

Composition of the cellular envelopes of Anabaena cylindrica.

Comparative chemical analyses were made of the walls of vegetative cells, heterocysts, and spores, and of the mucilage of Anabaena cylindrica. The wall of the vegetative cell is composed predominantly of amino compounds, with a mannose-rich carbohydrate component comprising only 18% of the dry weight. In contrast, 62% of the heterocyst wall and 41% of the spore wall is carbohydrate. The carbohydrate moieties of the heterocyst wall and spore wall are similar in that the ratio of glucose, mannose, galactose, and xylose is approximately 75:20:3:4 in both walls. It appears that, during the differentiation of a vegetative cell into either a spore or a heterocyst, a glucose-rich wall polysaccharide is produced that is different from the polysaccharide component of the wall of the vegetative cell and of the sheath. In the case of the heterocyst, the wall was estimated to account for approximately 52% of the dry weight of the whole cell.

Amino Acids↗