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Biomedical subjects

A T Young

Publications and source records attributed to A T Young.

At least 19 recordsLinked to original sources
PubMed2003

Correlation between exchange bias and pinned interfacial spins.

Using x-ray magnetic circular dichroism, we have detected the very interfacial spins that are responsible for the horizontal loop shift in three different exchange bias sandwiches, chosen because of their potential for device applications. The "pinned" uncompensated interfacial spins constitute only a fraction of a monolayer and do not rotate in an external magnetic field since they are tightly locked to the antiferromagnetic lattice. A simple extension of the Meiklejohn and Bean model is proposed to account quantitatively for the exchange bias fields in the three studied systems from the experimentally determined number of pinned moments and their sizes.

Journal Article↗
PubMed2002

Variable linear polarization from an X-ray undulator.

A new X-ray undulator has been designed and constructed which produces linearly polarized X-rays in which the plane of polarization can be oriented to a user selectable angle, from horizontal to vertical. Based on the Apple-II elliptically polarizing undulator (EPU), the undulator rotates the angle of the linear polarization by a simple longitudinal motion of the undulator magnets. Combined with the circular and elliptical polarization capabilities of the EPU operating in the standard mode, this new undulator produces soft X-ray radiation with versatile polarization control. This paper describes the magnetic structure of the device and presents an analysis of the magnetic field with varying undulator parameters. The variable linear polarization capability is then exhibited by measuring the X-ray absorption spectrum of an oriented polytetrafluoroethylene thin film. This experiment, which measures the linear dichroism of the sample at two peaks near the C 1s absorption edge, demonstrates the continuous polarization rotation capabilities of the undulator.

Journal Article↗
PubMed2002

Circular dichroism in K-shell ionization from fixed-in-space CO and N2 molecules.

We have measured the angular distributions of 1s photoelectrons excited by circularly and linearly polarized light from fixed-in-space CO and N2 molecules, in the vicinity of their shape resonances. A strong circular dichroism, i.e., a strong dependence on the sense of rotation of the polarization vector of the photons, is found for both molecules. State-of-the-art one-electron multiple scattering and partially correlated random phase approximation calculations are in good agreement with many, but not all, aspects of the experimental data.

Journal Article↗
PubMed2001

Nonviral transfection of intact pancreatic islets.

Ex vivo gene transfer offers a potential means to introduce genes into cells, which may play an important role in preventing graft rejection and inducing graft tolerance. This study examined the efficiency and toxicity of several lipid-based transfection reagents (LipofectAMINE, DOTAP, and DOSPER) in intact pancreatic islets. Isolated islets were transfected with a pCMV-beta-galactosidase plasmid using several DNA/liposome ratios (1:12) of liposomes (3-72 microl) and DNA (3 and 6 microg). Transfection efficiency was quantified by microscopic evaluation of beta-galactosidase gene expression in whole intact islets. Functionality of the transfected islets was measured by insulin response to glucose solutions. All transfection reagents evaluated in this study transfected cells within the islets. As expected, untransfected controls and transfected islets with DNA alone did not express beta-gal. The highest transfection efficiency and functional viability were obtained following a 48-h incubation after exposure to the transfection mixtures as follows: 3 microl DNA and 18 microl DOTAP/ml (1:6 ratio), 6 microg DNA and 12 microl DOSPER/ml (1:2 ratio), or 6 microg DNA and 12 microl Lipofect-AMINE/ml (1:2 ratio). The highest rate of transfected cells per islet was obtained using DOTAP. In vitro functionality was not significantly different between DOTAP and nontreated controls. However, optimal transfection efficiency doses of LipofectAMINE and DOSPER significantly reduced the stimulated insulin response of the transfected islets (p < 0.05, ANOVA). The calculated stimulation index (SI) was 7.8+/-0.6 (mean +/- SEM) for DOTAP-transfected islets compared with 8.4+/-0.5 for nontransfected control islets (p = ns). The SI of DOSPER- and LipofectAMINE-transfected islets was significantly lower (6.1+/-0.5 and 3.4+/-0.5, respectively, p < 0.05). Lipid-based transfection using DOTAP at a DNA/lipid ratio of 1:6 provides an effective means of ex vivo gene delivery without compromising in vitro functionality of the transfected islets.

Animals↗
PubMed2000

Sunset science. III. Visual adaptation and green flashes.

Photographs of green flashes do not preclude a role for physiological effects in these phenomena. While green flashes are certainly not after-images, there is compelling evidence that adaptation in the visual system strongly affects the perceived color of most sunset green flashes. Furthermore, the retinal image of the setting Sun is usually bright enough to bleach most of the red-sensitive photopigment in a few seconds, making the yellow stage of a sunset flash appear green. Even in air so hazy that no green light reaches the eye, a yellow flash may occur and appear green. Many, but not all, visual observations of sunset green flashes are of this yellow flash. The yellow portion of sunset green flashes helps explain their reported durations, which exceed those expected for the appearance of green light alone.

Adaptation, Physiological↗
PubMed1999

Anterior only fusion for scoliosis in patients with myelomeningocele.

A series of patients with single major scoliosis curvatures attributable to spina bifida treated by anterior only spinal fusion was studied for 2 years to determine whether the infection rate could be decreased, adequate correction and pelvic balance could be provided, and posterior surgery could be avoided in these patients. Anterior surgery alone was performed for thoracolumbar scoliosis greater than 45 degrees if the compensatory thoracic curve was less than 40 degrees and there was no significant junctional kyphosis. Fourteen patients were treated at a mean age of 11.9 years (range, 7-16 years), with a mean curve of 64 degrees (range, 51 degrees-85 degrees), and motor levels distributed from T10-L4. Thirteen patients had prior neurosurgery for tether, syrinx, or Arnold-Chiari malformation. The spine was fused over a mean of seven vertebrae. A 3/16 inch Texas Scottish Rite Hospital rod was used most commonly (10 patients). Blood loss averaged 1100 cc. The mean curve correction was 57% at 40 months after surgery. Loss of correction occurred primarily by adding on outside the instrumented area. Mean pelvic obliquity was improved from 16 degrees to 9 degrees. There was one superficial infection. Results were good in five patients, fair in four, and poor in five. Failures were attributable to proximal decompensation in two patients who required revision surgery (two), neurologic deterioration in two, and screw pullout in one. Both patients with decompensation had syringomyelia. Both patients with neurologic deterioration had large curves (> 75 degrees). Both patients recovered after rod removal. Retrospectively, by eliminating patients with syrinx or with a curve greater than 75 degrees, all poor results would be eliminated. Anterior only fusion and instrumentation may have significant advantages, but only for selected patients with thoracolumbar curves less than 75 degrees, compensatory curves less than 40 degrees, no increased kyphosis, and no syrinx. Quadriceps function should be monitored. On the basis of this preliminary experience, continued use of this approach using stricter selection seems warranted.

Activities of Daily Living↗
PubMed1995

Phosphatidylinositol 3-kinase binding to polyoma virus middle tumor antigen mediates elevation of glucose transport by increasing translocation of the GLUT1 transporter.

Elevation in the rate of glucose transport in polyoma virus-infected mouse fibroblasts was dependent upon phosphatidylinositol 3-kinase (PI 3-kinase; EC 2.7.1.137) binding to complexes of middle tumor antigen (middle T) and pp60c-src. Wild-type polyoma virus infection led to a 3-fold increase in the rate of 2-deoxyglucose (2DG) uptake, whereas a weakly transforming polyoma virus mutant that encodes a middle T capable of activating pp60c-src but unable to promote binding of PI 3-kinase induced little or no change in the rate of 2DG transport. Another transformation-defective mutant encoding a middle T that retains functional binding of both pp60c-src and PI 3-kinase but is incapable of binding Shc (a protein involved in activation of Ras) induced 2DG transport to wild-type levels. Wortmannin (< or = 100 nM), a known inhibitor of PI 3-kinase, blocked elevation of glucose transport in wild-type virus-infected cells. In contrast to serum stimulation, which led to increased levels of glucose transporter 1 (GLUT1) RNA and protein, wild-type virus infection induced no significant change in levels of either GLUT1 RNA or protein. Nevertheless, virus-infected cells did show increases in GLUT1 protein in plasma membranes. These results point to a posttranslational mechanism in the elevation of glucose transport by polyoma virus middle T involving activation of PI 3-kinase and translocation of GLUT1.

Amino Acid Sequence↗
PubMed1989

Phosphorylation of middle T by pp60c-src: a switch for binding of phosphatidylinositol 3-kinase and optimal tumorigenesis.

Substitution of phenylalanine for tyrosine 315 of the polyoma virus middle T (mT) protein lowers the incidence and limits the spectrum of tumors induced following inoculation of the virus into newborn mice. This substitution removes the major site of phosphorylation by pp60c-src without altering the ability of mT to associate with or to activate pp60c-src. The mutant mT fails to show binding of a phosphatidylinositol 3-kinase (Ptdlns 3-kinase) activity that is normally present in wild-type mT complexes. Furthermore, an anti-peptide antiserum that specifically recognizes mT lacking phosphate at tyrosine 315 precipitates binary (mT-pp60c-src) but not ternary (mT-pp60c-src-Ptdlns 3-kinase) complexes from wild-type infected cell extracts. Reprecipitation with either anti-pp60c-src or anti-mT serum brings down ternary complexes containing mT phosphorylated on tyrosine 315. Phosphorylation of mT by pp60c-src in vivo is therefore a critical event for binding of Ptdlns 3-kinase and for expression of the full tumorigenic potential of the virus.

Amino Acid Sequence↗
PubMed1989

Phosphatidylinositol 3-phosphate is present in normal and transformed fibroblasts and is resistant to hydrolysis by bovine brain phospholipase C II.

The transforming protein of polyoma virus, middle T antigen, associates with two cellular enzymes, pp60c-src, a protein tyrosine kinase, and a phosphatidylinositol kinase that forms phosphatidylinositol 3-phosphate. The formation of a ternary complex of these proteins is essential for complete transformation and maximal tumor induction by the virus. A mutant virus encoding an altered middle T protein that activates pp60c-src but fails to bind phosphatidylinositol kinase is partially defective in transformation. We have confirmed, using an enzymological method, that the product of the in vitro reaction catalyzed by middle T-pp60c-src-phosphatidylinositol kinase complexes is phosphatidylinositol 3-phosphate (PtdIns(3)P), as previously reported (Whitman, M., Downes, C. P., Keeler, M., Keller, T., and Cantley, L. (1988) Nature 332, 644-646). PtdIns(3)P is present in normal as well as virus-infected and transformed cells at levels ranging from 0.6 to 2.6% of the major phosphatidylinositol phosphate isomer, phosphatidylinositol 4-phosphate (PtdIns(4)P). Steady-state levels of PtdIns(3)P do not appear to be affected by the expression of middle T in cells. PtdIns(3)P is not hydrolyzed by bovine brain phospholipase C II, which readily cleaves PtdIns(4)P and other phosphatidylinositols. This result underscores the likelihood that the metabolism of PtdIns(3)P is distinct from that of PtdIns(4)P and raises further questions regarding a possible role of PtdIns(3)P in normal and neoplastic cell growth.

Animals↗
PubMed1989

Sulfur, ultraviolet radiation, and the early evolution of life.

The present biosphere is shielded from harmful solar near ultraviolet (UV) radiation by atmospheric ozone. We suggest here that elemental sulfur vapor could have played a similar role in an anoxic, ozone-free, primitive atmosphere. Sulfur vapor would have been produced photochemically from volcanogenic SO2 and H2S. It is composed of ring molecules, primarily S8, that absorb strongly throughout the near UV, yet are expected to be relatively stable against photolysis and chemical attack. It is also insoluble in water and would thus have been immune to rainout or surface deposition over the oceans. The concentration of S8 in the primitive atmosphere would have been limited by its saturation vapor pressure, which is a strong function of temperature. Hence, it would have depended on the magnitude of the atmospheric greenhouse effect. Surface temperatures of 45 degrees C or higher, corresponding to carbon dioxide partial pressures exceeding 2 bars, are required to sustain an effective UV screen. Two additional requirements are that the ocean was saturated with sulfite and bisulfite, and that linear S8 chains must tend to reform rings faster than they are destroyed by photolysis. A warm, sulfur-rich, primitive atmosphere is consistent with inferences drawn from molecular phylogeny, which suggest that some of the earliest organisms were thermophilic bacteria that metabolized elemental sulfur.

Atmosphere↗
PubMed1988

Percutaneous intrarenal marsupialization of a perirenal cystic collection--endocystolysis.

We report a case of a recurrent perirenal cyst after 4 previous attempts to obliterate the cyst by more conventional means percutaneously and by open surgery. Endocystolysis, a technique for the internal marsupialization of a cyst into the renal collecting system, was used successfully to obliterate the cyst. This case and the technique of endocystolysis are described in detail.

Adult↗
PubMed1988

Lower-extremity venous thrombosis: comparison of venography, impedance plethysmography, and intravenous manometry.

This study was undertaken to compare impedance plethysmography with lower-extremity venography and venous manometry in the diagnosis of acute deep venous thrombosis (DVT) of the lower extremity. Ninety-six extremities were studied. In this population, in which the prevalence of acute DVT was 43.8%, plethysmography had a sensitivity of 86.8% and a specificity of 72.0%. The predictive value of abnormal findings at plethysmography was 70.2%, and the predictive value of normal findings at plethysmography was 87.8%. Venous manometry was performed successfully in 89 extremities. A statistically significant difference was shown in the mean intravenous pressure between patients with and without acute DVT. However, there was considerable overlap between the two populations, limiting the predictive value of impedance plethysmography in any given patient.

Adult↗
PubMed1987

Limited usefulness of carbon dioxide as a contrast agent for cholangiography.

Carbon dioxide (CO2) was unsuccessfully used as a biliary contrast agent in 9 of 10 patients undergoing percutaneous transhepatic cholangiography prior to biliary drainage. The technique involved hand injection of 10-20 cc CO2 through the Chiba needle in an attempt to fill preferentially the anterior biliary radicals. Although CO2 remains a useful agent in many instances, particularly for percutaneous nephrostomy, its usefulness in the biliary tract is severely limited.

Carbon Dioxide↗
PubMed1987

Retrieving the Amplatz retrievable vena cava filter.

The new Amplatz retrievable filter was placed 15 times into the inferior vena cava (IVC) of 7 dogs. Retrieval of the filter was attempted in 11 cases after 1 week and in 3 cases after 2 weeks. The retrieval was successful and without complication in all 14 cases. The 15th placement resulted in thrombotic occlusion of the IVC, and no retrieval was attempted.

Animals↗
PubMed1987

Bone marrow in leukemia and aplastic anemia: MR imaging before, during, and after treatment.

Serial magnetic resonance (MR) studies of the cervical bone marrow were performed in five patients undergoing bone marrow transplantation for chronic granulocytic leukemia and in four patients with aplastic anemia who were treated with antilymphocytic globulin. Findings were compared with those from a group of healthy volunteers. Chemical shift imaging techniques were used to exploit the presence of protons in fat and water in the red marrow. Characteristic changes were seen in aplastic anemia before treatment, but derivation of images representing fat and water fractions was necessary to distinguish leukemic marrow. Acute changes during the treatment of leukemia may reflect the effects of chemotherapy and radiation therapy, whereas changes in the chronic phase of both diseases may prove useful in predicting treatment outcome. MR studies are likely to be useful in the assessment and treatment of hematologic disorders.

Adolescent↗