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Biomedical subjects

J C Taylor

Publications and source records attributed to J C Taylor.

At least 37 records · Page 2Linked to original sources
PubMed1998

Effects of joint configuration for the arc welding of cast Ti-6Al-4V alloy rods in argon.

STATEMENT OF PROBLEM: Titanium and its alloys are more commonly used in prosthodontics and welding has become the most common modality for their joining. Studies on the welding of titanium and its alloys have not quantified this value, though its importance has been suggested. PURPOSE: This study compared the strength and properties of the joint achieved at various butt joint gaps by the arc-welding of cast Ti-6Al-4V alloy tensile bars in an argon atmosphere. MATERIAL AND METHODS: Forty of 50 specimens were sectioned and welded at four gaps. All specimens underwent tensile testing to determine ultimate tensile strength and percentage elongation, then oxygen analysis and scanning electron microscopy. RESULTS: As no more than 3 samples in any group of 10 actually fractured in the weld itself, a secondary analysis that involved fracture location was initiated. There were no differences in ultimate tensile strength or percentage elongation between specimens with weld gaps of 0.25, 0.50, 0.75, and 1.00 mm and the as-cast specimens. There were no differences in ultimate tensile strength between specimens fracturing in the weld and those fracturing in the gauge in welded specimens; however, as-cast specimens demonstrated a higher ultimate tensile strength than welded specimens that fractured in the weld. Specimens that fractured in the weld site demonstrated less ductility than those that fractured in the gauge in both welded and as-cast specimens, as confirmed by scanning electron microscopy examination. The weld wire showed an oxygen scavenging effect from the as-cast parent alloy. CONCLUSIONS: The effects of the joint gap were not significant, whereas the characteristics of the joint itself were, which displayed slightly lower strength and significantly lower ductility (and thus decreased toughness). The arc-welding of cast titanium alloy in argon atmosphere appears to be a reliable and efficient prosthodontic laboratory modality producing predictable results, although titanium casting and joining procedures must be closely controlled to minimize heat effects and oxygen contamination.

Alloys↗
PubMed1997

"Shattered illusions--the Thiepval Barracks bombing, 7 October 1996".

The provisional IRA's ceasefire ended abruptly with the Canary Wharf bombing in London in February 1996. Hopes that violence would not return to Northern Ireland were shattered by the explosion of two car bombs in the headquarters of the British Army in Ulster in October 1996. The second bomb specifically targeted medical staff treating casualties from the first explosion. This article describes the medical aspects of this incident, including the extensive use of critical incident stress debriefing, and emphasises the implications for the major incident plans of medical centres and military hospitals.

Blast Injuries↗
PubMed1996

The multidrug resistance P-glycoprotein modulates cell regulatory volume decrease.

Cell volume is frequently down-regulated by the activation of anion channels. The role of cell swelling-activated chloride channels in cell volume regulation has been studied using the patch-clamp technique and a non-invasive microspectrofluorimetric assay for changes in cell volume. The rate of activation of these chloride channels was shown to limit the rate of regulatory volume decrease (RVD) in response to hyposmotic solutions. Expression of the human MDR1 or mouse mdr1a genes, but not the mouse mdr1b gene, encoding the multidrug resistance P-glycoprotein (P-gp), increased the rate of channel activation and the rate of RVD. In addition, P-gp decreased the magnitude of hyposmotic shock required to activate the channels and to elicit RVD. Tamoxifen selectively inhibited both chloride channel activity and RVD. No effect on potassium channel activity was elicited by expression of P-gp. The data show that, in these cell types, swelling-activated chloride channels have a central role in RVD. Moreover, they clarify the role of P-gp in channel activation and provide direct evidence that P-gp, through its effect on chloride channel activation, enhances the ability of cells to down-regulate their volume.

3T3 Cells↗
PubMed1996

Monovalent cation activation and kinetic mechanism of inosine 5'-monophosphate dehydrogenase.

Human type II inosine 5'-monophosphate dehydrogenase has been purified to homogeneity from an Escherichia coli strain that express large quantities of the enzyme from the cloned gene. Steady state kinetic studies have been used to characterize the activation by monovalent cations, including Li+, Na+, K+, Rb+, Cs+, Tl+, NH4+, and N(CH3)4+. The enzyme has less than 1% of the maximal activity in the absence of an added monovalent cation, such as K+, Na+, Rb+, Tl+, or NH4+. The enzyme is activated by K+ and Tl+ at lower concentrations than those of other monovalent cations. Li+ and N(CH3)4+ do not activate the enzyme, nor do they inhibit the K(+)-activated enzyme, implying that ionic radius is important in binding selectivity. The Km values for both substrates and Vmax differ with different monovalent cations. Initial velocity and product inhibition kinetic data are consistent with an ordered steady state mechanism in which the enzyme binds K+ first, TMP second, and then NAD; the product NADH is released before xanthosine 5'-monophosphate. Substrate and product binding experiments support this mechanism and show the presence of one substrate binding site per subunit. Several rate constants were obtained from a computer simulation of the complete steady state rate equation.

Base Sequence↗
PubMed1996

Medflight.

Explore the source record for details and available documents.

Air Ambulances↗
PubMed1995

Prenatal diagnosis of familial ring 21 chromosome.

Ring chromosome 21 is a rare chromosome anomaly often associated with mental retardation and dysmorphic features. Less commonly, the ring chromosome can be familial and associated with a normal phenotype. Phenotypically normal female carriers, however, are at increased risk of having children with Down syndrome, mosaic monosomy 21, and variable duplication or deletion of chromosome 21. Because of the relative mitotic and meiotic instability of ring chromosomes, abnormal cytogenetic findings encountered during prenatal diagnosis may not reflect the true genetic status of the fetus. This is a report of a phenotypically normal female carrier of a familial ring 21 chromosome. Prenatal diagnosis on her twin pregnancy revealed a mosaic 46,XX,r(21)(p13;q22) (77 per cent)/45,XX,-21 in one fetus and a normal male karyotype in the second. The pregnancy was carried to term. Both infants are completely normal, with a non-mosaic ring 21 karyotype from the lymphocytes of one twin. The diagnostic uncertainty and problematic genetic counselling related to fetal cytogenetic abnormalities are the subjects of this report.

Adult↗
PubMed1994

Escape behavior in task situations: task versus social antecedents.

We designed an investigation to differentiate two types of challenging behaviors occurring in teaching situations: those evoked by task stimuli (i.e., task avoidance), and those evoked by social stimuli present in teaching situations (i.e., social avoidance). Four students with developmental disabilities who exhibited challenging behaviors in teaching situations were exposed to social interaction in a play situation and task demands in a teaching situation. Results indicated that the students exhibited two distinct behavior patterns. Two of the students exhibited a behavior pattern consistent with task avoidance and the other two students exhibited a behavior pattern consistent with social avoidance. Implications concerning task versus social avoidance and the need for more fine-grained analyses of the stimuli associated with escape behavior are discussed.

Autistic Disorder↗
PubMed1994

Can a drawover vaporizer be a pushover?

Bench testing was carried out to establish whether the vapour output from an OMV50 vaporizer, as used in the Triservice apparatus, differs according to whether the carrier gas is either drawn or pushed through the vaporizer. Results show that the differences in output concentration between the two modes were clinically insignificant.

Anesthesia, Inhalation↗
PubMed1994

Subdural block--further points.

An obstetric epidural performed for analgesia showed a changing pattern of neurological block. The original features suggestive of a subdural block were complicated when aspiration of cerebrospinal fluid from the catheter became possible. Subsequent management as a continuous subarachnoid catheter allowed delivery.

Adult↗
PubMed1994

Generating hypotheses about the function of student problem behavior by observing teacher behavior.

We examined whether, as predicted by research on child effects, we could generate hypotheses about the function of student problem behavior by observing the amount of attention teachers provided to students. In the first phase of the study, we observed the amount of attention teachers distributed among small groups of students who exhibited problem behavior in individual or small-group instructional settings (problem behavior presumably maintained by attention or escape). Based on the amount of attention each student received, we generated hypotheses about the function of his or her problem behavior. In the second phase of the study, we determined the accuracy of these predictions by conducting a brief functional assessment with each student. Results confirmed that, for 14 of the 15 students, we were able to generate accurate hypotheses about the function of their problem behavior. These results suggest the potential efficacy of using the amount of attention teachers distribute among groups of students to generate empirically based hypotheses about the function of student problem behavior maintained by attention and/or escape. These results also illustrate the efficiency of this procedure; by observing teacher behavior, we were able to generate hypotheses about the function of problem behavior for several students at one time.

Attention↗
PubMed1993

The ORF1 of the gentamicin-resistance operon (aac) of Pseudomonas aeruginosa encodes adenosine 5'-phosphosulphate kinase.

The gentamicin-resistance operon of Pseudomonas aeruginosa (aac) contains two cistrons for which only the second gene product has an identified function. The 813bp second cistron (ORF2) encodes a protein that confers gentamicin resistance by catalysis of the transfer of an acetyl group from acetyl Coenzyme A to gentamicin. The first open reading frame (ORF1) encodes a 23.9 kDa protein that we have found, by enzyme activity and immunological reactivity, to be adenosine-5'-phosphosulphate (APS) kinase. APS kinase catalyses the transfer of the gamma phosphoryl group of ATP to the 3'-hydroxyl group of APS. The 70% sequence similarity between the Pseudomonas and Escherichia coli APS kinases suggests that the Pseudomonas enzyme may catalyse phosphoryl transfer to the 3'-hydroxyl group of other nucleotides such as dephosphocoenzyme A, as does the purified E. coli APS kinase. In extracts of pseudomonad cells we have also detected a higher molecular mass (70kDa) protein that cross-reacts with an anti-E. coli APS kinase antibody. This cross-reactive protein is also present in Pseudomonas strains lacking the gentamicin-resistance plasmid, and apparently reflects an APS kinase analogous to the nodQ-encoded high-molecular-weight APS kinase present in Rhizobium meliloti. Production of the Pseudomonas aac APS kinase was repressed by cysteine when expressed in E. coli, as is E. coli APS kinase. However, cysteine did not repress production of the Pseudomonas enzyme when the aac ORF1-encoded enzyme was expressed in a Pseudomonas strain, indicating differential regulation of gene expression in the two organisms.

Amino Acid Sequence↗
PubMed1993

Isozymes of S-adenosylmethionine synthetase are encoded by tandemly duplicated genes in Escherichia coli.

The sole biosynthetic route to S-adenosylmethionine, the primary biological alkylating agent, is catalysed by S-adenosylmethionine synthetase (ATP:L-methionine S-adenosyltransferase). In Escherichia coli and Salmonella typhimurium numerous studies have located a structural gene (metK) for this enzyme at 63 min on the chromosomal map. We have now identified a second structural gene for S-adenosylmethionine synthetase in E. coli by DNA hybridization experiments with metK as the probe; we denote this gene as metX. The metX gene is located adjacent to metK with the gene order speA metK metX speC. The metK and metX genes are separated by approximately 0.8 kb. The metK and the metX genes are oriented convergently as indicated by DNA hybridization experiments using sequences from the 5' and 3' ends of metK. The metK gene product is detected immunochemically only in cells growing in minimal media, whereas the metX gene product is detected immunochemically in cells grown in rich media at all growth phases and in stationary phase in minimal media. Mutants in metK or metX were obtained by insertion of a kanamycin resistance element into the coding region of the cloned metK gene (metK::kan) followed by use of homologous recombination to disrupt the chromosomal metK or metX gene. The metK::kan mutant thus prepared does not grow on minimal media but does grow normally on rich media, while the corresponding metX::kan mutant does not grow on rich media although it grows normally on minimal media. These results indicate that metK expression is essential for growth of E. coli on minimal media and metX expression is essential for growth on rich media. Our results demonstrate that AdoMet synthetase has an essential cellular and/or metabolic function. Furthermore, the growth phenotypes, as well as immunochemical studies, demonstrate that the two genes that encode S-adenosylmethionine synthetase isozymes are differentially regulated. The mutations in metK and metX are highly unstable and readily yield kanamycin-resistant cells in which the chromosomal location of the kanamycin-resistance element has changed.

Bacterial Proteins↗