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Biomedical subjects

T Holder

Publications and source records attributed to T Holder.

8 recordsLinked to original sources
PubMed2005

Supra-maximal effort and reaction and movement times in a non-compatible response time task.

AIM: The primary purpose of this study was to examine the effect of attempting to exercise supra-maximally on reaction time and movement time in a non-compatible response time task. METHODS: Subjects (n=9) undertook a 4-choice non-compatible response time test at rest, while cycling at 70 rpm with a resistance of 35 W (low intensity exercise), cycling at 70% of their maximum power output (MPO), cycling at 100% MPO and attempting to cycle at 70 rpm, with a resistance that was 28 W greater than the resistance required to elicit MPO (supra-maximal effort). RESULTS: Reaction time, movement time, intra-individual variations in reaction time and movement time at each exercise intensity were compared by a series of repeated measures analyses of variance. A significant effect of exercise was shown for movement time, F(4,32)=6.05, p<0.001, eta2=0.44, Power=0.97 and intra-individual variation in reaction time, F(4,32)=4.98, p<0.005, eta2=0.38, Power=0.93. For movement time, Tukey post-hoc tests showed that performance at rest was significantly slower than that during exercise at 70%, 100% MPO and supra-maximal effort. Performance at low intensity exercise was significantly slower than that at MPO. For intra-individual variations in reaction time, Tukey tests found that variations under supra-maximal effort and MPO were significantly greater than those at low intensity and 70% MPO. CONCLUSIONS: It was concluded that exercise facilitates speed of movement when the limbs used for the motor task are not the ones that are being exercised. Reaction time during maximal and supra-maximal exercise demonstrates large intra-individual variations.

Adult↗
PubMed2004

Quantification of groundwater contamination in an urban area using integral pumping tests.

In this paper, the integral groundwater investigation method is used for the quantification of PCE and TCE mass flow rates at an industrialized urban area in Linz, Austria. In this approach, pumping wells positioned along control planes perpendicular to the groundwater flow direction are operated for a time period on the order of days and sampled for contaminants. The concentration time series of the contaminants measured during operation of the pumping wells are then used to determine contaminant mass flow rates, mean concentrations and the plume shapes and positions at the control planes. The three control planes used in Linz were positioned downstream of a number of potential source zones, which are distributed over the field site. By use of the integral investigation method, it was possible to identify active contaminant sources, quantify the individual source strength in terms of mass flow rates at the control planes and estimate the contaminant plume position relative to the control planes. The source zones emitting the highest PCE and TCE mass flow rates could be determined, representing the areas where additional investigation and remediation activities will be needed. Additionally, large parts of the area investigated could be excluded from further investigation and remediation activities.

Austria↗
PubMed2001

Functional dynamics in the active site of the ribonuclease binase.

Binase, a member of a family of microbial guanyl-specific ribonucleases, catalyzes the endonucleotic cleavage of single-stranded RNA. It shares 82% amino acid identity with the well-studied protein barnase. We used NMR spectroscopy to study the millisecond dynamics of this small enzyme, using several methods including the measurement of residual dipolar couplings in solution. Our data show that the active site of binase is flanked by loops that are flexible at the 300-micros time scale. One of the catalytic residues, His-101, is located on such a flexible loop. In contrast, the other catalytic residue, Glu-72, is located on a beta-sheet, and is static. The residues Phe-55, part of the guanine base recognition site, and Tyr-102, stabilizing the base, are the most dynamic. Our findings suggest that binase possesses an active site that has a well-defined bottom, but which has sides that are flexible to facilitate substrate access/egress, and to deliver one of the catalytic residues. The motion in these loops does not change on complexation with the inhibitor d(CGAG) and compares well with the maximum k(cat) (1,500 s(-1)) of these ribonucleases. This observation indicates that the NMR-measured loop motions reflect the opening necessary for product release, which is apparently rate limiting for the overall turnover.

Endoribonucleases↗
PubMed1998

Education on health risks of smoking in Magadan, Russia.

PURPOSE: The purpose of this project was to educate young Russians on the health risks of smoking. METHOD: The American Cancer Society, Alaska Division, sponsored a project to deliver its teaching modules on the health risks of tobacco use to first- through third-graders in Magadan, Russia. Starting with a $4,400 (U.S.) contribution designated for this purpose, a young teacher, Irina Alishova, was contacted in Magadan in 1993. She translated the modules of the American Cancer Society oriented to the first- to the third-grade level. Irina also made contact with the Magadan school system, specifically the principal of Middle School Number 29, Alla Vakulyuk. Principal Vakulyuk encouraged the project and worked with the other schools in the Magadan school system. RESULTS: Throughout the 1993-94 school year, nearly all of the first- and second-grade classes and a portion of the third-grade classes received and participated in the 50-minute teaching module. An American representative for the American Cancer Society observed one of the classes and noted thoughtful and enthusiastic participation by the schoolchildren.

Adolescent↗