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Biomedical subjects

K R Koch

Publications and source records attributed to K R Koch.

7 recordsLinked to original sources
PubMed2006

Relative abundance and survival of the tick Amblyomma americanum collected from sunlit and shaded habitats.

The population density of host-searching nymphal and adult lone star ticks, Amblyomma americanum (L.) (Acari: Ixodidae), was determined at the Robinson tract of the Kansas Ecological Reserves and a private farm 5 km north-west of the Robinson tract using standard drag cloth methods. Nymphs, males and females were counted and collected weekly from shaded habitats and adjacent sunlit habitats from mid-May through late July, 2003. Of the 1598 nymphs and 549 males collected by drag sampling, 74.0% and 72.1%, respectively, were collected from shaded sections of the habitats, whereas 77.3% of 472 females were found in sunlit sections. A. americanum collected during each sampling period were maintained unfed at >95% relative humidity and a 14 : 10 h photoperiod, and survival was recorded weekly until all ticks had died. Survival of nymphs, males and females did not differ between ticks collected in the shade vs. those collected in the sun. Nymphs survived significantly longer than adults, whereas male and female survival did not differ from each other. These results suggest that host-searching A. americanum populations may partition their environment to increase the chances of coming into contact with a potential vertebrate host.

Animals↗
PubMed2002

State anxiety responses to 60 minutes of cross training.

OBJECTIVES: Significant reductions in state anxiety following bouts of aerobic exercise have been consistently noted, whereas changes are generally absent after acute resistance training. However, the influence of a single exercise session involving both modes on state anxiety has not been examined. METHODS: To address this, state anxiety responses to 60 minutes of cross training were examined in 16 collegiate athletes (12 women, four men). Each subject completed two cross training exercise sessions (30 minutes of resistance training, 30 minutes of bicycle ergometry) in which the order of the exercises was reversed, with a minimum of one week between sessions. Each exercise mode was completed at about 70% of maximum. State anxiety (SAI-Y1) was assessed five minutes before, and 0, 10, and 60 minutes after exercise. RESULTS: Repeated measures analysis of variance showed a significant (p<0.05) main effect for time. However, the main effect for order and the order by time interaction were not significant. Post hoc analysis showed that state anxiety was reduced (p<0.05) from baseline (mean (SD) = 34.8 (7.9)) at 10 minutes (32.1 (7.5)) and 60 minutes (30.4 (5.9)) after exercise, but not at 0 minutes (33.8 (6.9)). CONCLUSIONS: The results indicate that combined sessions of aerobic and resistance exercise are associated with reductions in state anxiety, and that the order in which the exercise is completed does not influence this response.

Adolescent↗
PubMed2001

Modeling platinum group metal complexes in aqueous solution.

We construct force fields suited for the study of three platinum group metals (PGM) as chloranions in aqueous solution from quantum chemical computations and report experimental data. Density functional theory (DFT) using the local density approximation (LDA), as well as extended basis sets that incorporate relativistic corrections for the transition metal atoms, has been used to obtain equilibrium geometries, harmonic vibrational frequencies, and atomic charges for the complexes. We found that DFT calculations of [PtCl(6)](2-).3H(2)O, [PdCl(4)](2-).2H(2)O, and [RhCl(6)](3-).3H(2)O water clusters compared well with molecular mechanics (MM) calculations using the specific force field developed here. The force field performed equally well in condensed phase simulations. A 500 ps molecular dynamics (MD) simulation of [PtCl(6)](2-) in water was used to study the structure of the solvation shell around the anion. The resulting data were compared to an experimental radial distribution function derived from X-ray diffraction experiments. We found the calculated pair correlation functions (PCF) for hexachloroplatinate to be in good agreement with experiment and were able to use the simulation results to identify and resolve two water-anion peaks in the experimental spectrum.

Journal Article↗
PubMed1992

Membrane fluidity of platelets and erythrocytes in patients with Alzheimer's disease and the effect of small amounts of aluminium on platelet and erythrocyte membranes.

The membrane fluidity of platelet and erythrocyte membranes in 10 Alzheimer's disease patients and 9 age-matched controls was studied. The platelet membranes of patients with Alzheimer's disease were found to be significantly more fluid than those of controls (p less than 0.02). However, erythrocyte membranes of Alzheimer patients were less fluid (more viscous) than those of controls (p less than 0.05). On further investigation of platelet and erythrocyte membranes obtained from healthy volunteers, the fluidity was found to change with increasing aluminium concentrations. When aluminium ammonium sulphate (0.01-10 microM) was added to membrane suspensions, the fluidity of platelet membranes was increased, whereas the fluidity of erythrocyte membranes was decreased (i.e. the microviscosity was increased).

Aluminum↗
PubMed1992

Identification of indigo-related pigments produced by Escherichia coli containing a cloned Rhodococcus gene.

Pigments produced by Escherichia coli containing a cloned piece of DNA from Rhodococcus sp. ATCC 21145 were extracted in chloroform and separated into blue and pink components. Evidence from TLC, NMR spectroscopy, absorption spectrum analysis and solubility behaviour suggested that the blue pigment was indigo and the pink pigment was indirubin, a structural isomer of indigo. The proposed pathway for pigment production on LB agar involves the conversion of tryptophan to indole by tryptophanase of E. coli and the oxidation of indole to indigo by the product of the cloned Rhodococcus DNA insert.

Chromatography, Thin Layer↗
PubMed1990

Quantitative determination of aluminium in tea by means of aluminium-27 nuclear magnetic resonance spectroscopy.

A method for determining the Al levels in tea leaf digests and tea infusions by means of 27Al nuclear magnetic resonance (NMR) spectroscopy is described. Quantitative results down to 2.0 micrograms cm-3 of Al in 0.5-cm-3 acidified samples are readily obtainable in standard 5-mm NMR tubes. An acceptable quantitative determination is achieved by using an internal Al standard in a 1-mm capillary in conjunction with europium nitrate as a shift reagent.

Aluminum↗