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At least 1,045 records · Page 58Linked to original sources
PubMed2002

Measuring acid volatile sulphide in floodplain lake sediments: effect of reaction time, sample size and aeration.

For the routine measurement of acid volatile sulphide (AVS) in floodplain lake sediments, an earlier published diffusion method was adapted and optimised. We evaluated the effect of reaction time, sample weight and passive sample aeration on AVS recovery, and determined the method's reproducibility. The optimal reaction time was 4 h. Losses of AVS due to sample aeration did not occur within 15 min of sample-air contact. Relative standard deviation was <2.5% for known sulphide solutions, was between 10% and 15% for AVS concentrations in sediments and <12% for SEM concentrations in sediments, generally. Sediment samples with known SEM and AVS content were used to compare results of the developed method with the purge-and-trap method. There is a good agreement with the purge-and-trap method for SEM concentrations. AVS concentrations measured with the diffusion method are higher than with the purge-and-trap method. We conclude that the adapted diffusion method is well suited for the routine measurement of AVS concentrations in floodplain sediments.

Environmental Monitoring↗
PubMed1986

Folic acid and chromosome breakage. IV. Variance estimates from longitudinal studies of normal individuals and their implications for sample size and power to detect differences between populations.

The frequency of chromosome aberrations was studied in minimal essential medium (MEM) with and without folic acid (FA) in lymphocytes of 4 normal individuals, each sampled 12 times over a 1-year period. The cells cultured without FA had significantly more breaks and gaps. In both media about 75% of aberrations were classified as gaps. Calculations based on variance estimates suggest that the use of medium without FA could enhance the statistical power to distinguish differences in proportions of chromosome breakage between groups in the same study.

Analysis of Variance↗
PubMed1985

Effects of heat conduction and sample size on ultrasonic absorption measurements.

The absorption coefficient of a material can be determined by measuring the heating which occurs as a result of ultrasonic irradiation. When narrow focused beams are used to heat a sample, or when the available volume of a material is restricted to small dimensions, then the effect of heat conduction to surrounding unheated regions becomes significant, complicating the relation between measured temperatures and acoustic parameters. In this paper new analytical expressions, which account for radial and axial heat flow in a medium, are derived for the case of Gaussian-shaped ultrasonic beam patterns in thin or semi-infinite absorbing materials. Solutions are given for temperature histories resulting from an ultrasonic impulse (pulse decay method) or a step input (rate of heating method). The use of these equations in absorption measurements is discussed, and experimental results are given. These expressions provide flexibility in choice of laboratory ultrasonic parameters, and the results are especially useful for many biomedical measurements where the volume of tissue available is restricted.

Hyperthermia, Induced↗
PubMed2004

Spatial distribution patterns of malaria vectors and sample size determination in spatially heterogeneous environments: a case study in the west Kenyan highland.

The current study examined temporal and spatial distribution patterns of anopheline malaria vectors in a highland site and determined the number of houses to be sampled to achieve the targeted precision level. Adult mosquito sampling was conducted seasonally in May and August 2002 in a 3 by 3-km2 area, and in November 2002 and February 2003 in an expanded 4 by 4-km2 area in Kakamega District, western Kenya. Anopheles gambiae Giles was the predominant malaria vector species, constituting 84.6% of the specimens, whereas Anopheles funestus Giles constituted 15.4% of the vector populations. An. gambiae abundance increased by six- to eight-fold in the long rainy season over the dry seasons, but An. funestus abundance peaked 3 mo after the long rainy season. For both species, the coefficient of variation was larger than 1, suggesting that the distribution of mosquito adults was aggregated. Mosquito clustering occurred in houses <400 m from a valley bottom. The negative binomial distribution was accepted in one sample period (August 2002) for An. gambiae and in two sampling periods (May and August 2002) for An. funestus. Taylor's power law analyses indicated that An. gambiae distribution was more aggregated in the wet seasons than in the dry seasons, whereas the degree of aggregation of An. funestus was similar in all four seasons. The minimum number of houses required to estimate anopheline female abundance within the commonly acceptable precision level (0.2) should be 17 houses per km2 for An. gambiae and 42 houses per km2 for An. funestus. The potential factors causing aggregated anopheline mosquito distribution are discussed.

Animals↗