A note on exact solutions of two prey-predator equations

Exact solutions are obtained and discussed for classes of Lotka-Volterra and Leslie-Gower systems governing the interaction of two species. The classes are defined by certain constraints which are imposed on the time-dependent parameters of the equations. A general result for such systems is that each species is characterised by two time-scales: one representing natural growth and the other, the interdependence of the species.     

A note on the nomenclature of two European cockles

The confused nomenclature concerning two European cockles is discussed. Reasons are given to support the genus name Cerastoderma in preference to Cardium and the use of the specific name glaucum in place of lamarcki.
It is concluded that the correct names of the two cockles under discussion are Cerastoderma edule (L.) and Cerastoderma glaucum (Poiret).     

A note on 'plotless' methods for estimating bacterial cell densities

R oser , D., N edwell , D.B. & G ordon , A. 1984. A note on "plotless" methods for estimating bacterial cell densities. Journal of Applied Bacteriology 56 , 343–347.
'Plotless' techniques for determining population densities have been developed for, and applied to, higher plant populations. They can often be carried out more rapidly than techniques involving total counts of individuals in plots, or quadrants, but such plotless techniques have not been generally applied to the estimation of densities of bacterial cells. Direct microscopical counting of cell numbers in a field of view, an example of a plot-related method, has been traditionally used for micro-bial cell counts. In this study 'plot' and 'plotless' methods on a variety of bacterial samples are compared. Estimates of bacterial cell density were obtained by measuring the distance of cells from a fixed point in a field of view. The values, which were more rapidly obtained, were directly correlated with total cell counts. Although there was some apparent deviation from a perfect 1:1 relationship with total counts, as indicated by a correlation coefficient less than 1.0, there were no significant differences between the replicated counts of bacteria on samples of tissue from the surface of Hypholoma basidiocarps ( P < 0.05). This indicated that the methods of enumeration were comparable. The distance-related estimates could readily be obtained from fields of view with cell densities varying over several orders of magnitude. It was more rapidly applied, particularly at high density, and the method was applicable not only to random cell distributions but also to the non-random distributions encountered when microbial cells aggregated into micro-colonies. The method appears to be particularly well-suited for automated, digitized, direct counting procedures, as well as to estimating bacterial numbers on membrane filters and natural substrates.     

Biological detection of low radiation doses by combining results of two microarray analysis methods

The accurate determination of the biological effects of low doses of pollutants is a major public health challenge. DNA microarrays are a powerful tool for investigating small intracellular changes. However, the inherent low reliability of this technique, the small number of replicates and the lack of suitable statistical methods for the analysis of such a large number of attributes (genes) impair accurate data interpretation. To overcome this problem, we combined results of two independent analysis methods (ANOVA and RELIEF). We applied this analysis protocol to compare gene expression patterns in Saccharomyces cerevisiae growing in the absence and continuous presence of varying low doses of radiation. Global distribution analysis highlights the importance of mitochondrial membrane functions in the response. We demonstrate that microarrays detect cellular changes induced by irradiation at doses that are 1000-fold lower than the minimal dose associated with mutagenic effects.     

A note on two uses for impedimetry in brewing microbiology

The forcing test used in the brewing industry is shortened from a few weeks to a few days using a new protocol employing impedimetry. The generation times of four different brewing yeasts growing in brewery wort were calculated from measurements obtained using impedimetry.     

A note on the scent-marking behavior of two captive-reared feral boars

Male swine are known to scent-mark, but the relationship of this behavior to social rank is unknown and quantitative data for other aspects of the behavior are lacking. A known dominant-subordinate pair of captive-reared feral boars was tested to determine latent periods and frequencies of each type of scent marking exhibited after being stimulated by exposure to feral sows. The boars exhibited metacarpal and preputial scent marking, but not tusk-gland marking. When paired, the dominant boar scent-marked significantly more often than the subordinate, with no significant differences in latent periods. When tested alone, the dominant boar did not mark at all. The subordinate boar did scent-mark when isolated, and frequencies and latent periods did not difder significantly from when paired with the dominant animal. These results suggest that scent-marking behavior varies according to dominance rank and may be influenced by the immediate social environment of the animal.     

A genetic association test through combining two independent tests

Gene- and pathway-based variant association tests are important tools in finding genetic variants that are associated with phenotypes of interest. Although some methods have been proposed in the literature, powerful and robust statistical tests are still desirable in this area. In this study, we propose a statistical test based on decomposing the genotype data into orthogonal parts from which powerful and robust independent p-value combination approaches can be utilized. Through a comprehensive simulation study, we compare the proposed test with some existing popular ones. Our simulation results show that the new test has great performance in terms of controlling type I error rate and statistical power. Real data applications are also conducted to illustrate the performance and usefulness of the proposed test.     

Practising methods of age determination. Comments on methods combining multiple age indicators

For some time, trends in age determination of skeletons have tended to shift from methods using single age indicators to methods combining multiple age indicators. Evidently the latter are expected to offer more balanced age assessments. If one decides to apply a method using multiple age indicators, a choice can be made between two «current» methods, both based on non-metrical age indicators: the socalled Complex Method of Acsádi and Nemeskéri, statistically elaborated by Sjøvold (WEA, 1980), and the so-called Multifactorial Method of Lovejoy et al., 1985a. Comments are given on practical applicability and supposed confidence.     

A note on chromosomes of two species of tree shrews (Tupaiidae)

Karyological studies of five tree shrews showed a diploid number 2n=60 forTupaia glis and 2n=66 forTupaia minor. The Y chromosome ofTupaia glis was found to be a medium-sized submetacentric chromosome in contrast to earlier data in the literature. The karyotype of a femaleTupaia minor showed five pairs of metacentric and submetacentric chromosomes and 28 pairs of acrocentric chromosomes.     

A note on two liquid scintillation fluors useful for primary production work

Summary Two liquid scintillation fluors, the first using a 2-methoxyethanol/toluene solvent, the second a Triton X-100/toluene solvent, are discussed. Data presented indicate that the technique using the 2-methoxyethanol/toluene solvent produces higher d.p.m. than does solid support counting. The Triton X-100/toluene solvent fluor is suggested for measuring aqueous samples such as algal excretion products and ¹⁴C stock solutions.     

A note on the use of dextran in blood cultures monitored by conductance methods

The incorporation of dextran into broth for the detection of bacteraemia by conductance monitoring is recommended to eliminate the effect of sedimenting blood cells which may mask early signals from bacteria. Broth containing ten times the recommended concentration of dextran was tested with a wide range of bacteria without demonstrating any reduction in growth or rate of change of conductance.     

A note on the use of dextran in blood cultures monitored by conductance methods

The incorporation of dextran into broth for the detection of bacteraemia by conductance monitoring is recommended to eliminate the effect of sedimenting blood cells which may mask early signals from bacteria. Broth containing ten times the recommended concentration of dextran was tested with a wide range of bacteria without demonstrating any reduction in growth or rate of change of conductance.