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At least 37 records · Page 2Linked to original sources
PubMed1988

Interaction of temperature and other environmental variables influencing plant distribution.

Statistical analyses of the relationships between the patterns of distribution of plants with C4 photosynthesis and Crassulacean acid metabolism (CAM) have revealed a variety of correlations with environmental variables. The worldwide abundance of C4 grasses, relative to C3 grasses, is highly positively correlated with growing season temperature. However, microscale analyses have revealed that C4 grasses are more abundant than C3 grasses in habitats with high levels of solar irradiance and low moisture availability. There are numerous exceptions to these generalizations. C4 dicots generally are more abundant in habitats characterized by high rates of evaporation. Species possessing CAM occur in habitats having low levels of soil moisture store. In the Cactaceae such habitats also have very high potential rates of evaporation and the CAM pathway is the primary mechanism of the uptake of atmospheric CO2. In contrast many species of the Crassulaceae grow in habitats with lower potential rates of evaporation and the CAM pathway is less important or not used at all in the uptake of atmospheric CO2.

Environment↗
PubMed1990

Computerized ultrasound B-scan texture analysis of experimental fatty liver disease: influence of total lipid content and fat deposit distribution.

Statistical pattern recognition procedures allow a quantitative description of ultrasound-B-scan image texture. According to well-established animal models, different types of fatty liver disease were induced in female Wistar rats. For the correlation of the computerized ultrasound image with its underlying histology a variable tissue model based on histomorphological data, texture analysis of the histological image and biochemical measurements of total lipid, water and hydroxyproline content was created. Whereas a regional arrangement of large fat deposits leads to a significant increase in the "mean grey level" (measure of image brightness) of the ultrasound-B-scan image, there is no difference in image brightness between normal liver tissue and liver steatosis for the tissue model with diffuse homogeneous fatty infiltration. It is demonstrated by multiple linear regression analysis that the "mean grey level" of the ultrasound-B-scan image depends not only on total lipid content but even more on the histomorphological fat deposit distribution.

Animals↗
PubMed1992

Gamma distribution and house 222Rn measurements.

The statistical distribution of 222Rn measurements from basements and first floors of homes in northeastern Pennsylvania was investigated. The gamma distribution was statistically significantly superior to the normal distribution (p less than 0.005) in describing the frequency distribution of the logarithm of observed 222Rn levels. The fit to the data was closer both in the central portion and in the upper tail. The gamma distribution has certain characteristics that make it generally useful in the study of environmental toxic agents where several different exposures over a lifetime occur and must be combined, as for risk assessment or for statistical power calculations for epidemiologic studies.

Air Pollution, Indoor↗
PubMed1988

Analysis of finite mixture of distributions: a statistical tool for biological classification problems.

A microcomputer program to analyze finite mixtures of normal, binomial, Poisson or exponential distributions by a maximum likelihood estimation procedure is described. The program is coded in Turbo Pascal. Some theoretical and practical aspects of the compound distributions are discussed, mainly mathematical characteristics, fitting procedures and tests of hypotheses. The statistical tool, which is a cluster analysis technique, is presented in a general context for applications in biology. In particular an ecological example is briefly described: the age class structure resolution of a white-tailed deer population. To improve the usefulness for classification purposes, the link with discriminant analysis is examined. For a successful analysis of finite mixture of distributions the need for a large sample size is emphasized.

Age Factors↗
PubMedDate not supplied

Dimensions of homo- and heteropolymeric sections of DNA synthesized by reverse transcription from globin mRNA matrices.

The lengths of globin messenger RNAs, isolated from rabbit and pigeon reticulocytes, and single-stranded complementary DNAs, synthesized from mRNA in presence of RNA-directed DNA-polymerase and oligo(dt) have been investigated by polyacrylamide gel electrophoresis under denaturing conditions. The cDNA preparations contained a fraction which corresponded in length to the alpha and beta chains of the mRNA used as a matrix. The lengthwise distribution of poly(A) sequences, isolated from globin mRNAs, corresponded to a statistical distribution, with a maximum at 75-80 nucleotides and with a maximum length of approximately 150 nucleotides. The lengthwise distribution of poly(dt) sequences, isolated from cDNA, corresponded to the poly(A) sequence distribution. It was concluded that: 1) cDNA is heterogeneous with respect to the length of poly(dt) sequences located at the 5' end of the molecule; 2) there was no selective use as primer of only that oligo(dt) which was located within the complex formed with the 5' end of the mRNA poly(A) sequence; 3) the heterogeneity of poly(DT) corresponded qualitatively to two models of template-primer interaction: selective use as a true primer of the oligonucleotide located in the complex formed with the 3' end of mRNA, and a statistical distribution of primer along the poly(A) sequence; and 4) the heterogeneity of the homopolymeric section of the cDNA may affect the kinetics of hybridization with mRNA, which possibly explains the previously observed [1] anomalous dependence of the hybridization rate on time.

Animals↗
PubMed1977

Statistical comparison of power spectra: a computer program.

A general computer program, of interest to neurobiologists, for comparison of uncorrelated power spectra is presented. The program, ALPHAF, is written in Fortran V language and is easily compiled and executed in any computer with a Fortran software package. The purpose of the program is to read power spectral density (PSD) values into a computer from digital tape and then perform the following functions: (1) compute and report power; (2) compute and report averages of the computed power values over selected frequency bands and (3) compute and report statistical standardised normal distributions for a frequency spectrum of interest. The standardised normal distribution statistic is derived by using equation 7.20, page 250 of Random data: Analysis and measurement procedures (Bendat and Piersol, 1971).

Computers↗