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At least 757 records · Page 42Linked to original sources
PubMed1981

Theory on prospect of population evolution processes.

This paper is aimed at investigating the dynamic process of population growth applied to population of the People's Republic of China. The discrete and continuous models of population evolution process are revised and adjusted to suit the social conditions of China. The relationship between two kinds of models is established. A series of new formulae of demographic indices are studied and defined as functions on the negative space of generalized solutions of the population equation. Based on survey data collected in China for recent years, the prospect of population growth according to different projections is offered for a one-hundred-year period from now on.

Demography↗
PubMed2003

Modeling controlled nutrient release from a population of polymer coated fertilizers: statistically based model for diffusion release.

A statistically based model for describing the release from a population of polymer coated controlled release fertilizer (CRF) granules by the diffusion mechanism was constructed. The model is based on a mathematical-mechanistic description of the release from a single granule of a coated CRF accounting for its complex and nonlinear nature. The large variation within populations of coated CRFs poses the need for a statistically based approach to integrate over the release from the individual granules within a given population for which the distribution and range of granule radii and coating thickness are known. The model was constructed and verified using experimentally determined parameters and release curves of polymer-coated CRFs. A sensitivity analysis indicated the importance of water permeability in controlling the lag period and that of solute permeability in governing the rate of linear release and the total duration of the release. Increasing the mean values of normally distributed granule radii or coating thickness, increases the lag period and the period of linear release. The variation of radii and coating thickness, within realistic ranges, affects the release only when the standard deviation is very large or when water permeability is reduced without affecting solute permeability. The model provides an effective tool for designing and improving agronomic and environmental effectiveness of polymer-coated CRFs.

Diffusion↗
PubMed1990

Incidence of cancer of the lung, stomach, breast, and cervix in the USSR: pattern and trends.

The most frequent fatal malignant tumors in the Soviet Union are cancers of the lung, stomach, breast, and cervix uteri. From incidence statistics and population estimates provided by the Department of Statistics of the Ministry of Health, age-adjusted incidence rates for the period 1971-87, using the World standard population, have been computed for the USSR as a whole and for each of the 15 Soviet republics. For six republics believed to have the highest quality of data and relatively homogeneous populations, time-trends are examined over the period. There is important geographical variation in the incidence of malignant tumors in the Soviet Union. The differences between high and low incidence areas are four-fold for cancer of the lung and stomach, three-fold for cancer of the breast and two-fold for cancer of the cervix. Overall in the six republics for which time-trends are examined, cancers of the lung and breast have increased, cancers of the stomach and cervix have decreased. There are some variations in specific age groups in some republics.

Adult↗
PubMed2006

[Segmenting lung fields in serial chest radiographs using both population and patient-specific shape statistics].

This paper presents a new deformable model using both population-based and patient-specific shape statistics to segment lung fields from serial chest radiographs. First, a modified scale-invariant feature transform (SIFT) local descriptor is used to characterize the image features in the vicinity of each pixel, so that the deformable model deforms in a way that seeks for the region with similar SIFT local descriptors; second, the deformable model is constrained by both population-based and patient-specific shape statistics. At first, population-based shape statistics plays an leading role when the number of serial images is small, and gradually, patient-specific shape statistics plays a more and more important role after a sufficient number of segmentation results on the same patient have been obtained. The proposed deformable model can adapt to the shape variability of different patients, and obtain more robust and accurate segmentation results.

Algorithms↗
PubMed2003

The loss of statistical power to distinguish populations when certain samples are ambiguous.

Case-control studies are used to map loci associated with a genetic disease. The usual case-control study tests for significant differences in frequencies of alleles at marker loci. In this paper, we consider the problem of comparing two or more marker loci simultaneously and testing for significant differences in haplotype rather than allele frequencies. We consider two situations. In the first, genotypes at marker loci are resolved into haplotypes by making use of biochemical methods or by genotyping family members. In the second, genotypes at marker loci are not resolved into haplotypes, but, by assuming random mating, haplotypes can be inferred using a likelihood method such as the expectation-maximization (EM) algorithm. We assume that a causative locus has two alleles with a multiplicative effect on the penetrance of a disease, with one allele increasing the penetrance by a factor pi. We find, for small values of pi-1 and large sample sizes, asymptotic results that predict the statistical power of a test for significant differences in haplotype frequencies between cases and a random sample of the population, both when haplotypes can be resolved and when haplotypes have to be inferred. The increase in power when haplotypes can be resolved can be expressed as a ratio R, which is the increase in sample size needed to achieve the same power when haplotypes are resolved over when they are not resolved. In general, R depends on the pattern of linkage disequilibrium between the causative allele and the marker haplotypes but is independent of the frequency of the causative allele and, to a first approximation, is independent of pi. For the special situation of two di-allelic marker loci, we obtain a simple expression for R and its upper bound.

Alleles↗
PubMed1997

Recent fertility and mortality trends among aboriginal and nonaboriginal populations of central Siberia.

We examine mortality and fertility patterns of aboriginal (primarily Evenki and Keto) and Russian (i.e., nonaboriginal) populations from the Baykit District of Central Siberia for the period 1982-1994. Mortality rates in the aboriginal population of Baykit are substantially greater than those observed in the Russians and are comparable to levels recently reported for other indigenous Siberian groups. Infant mortality rates average 48 per 1000 live births among Baykit aboriginals, three times greater than the Russians of the district (15 per 1000 births) and more than double the rates for Inuit and Indian populations of Canada. Similarly, crude death rates of the Baykit aboriginals are twice as high as those observed in either the Baykit Russians or the Canadian aboriginal populations (13 vs 6-7 deaths per 1000 individuals). Birth rates of the indigenous population of Baykit are higher than those of the Russians (33 vs. 15 births per 1000 individuals) but are comparable to those of Canadian aboriginal groups. Violence and accidents are the leading causes of adult male mortality in both ethnic groups, whereas circulatory diseases have emerged as the prime cause of death in women. The greater male mortality resulting from violence and accidents is a widely observed cross-cultural phenomenon. The emergence of circulatory diseases as a major mortality risk for women, however, appears to be linked to specific lifestyle changes associated with Soviet reorganization of indigenous Siberian societies. Marked declines in mortality and increases in fertility were observed in the Baykit aboriginal population during the mid to late 1980s with the government's implementation of anti-alcohol policies. The decline in mortality, however, was largely erased during the early 1990s, as the region became increasingly isolated and marginalized following the collapse of the Soviet Union. Demographic trends in the Baykit District suggest that because the indigenous groups have become more isolated, many are returning to a more traditional subsistence lifestyle.

Adult↗
PubMed2000

Analysis of anesthesia physician resources: projected Ontario deficit in 2005.

PURPOSE: To clarify the recent perception of shortfalls in anesthesia physician resources, two models were used to assess these resources in Ontario, Canada. METHODS: Two models, demand-based and benchmarking, were used. In the demand-based model estimated future supply and attrition were obtained from information on Ontario Ministry of Health funded trainees. Data from the Canadian Residents Matching Service and the Association of Canadian University Departments of Anesthesia were also used. Current demand was identified from a telephone survey of Departments of Anesthesia in ten Ontario cities. The number of anesthesia practitioners in Ontario was estimated from the 1996 Canadian Anesthesiologists' Society Physician Resource Database (CASPRD) in the demand-based model. In the benchmarking model, using Alberta as the closest published analogue to Ontario, the annual specialist growth rate in Ontario since 1986 was calculated in the literature as 2.8%/yr for 1986-1994. The number of anesthesiologists in Ontario from the 1986 CASPRD was used to calculate need based on that growth rate. Results are compared with population to anesthesiologist (P/A) ratios calculated from Statistics Canada population data and physician numbers from CASPRD. RESULTS: A shortfall in the number of anesthesiologists has been identified. The P/A ratio worsened by 17.6% from 1986 to 1996. The demand-based model indicated that the shortfall is increased from a current deficit of 40 to 68 by 2005, using CASPRD. Benchmarking showed that the estimated shortfall in 1994 was 131. CONCLUSION: This conservative approach indicates that the shortfall in anesthesiologist physician resources will worsen by 2005.

Adult↗