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Biomedical subjects

A Dewanji

Publications and source records attributed to A Dewanji.

16 recordsLinked to original sources
PubMed2005

A generalized Luria-Delbrück model.

We develop extensions of the Luria-Delbrück model that explicitly consider non-exponential growth of normal cells and a birth-death process with mean exponential or Gompertz growth of mutants. Death of mutant cells can be important in clones arising during cancer progression. The use of a birth-death process for growth of mutant cells, as opposed to a pure birth process as in previous work on the Luria-Delbrück model, leads to a large increase in the extra Poisson variation in the size of the mutant cell populations, which needs to be addressed in statistical analyses. We also discuss connections with previous work on carcinogenesis models.

Cell Growth Processes↗
PubMed1999

Two stage model for carcinogenesis: number and size distributions of premalignant clones in longitudinal studies.

The two stage clonal expansion model of carcinogenesis provides a convenient biologically based framework for the description of toxicologic and epidemiologic data on carcinogenesis. Under this model, a cancer cell is generated following the occurrence of two critical mutations in a single stem cell. Initiated cells that have sustained the first mutation undergo a stochastic birth-death process resulting in clonal expansion of the initiated cell population. In this article, we consider the analysis of longitudinal data on the number and size of premalignant clones, formed by clonal expansion of initiated cells. In particular, the joint distribution of the number of premalignant clones observed at different points in time in the same subject is derived. The application of these results in the statistical analysis of longitudinal data on the number and size of premalignant clones observed in initiation-promotion experiments is indicated.

Animals↗
PubMed1998

Projection of HIV infection in Calcutta.

Starting with the base year of 1991, the HIV infection projection for 1992-99 for the total, as well as various high-risk sub-populations of Calcutta, the first of its kind is provided. These projections are based on statistical methodology developed in this paper. Our methodology for spread of HIV infection takes into account various social interactions and practices and also uses available data. Rates of these interactions and practices and estimates of demographic parameters used in making projections were obtained primarily from surveys and census data. Since one of these estimated rates, that of HIV transmission rate through heterosexual encounters between an infected and an uninfected had a large range, we have provided two sets of projections based on the largest of these rates (worst-case scenario) and another that is consistent with the available data. The total projection of the number of HIV infected cases in Calcutta for 1999 is between 49,000 and 1,26,000. Separate projections are also provided for high-risk sub-groups. Among these, the sex workers expectedly will continue to manifest the highest numbers of newly infected cases. The temporal rate of increase in prevalence is projected to be alarmingly higher in the general population than even among sex workers, although the actual prevalence will continue to be the lowest in the general population compared to all other sub-groups of the population.

Female↗
PubMed1997

Extractability and nutritional value of leaf protein from tropical aquatic plants.

In a study conducted on the extraction of protein from the leaves of 30 freshwater aquatic plants, the highest standing crop fresh yield was found in Typha latifolia (2650 g/m2). The Bio-Medical Data Processing (BMDP) K-means clustering program with K = 2 showed that 11 of the 30 plants had a high protein nitrogen extractability as well as a high nitrogen content of the extracted protein. Among these, leaf protein from Allmania nodiflora had the highest content of crude protein (62.7%) and beta-carotene (782.4 micrograms/g). Leaf protein prepared from Hygrophila spinosa, Ottelia alismoides and Polygonum barbatum had low in-vitro digestibility. The levels of alkaloids and polyphenols were lower in the extracted protein compared to that present in the original leaf sample.

Dietary Proteins↗
PubMed1996

A biologically based model for the analysis of premalignant foci of arbitrary shape.

In many animal carcinogenesis experiments, quantitative data on putative premalignant foci are now routinely collected. Moolgavkar et al. [Carcinogenesis 11:1271 (1990)] considered the analysis of such data from a rat hepatocarcinogenesis experiment within the framework of a two-stage model for carcinogenesis using the assumption that the premalignant clones were spherical. This assumption seems questionable in many organs, including the liver. In this paper, it is relaxed and arbitrary shapes are allowed for the clones. The proposed method is illustrated by reanalysis of the data considered in the earlier paper. The new analysis yields parameter estimates that are more plausible biologically than those of the original analysis.

Animals↗
PubMed1993

Chemical composition of two semi-aquatic plants for food use.

The seasonal variation in the nutrient composition of Enhydra fluctuans and Marsilea quadrifolia, two edible semi-aquatic plants, was studied in order to promote their consumption as green leafy vegetables. Both plants had a high crude protein content throughout all harvesting seasons. Enhydra fluctuans had a low ash content and was a good source of beta-carotene (3.7 to 4.2 mg/100 g on a fresh weight basis). Marsilea quadrifolia exhibited wide fluctuations between seasons and was not very promising in nutrient composition when compared to other commonly used green leafy vegetables.

Carotenoids↗
PubMed1993

Working status and anxiety levels of urban educated women in Calcutta.

The primary objective of the present study was to assess the impact of out-of-home employment on anxiety levels of mothers. A study group of working mothers resident in Calcutta (India) was compared with a socioeconomically similar group of non-working mothers with respect to their anxiety level, measured by the Anxiety Scale Questionnaire, in terms of the total anxiety score and its various personality components. The possible relationships between anxiety score and age of these mothers as well as their children were studied. Non-working mothers showed higher anxiety levels than their working counterparts with respect to the total anxiety score as well as its components, although the differences were statistically non-significant. The anxiety scores of non-working mothers showed increasing values with increasing age of children. This trend was absent among the working mothers. The age of these mothers was not related to their anxiety level.

Adaptation, Psychological↗
PubMed1993

A Weibull model for the estimation of tumorigenic potency.

In this paper, a new method of estimating tumorigenic potency is proposed that takes into account information on survival and, when available, the underlying cause of death. Specifically, Weibull distributions are used to describe the time to tumor occurrence (X), the time to death as a result of tumor occurrence (Y), and the time of death from causes other than tumor occurrence (Z). The distributions of X and Y are related via a lethality parameter p lying between 0 (incidental tumors) and 1 (rapidly fatal tumors). The index of tumorigenic potency is defined as the dose inducing a specified excess tumor response rate (in the range of 25%-50%) following exposure for an extended period encompassing most of the expected lifespan. Application of the proposed method is illustrated using several data sets taken from the literature.

2-Acetylaminofluorene↗
PubMed1991

Two-mutation model for carcinogenesis: joint analysis of premalignant and malignant lesions.

A model for carcinogenesis that postulates two rate-limiting events for malignant transformation is a generalization of the recessive oncogenesis hypothesis, according to which inactivation of homologous tumor suppressor genes leads to cancer. This model has been shown to be consistent with a large body of epidemiologic and experimental data and has recently been used for the analysis of altered hepatic foci in rodents. These foci are considered to be premalignant lesions. In this paper the necessary mathematics for the joint analysis of premalignant and malignant lesions are developed within the framework of this model.

Animals↗
PubMed1989

Cigarette smoking and lung cancer: reanalysis of the British doctors' data.

Attention has focused recently on the recessive oncogenesis model, according to which inactivation of both alleles of specific genes leads to cancer. A mathematical formulation of this model was fitted to the lung cancer incidence data from a cohort study among British doctors. The model described the data well. One implication is that age influences lung cancer risk among smokers independently of duration of smoking. A study of dose-response within the framework of the model shows that the data are consistent with various interpretations regarding the relative importance of daily level of smoking and duration of smoking in determining lung cancer risk.

Adult↗
PubMed1986

Nonparametric methods for survival/sacrifice experiments.

In many carcinogenicity studies, the time to disease occurrence is not clinically observable; a survival/sacrifice experiment is considered for nonparametric inference about the rate of disease occurrence. A multistate model for disease development and death is considered and an algorithm of the EM type for maximum likelihood estimation is obtained. Questions of identifiability and estimability are addressed. Under the model, interval hazards for disease occurrence are identifiable for intervals defined by the sacrifice times. A score test is developed appropriate for the comparison of two groups with respect to disease development without need of any assumption concerning lethality of the disease concerned.

Animals↗