Showing papers on "Population published in 1975"

Period Three Implies Chaos

Abstract: The way phenomena or processes evolve or change in time is often described by differential equations or difference equations. One of the simplest mathematical situations occurs when the phenomenon can be described by a single number as, for example, when the number of children susceptible to some disease at the beginning of a school year can be estimated purely as a function of the number for the previous year. That is, when the number x n+1, at the beginning of the n + 1st year (or time period) can be written $${x_{n + 1}} = F({x_n}),$$ (1.1) where F maps an interval J into itself. Of course such a model for the year by year progress of the disease would be very simplistic and would contain only a shadow of the more complicated phenomena. For other phenomena this model might be more accurate. This equation has been used successfully to model the distribution of points of impact on a spinning bit for oil well drilling, as mentioned if [8, 11] knowing this distribution is helpful in predicting uneven wear of the bit. For another example, if a population of insects has discrete generations, the size of the n + 1st generation will be a function of the nth. A reasonable model would then be a generalized logistic equation $${x_{n + 1}} = r{x_n}[1 - {x_n}/K].$$ (1.2)

The Fire of Life: An Introduction to Animal Energetics

Abstract: A study of the evolution of bioenergetics, this book examines total starvation and the physical aspects of metabolism, as well as the metabolism of the starving animal. It discusses food as fuel and looks at food and population.

Some Problems and Misconceptions Related to the Construct of Internal Versus External Control of Reinforcement

Abstract: Research involving perceived internal versus external control of reinforcement as a personality variable has been expanding at a rapid rate. It seems clear that for some investigators there are problems associated with understanding the conceptualization of this construct as well as understanding the nature and limitations of methods of measurement. This article attempts to discuss in detail (a) the place of this construct within the framework of social learning theory, (b) misconceptions and problems of a theoretical nature, and (c) misuses and limitations associated with measurement. Problems of generalityspecificity and unidimensionality-multidimensionality are discussed as well as the logic of predictions from test scores. Estimates of the number of published articles dealing with some aspect of internal versus external control of reinforcement (sometimes referred to as "locus of control") vary, but it is clear that there are well over 600 studies. The number of unpublished investigations, master's theses, and doctoral dissertations dealing with this topic are impossible to estimate. Most of these studies have been published in the last IS years, and there seems to be still an active, if not increasing, interest in the topic. The concept deals both with situational parameters and individual differences, although the bulk of the studies have been concerned with the latter. One can only speculate on the surprising popularity of this concept as a subject for psychological investigations. Interest in this concept surely must be related to some persistent social problems, which in turn are related to the tremendous growth in population, increasing complexity of society, and the subsequent feeling of powerlessness that seems to permeate all levels of society, at least in Western culture. The research referred to above has produced some important and some well-replicated findings. It has also produced a series of studies that appear to reflect a basic misunderstanding of the nature of the variables and measurement devices used to assess individual differences. It is Requests for reprints should be sent to Julian B. Rotter, Department of Psychology, University of Connecticut, Storrs, Connecticut 06268.

Ecology and Evolution of Communities

Abstract: Introduction Martin L. Cody and Jared M. Diamond Bibliography of Robert MacArthur I. The Evolution of Species Abundance and Diversity 1. Evolution in Communities Near Equilibrium Richard Levins 2. Population Fluctuations, Community Stability, and Environmental Variability Egbert G. Leigh, Jr. 3. Environmental Fluctuations and Species Diversity John W. MacArthur 4. Patterns of Species Abundance and Diversity Robert M. May 5. On Continental Steady States of Species Diversity Michael L. Rosenzweig II. Competitive Strategies of Resource Allocation 6. Selection for Optimal Life Histories in Plants William M. Schaffer and Madhav D. Gadgil 7. Prey Characteristics and Predator Niche Width Henry A. Hespenheide 8. The Temporal Component of Butterfly Species Diversity Arthur M. Shapiro 9. Markovian Processes of Forest Succession Henry S. Horn III. Community Structure 10. Towards a Theory of Continental Species Diversities Martin L. Cody 11. Ecomorphological Configurations and Convergent Evolution James R. Karr and Frances C. James 12. Niche Relations of Desert Lizards Eric R. Pianka 13. Geographical Ecology of Desert Rodents James H. Brown 14. Assembly of Species Communities, Jared M. Diamond 15. Structure of Stream Communities Ruth Patrick 16. Some Mechanisms Producing Structure in Natural Communities Joseph H. Connell IV. Outlook 17. Variations on a Theme by Robert MacArthur G. Evelyn Hutchinson 18. Applied Biogeography Edward 0. Wilson and Edwin 0. Willis Index Contributors

Packet Switching in Radio Channels: Part II--The Hidden Terminal Problem in Carrier Sense Multiple-Access and the Busy-Tone Solution

Abstract: We consider a population of terminals communicating with a central station over a packet-switched multiple-access radio channel. The performance of carrier sense multiple access (CSMA) [1] used as a method for multiplexing these terminals is highly dependent on the ability of each terminal to sense the carrier of any other transmission on the channel. Many situations exist in which some terminals are "hidden" from each other (either because they are out-of-sight or out-of-range). In this paper we show that the existence of hidden terminals significantly degrades the performance of CSMA. Furthermore, we introduce and analyze the busy-tone multiple-access (BTMA) mode as a natural extension of CSMA to eliminate the hidden-terminal problem. Numerical results giving the bandwidth utilization and packet delays are shown, illustrating that BTMA with hidden terminals performs almost as well as CSMA without hidden terminals.

Sociobehavioral determinants of compliance with health and medical care recommendations.

Abstract: Over the past two decades, hundreds of articles, editorials, and commentaries have been published describing the considerable disruptive effects on quality of care of individuals noncompliance with health and medical advice While much research has been directed at determining factors responsible for poor compliance, past studies have tended to focus upon easily measured characteristics of the patients, regimen, or illness which, unfortunately, are usually neither predictive nor alterable This paper systematically reviews the literature on patient acceptance of recommended health behaviors, attempting to find social-psychological and related variables which have proven to be consistent predictors of compliance The review suggests that certain health beliefs (especailly personal estimates of vulnerability to, and seriousness of, the disease, and faith in the efficacy of care), health-related motivations, perceptions of psychological and other costs of the recommended action, various aspects of the doctor-patient relationship, and social influence are the most productive dimensions for present intervention and further exploration Building upon an earlier formulation, an hypothesized model is presented which combines these elements for explaining and predicting compliance behavior Further research should, with standardized questionnaires and analysis techniques, employ prospective, experimental designs for a variety of population groups, settings, and regimens, to evaluate the ability of practical attempts to modify the model variables and thus enhance compliance

Visualization of nucleolar organizer regions im mammalian chromosomes using silver staining

Abstract: A simple ammoniacal silver staining procedure, designated Ag-AS, differentially stains the chromosomal locations of ribosomal DNA in certain mammalian species. This was critically demonstrated by Ag-AS staining of the nucleolus organizer regions in karyotypes of the same species and cell lines used for locating the ribosomal cistrons by DNA/RNA in situ hybridization. With Ag-AS, silver stained NORs (Ag-NORs) are visualized as black spherical bodies on yellow-brown chromosome arms. Ag-NORs were visualized throughout mitosis at the secondary constrictions in the rat kangaroo, Seba's fruit bat, Indian muntjac, and Rhesus monkey. The Chinese hamster and cattle have telomeric Ag-NORs, the mouse subcentromeric Ag-NORs, and the field vole Ag-NORs as minute short arms or choromosomal satellites. Ag-NORs occur at both secondary constrictions and at telomeres in the cotton rat. Variability in Ag-NOR pattern included differences in the number of Ag-NORs per cell within a cell population, size of Ag-NORs among chromosomes of a complement, and presence of Ag-NOR on particular chromosomes in two cell lines of the Chinese hamster. The available cytochemical data suggest that the Ag-AS reaction stains chromosomal proteins at the NOR rather than the rDNA itself.

A Model for Tropic Interaction

Abstract: A nonlinear function general enough to include the effects of feeding saturation and intraspecific consumer interference is used to represent the transfer of material or energy from one trophic level to another. The function agrees with some recent experimental data on feeding rates. A model using this feeding rate function is subjected to equilibrium and stability analyses to ascertain its mathematical implications. The anaylses lead to several observations; for example, increases in maximum feeding rate may, under certain circumstances; result in decreases in consumer population and mutal interference between consumers is a major stabilizing factor in a nonlinear system. The analyses also suggest that realistic classes of consumer—resource models exist which do not obey Kolmogorov's Criteria but are nevertheless globally stable. See full-text article at JSTOR

Substance p: localization in the central nervous system and in some primary sensory neurons

Abstract: Antibodies to substance P with a high titer have been produced and used in immunohistochemical studies on the peripheral and central nervous system of the rat and the cat. Evidence was obtained for the localization of substance P in a certain population of primary sensory neurons, probably small nerve cells with unmyelinated processes. Substance P or a peptide similar to it was also observed in cell bodies in the medial habenula and in probable nerve terminals in many brain areas. The results give morphological support for a transmitter (or modulator) role of substance P in the nervous system.

Nonlinear Aspects of Competition Between Three Species

Abstract: It is shown that for three competitors, the classic Gause–Lotka–Volterra equations possess a special class of periodic limit cycle solutions, and a general class of solutions in which the system exhibits nonperiodic population oscillations of bounded amplitude but ever increasing cycle time. Biologically, the result is interesting as a caricature of the complexities that nonlinearities can introduce even into the simplest equations of population biology ; mathematically, the model illustrates some novel tactical tricks and dynamical peculiarities for 3-dimensional nonlinear systems.

Separation of subfragment-1 isoenzymes from rabbit skeletal muscle myosin.

Abstract: RABBIT skeletal muscle myosin is composed of two heavy chains and four light chains1. Two classes of light chains can be distinguished both chemically and functionally. Within the class of essential light chains (those which cannot be removed without loss of ATPase activity), two chemically related but pheno-typically distinct proteins have been identified2, both of which are present in single fibres of fast-twitch muscles3. The existence of both phenotypes within a single psoas muscle cell indicates that either there is a single population of myosin molecules with a different alkali light chain on each subfragment-1 head, or there are at least two populations of myosin present. Densitometric and radiochemical methods have shown that there is an unequal distribution of these two light chains; this supports the hypothesis that myosin isoenzymes occur in histochemically homogeneous muscles3–5 which cannot be attributed to the presence of contaminating slow-twitch fibres. The presence of different heavy chains also is indicated by the observation of amino acid substitutions in certain peptide sequences6,7. Thus fast-twitch muscles contain myosin showing heterogeneity of both light and heavy chains, suggesting isoenzyme populations, but so far these have not been separated, nor have the proteolytic subfragments derived from them.

Increased risk of endometrial carcinoma among users of conjugated estrogens.

Abstract: The possibility that the use of conjugated estrogens increases the risk of endometrial carcinoma was investigated in patients and a twofold age-matched control series from the same population. Conjugated estrogens (principally sodium estrone sulfate) use was recorded for 57 per cent of 94 patients with endometrial carcinoma, and for 15 per cent of controls. The corresponding point estimate of the (instantaneous) risk ratio was 7.6 with a one-sided 95 per cent lower confidence limit of 4.7. The risk-ratio estimate increased with duration of exposure: from 5.6 for 1 to 4.9 years exposure to 13.9 for seven or more years. The estimated proportion of cases related to conjugated estrogens, the etiologic fraction, was 50 per cent with a one-sided 95 per cent lower confidence limit of 41 per cent. These data suggest that conjugated estrogens have an etiologic role in endometrial carcinoma.

Association of exogenous estrogen and endometrial carcinoma.

Abstract: To determine the association between the incidence of endometrial cancer and the use of estrogen in menopausal and post-menopausal women, we retrospectively compared 317 patients with adenocarcinoma of the endometrium with an equal number of matched controls having other gynecologic neoplasms; 152 patients used estrogen, as compared to 54 of 317 controls. Thus, the risk of endometrial cancer was 4.5 times greater among women exposed to estrogen therapy. When estrogen use was adjusted for concomitant variables such as obesity, hypertension, diabetes, parity, referral pattern, age at diagnosis, year of diagnosis and other gynecologic neoplasms, the magnitude of the increased relative risk was associated with several of these variables, and was highest in patients without obesity and hypertension. Exogenous estrogen therapy is associated with an increased risk of endometrial carcinoma, but this increased relative risk is less apparent in patients with physiologic characteristics previously associated with an increased risk.

Anxiety, restraint, and eating behavior.

Abstract: It was hypothesized that individual differences in eating behavior based on the distinction between obese and normal subjects could be demonstrated within a population of normal subjects classified as to the extent of restraint chronically exercised with respect to eating. Restrained subjects resembled the obese behaviorally, and unrestrained subjects resembled normals. This demonstration was effected in the context of a test .of the psychosomatic hypothesis of obesity. The results indicated that although some individuals may eat more when anxious, there is little empirical support for the notion that eating serves to reduce anxiety. An explanation for this apparent inconsistency was offered. The role of anxiety as a possible causal agent in obesity has recently been subjected to experimental analysis. Schachter, Goldman, and Gordon (1968) hypothesized that although anxiety would decrease eating in normal-weight subjects by inhibiting gastric contractions and releasing sugar into the bloodstream, it would have little if any effect on the obese, who do not eat on the basis of internal physiological state. These predictions were confirmed, with normal-weight subjects eating substantially less (34%) when anxious and the obese eating nonsignificantly more (15%). Schachter et al. (1968) concluded that the psychosomatic hypothesis of obesity —that the obese in effect confuse hunger with negative affect (Bruch, 1961) and thus overeat in response to aversive emotional states (Kaplan & Kaplan, 1957)— had failed to find confirmation. Obese subjects did not eat more when anxious and did not exhibit significant anxiety reduction as a consequence of eating.

Plasmid-controlled colonization factor associated with virulence in Esherichia coli enterotoxigenic for humans.

Abstract: An enterotoxin-producing strain of Escherichia coli isolated from a case of cholera-like diarrhea (E. coli strain H-10407) was found to possess a surface-associated colonization factor. Colonization was manifested as the ability of small inocula (10(5) bacteria) to attain large (10(9)) populations in the infant rabbit intestine with a concomitant diarrheal response. A laboratory-passed derivative of E. coli H-10407, designated H-10407-P, failed to exhibit an increase in population in the infant rabbit and also failed to induce diarrhea. Cell-free culture supernatant fluids of E. coli H-10407 and H-10407-P produced equivalent enterotoxic responses in infant and in adult rabbits. Specific anti-colonization factor antiserum was produced by adsorbing hyperimmune anti-H-10407 serum with both heat-killed and living cells E. coli H-10407-P. This specific adsorbed serum protected infant rabbits from challenge with living E. coli H-10407 although the serum did not possess bactericidal activity. The anti-colonization factor serum did not agglutinate a strain of E. coli K-12 possessing the K88 colonization factor peculiar to E. coli enterotoxigenic for swine. By electron microscopy it was demonstrated that E. coli H-10407, but not H10407-, possessed pilus-like surface structures which agglutinated with the specific adsorbed (anti-colonization factor) antiserum. E. coli H-10407 possessed three species of plasmid deoxyribonucleic acid, measuring 60 X 10(6), 42 X 10(6), and 3.7 X 10(6) daltons, respectively. E. coli H-10407-P possessed only the 42 X 10(6)- and the 3.7 X 10(6)-dalton plasmid species. Spontaneous loss of the specific H-10407 surface-associated antigen was accompanied by loss of the 60 X 10(6)-dalton species of plasmid deoxyribonucleic acid and loss of colonizing ability. Thus, it is concluded that the E. coli colonization factor described here is a virulence factor which may play an important and possibly essential role in naturally occurring E. coli enterotoxic diarrhea in man.

An autoradiographic study of the time of origin and the pattern of granule cell migration in the dentate gyrus of the rat

Abstract: The dentate gyrus of the rat contains about 600,000 granule cells. These small neurons are generated over a prolonged period from the 14th day of gestation until sime time after the second postnatal week. The majority of the cells pass through their last phase of DNA synthesis in the postnatal period, and during the peak period of cell generation, between the fifth and seventh days after birth, up to 50,000 granule cells are formed each day. Contrary to earlier reports, most of the cells pass through their last mitotic division either within the stratum granulosum itself, or within the hilar region of the developing gyrus. The precursor population of cells in the hilar region must therefore constitute a pool of true neuroblasts. The origin of this pool of cells has not been definitely established but it seems probable that its cells are derived from the neuroepithelium lining the lateral ventricle adjacent to the region from which the hippocampal pyramidal cells are generated. Examination of the final location of granule cells labeled at different stages reveals three distinct morphogenetic gradients in the gyrus. The cells in the dorsal blade tend to be formed earlier than those in the ventral blade; cells in the more caudal (or temporal) portions of the gyrus are generated earlier than those in more rostral (or septal) regions; and in all regions the more superficial neurons in the stratum granulosum are formed earlier than the deeper granule cells. The bearing of some of these findings on the development and organization of the connections of the dentate gyrus is discussed.

Social Class and Psychiatric Disturbance among Women in an Urban Population

Abstract: While an association between social status and prevalence of psychiatric disurbance has often been reported, little has been established about aetiology or its significance for social class differences. In a survey of a random sample of women living in south London a large class difference in the prevalence of psychiatric disturbance was found. This difference is particularly great among women with young children at home. This paper examines why working class women have a greater prevalence of (i) conditions with an onset in the year before interview and (ii) conditions that have lasted longer than one year. Severe life-events and major long term difficulties occurring in the year before onset play an important aetiological role. However although these aetiological agents are more common among working class women, they only explain a small part of the social class differences. The class difference is essentially due not to the greater frequency of events and difficulties but to the much greater likelihood...

A model for trophic interaction

Abstract: A nonlinear function general enough to include the effects of feeding saturation and intraspecific consumer interference is used to represent the transfer of material or energy from one trophic level to another. The function agrees with some recent experimental data on feeding rates. A model using this feeding rate function is subjected to equilibrium and stability analyses to ascertain its mathematical implications. The analyses lead to several observations; for example, increases in maximum feeding rate may, under certain circum- stances, result in decreases in consumer population and mutual interference between consumers is a major stabilizing factor in a nonlinear system. The analyses also suggest that realistic classes of consumer-resource models exist which do not obey Kolmogorov's Criteria but are nevertheless globally stable.

Cell death in the development of the lateral motor column of the chick embryo.

Abstract: Cell counts were made in the lumbar lateral motor column (l.m.c.) of chick embryos of 5.5, 6, 7, 8, 9, 12, 18 days of incubation and five days posthatching (n = equals; 68). Only nuclei with nucleoli were counted and corrections were made for double counting (Abercrombie, 1946). The population attains a peak value of over 20,000 cells (corrected figure: over 17,000) at 5.5–6.5 days = stages 28 and 29 (Hamburger and Hamilton, 1951). The l.m.c. loses between 7,000 and 8,000 cells between days 6.5 and 9.5, (between stages 29 and 36). In other words, 60% of the population survive. A plateau of approximately 12,300 cells (corrected figure: 10,300) is maintained throug five days posthatching. Massive cell degeneration was observed in 7- and 8-day embryos. Counts of distinctly pyknotic cells indicate that at least 5–6% of the total population is in the process of degeneration at any particular time. This figure is probably an underestimation; hence it is virtually certain that the depletion of the l.m.c. is due entirely to cell death. Arguments are presented in support of the hypothesis that the naturally occurring cell death in the l.m.c. is due to the failure of their axons to survive in a competion process at the periphery. Observations of the time pattern of muscle differentiation and their neurotization in the leg further endorse this hypothesis. However, it is not clear whether the axons compete for contact sites on muscle fibers or for a “trophic” agent.

Toward a Subcultural Theory of Urbanism

Abstract: Wirth's (1938) theory of urban life has been eclipsed in recent years by a perspective that denies the importance of ecological factors. This view, though more accurate than Wirth's, fails to account for the pervasive "unconventionality" (deviance, invention, etc.) of urban life. A model is presented here to remedy that problem; it reintroduces the variable of size but in a manner distinct from Writh's. Population concentration produces a diversityof subcultures, strengthens them, and fosters diffusion among them. Together, these three mediating variables account for urban unconventionality. The four propositions of the theory and three others deducible from it are examined against existing research.

A theory of evolution above the species level.

Abstract: Gradual evolutionary change by natural selection operates so slowly within established species that it cannot account for the major features of evolution. Evolutionary change tends to be concentrated within speciation events. The direction of transpecific evolution is determined by the process of species selection, which is analogous to natural selection but acts upon species within higher taxa rather than upon individuals within populations. Species selection operates on variation provided by the largely random process of speciation and favors species that speciate at high rates or survive for long periods and therefore tend to leave many daughter species. Rates of speciation can be estimated for living taxa by means of the equation for exponential increase, and are clearly higher for mammals than for bivalve mollusks.

An economic framework for fertility analysis.

Abstract: An economic framework for fertility analysis is discussed. When the theory of consumer behavior is applied to childbearing fertility is viewed as the consumer demand for children over other goods. Standard economic theory limits the determinants of fertility to 1) the demand for children and 2) the cost of fertility regulation. The broader economic theory presented here includes child production potential as a determinant in human fertility. Production potential allows for the application of consumer behavior theory to a greater number of world conditions such as nonmarital fertility fluctuation in fertility in premodern times the decline in fertility in industrialized societies and the distinctions made between social vs. individual control of fertility.

A new analysis of allogeneic interactions.

Abstract: Allogeneic reactions have conventionally been considered as typical immune responses by one population of cells to antigens present on the other. This view is inadequate, since it does not explain many features of these reactions, among which are: (1) reactivity is much higher between different strains within a species than between species, in spite of the much greater antigenic disparity in the second case; (2) a very high proportion of cells may respond to allogeneic stimuli; (3) major histocompatibility differences are not essential for vigorous allogeneic reactions; (4) the responding population need not be immunologically competent to respond to antigens of the stimulating population; (5) the stimulating population must be both metabolically active and immunocompetent. We have tried to produce a model of cell interaction which will account for these and other anomalies, which at the same time explaining both normal antigenic stimulation (through cell-cell cooperation) and allogeneic interactions as examples of the same basic mechanisms. The model is based on the Bretscher-Cohn scheme of cell interaction. An allogeneic reaction is seen as having two stages: (1) Cells come together when antibody receptors on cells of one population combine with antigens on cells of the other. To this extent, our model is the same as the conventional one. It need not be the responding population which has the receptors, however. (2) A species-specific proliferation signal passes between the cells. This is the same signal as is involved in normal antibody induction. Even antigen-receptor bonds which are very weak may result in effective stimulation of one or both partners because of enhancing effect of this signal, and because the antigens involved are probably repeated over the cell surface, enabling multipoint binding. This explains the very proportions of cells which proliferate. The exact outcome of any allogeneic interaction will depend on which of the two populations have antibody receptors for antigens on the other, which can produce the proliferative stimulus, and which can respond to either the proliferative signal alone or to this stimulus plus antigen.