Self-Reported Substantial 1-Year Weight Change Among Men and Women in the United States

Population-based data have not been readily available on relatively short-term changes in weight. Therefore, we sought to determine the nature of self-reported substantial (> 10%) weight change over one year in a representative sample of the US population which participated in the 1989 National Health Interview Survey (NHIS). Across all ages, a larger proportion of women than men reported both weight loss as well as weight gain of any amount (18.9% vs. 16.1% for weight loss and 20.0% vs. 16.1% for weight gain). In sex-specific logistic regression analyses, significant risk factors common to both sexes for substantial weight loss included divorced/separated marital status, smoking, increased number of blood pressure checks, increased BMI (body mass index) and increased number of bed days. Black race reduced the risk of weight loss for both men and women. Sex-specific risk factors for weight loss in men only were widowhood or never married marital status, while increasing age was a protective factor in women only. Concerning weight gain > 10% over the past year, increased number of blood pressure checks and having one or more diabetic parents were significant risk factors among both men and women; while never being married, increased age, BMI, and education exerted a protective effect in both sexes. For women only, risk factors for weight gain included black race, increased number of contacts with a health professional, and being unemployed. Intention to lose weight was associated with both weight gain and weight loss in both sexes, although it did not serve as a confounder in any of these relationships. A greater likelihood of substantial weight loss among women relative to men was diminished for persons with higher BMI, higher number of blood pressure checks, being widowed, divorced or separated, and intention to lose weight. A greater likelihood of substantial weight gain among women relative to men was diminished for persons with low BMI. The results of this cross-sectional study of weight change, involving a one-year follow-up period, generally correspond with the results obtained by longitudinal studies involving a longer follow-up.     

向日葵籽实产量预测数学模型的研究

根据2年10个点次的田间试验结果建立了由数粒法、盘重法和盘径法预测向日葵籽实产量的回归数学模型,并根据1994年4个点次的产量实测结果对各模型的可靠性进行了验证．结果表明,三种方法建立的模型均有效、可靠．但在我国向日葵科研和生产实践中,以盘径法最为实用,建议推广应用．     

On some formulas in a partnership model from the perspective of a semi-Markov process

Many deterministic models of sexually transmitted diseases, as well as population models in general, contain elements of stochastic or statistical reasoning. An example of such a model is that of Dietz and Hadeler (1988) concerning sexually transmitted diseases in which there is partnership formation and dissolution. Among the interesting formulas in this paper, which enter into the analysis of the model, are those for the expected number of partners a male or female has during a lifetime. To a probabilist such formulas suggest the possibility that some stochastic process may be constructed so as to yield these formulas as well as others that may be of interest. The principal purpose of this paper is to demonstrate that such a stochastic process does indeed exist in the form of a three state semi-Markov process in continuous time with stationary laws of evolution and with a one-step density matrix determined by four parameters which were interpreted as constant latent risk functions in the classical theory of competing risks. This construction of a semi-Markov process not only provides a framework for the systematic derivation of the formulas of Dietz and Hadeler but also suggests pathways,for extensions to the age-dependent case.This research was partially supported by NATO Grant D.890350     

A cross-diffusion model of forest boundary dynamics

A simple mathematical model of mono-species forest with two age classes which takes into account seed production and dispersal is presented in the paper. This reaction — diffusion type model is then reduced by means of an asymptotic procedure to a lower dimensional reaction — cross-diffusion model. The existence of standing and travelling wave front solutions corresponding to the forest boundary is shown for the later model. On the basis of the analysis, possible changes in forest boundary dynamics caused by antropogenic impacts are discussed.     

Bifurcation analysis of periodic SEIR and SIR epidemic models

The bifurcations of the periodic solutions of SEIR and SIR epidemic models with sinusoidally varying contact rate are investigated. The analysis is carried out with respect to two parameters: the mean value and the degree of seasonality of the contact rate. The corresponding portraits in the two-parameter space are obtained by means of a numerical continuation method. Codimension two bifurcations (degenerate flips and cusps) are detected, and multiple stable modes of behavior are identified in various regions of the parameter space. Finally, it is shown how the parametric portrait of the SEIR model tends to that of the SIR model when the latent period tends to zero.     

Modelling the effect of treatment and behavioral change in HIV transmission dynamics

In this paper we analyze a model for the HIV-infection transmission in a male homosexual population. In the model we consider two types of infected individuals. Those that are infected but do not know their serological status and/or are not under any sort of clinical /therapeutical treatment, and those who are. The two groups of infectives differ in their incubation time, contact rate with susceptible individuals, and probability of disease transmission. The aim of this article is to study the roles played by detection and changes in sexual behavior in the incidence and prevalence of HIV. The analytical results show that there exists a unique endemic equilibrium which is globally asymptotically stable under a range of parameter values whenever a detection /treatment rate and an indirect measure of the level of infection risk are sufficiently large. However, any level of detection/ treatment rate coupled with a decrease of the transmission probability lowers the incidence rate and prevalence level in the population. In general, only significant reductions in the transmission probability (achieved through, for example, the adoption of safe sexual practices) can contain effectively the spread of the disease.     

Species composition of dabbling duck assemblages: ecomorphological patterns compared with null models

Ecomorphological patterns of breeding dabbling duck (Anas spp.) assemblages were studied in six regions in northern Europe. Observed spacings among species in terms of bill lamellar density and body length were compared with expected spacings based on null models incorporating different levels of constraints (regional species pools, species relative abundances, lake size and habitat requirements of species). Deviations of observed spacings from expected ones were compared with prey abundance and prey size diversity in the lakes. Observed spacings in terms of body length, but not in terms of bill lamellar density, were greater than expected on the basis of null models. The most abundant species were generally relatively more different than less abundant species in terms of body length but not in terms of bill lamellar density. Deviations between observed and expected spacings in terms of body length were more like those predicted by the competition hypothesis in lakes with low food abundance than in lakes with high food abundance. Patterns in bill lamellar spacings were not related to food abundance nor to food size diversity. In general, patterns in body length spacings were consistent with the competition hypothesis whether the null model used in comparisons was constrained or not.     

Presence of double‐stranded RNAs and virus‐like particles in the entomopathogenic fungus Metarhizium anisopliae

Nucleic acids from 41 strains of Metarhizium anisopliae, obtained from different parts of the world were extracted and examined by electrophoresis. Strong bands of double‐stranded RNA (dsRNA) were detected in two isolates from Brazil, V215 and V291, which had, respectively, 13 and 9 distinct bands ranging in size from ca. 0.75 to 3.5 kb. Icosahedral virus‐like particles (VLPs) (ca. 33 nm in diameter) were observed by transmission electron microscopy in extracts of these isolates. The VLPs and dsRNA were both absent from a clone of the isolate V291 which had been subcultured successively on solid medium. Bioassays against the aphid Myzus persicae showed no detectable difference in virulence between the clone of V291 which contained dsRNA and the clone that did not.     

Normoxic and anoxic heat output of the freshwater bivalves Pisidium and Sphaerium

In fasting Pisidium amnicum and Sphaerium corneum, regular periods of behavioural and metabolic quiescence were shown to occur in the normoxic, constant environment of the flow-through chamber of a heat-flow microcalorimeter. The metabolic rate was suppressed to 7.5% of normal at 10° C and to 8.5–9.7% at 20° C for periods exceeding the period of active metabolism by a factor of 3.5 at 10° C and 8.3 at 20° C. The rate of heat output during normoxic quiescence was equal to that during environmental anoxia, suggesting spontaneous achievement of body anoxia by complete shell closure. The mass-specific integrated heat output during closure periods was independent of size. Parallel observations on clam behaviour suggested that metabolic quiescence coincided with shell closure, and bursts of heat flow with active ventilation. Shell closure was accompanied by pronounced bradycardia, down to 20% of the active rate. In a constant environment, the rhythmic quiescence is regulated by shell closure which is probably triggered by lack of food. Regular quiescence of fasting bivalves may conserve energy reserves considerably, the amount depending on the possible excretion rate of the end products, and the post-quiescence recovery costs, which were not measured. Heat output during the active period was close to the average metabolic rate found earlier for Sphaeriidae. However, all the values determined so far are likely to be underestimates of the natural metabolism because the effects of digestion and growth are not included.     

Simulation of nitrogen assimilation by heterotrophic soil microbial biomass

Assimilation of N by heterotrophic soil microbial biomass is associated with decomposition of organic matter in the soil. The form of N assimilated can be either low molecular weight organic N released from the breakdown of organic matter (direct assimilation), or NH⁺₄ and NO⁻₃ from the soil inorganic N pool, into which mineralized organic N is released (mineralization immobilization turnover). The kinetics of C and N turnover in soil is quantifiable by means of computer simulation models. NCSOIL was constructed to represent the two assimilation schemes. The rate of N assimilation depends on the rate of C assimilation and microbial C/N ratio, thereby rendering it independent of the assimilation scheme. However, if any of the N forms is labeled, a different amount of labeled N assimilation will be simulated by the different schemes. Experimental data on inorganic N and ¹⁵N and on organic ¹⁵N dynamics in soils incubated with ¹⁵N added as NH⁺₄ or organic N were compared with data simulated by different model schemes. Direct assimilation could not account for the amount of ¹⁵N assimilated in any of the experimental treatments. The best fit of the model to experimental data was obtained for the mineralization immobilization turnover scheme when both NH⁺₄ and NO⁻₃ were assimilated, in proportion to their concentration in the soil.