The relationship between serial monogamy and rape in the United States (1960-1995).

In mating systems where individuals pair, separate and re-pair repeatedly (i.e. serial monogamy), some males monopolize more than one female's reproductive life span and thus leave other males effectively mateless. Males who cannot secure females through traditional methods may seek alternatives, such as rape, to ensure gene passage into future generations. Analysis of US government records shows that (i) divorce and remarriage patterns in the United States are likely to increase the variance in male reproductive success, and (ii) rates of divorce and rape correlate positively. The former result suggests that serial monogamy increases the variance in male, relative to female, reproductive success and the latter result suggests that this variance influences the frequency of rape in American society. Because raped females sometimes become pregnant and take these pregnancies to term, our results indicate that rape has current adaptive significance.

Fever in honeybee colonies.

Honeybees, Apis spp., maintain elevated temperatures inside their nests to accelerate brood development and to facilitate defense against predators. We present an additional defensive function of elevating nest temperature: honeybees generate a brood-comb fever in response to colonial infection by the heat-sensitive pathogen Ascosphaera apis. This response occurs before larvae are killed, suggesting that either honeybee workers detect the infection before symptoms are visible, or that larvae communicate the ingestion of the pathogen. This response is a striking example of convergent evolution between this "superorganism" and other fever-producing animals.

Stability analysis of two linear accommodation and convergence models.

PURPOSE: To perform time domain stability analysis on two widely accepted linear models of accommodation and convergence. METHODS: For each model, the governing differential equations were used to compute the system matrix. The system matrices were used to calculate the respective trace and determinant from which eigen-vectors and eigenvalues were quantified. These characteristic numbers fully identified and classified the fixed points of each model and, thus, their stability. RESULTS: Controller gains, time constants, and accommodation and convergence cross-links determined model stability. Accommodation and convergence cross-links have the greatest influence on stability. A model-specific transition between stabilities was identified as the product of these cross-links, AC.CA(CRITICAL). For each model, three types of fixed points are described and displayed graphically: stable node, line of nonisolated fixed points, and saddle. CONCLUSION: We demonstrated the stability analysis of a two-dimensional linear system, working only in the time domain. The benefit of time-domain stability analysis is that it can be extended to nonlinear systems when frequency domain analysis techniques fail. Given that we live in a fundamentally nonlinear world and that the use and application of computational models is extensive, this is a valuable and important tool.

An extension of an accommodation and convergence model of emmetropization to include the effects of illumination intensity.

The Flitcroft (1998) emmetropization model incorporates a classical model of accommodation and convergence with blur-driven feedback control of eye growth. We have modified this model by incorporating the effects of illumination (with or without extensive near work) on accommodation, vergence, pupil diameter and emmetropization. In addition to replicating Flitcroft's results, we show that (1) decreased illumination and (2) a low convergence accommodation/convergence (CAC) ratio exacerbate the progression of near-work-induced myopia. Our model further indicates that prescription of negative lenses, under these conditions, augments the advancement of myopia.

Refraction and keratometry: departures from and transformations toward multivariate normality.

The multivariate distributional properties of refraction and keratometric data were investigated across eyes with power represented in the coordinate system introduced by Deal and Toop. Normality and departure from normality were assessed with the aid of chi 2 and normal probability plots and by the comparison of multivariate sample skewness and kurtosis with critical values. Two of the three data sets show significant departure from normality in each of the marginal distributions and, therefore, the joint distribution too. The keratometric data were normally distributed along the line of spherical powers but departed from normality in the astigmatic plane. Marginal transformations are used to reduce the departure from normality where necessary. The transformation that was found to be successful is essentially an example of a Box/Cox transformation involving a shift, ci, and an exponent, gamma i, where i = 1,2,3. For two of the data sets, the values of the exponent, gamma i, result in a transformation that is similar to a modified square root transformation.