This paper presents a physics-based macroscale model for the densification of dry snow which provides for a smooth transition between densification by grain-boundary sliding (stage 1) and densification by power-law creep (stage 2). The model uses established values of the stage 1 and 2 densification rates away from the transition zone and two transition parameters with a simple physical basis: the transition density and the half-width of the transition zone. It has been calibrated using density profiles from the SUMup database and physically based expressions for the transition parameters have been derived. The transition model produces better predictions of the depth of the nominal bubble close-off horizon than the Herron and Langway model, both in its classical form and in a recent version with re-optimised densification rates.

A log-coffin excavated in the early nineteenth century proved to be well enough preserved in the early twenty-first century for the full armoury of modern scientific investigation to give its occupants and contents new identity, new origins and a new date. In many ways the interpretation is much the same as before: a local big man buried looking out to sea. Modern analytical techniques can create a person more real, more human and more securely anchored in history. This research team shows how.

A population genetics model of the role of asymmetric pairing and unequal exchange in the stabilization of transposable element copy number in natural populations is proposed and analysed. Monte Carlo simulations indicate that the approximations incorporated into the analysis are robust in the relevant parameter ranges. Given several simple assumptions concerning transposition and excision, equal and unequal exchange, and chromosome structure, predictions of the relative numbers of transposable elements in various regions of the Drosophila melanogaster genome are compared to the observed distribution of roo/B104 elements across chromosomal regions with differing rates of exchange, and between X chromosomes and autosomes. There is no indication of an accumulation of elements in the distal regions of chromosomes, which is expected if unequal exchange is reduced concomitantly with normal crossing over in the distal regions. There is, however, an indication of an excess of elements relative to physical length in the proximal regions of the chromosomes, which also have restricted crossing over. This observation is qualitatively consistent with the model's predictions. The observed distribution of elements between the mid-sections of the X chromosomes and autosomes is consistent with the predictions of one of two models of unequal exchange.

The numbers of members of three families of copia-like elements were counted on twenty X, 2nd and 3rd chromosomes collected from a natural population of Drosophila melanogaster. Theoretical predictions were computed for two models of copy number stabilization: (1) element frequencies are regulated by a simple genetic process such as copy number dependent transposition or excision, independent of chromosomal location; (2) elements are eliminated by natural selection against mutational effects of their insertion into the chromosome. Since insertions into the X can be expected to suffer more selection than autosomal insertions, due to expression of mutant phenotypes in the hemizygous state, hypothesis 2, called the disproportional model, predicts that the proportion of elements on the X will be smaller than the proportion of the genome contributed by the X, while hypothesis 1, called the equiproportional model, predicts that this proportionality will be unaffected. Two of the elements, 297 and roo, showed no evidence for deficiency of X-linked elements, but the data for a third element, 412, were consistent with the prediction based on the selective model.

These results indicate that simple selection against mutational effects of insertions of transposable elements is not generally adequate to account for their distribution within populations. We argue that a mechanism such as recombination between elements at different chromosomal sites, leading to rearrangements with highly deleterious, dominant effects could play a role in stabilizing copy number. This process would lead to a higher abundance of elements in genomic regions with restricted crossing over. We present some data indicating such an effect, and discuss possible interpretations.

Scholars often use roll-call votes to study legislative behaviour. However, many legislatures only conclude a minority of decisions by roll call. Thus, if these votes are not a random sample of the universe of votes cast, scholars may be drawing misleading inferences. In fact, theories over why roll-call votes are requested would predict selection bias based on exactly the characteristics of legislative voting that scholars have most heavily studied. This article demonstrates the character and severity of this sampling problem empirically by examining European Parliament vote data for a whole year. Given that many legislatures decided only a fraction of their legislation by roll call, these findings have potentially important implications for the general study of legislative behaviour.