Impact-Induced Melting of Near-Surface Water Ice on Mars

All fresh and many older Martian craters with diameters greater than a few km are surrounded by ejecta blankets which appear fluidized, with morphologies believed to form by entrainment of liquid water. We present cratering simulations investigating the outcome of 10 km s–1 impacts onto models of the Martian crust, a mixture of basalt and ice at an average temperature of 200 K. Because of the strong impedance mismatch between basalt and ice, the peak shock pressure and the pressure decay profiles are sensitive to the mixture composition of the surface. For typical impact events, about 50% of the excavated ground ice is melted by the impact-induced shock. Pre-existing subsurface liquid water is not required to form observed fluidized ejecta morphologies, and the presence of rampart craters on different age terranes is a useful probe of ground ice on Mars over time

Multidimensionality of Entrepreneurial Firm-level Processes: Do the Dimensions Covary?

Covariance (or not) among the first-order dimensions of firm-level entrepreneurial processes underpins a fundamental and non-trivial difference between the entrepreneurial orientation and entrepreneurial posture constructs. Utilizing a typology developed for multi-dimensional constructs, we operationalized each construct according to its specific conceptualization (relationships among the dimensions) and compared and contrasted each construct in an identical nomological network. Although we found support for both theories, the entrepreneurial orientation construct was more robust in explaining additional variance in growth. Additionally, our findings suggest that the means through which the first-order dimensions are operationalized—latent vs. summates— significantly affect the analysis

Links between parental life histories of wild salmon and the telomere lengths of their offspring

The importance of parental contributions to offspring development and subsequent performance is self-evident at a genomic level; however, parents can also affect offspring fitness by indirect genetic and environmental routes. The life history strategy that an individual adopts will be influenced by both genes and environment; and this may have important consequences for offspring. Recent research has linked telomere dynamics (i.e. telomere length and loss) in early life to future viability and longevity. Moreover, a number of studies have reported a heritable component to telomere length across a range of vertebrates, though the effects of other parental contribution pathways have been far less studied. By using wild Atlantic salmon with different parental life histories in an experimental split-brood IVF mating design and rearing the resulting families under standardised conditions, we show that there can be significant links between parental life history and offspring telomere length (studied at the embryo and fry stage). Maternal life history traits, in particular egg size, were most strongly related to offspring telomere length at the embryonic stage, but then became weaker through development. In contrast, paternal life history traits, such as the father's growth rate in early life, had a greater association in the later stages of offspring development. However, offspring telomere length was not significantly related to either maternal or paternal age at reproduction, nor to paternal sperm telomere length. This study demonstrates both the complexity and the importance of parental factors that can influence telomere length in early life

The spherically symmetric collapse of a massless scalar field

We report on a numerical study of the spherically symmetric collapse of a self-gravitating massless scalar field. Earlier results of Choptuik(1992, 1994) are confirmed. The field either disperses to infinity or collapses to a black hole, depending on the strength of the initial data. For evolutions where the strength is close to but below the strength required to form a black hole, we argue that there will be a region close to the axis where the scalar curvature and field energy density can reach arbitrarily large levels, and which is visible to distant observersComment: 23 pages, 16 figures, uuencoded gzipped postscript This version omits 2 pages of figures. This file, the two pages of figures and the complete paper are available at ftp://ftp.damtp.cam.ac.uk/pub/gr/rsh100

Shorter juvenile telomere length is associated with higher survival to spawning in migratory Atlantic salmon

The risk of mortality associated with a long-distance migration will depend on an animal's physiological state, as well as the prevailing ecological conditions. Here we assess whether juvenile telomere length, which in endotherms has been shown to be a biomarker of physiological state and expected lifespan, predicts whether wild Atlantic salmon Salmo salar successfully complete their marine migration. Over 1800 juvenile fish were trapped, measured, PIT-tagged and a tissue biopsy taken when migrating as juveniles down-river towards the sea. Survivors of the marine phase of the life cycle were then re-trapped and re-sampled when returning to the river to spawn as sexually mature adults, 1.5-2.5 years later. Most individuals experienced a reduction in telomere length during the marine migratory phase of their life cycle. While the relative rate of telomere loss was greater in males than females, telomere loss was unrelated to growth at sea. Contrary to expectations, salmon that had the shortest telomeres at the time of the outward migration had the greatest probability of surviving through to the return migration. This effect, independent of body size, may indicate a trade-off between investment in readiness for marine life (which favours high glucocorticoid levels, known to increase telomere attrition in other vertebrate species) and investment in telomere maintenance. Survival was also significantly influenced by the seasonal timing of outward migration, with the fish migrating downstream earliest in the spring having the highest probability of return. This study reveals that telomere length is associated with survival, although in ways that contrast with patterns seen in endotherms. This illustrates that while telomeres may be universally important for chromosome protection, the potential for telomere dynamics to predict performance may vary across taxa

CBS domains form energy-sensing modules whose binding of adenosine ligands is disrupted by disease mutations

CBS domains are defined as sequence motifs that occur in several different proteins in all kingdoms of life. Although thought to be regulatory, their exact functions have been unknown. However, their importance was underlined by findings that mutations in conserved residues within them cause a variety of human hereditary diseases, including (with the gene mutated in parentheses): Wolff-Parkinson-White syndrome (γ2 subunit of AMP-activated protein kinase); retinitis pigmentosa (IMP dehydrogenase-1); congenital myotonia, idiopathic generalized epilepsy, hypercalciuric nephrolithiasis, and classic Bartter syndrome (CLC chloride channel family members); and homocystinuria (cystathionine β-synthase). AMP-activated protein kinase is a sensor of cellular energy status that is activated by AMP and inhibited by ATP, but the location of the regulatory nucleotide-binding sites (which are prime targets for drugs to treat obesity and diabetes) was not characterized. We now show that tandem pairs of CBS domains from AMP-activated protein kinase, IMP dehydrogenase-2, the chloride channel CLC2, and cystathionine β-synthase bind AMP, ATP, or S-adenosyl methionine,while mutations that cause hereditary diseases impair this binding. This shows that tandem pairs of CBS domains act, in most cases, as sensors of cellular energy status and, as such, represent a newly identified class of binding domain for adenosine derivatives

On the Use of Stream Control Transmission Protocol (SCTP) with IPsec

This document describes functional requirements for IPsec (RFC 2401) and Internet Key Exchange (IKE) (RFC 2409) to facilitate their use in securing SCTP (RFC 2960) traffic

On the Use of Stream Control Transmission Protocol (SCTP) with IPsec

This document describes functional requirements for IPsec (RFC 2401) and Internet Key Exchange (IKE) (RFC 2409) to facilitate their use in securing SCTP (RFC 2960) traffic