Origin and Evolution of Saturn's Ring System

The origin and long-term evolution of Saturn's rings is still an unsolved problem in modern planetary science. In this chapter we review the current state of our knowledge on this long-standing question for the main rings (A, Cassini Division, B, C), the F Ring, and the diffuse rings (E and G). During the Voyager era, models of evolutionary processes affecting the rings on long time scales (erosion, viscous spreading, accretion, ballistic transport, etc.) had suggested that Saturn's rings are not older than 100 My. In addition, Saturn's large system of diffuse rings has been thought to be the result of material loss from one or more of Saturn's satellites. In the Cassini era, high spatial and spectral resolution data have allowed progress to be made on some of these questions. Discoveries such as the ''propellers'' in the A ring, the shape of ring-embedded moonlets, the clumps in the F Ring, and Enceladus' plume provide new constraints on evolutionary processes in Saturn's rings. At the same time, advances in numerical simulations over the last 20 years have opened the way to realistic models of the rings's fine scale structure, and progress in our understanding of the formation of the Solar System provides a better-defined historical context in which to understand ring formation. All these elements have important implications for the origin and long-term evolution of Saturn's rings. They strengthen the idea that Saturn's rings are very dynamical and rapidly evolving, while new arguments suggest that the rings could be older than previously believed, provided that they are regularly renewed. Key evolutionary processes, timescales and possible scenarios for the rings's origin are reviewed in the light of tComment: Chapter 17 of the book ''Saturn After Cassini-Huygens'' Saturn from Cassini-Huygens, Dougherty, M.K.; Esposito, L.W.; Krimigis, S.M. (Ed.) (2009) 537-57

Ballistic helmets – Their design, materials, and performance against traumatic brain injury

Protecting a soldier’s head from injury is critical to function and survivability. Traditionally, combat helmets have been utilized to provide protection against shrapnel and ballistic threats, which have reduced head injuries and fatalities. However, home-made bombs or improvised explosive devices (IEDs) have been increasingly used in theatre of operations since the Iraq and Afghanistan conflicts. Traumatic brain injury (TBI), particularly blast-induced TBI, which is typically not accompanied by external body injuries, is becoming prevalent among injured soldiers. The responses of personal protective equipment, especially combat helmets, to blast events are relatively unknown. There is an urgent need to develop head protection systems with blast protection/mitigation capabilities in addition to ballistic protection. Modern military operations, ammunitions, and technology driven war tactics require a lightweight headgear that integrates protection mechanisms (against ballistics, blasts, heat, and noise), sensors, night vision devices, and laser range finders into a single system. The current article provides a comparative study on the design, materials, and ballistic and blast performance of the combat helmets used by the US Army based on a comprehensive and critical review of existing studies. Mechanisms of ballistic energy absorption, effects of helmet curvatures on ballistic performance, and performance measures of helmets are discussed. Properties of current helmet materials (including Kevlar® K29, K129 fibers and thermoset resins) and future candidate materials for helmets (such as nano-composites and thermoplastic polymers) are elaborated. Also, available experimental and computational studies on blast-induced TBI are examined, and constitutive models developed for brain tissues are reviewed. Finally, the effectiveness of current combat helmets against TBI is analyzed along with possible avenues for future research

On the development of the brown spider Loxosceles gaucho Gertsch (Araneae, Sicariidae): the nympho-imaginal period

Observations of the developmental biology of Loxosceles gaucho Gertsch, 1967, the brown spider of southeastern Brazil are scarce. The present study reports the method of individualized rearing of 18 populations of L. gaucho, kept in laboratory under varied diet conditions, and characterizes their nympho-imaginal period as well as factors related to their reproduction. Females built the first egg sac about 20 days after copulation and nymphs hatched 40 days after the laying date. Average offspring was 61.3 spiderlings and females usually built three to four successive egg sacs in a period of five to seven months. First nymphs initiated their predatory activity between the 5th and 8th days after hatching and the majority reached adulthood within six moults (range of five to eight) in approximately 15 to 17 months (male) and 15.5 to 18 months (female). The average sex ratio equaled 1.0:1.7 (male:female). The wide individual variability of this species intermoult intervals is herewith expressed by the "intermoult rate", which was fairly uniform for both intra and interpopulations and gives a relevant aspect for a general idea of the life cycles of spiders