Capturing the S in segregation: a simple model of flowing granular mixtures in rotating drums

Flowing granular mixtures in rotating cylindrical drums arise in numerous industrial settings and are of great technological significance worldwide. To date, the development of a robust mathematical model for this process remains an open research problem. However, simple mathematical models may be developed that capture some of the underlying mechanisms, including segregation. The key lies in the analysis of the flowing surface layer whose profile is characteristically S-shaped: past models have shown that capturing this characteristic is an essential ingredient in predicting segregation. Using secondary to first-year undergraduate level mathematics, an analysis is presented of the flowing surface layer, which leads to an S-shaped profile. This problem presents an ideal case study for teaching applied mathematics and modelling. Interesting simulations that aid the visualization of this problem can be downloaded from the web, and simple classroom demonstrations of this process can be assembled with no specialized equipment.     

Dense electron-positron plasmas and ultraintense γ rays from laser-irradiated solids

In simulations of a 10 PW laser striking a solid, we demonstrate the possibility of producing a pure electron-positron plasma by the same processes as those thought to operate in high-energy astrophysical environments. A maximum positron density of 10(26) m(-3) can be achieved, 7 orders of magnitude greater than achieved in previous experiments. Additionally, 35% of the laser energy is converted to a burst of γ rays of intensity 10(22) W cm(-2), potentially the most intense γ-ray source available in the laboratory. This absorption results in a strong feedback between both pair and γ-ray production and classical plasma physics in the new "QED-plasma" regime.     

Microbiology: impact on research in life sciences.

In this essay with a flavor of science history, the influence of imaging techniques, as compared to other research strategies, on microbiologic investigations is discussed. Using a few selected examples, to what degree microbiology became a leading science during the last 50 years in gaining knowledge in life sciences, particularly with regard to molecular genetics and more recently molecular evolution is also discussed.     

Morphologie von Leberglykogen

Zusammenfassung Es werden elektronenmikroskopische Aufnahmen von verschiedenen Leberglykogenen gezeigt und die Artefakte verschiedener Pr?parationsmethoden untersucht.     

VALIS: A split-conservative scheme for the relativistic 2D Vlasov–Maxwell system

An accurate treatment of the relativistic Vlasov–Maxwell system is of fundamental importance to a broad range of plasma physics topics, including laser–plasma interaction, transport in solar and magnetospheric plasmas and magnetically confined plasmas. This paper introduces VALIS: an algorithm for the numerical solution of the Vlasov–Maxwell system in two spatial dimensions and two momentum dimensions.     

The application of fracture mechanics to the impact behaviour of rubber-toughened polyamides

Rubber-modification of polyamide is a widely-applied method of improving material resistance under high strain rate loading. The processing conditions used for preparing such two-phase blends strongly influence their structure and thus their subsequent impact properties. In the present work the relationships between production parameters, phase structure and impact resistance have been studied, and the rǒle of the rubber phase in promoting energy absorption investigated. It has been found that improved impact resistance, defined as a combination of high resistance to crack initiation and to crack propagation, is achieved by decreasing the polyamide phase viscosity while increasing the extrusion and injection temperatures, the mixing shear rate and the rubber phase volume fraction; an EPR modifier offers superior performance to a polybutadiene modifier; the dominant mechanisms of energy-absorption are shearing and void formation, there being no clear evidence of crazing; the J-integral technique of plastic fracture mechanics can be applied to Charpy impact testing; TEM allied with image analysis techniques provides quantitative morphological information on polymer blends.