UV Circular Polarisation in Star Formation Regions : The Origin of Homochirality?

Ultraviolet circularly polarised light has been suggested as the initial cause of the homochirality of organic molecules in terrestrial organisms, via enantiomeric selection of prebiotic molecules by asymmetric photolysis. We present a theoretical investigation of mechanisms by which ultraviolet circular polarisation may be produced in star formation regions. In the scenarios considered here, light scattering produces only a small percentage of net circular polarisation at any point in space, due to the forward throwing nature of the phase function in the ultraviolet. By contrast, dichroic extinction can produce a fairly high percentage of net circular polarisation (∼10%) and may therefore play a key role in producing an enantiomeric excessPeer reviewe

The Recent Excitement in High-Density QCD

Over the past few months, the theory of QCD at high density has been advanced considerably. It provides new perspectives on, and controlled realizations of, confinement and chiral symmetry breaking. Here I survey the recent developments, and suggest a few directions for future work.Comment: LaTeX, 16 pages, 2 figures. Invited talk at PANIC `99, Uppsala, Sweden, June 199

Magnetohydrodynamic models of astrophysical jets

In this review, analytical results obtained for a wide class of stationary axisymmetric flows in the vicinity of compact astrophysical objects are analyzed, with an emphasis on quantitative predictions for specific sources. Recent years have witnessed a great increase in understanding the formation and properties of astrophysical jets. This is due not only to new observations but also to advances in analytical theory which has produced fairly simple relations, and to what can undoubtedly be called a breakthrough in numerical simulation which has enabled confirmation of theoretical predictions. Of course, we are still very far from fully understanding the physical processes occurring in compact sources. Nevertheless, the progress made raises hopes for near-future test observations that can give insight into the physical processes occurring in active astrophysical objects.Comment: 40 pages, translated by K.A.Postnov, edited by A.Radzi

Twenty Five Years of Asymptotic Freedom

On the occasion of the 25th anniversary of Asymptotic Freedom, celebrated at the QCD Euroconference 98 on Quantum Chromodynamics, Montpellier, July 1998, I described the discovery of Asymptotic Freedom and the emergence of QCD.Comment: 35 pages, LaTe

Biomechanics

Biomechanics is a vast discipline within the field of Biomedical Engineering. It explores the underlying mechanics of how biological and physiological systems move. It encompasses important clinical applications to address questions related to medicine using engineering mechanics principles. Biomechanics includes interdisciplinary concepts from engineers, physicians, therapists, biologists, physicists, and mathematicians. Through their collaborative efforts, biomechanics research is ever changing and expanding, explaining new mechanisms and principles for dynamic human systems. Biomechanics is used to describe how the human body moves, walks, and breathes, in addition to how it responds to injury and rehabilitation. Advanced biomechanical modeling methods, such as inverse dynamics, finite element analysis, and musculoskeletal modeling are used to simulate and investigate human situations in regard to movement and injury. Biomechanical technologies are progressing to answer contemporary medical questions. The future of biomechanics is dependent on interdisciplinary research efforts and the education of tomorrow’s scientists

Applicability Evidence of Constructal Design in Structural Engineering: Case Study of Biaxial Elasto-Plastic Buckling of Square Steel Plates with Elliptical Cutout

The application of the Constructal Design method in Heat Transfer and Fluid Mechanics areas is an already consecrated approach to geometrically evaluate these flow engineering systems. However, this approach in Mechanics of Materials realm is not yet widely used, since one can find only few publications about it in literature. The Constructal Design is based on the Constructal Law, a physical law that explains the universal phenomenon of evolution of any finite size flow system. Therefore, the main goal here is to show that the Constructal Design can also be used in dedicated Structural Engineering problems as an effective method for geometric evaluation. The obtained results prove the Constructal Design applicability definitively in Mechanics of Materials

Quantitative 3D orientation analysis of particles and voids to differentiate hand-built pottery forming techniques using X-ray microtomography and neutron tomography

This article describes the quantitative analysis of the 3D orientation of objects (i.e. particles and voids) within pottery fabrics to differentiate two categories of pottery hand-building primary forming techniques, specifically percussion-building and coil-building, comparing the use of two independent non-destructive imaging modalities, X-ray microtomography (µ-CT) and neutron tomography (NT). For this purpose, series of experimental organic-tempered vessels and coil sections were analysed. For both imaging modalities, two separate systems were employed for quantitatively describing both the orientation of individual objects, as well as the collective preferential alignment of objects within samples, utilising respectively polar and azimuth angles within a spherical coordinate system, and projected sizes within a positive Cartesian coordinate system. While the former provided full descriptions of the orientations of objects within 3D space, the latter, through a ratio dubbed here the ‘Orientation Index’ (OI), gave a simple numerical value with which the investigated samples were differentiated according to forming technique. Both imaging modalities were able to differentiate between coil-built and percussion-built vessels with a high degree of confidence, with the strength of these findings additionally demonstrated through extensive statistical modelling using Monte Carlo simulations. Despite differences in resolution and differences in the attenuation of X-rays and neutrons, µ-CT and NT were shown to provide comparable results. The findings presented here broadly agree with earlier studies; however, the quantitative and three-dimensional nature of the results enables more subtle features to be identified, while additionally, in principle, the non-destructive nature of both imaging techniques facilitates such structural analysis without recourse to invasive sampling