A critical evaluation of two Reissner–Mindlin type models for composite laminated plates

The purpose of this paper is to critically evaluate two Reissner–Mindlin type theories developed recently for composite laminated plates, namely, VAPAS (Variational Asymptotic Plate And Shell analysis) and EFSDT (Enhanced First-Order Shear-Deformation Theory). The fundamentals of both models are briefly summarized along with their unique features in comparison to most other existing models. The similarities and differences between VAPAS and EFSDT are also examined. Exact solutions of three-dimensional elasticity theory for the cylindrical bending problems are used as the arbiter to assess the accuracy of both models. Such a systematic assessment demonstrates that both models have achieved an excellent compromise between the layer-wise theories, which are accurate but computationally demanding, and the first-order shear deformation theories, which are computationally cheap but not accurate.     

Use of measurements from an imaging sensor for precision targettracking

The extraction of measurements for precision tracking of the centroid of a target from a forward-looking infrared imaging sensor is presented. The size of the image of the target is assumed to be small, i.e. around 10 pixels. The statistical characterization of the centroid of the target is obtained. Similarly, the statistical properties of the image correlation of two frames, which measures the target offset, are derived. Explicit expressions that map the video noise statistics into measurement noise statistics are obtained. The offset measurement noise is shown to be autocorrelated. State variable models for tracking the target centroid with these measurements are then presented. Simulation results and quantitative conclusions about achievable subpixel tracking accuracy are given. It is shown that the filter that models the autocorrelated measurement noise provides the best performance     

Physical events in the track structure of heavy ions and their relation to alterations of biomolecules.

Heavy charged particles interacting with biological cells can produce a wide variety of different physical, chemical and biological consequences. A rigorous identification of relevant chemical and biological alterations of biomolecules in cells, however, is still lacking and, thus, it is difficult to identify the potential biological importance of different early physical events. In addition, due to experimental and theoretical problems also little is known about the details of energy transfer, -absorption and -decay from projectiles to atoms/molecules in condensed targets; this is particularly true for not completely stripped heavy ions. Nevertheless, one might conclude from available data that higher densities of physical energy absorption events have a significantly higher probability to lead to qualitatively more severe biochemical alterations as regards the induction of DNA double strand breaks and of chromatin damage. It is not very likely that energy migration along the DNA molecule in biological cells over long distances plays a significant role as contributor to these biological radiation effects.     

Two centuries of study of Algol systems

The periodicity of the light variation of Algol, discovered just over 200 years ago, may be regarded as the beginning of the study of eclipsing binary systems, especially those of the Algol type. Such studies, however, gained no real momentum until Vogel, 100 years ago, demonstrated by spectroscopy that the binary hypothesis of Algol's light changes is, in its essentials, correct. Three elements were needed to give us our modern notions of evolution by mass-transfer, namely: (i) results of combined analysis of light-curves and velocity-curves, (ii) evidence of circumstellar matter within binary systems and (iii) the notion that at least one component of an Algol system was near the limit of dynamical stability. All three entered the literature within about a decade, approximately halfway through the second century of eclipsing-binary studies; but it is the computational and instrumental developments of the last 25 years that have made real progress possible. We still lack commensurate theoretical developments, and the whole question of the contribution of Algol systems to the development of the Galaxy has barely been considered.     

Optimised radiative cooling of infrared space telescopes and applications to possible missions

General principles are outlined for the design of space infrared telescopes intended to cool by radiation to the lowest temperatures attainable without the use of on-board cryogens, and assuming on-orbit cooling after a warm launch. Maximum protection from solar and earth heating, maximum radiating area and efficiency and minimum absorbing area and absorptivity are the obvious basic criteria. The optimised design is a short, fat telescope surrounded by a series of radiation shields, each cooled by its own radiator. Maximising the longitudinal conductivity of the radiation shields and of the telescope tube itself is important both to the on-orbit cooling time and the final achieveable temperature. Realistic designs take between 80 and 200 days to cool to within a few degrees of equilibrium temperatures, depending on the materials used. Great advantages accrue from the use of an orbit distant from earth. Both simple models and detailed simulations suggest that temperatures of 30 to 40 K are attainable in high earth orbits. Placing a radiatively cooled telescope in a halo orbit around the Lagrangian point L2 is a particularly attractive option and significantly lower temperatures can be achieved there than in Earth orbit. Optimised radiative cooling is an important element of the small Japanese mission SMIRT. We suggest that a combination of an ESA Medium-sized Mission with a NASA Explorer to send a 2m+ telescope to an L2 halo orbit would provide a cost-effective and powerful long-duration facility for the early 21st century.