Defects in Chiral Columnar Phases: Tilt Grain Boundaries and Iterated Moire Maps

Biomolecules are often very long with a definite chirality. DNA, xanthan and poly-gamma-benzyl-glutamate (PBLG) can all form columnar crystalline phases. The chirality, however, competes with the tendency for crystalline order. For chiral polymers, there are two sorts of chirality: the first describes the usual cholesteric-like twist of the local director around a pitch axis, while the second favors the rotation of the local bond-orientational order and leads to a braiding of the polymers along an average direction. In the former case chirality can be manifested in a tilt grain boundary phase (TGB) analogous to the Renn-Lubensky phase of smectic-A liquid crystals. In the latter case we are led to a new "moire" state with twisted bond order. In the moire state polymers are simultaneously entangled, crystalline, and aligned, on average, in a common direction. In the moire state polymers are simultaneously entangled, crystalline, and aligned, on average, in a common direction. In this case the polymer trajectories in the plane perpendicular to their average direction are described by iterated moire maps of remarkable complexity, reminiscent of dynamical systems.Comment: plain TeX, (33 pages), 17 figures, some uufiled and included, the remaining available at ftp://ftp.sns.ias.edu/pub/kamien/ or by request to [email protected]

Perspectives and challenges for the use of radar in biological conservation

Radar is at the forefront for the study of broad-scale aerial movements of birds, bats and insects and related issues in biological conservation. Radar techniques are especially useful for investigating species which fly at high altitudes, in darkness, or which are too small for applying electronic tags. Here, we present an overview of radar applications in biological conservation and highlight its future possibilities. Depending on the type of radar, information can be gathered on local- to continental-scale movements of airborne organisms and their behaviour. Such data can quantify flyway usage, biomass and nutrient transport (bioflow), population sizes, dynamics and distributions, times and dimensions of movements, areas and times of mass emergence and swarming, habitat use and activity ranges. Radar also captures behavioural responses to anthropogenic disturbances, artificial light and man-made structures. Weather surveillance and other long-range radar networks allow spatially broad overviews of important stopover areas, songbird mass roosts and emergences from bat caves. Mobile radars, including repurposed marine radars and commercially dedicated ‘bird radars’, offer the ability to track and monitor the local movements of individuals or groups of flying animals. Harmonic radar techniques have been used for tracking short-range movements of insects and other small animals of conservation interest. However, a major challenge in aeroecology is determining the taxonomic identity of the targets, which often requires ancillary data obtained from other methods. Radar data have become a global source of information on ecosystem structure, composition, services and function and will play an increasing role in the monitoring and conservation of flying animals and threatened habitats worldwide

Modeling of contact deformations between a synthetic human and its environment

Many problems exist in synthetic human modeling because of the limitations of current models. The paper discusses the use of finite-element analysis for the computer animation of humans in contact with their environment. The authors' hybrid animation system is described, and the deformations due to contact forces generated during the pressing of a soft ball by a finger are modeled using FEM-based simulation of the environment and of the skin. An appropriate algorithm is presented. The limitations of the current system are discussed, and directions for further research are identified

The use of finite element theory for simulating object and human body deformations and contacts

A method for combining image synthesis and modeling based on a finite element method (FEM) to get realistic intelligent images is presented. FEM is used for modeling both elastically and plastically, deformations of objects and impacts with or without penetration between deformable objects. The concept of deformable objects is applied to human flesh to improve the behavior of synthetic human grasping and walking. The authors also discuss the introduction of this method in an animation system based on the concept of intelligent synthetic actors with automatic motion control performed using AI and robotics techniques. In particular, motion is planned at a task level and computed using physical law

Smoothed Particles: A new paradigm for animating highly deformable bodies

This paper presents a new formalism for simulating highly deformable bodies with a particle system. Smoothed particles represent sample points that enable the approximation of the values and derivatives of local physical quantities inside a medium. They ensure valid and stable simulation of state equations that describe the physical behavior of the material