Electron Impact Ionization Close to the Threshold: Classical Calculations

In this paper we present Classical Trajectory Monte Carlo (CTMC) calculations for single and multiple electron ionization of Argon atoms and ions in the threshold region. We are able to recover the Wannier exponents a for the power-law behavior of the cross section s versus excess energy: the exact value of the exponent as well as the existence of its saturation for multiple ionization appear to be related to how the total binding energy is shared between target electrons.Comment: 9 pages. To be published in Journal of Physics

Light-Responsive Springs from Electropatterned Liquid Crystal Polymer Networks

Future robotic systems will have to adapt their operation to dynamic environments and therefore their development will require the use of active soft components. Bioinspired approaches toward novel actuation materials for active components rely on integrating molecular machines in soft matter, and ensuring that their nanoscale movement is amplified to the macroscale, where mechanically relevant motion is generated. This approach is successfully used in the design of photoresponsive soft springs and other mechanically active materials. Here, this study reports on a new approach where the operation of photoswitches and chiral liquid crystals are combined with an original and mask-free microscopic patterning method to generate helix-based movement at the macroscale, including light-driven winding and unwinding accompanied with inversion of handedness. The microscopic patterning is the result of the unique organization of cholesteric liquid crystals under weak electric field. At a higher level, the pitch and the handedness of the active springs are defined by the imprinted pattern and the angle at which the spring ribbons are cut in the material. These findings are likely to enable soft and responsive robotic systems, and they show how transmission of molecular operation into macroscale functional movement is enabled by materials design across multiple hierarchical levels.</p

Chaotic features in classical scattering processes between ions and atoms

A numerical study has been done of collisions between protons and hydrogen atoms, treated as classical particles, at low impact velocities. The presence of chaos has been looked for by investigating the processes with standard techniques of the chaotic--scattering theory. The evidence of a sharp transition from nearly regular scattering to fully developed chaos has been found at the lower velocities.Comment: 10 pages, Latex, 3 figures (available upon request to the authors), submitted to Journal of Physics

Light-Fueled Nanoscale Surface Waving in Chiral Liquid Crystal Networks

Nano-and micro-actuating systems are promising for application in microfluidics, haptics, tunable optics, and soft robotics. Surfaces capable to change their topography at the nano-and microscale on demand would allow control over wettability, friction, and surface-driven particle motility. Here, we show that light-responsive cholesteric liquid crystal (LC) networks undergo a waving motion of their surface topography upon irradiation with light. These dynamic surfaces are fabricated with a maskless one-step procedure, relying on the liquid crystal alignment in periodic structures upon application of a weak electric field. The geometrical features of the surfaces are controlled by tuning the pitch of the liquid crystal. Pitch control by confinement allows engineering one-dimensional (1D) and two-dimensional (2D) structures that wave upon light exposure. This work demonstrates the potential that self-organizing systems might have for engineering dynamic materials, and harnessing the functionality of molecules to form dynamic surfaces, with nanoscale precision over their waving motion

A Proposal for an Environmental Decision Support System at the Regional Level: Concepts, Support Methodology, Tools and their Terminology

One of the goals of IIASA's research activities in the area of environmental quality modeling is the integration of data and models in a unified framework to assist decision makers with the management of complex environmental systems. Building on IIASA's work undertaken within the WELMM (Water, Energy, Land, Materials and Manpower) project of the former Resources and Environment Area and the work on Decision Support Systems of the former Management and Technology Area, a conceptual framework for an environmental decision support system (EDSS) has been developed and is presented in this paper. The proposed EDSS has been developed with the interest and the financial support of the CSI, the Center for Information Systems of the Regional Government of Piemonte, Italy. The main issue addressed by this paper is to devise a system assisting decision makers in tackling environmental problems at the regional level. These decisions are typically characterized by a combination of both structured (formalizable, described in a quantitative model) and unstructured elements (incomplete information, undefined cause-effect relationships, influence of political objectives, public perception, consideration of aesthetics, etc.). The proposed EDSS enables the user to use models and data, of relevance to a particular task, which are embedded in the EDSS in the form of a process information system. The specific feature of this process information system is that it contains processes of anthropogenic nature (the socio-economic activities being the cause of environmental impacts like power plants, industrial production units, etc.) as well as natural processes determining the spatial/temporal distribution and the extent of environmental quality changes (like the dispersion and deposition of air pollutants and their effect on human population, vegetation and wildlife). The system ensures that the data and models, which have been developed in the context of specific EDSS applications are documented right from the outset and become thus equally available for further use. This becomes especially important in view of the long-term effort to be put into the development of data and models dealing with the large number of environmental problems that governments, industry and academic institutions are confronted with at the regional level

Humidity-responsive actuators from integrating liquid crystal networks in an orienting scaffold

Developing shape-shifting materials requires combining the flexibility needed by shape-shifting properties, with the toughness that is demanded to maintain their mechanical performance. Typically, in liquid crystal networks, the amplitude of the shape transformation can be hindered by large cross-linking densities. Here, we argue that a promising strategy to address this limitation consists in integrating liquid crystal networks into an anisotropic and porous material that acts as an orienting scaffold. This strategy shows similarities with the principles of stimuli-responsive deformation in plants, where inflexible elements with specific orientations are integrated into a stimuli-responsive matrix. By aligning liquid crystals in a porous polypropylene orienting scaffold, we demonstrate liquid crystal networks that respond to humidity with a shape change, yet they display high elastic modulus and toughness. Various chiral shapes can be generated in single and double layers of these films, and the complexity of their actuation modes is enhanced, including twisting, curling or winding. We anticipate that these hybrid composites and the strategy they embody can find application to other stimuli-responsive anisotropic soft materials