Carbon-rich particles in Comet Halley

The majority of particles detected in the coma of Comet Halley contain carbon atoms; many of these grains appear to consist preponderately or only of light elements. These light-element particles may be composed of organic compounds. Of the possible combinations of the elements hydrogen, carbon, nitrogen, and oxygen, numerous examples are found of particles containing the combinations (H,C,O,N), (H,C,N), (H,C,O), and (H,C). These results may bear on the recent detection of polyoxymethylene fragments, the observation of cyanojets (CN patterns consistent with release from solid particles), the possible presence of cyanopolyacetylenes or HCN polymer and the make-up of the CHON particles. If cometary matter could reach the surface of the earth without complete disruption, these diverse organic and mixed particles could create unique microenvironments, possibly with significant or even pivotal prebiotic chemical activity. Here a speculative insight into possible relationships between carbon in comets and carbon in life is given, as well as a brief overview of on-going analysis of data from the highly successful Particle Impact Analyzer (PIA) experiment flown on the Giotto spacecraft for the flyby of Comet Halley (development and implementation of PIA was under the direction of J. Kissel of the Max Planck Institute for Kernphysik, Heidelberg). PIA is a time-of-flight analyzer which obtains mass spectra of ions from individual particles impacting on a Pt-Ag foil target within the instrument

Implementation of a robotic flexible assembly system

As part of the Intelligent Task Automation program, a team developed enabling technologies for programmable, sensory controlled manipulation in unstructured environments. These technologies include 2-D/3-D vision sensing and understanding, force sensing and high speed force control, 2.5-D vision alignment and control, and multiple processor architectures. The subsequent design of a flexible, programmable, sensor controlled robotic assembly system for small electromechanical devices is described using these technologies and ongoing implementation and integration efforts. Using vision, the system picks parts dumped randomly in a tray. Using vision and force control, it performs high speed part mating, in-process monitoring/verification of expected results and autonomous recovery from some errors. It is programmed off line with semiautomatic action planning

Emissitivity of hydrogen atoms at high temperature

A method is described for making estimates of the total emissivity of hydrogen in the temperature and pressure ranges where hydrogen atoms predominate under equilibrium conditions. For a typical geometrical depth of 50 cm, and temperatures of the order of 12 500ºK and higher, with pressures of the order of 100 atmos and higher, the emissivity approaches unity (є ≳ 0.95), while for temperatures of the order of 9500ºK and lower, with pressures of the order of 10 atmos and lower, the emissivity approaches zero (є ≾ 0.05). The variations of the emissivity between these approximate limits are shown graphically as functions of temperature and pressure with the geometrical depth set at 50 cm. The variation of the emissivity with geometrical depth is also shown graphically at 12 600ºK and 20 atmos

Reentrance of disorder in the anisotropic shuriken Ising model

For a material to order upon cooling is common sense. What is more seldom is for disorder to reappear at lower temperature, which is known as reentrant behavior. Such resurgence of disorder has been observed in a variety of systems, ranging from Rochelle salts to nematic phases in liquid crystals. Frustration is often a key ingredient for reentrance mechanisms. Here we shall study a frustrated model, namely the anisotropic shuriken lattice, which offers a natural setting to explore an extension of the notion of reentrance between magnetic disordered phases. By tuning the anisotropy of the lattice, we open a window in the phase diagram where magnetic disorder prevails down to zero temperature. In this region, the competition between multiple disordered ground states gives rise to a double crossover where both the low- and high-temperature regimes are less correlated than the intervening classical spin liquid. This reentrance of disorder is characterized by an entropy plateau, a multi-step Curie law crossover and a rather complex diffuse scattering in the static structure factor. Those results are confirmed by complementary numerical and analytical methods: Monte Carlo simulations, Husimi-tree calculations and an exact decoration-iteration transformation.Comment: 16 pages, 13 figure

Mars aqueous chemistry experiment

The Mars Aqueous Chemistry Experiment (MACE) is designed to conduct a variety of measurements on regolith samples, encompassing mineral phase analyses, chemical interactions with H2O, and physical properties determinations. From these data, much can be learned or inferred regarding the past weathering environment, the contemporaneous soil micro-environments, and the general chemical and physical state of the Martian regolith. By analyzing both soil and duricrust samples, the nature of the latter may become more apparent. Sites may be characterized for comparative purposes and criteria could be set for selection of high priority materials on future sample return missions. Progress for the first year MACE PIDDP is reported in two major areas of effort: (1) fluids handling concepts, definition, and breadboard fabrication and (2) aqueous chemistry ion sensing technology and test facility integration. A fluids handling breadboard was designed, fabricated, and tested at Mars ambient pressure. The breadboard allows fluid manipulation scenarios to be tested under the reduced pressure conditions expected in the Martian atmosphere in order to validate valve operations, orchestrate analysis sequences, investigate sealing integrity, and to demonstrate efficacy of the fluid handling concept. Additional fluid manipulation concepts have also been developed based on updated MESUR spacecraft definition. The Mars Aqueous Chemistry Experiment Ion Selective Electrode (ISE) facility was designed as a test bed to develop a multifunction interface for measurements of chemical ion concentrations in aqueous solution. The interface allows acquisition of real time data concerning the kinetics and heats of salt dissolution, and transient response to calibration and solubility events. An array of ion selective electrodes has been interfaced and preliminary calibration studies performed