Interstellar dust models

Interstellar dust models, previously constrained only from the extinction curve, have been radically changed with the arrival of IRAS observations of the dust infrared emission. An important component of interstellar dust is likely to be made of small particles that show a fluctuating temperature upon impinging single photons and which can produce large near and mid infrared excesses ubiquitously observed in the Galaxy and external galaxies. The analysis of COBE data should soon improve our understanding of dust infrared emissivity and particularly for big grains in the submillimeter domain. We will discuss the key observations (spectral features, broad-band colors, correlations with gas tracers…) which put the best constraints on any dust models and show that the next generation of IR/submm satellites (ISO, SIRTF…) should improve our knowledge of interstellar dust composition and the dust redistribution of the stellar energy inside galaxies.     

LET dependence of cell death, mutation induction and chromatin damage in human cells irradiated with accelerated carbon ions.

We investigated the LET dependence of cell death, mutation induction and chromatin break induction in human embryo (HE) cells irradiated by accelerated carbon-ion beams. The results showed that cell death, mutation induction and induction of non-rejoining chromatin breaks detected by the premature chromosome condensation (PCC) technique had the same LET dependence. Carbon ions of 110 to 124keV/micrometer were the most effective at all endpoints. However, the number of initially induced chromatin breaks was independent of LET. About 10 to 15 chromatin breaks per Gy per cell were induced in the LET range of 22 to 230 keV/micrometer. The deletion pattern of exons in the HPRT locus, analyzed by the polymerase chain reaction (PCR), was LET-specific. Almost all of the mutants induced by 124 keV/micrometer beams showed deletion of the entire gene, while all mutants induced by 230keV/micrometer carbon-ion beams showed no deletion. These results suggest that the difference in the density distribution of carbon-ion track and secondary electron with various LET is responsible for the LET dependency of biological effects.     

Spectroscopic diagnostics applicable to the UV and EUV spectra of astrophysical sources

A bibliography is provided of the most reliable emission and absorption line ratio diagnostic calculations currently available for application to the spectra of astrophysical sources in the UV and EUV wavelength region (50–3000 Å). References are listed containing diagnostics for species in the Li through P isoelectronic sequences, as well as the iron ions Feii-Fexxiii and nickel ions Nixvii-Nixxv. Also given is the wavelength range for which diagnostic calculations are presented in each reference, along with the type of diagnostic considered. These include, for example, emission line ratios for determining electron temperatures and densities, and absorption line diagnostics for evaluating hydrogen densities.     

Certification of production-representative/productionsoftware-intensive systems for dedicated test and evaluation

Fundamental questions that arise in the certification of readiness for dedicated test and evaluation of software-intensive systems are addressed. They concern what comprises production-representative or production software, what are the software impacts on dedicated system operational test readiness, how software impacts should be considered in the certification process, and what are the retest/recertification requirements associated with software changes/modifications. A paradigm is proposed that answers these questions and outlines guidelines for implementing a solution to these issues. The paradigm is based on existing test and evaluation events and uses a combination of defense and commercial standards and definitions to propose criteria for software certification and retest or regression test     

Le silence éternel de ces espaces infinis?

During the last 40 years — the merest blip in world history — talk about Homo astronauticus has signalled a growing awareness that the passengers on planet Earth can, if they want, take off for other destinations. If the scale of past advances is a satisfactory measure of future possibilities, then the wish will be father of the achievement.     

2-D differential interferometer

A new type of differential interferometer based on holographic optical elements is developed, which allows the exact determination of a refractive index gradient field in two orthogonal directions. This interferometer will be used in TEXUS experiments to determine the temperature field in a convective liquid cell in which the temperature may be known at only one point.     

An approach to geometric reasoning in robotics

Anticipating the use of knowledge-based expert systems for robot task planning, a geometric reasoning is envisioned for the representation and manipulation of geometric information in a manner uniform with other knowledge. The general requirements for such a reasoner are outlined and a proposed architecture is described, built on four concepts: a class structure of spatial sets, features as subsets of those spatial sets, geometric abstractions as partial representations of features, and constraints as a mechanism for reasoning. An example implementation is built in an object-oriented environment and uses an underlying solids modeler, transparent to the end user     

Qualitative Reasoning methods for CELSS modeling.

Qualitative Reasoning (QR) is a branch of Artificial Intelligence that arose from research on engineering problem solving. This paper describes the major QR methods and techniques, which, we believe, are capable of addressing some of the problems that are emphasized in the literature and posed by CELSS modeling, simulation, and control at the supervisory level.     

Experimental and theoretical modeling of laser propulsion

Some schemes of laser propulsive systems are discussed. The question concerned with a body acceleration due to series of air blast waves generated by laser sparks is studied. For this purpose the numerical solutions of gasdynamic equations are found under appropriate initial conditions corresponding to the real ones. Radiative losses and spatial effects at the nozzle exit are taken into account. Theoretical results presented as coupling coefficients (equivalent to reciprocal thrust cost realizing under periodical pulse laser operation) are compared with the experiment. Using conical and parabolic nozzles irradiated by pulsed CO₂ laser the thrust cost about 2000 W/N is achieved which is close to the minimum possible one for the air blast wave-nozzle wall interaction. The main characteristics of laser propulsive jet are presented. Experimental results on recoil momentum transfered to solids under their evaporation by the pulsed CO₂-laser are presented as well. The question of plasma shielding effects on the momentum transfer under the vapour optical breakdown conditions is touched on.