Common DMS Technology For European In-Orbit Infrastructure

Europe is involved in 3 major space programs, ARIANE 5-COLUMBUS-HERMES, which will achieve operational use in the second half of year$ 90. These new pograms are requiring considerable technology inveatments and it is necessary to optimize them in view of available European funds. Data Management System (OMS) and associated technoloiies are one of the key areas of optimization

Terahertz conductivity of the heavy-fermion compound UNi2Al3

We have studied the optical properties of the heavy-fermion compound UNi2Al3 at frequencies between 100 GHz and 1 THz (3 cm^-1 and 35 cm^-1), temperatures between 2 K and 300 K, and magnetic fields up to 7 T. From the measured transmission and phaseshift of radiation passing through a thin film of UNi2Al3, we have directly determined the frequency dependence of the real and imaginary parts of the optical conductivity (or permittivity, respectively). At low temperatures the anisotropy of the optical conductivity along the a- and c-axes is about 1.5. The frequency dependence of the real part of the optical conductivity shows a maximum at low temperatures, around 3 cm^-1 for the a-axis and around 4.5 cm^-1 for the c-axis. This feature is visible already at 30 K, much higher than the Neel temperature of 4.6 K, and it does not depend on external magnetic fields as high as 7 T. We conclude that this feature is independent of the antiferromagnetic order for UNi2Al3, and this might also be the case for UPd2Al3 and UPt3, where a similar maximum in the optical conductivity was observed previously.Comment: 7 pages, 9 figure

An investigation into the conversion of specific carbon atoms in oleic acid and methyl oleate to particulate matter in a diesel engine and tube reactor

The paper is concerned with particulate formation from the fuels oleic acid and methyl oleate. In particular the paper reports, quantitatively, the propensity of individual carbon atoms in these two molecules in being converted to particulate. The conversion of individual carbon atoms to particulate was traced by 'labelling' individual carbon atoms in those two fuel molecules with isotopic carbon-13 (C) and then measuring how many of the labelled atoms was found in the particulate. This allowed the measuring of the conversion rates of individual fuel carbon atoms to particulate. In the case of oleic acid, three carbon atoms were selected as being particularly relevant to particulate formation, and C labelled. One of the carbon atoms was double bonded to the oxygen atom on the carboxylic acid group; and the other two were part of the oleic acid molecule alkyl chain and double bonded to each other. In the case of the methyl oleate, one carbon atom was C labelled. This was the carbon atom that was double bonded to one of the oxygen atoms of the ester group. Experimental results are presented for particulate matter (PM) formed in a laminar flow tube reactor, and also in a direct injection compression ignition engine. The tube reactor has been used for the pyrolysis of oleic acid and methyl oleate at 1300 °C, under oxygen-free conditions and at air-fuel equivalence ratios (λ) of 0.1, and 0.2. Samples of PM were also collected from the compression ignition engine at an intermediate engine load. Isotope ratio mass spectrometry (IRMS) has been used to determine the relative abundance of C in the initial fuel and in the resulting PM. Significant differences in the relative conversion rates of individual carbon atoms are reported; a negligible contribution to PM from the carbon atom directly bonded to two oxygen atoms was found in both the engine and reactor. The labelling technique used in this paper requires low quantities of C labelled molecules to enrich otherwise unlabelled oleic acid; enrichment is at volumetric concentrations typically less than 0.7% (v/v). In addition, emissions data from the engine and tube reactor, including unburned hydrocarbons, CO, CO, NO, and PM size and number distributions measured by differential mobility spectrometer, are also presented

Caractéristiques moléculaires de l'immunité des plantes induite par les rhizobactéries non pathogènes

Molecular characteristics of the rhizobacteria-triggered plant immunity. Recognition of certain non-pathogenic rhizobacteria by plants can trigger a systemic resistance reaction that renders the host less susceptible to subsequent infection by a virulent agent. Used in combination with other approaches, this induced systemic resistance (ISR) phenomenon is considered as a promising strategy for plant disease control both in greenhouse cultures and under field conditions. This review emphasizes the molecular aspects of this three-step process involving sequentially the perception by plant cells of elicitors produced by the inducing agents that initiates the phenomenon, signal transduction that is needed to propagate the induced state systemically through the plant and expression of defense mechanisms sensu stricto that limit or inhibit pathogen penetration into the host tissues. The current state of knowledge about rhizobacteria-stimulated ISR is discussed in parallel with the better characterized systemic acquired resistance induced by incompatible pathogens

Isotopic fractionation of Cu in tektites

Tektites are terrestrial natural glasses of up to a few centimeters in size that were produced during hypervelocity impacts on the Earth’s surface. It is well established that the chemical and isotopic composition of tektites is generally identical to that of the upper terrestrial continental crust. Tektites typically have very low water content, which has generally been explained by volatilization at high temperature; however, the exact mechanism is still debated. Because volatilization can fractionate isotopes, comparing the isotopic composition of volatile elements in tektites with those of their source rocks may help to understand the physical conditions during tektite formation.Interestingly, volatile chalcophile elements (e.g., Cd and Zn) seem to be the only elements for which isotopic fractionation is known so far in tektites. Here, we extend this study to Cu, another volatile chalcophile element. We have measured the Cu isotopic composition for 20 tektite samples from the four known different strewn fields. All of the tektites (except the Muong Nong-types) are enriched in the heavy isotopes of Cu (1.98 < δ65Cu < 6.99) in comparison to the terrestrial crust (δ65Cu ≈ 0) with no clear distinction between the different groups. The Muong Nong-type tektites and a Libyan Desert Glass sample are not fractionated (δ65Cu ≈ 0) in comparison to the terrestrial crust. To refine the Cu isotopic composition of the terrestrial crust, we also present data for three geological reference materials (δ65Cu ≈ 0).An increase of δ65Cu with decreasing Cu abundance probably reflects that the isotopic fractionation occurred by evaporation during heating. A simple Rayleigh distillation cannot explain the Cu isotopic data and we suggest that the isotopic fractionation is governed by a diffusion-limited regime. Copper is isotopically more fractionated than the more volatile element Zn (δ66/64Zn up to 2.49‰). This difference of behavior between Cu and Zn is predicted in a diffusion-limited regime, where the magnitude of the isotopic fractionation is regulated by the competition between the evaporative flux and the diffusive flux at the diffusion boundary layer. Due to the difference of ionic charge in silicates (Zn2+ vs. Cu+), Cu has a diffusion coefficient that is larger than that of Zn by at least two orders of magnitude. Therefore, the larger isotopic fractionation in Cu than in Zn in tektites is due to the significant difference in their respective chemical diffusivity

Quantification of the Fraction of Particulate Matter Derived from a Range of C-13-Labeled Fuels Blended into Heptane, Studied in a Diesel Engine and Tube Reactor

This paper presents the results of an experimental study that was carried out to determine the conversion rates to particulate matter (PM) of several liquid fuel hydrocarbon molecules and specific carbon atoms within those molecules. The fuels investigated (ethanol, n-propanol, i-propanol, acetone, and toluene) were blended in binary mixtures with n-heptane to a level of 10 mol percent. The contribution of the additive molecules to PM was quantified using a carbon-13 (13C) labeling experiment, in which the fuel of interest was enriched with 13C to serve as an atomic tracer. Measurement of the 13C/12C in the fuel and in the resulting PM was carried out using isotope ratio mass spectrometry. The fuel binary mixtures were tested under pyrolysis conditions in a tube reactor and also combusted in a direct injection compression ignition engine. In the tube reactor, samples were generated under oxygen-free pyrolysis conditions and at a temperature of 1300 °C, while the engine experiments were carried out at an intermediate load. Both in the tube reactor and in the engine it was found that, dependent on the fuel molecular structure, there were significant differences in the overall conversion rates to PM of the fuel molecules and of the “submolecular” carbon atoms. A separate experiment was also carried out in the compression ignition engine, with n-heptane as fuel, in order to determine the contribution of the engine lubrication oil to exhaust PM; the results showed that a significant portion (∼60%) of the total particulate was derived from the lubrication oil

Closure of the Clymene Ocean and formation of West Gondwana in the Cambrian: Evidence from the Sierras Australes of the southernmost Rio de la Plata craton, Argentina

The formation of Gondwana took place across a series of Brasiliano?Pan African suture zones that record late Neoproterozoic to earliest Paleozoic collisions between Precambrian cratons. In South America, an internal suture zone marks the disappearance of the Clymene Ocean that separated the Amazon craton from the São Francisco and Rio de la Plata cratons. New geochronological data from the southern end of this massive collision zone in the Sierras Australes of central-eastern Argentina document Paleoproterozoic crust and suggest an Ediacaran age for the oldest sedimentary rocks. These two observations extend the known limit of the Rio de la Plata craton at least 200 km SW of previous estimates. New data also confirm the occurrence oflate Ediacaran to late Cambrian magmatism in the Sierras Australes. The age of these hypabyssal to volcanic rocks corresponds to igneous events in the Pampean belt along the western margin of the Rio de la Plata craton, although the shallow levelmagma emplacement in the Sierra da Ventana study area contrasts with the deeply exhumed rocks of the Pampean orogeny type locality. These new age data are compared with a broad compilation of geochronological age Clymene collision belts to the north, the Paraguai and Araguaia belts. The close overlap of the timing of orogenesis indicates the age of Clymene ocean closure in its northern reaches. In the south, the Pampean belt was unconfined, allowing continued tectonic activity and crustal accretion throughout the Paleozoic.Fil: Tohver, E.. University of Western Australia; AustraliaFil: Cawood, P. P.. University of Western Australia; Australia. University of St. Andrews; Reino UnidoFil: Rossello, Eduardo Antonio. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria; ArgentinaFil: Jourdan, J.. Curtin University; Australi

Observing the anisotropic optical response of the heavy-fermion compound UNi2Al3

The optical conductivity of heavy fermions can reveal fundamental properties of the charge carrier dynamics in these strongly correlated electron systems. Here we extend the conventional techniques of infrared optics on heavy fermions by measuring the transmission and phase shift of THz radiation that passes through a thin film of UNi2Al3, a material with hexagonal crystal structure. We deduce the optical conductivity in a previously not accessible frequency range, and furthermore we resolve the anisotropy of the optical response (parallel and perpendicular to the hexagonal planes). At frequencies around 7cm^-1, we find a strongly temperature-dependent and anisotropic optical conductivity that - surprisingly - roughly follows the dc behavior.Comment: 3 pages, 2 figures, accepted for proceedings of QCnP 200

Evidence for multiband superconductivity in the heavy fermion compound UNi2Al3

Epitaxial thin films of the heavy fermion superconductor UNi2Al3 with Tc{max}=0.98K were investigated. The transition temperature Tc depends on the current direction which can be related to superconducting gaps opening at different temperatures. Also the influence of the magnetic ordering at TN=5K on R(T) is strongly anisotropic indicating different coupling between the magnetic moments and itinerant charge carriers on the multi-sheeted Fermi surface. The upper critical field Hc2(T) suggests an unconventional spin-singlet superconducting state.Comment: 4 pages, 6 figures revised version: inset of fig. 2 changed, fig. 3 added accepted for pub. in Phys. Rev. Lett. (estimated 9/04