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Trigonometric parallaxes have been measured by Dahn et al. (2002) for 28 cool dwarfs and brown dwarfs, including 17 L dwarfs and three T dwarfs. Broadband CCD and near-IR photometry (VRIz*JHK) have been obtained for these objects and for 24 additional late-type dwarfs. These data have been supplemented with astrometry and photometry from the literature, including parallaxes for the brighter companions of ten L and two T dwarfs. The absolute magnitudes and colors are reviewed here. The I - J color and the spectral type are both good predictors of absolute magnitude for late-M and L dwarfs. MJ becomes monotonically fainter with I - J color and with spectral type through late-L dwarfs, then brightens for early-T dwarfs. In contrast, the J - K color correlates poorly with absolute magnitude for L dwarfs. Using several other parameters from the literature (Li detection, Hα emission strength, projected rotation velocity, and tangential velocity), we fail to uncover any measurable parameter that correlates with the anomalous J - K color.
The first type II radio burst to be observed at frequencies below the ionospheric cutoff was recorded by the Goddard radio astronomy experiment on the Interplanetary Monitoring Platform, IMP-6. It occurred on June 30, 1971; a tracing made from the intensity contour plot of the radio data is shown in Figure 1. On the original, intensity contours were plotted in dB above background as a function of frequency and time. The figure shows 32 discrete frequencies from 4.9 MHz to 30 kHz received by the IMP-6 experiment. The time scale covers a period of almost five hours. During this time, five individual type III bursts and one group of type III's occurred; they are shown by their outlines to be drifting rapidly from high to low frequencies. The relatively narrow-band, slowly-drifting radiation with clearly defined fundamental and second harmonic is the type II. The average drift rate, represented by the straight lines drawn through the burst, is approximately 2.5 kHz min−1 in this frequency range, and is roughly 100 times slower than that of the type III bursts. The ovals defining the type II emission were traced from the record and show modulation of the signal caused by the spin of the satellite and the resultant sweeping of the antenna pattern of the dipole across the source direction. On the original record, the outlines of the type III's are also filled with a pattern of modulation ovals that were omitted from the figure for clarity. The shaded portion of the record at the lower frequencies represents magnetospheric noise.
The present triennial commission report embraces mainly activities in wide angle, optical astrometry. With the successful development and application of new techniques from Earth (e.g. optical interferometry, CCD’s) and space (Hipparcos mission and new projects) the sub-division between Commissions 8 (Positional Astrometry) and 24 (Photographic Astrometry) has become questionable. During the GA at Kyoto in 1997 all steps for a merger of both commissions have been taken. The final merging will take place at the forthcoming GA in Manchester. For a more complete overview on astrometrical work done in the past triennium the reader should also take notice of the report of Commission 24.
The ALFA mission is designed to map the entire sky at frequencies between approximately 0.3 and 30 MHz with angular resolution limited by interstellar and interplanetary scattering. Most of this region of the spectrum is inaccessible from the ground because of absorption and refraction by the Earth’s ionosphere. A wide range of astrophysical questions concerning solar system, galactic, and extragalactic objects could be answered with high resolution images at low frequencies, where absorption effects and coherent emission processes become important and the synchrotron lifetimes of electrons are comparable to the age of the universe.
The second Advanced Technology Satellite (ATS-II) carries a radio-astronomy experiment designed to perform radio-noise measurements in the range 0·5 to 3·0 MHz from above the terrestrial ionosphere. The spacecraft was launched into an 11000-km apogee, 180-km perigee orbit on April 6, 1967, and since there was considerable solar activity in the ensuing months it is possible to present a preliminary description of the kind of solar observations this experiment will provide.
A study program was initiated at the Goddard Space Flight Center in 1962 to survey the astronomical observations most readily and profitably performed by an orbiting radio observatory, to analyze the antenna configurations most appropriate for such a mission and to develop the radiometers and other supporting instrumentation required for a radio astronomy satellite. This study has culminated in the conceptual design of a spacecraft intended solely for radio astronomical observations at wavelengths beyond the ionospheric cut-off. By utilizing long (250 m) antenna elements with a terminating resistance placed an odd number of quarter-wavelengths from the end, a V-antenna can be formed having a beamwidth less than 30° and an 18 db front-to-back ratio over a band of frequencies near 5 MHz. Proper combinations of four such long elements in a double-V or X configuration, furthermore can be made to yield some gain over a, dipole for observations as low as 0.3 MHz. A step-frequency, Ryle-Vonberg radiometer which employs an all solid-state-component comparison noise source has been developed to perform over a 70 db dynamic range with a relative accuracy of ± 0.5 db. A simple, precise instrument to measure both the resistive and reactive components of antenna impedance has also been developed for satellite use. Observations with this system from a gravity-gradient stabilized spacecraft in a 6000 km orbit would afford significant contributions to galactic studies, solar physics, and planetary astronomy by extending radio observations to frequencies in the range 0 3 to 10 MHz.
We present simultaneous energetic electron and solar radio observations from the ISEE−3 spacecraft of several solar type III radio bursts. The UC Berkeley energetic particle experiment measures from 2 to ~ 103 keV with good energy and pitch angle resolution while the Meudon/GSFC radio experiment tracks type III radio bursts at 24 frequencies in the range 30 kHz—2 MHz.
Three dimensional “snapshots” of the large scale solar magnetic field topology as well as the solar wind electron density distribution from about 0.1 to 1 AU are obtained by tracking traveling solar radio bursts at hectometer and kilometer wavelengths with instruments aborad the ISEE-3 satellite and the HELIOS-2 solar probe. Both instruments observe in the frequency range from 30 kHz to 1 MHz and both are equipped with dipole antennas located in the vehicle spin plane. ISEE-3 also has a dipole along the spin axis and the signals from the two ISEE-3 antennas are combined to give the azimuth and elevation angles of the radio source. Triangulation between HELIOS-2 and ISEE-3 provides the additional observation necessary to uniquely determine the position of the radio source in space at each observing frequency. The techniques will be outlined, and illustrated by an example of the three dimensional field geometry and electron density distribution determined by the observations.
Biomaterials are widely used for dental implants, orthopedic devices, cardiac pacemakers and catheters. One of the main concerns on using bio-implants is the risk of infection on the materials used. In this study, our aim is to quantify the effect of controlled surface roughness on the infection resistance of the titanium based bio-materials which are commonly used for orthopedic devices and dental implants. To modify the surface roughness of the surfaces in a controlled manner, Chemical Mechanical Polishing (CMP) technique, which is extensively used in semiconductor industry for the planarization of the interlayer dielectrics and metals, is utilized. To determine the infection resistance of the created films with varying surface roughness, bacteria growth response was studied on titanium plates after CMP.
We present experimental results supporting physics-based ejecta model development, where our main assumption is that ejecta form as a special limiting case of a Richtmyer–Meshkov (RM) instability at a metal–vacuum interface. From this assumption, we test established theory of unstable spike and bubble growth rates, rates that link to the wavelength and amplitudes of surface perturbations. We evaluate the rate theory through novel application of modern laser Doppler velocimetry (LDV) techniques, where we coincidentally measure bubble and spike velocities from explosively shocked solid and liquid metals with a single LDV probe. We also explore the relationship of ejecta formation from a solid material to the plastic flow stress it experiences at high-strain rates () and high strains (700 %) as the fundamental link to the onset of ejecta formation. Our experimental observations allow us to approximate the strength of Cu at high strains and strain rates, revealing a unique diagnostic method for use at these extreme conditions.
Subduction-related accretion of fault-defined tracts built up the Southern Uplands terrane during the final stages of closure of the Iapetus Ocean (Llandovery to Wenlock). Contrasts in depositional environment and pronounced differences in geochemical composition, provenance studies and metamorphic grade across the Laurieston Fault between the Gala and Hawick groups, suggests that it has a greater regional significance than most other tract-bounding structures. Initiated by underthrusting, and acting as a locus for subsequent sinistral strike-slip, the fault overlies a regional gravity anomaly gradient that is interpreted to be due, in part, to a concealed NW-ward dipping shallow basement surface. This is modelled as an open ramp in the NE that steepens to a near-vertical step along-strike to the SW. A change in structural geometry noted at the Laurieston Fault, with excision of accretionary tracts, is related to a period of oblique closure of the Iapetus Ocean. The youngest Gala Group tracts were accreted during a period of intense transpression to form a regional strike-slip duplex over the shallow basement ramp with termination of the tracts at the Laurieston Fault, its surface expression. The ramp acted as an obstacle to forward-breaking thrust progress, forcing the out-of-sequence thrusting and repetitive thrust imbrication noted in the eastern Southern Uplands. Upper Palaeozoic reactivation of this basement structure may have transferred strain between extensional Permian basins.
Part of a strategy for evaluating the compliance of geologic repositories with Federal regulations is a modeling approach that would provide realistic release estimates for a particular configuration of the engineered-barrier system. The objective is to avoid worst-case bounding assumptions that are physically impossible or excessively conservative and to obtain probabilitistic estimates of (1) the penetration time for metal barriers and (2) radionuclide-release rates for individually simulated waste packages after penetration has occurred. The conceptual model described in this paper will assume that release rates are explicitly related to such time-dependent processes as mass transfer, dissolution and precipitation, radionuclide decay, and variations in the geochemical environment. The conceptual model will take into account the reduction in the rates of waste-form dissolution and metal corrosion due to a buildup of chemical reaction products. The sorptive properties of the metal-barrier corrosion products in proximity to the waste form surface will also be included. Cumulative releases from the engineered-barrier system will be calculated by summing the releases from a probabilistically generated population of individual waste packages.
Mild steels are considered to be strong candidates for waste package structural barrier (e.g., overpack) applications in salt repositories. Corrosion rates of these materials determined in autoclave tests utilizing a simulated intrusion brine based on Permian Basin core samples are low, generally μm (1 mil) per year. When the steels are exposed to moist salts containing simulated inclusion brines, the corrosion rates are found to increase significantly. The magnesium in the inclusion brine component of the environment is believed to be responsible for the increased corrosion rates.
The Basalt Waste Isolation Project (BWIP) is conducted for the U.S. Department of Energy (DOE) by Rockwell Hanford Operations (Rockwell). The BWIP has undertaken an experimental program to test the behavior of defense waste glass under conditions relevant to a repository in basalt. Three autoclave experiments utilizing a nonradioactive simulated waste glass (Savannah River Laboratory (SRL) Type 131/TDS-3A) have been completed. Monolithic discs and crushed glass particles were reacted with crushed basalt and synthetic basalt groundwater for ∼1 yr at temperatures of 90 °C to 150 °C. The crushed qlass proved considerably more reactive than the monoliths at similar temperatures. Raising the temperature from 90 °C to 150 °C produced a striking increase in the extent of glass alteration. At 150 °C, essentially all of the boron and most of the sodium in the glass particles were released. The major reaction products in all three experiments were smectite clay and zeolites. The two tests utilizing crushed glass also yielded analcime. Nickel, cesium, and strontium, important elements in defense waste, were released from the glass in small quantities. The nickel was incorporated into the clay, while the cesium was incorporated into the analcime.
Sorption isotherms and apparent concentration limits for Tc(VII) and Np(V) for a variety of groundwater/basalt systems were determined using Grande Ronde basalt samples representative of the Hanford Site candidate high-level waste repository. Under oxic redox conditions (air present), little or no sorption of technetium was observed; neptunium exhibited low to moderate sorption ratios. Under anoxic redox conditions (oxygen-free), low to moderate sorption of technetium was often observed, but the extent of sorption was highly dependent upon the groundwater composition and the method of pretreatment (if any) of the basalt. Sorption isotherms for technetium under reducing redox conditions (hydrazine added) indicate an apparent concentration limit of approximately 10−6 mol/L Tc. No apparent concentration limit was found for neptunium for concentrations in groundwater up to.∼10−6 mol/L and 8 × 10−7 mol/L under oxic and reducing (hydrazine added) redox conditions, respectively.
Valence control and valence analysis experiments suggest that the sorption or precipitation of Tc and Np from groundwater in the presence of basalt may result from a heterogeneous reaction occurring on the surface of the basalt. One of the critical factors of this reduction reaction appears to be the accessibility of the reactive ferrous iron component of the basalt. The laboratory simulation of groundwater redox conditions representative of the repository environment through the use of solution phase redox reagents is of questionable validity, and information obtained by such experimental methods may not be defensible for site performance assessment calculations. Anoxic experiments conducted in an argon-filled glove box appear better suited for the laboratory simulation of in situ redox conditions.
The pyrochlore structure type, A1−2 B2 O6 Y0−1, is a common phase in polycrystalline waste forms. A principal concern has been the effect of alpharecoil events on the longterm stability of these phases. Naturally occurring minerals of the pyrochlore group provide an example of the full range of radiation effects from fully crystalline to xray diffraction amorphous (the metamict state). Xray absorption spectroscopy is used to investigate the coordination geometry of Tisites in metamict and annealed (1,000°C) pyrochlores. The principal effects in the fullydamaged material (∼4026 alpha events/m3) compared to annealed samples include an increase in the asymmetry of the Tisite and a slight reduction in bond length and coordination number.
The electrical properties associated with diamond charged particle- and photo-detectors were studied using charged particle-induced conductivity (CPIC) and photo-induced conductivity (PIC). The collection distance d, the product of the excess carrier mobility μ excess carrier lifetime T and electric field E, was used to characterize the diamonds. X-ray diffraction, Raman spectroscopy, photoluminescence, SEM and TEM were performed on CVD diamond detectors to investigate the limitations of the electrical properties. Correlations were found between the electrical properties and the material characterizations.