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Modified version of process for making SiC-fiber/SiC-matrix composite material reduces damage to SiC (SCS-6) fibers and to carbon-rich coatings on fibers. Modification consists of addition of second polymer-infiltration-and-pyrolysis step to increase carbon content of porous matrix before infiltration with liquid silicon or silicon alloy.
The most important nebular fractionation affecting the siderophile elements is the metal-silicate fractionation process and its relationship to the chondrule formation process is poorly understood. Understanding these processes is important in terms of understanding the expected compositional range for planetary building blocks. In a general way the composition of chondrites can be derived from the composition of the CI chondrites by addition or subtraction of a refractory component similar to CAI's (in some cases with a Mg2SiO4 component) and by addition or subtraction of Fe metal. Thus normalization to Fe produces the least spread in the normalized abundances of most siderophile elements relative to CI abundances. Detailed bulk chemical studies of chondrules have shown that their siderophile elements have refractory-element siderophile-element signatures (for example, Ir/Ni) that are similar to the bulk meteorites, but distinct among the different chondrite groups. This data suggests that the chondrules were not supplied to the chondrule groups from a single homogeneous source, and that each chondrite group's characteristic siderophile-element signature was established before chondrule formation. These authors make a further inference that all siderophile-lithophile-element fractionation occurred before chondrule formation, but recent discoveries and observations suggest this is not true. The discovery of the metal-rich CH meteorites, the recognition of the role of aerodynamic forces in the solar nebula, and the possible role of metal-silicate segregation during the chondrule formation process suggests that metal-silicate fractionation occurred before, during and after chondrule formation.
Mixed-phase clouds (MPCs) have been identified as significant contributors to uncertainties in climate projections, attributable to model representation of processes controlling the formation and loss of supercooled water droplets and ice particles from the atmosphere. Arctic MPCs are commonly widespread and long-lived, with sustained ice crystal formation processes that challenge current understanding. This study examines the ice-nucleating particle (INP) reservoir dynamics governing immersion-mode heterogeneous freezing in an observed case of Arctic MPCs using a simplified 1D aerosol-cloud model. The model setup includes prescribed dynamical forcings and thermodynamic profiles, and represents INPs as multicomponent and polydisperse particle size distributions. Diagnostic and prognostic approaches to immersion freezing parameterization are compared, including time-independent (singular) number- and surface area-based descriptions and a time-dependent description following classical nucleation theory (CNT). The choice of freezing parameterization defines the size of the INP reservoir. The CNT-based description yields an orders of magnitude larger INP reservoir than the singular parameterizations, which is the dominant factor for sustained ice crystal formation. The efficiency of the freezing process and cloud cooling are of secondary importance. A diagnostic treatment neglecting INP loss is only accurate when the INP reservoir size is large and INP depletion weak. Since a larger INP reservoir sustains ice crystal formation substantially longer, and ice water path scales with ice crystal concentrations for the conditions considered, resolving the source of differences in INP reservoir dynamics due to model implementation is a high priority for advancing climate model physics.
The possibility of diamond formation in radiation processes was checked by studying diamond contents in carburanium sample. The diamonds were not found and this result is discussed. At present one possible process of formation of nanometer-size diamond crystals in some meteorites and Earth's diamonds (carbonado), the radiation mechanism, is suggested: the formation of diamonds from carbonaceous matter in tracks of U fragment fissions and heavy fragmentation due to the action of energetic particles of cosmic rays. Bjakov et. al. have carried out the calculations and shown that the volume of formed diamonds in carbonaceous chondrites by radiation processes corresponds to discovery of diamond volume in chondrites. The discovery by Ozima et. al. of the unsupported fission of Xe and Kr in carbonado supports the supposition that carbonado could be formed by radiation processes. The possibility of diamond formation in radiation processes leads to the study of diamond contents in Earth's samples enriched by uranium and carbon. The attempt to release the diamonds from carburanium was undertaken.
Adrenocorticotropin (ACTH) was administered to rats at different times following adrenalectomy. Adrenocorticotropin caused a significant increase in the formation of heparin complexes even in the absence of stress factor. When ACTH secretion is blocked, immobilization stress is not accompanied by an increase in the process of complex formation. The effect of ACTH on the formation of heparin complexes was mediated through its stimulation of the adrenal cortex.
The MER Opportunity Athena Science team has described spheroidal hematite nodules in sediments at Meridiani Planum on Mars [1]. They were informally referred to as "Blueberries" in the initial press releases and for brevity that is the name to be used in this abstract. Not all spheroidal objects in sediments are nodular concretions, but this paper will discuss the diagenetic processes possibly relevant to understanding the origin of the Blueberries. There are many occurrences of spheroidal diagenetic concretions in terrestrial sediments and detailed work has been done to understand the processes of their formation. In particular, it is possible to reconstruct the controls on their shapes and compositions, both mineral and chemical. Although there may not be good analogs for the Meridiani Planum hematite spherules on Earth, it may be possible to deduce the former environmental conditions that led to their formation and whether they might retain (or even be) biosignatures.
Analyses of slicing processes and junction formation processes are presented. A simple method for evaluation of the relative economic merits of competing process options with respect to the cost of energy produced by the system is described. An energy consumption analysis was developed and applied to determine the energy consumption in the solar module fabrication process sequence, from the mining of the SiO2 to shipping. The analysis shows that, in current technology practice, inordinate energy use in the purification step, and large wastage of the invested energy through losses, particularly poor conversion in slicing, as well as inadequate yields throughout. The cell process energy expenditures already show a downward trend based on increased throughput rates. The large improvement, however, depends on the introduction of a more efficient purification process and of acceptable ribbon growing techniques.
Attention is given to the fact that a significant fraction of the chondrules from ordinary chondrites contain silicate grains that survived the chondrule formation process without melting. Typically, these grains consist of coarse olivine, rarely orthopyroxene, crystals located in the core of chondrules and displaying a zoning that is inconsistent with crystallization from a silicate melt. It is noted that the relict grains still preserve the imprint of processes that occurred in the solar nebula and, in some cases, may include the isotopic record of interstellar grains. Information is presented on the chondrule precursor materials and the process of chondrule formation which was acquired by a compositional and textural study of three of the most unequilibrated type 3 ordinary chondrites.
This paper considers the concept of magnetic reconnection from a general point of view, with special consideration given to magnetic reconnection in nonvanishing magnetic fields, i.e., finite-B reconnection as distinct from zero-B reconnection. It is shown that the electric field component parallel to the magnetic field (E-parallel) plays a crucial physical role in finite-B reconnection. Two theorems involving E-parallel are proposed. The first defines a necessary and sufficient condition of E-parallel for global reconnection to occur. The second theorem is concerned with the change of magnetic helicity to E-parallel for cases where the electric field vanishes at large distances. The general magnetic reconnection concept is tested by applying it to the process of plasmoid formation process.
The flame structure and soot-formation (soot nucleation and growth) properties of axisymmetric laminar coflowing jet diffusion flames were studied experimentally. Test conditions involved acetylene-nitrogen jets burning in coflowing air at atmospheric pressure. Measurements were limited to the axes of the flames and included soot concentrations, soot temperatures, soot structure, major gas species concentrations, radical species (H, OH, and O) concentrations, and gas velocities. The results show that as distance increases along the axes of the flames, detectable soot formation begins when significant H concentrations are present, and ends when acetylene concentrations become small. Species potentially associated with soot oxidation-O2, CO2, H2O, O, and OH-are present throughout the soot-formation region so that soot formation and oxidation proceed at the same time. Strong rates of soot growth compared to soot nucleation early in the soot-formation process, combined with increased rates of soot nucleation and oxidation as soot formation proceeds, causes primary soot particle diameters to reach a maximum relatively early in the soot-formation process. Aggregation of primary soot particles proceeds, however, until the final stages of soot oxidation. Present measurements of soot growth (corrected for soot oxidation) in laminar diffusion flames were consistent with earlier measurements of soot growth in laminar premixed flames and exhibited encouraging agreement with existing hydrogen-abstraction/carbon-addition (HACA) soot growth mechanisms in the literature that were developed based on measurements within laminar premixed flames. Measured primary soot particle nucleation rates in the present laminar diffusion flames also were consistent with corresponding rates measured in laminar premixed flames and yielded a crude correlation in terms of acetylene and H concentrations and the temperature.
The flame structure and soot-formation (soot nucleation and growth) properties of axisymmetric laminar coflowing jet diffusion flames were studied experimentally. Test conditions involved acetylene-nitrogen jets burning in coflowing air at atmospheric pressure. Measurements were limited to the axes of the flames and included soot concentrations, soot temperatures, soot structure, major gas species concentrations, radical species (H, OH, and O) concentrations, and gas velocities. The results show that as distance increases along the axes of the flames, detectable soot formation begins when significant H concentrations are present, and ends when acetylene concentrations become small. Species potentially associated with soot oxidation--O2, CO2, H2O, O, and OH-are present throughout the soot-formation region so that soot formation and oxidation proceed at the same time. Strong rates of soot growth compared to soot nucleation early in the soot-formation process, combined with increased rates of soot nucleation and oxidation as soot formation proceeds, causes primary soot particle diameters to reach a maximum relatively early in the soot-formation process. Aggregation of primary soot particles proceeds, however, until the final stages of soot oxidation. Present measurements of soot growth (corrected for soot oxidation) in laminar diffusion flames were consistent with earlier measurements of soot growth in laminar premixed flames and exhibited encouraging agreement with existing hydrogen-abstraction/carbon-addition (HACA) soot growth mechanisms in the literature that were developed based on measurements within laminar premixed flames. Measured primary soot particle nucleation rates in the present laminar diffusion flames also were consistent with corresponding rates measured in laminar premixed flames and yielded a crude correlation in terms of acetylene and H concentrations and the temperature.
The flame structure and soot-formation (soot nucleation and growth) properties of axisymmetric laminar coflowing jet diffusion flames were studied experimentally. Test conditions involved acetylene-nitrogen jets burning in coflowing air at atmospheric pressure. Measurements were limited to the axes of the flames and included soot concentrations, soot temperatures, soot structure, major gas species concentrations, radical species (H, OH, and O) concentrations, and gas velocities. The results show that as distance increases along the axes of the flames, detectable soot formation begins when significant H concentrations are present, and ends when acetylene concentrations become small. Species potentially associated with soot oxidation-O2, CO2, H2O, O, and OH-are present throughout the soot-formation region so that soot formation and oxidation proceed at the same time. Strong rates of soot growth compared to soot nucleation early in the soot-formation process, combined with increased rates of soot nucleation and oxidation as soot formation proceeds, causes primary soot particle diameters to reach a maximum relatively early in the soot-formation process. Aggregation of primary soot particles proceeds, however, until the final stages of soot oxidation. Present measurements of soot growth (corrected for soot oxidation) in laminar diffusion flames were consistent with earlier measurements of soot growth in laminar premixed flames and exhibited encouraging agreement with existing hydrogen-abstraction/carbon-addition (HACA) soot growth mechanisms in the literature that were developed based on measurements within laminar premixed flames. Measured primary soot particle nucleation rates in the present laminar diffusion flames also were consistent with corresponding rates measured in laminar premixed flames and yielded a crude correlation in terms of acetylene and H concentrations and the temperature.
The rare earth elements (REEs) are concentrated in CAIs by approx. 20 times the chondritic average [e.g., 1]. The REEs in CAIs are important to understand processes of CAI formation including the role of volatilization, condensation, and fractional crystallization [1,2]. REE measurements are a well established application of ion microprobes [e.g., 3]. However the spatial resolution of REE measurements by ion microprobe (approx.20 m) is not adequate to resolve heterogeneous distributions of REEs among/within minerals. We have developed methods for measuring REE with the NanoSIMS 50L at smaller spatial scales. Here we present our initial measurements of REEs in melilite and fassaite in an Allende Type-A CAI with the JSC NanoSIMS 50L. We found that the key parameters for accurate REE abundance measurements differ between the NanoSIMS and conventional SIMS, in particular the oxide-to-element ratios, the relative sensitivity factors, the energy distributions, and requisite energy offset. Our REE abundance measurements of the 100 ppm REE diopside glass standards yielded good reproducibility and accuracy, 0.5-2.5 % and 5-25 %, respectively. We determined abundances and spatial distributions of REEs in core and rim within single crystals of fassaite, and adjacent melilite with 5-10 m spatial resolution. The REE abundances in fassaite core and rim are 20-100 times CI abundance but show a large negative Eu anomaly, exhibiting a well-defined Group III pattern. This is consistent with previous work [4]. On the other hand, adjacent melilite shows modified Group II pattern with no strong depletions of Eu and Yb, and no Tm positive anomaly. REE abundances (2-10 x CI) were lower than that of fassaite. These patterns suggest that fassaite crystallized first followed by a crystallization of melilite from the residual melt. In future work, we will carry out a correlated study of O and Mg isotopes and REEs of the CAI in order to better understand the nature and timescales of its formation process and subsequent metamorphic history.
The digital processing requirements of several algorithms for extracting the spectrum of a detected synthetic aperture radar (SAR) image from the raw SAR data are described and compared. The most efficient algorithms for image spectrum extraction from raw SAR data appear to be those containing an intermediate image formation step. It is shown that a recently developed compact formulation of the image spectrum in terms of the raw data is computationally inefficient when evaluated directly, in comparison with the classical method where matched-filter image formation is an intermediate result. It is also shown that a proposed indirect procedure for digitally implementing the same compact formulation is somewhat more efficient than the classical matched-filtering approach. However, this indirect procedure includes the image formation process as part of the total algorithm. Indeed, the computational savings afforded by the indirect implementation are identical to those obtained in SAR image formation processing when the matched-filtering algorithm is replaced by the well-known 'dechirp-Fourier transform' technique. Furthermore, corrections to account for slant-to-ground range conversion, spherical earth, etc., are often best implemented in the image domain, making intermediate image formation a valuable processing feature.
This paper examines the global interaction of the solar wind with the geomagnetic field, using a newly developed three-dimensional high-precision MHD simulation code which employs the fourth-order Runge-Kutta-Gill scheme in time and the direct finite-difference method in space, and which allows much less numerical error than the conventional code. The simulation reveals in detail the formation processes of the magnetosphere and the bow shock, as well as the plasma sheet formation process. It is shown that, contrary to the conventional understanding, no Kelvin-Helmholtz instability occurs along the magnetopause in an ideal MHD.
Sensorimotor control tests show that mastering operational skills occurs under conditions that stimulate the operator to independent active analysis and summarization of current information with the goal of clarifying the signs and the integral images that are a model of the situation. Goal directed determination of such an image requires inner and external speech, activates and improves the thinking of the operator, accelerates the training process, increases its effectiveness, and enables the formation of strategies in anticipating the course of events.
Almost seventy percent of fire related deaths are caused by the inhalation of toxins such as CO and soot that are produced when fires become underventilated.(1) Although studies have established the importance of CO formation during underventilated burning,(2) the formation processes of CO (and soot) in underventilated fires are not well understood. The goal of the COSMIC project is to study the formation processes of CO and soot in underventilated flames. A potential way to study CO and soot production in underventilated flames is the use of inverse diffusion flames (IDFs). An IDF forms between a central air jet and a surrounding fuel jet. IDFs are related to underventilated flames because they may allow CO and soot to escape unoxidized. Experiments and numerical simulations of laminar IDFs of CH4 and C2H4 were conducted in 1-g and micro-g to study CO and soot formation. Laminar flames were studied because turbulent models of underventilated fires are uncertain. Microgravity was used to alter CO and soot pathways. A IDF literature survey, providing background and establishing motivation for this research, was presented at the 5th IWMC.(3) Experimental results from 1-g C2H4 IDFs and comparisons with simulations, demonstrating similarities between IDFs and underventilated fires, were presented at the 6th IWMC.(4) This paper will present experimental results from micro-g and 1-g IDFs of CH4 and C2H4 as well as comparisons with simulations, further supporting the relation between IDFs and underventilated flames.
This paper describes a modified polar format algorithm for SAR image-formation processing. the algorithm focuses raw data assuming a spherical reference surface (ground surface), and, unlike standard polar format algorithms, it assumes spherical rather than planar signal wavefronts.