Low gravity containerless processing of immiscible gold rhodium alloys

Under normal one-g conditions immiscible alloys segregate extensively during solidification due to sedementation of the more dense of the immiscible liquid phases. However, under low-g conditions it should be possible to form a dispersion of the two immiscible liquids and maintain this dispersed structure during solidification. Immiscible (hypermonotectic) gold-rhodium alloys were processed in the Marshall Space Flight Center 105 meter drop tube in order to investigate the influence of low gravity, containerless solidification on their microstructure. Hypermonotectic alloys composed of 65 atomic % rhodium exhibited a tendency for the gold rich liquid to wet the outer surface of the containerless processed samples. This tendency led to extensive segregation in several cases. However, well dispersed microstructures consisting of 2 to 3 micron diameter rhodium-rich spheres in a gold-rich matrix were produced in 23.4 atomic % rhodium alloys. This is one of the best dispersions obtained in research on immiscible alloy-systems to data

Influence of a magnetic field during directional solidification of MAR-M 246 + Hf superalloy

An area that has been almost totally overlooked in the optimization of properties in directionally solidified superalloys is the control of microstructural features through the application of a magnetic field during solidification. The influence of a magnetic field on the microstructural features of a nickel-base superalloys is investigated. Studies were performed on the dendritic MAR-M 246+Hf alloy, which was solidified under both a 5 K gauss magnetic field and under no-applied-field conditions. The possible influences of the magnetic field on the solidification process were observed by studying variations in microstructural features including volume fraction, surface area, number, and shape of the carbide particles. Stereological factors analyzed also included primary and secondary dendrite arm spacing and the volume fraction of the interdendritic eutectic constituent. Microprobe analysis was performed to determine the chemistry of the carbides, dendrites, and interdendritic constituents, and how it varied between field and no-field solidification samples. Experiments involving periodic application and removal of the magnetic field were also performed in order to permit a comparison with structural variations observed in a MAR-M 246+Hf alloy solidified during KC-135 high-g, low-g maneuvers

A multi-microcomputer intercommunication structure and multi-tasking algorithm

A recursive interconnection structure for multiple microcomputer systems is described. The average path length through such structures was computed, and the results were used as a measure of performance. Other characteristics such as flexibility, locality and complexity were also considered. An experimental dual-processor configuration was constructed and programmed to execute a producer-consumer multi-tasking algorithm, using a semaphore-protected queuing system in shared memory. The execution time was recorded, and was compared to the execution time of an optimized uniprocessor program. The results indicated that multiple microcomputer systems in general, and recursive structures in particular, are very promising, provided that sufficient attention is paid to task partitioning and interprocessor communications

Containerless low gravity processing of glass forming and immiscible alloys

Under normal one-g conditions immiscible alloys segregate extensively during solidification due to sedimentation of the more dense of the immiscible liquid phases. Immiscible (hypermonotectic) gold-rhodium alloys were processed in the 100 meter drop tube under low gravity, containerless conditions to determine the feasibility of producing dispersed structures. Three alloy compositions were utilized. Alloys containing 10 percent by volume of the gold-rich hypermonotectic phase exhibited a tendency for the gold-rich liquid to wet the outer surface of the samples. This wetting tendency led to extensive segregation in several cases. Alloys containing 80 and 90 percent by volume of the gold-rich phase possessed completely different microstructures from the 10 percent samples when processed under low-g, containerless conditions. Several samples exhibited microstructures consisting of well dispersed 2 to 3 microns diameter rhodium-rich spheres in a gold-rich matrix

University of Colorado: 1970 Summer Field Season in East Baffin Island

... Field work continued on [the late glacial and neoglacial chronology and recent crustal movements] program with the main emphasis being shifted to Narpaing Fiord and outer Okoa Bay. Marine limits were measured at many localities in the two areas and some samples of marine shells were collected for dating ... Studies continued on the task of subdividing the glacial deposits on the basis of a number of weathering criteria such as: depth of pitting, surface texture of boulders, soil development, X-ray analysis for clay minerals and Free-iron content. The combined results suggest several episodes of glaciation with a general decrease of glacier area and volume throughout the Wisconsin. ... A tentative lichen growth-curve is being developed based on a variety of evidence, and it is considered that the graph may usefully be extended back to 8,000 or 10,000 years ago. Work on a series of corrie moraines at the heads of Narpaing and Quajon fiords suggests that the outermost south-facing moraines at 600 m.a.s.l. may be 15,000 years old whereas the north-facing moraines at 550 m.a.s.l. are 8,000 to 10,000 years old. ... A series of 7 weather stations were established at different exposures and elevations in the area between the head of Quajon and Narpaing fiords. ... Mass budgets were measured in early June and mid-August using a variety of methods. Stakes, probing and pits were used to detail the progress of melting during the ablation season. In early June the specific net budget was + 0.42 cm ± 0.06 and in mid-August was + 0.38 ± 0.06 cm water equivalent. In complete contrast to 1969, no ice was showing on the glacier and the summer melt had been compensated by snowfalls throughout the "ablation" season. Surface lowering amounted to about 45 cm of snow and this was nearly identical to the mass added in the growth of superimposed ice. Because of low temperatures the glacier was acting nearly as a closed system. ..

A mean-removed variation of weighted universal vector quantization for image coding

Weighted universal vector quantization uses traditional codeword design techniques to design locally optimal multi-codebook systems. Application of this technique to a sequence of medical images produces a 10.3 dB improvement over standard full search vector quantization followed by entropy coding at the cost of increased complexity. In this proposed variation each codebook in the system is given a mean or 'prediction' value which is subtracted from all supervectors that map to the given codebook. The chosen codebook's codewords are then used to encode the resulting residuals. Application of the mean-removed system to the medical data set achieves up to 0.5 dB improvement at no rate expense

University of Colorado 1974 Field Season in Eastern Baffin Island

The summer of 1974 saw one of the largest research parties the University of Colorado has been able to mount operating along the eastern coast of Baffin Island. The early and widespread break-up of sea ice greatly assisted in the completion of the field programme in which a total of sixteen persons were involved. In addition to members of the University staff, the following individuals from other institutions also participated. In the programme: a member of the Department of Micropalaeontology of the University of Aarhus, Denmark; a soil scientist from the University of Pennsylvania, U.S.A.; a Quaternary geologist from Brock University, Ontario, Canada; and a Quaternary geologist from Grand Valley State College, Michigan, U.S.A. ... Raised marine sediments and tills were investigated on Broughton Island and northwards along the coast to Quajon Fiord. Specific attention was focused on collecting samples for micro-faunal analysis and delimiting different marine episodes. In addition, a number of sites were revisited on Broughton Island and northwards along the coast to Kivitoo and Quajon Fiord. Large (1000-g and over) samples of marine shells were collected from sites previously given dates of over 30,000 years BP. ... One field party mapped the southern part of the Baffin Island National Park, giving particular attention to (a) the delimitation of glacial periods on the basis of surface weathering of boulders, and (b) determining the elevation of local marine limits and lower strandlines. The latter research was concentrated on the mapping of the southern shore of Cumberland Peninsula, from outer Kingnait Fiord westward to the head of Cumberland Sound. ... Soil scientists established a soil chronosequence, and investigated the range of soil types existing within the southern part of Cumberland Peninsula. They sent samples south from laboratory analysis. Plant collection: Specimens of vascular plants, mosses and lichens were collected from Broughton Island and from the head of Maktak Fiord, and sent to the University of Colorado Museum. By December 1974, a total of 86 vascular plants had been identified. Climatological studies in relation to fast ice: Work done during the summer of 1974 concludes the field-measurement phase of the University of Colorado's study of the surface energy budgets of fast ice at Broughton Island. A micrometeorological station was operated at a site approximately one kilometre south of Broughton settlement, from late May until local break-up in early July. The programme of observation consisted of the periodic taking of profiles of wind, temperature and relative humidity; the continuous measurement of temperature at two metres, and net radiation over both saturated and unsaturated surfaces; and transects of surface short-wave albedo. Salinity and temperature profiles in the ice and water were taken every 304 days. Comparative analysis of the data for 1972-74 is now in progress in relation to the observed ice regime. The 1974 data should provide better estimates of the turbulent flux components of the energy budget than it was possible to make in previous summers. Meteorological observations were continued near the base of the Broughton Island operations through mid-August. Results are now available of four summers and two winters of standard meteorological observations, and global solar and net radiation measurements as well. The Atmospheric Environment Service Cooperative Observer station, with its twice-daily measurements of maximum and minimum temperatures and of precipitation, is now into its fourth calendar year of operation. The summer of 1974 was unusually mild. The mean ablation seasonal temperature was 3.9°C at the Broughton DEW line weather station. In contrast, 1972 was the coldest (-1.2 C°). The early part of June 1974 was dominated by anticyclonic synoptic weather patterns which greatly accelerated the fast ice ablation rate to give the earliest break-up in five years. Satellite-observed conce ntrations of pack ice in Davis Strait in late May were less than at the same time in 1973. With the resurvey of the "Boas" Glacier (67 35 N, 65 16 W) in August 1974, the mass balance measurements were extended to five balance years. Accurate measurements were not possible, because most ablation poles melted out during the warm summer of 1974. However, it is estimated that the net specific balance for the 1973-74 budget year was approximately -0.5 m water equivalent (w.e.). ... Analysis of the past five budget years shows that (a) the "Boas" Glacier exhibited a two-year alternation of large mass gains and losses during the first four years, and (b) the estimated net specific mass balance for the five-year period was -0.16 m w.e., in spite of the total net mass gains of 0.38 m w.e. during the first four years. ..

University of Colorado: 1971 Summer Field Season in East Baffin Island

Research was continued by University of Colorado faculty and graduate students in the area of Cumberland Peninsula. Baffin Island, Northwest Territories. The work was divided into four main phases: 1) studies on the glacial chronology of the Penny Ice Cap and local mountain ice caps; 2) the mass balance of the Boas Glacier; 3) air-sea interactions using ground stations, instrumented aircraft and satellite data; and 4) evaluation of climatic trends. ..

A study of surface tension driven segregation in monotectic alloy systems

The compatibilities of various monotectic alloy systems with several different crucible materials were evaluated. The study was carried out using small candidate alloy samples of compositions that produced fifty volume percent of each liquid phase at the monotectic temperature. Compatibility was based on the evaluation of the wetting tendency of the two immiscible phases with the crucible material in a one-g solidified sample. Three types of wetting phenomena were observed during the evaluation. Type 1 indicates an alloy-crucible combination where the L2 phase preferentially wets the crucible material. Since L2 is usually the minority phase in desirable alloys, this material combination would be difficult to process and is therefore considered incompatible. Type 2 behavior indicates an alloy-crucible combination where the L1 phase preferentially wets the crucible material. This type of combination is considered compatible since surface tension effects should aid in processing the alloy to a useful form. Type 3 indicates any combination that leads to major reactions between the alloy and crucible material, gas entrapment, or separation of the metal from the crucible wall. Additional compatibility evaluations would have to be carried out on combinations of this category. The five alloy systems studied included aluminum-bismuth, copper-lead, aluminum-indium, aluminum-lead and cadmium-gallium. The systems were combined with crucibles of alumina, boron nitride, mullite, quartz, silicon carbide and zirconia

Immiscible phase incorporation during directional solidification of hypermonotectics

Solidification processes in immiscible samples were investigated by directly observing the events taking place at the solid-liquid interface during directional solidification. Visualization of these events was made possible through the use of a transparent metal analog system and a temperature gradient stage assembly fitted to an optical microscope. The immiscible transparent analog system utilized was the succinonitrile-glycerol system. This system has been shown to exhibit the same morphological transitions as observed in metallic alloys of monotectic composition. Both monotectic and hypermonotectic composition samples were directionally solidified in order to gain an improved understanding of the manner in which the excess hypermonotectic liquid is incorporated into the solidifying structure. The processing conditions utilized prevented sedimentation of the excess hypermonotectic liquid by directionally solidifying the samples in very thin (13 microns), horizontally oriented cells. High thermal gradient to growth rate ratios (G/R) were used in an effort to prevent constitutional supercooling and the subsequent formation of L(sub 2) droplets in advance of the solidification front during the growth of fibrous composite structures. Results demonstrated that hypermonotectic composites could be produced in samples up to two weight percent off of the monotectic composition by using a G/R ratio greater than or equal to 4.6 x 10(exp 4) C(s)/mm(sup 2) to avoid constitutional supercooling. For hypermonotectic samples processed with G/R ratios below 4.6 x 10(exp 4) C(s)/mm(sup 2), constitutional supercooling occurred and resulted in slight interfacial instability. For these samples, two methods of incorporation of the hypermonotectic liquid were observed and are reported. The correlation between the phase spacing, lambda, and the growth rate, R, was examined and was found to obey a relationship generally associated with a diffusion controlled coupled growth process. For samples with compositions ranging from the monotectic composition up to 2 percent off of the monotectic composition, data indicated that the square of the phase spacing (lambda) varied linearly with the inverse of the growth rate (R)