20,098 research outputs found
Applications of high thermal conductivity composites to electronics and spacecraft thermal design
Recently, high thermal conductivity continuous graphite fiber reinforced metal matrix composites (MMC's) have become available that can save much weight over present methods of heat conduction. These materials have two or three times higher thermal conductivity in the fiber direction than the pure metals when compared on a thermal conductivity to weight basis. Use of these materials for heat conduction purposes can result in weight savings of from 50 to 70 percent over structural aluminum. Another significant advantage is that these materials can be used without the plumbing and testing complexities that accompany the use of liquid heat pipes. A spinoff of this research was the development of other MMC's as electronic device heat sinks. These use particulates rather than fibers and are formulated to match the coefficient of thermal expansion of electronic substrates in order to alleviate thermally induced stresses. The development of both types of these materials as viable weight saving substitutes for traditional methods of thermal control for electronics packaging and also for spacecraft thermal control applications are the subject of this report
Move-minimizing puzzles, diamond-colored modular and distributive lattices, and poset models for Weyl group symmetric functions
The move-minimizing puzzles presented here are certain types of one-player
combinatorial games that are shown to have explicit solutions whenever they can
be encoded in a certain way as diamond-colored modular and distributive
lattices. Such lattices can also arise naturally as models for certain
algebraic objects, namely Weyl group symmetric functions and their companion
semisimple Lie algebra representations. The motivation for this paper is
therefore both diversional and algebraic: To show how some recreational
move-minimizing puzzles can be solved explicitly within an order-theoretic
context and also to realize some such puzzles as combinatorial models for
symmetric functions associated with certain fundamental representations of the
symplectic and odd orthogonal Lie algebras
A PRELIMINARY FEASIBILITY FOR ESTABLISHING A MULTI-SPECIES MEAT PROCESSING PLANT IN SOUTHWESTERN NORTH DAKOTA
The number of small commodity livestock slaughter plants in the Upper Northern Plains region continues to decline. Significant factors contributing to this decline include: 1) pressure to consolidate, thereby capturing economies of scale; 2) relatively stringent federal inspection specifications, along with; 3) HACCP (Hazardous Analysis Critical Control Points) requirements. At the same time, consumer demand (markets) for specialty, selected, and exotic meats appears to be growing. For example, the recent market successes in Europe evidenced by the North American Bison Cooperative based in New Rockford, North Dakota. Several alternative livestock producer groups have emerged which include lamb, ratite, elk, deer, goat, poultry, rabbit, specialty beef, and organic livestock. These groups have expressed a need for slaughter and processing facilities to meet market demand. The economic question which then becomes foremost to developing a viable business enterprise is: "What is the critical threshold volume (CTV) of product required to succeed in terms of economic profit?" Specialty livestock is relatively new and production volume small in comparison to established commodity livestock such as cattle or hogs. This fact led researchers to consider the preliminary feasibility of a multi-species processing facility as a means of addressing the expressed need.multi-species, specialty meats, specialty livestock, alternative livestock, economies of scale, HACCP (Hazardous Analysis Critical Control Points), slaughter plants, processing plants, Community/Rural/Urban Development, Agribusiness,
The transient response of global-mean precipitation to increasing carbon dioxide levels
The transient response of global-mean precipitation to an increase in atmospheric carbon dioxide levels of 1% yr(-1) is investigated in 13 fully coupled atmosphere-ocean general circulation models (AOGCMs) and compared to a period of stabilization. During the period of stabilization, when carbon dioxide levels are held constant at twice their unperturbed level and the climate left to warm, precipitation increases at a rate of similar to 2.4% per unit of global-mean surface-air-temperature change in the AOGCMs. However, when carbon dioxide levels are increasing, precipitation increases at a smaller rate of similar to 1.5% per unit of global-mean surface-air-temperature change. This difference can be understood by decomposing the precipitation response into an increase from the response to the global surface-temperature increase (and the climate feedbacks it induces), and a fast atmospheric response to the carbon dioxide radiative forcing that acts to decrease precipitation. According to the multi-model mean, stabilizing atmospheric levels of carbon dioxide would lead to a greater rate of precipitation change per unit of global surface-temperature change
Visualising the structure of document search results: A comparison of graph theoretic approaches
This is the post-print of the article - Copyright @ 2010 Sage PublicationsPrevious work has shown that distance-similarity visualisation or âspatialisationâ can provide a potentially useful context in which to browse the results of a query search, enabling the user to adopt a simple local foraging or âcluster growingâ strategy to navigate through the retrieved document set. However, faithfully mapping feature-space models to visual space can be problematic owing to their inherent high dimensionality and non-linearity. Conventional linear approaches to dimension reduction tend to fail at this kind of task, sacrificing local structural in order to preserve a globally optimal mapping. In this paper the clustering performance of a recently proposed algorithm called isometric feature mapping (Isomap), which deals with non-linearity by transforming dissimilarities into geodesic distances, is compared to that of non-metric multidimensional scaling (MDS). Various graph pruning methods, for geodesic distance estimation, are also compared. Results show that Isomap is significantly better at preserving local structural detail than MDS, suggesting it is better suited to cluster growing and other semantic navigation tasks. Moreover, it is shown that applying a minimum-cost graph pruning criterion can provide a parameter-free alternative to the traditional K-neighbour method, resulting in spatial clustering that is equivalent to or better than that achieved using an optimal-K criterion
The Lopsidedness of Present-Day Galaxies: Results from the Sloan Digital Sky Survey
Large-scale asymmetries in the stellar mass distribution in galaxies are
believed to trace non-equilibrium situations in the luminous and/or dark matter
component. These may arise in the aftermath of events like mergers, accretion,
and tidal interactions. These events are key in the evolution of galaxies. In
this paper we quantify the large-scale lopsidedness of light distributions in
25155 galaxies at z < 0.06 from the Sloan Digital Sky Survey Data Release 4
using the m = 1 azimuthal Fourier mode. We show that the lopsided distribution
of light is primarily due to a corresponding lopsidedness in the stellar mass
distribution. Observational effects, such as seeing, Poisson noise, and
inclination, introduce only small errors in lopsidedness for the majority of
this sample. We find that lopsidedness correlates strongly with other basic
galaxy structural parameters: galaxies with low concentration, stellar mass,
and stellar surface mass density tend to be lopsided, while galaxies with high
concentration, mass, and density are not. We find that the strongest and most
fundamental relationship between lopsidedness and the other structural
parameters is with the surface mass density. We also find, in agreement with
previous studies, that lopsidedness tends to increase with radius. Both these
results may be understood as a consequence of several factors. The outer
regions of galaxies and low-density galaxies are more susceptible to tidal
perturbations, and they also have longer dynamical times (so lopsidedness will
last longer). They are also more likely to be affected by any underlying
asymmetries in the dark matter halo.Comment: 42 pages, 13 figures, 3 tables, accepted to Ap
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