9,646 research outputs found
Development of an Emulation-simulation Thermal Control Model for Space Station Application
Analysis techniques to evaluate the effects of changing thermal loads and the methods utilized to control temperature distributions in the orbital space station are essential. Analysis techniques including a user-friendly computer program, were developed which should prove useful in thermal design and system analysis of the the space station. The program uses a data base and user input to compute costs, sizes, and power requirements for individual components and complete systems. User input consists of selecting mission parameters, selecting thermal acquisition configurations, transport systems and distances, and thermal rejection configurations
Modeling of transient heat pipe operation
The overall goal is to gain a better understanding of the transient behavior of heat pipes operating under both normal and adverse conditions. Normal operation refers to cases where the capillary structure remains fully wetted. Adverse operation occurs when drying, re-wetting, choking, noncontinuum flow, freezing, thawing etc., occur within the heat pipe. The work was redirected towards developing the capability to predict operational behavior of liquid metal heat pipes used for cooling aerodynamic structures. Of particular interest is the startup of such heat pipes from an initially frozen state such as might occur during re-entry of a space vehicle into the Earth's atmosphere or during flight of hypersonic aircraft
Modeling of Transient Heat Pipe Operation
The major goal of this project is to develop mathematical models of heat pipes which can be used to predict transient behavior under normal and adverse conditions. The models and solution techniques are to be formulated so that they can be incorporated into existing NASA structural design codes. The major parameters of interest are heat flux distribution, temperature distribution, working fluid pressure distribution, fluid and containment thermal and mechanical properties and geometry. Normal transient operation is taken to be operating conditions where the capillary structure remains fully wetted. Adverse transient operation occurs when drying, re-wetting, choking, non-continuum flow, thawing, freezing, etc., occur in the internal heat pipe working fluid
Modeling of transient heat pipe operations
An analysis of the steady, compressible, one-dimensional, laminar flow of sodium vapor is presented for a case of a flat plate-type heat pipe with asymmetrical boundary conditions. In addition, shear stress at the liquid-vapor interface, variations of vapor quality, and momentum and energy factors are considered. A similarity solution for a semiporous channel is used to provide the velocity profile at cross sections
Development of an emulation-simulation thermal control model for space station application
Many features were added to the Thermal Control System (TCS) program to increase its user-friendliness. Several apparent inconsistencies were identified. In some instances, these have led to modifications to the source programs. With the summary line-sizing information, the user can more readily compare the TCS program results with other available data. Two mathematical models were completed: one deals with sizing and analysis of bus heat exchangers and the other provides a means of analyzing a variety of heat pipe radiator designs. A generic heat pipe model was added to the TCS Analysis Program
Uranium distribution as a proxy for basin-scale fluid flow in distributive fluvial systems
This work was supported by the Fluvial Systems Research Group sponsors BG Group, BP, Chevron, ConocoPhilips, and Total. We thank reviews from Martin Stokes, an anonymous reviewer and Editor Stuart Jones.Peer reviewedPostprin
Development of an emulation-simulation thermal control model for space station application
The goal of this program is to develop an improved capability for comparing various techniques for thermal management in the space station. The work involves three major tasks: Develop a Technology Options Data Base (Task 1); Complete Development of a Space Station Thermal Control Technology Assessment Program (Task 2); and Develop and Evaluate Emulation Models (Task 3)
Thermodynamics of beta-amyloid fibril formation
Amyloid fibers are aggregates of proteins. They are built out of a peptide
called --amyloid (A) containing between 41 and 43 residues,
produced by the action of an enzyme which cleaves a much larger protein known
as the Amyloid Precursor Protein (APP). X-ray diffraction experiments have
shown that these fibrils are rich in --structures, whereas the shape of
the peptide displays an --helix structure within the APP in its
biologically active conformation. A realistic model of fibril formation is
developed based on the seventeen residues A12--28 amyloid peptide, which
has been shown to form fibrils structurally similar to those of the whole
A peptide. With the help of physical arguments and in keeping with
experimental findings, the A12--28 monomer is assumed to be in four
possible states (i.e., native helix conformation, --hairpin, globular
low--energy state and unfolded state). Making use of these monomeric states,
oligomers (dimers, tertramers and octamers) were constructed. With the help of
short, detailed Molecular Dynamics (MD) calculations of the three monomers and
of a variety of oligomers, energies for these structures were obtained. Making
use of these results within the framework of a simple yet realistic model to
describe the entropic terms associated with the variety of amyloid
conformations, a phase diagram can be calculated of the whole many--body
system, leading to a thermodynamical picture in overall agreement with the
experimental findings. In particular, the existence of micellar metastable
states seem to be a key issue to determine the thermodynamical properties of
the system
Agricultural Policy: High Commodity and Input Prices
Because of high commodity prices, beginning in 2006, subsidies to farmers in the United States, the European Union, and Canada have been reduced significantly. However, significant losses have been experienced by the red meat sector, along with escalating food prices. Because of rising input costs, the “farm boom†may not be as great as first thought. Ethanol made from corn and country-of-origin labeling cloud the U.S. policy scene. Higher commodity prices have caused some countries to lower tariff and non-tariff barriers, resulting in freer commodity trade worldwide. Policymakers should attempt to make these trade-barrier cuts permanent and should rethink current policy legislation to deal with the possibility of a collapse of world commodity markets. Agricultural commodity prices have dropped significantly since early 2008.agricultural policy, high commodity prices, input prices, Agricultural and Food Policy,
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