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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 379 records · Page 21
All sourcesNASA NTRSDOE OSTI
DOE OSTI2010

Distribution of annihilation luminosities in dark matter substructure

We calculate the probability distribution function (PDF) of the expected annihilation luminosities of dark matter subhalos as a function of subhalo mass and distance from the Galactic center using a semianalytical model of halo evolution. We find that the PDF of luminosities is relatively broad, exhibiting a spread of as much as an order of magnitude at fixed subhalo mass and halo-centric distance. The luminosity PDF allows for simple construction of mock samples of {gamma}-ray luminous subhalos and assessment of the variance in the predicted {gamma}-ray signals from dark matter annihilation. Other applications include quantifying the variance among the expected luminosities of dwarf spheroidal galaxies, assessing the level at which dark matter annihilation can be a contaminant in the expected {gamma}-ray signal from other astrophysical sources, as well as estimating the level at which nearby subhalos can contribute to the antimatter flux.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2011

QCD Resummation for Jet Substructures

We provide a novel development in jet physics by predicting the energy profiles of light-quark and gluon jets in the framework of perturbative QCD. Resumming large logarithmic contributions to all orders in the coupling constant, our predictions are shown to agree well with Tevatron CDF and Large Hadron Collider CMS data. We also extend our resummation formalism to the invariant mass distributions of light-quark and gluon jets produced in hadron collisions. The predicted peak positions and heights in jet mass distributions are consistent with CDF data within uncertainties induced by parton distribution functions.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2018

Using a Dynamic Substructuring Approach to Model the Effects of Acoustic Damping in Coupled Acoustic-Structure Systems

Acoustic-structure coupling can substantially alter the frequency response of air-filled structures. Coupling effects typically manifest as two resonance peaks at frequencies above and below the resonant frequency of the uncoupled structural system. In this study, a dynamic substrucuring approach is applied to a simple acoustic-structure system to expose how the system response depends on the damping in the acoustic subsystem. Parametric studies show that as acoustic damping is increased, the frequencies and amplitudes of the coupled resonances in the structural response undergo a sequence of changes. For low levels of acoustic damping, the two coupled resonances have amplitudes approximating the corresponding in vacuo resonance. As acoustic damping is increased, resonant amplitudes decrease dramatically while the frequency separation between the resonances tends to increase slightly. When acoustic damping is increased even further, the separation of the resonant frequencies decreases below their initial separation. Finally, at some critical value of acoustic damping, one of the resonances abruptly disappears, leaving just a single resonance. Counterintuitively, increasing acoustic damping beyond this point tends to increase the amplitude of the remaining resonance peak. Finally, these results have implications for analysts and experimentalists attempting to understand, mitigate, or otherwise compensate for the confounding effects of acoustic-structure coupling in fluid-filled test structures.

42 ENGINEERING↗
DOE OSTI2018

And So Ad Infinitum: The Search for Quark and Lepton Substructure

The Victorian era mathematician, Augustus de Morgan wrote, “Great fleas have little fleas upon their backs to bite ‘em, And little fleas have lesser fleas, and so ad infinitum.” This parody of Jonathan Swift’s 1733 poem On Poetry: A Rhapsody arose from a literary history, but it is rather easy to see a metaphor for nature in these words. The saga of the search for the ultimate constituents of matter has long been one of finding a seemingly fundamental structure that, in turn, was found to be made of even smaller building blocks. Matter is made of molecules. Molecules are in turn made of atoms, which are themselves made of electrons and atomic nuclei. Furthermore, the nucleus consists of protons and neutrons, and these nucleons are composed of quarks.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2019

Substructure of Intermetallic Thin-Film Cu{sub 3}Sn

The crystalline structure of intermetallic Cu{sub 3}Sn synthesized by successively condensing thin layers of copper and tin on a substrate at 150°C has been studied. Cu{sub 3}Sn compound exists in a very narrow homogeneity range and has a long-period close-packed ordered D0{sub 19} superstructure. It has been found that the crystal lattice exhibits many slip traces associated with dislocation motion. The dislocation motion is due to the stressed state of the crystal, which can be characterized as uniform extension. Electron micrographs show that slip traces in the Cu{sub 3}Sn crystal are parallel to the ( 1-bar 1-bar 21) and (11 2-bar 1) planes belonging to pyramidal slip system II, which is a main slip system along with pyramidal and basal ones. Slip traces result from the motion of partial dislocations, as indicated by the amount of slip, which is equal to half the interplanar distance. Since the crystal is ordered, slip is accomplished by a pair of superpartial dislocations and a slip trace may be a superstructural or complex stacking fault.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗