15 research outputs found
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Ultra high temperature ceramics for hypersonic vehicle applications.
HfB{sub 2} and ZrB{sub 2} are of interest for thermal protection materials because of favorable thermal stability, mechanical properties, and oxidation resistance. We have made dense diboride ceramics with 2 to 20 % SiC by hot pressing at 2000 C and 5000 psi. High-resolution transmission electron microscopy (TEM) shows very thin grain boundary phases that suggest liquid phase sintering. Fracture toughness measurements give RT values of 4 to 6 MPam{sup 1/2}. Four-pt flexure strengths measured in air up to 1450 C were as high as 450-500 MPa. Thermal diffusivities were measured to 2000 C for ZrB{sub 2} and HfB{sub 2} ceramics with SiC contents from 2 to 20%. Thermal conductivities were calculated from thermal diffusivities and measured heat capacities. Thermal diffusivities were modeled using different two-phase composite models. These materials exhibit excellent high temperature properties and are attractive for further development for thermal protection systems
All-sky search for time-integrated neutrino emission from astrophysical sources with 7 years of IceCube data
Since the recent detection of an astrophysical flux of high energy neutrinos,
the question of its origin has not yet fully been answered. Much of what is
known about this flux comes from a small event sample of high neutrino purity,
good energy resolution, but large angular uncertainties. In searches for
point-like sources, on the other hand, the best performance is given by using
large statistics and good angular reconstructions. Track-like muon events
produced in neutrino interactions satisfy these requirements. We present here
the results of searches for point-like sources with neutrinos using data
acquired by the IceCube detector over seven years from 2008--2015. The
discovery potential of the analysis in the northern sky is now significantly
below , on average
lower than the sensitivity of the previously published analysis of four
years exposure. No significant clustering of neutrinos above background
expectation was observed, and implications for prominent neutrino source
candidates are discussed.Comment: 19 pages, 17 figures, 3 tables; ; submitted to The Astrophysical
Journa
The contribution of Fermi-2LAC blazars to the diffuse TeV-PeV neutrino flux
The recent discovery of a diffuse cosmic neutrino flux extending up to PeV
energies raises the question of which astrophysical sources generate this
signal. One class of extragalactic sources which may produce such high-energy
neutrinos are blazars. We present a likelihood analysis searching for
cumulative neutrino emission from blazars in the 2nd Fermi-LAT AGN catalogue
(2LAC) using an IceCube neutrino dataset 2009-12 which was optimised for the
detection of individual sources. In contrast to previous searches with IceCube,
the populations investigated contain up to hundreds of sources, the largest one
being the entire blazar sample in the 2LAC catalogue. No significant excess is
observed and upper limits for the cumulative flux from these populations are
obtained. These constrain the maximum contribution of the 2LAC blazars to the
observed astrophysical neutrino flux to be or less between around 10
TeV and 2 PeV, assuming equipartition of flavours at Earth and a single
power-law spectrum with a spectral index of . We can still exclude that
the 2LAC blazars (and sub-populations) emit more than of the observed
neutrinos up to a spectral index as hard as in the same energy range.
Our result takes into account that the neutrino source count distribution is
unknown, and it does not assume strict proportionality of the neutrino flux to
the measured 2LAC -ray signal for each source. Additionally, we
constrain recent models for neutrino emission by blazars.Comment: 18 pages, 22 figure
Neutrino interferometry for high-precision tests of Lorentz symmetry with IceCube
We acknowledge the support from the following agencies: USAâUS National Science FoundationâOffice of Polar Programs, US National Science FoundationâPhysics Division, Wisconsin Alumni Research Foundation, Center for High Throughput Computing (CHTC) at the University of WisconsinâMadison, Open Science Grid (OSG), Extreme Science and Engineering Discovery Environment (XSEDE), US Department of EnergyâNational Energy Research Scientific Computing Center, Particle astrophysics research computing centre at the University of Maryland, Institute for Cyber-Enabled Research at Michigan State University and Astroparticle physics computational facility at Marquette University; BelgiumâFunds for Scientific Research (FRS-FNRS and FWO), FWO Odysseus and Big Science programmes, and Belgian Federal Science Policy Office (Belspo); GermanyâBundesministerium fĂŒr Bildung und Forschung (BMBF), Deutsche Forschungsgemeinschaft (DFG), Helmholtz Alliance for Astroparticle Physics (HAP), Initiative and Networking Fund of the Helmholtz Association, Deutsches Elektronen Synchrotron (DESY), and High Performance Computing cluster of the RWTH Aachen; SwedenâSwedish Research Council, Swedish Polar Research Secretariat, Swedish National Infrastructure for Computing (SNIC), and Knut and Alice Wallenberg Foundation; AustraliaâAustralian Research Council; CanadaâNatural Sciences and Engineering Research Council of Canada, Calcul QuĂ©bec, Compute Ontario, Canada Foundation for Innovation, WestGrid and Compute Canada; DenmarkâVillum Fonden, Danish National Research Foundation (DNRF); New ZealandâMarsden Fund; JapanâJapan Society for Promotion of Science (JSPS) and Institute for Global Prominent Research (IGPR) of Chiba University; KoreaâNational Research Foundation of Korea (NRF); SwitzerlandâSwiss National Science Foundation (SNSF); UKâScience and Technology Facilities Council (STFC) and The Royal Society
CubeStack Wafer Adapter for CubeSats on Small Launch Vehicles
The CubeSat has progressively evolved from a platform for student projects to become a viable spacecraft configuration utilized by numerous government and commercial organizations. The Poly Picosatellite Orbital Deployer (P-POD), from Cal Poly, San Luis Obispo, is the common dispenser for the 3U (three-CubeSat) configuration, and CubeSats are typically launched from dispensers as tertiary payloads, often attached onto an unused surface of the launch vehicle for deployment after completion of the primary mission. The proliferation of CubeSats throughout the small satellite community gives rise to the requirement for more launch opportunities via the addition of multi-payload adapters, coupled with the development of more capable dispensers having 6U and larger form factors. LoadPath and CSA Engineering, under contract to the Air Force Research Laboratory Space Vehicles Directorate, are developing a multi-payload adapter for CubeSats in support of government and commercial missions. The CubeStack adapter is a 10-inch-tall âwaferâ similar to the NanoSat Launch Adapter System (NLAS) adapter developed at NASA Ames. The wafer mounts between the rocket upper stage and its primary payload and accommodates eight 3U dispensers, e.g. P-PODs, four 6U CubeSat dispensers, or other combinations of 3U and 6U dispensers. The modular CubeStack wafer features both 38.81 inch and 24.00 inch primary-spacecraft interfaces and is sized for several launch vehicles including Athena, Minotaur I, Taurus, Pegasus and Falcon 1. CubeStack was developed using requirements derived from launch vehicle specifications, customer needs, and lessons learned from the NLAS adapter fabrication and test. CubeStack features include a small part count, minimized weight, and ease of satellite dispenser integration. The CubeStack is expected to be available in 2012. This paper describes the CubeStack development program and design requirements, presents test and validation plans, and details the spacecraft and launch vehicle interfaces
The contribution of Fermi-2LAC blazars to the diffuse TeV-PeV neutrino flux
The recent discovery of a diffuse cosmic neutrino flux extending up to PeV energies raises the question of which astrophysical sources generate this signal. One class of extragalactic sources which may produce such high-energy neutrinos are blazars. We present a likelihood analysis searching for cumulative neutrino emission from blazars in the 2nd Fermi-LAT AGN catalogue (2LAC) using an IceCube neutrino dataset 2009-12 which was optimised for the detection of individual sources. In contrast to previous searches with IceCube, the populations investigated contain up to hundreds of sources, the largest one being the entire blazar sample in the 2LAC catalogue. No significant excess is observed and upper limits for the cumulative flux from these populations are obtained. These constrain the maximum contribution of the 2LAC blazars to the observed astrophysical neutrino flux to be or less between around 10 TeV and 2 PeV, assuming equipartition of flavours at Earth and a single power-law spectrum with a spectral index of . We can still exclude that the 2LAC blazars (and sub-populations) emit more than of the observed neutrinos up to a spectral index as hard as in the same energy range. Our result takes into account that the neutrino source count distribution is unknown, and it does not assume strict proportionality of the neutrino flux to the measured 2LAC -ray signal for each source. Additionally, we constrain recent models for neutrino emission by blazars
Mg-Al-LDH, Component of the Secondary Phases
The IceCube Neutrino Observatory has observed a diffuse flux of TeV-PeV astrophysical neutrinos at 5.7Ï significance from an all-flavor search. The direct detection of tau neutrinos in this flux has yet to occur. Tau neutrinos become distinguishable from other flavors in IceCube at energies above a few hundred TeV, when the cascade from the tau neutrino charged current interaction becomes resolvable from the cascade from the tau lepton decay. This paper presents results from the first dedicated search for tau neutrinos with energies between 214 TeV and 72 PeV in the full IceCube detector. The analysis searches for IceCube optical sensors that observe two separate pulses in a single event - one from the tau neutrino interaction and a second from the tau decay. No candidate events were observed in three years of IceCube data. For the first time, a differential upper limit on astrophysical tau neutrinos is derived around the PeV energy region, which is nearly 3 orders of magnitude lower in energy than previous limits from dedicated tau neutrino searches