115 research outputs found
An aircraft Earth station for general aviation
While the focus has been international commercial air traffic, an opportunity exists to provide satellite communications to smaller aircraft. For these users equipment cost and weight critically impact the decision to install satellite communications equipment. Less apparent to the operator is the need for a system infrastructure that will be supported both regionally and internationally and that is compatible with the ground segment being installed for commercial aeronautical satellite communications. A system concept is described as well as a low cost terminal that are intended to satisfy the small aircraft market
Cosmic dust fertilization of glacial prebiotic chemistry on early Earth
Earth’s surface is deficient in available forms of many elements considered limiting for prebiotic chemistry. In contrast, many extraterrestrial rocky objects are rich in these same elements. Limiting prebiotic ingredients may, therefore, have been delivered by exogenous material; however, the mechanisms by which exogeneous material may be reliably and non-destructively supplied to a planetary surface remains unclear. Today, the flux of extraterrestrial matter to Earth is dominated by fine-grained cosmic dust. Although this material is rarely discussed in a prebiotic context due to its delivery over a large surface area, concentrated cosmic dust deposits are known to form on Earth today due to the action of sedimentary processes. Here we combine empirical constraints on dust sedimentation with dynamical simulations of dust formation and planetary accretion to show that localized sedimentary deposits of cosmic dust could have accumulated in arid environments on early Earth, in particular glacial settings that today produce cryoconite sediments. Our results challenge the widely held assumption that cosmic dust is incapable of fertilizing prebiotic chemistry. Cosmic dust deposits may have plausibly formed on early Earth and acted to fertilize prebiotic chemistry
The HOSTS survey: evidence for an extended dust disk and constraints on the presence of giant planets in the Habitable Zone of Leo
The young (50-400 Myr) A3V star Leo is a primary target to study the
formation history and evolution of extrasolar planetary systems as one of the
few stars with known hot (1600K), warm (600K), and
cold (120K) dust belt components. In this paper, we present deep
mid-infrared measurements of the warm dust brightness obtained with the Large
Binocular Telescope Interferometer (LBTI) as part of its exozodiacal dust
survey (HOSTS). The measured excess is 0.47\%0.050\% within the central
1.5 au, rising to 0.81\%0.026\% within 4.5 au, outside the habitable zone
of ~Leo. This dust level is 50 10 times greater than in the solar
system's zodiacal cloud. Poynting-Robertson drag on the cold dust detected by
Spitzer and Herschel under-predicts the dust present in the habitable zone of
~Leo, suggesting an additional delivery mechanism (e.g.,~comets) or an
additional belt at 5.5 au. A model of these dust components is provided
which implies the absence of planets more than a few Saturn masses between
5 au and the outer belt at 40 au. We also observationally constrain
giant planets with the LBTI imaging channel at 3.8~m wavelength. Assuming
an age of 50 Myr, any planet in the system between approximately 5 au to 50 au
must be less than a few Jupiter masses, consistent with our dust model. Taken
together, these observations showcase the deep contrasts and detection
capabilities attainable by the LBTI for both warm exozodiacal dust and giant
exoplanets in or near the habitable zone of nearby stars.Comment: 11 pages, 9 figures, accepted for publication in Astronomical Journa
Sound production and pectoral spine locking in a Neotropical catfish (Iheringichthys labrosus, Pimelodidae)
Extended Donor Iliac Arterial Patch for Vascular Reconstruction During Pancreas Transplantation
Iliac arteries in allograft pancreas recipients may be compromised by the patient\u27s underlying disease or previous surgical intervention. We describe a previously unreported arterial reconstruction using an extended segmental common/external iliac artery patch with anastomosis of the pancreatic Y-graft to the patch internal iliac artery, and review the options for arterial reconstruction reported by others. This technique may find application in both pancreas and kidney transplantation to salvage a damaged or diseased iliac artery
Extended Donor Iliac Arterial Patch for Vascular Reconstruction During Pancreas Transplantation
Iliac arteries in allograft pancreas recipients may be compromised by the patient\u27s underlying disease or previous surgical intervention. We describe a previously unreported arterial reconstruction using an extended segmental common/external iliac artery patch with anastomosis of the pancreatic Y-graft to the patch internal iliac artery, and review the options for arterial reconstruction reported by others. This technique may find application in both pancreas and kidney transplantation to salvage a damaged or diseased iliac artery
- …