62 research outputs found
The First Three Rungs of the Cosmological Distance Ladder
It is straightforward to determine the size of the Earth and the distance to
the Moon without making use of a telescope. The methods have been known since
the 3rd century BC. However, few amateur or professional astronomers have
worked this out from data they themselves have taken. Here we use a gnomon to
determine the latitude and longitude of South Bend, Indiana, and College
Station, Texas, and determine a value of the radius of the Earth of 6290 km,
only 1.4 percent smaller than the true value. We use the method of Aristarchus
and the size of the Earth's shadow during the lunar eclipse of 2011 June 15 to
derive an estimate of the distance to the Moon (62.3 R_Earth), some 3.3 percent
greater than the true mean value. We use measurements of the angular motion of
the Moon against the background stars over the course of two nights, using a
simple cross staff device, to estimate the Moon's distance at perigee and
apogee. Finally, we use simultaneous CCD observations of asteroid 1996 HW1
obtained with small telescopes in Socorro, New Mexico, and Ojai, California, to
derive a value of the Astronomical Unit of (1.59 +/- 0.19) X 10^8 km, about 6
percent too large. The data and methods presented here can easily become part
of a beginning astronomy lab class.Comment: 34 pages, 11 figures, accepted for publication in American Journal of
Physic
Study of radioisotope safety devices for electric propulsion system, Volume 1: Summary report
A new reference design was prepared for the 5 kW(e) thermionic power supply. The safety equipment in this design is a passive containment system which does not rely on the operation of any mechanisms such as a launch escape rocket or deployment of parachutes. It includes: (1) a blast shield to protect against the explosion of the launch vehicle; (2) a combination of refractory thermal insulation and heat storage material to protect against a sustained launch pad fire; (3) a reentry body with a spherical nose and a large conical flare at the aft end to stabilize the reentry attitude and lower the terminal velocity in air; (4) composite graphite thermal protection to sustain the reentry heat pulse; (5) crushable honeycomb behind the nose to limit the deceleration of the radioisotope source due to impact on land at terminal velocity; (6) a double-walled secondary containment vessel surrounding the isotopic capsules; (7) neutron shielding to reduce external dose rates; (8) an auxiliary cooling system employing redundant heat pipes to remove the radioactive decay heat from the heat source and reject it to the surroundings or to a forced convection loop
CCAT-prime: a novel telescope for submillimeter astronomy
The CCAT-prime telescope is a 6-meter aperture, crossed-Dragone telescope,
designed for millimeter and sub-millimeter wavelength observations. It will be
located at an altitude of 5600 meters, just below the summit of Cerro
Chajnantor in the high Atacama region of Chile. The telescope's unobscured
optics deliver a field of view of almost 8 degrees over a large, flat focal
plane, enabling it to accommodate current and future instrumentation fielding
>100k diffraction-limited beams for wavelengths less than a millimeter. The
mount is a novel design with the aluminum-tiled mirrors nested inside the
telescope structure. The elevation housing has an integrated shutter that can
enclose the mirrors, protecting them from inclement weather. The telescope is
designed to co-host multiple instruments over its nominal 15 year lifetime. It
will be operated remotely, requiring minimum maintenance and on-site activities
due to the harsh working conditions on the mountain. The design utilizes
nickel-iron alloy (Invar) and carbon-fiber-reinforced polymer (CFRP) materials
in the mirror support structure, achieving a relatively temperature-insensitive
mount. We discuss requirements, specifications, critical design elements, and
the expected performance of the CCAT-prime telescope. The telescope is being
built by CCAT Observatory, Inc., a corporation formed by an international
partnership of universities. More information about CCAT and the CCAT-prime
telescope can be found at www.ccatobservatory.org.Comment: Event: SPIE Astronomical Telescope + Instrumentation, 2018, Austin,
Texas, USA; Proceedings Volume 10700, Ground-based and Airborne Telescopes
VII; 107005X (2018
Current ecotoxicity testing needs among selected U.S. federal agencies
U.S. regulatory and research agencies use ecotoxicity test data to assess the hazards associated with substances that may be released into the environment, including but not limited to industrial chemicals, pharmaceuticals, pesticides, food additives, and color additives. These data are used to conduct hazard assessments and evaluate potential risks to aquatic life (e.g., invertebrates, fish), birds, wildlife species, or the environment. To identify opportunities for regulatory uses of non-animal replacements for ecotoxicity tests, the needs and uses for data from tests utilizing animals must first be clarified. Accordingly, the objective of this review was to identify the ecotoxicity test data relied upon by U.S. federal agencies. The standards, test guidelines, guidance documents, and/or endpoints that are used to address each of the agencies’ regulatory and research needs regarding ecotoxicity testing are described in the context of their application to decision-making. Testing and information use, needs, and/or requirements relevant to the regulatory or programmatic mandates of the agencies taking part in the Interagency Coordinating Committee on the Validation of Alternative Methods Ecotoxicology Workgroup are captured. This information will be useful for coordinating efforts to develop and implement alternative test methods to reduce, refine, or replace animal use in chemical safety evaluations
Price-Based Unit Commitment Electricity Storage Arbitrage with Piecewise Linear Price-Effects
Effects of predator exposure on baseline and stress‐induced glucocorticoid hormone concentrations in pumpkinseed Lepomis gibbosus
We compared baseline and maximal cortisol concentrations between predator exposure and prey blood samples in pumpkinseed Lepomis gibbosus, captured using a standardised fishing event underneath osprey Pandion haliaetus nests and away from osprey nests. We did not detect differences in cortisol or glucose between sites. These findings suggest that predictable sources of predation risk may not confer stress-related costs in teleosts
Review of mathematical programming applications in water resource management under uncertainty
Improvement of ERA by speech-specific stimulation and correction of amplitude and latency behaviour
Sind internationale Studierende der Humanmedizin wirklich schlechter als ihre deutschen KommilitonInnen? Projekt zur Betreuung von internationalen Studierenden an der Medizinischen Fakultät Freiburg
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