30,900 research outputs found
Electro-optic modulator for infrared laser using gallium arsenide crystal
Gallium arsenide electro-optic modulator used for infrared lasers has a mica quarter-wave plate and two calcite polarizers to amplitude or phase modulate an infrared laser light source in the wavelength range from 1 to 3 microns. The large single crystal has uniformly high resistivities, is strain free, and comparable in quality to good optical glass
Development of a 10.6-micron laser modulator
Electro-optic coefficient of gallium arsenide measured at wavelengths from 2 to 12 microns by 10.6 micron laser modulato
Attitude determination of the spin-stabilized Project Scanner spacecraft
Attitude determination of spin-stabilized spacecraft using star mapping techniqu
High Resolution CO and H2 Molecular Line Imaging of a Cometary Globule in the Helix Nebula
We report high resolution imaging of a prominent cometary globule in the
Helix nebula in the CO J=1-0 (2.6 mm) and H2 v=1-0 S(1) (2.12 micron) lines.
The observations confirm that globules consist of dense condensations of
molecular gas embedded in the ionized nebula. The head of the globule is seen
as a peak in the CO emission with an extremely narrow line width (0.5 km/s) and
is outlined by a limb-brightened surface of H2 emission facing the central star
and lying within the photo-ionized halo. The emission from both molecular
species extends into the tail region. The presence of this extended molecular
emission provides new constraints on the structure of the tails, and on the
origin and evolution of the globules.Comment: 12 pages, 3 figures. To appear in The Astrophysical Journal Letter
Traveling-wave photodetector has sub-nanosecond response
Mercury-doped germanium photodetector uses waveguide which increases the absorption of microwave energy within the photodetectors. Waveguide and photodetector are placed in liquid helium Dewar and cooled. A carbon dioxide laser is light source and klystron provides microwave energy. Measured response times are approximately 1 nanosecond
High frequency sampling of the 1984 spring bloom within the mid-Atlantic Bight: Synoptic shipboard, aircraft, and in situ perspectives of the SEEP-I experiment
Moorings of current meters, thermistors, transmissometers, and fluorometers on the mid-Atlantic shelf, south of Long Island, suggest a cumulative seaward export of perhaps 0.35 g C/sq m/day between the 80 and 120 m isobaths during February-April 1984. Such a horizontal loss of algal carbon over the lower third of the water column would be 23 to 78% of the March-April 1984 primary production. This physical carbon loss is similar to daily grazing losses from zooplankton of 32-40% of the algal fixation of carbon. Metabolic demands of the benthos could be met by just the estimated fecal pellet flux, without direct consumption of algal carbon, while bacterioplankton needs could be served by excretory release of dissolved organic matter during photosynthesis. Sediment traps tethered 10 m off the bottom at the 120 m isobath and 50 m above the 500 m isobath caught as much as 0.16 to 0.26 g C /sq m/day during March-April 1984, in reasonable agreement with the flux estimated from the other moored instruments
High mass star formation in the infrared dark cloud G11.11-0.12
We report detection of moderate to high-mass star formation in an infrared
dark cloud (G11.11-0.12) where we discovered class II methanol and water maser
emissions at 6.7 GHz and 22.2 GHz, respectively. We also observed the object in
ammonia inversion transitions. Strong emission from the (3,3) line indicates a
hot (~60 K) compact component associated with the maser emission. The line
width of the hot component (4 km/s), as well as the methanol maser detection,
are indicative of high mass star formation. To further constrain the physical
parameters of the source, we derived the spectral energy distribution (SED) of
the dust continuum by analysing data from the 2MASS survey, HIRAS, MSX, the
Spitzer Space Telescope, and interferometric 3mm observations. The SED was
modelled in a radiative transfer program: a) the stellar luminosity equals 1200
L_sun corresponding to a ZAMS star of 8 M_sun; b) the bulk of the envelope has
a temperature of 19 K; c) the mass of the remnant protostellar cloud in an area
8x10^17 cm or 15 arcsec across amounts to 500M_sun, if assuming standard dust
of the diffuse medium, and to about 60 M_sun, should the grains be fluffy and
have ice mantles; d) the corresponding visual extinction towards the star is a
few hundred magnitudes. The near IR data can be explained by scattering from
tenuous material above a hypothetical disk. The class II methanol maser lines
are spread out in velocity over 11 km/s. To explain the kinematics of the
masing spots, we propose that they are located in a Kepler disk at a distance
of about 250 AU. The dust temperatures there are around 150 K, high enough to
evaporate methanol--containing ice mantles.Comment: 10 pages, 6 figures, Accepted for publication in Astronomy &
Astrophysics Journa
The Stealth Biplane: a Proposal in Response to a Low Reynolds Number Station Keeping Mission
The Stealth Biplane is conceived and constructed to serve as a remotely piloted vehicle designed to navigate a low-level figure-eight course at a target Reynolds number of 100,000. This flight vehicle will combine the latest in lightweight radio controlled hardware in conjunction with current low Reynolds number aerodynamic research to demonstrate feasible operation in a variety of applications. These potential low Reynolds number applications include high altitude atmospheric sampling, search and rescue, and even law enforcement. Design specs and fabrication technique are discussed
Allocation in Practice
How do we allocate scarcere sources? How do we fairly allocate costs? These
are two pressing challenges facing society today. I discuss two recent projects
at NICTA concerning resource and cost allocation. In the first, we have been
working with FoodBank Local, a social startup working in collaboration with
food bank charities around the world to optimise the logistics of collecting
and distributing donated food. Before we can distribute this food, we must
decide how to allocate it to different charities and food kitchens. This gives
rise to a fair division problem with several new dimensions, rarely considered
in the literature. In the second, we have been looking at cost allocation
within the distribution network of a large multinational company. This also has
several new dimensions rarely considered in the literature.Comment: To appear in Proc. of 37th edition of the German Conference on
Artificial Intelligence (KI 2014), Springer LNC
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