1,277 research outputs found
DSN 64-meter antenna L-band (1668-MHz) microwave system performance overview
In 1985, L-band (1668 MHz) receive-only feed systems were installed on the three Deep Space Network 64 meter antennas to provide tracking support for two non-NASA spacecraft. The specifications, design approach, and operational test results are presented. The L-band microwave system met all of its tracking goals and is currently being upgraded to include a C-band (5000 MHz) uplink
Improving High School Graduation Rates Among Males of Color
Young males of color constitute a disproportionately high percentage of our nation's non-high school graduate population. Data from the U.S. Census Bureau's American Community Survey show that in 2012, 7% of all U.S. 16- to 24-year-olds were not enrolled in school and had not earned a high school diploma or equivalency credential. That same year, for the same age group, this rate (called the status dropout rate) was 10.9% for Black males, 15.0% for Hispanic males, and 14.8% for American Indian/ Alaska Native males. For each of these ethnicities, the status dropout rate for females was significantly lower (U.S. Department of Education, National Center for Education Statistics, 2014, Table 219.80). The U.S. Census Bureau data also show a positive correlation between the incidence of young dropouts and levels of family poverty
Lineaments in coastal plain sediments as seen in ERTS imagery
Examination of satellite imagery over the Atlantic Coastal Plain near Washington, D. C. shows numerous lineaments, which cannot be accounted for by any known cultural or natural features. At least some of these lineaments represent the surface expression of faults, for one of them has been correlated with the outcrop of a fault that had been traced for several miles in southern Prince Georges County, Maryland. If a substantial number of these lineaments do indeed represent fault traces, the fact that they show on the surface suggests that the geologic history of the Coastal Plain is much more complex than has previously been recognized, and that faulting may have occurred in the Holocene, much later than has generally been recognized. The importance that such recent movements could have on future development of the Coastal Plain should be emphasized
Simulations of partially coherent focal plane imaging arrays: Fisher matrix approach to performance evaluation
Focal plane arrays of bolometers are increasingly employed in astronomy at
far--infrared to millimetre wavelengths. The focal plane fields and the
detectors are both partially coherent in these systems, but no account has
previously been taken of the effect of partial coherence on array performance.
In this paper, we use our recently developed coupled--mode theory of detection
together with Fisher information matrix techniques from signal processing to
characterize the behaviour of partially coherent imaging arrays. We investigate
the effects of the size and coherence length of both the source and the
detectors, and the packing density of the array, on the amount of information
that can be extracted from observations with such arrays.Comment: 14 pages, 7 figures, submitted to MNRAS 7th March 200
Modal decomposition of astronomical images with application to shapelets
The decomposition of an image into a linear combination of digitised basis
functions is an everyday task in astronomy. A general method is presented for
performing such a decomposition optimally into an arbitrary set of digitised
basis functions, which may be linearly dependent, non-orthogonal and
incomplete. It is shown that such circumstances may result even from the
digitisation of continuous basis functions that are orthogonal and complete. In
particular, digitised shapelet basis functions are investigated and are shown
to suffer from such difficulties. As a result the standard method of performing
shapelet analysis produces unnecessarily inaccurate decompositions. The optimal
method presented here is shown to yield more accurate decompositions in all
cases.Comment: 12 pages, 17 figures, submitted to MNRA
Recent advances in superconducting-mixer simulations
Over the last few years, considerable progress have been made in the development of techniques for fabricating high-quality superconducting circuits, and this success, together with major advances in the theoretical understanding of quantum detection and mixing at millimeter and submillimeter wavelengths, has made the development of CAD techniques for superconducting nonlinear circuits an important new enterprise. For example, arrays of quasioptical mixers are now being manufactured, where the antennas, matching networks, filters and superconducting tunnel junctions are all fabricated by depositing niobium and a variety of oxides on a single quartz substrate. There are no adjustable tuning elements on these integrated circuits, and therefore, one must be able to predict their electrical behavior precisely. This requirement, together with a general interest in the generic behavior of devices such as direct detectors and harmonic mixers, has lead us to develop a range of CAD tools for simulating the large-signal, small-signal, and noise behavior of superconducting tunnel junction circuits
Characteristic Functions Describing the Power Absorption Response of Periodic Structures to Partially Coherent Fields
Many new types of sensing or imaging surfaces are based on periodic thin
films. It is explained how the response of those surfaces to partially coherent
fields can be fully characterized by a set of functions in the wavenumber
spectrum domain. The theory is developed here for the case of 2D absorbers with
TE illumination and arbitrary material properties in the plane of the problem,
except for the resistivity which is assumed isotropic. Sum and difference
coordinates in both spatial and spectral domains are conveniently used to
represent the characteristic functions, which are specialized here to the case
of periodic structures. Those functions can be either computed or obtained
experimentally. Simulations rely on solvers based on periodic-boundary
conditions, while experiments correspond to Energy Absorption Interferometry
(EAI), already described in the literature. We derive rules for the convergence
of the representation versus the number of characteristic functions used, as
well as for the sampling to be considered in EAI experiments. Numerical
examples are given for the case of absorbing strips printed on a semi-infinite
substrate.Comment: Submitted to JOSA
Simulations of astronomical imaging phased arrays
We describe a theoretical procedure for analyzing astronomical phased arrays
with overlapping beams, and apply the procedure to simulate a simple example.
We demonstrate the effect of overlapping beams on the number of degrees of
freedom of the array, and on the ability of the array to recover a source. We
show that the best images are obtained using overlapping beams, contrary to
common practise, and show how the dynamic range of a phased array directly
affects the image quality.Comment: 16 pages, 26 figures, submitted to Journal of the Optical Society of
America
- …