4,741 research outputs found
A flexible telerobotic system for space operations
The objective and design of a proposed goal-oriented knowledge-based telerobotic system for space operations is described. This design effort encompasses the elements of the system executive and user interface and the distribution and general structure of the knowledge base, the displays, and the task sequencing. The objective of the design effort is to provide an expandable structure for a telerobotic system that provides cooperative interaction between the human operator and computer control. The initial phase of the implementation provides a rule-based, goal-oriented script generator to interface to the existing control modes of a telerobotic research system, in the Intelligent Systems Research Lab at NASA Research Center
On Observing Top Quark Production at the Tevatron
A technique for separating top quark production from Standard Model
background events is introduced. It is applicable to the channel in which one
top quark decays semi-leptonically and its anti-quark decays hadronically into
three jets, or vice versa. The method is shown to discriminate dramatically
between Monte Carlo generated events with and without simulated top quarks of
mass around 120 GeV and above. The simulations were performed with CDF detector
characteristics incorporated, showing that the method is applicable to existing
data.Comment: 8 pages, TUFTS-TH-92-G01 (Two minor TeX mistakes corrected
Pregnancy and cardiac disease
PKMedical disorders in pregnancy are one of the top five causes of maternal mortality in South Africa (SA), cardiac disease (CD) being the main contributor to this group. In developed countries, surgically corrected congenital heart disease (CHD) comprises the greater
proportion of maternal deaths from CD. In SA and other developing countries, acquired heart disease such as rheumatic heart disease and cardiomyopathies are the major causes, although CHD remains significantly represented. Both congenital and acquired cardiac lesions may present for the first time during pregnancy. CD may also occur for the first time during or after pregnancy, e.g. peripartum cardiomyopathy. The risk to both the mother and the fetus increases exponentially with the complexity of the underlying disease. Generally, the ability to tolerate a pregnancy is related to: (i) the haemodynamic significance of any lesion; (ii) the functional class – New York Heart Association classes III and IV have poorer outcomes; (iii) the presence of cyanosis; and (iv) the presence of pulmonary hypertension. While the ideal time to assess these factors is before conception, women frequently present when already pregnant. This review discusses risk assessment and management of CD in pregnant women and the role of a combined cardiology and
obstetric clinic
The reconfigurable Josephson circulator/directional amplifier
Circulators and directional amplifiers are crucial non-reciprocal signal
routing and processing components involved in microwave readout chains for a
variety of applications. They are particularly important in the field of
superconducting quantum information, where the devices also need to have
minimal photon losses to preserve the quantum coherence of signals.
Conventional commercial implementations of each device suffer from losses and
are built from very different physical principles, which has led to separate
strategies for the construction of their quantum-limited versions. However, as
recently proposed theoretically, by establishing simultaneous pairwise
conversion and/or gain processes between three modes of a Josephson-junction
based superconducting microwave circuit, it is possible to endow the circuit
with the functions of either a phase-preserving directional amplifier or a
circulator. Here, we experimentally demonstrate these two modes of operation of
the same circuit. Furthermore, in the directional amplifier mode, we show that
the noise performance is comparable to standard non-directional superconducting
amplifiers, while in the circulator mode, we show that the sense of circulation
is fully reversible. Our device is far simpler in both modes of operation than
previous proposals and implementations, requiring only three microwave pumps.
It offers the advantage of flexibility, as it can dynamically switch between
modes of operation as its pump conditions are changed. Moreover, by
demonstrating that a single three-wave process yields non-reciprocal devices
with reconfigurable functions, our work breaks the ground for the development
of future, more-complex directional circuits, and has excellent prospects for
on-chip integration
Luminous Infrared Galaxies With the Submillimeter Array. III. The Dense Kiloparsec Molecular Concentrations of Arp 299
We have used high resolution (~2.3") observations of the local (D = 46 Mpc)
luminous infrared galaxy Arp 299 to map out the physical properties of the
molecular gas which provides the fuel for its extreme star formation activity.
The 12CO J=3-2, 12CO J=2-1 and 13CO J=2-1 lines were observed with the
Submillimeter Array and the short spacings of the 12CO J=2-1 and J=3-2
observations have been recovered using James Clerk Maxwell Telescope single
dish observations. We use the radiative transfer code RADEX to estimate the
physical properties (density, column density and temperature) of the different
regions in this system. The RADEX solutions of the two galaxy nuclei, IC 694
and NGC 3690, are consistent with a wide range of gas components, from warm
moderately dense gas with T_{kin} > 30 K and n(H_{2}) ~ 0.3 - 3 x 10^{3}
cm^{-3} to cold dense gas with T_{kin} ~ 10-30 K and n(H_{2}) > 3 x 10^{3}
cm^{-3}. The overlap region is shown to have a better constrained solution with
T_{\rm{kin}}$ ~ 10-50 K and n(H_{2}) ~ 1-30 x 10^{3} cm^{-3}. We estimate the
gas masses and star formation rates of each region in order to derive molecular
gas depletion times. The depletion times of all regions (20-60 Myr) are found
to be about 2 orders of magnitude lower than those of normal spiral galaxies.
This rapid depletion time can probably be explained by a high fraction of dense
gas on kiloparsec scales in Arp 299. We estimate the CO-to-H_{2} factor,
\alpha_{co} to be 0.4 \pm 0.3 (3 x 10^{-4}/ x_{CO}) M_{sol} (K km s^{-1}
pc^{2})^{-1} for the overlap region. This value agrees well with values
determined previously for more advanced merger systems.Comment: 24 pages, 4 figures, ApJ accepte
Planar multilayer circuit quantum electrodynamics
Experimental quantum information processing with superconducting circuits is
rapidly advancing, driven by innovation in two classes of devices, one
involving planar micro-fabricated (2D) resonators, and the other involving
machined three-dimensional (3D) cavities. We demonstrate that circuit quantum
electrodynamics can be implemented in a multilayer superconducting structure
that combines 2D and 3D advantages. We employ standard micro-fabrication
techniques to pattern each layer, and rely on a vacuum gap between the layers
to store the electromagnetic energy. Planar qubits are lithographically defined
as an aperture in a conducting boundary of the resonators. We demonstrate the
aperture concept by implementing an integrated, two cavity-modes, one
transmon-qubit system
Space Station Freedom data management system growth and evolution report
The Information Sciences Division at the NASA Ames Research Center has completed a 6-month study of portions of the Space Station Freedom Data Management System (DMS). This study looked at the present capabilities and future growth potential of the DMS, and the results are documented in this report. Issues have been raised that were discussed with the appropriate Johnson Space Center (JSC) management and Work Package-2 contractor organizations. Areas requiring additional study have been identified and suggestions for long-term upgrades have been proposed. This activity has allowed the Ames personnel to develop a rapport with the JSC civil service and contractor teams that does permit an independent check and balance technique for the DMS
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