81,967 research outputs found
A very wide frequency band pulsed/IF radar system
A pulsed/IF radar for compact range radar cross section measurements has been developed which converts RF returns to a fixed IF, so that amplification and grating may be performed at one frequency. This permits the use of components which have optimal performance at this frequency which results in a corresponding improvement in performance. Sensitivity and dynamic range are calculated for this system and compared with our old radar, and the effect of pulse width on clutter level is also studied. Sensitivity and accuracy tests are included to verify the performance of the radar
Implications of an r-mode in XTE J1751-305: Mass, radius and spin evolution
Recently Strohmayer and Mahmoodifar presented evidence for a coherent
oscillation in the X-ray light curve of the accreting millisecond pulsar XTE
J1751-305, using data taken by RXTE during the 2002 outburst of this source.
They noted that a possible explanation includes the excitation of a non-radial
oscillation mode of the neutron star, either in the form of a g-mode or an
r-mode. The r-mode interpretation has connections with proposed spin-evolution
scenarios for systems such as XTE J1751-305. Here we examine in detail this
interesting possible interpretation. Using the ratio of the observed
oscillation frequency to the star's spin frequency, we derive an approximate
neutron star mass-radius relation which yields reasonable values for the mass
over the range of expected stellar radius (as constrained by observations of
radius-expansion burst sources). However, we argue that the large mode
amplitude suggested by the Strohmayer and Mahmoodifar analysis would inevitably
lead to a large spin-down of the star, inconsistent with its observed spin
evolution, regardless of whether the r-mode itself is in a stable or unstable
regime. We therefore conclude that the r-mode interpretation of the observed
oscillation is not consistent with our current understanding of neutron star
dynamics and must be considered unlikely. Finally we note that, subject to the
availability of a sufficiently accurate timing model, a direct
gravitational-wave search may be able to confirm or reject an r-mode
interpretation unambiguously, should such an event, with a similar inferred
mode amplitude, recur during the Advanced detector era.Comment: 8 pages, 3 figures; submitted to MNRA
Prospects for Extrasolar "Earths" in Habitable Zones
We have shown that Earth-mass planets could survive in variously restricted
regions of the habitable zones (HZs) of most of a sample of nine of the 102
main-sequence exoplanetary systems confirmed by 19 November 2003. In a
preliminary extrapolation of our results to the other systems, we estimate that
roughly a half of these systems could have had an Earth-mass planet confined to
the HZ for at least the most recent 1000 Ma. The HZ migrates outwards during
the main-sequence lifetime, and so this proportion varies with stellar age.
About two thirds of the systems could have such a planet confined to the HZ for
at least 1000 Ma at sometime during the main-sequence lifetime. Clearly, these
systems should be high on the target list for exploration for terrestrial
planets. We have reached this conclusion by launching putative Earth-mass
planets in various orbits and following their fate with mixed-variable
symplectic and hybrid integrators. Whether the Earth-mass planets could form in
the HZs of the exoplanetary systems is an urgent question that needs further
study.Comment: 7 pages, 2 figure
Hydrazine electrolysis for spacecraft propulsion. Analysis and test of a dual-mode gas and liquid system Final report
Dual-mode hydrazine electrolysis for spacecraft propulsion syste
Oral Health Advice for People With Serious Mental Illness
People with serious mental illness experience an erosion of functioning in day-to-day life over a protracted period of time. There is also evidence to suggest that people with serious mental illness have a greater risk of experiencing oral disease and have greater oral treatment needs than the general population. However, oral health has never been seen as a priority in people suffering with serious mental illness
Effect of exhaust nozzle configuration on aerodynamic and acoustic performance of an externally blown flap system with a quiet 6:1 bypass ratio engine
A highly suppressed TF-34 engine was used to investigate engine and flap interaction noise associated with an externally blown flap STOL powered lift system. Noise, efficiency, and velocity decay characteristics of mixed and separate flow exhaust systems including convergent, co-annular, and lobed designs were determined with the engine operating alone. Noise data were then obtained for several of the exhaust configurations with the engine blowing a wing-flap segment. Noise for both the engine alone and the engine with blown flaps showed substantial differences for the various exhaust configurations tested. The differences in observed noise are related primarily to nozzle effective exhaust velocity, flap impingement velocity, and noise spectral shape
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Portable Perimetry Using Eye-Tracking on a Tablet Computer—A Feasibility Assessment
Purpose: Visual field (VF) examination by standard automated perimetry (SAP) is an important method of clinical assessment. However, the complexity of the test, and its use of bulky, expensive equipment makes it impractical for case-finding. We propose and evaluate a new approach to paracentral VF assessment that combines an inexpensive eye-tracker with a portable tablet computer (“Eyecatcher”).
Methods: Twenty-four eyes from 12 glaucoma patients, and 12 eyes from six age-similar controls were examined. Participants were tested monocularly (once per eye), with both the novel Eyecatcher test and traditional SAP (HFA SITA standard 24-2). For Eyecatcher, the participant's task was to simply to look at a sequence of fixed-luminance dots, presented relative to the current point of fixation. Start and end fixations were used to determine locations where stimuli were seen/unseen, and to build a continuous map of sensitivity loss across a VF of approximately 20°.
Results: Eyecatcher was able to clearly separate patients from controls, and the results were consistent with those from traditional SAP. In particular, mean Eyecatcher scores were strongly correlated with mean deviation scores (r2 = 0.64, P < 0.001), and there was good concordance between corresponding VF locations (∼84%). Participants reported that Eyecatcher was more enjoyable, easier to perform, and less tiring than SAP (all P < 0.001).
Conclusions: Portable perimetry using an inexpensive eye-tracker and a tablet computer is feasible, although possible means of improvement are suggested.
Translational Relevance: Such a test could have significant utility as a case finding device
Development of a high temperature battery first quarterly technical report
High temperature battery development - zeolites, anode and cathode couples, and molten salt
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