97,872 research outputs found
Folded traveling wave maser structure Patent
Design of folded traveling wave maser structur
Analysis of a spacecraft instrument ball bearing assembly lubricated by a perfluoroalkylether
An analysis of a spacecraft instrument ball bearing assembly, subjected to a scanning life test, was performed to determine the possible case of rotational problems involving these units aboard several satellites. The analysis indicated an ineffective transfer of a fluorinated liquid lubricant from a phenolic retainer to the bearing balls. Part of the analysis led to a novel HPLC separation method employing a fluorinated mobile phase in conjunction with silica based size exclusion columns
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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
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
Pressure-viscosity measurements for several lubricants to 5.5 x 10 to the 8th power Newtons per square meter (8 x 10 to the 4th psi) and 149 C (300 F)
A capillary viscometer was used to measure viscosity as a function of pressure, temperature, and shear stress for a number of lubricants. The conditions under which the measurements were made are specified. The results obtained for each material are analyzed. It was determined that all pressure-viscosity coefficients decreased with increasing temperature. Data from other techniques such as optical elastohydrodynamics, oscillating crystal, and low shear capillary viscometry were compared with the results obtained
Energy-momentum balance in quantum dielectrics
We calculate the energy-momentum balance in quantum dielectrics such as
Bose-Einstein condensates. In agreement with the experiment [G. K. Campbell et
al. Phys. Rev. Lett. 94, 170403 (2005)] variations of the Minkowski momentum
are imprinted onto the phase, whereas the Abraham tensor drives the flow of the
dielectric. Our analysis indicates that the Abraham-Minkowski controversy has
its root in the Roentgen interaction of the electromagnetic field in dielectric
media
Evaluation of a Multizone Impedance Eduction Method
A computational study is used to evaluate the PyCHE impedance eduction method developed at the NASA Langley Research Center. This method combines an aeroacoustic duct propagation code based on numerical solution to the convected Helmholtz equation with a global optimizer that uses the Differential Evolution algorithm. The efficacy of this method is evaluated with acoustic pressure data simulated to represent that measured with one-zone, two-zone, and three-zone liners mounted in the NASA Langley Grazing Flow Impedance Tube. The PyCHE method has a normalized impedance error of approximately 0.2 for (uniform) one-zone liners with a length of at least 5, and produces quite reasonable results for liners as short as 2. Whereas the impedance of the liner has an effect on eduction accuracy, the amount of attenuation is shown to be the dominant parameter. Similar results are observed for two-zone liners, for which the impedance of each zone is unique. The two-zone results also indicate it is more difficult to accurately educe resistance than reactance, and a zone length of at least 6 (slightly longer than for uniform liners) is needed to limit the normalized error to 0.2. The PyCHE method is also demonstrated to successfully educe the impedances for each zone of a three-zone liner. These results are sufficiently encouraging to warrant the continued usage of the PyCHE impedance eduction method for single and multizone liners
Structural modeling for control design (articulated multibody component representation)
High gain, high frequency flexible responses in gimbaled multibody systems are discussed. Their origin and physical significance are described in terms of detailed mass and stiffness modeling at actuator/sensor interfaces. Guyan Reduction, Generalized Dynamic Reduction, inadequate mass modeling detail, as well as system mode truncation, are shown to suppress the high gain high frequency response and thereby lose system flexibility important for stability and performance predictions. Model validation by modal survey testing is shown to risk similar loss of accuracy. Difficulties caused by high frequency responses in component mode simulations, such as DISCOS, and also linearized system mode simulations, are described, and approaches for handling these difficulties are discussed
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