4,029 research outputs found
Rotorcraft flight research with emphasis on rotor systems
Over fifty years of contributions by NASA and the Army through rotor systems flight research were examined with an emphasis on the last 25 years. During this time, the helicopter has gone from an abnormality that did a few useful things to a vehicle that is a necessity to life in this country and a major part of all military forces in the world. Major data acquisition programs like the H-34 and White Cobra have been undertaken that have increased the understanding of the aerodynamic behavior of the rotor system. Specialized programs like the Ogee tip on the UH-1 and the flight tests of the hingeless rotor helicopters, the XH-13 and XH-51N, contributed greatly to the understanding of these technologies. The extensive airfoil test program also undertaken on the White Cobra provided valuable data on advanced airfoil configurations
Cyclopentadiene evolution during pyrolysis-gas chromatography of PMR polyimides
The effect of formulated molecular weight (FMW), extent of cure, and cumulative aging on the amount of cyclopentadiene (CPD) evolved from Polymerization of Monomeric Reactants (PMR) polyimides were investigated by pyrolysis-gas chromotography (PY-GC). The PMR polyimides are additional crosslinked resins formed from an aromatic diamine, a diester of an aromatic tetracarboxylic acid and a monoester of 5-norbornene-2, 3-dicarboxylic acid. The PY-GC results were related to the degree of crosslinking and to the thermo-oxidative stability (weight loss) of PMR polyimides. Thus, PY-GC has shown to be a valid technique for the characterization of PMR polyimide resins and composites via correlation of the CPD evolved versus the thermal history of the PMR sample
The Impact of Income on Mortality: Evidence from the Social Security Notch
There is widespread and longstanding agreement that life expectancy and income are positively correlated. However, it has proven much more difficult to establish a causal relationship since income and health are jointly determined. We use a major change in the Social Security law as exogenous variation in income to examine the impact of income on mortality in an elderly population. The legislation created a notch' in Social Security benefits based upon date of birth; those born before January 1, 1917 generally receive higher benefits than those born afterwards. We compare mortality rates after age 65 for males born in the second half of 1916 and the first half of 1917. Data from restricted-use versions of the National Mortality Detail File combined with Census data allows us to count all deaths among elderly Americans between 1979 and 1993. We find that the higher income group has a statistically significantly higher mortality rate, contradicting the previous literature. We also find that the younger cohort responded to lower incomes by increasing post-retirement work effort. These results suggest that moderate employment has beneficial health effects for the elderly.
Sources of Health Insurance Coverage in Georgia 2007 - 2008
An opportunity to identify gaps in health insurance coverage among Georgians, barriers to coverage, and strategies to facilitate access to affordable coverage
Monitoring Frequency of IntraāFraction Patient Motion Using the ExacTrac System for LINACābased SRS Treatments
Purpose: The aim of this study was to investigate the intraāfractional patient motion using the ExacTrac system in LINACābased stereotactic radiosurgery (SRS).
Method: A retrospective analysis of 104 SRS patients with kilovoltage imageāguided setup (Brainlab ExacTrac) data was performed. Each patient was imaged preātreatment, and at two time points during treatment (1st and 2nd midātreatment), and bony anatomy of the skull was used to establish setup error at each time point. The datasets included the translational and rotational setup error, as well as the time period between image acquisitions. After each image acquisition, the patient was repositioned using the calculated shift to correct the setup error. Only translational errors were corrected due to the absence of a 6D treatment table. Setup time and directional shift values were analyzed to determine correlation between shift magnitudes as well as time between acquisitions.
Results: The average magnitude translation was 0.64 Ā± 0.59 mm, 0.79 Ā± 0.45 mm, and 0.65 Ā± 0.35 mm for the preātreatment, 1st midātreatment, and 2nd midātreatment imaging time points. The average time from preātreatment image acquisition to 1st midātreatment image acquisition was 7.98 Ā± 0.45 min, from 1st to 2nd midātreatment image was 4.87 Ā± 1.96 min. The greatest translation was 3.64 mm, occurring in the preātreatment image. No patient had a 1st or 2nd midātreatment image with greater than 2 mm magnitude shifts.
Conclusion: There was no correlation between patient motion over time, in direction or magnitude, and duration of treatment. The imaging frequency could be reduced to decrease imaging dose and treatment time without significant changes in patient position
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