Fabrication of cooled, graphite-lined structures

Improved method of fabricating cooled graphite-lined thrust chamber has been developed. Layer of nickel is electrodeposited onto outer surface of machined and contoured graphite liner. Coolant passages are machined into nickel layer, filled with wax, outer shell electroformed over this, and wax removed. Tests in flox/methane rocket engine were completely successful

Fabrication of large tungsten structures by chemical vapor deposition

Process is accomplished by reducing tungsten hexafluoride with hydrogen. Metallic tungsten of essentially 100 percent purity and density is produced and built up as dense deposit on heated mandrel assembly. Process variations are building up, sealing or bonding refractory metals at temperatures below transition temperatures of base metal substrates

A graphite-lined regeneratively cooled thrust chamber

Design concepts, based on use of graphite as a thermal barrier for regeneratively cooled FLOX-methane thrust chambers, have been screened and concepts selected for detailed thermodynamic, stress, and fabrication analyses. A single design employing AGCarb-101, a fibrous graphite composite material, for a thermal barrier liner and an electroformed nickel structure with integral coolant passages was selected for fabrication and testing. The fabrication processes and the test results are described and illustrated

Investigation of advanced regenerative thrust chamber designs Final report

Fabrication and thermal performance of regeneratively cooled fluorine hydrogen thrust chambe

Development of a thermal barrier coating for use on a water-cooled nozzle of a solid propellant rocket motor Final report

Thermal barrier coating for use on water cooled nozzle of solid propellant rocket engin

The effect of unilateral blood flow restriction on temporal and spatial gait parameters

© 2019 The Authors Blood flow restriction walking (BFR-W) is becoming more frequently used in aerobic and strength training and it has been proposed that BFR-W can be used in clinical populations. BFR-W may change gait stability yet few studies have assessed gait changes during or following BFR-W. The aim of this study was to assess if spatial-temporal gait parameters change during and following BFR-W. Twenty-four participants completed two walking sessions (>48-hours apart); 1) Unilateral BFR-W applied at the dominant thigh, 2) walking without BFR. In each session participants performed a 5-min warmup, 15-min walking intervention and 10-min active recovery. The warmup and active recovery were performed without BFR on both days. Measurements were attained at baseline, during the intervention and post-intervention using the GAITRite®. Linear mixed models were applied to each measured variable. Fixed factors were timepoint (warmup, intervention, and active recovery), condition (BFR-W and control walking) and condition × timepoint. Random factors were subject and subject × condition. Participants took shorter (3.2-cm (mean difference), CI95%: 0.8–5.6-cm) and wider strides (1.4-cm, CI95%: 0.9–1.9-cm) during BFR-W. For single leg measures, participants took shorter steps (2.8-cm, CI95%: 1.7–4.0-cm) with a faster single support time (7.5-ms, CI95%: 2.9–12.0-ms) on the non-dominant (unoccluded) leg during BFR-W compared to the non-dominant leg during control walking. There were no differences in step length and single support time between the dominant (occluded) leg during BFR-W compared to the dominant leg during control walking. There were no significant changes in velocity, cadence or double support time between BFR-W and control walking (P > 0.05). BFR-W caused small transient changes to several gait parameters. These changes should be considered when using BFR-W in clinical populations

Hole doping dependences of the magnetic penetration depth and vortex core size in YBa2Cu3Oy: Evidence for stripe correlations near 1/8 hole doping

We report on muon spin rotation measurements of the internal magnetic field distribution n(B) in the vortex solid phase of YBa2Cu3Oy (YBCO) single crystals, from which we have simultaneously determined the hole doping dependences of the in-plane Ginzburg-Landau (GL) length scales in the underdoped regime. We find that Tc has a sublinear dependence on 1/lambda_{ab}^2, where lambda_{ab} is the in-plane magnetic penetration depth in the extrapolated limits T -> 0 and H -> 0. The power coefficient of the sublinear dependence is close to that determined in severely underdoped YBCO thin films, indicating that the same relationship between Tc and the superfluid density is maintained throughout the underdoped regime. The in-plane GL coherence length (vortex core size) is found to increase with decreasing hole doping concentration, and exhibit a field dependence that is explained by proximity-induced superconductivity on the CuO chains. Both the magnetic penetration depth and the vortex core size are enhanced near 1/8 hole doping, supporting the belief by some that stripe correlations are a universal property of high-Tc cuprates.Comment: 12 pages, 13 figure

Mesolensing Explorations of Nearby Masses: From Planets to Black Holes

Nearby masses can have a high probability of lensing stars in a distant background field. High-probability lensing, or mesolensing, can therefore be used to dramatically increase our knowledge of dark and dim objects in the solar neighborhood, where it can discover and study members of the local dark population (free-floating planets, low-mass dwarfs, white dwarfs, neutron stars, and stellar mass black holes). We can measure the mass and transverse velocity of those objects discovered (or already known), and determine whether or not they are in binaries with dim companions. We explore these and other applications of mesolensing, including the study of forms of matter that have been hypothesized but not discovered, such as intermediate-mass black holes, dark matter objects free-streaming through the Galactic disk, and planets in the outermost regions of the solar system. In each case we discuss the feasibility of deriving results based on present-day monitoring systems, and also consider the vistas that will open with the advent of all-sky monitoring in the era of the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS), and the Large Synoptic Survey Telescope (LSST).Comment: To appear in the Astrophysical Journal; 10 pages, no figure

Between session reliability of heel-to-toe progression measurements in the stance phase of gait

© 2018 Ade et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. The objective of the current study was to determine the test-retest reliability of heel-to-toe progression measures in the stance phase of gait using intraclass correlation coefficient (ICC) analysis. It has been proposed that heel-to-toe progression could be used as a functional measure of ankle muscle contracture/weakness in clinical populations. This was the first study to investigate the test-retest reliability of this measure. Eighteen healthy subjects walked over the GAITRite® mat three times at a comfortable speed on two sessions (≥ 48 hours apart). The reliability of the heel-to-toe progression measures; heel-contact time, mid-stance time and propulsive time were assessed. Also assessed were basic temporal-spatial parameters; velocity, cadence, stride length, step length, stride width, single and double leg support time. Reliability was determined using the ICC(3,1) model and, fixed and proportional biases, and measures of variability were assessed. Basic gait temporal-spatial parameters were not different between sessions (p > 0.05) and had excellent reliability (ICC(3,1) range: 0.871–0.953) indicating that subjects walked similarly between sessions. Measurement of heel-to-toe progression variables were not different between sessions (p > 0.05) and had excellent reliability (ICC(3,1) range: 0.845–0.926). However, these were less precise and more variable than the measurement of standard temporal-spatial gait variables. As the current study was performed on healthy populations, it represents the ‘best case’ scenario. The increased variability and reduced precision of heel-to-toe progression measurements should be considered if being used in clinical populations

Constraints on Cosmological Models from Hubble Space Telescope Observations of High-z Supernovae

We have coordinated Hubble Space Telescope photometry with ground-based discovery for three supernovae: two SN Ia near z~0.5 (SN 1997ce, SN 1997cj) and a third event at z=0.97 (SN 1997ck). The superb spatial resolution of HST separates each supernova from its host galaxy and leads to good precision in the light curves. The HST data combined with ground-based photometry provide good temporal coverage. We use these light curves and relations between luminosity, light curve shape, and color calibrated from low-z samples to derive relative luminosity distances which are accurate to 10% at z~0.5 and 20% at z=1. The redshift-distance relation is used to place constraints on the global mean matter density, Omega_matter, and the normalized cosmological constant, Omega_Lambda. When the HST sample is combined with the distance to SN 1995K (z=0.48), analyzed by the same precepts, it suggests that matter alone is insufficient to produce a flat Universe. Specifically, for Omega_matter+Omega_Lambda=1, Omega_matter is less than 1 with >95% confidence, and our best estimate of Omega_matter is -0.1 +/- 0.5 if Omega_Lambda=0. Although the present result is based on a very small sample whose systematics remain to be explored, it demonstrates the power of HST measurements for high redshift supernovae.Comment: Submitted to ApJ Letters, 3 figures, 1 plate, additional tabl