6,857 research outputs found
Preliminary estimates of radiation exposures for manned interplanetary missions from anomalously large solar flare events
Preliminary estimates of radiation exposures for manned interplanetary missions resulting from anomalously large solar flare events are presented. The calculations use integral particle fluences for the February 1956, November 1960, and August 1972 events as inputs into the Langley Research Center nucleon transport code BRYNTRN. This deterministic code transports primary and secondary nucleons (protons and neutrons) through any number of layers of target material of arbitrary thickness and composition. Contributions from target nucleus fragmentation and recoil are also included. Estimates of 5 cm depth doses and dose equivalents in tissue are presented behind various thicknesses of aluminum, water, and composite aluminum/water shields for each of the three solar flare events
Solar-flare shielding with Regolith at a lunar-base site
The Langley high energy nucleon transport computer code BRYNTRN is used to predict time-integrated radiation dose levels at the lunar surface due to high proton flux from solar flares. The study addresses the shielding requirements for candidate lunar habitat configurations necessary to protect crew members from these large and unpredictable radiation fluxes. Three solar proton events have been analyzed, and variations in radiation intensity in a shield medium due to the various primary particle energy distributions are predicted. Radiation dose predictions are made for various slab thicknesses of a lunar soil model. Results are also presented in the form of dose patterns within specific habitat configurations shielded with lunar material
Liquid cryogenic lubricant
Fluorinated polyethers are suitable lubricants for rolling-element bearings in cryogenic systems. Lubrication effectiveness is comparable to that of super-refined mineral oil lubricants operating at room temperature
Validation of a smartphone app to map social networks of proximity
Social network analysis is a prominent approach to investigate interpersonal
relationships. Most studies use self-report data to quantify the connections
between participants and construct social networks. In recent years smartphones
have been used as an alternative to map networks by assessing the proximity
between participants based on Bluetooth and GPS data. While most studies have
handed out specially programmed smartphones to study participants, we developed
an application for iOS and Android to collect Bluetooth data from participants
own smartphones. In this study, we compared the networks estimated with the
smartphone app to those obtained from sociometric badges and self-report data.
Participants (n=21) installed the app on their phone and wore a sociometric
badge during office hours. Proximity data was collected for 4 weeks. A
contingency table revealed a significant association between proximity data
(rho = 0.17, p<0.0001), but the marginal odds were higher for the app (8.6%)
than for the badges (1.3%), indicating that dyads were more often detected by
the app. We then compared the networks that were estimated using the proximity
and self-report data. All three networks were significantly correlated,
although the correlation with self-reported data was lower for the app (rho =
0.25) than for badges (rho = 0.67). The scanning rates of the app varied
considerably between devices and was lower on iOS than on Android. The
association between the app and the badges increased when the network was
estimated between participants whose app recorded more regularly. These
findings suggest that the accuracy of proximity networks can be further
improved by reducing missing data and restricting the interpersonal distance at
which interactions are detected.Comment: 20 pages, 5 figure
Using Bluetooth Low Energy in smartphones to map social networks
Social networks have an important role in an individual's health, with the
propagation of health-related features through a network, and correlations
between network structures and symptomatology. Using Bluetooth-enabled
smartphones to measure social connectivity is an alternative to traditional
paper-based data collection; however studies employing this technology have
been restricted to limited sets of homogenous handsets. We investigated the
feasibility of using the Bluetooth Low Energy (BLE) protocol, present on users'
own smartphones, to measure social connectivity. A custom application was
designed for Android and iOS handsets. The app was configured to simultaneously
broadcast via BLE and perform periodic discovery scans for other nearby
devices. The app was installed on two Android handsets and two iOS handsets,
and each combination of devices was tested in the foreground, background and
locked states. Connectivity was successfully measured in all test cases, except
between two iOS devices when both were in a locked state with their screens
off. As smartphones are in a locked state for the majority of a day, this
severely limits the ability to measure social connectivity on users' own
smartphones. It is not currently feasible to use Bluetooth Low Energy to map
social networks, due to the inability of iOS devices to detect another iOS
device when both are in a locked state. While the technology was successfully
implemented on Android devices, this represents a smaller market share of
partially or fully compatible devices.Comment: 6 pages, 1 tabl
Lubricant and additive effects on spur gear fatigue life
Spur gear endurance tests were conducted with six lubricants using a single lot of consumable-electrode vacuum melted (CVM) AISI 9310 spur gears. The sixth lubricant was divided into four batches each of which had a different additive content. Lubricants tested with a phosphorus-type load carrying additive showed a statistically significant improvement in life over lubricants without this type of additive. The presence of sulfur type antiwear additives in the lubricant did not appear to affect the surface fatigue life of the gears. No statistical difference in life was produced with those lubricants of different base stocks but with similar viscosity, pressure-viscosity coefficients and antiwear additives. Gears tested with a 0.1 wt % sulfur and 0.1 wt % phosphorus EP additives in the lubricant had reactive films that were 200 to 400 (0.8 to 1.6 microns) thick
Study of ball bearing torque under elastohydrodynamic lubrication
Spinning and rolling torques were measured in an angular-contact ball bearing with and without a cage under several lubrication regimes in a modified NASA spinning torque apparatus. Two lubricants were used, a di-2 ethylhexyl sebacate and a synthetic paraffinic oil, at shaft speeds of 1000, 2000, and 3000 rpm and bearing loads from 10 lbs to 90 lbs. An analytical model was developed from previous spinning friction models to include rolling with spinning under lubrication regimes from thin film to flooded conditions. The bearing torque values have a wide variation, under any condition of speed and load, depending on the amount of lubricant present in the bearing. The analytical model compared favorably with experimental results under several lubrication regimes
Radiation exposure for manned Mars surface missions
The Langley cosmic ray transport code and the Langley nucleon transport code (BRYNTRN) are used to quantify the transport and attenuation of galactic cosmic rays (GCR) and solar proton flares through the Martian atmosphere. Surface doses are estimated using both a low density and a high density carbon dioxide model of the atmosphere which, in the vertical direction, provides a total of 16 g/sq cm and 22 g/sq cm of protection, respectively. At the Mars surface during the solar minimum cycle, a blood-forming organ (BFO) dose equivalent of 10.5 to 12 rem/yr due to galactic cosmic ray transport and attenuation is calculated. Estimates of the BFO dose equivalents which would have been incurred from the three large solar flare events of August 1972, November 1960, and February 1956 are also calculated at the surface. Results indicate surface BFO dose equivalents of approximately 2 to 5, 5 to 7, and 8 to 10 rem per event, respectively. Doses are also estimated at altitudes up to 12 km above the Martian surface where the atmosphere will provide less total protection
Estimates of galactic cosmic ray shielding requirements during solar minimum
Estimates of radiation risk from galactic cosmic rays are presented for manned interplanetary missions. The calculations use the Naval Research Laboratory cosmic ray spectrum model as input into the Langley Research Center galactic cosmic ray transport code. This transport code, which transports both heavy ions and nucleons, can be used with any number of layers of target material, consisting of up to five different arbitrary constituents per layer. Calculated galactic cosmic ray fluxes, dose and dose equivalents behind various thicknesses of aluminum, water and liquid hydrogen shielding are presented for the solar minimum period. Estimates of risk to the skin and the blood-forming organs (BFO) are made using 0-cm and 5-cm depth dose/dose equivalent values, respectively, for water. These results indicate that at least 3.5 g/sq cm (3.5 cm) of water, or 6.5 g/sq cm (2.4 cm) of aluminum, or 1.0 g/sq cm (14 cm) of liquid hydrogen shielding is required to reduce the annual exposure below the currently recommended BFO limit of 0.5 Sv. Because of large uncertainties in fragmentation parameters and the input cosmic ray spectrum, these exposure estimates may be uncertain by as much as a factor of 2 or more. The effects of these potential exposure uncertainties or shield thickness requirements are analyzed
New generalized rheological model for lubrication of a ball spinning in a nonconforming groove
The elastohydrodynamic theory for predicting the spinning friction of a ball in a nonconforming groove was modified to incorporate a rheological model. The rheological model is based on the exponential pressure viscosity relation for low shear stresses, but at high shear rates and pressures, the relation is altered to one in which the shear stress is porportional to the normal stress. The model was fitted to experimental spinning torques for four different lubricants: a synthetic paraffinic lubricant, di-2-ethylhexyl sebacate, a super-refined naphthenic mineral oil, and a polyphenyl ether (5P4E). Good agreement between the model and experiment was found
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