1,910 research outputs found
Analysis of Compression Pad Cavities for the Orion Heatshield
Current results of a program for analysis of the compression pad cavities on the Orion heatshield are reviewed. The program was supported by experimental tests, engineering modeling, and applied computations with an emphasis on the latter presented in this paper. The computational tools and approach are described along with calculated results for wind tunnel and flight conditions. Correlations of the computed results are shown which can produce a credible prediction of heating augmentation due to cavity disturbances. The models developed for use in preliminary design of the Orion heatshield are presented
Persistent, Widespread Pulsating Aurora: A Case Study
Observations of a pulsating aurora event occurring on February 11, 2008, using the THEMIS all-sky imager array, indicate a spatially and temporally continuous event with a duration of greater than 15 hours and covering a region with a maximum size of greater than 9 hours MLT. The optical pulsations are at times locally interrupted or drowned out by auroral substorm activity, but are observed in the same location once the discrete aurora recedes. The pulsations following the auroral breakup appear to be brighter and have a larger patch size than pre-substorm. This suggests that, while the onset of pulsating aurora is not necessarily dependent upon a substorm precursor, the pulsations are affected and possibly enhanced by the substorm process. The long duration of such pulsating aurora events, enduring for several hours without interruption, is far longer than the expected recovery phase of a substorm, suggesting that pulsating aurora is not strictly a recovery phase phenomenon
Ultrafast Spin Dynamics in Nickel
The spin dynamics in Ni is studied by an exact diagonalization method on the
ultrafast time scale. It is shown that the femtosecond relaxation of the
magneto-optical response results from exchange interaction and spin-orbit
coupling. Each of the two mechanisms affects the relaxation process
differently. We find that the intrinsic spin dynamics occurs during about 10 fs
while extrinsic effects such as laser-pulse duration and spectral width can
slow down the observed dynamics considerably. Thus, our theory indicates that
there is still room to accelerate the spin dynamics in experiments.Comment: 4 pages, Latex, 4 postscript figure
Tunneling Anisotropic Magnetoresistance in Co/AlOx/Au Tunnel Junctions
We observe spin-valve-like effects in nano-scaled thermally evaporated
Co/AlOx/Au tunnel junctions. The tunneling magnetoresistance is anisotropic and
depends on the relative orientation of the magnetization direction of the Co
electrode with respect to the current direction. We attribute this effect to a
two-step magnetization reversal and an anisotropic density of states resulting
from spin-orbit interaction. The results of this study points to future
applications of novel spintronics devices involving only one ferromagnetic
layer.Comment: 11 pages, 5 figures. Accpted for publishing on Nano Letters, 200
Signatures of stirring and mixing near the Gulf Stream front
In October, 1986 the surface waters adjacent to the Gulf Stream front were surveyed with an undulating profiler to describe the finescale structure of the mixed layer. The profiler was a Seasoar equipped with a CTD and fluorometer. The survey first defined the structure of a cyclonic eddy which resembled frontal eddies of the South Atlantic Bight in sea surface temperature imagery. The Seasoar transects revealed, however, that the cyclonic eddy lacked a cold dome typically seen in frontal eddies. Farther downstream the Seasoar defined the structure of streamers of Gulf Stream and Shelf water wrapped about the southern edge of a warm-core ring. The streamers had lateral and along-axis dimensions on the order of ≈ 10 km and 100 km, respectively, and were bordered by narrow intrusive features. The temporal history of the streamers was described from SST imagery, and the surface flow derived from ship\u27s drift vectors. CTD casts taken while following an isopycnal float provided a means to examine the structure of the intrusive features. Interleaving was evident at the boundaries of the streamers and intrusive features where high conductivity Cox numbers were concentrated, suggesting elevated microstructure activity. The Turner angle distribution, indicating either saltfingering or diffusive convection, did not correlate well with the Cox number distribution. This is interpreted as evidence that lateral, rather than diapycnal, mixing was the process mediating the exchange of properties at the boundaries of contrasting water types. In contrast to physical properties, the distribution of fluorescence showed relatively less structure in the surface layer between the ring and Gulf Stream front. In the surface layers of the two streamers the pigment and bacterial biomass, and the diatom species composition, were typical of Slope water communities. We hypothesize that small-scale mixing processes concentrated at the boundaries of the streamers were the mechanism by which Slope water plankton were seeded into streamers of different hydrographic origins. Presumably, high netplankton growth rates allowed the Slope water species to dominate the communities in the streamers
Psychosocial and cognitive multimorbidity and health-related quality of life and symptom burden in older adults with atrial fibrillation: The systematic assessment of geriatric elements in atrial fibrillation (SAGE-AF) cohort study
BACKGROUND: Depression, anxiety, and cognitive impairments occur in up to 40 % of adults with AF and are associated with poorer health-related quality of life (HRQoL) and higher symptom burden. However, it is unknown how often these impairments co-occur, or multimorbidity, and how multimorbidity effects HRQoL and symptom burden.
METHODS: Patients with AF age \u3e /=65 years with a CHA2DS2VASC risk score \u3e /= 2 and eligible for oral anticoagulation therapy were recruited from five clinics in a prospective cohort study. Participants completed validated measures of depression (PHQ9) and anxiety (GAD7), cognitive impairment (MoCA), and HRQOL and AF symptom burden (AFEQT). Multinomial logistic regression was used.
RESULTS: Participants (N = 1244, 49 % female) were on average 76 +/- 7 years; 86 % were non-Hispanic white. Approximately 35 % of participants had 1 impairment, 17 % had 2 impairments and 8% had 3 impairments; 39 % had none of the 3 impairments examined. Compared to participants with no impairments, patients with 1, 2 and 3 impairments had higher odds of poor HRQoL (adjusted OR [AOR] = 1.77, 95 % CI 1.21, 2.60; AOR = 6.64, 95 % CI 4.43, 9.96; and AOR = 7.50, 95 % CI 4.40, 12.77, respectively) and those with 2 and 3 impairments had higher odds of high symptom burden (AOR = 3.69 95 % CI 2.22, 6.13; and AOR = 5.41 95 % CI 2.85, 10.26).
CONCLUSIONS: Psychosocial/cognitive multimorbidity is common among older adults with AF and is associated with poor HRQoL and high symptom burden. Clinicians might consider incorporating psychosocial and cognitive screens into routine care as this may identify a high-risk population
Two-neutron transfer reaction mechanisms in C(He,He)C using a realistic three-body He model
The reaction mechanisms of the two-neutron transfer reaction
C(He,He) have been studied at 30 MeV at the TRIUMF ISAC-II
facility using the SHARC charged-particle detector array. Optical potential
parameters have been extracted from the analysis of the elastic scattering
angular distribution. The new potential has been applied to the study of the
transfer angular distribution to the 2 8.32 MeV state in C, using
a realistic 3-body He model and advanced shell model calculations for the
carbon structure, allowing to calculate the relative contributions of the
simultaneous and sequential two-neutron transfer. The reaction model provides a
good description of the 30 MeV data set and shows that the simultaneous process
is the dominant transfer mechanism. Sensitivity tests of optical potential
parameters show that the final results can be considerably affected by the
choice of optical potentials. A reanalysis of data measured previously at 18
MeV however, is not as well described by the same reaction model, suggesting
that one needs to include higher order effects in the reaction mechanism.Comment: 9 pages, 9 figure
Spring plankton dynamics in the Eastern Bering Sea, 1971-2050 : mechanisms of interannual variability diagnosed with a numerical model
A new planktonic ecosystem model was constructed for the Eastern Bering Sea based on observations from the 2007-2010 BEST/BSIERP (Bering Ecosystem Study/Bering Sea Integrated Ecosystem Research Program) field program. When run with forcing from a data-assimilative ice-ocean hindcast of 1971-2012, the model performs well against observations of spring bloom time evolution (phytoplankton and microzooplankton biomass, growth and grazing rates, and ratios among new, regenerated, and export production). On the southern middle shelf (57°N, station M2), the model replicates the generally inverse relationship between ice-retreat timing and spring bloom timing known from observations, and the simpler direct relationship between the two that has been observed on the northern middle shelf (62°N, station M8). The relationship between simulated mean primary production and mean temperature in spring (15 February to 15 July) is generally positive, although this was found to be an indirect relationship which does not continue to apply across a future projection of temperature and ice cover in the 2040s. At M2, the leading direct controls on total spring primary production are found to be advective and turbulent nutrient supply, suggesting that mesoscale, wind-driven processes - A dvective transport and storminess - may be crucial to long-term trends in spring primary production in the southeastern Bering Sea, with temperature and ice cover playing only indirect roles. Sensitivity experiments suggest that direct dependence of planktonic growth and metabolic rates on temperature is less significant overall than the other drivers correlated with temperature described above
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