26,817 research outputs found
Evaluation of the metabolic cost of locomotion in an Apollo space suit
Evaluation of metabolic cost of locomotion in Apollo space sui
Observations on lunar gravity simulation
Physiological factors in astronaut performance in simulated lunar gravit
Tweed in Martensites: A Potential New Spin Glass
We've been studying the ``tweed'' precursors above the martensitic transition
in shape--memory alloys. These characteristic cross--hatched modulations occur
for hundreds of degrees above the first--order shape--changing transition. Our
two--dimensional model for this transition, in the limit of infinite elastic
anisotropy, can be mapped onto a spin--glass Hamiltonian in a random field. We
suggest that the tweed precursors are a direct analogy of the spin--glass
phase. The tweed is intermediate between the high--temperature cubic phase and
the low--temperature martensitic phase in the same way as the spin--glass phase
can be intermediate between ferromagnet and antiferromagnet.Comment: 18 pages and four figures (included
Importance of Mild Hyperoxaluria in the Pathogenesis of Urolithiasis - New Evidence from Studies in the Arabian Peninsula
The hypothesis that mild hyperoxaluria is more important than hypercalciuria in the pathogenesis of urolithiasis is re-examined in the light of new evidence. Small increments in urinary oxalate in the normal to high-normal range are much more critical than similar rises in urinary calcium for increasing the relative supersaturation of urine with respect to calcium oxalate, the oxalate/calcium ratio in urine, the total volume of calcium oxalate crystals excreted, the proportion of abnormally large crystals and aggregates of calcium oxalate and the severity of the disorder as defined by the recurrence rate of stone-formation. Data from the Arabian Peninsula, where the prevalence of calcium-containing stones is considerably higher than in the West, have shown that this occurs in spite of the almost complete absence of hypercalciuria. On the other hand, there is a strong association between stone-formation and the occurrence of mild hyperoxaluria. The life-time expectancy of stone-formation in men from various countries is strongly correlated with the average daily excretion of oxalate in the urine of the normal men in these countries. This relationship extends to include patients with enteric and hereditary hyperoxaluria. There is no such relationship, however, between the life-time expectancy of stones and urinary calcium excretion in the same populations.
Studies on the regulation of urinary oxalate indicate that it is largely controlled by the quantity of free dietary oxalate available for absorption in the lower intestine. This can be calculated from the intakes of calcium and oxalate and the urinary excretion of calcium
Numerical analysis of flow non-uniformity in the hot gas manifold of the Space Shuttle main engine
Three-dimensional viscous flow in a conceptual hot gas manifold (HGM) for the Space Shuttle Main Engine High Pressure Fuel Turbopump (SSME HPFTP) was numerically analyzed. A finite difference scheme was used to solve the Navier-Stokes equations. The exact geometry of the SSME HGM was modeled using boundary fitted curvilinear coordinates and the General Interpolants Method (GIM) code. Slight compressibility of the subsonic flow was modeled using a linearized equation of state with artificial compressibility. A time relaxation method was used to obtain a steady state solution. The feasibility and potential usefulness of computational methods in assisting the design of SSME components which involves the flow of fluids within complex geometrical shapes is demonstrated
The Angular Diameter and Fundamental Parameters of Sirius A
The Sydney University Stellar Interferometer (SUSI) has been used to make a
new determination of the angular diameter of Sirius A. The observations were
made at an effective wavelength of 694.1 nm and the new value for the
limb-darkened angular diameter is 6.048 +/- 0.040mas (+/-0.66%). This new
result is compared with previous measurements and is found to be in excellent
agreement with a conventionally calibrated measurement made with the European
Southern Observatory's Very Large Telescope Interferometer (VLTI) at 2.176
microns (but not with a second globally calibrated VLTI measurement). A
weighted mean of the SUSI and first VLTI results gives the limb-darkened
angular diameter of Sirius A as 6.041 +/- 0.017mas (+/-0.28%). Combination with
the Hipparcos parallax gives the radius equal to 1.713 +/- 0.009R_sun. The
bolometric flux has been determined from published photometry and
spectrophotometry and, combined with the angular diameter, yields the emergent
flux at the stellar surface equal to (5.32+/- 0.14)x10^8 Wm^-2 and the
effective temperature equal to 9845 +/- 64 K. The luminosity is 24.7 +/- 0.7
L_sun.Comment: Accepted for publication in PAS
Diffuse Neutron Scattering Study of Relaxor Ferroelectric (1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3(PZN-xPT)
Diffuse neutron scattering is a valuable tool to obtain information about the
size and orientation of the polar nanoregions that are a characteristic feature
of relaxor ferroelectrics. In this paper, we present new diffuse scattering
results obtained on Pb(Zn1/3Nb2/3)O3 (PZN for short) and
(1-x)Pb(Zn1/3Nb2/3)O3-xPbTiO3(PZN-xPT)single crystals (with x=4.5 and 9%),
around various Bragg reflections and along three symmetry directions in the
[100]-[011] zone. Diffuse scattering is observed around reflections with mixed
indices, (100), (011) and (300), and along transverse and diagonal directions
only. No diffuse scattering is found in longitudinal scans. The diffuse
scattering peaks can be fitted well with a Lorentzian function, from which a
correlation length is extracted. The correlation length increases with
decreasing temperatures down to the transition at Tc, first following a
Curie-Weiss law, then departing from it and becoming flat at very low
temperatures. These results are interpreted in terms of three temperature
regions: 1) dynamic polarization fluctuations (i.e. with a finite lifetime) at
high temperatures, 2) static polarization reorientations (condensation of polar
nanoregions) that can still reorient as a unit (relaxor behavior) at
intermediate temperatures and 3) orientational freezing of the polar
nanoregions with random strain fields in pure PZN or a structural phase
transition in PZN-xPT at low temperatures. The addition of PT leads to a
broadening of the diffuse scattering along the diagonal ([111]) relative to the
transverse ([100]) direction, indicating a change in the orientation of the
polar regions. Also, with the addition of PT, the polar nanoregions condense at
a higher temperature above Tc.Comment: AIP 6x9 style files, 9 pages, 5 figures, Conference-Fundamental
Physics of Ferroelectrics 200
- …