54,352 research outputs found
Local measurements in turbulent flows through cross correlation of optical signals
Crossed beam correlation method measures turbulent fluctuations in transonic and supersonic flows. Two collimated beams of radiation are crossed at the point of interest in the flow, and the power loss of each beam is measured with two independent photodetectors, which yield information about the turbulent properties
Fractal Droplets in Two Dimensional Spin Glasses
The two-dimensional Edwards-Anderson model with Gaussian bond distribution is
investigated at T=0 with a numerical method. Droplet excitations are directly
observed. It turns out that the averaged volume of droplets is proportional to
l^D with D = 1.80(2) where l is the spanning length of droplets, revealing
their fractal nature. The exponent characterizing the l dependence of the
droplet excitation energy is estimated to be -0.42(4), clearly different from
the stiffness exponent for domain wall excitations.Comment: 4 pages 4 figure
Fatalism and Future Contingents
In this paper I address issues related to the problem of future contingents and
the metaphysical doctrine of fatalism. Two classical responses to the problem of
future contingents are the third truth value view and the all-false view. According to
the former, future contingents take a third truth value which goes beyond truth and
falsity. According to the latter, they are all false. I here illustrate and discuss two
ways to respectively argue for those two views. Both ways are similar in spirit and
intimately connected with fatalism, in the sense that they engage with the doctrine
of fatalism and accept a large part of a standard fatalistic machinery
Evaluation of the effect of crack closure on fatigue crack growth of simulated short cracks
A test program was performed to determine the influence of crack closure on fatigue crack growth (FCG) rates of short cracks. By use of the standard compact tension specimen, test procedures were devised to evaluate closure loads in the wake of the crack behind its tip. The first procedure determined the magnitude of crack closure as a function of the fatigued crack wave by incrementally removing the contacting wake surfaces and measuring closure load at each increment. The second procedure used a low-high loading sequence to simulate short crack behavior. Based on the results, it was concluded that crack closure is not the major reason for the more rapid growth of short cracks as compared to long crack growth
Influence of fatigue crack wake length and state of stress on crack closure
The location of crack closure with respect to crack wake and specimen thickness under different loading conditions was determined. The rate of increase of K sub CL in the crack wake was found to be significantly higher for plasticity induced closure in comparison to roughness induced closure. Roughness induced closure was uniform throughout the thickness of the specimen while plasticity induced closure levels were 50 percent higher in the near surface region than in the midthickness. The influence of state of stress on low-high load interaction effects was also examined. Load interaction effects differed depending upon the state of stress and were explained in terms of delta K sub eff
Stability of Elastic Glass Phases in Random Field XY Magnets and Vortex Lattices in Type II Superconductors
A description of a dislocation-free elastic glass phase in terms of domain
walls is developed and used as the basis of a renormalization group analysis of
the energetics of dislocation loops added to the system. It is found that even
after optimizing over possible paths of large dislocation loops, their energy
is still very likely to be positive when the dislocation core energy is large.
This implies the existence of an equilibrium elastic glass phase in three
dimensional random field X-Y magnets, and a dislocation free,
bond-orientationally ordered ``Bragg glass'' phase of vortices in dirty Type II
superconductors.Comment: 12 pages, Revtex, no figures, submitted to Phys Rev Letter
Research opportunities in loss of red blood cell mass in space flight
Decreases of red blood cell mass and plasma volume have been observed consistently following manned space flights. Losses of red cell mass by United States astronauts have averaged 10 to 15% (range: 2 to 21%). Based on postflight estimates of total hemoglobin, Soviet cosmonauts engaged in space missions lasting from 1 to 7 months have exhibited somewhat greater losses. Restoration of red cell mass requires from 4 to 6 weeks following return to Earth, regardless of the duration of space flight
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