13,825 research outputs found
Characterization of crack growth under combined loading
Room-temperature static and cyclic tests were made on 21 aluminum plates in the shape of a 91.4x91.4-cm Maltese cross with 45 deg flaws to develop crack growth and fracture toughness data under mixed-mode conditions. During cyclic testing, it was impossible to maintain a high proportion of shear-mode deformation on the crack tips. Cracks either branched or turned. Under static loading, cracks remained straight if shear stress intensity exceeded normal stress intensity. Mixed-mode crack growth rate data compared reasonably well with published single-mode data, and measured crack displacements agreed with the straight and branched crack analyses. Values of critical strain energy release rate at fracture for pure shear were approximately 50% higher than for pure normal opening, and there was a large reduction in normal stress intensity at fracture in the presence of high shear stress intensity. Net section stresses were well into the inelastic range when fracture occurred under high shear on the cracks
A Rigorous Proof of Fermi Liquid Behavior for Jellium Two-Dimensional Interacting Fermions
Using the method of continuous constructive renormalization group around the
Fermi surface, it is proved that a jellium two-dimensional interacting system
of Fermions at low temperature remains analytic in the coupling constant
for where is some numerical constant
and is the temperature. Furthermore in that range of parameters, the first
and second derivatives of the self-energy remain bounded, a behavior which is
that of Fermi liquids and in particular excludes Luttinger liquid behavior. Our
results prove also that in dimension two any transition temperature must be
non-perturbative in the coupling constant, a result expected on physical
grounds. The proof exploits the specific momentum conservation rules in two
dimensions.Comment: 4 pages, no figure
Quantifying the Bull's Eye Effect
We have used N-body simulations to develop two independent methods to
quantify redshift distortions known as the Bull's Eye effect (large scale
infall plus small scale virial motion). This effect depends upon the mass
density, , so measuring it can in principle give an estimate of this
important cosmological parameter. We are able to measure the effect and
distinguish between its strength for high and low values of . Unlike
other techniques which utilize redshift distortions, one of our methods is
relatively insensitive to bias. In one approach, we use path lengths between
contour crossings of the density field. The other is based upon percolation. We
have found both methods to be successful in quantifying the effect and
distinguishing between values of . However, only the path lengths
method exhibits low sensitivity to bias.Comment: 21 pages, 5 figures, 3 tables; Replaced version - minor corrections,
replaced figure 2; To appear in ApJ, Jan. 20, 200
Design of an RSFQ Control Circuit to Observe MQC on an rf-SQUID
We believe that the best chance to observe macroscopic quantum coherence
(MQC) in a rf-SQUID qubit is to use on-chip RSFQ digital circuits for
preparing, evolving and reading out the qubit's quantum state. This approach
allows experiments to be conducted on a very short time scale (sub-nanosecond)
without the use of large bandwidth control lines that would couple
environmental degrees of freedom to the qubit thus contributing to its
decoherence. In this paper we present our design of a RSFQ digital control
circuit for demonstrating MQC in a rf-SQUID. We assess some of the key
practical issues in the circuit design including the achievement of the
necessary flux bias stability. We present an "active" isolation structure to be
used to increase coherence times. The structure decouples the SQUID from
external degrees of freedom, and then couples it to the output measurement
circuitry when required, all under the active control of RSFQ circuits.
Research supported in part by ARO grant # DAAG55-98-1-0367.Comment: 4 pages. More information and publications at
http://www.ece.rochester.edu:8080/users/sde/research/publications/index.htm
GALEX Observations of CS and OH Emission in Comet 9P/Tempel 1 During Deep Impact
GALEX observations of comet 9P/Tempel 1 using the near ultraviolet (NUV)
objective grism were made before, during and after the Deep Impact event that
occurred on 2005 July 4 at 05:52:03 UT when a 370 kg NASA spacecraft was
maneuvered into the path of the comet. The NUV channel provides usable spectral
information in a bandpass covering 2000 - 3400 A with a point source spectral
resolving power of approximately 100. The primary spectral features in this
range include solar continuum scattered from cometary dust and emissions from
OH and CS molecular bands centered near 3085 and 2575 A, respectively. In
particular, we report the only cometary CS emission detected during this event.
The observations allow the evolution of these spectral features to be tracked
over the period of the encounter. In general, the NUV emissions observed from
Tempel 1 are much fainter than those that have been observed by GALEX from
other comets. However, it is possible to derive production rates for the parent
molecules of the species detected by GALEX in Tempel 1 and to determine the
number of these molecules liberated by the impact. The derived quiescent
production rates are Q(H2O) = 6.4e27 molecules/s and Q(CS2) = 6.7e24
molecules/s, while the impact produced an additional 1.6e32 H2O molecules and
1.3e29 CS2 molecules, a similar ratio as in quiescent outgassing.Comment: 15 pages, 4 figures, accepted for publication in the Astrophysical
Journa
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