11,287 research outputs found
A total life prediction model for stress concentration sites
Fatigue crack growth tests were performed on center crack panels and radial crack hole samples. The data were reduced and correlated with the elastic parameter K taking into account finite width and corner crack corrections. The anomalous behavior normally associated with short cracks was not observed. Total life estimates for notches were made by coupling an initiation life estimate with a propagation life estimate
Wind tunnel tests of Space Shuttle external tank insulation material in the aerothermal tunnel at elevated (1440 deg F) total temperatures
Tests of the space shuttle external tank foam insulation were conducted in the von Karman Gas Dynamics Facility Tunnel C. For these tests, Tunnel C was run at Mach 4 with a total temperature of 1440 F and a total pressure which varied from 30-100 psia. Cold wall heating rates were changed by varying the test article support wedge angle and by adding and removing a shock generator or a cylindrical protuberance. Selected results are presented to illustrate the test techniques and typical data obtained
Rational approximation and arithmetic progressions
A reasonably complete theory of the approximation of an irrational by
rational fractions whose numerators and denominators lie in prescribed
arithmetic progressions is developed in this paper. Results are both, on the
one hand, from a metrical and a non-metrical point of view and, on the other
hand, from an asymptotic and also a uniform point of view. The principal
novelty is a Khintchine type theorem for uniform approximation in this context.
Some applications of this theory are also discussed
Complete chaotic synchronization in mutually coupled time-delay systems
Complete chaotic synchronization of end lasers has been observed in a line of
mutually coupled, time-delayed system of three lasers, with no direct
communication between the end lasers. The present paper uses ideas from
generalized synchronization to explain the complete synchronization in the
presence of long coupling delays, applied to a model of mutually coupled
semiconductor lasers in a line. These ideas significantly simplify the analysis
by casting the stability in terms of the local dynamics of each laser. The
variational equations near the synchronization manifold are analyzed, and used
to derive the synchronization condition that is a function of the parameters.
The results explain and predict the dependence of synchronization on various
parameters, such as time-delays, strength of coupling and dissipation. The
ideas can be applied to understand complete synchronization in other chaotic
systems with coupling delays and no direct communication between synchronized
sub-systems.Comment: 22 pages, 6 figure
Simulation of MeV/atom cluster correlations in matter
We present an efficient algorithm able to predict the trajectories of individual cluster constituents as they penetrate relatively thick amorphous targets. Our algorithm properly treats both the intracluster Coulomb repulsion and the collisions between cluster constituents and target atoms. We have compared our simulation predictions to experimental measurements of the distribution of lateral exit velocities, and demonstrated that the in-target Coulomb explosion of 2MeV/atom carbon clusters in carbon foils must be shielded with a screening length of less than 2.5 Å. We also present a simple phenomenological model for the suppression of the exit-side charge of ions in clusters which depends on the enhanced ionization potential that an electron near an ion feels due to the ion’s charged comoving neighbors. By using our simulation algorithm we have predicted the exit correlations of the cluster constituents and verified that the charge suppression model fits the observed charge suppression of ions in clusters to within the experimental uncertainties
Privacy-preserving architecture for forensic image recognition
Forensic image recognition is an important tool in many areas of law enforcement where an agency wants to prosecute possessors of illegal images. The recognition of illegal images that might have undergone human imperceptible changes (e.g., a JPEG-recompression) is commonly done by computing a perceptual image hash function of a given image and then matching this hash with perceptual hash values in a database of previously collected illegal images. To prevent privacy violation, agencies should only learn about images that have been reliably detected as illegal and nothing else. In this work, we argue that the prevalent presence of separate departments in such agencies can be used to enforce the need-to-know principle by separating duties among them. This enables us to construct the first practically efficient architecture to perform forensic image recognition in a privacy-preserving manner. By deriving unique cryptographic keys directly from the images, we can encrypt all sensitive data and ensure that only illegal images can be recovered by the law enforcement agency while all other information remains protected
Music as a mirror: the ‘‘choosing my personal theme song’’ exercise
When asked to describe their strengths people rarely refer to their natural knowledge, skills, abilities, and talents. From this we may assume that many are unaware of their individual strengths or at the very least take them for granted. Music lyrics are particularly salient symbols available in the minds of students and can be powerful tools for learning more about themselves and others. This knowledge is valuable as they continue in their own personal evolution as they discern greater distinctions between themselves and the world around them. The interactive exercise presented here uses music to help students look in the ‘mirror,’ reflect on their observations, and increase their self-awareness
Deep MMT Transit Survey of the Open Cluster M37 IV: Limit on the Fraction of Stars With Planets as Small as 0.3 R_J
We present the results of a deep (15 ~< r ~< 23), 20 night survey for
transiting planets in the intermediate age open cluster M37 (NGC 2099) using
the Megacam wide-field mosaic CCD camera on the 6.5m MMT. We do not detect any
transiting planets among the ~1450 observed cluster members. We do, however,
identify a ~ 1 R_J candidate planet transiting a ~ 0.8 Msun Galactic field star
with a period of 0.77 days. The source is faint (V = 19.85 mag) and has an
expected velocity semi-amplitude of K ~ 220 m/s (M/M_J). We conduct Monte Carlo
transit injection and recovery simulations to calculate the 95% confidence
upper limit on the fraction of cluster members and field stars with planets as
a function of planetary radius and orbital period. Assuming a uniform
logarithmic distribution in orbital period, we find that < 1.1%, < 2.7% and <
8.3% of cluster members have 1.0 R_J planets within Extremely Hot Jupiter (EHJ,
0.4 < T < 1.0 day), Very Hot Jupiter (VHJ, 1.0 < T < 3.0 days) and Hot Jupiter
(HJ, 3.0 < T < 5.0 days) period ranges respectively. For 0.5 R_J planets the
limits are < 3.2%, and < 21% for EHJ and VHJ period ranges, while for 0.35 R_J
planets we can only place an upper limit of < 25% on the EHJ period range. For
a sample of 7814 Galactic field stars, consisting primarily of FGKM dwarfs, we
place 95% upper limits of < 0.3%, < 0.8% and < 2.7% on the fraction of stars
with 1.0 R_J EHJ, VHJ and HJ assuming the candidate planet is not genuine. If
the candidate is genuine, the frequency of ~ 1.0 R_J planets in the EHJ period
range is 0.002% < f_EHJ < 0.5% with 95% confidence. We place limits of < 1.4%,
< 8.8% and < 47% for 0.5 R_J planets, and a limit of < 16% on 0.3 R_J planets
in the EHJ period range. This is the first transit survey to place limits on
the fraction of stars with planets as small as Neptune.Comment: 61 pages, 19 figures, 5 tables, replaced with the version accepted
for publication in Ap
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