21,304 research outputs found
Quaternary and quinary modifications of eutectic superalloys strengthened by delta Ni3Cb lamellae and gamma prime Ni3Al precipitates
By means of a compositional and heat treatment optimization program based on the quaternary gamma/gamma prime-delta, a tantalum modified gamma/gamma prime-delta alloy with improved shear and creep strength combined with better cyclic oxidation resistance was identified. Quinary additions, quaternary adjustments, and heat treatment were investigated. The tantalum modified gamma/gamma prime-delta alloy possessed a slightly higher liquidus temperature and exhibited rupture strength exceeding NASA VIA by approximately three and one-half Larson-Miller parameters (C = 20) above 1000 C. Although improvements in longitudinal mechanical properties were achieved, the shear and transverse strength property goals of the program were not met and present a continuing challenge to the alloy metallurgist
Constitutive and life modeling of single crystal blade alloys for root attachment analysis
Work to develop fatigue life prediction and constitutive models for uncoated attachment regions of single crystal gas turbine blades is described. At temperatures relevant to attachment regions, deformation is dominated by slip on crystallographic planes. However, fatigue crack initiation and early crack growth are not always observed to be crystallographic. The influence of natural occurring microporosity will be investigated by testing both hot isostatically pressed and conventionally cast PWA 1480 single crystal specimens. Several differnt specimen configurations and orientations relative to the natural crystal axes are being tested to investigate the influence of notch acuity and the material's anisotropy. Global and slip system stresses in the notched regions were determined from three dimensional stress analyses and will be used to develop fatigue life prediction models consistent with the observed lives and crack characteristics
Techniques for improving reliability of computers
Modular design techniques improve methods of error detection, diagnosis, and recovery. Theoretical computer (MARCS (Modular Architecture for Reliable Computer Systems)) study deals with postulated and modeled technology indigenous to 1975-1980. Study developments are discussed
The Effects of Laser Radiation on Exposed Dentine Surfaces in the Treatment of Dentine Sensitivity. An In Vitro Study.
Aim: This in vitro pilot study was undertaken to investigate the effects of Neodymium: Yttrium Aluminium Garnet
(Nd:YAG), Erbium: Yttrium Aluminium Garnet (Er:YAG) and Helium Neon (HeNe) laser radiation on dentine surfaces in
extracted human teeth.
Material and Methods: Instrumented root surfaces and etched and unetched dentine discs were irradiated with a
Nd:YAG laser operating at 3.5, 3.75 or 4W or an Er:YAG laser operating at 60, 80, 100mJ or with a HeNe laser. Results:
The Nd:YAG laser produced melting and resolidification of dentine on all surfaces while the Er:YAG laser produced
craters with closed tubules in root surfaces, but open tubules in dentine discs. The HeNe laser produced no apparent
surface alteration. Both lased and unlased control surfaces were compared using Scanning Electron Microscopy (SEM).
Conclusions: Irradiation with the Nd:YAG and Er:YAG lasers caused significant disruption of the dentine surfaces
on both root surfaces and also on dentine discs. Nd:YAG radiation produced irregular melting and resolidification of the
dentine surface with some occlusion of open dentine tubules. Er:YAG radiation caused ablation of dentine and produced
craters with open tubules in the dentine discs, but closed tubules on most root surfaces. Irradiation using a HeNe laser
produced no noticeable surface effect
Models of the ICM with Heating and Cooling: Explaining the Global and Structural X-ray Properties of Clusters
(Abridged) Theoretical models that include only gravitationally-driven
processes fail to match the observed mean X-ray properties of clusters. As a
result, there has recently been increased interest in models in which either
radiative cooling or entropy injection play a central role in mediating the
properties of the intracluster medium. Both sets of models give reasonable fits
to the mean properties of clusters, but cooling only models result in fractions
of cold baryons in excess of observationally established limits and the
simplest entropy injection models do not treat the "cooling core" structure
present in many clusters and cannot account for entropy profiles revealed by
recent X-ray observations. We consider models that marry radiative cooling with
entropy injection, and confront model predictions for the global and structural
properties of massive clusters with the latest X-ray data. The models
successfully and simultaneously reproduce the observed L-T and L-M relations,
yield detailed entropy, surface brightness, and temperature profiles in
excellent agreement with observations, and predict a cooled gas fraction that
is consistent with observational constraints. The model also provides a
possible explanation for the significant intrinsic scatter present in the L-T
and L-M relations and provides a natural way of distinguishing between clusters
classically identified as "cooling flow" clusters and dynamically relaxed
"non-cooling flow" clusters. The former correspond to systems that had only
mild levels (< 300 keV cm^2) of entropy injection, while the latter are
identified as systems that had much higher entropy injection. This is borne out
by the entropy profiles derived from Chandra and XMM-Newton.Comment: 20 pages, 15 figures, accepted for publication in the Astrophysical
Journa
An alternative derivation of the gravitomagnetic clock effect
The possibility of detecting the gravitomagnetic clock effect using
artificial Earth satellites provides the incentive to develop a more intuitive
approach to its derivation. We first consider two test electric charges moving
on the same circular orbit but in opposite directions in orthogonal electric
and magnetic fields and show that the particles take different times in
describing a full orbit. The expression for the time difference is completely
analogous to that of the general relativistic gravitomagnetic clock effect in
the weak-field and slow-motion approximation. The latter is obtained by
considering the gravitomagnetic force as a small classical non-central
perturbation of the main central Newtonian monopole force. A general expression
for the clock effect is given for a spherical orbit with an arbitrary
inclination angle. This formula differs from the result of the general
relativistic calculations by terms of order c^{-4}.Comment: LaTex2e, 11 pages, 1 figure, IOP macros. Submitted to Classical and
Quantum Gravit
Evolution of clouds in radio galaxy cocoons
This letter presents a numerical study of the evolution of an emission line
cloud of initial density 10 cm, temperature K, and size 200 pc,
being overtaken by a strong shock wave. Whereas previous simple models proposed
that such a cloud would either be completely destroyed, or simply shrink in
size, our results show a different and more complex behaviour: due to rapid
cooling, the cloud breaks up into many small and dense fragments, which can
survive for a long time. We show that such rapid cooling behaviour is in fact
expected for a wide range of cloud and shock properties. This process applies
to the evolution of emission line clouds being overtaken by the cocoon of a
radio jet. The resulting small clouds would be Jeans unstable, and form stars.
Our results thus give theoretical credibility to the process of jet induced
star formation, one of the explanations for the alignment of the optical/UV and
radio axis observed in high redshift radio galaxies.Comment: 4 pages, 2 figures, movies available at
http://www.strw.leidenuniv.nl/TheoryGroup/IG-Cloud.htm
Assessing Human Error Against a Benchmark of Perfection
An increasing number of domains are providing us with detailed trace data on
human decisions in settings where we can evaluate the quality of these
decisions via an algorithm. Motivated by this development, an emerging line of
work has begun to consider whether we can characterize and predict the kinds of
decisions where people are likely to make errors.
To investigate what a general framework for human error prediction might look
like, we focus on a model system with a rich history in the behavioral
sciences: the decisions made by chess players as they select moves in a game.
We carry out our analysis at a large scale, employing datasets with several
million recorded games, and using chess tablebases to acquire a form of ground
truth for a subset of chess positions that have been completely solved by
computers but remain challenging even for the best players in the world.
We organize our analysis around three categories of features that we argue
are present in most settings where the analysis of human error is applicable:
the skill of the decision-maker, the time available to make the decision, and
the inherent difficulty of the decision. We identify rich structure in all
three of these categories of features, and find strong evidence that in our
domain, features describing the inherent difficulty of an instance are
significantly more powerful than features based on skill or time.Comment: KDD 2016; 10 page
- …