11,200 research outputs found
Using AI/expert system technology to automate planning and replanning for the HST servicing missions
This paper describes a knowledge-based system that has been developed to automate planning and scheduling for the Hubble Space Telescope (HST) Servicing Missions. This new system is the Servicing Mission Planning and Replanning Tool (SM/PART). SM/PART has been delivered to the HST Flight Operations Team (FOT) at Goddard Space Flight Center (GSFC) where it is being used to build integrated time lines and command plans to control the activities of the HST, Shuttle, Crew and ground systems for the next HST Servicing Mission. SM/PART reuses and extends AI/expert system technology from Interactive Experimenter Planning System (IEPS) systems to build or rebuild time lines and command plans more rapidly than was possible for previous missions where they were built manually. This capability provides an important safety factor for the HST, Shuttle and Crew in case unexpected events occur during the mission
Spectropolarimetric observations of Herbig Ae/Be Stars I: HiVIS spectropolarimetric calibration and reduction techniques
Using the HiVIS spectropolarimeter built for the Haleakala 3.7m AEOS
telescope in Hawaii, we are collecting a large number of high precision
spectropolarimetrc observations of stars. In order to precisely measure very
small polarization changes, we have performed a number of polarization
calibration techniques on the AEOS telescope and HiVIS spectrograph. We have
extended our dedicated IDL reduction package and have performed some hardware
upgrades to the instrument. We have also used the ESPaDOnS spectropolarimeter
on CFHT to verify the HiVIS results with back-to-back observations of MWC 361
and HD163296. Comparision of this and other HiVIS data with stellar
observations from the ISIS and WW spectropolarimeters in the literature further
shows the usefulness of this instrument.Comment: 35 pages, 44 figures, Accepted by PAS
Structural and chemical embrittlement of grain boundaries by impurities: a general theory and first principles calculations for copper
First principles calculations of the Sigma 5 (310)[001] symmetric tilt grain
boundary in Cu with Bi, Na, and Ag substitutional impurities provide evidence
that in the phenomenon of Bi embrittlement of Cu grain boundaries electronic
effects do not play a major role; on the contrary, the embrittlement is mostly
a structural or "size" effect. Na is predicted to be nearly as good an
embrittler as Bi, whereas Ag does not embrittle the boundary in agreement with
experiment. While we reject the prevailing view that "electronic" effects
(i.e., charge transfer) are responsible for embrittlement, we do not exclude
the role of chemistry. However numerical results show a striking equivalence
between the alkali metal Na and the semi metal Bi, small differences being
accounted for by their contrasting "size" and "softness" (defined here). In
order to separate structural and chemical effects unambiguously if not
uniquely, we model the embrittlement process by taking the system of grain
boundary and free surfaces through a sequence of precisely defined gedanken
processes; each of these representing a putative mechanism. We thereby identify
three mechanisms of embrittlement by substitutional impurities, two of which
survive in the case of embrittlement or cohesion enhancement by interstitials.
Two of the three are purely structural and the third contains both structural
and chemical elements that by their very nature cannot be further unravelled.
We are able to take the systems we study through each of these stages by
explicit computer simulations and assess the contribution of each to the nett
reduction in intergranular cohesion. The conclusion we reach is that
embrittlement by both Bi and Na is almost exclusively structural in origin;
that is, the embrittlement is a size effect.Comment: 13 pages, 5 figures; Accepted in Phys. Rev.
Convergence of simple adaptive Galerkin schemes based on h − h/2 error estimators
We discuss several adaptive mesh-refinement strategies based on (h − h/2)-error estimation. This class of adaptivemethods is particularly popular in practise since it is problem independent and requires virtually no implementational overhead. We prove that, under the saturation assumption, these adaptive algorithms are convergent. Our framework applies not only to finite element methods, but also yields a first convergence proof for adaptive boundary element schemes. For a finite element model problem, we extend the proposed adaptive scheme and prove convergence even if the saturation assumption fails to hold in general
Avascular necrosis of the hip and diffuse idiopathic skeletal hyperostosis during long-term isotretinoin treatment of epidermolytic ichthyosis due to a novel deletion mutation in KRT10
Calibrated Sub-Bundles in Non-Compact Manifolds of Special Holonomy
This paper is a continuation of math.DG/0408005. We first construct special
Lagrangian submanifolds of the Ricci-flat Stenzel metric (of holonomy SU(n)) on
the cotangent bundle of S^n by looking at the conormal bundle of appropriate
submanifolds of S^n. We find that the condition for the conormal bundle to be
special Lagrangian is the same as that discovered by Harvey-Lawson for
submanifolds in R^n in their pioneering paper. We also construct calibrated
submanifolds in complete metrics with special holonomy G_2 and Spin(7)
discovered by Bryant and Salamon on the total spaces of appropriate bundles
over self-dual Einstein four manifolds. The submanifolds are constructed as
certain subbundles over immersed surfaces. We show that this construction
requires the surface to be minimal in the associative and Cayley cases, and to
be (properly oriented) real isotropic in the coassociative case. We also make
some remarks about using these constructions as a possible local model for the
intersection of compact calibrated submanifolds in a compact manifold with
special holonomy.Comment: 20 pages; for Revised Version: Minor cosmetic changes, some
paragraphs rewritten for improved clarit
Two-finger selection theory in the Saffman-Taylor problem
We find that solvability theory selects a set of stationary solutions of the
Saffman-Taylor problem with coexistence of two \it unequal \rm fingers
advancing with the same velocity but with different relative widths
and and different tip positions. For vanishingly small
dimensionless surface tension , an infinite discrete set of values of the
total filling fraction and of the relative
individual finger width are selected out of a
two-parameter continuous degeneracy. They scale as
and . The selected values of differ from
those of the single finger case. Explicit approximate expressions for both
spectra are given.Comment: 4 pages, 3 figure
Application of Dynamic System Identification to Timber Beams - part I
In this first part of a two-part paper, development of a method of dynamic system identification for timber beams is presented with an analytical verification of the method using a finite-element model. A method of global nondestructive evaluation for identifying local damage and decay in timber beams is investigated in this paper. Experimental modal analysis is used in conjunction with a previously developed damage localization algorithm. The damage localization algorithm utilizes changes in modal strain energy between the mode shapes of a calibrated model, representing the undamaged state of the beam of interest, and the experimentally obtained mode shapes for a timber beam. Analytical evaluations were performed to demonstrate and verify the use of this method of global nondestructive evaluation for the localization of damage or decay in timber beams. In a companion paper, experimental laboratory tests are presented that verify the use of dynamic system identification to locate damage within timber beams
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