9,736 research outputs found
Etching of aluminum for bonding Patent
Etching aluminum alloys with aqueous solution containing sulfuric acid, hydrofluoric acid, and an alkali metal dischromate for adhesive bondin
Flaw Selection Strategies for Partial-Order Planning
Several recent studies have compared the relative efficiency of alternative
flaw selection strategies for partial-order causal link (POCL) planning. We
review this literature, and present new experimental results that generalize
the earlier work and explain some of the discrepancies in it. In particular, we
describe the Least-Cost Flaw Repair (LCFR) strategy developed and analyzed by
Joslin and Pollack (1994), and compare it with other strategies, including
Gerevini and Schubert's (1996) ZLIFO strategy. LCFR and ZLIFO make very
different, and apparently conflicting claims about the most effective way to
reduce search-space size in POCL planning. We resolve this conflict, arguing
that much of the benefit that Gerevini and Schubert ascribe to the LIFO
component of their ZLIFO strategy is better attributed to other causes. We show
that for many problems, a strategy that combines least-cost flaw selection with
the delay of separable threats will be effective in reducing search-space size,
and will do so without excessive computational overhead. Although such a
strategy thus provides a good default, we also show that certain domain
characteristics may reduce its effectiveness.Comment: See http://www.jair.org/ for an online appendix and other files
accompanying this articl
Measurement of transient strain and surface temperature on simulated turbine blades using noncontacting techniques
Noncontacting techniques were used to measure strain and temperature in thermally cycled simulated turbine blades. An electro-optical extensometer was used to measure the displacement between parallel targets mounted on the leading edge of the blades throughout a complete heating and cooling cycle. An infrared photographic pyrometry method was used to measure blade steady state surface temperature. The blade was cyclically heated and cooled by moving it into and out of a Mach 1 hot-gas stream. Transient leading edge strain and steady state surface temperature distributions are presented for blades of three different configurations
Land landing couch dynamics computer program
Computer programs perform landing stability studies of mechanical impact system designs for advanced spacecraft. The programs consider variation in spacecraft vertical and horizontal velocity, attitude and orientation, shock strut load-stroke characteristics, and ground coefficient of friction
Systoles of Arithmetic Hyperbolic Surfaces and 3-manifolds
Our main result is that for all sufficiently large , the set of
commensurability classes of arithmetic hyperbolic 2- or 3-orbifolds with fixed
invariant trace field and systole bounded below by has density one
within the set of all commensurability classes of arithmetic hyperbolic 2- or
3-orbifolds with invariant trace field . The proof relies upon bounds for
the absolute logarithmic Weil height of algebraic integers due to Silverman,
Brindza and Hajdu, as well as precise estimates for the number of rational
quaternion algebras not admitting embeddings of any quadratic field having
small discriminant. When the trace field is , using work of
Granville and Soundararajan, we establish a stronger result that allows our
constant lower bound to grow with the area. As an application, we
establish a systolic bound for arithmetic hyperbolic surfaces that is related
to prior work of Buser-Sarnak and Katz-Schaps-Vishne. Finally, we establish an
analogous density result for commensurability classes of arithmetic hyperbolic
3-orbifolds with small area totally geodesic -orbifolds.Comment: v4: 17 pages. Revised according to referee report. Final version. To
appear in Math. Res. Let
Demonstration of the Zero-Crossing Phasemeter with a LISA Test-bed Interferometer
The Laser Interferometer Space Antenna (LISA) is being designed to detect and
study in detail gravitational waves from sources throughout the Universe such
as massive black hole binaries. The conceptual formulation of the LISA
space-borne gravitational wave detector is now well developed. The
interferometric measurements between the sciencecraft remain one of the most
important technological and scientific design areas for the mission.
Our work has concentrated on developing the interferometric technologies to
create a LISA-like optical signal and to measure the phase of that signal using
commercially available instruments. One of the most important goals of this
research is to demonstrate the LISA phase timing and phase reconstruction for a
LISA-like fringe signal, in the case of a high fringe rate and a low signal
level. We present current results of a test-bed interferometer designed to
produce an optical LISA-like fringe signal previously discussed in the
literature.Comment: find minor corrections in the CQG versio
Towards a Principled Representation of Discourse Plans
We argue that discourse plans must capture the intended causal and
decompositional relations between communicative actions. We present a planning
algorithm, DPOCL, that builds plan structures that properly capture these
relations, and show how these structures are used to solve the problems that
plagued previous discourse planners, and allow a system to participate
effectively and flexibly in an ongoing dialogue.Comment: requires cogsci94.sty, psfig.st
Universality in Three- and Four-Body Bound States of Ultracold Atoms
Under certain circumstances, three or more interacting particles may form
bound states. While the general few-body problem is not analytically solvable,
the so-called Efimov trimers appear for a system of three particles with
resonant two-body interactions. The binding energies of these trimers are
predicted to be universally connected to each other, independent of the
microscopic details of the interaction. By exploiting a Feshbach resonance to
widely tune the interactions between trapped ultracold lithium atoms, we find
evidence for two universally connected Efimov trimers and their associated
four-body bound states. A total of eleven precisely determined three- and
four-body features are found in the inelastic loss spectrum. Their relative
locations on either side of the resonance agree well with universal theory,
while a systematic deviation from universality is found when comparing features
across the resonance.Comment: 16 pages including figures and Supplementary Online Materia
Was ist Religion? Eine kritische Diskussion
Der Artikel diskutiert oft verhandelte Probleme der Erstellung eines wissenschaftlich brauchbaren Religionsbegriffs und unterbreitet einen Vorschlag zur Lösung einiger dieser Probleme. In Abgrenzung von Positionen, die von der Entbehrlichkeit eines allgemeinen Religionsbegriffes ausgehen, trägt er zunächst Argumente zusammen, die für die Erarbeitung einer wissenschaftlich verwendbaren Religionsdefinition sprechen. Dann diskutiert er in Religionswissenschaft und Religionssoziologie gebräuchliche Ansätze zur Definition von Religion: substanzielle, funktionalistische und diskursive Ansätze. Schließlich entwirft er einen eigenen Vorschlag zur Religionsdefinition, der substanzielle und funktionalistische Argumente kombiniert und den Anspruch erhebt, definitorische Trennschärfe und Weite miteinander zu verbinden und sowohl an das Selbstverständnis der Religionsangehörigen anzuknüpfen als es auch zu überschreiten.This essay deals with often disputed problems concerning the definition of an academically suitable term of religion and presents a suggestion for the solution of some of these problems. In order to distinguish it from positions that presume the dispensability of a general term of religion it first compiles arguments in favour of the determination of an academically applicable term of religion: substantial, functional and discursive approaches. Finally it formulates an own suggestion for the definition of religion which combines substantial and functional arguments and claims to link the selectivity by definition with a wide spectrum and both to take up the self-conception of the affiliated with a religion and to go beyond it.<br
Timing and Characterization of the Change in the Redox State of Uranium in Precambrian Surface Environments: A Proxy for the Oxidation State of the Atmosphere
The redox-sensitive geochemical behavior of uranium permits the use of Th/U ratios as a geochemical proxy for the oxidation state of the atmosphere and oceans during sedimentary processes. Due to the effects of post-depositional uranium mobility on Th/U ratios during events involving oxygenated fluids, direct measurements of Th/U ratios are often misleading, but the whole rock Pb isotope composition may be used to determine a sample¡¦s apparent time-integrated Th/U ratio (ƒÛa) and the timing associated with the onset of the U-Th-Pb geochemistry. Rare earth element (REE) concentrations were determined by isotope dilution mass spectrometry to evaluate the influence of multiple provenance components and potential mobility of Th, U, and Pb during post-depositional processes on the Th/U ratio. The Pb isotope compositions and REE concentrations were determined for six Paleoproterozoic sedimentary sequences, which were the focus of previous studies involving the timing of the rise of atmospheric oxygen. The Mount McRae Shale, Huronian Supergroup, and Zaonezhskaya Formation have been interpreted as experiencing post-depositional alteration (perhaps associated with orogenic events) due to Pb-Pb ages that are younger than the likely depositional age and observed fractionation of REE in chondrite normalized REE patterns and interelement REE ratios (e.g. La/Nd, La/Yb, Eu/Eu*). Similar geochemical proxies have been interpreted as sedimentary geochemical features of the Timeball Hill Formation, Hotazel Formation, and Sengoma Argillite Formation. This study of Paleoproterozoic sedimentary units constrains the onset of U-Th decoupling, most likely due to the onset of oxidative weathering conditions, began by 2.32 Ga, the latest
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