69,126 research outputs found
Duty cycle testing and performance evaluation of the SM-229 teleoperator
The first known experimental studies and analyses of teleoperator performance for specific duty cycles are discussed. The results are presented in two distinct areas as position usage patterns, and as three-dimensional power grids. The position usage patterns are a valuable means to assess the available motion range. The power grids are a unique concept for evaluating joint performance. Final conclusions contain recommendations to upgrade the teleoperator for optimum performance
Symmetry causes a huge conductance peak in double quantum dots
We predict a huge interference effect contributing to the conductance through
large ultra-clean quantum dots of chaotic shape. When a double-dot structure is
made such that the dots are the mirror-image of each other, constructive
interference can make a tunnel barrier located on the symmetry axis effectively
transparent. We show (via theoretical analysis and numerical simulation) that
this effect can be orders of magnitude larger than the well-known universal
conductance fluctuations and weak-localization (both less than a conductance
quantum). A small magnetic field destroys the effect, massively reducing the
double-dot conductance; thus a magnetic field detector is obtained, with a
similar sensitivity to a SQUID, but requiring no superconductors.Comment: 5pages 3 figures and an appendix ONLY in arXiv versio
Engineering an all-optical route to ultracold molecules in their vibronic ground state
We propose an improved photoassociation scheme to produce ultracold molecules
in their vibronic ground state for the generic case where non-adiabatic effects
facilitating transfer to deeply bound levels are absent. Formation of molecules
is achieved by short laser pulses in a Raman-like pump-dump process where an
additional near-infrared laser field couples the excited state to an auxiliary
state. The coupling due to the additional field effectively changes the shape
of the excited state potential and allows for efficient population transfer to
low-lying vibrational levels of the electronic ground state. Repetition of many
pump-dump sequences together with collisional relaxation allows for
accumulation of molecules in v=0.Comment: Phys. Rev. A, in pres
A tour of bordered Floer theory
Heegaard Floer theory is a kind of topological quantum field theory,
assigning graded groups to closed, connected, oriented 3-manifolds and group
homomorphisms to smooth, oriented 4-dimensional cobordisms. Bordered Heegaard
Floer homology is an extension of Heegaard Floer homology to 3-manifolds with
boundary, with extended-TQFT-type gluing properties. In this survey, we explain
the formal structure and construction of bordered Floer homology and sketch how
it can be used to compute some aspects of Heegaard Floer theory.Comment: 13 pages, 7 figure
Environmental fatigue of an Al-Li-Cu alloy. Part 1: Intrinsic crack propagation kinetics in hydrogenous environments
Deleterious environmental effects on steady-state, intrinsic fatigue crack propagation (FCP) rates (da/dN) in peak aged Al-Li-Cu alloy 2090 are established by electrical potential monitoring of short cracks with programmed constant delta K and K(sub max) loading. The da/dN are equally unaffected by vacuum, purified helium, and oxygen but are accelerated in order of decreasing effectiveness by aqueous 1 percent NaCl with anodic polarization, pure water vapor, moist air, and NaCl with cathodic polarization. While da/dN depends on delta K(sup 4.0) for the inert gases, water vapor and chloride induced multiple power-laws, and a transition growth rate 'plateau'. Environmental effects are strongest at low delta K. Crack tip damage is ascribed to hydrogen embrittlement because of the following: (1) accelerated da/dN due to part-per-million levels of H2O without condensation; (2) impeded molecular flow model predictions of the measured water vapor pressure dependence of da/dN as affected by mean crack opening; (3) the lack of an effect of film-forming O2; (4) the likelihood for crack tip hydrogen production in NaCl, and (5) the environmental and delta K-process zone volume dependencies of the microscopic cracking modes. For NaCl, growth rates decrease with decreasing loading frequency, with the addition of passivating Li2CO3, and upon cathodic polarization. These variables increase crack surface film stability to reduce hydrogen entry efficiency. The hydrogen environmental FCP resistance of 2090 is similar to other 2000 series alloys and is better than 7075
Bordered Floer homology and the spectral sequence of a branched double cover II: the spectral sequences agree
Given a link in the three-sphere, Ozsv\'ath and Szab\'o showed that there is
a spectral sequence starting at the Khovanov homology of the link and
converging to the Heegaard Floer homology of its branched double cover. The aim
of this paper is to explicitly calculate this spectral sequence in terms of
bordered Floer homology. There are two primary ingredients in this computation:
an explicit calculation of bimodules associated to Dehn twists, and a general
pairing theorem for polygons. The previous part (arXiv:1011.0499) focuses on
computing the bimodules; this part focuses on the pairing theorem for polygons,
in order to prove that the spectral sequence constructed in the previous part
agrees with the one constructed by Ozsv\'ath and Szab\'o.Comment: 85 pages, 19 figures, v3: Version to appear in Journal of Topolog
Investigation of Heat Transfer From
The convective heat transfer from the surface of an ellipsoidal forebody of fineness ratio 3 and 20-inch maximum diameter was investigated in clear air for both stationary and rotating operation over a range of conditions including air speeds up to 240 knots, rotational speeds up to 1200 rpm, and angles of attack of 0 deg, 3 deg, and 6 deg. The results are presented in the form of heat-transfer coefficients and the correlation of Nusselt and Reynolds numbers. Both a uniform surface temperature and a uniform input heater density distribution were used. The experimental results agree well with theoretical predictions for uniform surface temperature distribution. Complete agreement was not obtained with uniform input heat density in the laminar-flow region because of conduction effects. No significant effects of rotation were obtained over the range of airstream and rotational speeds investigated. Operation at angle of attack had only minor effects on the local heat transfer. Transition from laminar to turbulent heat transfer occurred over a wide range of Reynolds numbers. The location of transition depended primarily on surface roughness and pressure and temperature gradients. Limited transient heating data indicate that the variation of surface temperature with time followed closely an exponential relation
The Astronomy of the Kamilaroi People and their Neighbours
The Kamilaroi people and their neighbours, the Euahlayi, Ngemba, and
Murrawarri, are an Aboriginal cultural grouping located in the northwest and
north central of New South Wales. They have a rich history, but have been
missed in much of the literature concerned with sky knowledge in culture. This
study collected stories, some of which have not previously been reported in an
academic format, from Aboriginal people practicing their culture, augmented
with stories from the literature, and analysed the data to create a database of
sky knowledge that will be added to the larger body of Aboriginal cultural
knowledge in Australia. We found that there is a strong sky culture reflected
in the stories, and we also explored the stories for evidence of an
ethnoscientific approach to knowledge of the sky.Comment: 28 pages, 9 figure
Heegaard Floer homology as morphism spaces
In this paper we prove another pairing theorem for bordered Floer homology.
Unlike the original pairing theorem, this one is stated in terms of
homomorphisms, not tensor products. The present formulation is closer in spirit
to the usual TQFT framework, and allows a more direct comparison with
Fukaya-categorical constructions. The result also leads to various dualities in
bordered Floer homology.Comment: 57 pages, 14 figures; v2: many updates, including changing
orientation conventions, which changed the signs in many theorem
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