38,265 research outputs found
Nanomechanical detection of the spin Hall effect
The spin Hall effect creates a spin current in response to a charge current
in a material that has strong spin-orbit coupling. The size of the spin Hall
effect in many materials is disputed, requiring independent measurements of the
effect. We develop a novel mechanical method to measure the size of the spin
Hall effect, relying on the equivalence between spin and angular momentum. The
spin current carries angular momentum, so the flow of angular momentum will
result in a mechanical torque on the material. We determine the size and
geometry of this torque and demonstrate that it can be measured using a
nanomechanical device. Our results show that measurement of the spin Hall
effect in this manner is possible and also opens possibilities for actuating
nanomechanical systems with spin currents.Comment: 5 pages + 2 pages supplementary material, 4 figures tota
Exploiting replication in distributed systems
Techniques are examined for replicating data and execution in directly distributed systems: systems in which multiple processes interact directly with one another while continuously respecting constraints on their joint behavior. Directly distributed systems are often required to solve difficult problems, ranging from management of replicated data to dynamic reconfiguration in response to failures. It is shown that these problems reduce to more primitive, order-based consistency problems, which can be solved using primitives such as the reliable broadcast protocols. Moreover, given a system that implements reliable broadcast primitives, a flexible set of high-level tools can be provided for building a wide variety of directly distributed application programs
Reliable broadcast protocols
A number of broadcast protocols that are reliable subject to a variety of ordering and delivery guarantees are considered. Developing applications that are distributed over a number of sites and/or must tolerate the failures of some of them becomes a considerably simpler task when such protocols are available for communication. Without such protocols the kinds of distributed applications that can reasonably be built will have a very limited scope. As the trend towards distribution and decentralization continues, it will not be surprising if reliable broadcast protocols have the same role in distributed operating systems of the future that message passing mechanisms have in the operating systems of today. On the other hand, the problems of engineering such a system remain large. For example, deciding which protocol is the most appropriate to use in a certain situation or how to balance the latency-communication-storage costs is not an easy question
Inhibition Effect of Vernonia amygdalina Extract on the Corrosion of Mild Steel Reinforcement in Concrete in 3.5M NaCl Environment
The inhibition effect of Vernonia amygdalina (bitter leaf) extract on the corrosion behaviour of embedded mild steel rebar in concrete has been investigated by electrochemical potential measurement, pH and gravimetric (weight loss) methods. The results were further analysed using the two-factor ANOVA test. The experiments were performed using bitter leaf extract as a green inhibitor in 3.5% sodium chloride solution. Inhibitor extracts concentrations of 25, 50 75, and 100% were prepared from the fresh leaves of Vernonia amygdalina with distilled water. The voltage (potential) measurements were recorded with a digital voltmeter and a copper-copper sulphate electrode as the reference electrode. The pH of the test medium was measured by a pH meter. Compressive strength of each of the block samples was determined after the experiments. Weight loss values were obtained from the weight loss method (gravimetric) and the inhibitor efficiency was computed from the corrosion rate of each of the tested samples. Results showed that varied concentration of Vernonia amygdalina and the test exposure time significantly affect both the corrosion potential of embedded steel rebar in concrete and the pH of the medium. The outcome of the ANOVA test confirmed the results at 95 % confidence, and further showed that concentration of Vernonia amygdalina had greater effect on potential measurements, whereas, exposure time had greater effect on pH measurements. Vernonia amygdalina extract gave good corrosion inhibition performance of the embedded steel rebar in concrete at 25%, 50% and 75% concentrations in NaCl test medium. The highest inhibition efficiency of 90.08 % was achieved at 25% concentration, the lowest inhibitor concentration used
A Possible Resolution of the Black Hole Information Puzzle
The problem of information loss is considered under the assumption that the
process of black hole evaporation terminates in the decay of the black hole
interior into a baby universe. We show that such theories can be decomposed
into superselection sectors labeled by eigenvalues of the third-quantized baby
universe field operator, and that scattering is unitary within each
superselection sector. This result relies crucially on the quantum-mechanical
variability of the decay time. It is further argued that the decay rate in the
black hole rest frame is necessarily proportional to , where
is the total entropy produced during the evaporation process,
entailing a very long-lived remnant.Comment: 15 pages, 3 uuencoded figures. Revised version contains some
notational simplification
Very Long Baseline Array Imaging of Type-2 Seyferts with Double-Peaked Narrow Emission Lines: Searches for Sub-kpc Dual AGNs and Jet-Powered Outflows
This paper presents Very Long Baseline Array (VLBA) observations of 13
double-peaked [O III] emission-line type-2 Active Galactic Nuclei (AGNs) at
redshifts 0.06 < z < 0.41 (with a median redshift of z~0.15) identified in the
Sloan Digital Sky Survey. Such double-peaked emission-line objects may result
from jets or outflows from the central engine or from a dual AGN. The VLBA
provides an angular resolution of <~10 pc at the distance of many of these
galaxies, sufficient to resolve the radio emission from extremely close dual
AGNs and to contribute to understanding the origin of double-peaked [O III]
emission lines. Of the 13 galaxies observed at 3.6 cm (8.4 GHz), we detect six
at a 1\sigma\ sensitivity level of ~0.15 mJy/beam, two of which show clear jet
structures on scales ranging from a few milliarcseconds to tens of
milliarcseconds (corresponding to a few pc to tens of pc at a median redshift
of 0.15). We suggest that radio-loud double-peaked emission-line type-2 AGNs
may be indicative of jet produced structures, but a larger sample of
double-peaked [O III] AGNs with high angular resolution radio observations will
be required to confirm this suggestion.Comment: 14 pages, 7 figures; ApJ in pres
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