353 research outputs found
Sublinear Estimation of Weighted Matchings in Dynamic Data Streams
This paper presents an algorithm for estimating the weight of a maximum
weighted matching by augmenting any estimation routine for the size of an
unweighted matching. The algorithm is implementable in any streaming model
including dynamic graph streams. We also give the first constant estimation for
the maximum matching size in a dynamic graph stream for planar graphs (or any
graph with bounded arboricity) using space which also
extends to weighted matching. Using previous results by Kapralov, Khanna, and
Sudan (2014) we obtain a approximation for general graphs
using space in random order streams, respectively. In
addition, we give a space lower bound of for any
randomized algorithm estimating the size of a maximum matching up to a
factor for adversarial streams
Effect of Web Opening Location on Fatigue Assessment of H Section Steel Beams
In the last decades, steel beams with web opening were used extensively as useful structural and architectural elements due to their many advantages. In this research, steel beams with web opening subjected to static loading were modelled using the multi-purpose finite element software ANSYS and the finite element results were compared with previous research. Then, steel beams with a single web opening subjected to fatigue loading were investigated numerically. The effect of changing the location of web opening on the fatigue assessment of H section steel beams with web opening was studied taking normal stress into account. It was clear that, normal stress fatigue life of the steel beams was affected significantly by changing web opening location along the beam span when compared to a beam with solid web while the beam span, opening size and steel section were kept constant. The most convenient location of web opening along the beam span was found to be at mid span
Nafion®/poly(vinyl alcohol) blends: effect of composition and annealing temperature on transport properties
Journal of Membrane Science, 282(1-2): pp. 217-224. http://www.elsevier.com/wps/find/journaldescription.cws_home/502692/description?navopenmenu=1In this study, the transport properties (proton conductivity and methanol permeability) of Nafion® 117, solution-cast Nafion®, poly(vinyl alcohol) (PVA), and Nafion®/PVA blend membranes were measured as a function of annealing temperature (60-250oC) and blend composition for application to the direct methanol fuel cell (DMFC). A Nafion®/PVA blend membrane at 5 wt% PVA (annealed at 230oC) resulted in similar proton conductivity, but 3 times lower methanol permeability compared to Nafion® 117. In addition, an unusual trend was observed in Nafion®/PVA (50 wt% PVA) blend membranes, where proton conductivity remained relatively constant, but methanol permeability decreased by approximately one order of magnitude with increasing annealing temperature. Infrared spectroscopy reveals a band shift in the hydroxyl peak to higher wavenumbers in Nafion®/PVA blends (25-90 wt% PVA) with increasing annealing temperature suggesting an increase in the interaction between the hydroxyl groups in PVA and the sulfonic acid groups in Nafion®. For Nafion® alone, proton and methanol transport rates increased and then decreased with increasing annealing temperature with a maximum at 210oC for both solution-cast and as-received (extruded) Nafion®. This trend coincides with two transition temperatures observed by other investigators using differential scanning calorimetry, suggesting that transport properties are affected by morphological changes in Nafion®
Optimization of Reduction Process of Egyptian Ilmenitevia Metallothermic reactions
It is important to develop technologies for the production of master alloys for industrial applications. Detailed research on reduction of titanium from Egyptian ilmenite by an aluminothermic process in a graphite Crucible was charged by the mixture of ilmenite, flux, aluminum was investigated. This paper study the effect of aluminum feed (10%- 35%), flux material (type, and amount), and temperature preheat from 50 oC to 400 oC and time of preheating from 0.5 hr. to 3 hrs. Then, the metallic samples formed by the reduction were analyzed using X-ray diffraction, scanning electron microscopy. The mixed fluxes were strongly and successfully reduced ilmenite to a high-purity master alloy with small amounts of detected impurities. Key words: Aluminothermic, Egyptian ilmenite, flux, ferrotitanium, master alloy DOI: 10.7176/CMR/11-7-04 Publication date:September 30th 2019
Inter-arrival times of message propagation on directed networks
One of the challenges in fighting cybercrime is to understand the dynamics of
message propagation on botnets, networks of infected computers used to send
viruses, unsolicited commercial emails (SPAM) or denial of service attacks. We
map this problem to the propagation of multiple random walkers on directed
networks and we evaluate the inter-arrival time distribution between successive
walkers arriving at a target. We show that the temporal organization of this
process, which models information propagation on unstructured peer to peer
networks, has the same features as SPAM arriving to a single user. We study the
behavior of the message inter-arrival time distribution on three different
network topologies using two different rules for sending messages. In all
networks the propagation is not a pure Poisson process. It shows universal
features on Poissonian networks and a more complex behavior on scale free
networks. Results open the possibility to indirectly learn about the process of
sending messages on networks with unknown topologies, by studying inter-arrival
times at any node of the network.Comment: 9 pages, 12 figure
Revisiting the Direct Sum Theorem and Space Lower Bounds in Random Order Streams
Estimating frequency moments and distances are well studied problems in the adversarial data stream model and tight space bounds are known for these two problems. There has been growing interest in revisiting these problems in the framework of random-order streams. The best space lower bound known for computing the frequency moment in random-order streams is by Andoni et al., and it is conjectured that the real lower bound shall be . In this paper, we resolve this conjecture. In our approach, we revisit the direct sum theorem developed by Bar-Yossef et al. in a random-partition private messages model and provide a tight space lower bound for any -pass algorithm that approximates the frequency moment in random-order stream model to a constant factor. Finally, we also introduce the notion of space-entropy tradeoffs in random order streams, as a means of studying intermediate models between adversarial and fully random order streams. We show an almost tight space-entropy tradeoff for distance and a non-trivial tradeoff for distances
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Triply resonant coupled-cavity electro-optic modulators for RF to optical signal conversion
We propose an on-chip triply resonant electro-optic modulator architecture for RF-to-optical signal conversion and provide a detailed theoretical analysis of the optimal "circuit-level" device geometries and their performance limits. The designs maximize the RF-optical conversion efficiency through simultaneous resonant enhancement of the RF drive signal, a continuous-wave (CW) optical pump, and the generated optical sideband. The optical pump and sideband are resonantly enhanced in respective supermodes of a two-coupled-cavity optical resonator system, while the RF signal can be enhanced in addition by an LC circuit formed by capacitances of the optical resonator active regions and (integrated) matching inductors. We show that such designs can offer 15-50 dB improvement in conversion efficiency over conventional microring modulators. In the proposed configurations, the photon lifetime (resonance linewidth) limits the instantaneous RF bandwidth of the electro-optic response but does not limit its central RF frequency. The latter is set by the coupling strength between the two coupled cavities and is not subject to the photon lifetime constraint inherent to conventional singly resonant microring modulators. This feature enables efficient operation at high RF carrier frequencies without a reduction in efficiency commonly associated with the photon lifetime limit and accounts for 10-30 dB of the total improvement. Two optical configurations of the modulator are proposed: a "basic" configuration with equal Q-factors in both supermodes, most suitable for narrowband RF signals, and a "generalized" configuration with independently tailored supermode Q-factors that supports a wider instantaneous bandwidth. A second significant 5-20 dB gain in modulation efficiency is expected from RF drive signal enhancement by integrated LC resonant matching, leading to the total expected improvement of 15-50 dB. Previously studied triply-resonant modulators, with coupled longitudinal [across the free spectral range (FSR)] modes, have large resonant mode volume for typical RF frequencies, which limits the interaction between the optical and RF fields. In contrast, the proposed modulators support maximally tightly confined resonant modes, with strong coupling between the mode fields, which increases and maintains high device efficiency across a range of RF frequencies. The proposed modulator architecture is compact, efficient, capable of modulation at high RF carrier frequencies and can be applied to any cavity design or modulation mechanism. It is also well suited to moderate Q, including silicon, implementations, and may be enabling for future CMOS RF-electronic-photonic systems on chip.</p
Adversary lower bounds for nonadaptive quantum algorithms
International audienceWe present general methods for proving lower bounds on the query complexity of nonadaptive quantum algorithms. Our results are based on the adversary method of Ambainis
Priority diffusion model in lattices and complex networks
We introduce a model for diffusion of two classes of particles ( and )
with priority: where both species are present in the same site the motion of
's takes precedence over that of 's. This describes realistic situations
in wireless and communication networks. In regular lattices the diffusion of
the two species is normal but the particles are significantly slower, due
to the presence of the particles. From the fraction of sites where the
particles can move freely, which we compute analytically, we derive the
diffusion coefficients of the two species. In heterogeneous networks the
fraction of sites where is free decreases exponentially with the degree of
the sites. This, coupled with accumulation of particles in high-degree nodes
leads to trapping of the low priority particles in scale-free networks.Comment: 5 pages, 3 figure
Non-locality and Communication Complexity
Quantum information processing is the emerging field that defines and
realizes computing devices that make use of quantum mechanical principles, like
the superposition principle, entanglement, and interference. In this review we
study the information counterpart of computing. The abstract form of the
distributed computing setting is called communication complexity. It studies
the amount of information, in terms of bits or in our case qubits, that two
spatially separated computing devices need to exchange in order to perform some
computational task. Surprisingly, quantum mechanics can be used to obtain
dramatic advantages for such tasks.
We review the area of quantum communication complexity, and show how it
connects the foundational physics questions regarding non-locality with those
of communication complexity studied in theoretical computer science. The first
examples exhibiting the advantage of the use of qubits in distributed
information-processing tasks were based on non-locality tests. However, by now
the field has produced strong and interesting quantum protocols and algorithms
of its own that demonstrate that entanglement, although it cannot be used to
replace communication, can be used to reduce the communication exponentially.
In turn, these new advances yield a new outlook on the foundations of physics,
and could even yield new proposals for experiments that test the foundations of
physics.Comment: Survey paper, 63 pages LaTeX. A reformatted version will appear in
Reviews of Modern Physic
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