Three dimensional (3D) microstructure-based modeling of interfacial decohesion in particle reinforced metal matrix composites

Modeling and prediction of the overall elastic–plastic response and local damage mechanisms in heterogeneous materials, in particular particle reinforced composites, is a very complex problem. Microstructural complexities such as the inhomogeneous spatial distribution of particles, irregular morphology of the particles, and anisotropy in particle orientation after secondary processing, such as extrusion, significantly affect deformation behavior. We have studied the effect of particle/matrix interface debonding in SiC particle reinforced Al alloy matrix composites with (a) actual microstructure consisting of angular SiC particles and (b) idealized ellipsoidal SiC particles. Tensile deformation in SiC particle reinforced Al matrix composites was modeled using actual microstructures reconstructed from serial sectioning approach. Interfacial debonding was modeled using user-defined cohesive zone elements. Modeling with the actual microstructure (versus idealized ellipsoids) has a significant influence on: (a) localized stresses and strains in particle and matrix, and (b) far-field strain at which localized debonding takes place. The angular particles exhibited higher degree of load transfer and are more sensitive to interfacial debonding. Larger decreases in stress are observed in the angular particles, because of the flat surfaces, normal to the loading axis, which bear load. Furthermore, simplification of particle morphology may lead to erroneous results

Distortion-Memory Tradeoffs in Cache-Aided Wireless Video Delivery

Mobile network operators are considering caching as one of the strategies to keep up with the increasing demand for high-definition wireless video streaming. By prefetching popular content into memory at wireless access points or end user devices, requests can be served locally, relieving strain on expensive backhaul. In addition, using network coding allows the simultaneous serving of distinct cache misses via common coded multicast transmissions, resulting in significantly larger load reductions compared to those achieved with conventional delivery schemes. However, prior work does not exploit the properties of video and simply treats content as fixed-size files that users would like to fully download. Our work is motivated by the fact that video can be coded in a scalable fashion and that the decoded video quality depends on the number of layers a user is able to receive. Using a Gaussian source model, caching and coded delivery methods are designed to minimize the squared error distortion at end user devices. Our work is general enough to consider heterogeneous cache sizes and video popularity distributions.Comment: To appear in Allerton 2015 Proceedings of the 53rd annual Allerton conference on Communication, control, and computin

The approximate f-core and the utopia payoff for infinite assignment games

Assignment problems where both sets of agents are countably infinite, the so-called infinite assignment problems, are studied as well as the related assignment games. Further, two solutions for these games are studied. The first one is the approximate f-core for games with a finite value. This particular solution takes into account that due to organisational limitations only finite groups of agents can protest against proposals of profit distributions. Second, we study the utopia payoff, the perfect proposal in which each agent receives the maximal amount he can get. \u

Purificació catalítica d'hidrogen en microcanals

En aquest treball mostrem el funcionament d'un microdispositiu catalític dissenyat al nostre grup de recerca per purificar de manera catalítica i selectiva monòxid de carboni en presència d'hidrogen. Hem aconseguit desenvolupar un mètode per recobrir amb èxit els seus canals, d'entre 2 i 4 μm de diàmetre, amb una capa homogènia d'òxid de titani de només uns 100 nm de gruix. Sobre aquesta fina capa s'han ancorat unes nanopartícules d'or innovadores embolcallades amb lligands rics en silici que presenten una gran estabilitat i activitat per oxidar selectivament el monòxid de carboni (CO-PrOx) en un rang de temperatures comprès entre els 363 i els 473 K. El microreactor representa una intensificació del procés d'oxidació selectiva de CO i, gràcies a la reducció d'escala obtinguda en aquesta microestructura (en comparació amb reactors de parets catalítiques convencionals), s'han obtingut activitats específiques (quantitat de CO convertit per unitat de volum de reactor) cent vegades majors treballant a la mateixa temperatura i amb les mateixes mescles d'alimentació. Així, doncs, el microreactor desenvolupat resulta molt atractiu per realitzar la reacció de CO-PrOx a microescala i per ser combinat amb una etapa de reformació prèvia. L'acoblament d'ambdós processos per alimentar piles de combustible de baixa temperatura ofereix noves possibilitats dins del món de la tecnologia del vector hidrogen i, en concret, per a aplicacions de petita escala i portàtils.This paper describes the operation of a catalytic microdevice designed by our research group to catalytically and selectively purify carbon monoxide in the presence of hydrogen. We have developed a method of successfully coating channels of only 2-4 μm in diameter with a homogenous 100 nm-thick titanium oxide layer. Novel gold nanoparticles protected with a Si-rich shell have been anchored onto this thin layer. The gold nanoparticles show great stability and activity in preferentially oxidizing carbon monoxide (CO-PrOx) in a temperature range of 363 to 473 K. The microreactor intensifies the CO selective oxidation process. Due to the scale reduction achieved in this structure (compared to conventional catalytic wall reactors), specific activities (amount of converted CO per reactor volume) that are 100 times larger were obtained, operating at the same temperature level and with the same feed mixtures. Consequently, this microreactor is very interesting for performance of the CO-PrOx reaction at microscale and for combination with a preliminary reforming stage. The connection of both processes to feed low-temperature fuel cells offers new possibilities in hydrogen technology and, particularly, in small-scale and portable applications