Grating-assisted non-linear directional coupler based optical switch with reduced critical power

We present a novel design of an optical switch based on grating-assisted non-linear directional coupler (GANDC) which consists of two non-identical waveguides, with a periodic refractive index perturbation in between the waveguides, along the direction of propagation. The proposed design of the optical switch reduces the critical power by a factor ~25, as compared to the conventional non-linear directional coupler-based switch, with potential applications in photonics.     

Experimental and theoretical investigation of forming limit diagram for Ti-6Al-4 V alloy at warm condition

Forming limit diagram (FLD) is an important performance index to describe the maximum limit of principal strains that can be sustained by sheet metals till to the onset of localized necking. It is useful tool to access the forming severity of a drawing or stamping processes. In the present work, FLD has been determined experimentally for Ti-6Al-4 V alloy at 400 °C by conducting a hemispherical dome test with specimens of different widths. Additionally, theoretical FLDs have been determined using Marciniak Kuczynski (M-K) model. Various yield criteria namely: Von Mises, Hill 1948, Hill 1993 and Cazacu Barlat in combination with different hardening models viz., Hollomon power law (HPL), Johnson-Cook (JC), modified Johnson-Cook (m-JC), modified Arrhenius (m-Arr.), modified Zerilli–Armstrong (m-ZA) have been used in M-K analysis for theoretical FLD prediction. The material properties required for determination of yield criteria and hardening models constants have been calculated using uniaxial tensile tests. The predicted theoretical FLDs results are compared with experimental FLD. It can be observed that influence of yield criterion in M-K analysis for theoretical FLD prediction is predominant than the hardening model. Based on the results; it is observed that the theoretical FLD using Cazacu Barlat and Hill 1993 yield criteria with m-Arr. hardening model has a very good agreement with experimental FLD.     

Electric-Field Induced Morphological Transitions in Elastic Contact Instability of Soft Solid Films

A soft elastic film, when placed in adhesive proximity with a contactor in a crack-like geometry, spontaneously undergoes a surface instability to form finger patterns with a characteristic wavelength of approximately 4h, where h is the film thickness. We study the morphological evolution and control of this elastic contact instability under the influence of an external electric field. The distinct electric field induced morphological changes, leading to the formation of two-dimensional hexagonally arranged pillars, large-amplitude fingers, and straightening of contact edge, which are studied comprehensively. The conditions for the evolution of morphologically distinct patterns are governed by the film parameters, such as its shear modulus and thickness. A theoretical model and its stability analysis provide an approximate estimate of the critical voltage required for the onset of changes and its scaling with the film parameters (thickness and shear modulus). Further, three-dimensional simulations based on energy minimization are presented to provide important clues regarding the physics of pattern evolution on soft elastic interfaces.     

Rheograms of cellulosic polymers from the melt flow index

Data on the variation of melt viscosity over a wide range of shear rates and temperatures are necessary in the processing of cellulosic polymers. An effective method has been proposed to estimate the viscosity vs. shear rate flow curves of a cellulosic resin at temperatures relevant to the processing conditions, from its melt flow index and glass transition temperature. The method involves the use of a master curve obtained by coalescing the rheograms of various grades in terms of a modified viscosity, η˙MFI, and a modified shear rate, γ˙/MFI. Master curves have been reported for cellulose esters and ethers.     

Performance analysis of Virtual Mobility Domain scheme vs. IPv6 mobility protocols

The population of mobile users seeking connectivity to the Internet has been growing over the years, spurred by the capabilities of handsets and the increasing rich Internet content and services. Mobility management to enable efficient Internet access for users on the move is thus gaining significance. IETF has standardized several protocols such as Mobile IPv6, Hierarchical Mobile IPv6, and Proxy Mobile IPv6 to provide mobility management on the IP network. With future Internet design initiatives gaining momentum, it is important that these initiatives consider mobility management as an integral part of the design. In this article, we introduce the concept of Virtual Mobility Domain and describe the main features and key strengths of Virtual Mobility Domain that are designed to provide mobility management in a newly proposed tiered Internet architecture. Instead of IP addressing, the proposed Virtual Mobility Domain uses a tiered-addressing scheme to identify a mobile node with a single address regardless of its location. The tiered addressing provides a dynamic address length which brings less signaling overhead and scalable management. We also propose a collaborative network-based mobility management mechanism to provide low-latency handoffs and less processing-overhead on the mobile node compared to the IPv6-based protocols. The proposed mobility scheme unifies inter and intra-domain mobility management by introducing common anchor cloud concept which provides a distributed management and seamless mobility experience. We present comparative qualitative and quantitative performance analysis of Virtual Mobility Domain and aforementioned IPv6-based mobility protocols for Intra-AS roaming support. We examine handoff latency and signaling overhead performance of each protocol based on numerical results retrieved from analytical models and OPNET modeler based simulations. The results from a comparative performance study show the potential for more efficient mobility management under the proposed Internet architecture.     

Categorizing facial expressions: a comparison of computational models

Recognizing expressions is a key part of human social interaction, and processing of facial expression information is largely automatic for humans, but it is a non-trivial task for a computational system. The purpose of this work is to develop computational models capable of differentiating between a range of human facial expressions. Raw face images are examples of high-dimensional data, so here we use two dimensionality reduction techniques: principal component analysis and curvilinear component analysis. We also preprocess the images with a bank of Gabor filters, so that important features in the face images may be identified. Subsequently, the faces are classified using a support vector machine. We show that it is possible to differentiate faces with a prototypical expression from the neutral expression. Moreover, we can achieve this with data that has been massively reduced in size: in the best case the original images are reduced to just 5 components. We also investigate the effect size on face images, a concept which has not been reported previously on faces. This enables us to identify those areas of the face that are involved in the production of a facial expression.     

Sharc: managing CPU and network bandwidth in shared clusters

We argue the need for effective resource management mechanisms for sharing resources in commodity clusters. To address this issue, we present the design of Sharc-a system that enables resource sharing among applications in such clusters. Sharc depends on single node resource management mechanisms such as reservations or shares, and extends the benefits of such mechanisms to clustered environments. We present techniques for managing two important resources-CPU and network interface bandwidth-on a cluster-wide basis. Our techniques allow Sharc to 1) support reservation of CPU and network interface bandwidth for distributed applications, 2) dynamically allocate resources based on past usage, and 3) provide performance isolation to applications. Our experimental evaluation has shown that Sharc can scale to 256 node clusters running 100,000 applications. These results demonstrate that Sharc can be an effective approach for sharing resources among competing applications in moderate size clusters.     

Guest Editors' Introduction: Dynamic Information Dissemination

Dissemination and delivery of rapidly changing information to large user communities remains a challenge on the Web. Consequently, we need techniques to disseminate such data as efficiently as possible. To this end, researchers are focusing on new approaches to building efficient, resilient, and scalable content-distribution networks.