Design of laminated composite structures for optimum fiber direction and layer thickness,using optimality criteria

In this study, two optimality criteria are presented for optimum design of composite laminates using finite element method. Thickness of the layers and fiber orientation angles in each finite element are considered as the design variables. It will be shown that the optimum design of composite laminates with varying fiber orientations and layers thicknesses may be found by using these optimality criteria in an efficient way, without performing the sensitivity analysis.     

SYMBOLIC COMPUTATION OF ROBOT DYNAMIC PARAMETERS

Optimal performance of robot manipulators can be achieved only by utilizing advanced control algorithms. However, precise control of robot motion requires the use of accurate dynamic models, which are very complicated due to varying arm geometric configuration, uncertain effects of load handling on the dynamic stability of the arm, and the high degree of nonlinearty and coupling exhibited between different links. Therefore, an efficient and fast method for on-line tuning of robot dynamic parameters must be devised. In this work a simplified model based on Lagrange-Euler dynamics is developed. The proposed method is simple and systematic for the extraction and identification of robot dynamic parameters. The dynamic parameters are then formulated as a regression model. This model is used to generate the closed-form solution of the dynamics. The analysis in this work is based on a set of compiled data for the Stanford arm to facilitate the study of the dynamic performance and closed-loop solutions of robot manipulators. For the derivation of the dynamics MAPLE (symbolic computer algebra language) is used.     

Access and service convergence over the mobile internet – A survey

Next generation heterogeneous wireless networks are expected to interwork with Internet Protocol (IP)-based infrastructures. Conventional network services operate like silos in that a specific set of services are offered over a specific type of access network. It is desirable for users to be able to roam between fixed and mobile networks that employ different access technologies. Therefore, mobility management with quality of service (QoS) support is of particular importance and one of the driving forces of convergence. Since service providers often provide more than one service to their subscribers, it is important to facilitate convergence of network charging architecture through a common charging framework. One of the main issues of IP-based convergence is security and privacy. This requires coordination of different security policies in diverse networks that have different security levels and capabilities. The business case for migration to an IP-based platform motivates operators to deliver more powerful services for customers as well as a better user experience. This paper provides an overview of converged mobile Internet architectures and their implications on QoS, charging/billing and security, as well as emerging business models for telecommunication services.     

Automatic detection of depression symptoms in twitter using multimodal analysis

The Journal of Supercomputing - Depression is the most prevalent mental disorder that can lead to suicide. Due to the tendency of people to share their thoughts on social platforms, social data...     

Population variation in genetic programming

A new population variation approach is proposed, whereby the size of the population is systematically varied during the execution of the genetic programming process with the aim of reducing the computational effort compared with standard genetic programming (SGP). Various schemes for altering population size under this proposal are investigated using a comprehensive range of standard problems to determine whether the nature of the “population variation”, i.e. the way the population is varied during the search, has any significant impact on GP performance. The initial population size is varied in relation to the initial population size of the SGP such that the worst case computational effort is never greater than that of the SGP. It is subsequently shown that the proposed population variation schemes do have the capacity to provide solutions at a lower computational cost compared with the SGP.     

(Approximate) Uncertain Skylines

Given a set of points with uncertain locations, we consider the problem of computing the probability of each point lying on the skyline, that is, the probability that it is not dominated by any other input point. If each point’s uncertainty is described as a probability distribution over a discrete set of locations, we improve the best known exact solution. We also suggest why we believe our solution might be optimal. Next, we describe simple, near-linear time approximation algorithms for computing the probability of each point lying on the skyline. In addition, some of our methods can be adapted to construct data structures that can efficiently determine the probability of a query point lying on the skyline.     

Formation control of VTOL UAV vehicles under switching-directed interaction topologies with disturbance rejection

This paper addresses the adaptive formation control of a group of vertical take-off and landing (VTOL) unmanned aerial vehicles (UAV) with switching-directed interaction topologies. In addition, to tackle the adverse effect of disturbances, a couple of smooth bounded estimators are involved in the procedure design. Exploiting an extraction algorithm, we take advantage of the fully actuated rotational dynamics, to control the translational dynamics of each vehicle. We propose a distributed control scheme such that all vehicles track a desired reference velocity signal while keeping a desired prespecified formation. In this framework, the underlying topology of the agents may switch among several directed graphs, each having a spanning tree. The stability of the overall closed-loop system is proved through Lyapunov function. Finally, simulation results are given to better highlight the effectiveness of the proposed control scheme.     

Dynamic Connectivity for Axis-Parallel Rectangles

In this paper we give a fully dynamic data structure to maintain the connectivity of the intersection graph of n axis-parallel rectangles. The amortized update time (insertion and deletion of rectangles) is and the query time (deciding whether two given rectangles are connected) is O(1). It slightly improves the update time (O(n ^0.94)) of the previous method while drastically reducing the query time (near O(n ^1/3)). In addition, our method does not use fast matrix multiplication results and supports a wider range of queries. This work has been supported by an NSERC grant.     

Thermal management modeling for cylindrical lithium-ion battery packs considering safety and lifespan

Journal of Mechanical Science and Technology - Different battery thermal management (BTM) for a 18650 cylindrical Li-ion battery pack were simulated based on the lumped model. Phase change material...     

Molecular simulations of the solubility of gases in polyethylene below its melting temperature

We have employed Monte Carlo simulations in the osmotic ensemble to study the solubility of three different gases (N₂, CH₄, CO₂) in polyethylene. The simulations are performed at temperatures below the polymer melting point. Although under such conditions, polyethylene is in a semicrystalline state, we have used simulation boxes containing only a purely amorphous material. We show that under such circumstances, computed solubilities are 4-5 times larger than experimental data. We therefore introduce an original use of the osmotic ensemble to implicitly account for the effects of the complex morphology of semicrystalline materials on gas solubility. We have made the assumption that i) the network formed by polymer chains trapped between different crystallites and ii) the changes in local density from crystalline regions to purely amorphous regions, may be both represented by an ad-hoc constraint exerted on the amorphous phase. A single constraint value emerges, independent of the gas nature, characteristic of the crystalline degree of the polymer. It is concluded that the role of this constraint is mostly to reproduce the effective density of the permeable phase of the real material, indirectly giving insights into the morphology of a semicrystalline polymer.