Web Server Performance Modeling

The advent of Web technology has made Web servers core elements of future communication networks. Although the amount of traffic that Web servers must handle has grown explosively during the last decade, the performance limitations and the proper tuning of Web servers are still not well understood. In this paper we present an end-to-end queueing model for the performance of Web servers, encompassing the impacts of client workload characteristics, server harware/software configuration, communication protocols, and interconnect topologies. The model has been implemented in a simulation tool, and performance predictions based on the model are shown to match very well with the performance of a Web server in a test lab environment. The simulation tool forms an excellent basis for development of a Decision Support System for the configuration tuning and sizing of Web servers.     

EFFECTIVE IMPLEMENTATION OF CONSERVATIVE MODEL BASED CONTROL ALGORITHM

Recently a digital control algorithm, known as Conservative Model Based Controller (CMBC) with superior performance compared to many other currently popular controllers was discussed in the literature. It provides offset-free performance; however a large number of terms will have to be included in the algorithm to achieve this. This paper describes two modifications to ensure zero offset with limited number of terms in the algorithm. These modifications are evaluated through simulation by considering a few typical first order with dead time (FODT) processes. Both modifications provide offset-free performance, and either could be employed depending on the nature of the process response data on hand.     

Time tick based method for measuring static errors of ADC

This paper presents a novel Time Tick based Built In Self Test (TT BIST) for measuring the static errors of an Analog to Digital Converter (ADC). The proposed method determines the period elapsed during transition between two consecutive digital levels and compares it with the ideal period of transition. A counter that works, at higher speed relative to the sampling rate of the ADC under test, is used. It counts the number of time ticks occurred during every transition. The required ramp signal is generated dynamically, using current source with digital switch for selecting the equivalent test signal. Further to support testing of errors in ratiometric ADC, a slope conditioning module is also implemented. The entire computation cycle is done in a single ramp cycle whereas in conventional histogram method multiple waveforms are required. Thus, the proposed TT method requires less time to achieve desired accuracy levels by choosing the appropriate slope of the ramp signal.     

Generalized Universal Reynolds Equation for Variable Properties Fluid-Film Lubrication and Variable Geometry Self-Acting Bearings

The present article represents a theoretical further development of Dowson's equation (1). The developments presented herein start from the fundamental Dowson concept and proceed to a final generalization, which, by using a spherical coordinate system, accounts for the previously neglected curvature effect. The generalization brought about by this system of coordinates allows the derivation of the Generalized Universal Reynolds Equation (GURE) to best suit liquid and gas film lubrication, with variable properties. This single equation can now be customized by a simple change in angle, allowing all common classes of self-acting bearings to be modeled. Dowson's development in Cartesian coordinates lends itself only to geometries of small curvatures when compared to the film thickness and thus can be unwrapped. GURE's flexibility of spherical coordinates eliminates the minimal curvature assumption for Cartesian geometries. GURE provides a single-equation approach to cylindrical journal bearings, flat-plate thrust bearings, and conical and spherical bearings.     

Analysis of ARROW Waveguide Based Microcantilever for Sensing Application

Wireless Personal Communications - Analysis of microcantilever beam and anti-resonant reflecting optical waveguide (ARROW) microcantilever waveguides are presented in this work. The silicon nitride...     

Energy‐efficient resource allocation for device‐to‐device communication through noncooperative game theory

Wireless network with high data rate applications has seen a rapid growth in recent years. This improved quality of service (QoS) leads to huge energy consumption in wireless network. Therefore, in order to have an energy‐efficient resource allocation in cellular system, a device‐to‐device (D2D) communication is the key component to improve the QoS. In this paper, we propose a noncooperative game (NCG) theory approach for resource allocation to improve energy efficiency (EE) of D2D pair. A three‐tier network with macrocell base station (MBS), femtocell base station (FBS), and D2D pair is considered, which shares the uplink resource block. A resource allocation strategy with constraints is arrived, which maintains minimum throughput for each user in the network. The proposed resource allocation strategy optimizes the EE of D2D pair in the three‐tier network, which achieves Nash equilibrium (NE) and Pareto optimality (PO). Simulation results validate that EE is uniform and optimum for all D2D pair, which converges to NE when channel is static and it converges to PO when the channel is dynamic.     

A Novel Coverage Improved Deployment Strategy for Wireless Sensor Network

Coverage of the bounded region gets importance in Wireless Sensor Network (WSN). Area coverage is based on effective surface coverage with a minimum number of sensor nodes. Most of the researchers contemplate the coverage region of interest as a square and manifest the radio ranges as a circle. The area of a circle is much higher than the area of a square because of the perimeter. To utilize the advantage of the circle, the coverage region of interest is presumed as a circle for sensor node deployment. This paper proposes a novel coverage improved disc shape deployment strategy. Comparative analysis has been observed between circle and square regions of interest based on the cumulative number of sensor nodes required to cover the entire region. A new strategy named as disc shape deployment strategy is also proposed. Traditional hexagon and strip-based deployment strategies are compared with the disc shape deployment strategy. The simulation result shows that the circle shape coverage region of interest extremely reduces the required number of sensor nodes. The proposed deployment strategy provides desirable coverage, and it requires few more sensor nodes than hexagon shape deployment strategy.

     

Online 3-D tracking of suspension living cells imaged with phase-contrast microscopy

Neural stem cells/neural progenitors (NSCs/NPs) are cells that give rise to the main cell types of the nervous system: oligodendrocytes, neurons, and astrocytes. Studying NSCs/NPs with time-lapse microscopy is critical to the understanding of the biology of these cells. However, NSCs/NPs are very sensitive to phototoxic damage, and therefore, fluorescent dyes cannot be used to follow these cells. Also, since in most of NSC/NP-related experiments, a large number of cells neesd to be monitored. Consequently, the acquisition of a huge amount of images is required. An additional difficulty is related to our original suspension living, tracking objective, behavior much closer to the natural, in vivo, way of development of the cells. Indeed, unlike adherent cells, suspension cells float freely in a liquid solution, thus, making their dynamics very different from that of adherent cells. As a result, existing visual tracking algorithms that have primarily been developed to track adherent cells are no longer adequate to tackle living cells in suspension. This paper presents a novel automated 3-D visual tracking of suspension living cells for time-lapse image acquisition using phase-contrast microscopy. This new tracking method can potentially strongly impact on current 3-D video microscopy methods, paving the way for innovative analysis of NSCs/NPs and as a result, on the study of neurodegenerative diseases.