Effect of Space Charge on Polarization Reversal Currents in a Vinylidene Fluoride/Trifluoroethylene Copolymer

Polyvinylidene fluoride and its copolymers with trifluoroethylene and tetrafluoroethylene are ferroelectric. Reversal of polarization in these polymers is known to occur by a rotation of the polar molecular chains, in response to an externally applied electric field. Recent evidence suggests that the dynamics of polarization reversal can be affected by movement of space charges in the amorphous phase of the polymers. If a 75/25 mol.% vinylidene fluoride/trifluoro-ethylene (VF₂/VF₃) copolymer is poled at elevated temperature, the subsequent polarization reversal currents show large asymmetry and significant shifts in successive reversals. The field required to reverse the polarization in such high-temperature poled material is significantly larger than the normal coercive field. The asymmetry in the reversal currents is consistent with the presence of local fields within the polymer, generated by space charge which accumulates during the poling process. The subsequent movement of this space charge causes the shift in successive reversal currents. The variation of reversal current with temperature indicates that the movement of space charge within the copolymer is a thermally activated process.     

Pressure effects in multiphase binary diffusion couples

A systematic study has been carried out of the effect of pressure upon growth kinetics of intermediate phases formed in diffusion couples in the binary systems Ni-Al, U-A1, and U-Cu. Even though applied pressures greater than 100 MPa and long times were investigated little or no pressure effect was observed, in disagreement with previous literature reports. The magnitude of observed pressure effects falls within that expected by closure of Kirkendall porosity.     

A 40-43-Gb/s clock and data recovery IC with integrated SFI-5 1:16 demultiplexer in SiGe technology

A fully integrated OC-768 clock and data recovery IC with SFI-5 1:16 demultiplexer is designed in a 120-GHz/100-GHz (f/sub T//f/sub MAX/) SiGe technology. The 16 2.5-Gb/s outputs and additional deskew channel are compliant with the Serdes Framer Implementation Agreement Level 5 specification. The measured bit-error rate is <10/sup -15/. The measured jitter tolerance exceeds the mask specified in G.8251. The IC operates with 1.8-V and -5.2-V supplies and dissipates 7.5 W.     

On The Formation of Macrosegregations in

The effect of the natural convection on the formation of macrosegregations has been experimentally and theoretically analyzed. The Sn-10 pct Pb and Pb-15 pct Sn alloys were unidirectionally solidified. The temperature gradient and the solidification direction were perpendicular to the gravity vector. The concentration and temperature gradients in the samples cause natural con- vection. Large macrosegregations were observed in the sample. Two different convection modes were found in the two alloys caused by different density gradients in the two-phase region. This difference in convection causes an enrichment of Pb in the lower part of the last solidified regions in the Sn-10 pct Pb alloy and an enrichment of Sn in the upper part in the Pb-15 pct Sn alloy. Computer simulation of the convection mode models the convection pattern and the solidification process during which macrosegregation occurs. Formerly with the Department of Casting Formerly with the Department of Casting     

Enhancing multicast security of cognitive radio networks with antenna correlations over Nakagami-m fading channels

In this paper, we investigate the impact of diversity and antenna correlations on the secrecy capacity and outage performance of a cognitive radio multicast network over Nakagami-m fading channels analytically. The proposed network consists of single primary and secondary user, multiple primary and secondary receivers, and multiple eavesdroppers. It is assumed that each user is equipped with single antenna while all the primary and secondary receivers, and eavesdroppers are equipped with multiple antennas. The primary and secondary users transmit their common messages to the respective receivers in the presence of multiple eavesdroppers. A mathematical model is developed to ensure successful reception of confidential information to the primary receivers protecting the activities of eavesdroppers neglecting the effect of interference due to secondary user. In order to analyze the security of the proposed model, closed-form analytical expressions have been derived for the secrecy multicast capacity, the secure outage probability for multicasting and the probability of non-zero secrecy multicast capacity. Analytical results are justified via Monte-Carlo simulations.

     

Performance enhancement of traffic information gathering (PEnTInG) algorithm for vehicular ad‐hoc networks

Vehicular ad‐hoc networks (VANETs) play a vital role in today's context of vehicular traffic. In this paper, clusters of vehicles are created on the basis of average speed of the vehicles. One cluster communicates with the next cluster through a cluster head and also share the same information with next cluster heads and installed road side units (RSUs). By using this technique, we can solve the problem of rough driving behavior and road terrorism which is due to speed variation of vehicles and fake information dissemination by the drivers. Many a times, drivers may spread fake accident‐related information into the network which is a serious cause of concern in VANETs. It is ensured that such drivers are not allowed to spread wrong information in the network to avoid accidents. To solve this problem, we developed performance enhancement of traffic information gathering (PEnTInG) algorithm that selects only those drivers/vehicles as cluster heads in a cluster who has maximum value of the cluster head factor (CHF). The CHF is derived by considering different weights in range of 0 to 1 of relative average speed, time to leave, trust factor, and neighborhood degree. Further, the elected cluster head shares and stores the same information with the RSUs. In case, a driver wants to disseminate fake or wrong information in a network, then that vehicle driver can be easily tracked by the local authority by accessing RSU data. Simulation results show that the stability of PEnTInG is increased by 25% against the existing schemes viz. lowest‐ID, MCMF, and cluster‐based technique.     

ETPS-MAC: Energy Traffic Priority Scheduling-based QoS-aware MAC protocol for hierarchical WSNs

The evolution of the wireless sensor network (WSN) in recent years has reached its greatest heights and applications are increasing day by day, one such application is Smart Monitoring Systems (SMSs) which is in vision of implementation in every urban and rural areas. The implementation of WSN architecture in SMS needs an intelligent scheduling mechanism that efficiently handles the dynamic traffic load without sacrificing the energy efficiency of network. This paper presents a centralized TDMA scheduling based medium access control (MAC) protocol, called Energy Traffic Priority Scheduling MAC (ETPS-MAC) that accommodates variable traffic load while maintaining Quality-of-Service (QoS) assurance in hierarchical WSNs. The ETPS-MAC protocol employs priority scheduling algorithm which considers two factors for assigning priority, the energy factor and the traffic load factor to avoid packet buffering and maintains minimum data packet delay in case of high traffic load. Moreover, a novel rank-based clustering mechanism in FPS-QMAC protocol prolongs the network lifetime by minimizing the distance between the cluster head (CH) and the base station (BS). Both analytical and simulation models demonstrate the superiority of the ETPS-MAC protocol in terms of energy consumption, transmission delay, data throughput and message complexity when compared with the existing TDMA based MAC protocols.     

Kinematics,Dynamics and Power Consumption Analyses for Turning Motion of a Six-Legged Robot

This paper deals with kinematics, dynamics and power consumption analyses of a six-legged robot generating turning motions to follow a circular path. Direct and inverse kinematics analysis has been carried out for each leg in order to develop an overall kinematics model of the six-legged robot. It aims to estimate energy-optimal feet forces and joint torques of the six-legged robot, which are necessary to have for its real-time control. To determine the optimum feet forces, two approaches are developed, such as minimization of norm of feet forces and minimization of norm of joint torques using a least square method, and their performances are compared. The developed kinematics and dynamics models are tested through computer simulations for generating turning motion of a statically stable six-legged robot over flat terrain with four different duty factors. The maximum values of feet forces and joint torques decrease with the increase of duty factor. A power consumption model has been derived for the statically stable wave gaits to minimize the power requirement for both optimal foot force distributions and optimal foot-hold selection. The variations of average power consumption with the height of the trunk body and radial offset have been analyzed in order to find out energy-optimal foothold. A parametric study on energy consumption has been carried out by varying angular velocity of the robot to minimize the total energy consumption during locomotion. It has been found that the energy consumption decreases with the increase of angular velocity for a particular traveled distance.