Friction and dry sliding wear behavior of carbon and glass fabric reinforced vinyl ester composites

Friction and dry sliding wear behavior of glass and carbon fabric reinforced vinyl ester composites have been presented. The results show that the coefficient of friction and wear rate increased with increase in load/sliding velocity and depends on type of fabric reinforcement and temperature at the interphase. The excellent tribological characteristics were obtained with carbon fiber in vinyl ester. It is believed that a thin film formed on counterface was seems to be effective in improving the tribological characteristics. The worn surfaces examined through SEM, showed higher levels of broken glass fiber in vinyl ester compared to carbon-vinyl ester composites.     

Optimization of friction welding of tube-to-tube plate using an external tool by Taguchi method and genetic algorithm

Numerous advancements have been occurring in the field of materials processing. Friction welding is an important solid-state joining technique. In this research project, friction welding of tube-to-tube plate using an external tool (FWTPET) has been performed, and the process parameters have been prioritized using Taguchi??s L₂₇ orthogonal array. Genetic algorithm (GA) is used to optimize the welding process parameters. The practical significance of applying GA to FWTPET process has been validated by means of computing the deviation between predicted and experimentally obtained welding process parameters.     

Dry Sliding Wear Behavior of Titanium–(TiB+TiC) in situ Composite Developed by Spark Plasma Sintering

The present study provides insight into the dry sliding wear behavior of Ti-(TiB+TiC) in situ composite. The composite was developed from a Ti-B₄C powder mixture in three different proportions. The evolution of the morphology and in situ phase formation were characterized using optical microscopy, X-ray diffraction, scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDS). The sintered Ti-(TiB+TiC) composite showed an improved hardness and wear resistance with increasing TiB and TiC particulates. The friction and wear characteristics of the Ti-(TiB+TiC) composite were investigated using a pin-on-disc tester and were evaluated using SEM and EDS.     

Rate scheduling in multiple antenna downlink wireless systems

We consider scheduling strategies for multiantenna and multibeam cellular wireless systems for high-speed packet data services on the downlink. We establish a fundamental connection between the stability region of the queuing system and the set of feasible transmission rates, which provides the basis for the scheduling algorithm proposed in this paper. Transmission using adaptive steerable beams and fixed sector beams are considered and average delay versus throughput results are obtained through simulations for the proposed scheduling scheme in each case. While in single antenna systems multiuser diversity gains are achieved by the scheduling algorithms that transmit to a single user in each scheduling interval, our results show that with multiple antennas, transmitting to a carefully chosen subset of users has superior performance. The multiantenna scheduling problem is closely related to the problem of coordinated scheduling for transmission through multiple base stations, where a user can receive signals from several base stations simultaneously. We consider the special case when three single-antenna base stations are allowed to cooperate and transmit to the users in the triangular region between the base stations and propose scheduling strategies that demonstrate significant gains.     

Using a virtual security testbed for digital forensic reconstruction

This paper presents ViSe, a virtual security testbed, and demonstrates how it can be used to efficiently study computer attacks and suspect tools as part of a computer crime reconstruction. Based on a hypothesis of the security incident in question, ViSe is configured with the appropriate operating systems, services, and exploits. Attacks are formulated as event chains and replayed on the testbed. The effects of each event are analyzed in order to support or refute the hypothesis. The purpose of the approach is to facilitate reconstruction experiments in digital forensics. Two examples are given to demonstrate the approach; one overview example based on the Trojan defense and one detailed example of a multi-step attack. Although a reconstruction can neither prove a hypothesis with absolute certainty nor exclude the correctness of other hypotheses, a standardized environment, such as ViSe, combined with event reconstruction and testing, can lend credibility to an investigation and can be a great asset in court.     

An IEEE 802.11 and 802.16 WLAN Wireless Transmitter Baseband Architecture with a 1.2-V, 600-MS/s, 2.4-mW DAC

In this paper, we propose a transmitter baseband architecture for the present and up-coming WLAN applications (IEEE 802.11a/g, 802.11n, 802.16), based on a 600-MS/s current-steering DAC with a passive output load, to perform the baseband signal processing, avoiding the use of any active analog reconstruction filter. The DAC, fabricated in a 0.13-μm CMOS technology, consumes 2.4 mW from a 1.2-V single supply voltage. The DAC exhibits 68 dB of SFDR at full-scale for a 12-MHz input signal frequency and 9.7 bits of full-scale dynamic range in the bandwith from dc to 10 MHz.     

Densification of Al 5083 Mechanically Alloyed Powder by Equal Channel Angular Pressing

Equal channel angular pressing (ECAP), one of the most important methods in SPD, is used for the consolidation of mechanically alloyed Al 5083 powder. This paper mainly focuses on the densification of Al 5083 mechanically alloyed powder by ECAP with and without application of back pressure up to three passes with four different routes at room temperature. Aluminum can is used to encapsulate the powder. The particle size, crystallite size, microstructure and density were evaluated by scanning electron microscope and X-ray diffraction peak profile analysis. The crystallite size was measured by Williamson Hall analysis. Density and hardness were increased with increasing number of passes and upon sintering after ECAP. Good densification as well as good powder bonding was observed after three passes of ECAP.