A Receiver-Driven Transport Protocol for the Web

In this paper, we present a receiver-oriented, request/response protocol for the Web that is compatible with the dynamics of TCP's congestion control algorithm. The protocol, called WebTP, is designed to be completely receiver-based in terms of transport initiation, flow-control and congestion-control. We propose a dual window-cum-rate based congestion control mechanism that is compatible with parallel TCP flows, and in fact interacts better with a congested network state. In support of our receiver-driven design, we developed a novel retransmission scheme that is robust to delay variations. The resulting flows achieve efficient network utilization and are qualitatively fair in their interaction amongst themselves and even with competing TCP flows. The paper also provides detailed simulation results to support the protocol design.     

Ultra-low breakdown voltage and origin of 1/f(2) noise in metallic nanorod arrays

The application of a dc voltage to an array of copper nanorods causes field evaporation of atoms from the tips, resulting in their progressive sharpening and a further increase in the local field. The process is self-limited by the build-up of space charge on the nanorod tips. From an analysis of the conductance noise recorded across the nanorod array, we show that the conduction mechanism bears a strong analogy with the stick-slip problem in sliding friction. The in situ sharpening results in an unprecedented lowering of the breakdown voltage of air by over 90%, as compared to plane parallel electrodes.     

Wear resistance of laser-deposited boride reinforced Ti-Nb–Zr–Ta alloy composites for orthopedic implants

The inherently poor wear resistance of titanium alloys limits their application as femoral heads in femoral (hip) implants. Reinforcing the soft matrix of titanium alloys (including new generation β-Ti alloys) with hard ceramic precipitates such as borides offers the possibility of substantially enhancing the wear resistance of these composites. The present study discusses the microstructure and wear resistance of laser-deposited boride reinforced composites based on Ti–Nb–Zr–Ta alloys. These composites have been deposited using the LENS™ process from a blend of elemental Ti, Nb, Zr, Ta, and boron powders and consist of complex borides dispersed in a matrix of β-Ti. The wear resistance of these composites has been compared with that of Ti–6Al–4V ELI, the current material of choice for orthopedic femoral implants, against two types of counterfaces, hard Si₃N₄ and softer SS440C stainless steel. Results suggest a substantial improvement in the wear resistance of the boride reinforced Ti–Nb–Zr–Ta alloys as compared with Ti–6Al–4V ELI against the softer counterface of SS440. The presence of an oxide layer on the surface of these alloys and composites also appears to have a substantial effect in terms of enhanced wear resistance.     

Supersonic cavity flows over concave and convex walls

Supersonic cavity flows are characterized by compression and expansion waves, shear layer, and oscillations inside the cavity. For decades, investigations into cavity flows have been conducted, mostly with flows at zero pressure gradient entering the cavity in straight walls. Since cavity flows on curved walls exert centrifugal force, the features of these flows are likely to differ from those of straight wall flows. The aim of the present work is to study the flow physics of a cavity that is cut out on a curved wall. Steady and unsteady numerical simulations were carried out for supersonic flow through curved channels over the cavity with L/H = 1. A straight channel flow was also analyzed which serves as the base model. The velocity gradient along the width of the channel was observed to increase with increasing the channel curvature for both concave and convex channels. The pressure on the cavity floor increases with the increase in channel curvature for concave channels and decreases for convex channels. Moreover, unsteady flow characteristics are more dependent on channel curvature under supersonic free stream conditions.     

Performance Analysis of Relay-Assisted Cooperative Systems in Correlated Fading Channels

In this paper, the effect of fading correlation at the receiving elements of a linear antenna array in a relay-assisted cooperative single-input multiple-output (SIMO) system has been investigated over flat Rayleigh fading channels. Considering a model of local scatterer around the source and relay nodes and uniform angle of arrival (AOA) distribution, the spatial cross-correlation analysis is presented and extensive simulation studies are performed to determine the envelope correlation as a function of antenna spacing, mean AOA and angular spread. Error performance analysis for coherent binary and quaternary modulations are presented for fixed-gain amplify-and-forward (AF) and fixed decode-and-forward (DF) relaying with dual diversity maximal-ratio combiner (MRC) receiver array. Error probability in terms of bit error probability (BEP) and symbol error probability (SEP) is evaluated to study the effect of relevant parameters on the correlation performance. The presented results establish the fact that fixed DF relay network performs relatively well than fixed-gain AF relaying. Superior performance of dual-hop cooperative SIMO system over conventional single-hop SIMO system has also been observed.     

Laser deposited biocompatible Ca–P coatings on Ti–6Al–4V: Microstructural evolution and thermal modeling

A high intensity continuous wave diode pumped ytterbium laser source was used to deposit Ca–P coatings on a Ti–6Al–4V biocompatible alloy in order to generate a physically textured surface, enhancing osseointegration. Scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM) and energy dispersive spectroscopy (EDS) studies were coupled with X-ray and micro diffraction work to determine the structure, composition, and phases present in various zones of a sample prepared across the coating/substrate interaction zone. Three-dimensional thermal modeling was also carried out to determine the cooling rate and maximum temperature experienced by different regions of the substrate. Combining these results provide us with valuable insights regarding the thermo-physical as well as chemical interactions that take place across the coating–substrate interface.     

A bi-phase enabled serial acquisition system for remote processing of digitized ECG

This paper presents an approach for acquiring digitized ECG samples in a personal computer using an offline communication technique. For this, two standalone embedded modules are placed at the two ends of the communication link. The transmit end module collects ECG samples from the source and stores them in a RAM. Finally it converts each data byte into a bi-phase encoded bit stream for transmission using a standard telephone set through post office telephone line. The receive-end module, coupled with the telephone receiver decodes the ECG data, and then delivers them to a desktop computer through the serial port. An application software in the computer is used to store these samples for visual inspection. The detailed architecture and test results are discussed with synthetic ECG data available from PTB diagnostic ECG database (ptb-db) under Physionet.