TCP with header checksum option for wireless links: An analytical approach towards performance evaluation

TCP performs poorly in wireless mobile networks due to large bit error rates. Basically, the TCP sender responds to these losses as if they were due to congestion in the network, and reduces the congestion window unnecessarily. In earlier work, it has been shown that adding a TCP header checksum is very useful in differentiating between congestion loss and corruption loss. With the modified TCP, receivers can explicitly indicate corruption of received packets by generating “Explicit Loss Notifications (ELNs).” This paper focuses on an analytical study of this modified TCP protocol. We derive an expression for the probability of a receiver generating successful ELN, assuming a generic link layer protocol for data transfer over wireless links. Next, we develop an analytical approach for TCP throughput evaluation under the modified scheme. We compare the throughput results obtained by analysis and simulation, and find very close agreement between the two sets. We also compare the performance of the modified scheme with the standard NewReno TCP, and find considerable improvement in data throughput over wireless links.     

Bioinspired Hydrogel Interferometer for Adaptive Coloration and Chemical Sensing

Living organisms ubiquitously display colors that adapt to environmental changes, relying on the soft layer of cells or proteins. Adoption of soft materials into an artificial adaptive color system has promoted the development of material systems for environmental and health monitoring, anti‐counterfeiting, and stealth technologies. Here, a hydrogel interferometer based on a single hydrogel thin film covalently bonded to a reflective substrate is reported as a simple and universal adaptive color platform. Similar to the cell or protein soft layer of color‐changing animals, the soft hydrogel layer rapidly changes its thickness in response to external stimuli, resulting in instant color change. Such interference colors provide a visual and quantifiable means of revealing rich environmental metrics. Computational model is established and captures the key features of hydrogel stimuli‐responsive swelling, which elucidates the mechanism and design principle for the broad‐based platform. The single material–based platform has advantages of remarkable color uniformity, fast response, high robustness, and facile fabrication. Its versatility is demonstrated by diverse applications: a volatile‐vapor sensor with highly accurate quantitative detection, a colorimetric sensor array for multianalyte recognition, breath‐controlled information encryption, and a colorimetric humidity indicator. Portable and easy‐to‐use sensing systems are demonstrated with smartphone‐based colorimetric analysis.     

Structural aspects of alpha-omega transformation in group IV transition metals and alloys

The three most common crystal structures encountered in group IV transition metals Ti, Zr, and Hf and alloys based on them, under different temperature, pressure and alloy concentration conditions, are hcp(α), bcc (β) and simple hexagonal (ω). Although the structural relations of α?β andβ?ω transformations are well understood, the same is not true for α→ω phase change, which occurs at high pressures. We have done high pressure experiments on Ti-V alloys, followed by electron diffraction to study this. These patterns from pressure treated foils of alloys Ti₉₅ V₅ and Ti₉₁ V₉ showed the presence ofβ-phase with fourω variants. Some of them showed the existence of all three phases, α,β andω, with the number of variants given by the lattice correspondence matrix, derived through the orientation relations of α →β andβ →ω. This is a clear evidence that the α →ω transformation proceedsvia theβ-phase. The atomic rearrangements required forα →ω are found to be much smaller if the path is via theβ-phase, rather than the earlier model of Silcock.     

Twin-Boundary cavitation during creep in aged type 304 stainless steel

A transition from grain-to twin-boundary cavitation was observed in Type 304 stainless steel specimens aged at 593 and 649°C (1100 and 1200°F) and creep tested at 593°C (1100°F) and 207 MPa (30 ksi). Evidence of twin-boundary cavitation was also observed in unaged specimens tested at 649°C (1200°F) and 193 MPa (28 ksi). This same behavior was also found in aged Type 316 stainless steel. Several possible reasons have been suggested for the absence of frequently observed grain-boundary cavitation and its transition to twin-boundary cavitation.     

Elevated temperature tensile properties of powder metallurgy Ni3Al alloyed with chromium and zirconium

The tensile properties of hot extruded powders of Ni-24.1Al, Ni-19.1Al-8.5Cr, and Ni-17.4Al-7.9Cr-0.5Zr have been evaluated from room temperature to 1000° C. These powder metallurgy materials have a fine grain size that results in relatively little increase in yield stress with increasing temperature compared to coarse-grained or single-crystal materials. The alloy containing chromium and zirconium shows greatly reduced dynamic embrittlement in the temperature range 600 to 800° C where the unalloyed aluminide exhibits brittle behaviour. The Cr- and Cr + Zr-containing alloys deform superplastically above 900° C. The mechanism of superplastic deformation appears to be predominantly grain-boundary sliding.     

6G Communication Networks: Introduction,Vision, Challenges,and Future Directions

Wireless Personal Communications - In the fastest-growing world, technological innovation and industrial transformation are accelerating. The enhancement of Information and Communication Technology...     

A Low Profile Ultra-Wideband Antenna Design with Reconfigurable Notch-Bands for Wideband and Narrowband Applications

Wireless Personal Communications - A novel low profile ultra-wideband antenna design has been presented in this work, that offers switchable band-notch characteristics suitable for both wideband...