Electrical and Thermal Properties of Twin-Screw Extruded Multiwalled Carbon Nanotube/Epoxy Composites

This paper presents the experimental results of dispersing multiwalled carbon nanotubes (MWNTs) into epoxy (space grade structural adhesive) nanocomposites using co-rotating twin screw extrusion process. Two sets of specimens were prepared; set 1 with ultrasonication for predispersing MWNT before extrusion and set 2 direct dispersion of MWNT in the extruder. MWNT was loaded up to 8 vol.% in both the sets. The specimens were characterized for room temperature volume and surface resistivities as per ASTM D257 using Keithley Model 6517 and for thermal conductivity in the temperature range ?50 to 150 °C as per ASTM E 1530 using Thermal Conductivity Instrument (TCI) 2022 SX211. The volume resistivity of sets 1 and 2 decreased to an extent of 10¹¹ and 10⁹ respectively. The surface resistivity drop was of the order of 10⁹ for both the sets. These drops corresponded to the maximum MWNT loading of 8 vol.%. Electrical conductivity values of the specimens were fitted into the Power Law Model to evaluate the critical exponent. Both sets 1 and 2 showed increase in thermal conductivity with increase in temperature in the testing range. Thermal conductivity increased with increase in filler loading and the maximum increase was 60% at 150 °C in case of 8 vol.% MWNT nanocomposites for set 1. The corresponding value for the set 2 was 25%. Thermal conductivity values were predicted using Lewis Nielson model. DSC of the specimens showed increase in glass transition temperature with increase in filler loading. The dispersion of the nanofillers was studied using SEM and the surface morphology using AFM.     

Midwavelength Infrared Avalanche Photodiode Using InAs–GaSb Strain Layer Superlattice

InAs-GaSb strain layer superlattice p⁺-n^--n avalanche photodiodes (APDs) are fabricated using a newly introduced electron-beam aided zinc sulfide deposition. Temperature-dependent measurements were performed on 300 times 300 mum² mesa etched APDs. The effect of passivation was also studied on the diode characteristics and APD performances. Temperature-dependent gain strongly correlates with avalanche mechanism.     

A Visible and Near-Infrared Light-Fueled Omnidirectional Twist-Bend Crawling Robot

In recent years, although light-driven soft actuators have attracted intense scientific attention and achieved remarkable progress, the design and construction of an intelligent robotic system with maneuverability, self-adaptability, untethered control, and greater freedom of action, in particular the omnidirectional motion capability on a plane, remains challenging. Herein, four types of photo-thermal fillers and an unprecedented twist-bend actuation mode is introduced into a liquid crystal elastomer-based soft robot. The obtained twist-bend crawling robot not only exhibits in situ rotation, four-way turning, and four-way linear motion under light irradiation with four wavelength bands (520, 655, 808, and 980 nm), but also demonstrates the ability to avoid obstacles in complex geographical environments. This work may bring a new perspective for fabrication and development of soft robots that can adapt to dynamic and complex environmental conditions.     

Vector-extrapolated fast maximum likelihood estimation algorithms for emission tomography

A new class of fast maximum-likelihood estimation (MLE) algorithms for emission computed tomography (ECT) is developed. In these cyclic iterative algorithms, vector extrapolation techniques are integrated with the iterations in gradient-based MLE algorithms, with the objective of accelerating the convergence of the base iterations. This results in a substantial reduction in the effective number of base iterations required for obtaining an emission density estimate of specified quality. The mathematical theory behind the minimal polynomial and reduced rank vector extrapolation techniques, in the context of emission tomography, is presented. These extrapolation techniques are implemented in a positron emission tomography system. The new algorithms are evaluated using computer experiments, with measurements taken from simulated phantoms. It is shown that, with minimal additional computations, the proposed approach results in substantial improvement in reconstruction.     

A Comparison of Bit-Parallel and Bit-Serial Architectures for WDM Networks

Wavelength division multiplexing (WDM) is emerging as a viable solution to reduce the electronic processing bottleneck in very high-speed optical networks. A set of parallel and independent channels are created on a single fiber using this technique. Parallel communication utilizing the WDM channels may be accomplished in two ways: (i) bit serial, where each source-destination pair communicates using one wavelength and data are sent serially on this wavelength; and (ii) bit parallel, where each source-destination pair communicates using a subset of channels and data are sent in multiple-bit words. Three architectures are studied in the paper: single-hop bit-serial star, single-hop bit-parallel star, and multi-hop bit-parallel shufflenet. The objective of this paper is to evaluate these architectures with respect to average packet delay, network utilization, and link throughput. It is shown that the Shufflenet offers the lowest latency but suffers from high cost and low link throughput. The star topology with bit-parallel access offers lower latency than the bit-serial star, but is more expensive to implement.     

Analog and radio-frequency performance analysis of silicon-nanotube MOSFETs

This work presents a comparative study of the influence of various parameters on the analog and RF properties of silicon-nanotube MOSFETs and nanowire-based gate-all-around (GAA) MOSFETs. The important analog and RF performance parameters of SiNT FETs and GAA MOSFETs, namely drain current (I_d), transconductance to drain current ratio (g_m/I_d), I_on/I_off, the cut-off frequency (f_T) and the maximum frequency of oscillation (f_MAX) are evaluated with the help of Y- and H-parameters which are obtained from a 3-D device simulator, ATLAS^TM. It is found that the silicon-nanotube MOSFETs have far more superior analog and RF characteristics (g_m/I_d, f_T and f_MAX) compared to the nanowire-based gate-all-around GAA MOSFETs. The silicon-nanotube MOSFET shows an improvement of~2.5 and 3 times in the case of f_T and f_MAX values respectively compared with the nanowire-based gate-all-around (GAA) MOSFET.     

De-Duplication Complexity of Fingerprint Data in Large-Scale Applications

De-duplication using biometrics has gained much attention from research communities as it provides a unique identity for each and every individual among the large population.De-duplication is the process of removing the instances of multiple enrollments by the same person using the person’s biometric data.An important issue in the large-scale de-duplication applications is the speed of matching and the accuracy of the matching because the number of persons to be enrolled runs into millions.This paper presents an efficient method to improve the accuracy of fingerprint de-duplication in de-centralized manner.De-duplication accuracy decreases because of the noise present in the data,which would cause improper slap fingerprint segmentation.In this paper,an attempt is made to remove the noise present in the data by using binarization of slap fingerprint images and region labeling of desired regions with 8-adjacency neighborhood.The distinct feature of this technique is to remove the noise present in the data for an accurate slap fingerprint segmentation and improve the de-duplication accuracy.Experimental results demonstrate that the fingerprint segmentation rate and de-duplication accuracy are improved significantly.     

Autonomous Self-Sustained Liquid Crystal Actuators Enabling Active Photonic Applications

Advances in biomimicry have led to the rise of advanced robotics, posing promising revolutions across a variety of fields. Programmable self-sustained actuation in nature, such as human's heart beating, bird's wingbeats, and penguin's waddling, are intriguing and inspiring but challenging for device innovation, which hinders the emergence of autonomous self-feedback applications, especially in optics and photonics. Herein, the design, fabrication, and operation of crosslinked liquid crystal actuators are described that combine the programming of microstructures and the engineering of macroscopic shape morphing for active optics and photonics. The actuators consist of twisted nematic liquid crystal molecules with both elastic and optical anisotropies, resulting in large bending deformations in response to heat. Programmable bending motions and self-sustained waddling oscillations are demonstrated, further contributing to the achievements of dynamic 2D beam steering and self-sustained light field modulation. It is envisioned that these actuators with self-sustained performances without requiring turning the stimulus on-off will find applications in autonomous active optical systems, photonic applications, as well as self-governing robotics with the core feature of thermo-mechanical-optical transduction.     

Challenges and opportunities for next-generation intracortically based neural prostheses

Neural prosthetic systems aim to help disabled patients by translating neural signals from the brain into control signals for guiding computer cursors, prosthetic arms, and other assistive devices. Intracortical electrode arrays measure action potentials and local field potentials from individual neurons, or small populations of neurons, in the motor cortices and can provide considerable information for controlling prostheses. Despite several compelling proof-of-concept laboratory animal experiments and an initial human clinical trial, at least three key challenges remain which, if left unaddressed, may hamper the translation of these systems into widespread clinical use. We review these challenges: achieving able-bodied levels of performance across tasks and across environments, achieving robustness across multiple decades, and restoring able-bodied quality proprioception and somatosensation. We also describe some emerging opportunities for meeting these challenges. If these challenges can be largely or fully met, intracortically based neural prostheses may achieve true clinical viability and help increasing numbers of disabled patients.     

An Adaptive Learning Scheme for Medium Access with Channel Reservation in Wireless Networks

Providing effective medium access for wireless networks is a challenging task. Most of the existing protocols of IEEE 802.11 Medium Access Control (MAC) work towards the goal of achieving effective channel access by developing various backoff procedures. In this paper, we make an attempt to develop a new medium access protocol named Learning Automata (LA) based Wireless Channel Reservation (LAWCR). We use an LA approach to implement reservation for channel access for single hop wireless networks. Also, sequence procedure is used to improve the reservation mechanism. The performance of the proposed LAWCR scheme show significant improvements over the legacy DCF protocol with respect to important criteria such as the average time spent in the buffer and the throughput.