Firework inspired load balancing approach for wireless sensor networks

Wireless Networks - In Wireless Sensor Networks (WSNs), where power consumption is a huge concern, the improvement of the network’s lifetime is an area of constant study and innovation. The...     

Routing Protocols in Delay Tolerant Networks: Comparative and Empirical Analysis

Wireless Personal Communications - A Delay Tolerant Network (DTN) is a network capable of handling long delays and data loss efficiently in various challenged scenarios and environments. Owing to...     

Design and Characterization of a W-Band Folded-Waveguide Slow-Wave Structure

A single-section slow-wave structure for a W-band folded-waveguide traveling-wave tube with operating bandwidth of around 4% was designed for delivering the output power of 50 W at the operating voltage of 13.5 kV and operating beam current of 80 mA. The design was carried out using analytical formulations and 3D electromagnetic simulations. The beam-wave interaction analysis was carried out using large signal Lagrangian analysis and particle-in-cell simulation. The folded-waveguide slow-wave structure along with input-output couplers and RF windows were fabricated. Cold test measurements were carried out for dispersion characteristics of the slow-wave structure and voltage standing-wave ratio and insertion loss characteristics of the RF window. The measured cold circuit parameters show close agreement with the analysis.     

Effect of Electromigration on the Mechanical Performance of Sn-3.5Ag Solder Joints with Ni and Ni-P Metallizations

The effect of moderate electric current density (1 × 10³ to 3 × 10³ A/cm²) on the mechanical properties of Ni-P/Sn-3.5Ag/Ni-P and Ni/Sn-3.5Ag/Ni solder joints was investigated using a microtensile test. Thermal aging was carried out at 160°C for 100 h while the current was passed. The interfacial microstructure and intermetallic compound (IMC) growth were analyzed. It was found that, at these levels of current density, there were no observable voids or hillocks. Samples aged at 160°C without current stressing failed mostly inside the bulk solder with significant prior plastic deformation. The passage of current was found to cause brittle failure of the solder joints and this tendency for brittle failure increased with increasing current density. Fractographic analysis showed that, in most of the electrically stressed samples, fracture occurred at the interface region between the solder and the joining metals. The critical current density that caused brittle fracture was about 2 × 10³ A/cm². Once brittle fracture occurred, the tensile toughness, defined as the energy per unit fractured area, was usually lower than ~5 kJ/m², compared with the case of ductile fracture where this value was typically greater than ~9 kJ/m². When comparing the two types of joint, the brittle failure was found to be more severe with the Ni than with the Ni-P joint. This work also found that the passage of electric current affects the IMC growth rate more significantly in the Ni than in the Ni-P joint. In the case of the Ni joint, the Ni₃Sn₄ IMC at the anode side was appreciably thicker than that formed at the cathode side. However, in the case of electroless Ni-P metallization, this difference was much smaller.     

Copper@ZIF-8 Core-Shell Nanowires for Reusable Antimicrobial Face Masks

SARS-CoV-2 and other respiratory viruses spread via aerosols generated by infected people. Face masks can limit transmission. However, widespread use of disposable masks consumes tremendous resources and generates waste. Here, a novel material for treating blown polypropylene filtration media used in medical-grade masks to impart antimicrobial activity is reported. To produce thin copper@ZIF-8 core-shell nanowires (Cu@ZIF-8 NWs), Cu NWs are stabilized using a pluronic F-127 block copolymer, followed by growth of ZIF-8 to obtain uniform core-shell structures. The Cu@ZIF-8 NWs are applied to filtration media by dip coating. Aerosol filtration efficiency decreases upon exposure to ethanol (solvent for dip-coating), but increases with addition of Cu@ZIF-8 NWs. Cu@ZIF-8 NWs shows enhanced antibacterial activity, compared to Cu NWs or ZIF-8 alone, against Streptococcus mutans and Escherichia coli. Antiviral activity against SARS-CoV-2 is assayed using virus-infected Vero E6 cells, demonstrating 55% inhibition of virus replication after 48 h by 1 µg of Cu@ZIF-8 NWs per well. Cu@ZIF-8 NWs’ cytotoxicity is tested against four cell lines, and their effect on inflammatory response in A549 cells is examined, demonstrating good biocompatibility. This low-cost, scalable synthesis and straightforward deposition of Cu@ZIF-8 NWs onto filter media has great potential to reduce disease transmission, resource consumption, and environmental impact of waste.     

Two-stage decision making policy for opportunistic spectrum access and validation on USRP testbed

“Recently, various paradigms, for instance, device-to-device communications, LTE-unlicensed and cognitive radio based on an opportunistic spectrum access (OSA) are being envisioned to improve the average spectrum utilization. In OSA, secondary (unlicensed) users (SUs) need decision making policies (DMPs) to identify and transmit over optimum frequency bands without any interference to the primary (licensed) users as well as minimize the number of collisions among SUs. In this paper, we have proposed a two-stage DMP consisting of Bayesian Multi-armed Bandit algorithm to accurately characterize the frequency band statistics independently at each SU and frequency band selection scheme for orthogonalization of SUs. The analytical and simulation results show that the proposed DMP leads to 45% improvement in the average spectrum utilization compared to 36–39% in the existing DMPs. Furthermore, the number of collisions are 58.5% lower in the proposed DMP making SU terminals energy-efficient. The performance of the proposed DMP has been verified on the proposed USRP testbed in real radio environment and the experimental results closely match the simulated results .”     

Radiation characteristics and generation of higher-order modes of circular microstrip antennas

The characteristics of higher-order modes of circular micro-strip antennas, such as radiation pattern, directivity, bandwidth, efficiency, and location of the feedpoint to match a 50?line, are studied, and the effects of varying the substrate parameters are investigated. A multifeed technique to generate any particular mode is also presented.     

Analysis of a two unit standby system with partial failure and two types of repairs

A two dissimiliar unit standby system is analysed. The priority unit can either be in normal or partial operative mode. When the unit fails from the partial mode, it undergoes minor repair and the unit becomes operative with different failure rate. If this unit fails again, it goes to major repair after which it works as good as new. The standby unit while in use is either operative or failed. This non priority unit fails without passing through the partial failure mode and undergoes only one type of repair with different repair time distribution. Failure and repair time distributions are negative exponential and general respectively. Regenerative technique in MRP is applied to obtain several reliability characteristics of interest to system designers.     

Optimal allocation of cost to detectors in a two-unit series system

A two-unit series system, in which each unit is equipped with a separate detector to detect failure, is considered. The probability that a detector operates successfully at the time of need (i.e. when system fails) is a function of cost spent on the detector. The problem is that of allocation of total resources (cost) to the two detectors such that the overall expected profit is maximized. The optimization problem has been formulated. Two examples are included to show the uses of results.     

A Hybrid Fractal Metamaterial Inspired Multiband Antenna for Wireless Applications

Wireless Personal Communications - In this paper a multiband (hepta-band) antenna loaded with hybrid fractal structures and metamaterial cell (SRR/CSRR) is proposed to cover the wireless...