Micromechanical study on the deformation behaviour of directionally solidified NiAl-Cr eutectic composites

In this work, we employed micromechanical techniques on directionally solidified NiAl-Cr prepared at different solidification speeds, to understand the effect of processing conditions and the role of individual phases and interfaces on the deformation behaviour. The observations from the different tests suggest that the interface between the fiber and the matrix dominates the deformation of DS NiAl-Cr eutectic alloys by providing additional mobile dislocation generation sites at the interface

Design of Square Patch Microstrip Antenna for Circular Polarization Using IE3D Software

Communication between humans was first by sound through voice. With the desire for slightly more distance communication came, devices such as drums, then, visual methods such as signal flags and smoke signals were used. These optical communication devices, of course, utilized the light portion of the electromagnetic spectrum. It has been only very recent in human history that the electromagnetic spectrum, outside the visible region, has been employed for communication, through the use of radio. One of humankind’s greatest natural resources is the electromagnetic spectrum and the antenna has been instrumental in harnessing this resource.The thesis provides a detailed study of how to design and fabricate a probe-fed Square Microstrip Patch Antenna using IE3D software and study the effect of antenna dimensions Length (L), and substrate parameters relative Dielectric constant (εr), substrate thickness (t) on the Radiation parameters of Bandwidth and Beam-width

Fusarium pallidoroseum: A potential entomopathogenic agent for the biological management of Aphis gossypii

With rising need of switching over to sustainable agricultural practices, utilization of entomopathogenic fungi (EPF) as biocontrol agents, provides better substitute against chemical pesticides- having several side-effects. Therefore, an attempt have been made to explore the potential EPF fungi that could be incorporated into IPM practices for control of Helicoverpa armigera Hubner and Aphis gossypii Glover. Regarding this, an entomopathogenic fungus, Fusarium pallidoroseum (Cooke) Sacc, was isolated from natural population of H. armigera infesting chickpea (Cicer arietinum L.) and explored efficacy under in-vitro & field conditions. The findings of present investigation shows efficacy of F. pallidoroseum as potential biocontrol agent against okra aphid (A. gossypii), as it inflicted initial mortality of 43.33% nymphs on 2nd day and lead to complete annihilation (93.33%) of nymph population on 8th day of spore suspension application at 1x1010 spores/mL concentration. The observations against adult okra aphid clearly demonstrated that spraying of 1 x 1010 spores/mL of F. pallidoroseum resulted 66.67% mortality after 8th days of spraying. Increased mortality was recorded with increase in spore suspension concentrations. The LC50 & LC90 value for F. pallidoroseum against nymphs of A. gossypii was recorded 3.79 x 105 and 2.74 x 108, respectively. The findings were used to develop  formulations (1 × 104  to 1 × 1010 spore suspension/mL conc),  and tested  at field-level. The results showed that formulation at 1 x 1010 spores/mL conc was most effective against A. gossypii, recorded 93.33% mortality of nymphs & 66.67% mortality of adults; could be used under IPM practices

Functionality enhancement of two-dimensional transition metal dichalcogenide-based transistors

Atomically thin molybdenum disulfide (MoS₂) and tungsten diselenide (WSe₂), members of the transition metal dichalcogenide family, have emerged as prototypical two-dimensional semiconductors with a multitude of interesting properties and promising device applications spanning all realms of electronics and optoelectronics. While possessing inherent advantages over conventional bulk semiconducting materials (such as Si, Ge and III-Vs) in terms of enabling ultra-short channel and, thus, energy efficient field-effect transistors, the mechanically flexible and transparent nature of 2D MoS₂ and WSe₂ make them even more attractive for use in ubiquitous flexible and transparent electronic systems. However, before the fascinating properties of these materials can be effectively harnessed and put to good use in practical and commercial applications, several important technological roadblocks pertaining to their contact, doping and mobility engineering must be overcome. This dissertation reviews the important technologically relevant properties of semiconducting 2D TMDs followed by a discussion of the performance projections of, and the major engineering challenges that confront, 2D MoS₂ and WSe₂-based devices. Finally, this dissertation provides a comprehensive insight into two novel and promising engineering solutions that can be employed to address the all-important issues of contact resistance, controllable and area-selective doping, and charge carrier mobility enhancement (electrons in MoS₂ and holes in WSe₂) in these devices. Specifically, this work sheds light upon the interfacial-oxygen-vacancy mediated n-doping of MoS₂ by high-κ dielectrics, such as HfO₂, Al₂O₃ and TiO₂, using detailed experimental characterizations and theoretical calculations. This n-doping effect on MoS₂ by high-κ dielectrics is proposed as a mechanism responsible for the performance enhancement observed in MoS₂ devices upon encapsulation in high-κ dielectric environments. This work also sheds light upon the band structure engineering and p-doping of layered WSe₂ using a simple and facile one-step chemical functionalization technique utilizing ammonium sulfide solution. Detailed experimental and theoretical studies once again reveal the underlying mechanism responsible for the p-doping in WSe₂ after chemical treatment. Results show that the doping techniques presented in this dissertation can easily be adapted to obtain high-performance FETs based on 2D MoS₂ and WSe₂. Finally, some future research directions, based on the work presented in this dissertation, are highlighted.Electrical and Computer Engineerin

Accelerated Carrier Recombination by Grain Boundary/Edge Defects in MBE Grown Transition Metal Dichalcogenides

Defect-carrier interaction in transition metal dichalcogenides (TMDs) play important roles in carrier relaxation dynamics and carrier transport, which determines the performance of electronic devices. With femtosecond laser time-resolved spectroscopy, we investigated the effect of grain boundary/edge defects on the ultrafast dynamics of photoexcited carrier in MBE grown MoTe2 and MoSe2. We found that, comparing with exfoliated samples, carrier recombination rate in MBE grown samples accelerates by about 50 times. We attribute this striking difference to the existence of abundant grain boundary/edge defects in MBE grown samples, which can serve as effective recombination centers for the photoexcited carriers. We also observed coherent acoustic phonons in both exfoliated and MBE grown MoTe2, indicating strong electron-phonon coupling in this materials. Our measured sound velocity agrees well with previously reported result of theoretical calculation. Our findings provide useful reference for the fundamental parameters: carrier lifetime and sound velocity, reveal the undiscovered carrier recombination effect of grain boundary/edge defects, both of which will facilitate the defect engineering in TMD materials for high speed opto-electronics

An overview of the genus Dioscorea L. (Dioscoreaceae) in India

The present paper depicts an overview and elucidated assessment of published data and herbarium records on the diversity, distribution pattern, endemism and threat status of Dioscorea spp. to get availed with extant stature and design strategies for its effective conservation. Dioscorea nested under family Dioscoreceae is a pantropical genus comprising about 682 species. In India, the genus is known to possess 42 taxa (41 species and one variety). Dioscorea L. is highly regarded for its nutritional and medicinal values having a significant role in pharmaceutical and nutraceutical industries. Several species of Dioscorea contain various biologically active molecules that show anti-arthritic, anti-inflammatory and anti-fertility effects and thereby known for alleviating medicinal curses