Role of Strain on Electronic and Mechanical Response of Semiconducting Transition-Metal Dichalcogenide Monolayers: an ab-initio study

We characterize the electronic structure and elasticity of monolayer transition-metal dichalcogenides MX2 (M=Mo, W, Sn, Hf and X=S, Se, Te) with 2H and 1T structures using fully relativistic first principles calculations based on density functional theory. We focus on the role of strain on the band structure and band alignment across the series 2D materials. We find that strain has a significant effect on the band gap; a biaxial strain of 1% decreases the band gap in the 2H structures, by as a much 0.2 eV in MoS2 and WS2, while increasing it for the 1T materials. These results indicate that strain is a powerful avenue to modulate their properties; for example, strain enables the formation of, otherwise impossible, broken gap heterostructures within the 2H class. These calculations provide insight and quantitative information for the rational development of heterostructures based on these class of materials accounting for the effect of strain.Comment: 16 pages, 4 figures, 1 table, supplementary materia

The dynamics of copper intercalated molybdenum ditelluride

Layered transition metal dichalcogenides are emerging as key materials in nanoelectronics and energy applications. Predictive models to understand their growth, thermomechanical properties and interactions with metals are needed in order to accelerate their incorporation into commercial products. Interatomic potentials enable large-scale atomistic simulations at the device level, beyond the range of applications of first principle methods. We present a ReaxFF reactive force field to describe molybdenum ditelluride and its interactions with copper. We optimized the force field parameters to describe the properties of layered MoTe2 in various phases, the intercalation of Cu atoms and clusters within its van der Waals gap, including a proper description of energetics, charges and mechanical properties. The training set consists of an extensive set of first principle calculations computed from density functional theory. We use the force field to study the adhesion of a single layer MoTe2 on a Cu(111) surface and the results are in good agreement with density functional theory, even though such structures were not part of the training set. We characterized the mobility of the Cu ions intercalated into MoTe2 under the presence of an external electric fields via molecular dynamics simulations. The results show a significant increase in drift velocity for electric fields of approximately 0.4 V/A and that mobility increases with Cu ion concentration.Comment: 21 pages, 9 Figure

Effect of Ketamine on Social Avoidance in Socially Defeated Male and Female Syrian Hamsters

Social stress can cause or exacerbate neuropsychiatric illnesses such as depression. Unfortunately, currently available treatments for these disorders are slow to take effect and are often ineffective. One promising novel treatment option is the anesthetic ketamine, which may have rapid-acting antidepressant effects in humans and rodents. These rodent studies, however, have primarily used artificial stressors to produce depression-like responses. Our lab uses an ethologically relevant rodent model of social stress in Syrian hamsters. We tested whether a single, intraperitoneal dose of ketamine reduces social avoidance, a common symptom of mental disorders, in male and female Syrian hamsters that have experienced social stress. Social avoidance was tested one day after ketamine injection. Eight days later, subjects were defeated again, and tested for avoidance the following day. Ketamine reduced avoidance one day but not nine days post-injection. These data suggest that ketamine can act rapidly to prevent depressive-like responses to social stress

High Voltage Direct Current Energy Transmission Using Modular Multilevel Converters

This thesis focus on high voltage direct current (HVdc) energy transmission using modular multilevel converter (MMC) based terminals. It provides a brief comparison between different HVdc technologies, focusing on voltage source converters (HVdc-VSC) with the MMC-based terminal emerging as the topology of choice for ratings less than 1 GW. The controllers for a two-terminal HVdc-link are analyzed and Matlab/SimulinkTM simulation models are presented. The simplified models and full Matlab/SimulinkTM based model are used to select the gains for the MMC controllers. Simulation results carried out on the full model validated the proposed methodologies. A new control technique that eliminates the voltage sensors on the grid side normally used to synchronize the MMC-based terminal with the grid is proposed. The performance of proposed technique was evaluated through Matlab/SimulinkTM simulations by considering inverter operation. The sensorless technique is able to synchronize a MMC-based inverter terminal to a grid under non-ideal conditions as well to accurately detect changes in the grid voltages. Finally, an analysis of the impact that a 15-kV SiC IGBT would have on HVdc MMC-based terminals is presented. The analysis evaluates parasitic inductances within the sub-module (SM) of an MMC, changes on the required SM capacitance, and impact on the voltage waveform THD. The evaluations showed that the 15-kV SiC IGBT would be only suitable if the module is rated 400 A or greater

A Low Complexity 6DoF Magnetic Tracking System For Biomedical Applications

L'abstract è presente nell'allegato / the abstract is in the attachmen