Origin of layer dependence in band structures of two-dimensional materials

We study the origin of layer dependence in band structures of two-dimensional materials. We find that the layer dependence, at the density functional theory (DFT) level, is a result of quantum confinement and the non-linearity of the exchange-correlation functional. We use this to develop an efficient scheme for performing DFT and GW calculations of multilayer systems. We show that the DFT and quasiparticle band structures of a multilayer system can be derived from a single calculation on a monolayer of the material. We test this scheme on multilayers of MoS$_2$, graphene and phosphorene. This new scheme yields results in excellent agreement with the standard methods at a fraction of the computation cost. This helps overcome the challenge of performing fully converged GW calculations on multilayers of 2D materials, particularly in the case of transition metal dichalcogenides which involve very stringent convergence parameters

Substrate screening effects on the quasiparticle band gap and defect charge transition levels in MoS2_2

Monolayer MoS$_2$ has emerged as an interesting material for nanoelectronic and optoelectronic devices. The effect of substrate screening and defects on the electronic structure of MoS$_2$ are important considerations in the design of such devices. Here, we present ab initio density functional theory (DFT) and GW calculations to study the effect of substrate screening on the quasiparticle band gap and defect charge transition levels (CTLs) in monolayer MoS$_2$. We find a giant renormalization to the free-standing quasiparticle band gap by 350 meV and 530 meV in the presence of graphene and graphite as substrates, respectively. Our results are corroborated by recent experimental measurements on these systems using scanning tunneling spectroscopy and photoluminescence excitation spectroscopy. Sulfur vacancies are the most abundant native defects found in MoS$_2$. We study the CTLs of these vacancies in MoS$_2$ using the DFT+GW formalism. We find (+1/0) and (0/-1) CTLs appear in the pristine band gap of MoS$_2$. Substrate screening results in renormalization of the (0/-1) level, with respect to the valence band maximum (VBM), by the same amount as the gap. This results in the pinning of the (0/-1) level about $\sim$500 meV below the conduction band minimum for the free-standing case as well as in the presence of substrates. The (+1/0) level, on the other hand, lies less than 100 meV above the VBM for all the cases

Early Detection and Prevention of DDOS attack on VANET

Growing number of vehicles in use has ushered in the service to provide human and resource safety. The present trend calls for the application of technology to automate safety measures in road traffic and since has been known as Intelligent Transport System (ITS). Vehicular Ad hoc Network is like a fork to Mobile Ad hoc Network , where the nodes are mobile vehicles moving in constrained road topology. VANET networks are envisioned to be used in practical ITS systems around the world. A network standard has been developed as Wireless Access In Vehicular Environment (IEEE 802.11p) to be used in VANET which is an amendment to IEEE 802.11 standard. With every new technological applications especially computers and network applications, come new security challenges. Every network in modern day is susceptible to security attacks and VANET is no exception. The most infamous of those attacks is the Distributed Denial of Service Attack which is unavoidable because unlike other security attacks the data packets used in it are legitimate packets. In this thesis work previous solutions are reviewed and a new offensive measure for detection, mitigation and prevention has been propose

Comparison of the efficacy of combined epidural anesthesia with general anaesthesia alone to attenuate hemodynamic responses and perioperative analgesia in laparoscopic cholecystectomy patients

Background: The aim of the study was to compare the efficacy of combined GA-Epidural Anesthesia (CEGA) with GA alone to attenuate hemodynamic responses and perioperative analgesia.Method: Authors conducted a prospective, randomized, double blind study, in which 60 patients undergoing laparoscopic cholecystectomy. Group A received (n=30) received GA and Group B (n=30) received combined GA and Epidural Anaesthesia (CEGA). Authors analyzed the effect of combined epidural general anaesthesia as compared to plain general anaesthesia with regard to hemodynamic parameters (heart rate, systolic and diastolic blood pressure), intraoperative anaesthetic requirement (intraoperative requirement of propofol), recovery score and postoperative analgesia (VAS score).Results: Authors found significant decrease in the heart rate, systolic and diastolic blood pressure in response to stress response to pneumoperitoneum in combined epidural general anaesthesia (CEGA) group compared to plain general anaesthesia (GA) group. Total amount of propofol required intraoperatively was less in CEGA group than in GA group. Recovery score and pain score (VAS) score were also compared which were better in CEGA group than in GA group. There were no significant intraoperative and postoperative complications noted in both the groups.Conclusion: Authors concluded that the use of epidural along with general anaesthesia helps in attenuating hemodynamic changes due to stress response to pneumoperitoneum, which results in maintaining stable intraoperative and postoperative hemodynamics during laparoscopic cholecystectomy surgery. Combining epidural to general anaesthesia results in rapid recovery as compared to plain general anaesthesia and also helps in providing good postoperative analgesia