Sliding mode control of an unmanned air-vehicle system

The objective of this study is to design a Controller that is stable under varying conditions of system parameters from the trim conditions and also robust for parametric variation for an Unmanned Air Vehicle (UAV) System. The PID and Sliding Mode Controller are the control models for the UAV system that are studied, designed and analyzed. The proposed Sliding Mode Controller was applied to a nonlinear second order system (Single Input Single Output (SISO)) and tested for stability and robustness of the system for parametric variation. The control model indicated chattering effect with switching (signum) function. Therefore, in order to negate this chattering effect Saturation and ATAN functions were proposed for the control input. It was observed that the modified system demonstrated robustness in presence of parameter uncertainties such as inertial mass, stiffness, damping, input gain and nonlinear gain. The same model is tested with a PID Controller and observed that the controller is stable but the tracking error is 10 times more than the sliding mode controller, this is due to inability of the linear PID controller to control nonlinear systems. The sliding mode controller was then extended to control a Single Input Two Output system for parametric variation. It was observed that the controller was able to stabilize the system and make the system robust. Then, Sliding Mode Controller based on Switching theory and Lyapunov\u27s theory was designed for Unmanned Air Vehicle System under uncertainty conditions. Stable sliding mode and robust asymptotic stability in uncertain UAV systems were investigated for variation in Velocity and Angle of Attack parameters. Finally, simulation results are presented to show the effectiveness of the design method

Capacity-Achieving Coding Mechanisms: Spatial Coupling and Group Symmetries

The broad theme of this work is in constructing optimal transmission mechanisms for a wide variety of communication systems. In particular, this dissertation provides a proof of threshold saturation for spatially-coupled codes, low-complexity capacity-achieving coding schemes for side-information problems, a proof that Reed-Muller and primitive narrow-sense BCH codes achieve capacity on erasure channels, and a mathematical framework to design delay sensitive communication systems. Spatially-coupled codes are a class of codes on graphs that are shown to achieve capacity universally over binary symmetric memoryless channels (BMS) under belief-propagation decoder. The underlying phenomenon behind spatial coupling, known as “threshold saturation via spatial coupling”, turns out to be general and this technique has been applied to a wide variety of systems. In this work, a proof of the threshold saturation phenomenon is provided for irregular low-density parity-check (LDPC) and low-density generator-matrix (LDGM) ensembles on BMS channels. This proof is far simpler than published alternative proofs and it remains as the only technique to handle irregular and LDGM codes. Also, low-complexity capacity-achieving codes are constructed for three coding problems via spatial coupling: 1) rate distortion with side-information, 2) channel coding with side-information, and 3) write-once memory system. All these schemes are based on spatially coupling compound LDGM/LDPC ensembles. Reed-Muller and Bose-Chaudhuri-Hocquengham (BCH) are well-known algebraic codes introduced more than 50 years ago. While these codes are studied extensively in the literature it wasn’t known whether these codes achieve capacity. This work introduces a technique to show that Reed-Muller and primitive narrow-sense BCH codes achieve capacity on erasure channels under maximum a posteriori (MAP) decoding. Instead of relying on the weight enumerators or other precise details of these codes, this technique requires that these codes have highly symmetric permutation groups. In fact, any sequence of linear codes with increasing blocklengths whose rates converge to a number between 0 and 1, and whose permutation groups are doubly transitive achieve capacity on erasure channels under bit-MAP decoding. This pro-vides a rare example in information theory where symmetry alone is sufficient to achieve capacity. While the channel capacity provides a useful benchmark for practical design, communication systems of the day also demand small latency and other link layer metrics. Such delay sensitive communication systems are studied in this work, where a mathematical framework is developed to provide insights into the optimal design of these systems

Application of Elliptical Curve Cryptography in Empowering Cloud Data Security

Cloud computing is one of the most preferable and used technologies in IT Industry in the present scenario. Providing security to cloud data in cloud environment has become popular feature in industry and academic research. Cloud Computing is a conceptual concept based on technology that is widely used by many companies these days. The Elliptical Curve Cryptography algorithm ensures the integrity and authentication of secure communications with non-repudiation of communication and data confidentiality. Elliptical Curve Cryptography is also known as a public key cryptography technique based on the elliptic curve theory that can be used to create a fast, small, more efficient and unpredictable cryptographic key. This paper provides authentication and confidentiality to cloud data using Elliptical Curve Cryptography. This paper attempts to evolve cloud security and cloud data security by creating digital signatures and encryption with elliptical curve cryptography. The proposed method is an attempt to provide security to encryption keys using access control list, wherein it lists all the authorized users to give access to the encryption keys stored in cloud

Density-driven instabilities of miscible fluids in a capillary tube : linear stability analysis

Erworben im Rahmen der Schweizer Nationallizenzen (http://www.nationallizenzen.ch)A linear stability analysis is presented for the miscible interface formed by placing a heavier fluid above a lighter one in a vertically oriented capillary tube. The analysis is based on the three-dimensional Stokes equations, coupled to a convection-diffusion equation for the concentration field, in cylindrical coordinates. A generalized eigenvalue problem is formulated, whose numerical solution yields both the growth rate and the two-dimensional eigenmodes as functions of the governing parameters in the form of a Rayleigh number and a dimensionless interfacial thickness. The dispersion relations show that for all values of the governing parameters the three-dimensional mode with an azimuthal wavenumber of 1 represents the most unstable disturbance. The stability results also indicate the existence of a critical Rayleigh number of about 920, below which all perturbations are stable. The growth rates are seen to reach a plateau for Rayleigh numbers in excess of 10^6 . In order to analyse the experimental observations by Kuang et al.(2002), which show that a small amount of net flow can stabilize the azimuthal instability mode and maintain an axisymmetric evolution, a base flow of Poiseuille type is included in the linear stability analysis. Results show that a weak base flow leads to a slight reduction of the growth rates of both axisymmetric and azimuthal modes. However, within the velocity interval that could be analysed in the present investigation, there is no indication that the axisymmetric mode overtakes its azimuthal counterpart

Correction to: Gender-Based Differences in Abdominal Aortic Aneurysm Rupture: A Retrospective Study; Review of COVID-19 Vaccines Approved in the United States of America for Emergency Use; Review of COVID-19 Variants and COVID-19 Vaccine Efficacy: What the Clinician Should Know?

Correction to: Gender-Based Differences in Abdominal Aortic Aneurysm Rupture: A Retrospective Study; Review of COVID-19 Vaccines Approved in the United States of America for Emergency Use; Review of COVID-19 Variants and COVID-19 Vaccine Efficacy: What the Clinician Should Know

Density-driven instabilities of variable-viscosity miscible fluids in a capillary tube

A linear stability analysis is presented for variable-viscosity miscible fluids in an unstable configuration; that is, a heavier fluid placed above a lighter one in a vertically oriented capillary tube. The initial interface thickness is treated as a parameter to the problem. The analysis is based on the three-dimensional Stokes equations, coupled to a convection-diffusion equation for the concentration field, in cylindrical coordinates. When both fluids have identical viscosities, the dispersion relations show that for all values of the governing parameters the three-dimensional mode with an azimuthal wave number of one represents the most unstable disturbance. The stability results also indicate the existence of a critical Rayleigh number of about 920, below which all perturbations are stable. For the variable viscosity case, the growth rate does not depend on which of the two fluids is more viscous. For every parameter combination the maximum of the eigenfunctions tends to shift toward the less viscous fluid. With increasing mobility ratio, the instability is damped uniformly. We observe a crossover of the most unstable mode from azimuthal to axisymmetric perturbations for Rayleigh numbers greater than 10(5) and high mobility ratios. Hence, the damping influence is much stronger on the three-dimensional mode than the corresponding axisymmetric mode for large Rayleigh numbers. For a fixed mobility ratio, similar to the constant viscosity case, the growth rates are seen to reach a plateau for Rayleigh numbers in excess of 10(6). At higher mobility ratios, interestingly, the largest growth rates and unstable wave numbers are obtained for intermediate interface thicknesses. This demonstrates that, for variable viscosities, thicker interfaces can be more unstable than their thinner counterparts, which is in contrast to the constant viscosity result where growth rate was seen to decline monotonically with increasing interface thickness

Review of COVID-19 Variants and COVID-19 Vaccine Efficacy: What the Clinician Should Know?

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a beta coronavirus that belongs to the Coronaviridae family. SARS-CoV-2 is an enveloped spherical-shaped virus. The ribonucleic acid (RNA) is oriented in a 5’-3’direction which makes it a positive sense RNA virus, and the RNA can be read directly as a messenger RNA. The nonstructural protein 14 (nsp14) has proofreading activity which allows the rate of mutations to stay low. A change in the genetic sequence is called a mutation. Genomes that differ from each other in genetic sequence are called variants. Variants are the result of mutations but differ from each other by one or more mutations. When a phenotypic difference is demonstrated among the variants, they are called strains. Viruses constantly change in two different ways, antigenic drift and antigenic shift. SARS-CoV-2 genome is also prone to various mutations that led to antigenic drift resulting in escape from immune recognition. The Center of Disease Control and Prevention (CDC) updates the variant strains in the different classes. The classes are variant of interest, variant of concern and variant of high consequence. The current variants included in the variant of interest by the USA are: B.1.526, B.1.525, and P.2; and those included in the variant of concern by the USA are B.1.1.7, P.1, B.1.351, B.1.427, and B.1.429. The double and triple mutant variants first reported in India have resulted in a massive increase in the number of cases. Emerging variants not only result in increased transmissibility, morbidity and mortality, but also have the ability to evade detection by existing or currently available diagnostic tests, which can potentially delay the diagnosis and treatment, exhibit decreased susceptibility to treatment including antivirals, monoclonal antibodies and convalescent plasma, possess the ability to cause reinfection in previously infected and recovered individuals, and vaccine breakthrough cases in fully vaccinated individuals. Hence, continuation of precautionary measures, genomic surveillance and vaccination plays an important role in the prevention of spread, early identification of variants, prevention of mutations and viral replication, respectively

Shapes and dynamics of miscible liquid/liquid interfaces in horizontal capillary tubes

We report optical observations of the dissolution behaviour of glycerol/water, soybean oil/hexane, and isobutyric acid (IBA)/water binary mixtures within horizontal capillary tubes. Tubes with diameters as small as were initially filled with one component of the binary mixture (solute) and then immersed into a solvent-filled thermostatic bath. Both ends of the tubes were open, and no pressure difference was applied between the ends. In the case of glycerol/water and soybean oil/hexane mixtures, we managed to isolate the dissolution (the interfacial mass transfer) from the hydrodynamic motion. Two phase boundaries moving from the ends into the middle section of the tube with the speeds ( and d are the coefficient of diffusion, time and the diameter of the tube, respectively) were observed. The boundaries slowly smeared but their smearing occurred considerably slower than their motion. The motion of the phase boundaries cannot be explained by the dependency of the diffusion coefficient on concentration, and should be explained by the effect of barodiffusion. The shapes of the solute/solvent boundaries are defined by the balance between gravity and surface tension effects. The contact line moved together with the bulk interface: no visible solute remained on the walls after the interface passage. Changes in temperature and in the ratio between gravity and capillary forces altered the apparent contact angles. The IBA/water system had different behaviour. Below thecritical (consolute) point, no dissolution was observed: IBA and water behaved like two immiscible liquids, with the IBA phase being displaced from the tube by capillary pressure (the spontaneous imbibition process). Above the critical point, two IBA/water interfaces could be identified, however the interfaces did not penetrate much into the tube<br/