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关键词： Mathematics   Computer science   Construction   Coding theory   Graphs   Error correction & detection   Eigen values   Approximation   Codes   Algorithms   Binary system   Linear codes   Linear algebra  

摘要： Our adventures take us through several problems related to decoding a class of error-correcting codes known as direct sum codes. These codes are obtained from a base code C0 ⊆ F2n by summing the entries of each codeword on a collection of subsets W ⊆ [n]k to yield a code C ⊆ F2W. If the collection W has a particular expansion property, the resulting direct sum code C will have a large minimum distance and (as we show) an efficient decoding algorithm. In our first adventure (Chapter 2, joint work with Vedat Levi Alev, Fernando Granha Jeronimo, Shashank Srivastava, and Madhur Tulsiani), we develop a list decoding algorithm for a generalization of direct sum codes where the direct sum can be replaced by any suitable "lifting'' operation. The algorithm creates a Sum-of-Squares program for list decoding, the solution to which allows the desired list of codewords to be recovered through rounding. We apply the general decoding framework to obtain list decoding algorithms for direct sum codes constructed using a collection W which is either the set of walks of k vertices on an expander graph or the set of k-sized faces of a high-dimensional expander. Our second adventure (Chapter 3, joint work with Fernando Granha Jeronimo, Shashank Srivastava, and Madhur Tulsiani) is adapting the results of Chapter 2 to decode Ta-Shma's [STOC 2017] direct sum codes. These codes are ε-balanced, meaning any two codewords have distance between 1/2-ε/2 and 1/2+ε/2, and have rate nearly achieving the Gilbert–Varshamov bound of Ω(ε2). Decoding is accomplished using the direct sum list decoding framework in an inductive process that sidesteps its suboptimal parameter requirements. This process can perform both unique and list decoding for Ta-Shma's codes, though at a list decoding radius smaller than the minimum distance.

关键词： Design   Acoustics   Histology   Computer science   Endocrinology   Medicine   Morphology   Polymer chemistry  

摘要： This thesis examined the effects of combination inhaled corticosteroids (ICs) on the stability of six aerodynamic measures of phonation utilizing a traditional benchtop model with leporine larynges. The motivation for this study was based on the increase of voice disorders associated with IC use in recent years. The aerodynamic measures examined were phonation threshold pressure (PTP), phonation threshold flow (PTF), onset resistance, sustained pressure, sustained flow, and sustained resistance. Leporine larynges were selected as the model for this study due to histological similarities between leporine and human vocal folds that make them ideal for translational research. Rabbits were either exposed to saline solution or ICs for 8 weeks before being sacrificed. After being sacrificed, larynges were excised and dissected. After dissection, the larynges were mounted on a benchtop, the aerodynamic data were gathered, and stability over multiple phonation trials was calculated. The results indicate that the variation between individual rabbits across the measures did not differ significantly. However, after controlling for trial, the average variation of the groups across all trials did differ significantly. PTP and sustained pressure were more variable for the inhaler group, while PTF, sustained flow, onset resistance, and sustained resistance were more variable for the control group. These results suggest that some level of variability in aerodynamic measures both within and between subjects is to be expected when using the leporine benchtop model. Furthermore, while IC exposure does not seem to impact within-subject variability, it does influence between-subjects variability.

关键词： Drones   Security   Privacy   Ad hoc networks   Tutorials   Encryption   Computer science   Blockchain   drone applications   drone security   fog computing   machine learning   software defined networks   UAV  

摘要： Drone security is currently a major topic of discussion among researchers and industrialists. Although there are multiple applications of drones, if the security challenges are not anticipated and required architectural changes are not made, the upcoming drone applications will not be able to serve their actual purpose. Therefore, in this paper, we present a detailed review of the security-critical drone applications, and security-related challenges in drone communication such as DoS attacks, Man-in-the-middle attacks, De-Authentication attacks, and so on. Furthermore, as part of solution architectures, the use of Blockchain, Software Defined Networks (SDN), Machine Learning, and Fog/Edge computing are discussed as these are the most emerging technologies. Drones are highly resource-constrained devices and therefore it is not possible to deploy heavy security algorithms on board. Blockchain can be used to cryptographically store all the data that is sent to/from the drones, thereby saving it from tampering and eavesdropping. Various ML algorithms can be used to detect malicious drones in the network and to detect safe routes. Additionally, the SDN technology can be used to make the drone network reliable by allowing the controller to keep a close check on data traffic, and fog computing can be used to keep the computation capabilities closer to the drones without overloading them.

关键词： Industrial engineering   Computer science   Geographic information science   Artificial intelligence  

摘要： Deep Learning has found great success in the field of Computer Vision and Natural Language Processing due to the increase in computing power and data availability. Echolocation is the phenomenon of locating objects by sending out a source call in the environment and listening for echoes reflected from those objects. Mammals such as bats and whales use echolocation for navigation and prey hunting. They posses this enhanced ability where they can locate both stationary and moving objects with high precision. Echolocation can be used by autonomous systems to navigate in low light environments and can also be used in privacy constrained surveillance. In this work, we tackle a variant of echolocation where we try to predict 2D location coordinates (i.e (x,y)) of a single object. We also extend it to locate two objects. An experimental setup was designed to collect the data necessary in testing our hypothesis. A Convolution Neural Network based model is designed for object location prediction problem. The proposed model and methodology result in average prediction accuracy of (x ± 0.08, y ± 0.08) for single object detection. The current experimental design suffered from bias in samples collected and hence a few bias correcting techniques are also discussed. Finally, current challenges and a few future directions are discussed for echolocation using an experimental approach.

关键词： Computer science   Artificial intelligence   Information technology  

摘要： The research paper focused on machine learning forensics resources to help prevent or limit the success of ransomware attacks on the supply chain. The research highlighted why the supply chain is susceptible to ransomware attacks and how machine learning forensics can help lower risk by performing efficient analysis and predicting future malware variants. The research is significant due to the increase of successful ransomware attacks on the supply chain in the transition to a large remote workforce during the Coronavirus pandemic. In addition, the supply chain suffers greatly from ransomware attacks because victims tend to surrender money to their attackers. As a result, victims spend significant money to restore their computer systems and suffer reputational damage. Therefore, the supply chain needs to invest in intelligent technology such as machine learning forensics to defend against cyberattacks that continue to increase sophistication and occurrence.

关键词： Phase transitions   Energy   Viscosity   Algorithms   Fluid dynamics   Contact angle   Equilibrium   Interfaces   Computer science   Fluid mechanics   Mechanics   Physics  

摘要： Ternary fluid systems (and specifically the ones involving two liquids and a gas phase) are of special interest for a variety of practical applications, such as combustion engines, ink-jet printing, and oil recovery. The physics and dynamics of these systems involves a complex interplay of capillary, viscous and inertial forces. For such flows, some fundamental information such as the velocity field, strains, and stresses, usually cannot be observed in experiments. On the other hand, analytic descriptions struggle to account for complex boundary conditions at multiple interfaces. In this context, numerical approaches are able of revealing hidden details, and provide the missing link between experiments and theory. Additionally, numerical approaches allow to easily tune a variety of physical parameters over a broad range of values, usually difficult to access experimentally, allowing a broader and deeper understanding. In this thesis, I employ and further develop a ternary free energy lattice Boltzmann method (LBM) to investigate two fundamental problems involving ternary fluid systems. The first problem focuses on the fluid flow and contact line dynamics of ternary fluids in presence of solid boundaries. To this aim, I propose three alternative schemes for solid boundaries for ternary fluids within the lattice Boltzmann framework. After benchmarking both static and dynamic properties, I focus on a system consisting of a train of two immiscible drops (bislug) confined within a long channel. By imposing a capillary force imbalance through the wetting boundaries for different phases, the bislug is self-propelled, and the steady velocity can be readily tuned by setting the bislug length. This will allow to extract simultaneous information on the contact line dynamics for all interfaces, evaluating the role of surface tension, density and viscosity contrast between phases. The second and main problem focuses on the collision between immiscible drops surrounded by a low-d

关键词： Traffic flow   Linear programming   Algorithms   Bandwidths   Optimization techniques   Traffic congestion   Sensors   Vehicles   Traffic control   Civil engineering   Computer science   Engineering   Transportation  

摘要： In today’s world, Traffic congestion in arterials is one of the major challenges faced by traffic engineers. A technique that has been widely used to solve this problem is to coordinate the individual intersections in the network to provide the drivers with an opportunity to pass through the network without stopping. This paper proposes a new approach to design traffic signal plans for effective signal coordination for smooth progression of traffic through arterials. All the methods used as of now to solve the challenge of providing coordination is solved either by using fixed smaller cycle lengths or by making use of detection. Using smaller cycle lengths immediately eliminates the possibility of providing larger green bands. On the other hand, using detection often results in stopping the green band to service a low demand in the minor street. The signal plans designed by this approach increases the capacity of the green bands for the coordinated movement by using a larger super cycle. This gives an opportunity for drivers to pass through successive intersections without having to stop. The minor movements in the individual intersections are serviced multiple times in a single signal cycle to reduce high delays. The ideal cycle length for a given bandwidth is important to identify to get the optimum signal plan for a given dataset. Delays for various movements are compared for different cycle lengths to identify the ideal cycle length. The study also looks at the performance of the new approach with MAXBAND in terms of bandwidth capacity, bandwidth efficiency and the delays. The volume of traffic in the network in one the key factors that affect the performance of signalized intersections. The impact of higher left turning volumes and higher side street volumes are often an important reason for inability to provide longer green bands. The paper investigates the performance of the new approach in these limiting conditions.

关键词： Estimation   Social networking (online)   Blogs   Licenses   Computer science   Urban areas   Cultural differences   Cultural differences   home location estimation   online social networks   Twitter   user profile  

摘要： Social media is used all over the world. Although the home location attribute is available anywhere, few studies have been conducted on the differences in the performance of home location estimation between countries. Because social media is used differently in different countries, the difference between countries in terms of users' relationships needs to be investigated. We consider the performance of graph-based home location estimation in capturing users' relationships, as it is affected by users' social media usage. We analyze user profiles in 10 countries by graph-based estimation and find that some profile attributes, in particular, contribute to the estimation performance for all the countries examined.

关键词： Data processing   Telescopes   Software   Interferometry   Satellites   Parameter estimation   Aerospace engineering   Astronomy   Computer science   Engineering   Optics  

关键词： Energy   Computer science   Design   Materials science  

摘要： Metal laser powder bed fusion (L-PBF) allows for production of complex components using the energy from a laser to locally melt micron-sized powder following a layer-wise approach. Considerable scientific efforts are focused on addressing the influence of the process parameters on the melting stability and the control of material properties, while developing necessary monitoring and characterization tools. The importance of the process atmosphere has largely been undermined in favour of first order parameters connected to the laser scanning. The role of the atmosphere has been limited to the reduction of the operating residual oxygen level down to typically 1000 ppm. This thesis focuses on providing knowledge on the influence of the process atmosphere on the laser metal powder interaction during L-PBF and the resulting properties of the built material in terms of generated defects, microstructure and mechanical properties. Different purities and compositions of generated atmospheres have been investigated to manufacture the most used materials in the field, namely 316L stainless steel, Alloy 718 and Ti-6Al-4V. The scope of process gases was extended from the traditionally employed argon to also include nitrogen, helium and mixtures of argon and helium. Purities from the typical 1000 ppm O2 threshold down to a few ppm were achieved using external monitoring of the atmosphere on both industrial- and laboratory-scale production machines. The investigated materials displayed different sensitivities to the atmosphere composition. 316L stainless steel had limited differences in terms of composition and strength when processed with high purity argon or nitrogen. Only processing with a built-in nitrogen generator, with which the process starts as soon as 10000 ppm residual O2 is reached, led to the increased oxidation of spatter particles and the appearance of large lack-of-fusion defects. A reduction in residual oxygen down to few ppm allowed to significantly hinder the de