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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
461

Mode Matching sensing in Frequency Dependent Squeezing Source for Advanced Virgo plus

Grimaldi, Andrea 07 February 2023 (has links)
Since the first detection of a Gravitational Wave, the LIGO-Virgo Collaboration has worked to improve the sensitivity of their detectors. This continuous effort paid off in the last scientific run, in which the collaboration detected an average of one gravitational wave per week and collected 74 candidates in less than one year. This result was also possible due to the Frequency Independent Squeezing (FIS) implementation, which improved the Virgo detection range for the coalescence between two Binary Neutron Start (BNS) of 5-8\%. However, this incredible result was dramatically limited by different technical issues, among which the most dangerous was the mismatch between the squeezed vacuum beam and the resonance mode of the cavities. The mismatch can be modelled as a simple optical loss in the first approximation. If the beam shape of squeezed vacuum does not match the resonance mode, part of its amplitude is lost and replaced with the incoherent vacuum. However, this modelisation is valid only in simple setups, e.g. if we study the effect inside a single resonance cavity or the transmission of a mode cleaner. In the case of a more complicated system, such as a gravitational wave interferometer, the squeezed vacuum amplitude rejected by the mismatch still travels inside the optical setup. This component accumulates an extra defined by the characteristics of the mismatch, and it can recouple into the main beam reducing the effect of the quantum noise reduction technique. This issue will become more critical in the implementation of the Frequency Dependent Squeezing. This technique is an upgrade of the Frequency Independent Squeezing one. The new setup will increase the complexity of the squeezed beam path. The characterisation of this degradation mechanism requires a dedicated wavefront sensing technique. In fact, the simpler approach based on studying the resonance peak of the cavity is not enough. This method can only estimate the total amount of the optical loss generated by the mismatch, but it cannot characterise the phase shift generated by the decoupling. Without this information is impossible to estimate how the mismatched squeezed vacuum is recoupled into the main beam, and this limits the possibility to foreseen the degradation of the Quantum Noise Reduction technique. For this reason, the Padova-Trento Group studied different techniques for characterising Mode Matching. In particular, we proposed implementing the Mode Converter technique developed by Syracuse University. This technique can fully characterise the mismatch of a spherical beam, and it can be the first approach to monitoring the mismatch. However, this method is not enough for the Frequency Dependent Squeezer source since it cannot detect the mismatch generated by the astigmatism of the incoming beam. In fact, the Frequency Dependent Squeezer Source case uses off-axis reflective telescopes to reduce the power losses generated by transmissive optics. This setup used curved mirrors that induce small astigmatic aberrations as a function of the beam incident angle. These aberrations are present by design, and the standard Mode Converter Technique will not detect them. To overcome this issue, I proposed an upgrade of the Mode Converter technique, which can extend the detection to this kind of aberration.
462

On Independent Reference Priors

Lee, Mi Hyun 09 January 2008 (has links)
In Bayesian inference, the choice of prior has been of great interest. Subjective priors are ideal if sufficient information on priors is available. However, in practice, we cannot collect enough information on priors. Then objective priors are a good substitute for subjective priors. In this dissertation, an independent reference prior based on a class of objective priors is examined. It is a reference prior derived by assuming that the parameters are independent. The independent reference prior introduced by Sun and Berger (1998) is extended and generalized. We provide an iterative algorithm to derive the general independent reference prior. We also propose a sufficient condition under which a closed form of the independent reference prior is derived without going through the iterations in the iterative algorithm. The independent reference prior is then shown to be useful in respect of the invariance and the first order matching property. It is proven that the independent reference prior is invariant under a type of one-to-one transformation of the parameters. It is also seen that the independent reference prior is a first order probability matching prior under a sufficient condition. We derive the independent reference priors for various examples. It is observed that they are first order matching priors and the reference priors in most of the examples. We also study an independent reference prior in some types of non-regular cases considered by Ghosal (1997). / Ph. D.
463

Time-Variant Components to Improve Bandwidth and Noise Performance of Antennas

Loghmannia, Pedram 18 January 2021 (has links)
Without noise, a wireless system would be able to transmit and receive signals over an arbitrary long-distance. However, practical wireless systems are not noise-free, leading to a limited communication range. Thus, the design of low-noise devices (such as antennas, amplifiers, and filters) is essential to increase the communication range. Also, it is well known that the noise performance of a receiving radio is primarily determined by the frontend including the antenna, filter, and a low-noise amplifier. In our first design, we intend to reduce the noise level of the receiving system by integrating a parametric amplifier into the slot antenna. The parametric amplifier utilizes nonlinear and/or time-variant properties of reactive elements (capacitors and/or inductors) to amplify radio frequency signals. Also, the parametric amplifier offers superior noise performance due to its reactive nature. We utilize the parametric amplifier to design a low-noise active matching circuit for electrically small antennas in our second design. Using Chu's limit and the Bode-Fano bound, we show a trade-off between the noise and bandwidth of the electrically small antennas. In particular, to make the small antenna wideband, one needs to introduce a mismatch between the antenna and the amplifier. Due to the mismatch, the effect of the low-noise amplifier becomes even more critical and that is why we choose the parametric amplifier as a natural candidate. As a realized design, a loop antenna is configured as a receiver, and the up-converter parametric amplifier is connected to it leading to a low-noise and wideband active matching circuit. The structure is simulated using a hybrid simulation technique and its noise performance is compared to the transistor counterpart. Our simulation and measurement results show more than 20 times bandwidth improvement at the expense of a 2 dB increase in the noise figure compared to the passive antenna counterpart. / Doctor of Philosophy / Nowadays, there is a high demand for compact and high-speed electronic devices such as cellphones, tablets, laptops, etc. It is therefore essential to design a miniaturized wideband antenna. Unfortunately, a trade-off exists between the bandwidth and gain of small antennas. The trade-off is based on some fundamental limits and extends to all small and passive antennas, regardless of their shape or structure. By using an active component such as an amplifier, the gain-bandwidth trade-off can be improved. However, we show that the active component adds noise to the receiving system leading to a new trade-off between noise and bandwidth in the receiving structures. In other words, utilizing the active component does not solve the problem and just replaces the gain-bandwidth trade-off with the noise-bandwidth trade-off. To improve the noise-bandwidth trade-off, we propose a new receiving structure in which we use the parametric amplifier instead of a commercially available transistor amplifier. The noise performance of the parametric amplifier is extremely better than the transistor amplifier leading to lower noise for the specified bandwidth. In particular, we improved the noise performance of the receiving system by 3 dB leading to doubling the communication distance.
464

Vision-Based Self-Motion Estimation in a Fixed-Wing Aerial Vehicle

Parks, Matthew Raymond 06 September 2006 (has links)
This paper describes a complete algorithm to estimate the motion of a fixed-wing aircraft given a series of digitized flight images. The algorithm was designed for fixed-wing aircraft because carefully procured flight images and corresponding navigation data were available to us for testing. After image pre-processing, optic flow data is determined by automatically finding and tracking good features between pairs of images. The image coordinates of matched features are then processed by a rigid-object linear optic flow-motion estimation algorithm. Input factors are weighed to provide good testing techniques. Error analysis is performed with simulation data keeping these factors in mind to determine the effectiveness of the optic flow algorithm. The output of this program is an estimate of rotation and translation of the imaged environment in relation to the camera, and thereby the airplane. Real flight images from NASA test flights are used to confirm the accuracy of the algorithm. Where possible, the estimated motion parameters are compared with recorded flight instrument data to confirm the correctness of the algorithm. Results show that the algorithm is accurate to within a degree provided that enough optic flow feature points are tracked. / Master of Science
465

Assessing the Impact of the Jepara Furniture Value Chain Project

Clements, Corinna 07 September 2016 (has links)
This thesis assesses the impact of the Jepara Furniture Value Chain (FVC) project, which was conducted by the Center for International Forestry Research (CIFOR) to address challenges faced by small-scale furniture producers in Jepara, Indonesia. This assessment focuses on the effect of membership in the APKJ, a producer association started as part of the project. The propensity score for association membership was estimated using unchanging firm and owner characteristics, as well as information recalled about firm operations in 2009 (before the association was formed). Propensity score matching was used to compare outcome variables of association members and non-members. Results suggest that membership in the APKJ does not have a significant effect on profit levels. Using differenced current and recalled marketing and production behaviors as outcome variables with propensity score matching indicates that members have improved their bargaining position and marketing behaviors more than non-members since 2009. Additionally, APKJ members are more likely to have obtained certificates of timber legality / Master of Science
466

An Exploration of Circuit Similarity for Discovering and Predicting Reusable Hardware

Zeng, Kevin 27 April 2016 (has links)
A modular reuse-based design methodology has been one of the most important factors in improving hardware design productivity. Traditionally, reuse involves manually searching through repositories for existing components. This search can be tedious and often unfruitful. In order to enhance design reuse, an automated discovery technique is proposed: a reference circuit is compared with an archive of existing designs such that similar circuits are suggested throughout the design phase. To achieve this goal, methods for assessing the similarity of two designs are necessary. Different techniques for comparing the similarity of circuits are explored utilizing concepts from different domains. A new similarity measure was developed using birthmarks that allows for fast and efficient comparison of large and complex designs. Applications where circuit similarity matching can be utilized are examined such as IP theft detection and reverse engineering. Productivity experiments show that automatically suggesting reusable designs to the user could potentially increase productivity by more than 34% on average. / Ph. D.
467

Empirical Analysis of Algorithms for the k-Server and Online Bipartite Matching Problems

Mahajan, Rutvij Sanjay 14 August 2018 (has links)
The k–server problem is of significant importance to the theoretical computer science and the operations research community. In this problem, we are given k servers, their initial locations and a sequence of n requests that arrive one at a time. All these locations are points from some metric space and the cost of serving a request is given by the distance between the location of the request and the current location of the server selected to process the request. We must immediately process the request by moving a server to the request location. The objective in this problem is to minimize the total distance traveled by the servers to process all the requests. In this thesis, we present an empirical analysis of a new online algorithm for k-server problem. This algorithm maintains two solutions, online solution, and an approximately optimal offline solution. When a request arrives we update the offline solution and use this update to inform the online assignment. This algorithm is motivated by the Robust-Matching Algorithm [RMAlgorithm, Raghvendra, APPROX 2016] for the closely related online bipartite matching problem. We then give a comprehensive experimental analysis of this algorithm and also provide a graphical user interface which can be used to visualize execution instances of the algorithm. We also consider these problems under stochastic setting and implement a lookahead strategy on top of the new online algorithm. / MS / Motivated by real-time logistics, we study the online versions of the well-known bipartite matching and the k-server problems. In this problem, there are servers (delivery vehicles) located in different parts of the city. When a request for delivery is made, we have to immediately assign a delivery vehicle to this request without any knowledge of the future. Making cost-effective assignments, therefore, becomes incredibly challenging. In this thesis, we implement and empirically evaluate a new algorithm for the k-server and online matching problems.
468

Energy Harvesting IC Design for an Electromagnetic Generator Based on the Split Capacitor Approach

Dancy, Alant'e Jaquan 18 September 2018 (has links)
The proposed energy harvesting system intends to harvest vibrational energy via an electromagnetic generator (EMG). The proposed circuit intends to extract maximum power from the EMG by utilizing the maximum power transfer theorem which states that maximum power is transferred to the load when the source resistance equals the load resistance. The proposed circuit is a synchronous split-capacitor boost converter operating in boundary conduction mode (BCM) to achieve impedance matching and therefore maximum power transferred to the load. The circuit topology combines the rectifier and power stage to reduce power loss of the power management integrated circuit (PMIC). The proposed circuit is designed and fabricated in 130 nm BiCMOS technology. The circuit is validated through schematic level simulations and post-layout simulations. The results conclude the proposed circuit and control operates in a manner to achieve BCM. / Master of Science / Tracking and monitoring systems and products has become more prevalent in our society. Consumers want to know when a package they ordered will arrive. Grocery stores would like to track a produce from harvest to the shelves, ensuring their produce is safe to eat. Produce should be kept around 0 °C and if it exceeds that anywhere during the supply chain, the store should be alerted. Wireless sensor nodes (WSNs) are such devices that would be able to monitor the temperature of produce or the location of a package. These devices must be small, reliable, long-life and cost efficient. Using a battery to power WSNs is an inconvenience as the battery must be replaced often. The proposed circuit enables a self-sufficient WSN that is compact, dependable, long-lasting and economical when deployed at large scale. The proposed circuit has been designed, fabricated and proven through simulations.
469

Robust Exact Algorithms for the Euclidean Bipartite Matching Problem

Gattani, Akshaykumar Gopalkrishna 06 July 2023 (has links)
The minimum cost bipartite matching problem is a well-studied optimization problem in computer science and operations research, with wide-ranging applications in fields such as machine learning, economics, transportation, logistics and biology. A special instance of this problem is the computation of the p-Wasserstein distance which we define next. Given a complete bipartite graph with two disjoint sets of n points in d-dimensional Euclidean space and an integer p ≥ 1, let the cost of an edge be the p-th power of the Euclidean distance between its endpoints. The objective of this problem is to find a minimum-cost matching in this complete bipartite graph. The Hungarian algorithm is a classical method that solves this problem in O(n^3) time. There are many algorithms that have a run time better than that of the Hungarian algorithm if the graphs have non-negative integer edge costs bounded by C. Since the input points have real-valued coordinates and the Euclidean distances can be irrational, such algorithms only return an approximate matching. Thus, the Hungarian algorithm remains the fastest known algorithm to compute an exact matching. In this thesis, we implement a new algorithm in the divide and conquer framework that computes the exact p-Wasserstein distance and has a run time asymptotically better than the Hungarian algorithm for stochastic point sets. Inspired by the techniques used in the algorithm, we also design an alternate version of the Hungarian algorithm that uses a grid- based approach. Our experimental analysis shows that both of our algorithms significantly outperform the classical Hungarian algorithm. / Master of Science / Suppose we have two sets of equal number of items and a list of compatible pairs of items, where a pair is considered compatible if its items belong to different sets. A perfect matching is a subset of compatible pairs where each item is paired with exactly one other item. When trying to find a perfect matching, there may be multiple options, and minimizing the cost of the perfect matching is often desired. This is referred to as the minimum cost bipartite matching problem, which is extensively studied due to its importance in algorithmic theory and operations research. A special instance of this problem is the calculation of the p- Wasserstein distance. It has many practical applications in fields such as machine learning, economics, transportation, logistics and biology. The Hungarian algorithm is the only known algorithm that can compute the exact p-Wasserstein distance. Therefore, our focus is to develop exact algorithms for this problem that perform better than the Hungarian algorithm and can scale efficiently to large datasets.
470

A Novel Method to Locate Targets Using Active Vision and Robotic Inertial Navigation Data

Simone, Matthew James 06 July 2006 (has links)
Unmanned vehicles are increasingly being used for mobile sensing missions. These missions can range from target acquisition to chemical and biological sensing. The reason why these vehicles are increasingly being used is because they can carry many different types of sensors and can function as a cheap platform for carrying these sensors. The sensing that will be explained in this thesis is target acquisition. Target acquisition is the act of locating the exact position of an "area of interest." Currently this task can be completed with different types of complex range sensors. This thesis presents a type of target acquisition scheme for unmanned vehicles that will use a combination of cheap, simple vision sensors and robot inertial navigation data in order to accurately measure the location of a target in real world coordinates. This thesis will first develop an accurate waypoint driving algorithm that will either use dead reckoning or GPS/ compass sensors. We will then develop a robust target extraction algorithm that will be able to pick out a target in an image. After this is completed we will develop an algorithm that will be used to find the distance to the target from the robot. This algorithm will be based on a type of active vision system. Finally we will integrate all of these algorithms together in order to develop a target extraction technique that will be able to accurately find the distance to the target. With the distance we can then find the real world location of the target. / Master of Science

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