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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.
81

Diversité structurelle et évolution contrastée des génomes cytoplasmiques des plantes à fleurs : une approche phylogénomique chez les Oleaceae / Structural diversity and contrasted evolution of cytoplasmic genomes in flowering plants : a phylogenomic approach in Oleaceae

Van de Paer, Céline 19 December 2017 (has links)
Chez les plantes, la dynamique structurelle et l'évolution concertée des génomes nucléaire et cytoplasmiques restent peu documentées. L'objectif de cette thèse était d'étudier la diversité structurelle et l'évolution des mitogénomes et des plastomes chez les Oleaceae à l'aide d'une approche de phylogénomique. Nous avons d'abord assemblé des mitogénomes à partir de données de séquençage de faible couverture, obtenues à partir de matériel frais et d'herbier. Une grande variation de structure du mitogénome a été observée chez l'olivier, et un gène chimérique potentiellement associé à un type de stérilité mâle a été identifié. Enfin, nous avons étudié l'évolution des plastomes et des gènes mitochondriaux chez les Oleaceae. Une accélération de l'évolution du plastome a été observée dans deux lignées indépendantes. Ce changement de trajectoire évolutive pourrait être la conséquence d'une transmission occasionnelle de plastes par le pollen, modifiant les pressions sélectives sur certains gènes. / In plants, the structural dynamics and concerted evolution of nuclear and cytoplasmic genomes are poorly understood. The objective of this thesis was to study the structural diversity and evolution of mitogenomes and plastomes in the family Oleaceae with a phylogenomic approach. First, we assembled mitogenomes from low-coverage sequencing data obtained from live and herbarium material. Considerable structural variation of mitogenomes was observed in the olive, and a chimeric gene potentially associated to a type of male sterility was detected. Finally, we studied the evolution of plastomes and mitochondrial genes in the Oleaceae. Accelerated evolution of plastomes was observed in two independent lineages. This change of evolutionary rate could be the consequence of an occasional transmission of plastids with pollen, modifying selective pressures on some genes.
82

Condition monitoring of axial piston pump

Li, Zeliang Eric 30 November 2005
<p>Condition Monitoring is an area that has seen substantial growth in the last few decades. The purpose for implementing condition monitoring in industry is to increase productivity, decrease maintenance costs and increase safety. Therefore, condition monitoring can be used not only for planning maintenance but also for allowing the selection of the most efficient equipment to minimize operating costs. </p><p>Hydraulic systems are widely used in industry, aerospace and agriculture and are becoming more complex in construction and in function. Reliability of the systems must be supported by an efficient maintenance scheme. Due to component wear or failure, some system parameters may change causing abnormal behaviour in each component or in the overall circuit. Research in this area has been substantial, and includes specialized studies on artificial fault simulation at the University of Saskatchewan. In this research, an axial pump was the focus of the study. In an axial piston pump, wear between the various faces of components can occur in many parts of the unit. As a consequence, leakage can occur in locations such as between the valve plate and barrel, the drive shaft and oil wiper, the control piston and piston guide, and the swash plate and slippers. In this study, wear (and hence leakage) between the pistons and cylinder bores in the barrel was of interest. Researchers at the University of Saskatchewan, as well as at other research institutions, have been involved in studies to detect wear in pumps using a variety of condition monitoring algorithms. However, to verify the reliability and indeed, limitations of some of the approaches, it is necessary to test the algorithms on systems with real leakage. To introduce actual wear in the piston of pumps can be very difficult and very expensive. Hence, introducing piston wear in an artificial manner would be of great benefit in the evaluation of various condition monitoring techniques.</p><p>Since leakage is a direct consequence of piston wear, it is logical to conclude that varying the leakage in some prescribed manner can be used to artificially simulate wear. A prime concern, therefore, is to be able to precisely understand the dynamic relationships between the wear and leakage and the effect it has on the output flow or pressure waveform from the pump.</p><p>Introducing an artificial leakage to simulate the wear of pistons is a complex task. The creation of an artificial leakage path was not simply a process of providing a resistive short to the tank at the outlet of the pump port as was done in other studies. The objective was to create a leakage environment that would simulate leakage from a single piston (or combination of several pistons thereof). The complexity of the flow and pressure ripple waveforms (which various condition monitoring algorithms did require) was such that a more comprehensive leakage behaviour had to be modeled and experimentally created. A pressure control servo valve with a very high frequency response was employed to divert the flow from the pump outlet with a prescribed waveform directly to the tank to simulate the piston leakage from the high pressure discharge chamber to the pump case drain chamber as the simulated worn piston made contact with the high pressure chamber. The control algorithm could mimic the action of a single worn piston at various degrees of wear. The experimental results indicated that the experimental system could successfully introduce artificial leakage into the pump which was quite consistent with a unit with a real worn piston. Comparisons of the pressure ripples from an actual faulty pump (worn piston) and the artificial faulty pump (artificial leakage) are presented.</p>
83

Condition monitoring of axial piston pump

Li, Zeliang Eric 30 November 2005 (has links)
<p>Condition Monitoring is an area that has seen substantial growth in the last few decades. The purpose for implementing condition monitoring in industry is to increase productivity, decrease maintenance costs and increase safety. Therefore, condition monitoring can be used not only for planning maintenance but also for allowing the selection of the most efficient equipment to minimize operating costs. </p><p>Hydraulic systems are widely used in industry, aerospace and agriculture and are becoming more complex in construction and in function. Reliability of the systems must be supported by an efficient maintenance scheme. Due to component wear or failure, some system parameters may change causing abnormal behaviour in each component or in the overall circuit. Research in this area has been substantial, and includes specialized studies on artificial fault simulation at the University of Saskatchewan. In this research, an axial pump was the focus of the study. In an axial piston pump, wear between the various faces of components can occur in many parts of the unit. As a consequence, leakage can occur in locations such as between the valve plate and barrel, the drive shaft and oil wiper, the control piston and piston guide, and the swash plate and slippers. In this study, wear (and hence leakage) between the pistons and cylinder bores in the barrel was of interest. Researchers at the University of Saskatchewan, as well as at other research institutions, have been involved in studies to detect wear in pumps using a variety of condition monitoring algorithms. However, to verify the reliability and indeed, limitations of some of the approaches, it is necessary to test the algorithms on systems with real leakage. To introduce actual wear in the piston of pumps can be very difficult and very expensive. Hence, introducing piston wear in an artificial manner would be of great benefit in the evaluation of various condition monitoring techniques.</p><p>Since leakage is a direct consequence of piston wear, it is logical to conclude that varying the leakage in some prescribed manner can be used to artificially simulate wear. A prime concern, therefore, is to be able to precisely understand the dynamic relationships between the wear and leakage and the effect it has on the output flow or pressure waveform from the pump.</p><p>Introducing an artificial leakage to simulate the wear of pistons is a complex task. The creation of an artificial leakage path was not simply a process of providing a resistive short to the tank at the outlet of the pump port as was done in other studies. The objective was to create a leakage environment that would simulate leakage from a single piston (or combination of several pistons thereof). The complexity of the flow and pressure ripple waveforms (which various condition monitoring algorithms did require) was such that a more comprehensive leakage behaviour had to be modeled and experimentally created. A pressure control servo valve with a very high frequency response was employed to divert the flow from the pump outlet with a prescribed waveform directly to the tank to simulate the piston leakage from the high pressure discharge chamber to the pump case drain chamber as the simulated worn piston made contact with the high pressure chamber. The control algorithm could mimic the action of a single worn piston at various degrees of wear. The experimental results indicated that the experimental system could successfully introduce artificial leakage into the pump which was quite consistent with a unit with a real worn piston. Comparisons of the pressure ripples from an actual faulty pump (worn piston) and the artificial faulty pump (artificial leakage) are presented.</p>
84

In vitro evaluation of bacterial penetration around varnish-lined amalgam restorations a thesis submitted in partial fulfillment ... pedodontics /

Vonk, James D. January 1969 (has links)
Thesis (M.S.)--University of Michigan, 1969.
85

In vitro evaluation of bacterial penetration around varnish-lined amalgam restorations a thesis submitted in partial fulfillment ... pedodontics /

Vonk, James D. January 1969 (has links)
Thesis (M.S.)--University of Michigan, 1969.
86

Security of Big Data: Focus on Data Leakage Prevention (DLP)

Nyarko, Richard January 2018 (has links)
Data has become an indispensable part of our daily lives in this era of information age. The amount of data which is generated is growing exponentially due to technological advances. This voluminous of data which is generated daily has brought about new term which is referred to as big data. Therefore, security is of great concern when it comes to securing big data processes. The survival of many organizations depends on the preventing of these data from falling into wrong hands. Because if these sensitive data fall into wrong hands it could cause serious consequences. For instance, the credibility of several businesses or organizations will be compromised when sensitive data such as trade secrets, project documents, and customer profiles are leaked to their competitors (Alneyadi et al, 2016).  In addition, the traditional security mechanisms such as firewalls, virtual private networks (VPNs), and intrusion detection systems/intrusion prevention systems (IDSs/IPSs) are not enough to prevent against the leakage of such sensitive data. Therefore, to overcome this deficiency in protecting sensitive data, a new paradigm shift called data leakage prevention systems (DLPSs) have been introduced. Over the past years, many research contributions have been made to address data leakage. However, most of the past research focused on data leakage detection instead of preventing against the leakage. This thesis contributes to research by using the preventive approach of DLPS to propose hybrid symmetric-asymmetric encryption to prevent against data leakage.  Also, this thesis followed the Design Science Research Methodology (DSRM) with CRISP-DM (CRoss Industry Standard Process for Data Mining) as the kernel theory or framework for the designing of the IT artifact (method). The proposed encryption method ensures that all confidential or sensitive documents of an organization are encrypted so that only users with access to the decrypting keys can have access. This is achieved after the documents have been classified into confidential and non-confidential ones with Naïve Bayes Classifier (NBC).  Therefore, any organizations that need to prevent against data leakage before the leakage occurs can make use of this proposed hybrid encryption method.
87

Modeling and reduction of gate leakage during behavioral synthesis of nanoscale CMOS circuits.

Velagapudi, Ramakrishna 05 1900 (has links)
The major sources of power dissipation in a nanometer CMOS circuit are capacitive switching, short-circuit current, static leakage and gate oxide tunneling. However, with the aggressive scaling of technology the gate oxide direct tunneling current (gate leakage) is emerging as a prominent component of power dissipation. For sub-65 nm CMOS technology where the gate oxide (SiO2) thickness is very low, the direct tunneling current is the major form of tunneling. There are two contribution parts in this thesis: analytical modeling of behavioral level components for direct tunneling current and propagation delay, and the reduction of tunneling current during behavioral synthesis. Gate oxides of multiple thicknesses are useful in reducing the gate leakage dissipation. Analytical models from first principles to calculate the tunneling current and the propagation delay of behavioral level components is presented, which are backed by BSIM4/5 models and SPICE simulations. These components are characterized for 45 nm technology and an algorithm is provided for scheduling of datapath operations such that the overall tunneling current dissipation of a datapath circuit under design is minimal. It is observed that the oxide thickness that is being considered is very low it may not remain constant during the course of fabrication. Hence the algorithm takes process variation into consideration. Extensive experiments are conducted for various behavioral level benchmarks under various constraints and observed significant reductions, as high as 75.3% (with an average of 64.3%).
88

Měření těsnosti hermetických prostor na JE / Tightness measurement of hermetic compartments in NPP

Sklenár, Ondrej January 2011 (has links)
This diploma thesis deals with measuring the tightness of the hermetic area of nuclear power plant in the way of improving safety. Describes the layout and function of this area - the primary circuit of NPP with WWER 440/213 reactors, as well as methodology for leakage search and leakage calculation procedures. Personal contribution to the issue is a proposal improving tightness of the current state in hermetic area of NPP Jaslovské Bohunice – transition of jacketed pipe designed to collect water from the floor in the box of the steam generator to the heat exchanger of the shower system. This system belongs to the safety system designed to reduce pressure in the LOCA type of accident.
89

Statistical Leakage Estimation Using Artificial Neural Networks

Muralidharan Nair, Mithun January 2014 (has links)
No description available.
90

Towards Comprehensive Side-channel Resistant Embedded Systems

Yao, Yuan 17 August 2021 (has links)
Embedded devices almost involve every part of our lives, such as health condition monitoring, communicating with other people, traveling, financial transactions, etc. Within the embedded devices, our private information is utilized, collected and stored. Cryptography is the security mechanism within the embedded devices for protecting this secret information. However, cryptography algorithms can still be analyzed and attacked by malicious adversaries to steal secret data. There are different categories of attacks towards embedded devices, and the side-channel attack is one of the powerful attacks. Unlike analyzing the vulnerabilities within the cryptography algorithm itself in traditional attacks, the side-channel attack observes the physical effect signals while the cryptography algorithm runs on the device. These physical effects include the power consumption of the devices, timing, electromagnetic radiations, etc., and we call these physical effects that carry secret information side-channel leakage. By statistically analyzing these side-channel leakages, an attacker can reconstruct the secret information. The manifestation of side-channel leakage happens at the hardware level. Therefore, the designer has to ensure that the hardware design of the embedded system is secure against side-channel attacks. However, it is very arduous work. An embedded systems design including a large number of electronic components makes it very difficult to comprehensively capture every side-channel vulnerability, locate the root cause of the side-channel leakage, and efficiently fix the vulnerabilities. In this dissertation, we developed methodologies that can help designers detect and fix side-channel vulnerabilities within the embedded system design at low cost and early design stage. / Doctor of Philosophy / Side-channel leakage, which reveals the secret information from the physical effects of computing secret variables, has become a serious vulnerability in secure hardware and software implementations. In side-channel attacks, adversaries passively exploit variations such as power consumption, timing, and electromagnetic emission during the computation with secret variables to retrieve sensitive information. The side-channel attack poses a practical threat to embedded devices, an embedded device's cryptosystem without adequate protection against side-channel leakage can be easily broken by the side-channel attack. In this dissertation, we investigate methodologies to build up comprehensive side-channel resistant embedded systems. However, this is challenging because of the complexity of the embedded system. First, an embedded system integrates a large number of components. Even if the designer can make sure that each component is protected within the system, the integration of the components will possibly introduce new vulnerabilities. Second, the existing side-channel leakage evaluation of embedded system design happens post-silicon and utilizes the measurement on the prototype of the taped-out chip. This is too late for mitigating the vulnerability in the design. Third, due to the complexity of the embedded system, even though the side-channel leakage is detected, it is very hard to precisely locate the root cause within the design. Existing side-channel attack countermeasures are very costly in terms of design overhead. Without a method that can precisely identify the side-channel leakage source within the design, huge overhead will be introduced by blindly add the side-channel countermeasure to the whole design. To make the challenge even harder, the Power Distribution Network (PDN) where the hardware design locates is also vulnerable to side-channel attacks. It has been continuously demonstrated by researchers that attackers can place malicious circuits on a shared PDN with victim design and open the opportunities for the attackers to inject faults or monitoring power changes of the victim circuit. In this dissertation, we address the challenges mentioned above in designing a side-channel-resistant embedded system. We categorize our contributions into three major aspects—first, we investigating the effects of integration of security components and developing corresponding countermeasures. We analyze the vulnerability in a widely used countermeasure - masking, and identify that the random number transfer procedure is a weak link in the integration which can be bypassed by the attacker. We further propose a lightweight protection scheme to protect function calls from instruction skip fault attacks. Second, we developed a novel analysis methodology for pre-silicon side-channel leakage evaluation and root cause analysis. The methodology we developed enables the designer to detect the side-channel leakage at the early pre-silicon design stage, locate the leakage source in the design precisely to the individual gate and apply highly targeted countermeasure with low overhead. Third, we developed a multipurpose on-chip side-channel and fault monitoring extension - Programmable Ring Oscillator (PRO), to further guarantee the security of PDN. PRO can provide on-chip side-channel resistance, power monitoring, and fault detection capabilities to the secure design. We show that PRO as application-independent integrated primitives can provide side-channel and fault countermeasure to the design at a low cost.

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