Vibro-impact systems are extensively used in engineering and physics field, such as impact damper, particle accelerator, etc. These systems are most basic elements of many real world applications such as cars and aircrafts. Such vibro-impact systems possess both the continuous characteristics as continuous dynamical systems and discrete characteristics introduced by impacts at the same time. Thus, an appropriately developed discrete mapping system is required for such vibro-impact systems in order to simplify investigation on the complexity of motions. In this dissertation, a few vibro-impact oscillators will be investigated using discrete maps in order to understand the dynamics of vibro-impact systems. Before discussing the nonlinear dynamical phenomena and behaviors of these vibro-impact oscillators, the theory for nonlinear discrete systems will be applied to investigate a two-dimensional discrete system (Henon Map). And the complete dynamics of such a nonlinear discrete dynamical system will be presented using the inversed mapping method. Neimark bifurcations in such a discrete system have also drawn a lot of interest to the author. The Neimark bifurcations in such a system have actually formed a boundary dividing the stable solution of positive and negative maps (inversed mapping). For the first time, one is able to obtain a complete prediction of both stable and unstable solutions in such a discrete dynamical system. And a detailed parameter map will be presented to illustrate how changes of parameters could affect the different solutions in such a system. Then, the theory of discontinuous dynamical systems will be adopted to investigate the vibro-impact dynamics in several vibro-impact systems. First, the bouncing ball dynamics will be analytically discussed using a single discrete map. Different types of motions (periodic and chaotic) will be presented to understand the complex behavior of this simple model. Analytical condition will be expressed using switching phase of the system in order to easily predict stick and grazing motion. After that, a horizontal impact damper model will be studied to show how complex periodic motions could be developed analytically. Complete set of symmetric and asymmetric periodic motions can also be easily predicted using the analytical method. Finally, a Fermi-Accelerator being excited at both ends will be discussed in detail for application. Different types of motions will be thoroughly studied for such a vibro-impact system under both same and different excitations.

Chlamydia trachomatis is a Gram-negative, obligate intracellular pathogen that is the causative agent of sexually transmitted infections and the ocular disease trachoma. Chlamydia trachomatis undergoes a biphasic developmental cycle differentiating between the infectious elementary body (EB) and the replicative reticulate body (RB). Under certain stress conditions, C. trachomatis can stall its developmental cycle and enter an aberrant state termed persistence. While in a persistent state, C. trachomatis is refractory toward antibiotics, can evade the host immune response, and becomes undetectable using standard clinical detection methods. Environmental and other pathogenic microbes are known to utilize partner switching mechanisms (PSM) to regulate sigma factors used to initiate a stress response. For this reason, this study focuses on the chlamydial PSM, its role in regulating the availability of the housekeeping sigma factor σ66, and its role in the developmental cycle and stress response of C. trachomatis. The chlamydial PSM is composed of five known proteins: the anti-sigma factor RsbW, two anti-anti-sigma factors RsbV1 and RsbV2, a regulatory phosphatase RsbU, and a second phosphatase-like protein CTL0852. In order to test the role of the PSM in the chlamydial stress response, a panel of C. trachomatis rsbV1 mutants were generated, persistence inducing iron starvation and tryptophan starvation cell culture conditions were optimized, and growth of the rsbV1 mutants under iron starvation conditions were assayed. No significant differences were seen between rsbV1 mutants under iron starvation nor recovery conditions as determined by progeny production and inclusion size analysis. Furthermore, this study generated PSM protein producing Escherichia coli strains for in vitro protein work and performed operon mapping of the PSM genes of C. trachomatis to help aid in future studies of the chlamydial PSM by facilitating the development of new chlamydial PSM mutants. This study gives phylogenetic support to the classification of ctl0852 as a chlamydial PSM gene by comparing relative mutations rates of PSM genes across chlamydial species.

Mobile networks are highly unpredictable and might be unreliable for real-time mobile video streaming due to various wireless network conditions. Video frames could be delayed or lost and could affect the perceived quality of a video stream. The time-sensitive nature of real-time video streaming is to deliver the video frames to the mobile devices and to provide smooth playback. This study examines the concept of streaming the video frames over two wireless channels from the server to the mobile device in order to play the complete video frame sequence to the mobile users. The simulator is been developed to provide a reliable video streaming until if there is a missing frame(s). A switching mechanism is been implemented in the client side to switch between the video streams to replace the missing frames. This will provide a smooth playback of the video stream and perceived video quality to the mobile user.

abstract: Humans have an excellent ability to analyze and process information from multiple domains. They also possess the ability to apply the same decision-making process when the situation is familiar with their previous experience. Inspired by human's ability to remember past experiences and apply the same when a similar situation occurs, the research community has attempted to augment memory with Neural Network to store the previously learned information. Together with this, the community has also developed mechanisms to perform domain-specific weight switching to handle multiple domains using a single model. Notably, the two research fields work independently, and the goal of this dissertation is to combine their capabilities. This dissertation introduces a Neural Network module augmented with two external memories, one allowing the network to read and write the information and another to perform domain-specific weight switching. Two learning tasks are proposed in this work to investigate the model performance - solving mathematics operations sequence and action based on color sequence identification. A wide range of experiments with these two tasks verify the model's learning capabilities. / Dissertation/Thesis / Masters Thesis Computer Science 2020

The phylum of Chlamydiota is composed of gram negative obligate intracellular bacteria that live as symbionts of diverse eukaryotes, from protists to animals and humans. Members of the phylum can be split into two groups: the environmental Chlamydia, which includes symbionts of amoeba, and the pathogenic Chlamydia, which includes species infecting animals, birds, and humans and includes Chlamydia trachomatis the leading cause of reportable, bacterial sexually transmitted infections and the ocular infection, trachoma. The characterized phylum members undergo a biphasic developmental cycle alternating between the infectious elementary body (EB) and the replicative reticulate body (RB), with each form having distinct morphological and physiological properties. Differentiation between these forms occurs within a host cell membrane-derived vacuole termed the inclusion. The molecular mechanisms governing and executing bacterial development and RB growth remain unclear. The essentiality and uniqueness of development makes it a prime target for the development of novel, chlamydial-specific therapeutics. Reductive evolution has resulted in the loss of or fragmentation of numerous metabolic pathways, particularly in the pathogenic Chlamydia (~1 Mbp genome) as compared to the environmental Chlamydia (~2.5 Mbp). We hypothesize that the bacterium senses environmental changes (host cytoplasm) to ensure that development and growth coincide with host cell energy and metabolite levels. We predict that an encoded partner switching mechanism (PSM) plays a key role in: 1) regulation of growth by acting as a molecular throttle through regulation of the housekeeping sigma factor, and 2) differentiation by impacting the composition of the sigma factor pool allowing for transcriptional changes needed for developmental transitions. We also predict that PSM regulation occurs through sensing of nucleotide triphosphates, TCA-cycle intermediates, metal concentrations, and redox. Canonical PSMs have a PP2C-type sensor phosphatase (SP), an anti-sigma factor (ASF, serine kinase), an anti-anti-sigma factor (AASF, substrate of the SP and ASF) and a stress-response related alternative sigma factor. The PSM in pathogenic Chlamydia is atypical, and despite its reduced genome, is comprised of two SPs (RsbU which responds to α-ketoglutarate and CTL0852), two AASFs (RsbV1 and RsbV2), one ASF (RsbW), and, unusually, the ASF regulates the availability of the “housekeeping” sigma factor, σ66. To test our hypotheses, we first constructed and purified a variety of amino acid point mutants of the two AASFs, ASF, and the SP for in vitro analyses. Kinase and phosphatase activity towards RsbV1/V2 was measured in the presence of different metals, phosphate donors, and pH and redox conditions. Phos-tag acrylamide gels were used to assess protein phosphorylation status. We discovered that metalation impacts enzyme activity and the substrate specificity of RsbU, and that RsbW can use multiple phosphate donors. Prior work, and our data, found that RsbW and RsbU have higher enzymatic activity towards RsbV1 than RsbV2, leading us to explore the importance of RsbV2 in chlamydial biology. Genome gazing revealed that environmental Chlamydia possess a single AASF, and bioinformatic analyses support that it is more similar to RsbV2 than RsbV1 suggesting that the pathogenic Chlamydia gained RsbV1. Comparing the biochemical features of the two AASFs provides potential reasons for the different enzyme affinities. To flesh out the in vivo importance of each AASF, we characterized bacterial growth, infectious progeny production, and the levels of RsbV1/V2 in a cell culture infection model using a collection of C. trachomatis L2 rsbV1 null or rsbV2 knockdown strains. We also overexpressed the AASFs in strains grown with different glucose levels. Note that C. trachomatis is an auxotroph for glucose-6-phosphate. In normal chlamydial culture glucose medium levels, the rsbV1 null strain showed an ~1 log reduction in infectious progeny numbers while the rsbV2 knockdown or AASF overexpression strains had no defects. We also observed that the rsbV1 null strain has a developmental delay and exhibits growth differences in response to glucose levels, i.e. a functional PSM seems to set a “growth cap” in response to different glucose availability. Immunoblotting analysis of RsbV1/V2 demonstrated the presence of both proteins throughout development, and protein levels remained the same in low or high glucose levels and in the wild type or rsbV1 null strains (measuring RsbV2 only for the RsbV1 null strain). These results tell us that the AASF levels have minimal impact on chlamydial biology, suggesting that phosphorylation status is key to regulation. To assess phosphorylation, we used protein pulldown assays and Phos-tag gels to assess RsbV1 and RsbV2 phosphorylation during development. Both RsbV1 and RsbV2 were phosphorylated during the EB stage, which is similar to our prior results using Chlamydia caviae. In conjunction with the in vivo phosphorylation data, we hypothesize that stage-dependent inhibition of AASF/RsbW interactions frees RsbW to sequester σ66. Reduced pools of σ66 would promote RB-EB conversion through increased RNAP binding to the late gene sigma factors σ54 and σ28. Supporting this model, overexpression of a non-phosphorylatable RsbV2 S55A mutant (an RsbW “trap”), but not overexpression of RsbV1 S56A, resulted in a 3 log reduction in infectious progeny production without gross changes in inclusion morphology or bacterial numbers, while causing a reduction in σ54 and σ28 regulated EB-specific proteins and inhibition of RB-EB transition shown via transmission electron microscopy. As an alternative approach to assess the consequence of reduced “free” RsbW, we used a CRISPRi knockdown system targeting rsbW and observed a reduction in infectious progeny production under some conditions, which is consistent with the RsbV2 S55A expression strain results. The rsbW CRISPRi-associated phenotype was weaker than the RsbV2 S55A phenotype. As bacterial redox status changes throughout development (RBs are reduced and EBs are oxidized), we also assessed whether the cysteine-rich proteins RsbV2 and RsbW were redox responsive. In parallel to the unique AASF expansion in the pathogenic Chlamydia, RsbV2 in the pathogenic Chlamydia has a CXCC motif that is not found in the RsbV homolog in the environmental Chlamydia. Our in vitro studies found that, under oxidizing conditions, RsbV2 is dimerized, and the dimer form inhibits phosphorylation of RsbV2 by RsbW. We predict that retention of RsbV2 after RsbV1 acquisition has been selected for, in part, owing to a unique redox-sensing role compared to RsbV1 and that the presence of two AASFs enables more sensitive tuning of growth and development in response to metabolite levels. The different phenotypes when overexpressing non-phosphorylatable RsbV1 and RsbV2 also hints at a potential non-PSM or expanded PSM role for RsbV1. The in vitro redox findings need to be further explored in an in vivo model. Collectively, we think the expansion of the PSM, in addition to other gene gain events, facilitated infection of multi-cellular organisms. Additionally, our data support that the PSM regulates growth/cell differentiation in response to energy/nutrients, and that redox levels and biochemical features of RsbV1 and RsbV2 govern PSM-component interactions. As disruption of normal PSM function significantly reduces production of infectious progeny, compounds targeting the PSM components could serve as novel, narrow spectrum inhibitors.

This paper deals with mechanical switch in circuit breaker designed for low voltage. The goal of this thesis was to analyze switching mechanism both theoretically and practically. Theoretical analysis consist of study different types of switching mechanism and analytical calculations of acceleration speed and trajectory. Practical analysis has been made taking a video with high speed camera of real switching mechanism of a circuit breaker and software analysis of the data. The next part of a thesis is about 3D modeling, animating and simulating of a switchgear switching mechanism.

<div>Silicon based semiconductor technology is facing more and more challenges to continue the Moore's law due to its fundamental scaling limitations. To continue the pace of progress of device performance for both logic and memory devices, researchers are exploring new low-dimensional materials, e.g. nanowire, nanotube, graphene and hexagonal boron nitride. Transition metal dichalcogenides (TMDs) are attracted considerable attention due their atomically thin nature and proper bandgap at the initial study. Recently, more and more interesting properties are found in these materials, which will bring out more potential usefulness for electronic applications. Competing with the silicon device performance is not the only goal in the potential path finding of beyond silicon. Low-dimensional materials may have other outstanding performances as an alternative materials in many application realms. </div><div><br></div><div>This thesis explores the potential of TMD based devices in memory and logic applications. For the memory application, TMD based vertical devices are fully studied. Two-terminal vertical transition metal dichalcogenide (TMD) based memory selectors were firstly built and characterized, exhibiting better overall performance compared with some traditional selectors. Polymorphism is one of unique properties in TMD materials. 2D phase engineering in TMDs attracted great attention. While electric switching between semiconductor phase to metallic phase is the most desirable. In this thesis, electric field induced structural transition in MoTe₂ and Mo_1-xW_xTe₂ is firstly presented. Reproducible bipolar resistive random access (RRAM) behavior is observed in MoTe₂ and Mo_1-xW_xTe₂ based vertical devices. Direct confirmation of a phase transition from a 2H semiconductor to a distorted 2H_d metallic phase was obtained after applying an electric field. Set voltage is changed with flake thickness, and switching speed is less than 5 ns. Different from conventional RRAM devices based on ionic migration, the MoTe₂-based RRAMs offer intrinsically better reliability and control. In comparison to phase change memory (PCM)-based devices that operate based on a change between an amorphous and a crystalline structure, our MoTe₂-based RRAM devices allow faster switching due to a transition between two crystalline states. Moreover, utilization of atomically thin 2D materials allows for aggressive scaling and high-performance flexible electronics applications. Both of the studies shine lights on the new application in the memory field with two-dimensional materials.<br></div><div><br></div><div>For the logic application, the ultra thin body nature of TMDs allows for more aggressive scaling compared with bulk material - silicon. Two aspects of scaling properties in TMD based devices are discussed, channel length scaling and channel width scaling. A tunability of short channel effects in MoS₂ field effect transistor (FET) is reported. The electrical performance of MoS₂ flakes is governed by an unexpected dependence on the effective body thickness of the device which in turn depends on the amount of intercalated water molecules that exist in the layered structure. In particular, we observe that the doping stage of a MoS₂ FET strongly depends on the environment (air/vacuum). For the channel width scaling, the impact of edge states in three types of TMDs, metallic T_d-phase WTe₂ as well as semiconducting 2H-phase MoTe₂ and MoS₂ were explored, by patterning thin flakes into ribbons with varying channel widths. No obvious charge depletion at the edges is observed for any of these three materials, which is different from what has been observed in graphene nanoribbon devices. </div>