Performance and reliability modelling of computing systems using spectral expansion

PhD ThesisThis thesis is concerned with the analytical modelling of computing and other discrete event systems, for steady state performance and dependability. That is carried out using a novel solution technique, known as the spectral expansion method. The type of problems considered, and the systems analysed, are represented by certain two-dimensional Markov-processes on finite or semi-infinite lattice strips. A sub set of these Markov processes are the Quasi-Birth-and-Death processes. These models are important because they have wide ranging applications in the design and analysis of modern communications, advanced computing systems, flexible manufacturing systems and in dependability modelling. Though the matrixgeometric method is the presently most popular method, in this area, it suffers from certain drawbacks, as illustrated in one of the chapters. Spectral expansion clearly rises above those limitations. This also, is shown with the aid of examples. The contributions of this thesis can be divided into two categories. They are, • The theoretical foundation of the spectral expansion method is laid. Stability analysis of these Markov processes is carried out. Efficient numerical solution algorithms are developed. A comparative study is performed to show that the spectral expansion algorithm has an edge over the matrix-geometric method, in computational efficiency, accuracy and ease of use. • The method is applied to several non-trivial and complicated modelling problems, occuring in computer and communication systems. Performance measures are evaluated and optimisation issues are addressed

Suppression of Defective Motor Patterns in Parkinsonian C. elegans

Parkinson’s disease (PD) is a progressive neurodegenerative disorder that is caused partly by the loss of dopamine producing neurons. Dopamine is a conserved neuromodulator that aids in the transition between different motor patterns such as swimming, walking, or running. This can be observed across many species, including mice, flies, and nematodes. The cat-2 mutant strain of the nematode C. elegans has a deletion in the gene encoding tyrosine hydroxylase, an enzyme required to synthesize dopamine. Our lab recently demonstrated that the cat-2 mutant shares aspects of PD patient dysfunction through its inability to transition normally between the “swimming” and “crawling” patterns of motion. Currently, PD treatments focus on boosting residual dopamine signaling and are not available to maintain motor function once dopamine neurons completely degenerate. To search for ways to overcome motor dysfunction in the absence of dopamine, we performed a forward genetic screen to identify mutations that suppress poor swim-to-crawl motor transition in cat-2 mutant. We found several suppressor mutants that improve motor function. Further characterization can identify molecular pathways that can be altered to improve motor function in the absence of dopamine. This information could provide insight into repair of dopamine-deficient neural circuitry in higher level animals and possible approaches to help late stage PD patients.Neuroscienc

Shock reduction methods for electronic components in a projectile

Electronic components within a projectile are subjected to severe loads over extremely short duration. Failure of these components is likely to have negative implications to projectile or mission. While experimental data can be helpful in understanding the failure phenomena, collecting such data is difficult. There are also limitations on the reliability of shock sensors under these circumstances. Finite Element Modeling can offer a means to better understand the behavior of these components. It can also be used to design better techniques to mitigate the shocks these components are subjected to. A model of a projectile and gun barrel is presented. The model is subjected to a realistic launch pressure time-history. The projectile is modified to include a one-pound mass that represents a typical electronic package. The electronic package is supported by a steel plate. Efforts were put in this research to find a suitable material that reduces the shock transmitted to the 1-pound payload. A composite material with carbon fiber reinforced in an epoxy matrix has been considered to start with. The effect of fiber volume fraction has been studied by varying it from 30%-70%. The model includes effects of friction between the gun barrel and projectile. Effects of the flexibility of the gun barrel and its boundary conditions are also considered. A parametric study of the effects of changing the thickness of the supporting plate on acceleration transmitted to the electronic package within and outside the gun barrel is presented. Sensitivity of payload mounting location is also studied

Quasi-Static and Impact Characterization of Sandwich Structures with an Iso-Grid Stiffened Syntactic Foam Core

In this study, a novel hybrid sandwich structure with an integrated, iso-grid stiffened syntactic foam core was fabricated and evaluated by impact test and static test. Sandwich beams with different grid cell areas were prepared using a pin-guided dry weaving process. Low velocity impact test on different locations (rib, node, and bay) was conducted with varying hammer weight and impact velocities by an instrumented impact testing machine. Ultrasonic C-scan was utilized before and after impact to identify the damage induced by impact. Scanning Electron Microscopy observation was also implemented to visualize the impact damage at micro- length scale. Compressions after impact (CAI) tests per an anti-buckling test fixture were conducted to evaluate the residual strength and stiffness of the impact damaged sandwich plate specimens. In order to validate the experimental results, Finite Element Analysis was conducted on unimpacted specimens of different Groups. Parametric study was also conducted to study how different parameters affect the strength of the iso-grid stiffened sandwich structures. The test results show that the novel sandwich structure has a higher capacity to transfer impact energy elastically. It leads the sandwich plate towards quasi-static impact response. The propagation energy, the energy absorbed for damage creation and propagation, is reduced. The damage is more localized and confined to the bay directly under impact or adjacent bays. It is found that the bay area is one of the most important design parameters for the iso-grid pattern investigated. The residual strength and residual modulus of iso-grid structures is found to be higher than that of laminates. Impact damage on iso-grid structures is confined to a smaller area when compared to laminates

A New Receiver for a Digital Passband System with CPSK Modulation: The STTS-CPSK Receiver

671-677Telecommunications industry is expanding vastly with huge infrastructure requiring huge sums of money for investment1,2. Reliability of the system3,4, efficient utilization of resources1,2, and safety of the users and the environment are paramount towards providing high quality efficient telecom services at affordable prices1,2. This paper deals with an important scientific investigation for the development of the STTS-CPSK receiver for pass band applications5,6 . This is a new receiver being developed with the inspiration from the previously developed STTS-MF receiver for baseband applications. This is carried out considering transmission of p-q signals (p-q signals represent correlated digital signals) through AWGN channel. Performance-comparison studies of the conventional STS-CPSK receiver and the new STTS-CPSK receiver are carried out for a wide range of signal and system parameters 0.0 ≤ p,q ≤ 1.0 and-10 dB ≤ SNR ≤ 10 dB. Performance superiority of the STTS-CPSK receiver is established for 0.0 ≤ p,q ≤ 1.0, -2 dB ≤ SNR ≤ 10 dB, and illustrated. Thus, this work has important implications towards efficient utilization of bandwidth, and also in greening of communication technologies which is highly needed. The latter is because the performance-improvement, achieved in case of STTS-CPSK receiver, can be translated into an equivalent advantage of EMF-reduction appropriately

MCI Detection using fMRI time series embeddings of Recurrence plots

The human brain can be conceptualized as a dynamical system. Utilizing resting state fMRI time series imaging, we can study the underlying dynamics at ear-marked Regions of Interest (ROIs) to understand structure or lack thereof. This differential behavior could be key to understanding the neurodegeneration and also to classify between healthy and Mild Cognitive Impairment (MCI) subjects. In this study, we consider 6 brain networks spanning over 160 ROIs derived from Dosenbach template, where each network consists of 25-30 ROIs. Recurrence plot, extensively used to understand evolution of time series, is employed. Representative time series at each ROI is converted to its corresponding recurrence plot visualization, which is subsequently condensed to low-dimensional feature embeddings through Autoencoders. The performance of the proposed method is shown on fMRI volumes of 100 subjects (balanced data), taken from publicly available ADNI dataset. Results obtained show peak classification accuracy of 93% among the 6 brain networks, mean accuracy of 89.3% thereby illustrating promise in the proposed approach.Comment: 4 pages, 5 figure