761 research outputs found
Factorization of isometries of hyperbolic 4-space and a discreteness condition:
No full textGilman's NSDC condition is a sufficient condition for the discreteness of a two generator subgroup of PSL(2,C). We address the question of the extension of this condition to subgroups of isometries of hyperbolic 4-space. While making this new construction, namely the NSDS condition, we are led to ask whether every orientation preserving isometry of hyperbolic 4-space can be factored into the product of two half-turns. We use some techniques developed by Wilker to first, define a half-turn suitably in dimension 4 and then answer the former question. It turns out that defining a half-turn in this way in any dimension n enables us to generalize some of Gilman's theorems to dimension greater than or equal to 4. We also give an exposition on part of Wilker's work and give new proofs for some of his results.Ph.D.Includes bibliographical references (p. 52-53)by Karan Mohan Pur
Bibliographics for the 983 eprints in the live archives of E-LIS : trends and status report up to 7th July 2004, based on author-self-archiving metadata
No full textThe priority for ideas and philosophy related to "Network Theory" have been traced back and documented by Braun(2004),and credit goes to Karinthy(1929).The IT has empowered to realise it, as the most practical phenomena and it is no more a humour. The OAI (Open Archives Initiatives)and ACIS (Academic Contributor Information System)are progressive in the direction ,which may lead to realise the "Collective Genius" at global level. Focus of present study is on Author-Self-Archiving (A-S-A)Metadata of the 983 Eprints in the Live Archives of the E-LIS (EPrints of Library and Information Science),which were approved till 7th July 2004.The A-S-A Metadata was used for librametric analysis. Self-explanatory bibliographics are illustrated.The highlights include: Conference papers (34%); highest approval, June 2004 (28%); published archives (76%);not refereed (52%); not in public domain (60%); highest self-archiving-author (De Robbio, Antonella).The Nos. of EPrints having single JITA domain specifications were: Theoretical and general aspects of libraries and information(27); Information use and sociology of information(80);Users,literacy and reading(13);Libraries as physical collections(30);Publishing and legal issues(57);Management(13);Industry, profession and education(36);Information sources, supports, channels(113) ; Information treatment for information services, Information functions and techniques (101); Technical services libraries, archives and museums(25); Housing technologies(1); Information technology and library technology(92); and Inter-domainery (395) i.e. having specifications of two or more than two JITA classes
Designing a successful library school field experience
No full textTo share the library school field experience paradigm that the authors developed after their successful participation as a supervisor and student.
Design/methodology/approach – A review of field experience literature is provided. The field experience paradigms and perspectives pertaining to the supervisor and the student are explained. The paradigm is suggested as a model for field experience participants and their supervisors.
Findings – The field experience paradigm for the supervisors elucidates the stages – planning, training, mentoring and evaluation. The paradigm for students explains the phases – awareness, interests, planning and participation.
Research limitations/implications – The focus of the field experience, from which the paradigm emanated, was to train and prepare the student for agricultural librarianship in an academic library. The application of the paradigm may vary for different situations.
Practical implications – The paradigm is expected to be useful for supervisors and students of field experience programs.
Originality/value – This paradigm stems from the participation of the authors as a field experience supervisor and student. The steps and methods the authors followed will help advance future field experience programs
Rethinking web platform extensibility
No full textThe modern Web platform provides an extensible architecture that lets third party extensions, often untrusted, enhance and customize the Web browser and the Web applications. While the prevalence of extensions for both browsers and applications has been instrumental in making the Web browser hugely successful, there are two critical issues that the designers of the modern Web platform have not yet tackled in a principled manner. First, both the third party extensions and the extensible components of the Web platform include numerous vulnerabilities, which can compromise the security and privacy of end users. Second, the black-box and opaque nature of the Web platform limits the extent of extensibility achievable for Web developers, thereby hampering the development of novel browser-based user applications. This dissertation develops new tools and techniques to address the problem of insecure extensibility in the Web platform, proposes novel language and system level solutions to make extensibility a first class primitive for developing Web software, and demonstrates that these methods are applicable to real-world Web applications and Web browser extensions. Specifically, this dissertation makes the following three contributions. First, it studies and characterizes the problem of insecure JavaScript-based Web browser extensions using a specialized program analysis system, Sabre, which leverages JavaScript-level information flow mechanism to detect violations in client’s confidentiality and integrity arising from execution of untrusted extensions. Second, it formalizes the concept of transactions for JavaScript and implements Transcript, a language runtime system that allows hosting principals, i.e., Web browser and Web applications, to isolate untrusted JavaScript-based extensions using speculative execution. Lastly, this dissertation presents the design and implementation of Atlantis, a novel, extensible browser architecture that allows Web applications to define their own runtime environment and become more secure and robust. Atlantis enables developers with primitives to manage the Web application’s security and privacy, and removes their dependence on opaque, legacy Web interfaces.Ph. D.Includes bibliographical referencesby Mohan Dhawa
INSPEC database analysis for Knowledge Management records
No full textThe study deals with the Knowledge Management papers covered in the INSPEC, an international database on Information Science, Physical Sciences, Engineering and Computer Sciences. The papers have been analysed in terms of their content and other scientometric parameters
Physically interpretable machine learning methods for transcription factor binding site identification using principled energy thresholds and occupancy:
No full textRegulation of gene expression is pivotal to cell behavior. It is achieved predominantly by transcription factor proteins binding to specific DNA sequences (sites) in gene promoters. Identification of these short, degenerate sites is therefore an important problem in biology. The major drawbacks of the probabilistic machine learning methods in vogue are the use of arbitrary thresholds and the lack of biophysical interpretations of statistical quantities. We have developed two machine learning methods and linked them to the biophysics of transcription factor binding by incorporating simple physical interactions. These methods estimate site binding energy, recognizing that it determines a site's function and evolutionary fitness. They use the occupancy probability of a transcription factor on a DNA sequence as the discriminant function because it has a straightforward physical interpretation, forms a bridge between binding energy and evolutionary fitness, and has a natural threshold for classifying sequences into sites that allows establishing the threshold in a principled manner. Our methods incorporate additional characteristics of sites to enhance their identification. The first method, based on a hidden Markov model (HMM), identifies self-overlapping sites by combining the effects of their alternative binding modes. It learns the threshold by training emission probabilities using unaligned sequences containing known sites and estimating transition probabilities to reflect site density in all promoters in a genome. While identifying sites, it adjusts parameters to model site density changing with the distance from the transcription start site. Moreover, it provides guidance for designing padding sequences in experiments involving self-overlapping sites. Our second method, the Phylogeny-based Quadratic Programming Method of Energy Matrix Estimation (PhyloQPMEME), integrates evolutionary conservation to reduce false positives while identifying sites. It learns the threshold by solving an iterative quadratic programming problem to optimize the distribution of correlated binding energies of neutrally evolving orthologous sequences while restricting the values of binding energies of known sites and their orthologs. We have used the NF-κB transcription factor family as a case study for both methods and gained new insights into its biology.Ph.D.Includes bibliographical references (p. 210-226)by Amar Mohan Drawi
Clustering based causal topic mining
No full textEvents in the world generate an enormous amount of textual data like tweets and news articles. These events also manifest in the form of changes to time-series numeric data. This thesis deals with the problem of extracting these events from the timestamped document collection in the form of topics that cause a change in a time-series. We develop a conceptual framework for that can be used to analyze different causal topic mining algorithms. We also propose two novel clustering based algorithms - cCTM-CF and cCTM-CoF to generate causal topics. We evaluate these algorithms both qualitatively, and quantitatively by comparing their coherence and correlation scores to that of the baseline generative causal topic model - gCTM. We found that cCTM-CoF performs 35% and 62.5% better according to these metrics as compared to the baseline.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2019-05-01The student, Vishaal Mohan, accepted the attached license on 2017-04-24 at 14:23.The student, Vishaal Mohan, submitted this Thesis for approval on 2017-04-24 at 14:28.This Thesis was approved for publication on 2017-04-25 at 11:02.DSpace SAF Submission Ingestion Package generated from Vireo submission #11014 on 2017-08-10 at 14:32:32Made available in DSpace on 2017-08-10T19:52:22Z (GMT). No. of bitstreams: 2
MOHAN-THESIS-2017.pdf: 386969 bytes, checksum: 59c2389baaf5254174bf10112078b1c6 (MD5)
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Previous issue date: 2017-04-25Embargo set by: Colleen Fallaw for item 102679
Lift date: 2019-08-10T21:25:30Z
Reason: Author requested closed access (OA after 2yrs) in Vireo ETD systemLimited Restriction Lifted for Item 102679 on 2019-08-11T09:15:39Z
Optimal fuel cell power extraction
No full textThe need for alternative energy sources has never been higher and one such clean energy source, the fuel cells are popular because of their ability to generate energy from naturally available clean fuels. At present however, fuel cells remain some extent away from full commercialization largely due to its high operating costs which can be reduced through optimal and efficient power extraction.Master of Science (Power Engineering
Refinement of solutions to the linear complimentarity problem
No full textNash equilibrium;game theaory;matrices
Direct torque control of three-level inverter fed IPMSM drive
No full textClassical direct torque control (DTC) suffers from problems such as high torque ripples, variable inverter switching frequency and flux drooping at low speeds. Traditionally, two-level inverters are employed in direct torque controlled motor drives. The torque and flux regulation in DTC drives can be improved if three-level inverters are used instead of two-level inverters; the increase in the degree of freedom for voltage vector selection means that the rotational speed of stator flux can be more precisely controlled to attain a superior regulation of torque and flux. At the same time, the broad review presented on the existing three-level inverter fed DTC (3L-DTC) methods at the beginning of this thesis reveal that the integration of three-level inverters into switching table based DTC drives is complicated and does not readily alleviate the shortcomings of classical DTC. Firstly, 3L-DTC drives are typically intended for use in higher power motors and therefore, the average inverter switching frequency has to be kept as low as possible to maximize the drive efficiency. However, if low switching frequencies are used, torque and flux ripples in 3L-DTC schemes can still be excessive and detrimental. Secondly, the inverter inherent switching constraints due to smooth voltage vector switching and neutral point voltage fluctuations, which are essential to reduce low order THD and ensure safe operation, must be respected.
This study focuses on the incorporation of three-level inverters into DTC drives. A number of 3L-DTC strategies incorporating a three-level neutral point clamped (3L-NPC) inverter, one of the most frequently used multilevel inverter in variable speed drives, are proposed and experimentally verified for the control of an interior permanent magnet synchronous motor (IPMSM). The torque variation rates or slopes of permanent magnet synchronous motors are considerably larger than the minimum rate required for the proper regulation of torque during steady state. Consequently, the application of a single voltage vector within one switching period in classical DTC leads to large ripples of torque. Duty cycle based DTC (DDTC) method, in which more than one voltage vectors is applied within each switching cycle, is an effective way to reduce the torque ripples. With the DDTC method, the biggest challenge is to determine the appropriate voltage vectors and their respective duty ratios. The handful of DDTC methods in literature for 3L-DTC drives uses parameter dependent and complicated techniques for duty ratio determination. Furthermore, no consideration is given to the aforementioned inverter switching constraints in selecting the voltage vectors.
In this thesis, a comprehensive analysis is carried out to investigate the typical variation rates of torque and flux in a 3L-DTC IPMSM. Based on this analysis, a novel DDTC method using two voltage vectors, one active and one passive within one switching cycle is proposed. For duty ratio calculation, torque ripple root mean square minimization (TR-RMSM) with minimal parameter dependency is developed, taking into account the dynamics of torque and flux characteristics in an IPMSM. In addition, proper switching techniques are introduced to overcome the problem of smooth voltage vector switching and large neutral point voltage fluctuations.
Ideally for optimal torque ripple reduction, the active and passive voltage vectors applied within each switching cycle in DDTC methods should have opposing variation rates of torque. For instance, the inclusion of a zero voltage vector as a passive vector is necessary for 3L-DTC drives to optimize the torque ripple reduction during medium to low speeds. However, this is not always possible considering the smooth voltage vector switching criteria, which limits the switching transitions to be between adjacent voltage vectors. Therefore, a new DDTC method employing three voltage vectors (one active and two passive) in one switching cycle is proposed in this thesis. The application of three vectors, however, complicates the direct application of TR-RMS method for duty ratio calculations. Consequently, a simplified duty ratio calculation technique which regulates the duty ratio of the non-zero passive vector according to the angular velocity of the motor is developed. Regulating the duty ratio of one passive vector means that aforementioned TR-RMSM method with minimal parameter dependency can be applied.
The low speed performance of 3L-DTC drives is typically affected by poor flux regulation, otherwise known as flux drooping. Flux drooping will increase the lower order harmonics in the output, and thus, affect the efficiency of the drive system. The back emf of the motor is low at low speeds and therefore, voltage vectors with smaller magnitudes are used more frequently. During heavy loads, the significant voltage drop across the stator resistance will cause the stator flux to droop. In order to alleviate the flux drooping issue during low speed, the use of virtual voltage vectors, which are synthesized from two adjacent vectors with smaller magnitudes, are proposed. The proposed method is evaluated through experiments carried out at 3% of the test IPMSMs rated speed. Results confirm that the effects of flux drooping at low speed are mitigated through the use virtual short voltage vectors.
Although the regulation of torque and flux is improved significantly by the proposed DDTC methods, they do not solve the issue of variable inverter switching frequency. The inconsistent variation of torque slope and the usage of fixed torque hysteresis bandwidth are the main causes for variable switching frequency in DTC drives. To attain a constant inverter switching frequency with improved torque and flux regulation, a simple torque regulator, consisting of a PI controller and triangular carriers, is proposed in place of the conventional torque hysteresis controller. The PI controller is used to negate the large variations in torque slope, which is desirable for reducing torque ripples. Then, the output of the PI controller is compared against triangular carriers to attain a constant switching frequency. Detailed analysis and design guidelines for the proposed torque regulator using small signal modeling are presented. In addition, the parametric robustness of the proposed method is experimentally verified.
Almost all of the existing DTC strategies used in multilevel inverter fed DTC (MLI-DTC) drives including the DDTC and constant switching frequency based methods proposed in this thesis are inverter specific. i.e., the level of hysteresis controllers and the proposed switching tables are designed specifically for inverters with a certain number of voltage levels. Therefore, these methods are not readily applicable to generic n-level multilevel inverters. In order to overcome this inconvenience, the proposed CSF strategy is extended to be generalized for inverters possessing any number of voltage levels by using a simple voltage vector decomposition technique. A comparative study with a prior art and parametric sensitivity analysis are presented to verify the effectiveness and robustness of the proposed MLI-DTC method.Doctor of Philosophy (EEE
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