• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 442
  • 79
  • 76
  • 38
  • 28
  • 22
  • 9
  • 8
  • 5
  • 4
  • 4
  • 4
  • 4
  • 3
  • 3
  • Tagged with
  • 866
  • 98
  • 81
  • 79
  • 70
  • 60
  • 60
  • 57
  • 54
  • 47
  • 47
  • 47
  • 42
  • 41
  • 40
  • 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.
761

Algebarske strukture oslabljenih mreža i primene / Algebraic structures of weakened lattices and applications

Lazarević Vera 13 July 2001 (has links)
<p>Ako je&nbsp; Lalgebarska mreža i&nbsp; a kodistributivan elemenat u L, onda sve klase kongruencije&nbsp; (pa indukovane homomorfizmom&nbsp; ma : xi&mdash; &gt;&nbsp; a&nbsp;&nbsp; A x imaju najveće elemente. Najveći elemenat klase kojoj&nbsp; x E Lpripada je označen sa&nbsp; x.Ako je&nbsp; *a binarna op&shy;eracija definisana sa x *ay = (x A y)&nbsp; V&nbsp; (x A y),onda je istraživana struktura&nbsp; (L, *a), i odgovarajući poset ( L, &lt;&raquo;). Kao primer takve strukture posmatrana je algebra slabih kongruencija&nbsp; (CwA, *a), gde je *a specijalna grafička kompozicija. Dobijeni rezultati daju prirodne posledice u strukturi slabih kongruencija. Data je primena ovih rezultata u univerzalnoj algebri. Njihovom primenom karakterizuje se CEP i Hamiltonovo svojstvo. Dat je potreban i dovoljan uslov da poset (L, &lt; -) bude mreža i ovi rezultati su primenjeni na mrežu slabih kongruencija.</p> / <p>If&nbsp; Lis an algebraic lattice and&nbsp; a codistributive element in&nbsp; L,then all the classes of the congruences&nbsp; 4&gt;a determined by the homomorphism&nbsp; ma :&nbsp; x&nbsp; \&mdash; &gt;&nbsp; a Ax&nbsp;&nbsp; have top elements. The top element of the class which to belongs an&nbsp; x&nbsp;&nbsp; &euro;&nbsp; Lis denoted by&nbsp; x.&nbsp;&nbsp; If *a is a binary operation defined by&nbsp; x&nbsp; *ay=&nbsp; (xA y)&nbsp; V&nbsp; (xA y),then we investigate the<br />structure&nbsp; (L,*a), and the corresponding poset&nbsp; (L, &lt; t ). Asan example of such a structure we observe an algebra of weak congruences ( C w A , * a),where *a is a special graphical composition. We obtain natural conse&shy; quences of the mentioned results to the structure weak congruences. An application in universal algebra is presented, for example, we characterized CEP and Hamiltonian property. Necessary and sufficient conditions for a poset&nbsp; (L,&lt;*) to be a lattice are given, and the results are applied in the case of weak congruence lattices.</p>
762

Charakterisierungen schwacher Kompaktheit in Dualräumen / Characterizations of weak compactness in dual spaces

Möller, Christian 15 September 2003 (has links)
In this thesis we present an extensive characterization of weak* sequentially precompact subsets of the dual of a sequentially order complete M-space with an order unit. This central part of the thesis generalizes results due to H.H. Schaefer and X.D. Zhang showing that small weak* compact subsets of the dual of a space of bounded measurable real-valued functions (continuous real-valued functions on a compact quasi-Stonian space) are weakly compact. Moreover, while the proofs of Schaefer and Zhang use measure theoretical arguments, the arguments presented here are purely elementary and are based on the well-known result, that the space l1 has the Schur property. Finally some applications are given. For example, we investigate compact or sequentially precompact subsets, which consist of order-weakly compact operators, in the space of continuous linear operators defined on a sequentially order complete Riesz space with values in a Banach space provided with the strong operator topology: as an immediate consequence of the results, we can easily deduce extended versions of the Vitali-Hahn-Saks theorem for vector measures. For this we need a generalization of the Yosida-Hewitt decomposition theorem, which is proved here with other techniques like the factorization of an order-weakly compact operator through a Banach lattice with order continuous norm.
763

Essais en économetrie et économie de l'éducation

Tchuente Nguembu, Guy 07 1900 (has links)
No description available.
764

Elektronenspinresonanz in Systemen mit ferromagnetischen Korrelationen

Förster, Tobias 21 October 2011 (has links)
Die Arbeit befasst sich mit der Elektronenspinresonanz (ESR) stark korrelierter Elektronensysteme mit ferromagnetischen Wechselwirkungen. Es wurden dafür Messungen an den Kondogitter-Systemen CeRuPO und CeOsPO, der Dotierungsreihe CeFeAs1-xPxO, den niederdimensionalen frustrierten Quadratgittern AA’VO(PO4)2 sowie in dem schwach ferromagnetischen Metall Nb1-yFe2+y durchgeführt. Alle Verbindungen zeigen entweder eine ferromagnetische Ordnung oder befinden sich in der Nähe einer ferromagnetischen Instabilität, die die Eigenschaften des stark korrelierten Systems beeinflusst.:Abkürzungsverzeichnis xi Einleitung 1 1 Theoretische Modelle 5 1.1 Auswirkungen des Kristallfeldes 1.2 Phasenübergänge, Landau-Ginzburg Theorie und Quantenphasenübergänge 1.3 Physik Niederdimensionaler Spin-Systeme 1.3.1 Das zweidimensionale XY-Modell 1.3.2 Das J1-J2-Modell auf dem Quadratgitter 1.4 4f-Magnetismus, Kondoeffekt und Kondogitter 1.4.1 Vom freien Elektronengas zur Landau-Fermi-Flüssigkeit 1.4.2 Kondo-Effekt, RKKY-Wechselwirkung und Schwere Fermionen Systeme 1.4.3 Cer: 4f-Magnetismus 1.5 Schwach magnetische Metalle 1.5.1 Pauli-Suszeptibilität und spontan aufgespaltene Bänder 1.5.2 Spinfluktuationen in itineranten Magneten und marginale Fermiflüssigkeit 1.6 Dichtefunktionaltheorie 2 Grundlagen der Elektronenspinresonanz 31 2.1 Prinzip der magnetischen Resonanz und ESR Parameter 2.1.1 Linienform 2.1.2 Intensität 2.1.3 g-Faktor 2.1.4 Linienbreite und Spin-Relaxation 2.2 Experimenteller Aufbau 2.3 ESR in niederdimensionalen Systemen 2.4 ESR an Metallen und Kondogitter Systemen 2.4.1 Auswirkungen der Wechselwirkungen zwischen lokalen Momenten und Leitungselektronen auf die ESR 2.4.2 ESR in Kondogittersystemen 2.5 Leitungselektronenspinresonanz 2.5.1 Linienform in der LESR 2.5.2 Elliot-Yafet Theorie und ihre Verallgemeinerung 2.6 ESR an magnetischen Phasenübergängen 3 ESR in CeTPO (T=Ru, Os) und CeFeAs1-xPxO 59 3.1 Die Eigenschaften von CeTPO (T=Ru, Os) & CeFeAs1-xPxO 3.1.1 Das ferromagnetische Kondogitter CeRuPO 3.1.2 Das antiferromagnetische Kondogitter CeOsPO 3.1.3 Die Dotierungsreihe CeFeAs1-xPxO 3.2 CeRuPO und CeOsPO: Die Bedeutung FM Fluktuationen für die Beobachtbarkeit der ESR in Kondo-Gitter Systemen 3.3 ESR an CeRuPO Einkristallen 3.3.1 Anisotropie und Temperaturverhalten des g-Faktors 3.3.2 Anisotropie und Temperaturverhalten der Linienbreite 3.4 Entwicklung der ESR in der Dotierungsreihe CeFeAs1-xPxO 3.4.1 CeFeAs0.7P0.3O - Supraleitung und Ferromagnetismus 3.5 Zusammenfassung ESR in CeTPO und CeFeAs1-xPxO 4 ESR in den frustrierten Quadratgittern AA’VO(PO4)2 97 4.1 Struktur und magnetische Eigenschaften AA’VO(PO4)2 4.2 ESR an polykristallinen SrZnVO(PO4)2 & BaCdVO(PO4)2 4.2.1 SrZnVO(PO4)2 4.2.2 BaCdVO(PO4)2 4.3 ESR an Pb2VO(PO4)2-Einkristallen 4.3.1 Anisotropie der Resonanz 4.3.2 Temperaturabhängigkeit 4.4 Zusammenfassung der ESR in den frustrierten Quadratgittern 7 4.4.1 Analyse der Linienbreitendivergenz am Phasenübergang 5 Leitungselektronenspinresonanz in Nb1-yFe2+y 125 5.1 Das magnetische Phasendigramm von Nb1-yFe2+y 5.2 LESR in polykristallinen Nb1-yFe2+y 5.2.1 Proben mit ferromagnetischer Ordnung 5.2.2 Proben mit SDW-Ordnung 5.2.3 Zusammenfassung polykristalline Proben 5.3 Bandstruktur und verallgemeinerte Elliot-Yafet-Theorie in NbFe2 5.4 LESR in einkristallinen Proben von Nb1-yFe2+y 5.4.1 Fe-reicher Einkristall: y=0.016 5.4.2 Stöchiometrischer Einkristall: NbFe2 5.4.3 Nb-reicher Einkristall: y=-0.008 5.5 Zusammenfassung LESR in Nb1-yFe2+y 6 Zusammenfassung und Ausblick Anhang A.1 Das zweite Moment der Dipol-Dipol-Wechselwirkung A.2 Untersuchte CeFeAs1-xPxO-Proben Literaturverzeichnis
765

Improved Methods for Phased Array Feed Beamforming in Single Dish Radio Astronomy

Elmer, Michael James 09 July 2012 (has links) (PDF)
Among the research topics needing to be addressed to further the development of phased array feeds (PAFs) for radio astronomical use are challenges associated with calibration, beamforming, and imaging for single dish observations. This dissertation addresses these concerns by providing analysis and solutions that provide a clearer understanding of the effort required to implement PAFs for complex scientific research. It is shown that calibration data are relatively stable over a period of five days and may still be adequate after 70 days. A calibration update system is presented with the potential to refresh old calibrators. Direction-dependent variations have a much greater affect on calibration stability than temporal variations. There is an inherent trade-off in beamformer design between achieving high sensitivity and maintaining beam pattern stability. A hybrid beamformer design is introduced which uses a numerical optimizer to balance the trade-off between these two conflicting goals to provide the greatest sensitivity for a desired amount of pattern control. Relative beam variations that occur when electronically steering beams in the field of view must be reduced in order for a PAF to be useful for source detection and imaging. A dual constraint beamformer is presented that has the ability to simultaneously achieve a uniform main beam gain and specified noise response across all beams. This alone does not reduce the beam variations but it eliminates one aspect of the problem. Incorporating spillover noise control through the use of rim calibrators is shown to reduce the variations between beams. Combining the dual constraint and rim constraint beamformers offers a beamforming option that provides both of these benefits.
766

Concepts of Divine Action for a Theistic Approach to Psychology

Melling, Brent S. 27 June 2013 (has links) (PDF)
Recent years have seen increased interest in using theism (the perspective that assumes that God is currently actively in the world) as a conceptual framework for scientific inquiry. This interest has built particular momentum in psychology where several scholars have expressed that traditional naturalistic approaches limit understanding and investigation of psychology's subject matter and thus are insufficient to fully account for human phenomena. Others have previously made the case for the consideration of theism as a legitimate alternative basis for psychological theory, research, and practice. This dissertation begins with that consideration and examines what would be required to move a theistic approach to psychology forward. In other words, if God is assumed to be active in the world (including the psychological world-theism), what difference would that make for the ideas, methods, and practices of psychology? As the current activity of God is the foundational assumption of theism, clarity about what that activity would entail is especially essential for those seeking to develop a theistic approach to psychology and to describe how their discipline would be different from that perspective. Unfortunately, there is currently a lack of clear and explicitly articulated conceptions of God's actions in and for psychology. This dissertation provides a conceptual analysis of the activity of God that synthesizes disparate approaches to divine action into a tentative conceptualization or taxonomic schema. This schema organizes the scholarly literature from across several major traditions into six major heads and elucidates multiple subordinate concepts. The conceptualization serves as an orientation to important issues such as strong v weak theisms, the limitations of naturalism, and practical theistic applications for psychology. Detailed illustrations of these concepts as applied to psychological theory, research (both in the qualitative and quantitative modes), and practice further demonstrate the utility of such a conceptualization. These examples provide a specific focus on the unique contributions of a theistic perspective over and against those of naturalism.
767

WEAKLY SUPERVISED CHARACTERIZATION OF DISCOURSES ON SOCIAL AND POLITICAL MOVEMENTS ON ONLINE MEDIA

Shamik Roy (16317636) 14 June 2023 (has links)
<p>Nowadays an increasing number of people consume, share, and interact with information online. This results in posting and counter-posting on online media by different ideological groups on various polarized topics. Consequently, online media has become the primary platform for political and social influencers to directly interact with the citizens and share their perspectives, views, and stances with the goal of gaining support for their actions, bills, and legislation. Hence, understanding the perspectives and the influencing strategies in online media texts is important for an individual to avoid misinformation and improve trust between the general people and the influencers and the authoritative figures such as the government.</p> <p><br></p> <p>Automatically understanding the perspectives in online media is difficult because of two major challenges. Firstly, the proper grammar or mechanism to characterize the perspectives is not available. Recent studies in Natural Language Processing (NLP) have leveraged resources from social science to explain perspectives. For example, Policy Framing and Moral Foundation Theory are used for understanding how issues are framed and the moral appeal expressed in texts to gain support. However, these theories often fail to capture the nuances in perspectives and cannot generalize over all topics and events. Our research in this dissertation is one of the first studies that adapt social science theories in Natural Language Processing for understanding perspectives to the extent that they can capture differences in ideologies or stances. The second key challenge in understanding perspectives in online media texts is that annotated data is difficult to obtain to build automatic methods to detect the perspectives, that can generalize over the large corpus of online media text on different topics. To tackle this problem, in this dissertation, we used weak sources of supervision such as social network interaction of users who produce and interact with the messages, weak human interaction, or artificial few-shot data using Large Language Models. </p> <p><br></p> <p>Our insight is that various tasks such as perspectives, stances, sentiments toward entities, etc. are interdependent when characterizing online media messages. As a result, we proposed approaches that jointly model various interdependent problems such as perspectives, stances, sentiments toward entities, etc., and perform structured prediction to solve them jointly. Our research findings showed that the messaging choices and perspectives on online media in response to various real-life events and their prominence and contrast in different ideological camps can be efficiently captured using our developed methods.</p>
768

Voltage Source Converters with Energy Storage Capability

Xie, Hailian January 2006 (has links)
This project deals with voltage source converters with energy storage capability. The main objective is to study the possible benefits of energy storage to a power system with a VSC as the interface between them. First of all, a converter control system is proposed for a two level VSC. In the conventional converter control, the control system usually takes the voltage measured at the point where the converter is connected and calculates the reference voltage for the converter; with a modulation system the converter then produces the required 'average voltage'. In this project, a novel flux modulation scheme, combined with the deadbeat current control strategy, is proposed. The current controller is capable of controlling both positive and negative sequence current components. With flux modulation, the control system measures the bus flux and commands the converter to generate the required flux. Based on the proposed control strategies, several application studies have been carried out. The first application study investigates the effect of energy storage on the power quality at the point of common coupling when a system is subject to load disturbances. The voltage at PCC in a weak network is very sensitive to load changes. A sudden change in active load will cause both a phase jump and a magnitude fluctuation in the bus voltage, whereas reactive load changes mainly affect the voltage magnitude. With the addition of energy storage to a StatCom, it is possible to compensate for the active power change as well as providing reactive power support. In this thesis, some effective active power compensation schemes are proposed. Simulations and experiments have been performed to verify the compensation schemes. The results show that a StatCom with energy storage can significantly reduce phase jumps and magnitude deviations of the bus voltage. pact of the energy storage on the performance of weak systems under fault conditions has been investigated. The investigation was done by studying an example system. The system model was established based on a real system, in which some induction motors driving pumps along a pipeline are fed from a radial transmission line. Studies show that for a weak system with induction motor loads, a StatCom with certain energy storage capacity will effectively improve the system recovery after faults. Although this incurs extra cost for the increasing dc voltage rating and size of the dc side capacitor, the overall rating of the converter can be reduced by utilization of the proposed active power compensation scheme. The last case study investigates the possible use of a StatCom with energy storage to improve the power quality at the point of common coupling where a cyclic load is connected. Studies show that by providing both fast reactive and fast active power support to the network, not only the voltage magnitude can be well controlled, but also the voltage phase jump can be reduced significantly. / QC 20101124
769

Weak core solution for the non-transferable utility kidney exchange game

Collette, Raphaël 08 1900 (has links)
Plusieurs pays possèdent des programmes de don croisé de rein (PDCR). Le but de ces programmes est d’aider les patients ayant un donneur incompatible à obtenir une greffe, en échangeant les donneurs incompatibles entre les patients. Pour pouvoir obtenir des bassins de paires incompatibles de plus grande taille, il est possible d’élargir les PDCR pour y inclure plusieurs pays ou hôpitaux. Par contre, on doit s’attendre à ce que ces derniers agissent de façon stratégique pour maximiser le nombre de leurs patients obtenant une greffe. Avec ce cadre, on peut définir le problème de don croisé de rein à plusieurs agents. Dans ce mémoire, nous modélisons ce problème comme un jeu coopératif à utilité non- transférable et nous présentons le noyau faible comme solution à ce jeu. Nous étudions empiriquement notre solution sur des exemples basés sur des données réelles et montrons qu’elle est atteignable en pratique. Nous comparons aussi le noyau faible à une autre solution présente dans la littérature: les couplages résistants aux rejets. / In various countries, kidney paired donation programs (KPDs) are implemented. These programs aim to help patients with an incompatible donor to obtain a transplant by swapping the donors between the patients. In order to increase the size of the pool of incompatible patient-donor pairs and potentially enhance patient benefits, KPDs can be extended to include multiple countries or hospitals. However, unlike existing nationwide KPDs, strategic behaviour from these entities (agents) is to be expected. This gives rise to the multi-agent kidney exchange problem. In this work, we model for the first time this problem as a non-transferable utility game. We also propose and argue in favour of the use of the weak core as a solution concept for the game. Using integer programming tools, we empirically study our solution concept on instances from the literature, which are derived from real-world data, and show that it is attainable in practice. We also compare the weak core to another recently presented solution concept from the literature, the rejection-proof matching.
770

Detection of Sparse and Weak Effects in High-Dimensional Supervised Learning Problems, Applied to Human Microbiome Data / Detektering av glesa och svaga effekter i högdimensionella övervakade inlärningsproblem, tillämpat på mikrobiomdata från människor

Lindahl, Fred January 2020 (has links)
This project studies the signal detection and identification problem in high-dimensional noisy data and the possibility of using it on microbiome data. An extensive simulation study was performed on generated data using as well as a microbiome dataset collected on patients with Parkinson's disease, using Donoho and Jin's Higher criticism, Jager and Wellner's phi-divergence-based goodness-of-fit-test and Stepanova and Pavlenko's CsCsHM statistic . We present some novel approaches based on established theory that perform better than existing methods and show that it is possible to use the signal identification framework to detect differentially abundant features in microbiome data. Although the novel approaches produce good results, they lack substantial mathematical foundations and should be avoided if theoretical rigour is needed. We also conclude that while we have found that it is possible to use signal identification methods to find abundant features in microbiome data, further refinement is necessary before it can be properly used in research. / Detta projekt studerar signaldetekterings- och identifieringsproblemet i högdimensionell brusig data och möjligheten att använda det på mikrobiomdata från människor. En omfattande simuleringsstudie utfördes på genererad data samt ett mikrobiomdataset som samlats in på patienter med Parkinsons sjukdom, med hjälp av ett antal goodness-of-fit-metoder: Donoho och Jins Higher criticis , Jager och Wellners phi-divergenser och Stepanova och Pavelenkos CsCsHM. Vi presenterar några nya tillvägagångssätt baserade på vedertagen teori som visar sig fungera bättre än befintliga metoder och visar att det är möjligt att använda signalidentifiering för att upptäcka olika funktioner i mikrobiomdata. Även om de nya metoderna ger goda resultat saknar de betydande matematiska grunder och bör undvikas om teoretisk formalism är nödvändigt. Vi drar också slutsatsen att medan vi har funnit att det är möjligt att använda signalidentifieringsmetoder för att hitta information i mikrobiomdata, är ytterligare experiment nödvändiga innan de kan användas på ett korrekt sätt i forskning.

Page generated in 0.2768 seconds