1,721,088 research outputs found
Spanning subgraphs in graphs and hypergraphs
No full textThis thesis consists of three new fundamental results on the existence of spanning subgraphs in graphs and hypergraphs. Cycle Factors in Graphs: A classical conjecture of El-Zahar states that if H is a graph consisting of r vertex disjoint cycles of length n_1, n_2, ldots , n_r, and G is a graph on n = n_1+n_2 + ... +n_r vertices with minimum degree at least [sigmar/i=1 n_1/2
then G contains H as a subgraph. A proof of this conjecture for graphs withn[greater than or less than] n_0 was announced by S. Abbasi (1998) using the Regularity Lemma-Blow-up Lemma method. We give a new, ``de-regularized" proof of the conjecture for large graphs that avoids the use of the Regularity Lemma, and thus the resulting n_0 is much smaller. Perfect Matching in three-uniform hypergraphs A perfect matching in a three-uniform hypergraph on n=3k vertices is a subset of n/3 disjoint edges. We prove that if is a three-uniform hypergraph on vertices such that every vertex belongs to at least {n-1choose 2} - {2n/3choose 2}+1 edges, then H contains a perfect matching. We give a construction to show that our result is best possible. Perfect Matching in four-uniform hypergraphs A perfect matching in a four-uniform hypergraph is a subset of lfloorfrac{n}{4}
floor disjoint edges. We prove that if H is a sufficiently large four-uniform hypergraph on n=4k vertices such that every vertex belongs to more than ${n-1choose 3} - {3n/4 choose 3} edges, then H contains a perfect matching. Our bound is tight and settles a conjecture of Hán, Person and Schacht (2009).Ph.D.Includes bibliographical referencesIncludes vitaby Imdadullah Kha
Highly Functional and Electrochemically Active Spinel Materials for Solid Oxide Fuel Cells
No full textSolid Oxide Fuel Cell, Solid Oxide Electrolysis, Spinel, Interconnect, Cathode, High Perfor-mance Oxidation Reduction Reaction, Oxygen Evolution Reaction.prohibitionⅠ. Introduction 1
ⅠI. Background 5
2.1 Solid Oxide Fuel Cells (SOFCs) 5
2.2 SOFC materials 7
2.2.1 Anode 7
2.2.2 Electrolyte 8
2.2.3 Cathode 9
2.2.4 Interconnect 11
2.3 Experimental Methods 14
2.3.1 Electrochemical Impedance Spectroscopy (EIS 14
2.3.2 Current-Voltage (C-V) measurements 15
2.4 Potential Losses of SOFC 15
2.4.1 Activation Polarization 15
2.4.2 Ohmic Polarization 16
2.4.3 Concentration Polarization 16
III. Structure and Electrical Properties of Mn1.4-0.5xCo1.4-0.5xCuxY0.1O4 (0.1 ≤ x ≤ 0.5) Spi-nel
Protective Coatings for Solid Oxide Fuel Cell Interconnect.
3.1 Introduction 22
3.2 Experimental Section 25
3.2.1 Material SynTheses 25
3.2.2 Preparation of the Coatings 25
3.2.3 Electrochemical measurement 26
3.2.4 Non-Isothermal Oxidation Test 26
3.2.5 Characterization 26
3.3 Results and Discussion 27
3.3.1 Powder Characterization 27
3.3.2 Electrochemical Performance 29
3.3.3 Oxidation Behavior 34
3.4 Conclusion 35
IV. High performing Mn1.3Co1.3Cu0.4O4 Spinel Based Composite Cathodes for
Intermediate Temperature Solid Oxide Fuel Cells.
4.1 Introduction 46
4.2 Experimental Section 48
4.2.1 Material Preparation 48
4.2.2 Cell Fabrication 48
4.2.3 Characterization 49
4.3 Results and Discussion 50
4.3.1 Powder Characterization 51
4.3.2 Ultraviolet-Visible Absorption 52
4.3.3 Electrochemical Properties 53
4.4 Conclusion 57
V. High Performing Nanostructured Mn1.3Co1.3Cu0.4O4 spinel Cathode for Intermediate
Temperature Solid Oxide Fuel Cells via an Infiltration Technique.
5.1 Introduction 68
5.2 Experimental Part 70
5.2.1 Material SynTheses 70
5.2.2 Cell Preparation 70
5.2.3 Characterization 71
5.3 Results and Discussion 72
5.3.1 Phase Structure and Chemical Compatibility 72
5.3.2 Wetting Contact Angle 72
5.3.3 Microstructure Analysis 73
5.3.4 Area Specific Resistance of MCCO infiltrated ScSZ cathode 73
5.3.5 Optimization by Precursor Solution Control 74
5.3.6 Optimization Microstructure and Electrochemical Properties 75
5.4 Conclusion 76
VI. High Performing Cobalt Iron Based Composite Cathode for Reversible Solid Oxide
Cells at Reduced Temperature.
6.1 Introduction 87
6.2 Experimental Section 89
6.2.1 Material SynTheses 89
6.2.2 Cell Fabrication 90
6.2.3 Characterization 91
6.3 Results and Discussion 91
6.3.1 Phase Analysis 92
6.3.2 Oxidation state of CFO Elements 92
6.3.3 Electrical Conductivity Analysis 93
6.3.4 Thermal Expansion Coefficient (TEC) Analysis 93
6.3.5 Chemical Compatibility 94
6.3.6 Electrical Properties 94
4.4 Conclusion 96
VII Summary 107
VIII. References 113DoctordCollectio
Highly conductive and stable Mn1.35Co1.35Cu0.2Y0.1O4 spinel protective coating on commercial ferritic stainless steels for intermediate-temperature solid oxide fuel cell interconnect applications
No full textChromia scale growth and Cr evaporation of ferritic stainless steel interconnects are known to be major causes of serious degradation of the solid oxide fuel cell (SOFC) stack. The development of suitable ceramic coating materials on the metallic interconnects has been demonstrated as an effective way to address these challenges. Herein, we developed a Mn1.35Co1.35Cu0.2Y0.1O4 (MCCY) spinel material via a facile glycine-nitrate process as a protective coating on a metallic interconnect (SUS 441). Crystal structure and surface charge state analysis of the MCCY material revealed that co-doping of Y and Cu into the (Mn,Co)3O4 spinel resulted in redistribution of the Mn ions (Mn3+ and Mn4+) into the octahedral site, which increased the electrical conduction by enhanced small polaron hopping. Accordingly, the MCCuY-coated interconnect exhibited ∼8 times lower area specific resistance (ASR) than that of the undoped Mn1.5Co1.5O4 (MCO) coated interconnect. Moreover, time-dependent ASR behavior of MCCuY-coated sample was monitored in-situ using electrochemical impedance spectroscopy at 650 °C, showing excellent stability with no observable change for >1000 h, while the ASR of the MCO-coated sample was raised by ∼71%. After 1000 h operation, we found strong adhesion between the MCCuY coating and the metallic interconnect as well as remarkably restricted Cr diffusion into the coating layer. Furthermore, the parabolic constant associated with the oxidation kinetics of the MCCuY-coated substrate (8.25 × 10−11 mg2 cm−4 s−1) was ∼1 order of magnitude lower than that of the MCO-coated one (7.34× 10−10 mg2 cm−4 s−1) at 650 °C after 1000 h measurement. These results demonstrate that the MCCuY is a highly promising coating material of metallic interconnects for intermediate-temperature SOFC applications. © 2019 Hydrogen Energy Publications LLC1
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Tree Packing in Complete Graph
No full textA conjecture of Gy´arf´as and Lehel asks if the sequence of trees T1, T2, ..., Tn, where Ti is a tree on i vertices, can be packed into Kn. We show that if each Ti is restricted to a star or a path, then the sequence can be packed. We also give an explicit construction for a restricted case when the paths and stars alternate.Technical report DCS-TR-68
Variations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
No full textWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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