8,790 research outputs found
Influence of Cr on microstructure and elastocaloric effect in Ni-Mn-In-Co-Cr polycrystalline alloys
No full textNi-Mn-based metamagnetic shape memory alloys have been proposed as potential elastocaloric refrigerants. The intrinsic brittleness of the alloys has limited their cooling application. Introducing a soft second phase is an effective way to reduce the brittleness. From the viewpoint of application, the effect of second phase on elastocaloric effect should be illustrated. In this paper, we have investigated the microstructure, martensitic transformation and elastocaloric effect of Ni45Mn37-xIn13Co5Crx (x = 0, 1 and 2) polycrystalline alloys. Single-phase and precipitates-containing microstructures are obtained for the undoped and doped alloys, respectively. The precipitates in Cr-doped alloys enhances the fracture strength but significantly hinders the martensitic transformation. Balancing the fracture strength and martensitic transformation, the Ni45Mn36In13Co5Cr alloy with small amount of precipitates along grain boundaries exhibits large cooling effects of 4-6 K in the temperature range of 317-353 K. (C) 2018 Elsevier B.V. All rights reserved
CR Li-Yau-Hamilton Inequality and its Applications
No full text這篇文章包含三大部分，第一部分證明矩陣形式的 Li-Yau-Hamilton Harnack 不等式。第二部份延續第一部分的工作，推廣至(1,1)-form 形式的 Li-Yau-Hamilton Harnack 不等式。第三部份將應用這不等式証明柯西黎曼上的 Gap 定理。In the first part of thesis, we first derive the CR analogue of matrix Li-Yau-Hamilton
inequality for a positive solution to the CR heat equation in a closed pseudohermitian (2n+1)-
manifold with nonnegative bisectional curvature and bitorsional tensor. We then obtain the
CR Li-Yau gradient estimate in a standard Heisenberg group. Finally, we extend the CR
matrix Li-Yau-Hamilton inequality to the case of Heisenberg groups. As a consequence, we
derive the Hessian comparison property in the standard Heisenberg group.
In the second part, we study the CR Lichnerowicz-Laplacian heat equation deformation of
(1; 1)-tensors on a complete strictly pseudoconvex CR (2n+1)-manifold and derive the linear
trace version of Li-Yau-Hamilton inequality for positive solutions of the CR Lichnerowicz-
Laplacian heat equation. We also obtain a nonlinear version of Li-Yau-Hamilton inequality
for the CR Lichnerowicz-Laplacian heat equation coupled with the CR Yamabe flow and
trace Harnack inequality for the CR Yamabe flow.
In the last part, by applying a linear trace Li-Yau-Hamilton inequality for a positive
(1; 1)-form solution of the CR Hodge-Laplace heat equation and monotonicity of the heat
equation deformation, we obtain an optimal gap theorem for a complete strictly pseudocovex
CR (2n+1)-manifold with nonnegative pseudohermitian bisectional curvature and vanishing
torsion. We prove that if the average of the Tanaka-Webster scalar curvature over a ball of
radius r centered at some point o decays as o(r^-2 ), then the manifold is flat.1. Abstract v
2. Introduction 1
2.1. CR Li-Yau Gradient Estimate and Harnack Inequality 2
2.2. CR Matrix Li-Yau-Hamilton Inequality 4
2.3. CR Linear Trace Li-Yau-Hamilton Inequality and Gap Theorem 6
2.4. The Coupled CR Yamabe Flow 7
3. Preliminary 10
4. CR Matrix Li-Yau-Hamilton Harnack Inequality 12
4.1. CR Matrix Li-Yau-Hamilton Inequality 15
4.2. The CR Gradient Estimate and Harnack inequality in Heisenberg Groups 20
4.3. Complete noncompact case 25
5. Linear Trace Li-Yau-Hamilton inequality 31
5.1. The CR Bochner-Weitzenbock Formula 35
5.2. Linear Trace Li-Yau-Hamilton Inequality 39
5.3. Nonlinear Version for Li-Yau-Hamilton Inequality 50
6. CR Gap Theorem 58
6.1. CR Moment-Type Estimates 59
6.2. CR Lichnerowicz-Laplacian heat equation 63
6.3. Proof of CR Optimal Gap Theorem 67
Appendix A. 71
References 7
Cr(VI) and Cr(III)-Based Conversion Coatings on Zinc
No full textWith the aims of understanding the protective mechanism of chromate conversion coatings and developing alternatives to chromate treatments, the physical natures and corrosion properties of Cr(VI) and Cr(III) treated zinc have been investigated in this work. The Cr(VI) treatments were carried out in dichromate and sulfuric acid solution with different dipping times. The Cr(III) treatments were carried out in two commercial solutions (A and B). The thickness of the coatings was measured using ellipsometry. The morphologies and the compositions of the treated zinc have been studied by means of SEM, AFM, AES, FTIR and XPS. The drying temperature influence on the corrosion performance of the Cr(VI)âtreated zinc has been investigated. The Volta potential in treated and untreated areas has been measured using scanning Kelvin probe (SKP) and SKPFM. The corrosion behavior of the Cr(VI) and Cr(III) treated zinc has been investigated using polarization, electrochemical impedance measurements (EIS), and salt spray tests. Both Cr(VI) and Cr(III) species were detected by XPS in the outermost layer of the Cr(VI) coatings, while no Cr(VI) species was found in the Cr(III) coatings. AES depth profile results show that chromium oxides are the main components in the Cr(VI) coatings. Zinc oxide is mainly located at the chromium oxides / zinc interface. The Cr(III) coating is a mixture of chromium oxides and zinc oxide. Both the Cr(VI) and the Cr(III) treatments can supply corrosion protection to zinc. The corrosion resistance of the Cr(III)-B coating is greater than that of the Cr(III)-A coating. However, the inhibition of the corrosion of zinc by Cr(VI) coating is more effective than by the Cr(III) coatings. The inhibition of the corrosion of zinc by the Cr(VI) and the Cr(III) treatments is discussed, and future research topics are suggested.Mechanical, Maritime and Materials Engineerin
Influences of chemical compositions and molecular weights of humic acids on Cr (VI) reduction
No full textHumic acids (HAs) are one of the major components in soils which influence greatly the behavior and fate of heavy metals in the environment. Due to the high chemical and structural heterogeneities of HAs, of which domains in humic substances involved in Cr (VI) removal are barely understood. Thus, in the study, a repetitive extract and ultrafiltration techniques were used to fractionate HA into several fractions containing various proportions of aliphatic and aromatic carbons and molecular weights. Three fractions (denoted as F1, F2, and F3) and five molecular weights (MWs) of HAs (Bulk, >100kD, 50-100kD, <10kD) were obtained by a repetitive extraction method and by using a hollow-fiber tangential flow filtration (TFF) system, respectively, from a Yangming Mountain peat soil, Taiwan. In the study, the chemical properties of each HA fraction were characterized by FTIR and 13C-NMR spectroscopy before and after reaction with Cr(VI). Spectral analyses found that the contents of aromatic and oxygen-containing C decreased with a progressive extraction, and lower molecular weights of HAs contained more aromatic carbons and carboxyl groups. The interactions of each HA fractions with Cr(VI) showed that Cr (VI) removal could be enhanced under illumination, and the removal was attributed to Cr(VI) reduction. The redox product, i.e, Cr(III), was either adsorbed on residual HAs or released into the solution. A higher aromatic C content and a smaller molecular weight of humic acid exhibited a greater efficiency for Cr(VI) reduction, and the 13C NMR and FTIR results indicated that the carboxyl and phenolic groups enriched in these domains of HAs were responsible for the enhancement of Cr (VI) reduction. Time-dependent FTIR and 13C NMR spectra suggested that the activated sites on HA were rapidly consumed or dissolved into the solutions upon Cr(VI) oxidation. Thus, Cr(VI) may react directly with dissolved organic C (DOC) in the solution instead of on the surfaces of HA fractions. In conclusion, the O-containing groups of HAs were dominant sites for Cr(VI) reduction; however, the redox reactions proceeded very slowly unless the light participated to the reaction. With an increase of DOC concentrations upon Cr(VI) interactions with HAs, this study highlighted the possibilities that DOC derived from HAs may react with Cr(VI) much longer to complement the slow reactions between these two reactants. Thus, HAs may still have a profound effect to Cr(VI) reduction in a soil system.ABSTRACT I
CONTENTS III
TABLES VII
FIGURES VIII
CHAPTER 1 INTRODUCTION 1
CHAPTER 2 LITERATURE REVIEWS 2
2.1 Humic substances 2
2.2 The reaction of humic acids and heavy metals 4
2.3 Ultrafiltration 6
2.4 Humic Acids Under UV lights 8
2.5 ….Chromium 9
2.5.1 The source of chromium 9
2.5.2 Cr(III) 10
2.5.3 Cr(VI) 12
2.6 …The Reaction between Humic Acids and Chromium 15
CHAPTER 3 MATERIALS AND METHODS 16
3.1 The experiment design 16
3.2. Repetitive extraction of HAs 18
3.2.1. HA extracted from the peat soil. 18
3.2.2. Fractionation of HA by ultrafiltration 21
3.2.2.1. Advantages of TFF system. 21
3.2.2.2. Fractionation of various MWs from HAs using a Hollow Fiber TFF system. 22
3.4 Characterization of humic acids 25
3.4.1 Estimation of apparent MWs of HAs using high-Performance Size-Exclusion Chromatography (HPSEC) 25
3.4.2 Fourier transform infrared spectroscopy 27
3.4.3 13 C CP-MAS Nuclear Magnetic Resonance Spectroscopy 27
3.5 Humic acids reaction with Cr(VI) 28
3.5.1 Preparation of Cr(VI) regent 28
3.5.2 Removal kinetics of Cr(VI) 28
3.5.2.1 Cr(VI) removal by HA derived from repetitive extraction in the dark. 28
3.5.2.2. Cr (VI) removal by HA derived from repetitive extraction under illumination. 29
3.5.2.3. Cr(VI) removal by HA with various MWs under illumination. 30
3.5.3 Effect of initial Cr(VI) concentrations on HA structures 33
3.6 Chromium analysis 34
3.6.1 Cr (VI) 34
3.6.2 Total Cr 34
CHAPTER 4 RESULT AND DISCUSSION 36
4.1 Characterization of humic acids 36
4.1.1 FTIR 36
4.1.2 13C NMR 39
4.2 High-Performance Size-Exclusion Chromatography 41
4.3 Removal of Cr(VI) on humic acids 45
4.3.1 HA fractions derived from repetitive extraction 45
4.3.1.1 The kinetics of Cr(VI) removing. 45
4.3.1.2 Cr (VI) removal on HAs involving adsorption and reduction reactions. 47
4.3.2 The fractions of TFF systems 51
4.3.2.1 Photo-induced Cr(VI) reduction. 51
4.3.2.2 Influence of TOC on Cr(VI) reduction 57
4.4 The structure analysis of humic acids after reaction with Cr(VI) 60
4.4.1 13C CP-MAS Nuclear Magnetic Resonance Spectroscopy 60
4.4.1.1. F1 fraction of HAs. 60
4.4.1.2. Comparisons of Cr(VI) reduction on F1, F2, and F3 fractions of HAs. 64
4.4.1.3 Kinetic changes of chemical structures of F1 as influenced by Cr(VI). 69
4.4.2 FTIR 74
4.4.2.1 F1 fraction of HA. 74
4.4.2.2 F2 and F3 fractions of HA. 78
4.4.2.3 Influence of reaction time on the functionl groups of HA fractions. 81
4.4.2.4. Concentration effects. 85
CHAPTER 5 CONCLUSION 91
REFERENCES 9
Site occupation in the Cr-Ru and Cr-Os ? phases
No full textThe site occupation in the Cr-Ru and Cr-Os ? phases is computed as a function of temperature. Generally, in ? phases the larger atoms occupy the sites with larger coordinations numbers, as can be explained on the basis of atomic-size and electronic structure. However, for Cr2Ru and Cr2Os the atomic-size argument predicts that Ru and Os occupy the sites with larger coordination numbers, whereas the reasoning based on the approximate degeneracies of electronic levels predicts that Cr occupies those sites. By comparing these predictions with the theoretically computed and the experimentally measured site occupations, the atomic-size and electronic arguments can be judged on their predictive merits.Materials Science and EngineeringMechanical, Maritime and Materials Engineerin
Synergy of photocatalysis and adsorption for simultaneous removal of Cr(VI) and Cr(III) with TiO2 and titanate nanotubes
No full textAn one-step efficient simultaneous removal of Cr(VI) and Cr(III) was achieved with mixture of TiO2 and titanate nanotubes (TNTs). Unlike the conventional two-step Cr removal with a first photocatalytic reduction of Cr(VI) and a subsequent adsorption of Cr(III), the proposed single process significantly reduced reaction time (over 50%). The synergy of photocatalysis and adsorption played an important role in enhancing Cr removal process. The synergetic mechanism was interpreted and indirectly confirmed with H2O2 variation during photocatalysis. The instant transfer of the reduced Cr from TiO2 surface to TNTs interlayer greatly promoted the release of photocatalytic sites of TiO2, which in turn considerably enhanced photocatalytic activity of TNTs by inhibiting electron hole pairs recombination. The optimum condition for the whole process was at pH 5. Adsorption of Cr(III) was primarily in the interlayer of TNTs at pH <= 5. However, higher pH would lead to precipitation of Cr(OH)(3) onto TNTs as observed by X-ray photoelectron spectroscopy (XPS). Addition of Ca2+ could promoted photocatalysis owing to its ionic bridging function and form of equivalent to TiOH+-Cr(VI)-Ca2+-Cr(VI) linkages, while SO42- only slightly inhibited photo-reduction of Cr(VI), indicating good synergy of photocatalysis and adsorption even at high ionic strength of electrolyte. Besides, the desorbed TNTs could be easily regenerated by remedying the damaged tubular structure and reused for Cr removal with excellent performance. The outstanding synergetic effects with essential explanation of the mechanism make this study not only fundamentally important but also potentially practical applicable. (C) 2014 Elsevier Ltd. All rights reserved.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000333781300002&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Engineering, EnvironmentalEnvironmental SciencesWater ResourcesSCI(E)[email protected]
Nonlinear influence of excess Mn on the magnetoelastic transition in (Mn,Cr)<sub>2</sub>Sb
No full textThe influence of excess Mn on the magnetoelastic ferromagnetic-to-antiferromagnetic transition Tt in the magnetocaloric compound (Mn,Cr)2Sb has been studied. With increasing excess Mn the magnetoelastic transition temperature for (Mn,Cr)2Sb initially increases and then decreases. This trend is accompanied by a strong reduction of the (Mn,Cr)Sb secondary phase. With increasing excess Mn a higher Cr content was found in the (Mn,Cr)Sb secondary phase in comparison to the matrix phase. This competition for Cr leads to a nonlinear dependence of Tt with increasing excess Mn at a fixed nominal Cr content. However, we observed that Tt depends linear on the c/a ratio for a wide range of temperatures from 170 to 350 K. A compositional diagram of the c/a ratio was constructed to assist the selection of (Mn,Cr)2Sb alloys with a desired transition temperature.RST/Fundamental Aspects of Materials and Energ
Columnar metallomesogens derived from 1,3,4-oxadiazoles and X-ray crystal structure of dichlorobis[2,5-bis(3,4,5-trimethoxyphenyl)-1,3,4-oxadiazole]palladium(II)
No full textUltradifferentiable CR Manifolds
No full textIn this article, the notion of ultradifferentiable CR manifold is introduced and an ultradifferentiable regularity result for finitely nondegenerate CR mappings is proven. Here, ultradifferentiable means with respect to Denjoy–Carleman classes defined by weight sequences. Furthermore, the regularity of infinitesimal CR automorphisms on ultradifferentiable abstract CR manifolds is investigated.© The Author(s) 201
elliegiulietti/V-Cr-Ti-for-Fusion-Reactors: Vanadium_Alloys (V-Cr-Ti)_for_Fusion_Reactors_AM_Study_Release_v1.0
No full text<h2>Vanadium Alloys (V-Cr-Ti) for Fusion Reactors AM Study</h2>
<p>This repository contains the research and experimental data related to the study on vanadium alloys (specifically V-Cr-Ti alloys, V44 and V1515) for fusion reactors using additive manufacturing (AM) techniques.</p>
<h3>Overview</h3>
<p>Vanadium alloys are potential materials for nuclear fusion reactors due to their structural durability and irradiation resistance. This study focuses on investigating the viability of V-Cr-Ti alloys for AM procedures, aiming to understand crack behaviour and optimise laser parameters for better melt track formation.</p>
<h3>Key Findings</h3>
<ul>
<li>Experimental investigations involved varying laser power and speed on V-Cr-Ti alloys (V44 and V1515) to observe crack behaviour across melt tracks on a laser powder bed fusion (LPBF) machine.</li>
<li>Main types of cracks associated with AM melt tracks were identified, including liquation cracks (LC), solidification cracks (SC), and solid-state cracks (SSC).</li>
<li>Qualitative analysis involved visually determining crack types using optical microscopes and scanning electron microscopy (SEM), while quantitative analysis measured crack density using ImageJ software.</li>
<li>Results indicate that high laser power and low laser speeds result in increased cracking, while low laser power with a mid-range of laser speeds result in less cracking and a more optimal melt track.</li>
<li>An operating window between 60 and 150 W laser power and 850 to 1500 mm/s has been identified, with further studies required for confirmation and comparison to powder processing.</li>
</ul>
<h3>Future Directions</h3>
<ul>
<li>Future studies should focus on comparing data with similar alloys, refining laser parameters, and exploring microstructural properties for deeper insights into crack formation mechanisms.</li>
<li>Sharing of experimental data to facilitate accessibility and reusability for the scientific community.</li>
</ul>
<h3>Dissertation Details</h3>
<p>Dissertation submitted to the University of Sheffield in partial fulfilment of the requirements for the degree of Master of Engineering.
Dissertation title: Vanadium Alloys for Fusion Reactors: Determining their Viability for Additive Manufacturing Procedures.
Author: Ellie Giulietti
Supervisor: Dr Russell Goodall
May 2024</p>
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