440 research outputs found
Negative and zero thermal expansion in alpha-(Cu2-xZnx)V2O7 solid solutions
No full textNegative or zero thermal expansion (NTE or ZTE) of materials is intriguing for controllable thermal expansion. We report a series of orthorhombic alpha-Cu2-xZnxV2O7 (x = 0, 0.1, 0.2), in which the volumetric coefficients of thermal expansion are successfully tuned from -10.19 * 10-6 K-1 to -1.58 * 10-6 K-1 in the temperature range of 100-475 K by increasing the content of Zn2+. It has been revealed that the transverse vibrations of oxygen bonded with vanadium are dominant in the contraction of the bc plane, leading to the overall volume NTE in alpha-Cu2V2O7. The introduction of Zn2+ densifies the crystal structure, which is presumed to suppress the space of transverse vibrations and results in the ZTE in alpha-Cu1.8Zn0.2V2O7. This work presents an effective method to realize ZTE in anisotropic framework systems
Advances and challenges in marine litter pollution
No full textNo abstracts are to be cited without prior reference to the author.Conveners: Thomas Maes (UK), Andy Booth (Norway), Francios Galgani (France), Chengjun Sun (PICES)
Due to the cancellation of ICES ASC 2020, some contributions submitted that year were also included in ASC 2021.</p
A study of biomarker analysis in association with type 1 diabetes and their shared features in rheumatoid arthritis
No full textType 1 diabetes (T1D) is mediated by abnormal immune system (autoimmunity) that targeting specifically to self insulin-producing cells (β-cells). People with T1D require treatments based on life-long insulin substitution. In addition to the damages in health caused by T1D complications, the complexity of insulin treatment and the fear of glucose dysregulation often place extra burden to the affected family. There is a current need for better understanding of the disease etiology therefore guide the construction of successful prediction and prevention strategies for the disease.There are many immune-related genes playing important roles in T1D etiology. In addition, there is a trend of autoimmune diseases segregating within individuals and families where those genes are critically involved. Exploration of these genes can provide knowledge related to the disease pathogenesis. In my studies, we select two genes functioning in the immune system and explored their potential roles in T1D. In addition, we analyzed the association between HLA alleles and T1D autoimmune markers (autoantibodies) in rheumatoid arthritis patients.Killer cell immunoglobulin like receptors (KIRs) is a group of receptors expressed on the surface of natural killer cells and subgroups of T cells. KIRs could accelerate autoimmune diabetes in rodent models. However their roles in human T1D are not clear. In Study I, we studied the T1D association of KIR genes and their combination with HLA-C ligand genes in Chinese Han population. Our results indicated that KIR modifies the T1D association of HLA-C ligand genes. Recent studies indicated that KIRs exert their function in a collective fashion and their effects can initiate as early as life in uterus by maternal-fetal interaction. Therefore in Study II, we studied the T1D association with the collection of maternal KIR genes and their combination with fetal HLA-C ligand genes in the Chinese Han population. Results from study II indicated that the accumulation of maternal activating KIRs along with fetal HLA-C2 genes predispose T1D in the fetus.Alpha-B crystallin (encoded by CRYAB) is a major autoimmune target in multiple sclerosis (an autoimmune disease occurred in central nervous system). In Study III, we tested the association between CRYAB gene and islet autoantibodies in T1D using two well-established Swedish cohorts. Our results suggested that genetic variant in the promoter region of CRYAB is associated with increased T1D risk and islet autoantibodies in T1D patients.In Study IV, we aimed to identify genetic factors that cause the aggregation of the two autoimmune disorders, T1D and rheumatoid arthritis (RA). We measured islet autoantibodies among RA patients and analyzed the association between HLA and islet autoantibodies in RA patients and in subgroups of RA positive for anti-citrullinated protein antibodies. We identified that HLA DR4 alleles were associated with increased islet autoantibodies in RA patients, however HLA DR3 alleles were the major genetic contributors toward elevated islet autoantibodies among RA patients positive for both anti-CCP and anti-CEP-1.In conclusion, our studies indicated that KIR, CRYAB are among the genetic factors predisposing T1D. In addition, HLA alleles are the major contributors to the presence of islet autoantibodies among RA patients.List of scientific papersI. Zhi D, Sun C, Sedimbi SK, Luo F, Shen S, Sanjeevi CB. Killer cell immunoglobulin-like receptor along with HLA-C ligand genes are associated with type 1 diabetes in Chinese Han population. Diabetes/metabolism research and reviews. 2011 Nov;27(8):872-7. https://doi.org/10.1002/dmrr.1264 II. Sun C, Luo F, Zhi D, Sanjeevi CB. Interactions between maternal killer cellimmunoglobulin receptor genes and fetal HLA ligand genes contribute toType 1 diabetes susceptibility. [Manuscript]III. Sun C, Sedimbi SK, Ashok AK, Sanjeevi CB; Swedish Childhood Diabetes and the Diabetes Incidence in Sweden Study Groups. CRYAB-650 C>G (rs2234702) affects susceptibility to Type 1 diabetes and IAA-positivity in Swedish population. Human immunology. 2012 Jul;73(7):759-66. https://doi.org/10.1016/j.humimm.2012.04.004 IV. Sun C, Ramelius A, Israelsson L, Lernmark Å, Klareskog L, Sanjeevi CB. Autoantibodies against Type 1 Diabetes autoantigens in RheumatoidArthritis. [Manuscript]</p
Localized Symmetry Breaking for Tuning Thermal Expansion in ScF3 Nanoscale Frameworks
No full textThe local symmetry, beyond the averaged crystallographic structure, tends to bring unusual performances. Negative thermal expansion is a peculiar physical property of solids. Here, we report the delicate design of the localized symmetry breaking to achieve controllable thermal expansion in ScF3 nanoscale frameworks. Intriguingly, an isotropic zero thermal expansion is concurrently engineered by localized symmetry breaking, with a remarkably low coefficient of thermal expansion of about +4.0 × 10−8/K up to 675 K. This mechanism is investigated by the joint analysis of atomic pair distribution
function of synchrotron X-ray total scattering and extended X-ray absorption fine structure spectra. A localized rhombohedral distortion presumably plays a critical role in stiffening ScF3 nanoscale frameworks and concomitantly suppressing transverse thermal vibrations of fluorine atoms. This physical scenario is also theoretically corroborated by the extinction of phonon modes with negative Grüneisen parameters in rhombohedral ScF3. The
present work opens an untraditional chemical modification route to achieve controllable thermal expansion by breaking local symmetries in materials
Development of a flat crystal X-ray emission spectrometer and applications of X-ray spectroscopy to the study of 3d transition metal-based metal-organic framework materials
No full textMetal Organic Frameworks (MOFs) are extended 3-dimensional structures that arecrafted by joining together metal ions/clusters with organic linkers. Specific attributes of MOFs can be tuned by varying the metal and linker composition. This tunability, together with the large surface area produced by their permanent microporosity, has shown great promise in various adsorption-based applications such as, small molecule separation, storage, and delivery. More recently MOF magnetic and electronic properties have been explored for applications such as catalysis, chemical sensing and switching. MOF utility depends on the interaction between guest molecules contained within the porous network and the framework itself. This host-guest communication, however, is often not well understood due to the complexity of the 3-dimensional structures. Traditional characterization methods have limited utility for studying such interactions in solid state materials.
This dissertation aims to expand the understanding of MOF structure and electronic properties by using X-ray spectroscopy methods to probe the host-guest interactions in the frameworks as well as their corresponding electronic structure changes. A long-range goal of this research is to develop advanced X-ray spectroscopy techniques for both ex-situ and in-situ studies of MOF systems. This is accomplished, in part, via interrogation of two specific well-known MOF systems with a variety of X-ray techniques and confirming previously known information as well as reporting on new information that can be gleaned from the interrogations. The other focus of the research is the development of two new spectrometers designed for X-ray emission studies, with improvements in the resolution and data acquisition, making the process faster and easier while providing high quality data.Ph.D.Includes bibliographical reference
Isotropic Zero Thermal Expansion and Local Vibrational Dynamics in (Sc,Fe)F3
No full textScandium fluoride (ScF3) exhibits a pronounced negative thermal expansion (NTE), which can be suppressed and ultimately transformed into an isotropic zero thermal expansion (ZTE) by partially substituting Sc with Fe in (Sc0.8Fe0.2)F3 (Fe20). The latter displays a rather small coefficient of thermal expansion of −0.17 × 10−6/K from 300 to 700 K. Synchrotron X-ray and neutron pair distribution functions confirm that the Sc/ Fe−F bond has positive thermal expansion (PTE). Local vibrational dynamics based on extended X-ray absorption fine structure indicates a decreased anisotropy of relative vibration in the Sc/Fe−F bond. Combined analysis proposes a delicate balance between the counteracting effects of the chemical bond PTE and NTE from transverse vibration. The present study extends the scope of isotropic ZTE compounds and, more significantly, provides a complete local vibrational dynamics to shed light on the ZTE mechanism in chemically tailored NTE compounds
Spectroscopic interrogation of metal ligation and photoactive properties in metal-organic frameworks
No full textMetal-organic frameworks (MOFs), a class of crystalline hybrid materials, have been studied for a variety of applications ranging from gas sorption to photocatalysis. While the topic of most MOF research focuses on the application of the material, it is important to first understand the structure-function relationship. The adsorption-based functionalities of porous metal-organic framework (MOF) materials that lead to applications such as catalysis and gas separation rely on specific host–guest interactions often involving open metal sites within the nodes of the framework. These interactions are difficult to probe on the molecular level and consequently poorly understood. Spectroscopic methods provide the necessary molecular level information on local metal coordination and electronic structure. In this thesis, steady-state and time resolved optical, x-ray, and vibrational spectroscopic methods are all used to gain molecular level insight, and sometimes a conjunction of techniques are needed to provide a comprehensive answer. Namely, valence-to-core X-ray emission spectroscopy has proven to be exceptionally sensitive to ligand identity, however, for a complete understanding of ligand identity and the nature of the interaction within a given framework, results were complimented with other spectroscopic methods such as Raman spectroscopy and X-ray absorption spectroscopy. Additionally, element specific techniques like X-ray spectroscopic methods, specifically X-ray transient absorption spectroscopy offer element specific excited state information that eludes assignment via convention methods. A brief summary of each chapter is provided below.Ph.D.Includes bibliographical reference
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