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Shift Symmetries and AdS/CFT
No full textAbstract
Massive fields on anti-de Sitter (AdS) space enjoy galileon-like shift symmetries at particular values of their masses. We explore how these shift symmetries are realized through the boundary conformal field theory (CFT), at the level of the 2-point functions. In the alternate quantization scheme in which the dual conformal field gets the smaller ∆− conformal dimension, the shift symmetry is realized as a gauge symmetry in the dual CFT, so that only shift invariant operators are true conformal primary fields. In the standard quantization scheme the shift symmetry acts on the source, leading to Ward identities that take the form of integral constraints.</jats:p
Children\u27s Stress in the Time of COVID-19: Relationships with School, Social and Recreational Experiences
No full textIntroduction: In response to the public health threats during the pandemic, many schools shifted to online instructional delivery, and many children experienced changes to their social and recreational activities. While an emerging body of literature is documenting these changes or how these experiences may be related to parents\u27 and children\u27 functioning, no known study has examined all of these constructs. We investigated the degree to which schooling, social, and recreational experiences during the COVID-19 pandemic influenced the stress levels of school-age children. Further, recognizing the interconnectedness of parents’ and children\u27s lives, we examined whether parental stress mediated the relations between children\u27s experiences and child stress. Method: Parents of school-age children (N = 701) completed an online questionnaire with items focused on school modality (i.e., fully online or not), sufficiency of school resources, change in relationships, change in social/recreational activities, parental stress, and child stress. Results: The findings indicated that fully online school was not associated with child stress. Lower sufficiency of school resources, greater change in relationships, and greater change in social/recreational activities predicted higher child stress. Parental stress fully or partially mediated these relations. Discussion: Implications for educators are provided.</p
Social and moral psychology of COVID-19 across 69 countries
No full textAbstractThe COVID-19 pandemic has affected all domains of human life, including the economic and social fabric of societies. One of the central strategies for managing public health throughout the pandemic has been through persuasive messaging and collective behaviour change. To help scholars better understand the social and moral psychology behind public health behaviour, we present a dataset comprising of 51,404 individuals from 69 countries. This dataset was collected for the International Collaboration on Social & Moral Psychology of COVID-19 project (ICSMP COVID-19). This social science survey invited participants around the world to complete a series of moral and psychological measures and public health attitudes about COVID-19 during an early phase of the COVID-19 pandemic (between April and June 2020). The survey included seven broad categories of questions: COVID-19 beliefs and compliance behaviours; identity and social attitudes; ideology; health and well-being; moral beliefs and motivation; personality traits; and demographic variables. We report both raw and cleaned data, along with all survey materials, data visualisations, and psychometric evaluations of key variables.</jats:p
A proof-of-concept randomized crossover clinical trial of a first-in-class vasopressin 1a receptor antagonist for PTSD: Design, methods, and recruitment
No full textMolecular Rearrangements of Fluoropolymers as it Relates to Thermomechanical Behavior of Films
No full textThermal phase transitions of fluoropolymers have been identified to have significant influence on molecular rearrangement; ultimately influencing the performance of extruded films due to the changing thermomechanical properties. Theory describes how semi-crystalline polymers, when exposed to said thermal phase transitions, can form metastable crystals. Extruded fluoropolymer films are used in applications that utilize their stability in extreme environments (i.e., high heat) therefore they will be exposed to temperatures above their Tg values. Since fluoropolymers are classified as semi-crystalline polymers, when exposed to temperatures above the Tg, these crystalline regions may experience reorganization and relaxation of internal residual stresses produced during film extrusion; if the crystallites are not in equilibrium, (i.e., energetically the most optimal conformation), poor macroscopic properties may result, such as anisotropic film shrinkage. Due to their chemical stability, it is unlikely that they would experience chemical changes or degradation so it is a reasonable hypothesis that these fluoropolymers will undergo some sort of physical change such as residual stress relaxation (due to thermal history induced during extrusion) and/or molecular rearrangements (due to thermal phase transitions).It has been demonstrated in literature, that this volumetric change in the fluoropolymer film will influence the thermomechanical properties. If the fluoropolymer films are constrained, the residual stress will not be able to relax outwardly and will wrinkle as a result. The goal of this Master\u27s Thesis is to gain a deeper understanding of how the thermal phase transitions of fluoropolymers influence molecular rearrangement and how it relates to the thermomechanical behavior of films, in an effort to optimize film processing and improve application performance
Analysis of Residual Stresses and Their Impact on the Subsurface Crack Growth Behavior in Modern Steel Rails
No full textRailroads are an essential mode of transportation for people and goods worldwide, and steel rails are a critical component of this infrastructure. However, steel rails are subjected to various forms of loading during their service life, which can lead to the formation and propagation of fatigue cracks, compromising their structural integrity. The presence of subsurface cracks can compromise the structural integrity of the rail and increase the risk of catastrophic failure, such as "detail fracture", which is related to high tensile residual stresses induced during rail manufacturing. Therefore, it is essential to understand the mechanical behavior of the rail for the loading conditions to which it will be subjected.This dissertation aims to investigate the mechanical behavior of steel rails, including their mechanical properties, fatigue performance, and fracture mechanisms, and how they relate to residual stresses induced by the roller straightening process. A parametric study using finite element method (FEM) simulation will be conducted to examine the spatial variation of yield strength and plastic hardening within the rail profile and its effect on residual stress distribution. Furthermore, a comprehensive FEM simulation will be conducted to investigate rail fracture mechanisms originating from shelling defects, with a particular focus on the transition between shell cracks and detail fractures. The main efforts will be on filling the gap in the literature by characterizing the transition between shell cracks and detail fractures, where few studies have focused on finite element modeling. Ultimately, the research presented in this dissertation will contribute to the ongoing efforts to enhance the integrity and reliability of railroad infrastructure and prevent derailments
Assessing the Efficacy of Process-Specific Topology Optimization for Direct-Ink Write 3D-Printed Hierarchical Composites and Structures
No full textPolymers are ubiquitous in modern society. From food packaging to structural components inaerospace applications, plastics can be found. For applications like the latter, there is a requirement for exceptional performance characteristics - whether that be with respect to mechanical stiffness or strength, thermal or electrical conductivity, or other desirable engineering outcomes. As a result, much effort has been exerted in industry and academia toward optimizing the performance of structural components made out of polymers. Performance optimization of structural components, generally speaking, is a multi-layered problem. One layer of this problem is the material design problem – tailoring the properties of the material (by changing/adding to the manufacturing process, leveraging composites, etc.) in the desired component to have certain characteristics. Another layer is the structural design problem – the geometric features of the component (such as shape and topology) that govern its performance in service, such as under mechanical or thermal loading. For polymers, additive manufacturing (AM) is a tool which is very amenable to tailoring, both in terms of material behavior and structural geometry. Its use, in conjunction with structural optimization techniques (e.g. topology optimization, or TO) is the subject of this thesis. First, numerical and experimental benchmarking is presented on minimum mechanical compliance optimization and material extrusion AM techniques (fused filament fabrication, or FFF, and direct-ink writing, or DIW). A major focus of the benchmarking work is the analysis of the impact of mechanical anisotropy and material extrusion orientation on the outcomes of minimum compliance TO designs. Finite element calculations are performed using Matlab scripts and commercial software (ABAQUS) to complement flexural testing of AM specimens made of ABS polymer or epoxy-based polymer matrix composite inks. Next, analysis of multi-material topology optimization (MMTO) and multi-material additive manufacturing (MMAM) is presented. An analysis of choices regarding extrusion of material at the interfaces between materials is presented with corresponding experimental testing (e.g., printing and flexural testing) of specimens with disparate interface designs. Finally, numerical work towards the multi-material thermomechanical optimization of structures with orthotropic material behavior is presented. The main contributions of the thesis work lie in: (i) establishing baseline numerical and experimental evaluations of TO/AM structures using standard TO and AM methods (e.g. SIMP, material-extrusion AM with common infill patterns) (ii) quantifying the impact of process-specific design methodologies for the orientation design of orthotropic composites (iii) presenting a new application of optimization in multiphysics and multi-material TO for isotropic/orthotropic materials that considers elastic compliance and thermal conductance and (iv) initial experimental assessments of printing methodologies for their integrity at material interfaces in multi-material TO structures
Multi-peptide presentation and organization in 3D-printed scaffolds drives osteochondral tissue formation
No full textFunctional repair of osteochondral (OC) tissue remains challenging because the transition from bone to cartilage presents gradients in biochemical and physical properties necessary for joint function. Osteochondral regeneration requires strategies that restore the spatial composition and organization found in the native tissue. Several biomaterial approaches have been developed to guide chondrogenic and osteogenic differentiation of human mesenchymal stem cells (hMSCs). These strategies must be coupled with advanced manufacturing techniques to achieve precise spatial control of biochemical signaling. 3D printing has rapidly become a popular method for creating highly tunable multi-material constructs with complex architectures that can be customized and scaled for in vivo translation. Our lab has developed a platform that achieves surface functionalization of scaffolds in a single fabrication step by solvent-cast 3D printing peptide-functionalized polymers. This 3D printing strategy enables unprecedented control of surface peptide presentation and spatial organization within a continuous construct. Peptide-poly(caprolactone) (PCL) conjugates were synthesized bearing hyaluronic acid (HA)-binding (HAbind–PCL) or mineralizing (E3–PCL) peptides, which have been shown to promote hMSC chondrogenesis or osteogenesis, respectively. Scaffolds presenting both cartilage-promoting and bone-promoting peptides had a synergistic effect that enhanced hMSC chondrogenic and osteogenic differentiation in the absence of differentiation factors compared to scaffolds without peptides or only one peptide. Notably, multi-peptide organization significantly influenced hMSC response. Scaffolds presenting HAbind and E3 peptides in discrete opposing zones promoted hMSC osteogenic behavior. In contrast, presenting both peptides homogeneously throughout the scaffolds drove hMSC differentiation towards a mixed population of articular and hypertrophic chondrocytes. These significant results indicated that hMSC behavior was driven by dual-peptide presentation and organization. An ex vivo equine explant model was developed to evaluate scaffold-directed tissue formation in a native-like environment. The downstream potential of this platform is the ability to fabricate biomaterials with spatially controlled biochemical cues to guide functional tissue regeneration in situ without the need for differentiation factors
Process Coordination in RDMA-Enabled Data Management Systems
No full textState-of-the-art distributed systems consist of multicore machines connected via a high-performance network. This is the standard deployment to meet the needs of modern applications. With the advent of new hardware, like remote direct memory access (RDMA), the overhead of network communication in such clusters has dramatically decreased, enabling data access latency within an order of magnitude of local memory access. Furthermore, the ability of RDMA to access memory over the network without involving a remote process breaks the conventional distributed communication model based on message-passing. Lower communication costs and a shared-memory-like abstraction are new considerations changing the landscape of prevailing distributed system design assumptions. This dissertation explores how processes can leverage this abstraction when coordinating concurrent tasks and develops techniques for RDMA-enabled systems. Theoretical frameworks are coupled with practical assumptions, rooted in the guarantees of RDMA implementations, to offer a holistic view of process coordination via RDMA. Consistent access to shared data is a central problem in this domain. Several techniques are presented in this regard and are leveraged to develop novel strategies for process coordination, spanning mutual exclusion, consensus, and concurrent data structures supporting linearizable range queries. A core emphasis is given to how hardware guarantees influence the manner in which local and remote processes communicate in RDMA-enabled systems
Rational Design of Fluoroalkylated Transition Metal Complexes for Fluoroalkylation Reactions
No full textThere is a continuous demand to develop better ways to incorporate fluoroalkyl groups into organic molecules, as such functionalities are known to facilitate the stability, reactivity, and conformational bias of their parent molecule. The interest in fluoroalkylation chemistry has created a need for better synthetic methodologies to access fluoroalkylated transition metal complexes. In comparison with second- and third-row transition metals, first-row transition metals are more desirable catalysts due to their lower cost and higher natural abundance.The first part of this dissertation briefly describes the synthesis of various perfluoroethylated nickel(II) complexes ([LnNi(CF2CF3)2], L = MeCN, bipyridine, pyridine) and their use in catalytic pentafluoroethylation of (hetero)arenes. Additionally, we describe the design of a partially fluorinated trifluoroethylated nickel(II) precatalyst ([(bipyridine)Ni(CH2CF3)2]) for Suzuki-type trifluoroethylation reactions between (hetero)arylboronic acids and a variety of alkyl halides.While routes to fluoroalkylated nickel complexes have been well-developed, the preparation of related cobalt complexes remains challenging and limited. To fill a void in this knowledge, the second part of this dissertation describes simple synthetic routes to afford a family of perfluoroalkylated cobalt(III) complexes ([Co-Rf], Rf = CF3, C2F5, n- C3F7, C4F8). Electrochemical analyses reveal that [(MeCN)4Co(C2F5)2][PF6] is more easily reduced compared to [(MeCN)3Co(C2F5)3], which has implications for the development of redox-triggered reactions involving the intermediacy of cobalt(II). Notably, a variety of well-defined perfluorometallacyclopentane complexes of cobalt ([Co(C4F8)]) have alsobeen synthesized and fully characterized for the first time. Access to these perfluoroalkylated cobalt complexes provides a foundation to explore less expensive and more diverse approaches to potential fluoroalkylation reactions.Lastly, the efforts to an optimized synthesis of the artificial nucleoside bearing the 5-(pyrimidin-2-yl)-pyrrolo[3,2-b]pyridine (PPP) motif are detailed in this dissertation. Our preliminary findings provide a foundation to further coordinate this unique chelating ligand with different transition metals within duplex DNA. The resulting metal-chelating artificial nucleoside is proposed to more closely resembled naturally occurring DNA base pairs whose function is not to support an internal metal-mediated base pair but rather to coordinate metals for labeling purposes and/or to perform bio-orthogonal reaction chemistries in the chiral environment of the major groove of duplex DNA