587 research outputs found

    Functional Nanomaterials and Polymer Nanocomposites: Current Uses and Potential Applications

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    This book covers a broad range of subjects, from smart nanoparticles and polymer nanocomposite synthesis and the study of their fundamental properties to the fabrication and characterization of devices and emerging technologies with smart nanoparticles and polymer integration

    Polymer-Ligated Nanocrystals with Tunable Dimensions, Compositions, and Architectures

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    The ability to produce monodisperse nanocrystals with stable and tunable surface chemistry is of key importance to render investigation into their size- and shape-dependent physical properties and thus an array of applications including electronics, photonics, catalysis, sensors, energy storage, information technology, bionanotechnology, etc. In this context, nonlinear block copolymer nanoreactor has emerged as a general and robust route to synthesis of a gallery of nanocrystals with precisely controlled sizes, shapes, compositions, and surface chemistry. In this thesis, I capitalized on a set of rationally designed star-like and bottlebrush-like block copolymer to template the growth of a host of functional 0D and 1D nanocrystals with controlled dimensions, compositions, and architectures, and scrutinize the dependence of physical properties and energy-related applications on their size, shape, and surface chemistry. First, a series of star-like copolymers were synthesized via sequential atom transfer radical polymerization (ATRP) of tert-butyl acrylate (tBA) and styrene from star-like macroinitiators, brominated β-cyclodextrin (β-CD). Due to the living nature of ATRP, the molecular weight of each polymer block can be precisely controlled by simply tuning polymerization time and a low polydispersity index (PDI) can be achieved. The inner hydrophobic poly(tert-butyl acrylate) (PtBA) blocks were then converted into hydrophilic poly(acrylic acid) (PAA), which strongly coordinates with the metal moieties of precursors of targeted nanocrystals, leading to the nucleation and growth of nanocrystals confined within the space occupied by the PAA blocks. As a result, the size and shape of nanocrystals can be readily controlled by the molecular weight of PAA blocks (i.e., diameter of nanoparticles). Moreover, the outer PS blocks, originally covalently linked to the inner PAA blocks, form a layer of permanently anchored ligands on the nanocrystal surface to enable stable surface chemistry. This synthetic strategy were successfully applied for preparing a diversity of functional nanoparticles for the investigation into their physical properties and applications. Specifically, this judiciously designed nanoreactor was utilized to craft monodispersed magnetic spinel CoFe2O4 nanoparticles, which was studied for their magnetic and surface chemistry related electrocatalytic activity. It was the first systematic scrutiny of the influence of spin-pinning effect in spinel nanoparticles realized via surface reconstruction on the oxygen evolution reaction (OER). Second, using the same chemistry, 1D bottlebrush-like PAA-b-PS templates can be realized by employing brominated cellulose (Cell-Br) as macroinitiators. Due to the larger number of side chains on one Cell-Br macroinitiator (ranging from about 40 chains to more than 150 chains), high quality bottlebrush-like block copolymers are more challenging to synthesize than star-like block copolymers, which only have 21 arms. Systematic scrutiny was made to investigate the reaction conditions (e.g., catalyst ratio, ligand ratio, reaction concentration, degassing method, etc.) that affect the uniform growth of the highly dense block copolymer side chains, which has a determining effect on the quality of the bottlebrush-like templates and their application as nanoreactors for the synthesis of 1D nanocrystals. In addition to focusing on the precise synthesis of 0D and 1D nanocrystals via nanoreactor strategy, this thesis also covers the practical application of multi-functional nanocomposites. In this work, a ternary nanocomposite consisting of antibacterial silver (Ag) NPs, photocatalytic titania oxide (TiO2) NPs, and upconverting NPs are prepared, manifesting a greatly enhanced biocidal performance under ambient environment. It was found that the visible light (blue) and ultraviolet (UV) light which were converted from near infrared (NIR) radiation by the NaYF4@Yb:Tm upconverting NPs can be effectively absorbed by Ag and TiO¬2 NPs to generate electrons and electron-hole pairs, respectively. Reactive oxygen species (ROS) could then be produced from the reactions between environment and the electrons and holes to terminate bacteria. The outstanding antibacterial performance of this nanocomposite system renders it the potential to be used in food packaging industry. Moreover, reversible photo responsive Ruddlesden-Popper 2D perovskite nanoplatelets were explored in this thesis. Colloidal two-dimensional RP perovskite nanoplatelets with a general formula L2(ABX3)n-1BX4 are a rapidly emerging type of semiconductor materials with excellent optical and electronic properties. Research on the functional organic spacers (L) has become a popular direction in the past several years. Inspired by our previous research about reversible photo-crosslinkable nanoparticles realized by capitalizing on star-like nanoreactors with photo responsive coumarin containing repeat units in the outer block, the preparation of RP lead halide perovskite nanoplatelets with coumarin containing ammonium as organic spacers was attempted. Molecular modification and mixed organic spacer strategies were adopted to overcome the solubility limitation of coumarin containing molecules in non-polar solvents. Such coumarin containing 2D perovskite nanoplatelets will undergo controllable and reversible layer-by-layer crosslinking and de-crosslinking under radiation of certain wavelength, leading to many intriguing and tunable optical and electronic properties.Ph.D

    LIPIcs, Volume 251, ITCS 2023, Complete Volume

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    LIPIcs, Volume 251, ITCS 2023, Complete Volum

    Engineering a Preprocessor for Symmetry Detection

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    State-of-the-art solvers for symmetry detection in combinatorial objects are becoming increasingly sophisticated software libraries. Most of the solvers were initially designed with inputs from combinatorics in mind (nauty, bliss, Traces, dejavu). They excel at dealing with a complicated core of the input. Others focus on practical instances that exhibit sparsity. They excel at dealing with comparatively easy but extremely large substructures of the input (saucy). In practice, these differences manifest in significantly diverging performances on different types of graph classes. We engineer a preprocessor for symmetry detection. The result is a tool designed to shrink sparse, large substructures of the input graph. On most of the practical instances, the preprocessor improves the overall running time significantly for many of the state-of-the-art solvers. At the same time, our benchmarks show that the additional overhead is negligible. Overall we obtain single algorithms with competitive performance across all benchmark graphs. As such, the preprocessor bridges the disparity between solvers that focus on combinatorial graphs and large practical graphs. In fact, on most of the practical instances the combined setup significantly outperforms previous state-of-the-art

    Analog Photonics Computing for Information Processing, Inference and Optimisation

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    This review presents an overview of the current state-of-the-art in photonics computing, which leverages photons, photons coupled with matter, and optics-related technologies for effective and efficient computational purposes. It covers the history and development of photonics computing and modern analogue computing platforms and architectures, focusing on optimization tasks and neural network implementations. The authors examine special-purpose optimizers, mathematical descriptions of photonics optimizers, and their various interconnections. Disparate applications are discussed, including direct encoding, logistics, finance, phase retrieval, machine learning, neural networks, probabilistic graphical models, and image processing, among many others. The main directions of technological advancement and associated challenges in photonics computing are explored, along with an assessment of its efficiency. Finally, the paper discusses prospects and the field of optical quantum computing, providing insights into the potential applications of this technology.Comment: Invited submission by Journal of Advanced Quantum Technologies; accepted version 5/06/202

    Precision Studies of QCD in the Low Energy Domain of the EIC

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    The manuscript focuses on the high impact science of the EIC with objective to identify a portion of the science program for QCD precision studies that requires or greatly benefits from high luminosity and low center-of-mass energies. The science topics include (1) Generalized Parton Distributions, 3D imagining and mechanical properties of the nucleon (2) mass and spin of the nucleon (3) Momentum dependence of the nucleon in semi-inclusive deep inelastic scattering (4) Exotic meson spectroscopy (5) Science highlights of nuclei (6) Precision studies of Lattice QCD in the EIC era (7) Science of far-forward particle detection (8) Radiative effects and corrections (9) Artificial Intelligence (10) EIC interaction regions for high impact science program with discovery potential. This paper documents the scientific basis for supporting such a program and helps to define the path toward the realization of the second EIC interaction region.Comment: 103 pages,47 figure

    Algorithms Transcending the SAT-Symmetry Interface

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    Dedicated treatment of symmetries in satisfiability problems (SAT) is indispensable for solving various classes of instances arising in practice. However, the exploitation of symmetries usually takes a black box approach. Typically, off-the-shelf external, general-purpose symmetry detection tools are invoked to compute symmetry groups of a formula. The groups thus generated are a set of permutations passed to a separate tool to perform further analyzes to understand the structure of the groups. The result of this second computation is in turn used for tasks such as static symmetry breaking or dynamic pruning of the search space. Within this pipeline of tools, the detection and analysis of symmetries typically incurs the majority of the time overhead for symmetry exploitation. In this paper we advocate for a more holistic view of what we call the SAT-symmetry interface. We formulate a computational setting, centered around a new concept of joint graph/group pairs, to analyze and improve the detection and analysis of symmetries. Using our methods, no information is lost performing computational tasks lying on the SAT-symmetry interface. Having access to the entire input allows for simpler, yet efficient algorithms. Specifically, we devise algorithms and heuristics for computing finest direct disjoint decompositions, finding equivalent orbits, and finding natural symmetric group actions. Our algorithms run in what we call instance-quasi-linear time, i.e., almost linear time in terms of the input size of the original formula and the description length of the symmetry group returned by symmetry detection tools. Our algorithms improve over both heuristics used in state-of-the-art symmetry exploitation tools, as well as theoretical general-purpose algorithms

    Design Strategies for Polysaccharide Hydrogels Used in Soft Tissue Engineering : Modification, Testing and Applications of Gellan Gum

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    Hydrogels are water-swollen polymer networks which provide an aqueous, three- dimensional environment and can mimic the biological cell environment and tissue architecture. Therefore, hydrogels are a valuable class of biomaterials for tissue engineering purposes that can be modified to support a specific application, such as the encapsulation of cells or as implantable device. Gellan gum is a microbial polysaccharide that readily forms self-supporting hydrogels in the presence of ions, and that has been investigated for medical applications due to its biocompatibility. However, due to its lack of innate cell recognition sites in its structure, gellan gum is highly inert and does not elicit any cell response required for in vitro cell culture or in vivo tissue integration. Here, the possibilities to chemically modify gellan gum and render it bioactive for cell culture purposes are explored. The investigated modifications include purification, oxidation, reductive scissoring, as well as blending and chemical crosslinking, and are initially reviewed for their biocompatibility and ability to form hydrogels. The modified materials were assessed for their mechanical and viscoelastic properties, and basic cell response using the human fibroblast line WI-38. The cells were seeded either 2D on the surface of a gelated sample or encapsulated in the 3D hydrogel. Similarly, more advanced cell lines, such as human adipose stem cells, bone marrow-derived stem cells and a vascular co-culture model, were investigated using some of the formulations, and evaluated using different microscopic techniques. Furthermore, extrusion bioprinting was investigated as biofabrication method, and tissue response in vivo of cell-free hydrogels was ascertained by subcutaneous implantation. In conclusion, the aim of thesis was to examine different modification approaches for the hydrogel gellan gum, but also to present a wholistic assessment protocol of modified hydrogel. Gellan gum acts as model polymer with the intent of projecting the design strategies and evaluation insights onto other polysaccharides and hydrogels. It has proven to be a suitable base polymer to create a material library with various mechanical and bioactive properties

    Design, expression, and characterization of FimH antigen as single recombinant protein or exposed on nanoparticles

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    Uropathogenic Escherichia coli (UPEC) accounts for approximately 85% of all urinary tract infections (UTIs), causing a global economic burden. E. coli is one of the pathogens mentioned in the ESKAPEE list drafted by OMS, meaning that the increasing antibiotic resistance acquired by UPEC is and will be a serious health problem in the future. Amongst the immunogenic antigens exposed on the surface of UPEC, FimH represent a potential target for vaccine development, since it is involved in the early stages of infection. As already demonstrated, immunizations with FimH elicit functional antibodies that prevent UPEC infections even though the number of doses required to elicit a strong immune response is not optimal. In this work, we aimed to stabilize FimH as a soluble recombinant antigen exploiting the donor strand complementation mechanism by generating different chimeric constructs constituted by FimH and FimG donor strand. To explore the potential of self-assembling nanoparticles to display FimH through genetic fusion, different constructs have been computationally designed and produced. In this work a structure-based design, using available crystal structures of FimH and three different NPs was performed to generate different constructs with optimized properties. Despite the different conditions tested, all the constructs designed (single antigen or chimeric NPs), resulted to be un-soluble proteins in E. coli. To overcome this issue a mammalian expression system has been tested. Soluble antigen expression was achieved for all constructs tested in the culture supernatants. Three novel chimeric NPs have been characterized by transmission electron microscopy (TEM) confirming the presence of correctly assembled NPs displaying UPEC antigen. In vivo study has shown a higher immunogenicity of the E. coli antigen when displayed on NPs surface compared to the single recombinant antigen. The antibodies elicited by chimeric NPs showed a higher functionality in the inhibition of bacterial adhesion
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