The Experts below are selected from a list of 4572 Experts worldwide ranked by ideXlab platform
L.m. Young - One of the best experts on this subject based on the ideXlab platform.
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Characterization of the roles of electrochemistry, convection and crack chemistry in stress corrosion cracking
1995Co-Authors: Peter L. Andresen, L.m. YoungAbstract:Understanding the role of Ionic Current Flow within a crack and near the crack tip is fundamental to modeling of environmentally assisted crack advance. Critical conceptual issues and models related to Ionic Current Flow within cracks, and the associated ``crevice`` chemistry and metal oxidation that results, are presented and examined in the light of experimental evidence. Various advanced techniques have been developed to evaluate the roles of electrochemistry, transport, and crack chemistry in stress corrosion cracking, with emphasis on high temperature ``pure`` water. These include high resolution crack length measurement by dc potential drop performed simultaneously with microsampling, electrochemical microprobe mapping, microinjection of species, and micropolarization of the crack. Conceptual issues addressed include the importance of the corrosion potential vs. oxidant concentration, the absence of oxidants and associated low corrosion potential within cracks, the location and role of macrocell Currents associated with potential gradients from differential aeration cells, the localized nature of the microcell Currents associated with dissolution at the crack tip, the importance of pH and adsorbed species on repassivation and crack advance, and the role of convection in crack chemistry and crack advance. Correct concepts are shown to be an essential pre-cursor to quantitative modeling.
Peter L. Andresen - One of the best experts on this subject based on the ideXlab platform.
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Characterization of the roles of electrochemistry, convection and crack chemistry in stress corrosion cracking
1995Co-Authors: Peter L. Andresen, L.m. YoungAbstract:Understanding the role of Ionic Current Flow within a crack and near the crack tip is fundamental to modeling of environmentally assisted crack advance. Critical conceptual issues and models related to Ionic Current Flow within cracks, and the associated ``crevice`` chemistry and metal oxidation that results, are presented and examined in the light of experimental evidence. Various advanced techniques have been developed to evaluate the roles of electrochemistry, transport, and crack chemistry in stress corrosion cracking, with emphasis on high temperature ``pure`` water. These include high resolution crack length measurement by dc potential drop performed simultaneously with microsampling, electrochemical microprobe mapping, microinjection of species, and micropolarization of the crack. Conceptual issues addressed include the importance of the corrosion potential vs. oxidant concentration, the absence of oxidants and associated low corrosion potential within cracks, the location and role of macrocell Currents associated with potential gradients from differential aeration cells, the localized nature of the microcell Currents associated with dissolution at the crack tip, the importance of pH and adsorbed species on repassivation and crack advance, and the role of convection in crack chemistry and crack advance. Correct concepts are shown to be an essential pre-cursor to quantitative modeling.
Doroschak, Kathryn Jean - One of the best experts on this subject based on the ideXlab platform.
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Computational design and sensing algorithms for nanopore-based molecular tagging and peptide detection
2021Co-Authors: Doroschak, Kathryn JeanAbstract:Thesis (Ph.D.)--University of Washington, 2021Molecular sensing provides a window into the complex world of otherwise invisible molecules, allowing us to measure protein abundance or sequence DNA, for example. Commercially available nanopore arrays have already made DNA sequencing less expensive and more portable than existing platforms, and they have recently emerged as potential tools for general purpose molecular sensing. Nanopore arrays record a time series of Ionic Current observations and do not intrinsically detect any particular types of molecules; any molecule that can physically Flow through the pore will partially block the Ionic Current Flow in unique ways depending on its physical properties, producing a characteristic Current trace. Since only DNA and RNA sequencing are officially supported, any applications beyond straightforward DNA sequencing require developing novel computational pipelines and algorithms to extract biologically relevant information. Here I present computational methods for three novel uses of commercial nanopore devices: (1) Porcupine, a molecular tagging system using custom designed nanopore-orthogonal DNA molecular bits (molbits); (2) Big Bits, a DNA data storage implementation using sequentially encoded molbits; and (3) Poretitioner, a pipeline for identifying NanoporeTERs (NTERs, Nanopore-addressable protein Tags Engineered as Reporters) and other engineered molecules. In each chapter, I present my contributions to novel computational analysis of nanopore data for these applications. Briefly, Porcupine labels physical objects using molecular tags. These tags encode digital information via the presence and absence of molbits, which I algorithmically designed to produce visually unique nanopore signals. The tags are later read back and decoded directly from the nanopore Ionic Current trace using a convolutional neural network (CNN). Big Bits extends upon this, using design principles from Porcupine to encode even more information for DNA data storage. Instead of using presence or absence to encode information, molbits in Big Bits are encoded sequentially. In the Poretitioner pipeline, I extract Ionic Current for captured peptides, then filter, classify, and quantify them using components built by both myself and others that can be tuned for various molecules
Acharjee, Mitu Chandra - One of the best experts on this subject based on the ideXlab platform.
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Characterization of Protein Aggregation Using a Solid-State Nanopore Device
ScholarWorks@UARK, 2021Co-Authors: Acharjee, Mitu ChandraAbstract:Protein aggregation has been linked to many chronic and devastating neurodegenerative human diseases and is also strongly associated with aging. In the case of neurodegenerative diseases, α, β tubulins and tau proteins dissociate in a neuron cell and aggregate both intra and extra-cellularly. Tau and tubulin aggregations were found as one of the major causes of many neurodegenerative diseases, such as Parkinson’s, Picks, Alzheimer’s, Huntington, and Prion. Finding the state and mechanism of protein aggregation is significant. In this work, tau and tubulin aggregations were detected in Ionic solutions using the solid-state nanopore technique. Besides tau and tubulin, aggregations of β-lactoglobulin were characterized using solid-state nanopore to understand amyloid plaques formation in Alzheimer’s disease. The nanopores (6-30 nm in diameter) were fabricated in a silicon nitride membrane on a silicon substrate by combination of focused ion beam milling and ion beam sculpting. Protein molecules were driven through nanopores by applied voltages (60-210 mV) in Ionic solution (0.1M – 2M KCl). A protein molecule passing through a pore will partially block Ionic Current Flow through the nanopore due to an increase in pore resistance which generates a Current drop event that can be recorded. The amplitudes of Ionic Current drops were proportional to the excluded volume of protein molecules. Protein aggregations were detected by comparing the Current blockage signals of monomer and aggregated proteins. Results of this research showed that solid-state nanopores were highly sensitive in the detection of dimeric to heptameric aggregations in Ionic solutions at different pH salt concentrations, and voltages. Protein aggregations measured using AFM scanning were consistent with nanopore results
Hagan Bayley - One of the best experts on this subject based on the ideXlab platform.
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Semisynthetic protein nanoreactor for single-molecule chemistry.
Proceedings of the National Academy of Sciences, 2015Co-Authors: Joongoo Lee, Hagan BayleyAbstract:The covalent chemistry of individual reactants bound within a protein pore can be monitored by observing the Ionic Current Flow through the pore, which acts as a nanoreactor responding to bond-making and bond-breaking events. In the present work, we incorporated an unnatural amino acid into the α-hemolysin (αHL) pore by using solid-phase peptide synthesis to make the central segment of the polypeptide chain, which forms the transmembrane β-barrel of the assembled heptamer. The full-length αHL monomer was obtained by native chemical ligation of the central synthetic peptide to flanking recombinant polypeptides. αHL pores with one semisynthetic subunit were then used as nanoreactors for single-molecule chemistry. By introducing an amino acid with a terminal alkyne group, we were able to visualize click chemistry at the single-molecule level, which revealed a long-lived (4.5-s) reaction intermediate. Additional side chains might be introduced in a similar fashion, thereby greatly expanding the range of single-molecule covalent chemistry that can be investigated by the nanoreactor approach.
