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605 results on '"Liu, Yiyun"'

3. Profiling Intact Glycosphingolipids with Automated Structural Annotation and Quantitation from Human Samples with Nanoflow Liquid Chromatography Mass Spectrometry

Author

Schindler, Ryan L, Oloumi, Armin, Tena, Jennyfer, Alvarez, Michael Russelle S, Liu, Yiyun, Grijaldo, Sheryl, Barboza, Mariana, Jin, Lee-Way, Zivkovic, Angela M, and Lebrilla, Carlito B

Subjects
Medical Biochemistry and Metabolomics, Analytical Chemistry, Biomedical and Clinical Sciences, Chemical Sciences, Humans, Glycosphingolipids, Liquid Chromatography-Mass Spectrometry, Reproducibility of Results, Chromatography, Liquid, Sphingolipids, Chromatography, High Pressure Liquid, Other Chemical Sciences, Medical biochemistry and metabolomics, Analytical chemistry, Chemical engineering
Abstract

Sphingolipids are an essential subset of bioactive lipids found in most eukaryotic cells that contribute to membrane biophysical properties and are involved in cellular differentiation, recognition, and mediating interactions. The described nanoHPLC-ESI-Q/ToF methodology utilizes known biosynthetic pathways, accurate mass detection, optimized collision-induced disassociation, and a robust nanoflow chromatographic separation for the analysis of intact sphingolipids found in human tissue, cells, and serum. The methodology was developed and validated with an emphasis on addressing the common issues experienced in profiling these amphipathic lipids, which are part of the glycocalyx and lipidome. The high sensitivity obtained using nanorange flow rates with robust chromatographic reproducibility over a wide range of concentrations and injection volumes results in confident identifications for profiling these low-abundant biomolecules.

Published
2024

11. Progressive Knowledge Transfer Based on Human Visual Perception Mechanism for Perceptual Quality Assessment of Point Clouds

Author

Liu, Qi, Liu, Yiyun, Su, Honglei, Yuan, Hui, and Hamzaoui, Raouf

Subjects
Computer Science - Computer Vision and Pattern Recognition, Electrical Engineering and Systems Science - Image and Video Processing
Abstract

With the wide applications of colored point cloud in many fields, point cloud perceptual quality assessment plays a vital role in the visual communication systems owing to the existence of quality degradations introduced in various stages. However, the existing point cloud quality assessments ignore the mechanism of human visual system (HVS) which has an important impact on the accuracy of the perceptual quality assessment. In this paper, a progressive knowledge transfer based on human visual perception mechanism for perceptual quality assessment of point clouds (PKT-PCQA) is proposed. The PKT-PCQA merges local features from neighboring regions and global features extracted from graph spectrum. Taking into account the HVS properties, the spatial and channel attention mechanism is also considered in PKT-PCQA. Besides, inspired by the hierarchical perception system of human brains, PKT-PCQA adopts a progressive knowledge transfer to convert the coarse-grained quality classification knowledge to the fine-grained quality prediction task. Experiments on three large and independent point cloud assessment datasets show that the proposed no reference PKT-PCQA network achieves better of equivalent performance comparing with the state-of-the-art full reference quality assessment methods, outperforming the existed no reference quality assessment network.

Published
2022

16. A Formal Model of Checked C

Author

Li, Liyi, Liu, Yiyun, Postol, Deena L., Lampropoulos, Leonidas, Van Horn, David, and Hicks, Michael

Subjects
Computer Science - Programming Languages, Computer Science - Software Engineering, D.3.1
Abstract

We present a formal model of Checked C, a dialect of C that aims to enforce spatial memory safety. Our model pays particular attention to the semantics of dynamically sized, potentially null-terminated arrays. We formalize this model in Coq, and prove that any spatial memory safety errors can be blamed on portions of the program labeled unchecked; this is a Checked C feature that supports incremental porting and backward compatibility. While our model's operational semantics uses annotated ("fat") pointers to enforce spatial safety, we show that such annotations can be safely erased: Using PLT Redex we formalize an executable version of our model and a compilation procedure from it to an untyped C-like language, and use randomized testing to validate that generated code faithfully simulates the original. Finally, we develop a custom random generator for well-typed and almost-well-typed terms in our Redex model, and use it to search for inconsistencies between our model and the Clang Checked C implementation. We find these steps to be a useful way to co-develop a language (Checked C is still in development) and a core model of it., Comment: This is an extended version of a paper that appears at the 2022 Computer Security Foundations Symposium

Published
2022

30. Study of Cu-exchanged CHA catalysts for the Selective Catalytic Reduction (SCR) reaction

Author

Liu, Yiyun

Abstract

Eliminating the harmful NOx, which is the major pollutant in the exhaust gas of diesel engines, has long been the pursue of scientists. Cu-chabazite (Cu-CHA) zeolites system developed in 2008 is shown to be an efficient and thermal stable catalyst in the deNOx NH3-SCR reaction and has received intense study since then. Aiming to further improve its catalytic activity, a wide range of characterization techniques has been developed and applied to study the well-defined structures and catalysis. Study of SCR reaction over the Cu-CHA catalysts demands the understanding of active Cu sites, for which loading-dependent behaviour is first studied with UV-Vis spectroscopy and ex-situ EPR spectroscopy together with the reaction evaluation. To further investigate different Cu species, the combination of H2-TPR, NH3-TPD and EPR spectroscopy were applied to quantify the Cu speciation in the catalysts, from which the sequential domination of 2AlCu, 1AlCu and CuO species with increasing Cu loadings was observed. Subsequent study of dehydration and hydrothermal aging processes with EPR also reveals the transformation of Cu species from 1AlCu to 2AlCu through the formation of hydrated complexes and the decomposition of CuOx clusters. On the other hand, the interaction between Cu-CHA catalysts and SCR reactants was studied with in situ FTIR and operando NEXAFS, showing the adsorption of NO and NH3 molecules respectively. Aiming to uncover the key species in the SCR reaction and reveal the origin of different reactivity for 1AlCu and 2AlCu sites, the samples with different Cu distribution was studied with operando X-ray spectroscopy under SCR conditions. With the combination of HERFD-XANES, vtc-XES and time-resolved XAS at transient states, key intermediate CuNOx species is observed to be preferentially formed on the 1AlCu sites, while a framework coordinated CuI(NH3)xOfw species is identified to be the real species causing NH3 inhibition effect, hindering the re-oxidation of CuI especially at 2AlCu sites.

Published
2021

38. Pemphigus-associated desmoglein-specific IgG1 and IgG4 have a dominant agalactosylated glycan modification

Author

Oloumi, Armin, primary, Le, Stephanie T., additional, Liu, Yiyun, additional, Herbert, Samantha, additional, Ji-Xu, Antonio, additional, Merleev, Alexander A., additional, Kruglinskaya, Olga, additional, Artounian, Kimberly, additional, Park, Dayoung, additional, Marusina, Alina I., additional, Zone, John J., additional, Feldman, Ron, additional, Lebrilla, Carlito B., additional, and Maverakis, Emanual, additional

Published
2024
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