Browsing by Author "Li, H"

Now showing 1 - 7 of 7
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    Anomalous periodicity of magnetic interference patterns in encapsulated graphene Josephson junctions
    (Physical Review Research) Ke, CT; Draelos, AW; Seredinski, A; Wei, MT; Li, H; Hernandez-Rivera, M; Watanabe, K; Taniguchi, T; Yamamoto, M; Tarucha, S; Bomze, Y; Borzenets, IV; Amet, F; Finkelstein, G
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    Chiral quasiparticle tunneling between quantum Hall edges in proximity with a superconductor
    (Physical Review B, 2019-09-10) Wei, MT; Draelos, AW; Seredinski, A; Ke, CT; Li, H; Mehta, Y; Watanabe, K; Taniguchi, T; Yamamoto, M; Tarucha, S; Finkelstein, G; Amet, F; Borzenets, IV
    © 2019 American Physical Society. We study a two-terminal graphene Josephson junction with contacts shaped to form a narrow constriction, less than 100nm in length. The contacts are made from type-II superconducting contacts and able to withstand magnetic fields high enough to reach the quantum Hall regime in graphene. In this regime, the device conductance is determined by edge states, plus the contribution from the constricted region. In particular, the constriction area can support supercurrents up to fields of ∼2.5T. Additionally, enhanced conductance is observed through a wide range of magnetic fields and gate voltages. This additional conductance and the appearance of supercurrent is attributed to the tunneling between counterpropagating quantum Hall edge states along opposite superconducting contacts.
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    Computational Analyses of Physiologic Effects After Midvault Repair Techniques in Rhinoplasty
    (FACE, 2023-03) Avashia, YJ; Martin, HL; Frank-Ito, DO; Hodges, KZ; Trotta, RT; Li, H; Lowry, C; Woodard, CR; Allori, AC; Marcus, JR
    Background: Midvault reconstruction is an essential element of functional rhinoplasty. An improved understanding of airflow patterns after spreader graft (SG) or spreader flap (SF) techniques can inform surgical techniques based on individual anatomy. Objectives: The objective of this study was to compare the physiologic changes related to nasal function after midvault reconstruction with SF and SG. Methods: Soft tissue elevation (STE), SG, and SF were performed in sequence on 5 cadaveric specimens. Computational modeling was used to simulate airflow, heat transfer, and humidity in three-dimensional nasal airway reconstructions of each specimen. Results: Median bilateral airflow-rates (L/min) were similar for STE (29.4), SF (27.6), and SG (28.9), and were not statistically significant (STE vs SF: P = 1.0, power = 5%; STE vs SG: P = .31, power = 16%; SF vs SG: P = .42, power = 14%). Both SF and SG had increased unilateral airflow volume (L/min) through the more obstructed nasal passage (median: STE 10.3, SF 12.2, SG 12.7), but these differences were not significant (STE vs SF: P = .19, power = 24%; STE vs SG P = .19, power = 30%). Furthermore, SF and SG had decreased unilateral nasal resistance (Pa s/mL) on the more obstructed side (median: STE 0.085, SF 0.072, SG 0.062) (STE vs SF: P = .13, power = 23%; STE vs SG P = .13, power = 24%). For all 3 models, heat flux distribution was greater in the anterior portion of the nasal passage than the posterior portions. Conclusions: Differences in nasal airflow and resistance after SF and SG were not statistically significant, but both procedures resulted in higher airflow rates and decreased nasal resistance through the more obstructed nasal passage.
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    High Multiplicity Infection by HIV-1 in Men Who Have Sex with Men.
    (PLoS pathogens, 2010) Li, H; Bar, KJ; Wang, S; Decker, JM; Chen, Y; Sun, C; Salazar Gonzalez, JF; Salazar, MG; Learn, GH; Morgan, CJ; Schumacher, JE; Hraber, P; Giorgi, EE; Bhattacharya, T; Korber, BT; Perelson, AS; Eron, JJ; Cohen, MS; Hicks, CB; Haynes, BF; Markowitz, M; Keele, BF; Hahn, BH; Shaw, GM
    Elucidating virus-host interactions responsible for HIV-1 transmission is important for advancing HIV-1 prevention strategies. To this end, single genome amplification (SGA) and sequencing of HIV-1 within the context of a model of random virus evolution has made possible for the first time an unambiguous identification of transmitted/founder viruses and a precise estimation of their numbers. Here, we applied this approach to HIV-1 env analyses in a cohort of acutely infected men who have sex with men (MSM) and found that a high proportion (10 of 28; 36%) had been productively infected by more than one virus. In subjects with multivariant transmission, the minimum number of transmitted viruses ranged from 2 to 10 with viral recombination leading to rapid and extensive genetic shuffling among virus lineages. A combined analysis of these results, together with recently published findings based on identical SGA methods in largely heterosexual (HSX) cohorts, revealed a significantly higher frequency of multivariant transmission in MSM than in HSX [19 of 50 subjects (38%) versus 34 of 175 subjects (19%); Fisher's exact p = 0.008]. To further evaluate the SGA strategy for identifying transmitted/founder viruses, we analyzed 239 overlapping 5' and 3' half genome or env-only sequences from plasma viral RNA (vRNA) and blood mononuclear cell DNA in an MSM subject who had a particularly well-documented virus exposure history 3-6 days before symptom onset and 14-17 days before peak plasma viremia (47,600,000 vRNA molecules/ml). All 239 sequences coalesced to a single transmitted/founder virus genome in a time frame consistent with the clinical history, and a molecular clone of this genome encoded replication competent virus in accord with model predictions. Higher multiplicity of HIV-1 infection in MSM compared with HSX is consistent with the demonstrably higher epidemiological risk of virus acquisition in MSM and could indicate a greater challenge for HIV-1 vaccines than previously recognized.
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    Interactions of oxygen radicals with airway epithelium.
    (Environ Health Perspect, 1994-12) Wright, DT; Cohn, LA; Li, H; Fischer, B; Li, CM; Adler, KB
    Reactive oxygen species (ROS) have been implicated in the pathogenesis of numerous disease processes. Epithelial cells lining the respiratory airways are uniquely vulnerable regarding potential for oxidative damage due to their potential for exposure to both endogenous (e.g., mitochondrial respiration, phagocytic respiratory burst, cellular oxidases) and exogenous (e.g., air pollutants, xenobiotics, catalase negative organisms) oxidants. Airway epithelial cells use several nonenzymatic and enzymatic antioxidant mechanisms to protect against oxidative insult. Nonenzymatic defenses include certain vitamins and low molecular weight compounds such as thiols. The enzymes superoxide dismutase, catalase, and glutatione peroxidase are major sources of antioxidant protection. Other materials associated with airway epithelium such as mucus, epithelial lining fluid, and even the basement membrane/extracellular matrix may have protective actions as well. When the normal balance between oxidants and antioxidants is upset, oxidant stress ensues and subsequent epithelial cell alterations or damage may be a critical component in the pathogenesis of several respiratory diseases. Oxidant stress may profoundly alter lung physiology including pulmonary function (e.g., forced expiratory volumes, flow rates, and maximal inspiratory capacity), mucociliary activity, and airway reactivity. ROS may induce airway inflammation; the inflammatory process may serve as an additional source of ROS in airways and provoke the pathophysiologic responses described. On a more fundamental level, cellular mechanisms in the pathogenesis of ROS may involve activation of intracellular signaling enzymes including phospholipases and protein kinases stimulating the release of inflammatory lipids and cytokines. Respiratory epithelium may be intimately involved in defense against, and pathophysiologic changes invoked by, ROS.
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    Joint estimation of multiple high-dimensional precision matrices
    (Statistica Sinica, 2016-04-01) Cai, TT; Li, H; Liu, W; Xie, J
    Motivated by analysis of gene expression data measured in different tissues or disease states, we consider joint estimation of multiple precision matrices to effectively utilize the partially shared graphical structures of the corresponding graphs. The procedure is based on a weighted constrained l∞/l1 minimization, which can be effectively implemented by a second-order cone programming. Compared to separate estimation methods, the proposed joint estimation method leads to estimators converging to the true precision matrices faster. Under certain regularity conditions, the proposed procedure leads to an exact graph structure recovery with a probability tending to 1. Simulation studies show that the proposed joint estimation methods outperform other methods in graph structure recovery. The method is illustrated through an analysis of an ovarian cancer gene expression data. The results indicate that the patients with poor prognostic subtype lack some important links among the genes in the apoptosis pathway.
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    Supercurrent in Graphene Josephson Junctions with Narrow Trenches in the Quantum Hall Regime
    (MRS Advances, 2018-01-01) Seredinski, A; Draelos, A; Wei, MT; Ke, CT; Fleming, T; Mehta, Y; Mancil, E; Li, H; Taniguchi, T; Watanabe, K; Tarucha, S; Yamamoto, M; Borzenets, IV; Amet, F; Finkelstein, G
    © 2018 Materials Research Society. Coupling superconductors to quantum Hall edge states is the subject of intense investigation as part of the ongoing search for non-abelian excitations. Our group has previously observed supercurrents of hundreds of picoamperes in graphene Josephson junctions in the quantum Hall regime. One of the explanations of this phenomenon involves the coupling of an electron edge state on one side of the junction to a hole edge state on the opposite side. In our previous samples, these states are separated by several microns. Here, a narrow trench perpendicular to the contacts creates counterpropagating quantum Hall edge channels tens of nanometres from each other. Transport measurements demonstrate a change in the low-field Fraunhofer interference pattern for trench devices and show a supercurrent in both trench and reference junctions in the quantum Hall regime. The trench junctions show no enhancement of quantum Hall supercurrent and an unexpected supercurrent periodicity with applied field, suggesting the need for further optimization of device parameters.