Browsing by Author "Zhang, Hui"

Now showing 1 - 7 of 7
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    Chiral and Achiral Nanodumbbell Dimers: The Effect of Geometry on Plasmonic Properties
    (American Chemical Society, 2016) Smith, Kyle W.; Zhao, Hangqi; Zhang, Hui; Sánchez -Iglesias, Ana; Grzelczak, Marek; Wang, Yumin; Chang, Wei-Shun; Nordlander, Peter; Liz-Marzán, Luis; Link, Stephan; Laboratory for Nanophotonics
    Metal nanoparticles with a dumbbell-like geometry have plasmonic properties similar to those of their nanorod counterparts, but the unique steric constraints induced by their enlarged tips result in distinct geometries when self-assembled. Here, we investigate gold dumbbells that are assembled into dimers within polymeric micelles. A single-particle approach with correlated scanning electron microscopy and dark-field scattering spectroscopy reveals the effects of dimer geometry variation on the scattering properties. The dimers are prepared using exclusively achiral reagents, and the resulting dimer solution produces no detectable ensemble circular dichroism response. However, single-particle circular differential scattering measurements uncover that this dimer sample is a racemic mixture of individual nanostructures with significant positive and negative chiroptical signals. These measurements are complemented with detailed simulations that confirm the influence of various symmetry elements on the overall peak resonance energy, spectral line shape, and circular differential scattering response. This work expands the current understanding of the influence self-assembled geometries have on plasmonic properties, particularly with regard to chiral and/or racemic samples which may have significant optical activity that may be overlooked when using exclusively ensemble characterization techniques.
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    Circulating ACE2-expressing extracellular vesicles block broad strains of SARS-CoV-2
    (Springer Nature, 2022) El-Shennawy, Lamiaa; Hoffmann, Andrew D.; Dashzeveg, Nurmaa Khund; McAndrews, Kathleen M.; Mehl, Paul J.; Cornish, Daphne; Yu, Zihao; Tokars, Valerie L.; Nicolaescu, Vlad; Tomatsidou, Anastasia; Mao, Chengsheng; Felicelli, Christopher J.; Tsai, Chia-Feng; Ostiguin, Carolina; Jia, Yuzhi; Li, Lin; Furlong, Kevin; Wysocki, Jan; Luo, Xin; Ruivo, Carolina F.; Batlle, Daniel; Hope, Thomas J.; Shen, Yang; Chae, Young Kwang; Zhang, Hui; LeBleu, Valerie S.; Shi, Tujin; Swaminathan, Suchitra; Luo, Yuan; Missiakas, Dominique; Randall, Glenn C.; Demonbreun, Alexis R.; Ison, Michael G.; Kalluri, Raghu; Fang, Deyu; Liu, Huiping
    The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused the pandemic of the coronavirus induced disease 2019 (COVID-19) with evolving variants of concern. It remains urgent to identify novel approaches against broad strains of SARS-CoV-2, which infect host cells via the entry receptor angiotensin-converting enzyme 2 (ACE2). Herein, we report an increase in circulating extracellular vesicles (EVs) that express ACE2 (evACE2) in plasma of COVID-19 patients, which levels are associated with severe pathogenesis. Importantly, evACE2 isolated from human plasma or cells neutralizes SARS-CoV-2 infection by competing with cellular ACE2. Compared to vesicle-free recombinant human ACE2 (rhACE2), evACE2 shows a 135-fold higher potency in blocking the binding of the viral spike protein RBD, and a 60- to 80-fold higher efficacy in preventing infections by both pseudotyped and authentic SARS-CoV-2. Consistently, evACE2 protects the hACE2 transgenic mice from SARS-CoV-2-induced lung injury and mortality. Furthermore, evACE2 inhibits the infection of SARS-CoV-2 variants (α, β, and δ) with equal or higher potency than for the wildtype strain, supporting a broad-spectrum antiviral mechanism of evACE2 for therapeutic development to block the infection of existing and future coronaviruses that use the ACE2 receptor.
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    Effect of oils, soap and hardness on the stability of foams
    (2004) Zhang, Hui; Miller, Clarence A.
    A systematic study of foam stability in the presence of model nonpolar oils and their mixtures with oleic acid was conducted for two commonly used surfactants (anionic and nonionic) under neutral and alkaline conditions with different amounts of dissolved calcium. In some cases insoluble calcium soap or microemulsions formed in situ. Measurements of the rate of collapse of a foam column were supplemented by microscopic observations of individual foam and "pseudoemulsion" films and by measurement of equilibrium and dynamic surface and interfacial tensions. In the absence of calcium soap use of equilibrium values of conventional entry E, spreading S, and bridging B coefficients was adequate to explain the effect of oils on stability of foams containing the nonionic surfactant. For the anionic surfactant E must be modified to account for electrostatic repulsion in the pseudoemulsion film. Calcium soap particles at the oil-water interface facilitate entry of oil drops and the associated bridging of foam films or Plateau borders, producing a substantial antifoam effect. When this synergistic effect occurs, conventional values of E govern oil entry. In some cases for oils that were mixtures of triolein and oleic acid foam is unstable during foam formation and initial foam drainage but stable at later times, behavior which is explained by calculating transient values of E, S, and B. Addition of n-dodecanol produced significant stabilization of foams of the anionic surfactant containing dispersed oil drops both when calcium soap was present and when high levels of calcium had destabilized the foam at neutral pH. ESB theory proved useful in predicting this effect. An amine oxide surfactant was less effective as a foam booster. In the absence of oil, calcium soap particles can destabilize foams of both surfactants. A model for predicting the precipitation boundary including the enhancement of calcium content in the electrical double layers of surfactant micelles yielded results in agreement with experiment. Foam was less stable while precipitation was occurring (hours) than at equilibrium, perhaps because calcium oleate, which initially formed at the interfaces, was extracted as oleate concentration decreased to its equilibrium value.
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    From tunable core-shell nanoparticles to plasmonic drawbridges: Active control of nanoparticle optical properties
    (AAAS, 2015) Byers, Chad P.; Zhang, Hui; Swearer, Dayne F.; Yorulmaz, Mustafa; Hoener, Benjamin S.; Huang, Da; Hoggard, Anneli; Chang, Wei-Shun; Mulvaney, Paul; Ringe, Emilie; Halas, Naomi J.; Nordlander, Peter; Link, Stephan; Landes, Christy F.
    The optical properties of metallic nanoparticles are highly sensitive to interparticle distance, giving rise to dramatic but frequently irreversible color changes. By electrochemical modification of individual nanoparticles and nanoparticle pairs, we induced equally dramatic, yet reversible, changes in their optical properties. We achieved plasmon tuning by oxidation-reduction chemistry of Ag-AgCl shells on the surfaces of both individual and strongly coupled Au nanoparticle pairs, resulting in extreme but reversible changes in scattering line shape. We demonstrated reversible formation of the charge transfer plasmon mode by switching between capacitive and conductive electronic coupling mechanisms. Dynamic single-particle spectroelectrochemistry also gave an insight into the reaction kinetics and evolution of the charge transfer plasmon mode in an electrochemically tunable structure. Our study represents a highly useful approach to the precise tuning of the morphology of narrow interparticle gaps and will be of value for controlling and activating a range of properties such as extreme plasmon modulation, nanoscopic plasmon switching, and subnanometer tunable gap applications.
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    Gradient Methods for Convex Minimization: Better Rates Under Weaker Conditions
    (2013-03) Zhang, Hui; Yin, Wotao
    The convergence behavior of gradient methods for minimizing convex differentiable functions is one of the core questions in convex optimization. This paper shows that their well-known complexities can be achieved under conditions weaker than the commonly assumed ones. We relax the common gradient Lipschitz-continuity condition and strong convexity condition to ones that hold only over certain line segments. Specifically, we establish complexities O(R/eps) and O(sqrt(R/eps)) for the ordinary and accelerate gradient methods, respectively, assuming that ∇f is Lipschitz continuous with constant R over the line segment joining x and x-∇f/R for each x in the domain of f. Then we improve them to O((R/ν) log(1/eps)) and O(sqrt(R/ν) log(1/eps)) for function f that also satisfies the secant inequality (∇f(x))T(x-x*)> ≥ ν||x-x*||2 for each x in the domain of f and its projection x* to the minimizer set of f. The secant condition is also shown to be necessary for the geometric decay of solution error. Not only are the relaxed conditions met by more functions, the restrictions give smaller R and larger ν than they are without the restrictions and thus lead to better complexity bounds. We apply these results to sparse optimization and demonstrate a faster algorithm.
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    MMS: An Autonomic Network-Layer Foundation for Network Management
    (2008-12-03) Gogineni, Hemant; Greenberg, Albert; Maltz, David A.; Ng, T. S. Eugene; Yan, Hong; Zhang, Hui
    Networks cannot be managed without communication among geographically distributed network devices and control agents. Unfortunately, computer networks today lack an autonomic mechanism that enables such communications, and the stopgap solutions used in practice are seriously flawed. To address the problem, this paper presents the design and implementation of the Meta-Management System (MMS), a network-layer subsystem that provides robust and universal support for management plane communications. The MMS is autonomic, able to self-configure, self-heal, self-optimize, and self-protect. Furthermore, it is efficient, scalable, and evolvable. We demonstrate the practicality of the MMS via a fully functional implementation that runs on commodity hardware. The MMS software is freely available.
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    Necessary and Sufficient Conditions of Solution Uniqueness in l1 Minimizationms
    (2012-08) Zhang, Hui; Yin, Wotao; Cheng, Lizhi
    This paper shows that the solutions to various convex l1 minimization problems are unique if and only if a common set of conditions are satisfied. This result applies broadly to the basis pursuit model, basis pursuit denoising model, Lasso model, as well as other l1 models that either minimize f(Ax-b) or impose the constraint f(Ax-b) <= sigma, where f is a strictly convex function. For these models, this paper proves that, given a solution x* and defining I=supp(x*) and s=sign(x*I), x is the unique solution if and only if AI has full column rank and there exists y such that A'Iy=s and |a'iy|<1 for i not in I. This condition is previously known to be sufficient for the basis pursuit model to have a unique solution supported on I. Indeed, it is also necessary, and applies to a variety of other l1 models. The paper also discusses ways to recognize unique solutions and verify the uniqueness conditions numerically.