Browsing by Author "Li, Xiang"
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Item A COMPACT TWO-STEP LASER TIME-OF-FLIGHT MASS SPECTROMETER FOR IN SITU ANALYSIS OF PLANETARY SURFACES(2015-09-16) Getty, Stephanie A.; Brinckerhoff, William B.; Cornish, Timothy J.; Grubisic, Andrej; Li, Xiang; Uckert, KyleItem Development of chromatofocusing techniques employing mixed-mode column packings for protein separations.(Elsevier B.V, 2013-11-06) Frey, Douglas D.; Guo, Hui; Li, XiangRecent studies reported in the literature using mixed-mode chromatography (MMC) column packings have shown that multiple modes of interactions between the column packing and proteins can be usefully exploited to yield excellent resolution as well as salt-tolerant adsorption of the target protein. In this study, a mixed-mode separation method using commercially available column packings was explored which combines the techniques of hydrophobic-interaction chromatography and chromatofocusing. Two different column packings, one based on mercapto-ethyl-pyridine (MEP) and the other based on hexylamine (HEA) were investigated with regard to their ability to separate proteins when using internally generated, retained pH gradients. The effects of added salt and urea on the behavior of the retained pH gradient and the protein separation achieved when using MMC column packings for chromatofocusing were also investigated. Numerical simulations using methods developed in previous work were shown to agree with experimental results when using reasonable physical parameters. These numerical simulations were also shown to be a useful qualitative method to select the compositions of the starting and elution buffers in order to achieve desired shapes for the pH and ionic strength gradients. The use of the method to fractionate blood serum was explored as a prototype example application.Item Estimation of Surface and Top-of-Atmosphere Shortwave Irradiance in Biomass-Burning Regions during SCAR-B(AMS, 2000-10-01) Christopher, Sundar A.; Li, Xiang; Welch, Ronald M.; Reid, Jeffrey S.; Hobbs, Peter V.; Eck, Thomas; Holben, BrentUsing in situ measurements of aerosol optical properties and ground-based measurements of aerosol optical thickness (τₛ) during the Smoke, Clouds and Radiation—Brazil (SCAR-B) experiment, a four-stream broadband radiative transfer model is used to estimate the downward shortwave irradiance (DSWI) and top-of-atmosphere (TOA) shortwave aerosol radiative forcing (SWARF) in cloud-free regions dominated by smoke from biomass burning in Brazil. The calculated DSWI values are compared with broadband pyranometer measurements made at the surface. The results show that, for two days when near-coincident measurements of single-scattering albedo ω₀ and τₛ are available, the root-mean-square errors between the measured and calculated DSWI for daytime data are within 30 W m⁻². For five days during SCAR-B, however, when assumptions about ω₀ have to be made and also when τₛ was significantly higher, the differences can be as large as 100 W m⁻². At TOA, the SWARF per unit optical thickness ranges from -20 to -60 W m⁻² over four major ecosystems in South America. The results show that τₛ and ω₀ are the two most important parameters that affect DSWI calculations. For SWARF values, surface albedos also play an important role. It is shown that ω₀ must be known within 0.05 and τₛ at 0.55 ?m must be known to within 0.1 to estimate DSWI to within 20 W m⁻². The methodology described in this paper could serve as a potential strategy for determining DSWI values in the presence of aerosols. The wavelength dependence of τₛ and ω₀ over the entire shortwave spectrum is needed to improve radiative transfer calculations. If global retrievals of DSWI and SWARF from satellite measurements are to be performed in the presence of biomass-burning aerosols on a routine basis, a concerted effort should be made to develop methodologies for estimating ω₀ and τₛ from satellite and ground-based measurements.Item I Can See the Light: Attacks on Autonomous Vehicles Using Invisible Lights(Association for Computing Machinery, 2021-11-15) Wang, Wei; Yao, Yao; Liu, Xin; Li, Xiang; Hao, Pei; Zhu, TingThe camera is one of the most important sensors for an autonomous vehicle (AV) to perform Environment Perception and Simultaneous Localization and Mapping (SLAM). To secure the camera, current autonomous vehicles not only utilize the data gathered from multiple sensors (e.g., Camera, Ultrasonic Sensor, Radar, or LiDAR) for environment perception and SLAM but also require the human driver to always realize the driving situation, which can effectively defend against previous attack approaches (i.e., creating visible fake objects or introducing perturbations to the camera by using advanced deep learning techniques). Different from their work, in this paper, we in-depth investigate the features of Infrared light and introduce a new security challenge called I-Can-See-the-Light- Attack (ICSL Attack) that can alter environment perception results and introduce SLAM errors to the AV. Specifically, we found that the invisible infrared lights (IR light) can successfully trigger the image sensor while human eyes cannot perceive IR lights. Moreover, the IR light appears magenta color in the camera, which triggers different pixels from the ambient visible light and can be selected as key points during the AV's SLAM process. By leveraging these features, we explore to i) generate invisible traffic lights, ii) create fake invisible objects, iii) ruin the in-car user experience, and iv) introduce SLAM errors to the AV. We implement the ICSL Attack by using off-the-shelf IR light sources and conduct an extensive evaluation on Tesla Model 3 and an enterprise-level autonomous driving platform under various environments and settings. We demonstrate the effectiveness of the ICSL Attack and prove that current autonomous vehicle companies have not yet considered the ICSL Attack, which introduces severe security issues. To secure the AV, by exploring unique features of the IR light, we propose a software-based detection module to defend against the ICSL Attack.