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Xi Zhao

Publications and source records attributed to Xi Zhao.

47 records · Page 3Linked to original sources
arXiv2020

Informative Scene Decomposition for Crowd Analysis, Comparison and Simulation Guidance

Crowd simulation is a central topic in several fields including graphics. To achieve high-fidelity simulations, data has been increasingly relied upon for analysis and simulation guidance. However, the information in real-world data is often noisy, mixed and unstructured, making it difficult for effective analysis, therefore has not been fully utilized. With the fast-growing volume of crowd data, such a bottleneck needs to be addressed. In this paper, we propose a new framework which comprehensively tackles this problem. It centers at an unsupervised method for analysis. The method takes as input raw and noisy data with highly mixed multi-dimensional (space, time and dynamics) information, and automatically structure it by learning the correlations among these dimensions. The dimensions together with their correlations fully describe the scene semantics which consists of recurring activity patterns in a scene, manifested as space flows with temporal and dynamics profiles. The effectiveness and robustness of the analysis have been tested on datasets with great variations in volume, duration, environment and crowd dynamics. Based on the analysis, new methods for data visualization, simulation evaluation and simulation guidance are also proposed. Together, our framework establishes a highly automated pipeline from raw data to crowd analysis, comparison and simulation guidance. Extensive experiments and evaluations have been conducted to show the flexibility, versatility and intuitiveness of our framework.

cs.GR↗
arXiv2019

Cooper minimum of high-order harmonic spectra from MgO crystal in an ultrashort laser pulse

Cooper minimum structure of high-order harmonic spectra from atoms or molecules has been extensively studied. In this paper, we demonstrate that the crystal harmonic spectra from an ultrashort mid-infrared laser pulse also exhibit the Cooper minimum characteristic. Based on the accurate band dispersion and k-dependent transition dipole moment (TDM) from the first-principle calculations, it can be found that the harmonic spectra from MgO crystal along Γ-X direction present a dip structure in the plateau, which is originated from the valley of TDM by examining the distribution of the harmonic intensity at the k-space. The Cooper minimum feature in crystal HHG will pave a new way to retrieve the band information of solid materials by using HHG from the ultrashort mid-infrared laser pulse.

physics.atm-clus↗
arXiv2019

Retrieving Similar Trajectories from Cellular Data at City Scale

Retrieving similar trajectories from a large trajectory dataset is important for a variety of applications, like transportation planning and mobility analysis. Unlike previous works based on fine-grained GPS trajectories, this paper investigates the feasibility of identifying similar trajectories from cellular data observed by mobile infrastructure, which provide more comprehensive coverage. To handle the large localization errors and low sample rates of cellular data, we develop a holistic system, cellSim, which seamlessly integrates map matching and similar trajectory search. A set of map matching techniques are proposed to transform cell tower sequences into moving trajectories on a road map by considering the unique features of cellular data, like the dynamic density of cell towers and bidirectional roads. To further improve the accuracy of similarity search, map matching outputs M trajectory candidates of different confidence, and a new similarity measure scheme is developed to process the map matching results. Meanwhile, M is dynamically adapted to maintain a low false positive rate of the similarity search, and two pruning schemes are proposed to minimize the computation overhead. Extensive experiments on a large-scale dataset and real-world trajectories of 1701 km reveal that cellSim provides high accuracy (precision 62.4% and recall of 89.8%).

eess.SP↗
arXiv2018

Tubeless Siphon Flow of Room Temperature Liquid Metal

Tubeless siphon flow of liquid metal was made possible by way of sucking the fluid via a syringe pump with a rubber tube. Through adjusting the flow rate and tube diameter, the liquid column height and diameter can be changed accordingly. A theoretical model was derived to predict the flow configuration thus enabled. Adding micro copper particles evidently increased the extensional viscosity of liquid metal. With the increase of particle concentration, the enhancement of tubeless siphon becomes more remarkable. The intermetallic compound CuGa2 produced by corrosion was considered as the reason for the variation of rheological property of liquid metal.

physics.flu-dyn↗
arXiv2018

A Theory of Enzyme Chemotaxis: Comparison Between Experiment and Model

Enzymes show two distinct transport behaviors in the presence of their substrates in solution. First, their diffusivity enhances with increasing substrate concentration. In addition, enzymes perform directional motion toward regions with high substrate concentration, termed chemotaxis. While a variety of enzymes has been shown to undergo chemotaxis, there remains a lack of quantitative understanding of the phenomenon. Here, we provide a general expression for the active movement of an enzyme in a concentration gradient of its substrate. The proposed model takes into account both the substrate-binding and catalytic turnover step, as well as the enhanced diffusion effect. We have experimentally measured the chemotaxis of a fast and a slow enzyme: urease under catalytic conditions, and hexokinase for both full catalysis and for simple non-catalytic substrate binding. There is good agreement between the proposed model and the experiments. The model is general, has no adjustable parameters, and only requires three experimentally defined constants to quantify chemotaxis: enzyme-substrate binding affinity (Kd), Michaelis-Menten constant (KM) and level of diffusion enhancement in the associated substrate (α).

physics.bio-ph↗
arXiv2017

A multi-candidate electronic voting scheme with unlimited participants

In this paper a new multi-candidate electronic voting scheme is constructed with unlimited participants. The main idea is to express a ballot to allow voting for up to k out of the m candidates and unlimited participants. The purpose of vote is to select more than one winner among $m$ candidates. Our result is complementary to the result by Sun peiyong$'$ s scheme, in the sense, their scheme is not amenable for large-scale electronic voting due to flaw of ballot structure. In our scheme the vote is split and hidden, and tallying is made for $G\ddot{o}del$ encoding in decimal base without any trusted third party, and the result does not rely on any traditional cryptography or computational intractable assumption. Thus the proposed scheme not only solves the problem of ballot structure, but also achieves the security including perfect ballot secrecy, receipt-free, robustness, fairness and dispute-freeness.

cs.CR↗
arXiv2017

Transformable Soft Quantum Device based on Liquid Metals with Sandwiched Liquid Junctions

Quantum tunneling effect has been an important issue in both fundamental science and practical applications. Classical quantum tunneling devices are generally rigid in structures which may encounter technical difficulties during fabrication, functional tuning and shape adapting. Here through introducing the room-temperature liquid metals as two conductive electrodes and a soft even liquid insulating layer sandwiched between them, we proposed a conceptually innovative all-soft or liquid quantum device which would help realize a couple of unconventional quantum capabilities such as flexibility, deformability, transformability, and reconfigurability, etc. which may not be easily offered by a rigid quantum device. Representative structural configurations to make such transformable quantum devices via sandwiching various liquid metal-insulating layer-liquid metal (LM-IL-LM) components are suggested. The feasibility for making such an all-soft quantum device is interpreted through experimental evidences and theoretical evaluations. Potential future applications of the proposed devices in a group of emerging fields including intelligent quantum systems and quantum computing are prospected.

physics.app-ph↗
arXiv2017

Improving Shadow Suppression for Illumination Robust Face Recognition

2D face analysis techniques, such as face landmarking, face recognition and face verification, are reasonably dependent on illumination conditions which are usually uncontrolled and unpredictable in the real world. An illumination robust preprocessing method thus remains a significant challenge in reliable face analysis. In this paper we propose a novel approach for improving lighting normalization through building the underlying reflectance model which characterizes interactions between skin surface, lighting source and camera sensor, and elaborates the formation of face color appearance. Specifically, the proposed illumination processing pipeline enables the generation of Chromaticity Intrinsic Image (CII) in a log chromaticity space which is robust to illumination variations. Moreover, as an advantage over most prevailing methods, a photo-realistic color face image is subsequently reconstructed which eliminates a wide variety of shadows whilst retaining the color information and identity details. Experimental results under different scenarios and using various face databases show the effectiveness of the proposed approach to deal with lighting variations, including both soft and hard shadows, in face recognition.

cs.CV↗
arXiv2017

Surfing Liquid Metal Droplet on the Same Metal Bath via Electrolyte Interface

We reported a phenomenon that when exerting an electric field gradient across a liquid metal/electrolyte interface, a droplet of the same liquid metal can persistently surf on the interface without coalescence. A thin layer of the intermediate solution, which separates the droplet from direct metallic contacting and provides the levitating force, is responsible for such surfing effect. The electric resistance of this solution film is measured and the film thickness is further theoretically calculated. The fact that the levitating state can be switched on and off via a controlled manner paves a way for reliable manipulation of liquid metal droplet.

physics.flu-dyn↗
arXiv2017

Exothermicity is not a necessary condition for enhanced diffusion of enzymes

Recent experiments have revealed that the diffusivity of exothermic and fast enzymes is enhanced when they are catalytically active, and different physical mechanisms have been explored and quantified to account for this observation. We perform measurements on the endothermic and relatively slow enzyme aldolase, which also shows substrate-induced enhanced diffusion. We propose a new physical paradigm, which reveals that the diffusion coefficient of a model enzyme hydrodynamically coupled to its environment increases significantly when undergoing changes in conformational fluctuations in a substrate-dependent manner, and is independent of the overall turnover rate of the underlying enzymatic reaction. Our results show that substrate-induced enhanced diffusion of enzyme molecules can be explained within an equilibrium picture, and that the exothermicity of the catalyzed reaction is not a necessary condition for the observation of this phenomenon.

physics.bio-ph↗