Jiawan Zhang

Improvements of Juang 's Password-Authenticated Key Agreement Scheme Using Smart Cards

In the IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, vol. 55, no. 6, Juang et al.proposed a password-authenticated key agreement scheme using smart cards. Although the scheme of Juang et al. has many benefits, we find that it suffers from three weaknesses: 1) inability of the password-changing operation; 2) the session-key problem; and 3) inefficiency of the double secret keys. Therefore, we propose an improved scheme to overcome the weaknesses and maintain the benefits of the original scheme. In addition, our improved scheme reduces the storage and computation costs on the smart card compared with the scheme of Juang et al. We believe that our improved scheme is more suitable for real-life applications than that of Juang et al.

Effects of TiO 2 particles on surface charge of epoxy nanocomposites

Epoxy used as insulating material in electronic and electrical devices plays an important role in system reliability. Addition of nanoparticles into epoxy can improve the insulating properties compared with undoped material. However, due to the change of the material structure, trap characteristics and charge behaviors are altered as a consequence. This possibly leads to distortion of electric field that can result in degradation of the insulation. From the viewpoint of safety, it is necessary to investigate charge behavior of epoxy nanocomposites. This paper presents study aimed at clarifying the effect of nano-filler concentration on surface charge accumulation and decay behaviors of epoxy/TiO2 nanocomposites. Samples were prepared by dispersing nano-scale TiO2 into epoxy by mixing with shear force. Corona charging tests were performed at room temperature with a relative humidity of ~ 40%. The charge distribution was measured by means of an electrostatic voltmeter. Obtained results show the dependence of the charge density as well as the charge decay rate upon the concentration of TiO2, varying as a function of the charge polarity, charging time and charging voltage. It is suggested that the charge dynamics is dependent upon the characteristics of localized surface states that are altered by the nanoparticles.

Interactive Visual Discovering of Movement Patterns from Sparsely Sampled Geo-tagged Social Media Data

Social media data with geotags can be used to track peoples movements in their daily lives. By providing both rich text and movement information, visual analysis on social media data can be both interesting and challenging. In contrast to traditional movement data, the sparseness and irregularity of social media data increase the difficulty of extracting movement patterns. To facilitate the understanding of peoples movements, we present an interactive visual analytics system to support the exploration of sparsely sampled trajectory data from social media. We propose a heuristic model to reduce the uncertainty caused by the nature of social media data. In the proposed system, users can filter and select reliable data from each derived movement category, based on the guidance of uncertainty model and interactive selection tools. By iteratively analyzing filtered movements, users can explore the semantics of movements, including the transportation methods, frequent visiting sequences and keyword descriptions. We provide two cases to demonstrate how our system can help users to explore the movement patterns.

Detecting photographic composites using shadows

Image compositing technology has become popular for tampering with digital photographies. We describe how such composites can be detected by enforcing the geometric and photometric constraints from shadows. In particular, we explore (i) the imaged shadow relations that are modeled by the planar homology, and (ii) the color characteristics of the shadows measured by the shadow matte. Our approach efficiently extracts these constraints from a single image and makes use of them for the digital forgery detection. Experimental results on visually plausible images demonstrate the performance of the proposed method.

Video dehazing with spatial and temporal coherence

This paper describes a new framework for video dehazing, the process of restoring the visibility of the videos taken under foggy scenes. The framework builds upon techniques in single image dehazing, optical flow estimation and Markov random field. It aims at improving the temporal and spatial coherence of the dehazed video. In this framework, we first extract the transmission map frame-by-frame using guided filter, then estimate the forward and backward optical flow between two neighboring frames to find the matched pixels. The flow fields are used to help us building an MRF model on the transmission map to improve the spatial and temporal coherence of the transmission. The proposed algorithm is verified in both real and synthetic videos. The results demonstrate that our algorithm can preserve the spatial and temporal coherence well. With more coherent transmission map, we get better refocusing effect. We also apply our framework on improving the video coherence on the application of video denoising.

A new design of wearable token system for mobile device security

Increasingly, todays mobile devices provide users a high level of convenience and flexibility. But, mobile devices are vulnerable to theft and loss, greatly increasing the likelihood of exposing sensitive data. To address this problem, Corner and Noble gave the concept of transient authentication and built a wearable token system, called ZIA system. In this paper, we design a new wearable token system using the idea of transient authentication. Our system not only preserves the same security characteristics as ZIA system, but also is more effective than ZIA system. In our system, careful key management and prudent communication mechanism allow significant performance enhancements. Due to the power constraint of the wearable token and the wireless link, the lower the costs are, the greater the chance of success the wearable token system has in practical implementation.

MIFT: a mirror reflection invariant feature descriptor

In this paper, we present a mirror reflection invariant descriptor which is inspired from SIFT. While preserving tolerance to scale, rotation and even affine transformation, the proposed descriptor, MIFT, is also invariant to mirror reflection. We analyze the structure of MIFT and show how MIFT outperforms SIFT in the context of mirror reflection while performs as well as SIFT when there is no mirror reflection. The performance evaluation is demonstrated on natural images such as reflection on the water, non-rigid symmetric objects viewed from different sides, and reflection in the mirror. Based on MIFT, applications to image search and symmetry axis detection for planar symmetric objects are also shown.

Maximum Cohesive Grid of Superpixels for Fast Object Localization

This paper addresses a challenging problem of regularizing arbitrary super pixels into an optimal grid structure, which may significantly extend current low-level vision algorithms by allowing them to use super pixels (SPs) conveniently as using pixels. For this purpose, we aim at constructing maximum cohesive SP-grid, which is composed of real nodes, i.e SPs, and dummy nodes that are meaningless in the image with only position-taking function in the grid. For a given formation of image SPs and proper number of dummy nodes, we first dynamically align them into a grid based on the centroid localities of SPs. We then define the SP-grid coherence as the sum of edge weights, with SP locality and appearance encoded, along all direct paths connecting any two nearest neighboring real nodes in the grid. We finally maximize the SP-grid coherence via cascade dynamic programming. Our approach can take the regional objectness as an optional constraint to produce more semantically reliable SP-grids. Experiments on object localization show that our approach outperforms state-of-the-art methods in terms of both detection accuracy and speed. We also find that with the same searching strategy and features, object localization at SP-level is about 100-500 times faster than pixel-level, with usually better detection accuracy.

Cube2Video: Navigate Between Cubic Panoramas in Real-Time

Online virtual navigation systems enable users to hop from one 360° panorama to another, which belong to a sparse point-to-point collection, resulting in a less pleasant viewing experience. In this paper, we present a novel method, namely Cube2Video, to support navigating between cubic panoramas in a video-viewing mode. Our method circumvents the intrinsic challenge of cubic panoramas, i.e., the discontinuities between cube faces, in an efficient way. The proposed method extends the matching-triangulation-interpolation procedure with special considerations of the spherical domain. A triangle-to-triangle homography-based warping is developed to achieve physically plausible and visually pleasant interpolation results. The temporal smoothness of the synthesized video sequence is improved by means of a compensation transformation. As experimental results demonstrate, our method can synthesize pleasant video sequences in real time, thus mimicking walking or driving navigation.

Effect of nanosecond rise time of pulse voltage on the surface charge of Epoxy/TiO 2 nanocomposites

Polymeric insulating materials exposed to pulse voltage with a nanosecond rise time in pulsed power have drawn increasing attention. Surface charge accumulation and decay on the charged polymers are very important parameters related to discharge. Nanocomposite technology has been used to improve the electrical properties of polymeric insulating materials. Therefore, it must be confirmed whether the nanosecond rise time of pulse voltage on the dynamic behaviour of surface charge on polymeric nanocomposites is different from that without nanoparticles. In this paper, we attempted to clarify the effect of the rise time on the electrical properties of epoxy/TiO2 nanocomposites focusing on surface charge accumulation and decay. Samples were prepared by dispersing nano-scale TiO2 particles into epoxy (EX) by mixing with shear force. Corona charging tests were performed at room temperature with a relative humidity of ~40%. The charge distribution was measured by means of an electrostatic voltmeter. The results show that the rise time plays an important role in the accumulating charge as well as the charge decay rate and varies with the concentration of nanoparticles and charge polarity. It is suggested that charge dynamics are dependent upon the rise time.