Real-Time Misbehavior Detection in IEEE 802.11e Based WLANs

The Enhanced Distributed Channel Access (EDCA) specification in the IEEE 802.11e standard supports heterogeneous backoff parameters and arbitration inter-frame space (AIFS), which makes a selfish node easy to manipulate these parameters and misbehave. In this case, the network-wide fairness cannot be achieved any longer. Many existing misbehavior detectors, primarily designed for legacy IEEE 802.11 networks, become inapplicable in such a heterogeneous network configuration. In this paper, we propose a novel real-time hybrid-share (HS) misbehavior detector for IEEE 802.11e based wireless local area networks (WLANs). The detector keeps updating its state based on every successful transmission and makes detection decisions by comparing its state with a threshold. We develop mathematical analysis of the detector performance in terms of both false positive rate and average detection rate. Numerical results show that the proposed detector can effectively detect both contention window based and AIFS based misbehavior with only a short detection window.Comment: Accepted to IEEE Globecom 201

Extensional viscosity of copper nanowire suspensions in an aqueous polymer solution

Suspensions of copper nanowires are emerging as new electronic inks for next-generation flexible electronics. Using a novel surface acoustic wave driven extensional flow technique we are able to perform currently lacking analysis of these suspensions and their complex buffer. We observe extensional viscosities from 3 mPa$\cdot$s (1 mPa$\cdot$s shear viscosity) to 37.2 Pa$\cdot$s via changes in the suspension concentration, thus capturing low viscosities that have been historically very challenging to measure. These changes equate to an increase in the relative extensional viscosity of nearly 12,200 times at a volume fraction of just 0.027. We also find that interactions between the wires and the necessary polymer additive affect the rheology strongly. Polymer-induced elasticity shows a reduction as the buffer relaxation time falls from 819 to 59 $\mu$s above a critical particle concentration. The results and technique presented here should aid in the future formulation of these promising nanowire suspensions and their efficient application as inks and coatings.Comment: 7 pages, 5 figures, under review for Soft Matter RS

Effects of Shell on Bore center Annular Shaped Charges Formation and Penetrating into Steel Targets

Annular shaped charge can efficiently create large penetration diameter, which can solve the problem of small penetration diameter of a traditional shaped charge, and thus meeting the requirements of large penetration diameter in some specific situations. In this paper, the influence of five kinds shell structures, i.e. no shell, aluminum shell with thickness of 2.0 mm and steel shell with thickness of 2.0 mm, 3.0 mm and 4.0 mm, on bore-center annular shaped charges (BCASCs) formation and penetrating steel targets was investigated by numerical simulations and experiments. The numerical simulation results are in good agreement with the experimental results. The results showed that, from no shell to aluminum shell of 2.0 mm and then to steel shell of 2.0 mm, 3.0 mm and 4.0 mm for BCASCs, the diameter and radial velocity of projectile head decrease, the axial velocity of BCASC projectiles increases gradually, the penetration diameter of the targets decreases, and the penetration depth increases. The penetration diameter caused by the BCASC with no shell is the largest, being 116.0 mm (1.16D), D is the charge diameter. The penetration depth caused by the BCASC with steel shell of 4.0 mm thickness is the deepest, being 76.4 mm (0.76D)

Tree-like alumina nanopores generated in a non-steady-state anodization{

Novel tree-like alumina nanopores were reproducibly obtained in non-steady-state anodization conditions by exponential decrease of anodization potential. The mechanism of pore formation was thought to be due to a combination of electrical treeing and mechanic stress in the growth process. Furthermore, some interesting properties from gold nanotrees were observed showing that the tree-like nanopores will be new templates towards fabrication of nanotrees from a variety of materials possibly exhibiting new shape-dependent properties. Nanoporous alumina formed by electrochemical anodization of aluminium in acid electrolytes has been extensively studied for more than 50 years. 1 Wood's model 2 and further modified models 3,4 can give satisfactory interpretations of many experimental phenomena, such as monodispersity of pore size distribution, linear dependence of pore diameter and inter-pore distance on the applied anodization potential. However, these models cannot easily explain well some recent findings, such as selfordered pore growth in two-step anodization, 5,6 self-ordering under high-field anodization 7,8 and at burning potential, 9 guided pore growth by imprint lithography, 10,11 etc. In order to understand the self-ordering pore growth mechanism, repulsive interactions between the pores 12 and high electric field theory 7-9 have been proposed. In contrast to the extensive research efforts on steady-state anodization, non-steady-state anodization has been given little attention. Here, it was found that unexpected tree-like alumina nanopores were generated in non-steady-state anodization when the anodization potential was decreased exponentially in a stepwise way. The development of pores is more like that of tree or root in nature, which cannot be simply explained by Wood's models. 17,18 Scheme 1 illustrates the fabrication process of tree-like alumina nanopores. Firstly, ordered nanopore arrays were fabricated via well-established two-step anodization in oxalic acid at 40 V (see details in ESI{). The nanopores have a depth of y2 mm, and a diameter of y35 nm. Then, the anodization potential was decreased exponentially from 40 V to 5 V. The change of the applied anodization potential as a function of time is shown i

Optimized gold nanoshell ensembles for biomedical applications

We theoretically study the properties of the optimal size distribution in the ensemble of hollow gold nanoshells (HGNs) that exhibits the best performance at in vivo biomedical applications. For the first time, to the best of our knowledge, we analyze the dependence of the optimal geometric means of the nanoshells’ thicknesses and core radii on the excitation wavelength and the type of human tissue, while assuming lognormal fit to the size distribution in a real HGN ensemble. Regardless of the tissue type, short-wavelength, near-infrared lasers are found to be the most effective in both absorption- and scattering-based applications. We derive approximate analytical expressions enabling one to readily estimate the parameters of optimal distribution for which an HGN ensemble exhibits the maximum efficiency of absorption or scattering inside a human tissue irradiated by a near-infrared laser

Text-based Person Search in Full Images via Semantic-Driven Proposal Generation

Finding target persons in full scene images with a query of text description has important practical applications in intelligent video surveillance.However, different from the real-world scenarios where the bounding boxes are not available, existing text-based person retrieval methods mainly focus on the cross modal matching between the query text descriptions and the gallery of cropped pedestrian images. To close the gap, we study the problem of text-based person search in full images by proposing a new end-to-end learning framework which jointly optimize the pedestrian detection, identification and visual-semantic feature embedding tasks. To take full advantage of the query text, the semantic features are leveraged to instruct the Region Proposal Network to pay more attention to the text-described proposals. Besides, a cross-scale visual-semantic embedding mechanism is utilized to improve the performance. To validate the proposed method, we collect and annotate two large-scale benchmark datasets based on the widely adopted image-based person search datasets CUHK-SYSU and PRW. Comprehensive experiments are conducted on the two datasets and compared with the baseline methods, our method achieves the state-of-the-art performance