基于多天线的机器人定位和高效节能无线互联网络(英文)

基于生物行为启发的协同机器人集群具有广泛的应用前景。然而,一个通常假定成立但还没有得以适当解决的问题是机器人之间通过无线通信实现动态的相互之间的定位。本文研究了用多天线实现群集机器人网的技术。沿着接收信号在路径中的功率梯度,一个装有单天线的机器人可以跟踪搜索出未知信号源的方向。用3个适当装置的可以感知载波信号不同相移的天线,一个机器人可以确定未知信号源的位置。根据各自测到的未知信号源的距离,3个机器人通过协作通信可以确定未知信号源的位置。在知道2个夹角和1个边长的情况下,3个机器人可以确定彼此之间的几何关系。在彼此之间知道位置关系的情况下,可以采用聚束技术对着想要的机器人接收或发射信号,从而提高功率效率,延长机器人的生命。这些技术可以从二维扩展到诸如爬墙机器人的三维应用情景。     

Wirelessly lockpicking a smart card reader

With more than 300 million cards sold, HID iClass is one of the most popular contactless smart cards on the market. It is widely used for access control, secure login and payment systems. The card uses 64-bit keys to provide authenticity and integrity. The cipher and key diversification algorithms used in iClass are proprietary, and little information about them is publicly available. In this paper, we have reverse engineered all security mechanisms in the card including cipher, authentication protocol and also key diversification algorithms, which we publish in full detail. Furthermore, we have found six critical weaknesses that we exploit in two attacks, one against iClass Standard and one against iClass Elite (a.k.a., iClass High Security). In order to recover a secret card key, the first attack requires one authentication attempt with a legitimate reader and \(2^{22}\) queries to a card. This attack has a computational complexity of \(2^{40}\) MAC computations. The whole attack can be executed within a day on ordinary hardware. Remarkably, the second attack which is against iClass Elite is significantly faster. It directly recovers the system-wide master key from only 15 authentication attempts with a legitimate reader. The computational complexity of this attack is lower than \(2^{25}\) MAC computations, which means that it can be fully executed within 5 seconds on an ordinary laptop.     

Practical static analysis of context leaks in Android applications

Android native applications, written in Java and distributed in APK format, are widely used in mobile devices. Their specific pattern of use lets the operating system control the creation and destruction of resources, such as activities and services (contexts). Programmers are not supposed to interfere with such life cycle events. Otherwise, contexts might be leaked, ie, they will never be deallocated from memory, or be deallocated late, leading to memory exhaustion and frozen applications. In practice, it is easy to write incorrect code, which hinders garbage collection of contexts and leads to context leakages. In this work, we present a novel static analysis method that finds context leaks in Android code. We apply this analysis to APKs translated into Java bytecode. We provide a formal analysis of our algorithms and suggest further research directions for improving precision by combining different approaches. We discuss the results of a large number of experiments with our analysis, which reveal context leaks in many widely used applications from the Android marketplace. This shows the practical usefulness of our technique and its superiority w.r.t. the well-known Lint and Infer static analysis tools. We estimate the amount of memory saved by the collection of the leaks found and explain, experimentally, where programmers often go wrong and limitations of our tool. Such lessons could be used for designing of a sound or more powerful static analysis tool. This work can be considered as a practical application of software analysis techniques to solve practical problems.     

Correlation between the defect structure and the residual stress distribution in ZnO visualized by TEM and Raman microscopy

A deep understanding of the appearance and distribution of residual stresses in ZnO is of high importance as mechanical stresses directly influence its electrical and optical properties. In this paper we investigate the correlation between residual stresses and the plastic deformation below a micro indent placed on a prism plane of a ZnO single crystal. The residual stress field was mapped by means of confocal Raman microscopy. A cross section was studied by transmission electron microscopy and cathodoluminescence to visualize defect structures. In the Raman measurement bands of residual stresses were observed. The analysis of the defect structure showed that the residual stress distribution corresponds to crystallographic directions which are known to be the preferred directions for plastic deformation. The preparation of lamellae by FIB strongly alters both the residual stress state as well as the defect density caused by plastic deformation.     

Kinetic Studies of Mullite Synthesis from Alumina Nanoparticles and a Preceramic Polymer

The crystallization kinetics of mullite formation in a diphasic precursor consisting of a silicone resin filled with commercial γ-alumina nanoparticles (15 nm mean particle size, specific surface area of 100 m²/g), heated in air from 1250° to 1350°C, was studied by X-ray diffraction. Transitional γ-alumina and amorphous silica from the pyrolysis of the preceramic polymer exhibited a remarkable reactivity, as demonstrated by a very low incubation time (from 500 s at 1250°C to 20 s at 1350°C), a high mullite yield (about 80 vol%, after 100 s at 1350°C), and a low activation energy for nucleation (677±60 kJ/mol). The activation energy values found were lower than those reported previously for other diphasic systems, including sol–gel precursors. Besides the high specific surface of nanosized γ-alumina particles, the low energy barrier could be attributed to the highly reactive silica deriving from the oxidation of Si–CH₃ bonds in the silicone and to the homogeneous dispersion of the nanosized filler inside the preceramic polymer. Furthermore, the possibility of applying plastic shaping processing methods to the mixture of a preceramic polymer and nanosized filler makes this approach particularly valuable, in comparison, for instance, with sol–gel based alternatives.     

Density functional computational studies on the intermediate stage of the ribose and glycine Maillard reaction: Formation of deoxyosones in aqueous solution

Mechanisms in an aqueous solution of the Maillard reaction are proposed under several pH conditions for the interaction of glycine with cyclic ribose (c-Rib) and open-chain ribose (Rib). According to the Gibbs free energy relationships as well as internal energies values derived from our density functional theory calculations, the c-Rib/Rib + DGly (glycine) are the most favourable reaction pathways for the formation of deoxyosones under basic conditions, where Rib is more reactive than c-Rib. The intermediate stage of the Maillard reaction leads to the formation of deoxyosones.     

Performance of a single-phase hybrid and nanocomposite polyelectrolyte in classical electrochromic devices

In this paper, we discuss the high stability of a single-phase hybrid polyelectrolyte (SPHP) and nanocomposite hybrid polyelectrolyte (NHP) in a large electrochromic (EC) device (5 cm × 10 cm) mounted with different electrodes. The electrochromic device (K-glass/FTO/WO₃/SPHP/CeO₂-TiO₂/FTO/K-glass—ECI, K-glass/FTO/WO₃/NHP/CeO₂-TiO₂/FTO/K-glass—ECII,) exhibited excellent color and bleach reversibility, high coloration efficiency (CE) (>35 cm²/C) from the first cycle up to more than 60,000 CA cycles, and a maximum constant rate of deintercalation/intercalation (O_out/Q_in = 1). Also, the life time of the EC device with Nb₂O₅:Mo (K-glass/FTO/Nb₂O₅:O/SPHP/CeO₂-TiO₂/FTO/K-glass—ECIII) was prolonged to up to more than 10,000 cycles with a fairly stable coloration efficiency (around 19 cm²/C) and O_out/Q_in = 1. The SPHP and NHP were tested in a large EC device with different configurations to evaluate its successful performance. In conclusion, its remarkable behavior and high stability render this material an excellent candidate for application in EC devices.