Countermeasures for Primary User Emulation Attack: A Comprehensive Review

Wireless Personal Communications - Cognitive radio (CR) is a flexible wireless network that can solve the scarcity and underutilization problem of the spectrum by permitting unlicensed users to...     

模拟引潮力作用下岩石破坏前兆的实验研究 --加卸载响应比(LURR)理论和能量加速释放(AER)

大地震前加卸载响应比升高和能量加速释放这2种现象可以用来对地震进行中期预报。同时,加卸载响应比升高和能量加速释放有相同的物理机制。实验对于揭示地壳岩石的变形和破坏规律是非常重要的。在三轴应力条件下进行了岩石破坏声发射实验,声发射技术是研究岩石变形破坏微观机理的重要手段。为了模拟日月引潮力对地球的加载和卸载作用,在一常数加载率的轴向压力作用下,叠加上微小的正弦扰动,力求能够模拟地下岩石复杂的受力状态。实验过程中记录到大量的声发射信息,声发射记录包括声发射发生的时间、空间坐标和振幅,它能够反映岩石试件内部每一个损伤(微裂纹)发生的时间、地点和强度。利用声发射记录系统地分析了岩石试件破坏前能量释放及加卸载响应比的演化情况,结果显示,岩石试件宏观破坏前出现了能量加速释放及加卸载响应比剧增这2种前兆现象,从而对地震临界点理论给予了实验支持,同时也为地震预测提供了实验依据。     

Retarding Thermal Degradation in Hybrid Perovskites by Ionic Liquid Additives

Recent years have witnessed considerable progress in the development of solar cells based on lead halide perovskite materials. However, their intrinsic instability remains a limitation. In this context, the interplay between the thermal degradation and the hydrophobicity of perovskite materials is investigated. To this end, the salt 1‐(4‐ethenylbenzyl)‐3‐(3,3,4,4,5,5,6,6,7,7,8,8,8‐tridecafluorooctylimidazolium iodide (ETI), is employed as an additive in hybrid perovskites, endowing the photoactive materials with high thermal stability and hydrophobicity. The ETI additive inhibits methylammonium (MA) permeation in methylammonium lead triiodide (MAPbI₃) occurring due to intrinsic thermal degradation, by inhibiting out‐diffusion of the MA⁺ cation, preserving the pristine material and preventing decomposition. With this simple approach, high efficiency solar cells based on the unstable MAPbI₃ perovskite are markedly stabilized under maximum power point tracking, leading to greater than twice the preserved efficiency after 700 h of continuous light illumination and heating (60 °C). These results suggest a strategy to tackle the intrinsic thermal decomposition of MAI, an essential component in all state‐of‐the‐art perovskite compositions.     

A New Fourth-Order Compact Off-Step Discretization for the System of 2D Nonlinear Elliptic Partial Differential Equations

This paper discusses a new fourth-order compact off-step discretization for the solution of a system of two-dimensional nonlinear elliptic partial differential equations subject to Dirichlet boundary conditions. New methods to obtain the fourth-order accurate numerical solution of the first order normal derivatives of the solution are also derived. In all cases, we use only nine grid points to compute the solution. The proposed methods are directly applicable to singular problems and problems in polar coordinates, which is a main attraction. The convergence analysis of the derived method is discussed in detail. Several physical problems are solved to demonstrate the usefulness of the proposed methods.     

Hydrothermal transformations of organic matter of low permeability rocks from domanic formation of the romashkino oil field

Abstract

The oil generating potential of Domanic rocks from Dankov–Lebedyan horizon of the Zelenogorsk area of Romashkino oil field was evaluated by Rock-Eval pyrolysis technique. The result of given method depends on the content, composition, and thermal stability of organic matter in rocks. During hydrothermal processes, the distinctive conversion behavior of organic matter at temperatures of 200°С, 250°С, 300°С, and 350°С in CO₂ environment was revealed. The yield of obtained aquathermolysis products and their quality were evaluated. The results of the studies suggest that low-permeability carbonate rocks of the Dankov–Lebedyan horizon contain productive beds with content of C_org 1.89–3.03%, which when developed using thermal methods, can become an additional source of liquid hydrocarbons.     

Three-Dimensional Diffraction Tomography Using Filtered Backpropagation and Multiple Illumination Planes

In this paper, a three-dimensional (3-D) extension of the well-known filtered-backpropagation (FBP) algorithm is presented with the aim of taking into account scattered-field-data measurements obtained using incident directions not restricted in a single plane. The FBP algorithm has been extensively used to solve the two-dimensional inverse-scattering problem under the first-order Born and Rytov approximations for weak scatterers. The extension of this algorithm in three dimensions is not straightforward, because the task of collecting the data needed to obtain a low-pass filtered version of the scattering object, taking into account all spatial frequencies within a radius of radic2k₀, and of incorporating these data to the FBP algorithm, needs to be addressed. A simple extension using incident field directions restricted to a single plane (illumination plane) leaves a region of spatial frequencies of the sphere of radius radic2k ₀ undetermined. The locus of these spatial frequencies may be crucial for the accurate reconstruction of objects which do not vary slowly along the axis perpendicular to the illumination plane. The proposed 3-D FBP algorithm presented here is able to incorporate the data collected from more than one illumination plane and to ensure the reliability of the reconstruction results     

Estimation of temperature distribution inside tissues heated byinterstitial RF electrode hyperthermia systems

The computational method presented relies on a semi-infinite tissue model. The needle-shaped RF electrodes are modeled with elongated spheroids. The heat transfer problem is treated in three dimensions. The localized current fields set up inside the tissue from the discrete implants are computed by using electrostatic methods, and the bioheat diffusion equation under a steady-state condition is solved to determine the temperature distributions inside superficial tissues. A Green's-function technique is applied to solve the bioheat transfer equation. The heat removal due to blood circulation is also taken into account. Analytical techniques are used to treat the singularities in the vicinity of implanted electrodes. Numerical results are presented for several electrode configurations