偏振选择可调谐双带太赫兹吸收器

提出并研究了一种偏振选择可调谐双带太赫兹吸收器。吸收器由顶层方形劈裂石墨烯环、中间SiO₂介质层以及底层金反射层组成。基于时域有限差分法的仿真结果显示,该吸收器在不同偏振光入射下均可以实现双带高效率吸收。x偏振光时在7.86和12.63THz处的吸收率分别为97.9%和91.2%;y偏振光时在6.30和10.52THz处的吸收率分别为94.1%和93.2%。通过改变石墨烯费米能级,可以对两个偏振的双带吸收峰波长进行调谐。此外,研究了介质层厚度和石墨烯劈裂环的物理参数对共振吸收峰的影响。因为在两个偏振状态下都能产生双带高吸收,所以此吸收器在太赫兹偏振成像、太赫兹传感、选择性光谱检测和偏振复用等领域有重要的潜在应用价值。     

多核CPU下的K-means遥感影像分类并行方法

针对海量遥感影像快速分类的应用需求,提出一种基于K-means算法的遥感影像并行分类方法.该方法结合CPU下进程级与线程级模式的并行特征,设计融合进程级与线程级并行的两阶段数据粒度划分方法和任务调度方法,在保证精度的基础上实现并行加速.利用大数据量的多尺度遥感影像进行实验,结果表明:所提并行方法可大大减少遥感影像的分类时间,取得了良好的加速比(13.83),并可达到负载均衡,从而解决了大区域遥感影像快速分类的问题.     

An adaptive updating protocol for reducing moving object database workload

In the last decade, spatio-temporal database research focuses on the design of effective and efficient indexing structures in support of location-based queries such as predictive range queries and nearest neighbor queries. While a variety of indexing techniques have been proposed to accelerate the processing of updates and queries, not much attention has been paid to the updating protocol, which is another important factor affecting the system performance. In this paper, we propose a generic and adaptive updating protocol for moving object databases with less number of updates between objects and the database server, thereby reducing the overall workload of the system. In contrast to the approach adopted by most conventional moving object database systems where the exact locations and velocities last disclosed are used to predict their motions, we propose the concept of Spatio-temporal safe region to approximate possible future locations. Spatio-temporal safe regions provide larger space of tolerance for moving objects, freeing them from location and velocity updates as long as the errors remain predictable in the database. To answer predictive queries accurately, the server is allowed to probe the latest status of objects when their safe regions are inadequate in returning the exact query results. Spatio-temporal safe regions are calculated and optimized by the database server with two contradictory objectives: reducing update workload while guaranteeing query accuracy and efficiency. To achieve this, we propose a cost model that estimates the composition of active and passive updates based on historical motion records and query distribution. More system performance improvements can be obtained by cutting more updates from the clients, when the users of system are comfortable with incomplete but accuracy bounded query results. We have conducted extensive experiments to evaluate our proposal on a variety of popular indexing structures. The results confirm the viability, robustness, accuracy and efficiency of our proposed protocol.     

高效的基于证书可验证加密签名方案

针对传统公钥密码体制中存在的公钥证书管理问题和基于身份密码体制中存在的密钥托管问题,以及互联网上交易过程中存在的不公平性,将基于证书签名体制(CBS)与可验证加密签名(VES)相结合,提出了一种基于证书可验证加密签名体制CBVES。首先,定义了基于证书可验证加密签名方案的安全模型;然后,基于k-CAA问题和Squ-CDH问题的困难性,构造一个新的基于证书的可验证加密签名方案,并在随机预言机模型下证明了其安全性。与已有的基于证书可验证加密签名方案相比,所提出的方案是高效的,所需的计算量小,且具有需要仲裁人和指定验证人合作才能从可验证加密签名提取普通签名的优点。     

钻井液密度低就能保护油气层吗?

钻井过程中,正向压差对油气层既有污染的一面,又有保护的一面,关键在于能否迅速形成牢固而致密的滤饼。平衡钻井或近平衡钻井由于压差过小,对高质量滤饼的形成和巩固不利,所以更易造成油气层污染。若采用屏蔽暂堵技术,适当高的正向压差有利于迅速形成强度高、致密性好的滤饼,同时兼顾了井控安全和井壁稳定,所以更有利于保护油气层。     

按信包传递最小普查图研究

普查是信息网络中结点之间的一种常见的也是重要的信息传递方式，在普查过程中，网络所有结点的信息按一定的约束条件传递到终结点。本文定义并讨论了按信包传递最小普查图ｐ－ｍｅｇ，给出了最小普查时间ｔｐ（ｎ）的公式，在讨论了最小普查图与最小广播图的关系之后，指出了识别一个图是否为最小普查图的问题是ＮＰ完全问题，而且对ｐ＝１，２，３完全解决了ｐ－ｍｅｇ的构造问题，对ｐ＝２＾ｋ给出ｎ＝ｍ．２＾ｋ时ｐ－ｍｅｇ的构     

QPL-Y高强度井壁封固剂在随钻防漏堵漏工艺中的应用

中原油田钻调整井时常发生恶性漏失,特点是漏失层位多,漏层微裂缝尺寸随压力波动而变化。选用QPL-Y高强度井壁封固剂配成随钻防漏堵漏钻井液后,不同粒径的微细活化颗粒随钻井液进入漏层,形成水化铝酸钙、水化硫铝酸钙等水化产物,与微细活性纤维、膨润土颗粒、沥青颗粒和高聚物分子等形成网架结构,在高温高压下凝结固化,将破碎性裂缝漏层牢固地粘结封固起来,提高漏层的承压能力。经文51-191等6口井试验,成功率为100%。     

强粘接性堵漏技术在中原油田的应用

针对漏失通道的尺寸、形状随井内压力变化的复杂井漏，提出了“强粘接性”概念。介绍了强粘接性堵漏剂的室内试验及现场应用情况。探讨了强粘接性堵漏机理及粘接强度影响因素。现场实践证明，强粘接性堵漏与常规封堵相比，能大幅度地提高地层承压能力，并具有施工简便、成本低廉和可靠性强等特点，为今后复杂地层堵漏技术的发展提供了新的思路     

A regularized approach for frictional impact dynamics of flexible multi-link manipulator arms considering the dynamic stiffening effect

The present study offers a regularized approach for multi-link flexible manipulator arms with frictional impacts. The complex risks of global dynamics simulation, which involve nonlinear frictional impact, stick–slip, and foreshortening deformation, as well as multi-scale numerical problems, were implemented. The system is described as an assembly of \(n\) flexible links connected by \(n\) rotary joints. The stretching, bending, and the torsional deformations of the flexible links were considered in addition to the flexibility and mass of the joint. The introduction of a contact force potential energy approach transformed the non-differentiable functions of the normal and tangential frictions into differentiable ones, thereby generating Lagrange equations for the general recursive formulation of the systems. A numerical simulation for the double pendulum and spatial manipulator arms collision with targets was generated, thereby allowing the calculation of the frequent switching between the stick/sliding and forward/backward sliding. Several normal contact and friction models were adopted, and their corresponding results were analyzed. The generated ordinary differential equations of the proposed smoothed algorithm were solved using explicit solvers to verify any improvements in the global computational efficiency of the frictional collision dynamics for the flexible manipulator arms.     

Appearance of Superconductivity at 15.9 K in Layered V<Subscript>2</Subscript>AlN

A bulk polycrystalline sample with the nominal compositions represented by V₂AlN_1?δ was synthesized by a two-step solid-state reaction. The structural characterization has been done via X-ray diffraction, followed by Rietveld refinements, which revealed that the layered V₂AlN is crystalized in cubic Fm3m space group with lattice parameters a = b = c = 6.127 Å. Both DC resistivity and magnetization measurements confirmed that V₂AlN is a bulk superconductor with superconducting transition temperature (T _c ) of 15.9 K.