基于IPFIX的DNS异常行为检测方法

提出了一种基于IPFIX（IP数据流信息输出）网络流量数据准确检测可疑和异常DNS、识别DNS流量放大攻击行为的算法。该算法已在清华大学校园网实际部署运行,能够有效检测到校园网内部DNS的异常行为并发送告警信息,从而及时控制攻击行为,实现异常流量的及时监测和预警。     

基于深度特征学习的网络流量异常检测方法

针对网络流量异常检测过程中提取的流量特征准确性低、鲁棒性差导致流量攻击检测率低、误报率高等问题,该文结合堆叠降噪自编码器(SDA)和softmax,提出一种基于深度特征学习的网络流量异常检测方法。首先基于粒子群优化算法设计SDA结构两阶段寻优算法:根据流量检测准确率依次对隐藏层层数及每层节点数进行寻优,确定搜索空间中的最优SDA结构,从而提高SDA提取特征的准确性。然后采用小批量梯度下降算法对优化的SDA进行训练,通过最小化含噪数据重构向量与原始输入向量间的差异,提取具有较强鲁棒性的流量特征。最后基于提取的流量特征对softmax进行训练构建异常检测分类器,从而实现对流量攻击的高性能检测。实验结果表明:该文所提方法可根据实验数据及其分类任务动态调整SDA结构,提取的流量特征具有更高的准确性和鲁棒性,流量攻击检测率高、误报率低。     

基于分形特性的宏观网络流量异常分析

基于宏观网络流量汇聚的分形结构,从流量的全局标度指数和局部标度指数出发,对流量异常进行定性和定量分析.利用多分形奇异谱和Lipschitz正则性分布分析流量异常的分形参数,试图找出这些参数的变化轨迹与异常出现的对应关系.实验结果表明异常的发生在奇异谱和Lipschitz正则性分布中确实有明显的体现.基于此特性构建了新的多分形异常检测算法并设计了新的检测框架,对DARPA 1999年数据的实验表明,算法在低误报率的前提下,达到了较高的检测率,优于EMERALD算法.     

基于机器学习的网络异常流量检测研究

异常流量检测需要在海量的数据流中检测出网络流量异常,传统的异常流量检测无法自学习和自演进,在复杂、多变的网络环境下面临巨大挑战。机器学习的方法在完成异常流量检测的同时,可以不断地对新的异常流量进行标记和学习,不断地完善异常流量检测系统,提高异常流量检测系统的准确度,并可对未知的异常进行预测与分类。文章对基于机器学习的网络异常流量检测进行分析和比较,包括监督学习、非监督学习、半监督学习下的异常流量检测,指出了基于机器学习的异常流量检测技术的未来发展方向。     

基于局部异常因子的信息网络流量异常检测

网络流量异常问题是网络遭受攻击的一种表现,通常会引起网络丢包、网络延迟、甚至造成网路堵塞和瘫痪,严重威胁着网络性能和安全。因此,对于网络流量异常进行有效检测,对保障网络的正常运行具有重要意义。设计了一种基于局部异常因子的信息网络流量异常检测方案,在局部异常因子算法的基础上通过MVC模型,采用了SOA结构,通过计算最邻近点的K值,实现网络流量异常检测。在仿真实验中人为制造异常点,对比本文方法与传统方法的检测效果,结果表明设计的方案优于传统异常检测方法。     

网络安全异常检测技术研究

本文提出构建流量异常检测模块和分析模块,并结合BP神经网络等算法,对网络流量特征值进行提取,从而对误差阈值、权值、隐含层个数等进行改进;采用联合熵算法对流量分析模块进行构建,从而通过熵值的变化来查看网络的异常,以此更好的实现对网络异常的检测。     

基于数据挖掘的异常网络流量分析与检测研究

异常网络流量是指会对正常的网络应用造成不良影响的流量模式,早期网络规模小,数据量小,网络管理员就可分析出网络中的异常流量。随着网络规模的不断扩大,必须应用自动化、智能化技术处理网络异常流量,才能满足网络用户对网络应用安全的需求,在这种背景下出现了异常网络流量检测技术。文章提出一种基于数据挖掘技术的异常网络流量检测系统,给出系统的主要组成模块及主要设计流程,详细说明了数据挖掘模块,通过神经网络技术的应用提高了异常网络流量检测的效率及效果。     

基于AR模型的网络异常检测

在网络流量管理中流量异常的一般检测方法是阈值监控，文章提出一种新的异常检测方法，选取适当的SNMP管理信息库变量，建立对相关变量的局部AR（自回归）模型，检测并分析一种服务器故障引起的流量异常，获得该故障的特征向量模型；该检测方法比阈值方法有更强的检测功能，并与传统GLR测试方法进行对比。     

一种互联网宏观流量异常检测方法

网络流量异常指网络中流量不规则地显著变化。网络短暂拥塞、分布式拒绝服务攻击、大范围扫描等本地事件或者网络路由异常等全局事件都能够引起网络的异常。网络异常的检测和分析对于网络安全应急响应部门非常重要,但是宏观流量异常检测需要从大量高维的富含噪声的数据中提取和解释异常模式,因此变得很困难。文章提出一种分析网络异常的通用方法,该方法运用主成分分析手段将高维空间划分为对应正常和异常网络行为的子空间,并将流量向量影射在正常子空间中,使用基于距离的度量来检测宏观网络流量异常事件。     

一种基于相似度的DDoS攻击检测方法

在分析了网络流量构成的基础上,提出了基于相似度的DDoS检测方法。这种方法不是简单的根据流量的突变来检测网络状况,而是从分析攻击对流量分布的影响着手。首先对网络流量进行高频统计,然后对其相邻时刻进行相似度分析,根据相似度的变化来发现异常。从大量的实验结果可以看出基于相似度的检测方法能够比较有效的发现大流量背景下,攻击流量并没有引起整个网络流量显著变化的DDoS攻击,因此更适合大规模网络的异常检测。     

Curved crystal spectrometer for the measurement of X-ray lines from laser-produced plasmas

In order to diagnose the laser-produced plasmas, a focusing curved crystal spectrometer has been developed for measuring the X-ray lines radiated from a laser-produced plasmas. The design is based on the fact that the ray emitted from a source located at one focus of an ellipse will converge on the other focus by the reflection of the elliptical surface. The focal length and the eccentricity of the ellipse are 1350 mm and 0.9586, respectively. The spectrometer can be used to measure the X- ray lines in the wavelength range of 0.2-0.37 nm, and a LiF crystal （200） （2d = 0.4027 nm） is used as dispersive element covering Bragg angle from 30° to 67.5°. The spectrometer was tested on Shengnang- Ⅱ which can deliver laser energy of 60-80 J/pulse and the laser wavelength is 0.35 μm. Photographs of spectra including the 1 s2p ^1P1-1s^2 ^1S0 resonance line（w）, the 1s2p ^3P2-1s^2 1S0 magnetic quadrupole line（x）, the 1s2p ^3P1-1 s^2 ^1S0 intercombination lines（y）, the 1 s2p ^3S~1-1 s^2 ^1S0 forbidden line（z） in helium-like Ti Ⅹ Ⅺ and the 1 s2s2p ^2P3/2-1 s622s ^2S1/2 line（q） in lithium-like Ti Ⅹ Ⅹhave been recorded with a X-ray CCD camera. The experimental result shows that the wavelength resolution（λ/△ 2） is above 1000 and the elliptical crystal spectrometer is suitable for X-ray spectroscopy.     

Preparation and Characterization of TaN ALD Precursors

High purity organic-tantalum precursors for thin film ALD TaN were synthesized and characterized.Vapor pressure and thermal stability of these precursors were studied.From the vapor pressure analysis,it was found that TBTEMT has a higher vapor pressure than any other published liquid TaN precursor,including TBTDET,TAITMATA,and IPTDET.Thermal stability of the alkyl groups on the precursors was investigated using a 1H NMR technique.The results indicated that the tertbutylimino group is the most stable group on TBTDET and TBTEMT as compared to the dialkylamido groups.Thermal stability of TaN precursors decreased in the following order:TBTDET ＞ PDMAT ＞ TBTEMT.In conclusion,precursor vapor pressure and thermal stability were tuned by making slight variations in the ligand sphere around the metal center.     

Electronic Structure of Semiconductor Nanocrystals

This paper reviews our recent development of the use of the large-scale pseudopotential method to calculate the electronic structure of semiconductor nanocrystals, such as quantum dots and wires, which often contain tens of thousands of atoms. The calculated size-dependent exciton energies and absorption spectra of quantum dots and wires are in good agreement with experiments. We show that the electronic structure of a nanocrystal can be tuned not only by its size,but also by its shape. Finally,we show that defect properties in quantum dots can be significantly different from those in bulk semiconductors.     

Critical Stage Rule-Based Real Time Dispatch（RTD）System in Highly-Mixed-Products （HMP） FAB

An improving utilization and efficiency of critical equipments in semiconductor wafer fabrication facilities are concerned. Semiconductor manufacturing FAB is one of the most complicated and cost sensitive environments. A good dispatching tool will make big difference in equipment utilization and FAB output as a whole. The equipment in this paper is In-Line DUV Scanner. There are many factors impacting utilization and output on this equipment group. In HMP environment one of the issues is changing of reticule in this area and idle counts due to load unbalance between equipments. Here we'll introduce a rule-based RTD system which aiming at decreasing the number of recipe change and idle counts among a group of scanner equipment in a high-mixed-products FAB.     

GaAsSb/InAlAs PA DHBTs Grown by Production MBE

The epi material growth of GaAsSb based DHBTs with InAlAs emitters are investigated using a 4 × 100mm multi-wafer production Riber 49 MBE reactor fully equipped with real-time in-situ sensors including an absorption band edge spectroscope and an optical-based flux monitor. The state-of-the-art hole mobilities are obtained from 100nm thick carbon-doped GaAsSb. A Sb composition variation of less than ± 0.1 atomic percent across a 4 × 100mm platen configuration has been achieved. The large area InAlAs/GaAsSb/InP DHBT device demonstrates excellent DC characteristics,such as BVCEO＞6V and a DC current gain of 45 at 1kA/cm2 for an emitter size of 50μm × 50μm. The devices have a 40nm thick GaAsSb base with p-doping of 4. 5 × 1019cm-3 . Devices with an emitter size of 4μm × 30μm have a current gain variation less than 2% across the fully processed 100mm wafer. ft and fmax are over 50GHz,with a power efficiency of 50% ,which are comparable to standard power GaAs HBT results. These results demonstrate the potential application of GaAsSb/InP DHBT for power amplifiers and the feasibility of multi-wafer MBE for mass production of GaAsSb-based HBTs.     

Influence of polarization extinction ratio on distributed polarization coupling detection

Distributed polarization coupling in polarization-maintaining fibers can be detected by using a white light Michelson interferometer. This technique usually requires that only one polarization mode is excited. However, in practical measurement, the injection polarization direction could not be exactly aligned to one of the principal axes of the PMF, so the influence of the polarization extinction ratio should be considered. Based on the polarization coupling theory, the influence of the incident polarization extinction on the measurement result is evaluated and analyzed, and a method for distributed polarization coupling detection is developed when both two orthogonal eigenmodes are excited.     

Noise character analysis and the restraint of self-pulsation laser diodes

We calculate the Langevin noise sources of self-pulsation laser diodes, analyze the effects of active region noise and saturable-absorption region noise on the power fluctuation as well as period fluctuation, and propose a novel method to restrain the noise effects. A visible SIMULINK model is established to simulate the system, The results indicate that the effects of noise in absorption region can be ignored; that with the increase of DC injecting current, the noise effects enhance power jitter, and nevertheless, the period jitter is decreased; and that with external sinusoidal current modulating the self-pulsation laser diode, the noise-induced power jitter and period jitter can be suppressed greatly. This work is valuable for clock recovery in all-optical network.     

High-quality single-crystal CdSe nanoribbons and their optical properties

Large-scale synthesis of single-crystal CdSe nanoribbons is achieved by a modified thermal evaporation method, in which two-step-thermal-evaporation is used to control CdSe sources＇ evaporation. The synthesized CdSe nanoribbons are usually several micrometers in width, 50 nm in thickness, and tens to several hundred micrometers in length. Studies have shown that high-quality CdSe nanoribbons with regular shapes can be obtained by this method. Room-temperature photolumines-cence indicates that the lasing emission at 710 nm has been observed under optical pumping （266 nm） at power densities of 25-153 kW/cm^2. The full width half maximum （FWHM） of the lasing mode is 0.67 nm     

Propagation of hermite-cosh-gaussian beams passing through ABCD optical system with an annular aperture

By using the expansion of the aperture function into a finte sum of complex Gaussian functions, the corresponding analytical expressions of Hermite-cosh-Gaussian beams passing through annular apertured paraxially and symmetrically optical systems written in terms of ABCD matrix were derived, and they could reduce to the cases with squared aperture. In a similar way, the corresponding analytical expressions of cosh-Gaussian beams through annular apertured ABCD matrix were also given. The method could save more calculation time than that by using the diffraction integral formula directly.     

中国建立EB级存储实验室,致力云计算应用(英文)

正With the support of 863 programs,Sugon Information Industry Co.,Ltd.,set up a dawning EB-class storage laboratory to address massive data storage requirements and largescale cloud computing demonstration applications.The Dawning EB-class cloud storage system adopts advanced fault-tolerant architecture,efficient data fault-tolerant algorithms with user authentication and data encryption policies to deal with the"lost""wrong"and"stolen"problems of data for ensuring the reliability and safety of the EB-class storage system in the public network application environments.The Dawning EB-class Storage Laboratory taking advan-