基于多特征的域间路由节点安全状态评估方法

域间路由节点安全状态评估能够实现对BGP节点安全状态的直观、实时描述,可为制定合理的安全策略,及时定位、抑制异常路由事件提供数据参考.然而由于完整的异常域间路由集难以获取,使得传统基于数据融合的状态评估方法不再适用.分析BGP节点间交互路由过程中存在的统计特征以及这些特征与域间路由节点安全状态的关系,进而提出一种基于多特征的安全状态评估方法.以平均路径长度和路由事件发生频率等属性为安全特征,并借鉴云模型理论转换定量特征为定性概念的思想,构建域间路由安全特征云,将正常态下的多属性综合安全特征转换为安全正常态,然后通过度量安全特征偏离正常态的程度来计算节点偏离正常态的程度,由此得到域间路由节点面临安全威胁的概率.实验结果表明,该方法能够实现对域间路由节点安全状态的评估,准确性高、实时性强,可为域间路由系统的安全稳定运行提供有力支撑.     

Plasma sheet stretching accompanied by field aligned energetic ion fluxes observed by the NUADU instrument aboard TC-2

The NUADU (NeUtral Atom Detector Unit) instrument aboard TC-2 recorded 4л solid angle images of charged particles (E >180 keV) spiraling around the magnetic field lines in the near-Earth plasma sheet (at ~ -7 RE, equatorial dawn-to-night side) during a geomagnetic storm (Dst =-219 nT) on August 24, 2005. Energetic ion beam events characterized by symmetrical, ring-like, solid angle distributions around ambient magnetic field lines were observed during a 34-minute traversal of the plasma sheet by the TC-2 spacecraft. Also, observations during these multiple crossings of the plasma sheet were monitored by the magnetometer experiment (FGM) aboard the same spacecraft. During each crossing, a whistler-mode chorus enhancement was observed in the anisotropic area by the TC-2 low frequency electromagnetic wave detector (LFEW/TC-2) at a frequency just above that of the local lower hybrid wave. A comparison of the ion pitch angle distribution (PAD) map with the ambient magnetic field shows that an enhancement in the field aligned energetic ion flux was accompanied by tailward stretching of the magnetic field lines in the plasma sheet. In contrast, the perpendicular ion-flux enhancement was accompanied by a signature indicating the corresponding shrinkage of the magnetic field lines in the plasma sheet. Since both parallel ion-flux and perpendicular ion-flux enhancements occurred intermittently, the data were interpreted to imply a dynamical, oscillatory process of the magnetic field line (stretching and shrinking) in the near-Earth plasma sheet, which might have acted to help establish an interaction region in this area which would support continuous aurora-substorm triggering during the ongoing magnetic storm. The whistler-mode chorus may have been produced due to ion gyro-resonance during particle pitch angle diffusion after the plasma sheet compression.     

Observations of kinetic Alfvén waves by THEMIS near a substorm onset

Low frequency electromagnetic fluctuations in the vicinity of a magnetospheric substorm onset were investigated using simultaneous observations by THEMIS multiple probes in the near-Earth plasma sheet in the magnetotail.The observations indicate that in the vicinity of a substorm onset,kinetic Alfvén waves can be excited in the high-βplasma sheet(β=2μ0nT/B 2 ,the ratio of plasma thermal pressure to magnetic pressure)within the near-Earth magnetotail.The kinetic Alfvén wave has a small spatial scale in the high-βplasma.The parallel electric field accompanying kinetic Alfvén waves accelerates the charged particles along the magnetic field.The kinetic Alfvén waves play an important role in the substorm trigger process,and possibly in the formation of a substorm current wedge.     

Continuous tailward flow in the near-Earth magnetotail observed by TC-1 satellite

On July 11, 2004, a substorm process in the period of continuous tailward flow was observed by the joint exploration of the TC-1, IMAGE and ACE satellites. The substorm observed by the TC-1 in the near-Earth has three stages: the growth phase (from 11:43 to 12:19), the pre-expansion process (from 12:19 to 12:28) and the dipolarization process. The auroral brightening was at 12:26 recorded by the FUV instrument on IMAGE, and the dipolarization occurred two minutes later. During the 45 min period of the tailward flow, the magnetotail experienced the growth phase and the pre-expansion process. When the dipolarization process began, the TC-1 entered the plasma sheet and observed a high speed earthward flow. The field-aligned tailward flow is characterized by the low temperature and high density, which is consistent with the properties of the flow from the ionosphere detected in the near-Earth magnetotail by other satellites. The tailward flow is closely related with the southward interplanetary magnetic field (IMF), and may have an important effect on the substorm.     

Convective high-speed flow and field-aligned high-speed flows explored by TC-1

From June 1, 2004 to October 31, 2006, a total 465 high-speed flow events are observed by the TC-1 satellite in the near-Earth region （-13 RE〈X〈-9 RE, ｜Y｜〈10 RE, ｜Z＋〈5 RE）, Based on the angle between the flow and the magnetic field, the high-speed flow events are further divided into two types, that is, field-aligned high-speed flow （FAHF） in the plasma sheet boundary and convective bursty bulk flow （BBF） in the center plasma sheet, Among the total 465 high-speed flow events, there are 371 FAHFs, and 94 BBFs, The CHF are mainly concentrated in the plasma sheet, the intersection angle between the flow and the magnetic field is larger, the magnetic field intensity is relatively weak, The FHF are mainly distributed near the boundary layer of the plasma sheet, the intersection angle between the flow and magnetic field is smaller, and the magnetic field intensity is relatively strong, The convective BBFs have an important effect on the substorm,     

Variation of dependence of the cusp location at different altitude on the dipole tilt

Using the Cluster cusp crossings data, dependence of the cusp location at the mid-altitude on the geomagnetic dipole tilt during northward IMF is studied. The results show that the cusp center moves 0.051° Invariant Latitude (ILAT) upon the increase of 1° in the dipole tilt angle at the average altitude of 5.8 R_E (Earth radius). According to the present results obtained at the altitude of the Cluster orbit and previous results obtained at other altitudes of other satellite orbits, it is found that the higher the altitude in the cusp region is, the bigger the dependence of cusp location on the dipole tilt angle will be. If the altitude increases by 1 R_E in the cusp region, the dependence will increase by 0.012° ILAT upon the increase of 1° in the dipole tilt angle. Some possible physical mechanisms are discussed and it shows that the cusp location will be more sensitive to the solar wind dynamic pressure if the altitude is high.     

温度对氟氧化物玻璃陶瓷中Tm3+荧光强度的影响

采用不同波长的红色脉冲光, 激发镶嵌有LaF₃:Tm³⁺纳米晶体颗粒的透明氟氧化物玻璃陶瓷样品, 测量了不同环境温度下样品的荧光发射谱, 记录了荧光发射强度随环境温度的变化规律.实验结果显示, 在643.2 nm 脉冲光激发下, 上转换454 nm 在100~200 K 的温度范围内有很强的荧光发射, 并且荧光强度随着环境温度的降低先增强而后减弱; 当采用656.0 和638.0 nm 脉冲光激发样品时, 上转换荧光发射强度随环境温度的降低而逐渐增强, 其中643.2 和638.0 nm 脉冲光激发下的上转换效率高于656.0 nm 激发时的结果, 表明波长接近于激发态吸收的激发光泵浦样品时, 更容易实现Tm³⁺的频率上转换. 最后, 从基质声子分布特点等方面对实验结果给出了合理的解释.     

Graphene-based ambipolar electronics for radio frequency applications

Graphene is considered as a promising material to construct field-effect transistors (FETs) for high frequency electronic applications due to its unique structure and properties,mainly including extremely high carrier mobility and saturation velocity,the ultimate thinnest body and stability.Through continuously scaling down the gate length and optimizing the structure,the cut-off frequency of graphene FET (GFET) was rapidly increased and up to about 300 GHz,and further improvements are also expected.Because of the lack of an intrinsic band gap,the GFETs present typical ambipolar transfer characteristic without off state,which means GFETs are suitable for analog electronics rather than digital applications.Taking advantage of the ambipolar characteristic,GFET is demonstrated as an excellent building block for ambipolar electronic circuits,and has been used in applications such as highperformance frequency doublers,radio frequency mixers,digital modulators,and phase detectors.     

The distribution characteristics of the flows in the near-Earth region： TC-1 observational results

TC-1 observational results clearly indicate that the velocity of the flows in the near-Earth region is dependent on the satellite location. The flow speed decreases while satellite moves close to the Earth. The plasma flow in the region close to the Earth tends to drift into the midnight region from the dawn and dusk region while the flow in the region away from the Earth shows an opposite drift. The observational results also show that the tailward flows are mainly located in the plasma sheet boundary while the earthward flow becomes dominant in the plasma sheet. It is found that both the strong tailward and earthward flows are distributed in the region around X= -11 Re, which coincides with the trigger region of the substorm onset. Hence, it may suggest that the flows are related with the trigger of the substorm onset. In addition, the BBFs coming from the mid-tail maily distributed in the region where X〈-9R E a n d ｜Z｜ 〈 3 R E that differs from the convection.     

Responses of properties in the plasma sheet and at the geosynchronous orbit to interplanetary shock

On July 22, 2004, the WIND spacecraft detected a typical interplanetary shock. There was sustaining weak southward magnetic field in the preshock region and the southward field was suddenly enhanced across the shock front （i.e., southward turning）. When the shock impinged on the magnetosphere, the magnetospheric plasma convection was abruptly enhanced in the central plasma sheet, which was directly observed by both the TC-1 and Cluster spacecraft located in different regions. Simultaneously, the Cluster spacecraft observed that the dawn-to-dusk electric field was abruptly enhanced. The variations of the magnetic field observed by TC-1, Cluster, GOES-10 and GOES-12 that were distributed in different regions in the plasma sheet and at the geosynchronous orbit are obviously distinct. TC-1 observations showed that the magnetic intensity kept almost unchanged and the elevation angle decreased, but the Cluster spacecraft, which was also in the plasma sheet and was further from the equator, observed that the magnetic field was obviously enhanced. Simultaneously, GOES-12 located near the midnight observed that the magnetic intensity sharply increased and the elevation angle decreased, but GOES-10 located in the dawn side observed that the magnetic field was merely compressed with its three components all sharply increasing. Furthermore, the energetic proton and electron fluxes at nearly all channels observed by five LANL satellites located at different magnetic local times （MLTs） all showed impulsive enhancements due to the compression of the shock. The responses of the energetic particles were much evident on the dayside than those on the nightside. Especially the responses near the midnight were rather weak. In this paper, the possible reasonable physical explanation to above observations is also discussed. All the shock-induced responses are the joint effects of the solar wind dynamic pressure pulse and the magnetic field southward turning.