Joint observations of sporadic sodium and sporadic E layers at middle and low latitudes in China

Sporadic sodium layers (SSLs) were studied with sodium (Na) lidar at Beijing (40.5°N, 116.0°E) and Haikou (19.5°N, 109.1°E) in China. The altitude distribution, strength factors, and occurrence time of SSL and sporadic E (E_s) layer events were statistically analyzed at both observing sites. SSL occurrence had a maximum near 22:00 local time, and E_s layer occurrence had a maximum before midnight. The altitude distributions of SSL and E_s layer events were better correlated at Haikou than at Beijing. All the average values of height and strength factor for SSL and E_s layer events, as well as the average of the maximum frequency that can be reflected by the E_s layer (f_oE_s), at Beijing were higher than those at Haikou. A better correlation between SSL and E_s layer events was also found at Haikou, and the formation of SSLs was considered to likely depend on the seasonal variability of chemical and dynamical processes.     

Downward current electron beams observed at the dipolarization front

The strong field-aligned pitch angle distribution of electrons is observed right at the dipolarization front (DF) before the arriving of a high speed flow when the four Cluster satellites are traveling in the magnetotail around 15 R E on July 22, 2001. The increased electron fluxes only last for a short time period at the DF, corresponding to just a few bouncing periods for 1 keV electrons. The field-aligned current contributed by these electrons agrees well with that calculated by the magnetic field observations by four satellites at the front. These electron streams are found in the energy range of 0.2-2 keV, peak around 1 keV. It is suggested that these downward current electrons may be originated near the aurora region by some kinds of potential structure. The occurrence of these electrons implies that the formation of the dipolarization front and the associated field-aligned current play an important role in the magnetosphere-ionosphere coupling.     

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,     

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.     

Angular dependent NEXAFS study of the molecular orientation of PTCDA multilayers on Au （111） surface

The molecular orientation of perylene-3,4,9,10-tetracarboxylic acid dianhydride (PTCDA) multilayers adsorbed on Au (111) surface has been investigated using angular dependent O K-edge near edge X-ray absorption fine structure (NEXAFS) spectroscopy. The significant angular dependence of important resonant structures (π* and σ*) reveals that PTCDA molecules adopt an ordered geometry on the substrate surface. The average tilt angle of the PTCDA molecular planes is 27°±10° from the Au (111) surface.     

喷射策略对某重型柴油机高原燃烧特性的影响

为研究高原条件下不同喷射策略对某重型柴油机燃烧特性的影响。建立基于ECFM-3Z燃烧模型的某增压柴油机燃烧室三维模型并将其与平原台架试验结果进行对比验证,分析在海拔4 550 m条件下不同喷射策略对柴油机缸内燃烧过程的影响。结果表明,随着喷油提前角增大,单次喷射时缸内高温区域缩小,温度分布变得均匀,缸内预混合燃烧增强。和平原条件下的结果相比,喷油提前角的增大可以减少碳烟的排放但是增加了NO_x的排放。采用多次喷射策略时,预喷的提前可以使燃油与空气混合更充分,从而有助于主喷燃油更好地燃烧,功率能够得到进一步提升,较单次喷射NO_x排放增加,碳烟排放减少。根据模拟结果最终选择预喷提前角为22°CA BTDC和主喷提前角为2°CA BTDC的喷射策略,示功图面积较单次喷射相比有所提高,可恢复至平原的85.6%。     

Sunlit boundary ionospheric response to the great flare on Oct. 28, 2003

The sudden increase in X-ray and EUV flux duringthe outburst of a large flare greatly elevate the electrondensity of the ionosphere, causing sudden ionosphericdisturbances (SIDs), such as sudden wave fadeout (SFD),sudden phase anomaly (SPA), sudden frequency deviation(SFD) and sudden increase in total electron content(SITEC)[1—4]. Two review articles addressed SIDs in detailrecently[5,6]. Due to the limitation of observing methods,the global ionospheric morphology during solar flares…     

Numerical simulation of ionization enhancement in the topside ionosphere of cusp foot-point region caused by low energy particle precipitation

The Graz Ionospheric Flux Tube Simulations (GIFTS) has been improved. The improved GIFTS model was used to numerically investigate the energy particle precipitation on the distribution of electron density in the ionospheric cusp foot-point region under conditions of large plasma convection during magnetic storm. After including the effects of low energy incident particles, the ionospheric electron densities increase remarkably above altitude of ∼250 km, showing a peak at about 350 km. The percent enhancements of electron densities increase gradually with altitude, exceeding 60% near the upper boundary of the calculation. The calculated ionospheric F ₂-peak was remarkably enhanced and lifted up by the incident low energy electrons. Biography: CAI Hongtao(1976–), male, Associate professor, Ph.D., research direction: polar magnetosphere and ionosphere.     

Relocation of the mainshock and aftershock sequences of M S7.0 Sichuan Lushan earthquake

The mainshock of April 20, 2013 Sichuan Lushan M _S7.0 earthquake was relocated using a 3-D velocity model. Double difference algorithm was applied to relocate aftershock sequences of Lushan earthquake. The locations of 2405 aftershocks were determined. The location errors in E-W, N-S and U-D direction were 0.30, 0.29 and 0.59 km on average, respectively. The location of the mainshock is 102.983°E, 30.291°N and the focal depth is 17.6 km. The relocation results show that the aftershocks spread approximately 35 km in length and 16 km in width. The dominant distribution of the focal depth ranges from 10 to 20 km. A few earthquakes occurred in the shallow crust. Focal depth profiles show fault planes dip to the northwest, manifested itself as a listric thrust fault. The dip angle is steep in the shallow crust and gentle in the deep crust. Although the epicenters of aftershocks distributed mainly along both sides of the Shuangshi-Dachuan fault, the seismogenic fault may be a blind thrust fault on the eastern side of the Shuangshi-Dachuan fault. Earthquake relocation results reveal that there is a southeastward tilt aftershock belt intersecting with the seismogenic fault with y-shape. We speculate it is a back thrust fault that often appears in a thrust fault system. Lushan earthquake triggered the seismic activity of the back thrust fault.     

Investigation of solvent extraction with GC/MS and residue with TG-FTIR from high-temperature coal tar

A high-temperature coal tar(HTCT) was sequentially extracted with petroleum ether(PE),ethyl acetate(EA),and acetone with ultrasonic irradiation to afford extracts 1 to 3(E_1 to E_3),respectively,and acetone residue.The gas chromatography/mass spectrometry(GC/MS) analysis of all extracts show that E_1 is mainly composed of di- and tricyclic arenes such as naphthalenes,phenanthrene,anthracene,etc.,whereas high contents of heteroatomic compounds and four or more ring arenes were found in E_2 and E_3,respectively.The pyrolysis process of acetone residue was studied with a thermogravimetric(TG) analyzer equipped with Fourier transform infrared(FTIR) spectrometer.The results indicate that volatiles were mainly released at 380-560 ℃,and the maximum mass loss rate occurred at 492 ℃.     

不同战场环境下超低空导弹目标抗多径方法

多径干扰是影响超低空探测的主要因素,针对防空导弹对超低空导弹目标探测问题,研究了不同战场环境下的抗多径方法。采用物理光学法与等效电磁流混合方法(PO+MEC)快速获取导弹目标的电磁散射特性,结合传统的四路径模型,并引入导引头天线方向图对其进行修正,提取出不同战场环境下超低空导弹目标的多径干扰。仿真结果表明,不同的战场环境对应着不同的布儒斯特角,混凝土、半干地、干地和湿地环境下所对应的布儒斯特角分别为30°、26.5°、21.5°和10.5°;当导引头采用VV极化方式以布儒斯特角下视探测超低空导弹目标时,多径干扰达到极小水平,所接收信号的信干比达到极大水平,此时导引头对于超低空导弹目标的探测能力最强,目标回波最为明显。仿真结果对于防空导弹弹道优化具有借鉴意义,为超低空对抗打下基础。     

蜻蜓柔性后翅模型的气动效能分析

为探究柔性材料对蜻蜓滑翔时气动特性的影响,通过数值仿真的方法,研究杨氏模量为3800 MPa,泊松比为0.18的三维柔性蜻蜓后翅模型在不同雷诺数和迎角滑翔时的气动效能和气动力作用下的结构变形.结果表明:柔性蜻蜓后翅在气动力的作用下会产生明显的弯曲扭转变形,且变形程度随着雷诺数和迎角的增大而增大,其中该扭转变形会使蜻蜓滑翔的实际迎角减小;由于产生了使迎角减少的扭转变形,使得在迎角为5°～30°滑翔时,升力系数减少了9％ ～45％,失速迎角增大10°以上;小迎角滑翔时,升力系数随速度增大而减小,大迎角滑翔时,升力系数与速度无明显相关性;大迎角滑翔时,在气流分离和柔性蜻蜓翼大角度扭转的作用下,上翼面的负压区向后缘移动,增加了负压区面积,增大了失速迎角,有利于提高蜻蜓飞行时的机动性.可见虽然柔性材料虽然会牺牲蜻蜓滑翔时的气动效能,但有助于蜻蜓高速大迎角飞行,提高了蜻蜓的机动性.     

Latitudinal shift and tilt of the ring current during magnetic storms

The equatorial ring current (ERC) theory suggested that the distribution of global disturbed horizontal geomagnetic field only depends on the cosine of station’s latitude. However, we always observe a larger ΔH at higher latitude stations than lower ones, implying that the ERC could tilt or/and shift with respect to the equatorial plane during intense storms. In this paper, we analyze 11 intense magnetic storms from 2000 to 2004, and introduce two configurational factors to characterize the topology of storm time ring current. The results show that ERC has occasionally deviated off equatorial plane with both tilt angle δ_t≈13°―25° and latitude shift δ_s≈0°―21.8°. The ground disturbed field distribution should be improved as ΔH_k = ΔH_maxcos(φ_k-δ ), which agree well with the geomagnetic observations.     

结冰风洞变截面拐角数值计算与实验研究

为了降低变截面拐角流动损失,提高拐角出口速度均匀性,采用数值计算与实验相结合的方式研究了某型结冰风洞变截面拐角流动情况。研究结果表明:在未安装导流片的情况下变截面拐角流动会出现旋涡,造成能量损失,并会导致拐角下游速度均匀性较差;圆弧直线型导流片能够改善变截面拐角流动,降低整个流道压力损失;预偏角的选取对拐角流动具有较大影响,当预偏角为0°和2.5°时拐角段损失系数较小,随着预偏角增大为5°、7.5°、10°拐角段损失不断增加。     

锯齿形PDC刀具的破岩特性及温度场

聚晶金刚石复合片(polycrystalline diamond compact, PDC)刀具的结构是影响钻头性能的重要因素,锯齿形PDC刀具性能较好但研究较少,缺乏相关理论支撑。因此,基于弹塑性力学及Drucker-Prager准则构建了刀具与岩石的有限元模型,对锯齿形PDC及常规PDC刀具的破岩和温度场进行对比研究。结果表明,锯齿形PDC通过剪切和犁碎的方式破岩,有效且明显提升了破岩效率。锯齿形PDC较常规PDC切削力均值减小约20%,波动明显更小。后倾角变大,其切削力增加,破岩比能先增加减小又增加,存在最佳后倾角10°～15°;切削深度增大,切削力变大,破岩比能先减小后增加,存在临界切深1.5～2 mm;锯齿数增加,刀具的切削力与破岩比能先增加后减小,3个锯齿为最佳。温度场研究结果表明,锯齿形PDC比常规PDC刀具散热面积大,热稳定性更好,工作参数与温度变化之间存在规律。研究深度揭示了锯齿形PDC刀具的破岩特性以及温度场,对PDC刀具优化及高性能钻头布齿具有较为重要的指导意义。     

Statistical survey on the magnetic field in magnetotail current sheets: Cluster observations

The distribution properties of the magnetic field in magnetotail current sheets have been explored statistically with the magnetic measurement data of the Cluster mission from June to November of the years 2001–2005. It is found that, on average, the strength of the magnetic field and its B_z component in the current sheet are weaker in the region close to midnight but stronger near the dawnside and duskside flanks, which implies that, in general, a thinner current sheet occurs near midnight and thicker ones near both flanks. The occurrence of tail current sheet flapping is higher on both flanks than in the midnight region, although it is most frequent in the dawn flank. Current sheets with a negative B_z component or a strong B_y component have a higher probability of occurring at magnetic local times of 21:00–01:00, indicating that magnetic activity, e.g. magnetic reconnection and current disruption occur more frequently there. Statistically, the probability distributions of the B_y component and the tilt angle of magnetic field lines in the current sheet are approximately normal distributions, and the occurrence probability of the flattened current sheet is about one third that of the normal current sheet. The magnetic field and B_z component in the current sheet mainly vary from 1 nT to 10 nT. The B_y component in the tail central current sheet is on average twice the IMF B_y at 1 AU.     

A distance regular graph of typeE 1° E d

In this note, the distance regular graph of typeE _1° E _d is considered and some characterization of the type graph is given. The results generalize the characterization of tight distance regular graphs.     

Correlation between intrinsic dipole moment and pyroelectric coefficient of Fe-Mg tourmaline

Single-crystal X-ray diffraction structural data of four Fe-Mg tourmalines with different Fe contents from Xinjiang, Sichuan, and Yunnan Provinces, China, were collected at room temperature and ?100℃. The intrinsic dipole moments of polyhedra and the total intrinsic dipole moment of the unit cell were calculated. By comparing the intrinsic electric dipole moments of the X, Y, Z, T, and B site polyhedra, it is found that the T site polyhedron makes the greatest contribution to the total intrinsic dipole moment. The pyroelectric coefficients of four Fe-Mg tourmalines were experimentally determined, and the influence of intrinsic dipole moments on their pyroelectric properties was investigated. The experimental results show that, compared with the case at room temperature, the intrinsic dipole moments change with the total Fe content at ?100℃ in a completely different way. With the decrease of temperature, the total intrinsic dipole moments of tourmaline decrease. Over the same temperature interval, the pyroelectric coefficients increase with the increase in intrinsic dipole moment.     

移动机器人空间姿态测量系统研究与设计

未知环境中机器人的自主导航研究一直是非常具有挑战性的前沿课题,要求机器人在定向移动之前必须先调整好自己的空间姿态;捷联惯性导航对空间姿态信息有明确的定义,具体通过倾斜角、方位角和工具面角来体现;针对目前已公开的空间姿态信息的解算数学模型存在缺陷的问题,结合空间坐标变换、空间直线方程和狗腿角的定义推导出倾斜角、磁方位角和工具面角的数学模型,并利用三轴加速度计和三轴磁强计给出具体的实现方案;测试结果表明:该方案能获得正确的空间姿态数据,倾斜角误差在±0.1°以内,磁方位角和工具面角误差在±1.5°以内,且成本低廉,体积小巧,是测量空间姿态的理想选择。     

Temperature dependence of surface enhanced Raman scattering on C<Subscript>70</Subscript>

The temperature dependence of surface enhanced Raman scattering of the C70 molecule is reported. The Raman scattering of C70 molecules adsorbed on the surface of a silver mirror was measured at different temperatures. The experimental results indicate that the relative intensities of the Raman features vary with the temperature of the sample. When the temperature decreases from room temperature to 0℃, the relative intensifies of certain Raman bands decrease abruptly. If we like the strongest band 1565cm^-1 as a standard value 100, the greatest decrease approaches to 43%. However, with the further decrease in the temperature these relative intensities increase and resume the value at room temperature. And such a temperature dependence is reversible. Our results show that the adsorption state of the C70 molecules on the silver surface around 0℃ changes greatly with the temperature, resulting in a decrease in relative intensities for some main Raman features of C70 molecule. When the temperature is lower than 0℃, the adsorption state changes continually and more slowly. Synchronously, eight new Raman features, which have not ever been reported in fiterature, are observed in our experiment and this enriches the basic information of the vibrational modes for C70 molecule.