Imaging Borrelly

The nucleus, coma, and dust jets of short-period Comet 19P/Borrelly were imaged from the Deep Space 1 spacecraft during its close flyby in September 2001. A prominent jet dominated the near-nucleus coma and emanated roughly normal to the long axis of nucleus from a broad central cavity. We show it to have remained fixed in position for more than 34 hr, much longer than the 26-hr rotation period. This confirms earlier suggestions that it is co-aligned with the rotation axis. From a combination of fitting the nucleus light curve from approach images and the nucleus' orientation from stereo images at encounter, we conclude that the sense of rotation is right-handed around the main jet vector. The inferred rotation pole is approximately perpendicular to the long axis of the nucleus, consistent with a simple rotational state. Lacking an existing IAU comet-specific convention but applying a convention provisionally adopted for asteroids, we label this the north pole. This places the sub-solar latitude at ∼60° N at the time of the perihelion with the north pole in constant sunlight and thus receiving maximum average insolation.     

INTEGRAL observations of TeV plerions

Amongst the sources seen in very high gamma-rays several are associated with Pulsar Wind Nebulae (“TeV plerions”). The study of hard X-ray/soft gamma-ray emission is providing an important insight into the energetic particle population present in these objects. The unpulsed emission from pulsar/pulsar wind nebula systems in the energy range accessible to the INTEGRAL satellite is mainly synchrotron emission from energetic and fast cooling electrons close to their acceleration site. Our analyses of public INTEGRAL data of known TeV plerions detected by ground based Cherenkov telescopes indicate a deeper link between these TeV plerions and INTEGRAL detected pulsar wind nebulae. The newly discovered TeV plerion in the northern wing of the Kookaburra region (G313.3+0.6 powered by the middle aged PSR J1420-6048) is found to have a previously unknown INTEGRAL counterpart which is besides the Vela pulsar the only middle aged pulsar detected with INTEGRAL. We do not find an INTEGRAL counterpart of the TeV plerion associated with the X-ray PWN “Rabbit” G313.3+0.1 which is possibly powered by a young pulsar.     

Outgassing-induced effects in the rotational state of comet 67P/Churyumov—Gerasimenko during the Rosetta mission

The new target of the Rosetta mission is comet 67P/Churyumov-Gerasimenko (hereafter 67P/C-G). In order to support the planning of the mission, in particular the strategy during the mapping and landing phases, we have performed numerical simulations of the rotational evolution of a comet in the orbit of 67P/C-G. In these simulations, the currently known observational constraints have been taken into account and a large set of initial conditions were considered. For most of the simulations, we observe that the sublimation-induced torques produce significant changes in the rotational parameters of a 67P/C-G-like comet. Typical rates of change for the spin period from the rendezvous up to the end of the nominal mission range from 0.001 to depending on different circumstances as described in the text. At perihelion, rates of change of the orientation of the angular momentum vector amount to about 0.01-. These simulations suggest that a specific strategy should be defined in order to monitor likely variations of the rotational parameters. As an example we show a possible optimized schedule for observations with the OSIRIS instrument to determine the rotational parameters of comet 67P/C-G and their possible evolution.     

A giant crater on 90 Antiope?

Mutual event observations between the two components of 90 Antiope were carried out in 2007-2008. The pole position was refined to λ₀ = 199.5 ± 0.5° and β₀ = 39.8 ± 5° in J2000 ecliptic coordinates, leaving intact the physical solution for the components, assimilated to two perfect Roche ellipsoids, and derived after the 2005 mutual event season (Descamps, P., Marchis, F., Michalowski, T., Vachier, F., Colas, F., Berthier, J., Assafin, M., Dunckel, P.B., Polinska, M., Pych, W., Hestroffer, D., Miller, K., Vieira-Martins, R., Birlan, M., Teng-Chuen-Yu, J.-P., Peyrot, A., Payet, B., Dorseuil, J., Léonie, Y., Dijoux, T., 2007. Figure of the double Asteroid 90 Antiope from AO and lightcurves observations. Icarus 187, 482-499). Furthermore, a large-scale geological depression, located on one of the components, was introduced to better match the observed lightcurves. This vast geological feature of about 68 km in diameter, which could be postulated as a bowl-shaped impact crater, is indeed responsible of the photometric asymmetries seen on the “shoulders” of the lightcurves. The bulk density was then recomputed to 1.28 ± 0.04 g cm⁻³ to take into account this large-scale non-convexity. This giant crater could be the aftermath of a tremendous collision of a 100-km sized proto-Antiope with another Themis family member. This statement is supported by the fact that Antiope is sufficiently porous (∼50%) to survive such an impact without being wholly destroyed. This violent shock would have then imparted enough angular momentum for fissioning of proto-Antiope into two equisized bodies. We calculated that the impactor must have a diameter greater than ∼17 km, for an impact velocity ranging between 1 and 4 km/s. With such a projectile, this event has a substantial 50% probability to have occurred over the age of the Themis family.     

CCD-photometry and pole coordinates for eight asteroids

The long time photometric observations were carried out for eight asteroids: (122) Gerda, (153) Hilda, (190) Ismene, (221) Eos, (411) Xanthe, (679) Pax, (700) Auravictrix, (787) Moskva. New rotation periods have been determined for the asteroids (153) Hilda (5.959 h) and (411) Xanthe (11.408 h), and known rotation periods for some of the others have been confirmed. Using our data and others data we have estimated new pole coordinates for the observed asteroids.     

IERS1996规范中地球引力势模型和测量模型的改进

简要而系统地介绍ＩＥＲＳ１９９６规范采用的地球引力势模型和各种测量模型,着重叙述了其与ＩＥＲＳ１９９２标准相比所作的改进。规范用ＪＧＭ－３地球引力势模型取代ＧＥＭ－Ｔ３模型,在计算地球潮汐形变产生的附加势时展开到３阶,并考虑了地幔的滞弹效应。在测站位移的计算中,规范引入了３倍洛夫数,计及地幔的滞弹性,引入了计算冰后期回弹的ＩＣＥ－４Ｇ模型,列出了改正ＶＬＢＩ观测中天线形变改正的公式。关于地球自转和     

Rotation Of Trajectories In Lagrangian Stochastic Models Of Turbulent Dispersion

We present a new measure for the rotation of Lagrangian trajectories in turbulence that simplifies and generalises that suggested by Wilson and Flesch ( Boundary-Layer Meteorol. 84, 411–426). The new measure is the cross product of the velocity and acceleration and is directly related to the area, rather than the angle, swept out by the velocity vector. It makes it possible to derive a simple but exact kinematic expression for the mean rotation of the velocity vector and to partition this expression into terms that are closed in terms of Eulerian velocity moments up to second order and unclosed terms. The unclosed terms arise from the interaction of the fluctuating part of the velocity and the rate of change of the fluctuating velocity.We examine the mean rotation of a class of Lagrangian stochastic models that are quadratic in velocity for Gaussian inhomogeneous turbulence. For some of these models, including that of Thomson ( J. Fluid Mech. 180, 113–153), the unclosed part of the mean rotation vanishes identically, while for other models it is non-zero. Thus the mean rotation criterion clearly separates the class of models into two sets, but still does not provide a criterion for choosing a single model.We also show that models for which = 0 are independent of whether the model is derived on the assumption that total Lagrangian velocity is Markovian or whether the fluctuating part is Markovian.     

基于广义旋转法双九点格式标量波方程数值模拟

前人虽然基于传统旋转法提出了四阶精度最优17点差分格式,用于提高频率域地震波场数值模拟精度,但其仅适用于等网格间距的情形.这大大限制了该格式的使用范围.为了进一步提高17点有限差分格式的数值精度并将其推广到矩形网格,本文基于二阶精度有限差分算子利用广义旋转法提出了双九点格式,由于其差分格点与前人17点格式在分布上一样,所以也可称为二阶精度最优17点格式,但由差分格式构造原理上来讲,称其为双九点格式更妥.前人四阶精度17点格式仅为本文等网格间距情形时的特殊情况,本文方法单位波长网格点数仅需要2.2个即可.本文格式在继承传统旋转法良好几何旋转性质的同时,拥有平均导数方法适用于矩形网格的特点,和平均导数法所得的广义17点格式相比,本文格式数值精度更高,数值频散抑制性能和差分算子对称性更好.同时,本文双九点格式方法和思想对于后人借助传统九点格式的构造方法将其扩展到17点格式求解各类波动方程具有十分重要的意义.     

催化电解杀菌与次氯酸钠杀菌的对比

油田回注水催化电解杀菌与次氯酸钠杀菌在杀菌机理、效果及应用成本3方面的对比结果表明,催化电解产生有效氯是主要的杀菌机理.催化电解产生的有效氯质量浓度与电解时间呈线性关系,杀菌率随着有效氯质量浓度的增大而增大.定量杀菌的对比结果表明,油田回注水催化电解杀菌比次氯酸钠杀菌效果好,且不须投加任何药剂,只消耗电能,运行成本低.