基于遗传算法的地磁匹配搜索策略

为降低导航成本,提出仅利用磁测计和里程计的地磁场匹配定位方法.为解决搜索空间过大的问题,提出以遗传算法在匹配区域搜索可能路径的方法.该方法以相关性度量作为适应度函数,交叉与变异仅针对点列的相对关系完成,提出用局部适应度函数自适应调整交叉概率与变异概率.仿真结果表明,该方法可以有效完成地磁匹配导航中任意形状路径的匹配.     

最大熵磁共振成象理论

由于在实际磁共振成象系统中，只能得到有限的频谱数据，利用传统的ＦＦＴ方法重建磁共振图象，将导致截断的伪影和低的分辨率。本文提出了一种基于ＡＲ模型的最大熵磁共振成象算法，利用ＡＲ模型外推未知频谱数据，替代了ＦＦＴ方法的填零法重建，并利用了ＢＵＲＧ算法中的ＡＲ模型参数计算的有效性，不仅消除了截断伪影、抑制噪声、提高了分辨率，而且使重建时间与ＦＦＴ方法相当，完全适用于临床应用。     

Solar cycle and latitude dependence of high-beta suprathermal plasma conditions in interplanetary space between 1.3 and 5.4 AU

The analysis of energetic particles and magnetic field measurements from the Ulysses spacecraft has shown that in a series of events, the energy density contained in the suprathermal tail particle distribution is comparable to or larger than that of the magnetic field, creating conditions of high-beta plasma. In this work we analyze periods of high-beta suprathermal plasma occurrences (β_ep > 1) in interplanetary space, using the ratio (β_ep) of the energetic particle (20 keV to ∼5 MeV) and magnetic field energy densities from measurements covering the entire Ulysses mission lifetime (1990–2009) in order to reveal new or to reconfirm some recently defined interesting characteristics. The main key-results of the work are summarized as follows: (i) we verify that high-beta events are detected within well identified regions corresponding mainly to the vicinity of shock surfaces and magnetic structures, and associated with energetic particle intensity enhancements due to (a) reacceleration at shock-fronts and (b) unusually large magnetic field depressions. (ii) We define three considerable features for the high-beta events, concentrated on the next points: (a) there is an appreciable solar-activity influence on the high-beta events, during the maximum and middle solar-cycle phase, (b) the annual peak magnitude and the number of occurrences of high events are well correlated with the sunspot number, (c) the high-beta suprathermal plasma events present a spatial distribution in heliographic latitudes (HL) up to ∼±80°, and a specific important concentration on the low (−25° ? HL < −6°, 6° < HL ? 25°) and median (−45° ? HL < −25°, 25° < HL ? 45°) latitudes. We also reconfirm by a statistical analysis the results of Marhavilas and Sarris (2011), that the high-beta suprathermal plasma (β_ep > 1) events are characterized by a very large parameter β_ep (up to 1732.5), a great total duration (406 days) and a large percentage of the Ulysses-mission lifetime (which is equal to 6.34% of the total duration with usable measurements, and 11.3% of the duration in presence of suprathermal particles events).     

A heuristic derivation of an improved analytical theory for perpendicular diffusion of charged particles

A heuristic derivation of an improved nonlinear guiding center theory for perpendicular diffusion of charged particles is presented. This new derivation complements previous work which is based on an indirect solution of the Fokker–Planck equation. The new derivation confirms the improved theory for diffusion of charged particles and makes the validity of the theory plausible.     

Upper limit of the total magnetic flux in an active region according to the photometric-magnetic dynamical model

The photometric-magnetic dynamical model handles the evolution of an individual sunspot as an autonomous nonlinear, though integrable, dynamical system. One of its consequences is the prediction of an upper limit of the sunspot areas. This upper limit is analytically expressed by the model parameters, while its calculated value is verified by the observational data. In addition, an upper limit for the magnetic strength inside the sunspot is also predicted, and then, we obtain the following significant result: The upper limit of the total magnetic flux in an active region is found to be of about 7.23 × 10²³ Mx, namely, phenomenologically equal to the magnetic flux concentrated in the totality of the granules of the quiet Sun, having a typical maximum magnetic strength of about 12G. Therefore, the magnetic flux concentrated in an active region cannot exceed the magnetic flux concentrated in the photosphere as a whole.     

Modelling and observations of photospheric magnetic helicity

Mounting observational evidence of the emergence of twisted magnetic flux tubes through the photosphere have now been published. Such flux tubes, formed by the solar dynamo and transported through the convection zone, eventually reach the solar atmosphere. Their accumulation in the solar corona leads to flares and coronal mass ejections. Since reconnections occur during the evolution of the flux tubes, the concepts of twist and magnetic stress become inappropriate. Magnetic helicity, as a well preserved quantity, in particular in plasma with high magnetic Reynolds number, is a more suitable physical quantity to use, even if reconnection is involved.     

Viewing radiation signatures of solar energetic particles in interplanetary space

A current serious limitation on the studies of solar energetic particle (SEP) events is that their properties in the inner heliosphere are studied only through in situ spacecraft observations. Our understanding of spatial distributions and temporal variations of SEP events has come through statistical studies of many such events over several solar cycles. In contrast, flare SEPs in the solar corona can be imaged through their radiative and collisional interactions with solar fields and particles. We suggest that the heliospheric SEPs may also interact with heliospheric particles and fields to produce signatures which can be remotely observed and imaged. A challenge with any such candidate signature is to separate it from that of flare SEPs. The optimum case for imaging high-energy (E > 100 MeV) heliospheric protons may be the emission of π⁰-decay γ-rays following proton collisions with solar wind (SW) ions. In the case of E > 1 MeV electrons, gyrosynchrotron radio emission may be the most readily detectible remote signal. In both cases we may already have observed one or two such events. Another radiative signature from nonthermal particles may be resonant transition radiation, which has likely already been observed from solar flare electrons. We discuss energetic neutrons as another possible remote signature, but we rule out γ-ray line and 0.511 MeV positron annihilation emission as observable signatures of heliospheric energetic ions. We are already acquiring global signatures of large inner-heliospheric SW density features and of heliosheath interactions between the SW and interstellar neutral ions. By finding an appropriate observable signature of remote heliospheric SEPs, we could supplement the in situ observations with global maps of energetic SEP events to provide a comprehensive view of SEP events.     

Features of mass supply and flows related with reconnection in the solar corona

Symmetrical broadening in the emission spectral lines is the ultimate observational effect of magnetic reconnection in the solar corona. Reconnection can create plasmas of very different temperatures and, hence, very different electrical conductivities in the corona. The electrodynamical effect of such a mass supply is considered. Electromagnetic expulsion force, different from Parker's well-known magnetic buoyancy force, can effectively balance gravity in prominences and generate fast vortex flows in the vicinity of fine threads inside prominences. The possibility of observing this effect from SOHO is discussed.     

结构隔绝内-外空间的流-热-固耦合仿真应用

为验证和指导高速飞行器的防隔热设计,准确地模拟气动热产生的热量穿透防隔热材料进而影响舱内温度空间分布和时间变化的过程,研究了一种同时求解机体外流场及气动热、机体结构传热及舱内流场温度场仿真计算方法,其中的传热方式包括热传导、热对流及热辐射。采用两套计算模型、两种求解器、一个数据交换文件的计算结构,构建了一种针对流场-热-结构的多场耦合分析方法,实现了对固体隔绝内外流场温度动态变化问题的仿真分析。最后通过计算实例验证了整套计算方法,得到的飞行器舱内温度变化特性能够用于指导高速飞行器的防隔热设计。     

Evolution of binaries with chemically peculiar primaries

The chemically peculiar (CP) stars are classified into subgroups based on the type of peculiarities. A significant fraction of these are known to be binaries. The faster evolution of the massive component leads to a white dwarf or a neutron star. Further evolution of the binary is analysed taking into consideration, the orbital parameters, effect of magnetic field, spectroscopic peculiarities and finally the statistics of CP binaries and Low Mass X-ray Binaries (LMXB).

The possible consequences of the evolution to lead to the formation of Magnetic Cataclysmic Variables (MCV) and LMXB are discussed.