共查询到20条相似文献，搜索用时 31 毫秒
1.
加快模型试验中水的渗流速率对库岸滑坡研究意义重大。考虑滑坡渗流特性,基于电磁驱动原理,在滑坡模型中施加相互垂直的电场、磁场,推导出孔隙水受力公式,根据电渗固结理论,推导水分迁移速率v与电压Ve、磁场强度B的关系式,进而获得时间相似比,实现了通过电磁场强度来控制滑坡模型水分迁移速率,改进模型试验,为研究库水位升降对滑坡的影响提供条件。通过试验进行验证：电磁场对水分迁移速度的影响具有显著效果,且电压大小对模型的稳定渗流场影响较小。说明在不改变模型材料参数的条件下,改变磁场强度和电压可获得任意孔隙水的渗流速度,为研究库水位波动条件下的滑坡演化机制奠定基础。 相似文献
2.
D. V. Klepikov B. P. Filippov A. Ajabshirizadeh Yu. V. Platov 《Astronomy Reports》2006,50(10):834-841
The behavior of magnetic foci—intersection points of tangents to ray structures in the polar corona of the Sun—is studied. This behavior reflects the evolution of the large-scale magnetic field near the poles, and is one of only a few sources of information on the polar magnetic field of the Sun. For the first time, the positions of the magnetic foci are plotted as a function of the solar-cycle phase for a full cycle, based not only on total-eclipse images but also on daily coronal observations in the FeIX and FeX (171 Å) lines carried out with the EIT telescope on the SOHO satellite. The temporal behavior of the foci over a cycle differs appreciably from that inferred from isolated observations during eclipses. The curve agrees fairly well with the model of the global-field evolution suggested by us previously. 相似文献
3.
The evolution of a system of electrons with a given initial distribution in an external magnetic field is considered. An equation describing the evolution of the electron distribution function in a uniform magnetic field is derived for the case of arbitrarily relativistic electrons, and an exact solution to this equation is found. Asymptotics of this solution corresponding to the cases of synchrotron radiation and relativistic dipole radiation are calculated, and the evolution of the radiation spectra for these limiting cases is analyzed. The curvature of the magnetic field lines is taken into account phenomenologically, which demonstrates the presence of an exponential dependence in the case of synchrotron radiation. 相似文献
4.
地磁场源于地核流体的运动,至少已有约35亿年历史.地磁场的起源及演化一直是地球科学研究的前沿领域之一,这是因为它既是地球宜居环境的重要保障,也是探究地球系统各圈层联系的重要途径.本文重点围绕保留在岩石中的"深时"古地磁场记录,分析在地球内部磁场的形成与维持、地磁场极性倒转、以及地磁场强度变化等古地磁场研究三个方面的主要... 相似文献
5.
古地磁学是一门典型的交叉学科,通过综合地质学、地球物理学、环境科学等学科相关方法,分析天然样品中记录的磁学信息,深入研究地磁场演化、地球动力学过程、古环境与古气候演化等.自20世纪中叶以来,古地磁学在各研究领域得到快速发展,通过进一步与其他学科交叉,衍生出诸多新兴方向.首先回顾了古地磁学的发展历史与基础研究领域.在此基础上,重点介绍了高精度卫星磁测与相关研究新领域、月球与火星磁学研究的新进展.同时,对古地磁学与高精度磁测等方法集成在地磁场演化、板块构造、深部结构、月球磁场演化、火星磁场及环境演化等方面的综合应用进行了讨论.最后,对古地磁学未来的潜在研究方向进行了展望. 相似文献
6.
A physical model and two-dimensional numerical method for computing the evolution and spectra of protostellar clouds are described. The physical model is based on a system of magneto-gas-dynamical equations, including ohmic and ambipolar diffusion, and a scheme for calculating the thermal and ionization structure of a cloud. The dust and gas temperatures are determined when calculating the thermal structure of the cloud. The results of computing the dynamical and thermal structure of the cloud are used to model the transfer of continuum and molecular-line radiation in the cloud. Results are presented for clouds in hydrostatic and thermal equilibrium. The evolution of a rotating magnetic protostellar cloud that is compressed starting from a quasi-static equilibrium state is also considered. Spectral maps for optically thick lines of linear molecules are analyzed. The influence of the magnetic field and rotation can lead to a redistribution of angular momentum in the cloud and the formation of a characteristic rotational-velocity structure. As a result, the distribution of the velocity centroid of the molecular lines can acquire an hourglass shape. It is planned in future to use the developed program package and a model for the chemical evolution of clouds to interpret and model in detail observed starless and protostellar cores. 相似文献
7.
E. A. Mikhailov 《Astronomy Reports》2017,61(9):739-746
It is currently generally believed that magnetic fields in the disks of spiral galaxies are generated by the dynamo mechanism, which is based on the joint action of differential rotation and the alpha effect, associated with turbulent motions in the interstellar gas. Together with their disks, outer rings are also encountered in galaxies, where magnetic fields may be present. In earlier studies, the generation of magnetic fields has been described in a planar approximation, whose essence is that the size of rings perpendicular to the plane of the galaxy is much smaller than their size in the radial direction. However, it is plausible that these sizesmay sometimes be comparable, so that it would be more logical to suppose that a ring has a toroidal form. A model for a dynamo in a toroidal ring is constructed in this study. This model describes the magnetic field using two functions, corresponding to the toroidal component of the field and the part of the vector potential characterizing its poloidal component. The possible generation of magnetic field in various cases is shown, with both quadrupolar symmetry (close to the fields obtained in the planar approximation) and dipolar symmetry (when two layers with oppositely directed magnetic fields form in the ring). The parameter values for which the generation of fields with one or the other type of symmetry is possible are estimated. The results can also be used to describe the evolution of the magnetic fields in other toroidal astrophysical objects. 相似文献
8.
Yu. V. Glagolevskij 《Astronomy Reports》2013,57(1):56-64
Measurements of the longitudinal magnetic field of the CP star HD 62140 with high accuracy (σ ～ 50 G) are used to construct a magnetic-dipole model for this star. The model describes the observed phase dependence of the field very well, supporting the idea that CP stars have dipolar magnetic fields. Based on an analysis of the CP stars HD 32633 and HD 142301, which were earlier suggested to have dipoles shifted perpendicular to the dipole axis, it is concluded that the only possible models in this case have one or two shifted dipoles, with the distance between the monopoles being comparable to the stellar radius. Such configurations may occur as a consequence of deformations of the field in early stages of the star’s evolution, due to the accretion of higher-mass objects or a merger with another component, as well as the influence of a convective core. 相似文献
9.
Analysis of long-term measurements of solar magnetic fields and the flux of UV radiation from the Sun indicates a cause-effect relationship between activity complexs, their residual magnetic fields, and coronal holes. A comparison of the background magnetic fields of the Sun and the evolution of former activity complexes reveals unipolar magnetic regions that form after the decay of these complexes. The latitude and time evolution of unipolar magnetic regions in solar cycles 21–24 is studied. A North-South asymmetry in solar activity is manifest in the distribution of unipolar regions migrating toward higher latitudes. It is shown that, when residual magnetic fields of the opposite polarity reach the polar regions, this leads to a sign change of the polar magnetic field and a decrease in the area of polar coronal holes, or even their complete disappearance. These interactions can explain the triple sign change of the polar magnetic field of the Sun in cycle 21 and the short-term polarity reversals observed in 2010 and 2011. 相似文献
10.
南海西北部壳体新构造运动及其演化模式 总被引：1，自引：0，他引：1
本文根据南海西北部壳体的地形地貌、重磁场异常和地壳结构特征和岩石圈动力学环境，对穿过莺歌海盆地和西沙海槽的地震剖面进行解释。把本区新构造运动类型划分为拉张型、挤压型、平移剪切型和旋动型，并对其构造演化模式进行了初步分析。结果发现，南海西北部在漫长的地质历史中，曾经历复杂的动力学演变过程，从中生代到新生代，本区在周缘岩石圈壳体作用下，经历挤压、拉张、复杂应力调整和现代挤压收缩四个演化阶段。 相似文献
11.
We present the results of two-dimensional calculations of a magneto-rotational (MR) supernova explosion with a collapsing core for various core masses, rotational angular momenta, and magnetic-field configurations. It is shown that the MR mechanism produces an explosion energy that corresponds to observed values. The form of the explosion depends substantially on the initial configuration of the magnetic field. MR instability develops during the evolution of the magnetic field in an MR supernova explosion, resulting in an exponential increase of all components of the magnetic field, thereby substantially decreasing the time scale of the MR explosion. The energy of the supernova increases with the core’s mass and initial rotational energy. 相似文献
12.
地质力学磁力模型试验利用电磁力（场）模拟重力（场）的原理研究地质力学工程问题,采用的相似材料由铁磁材料与岩土体混合而成。铁磁材料在磁场中的受力方向和大小与所处空间的磁通密度梯度的大小和方向有关,为了模拟均匀的重力场,需要得到在一定空间范围内磁通密度梯度大小相同、方向单一的磁场。根据电磁学基本原理,构建了3种磁路形式以获得磁通密度梯度相对均匀的磁场,对磁力模型试验相似材料进行加载。对比3种磁路,在最佳试验区内开放式磁路对磁场的利用率更高,所以在电流相同条件下等到的磁通密度梯度的量值也更大。与另两种磁路形式相比,尽管半开放式磁路在重量和工作效率上的性能不及开放式和封闭式磁路,但其最佳试验空间的磁通密度梯度的均匀性最好,误差在5%以内,半开放式磁路可以作为地质力学磁力模型试验的磁场发生装置。 相似文献
13.
The spins of supermassive black holes in FR I and FR II radio galaxies are estimated using two models for the generation of the relativisitic jets, based on the Blandford–Znajek and Blandford–Payne mechanisms: the hybrid model of Meier and a flux-trapping model. The magnetic field at the event horizon is estimated assuming equipartition between the energy densities of the magnetic field and the accreting material. The magnetic field near the inner edge of the accretion disk is estimated assuming equipartition between the magnetic pressure and the radiation pressure, and also assuming proportionality between the magnetic field and the spin. In the case of FR I objects, both mechanisms for the generation of the jets (the hybrid model of Meier and a flux-trapping model) are efficient. For the FR II objects, equipartition between the energy densities of the magnetic field and the accretion flow facilitates stronger retrograde rotation of the supermassive black hole. Plots of spin versus mass suggest a predominantly chaotic character for the accretion in both types of radio galaxies. 相似文献
14.
东北印度洋地理位置独特,其沉积物记录了青藏高原隆升及孟加拉扇的“源-汇”过程、印度季风与东亚季风的“海-气”交互作用、印-太暖池热传输的演变与高纬气候之间的相位关系等关键信息,是喜马拉雅地区“构造-气候-沉积”耦合演化的良好记录载体,是探讨多圈层相互作用、探索古气候与古环境演化的理想“窗口”。本文系统总结了近年来有关东北印度洋季风与表层环流特征、沉积物组成及物源、气候环境演化以及环境磁学记录等方面的研究进展。分析表明,东北印度洋为典型的季风风场,表层环流受季风影响强烈,夏季和冬季环流差异明显。沉积物类型丰富,包括河流输运而来的陆源碎屑、钙质和硅质为主的生物沉积以及火山物质等。但目前对于该区域的沉积物的具体组成、“源-汇”过程、迁移历史、季风演化与青藏高原隆升、高纬气候变化之间相互关系等方面的认识尚存在较大的分歧。同时,受样品获取难度大、磁学信号稀释严重等因素的限制,环境磁学作为一种在示踪沉积物物质来源、恢复古气候和古环境等方面被普遍认可的技术手段,在东北印度洋区并没有得到充分的发挥与应用。因此,未来需要在前人研究的基础上,将目光向东北印度洋更南、更深处延伸,对其“源-汇”过程进行全面分析。在研究方法上进一步拓展,采用更高精度的技术手段提取磁学信号,加大环境磁学的应用,寻找有效的替代性指标,解决该地区季风演化、古海洋环境变化等气候环境问题,为该地区环境气候研究提供新认识。并尝试开展地磁场长期变化(paleosecular variation, PSV)研究,建立东北印度洋的PSV记录,辅助修正全球地磁场模型,探究地球深部动力过程。 相似文献
15.
G. A. Shul’man 《Astronomy Reports》2011,55(3):267-274
A Fermi-gas model for the atomic nucleus in the presence of a quantizing magnetic field is considered. The energy of the magnetized
neutrons is determined taking into account the Pauli paramagnetism, and the energy of the magnetized protons taking into account
Landau diamagnetism and Pauli paramagnetism. To determine the characteristics of the proton-gas energy in a quantizing magnetic
field, we use a model for the proton motion in which the initial energy of the proton and the magnetic field strength enable
estimation of the maximum Landau quantum number. The latter characterizes the proton motion perpendicular to the direction
of the magnetic field. Due to the occupation of Landau levels by protons, it is possible to estimate the kinetic energy for
continuous motion along the magnetic field from zero to a certain finite value. As a result, the magnetic field of a certain
strength facilitates neutron evaporation from the nucleus and increases the stability of the protons in the nucleus. 相似文献
16.
The evolution of photospheric velocities from the first minutes after the emergence of fresh magnetic flux and the formation
of the first pores in active region NOAA 10488 is studied with a time resolution of 1 min and spatial resolution of 4″. The
emerging magnetic flux of a major active region is initially a bundle of magnetic-flux loops. Some of these loops erupt through
the system of supergranular cells with speeds of up to 1 km/s within 15–25 min and form pores and small spots. It is suggested
that the development of a pore represents the emergence of a horizontal magnetic field, which is converted into elements with
a strong vertical magnetic field. The region of ascending plasma initially coincides with the zero line of a bipolar magnetic
pair. Downflow and upflow regions are related to and appear with the development of pores. During the first hours of their
evolution, the trailing-polarity pores exhibit downflows with mean speeds of ∼500 m/s, while upflows with speeds of ∼250 m/s
dominate near the leading-polarity pores. It is concluded that a matter flow from the leading to the trailing end is present
in the rising loop of a magnetic flux tube, in agreement with well-known numerical-simulation results. The flow that develops
in the magnetic-flux tube erupting through the convection zone persists when pores and small spots emerge in the photosphere,
at least during the first hours of their evolution. 相似文献
17.
M. Yu. Reshetnyak 《Doklady Earth Sciences》2018,478(2):224-227
A 2-D mean field geodynamo model with the algebraic form of nonlinearity is considered. The geostrophic alpha-effect and differential rotation are taken from the 3-D models of convection in the liquid core of the Earth. The analysis reveals that these both are located in different spatial areas, and their correlation is no more than ten percent. The model allows typical Z-distributions of the poloidal magnetic field to be generated within the Taylor cylinder. On the surface, this field configuration corresponds to the magnetic dipole. Because of the spatial homogeneity of the magnetic field in the cylinder, dissipation of the field is small, which causes its greater amplitude in this region. Owing to the simple form of alpha-effect quenching by the magnetic field, the model can be used to generate a magnetic field over geological times. 相似文献
18.
The evolution of the angle between the magnetic moment and rotation axis of radio pulsars (inclination angle) is considered taking into account the presence of a non-dipolar magnetic field at the neutron-star surface and superfluid neutrons in the stellar interior. It is assumed that the total loss of angular momentum by the pulsar can be represented as a sum of magnetodipole and current losses. The neutron star is treated as a two-component system consisting of a charged component (including protons and electrons, as well as the crust, which is rigidly coupled with them, and normal neutrons) and a superfluid core. The components interact through scattering of degenerate electrons on magnetized Feynman-Onsager vortices. If a superfluid core is absent, then, in spite of the presence of stable equilibrium inclination angles, the rate with which these are reached is so slow that most pulsars do not have sufficient time to approach them during their lifetimes. The presence of superfluid neutrons results, first, in faster evolution of the inclination angle and, second, in the final stage of the evolution being either an orthogonal or a coaxial state. The proposed model fits the observations better in the case of small superfluid cores. 相似文献
19.
在某些浅水区域中, 常有大量工程障碍, 如磁性柱状体。依据磁性柱状体的特点, 从顺轴磁化无限延深柱状磁性体这一简化数学模型的磁场分析入手, 进而对更近实际的顺轴磁化有限延深柱状磁性体的磁场及其梯度场的分布规律进行讨论, 并据此提出了采用水平磁梯度测量法对磁性柱状体磁特性实施探测的可取途径。 相似文献
20.
The global component of the large-scale magnetic field is identified using two methods applied to Stanford Observatory data on the photospheric magnetic field obtained in 1976–2000. Two significantly different phases are observed in the evolution of the global magnetic field detected during the 11-year cycle. Phase I includes the cycle growth and maximum, while Phase II includes the cycle decay and minimum. During Phases I and II of the 11-year cycle, two different processes dominate both the magnetic-field generation and the solar activity as a whole. At lower latitudes, Phase I demonstrates a longitudinal splitting of the magnetic field, which takes the form of stripes of opposite polarities located parallel to the equator. The long dimensions of these stripes are grouped near 90° and 180°. The global magnetic field rotates as a rigid body with a period that is appreciably shorter than the Carrington-rotation period and reaches about 27.225 days. During reversals of the polarity of the global magnetic field, the field displays opposite signs in antipodal longitude intervals with lengths of about 135°. Thus, the equatorial dipolar field is clearly manifest during Phase I. Transitional longitude intervals with widths of 45° located between 135° intervals correspond to the positions of active longitudes of sunspots, indicating a close relationship between the global and local magnetic fields. 相似文献