Study of electromagnetic characteristics of stress distribution and sudden changes in the mining of gob-surrounded coal face

The incidence of dynamic coal or rock disasters is closely related to the distribution of stress in the surrounding rock. Our experiments show that electromagnetic radiation （EMR） signals are related to the state of stress of a coal body. The higher the stress, the more intense the deformation and fractures of a coal body and the stronger the EMR signals. EMR signals reflect the degrees of concentrated stress of a coal body and danger of a rock burst. We selected EMR intensity as the test index of the No.237 gob-surrounded coal face in the Nanshan coal mine. We tested the EMR characteristics of the stress distribution on the strike, on the incline and in the interior of the coal body. The EMR rule of rock bursts, caused by sudden changes in stress, is analyzed. Our research shows that EMR technology can be not only used to test qualitatively the stress distribution of the surrounding rock, but also to predict a possible occurrence of rock burst. Based on this, effective distress measures are used to eliminate or at least weaken the incidence of rock bursts. We hooe that safetv in coalmines will be enhanced.

An Extended Model for Coexistence of Superconductivity and Paramagnetism in High-T_c Superconductors

In the present work, the total magnetization in superconducting state is separated into critical state and paramagnetic components in terms of an H（x）-dependent magnetic flux density. Utilizing this model, we reproduce successfully M-H curves measured by Sandu et al. [Phys. Rev. B 74 （2006） 184511] and Sandu et al. [J. Supercond. Incorp. Novel Magn. 17 （2004） 701] for different forms of Jc.

Effect of liquid-solid ratio on the morphology,structure,conductivity,and electromagnetic characteristics of iron particles

Using a ball-milling technique,polymorphous iron particles were prepared by changing only the liquid-solid ratioλ.Effects of λon their morphology,structure,conductivity,and electromagnetic properties were studied.The results show that an increase ofλfrom 0 to 0.25 causes a nonlinear decrease of the conductivity in the ranges of 88.50-2.25 S cm-1 and a regular variation of the electromagnetic parameters,corresponding to the as-obtained iron particles.This is ascribed to a combination of the increased shape anisotropy and the decreased fresh surface with active atoms deriving from the weakened welding-on action and the enhanced micro-malleation action in the ball-milling process.Hereinto,the iron flakes formed at wet-milling with λ=0.08-0.25 have lower conductivity,higher permittivity and permeability,and more excellent absorption property compared with the irregular iron particles obtained at dry-milling withλ=0.It is a consequence of the synergistic effect of dielectric relaxation loss,exchange energy and conductance loss originating from the flake-shape structures.This indicates that the morphology,structure,conductivity,and electromagnetic properties of the products can be effectively controlled by changingλ.

Observational connection between local high-temperature phenomena within magnetic clouds and the Sun

Magnetic clouds(MCs) frequently show abnormal high-ionization states of heavy ions. The abnormal high-charge distributions are related to the coronal temperature of their source regions. We examined the plasma and magnetic field data of 74 MCs observed by the Advanced Composition Explorer from February 1998 to December 2008. We determined that 14 of the 74 events showed local high-temperature phenomena. We analyzed the correlation between proton temperature and O7/O6ratio(or high mean Fe charge state ?Fe?) within the local high-temperature regions in the 14 MCs. Results show that proton temperature and O7/O6 ratio(or high mean Fe charge state) had good correlations in nine MCs, but had no evident correlation in the other five MCs. The local high-temperature phenomena within the nine MCs have resulted from the Sun.

NiaSi2O5（OH）4 Multi-Walled Nanotubes with Tunable Magnetic Properties and Their Application as Anode Materials for Lithium Batteries

Highly crystalline and thermally stable pure multi-walled Ni3Si2O5（OH）4 nanotubes with a layered structure have been synthesized in water at a relatively low temperature of 200-210 ℃ using a facile and simple method. The nickel ions between the layers could be reduced in situ to form size-tunable Ni nanocrystals, which endowed these nanotubes with tunable magnetic properties. Additionally, when used as the anode material in a lithium ion battery, the layered structure of the Ni3Si2O5（OH）4 nanotubes provided favorable transport kinetics for lithium ions and the discharge capacity reached 226.7 mA.h.g-1 after 21 cycles at a rate of 20 mA.g-1, Furthermore, after the nanotubes were calcined （600 ℃, 4 h） or reduced （180℃ 10 h）, the corresponding discharge capacities increased to 277.2 mA.h.g-1 and 308.5 mA.h.g-1, respectively.

High-permittivity Sb_(2)S_(3) single-crystal nanorods as a brand-new choice for electromagnetic wave absorption

The application of antimony sulfide(Sb_(2)S_(3))has been limited mainly to the energy storage and photoelectric conversion fields.However,in this work,the application of Sb_(2)S_(3) is extended to the field of electromagnetic(EM)wave absorption for the first time.High-permittivity Sb_(2)S_(3) singlecrystal nanorods were prepared successfully and exhibited excellent performance,with a low reflection loss of -65.9 dB(13.0 GHz,3.8 mm)and an ultra-wide effective absorption bandwidth of 9.5 GHz(8.5-18.0 GHz,4.1 mm).After excluding the general absorption mechanisms,including conductive losses,interfacial polarization,and dipole polarization,the distinctive single-crystal volume polarization affected by shape anisotropy was proposed.This work not only meets the challenge of a single-component dielectric material design but also introduces a new concept for construction of efficient dielectric EM wave absorption material.

Controlled synthesis and shape-dependent electromagnetic wave absorption characteristics of porous Fe_3O_4 sub-micro particles

Porous Fe3O4 sub-micro particles with sphere-like, cube-like and walnut-like morphologies were obtained by a two-step process, and the electromagnetic properties of the Fe3O4 particle/wax composites were investigated. The reflect loss was less than -20 dB for all of the composites in different frequency ranges. The cube-like and walnut-like Fe3O4 composites exhibit improved complex permittivity and permeability and dual-frequency and wide bandwidth absorption characteristics, which is mainly attributed to the larger shape anisotropy. Such a high absorption property indicates that these porous Fe3O4 particles with various morphologies are very promising for electromagnetic wave absorptive materials.