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101.
This paper introduced systematically the present situation of the research on theory andtechnology for hard roof control of coal face in Chinese collieries.  相似文献   
102.
针对IFC(建设和设备管理行业工业基础类)标准表达建筑信息模型(BIM)的复杂性问题,分析了IFC标准体系构成的主要思想和BIM模型表达过程的核心环节。在研究IFC标准体系的基础上,梳理了各层之间的资源组织情况。利用一个矩形梁实例,从建筑实体对象、材料属性、关系组织和几何表达等方面,对IFC标准表达BIM模型的过程进行了深入分析,通过分析得到了IFC标准描述建筑信息模型的4个关键要素。  相似文献   
103.
Nano hexahydro-l,3,5-trinitro-l,3,5-triazine (RDX) was prepared using a bi-directional rotation mill and dried under different conditions (liquid, temperature and drying). It shows that the samples cake seriously and the particles grow up obviously by ordinary drying in different liquids at 70 ℃, which occurs again after vacuum drying. With the increase of temperature, the degrees of caking and aggregation are enhanced. Well dispersed sample maintaining constant particle size is extracted by supercritical drying, especially freeze drying. Furthermore, the me- chanical sensitivities of I-RDX, O-RDX and F-RDX, of which the average sizes are 88.03 μm, 15.32 μm and 0.16 μm, respectively, are evaluated. Compared with I-RDX, the friction, impact and shock sensitivities of O-RDX are slightly lower. However, the friction, impact and shock sensitivities of F-RDX are reduced by 30%, 99.0% and 59.9%, respectively.  相似文献   
104.
液压凿岩设备在我国地下矿山的应用   总被引:1,自引:0,他引:1  
十多年来,我国液压凿岩设备的研制和使用进展很大。地下矿山除了使用我国自行设计、研制的产品外,还使用根据技术引进合同生产的产品,也有一些矿山直接从国外购买,本文着重介绍这些液压凿岩设备在金属矿山、黄金和化工等矿山的应用情况。  相似文献   
105.
Uniform and beads free fibers of pristine syndiotactic PMMA (s-PMMA), isotactic PMMA (i-PMMA), and their blends in the ratio of s:i = 3:1, 1:1 and 1:3 were successfully prepared using the electrospinning technique. The tactic PMMA blend fibers showed unique thermal stability and glass transition temperatures compared to their pristine counterparts. An interesting endotherm peak was observed for the s:i = 1:3 electrospun fibers, which might indicate a complex formation between the two tactic PMMAs. Systematic surface functionalities study by attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) revealed the interactions between these two tactic PMMAs. Biocompatibility of tactic PMMA and their blend fibers was first time comparably investigated using HeLa as the model mammalian cell line; an intriguing observance was first revealed that the blend fibers showed better biocompatibility than both pristine ones, though the behind mechanism is not well understood yet.  相似文献   
106.
TiB2 powders were synthesized by borothermal reduction in nanoscale TiO2 with boron under vacuum. Reaction processes were investigated, and the effect of by‐product B2O3 was evaluated. Results showed that TiO2 was firstly reduced by boron to form TiBO3 and Ti2O3, and then to produce TiB2 and B2O3 with increasing temperature. The reaction processes of TiB2 powders synthesis included two‐step reduction in TiO2 by boron and the removal of B2O3. The presence of B2O3, which was previously reported as the most important factor in promoting the coarsening of ZrB2 and HfB2 powders by borothermal reduction, did not lead to significant coarsening of TiB2 powders. Due to the minor effect of B2O3, TiB2 powders with small particle size and low oxygen content could be prepared by direct heat treatment of TiO2 and boron at 1550°C under vacuum for 1 h. The particle size and oxygen content of synthesized TiB2 powders were ~0.9 μm and ~1.7 wt%, respectively.  相似文献   
107.
Ag2MoO4 ceramic was prepared by using the solid‐state reaction method, which could be sintered at 450°C for 2 h, having a relative permittivity of 8.08, a Qf value of 17 000 GHz, and a temperature coefficient of resonance frequency about ?133 ppm/°C. Ag2MoO4 ceramic was chemically compatible with silver but reacted seriously with aluminum to form (Ag0.5Al0.5)MoO4 during the sintering. The fitting of infrared spectra and the Shannon's additive rule were employed to study intrinsic dielectric behaviors of the ceramics at microwave region. Ionic displacive polarization and the electronic polarization contributed almost equally to the dielectric permittivity of the ceramic at microwave region. The Ag2MoO4 ceramics could be a good candidate for ultra‐low temperature co‐fired microwave devices.  相似文献   
108.
Inspired by pressure resistance welding of metallic materials, herein we describe how two MAX phases—Ti3SiC2 and Ti3AlC2—were successfully joined by a rapid electric current heating method in a pulsed electric current sintering furnace. No welding agent was employed and the total processing time was less than 6 min. When the bulk temperature of the joint couple exceeded 1070°C, good joints, with shear strength above 50 MPa, were achieved in both homo‐ and heterojunction joints.  相似文献   
109.
The presented study investigates the flow length and the corresponding fiber content distribution in the injection‐moulded natural fiber reinforced thermoplastics and its relation to fiber type and processing parameters such as injection pressure, temperature, injection rate and mould tempering by increasing die temperature. In this research, polypropylene compounds with nominally 30 wt % hemp and sisal fibers are investigated. The influence of the injection pressure (500 and 1000 bar), melt temperature (180°C, 200°C, and 220°C), and die temperature (23°C and 80°C) on the fiber content distribution all over the sample is investigated. An increasing linear trend of fiber content along the spiral length is observed as an evidence of a fiber/polymer multiflow system. A pattern for fiber content distribution with respect to the fiber length along the injected spiral can be distinguished, where the longer fibers are usually found at the end of the injected part and the shorter fibers remain near mould entrance point. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39861.  相似文献   
110.
This study mainly focuses on the formation of isotactic polypropylene (iPP) blend morphologies with microspheres and distinct bead–string spherulites. iPP microspheres have been prepared by a simple and convenient strategy through either an isothermal or a nonisothermal crystallization process based on the macrophase‐separated structure in molten state of iPP/olefin block copolymer (OBC) blend. The dimension of the iPP spheres can be adjusted easily from about 1 µm to >10 µm by controlling the compatibility and annealing conditions. It was found that any of the following three parameters, the molecular structure of OBC (particularly the octene content), molecular weight of iPP, and annealing condition can be rescaled with others in controlling the dimension of the iPP microspheres. The mechanism of the formation of iPP microspheres was studied in detail. Surprisingly, the typical spinodal decomposition morphology with interconnected or thin sheet structure is the precursor of these microspheres. During the subsequent annealing process, it breaks up and further coarsens into spherical structure. In addition, distinct spherulites with a bead–string substructure have been obtained during the isothermal crystallization. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40863.  相似文献   
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