浅谈短波天线的维护和保养

随着小功率短波实验台的不断建设，如何更好的利用和维护天线成了各短波实验台站关注的问题。本文以我台的垂直笼型天线为例进行介绍。垂直笼型天线在短波广播频段的中低频段具有较强的地波全向辐射能力，主要用于对城区和附近周边地区进行压制干扰。     

M1080B无心外圆磨床改进

M1080B无心外圆磨床砂轮及导轮宽度较窄,磨削轴承套圈外圆时,磨削效率低,托板架调整较为繁琐、皮带打滑、磨损较为严重。针对上述问题,提出了相应的解决办法,提高了磨削效率。     

Quantitative analysis of CO2 hydrate formation in porous media by proton NMR

Gas hydrate is a nonstoichiometric crystal compound formed from water and gas. Most nonvisual studies on gas hydrate are unable to detect how much water is converted to hydrates, and thus, the hydrate stoichiometry calculations are inaccurate. This study investigated the CO₂ hydrate formation process in porous media directly and quantitatively. The characteristics of the time-variable consumption of hydrate formation indicated a two-stage formation, hydrate enclathration and continuous occupancy. The enclathration stage occurred in the first 20 min of the formation when considerable heat is released. The continuous occupancy stage lasted longer than the hydrate enclathration because the empty cages in previously formed hydrates would also be occupied. The higher formation pressures can accelerate water consumption and increase cage occupancy. The compositions of completely formed CO₂ hydrates at 2.7, 3.0, and 3.3 MPa and 275.15 K were determined as CO₂·6.90H₂O, CO₂·6.70H₂O, and CO₂·6.49H₂O, respectively.     

Experiments on the thermal activation of hydrogen release of NaBH4-sodalites characterized by IR- and MAS-NMR spectroscopy

New results on the reactions of the (BH₄)-anion enclathrated in the cages of sodalites are reported. Hydrothermally synthesized NaBH₄-sodalites (?Na₈(BH₄)₂?[SiAlO₄]₆) always contain hydro-sodalite type cages (?Na₃(H₂O)₄?[SiAlO₄]₃). With increasing temperature dehydration occurs. Above 250 °C a limited reaction of the residual water is going on with (BH₄)-cage fillings releasing hydrogen and the appearance of certain borate specifications enclosed in the sodalite cages. The effect of a reaction of oxygen with the (BH₄)-anions in the sodalite-cages at temperatures above 400 °C is also shown. The degree of (BH₄)-conversion using wet and dry N₂ stream is further followed by IR and MAS NMR investigations. External supply of water largely enhances the degree of reaction, e.g. at 400 °C from 16% to 44% loss of (BH₄)-absorption intensity. However, ¹¹B MAS NMR shows 8% and 22% of a conversion of (BH₄)-cage fillings into new borate species in dry and wet N₂ stream, respectively. These lower values are explained by a loss of B-ions via formation and evaporation of BH₃ from the sodalite. Further evaluation of the ¹¹B MAS NMR spectra could resolve the formation of (B(OH)₃)^-, (BO(OH)₂)^-, (B(OH)₄)^- along with unreacted (BH₄)-species in the cages. ¹H-MAS NMR shows a ?3.8 ppm signal related to cage isolated (OH)^-, which suggests an initial reaction step via (H⁺ + BH₄^?) to (BH₃ + H₂). The formation of (B(OH)₃), however, also indicated sufficient water for a reaction of BH₃ releasing further hydrogen. The formation of (BH₃) could be observed in temperature dependent IR investigations at temperatures above 400 °C.     

建筑物金属构架对近区雷击的磁场屏蔽效果

基于电路法计算分析近区雷击时建筑物金属构架的磁场蔽效果，并进行了实验验证。研究表明，金属构架对脉冲磁场有屏蔽效果。磁场屏蔽系数以构架网格为单位呈阶梯式分布，其效果是使得建筑物内的磁场分布趋于均匀。     

长螺旋钻孔泵压混凝土振插钢筋笼施工工艺

介绍了长螺旋钻孔泵压混凝土振插钢筋笼施工工艺原理、施工方法及其特点,指出长螺旋钻孔中心泵压混凝土振插钢筋笼施工工艺是一种噪音小、无污染、施工机械化程度高的新型工艺,以推广该施工工艺。     

1m厚44 m深地下连续墙的施工工艺

结合地下铁道工程施工技术标准，重点阐述了1m厚44m深地下连续墙的施工方法，对幅段接头、钢筋笼的制作及吊装进行了较深入的研究和探讨，对类似施工具有一定的参考价值。     

长螺旋反插钢筋笼基础桩施工工艺

结合具体工程实例，介绍了后插钢筋笼成桩施工工艺，对各工艺流程的施工过程进行了详细阐述，并就关键工序的控制进行了探讨，分析了该工程采用长螺旋反插钢筋笼基础桩的施工效果，以推广该施工工艺。     

后植入钢筋笼灌注桩成桩施工工法的应用

万通中心工程东西长135.00m,南北宽100.00m,是由2幢23层和2幢24层的甲级写字楼组成,地下室4层。基坑深度分别为17.80m和18.85m,采用桩锚支护体系。护坡桩共计303根。由于施工场地小,采用直径为600mm的护坡桩,桩长21.80 m和22.85 m两种,钢筋笼主筋为25×14和25×18。1施工工法的选择场区位于永定河冲洪积扇的中下部,地形平坦。勘察所揭露的地层上部为人工填土,下部为第四系冲洪积物。目前桩基施工的工法较多,施工中选择的余地较大。因此要根据工程特点、现场平面布置、土层分布、地下水位、工期甚至工程造价的情况,选择适合的施工工法。由于…     

浅析钻孔灌注桩的施工技术和质量控制

结合运城绕城高速公路西南段路基、桥涵工程的钻孔灌注桩施工经验,就如何在各个施工环节中充分重视、精心施工、加强质量管理等问题进行了探讨,以便有效地对桩基施工质量加以控制。