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811.
利用对称性计算第二类曲线积分与曲面积分的方法 总被引:2,自引:1,他引:1
由于第二类曲线积分与曲面积分涉及到方向性问题,因此利用对称性来计算较为困难,文中给出了利用对称性计算第二类曲线积分与曲面积分的方法,并证明了方法的可行性,并通过实例表明,此方法有时能起到简化计算的作用. 相似文献
812.
Air–sea fluxes in the Caribbean Sea are presented based on measurements of partial pressure of CO2 in surface seawater, pCO2sw, from an automated system onboard the cruise ship Explorer of the Seas for 2002 through 2004. The pCO2sw values are used to develop algorithms of pCO2sw based on sea surface temperature (SST) and position. The algorithms are applied to assimilated SST data and remotely sensed winds on a 1° by 1° grid to estimate the fluxes on weekly timescales in the region. The positive relationship between pCO2sw and SST is lower than the isochemical trend suggesting counteracting effects from biological processes. The relationship varies systematically with location with a stronger dependence further south. Furthermore, the southern area shows significantly lower pCO2sw in the fall compared to the spring at the same SST, which is attributed to differences in salinity. The annual algorithms for the entire region show a slight trend between 2002 and 2004 suggesting an increase of pCO2sw over time. This is in accord with the increasing pCO2sw due the invasion of anthropogenic CO2. The annual fluxes of CO2 yield a net invasion of CO2 to the ocean that ranges from − 0.04 to − 1.2 mol m− 2 year− 1 over the 3 years. There is a seasonal reversal in the direction of the flux with CO2 entering into the ocean during the winter and an evasion during the summer. Year-to-year differences in flux are primarily caused by temperature anomalies in the late winter and spring period resulting in changes in invasion during these seasons. An analysis of pCO2sw before and after hurricane Frances (September 4–6, 2004), and wind records during the storm suggest a large local enhancement of the flux but minimal influence on annual fluxes in the region. 相似文献
813.
采用粉末冶金技术,制备了铜基陶瓷强化摩擦材料.通过定速摩擦试验机,测试了摩擦压力、摩擦速度和干湿条件对材料摩擦磨损性能的影响.结果表明:在干摩擦条件下,系数大于0.3,摩擦系数稳定.摩擦压力在0.5~0.6 MPa范围时,摩擦系数处于较低值.随摩擦压力的变化,磨损率变化不大.当摩擦速度为2 000 r/m in时,摩擦系数最大.湿摩擦条件下摩擦系数低于干摩擦条件下的摩擦系数. 相似文献
814.
815.
结合几种常用上面层沥青混合料的路用性能试验数据,讨论了各类沥青混合料的路用性能的优劣,并提出适用于湖北地区高等级公路沥青路面上面层的沥青混合料类型。 相似文献
816.
50年来我国铁路车辆闸瓦(闸片)的发展 总被引:1,自引:0,他引:1
介绍了我国铁路车辆闸瓦(闸片)50年来的发展,对不同材质的闸瓦(闸片)从试验到应用的情况做了综述。 相似文献
817.
3D轴焊接构架式转向架重车过曲线轮轨横向力超标原因分析 总被引:3,自引:0,他引:3
根据转向架结构理论分析和动力学仿真计算,对3D轴焊接构架式转向架通过曲线时重车轮轨横向力偏大的原因进行分析。认为3D轴焊接构架式转向架的主、副摩擦面摩擦系数偏大,使重车通过曲线时斜楔处于卡死状态,轮对轴箱纵向呈刚性定位,从而导致重车过曲线时轮轨横向力偏大。提出只要将斜楔副摩擦面的摩擦系数减小至0.1左右,则在轮轨纵向蠕滑力的作用下,轴箱斜楔纵向就不会被卡死,而且轮对纵向定位刚度只由轴箱弹簧提供,可以有效地降低重车过曲线时的轮轨横向力。线路动力学试验证明理论分析和仿真计算的结果是正确的。 相似文献
818.
819.
船体B样条曲面的数学描述及计算机方法 总被引:10,自引:0,他引:10
叙述了三次B样条曲面的特点、数学描述、船体曲面片的拼接和曲面边界的处理,最后给出船体曲面设计产例,证明所述方法的正确法。 相似文献
820.
Climate changes in the subtropical South-east Atlantic turn out to be well described by the St. Helena Island Climate Index (HIX) and observed fluctuations are in good agreement with inter-decadal variability of the entire South Atlantic Ocean. Year-to-year variations of the averaged austral winter HIX (July–September), representative of the main upwelling season, were compared with (i) corresponding averages of the geostrophic alongshore component of the south-east trade wind (SET) between St. Helena Island in the south-west and Luanda/Angola in the north-east, (ii) the meridional distribution of surface waters colder than 13 °C to characterise intense Benguela upwelling (IBU), and (iii) the meridional position of the Angola-Benguela Frontal Zone (ABFZ) determined by means of sea surface temperature images for offshore distances between 50 and 400 km. Temporal changes of these parameters were investigated and showed that the frequency of consecutive years of strong and relaxed Benguela upwelling is characterised by a quasi-cycle of about 11–14 years. It is proposed that the index of the winter HIX may be used as a ‘surveyor’s rod' to describe interannual changes in the Benguela upwelling regime as well as those of the embedded marine ecosystem. 相似文献