目的:探究阳极经颅直流电刺激(a-tDCS)结合抗阻训练对健康成年人下肢力量和无氧功率的训练效果。方法:选取30名有丰富抗阻训练经验的(19.70±1.47)岁健康成年人,并随机分配到复合训练组(a-tDCS+抗阻训练,n=15)和单一训练组(n=15);2...目的:探究阳极经颅直流电刺激(a-tDCS)结合抗阻训练对健康成年人下肢力量和无氧功率的训练效果。方法:选取30名有丰富抗阻训练经验的(19.70±1.47)岁健康成年人,并随机分配到复合训练组(a-tDCS+抗阻训练,n=15)和单一训练组(n=15);2组受试者每周均进行2次颈后杠铃深蹲训练,复合训练组需要在每次深蹲训练前进行20 min a-tDCS(电流2mA)干预,训练时长为5周;采用双因素重复测量方差分析(干预方式×测试阶段),探讨上述自变量对受试者的下肢最大力量和无氧功率指标的影响,包括峰值功率(PP)、平均功率(AP)以及功率衰减(PD)。结果:5周训练干预后,2组受试者后测的1RM深蹲成绩相较前测均有显著提高(p<0.05),且复合训练组受试者1RM深蹲成绩的提高效果显著于单一训练组〔复合训练组(19.20±7.38)kg对比单一训练组(12.27±8.66)kg,p<0.05〕;复合训练组和单一训练组的PP、AP、PD在干预前后的差异均不显著(p>0.05)。结论:a-tDCS结合抗阻训练对下肢肌力的增强作用显著于单一抗阻训练,a-tDCS可以作为健康成年人增强下肢力量的一种辅助训练方法。展开更多
鲁汶流是东印度洋海区低盐暖水向极传输的主要途径,不仅显著调节低纬-高纬海区间的温盐分配,也极大影响澳大利亚西岸降水,理解其在地质历史时期的变化及影响因素,对于认识区域和全球气候变化具有重要意义。本次研究将鲁汶流区采集的SO18...鲁汶流是东印度洋海区低盐暖水向极传输的主要途径,不仅显著调节低纬-高纬海区间的温盐分配,也极大影响澳大利亚西岸降水,理解其在地质历史时期的变化及影响因素,对于认识区域和全球气候变化具有重要意义。本次研究将鲁汶流区采集的SO18588孔岩芯上部63 cm沉积物作为研究材料,并以1 cm为间隔对其进行采样,共计获得63个沉积物样品。通过对这些沉积物样品进行研究,发现在SO18588站处浮游有孔虫热带表层水种Trilobatus sacculifer的相对丰度比浮游有孔虫热带-亚热带表层水种Globigerinoides ruber的相对丰度更适合被用于指示鲁汶流强度变化;之后,利用浮游有孔虫热带表层水种T.sacculifer的相对丰度,重建了32 ka B. P.以来鲁汶流的强度变化,并与已发表的古海洋和古气候学记录进行了对比。结果显示,鲁汶流强度的冰期-间冰期变化受海平面升降和类厄尔尼诺-南方涛动气候态共同调控:冰期时海平面下降,类厄尔尼诺态强化,导致鲁汶流减弱;间冰期时,海平面上升,类拉尼娜态发育,造成鲁汶流增强。9.5~0 ka B. P.期间,鲁汶流强度的持续弱化,可能归因于澳洲冬季风的减弱和早全新世类拉尼娜格局向现代类厄尔尼诺格局转变所造成的厄尔尼诺事件频发;9.5 ka B. P.左右鲁汶流强度事件性地突然减弱,可能与海平面上升所导致的卡里马塔海峡贯通、印尼穿越流表层流被抑制有关。展开更多
Acoustic Doppler current profiler （ADCP） receives echoes from sound scatterers, then their speed is calcu- lated by the Doppler effect. In the open ocean, most of these backscatterers are from the plankton. The soun...Acoustic Doppler current profiler （ADCP） receives echoes from sound scatterers, then their speed is calcu- lated by the Doppler effect. In the open ocean, most of these backscatterers are from the plankton. The sound scatterers descend down to depth at around dawn, their mean speed is 2.9 cm/s, then they ascend up to the surface layer at around dusk with a mean speed of 2.1 cm/s, in the Luzon Strait. The descending speed is faster, which suggests that this zooplankton population may accelerate its downward migration under the action of the gravity. The vertical distribution of a mean volume backscattering strength （MVB- S） in the nighttime has two peaks, which locate near the upper and lower boundary layers of halocline, respectively. However, the backscatterers only aggregate near the surface layer in the daytime. The diel ver- tical migration （DVM） of sound scatterers has several characteristic patterns, it is stronger in summer, but weaker in winter, and the maximum peak occurs in September. The DVM occurrence is synchronous with the seawater temperature increasing at around dawn and dusk, it may affect the ocean mixing and water stratification,展开更多
【目的】旨在实现压铸镁合金高质量焊接,其是拓宽镁合金在工业领域应用的关键。【方法】为改善压铸镁合金常规交流非熔化极惰性气体保护焊(Tungsten inert gas welding,TIG)接头质量,利用超声频电信号激发电弧,产生作用于电弧及熔池的超...【目的】旨在实现压铸镁合金高质量焊接,其是拓宽镁合金在工业领域应用的关键。【方法】为改善压铸镁合金常规交流非熔化极惰性气体保护焊(Tungsten inert gas welding,TIG)接头质量,利用超声频电信号激发电弧,产生作用于电弧及熔池的超声,对比研究超声电弧对AZ31B压铸镁合金平板对接接头的成形、金相组织及力学性能的影响。【结果】结果表明,超声电弧可以提高焊缝成形性能、细化焊缝组织以及提高接头的强度和塑性。与常规TIG相比,施加超声激励扩展了焊缝中下部熔宽,使得接头表面和边界熔化均匀,焊缝晶粒得到细化。同时,抑制了第二相的聚集和长大,促进其在焊缝中的均匀分布;接头的平均抗拉强度为212 MPa,达到母材的80.9%,断后伸长率由5.1%增高至8.5%;未施加超声电弧的接头拉伸试样在焊缝中断裂,引入超声电弧的接头拉伸试样在热影响区断裂,断口均呈现出准解理断裂的特征。【结论】超声电弧的引入有助于改善压铸镁合金焊接质量,显著提高接头力学性能。展开更多
Medium strength aluminium alloy （Al-Mg-Si alloy） has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to weight ratio, such as transportable bridge girders, military v...Medium strength aluminium alloy （Al-Mg-Si alloy） has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding process for aluminium alloy is frequently TIG （tungsten inert gas） welding due to its comparatively easier applicability and better economy.In the case of single pass TIG welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The use of pulsed current parameters has been found to improve the mechanical properties of the welds compared to those of continuous current welds of this alloy due to grain refinement occurring in the fusion zone. A mathematical model has been developed to predict pitting corrosion potential of pulsed current TIG welded AA6061 aluminium alloy.Factorial experimental design has been used to optimize the experimental conditions. Analysis of variance technique has been used to find out the significant pulsed current parameters. Regression analysis has been used to develop the model. Using the developed model pitting corrosion potential values have been estimated for different combinations of pulsed current parameters and the results are analyzed in detail.展开更多
级联型混合直流系统受端的模块化多电平换流器高压直流系统(modular multilevel converter high voltage direct current,MMC-HVDC)和电网换相换流器高压直流系统(line commutated converter high voltage direct current,LCC-HVDC)会...级联型混合直流系统受端的模块化多电平换流器高压直流系统(modular multilevel converter high voltage direct current,MMC-HVDC)和电网换相换流器高压直流系统(line commutated converter high voltage direct current,LCC-HVDC)会因馈入点电气距离较近而存在强相互作用关系。为明确级联型混合直流馈入系统中MMC-HVDC对LCC-HVDC系统强度的影响,提出考虑幅值和相位的MMC等效电流源的简化等效方法,基于所提MMC等效原理将级联型混合直流馈入系统等效成单馈入LCC-HVDC系统,分析等效单馈入系统的参数计算方法,并提出等效单馈入短路比评估指标。最后通过该指标分析归纳了不同控制方式、不同电气距离下等效单馈入系统的系统强度变化情况,即为MMC-HVDC对LCC-HVDC系统强度的影响规律。机理分析和基于PSCDAD/EMTDC、MATLAB的仿真结果表明,所提等效方法具有有效性且所提指标能很好地反应MMC-HVDC对LCC-HVDC系统强度的影响。展开更多
文摘目的:探究阳极经颅直流电刺激(a-tDCS)结合抗阻训练对健康成年人下肢力量和无氧功率的训练效果。方法:选取30名有丰富抗阻训练经验的(19.70±1.47)岁健康成年人,并随机分配到复合训练组(a-tDCS+抗阻训练,n=15)和单一训练组(n=15);2组受试者每周均进行2次颈后杠铃深蹲训练,复合训练组需要在每次深蹲训练前进行20 min a-tDCS(电流2mA)干预,训练时长为5周;采用双因素重复测量方差分析(干预方式×测试阶段),探讨上述自变量对受试者的下肢最大力量和无氧功率指标的影响,包括峰值功率(PP)、平均功率(AP)以及功率衰减(PD)。结果:5周训练干预后,2组受试者后测的1RM深蹲成绩相较前测均有显著提高(p<0.05),且复合训练组受试者1RM深蹲成绩的提高效果显著于单一训练组〔复合训练组(19.20±7.38)kg对比单一训练组(12.27±8.66)kg,p<0.05〕;复合训练组和单一训练组的PP、AP、PD在干预前后的差异均不显著(p>0.05)。结论:a-tDCS结合抗阻训练对下肢肌力的增强作用显著于单一抗阻训练,a-tDCS可以作为健康成年人增强下肢力量的一种辅助训练方法。
文摘鲁汶流是东印度洋海区低盐暖水向极传输的主要途径,不仅显著调节低纬-高纬海区间的温盐分配,也极大影响澳大利亚西岸降水,理解其在地质历史时期的变化及影响因素,对于认识区域和全球气候变化具有重要意义。本次研究将鲁汶流区采集的SO18588孔岩芯上部63 cm沉积物作为研究材料,并以1 cm为间隔对其进行采样,共计获得63个沉积物样品。通过对这些沉积物样品进行研究,发现在SO18588站处浮游有孔虫热带表层水种Trilobatus sacculifer的相对丰度比浮游有孔虫热带-亚热带表层水种Globigerinoides ruber的相对丰度更适合被用于指示鲁汶流强度变化;之后,利用浮游有孔虫热带表层水种T.sacculifer的相对丰度,重建了32 ka B. P.以来鲁汶流的强度变化,并与已发表的古海洋和古气候学记录进行了对比。结果显示,鲁汶流强度的冰期-间冰期变化受海平面升降和类厄尔尼诺-南方涛动气候态共同调控:冰期时海平面下降,类厄尔尼诺态强化,导致鲁汶流减弱;间冰期时,海平面上升,类拉尼娜态发育,造成鲁汶流增强。9.5~0 ka B. P.期间,鲁汶流强度的持续弱化,可能归因于澳洲冬季风的减弱和早全新世类拉尼娜格局向现代类厄尔尼诺格局转变所造成的厄尔尼诺事件频发;9.5 ka B. P.左右鲁汶流强度事件性地突然减弱,可能与海平面上升所导致的卡里马塔海峡贯通、印尼穿越流表层流被抑制有关。
基金The National Basic Research Program of China under contract Nos 2007CB816003,2011CB403503 and 2012CB955601the National Natural Science Foundation of China under contract Nos 41176020 and 41176021the Scientific Research Fund of the Second Institute of Oceanography,State Oeanic Administration,under contract Nos JT1006 and JG1009
文摘Acoustic Doppler current profiler （ADCP） receives echoes from sound scatterers, then their speed is calcu- lated by the Doppler effect. In the open ocean, most of these backscatterers are from the plankton. The sound scatterers descend down to depth at around dawn, their mean speed is 2.9 cm/s, then they ascend up to the surface layer at around dusk with a mean speed of 2.1 cm/s, in the Luzon Strait. The descending speed is faster, which suggests that this zooplankton population may accelerate its downward migration under the action of the gravity. The vertical distribution of a mean volume backscattering strength （MVB- S） in the nighttime has two peaks, which locate near the upper and lower boundary layers of halocline, respectively. However, the backscatterers only aggregate near the surface layer in the daytime. The diel ver- tical migration （DVM） of sound scatterers has several characteristic patterns, it is stronger in summer, but weaker in winter, and the maximum peak occurs in September. The DVM occurrence is synchronous with the seawater temperature increasing at around dawn and dusk, it may affect the ocean mixing and water stratification,
文摘【目的】旨在实现压铸镁合金高质量焊接,其是拓宽镁合金在工业领域应用的关键。【方法】为改善压铸镁合金常规交流非熔化极惰性气体保护焊(Tungsten inert gas welding,TIG)接头质量,利用超声频电信号激发电弧,产生作用于电弧及熔池的超声,对比研究超声电弧对AZ31B压铸镁合金平板对接接头的成形、金相组织及力学性能的影响。【结果】结果表明,超声电弧可以提高焊缝成形性能、细化焊缝组织以及提高接头的强度和塑性。与常规TIG相比,施加超声激励扩展了焊缝中下部熔宽,使得接头表面和边界熔化均匀,焊缝晶粒得到细化。同时,抑制了第二相的聚集和长大,促进其在焊缝中的均匀分布;接头的平均抗拉强度为212 MPa,达到母材的80.9%,断后伸长率由5.1%增高至8.5%;未施加超声电弧的接头拉伸试样在焊缝中断裂,引入超声电弧的接头拉伸试样在热影响区断裂,断口均呈现出准解理断裂的特征。【结论】超声电弧的引入有助于改善压铸镁合金焊接质量,显著提高接头力学性能。
文摘Medium strength aluminium alloy （Al-Mg-Si alloy） has gathered wide acceptance in the fabrication of light weight structures requiring a high strength-to weight ratio, such as transportable bridge girders, military vehicles, road tankers and railway transport systems. The preferred welding process for aluminium alloy is frequently TIG （tungsten inert gas） welding due to its comparatively easier applicability and better economy.In the case of single pass TIG welding of thinner section of this alloy, the pulsed current has been found beneficial due to its advantages over the conventional continuous current process. The use of pulsed current parameters has been found to improve the mechanical properties of the welds compared to those of continuous current welds of this alloy due to grain refinement occurring in the fusion zone. A mathematical model has been developed to predict pitting corrosion potential of pulsed current TIG welded AA6061 aluminium alloy.Factorial experimental design has been used to optimize the experimental conditions. Analysis of variance technique has been used to find out the significant pulsed current parameters. Regression analysis has been used to develop the model. Using the developed model pitting corrosion potential values have been estimated for different combinations of pulsed current parameters and the results are analyzed in detail.
文摘级联型混合直流系统受端的模块化多电平换流器高压直流系统(modular multilevel converter high voltage direct current,MMC-HVDC)和电网换相换流器高压直流系统(line commutated converter high voltage direct current,LCC-HVDC)会因馈入点电气距离较近而存在强相互作用关系。为明确级联型混合直流馈入系统中MMC-HVDC对LCC-HVDC系统强度的影响,提出考虑幅值和相位的MMC等效电流源的简化等效方法,基于所提MMC等效原理将级联型混合直流馈入系统等效成单馈入LCC-HVDC系统,分析等效单馈入系统的参数计算方法,并提出等效单馈入短路比评估指标。最后通过该指标分析归纳了不同控制方式、不同电气距离下等效单馈入系统的系统强度变化情况,即为MMC-HVDC对LCC-HVDC系统强度的影响规律。机理分析和基于PSCDAD/EMTDC、MATLAB的仿真结果表明,所提等效方法具有有效性且所提指标能很好地反应MMC-HVDC对LCC-HVDC系统强度的影响。
