Dynamics and manipulation of ferroelectric domain walls in bismuth ferrite thin films     

Shuyu Xiao  Yaming Jin  Xiaomei Lu  Sang-Wook Cheong  Jiangyu Li  Yang Li  Fengzhen Huang  Jinsong Zhu 《国家科学评论(英文版)》2020,7(2):278

Ferroelectric domain walls differ from domains not only in their crystalline and discrete symmetry, but also in their electronic, magnetic, and mechanical properties. Although domain walls provide a degree of freedom to regulate the physical properties at the nanoscale, the relatively lower controllability prevents their practical applications in nano-devices. In this work, with the advantages of 3D domain configuration detection based on piezoresponse force microscopy, we find that the mobility of three types of domain walls (tail-to-tail, head-to-tail, head-to-head) in (001) BiFeO₃ films varies with the applied electrical field. Under low voltages, head-to-tail domain walls are more mobile than other domain walls, while, under high voltages, tail-to-tail domain walls become rather active and possess relatively long average lengths. This is due to the high nucleation energy and relatively low growth energy for charged domain walls. Finally, we demonstrate the manipulation of domain walls through successive electric writings, resulting in well-aligned conduction paths as designed, paving the way for their application in advanced spintronic, memory and communication nano-devices.  相似文献   

黄河流域土地利用时空格局演变及驱动力   总被引：10，自引：0，他引：10  

张佰发  苗长虹 《资源科学》2020,42(3):460-473

土地利用时空格局是人类与自然相互作用状况的重要表征。研究黄河流域土地利用时空格局及其驱动因素,厘清土地利用类型转换及粮食保障用地、生态保育用地、城乡建设用地的时空变化特征,可为黄河流域生态保护和高质量发展国家重大战略的规划制定与实施提供参考。本文基于土地利用类型转移矩阵和空间自相关,从城市群、省、市、县多尺度入手,利用7期土地利用数据对黄河流域1970—2015年土地利用状况及变化进行探究。结果表明：①黄河流域生态保育用地和耕地占比多年平均值分别为79.04%和18.64%,表明生态保护和粮食生产是其两大主体功能;②城乡建设用地占比逐年提高,城市群地区是建设用地扩张的主体空间;③黄河流域耕地、生态保育用地和城乡建设用地各节点年份Moran’s I均大于0.75,表明3种功能类型用地具有强空间正向集聚效应,呈现出“凹”字型分布格局;④城乡建设用地扩张以牺牲耕地为代价,同时部分农村居民点用地逐渐转化为城镇用地;⑤人口规模和经济发展是促进土地利用变化的核心因素,驱动力因素存在区域差异,在黄河下游的山东、河南,经济水平达到一定规模后,伴随经济再发展不会出现大规模城乡建设用地扩张。  相似文献   

Effects of oncoming target velocities on rapid force production and accuracy of force production intensity and timing     

Yoichi Ohta 《Journal of sports sciences》2017,35(23):2304-2312

The present study aimed to clarify the effects of oncoming target velocities on the ability of rapid force production and accuracy and variability of simultaneous control of both force production intensity and timing. Twenty male participants (age: 21.0 ± 1.4 years) performed rapid gripping with a handgrip dynamometer to coincide with the arrival of an oncoming target by using a horizontal electronic trackway. The oncoming target velocities were 4, 8, and 12 m · s^?1, which were randomly produced. The grip force required was 30% of the maximal voluntary contraction. Although the peak force (Pf) and rate of force development (RFD) increased with increasing target velocity, the value of the RFD to Pf ratio was constant across the 3 target velocities. The accuracy of both force production intensity and timing decreased at higher target velocities. Moreover, the intrapersonal variability in temporal parameters was lower in the fast target velocity condition, but constant variability in 3 target velocities was observed in force intensity parameters. These results suggest that oncoming target velocity does not intrinsically affect the ability for rapid force production. However, the oncoming target velocity affects accuracy and variability of force production intensity and timing during rapid force production.  相似文献   

体校学生田径训练中单足跳发展下肢爆发力的研究     

关革 《哈尔滨体育学院学报》2010,28(2):107-108,111

文章对体校学生爆发力训练进行了理论研究,提出了爆发训练的专项性原则及应注意的问题,并确定了体校学生单腿训练的依据及方法,希望借此对体校的教学与训练提供一定参考。  相似文献   

论田径运动员爆发力的训练     

邱晓桦  林国忠 《体育科技文献通报》2010,18(10):35-36

爆发力是多数田径运动员取得优异成绩的素质基础,本文采用文献法,从爆发力的生理学机制出发,对发展田径运动员爆发力的途径,爆发力训练方法,以及训练时的注意事项加以论述。提出了一些发展田径运动员爆发力的训练方法,以期能最大限度地挖掘运动员的爆发力潜能,达到提高运动成绩的目的。  相似文献   

论“阴阳合同”的法律效力——以王栋合同门事件为例          下载免费PDF全文

张红华  郑鹭宾  缪志伟 《武汉体育学院学报》2010,44(2):42

以王栋合同门事件为例,从登记备案与合同效力的关系、合同是否为双方的真实意思表示、是否以新签订的合同为准和合同是否存在无效情形等方面分析"阴合同"、"阳合同"的法律效力.认为在王栋"合同门"事件中应以未在足协备案的"阴合同"为准,但总体上"阴阳合同"的效力是不确定的,应当加强监管,完善体育立法,订立集体合同,改革转会制度.  相似文献   

合理使用与许可使用的异同及适用     

刘志刚 《图书馆建设》2005,(5):1-4

版权法自产生之初,就在对版权是保护还是限制这个问题上陷入两难境地。一方面要鼓励和保护优秀作品的创作与传播;另一方面必须出于对社会公共利益的兼顾而对版权人权利加以限制。总的来看,这种限制主要包括合理使用和许可使用两个方面。  相似文献   

浅论邓小平对青少年成长的关怀     

周慧敏 《六盘水师范高等专科学校学报》2004,16(5):33-34

邓小平同志始终以博大的胸怀和深邃的目光,站在党和国家前途命运的高度,十分关怀青少年的成长。多次向青年发出号召要做“四有”新人,要学习,要参加社会实践,并鼓励大量派遣青少年出国留学,培养了大量的青年专家。  相似文献   

Impact absorption of tennis shoe-surface combinations     

S.?J.?DixonEmail author  V.?H.?Stiles 《Sports Engineering》2003,6(1):1-9

The aim of this study was to investigate, for typical shoes and surfaces used in tennis, the relative role of the shoe and surface in providing cushioning during running. Five test surfaces ranging from concrete to artificial turf were selected, together with two shoe models. Impact absorbing ability was assessed mechanically using drop test procedures and biomechanically using peak magnitude and rate of loading of impact force and peak in-shoe pressure data at the lateral heel. Differences in biomechanical variables between shoe-surface combinations were identified using a two-way ANOVA (p < 0.05). Mechanical test results were found to rank the surfaces in the same order regardless of the shoe model, suggesting that the surface is influential in providing cushioning. However, for all mechanical and biomechanical (p < 0.05) variables representing impact absorbing ability, it was found that the difference between shoes was markedly greater than the differences between surfaces. The peak heel pressure data were found to rank the surfaces in the same order as the mechanical tests, while impact force data were not as sensitive to the changes in surface. Correlations between mechanical and biomechanical impact absorption highlighted the importance of testing the shoe-surface combination in mechanical tests, rather than the surface alone. In conclusion, mechanical testing of the shoe-surface combination was found to provide a strong predictor of the impact absorbing ability during running if pressure data were used. In addition, for typical shoe-surface combinations in tennis, the shoe was found to have more potential than the surface to influence impact loading during running. Finally, in-shoe pressure data were found to be more sensitive than force plate data to changes in material cushioning.  相似文献   

大型集装箱船的总纵强度实用计算方法     

吴善刚  邱文昌 《上海海事大学学报》1998,(3)

以我国１９９６年《钢质海船入级与建造规范》对大型集装箱船的总纵强度的要求为标准,讨论了具体装载状态下船舶总纵强度的校核方法,并着重探讨了在资料不完整的情况下与总纵强度校核有关的船舶资料的计算制作方法。  相似文献