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<正>根据艾宾浩斯遗忘曲线规律,任何学习若不及时复习就会出现大幅度遗忘的现象.高中阶段课程繁多,学生每天所接受的知识信息量大,如何提高复习质量决定了学生的学习效率.尤其是数学学科,大量的公式、定理、法则与数学思想方法等需要学生掌握,只有及时、高效的复习,才能完善学生的知识储备,帮助学生建构系统的认知体系[1].若将高中数学的新课教学喻为“画龙”的过程,那么复习则属于“点睛”.随着新课改的推进,高考试题常出常新, 相似文献
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采用溶胶-凝胶法制备了La_(1-x)Ca_xCrO_3(x=0~0.335)多晶样品,并研究其磁性.La_(1-x)Ca_xCrO_3的奈尔温度随掺钙量的增加而降低,在零场冷却模式下外加磁场为10Oe时,La_(1-x)Ca_xCrO_3样品的磁化率-温度曲线均出现负磁化现象,这是该体系中负磁化现象的首次报道.La_(0.665)Ca_(0.335)CrO_3在50K下的磁化率数值远高于其他样品,且其负磁化行为随着外场强度增大而被抑制,说明体系可能同时存在铁磁性相与抗磁性相,外加磁场较低时,铁磁信号被抑制,呈现出温度依赖的负磁化行为;外加磁场较高时,铁磁性信号与负磁性信号叠加,呈现出反铁磁转变特性. 相似文献
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采用溶胶-凝胶法制备了名义Y_(1-x)AE_xCrO_3(AE=Mg,Ca;x=0~1/3)多晶样品,并研究其晶体结构、磁性、输运性质.Y_(0.9)Ca_(0.1)CrO_3晶格常数及晶胞体积相对于YCrO_3减小,这是Cr~(3+)由于电荷补偿机制向Cr~(4+)转变进而增大CrO~6八面体畸变程度的结果.碱土金属掺杂几乎不改变YCrO_3的反铁磁转变温度(~138K),但会导致体系有效磁矩明显降低.Y_(0.9)Ca_(0.1)CrO_3的M-H曲线呈现出未饱和的明显铁磁Loop,由体系倾斜的G型反铁磁序造成;Y_(0.9)Ca_(0.1)CrO_3输运性质呈现出lnρ与1000/T的线性相关关系,由于晶格畸变场导致的小极化子受热激活剧烈跳跃,体系电阻率随着温度升高显著降低. 相似文献
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为了能够直接感受电磁感应作用的效果,设计制作了电磁炮模型.该模型主要由线圈和电容器组成,电容对线圈放电,线圈内部产生磁场,在磁场力作用下线圈发射弹丸.以影响电磁线圈炮弹丸发射速度的3个因素为研究对象,探究在50V直流充电电压的情况下弹丸的最大发射速度与电容等因素的关系. 相似文献
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Fountain codes provide an efficient way to transfer information over erasure channels like the Internet. LT codes are the first codes fully realizing the digital fountain concept. They are asymptotically optimal rateless erasure codes with highly efficient encoding and decoding algorithms. In theory, for each encoding symbol of LT codes, its degree is randomly chosen according to a predetermined degree distribution, and its neighbours used to generate that encoding symbol are chosen uniformly at random. Practical implementation of LT codes usually realizes the randomness through pseudo-randomness number generator like linear congruential method. This paper applies the pseudo-randomness of chaotic sequence in the implementation of LT codes. Two Kent chaotic maps are used to determine the degree and neighbour(s) of each encoding symbol. It is shown that the implemented LT codes based on chaos perform better than the LT codes implemented by the traditional pseudo-randomness number generator. 相似文献
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In this paper, one-state on-off intermittency and two-state on-off intermittency are generated in two five- dimensional continuum systems respectively. In each system, a two-dimensional subsystem is driven by the Rossler chaotic system. The parameter conditions under which the on-off intermittency occurs are discussed in detail. The statistical property of the intermittency is investigated. It is shown that the distribution of the laminar phase duration time follows a power law with an exponent of -3/2, which is a signature of on-off intermittency. Moreover, the phenomenon of intermingled basins is observed when attractors in the two symmetric invariant subspaces are stable. We provide an effective way to generate on-off intermittency based on a chaotic system, which is important for application and theoretical study. 相似文献