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文洁若 《中学生阅读(初中版)》2023,(Z1):89-94
<正>(1)一九九八年夏秋之交,雨接连下了二十几天,天空才放晴。断流多年的西辽河躁动不安,河水暴涨。终于有一日冲破了堤坝,向下游奔涌而去。(2)“暴走”的洪水冲刷过田野,直奔我的家乡科尔沁左翼后旗,却在二道壕村北十余里开外,被一道高高的壕堤拦住去路。洪水在壕堤下日夜咆哮。 相似文献
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胡李萍 《数学学习与研究(教研版)》2014,(8):106
随着近世代数的不断完善,以及平面几何研究工具的不断发展,尺规作图这一早在古希腊时期提出的最原始的数学问题,在我们的实践教学中越来越不被重视.在我们的平面几何教学工作中,我们也越来越多地忽视了尺规作图对提高学生创新力的重要作用.本文将结合教学案例来说明尺规作图在开发学生创新性思维方面的积极作用. 相似文献
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凌夫 《语文世界(高中版)》2006,(10):40
《螺旋形防波堤》是大地雕塑艺术。大地雕塑艺术是一种新的雕塑类型。它通过对大自然景物进行人为的加工,如开挖、堆叠、包装等,改变原来的面貌,营造一个新的人工的艺术景观。这类作品是在许多人共同参与下完成的,不能永久性保存,只能采用摄影和摄像的手段传播。1970年,美国雕塑家史密斯(1938～1973)在美国犹他州大盐湖修筑了螺旋形防波堤。他采用了大盐湖周围的烂泥、黑色岩石等作材料,用推土机和其他先进设备筑成一条螺旋形的堤。堤坝从岸边向水面伸出1.5公里,人可以在上面行走。由于湖水持续不断地波动,受水的侵蚀作用所留下的盐的沉淀物… 相似文献
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目的:本文旨在建立简单实用的饱和软黏土不排水强度损伤弱化模型,应用于波浪循环荷载作用下沉箱式防波堤与软土地基相互作用的非线性数值计算,为解决防波堤软土强度弱化计算问题提供有效途径。创新点:1.基于不排水强度循环损伤弱化机理,得到软黏土不排水强度随循环荷载作用次数和应力水平的变化规律;2.结合Tresca屈服准则进行数值开发,应用于波浪循环荷载作用下沉箱式防波堤与软土地基相互作用的数值计算。方法:1.引入累积塑性变形相关的损伤变量表征土体结构性的损伤和重塑对软黏土不排水强度弱化的影响(公式(3)和(11));2.建立软黏土不排水强度随循环荷载作用次数和应力水平变化的损伤弱化模型(公式(14));3.结合Tresca屈服准则,实现软黏土不排水强度损伤弱化的数值计算过程(图9);4.针对烟台软黏土动三轴试验数据进行分析,对模型及其数值开发过程进行验证(图11和12);5.将模型应用到软土地基上沉箱式防波堤数值运算,分析软土地基响应,验证模型的有效性(图15~18)。结论:1.在临界循环应力比以下,损伤变量和归一化最大孔压比随循环荷载作用次数的增加逐渐增大,并趋于稳定;随循环应力比增大逐渐增大。循环后不排水强度折减系数随着循环荷载作用次数和循环应力比的增加而减小。2.有限元数值开发过程是正确的,不排水强度损伤弱化模型是合理的。3.该模型简单实用,可应用于波浪等循环荷载作用下沉箱式防波堤与软土地基相互作用的非线性数值计算,且能模拟循环荷载下软土地基的孔隙水压力增长以及不排水强度弱化等响应。软土地基的响应主要分布在基床两趾及正下方的软土层上部。 相似文献
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《义务教育数学课程标准(2011年版)》虽然将尺规作图作为课程内容,但由于初中教科书将尺规作图编排靠后,影响了尺规作图发挥其应有的教育价值.2017年,日本文部科学省颁布了自2021年开始实施的《初中学习指导要领》,在最新“要领”的指导下日本初中教科书将尺规作图置于平面几何章节之首,设计有趣的情境,以作图为线索串联几何知识,并给出作图的思考方式.“他山之石,可以攻玉”,日本初中教科书尺规作图的编排可以给我国课程标准与教科书的编写带来一些启示. 相似文献
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一、"补位法"简介
当游标卡尺的读数为整毫米数时(以整数为数值,毫米为单位),游标和主尺将同时有两处刻度线重合(游标的最前一条和最后一条刻度线分别和主尺的两条刻度线重合).当游标卡尺的左、右测量爪合在一起时,游标卡尺的读数为零毫米,此时游标和主尺亦同时有两处刻度线重合.而在其他情况下,游标和主尺只在一处有刻度线重合. 相似文献
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袁永康 《中国科教创新导刊》2004,(10):33
高速渡船产生的冲刷作用会导致严重的问题,特别是在浅水中。它曾经导致过致使小型船只倾覆、岸边日光浴者四散逃命的怪异波浪。海军设计师们在计算机上进行了流体动力学仿真研究,以预测各种给定的船体设计所产生的冲刷作用。结果发现形状、最高速度和排水量等因素对冲刷作用有影响。但研究人员却决定反其道而行之。他们先确定了把80米长双体渡船冲刷作用降低25%的目标,然后反方向运行此模型,以此确定哪种船形能够实现他们的目标。研究人员分别设计了用于深水和浅水的优化船形。然后他们把这两种船形组合起来,成为一种折衷的形状。它没有采取… 相似文献
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This paper investigates the wave attenuation properties of the double trapezoidal submerged breakwaters on the flat-bed by conducting physical experiments subjected to linear and cnoidal incident waves.The method of Goda’s two points is used to separate the heights of incident,reflected and transmitted waves based on the experimental data.The possible factors affecting the wave attenuation properties of the double trapezoidal submerged breakwaters(i.e.,the relative submerged water depth,relative breakwater spacing,wave steepness and relative wave height) are investigated with respect to the reflection and transmission coefficients.The results show that there is a range,within which the breakwater spacing has little impact on the reflection coefficient,and the transmission coefficient tends to be a constant.The influence of the wave steepness is reduced while the breakwater spacing is too large or too small.Within the range of the relative wave height tested in this study,the reflection and transmission coefficients increase and decrease with the relative wave height,respectively.The double trapezoidal submerged breakwaters model indicates a good attenuation effect for larger wave steepness,big relative wave height and within the range of the relative breakwater spacing between 12.5 and 14 according to linear and cnoidal waves.The changes of wave energy spectra between the double submerged breakwaters on the flat-bed are investigated by the fast Fourier transform(FFT) method,showing that wave energy dissipation can be reached more effectively when the relative breakwater spacing is 12.5. 相似文献
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通过丹江口水库36年实测资料的分析研究认为:变动回水区的泥沙冲淤具有两冲一淤的周期性特点,冲淤分布受坝前两个运用水位所控制;年内具有汛、枯期两大造床期,有两个对应造床期的纵剖面;变动回水区的淤积自上至下逐段发展.由于淤积,汉库回水区有效库容损失较大. 相似文献
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In this paper we propose a degradation model to describe the damage-dependent behavior of saturated soft clay under cyclic loading, which is then applied to the analysis of a caisson breakwater. The degree of damage and remolding of soft clay is quantified by a damage parameter related to the accumulated plastic deviatoric strain. Through the correlation between the maximum pore pressure and the undrained strength of soft clay, we obtain a damage-dependent degradation model that employs the post-cyclic undrained strength degradation coefficient in terms of the cyclic stress ratio and the number of cycles. Based on the Tresca yield criterion, the degradation model of undrained strength of soft clay is numerically implemented in the user interface USDFLD of ABAQUS. The performance of this model is verified by a comparison between numerical results (finite element method) and experimental data (cyclic triaxial test). The model is applied to the numerical simulation of a caisson breakwater resting on a partially sand-filled soft clay seabed under cyclic wave loading. The cyclic stress distribution, pore pressure development, and strength degradation of the seabed soil are presented to illustrate the applicability and efficiency of the model in the analysis of the interaction between offshore structures and soft ground. 相似文献
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文章针对高校统战人物档案建设存在的建档意识薄弱、材料分散、收集不全等问题,提出了高校统战人物档案纳入学校人事档案集中管理、建立协调机制确保统战人物档案材料的收集完整、开展统战人物档案的适度开发利用等对策建议。 相似文献
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The dynamic stress path of a rock and soil mass under seismic action has a crucial influence on its catastrophic behavior. In soil dynamics, earthquakes are commonly simplified as vertically incident shear waves and the seismic stresses in soil are estimated based on rigid foundation models. However, the great effect of P-waves should not be overlooked in strong earthquakes, which have happened frequently in recent years. The characteristics of the dynamic stress path under longitudinal waves with significant oblique incidence are still unclear. Analytical formulas for the seismic stresses at any depth of a semi-infinite elastic space under obliquely incident P-waves are derived, which degenerate into the traditional rigid foundation method in soil dynamics when both the incident angle and Poisson’s ratio are taken as zero. Here, we reveal the fundamental characteristics of a dynamic stress path under obliquely incident P-waves. The stress path is proved mathematically to be an oblique ellipse in the plane of normal stress difference and horizontal shear stress. We identify factors affecting the stress path, including the incident angle, Poisson’s ratio, and depth corresponding to unit wavelength. The possible variation in the range of an oblique elliptic stress path is systematically analyzed, which lays a theoretical foundation for further study of the dynamic response of sites under obliquely incident seismic waves. 相似文献
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前牙外伤折断、牙髓暴露,或近中和远中深龋因咬硬物而折断者,较为常见,采用根管螺纹钉做固位装置,用光固化复合树脂修复牙冠,修复体不但固位牢,而且形态逼真,色泽自然,操作简便,深受患者欢迎。作者自1994年6月至1996年12月收治了34人,45颗牙。临床效果满意。 相似文献
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以蚕豆根尖为材料,研究厕洁灵、丝毛剂和蔬果清洗剂对蚕豆根尖细胞的遗传毒性.利用不同浓度的厕洁灵、丝毛剂和蔬果清洗剂为诱变剂,测定蚕豆根尖细胞的微核率和染色体畸变率.结果：不同浓度的洗涤剂能诱发较高频率的微核,还能诱导染色体产生多种类型的染色体畸变.结论：三种洗涤剂对植物根尖细胞具有明显的致突变效应,有一定的遗传毒性;其中洁厕剂的毒性最大,丝毛剂次之,果蔬洗涤剂最弱. 相似文献
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量词为动量的“A1一量A2一量”格式中“一+动量”结构都是表示动态事件的名词性短语,它们和前面的形容词之间在语义上是性状拥有者和性状之间的关系。整个格式的语法意义是:动作行为以不同性状交替延续;在运用中格式主要有三个方面的不同功能。 相似文献
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褚志刚 《重庆大学学报(英文版)》2003,2(2)
1. Introduction In order to improve the driving operation performance, the front suspension of a vehicle is generally of McPherson independent style, which can simplify the structure, lighten the unsprung mass, and conveniently arrange the engine and steering system. Moreover, it can adapt to many types of springs and is of advantage to adjust the height of the vehicle. In such a system, the axis of the kingpin is the line between the upper damper end and the intersection of the transverse ar… 相似文献
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The random wave load is applied to dynamic response analysis of circular caisson breakwater. The motion process of circular caisson breakwater is classified as rotation motion mode and rotation-and-sliding motion mode. The dynamic model system composed of damper-antislider to control the lateral sliding is introduced, and corresponding dynamic equations of two motion modes are established. The formulas to calculate added mass and new conversion relation of the unit rotational stiffness coefficient are put forward according to the characteristic of the circular caisson breakwater. An engineering case is calculated by a program compiled in Fortran language using proposed dynamic model and method. The validity of the model is calibrated. 相似文献