Analysis of wave propagation in a functionally graded nanobeam resting on visco-Pasternak＇s foundation

Wave propagation analysis for a functionally graded nanobeam with rectangular cross-section resting on visco-Pasternak＇s foundation is studied in this paper. Timoshenko＇s beam model and nonlocal elasticity theory are employed for formulation of the problem. The equations of motion are derived using Hamilton＇s principals by calculating kinetic energy, strain energy and work due to viscoelastic foundation. The effects of various parameters such as wavenumber, non-homogeneous index, nonlocal parameter and three parameters of foundation are performed on the phase velocity of the nanobeam. The obtained results indicate that some parameters such as non-homogeneous index, nonlocal parameter and wavenumber have significant effect on the response of the system.

Transverse free vibration analysis of a tapered Timoshenko beam on visco-Pasternak foundations using the interpolating matrix method

The characteristics of transverse free vibration of a tapered Timoshenko beam under an axially conservative compression resting on visco-Pasternak foundations are investigated by the interpolating matrix method. The research is executed in view of a three-parameter foundation which includes the eff ects of the Winkler coeffi cient, Pasternak coeffi cient and damping coeffi cient of the elastic medium. The governing equations of free vibration of a non-prismatic Timoshenko beam under an axially conservative force resting on visco-Pasternak foundations are transformed into ordinary diff erential equations with variable coeffi cients in light of the bending rotation angle and transverse displacement. All the natural frequencies orders together with the corresponding mode shapes of the beam are calculated at the same time, and a good convergence and accuracy of the proposed method is verifi ed through two numerical examples. The infl uences of foundation mechanical characteristics together with rotary inertia and shear deformation on natural frequencies of the beam with diff erent taper ratios are analyzed. A comprehensive parametric numerical study is carried out emphasizing the primary parameters that describe the dynamic property of the beam.

Vibration suppression of magnetostrictive laminated beams resting on viscoelastic foundation

The vibration suppression analysis of a simply-supported laminated composite beam with magnetostrictive layers resting on visco-Pasternak’s foundation is presented.The constant gain distributed controller of the velocity feedback is utilized for the purpose of vibration damping.The formulation of displacement field is proposed according to Euler-Bernoulli’s classical beam theory(ECBT),Timoshenko’s first-order beam theory(TFBT),Reddy’s third-order shear deformation beam theory,and the simple sinusoidal shear deformation beam theory.Hamilton’s principle is utilized to give the equations of motion and then to describe the vibration of the current beam.Based on Navier’s approach,the solution of the dynamic system is obtained.The effects of the material properties,the modes,the thickness ratios,the lamination schemes,the magnitudes of the feedback coefficient,the position of magnetostrictive layers at the structure,and the foundation modules are extensively studied and discussed.

New artificial boundary condition for saturated soil foundations

Anew artificial boundary model based on multi-directional transmitting and viscous-spring artificial boundary theories is proposed to absorb stress waves in a saturated soil foundation in dynamic analysis. Since shear waves （S-waves） are the same in a saturated soil foundation and a single-phase medium foundation, a tangential visco-elastic boundary condition for a single-phase medium foundation can also be used for saturated soil foundations. Thus, the purpose of the artificial boundary proposed in this paper is primarily to absorb two types of P-waves in a saturated soil foundation. The main idea is that the stress of the P-waves in the saturated soil foundation is decomposed into two types. The first type of stress, δra＇ is absorbed by the first artificial boundary. The second type of stress, δrb, is balanced by the stress generated by the second artificial boundary. Ultimately, both types of P-waves （fast-P-waves and slow-P-waves） are absorbed by the artificial boundary model proposed in this paper. In particular, note that the fast-P-waves and slow-P-waves are absorbed at the position of the first boundary. Thus, the artificial boundary model proposed herein can simultaneously absorb P-fast waves, P-slow waves and shear waves. Finally, a numerical example is given to examine the proposed artificial boundary model, and the results show that it is very accurate.

Quasi-Green’s function method for free vibration of clamped thin plates on Winkler foundation

The quasi-Green＇s function method is used to solve the free vibration problem of clamped thin plates on the Winkler foundation. Quasi-Green＇s function is established by the fundamental solution and the boundary equation of the problem. The function satisfies the homogeneous boundary condition of tile problem. The mode-shape differential equation of the free vibration problem of clamped thin plates on the Winkler foundation is reduced to the Fredholm integral equation of the second kind by Green＇s formula. The irregularity of the kernel of the integral equation is overcome by choosing a suitable form of the normalized boundary equation. The numerical results show the high accuracy of the proposed method.

Free Vibration Analysis of FG-CNTRC Cylindrical Pressure Vessels Resting on Pasternak Foundation with Various Boundary Conditions

This study focuses on vibration analysis of cylindrical pressure vessels constructed by functionally graded carbon nanotube reinforced composites(FG-CNTRC).The vessel is under internal pressure and surrounded by a Pasternak foundation.This investigation was founded based on two-dimensional elastic analysis and used Hamilton’s principle to drive the governing equations.The deformations and effective-mechanical properties of the reinforced structure were elicited from the first-order shear theory(FSDT)and rule of mixture,respectively.The main goal of this study is to show the effects of various design parameters such as boundary conditions,reinforcement distribution,foundation parameters,and aspect ratio on the free vibration characteristics of the structure.

Maternal Health Care in Cox’s Bazar, Bangladesh: A Survey of Midwifery Experience at Hope Foundation and a Review of the Literature

Background: The Ministry of Health and Family Welfare of the Government of Bangladesh developed a midwifery education strategy in 2011 and starting in 2013, BRAC University developed a three-year Diploma in Midwifery. A survey was developed to understand the challenges of the newly graduated midwives and to identify resource and educational needs. The survey feedback will help develop and strengthen curriculum for primary and postgraduate midwifery training. Methods: A 30-question survey was given to midwives at the Hope Hospital in Cox’s Bazar and at the birth centers in the surrounding rural communities. Questions explored the midwives’ clinical experience, patient problems in the prenatal, intrapartum, and postnatal period, and asked about what education;training and clinical resources were needed. Results: Thirty-two midwives answered the surveys. The midwives’ average time from graduation from the midwifery diploma program was sixteen months. All the respondents felt comfortable managing most maternal issues but felt further training was important. They also identified the lack of many clinical resources including blood products, medicines, vaccines, and ultrasound. They identified significant maternal health issues among their patients including adolescent pregnancy, malnutrition, anemia, sexual violence, pregnancy-induced hypertension, hemorrhage, low birth weight infants, prolonged and obstructed labors. Conclusion: Training and increasing the number of midwives are crucial strategies for reducing maternal and neonatal mortality. There is a significant need for long-term placement and commitment of midwives to rural areas in Bangladesh. Health systems and organizations employing midwives must be accountable for the continuing education, mentorship, and supportive needs of midwives.

LIRR's Project of “Study on Spalling Mechanism Mechanism of Dense Refractory Castables by Rapid Heating-up” Being Obtained the Support from National Natural Natural Science Foundation of China

LIRR＇s Priject of ＂Research on Spalling Mechanism Due to Rapid Heating-up of Dense Refractory Castables＂ declared by Wang Zhanmin,vice-president of LIRR,will gain the fund support from National Natural Science Foundation of China in 2011.

Methods for Estimating the Ultimate Bearing Capacity of Layered Foundations

The Meyerhof and Hanna′s(M-H) method to estimate the ultimate bearing capacity of layered foundations was improved. The experimental results of the load tests in Tianjin New Harbor were compared with predictions with the method recommended by the code for the foundations of harbor engineering, i.e. Hansen′s method and the improved M-H method. The results of the comparisons implied that the code and the improved M-H method could give a better prediction.

Influence of Soil-Foundation Interaction Properties on Oscillations of the System “Building-Building” and “Building-Stack-Like Structure”

Seismic oscillations of the “building-building” system which is interconnected buildings built close to each other, and “building-stack-like structure” system which is adjacent and connected in different ways to existing building are considered in the paper. Different types of connections, such as dampers, including the ones suggested by the authors, are studied. Seismic impact is given as a harmonic function and various existing accelerograms, including synthesized ones. Distinctive feature of this paper from previously published ones [1] [2] is the fact that the emphasis falls on the influence of soil-foundation interaction properties, which are described using various models of load-displacement connections. Calculation results are compared in the case of representation of the building as concentrated masses and spatial systems. Ways to reduce seismic response of buildings during the earthquakes are pointed out. Results of experimental studies are given in the paper and are compared with calculations.

Numeric simulation analysis of load-settlement relation of pile in layer foundation

Considering the level distribution of soil layers, the soils surrounding pile are simulated with level finite layer elements. Supposing that the vertical deformation of the soil elements surrounding pile varies in the form of exponent function with radial distance, and considering the nonlinear constitutive relation of stress and strain, the stiffness matrix is established. The mechanics behavior of the pile—soil interface is simulated with a nonlinear interface element. This method can truly express the behavior of the pile-soil system. The load-settlement relation Q-S curves of two big diameter prototype piles on bearing test are analyzed, and satisfying results are obtained. This method is reasonable in theory and feasible in engineering.

基于Q-s曲线的大型LNG储罐桩板基础沉降计算方法

试桩Q-s曲线体现了现场桩基荷载和沉降的关系。文章以某LNG储罐桩板基础为背景,提出利用Q-s曲线求出桩端土层变形模量的方法,并考虑桩板共同作用的求解桩板基础沉降的方法。该方法将桩基模拟为非线性弹簧,弹簧刚度取自Q-s曲线,采用MIDAS进行建模求解,可得到设计需要的筏板和桩基的沉降等高线图以及轴力和弯矩图,用于指导设计。与仅考虑线性地弹簧系数的规范方法进行对比,该方法精度更高,与实际情况更加相符。该方法可针对不同位置的桩基输入不同的非线性弹簧,可用于解决复杂不均匀地层桩筏基础沉降计算的问题。

Bending the Foundation Beam on Elastic Base by Two Reaction Coefficient of Winkler’s Subgrade

A new method for analysis of counter beams is presented in the paper. The analysis has taken into account their stiffness EI, Winkler’s space with modulus of subgrade reaction k and equality deformities of the foundation beam with the ground. The solution is found by using the numerical analysis of the Winkler’s model, with variation of different moduli of the subgrade reaction k2 outside the force zone r, while under the force P exists the modulus of the subgrade reaction k, up to the definition of minimum bending moments. The exponential function k2(r), as the geometric position of the minimum moments is approximately assumed. From the potential energy conditions of the reciprocity of displacement and reaction, the width of the zone r and the modulus of the subgrade reaction k2 are explicitly determined, introducing in the calculation initial and calculation soil displacement wsi successively. At the end of the paper, it presented numerical example in which the influence of k and k2 values on bending moments of the counter beam is analyzed. The essential idea of this paper is to decrease the quantity of the reinforcement in the foundations, beams, i.e. to obtain a cost-efficient foundation construction.

基于MSB二维标记的加密图像可逆数据隐藏

针对基于标记编码的加密图像可逆数据隐藏存在图像冗余未充分利用和信息泄露问题,提出一种基于MSB(Most Significant Bit)二维标记的加密图像可逆数据隐藏(Reversible Data Hiding in Encrypted Image,RDH-EI)算法.为提高算法的嵌入容量,在二维标记图生成阶段,根据原始与预测像素值构造出差异序列,生成MSB二维标记(l1,l2).第一维l1和第二维l2分别记录原始与预测像素值初始连续相同MSBs位数和后继连续相反MSBs(Subsequent Consecutive Opposite MSBs,SCO-MSBs)位数.SCO-MSBs的使用提高像素冗余的利用率,结合范式哈夫曼编码实现嵌入容量的提升.为提高算法的安全性,在伪标记图与加密图像构造阶段,将二维标记图生成的编码流与保存所有辅助信息的额外数据流进行有效信息合并生成原始流后加密,同时在构造加密图像过程中生成用于标识可嵌入位置的伪标记图.原始流加密能有效防止图像信息泄露,伪标记图则用于确定嵌入的预留空间位置.实验结果表明,与现有同类算法相比,本文算法能防止标记图泄露并抵抗唯密文攻击,嵌入容量提高0.208 bpp以上,且算法实现完全可逆的同时,运行时间将近现有算法的1/4.

竖向入射S波作用下单桩水平地震响应简化解析方法

基于连续介质模型并考虑桩-土运动相互作用,将单桩视为一维线弹性梁,研究了竖向入射S波作用下的单桩水平地震响应问题。将竖向入射S波模拟为基岩水平位移,基于平面应变模型建立的土体控制方程,推导出地震作用下土体水平动力阻抗函数表达式。将土体阻抗代入单桩控制方程并联立桩-土接触条件及桩顶和桩底的边界条件,得出了竖向入射S波作用下单桩的地震响应解析解。通过将所得解与已有文献理论解和有限元结果进行对比,验证了该方法的合理性。基于所得理论解进行参数分析得出:桩-土模量比的增加可以明显降低桩-土运动相互作用因子的最小值,而较大桩身长径比以及土体滞回阻尼对桩-土运动相互作用因子的影响较小;对于桩顶水平地震放大因子来说,桩-土模量比的增加仅在高共振频率处抑制其幅值,较大桩身长径比对其影响较小,而滞回阻尼比的增加会显著抑制共振频率处的幅值;桩身地震响应仅在较小桩径比时受桩-土模量比的影响明显,并随桩-土模量比的增加而降低。

The Historical Logic on the Basic Theory of Physics—A Summary on the Cosmic Continuum Theory

Any scientific system has a unified basic theory. But physics has no unified basic theory in the modern sense. Classical mechanics, relativity and quantum mechanics have their own basic concepts, categories and principles, so none of them can be regarded as true basic theories of physics. Cosmic Continuum Theory holds that the continuity and discreteness of the universe are fundamental issues related to the unification of physics. Because the contradiction between quantum non-locality and local reality is the fundamental obstacle to the unification of physics, while locality and non-locality correspond to the continuity and discreteness of physical reality respectively. The cosmic continuum theory introduces mathematical continuum and axiomatic ideas to reconstruct the basic theory of physics, and by the correspondence of existence and its dimensions to achieve the unification of the essence of physical reality, by introducing the cosmic continuum hypothesis to achieve the unification of the continuity and discreteness of physical reality, by introducing axiomatic methods to achieve formal unification of the foundations on physics. From the perspective of Cosmic Continuum, classical mechanics, relativity and quantum mechanics are no longer the basic theories of physics, but three branch theories of physics that are respectively applicable to macroscopic, cosmoscopic and microcosmic systems.

基于L_(2)灵敏度最小化的数字滤波器状态空间实现稀疏化方法

为解决传统数字滤波器在有限精度实现时因有限字长(Finite Word Length,FWL)效应导致滤波器性能下降的问题,提出一种L_(2)灵敏度最小化的数字滤波器状态空间实现稀疏化方法.推导前向差分算子数字滤波器结构传输函数及其等效状态空间实现,根据可控及可观格莱姆矩阵得到基于相似变换矩阵的L_(2)灵敏度表达式,并进行稀疏化校准,将L_(2)灵敏度最小化问题转换为凸函数求最值问题,求导得到L_(2)灵敏度最小化表达式,代回即得前向差分算子数字滤波器的稀疏化状态空间实现.仿真结果表明,所提方法设计的数字滤波器具有更好的抗FWL效应.

Logistic和Gompertz曲线及其最优组合模型在沉降预测中的运用

堆载预压法处理的软土地基沉降变化规律与Logistic和Gompertz曲线的变化规律极为相似,有着明显的出生、成长和成熟的过程。通过对Logistic和Gompertz曲线参数的合理取值,能够较好地拟合S—t曲线,预估最终沉降量。同时,以平均绝对百分误差最小为目标,建立了组合预测模型,拟合结果显示,该组合模型对于S—t曲线的拟合,比Logistic和Gompertz曲线更具优越性。

U-G-F-S协作下的中小学教师专业发展模式建构研究——基于田家炳基金会协同教师教育的实践与思考

U-G-F-S中小学教师专业发展模式是田家炳基金会(Foundation)参与高校(University)、地方政府(Government)、中小学(School)促进教师专业发展形成的四方协同共生新机制。模式以互惠共生,民主协商,资源互补和主动发展为理念,以转变教师专业发展理念、优化教师专业发展资源、建构教师专业发展协同机制、培养时代良师、促进学校整体性发展为目标,强化四方联动,形成教师专业发展共同体。运行机制是基金会协同地方政府错位实施教师专业发展;大学依托优势团队协同诊脉中小学教师专业发展需求;大学协同精准规划教师专业发展课程方案;尝试汰选机制,实施发展性培训。

基于D-S证据理论的深基坑施工风险评价

随着地下工程的迅速发展,深基坑工程被广泛应用且其施工复杂性与风险性急剧增加。针对深基坑施工风险因素的特点建立了风险评价指标体系,运用D-S证据理论构建了深基坑施工风险评价模型。基于评价模型,根据专家意见计算指标mass函数,采用COWA算子对各指标集成赋权,并采用证据理论的层次递归合成算法对多层次指标进行合成,对合成结果进行排序;并通过实例分析验证该模型的实用性与有效性,为深基坑施工过程的风险控制提供有益参考。