局部覆盖约束层阻尼梁动力学问题的解析解

采用传递函数方法对局部覆盖约束层阻尼梁进行了动力学分析。由Hamilton原理导出了约束层阻尼梁的运动方程和边界条件,经Laplace变换后引入状态向量建立了系统的状态空间方程,由边界条件和连接条件共同构成的定解条件,利用传递函数方法求解方程得到了系统的固有频率、损耗因子和频响曲线。算例计算结果与相关文献或NAS-TRAN计算结果吻合良好,验证了传递函数方法的有效性和精确性,且本文方法更适合于阻尼层粘弹性材料采用随频率变化的复模量模型的情况。同时还讨论了约束层阻尼的位置和覆盖率对系统固有频率和损耗因子的影响,为今后的优化研究奠定了基础。     

线弹性问题的locking-free双参数元

文中运用双参数法提出了一个4参数的四边形非协调有限元,讨论了该单元对纯位移边界条件下的均匀介质线弹性方程的逼近问题.证明了在材料几乎不可压时单元对弹性问题的一致最优收敛性,数值试验验证了理论分析结果.并通过构造后处理算子,得到了超收敛结果.所有的分析结果都可以推广到三维情形.     

Atomic Layer Deposition of Tunnel Barriers for Superconducting Tunnel Junctions

We demonstrate a technique for creating high quality, large area tunnel junction barriers for normal–insulating–superconducting or superconducting–insulating–superconducting tunnel junctions. We use atomic layer deposition and an aluminum wetting layer to form a nanometer scale insulating barrier on gold films. Electronic transport measurements confirm that single-particle electron tunneling is the dominant transport mechanism, and the measured current–voltage curves demonstrate the viability of using these devices as self-calibrated, low temperature thermometers with a wide range of tunable parameters. This work represents a promising first step for superconducting technologies with deposited tunnel junction barriers. The potential for fabricating high performance junction refrigerators is also highlighted.     

Two Layer Symmetric Cryptography Algorithm for Protecting Data fromAttacks

Many organizations have insisted on protecting the cloud server from the outside, although the risks of attacking the cloud server are mostly from the inside. There are many algorithms designed to protect the cloud server from attacks that have been able to protect the cloud server attacks. Still, the attackers have designed even better mechanisms to break these security algorithms. Cloud cryptography is the best data protection algorithm that exchanges data between authentic users. In this article, one symmetric cryptography algorithm will be designed to secure cloud server data, used to send and receive cloud server data securely. A double encryption algorithm will be implemented to send data in a secure format. First, the XOR function will be applied to plain text, and then salt technique will be used. Finally, a reversing mechanism will be implemented on that data to provide more data security. To decrypt data, the cipher text will be reversed, salt will be removed, and XOR will be implemented. At the end of the paper, the proposed algorithm will be compared with other algorithms, and it will conclude how much better the existing algorithm is than other algorithms.     

一个二阶收敛的平面弹性问题Locking-free三角形元

对于纯位移平面弹性问题,以往构造的单元的能量模误差多是一阶收敛的,本文在不完全三次多项式空间中,基于div→v ∈ P1的限制构造了一个14自由度的非协调三角形单元,该单元是Locking-free的,且能量模和L2-模误差分别达到了二阶和三阶收敛,并且通过数值实验验证了该单元的理论结果.     

Homogeneous Solutions of a Skew-Symmetric Problem with Mixed Boundary Conditions for a Piezoceramic Layer

On the basis of a modified scheme of homogeneous solutions significantly simplifying the Lur'e scheme, we construct homogeneous solutions for a piezoceramic layer with mixed boundary conditions imposed on its faces. We consider an electroelastic state skew-symmetric about the median plane of the layer. It is shown that the corresponding homogeneous solutions do not contain biharmonic terms and the components of the conjugate electroelastic field in the layer have the form of Fourier series with respect to the coordinate x ₃.     

Elasticity Solution of a Laminated Clamped Cylindrical Shell with Piezoelectric Layer under Dynamic Load

Dynamic elasticity solution for a clamped, laminated cylindrical shell with two orthotropic layers bounded with a piezoelectric layer and subjected to impulse load distributed on inner surface is presented. The piezoelectric layer serves as sensor/actuator. The governing elasticity PDE equations are reduced to ordinary differential equations by means of Legendre polynomial expansion for displacement and electric potential in the axial direction. The resulting equations are transferred into state space form and reduced to an eigenvalue problem by using Galerkin's finite element in radial direction. The static and dynamic results are presented for [0/90/Piezo] lamination. The radius to thickness ratio effect on dynamic behavior is studied. The results are compared for different thickness ratios and applied electric loads with simply-supported shell results. Time responses for sensor and actuated shell are presented and natural frequencies are compared with simply-supported shell results.     

弹性接触问题的最小二乘混合变分形式

采用最小二乘法对弹性接触问题提出了一种新的混合变分形式，对该变分问题解的存在唯一性进行了论证。     

《多点敷设支撑层的粘弹性约束阻尼梁振动分析》

针对夹层约束阻尼梁结构的减振特性进行深入研究,在其基础上扩展多处敷设增设支撑层的约束阻尼,建立了多点铺设增设支撑层约束阻尼梁的振动特性模型,利用粘弹性材料的Maxwell模型、假设模态法、有限元理论和力学原理,结合功能特性方程和Lagrange方程,导出了增设支撑层约束阻尼梁的振动位移响应方程。通过对敷设双支撑约束阻尼简支梁在支撑层厚度变化的参数研究,可以看到增设适当厚度的支撑层能够达到更好的减振效果。     

Bending of a Layer with Through Tunnel Cuts and Free-Sliding End Faces

We propose a new procedure for the solution of mixed three-dimensional skew-symmetric problems of the theory of elasticity for a layer weakened by through tunnel cracks. The boundary-value problem is reduced to a system of 3k (k = 1, 2, ...) one-dimensional singular integral equations. We present some results of numerical calculations of the stress intensity factors.     

Variational Principle for the Temperature Problem of the Elasticity Theory for Stresses

The variational formulation of a problem is frequently used in strength analysis of parts and structural elements. The authors present a variational principle whose Euler's equations are the differential equations of thermoelasticity for stresses.     

Analytic Solution of the Plane Problem of the Theory of Elasticity for a Nonuniform Strip

We construct the analytic solution of the plane problem of the theory of elasticity in stresses for a strip nonuniform across the width. To deduce the key equations, we perform the direct integration of the original differential balance and continuity equations. In the space of Fourier transforms, the key equations are reduced to an integral Volterra equation of the second kind, which is solved by the method of successive approximations.__________Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 41, No. 1, pp. 114–116, January–February, 2005.     

Parametric Excitation of Marangoni Instability in a Heated Thin Layer Covered by Insoluble Surfactant

The paper presents the analysis of the impact of vertical periodic vibrations on the long-wavelength Marangoni instability in a liquid layer with poorly conducting boundaries in the presence of insoluble surfactant on the deformable gas-liquid interface. The layer is subject to a uniform transverse temperature gradient. Linear stability analysis is performed in order to find critical values of Marangoni numbers for both monotonic and oscillatory instability modes. Longwave asymptotic expansions are used. At the leading order, the critical values are independent on vibration parameters; at the next order of approximation we obtained the rise of stability thresholds due to vibration.     

Symmetric Problem of Stable Interaction of Cracks with Thin Rigid Inclusions in a Three-Dimensional Matrix

By the method of boundary integral equations, we solve the problem of interaction of coplanar circular cracks with thin rigid inclusions in an unbounded elastic matrix under the action of normal loads applied to the crack surfaces and harmonic as functions of time. The inertial effects of the distribution of stresses along the crack contour are analyzed with regard for the presence of neighboring macroinclusions of fixed mass. The corresponding static solutions are obtained in the limiting case where the wave numbers are equal to zero.     

Broadband Light Absorption and Efficient Charge Separation Using a Light Scattering Layer with Mixed Cavities for High‐Performance Perovskite Photovoltaic Cells with Stability

CH₃NH₃PbI₃ is one of the promising light sensitizers for perovskite photovoltaic cells, but a thick layer is required to enhance light absorption in the long‐wavelength regime ranging from PbI₂ absorption edge (500 nm) to its optical band‐gap edge (780 nm) in visible light. Meanwhile, the thick perovskite layer suppresses visible‐light absorption in the short wavelengths below 500 nm and charge extraction capability of electron–hole pairs produced upon light absorption. Herein, we find that a new light scattering layer with the mixed cavities of sizes in 100 and 200 nm between transparent fluorine‐doped tin oxide and mesoporous titanium dioxide electron transport layer enables full absorption of short‐wavelength photons (λ < 500 nm) to the perovskite along with enhanced absorption of long‐wavelength photons (500 nm < λ < 780 nm). Moreover, the light‐driven electric field is proven to allow efficient charge extraction upon light absorption, thereby leading to the increased photocurrent density as well as the fill factor prompted by the slow recombination rate. Additionally, the photocurrent density of the cell with a light scattering layer of mixed cavities is stabilized due to suppressed charge accumulation. Consequently, this work provides a new route to realize broadband light harvesting of visible light for high‐performance perovskite photovoltaic cells.     

Distribution of Residual Stresses Induced by Axially Symmetric Plastic Strains in a Layer

By using the direct method of integration of the resolving equations of an axially symmetric problem of the theory of elasticity for a layer in stresses, we find residual stresses for a given field of plastic strains. For plastic strains symmetric about the median surface of the layer, we performed the numerical analysis of the distribution of residual stresses. It is shown that stresses undergo significant redistributions over the thickness of the layer as the drop of plastic strains in the indicated direction increases.