无约束修正Timoshenko梁的冲击问题

介绍了修正后的Timoshenko梁运动方程,并比较了修正Timoshenko梁与经 典Timoshenko梁的运动方程. 推导了考虑剪切变形引起的转动惯量的修正Timoshenko 梁的正交条件,推导了集中质量对无约束修正Timoshenko梁的正碰撞对梁所引起的瞬态冲 击响应公式,并用算例进行了分析,且与集中质量对经典的无约束Timoshenko梁的正碰撞 对梁所引起的冲击响应进行了比较,另外还用算例分析了梁的刚度的变化和冲击质量比对其 冲击响应产生的影响.     

Studies on structural safety in stochastically excited Duffing oscillator with double potential wells

The effects of the Gaussian white noise excitation on structural safety due to erosion of safe basin in Duffing oscillator with double potential wells are studied in the present paper. By employing the well-developed stochastic Melnikov condition and Monte–Carlo method, various eroded basins are simulated in deterministic and stochastic cases of the system, and the ratio of safe initial points (RSIP) is presented in some given limited domain defined by the system’s Hamiltonian for various parameters or first-passage times. It is shown that structural safety control becomes more difficult when the noise excitation is imposed on the system, and the fractal basin boundary may also appear when the system is excited by Gaussian white noise only. From the RSIP results in given limited domain, sudden discontinuous descents in RSIP curves may occur when the system is excited by harmonic or stochastic forces, which are different from the customary continuous ones in view of the first-passage problems. In addition, it is interesting to find that RSIP values can even increase with increasing driving amplitude of the external harmonic excitation when the Gaussian white noise is also present in the system. The project supported by the National Natural Science Foundation of China (10302025 and 10672140). The English text was polished by Yunming Chen.     

一步法直接合成碳酸二甲酯催化剂

采用浸渍法以MgO、海泡石（Sep）。γ-Al2O3为载体,制备了一系列金属盐Lewis酸-无机碱双组分负载型催化剂,以环氧丙烷（PO）一步合成碳酸二甲酯（DMC）反应为探针。考察了催化剂的不同载体活性组分和反应条件对合成DMC的产率及选择性的影响。结果表明,催化剂的活性次序为：NaOH—LiCl／MgO）NaOH—LiCl／Sep）NaOH—LiCl／γ-Al2O3;选择性的次序为：NaOH—LiCl／Sep）NaOH—LiCl／MgO）NaOH—LiCl／γ-Al2O3。NaOH—LiCl／SeP催化剂具有较高的活性和选择性;其最佳反应条件为：反应温度160℃。反应时间5h,甲醇与PO的量之比为1：1。在最佳条件下。PO转化率为82．6％,DMC的产率达到7．68％。     

模糊选择函数半序合理的充分条件

在G?del t-模下,研究了模糊选择函数的半序合理性.首先给出了模糊选择函数的合理性条件FA1.然后研究了该条件与模糊选择函数半序合理性之间的关系,得到了半序合理的一个充分条件.     

锥形模圆柱体超塑性挤压非局部摩擦分析

为了考虑金属材料表面微凸结构对模具与工件接触区域上的非局部摩擦效应,在锥形模圆柱体超塑性挤压加工分析中,采用Oden等提出的非局部摩擦定律代替经典的库仑摩擦定律,利用主应力法或工程法建立了相应问题的积微分形式的力平衡方程.在简化的情况下,采用摄动法求得所论问题的近似解,并分析了影响应力的非局部效应的相关因素.     

Bias dependence of a deep submicron NMOSFET response to total dose irradiation

Deep submicron n-channel metal-oxide-semiconductor field-effect transistors (NMOSFETs) with shallow trench isolation (STI) are exposed to ionizing dose radiation under different bias conditions.The total ionizing dose radiation induced subthreshold leakage current increase and the hump effect under four different irradiation bias conditions including the worst case (ON bias) for the transistors are discussed.The high electric fields at the corners are partly responsible for the subthreshold hump effect.Charge trapped in the isolation oxide,particularly at the Si/SiO 2 interface along the sidewalls of the trench oxide creates a leakage path,which becomes a dominant contributor to the offstate drain-to-source leakage current in the NMOSFET.Non-uniform charge distribution is introduced into a threedimensional (3D) simulation.Good agreement between experimental and simulation results is demonstrated.We find that the electric field distribution along with the STI sidewall is important for the radiation effect under different bias conditions.     

液体表面张力系数测定实验的几点分析

用拉脱法测定水的表面张力系数实验中，用焦利氏秤测定（Ｆ—Ｗ）时，确定焦利氏秤标尺读数Ｌ１、Ｌ２的位置有两种方法。本文旨在详细分析这两种方法隐含的实验条件和对实验结果的影响．并进行比较，得出结论。     

复相系平衡条件及平衡稳定性条件的分析

复相系平衡条件及平衡稳定性条件的分析曾丹苓（重庆大学热力工程系重庆６３００４４）关键词复相系，平衡条件，平衡稳定性条件１引言汽液相变是工程上常见的现象，它是一个复杂的物理过程，涉及到传热传质、相转变、表面现象、流体流动及工质热物性等领域，但从热力学的...     

Directivity calculation with experimental verification for a conformal array of underwater acoustic transducers

The radiation directivity of a complicated conformal array of underwater acoustic transducers is presented based on the boundary ＂element method. It includes the element directivity of each transducer, the natural beam pattern and the controlled beam pattern of the transducer array. At first, the boundary element model of the conformal array is built up, and then the boundary condition is exerted on the model according to the design and environment in which the transducer array is used, and the radiation directivity of the conformal array is calculated. An experiment has been done to measure the directivity in an anechoic water tank. The calculated and the experimental results are compared and analyzed. They are consistent to each other. It is shown that the boundary element method together with the detailed calculations is successful to simulate and predict the radiation directivity of an underwater acoustic transducer array.     

热处理条件对PVA薄膜阻氢性能的影响

采用XRD测定了PVA薄膜在不同热处理条件下的结晶度,并用自行设计的渗氢系数测量系统研究了在不同热处理条件下的PVA薄膜阻氢性能的变化规律。结果表明,PVA薄膜的热处理温度越高,其结晶度越高,越有利于提高PVA薄膜的阻氢性能,但热处理温度宜选择在180℃以下,以防止PVA薄膜热降解,另一方面,在PVA的玻璃化转变温度以下进行热处理同样能够提高PVA薄膜的阻氢性能,而醇解度较低的PVA薄膜在玻璃化转变温度以下经热处理后的阻氢性能提高的幅度较大。