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81.
样本均值Bootstrap逼近的收敛速度 总被引:1,自引:0,他引:1
本文进一步研究Bootstrap逼近的收敛速度,在随机变量的(2+δ)阶矩(0≤δ<2)有限的情况下,讨论标准化样本均值的分布与它的Bootstrap逼近之间差的一致收敛速度,以及这种逼近与正态分布之间差的一致收敛速度。 相似文献
82.
The article presents the preliminary studies for the prototyping of a spherical parallel robot for miniaturized assembly applications.
The closed-form solution of robot’s kinematics allowed to optimize its (rotation) workspace by taking into account all singularity
surfaces and the maximum strokes of the linear actuators. Then, in view of flexures design, the maximum rotations of the passive
joints have been calculated and finally the design of the legs and of the whole robot has been carried out by means of a FEM
software, with due regard to the non-linearities arising from large displacements. 相似文献
83.
84.
Hybrid fiber laser-arc welding (HLAW) process was applied to a novel hot-rolled Nb-Ti-Mo microalloyed steels of 8 mm thickness. The steel is primarily used to manufacture automotive and construction machinery components, etc. To elucidate the effect of heat input on geometry, microstructure and mechanical properties, different heat inputs (3.90, 5.20 and 7.75 kJ/cm) were used by changing the welding speeds. With increased heat input, the depth/width of penetration was decreased, and the geometry of fusion zone (FZ) changed to “wine cup-like” shape. In regard to the microstructural constituents, the martensite content was decreased, but granular bainite (GB) content was increased. The main microstructural difference was in the FZ cross-section at 7.75 kJ/cm because of the effect of thermal source on the top and bottom. The microstructure of the top part consisted of GB, grain boundary ferrite, and acicular ferrite, while the bottom part was primarily lath martensite. The hardness distribution was similar for different heat inputs. Hardness in FZ, coarse-grained HAZ and mixed-grained HAZ was higher than the base metal (BM), but for the fine-grained HAZ was similar or marginally less than the base metal (BM). Tensile strain was concentrated in the BM such that the fracture occurred in this region. In summary, the geometry, microstructure, and mechanical properties of weld joints were superior at heat input of 5.20 kJ/cm. 相似文献
85.
新型人工关节仿生润滑系统设计及滑液摩擦学特性研究 总被引:12,自引:3,他引:12
通过摩擦学系统分析,指出了目前人工关节无润滑系统的结构缺陷.为解决此缺陷,提出了一种包括生物滑液、人工关节摩擦配副和仿生关节囊的新型人工仿生关节摩擦学系统结构,并对系统设计以及其改善现有人工关节系统润滑的潜在优越性进行了讨论.采用销-盘摩擦磨损试验机对影响人工关节仿生润滑系统摩擦学性能的滑液进行了模拟试验前的快速初步评价.结果表明,滑液可显著改善人工关节副的摩擦学特性,但其效果同系统条件及其结构元素有关.在研制仿生滑液和设计其摩擦学特性模拟试验方法时,必须结合这些影响因素进行设计和试验. 相似文献
86.
87.
A new compact pressure wave refrigerator has been designed and manufactured at the Shock Wave Research Center, Institute of Fluid Science, Tohoku University. The performance of this device was investigated for combinations of major operational parameters, such as the rotational speed of gas distributor, the length of expansion tubes, the input gas pressure. The maximum temperature decrease of 20 K has been measured. Some theoretical consideration to the efficiency of the pressure wave refrigerator and two-dimensional numerical simulations were carried out in order to understand the wave interactions that take place inside the device.Received: 26 May 2003, Accepted: 12 August 2003, Published online: 14 October 2003
Correspondence to: T. Saito 相似文献
88.
T. Touhei 《Archive of Applied Mechanics (Ingenieur Archiv)》2002,72(1):13-38
Summary The complete eigenfunction expansion form of the Green's function for a 3-D elastic layered half-space in the frequency domain
is derived in this paper. The expression of the Green's function presented here is an extension of that represented by the
residue terms and the branch line integrals given by Lamb [1]. The present expression, however, clarifies the mathematical
common frame between the residue terms and the branch line integrals with respect to the eigenfunctions and energy integrals.
For the derivation, the concept of an energy integral for the improper eigenfunctions is newly developed. The improper eigenfunctions,
which can be found in the wavenumbers for the branch cuts, are not in L
2 space, so the definition of the energy integral requires some treatment. The energy integral is defined as the limit of the
inner product of the improper eigenfunction and the definition function of the improper eigenfunction, for which the inner
product remains finite. Via the definition of the energy integral, the kernel of the branch line integral is decomposed into
the improper eigenfunction, and the complete eigenfunction expansion form of the Green's function is derived. The Green's
function can thus be expressed by summation of normal modes, complex modes pointed out in [2], the integral of the improper
eigenfunction and the residue at k=0 due to the singularity of the horizontal wavefunction.
Received 3 May 2001; accepted for publication 23 August 2001 相似文献
89.
90.
Abstract The effect of poly(methyl methacrylate) [PMMA], with different molecular weights on the mechanical properties of a polymerized BisGMA/TEGDMA base monomer resin was investigated. With the aid of acetone solvent, PMMA could be readily dissolved in BisGMA/TEGDMA mixtures. The addition of PMMA can significantly improve the compressive strengths and decrease the Knoop hardness values of the BisGMA/TEGDMA/PMMA semi-IPNs. The thermal expansion coefficients rapidly increased before Tg, and decreased after T g. The observed properties could be attributed to the effect of the molecular weight of the PMMA on the phase structures of the semi-IPNs. 相似文献