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排序方式: 共有56条查询结果,搜索用时 234 毫秒
1.
Behrooz?HassaniEmail author Mostafa?Khanzadi S.?Mehdi?Tavakkoli 《Structural and Multidisciplinary Optimization》2012,45(2):223-233
The Isogeometric Analysis (IA) method is applied for structural topology optimization instead of finite elements. For this
purpose, a control point based Solid Isotropic Material with Penalization (SIMP) method is employed and the material density
is considered as a continuous function throughout the design domain and approximated by the Non-Uniform Rational B-Spline
(NURBS) basis functions. To prevent the formation of layouts with porous media, a penalization technique similar to the SIMP
method is used. For optimization an optimality criteria is derived and implemented. A few examples are presented to demonstrate
the performance of the method. It is shown that, dissimilar to the element based SIMP topology optimization, the resulted
layouts by this method are independent of the number of the discretizing control points and checkerboard free. 相似文献
2.
Kazem Tahmasebi Mohammad Maleki Shahraki Touraj Ebadzadeh 《Materials and Manufacturing Processes》2018,33(8):817-821
Coarse-grained ZnO varistors for low-voltage applications were prepared by microwave sintering technique under different soaking times of 5–150?min. For comparison, a low-voltage ZnO varistor was also prepared through a conventional sintering process. Microwave sintering remarkably enhanced the grain growth rate of ZnO varistors. Average grain size of the sample prepared by microwave sintering in 15?min was about 20?µm, which is similar to the grain size of sample prepared conventionally in 150?min time. In addition to grain growth, an increase in microwave sintering time led to precipitation of zinc titanate (Zn2TiO4) on the top surface of samples which sintered for long dwell times. X-ray diffraction and scanning electron microscopy results from different points of the samples declared that precipitation of Zn2TiO4 phase is due to the high rate of bismuth evaporation of Bi-rich liquid from top surface and the reaction between remaining titanium ions on the surface with ZnO. The results showed that increasing sintering time from 5 to 150?min increased the grain size from 14 to 33?µm, consequently, the breakdown field decreased from 90 to 27?V/mm, respectively. These changes led to a switch in the varistor application, from low to very low voltage. 相似文献
3.
Alireza Tavakkoli Mircea Nicolescu George Bebis Monica Nicolescu 《Machine Vision and Applications》2009,20(6):395-409
Most methods for foreground region detection in videos are challenged by the presence of quasi-stationary backgrounds—flickering
monitors, waving tree branches, moving water surfaces or rain. Additional difficulties are caused by camera shake or by the
presence of moving objects in every image. The contribution of this paper is to propose a scene-independent and non-parametric
modeling technique which covers most of the above scenarios. First, an adaptive statistical method, called adaptive kernel
density estimation (AKDE), is proposed as a base-line system that addresses the scene dependence issue. After investigating
its performance we introduce a novel general statistical technique, called recursive modeling (RM). The RM overcomes the weaknesses
of the AKDE in modeling slow changes in the background. The performance of the RM is evaluated asymptotically and compared
with the base-line system (AKDE). A wide range of quantitative and qualitative experiments is performed to compare the proposed
RM with the base-line system and existing algorithms. Finally, a comparison of various background modeling systems is presented
as well as a discussion on the suitability of each technique for different scenarios. 相似文献
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5.
Jahangiry Hassan A. Gholhaki Majid Naderpour H. Tavakkoli S. Mehdi 《International Journal of Mechanics and Materials in Design》2021,17(4):947-967
International Journal of Mechanics and Materials in Design - This article aims to utilize IsoGeometric analysis (IGA) and Level set method for topology optimization of elastoplastic plane stress... 相似文献
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9.
Sushilov NV Tavakkoli J Cobbold RS 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2001,48(1):274-284
Based on the method proposed by Donnelly and Ziolkowski [1], [2], a new general solution has been obtained for the isotropic/homogeneous scalar wave equation in cylindrical coordinates. It is shown that well-known limited diffraction beams such as Durnin's Bessel beams [4], Lu and Greenleaf's X-wave [15], localized waves of Donnelly and Ziolkowski [1], [2], and limited-diffraction, band-limited waves of Li and Bharath [19], [20] can be obtained from this generic solution as particular cases. In addition, we have obtained new X-wave solutions and have calculated the field characteristics for one of them using a finite aperture realization. It is shown that with a proper choice of the free parameter values, well-behaved X-waves with narrow beamwidths and large depths of field can be achieved. For similar source spectra, the results are compared with Lu and Greenleaf's zeroth-order X-wave, and it is shown that the depth of field and beamwidth are very comparable. 相似文献
10.
Saeed Hesaraki Touraj Ebadzadeh Shaghayegh Ahmadzadeh-Asl 《Journal of materials science. Materials in medicine》2010,21(7):2141-2149
In this study, bioceramic nanocomposites were synthesized by sintering compacted bodies of hydroxyapatite (HA) mixed with
5 or 15 wt% nanosilicon carbide at 1100 or 1200°C in a reducing atmosphere. Pure hydroxyapatite was also prepared for comparison.
Phase compositions, structural and physical properties of the composites were studied using appropriate techniques. Some in
vitro biological properties of the composites were also investigated by using newrat calvaria osteoblastic cells. X-ray diffraction
analysis indicated that tricalcium phosphate (TCP) comprising negligible α-TCP and considerable β-TCP were formed in composites
during sintering meanwhile hydroxyapatite and silicon carbide (SiC) were also existed in the composition. Based on the results,
that composite made of 5 wt% nanosilicon carbide exhibited higher bending strength, fracture toughness and bulk density than
pure HA and composite with 15 wt% silicon carbide. The scanning electron microscopy coupled with energy dispersive X-ray analysis
revealed that the addition of nanosilicon carbide suppressed the grain growth and yielded a feature of island-type clusters
consisting of blistered calcium phosphate (HA and TCP) and SiC grains. Also, in this study, better proliferation rate and
alkaline phosphatase activity were observed for the osteoblastic cells seeded on top of the composites compared to pure HA.
Overall, the results indicated that the composite of 95 wt% hydroxyapatite and 5 wt% SiC exhibited better mechanical and biological
properties than pure HA and further addition of SiC failed strength and toughness. 相似文献