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91.
P. Wang I. M. Hutchings S. J. Duncan L. Jenkins E. Woo 《Journal of Materials Science》2006,41(15):4847-4859
This paper presents research work on the characteristics and micro mechanism of strain whitening of a thermoplastic olefin material. Systematic tensile tests have been carried out to investigate the relation between strain whitening extent and external factors, including the deformation employed and the environmental temperature. A new optical method has been developed for the measurement of strain on polymer tensile samples. Applying this method relation between whitening level (grey level change) and strain has been studied. A new concept of ‘strain whitening sensitivity’ has been proposed and defined as the strain whitening induced by unit deformation or strain. Non-monotonic relation between whitening level and strain has been found. Strained and fractured samples were observed with A JEOL 5800 LV SEM for the micro mechanism investigation. The change of microstructure on the sample surface has been extensively observed and the combined effects of small ridges and micro-voids on the scattering efficiency of the strained surface were regarded as reasons for the non-monotonic relation between whitening level and strain. 相似文献
92.
Technological advancements have led to an increase in demand for fabrication of small and cheap miniature components or parts, especially in the medical and electronic fields. In this research work, micro-rods of varying lengths and diameters were molded using a specially designed tabletop injection molding machine. The main purpose was to investigate whether complete filling of the microcavities was possible and whether small cavity openings will restrict melt flow into the cavities.
Process parameters, such as injection pressure, mold temperature and melt temperature were varied. The micro-rods obtained were analyzed with Scanning Electron Micrographs (SEM). The results showed that injection pressure was the most important parameter for microinjection molding. The use of a vacuum system also yielded better results. 相似文献
Process parameters, such as injection pressure, mold temperature and melt temperature were varied. The micro-rods obtained were analyzed with Scanning Electron Micrographs (SEM). The results showed that injection pressure was the most important parameter for microinjection molding. The use of a vacuum system also yielded better results. 相似文献
93.
Electromagnetic shielding properties of soft magnetic metal and ferrite composites for application to suppress noise in a radio frequency range 总被引:1,自引:0,他引:1
Yong Woon Yun Sang Woo Kim Gwang Yoon Kim Yoon Bae Kim Yeo Chun Yun Kyung Sup Lee 《Journal of Electroceramics》2006,17(2-4):467-469
Electromagnetic shielding properties of soft magnetic metal alloy (Fe-Al-Si) flakes and Ni-Zn ferrite composites for effective
suppression of broadband and high frequency noise were investigated. In the soft magnetic composites, the maxima of reflection
loss were shifted to high frequency with increase in content of Ni-Zn ferrite. The composites with content of 50 and 70% ferrite
exhibited broadband absorptive characteristics. The broadband character- istics might be caused by the extended resonance
due to an overlap between imaginary permeability and permittivity of the two composites over the frequency range from 2 to
10 GHz. 相似文献
94.
The influence of complex dopants including donor and acceptor ions on microstructure and electrical properties of PZT (Zr/Ti
= 53/47) ceramics was investigated. The prepared PZT ceramics modified with complex soft dopants, La+3 and Nb+5, showed that the piezoelectric properties were enhanced and stable with the compositional variations, which made it possible
to establish the higher reliability and reproducibility of the piezoelectric performances. For 1.0 mol% La and 1.2 mol% Nb
doped composition, the maximum value, k
P
= 0.66, was obtained. Unlike single element doping, the complex doping of both the donor and acceptor ions caused various
compensation effects for the piezoelectric properties of the PZT ceramics. The improved piezoelectric properties, i.e., enhanced
Q
m
with remaining higher k
p
, were obtained in the PZT composition complexly doped with La+3 and Fe+3. For 1.0 mol% La and 2.0 mol% Fe doped PZT composition, relatively high Q
m
and k
p
values of 580 and 0.53, respectively, were obtained. It was also shown that the PZT composition had the rather lowered dielectric
constant, ε
r
= 800, and considerably low loss, tanδ = 0.003. By changing the dopants compositions, the properties can also be tailored
over wider range. 相似文献
95.
Sung Hwan Hwang Dae Dong Seo Jae Yong An Myeong-Hyun Kim Woo Chang Choi Sung Ryul Cho Sang Hwan Lee Hyo-Hoon Park Han Seo Cho 《Advanced Packaging, IEEE Transactions on》2006,29(3):457-462
We propose an advanced structure of optical subassembly (OSA) for packaging of the vertical-cavity surface-emitting laser (VCSEL) array, using (111) facet mirror of the V-groove ends formed in a silicon optical bench (SiOB) and angled fiber apertures. The feature of our OSA can provide a low optical crosstalk between neighboring channels, a low feedback reflection, and a large misalignment tolerance along the V-groove. We describe the optimized design of fiber angle, VCSEL position, and fiber position. The fabricated OSA structure consists of 12 channels of angled fiber array, 54.7/spl deg/ V-grooves, Au-coated mirrors on (111) end facet of the V-grooves, and flip-chip-bonded VCSEL array on a SiOB. In this structure, the beam emitted from the VCSEL is deflected at the 54.7/spl deg/ mirror of (111) end facet and propagated into the angled fiber. The angled fiber array was polished by 57/spl deg/. Fabricated OSAs showed a coupling efficiency of 30%-50% that is 25 times larger than that obtained from an OSA with a vertically flat fiber array. Our OSA showed large misalignment tolerance of about 90 /spl mu/m along the longitudinal direction in the V-groove. We fabricated a parallel optical transmitter module using the OSA and demonstrated 12 channels /spl times/2.5 Gb/s data transmission with a clear eye diagram. 相似文献
96.
Kim H. Nam B.-G. Sohn J.-H. Woo J.-H. Yoo H.-J. 《Solid-State Circuits, IEEE Journal of》2006,41(11):2373-2381
A 32-bit fixed-point logarithmic arithmetic unit is proposed for the possible application to mobile three-dimensional (3-D) graphics system. The proposed logarithmic arithmetic unit performs division, reciprocal, square-root, reciprocal-square-root and square operations in two clock cycles and powering operation in four clock cycles. It can program its number range for accurate computation flexibility of 3-D graphics pipeline and eight -region piecewise linear approximation model for logarithmic and antilogarithmic conversion to reduce the operation error under 0.2%. Its test chip is implemented by 1-poly 6-metal 0.18-mum CMOS technology with 9-k gates. It operates at the maximum frequency of 231 MHz and consumes 2.18 mW at 1.8-V supply 相似文献
97.
98.
Time-accurate Navier-Stokes simulation of vortex convection using an unstructured dynamic mesh procedure 总被引:1,自引:0,他引:1
A two-dimensional Navier-Stokes flow solver is developed for the simulation of unsteady flows on unstructured adaptive meshes. The solver is based on a second-order accurate implicit time integration using a point Gauss-Seidel relaxation scheme and a dual time-step subiteration. A vertex-centered, finite-volume discretization is used in conjunction with Roe’s flux-difference splitting. The Spalart-Allmaras one equation model is employed for the simulation of turbulence. An unsteady solution-adaptive dynamic mesh scheme is used by adding and deleting mesh points to take account of spatial and temporal variations of the flowfield. Unsteady viscous flow for a traveling vortex in a free stream is simulated to validate the accuracy of the dynamic mesh adaptation procedure. Flow around a circular cylinder and two blade-vortex interaction problems are investigated for demonstration of the present method. Computed results show good agreement with existing experimental and computational results. It was found that unsteady time-accurate viscous flows can be accurately simulated using the present unstructured dynamic mesh adaptation procedure. 相似文献
99.
Kai Tang Ming-En Wang Lin-Lin Chen Shuo-Yan Chou Tony C. Woo Ravi Janardane 《Computer aided design》1997,29(12):825-836
A translational sweep is the translating of a polygon, called the generatrix G, around another polygon, called the directrix D, under two conditions: (1) G is always in contact with D; and (2) the interiors of G and D do not intersect. Three classes of translational sweep are studied, including the case in which both G and D are convex; the case in which G is convex, D monotone; and the case in which both are monotone. Efficient algorithms for computing the trajectory and the swept area as well as geometric and computational properties are presented for each class. A notion called the inverse generatrix, which reveals a duality between the trajectory and the swept polygon, is introduced to reduce complexity. 相似文献
100.
Electronic Business using eXtensible Markup Language (ebXML) Business Process Specification Schema (BPSS) supports the specification of the set of elements required to configure a runtime system in order to execute a set of ebXML business transactions. The BPSS is available in two stand-alone representations; a UML version and an XML version. Due to the limitations of UML notations and XML syntax, however, the current ebXML BPSS specification is insufficient to formally specify semantic constraints of modeling elements. In this study, we propose a classification scheme for BPSS semantic constraints, and describe how to represent those semantic constraints formally using Object Constraint Language. As a way to verify a particular Business Process Specification (BPS) with formal semantic constraint modeling, we suggest a rule-based approach to represent the formal semantic constraints, and describe a detail mechanism to apply the rule-based specified constraints to the BPS in a prototype implementation. 相似文献