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71.
To address the wide variety of solder joint configurations, the authors have developed and applied a physics-of-failure model to predicting the service life of solder joints under thermal cycling conditions. The wide variety of solder joint geometries, materials and environments makes it impractical to develop and apply empirical models to predicting the service life of solder joint interconnects. On the other hand, a physics-of-failure model that describes the failure mechanisms in solder joints can be applied to a wide range of conditions. The physics-of-failure model framework is described and a model is demonstrated for predicting the failure of a leadless surface mount solder joint under slow thermal cycling conditions. 相似文献
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The crystalline phases prepared by calcination at 350°C of amorphous iron molybdate precipitates with different chemical composition have been studied by magnetic susceptibility and EPR measurements. The magnetic susceptibility parameters and peak-to-peak resonance linewidth are defined for the stoichiometric Fe2(MoO4)3.At MotoFe ratios in the precursors higher than 1.5 the crystal products contain lattice defects changing the values of the intensive magnetic parameters. 相似文献
74.
Automatic Creation of Object Hierarchies for Ray Tracing 总被引:7,自引:0,他引:7
Intersection calculations dominate the run time of canonical ray tracers. A common algorithm to reduce the number of intersection tests required is the intersection of rays with a tree of extents, rather than the whole database of objects. A shortcoming of this method is that these trees are difficult to generate. Additionally, manually generated trees can be poor, greatly reducing the run-time improvement available. We present methods for evaluation of these trees in approximate number of intersection calculations required and for automatic generation of good trees. These methods run in O(nlogn) expected time where n is the number of objects in the scene. We report some examples of speedups. 相似文献
75.
Gangxiang Shen Sanjay K. Bose Tee Hiang Cheng Chao Lu Teck Yoong Chai 《International Journal of Communication Systems》2001,14(4):407-418
The performance of WDM networks using shortest path routing is studied under wavelength continuous (WC) and non‐continuous (NWC) constraints and dynamic traffic loading. Approximate analytical models are presented for the performance studies of such systems. Results of numerical calculations based on these models and simulations are given for different network topologies for the purposes of comparison. These analytical and simulation results are used to study the performance of these WDM networks under dynamic traffic loading. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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L. C. Hastie S. L. Cooksley F. Scougall M. R. Young P. J. Boon M. J. Gaywood 《河流研究与利用》2004,20(8):1001-1013
The spatial distribution and associated physical habitat of endangered freshwater pearl mussels (Margaritifera margaritifera) in a 145 km stretch of the River Spey, northeast Scotland, were investigated. The overall size of the Spey M. margaritifera population was estimated to be in the order of 10 million. Mussel distributions were compared with River Corridor Survey (RCS) macrohabitat data and found to be positively associated with coarse riverbed substrata, ‘fast‐flowing’ waters, riparian woodland, and river bends; and negatively associated with shingle bars, flood barriers, ‘slow‐flowing’ waters, eroding cliffs and aquatic macrophytes. Significant positive relationships between mussel density and channel slope, width and bank height, were also observed. Binary logistic regression models (based on four to six features) were used to predict the presence/absence of mussels or the occurrence of ‘optimal’ mussel habitat (i.e. mussel density >1 m?2) at any given site. Overall predictive success rates of 79% and 78% were achieved, respectively. Discriminant function models (based on five variables) were also used, with predictive success rates of 78% and 88%, respectively. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
78.
Chou Yong Tan Ramesh Singh Yee Ching Teh Yoke Meng Tan Boon Kar Yap 《International Journal of Applied Ceramic Technology》2015,12(2):437-442
In this work, the sinterability of forsterite powder synthesized via solid‐state reaction was investigated. X‐ray diffraction (XRD) analyses indicate that the synthesized powder possessed peaks that correspond to stoichiometric forsterite. Scanning electron micrographs revealed that the powders were formed agglomerates, which were made up of loosely packed fine particles. Subsequently, the forsterite powders were cold isostatically pressed into a disk shape under 200 MPa and sintered in air at temperature ranging from 1200°C to 1500°C (interval of 50°C) with ramp rate of 10°C/min and dwelling time of 2 h. The sinterability of each sintered samples was examined in terms of phase stability, relative density, Vickers hardness, fracture toughness, and microstructural examination. XRD examination on all the sintered samples exhibited pure forsterite, in which the generated peaks were found to be in a good agreement with JCPDS card no. 34‐0189. The densification of forsterite progressed to reach a maximum relative density of ~91% at 1500°C. This study also revealed that high‐strength forsterite ceramic can be synthesized via solid‐state reaction as forsterite attained favorable mechanical properties, having fracture toughness of 4.88 MPam1/2 and hardness of 7.11 GPa at 1400°C. 相似文献
79.
Joni Polili Lie Boon Poh Ng Chong Meng Samson See 《International Journal of Communication Systems》2010,23(12):1537-1553
In this paper, we propose a direction finding (DF) receiver for ultra wideband impulse radio (UWB‐IR) signal in a realistic multipath environment. The receiver uses an array of antenna, where each antenna is connected to a proposed propagation‐delay estimation structure. The advantage of the proposed structure is that it outputs a trapezoidal signal whose amplitude reflects the propagation delay and thus relaxes the sampling rate requirement of the analog‐to‐digital‐converter (ADC). The angle‐of‐arrival (AOA) is estimated from the vector of propagation delays measured with respect to reference antenna. Because these estimated delays contain outliers, we propose a simple AOA estimation algorithm based on minimum fractional‐distance search. Experimental results based on simulation show that the proposed DF receiver achieves better performance compared with the minimum ?1‐ and ?2‐based (least‐squares based) distance search. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
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