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991.
M. Gunawan E. H. Wong S. G. Mhaisalkar L. T. Davila Yu Hong J. F. J. M. Caers T. K. Tsai 《Journal of Electronic Materials》2004,33(9):1041-1047
Adhesive interconnections are considered to be attractive alternatives to lead or lead-free solder interconnects because of
their lower processing temperatures and extendability to fine pitch applications. However, reliability issues, such as moisture-induced
delamination and viscoelastic relaxation of the adhesive in both steady-state and cyclic loading, continue to pose a challenge
to widespread implementation. To date, the static and cyclic relaxation characteristics of nonconductive adhesives (NCAs)
are yet to be understood. This paper attempts to provide insights into this static and cyclic relaxation behavior through
experimental characterization and modeling. The viscoelastic property of a typical NCA material was characterized, and a simulation
program with integrated circuit emphasis (SPICE) modeling program was used to model the cyclic relaxation behavior. The modeling
results were successfully validated with a series of experiments. This showed that cyclic relaxation of the adhesive can be
successfully modeled using linear-viscoelastic property. The phenomenon of slower relaxation of the adhesive under cyclic
loading than that in static loading suggests that accelerated reliability testing used in solder-joint fatigue durability
investigations may not be directly applicable to the adhesive interconnections. A rework methodology applicable to adhesive
interconnects using cyclic loading has also been proposed. 相似文献
992.
基于等效时间的混凝土绝热温升、热传导方程,考虑温度对早期混凝土水化热化学反应速率和徐变特性的影响,计算了大体积混凝土墙中心的温升。采用裂缝带模型计算温度裂缝,用半解析迭代法进行了混凝土墙的温度应力和开裂计算。 相似文献
993.
Ning Y. Wong Y.S. Fuh J.Y.H. Loh H.T. 《Automation Science and Engineering, IEEE Transactions on》2006,3(1):73-80
This paper discusses the effect of geometric shape on the accuracy of direct metal laser sintering (DMLS) prototypes. The percentage shrinkages due to different shapes are investigated and their empirical relationship is determined. A new speed-compensation (SC) method is proposed to reduce uneven shrinkage affected by the two-dimensional geometric shape at each layer. From case studies conducted, the optimized SC method is found to be efficient in improving the accuracy of prototypes fabricated. Note to Practitioners-This paper aims to address the problem of dimensional errors of parts built by the direct metal laser sintering (DMLS) process. Existing compensation approaches are normally based on a general relationship between the nominal dimensions and the errors after sintering. However, the effect arising from different geometric shapes is not considered. A new approach is proposed using different scan speed settings to compensate for the effect of geometric shapes to improve the dimensional accuracy of the entire part. During processing, the laser sinters along the trajectory are guided by the hatch vectors or dexel. An appropriate experimental method is used to establish the relationship for different scan speeds with the dexel length to the final accuracy. When building the part, the laser scan speed is adjusted dynamically according to the dexel length which varies with the geometric shape of the part. The case study demonstrates that the proposed method can generate correct speed settings to effectively increase the dimensional accuracy of the final part. Although this method has been developed based on the DMLS process, it is also applicable to other laser sintering processes. In future research, other process parameters, such as laser power, will be considered independently, or together with the scan speed, for possible further improvement on the dimensional accuracy. 相似文献
994.
M. K. Yoo K. Y. Cho H. H. Song Y. J. Choi J. W. Kwon M. K. Kim J. H. Lee W. R. Wee C. S. Cho 《Drug development and industrial pharmacy》2005,31(4):455-463
The system was designed to use Poloxamer as a vehicle for ophthalmic drug delivery using in situ gel formation property. To enhance the wound healing and cell adhesion as well as transparency of Poloxamer hydrogel, chondroitin 6-sulfate (C6S) was introduced into Poloxamer. For this purpose, mono amine-terminated Poloxamer (MATP), which was end-capped with ethylene amine group only in one side of terminal hydroxyl groups of Poloxamer, was synthesized. Subsequently, C6S-graft-Poloxamer copolymer (C6S-g-Poloxamer) was prepared by reaction between the amine groups of MATP and carboxyl groups of C6S in the presence of 1-ethyl-3-(3-dimethylaminopropyl)-carboimide (EDC). The coupling of MATP with C6S was clarified by 1H-NMR and FT-IR spectroscopy. The gelation temperature of graft copolymers was determined by measuring the temperature at which immobility of the meniscus in each solution was first noted. Release behavior of ciprofloxacin from C6S-g-Poloxamer hydrogel in vitro was investigated as a function of C6S content in the graft copolymer by a spectrophotometric assay at 287 nm using an UV spectrophotometer. Differences in the adhesion and morphology of human lens cell between Poloxamer- and C6S-g-Poloxamer-coated surfaces were also investigated. The gelation temperatures of C6S-g-Poloxamer copolymers were lowered with increasing of the concentration of the copolymer and decreasing of C6S content. The release of ciprofloxacin from the graft copolymer was sustained compared with Poloxamer itself and decreased with increasing the content of C6S in the copolymer due to the in situ gel formation of the copolymer and viscous properties of C6S. Human lens cells (B3) adhered to C6S-g-Poloxamer-coated surface were observed as transformed shapes after 2 days. The bioadhesive and thermally gelling of these graft copolymers will be expected to be an excellent drug carrier for the prolonged delivery to surface of the eye. 相似文献
995.
Shang H. Okorn-Schimdt H. Ott J. Kozlowski P. Steen S. Jones E.C. Wong H.-S.P. Hanesch W. 《Electron Device Letters, IEEE》2003,24(4):242-244
In this letter, we report germanium (Ge) p-channel MOSFETs with a thin gate stack of Ge oxynitride and low-temperature oxide (LTO) on bulk Ge substrate without a silicon (Si) cap layer. The fabricated devices show 2 /spl times/ higher transconductance and /spl sim/ 40% hole mobility enhancement over the Si control with a thermal SiO/sub 2/ gate dielectric, as well as the excellent subthreshold characteristics. For the first time, we demonstrate Ge MOSFETs with less than 100-mV/dec subthreshold slope. 相似文献
996.
Antioxidant activities of aqueous extracts of selected plants 总被引:1,自引:0,他引:1
The antioxidant properties of 25 edible tropical plants, expressed as Trolox equivalent antioxidant capacity (TEAC), were studied using DPPH (1,1-diphenyl-2-picrylhydrazyl free radical) scavenging and reducing ferric ion antioxidant potential (FRAP) assays. Their cupric ion chelating activities (CCA) and total polyphenol contents (TPC) were also determined. A strong correlation between TEAC values obtained for the DPPH assay (TEACDPPH) and those for the FRAP assay (TEACFRAP) implied that compounds in the extracts were capable of scavenging the DPPH free radical and reducing ferric ions. A satisfactory correlation of TPC with TEACDPPH and TEACFRAP suggested that polyphenols in the extracts were partly responsible for the antioxidant activities while its correlation with CCA was poor, indicating that polyphenols might not be the main cupric ion chelators. Principal component analysis (PCA) indicated that TEACDPPH, TEACFRAP and TPC contributed to the total variation in the antioxidant activities of the plants. 相似文献
997.
Optical switching is demonstrated using movable integrated optical waveguides fabricated on silicon-on-insulator substrates. The switching effect is produced by the voltage-controlled micromechanical deflection of the movable waveguides. The dynamic response of the deflection is studied. A contrast ratio of 12 dB of switching is obtained using an applied voltage of less than 10 V. At 20 V, the contrast ratio is about 40 dB 相似文献
998.
Chi Wan Sung Wing Shing Wong 《Vehicular Technology, IEEE Transactions on》1997,46(3):676-686
Generally, the channel-assignment problem (CAP) for mobile cellular systems is solved by graph-coloring algorithms. These algorithms, though sometimes can yield an optimal solution, do not supply any information on whether an optimal solution has been found or bow far away it is from the optimum. In view of these undesirable features, two relevant results are presented. First, a lower bound for the minimum number of channels required to satisfy a given call-traffic demand is derived. This lower bound is tighter than the existing ones under certain conditions and can be used as a supplement for other approximate algorithms. Second, we propose an efficient heuristic algorithm to solve this problem. Although the CAP is nondeterministic polynomial (NP) complete in general, our algorithm provides an optimal solution for a special class of network topologies. For the general case, promising results are obtained, and numerical examples show that our algorithm has a better performance than many existing algorithms 相似文献
999.
Chuan-Jane Chao Shyh-Chyi Wong Chi-Hung Kao Ming-Jer Chen Len-Yi Leu Kuang-Yi Chiu 《Semiconductor Manufacturing, IEEE Transactions on》2002,15(1):19-29
The paper presents a complete characterization of on-chip inductors fabricated in BiCMOS technology. First, a study of the scaling effect of inductance on geometry and structure parameters is presented to provide a clear guideline on inductor scaling with suitable quality factors. The substrate noise analysis and noise reduction techniques are then investigated. It is shown that floating well can improve both quality factor and noise elimination by itself under 3 GHz and together with a guard ring above 3 GHz. Finally, for accurate circuit simulations, a new inductor model is developed for predicting the skin effect and eddy effect and associated quality factor and inductance. 相似文献
1000.
Burker Eileen J.; Wong Henry; Sloane Philip D.; Mattingly Dianne; Preisser John; Mitchell C. Madeline 《Canadian Metallurgical Quarterly》1995,10(1):104
Fear of falling may constitute an independent risk factor for disability, leading older people to unnecessarily restrict their activity. Sixty older adults with chronic dizziness and 66 healthy controls were studied to help clarify the interrelationships among demographic factors, psychological status, physical health, and fear of falling. Chronic dizziness was strongly associated with fear of falling; among dizzy patients, nearly half (47%) expressed fear of falling, in comparison with 3% of controls. In participants with dizziness, 3 factors predicted fear of falling: an activity of daily living score, the revised Symptom Checklist 90 Depression (L. R. Derogatis, 1983) score, and stability when standing with feet together. These results support the concept that fear of falling is multiply determined and that psychological factors play a major role in influencing the symptoms and responses in many older patients with dizziness. (PsycINFO Database Record (c) 2011 APA, all rights reserved) 相似文献