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41.
Conducting drop tests to investigate impact behavior and identify failure mechanisms of small-size electronic products is
generally expensive and time-consuming. Nevertheless, strict drop/impact performance criteria for hand-held electronic products
such as cellular phones play a decisive role in the design because they must withstand unexpected shocks. The design of product
durability on impact has heavily relied on the designer's intuition and experience. In this study, a reliable drop/impact
simulation for a cellular phone is carried out using the explicit code LS-DYNA. Subsequently globallocal experimental verification
is accomplished by means of high-speed photography and impact response measurement. Using this methodology, we predict potential
damage locations in a cellular phone and compare them with real statistical data. It is envisaged that development of a reliable
methodology of drop/impact simulation will provide us with a powerful and efficient vehicle for improvement of the design
quality and reduction of the product development cycle. 相似文献
42.
S. Park 《Acta Mathematica Hungarica》1998,81(1-2):155-161
A closed multimap T : X ? X having the KKM property has a fixed point whenever X is a compact convex set satisfying a certain topological condition. Our new result properly generalizes a known one due to W. K. Kim [4]. 相似文献
43.
In this paper we present numerical methods for computations of nonequilibrium hypersonic flow of air around bodies including chemical reaction effects and present numerical result of the flow over concave corners. We developed implicit finite difference method to overcome numerical difficulties associated with the lack of resolution behind the shock and near the body. Using our method we were able to find details of the flow properties near the shock and body and were able to continue the computation of the flow for a long distance from the corner of the body. 相似文献
44.
The nucleation and grain growth of the Ge2Sb2Te5 (GST) thin films were studied using high voltage electron microscope operated at 1250 kV. As a result, we have found that 2 nm-sized nucleus forms as a cluster which atoms are arranged regularly at the stage of nucleation prior to the formation of grains having crystal structure. The high-resolution transmission electron microscopy study and fast-Fourier transformations revealed that coexistence of face-centered-cubic (FCC) and hexagonal structure occurs, and formation of twin defect is found in the hexagonal structure during the grain growth as the annealing temperature is increased. GST grain having the hexagonal structure grow from the surface, and the growth proceeded perpendicular to the [0 0 0 1], namely the path parallel to the (0 0 0 1) plane. Consequently, grain growth to a large-scale result in a lengthened shape. 相似文献
45.
N. Jiten Singh Adriana C. Olleta Anupriya Kumar Mina Park Hai-Bo Yi Indrajit Bandyopadhyay Han Myoung Lee P. Tarakeshwar Kwang S. Kim 《Theoretical chemistry accounts》2006,115(2-3):127-135
In earlier studies, the interactions of isolated ionic species with various solvents were investigated using ab initio calculations.
The ionic species investigated included cations (proton, hydronium, ammonium, and metal cations) and anions (single electron,
hydroxide, and halide anions). However in the present study, we investigate the interactions of these ionic species with the
solvent in the presence of other competing ionic species. We also elaborate on how the information obtained from these extensive
studies have been employed in designing and synthesizing various kinds of novel ionophores and receptors. 相似文献
46.
Seoung-Soo Lee Ho-In Park Chung-Hyung Joh Song-Ho Byeon 《Journal of solid state chemistry》2007,180(12):3529-3534
Three different synthetic methods, the liquid phase process in HCl solution, the solvothermal reaction, and the surfactant-assisted solvothermal reaction, were explored to selectively control the particle shape and to enhance the luminescence intensity of the PbFCl-type red-emitting oxychloride phosphors LnOCl:Eu (Ln=La and Gd). The solvothermal pressure facilitated the low-temperature crystallization of the rod-shape particles for both Ln=La and Gd. It is noted that LaOCl:Eu nanorods show highly porous particle surface and quite low photoemission intensity. In contrast, the solvothermal synthesis could highly enhance the red-emission of GdOCl:Eu with no porous surface so as to be comparable to that of commercial Y2O3:Eu phosphor. An addition of surfactant material during solvothermal reaction yielded a rhomboidal-shape phosphor particles with no porous surface for both Ln=La and Gd. Interestingly, the elimination of surface porosity by using a surfactant significantly increased the emission intensity of LaOCl:Eu. It is proposed that the application of solvothermal technique for the synthesis of the PbFCl-type oxychloride phosphors is very effective to selectively control the particle shape and consequently to enhance the photoemission intensity if we use an appropriate surfactant material. 相似文献
47.
We consider a SA-SA' critical point in the presence of a symmetry-breaking external magnetic (electric) field with a positive magnetic (dielectric) anisotropy or a dislocation layer. Via a renormalization group analysis of the model hamiltonian, we show that the upper critical dimensions below which mean-field theory breaks down is dc = 2·5. Thus the SA-SA' transition in three dimensions becomes mean-field like in the presence of a symmetry-breaking field. We estimate the reduced temperature region where we can expect to see the mean field SA-SA' critical point in the presence of a magnetic field or a dislocation layer. 相似文献
48.
Hyeong Taek Ham Yeong Suk Choi Mu Guen Chee In Jae Chung 《Journal of polymer science. Part A, Polymer chemistry》2006,44(1):573-584
This work is to make carbon nanotubes dispersible in both water and organic solvents without oxidation and cutting nanotube threads. Polystyrene‐singlewall carbon nanotube (PS‐SWNT) composites were prepared with three different methods: miniemulsion polymerization, conventional emulsion polymerization, and mixing SWNT with PS latex. The two factors, crosslinking and surface coverage of PS are important factors for the mechanical and electrical properties, including dispersion states of SWNT in various solvents. The PS‐SWNT composite prepared via a conventional emulsion polymerization showed SWNT bundles entirely covered with PS, whereas the PS‐SWNT composite prepared via a miniemulsion polymerization showed SWNT partially covered with crosslinked PS nanoparticles. The method of mixing SWNTs with PS latex did not show the well dispersed state of carbon nanotubes because PS was not crosslinked and was dissolved in a solvent, and nanotubes separated from PS precipitated. So the PS nanoparticle‐SWNT composite had lower electrical resistance, and higher mechanical strength than the other composites made by the latter two methods. As the amount of SWNT increases, the bare surface area of SWNT increases and the electrical conductivity increases in the composite made by the miniemulsion polymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 573–584, 2006 相似文献
49.
Jin Kyu Park Dong Hun Lee Bok Ju Song Jae Buem Oh Hwan Kyu Kim 《Journal of polymer science. Part A, Polymer chemistry》2006,44(3):1326-1342
We have designed and synthesized novel perfluorinated polyimides with 3D controlled structure. At first, we successfully developed the new synthetic routes to diamines with pendant bulky perfluorinated aromatic units in a multi‐step synthetic procedure. Novel perfluorinated polyimides were prepared in a two‐step reaction in N‐methyl‐2‐pyrrolidinone (NMP) solution: The first step was for the synthesis of polyamic acids (PAAs) and the second reaction was for the imidization of PAA. The polymer yield was over 89% and the inherent viscosity of PAAs was in the range of 0.24–0.36 dL/g. The thin films were prepared by spin‐coating the PAA solution in NMP onto various substrates such as a Si wafer or a KBr pellet, dried at 80 °C and further cured at 230 °C. The resultant polyimides are thermally stable over 400 °C. The refractive index and birefringence of the resultant polyimides are 1.5858–1.6452 and 0.01–0.005, respectively. The refractive index of polyimide decreases with increasing the fluorine content. The copolymerization and the ether linkages into the backbone reduce the birefringence of polyimides. Surprisingly, the pendant ether linkage is not a crucial factor in reducing the polyimide birefringence. Their birefringence is comparatively very low, compared with that of previous polyimides. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1326–1342, 2006 相似文献
50.
Chae Kyu Kim Eun Seok Song Hyung Joo Kim Chiyoung Park Young Chul Kim Jai Kyeong Kim Jae Woong Yu Chulhee Kim 《Journal of polymer science. Part A, Polymer chemistry》2006,44(1):254-263
We have synthesized conjugated dendrimer with triazine peripheries, and their luminescence properties were investigated. The dendrimers consist of dendritic triazine wedges for electron transport, distyrylbenzene core as an emitting moiety, and t‐butyl peripheral groups for good processing properties. The dendrimers have LUMO values of about ?2.7 eV possibly because of the triazine moiety with high electron affinity. Photoluminescence study indicates that energy transfer occurs from the triazine wedges to the stilbene bridge, and finally to the core chromophore units due to a cascade decrease of bandgap from the peripheral wedge to core moiety. Therefore, the emission wavelength was determined by the structure of the core unit. The energy transfer efficiency of distyrylbenzene‐cored dendrimers was about 75 and 55% for Trz‐1GD‐DSB and Trz‐2GD‐DSB, respectively. A preliminary electroluminescence property also was investigated. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 254–263, 2006 相似文献