[en] The response of the near-band-edge photoluminescence (PL) emission of ZnO thin films to annealing and the electric field's action was investigated. These processes separately caused similar changes in the PL spectrum. The donor bound exciton emission at 3.36 eV, which is attributed to bulk defects, demonstrated invariance to any exposure, while the intensity of the 3.33-eV emission line decreased after annealing in nitrogen gas and was restored after annealing in an oxygen atmosphere. On the other hand, application of an electrical field during laser illumination resulted in the same change in the PL spectrum. The transition of defects related to the 3.33-eV emission from a radiative to a non-radiative state (and inversely) through the capture (release) of electrons was proposed as the mechanism responsible for the observed changes in the optical properties. The desorption of oxygen from the surface of the ZnO film during annealing in N2 or the motion of photogenerated electrons toward the surface during laser illumination were suggested to be the cause of this capture process.

[en] In this study the cycloaddition of glycidyl methacrylate (GMA) and CO₂ using ionic liquid as catalyst was performed for the technology of CO₂ reduction. The structure of synthesized cyclic carbonate, [2-oxo-1,3-dioxolan-4-yl]methacrylate (DOMA) was analyzed and confirmed by FT-IR and ¹H-NMR. The change in conversion with respect to reaction time was investigated using ¹H-NMR. Interestingly, the ionic polymerization of vinyl groups and crosslinking reaction between cyclic carbonate rings of DOMA were observed following completion of cycloaddition

[en] We have fabricated Si nanocrystals utilizing nanometer-sized Pt islands acting as etching-masks on SiO_x/amorphous-Si/SiO_x/p-Si (1 0 0) thin films. In the measurement of transmission electron microscopy the Si nanocrystals embedded in SiO₂ were observed, and in the measurement of cathodoluminescence spectroscopy at 77 K Si nanocrystal-related peaks were observed at 462 and 647 nm. For the Al/SiO₂/nanocrystalline-Si/SiO₂/p-Si capacitor structure, a hysteretic behavior with the flatband voltage shift of 0.592 V was observed in the measurement of capacitance-voltage characteristic at 300 K. These results indicate that Si nanocrystals can be formed by using a nanosized Pt island etching-mask, and that Si nanocrystals embedded in SiO₂ layer act as Si quantum dots which hold promise potential applications

[en] Curved structural members are widely seen in our surroundings, such as railway supports in playgrounds resembling a c-ring structure. The common geometry of the curved member consists of a segment of a circular ring with a uniform width. The curved section is of constant width in most cardiovascular stents. This study focuses on curved strut members whose width changes along the curved segment. The location of the maximum equivalent stress varies depending on the manner in which the width changes. When the width is constant or larger toward the top, the maximum equivalent stress is developed at the top. Meanwhile, when the area is reduced toward the bottom, the largest equivalent stress is developed some distance from the top. Simple equations, based on the mechanics of materials and the theory of elasticity, were compared favorably with the results from finite element analysis. Included are elaborations of the distribution of the change of stress. The suggested strategy of changing the width, with refinements, could be applied to the optimal design of structural members, including pipes and medical devices such as stents

[en] A radiologic study of 139 dentigerous cysts (128 patients) indicated the followings: 1. There was higher incidence in males (62.99%) than in females (37.01%). The most common age group was 11-20 years and the average age was 23.6 years. 2. The most common clinical symptoms was swelling of the jaws (49 cases, 33.09%), and no symptoms was presented in 26 cases (18.71%). 3. Dentigerous cysts were found to be slightly more common in the maxilla (53.24%) than in the mandible (46.76%) and there was almost no difference in occurrence between right and left side. The maxillary supernumerary tooth was the most frequent site of the dentigerous cyst and no dentigerous cyst was found to be related to a deciduous tooth. 4. The most common radiographic findings was root resorption of the adjacent teeth (33.09%), and the central dentigerous cysts were 78 cases (56.12%), the lateral dentigerous cysts were 61 cases (43.88%). 5. The increased radiolucency at the crown portion of the tooth in a cystic cavity was seen in 44 cases (31.65%), and a case of dentigerous cyst was found in a edentulous patient, and 16 cases of multiple dentigerous cysts were found in 5 patients. 6. The ameloblastic changes in 8 cases, the keratinization of the cyst wall in 2 cases, and a case of epidermoid carcinoma were confirmed microscopically.

[en] The oscillatory magnetoresistance (Shubnikov-de Hass) effect has been used to investigate the two-dimensional electron gas in Al_xGa_1-xAs/GaAs single quantum wells and heterostructures grown by molecular beam epitaxy. The electron carrier density of the subband can be obtained clearly by digitizing the data linearly in terms of 1/B and fast Fourie transformation of the data by computer. Comparisons between these analyses and the period of oscillation of each subband obtained from the slope of a plot of reciprocal magnetic field vs the number of oscillation peaks for these samples will be discussed, as will determination of the mobility of the subband using the onset position of the oscillations and a plot ln(amplitude) vs I/B. (Author)

[en] Influence of material shear nonlinearity on multidirectional laminates in terms of failure envelopes was investigated. In applying classic laminate theory, elastic constants were employed in transverse and longitudinal directions, while initial shear modulus was substituted by the secant shear modulus, which was achieved by means of Ramberg-Osgood model. The fracture curves were generated from maximum stress, Tsai-Wu and Puck criteria. The similarities and differences between nonlinear and linear shear models can be expressed in terms of symmetric balanced laminates [±θ°]2s and asymmetric laminates [0°₂/±θ°], which are both arranged by material E-glass/MY750 oriented at different directions. All σ₁ - σ₂ failure envelopes due to material nonlinearity extend outward in tensile and compressive directions, but the phenomenon is not obvious with increasing ply angles. Similarly, the differences of all σ₁ - τ₁₂ failure envelopes between nonlinear shear analysis and linear shear analysis are decreasing with increased ply angles. Ply orientations and loading directions are involved in the effect of nonlinear shear properties on failure envelopes. According to the failure modes obtained from maximum stress criterion, it is reasonably derived that the influence of material shear nonlinearity will lead whether the failure envelopes from the other two failure criteria are more conservative or not.

[en] Self-assembled, one dimensional (1-D) Zn1−xCdxS nanostructures with a Cd composition of x = 0.11 have been successfully fabricated on indium-tin-oxide/glass substrates by using a coevaporation method in the absence of any catalyst. The structures and the morphologies of these nanostructures were studied using X-ray diffraction and high-resolution transmission electron microscopy. X-ray photoelectron spectroscopy confirmed that the Cd ions occupied the Zn sites in the ZnCdS nanowire. The fabricated ZnCdS nanostructures exhibited various shapes, such as hexagonal nanorods (H-NRs), cylindrical nanorods (C-NRs), nanoneedles (NNs), nanowires (NWs) and nanodumbbells (NDs), for different substrate temperatures. Increasing the substrate temperature resulted in the formation of nanostructures with smaller diameters. The shape-controllable growth of ZnCdS 1-D nanostructures might result in the development of a high-efficiency nano-solar cell.

[en] The effects of implanted N ions on both electrical and magnetic characteristics of Mn-implanted p-type GaN were studied. compared with Mn-implanted sample, the Curie temperature and magnetic moment of (Mn+N)-implanted GaN significantly increased. When N ions were implanted, Mn-N compounds of Mn₆N_2.58 drastically decreased and the concentration of N vacancies was also reduced, leading to the increase in sheet resistivity. The photoluminescence peak at 2.92 eV shifted to 2.86 eV and became strong with the N-implantation, indicating that effective hole concentration increases due to an enhanced activation of Mn impurities in GaN. Consequently, the enhancement of ferromagnetic property by N implantation originated due to the increase in hole concentration via the enhanced Mn activation in GaN and due to the suppression of production of Mn+N compounds. (author)

[en] Light emission from a poly-[3-(2-benzotriazolo)-ethylthiophene]/indium tin oxide (PBET/ITO) structure under electron beam excitation was investigated. Two peaks at 580 nm (green) and 620 nm (orange) are observed under low excitation. An ultraviolet (UV) emission centered at 347 nm appeared under high current excitation. The ratio of the UV/green-orange band intensities increases with an increase of the current density and with a decrease of temperature. Stimulated emission and lasing from the polythiophene derivative structure are observed at high current density. (copyright 2004 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)