A hexagonal array of low-aspect-ratio silicon nanodisks is formed on a silicon thin film and the optical absorption and photocurrent properties are studied. Numerical simulations reveal that the nanodisk array possesses the toroidal dipole modes that tightly confine incoming light in a silicon region below the nanodisks. The field confinement brings about narrow-band absorption when the extinction coefficient (κ) is very small, for example, κ = 10–2∼10–3. This suggests that defect-related sub-band gap absorption of silicon can be enhanced by utilizing the modes. Transmittance spectra of fabricated devices reveal that narrow dips assigned to the toroidal dipole resonances appear in the sub-band gap region. At the resonance wavelengths, the photocurrent is substantially enhanced; the enhancement factor reaches 30-fold. The observed narrow-band photodetection can be used as a current-detection-type refractive index sensor operating in the near-infrared range.

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Abstract:The recent design requirement for a pile foundation often causes the pile head joint (hereafter, pile cap) to overcrowd the arrangement of reinforcements and to expand the dimensions. In order to solve this problem without increasing in dimension of the pile cap, the introduction of lateral prestress to the pile cap may be effective in improving the shear capacity. In the present study, the validity of analytical models is verified first by comparing the results through 3D FEM approaches against the test results performed on a partial pile foundation previously. After that, the improvement of earthquake resistance and durability by introducing lateral prestress to pile caps are investigated based on the triaxial state of stress. The analysis results indicated that the lateral prestress controls the shear crack effectively and increases the shear capacity of the pile cap by over 30 percent. However, some vertical tension reinforcements yielded in this analysis, therefore the introduction of vertical prestress in addition to lateral prestress to the pile cap may prevent yielding of vertical reinforcements and further improve the shear capacity.

3-D finite element analyses were conducted on post-tensioned precast concrete frames to investigate the shear behaviors of beam-column joints having some openings through sheaths. The compressive damage and confining effect in the beam-column joints were numerically estimated based on the 3-D stress state. Analytical results indicated that the shear strength of the beam-column joint decreased considerably with increasing opening ratio without beams installed orthogonally. If, however, the orthogonal beams were installed, the shear strength of the beam-column joint increased by 20 % and the decrease in shear strength due to opening was softened because a high confining pressure was generated.