Analysis of Asymmetrical Deformation of Surface and Oblique Pipeline Caused by Shield Tunneling along Curved Section

The deformation of existing pipelines caused by the tunneling of a shield machine along curved sections has not been sufficiently researched, and a corresponding theoretical prediction formula is lacking. This paper derives a prediction formula for the deformation of an existing pipeline caused by shield machine tunneling along a curved section. Further, a finite difference model (FDM) corresponding to an actual project is built. Finally, the deformation of the surface and existing pipelines caused by shield machine tunneling along the curved section is analyzed. The research results show that the results of theoretical prediction, FDM calculation, and field monitoring data are consistent. In addition, the deformation of the surface and the existing pipeline are asymmetrically distributed when the shield machine tunnels along the curve section instead of symmetrically distributed (for straight line segment). When the pipeline is perpendicular to the tunnel axis, the maximum deformation position of the existing pipeline deviates from the tunnel axis by about 0.5 times the tunnel radius. In addition, as the angle β between the pipeline axis and the tunnel axis increases, the maximum deformation position of the pipeline gradually approaches the tunnel axis

Maize Seed Variety Classification Using the Integration of Spectral and Image Features Combined with Feature Transformation Based on Hyperspectral Imaging

Hyperspectral imaging (HSI) technology has been extensively studied in the classification of seed variety. A novel procedure for the classification of maize seed varieties based on HSI was proposed in this study. The optimal wavelengths for the classification of maize seed varieties were selected using the successive projections algorithm (SPA) to improve the acquiring and processing speed of HSI. Subsequently, spectral and imaging features were extracted from regions of interest of the hyperspectral images. Principle component analysis and multidimensional scaling were then introduced to transform/reduce the classification features for overcoming the risk of dimension disaster caused by the use of a large number of features. Finally, the integrating features were used to develop a least squares–support vector machines (LS–SVM) model. The LS–SVM model, using the integration of spectral and image features combined with feature transformation methods, achieved more than 90% of test accuracy, which was better than the 83.68% obtained by model using the original spectral and image features, and much higher than the 76.18% obtained by the model only using the spectral features. This procedure provides a possible way to apply the multispectral imaging system to classify seed varieties with high accuracy

High-efficiency Terahertz-wave generation in silicon membrane waveguides

Terahertz (THz) wave generation via four-wave mixing (FWM) in silicon membrane waveguides is investigated with mid-infrared pump. The silicon membrane waveguides with width of 12 μm and heights varied from 14 μm to 17 μm, which can confine the THz-wave ranging from 7.5 THz to 10 THz due to the large refractive index contrast of the waveguide core and cladding, are designed to realize the collinear phase matching for THz-wave generation via FWM. Compared with the conventional parametric amplification or wavelength conversion based on FWM in silicon waveguides, which needs a pump wavelength located in the anomalous group-velocity dispersion (GVD) regime to realize broad phase matching, the pump wavelength located in the normal GVD regime is required to realize phase matching because of the large signal-pump frequency detuning. Phase matching for a tunable THz-wave ranging from 8.57 THz to 10 THz can be realized by tuning the pump wavelength from 4.2 μm to 4.4 μm in the silicon waveguide with rib height of 15 μm. Whilst, the phase matching bandwidth of THz-wave ranging from 7.7 THz to 10 THz can be achieved by tailoring the waveguide height from 14 μm to 17 μm when the pump wavelength is 4.3μm. Moreover, the conversion efficiency of the THz-wave generation is studied with different pump wavelengths and waveguide heights, the maximum conversion efficiency of 1.25 % at 9.2 THz can be obtained in a 6-mm long silicon waveguide when the pump wavelength is 4.3 μm and the waveguide height is 15 μm

Multi-channel terahertz wavelength division demultiplexer with defects-coupled photonic crystal waveguide

Terahertz (THz) wavelength division demultiplexer based on a compact defects-coupled photonic crystal waveguide is proposed and demonstrated numerically. This device consists of an input waveguide that perpendicularly coupled with a series of defects cavities, each of which captures the resonance frequency from the input waveguide. Coupled-mode theory and finite element method are used to analyze the transmission properties of the structure. It is found that the transmission wavelength centered around 1THz can be adjusted by changing the geometrical parameters of defects cavities, which equals to THz waves generated by optical methods such as difference frequency generation and optical rectification. Applications in this frequency range are urgently needed. Furthermore, the highest transmission efficiency of 0.94 can be achieved when a perfect wavelength-selective mirror is set in the output waveguide

Widely tunable femtosecond optical parametric oscillator based on silicon-on-insulator waveguides

A femtosecond optical parametric oscillator (OPO) based on silicon-on-insulator (SOI) waveguide is proposed and analyzed numerically. By utilizing split-step Fourier method (SSFM), it is demonstrated that ultra-wide tunable wavelength femtosecond pulse can be realized under the phase matching condition. Due to the interaction between nonlinearity and flexible dispersion design, the output signal wavelength can be tuned from 1645 to 1805 nm and the idler wavelength can be tuned from 1350 to 1456 nm. Moreover, the peak power of the output signal pulse exceeds 10 W from 1700 to 1770 nm with the pump peak power 50 W. The proposed OPO exhibits compact configuration and can find important applications in integrated broadband optical source.

Engineering of phase matching for mid-infrared coherent anti-Stokes Raman wavelength conversion with orthogonally polarized pump and Stokes waves in silicon-on-sapphire waveguides

The conversion efficiency of mid-infrared wavelength conversion based on coherent anti-Stokes Raman scattering with TE-polarized pump and TM-polarized Stokes waves is theoretically investigated in silicon-on-sapphire (SOS) waveguides. The peak conversion efficiency of -10 dB is obtained when the linear propagation loss is 1 dB/cm at Delta k = 0; however, it is reduced to -13.6 dB when the linear propagation loss is 2 dB/cm. The phase matching for wavelength conversion with orthogonally polarized pump and Stokes waves can be realized by engineering the birefringence in SOS waveguides, because proper phase mismatch induced by birefringence together with material dispersion-induced phase mismatch can counteract the large phase mismatch induced by waveguide dispersion. Moreover, compared with the phase matching for identically polarized pump and Stokes waves, the phase matching for orthogonally polarized pump and Stokes waves can be realized in a SOS waveguide with much smaller cross section, which reduces the power requirement for optical systems. (C) 2013 Optical Society of Americ

Numerical analysis of pulse signal restoration by stochastic resonance in a buckled microcavity

A novel scheme is proposed to restore weak pulse signals immersed in noise by stochastic resonance based on photothermal-effect-induced optical bistability in a buckled dome microcavity. The bistable properties of the dome microcavity are analyzed with different initial detuning wavelengths and effective cavity lengths, and bistable transmission can be obtained for input powers in submilliwatt range. A theoretical model is derived to interpret the nonlinear process of pulse signal recovery through double-well potential theory. The cross-correlation coefficient between output signals and pure input pulses is calculated to quantitatively analyze the influence of noise intensity on stochastic resonance. A cross-correlation gain of 7 is obtained, and the noise-hidden signal can be recovered effectively though the buckled dome microcavity with negligible distortion. The simulation results show the potential of using this structure to restore low-level or noise-hidden pulse signals in all-optical integrated systems. (C) 2016 Optical Society of Americ