Design method for eliminating spectral line tilt in a multiple sub-pupil ultra-spectral imager (MSPUI).

A multiple sub-pupil ultra-spectral imaging system designed with a single spectrometer and detector can simultaneously detect multiple-channel spectra with ultra-high spectral resolution. However, due to using a prism in the system's front end, the nonlinear dispersion introduces spectral line tilt in the imaging spectra. This phenomenon can lead to bias in the final spectral data. To eliminate this issue, we propose a new design by introducing a second prism to correct this spectral tilt in the system. The angle of spectral line tilt generated by the nonlinear dispersion of the first prism is derived. It provides the theoretical basis for characterizing the second complementary prism. Finally, a UV multiple sub-pupil ultra-spectral imaging system is designed. The system employs two pupil separation prisms and one flat panel array to segment the pupil in three channels, each operating within spectral ranges of 180∼210 nm, 275∼305 nm, and 370∼400 nm, respectively. The spectral resolutions in all three channels are better than 0.1 nm. The corrected spectral line tilt is less than 1/3 of a pixel in the two channels with pupil separation prisms. At a Nyquist frequency of 30 lp/mm, the modulation transfer functions of all three channels are greater than 0.7, ensuring imaging quality. The design results indicate that the method proposed in this paper, utilizing complementary prisms, can effectively correct the spectral line tilt caused by the nonlinear dispersion of the pupil separation prisms. This design approach can be a reference for developing multiple sub-pupil ultra-spectral imaging systems.

A Comparative Study on Microstructure, Segregation, and Mechanical Properties of Al-Si-Mg Alloy Parts Processed by GISS-HPDC and SEED-HPDC.

There are multiple routes to prepare semi-solid slurries with a globular microstructure for semi-solid forming. The variations in the microstructure of semi-solid slurries prepared using different routes may lead to significant differences in the flow behavior and mechanical properties of rheo-diecasting parts. Therefore, it is crucial to have a comprehensive understanding of the microstructure evolution associated with different slurry preparation routes and their resulting effects. In this study, the gas-induced semi-solid process (GISS) and the swirl enthalpy equilibrium device (SEED) routes were employed to prepare semi-solid Al-Si-Mg slurries for their simplicity and productivity in potential industrial applications. The prepared slurries were then injected into the shoot sleeves of a high-pressure die casting (HPDC) machine to produce tensile test bars. Subsequently, the bars underwent T6 treatment to enhance their mechanical properties. The microstructure, segregation, and mechanical properties of the samples were investigated and compared with those of conventional HPDC. The results indicated that the GISS and SEED can produce semi-solid slurries containing a spherical α-Al primary phase, as opposed to the dendritic structure commonly found in conventional castings. The liquid fraction had a significant effect on the flow behavior, resulting in variations in liquid segregation and mechanical properties. It was observed that a higher solid fraction (>75%) had a suppressing effect on surface liquid segregation. In addition, the tendency for liquid segregation gradually increased along the filling direction due to the special flow behavior of the semi-solid slurry with a low solid fraction. Furthermore, under the same die-casting process parameters, the conventional HPDC samples exhibit higher yield stress (139 ± 3 MPa) compared to SEED-HPDC and GISS-HPDC samples, which may be attributed to the small grain size and the distribution of eutectic phases. After undergoing the T6 treatment, both SEED-HPDC and GISS-HPDC samples showed a significant improvement in yield and tensile strength. These improvements are a result of solution and precipitation strengthening effects as well as the spheroidization of the eutectic Si phase. Moreover, the heat-treated SEED-HPDC samples demonstrate higher ultimate strength (336 ± 5 MPa) and elongation (13.7 ± 0.3%) in comparison to the GISS-HPDC samples (307 ± 4 MPa, 8.8 ± 0.2%) after heat treatment, mainly due to their low porosity density. These findings suggest that both GISS-HPDC and SEED-HPDC processes can be utilized to produce parts with favorable mechanical properties by implementing appropriate heat treatments. However, further investigation is required to control the porosities of GISS-HPDC samples during heat treatment.