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A Fourier transform spectrometer (FTS) has been used to observe solar activities due to its ultra-high spectral resolution. However, the FTS in-band spectra are usually distorted and some artifacts appear in out-of-band regions due to nonlinear effects. Therefore, the FTS nonlinear problem must be corrected. In this study, we proposed a novel method to correct the nonlinear effects using simulated annealing. We simulated several nonlinear spectra to evaluate the performance of our method. The calculated quadratic coefficients are extremely close to the given values, demonstrating that the method is effective and accurate. The proposed method is further used to correct the blackbody and solar spectra with nonlinearity obtained by Bruker IFS-125HR installed at the Huairou Solar Observing Station, which is a pathfinder for the accurate infrared magnetic field measurements of the Sun project. To the blackbody spectra, the nonlinearity in low- and high-frequency regions are corrected by 89.09% and 60.84%. The nonlinear correction of the solar spectra in the low- and high-frequency regions have reached 65.34% and 81.04%, respectively. These results prove that our method can correct the nonlinear problem to improve the data accuracy.

A method of identifying positron/electron species from the cosmic rays was studied in the DArk Matter Particle Explorer (DAMPE) experiment. As there is no onboard magnet on the satellite, the different features imposed by the geomagnetic field on these two species were exploited for the particle identification. Application of this method to the simulation of on-orbit electrons/positrons/protons and the real flight data proves that separately measuring the CR positrons/electrons with DAMPE is feasible, though limited by the field of view for the present observation data. Further analysis on the positron flux with this method can be expected in the future.

The Stokes polarimeter based on liquid crystal variable retarders (LCVRs) is envisaged as a promising novel technique for polarization measurement in space applications due to the inherent advantage of eliminating the need for conventional rotating polarizing optics and increasing the measuring speed. However, the intrinsic multi-beam interference in LCVRs limits its polarization accuracy by several percent. How to eliminate the influence of the interference effect becomes an urgent issue for the liquid-crystal-based Stokes polarimeter. The present study introduces a simplified but effective interference model based on the thin-film optics and polarized light theory to simulate the relationship between the interference effect of the LCVRs-based Stokes polarimeter and the polarization accuracy. The simulation results show that the transmittance variation of LCVR with the derived voltage is caused by multi beam interference between the indium tin oxide (ITO) film and the liquid crystal within LCVR, which produces a few percent of instrumental polarization. The instrumental polarization is about 0.01 and different for different wavelengths. An optimization method was proposed to reduce the instrumental polarization to 0.002, effectively improving the polarization sensitivity of the Stokes polarimeter limited by the interference. In addition, an experimental setup was built up to measure and analyze the influence of the interference effect of the LCVRs-based Stokes polarimeter on the polarization accuracy before and after the optimization. The experiment results are in good agreement with the simulation.

The nonequilibrium spin accumulation on a one-dimensional (1D) mesoscopic Rashba ring is investigated with unpolarized current injected through ideal leads. Due to the Rashba spin-orbit (SO) coupling and back-scattering at the interfaces between the leads and the ring, a beating pattern is formed in the fast oscillation of spin accumulation. If every beating period is complete, a plateau is formed, where the variation of spin accumulation with the external voltage is slow, but if new incomplete periods emerge in the envelope function, a transitional region appears. This plateau structure and the beating pattern are related to the tunnelling through spin-dependent resonant states. Because of the Aharonov-Casher (AC) effect, the average spin accumulation oscillates quasi-periodically with the Rashba SO coupling and has a series of zeros. In some situations, the direction of the average spin accumulation can be reversed by the external voltage in this 1D Rashba ring.

The interplay between the Fano effect and electronic correlations in a double-quantum-dot (DQD) structure is investigated by the finite-U slave-boson mean-field method, and the focus is put on the influence of the Aharonov–Bohm (AB) effect on the transport properties. In the singly occupied regime, with weak antiferromagnetic correlation, the Fano–Kondo effect greatly suppresses the conductance G, whereas the strong parity splitting blocks the path through the DQD, which is similar to the time-reversal symmetric case. At the particle–hole symmetric point the peak usually still exists in the would-be peak-zero structure, but with the magnetic flux increased the zero is enhanced and eventually removed at quarter of a flux quantum. Results similar to the frequency doubling of AB oscillation and the 'pinning' of the AB maximum can be found, which account for the appearance of a new transmission zero in the variation of G with the energy levels on dots.

We investigate how the competition between Kondo and antiferromagnetic (AF) correlations influences the Josephson current through double quantum dots (DQDs) and focus our attention on the situation where the superconducting energy gap is smaller than the Kondo temperature. The finite-U slave-boson mean-field method is adopted to treat electronic correlations. With weak AF correlation, two Kondo spin singlets yield two Andreev bound states below the Fermi level, and the low tunnelling probability through these singlet states leads to small critical Josephson current Jc. Strong AF correlation results in a singlet between the two localized spins, and only in a certain range can one bound state be found. At an intermediate point, the competition between the Kondo and AF correlations leads to a peak in the critical Josephson current, where just one bound state is formed in the gap. The strong parity splitting causes the double occupancy on the bonding orbital of two dots, and no Andreev bound state is found with Jc approaching zero.

We investigate the influence of an external voltage V0 on conductance G through a quantum dot (QD), which is side-coupled to a quantum wire of length LW, whose two ends are weakly connected to leads. In our calculation, the poor man's scaling law and slave-boson mean-field method are employed. With V0 increased, a series of resonant regions is formed and G exhibits different properties in and out of these regions, which is the universal result of the finite-size effect on the Kondo correlation. In symmetric structures, the would-be resonant regions corresponding to odd wavefunctions are removed. If the symmetry is broken by changing the QD position, those regions will be recovered. In two asymmetric structures with their wire lengths being LW and LW+1, respectively, the two sets of resonant regions intersect with each other. These symmetry-related phenomena characterize side-coupled QD structures. With the barrier width increased, the number of resonant regions is increased, too.

The influence of the Fano effect and the Kondo and antiferromagnetic (AF) correlations on the transport properties through a double quantum dot (DQD) structure is investigated by the finite-U slave-boson mean field method. In the singly-occupied regime, with weak AF correlation, the Fano–Kondo effect greatly reduces the conductance G no matter whether the transmissivity through the direct channel is high or low, whereas the strong parity splitting leads to the blockade of the channel through the DQDs. At the particle–hole symmetric point, when the Kondo and AF correlations are comparable with each other, their competition results in a resonant conductance peak, which is accompanied with a transmission zero due to the Fano effect. This peak-zero structure is a counterpart of the characteristic asymmetric line shape and governs the variational trend of G with the energy levels on dots. The qualitative relations between the positions of those peaks and zeros with the transmissivity through the direct channel are obtained via a fitting method.

The internal friction for Ti-Ni-Cu shape memory alloys (SMAs) was measured in the Hz and kHz range. The peak temperature in the Hz range is independent of the measuring frequencies. Only in the tens of kHz range does the peak temperature shift with the frequencies, showing a thermally activated progress with = 0e-B/Tc - T, characteristic of viscous motion of domain walls, instead of the Arrhenius relation. Taking into account the change of the density of the domain walls during the phase transformation, we modified the Q-1-formula by using a model of viscous motion of domain walls, obtaining a good result in agreement with the experimental data. Additionally, corresponding parameters, which play a key role in the shape memory effect, such as the viscosity coefficient and the effective pinning force constant, were obtained.

Direct observation of the domain-inverted regions in LiNbO3 formed by proton exchange followed by heat treatment is performed by using transmission electron microscopy. A charged straight 180° twinning domain boundary was revealed and compared with winding domain boundaries in LiNbO3 grown by Czochralski method. Obtained results are significant to studying the mechanism of domain inversion and morphology of inversion domains.

Field-induced periodic domain reversal has been achieved in a 0.5 mm thick, c-cut sample with Al electrodes by optimizing fabrication conditions. The quality of the sample has been tested by measuring the efficiency of second harmonic blue light generation and its tuning behaviour.

The domain inversion in LiNbO3 is fabricated by proton exchange and rapid heat treatment. The proton concentration is measured by secondary-ion mass spectroscopy. A modified diffusion model is proposed, the result of which agrees well with the measured data. Comparisons with the existing models are made, which suggests that our model may be more extensively applicable.

Domain-inverted structures in LiNbO3 are fabricated by proton exchange followed by rapid heat treatment. The domain inversion mechanism is discussed in relationship to the pyroelectric field and to the concentration gradient of protons.

We show that the generalized short pulse equation is nonlinearly self-adjoint with differential substitution. Moreover, any adjoint symmetry is a differential substitution of nonlinear self-adjointness, and vice versa. Consequently, the general conservation law formula is constructed and new conservation laws for some special cases are found.

Domain reversal in LiTaO3 with period 6.5 mu m and 1:3 duty cycle has been obtained by using a partially switching technique in a 0.25 mm thick sample. A CW second-order quasi-phase-matched second-harmonic-generation experiment yielded a 12 mu W, 407 nm blue light output for 200 mW, 814 nm fundamental input. The technique can be used for the fabrication of the periodic poled LiTaO3 for bulk violet and ultraviolet second-harmonic generation and for the fabrication of other ferroelectric microstructure materials.

The quantum anomalous Hall (QAH) effect in kagome lattices is investigated in the presence of both Rashba spin–orbit coupling and an exchange field. In addition to the gap at the Dirac points as found in graphene, a new topological energy gap is opened at the Γ point. With the Fermi energy lying in the first gap, the Chern number 𝒞 = 2 as in graphene, whereas with it lying in the second one, 𝒞 = 1. The distribution of Berry curvature is obtained to reveal the nontrivial topological properties in momentum space. For stripes with ‘armchair’ and ‘zigzag’ edges, the topological characteristics of gapless edge states on the genus g = 2 Riemann surface are studied. The obtained nonzero winding numbers also demonstrate the QAH effect.

The differential conductance through a normal metal–insulator–normal metal–superconductor (NINS) junction on graphene is obtained via numerical calculation of the Dirac–Bogoliubov–de Gennes equation. A series of sub-gap peaks of differential conductance can be found no matter whether the Andreev reflection is specular or standard. In the meantime, the differential conductance displays an oscillatory behaviour as a function of the effective barrier strength even if the Fermi surface mismatch is large. In the two limiting situations with the superconducting gap much smaller or much larger than the Fermi energy, all of the oscillations are in the same phase, and the number and positions of the sub-gap peaks are determined only by the distance between the NI and NS interfaces. In the intermediate regime with the Andreev retro-reflection crossing over to a specular one, however, a phase shift appears between any two different oscillations. The number and positions of the sub-gap peaks are related not only to that distance but also to the effective barrier strength.

The transport properties of a mesoscopic hybrid four-terminal Rashba ring are investigated along the lines of Blonder, Tinkham and Klapwijk and our attention is focused on the influence of Andreev reflection. Although the resonant peak and zero conductance resulting from spin-dependent quantum interference are destroyed by incoherent addition in this four-terminal structure, the total longitudinal electron conductance is still enhanced by the Andreev contribution. However, the contribution of the Andreev reflection to the spin Hall conductance in this mesoscopic Rashba ring is negative and the total spin Hall conductance is reduced. These results are robust to an external magnetic flux.

The thermoelectric properties of double quantum dot (DQD) systems are investigated and our attention is focused on the interplay between the Fano effect and electronic correlations. If the antiferromagnetic (AF) correlation is weak, the derivative of thermopower with the energy level on dots is positive at the particle–hole symmetric point. With the Fano effect introduced, it becomes negative due to the Fano–Kondo effect. The competition between the Kondo and AF correlations yields a zero in the derivative, and with the direct channel open, in the vicinity of that zero, the derivative undergoes an almost discontinuous hopping with its sign reversed. Away from the particle–hole symmetric point, the variation of thermopower is also related to that interplay. Compared with conductance, thermopower can provide more information on the DQD systems. These results are robust to asymmetry and can be verified in experiments with temperature lower than the Kondo temperature.

The ballistic transport through a mesoscopic zigzag Rashba wire is studied via the Green function technique and the spin transmission is investigated with an unpolarized charge current injected. These results are compared with those of a straight wire, and show that to generate a nonzero spin conductance in the longitudinal direction, the mirror symmetry with respect to that direction must be broken. This necessary condition is satisfied in the zigzag wire. Its ballistic transport properties are also affected by the spin-dependent quantum interference effect, resulting from the Rashba spin–orbit coupling and scattering at corners and at interfaces between the wire and the leads. Mixing between different pairs of transverse modes is crucial for spin transmission, and only if more than one pair of modes are open can a measurable spin-polarized current be obtained in the longitudinal direction. These results provide one way to generate an artificially controllable spin-polarized current in mesoscopic Rashba systems.