Analysis of high-temperature performance of 4H-SiC avalanche photodiodes in both linear and Geiger modes

The high-temperature performance of 4H-SiC ultraviolet avalanche photodiodes(APDs)in both linear and Geiger modes is extensively investigated.During the temperature-dependent measurements,a fixed bias voltage is adopted for the device samples,which is much more practical and important for high-temperature applications.The results show that the fabricated 4H-SiC APDs are very stable and reliable at high temperatures.As the temperature increases from room temperature to 425 K,the dark current at 95%of the breakdown voltage increases slightly and remains lower than40 pA.In Geiger mode,our 4H-SiC APDs can be self-quenched in a passive-quenching circuit,which is expected for highspeed detection systems.Moreover,an interesting phenomenon is observed for the first time:the single-photon detection efficiency shows a non-monotonic variation as a function of temperature.The physical mechanism of the variation in hightemperature performance is further analyzed.The results in this work can provide a fundamental reference for researchers in the field of 4H-SiC APD ultraviolet detectors.

Weakly nonlinear multi-mode Bell-Plesset growth in cylindrical geometry

Bell-Plesset(BP)effect caused perturbation growth plays an important role in better understanding of characteristics of the convergence effect.Governing equations for multi-mode perturbation growth on a cylindrically convergent interface are derived.The second-order weakly nonlinear(WN)solutions for two-mode perturbations at the interface which is subject to uniformly radical motion are obtained.Our WN theory is consistent with the numerical result in terms of mode-coupling effect in converging Richtmyer-Meshkov instability.Nonlinear mode-coupling effects will cause irregular deformation of the convergent interface.The mode-coupling behavior in convergent geometry depends on the mode number,Atwood number A and convergence ratio Cr.The A=-1.0 at the interface results in larger perturbation growth than A=1.0.The growth of generated perturbation modes from two similar modes at the initial stage are smaller than that from two dissimilar modes.

Magnetohydrodynamic Kelvin-Helmholtz instability for finite-thickness fluid layers

We have derived the analytical formulas for the Kelvin-Helmholtz instability(KHI)of two superposed finite-thickness fluid layers with the magnetic field effect into consideration.The linear growth rate of KHI will be reduced when the thickness of the fluid with large density is decreased or the thickness of fluid with small density is increased.When the thickness and the magnetic field act together on the KHI,the effect of thickness is more obvious when the magnetic field intensity is weak.The magnetic field transition layer destabilizes(enforces)the KHI,especially in the case of small thickness of the magnetic field transition layer.When considering the effect of magnetic field,the linear growth rate of KHI always decreases after reaching the maximum with the increase of total thickness.The stronger the magnetic field intensity is,the more obvious the growth rate decreases with the total thickness.Thus,it should be included in applications where the effect of fluid thickness on the KHI cannot be ignored,such as in double-cone ignition scheme for inertial confinement fusion.

Weakly Nonlinear Rayleigh–Taylor Instability in Cylindrically Convergent Geometry

The Rayleigh–Taylor instability（RTI） in cylindrical geometry is investigated analytically through a second-order weakly nonlinear（WN） theory considering the Bell–Plesset（BP） effect. The governing equations for the combined perturbation growth are derived. The WN solutions for an exponentially convergent cylinder are obtained. It is found that the BP and RTI growths are strongly coupled, which results in the bubble-spike asymmetric structure in the WN stage. The large Atwood number leads to the large deformation of the convergent interface. The amplitude of the spike grows faster than that of the bubble especially for large mode number m and large Atwood number A. The averaged interface radius is small for large mode number perturbation due to the mode-coupling effect.

Effect of initial phase on the Rayleigh–Taylor instability of a finite-thickness fluid shell

Rayleigh–Taylor instability(RTI) of finite-thickness shell plays an important role in deep understanding the characteristics of shell deformation and material mixing. The RTI of a finite-thickness fluid layer is studied analytically considering an arbitrary perturbation phase difference on the two interfaces of the shell. The third-order weakly nonlinear(WN) solutions for RTI are derived. It is found the main feature(bubble-spike structure) of the interface is not affected by phase difference. However, the positions of bubble and spike are sensitive to the initial phase difference, especially for a thin shell(kd < 1), which will be detrimental to the integrity of the shell. Furthermore, the larger phase difference results in much more serious RTI growth, significant shell deformation can be obtained in the WN stage for perturbations with large phase difference. Therefore, it should be considered in applications where the interface coupling and perturbation phase effects are important, such as inertial confinement fusion.

Click synthesis and dye extraction properties of novel thiacalix[4]arene derivatives with triazolyl and hydrogen bonding groups

Using a click reaction between alkynylthiacalix[4]arene and ethyl 2-azidoacetate followed by an ammonolysis with ethanolamine,leucinol and hydrazine hydrate,respectively,three novel thiacalix [4]arene derivatives 4,5 and 6 with triazolyl and hydrogen bonding groups（NH and OH） were synthesized in high yields.They exhibited excellent extraction capability for six anionic and cationic dyes.The flexible cavity,π-triazole rings and hydrogen bonding groups all play crucial roles in dye complexation.

Thiacalix[4]arene 1,2,3-triazole-polyethylene glycol polymers:Synthesis and dye adsorption properties

By reacting alkynylthiacalix[4]arenes with polyethylene glycol azido compounds,a series of novel thiacalix[4]arene 1,2,3-triazole-polyethylene glycol netty polymers were conveniently prepared in good yields.Their structures and morphologies were studied by ^1H NMR,IR.and elemental analysis and SEM images.On average,approximately 28-31 thiacalixarene units exist in each polymeric molecule.These novel polymers possess excellent adsorption ability for both cationic and anionic dyes.The saturation adsorption capacity for Congo red reached 1.3-1.4 mmol/g.They exhibit high and stable adsorption ability in the scope of pH 5-9,and maintain good properties in five cycles.