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<jats:title>Abstract</jats:title> <jats:p>The digital coding metasurfaces need several kinds of meta-particle structures to obtain corresponding electromagnetic wave responses and require time-consuming optimization. In this paper, we present train-symbol-shaped meta-particles with various orientations utilizing Pancharatnam–Berry (PB) phase to achieve 1-, 2-, and 3-bit digital coding metasurfaces. Terahertz wave scattering patterns of the coding metasurfaces with regular and random sequences are given and discussed. They have strongly suppressed backward scattering with approximately −13.5 dB radar cross section (RCS) reduction in a wide band range from 0.85 THz to 1.6 THz. The proposed digital coding metasurfaces provide a simple way and new opportunities for manipulating terahertz wave scattering with polarization independence.</jats:p>

<jats:p>We perform an experimental study of the multi-orbital effect on the high-order harmonic generation (HHG) from aligned N<jats:sub>2</jats:sub> molecules in both linearly and elliptically polarized intense laser fields. Measured by a home-built extreme ultraviolet (XUV) flat grating spectrometer with the pump–probe method, the angular distributions of different orders of HHG are obtained, which show distinctive behaviors for harmonics in the plateau and the cut-off regions. The ellipticity dependence of HHG is investigated by aligning the molecular axis parallel or perpendicular to the laser polarization. Our results indicate that both the highest occupied molecular orbital (HOMO) as well as the lower one (HOMO-1) contribute to the HHG of N<jats:sub>2</jats:sub> molecules, in either linearly or elliptically polarized intense laser field. The study paves the way for understanding the ultrafast electron dynamics of molecules exposed to an intense laser field.</jats:p>

<jats:p>We report a direct blue-diode-pumped wavelength tunable Kerr-lens mode-locked Ti: sapphire laser. Central wavelength tunability as broad as 89 nm (736–825 nm) is achieved by adjusting the insertion of the prism. Pulses as short as 17 fs are generated at a central wavelength of 736 nm with an average output power of 31 mW. The maximum output power is 46.8 mW at a central wavelength of 797 nm with a pulse duration of 46 fs.</jats:p>

<jats:p>It is well known that the radiation efficiency of an acoustic dipole is very low, increasing the radiation efficiency of an acoustic dipole is a difficult task, especially in an ordinary waveguide. In addition, current acoustic superlenses all utilize in-phase sources to do the super-resolution imaging, it is almost impossible to realize super-resolution imaging of an acoustic dipole. In this paper, after using the Helmholtz resonator arrays (HRAs) which are placed at the upper and lower surfaces of the waveguide, we observe a large dipole radiation efficiency at the certain frequency, which gives a method to observe an acoustic dipole in the far field and offers a novel model which is promising to realize the superlens with a source of an acoustic dipole. We discuss how the arrangement of HRAs affects the transmission of the acoustic dipole.</jats:p>

<jats:p>Fluctuation phenomena commonly exist in arc plasmas, limiting the application of this technology. In this paper, we report an investigation of fluctuations of arc plasmas in an arc plasma torch with multiple cathodes. Time-resolved images of the plasma column and anode arc roots are captured. Variations of the arc voltage, plasma column diameter, and pressure are also revealed. The results indicate that two well-separated fluctuations exist in the arc plasma torch. One is the high-frequency fluctuation (of several thousand Hz), which arises from transferring of the anode arc root. The other is the low-frequency fluctuation (of several hundred Hz), which may come from the pressure variation in the arc plasma torch. Initial analysis reveals that as the gas flow rate changes, the low-frequency fluctuation shows a similar variation trend with the Helmholtz oscillation. This oscillation leads to the shrinking and expanding of the plasma column. As a result, the arc voltage shows a sinusoidal fluctuation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Dip-coated double-wall carbon nanotubes (DWCNTs) and titanium dioxide (TiO<jats:sub>2</jats:sub>) sol have been prepared and smeared onto the tip of a conductive iron needle which serves as the corona discharge anode in a needle–cylinder corona system. Compared with the discharge electrode of a CNT-coated needle tip, great advancements have been achieved with the TiO<jats:sub>2</jats:sub>/CNT-coated electrode, including higher discharge current, ionic wind velocity, and energy conversion efficiency, together with lower corona onset voltage and power consumption. Several parameters related to the discharge have been phenomenologically and mathematically studied for comparison. Thanks to the morphology reorientation of the CNT layer and the anti-oxidation of TiO<jats:sub>2</jats:sub>, better performance of corona discharge induced wind generation of the TiO<jats:sub>2</jats:sub>/CNT-coated electrode system has been achieved. This novel decoration may provide better thoughts about the corona discharge application and wind generation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The melting of crystals is one of the most common and general phase transition phenomena. However, the mechanism of crystal melting is not well understood, and more experimental measurements and explorations are still needed. The mechanical spectra of propylene carbonate and 1,3-propanediol during the crystal melting processes are measured by the reed vibration mechanical spectroscopy for liquids (RMS-L) for the first time. The experimental results show that as the temperature increases, the real part of the complex Young modulus first decreases slowly, and then quickly drops to zero; meanwhile, its imaginary part increases slowly at first, then goes up and drops quickly to zero, showing a peak of internal friction. Preliminary analyses indicate that both the real and imaginary parts can present some characteristics of the melting process, such as the transition from the disconnected liquid regions to the connected liquid regions, that from the connected crystal regions to the disconnected crystal regions, and so on. In addition, the results show that the melting rate per unit volume of crystalline phase versus temperature satisfies the Arrhenius relation at the initial stage of melting, and deviates from this relation as the temperature increases to a certain value. Therefore, the RMS-L will provide an effective supplement for the further study of melting.</jats:p>

<jats:p>Ceramics usually have irregular grains, cracking, or porosity, which result in their lightproof. Y<jats:sub>2</jats:sub>Mo<jats:sub>3</jats:sub>O<jats:sub>12</jats:sub> ceramics have more porosity due to the heavy hygroscopicity. Introducing ZnLi to Y<jats:sub>2</jats:sub>Mo<jats:sub>3</jats:sub>O<jats:sub>12</jats:sub> could form regular grains, reduce cracking and porosity. With increasing the content of ZnLi, the grain shapes self-assembly gradually and then the laser scattering and transmittance improve. The laser scattering property and transmittance of diverging rays become the best in ceramics <jats:inline-formula> <jats:tex-math><?CDATA ${{\rm{Y}}}_{2-x}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Y</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> <mml:mo>−</mml:mo> <mml:mi>x</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_096501_ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>(ZnLi)<jats:sub> <jats:italic>x</jats:italic> </jats:sub>Mo<jats:sub>3</jats:sub>O<jats:sub>12</jats:sub> (<jats:italic>x</jats:italic>=1.0 and 1.2) with regular grains and low thermal expansion. The formation mechanism of regular grains is ascribed to the substitutions of Zn<jats:sup>2+</jats:sup> and Li<jats:sup>+</jats:sup> for Y<jats:sup>3+</jats:sup> in Y<jats:sub>2</jats:sub>Mo<jats:sub>3</jats:sub>O<jats:sub>12</jats:sub> resulting in the preferential growth. The investigation in laser scattering, transmittance and low thermal expansion behaviors of <jats:inline-formula> <jats:tex-math><?CDATA ${{\rm{Y}}}_{2-x}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi mathvariant="normal">Y</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> <mml:mo>−</mml:mo> <mml:mi>x</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_096501_ieqn4.gif" xlink:type="simple" /> </jats:inline-formula>(ZnLi)<jats:sub> <jats:italic>x</jats:italic> </jats:sub>Mo<jats:sub>3</jats:sub>O<jats:sub>12</jats:sub> could pave a way to weaken the strong-laser attack from the high-power laser weapon and the other.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report theoretical studies on the newly discovered novel Josephson effect and scanning tunneling spectroscopy (STS) at the interface of strontium titanate/lanthanum aluminate (STO/LAO). With a phenomenological boson–fermion model, the density of states is calculated and the results are consistent with the STS experiments. A typical calculation of Josephson effect is performed, and it is in qualitative agreement with the experiments. The calculations indicate that the gap states come from the pairing of quasi-particles with a finite total momentum and the Josephson current comes from the tunneling of quasi-particle pairs with zero momentum. The quasi-particles are Bogoliubov quasi-particles. Moreover, the fits using Kulikʼs formula imply that the Josephson junction at the STO/LAO interface has a point contact with the clean superconductor limit.</jats:p>

<jats:p>The optical properties of the type-II lineup In<jats:sub> <jats:italic>x</jats:italic> </jats:sub>Al<jats:sub>1−<jats:italic>x</jats:italic> </jats:sub>N–Al<jats:sub>0.59</jats:sub>Ga<jats:sub>0.41</jats:sub>N/Al<jats:sub>0.74</jats:sub>Ga<jats:sub>0.26</jats:sub>N quantum well (QW) structures with different In contents are investigated by using the six-by-six <jats:italic>K</jats:italic>–<jats:italic>P</jats:italic> method. The type-II lineup structures exhibit the larger product of Fermi–Dirac distribution functions of electron <jats:inline-formula> <jats:tex-math><?CDATA ${f}_{{\rm{c}}}^{n}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">c</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_097801_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> and hole <jats:inline-formula> <jats:tex-math><?CDATA $(1-{f}_{{\rm{v}}}^{{\rm{U}}m})$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">v</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">U</mml:mi> <mml:mi>m</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo stretchy="false">)</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_097801_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> and the approximately equal transverse electric (TE) polarization optical matrix elements (<jats:inline-formula> <jats:tex-math><?CDATA $|{M}_{x}{|}^{2})$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">|</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>x</mml:mi> </mml:mrow> </mml:msub> <mml:msup> <mml:mrow> <mml:mo stretchy="false">|</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">)</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_097801_ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> for the c1–v1 transition. As a result, the peak intensity in the TE polarization spontaneous emission spectrum is improved by 47.45%–53.84% as compared to that of the conventional AlGaN QW structure. In addition, the type-II QW structure with <jats:inline-formula> <jats:tex-math><?CDATA $x\sim 0.17$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>x</mml:mi> <mml:mo>∼</mml:mo> <mml:mn>0.17</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_097801_ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> has the largest TE mode peak intensity in the investigated In-content range of 0.13–0.23. It can be attributed to the combined effect of <jats:inline-formula> <jats:tex-math><?CDATA $|{M}_{x}{|}^{2}$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">|</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>x</mml:mi> </mml:mrow> </mml:msub> <mml:msup> <mml:mrow> <mml:mo stretchy="false">|</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_097801_ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math><?CDATA ${f}_{{\rm{c}}}^{n}(1-{f}_{{\rm{v}}}^{{\rm{U}}m})$?></jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">c</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>n</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>−</mml:mo> <mml:msubsup> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">v</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">U</mml:mi> <mml:mi>m</mml:mi> </mml:mrow> </mml:msubsup> <mml:mo stretchy="false">)</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpb_28_9_097801_ieqn6.gif" xlink:type="simple" /> </jats:inline-formula> for the c1–v1, c1–v2, and c1–v3 transitions.</jats:p>