Molecular dynamics of CO in few-cycle laser fields

We experimentally study the ionization, fragmentation and Coulomb explosion of CO using 6 fs laser pulses. Different from previous observations in tens or hundreds of femtoseconds laser pulses, strong charge asymmetric dissociation and CO²⁺ are observed in the current intense few-cycle laser field.     

Study of free convective boundary layer of isothermal lateral surface of axisymmetrical horizontal body

Approximate analytical solution of simplified Navier–Stokes and Fourier–Kirchhoff equations describing free convective heat transfer from isothermal surface has been presented. It is supposed that the surface has the horizontal axis of symmetry and its axial cross-section lateral boundary is a concave function. The equation for the boundary layer thickness is derived for typical for natural convection assumptions. The most important are that the convective fluid flow is stationary and the normal to the surface component of velocity is negligibly small in comparison with the tangential one. The theoretical results are verified by two characteristic cases of the revolution surfaces namely for horizontal conic and vertical round plate. Both limits of presented solution coincide with known formulas.     

MHD mixed convection of a viscous dissipating fluid about a permeable vertical flat plate

The problem of steady laminar magnetohydrodynamic (MHD) mixed convection heat transfer about a vertical plate is studied numerically, taking into account the effects of Ohmic heating and viscous dissipation. A uniform magnetic field is applied perpendicular to the plate. The resulting governing equations are transformed into the non-similar boundary layer equations and solved using the Keller box method. Both the aiding-buoyancy mode and the opposing-buoyancy mode of the mixed convection are examined. The velocity and temperature profiles as well as the local skin friction and local heat transfer parameters are determined for different values of the governing parameters, mainly the magnetic parameter, the Richardson number, the Eckert number and the suction/injection parameter, f_w. For some specific values of the governing parameters, the results agree very well with those available in the literature. Generally, it is determined that the local skin friction coefficient and the local heat transfer coefficient increase owing to suction of fluid, increasing the Richardson number, Ri (i.e. the mixed convection parameter) or decreasing the Eckert number. This trend reverses for blowing of fluid and decreasing the Richardson number or decreasing the Eckert number. It is disclosed that the value of Ri determines the effect of the magnetic parameter on the momentum and heat transfer.     

Critical electric fields of AlGaN in AlGaN-based vertical conducting diodes on -SiC substrates

We have succeeded in obtaining high critical electric fields from AlGaN layers using the p-InGaN/i-Al_xGa_1−xN/n-Al_xGa_1−xN (x=0–0.22) vertical conducting diodes grown on n-SiC substrates by low-pressure metalorganic vapor phase epitaxy (MOVPE). The breakdown voltage (V_B) increases with increasing Al composition of the AlGaN layer. The corresponding critical electric fields are calculated to be 2.4 MV/cm for GaN and 3.5 MV/cm for Al_0.22Ga_0.78N. The critical electric field is proportional to the bandgap energy to a power of 2.5. This bandgap energy dependence is much stronger than that in the empirical expression proposed by Sze and Gibbons. The figure of merit, , increases with increasing Al composition, indicating the AlGaN-based p–i–n diodes are promising for high-power and high-temperature electronic device applications.     

Theoretical Analysis on Magnetic Properties of Conjugated Organic Molecules Containing Borepin

Theoretical study about the magnetic properties of conjugated organic molecules containing borepin with π current density was carried out. 1-(2,4,6-Trimethylphenyl)borepin moiety is the center and other different groups are situated on the both β sides, which are named molecules 1-12 as theoretical model in order to establish the relationship between aromaticity and geometry variation of borepin. The optimized molecular structures of molecules 1-12 are almost keeping planar and the C2-C3 bond length of borepin turns longer from molecule 1 to molecule 12. Different borepin-annulated ring could change the conjugated effect of π-electron between borepin and these borepin-annulated rings. Moreover, the molecule presents antiaromaticity, in other words, the molecule became unstable when the C2-C3 bond length of borepin extended more than ca. 0.1417 nm. But the β position fragment and substituent groups of borepin are not affected in this case, they are still steady. However, the central borepin ring current is counteracted by symmetrical overlap of it with affiliated borepin-annulated ring current. Hence, the central borepin ring breaking would be liable to occur. These molecules have higher vertical ionization potentials(VIPs) and lower vertical electron affinities(VEAs), which suggests that these molecules could easily exist in anionic form.     

Ab initio Study on Ionization Energies of 3-Amino-1-propanol

Fourteen conformers of 3-amino-1-propanol as the minima on the potential energy surface are examined at the MP2/6-311++G** level. Their relative energies calculated at B3LYP, MP3 and MP4 levels of theory indicated that two most stable conformers display the in-tramolecular OH…N hydrogen bonds. The vertical ionization energies of these conformers calculated with ab initio electron propagator theory in the P3/aug-cc-pVTZ approximation are in agreement with experimental data from photoelectron spectroscopy. Natural bond orbital analyses were used to explain the differences of IEs of the highest occupied molec-ular ortibal of conformers. Combined with statistical mechanics principles, conformational distributions at various temperatures are obtained and the temperature dependence of pho-toelectron spectra is interpreted.     

不同连接方案下垂直场线圈的性能研究

基于热-结构耦合分析了欧姆热和等离子体辐照引起的垂直场线圈的温度变化,对垂直场线圈在不同连接方式下的电气参数进行了研究,提出了一种优化的线圈连接方案。计算结果表明,该优化方案有助于改善垂直场线圈的响应性能,并提高其对等离子体的控制能力。     

基于多轴差分光学吸收光谱探测的北京春季气溶胶垂直廓线

气溶胶垂直廓线是评估污染物来源、输送等途径的必要手段。气溶胶污染对环境和人体健康带来直接的影响。该研究于2019年4-5月,利用中国科学院大气物理研究所（39.98°N,116.39°E）的地基多轴差分光学吸收光谱（MAX-DOAS）仪,对北京地区春季大气光谱垂直廓线进行了观测。凭借MAX-DOAS实时、在线、连续的观测优势,能有效的对气溶胶进行监测。MAX-DOAS基于最优估算法（OEM）以及最小二乘光谱拟合法,并以辐射传输模型SCIATRAN作为前向模型,利用海德堡廓线（HEIPRO）算法反演得到气溶胶消光系数的垂直廓线,通过对气溶胶消光系数在其路径的积分获得气溶胶光学厚度（AOD）。利用地基太阳光度计观测的AOD和高塔观测的颗粒物质量浓度垂直廓线,分别与MAX-DOAS观测的AOD和气溶胶消光系数垂直廓线进行对比,验证MAX-DOAS算法的适用性。研究结果表明,MAX-DOAS与太阳光度计观测AOD结果,相关系数为0.92,斜率为0.89。三层气溶胶消光系数与PM_2.5质量浓度的皮尔森相关系数从低处到高处分别达到0.69（60 m）,0.77（160 m）和0.75（280 m）。并且,将气溶胶平均消光系数和对应三层（60,160和280 m）的PM_2.5平均质量浓度对比,发现两者趋势一致。同样的,为了验证MAX-DOAS是否具备准确识别污染物的长距离输送的能力,我们通过Angstrom指数确定沙尘天气,通过计算梯度理查森数和边界层高度确定静稳天气,分析了在特殊天气条件下,MAX-DOAS能够对沙尘和静稳天气做出及时、准确的响应。分析气溶胶平均消光系数,发现气溶胶垂直廓线随高度升高呈现指数衰减变化的趋势,并且气溶胶消光系数均值在1.5 km高度处约为近地面的50%左右,而在1.5 km以上消光系数会随着高度的增加而快速减小。当高度达到2 km左右时,气溶胶消光系数均值下降到了0.1 km-1。以上结果表明MAX-DOAS探测大气气溶胶垂直廓线具有较高的适用性。     

P(St-AM)核壳聚合物微球的制备及其光子晶体膜

采用一步乳液聚合法,调节引发剂用量,制备了不同粒径的具有核壳结构的功能性聚(苯乙烯-丙烯酰胺)乳胶微球.用透射电子显微镜表征了乳胶微球的核壳结构和粒径,所制微球的粒径分别为195,217,234和255 nm.用红外光谱对微球的化学成分进行了表征,证实聚丙烯酰胺已包覆在聚苯乙烯外层.通过竖直沉积自组装法制备了聚合物微球的光子晶体薄膜.扫描电子显微镜表征了所制光子晶体膜的表面形貌,反射和透射光谱表征了光子禁带.结果表明,聚合物微球以面心立方紧密堆积,其(111)面与基底平行;微球粒径不同,光子晶体的光子禁带不同.制备了不同光子禁带的光子晶体,禁带分别位于473,515,574和630 nm,相应的薄膜分别呈蓝色、绿色、黄色和红色,对于光子晶体的拓展和应用具有重要的意义.