Large oscillator strength excitons in PbGa2S4 crystals

Exciton states with a large oscillator strength (transverse-longitudinal splitting of 50 meV) and binding energy of 290 meV have been observed in PbGa₂S₄ crystals. The ground exciton states are stable up to the room temperature. The ground (n = 1) exciton state and two excited (n = 2 and n = 3) states of the short-wavelength B-excitons series were observed at low temperature (T = 10 K). The ground (n = 1) and the excited (n = 2) states of the long-wavelength A-exciton series were also revealed. The exciton Bohr radius of the ground exciton state was determined to be 70 Å for the A-exciton and 10 Å for the B-exciton. The band splitting and the main parameters of excitons have been determined from the calculation of the reflectivity spectra contours. The group theory analysis of the band symmetry was performed and the scheme of bands responsible for exciton transitions in the center of the Brillouin zone was proposed.     

关于算子形式的Bohr不等式的推广

采用算子论中的方法和技巧,研究了Bohr不等式的有界线性算子形式的推广,并且给出一些算子不等式,这样对文[4-5]中的结果进行了推广.进一步研究了Bohr不等式在算子范数上的性质,推广了文[6]中的相关结果.     

物理学中的自然单位方法

分析了物理学中自然单位的特点，用自然单位方法给出了原子物理学中玻尔理论的全部结果．     

Practical calculations of stopping powers for intermediate energy electrons in some elemental solids

This study presents calculation results of the stopping power (SP) of electrons of kinetic energy from 10 eV to 100 keV for some elemental solids. The method is based on utilization of the modified Bethe-Bloch SP expression and analytical expression for effective atomic electron number and effective mean excitation energies of target atoms, and for effective charge of incoming electrons, Sugiyama’s semi-empirical formula is embedded in the formula. An analytical expression for the practical SP calculations using Bethe approximation and Thomas-Fermi model of atom is taken from an pervious study and the calculated results of the SPs from this formula for electrons in some elemental solids, such as Al, Si, Cr, Ni, Cu, Ge, Pd, Ag, Pt, and Au, are calculated and rigorously compared with experimental data, Penelope code results and with results of other calculations such as the non-relativistic Bethe SP equation and the empirical modification of the Bethe equation by Joy and Luo. The results are found to be in good agreement for some targets but some limited agreement for some energies and targets is also observed.     

A review of the growth of V2O5 films from 1885 to 2010

This year is the 125th anniversary of the first synthesis of V₂O₅ gels. The fascinating properties and wide application range of V₂O₅ thin films have attracted significant attention over the past decades. Its wide optical band gap, layered structure, good chemical and thermal stability and excellent thermoelectric and electrochromic properties have made V₂O₅ a promising material for industrial applications such as gas sensors, electrochromic devices, optical switching devices, and reversible cathode materials for Li batteries. Gels were the first form in which V₂O₅ was synthesized at the end of the 19th century. Interest started to grow in the 1980s due to the discovery of their semiconducting properties and their use in antistatic coatings in the photographic industry. The rapid development of the sol-gel process brought new interest in V₂O₅ gels. Following a short discussion of vanadium oxides and V₂O₅, I summarize all thin film preparation techniques known up to now and use reported optical band gaps to characterize different growth methods. An estimation of the Bohr radius for V₂O₅ is also presented. This article provides an up-to-date review of more than a century (1885-2010) of research on the growth of vanadium oxide thin films. Nonetheless, due to the huge number of publications in the field, only those are selected and described which, according to the author, contribute the most to the field's further development.     

Charge transport in lead sulfide quantum dots/phthalocyanines hybrid nanocomposites

A hybrid composite of non-aggregated lead sulfide (PbS) nanoparticles of average size 5.8 ± 1 nm embedded within a film of an octaalkyl substituted metal-free phthalocyanine (Compound 2) was prepared on interdigitated gold electrodes by mild acidic treatment of newly synthesised octasubstituted lead phthalocyanine analogue (Compound 1) in solid state phase. This nanocomposite film shows an enhancement of in-plane electrical conductivity over that of a film of octaalkyl substituted metal-free phthalocyanine alone by nearly 65%. This observation is consistent with the formation of charge complex compound as indicated by Raman and XPS data. The presence of PbS in the composite was examined on the basis of XRD peak positions which are comparable with those of bulk PbS. A band gap of 2.22 eV was calculated from optical absorption data using Tauc's law, implying quantum confinement. The mono dispersal behaviour of PbS nanoparticles was established from TEM and XRD studies. The hopping conduction mechanism is found to be primarily responsible for charge transport in the hybrid nanocomposite film with the hopping distance larger than PbS diameter.     

船舶主柴油机燃油波尔滤器的改进方案设计

船舶主柴油机是船舶安全航行的心脏,而燃油波尔滤器担负着燃油过滤与净化的重要任务,是为主柴油机提供可靠、洁净燃油的重要设备。本文主要针对目前燃油波尔滤器工作存在的诸多问题,介绍了燃油波尔滤器的结构及工作原理,分析了设备存在的不足;并通过流体力学相关计算和设备工作性能要求,提出了系统改进设计方案,从而为下一步船舶修理提供改造依据,最终达到提高设备工作稳定性和保障主柴油机安全运行的目的。     

Bose–Einstein Condensation of Indirect Excitons in Coupled Quantum Wells

We study the ground-state properties of a quasi-two-dimensional Bose–Einstein condensate of indirect excitons, which are confined in an anisotropic harmonic potential. Incorporating the interactions, we calculate the order parameter variationally. The difficulties in the detection of a Bose–Einstein condensate are also discussed, along with possible ways which would overcome them.     

基于Kp微扰算法的磁场中MMM信号特征的研究

金属磁记忆(MMM)法可以对铁磁性金属构件微观损伤区域进行早期预判和评估,但是磁记忆信号很容易受到外界强磁场的干扰,给检测结果带来偏差。为研究磁场强度对磁记忆信号的影响规律,采用Kp微扰算法,在K空间,通过有效玻尔磁子数p建立多元超原胞磁力学模型,计算在外界磁场作用下,磁力学定量变化关系。研究结果表明,在外界磁场作用下,电子轨道运动增强,晶格结构发生畸变,原子磁矩增大。当磁场较小时,磁记忆信号随外界磁场强度增大而线性增大;当磁场强度达到临界值时,原子磁矩近似等于独立原子的磁矩,磁记忆信号趋于定值;当磁场强度大于临界值以后,应力集中区的磁记忆信号将被磁场覆盖。磁记忆检测实验结果与理论分析结果具有很好的一致性。