不同壁面结构与传热情形下低温壁面结霜特性

壁面结霜致使低温换热设备传热性能下降,甚而产生设备安全和生产安全问题。通过实验研究了涂覆疏水涂料壁面结构的结霜特性,不同倾斜角度壁面的水滴凝结与滑落特性,以及添置了太阳能吸热膜的表面传热特性。结果表明:涂有疏水材料的壁面较普通壁面初始结霜时间能延迟约10分钟;一定的壁面倾斜角度通过影响水滴的滚动角,促进凝结的水滴滑落,可阻碍霜层生长;当换热壁面利用太阳能吸热膜对低温壁面进行补热时,吸热量为5.27J/cm2,为普通壁面的1.44倍。这些改进措施可以减少冷壁面结霜量,有助于提升低温设备传热效果。     

Theoretical Analysis of Interference Nanolithography of Surface Plasmon Polaritons without a Match Layer

Interference nanolithography techniques based on long-range surface plasmon polaritons （LR-SPP） are hardly ever achieved by experiments at present. One key reason is that suitable liquid materials are difflcult to find as the match layer connects the metal film and the resist. We redesign a Kretschmann-Raether structure for interference lithography. A polymer layer is coated under the metal film, and an air layer is placed between the polymer layer and the resist layer. This design not only avoids the above-mentioned question of the match layer, but also can form a soft contact between the polymer layer and the resist layer and can protect the exposure pattern. Simulation results confirm that a device with an appropriately thick polymer layer can form high intensity and contrast interference fringes with a critical dimension of about λ/7 in the resist. In addition, the fabrication of the device is very easy.     

Surface solitons supported by one-dimensional composite Bessel optical lattices

We address the existence of surface solitons at an interface in a defocusing cubic medium with an imprinted one-dimensional （1D） composite Bessel optical lattice. This setting is composed of two Bessel lattices with different orders and different modulation depths, separated beside both sides of an interface. Stability analysis and numerical propagation simulations prove that solitons supported by the model are dynamically stable in the entire domain of their existence. The order of lattice determines the shape of soliton, and the amplitude of soliton depends on the lattice modulation depth. The experimental realization of the scheme is also proposed. Our results may provide another effective way of controlling the shapes of surface solitons and thus their evolutions by introducing a new freedom degree.     

The spreading behaviour of perfluoropolyether droplets on solid surfaces

The spread of perfluoropolyether （PFPE） droplets on solid surfaces has been measured from the top-down view through a microscope system. Effects of substrates, molecular weight and end-group functionality on spreading of the PFPE droplets have been studied experimentally and the results were compared with those by molecular dynamics （MD） simulations. Silicon wafer and diamond-like carbon （DLC） substrates were used to study the effect of substrates on spreading. Two types of PFPE, Z-dol and Z-tetraol, with the same chain structure and various molecular weights （2000 and 4000 g/mol） were employed in experiments. Effect of molecular weight has been investigated through comparing the spreading of Z-dol 2000 and Z-dol 4000, and it is found that the increase of molecular weight will decrease the mobility of PFPE. Comparison between spreading of Z-dol and Z-tetraol of the same molecular weight proved that functional end group plays a significant role on the spreading of PFPE, which confirmed the MD simulation results.     

Analytic solutions for degenerate Raman-coupled model

The Raman-coupled interaction between an atom and a single mode of a cavity field is studied. For the cases in which a light field is initially in a coherent state and in a thermal state separately, we have derived the analytic expressions for the time evolutions of atomic population difference W, modulus B of the Bloch vector, and entropy E. We find that the time evolutions of these quantities are periodic with a period of π. The maxima of W and B appear at the scaled interaction time points τ- = kπ（k = 0, 1, 2,...）. At these time points, E = 0, which shows that the atom and the field are not entangled. Between these time points, E ≠ 0, which means that the atom and the field are entangled. When the field is initially in a coherent state, near the maxima, the envelope of W is a Gaussian function with a variance of 1/（4n^-）（n^- is the mean number of photons）. Under the envelope, W oscillates at a frequency of n^-/π. When the field is initially in a thermal state, near the maxima, W is a Lorentz function with a width of 1/n^-.     

遗传算法用于多组分拉曼光谱定量分析的研究

拉曼光谱是一种分子散射光谱,利用物质的特征拉曼光谱,可实现对其结构、成分、浓度等的检测.多组分物质拉曼光谱的定量分析是一个有待深入研究的课题.采用遗传算法程序对10组分的混合矿石样品的拟合拉曼光谱数据进行了分析,对同一条件下算法多次计算的结果和不同条件下算法的表现进行了讨论,分析了算法设计和基本参数的不同对算法收敛速度以及对计算结果的精确性和稳定性的影响,验证了遗传算法用于多组分样品拉曼光谱数据分析的可行性、有效性和精确性.     

磁场下合成Fe3O4粉体的隧道磁阻

通过在半金属Fe₃O₄合成过程中外加磁场的方法，改变样品粒子的表面结晶状态和晶格缺陷，研究了由此引起的Fe₃O₄输运性质的变化.合成的Fe₃O₄粉体的主要导电机理均为自旋极化隧穿和高阶跃迁电导，电阻随温度升高成指数降低，电阻与电压显示了非线形相关性，磁阻与磁场的关系为蝴蝶形，是典型的隧道磁阻特征.与没有外加磁场时合成的样品比较，外加磁场合成的样品显示了更低的电阻和更高的磁阻.     

人造复眼成像系统研究的新进展

人造复眼成像系统具有体积小、功耗低、视角范围广等优点，是一种应用前景非常广阔的光成像系统。综述了人造复眼成像系统的研究背景及最新的研究进展，其中包宿基于不同仿生设计理念的各种新型人造复眼结构以及能够实现诸如彩色成像、指纹识别、全视角成像等新功能的实验系统；展望了人造复眼成像系统今后的研究方向。     

模具钢表面激光毛化工艺的试验研究

以模具工业45^#钢摩擦学设计及性能要求为基础，分析了激光毛化模具钢表面形貌的形成机理及其关键的影响因素。采用灯泵浦Nd：YAG脉冲激光器在试样表面进行激光毛化工艺试验，获得了合理的激光毛化参数范围：激光峰值功率0．8～1．6kW，离焦量-1．4～-0．4mm、＋0．4～4-1．4mm，辅助气体压力〉0．2MPa，脉宽1．8ms。采用功率增益和氧气保护，可加工出预先设定的微火山口状毛化形貌。微凹坑形貌的成功获得对于提高拉伸模具的摩擦磨损性能，进一步掌握激光毛化参数与材料的作用规律，提供了有效的数据参考。     

分布式拉曼光纤放大器动态增益控制研究

介绍了动态增益控制的必要性，对动态拉曼传输方程进行了简化，并将其以矩阵形式表示，从而减少了方程的数量，提高了计算速度。由拉曼传输耦合方程推出一种适用于分布式拉曼放大器实时控制的自动控制算法。考虑工程需要，该算法忽略了噪声功率、泵浦间的受激拉曼效应，以及信号和泵浦间受激拉曼效应对泵浦功率的损耗。结果表明该算法能够达到快速抑制输入信号功率突变引起的输出功率／增益波动的目的。