Dimensional variation in production of high-aspect-ratio micro-pillars array by micro powder injection molding

Micro powder injection molding (μPIM) is one of the potential processes for the mass production of metallic microstructures and micro components. Here, μPIM is the miniaturization of conventional PIM, which involves four processing steps: mixing, injection molding, debinding and sintering. This paper looks into the feasibility and effectiveness of μPIM as a key mass production process for the fabrication of metallic micro components. For it to be an effective re-production process, it is imperative to examine how well parts can be duplicated/fabricated from a master mold. In this work, the dimensional variation of high-aspect-ratio micro-pillars arrays, in particular the dimensional shrinkage, global warpage, and surface roughness at each stage of the μPIM process for a range of molding pressures, are quantified and compared in detail. The sensitivity of the dimensional variation of the microstructures to the packing pressure is reported. The mechanism behind the dimensional variation is analyzed. PACS 81.20.Ev; 81.20.Hy; 81.70.Fy; 07.60.Ly; 81.05.-t     

A side-coupled photonic crystal filter with sidelobe suppression

This paper presents the theoretical model and the optimization method to suppress the sidelobes of side-coupled photonic crystal filters. Numerical verification shows a good agreement between the theoretical method and the finite-difference time-domain simulation, but the theoretic method does not involve the time-consuming computation. The theoretical method also presents a better physical image for choosing the critical parameters, such as the quality factor, phase shift and the number of resonators. Based on the theoretical model, two optimization methods (chirp and cascading) are proposed to deeply suppress the sidelobes. They also show more flexibility in controlling the bandwidth and steepness of the roll-off in the filter. PACS 42.70.Qs     

Generation of red light at 660 nm by frequency doubling a Nd:YAG laser with periodically-poled stoichiometric LiTaO<Subscript>3</Subscript>

High power red light was generated from a periodically-poled stoichiometric LiTaO₃ (PPSLT) by single-pass frequency doubling of a diode-side-pumped, Q-switched Nd:YAG laser at 1319 nm. An average power of 2.4 W of the 660 nm red light was obtained at the fundamental power of ∼5.4 W with the conversion efficiency up to 44.4% and with low fluctuation down to 2%. The high efficiency and stability at the red output indicate that it is a practical method to construct a reliable compact red laser. PACS 42.70.Mp; 42.79.Nv; 42.55.Xi     

Hydrothermal synthesis and Magnetocaloric effect of La0.5Ca0.3Sr0.2MnO3

The hydrothermal synthesis and magnetic entropy change for the perovskite manganite La_0.5Ca_0.3Sr_0.2MnO₃ have been studied. The La_0.5Ca_0.3Sr_0.2MnO₃ can be produced as phase-pure, crystalline powders in one step from solutions of metal salts in aqueous potassium hydroxide solution at a temperature of 513 K in 72 h. Scanning electron microscopy shows that the materials are made up of cuboid-shaped particles in typical dimension of 4.0×2.5×1.6 μm. Heat treatment can improve the magnetocaloric effect for the hydrothermal sample. The maximum magnetic entropy change ΔS_M for the as-prepared sample is 0.88 J kg⁻¹ K⁻¹ at 315 K for a magnetic field change of 2.0 T. It increases to 1.52 J kg⁻¹ K⁻¹, near its Curie temperature (317 K) by annealing the sample at 1473 K for 6 h. The hydrothermal synthesis method is a feasible route to prepare high-quality perovskite material for magnetic refrigeration application.     

一种识别液体中粒状物的数字图象法软件的基本原理

本文介绍了一种识别液体中粒状物的数字图象法软件的基本原理,说明了软件中确定背景灰度门槛值的原则,发展了从背景中分离粒状物并对粒状物的大小和数目进行统计的算法。对整个软件进行了初步验证。     

Field Quantization and Spontaneous Emission in Left-handed Material

Recently, research on left-handed materials （LHMs） has attracted considerable attentions. The LHMs are a kind of man-made metameterials which have negative permittivity and negative permeability. These metameterials have many novel properties such as inverse light pressure, and reverse Doppler effect, which lead to many potential applications of LHMs such as superlenses which, in principle, can achieve arbitrary subwavelength resolution. However, though the properties mentioned above are seen to be classical, the quantum phenomena in LHMs have also attracted attentions such as the modified spontaneous emission of atoms in LHME.     

火工品可靠性试验数据的综合分析方法

升降法试验数据和固定刺激量下的成败型试验数据,是两种最常见的火工品可靠性试验数据．我们应用Markov链,研究了升降法试验数据下,感度分布参数的极大似然估计的特性．在此基础上,应用Bootstrap方法和Bayes方法,给出了综合分析两种试验数据的方法．最后,将该方法应用于520底火的可靠性鉴定,得出了有益的结论．     

Simulation of island aggregation influenced by substrate temperature, incidence kinetic energy and intensity in pulsed laser deposition

Using kinetic Monte Carlo method, we have simulated a pulsed energetic growth process in pulsed laser deposition. During the growth of film, substrate temperature mainly influences upon film morphology by directly enhancing the adatom mobility through the temperature-dependent thermal vibration. By contrast, the effect of incidence kinetic energy on film growth is complex resulting from the collisions between the incident particles and the adatoms. The results show that improving incident kinetic energy cannot significantly accelerate the migration rate of adatom but change surface microstructure and promote single adatom formation resulting in more island aggregation density. Moreover, since pulse-influx characterizes pulsed laser deposition, the intensity per pulse contributes to the evolvement of nucleation density and the results illustrate that a general scaling law different from ordinary power law still exists in energetic growth of pulsed laser deposition.