SMT质量控制

SMT在电子装配业不断发展,地位日渐重要.文中从装配准备、贴片、焊膏丝印和回流焊接等角度探讨了SMT的质量控制问题,提出了相应的质量控制措施.     

杂环类农药废水的深度处理工艺

杂环类农药废水因其有机物含量高、毒性大而成为水处理的难题。本文介绍了膜生物反应器／高级氧化／超滤组合工艺作为杂环类农药废水深度处理方法，并对该工艺的构筑物参数、经济成本及运行结果进行分析。实验结果表明该法对杂环类农药废水有较好的处理效果，并具有运行成本低、占地面积小的特点。     

Summarization and Analysis on the Synthesis Schemes of Glufosinate-Ammonium

Glufosinate-ammonium is a highly efficient, non-selective herbicide. The former synthesis schemes of glufosinate-ammonium were introduced and analyzed, the main of which are Arbuzov synthesis method, method under catalyzer and high pressure, targeted method under low temperature, Gabriel synthesis method, Zelinsky-Strecher synthetic method, synthetic method with chiral-synthon, and several special methods such as with enzyme or stereochemistry. Based on the structure and synthesis characteristic of glufosinate-ammonium as well as Arbuzov reaction and Michael reaction, a novel and reasonable scheme, which was named Arbuzov-Michael method, was put forward as the more economical one with simpler raw reagents and less waste.     

First-principles predictions of potential hydrogen storage materials: Novel sandwich-type ethylene dimetallocene complexes

The hydrogen storage capacities of a sandwich-type ethylene dimetallocene complex (Cp₂Ti₂C₂H₄) are studied using first-principles calculations. It is found that the TiC₂H₄Ti molecule can intercalate into the two cyclopentadienyl (Cp) rings and form a stable sandwich-type complex. Each Ti atom can adsorb a maximum of three H₂ molecules, which corresponds to a gravimetric storage capacity of 4.73 wt%. This hydrogen storage capacity is close to the 2015 target of 5.5% set by the US Department of Energy (DOE) in 2009. Furthermore, the Cp₂Ti₂C₂H₄ molecule proposed in this paper is favorable for both adsorption and desorption of hydrogen molecules at room temperature and ambient pressure because its average binding energy of 0.34 eV/H₂.     

Variable-dimensional vector modulation for perceptual-based DWT blind audio watermarking with adjustable payload capacity

A variable-dimensional vector modulation (VDVM) scheme is introduced to maximize the efficiency of the norm-space DWT-based blind audio watermarking technique. This flexible scheme allows the watermarking algorithm to reach a balance between robustness and capacity, while the imperceptivity is always ensured. The imperfection of applying quantization index modulation in the open-loop case has been rectified. The effectiveness of the proposed scheme is proven using the perceptual evaluation of audio quality (PEAQ) and bit error rates of recovered watermarks under various signal processing attacks. Experimental results show that the proposed VDVM scheme is comparable to other recently developed methods in robustness and imperceptivity even at a capacity as high as 301.46 bps. Such a capacity can be further doubled by halving the dimension of the involved DWT vector, while the robustness is still maintained at a satisfactory level.     

Luminescence at 2.8 μm: Er3+-doped chalcogenide micro-waveguide

This paper reports the fabrication of luminescent optical rib/ridge waveguides made of erbium doped Ga-Ge-Sb-S films deposited by RF magnetron sputtering. Several fluorescence emissions of Er³⁺ ions from the visible to the middle infrared spectral domain were clearly observed within the films. The study of the ⁴I_13/2 level lifetime enabled development of a suitable annealing treatment of the films to reach the value of the bulk counterpart while the variation in surface roughness was limited, thus ensuring reasonable optical losses (0.7–0.9 dB/cm). Amplification experiments were carried out at 1.54 μm leading to complete characterization of the erbium-doped micro-waveguide with ∼3.4 dB/cm on/off gain. A demonstration of mid-IR photoluminescence from Er³⁺-doped chalcogenide micro-waveguide was recorded at ∼2.76 μm. The multi-luminescence from the visible to mid-IR generated using erbium doped chalcogenide waveguiding micro-structures might find easy-to-use applications concerning telecommunication technologies or on-chip optical sensors for which luminescent sources or amplifiers operating at different wavelengths are required.     

Design and Analysis of MEMS Comb Drive Capacitive Accelerometer for SHM and Seismic Applications

This work presents the design of a MEMS accelerometer that is specifically intended for Structural Health Monitoring (SHM) applications where sensing low frequency low amplitude accelerations with high resolution is essential. The surface micromachined comb drive capacitance accelerometer structure has been considered in this design. The simulation experiments conducted on these devices using IntelliSuite MEMS design tool show that it has excellent displacement sensitivity of 21.39 μm/g, a capacitive sensitivity of 1.22 pF/g and voltage sensitivity of 1783 mV/g/V when it is designed to measure 0–0.1 g. Further, it is seen that it has a very low noise floor of 1.32 μg/√Hz and therefore high resolution. Since the accelerations can be as low as 0.04 g in SHM applications, excellent resolution is the primary goal in this design. Further, one more sensor specifically meant for strong motion seismic application has also been reported. This device has a bandwidth of 0–250 Hz and a noise floor of 5.612 μg/√Hz in addition to a sensor level voltage sensitivity of 97.9 mV/g/V. Finally, the comparison of these results with other similar devices reported in the past clearly illustrates the comparable performance of the present devices. Further, these devices, unlike the commercial low frequency accelerometers and other similar devices reported in the past can be fabricated by surface micromachining and CMOS compatible processes.     

Transition metal atom embedded graphene for capturing CO: A first-principles study

The adsorption of CO and H₂ on single-metal-atom (Fe, Co, Ni and Cu) embedded graphene (M-G) has been studied using density functional theory calculations. Fe-G and Co-G can capture up to three CO molecules per metal atom strongly, but tend to weakly or not adsorb H₂ molecules. Under standard conditions (298.15 K and 1 bar), they show a high adsorption selectivity ratio for CO over H₂. The density of states analysis reveals that the strong adsorption between CO and Fe(Co)-G results from the hybridization between d states of Fe (Co) and sp states of CO. Our findings suggest that Fe-G and Co-G can be used as a filter membrane for removing CO efficiently in the feed gas of hydrogen fuel cells.     

CFD analysis of the ITER first wall 06 panel. Part I: Model set-up and flow distribution

The first detailed Computational Fluid Dynamics (CFD) analysis of the FW06 panel of the ITER shielding blanket is presented in two companion papers. In this Part I we introduce the problem, define the model together with its input and discuss the results with particular reference to the hydraulics of the water coolant. The pressure drop across the panel is computed, together with the distribution of the flow among the different channels. Different design options are studied, with particular reference to the minimization of stagnation/recirculation regions.