粉末冶金材料激光深熔焊接光致等离子体行为及控制

采用LSM2 4 0型全自动CO2 激光焊接机焊接粉末材料 ,研究不同粉末材料产生等离子体所需的临界激光功率。粉末配方为 :Fe粉 +15 %羟基Fe粉 ,Co粉 ,Ni粉 +15 %羟基Ni粉三种试样。研究结果表明 ,Fe ,Co ,Ni三种试样在CO2 激光作用下产生金属蒸气时的临界激光功率密度IC 为ICFe >ICCo >ICNi;等离子体得以有效控制的下限临界气流量QS 为QFeS 相似文献   

堪为物理学第三分支的计算物理

本文是作者1982年在中国访问时所作的讲演,论述物理学各领域的前沿工作,用许多事例说明计算物理对推动物理理论的重大意义。文中还指出计算物理在其性质、方法及需要等方面不同于和独立于解析的理论物理和实验物理,而成为物理学的第三分支。     

Authorship verification using deep belief network systems

This paper explores the use of deep belief networks for authorship verification model applicable for continuous authentication (CA). The proposed approach uses Gaussian units in the visible layer to model real‐valued data on the basis of a Gaussian‐Bernoulli deep belief network. The lexical, syntactic, and application‐specific features are explored, leading to the proposal of a method to merge a pair of features into a single one. The CA is simulated by decomposing an online document into a sequence of short texts over which the CA decisions happen. The experimental evaluation of the proposed method uses block sizes of 140, 280, 500 characters, on the basis of the Twitter and Enron e‐mail corpuses. Promising results are obtained, which consist of an equal error rate varying from 8.21% to 16.73%. Using relatively smaller forgery samples, an equal error rate varying from 5.48% to 12.3% is also obtained for different block sizes.     

The effects of etching and deposition on the performance and stress evolution of open through silicon vias

The effects of silicon etching using the Bosch process and LPCVD oxide deposition on the performance of open TSVs are analyzed through simulation. Using an in-house process simulator, a structure is generated which contains scalloped sidewalls as a result of the Bosch etch process. During the LPCVD deposition step, oxide is expected to be thinner at the trench bottom when compared to the top; however, additional localized thinning is observed around each scallop. The scalloped structure is compared to a structure where the etching step is not performed, but rather a flat trench profile is assumed. Both structures are imported into a finite element tool in order to analyze the effects of processing on device performance. The scalloped structure is shown to have an increased resistance and capacitance when compared to the flat TSV. Additionally, the scalloped TSV does not perform as well at high frequencies, where the signal loss is shown to increase. However, the scallops allow the TSV to respond better to an applied stress. This is due to the scallops’ enhanced range of motion and displacement, meaning they can compensate for the stress along the entire sidewall and not only on the TSV top, as in the flat structure.     

Viscosity dependence of electrochemical etching for gold tip fabrication

We suggest an electrochemical etching method with viscous etchant to enhance the sharpness of tip of scanning probe microscope. The viscosity of the etchant mixed with HCl solution and glycerol was used as a control parameter in addition to the voltage applied to the tip. In order to improve the sharpness of the tip, a nano-scale meniscus formed between the end of the tip and the liquid level was used. The shapes, aspect ratios, and radii of tips were measured depending on the concentration of the etchant. It was found that the tip etched with the mixed liquid with glycerol was sharper than the tip with the pure HCl solution. This can be explained by the fact that the meniscus formed by viscous liquid is maintained with a thinner diameter and causes final etching until the meniscus bridge is ruptured.     

量子阱层和垒层具有不同Al组分的270/290/330nm AlGaN基深紫外LED光电性能

为了研究AlGaN量子阱层和垒层中Al组分不同对AlGaN基深紫外发光二极管(LED)光电性能的影响,本文利用MOCVD生长、光刻和干法刻蚀工艺制备了AlGaN量子阱层和垒层具有不同Al组分的270/290/330nm深紫外LED,通过实验和数值模拟计算方法发现,量子阱层和垒层中具有低Al组分紫外LED的AlGaN材料具有较低的位错密度、较高的光输出功率和外量子效率。通过电流-电压(I-V)曲线拟合出的较大的理想因子(3.5)和能带结构图表明,AlGaN深紫外LED的电流产生是隧穿机制占据主导作用,这是因为高Al组分AlGaN量子阱中强极化场造成了有源层区域较大的能带弯曲和电势降。     

A picosecond widely tunable deep-ultraviolet laser for angle-resolved photoemission spectroscopy

We develop a picosecond widely tunable laser in a deep-ultraviolet region from 175 nm to 210 nm,generated by two stages of frequency doubling of a 80-MHz mode-locked picosecond Ti:sapphire laser.A β-BaB2O4 walk-off compensation configuration and a KBe2BO3F2 prism-coupled device are adopted for the generation of second harmonic and fourth harmonics,respectively.The highest power is 3.72 mW at 193 nm,and the fluctuation at 2.85 mW in 130 min is less than ±2%.