江口拱坝坝基渗流场有限元法分析

运用固定网格结点虚流量法及排水子结构技术，对江口拱坝坝基的防渗与排水渗控制施、两岸山体边界条件、隔水岩层阻渗及岩体成层产状等因素在影响坝基渗流场特性中的具体作用进行了计算分析。结果表明，排水子结构技术在精细求解复杂坝基渗流场中具有明显的优势，它在理论和算法上严密，完全能仿真模拟各个排水孔的几何尺寸及排水降压的真实水力行为，不仅能明显地提高计算效率，还能使渗流场的精度大大提高。     

氧化锆增韧陶瓷的相变及相变增韧

本文阐述了氧化锆增韧陶瓷（ＺＴＣ）的相变增韧机理，并探讨了热处理工艺对ＺＴＣ的相变及显微组织的影响规律。     

Crack Branching in All-Oxide Ceramic Composites

The existence of oxidation embrittlement in previously developed ceramic-matrix composite (CMC) systems at intermediate temperatures (500–900°C) has motivated the development of all-oxide CMCs. Studies of the damage tolerance of an all-oxide CMC suggest that it relies on distributing fiber bundles heterogeneously in a porous matrix with a thin matrix-only region surrounding each bundle. For such composites, loading in the direction of the fibers causes cracks to first commence in the fiber bundles, breaching both the matrix and fibers within each bundle. These fiber-bundle cracks then branch in the matrix-rich region, parallel to the load, forming stable H-shaped cracks. The mechanics behind one mechanism controlling the competition between branching and continued extension of a preexistent fiber-bundle crack in a unidirectional all-oxide CMC are provided in this paper. Both plane-strain and axisymmetric cases are studied using an integral equation method as well as a numerical method based on finite elements. With no elastic mismatch assumed between the fiber and matrix, a single nondimensional combination, E Ω/σ_∞, emerges as the key parameter that governs the tendency of the crack to branch (where E is Young's modulus, Ω is the thermal misfit strain between the fiber bundle and matrix, and σ_∞ is the stress applied parallel to the fiber axis). Quantitative estimates of the conditions under which the branching of the bundle crack is favored are presented.     

Detection of severity of coronary stenosis by quantitative myocardial tomography with Tc-99m-MIBI at rest

To evaluate the role of myocardial tomography with Tc-99m-MIBI (MB) in detecting abnormal coronary arteries, 34 patients with myocardial infarction underwent resting quantitative SPEC with MB and coronary arteriography within one month. When segmental MB uptake was < 560% of the left ventricular peak activity, there was 88% probability that a totally occluded or severely stenosed coronary artery (stenosis > 90%) was involved. There was 82% probability of finding no significant stenosis of coronary arteries in the normal myocardial segments. In the myocardial segments supplied by occluded coronary arteries, there was significantly higher MB uptake in the segments with good collateral circulation as compared with those subtended by a vessel totally occluded with poor collateral circulation (P < 0.05). The sensitivity and specificity of detecting abnormal coronary artery by quantitative analysis of myocardial tomography was 87% and 90% respectively. It is suggested that quantitative analysis of myocardial tomography with MB can differentiate between myocardial segments supplied by severely stenosed and normal coronary artery and evaluate the existence of collateral circulation.     

电脉冲快速退火对铁基非晶合金性能的影响

采用大电流交流脉冲对非晶Ｆｅ７８Ｂ１３Ｓｉ９合金进行了去应力退火。初步探讨了电脉冲加热对加热速率和该合金内应力释放、退火脆化以及最终软磁性影响的基本规律。结果表明：电脉冲加热可以得到远高于常规退火的加热速率，选择合适工艺参数可使非晶合金内应力释放９０％，软磁性（Ｈ＿ｃ和Ｂ＿ｓ）达常规退火后的９５％以上，与此同时使合金的延性（断裂应变ε＿ｆ）维持在０．９以上，从而有望实现非晶合金磁性与延性的合理配合。     

真空微电子三极管几何参数的设计考虑

真空微电子三极管是近年来兴起与发展的真空微电子学中的一类重要器件。本文从真空微三极管的工作特性出发,分析了这类器件中所需考虑的几何参数和工作特性的关系,并给出了一些理论和实验公式,为今后的设计提供一些参考。     

Association of herpes zoster ophthalmicus with acquired immunodeficiency syndrome and acute retinal necrosis

We conducted a review to investigate the prevalence of human immunodeficiency virus (HIV), or acquired immunodeficiency syndrome (AIDS), in patients with herpes zoster ophthalmicus, as well as the incidence of acute retinal necrosis after herpes zoster ophthalmicus. All charts of patients seen at our institution between 1987 and 1992 with a primary diagnosis of herpes zoster ophthalmicus were reviewed. Of 112 patients with herpes zoster ophthalmicus, 29 (26%) had HIV or AIDS. All these patients were younger than 50 years at the time of diagnosis. Five of 29 (17%) immunocompromised patients had acute retinal necrosis after herpes zoster ophthalmicus. No acute retinal necrosis was identified in the nonimmunocompromised patients after herpes zoster ophthalmicus. We recommend that all patients younger than 50 years who have herpes zoster ophthalmicus at initial examination be tested for HIV. Additionally, HIV-infected patients should be monitored closely after herpes zoster ophthalmicus for development of acute retinal necrosis. Long-term oral prophylactic as well as initial high-dose intravenous acyclovir may be appropriate in HIV-infected individuals with herpes zoster.     

SiCf/O′-SiAlON composite: properties and oxidation retained properties

A composite of O′SiAlON (Si_2-xAl_xN_2-xO_1+x, with x 0.14) reinforced with 20 vol.% SiC monofilaments was fabricated by hot-pressing, at 1600°C, for 2 h under 34 MPa pressure. The mechanical and interfacial properties of the composites, as-fabricated as well as post-oxidized, were, investigated. The composite exhibited a significant improvement in ultimate flexure strength (640 MPa) and work of fracture (42 kJ m⁻²) compared with that (350 MPa and 1.8 kJ m⁻², respectively) of the monolithic material. These mechanical properties were slightly increased after the composite was heat treated for 24 h in air at 1200 and 1300°C. However, the composite exhibited a significant degradation in ultimate strength, while the work of fracture (WOF) remained unchanged after exposure in air at temperatures beyond 1400°C. The as-fabricated composite revealed a low interfacial shear strength (6.2 MPa) and a frictional sliding stress (3.2 MPa). After the composite was oxidized at elevated temperatures, the interfacial bonding and sliding stresses were reduced to noticeable extents, resulting from the degradation of the carbon coating layer of the SiC monofilaments.