Reoperations after operation on the thoracic aorta: etiology, surgical techniques, and prevention

Recurrent aortic aneurysms, persistent or new dissection, new onset of valvular and coronary artery disease, graft infection, and prosthetic endocarditis are not rare after thoracic aortic operations; they can be difficult to diagnose and represent a formidable surgical challenge. Between 1977 and 1991, 876 operations were performed on the thoracic aorta in our institution: 340 in dissections, 299 in true aneurysms, 150 for aortic remodeling and external wall support during aortic valve replacement, and 87 for miscellaneous causes. During the same period, there were 193 additional reoperations. Vascular reoperations on abdominal aorta and peripheral arteries accounted for 73 cases and are not further discussed in this study. The reasons for reoperation (n = 130) in 120 patients were: failure of biologic valves (n = 23); aneurysm recurrence in a proximal or distal aortic segment (n = 21); pseudoaneurysm formation at suture lines (n = 13); new dissection or dilatation involving ascending aorta (n = 11), aortic arch (n = 13), and descending aorta (n = 10); aneurysm after aortic remodeling (n = 13); new onset of valvular disease (n = 5); and new onset of coronary disease (n = 5). Infected aortic graft and prosthetic endocarditis accounted for 10 reoperations, and a planned two-staged procedure was performed in 6 patients. Omitting the failed biologic valves, reoperations were performed on the aortic segment previously operated on in 69.3% of the cases and on other thoracic segments in 30.7%. Overall hospital mortality rate after reoperation was 5.8%. A significant decrease in operative mortality was observed in the most recent period (3.0% between 1989 and 1991). Reoperations are technically demanding, and some of them are preventable; therefore (1) graft inclusion technique should be abandoned in ascending aortic operation due to formation of false aneurysms; (2) in patients with Marfan syndrome, complete repair of the diseased aorta should be attempted during the initial operation; (3) aortic arch dissection should be repaired definitively during the first operation in low-risk patients; (4) biological valves should be avoided in aneurysm operations; and (5) homograft replacement is the treatment of choice in prosthetic endocarditis or in infected composite graft after an aortic valve or ascending aortic operation.     

凸非球面补偿检验的工艺球面分析解

本文从三级像差理论出发,推导了几种工艺球面检验凸二次曲面的计算公式。根据这些公式计算结果,进行了光路追迹,给出了这些公式对凸二次曲面的补偿范围;并讨论了几种特殊情况下的平面解。     

关于Vague集的模糊熵及其构造

本文分析了Vague集的性质,给出了将Vague集变换为Fuzzy集的转换函数,并讨论了其性质。分析了关于Vague集的模糊熵的直观特性,在此基础上我们给出了Vague集的模糊熵的定义。最后给出了一个关于Vague集的模糊熵的构造方法。     

Dynamic range of coherent analog fiber-optic links

We investigate the performance of coherent analog optical links employing amplitude modulation (AM), phase modulation (PM), and frequency modulation (FM). The performance of these coherent links is compared to that of AM direct-detection (DD) links. The signal-to-noise ratios, nonlinearities, and-spurious-free dynamic ranges (SFDR's) of the foregoing links are evaluated. We calculate the SFDR for links using DFB and Nd:YAG lasers with typical linewidths of 10 MHz and 5 kHz, respectively. The performance of PM and FM links is dominated by phase noise above a critical value of received optical power. For a linewidth of 10 MHz, and SFDR's of PM and FM links are 30 and 31 dB, respectively, for a received optical power above -27 dBm in a 1 GHz bandwidth. For a linewidth of 5 kHz, the corresponding SFDR's above a received power level of 0 dBm are 51 and 53 dB. The performance of DD and AM links is dominated by RIN above a critical value of received optical power. For a RIN level of -155 dB/Hz, the SFDR's of DD and AM links are 49 and 47 dB, respectively, for a received optical power of 10 dBm in a 1 GHz bandwidth. The SFDR's of the DD and coherent links used for transmission of subcarrier-multiplexed (SCM) signals are also derived. We evaluate target laser parameters needed by a number of different applications. For AM video and antenna remoting applications, linewidths of <1 and <3 kHz are required to use PM and FM links, respectively. For FM video, linewidths of <150 and <350 MHz are required to use PM and FM links. For SCM digital applications, linewidths of <80 and <200 MHz are required to use PM and FM links. The paper concludes with a discussion of system implementation issues, including linearization, optical frequency modulation, balanced receivers, and IF issues     

ZrO_2（Y－TZP）－Si_3N_4复合材料中抑制ZrN生成研究

研究了气氛加压烧成ＺｒＯ２（Ｙ－ＴＺＰ）－Ｓｉ３Ｎ４复合材料中抑制ＺｒＮ生成工艺问题，相组成分析表明：无论添加２０ｗｔ％工业ＺｒＯ２或者Ｙ－ＴＺＰ（３ｍｏｌ％Ｙ。Ｏ。）的氯化硅复合材料，在低于１８５０℃，３ＭＰａｋ气压力下烧成，表面无ＺｒＮ生成．通过加入有效的烧结助剂（Ｙ。Ｏａ＋ＡＩ。Ｏｓ）、增加埋粉中ＳＩＯ分压以及增加保护气氛氮气压力，适当的烧成条件等工艺措施可有效地抑制ＺｒＮ的生成．实验还证实了ＺｒＮ很容易氧化，含有ＺｒＮ的ＺｒＯ。（Ｙ－ＴＺＰ）－ＳｉｓＮ。复合材料试样经９００℃，０．ｓｈ热处理已粉碎性裂开．     

Sheep pulmonary adenomatosis: a unique model of retrovirus-associated lung cancer

Sheep pulmonary adenomatosis (SPA) is a contagious bronchiolo-alveolar carcinoma of sheep associated with an exogenous type D/B retrovirus known as jaagsiekte sheep retrovirus (JSRV). SPA represents a unique model for lung cancer, and studies on its aetiopathogenesis can provide further insight into the mechanisms of epithelial neoplasms.     

HfOxNy的场发射特性

用直流溅射和高温退火相结合的方法制备了HfOxNy薄膜并测试了其场发射性能,发现其具有较低的开启电场、较大的发射电流密度以及很好的发射稳定性.高压"锻炼"对提高HfOxNy场发射性能起着关键作用,这与高压"锻炼"下薄膜内部结构和表面性质的改变有关.对场发射机理的研究表明,HfOxNy的场发射符合经典的FN隧穿理论.     

加强无线电管理,日常监督检查势在必行

随着社会经济的迅速发展,无线电通信事业取得了很大进步,无线电通信广泛应用于各行各业,在经济发展、社会进步中发挥了重要的作用.但目前一些单位和个人无视国家有关频率管理和无线电设备管理的有关法规,擅自占用频率和非法设台情况比较严重,极大地损害了电磁环境和秩序,干扰了航空导航、公安、消防、护林防火、“三防”等重要通信业务,对无线电通信的可持续性发展造成了极大隐患,加强无线电管理日常监督检查势在必行.     

数字混沌扩频序列的盲估计

混沌序列具有非线性、宽带类噪声、大的码族、任意长的周期且容易产生的特性,因此在扩频通信系统中很有实用价值。本文将文献[1]中对伪随机扩频序列盲估计的方法推广应用到混沌扩频通信中,并对其不足提出了改进方法。在只知道扩频码周期而无其它任何先验知识的条件下,利用特征值分析的方法可以对数字混沌直扩序列进行盲估计,仿真实验证明了该方法的有效性。     

Flammability and thermal stability studies of ABS/Montmorillonite nanocomposite

Acrylonitrile–butadiene–styrene (ABS)/montmorillonite nanocomposites have been prepared using a direct melt intercalation technique by blending ABS and organophilic clay of two different particle sizes: OMTa (5 µm) and OMTb (38 µm). Their structure and flammability properties were characterized by X‐ray diffraction, high resolution electronic microscopy (HREM), thermogravimetric analysis (TGA) and cone calorimeter experiments. The results of HREM showed that ABS/5 wt% OMTa nanocomposite was a kind of intercalated–delaminated structure, while ABS/5 wt% OMTb nanocomposite was mainly an intercalated structure. The nanocomposites showed a lower heat release rate peak and higher thermal stability than the original ABS by TGA and cone calorimeter experiments. Also, the intercalated nanocomposite was more effective than an exfoliated–intercalated nanocomposite in fire retardancy. Copyright © 2003 Society of Chemical Industry