微类星体带来的谜团

与普通的观点相反 ,黑洞是个挑剔的食客。尽管这些重达数十亿太阳质量的巨兽每年可以吞食一个太阳质量的物质 ,但是它却为类星体提供动力而且会喷出等质量的物质     

REDUCING FIBER LOSS IN LABORATORY-AND MILL-SCALE FLOTATION DEINKING USING SURFACTANT SPRAY TECHNOLOGY

INTRODUCTIONDuring the past few years, the use of recycled fiber has increased dramatically due to the shortage of fiber resources and restrictive environmental regulations on paper landfills. Since the successful application of flotation in the paper recycling industry from the minerals industry in 1980s, flotation deinking has become a necessary process for ink removal from wastepaper in many paper recycling mills. The deinking chemistry and the physicochemical interactions among air bub…     

腹腔镜肾部分切除术治疗局限性肾细胞癌27例

目的:探讨经腹腔镜肾部分切除术治疗局限性肾细胞癌的手术技巧和近期疗效.方法:选择T1期、单发肿瘤,平均肿瘤直径4.0 cm(3.0～7.0 cm)的局限性肾细胞癌27例, 术中用内镜bulldog钳阻断肾动脉;用剪刀或超声刀在距离肿瘤边缘0. 5～1.0 cm处进行局部切除;肾切除床内置Surgicel薄片卷垫后,间断缝合肾实质,创面边缘喷涂FloSeal明胶基质以防延迟出血.术中冰冻确定切缘阴性.结果:27例手术均获成功,无术中、术后并发症.手术时间平均110 min;热缺血时间20～55 min,平均32 min;术中出血量平均150 mL.术后随访平均6个月,未见肿瘤局部复发,未见转移.结论:腹腔镜肾部分切除术治疗局限性肾细胞癌安全可靠,短期随访效果肯定.     

绘制人类基因组图

人体的46条染色体的DNA核心是四种碱基形成的30亿个碱基对。这四种碱基(腺嘌呤,胞嘧啶、鸟嘌呤、胸腺嘧啶)是复杂的DNA分子的主要成分。一个典型的基因是由1,000～3,000个碱基对组     

电磁兼容与电磁干扰测试方法评述

今天在电视设备、计算机、微波炉、汽车等产品中广泛地使用了各种电子设备和数字电路,从而使周围的电磁环境日趋复杂。电磁能量污染环境,其影响几乎涉及到每一个领域。电磁环境的复杂性一方面表现在电磁环境可能影响所使用的电子设备的正常工作,另一方面所使用的电子设备又可能产生电磁干扰,影响其它电子设备。电磁兼容与电磁干扰问题已经引起了广泛的重视,世界各工业发达国家都投入了巨大的人力和物力对它进行认真研究。为配合我国有关部门开展对这门学科的研究和探讨,特摘译了这篇文章的部分内容,以供参考。 这篇综述性文章详细地讨论了评价各种电子设备和系统的电磁兼容和电磁干扰特性所使用的电磁辐射和敏感度测量方法。着重讨论了使用开阔场、横电磁波室、混响室和微波暗室等测试场地的测试方法,介绍了这些测试方法的优点和局限性、技术基础和合理性以及测试结果的处理。文章的引言回顾了电磁兼容和电磁干扰的研究历史,介绍了国际上先后制定的有关标准和推行这些标准的机构,并指出影响测试方法的主要因素。以美国标准局为背景,介绍了他们所采用的方法。文章的第二部分介绍了开阔场测量的用途、组成、优缺点,并讨论了与测量误差有关的问题。第三部分介绍了横电磁波室的来由、原理、用途、优缺点及测     

中国谷物收获机械的经济比较(摘译)

今天中国与1848年的美国在谷物收获方面有许多类似的和不同的地方,两者都以手工收割为主,然而现时的中国比19世纪中叶的美国人口密度要高得多。农村丰富的劳动力和小型的农业经营规模是发展机械化的两大障碍。推动当初北美实现机械化的许多条件在中国并不具备。     

Regulation of polarized extension and planar cell polarity in the cochlea by the vertebrate PCP pathway

The mammalian auditory sensory organ, the organ of Corti, consists of sensory hair cells with uniformly oriented stereocilia on the apical surfaces and has a distinct planar cell polarity (PCP) parallel to the sensory epithelium. It is not certain how this polarity is achieved during differentiation. Here we show that the organ of Corti is formed from a thicker and shorter postmitotic primordium through unidirectional extension, characteristic of cellular intercalation known as convergent extension. Mutations in the PCP pathway interfere with this extension, resulting a shorter and wider cochlea as well as misorientation of stereocilia. Furthermore, parallel to the homologous pathway in Drosophila melanogaster, a mammalian PCP component Dishevelled2 shows PCP-dependent polarized subcellular localization across the organ of Corti. Taken together, these data suggest that there is a conserved molecular mechanism for PCP pathways in invertebrates and vertebrates and indicate that the mammalian PCP pathway might directly couple cellular intercalations to PCP establishment in the cochlea.     

微纳米加工技术

无论是集成电路技术,还是微系统技术或纳米技术,其共同特征是功能结构的尺寸在微米或纳米范围,因此可以统称为微纳米技术。功能结构的微纳米化带来的不仅仅是能源与原材料的节省,而且导致多功能的高度集成和生产成本的大大降低。微纳米技术依赖于微纳米尺度的功能结构与器件。实现功能结构微纳米化的基础是先进的微纳米加工技术。本书作者力求全面介绍微纳米加工方面的各种技术,并且介绍了微纳米加工技术的最新进展。     

郯庐断裂带形成演化的年代学研究

通过对郯庐断裂带东侧张八岭蓝片岩带内白云母＾４０Ａｒ－＾３９Ａｒ年龄、断裂带内片麻状花岗岩中钾长石＾４０Ａｒ－＾３９Ａｒ年龄以及断裂带内断层泥Ｋ－Ａｒ、ＥＳＲ年龄的测定,并结合有关的地质和古地磁资料,厘定了籽庐断裂带形成和演化的过程：（１）三叠纪（２４４～２０９Ｍａ）由于华北与扬子地块碰撞,郯庐断裂带形成为其主要左行平稳时期;（２）侏罗纪（１８９～１６４Ｍａ）时郯庐断裂东侧下扬子地块可能经历了逆时     

Growth and microstructure of AlN whiskers and dendrites

AlN whiskers or dendrites were synthesized with asublimation-recrystallization method by using Al, AlN powders and some additives as raw materials.Whiskers with different sizes that featured high purity and good crystallinity were obtained by controlling temperature and gas supersaturation in the reaction container. The whiskers were described as long and straight single crystals of approximately 1-30 μm in diameter by the centimeter range in length. However, AlN dendrites were about 1mm in diameter by 0.5cm in length,and showed an obviously preferential growth orientation, i.e., perpendicular to[2111] and[1011] planes. It is concluded that the whiskers or dendrites grow via the vapor-solidmechanism.