Effect of ricin,of its subunits and of modeccin on cAMP level in Yoshida ascites cells

Summary The B chain of ricin strongly decreases the PGE₁-enhanced level of cAMP in Yoshida ascites sarcoma cells, whereas the A chain is ineffective. Modeccin does not have any effect.Acknowledgments. We thank E. Lorenzoni for preparing ricin and modeccin. The work was aided by a contract from The Consiglio Nazionale delle Ricerche, Rome, within The Piano Finalizzato Controllo della crescita neoplastica and by Pallotti's legacy for cancer research.     

Influence of fire and juniper encroachment on birds in high-elevation sagebrush steppe

We examined relationships between high-elevation sagebrush ( Artemisia spp.) steppe habitats altered by prescribed fire and western juniper ( Juniperus occidentalis ) encroachment on breeding distributions of Brewer's Sparrows ( Spizella breweri ), Vesper Sparrows ( Pooecetes gramineus ), Green-tailed Towhees ( Pipilo chlorurus ), and Sage Thrashers ( Oreoscoptes montanus ) on Steens Mountain in southeastern Oregon. In 2000 we conducted fixed-radius point count surveys at 172 sites encompassing burned and unburned sagebrush habitat and a range of juniper densities. For each bird species we developed habitat models using local variables measured in the field and landscape variables derived from remotely sensed data. Akaike's Information Criterion (AIC c ) was used to select the best-approximating model from a suite of a priori candidate models. Brewer's Sparrows, Sage Thrashers, and Green-tailed Towhees were positively related to increasing local sagebrush cover or percent sagebrush in the landscape, whereas Vesper Sparrows were negatively associated with sagebrush cover and positively related to increases in sagebrush fragmentation at local and landscape scales. Including a measure of juniper encroachment substantially improved models for all species in the analysis. Green-tailed Towhees showed a curvilinear response to the amount of juniper in the landscape. All other species showed a strong negative relationship with juniper. Our results indicate that, although changes in sagebrush habitat associated with fire had a negative influence on sagebrush birds, juniper encroachment due to fire suppression also impacted this high-elevation sagebrush bird community.     

唐宋文人审美情趣的嬗变——论山水画的兴起发展

唐宋作为中国文化发展的又一鼎盛与重要转折时期,其绘画也是瑰丽多姿。而文人是社会意识的代表,他们所体现出来的审美追求,最为充分地表现中国绘画的社会主流审美情趣。中国的艺术精神,可说由唐代水墨淡彩山水的出现而完成了它自身性格所要求的形式,才完成了文人进入绘画主流审美意识的舞台。随着社会思潮的不断变迁,山水画取代了人物画却在其后不远的北宋时代迎来了它的高峰。     

Premature ageing in mice expressing defective mitochondrial DNA polymerase

Point mutations and deletions of mitochondrial DNA (mtDNA) accumulate in a variety of tissues during ageing in humans, monkeys and rodents. These mutations are unevenly distributed and can accumulate clonally in certain cells, causing a mosaic pattern of respiratory chain deficiency in tissues such as heart, skeletal muscle and brain. In terms of the ageing process, their possible causative effects have been intensely debated because of their low abundance and purely correlative connection with ageing. We have now addressed this question experimentally by creating homozygous knock-in mice that express a proof-reading-deficient version of PolgA, the nucleus-encoded catalytic subunit of mtDNA polymerase. Here we show that the knock-in mice develop an mtDNA mutator phenotype with a threefold to fivefold increase in the levels of point mutations, as well as increased amounts of deleted mtDNA. This increase in somatic mtDNA mutations is associated with reduced lifespan and premature onset of ageing-related phenotypes such as weight loss, reduced subcutaneous fat, alopecia (hair loss), kyphosis (curvature of the spine), osteoporosis, anaemia, reduced fertility and heart enlargement. Our results thus provide a causative link between mtDNA mutations and ageing phenotypes in mammals.     

湿型砂三性能自动快速测定方法及其测定仪

本文研究一种湿型砂三性能自动快速测定方法及其测定仪。该方法是直接测定紧实率的试样的透气压力和湿压强度,代入由试验建立的二元线性回归方程求得标准工艺试样的透气性和湿压强度。该仪器采用用移传感器测定紧实率,用压力传感器测定湿压强度,用气压传感器测定透气压力。仪器的动作程序、检测信号的采集、数据处理及打印险测结果等均由微机控制,自动运行。本方法简单,快速和准确。该仪器采用气压传动,结构简单,制造容易。     

碳纤维表面处理及其复合材料界面优化的研究Ⅰ．低温等离子处理对碳纤维表面的作用

通过碳纤维表面的扫描电镜观察与复丝力学性能测定，发现等离子处理对纤维的模量几乎没有影响，而强度随着处理功率的增加和时间的延长稍有下降，在外观上仅表现为纤维表面纵向沟槽的加深。氩气等离子比氧化性空气等离子的损伤小。通过碳纤维表面的Ｘ射线光电子能谱分析，结合喇曼光谱的研究，还发现等离子处理的有效深度达到１５ｍｍ左右。其作用是蚀刻去碳纤维表面脂肪链结构，产生石墨等晶体结构富集的高能表面。