An iridium abundance anomaly at the palynological cretaceous-tertiary boundary in northern new Mexico

An iridium abundance anomaly, with concentrations up to 5000 parts per trillion over a background level of 4 to 20 parts per trillion, has been located in sedimentary rocks laid down under freshwater swamp conditions in the Raton Basin of northeastern New Mexico. The anomaly occurs at the base of a coal bed, at the same stratigraphic position at which several well-known species of Cretaceous-age pollen became extinct.     

Detection of a red supergiant progenitor star of a type II-plateau supernova

We present the discovery of a red supergiant star that exploded as supernova 2003gd in the nearby spiral galaxy M74. The Hubble Space Telescope (HST) and the Gemini Telescope imaged this galaxy 6 to 9 months before the supernova explosion, and subsequent HST images confirm the positional coincidence of the supernova with a single resolved star that is a red supergiant of 8(+4)(-2) solar masses. This confirms both stellar evolution models and supernova theories predicting that cool red supergiants are the immediate progenitor stars of type II-plateau supernovae.     

Graduate students' teaching experiences improve their methodological research skills

Science, technology, engineering, and mathematics (STEM) graduate students are often encouraged to maximize their engagement with supervised research and minimize teaching obligations. However, the process of teaching students engaged in inquiry provides practice in the application of important research skills. Using a performance rubric, we compared the quality of methodological skills demonstrated in written research proposals for two groups of early career graduate students (those with both teaching and research responsibilities and those with only research responsibilities) at the beginning and end of an academic year. After statistically controlling for preexisting differences between groups, students who both taught and conducted research demonstrate significantly greater improvement in their abilities to generate testable hypotheses and design valid experiments. These results indicate that teaching experience can contribute substantially to the improvement of essential research skills.     

RELATION OF SEVERAL PEDOLOGICAL CHARACTERISTICS TO ENGINEERING QUALITIES OF SOIL

An attempt to predict engineering qualities which are needed in soil evaluation and to enhance nonagricultural use of soil survey data was made. Data from a variety of soils were subjected to simple correlation and multiple regression analyses to relate three pedologic characteristics: clay content, cation-exchange capacity (CEC), and organic matter content to two engineering qualitites: plasticity index, and optimum moisture. Simple correlation coefficients showed that clay content and CEC correlated significantly with the engineering determinations. The relationship between organic matter content and these engineering determinations was weaker. Multiple regression analyses showed that the three pedologic characteristics accounted for most of the variation in each of the engineering qualities, and that prediction was feasible.     

EMS诱变对鹰嘴紫云英种子萌发及幼苗表型特征的影响

【目的】筛选适宜鹰嘴紫云英的 EMS 诱变条件。【方法】以鹰嘴紫云英品种甘绿 2 号种子为试验材料,采用不同浓度（0、0. 2%、0. 4%、0. 6%、0. 8%）的甲基磺酸乙酯（EMS）进行不同时间（2、4、 6、8 h）的诱变处理,探究 EMS 对鹰嘴紫云英种子萌发特征及表型变化的影响。【结果】低浓度和短时间 EMS 处理促进鹰嘴紫云英种子的萌发,随 EMS 浓度升高和诱变时间的增加,对鹰嘴紫云英种子萌发产生抑制作用。种子浸出液电导率随诱变条件的加深呈上升趋势,在 2~6 h 时,萌发期发芽率、发芽势、幼苗苗长和根长均随处理时间和诱变浓度的增加呈先升高后降低的趋势,在 8 h 处理下,随 EMS 浓度的增加呈逐渐降低趋势,EMS 浓度在 0. 8% 时,种子发芽率和发芽势均达到最低,较对照分别降低了 54. 45% 和 56. 67%;经形态学筛选,发现有鹰嘴紫云英幼苗表现出幼苗矮小、停滞生长、叶片黄化、宽叶、窄叶、叶片发紫、诸多病斑等特殊变异性状。【结论】0. 8%EMS 处理 6 h 可作为最佳诱变组合;幼苗的生长随诱变时间和浓度增加而明显受到抑制,且表型变异类型也逐步增多。     

17种报春苣苔属植物的组培苗移栽季节研究

探讨不同季节对报春苣苔属植物组培苗移栽成活的影响,为其今后组培苗工厂化、规模化生产提供技术支持.以17种报春苣台属植物的组培生根苗为材料,研究季节对移栽成活的影响,分析不同物种间在同一季节的移栽成活差异以及同一物种在4个不同季节的移栽成活差异.大部分种类在春季移栽具有较高的成活率;成活率最高与最低的种类为三苞报春苣苔和...     

不同处理方法对美国截叶胡枝子种子发芽的影响

截叶胡枝子(Lespedezacunecta)是原产于亚洲东部的一种多年生的豆科植物,在我国南方地区野生分布很广。它具有耐瘠、耐旱、耐酸、耐热、固土能力强、适应性广等特性,在国外也颇受重视。我国于1983年从美国引种,通过对其生物学和生态学特性、经济性状和栽培技术研究证明,引进的美国截叶胡枝子在人工栽培条件下,表现出良好的经济性状,是南方草地改良的希望种子。但是在生产中,由于其硬实的存在,使得种子的发芽率很低,往往造成出苗困难和草地建植缓慢,甚至出现严重缺苗断垄的现象,直接影响田间产量,限制了它的进一步推广应用。试验采用不同处…