离石区玉米高产创建展示措施与体会

离石区通过实施玉米高产创建示范展示,实现了玉米产量持续高产。     

硫酸钛为钛源制备二氧化钛的实验条件研究

实验以硫酸钛为钛源、尿素为沉淀剂、聚乙二醇600为分散剂,采用均匀沉淀法制备二氧化钛粉末。主要讨论了影响沉淀形成时间的主要因素:尿素的用量及加入方法、聚乙二醇的用量、以及水浴的温度等。实验结果表明,以硫酸钛为钛源、尿素为沉淀剂、聚乙二醇600为分散剂,采用均匀沉淀法制备二氧化钛粉末最佳反应条件为:在水浴加热343 K条件下,将尿素缓慢滴加到硫酸钛和聚乙二醇600的混合液中,硫酸钛和聚乙二醇600的混合液在磁力搅拌器搅拌时滴加尿素,用硫酸调节pH在1.5~2,保持硫酸钛、尿素和聚乙二醇600的摩尔比1∶12∶0.01。     

中国特色经济地理学构建初探

通过分析西方发达国家与我国不同的经济发展阶段、经济地理学的学科定位及国家社会文化环境,探索中国特色经济地理学的特殊之处,提出构建中国特色经济地理学的可能性.总结中国特色经济地理学构建的三个重要基点:反映发展中大国快速发展的经济地理特殊事实并给出解释;基于地理学的研究框架并吸纳经济学的相关理论;中国特殊的政治制度和文化传统对经济地理现象的重要影响.     

生化实验室在实践教学中的课程协调和管理作用

自2011年以来,为实现培养医学生动手能力、批判性思维和创新能力的教学目标,作为基础实验课程的生物化学与分子生物学实验在实验内容和课程设置方面进行了一系列的改革,循序渐进,由浅入深,同时突出小班化精英化的教育特色,最大限度地使学生受益。在整个课程的实施过程中,生物化学与分子生物学实验室作为实践课程开展的核心部门,无论是在课程准备,课程安排,还是在教学资源分配和课程内容改革中,都起到了有利的协调和管理作用,最大限度地服务于实践教学,使实验课程在良好有序的环境中发展前行。     

A very faint core-collapse supernova in M85

An anomalous transient in the early Hubble-type (S0) galaxy Messier 85 (M85) in the Virgo cluster was discovered by Kulkarni et al. on 7 January 2006 that had very low luminosity (peak absolute R-band magnitude M(R) of about -12) that was constant over more than 80 days, red colour and narrow spectral lines, which seem inconsistent with those observed in any known class of transient events. Kulkarni et al. suggest an exotic stellar merger as the possible origin. An alternative explanation is that the transient in M85 was a type II-plateau supernova of extremely low luminosity, exploding in a lenticular galaxy with residual star-forming activity. This intriguing transient might be the faintest supernova that has ever been discovered.     

West Nile virus emergence and large-scale declines of North American bird populations

Emerging infectious diseases present a formidable challenge to the conservation of native species in the twenty-first century. Diseases caused by introduced pathogens have had large impacts on species abundances, including the American chestnut, Hawaiian bird species and many amphibians. Changes in host population sizes can lead to marked shifts in community composition and ecosystem functioning. However, identifying the impacts of an introduced disease and distinguishing it from other forces that influence population dynamics (for example, climate) is challenging and requires abundance data that extend before and after the introduction. Here we use 26 yr of Breeding Bird Survey (BBS) data to determine the impact of West Nile virus (WNV) on 20 potential avian hosts across North America. We demonstrate significant changes in population trajectories for seven species from four families that concur with a priori predictions and the spatio-temporal intensity of pathogen transmission. The American crow population declined by up to 45% since WNV arrival, and only two of the seven species with documented impact recovered to pre-WNV levels by 2005. Our findings demonstrate the potential impacts of an invasive species on a diverse faunal assemblage across broad geographical scales, and underscore the complexity of subsequent community response.     

Non-volcanic tremor driven by large transient shear stresses

Non-impulsive seismic radiation or 'tremor' has long been observed at volcanoes and more recently around subduction zones. Although the number of observations of non-volcanic tremor is steadily increasing, the causative mechanism remains unclear. Some have attributed non-volcanic tremor to the movement of fluids, while its coincidence with geodetically observed slow-slip events at regular intervals has led others to consider slip on the plate interface as its cause. Low-frequency earthquakes in Japan, which are believed to make up at least part of non-volcanic tremor, have focal mechanisms and locations that are consistent with tremor being generated by shear slip on the subduction interface. In Cascadia, however, tremor locations appear to be more distributed in depth than in Japan, making them harder to reconcile with a plate interface shear-slip model. Here we identify bursts of tremor that radiated from the Cascadia subduction zone near Vancouver Island, Canada, during the strongest shaking from the moment magnitude M(w) = 7.8, 2002 Denali, Alaska, earthquake. Tremor occurs when the Love wave displacements are to the southwest (the direction of plate convergence of the overriding plate), implying that the Love waves trigger the tremor. We show that these displacements correspond to shear stresses of approximately 40 kPa on the plate interface, which suggests that the effective stress on the plate interface is very low. These observations indicate that tremor and possibly slow slip can be instantaneously induced by shear stress increases on the subduction interface-effectively a frictional failure response to the driving stress.     

Clathrate nanostructures for mass spectrometry

The ability of mass spectrometry to generate intact biomolecular ions efficiently in the gas phase has led to its widespread application in metabolomics, proteomics, biological imaging, biomarker discovery and clinical assays (namely neonatal screens). Matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization have been at the forefront of these developments. However, matrix application complicates the use of MALDI for cellular, tissue, biofluid and microarray analysis and can limit the spatial resolution because of the matrix crystal size (typically more than 10 mum), sensitivity and detection of small compounds (less than 500 Da). Secondary-ion mass spectrometry has extremely high lateral resolution (100 nm) and has found biological applications although the energetic desorption/ionization is a limitation owing to molecular fragmentation. Here we introduce nanostructure-initiator mass spectrometry (NIMS), a tool for spatially defined mass analysis. NIMS uses 'initiator' molecules trapped in nanostructured surfaces or 'clathrates' to release and ionize intact molecules adsorbed on the surface. This surface responds to both ion and laser irradiation. The lateral resolution (ion-NIMS about 150 nm), sensitivity, matrix-free and reduced fragmentation of NIMS allows direct characterization of peptide microarrays, direct mass analysis of single cells, tissue imaging, and direct characterization of blood and urine.