Measuring spacetime: from the big bang to black holes

Space is not a boring static stage on which events unfold over time, but a dynamic entity with curvature, fluctuations, and a rich life of its own. Spectacular measurements of the cosmic microwave background, gravitational lensing, type Ia supernovae, large-scale structure, spectra of the Lyman alpha forest, stellar dynamics, and x-ray binaries are probing the properties of spacetime over 22 orders of magnitude in scale. Current measurements are consistent with an infinite flat everlasting universe containing about 30% cold dark matter, 65% dark energy, and at least two distinct populations of black holes.     

How big is the universe of exons?

If genes have been assembled from exon subunits, the frequency with which exons are reused leads to an estimate of the size of the underlying exon universe. An exon database was constructed from available protein sequences, and homologous exons were identified on the basis of amino acid identity; statistically significant matches were determined by Monte Carlo methods. It is estimated that only 1000 to 7000 exons were needed to construct all proteins.     

联苯肼酯在草莓上的残留降解及其安全使用

为评价联苯肼酯在草莓上的环境安全性,采用田间试验方法,研究了设施栽培条件下联苯肼酯在草莓上的消解动态和残留情况,并据此对实际生产中的用药模式进行调整,探索最适安全间隔期。结果表明,联苯肼酯2 000倍液施药1次,其在设施栽培草莓上的半衰期为3.15 d;设施栽培草莓上联苯肼酯的残留量受施药浓度、施药次数影响,残留风险与田间用药剂量、用药次数呈正相关。参考国外农药残留限量标准,建议在设施栽培条件下,按常规方法及作用剂量施药;在施药2~3次的情况下,草莓的安全采收间隔期为3 d;随着施药浓度或施药次数增加,安全间隔期应适当延长。     

耕地重金属污染与安全利用

耕地土壤是人类社会赖以生存的重要资源之一,为农作物生长提供必要的养分和物质基础。然而,随着工业化和农业现代化的快速发展,重金属污染耕地土壤的问题日益严重。重金属污染不仅危害农产品质量安全,还会通过食物链危害人类健康。本文对耕地土壤重金属污染情况、重金属污染对作物、环境和健康的影响以及重金属污染耕地的安全利用技术进行汇总分析,以期为耕地土壤重金属污染治理修复和安全利用提供参考。     

大数据时代下的图书馆用户信息管理及应用探析

大数据时代,大数据充斥在人们生活的各个方面,各个专业、各个领域也受到大数据的影响.在此背景下,要充分利用云计算技术,对用户信息进行分析和鉴定,以掌握用户的信息需求,充分发挥图书馆用户信息管理在图书馆管理和发展中的重要作用.     

HACCP与绿色畜产品生产

文章简要介绍了 HACCP的概念、历史、主要内容以及与绿色畜产品生产的关系 ,供国内同行参考。