单选题
柴油的十六烷值，一般为（）。
发布日期：2020-12-11
10-20
20-40
40-60
60-80
试题解析
十六烷值
十六烷值是衡量柴油在压燃式发动机中发火性能的重要指标。十六烷值越高，表明柴油的发火性能好、滞燃期短、燃烧均匀、发动机发动平稳。十六烷值低则表明燃烧发火困难，滞燃期长，发动机工作状态粗暴。但十六烷值过高，也将会由于局部不完全燃烧，而产生少量黑色排烟。
- 中文名
- 十六烷值
- 作用
- 衡量柴油在
- 外文名
- Cetane number
- 公式
- 442.8-462.9
柴油
柴油，是轻质石油产品，复杂烃类（碳原子数约10～22）混合物，为柴油机燃料，主要由原油蒸馏、催化裂化、热裂化、加氢裂化、石油焦化等过程生产的柴油馏分调配而成，也可由页岩油加工和煤液化制取，分为轻柴油（沸点范围约180～370℃）和重柴油（沸点范围约350～410℃）两大类。广泛用于大型车辆、铁路机车、船舰。柴油最重要用途是用于车辆、船舶的柴油发动机。与汽油机相比，柴油机热效率高，燃油消耗率低。柴油具有低能耗，所以一些小型汽车甚至高性能汽车也改用柴油。2017年10月27日，世界卫生组织国际癌症研究机构公布的致癌物清单初步整理参考，柴油,轻馏分在3类致癌物清单中。
- 中文名
- 柴油
- 主要成分
- 复杂烃类混合物
- 外文名
- diesel oil
- 分类
- 轻柴油、重柴油
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[A] The work builds on a study published last year by Shinya Yamanaka of Kyoto University in Japan, which showed that mouse tail cells could be transformed into ES-like cells by inserting four genes (Science Now, 3 July 2006).Those genes are normally switched off after embryonic cells differentiate into the various cell types. In June this year, Yamanaka and another group reported that the cells were truly pluripotent, meaning that they had the potential to grow into any tissue in the body (Science Now, 6 June). [B] In the new work, Yamanaka and his colleagues used a retrovirus to ferry into adult cells the same four genes they had previously used to reprogram mouse cells: OCT3/4, SOX2, KLF4, and c-MYC. They reprogrammed cells taken from the facial skin of a 36-year-old woman and from connective tissue from a 69-year-old man. Roughly one iPS cell line was produced for every 5,000 cells the researchers treated using the technique, an efficiency that enabled them to produce several cell lines from each experiment. [C] Now the race to repeat the feat in human cells has ended in a tie: Two groups report today that they have reprogrammed human skin cells into so-called induced pluripotent cells (iPSs). In a paper published online in Cell, Yamanaka and his colleagues show that their mouse technique works with human cells as well. And in a paper published online in Science, James Thomson of the University of Wisconsin, Madison, and his colleagues report success in reprogramming human cells, again by inserting just four genes, two of which are different from those Yamanaka uses. [D] Once the kinks are worked out, “the whole field is going to completely change,” says stem cell researcher Jose Cibelli of Michigan State University in East Lansing. “People working on ethics will have to find something new to worry about.” [E] Thomson’s team started from scratch, identifying its own list of 14 candidate reprogramming genes. Like Yamanaka’s group, the team used a systematic process of elimination to identify four factors: OCT3 and SOX2, as Yamanaka used, and two different genes, NANOG and LIN28. The group reprogrammed cells from fetal skin and from the foreskin of a newborn boy. The researchers were able to transform about one in 10,000 cells, less than Yamanaka’s technique achieved, Thomson says, but still enough to create several cell lines from a single experiment. [F] Scientists have managed to reprogram human skin cells directly into cells that look and act like embryonic stem (ES) cells. The technique makes it possible to generate patient-specific stem cells to study or treat disease without using embryos or oocytes—and therefore could bypass the ethical debates that have plagued the field. “This is like an earthquake for both the science and politics of stem cell research,” says Jesse Reynolds, policy analyst for the Center for Genetics and Society in Oakland, California. [G] Although promising, both techniques share a downside. The retroviruses used to insert the genes could cause tumors in tissues grown from the cells. The crucial next step, everyone agrees, is to find a way to reprogram cells by switching on the genes rather than inserting new copies. The field is moving quickly toward that goal, says stem cell researcher Douglas Melton of Harvard University. “It is not hard to imagine a time when you could add small molecules that would tickle the same networks as these genes” and produce reprogrammed cells without genetic alterations, he says.(此文选自Science2007年刊) Order:
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