Precipitation: its acidic nature

A comparison of the free hydrogen ion concentration and the total hydrogen ion concentration of rain samples shows that rain is a weak acid. The weak acid nature of rain casts doubt on the concepts that the acidity of rain is increasing and that these increases are due to strong acids such as sulfuric acid.     

DNA of Rous sarcoma virus: its nature and significance

Purified preparations of Rous sarcoma virus (an avian tumor virus with an RNA genome) contain small amounts of double-stranded DNA. This DNA cannot be hybridized to viral RNA, but will reanneal completely with the DNA of avian cells. Extensive substitution of bromodeoxyuridine for thymidine in "viral" DNA does not photosensitize the biological activity of the virus. These observations indicate that the DNA associated with Rous sarcoma virus is derived from the DNA of the avian host cell, and is probably devoid of any function in the life cycle of the virus.     

Plasma saluretic activity: its nature and relation to oxytocin analogs

Plasma natriuretic activity was evoked in cows and dogs by infusion of saline with or without dextran. Deproteinized samples were fractionated on both Sephadex and Bio-Gel columns; the activity was separated, the approximate molecular weight being in the region of 1000. Incubation with chymotrypsin destroyed the activity, suggesting that it might be a polypeptide. A similar activity in blood resulted from intracarotid injection of either oxytocin or either of two synthetic analogs. Possibly the latter are saluretic by virtue of a releasing action on some intracranial structure for another natriuretic peptide.     

Red cochineal dye (carminic Acid): its role in nature

Carminic acid, the well-known red dyestuff from cochineal insects (Dactylopius spp.), is a potent feeding deterrent to ants. This deterrency may be indicative of the natural function of the compound, which may have evolved in cochineals as a chemical weapon against predation. The behavior of an unusual predator is described-the carnivorous caterpillar of a pyralid moth (Laetilia coccidivora)-which is undeterred by carminic acid and feeds on cochineals. The animal has the remarkable habit of utilizing the ingested carminic acid for defensive purposes of its own.     

Ciguatoxin: isolation and chemical nature

Ciguatoxin, the agent responsible for ciguatera, a disease produced in humans from ingestion of certain fishes, has been isolated from specimens of the moray eel, Gymnothorax javanicus. The toxin is apparently a lipid containing quaternary nitrogen, hydroxyl, and carbonyl functions.     

Cystathioninuria: nature of the defect

A homogenate of liver obtained by biopsy from two patients with cystathioninuria, an inborn error of metabolism, cleaved radioactive cystathionine only slightly until an excess of pyridoxal phosphate was added. The apoenzyme failed to bind the coenzyme normally. Pyridoxine therapy of familial cystathioninuria thus has a sound basis.     

Deoxyribonucleic acid antibody: a method to detect its primary interaction with deoxyribonucleic acid

Antibody to DNA in human serums can be detected by the ammonium sulfate method. This sensitive and specific technique, which measures the primary interaction between DNA and antibody to DNA, is based on the observation that free DNA is soluble in 50-percent saturated ammonium sulfate whereas antibody-bound DNA is insoluble.     

天然气管道压缩机组及其在国内的应用与发展

概述了天然气管道压缩机和驱动机的分类与选型,比较了离心机和往复机、燃机驱动和电机驱动方式在管道应用中的优缺点和适用范围;介绍了现阶段国内外管道压缩机和驱动机的技术发展现状与市场资源情况,指出专业的长输管道离心压缩机的制造商以欧美国家为主。在此基础上,回顾了国内天然气管道压缩机组的发展历史,分析了其应用现状,介绍了管道压缩机国产化方案,探讨了在制造、运行和维护等方面需要重点关注的问题和发展趋势,例如燃机大修本地化、多机组站场余热利用、优化压缩机组运行管理等,对于下一阶段管道建设和运行中管道压缩机组的选型和使用有一定的借鉴意义。     

六六六在自然界中的环境行为及其危害消除研究现状

针对有机氯杀虫剂六六六生产使用状况、毒性及环境行为,对近20年来六六六的生物降解和非生物降解的研究给予了全面阐述和综合评价,并提出了今后在环境监测和污染治理方面可能的研究动向。     

Clouds of venus: evidence for their nature

The linear polarization of sunlight multiply scattered by the atmosphere, and cloud particles of Venus has been computed and compared with observations over the wavelength range from the ultraviolet to the infrared region. The following properties of the visible cloud layer are derived: the refractive index of the cloud particles is 1.45 +/- 0.02 at a wavelength of 0.55 micron, and there is an indication of a slight decrease in the value from the ultraviolet to the near-infrared region; the mean particle radius is very near 1 micron, and most of the particles are spherical; the cloud layer occurs high in the atmosphere where the pressure is about 50 millibars (equivalent to an altitude of approximately 20 kilometers on the earth). The results for the index of refraction eliminate the possibility that the visible clouds are composed of pure water or ice.