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If the unexplained fission xenon component in meteorites is due to a volatile superheavy element, this element must have had a heat of vaporization of 54 +/- 3 kilocalories per mole and a normal boiling point of 2500 degrees +/- 400 degrees K. The prime candidates are elements 111 and 115, followed by 113, 114, 112, and 116. Elements 105 to 110 are not volatile enough and can therefore be excluded. 相似文献
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Armbrust EV Berges JA Bowler C Green BR Martinez D Putnam NH Zhou S Allen AE Apt KE Bechner M Brzezinski MA Chaal BK Chiovitti A Davis AK Demarest MS Detter JC Glavina T Goodstein D Hadi MZ Hellsten U Hildebrand M Jenkins BD Jurka J Kapitonov VV Kröger N Lau WW Lane TW Larimer FW Lippmeier JC Lucas S Medina M Montsant A Obornik M Parker MS Palenik B Pazour GJ Richardson PM Rynearson TA Saito MA Schwartz DC Thamatrakoln K Valentin K Vardi A Wilkerson FP Rokhsar DS 《Science (New York, N.Y.)》2004,306(5693):79-86
Diatoms are unicellular algae with plastids acquired by secondary endosymbiosis. They are responsible for approximately 20% of global carbon fixation. We report the 34 million-base pair draft nuclear genome of the marine diatom Thalassiosira pseudonana and its 129 thousand-base pair plastid and 44 thousand-base pair mitochondrial genomes. Sequence and optical restriction mapping revealed 24 diploid nuclear chromosomes. We identified novel genes for silicic acid transport and formation of silica-based cell walls, high-affinity iron uptake, biosynthetic enzymes for several types of polyunsaturated fatty acids, use of a range of nitrogenous compounds, and a complete urea cycle, all attributes that allow diatoms to prosper in aquatic environments. 相似文献
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FTV Pereira FC Braga KC Burioli JR Kfoury Jr LJ Oliveira PC Papa AF Carvalho CE Ambrósio FW Bazer MA Miglino 《Reproduction in domestic animals》2010,45(5):907-914
The objectives of this investigation were to understand transplacental transport of iron by secreted uteroferrin (UF) and haemophagous areas of water buffalo placenta and clarify the role(s) of blood extravasation at the placental‐maternal interface. Placentomes and interplacentomal region of 51 placentae at various stages of gestation were fixed, processed for light and transmission electron microscopy, histochemistry and immunohistochemistry. Haemophagous areas were present in placentomes collected between 4 and 10 months of pregnancy. Perl’s reaction for ferric iron was negative in placentomes, but positive in endometrial glands. Positive staining for UF indicated areas in which it was being taken up by phagocytosis and/or fluid phase pinocytosis in areolae of the interplacentomal mesenchyme, with little staining in endometrial stroma. Imunohistochemistry detected UF in trophectoderm of haemophagous regions of placentomes and in other parts of the foetal villous tree, but the strongest immunostaining was in the epithelial cells and lumen of uterine glands. Ultrastructural analyses indicated that erythrophagocytosis was occurring and that erythrocytes were present inside cells of the chorion that also contained endocytic vesicles and caveolae. Results of this study indicate that both the haemophagous areas of placentomes and the areolae at the interface between chorion and endometrial glands are important sites for iron transfer from mother to foetal‐placental tissues in buffalo throughout pregnancy. 相似文献
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A barred chondrule in the Ngawi meteorite contains a magnetite spherule embedded in it. The collision between these two objects fractured and partially remelted the chondrule, an indication that the impact velocity was 10(5) to 10(6) centimeters per second. This observation supports Cameron's and Whipple's recent predictions that grains achieved high velocities in the nebula and that the resulting impacts provide a suitable chondrule-forming mechanism. 相似文献
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DE Boerner RD Kurtz JA Craven GM Ross FW Jones WJ Davis 《Science (New York, N.Y.)》1999,283(5402):668-670
The subcrustal lithosphere underlying the southern Archean Churchill Province (ACP) in western Canada is at least one order of magnitude more electrically conductive than the lithosphere beneath adjacent Paleoproterozoic crust. The measured electrical properties of the lithosphere underlying most of the Paleoproterozoic crust can be explained by the conductivity of olivine. Mantle xenolith and geological mapping evidence indicate that the lithosphere beneath the southern ACP was substantially modified as a result of being trapped between two nearly synchronous Paleoproterozoic subduction zones. Tectonically induced metasomatism thus may have enhanced the subcrustal lithosphere conductivity of the southern ACP. 相似文献
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Rapid, sensitive bioluminescent reporter technology for naphthalene exposure and biodegradation 总被引:1,自引:0,他引:1
King JM Digrazia PM Applegate B Burlage R Sanseverino J Dunbar P Larimer F Sayler GS 《Science (New York, N.Y.)》1990,249(4970):778-781
A bioluminescent reporter plasmid for naphthalene catabolism (pUTK21) was developed by transposon (Tn4431) insertion of the lux gene cassette from Vibrio fischeri into a naphthalene catabolic plasmid in Pseudomonas fluorescens. The insertion site of the lux transposon was the nahG gene encoding for salicylate hydroxylase. Luciferasemediated light production from P. fluorescens strains harboring this plasmid was induced on exposure to naphthalene or the regulatory inducer metabolite, salicylate. In continuous culture, light induction was rapid (15 minutes) and was highly responsive to dynamic changes in naphthalene exposure. Strains harboring pUTK21 were responsive to aromatic hydrocarbon contamination in Manufactured Gas Plant soils and produced sufficient light to serve as biosensors of naphthalene exposure and reporters of naphthalene biodegradative activity. The robust and sensitive nature of the bioluminescent reporter technology suggests that new sensing methods can be developed for on-line process monitoring and control in complex environmental matrices. 相似文献
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An unusual carbon-rich material found in the Abee meteorite is highly enriched in volatile elements, by factors of 10(4) relative to the case for nonvolatile elements. Volatile-rich material of this type might form in the solar nebula toward the end of accretion, when small amounts of residual dust acquire all the uncondensed volatile elements. The mercury enrichment factor of 8500 could explain the paradox of the excess abundance of this element in meteorites. 相似文献
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When confronted with a novel familial disorder, veterinarians should consult McKusick's catalogue of inherited disorders in humans, called Mendelian Inheritance in Man (MIM), or its online version (OMIM), to see whether a similar disorder has been reported in humans. They should also consult the other readily available sources of comparative information on mice and domesticated species. Increasingly, such consultations can be conducted on the Internet via the World Wide Web. If it is thought that an animal disorder is homologous with a human disorder, publications describing the animal disorder should include the MIM number(s) for that disorder. Future research can then test the hypothesis of homology, until a consensus is reached. 相似文献