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41.
42.
PC Sereno DB Dutheil M Iarochene HCE Larsson GH Lyon PM Magwene CA Sidor DJ Varricchio JA Wilson 《Science (New York, N.Y.)》1996,272(5264):986-991
Late Cretaceous (Cenomanian) fossils discovered in the Kem Kem region of Morocco include large predatory dinosaurs that inhabited Africa as it drifted into geographic isolation. One, represented by a skull approximately 1.6 meters in length, is an advanced allosauroid referable to the African genus Carcharodontosaurus. Another, represented by a partial skeleton with slender proportions, is a new basal coelurosaur closely resembling the Egyptian genus Bahariasaurus. Comparisons with Cretaceous theropods from other continents reveal a previously unrecognized global radiation of carcharodontosaurid predators. Substantial geographic differentiation of dinosaurian faunas in response to continental drift appears to have arisen abruptly at the beginning of the Late Cretaceous. 相似文献
43.
A tunnel in the large ribosomal subunit revealed by three-dimensional image reconstruction 总被引:14,自引:0,他引:14
A better understanding of the molecular mechanism of protein biosynthesis depends on the availability of a reliable model for the ribosome particle. The application of a diffraction technique, namely, three-dimensional image reconstruction from two-dimensional sheets of the large ribosomal subunits of Bacillus stearothermophilus at a resolution of 30 angstroms is described. The resulting three-dimensional model shows at least four projecting arms, arranged radially near the presumed interface with the 30S subunit. The projecting arms are positioned around a cleft, which turns into a tunnel with a length of 100 to 120 angstroms and a diameter of up to 25 angstroms. This tunnel spans the particle and may provide the path taken by the nascent polypeptide chain. 相似文献
44.
E. K. Leonard D. L. Pearl R. L. Finley N. Janecko A. S. Peregrine R. J. Reid‐Smith J. S. Weese 《Zoonoses and public health》2011,58(2):140-149
The purpose of this study was to determine pet‐related management factors that may be associated with the presence of Salmonella spp. in feces of pet dogs from volunteer households. From October 2005 until May 2006, 138 dogs from 84 households in Ontario were recruited to participate in a cross‐sectional study. Five consecutive daily fecal samples were collected from each dog and enrichment culture for Salmonella spp. was performed. A higher than expected number of the dogs (23.2%; 32/138) had at least one fecal sample positive for Salmonella, and 25% (21/84) of the households had at least one dog shedding Salmonella. Twelve serotypes of Salmonella enterica subsp. enterica were identified, with the predominant serotypes being Typhimurium (33.3%; 13/39), Kentucky (15.4%; 6/39), Brandenburg (15.4%; 6/39) and Heidelberg (12.8%; 5/39). Univariable logistic regression models were created with a random effect for household to account for clustering. Statistically significant risk factors for a dog testing positive included having contact with livestock, receiving a probiotic in the previous 30 days, feeding a commercial or homemade raw food diet, feeding raw meat and eggs, feeding a homemade cooked diet, and having more than one dog in the household. In two‐variable models that controlled for feeding raw food, the non‐dietary variables were no longer statistically significant. These results highlight the potential public health risk of including raw animal products in canine diets. 相似文献
45.
Van Boven M Laga M Leonard S Busson R Holser R Decuypere E Flo G Lievens S Cokelaere M 《Journal of agricultural and food chemistry》2003,51(5):1260-1264
Jojoba seed meal shows appetite-suppressing activity due to the presence of simmondsin. This pharmacological activity disappears with treatment of the meal with sodium hydroxide. To elucidate this mechanism of inactivation, the reaction of simmondsin in 1 N NaOH at 20 degrees C was monitored as a function of time. The end products of the reaction as well as intermediates were isolated and identified. The half-life of simmondsin was approximately 60 min with d-glucose and 2-hydroxy-3-methoxyphenylacetonitrile as reaction end products. The reaction mechanism could be elucidated by the isolation of isosimmondsin and a simmondsin lactone derivative. Those compounds were isolated and purified by a combination of column chromatography and HPLC and identified mainly by HRMS and NMR spectroscopy. 相似文献
46.
Robert L. Leonard Charles R. Goldman Gene E. Likens 《Water, air, and soil pollution》1981,15(2):153-167
Precipitation samples were collected at Davis and Lake Tahoe, California, in 1972–73 and 1977–78 and analyzed for pH and major cations and anions. Rain and snow in this region of northern California are derived primarily from winter cyclonic storms which move easterly from the Pacific Ocean over Davis and then Lake Tahoe. Precipitation at both sites was found to be more acid than water in equilibrium with atmospheric CO2. Acidity at Lake Tahoe apparently increased over the 5-yr period of the study. Sulfate was the dominant acid anion in 1972–73 (not measured in 1977–78). A major source of sulfate in precipitation was probably industry in the San Francisco Bay Area, upwind of the study sites. Automobile exhaust emissions throughout the region, which contains three major interstate highways and several large urban centers, contribute both sulfate and nitrate precursors to the atmosphere. As in the Eastern United States, these strong acid anions are influencing precipitation chemistry in northern California, including the Sierra Nevada mountains. 相似文献
47.
S Divakaran Leonard G Obaldo Ian P Forster 《Journal of agricultural and food chemistry》2002,50(3):464-467
Chromic oxide is used as an inert marker to measure apparent digestibility of feeds in insects, terrestrial, and aquatic animals. Quantitative determination of chromic oxide content in the sample requires the oxidation of water insoluble trivalent chromic oxide to its water-soluble hexavalent form. The two commonly used oxidizing agents are 70% perchloric acid or a mixture of sodium molybdate, sulfuric, and perchloric acid. Chromic oxide content of the oxidized solution is then measured against known standards either directly by spectrophotometry in the visible range at 350, 370, or 440 nm or after forming a colored complex with diphenylcarbazide (DPC) by colorimetry at 540 nm. This study compared the two methods of oxidation followed by spectrophotometry at the three wavelengths and by DPC colorimetry. DPC colorimetry gave precise results than the direct measurement of dichromate ion, irrespective of the method of oxidation used. Ash from samples oxidized by perchloric acid and quantified by DPC colorimetry gave a better measure of actual chromic oxide content as compared to the other methods tested. 相似文献
48.
Summary Isozyme analyses of genetic diversity in Vigna unguiculata were performed to determine genetic relationships and level of genetic diversity between wild and cultivated cowpea. Thirty-four cultivated accessions of V. unguiculata, 56 wild accessions of V. unguiculata, and six accessions representing five related wild Vigna species were analyzed. Ten enzyme systems were polymorphic within Vigna unguiculata: AAT, ACO, G6PDH, DIAP, LAP, MUE, ME MDH, PRX, and SOD. Fourteen of 24 putative loci (58%) were polymorphic within wild V. unguiculata, but only one locus (4%) was polymorphic within cultivated cowpea; when five related Vigna species were examined, 21 of the 24 bands of activity showed polymorphisms (88%) adding 33 alleles to the 48 identified within V. unguiculata. In one F2 population of 68 plants (UCDVg 36 × UCDVg 21) a loose linkage was indicated between Diap-2 and G6pd-1 (2 = 15.39; p = 0.004) with an estimated distance of 36.0 cM ± 5.02 (recombination (r) = 0.31). Also in another F2 population of 38 plants (CB 88 × UCDVg 21) a loose linkage was indicated between Lap-1 and Prx (\gC2 = 9.62; p = 0.047) with an estimated distance of 39.8 cM ± 7.0 (r = 0.33). Total genetic diversity (HT) was 0.085 over all of the accessions including the one classified as V. nervosa. Within accession diversity (Hs) approached zero and between accession diversity (Dsi) was responsible for all of the genetic diversity present. Therefore the coefficient of gene differentiation (GST = DSTIIT) approached 1. Absolute gene differentiation (Dm) was 0.087. Two of the nine segregations in this study were skewed. In general, results of this study concurred with the taxonomic classification within V. unguiculata and provided a strong indication that a severe genetic bottleneck occurred during the domestication process of cowpea.Abbreviations AAT
aspartate amino-transferase
- ACO
aconitase
- ALD
aldolase
- AUS
Australia
- BDI
Burundi
- BWA
Botswana
- CHN
China
- CMR
Cameroon
- DIAP
diaphorase
- DZA
Algeria
- ETH
Ethiopia
- G6PDH
glucose-6-phosphate dehydrogenase
- GDH
glutamate dehydrogenase
- GHA
Ghana
- GUY
Guyana
- IDH
isocitrate dehydrogenase
- IND
India
- KEN
Kenya
- LAO
Laos
- LAP
leucine aminopeptidase
- MDH
malate dehydrogenase
- ME
malic enzyme
- MEX
Mexico
- MOZ
Mozambique
- MUE
methylumelliferyl-esterase
- MWI
Malawi
- MYS
Malaysia
- NER
Niger
- NGA
Nigeria
- PRX
peroxidase
- RBSC
ribulose-bisphosphate carboxylase
- SEN
Senegal
- SLE
Sierra Leone
- SOD
superoxide dismutase
- TGO
Togo
- TZA
Tanzania
- USA
United States of America
- XDH
xanthine dehydrogenase
- ZAF
South Africa
- ZAR
Zaire
- ZIM
Zimbabwe
- ZMB
Zambia 相似文献
49.
50.
Ashir Kumar Mark C. Leonard Ronald P. Cleveland 《Comparative immunology, microbiology and infectious diseases》1989,12(4):91-94
Immunosuppressive agents were given to baby guinea pigs to develop a leukocytopenic baby guinea pig model. Azathioprine in different doses, and cyclophosamide and methylprednisolone combinations did not result in predictable leukocytopenia without significant mortality. A combination of azathioprine 20mg and cyclophosphamide 20mg administered once daily for 5 days to 42 baby guinea pigs resulted in a mean white blood cell count of 2531/mm3 ±1198 (a reduction of 3931 ± 1413 from pretreatment values). The mean counts for polymorphonuclear leukocytes and lymphocytes on day 6 were 398/mm3 and 2035/mm3, respectively. Only 7% mortality was seen in these animals. This model can be utilized to study a variety of bacterial and viral infections in “immunocompromised hosts”. 相似文献