A 6-year-old Rottweiler with weight loss     

P. CLARK  CL SWENSON  CM DRENEN 《Australian veterinary journal》1997,75(10):709-709

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Selection parameters for resistance to Fusarium oxysporum f. sp. cubense race 1 and race 4 on diploid banana (Musa acuminata Colla)     

R. Morpurgo  S. V. Lopato  R. Afza  F. J. Novak 《Euphytica》1994,75(1-2):121-129

Summary Shoot tip cultures from banana clones susceptible and resistant to Fusarium oxysporum f. sp. cubense (FOC) race 1 and race 4 were grown in vitro in the presence of different concentrations of fusaric acid and fungal crude filtrates or inoculated with a conidial suspension of FOC to assess correlation between in vivo and in vitro behaviour. Explants were susceptible to both filtrate and fusaric acid irrespective to their known field resistance/susceptibility response. No clear linkage between in vivo and in vitro behaviour was observed and our results suggest that the use of crude filtrate or non-host specific toxin (fusaric acid) in a screening programme for selecting a novel resistant genotype of Musa to FOC is not feasible. When peroxidase activity was used as a parameter to discriminate between sesceptibility and tolerance, results were in good agreement with field response of host plant to pathogens. Early enzymatic activity increased in the incompatible host-pathogen interaction but not in the compatible interaction.Abbreviations IBA Indolebutyric acid - 2iP 6-dimethylallylamino-purine - VCG Vegetative Compatibility Group - FOC Fusarium oxysporum f. sp. cubense - IEF isoelectrofocusing  相似文献   

Nuclear DNA content and in vitro induced somatic polyploidization cassava (Manihot esculenta Crantz) breeding     

F. Awoleye  M. van Duren  J. Dolezel  F. J. Novak 《Euphytica》1994,76(3):195-202

Summary The diploid (2C) amount of DNA in cassava (Manihot esculenta Crantz) is 1.67 picograms (pg) per cell nucleus. This value corresponds to 772 mega-base pairs in the haploid genome. The size of the nuclear genome in cassava is very small in comparison with other Angiosperms. Flow cytometry techniques were used to screen ploidy levels in a large population of in vitro plantlets treated with colchicine and oryzalin (3,5-dinitro-N⁴,N-dipropylsulphate). Culture of axillary node cuttings for 48 hours in liquid medium supplemented with 2.5 to 5.0 mM colchicine in combination with 2% dimethyl sulfoxide (DMSO) resulted in a high frequency (23 to 42%) of non-chimeric tetraploids in the V₃ generation. Although mixoploidy may persist in as many as four cycles of vegetative propagation of node cuttings, solid (non-chimeric) tetraploids can be identified by flow cytometry among in vitro plantlets and then rapidly propagated for field testing. A somatic polyploidization system is proposed for implementation in cassava breeding programmes.Dedicated to the memory of the late Dr. Novak. Correspondence to M. van Duren  相似文献   

Outbreak of West Nile virus in North America     

Spielman A  Andreadis TG  Apperson CS  Cornel AJ  Day JF  Edman JD  Fish D  Harrington LC  Kiszewski AE  Lampman R  Lanzaro GC  Matuschka FR  Munstermann LE  Nasci RS  Norris DE  Novak RJ  Pollack RJ  Reisen WK  Reiter P  Savage HM  Tabachnick WJ  Wesson DM 《Science (New York, N.Y.)》2004,306(5701):1473-5; author reply 1473-5

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Thermal Structure and Energy Influx to the Day-and Nightside Venus Ionosphere     

Knudsen WC  Spenner K  Whitten RC  Spreiter JR  Miller KL  Novak V 《Science (New York, N.Y.)》1979,205(4401):105-107

Pioneer Venus in situ measurements made with the retarding potential analyzer reveal strong variations in the nightside ionospheric plasma density from location to location in some orbits and from orbit to orbit. The ionopause is evident at night as a relatively abrupt decrease in the thermal plasma concentration from a few hundred to ten or fewer ions per cubic centimeter. The nightside ion and electron temperatures above an altitude of 250 kilometers, within the ionosphere and away from the terminator, are comparable in magnitude and have a value at the ionopause of approximately 8000 K. The electron temperature increases from a few tens of thousands of degrees Kelvin just outside the ionopause to several hundreds of thoussands of degrees Kelvin further into the shocked solar wind. The coldest ion temperatures measured at an altitude of about 145 kilometers are 140 to 150 K and are still evidently above the neutral temperature. Preliminary day-and nightside model ion and electron temperature height profiles are compared with measured profiles. To raise the model ion temperature to the measured ion temperature on both day-and nightsides, it was necessary to include an ion energy source of the order of 4 x 10(-3) erg per square centimeter per second, presumably Joule heating. The heat flux through the electron gas from the solar wind into the neutral atmosphere averaged over day and night may be as large as 0.05 erg per square centimeter per second. Integrated over the planet surface, this heat flux represents one-tenth of the solar wind energy expended in drag on the sunward ionopause hemisphere.  相似文献   

Excited singlet absorption in 1,2-benzanthracene by the use of nanosecond laser photolysis and spectroscopy     

J R Novak  M W Windsor 《Science (New York, N.Y.)》1968,161(848):1342-1343

Using the technique of laser photolysis and spectroscopy, we have observed excited singlet state absorption bands in 1,2-benzanthracene at 560 and 520 nanometers. The bands decay in less than 50 nanoseconds and are replaced by the known absorption spectrum of the lowest triplet state.  相似文献   

Achievement in mathematics     

Novak JD  Ridley DR 《Science (New York, N.Y.)》1984,223(4642):1248

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Searching the world wide Web   总被引：8，自引：0，他引：8  

S Lawrence  CL Giles 《Science (New York, N.Y.)》1998,280(5360):98-100

The coverage and recency of the major World Wide Web search engines was analyzed, yielding some surprising results. The coverage of any one engine is significantly limited: No single engine indexes more than about one-third of the "indexable Web," the coverage of the six engines investigated varies by an order of magnitude, and combining the results of the six engines yields about 3.5 times as many documents on average as compared with the results from only one engine. Analysis of the overlap between pairs of engines gives an estimated lower bound on the size of the indexable Web of 320 million pages.  相似文献   

Natural emissions of oxidant precursors     

Joan H. Novak  Thomas E. Pierce 《Water, air, and soil pollution》1993,67(1-2):57-77

This paper provides an overview of the sources, the estimation methodology, and the relative amounts of natural hydrocarbon and NO_x emissions. The most recent estimate of natural nonmethane hydrocarbon (NMHC) emissions for the United States is 28 Tg yr^?1. This compares with 20 Tg yr^?1 for anthropogenic NMHC sources. The southeastern and southcentral portions of the United States account for approximately 43% of the annual U.S. natural NMHC estimate. These emissions exhibit strong diurnal and seasonal dependencies related to temperature, solar radiation, and active biomass. Forests are the primary vegetative source of hydrocarbons. The major sources of natural NO_X emissions in North America are biomass burning, lightning, and microbial activity in soil. We present a comparison of hourly gridded NO_X emissions from lightning, soil, and man-made sources for the northeastern United States. We also provide results from preliminary investigations of the sensitivity of O₃ predictions from the U.S. Environmental Protection Agency's Regional Oxidant Model to natural NMHC and nitric oxide emissions.  相似文献   

Increased tolerance to annual ryegrass toxicity in sheep given a supplement of cobalt     

SC DAVIES  CL WHITE†  IH WILLIAMS 《Australian veterinary journal》1995,72(6):221-224

SUMMARY To determine whether oral cobalt supplements could modify the clinical onset of annual ryegrass toxicity, groups (n = 5) of sheep were dosed orally with 0, 4 or 16 mg cobalt/day. After 3 weeks on this treatment, toxic ryegrass seed was added to their feed to provide 0, 0.15 and 0.30 mg corynetoxins/kg body weight, daily. Sheep receiving cobalt ingested 30% more toxin than did unsupplemented sheep before clinical signs developed (P = 0.03). There was no significant difference between groups receiving 4 and 16 mg cobalt. The results showed that cobalt delayed, but did not prevent, the onset of clinical signs of annual ryegrass toxicity.  相似文献