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排序方式: 共有152条查询结果,搜索用时 15 毫秒
91.
PV Hobbs JS Reid RA Kotchenruther RJ Ferek R Weiss 《Science (New York, N.Y.)》1997,275(5307):1776-1778
Airborne measurements in smoke from biomass burning in Brazil have yielded optical parameters that permit an improved assessment of the effects of smoke on Earth's radiation balance. The global-mean direct radiative forcing due to smoke from biomass burning worldwide is estimated to be no more than about -0.3 watt per square meter (cooling), compared with +2.45 watts per square meter (warming) due to anthropogenic greenhouse gases. On regional scales, direct radiative forcing due to smoke can be large and might indirectly affect global climate. 相似文献
92.
PT HOOPER RA LUNT AR GOULD AD HYATT GM RUSSELL JA KATTENBELT SD BLACKSELL LA REDDACLIFF PD KIRKLAND RJ DAVIS PJK DURHAM AL BISHOP J WADDINGTON 《Australian veterinary journal》1999,77(8):529-536
OBJECTIVE: To determine the cause of an epidemic of blindness in kangaroos. DESIGN AND PROCEDURES: Laboratory examinations were made of eyes and brains of a large number of kangaroos using serological, virological, histopathological, electron microscopical, immunohistochemical methods, and PCR with cDNA sequencing. In addition, potential insect viral vectors identified during the disease outbreak were examined for specific viral genomic sequences. SAMPLE POPULATION: For histopathological analysis, 55 apparently blind and 18 apparently normal wild kangaroos and wallabies were obtained from New South Wales, Victoria, South Australia, and Western Australia. A total of 437 wild kangaroos and wallabies (including 23 animals with apparent blindness) were examined serologically. RESULTS: Orbiviruses of the Wallal and Warrego serogroups were isolated from kangaroos affected with blindness in a major epidemic in south-eastern Australia in 1994 and 1995 and extending to Western Australia in 1995/96. Histopathological examinations showed severe degeneration and inflammation in the eyes, and mild inflammation in the brains. In affected retinas, Wallal virus antigen was detected by immunohistochemical analysis and orbiviruses were seen in electron microscopy. There was serological variation in the newly isolated Wallal virus from archival Wallal virus that had been isolated in northern Australia. There were also variations of up to 20% in genotype sequence from the reference archival virus. Polymerase chain reactions showed that Wallal virus was present during the epidemic in three species of midges, Culicoides austropalpalis, C dycei and C marksi. Wallal virus nucleic acid was also detected by PCR in a paraffin-embedded retina taken from a blind kangaroo in 1975. CONCLUSION: Wallal virus and perhaps also Warrego virus are the cause of the outbreak of blindness in kangaroos. Other viruses may also be involved, but the evidence in this paper indicates a variant of Wallal virus, an orbivirus transmitted by midges, has the strongest aetiological association, and immunohistochemical analysis implicates it as the most damaging factor in the affected eyes. 相似文献
93.
CM Volk JW Elkins DW Fahey RJ Salawitch GS Dutton JM Gilligan MH Proffitt M Loewenstein JR Podolske K Minschwaner JJ Margitan KR Chan 《Science (New York, N.Y.)》1996,272(5269):1763-1768
Airborne in situ observations of molecules with a wide range of lifetimes (methane, nitrous oxide, reactive nitrogen, ozone, chlorinated halocarbons, and halon-1211), used in a tropical tracer model, show that mid-latitude air is entrained into the tropical lower stratosphere within about 13.5 months; transport is faster in the reverse direction. Because exchange with the tropics is slower than global photochemical models generally assume, ozone at mid-latitudes appears to be more sensitive to elevated levels of industrial chlorine than is currently predicted. Nevertheless, about 45 percent of air in the tropical ascent region at 21 kilometers is of mid-latitude origin, implying that emissions from supersonic aircraft could reach the middle stratosphere. 相似文献
94.
High-pressure diamond-cell experiments indicate that the iron-magnesium partitioning between (Fe,Mg)SiO3-perovskite and magnesiowustite in Earth's lower mantle depends on the pressure, temperature, bulk iron/magnesium ratio, and ferric iron content. The perovskite stability field expands with increasing pressure and temperature. The ferric iron component preferentially dissolves in perovskite and raises the apparent total iron content but had little effect on the partitioning of the ferrous iron. The ferrous iron depletes in perovskite at the top of the lower mantle and gradually increases at greater depth. These changes in iron-magnesium composition should affect geochemical and geophysical properties of the deep interior. 相似文献
95.
MG Kivelson KK Khurana RJ Walker CT Russell JA Linker DJ Southwood C Polanskey 《Science (New York, N.Y.)》1996,273(5273):337-340
During the inbound pass of the Galileo spacecraft, the magnetometer acquired 1 minute averaged measurements of the magnetic field along the trajectory as the spacecraft flew by Io. A field decrease, of nearly 40 percent of the background jovian field at closest approach to Io, was recorded. Plasma sources alone appear incapable of generating perturbations as large as those observed and an induced source for the observed moment implies an amount of free iron in the mantle much greater than expected. On the other hand, an intrinsic magnetic field of amplitude consistent with dynamo action at Io would explain the observations. It seems plausible that Io, like Earth and Mercury, is a magnetized solid planet. 相似文献
96.
Francesco Fazio Giuseppe PiccioneStefania Casella PhD student PhD Anna AssenzaVanessa Messina PhD student PhD Giovanni Caola Full Professor 《Journal of Equine Veterinary Science》2010
The effect of acute exercise on serum homocysteine (sHCy) concentration was examined in 10 horses; five Sella Italiana and five Thoroughbreds. All horses underwent standard training before the study (show jumping for Sella Italiana horses and gallop racing for Thoroughbreds). For the study, blood samples were taken at rest, immediately after exercise, and during a recovery period (30 and 60 minutes after exercise) by external jugular venipuncture. sHCy values were determined by high-performance liquid chromatography. Heart rate and blood lactate were monitored to quantify the workloads. In show jumpers, there was a significant effect of sampling time on sHCy (P < .01), which increased significantly after exercise as compared with at rest. In Thoroughbreds, no statistically significant differences were observed in sHCy over time (F(3,12) = 0.89, P = .05). The baseline values of sHcy were higher in Thoroughbreds than in show jumpers (P < .0002). We infer that physical activity causes biochemical changes that can influence the metabolic pathway of homocysteine in show jumpers, whereas the absence of a significant effect of exercise in Thoroughbreds may reflect an adaptive response of the enzymatic antioxidant defense system. 相似文献
97.
AD Brandon RJ Walker JW Morgan MD Norman HM Prichard 《Science (New York, N.Y.)》1998,280(5369):1570-1573
Osmium isotopic analyses of picritic lavas from Hawaii show enrichments in the osmium-186/osmium-188 ratio (186Os/188Os) of 0. 008 to 0.018%, relative to a chondritic upper mantle, that are positively correlated with enrichments in 187Os/188Os of 5.4 to 9.0%. The most viable mechanism to produce these coupled 186Os and 187Os enrichments is by addition of 0.5 to 1 weight percent of outer core metal to a portion of the D" layer and subsequent upwelling of the mixture. These data suggest that some plumes originate at the core-mantle boundary and that Os isotopes may be used to distinguish plumes derived from shallow versus deep mantle sources. 相似文献
98.
RJ HYLAND 《Australian veterinary journal》2002,80(1):54-56
An adult male Macquarie turtle was presented for examination after swallowing a fish hook. Radiographs taken to determine the position of this foreign body within the gastrointestinal tract revealed the fish hook lodged in the turtle's oesophagus. Surgical removal of the fish hook involved an approach through the soft tissues of the lateral neck. The turtle recovered well and was returned to the wild. 相似文献
99.
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