Time scales in atmospheric chemistry: coupled perturbations to N2O, NOy, and O3     

MJ Prather 《Science (New York, N.Y.)》1998,279(5355):1339-1341

Nitrous oxide (N2O) is one of the top three greenhouse gases whose emissions may be brought under control through the Framework Convention on Climate Change. Current understanding of its global budget, including the balance of natural and anthropogenic sources, is largely based on the atmospheric losses calculated with chemical models. A representative one-dimensional model used here describes the photochemical coupling between N2O and stratospheric ozone (O3), which can easily be decomposed into its natural modes. The primary, longest lived mode describes most of the atmospheric perturbation due to anthropogenic N2O sources, and this pattern may be observable. The photolytic link between O3 and N2O is identified as the mechanism causing this mode to decay 10 to 15 percent more rapidly than the N2O mean atmospheric lifetime, affecting the inference of anthropogenic sources.  相似文献   

In situ measurements of organics, meteoritic material, mercury, and other elements in aerosols at 5 to 19 kilometers   总被引：1，自引：0，他引：1  

DM Murphy  DS Thomson  MJ Mahoney 《Science (New York, N.Y.)》1998,282(5394):1664-1669

In situ measurements of the chemical composition of individual aerosol particles at altitudes between 5 and 19 kilometers reveal that upper tropospheric aerosols often contained more organic material than sulfate. Although stratospheric aerosols primarily consisted of sulfuric acid and water, many also contained meteoritic material. Just above the tropopause, small amounts of mercury were found in over half of the aerosol particles that were analyzed. Overall, there was tremendous variety in aerosol composition. One measure of this diversity is that at least 45 elements were detected in aerosol particles. These results have wide implications for the complexity of aerosol sources and chemistry. They also offer possibilities for understanding the transport of atmospheric aerosols.  相似文献   

Gold nanoelectrodes of varied size: transition to molecule-like charging   总被引：1，自引：0，他引：1  

S Chen  RS Ingram  MJ Hostetler  JJ Pietron  RW Murray  TG Schaaff  JT Khoury  MM Alvarez  RL Whetten 《Science (New York, N.Y.)》1998,280(5372):2098-2101

A transition from metal-like double-layer capacitive charging to redox-like charging was observed in electrochemical ensemble Coulomb staircase experiments on solutions of gold nanoparticles of varied core size. The monodisperse gold nanoparticles are stabilized by short-chain alkanethiolate monolayers and have 8 to 38 kilodaltons core mass (1.1 to 1.9 nanometers in diameter). Larger cores display Coulomb staircase responses consistent with double-layer charging of metal-electrolyte interfaces, whereas smaller core nanoparticles exhibit redox chemical character, including a large central gap. The change in behavior is consistent with new near-infrared spectroscopic data showing an emerging gap between the highest occupied and lowest unoccupied orbitals of 0.4 to 0.9 electron volt.  相似文献   

ULTRASONOGRAPHIC APPEARANCE AND CLINICAL FINDINGS IN 14 DOGS WITH GALLBLADDER MUCOCELE     

JG Besso  DEDV  RH Wrigley  BVSc  MS DVR  JM Gliatto  VMD CRL Webster  DVM 《Veterinary radiology & ultrasound》2000,41(3):261-271

Fourteen dogs with enlarged gallbladders and immobile stellate or finely striated bile patterns on ultrasound are described. Smaller breeds and older dogs were overrepresented, with 4/14 Cocker Spaniels. Most dogs presented for nonspecific clinical signs such as vomiting, anorexia and lethargy. Abdominal pain, icterus and hyperthermia were the most common findings on physical examination. All dogs except one had serum elevation of total bilirubin and/or alkaline phosphatase, alanine aminotransferase and gamma glutamyl transferase. All dogs were diagnosed with a gallbladder mucocele upon histologic and/or macroscopic evaluation. Ultrasonographically, mucoceles are characterized by the appearance of the stellate or finely striated bile patterns and differ from biliary sludge by the absence of gravity dependent bile movement. On ultrasound, gallbladder wall thickness and wall appearance were variable and nonspecific. The cystic or common bile duct were normal sized in 5 dogs although all 5 had evidence of biliary obstruction at surgery or necropsy. Loss of gallbladder wall integrity and/or gallbladder rupture were present in 50% of the dogs, all located in the fundus. Gallbladder wall discontinuity on ultrasound indicated rupture whereas neither bile patterns predicted the likelihood of gallbladder rupture. Pericholecystic hyperechoic fat or fluid were suggestive of but not diagnostic for a gallbladder rupture. Cholecystectomy appears to be an appropriate treatment for mucoceles, if not to treat a gallbladder rupture, at least in most dogs to prevent it since gallbladder wall necrosis was identified by histology in 9 of 10 dogs. Mucosal hyperplasia was present in all gallbladders examined histologically. Positive aerobic bacterial culture was obtained from bile in 6 of 9 dogs. Cholecystitis was diagnosed histologically in 5 dogs and 4 dogs had signs of gallbladder infection solely upon bacterial bile culture. Gallbladder infection was not present with all the mucoceles suggesting that biliary stasis and mucosal hyperplasia may be the primary factors involved in mucocele formation. Based on the results of our study, we suggest two alternate courses of action in the presence of a distended gallbladder with an immobile ultrasonographic stellate or finely striated bile pattern: a cholecystectomy when clinical or biochemical signs of hepatobiliary disease are present or a medical treatment (antibiotics and choleretics) and patient monitoring by follow-up ultrasound examinations when the patient does not have clinical or biochemical abnormalities. An aerobic bile culture should be obtained in all patients, by ultrasound-guided fine needle aspirate or at surgery.  相似文献   

Vermicomposting of sewage sludge: Effect of bulking materials on the growth and reproduction of the earthworm Eisenia andrei     

Jorge Domínguez  Clive A. Edwards  Michelle Webster 《Pedobiologia》2000,44(1)

The effect of different residual bulking agents (paper, cardboard, grass clippings, pine needles, sawdust and food wastes) in mixtures with sewage sludge (1:1 dry weight) on the growth and reproduction of Eisenia andrei, Bouché 1972 was studied in smallscale laboratory experiments with batches of sixty earthworms. The maximum weight achieved and the highest growth rate were attained in the mixture with food waste (755±18 mg and 18.6±0.6 mg day⁻¹ respectively) whereas the smallest size and the lowest growth rate was achieved in the mixture of sewage sludge with sawdust (572±18 mg and 11±0.7 mg day⁻¹ respectively). The earthworms showed much higher reproductive rates in the paper and cardboard mixtures (2.82±0.39 and 3.19±0.30 cocoons earthworm⁻¹ week⁻¹ respectively) compared to the control with sewage sludge alone (0.05±0.01 cocoons earthworm⁻¹ week⁻¹).  相似文献   

The Solar Acoustic Spectrum and Eigenmode Parameters     

F Hill  PB Stark  RT Stebbins  ER Anderson  HM Antia  TM Brown  TL Duvall  DA Haber  JW Harvey  DH Hathaway  R Howe  RP Hubbard  HP Jones  JR Kennedy  SG Korzennik  AG Kosovichev  JW Leibacher  KG Libbrecht  JA Pintar  EJ Rhodes  J Schou  MJ Thompson  S Tomczyk  CG Toner  R Toussaint  WE Williams 《Science (New York, N.Y.)》1996,272(5266):1292-1296

The Global Oscillation Network Group (GONG) project estimates the frequencies, amplitudes, and linewidths of more than 250,000 acoustic resonances of the sun from data sets lasting 36 days. The frequency resolution of a single data set is 0.321 microhertz. For frequencies averaged over the azimuthal order m, the median formal error is 0.044 microhertz, and the associated median fractional error is 1.6 x 10(-5). For a 3-year data set, the fractional error is expected to be 3 x 10(-6). The GONG m-averaged frequency measurements differ from other helioseismic data sets by 0.03 to 0.08 microhertz. The differences arise from a combination of systematic errors, random errors, and possible changes in solar structure.  相似文献   

Primary production of the biosphere: integrating terrestrial and oceanic components   总被引：32，自引：0，他引：32  

CB Field  MJ Behrenfeld  JT Randerson  P Falkowski 《Science (New York, N.Y.)》1998,281(5374):237-240

Integrating conceptually similar models of the growth of marine and terrestrial primary producers yielded an estimated global net primary production (NPP) of 104.9 petagrams of carbon per year, with roughly equal contributions from land and oceans. Approaches based on satellite indices of absorbed solar radiation indicate marked heterogeneity in NPP for both land and oceans, reflecting the influence of physical and ecological processes. The spatial and temporal distributions of ocean NPP are consistent with primary limitation by light, nutrients, and temperature. On land, water limitation imposes additional constraints. On land and ocean, progressive changes in NPP can result in altered carbon storage, although contrasts in mechanisms of carbon storage and rates of organic matter turnover result in a range of relations between carbon storage and changes in NPP.  相似文献   

EVALUATION OF ORAL IRON GALACTAN AS A METHOD OF IRON SUPPLEMENTATION FOR INTENSIVELY HOUSED SUCKING PIGLETS     

W. R. Webster  Corinne K.  Dimmock†  P. K. O'Rourke  † P. J. Lynch  § 《Australian veterinary journal》1978,54(7):345-348

SUMMARY Iron supplementation of piglets with oral galactan given as a single dose within 24 hours of birth was evaluated in a series of on farm trials. The growth rate of piglets receiving this treatment was faster than that of piglets receiving single injections of iron dextran or iron galactan at 3 days of age, or ferrous sulphate crystals orally at weekly intervals. Mean values for red cell parameters of oral iron galactan supplemented piglets at 2 to 4 weeks of age were lower than those of injected piglets but there was no clinical evidence of anaemia in any of the piglets.  相似文献   

Cold storage degradation of the herbicide metribuzin in field soil samples awaiting analysis     

G. R. Barrie Webster  Gerald J. Reimer 《Pest management science》1976,7(3):292-300

In conjunction with a study of herbicide degradation in the field, metribuzin (4-amino-6-tert-butyl-4,5-dihydro-3-methylthio-l,2,4-triazin-5-one) was shown to be degraded at-37±5°C in soil samples awaiting analysis. Products of this degradation process include the known derivatives DADK (6-tert-butyl-2,3,4,5-tetrahydro-l,2,4-triazine-3,5-dione) and DK (4-amino-6-tert-butyl-2,3,4,5-tetrahydro-l,2,4-triazine-3,5-dione) and these products themselves have been shown to be degraded further under the same storage conditions. Loss of the herbicide can be approximated using half order kinetics with respect to metribuzin; however, loss of both previously identified metabolites is most rapid when metabolite concentrations are highest. Assuming half order kinetics, samples of Almasippi very fine sandy loam containing metribuzin (0.5 mg/kg) can be expected to lose 50% of the herbicide in 282 days at - 37°, a period which is short enough to affect residue analysis results significantly should samples be stored for extended lengths of time prior to analysis. Implied in these results is the desirability of immediate analysis following collection of samples; otherwise rates of loss during storage must be determined to allow adjustment of results to compensate for residue losses in samples awaiting analysis.  相似文献   

Wildlife surveillance associated with an outbreak of lethal H5N2 avian influenza in domestic poultry   总被引：2，自引：0，他引：2  

V F Nettles  J M Wood  R G Webster 《Avian diseases》1985,29(3):733-741

Wildlife surveillance was conducted for influenza viruses in conjunction with the 1983-84 lethal H5N2 avian influenza epizootic in domestic poultry in Pennsylvania, New Jersey, Maryland, and Virginia. Virus-isolation attempts made on cloacal and tracheal swabs from 4,466 birds and small rodents within the quarantined areas and 1,511 waterfowl in nearby Maryland yielded only a single H5N2 isolate from a pen-raised chukar in Pennsylvania. Antibodies against hemagglutinin type 5 and/or neuraminidase type 2 were found in 33% of the aquatic birds tested; however, this finding could not be used to confirm previous H5N2 avian influenza virus activity because of the possibility of prior infections with multiple influenza subtypes. The low prevalence of lethal H5N2 avian influenza virus in wild birds and small rodents strongly indicated that these animals were not responsible for dissemination of the disease among poultry farms during the outbreak.  相似文献