Hydrogen radicals, nitrogen radicals, and the production of O3 in the upper troposphere     

PO Wennberg  TF Hanisco  L Jaegle  DJ Jacob  EJ Hintsa  EJ Lanzendorf  JG Anderson  R Gao  ER Keim  SG Donnelly  LAD Negro  DW Fahey  SA McKeen  RJ Salawitch  CR Webster  RD May  RL Herman  MH Proffitt  JJ Margitan  EL Atlas  SM Schauffler  F Flocke  CT McElroy  TP Bui 《Science (New York, N.Y.)》1998,279(5347):49-53

The concentrations of the hydrogen radicals OH and HO2 in the middle and upper troposphere were measured simultaneously with those of NO, O3, CO, H2O, CH4, non-methane hydrocarbons, and with the ultraviolet and visible radiation field. The data allow a direct examination of the processes that produce O3 in this region of the atmosphere. Comparison of the measured concentrations of OH and HO2 with calculations based on their production from water vapor, ozone, and methane demonstrate that these sources are insufficient to explain the observed radical concentrations in the upper troposphere. The photolysis of carbonyl and peroxide compounds transported to this region from the lower troposphere may provide the source of HOx required to sustain the measured abundances of these radical species. The mechanism by which NO affects the production of O3 is also illustrated by the measurements. In the upper tropospheric air masses sampled, the production rate for ozone (determined from the measured concentrations of HO2 and NO) is calculated to be about 1 part per billion by volume each day. This production rate is faster than previously thought and implies that anthropogenic activities that add NO to the upper troposphere, such as biomass burning and aviation, will lead to production of more O3 than expected.  相似文献   

Abrupt climate events 500,000 to 340,000 years ago: evidence from subpolar north atlantic sediments     

DW Oppo  JF McManus  JL Cullen 《Science (New York, N.Y.)》1998,279(5355):1335-1338

Subpolar North Atlantic proxy records document millennial-scale climate variations 500,000 to 340,000 years ago. The cycles have an approximately constant pacing that is similar to that documented for the last glacial cycle. These findings suggest that such climate variations are inherent to the late Pleistocene, regardless of glacial state. Sea surface temperature during the warm peak of Marine Isotope Stage 11 (MIS 11) varied by 0.5 degrees to 1 degrees C, less than the 4 degrees to 4.5 degrees C estimated during times of ice growth and the 3 degrees C estimated for glacial maxima. Coherent deep ocean circulation changes were associated with glacial oscillations in sea surface temperature.  相似文献   

Shipboard geophysical indications of asymmetry and melt production beneath the east pacific rise near the MELT experiment     

DS Scheirer  DW Forsyth  MH Cormier  KC Macdonald 《Science (New York, N.Y.)》1998,280(5367):1221-1224

Near the Mantle Electromagnetic and Tomography (MELT) Experiment, seamounts form and off-axis lava flows occur in a zone that extends farther to the west of the East Pacific Rise than to the east, indicating a broad, asymmetric region of melt production. More seamounts, slower subsidence, and less dense mantle on the western flank suggest transport of hotter mantle toward the axis from the west. Variations in axial ridge shape, axial magma chamber continuity, off-axis volcanism, and apparent mantle density indicate that upwelling is probably faster and more melt is produced beneath 17 degrees15'S than beneath 15 degrees55'S. Recent volcanism occurs above mantle with the lowest seismic velocities.  相似文献   

Magnetic Field and Plasma Observations at Mars: Initial Results of the Mars Global Surveyor Mission   总被引：2，自引：0，他引：2  

MH Acu?a  JEP Connerney  P Wasilewski  RP Lin  KA Anderson  CW Carlson  J McFadden  DW Curtis  D Mitchell  H Reme  C Mazelle  JA Sauvaud  C d'Uston  A Cros  JL Medale  SJ Bauer  P Cloutier  M Mayhew  D Winterhalter  NF Ness 《Science (New York, N.Y.)》1998,279(5357):1676-1680

The magnetometer and electron reflectometer investigation (MAG/ER) on the Mars Global Surveyor spacecraft has obtained magnetic field and plasma observations throughout the near-Mars environment, from beyond the influence of Mars to just above the surface (at an altitude of approximately 100 kilometers). The solar wind interaction with Mars is in many ways similar to that at Venus and at an active comet, that is, primarily an ionospheric-atmospheric interaction. No significant planetary magnetic field of global scale has been detected to date (<2 x 10(21) Gauss-cubic centimeter), but here the discovery of multiple magnetic anomalies of small spatial scale in the crust of Mars is reported.  相似文献   

Immunisation against ovine caseous lymphadenitis: efficacy of monocomponent Corynebacterium pseudotuberculosis toxoid vaccine and combined clostridial-corynebacterial vaccines   总被引：3，自引：0，他引：3  

DG EGGLETON  CV DOIDGE  HD MIDDLETON  DW MINTY 《Australian veterinary journal》1991,68(10):320-321

Sheep were immunised with Corynebacterium pseudotuberculosis toxoid formulated as a monocomponent vaccine with aluminium adjuvant or in combination with 5 clostridial antigens, and also in the combined form with sodium selenate. Immunised and control sheep were experimentally infected 16 days after vaccination and slaughtered and inspected after a further 3 months to determine their resistance to infection. All 3 vaccines afforded an equal and high level of protection; 91% of vaccinated sheep exhibiting no lesions of caseous lymphadenitis compared with 51.5% affected sheep in the control group. Average lesion counts were 1.2 per affected vaccinated sheep and 4.5 per affected control sheep. Antitoxin responses to the clostridial toxoids incorporated in the combined vaccines were not affected by inclusion of the C pseudotuberculosis toxoid or the sodium selenate.  相似文献   

Immunisation against ovine caseous lymphadenitis: comparison of Corynebacterium pseudotuberculosis vaccines with and without bacterial cells   总被引：2，自引：0，他引：2  

DG EGGLETON  HD MIDDLETON  CV DOIDGE  DW MINTY 《Australian veterinary journal》1991,68(10):317-319

Sheep were immunised with Corynebacterium pseudotuberculosis vaccines prepared from cell-free toxoid or from toxoid with formalin-killed cells of C pseudotuberculosis added. Resistance of sheep to infection was tested 6 months after immunisation by inoculation with caseous lymphadenitis pus. The outcome was assessed 3 months later by slaughter and inspection of the sheep for lesions of caseous lymphadenitis. immunised sheep were adequately protected against infection as shown by a significant reduction in the number of sheep exhibiting lesions compared with control sheep, and by fewer abscesses in affected vaccinated sheep than in affected control sheep. The protective potency of the vaccines was not improved by the inclusion of cells of C pseudotuberculosis.  相似文献   

The hypocholesterolemic and antioxidative effect of dietary diosgenin and chromium chloride supplementation on high-cholesterol fed Japanese quails     

Al-Matubsi HY  Nasrat NA  Oriquat GA  Abu-Samak M  Al-Mzain KA  Salim M 《Pakistan journal of biological sciences: PJBS》2011,14(7):425-432

The current study investigated the effect of natural diosgenin extracted from fenugreek seeds, in comparison with the pure standard diosgenin, plus chromium chloride (CrCl3) supplementation on high-cholesterol fed Japanese quails. Quails were randomly divided into four groups. Group one (n = 25) fed experimental diet only (control; contained basal diet supplemented with 1% cholesterol), group 2 (n = 20) fed experimental diet supplemented with CrCl3 only (400 microg kg(-1) of body weight), groups 3 and 4 (n = 30 per group) were fed experimental diet supplemented with either 0.5% (w/w) of extracted diosgenin plus CrCl3 or pure standard diosgenin (0.5%) plus CrCl3 respectively, for 12 days. Blood samples were collected at days 0 and 12 for measuring levels of lipid profile. The work was carried out at Applied Science University and Amman University, Amman, Jordan during the period from October 2009 through October 2010. The mean levels of total cholesterol (TC) in control quails at d12 was significantly (p < 0.01) increased compare to those at d0. Supplementation of diet with CrCl3 alone or CrCl3 with diosgenin either extracted or pure standard for 12 days showed a significant (p < 0.01) decrease in TC and low density lipoprotein cholesterol (LDL-C) levels as compared to those in the control quails. While, high density lipoprotein cholesterol (HDL-C) increased significantly (p < 0.01) in quails supplemented with diosgenin and CrCl3. At d12, the mean Superoxide Dismutase (SOD) activities in erythrocytes of quails in all supplemented groups was significantly (p < 0.01) increased as compared to those in control group and was more pronounced in erythrocytes of quails supplemented with pure standard diosgenin plus CrCl3. These results indicated that the combined diosgenin and CrCl3 supplementation to high-cholesterol fed quails might induce a protective effect by both regulating lipid and antioxidative damage.  相似文献   

A strategy for designing multi-taxa specific reference gene systems. example of application--ppi phosphofructokinase (ppi-PPF) used for the detection and quantification of three taxa: maize (Zea mays), cotton (Gossypium hirsutum) and rice (Oryza sativa)   总被引：2，自引：0，他引：2  

Chaouachi M  Giancola S  Romaniuk M  Laval V  Bertheau Y  Brunel D 《Journal of agricultural and food chemistry》2007,55(20):8003-8010

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The potential for respiratory droplet-transmissible A/H5N1 influenza virus to evolve in a mammalian host     

Russell CA  Fonville JM  Brown AE  Burke DF  Smith DL  James SL  Herfst S  van Boheemen S  Linster M  Schrauwen EJ  Katzelnick L  Mosterín A  Kuiken T  Maher E  Neumann G  Osterhaus AD  Kawaoka Y  Fouchier RA  Smith DJ 《Science (New York, N.Y.)》2012,336(6088):1541-1547

Avian A/H5N1 influenza viruses pose a pandemic threat. As few as five amino acid substitutions, or four with reassortment, might be sufficient for mammal-to-mammal transmission through respiratory droplets. From surveillance data, we found that two of these substitutions are common in A/H5N1 viruses, and thus, some viruses might require only three additional substitutions to become transmissible via respiratory droplets between mammals. We used a mathematical model of within-host virus evolution to study factors that could increase and decrease the probability of the remaining substitutions evolving after the virus has infected a mammalian host. These factors, combined with the presence of some of these substitutions in circulating strains, make a virus evolving in nature a potentially serious threat. These results highlight critical areas in which more data are needed for assessing, and potentially averting, this threat.  相似文献   

Mercury Cycling in Lake Gordon and Lake Pedder,Tasmania (Australia). II: Catchment Processes     

Bowles  Karl C.  Apte  Simon C.  Maher  William A.  Blühdorn  David R. 《Water, air, and soil pollution》2003,147(1-4):25-38

The sources and concentrations of total mercury (total Hg) and methylmercury (MeHg) in the upper catchment of the Lake Gordon/Lake Pedder system in Tasmania, Australia were investigated. The catchment area, which contains over 50% wetlands, is located in a temperate region with no obvious point sources of mercury. Surface waters in the region had concentrations of total Hg ranging from 1.2 to 14.4 ng L^-1 and MeHg from < 0.04 to 1.4 ng L^-1. MeHg concentrations were seasonally dependent, with the highest concentrations occurring in summer. Sediments/soils in the catchment had concentrations of total Hg ranging from 4.0 to 194 ng g^-1 and MeHg from <0.02 to 20.1 ng g^-1. The low concentrations of total Hg confirmed that this region is pristine as regards mercury and has no geological enrichment of total Hg. The highest total Hg and MeHg concentrations in both sediment/soils and waters were found in bogs whereas the lowest concentrations typically occurred on the wetlandplains. MeHg concentrations, in bog and swamp sediments were correlatedwith the organic matter content (r = 0.942, P < 0.001). Acid volatile sulfide (AVS) measurements indicate that in most sediments AVS was greater than total Hg. Given the high reactivity of inorganic mercury and sulfide, this suggests that most of the particulate mercury in sediments is present as mercuric sulfide. The yield of MeHg from the catchment was estimated to be 3.2 mg ha^-1 yr^-1 and is higher than published rates measured in non-contaminated temperate catchments in the northern hemisphere. The higher yield was attributed to the generally warmer climatic conditions that favour net methylation and the relatively high rainfall (2–3 m yr^-1) of the region, which supplies reactive inorganic mercury to the active zones ofmercury methylation and also flushes MeHg from the catchment.  相似文献