Further studies of the temperature dependence of the rate coefficients for the reactions of OH with a series of ethers under simulated atmospheric conditions     

Marco Semadeni  David W. Stocker  J. Alistair Kerr 《Journal of Atmospheric Chemistry》1993,16(1):79-93

The following temperature-dependent rate coefficients (k/cm³ molecule^–1 s^–1) of the reactions of hydroxyl radicals with aliphatic ethers have been determined over the temperature range 247–373 K by a competitive flow technique: diethyl ether,k _OH=5.2×10^–12 exp[(262±150)/T]; methyln-butyl ether,k _OH=5.4×10^–12 exp[(309±150)/T]; ethyln-butyl ether,k _OH=7.3×10^–12 exp[(335±150)/T]; di-n-butyl ether,k _OH=5.5×10^–12 exp[(502±150)/T] and di-n-pentyl ether,k _OH=8.5×10^–12 exp[(417±150)/T]. The data have been measured relative to the rate coefficientk(OH + 2,3-dimethylbutane)=6.2×10^–12 cm³ molecule^–1 s^–1 independent of temperature.Previous discrepancies in the room-temperature rate coefficients for the OH reactions with ethyln-butyl ether and di-n-butyl ether, obtained in the flow and static experiments of Bennett and Kerr (J. Atmos. Chem. 8, 87–94, 1989;10, 29–38, 1990) compared with those of Wallingtonet al. (Int. J. Chem. Kinet. 20, 541–547, 1988;21, 993–1001, 1989) and of Nelsonet al. (Int. J. Chem. Kinet. 22, 1111–1126, 1990) have been resolved. The results are considered in relation to the available literature data and evaluated rate expressions are deduced where possible. The data are also discussed in terms of structure-activity relationships.  相似文献   

Intercomparison of remote measurements of stratospheric NO and NO2     

H. K. Roscoe  B. J. Kerridge  S. Pollitt  N. Louisnard  J. M. Flaud  C. Camy-Peyret  C. Alamichel  J-P. Pommereau  T. Ogawa  N. Iwagami  M. T. Coffey  W. Mankin  W. F. J. Evans  C. T. McElroy  J. Kerr 《Journal of Atmospheric Chemistry》1990,10(2):111-144

During the 1982 and 1983 Balloon Intercomparison Campaigns, the vertical profile of stratospheric NO₂ was measured remotely by nine instruments and that of NO by two. Total overhead columns were measured by two more instruments. Between 30 and 35km, where measurements overlapped, agreement between NO profiles was within ±30%, which is better than the accuracies claimed by the experimenters. Between 35 and 40km there was similarly good agreement between NO₂ profiles, but below 30km, differences of greater than a factor three were found. In the second Campaign, NO₂ values from most instruments agreed within their quoted errors, except that the Oxford radiometer gave much lower values; but the first Campaign and the column measurements show a more uniform spread of results.These differences below 30km could not be resolved, but new laboratory measurements are planned which should do so.  相似文献   

Near-infrared spectroscopy of (proto)-planetary nebulae: molecular hydrogen excitation as an evolutionary tracer     

Christopher J. Davis  Michael D. Smith  Luke Stern  Thomas H. Kerr  Jean E. Chiar 《Monthly notices of the Royal Astronomical Society》2003,344(1):262-282

We present an in-depth analysis of molecular excitation in 11 H₂-bright planetary and protoplanetary nebulae (PN and PPN). From newly acquired K -band observations, we extract a number of spectra at positions across each source. H₂ line intensities are plotted on 'column density ratio' diagrams so that we may examine the excitation in and across each region. To achieve this, we combine the shock models of Smith, Khanzadyan & Davis with the photodissociation region (PDR) models of Black & van Dishoeck to yield a shock-plus-fluorescence fit to each data set.
Although the combined shock + fluorescence model is needed to explain the low- and high-energy H₂ lines in most of the sources observed (fluorescence accounts for much of the emission from the higher-energy H₂ lines), the relative importance of shocks over fluorescence does seem to change with evolutionary status. We find that shock excitation may well be the dominant excitation mechanism in the least evolved PPN (CRL 2688 – in both the bipolar lobes and in the equatorial plane) and in the most evolved PN considered (NGC 7048). Fluorescence, on the other hand, becomes more important at intermediate evolutionary stages (i.e. in 'young' PN), particularly in the inner core regions and along the inner edges of the expanding post-asymptotic giant branch (AGB) envelope. Since H₂ line emission seems to be produced in almost all stages of post-AGB evolution, H₂ excitation may prove to be a useful probe of the evolutionary status of PPN and PN alike. Moreover, shocks may play an important role in the molecular gas excitation in (P)PN, in addition to the low- and/or high-density fluorescence usually attributed to the excitation in these sources.  相似文献   

Functional,Phylogenetic and Host-Geographic Signatures of <Emphasis Type="Italic">Labyrinthula</Emphasis> spp. Provide for Putative Species Delimitation and a Global-Scale View of Seagrass Wasting Disease     

Daniel?L.?MartinEmail author  Ylenia?Chiari  Emily?Boone  Timothy?D.?Sherman  Cliff?Ross  Sandy?Wyllie-Echeverria  Joseph?K.?Gaydos  Anne?A.?Boettcher 《Estuaries and Coasts》2016,39(5):1403-1421

Seagrass meadows form ecologically and economically valuable coastal habitat on every continental margin except the Antarctic, but their areal extent is declining by approximately 2–5 % per year. Seagrass wasting disease is a contributing factor in these declines, with the protist Labyrinthula identified as the etiologic agent. To help elucidate the role of Labyrinthula spp. in global seagrass declines, we surveyed roughly one fourth of all seagrass species to identify Labyrinthula diversity at the strain and/or species level, combining results from culturing methods and two common nuclear DNA markers: the ITS and 18S regions of the ribosomal RNA gene complex. After assaying a subset of the resulting isolates (of which 170 were newly sequenced), we produced a cladogenic context for putative seagrass-pathogenic versus non-pathogenic Labyrinthula while also defining host and geographic ranges. Assays also suggest that pathogenicity is consistently high (when present; and, even when comparing susceptibility of US East- versus West Coast Zostera marina hosts) while virulence is variable, that some isolate-host combinations have the potential for host cross-infection, and that several modes of transmission can be effective. Taken together, these data provide additional means for delimiting putative species of Labyrinthula, suggesting at least five seagrass-pathogenic and perhaps ten or more non-pathogenic marine “species”, yielding a working definition for ecologists and epidemiologists attempting to reconcile the sundry data related to seagrass wasting disease.  相似文献   

Incorporating spatial variation in housing attribute prices: a comparison of geographically weighted regression and the spatial expansion method   总被引：10，自引：3，他引：7  

Christopher Bitter  Gordon F. Mulligan  Sandy Dall’erba 《Journal of Geographical Systems》2007,9(1):7-27

Hedonic house price models typically impose a constant price structure on housing characteristics throughout an entire market area. However, there is increasing evidence that the marginal prices of many important attributes vary over space, especially within large markets. In this paper, we compare two approaches to examine spatial heterogeneity in housing attribute prices within the Tucson, Arizona housing market: the spatial expansion method and geographically weighted regression (GWR). Our results provide strong evidence that the marginal price of key housing characteristics varies over space. GWR outperforms the spatial expansion method in terms of explanatory power and predictive accuracy.

Christopher BitterEmail:

  相似文献   

EDI convection measurements at 5–6 RE in the post-midnight region     

J. M. Quinn  G. Paschmann  N. Sckopke  V. K. Jordanova  H. Vaith  O. H. Bauer  W. Baumjohann  W. Fillius  G. Haerendel  S. S. Kerr  C. A. Kletzing  K. Lynch  C. E. McIlwain  R. B. Torbert  E. C. Whipple 《Annales Geophysicae》1999,17(12):1503-1512

We present the first triangulation measurements of electric fields with the electron drift instrument (EDI) on Equator-S. We show results from five high-data-rate passes of the satellite through the near-midnight equatorial region, at geocentric distances of approximately 5–6 R_E, during geomagnetically quiet conditions. In a co-rotating frame of reference, the measured electric fields have magnitudes of a few tenths of mV/m, with the E × B drift generally directed sunward but with large variations. Temporal variations of the electric field on time scales of several seconds to minutes are large compared to the average magnitude. Comparisons of the “DC” baseline of the EDI-measured electric fields with the mapped Weimer ionospheric model and the Rowland and Wygant CRRES measurements yield reasonable agreement.  相似文献   

Slant Column Measurements of O3 and NO2 During the NDSC Intercomparison of Zenith-Sky UV-Visible Spectrometers in June 1996     

H. K. Roscoe  P. V. Johnston  M. Van Roozendael  A. Richter  A. Sarkissian  J. Roscoe  K. E. Preston  J-C. Lambert  C. Hermans  W. DeCuyper  S. Dzienus  T. Winterrath  J. Burrows  F. Goutail  J-P. Pommereau  E. D'Almeida  J. Hottier  C. Coureul  R. Didier  I. Pundt  L. M. Bartlett  C. T. McElroy  J. E. Kerr  A. Elokhov  G. Giovanelli  F. Ravegnani  M. Premuda  I. Kostadinov  F. Erle  T. Wagner  K. Pfeilsticker  M. Kenntner  L. C. Marquard  M. Gil  O. Puentedura  M. Yela  D. W. Arlander  B. A. Kastad Hoiskar  C. W. Tellefsen  K. Karlsen Tornkvist  B. Heese  R. L. Jones  S. R. Aliwell  R. A. Freshwater 《Journal of Atmospheric Chemistry》1999,32(2):281-314

In June 1996, 16 UV-visible sensors from 11 institutes measured spectra of the zenith sky for more than 10 days. Spectra were analysed in real-time to determine slant column amounts of O3 and NO2. Spectra of Hg lamps and lasers were measured, and the amount of NO2 in a cell was determined by each spectrometer. Some spectra were re-analysed after obvious errors were found. Slant columns were compared in two ways: by examining regression analyses against comparison instruments over the whole range of solar zenith angles; and by taking fractional differences from a comparison instrument at solar zenith angles between 85° and 91°. Regression identified which pairs of instruments were most consistent, and so which could be used as universal comparison instruments. For O3, regression slopes for the whole campaign agreed within 5% for most instruments despite the use of different cross-sections and wavelength intervals, whereas similar agreement was only achieved for NO2 when the same cross-sections and wavelength intervals were used and only one half-day's data was analysed. Mean fractional differences in NO2 from a comparison instrument fall within ±7% (1-sigma) for most instruments, with standard deviations of the mean differences averaging 4.5%. Mean differences in O3 fall within ±2.5% (1- sigma) for most instruments, with standard deviations of the mean differences averaging 2%. Measurements of NO2 in the cell had similar agreement to measurements of NO2 in the atmosphere, but for some instruments measurements with cell and atmosphere relative to a comparison instrument disagreed by more than the error bars.  相似文献   

The geochemistry and petrogenesis of the late-Cretaceous picrites and basalts of Curaçao,Netherlands Antilles: a remnant of an oceanic plateau     

A. C. Kerr  John Tarney  Giselle F. Marriner  Gerard T. Klaver  Andrew D. Saunders  Matthew F. Thirlwall 《Contributions to Mineralogy and Petrology》1996,124(1):29-43

The island of Curaçao in the southern Caribbean Sea is composed mainly of a thick sequence (>5?km) of pillow lavas, grading upwards from picrites at the base of the exposed section, to basalts nearer the top. Modelling suggests that picrites are related to the basalts by fractional crystallisation. Initial radiogenic isotope ratios of the picrites have a restricted compositional range: ?_Nd=+6.1 to +6.6, ⁸⁷Sr/⁸⁶Sr=0.70296–0.70319; whereas the basalts display a wider range of compositions: ?_Nd=+6.6 to +7.6, ⁸⁷Sr/⁸⁶Sr=0.70321–0.70671. This variation in isotope ratios between basalts and picrites may be due to the assimilation of altered oceanic crust (or possibly partial melts of such crust) by a picritic magma along with fractional crystallisation. The relatively narrow range of Nd and Pb isotopic compositions in the Curaçao lavas suggests either that the source region was homogeneous, or that melts from a heterogeneous mantle source were well mixed before eruption. Chondritic to slightly light rare earth element enriched patterns, combined with long-term light rare earth element depletion (positive ?_Nd), suggest that the lavas were formed by polybaric melting of spinel lherzolite, with small a contribution from garnet lherzolite melts. High-MgO lavas, the absence of a subduction related chemistry, and the chemical similarity to other oceanic plateaux, suggest a mantle plume origin for the Curaçao lava succession. The Curaçao volcanic sequence is part of an oceanic plateau formed at about 88–90?Ma, fragments of which are dispersed around the Caribbean as well as being obducted onto the western margin of Colombia and Ecuador. The occurrence of high-Mg lavas throughout this Cretaceous Caribbean–Colombian igneous province requires anomalously hot mantle (>200^°?C hotter than ambient upper mantle) over a large part of a putative plume head, which is inconsistent with some mantle plume models.  相似文献   

NEW LEGISLATION OF INTEREST TO GEOGRAPHERS     

John Kerr Rose 《The Professional geographer》1966,18(3):171-172

  相似文献   

THE DESIGN AND TESTING OF GEOPHONES AND THEIR AMPLIFIERS.     

E. C. Bullard  C. Kerr Grant 《Geophysical Journal International》1938,4(5):341-350

  相似文献