Seasonal changes in the daily emission rates of terpenes by Quercus ilex and the atmospheric concentrations of terpenes in the natural park of Montseny, NE Spain     

Joan Llusia  Josep Pe?uelas  Roger Seco  Iolanda Filella 《Journal of Atmospheric Chemistry》2012,69(3):215-230

We studied the daily patterns in the rates of terpene emissions by the montane holm oak, Quercus ilex, in three typical days of winter and three typical days of summer in Montseny, a natural park near Barcelona, and related them to the air concentrations of terpenes, ozone and NO₂. Terpene emission rates were about 10 times higher in summer than in winter. Emissions virtually stopped in the dark. In both seasons, rates of terpene emissions were well correlated with light, air temperature and relative humidity. Rates of emissions were also correlated with stomatal conductance and the rates of transpiration and photosynthesis. Almost all the individual terpenes identified followed the same pattern as total terpenes. The most abundant terpene was ??-pinene, followed by sabinene + ??-pinene, limonene, myrcene, camphene and ??-phellandrene. Atmospheric terpene concentrations were also about 10 times higher in summer than in winter. A significant diurnal pattern with maxima at midday was observed, especially in summer. The increase by one order of magnitude in the concentrations of these volatile isoprenoids highlights the importance of local biogenic summer emissions in these Mediterranean forested areas which also receive polluted air masses from nearby or distant anthropic sources. Atmospheric concentrations of O₃ and NO₂ were also significantly higher in summer and at midday hours. In both seasons, concentrations of O₃ were significantly correlated with concentrations of terpenes and NO₂ in the air and with rates of terpene emission.  相似文献   

Recent advances in mountain climate research     

Roger G. Barry 《Theoretical and Applied Climatology》2012,110(4):549-553

The paper provides a brief overview of recent advances in selected areas of mountain climate research. It addresses the contrasting vertical precipitation gradients in the Alps and in central Asia, snow line in the Alps, orographic precipitation in North America, the Mesoscale Alpine Programme wind studies, automatic weather stations in mountains, satellite remote sensing of glacier changes, and temperature change at high elevations. The evidence for altitudinal differences in the temperature response to recent warming is discussed.  相似文献   

Periodicities in the high-mass X-ray binary system RX J0146.9+6121/LS I+61°235     

Gordon E. Sarty  László L. Kiss  Richard Huziak  Lionel J. J. Catalan  Diane Luciuk  Timothy R. Crawford  David J. Lane  Roger D. Pickard  Thomas A. Grzybowski  Pere Closas  Helen Johnston  David Balam  Kinwah Wu 《Monthly notices of the Royal Astronomical Society》2009,392(3):1242-1252

The high-mass X-ray binary RX J0146.9+6121, with optical counterpart LS I+61°235 (V831 Cas), is an intriguing system on the outskirts of the open cluster NGC 663. It contains the slowest Be type X-ray pulsar known with a pulse period of around 1400 s and, primarily from the study of variation in the emission line profile of Hα, it is known to have a Be decretion disc with a one-armed density wave period of approximately 1240 d. Here we present the results of an extensive photometric campaign, supplemented with optical spectroscopy, aimed at measuring short time-scale periodicities. We find three significant periodicities in the photometric data at, in order of statistical significance, 0.34, 0.67 and 0.10 d. We give arguments to support the interpretation that the 0.34 and 0.10 d periods could be due to stellar oscillations of the B-type primary star and that the 0.67 d period is the spin period of the Be star with a spin axis inclination of  23⁺¹⁰₋₈  degrees. We measured a systemic velocity of  −37.0 ± 4.3 km s⁻¹  confirming that LS I+61°235 has a high probability of membership in the young cluster NGC 663 from which the system's age can be estimated as 20–25 Myr. From archival RXTE All Sky Monitor (ASM) data we further find 'super' X-ray outbursts roughly every 450 d. If these super outbursts are caused by the alignment of the compact star with the one-armed decretion disc enhancement, then the orbital period is approximately 330 d.  相似文献   

The fresnel interferometric imager     

Laurent Koechlin  Denis Serre  Paul Deba  Roser Pelló  Christelle Peillon  Paul Duchon  Ana Ines Gomez de Castro  Margarita Karovska  Jean-Michel Désert  David Ehrenreich  Guillaume Hebrard  Alain Lecavelier des Etangs  Roger Ferlet  David Sing  Alfred Vidal-Madjar 《Experimental Astronomy》2009,23(1):379-402

The Fresnel Interferometric Imager has been proposed to the European Space Agency (ESA) Cosmic Vision plan as a class L mission. This mission addresses several themes of the CV Plan: Exoplanet study, Matter in extreme conditions, and The Universe taking shape. This paper is an abridged version of the original ESA proposal. We have removed most of the technical and financial issues, to concentrate on the instrumental design and astrophysical missions. The instrument proposed is an ultra-lightweight telescope, featuring a novel optical concept based on diffraction focussing. It yields high dynamic range images, while releasing constraints on positioning and manufacturing of the main optical elements. This concept should open the way to very large apertures in space. In this two spacecraft formation-flying instrument, one spacecraft holds the focussing element: the Fresnel interferometric array; the other spacecraft holds the field optics, focal instrumentation, and detectors. The Fresnel array proposed here is a 3.6 ×3.6 m square opaque foil punched with 10⁵ to 10⁶ void “subapertures”. Focusing is achieved with no other optical element: the shape and positioning of the subapertures (holes in the foil) is responsible for beam combining by diffraction, and 5% to 10% of the total incident light ends up into a sharp focus. The consequence of this high number of subapertures is high dynamic range images. In addition, as it uses only a combination of vacuum and opaque material, this focussing method is potentially efficient over a very broad wavelength domain. The focal length of such diffractive focussing devices is wavelength dependent. However, this can be corrected. We have tested optically the efficiency of the chromatism correction on artificial sources (500 < λ < 750 nm): the images are diffraction limited, and the dynamic range measured on an artificial double source reaches 6.2 10^− 6. We have also validated numerical simulation algorithms for larger Fresnel interferometric arrays. These simulations yield a dynamic range (rejection factor) close to 10^− 8 for arrays such as the 3.6 m one we propose. A dynamic range of 10^− 8 allows detection of objects at contrasts as high as than 10^− 9 in most of the field. The astrophysical applications cover many objects in the IR, visible an UV domains. Examples are presented, taking advantage of the high angular resolution and dynamic range capabilities of this concept.  相似文献   

Diagenesis of plant biopolymers: Decay and macromolecular preservation of Metasequoia     

Neal S. Gupta  Hong Yang  Qin Leng  Derek E.G. Briggs  George D. Cody  Roger E. Summons 《Organic Geochemistry》2009,40(7):802-809

Analysis of modern Metasequoia leaves revealed the presence of the structural polyester cutin, guaiacyl lignin units and polysaccharides. Analysis of environmentally decayed Metasequoia leaves revealed that guaiacyl lignin units and cellulose were degraded more than vinyl phenol (the last being the primary pyrolysis product of cutin and plant cuticles) suggesting that cutin is more stable than lignin and cellulose during degradation, contrary to some previous studies. This observation is supported by electron microscopy showing changes in the cellular structure and cuticle of modern, decayed and fossil Metasequoia leaves. Metasequoia fossils from the Eocene of Republic (Washington State) showed a significant aliphatic component, but biopolymeric lignin and polysaccharides were not detected. Fossils from the Eocene of Axel Heiberg revealed the presence of lignin and an aliphatic polymer up to C₂₉ with cellulose, and fossils from the Miocene Clarkia deposit (Idaho) revealed lignin and an aliphatic polymer up to C₂₇ without any polysaccharides. Modern Metasequoia needles heated experimentally in confined conditions generated a macromolecular composition with an aliphatic polymer up to C₃₂ and additional phenolic compounds similar to those present in the fossils. Experimental heating of cutin is known to generate an aliphatic polymer with carbon chain length units <C₂₀. Thus, the n-alkyl component with chain length units >C₂₀ in the heated Metasequoia needles is a product of incorporation of longer chain plant waxes, indicated by the odd/even predominance of the >C₂₇ n-alkanes. The resistant nature of cutin compared to lignin and polysaccharides explains the presence of an n-alkyl component (<C₂₀) in fossil leaves even when polysaccharides are absent and lignin has decayed; cutin and its diagenetically altered products contribute significantly to the presence of aliphatic components in terrestrially derived sedimentary organic matter.  相似文献   

A cryo-SEM study of aggregate and floc structure changes during clay settling and raking processes     

Jianhua Du  Rada A. Pushkarova  Roger St.C. Smart 《International Journal of Mineral Processing》2009,93(1):66-72

The destabilization of kaolinite suspension by anionic flocculant addition occurs in three zones; free settling, hindered settling and compression which usually includes a final bed raking process in mineral processing practice. This paper reports changes in the kaolinite aggregate and floc structures in the different settling and raking zones by cryo-vitrification/cryo-SEM techniques with image analysis combining micro- and macro-flocs. Cryo-SEM images indicate that, even during free settling, fine clay particles are bridged predominantly in edge–edge (E–E) with some face–face (F–F) configurations forming single, small flocs and some chain structures. When these small flocs and chains settle into the hindered settling zone, the collision between flocs and chains results in “honeycomb” network structures formed with lateral chain-like extension. The settled bed consists of these honeycomb structures with both inter-aggregate and intra-aggregate trapped water and has relatively low bed density (e.g. < 12 wt.% for a 2 wt.% slurry). The effect of the raking process in dramatically improving thickener underflow solids has been extensively studied but the structural changes in flocs and aggregates in this process are less well defined. Raking the compression zone for 1 h at 3 rpm can release some of the trapped water in the “honeycomb” structure and the bed density for 2 wt.% slurry improves dramatically to more than 36 wt.%. Cryo-SEM illustrates the extensive restructuring of flocs from predominantly E–E to predominantly F–F in many areas. The STructural IMage ANalysis (STIMAN) software is used to combine a series of images at magnifications from 1000× to 8000×, including both macro- and micro-flocs. This structural analysis comparing the un-raked and raked bed samples gives increases in total particle area of 30% and in relative particle area of 6%. The relatively low energy rake action of the shear stress results in the disruption of the E–E chains and the honeycomb structure, partly releasing the trapped water and inducing some E–E to F–F aggregate restructuring are clearly illustrated in these results.  相似文献   

Climate change impact on water and salt balances: an assessment of the impact of climate change on catchment salt and water balances in the Murray-Darling Basin, Australia     

Jenet Austin  Lu Zhang  Roger N. Jones  Paul Durack  Warrick Dawes  Peter Hairsine 《Climatic change》2010,100(3-4):607-631

Climate change has potentially significant implications for hydrology and the quantity and quality of water resources. This study investigated the impacts of climate change and revegetation on water and salt balance, and stream salt concentration for catchments within the Murray-Darling Basin, Australia. The Biophysical Capacity to Change model was used with climate change scenarios obtained using the CSIRO DARLAM 125 (125 km resolution) and Cubic Conformal (50 km resolution) regional climate models. These models predicted up to 25% reduction in mean annual rainfall and a similar magnitude of increase in potential evapotranspiration by 2070. Relatively modest changes in rainfall and temperature can lead to significant reductions in mean annual runoff and salt yield and increases in stream salt concentrations within the Basin. The modelled reductions in mean annual runoff were up to 45% in the wetter/cooler southern catchments and up to 64% in the drier/hotter western and northern catchments. The maximum reductions in salt yield were estimated to be up to 34% in the southern catchments and up to 49% in the northern and western catchments. These changes are associated with average catchment rainfall decreases of 13 to 21%. The results suggest that percentage changes in rainfall will be amplified in runoff. This study demonstrates that climate change poses significant challenges to natural resource management in Australia.  相似文献   

Effects of Bubbles and Sea Spray on Air–Sea Exchange in Hurricane Conditions     

Alexander Soloviev  Roger Lukas 《Boundary-Layer Meteorology》2010,136(3):365-376

The lower limit on the drag coefficient under hurricane force winds is determined by the break-up of the air–sea interface due to Kelvin–Helmholtz instability and formation of the two-phase transition layer consisting of sea spray and air bubbles. As a consequence, a regime of marginal stability develops. In this regime, the air–sea drag coefficient is determined by the turbulence characteristics of the two-phase transition layer. The upper limit on the drag coefficient is determined by the Charnock-type wave resistance. Most of the observational estimates of the drag coefficient obtained in hurricane conditions and in laboratory experiments appear to lie between the two extreme regimes: wave resistance and marginal stability.  相似文献   

Analysis of Urban Atmosphere Plume Concentration Fluctuations   总被引：1，自引：1，他引：0  

Dennis Finn  Kirk L. Clawson  Roger G. Carter  Jason D. Rich  Chris Biltoft  Martin Leach 《Boundary-Layer Meteorology》2010,136(3):431-456

Concentration variability in the fast-response tracer dataset for continuous, near-surface, point source releases in the urban core from the Joint Urban 2003 field study is analyzed. Concentration variability for conditionally and unconditionally sampled time series is characterized by probability densities, concentration fluctuation intensity, skewness, and kurtosis. Significant day-night differences in plume dispersion are observed. Relative to daytime, nighttime plumes were more likely to have reduced concentration fluctuation intensities, higher normalized surface concentrations, suppressed vertical mixing, and a greater prevalence of Gaussian-like distributions rather than log-normal or mixed mode distributions. This was in spite of the similar stability and turbulence conditions in the urban core for day and night. The potential roles of flow meander and thermal stability in explaining these differences are examined. Probability densities of concentration are found to be a strong function of fluctuation intensity. There are few differences in probability densities between day and night when classified by fluctuation intensity. There are no appreciable differences between conditional and unconditional probability densities and only small differences between conditional and unconditional sampling statistics relative to the larger differences usually observed in more homogeneous settings. Fluctuation intensity, skewness, and kurtosis are higher for the daytime experiments, and closer to the source, but show little difference between conditional and unconditional results over most of their range of values. The log-normal distribution provides a better overall fit to a broader range of the dataset than the exponential or clipped-normal distributions.  相似文献   

Spatial Data Analysis: Theory and Practice. By ROBERT HAINING (Cambridge: Cambridge University Press, 2003). [Pp. xx+432]. ISBN 0-521-77437-3. Price £29.95 Paperback. ISBN 0-521-77319-9. Price £80. Hardback     

Roger Bivand 《International journal of geographical information science》2013,27(3):300-301

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