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排序方式: 共有625条查询结果,搜索用时 31 毫秒
61.
Past and future polar amplification of climate change: climate model intercomparisons and ice-core constraints 总被引:1,自引:0,他引:1
V. Masson-Delmotte M. Kageyama P. Braconnot S. Charbit G. Krinner C. Ritz E. Guilyardi J. Jouzel A. Abe-Ouchi M. Crucifix R. M. Gladstone C. D. Hewitt A. Kitoh A. N. LeGrande O. Marti U. Merkel T. Motoi R. Ohgaito B. Otto-Bliesner W. R. Peltier I. Ross P. J. Valdes G. Vettoretti S. L. Weber F. Wolk Y. Yu 《Climate Dynamics》2006,27(4):437-440
62.
This study represents the first detailed investigation of platinum-group elements (PGEs) in road-deposited sediment (RDS) in Hawaii, USA. Thirty-three sample locations, in two urban watersheds in Honolulu, Oahu, Hawaii were sampled. The <63 μm fraction of RDS was digested with aqua regia, followed by matrix separation with Dowex AG50-X8 cation exchange resin. PGEs were analyzed with inductively coupled plasma-mass spectrometry (ICP-MS) equipped with a desolvating nebulizer. Concentrations of Rh, Pd and Pt in residential streets reached 64, 105 and 506 ng/g, respectively. Maximum enrichment ratios, computed as RDS concentrations relative to baseline values, exceeded 400, indicating a significant anthropogenic signal with the sequence Rh > Pt > Pd. Iridium concentrations were uniformly low <1 ng/g, and enrichment ratios support a geogenic source. Significant interelement PGE correlations (Pd–Pt–Rh), combined with the magnitude of PGE pair-wise ratios (Pt/Pd, Pt/Rh and Pd/Rh), and relative percentages comparable to European RDS and roadside soil in Indiana, USA all suggest an automobile source. Attrition of PGE-loaded automobile catalytic converters and subsequent loss to the environment by exhaust emissions explains the significant environmental signal of PGEs in road environments of Hawaii. Further PGE work is required to quantify urban transport paths as PGEs are known to bioaccumulate, cause cellular damage and may have detrimental human health effects. 相似文献
63.
R. S. Ross A. Chakraborty A. Chen L. Stefanova S. Sirdas T. N. Krishnamurti 《Meteorology and Atmospheric Physics》2007,98(3-4):137-174
Summary Climate variations in the Caribbean, largely manifest in rainfall activity, have important consequences for the large-scale
water budget, natural vegetation, and land use in the region. The wet and dry seasons will be defined, and the important roles
played by the El Ni?o-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO) in modulating the rainfall during
these seasons will be discussed.
The seasonal climate forecasts in this paper are made by 13 state of the art coupled atmosphere-ocean general circulation
models (CGCMs) and by the Florida State University Synthetic Superensemble (FSUSSE), whose forecasts are obtained by a weighted
combination of the individual CGCM forecasts based on a training period. The success of the models in simulating the observed
1989–2001 climatology of the various forecast parameters will be examined and linked to the models’ success in predicting
the seasonal climate for individual years. Seasonal forecasts will be examined for precipitation, sea-surface temperature (SST), 2-meter air temperature, and
850 hPa u- and v-wind components during the period 1989–2001. Evaluation metrics include root mean square (RMS) error and Brier skill score.
It will be shown that the FSUSSE is superior to the individual CGCMs and their ensemble mean both in simulating the 1989–2001
climatology for the various parameters and in predicting the seasonal climate of the various parameters for individual years.
The seasonal climate forecasts of the FSUSSE and of the ensemble mean of the 13 state of the art CGCMs will be evaluated for
years (during the period 1989–2001) that have particular ENSO and NAO signals that are known to influence Caribbean weather,
particularly the rainfall. It will be shown that the FSUSSE provides superior forecasts of rainfall, SST, 2-meter air temperature,
and 850 hPa u- and v-wind components during dry summers that are modulated by negative SOI and/or positive NAO indices. Such summers have become
a feature of a twenty-year pattern of drought in the Caribbean region. The results presented in this paper will show that
the FSUSSE is a valuable tool for forecasting rainfall and other atmospheric and oceanic variables during such periods of
drought. 相似文献
64.
This paper introduces, explains, and describes methods for addressing the issues of permanence, leakage, and additionality
(PLA) of agricultural soil carbon sequestration (ASCS) activities at the project level. It is important to cast these as project-level
issues, because they relate to the integrity and consistency of using location-specific ASCS projects as an offset against
GHG emissions generated in other sectors (e.g., energy). The underlying objective is to understand and quantify what the net
carbon benefits of an ASCS project are once we account for the fact that (1) the sequestered carbon may be stored impermanently,
(2) the project may displace emissions outside the project boundaries (leakage), and (3) the project’s carbon sequestration
may not be entirely additional to what would have occurred anyway under business-as-usual (no project) conditions. This article
evaluates methods for identifying and estimating PLA and gauges the potential magnitude of these effects on the economic returns
to a project.
This work reflects ongoing collaborative efforts of the authors and Bruce McCarl (Texas A&M University), Allan Sommer, Jui-Chen
Yang, and Laurel Clayton (RTI International), Sandra Brown (Winrock International), Ken Andrasko and Ben DeAngelo (US EPA),
and various participants in the World Resources Institute/World Business Council workgroup to develop GHG project reporting
protocols. All opinions, errors and omissions are those of the authors only. 相似文献
65.
Nancy L. Ross 《Physics and Chemistry of Minerals》1998,25(8):597-602
The crystal structure of orthorhombic (Pbnm) ScAlO3 perovskite has been refined to 5 GPa using single-crystal X-ray diffraction. The compression of the structure if anisotropic
with β
a
=1.39(3)×10−3 GPa−1, β
b
=1.14(3)×10−3 GPa−1 and β
c
=1.84(3)×10−3 GPa−1. The isothermal bulk modulus of ScAlO3, K
T
, determined from fitting a Birch-Murnaghan equation of state (K
′
T
=4) to the volume compression data is 218(1) GPa. The interoctahedral angles to not vary significantly with pressure, and
the compression of the structure is entirely attributable to compression of the AlO6 octahedra. The compressibilities of the constituent AlO6 and ScO12 are well matched: βAl−O=1.6×10−3 GPa−1 and βSc−O=1.5×10−3 GPa−1. Therefore the distortion of the structure shows no significant change with increasing pressure.
Received: 18 August 1997 / Revised, accepted: 11 November 1997 相似文献
66.
A. J. Young R. R. Ross & A. C. Fabian 《Monthly notices of the Royal Astronomical Society》1998,300(1):L11-L15
We propose a model for the source of the X-ray background (XRB) in which low-luminosity active nuclei ( L ∼ 1043 erg s−1 ) are obscured ( N ∼ 1023 cm−2 ) by nuclear starbursts within the inner ∼ 100 pc. The obscuring material covers most of the sky as seen from the central source, rather than being distributed in a toroidal structure, and hardens the averaged X-ray spectrum by photoelectric absorption. The gas is turbulent with velocity dispersion ∼ few × 100 km s−1 and cloud–cloud collisions lead to copious star formation. Although supernovae tend to produce outflows, most of the gas is trapped in the gravity field of the star-forming cluster itself and the central black hole. A hot ( T ∼ 106 − 107 K) virialized phase of this gas, comprising a few per cent of the total obscuring material, feeds the central engine of ∼ 107 M⊙ through Bondi accretion, at a sub-Eddington rate appropriate for the luminosity of these objects. If starburst-obscured objects give rise to the residual XRB, then only 10 per cent of the accretion in active galaxies occurs close to the Eddington limit in unabsorbed objects. 相似文献
67.
PHOTOGRAMMETRY AND THE SCANNING ELECTRON MICROSCOPE 总被引:1,自引:0,他引:1
The scanning electron microscope forms images of the surfaces of objects located in a vacuum specimen chamber. A fine beam of electrons scans the surface in synchronism with a cathode ray tube whose spot brightness is modulated by the secondary electron signal emanating from the specimen. The system is capable of giving a large depth of focus and thus allows different projections of the specimen to be photographed by tilting the specimen between successive exposures. From a knowledge of the geometry of the projection (which is central or perspective, but may be justifiably treated as a parallel or orthogonal case for high magnification images), it is therefore possible to proceed to three dimensional analyses from the measurement of parallaxes. Part I of this paper deals with the practical problems resulting from mechanical design limitations of specimen stages and plotting instruments, as well as the nature and sources of image distortions. Part II deals with the practical features of the successful plotting instruments designed especially for the solution of a standardised scanning electron microscope problem in which the magnification of the two members of a stereoscopic pair of images is held constant, the angle of divergence of the peripheral “rays” of the projection from the central “ray” is assumed to be negligible (which is the case for high magnification images) and the tilt angle difference between the two specimen attitudes is constant. 相似文献
68.
Z. Reiss B. Luz A. Almogi-Labin E. Halicz A. Winter M. Wolf D. A. Ross 《Quaternary Research》1980,14(3):294-308
The quantitative distribution of planktonic foraminifera, pteropods, and coccolithophorids, as well as oxygen-isotope variations were analyzed in four deep-sea cores from the Gulf of Aqaba (Elat) and the northernmost Red Sea. The core record covers about 150,000 yr. Detailed stratigraphic subdivision is facilitated by combining all calcareous plankton groups. Time-stratigraphic correlation and dating beyond the radiocarbon range are possible by comparison of the oxygen-isotope curves. During the glacial maximum salinity rose to more than 50‰, while winter temperature of the upper waters fell by at least 4°C compared to the present. The rise in salinity can be accounted for by sea-strait dynamics and lowering of sea level. The Gulf of Aqaba and the Red Sea were continuously connected through the Straits of Tiran, and there is no indication of desiccation during the glacial maximum. 相似文献
69.
The Miocene-Oligocene volcanism of this region is part of the larger Tertiary volcanic province found throughout E. Australia. Within the S.E. Queensland region, the volcanism is strongly bimodal, and has emanated from six major centres, and many additional smaller centres. The mafic lavas (volumetrically dominant) range continuously from ne-normative through to Q-normative and are predominantly andesine-normative; Mg/Mg+Fe (atomic ratios range from 30–60; K2O ranges from 0.42–2.93%, and TiO2 from 0.81–3.6%.Phenocryst contents are low (averaging 6.7 vol.%), and comprise olivine (Fa18–75; Cr-spinel inclusions occur locally in Mg-rich phenocrysts), plagioclase (An25–68), and less commonly augite, which is relatively aluminous in lavas of the Springsure volcanic centre. Very rare aluminous bronzite occurs in certain Q-normative lavas. Groundmass minerals comprise augite, olivine (Fa33–77), feldspar (ranging from labradorite through to anorthoclase and sanidine), Fe-Ti oxides, and apatite. Within many of the Q-normative lavas, extensive development of subcalcic and pigeonitic pyroxenes occurs, and also relatively rarely orthopyroxene. Mineralogically, the ne- and ol-normative lavas, and some of the Q-normative lavas are indistinguishable, and in view of the gradations in chemistry, the term hawaiite has been extended to cover these lavas. The term tholeiitic andesite is used to describe the Q-normative lavas containing Ca-poor pyroxenes as groundmass phases.Megacrysts of aluminous augite, aluminous bronzite, olivine, ilmenite, and spinel sporadically occur within the lavas, and their compositions clearly indicate that they are not derived from the Upper Mantle. Rare lherzolite xenoliths are also found.The petrogenesis of these mafic lavas is approached by application of the thermodynamic equilibration technique of Carmichael et al. (1977), utilizing three parental mineral assemblages that could have been in equilibrium with the magmas at P and T. The models are: (a) standard upper mantle mineralogy; (b) an Fe-enriched upper mantle model (Wilkinson and Binns 1977); (c) lower crust mineralogy, based on analysed megacryst compositions. The calculations suggest that these mafic magmas were not in equilibrium with either mantle model prior to eruption, but show much closer approaches to equilibrium with the lower crust model. Calculated equilibration temperatures and pressures (for the lower crust model) range from 995°–l,391° C (average 1,192), and 7.2–16.3 kb (average 12.4). These results are interpreted in terms of a model of intrusion and magma fractionation within the crust-mantle interface region, with consequent crustal underplating and thickening beneath the Tertiary volcanic regions. Some support for the latter is provided by regional isostatic gravity anomalies and physiographic considerations. 相似文献
70.