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  • 1
    Publikationsdatum: 2015-09-10
    Beschreibung: During the last decade, the widely distributed shrublands in northern China have shown significant signs of recovery from desertification, the result of widespread conservation practices. However, to support the current efforts in conservation, more knowledge is needed on surface energy partitioning and its biophysical controls. Using eddy-covariance measurements made over a semi-arid shrubland in northwest China in 2012, we examined how surface energy-balance components vary on diurnal and seasonal scales, and how biophysical factors control bulk surface parameters and energy exchange. Sensible heat flux ( H ) exceeded latent heat flux ( λE ) during most of the year, resulting in an annual Bowen ratio ( β , i.e. H / λE ) of 2.0. λE exceeded H only in mid-summer when frequent rainfall co-occurred with the seasonal peak in leaf area index ( LAI ). Evapotranspiration reached a daily maximum of 3.3 mm day −1 , and summed to 283 mm yr −1 . The evaporative fraction ( EF , i.e. λE / R n ), Priestley-Taylor coefficient ( α ), surface conductance ( g s ) and decoupling coefficient ( Ω ) were all positively correlated with soil water content ( SWC ) and LAI . The direct enhancement of λE by high vapor pressure deficit ( VPD ) was buffered by a concurrent suppression of g s . The g s played a direct role in controlling EF and α by mediating the effects of LAI , SWC and VPD . Our results highlight the importance of adaptive plant responses to water scarcity in regulating ecosystem energy partitioning, and suggest an important role for revegetation in the reversal of desertification in semi-arid areas. This article is protected by copyright. All rights reserved.
    Print ISSN: 0885-6087
    Digitale ISSN: 1099-1085
    Thema: Architektur, Bauingenieurwesen, Vermessung , Geographie
    Publiziert von Wiley
    Standort Signatur Erwartet Verfügbarkeit
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  • 2
    Publikationsdatum: 2013-06-07
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
    Standort Signatur Erwartet Verfügbarkeit
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  • 3
    Publikationsdatum: 2015-01-15
    Beschreibung: A fundamental statement in diffusion theory is provided by the so-called theorem on reduced dimensionality . The latter theorem is saying that if the dimensionality of the turbulence is reduced, charged particles are tied to a single magnetic field line. If there is pitch-angle scattering and therewith parallel diffusion, this usually means that perpendicular transport is subdiffusive. Subdiffusive transport was found in numerous simulations for slab turbulence. However, it was unclear whether the theorem is valid for other models with reduced dimensionality such as the two-dimensional model. In the current paper, we simultaneously trace magnetic field lines and energetic particles and we compute the distance between the particle and the initial field line. We confirm the aforementioned theorem for slab turbulence but we cannot confirm it for two-dimensional turbulence. We also show that particles are not tied to field lines for two-component turbulence.
    Print ISSN: 1070-664X
    Digitale ISSN: 1089-7674
    Thema: Physik
    Standort Signatur Erwartet Verfügbarkeit
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  • 4
    Publikationsdatum: 2016-02-26
    Beschreibung: Ammonia nitrogen and salinity tolerance of Penaeus monodon from eight selected breeding families were evaluated at the concentration of 67.65 mg L−1 ammonia-N and reducing salinity from 15 to 0 ‰. The final survi...
    Digitale ISSN: 2193-1801
    Thema: Allgemeine Naturwissenschaft
    Publiziert von SpringerOpen
    Standort Signatur Erwartet Verfügbarkeit
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  • 5
    Publikationsdatum: 2012-04-28
    Beschreibung: It is very important to predict the shock arrival times (SATs) at Earth for space weather practice. In this paper we use the energy of soft X-ray during solar flare events to help predict the SATs at Earth. We combine the soft X-ray energy and SAT prediction models previously developed by researchers to obtain two new methods. By testing the methods with the total of 585 solar flare events following the generation of a metric type II radio burst during the Solar Cycle 23 from September 1997 to December 2006, we find that the predictions of SATs at Earth could be improved by significantly increasing PODn, the proportion of events without shock detection that were correctly forecast. PODn represents a method's ability in forecasting the solar flare events without shocks arriving at the Earth, which is important for operational predictions.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
    Standort Signatur Erwartet Verfügbarkeit
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  • 6
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    Unbekannt
    American Physical Society (APS)
    Publikationsdatum: 2012-05-12
    Beschreibung: Author(s): G. Li, B. Miao, Q. Hu, and G. Qin A Reply to the Comment by S. Perri and V. Carbone. [Phys. Rev. Lett. 108, 199502] Published Fri May 11, 2012
    Schlagwort(e): Comments
    Print ISSN: 0031-9007
    Digitale ISSN: 1079-7114
    Thema: Physik
    Standort Signatur Erwartet Verfügbarkeit
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  • 7
    Publikationsdatum: 2011-03-22
    Beschreibung: Author(s): G. Li, B. Miao, Q. Hu, and G. Qin The MHD turbulence theory developed by Iroshnikov and Kraichnan predicts a k^{-1.5} power spectrum. Solar wind observations, however, often show a k^{-5/3} Kolmogorov scaling. Based on 3 years worth of Ulysses magnetic field data where over 28 000 current sheets are identified, we propose that th... [Phys. Rev. Lett. 106, 125001] Published Mon Mar 21, 2011
    Schlagwort(e): Plasma and Beam Physics
    Print ISSN: 0031-9007
    Digitale ISSN: 1079-7114
    Thema: Physik
    Standort Signatur Erwartet Verfügbarkeit
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  • 8
    Publikationsdatum: 2014-02-15
    Beschreibung: Scheelite is well developed in hydrothermal deposits, providing a window into genetic processes and facilitating comparative studies, however, few studies have focused on characterizing scheelite in skarn-type W-Mo deposits. The primary ore mineral in the Jitoushan and Baizhangyan skarn-type W-Mo deposits (Anhui Province, Eastern China), scheelite was analyzed for major, trace, and rare earth element (REE) abundance and for Sr-Nd isotopes. The analysis revealed two unique geochemical characteristics that distinguish the scheelite from skarn-type W-Mo deposits to that from vein-type Au-W and porphyry-type W-Mo deposits: higher Mo content with a negative correlation between MoO 3 and WO 3 and a strong HREE depletion. Skarn-type scheelite mainly inherited REE signatures from ore-forming fluids, and the early precipitation of skarn minerals (e.g., garnet, diopside, and amphibole) has most likely resulted in the observed strong HREE depletion in scheelite and the decoupling of LREEs and HREEs. Of the numerous substitution mechanisms suggested by previous workers, 3Ca 2+ = 2REE 3+ + Ca (where Ca is a Ca-site vacancy) is preferred for the substitution of REE 3+ for Ca 2+ and in this study, particularly given the low salinity of ore fluids. As the scheelite Eu anomalies were inherited from ore-forming fluids with variable redox conditions and pH, the complex dEu/Mo correlation indicates that Mo increasingly entered the scheelite under oxidizing conditions and reached a maxim at dEu values of 0.8 to 1. In contrast, under reducing conditions, Mo contents in scheelite decrease gradually and Mo is precipitated as molybdenite as a result of the change in dominant valence state. Unlike the Sr-Nd isotope compositions of scheelite from vein-type Au-(W) and W-(Sb-Au) deposits, the scheelite from skarn-type W-Mo deposits has low ( 143 Nd/ 144 Nd)(t) (most 〈0.5125) and intermediate ( 87 Sr/ 86 Sr)(t) values (most between 0.708 and 0.715). The eNd(t) values of the scheelite varied from –16 to –12.3 in the Baizhangyan deposit and from –9.5 to –9.1 in the Jitoushan deposit, indicating that the ore-forming materials in the two W-Mo deposits were mainly derived from crustal sources.
    Print ISSN: 0003-004X
    Digitale ISSN: 1945-3027
    Thema: Geologie und Paläontologie
    Standort Signatur Erwartet Verfügbarkeit
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  • 9
    Publikationsdatum: 2014-03-28
    Beschreibung: Supercritical carbon dioxide (scCO 2 ) processing has been proven as a method for preparing polymer/montmorillonite (MMT) nanocomposites with improved platelet dispersion. The influence of scCO 2 processing on the shape and size of the MMT tactoid/platelet, which is of great importance to the final platelet dispersion in the polymer matrix, is scarcely reported in the literature. In the present study, the pristine MMT was first surface modified with 3-glycidoxypropyltrimethoxysilane (the grafted MMT is labeled as GMMT), and then intercalated using three kinds of intercalating agents, myristyltrimethylammonium bromide (MTAB), tetradecyltrihexylphosphonium chloride (TDTHP), and ethoxyltriphenylphosphonium chloride (ETPC), in water or scCO 2 , to study the effect of intercalating agent type and intercalation method on the morphology and thermal properties of GMMT, as a part of a program devoted to the synthesis of polymer/MMT nanocomposites. The structure of intercalated GMMT was characterized by thermogravimetric analysis, X-ray powder diffraction, and scanning electron microscopy (SEM). The optimum intercalation conditions in scCO 2 were established by trying a range of reaction times and pressures. The structures of intercalated GMMT obtained under optimum scCO 2 conditions and water were compared. The basal spacing of GMMT intercalated in scCO 2 was almost the same as that in water, and both were obviously larger than that of GMMT. The GMMT exhibited a compact spherical morphology (examined using SEM), and the surface structures (including surface morphology, surface roughness, and surface compactness) of samples intercalated in water became ‘less compact’ and the degree of the ‘compactness’ of samples intercalated in scCO 2 decreased further. Whether in water or scCO 2 , samples intercalated with TDTHP exhibited a larger basal spacing and the extent of disorder increased compared to that for samples intercalated with MTAB. The pristine MMT was also intercalated for comparison and silane grafting was proven to contribute to the increased basal spacing and ‘less compact’ surface structure.
    Print ISSN: 0009-8604
    Digitale ISSN: 1552-8367
    Thema: Geologie und Paläontologie
    Publiziert von Clay Minerals Society
    Standort Signatur Erwartet Verfügbarkeit
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  • 10
    Publikationsdatum: 2011-09-09
    Beschreibung: The Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on board the Canadian SCISAT-1 satellite (launched in August 2003) measures over 30 different atmospheric species, including six nitrogen trace gases that are needed to quantify the stratospheric NOy budget. We combine volume mixing ratio (VMR) profiles for NO, NO2, HNO3, N2O5, ClONO2, and HNO4 to determine a zonally averaged NOy climatology on monthly and 3 month combined means (December–February, March–May, June–August, and September–November) at 5° latitude spacing and on 33 pressure surfaces. Peak NOy VMR concentrations (15–20 ppbv) are situated at about 3 hPa (∼40 km) in the tropics, while they are typically lower at about 10 hPa (∼30 km) in the midlatitudes. Mean NOy VMRs are similar in both the northern and southern polar regions, with the exception of large enhancements periodically observed in the upper stratosphere and lower mesosphere. These are primarily due to enhancements of NO due to energetic particle precipitation and downward transport. Other features in the NOy budget are related to descent in the polar vortex, heterogeneous chemistry, and denitrification processes. Comparison of the ACE-FTS NOy budget is made to both the Odin and ATMOS NOy data sets, showing in both cases a good level of agreement, such that relative differences are typically better than 20%. The NOy climatological products are available through the ACE website and are a supplement to the paper.
    Print ISSN: 0148-0227
    Thema: Geologie und Paläontologie , Physik
    Publiziert von Wiley im Namen von American Geophysical Union (AGU).
    Standort Signatur Erwartet Verfügbarkeit
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