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  • Articles  (66)
  • Geosciences  (66)
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  • Articles  (66)
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  • 1
    Publication Date: 2015-12-24
    Description: The Sanjiang Plain (SJP) wetland is the largest freshwater marshland in China. Peatlands were initiated early and are widely distributed across the SJP and form a large carbon (C) pool. Consequently, there is a growing interest in understanding past, present, and future peatland dynamics. Most studies on peatland dynamics have been carried out on boreal and subarctic region; however, there are limited data about peatland dynamics on temperate region, such as SJP wetland, which is sensitive to climate change and human disturbance. Here, we presented a data synthesis of basal peat ages, peatland area, and peat C accumulation rate in the SJP to examine Holocene peatland dynamics and climate sensitivity, along with total C storage and their future fate. We show that peatland initiation in the SJP started in the early Holocene, but the most intense period of peatland initiation occurred during the late Holocene, when the climate was colder and drier than the early and mid-Holocene. And the C accumulation rate also continued to increase during the late Holocene. Our results suggest that insolation and monsoon intensity as well as the local topographic characteristics and hydrology during the late Holocene in the SJP might have played an important role in causing the highest rates of peatland initiation and C accumulation. Based on the Second National Wetland Resources Survey data, we estimated that the total peatland covered an area of about 10,520 km 2 on the SJP and currently stores ~0.26 Pg C. However, human activities, together with the widespread warming on the SJP over the past 60 years, not only reduce the area of wetlands but also have switched it from being a net C sink to a significant C source.
    Print ISSN: 0959-6836
    Electronic ISSN: 1477-0911
    Topics: Geography , Geosciences
    Published by Sage
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  • 2
    Publication Date: 2014-06-03
    Description: A stochastic approach has been developed to model the positions of BC/dust internally mixed with two snow-grain types: hexagonal plate/column (convex) and Koch snowflake (concave). Subsequently, light absorption and scattering analysis can be followed by means of an improved geometric-optics approach coupled with Monte Carlo photon tracing to determine BC/dust single-scattering properties. For a given shape (plate, Koch snowflake, spheroid, or sphere), the action of internal mixing absorbs substantially more light than external mixing. The snow-grain shape effect on absorption is relatively small, but its effect on asymmetry factor is substantial. Due to a greater probability of intercepting photons, multiple inclusions of BC/dust exhibit a larger absorption than an equal-volume single inclusion. The spectral absorption (0.2 – 5  μ m) for snow grains internally mixed with BC/dust is confined to wavelengths shorter than about 1.4  μ m, beyond which ice absorption predominates. Based on the single-scattering properties determined from stochastic and light absorption parameterizations and using the adding/doubling method for spectral radiative transfer, we find that internal mixing reduces snow albedo substantially more than external mixing and that the snow-grain shape plays a critical role in snow albedo calculations through its forward scattering strength. Also, multiple inclusion of BC/dust significantly reduces snow albedo as compared to an equal-volume single sphere. For application to land/snow models, we propose a two-layer spectral snow parameterization involving contaminated fresh snow on top of old snow for investigating and understanding the climatic impact of multiple BC/dust internal mixing associated with snow grain metamorphism, particularly over mountain/snow topography.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
    Publication Date: 2013-03-22
    Description: A bstract A thalattosaur taxon, Concavispina biseridens , was recently named and briefly described. It is described here in detail and compared with other thalattosaurs, especially Xinpusaurus. Concavispina is characterized by a long skull, measuring approximately half the length of presacral portion of the vertebral column, two rows of blunt teeth on the anterior part of the maxilla, and neural spines that have convex anterior or posterior margins and V-shaped notches in their dorsal margins. Concavispina differs from all thalattosaurs except Xinpusaurus in that the anterior end of the maxilla is curved dorsally, less than five cervical vertebrae are present, and the proximal end of the humerus is wider than the distal end. Phylogenetic analysis of 40 characters suggests that Miodentosaurus occupies a basal position within Askeptosauridea, Paralonectes is the basalmost member of Thalattosauridea, Concavispina may form a clade with Xinpusaurus , and Chinese thalattosaurs do not have a close relationship with eastern Pacific forms as suggested by previous studies. Concavispina may have been similar to Xinpusaurus in overall locomotor style, but probably had a poorer swimming ability. Concavispina likely differed from Xinpusaurus in diet, for example by depending on softer food.
    Print ISSN: 0022-3360
    Electronic ISSN: 1937-2337
    Topics: Geosciences
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  • 4
    Publication Date: 2015-11-18
    Description: Solar irradiance changes are thought to play an important role in natural climate variability. How the hydrological conditions were affected by solar irradiance in westerly-controlled arid central Asia (ACA) on decadal/centennial timescales remains poorly understood because of the lack of high-quality records. Here, we integrate 1.2-year-resolution x-ray fluorescence (XRF) scanner-derived carbonate accumulation estimates with 6-year-resolution biomarker and magnetic records in a well-preserved shoreline core from Lake Manas, northwestern China, to reconstruct lake level fluctuations and potential solar imprints over the last millennium. Besides the generally confirmed cool-wet/warm-dry climate pattern in ACA, our data also consistently show frequent and substantial lake level fluctuations, resembling solar activity changes, especially during the ‘Little Ice Age’. Wavelet spectral analyses of our XRF data indicate strong 8- to 16-year, 64- to 128-year and 128- to 256-year cycles, coinciding with the ~11-year Schwabe cycle, ~70- to 100-year Gleissberg cycle, and the ~200-year Suess-de Vries cycle. We therefore suggest the existence of solar imprints on effective moisture fluctuations in ACA over the last millennium, and the potential occurrence of the Schwabe cycle even during the solar minima.
    Print ISSN: 0959-6836
    Electronic ISSN: 1477-0911
    Topics: Geography , Geosciences
    Published by Sage
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  • 5
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Journal of Crystal Growth 132 (1993), S. 609-610 
    ISSN: 0022-0248
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Rock mechanics and rock engineering 23 (1990), S. 261-273 
    ISSN: 1434-453X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Notes: Summary First, Class II behaviour of rock is discussed with a spring model. The model is characterized by non-uniform failure, which agrees qualitatively with common experimental observation, and shows not only class I but also class II behaviour depending on strength variation of springs. Focusing on the difference between class I and class II behaviour in actual rocks, unloading-reloading tests were conducted in the post-failure region. From the test results, it was found that for both class I and class II rocks, the elastic strain tends to decrease in the post-failure region as the loadbearing capacity deteriorates. The results also show that a remarkable difference between class I and class II categories is the magnitude of non-elastic strain. That is, if non-elastic strain increases faster that elastic strain decreases, then rock shows class I behaviour, and in the opposite case class II behaviour. In general, the non-elastic strain increases with confining pressure and in some cases, rock behaviour changes from class II to class 1 at higher confining pressure.
    Type of Medium: Electronic Resource
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  • 7
    Publication Date: 2015-04-16
    Description: The title compound, C19H20N4O3S, was synthesized by refluxing equimolar amounts of 1-phenyl-3-methyl-4-propionylpyrazol-5-one and benzenesulfonyl hydrazide in ethanol. The compound crystallizes in the keto form and the carbonyl O atom forms an intramolecular N—H...O hydrogen bond with the neighbouring NH group. There is also C—H...O short contact involving the neighbouring phenyl ring. Probably as a result of this, the phenyl ring is inclined to the pyrazolone ring by only 7.58 (12)°. The dihedral angle between the phenyl ring and the benzenesulfonyl ring is 22.78 (11)°. In the crystal, molecules are linked by pairs of N—H...O hydrogen bonds, forming inversion dimers with an R22(14) ring motif. The dimers are linked via pairs of C—H...O hydrogen bonds, forming chains propagating along [100].
    Keywords: crystal structurepyrazolone derivativehydrogen bondingpolymer chain
    Electronic ISSN: 1600-5368
    Topics: Chemistry and Pharmacology , Geosciences
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  • 8
    Publication Date: 2015-12-30
    Description: For more than a decade, scientists have argued about the warmth of the current interglaciation. Was the warmth of the pre-industrial late Holocene natural in origin, the result of orbital changes that had not yet driven the system into a new glacial state? Or was it in considerable degree the result of humans intervening in the climate system through greenhouse gas emissions from early agriculture? Here we summarize new evidence that moves this debate forward by testing both hypotheses. By comparing late Holocene responses to those that occurred during previous interglaciations (in part 2), we assess whether the late Holocene responses look different (and thus anthropogenic) or similar (and thus natural). This comparison reveals anomalous (anthropogenic) signals. In part 3, we review paleoecological and archaeological syntheses that provide ground-truth evidence on early anthropogenic releases of greenhouse gases. The available data document large early anthropogenic emissions consistent with the anthropogenic ice-core anomalies, but more information is needed to constrain their size. A final section compares natural and anthropogenic interpretations of the δ 13 C trend in ice-core CO 2 .
    Print ISSN: 8755-1209
    Topics: Geosciences
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
    Publication Date: 2016-06-10
    Description: This study extends the linear spectral-element method (SEM) program SPECFEM3D to include nonlinear constitutive relationships. The iterations for solving the nonlinear equations are bypassed considering that the explicit integration used in the code requires a very small time increment; as a result, the high efficiency of the original linear procedure is preserved. This nonlinear code allows us to perform a deterministic seismic-hazard analysis that considers the nonlinear behaviors of the propagation path and local site for an engineering site. After checking its accuracy against the commercial finite-element method program ABAQUS, the extended nonlinear SEM is used to investigate the effect of noncausative faults on the seismic ground motion at the Dagangshan dam site in Southwest China. The analysis of the study case shows that the isolation effect of noncausative faults is dependent on the fault-source relative position, and the nonlinear responses of the faults are sensitive to earthquake magnitude.
    Print ISSN: 0037-1106
    Electronic ISSN: 1943-3573
    Topics: Geosciences , Physics
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  • 10
    Publication Date: 2014-05-04
    Description: The recent launching of Van Allen probes provides an unprecedent opportunity to investigate variations of the radiation belt relativistic electrons. During the March 17–19 2013 storm, the Van Allen probes simultaneously detected strong chorus waves and substantial increases in fluxes of relativistic (2–4.5 MeV) electrons around L  = 4.5. Chorus waves occurred within the lower-band 0.1–0.5 f ce (the electron equatorial gyrofrequency), with a peak spectral density ~10 −4 nT 2 /Hz. Correspondingly, relativistic electron fluxes increased by a factor of 10 2 –10 3 during the recovery phase compared to the main phase levels. By means of a Gaussian fit to the observed chorus spectra, the drift and bounce-averaged diffusion coefficients are calculated and then used to solve a 2D Fokker-Planck diffusion equation. Numerical simulations demonstrate that the lower-band chorus waves indeed produce such huge enhancements in relativistic electron fluxes within 15 hours, fitting well with the observation.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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