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  • 1
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    Percolation connectivity, pore size and gas apparent permeability: network simulations and comparison to experimental data (2017)
    Wiley
    Details
    Publication Date: 2017-07-01
    Description: We modeled single-phase gas flow through porous media using percolation networks. Gas permeability is different from liquid permeability. The latter is only related to the geometry and topology of the pore space while the former depends on the specific gas considered and varies with gas pressure. As gas pressure decreases, four flow regimes can be distinguished as viscous flow, slip flow, transition flow and free molecular diffusion. Here, we use a published conductance model presumably capable of predicting the flow rate of an arbitrary gas through a cylindrical pipe in the four regimes. We incorporated this model into pipe network simulations. We considered 3D simple cubic, BCC and FCC lattices, in which we varied the pipe radius distribution and the bond coordination number. Gas flow was simulated at different gas pressures. The simulation results showed that the gas apparent permeability k app obeys an identical scaling law in all three lattices, k app ~( z - z c ) β , where the exponent β depends on the width of the pipe radius distribution, z is the mean coordination number and z c its critical value at the percolation threshold. Surprisingly, ( z - z c ) had a very weak effect on the ratio of the apparent gas permeability to the absolute liquid permeability, k app / k abs , suggesting that the Klinkenberg gas slippage correction factor is nearly independent of connectivity. We constructed models of k app and k app / k abs based on the observed power law and tested them by comparison with published experimental data on glass beads and other materials.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Lower Thermospheric Enhanced Sodium Layers Observed at Low Latitude and Possible Formation: Case Studies (2013)
    Wiley
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    Publication Date: 2013-02-28
    Description: [1]  We report two lower thermospheric enhanced sodium layer (TeSL) cases observed at a low latitude station, Lijiang, China (26.7°N, 100.0°E), on March 10 and April 10, 2012, respectively. The TeSLs in the two cases were located at altitudes near 122 and 112 km, respectively. In addition, strong sporadic sodium layers (SSLs) near 100 km accompanied the TeSL observed on March 10, 2012. Both the TeSLs and SSLs exhibited tidal-induced downward motion. The adjacent ground-based and space-borne ionospheric radio observations showed strong Es layers before the appearance of the TeSLs, suggesting an " Es – TeSLs (SSLs)" chain formed through the tidal wind shear mechanism. Assuming that the vertical tidal wavelengths remain unchanged, it is found that in different regions caused by the tidal wind shear, different TeSLs evolution processes are expected: (1) in a tidal-convergence region, a TeSL/SSL with a downward propagation phase is enhanced due to a rapid decrease in the Na + lifetime at the lower altitude; (2) in an ion convergence-divergence interface region, a TeSL/SSL will still follow the tidal downward phase progression, but sodium density does not exhibit evident enhancement; and (3) when a TeSL/SSL enters into a tidal wind-divergence zone, the layer density tends to decrease.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
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    Blind Thrusting, Surface Folding and the Development of Geological Structure in the Mw 6.3 2015 Pishan (China) Earthquake (2017)
    Wiley
    Details
    Publication Date: 2017-10-25
    Description: The relationship between individual earthquakes and the longer-term growth of topography and of geological structures is not fully understood, but is key to our ability to make use of topographic and geological datasets in the contexts of seismic hazard and wider-scale tectonics. Here we investigate those relationships at an active fold-and-thrust belt in the southwest Tarim Basin, Central Asia. We use seismic waveforms and interferometric synthetic aperture radar (InSAR) to determine the fault parameters and slip distribution of the 2015 M w  6.3 Pishan earthquake - a blind, reverse-faulting event dipping towards the Tibetan Plateau. Our earthquake mechanism and location correspond closely to a fault mapped independently by seismic reflection, indicating that the earthquake was on a pre-existing ramp fault over a depth range of ∼9–13 km. However, the geometry of folding in the overlying fluvial terraces cannot be fully explained by repeated coseismic slip in events such as the 2015 earthquake nor by the early postseismic motion shown in our interferograms; a key role in growth of the topography must be played by other mechanisms. The earthquake occurred at the Tarim-Tibet boundary, with the unusually low dip of 21° . We use our source models from Pishan and a 2012 event to argue that the Tarim Basin crust deforms only by brittle failure on faults whose effective coefficient of friction is ≤0.05±0.025. In contrast, most of the Tibetan crust undergoes ductile deformation, with a viscosity of order 10 20 –10 22  Pa s. This contrast in rheologies provides an explanation for the low dip of the earthquake fault plane.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
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    Estimation of atmospheric aerosol composition from ground-based remote sensing measurements of sun-sky radiometer (2016)
    Wiley
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    Publication Date: 2016-12-27
    Description: Remote sensing provides aerosol loading information, but to address climate and air quality model validation, there are additional needs to acquire aerosol composition information. In this study, a comprehensive aerosol composition model is established to quantify black carbon (BC), brown carbon (BrC), mineral dust (DU), particulate organic matters (POM), ammonium sulfate-like (AS), sea salt (SS) and aerosol water uptake (AW). We develop forward modeling of aerosol components, including microphysical parameters (real and imaginary refractive indices, volume fraction ratio of fine to coarse mode and sphericity) and hygroscopic growth models, and propose an optimization scheme to estimate the components. The uncertainties caused by input parameters are also assessed. Sun-sky radiometer measurements, meteorological data and chemical measurements obtained during a campaign in Huairou, Beijing, are processed to estimate aerosol components, which are further compared with in-situ synchronous chemical measurements. The results show generally good consistencies between remotely estimated and measured components (e.g., correlation coefficients for BC, BrC, AS and PM 2.5 lie in about 0.8-0.9). The comparisons between modeled and observed microphysical parameters also show good agreements, with the exception of sphericity, which is likely caused by high uncertainties of this parameter. Sensitivity studies show that BC and BrC are highly sensitive to imaginary refractive index, while DU is strongly correlated to both volume size and sphericity. The performance of composition retrieval is expected to be improved when the sphericity uncertainty is significantly reduced.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 5
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    Density waves in Titan's upper atmosphere (2013)
    Wiley
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    Publication Date: 2013-12-17
    Description: [1]  Analysis of the Cassini Ion Neutral Mass Spectrometer data reveals the omnipresence of density waves in various constituents of Titan's upper atmosphere, with quasi-periodical structures visible for N 2 , CH 4 , 29 N 2 and some of the minor constituents. The N 2 amplitude lies in the range of ≈ 4%-16% with a mean of ≈ 8%. Compositional variation is clearly seen as a sequence of decreasing amplitude with increasing scale height. The observed vertical variation of amplitude implies significant wave dissipation in different constituents, possibly contributed by molecular viscosity for N 2 but by both molecular viscosity and binary diffusion for the others. A wave train with near horizontally propagating wave energy and characterized by a wavelength of ≈ 730 km and a wave period of ≈ 10 hr is found to best reproduce various aspects of the observations in a globally averaged sense. Some horizontal and seasonal trends in wave activity are identified, suggesting a connection between the mechanism driving the overall variability in the background atmosphere and the mechanism driving the waves. No clear association of wave activity with magnetospheric particle precipitation can be identified from the data.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    A case study of typhoon-induced gravity waves and the orographic impacts related to Typhoon Mindulle (2004) over Taiwan (2015)
    Wiley
    Details
    Publication Date: 2015-08-27
    Description: Atmospheric gravity waves (GWs) significantly influence global circulation. Deep convection, particularly that associated with typhoons, is believed to be an important source of gravity waves. Stratospheric gravity waves induced by Typhoon Mindulle (2004) were detected by the Atmospheric Infrared Sounder (AIRS). Semicircular GWs with horizontal wavelengths of 100–400 km were found over Taiwan through an inspection of AIRS radiances at 4.3 μ m. Characteristics of the stratospheric gravity waves generated by Typhoon Mindulle were investigated using the Weather Research and Forecasting (WRF) model. The initial and boundary data were determined by the high-resolution European Center for Medium-Range Weather Forecasts (ECMWF) re-analysis data. The WRF simulation reproduces the main features of Typhoon Mindulle and the significant GWs. The simulated GWs with horizontal wavelengths of 100–400 km match the AIRS observations: they propagate upward and eastward, and the westward components are mostly filtered in the stratosphere. By comparing the measured waves with a WRF simulation in the absent of orography (WRF-FLAT), we find that the orographic gravity waves (OGWs) generated by the flow of Typhoon Mindulle over the Central Mountain Range (CMR) in Taiwan account for approximately 50% of the total wave momentum flux in the troposphere. The dominant orientation of the OGW wave fronts is parallel to the CMR rideline. When entering into the stratosphere, OGW propagation is determined by the position of the typhoon center relative to the CMR.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
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  • 7
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    Relatively stable response of fruiting stage to warming and cooling relative to other phenological events (2016)
    Wiley
    In: Ecology
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    Publication Date: 2016-05-06
    Description: The timing of the fruit-set stage (i.e. start and end of fruit set) is crucial in a plant's life cycle, but its response to temperature change is still unclear. We investigated the timing of seven phenological events, including fruit-set dates during 3 years for six alpine plants transplanted to warmer (+ ~3.5 °C in soils) and cooler (- ~3.5 °C in soils) locations along an altitudinal gradient in the Tibetan area. We found that fruit-set dates remained relatively stable under both warming and cooling during the 3-years transplant experiment. Three earlier phenological events (emergence of first leaf, first bud set, and first flowering) and two later phenological events (first leaf coloring and complete leaf coloring) were earlier by 4.8-8.2 days °C −1 and later by 3.2-7.1 days °C −1 in response to warming. Conversely, cooling delayed the three earlier events by 3.8-6.9 days °C −1 and advanced the two later events by 3.2-8.1 days °C −1 for all plant species. The timing of the first and/or last fruit-set dates, however, did not change significantly compared to earlier and later phenological events. Statistical analyses also showed that the dates of fruit set were not significantly correlated or had lower correlations with changes of soil temperature relative to the earlier and later phenological events. Alpine plants may thus acclimate to changes in temperature for their fruiting function by maintaining relatively stable timings of fruit set compared with other phenological events to maximize the success of seed maturation and dispersal in response to short-term warming or cooling. This article is protected by copyright. All rights reserved.
    Print ISSN: 0012-9658
    Electronic ISSN: 1939-9170
    Topics: Biology
    Published by Wiley on behalf of The Ecological Society of America (ESA).
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  • 8
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    Along-axis variation in crustal thickness at the ultraslow spreading Southwest Indian Ridge (50°E) from a wide-angle seismic experiment (2015)
    Wiley
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    Publication Date: 2015-01-29
    Description: The Southwest Indian Ridge (SWIR) is characterized by an ultraslow spreading rate, thin crust and extensive outcrops of serpentinized peridotite. Previous studies have used geochemical and geophysical data to suggest the presence of a thicker crust at the central and shallowest portions of the SWIR, from the Prince Edward (35°30′E) to the Gallieni (52°20′E) fracture zones. Here we present a new analysis of wide-angle seismic data along the ridge 49°17′E - 50°49′E. Our main conclusions are as follows: 1) we find an oceanic layer 2 of roughly constant thickness and steep velocity gradient, underlain by a layer 3 with variable thickness and low velocity gradient; 2) the crustal thickness varies from c. 5 km beneath non-transform discontinuities (NTDs) up to c. 10km beneath a segment center; 3) the melt supply is focused in segment centers despite a small NTD between adjacent segments; 4) the presence of a normal upper mantle velocity indicates that no serpentinization occurs beneath this thick crust. Our observation of thick crust at an ultra-slow spreading ridge adds further complexity to relationships between crustal thickness and spreading rate, and supports previous suggestions that the extent of mantle melting is not a simple function of spreading rate, and that mantle temperature or chemistry (or both) must vary significantly along-axis. This article is protected by copyright. All rights reserved.
    Electronic ISSN: 1525-2027
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
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    New Konjac Glucomannan-PVA Composite Membrane for Application in Pervaporation Dehydration of Caprolactam Solution (2012)
    Wiley
    Details
    Publication Date: 2012-05-11
    Description: Konjac glucomannan (KGM)-polyvinyl alcohol (PVA) composite membranes were investigated with the aim of proposing an improved caprolactam pervaporation dehydration process. The composite membranes were characterized by FTIR, SEM, XRD and degree of swelling measurements. The effect of the proportion of KGM in the composite membranes on pervaporation performance was studied. The best separation factor was achieved with an appropriate content of KGM. Both too much and too little KGM can lead to a low separation factor. Besides, pervaporation performance data showed that a higher separation factor could result in lower caprolactam concentration and operating temperature. Evaluation results indicated that the separation performances of KGM-PVA composite membranes were strongly related to their intrinsic structure and to operating parameters. Polyvinyl alcohol (PVA) was modified by blending with Konjac glucomannan (KGM) to control water solubility as a KGM-PVA blend active layer. According to evaluation results, the separation performances of the novel KGM-PVA composite membranes were strongly related to their intrinsic structure and to operating parameters.
    Print ISSN: 0930-7516
    Electronic ISSN: 1521-4125
    Topics: Chemistry and Pharmacology , Process Engineering, Biotechnology, Nutrition Technology
    Published by Wiley
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  • 10
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    The impact of precipitating ice and snow on the radiation balance in global climate models (2011)
    Wiley
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    Publication Date: 2011-03-23
    Description: Climate models often ignore the radiative impact of precipitating hydrometeors. CloudSat retrievals provide the first means to distinguish between cloud versus precipitating ice mass and characterize its vertical structure. With this information, radiative transfer calculations are performed to examine the impact of excluding precipitating ice on atmospheric radiative fluxes and heating rates. The preliminary results show that such exclusion can result in underestimates of the reflective shortwave flux at the top of the atmosphere (TOA) and overestimates of the downwelling surface shortwave and emitted TOA longwave flux, with the differences being about 5–10 Wm−2 in the most convective and rainfall intensive areas and greatest for the TOA longwave flux. There are also considerable differences (∼10–25%) in the vertical profiles of shortwave and longwave heating, resulting in an overestimation (∼up to 10%) of the integrated column cooling. The implications of these results are that models that exclude these ice components are achieving TOA radiation balance through compensating errors as well as possibly introducing biases in atmospheric circulations.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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