Inter-annual variability of precipitation over Southern Mexico and Central America and its relationship to sea surface temperature from a set of future projections from CMIP5 GCMs and RegCM4 CORDEX simulations     

Ramón Fuentes-Franco  Erika Coppola  Filippo Giorgi  Edgar G. Pavia  Gulilat Tefera Diro  Federico Graef 《Climate Dynamics》2015,45(1-2):425-440

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First-principles investigation of the lattice vibrations in the alkali feldspar solid solution     

Artur Benisek  Edgar Dachs  Michael Grodzicki 《Physics and Chemistry of Minerals》2015,42(3):243-249

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On the nature of the excess heat capacity of mixing     

Artur Benisek  Edgar Dachs 《Physics and Chemistry of Minerals》2011,38(3):185-191

The excess vibrational entropy (ΔS _vib^ex) of several silicate solid solutions are found to be linearly correlated with the differences in end-member volumes (ΔV _i ) and end-member bulk moduli (Δκ _i ). If a substitution produces both, larger and elastically stiffer polyhedra, then the substituted ion will find itself in a strong enlarged structure. The frequency of its vibration is decreased because of the increase in bond lengths. Lowering of frequencies produces larger heat capacities, which give rise to positive excess vibrational entropies. If a substitution produces larger but elastically softer polyhedra, then increase and decrease of mean bond lengths may be similar in magnitude and their effect on the vibrational entropy tends to be compensated. The empirical relationship between ΔS _vib^ex, ΔV _i and Δκ _i , as described by ΔS _vib^ex = (ΔV _i  + mΔκ _i )f, was calibrated on six silicate solid solutions (analbite–sanidine, pyrope–grossular, forsterite–fayalite, analbite–anorthite, anorthite–sanidine, CaTs–diopside) yielding m = 0.0246 and f = 2.926. It allows the prediction of ΔS _vib^ex behaviour of a solid solution based on its volume and bulk moduli end-member data.  相似文献   

The Critical Richardson Number and Limits of Applicability of Local Similarity Theory in the Stable Boundary Layer   总被引：7，自引：7，他引：0  

Andrey A. Grachev  Edgar L Andreas  Christopher W. Fairall  Peter S. Guest  P. Ola G. Persson 《Boundary-Layer Meteorology》2013,147(1):51-82

Measurements of atmospheric turbulence made over the Arctic pack ice during the Surface Heat Budget of the Arctic Ocean experiment (SHEBA) are used to determine the limits of applicability of Monin–Obukhov similarity theory (in the local scaling formulation) in the stable atmospheric boundary layer. Based on the spectral analysis of wind velocity and air temperature fluctuations, it is shown that, when both the gradient Richardson number, Ri, and the flux Richardson number, Rf, exceed a ‘critical value’ of about 0.20–0.25, the inertial subrange associated with the Richardson–Kolmogorov cascade dies out and vertical turbulent fluxes become small. Some small-scale turbulence survives even in this supercritical regime, but this is non-Kolmogorov turbulence, and it decays rapidly with further increasing stability. Similarity theory is based on the turbulent fluxes in the high-frequency part of the spectra that are associated with energy-containing/flux-carrying eddies. Spectral densities in this high-frequency band diminish as the Richardson–Kolmogorov energy cascade weakens; therefore, the applicability of local Monin–Obukhov similarity theory in stable conditions is limited by the inequalities Ri < Ri _cr and Rf < Rf _cr. However, it is found that Rf _cr  =  0.20–0.25 is a primary threshold for applicability. Applying this prerequisite shows that the data follow classical Monin–Obukhov local z-less predictions after the irrelevant cases (turbulence without the Richardson–Kolmogorov cascade) have been filtered out.  相似文献   

Analysis of MESSENGER Gamma-Ray Spectrometer data from the Mercury flybys     

Edgar A. Rhodes  Larry G. Evans  Larry R. Nittler  Richard D. Starr  Ann L. Sprague  David J. Lawrence  Timothy J. McCoy  Karen R. Stockstill-Cahill  John O. Goldsten  Patrick N. Peplowski  David K. Hamara  William V. Boynton  Sean C. Solomon 《Planetary and Space Science》2011,59(15):1829-1841

During its three flybys of Mercury, the MESSENGER spacecraft made the first detection of gamma-ray emission from the planet's surface. With a closest approach distance of ∼200 km, the flybys provided an opportunity to measure elemental abundances of Mercury's near-equatorial regions, which will not be visited at low altitude during MESSENGER's orbital mission phase. Despite being limited by low planetary photon flux, sufficient counts were accumulated during the first two flybys to estimate bounds on abundances for some elements having relatively strong gamma-ray spectral peaks, including Si, Fe, Ti, K, and Th. Only for Si is the standard deviation σ sufficiently small to conclude that this element was detected with 99% confidence. Iron and potassium are detected at the 2−σ (95% confidence) level, whereas only upper bounds on Ti and Th can be determined. Relative to a Si abundance assumed to be 18 weight percent (wt%), 2−σ upper bounds have been estimated as 9.7 wt% for Fe, 7.0 wt% for Ti, 0.087 wt% for K, and 2.2 ppm for Th. The relatively low upper bound on K rules out some previously suggested models for surface composition for the regions sampled. Upper bounds on Fe/Si and Ti/Si ratios are generally consistent with Ti and Fe abundances estimated from the analysis of measurements by the MESSENGER Neutron Spectrometer during the flybys but are also permissive of much lower concentrations.  相似文献   

Predictions of MESSENGER Neutron Spectrometer measurements for Mercury's north polar region     

David J. Lawrence  John K. Harmon  William C. Feldman  John O. Goldsten  David A. Paige  Patrick N. Peplowski  Edgar A. Rhodes  Christina M. Selby  Sean C. Solomon 《Planetary and Space Science》2011,59(13):1665-1669

From radar images of Mercury's poles and MESSENGER Neutron Spectrometer (NS) measurements obtained during the spacecraft's flybys of Mercury, predictions of neutron count rates and their uncertainties are calculated for Mercury's north polar region as of the end of the MESSENGER primary orbital mission. If Mercury's poles contain large amounts of water ice, as has been suggested on the basis of the radar data, then during the one-year-long orbital mission the NS should detect signals indicative of excess polar hydrogen with a significance of at least 4σ, where σ is the standard deviation derived from Poisson counting statistics. If the polar deposits are not enriched with hydrogen, but are dominated by other elements, such as sulfur, then the MESSENGER neutron measurements should be able to confirm the absence of deposits having surface concentrations in excess of 50 wt% H₂O on permanently shadowed floors of craters near Mercury's north pole. Because of the large spatial footprint of the NS data, individual polar deposits will not be spatially resolved, but longitudinal asymmetries may be detected if residual systematic uncertainties are sufficiently low.  相似文献   

Heat capacity,entropy, and phase equilibria of dmitryivanovite     

Wenjun?YongEmail author  Edgar?Dachs  Artur?Benisek  Anthony?C.?Withers  Richard?A.?Secco 《Physics and Chemistry of Minerals》2012,39(3):259-267

The heat capacity (C _p ) of dmitryivanovite synthesized with a cubic press was measured in the temperature range of 5–664 K using the heat capacity option of a physical properties measurement system and a differential scanning calorimeter. The entropy of dmitryivanovite at standard temperature and pressure (STP) was calculated to be 110.1 ± 1.6 J mol⁻¹ K⁻¹ from the measured C _p data. With the help of new phase equilibrium experiments done at 1.5 GPa, the phase transition boundary between krotite and dmitryivanovite was best represented by the equation: P (GPa) = −2.1825 + 0.0025 T (K). From the temperature intercept of this phase boundary and other available thermodynamic data for krotite and dmitryivanovite, the enthalpy of formation and Gibbs free energy of formation of dmitryivanovite at STP were calculated to be −2326.7 ± 2.1 and −2,208.1 ± 2.1 kJ mol⁻¹, respectively. It is also inferred that dmitryivanovite is the stable CaAl₂O₄ phase at STP and has a wide stability field at high pressures whereas the stability field of krotite is located at high temperatures and relatively low pressures. This conclusion is consistent with natural occurrences (in Ca–Al-rich inclusions) of dmitryivanovite and krotite, where the former is interpreted as the shock metamorphic product of originally present krotite.  相似文献   

Heat capacity,entropy and phase equilibria of stishovite     

Wenjun?YongEmail author  Edgar?Dachs  Artur?Benisek  Richard?A.?Secco 《Physics and Chemistry of Minerals》2012,39(2):153-162

The low-temperature heat capacity (C _P) of stishovite (SiO₂) synthesized with a multi-anvil device was measured over the range of 5–303 K using the heat capacity option of a physical properties measurement system (PPMS) and around ambient temperature using a differential scanning calorimeter (DSC). The entropy of stishovite at standard temperature and pressure calculated from DSC-corrected PPMS data is 24.94 J mol⁻¹ K⁻¹, which is considerably smaller (by 2.86 J mol⁻¹ K⁻¹) than that determined from adiabatic calorimetry (Holm et al. in Geochimica et Cosmochimica Acta 31:2289–2307, 1967) and about 4% larger than the recently reported value (Akaogi et al. in Am Mineral 96:1325–1330, 2011). The coesite–stishovite phase transition boundary calculated using the newly determined entropy value of stishovite agrees reasonably well with the previous experimental results by Zhang et al. (Phys Chem Miner 23:1–10, 1996). The calculated phase boundary of kyanite decomposition reaction is most comparable with the experimental study by Irifune et al. (Earth Planet Sci Lett 77:245–256, 1995) at low temperatures around 1,400 K, and the calculated slope in this temperature range is mostly consistent with that determined by in situ X-ray diffraction experiments (Ono et al. in Am Mineral 92:1624–1629, 2007).  相似文献   

Outlier Problem in Evaluating Similarity Functions in the Stable Atmospheric Boundary Layer   总被引：1，自引：1，他引：0  

Andrey A. Grachev  Edgar L. Andreas  Christopher W. Fairall  Peter S. Guest  P. Ola G. Persson 《Boundary-Layer Meteorology》2012,144(2):137-155

The gradient-based similarity approach removes turbulent fluxes as governing parameters and replaces them with vertical gradients of mean wind speed and potential temperature. As a result, the gradient Richardson number, Ri, appears as a stability parameter instead of the Monin–Obukhov stability parameter z/L (L is the Obukhov length). The gradient-based scaling is more appropriate for moderate and very stable conditions when the gradients are large and their errors are relatively small whereas z/L becomes ambiguous in these conditions because turbulent fluxes are small. However, the gradient-based formulation is faced with a problem related to the influence of Ri outliers: outliers with high values of Ri can exist in conditions that are really near-neutral. These outliers are mapped into the very stable range in plots in which Ri is the independent variable and may lead to spurious dependencies for bin-averaged data (spurious bin-averaging). This effect is quite large for functions that are steep for the gradient-based scaling. The present study uses the Surface Heat Budget of the Arctic Ocean (SHEBA) data to examine the problem and proposes two methods, conditional analysis and independent binning, to limit the influence of outliers on bin-averaging. A disadvantage of the conditional analysis is associated with eliminating outliers based on criteria that could be considered as subjective. The independent bin-averaging method does not have this disadvantage, but the scatter of the bin-averaged points is higher than for the conditional analysis, rendering data analysis and interpretation difficult.  相似文献   

Arsenic mobility from anthropogenic impoundment sediments – Consequences of contamination to biota, water and sediments, Poša, Eastern Slovakia     

Edgar Hiller  L&#x;ubomír Jurkovi   Jozef Kordík  Igor Slaninka  Michal Jankulr  Juraj Majzlan  Jrg Gttlicher  Ralph Steininger 《Applied Geochemistry》2009,24(11):2175-2185

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