Spectroscopic properties of \hbox {Cr}^{3+} in the spinel solid solution \hbox {ZnAl}_{2-x}\hbox {Cr}_{x}\hbox {O}_4     

Louisiane Verger  Olivier Dargaud  Gwenaelle Rousse  Emese Rozsályi  Amélie Juhin  Delphine Cabaret  Marine Cotte  Pieter Glatzel  Laurent Cormier 《Physics and Chemistry of Minerals》2016,43(1):33-42

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Statistics of velocity centroids: effects of density–velocity correlations and non-Gaussianity     

A. Esquivel  A. Lazarian  S. Horibe  J. Cho  V. Ossenkopf  J. Stutzki 《Monthly notices of the Royal Astronomical Society》2007,381(4):1733-1744

We continue with our previous work on statistics of velocity centroids, to retrieve information about the scaling properties of an underlying turbulent velocity field from spectroscopic observations. We use synthetic data sets with extreme effects of velocity–density correlations that we create artificially, which also have a non-Gaussian distribution of fluctuations. We confirm that centroids can be used to obtain the scaling properties of the turbulent velocity when the ratio of the density dispersion to the mean density is less than unity, regardless of velocity–density correlations and non-Gaussianity. It was found that extreme velocity–density correlations can distort the statistics of velocity centroids, impeding the recovery of the turbulent velocity spectral index from centroids. We show that such correlations introduce high-order moments to the maps of centroids, which we disregarded in previous work, but that they are only important when the density dispersion is large in comparison with the mean density. It was also found that non-Gaussian velocity and/or density distort the statistics of centroids too, but to a lower degree than extreme cross-correlations.  相似文献   

Magnetic Reconnection and Turbulent Mixing: From ISM to Clusters of Galaxies     

A. Lazarian  J. Cho 《Astrophysics and Space Science》2004,289(3-4):307-318

Magnetic reconnection, or the ability of the magnetic field lines that are frozen in plasma to change their topology, is a fundamental problem of magnetohydrodynamics (MHD). Webriefly examine the problem starting with the well-known Sweet-Parker scheme, discuss effectsof tearing modes, anomalous resistivity and the concept of hyperresistivity. We show that the field stochasticity by itself provides a way toenable fast reconnection even if, at the scale of individual turbulent wiggles,the reconnection happens at the slow Sweet-Parker rate. We show that fast reconnectionallows efficient mixing of magnetic field in the direction perpendicular tothe local direction of magnetic field. While the idea of stochastic reconnection still requiresnumerical confirmation,our numerical simulations testify that mixing motions perpendicular to the local magnetic field are upto high degree hydrodynamical. This suggests that the turbulent heattransport should be similar to that in non-magnetized turbulent fluid, namely,should have a diffusion coefficient ～V _L L, whereV _L is the amplitude of the turbulent velocity and L is the scale of the turbulent motions. We present numericalsimulations which support this conclusion. The applicationof this idea to thermal conductivity in clusters of galaxies shows that thismechanism may dominate the diffusion of heat and may be efficient enoughto prevent cooling flow formation.  相似文献   

The Atmospheric Boundary Layer Over Baltic Sea Ice   总被引：4，自引：0，他引：4  

Burghard?BrümmerEmail author  Amèlie?Kirchg??ner  Gerd?Müller 《Boundary-Layer Meteorology》2005,117(1):91-109

A new parametrization for the surface energy balance of urban areas is presented. It is shown that this new method can represent some of the important urban phenomena, such as an urban heat island and the occurrence of a near-neutral nocturnal boundary layer with associated positive turbulent heat fluxes, unlike the traditional method for representing urban areas within operational numerical weather prediction (NWP) models. The basis of the new parametrization is simple and can be applied easily within an operational NWP model. Also, it has no additional computational expense compared to the traditional scheme and is hence applicable for operational forecasting requirements. The results show that the errors for London within the Met Office operational mesoscale model have been significantly reduced since the new scheme was introduced. The bias and root-mean-square (rms) errors have been approximately halved, with the rms error now similar to the model as a whole. The results also show that a seasonal cycle still exists in the model errors, but it is suggested that this may be caused by anthropogenic heat sources that are neglected in the urban scheme.The British Crowns right to retain a non-exclusive royalty-free license in and to any copyright is acknowledged.  相似文献   

THE NEW PETROLOGY     

CHARLES P.BERKEY 《地质学报》1922,(1)

I suppose that one is not far wrong in saying that Petrology is thescience of rocks.But we have not made ourselves very clear by saying it.To the average student of the subject.who must judge from what he is taught,  相似文献   

A note on linear dispersion and shoaling properties in extended Boussinesq equations   总被引：1，自引：0，他引：1  

C. Lee  Y. -S. Cho  S. B. Yoon 《Ocean Engineering》2003,30(14):1849-1867

A set of optimum parameter α is obtained to evaluate the linear dispersion and shoaling properties in the extended Boussinesq equations of [Madsen and Sorensen, 1992 and Nwogu, 1993], and [Chen and Liu, 1995]. Optimum α values are determined to produce minimal errors in each wave property of phase velocity, group velocity, or shoaling coefficient relative to the analytical one given by the Stokes wave theory. Comparisons are made of the percent errors in phase velocity, group velocity, and shoaling coefficient produced by the Boussinesq equations with a different set of optimum α values. The case with a fixed value of α = −0.4 is also presented in the comparison. The comparisons reveal that the optimum α value tuned for a particular wave property gives in general poor results for other properties. Considering all the properties simultaneously, the fixed value of α = −0.4 may give overall accuracies in phase velocity and shoaling coefficient for all the types of Boussinesq equations selected in this study.  相似文献   

Two-dimensional wave-current interaction with a locally enriched quadtree grid system     

Koo-Yong Park  Alistair G.L. Borthwick  Yong-Sik Cho   《Ocean Engineering》2006,33(2):247-263

Wave-induced currents may drive nearshore mixing and transport processes, including coastal pollutant dispersion, littoral drift, and long-term morphological changes through beach erosion and accretion. In this study, a numerical model is newly developed to simulate wave climate and localized currents in complicated coastal environments. The model developed is based on a quadtree grid system. The two-dimensional hydrodynamic governing equations are solved by using an explicit Adams-Bashforth finite difference scheme. Effects of wave breaking, shoaling, refraction, diffraction, wave-current interaction, set-up and set-down, turbulent mixing, bed friction, and shoreline movement are incorporated in the model. Results are presented for set-up at a beach in a flume due to normally incident waves, and longshore currents generated by oblique waves on a plane beach.  相似文献   

Changes in spatial variations of sap flow in Korean pine trees due to environmental factors and their effects on estimates of stand transpiration     

Minkyu Moon  Taekyu Kim  Juhan Park  Sungsik Cho  Daun Ryu  Sanguk Suh  Hyun Seok Kim 《山地科学学报》2016,13(6):1024-1034

It is difficult to scale up measurements of the sap flux density (Js) for the characterization of tree or stand transpiration (E) due to spatial variations in JS and their temporal changes. To assess spatial variations in the sap flux density of Korean pine (Pinus koraiensis) and their effects on E estimates, we measured the Js using Granier-type sensors. Within trees, the Js decreased exponentially with the radial depth, and the Js of the east aspects were higher than those of the west aspects. Among trees, there was a positive relationship between Js and the tree diameter at breast height, and this positive relationship became stronger as the transpiration demand increased. The spatial variations that caused large errors in E estimates (i.e., up to 110.8 % when radial variation was ignored) had varied systematically with environmental factors systematic characteristics in relation to environmental factors. However, changes in these variations did not generate substantial errors in the E estimates. For our study periods, the differences in the daily E (E _D) calculated by ignoring radial, azimuthal and tree-to-tree variations and the measured E _D were fairly constant, especially when the daily vapor pressure deficit (D__D) was higher than 0.6 kPa. These results imply that the effect of spatial variations changes on sap flow can be a minor source of error compared with spatial variations (radial, azimuthal and tree-to-tree variations) when considering E estimates.  相似文献   

A study on the predictability of the transition day from the dry to the rainy season over South Korea     

Sang-Min Lee  Ji-Eun Nam  Hee-Wook Choi  Jong-Chul Ha  Yong Hee Lee  Yeon-Hee Kim  Hyun-Suk Kang  ChunHo Cho 《Theoretical and Applied Climatology》2016,125(3-4):449-467

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Ambient air metallic elements (Mn,Fe, Zn,Cr, Cu,and Pb) pollutants sources study at a rural resident area near Taichung Thermal Power Plant and Industrial Park: 6-month observations     

Guor-Cheng Fang  Yuan-Jie Zhuang  Yu-Chen Kuo  Meng-Hsien Cho 《Environmental Earth Sciences》2016,75(7):587

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