Flow variability in the Strait of Gibraltar: The Mediterranean adjustment to tidal forcing

The vertical structure of the flow variability through the Strait of Gibraltar is studied based on the Gibraltar Experiment and the Word Ocean Circulation Experiment data sets. An analysis of the leading modes of velocity and density variability at the Strait of Gibraltar showed an adjustment of the water masses exchanged through the Strait. Mediterranean mass variations resulting from the water exchanged by barotropic tidal oscillations generate changes of the baroclinic component of the flow that damp these mass variations. This adjustment explains the previously observed fortnightly variation of the shear. Moreover, the adjustment is found to operate for the subinertial time scale flow variability forced by the atmospheric pressure. An analytical model aimed at reproducing variations of the velocity with time and in the vertical is derived. The model includes a depth-varying parameterisation of friction and takes into account density gradient fluctuations across the Strait. The model reproduces the main features of the flow, in particular the shear and the interface depth variations with the tide phase.     

A general approach to the modelling of contaminant transport through composite landfill liners with intact or leaking geomembranes

Finite‐element models of contaminant transport through composite landfill liners require highly refined meshes around the interface between the geomembrane and the clay layer, especially if leakage through holes in the geomembrane is considered. In addition, no general formulation for transport through leaking geomembranes can be found in the literature. The paper develops a general approach to time‐dependent contaminant migration through composite liners with intact or leaking geomembranes. Equations are derived for various combinations of system conditions including Dirichlet and Neumann boundary conditions in the waste, constant mass of contaminants in the waste, steady state or transient transport in the geomembrane, and steady state or transient seepage velocities in the mineral liner. The effect of the geomembrane on transport in the soil is converted into an equivalent boundary condition applicable at the top of the clay layer. Hence, only the media underlying the top geomembrane are explicitly represented in the numerical model, yielding a computationally efficient algorithm. The new formulation is validated in conjunction with finite‐layer, finite‐element and boundary‐element methods, by comparing its predictions to those of more conventional approaches which represent the geomembrane explicitly. The scope of the method is illustrated by modelling a landfill liner with a geomembrane leaking in five locations. Copyright © 2007 John Wiley & Sons, Ltd.     

Identification of shocked quartz by scanning cathodoluminescence imaging

Abstract— Quartz grains subjected to high‐strain‐rate shock waves owing to meteorite or cometary impact on Earth's surface commonly display shock lamellae. These lamellae appear as remarkably straight, thin, planar features (microstructures) in sets within which lamellae are essentially parallel to each other and spaced ≤ 20 μm apart. Two or more intersecting sets are typically present. Shock lamellae are commonly recognized and identified by optical methods, by use of the transmission electron microscope (TEM), and by etching polished sections and subsequent examination with a scanning electron microscope (SEM) operated in the secondary electron mode. We present here a method for observing planar microstructures in shocked quartz by using a cathodoluminescence (CL) detector attached to a SEM. The method relies on the fact that planar microstructures in quartz arising as a result of shock display no CL whatever; thus, they show up as distinct, thin, black lines on otherwise luminescent quartz grains. We used scanning CL imaging to study shocked quartz from the Ries Crater, Germany, a well‐known impact crater of Miocene age. We demonstrate that shock‐produced planar microstructures are clearly displayed in SEM‐CL images and can be distinguished from microfractures generated by tectonism, and subsequently filled with quartz, and other similar features not related to impact events. The SEM‐CL method provides a powerful supplement to other methods of identifying shocked quartz. It commonly provides better spatial resolution than does standard optical methods, and does not require etching of quartz grains. Further, it is easier and faster to use than are TEM methods, although it is not capable of the fine‐scale defect analysis possible with TEM.     

脉冲星星际闪烁的研究进展

综述了脉冲星星际闪烁观测研究的进展，对脉冲星星际闪烁现象，星际介质中电子密度涨落谱，散射等离子体在银河系中的分面等方面的最新研究结果作了介绍。星际闪烁现象和昨际介质的深入理解，使脉冲星星际闪烁已成为研究诸如脉冲星辐射区结构和脉冲星速度等脉冲星本身性质的重要工具。     

Investigation of the properties of electrostatic IA solitary wave structures in negative ion magneto-plasmas with superthermal electrons

A rigorous theoretical investigation is carried out in analyzing the excitation of electrostatic ion acoustic (IA) solitary wave (SW) structures in two dimensional negative ion magneto-plasmas with superthermal electrons (following κ type distribution). The Zakharov-Kuznetsov (ZK) equation is derived by employing the well known reductive perturbation method, and the analytical solution of ZK equation assists to find out the SW profiles along with their properties. The consequences of different plasma parameters (regarding our considered plasma system) variation on SW structures has been studied. It is found that magnetic field intensity, superthermal parameter κ and temperature of positive and negative ions as well as their densities significantly modify the basic characteristics (amplitude, width, etc.) of the SW waves. A comparison of the SW structures is also presented when the electrons are Maxwellian to when they are superthermal. The relevance of the findings of this work with astrophysical plasmas is briefly pointed out.     

A comparison between observed and analytical velocity dispersion profiles of 20 nearby galaxy clusters

We derive analytical expression for the velocity dispersion of galaxy clusters, using the statistical mechanical approach. We compare the observed velocity dispersion profiles for 20 nearby (z≤0.1) galaxy clusters with the analytical ones. It is interesting to find that the analytical results closely match with the observed velocity dispersion profiles only if the presence of the diffuse matter in clusters is taken into consideration. This takes us to introduce a new approach to detect the ratio of diffuse mass, M _diff , within a galaxy cluster. For the present sample, the ratio f=M _diff /M, where M the cluster’s total mass is found to has an average value of 45±12 %. This leads us to the result that nearly 45 % of the cluster mass is impeded outside the galaxies, while around 55 % of the cluster mass is settled in the galaxies.     

Radio frequency interference measurements in Indonesia

We report the first measurements of radio frequency spectrum occupancy performed at sites aimed to host the future radio astronomy observatory in Indonesia. The survey is intended to obtain the radio frequency interference (RFI) environment in a spectral range from low frequency 10 MHz up to 8 GHz. The measurements permit the identification of the spectral occupancy over those selected sites in reference to the allocated radio spectrum in Indonesia. The sites are in close proximity to Australia, the future host of Square Kilometre Array (SKA) at low frequency. Therefore, the survey was deliberately made to approximately adhere the SKA protocol for RFI measurements, but with lower sensitivity. The RFI environment at Bosscha Observatory in Lembang was also measured for comparison. Within the sensitivity limit of the measurement equipment, it is found that a location called Fatumonas in the surrounding of Mount Timau in West Timor has very low level of RFI, with a total spectrum occupancy in this measured frequency range being about 1 %, mostly found at low frequency below 20 MHz. More detailed measurements as well as a strategy for a radio quiet zone must be implemented in the near future.     

Application of multivariate approach in agrometeorological suitability zonation at northeast semiarid plains of Iran

At the present study, factor and cluster analysis were applied to evaluate the agrometeorological suitability zonation of 39 plains in Khorasan Razavi Province, NE Iran. For this purpose, the extracted 98 variables were processed, resulted in eight factors which explain about 90 % of the total variance. The explained variances of these factors are varied from 42.99 to 2.74 % for factors 1 and 8 after the Varimax rotation, respectively. The spatial classification maps of factor scores are extracted after the studied plains and the calculated scores were then classified by cluster analysis. It was revealed that five clusters were enough to classify the studied plains. The “negligible,” “low,” “moderate,” “high,” and “very high” classes included 4, 14, 9, 7, and 5 plains with 8.0, 35.6, 23.0, 15.1, and 18.3 % of the total surface area, respectively. The geographical distribution of the five major zones revealed that the plains with very high suitability are laid on the center and north parts of the study area, while the rest which are negligible and low suitability zones are mainly concentrated in the west, south, and southeast of the study area. Comparing the agrometeorological suitability between the corresponding zones revealed a general reducing trend from north to south along 3° geographical latitudes.     

Evaluation of wind erosion in the Tarim Basin based on parameter localization

Theoretical and Applied Climatology - Air density strongly constrains the characteristics of an airflow and the resulting flow of sand and therefore, it should not be neglected in sand transport...     

Statistical Relationship Between UVB(280-320nm) and Broadband Solar Radiation(295-2800nm) at a Subtropical Location(Qena,Egypt)

The present study quantifies the relationship between ultraviolet-B(UVB) and broadband solar radiation(G) at Qena,Egypt.Data from 10-year hourly integrated totals for both UVB and G on a horizontal surface were used to determine the best fit between the two radiation types.On the basis of the correlation of determination(r2),a second-order polynomial was determined to provide the best fit.For the purpose of developing an empirical model to estimate UVB,all of the cases of UVB and G from a nine-year study from 2001 to 2009 were introduced.Monthly and seasonal empirical models,as well as a general expression,were established for UVB as a function of G.The values of r2 ranged from 0.90 to 0.97.By using a new dataset of G,the estimated and the corresponding measured values of UVB were determined to be in good agreement whereby the values of r2 between the two ranged from 0.91 to 0.98.In addition,the significance and performance of the regression forms were evaluated with the aid of several statistical analysis procedures.The values of the index of modeling(d) and coefficient of modeling efficiency(ME) were close to one.Moreover,the values of RMSE,mean bias error(MBE),and mean absolute error(MAE) were lower than the experimental errors.On the basis of this analysis,it has been determined that the suggested regression forms can be used to estimate UVB when it difficult to obtain measurements or when measurements are available only for limited periods at the studied region.