Groundwater potential zone assessment in Wadi Watir area,Egypt using radar data and GIS

The exploration of new locations for possible groundwater potentiality is required to support the needs of urban and agricultural activities in arid regions such as Wadi Watir basin. The aim of this study is to locate new groundwater wells that can help overcome the water shortage. In order to define favorable zones for groundwater potentiality, several essential factors contributing to groundwater potentiality were identified. These factors include textural classification of alluvial deposits, lithological units, surface and subsurface structures, topographic parameters, geomorphological features and land use/land cover. A hydrogeological prospective model was developed using spatial data which represent these factors. For final groundwater potential map, all factors were converted to raster data to integrate spatially as important thematic layers based on weightage analysis. The groundwater potential map was classified to five classes including very poor to very good potential. The classes of groundwater potential map were checked against the distribution of the groundwater wells, Bedouin communities and agriculture areas, which present a general knowledge of groundwater potential in the study area.     

Effect of non-uniform station coverage on the inversion for earthquake rupture history for a Haskell-type source model

In order to determine how reliably one can invert accelerograms to determine the rupture process details, when the station configuration is less than optimal, we use the vertical component of synthetic accelerograms for a Haskell-type earthquake rupture model, at stations in the vicinity of a dip-slip fault and solve the inverse problem. Of the various station configurations used, one is a uniform distribution and the others are very non-uniform. Faults of two different aspect ratios are considered. We mainly use much larger spatial and temporal cell sizes in the inversion than we use to construct the artificial data. The fault mechanism and the fault area are taken as known in the inversions. To solve the inverse problem, we use the method of linear programming and stabilize the solution by the use of physical constraints. The constraints of positivity of the slip rates on the fault is used in all cases in this study. In some cases, additional physical constraints such as preassigning the final moment, the rupture speed, and so on, are also used. We find that using a cell size almost double the wavelength of interest, we are able to reproduce the solution of the problem, even when we add a small amount of random noise to the artificial data, provided the source medium structure is known. We show that the best station configuration is when the stations are on the hanging wall, due to the fact that they provide the best illumination of the fault surface. This provides an incentive to install permanent ocean bottom strong ground motion stations in subduction zones. We also analyzed the effect of the rupture propagation direction on the results of the inversion showing that even four stations are sufficient to retrieve the rupture process if they are in the forward direction of the rupture propagation; the results for this case are better than when the four stations are placed in the backward direction, even when their positions are such that they illuminate the fault in exactly the same way as the four stations in the forward direction. Thus azimuthal distribution and the resulting illumination of the fault as well as the relation of the position of the stations to the direction of rupture propagation are more important than simply the number of stations. Finally, we find that proper knowledge of source medium structure is essential to recover the source process details reliably and that poor knowledge of crustal structure cannot be compensated by adding stations or by additional constraints.     

Historical Trends of Organochlorine Pesticides in an Alpine Glacier

The significance of persistent organic pollutants, such as organochlorine compounds, as global contaminants in cold regions has been recognised for a long time. In particular, there is a growing interest on the role of high mountains as `cold condensers' for these chemicals. In this paper, for the first time, organochlorine pesticides (DDTs, HCHs, HCB) are analysed in an ice core sampled on a `cold' glacier in the Alps. Several methods were applied to achieve accurate dating of the core layers. Historical trends of organochlorine pesticides from the 1950s up to the year 2000 are reconstructed, showing, for each individual chemical, the influence of long range transport, as well as of local transport patterns. The role of mountain glaciers as natural archives for studying the local and global transport of persistent organic pollutants is highlighted, though results can be biased by volatilisation losses.     

An empirical evaluation of three elevation change symbolization methods along routes in bicycle maps

ABSTRACT

Elevation change is critical for choosing a route when bicycling. We detail an empirical study in which we comparatively evaluated three linear symbolization types (color hue, color-coded arrows, and elevation profiles) to depict elevation change in bicycle maps for two common bicycle route planning tasks: relative height detection and slope identification. Participants performed most accurately with the color-coded arrows for relative height detection tasks, whereas symbolization did not significantly influence map-use performance for slope identification. Participants preferred the elevation profile, in spite of their lowest performance with this method overall. Our rare empirical findings offer much needed new insights into the function and appropriateness of common elevation symbolization methods, specifically to identify elevation change in bicycle route planning tasks in urban areas where map display real estate is already very limited.     

The use of buffers to measure the pH of seawater

The pH of seawater can be measured in the field using potentiometric and spectrophotometric methods. The use of pH standards or buffers is an important aspect of the calibration of both methods in a laboratory on a common concentration scale. The buffers can also be used to monitor the performance of pH meter and spectrophotometer during a cruise. A procedure is described for the determination of the pH of seawater, where the proton concentration is expressed as moles kg-H₂O⁻¹ using seawater buffers. The buffers are prepared in synthetic seawater in the laboratory by the methods outlined by Bates and coworkers. We have prepared four buffers (Bis, Tris, Morpholine and 2-Aminopyridine) that cover a pH range from 6.8 to 8.8. The emf values of the buffers were measured with a H₂, Pt/AgCl, Ag electrode system after their preparation and bottling for use at sea. The measured emf values were found to be in good agreement (±0.05 mV) with the original measurements of Bates and coworkers from 0 to 45°C. The measured pH of these buffers are in good agreement (±0.001 pH units) with the values calculated from the equations of Dickson on the total pH scale based on Bates et al. Studies are underway to access the long term stability of these buffers. We have also used these buffers to calibrate systems used to make potentiometric and spectrophotometric measurements of pH on seawater relative to the H₂, Pt/Ag, AgCl electrode from 5 to 45°C.     

Monitoring the winds of hot stars with HST/GHRS

We present observations obtained with the Goddard High Resolution Spectrograph (GHRS) of three O-type stars: per (O7 III), Cep (O6 Iaf) and 10 Lac (O9 V). These observations show evidence of instabilities in the winds of all three stars, although not necessarily those expected from current models of structured winds.Based on observations with the NASA/ESAHubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA for NASA under contract NAS5-26555