Modeling nutrients profiles at the sediment–water interface. Calibration and validation from two climatically contrasted estuaries: Seine (France) and Somone (Senegal)

The dialysis porewater sampler, type Hesslein, allows sampling of sediment interstitial water according to a continuous gradient between sediment and the water column. Its equilibration time fluctuates according to the nature of sediment, so it has to be measured in each kind of sediment. The aim of this work is to develop a physical diffusion model in order to determine an equilibration time without using extensive field experiments. The model is validated by real nutrient concentration profiles obtained on two estuaries under different climates, moderate climate (estuary of the Seine) and tropical dry climate (estuary of Somone, Senegal). The results highlight that the equilibration of the dialysis porewater sampler is not homogeneous over the full sediment height investigated. Other sediment characteristics as compaction, rate of bioturbation or bacterial density must be taken into account in order to find a well-calculated value of the equilibration time.     

Archimedes spiral and the surface distribution of dark clouds in M31, III

The surface distribution of dark clouds along the major and minor axes were compiled to give a general formula expressing the surface distribution along both axes simultaneously. Absorption values were determined, assuming the parameters of the standard cloud model as a function of the distance from the two-dimensional distribution of dark clouds. Iso-cloud line numbers were drawn as a function of bothX andY. Two knots appeared in the new distribution function. This may announce the beign of the spiral arms. The knots may indicate the least possible number of the dark clouds per kiloparsec beyond which spiral structure may be possible. The projected distance of the two knots on the X-axis may correspond to some spiral features found by other investigators.     

Disaster prevention,disaster preparedness and local community resilience within the context of disaster risk management in Cameroon

This paper presents a simulation of three components of near-field ground shaking recorded during the main shock at three stations of the September 16, 1978, Tabas (M _w = 7.4), Iran, earthquake, close to the causative fault. A hybrid method composed of a discrete wavenumber method developed by Bouchon (Bouchon in Bull Seismol Soc Am 71:959–971, 1981; Cotton and Coutant in Geophys J Int 128:676–688, 1997) and a stochastic finite-fault modeling based on a dynamic corner frequency proposed by Motazedian and Atkinson (Bull Seismol Soc Am 95:995–1010, 2005), modified by Assatourians and Atkinson (Bull Seismol Soc Am 97:935–1949, 2007), is used for generating the seismograms at low (0.1–1.0 Hz) and high frequencies (1.0–20.0 Hz), respectively. The results are validated by comparing the simulated peak acceleration, peak velocity, peak displacement, Arias intensity, the integral of velocity squared, Fourier spectrum and acceleration response spectrum on a frequency-by-frequency basis, the shape of the normalized integrals of acceleration and velocity squared, and the cross-correlation with the observed time-series data. Each characteristic is compared on a scale from 0 to 10, with 10 being perfect agreement. Also, the results are validated by comparing the simulated ground motions with the modified Mercalli intensity observations reported by reconnaissance teams and showed reasonable agreement. The results of the present study imply that the damage distribution pattern of the 1978 Tabas earthquake can be explained by the source directivity effect.     

Rate of seawater intrusion estimated by geophysical methods in an arid area: Al Khabourah, Oman

Seawater intrusion and its spreading rate are the challenging problems in over-pumped coastal aquifers of arid zones like the Batinah region of Oman. The study delineates the saline plume, identifies saline/freshwater zones, and estimates the migration rate of the plume in the Al Khabourah area of the Batinah coast. Time domain electromagnetic surveys, aided by vertical electrical sounding surveys, and seismic refraction methods have defined the locus of the saline/freshwater interface in the area. The current (2007) interface position, when compared with that determined during 2002, indicates a prominent recession in the saline plume and suggests an average annual recession rate of 120 m. This recession may be attributed mainly to the recharging dam of Wadi Al Hawasinah, constructed in 1995, and the enforcement of new water resources legislation. This study reveals the shielding role of the recharging dam to counter advancing saline intrusion.     

Prospection géochimique dans le centre et le nordouest du Burkina Faso

After the discovery of a Zn-Ag massive sulphide deposit at Perkoa in 1982, following regional geochemical exploration in the Birimian belts of Boromo and Hounde, a joint project was carried out by UNDP (United Nations Development Programme) and BUMIGEB (Bureau des Mines et de la Géologie du Burkina) in Central and Northwest Burkina Faso. The same exploration approach was applied which has been successful in previous surveys: it is based on soil sampling at about 30 cm depth at a density ranging from 3.3 to 8 samples per km². The results obtained and the various problems encountered during exploration are presented in this paper. These problems are typical of the morphoclimatic conditions prevailing in semi-arid savanna regions of western Africa. Where the deep weathering profile, probably formed during former climatic episodes, is well preserved, residual laterites may alter the geochemical signature of mineralizations. North of the 14th parallel, windblown sand may cover large areas where geochemical sampling needs to be adapted: samples have to be collected at depth, in the saprolite, beneath the sand.Storage, processing and display of the numerous analytical data gathered for the last ten years, fully justified the development of a computer assisted processing unit which is now operational.

Résumé

Suite à la découverte en 1982 de l'amas sulfuré Zn-Ag de Perkoa par prospection géochimique régionale dans les sillons birrimiens de Boromo et de Houndé, un nouveau projet associant le PNUD (Programme des Nations Unies pour le Développement) et le BUMIGEB (Bureau des Mines et de la Géologie du Burkina) a été lancé dans le centre et le nord-ouest du pays en appliquant une démarche qui avait déjà fait ses preuves. Celle-ci s'appuie sur l'échantillonnage de sols, prélevés à environ 30 cm de profondeur, à une densité variant de 3,3 à 8 prélèvements au km².Sont présentés les résultats de cette campagne ainsi que les divers problèmes rencontrés. Ceuxci sont communs à toute prospection dans la zone tropicale sèche d'Afrique occidentale et résultent des situations pédologiques propres à cette zone climatique caractérisée localement soit par des cuirasses latéritiques, dont le caractère autochtone prédominant autorise les prélèvements géochimiques de surface, soit par des recouvrements éoliens. Ceux-ci sont principalement développés au nord du 14ème parallèle; ils nécessitent en général l'adaptation de l'échantillonnage, qui doit être réalisé, à une profondeur parfois importante, dans la saprolite.Le stockage des nombreuses données analytiques collectées depuis dix ans, leur traitement et leur visualisation ont justifié la mise en place d'une unité de traitement informatique maintenant opérationnelle.     

Spatial student enrolment at UAE University: A quantitative analysis

Very few geographic studies have been carried out on student enrolment in the Gulf region. To the best knowledge of the present author, no geographic study exists on student enrolment at the UAE University. This paper is primarily concerned with analyzing one of the prominent characteristics of UAE University students, ie the pattern of sex distribution, thereby hoping to fill a research gap in the geographical literature. The grand total of UAE University students has exceeded 12,000, with 78% females and 22% males. The females proportion is considered to be the highest when compared with other neighbouring countries. This study aims to analyze this particular characteristic in its spatial context. The analysis will be statistically tested by chi-square (x²) to determine to which extent the pattern differs from one area to another. The conclusion is that more male students from Abu Dhabi and Al-Ain areas and more female students from Dubai area come to study at UAE University than were expected.     

Earthquake risk assessment for the building inventory of Muscat,Sultanate of Oman

Little Andaman, the fourth largest island in the Andaman group of islands of India, was severely affected by the December 26, 2004, Indian Ocean tsunami generated by massive earthquake of moment magnitude 9.3 Mw which devastated the Andaman and Nicobar group of islands causing heavy damage to life and property. Due to hostile terrain conditions not much information was available on the extent of inundation and run-up along the island except for Hut Bay region. In order to study the vulnerability of the island to tsunami hazard, the inundation in the island due to the 2004 tsunami was studied using TUNAMI N2 numerical model and ENVISAT ASAR datasets. The extent of inundation derived from the SAR imagery was compared using the RTK-GPS field survey points collected in the Hut Bay regions immediately after the 2004 tsunami. The extent of inundation obtained from SAR images for the entire island was compared with inundation obtained from model. It was observed that the inundation obtained from the model matched well with inundation extent from SAR imagery for nearshore regions, while for low-lying areas and creeks large deviations were observed. In the absence of field datasets, the inundation derived from SAR imagery would be effective in providing ground data to validate the numerical models which can then be run for multiple scenarios for disaster mitigation and planning operation in areas that have hostile terrain conditions.     

A geometric method to determine the distances of galaxies

Es wird die Möglichkeit diskutiert, die Größenverteilungsfunktion von Kugelsternhaufen für die Entfernungsbestimmung von Galaxien zu nutzen.     

Evaluation and modification of some empirical and semi-empirical approaches for prediction of area-storage capacity curves in reservoirs of dams

The storage capacity of reservoirs is gradually reduced due to sediment accumulation that causes changes in the area-storage capacity (ASC) curves.Establishing these curves and predicting their future change is an important issue for planners,designers and operators of dams.Many empirical and semiempirical approaches have been suggested for establishing and predicting the future changes for these curves.In this study four empirical and semi-empirical methods were evaluated and three of them were modified to be used for the prediction of changes in the ASC curves due to sedimentation,based on the existing sedimentation survey data for 11 reservoirs in the USK For evaluation,these approaches were reviewed and used to determine sedimentation depth and establishing the ASC curves for the Mosul dam reservoir (MDR),which is the biggest hydraulic structure on the River Tigris in northern Iraq.MDR started operating in 1986 with a storage capacity of 11.11 km3 and a water surface area 380 km2 at normal operation stage (330 m a.s.l.).The results obtained from these methods were evaluated using observed bathymetric survey data that had been collected in 2011 after 25 years of the operation of the dam.The evaluation results showed three methods had presented more accurate results for estimating water depth or sedimentation depth at dam site with percentage error about 1.06-3.30％.Whilst for establishing ASC curves,one method presented good agreement result with survey data.Furthermore,ASC and sedimentation depths at dam site of MDR for periods 50,75,100 and 125 years were estimated using the modified approaches and the area reduction method.The results of the modified methods provided reasonable agreement when compared with the area reduction method proposed by the U.S.Bureau of Reclamation and the agreement became better with an increase in time period.     

X-Ray Spectral Study of AGN Sources Content in Some Deep Extragalactic XMM-Newton Fields

We undertake a spectral study of a sample of bright X-ray sources taken from six XMM-Newton fields at high galactic latitudes, where AGN are the most populous class. These six fields were chosen such that the observation had an exposure time more than 60 ksec, had data from the EPIC-pn detector in the full-Frame mode and lying at high galactic latitude |b|>25^∘. The analysis started by fitting the spectra of all sources with an absorbed power-law model, and then we fitted all the spectra with an absorbed power-law with a low energy black-body component model.The sources for which we added a black body gave an F-test probability of 0.01 or less (i.e. at 99% confidence level), were recognized as sources that display soft excess. We perform a comparative analysis of soft excess spectral parameters with respect to the underlying power-law one for sources that satisfy this criterion. Those sources, that do not show evidence for a soft excess, based on the F-test probability at a 99% confidence level, were also fitted with the absorbed power-law with a low energy black-body component model with the black-body temperature fixed at 0.1 and 0.2 keV. We establish upper limits on the soft excess flux for those sources at these two temperatures. Finally we have made use of Aladdin interactive sky atlas and matching with NASA/IPAC Extragalactic Database (NED) to identify the X-ray sources in our sample. For those sources which are identified in the NED catalogue, we make a comparative study of the soft excess phenomenon for different types of systems.