Theoretical infrared spectra of some model polycyclic aromatic hydrocarbons: effect of ionization     

De Frees DJ  Miller MD  Talbi D  Pauzat F  Ellinger Y 《The Astrophysical journal》1993,408(2):530-538

In order to test the hypothesis of ionized polycyclic aromatic hydrocarbons (PAHs) as possible carriers of the UIR bands, we realized a computational exploration on selected PAHs of small dimension in order to identify which changes ionization would induce on their IR spectra. In this study we performed ab initio calculations of the spectra of neutral and positively ionized naphthalene, anthracene, and pyrene. The results are significantly important. The frequencies in the cations are slightly shifted with respect to the neutral species, but no general conclusion can be reached from the three molecules considered. By contrast, the relative intensities of most vibrations are strongly affected by ionization, leading to a much better agreement between the calculated CH/CC vibration intensity ratios and those deduced from observations.  相似文献   

Pb-Zn (Ba) deposits of the oriental Saharan Atlas (north-east of Algeria): distribution,control and implications for mining exploration     

Haddouche Omar  Boutaleb Abdelhak  Chamam Madjid  Ysbaa Saadia  Hammouche Hanafi  Boubaya Djamel 《Arabian Journal of Geosciences》2016,9(5):422

Analysis and integration of geological/metallogenic data and digitally processed gravimetric/aeromagnetic data to the oriental Saharan Atlas domain were carried out to understand the spatial distribution and structural control on Pb-Zn (Ba) deposits of the oriental Saharan Atlas. The use of this combined technique suggests that most of mineral deposits appear to be regionally controlled by structural trends (subparallel NE-SW-trending) along margins of subsiding sedimentary basins. Mineralization occurs along or near major NE-SW-trending faults, locally intersected by NW-SE-trending faults. In addition, mineral deposits are usually either inside anticlinal hinge zones (example, Merouana, Ichmoul and Ain Mimoum ore deposits) or on the flanks of anticlinal structures (example, Ain Bougda ore deposit). In “diapiric zone”, mineral deposits are generally located on diapiric structures borders (peridiapiric concentrations), related to NE-SW/NE-SW and E-W-trending faults. Other mineral concentrations occurs along the margins of tectonic troughs zones (example, Morsott trough) resulting probably by NW-SE-trending deep faults movement. In summary, our research suggested that regional parameters, such as NE-SW/NW-SE-trending lineaments, intersections of these lineament zones and margins of subsiding sedimentary basins/diapiric structures, serve as significant indicators and provides a valuable framework for guiding the early stages of Pb-Zn (Ba) mineral exploration; other considerations must then be applied in this region, like integration of surficial geochemical anomalies that allows better delineation of targets for further mineral exploration.  相似文献   

Three-dimensional numerical and analytical study of horizontal group of square anchor plates in sand     

Hicham Mokhbi  Mekki Mellas  Abdelhak Mabrouki  Jean-Michel Pereira 《Acta Geotechnica》2018,13(1):159-174

In this paper, numerical and analytical methods are used to evaluate the ultimate pullout capacity of a group of square anchor plates in row or square configurations, installed horizontally in dense sand. The elasto-plastic numerical study of square anchor plates is carried out using three-dimensional finite element analysis. The soil is modeled by an elasto-plastic model with a Mohr–Coulomb yield criterion. An analytical method based on a simplified three-dimensional failure mechanism is developed in this study. The interference effect is evaluated by group efficiency η, defined as the ratio of the ultimate pullout capacity of group of N anchor plates to that of a single isolated plate multiplied by number of plates. The variation of the group efficiency η was computed with respect to change in the spacing between plates. Results of the analyses show that the spacing between the plates, the internal friction angle of soil and the installation depth are the most important parameters influencing the group efficiency. New equations are developed in this study to evaluate the group efficiency of square anchor plates embedded horizontally in sand at shallow depth (H = 4B). The results obtained by numerical and analytical solutions are in excellent agreement.  相似文献   

Bottom-up climate risk assessment of infrastructure investment in the Niger River Basin     

Y. B. Ghile  M. Ü. Taner  C. Brown  J. G. Grijsen  Amal Talbi 《Climatic change》2014,122(1-2):97-110

The Niger River is the third largest river in the African continent. Nine riparian countries share its basin, which rank all among the world’s thirty poorest. Existing challenges in West Africa, including endemic poverty, inadequate infrastructure and weak adaptive capacity to climate variability, make the region vulnerable to climate change. In this study, a risk-based methodology is introduced and demonstrated for the analysis of climate change impacts on planned infrastructure investments in water resources systems in the Upper and Middle Niger River Basin. The methodology focuses on identifying the vulnerability of the Basin’s socio-economic system to climate change, and subsequently assessing the likelihood of climate risks by using climate information from a multi-run, multi-GCM ensemble of climate projections. System vulnerabilities are analyzed in terms of performance metrics of hydroelectricity production, navigation, dry and rainy season irrigated agriculture, flooding in the Inner Delta of the Niger and the sustenance of environmental flows. The study reveals low to moderate risks in terms of stakeholder-defined threshold levels for most metrics in the 21st Century. The highest risk levels were observed for environmental flow targets. The findings indicate that the range of projected changes in an ensemble of CMIP3 GCM projections imply only relatively low risks of unacceptable climate change impacts on the present large-scale infrastructure investment plan for the Basin.  相似文献   

Petrology, isotope geochemistry and chemical budgets of oceanic gabbros-seawater interactions in the Equatorial Atlantic     

EL H. Talbi  J. Honnorez  N. Clauer  F. Gauthier-Lafaye  P. Stille 《Contributions to Mineralogy and Petrology》1999,137(3):246-266

 Petrological and chemical variations, as well as oxygen and strontium isotopic data are presented for metagabbros from the Romanche and Vema fracture zones. These rocks were affected by several types and degrees of alterations ranging from slight hydrothermal alteration to complete amphibolitization. Five major kinds of alteration processes ranging from late-magmatic deuteric alteration (stage I) to low temperature (<150 °C) alteration (stage V) were identified. Water-rock interactions between 300 and 650 °C are the most dominant interactions resulting in the most prevailing secondary mineralogical assemblages which characterize the amphibolite and/or greenschist facies (amphibole ± plagioclase ± epidote ± titanite ± chlorite ± prehnite). Hydrothermal alteration of these gabbroic rocks results in isotopic exchanges between rocks and seawater-derived fluids. These exchanges lead to decrease of gabbroic δ¹⁸O toward values as low as +3.9‰, and larger Sr isotopic variations than other oceanic gabbroic rocks (⁸⁷Sr/⁸⁶Sr ratios shift to 0.7029–0.7051). Calculation of a chemical budget indicates that metagabbros are hydrated and enriched in Fe and probably in Mg and Cl, while Si, Ca and Ti are released to the hydrothermal fluids. In addition to metamorphic recrystallization and geochemical transformation, hydrothermal alteration of oceanic gabbros contributes to the control of the global ocean geochemistry. Received: 8 March 1999 / Accepted: 12 July 1999  相似文献   

Flood forecasting based on an artificial neural network scheme     

Dtissibe  Francis Yongwa  Ari  Ado Adamou Abba  Titouna  Chafiq  Thiare  Ousmane  Gueroui  Abdelhak Mourad 《Natural Hazards》2020,104(2):1211-1237

Natural Hazards - Nowadays, floods have become the widest global environmental and economic hazard in many countries, causing huge loss of lives and materials damages. It is, therefore, necessary...  相似文献   

Uptake and fixation of Zn, Pb, and Cd by Thlaspi caerulescens: application in the cases of old mines of Mibladen and Zaida (West of Morocco)     

Safae Berrah El Kheir  Jamal Oubbih  Nadia Saidi  Abdelhak Bouabdli 《Arabian Journal of Geosciences》2008,1(2):87-95

Contaminated soils and mine tailings pose major environmental and agricultural problems worldwide. These problems may be partially solved by an emerging new technology: phytoremediation. This technique uses plants to extract soil contaminants from the ground. Thlaspi caerulescens is known to accumulate in their tissues several heavy metals from soil and aerial deposition. This study was conducted to screen plants growing on a contaminated site to determine their potential for metal accumulation. Seeds of T. caerulescens metallicolous have been collected in the vicinity of F.T. Laurent le Minier in the Pb–Zn mining district of les Malines (North of Montpellier, Southern France), and seeds of T. caerulescens non-metallicolous were sampled on Larzac Plateau (North of Montpellier, Southern France). Soil substrates were collected from a mine site of Mibladen and Zaida (West, Morroco). Cultivated plant and surface soil samples were analyzed for zinc, lead, and cadmium concentrations by inductively coupled plasma mass spectrometry. A non-metallicolous (NM) ecotype of T. caerulescens and a metallicolous (M) ecotype are compared for Pb, Cd, and Zn accumulation in shoot and root in five metal-contaminated soils and one uncontaminated soil. The growth of individuals from uncontaminated soil was greater than that of individuals from metal-contaminated soils. The NM populations had markedly higher root/shoot ratio compared to M populations. The results indicate that both ecotypes of T. caerulescens are highly tolerant of zinc and Cd. Ecotype NM had constitutively higher Zn uptake capacity than the M ecotype. T. caerulescens species accumulate higher amount of Zn and Cd in their tissues in polluted soil and, in both of the two ecotypes, the root Pb concentrations were much greater than those of the shoot Pb contents. From both uncontaminated and metal-contaminated soils, we conclude that T. caerulescens are interesting material for phytoremediation of zinc and cadmium.  相似文献   

Calculations on the rates, mechanisms, and interstellar importance of the reactions between C and NH₂ and between N and CH₂     

E. Herbst  R. Terzieva  D. Talbi 《Monthly notices of the Royal Astronomical Society》2000,311(4):869-876

The attempt to understand the temperature dependence of the HNC/HCN abundance ratio in interstellar clouds has been long standing and indecisive. In this paper we report quantum chemical and dynamical studies of two neutral–neutral reactions thought to be important in the formation of HNC and HCN, respectively – C+NH₂→HNC+H, and N+CH₂→HCN+H. We find that although these reactions do lead initially to the products suggested by astronomers, there is so much excess energy available in both reactions that the HCN and HNC products are able to undergo efficient isomerization reactions after production. The isomerization leads to near equal production rates of the two isomers, with HNC slightly favoured if there is sufficient rotational excitation. This result has been incorporated into our latest chemical model network of dense interstellar clouds.  相似文献   

Ground-Motion Hazard Values for Northern Algeria   总被引：2，自引：0，他引：2  

M. Hamdache  J. A. Peláez  A. Talbi  M. Mobarki  C. López Casado 《Pure and Applied Geophysics》2012,169(4):711-723

This study examines distinctive features of ground motion parameters in northern Algeria. An initial computation of seismic hazard in terms of horizontal peak ground acceleration (PGA) and spectral acceleration (SA) at different periods, damped at 5%, is carried out for three different types of soils (rock, stiff soils and soft soils) for return periods of 100 and 475 years. In addition, uniform hazard spectra (UHS) are computed for these two return periods at several locations in the region. Then, the UHS computed for different soil types are proposed as a starting point to define elastic design spectra for building-code purposes. We have used the well-known Newmark-Hall approach. As proposed in the most recent International Building Codes, the SA (0.2 s) value is used to establish the spectral region for lower periods (region controlled by acceleration), whereas the SA (1.0 s) value is used to establish the spectral region for intermediate periods (region controlled by velocity). We also obtained important relations, dependent on site condition, between SA (0.2 s), SA (1.0 s) or SA_max values, and the PGA, for both return periods of 100 and 475 years. Other relationships between PGA or SA_max values have also been derived for return periods of 100 and 475 years, in this case independent of site condition.  相似文献   

Soil metal pollution from former Zn–Pb mining assessed by geochemical and magnetic investigations: case study of the Bou Caid area (Tissemsilt,Algeria)     

Lynda Attoucheik  Neli Jordanova  Boualem Bayou  France Lagroix  Diana Jordanova  Said Maouche  Bernard Henry  Abdelhak Boutaleb 《Environmental Earth Sciences》2017,76(7):298

Former zinc and lead mines that have been operating for half a century are located in the massif of Bou Caid (Tissemsilt, Algeria). Hazardous heavy metals emitted from the mines are abundant in the surrounding soil and cause strong metal pollution in the region. This paper investigates the extent of lead and zinc mine activity derived pollution by characterizing both magnetic and geochemical properties of samples collected in the vicinity of the mines. The results of the magnetic study show the coexistence of magnetic minerals such as magnetite, hematite and goethite. Analyses on surface soils and weathered rocks suggest that hematite and goethite have ore-related lithogenic origins. Magnetic susceptibility shows a positive correlation with lead content when present in low-to-medium concentrations (< ~500 mg/kg). At higher lead concentrations, there is no correlation with magnetic susceptibility. The relationship between magnetic susceptibility and zinc content is not straightforward. These observations are explained by the higher affinity of Pb to iron oxides at lower pollution levels and their preferential bonding to carbonates when Pb and Zn contents are extremely high, as demonstrated by Iavazzo et al. (J Geochem Explor 113:56–67, 2012) in a study of former Zn–Pb mine in Morocco. Based on the general features of the spatial maps of field-measured magnetic susceptibility, mass-specific magnetic susceptibility, Pb and Zn contents, it is concluded that field magnetic measurements provide a good qualitative proxy of pollution spread out of the mining galleries, while laboratory measurements afford a more detailed investigation of the links between iron oxides and the main heavy metals in the ore.  相似文献