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1.
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
2.
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
3.
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
4.
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
5.
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 SAmax values, and the PGA, for both return periods of 100 and 475 years. Other relationships between PGA or SAmax values have also been derived for return periods of 100 and 475 years, in this case independent of site condition. 相似文献
6.
In the central part of the Bolivian Altiplano, the shallow groundwater presents electrical conductivities ranging from 0·1 to 20 mS/cm. In order to study the origin of this salinity pattern, a good knowledge is required of the geometry of the aquifer at depth. In this study, geophysics has been used to complement the sparse data available from drill holes. One hundred time‐domain electromagnetic (TDEM) soundings were carried out over an area of 1750 km2. About 20 geological logs were available close to some of the TDEM soundings. Three intermediate results were obtained from the combined data: (i) the relationship between the electrical conductivity of the groundwater and the formation resistivity, (ii) geoelectrical cross‐sections and (iii) geoelectrical maps at various depths. The limited data set shows a relationship between resistivity and the nature of the rock. From the cross‐sections, a conductive substratum with a resistivity of less than 1 Ω·m was identified at most of the sites at depths ranging from 50 to 350 m. This substratum could be a clay‐rich formation containing brines. Using derived relationships, maps of the nature of the formation (sandy, intermediate and clayey sediments) were established at depths of 10 and 50 m. Discrimination between sand and clays was impossible where groundwater conductivity is high (>3 mS/cm). In the central part of the area, where the groundwater conductivity is low, sandy sediments are likely to be present from the surface to a depth of more than 200 m. Clayey sediments are more likely to be present in the south‐east and probably constitute a hydraulic barrier to groundwater flow. In conclusion, the study demonstrates the efficiency of the TDEM sounding method to map conductive zones. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
7.
Comparison of seismicity declustering methods using a probabilistic measure of clustering 总被引：2，自引：1，他引：1
Abdelhak Talbi Kazuyoshi Nanjo Kenji Satake Jiancang Zhuang Mohamed Hamdache 《Journal of Seismology》2013,17(3):1041-1061
We present a new measure of earthquake clustering and explore its use for comparing the performance of three different declustering methods. The advantage of this new clustering measure over existing techniques is that it can be used for non-Poissonian background seismicity and, in particular, to compare the results of declustering algorithms where different background models are used. We use our approach to study inter-event times between successive earthquakes using earthquake catalog data from Japan and southern California. A measure of the extent of clustering is introduced by comparing the inter-event time distributions of the background seismicity to that of the whole observed seismicity. Theoretical aspects of the clustering measure are then discussed with respect to the Poissonian and Weibull models for the background inter-event time distribution. In the case of a Poissonian background, the obtained clustering measure shows a decrease followed by an increase, defining a V-shaped trend, which can be explained by the presence of short- and long-range correlation in the inter-event time series. Three previously proposed declustering methods (i.e., the methods of Gardner and Knopoff, Reasenberg, and Zhuang et al.) are used to obtain an approximation of the residual “background” inter-event time distribution in order to apply our clustering measure to real seismicity. The clustering measure is then estimated for different values of magnitude cutoffs and time periods, taking into account the completeness of each catalog. Plots of the clustering measure are presented as clustering attenuation curves (CACs), showing how the correlation decreases when inter-event times increase. The CACs demonstrate strong clustering at short inter-event time ranges and weak clustering at long time ranges. When the algorithm of Gardner and Knopoff is used, the CACs show strong correlation with a weak background at the short inter-event time ranges. The fit of the CACs using the Poissonian background model is successful at short and intermediate inter-event time ranges, but deviates at long ranges. The observed deviation shows that the residual catalog obtained after declustering remains non-Poissonian at long time ranges. The apparent background fraction can be estimated directly from the CAC fit. The CACs using the algorithms of Reasenberg and Zhuang et al. show a relatively similar behavior, with a time correlation decreasing more rapidly than the CACs of Gardner and Knopoff for shorter time ranges. This study offers a novel approach for the study of different types of clustering produced as a result of various hypotheses used to account for different backgrounds. 相似文献
8.
The stability of the power law scaling of earthquake recurrence time distribution in a given space–time window is investigated,
taking into account the magnitude of completeness and the effective starting time of aftershock sequences in earthquake catalogs
from Southern California and Japan. A new method is introduced for sampling at different distances from a network of target
events. This method allows the recurrence times to be sampled many times on the same area. Two power laws with unknown exponents
are assumed to govern short- and long-recurrence-time ranges. This assumption is developed analytically and shown to imply
simple correlation between these power laws. In practice, the results show that this correlation structure is not satisfied
for short magnitude cutoffs (m
c
= 2.5, 3.5, 4.5), and hence the recurrence time distribution departs from the power law scaling. The scaling parameters obtained
from the stack of the distributions corresponding to different magnitude thresholds are quite different for different regions
of study. It is also found that significantly different scaling parameters adjust the distribution for different magnitude
thresholds. In particular, the power law exponents decrease when the magnitude cutoff increases, resulting in a slower decrease
of the recurrence time distribution, especially for short time ranges. For example, in the case of Japan, the exponent p2 of the power law scaling at large recurrence times follows roughly the relation: , where m
c
is the magnitude cutoff. In case of Southern California, it is shown that Weibull distribution provides a better alternative
fit to the data for moderate and large time scales. 相似文献
9.
Fouzi Bellalem Abdelhak Talbi Hamou Djellit Hayet Ymmel Mourad Mobarki 《Journal of Seismology》2018,22(4):897-908
The region of Blida is characterized by a relatively high seismic activity, pointed especially during the past two centuries. Indeed, it experienced a significant number of destructive earthquakes such as the earthquakes of March 2, 1825 and January 2, 1867, with intensity of X and IX, respectively. This study aims to investigate potential seismic hazard in Blida city and its surrounding regions. For this purpose, a typical seismic catalog was compiled using historical macroseismic events that occurred over a period of a few hundred years, and the recent instrumental seismicity dating back to 1900. The parametric-historic procedure introduced by Kijko and Graham (1998, 1999) was applied to assess seismic hazard in the study region. It is adapted to deal with incomplete catalogs and does not use any subjective delineation of active seismic zones. Because of the lack of recorded strong motion data, three ground prediction models have been considered, as they seem the most adapted to the seismicity of the study region. Results are presented as peak ground acceleration (PGA) seismic hazard maps, showing expected peak accelerations with 10% probability of exceedance in 50-year period. As the most significant result, hot spot regions with high PGA values are mapped. For example, a PGA of 0.44 g has been found in a small geographical area centered on Blida city. 相似文献
10.
The area under study covers 3500 km2 in the upstream part of the closed catchment basin of the salt crust of Uyuni. This crust is a remnant of the saline Lake Tauca, which covered the area about 15,000 years ago. In the downstream part of the aquifer, the Cl concentration of ground water and Cl content in the unsaturated zone exceed 20 meq/L and 18 kg/m2, respectively. With the present hydrological conditions under semiarid conditions, the ground water residence time in the study area exceeds 3000 years. Transient simulations over 11,000 years were made using initial conditions as the retreat of Lake Tauca and taking into account a low recharge during the arid mid-Holocene period. The modeling simulates ground water flow, Cl transport, and ground water residence time. It includes the evaporation from the aquifer that leads to the accumulation of chloride in the unsaturated zone. Results of the modeling are consistent with the observations if it is assumed that the Cl previously accumulated in the unsaturated zone was flushed back into the aquifer around 2000 years B.P., contemporaneously with the end of the arid period. 相似文献