The clustering, number counts and morphology of extremely red (R–K > 5) galaxies to K≤ 21     

Nathan D. Roche  Omar Almaini  James Dunlop  R. J. Ivison  C. J. Willott 《Monthly notices of the Royal Astronomical Society》2002,337(4):1282-1298

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

Mahmoud El-Nouby ADAM  Khalafallah Omar KASSEM  Emad Ali AHMED 《大气和海洋科学快报》2013,(4):173-178

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.  相似文献   

Structure and seasonal variability of fish food webs in an estuarine tropical marine protected area (Senegal): Evidence from stable isotope analysis     

Djibril Faye  Luis Tito de Morais  Jean Raffray  Oumar Sadio  Omar Thiom Thiaw  Franois Le Loc&#x;h 《Estuarine, Coastal and Shelf Science》2011,92(4):69

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A scale-selective multilevel method for long-wave linear acoustics     

Stefan Vater  Rupert Klein  Omar M. Knio 《Acta Geophysica》2011,59(6):1076-1108

A new method for the numerical integration of the equations for one-dimensional linear acoustics with large time steps is presented. While it is capable of computing the “slaved” dynamics of short-wave solution components induced by slow forcing, it eliminates freely propagating compressible short-wave modes, which are under-resolved in time. Scale-wise decomposition of the data based on geometric multigrid ideas enables a scale-dependent blending of time integrators with different principal features. To guide the selection of these integrators, the discrete-dispersion relations of some standard second-order schemes are analyzed, and their response to high wave number low frequency source terms are discussed. The performance of the new method is illustrated on a test case with “multiscale” initial data and a problem with a slowly varying high wave number source term.  相似文献   

Comprehensive physicochemical study of dioctahedral palygorskite-rich clay from Marrakech High Atlas (Morocco)     

Benaissa Rhouta  Ezzouhra Zatile  Lahcen Bouna  Omar Lakbita  Francis Maury  Lahcen Daoudi  Marie Christine Lafont  M’Barek Amjoud  François Senocq  Amane Jada  Ahmed Aït Aghzzaf 《Physics and Chemistry of Minerals》2013,40(5):411-424

This study is devoted to the physicochemical and mineralogical characterizations of palygorskite from Marrakech High Atlas, Morocco. The raw clay and its Na⁺-saturated <2 μm fraction were characterized using chemical, structural, and thermal analytical techniques. Measurements of specific surface area and porous volume are reported. The clay fraction was found to be made up of 95 % of palygorskite and 5 % of sepiolite. An original feature of this palygorskite is its deficiency in zeolitic H₂O. The half-cell structural formula of its dehydrated form was determined on the basis of 21 oxygens to be (Si_7.92Al_0.08)(Mg_2.15Al_1.4Fe_0.4Ti_0.05 $ \square_{1} $ )(Ca_0.03Na_0.08K_0.04)O₂₁, while the hydrated form could be formulated as (Si_7.97Al_0.03)(Mg_2.17Al_1.46Fe_0.40Ti_0.05)(Ca_0.03Na_0.07K_0,03)O_20.18(OH)_1.94(OH₂)_3.88·2.43 H₂O. These formulas show that the (Al³⁺+Fe³⁺)/Mg²⁺ ratio is around 0.84, revealing a pronounced dioctahedral character. Further, inside its octahedral sheet, it was determined that the inner M₁ sites are occupied by vacancies, whereas the M₂ sites are shared between 90 % of trivalent cations (78 % for Al³⁺ and 22 % for Fe³⁺), 7.5 % of Mg²⁺, and 2.5 % of Ti⁴⁺, all of them linked to 1.94 of structural hydroxyls. The two remaining Mg²⁺ by half-cell occupy edge M₃ sites and are coordinated to 3.88 molecules of OH₂. Channels of this palygorskite are deficient in zeolitic H₂O since they contain only 2.43 H₂O molecules. A correlation was found between these results and the observation of very intense and well-resolved FTIR bands arising from dioctahedral domains (mainly Al₂OH, Fe₂OH, and AlFeOH) along with very small responses from a trioctahedral domain (Mg₃OH). Accordingly, a schematic representation of the composition of the octahedral sheet was proposed. The cation exchange capacity, specific surface area, and total pore volume were also assessed to be ca. 21.2 meq/100 g, 116 m²/g, and 0.458 cm³/g, respectively.  相似文献   

A priori testing of sparse adaptive polynomial chaos expansions using an ocean general circulation model database   总被引：1，自引：0，他引：1  

Justin Winokur  Patrick Conrad  Ihab Sraj  Omar Knio  Ashwanth Srinivasan  W. Carlisle Thacker  Youssef Marzouk  Mohamed Iskandarani 《Computational Geosciences》2013,17(6):899-911

This work explores the implementation of an adaptive strategy to design sparse ensembles of oceanic simulations suitable for constructing polynomial chaos surrogates. We use a recently developed pseudo-spectral algorithm that is based on a direct application of the Smolyak sparse grid formula and that allows the use of arbitrary admissible sparse grids. The adaptive algorithm is tested using an existing simulation database of the oceanic response to Hurricane Ivan in the Gulf of Mexico. The a priori tests demonstrate that sparse and adaptive pseudo-spectral constructions lead to substantial savings over isotropic sparse sampling in the present setting.  相似文献   

Abu Roash G dolomite reservoir characterization using seismic inversion technique, Horus field, Western Desert, Egypt     

Omar Mohamed Hassan Al Mahdy  Mohamed Salah Sedek 《Arabian Journal of Geosciences》2013,6(6):1769-1797

The main objective of this paper was the characterization of the reservoir (Abu Roash G dolomite) in terms of acoustic impedance from surface seismic data complemented by available well logs. To reach our target, a two-step procedure was followed: first, identification of the reservoir signatures using synthetic seismogram using Strata program in Hampson–Russell software and second, applying inversion technique to the post-stack seismic data using Strata program in Hampson–Russell software to obtain acoustic impedance profiles and maps. This procedure was applied to 12 3D seismic lines (six cross-lines, and six in-lines) from Horus field in Western Desert in Egypt after converting them from analog state to SEGY format by vectorization. Five wells had been used in this study. The outcome of this paper is an improved subsurface image of seismic data and achieving the reservoir characterization in a good way.  相似文献   

Multi-label class assignment in land-use modelling     

Hichem Omrani  Fahed Abdallah  Omar Charif  Nicholas T. Longford 《International journal of geographical information science》2013,27(6):1023-1041

During the last two decades, a variety of models have been applied to understand and predict changes in land use. These models assign a single-attribute label to each spatial unit at any particular time of the simulation. This is not realistic because mixed use of land is quite common. A more detailed classification allowing the modelling of mixed land use would be desirable for better understanding and interpreting the evolution of the use of land. A possible solution is the multi-label (ML) concept where each spatial unit can belong to multiple classes simultaneously. For example, a cluster of summer houses at a lake in a forested area should be classified as water, forest and residential (built-up). The ML concept was introduced recently, and it belongs to the machine learning field. In this article, the ML concept is introduced and applied in land-use modelling. As a novelty, we present a land-use change model that allows ML class assignment using the k nearest neighbour (kNN) method that derives a functional relationship between land use and a set of explanatory variables. A case study with a rich data-set from Luxembourg using biophysical data from aerial photography is described. The model achieves promising results based on the well-known ML evaluation criteria. The application described in this article highlights the value of the multi-label k nearest neighbour method (MLkNN) for land-use modelling.  相似文献   

Features of soil redistribution and major element migration in a karst hillslope of Southwest China     

Chang-shun Song  Hong-bing Ji  Howard Omar Beckford  Hua-shuo Chu  Kun Zhang  Shi-jie Wang 《山地科学学报》2018,15(9):1892-1908

In this study, we investigated the spatial characteristics of the rate of soil distribution and the mechanism of major element migration in a typical karst hillslope in Guangxi Province, Southwestern China. Soil redistribution was examined using ¹³⁷Cs technique under different hillslope components. With the combination of geochemical methods, the migration characteristics of major elements in soils of three hillslope components in both the horizontal and vertical directions were determined. Thirty-seven soil samples were collected and analyzed for ¹³⁷Cs and the major elements were determined. By using the profile distribution model the mean soil redistribution rates were found to be -17.01, 0.40 and -23.30 t ha^-1 yr^-1 in the summit (BYSD), shoulder (BYSY) and toeslope (BYSJ) components of the studied hillslope, respectively. In comparison to BYSD, the sesquioxides of Fe₂O₃ and TiO₂ tend to be enriched, whereas the alkalis (CaO, MgO, Na₂O and K₂O) tend to be depleted, both in the shoulder and toeslope components. Due to human and animal activities, the contents of CaO, MgO, K2O and Na₂O have somewhat increased within the topsoil. The results indicated that ¹³⁷Cs activities are significantly correlated with clay particles and organic matter, and are affected by the pedogenic process and vegatation. Overall, it maybe necessary to use techniques such as ¹³⁷Cs to investigate soil erosion with the combination of geochemical methods.  相似文献   

New methodology for urban seismic risk assessment from a holistic perspective   总被引：2，自引：0，他引：2  

Martha L. Carreño  Omar D. Cardona  Alex H. Barbat 《Bulletin of Earthquake Engineering》2012,10(2):547-565

The seismic risk evaluation usually works with a fragmented concept of risk, which depends on the scientific discipline in charge of the assessment. To achieve an effective performance of the risk management, it is necessary to define risk as the potential economic, social and environmental consequences due to a hazardous phenomenon in a period of time. This article presents a methodology which evaluates the seismic risk from a holistic perspective, which means, it takes into account the expected physical damage and also the conditions related to social fragility and lack of resilience, which favour the second order effects when a hazard event strikes an urban centre. This seeks to obtain results which are useful in the decision making process for risk reduction. The proposed method for urban seismic risk evaluation uses the fuzzy sets theory in order to handle qualitative concepts and variables involved in the assessment, the physical risk level and aggravation level, related to the social fragility and the lack of resilience, are evaluated and finally a total risk level is determinate.  相似文献