Coronal He+ λ304 radiation     

Imad A. Ahmad 《Solar physics》1977,53(2):409-415

The intensity of the He⁺ 304 coronal line relative to the H⁰ 1216 line, including the dominant contribution due to resonance scattering, is presented. All physical processes important in the corona are included. It is found that He⁺ 304 is a major contributor to the XUV corona, and that the sensitivity of the He⁺ 304/H⁰ 1216 intensity ratio to coronal temperature is very weak, supporting the belief that this ratio is a good indicator of the coronal helium abundance.  相似文献   

Microwave solar limb brightening     

I. A. Ahmad  M. R. Kundu 《Solar physics》1981,69(2):273-287

Previous models of microwave limb brightening have omitted the alignment of spicules along supergranule boundaries, have neglected the high temperature sheath around spicules, and have assumed an interspicular medium which was averaged over chromospheric network and non-network regions. We present a model which includes these factors. By constraining the model to conform to results from earlier UV and optical studies we are effectively left with two free parameters: the temperature at the core of the spicules, T _core, and (at solar minimum), the interspicular chromospheric network density model of the lower transition zone. The absence of limb brightening at the short millimeter wavelengths implies T _core 6000 k. Differences between the model and certain deconvolved observations near 9 mm are expected as a consequence of an extension of emission beyond the optical limb, predicted by the model, which affects the accuracy of the deconvolution technique. Unlike models which assume homogeneous spicules in a random distribution, ours does not require an abnormally high spicule area.  相似文献   

COMPARISON OF HEAVY METAL CONCENTRATIONS IN SURFACE SEDIMENT OF TANJUNG PIAI WETLAND WITH OTHER SITES RECEIVING ANTHROPOGENIC INPUTS ALONG THE SOUTHWESTERN COAST OF PENINSULAR MALAYSIA     

Chee Kong Yap Mew Seong Choh Franklin Edward Berandah Ahmad Ismail Soon Guan Tan 《湿地科学》2006,4(1):48-57

1 INTRODUCTIONOur sampling trip to Tanjung Piai wetland in2002 showed that the site had not been developed andrecognized yet as a wetland of international importance(Ramsar). Recently, our field trip in January 2005to the same site to collect sediment sam…  相似文献   

RKRV Potential Energy Curves, Dissociation Energies, γ-Centroids And Franck-Condon Factors Of YO, CrO, BN, ScO, SiO And AlO Molecules     

R.R. Reddy  Y. Nazeer Ahammed  K. Rama Gopal  P. Abdul Azeem  S. Anjaneyulu 《Astrophysics and Space Science》1998,262(2):223-240

The potential energy curves for the electronic ground states of astrophysically important YO, CrO, BN, ScO, SiO and AlO molecules are constructed techniques using the five-parameter Hulburt-Hirschfelder function. The estimated dissociation energies are 7.235±0.15, 4.337 ± 0.09, 3.917 ± 0.09, 6.899 ± 0.14, 8.181 ± 0.17 and 5.202 ± 0.11 eV for YO, CrO, BN, ScO, SiO and AlO, respectively. The estimated D₀ values are in reasonably good agreement with literature values. The r-Centroids and Franck-Condon factors for the bands of B^{2 +} – X^{2 +} of YO, B⁵ –X⁵ > of CrO, A³ – X³ of BN, B^{2 +} –X^{2 +} of ScO, E^{1 +} – X^{1 +} of SiO and D^{2 +} – X^{2 +} and B^{2 +} –X^{2 +} of AlO molecules have been determined. The Franck-Condon factors are evaluated by the approximate analytical method of Jarmain and Fraser. The absence of the bands in these systems is explained.  相似文献   

Influence of earthquake ground motion incoherency on multi-support structures   总被引：2，自引：1，他引：2  

杨庆山  M.Saiid Saiidi  王航  Ahmad Itani 《地震工程与工程振动(英文版)》2002,1(2):167-180

A linear response history analysis method is used to determine the influence of three factors: geometric incoherency, wave-passage, and local site characteristics on the response of multi-support structures subjected to differential ground motions. A one-span frame and a reduced model of a 24-span bridge, located in Las Vegas, Nevada are studied, in which the influence of each of the three factors and their combinations are analyzed. It is revealed that the incoherency of earthquake ground motion can have a dramatic influence on structural response by modifying the dynamics response to uniform excitation and inducing pseudo-static response, which does not exist in structures subjected to uniform excitation. The total response when all three sources of ground motion incoherency are included is generally larger than that of uniform excitation.  相似文献   

River suspended sediment load prediction based on river discharge information: application of newly developed data mining models     

Sinan Q. Salih  Ahmad Sharafati  Khabat Khosravi  Hossam Faris  Ozgur Kisi  Hai Tao 《水文科学杂志》2020,65(4):624-637

ABSTRACT

Suspended sediment load (SSL) is one of the essential hydrological processes that affects river engineering sustainability. Sediment has a major influence on the operation of dams and reservoir capacity. This investigation is aimed at exploring a new version of machine learning models (i.e. data mining), including M5P, attribute selected classifier (AS M5P), M5Rule (M5R), and K Star (KS) models for SSL prediction at the Trenton meteorological station on the Delaware River, USA. Different input scenarios were examined based on the river flow discharge and sediment load database. The performance of the applied data mining models was evaluated using various statistical metrics and graphical presentation. Among the applied data mining models, the M5P model gave a superior prediction result. The current and one-day lead time river flow and sediment load were the influential predictors for one-day-ahead SSL prediction. Overall, the applied data mining models achieved excellent predictions of the SSL process.  相似文献   

Integrative stochastic model standardization with genetic algorithm for rainfall pattern forecasting in tropical and semi-arid environments     

Sinan Q. Salih  Ahmad Sharafati  Isa Ebtehaj  Hadi Sanikhani  Ridwan Siddique  Ravinesh C. Deo 《水文科学杂志》2020,65(7):1145-1157

ABSTRACT

Climate patterns, including rainfall prediction, is one of the most complex problems for hydrologist. It is inherited by its natural and stochastic phenomena. In this study, a new approach for rainfall time series forecasting is introduced based on the integration of three stochastic modelling methods, including the seasonal differencing, seasonal standardization and spectral analysis, associated with the genetic algorithm (GA). This approach is specially tailored to eradicate the periodic pattern effects notable on the rainfall time series stationarity behaviour. Two different climates are selected to evaluate the proposed methodology, in tropical and semi-arid regions (Malaysia and Iraq). The results show that the predictive model registered an acceptable result for the forecasting of rainfall for both the investigated regions. The attained determination coefficient (R²) for the investigated stations was approx. 0.91, 0.90 and 0.089 for Mosul, Baghdad and Basrah (Iraq), and 0.80, 0.87 and 0.94 for Selangor, Negeri Sembilan and Johor (Malaysia).  相似文献   

Application of newly developed ensemble machine learning models for daily suspended sediment load prediction and related uncertainty analysis     

Ahmad Sharafati  Seyed Babak Haji Seyed Asadollah  Davide Motta 《水文科学杂志》2020,65(12):2022-2042

ABSTRACT

Ensemble machine learning models have been widely used in hydro-systems modeling as robust prediction tools that combine multiple decision trees. In this study, three newly developed ensemble machine learning models, namely gradient boost regression (GBR), AdaBoost regression (ABR) and random forest regression (RFR) are proposed for prediction of suspended sediment load (SSL), and their prediction performance and related uncertainty are assessed. The SSL of the Mississippi River, which is one of the major world rivers and is significantly affected by sedimentation, is predicted based on daily values of river discharge (Q) and suspended sediment concentration (SSC). Based on performance metrics and visualization, the RFR model shows a slight lead in prediction performance. The uncertainty analysis also indicates that the input variable combination has more impact on the obtained predictions than the model structure selection.  相似文献   

Groundwater vulnerability assessment and evaluation of human activity impact (HAI) within the Dead Sea groundwater basin,Jordan   总被引：3，自引：2，他引：1  

Ahmad Al-Hanbali  Akihiko Kondoh 《Hydrogeology Journal》2008,16(3):499-510

Groundwater vulnerability to contamination was determined within the Dead Sea groundwater basin, Jordan, using the DRASTIC model and evaluation of human activity impact (HAI). DRASTIC is an index model composed of several hydrogeological parameters and, in this study, the recharge parameter component was calculated as a function of rainfall, soil permeability, slope percentage, fault system, and the intersection locations between the fault system and the drainage system, based on the hydrogeologic characteristics of hard-rock terrain in an arid region. To evaluate the HAI index, a land use/cover map was produced using an ASTER VNIR image, acquired for September 2004, and combined with the resultant DRASTIC model. By comparing the DRASTIC and HAI indices, it is found that human activity is affecting the groundwater quality and increasing its pollution risk. The land use/cover map was verified using the average nitrate concentrations in groundwater associated with land in each class. A sensitivity analysis was carried out in order to study the model sensitivity. The analyses showed that the depth to water table and hydraulic conductivity parameters have no significant impact on the model, whereas the impact of vadose zone, aquifer media, and recharge parameters have a significant impact on the DRASTIC model.  相似文献   

Three-Dimensional Wideband Beamforming for Imaging Through a Single Wall   总被引：2，自引：0，他引：2  

Ahmad  F. Yimin Zhang Amin  M.G. 《Geoscience and Remote Sensing Letters, IEEE》2008,5(2):176-179

Through-the-wall imaging and urban sensing is an emerging area of research and development. The incorporation of the effects of signal propagation through wall material in producing an indoor image is important for reliable through-the-wall mission operations. We have previously analyzed wall effects, such as refraction and change in propagation speed, and designed a wideband beamformer for 2D imaging using line arrays. In this letter, we extend the analysis to 3D imaging via delay-and-sum beamforming in the presence of a single uniform wall. The third dimension provides valuable information on target heights that can be used for enhancing target discrimination/identification. Supporting simulation results are provided.  相似文献