On lattice reduction algorithms for solving weighted integer least squares problems: comparative study   总被引：2，自引：1，他引：1  

Shahram Jazaeri  Alireza Amiri-Simkooei  Mohammad Ali Sharifi 《GPS Solutions》2014,18(1):105-114

Decorrelation or reduction theory deals with identifying appropriate lattice bases that aid in accelerating integer search to find the optimal integer solution of the weighted integer least squares problem. Orthogonality defect has been widely used to measure the degree of orthogonality of the reduced lattice bases for many years. This contribution presents an upper bound for the number of integer candidates in the integer search process. This upper bound is shown to be a product of three factors: (1) the orthogonality defect, (2) the absolute value of the determinant of the inverse of the generator matrix of the lattice, and (3) the radius of the search space raised to the power of the dimension of the integer ambiguity vector. Four well-known decorrelation algorithms, namely LLL, LAMBDA, MLAMBDA, and Seysen, are compared. Many simulated data with varying condition numbers and dimensions as well as real GPS data show that the Seysen reduction algorithm reduces the condition number much better than the other algorithms. Also, the number of integer candidates, before and after the reduction process, is counted for all algorithms. Comparing the number of integer candidates, condition numbers, and orthogonality defect reveals that reducing the condition number and the orthogonality defect may not necessarily result in decreasing the number of integer candidates in the search process. Therefore, contrary to the common belief, reducing the orthogonality defect and condition number do not always result in faster integer least squares estimation. The results indicate that LAMBDA and MLAMBDA perform much better in reducing the number of integer candidates than the other two algorithms, despite having a larger orthogonality defect and condition number in some cases. Therefore, these two algorithms can speed up the integer least squares estimation problem in general and the integer ambiguity resolution problem in particular.  相似文献   

Development of fuzzy rule-based parameters for urban object-oriented classification using very high resolution imagery     

Alireza Hamedianfar 《国际地球制图》2013,28(3):268-292

Urban areas consist of spectrally and spatially heterogeneous features. Advanced information extraction techniques are needed to handle high resolution imageries in providing detailed information for urban planning applications. This study was conducted to identify a technique that accurately maps impervious and pervious surfaces from WorldView-2 (WV-2) imagery. Supervised per-pixel classification algorithms including Maximum Likelihood and Support Vector Machine (SVM) were utilized to evaluate the capability of spectral-based classifiers to classify urban features. Object-oriented classification was performed using supervised SVM and fuzzy rule-based approach to add spatial and texture attributes to spectral information. Supervised object-oriented SVM achieved 82.80% overall accuracy which was the better accuracy compared to supervised per-pixel classifiers. Classification based on the proposed fuzzy rule-based system revealed satisfactory output compared to other classification techniques with an overall accuracy of 87.10% for pervious surfaces and an overall accuracy of 85.19% for impervious surfaces.  相似文献   

Modelling of infiltration using artificial intelligence techniques in semi-arid Iran     

Parveen Sihag  Vijay P. Singh  Anastasia Angelaki  Vinod Kumar  Alireza Sepahvand  Evangelia Golia 《水文科学杂志》2013,58(13):1647-1658

ABSTRACT

Infiltration plays a fundamental role in streamflow, groundwater recharge, subsurface flow, and surface and subsurface water quality and quantity. In this study, adaptive neuro-fuzzy inference system (ANFIS), support vector machine (SVM) and random forest (RF) models were used to determine cumulative infiltration and infiltration rate in arid areas in Iran. The input data were sand, clay, silt, density of soil and soil moisture, while the output data were cumulative infiltration and infiltration rate, the latter measured using a double-ring infiltrometer at 16 locations. The results show that SVM with radial basis kernel function better estimated cumulative infiltration (RMSE = 0.2791 cm) compared to the other models. Also, SVM with M4 radial basis kernel function better estimated the infiltration rate (RMSE = 0.0633 cm/h) than the ANFIS and RF models. Thus, SVM was found to be the most suitable model for modelling infiltration in the study area.  相似文献   

Dynamic mechanism of turbulent flow in meandering channels: considerations for deflection angle     

Fariba Sadat Esfahani  Alireza Keshavarzi 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(5):1093-1114

To find turbulent flow structure inside meandering channels, three physical models of river meanders representing strongly curved bend, mild bend and elongated symmetrical meander loop were tested in this paper. Instantaneous velocity data in three dimensions were measured using Micro-ADV at different cross sections of these models. Depth averaged velocity vectors, streamwise velocity, secondary currents, turbulent and mean flow kinetic energy were investigated with respect to the sediment deposition pattern. In order to gain more regarding the force acting the sediment particles, three dimensional velocity fluctuations were analyzed in detailed inside the elongated symmetrical meander loop. Occurrence frequency, transition probability and angle of attack for different events were also computed for the points close to the bed. Of the present results, the importance of sweeps and ejections on sediment deposition can be detected. Further, distribution of bursting events is presented through the water column and compared the results with the previous works. Importantly, occurrence of fluctuating velocities in three dimensions at different locations inside the river meanders in addition to the effect of mean flow and turbulent components is responsible for sediment transport. Streamwise velocity distribution through the depth is also compared with some previous mathematical models. Researchers seeking the better control over the river morphology can apply this method without sacrificing much time and cost. This study is also included some insights to be pursued by future works.  相似文献   

Ellipsoidal Neumann geodetic boundary-value problem based on surface gravity disturbances: case study of Iran     

Mehdi Najafi-Alamdary  Alireza A. Ardalan  Seyed-Rohallah Emadi 《Studia Geophysica et Geodaetica》2012,56(1):153-170

An ellipsoidal Neumann type geodetic boundary-value problem (GBVP) for the computation of disturbing potential on the surface of the Earth based on the surface gravity disturbance as the boundary data is formulated. The solution methodology of the GBVP can be algorithmically summarized as follows: (i) using global navigation satellite systems (GNSS) coordinates of the gravity stations, the surface gravity disturbances are generated as the boundary data. (ii) Applying the deflection correction to the gravity disturbances to arrive at the derivative of the surface disturbing potential along the ellipsoidal normal. (iii) Removing the low frequencies part of the gravity field using harmonic expansion to degree and order 110. (iv) Using the short wavelength part of the corrected gravity disturbances derived in the previous section as the boundary data within the constructed GBVP to derive the short wavelength disturbing potential over the Earth surface. (v) The computed shortwave length signals of disturbing potentials are converted to disturbing potential values by restoring the removed effects.  相似文献   

A Poroelastic Description of Permeability Evolution     

Alireza Hassanzadegan  Günter Zimmermann 《Pure and Applied Geophysics》2014,171(7):1187-1201

Pore pressure changes in a geothermal reservoir, as a result of injection and/or production of water, result in changes of stress acting on the reservoir rock and, consequently, changes in the mechanical and transport properties of the rock. Bulk modulus and permeability were measured at different pressures and temperatures. An outcropping equivalent of Rotliegend reservoir rock in the North German Basin (Flechtinger sandstone) was used to perform hydrostatic tests and steady state fluid flow tests. Permeability measurements were conducted while cycling confining pressure; the dependence of permeability on stress was determined at a constant downstream pressure of 1 MPa. Also, temperature was increased stepwise from 30 to 140 °C and crack porosity was calculated at different temperatures. Although changes in the volumes of cracks are not significant, the cracks control fluid flow pathways and, consequently, the permeability of the rock. A new model was derived which relates microstructure of porosity, the stress–strain curve, and permeability. Porosity change was described by the first derivative of the stress–strain curve. Permeability evolution was ascribed to crack closure and was related to the second derivative of the stress–strain curve. The porosity and permeability of Flechtinger sandstone were reduced by increasing the effective pressure and decreased after each pressure cycle.  相似文献   

New biorthogonal potential–density basis functions     

Alireza Rahmati  Mir Abbas Jalali 《Monthly notices of the Royal Astronomical Society》2009,393(4):1459-1466

We use the weighted integral form of spherical Bessel functions and introduce a new analytical set of complete and biorthogonal potential–density basis functions. The potential and density functions of the new set have finite central values and they fall off, respectively, similar to   r ^{−(1+ l )}  and   r ^{−(4+ l )}  at large radii, where l is the latitudinal quantum number of spherical harmonics. The lowest order term associated with   l = 0  is the perfect sphere of de Zeeuw. Our basis functions are intrinsically suitable for the modelling of three-dimensional, soft-centred stellar systems and they complement the basis sets of Clutton-Brock, Hernquist & Ostriker and Zhao. We test the performance of our functions by expanding the density and potential profiles of some spherical and oblate galaxy models.  相似文献   

Kerman Clay Improvement by Lime and Bentonite to Be Used as Materials of Landfill Liner     

Alireza Firoozfar  Nasrin Khosroshiri 《Geotechnical and Geological Engineering》2017,35(2):559-571

Kerman province, located in the south eastern Iran, is dominated with clays which can be used in different projects. The liner system within a landfill is constructed to control leachate migration and can be constructed by low permeable natural soils or plastic lining materials, environmentally however, natural materials is preferred that usually need to be amended in order to meet requirements recommended by environmental agencies. This research examines the possibility of using the Kerman collapsible clay as a liner layer material. A set of laboratory test was conducted on pure soil samples and additive treated samples. The moderate collapse potential of the used soil is decreased with wet compaction and under the effect of additive-soil reactions. Laboratory investigations showed that lime and bentonite treatment improved the hydraulic conductivity. The results revealed hydraulic conductivities on the order of 10^?8 m/s. The obtained values met the 1.0E?07 m/s criterion required by Iranian standards. Unconfined compression tests were also performed on pure soil and additive amended samples. The unconfined compression strength values demonstrated gradual decreases with the addition of bentonite and considerable increases with adding lime such that with adding 1% lime the unconfined compression strength increased by 75%. This study verified that the Kerman collapsing clay can be used as a liner material using lime and bentonite as additives.  相似文献   

Fault diagnosis using noise modeling and a new artificial immune system based algorithm     

Farshid Abbasi  Alireza Mojtahedi  Mir Mohammad Ettefagh 《地震工程与工程振动(英文版)》2015,14(4):725-741

A new fault classification/diagnosis method based on artificial immune system(AIS) algorithms for the structural systems is proposed. In order to improve the accuracy of the proposed method, i.e., higher success rate, Gaussian and non-Gaussian noise generating models are applied to simulate environmental noise. The identification of noise model, known as training process, is based on the estimation of the noise model parameters by genetic algorithms(GA) utilizing real experimental features. The proposed fault classification/diagnosis algorithm is applied to the noise contaminated features. Then, the results are compared to that obtained without noise modeling. The performance of the proposed method is examined using three laboratory case studies in two healthy and damaged conditions. Finally three different types of noise models are studied and it is shown experimentally that the proposed algorithm with non-Gaussian noise modeling leads to more accurate clustering of memory cells as the major part of the fault classification procedure.  相似文献   

Experimental Investigation and Kinetic Modeling of p‐Nitrophenol and Phenol by Kissiris‐Immobilized Ralstonia eutropha in a Batch Reactor          下载免费PDF全文

Mahdi Motamedi  Alireza Habibi  Mohammad Maleki  Farzaneh Vahabzadeh 《洁净——土壤、空气、水》2015,43(2):237-243

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