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Energy spectrum of multi-radiation of X-rays in a low energy mather-type plasma focus device

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Chinese Physics B 2014年第6期23卷 375-380页

作者： farzin m.aghamir Reza A.Behbahani Department of Physics University of Tehran

The multi-radiation of X-rays was investigated with special attention to their energy spectrum in a mather-type plasma focus device （operated with argon gas）. The analysis is based on the effect of anomalous resistances. To study the energy spectrum, a four-channel diode X-ray spectrometer was used along with a special set of filters. The filters were suitable for detection of medium range X-rays as well as hard X-rays with energy exceeding 30 keV. The results indicate that the anomalous resistivity effect during the post pinch phase may cause multi-radiation of X-rays with a total duration of 300 ± 50 ns. The significant contribution of Cu-Kα was due to the medium range X-rays, nonetheless, hard X-rays with energies greater than 15 keV also participate in the process. The total emitted X-ray energy in the forms of Cu-K and Cu-K/3 was around 0.14 ± 0.02 （J/Sr） and 0.04 ±0.01 （J/Sr）, respectively. The total energy of the emitted hard X-ray （〉 15 keV） was around 0.12± 0.02 （J/Sr）.

关键词： mather-type plasma focus device hard X-rays multi-radiation tube multiple voltage peaks,anomalous resistances

Gain enhancement in two-stream free electron laser with a planar wiggler and an axial guide magnetic field

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Chinese Physics B 2012年第9期21卷 247-250页

作者： S.Saviz Z.Rezaei farzin m.aghamir Plasma Physics Research Center Science and Research BranchIslamic Azad University Department of Physics University of Tehran

The theory for a two-stream free electron laser （FEL） consisting of a relativistic electron beam transported alongthe axis of a planar wiggler in the presence of an axial guiding magnetic field is proposed and investigated. The electron trajectories and the small signal gain are derived. The characteristic of the linear gain and the normalized maximum gain are studied numerically. The result shows that the normalized maximum gain is considerably enhanced in comparison with that of the single stream. The effect of the difference between the energies of the two beams in this configuration of FEL is also considered, and we find that the gain is affected by the energy differences between groups 1 and 2.

关键词： wo-stream free-electron laser

The effects of self-fields on the electron trajectory in a two-stream free electron laser with a helical wiggler and an axial guiding magnetic field

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Chinese Physics B 2012年第10期21卷 251-254页

作者： S.Saviz E.Lashani farzin m.aghamir Plasma Physics Research Center Science and Research BranchIslamic Azad UniversityTehranP.O.Box 14665-678Iran Department of Physics University of TehranN.Kargar AveTehran 14399Iran

A theory for the two-stream free-electron laser（TSFEL） with a helical wiggler and an axial guide magnetic field is *** the analysis,the effects of self-fields are taken into *** analysis of the two-stream steady-state electron trajectories is given by solving the equation of *** calculations show that there are seven groups of orbits in the presence of self-fields instead of two groups reported in the absence of *** stability of the trajectories is studied numerically.

关键词： two-stream free electron laser electron trajectory

Effects of self-fields on electron trajectory and gain in two-stream electromagnetically pumped free-electron laser with ion channel guiding

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Chinese Physics B 2011年第7期20卷 158-164页

作者： S.Saviz farzin m.aghamir H.mehdian m.Ghorannevis Plasma Physics Research Center Science and Research BranchIslamic Azad UniversityTehranP.O.Box.14665-678Iran Department of Physics University of TehranN.Kargar AveTehran 14399Iran Department of Physics and Institute for Plasma Research Tarbiat Moallem University49Dr.Mofatteh avenueTehran 15614Iran

A theory for the two-stream free-electron laser with an electromagnetic wiggler （EmW） and an ion channel guiding is developed. In the analysis, the effects of self-fields have been taken into account. The electron trajectories and the small signal gain are derived. The stability of the trajectories, the characteristics of the linear gain and the normalized maximum gain are studied numerically. The dependence of the normalized frequency ω corresponding to the maximum gain on the ion-channel frequency is presented. The results show that there are seven groups of orbits in the presence of the self-fields, which are similar to those reported in the absence of the self-fields. It is also shown that the normalized gains of 2 groups decrease while the rest increase with the increasing normalized ion-channel frequency. Furthermore, it is found that the two-stream instability and the self-field lead to a decrease in the maximum gain except for group 4.

关键词： free electron laser two-stream

Landau damping in a bounded magnetized plasma column

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Chinese Physics B 2015年第2期24卷 287-294页

作者： H.Zakeri-Khatir F.m.aghamir Department of Physics University of Tehran

The damping decrement of Landau damping and the effect of thermal velocity on the frequency spectrum of a propagating wave in a bounded plasma column are *** magnetized plasma column partially filling a cylindrical metallic tube is considered to be collisionless and *** Landau damping is due to the thermal motion of charge carriers and appears whenever the phase velocity of the plasma waves exceeds the thermal velocity of *** analysis is based on a self-consistent kinetic theory and the solutions of the wave equation in a cylindrical plasma waveguide are presented using Vlasov and maxwell *** hybrid mode dispersion equation for the cylindrical plasma waveguide is obtained through the application of appropriate boundary conditions to the plasma-vacuum *** dependence of Landau damping on plasma parameters and the effects of the metallic tube boundary on the dispersion characteristics of plasma and waveguide modes are investigated in detail through numerical calculations.

关键词： Landau damping cylindrical plasma waveguide Vlasov equation dispersion characteristic

Analysis of Landau damping in radially inhomogeneous plasma column

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Chinese Physics B 2018年第5期27卷 365-373页

作者： H Rajabalinia-Jelodar m K Salem F m aghamir H Zakeri-Khatir Plasma Physics Research Center Science and Research BranchIslamic Azad University Department of Physics University of Tehran

The Landau damping behavior in a cylindrical inhomogeneous warm magnetized plasma waveguide has been *** radial inhomogeneity for different characteristic lengths（L0） with strong spatial dispersion has been taken into *** analyses have been considered for two limits ωce 〈 ωpe and ωce 〉 ωpe. Due to the radial inhomogeneity of the plasma, all essential equations for studying the Landau damping are calculated in the Bessel–Furrier and differential Bessel–Furrier expansions. The dependence of Landau damping on the inhomogeneity, temperature and external magnetic field for electrostatic modes is scrutinized and described in detail through numerical calculations. The associated numerical results are presented and discussed.

关键词： inhomogeneous warm plasma cylindrical plasma waveguide Landau damping electrostatic modes

Experimental investigation and prediction of free fall jet scouring using machine learning models

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International Journal of Sediment Research 2023年第3期38卷 405-420页

作者： farzin Salmasi Parveen Sihag John Abraham meysam Nouri Department of Water Engineering Faculty of Agriculture University of Tabriz Department of Civil Engineering Chandigarh University School of Engineering University of St.Thomas Minnesota Department of Water Engineering Faculty of Agriculture Urmia University Department of Civil Engineering Saeb University

The current study deals with the depth of scour at the location of impact between a free fall jet and a riverbed. The current study is based on extensive laboratory experiments that were designed to mimic full-scale behavior. The literature review shows that relations among hydraulic parameters for predicting the depth of scour are complex; therefore, six artificial intelligence techniques are used in the current study to capture these complex relation. A total of 120 observations are used for the analysis. Results from the experiments show that with increasing downstream water depth(h), the impinging jet causes increasingly turbulent currents and large vortices that increase the scouring of the riverbed. Increasing discharge per unit width(q) enhances the relative scour depth(D/H) while increasing the average diameter of the riverbed materials(d) decreases D/H, where D is maximum scour depth and H is the height of the falling jet. With increasing(particle Froude number Fr), the relative scour depth *** the current study the prediction accuracy of Gene Expression Programming(GEP), multivariate Adaptive Regression Spline(mARS), m5P Tree, Random Forest(RF), Random Tree(RT), and Reduces Error Pruning Tree(REP Tree) techniques are evaluated using the relative scour depth(D/(H-h)). The performance evaluation indices and graphical methods suggest that the GEP based model is more accurate than other prediction methods for the relative scour depth with a coefficient of determination(R2) equal to 0.8330 and 0.8270, a mean absolute error(mAE) equal to 0.1125 and 0.0902, root mean square error(RmSE) values of 0.1463 and 0.1116, and Willmott’s Index(WI) equal to 0.8998 and 0.9014, for the training and testing stages.

关键词： Free jet Scour Gene Expression Programming (GEP) Random Forest (RF) multivariate Adaptive Regression Spline (mARS)

Effects of chelating agents on the sol-gel synthesis of nano-zirconia:Comparison of the Pechini and sugar-based methods

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International Journal of minerals,metallurgy and materials 2020年第5期27卷 693-702页

作者： Faramarz Kazemi farzin Arianpour mahdiar Taheri Ali Saberi Hamid Reza Rezaie Department of mining and metallurgy Amirkabir University of TechnologyTehranIran Research and Application Center Kastamonu UniversityKastamonuTurkey College of Engineering and Computer Science The Australian National UniversityCanberraAustralia materials Processing Faculty of Engineering ScienceUniversity of BayreuthBayreuthGermany School of metallurgy and materials Engineering Iran University of Science and TechnologyTehranIran

This study focused on the comparison of the Pechini and sugar-based combustion synthesis methods to produce nano-zirconia. Zirconium hydroxide was utilized as metal precursor and citric acid, sucrose, and fructose were used as chelating agents, followed by calcination at 500, 600, and 700°C in air, respectively. Characterization was conducted by thermal analysis, specific surface area measurement, Fourier transform infrared spectroscopy, X-ray diffraction, and scanning and transmission electron microscopy. When sucrose and citric acid were used as chelating agents during synthesis, mixtures of monoclinic and tetragonal phases were formed after calcination at 600 and 700°C. In the fructose samples, the tetragonal structure was the unique characterized phase. The tetragonal parameters in the fructose samples were determined using the diffraction data and the lattice parameter ratio was proven to increase with the temperature increase. Compared with the citrate and sucrose samples, the largest specific surface area(27 m2·g-1) and smallest particle size(39.1 nm) were obtained for the fructose sample after calcination at 700°C. The study revealed the formation of single-phase stabilized tetragonal zirconia using fructose as chelating agent after calcination at 500°C, and the presence and formation mechanism of stabilized tetragonal phase were also discussed on the basis of the X-ray and electron diffraction studies.

关键词： zirconia nanopowder sol-gel sugar Pechini chelation

A New Stochastic model for Classifying Flexible measures in Data Envelopment Analysis

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Journal of the Operations Research Society of China 2021年第3期9卷 569-592页

作者： mansour Sharifi Ghasem Tohidi Behrouz Daneshian farzin modarres Khiyabani Department of mathematics Tabriz BranchIslamic Azad UniversityTabrizIran Department of mathematics Central Tehran BranchIslamic Azad UniversityTehranIran

The way to deal with flexible data from their stochastic presence point of view as output or input in the evaluation of efficiency of the decision-making units(DmUs)motivates new perspectives in modeling and solving data envelopment analysis(DEA)in the presence of flexible *** the orientation of flexible data is not pre-determined,and because the number of DmUs is fixed and all the DmUs are independent,flexible data can be treated as random variable in terms of both input and output *** a result,the selection of flexible variable as input or output for n DmUs can be regarded as binary random *** the randomness of choosing flexible data as input or output,we deal with DEA models in the presence of flexible data whose input or output orientation determines a binomial distribution *** study provides a new insight to classify flexible variable and investigates the input or output status of a variable using a stochastic *** proposed model obviates the problems caused by the use of the large m number and using its different values in previous *** addition,it can obtain the most appropriate efficiency value for decision-making units by assigning the chance of choosing the orientation of flexible variable to the model *** proposed method is compared with other available methods by employing numerical and empirical examples.

关键词： Data envelopment analysis Flexible variables Stochastic model Random variable Classifying