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Optical bistability and multistability in a defect slab doped by GaAs/AlGaAs multiple quantum wells

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Chinese Physics B 2016年第5期25卷 223-228页

作者： Seyyed Hossein Asadpour G Solookinejad M Panahi e ahmadi sangachin Department of Physics Marvdasht Branch Islamic Azad University

We proposed a new model for controlling the optical bistability（OB） and optical multistability（OM） in a defect slab doped with four-level GaAs/AlGaAs multiple quantum wells with 15 periods of 17.5 nm GaAs wells and 15-nm Al_（0.3）Ga_（0.7）As barriers. The effects of biexciton energy renormalization, exciton spin relaxation, and thickness of the slab on the OB and OM properties of the defect slab were theoretically investigated. We found that the transition from OB to OM or vice versa is possible by adjusting the controllable parameters in a lab. Moreover, the transmission, reflection, and absorption properties of the weak probe light through the slab were also discussed in detail.

关键词： optical bistability optical multistability quantum well nanostructure

Influence of Fano interference and incoherent processes on optical bistability in a four-level quantum dot nanostructure

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Chinese Physics B 2016年第3期25卷 205-209页

作者： Seyyed Hossein Asadpour G Solookinejad M Panahi e ahmadi sangachin Department of Physics Marvdasht Branch Islamic Azad University Marvdasht Iran

Role of Fano interference and incoherent pumping field on optical bistability in a four-level designed InGaN/GaN quantum dot nanostructure embedded in a unidirectional ring cavity are analyzed. It is found that intensity threshold of optical bistability can be manipulated by Fano interference. It is shown that incoherent pumping fields make the threshold of optical bistability behave differently by Fano interference. Moreover, in the presence of Fano interference the medium becomes phase-dependent. Therefore, the relative phase of applied fields can affect the behaviors of optical bistability and intensity threshold can be controlled easily.

关键词： optical bistability Fano interference incoherent pumping fields quantum dot nanostructure

enhanced Kerr nonlinearity in a quantized four-level graphene nanostructure

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Chinese Physics B 2016年第7期25卷 234-238页

作者： Ghahraman Solookinejad M Panahi e ahmadi Seyyed Hossein Asadpour Department of Physics Marvdasht Branch Islamic Azad University

In this paper, a new model is proposed for manipulating the Kerr nonlinearity of right-hand circular probe light in a monolayer of graphene nanostructure. By using the density matrix equations and quantum optical approach, the third-order susceptibility of probe light is explored numerically. It is realized that the enhanced Kerr nonlinearity with zero linear absorption can be provided by selecting the appropriate quantities of controllable parameters, such as Rabi frequency and elliptical parameter of elliptical polarized coupling field. Our results may be useful applications in future all-optical system devices in nanostructures.

关键词： Kerr nonlinearity graphene nanostructure linear absorption

Kinetics of Silver Dissolution in Nitric Acid from Ag-Au_(0.04)-Cu_(0.10) and Ag-Cu_(0.23) Scraps

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Journal of Materials Science & Technology 2006年第5期22卷 696-700页

作者： S.K.Sadrnezhaad e.ahmadi M.Mozammel Center of excellence for Advanced Processes of Production of Materials Department of Materials Science and engineering Sharif University of TechnologyTehranIran

Kinetics of dissolution of silver present in precious metal 26～85℃. Dissolution rate of silver was much faster than scraps in HNO3 was studied in temperature range of that of copper at all temperatures. effects of particle size, stirring speed, acid concentration and temperature on the rate of dissolving of silver were evaluated. Dissolution rate decreases with particle size and increases with temperature. Dissolving was accelerated with acid concentrations less than 10 mol/L. Concentrations greater than 10 mol/L resulted in slowing down of the dissolution rate. Shrinking core model with internal diffusion equation t/τ=1-3（1-x）^2/3＋2（1-x） could be used to explain the mechanism of the reaction. Silver extraction resulted in activation energies of 33.95 kJ/mol for Ag-Au0.04-Cu0.10 and 68.87 kJ/mol for Ag-Cu0.23 particles. Inter-diffusion of silver and nitrate ions through the porous region of the insoluble alloying layer was the main resistance to the dissolving process. Results were tangible for applications in recycling of the material from electronic silver-bearing scraps, dental alloys, jewelry, silverware and anodic slime precious metal recovery.

关键词： Silver Copper Kinetics, Dissolution Shrinking core model Internal diffusion

Photoactive area modification in bulk heterojunction organic solar cells using optimization of electrochemically synthesized ZnO nanorods

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Chinese Physics B 2015年第11期24卷 422-427页

作者： Mehdi ahmadi Sajjad Rashidi Dafeh Department of Physics Faculty of Science Vali-e-Asr University of Rafsanjan

In this work, ZnO nanorod arrays grown by an electrochemical deposition method are investigated. The crucial parameters of length, diameter, and density of the nanorods are optimized over the synthesize process and nanorods growth time. Crystalline structure, morphologies, and optical properties of ZnO nanorod arrays are studied by different techniques such as x-ray diffraction, scanning electron microscope, atomic force microscope, and UV-visible transmission spectra. The ZnO nanorod arrays are employed in an inverted bulk heterojunction organic solar cell of Poly （3-hexylthiophene）：[6- 6] Phenyl-（6） butyric acid methyl ester to introduce more surface contact between the electron transporter layer and the active layer. Our results show that the deposition time is a very important factor to achieve the aligned and uniform ZnO nanorods with suitable surface density which is required for effective infiltration of active area into the ZnO nanorod spacing and make a maximum interfacial surface contact for electron collection, as overgrowing causes nanorods to be too dense and thick and results in high resistance and lower visible light transmittance. By optimizing the thickness of the active layer on top of ZnO nanorods, an improved efficiency of 3.17% with a high FF beyond 60% was achieved.

关键词： electrochemical deposition density-controlled ZnO nanorods inverted polymer solar cells active area modification

THe eXPONeNTIAL OF QUASI BLOCK-TOePLITZ MATRICeS

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Acta Mathematica Scientia 2022年第3期42卷 1018-1034页

作者： elahe BOLOURCHIAN Bijan ahmadi KAKAVANDI Department of Applied Mathematics Faculty of Mathematical SciencesShahid Beheshti UniversityTehranIran

The matrix Wiener algebra,W_(N):=M_(N)(W)of order N>0,is the matrix algebra formed by N×N matrices whose entries belong to the classical Wiener algebraWof functions with absolutely convergent Fourier series.A block-Toeplitz matrix T(a)=[A_(i,j)]i,j≥0is a block semi-infinite matrix such that its blocks A_(i,j) are finite matrices of order N,A_(i,j)=A^(r,s) whenever i-j=r-s and its entries are the coefficients of the Fourier expansion of the generator a:T→M_(N)(C).Such a matrix can be regarded as a bounded linear operator acting on the direct sum of N copies of L^(2)(T).We show that exp(T(a))differes from T(exp(a))only in a compact operator with a known bound on its *** fact,we prove a slightly more general result:for every entire function f and for every compact operator e,there exists a compact operator F such that f(T(a)+e)=T(f(a))+*** call these T(a)+e′s matrices,the quasi block-Toeplitz matrices,and we show that via a computation-friendly norm,they form a Banach *** results generalize and are motivated by some recent results of Dario Andrea Bini,Stefano Massei and Beatrice Meini.

关键词： Toeplitz matrix infinite matrix block matrix exponential functional calculus

epileptic Seizures Diagnosis Using Amalgamated extremely Focused eeG Signals and Brain MRI

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Computers, Materials & Continua 2023年第1期74卷 623-639页

作者： Farah Mohammad Saad Al-ahmadi Department of Computer Science King Saud UniversityRiyadh11543Saudi Arabia

There exists various neurological disorder based diseases like tumor,sleep disorder,headache,dementia and *** these,epilepsy is the most common neurological illness in humans,comparable to *** is a severe chronic neurological illness that can be discovered through analysis of the signals generated by brain neurons and brain Magnetic resonance imaging(MRI).Neurons are intricately coupled in order to communicate and generate signals from human *** to the complex nature of electroencephalogram(eeG)signals and MRI’s the epileptic seizures detection and brain related problems diagnosis becomes a challenging *** based techniques and machine learning models are continuously giving their contributions to diagnose all such diseases in a better way than the normal process of *** performancemay sometime degrade due to missing information,selection of poor classification model and unavailability of quality data that are used to train the models for better *** research work is an attempt to epileptic seizures detection by using amulti focus dataset based on eeG signals and *** key steps of this work are:feature extraction having two different streams i.e.,eeGusingwavelet transformation along with SVD-entropy,and MRI using convolutional neural network(CNN),after extracting features fromboth streams,feature fusion is applied to generate feature vector used by support vector machine(SVM)to diagnose the epileptic *** the experimental evaluation and results comparison with the current state-of-the-art techniques,it has been concluded that the performance of the proposed scheme is better than the existing models.

关键词： epilepsy eeG MRI CNN SVM

Inverted polymer solar cells with employing of electrochemical-anodizing synthesized TiO_2 nanotubes

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Chinese Physics B 2016年第4期25卷 320-324页

作者： Mehdi ahmadi Sajjad Rashidi Dafeh Hamed Fatehy Department of Physics Faculty of Science Vali-e-Asr University of Rafsanjan

An inverted structure of polymer solar cells based on Poly（3-hexylthiophene）（P3HT）：[6-6] Phenyl-（6） butyric acid methyl ester （PCBM） with using thin films of TiO2 nanotubes and nanoparticles as an efficient cathode buffer layer is developed. A total of three cells employing TiO2 thin films with different thickness values are fabricated. Two cells use layers of TiO2 nanotubes prepared via self-organized electrochemical-anodizing leading to thickness values of 203 and 423.7 nm, while the other cell uses only a simple sol-gel synthesized TiO2 thin film of nanoparticles with a thickness of 100 nm as electron transport layer. experimental results demonstrate that TiO2 nanotubes with these thickness values are inefficient as the power conversion efficiency of the cell using 100-nm TiO2 thin film is 1.55%, which is more than the best power conversion efficiency of other cells. This can be a result of the weakness of the electrochemical anodizing method to grow nanotubes with lower thickness values. In fact as the TiO2 nanotubes grow in length the series resistance （Rs） between the active polymer layer and electron transport layer increases, meanwhile the fill factor of cells falls dramatically which finally downgrades the power conversion efficiency of the cells as the fill factor falls.

关键词： inverted polymer solar cells TiO2 nanotubes electrochemical-anodizing doctor blading

effects of Multiple Strengthening Treatments on Mechanical Properties and Stability of Nanoscale Precipitated Phases in an Aluminum-Copper-Lithium Alloy

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Journal of Materials Science & Technology 2010年第12期26卷 1078-1082页

作者： S.ahmadi H.Arabi A.Shokuhfar Department of Material Science Faculty of EngineeringTarbiat Modares UniversityTehranIran Center of excellence of Advanced Materials and Processing(CeAMP) Department of Metallurgy and Materials Science and EngineeringIran University of Science & Technology(IUST)NarmakTehranIran Department of Material Science Faculty of Mechanical EngineeringK.N.Toosi University of TechnologyTehranIran

effects of multiple strengthening treatments （i.e. ag mechanical properties and stability of nanoscale prec in this research. Various tests such as hardness, tensi ng either at three or four consecutive temperatures） on pitated phases in an AA2090 alloy have been evaluated e, electrical resistance, differential scanning calorimetric （DSC）, and transmission electron microscopy （TeM） have been performed. The results show that the ultimate tensile strength （UTS） and the yield strength of the samples aged at four consecutive temperatures （i.e. natural aging＋190℃＋150℃＋100℃） can be increased approximately to 660 and 610 MPa, respectively. It is also found that precipitation of T1 phase occurs during multiple aging process of the alloy and the higher amounts of enthalpies shown in DSC charts are linked to higher volume fraction of this precipitate. Furthermore, TeM observations reveal that T1 phase has plate shape morphology and its crystal structure is in the form of hcp with lattice parameters of a=0.467 nm and c=0.878 nm.

关键词： Multiple strengthening Thermo mechanical treatment (TMT) Selected area electron diffraction (SAeD) pattern Inter planar spacing (d)