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New Characterizations of Operator-Valued Bases on Hilbert Spaces

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Analysis in Theory and Applications 2017年第2期33卷 157-177页

作者： mohammad sadegh asgari Department of Mathematics Faculty of ScienceCentral Tehran BranchIslamic Azad UniversityP.O.Box 13185/768TehranIran

In this paper we study operator valued bases on Hilbert spaces and similar to Schauder bases theory we introduce characterizations of this generalized bases in Hilbert spaces. We redefine the dual basis associated with a generalized basis and prove that the operators of a dual g-basis are continuous. Finally we consider the stability of g-bases under small perturbations. We generalize two results of Krein- Milman-Rutman and Paley-Wiener [7] to the situation of g-basis.

关键词： g-bases dual g-bases g-biorthogonal sequence.

GENERALIZATIONS OF THE SUZUKI AND KANNAN FIXED POINT THEOREMS IN G-CONE METRIC SPACES

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Analysis in Theory and Applications 2012年第3期28卷 248-262页

作者： mohammad sadegh asgari Zohreh Abbasbigi Islamic Azad University

In this paper we develop the Banach contraction principle and Kannan fixed point theorem on generalized cone metric spaces. We prove a version of Suzuki and Kannan type generalizations of fixed point theorems in gener... 详细信息

关键词： fixed point D-metric space 2-metric space generalized cone metric space,Kannan mapping generalized Kannan mapping contractive mapping

On the Generality of Orthogonal Projections and e-Projections in Banach Algebras

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Advances in Pure Mathematics 2012年第5期2卷 318-322页

作者： mohammad sadegh asgari Seyedeh Sara Karimizad Hamidreza Rahimi Department of Mathematics Faculty of Science Islamic Azad University Central Tehran Branch Tehran Iran

In this paper we develop the orthogonal projections and e-projections in Banach algebras. We prove some necessary and sufficient conditions for them and their spectrums. We also show that the sum of two generalized orthogonal projections u and v is a generalized orthogonal projection if, uv=vu=0. Our results generalize the results obtained for bounded linear operators on Hilbert spaces.

关键词： Generalized Orthogonal Projection Orthogonal Projection Generalized e-Projection e-Projection

Risk factors for congenital nasolacrimal duct obstruction in children under two years of age

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国际眼科杂志 2025年第1期25卷 17-23页

作者： Rozhin Kasiri Gholamreza Khataminia Ali Kasiri mohammad sadegh Mirdehghan mohammad Armin Kasiri Infectious Ophthalmologic Research Center Ahvaz Jundishapur University of Medical SciencesAhvaz ***Iran Islamic Azad University Tehran Medical Sciences Tehran ***Iran

·AIM:To identify various risk factors that may play a significant role in the development of congenital nasolacrimal duct obstruction(CNLDO).·METHODS:This observational case-control study included a case group of 122 children less than two years of age with CNLDO who underwent probing and irrigation treatment at the ophthalmology department of Imam Khomeini Hospital in Ahvaz,Iran,from June 2022 to June2024.A control group of 122 age-matched children without CNLDO was also included for *** was collected from the children's medical records.·RESULTS:The study found a significant correlation between the occurrence of CNLDO and several maternal factors,such as preeclampsia,the use of levothyroxine,hypothyroidism,having more than three pregnancies(gravidity>3),natural pregnancy,and gestational diabetes ***,in children,factors,such as oxygen therapy,anemia,reflux,jaundice,and a family history of CNLDO in first-degree relatives were associated with CNLDO,and maternal preeclampsia and hypothyroidism were found to significantly increase the risk of developing CNLDO in children.·CONCLUSION:Given that CNLDO affects both premature and full-term children,the present findings may potentially facilitate the early identification of children and infants at risk of nasolacrimal duct obstruction,thereby preventing the onset of chronic dacryocystitis.

关键词： risk factors congenital nasolacrimal duct obstruction children

Analysis of Spray Evaporation in a Model Evaporating Chamber:Effect of Air Swirl

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Journal of Thermal Science 2023年第2期32卷 837-853页

作者： mohammad sadegh ABEDINEJAD Department of Mechanical Engineering Faculty of EngineeringAlzahra UniversityTehranIran

Spray evaporation of liquid fuels in a turbulent flow is a common process in various engineering applications such as *** between fuel droplets(discrete phase)and fluid flow(continuous phase)have a considerable effect on liquid fuel *** this paper,both the single-and two-phase modeling of liquid fuel injection into a model evaporating chamber are *** influences of important issues such as turbulence models,coupling between gas phase and droplets,secondary break-up and air swirling on the current spray simulation are ***,the shear stress transport turbulence model,Taylor analogy break-up and two-way coupling models are applied to simulate the two-phase *** and spray of fuel droplets in hot air are modeled employing an Eulerian-Lagrangian *** current results show an acceptable agreement with the *** the fuel atomizer,bigger droplets are detected near the spray edge and minor droplets are situated in the *** increasing the droplets axial position,the droplets diameter decreases with a finite *** smaller droplets have a deeper penetration,but their lifetime is smaller and they evaporate sooner.A linear relation between penetration and lifetime of smaller droplets is *** droplet penetration and mean axial velocity of gas phase are observed for no air swirling *** effect of variation of swirl number on the lifetime of droplets is almost *** enhancing the swirl number,the uniformity of droplet size distribution is reduced and some large droplets are formed up in the domain.

关键词： secondary break-up droplet evaporation air swirling fuel spray gas-droplets coupling

Production of ultra-transparent glass-ceramics via controlled crystallization of nanocrystals in the glassy matrix of LAST

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International Journal of Minerals,Metallurgy and Materials 2014年第1期21卷 71-76页

作者： mohammad sadegh Shakeri Materials and Energy Research Center(MERC)

Microstructural variation in glass-ceramics encompasses the range from nanocrystalline transparent materials to microcrystalline tough materials. In this investigation, the crystallization process was controlled for the development of ultra transparent LiEO-A1203-SiO2 glass-ceramics containing TiO2 as a nucleating agent （LAST）. Results of UV-Vis absorption spectra were compared with the expected theo- retical values calculated by the Rayleigh scattering method for the determination of ultra transparency. Results of the investigation illustrate that the control of crystallization increases the range of ultra transparency by the reduction of crystal size and their uniformity in the glassy matrix. Last but not the least, the optimized samples are ultra transparent approximately in the whole light wavelengths.

关键词： glass-ceramics transparency nanocrystals crystallization

Fabrication,microstructure,and optical properties of nanocrystalline transparent LAST glass ceramics containing CeO_2

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International Journal of Minerals,Metallurgy and Materials 2014年第4期21卷 401-407页

作者： mohammad sadegh Shakeri Materials and Energy Research Center (MERC)

In the present research, the effect of CeO2 dopant on the fabrication of transparent lithium aluminosilicate titanate （LAST） glass ceramics was investigated. Nanocrystallineβ-quartz solid solution （s.s.） was observed to be the main phase crystallized in this system. Com-parable refractive indices of the glassy matrix andβ-quartz s.s., as well as the incorporation of very fine grains size were determined as the main reasons for retaining the transparency of the glass ceramics. CeO2 was introduced as a suitable optical agent, playing a role as a network modifier in the glass ceramics, because it does not accelerate the growth process and retards the extended growth of crystals. Optical investi-gations indicate that the Fermi energy level, direct and indirect band gaps, and Urbach energy decrease with increasing nanocrystal content in the glassy matrix of specimens, which can be related to the expansion of conduction band, the enhancement of ionic bonds in the crystal lat-tice, and the enhancement of structural arrangement degree, respectively.

关键词： glass ceramics nanocrystals alurninosilicates titanates transparency optical properties

Effect of Y_2O_3 on the crystallization kinetics of TiO_2 nucleated LAS glass for the production of nanocrystalline transparent glass ceramics

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International Journal of Minerals,Metallurgy and Materials 2013年第5期20卷 450-455页

作者： mohammad sadegh Shakeri Materials and Energy Research Center (MERC) P.O. Box 31779-83634KarajIran

Crystallization kinetics of metastable B-quartz solid solution as a desirable phase for the production of trans- parent lithium aluminosilicate （LAS） glass ceramics was investigated in the presence of Y203. Accordingly, differential thermal analysis scans were performed thoroughly to study the mechanism of crystallization kinetics. The aim of this investigation is to discover the complicated mechanism of crystallization process in the presence of co-additives and ac- cordingly find a way for increasing the transparency of glass ceramics. It is shown that the bulk （3D） growth is intensively increased by the enhancement of Y203. Then again, reducing nucleation and increasing growth mechanisms were recog- nized for the LAS system in the presence of Y2O3. Results of the investigation illustrate that when co-additives are added to glasses, it is necessary to nucleate the optical component separately before the growth process.

关键词： glass ceramics lithium aluminosilicate yttria crystallization kinetics nanocrystals transparency

Nonlinear finite time attitude control of flexible spacecraft based on a novel output redefinition method

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Chinese Journal of Aeronautics 2023年第11期36卷 373-385页

作者： Seyed Majid ESMAEILZADEH mohammad sadegh ZEYGHAMI Department of Electrical Engineering Iran University of Science and TechnologyNarmakTehran 16846-13114Iran

A finite time attitude controller is designed for a flexible spacecraft based on a novel output redefinition method, in this paper. To make the flexible appendages vibration suppression effective, the appendage tip-point is selected as the output. First, a novel output redefinition method is proposed to overcome the non-minimum phase property of the dynamic model. The proposed method not only makes the system model minimum phase but also improves the attitude control system performance. Consequently, the precise attitude pointing and stabilization are ***, a nonlinear finite time H∞controller is designed based on the backstepping approach. For the situation where the modal variables measurements are not available, a modal observer is also designed. The simulation results show the effectiveness of the proposed method in the presence of the model uncertainties and environmental disturbances.

关键词： Finite time Output redefinition H1 control Attitude control Flexible spacecraft Backstepping Robust