Yaghoob Naimi
Abstract
A B S T R A C TWe present a comparative study based on Density Functional Theory (DFT), of the effect that different approximations such as exchange-correlation (XC) functional, effect of Hubbard U, TB-mBJ correction and optimized lattice constant strain have on the structural and electronic properties ...
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A B S T R A C TWe present a comparative study based on Density Functional Theory (DFT), of the effect that different approximations such as exchange-correlation (XC) functional, effect of Hubbard U, TB-mBJ correction and optimized lattice constant strain have on the structural and electronic properties of NaTiAs compound. At first, by using DFT based full-potential WIEN2k package we compare the total energy vs volume of ferromagnetic, antiferromagnetic and non-magnetic half-Heusler structures to obtain the more stable configuration phase and magnetic state. Calculations show that our compound is more stable in the half-Heusler beta-phase and the ferromagnetic state. Then, we investigate the structural and electronic properties of NaTiAs-beta by using LDA, PBEsol, WC and PBE XC functionals. Our results show that different XC functionals cannot lead to half metallicity. But when we use the GGA+U and TB-mBJ schemes with PBE parameterization, results indicate that the Fermi level cuts through the partially occupied band in majority spin channel while it is located in the gap between valence and conduction bands in the minority spin direction thus it demonstrates the half-metallic behavior of this compound, and the amount of a total magnetic moment is equal to . Furthermore, by applying at least optimized lattice constant strain, NaTiAs-beta becomes half metal. Examination of the elastic constants shows that the compound is stable. These types of compounds are candidates for making spintronic devices.
Zeinab Hajijamali-Arani; Tymaz Fatolahi-Khalkhali
Abstract
In this research, the photonic structure of an inverse linear tapered waveguide made of silicon nitride is investigated. This structure serves as a connector between a few micron-sized waveguides and sub-micrometer waveguides in photonic integrated circuits. Since the propagation of electromagnetic modes ...
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In this research, the photonic structure of an inverse linear tapered waveguide made of silicon nitride is investigated. This structure serves as a connector between a few micron-sized waveguides and sub-micrometer waveguides in photonic integrated circuits. Since the propagation of electromagnetic modes in the structure of waveguides, especially in tapered waveguides, depends on the shape, dimensions, and material of the waveguide, the investigations of various aspects of the mentioned geometric structure are analyzed. The distribution of electromagnetic field for guided modes in this structure is also studied. Considering the importance of the transmission spectrum of a waveguide for the design of integrated photonic circuits, this will be simulated using the 3D finite-difference time-domain (FDTD) method. Among the selected single-mode structures, an optimized structure with improved efficiency is obtained. This structure has a length of 100 μm, an output width of 1 μm, and an input width of 0.3 μm.
Mina shiri; Mehrdad Ghominejad; Mohammad Reza Pourkarimi
Abstract
In this paper, we model a two-qubit system of identical superconducting charge qubits, where Josephson junctions are coupled via a fixed capacitor. In this model, the effects of temperature, Josephson energy, and mutual coupling energy between the two qubits under increase or decrease of coherence and ...
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In this paper, we model a two-qubit system of identical superconducting charge qubits, where Josephson junctions are coupled via a fixed capacitor. In this model, the effects of temperature, Josephson energy, and mutual coupling energy between the two qubits under increase or decrease of coherence and dense coding capacity (DCC) examined. The results indicate that increasing temperature leads to a reduction in coherence and DCC, while mutual coupling energy contributes to increase in these two quantities. On the other hand, Josephson energy has an effect opposite to mutual coupling energy, reducing both coherence and DCC.
Parisa Mahmoudi
Abstract
Effective mixing of samples is a critical requirement in many biochemical processes. However, achieving fast and homogeneous mixing in microfluidic channels presents significant challenges due to the low Reynolds number characteristic of microscale fluid flows. This study introduces an active micromixer ...
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Effective mixing of samples is a critical requirement in many biochemical processes. However, achieving fast and homogeneous mixing in microfluidic channels presents significant challenges due to the low Reynolds number characteristic of microscale fluid flows. This study introduces an active micromixer with a non-symmetric lateral geometry that facilitates the application of electroosmotic flow, particularly near the inlet and, most notably, at the outlet of the mixing chamber. In this proposed configuration, input fluids are more rapidly and precisely subjected to efficient mixing, under very low applied voltages. As a result, a higher quality of fluid mixture is achieved throughout the mixing chamber, driven by vortices generated through electroosmotic stimulation as well as the sharp edges within the chamber. Additionally, the mixing quality is further modified by the electric field at the outlet of the mixing chamber. This performance reduces the effective mixing time, minimizes the required voltage amplitude, improves the Mixing Index, and ensures consistent and stable operation over time. According to the finite element simulation results, at an applied voltage of 0.1 volts, the mixing time is less than 2 seconds, and the Mixing Index is 0.98. Consequently, this design is highly safe and efficient for lab-on-a-chip microfluidic applications, where the integrity of the samples within the mixers must remain unchanged.
Mohsen Ruzbehani; naser Partovi Shabestari; hamid Ghaemi Bafghi
Abstract
Holographic diffraction gratings play a key role as dispersive optical elements in spectrometers, diode lasers, optical filters, and communication systems. This paper presents the design and development of an active stabilization system for maintaining the stability of interference fringes during the ...
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Holographic diffraction gratings play a key role as dispersive optical elements in spectrometers, diode lasers, optical filters, and communication systems. This paper presents the design and development of an active stabilization system for maintaining the stability of interference fringes during the recording process of holographic gratings. In holographic setups, interference fringes are susceptible to displacement due to factors such as environmental vibrations, temperature fluctuations, air currents, and laser source instability. Some of these disturbances, particularly random vibrations, can only be effectively managed using active control methods. In this paper, an active feedback system based on a PID controller is employed to stabilize the interference fringes. The fringes are detected using a CCD camera, and after software-based analysis, the displacement is compensated by adjusting the path of one of the laser beams using a piezoelectric actuator attached to a mirror. The piezoelectric device is controlled by applying an appropriate voltage. This method is capable of reducing environmental fluctuations to approximately λ/24 (for a wavelength of 442 nm), equivalent to about 18 nanometers.
Reza Mardani Ghahfarrokhi; Mohsen Ghasemi; Vishtasb Soleimanian
Abstract
In this research, the ZnSe/Ag/CdTe (ZAC) transparent conductive multilayer system designed and simulated. The optimal thickness of the layers determined to simultaneously obtain high transmittance and low electrical resistance simultaneously. To investigate the optical properties of the multilayer system, ...
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In this research, the ZnSe/Ag/CdTe (ZAC) transparent conductive multilayer system designed and simulated. The optimal thickness of the layers determined to simultaneously obtain high transmittance and low electrical resistance simultaneously. To investigate the optical properties of the multilayer system, the transmission spectrum, reflection, and effective energy band gap of the multilayer system determined. The optimal thicknesses for the ZnSe, Ag, and CdTe layers calculated to be 40 nm, 12 nm, and 35 nm, respectively. The results showed that the designed system can be used as an interlayer electrode in solar cells. For this purpose, a two-terminal tandem perovskite (CH3NH3PbI3) and silicon solar cell with the structure FTO/TiO2/Perovskite (CH3NH3PbI3)/Spiro-OMeTAD/ZAC/C-Si(n)/C-Si(p)/C-Si(p+)/Mo simulated using SCAPS software. The values of open circuit voltage (Voc), current density (Jsc), fill factor (FF), and power conversion efficiency (PCE) obtained as 1.62 V, 20.40 mA/cm2, 89.30%, and 29.51%, respectively. Generally, the results showed that the designed ZAC system has good potential for application in optoelectronic devices.
Fatemeh NematiRishakan; Reza Habibpourbisafar; Elaheh Javanshoor
Abstract
In this study, the structural, electronic, and optical properties of perovskite compounds Ba₃MBr₃ with nitrogen and phosphorus elements in the M-site were systematically investigated using density functional theory calculations. To increase the accuracy in modeling the electronic interactions, the ...
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In this study, the structural, electronic, and optical properties of perovskite compounds Ba₃MBr₃ with nitrogen and phosphorus elements in the M-site were systematically investigated using density functional theory calculations. To increase the accuracy in modeling the electronic interactions, the second-order generalized gradient approximation was used, and calculations were performed both with and without considering the effects of spin-orbit coupling. In order to improve the prediction of the band gap, a hybrid Heyd-Scuseria-Ernzerhof (HSE) functional was used. The results showed that in the absence of SOC, the compound Ba₃NBr₃ has an indirect band gap of 0.36 eV, and Ba₃PBr₃ has a gap of 0.85 eV. By applying the HSE functional, these values increased to 0.92 and 1.40 eV, respectively. Considering SOC, the band gap of both compounds decreased slightly, which was more pronounced in the nitrogen compound. Density of states analysis showed that the p orbitals of Br play a major role in the valence band, while the conduction band is mainly composed of d orbitals of Ba. Electron density maps also confirmed the presence of ion-covalent bonds, such that the Ba–N bond has a stronger covalent character than the Ba–P bond. Overall, this study shows that the type of element substituted in the M site, as well as relativistic effects, has a significant impact on the electronic structure and band gap of these materials. These findings could pave the way for the design of stable and lead-free perovskites for novel optoelectronic applications.
noushin dadashzadeh; Elnaz Poorreza
Abstract
Valveless micropumps are crucial components in microfluidic systems and lab-on-a-chip technology.
These pumps, utilizing specific mechanisms, can transport fluids at the microscale with minimal clogging and damage to biological materials. In this research, the performance of a valveless micropump under ...
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Valveless micropumps are crucial components in microfluidic systems and lab-on-a-chip technology.
These pumps, utilizing specific mechanisms, can transport fluids at the microscale with minimal clogging and damage to biological materials. In this research, the performance of a valveless micropump under laminar flow conditions (low Reynolds numbers) was numerically simulated. The aim of this simulation was to investigate the effect of flap height on pump efficiency and to better understand its operating mechanism. Results show that increasing the flap height leads to an increase in the volume of fluid pumped from left to right over time. By utilizing fluid-structure interaction, it was possible to analyze the fluid flow and structural deformations resulting from it.