فهرست مطالب علی اصغر شکری

Radiation damages have destructive effects on the electronic components of satellites. Due to financial reasons and the presence of different restrictions, the utilize of commercial components ended up common in short-term and low-altitude missions. The most effective method of protection against radiation is the use of shields. The results of calculations obtained from PSTAR and ESTAR software show that in case heavier metals are utilized, the energy range of particles to stop increases. The result of SHIELDOSE, MULASSIS, PSTAR, and ESTAR software calculations is that the amount of thickness of different materials for the radiation tolerance of commercial parts does not differ much in terms of condensation thickness. Also, there is no need for complex protection and it can be used the usual protections. The maximum thickness required for the radiation tolerance of commercial parts is 0.5 mm from the combination of Aluminum and Tantalum. In order to achieve the best result considering the mass budget, it is better to use polyethylene material. From the results of the calculations to change the permutations of the aluminum and polyethylene shields, it can be concluded that it is better to have the first layer of polyethylene and the next layer of Aluminum.

In this study, the thermoelectric properties of the system based on molybdenum disulfide and tungsten di-telluride in three compounds with two identical nano-ribbons of molybdenum disulfide and tungsten di-telluride in the upper and lower layer and also a structure with two We examine the different layer, one molybdenum disulfide and the other tungsten-di-telluride. These properties include electrical conductivity coefficient (G), thermal conductivity (κe), Seebeck coefficient or thermoelectric power (S) and efficiency coefficient (ZTe). which are suitable for the design of thermoelectric devices. The effect of two-dimensional heterogeneous structures and temperature on thermodynamic properties was investigated. The results show that molybdenum-disulfide/tungsten-di-telluride configuration with Armchair edge structure has the most desirable thermoelectric properties. The results of this article can be useful in the design of nano electric devices based on two-dimensional layers.

In this paper, the electrical transport properties of a quasi-one dimensional heterostructure based on the GaAs (such as quantum wire) are studied in the presence of the electron-phonon interaction, theoretically. In this regards, a homogeneous quasi-one dimensional quantum wire with a given length is considered which is coupled between two semi-infinite metal leads. Using the Hamiltonian of the system the framework of the tight binding method within the effective mass approximation, the electron transmission coefficient are studied as a function of the electron energy and also the applied filed frequency. Different values of the length as well as Al concentrations of the central region are considered. In order to investigate the electron-phonon effects, we consider a time and space dependent external field which is applied on each atoms in a linear chain within the harmonic approximation. The numerical results of this paper can have shed light on the electron-phonon impacts on the electron transport of the nanowire.

Perovskite solar cells (PSCs) are advancing swiftly due to their remarkable increase in power conversion efficiency (PCE) compared to traditional photovoltaic technologies. The main purpose of this study is to investigate the efficiency of two distinct PSCS structures that use  as an inorganic perovskite active layer. The calculations are based on the optoelectronic model of the solar cell and the use of the finite element method to solve the continuity equations for current and charge density. Therefore, the layer thicknesses of different materials (as ETL and Active layer) are modified to find the better power conversion efficiency of these solar cells. The obtained results of simulation calculations illustrate that the first structure FTO/ITO/  /PEDOT: PSS/Au exhibits a maximum power conversion efficiency of 11.37%, with a short circuit current of 14.47 (mA/cm^2) and an open circuit voltage of 0.96 (V) and while the FTO/TiO2/ /Spiro- OMETAD/Au structure shows a maximum power conversion efficiency of 10.57%. The greatest power conversion efficiency for the aforementioned designs is 80 nm for the electron transporting layer is 80 nm and 200 nm for the inorganic active layer, respectively. The results of this article can be useful in the design of new-generation solar cells based on inorganic perovskite layers.

One of the non-invasive methods of cancer treatment is photothermal laser therapy. Adding metal nanospheres and nanorods to tissue improves the healing process. On the other hand, temperature control is also essential to maintain healthy tissue. This article investigates the process of cancer treatment using laser and cobalt oxide nanoparticles as well as iron and copper metals. For this, we consider cobalt oxide nanospheres in a spherical cancer cell; Then, a number of cylindrical cobalt oxide nanorods are regarded in an aqueous hemisphere (as a cancer cell) and simulated with the help of COMSOL finite element approximation software. Appropriate boundary conditions are important for heat transfer on internal and external surfaces and temperature distribution should be obtained in different parts of the cell and nanoparticles. In addition, we investigated the magnetic and non-magnetic effects of iron and copper metals with the same laser intensity and similar boundary conditions. The calculation results show that the average temperature of the cell water volume during the first 0.8 microseconds of irradiation in the presence of cobalt oxide nanospheres is 43 degrees Celsius; also, in the presence of cobalt oxide nanorods, it reaches a temperature of 53 degrees Celsius. The average temperature of the water volume of the cell reaches 100 degrees Celsius in the presence of iron nanospheres and 100 degrees Celsius in the presence of copper nanorods with a steeper slope.

In this study, we investigate the properties of spin-dependent electrical transport in molecular nano structures through a heterogeneous molecular bridge of fullerene and the pentacene molecule as an electron acceptor and donor, coupled to two semiconductor copper electrodes. For this purpose, we determine the spin-dependent Hamilton for a single band and, using the Green function approach in the context of strong dependence, the dependence of the electrical conductivity properties of the spin-circuit interaction, as well as the applied voltage on this structure. . The results of the calculations show that the spin polarization is up to 80% effective in controlling the spin of the descending electrons. This heterogeneous molecular nano structure may be useful in the design of spintronic devices.

In this paper a new method in design and modeling of infrared detector HgCdTe in photoconductive mode ‎is presented. In this method after scrutiny mechanical, optical, electrical properties of semiconductor ‎HgCdTe and solving the photoconductive equations, software of equations is programmed and with initial ‎value and repeat cycle, their changes to key parameters such as thickness, wavelength and amount of ‎impurities are calculated and finally, performance of detector is optimized.‎ Modeling of photoconductive detector has been done in temperature of 300K and 2-6 µm wavelength range‎‎, according to obtained results, optimal specific detectivity  is 3×109 cmHz1/2W-1‎‏ ‏in 5.77 µm wavelength.‎

Due to their high efficiency and low ‎cost, electrostatic electron accelerators with a moderate energy,  are used in the industry. In an electrostatic accelerator, the acceleration tube plays the role of dividing ‎the potential of the high-voltage terminal so that it accelerates the beam incrementally in a straight line. In this ‎paper, an acceleration tube for a Dynamitron accelerator with a voltage of 500 kV is designed by CST Studio ‎Suite software. In this design, an electron gun with flat cathode, and a current of 50 mA was used.  In order to ‎extract the beam from the electron gun, two filters are used: electrodes and the lens electrode, with voltages of 495 and ‎‎481 kV, respectively; besides for electron acceleration, 13 electrodes with a potential step of 37 kV have been ‎designed. To hold the electrodes and prevent electrical discharges between the electrodes, insulating ‎sheets made of Pyrex are used. At the end of the acceleration tube, a 50mA beam current, a waist radius of less than 0.5 ‎mm, a 73nm radian emittance, and a 0.15μperv beam were obtained. The dimensions of the acceleration tube ‎and the results of investigating the change in the radius of the electrodes, the displacement and deviation of ‎the angles of the first electrode relative to the axis of the acceleration tube are presented in this paper‎.‎

When an ionizing beam enters a living cell, it interacts with the cellular material, thereby transferring some of its energy to it. In this study, the propagation of Auger electrons and their effects as DNA damage by some radionuclides, were analyzed using the Geant4-DNA Toolkit with the 1ZBB model. The 1ZBB model is selected from the protein data bank library which simulates the location of atoms in the sequence of cellular chromosomes. The average number of DSBs is shown as a function of energy. In this study, it is shown that the most damage is caused by Auger electrons with energies of less than 1 keV which corresponds to Auger electrons in layers M, N.

In this paper, the electrical properties of graphene and boron nitride are studied. The effect of the layers on each other and also the twisting of the layers on each other were studied. The presence of an additional layer creates additional levels, which, in the case of graphene, maintains the conductivity of the material, but reduces its mobility dramatically. The curvature of graphene and boron nitride increases the number of energy strips to eight. Increasing the bending angle leads to the movement of the point of attachment of the conduction edges and also to the movement of the capacity of the graphene to the center of the region of the brillouin. . In the case of boron nitride, the curvature transfers the band gap to the center of the brillouin region. This transmission increases with increasing the angles of twisting.

This study proposed a method to investigate the damage caused by Auger emitter radionuclide radiation. Materials &

This study investigated the detailed rate of breaks induced by iodine radionuclide at different intervals from the DNA center using the Geant4-DNA toolkit and based on the atomic geometric model.

The mean number of breaks in DNA is shown as a function of distance from the center of the DNA axis to the position of Auger emission radionuclide decay.

The highest damage occurs by electrons with energies below 1 keV, especially in the proximity of DNA.

In this work, using the tight-binding approximation and kinetic coefficient matrix, the electrical and thermoelectric properties of four different configurations of single/bilayer graphene junctions with armchair and zigzag edges are studied. These electrical transport properties include the electrical conductivity coefficients (G), thermal conductivity (κ_e), thermoelectric power (S) and figure of merit (ZTe), which are suitable for designing thermoelectronic devices. The numerical results show that the system can exhibit a metallic or semiconductive behavior with a special edge under different geometric conditions. This makes it possible to exhibit that the thermoelectric power and thermoelectric performance of a relatively large size under particular conditions. Also, the role of carriers (electron or hole) is clearly demonstrated in terms of electrical and thermoelectric properties. The results may be useful in designing nanoelectronic devices based on two-dimensional layers.

These days, the use of Rhenium 186 and 188 radionuclides in the production of various radiopharmaceuticals has grown considerably. These two radionuclides have good features such as emitting beta particles with appropriate range and energy, and gamma rays for imaging and evaluating biological distribution in cancer treatment. Regarding the energy and range of these radionuclides, Rhenium 186 with small range is suitable for treating small tumors; and Rhenium 188 with greater range is appropriate to destroy large tumors. In this study, the simultaneous production of these two radionuclides by natural rhenium irradiation for the production of a combined radiopharmaceutical, to treat tumors with various sizes has been investigated. For the purpose of this study, the irradiation of 1 mg of natural rhenium in a neutron flux of 3×1013 cm-2s-1 for 7 days was evaluated and the activity of the main products was calculated. Since the presence of impurities delivers an unwanted and excess dose to the patient, the presence and activity level of these radionuclides have also been studied. The results of the study showed that by the irradiation of natural rhenium, Rhenium 186 and 188 radionuclides can be produced simultaneously with the appropriate activity level for using the combination of both radionuclides. Also, theoretical calculations showed that the amount of produced impurities compared to the original products is negligible.

This paper presents the design of a thermionic electron gun with two different geometries, flat cathode and spherical cathode.The purpose of this research is to answer the question of which type of electron gun is suitable for industrial electrostatic accelerators. CST Studio software was used to design the guns. The desired specification in the design of a suitable thermionic gun, the maximum current  of  50 milliamper and the voltage 5 to 10 kilovolt, is selected for use in the dynamitron accelerator. The beam current, the waist beam radius, the waist beam position and the perveance of a flat cathode gun and spherical cathode gun were 49 and 49.8 mA, 3.2 and 0.45 mm, 36 and 24.3mm, 0.138 and 0.0498 μperv, respectively. Since the electron guns used in the industry have a perveance between 0.1 to 1 μperv therefore, an electron gun with a flat cathode with 0.138 μperv is more suitable.  On the other hand, it is easier and less costly to make it. That is why the gun with a flat cathode was chosen and its final dimensions are presented.

In this paper, we have investigated the transport properties of the Dirac fermions on a topological insulator surface in the presence of external electric and magnetic fields. For this reason, firstly we obtain the eigen energies (or eigenvalues) by using the Dirac Hamiltonian of the system for transmitted electrons via the surface and the Lorentz transformations. The conductance of the system is calculated by Landauer equation. Also, the effects of electric and magnetic fields are investigated on the conductance and Fano factor effect. The application of the present results may be useful in designing devices based on molecular electronics in nanoscale.

In recent years, due to electron transport properties of nanostructures based on carbon nanotubes, a lot of attention to design electronic devices in the field of nanotechnology has attracted. There are three types of carbon nanotubes in zigzag, armchair and chiral (asymmetrical) forms. Since the types of armchair are electrically conductive, by a combination with a metal such as zinc can be achieved by various means distinct applications. In this respect, we select different layers of circular connectors on the number of atoms of 10, 20 and 30, respectively, in the systems A-Zn10-A, A-Zn20-A and A-Zn30-A, where (A: armchair). Our calculations are based on the Green's function method within tight-binding approximation in the nearest neighbors in the framework of Landauer. The results are able to predict that devices with different functions such as quantum conductor wire, negative differential resistance and rectifier design. The results may be useful in the design of electronic devices at the nanometer scale.

The drugs that usually are applied as anticancer are toxins. These toxines are inorganic or organic molecules which harm normal cells as much as cancer cells. Resently, researchers are trying to find ways to develop targeted drugs (molecules) which kill cancer cells exclusively. Different methods have been developed for killing cancer cells .e.g. heating the toxic drugs by electromagnetic field or activate the drug locally by sound or heat waves. These methods are non- invasive.
In this research, two physical techniques were used to kill cancer cells, 528 Hz sound waves and Fe2O3 nanoparticles magnetic field. Nanoparticles were synthesized and cells were cultured. The viability of cells was conducted by MMT test. It was evident that the nanoparticles interacting with the cells membrane and the magnetic field applied on the sample changed the membrane structure. Considering the possibility of frequency and intensity change sound wavw is more applicables in short time

In the absence of lattice defects, pristine graphene and hydrogen-terminated armchair graphene nanoribbons are non-magnetic materials. The presence of vacancies extremely effect on the magnetic properties and they can produce remarkable spin polarization in these materials. In this study, using first principles calculations based on Kohn-Sham density functional theory (KS-DFT), the effect of the presence of vacancies on magnetic properties and spin polarization of monolayer and bilayer armchair graphene nanoribbons are investigated. The results show that the magnitude of magnetic moments depends on the number and configuration of vacancies, their distance from each other as well as from nanoribbon's edges.

In this paper, spin-dependent electrical transport properties are investigated in a single-crystal magnetic tunnel junction (MTJ) which consists of two ferromagnetic Fe electrodes separated by an MgO insulating barrier. These properties contain electric current, spin polarization and tunnel magnetoresistance (TMR). For this purpose, spin-dependent Hamiltonian is described for Δ1 and Δ5 bands in the transport direction. The transmission is calculated by Green's function formalism based on a single-band tight-binding approximation. The transport properties are investigated as a function of the barrier thickness in the limit of coherent tunneling. We have demonstrated that dependence of the TMR on the applied voltage and barrier thickness. Our numerical results may be useful for designing of spintronic devices. The numerical results may be useful in designing of spintronic devices.

In this paper، the effect of interface roughness has been studied on spin-dependent electronic transmission in a magnetic tunnel junctions (MTJs). The transfer matrix method and effective mass approximation are used for calcilating the transmission probability. The magnetic double barrier structure consists of two ferromagnetic semiconductor (FMS) barriers which seperated by a nonmagnetic layer that is connected to two nonmagnetic metal electrodes. The different components of spin-dependent transmission probabilities (direct and indirect) have been studied for different thicknesses of quantum which in case that roughness is distributed at the interfaces as some random islands. The results of calculation show that interface roughness effectively affects the electron transport through the double barrier structures. Because scattering and opening the new addition conduction channels have a main effect in reducing of the peak of transmission probabilities. Also، influence of the amount of interface roughness is studied on scattered components of transmission probabilities.

In this paper، we have investigated the spin-dependent transport properties and electron entanglement in a mesoscopic system، which consists of two semi-infinite leads (as source and drain) separated by a typical quantum wire with a given potential. The properties studied include current-voltage characteristic، electrical conductivity، Fano factor and shot noise، and concurrence. The calculations are based on the transfer matrix method within the effective mass approximation. Using the Landauer formalism and transmission coefficient، the dependence of the considered quantities on type of potential well، length and width of potential well، energy of transmitted electron، temperature and the voltage have been theoretically studied. Also، the effect of the above-mentioned factors has been investigated in the nanostructure. The application of the present results may be useful in designing spintronice devices.

In this paper، electronic properties of single-wall armchair and zigzag carbon nanotubes (CNTs) superlattices، n (12،0) /m (6،6) and n (12،0) /m (11،0) are investigated. For this reason، the topological defects of pentagon–heptagon pairs at interfaces of carbon hexagonal network appear. These defects break the symmetry of the system، and then change the electrical properties. The calculations include two parts: investigation of the structures in the absence and presence of the impurity effect، which are calculated by the nearest-neighbor tight binding model. Out numerical results can be useful in designing nanoelectronic devices based on carbon nanotubes.

In this paper, we examined the effect of gate voltage, bias voltage, contact geometries and the different bond lengths on the electrical transport properties in a nanostructure consisting of C60 molecule attached to two semi-infinite leads made of single wall carbon nanotubes in the coherent regime. Our calculation was based on the Green’s function method within nearest-neighbour tight-binding approximation. After the calculation was of transmission, the electrical current was obtained by the Landauer-Buttiker formula. Next, the effect of the mentioned factors was investigated in the nanostructure. The application of the present results may be useful in designing devices based on molecular electronics in nanoscale.