نشریه دفاع هوافضایی
پیاپی 1 (بهار 1401)

The use of telecommunication systems with high energy efficiency and high data rates along with the desired quality of services is the infrastructure of a command and control system (C4I) that should be used with the best quality of communication in times of crisis. The use of such a structure has a special place in modern defense systems. Therefore, the design of such systems has become a major challenge and a very important research field in the field of telecommunications. The increasing growth of wireless telecommunications and the high speed of multimedia data traffic and the presence of multiple users are associated with energy consumption, which has focused on energy efficiency and the optimal use of energy and power in telecommunications. Energy efficiency is considered as one of the major goals of wireless telecommunication systems design due to environmental and economic issues. . Multi-user multi-input multi-output systems are one of the new methods of telecommunications. In these systems, the use of hundreds of antennas in the base station improves energy efficiency. Increasing the number of system antennas increases the rate of information exchange, energy consumption and hardware, the introduction of a power selection model in multi-input multi-output multi-user systems increases energy efficiency. Important factors affecting energy efficiency are actual transmission power and power consumption in transmitter and receiver circuits, number of antennas, number of users and spatial correlation between antennas. In this paper, the algorithm for selecting the farthest antenna is proposed (antenna correlation), which leads to a significant improvement in energy efficiency compared to the conventional state.

In this paper, the optical properties of penta-boron carbide two-dimensional nanostructure (B2C) have been studied using simulations with computational codes based on density function theory based on initial calculations. The study of electronic properties shows that this two-dimensional nanostructure is an indirect semiconductor with an energy gap of 1.49 electron volts by the PBE approximation method. Study of optical properties of this nanostructure by PBE-GGA approximation method In addition to showing the agreement of optical aspects with the electronic properties of this two-dimensional monolayer, this nanostructure can in the future, as a suitable material in the design of electro-optical devices in industry Different to be used. According to the findings of this study based on the relatively high absorption rate and very low reflectivity of this nanomaterial in the visible spectrum, this nanostructure can be used for optical applications, especially in the design of solar energy devices and optical sensors with various applications in the defense industry.

Artillery weapons have an important role in low height artilleries. In the first step of these weapons, due to reach a stable and controllable projectile, aerodynamically, finding angle and the initial velocity are very essential. Until now, scientists have obtained these items by modelling based on ordinary differential equations. But, in this paper, fractional differential equations of the projectile motion, which are very efficient in artillery weapons and more compatible with nature, are introduced. Then some of its properties such as trajectory, range, flight time and maximum height are studied. In addition, an inverse projectile motion is considered, i.e., we consider a problem that we know the position of motion in a special time and then we obtain angle and the initial velocity. In this way, the shooting method is applied. This method is an efficient and applicable method for solving boundary value problems. Finally, in order to study the efficiency and accuracy of the method a numerical example is given.

In this paper, the method of second harmonic generation of longitudinal and transverse waves in cold, low-density and uniform non-magnetic plasma is invistigated, when a short pulse laser or lidar is propagated in the plasma medium and collision effects are considered. Also, the effect of external uniform magnetic field on the plasma is studied. The propagation of electromagnetic waves in isotropic plasma can produce odd harmonics, but magnetic field varies isotropic state and produce even harmonics. Using perturbation theory companents of electric field of first and second harmonic are calculated and the effects of successive reflections on the electric field amplitude of first and second harmonics and efficiency of reflection power of second harmonic are investigated. Also, with analysis of government equations the resulas are obtained. Finally, field amplitude of harmonics for zero and first perturbatins for different states are studied and variations of them in term o different parameters are plotted. Also, results and optimom conditions are discussed and some suggestions are offered.

In this study, first La2CuO4 perovskite nanostructures were prepared using sonochemical method. This method is one of the methods in chemistry that creates a uniform morphology. This synthesis was performed in a 2:1 molar ratio of copper and lanthanum and a time of 10 minutes and a power of 45 watts resulted in a better morphology. After synthesizing the desired semiconductor using detection analyzes such as XRD, FT-IR, VSM, DRS, BET theory and FE-SEM of the structure The comment was confirmed. After confirming the formation of the desired structure, photocatalytic tests were taken, which in the end, the dye Acid black1  had the highest amount of  99.11% degradation.

Inactive radars do not have a transmitter and can use different signal sources. These sources include AM and FM radio, digital and analog television, cell phone signals, satellite signals, and more. Using each of these resources has its own advantages and disadvantages. Among the recent signals, digital TV signal (DVBT) and FM radio have major advantages and have received more attention. This paper examines how to systematically calculate and locate targets on a passive radar using television signals. Also, the extraction of the dynamic range of this radar is studied and some requirements in this regard are examined.