مجله علوم و فناوری های پدافند نوین
سال دهم شماره 2 (پیاپی 36، تابستان 1398)

The investigation on the reduction of radar cross section (RCS) has been an interesting research subject in recent years. Plasma-based stealth is a RCS reduction technique associated with the reflection and absorption of incident EM wave by the plasma layer surrounding the structure. In this paper, an overview of the plasma stealth has been presented. The MCNPX codes are employed to calculate the density electron of air in STP conditions by the alpha decay. Then, the RCS of the flat conductive plate, in the presence and absence of plasma coatings created by alpha decay of nuclei, is simulated by FEM solving method in CST-studio. The most important aspect of the research is the attempt to optimize the RCS reduction by changing the plasma parameters created by the radioactive nuclei. The obtained results show a reduction of 7 to 11dB at RCS in the typical radar frequency range (2 to 12 GHz).

Laser guidance, is one of the most common methods in guided weapons. Due to the high precision of this method and its spot-shaped collision ability, it is widely used in modern warfare. The main part of these weapons is laser seeker, which can guide the  weapons to hit the target, based on the beams reflected from it. As a defensive action toward these weapons, and in order to deceive and distract the weapons route from its main paths and orientation toward the false target, a second reflective laser can be used. In this article, in order to achieve the specifications of the deceptive laser, first, the behavior of laser-guided weapons detector is simulated, then the detector testing system is designed and implemented. Based on simulations and tests, information on the dimensions, power, and time of laser beam decoding was obtained as follows. Changing the laser beam's dimensions of deception relative to the main beam has no effect on the detector's performance. To deceive the laser-guided weapon detector, only the laser beam power should increase the deception to the original laser beam.The more the laser beam decrypts in the early stages of the attack, the more likely it is to deception the operation. In the case where the power of the main beam and the deception beam is equal, the total deviation of the detector depends on the average deviation of each of the beams. If the laser beam's ratio of deception to the original laser beam is tripled, the detector will be more affected by the deception laser. 1- Changing the dimension of the deception spot rather than that of main spot has no effect on the performance of the detector.2-In order to deceive the laser- guided missile detector, the power of deception spot should only increase with the power of the main spot.3-If sending the deception spot takes place in the early stages of the attack, the deception operation is more likely to succeed. 4-In case the power of the main spot and deception are equal, the total deviation of the detector depends on the average deviation of each of the spots relative to the detector center. 5- If the power of deception spot is more than three times as much as that of the main spot, the detector is further affected by the deception spot.

The use of absorbent materials is one of the most common ways to prevent radar visibility. In this study, considering the application of radar  absorbing materials, two important materials, one with high dielectric coefficient  and other with high permeability coefficient, (Perovskite Ba0.7Sr0.3TiO3 and ferrite Mn0.5Zn0.5Fe2O4),  being  good candidate for radar-absorbing materials, have been synthesized with a specific stoichiometry  by sol-gel method and were characterized by X-ray diffraction and scanning electron microscopy. In order to determine the radar absorption rate, five different nanopowder was prepared and the pigment was prepared with an 828 Epoxy resin and placed on a non-adsorbent surface with an approximate thickness of 1  mm and the amount of radar absorption by using the network analyzer in the 8-12 GHz range has been investigated. The results showed that the absorption of waves in the 8-12 GHz range is dependent to the dielectric coefficient and the material with a high permeability coefficient does not have any influence in the absorption. The highest absorb ion rate was observed for a material with high dielectric coefficient  of -24dB at about 9.5 GHz.

Neutron focusing with specific energy and intensity distribution from neutron source plays an important role in various applications. In this paper, the effect of straight and elliptical guide systems for focusing on the neutron intensity on the target has been investigated for a neutron source as a Maxwell distribution in the range of wavelength from 0.5 to 5 angstroms. The simulations were performed using the Monte Carlo simulation code McStas and the effects of different parameters of straight and elliptical neutron guides on the neutrons intensity have been obtained. Then, the results of straight and elliptical guide systems are also compared. Studying the role of the straight and elliptical guide's length shows that increasing the guide length, the output intensity increases and after an optimal length, it decreases. The results show that for the straight guide, optimization of the distance between the source to the guide has the greatest effect on the intensity of the output neutrons versus wavelength, while for the elliptic guide, optimization of the source radius has the greatest effect. Finally, the results show that the performance of the elliptical guide is better than the straight guide.

In this study, the feasibilityof using the Ground Penetrating Radar (GPR) method to detect and locate subsurface utilities in various conditions has been investigated. To do this end, the performance of radar waves in detecting different material types in environmental conditions with different electrical conductivity has been studied. The GPR's performance criterion in this study is the resolution of the reflected waves in using radar systems with different central frequencies. The results indicate that the central frequency has a great influence on the size of the target with proper imaging. Moreover, the simulation results show that for central frequencies of 50, 250, 500 MHz, 1 GHz and 2 GHz, targets with sizes 125, 25, 6 and 3 cm cannot be detected, respectively. Estimated results on resolution are related to the radar wave propagation velocity in the media severely. Also, the estimated resolution values are valid for a medium with a wave propagation velocity equal to 0.15 m/ns (For example, alluvium with moderate grains or dry sand). Simulation results on martial type based on relative electromagnetic permittivity (Ɛ), sub-layer conductivity (δ) and layers thickness (D), show that the electrical conductivity had a higher effect on the GPR results with respect to the other parameters and layers with an electrical conductivity of less than 0.1 ohm-meter strongly weaken the amplitude of the transmitted wave and made it difficult to identify the target. Results show that with changing the central frequency in the GPR system, transmitted and reflected radar waves have different frequency content and pulse width in both frequency and time domain. As it is presented in the paper, short pulse width in time domain led to a broad band in frequency domain. Simulation results on substance type which is simulated by relative electromagnetic permittivity (Ɛ) parameter show that high relative permittivity led to receiving a reflected signal with high frequency content in frequency domain and recording strong amplitude in time domain. The simulation results show that soil conductivity attenuated electromagnetic waves severely. Based on simulated data for a target located in 1 m depth and a GPR system with dominant frequency equal to 500 MHz media with electrical resistivity more than 20 ohm.m does not affect the signal quality in radar waves. However, decreasing electrical resistivity by less than 2 ohm.m caused lack of penetration and without receiving any reflection from the target. The simulation results concluded that, using a GPR system in normal condition such as soil with 100 ohm.m, target and media relative permittivity respectively equal to 80 and 4 and target depth located in effective depth, reflected electromagnetic waves are recorded in different resolution. As results for 50, 250 500 and 2000 MHz central frequency 125, 25, 6 and 3 cm resolution is calculated respectively. Estimated results on resolution is related to radar wave propagation velocity in the media severely. Estimated resolution are valid wave propagation velocity equal to 0.15 m/ns. In the second part oof this study 2D simulation is performed. 2D simulation conducted for four different conditions. In all conditions 3 layers and 3 target is simulated. Ground penetrating radar data is simulated based on central frequency 50 MHz.  Finally, 2D simulation, synthetic cross-sections indicated that high conductivity of soils cause the less penetration and low-resolution results. In addition, attenuation parameter investigations show that value of high attenuation in silt and clay soils by two and four cause the very low-resolution data in ground penetrating radar method.

In this paper, band structure of one-dimensional photonic crystal consisting of two-layer dielectrics is calculated (The first layer is the vacuum and the second layer is ZnSe). Then, the photonic crystal band structure by- nonlinear characteristics of layers and different intensity radiation values -is calculated. The refractive index modification is applied for each layer and its effect on the electrical permittivity coefficients is calculated. Since the transmission and reflection coefficients of photonic crystal depends on the layer electrical permittivity, the band structure of crystal changes as the layer electrical permittivity change. The results show that by increasing the light radiation intensity, the frequency of the band gap branches decreases, therefore in TE and TM polarizations band gap branches shift slightly to lower frequencies. In addition it is shown that new band gap branches appeared at higher frequencies which indicates that crystal band structure can be controlled by the intensity of the radiation field. In order to demonstrate the practical ability of nonlinear optics, the band structure of photonic crystal is calculated in both regimes (linear and nonlinear optics) and compared with each other. These structures can be used as anti-reflective coatings that reduce reflections from the surface. In fact, by covering war devices with band gap controllable nonlinear optical photonic crystals, they can be hidden from the enemy's radar view.

The subject of this research is to investigating the advantages of a special stable resonator relative to the flat-symetric stable resonator scheme in high power pumped Nd:YAG lasers. At first a discussion about some convetional resonators used in high power Nd:YAG lasers is presented considering the advantages and shortcomes of each resonator scheme. Then by using distributed refractive power model(DRP), for a typical high power side pumped Nd:YAG laser ,and investigating the stability regions, a non symmetric resonator scheme is proposed which gives single transverse mode and demonstrates higher fundamental mode volume (12 times greater)  compared with flat-symetric scheme.  Also misalignment sensivity of the presented resonator has been studied and compared with flat-symetric resonator, using numerical calculation and simulation with GLAD software. The results of this research revealed that in high level of pumped power, it is also possible to achieve high fundamental mode volume and make the resonator stable due to thermal and mechanical disturbance.

The aim of this study is construction of graphs of concentration versus time at different distances from the primary pollution place of the HCN agent and also the production of well tabulated data for the amount of HCN released at different distances and heights from the location of primary pollution using the PHAST software. At different distances from the primary pollution place and 2 meters height from the ground, the maximum concentration of HCN was due to neutral weather condition. With increasing the distance from 2 meters above the ground, the concentration of HCN decreased while the duration of contamination in area increased. At a certain distance from the primary pollution place, with increasing the height, the concentration of HCN increased. The results of this study indicate that the neutral weather condition is the worst condition for defensive protection actions, because there was a higher concentration of HCN in the region, and the duration of contamination has also been higher.

One of the areas of biological defense is livestock and poultry threats and assessing the health risks of foodborne germs, including Salmonella, is of great importance in many aspects. Chicken meat is a good product for the transmission of this infection to consumers and is considered as a salmonella reservoir. The aim of this study is to reduce salmonella contamination in poultry carcasses which happened with the change in production and processing. In a study during 2014-2017, 383 pieces of poultry were randomly sampled. After the stages of purification and isolation of suspicious cultures, isolated Salmonella were confirmed by biochemical, serological and PCR tests. With using PCR method, 15 samples were positive for Salmonella. By applying the Instructions of the country's veterinary organization, the rate of polution has fallen sharply. Reducing salmonella contamination in poultry pieces is due to health control, packaging and identification of chicken carcasses in industrial slaughterhouses. Intentional and unintentional nonconformity with health issues in the production chain to chicken consumption will impose irreparable damage.

Tri-methyl chitosan is used to deliver genes, peptide drugs and vaccines through nasal and oral mucosal routes. This polymer is a chitosan derivative that the solubility in water has been enhanced by methylation of primary amine group and its convertion to quaternary amonium. During this process, O-methylation also occurs, reducing the water solubility of the product. The purpose of this study is to evaluate the toxicity of trimethyl chitosan with high molecular weight and high degree of quaternary amine. Thus, high molecular weight chitosan was used for the synthesis of dimethyl chitosan through the Eschweiler-Clarke methylation method. Then, to avoid the O-methylation, methylation was continued by Menshutkin reaction using iodomethane as alkylating agent in NMP solvent. The quaternized chitosan was characterized by NMR and FTIR spectroscopy methods. The cytotoxicity of the product was investigated on Caco-2 cells via MTT assay. Hemolytic activity of the synthesized polymer was evaluated using haemoglobin release test. The data were statistically analyzed by ANOVA and Tukey's multiple comparisons test. The results showed that the synthesized polymer had no toxicity on Caco2 cells (up to the concentration of 1 mg/ml) (p<0.001). Haemoglobin release test further confirmed the lack of toxicity of the polymer up to the mentioned concentration. In conclusion, the polymer can be envisaged as a carrier in biomaterials delivery.