مجله علوم و فناوری های پدافند نوین
سال چهارم شماره 3 (پیاپی 13، پاییز 1392)

One of passive defence principles is the immunization unit against the attacks to computer systems. Large set of attacks is occurred by malware to computer systems. Performance of existing techniques should be evaluated against malware attacks. In this regards, one of the approaches in this area is to perform the managed attacks by the produced malwares through intelligent engines. Most of anti-malware products may apply the detection techniques based on binary signature code to identify the malware. A family of computer malware called as metamorphic exists whose signature has been changed in each generation through applying the obfuscation techniques so that they cannot be identified by binary malware signature based detection techniques. In this paper, a metamorphic engine has been presented on the basis of learning cellular automata. This engine is capable to confront the detection techniques according to codes statistical analysis due to its dynamic nature, identification ability and creation of safety program’s similar codes with high similarity rate. This engine could be a suitable tool for assessing the performance of existing systems to encounter the possible attacks.

One of the most important issues in passive defense considerations is progressive collapse. For instant destruction of structural member due to different incidents such as deliberate or unexpected events, propagation of destruction to adjacent members and inability of building to achieve static alternative equilibrium conditions, progressive collapse occurs, which leads to partial or even total destruction. On the other hand, removing critical members in different buildings situations may have various progressive collapse potentials. Catenary action is a building rehabilitation mechanisms to achieve equilibrium alternative and stability of the structure. In this study, based on the sixth and tenth national building regulations and using vertical push nonlinear static analysis (Push-Down Analysis) and nonlinear dynamic time history analysis of steel bending frame structures, performance of the structure by removing columns in different locations and its effect on potential progressive collapse, are discussed. The results show that it has highest effect when a corner column is removed while it has lowest catenary action in building. Structural stability to achieve alternative equilibrium after columns removal, will improve by strengthening catenary action building performance.

Soil-buried structures are the most usual means of protection of strategic facilities against explosions. Surface explosions and underground detonations effects on buried structures have been analyzed in this study to evaluate the performance of several approaches which have been suggested to secure underground structures from blast induced damages. Blast induced pressures amplitudes have been evaluated through nonlinear dynamic analyses considering different soil types and results have been compared with conventional formulations. Granular soils have provided more protective efficiency in comparison with cohesive soils. Although concrete blanket does not produce considerable shield effect against blasts waves resulted from surface explosions but a void space or compressible materials under the concrete cover may increase its protectivity. Adjacent trenches or holes in vicinity of the buried structure have provided an effective protection against blast wave's propagation and their efficiency has been evaluated in this study considering different distances from the structure and from each other.

Service-oriented environments have distinctive characteristics, such as being dynamic, open and distributed. The evaluation of trust and reputation is very important in establishing secure interactions between web services in such environments. Many trust models have been developed based on feedback mechanisms. However, not all of them are able to detect false reputation outcome as a result of misleading data provided by raters. A key challenge to employ these models is to prevent user’s misbehavior in unfair feedbacks and ratings. In this paper, a new trust model based on ELECTRE TRI method is proposed to overcome such a challenge. To evaluate the effectiveness of the model, the results are compared with the well known RATEWeb model. Numerical results and performance evaluation of our model proves its ability in trust management as well as quick adaption of behavioral changes of service providers.

In this study, the synthesis and Nanocrystallites properties of one of the main semiconductors has been investigated which has high efficiency in detection, recognition and identification. Thus, PbS Nanocrystallites have been synthesized through wet chemistry using a capping agent (2-mercaptoethanol). Some properties including crystal, optic and morphology structure and the size of PbS Nanoparticles has been investigated through X-Ray diffraction, UV-VIS spectroscopy and STM (Scanning Tunneling Microscopy). The excitonic shoulders of PbS Nanoparticles become visible by cluster's shrinkage through VIS spectroscopy. 2-mercaptoethanol capping agent leads to handling of cluster size, and the increase of its concentration leads to much shifts in the shoulders. X-Ray diffraction approved the certain shoulders of PbS and the high purity of Nanoparticles, and the size of particles was calculated by Scherrer equation. Furthermore, based on STM, 4-5 nm Nanoparticles with high dispersion and spherical shape were observed. The innovation in this work is reaching PbS Nanoparticles with energy gap of around 4.1 eV which has not been reported in other papers so far.

Bearing capacity of shallow foundations under blast loading depends on various factors such as the severity of the explosion, buried depth of the foundation and its materials, but comprehensive study hasn’t been done on the impact of these factors on the bearing capacity of this kind of foundations. The method of calculating bearing capacity of foundations under blast loading follows that after applying initial stress due to the soil gravity, during different loading in each step, the foundation will be placed by uniform stress. After analysis of the model in the static mode, the model will be analyzed under the blast loading again, and then the average settlement of points below the foundation is calculated. This procedure is performed for various stress levels and finally the settlement-stress graphs are plotted. This stress increasing continues until the soil failed under the blast loading. Then bearing capacity of the foundation under the blast loading is estimated by the cross-tangent method on the settlement-stress graph. The results indicate reduction of the bearing capacity and the asymmetrical settlement of the foundation under blast loading. Also under the blast loading like the static condition, bearing capacity is increased by increasing the buried depth.

The Comprehensive Nuclear-Test-Ban Treaty Organization (CTBTO) uses a special detection method to verify activities for the member states of the organization. One of the systems based on these methods, is sampling system of airborne radioactive particles. The radionuclide monitoring is the only technique that provides the forensic or confirmatory evidence that a detected explosion is nuclear in nature. The radionuclide station including air sampler and detection unit, was designed to achieve a detection capability of not less than 90% within approximately 14 days for a 1 kt nuclear explosion in the atmosphere or from venting by an underground or underwater detonation. In this paper, SNOW WHITE® sampler has been investigated and some technical objections to this type of sampling system have been introduced. Finally, a sampling system that can resolve related technical problems (bugs), have been simulated and some suggestions to using at the treaty have been proposed.

Nowadays, due to the appearance of advanced aerial attack weapons, the usage of modern defence systems such as aerial target recognition systems could play a prominent role in a successful defence. The micromotion of rotating structures of radar targets is used, in many cases, as discriminant feature for their recognition. Possessing a general and accurate database of targets of interest can extremely affect the performance of feature extraction algorithms. Besides, the modeling of radar returns which contain informations about structural properties of the target, provides possibility of controlling the radar parameters and capability of arbitrarily selecting the target specifications. In this paper, the rotational micro-motions of the hovering helicopter main rotor blade tips are modeled as individual features of each helicopter in backscattered pulses with high range resolution ability. Although, the implementation of a pulse as narrow as the pulse used in this paper is not realizable with available technologies, it provides time domain analyzing of blade's micro-motions without taking their radar cross sections into account. In this paper, an algorithm is also designed and presented for estimating the rotational velocity of main rotor blade tips (i.e. v_rot) of four helicopter models. When the radar parameters such as pulse repetition frequency (PRF) and time on target (TOT) are improperly allocated, the backscattered pulses are not suitable to be used in the proposed v_rot estimation algorithm. Hence, above mentioned radar parameters are also evaluated.

Free-space optical communication has many advantages such as high bandwidth, high security and can be a good alternative for radio systems. The performance of this system could be degraded due to atmospheric turbulence. Turbulence-induced refractive index changes in the medium in the path between transmitter and receiver which leads fluctuation in light intensity on receiver. The gamma-gamma distribution is popularly accepted for modeling the received intensity fluctuations in the near-ground free-space optical communication. Turbulence can cause fading in mobile communication. In the third generation mobile communication systems, to overcome the fading phenomenon, multi-transmitter and multi-receiver MIMO structure is used. In this paper, mitigation of the turbulence effects, based on practical considerations, and using a MISO structure with space time-codes with aperture averaging method with gamma-gamma distribution has been studied. Simulation results show that the design link (MISO with 4 transmitter and 10km range) has BER of less than 10-6 even in the presence of strong turbulence.