Vojnotehnicki glasnik / Military Technical Courier

7-25

Authors: Mrdak Mihailo R.

The cermet coatings of WC-12wt.%Co are extensively used to improve the wear resistance of a wide range of technical components. This paper analyses the influence of the plasma gas flow of helium on the microstructure and mechanical properties of WC-12wt.%Co coatings deposited by plasma spraying at atmospheric pressure (APS). In order to obtain homogeneous and denser coatings, three different flows of He (8 l/min., 16 l/min. and 32 l/min.) were used in the research. With the application of He, coatings achieved higher values of hardness due to less degradation of the primary WC carbides. The main goal was to deposit dense and homogeneous layers of WC-12wt.%Co coatings with improved wear resistance for different applications. The test results of the microstructure of the layers were evaluated under a light microscope. The analysis of the microstructure and the mechanical properties of the deposited layers was made in accordance with the standard of Pratt-Whitney. The morphology of the powder particles and the microstructure of the best coating was examined on the SEM (scanning electron microscope). The evaluation of the mechanical properties of the layers was done by applying the HV0.3 method for microhardness testing and by applying tensile testing to test the bond strength. The research has shown that the flow of He plasma gas significantly affects the microstructure, the mechanical properties and the structure of WC-12 wt.%Co coatings.

37-58

Authors: Berber Stevan M.

Chaotic spreading sequences can increase secrecy and resistance to interception in signal transmission. Chaos-based CDMA systems have been well investigated in the case of flat fading and noise presence in the channel. However, these systems operating in wideband channels, characterized by the frequency selective fading and white Gaussian noise, have not been investigated to the level of understanding their practical applications. This paper presents a detailed mathematical model of a CDMA system based on chaotic spreading sequences. In a theoretical analysis, all signals are represented in the discrete time domain. Using the theory of discrete time stochastic processes, the probability of error expressions are derived in a closed form for a multi-user chaos based CDMA system. For the sake of comparison, the expressions for the probability of error are derived separately for narrowband and wideband channels. The application of the system interleaving technique is investigated in particular, which showed that this technique can substantially improve probability of error in the system. The system is simulated and the findings of the simulation confirmed theoretically expected results. Possible improvements in the probability of bit error due to multipath channel nature, with and without interleavers, are quantified depending on the random delay and the number of users in the system. In the analyzed system, a simplified version of the wideband channel model, proposed for modern wideband wireless networks, is used.

80-100

Authors: Dobratić Predrag S., Ristivojević Mileta R.

In the field of transmission and power transformation from the power engine to the working machine, gear pairs, are mostly used in mechanical engineering due to their compactness of the structure, high reliability and capacity. One way of improving the performance characteristics of gear pairs, and thus the gear transmitters, is to increase the number of simultaneously meshed pairs of teeth, or increasing the transverse contact ratio. To this end, this paper analyzes in detail the partial and simultaneous influence of the number of teeth and tooth profile shapes, moving through shifting coefficient and pressure angle, to the number of simultaneously meshed pairs of teeth. The obtained results allow us to define the optimum parameters of cylindrical gear pairs, in terms of the size of the transverse contact ratio.

121-127

Authors: Golodjaev Aleksandar Ivanovič

This paper shows a new way of dealing with the generators of pulsating infrared interferences and a new kind of fighting with infrared homing seekersas well as an analysis of this Air Force combat means and appropriate countermeasures. It is described how to upgrade infrared homing seekers to overcome generators of pulsating infrared interferences. The article describes an original method of setting false thermal targets using termite copper-aluminum and 'electron' alloy. The use of modernized types of heads against aerial targets makes generators of pulsating infrared interferences useless.

152-164

Authors: Bereš Paun J., Bereš Kristian P.

This paper presents problem solving using heuristics and operational research in order to make appropriate decisions in emergency situations with a particular emphasis on the application of a heuristic model of team training for emergency situations. It is intended for military command and teaching personnel as well as for civil defense personnel (Department of Emergency Management) and local government authorities (administrative district chiefs and mayors - commanders). The heuristic approach to problem solving should enable adequate decision making for command staff from the local to the national level after the proclamation of emergency and a state of emergency in some regions or the whole territory of Serbia.