Vojnotehnicki glasnik / Military Technical Courier

Number 4(63), 2015

11-24
Improvement of signal synchronization in GPS software receiver

Authors: Sokolović Vlada S., Marković Goran B., Dikić Goran D.

Abstract

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Number of views: 505

In GPS receivers, navigation bit allocation is performed throughout the process of signal tracking and detection. In the process of signal tracking, the locally generated signal must be synchronized with the received signal. The Costas phase-locked loop (PLL) behavior, which is often used for signal synchronization, is characterized by dominant tracking error sources. The resulting phase tracking errors are significant in the presence of weak signals, i.e. signals with the low signal-to-noise ratio (SNR). In order to improve the signal synchronization and enable signal tracking by the receiver, we here proposed the usage of a non-data-aided (NDA) phase estimator. Based on the practical processing of the GPS signals, it is shown that the applied NDA algorithm is more resistant to sudden changes in frequency (phase) of the input signal than the previously considered phase discriminator in the Costas PLL. Also, we have shown that the solution analyzed here exhibits more stable operation in signal tracking for a low SNR.

25-45
Improving a technology model for intermediate maintenance of radio-relay devices

Authors: Radonjić Vojkan M., Đukić Slobodan R., Jovanović Danko M., Ćirić Milenko P.

Abstract

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Number of views: 480

The work was conducted to investigate the manner of improving the technology of intermediate level maintenance of radio-relay devices. The Improved model of maintenance techniques will be applied in practice during corrective maintenance of radio-relay devices. The results obtained during the application of the proposed model will serve to draw conclusions about the effectiveness of the defined model of maintenance technology.

46-67
Morphology of powder particles produced by spray atomization and other processes

Authors: Mrdak Mihailo R.

Abstract

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Number of views: 500

The physical and mechanical properties of coatings are heavily influenced by the technologies of powder production and by the parameters of the plasma spray process. One of the most important parameters that affects the physical and mechanical properties of coatings is the morphology of powder particles - homogeneity, granulation and granulation range, directly related to the technologies of powder production. This paper describes the technological processses of powder production most commonly used and shows the SEM micrographs of powder morphologies. Depending on the manufacturing process, powder particles have different characteristics regarding their shape, size, specific gravity, purity, etc. Since these characteristics have a significant impact on the quality and properties of deposited coatings, it is necessary to possess knowledge about the characteristics of powders in order to better control the behavior of particles in the plasma jet, in order to produce the expected characteristics of the coating. Powders have a variety of characteristics to be set for the operating parameters of the deposition in order to obtain the desired coating characteristics.

68-98
Contribution to better understanding of logistics

Authors: Milenkov Marjan A., Dronjak Milan Ž., Parezanović Vladan D.

Abstract

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Number of views: 494

There are a number of definitions of logistics and logistics systems through which different authors, at different times and military, economic, market and social circumstances, tried to explain the essence of logistics as a branch of the art of war, business philosophy, scientific discipline, etc. Although logistics ia a very old area of human activity, which was improving along with the development of civilisation, its terms are still in the process of developing and they should be accepted as they appear and how they appear in different human activities.

99-115
Contribution to the modeling of a pneumatic semi-active control of vehicle suspension

Authors: Ketu Nabil S., Demić Miroslav M., Muždeka Slavko R., Krsmanović Milan M.

Abstract

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Number of views: 478

This paper contributes to the modeling of a semi-active control of a quarter vehicle model using air springs. A conventional mass-spring-damper model has been used along with an air spring. Based on the theory of thermodynamics, the dynamic equation of the air spring model was established. The simulation model was implemented using MATLAB and the transfer functions with varying parameters were calculated. The simulation results show that air spring pressure, the valve diameter, the dumping coefficient and the mechanical stiffness affect the dynamic response of the system. A semi-active control methodology was then established by controlling the valve diameter using two declinations of an on-off logic switch based on the velocity of the suspended mass and the relative velocity at both ends of the air spring. The obtained results show reduced oscillation amplitudes around the natural frequency of the system.

116-134
Planning and designing large energy systems with a special emphasis on their impact on the environment

Authors: Luburić Veselin D., Bakrač Saša T., Milanović Miško M.

Abstract

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Number of views: 512

This paper analyzes the impact of planning and designing large power systems on the environment, such as the DSP 400 kV optical cable from the Montenegrin coast to Pljevlja. It is a very complex and multidisciplinary project, and involves the analysis of a number of important factors and cause-effect relationships that such a system can produce. The analysis was guided by the fact that this is an atypical example, from the planned and implemented aspect unknown both on the national and wider regional level. For this reason, it is challenging to shed light on the consequences of any such system and structure, which is specific in many ways, and whose repercussions in the near future are still vague. The paper discussed European and international experiences as well as their perceptions of problems with similar solutions in practice.

135-165
Assessment of the security risk to people and property from ordnance explosion effects in the Serbian Armed Forces

Authors: Stojanović Dejan S.

Abstract

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Number of views: 554

The research goal is to enable prediction of events in the incoming period on the basis of a large number of collected relevant data that may represent a potential risk and the danger of ordnance explosion effects in the Army of Serbia. The realization of the objectives of the research requires the use of appropriate methods and techniques for dating and study of existing teoretical and practical solutions as well as proposing new ones in the areas of interest. During the research, the following scientific methods were used: comparative method, content analysis and positivist method. The investigation has covered situations which may arise at workplace due to various threats caused by both the human factor and chains of events, followed by the identification of potential forms of risk to people and property by ordnance explosion effects in the Army of Serbia. The collected data on potential forms of endangering people and property by ordnance explosion effects were analysed and their positive and negative consequences were discussed. The levels of safety risks to people and property from ordnance explosion effects are assessed and decisions are made about the forms of threat and to what extent they will be dealt with in the future.

166-191
Serbian Army and the risk management of accidents involving dangerous substances

Authors: Rutić Srđan Z., Inđić Dejan R.

Abstract

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Number of views: 458

The article describes the role and the place of the Serbian Army in the risk management of accidents involving dangerous substances as well as the activities such as taking measures for controlling chemical hazards, protection from chemical contamination and elimination of consequences. A method of plan drafting for the risk management in garrisons in case of accidents involving dangerous substances has been presented. Taking into account all the elements of the assessment of potential accidents involving dangerous substances and their mutual influence serves as a basis for planning and organising preparedness of units and institutions of the Army for accidents involving dangerous substances. The Serbian Army has a significant place and role in dealing with accidents with hazardous materials.

192-214
Preventive measures for safe and healthy working with mines in multinational operations

Authors: Kovačević Nenad V.

Abstract

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Number of views: 462

After the re-admission of the Republic of Serbia to the United Nations (UN), members of the Ministry of Defence ( MoD) and the Serbian Army Forces (SAF) have been engaged in multinational operations (MNOP). The first engagement of three military observers was in UN MNOP in East Timor (UNMISET) from 26.06.2002. Until the closing of the mission, there were five members of the MoD and SAF engaged. Currently, there are 247 members of the MoD in 10 UN MNOP worldwide, engaged in different roles. During UN multinational operations, one of the key problems is posed when encountering some kind of explosive ordnance (referred to in the article as MES). In order to avoid consequences of improper explosive ordnance handling, full attention has to be paid to prevention, i.e. good preparation, During the preparation of MoD and SAF members to be sent to UN MNOP, the main problems concern professional staff (a small number of qualified and trained instructors) and necessary literature. The paper presents a review of the currently available literature and the experience of the MoD and SAF members who were engaged in UN MNOP in dealing with explosive ordnance, notably mines.

215-223
Srećko Stopić: Synthesis of metallic nanosized particles by ultrasonic spray pyrolysis

Authors: Stopić Milena D.

Abstract

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Number of views: 682

Nanotechnology belongs to the key innovative technologies for powder production. Ultrasonic spray pyrolysis is a versatile method for the formation of nanosized particles of metals, oxides and composites. This work deals with Ag, Cu and Au nanoparticles formed by ultrasonic spray pyrolysis using the horizontal and vertical reactor. Furthermore, a direct synthesis of Ru-TiO2 and RuO2-TiO2 nanoparticles with the core and shell structure was investigated. The molar fractions of precursors, solvent type, and the process temperature play the crucial role in the formation of core and shell structures. Moreover, the influence of the reaction parameters (temperature, residence time, solution concentration and ultrasonic frequency) on the morphological characteristics of the prepared nanoparticles was studied. A decrease in the solution concentration decreases the final nanoparticle size. An increase in temperature from 150°C to 1000°C leads from an irregular form to a more spherical one. Subsequently, a model of metallic nanoparticle formation from an aerosol droplet could be proposed. Using ultrasonic spray pyrolysis, ideal spherical metallic particles were obtained at temperatures above the melting point. A scanning mobility particle sizer (SMPS) was used for the on-line determination of nanoparticle size distribution. The collection of nanosized particles was performed in an electrostatic field. The scale up of the ultrasonic spray pyrolysis method was successfully applied for the synthesis of silver powder from a water solution of silver nitrate.