Browse

71 - 80 of 947 items :

  • Materials Characterization and Properties x
  • Materials Sciences x
Clear All
Risk Assessment of the Adverse Events in Air Transportation

Abstract

In the field of security in transport distinguish risks related to flight safety and aviation security. Safety of flights is ensured through the reliability of aviation equipment and the qualification of the personnel who services and operates it, aviation security is a condition of protection from illegal interference in its activity. Risk management in civil aviation in the field of security is a relatively new direction of activity. Deep research in this area began only at the beginning of the XXI century. It is quite difficult to use the existing experience of risk management, accumulated in other spheres, as civil aviation has significant features. Various methods and schemes can be used to assess risks. The article discusses various options for predicting risks using the “event tree” and “risk factor tree” methods.

Open access
RPAS Satellite Communication Channel Based on IEEE 802.11b Standard

Abstract

Original models of RPAS communication channels based on IEEE 802.11b Standard, including both Base Station transmission within the Radio Line of Sight, and through the satellite using Beyond Radio Line of Sight, were built. Dependencies of the Bit Error Rate on the Signal-Noise Ratio for different payload data rates were obtained. Transponder nonlinearity and Base Station antenna diameter impact were analysed.

Open access
Ship Noise Level Analysis Based on the International Regulations

Abstract

The target of analyse was to determine the exposure levels to the staff on the vessel and ensure adequate measures are in place to minimize the exposure when necessary. Noise levels through the vessel will be compared to the noise code detailed in section 2 of this report. The measurement data results obtained at this survey will be analysed against the codes, as shown below. In addition, the measurement result table has the readings from 2007 during sea trials at the shipyard, Brodogradilište d.o.o. – Split. The analyse is to measure the exposure levels, through the accommodation and machinery spaces to determine the risk to staff working in these areas as well as making recommendations that could reduce the exposure levels.

Open access
Turbine Blade of Gas Turbine Engine Additional Unloading by Changing the Layout of the Gravity Centre of the Shroud Shelf

Abstract

The article describes the impact of the gas turbine engine low-pressure turbine blade shroud shelf on the blade profile stress position. Attention is focused directly on the impact of the location of the gravity centre of the shroud shelf on blade stress distribution at the three most critical points of the profile. The paper describes the details of the calculation and the required expressions provided, as well as the results of the calculation example with clear graphical dependencies.

Open access
Analysis of surface properties of Ti-Cu-Ox gradient thin films using AFM and XPS investigations

Abstract

The paper presents results of investigations on surface properties of transparent semiconducting thin films based on (Ti-Cu)oxide system prepared using multi-magnetron sputtering system. The thin films were prepared using two programmed profiles of pulse width modulation coefficient, so called V- and U-shape profiles. The applied powering profiles allowed fabrication of thin films with gradient distribution of Ti and Cu elements over the thickness of deposited layers. Optical investigations allowed determination of transparency of prepared films that reached up to 60 % in the visible part of optical radiation, which makes them attractive for the transparent electronics domain. Surface properties investigations showed that the surface of mixed (Ti-Cu)oxides was sensitive to adsorption, in particular to carbon dioxide and water vapor. Soft etching with argon ions resulted in surface cleaning from residuals, however, deoxidation of Cu-oxide components was also observed.

Open access
Characterization of CuO/n-Si heterojunction solar cells produced by thermal evaporation

Abstract

Copper(II) oxide (CuO) in powder form was evaporated thermally on the front surface of an n-Si (1 0 0) single crystal using a vacuum coating unit. Structural investigation of the deposited CuO film was made using X-ray difraction (XRD) and energy dispersive X-ray analysis (EDX) techniques. It was determined from the obtained results that the copper oxide films exhibited single-phase CuO properties in a monoclinic crystal structure. Transmittance measurement of the CuO film was performed by a UV-Vis spectrophotometer. Band gap energy of the film was determined as 1.74 eV under indirect band gap assumption. Current-voltage (I-V) measurements of the CuO/n-Si heterojunctions were performed under illumination and in the dark to reveal the photovoltaic and electrical properties of the produced samples. From the I-V measurements, it was revealed that the CuO/n-Si heterojunctions produced by thermal evaporation exibit excellent rectifying properties in dark and photovoltaic properties under illumination. Conversion efficiencies of the CuO/n-Si solar cells are comparable to those of CuO/n-Si produced by other methods described in the literature.

Open access
Decarburization of the Carbon Steel C45 During Annealing in Air

Abstract

In production it is necessary to achieve conditions that lead to the minimum decarburization of a steel product’s surfaces. In this study, the hypo-eutectoid carbon steel C45 was annealed in air in the temperature range T a = 600–1100 °C. The annealing times were between t a = ½ h and t a = 2 h. Different decarburizations occurred in different microstructures: ferrite–pearlite (T a = 600 °C and 700 °C, T a < AC1, no visible decarburization); ferrite–austenite (T a = 760 °C, AC1 < T a < AC3, visible decarburization); austenite at the beginning, ferrite– austenite after the incubation period (Ta = 850 °C, AC3 < T a < 912 °C, visible decarburization); and austenite (T a= 950 °C and 1100 °C, T a> 912 °C, visible decarburization and overheating of steel). The edges were more prone to decarburization and to overheating. Stress relieving, normalizing and annealing before quenching of the steel C45 can be carried out in air.

Open access
Effect of MgB2 additives on structure, electrical and thermal properties of Eu1Ba2Cu3O7

Abstract

The effect of MgB2 addition on the Eu1Ba2Cu3O7 (EBCO) ceramics was systematically studied. Series of Eu1Ba2Cu3O7 + x(MgB2) samples (x = 0 wt.%, 0.05 wt.%, 0.1 wt.%, 1 wt.%, 3 wt.%) were prepared using traditional solid state method. X-ray powder diffraction measurements were used for phase identification. The lattice parameters and orthorombicity decreased with MgB2 addition. A standard four point measurement method was used to determine transition temperatures Tc of superconducting samples. Tc values of the samples were decreasing with MgB2 concentration. TGA results indicate thermal stability of doped samples.

Open access
Electrical and optical properties of new Pr3+-doped PbWO4 ceramics

Abstract

Polycrystalline samples of new scheelite-type tungstates, Pb1−3x xPr2xWO4 with 0.0098 ⩽ x ⩽ 0.20, where denotes cationic vacancies have been successfully prepared by a high-temperature solid-state reaction method using Pr2(WO4)3 and PbWO4 as the starting reactants. The influence of the Pr3+ substitution in the scheelite framework on the structure and optical properties of prepared new ceramic materials has been examined using powder X-ray diffraction method (XRD) and UV-Vis-NIR spectroscopy. The results of dielectric studies of Pb1−3x xPr2xWO4 samples showed both low values of dielectric constant (below 14) and loss tangent (below 0.2). The electrical conductivity and thermoelectric power measurements revealed a low conductivity (∼2 × 10−9 S/m) and the sign change of thermoelectric power around the temperature of 366 K suggesting the p-n transition. These results are discussed in the context of vacancy, acceptor and donor levels as well as the Maxwell-Wagner model.

Open access
Enhancement in magnetic and electrical properties of Ni substituted Mg ferrite

Abstract

In this work, Ni substituted magnesium spinel ferrites having general formula Mg1−xNixFe2O4 (where x = 0.0, 0.1, 0.15, 0.2, 0.25 and 0.3) were synthesized by standard solid state reaction method. All the samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), vibrating sample magnetometer (VSM), DC resistivity measurements. X-ray diffraction analysis confirmed the single spinel phase. The lattice constant decreased with increasing Ni content due to the difference in the ionic radii of Mg2+ and Ni2+ ions. The FT-IR spectra reveled two prominent frequency bands in the wave number range of 400 cm−1 to 600 cm−1, which confirmed the cubic spinel structure of obtained compound and completion of chemical reaction. Magnetic studies revealed that the saturation magnetization increased with the substitution of Ni. The increase in magnetization was explained on the basis of distribution of magnetic and non-magnetic cations among A and B sites of the spinel lattice. A significant influence of cation distribution on DC electrical resistivity and activation energy was observed.

Open access