Papers by Keyword: Frequency

Abstract: The paper is based on dynamic modeling research and experimental results obtained for freshly compacted concrete under stationary vibration. Thus, computational relationships and laws for vibration parameters and dissipated energy will be presented. In correlation with the dissipated energy, it will be evidenced by the evolution of the compaction degree and the resistance of the concrete depending on the vibration duration. It is noted that significant correlations have been established between the displacement curve of the dissipated energy and the loop hysteresis area for several vibration frequencies specific to the dynamic compaction regime

Abstract: Various studies are being conducted on the application of DBD (Dielectric barrier discharges). The internal dielectric has a very important characteristic on DBD, thus we analyze of the characteristics on dielectric barrier discharges depending on the relative permittivity and frequency. Through simulation, the discharge voltage was calculated based on relative permittivity and frequency of real used dielectrics (Green sheet, Down dielectric, white dielectric). We investigate that increased relative permittivity and fast frequency occur the decrease of the firing voltage. Also, we investigate the frequency dependence of the dielectric constant and dielectric loss of dielectric layers measured at a frequency region of 100Hz to 10MHz. In a condition of drive within 1MHz, with regard to the change of real and imaginary part according to frequency, it has quite stable dielectric constant in the condition of drive within 1MHz.

Abstract: Deceptive promotions occur frequently on Taobao Mall, Jd Mall and other net-shopping platforms, which not only affecting the focus online store, but also having favorable or adverse impact on other competing online stores, and cause spillover effect. From the perspective of mass and frequency, this paper used the scenario experiment method to explore the effect of deceptive promotion’s characteristics on negative spillover effect to other competing online stores. The study found that the higher the mass of deceptive promotion is, the stronger negative spillover effect of deceptive promotion from the focus online store to competing online stores is, and the higher the frequency of deceptive promotion is, the stronger negative spillover effect of deceptive promotion from the focus online store to competing online stores is. Frequency moderates the effect of mass on negative spillover effect to competing online stores; under the condition of low-frequency, there are not significant differences between high-mass group and low-mass group; under the condition of high-frequency, spillover effect of high-mass group was significantly stronger than that of low-mass group. In practice, this paper explains the effect of the characteristics of deceptive promotions on spillover effect, which provides valuable reference for competing online stores to predict spillover effect of deceptive promotion effectively.

Abstract: Water plays a crucial role in the growth and development of species on Earth. Changes in the physicochemical properties of water have a large effect on the human activities. Researchers have researched and evaluated effects of electric current frequency on the physicochemical properties of distilled water samples. The effect of electric fields on the physicochemical properties of water allows it to identify the optimal treatment regimes that promote the intensification of various processes taking place in an aqueous medium or in the presence of water.

Abstract: The porous oxide TiO₂ ceramic film containing Ca and P is fabricated on the surface of pure titanium in the electrolyte of C₄H₆CaO₄-NaH₂PO₄ by micro-arc oxidation (MAO) method. The microscopic structure, elemental composition and phase components of Ceramic Film are studied with scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), 3D profilometer and etc. Results indicate that the ceramic film on pure titanium by micro-arc oxidation is a porous mixed crystal structure which contains anatase TiO₂ and rutile TiO₂, and that the film is mainly composed of such elements as Ti, O, Ca and P. With frequency increasing, the number of micropores increases, the hole is decreased in diameter, porosity and roughness,and the surface is more smooth. The increase of frequencies makes the ratio of Ca/P decrease, the relative content of anatase TiO₂ increase and rutile TiO₂ decrease.

Abstract: Drying masonry building structures using high-frequency electromagnetic radiation, so-called microwave technology in construction practice is becoming more common. It is an innovative method which can be used to remove excess moisture with significant speed. This article focuses on the description of physical phenomena that occurs during drying and compares the most commonly used processes for drying buildings. This article describes the heating of building materials (basement spaces built from full burnt bricks) using microwave radiation. It assesses the depth of the heating process achieved under different conditions while taking account of various moisture content of irradiated material and varied length of heating.

Abstract: The structure-property relationship of 0.3, 0.5 and 0.7mole% lanthanum (La₂O₃) doped Barium titanate (BaTiO₃) ceramics prepared by solid state sintering under different sintering conditions were investigated in this research. The raw materials were La₂O₃ (grain size=~80nm) and BaTiO₃ (grain size=100nm) powders. Field Emission Scanning Electron Microscope (FE-SEM) was used to examine grain size and surface morphology of sintered pellets & X-Ray Diffraction analysis was conducted to identify crystal structure. The results showed significantly improved grain size and electrical properties of BaTiO₃ for 0.5 mole% La₂O₃ with desired grain size (0.8-1.3μm), high densification (>90% theoretical density) and stable dielectric constant (12700) at room temperature (f=100Hz) by lowering curie temperature around 30^oC by sintering at 1300^oC for 8 hrs. A gradual deterioration follows with increased doping concentration. So the research revealed that proper La³⁺ concentration can inhibit grain size and lower Curie temperature hence significantly improving the electrical properties of BaTiO₃ ceramics.

Abstract: Based on the analysis of trends in the development of aviation and rocketry and ground transportation, the prospect of use of high-alloy steels, and titanium-based alloys with high strength, heat-and corrosion-resistant properties is established. It is shown, that high strength and elasticity of mentioned alloy groups adversely affect the dynamics of cutting process and the resistance of the cutting tool. Processing of small diameter holes is especially difficult due to the small longitudinal stability of the instrument, chip evacuation problems, grooves sticking to the surface almost zero cutting speed near the core. The results from the analysis of works of domestic and foreign scientists have shown that the message sent to the drill by ultrasonic vibrations of the small amplitude reduces axial force and cutting moment due to reduced friction caused by local thermal effects and relief of dislocation motion. At the same time, it is stated that the stable results of the effectiveness of ultrasound were not received in relation to the small diameter end tools until recently because of additional dynamic loads reducing the longitudinal stability and therefore it is impossible to report the instrument optimal oscillation amplitude to facilitate cutting. The working hypothesis of increase of efficiency of the ultrasonic drilling of small diameter holes proposes to consider correlation frequency supplied to the ultrasonic instrument, structural parameters and physical and mechanical properties of the material and to drive oscillations in the plane of the main cutting edges which would significantly reduce the magnitude of the oscillation amplitude. Experimental studies on ultrasound indentation, micro cutting and drilling titanium alloys have confirmed this hypothesis. It was established that at the moment the drill receives a message with the oscillation frequency of 30 kHz when machining titanium alloys, the axial cutting forces decrease by 70 – 80 % and the tool life increases by 2.2 times.

Abstract: This paper presents a solution for the real power control, generated by a synchronous generator belonging to a small hydroelectric power plant. The proposed control system is based on the simple feedback structure which contains also, a frequency correction loop. The mathematical models of all the elements from the control structure are detailed. Also, starting from these models, the real power controller (of Proportional – Integral – Derivative type) tuning procedure is presented. In the end of the paper, the simulations results of the control system are presented highlighting the obtained control performances. The proposed solution is a general one and it can be adapted with relative minor changes to any hydroelectric power plant.

Abstract: Vibration and noise are the dangers for equipment, human health and environment. Developing of a new Mg matrix composite with high damping performance and high strength rate has been acknowledged as an important approach for the reduction of vibrations and prevention of noise. In this paper, xHA/Mg-3Zn-0.5Zr (x=0.5wt.%, 1wt.%, 1.5wt.%) composites were prepared by vacuum induction melting and hot extruding. The microstructure and damping performance were observed and measured using an optical microscope and a dynamic thermomechanical analysis apparatus (DMA), respectively. The influence of HA and environmental factors (temperature, frequency and strain amplitude) on the damping performance of HA/Mg-3Zn-0.5Zr composites were studied. The results showed that the damping performance of HA/Mg-3Zn-0.5Zr composites increased with increasing HA content and strain amplitude. The damping mechanism was in line with the G-L theory and interface damping theory. The damping values were strongly amplified at 150-300°C. The plot of damping versus temperature showed a peak for the Mg-3Zn-0.5Zr-1HA composite at 235°C. The low frequency damping values of xHA/Mg-3Zn-0.5Zr were higher than the high frequency damping values. It is suggested that the change of damping by a variety of external factors is due to the presence of different dominant damping mechanism at different conditions. Furthermore, it was found that at increased HA content, the grain size of HA/Mg-3Zn-0.5Zr composites decreased and the tensile strength and elongation of HA/Mg-3Zn-0.5Zr composites improved. This work will be beneficial for the study of Mg based joint implant materials with high vibration damping performance.