Papers by Keyword: Duty Cycle

Abstract: The demand for and usage of radio spectrum over the last three decades have increased geometrically throughout the world as a result of daily increase in new wireless services and applications that are in need of radio spectrum. However, the current fixed allocation policy currently being using in radio spectrum management has made availability of radio spectrum for the new emerging wireless services and applications practically infeasible since all available radio spectrum had been allocated nationally and internationally. Nevertheless, results of recent radio spectrum occupancy measurements conducted in several parts of the world had revealed that most of the allocated radio spectrum under the current fixed allocation policy nationally and internationally was underutilized. In additional, the results of some of the spectrum occupancy measurements conducted also showed that the usage of most already allocated radio spectrum varies with time, space and frequency. In order to experimentally verify the actual radio spectrum usage in Nigeria, radio spectrum occupancy measurements were conducted in three major cities in South-West geopolitical zone of Nigeria. The analysis of the results of the radio spectrum occupancy measurements conducted show that the actual radio spectrum usage in the three cities follows the same pattern with the rest of the world with actual usage varies with time, space and frequency with actual overall percentage of occupancy less than 26.0%. The analysis of the results of the occupancy measurements conducted also show that while some allocated radio spectrum were sparsely used, some were medially used and some were heavily used.

Abstract: Plasma electrolytic oxidation (PEO) was used to form a protective layer on 5754 and 2024 aluminum alloys to improve the corrosion properties of the processed materials. The protective performances of the obtained coatings were studied by a combination of electrochemical methods and salt spray test. The absence of pitting corrosion after a 7-day test for the entire series of PEO-layers on aluminum alloys 5754 and 2024 was confirmed by scanning electron microscopy (SEM). Also, microcracks were detected only in the SEM-image for the most porous and thin PEO-coating formed on aluminum alloy 2024 at duty cycle = 0.06 and 30 min.

Abstract: Several studies have been made on cell growth by the ultrasound irradiation. It is important to change the output, irradiation time and duty cycle for cell growth. The duty cycle determined the proportion of the time that the ultrasound was “on”. We can control cell growth by changing these three terms. The purpose of this study is to find the optimum conditions for cell growth and examine a new factor to influence cell growth. Cell concentration was determined by measuring the absorbance with a spectrophotometer. In this study, the absorbance became highest on 10min ultrasound irradiation and the duty cycle of 67% in experimental conditions. However, when 30 min ultrasound irradiation and the duty cycles of 86%, the absorbance became close to the highest value too. The results suggested that, in addition to the duty cycle, the off time of ultrasound might also affect the cell growth.

Abstract: The current gain stability of a second generation of 1200 V rated SiC Junction Transistors (SJTs) under long-term DC and pulsed current operation is investigated. A 1000-hour long, 200 A/cm² DC current stress results in a ≈ 10% reduction of the current gain (β) during the early stages of the stress test, while the β is perfectly stable for the remainder (>90%) of the stress duration. The same amount of stress charge applied as a pulsed current in lieu of DC current results in similar extent of β degradation for the Gen-II SJTs. The pulsed current stressing is conducted at frequencies ranging from 50 kHz to 200 kHz, at a fixed duty cycle of 0.5.

Abstract: Plasma electrolytic oxidation (PEO) of commercially pure titanium VT1-0 was performed in phosphate electrolyte. High-frequency 200 kHz bipolar signal at a duty cycle D=0.1 was used to form the oxide coatings. Polymer-containing anticorrosion coatings were formed by applying polyvinylidene fluoride (PVDF) on the base PEO-coating. The results of electrochemical tests have showed a decrease of corrosion current density by 2 orders of magnitude (down to 1.5∙10^-10 А∙сm^-2) and the corresponding increase of the polarization resistance (up to 1.9∙10⁸ Оhm∙сm²) in comparison with the metallic substrate.

Abstract: The paper presents the results of the study of electrochemical and mechanical properties of PVDF/PEO-coatings formed on magnesium alloy MA8 by plasma electrolytic oxidation (PEO) and subsequent application of polyvinylidene fluoride (PVDF) on the PEO-layer. The oxide coatings were formed using a 300 Hz bipolar signal with duty cycle (D) 0.50. The analysis of electrochemical data has showed a decrease of corrosion currents by 3 orders of magnitude (down to 6.0·10^-9 А·сm^-2) and an increase of the polarization resistance by 3 orders of magnitude (up to 5.3·10⁶ Оhm·сm²) for the coatings formed by triple dipping (x3) of the PEO-layers into PVDF solution. Evaluation of the tribological properties of the (x3) PVDF/PEO-coatings has showed a significant increase of the wear resistance (the number of abrasion cycles resulting in complete destruction of the coating increased in 25 times) as compared to the base PEO-layer.

Abstract: Influence of the polarizing signal parameter used during plasma electrolytic oxidation (PEO) on the composition, morphology and properties of protective coatings formed on aluminum alloy in tartrate-containing electrolyte has been presented. It was established, that using of the short-pulse bipolar polarizing signal (τ=5 μs) facilitates the reduction of porosity and roughness of the formed PEO-layers. This, in turn, increases wearproof and protective corrosion characteristics of the treated alloy surface. Increasing the duty cycle (D) affects on the chemical composition and the thickness of the obtained coatings.

Abstract: Tin seleno telluride thin film was deposited by pulse electrodeposition onto fluorine doped tin oxide coated glass from aqueous solution containing Sn-EDTA, Na₂SeO₃ and TeO₂. The sample was deposited at a potential of-0.40 V vs Ag/AgCl with various duty cycle between 10% to 90% followed by annealing under nitrogen gas at 250°C for 30 minutes. The crystalline structure, morphology and photoresponse of the thin film was analyzed using X-ray diffraction (XRD), scanning electron microscopy and linear sweep photovoltammetry techniques. The XRD pattern shows polycrystalline cubic structure of SnSe_0.4Te_0.6 for film deposited at 50% duty cycle. The domain peak at 2θ=28.82^o shows a high intensity and a better photoresponse due to the small crystalline size. The tin seleno telluride thin film reflects the loose short rod type aggregates at 10%-50% duty cycle and dendritic structure was formed at deposition of 75% and above. The deposited tin seleno telluride is a p-type semicoductor and the band gap was found to be 1.60 eV with direct transition.

Abstract: A method to establish duty cycle was proposed based on wheel loader operating characteristics and features. Firstly, wheel loader operating characteristics, energy consumption and power distribution rules were summarized theoretically. Wheel loader energy consumption rules were explored through operating test. The features were extracted from testing data which can represent wheel loader operating rules. Finally, the duty cycle was composed according to the rules features arose in the actual operating test. The duty cycle will provide support for data files for hybrid wheel loader power system matching, computer simulation and dynamic analysis. Furthermore, the duty cycle will be helpful for traditional wheel loader dynamic matching, simulation analysis and numerical optimization.

Abstract: Micro EDM is a nonconventional machining method which has gained researcher’s attention during the past decade. After the success in industrial applications of EDM, focus has been to scale down the entire system to a smaller size. The capability of the process to machine extremely hard and difficult to machine materials has made it a suitable candidate for machining the next generation engineering materials. In this paper, an attempt has been made to develop μEDM setup with piezo actuated tool feed mechanism. The holes are machined on copper plates of thickness 300μm with varying process parameters like voltage, frequency and duty cycle. The design of experiment method has been used to carry out the experiments in a systematic manner. The quality of holes produced is studied using optical microscope and SEM images. The results obtained are presented in this paper.