Abstraction and context in requirements engineering: Toward a synthesis

Most requirements engineering (RE) research and practice embodies a philosophy that we will call abstractionism, which involves the building of simplified models of domains of discourse and proposed systems. Abstractionists make much use of formal models, such as goal dependency networks. An alternative design philosophy is contextualism, according to which the particularities of the context of use of a system must be understood in detail before the requirements can be derived. Contextualists use qualitative methods to uncover and help interpret these particularities. In this paper, we analyze what it would mean to combine the best features of abstractionism and contextualism, and we ground our discussion in an illustration of abstractionist and contextualist thinking about RE through goal refinement (GR). In the context of the domain of meeting scheduling, we contrast a wholly abstractionist approach to GR with one that incorporates data gathered using two ethnographic methods. In doing so, we consider each step of the abstractionist approach, illustrating where ethnographic data obtained in our work environment affects the model produced. As we proceed, we summarize the general lessons learned. We then discuss how other abstractionist and contextualist methods could be integrated.     

Analysis of the radiation resistance and gain of a full-wave dipole

The full-wave-dipole antenna is very seldom used in communication systems, and yet this type of antenna offers a very high gain. This is due to the high input impedance for the center-tap feeding-point antenna. The analysis of short-length and half-wavelength dipole antennas has been reported, in great detail previously, in texts. However, an analysis of the full-wave dipole antenna has not been detailed nor reported, either in texts or journals. Such an analysis is very significant, in order to understand more about this antenna's properties and potential applications for exploiting its high-gain benefits. The paper presents an analysis of the radiation resistance and gain of the full-wave-dipole antenna. This involves special integrations in the mathematics     

Kinetic and regeneration studies of photocatalytic magnetic separable beads for chromium (VI) reduction under sunlight

Physical adsorption and photocatalytic reduction of Cr(VI) in magnetic separable beads were investigated. In order to elucidate the kinetics of photocatalytic process, operating parameters such as catalyst dosage and the initial concentration were examined in detail. It was observed that the reduction rate of Cr(VI) increased with an increase in the catalyst loading, as this translated into an increase in the number of available active sites. Critical scrutiny of the percentage of the initial reduction rate versus time at various initial concentration of Cr(VI) revealed that the rate of substrate conversion decreased as the initial concentration increased. The kinetic analysis of the photoreduction showed that the removal of Cr(VI) satisfactory obeyed the pseudo first-order kinetic according to the Langmuir-Hinshelwood (L-H) model and the absorption of Cr(VI) on the magnetic beads surfaces was the controlling step in the entire reduction process. Furthermore, desorption experiments by elution of the loaded gels with sodium hydroxide indicated that the magnetic photocatalyst beads could be reused without significant losses of their initial properties even after 3 adsorption-desorption cycles.     

Synthesis and electrochemical performance of LiV3O8/carbon nanosheet composite as cathode material for lithium-ion batteries

To improve the rate capability and cyclability of LiV₃O₈ cathode for Li-ion batteries, LiV₃O₈ was modified by forming LiV₃O₈/carbon nanosheet composite. The LiV₃O₈/carbon nanosheet composite was successfully achieved via a hydrothermal route followed by a carbon coating process. The morphology and structural properties of the samples were investigated by X-ray diffraction (XRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). TEM observations demonstrated that LiV₃O₈/carbon composite has a very flat sheet-like morphology, with each nanosheet having a smooth surface and a typical length of 400-700 nm, width of 200-350 nm, and thickness of 10-50 nm. Each sheet was surrounded by a thick layer of amorphous carbon. Electrochemical tests showed that the LiV₃O₈/carbon composite cathode features long-term cycling stability (194 mAh g⁻¹ at 0.2 C after 100 cycles) and excellent rate capability (110 mAh g⁻¹ at 5 C, 104 mAh g⁻¹ at 10 C, and 82 mAh g⁻¹ at 20 C after 250 cycles). Electrochemical impedance spectra (EIS) indicated that the LiV₃O₈/carbon composite electrode has very low charge-transfer resistance compared with pristine LiV₃O₈, indicating the enhanced ionic conductivity of the LiV₃O₈/carbon composite. The enhanced cycling stability is attributed to the fact that the LiV₃O₈/carbon composite can prevent the aggregation of active materials, accommodate the large volume variation, and maintain good electronic contact.     

Chip morphology study in high speed drilling of Al�CSi alloy

Chip formation during drilling operation is greatly influenced by the cutting parameters such as cutting speed, feed rate, and drill geometry. However, not many studies have focused on the direct observation of the chip formation during high speed drilling. This paper investigates the effect of cutting speed and feed rate on the chip morphology during high speed drilling of aluminum?Csilicon alloys using carbide drill. Observation on the multiview characterization of the chips was carried out which includes free surface, back surface, and cross-section of top surface. Structure and shape alterations of the free and back surfaces were analyzed using a scanning electron microscope. Finally, different geometrical parameters of chip cross-section were measured in order to study the effect of cutting parameters on chip compression ratio and thrust force. It was found that increase in cutting speed significantly affects the chip morphology especially on the structure of free surface and cross-section of the chips. Results also showed that built-up edge on the rake face of tool played an important role on the formation of irregular pattern on the chip back surface.     

Synthesis and characterization of graphene–nickel oxide nanostructures for fast charge–discharge application

Graphene–metal oxide composites as anode materials for Li-ion batteries have been investigated extensively, but these attempts are mostly limited to moderate rate charge–discharge applications. Here, graphene–nickel oxide nanostructures have been synthesised using a controlled hydrothermal method, which enabled in situ formation of NiO with a coralloid nanostructure on graphene. Graphene/NiO (20%), graphene/NiO (50%) and pure NiO show stable discharge capacities of 185 mAh/g at 20 C (1 C = 300 mA/g), 450 mAh/g at 1 C, and 400 mAh/g at 1 C, respectively. High rate capability and good stability in prolonged charge–discharge cycling permit the application of the material in fast charging batteries for upcoming electric vehicles. To the best of our knowledge such fast rate performance of graphene/metal oxide composite as anode and such stability for pure NiO as anode have not been reported previously.     

Grid Harmonic and Control Delay Compensation for Three-phase Grid-connected VSIs in Small Wind Turbine Systems

Voltage space vector pulse-width modulation(SVPWM) has been widely applied to control current in threephase vohage source inverters (VSI).However,as a voltage type modulator,SVPWM has certain drawbacks compared with current type modulators for grid-connected applications.For a grid-connected VSI,the performance of existing current controllers based on SVPWM is compromised by grid harmonics,control delay and system nonlinearities such as switching dead time.Moreover,unlike current type PWM,SVPWM does not inherently have over-current protection.A novel SVPWM-based current controller is proposed for three-phase grid-connected VSIs for small wind turbine applications.To overcome the drawbacks of SVPWM,a grid harmonic compensation method is proposed along with compensation for control delays.Both simulation and experimental results have established excellent steady-state response and fast dynamic response of the current controller.In addition,the DSP-based control system has both improved real-time control performance and fast response for over-current protection.     

Heat transfer enhancement in light-emitting diode packaging employing different molar concentration of magnesium oxide thin films as a heat spreader

To solve thermal management difficulties created by miniaturization of light-emitting diode package, magnesium oxide thin film was spin coated on the aluminum 5052-grade substrate and employed for heat spreading and improvement of the thermal path for heat removal from light-emitting diode parcel to ambient. Thickness of different films of magnesium oxide was prepared from 0.6M and 0.8M precursors to find out the effects of films thickness and molar concentrations towards perfect heat spreading. Results from X-ray diffraction (XRD) proves the MgO thin film as cubic with the crystalline orientations of (200), (220), and (222). Good results were highlighted through 20 layers (0.6M) MgO thin film in respect to its transient thermal analysis compared with other layers from 0.6M and 0.8M and bare Al substrate; this was due to its nonporous and evenly distributed particles size (56.0 nm), film thickness (301.7 nm), surface roughness (121 nm), higher thermal conductivity (26.3 W/mK), and free from internal cracks and defects. Lower total thermal resistance (11.4 K/W), lower junction temperature (98.8°C), optimal thermal impedance (36.43°C), higher illumination from light-emitting diode, and operation within safe operating temperature range (2700-3000 K) for high-power light-emitting diodes were all recorded at 700 mA from the tested light-emitting diode mounted on 20 layers (0.6M) magnesium oxide thin film. This study consequently proved magnesium oxide thin film as an alternative heat spreader in lighting technology packaging.     

Scientometric review of advancements in the development of high-performance cathode for low and intermediate temperature solid oxide fuel cells: Three decades in retrospect

Solid oxide fuel cells (SOFCs) have the potential to replace conventional thermal power plants due to their high efficiency and low emission. As the activation loss of the cathode usually limits the SOFC performance, the development of high-performance and durable cathode materials has received extensive attention in the past few decades. It is therefore essential to keep track of the research progress to identify significant research gaps and future directions. In this study, we retrieved the bibliometric data of 1101 cutting-edge research articles focused on cathode development for SOFCs and conducted a scientometric review. Even though significant research in cathode development for intermediate to low temperature SOFCs started in the 1990s, significant growth in the research output appeared in the year 2000 and remarkably continued till 2010 before exhibiting a sinusoidal pattern. Overall, there is a record of average decadal progress in this research area. We found that only a small percentage of countries in the world (i.e., about 29%) are involved in the research for the development of intermediate to low temperature SOFC cathodes. A highlight of core assessment criteria for cathode developments is presented with a summary of the most recent articles (i.e., including those in 2021). This paper can help early-stage researchers, journal outlets, governments, funding authorities, and investors understand the current progress in this area and how close researchers are to a breakthrough that could lead to the commercialization of this emerging technology.