Engineering reports : open access最新文献

The present study focused on the quantitative determination of active compounds, antioxidant and antibacterial activities of leaf extracts of different Sonneratia species. The tested species including Sonneratia alba (SA), Sonneratia caseolaris (SC), and Sonneratia ovata Backer (SO) were collected from Can Gio Mangrove Forest, Vietnam. The methanol extract of SA leaves was found to contain the highest content of total flavonoids, total phenolics and gallic acid (4344.16 ± 51.78 μg/g dry mass). The highest luteolin-7-O-glucoside and luteolin amounts (5963.28 ± 59.77 and 234.33 ± 10.41 μg/g dry mass, respectively) were found in the methanol extract of SC leaves according to HPLC-DAD analysis. The methanol extracts of all three species exhibited strong DPPH radical scavenging activity while the ethanol extracts provided strong antibacterial activity against Staphylococcus aureus, Salmonella typhimurium, and Escherichia coli. By fractionating the extracts over a SiO₂ column using CHCl₃: EA: MeOH gradients, the fractions containing high purity luteolin and luteolin-7-glucoside from SC and high purity luteolin from SO were collected. Moreover, all fractions demonstrated significant DPPH free radical scavenging ability but the fraction enriched in gallic acid showed the highest activity. These findings show that SA is a promising source of gallic acid while SC can be potentially used for the extraction and isolation of luteolin-7-glucoside.

In contrast to single-phase materials the manufacturing process of composites creates multiscale interfaces among constituent materials and between laminar multilayers. Targeting the interfaces in these composite structures, this paper presents a perspective study on the impact safety of potential future composite rail vehicles. The aim is to conceptually explore the key role of interfacial discontinuities of composite material structures as they are a critical issue affecting the impact performance of future composite rail vehicles. Following a theoretical description, the issues are addressed in two parts. First, composite materials are characteristically analyzed from the perspective of their interfacial discontinuities within the materials and between the laminate multilayers to identify their influence. Second, the structural conditions required for crashworthiness are determined in relation to the dual requirements of global stability and local deformability for efficient energy absorption. The key findings are: (1) The interfacial discontinuities of the material phases and the designed structural assemblies need to be tailored for crashworthiness performance and (2) Global stability and locally deformability are the key dual requirements for the energy absorbing progressive deformations that are essential for application of composite for crashworthiness of rail vehicles. The research conceptually explores a key issue of the impact mechanics of composite structures from the perspective of impact safety of composite rail vehicles.

Nanocarbons including carbon nanotubes, graphene oxide, reduced graphene oxide and particularly graphene have unique properties such as high mechanical strength, thermally stable, highly conducting, high friction stability and lower specific wear rates, which can potentially provide synergically improved performance of advanced engineering materials and technologies for various fields of applications such as automotive, aerospace, and other industrial components. Development of phenolic resin-based nanocomposites comprised of nanocarbon material remained as a research focus to outperform different properties of conventional material based components. In application, phenolic resin is the most popular binder in frictional components development such as brake pads, brake linings, and clutch facings, particularly used in many of light and medium automotive brake pad applications. Specifically, the present review study aims to provide thorough discussion on the mechanical, tribological, and thermal performances of phenolic resin-based nanocomposites containing nanocarbon as a property modifier by comparing with the neat phenolic resin or with the composite containing other micro ingredients. As per presented overview, the analysis shows the significant improvement in some required application-based properties of phenolic resin-based nanocomposites such as tensile strength, young's modulus, impact strength, specific wear rate reduction, residue yield, and thermal conductivity due to the inclusion of nanocarbon, where the content of nanocarbons ranges about 0.5 wt% to 5 wt%. Hence nanocomposites synthesized using phenolic resin matrix with nanocarbons fillers found to have better mechanical strength, better wear resistance, and thermal stabilities when compared to pure phenolic resin and other composites.

So far shape memory alloys (SMA) are mostly characterized by their thermo-mechanical behavior due to the underlying thermal effect. In technical applications however, where their benefits like low weight and compact design become relevant, they are activated electrically. This work presents methods for a thorough and systematic characterization of SMA wire samples under Joule heating with the focus on aspects relevant for applications. The goal is to achieve a precise understanding of the sensor and actuator properties of SMA wire samples with different trainings under varying loads. All experiments are conducted on a custom designed test bench with a commercially available NiTi wire with 72 μm diameter, which enables the direct comparisons of tensile tests to actuation tests. The characterization consists of tensile tests and actuator tests with varying load and heating power for differently trained wire samples. The results vividly represent the influence of heating power, training and changing loads on stroke output, working point and the functional stability of SMA actuator wires. Especially, the evolution of the resistance signal and the influence of the R-phase on self-sensing is discussed. The proposed method enables to compare and choose the best suitable alloy with a fitting training for a desired application.

The transition from traditional to digital payment platforms is reshaping domestic revenue mobilization, with significant impacts on sectors like agriculture, health, business, education and economy. This transition, while presenting both challenges and opportunities, has the potential to foster economic growth and boost revenue mobilization. This paper investigates how digital taxation or electronic levy (e-levy) has shaped mobile money (MoMo) adoption in Ghana since the introduction of e-levy on digital financial transactions. The underlying theories supporting this study include the Technology Acceptance Model (TAM), Social Norm Theory (SNT), and Expectancy-Confirmation Theory (ECT). A cross-sectional design was employed, and data was collected from 206 participants (mobile network subscribers) through a self-administered online survey conducted and applied a partial least square structural equation modeling technique. The findings indicate that inherent innovativeness, the structure of the tax, and social tax compliance norms significantly influence citizens' compliance attitudes towards e-levy in the context of a developing country. Conversely, the study found that potential taxpayers' attitudes towards e-levy do not determine their intention to pay (actual use) e-levy. In this respect, recommendations to drive the digital taxation agenda among government revenue agencies in developing countries are (i) continuous inherent innovativeness on the part of the government, (ii) ensuring compliance attitudes towards e-levy, (iii) proper structuring of the tax components and (iv) ensuring ease of use of the system. These findings provide governments and revenue agencies, particularly those in developing countries, with valuable insights into citizens' behavioral change towards digital taxation on MoMo transactions. An effective convergence of the determinants discussed in this research would expedite government mobilization efforts for electronic levies and promote development.

In order to improve the wear and frictional behavior of the aluminum metal matrix composites, carbon nanotube, and fly ash were added as reinforcements. Powder metallurgy technique was used to fabricate the hybrid metal matrix composites. Experimentations were carried out using pin on disc type wear test rig. The analyzed experimental results showed that, in comparison to the pure aluminum and mono reinforcement combination, the wear loss and coefficient of friction of hybrid metal matrix composites were greatly reduced. It was noted that compared to pure aluminum wear loss was decreased to 89.58%, 86.97%, 83.3% by adding 0.25, 0.5, 0.75 wt% carbon nanotube (CNT), respectively. By the addition of 4, 8 and 16 wt% FA to pure Al wear loss was decreased to 83.85%, 89.58%, and 78.12%, respectively. It was also noted that compared to Al/8 wt% FA mono reinforced composites, wear loss was decreased to 77%, 71.26%, and 53.22% with the addition of 0.25, 0.5, 0.75 wt% CNT, respectively. With the addition of 4, 8, 16 wt% FA, wear loss decreased to 81%, 88%, and 75% over Al/0.25 wt% CNT composites, respectively. The microstructural study of the worn-out surfaces revealed low abrasive and adhesive wear by the presence of carbon nanotubes and fly ash in aluminum metal matrix. The reinforcing mechanisms of the wear and frictional properties were also discussed.

The paper analyzes how to improve the teaching of Operational Research, focusing on distance learning courses where professors and students are separated through space and time. This case study was done in a public Industrial Engineering undergraduate course, and the work structure is divided into three main parts: an exploratory-descriptive documentary analysis, application of free software, and evaluation of learning. The authors showed the feasibility of using the SageMath tool in the teaching-learning process. The study revealed the importance of developing alternative solutions to educational realities marked by economic and financial constraints, where structure teaching with free software is a ruling factor once Engineering education is not a similar global event everywhere. Distance learning is a phenomenon that has been growing over the last 20 years in Brazil, but this was one of the first experiences with the use of SageMath. So, it can serve as a reference for countries with socioeconomic conditions similar to Brazil. Also, this case study can help other professors to enhance their teaching in a distance learning context even in scarcity scenarios of educational resources. The software implementation would be justified in part of the groups studied.

The biochemical pathway for propionic acid (PA) production is an interesting alternative that can include the utilization of biomass as feedstock. This study evaluated the utilization of Agave bagasse (AB), a lignocellulosic residue, to produce PA by Propionibacterium acidipropinici in batch systems (125 mL-hermetic bottles and 1000 mL-bioreactor). The process included a steam explosion pretreatment at 142°C for 15 min and enzymatic hydrolysis, where solid loading (2.75% and 5% in pretreatment and 2.5%, 3.75%, and 5% in enzymatic hydrolysis) was evaluated. Furthermore, the enzymatic concentrations of 18.3 filter paper unit (FPU)/g_AB (1×) of Cellic® CTec2 and 1.5× and 3× were tested. The yields of total carbohydrates (TC) obtained at the two solid loadings tested in the pretreatment were statistically similar, but the 3x enzymatic concentration enhanced the yields of TC, glucose, and xylose (0.23 ± 0.01, 0.15 ± 0.01 and 0.03 ± 0.01 g/g_AB, respectively). The hydrolysates obtained under these conditions were evaluated as carbon sources for PA production, obtaining a productivity of 0.069 ± 0.006 g/L h and a yield product/substrate of 0.44 g_PA/g_TC. The control of pH in the culture reduced the fermentation time in the bioreactor by 52% compared with the hermetic bottles without pH control. The potential of hydrolysates as carbon sources for PA production was evidenced, as approximately 50% of the initial carbon was converted to this product. The observed yield product/substrate was similar to those reported from hydrolysates of diverse biomass types, pretreatments, or enzymatic cocktails and the same or related microorganisms. However, the system studied has advantages, such as not requiring the addition of chemical or detoxification stage, and lower temperature and time compared to other pretreatments.

The frequency-domain reflection (FDR) has been demonstrated to be a trustworthy technique in solving the defect location of power cable by field experiments. However, the location spectrum of the FDR requires manual window smoothing and can be disturbed by spurious peaks. Aiming at these shortcomings of FDR, a new method of cable defect location based on Burg power spectral (BPS) is introduced in this paper. The idea of this method is to use linear difference variance to fit the distribution of reflection coefficient spectrum and build an auto-regressive (AR) model. The Burg algorithm is employed to estimate the coefficients model and calculate the power distribution of the AR model. Then, the cable defects will be located by BPS with high precision and resolution. In this method, the fast Fourier transform (FFT) with windowed function is replaced by an AR model without windowed function. This suppressed the impact of spurious peaks or spectrum leakage in FFT on the localization defects, and the localization resolution is higher. Finally, we validate the feasibility and effectiveness of BPS through experiments conducted on a 500 m laboratory cable and a 9.6 km submarine cable.

Because of its improved formability, lower production costs, and mechanical properties, aluminum metal matrix composite is the highly intriguing engineering material. It can meet the needs of modern engineering applications used in the automotive, military, aerospace, and marine industries. Hybridization of reinforcement is adopted to develop tailor-made properties of composites for specific application. In this study, Al-B₄C-Gr hybrid composites were produced with varying graphene content (0.25, 0.50, 0.75, and 1 wt.%) and keeping boron carbide (10 wt.%) as constant, the effect of graphene proportion on the mechanical properties of produced composites was evaluated. It has been observed that increasing the Gr reinforcement particles in the synthesized composites improves the mechanical characteristics of the composites, such as raising the tensile strength to 215 Mpa and the hardness to 110 HV due to the presence and proper distribution of reinforcement in the matrix. When compared to the base alloy, the tensile strength and hardness of Al10B₄C0.75Gr composites rose by 27.174% and 67.290%, respectively. The dry sliding wear behavior of Al-10 wt.% B₄C-wt.%Gr hybrid composites confirms that graphene and B₄C particles in the matrix increase the wear resistance of the produced MMCs. The each parameter such as sliding distance, sliding velocity and load has its influence toward the better wear resistance of the developed composites and were discussed.