Search Results (72)

Rapid global urbanization poses complex challenges that demand advanced data-driven forecasting solutions for smart cities. Traditional statistical and standalone Long Short-Term Memory (LSTM) models often struggle to capture non-linear dynamics and long-term dependencies in urban time-series data. This review critically examines hybrid LSTM models that integrate LSTM with complementary algorithms, including CNN, GRU, ARIMA, and SVM. These hybrid architectures aim to enhance prediction accuracy, integrate diverse data sources, and improve computational efficiency. This study systematically reviews principles, trends, and real-world applications, quantitatively evaluating hybrid LSTM models using performance metrics such as mean absolute error (MAE), root mean square error (RMSE), and the coefficient of determination (R²), while identifying key study limitations. The case studies considered include traffic management, environmental monitoring, energy forecasting, public health, infrastructure assessment, and urban waste management. For example, hybrid models have achieved substantial accuracy improvements in traffic congestion forecasting, reducing their mean absolute error by up to 29%. Despite the inherent challenges related to structural complexity, interpretability, and data requirements, ongoing research on attention mechanisms, model compression, and explainable AI has significantly mitigated these limitations. Thus, hybrid LSTM models have emerged as vital analytical tools capable of robust spatiotemporal prediction, effectively supporting sustainable urban development and data-driven decision-making in evolving smart city environments. Full article

MnO₂-doped 9 mol% CaO-stabilized zirconia (CSZ) was investigated in terms of phase stability, microstructure, and mechanical properties before and after thermal cycling. As the MnO₂ content increased from 2 to 4 mol%, the monoclinic phase fraction decreased significantly (from 32.6% to 2.5%), while the tetragonal phase fraction increased (from 58.2% to 90.3%), indicating an enhanced phase stability comparable to fully stabilized ZrO₂. The cubic phase fraction decreased from 9.2% to 3.4% with 2–3 mol% MnO₂, but increased to 7.2% at 4 mol%. The 9 mol% CSZ showed a mixture of grains around 2 μm and 10 μm, while the MnO₂-doped CSZ exhibited only grains larger than 30 μm, suggesting that MnO₂ acted as a sintering aid. After thermal cycling, increasing the MnO₂ content from 2 to 4 mol% led to an increase in the monoclinic phase fraction (from 7.8% to 17.2%) and a decrease in the tetragonal phase fraction (from 53.6% to 21.8%). The Vickers hardness and wear resistance of MnO₂-doped CSZ were superior to those of undoped 9-CSZ, and improved as the MnO₂ doping level increased. These mechanical properties were maximized in the CSZ doped with 3 mol% MnO₂, and this trend persisted after thermal cycling. These results demonstrate that MnO₂ doping effectively enhances the phase stability and mechanical performance of CaO-partially stabilized zirconia under thermal stress cycling conditions. Full article

The emergence of numerous SARS-CoV-2 variants, characterized by mutations in the viral RNA genome and target proteins, has presented challenges for accurate COVID-19 diagnosis. To address this, we developed universal aptamer probes capable of binding to the spike proteins of SARS-CoV-2 variants, including highly mutated strains like Omicron. These aptamers were identified through protein-based SELEX using spike proteins from three key variants (D614G-substituted Wuhan-Hu-1, Delta, and Omicron) and virus-based SELEX, known as viro-SELEX. Leveraging these universal aptamers, we created a highly sensitive lateral flow assay (LFA) and an ultra-sensitive molecular diagnostic platform that integrates a novel rapid PCR technique, enabling fast and reliable detection across all SARS-CoV-2 variants. Full article

We investigated the phase transitions, mechanical properties, and chemical durability of a composition of 9 mol% CaO-stabilized zirconia (9CSZ) doped with 2–4 mol% CeO₂ under thermal stress against molten slag. The monoclinic phase fraction of 9CSZ was 7.14% at room temperature, and CSZ doped with 2–4 mol% CeO₂ showed a slightly lower value of 5.55–3.72%, with only a minor difference between them. The microstructure of 9CSZ doped with 2–3 mol% CeO₂ was similar to that of undoped 9CSZ, whereas the microstructure of 9CSZ doped with 4 mol% CeO₂ exhibited noticeable grain refinement. The mechanical properties of CSZ at room temperature tended to improve as the CeO₂ doping concentration increased. The Vickers hardness increased from 1088.4 HV to 1497.6 HV when the CeO₂ doping amount was 4 mol%, and the specific wear amount decreased from 1.5941 to 1.1320 × 10⁵ mm³/Nm. This tendency remained similar even after applying thermal stress. The monoclinic phase fraction of 9CSZ increased from 7.14% to 67.71% after the erosion experiment with the CaF₂-based slag. CeO₂-doped CSZ had a lower monoclinic phase fraction than CSZ after the erosion experiment, but as CeO₂ content increased from 2 to 4 mol%, the fraction rose to 4.07%, 30.85%, and 77.11%. Full article

Superhydrophobic surfaces, known for their exceptional water-repellent properties with contact angles exceeding 150°, are highly regarded for their effectiveness in applications including self-cleaning, antifouling, and ice prevention. However, the structural fragility and weak durability of conventional coating limit their long-term use. In this research, a new approach is proposed for the fabrication of long-lasting superhydrophobic surfaces using ethyl cyanoacrylate (ECA) and a primer. The application of the primer creates a curing rate disparity between the surface and bulk of the ECA layer, resulting in the formation of wrinkled microstructures essential for achieving superhydrophobicity. The fabricated surfaces were further functionalized through plasma treatment and hydrophobic silane (OTS) coating, enhancing their water-repellent properties. This straightforward and scalable method produced surfaces with excellent superhydrophobicity and robust adhesion to substrates. Durability tests, including roller abrasion and microscratch evaluations, indicated that the wrinkled structure and strong substrate adhesion contributed to sustained performance even under mechanical stress. Additionally, mechanical properties were assessed through nanoindentation, demonstrating enhanced resistance to physical damage compared to conventional superhydrophobic coatings. This study highlights the potential of ECA-based superhydrophobic surfaces for applications requiring durability and mechanical stability, such as architectural coatings, automotive exteriors, and medical devices. The approach offers a promising solution to the limitations of existing superhydrophobic technologies and opens new avenues for further research into wear-resistant and environmentally resilient coatings. Full article

A comprehensive review of recent advancements in applying deep reinforcement learning (DRL) to fluid dynamics problems is presented. Applications in flow control and shape optimization, the primary fields where DRL is currently utilized, are thoroughly examined. Moreover, the review introduces emerging research trends in automation within computational fluid dynamics, a promising field for enhancing the efficiency and reliability of numerical analysis. Emphasis is placed on strategies developed to overcome challenges in applying DRL to complex, real-world engineering problems, such as data efficiency, turbulence, and partial observability. Specifically, the implementations of transfer learning, multi-agent reinforcement learning, and the partially observable Markov decision process are discussed, illustrating how these techniques can provide solutions to such issues. Finally, future research directions that could further advance the integration of DRL in fluid dynamics research are highlighted. Full article

This paper presents advancements in the performance of digital phase-locked loop (DPLL)s, with a special focus on addressing the issue of required gain calibration in the time-to-digital converter (TDC) within phase-domain DPLL structures. Phase-domain DPLLs are preferred for their simplicity in implementation and for eliminating the delta–sigma modulator (DSM) noise inherent in conventional fractional-N designs. However, this advantage is countered by the critical need to calibrate the gain of the TDC. The previously proposed dual-interpolated TDC(DI-TDC) was proposed as a solution to this problem, but strong spurs were still generated due to the TDC resolution, which easily became non-uniform due to PVT variation, degrading performance. To overcome these problems, this work proposes a DPLL with a new calibration system that ensures consistent TDC resolution matching the period of the digitally controlled oscillator (DCO) and operating in both the foreground and background, thereby maintaining consistent performance despite PVT variations. This study proposes a DPLL using a calibrated dual-interpolated TDC that effectively compensates for PVT variations and improves the stability and performance of the DPLL. The PLL was fabricated in a 28-nm CMOS process with an active area of only 0.019 mm², achieving an integrated phase noise (IPN) performance of −17.5 dBc, integrated from 10 kHz to 10 MHz at a PLL output of 570 MHz and −20.5 dBc at 1.1 GHz. This PLL operates within an output frequency range of 475 MHz to 1.1 GHz. Under typical operating conditions, it consumes only 930 µW with a 1.0 V supply. Full article

This study investigates the mechanical and piezoresistive sensing properties of recycled carbon-fiber-reinforced polymer composites (rCFRPs) for self-sensing applications, which were prepared from recycled carbon fibers (rCFs) with fiber lengths of 6, 12, 18, and 24 mm using a vacuum infusion method. Mechanical properties of the rCFRPs were examined using uniaxial tensile tests, while sensing characteristics were examined by monitoring the in situ electrical resistance under cyclic and low fatigue loads. Longer fibers (24 mm) showed the superior tensile strength (92.6 MPa) and modulus (8.4 GPa), with improvements of 962.1% and 1061.1%, respectively. Shorter fibers (6 mm) demonstrated enhanced sensing capabilities with the highest sensitivity under low fatigue testing (1000 cycles at 10 MPa), showing an average maximum electrical resistance change rate of 0.7315% and a gauge factor of 4.5876. All the composites displayed a stable electrical response under cyclic and low fatigue loadings. These results provide insights into optimizing rCF incorporation, balancing structural integrity with self-sensing capabilities and contributing to the development of sustainable multifunctional materials. Full article

This paper presents a wideband fractional-N all-digital phase-locked loop (WBPLL) architecture featuring a triple-loop configuration capable of tuning frequencies from 1.9 to 6.1 GHz. The first and second loops, automatic frequency control (AFC) and counter-assisted phase-locked loop (CAPLL), respectively, perform coarse locking, while the third loop employs a digital sub-sampling architecture without a frequency divider for fine locking. In this third loop, fractional-N frequency synthesis is achieved using a delta-sigma modulator (DSM) and digital-to-time converter (DTC). To minimize area, digital modules such as counters, comparators, and differentiators used in the AFC and CAPLL loops are reused. Furthermore, a moving average filter (MAF) is employed to reduce the frequency overlap ratio of the digitally controlled oscillator (DCO) between the second and third loops, ensuring stable loop switching. The total power consumption of the WBPLL varies with the frequency range, consuming between 8.8 mW at the WBPLL minimum output frequency of 1.9 GHz and 12.8 mW at the WBPLL maximum output frequency of 6.1 GHz, all at a 1.0 V supply. Implemented in a 28 nm CMOS process, the WBPLL occupies an area of 0.055 mm². Full article

This study analyzes the impact of knowledge capital (KC), a key element of firms’ innovation and competitiveness, on stock returns during economic crises when sustainable competitiveness becomes particularly important. We analyze the impact of the Global Financial Crisis and COVID-19 as economic crises, focusing on manufacturing industries with a high proportion of investment shifts from physical capital to KC. Our findings indicate that KC is positively associated with stock returns during the Global Financial Crisis and COVID-19. This positive relationship is strengthened by the firm’s ability to leverage KC, as measured by greater product market share, higher Tobin’s Q, and larger cash holdings. This study emphasizes the protective role of KC during the economic crisis when the market pays more attention to corporate sustainability and provides implications to corporate managers and investors. Full article

Al–10%Si–2%Cu alloys have been widely used in high-value industries (e.g., aerospace and automobiles) because of their lower specific gravity; however, galvanic corrosion rendered these alloys to have poor corrosion resistance. Therefore, the microstructure and corrosion properties of Al–10%Si–2%Cu alloys were investigated with respect to the lanthanum (La) content. All Al alloy samples were synthesized using gravity casting, with added La contents of 0.00, 0.25, 0.50, 0.75, and 1.00 wt%, and were characterized using microstructural characteristics analysis and electrochemical tests. Adding 0.5 wt% La (xLa-0.5) indicated the finest structure, which had a 4% lower α-Al area fraction than the La-free alloy (xLa-0). However, the area fraction of a 1 wt% La-added (xLa-1) alloy was 2.4% higher than that of xLa-0. The corrosion current density (I_corr) of the xLa-0.5 was 1.09 μA/cm², representing a 68% decrease as compared to that of xLa-0, and xLa-0.5 reached the highest polarization resistance value (7.32 × 10³ Ω·cm²). The improvement in corrosion resistance of xLa-0.5 was due to the rapid and dense formation of a passivation layer induced by its fine structure, as well as the precipitated phase by enhancing the dispersibility of Cu. Full article

This study examines the relationship between intangible capital (IC) and stock performance during the two recent crisis periods, the GFC and COVID-19. By categorizing IC into Knowledge Capital (KC) and Organizational Capital (OC), we analyze the impact of each capital on the crisis return in the manufacturing sector. The results show that a greater KC and OC are significantly associated with higher crisis returns during both periods. In addition, we find evidence that generalist CEOs strengthen this relationship while specialist CEOs do not. Within firms led by a generalist CEO, the CEO’s tenure positively moderates the association between each factor of intangible capital and crisis period returns. This study emphasizes the pivotal role of KC and OC as a protective buffer against external shocks, particularly when the market pays more attention to corporate sustainability. Full article

This study investigated how process parameters of laser cladding affect the microstructure and mechanical properties of WC-12Co composite coating for use as a protective layer of continuous caster rolls. WC-Co powders, WC-Ni powders, and Ni-Cr alloy powder with various wear resistance characteristics were evaluated in order to determine their applicability for use as cladding materials for continuous caster roll coating. The cladding process was conducted with various parameters, including laser powers, cladding speeds, and powder feeding rates, then the phases, microstructure, and micro-hardness of the cladding layer were analyzed in each specimen. Results indicate that, to increase the hardness of the cladding layer in WC-Co composite coating, the dilution of the cladding layer by dissolution of Fe from the substrate should be minimized, and the formation of the Fe-Co alloy phase should be prevented. The mechanical properties and wear resistance of each powder with the same process parameters were compared and analyzed. The microstructure and mechanical properties of the laser cladding layer depend not only on the process parameters, but also on the powder characteristics, such as WC particle size and the type of binder material. Additionally, depending on the degree of thermal decomposition of WC particles and evolution of W distribution within the cladding layer, the hardness of each powder can differ significantly, and the wear mechanism can change. Full article

Understanding trends in the formation of the intermetallic compound (IMC) layer in Al/Fe bimetallic composites can aid in significantly improving their mechanical properties. However, it is currently challenging to predict IMC layer formation during hot-dip aluminizing. Furthermore, the results from previous studies are difficult to compare owing to the variation in the process parameters used. Therefore, to understand how temperatures and holding times affect the thickness and hardness properties of IMC layers, we investigated the interfacial properties of aluminized stainless steel in molten Al-Si-Mg. AISI 420 stainless steel was hot-dip aluminized in an Al–Si–Mg alloy melt for 10–120 min at four different temperatures: 700, 750, 800, and 850 °C. Morphology, type, and element distribution of the phases formed in the reaction layer and the reduction rate of the aluminizing process were studied. Notably, while the reaction layer thickness increased with increasing aluminizing temperature when the holding time was low, long-term reaction caused the reaction layer to become thicker at lower temperatures. The mechanism of this morphological transformation is discussed. The results demonstrated effective trends in controlling the morphology of the intermetallic compound layer with respect to various hot-dip Al plating process parameters. Full article

The urban heat island (UHI) effect poses a significant challenge for cities like Pohang, South Korea, which suffer from environmental pollution. Integrating a ventilation corridor into city planning can mitigate this issue. Despite wind’s potential as a resource for urban areas, its role remains under-studied in urban planning and design. To address this gap, this study analyzes the wind environment of Pohang City to identify effective strategies for reducing the UHI effect through the implementation of wind corridors, thereby enhancing the city’s thermal environment and sustainability. We used the KLAM_21 model to simulate and analyze the cold airflow. The results indicate that the land cover of Pohang, including residential and commercial areas, consists of urbanized dry areas. The wind direction over the past 10 years (2013–2022) has generally been west–southwest (247.5°). The cold air height and flow direction range expanded around the Hyeongsan River, eventually affecting the central city after 5 h. In the simulations, cold air accumulated above 30 m at specific locations near the valley’s base. After 2 h, the flow range of the cold air height increased. The green area ratio (GAR) and cold air speed positively correlated (+0.153). Thus, creating a wind-corridor forest could effectively address Pohang’s fine dust and UHI phenomena. Full article