Search Results (827)

Power converters are increasingly pushing toward higher switching frequencies, with current designs typically operating between tens of kilohertz and a few megahertz. The commercialization of gallium nitride (GaN) power transistors has opened new possibilities, offering performance far beyond the limitations of conventional silicon devices. Despite this promise, the potential of GaN technology remains underutilized. This paper explores the feasibility of achieving sub-gigahertz switching frequencies using GaN-based switch-mode power converters, a regime currently inaccessible to silicon-based counterparts. To reach such operating speeds, it is essential to understand and quantify the intrinsic frequency limitations imposed by GaN device physics and associated parasitics. Existing power conversion topologies and control techniques are unsuitable at these frequencies due to excessive switching losses and inadequate drive capability. This work presents a detailed, systematic study of GaN transistor behavior at high frequencies, aiming to identify both fundamental and practical switching limits. A compact analytical model is developed to estimate the maximum soft-switching frequency, considering only intrinsic device parameters. Under idealized converter conditions, this upper bound is derived as a function of internal losses and the system’s target efficiency. From this, a soft-switching figure of merit is proposed to guide the design and layout of GaN field-effect transistors for highly integrated power systems. The key contribution of this study lies in its analytical insight into the performance boundaries of GaN transistors, highlighting the roles of parasitic elements and loss mechanisms. These findings provide a foundation for developing next-generation, high-frequency, chip-scale power converters. Full article

Welding is a technological variant of the electric resistance spot-welding process in which the machined protrusion on the surface is heated and rapidly deformed, and the small molten zone formed at the interface is then forged to form the weld spot. The paper analyses the effects of projection welding parameter values for thin, low-carbon aluminized steel sheets. Two sets of 16 welded samples having three or five protrusions were performed and analyzed using the Taguchi method. The microstructural aspects were analyzed in cross sections made through the welded points, highlighting the expulsion or accumulated effects of the Al-Si alloy protective layer and the formation of intermetallic compounds. To estimate the effect of welding parameters, the samples were subjected to tensile strength tests, and the fracture mode was evaluated. It was found that the values of the breaking forces were close for the two types of samples analyzed, for identical values of the welding regime parameters, but the elongation at break was double in the case of samples with five protrusions. The breaking force increased from 10.9 kN for samples with three protrusions to 11.4 kN for samples with five protrusions, for the same values of welding parameters. Full article

In this work, the production of iron-containing powders by the electroplasma dispersion method was investigated under various discharge regimes and in electrolytes of different natures (NaCl and Na₂CO₃). The influence of technological parameters on particle morphology, phase composition, and elemental content was analyzed using X-ray diffraction (XRD), scanning electron microscopy with energy-dispersive spectroscopy (SEM/EDS), as well as laser particle size distribution analysis. It was found that the single-stage mode at 350 V in NaCl electrolyte led to the formation of predominantly irregularly shaped and fragmented particles, with a limited amount of spherical powders. The two-stage mode (350 V for 5 s followed by 250 V) in NaCl ensured a more stable formation of spherical particles with sizes of 60–80 μm; however, it was accompanied by intensive surface oxidation. The highest fraction of spherical powders was obtained in a Na₂CO₃ electrolyte under the two-stage mode, where homogeneous spheres with diameters of 20–75 μm and smooth surfaces were formed. According to EDS analysis, the powders consisted mainly of iron and oxygen, while in the samples synthesized in Na₂CO₃, the presence of sodium was detected, indicating the formation of mixed Na–Fe–O oxide phases. XRD confirmed the presence of a metallic α-Fe matrix along with oxide phases Fe₂O₃ and Fe₃O₄, while granulometric analysis (D50 ≈ 55 μm) revealed a relatively narrow particle size distribution. The obtained results demonstrate that variation in the discharge regime and electrolyte composition enables targeted control over the morphology and phase composition of the powders, making the electroplasma method a promising approach for producing metallic powders with tailored properties. Full article

This study examines the soliton dynamics in the time-fractional cubic–quintic nonlinear non-paraxial propagation model, applicable to optical signal processing, nonlinear optics, fiber-optic communication, and biomedical laser–tissue interactions. The fractional framework exhibits a wide range of nonlinear effects, such as self-phase modulation, wave mixing, and self-focusing, arising from the balance between cubic and quintic nonlinearities. By employing the Multivariate Generalized Exponential Rational Integral Function (MGERIF) method, we derive an extensive catalog of analytic solutions, multi-peakon structures, lump solitons, kinks, and bright and dark solitary waves, while periodic and singular solutions emerge as special cases. These outcomes are systematically constructed within a single framework and visualized through 2D, 3D, and contour plots under both anomalous and normal dispersion regimes. The analysis also addresses modulation instability (MI), interpreted as a sideband amplification of continuous-wave backgrounds that generates pulse trains and breather-type structures. Our results demonstrate that cubic–quintic contributions substantially affect MI gain spectrum, broadening instability bands and permitting MI beyond the anomalous-dispersion regime. These findings directly connect the obtained solution classes to experimentally observed routes for solitary wave shaping, pulse propagation, and instability and instability-driven waveform formation in optical communication devices, photonic platforms, and laser technologies. Full article

Optically levitated particles in high vacuum offer an exceptionally isolated mechanical platform for photonic control. Effective cooling of their center-of-mass motion is essential not only for enabling ultrasensitive precision sensing but also for opening access to the quantum regime where macroscopic superposition and nonclassical states can be realized. In this review, we present a comprehensive overview of recent advances in active feedback cooling, based on real-time photonic modulation, and passive feedback cooling, driven by optomechanical interactions within optical resonators. We highlight key experimental milestones, including ground state cooling in one and two dimensions, and discuss the emerging applications of these systems in force sensing, inertial metrology, and macroscopic quantum state preparation. Particular attention is given to novel proposals for probing quantum gravity, detecting dark matter and dark energy candidates, and exploring high-frequency gravitational waves. These advancements establish levitated optomechanical systems as a powerful platform for both high-precision metrology and the investigation of fundamental quantum phenomena. Finally, we discuss the current challenges and future prospects in cooling multiple degrees of freedom, device integration, and scalability toward future quantum technologies. Full article

This review provides a comprehensive synthesis of the coupled effect of temperature and solar radiation on photovoltaic (PV) module performance and lifespan. Although numerous investigations have examined these stressors in themselves, this research addresses their interrelationship and evaluates the way climatic conditions affect short-term performance fluctuation and long-term degradation mechanisms. The assessment consolidates outcomes from model strategies, laboratory tests, and field monitoring studies. Through the presentation of these findings in a narrative form, the paper identifies recurring difficulties in terms of the absence of shared assessment metrics and the low level of standardisation of long-term test regimes. Second, it underlines the importance of predictive modelling and live monitoring as important management tools for coupled stressors. Finally, the review points out research gaps and underscores future research avenues, including ongoing work towards the development of a coupling index, a composite measure being piloted in individual studies, and advancements in materials technology, predictive methodology, and durability testing. Full article

Bare sand patches are extensively distributed in dryland ecosystems, and their spatiotemporal evolution provides critical insights into regional eco-environmental changes. The Mu Us Sandy Land, a typical dryland region, exemplifies a distinctive mosaic distribution of bare sand and vegetation patches. Based on the Google Earth Engine (GEE) platform and Landsat time-series imagery (1986–2023), this study extracted multi-temporal bare sand patches using the random forest algorithm. We quantified their spatiotemporal dynamics and identified driving mechanisms through integration with natural/socioeconomic datasets. Key findings include the following: (1) The total area of bare sand patches decreased significantly after 2000, with an average annual reduction of 530.08 km² (p < 0.01), a rate markedly exceeding pre-2000 rates. (2) Before 2000, bare sand patches were widespread across the entire region; however, by 2023, only residual patches persisted in the northwestern regions. (3) The most significant reduction in bare sand patch area is attributable to the shrinkage of giant patches (>10 km²). (4) The spatial distribution of bare sand patches is primarily controlled by a combination of natural factors, including stream, precipitation, topography, and wind regime. (5) The principal drivers of the reduction in bare sand patch area are anthropogenic activities, such as the implementation of ecological restoration projects, advancements in agricultural technology, and transformations in breeding patterns. These findings provide a scientific foundation for desertification control and ecosystem management strategies in drylands. Full article

Climate change, marked by increasing temperatures and unpredictable rainfall, presents a significant challenge to the sustainable cultivation of runner beans (Phaseolus coccineus L.). These conditions underscore the urgent need for efficient resource management. Therefore, it is crucial to establish suitable irrigation regimes and nutritional conditions for runner bean cultivars. Furthermore, since genotype performance is strongly influenced by water availability and nutrient supply, understanding their interactive effects is essential for developing technologies that are adapted to climate change and sustain high yields of garden beans. In this context, the individual and combined effects of three runner bean cultivars (Cozia1, Cozia2, and Cozia3), two irrigation regimes (2000 and 2500 m³·ha⁻¹), and three fertilisation strategies (chemical, organic, and unfertilised) on some physiological, morphological, and biochemical parameters were assessed in this study. The field experiment was carried out in the north-eastern part of Romania over two consecutive growing seasons, following a randomized split–split plot design with three replications. The results showed that genotype had the most significant influence on the majority of traits, highlighting its dominant role over fertilization and irrigation. Under chemical fertilization and 2500 m³·ha⁻¹ irrigation, Cozia2 achieved the highest grain yield (3427.60 kg·ha⁻¹) and pod number (48.13), while Cozia1 combined with chemical fertilization under 2000 m³·ha⁻¹ irrigation recorded the highest total phenolic content (0.47 mg GAE·100 g⁻¹ d.w.). Among cultivars, Cozia2 was highly responsive to fertilisation and irrigation variation, showing both the highest and lowest values for pod number, seed weight, and seeds per pod depending on treatment. Notably, the highest photosynthetic assimilation rates were observed in Cozia2 × IR2 × UF and Cozia3 × IR1 × OR combinations. Based on the results of this study, Cozia3 under chemical fertilization is best suited for high yields under limited water (2000 m³·ha⁻¹), while Cozia2 is best suited when chemical fertilization is combined with higher irrigation (2500 m³·ha⁻¹). However, in the context of organic cultivation, Cozia3 is identified as the most suitable cultivar. Full article

Although laser cavitation was discovered half a century ago, novel geometries and regimes to excite this effect have been vigorously explored during the past few decades. This research is driven by a variety of applications of laser cavitation in demanding branches of science and technology, such as microfabrication, synthesis of nanoparticles, manipulation of cells, surgery, and lithotripsy. In this work, we combine experimental studies using high-repetition-rate imaging and numerical simulations to uncover a novel regime of the laser cavitation observed upon excitation of a liquid by a train of laser pulses with the pulse energy of 140 mJ and duration of 1.2 μs delivered through a quartz optical fiber. Once the lifetime of the initial cavitation bubble (excited by the first laser pulse) is larger than the period between pulses, which is 34.3 μs, the secondary pulses in the train pass the gas in a bubble and evaporate additional liquid. This results in the formation of a cascaded cavitation bubble of larger volume and elongated shape of $4.6$ mm length compared to $3.8$ mm in case of excitation by a single laser pulse. In addition, the results of acoustic measurements confirm the presence of shock waves in the applied liquid. Finally, potential applications of the uncovered laser cavitation regime are discussed. Full article

Twelve Polish pea varieties were malted, and their technological properties were assessed, using a congress mashing regime. Alpha-amylase addition was also used to determine whether external enzymes can improve the properties of the achieved worts. Malts from peas were characterized with poor saccharification time, but alpha-amylase allowed for the saccharification of starch from three different pea varieties (‘Gloriosa’, ‘Jantar’, and ‘Primavil’). Acquired worts were characterized with a low amount of fermentable sugars, which would be inadequate for production of beer with the typical alcohol content (4–6% v/v), albeit they possibly could be used as a substrate for the production of low-alcoholic beers. Additionally, the malting process changed the amount and the type of volatiles present in the pea malts, significantly increasing the concentration of pyrazines, while, at the same time, reducing concentration of terpenes. Full article

This review paper deals with Triply Periodic Minimal Surfaces (TPMS) and lattice structures as a new generation of heat exchangers. Especially, their manufacturing is becoming feasible with technological progress. While some intricate structures are fabricated, challenges persist concerning manufacturing limitations, cost-effectiveness, and performance under transient operating conditions. Studies reported that these complex geometries, such as diamond, gyroid, and hexagonal lattices, outperform traditional finned and porous materials in thermal management, particularly under forced and turbulent convection regimes. However, TPMS necessitates the optimization of geometric parameters such as cell size, porosity, and topology stretching. The complex geometries enhance uniform heat exchange and reduce thermal boundary layers. Moreover, the integration of high thermal conductivity materials (e.g., aluminum and silver) and advanced coolants (including nanofluids and ethylene glycol mixtures) further improves performance. However, the drawback of complex geometries, confirmed by both numerical and experimental investigations, is the critical trade-off between heat transfer performance and pressure drop. The potential of TPMS-based heatsinks transpires as a trend for next-generation thermal management systems, besides identifying key directions for future research, including design optimization, Multiphysics modeling, and practical implementation. Full article

Digitalization is reshaping entrepreneurship, yet the mechanisms that translate new technological possibilities into entrepreneurial intention remain poorly understood, especially for resource-constrained small and medium-sized enterprises (SMEs). Building on the Theory of Planned Behaviour, Entrepreneurial Risk-Taking Theory and Affordance Theory, this study proposes and tests an integrated model that captures how individual cognition, digital capability and platform-related risk interact to shape digital entrepreneurial intention (DEI). Survey data from 428 Greek SME owner-managers were analyzed with Partial Least Squares Structural Equation Modelling (PLS-SEM). Results show that entrepreneurial self-efficacy, financial risk tolerance, digital literacy and perceived platform affordances each exert significant positive effects on DEI, whereas perceived platform risk exerts a significant negative effect. Importantly, platform risk also dampens the positive impact of self-efficacy, revealing a boundary condition often overlooked in intention research. The findings position digital transformation as a double-edged phenomenon amplifying opportunity through affordances while simultaneously magnifying risk. The study advances theory by integrating risk perceptions and affordance recognition into a TPB framework, and it offers actionable guidance: policy makers should stabilize digital-regulatory regimes, platform providers should increase transparency and reliability, and SME support programs should blend digital-skills training with calibrated risk-management tools. Together, such measures can convert latent entrepreneurial confidence into resilient digital venture creation. This study contributes to theory by extending the Theory of Planned Behaviour with risk-sensitive boundary conditions, broadening Risk-Taking Theory to account for platform-specific uncertainties, and validating Affordance Theory in a digital SME context. Practically, it provides actionable guidance for entrepreneurs, policymakers, and platform operators on balancing digital capability development with systemic risk governance. Full article

Hydrogen-based technologies are growing, thanks to recent advancements in systems such as fuel cells and electrolyzers. The present work aims to develop a methodology for the definition of a fused health indicator to monitor the operating and health conditions of a solid oxide fuel cell system. A suitable degradation model was built to yield four trendable output indicators, which were subsequently merged to create the fused health indicator. Subsequently, the assessment of off-design conditions and two realistic scenarios (leakage and constant excess of air working regime) was carried out. The health indicator has proved suitable for fault detection, prognostic applications, control strategy improvement, and health management. In particular, the methodology has underlined the necessity of making the control strategy adaptive with respect to degradation. Through this approach, it is observed that reducing the solid oxide fuel cell temperature difference by 10 °C can result in a 1.2% increase in lifetime. In contrast, the leakage simulation reveals a decrease of about 10.5% in the health state after 100 h, resulting in about a 21% lower end-of-life. Full article

The reuse of buildings of documentary value, as an expression of authorship and of a research trajectory within the debate on contemporary architectural design, represents a sustainable retrofitting approach, as it enables the extension of the life cycle of buildings as a resource. The adaptive reuse of buildings entails several cultural and technical challenges for a balance between conservation and transformation. This topic lies in the Italian debate on the technological, energy and housing needs inadequacy of the housing stock. Within this scenario, the PINQuA—Programma Innovativo Nazionale per la Qualità dell’Abitare (Innovative National Programme for Housing Quality) constitutes an innovative factor in the process of upgrading socially, physically, and functionally degraded housing contexts. The paper investigates the sustainable redevelopment of architects Franco Purini and Laura Thermes’ residential building block in the Marianella neighbourhood in Northern Naples. The methodology is based on the identification of the conditions of authorship, the relationship with the values of the pre-existing elements of the urban environment, and the expression of 1980s architecture. The results of the design proposal are measured by indicators of environmental and energy performance. The design proposal develops a retrofitting approach for contemporary housing by maintaining the residential function and reusing public and collective spaces adapted to the new climate regime and social needs. Full article

This paper highlights recent activities associated with the design of an uninstalled open fan propulsor for next-generation civil aircraft in the high-subsonic flight regime. The concept comprises a transonic propeller–rotor and a subsequent guide vane, which are both subject to pitch-variability in order to account for the strong variations in flight conditions over the entire mission profile. The engine-scale design aimed for high technological maturity and to comply with a high number of industrially relevant requirements to ensure a competitive design, meeting performance requirements in terms of high efficiency levels at cruise and maximum climb conditions, operability in terms of stability margins, good acoustic characteristics, and structural integrity. During the design iterations, rapid 3D-RANS-based optimisations were only used as a conceptual design tool to derive sensitivities, which were used to support and justify major design choices in addition to established relations from propeller theory and common design practice. These design-driven optimisation efforts were complemented with more sophisticated CFD analysis focusing on rotor tip vortex trajectories and resulting in unsteady blade row interaction to optimise the guide vane clipping, as well as investigations of the entire propulsor under angle-of-attack conditions. The resulting open fan design will be the very basis for wind tunnel experiments of a downscaled version at low and high speed. Full article