Search Results (34,745)

The growing operational demands placed on small uncrewed aerial vehicles (UAVs) favor propulsion systems with high onboard energy density, which has renewed interest in micro-turbojet engines in the 100–500 N thrust class. Manufacturing these miniature, geometrically complex engines by subtractive machining or laser powder bed fusion (L-PBF) entails high capital expenditure and, in the case of L-PBF, a substantial feedstock energy burden, which limits their use on attritable (expendable) platforms. This paper is a narrative review; it does not fabricate, instrument, or test a micro-turbojet engine, and none of the arguments presented here constitute experimental validation. Its purpose is to assess, against the published evidence, whether fused filament fabrication (FFF) both in its high-performance polymer form and in its sinterable bound-metal form offers a credible manufacturing route for this engine class, and to identify where the evidence is insufficient. We examine a hybrid material strategy: high-performance thermoplastics (CF-PEEK, PEI) for cold-section lightweighting, and the shaping, debinding and sintering (SDS) route for bound-metal (17-4 PH, 316L, Inconel 718) and ceramic filaments in the hot section. Three findings temper the optimism of earlier accounts. First, a simplified per-part energy model, benchmarked against published life-cycle inventories, shows that the manufacturing-energy advantage of SDS over L-PBF is conditional on furnace loading: with the assumptions adopted here, batch sintering must accommodate roughly 15 or more parts per cycle before SDS becomes the lower-energy route, and a single-specimen comparison favors L-PBF. Second, a first-order conduction analysis indicates that the 2–5% residual porosity of sintered FFF metals lowers the through-wall temperature drop of a combustor liner by only a few kelvin, two orders of magnitude less than a thermal barrier coating, so residual porosity should not be presented as a thermodynamic benefit. Third, applying a classical admissible-roughness criterion to representative micro-turbojet blade chords and Reynolds numbers shows that as-built FFF surfaces exceed the admissible equivalent sand-grain roughness by a factor of three to seven, making aerodynamic post-processing a quantified requirement rather than a qualitative recommendation. We conclude that FFF is presently credible for static cold- and hot-section hardware on attritable platforms, that its use for rotating hot-section components is not supported by the available data, and that the economic case is stronger and better evidenced than the manufacturing-energy case. Full article

Long-term assessment of aging highway tunnels requires linking spatial geometry with time-dependent rock-lining interactions. This study examined the 1147 m left tube of the Jinan Tunnel after 23 years of service to identify deformation-sensitive zones and inform maintenance. The tunnel is excavated mainly in weathered Cambrian limestone, classified as Grade IV (poor) to Grade V (very poor) rock. Terrestrial laser scanning (TLS) point clouds were compared with the design profile to quantify radial deviations and clearance convergence. A representative Grade IV section with an approximately 100 m overburden was simulated for 100 years using Fast Lagrangian Analysis of Continua in Three Dimensions (FLAC3D) and a Burgers viscoelastic model. At LK32+370, the crown deviation reached 109 mm, compared with 87.8 mm at the right arch waist and 46.3 mm at the left sidewall. Alignment-scale average radial deviations were approximately 40–50 mm in central sections but 60–70 mm near the ends, and Grade V sections exhibited average deviations that were approximately 1.5 times those of Grade IV sections. Modeled crown displacement increased from approximately 1.6 to 2.6 mm between years 10 and 20. From years 5 to 50, lining horizontal stress at the crown increased from 5.1 to 8.5 MPa and lining vertical stress at the arch waist from 5.5 to 10.5 MPa, with the steepest growth during years 10–20 and slower growth thereafter. The resulting framework integrates full-profile TLS screening with creep-based interpretation to prioritize poor-rock, shallow-cover, weak-interlayer, and vulnerable lining zones. Because the TLS survey represents one late-life epoch, the field quantities are design-referenced deviations rather than pure 23-year deformation. Full article

Smart mobility is a core component of the smart city; it comprises various intelligent systems that make the city more safe, livable, efficient and sustainable. One of these system is the smart parking system (SPS). A smart parking system is known as the application of advanced information and communication technologies to the traditional parking system. It is a technology-driven approach that plays a crucial role in smart cities, particularly in improving traffic management. The smart parking system is a multi-faceted concept that integrates parking reservation, automatic payment, parking space detection, outside/inside guidance, data analytics, and user interaction interfaces. While various advanced technologies, such as Wireless Sensors Networks (WSNs), Internet of Things (IoT), Cloud Computing (CC), FoG computing, and Artificial Intelligence (AI), are involved in engineering and implementing these functional facets, Vehicular Ad Hoc Network (VANET) and its derivatives have received relatively limited interest in the literature of smart parking systems. Moreover, much of the literature primarily focuses on reducing parking search time outside parking facilities. However, drivers in practice often waste a significant amount of time inside the parking facility navigating for a free parking spot. In this work, we address two main functions in smart parking: a parking spot allocation mechanism and on-site parking real-time guidance. We developed an automatic parking spot allocation and in-parking guidance approach where the communication layer is modelled using IEEE 802.11p DRSC as the reference infrastructure. The simulation assumes a reliable channel and excludes lower-layer performance evaluation such as packet loss, congestion, latency, interferences, or coverage sensitivity. The reported improvements therefore characterize the application-layer benefit of pre-assignment reservation and spatial guidance, independent of the specific communication technology employed. The designed system, called in this paper VANET-guided, aims to significantly decrease the parking spot search time inside the parking facility. This paper presents a comparative evaluation study of a VANET-guided smart parking framework against a fully unguided baseline using NS-3.36.1, evaluating their performance across four key operational dimensions: lot occupancy, number of vehicles within facility, inter-arrival gap, and driver decision delay, with R = 30 statistically validated replications per experimental cell, using a series of Monte Carlo simulations under diverse traffic and mobility conditions. The guided system combines atomic server-side spot reservation, spatial allocation strategies, and a Kalman-filtered RSSI-based in-lot positioning pipeline, while the unguided baseline models realistic driver behavior, including cognitive decision delays, spot rejection, and concurrent spot competition. To address the structural asymmetry between the two systems, two intermediate baselines are evaluated: (i) an information-only configuration and (ii) a reservation-only configuration, providing an exploratory comparison of the respective roles of availability information, reservation, and spatial targeting. The findings indicate that the fully guided system (called in this paper VANET or VANET-guided) reduces mean parking search time by 28% to 71% relative to the fully unguided baseline across all tested occupancy levels, with statistical validation through 95% confidence interval analysis, paired t-test and Wilcoxon signed-rank test, practical effect sizes reported through Cohen’s d, and distributional statistics including standard deviation, coefficient of variation, and 90th–95th percentile search times. Full article

To enhance the comprehensive performance of laser cladding coatings, IN 625 alloy coatings were fabricated on Q345R steel substrates via laser cladding technology, followed by laser remelting treatment under varying laser energy densities. In this paper, the differences in microstructure and properties of the cladding layers without remelting and after laser remelting with different laser energy densities are studied. The experimental results show that laser remelting could effectively improve the surface roughness of the cladding layer. With the increase in laser energy density, the surface roughness initially decreased from 20.82 μm to 7.04 μm at 8 J/mm² and then increased to 10.28 μm at 12 J/mm². After laser remelting, the grain size of the cladding layer became more uniform, the number of equiaxed crystals increased, and the columnar crystals in the remelting area were broken to form short, rod-like columnar crystals. With the increase in laser energy density during remelting, the microhardness of the cladding layer gradually increased. The average microhardness of the cladding layer after remelting with 12 J/mm² laser energy density was about 265 HV_0.2, and the microhardness distribution was more uniform. With the increase in laser energy density, the corrosion resistance of the cladding-layer surface changed from an increase to a decrease. After remelting with a laser energy density of 8 J/mm², the cladding layer showed higher corrosion resistance, with the highest corrosion potential of −0.41 V and the minimum corrosion current density of 0.562 μA/cm². Full article

Automatic tree detection plays a significant role in terrain analysis, planning and decision-making across a range of sectors, including forestry, agriculture and road accessibility analysis. This article focuses on the automatic detection of individual trees from Airborne Laser Scanning (ALS) data. Existing methods have been developed mainly for forests and urban green spaces, where trees are characterised by extensive crowns; in orchards, they are primarily suitable for mature trees. There is therefore a need to refine detection methods dedicated to intensive orchards, taking into account both young and mature trees. The study utilised ALS data with a density of 12 points/m² on the basis of which a Canopy Height Model (CHM) was generated; the impact of various noise reduction methods on the effectiveness of tree detection was then compared. A new method for detecting treetops was proposed, Distance-Transform-Based Adaptive Non-Maximum Suppression (DTB-ANMS), combining adaptive reduction in local maxima with a radius dependent on the distance between potential vertices. Validation was carried out on 10 test areas comprising 2272 trees in young and mature orchards. The bilateral filter provided the best compromise between noise reduction and the preservation of fine crown structures, whilst DTB-ANMS achieved the highest overall performance (Precision 0.944, F1-score 0.875, Recall of 0.816), outperforming the classic Marker-Controlled Watershed and the local maxima method. The results indicate that publicly available, low-density ALS data can form the basis for an effective, low-cost tree inventory in intensive apple orchards. Full article

Agricultural machinery components are frequently exposed to abrasive wear, impact loading, and corrosive environments, leading to rapid material loss and premature failure. Laser cladding provides an effective route for surface strengthening and remanufacturing because of its low dilution, metallurgical bonding, and flexible material design. This review examines recent progress in wear-resistant laser-cladded coatings for agricultural machinery, focusing on coating materials, multiphase and multiscale structural design, process regulation, service evaluation, and engineering applications. Fe-, Ni-, and Co-based and high-entropy alloy coatings are compared together with particle reinforcement, in situ synthesis, gradient structures, auxiliary-field processing, and post-treatment. Multiscale modeling, data-driven prediction, and digital-twin approaches are also discussed in relation to process optimization and service assessment. Current evidence shows that coating design should be matched to the dominant failure mode rather than guided by hardness alone. Fe-based and graded coatings remain attractive for large-volume soil-engaging components, whereas high-entropy and composite coatings offer advantages under coupled wear, corrosion, and impact conditions. Further development requires standardized testing, comparable service data, and stronger links between laboratory evaluation and field validation. Full article

Laser powder bed fusion (L-PBF) of near-β titanium alloys typically produces coarse columnar grains and strong <001> textures, which induce anisotropic mechanical behavior. Here, 5 wt.% tantalum (Ta) particles were doped into Ti-5Al-5Mo-5V-3Cr (Ti-5553) powder to concurrently inhibit microstructural anisotropy and contribute to enhanced strength–ductility synergy via solidification modification. During the L-PBF process, unmelted Ta particles provided heterogeneous nucleation sites, while dissolved Ta generated local constitutional undercooling. Together, these effects reduced the average β-grain size from 47.23 ± 27.5 to 12.28 ± 11.8 μm and weakened the <001> texture, as well as increased yield strength from 870 to 990 MPa while retaining 28% elongation. After solution treatment and aging, Ti-5553-Ta reached a yield strength of 1196 MPa and 16.0% elongation. Local Ta-enriched precipitate-free zones and refined α precipitates contributed to the improved post-treatment ductility. Full article

Low-angle overhang structures in laser powder bed fusion (LPBF) experience strongly geometry-dependent thermal conditions because the underlying material progressively changes from consolidated solid to low-conductivity powder, which raises a fundamental question regarding the conventional use of a uniform inherent strain for efficient residual stress and distortion prediction. In this study, the dynamic inherent strain (DIS) method is employed to investigate the inherent strain behavior of LPBF overhang structures with different tilt-angles. The results reveal that after excluding the boundary-affected stages of the build, the representative inherent strain exhibits a systematic dependence on tilt-angle in both magnitude and tensor characteristics. Based on this angle dependence, compact angle-dependent expressions are established using trigonometric basis functions for engineering implementation. Comparisons with residual stress measurements at the experimentally investigated 30° and 90° geometries further indicate that angle-specific inherent strain assignment has a greater influence on the mechanical response toward the lower bound of the investigated angular range. Full article

Background/Objectives: Goat placenta extract (GPE), enriched with bioactive macromolecules, exhibits regenerative potential in both healthy and damaged cells. To enable targeted transport of these macromolecules to the buccal mucosa, potential delivery systems are required. The study aimed to evaluate the bioactivity of GPE on human gingival fibroblasts (HGFs) and to develop a GPE-loaded chitosome (CTS) mucoadhesive system for buccal delivery. Methods: The bioactivity of GPE was assessed in normal and chemotherapy-damaged HGF cells. GPE-loaded CTS was prepared, lyophilized, and then incorporated into an oral gel. The in vitro buccal deposition was visualized by confocal laser scanning microscopy. Results: GPE showed no cytotoxic effects at a concentration of 4000 µg/mL and significantly promoted the viability of both normal and 5-fluorouracil (5-FU)-treated HGF cells (p < 0.05). The GPE-loaded CTS formed nanosized vesicles and a positive surface charge, which may facilitate interactions with mucin. CTS and its loaded oral gel enhanced the delivery of macromolecular proteins into the buccal mucosa compared with gel alone. Conclusions: GPE promoted HGF viability and facilitated the recovery of 5-FU-induced gingival fibroblast injury. The CTS-loaded oral gel enhanced the buccal delivery of macromolecular protein, representing a promising strategy for oral mucosal regeneration and supportive care in chemotherapy-induced mucosal injury. Full article

Replacing conventional petroleum-based materials in printing technology with sustainable alternatives is an approach to reducing the environmental impact of printing processes. In this research, biodegradable printing plates based on polylactic acid (PLA), polycaprolactone (PCL), and silicon dioxide (SiO₂) nanoparticles were produced for embellishment printing applications, including relief printing and foil stamping. Structural properties were examined by scanning electron microscopy (SEM), while thermal behaviour was characterized using thermogravimetric analysis (TGA). Mechanical properties were defined through tensile testing, hardness, and surface roughness measurements. Printing plates were produced by laser engraving, and relief geometry was measured to evaluate printing plate feasibility. The plates were exposed to 80, 100, and 120 °C for 5, 10, and 15 min, followed by evaluation of mechanical properties, surface features, and relief stability. Initial functional assessment was conducted through printing trials to obtain embossed reliefs and foil-transferred prints. The results showed that SiO₂ nanoparticles increased thermal stability and stiffness and reduced thermally induced variations in hardness and thickness. SiO₂-containing plates exhibited engraved line dimensions closer to nominal values. All produced plates presented well-defined embossed elements, while successful foil transfer was achieved with PLA/PCL/SiO₂ 70/30/3, 80/20/3, and 90/10/3 formulations. The 80/20/3 and 90/10/3 blends showed the best foil stamping performance. Full article

Background: Antimicrobial resistance is a growing concern, and inappropriate prescribing may contribute to its rise. Variability among periodontists highlights the need to understand prescribing patterns and factors influencing antibiotic selection. We aim to assess antibiotic prescribing patterns and perceptions of resistance among Indian periodontists and evaluate factors associated with prescribing practices and selection of the antibiotic regimen perceived by respondents as most effective. Methods: A cross-sectional questionnaire survey was conducted among Indian periodontists (January–April 2024), distributed via institutional email and LinkedIn. Descriptive statistics summarized responses; chi-square/Fisher’s tests assessed associations with experience. Logistic regression was performed to identify factors associated with respondents’ selection of the antibiotic regimen perceived as most effective for periodontal therapy. Results: Of 500 invited, 328 responded (65.6%). Respondents were mostly female (67.7%), with a mean age of 32.25 ± 6.05 years; 50.3% had <5 years’ experience and 98.6% held an MDS in Periodontology. Amoxicillin plus metronidazole was the regimen most frequently perceived as effective by respondents (37.8%), followed by amoxicillin–clavulanic acid (35.4%) and amoxicillin alone (15.9%). Oral administration was preferred (89.0%). Prophylactic antibiotics were prescribed for infective endocarditis/CABG indications by 89.6%, while 48.2% did not prescribe after laser-assisted surgery. Experience was significantly associated with prescribing frequency and post-laser prescribing (p < 0.05); associations with crown lengthening and flap surgery lost significance after Bonferroni correction. Academic practice was associated with regimen selection univariably (OR = 0.56, 95% CI 0.34–0.93) but not after multivariable adjustment (aOR = 0.65, 95% CI 0.37–1.13). Most respondents (98.5%) viewed resistance as a growing concern. Conclusions: Prescribing practices varied with experience and practice setting. Amoxicillin plus metronidazole was most frequently considered effective, though no factor independently predicted selection. High awareness of resistance underscores the need for stronger antimicrobial stewardship in periodontal care. Full article

Terrestrial laser scanning (TLS) has become an important tool for the digital documentation of historic buildings, particularly where irregular geometries and restricted spaces limit conventional survey methods. This study develops and applies a TLS-based Scan-to-HBIM workflow for the documentation of La Casa de la Alquimia, a thirteenth-century domestic heritage building located in the Judería of Córdoba, within the UNESCO-listed historic centre. The workflow integrates TLS data acquisition, scan registration and cleaning, AI-assisted point-cloud classification, expert-led HBIM reconstruction, and deviation-based geometric validation. The results show that the TLS dataset supported the reliable reconstruction of a complex medieval domestic building. The AI-assisted classification tool was used as a practical support mechanism for organising dense point-cloud data before modelling, improving the visual separation of architectural elements and reducing repetitive manual filtering, while final modelling decisions remained dependent on expert interpretation. Deviation analysis showed a close correspondence between the HBIM geometry and the surveyed point cloud, with higher local deviations mainly associated with exposed stone masonry, curved transitions, and inherent historic deformations. HBIM-based renderings and a scan-based virtual tour were also produced as complementary outputs for spatial interpretation. The study indicates that a TLS-based Scan-to-HBIM workflow, supported by AI-assisted classification and geometric validation, can provide a reliable and transferable methodological reference for documenting comparable domestic heritage buildings under constrained real-world conditions. Full article

This study presents a detailed microanalysis and microstructural characterization of the multi-material 316L–IN718 system produced in a prior work by the powder binning method for Laser Powder Bed Fusion (L-PBF), in which these multi-material samples were fabricated in a single build and then mechanically tested. This effort extends the investigation by applying X-ray micro-computed tomography (Micro-CT), electron backscatter diffraction (EBSD), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD) techniques to specimens produced under the baseline single-scan condition to examine the interface transition in volumetric porosity, crystallographic structure, and elemental composition. Micro-CT analysis revealed that the interface region exhibited the highest void volume ratio among the three analyzed regions, reaching 0.91%, compared to 0.32% for 316L and 0.37% for IN718. The interface also contained the largest defects, including the only voids with volumes exceeding 500,000 µm³, indicating that critical flaws, while not widespread, were concentrated at the dissimilar material boundary. EDS line scanning across four locations along the interface confirmed a diffuse compositional transition that closely and consistently supports the interface width independently reported via microhardness for the same material pairing in the original study. EBSD mapping showed a gradual grain structure transition with coarser equiaxed grains on the 316L side, and the entire scan indexed successfully with a single face-centered cubic structure file, with no secondary or intermetallic phases detected at the resolution of the measurement. Collectively, these results explain the failure behavior reported previously: the compositionally strengthened, defect-rich interface sheds plastic strain into the adjacent, softer 316L, which fails first due to its lower strength and coarser void population. Under monotonic tensile loading, improving binning-based multi-material performance therefore depends primarily on strengthening or targeting defect-reduction strategies at the weaker 316L constituent. Full article

This work focuses on the design of non-Hermitian DFB lasers incorporating phase-shifted dielectric and metallic gratings, emphasizing the symmetry aspects of the complex refractive index profile. Conventional DFB lasers featuring dielectric Bragg gratings and metallic gratings are also investigated. The impact of the phase shift between the gratings, as well as facet boundary conditions, was analyzed in terms of threshold gain and gain contrast relative to the next-higher-order laser pole. Significant performance improvements were predicted for complex-coupled DFB lasers wherein the dielectric and metallic gratings are either in-phase or out-of-phase. In contrast, for PT-symmetric configurations, we found that reflection asymmetry, which was expected to further enhance DFB laser performance, is compromised by facet reflections. To address this issue, lasing must occur at the Bragg wavelength, and the contribution of the PT-symmetry-induced asymmetric reflection must be enhanced. The solution involves using high-reflectivity and anti-reflective facet coatings. Modeling results show a threshold gain as low as 26 dB/cm, with laser emission occurring exactly at the Bragg wavelength. The gain contrast relative to the next-higher mode reached 72 dB/cm. Such gain contrast should ensure extremely robust single-mode laser operation. These results also suggest better tolerance of optical feedback and, as a potential outcome, operation without an optical isolator. Full article

Remanufacturing damaged components with high-performance materials often produces heterogeneous coating–substrate interfaces, which can substantially influence the rolling contact fatigue performance of repaired components. In this study, the fatigue behavior of laser-remanufactured Inconel 625 (In625) coatings was systematically investigated using different substrate materials. Particular attention was paid to the effects of substrate selection and interfacial heterogeneity on crack initiation, interfacial damage accumulation, and cyclic contact failure under dry rolling-contact conditions. Two quantitative models were developed to evaluate the nominal strength and critical damage of the coating–substrate systems, respectively. The proposed models were validated against available interfacial failure and experimental data, and the relative fatigue performance of five In625/substrate systems was comparatively assessed. Rolling-contact-fatigue tests were subsequently conducted using different substrate materials, followed by detailed fractographic characterization of the coating surfaces and coating–substrate interfaces. The experimental results showed good agreement with the model predictions, confirming the effectiveness of the proposed evaluation framework. The results indicate that the fatigue failure behavior of laser-remanufactured In625 coatings is governed by the competition between fatigue damage accumulation induced by the maximum surface contact stress and interfacial damage accumulation associated with the maximum interfacial shear stress. Furthermore, the relationship between material-matching factors and interfacial critical damage was clarified. Based on the established interfacial fatigue-damage evolution model, the effects of material-matching factors on interfacial fatigue life were quantitatively determined. The findings demonstrate that substrate selection and heterogeneous interface properties play decisive roles in controlling crack initiation and cyclic contact failure in laser-remanufactured In625 coatings under the investigated dry-contact conditions. Full article