Search Results (256)

Internal fins are commonly utilized as a passive technique to enhance natural convection, but their efficiency depends on complex interplay between fin design, material properties, and convective strength. This study presents an extensive numerical analysis of buoyancy-driven flow in square cavities containing a single horizontal fin on the hot wall. Over 9000 simulations were conducted, methodically varying the Rayleigh number (Ra = 10 to 10⁵), Prandtl number (Pr = 0.1 to 10), and fin characteristics, such as length, vertical position, thickness, and the thermal conductivity ratio (up to 1000), to assess their overall impact on thermal efficiency. Thermal enhancements compared to scenarios without fins are quantified using local and average Nusselt numbers, as well as a Nusselt number ratio (NNR). The results reveal that, contrary to conventional beliefs, long fins positioned centrally can actually decrease heat transfer by up to 11.8% at high Ra and Pr due to the disruption of thermal plumes and diminished circulation. Conversely, shorter fins located near the cavity’s top and bottom wall edges can enhance the Nusselt numbers for the hot wall by up to 8.4%, thereby positively affecting the development of thermal boundary layers. A U-shaped Nusselt number distribution related to fin placement appears at Ra ≥ 10³, where edge-aligned fins consistently outperform those positioned mid-height. The benefits of high-conductivity fins become increasingly nonlinear at larger Ra, with advantages limited to designs that minimally disrupt core convective patterns. These findings challenge established notions regarding passive thermal enhancement and provide a predictive thermogeometric framework for designing enclosures. The results can be directly applied to passive cooling systems in electronics, battery packs, solar thermal collectors, and energy-efficient buildings, where optimizing heat transfer is vital without employing active control methods. Full article

Background and Objectives: Dental restorations can be composed of various materials, including amalgams and methacrylate-based resins. The health risks associated with the components of the restorative materials have always been a concern, even more so with the ageing of the restorations. As the micronucleus (MN) test is a standard, accessible, and minimally invasive technique for studying the genotoxic effect of clastogenic chemicals on oral mucosal cells, the current study was conducted to determine the frequency and morphological properties of MN in the exfoliated oral mucosal cells. Materials and Methods: A total of 115 aged composite and amalgam restorations were included in this study. Epithelial cells were collected from the gingival tissue adjacent to the restorations of each patient and stained with a hematoxylin–eosin (HE) stain. After evaluation of the slides, the results were subjected to statistical analysis using Chi-square tests. The level of significance was set at 0.05. Results: The mean number of MN was significantly lower for composite restorations compared to amalgam restorations. There were no statistically significant differences between composite restorations aged 1–5 years, 5–10 years, over 10 years, and amalgam restorations aged over 10 years in the location (p = 0.11), staining (p = 0.11), or morphological characteristics (p = 0.18) of the MN. Conclusions: Despite the main limitation of this study, the lack of a control group, our results suggest that long-term exposure to restorative fillings and the ageing of these materials can cause DNA damage locally in the adjacent sites of oral cavity. Full article

Based on admirable porous media performance and the popularity of additive manufacturing technology, gradient porous media are progressively being applied in increasing fields. In this study, convection heat transfer within a square vented cavity, partially occupied by two copper metal foam layers of $10$ and $20$ PPI saturated with nanofluid, was assessed numerically. The left wall was heated uniformly and non-uniformly by applying multi-frequency spatial heating following a sinusoidal function. Governing equations, including continuity, the Darcy–Brinkmann–Forchheimer model, and local thermal non-equilibrium energy equations, were adopted and solved by employing the finite volume method. The influences of relevant parameters, including nanoparticle concentrations $\left(0\%\le \phi \le 10\%\right)$, Reynolds number ($1\le Re\le 100$), inlet and outlet port aspect ratios $\left(0.1\le D/H\le 0.4\right)$, three outlet vent opening locations ($\left(S_o=0\right)$ left, ($S_o=\left(H/2-D/2\right)$) middle, and ($S_o=\left(H-D\right)$) right), sinusoidal offset temperature (${\theta }_o=0.5$, $1$), frequency ($f=1, 3, 5$), and amplitude ($A=0-1$), were examined. The results demonstrate that flow and heat transfer fields are impacted mainly by these parameters. Streamlines are more intensified at the upper-left corner when the outlet opening vent is shifted towards the right-corner upper wall. Fluid- and solid-phase Nusselt number increases $Re$, $D/H$, ${\theta }_o$, $A$, and $f$ are raised, specifically when $A\ge 0.3$. The Nusselt number remains constant when the frequency is raised from $3$ to $5$, definitely when $D/H\ge 0.25$. In uniform and non-uniform heating cases, the Nusselt number of both phases remains constant as the outlet port is shifted right for $Re\le 10$ and slightly for higher $Re$ as the outlet vent location is translated from left to right. Full article

Fluids that exhibit self-rewetting properties, such as aqueous long-chain alcohol solutions, display a unique quadratic relationship between surface tension and temperature and are marked by a positive gradient. This characteristic leads to distinctive patterns of thermocapillary convection and associated interfacial dynamics, setting self-rewetting fluids apart from normal fluids (NFs). The potential to improve heat transfer using self-rewetting fluids (SRFs) is garnering interest for use in various technologies, including low-gravity conditions and microfluidic systems. Our research aims to shed light on the contrasting behaviors of SRFs in comparison to NFs regarding interfacial transport phenomena. This study focuses on the thermocapillary convection in SRF layers with a deformable interface enclosed inside a closed container modeled as a square cavity, which is subject to nonuniform heating, represented using a Gaussian profile for the heat flux variation on one of its sides, in the absence of gravity. To achieve this, we have enhanced a central-moment-based lattice Boltzmann method (LBM) utilizing three distribution functions for tracking interfaces, computing two-fluid motions with temperature-dependent surface tension and energy transport, respectively. Through numerical simulations, the impacts of several characteristic parameters, including the viscosity and thermal conductivity ratios, as well as the surface tension–temperature sensitivity parameters, on the distribution and magnitude of the thermocapillary-driven motion are examined. In contrast to that in NFs, the counter-rotating pair of vortices generated in the SRF layers, due to the surface tension gradient at the interface, is found to be directed toward the SRF layers’ hotter zones. Significant interfacial deformations are observed, especially when there are contrasts in the viscosities of the SRF layers. The thermocapillary convection is found to be enhanced if the bottom SRF layer has a higher thermal conductivity or viscosity than that of the top layer or when distributed, rather than localized, heating is applied. Furthermore, the higher the magnitude of the effect of the dimensionless quadratic surface tension sensitivity coefficient on the temperature, or of the effect of the imposed heat flux, the greater the peak interfacial velocity current generated due to the Marangoni stresses. In addition, an examination of the Nusselt number profiles reveals significant redistribution of the heat transfer rates in the SRF layers due to concomitant nonlinear thermocapillary effects. Full article

This study numerically examines laminar natural convection within a square cavity that has a horizontally attached adiabatic fin on its heated vertical wall. The analysis employed the finite element method to investigate how fin position, length, thickness, and thermal conductivity affect heat transfer behavior over a broad spectrum of Rayleigh numbers (Ra = 10 to 10⁶) and Prandtl numbers (Pr = 0.1 to 10). The findings indicate that the geometric configuration and the properties of the fluid largely influence the thermal disturbances caused by the fin. At lower Ra values, conduction is the primary mechanism, resulting in minimal impact from the fin. However, as Ra rises, convection becomes increasingly significant, with the fin positioned at mid-height (Y_fin = 0.5), significantly improving thermal mixing and flow symmetry, especially for high-Pr fluids. Extending the fin complicates vortex dynamics, whereas thickening the fin improves conductive heat transfer, thereby enhancing convection to the fluid. A new fluid-focused metric, the normalized Nusselt ratio (NNR), is introduced to evaluate the true thermal contribution of fin geometry beyond area-based scaling. It exhibits a non-monotonic response to geometric changes, with peak enhancement observed at high Ra and Pr. The findings provide practical guidance for designing passive thermal management systems in sealed enclosures, such as electronics housings, battery modules, and solar thermal collectors, where active cooling is infeasible. This study offers a scalable reference for optimizing natural convection performance in laminar regimes by characterizing the interplay between buoyancy, fluid properties, and fin geometry. Full article

Compact, broadband, multi-channel RF chips with low loss and high integration are required for high-performance phased-array systems. Presented in this paper is a four-channel, multifunction RF chip operating in the 5–18 GHz frequency range that integrates broadband phase shifting, amplitude control, power amplification, and switching functions. The chip is designed to have flip-chip bonding and stacked gold bumps to enable the compact 3D integration of the GaAs pHEMT and Si-CMOS. To ensure high-density interconnects with minimal parasitic effects, a fan-in redistribution process is implemented. The RF front-end part of this chip, fabricated through a 0.15 µm GaAs pHEMT process, integrates 6-bit digital phase shifters, 6-bit digital attenuators, low-noise amplifiers (LNAs), power amplifiers (PAs), and single-pole double-throw (SPDT) switches. To enhance multi-channel isolation and reduce crosstalk between RF chips and digital circuits, high isolation techniques, including a ground-coupled shield layer in the fan-in process and on-chip shield cavities, are utilized, which achieve isolation levels greater than 41 dB between adjacent RF channels. The measurement results demonstrate a reception gain of 0 dB with ±0.6 dB flatness, an NF below 11 dB, and transmit gain of more than 10 dB, with a VSWR of below 1.6 over the entire 5–18 GHz frequency band. The 6-bit phase shifter achieves a root mean square (RMS) phase error below 2.5° with an amplitude variation of less than 0.8 dB, while the 6-bit attenuator exhibits an RMS attenuation error of below 0.5 dB and a phase variation of less than 7°. The RF and digital chips are heterogeneously integrated using flip-chip and fan-in technology, resulting in a compact chip size of 6.2 × 6.2 × 0.33 mm³. These results validate that this is a compact, high-performance solution for advanced phased-array radar applications. Full article

Mn(III)– and Co(III)–salen complexes (Mn-1 and Co-2) have been synthesized by a simple one-pot procedure through oxidation of Mn(II) and Co(II) precursors in air. X-ray structural analysis reveals that both complexes adopt similar coordination modes, including a typical square planar metal/salen coordination sphere, which is further occupied by two axial ligands, i.e., an acetate anion and a water molecule. Despite their structural similarity, they are not isomorphous given their distinct cell parameters. In the solid-state structures, both complexes exist as hydrogen-bonded dimers through hydrogen bonding interactions between the axially coordinating water molecules and outer O₄ cavity from another molecule of the complex. The reductive activity of both complexes has been explored. While the reaction of Mn-1 with potassium triethylborohydride was unsuccessful, leading to a complicated mixture, the use of Co-2 furnished the formation of a novel product (CoK-3) that was isolated as red crystals in reasonable yield. CoK-3 was characterized as a heterometallic dimer involving the coordination of a K⁺ ion within the O₄ cavity of a semi-hydrogenated salen/cobalt complex while the cobalt center has been reduced from Co(III) to Co(II). In addition, an attempt at reducing Co-2 with pinacolborane resulted in the isolation of crystals of Co-4, whose structure was determined as a simple square planar Co^II–salen complex. Finally, three complexes (Mn-1, Co-2 and CoK-3) have been investigated for their cytotoxic activities against two human breast cancer cell lines (MCF-7 and MDA-MB 468) and a normal breast epitheliel cell line (MCF-10A), with cisplatin used as a reference in order to discover potential drug candidates that may compete with cisplatin. The results reveal that Co-2 can be a promising drug candidate, specifically for the MCF-7 cancer cells, with minimal damage to healthy cells. Full article

With global energy demand surging and traditional energy resources diminishing, the solar absorber featuring optimized design shows substantial potential in areas like power generation. This study proposes a solar absorber that is insensitive to wide-angle incidence and polarization. It has a cylindrical structure with square holes, which is constructed from titanium nitride (TiN). The calculation results indicate that, for plane waves, the average absorption of this solar absorber across the wavelength range of 300–2500 nm reaches 92.4%. Moreover, its absorption rate of the solar spectrum corresponding to AM1.5 reaches 94.8%. The analysis of the characteristics within the electric and magnetic field profiles indicates that the superior absorption properties arise from a cooperative resonance effect. This effect originates from the interaction among surface plasmon resonance, guided-mode resonance, and cavity resonance. In this study, the geometric parameters of the solar absorber’s structure significantly influence its absorption performance. Therefore, we optimized these parameters to obtain the optimal values. Even at a large incident angle, this absorber maintains high absorption performance and shows insensitivity to the polarization angle. The findings expected from this study are likely to be of considerable practical importance within the realm of solar photothermal conversion. Full article

Dual-mode sensors are currently facing difficulties in achieving independent sensing of parameters as well as low sensitivity. In this paper, we propose a dual-mode sensor using the finite element method (FEM) based on a coupled silver–PDMS–gold (SPG) cavity. We coupled a square ring resonant cavity with a double-ring resonant cavity structure, thus identifying a unique resonant cavity structure. The square ring resonator is made of silver and a double-ring resonant cavity filled with PDMS. Our proposed SPG cavity can independently achieve temperature and refractive index sensing. The SPG cavity enables us to obtain the highest biosensing sensitivity of about 1030 nm/RIU and the highest temperature sensitivity of about 216 pm/K. In addition, SPG cavities have excellent tolerances for geometric parameters. Our results provide new methodologies for metasurface design for dual-mode sensing. Full article

Bolted connections are extensively utilized in aircraft structures, and accurately simulating these connections is a critical factor affecting the precision of vibration and noise response predictions for aircraft. This study focuses on an instrument compartment of a specific aircraft model, employing the virtual material method to simulate the bolted joints within the structure. Parameters for the virtual material layer were obtained through theoretical calculations combined with parameter identification methods, achieving precise modeling of the instrument compartment. By comparing the calculated modes with the experimental modes of the instrument compartment, it was found that the first four modal shapes from both calculation and experiment were completely consistent, with the error in natural frequencies within three percent. Subsequently, acoustic and vibration computations were performed using both the virtual material model and the tied constraint model, with comparisons made against experimental results. The findings indicate that the root mean square (RMS) acceleration response of the virtual material model was 11.23 g, closely matching the experimental value of 10.35 g. Additionally, the total sound pressure level inside the acoustic cavity was 136.98 dB, closely aligning with the experimental value of 135.76 dB. These results demonstrate that the virtual material method offers higher accuracy in structural acoustic and vibration calculations. Full article

To safeguard historic centers with masonry buildings in medium-high seismic areas, the local seismic response (LSR) should be used. These portions of the urban areas are commonly characterized by complex subsurface features (i.e., underground cavities, buried anthropic structures, and archeological remains) that could be responsible for unexpected amplifications at period intervals similar to the building’s ones. In this study, San Giustino’s Square (Chieti, Italy) was considered due to the differentiated damage caused by the 2009 L’Aquila earthquake mainshock (6 April 2009 at 3:32 CEST, 6.3 M_w). Out of the eight buildings overlooking the square, the structure that suffered the heaviest damage was the Justice Palace. Two-dimensional finite element analyses have been carried out in San Giustino’s square to predict the LSR induced by the seismic shear wave propagation. The influence of the Chieti hill, the anthropogenic shallow soil deposit, and the manmade cavity were investigated. The results outlined that the amplifications of the seismic shaking peaked between 0.2 and 0.4 s. The crest showed amplifications over a wide period range of 0.1–0.8 s with an amplification factor (FA) equal to 2. Throughout the square, FA = 2.0–2.4 was predicted due to the cavities and the filled soil thickness. The large amplified period range is considered responsible for the Justice Court damage. Full article

The purpose of this article is to inform the reader about the results of an experimental investigation into the appropriate manifold geometry for an air-cooled inverter, which is manufactured from an AlSi10Mg powder material using SLM technology. The best approach is to optimize the part geometry for SLM technology so that the placement of support structures required for model fabrication is eliminated as much as possible. A suitable solution was selected based on the design of the most appropriate cross-sectional shape of the openings with the smallest dimensional accuracy deviation and shape deformation. In the experiment, three test specimens were designed; each of them contained eight holes of different shapes, particularly square, rhombic, and circular, with a given range of sizes. The results of the experimental study can help designers select the optimal design of vents and cavities for the chosen AM technology, e.g., for conformal cooling systems. Full article

This in vitro study evaluated short-fiber-reinforced composite materials and fiber-reinforced restorations of endodontically treated molars with furcal perforation. The endodontic treatment and mesio-occlusal–distal cavity preparation of 126 two-rooted mandibular third molars were performed. Eighteen non-perforated teeth were restored with resin composite as the control group. Furcal perforations and repair were performed on 108 teeth that were divided into six experimental groups: resin composite (RC), everX Flow (EXF), everX Posterior (EXP), Bioblock (BB), modified transfixed (MT), and horizontal glass-fiber (HGF) groups (n = 18). Fracture resistance tests were performed at an angle of 30◦ using a universal testing machine under static loading, and fracture patterns were classified. Welch’s analysis of variance, Pearson chi-square, and Tamhane post hoc tests (p = 0.05) were used to analyze the data (p = 0.05). The highest fracture resistance values were seen with the HGF (596.305 N), followed by MT (540.365 N), BB (477.906 N), EXP (476.647 N), EXF (414.462 N), control (413.811 N), and RC (335.325 N) groups (p < 0.001). There was no significant difference between the BB and EXP groups or between the EXF and control groups (p > 0.05). In terms of the dominant fracture pattern, the HGF and MT groups were repairable and possibly repairable, whereas the control, RC, and EXP groups were unrepairable. The EXF and BB groups were almost equally divided between possibly repairable and unrepairable. Restorations using horizontal fiber techniques and short-fiber-reinforced materials increased the fracture resistance of endodontically treated teeth with furcal perforation. Full article

The main aim of this study is to achieve the numerical solution for the Navier–Stokes equations for incompressible, non-turbulent, and subsonic fluid flows with some Gaussian physical uncertainties. The higher-order stochastic finite volume method (SFVM), implemented according to the iterative generalized stochastic perturbation technique and the Monte Carlo scheme, are engaged for this purpose. It is implemented with the aid of the polynomial bases for the pressure–velocity–temperature (PVT) solutions, for which the weighted least squares method (WLSM) algorithm is applicable. The deterministic problem is solved using the freeware OpenFVM, the computer algebra software MAPLE 2019 is employed for the LSM local fittings, and the resulting probabilistic quantities are computed. The first two probabilistic moments, as well as the Shannon entropy spatial distributions, are determined with this apparatus and visualized in the FEPlot software. This approach is validated using the 2D heat conduction benchmark test and then applied for the probabilistic version of the 3D coupled lid-driven cavity flow analysis. Such an implementation of the SFVM is applied to model the 2D lid-driven cavity flow problem for statistically homogeneous fluid with limited uncertainty in its viscosity and heat conductivity. Further numerical extension of this technique is seen in an application of the artificial neural networks, where polynomial approximation may be replaced automatically by some optimal, and not necessarily polynomial, bases. Full article

The lattice Boltzmann method (LBM) is a finite element and finite volume method for studying the reaction rate, mass diffusion and concentration of species. We are used the LBM to investigate the effect of the Damköhler number (Da) and Reynolds number (Re) on the laminar flow in a channel with an open square cavity and a reactive bottom wall in two dimensions in a first-order chemical reaction. The reactant A is transported through the cavity, where it undergoes a reaction on the reactive surface, resulting in the synthesis of product B. The effect of Da < 1 on the reaction rate is negligible for all investigated Re values; the generation of product B is slower because of the effect of the momentum diffusivity on the velocity inside the cavity. For Re = 5 and 1 < Da ≤ 100, the concentration of B inside the cavity reaches the maximum for Da = 100, and A is absorbed almost entirely on the bottom of the cavity. In our simulations, we observed that for all values of Re and Da > 100, the effect of the momentum diffusivity is negligible in the cavity, and the reaction on the surface is almost instantaneous. Full article