Search Results (103)

Chemical endodontic irritants can lead to the demineralization of the inorganic tooth structure, its loss of integrity, microhardness changes, erosion, and an increased risk of fractures. We investigated the action of iron oxide nanomagnet particles (IONPs) as an irrigant solution for improving hardness and identifying the concentration of element ions in the root canal. There were six groups in total: a control group (no treatment) and experimental groups (UN: ultrasound agitation normal saline, UI: ultrasound agitation IONPs, MSI: magnetic field and endodontic needle with syringe agitation IONPs, MUI: magnetic field and ultrasound agitation IONPs, and EDTA: ethylenediaminetetraacetic acid). We hypothesized that IONPs with magnetic agitation would preserve microhardness better than EDTA. Vickers hardness testing was used to evaluate microhardness, which was then analyzed using energy-dispersive X-ray spectroscopy (EDS) to investigate the calcium/phosphorus ratio and the presence of iron. The IONP groups exhibit a higher VHN value than the EDTA group (p < 0.05). These results support our hypothesis, indicating that utilizing an IONP irrigant solution with an external magnetic field does not change microhardness but enhances it compared to the EDTA group, suggesting that employing an external magnetic field to deliver nanoparticles to the root canal wall does not affect the properties of the tooth structure compared to conventional instrumentation techniques, which lead to unnecessary loss of root structure. Full article

Based on the magnetic configuration of the China Astro-Torus-1 (CAT-1) levitated dipole device, this study investigated the confinement performance of common discharge gas ions under E × B transverse transport conditions induced by electric fields. By adjusting L-coil parameters to shift the inject location, it was found that when the loss boundary is in the outer weak-field region, most particles with large Larmor radii are lost after colliding with the wall, for particles with large pitch angles, the strongly anisotropic magnetic field causes particles across a broad range of energies to be lost through the X-point into the divertor. The study demonstrates that for particle kinetic energies between 100 and 300 eV, the CAT-1 device exhibits a loss cone angle θ_loss of approximately 58°, indicating favorable confinement performance. Full article

To investigate the impact of sand-laden flow on energy loss in Francis turbines, this study integrates entropy generation theory with numerical simulations conducted using ANSYS CFX. The mixture multiphase flow model and the SST k-ω turbulence model are employed to simulate the solid–liquid two-phase flow throughout the entire flow passage of the turbine at the Gengda Hydropower Station (Minjiang River Basin section, 103°17′ E and 31°06′ N). The energy loss characteristics under different off-design conditions are analyzed on the basis of the average sediment concentration during the flood season (2.9 kg/m³) and a median particle diameter of 0.058 mm. The results indicate that indirect entropy generation and wall entropy generation are the primary contributors to total energy loss, while direct entropy generation accounts for less than 1%. As the guide vane opening increases, the proportion of wall entropy generation initially rises and then decreases, while the total indirect entropy generation exhibits a non-monotonic trend dominated by the flow pattern in the draft tube. Entropy generation on the runner walls increases steadily with larger openings, whereas entropy generation on the draft tube walls first decreases and then increases. The variation in entropy generation on the guide vanes remains relatively small. These findings provide technical support for the optimal design and operation of turbines in sediment-rich rivers. Full article

The preservation of chilled fresh pork is an issue that has widely drawn significant attention. A novel microcapsule was developed in this study, specifically a composite plant essential oil microcapsule (CEO mps) prepared using gum arabic (GA) and an inclusion compound of allyl isothiocyanate (AITC) with β-cyclodextrin (β-CD), in which AITC is encapsulated within the cavity of β-CD molecules. In this formulation, AITC functions as an antibacterial agent, while the essential oils provide antioxidant properties that further enhance bacterial inhibition. The encapsulation ratio of AITC to β-CD was optimized at 1:1, with nuclear magnetic resonance (NMR) hydrogen spectroscopy confirming that AITC was incorporated into β-CD through its wider cavity. The morphology and structure of CEO mps were characterized using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and laser particle size analysis, and these were compared to those of AITC mps—microcapsules prepared with GA and β-CD as wall materials and AITC as the core material. The results indicated that CEO mps exhibited superior appearance and physical stability in comparison to AITC mps. The release rate of CEO mps was evaluated using gas chromatography–mass spectrometry (GC/MS), revealing sustained release characteristics. On day 12, cumulative releases for AITC, eugenol, cuminal, and thymol were 61.82%, 57.96%, 44.34%, and 38.65%. Finally, the efficacy of CEO mps in preserving chilled pork was assessed by measuring pH levels, total volatile base nitrogen (TVB-N), color parameters (L*, a*, b*), thiobarbituric acid-reactive substances (TBARSs), water loss, and total microbial counts. The results demonstrated that CEO mps significantly inhibited microbial growth in chilled pork, reduced TBARS and TVB-N values, and helped preserve meat color integrity, thereby effectively extending shelf life by approximately six days. Overall, the experimental findings confirmed that the developed CEO mps possess both antibacterial and antioxidant properties, thereby improving both the shelf life and organoleptic quality of chilled pork. Full article

The structure of yeast cells, which are rich in bioactive compounds, makes them an attractive encapsulation vehicle due to their antioxidant, antibacterial, and antimutagenic properties. In this study, black chokeberry extract was encapsulated with different wall materials (maltodextrin, gum arabic, mixture of maltodextrin and gum arabic, plasmolyzed yeast, and non-plasmolyzed yeast) by freeze-drying. While the highest encapsulation efficiency was obtained with maltodextrin (98.82%), non-plasmolyzed yeast (86.58%) emerged as a viable alternative to gum arabic. The largest particle size was observed in plasmolyzed yeast microcapsules. Yeast-coated capsules exhibited a spheroidal morphology. Differential Scanning Calorimetry revealed high thermal stability for all microcapsules, with the gum arabic-coated microcapsules demonstrating the greatest stability. After the simulated gastric and intestinal fluid treatment, plasmolyzed yeast provided the highest retention, with 63.45% and 77.55% of phenolics, respectively. The highest 2,2-Diphenyl-1-picrylhydrazyl (DPPH) activities were found in yeast microcapsules, with no significant difference between them. In 2,2′-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS^•+) scavenging activity, the least loss (approximately 10%) was observed in non-plasmolyzed yeast samples after intestinal digestion. These results showed that yeast can be used as an alternative coating material in the encapsulation of phenolics, and it contributes to the bioavailability of microcapsules with its protective effect during digestion. Full article

During slurry shield tunneling in hard rock or cobble strata, the discharge pipes suffer serve wear and damage. However, the effect mechanism of pipe wall wear defects on the flow characteristics of two-phase flow is unclear. In this study, a three-dimensional slurry particle model of pipeline transport was established using the coupled computational fluid dynamics–discrete element method (CFD-DEM) considering the pipe wall wear defect, and the typical pipeline forms of straight pipe and 90° elbow pipe were selected as the research targets. The results indicated that the localized wear defect of pipes can lead to increased inhomogeneity in the velocity distribution, generating localized low-flow zones and resulting in a reduced flow rate or stagnancy in parts of the pipe. Meanwhile, the wear defect of the pipe results in local shape changes, so that the fluid flow path through the pipe is no longer smooth, causing more vortex/turbulence and secondary flow, where an increased vortex promotes localized kinetic energy reduction and creates larger pressure losses at the elbow. In addition, for the elbow pipe without wear defect, the pressure drop of the elbow increases quadratically from an increase of 6.5% to an increase of 16.9%, with the maximum wear depth increasing from 4 mm to 19 mm. For the straight pipe without wear defect, the pressure drop of the elbow increases linearly, from an increase of 2.2% to an increase of 10.2% with the maximum wear depth increasing from 4 mm to 19 mm. The paper investigates the potential mechanism of pipe flow characteristics influenced by wear defect and provides practical guidelines for the efficient operation of a slurry shield circulating system. Full article

The cantilever-enhanced photoacoustic spectrometer is a sensitive instrument developed originally for trace gas measurements and has lately been successfully applied for measuring light-absorbing particles, such as aerosols. The finite inertia of aerosol particles can cause the particles to be deposited on the walls in the spectrometer’s flow channels, which creates a source of uncertainty for the measurement process. In this study, we characterized this inertial deposition in the spectrometer using finite element-based modeling. First, computational fluid dynamics was used to calculate the distribution of airflow within a 3D model of the spectrometer’s flow channels. Then, the trajectories of aerosol particles were computed to evaluate the inertial deposition losses. The modeling method was validated by computing inertial deposition for two known cases of laminar flow, namely particles flowing through a pipe with a 90-degree bend and a pipe with an abrupt contraction. The particle transmission of the photoacoustic spectrometer was experimentally measured. Differences and similarities between measured and modeled results are discussed. The modeled inertial deposition losses ranged from approximately 5% to 70% for particle diameters between 50 and 500 nm. This modeling approach provides valuable insight into the influence of particle size and flow rate on the inertial deposition and also pinpoints the physical location of the loss within the spectrometer, which is valuable for improving the measurement process. Full article

The heterobimetallic 15-MC-5 metallacrown of formula [CeCu₅(5mpzHA)₅(NO₃)(H₂O)₇]·2NO₃·7H₂O, designated MC-Ce, was synthesized using 5-methyl-2-pyrazinehydroxamic acid (5mpzHA) as a linker, reacting with Ce^III and Cu^II salts under mild conditions. Single-crystal X-ray diffraction analysis reveals a crown-like [Cu₅Ce(5mpzHA)₅] core, characteristic of a 15-MC-5 system, with five Cu^II atoms at the rim of the crown and the Ce^III ion occupying the dome of the crown, with water molecules, oxygen atoms and one nitrate anion filling the nine-coordination sphere around the Ce^III ion, which exhibits a distorted spherical tricapped trigonal prism geometry. The thermogravimetric analysis evidences successive mass losses due to the removal of water molecules and decomposition of the structure after 217 °C, whereas the PXRD analysis of the thermal decomposition residue reveals the presence of copper and copper/cerium oxide particles. These nanocomposite materials were also synthesized using the metallacrown MC-Ce under a hydrothermal method in the presence of multi-walled carbon nanotubes (MWCNTs), affording insights that this metallacrown can act as a source precursor for the synthesis of these mixed cerium/copper oxide nanomaterials. The experimental χMT value in MC-Ce at room temperature is 3.175 cm³ mol⁻¹ K, which is higher than the calculated one for one magnetically isolated Ce^III plus five Cu^II ions, probably due to the antiferromagnetic interactions among Cu^II ions within the metallacrown hoop plus the thermal depopulation of JZ sublevels of Ce^III ground state (5/2), which exhibit a small splitting under the anisotropic ligand field effects. The χMT decreases continuously until it reaches the value of 0.80 cm³ mol⁻¹ K at 10 K, reinforcing the presence of intramolecular antiferromagnetic interactions. Full article

Abutment scour is a major cause of bridge failures worldwide, leading to disruptions, economic losses, and loss of life. The present experimental study examines countermeasures against abutment scour using hooked-collar protections on vertical-wall and wing-wall abutments (at 45° and 60°) under different flow conditions. All 60 experiments were performed under sub-critical flow conditions by investigating scour around an abutment 20 cm long, 20 cm wide, and 25 cm tall. Two distinct values of the Froude number, 0.154 and 0.179, and a sediment particle diameter (d₅₀) of 0.88 mm were used throughout the experimental phase. The resulting equilibrium scour around the abutments was compared to those with collar and hooked-collar protections. It was determined that the maximum abutment scour depth reduction was 83.89% when hooked collars were placed on vertical wall abutments beneath the bed surface level, and for wing-wall abutments at 45° and 60°, it was 74.2% and 73.5%, respectively, at the bed surface level. Regression analysis was conducted to assess the non-dimensional scour depth (D_s/Y_f) and scour reduction (R_Ds/Y_f), with a high enough coefficient of determination (R² values of 0.96 and 0.93, respectively), indicating high confidence in the analysis. The sensitivity analysis findings demonstrate that the width of the collar (W_c) and L_a are the most influencing factors affecting D_s/Y_f and RD_s/Y_f. Full article

Silt removal is crucial for maintaining navigable waterways in harbors. Jet pumps, without moving parts, are highly suitable for underwater operations such as channel dredging in port environments. Despite their structural advantages in slurry handling, the prolonged transport of solid–liquid two-phase flows can lead to wear on the wall materials, resulting in decreased efficiency and potential pump failure. The wear characteristics of the jet pump walls due to sand particles of varying grain sizes were experimentally investigated. The characteristic of the sands having a higher distribution above the axis as they enter the jet pump was captured by a high-speed camera. The experiment recorded the variations in mass loss at different sections of the jet pump over a period of 120 h, identifying that backflow within the throat region is a significant contributor to wall wear. Scanning electron microscopy was employed to examine the microstructure of the abraded pump surfaces. It was found that there are noticeable differences in the surface wear microstructure across various pump areas, and that particles of different grain sizes result in distinct wear patterns on the pump surfaces. The underlying causes of this phenomenon were discussed from the perspective of particle motion. Full article

To investigate the lubrication characteristics in high-speed train gearboxes, a two-stage herringbone gearbox with an idle gear was analyzed. The lubricant flow and distribution were shown using the moving particle semi-implicit (MPS) method. A liquid film flow model was brought in to enhance the non-slip wall boundary conditions, enabling MPS to predict the film flow characteristics. This study investigates the influence of gear rotating speed, lubricant volume, and temperature on lubricant flow, liquid film distribution, lubrication state in the meshing zone, and churning power loss. The results indicate that lubrication characteristics depend on the splashing effect of rotating gears and lubricant fluidity. Increasing gear rotating speed and lubricant temperature can improve liquid film distribution on the inner wall, increase lubricant volume, and thus enhance film thickness. The lubricant particles in the meshing zone correlate positively with the gear rotating speed and lubricant volume, correlate negatively with a temperature above 20 °C, and decrease notably at low temperatures. Churning power loss mainly comes from the output gear. As lubricant volume and gear rotating speed increase, churning torque and power loss increase. Above 20 °C, viscosity decreases, reducing power loss; low temperatures lessen lubricant fluidity, reducing churning power loss. Full article

Polymers with a low dielectric constant (D_k) are promising materials for high-speed communication networks, which demand exceptional thermal stability, ultralow D_k and dissipation factor, and minimum moisture absorption. In this paper, we prepared a series of novel low-D_k polyimide films containing an MCM-41-type amino-functionalized mesoporous silica (AMS) via in situ polymerization and subsequent thermal imidization and investigated their morphologies, thermal properties, frequency-dependent dielectric behaviors, and water permeabilities. Incorporating 6 wt.% AMS reduced the D_k at 1 MHz from 2.91 of the pristine fluorinated polyimide (FPI) to 2.67 of the AMS-grafted FPI (FPI-g-AMS), attributed to the free volume and low polarizability of fluorine moieties in the backbone and the incorporation of air voids within the mesoporous AMS particles. The FPI-g-AMS films presented a stable dissipation factor across a wide frequency range. Introducing a silane coupling agent increased the hydrophobicity of AMS surfaces, which inhibited the approaching of the water molecules, avoiding the hydrolysis of Si–O–Si bonds of the AMS pore walls. The increased tortuosity caused by the AMS particles also reduced water permeability. All the FPI-g-AMS films displayed excellent thermooxidative/thermomechanical stability, including a high 5% weight loss temperature (>531 °C), char residue at 800 °C (>51%), and glass transition temperature (>300 °C). Full article

For the optimization of ventricular assist devices (VADs), flow simulations are crucial. Typically, these simulations assume single-phase flow to represent blood flow. However, blood consists of plasma and blood cells, making it a multiphase flow. Cell migration in such flows leads to a heterogeneous cell distribution, significantly impacting flow dynamics, especially in narrow gaps of less than 300 $\mathsf{\mu }$m found in VADs. In these areas, cells migrate away from the walls, forming a cell-free layer, a phenomenon not usually considered in current VAD simulations. This paper addresses this gap by introducing a viscosity model that accounts for cell migration in microchannels under VAD-relevant conditions. The model is based on local particle distributions measured in a microchannels with a blood analog fluid. We developed a local viscosity distribution for flows with particles/cells and a cell-free layer, applicable to both blood and analog fluids, with particle volume fractions of up to 5%, gap heights of 150 $\mathsf{\mu }$m, and Reynolds numbers around 100. The model was validated by comparing simulation results with experimental data of blood and blood analog fluid flow on wall shear stresses and pressure losses, showing strong agreement. This model improves the accuracy of simulations by considering local viscosity changes rather than assuming a single-phase fluid. Future developments will extend the model to physiological volume fractions up to 40%. Full article

The requirement for high-performance and energy-saving materials motivated the researchers to develop novel composite materials. This investigation focuses on utilizing aluminum alloy (A383) as the matrix material to produce hybrid metal matrix composites (HMMCs) incorporating boron carbide (B₄C) and multi-walled carbon nanotube (MWCNT) through a cost-effective stir casting technique. The synthesis of HMMCs involved varying the weight fractions of B₄C (2%, 4%, and 6%) and MWCNT (0.5%, 1%, and 1.5%). The metallographic study was carried out by field emission scanning electron microscopy (FESEM) mapped with EDS analysis. The results indicated a uniform dispersion and robust interfacial interaction between aluminum and the reinforced particles, significantly enhancing the mechanical properties. Micro-hardness and wear characteristics of the fabricated HMMCs were investigated using Vickers microhardness testing and the pin-on-disc tribometer setup. The disc is made of hardened chromium alloy EN 31 steel of hardness 62 HRC. The applied load was varied as 10N, 20N, 30N with a constant sliding speed of 1.5 m/s for different sliding distances. The micro-hardness value of composites reinforced with 1.5 wt% MWCNT and 6 wt% B₄C improved by 61% compared to the base alloy. Additionally, the wear resistance of the composite material improved with increasing reinforcement content. Incorporating 1.5% CNT and 6% B₄C as reinforcements results in the composite experiencing about a 40% reduction in wear loss compared to the unreinforced aluminum alloy matrix. Furthermore, the volumetric wear loss of the HMMCs was critically analyzed with respect to different applied loads and sliding distances. This research underscores the positive impact of varying the reinforcement content on the mechanical and wear properties of aluminum alloy-based hybrid metal matrix composites. Full article

Process design critically depends on the characterization of fuels and their kinetics under process conditions. This study steps beyond the fundamental methods of thermogravimetry to modulated (MTGA) and Hi-Res™ (high resolution) techniques to (1) add characterization detail and (2) increase the utility of thermal analysis data. Modulated TGA methods overlay sinusoidal functions on the heating rates to determine activation energy as a function of temperature with time. Under devolatilization conditions, Hi-Res™ TGA maintains a constant mass loss with time and temperature. These two methods, run independently or overlaid, offer additional analysis in which multiple samples at different heating rates are run to different final temperatures. Advanced methods allow researchers to use fewer samples by conducting fewer runs, targeting practical experimental designs, and quantifying errors easier. The parameters of the studies included here vary the heating rate at 10, 30, and 50 °C/min; vary gas-phase oxygen for pyrolysis or combustion conditions; and particle size ranges of 100–125 µm, 400–425 µm, and 600–630 µm. The two biomass fuels used in the studies are pinewood from Northern Sweden and wheat straw. The influence of torrefaction is also included at temperatures of 220, 250, and 280 °C. Apparent activation energy results align with the previous MTGA data in that combustion conditions yield higher values than pyrolysis conditions—200–250 kJ/mol and 175–225 kJ/mol for pine and wheat combustion, respectively, depending on pre-treatment. Results show the dependence of these parameters upon one another from a traditional thermal analysis approach, e.g., the Ozawa-Flynn-Wall method, as well as MTGA and Hi-Res™ thermogravimetric investigations to show future directions for thermal analysis techniques. Full article