Ra Values Research Articles

Optimization of sustainable polymer composites for surface metamorphosis in FDM processes

The demand for the development of sustainable manufacturing processes is enhanced by the necessity to optimize polymer composites, particularly in the context of fused deposition modeling (FDM). This research aims to enhance sustainable polymer composites to improve the surface metamorphosis during FDM processes. Various eco-friendly polymer matrices were integrated with novel composite reinforcements to evaluate their impact on surface quality, structural integrity, and the performance of FDM-printed components. Key surface features, including roughness (Ra), texture, and function, were quantified through both experimental and computational methods. The optimized composites led to a significant reduction in surface roughness, with Ra values improving by up to 45% compared to standard filaments. In addition, tensile strength was increased by 30% and flexural strength by 20% relative to unmodified polymer composites. Optimization strategies, guided by green chemistry principles and materials science, successfully enhanced surface finishes and functional properties, aligning with sustainability goals. The results demonstrate that optimized sustainable polymer composites can significantly improve the quality and performance of FDM prints, supporting more efficient and environmentally friendly manufacturing practices. This study contributes to advancing materials and processes in line with sustainability principles and surface engineering.

Numerical analysis of heat transfer in annulus composite material at different operation conditions

In this article natural air convection in an inclined annular cage in three dimensions is investigated numerically. This study will examine the impact of the radius ratio of an annulus on heat transfer employing two distinct methods to optimizing effective thermal conductivity: minimizing and maximizing. The annulus is built of graphite/epoxy laminated composite material. There are 12 fins attached to the inner cylinder of the two concentric cylinders that make up the annulus enclosure, which is filled with porous medium. Regarding the annulus's inclination angle “δ”, two scenarios—a horizontal annulus and a vertical annulus—are considered. Constant walls temperature boundary condition and steady state conditions apply to the system with 0.2, 0.3, 0.4 and 0.5 different radius ratio, inclination angle (0o and 90o), and modified Rayleigh number “Ra*” ranged from 10 to 500, The Nusselt number decreased for all parameters as the radius ratio Rr decreased, indicating a wider cold outer cylinder gap. For large values of modified Rayleigh number, the average Nu number ”Nuavg.” decreases with an increase in δ, and increases with a rise in the modified Rayleigh number; for low values of Ra*, δ has no effect. For horizontal, and vertical states “δ=0 o, and 90o respectively, at higher and lower thermal conductivity, the divergence of the average Nusselt is 5.1% and 10%, respectively. In horizontal cylinder adding fins on the inner cylinder is more substantial for due to its impeding effect, and NuL increases with cylinder length. For the outer cold cylinder, a link between Ra* and δ and the average Nusselt number has been established.

Hybrid Runge–Kutta and lattice Boltzmann methods: Three-dimensional study of magnetohydrodynamics effect on heat exchange of electronic devices

This study explores the impact of the magnetic field on heat transfer and entropy generation in a simulated electronic device using magnetohydrodynamic principles through a three-dimensional hybrid Runge–Kutta and lattice Boltzmann method. By varying Rayleigh number (Ra) from 103 to 106 and Hartmann number (Ha) between 0 and 100, the research evaluated the influence of these parameters on the average Nusselt number (⟨Nu⟩), heat exchange ratio (R), and entropy generation within a confined cavity. The results demonstrated that higher Ra values, particularly for Ra ≥105, significantly enhance convective heat transfer, as reflected by an increase in ⟨Nu⟩. However, introducing a magnetic field (Ha = 50, 100) diminishes this effect by damping fluid motion, resulting in a reduction of ⟨Nu⟩. The heat exchange ratio increases with Ra, reaching a peak value of 0.93 for Ha = 100 and Ra = 105, indicating improved heat dissipation under the magnetic influence. In terms of entropy generation, at low Ra (Ra = 103), thermal conduction is the predominant heat transfer mechanism, with entropy primarily generated due to thermal effects. As Ra increases to 106, the system shifted toward a convection-dominated regime, where entropy generated by viscous effects becomes more significant. Under stronger magnetic fields, particularly at Ha = 100, magnetic entropy generation emerges as a dominant factor, further increasing energy dissipation. These results suggested that magnetic fields can be strategically applied to optimize thermal management in electronic devices by controlling both heat transfer and entropy generation. The effectiveness of this approach, however, is highly dependent on the specific flow conditions and the strength of the applied magnetic field.

Numerical analysis of Nano-encapsulated PCM magnetohydrodynamics double-diffusive convection and entropy generation in vertical enclosures with porous layer

This study investigates the effects of Nano-Encapsulated Phase Change Materials (NEPCMs) on double diffusive free convection in a partially porous cavity, considering Soret-Dufour effects and magnetohydrodynamics. The problem is modeled using non-dimensional governing equations, solved numerically through a Galerkin finite element method. The research examines the influence of key parameters including Rayleigh number (Ra: 103–105), Darcy number (Da: 10–4 -10–1), Hartmann number (Ha:0−80), NEPCM volume fraction (ϕ:0−0.04), Lewis number (Le:0.1−10), fusion temperature (θf:0.1−0.9), and Stefan number (Ste:0.1−0.9) on heat and mass transfer characteristics and entropy generation. Results show that increasing Ra significantly enhances heat and mass transfer, with Nusselt and Sherwood numbers rising by 424.8 % and 547.3 % respectively as Ra increases from 103 to 105. Higher Da and ϕ improve heat transfer, while stronger magnetic fields suppress both heat and mass transfer. An optimal fusion temperature (θf=0.5) is identified for maximum heat transfer enhancement. Total entropy generation, considering thermal diffusion, nanofluid friction, magnetic effects, porous medium, and mass diffusion contributions, increases by 15,957 % with Ra and decreases by 42.5 % with increasing Ha. The Bejan number analysis reveals that non-thermal irreversibilities become increasingly dominant at higher Ra and Ha values. The study concludes that NEPCMs can effectively enhance heat transfer in partially porous cavities, with their performance strongly influenced by Ra, Da, and Ha. The findings provide valuable insights for optimizing thermal management systems incorporating NEPCMs, particularly in applications involving porous media and magnetic fields.

Magnetic mixed convection within wavy trapezoidal thermal energy storage systems using nano enhanced phase change material

The three-dimensional (3D) MHD mixed convection mode confined 3D wavy trapezoidal enclosure is examined. The bottom plane of the trapezoidal system is irregular, particularly a wavy plane with various undulation numbers \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:N$$\\end{document}. The forced convection phenomenon arises due to the displacement of the top region plane, whereas the porosity-enthalpy methodology characterizes the progression of charging. The heat transfer is enhanced using the nanoencapsulation phase change material (NePCM), consisting of Polyurethane as a shell and Nonadecane as a core, with water as the primary liquid base. The (GFEM) is used to treat the governing system, and a comparison between the HT (heat transmission) irreversibility and FF (fluid friction) irreversibility is performed using the function of the BeAvg. The significant findings revealed that parabolic behaviors for the melting ribbon curve are given at lower values of Re and higher values of Ha. Also, reducing the undulation number is better for obtaining a higher heat transmission rate. The average Nusselt number was lowered by 60% and 19%, respectively, at the highest Reynolds number when the Hartmann number increased from 0 to 100 and N from 2 to 8. Also, the values of \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\:Re$$\\end{document} between 1 and 100 improve the heat transfer rates up to 51%.

Web Based Dashboard of Airplane Turbulence Mitigation

Airplane accidents still occur frequently, one of which is caused by turbulence. To minimize the risk, an effective forecasting system is needed. This research focuses on developing a web-based dashboard for aircraft turbulence mitigation by considering factors such as convective cloud growth, Richardson number index, and wind shear. The dashboard was developed through four steps: requirement analysis, design, implementation, and verification. The Richardson number index (Ri) is calculated using a formula involving temperature and wind speed at different geopotential heights. Alert status is determined based on Ri values and other parameters, with three alert levels: 'Alert 1', 'Alert 2' and 'Alert 3'. The system provides alerts based on user input. If the cloud cover is less than 50%, the “Alert 1” status is displayed; if Ri < 0.25, the “Alert 2” status appears; and if the wind shear exceeds the threshold, the “Alert 3” status indicates that flights are prohibited. Pilot tests show that the system works well and the Ri calculation results are comparable to existing Richardson calculators. The dashboard allows users to access critical information related to turbulence and flight status in real-time, thereby improving flight safety. Timely alerts help in flight-related decision making. This research successfully developed a web-based dashboard for aircraft turbulence mitigation that works well. By monitoring convective cloud growth, Richardson number index, and wind shear, the system is able to provide relevant alerts to improve flight safety.

Asymmetry of Two-Dimensional Thermal Convection at High Rayleigh Numbers

While thermal convection cells exhibit left–right and top–bottom symmetries at low Rayleigh numbers (Ra), the emergence of coherent flow structures, such as elliptical large-scale circulation in Rayleigh–Bénard convection (RBC), breaks these symmetries as the Rayleigh number increases. Recently, spatial double-reflection symmetry was proposed and verified for two-dimensional RBC at a Prandtl number of 6.5 and Ra values up to 1010. In this study, we examined this new symmetry at a lower Prandtl number of 0.7 and across a wider range of Rayleigh numbers, from 107 to 1013. Our findings reveal that the double-reflection symmetry is preserved for the mean profiles and flow fields of velocity and temperature for Ra<109, but it is broken at higher Rayleigh numbers. This asymmetry at high Ra values is inferred to be induced by a flow-pattern transition at Ra=109. Together with the previous study, our results demonstrate that the Prandtl number has an important influence on the symmetry preservation in RBC.

Effect of an experimental desensitizer with a hydroxyapatite-capsaicin composite applied before in-office dental bleaching on hydrogen peroxide diffusion, color and surface changes.

To evaluate a prior application of an experimental desensitizer containing a hydroxyapatite-capsaicin composite (HAp-CAP) in different concentrations on hydrogen peroxide (HP) diffusion into the pulp chamber, bleaching efficacy (BE) and on physical and chemical alterations of the enamel surface after in-office bleaching. Forty sound premolars were randomized in five groups according to each experimental condition (n = 8): no bleaching (negative control), only bleaching (positive control), 0.1%, 1% and 5% of HAp-CAP. Four groups were submitted to in-office bleaching (HP 35%) post-desensitizer application. The HP concentration (µg/mL) on the pulp chamber was measured by UV-Vis spectrophotometer. The BE was measured by digital spectrophotometer (ΔEab, ΔE00 and ΔWID) before and after 7 days bleaching. Enamel tooth fragments obtained from twenty molars were submitted to the same experimental conditions and analyzed using FE-SEM and EDS, Vickers microhardness (VHN), Raman spectroscopy, and nanoroughness (Ra) by AFM to evaluate morphologic and chemical changes on enamel surface. All data were submitted to statistical analysis (α = 0.05). The groups treated with HAp-CAP exhibited a lower concentration of HP in the pulp chamber compared to only bleaching group (p < 0.05). There were no significant differences observed in BE between HAp-CAP groups and only bleaching group (p > 0.05). Only HAp-CAP 5% showed no significant differences in VHN values when compared to no bleaching group (p > 0.05). There were no significant differences among any group in Ra values (p > 0.05). The groups submitted to HAp-CAP showed a higher mineral concentration when compared to only bleaching group (p < 0.05). Desensitizers containing HAp-CAP up to 5% effectively reduce HP diffusion into the pulp chamber after in-office bleaching, without interfering to BE and Ra, as well as prevent enamel demineralization. The use of desensitizers containing HAp-CAP during in-office bleaching treatments offers a promising approach to reduce the risk of pulp irritation caused by hydrogen peroxide diffusion, without compromising the bleaching effectiveness or causing surface roughness.

Experimental study on mechanical response and crack evolution law of coal and sandstone under different stress environments.

In order to study the mechanical response and crack evolution law of different lithologic rock bodies under different stress environments in deep stress mines, based on the deviator stress theory, the actual triaxial disturbance unloading rock test system was used to simulate the stress occurrence environment of the original rock. The mechanical characteristics of different σ2 coal rock masses were studied, and the crack evolution law of coal and sandstone under different stress environments was analyzed. The results show that the increase of σ2 inhibits the deformation in the σ2 direction of coal and sandstone, promotes the expansion and deformation in the σ3 direction, and enhances its peak strength and elastic modulus. The development characteristics of internal cracks in rock mass are directly related to the stress environment, and the increase of σ2 promotes the increase of the proportion of coal RA value, weakens the proportion of sandstone RA value, aggravates the development of coal internal shear cracks, and inhibits the development of internal shear cracks in sandstone. The larger σ2, the greater the initial AE ringing count of coal and sandstone, and the greater the AE cumulative energy when the rock mass is finally damaged. At the same time, due to the self-organizing behavior in the process of crystal failure in sandstone, the cumulative energy curve of sandstone fluctuates in a step-like manner. The ringing count and cumulative energy increase suddenly, which can predict the imminent instability and failure of the rock, and the research results can provide an experimental basis for the sudden instability of deep high-stress roadways.

Flexural strength, surface roughness, and color stability of various CAD-CAM denture teeth materials.

To assess the flexural strength (FS), surface roughness, and color stability of additive manufactured (AM) and subtractive manufactured (SM) denture teeth materials, as well as the effect of thermocycling on these properties. Eighty strips (20/material type; 64×10×3.3mm) and 60 discs (15/material type; 12×4mm) were fabricated from four different denture teeth materials (Straumann, Flexcera, Ivoclar, and Candulor). The specimens were divided into two subgroups (nonthermal cycled and 5000 thermal cycled,10 per subgroup), and subjected to a 3-point test for FS using a universal testing machine at a crosshead speed of 5.0mm/min. Surface roughness (Ra, µm) and color differences (ΔE00) of disc specimens were measured before and after thermocycling using a noncontact optical profilometer and a spectrophotometer, respectively. The CIEDE2000 formula was used to calculate the color differences (ΔE00) before and after thermocycling. Data were analyzed using 2-way ANOVA followed by post hoc multiple comparison tests (α=0.05). There was no significant difference in flexural strength between nonthermal cycled SM materials (p=0.15), which were significantly higher than AM materials (p<0.001). The flexural strength values of all tested materials weresignificantly reduced after thermocycling (p<0.05). The material type had a significant effect on the Ra values (p<0.001), whereas thermocycling did not (p=0.81). After thermocycling, all materials exhibited color changes lower than the clinical perceptible threshold (ΔE00=2.7). Thermocycling decreased the FS of denture teeth materials manufactured with AM and SM, but did not affect the surface roughness. The FS values of SM groups were significantly higher than AM materials, irrespective of thermocycling. No clinically significant color changes of the denture teeth material were noted.

Combined buoyancy and Marangoni convective heat transport of CNT-water nanofluid in an open chamber with influence of magnetic field and isothermal solid block

This paper proposes combined buoyancy and Marangoni convective heat phenomenon of CNT water nano-liquid in an open chamber subject to isothermal solid block and magnetic field. The Finite Volume Method (FVM) is incorporated to discretize the transport modeled expressions and are solved by SIMPLE algorithm. A comparison study made to authenticate the inspiration of Marangoni convection, magnetic field and isothermal block with the former literatures and shows the reliable agreement. This study scrutinizes the impact of different parameters such as Rayleigh number, Hartmann number, Marangoni number and the nanoparticles concentration. The computational result of the present analysis is deliberated with the graphical representation of streamlines, isotherms contour, velocity fields and average Nusselt number. The overall heat transport rate of the chamber is greatly improved by the rising values of Ra and ϕ but follows a decreasing trend with Ha.

Enhancing the Spectral Sensitivity of Prism-Based SPR Sensors: The Role of Analyte RI

A theoretical approach is presented to significantly enhance the spectral sensitivity of prism-based SPR sensors. The spectral sensitivity of prism-based SPR sensors is derived based on the coupling conditions of SPR and might exceed 105 nm/RIU for analytes with large RI values when other sensor parameters are carefully considered, including the RI of the prism, the angle of incidence, and the SPR active material. The spectral sensitivity could be markedly enhanced, reaching up to 10,000 nm/RIU by fine-tuning the effective RI of the incident light to be slightly larger, specifically 0.01~0.02 RIU, than the RI of the analyte, which is attributed to the large dielectric permittivity of the SPR active material, the key factor for achieving high sensitivity. The dynamic range is 0.040 RIU in the case of high sensitivity, which is sufficient in most applications. Moreover, the spectral sensitivity could be pushed even higher, into the range of 106~108 nm/RIU, by positioning the effective RI of the incident light closer to that of the analyte. However, it requires a careful balance between optimizing the sensitivity and maintaining an acceptable dynamic range.

Dynamics of Changes in the Surface Area of Water Bodies in Subsidence Basins in Mining Areas

The Silesian Upland in southern Poland is known as a place where subsidence processes induced by mining activities occur in an area of nearly 1500 square kilometres, with many water bodies that formed in subsidence basins. This study concerned the dynamics of changes in the occurrence, boundaries and area of water bodies in subsidence basins (using orthoimagery from 1996 to 2023), as well as the assessment of the factors underlying the morphogenetic and hydrogenetic transformations of these basins. Within the subsidence basins covered by the study, water bodies occupied a total area that changed from 9.22 hectares in 1996 to 48.43 hectares in 2003, with a maximum of 52.30 hectares in 2009. The obtained figures testify to the extremely dynamic changes taking place in subsidence basins, which are unprecedented within such short time intervals in the case of other morphogenetic types of lakes and anthropogenic water bodies (for instance, from 1996 to 2003, the basin of the Brantka water body in Bytom underwent a more than two-fold change in its area, with RA values in the range of 54.4% to 131.9). A reflection of the dynamics of short-term changes in the water bodies in question in the period from 1996 to 2023 is the increase in the water area of the three studied water bodies, which was projected by linear regression to range from 0.09 hectares/year to 0.56 hectares/year. The area change trends, as determined by polynomial regression, suggest a slight decrease in the water table within the last few years, as well as within the next few years, for each of the studied basins.

Influence of material orientation, loading angle, and single-shot repetition of laser shock peening on surface roughness properties

Titanium alloy Ti6Al4V is extensively utilized in biomedical applications due to its excellent biocompatibility, corrosion resistance, and mechanical properties. The design of dental implant surface textures has changed throughout time to address issues with oral rehabilitation in both healthy and damaged bones. The longevity of an implant is significantly impacted by surface roughness. This study examines the use of laser shock peening (LSP) as a surface modification technique to improve the mechanical properties of implants. A numerical model is developed using the commercial finite elements software in ABAQUS/Explicit for simulating dynamic conditions. The aim of the study is to develop surface roughness parameters using computational methods such as studies have not yet been contemplated. The single shot angle, shot repeat, time, material orientation, and laser power are applied for the first time simultaneously to evaluate the impact of material orientation and loading angles on surface roughness parameters. The study showed that the developed computational model’s compressive residual stress was −578.45 MPa, while the experimental samples were −592.18 MPa. Consequently, the difference between the computational and experimental results was 2.32%. Without regard to material orientation or angle, the compressive residual stress of the samples under examination was found to be −578.450 MPa after three repetitions and to decreased to −1.620 MPa after four. These results demonstrate that by varying the material orientation and loading angle, the Ra value may be increased four times.

Contributions Regarding the Study of Pulsatility and Resistivity Indices of Uterine Arteries in Term Pregnancies-A Prospective Study in Bucharest, Romania.

Pregnancy is a complex stage in a woman's life, considering the physical and psychological changes that occur. The introduction of Doppler studies of the pregnant woman's vessels and those of the fetus has proven to be a useful tool in evaluating the maternal-fetal relationship. Objective: The study aims to assess the correlations of PI and RI values in term pregnancies. Methods: This analysis is based on the prospective evaluation of medical data from 60 patients who were admitted to the Obstetrics and Gynecology department of Saint Pantelimon Hospital in Bucharest, Romania, from May to August 2024. Among the examined parameters are patient age, blood pressure, amniotic fluid quantity, placenta location, and pulsatility and resistivity indices of uterine arteries. Results: A higher diastolic blood pressure is associated with higher mean PI and RI values, indicating that diastolic blood pressure has a significant correlation to these values. The mean RI shows a moderately negative and significant correlation, suggesting that a lower level of amniotic fluid is associated with a higher mean RI. Regarding the PI value of the uterine arteries, the p-value suggests that the difference between the groups with and without associated diseases is statistically significant. Placental insertion on the anterior or posterior uterine wall does not have a significant impact on the PI and RI values of the uterine arteries, but the values are higher in the contralateral part of the placental insertion. Conclusions: These results strengthen the evidence previously demonstrated. Uterine artery Doppler ultrasonography is an extremely useful tool in monitoring and managing high-risk pregnancies.

Effects of Er:YAG laser debonding on changes in the properties of dental zirconia.

To investigate changes in the optical and mechanical properties of novel zirconia ceramics applied in dentistry after Er:YAG laser debonding and to evaluate the feasibility and value of reusing zirconia restorations debonded by an Er:YAG laser. Four types of zirconia ceramics were investigated: self-glazed zirconia (SGZ), 3Y-TZP, 4Y-PSZ and 5Y-PSZ. Forty rectangular (25 mm*8 mm*1.5 mm) specimens were fabricated for each zirconia type, and a total of 160 specimens were manufactured. The zirconia specimens were divided into four subgroups according to the applied Er:YAG laser debonding process: the control group, 4 W laser group, 5 W laser group, and 6 W laser group. For each subgroup, 10 specimens were subjected to color tests (color difference (△E) and transparency parameter (TP) tests) and subsequent mechanical tests (flexural strength (FS), elastic modulus (EM), Vickers hardness (VH) and surface roughness (Ra) tests). The △E, TP, FS, EM, VH and Ra values were measured and calculated. One random sample from each subgroup was observed by SEM. Statistical analyses were performed by one-way ANOVA followed by post hoc comparisons (α = 0.05). The △E and TP values after Er:YAG laser debonding were not significantly different among the subgroups (P > 0.05). However, the 6 W laser group had the highest △E and lowest TP. The ranges of changes in △E and TP were below the clinically detectable threshold (△E = 1.2, △TP = 1.33). In terms of the mechanical properties, there were no significant differences in the FS, EM, VH or Ra among the subgroups. No obvious microcracks were detected on the surfaces of the zirconia specimens during SEM. Er:YAG laser debonding does not obviously affect the optical or mechanical properties of novel zirconia ceramics in dentistry. Moreover, it is potentially feasible and valuable to reuse zirconia restorations after Er:YAG laser debonding.

Risk Attribute Analysis and Risk of Adherence to Taking Medication for Pulmonary TB Patients at the Jayapura Regency Office

This study aims to analyze the Risk Attributes and risks of medication adherence in patients with pulmonary TB. Type of survey research designed by cross sectional. A sample of 81 people was taken using the purposive sampling technique. The results of the study were with the variable value of RA = -21%, RP=1(0.19-5.9), gender RA=18%, PR 1.7(0.9-3.3), education RA=-16%, PR =0.57. Work RA = 19%, RP = 2.12 (0.72-6.22). TB MDR RA =62%, RP=16 (5.2-48.4). Side effects of RA Drug = 30%, PR = 2.5 (1.2-4.88), History of Comorbidities RA = 61%, PR = 3.6(2.02-6.6), duration of treatment RA = 50% PR = 3.8 (2-7). The variable that contributes the most to medication adherence is MDR TB status.

Probing the Electronic Manifold of MgCl with Millimeter-Wave Spectroscopy and Theory: (3)2Σ+ and (4)2Σ+ States.

The millimeter/submillimeter spectrum of magnesium chloride (MgCl) has been observed in two new electronic excited states, (3)2Σ+ and (4)2Σ+, using direct absorption methods. The molecule was synthesized in a mixture of Cl2, argon, and magnesium vapor. For the (3)2Σ+ state, multiple rotational transitions were measured in the v = 0 level for all six isotopologues (24Mg35Cl, 24Mg37Cl, 25Mg35Cl, 25Mg37Cl, 26Mg35Cl, and 26Mg37Cl), as well as up to v = 13 for 24Mg35Cl. For the (4)2Σ+ state, less intense spectra were recorded for 24Mg35Cl (v = 0-2). Equilibrium rotational parameters were determined for both states for 24Mg35Cl, as well as rotational constants and 25Mg hyperfine parameters for the other isotopologues. A perturbation was observed between rotational levels of the two states due to an avoided crossing. Computations were also carried out at the CASPT2 and MRCISD+Q levels, and the resulting bond lengths for (3)2Σ+ and (4)2Σ+ states agree well with the experimental values of re = 2.536 and 2.361 Å. The computations show that the (3)2Σ+ state has a double-well potential; however, the state behaves as a single well with unperturbed vibrational levels up to v = 13 due to nonadiabatic interactions with the (4)2Σ+ state.

Comparison of the effects of laser systems and cold atmospheric plasma on the surface roughness and shear bond strength of flexible hybrid ceramics.

The aim of this study was to compare the effects of laser systems and cold atmospheric plasma (CAP) on the surface roughness (Ra) and shear bond strength (SBS) of flexible hybrid ceramics (FHCs). Eighty FHC samples were divided into 5 groups to be subjected to surface treatments (hydrofluoric acid (HFA), HFA + 5W Er: YAG laser (HFA + 5WE), HFA + 3W Er: YAG laser (HFA + 3WE), HFA + ultrafast fiber laser (HFA + FL), and CAP). The Er: YAG laser (AT Fidelis Plus III, Fotona, Slovenia) was operated with a 0.9mm diameter tip, delivering 250mJ and 150mJ per pulse, with output powers of 5W and 3W, and fluences of 23,623J/cm² and 14,157J/cm², respectively, at a frequency of 20Hz and a pulse duration of 600 µs for 30s. The FL (FiberLAST Inc., Turkey) was applied with a 7mm spot size, 1mJ pulse energy, 20W output power, 100kHz repetition rate, ultrashort pulse length (100 ns), and the fluence of 1,820J/cm² for 7s. The CAP (PiezoBrush PZ3, Relyon Plasma, Germany) applied to the surfaces for 80s at a treatment speed of 5 cm2/s and 100% plasma power. After the Ra values were measured, each group was divided into 2 subgroups to be cemented with total-etch (TE) and self-adhesive (SA) resin cements. The SBS of all the samples was measured. One sample was randomly selected from each group, and the fractured surfaces were examined by SEM analysis. The significance level was at P < 0.05. HFA + FL had the highest Ra values, and there was no significant difference between HFA + FL and HFA + 5WE (P > 0.05). There was no difference in Ra between CAP and HFA (P > 0.05). The highest SBS values were observed for the samples cemented with TE after HFA + FL. The difference between the SBS values of the groups cemented with TE after CAP, HFA + 5WE, HFA + 3WE, and HFA + FL was not significant (P < 0.05). The use of FL may be a promising method to improve SBS without causing thermal damage when using TE or SA cements. CAP can be recommended as a practical and safe treatment with SA cement because it is suitable for chairside use with a handheld device and does not change the physical properties of the material.

Study on the failure and acoustic emission characteristics of coal under graded cyclic loading and unloading stress paths

To study the influence of cyclic disturbance stress on the mechanical behavior of coal during mining, a gas containing coal fluid-solid coupling servo seepage experimental system was used to conduct experimental research on the acoustic emission (AE) characteristics of gas containing coal under two stress paths of graded cyclic loading and unloading. The AE characteristics of coal damage and failure processes under different cyclic stress paths were analyzed. The research results indicate that: (1) The overall characteristics of AE signals for both graded cyclic loading and unloading paths are basically the same. With increasing of the amount of graded cyclic loading or unloading, the AE count reaches its maximum value when reaching failure, and the cumulative ringing calculation of AE increases exponentially. (2) The AE signals under the graded cyclic loading or unloading path exhibit obvious zoning characteristics. In the low and medium stress regions, the AE signal basically satisfies the Kaiser effect, while reaching the high stress region before failure, the AE signal exhibits a significant Felicity effect. (3) The concentration coefficient of AE and the intensity coefficient of the Kaiser effect have been newly defined. They are used to quantitatively characterize the extent of the Kaiser effect of AEs under graded cyclic stress. It was found that as the variation of graded cyclic stress increases, the concentration coefficient and Kaiser effect intensity coefficient both show a decreasing trend. (4) Combining the AF and RA values of AE, it was found that the coal failure signals of the two stress paths were basically similar, that is, the overall failure was mainly tensile failure, and the signals of cyclic unloading tensile failure were significantly more than those of cyclic loading. The AE signal characteristics studied in this article are of great significance for predicting coal power disasters.