Cavity Wall Research Articles

Slow Translation of a Composite Sphere in an Eccentric Spherical Cavity

This semi-analytical study is presented examining the quasi-steady creeping flow caused by a soft (composite) spherical particle, which is a hard (impermeable) sphere core covered by a porous (permeable) layer, translating in an incompressible Newtonian fluid within a non-concentric spherical cavity along the line joining their centers. To solve the Brinkman and Stokes equations for the flow fields inside and outside the porous layer, respectively, general solutions are constructed in two spherical coordinate systems attached to the particle and cavity individually. The boundary conditions at the cavity wall and particle surface are fulfilled through a collocation method. Numerical results of the normalized drag force exerted by the fluid on the particle are obtained for numerous values of the ratios of core-to-particle radii, particle-to-cavity radii, the distance between the centers to the radius difference of the particle and cavity, and the particle radius to porous layer permeation length. For the translation of a soft sphere within a concentric cavity or near a small-curvature cavity wall, our drag results agree with solutions available in the literature. The cavity effect on the drag force of a translating soft sphere is monotonically increasing functions of the ratios of core-to-particle radii and the particle radius to porous layer permeation length. While the drag force generally rises with an increase in the ratio of particle-to-cavity radii, a weak minimum (surprisingly, smaller than that for an unconfined soft sphere) may occur for the case of low ratios of core-to-particle radii and of the particle radius to permeation length. This drag force generally increases with an increase in the eccentricity of the particle position, but in the case of low ratios of core-to-particle radii and particle radius to permeation length, the drag force may decrease slightly with increasing eccentricity.

Blackbody heat capacity at constant pressure

At first glance, the title of this work seems to be improper. And the reason is well known. Since blackbody pressure depends only on temperature, one cannot take the derivative of the thermodynamic quantities with respect to one of them, keeping the other constant. That is, the heat capacity at constant pressure, C P , as well as, the coefficient of thermal expansion, α, and the isothermal compressibility, κ T , are ill-defined quantities. This work will show that when the perfect conducting nature of the walls of a blackbody cavity is taken into account, C P , α and κ T are in fact well defined, and they are related by the usual thermodynamic relations, as expected. Two geometries will be considered, namely, a spherical shell and a cubic box. It will be shown that C P , α and κ T depend very much on the geometry of the cavity. Issues regarding thermodynamic stability will be addressed, revealing that they also depend on the cavity’s geometry. It is argued that these findings may be amenable to experimental verification.

Correlation between Gene polymorphism levels of serum matrix metalloproteinases with cavitary features and pulmonary fibrosis of the Patient tuberculosis multi-drug resistance using high-resolution computerized tomography of the Thorax

Matrix metalloproteinases (MMPs) are proteins that play a role in the inflammatory and remodeling processes caused by infections, including pulmonary tuberculosis (TB), especially multidrug resistance. This study aims to investigate the relationship between variations in MMP-1 and MMP-9 blood levels, cavity features such as number, diameter, and wall thickness, and the location of fibrosis in multidrug-resistant (MDR) and drug-sensitive (DS) tuberculosis patients. This study used a comparative cross-sectional study design. The subjects, who were outpatients at Abdoel Moelok Hospital, Lampung, Indonesia, had passed the ethical test. We divided the subjects into two groups: 34 in the MDR-TB group and 36 in the DS-TB group. An ELISA test determined the levels of MMP-1 and MMP-9, while the PCR-sequencing method determined the genotypes of MMP-1 and MMP-9. Additionally, we measured cavities and fibrosis using thoracic high-resolution computerized tomography (HRCT) imaging. In MDR-TB patients, there was a significant difference in the number of cavities larger than 6.6 mm in diameter, as well as cavity thickness, compared to DS-TB patients. The distribution of fibrosis in lung segments was also significantly different in MDR-TB compared to DS-TB. Although MMP-9 levels in the MDR-TB group were higher than in the DS-TB group, there was no statistically significant difference. Based on HRCT measurements, this study found a link between MDR-TB and DS-TB in terms of the number of cavities, the diameter of the cavities, the thickness of the cavity walls, and the location of fibrosis in the affected lung segments. There was no link between the MMP-1 (−1607G) and MMP-9 (C1562T) genotypes and the levels of MMP-1 and MMP-9 in the blood. The MMP-1 genotype in the two study groups was very different and was linked to twice as many cases of MDR-TB. In addition, there was a substantial difference in cavity wall thickness between the G/G MMP-1 1607 genotype and the T/T MMP-9 genotype in the two study groups.

Inner walls or vortices? Crescent-shaped asymmetries in ALMA observations of protoplanetary discs

ABSTRACT Crescent-shaped asymmetries are common in millimetre observations of protoplanetary discs and are usually attributed to vortices or dust overdensities. However, they often appear on a single side of the major axis and roughly symmetric about the minor axis, suggesting a geometric origin. In this work, we interpret such asymmetries as emission from the exposed inner cavity walls of inclined discs and use them to characterize their vertical extent. Here we focus on the discs around CIDA 9 and RY Tau, first modelling their observations in visibility space with a simple geometric prescription for the walls, and then exploring more detailed radiative transfer models. Accounting for the wall emission yields significantly better residuals than purely axisymmetric models, and we estimate the dust scale height of these systems to be 0.4 au at 37 au for CIDA 9 and 0.2 au at 12 au for RY Tau. Finally, we identify crescent-shaped asymmetries in twelve discs, nine of which have constraints on their orientation – in all cases, the asymmetry appears on the far-side of the disc, lending support to the hypothesis that they are due to their inner rims. Modelling this effect in larger samples of discs will help to build a statistical view of their vertical structure.

Exploration of heat transfer and entropy generation in an irregular wall cavity filled with Al2O3-water nanofluid

This study investigates 2-D natural convection heat transfer within an irregular wall cavity filled with nanofluid, employing a computational approach. The rough profile of the cavity surface is generated using the Weierstrass-Mandelbrot (W-M) function, and various parameters such as Rayleigh number ( 10 3 ≤ Ra ≤ 10 6 ), Knudsen number ( 0 ≤ Kn ≤ 1.5 ), solid volume fraction ( 0 ≤ ϕ ≤ 0.15 ), and amplitude of the irregular rough wall ( 0 ≤ A 1 ≤ 0.1 ) are varied. The nanofluid consists of water as the base fluid and aluminum oxide (Al2O3) nanoparticles. Heat transfer characteristics are analyzed using the Nusselt number (Nu), while entropy generation is quantified to optimize thermal system efficiency. Grid sensitivity analysis and validation against existing literature are conducted to ensure the accuracy of the numerical methodology. Notably, the study demonstrates that increasing the slip velocity at the cavity wall enhances convection within the cavity, leading to a substantial increase in Nu. At Ra = 106, the Nu increases by 53.52% when Kn changes from 0 to 1. Furthermore, the study highlights the significant influence of nanoparticle volume fraction on Nu, showing that as the volume fraction increases, Nu also increases, indicating improved convective heat transfer performance. The Nu for a cavity with an amplitude of 0.1 is roughly 2.5 times higher compared to a smooth-walled cavity at Ra = 106. Increased surface irregularity enhanced turbulence intensity and mixing, leading to stronger convective currents. The novelty of this study lies in examining natural convection in irregular shaped cavities with wall-slip conditions, which are common in practical applications such as solar collectors, microelectronic devices, energy storage units, industrial furnaces, etc. This study offers valuable insights into the thermal behavior of rough enclosures filled with nanofluids, which will facilitate the optimization of heat transfer systems to minimize energy losses.

Hydrated Calcium Silicate in Resin Composites for Prevention of Secondary Caries

Introduction and aimsThe gaps at the margins of restorative composite resin can increase as the carious process occurs underneath the materials, causing further demineralization along the tooth cavity wall. The aim of this study was to evaluate the effects of restorative resin composite containing hydrated calcium silicate (hCS) filler on enamel protection against demineralization by simulating microleakage between the test material and teeth in a cariogenic environment. MethodsThe experimental resin composites were composed of 70 wt.% filler, which was mixed with a glass filler and hCS in a weight ratio of 70.0% glass (hCS 0), 17.5% hCS + 52.5% glass (hCS 17.5), 35.0% hCS + 35.0% glass (hCS 35.0), and 52.5% hCS + 17.5% glass (hCS 52.5). A light-cured experimental resin composite disk was positioned over a polished bovine enamel disk, separated by a 30-µm gap, and immersed in artificial saliva with pH 4.0 for 15, 30, and 60 days. After the immersion period, the enamel disk was separated from the resin composite disk and evaluated using a microhardness tester, atomic force microscopy, and polarized light microscopy. The opposing sides of the enamel and resin composite disks were observed using scanning electron microscopy/energy dispersive X-ray spectrometry. ResultsThe enamel surface showed a significant increase in microhardness, decreased roughness, and remineralization layer as the proportion of hCS increased (P < .05). In the scanning electron microscopy image, the enamel surface with hCS 35.0 and 52.5 after all experimental immersion periods, showed a pattern similar to that of a sound tooth. ConclusionsThe results demonstrated that increasing the hCS filler level of restorative resin composites significantly decreased enamel demineralization. Clinical relevanceHydrated calcium silicate laced restorative resin composites may be a promising dental biomaterial for protecting teeth against demineralization and preventing secondary caries around restorations.

Numerical modeling of the heat and mass transfer of rarefied gas flows in a double-sided oscillatory lid-driven cavity

In micro/nano research and engineering applications, internal flows of rarefied gas in confined geometries with moving parts are of great interest. The rarefied gaseous flows in an oscillating lid-driven cavity are investigated numerically in this work, taking into account both the parallel and antiparallel motion of the driving walls. The discrete unified gas kinetic scheme (DUGKS) is applied to the evolution of the flow and temperature fields. The Shakhov collision model is incorporated into DUGKS to account for flows of non-unit Prandtl numbers. The validity of the Shakhov-DUGKS is confirmed in both single-sided oscillating and steady lid-driven cavity flows. The effects of gas compressibility, rarefaction, and lid oscillation frequency on the mass and heat transport are then thoroughly examined. The corresponding parameter spaces of the Mach, Knudsen and Stokes numbers are 0.16 ≤ Ma ≤ 1.2, 0.075 ≤ Kn ≤ 10 and 0.5 ≤ St ≤ 5, respectively. The shear force and Nusselt number Nu on the cavity walls, as well as the velocity, temperature, and heat flux lines in the cavity, are measured and analyzed. The results suggest that the anti-Fourier heat transfer phenomenon might also occur in the rarefied double-sided oscillating cavity flow. Nu is prone to non-simple harmonic oscillation in its evolution. Furthermore, in the parallel motion as opposed to the anti-parallel motion, the left wall experiences a greater intensity of heat transmission. Compressibility, expansion cooling, and viscous heating compete to provide the complicated flow and heat transfer characteristics found in cavities.

Diffusiophoresis of a Charged Soft Sphere in a Charged Spherical Cavity

The quasi-steady diffusiophoresis of a soft particle composed of an uncharged hard sphere core and a uniformly charged porous surface layer in a concentric charged spherical cavity full of a symmetric electrolyte solution with a concentration gradient is analyzed. By using a regular perturbation method with small fixed charge densities of the soft particle and cavity wall, the linearized electrokinetic equations relevant to the fluid velocity field, electric potential profile, and ionic concentration distributions are solved. A closed-form formula for the diffusiophoretic (electrophoretic and chemiphoretic) velocity of the soft particle is obtained as a function of the ratios of the core-to-particle radii, particle-to-cavity radii, particle radius to the Debye screening length, and particle radius to the permeation length in the porous layer. In typical cases, the confining charged cavity wall significantly influences the diffusiophoresis of the soft particle. The fluid flow caused by the diffusioosmosis (electroosmosis and chemiosmosis) along the cavity wall can considerably change the diffusiophoretic velocity of the particle and even reverse its direction. In general, the diffusiophoretic velocity decreases with increasing core-to-particle radius ratios, particle-to-cavity radius ratios, and the ratio of the particle radius to the permeation length in the porous layer, but increases with increasing ratios of the particle radius to the Debye length.

On the resonance frequency of the irregular shaped visco-acoustic Helmholtz cavity problem

In this paper we develop a closed-form mathematical solution for the resonance frequency of the axisymmetric irregular shaped visco-acoustic Helmholtz cavity problem. The solution is based on a conformal mapping that transforms the governing visco-acoustic equations of motion for the irregular cavity geometry into a new domain described by a set of orthogonal curvilinear coordinates. These orthogonal curvilinear coordinates have an important characteristic relative to the transformation of the physical boundary: the mapped domain is constructed such that the locus of all points for the length-wise profile of the physical boundary coincides with a constant value for a (quasi radial) coordinate in the new mapped domain. In these orthogonal curvilinear coordinates we obtain an analytical solution for the visco-acoustic equations of motion and exactly satisfy the no-slip fluid boundary conditions over the irregular shaped cavity walls by matching the coefficients of an orthogonal Legendre polynomial series representation for the non-uniform velocity on the cavity walls. The mathematical solution is an approximation to the extent that the scale factors chosen for the mapping consist of strictly the mutual-coupling terms of the true scale factors. Thus we analyze some results to understand the correlation of the analytical solution frequency response spectra with numerical finite element analyses of the idealized boundary conditions with various irregular shaped cavity geometries. The results for fundamental resonance frequency were found to exhibit good correlation with the results of finite element analyses over a significant range of fluid properties with different irregular cavity geometries. As the primary motivation for the derivation stems from the lack of a rapid yet accurate alternative to computationally intensive MultiPhysics FEA in the formulation of acoustic trendlines for sensor development, the solution’s acoustic impedance was applied as dispersive loading in a simple lumped parameter model of a fluid identification sensor for comparison. The resulting acoustic trendlines of the reduced (5 DOF) model were found to exhibit good correlation with the results of the MultiPhysics FEA (>105 DOF). Thus the solution was found to enable a closed-form analytical method for rapid construction of parametric studies in the practical design of fluid analysis sensors based on complex resonant cavity geometries.

Cavity Disinfection with Natural Agents and their Efficacy: A Review on Recent Literature

Abstract: The success of a dental restoration can be altered by the amount of residual bacteria present under the cavity which over time cause deterioration of adhesive cement by microleakage or secondary caries. Cavity disinfectant application on the cavity walls performs a cleansing action to decrease the bacterial load and improve the longevity of restorations. Although a wide variety of such chemical disinfectants have been in use, their cytotoxic effects have led to the increasing popularity of natural agents. These materials possess antimicrobial, antioxidant and anti-inflammatory properties, which effectively disinfect cavity walls while, at the same time, being cheaper, less toxic, and more patient-friendly. : Some of these agents have also been proven to improve the bond strength of resin to dentin by preventing collagen degradation and MMP inhibition. Propolis, aloe vera, chitosan, green tea, liquorice etc., are derived from parts of plants or animals and have been tested to be efficacious and, in some cases, superior to chemical alternatives without any erosive effect on dentin. : Although there is a lack of enough In vivo evidence to advocate the use of these products as an adjunct in dental therapy, recent studies have yielded promising results, which increases the scope for future clinical research. This review aims to highlight the properties and effectiveness of a few of such natural agents as potential cavity disinfectants.

Cold obstacle influence on nanofluid convection in porous cavity

Enclosure design has a substantial influence on thermal engineering procedures and technology, such as electronics, thermal exchangers, power engines, heating systems, solar panels, and nuclear power plants. Triangular enclosures with different aspect ratios are used for multiple-purpose optimization and enhanced thermal efficiency in microchannels. Triangle enclosures with cold cylinders are often used to reduce heat loss in thermal exchange devices and nanoscale thermal sinks. The objective of the current study is to explore the natural convection of a hybrid nanofluid within a wavy-bottom triangular porous cavity containing an embedded cold inverted triangle, all under the influence of an inclined magnetic field. The inner inverted triangle maintains a lower temperature, while the wavy bottom wall of the outer triangular cavity acts as an isothermal heat source at high temperatures. The space between the inner and outer triangles is filled with hybrid nanofluid (Ag–MgO– water). The numerical solution for the modeled mathematical framework is derived using the open-source finite element program COMSOL. A wavy triangle enclosure is used in this work to analyze key elements, such as the Hartmann number, Ha, the Rayleigh number, Ra, the volume fraction, ϕ, the Darcy number, Da, and the inclination, γ. The local distribution of streamlines, velocity profile, isotherms, and entropy production are demonstrated along with the average Nusselt number. The findings reveal that the heat transfer rate and the total entropy generation increase with increase in Da, while their values decrease with increase in Ha. The value of Nu is raised with increase in the volume fraction ϕ and Rayleigh number Ra. The velocity profile shows increase with increase in the volume fraction ϕ and Rayleigh number Ra.

Thermal analysis of hybrid nanoliquid contains iron-oxide (Fe3O4) and copper (Cu) nanoparticles in an enclosure

The major aim of this work is to analyze the thermophysical properties of hybrid nanoliquid inside a square lid driven enclosure under the effect of applied magnetic field and mixed convection. The Hybrid nanofluid is considered a suspension of Iron-oxide (Fe3O4) and Copper (Cu) nanoparticles into water. The cavity walls have varying properties such as top adiabatic wall is moving continuously while the lower wall is maintained at a high constant temperature, in addition, the vertical walls are kept at a low fixed temperature. The magnetic field is applied to the right vertical wall in a horizontal direction. Additionally, the effects of buoyancy forces caused by temperature gradients and shear forces caused by continuous lid motion are considered. The mathematical modelling of problem with all assumptions yields the nonlinear partial differential system. First this system is transferred into non-dimensional form and then transformed system is solved by using Galerkin finite element method (GFEM) along with Gaussian elimination method. Results for isotherms, streamlines and average Nusselt number are obtained versus Richardson number (0.1 ≤ Ri ≤ 15), Grashof number (10 ≤ Gr ≤ 10000), Hartmann number (0 ≤ Ha ≤ 100), volume fractions of solid nanoparticles (0.005 ≤ ϕ1 ≤ 0.02) and (0.005 ≤ ϕ2 ≤ 0.02). It is observed that the Richardson number and Grashof number have significant impacts on both flow velocity and temperature. In addition, concentration of hybrid nanoparticles improves the heat transfer performance. The obtained results may be crucial for thermal management in the cooling of electronics, heat exchangers, solar thermal collectors, industrial operations, medical equipment, HVAC systems, food processing, and renewable energy systems.

Magnetic impacts on double diffusion of a non‐Newtonian NEPCM in a grooved cavity: ANN model with ISPH simulations

AbstractEmploying phase change materials (PCMs) offers the advantage of storing and releasing thermal energy while ensuring temperature stability. This characteristic makes PCMs valuable for reducing energy usage across various industrial applications. To explore the magnetic effects on double diffusion of a non‐Newtonian nano‐encapsulated phase change material (NEPCM) in a grooved cavity, the present study combined the incompressible smoothed particle hydrodynamics (ISPH) approach with an artificial neural network (ANN) model. The grooved shape is made up of three constructed grooves: triangular, curved, and rectangular grooves. In the cavity's walls, three segments of boundaries are considered as , , and . The ANN model correctly predicted the mean Nusselt number and Sherwood number when merged with current ISPH simulations. The study's novelty lies in exploring three distinct thermal and mass scenarios regarding double diffusion of a non‐Newtonian NEPCM within an innovative grooved domain. The relevant parameters include the fractional‐time derivative , power‐law index , Rayleigh number , Hartmann number , Soret–Dufour numbers (Sr and Du), and Lewis number Le. The obtained simulations present the significance of distinct boundary conditions in changing the velocity field, heat capacity ratio, temperature, and concentration in a grooved cavity. The fractional parameter accelerates the shift from unstable to steady condition. The increase in from 1.1 to 1.5 results in a 44.5% drop in the velocity maximum. Because of the Lorentz effect of a magnetic field, increasing from 0 to 50 reduces the maximum velocity by 20.9%.

Clinical conduct of dentists in the treatment of deep dental carious lesions

Different techniques are employed to contain the carious process: non-invasive, microinvasive, and invasive, and with restorative needs. Thus, it is essential that dentists are duly updated regarding scientific evidence and perform with skill and precision the techniques proposed as treatment, being aware of the consequences and risks, and aiming at the most conservative therapy. Objective: To identify the clinical practices for the treatment of deep carious lesions used by dental surgeons of the Family Health Strategy (FHS) program of a Brazilian city. Material and methods: This was a quantitative and cross-sectional study carried out with 43 dental surgeons from the FHS program in the city of Sobral, State of Ceará, Brazil, using a Google Forms online questionnaire, containing questions related to the clinical criteria used during caries removal, deep dentin caries removal techniques, lining materials, survival rate of some treatments, in addition to sociodemographic data and questions regarding professional qualification. Results: Among those interviewed, 62.8% were aged between 25 and 30 years. Most dentists (58.7%) considered that the cavity floor should be hard at the end of the carious dentin removal, which demonstrates the non[1]adherence to Selective Carious Tissue Removal (SCTR) protocols. Only 25.6% considered SCTR a treatment with a chance of success and a 2-year survival rate greater than 80%. More than half of the interviewees (51.2%) disagreed with the maintenance of carious tissue in the axial/pulp walls of deep cavities to preserve pulp vitality. More invasive treatments were preferred in a greater proportion by dentists who work exclusively in the public sector (66.7%) compared to those who also work in the private sector (17.6%) [p=0.002], with an evident need for cariology education workshops and more studies on the topic. Conclusion: The dentists who participated in the study showed little adherence to less invasive techniques in the treatment of deep carious lesions.

Numerical study on natural convection in a saturated non Darcian porous medium under radiation and entropy generation effects

This work focuses on analyzing fluid flow, generation of entropy, and heat transfer during natural convection in a cavity enclosed with a non-Darcian saturated porous medium. The influence of viscous dissipation and thermal radiation are considered. The Lattice Boltzmann method is adopted to simulate the governing equations. The study discusses the general effect of dimensionless parameters on the fluid structure interaction properties, entropy generation and the thermal field. The parameters investigated include the Grashof number, Eckert number, Rayleigh number, Forchheimer Resistance, inverse Darcy, radiation parameter, and Prandtl number. The combination of studying dimensionless parameters on non-Darcian porous medium, along with the consideration of thermal radiation, viscous dissipation, and entropy analysis, has made this research valuable and worth pursuing. The findings reveal that the areas of high entropy generation are primarily located along the walls (vertical) of the cavity. Moreover, it is observed that as the inverse Darcy and Forchheimer resistance increase, their effect on the average Nusselt number diminishes for varying parameters of radiation. As the Prandtl number increases, the isotherms cluster along the walls (vertical) of the porous cavity. With high Grashof values, convection becomes turbulent, and the temperature distribution becomes non-uniform. Additionally, the entropy caused by heat and fluid friction decreases as the Forchheimer resistance increases.

Transient contribution of the sphenoid ala major to the socket of the temporomandibular joint in near-term fetuses.

The temporomandibular joint (TMJ) is a complex structure that plays a vital role in the movement of the jaw. Some anatomy and dental textbooks show that, at the medial margin, the TMJ capsule attaches to a suture between the sphenoid ala major and the temporal bone squamosa. In near-term fetuses, the ala major extends posterolaterally to approach the TMJ. In this study, we aimed to investigate the contribution of the sphenoid ala major to the socket of the TMJ in near-term fetuses. We examined histological sections from 22 human fetuses (approximately 15-40 weeks). At midterm, the lateral and superior walls of the TMJ cavity were formed by the temporal bone squamosa, whereas the ala major was distant from the joint. However, at near-term, the ala major formed the medial wall of almost the entire part of the joint cavity. The top of the TMJ was attached to both the squamosa and ala major, with the condylar head consistently separated from the sphenoid by the joint disk. We observed a significant descent of the middle cranial fossa in near-term fetuses, which brought the ala major close to the TMJ. This transient position of the TMJ near the sphenoid is likely due to brain enlargement and posterolateral growth of the ala major. After birth, occlusion causes the anterior growth of the mandibular fossa of the squamosa, which moves the ala major away from the TMJ. Similarly, the lateral growth of the sphenoid toward the squamosa suture may also stop in children.

Damage prediction and improvement method based on cutting mode of circular empty hole

Based on the theory of empty hole effect of cutting blasting, the Hopkinson effect and Saint–Venant principle are integrated to establish a two-dimensional calculation model of dynamic stress evolution of the holes wall, and then the dynamic fracture mechanism and damage distribution mode of the rock mass in the cutting area under the action of longitudinal waves are predicted. The results of the calculation and numerical simulation are verified by experiments, and the results show that: The time-varying stress function of the circular cavity wall conforms to the periodic dynamic evolution of the trigonometric function, and the theoretical calculation is consistent with the simulation results. Through the calculation of the round holes cut model and the square empty hole cut model, the change of the shape of the holes in the cut area changes the failure form of the surrounding rock mass. The circular empty hole wall is affected by the stress wave to produce "interval ring" destruction, and the effect of the reflected stretch wave is inhibited. The large range of rock mass in the square empty hole wall produces tensile and shear failure, and the rock mass collapses inward under the influence of the second stage stress. Among them, the empty space utilization rate of the square empty hole model is about 8.5 times that of the circular holes model. Vibration monitoring in the center of the cutting area shows that the vibration effect of the circular empty hole is larger than that of the square empty hole, and the proportion of rock breaking energy is lower.

Evaluation of exterior wall cavity fires using an intermediate scale test method

AbstractCavities form an integral part of many external wall systems (EWSs). Numerous external wall fires worldwide have been primarily due to combustible exterior cladding. However, the Grenfell Tower and Knowsley Heights fire incidents (in the UK) are examples where wall cavity materials have impacted fire spread. Wall cavity materials are typically regulated by small‐scale fire test methods which do not necessarily represent the actual fire conditions that can exist within wall cavities. This experimental study proposes an intermediate‐scale test (IST) protocol to examine cavity wall fire behaviour. This protocol is a modified version of the FM Global Cavity Fire Test method (within the FM 4411‐2020 series). The study examines a broad range of cavity materials including sarking, polyester insulation, phenolic foam, PIR, and EPS. A low‐intensity (6–8 kW) and high‐intensity (~80 kW) ignition sources were used to represent two types of cavity fire scenarios. These two fire sizes were shown to differentiate reaction to fire behaviour between these materials and explore the “tipping point” in resulting fire behaviour (which may lie between these two intensities). This proposed cavity fire test protocol provides a suitable “elevated fire risk assessment tool” for combustible cavity materials.

A Study on Nanoleakage of Apical Retrograde Filling of Premixed Calcium Silicate-Based Cement Using a Lid Technique.

This study aimed to compare the nanoleakage of retrograde fillings with premixed calcium silicate-based putty and mineral trioxide aggregate (MTA), using two different techniques (traditional and Lid). Sixty-four extracted human teeth were decoronated, then root canals and ends were instrumented for retrograde filling and divided into four groups according to the retrograde filling technique: the traditional and the Lid technique. Each group (n = 15) was filled with Ceraseal + Well-Root putty, Well-Root putty, Ceraseal + ProRoot MTA, and ProRoot MTA. The nanoleakage was evaluated using the Nanoflow device (IB Systems) on days 1, 3, 7, 15 and 30. Data were collected twice per second at the nanoscale (nL/s) and calculated after archiving the stabilization of fluid flow. The Kruskal-Wallis and Mann-Whitney U-tests were used for statistical analysis. All groups showed enhanced sealing ability over time. Regardless of filling materials, the Well-Root putty, Ceraseal+Well-Root putty, and Ceraseal+ProRoot MTA groups indicated less nanoleakage than the ProRoot MTA group in the first week of evaluation (p < 0.05). Although all groups did not show significant differences after 2 weeks, the Ceraseal+ProRoot MTA group leaked less than ProRoot MTA on Days 3 and 7 (p < 0.05). The scanning electron microscopic examined good adaptation to the cavity wall, which was similar to nanoleakage results. Premixed calcium silicate-based putty retrograde filling material alone and using the "lid technique" were shown to be faster and less prone to nanoleakage when compared to MTA.

Turbomachines seal flow resistance enhancement and leakage reduction based on flow control method with bow-shaped auxiliary teeth

Improving sealing performance without clearance reduction is important for the economic and safety operation of modern turbomachines. For this purpose, this study proposes the bow-shaped auxiliary teeth to reduce the leakage. One bow-shaped auxiliary tooth is installed after each seal tooth to guide the leakage jet towards the side wall of seal tooth. Then the leakage jet attaches itself to the inner wall of cavity. The Computational Fluid Dynamics method is used to calculate the flow field in the new seal. Results show that flow impingements, flow deflections, and enhanced vena contraction effect increase the leakage flow resistance and reduce the leakage velocity. The application of the bow-shaped auxiliary teeth reduces the leakage flow rate by 43.8–46.3 % compared with the labyrinth seal. Geometry parameters analysis shows that reducing the axial distance between seal tooth and bow-shaped auxiliary tooth, and increasing the central angle of bow-shaped auxiliary tooth are beneficial for leakage reduction. With the increase in the radius of bow-shaped auxiliary tooth, the leakage firstly decreases and then changes a little.