Axial Wall Research Articles

Effect of axial conduction in integral rough friction stir channels: experimental thermo-hydraulic characteristics analyses

Integral mini-channels fabricated in the metal substrate by friction stir channeling process are different from conventional mini-channels due to irregular shape, and large surface roughness. The effect of axial wall conduction on heat transfer in such mini-channels is significant, which could limit their utilisation as cooling channels in heat transfer based applications. Hence, in this study, we present an experimental analysis of the thermo-hydraulic performance of a friction stir channel to identify the axial wall conduction effect using de-ionized water as working fluid. The thermo-hydraulic performance parameters are analysed in the range of Reynolds number of 500 to 2100. The local wall temperature distribution along the length of the mini-channel is found to be non-uniform due to the significant axial wall conduction effect. The distinct pattern of numerical heat flux distribution is used as evidence to confirm the presence of axial wall conduction effect which is implied by the local wall temperature distribution. The higher average heat transfer and flow characteristics compared to the theoretical predictions for conventional mini-channels are observed as a result of simultaneously developing flow and the presence of surface roughness.

Volumetric analyses of restorative crown preparations in simulated-premolar and -molar teeth

Crowns or abutments of fixed partial denture tooth preparations to restore natural teeth or implant-supported restorations require tooth or abutment reduction in a tapered format. Low angulations of axial wall taper to the long axis of the tooth or abutment have been shown to increase the restoration’s stability during masticatory function with large occlusal loads. The tooth preparation and luting agent stabilize the restoration during these loading cycles to prevent dislodgement. Restoration dislodgement represents a catastrophic failure of the prosthesis in function. The preparation attributes contribute to prevent displacement failure and reduce luting agent tensile and shear stresses. Low axial wall taper levels increase resistance to rotational displacement. Increasing axial wall angulations produces negative consequences including reduced rotational resistance, reduced surface area and increased volume of remaining tooth structure. These three considerations have been shown to involve three variables: preparation vertical height, horizontal base width from rotational axis and rotational axis vertical height compared to the opposing axial resisting wall. Natural tooth preparations are completed by a restorative dentist with a hand-held high-speed handpiece with cutting instruments within the oral cavity; while implant-supported custom abutments are prepared in a similar manner but machined outside the oral cavity. As a result, the machined abutment is more controlled for ideal taper in inanimate materials compared to the intraoral tooth preparation on human vital tissues. This experimental study will analyze the preparation of simulated-vital tooth premolars and molars for volume loss at ideal and non-ideal axial wall angulations with variation of vertical heights and vital pulpal tissue volumes.

Fit of cobalt-chromium copings fabricated by the selective laser melting technology and casting method: A comparative evaluation using a profilometer

This study aimed to assess the marginal adaptation and internal fit of cobalt-chromium copings fabricated by the selective laser melting (SLM) and conventional techniques using a profilometer. In this in vitro study sample size was calculated to be a total of 10 in two groups (n = 5). A brass model was used that had a circular cross-section with a round shoulder margin with 0.5 mm thickness and axial walls with 10 mm length and 6° taper. The copings fabricated with both techniques (SLM and casting method) were placed on the model, and vertical marginal gap was measured using a profilometer. The internal fit of copings was assessed by weighing the light-body addition silicone applied inside them, which simulated the cement. Data were analyzed through parametric (Independent t-test) and nonparametric (Mann-Whitney U-test, Bootstrap, Spearman, and Pearson Correlation) analysis. All analyses were performed at a significant level (α = 0.05) using SPSS. The mean marginal gap in the casting group (132.93 ± ) was significantly higher than that in the SLM group (67.14 ± 15.67 μm) (P < 0.05). The mean weight of light-body silicone was 9.60 ± in the SLM and 8.70 ± 1.21 mg in the casting group. No significant difference was noted between the two groups regarding the internal fit (P > 0.05). The copings fabricated by the SLM technique showed a smaller vertical marginal gap compared to the casting group. However, the two groups were not significantly different in terms of internal fit.

Comparative evaluation of microleakage of conventional crowns and endocrowns using confocal laser scanning electron microscope – An in vitro study

Background and Aims: The purpose of this study was to compare the microleakage of conventional crowns and endocrowns using confocal laser scanning electron microscope. Materials and Methods: Thirty extracted human permanent mandibular molars were collected and sectioned parallel to the occlusal surface at 2 mm above the CEJ to deroof the pulp chamber. Endodontic treatment was performed. The gutta-percha was removed 1 mm below the orifice of each canal, and flowable resin composite was filled in the canals up to the level of the pulp chamber. Samples were then randomly divided into two groups with 15 teeth each according to the type of post endodontic restoration given – Group 1: conventional crowns and Group 2: endocrowns. In Group (1), teeth were restored with composite cores, wide circumferential deep chamfer margin (0.8 mm) was prepared at the CEJ and 2 mm from the occlusal surface, 1.5 mm were cut from the axial walls. In Group (2), preparation was performed by making a circular butt margin with a central retention cavity with rounded internal line angles. Impressions were made, crowns were fabricated, and cementation was done, followed by thermocycling. The specimens were coated with varnish up to 1 mm from the crown margins, placed in Rhodamine B dye for 60 h, rinsed thoroughly for 30 s, sectioned with hard tissue microtome and examined for microleakage. Statistical Analysis: Statistical analysis was accomplished with the Student t-test, and significance was predetermined at P Results: In this study, endocrowns (6.158) showed significantly low microleakage compared with conventional crowns (14.052). Conclusion: Endocrowns showed significantly lower microleakage.

An In Vitro Comparative Study to Assess Minimal Thickness Required for Monolithic Zirconia Crowns to Resist Fracture under Load on Rapid Prototyped Models

To evaluate and validate minimal thickness required for computer-aided designed (CAD) and computer-aided manufactured (CAM) monolithic zirconia crowns to withstand occlusal load. The study compares two systems. Forty-eight rapid prototype die models with varying occlusal reductions were fabricated. Group I samples had an axial wall height of 7.0 mm with occlusal reduction of 0.5 mm, group II had axial wall height 6.5 mm with occlusal reduction 1.0 mm, group III had axial wall height 6.0 mm with occlusal reduction of 1.5 mm. Control group IV had axial wall height 5.5 mm with occlusal reduction of 2.0 mm. Laboratories A (Czar) and B (3M) were provided with 24 samples each, 6 samples in each group for fabricating CAD/CAM monolithic zirconia crowns of 0.5, 1.0, 1.5, and 2 mm occlusal thickness, respectively, and cemented using resin-modified glass ionomer cement over the die models. Samples were loaded on a universal testing machine for fracture testing. Surface topography analysis of fractured specimens was done under the scanning electron microscope (SEM). The results were subjected to one-way analysis of variance (ANOVA) and honestly significant difference (HSD) Tukey test to analyze statistical significance at 0.05 levels. Samples of laboratory A performed superior to laboratory B. The t test showed fracture resistance of group AI (0.5 mm) > group BII (1.0 mm) and also group AIII (1.5 mm) > control of Lab B (2 mm). Monolithic zirconia crowns showed a favorable mechanical property to withstand occlusal load with minimal tooth preparation. The occlusal thickness of Czar with 0.5 mm is found to resist fracture under physiological masticatory load. Scanning electron microscope revealed increased voids in the microstructure of 3M, which lead to decreased fracture resistance. Preservation of tooth structure can be considered using monolithic crowns with minimal thickness of 1 mm.

A novel retentive type of dental implant prosthesis: marginal fitness of the cementless double crown type implant prosthesis evaluated by bacterial penetration and viability.

PURPOSEThis study aims to compare the marginal fitness of two types of implant-supported fixed dental prosthesis, i.e., cementless fixation (CL.F) system and cement-retained type.MATERIALS AND METHODSIn each group, ten specimens were assessed. Each specimen comprised implant lab analog, titanium abutment fabricated with a 2-degree tapered axial wall, and zirconia crown. The crown of the CL.F system was retained by frictional force between abutment and relined composite resin. In the cement-retained type, zinc oxide eugenol cement was used to set crown and abutment. All specimens were sterilized with ethylene oxide, immersed in Prevotella intermedia culture in a 50 mL tube, and incubated with rotation. After 48 h, the specimens were washed thoroughly before separating the crown and abutment. The bacteria that penetrated into the crown-abutment interface were collected by washing with 500 µL of sterile saline. The bacterial cell number was quantified using the agar plate count technique. The BacTiter-Glo Microbial Cell Viability Assay Kit was used to measure bacterial adenosine triphosphate (ATP)-bioluminescence, which reflects the bacterial viability. The t-test was performed, and the significance level was set at 5%.RESULTSThe number of penetrating bacterial cells assessed by colony-forming units was approximately 33% lower in the CL.F system than in the cement-retained type (P<.05). ATP-bioluminescence was approximately 41% lower in the CL.F system than in the cement-retained type (P<.05).CONCLUSIONThe CL.F system is more resistant to bacterial penetration into the abutment-crown interface than the cement-retained type, thereby indicating a precise marginal fit.

Numerical analysis on flow and heat transfer characteristics of supercritical pressure CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; in inclined tube

In this study, numerical simulation of flow and heat transfer of S-CO2 (supercritical CO2) in the inclined upward and downward smooth tubes with an inner diameter of 10 mm and a heating length of 2000 mm at an inclination angle of 45° were conducted. The SST k - ω low Reynolds number turbulence model was used, and the accuracy of the calculation model was verified by the experimental data of S-CO2 flowing upward in the vertical smooth tube. The variation characteristics of the axial and circumferential inner wall temperature T w,i and the convective heat transfer coefficient h were analyzed. The S-CO2 would undergo the phase change from a liquid-like to the vapor-like at the pseudocritical temperature T pc by assuming supercritical pseudo-boiling. Based on this assumption, the reasons for a difference in the wall temperature distribution at the top generatrix during S-CO2 flowing in different directions were studied. By the detailed analysis of the velocity distribution, thermophysical properties distribution, including specific heat capacity at constant pressure cp and thermal conductivity λ , and the turbulent kinetic energy k distribution in the cross-sections of the inclined circular tube, the heat transfer mechanism related to the wall temperature difference at upward and downward was studied. The results showed that the thickness of vapor-like film, axial velocity u , turbulent kinetic energy k , and the thickness of viscosity sub-layer δ y +=5 were the main factors affecting the difference in the wall temperature distribution at the top generatrix in different flow directions.

Thermal performance of phase change nano-emulsion in a rectangular minichannel with wall conduction effect

The minichannel heatsink is one of the small heat exchangers, having high heat capacity and being able to remove substantial heat within a very small volume, in line with the current demand for heat dissipation of electronic components. In the present study, the convection cooling characteristics in a rectangular minichannel considering wall conduction effect was investigated numerically. Numerical simulations are performed under 2% and 10% volume fractions of PCM particles (n-eicosan). The results reveal that the axial wall conduction plays a more pivotal role in the minichannels at the lower Reynolds number. Besides, the employment of phase change nano-emulsion in the working fluid in the rectangular minichannel suppresses the wall temperature and improves the heat transfer performance up to 4.23% and 9.36%, respectively, compared with the application of pure water. In addition, it is demonstrated that a high concentration of PCM particles may have detrimental effect on pressure drop and extended wall heat dissipation efficiency under certain circumstances thus the concentration of PCM particles needs careful selection.

Influence of speed sintering on the fit and fracture strength of 3-unit monolithic zirconia fixed partial dentures

Statement of problemSpeed sintering has been introduced to enable single-visit monolithic zirconia prostheses. However, the fit and fracture load of zirconia 3-unit monolithic fixed partial dentures (FPDs) after speed sintering are unknown. PurposeThe purpose of this in vitro study was to test the properties of zirconia 3-unit monolithic FPDs after speed sintering and to compare the properties with conventional sintering. Material and methodsA calibrated operator digitized an in vitro model with a complete coverage preparation of a maxillary right second premolar and second molar (n=12) by using the CEREC AC Omnicam (Dentsply Sirona) scanner. Twelve zirconia FPDs were designed (CEREC SW 4.1.1), and for each data set (n=12), 1 FPD was designed and milled 4 times (MCXL Premium; CEREC Zirconia; Dentsply Sirona), resulting in 4 identical monolithic FPDs (N=48). The FPDs were divided into 2 groups according to the sintering procedure (n=24): speed sintering (group S) by using the SpeedFire (Dentsply Sirona) and the conventional sintering (group C) by using the inFire HTC speed (Dentsply Sirona). All the FPDs were glazed by using glaze-spray and fired according to the sintering group. The SpeedFire (Dentsply Sirona) was used for group S, and the VACUMAT 6000M (VITA Zahnfabrik) was used for group C. The fit of the FPDs was evaluated with the replica technique by using polyvinyl siloxane and analyzed according to the measurement areas: marginal gap, chamfer area, axial wall, and occlusal area. Subsequently, groups S and C were further subdivided, and 12 specimens per group underwent artificial aging by thermomechanical loading in a mastication machine (50 N for 1.2×106 times at a frequency of 1.7 Hz and a thermal change in distilled water from 5 °C to 50 °C every 120 seconds), resulting in additional subgroups: group SA and group CA. For all the FPDs (groups S, C, SA, and CA), a fracture load measurement was conducted. The Kolmogorov-Smirnov test was used to examine the values of the fit and fracture load for normal distribution. The Mann-Whitney U test for the fit and a 2-way ANOVA for the fracture load were used to detect the differences among the groups (α=.05). ResultsGroup S showed a better marginal (P=.018) and occlusal (P<.001) fit than group C. For the fracture load values, no significant difference was found because of the sintering procedure (P=.070) or the interaction of the sintering procedure and artificial aging (P=.484). Artificial aging showed an impact (P=.024) with significantly lower values after aging. ConclusionsSpeed-sintered FPDs had equal and better values for the fit and fracture load than conventional sintering.

Comparative study of conjugate heat transfer in a single-phase flow in wavy and raccoon microchannels

Purpose This paper aims to emphasize on studying various geometrical modification performed in wavy and raccoon microchannel by manipulating parameters, i.e. waviness (γ), expansion factor (α), wall to fluid thermal conductivity ratio (ksf), substrate thickness to channel height ratio (dsf) and Reynolds number (Re) for obtaining optimum parameter(s) that leads to higher heat dissipation rate. Design/methodology/approach A three-dimensional solid-fluid conjugate heat transfer numerical model is designed to capture flow characteristics and heat transfer in single-phase laminar flow microchannels. The governing equations are solved using finite volume method. Findings The results are presented in terms of average base temperature, average Nusselt number, pressure drop, dimensionless local heat flux, dimensionless wall and bulk fluid temperature, local Nusselt number and performance factor including axial conduction number. Heat dissipation rate with raccoon microchannel configuration is found to be higher compared to straight and wavy microchannel. With waviness of γ = 0.167, and 0.267 in wavy and raccoon microchannel, respectively, performance factor attains maximum value compared to other waviness for all values of Reynolds number. It is also found that the effect of axial wall conduction in wavy and raccoon microchannel is negligible. Additionally, thermal performance of wavy and raccoon microchannel is compared with straight microchannel. Practical implications In recent past years, much complex design of microchannel has been proposed for heat transfer enhancement, but the feasibility of available manufacturing techniques to fabricate complex geometries is still questionable. However, fabrication of wavy and raccoon microchannel is easy, and their heat dissipation capability is higher. Originality/value This makes the difference in wall and bulk fluid temperature smaller. Thus, present work highlighted the dominance of axial wall conduction on thermal and hydrodynamic performance of wavy and raccoon microchannel under conjugate heat transfer situation.

Influence of angulation and height of tooth preparation on the distribution of tensions in prosthetic crowns for upper central incisor

Aim: it was to use tridimensional finite element analysis (FEA) to analyze the effect of height and angulation of prosthetic preparations on the distribution of stresses for lithium disilicate prosthetic crowns, the underlying resin cement, and the prosthetic preparation of a superior central incisor. Methods: a CAD modeling software, SolidWorks 2013, was used to generate three-dimensional virtual models comprising the dimensions of the preparation parameters. Three angles (6, 12 and 16 degrees) were simulated on the prepared walls and two wall heights were utilized (4 and 5 mm), for a total of six model groups according to the height and angulation of the walls. A vertical line in the Y-axis was used as a reference for determining the degrees of convergence (inclination of the preparations). The chamfer finish and preparation width were standardized for all groups. Results: the 4 mm preparations behaved more appropriately when the axial wall convergence was approximately 6 degrees. The 5 mm preparations required 12 degrees of angulation. In relation to resin cement, there was better stress distribution when the angle of incisal convergence was between 6 and 12 degrees. An increase to 16 degrees led to a considerable increase in peak stress at the preparation margin. Conclusion: it was concluded that the convergence of the axial walls of coronal preparations with 4 and 5 mm heights should be 6 and 12 degrees, respectively, to avoid high tension spikes in the underlying resin cement.

Numerical analysis of out-of-plane deformation of shear wall

An important factor in slender reinforced concrete shear wall design is the out-of-plane instability, identified as one of the main failure modes. Previous experimental researches had observed this failure in T-shape slender walls as well as rectangular walls. This paper describes the development of out-of-plane instability of slender shear walls with different end configuration which subjected to in-plane quasi-static lateral loading. Experimental results of a T-shape thin wall specimen which failed in out-of-plane mode were used for verification of the modelling, using finite element nonlinear static analysis. The numerical analysis results were in good agreement with the experimental results and the overall global response of shear wall can be predicted using finite element analysis. Series of models were developed to scrutinize the major sources governing the out-of-plane instability. Based on the investigation, shear to span ratio, axial load ratio, wall thickness, and different end configurations of the boundary element are identified as the main parameters governing the wall instability.

Influence of a Retentive Shoulder Design to Prevent Early Failure of Three Core Build-Ups.

This study evaluated the influence of a retentive shoulder design to prevent early failure of three resin composite build-ups on molars. Ninety-six intact extracted human maxillary third molars were assigned to two groups (n=48) based on occlusal, buccal cusps only and all cusps reduction. The groups were divided into two subgroups: pin retained and non-pin retained build-ups resulting in four groups (n=24), according the cusps reduction: pin retained/partial, pin retained/complete, non-pin retained/partial, non-pin retained/complete. Occlusal reduction was 3 mm with a semi-lunar retentive shoulder of 3 mm and an axial wall height of 1.5 mm. Groups were restored using a microhybrid, flowable or titanium reinforced resin composite. Modified self-curing acrylic resin provisional crowns were fabricated, cemented with non-eugenol temporary cement and thermal cycled. An instron machine applied tension to the provisional crowns parallel to the long axis of the tooth until dislodgement. A three-way analysis of variance was conducted on the influence of the variables on the retention of the core build-up. Ninety-three build-ups were retained under tensile load, while three core build-ups without pins were dislodged. Three-way analysis of variance showed no statistically significant difference between core build-ups using a retentive shoulder and pin retained core build-ups when tested under tensile load. With the advent of adhesive systems, increased surface area and retentive shoulder design can provide a retentive core foundation to prevent early failures of core build-ups during indirect restoration fabrication which will contribute to the longevity of final restorations.

Effect of the wall thermal boundary condition on the structure of a confined swirling diffusion flame

The present study focuses on the effect of the wall heat loss on a confined swirling diffusion flame. The objective is to assess the effect of changing the wall thermal boundary condition (i.e., from isothermal to adiabatic) on the flow structure, the flame shape, and the mixing behavior. Reynolds-averaged Navier–Stokes equations are solved. The diffusion flamelet model is employed in the simulation. The comparison of the numerical and experimental axial wall heat flux distributions shows a good agreement. The inner recirculation zone (IRZ) is shorter in the case of the adiabatic wall. It features higher negative axial velocities. The radial gradient of the axial velocity is higher which could enhance mixing and flame stability. The outer recirculation zone (ORZ) size does not change with the wall thermal boundary condition. Generally, the exit flow from the furnace decelerates due to the formation of the IRZ. This effect is more pronounced when the IRZ is longer, as the case when there is a wall heat loss. The flame is longer in the adiabatic wall case. However, its position relative to the burner exit does not change compared to the isothermal wall. In both cases, the flame is stabilized on the boundary of the IRZ. The mixing behavior is similar for the two wall thermal boundary conditions. However, the adiabatic wall case features a more fuel-rich mixture in the flame stabilization region, mainly due to the different velocity fields. Pockets of very fuel-rich mixtures are formed in the ORZ.

РЕЗУЛЬТАТЫ КРАЕВОЙ АДАПТАЦИИ МОНОЛИТНЫХ КОРОНОК ИЗ ДИОКСИДА ЦИРКОНИЯ

Subject. Edge clearance and mechanical strength are important factors for selecting all-ceramic zirconia crowns. The article presents the results of evaluating the regional adaptation of single monolithic zirconia crowns mounted on premolars and molars made using the CAD/CAM system.&#x0D; Objectives — a clinical assessment of the edge conformity and absolute marginal discrepancy of single monolithic zirconia crowns made by the CAD/CAM system and fixed on premolars and molars. &#x0D; Materials and methods. 75 patients (mean age 34.9 ± 3.77 years) with monolithic zirconia crowns fixed 6 months ago were examined. 3Shape software, Zenotec CAM Wieland Dental system, CNC Wieland Select milling machine, Zenostar translucent blanks were used. The measurements were performed in vivo. Marginal clearance and absolute marginal mismatch are measured with an optical microscope. All measured data were averaged based on four positions: edge, rounded shoulder, axial wall, and occlusal area. &#x0D; Results. 98 crowns were established: in 74.7 % of cases 1 crown was installed, in 20.0 % of cases — 2 crowns, in 5.3 % of cases — 3 crowns. 48 crowns are installed on premolars, 50 — on 1 and 2 molars. On the upper jaw 22 were fixed on premolars, 20 restorations on molars, 26 and 30 crowns on the lower jaw, respectively. The average value of the edge gap was 90.6 ± 20.71 μm, and the average values of the absolute edge discrepancy were 164.90 ± 22.28 μm. The marginal gap of premolars and molars averaged 90.8 ± 18.96 μm and 89.14 ± 21.0 μm, respectively, and the absolute boundary discrepancy was 165.82 ± 19.95 and 163.11 ± 22.37 μm, respectively.&#x0D; Conclusion. The results of the marginal fit and the absolute marginal divergence of monolithic crowns based on zirconium dioxide are within the limits of clinical acceptability. 2. It is necessary to take measurements before and after the sintering process.

Finite-element analysis of mandibular first molar with two marginal designs of endocrown for the repair of different defects

This study aimed to evaluate the stress distribution of the mandibular first molar with different thicknesses and heights of the axial wall restored by the endocrown with two marginal designs and thus provide a theoretical basis for selecting clinical preparation through the finite-element method. Two marginal endocrowns of the mandibular first molar with different axial-wall thicknesses (t=1, 2, 3 mm) and heights (h=2, 3, 4 mm) were established. Group A was the butt-joint design, whereas group B was the shoulder-surrounded design. After applying vertical and oblique loads , the size and distribution of the maximum principal stress and equivalent stress of residual tooth tissue were recorded. The maximum principal stress and equivalent stress distribution of residual tooth tissue were similar among different models. Group A showed a lower maximum principal stress and equivalent stress than group B at the same thickness and height under vertical load. Meanwhile, under oblique load, the maximum principal stress values of groups A and B decreased with increased thickness at constant height. Group A showed lower equivalent stress than group B at the same thickness and height of 2 and 3 mm. However, when the height was 4 mm, the trend was reversed. In mastication, when bearing the vertical force, the retention of the butt-joint marginal endocrown preferred to the shoulder-surrounded one. Given the higher axial wall of the shoulder-surrounded marginal endocrown, it showed better ability to bear the oblique force than the butt-joint one.

P4131Abnormal flow pattern in the main pulmonary artery of Marfan patients is related to local dilation

Abstract Introduction Marfan syndrome (MFS) is a hereditary connective tissue disorder caused by mutation in the FBN1 gene. Main pulmonary artery (MPA) dilation is very prevalent in MFS patients. Indeed, the old Ghent nosology considered main pulmonary artery (MPA) dilation as diagnostic criterion of MFS patients. Although clinical complications related to pulmonary dilation in MFS are rare, this may potentially lead to MPA dissection or be a marker of vascular disease in MFS. Studies regarding potential causes of MPA dilation in MFS patients are very scarce. Purpose Through 4D flow CMR, we aimed to assess whether flow abnormalities exist in the MPA of MFS patients and their relation to local diameter. Methods Fifty-five consecutive Marfan syndrome adults (MFS) and 22 healthy volunteers (HV) were prospectively enrolled. All subjects underwent non-contrast-enhanced 4D flow-MRI, obtaining 4D flow field and a 3D angiography. The MPA was segmented from the 3D angiography, and the segmentation was used to mask 4D velocity data. Four, equidistant analysis planes were placed in the MPA between the pulmonary valve and the pulmonary artery bifurcation. Common descriptors of large arteries hemodynamics were computed at each plane: maximum velocity, systolic flow reversal ratio (a descriptor of the amount of systolic backward flow) and circumferentially-averaged axial and circumferential wall shear stress (WSS). Pulmonary artery diameters were measured on axial images. MPA dilation was defined as a diameter larger than 27 mm in women and 29 mm in men. Systolic (SBP) and diastolic (DBP) systemic blood pressure were measured at the brachial artery with a calibrated cuff immediately after the scan. Results Compared with HV, MFS patients presented similar age, BSA, SBP and maximum blood velocity, but had larger MPA diameter (27.8 vs 25.1 mm, p&lt;0.001) and higher DBP (75.5 vs 66.8 mmHg, p=0.003). According to the used threshold, 45% (27) of MFS patients had MPA dilation. Compared with HV, Marfan patients presented an increased systolic flow reversal ratio in the proximal part of the MPA (Figure 1). In MFS patients axial WSS was reduced in central sections of the MPA, while the circumferential component was not difference with respect to HV. All these flow abnormalities were also present in the subset of 28 MFS patients without pulmonary artery dilation. In multivariable analysis, MPA diameter was independently related to age (B=0.056; p=0.032), sex (B=−2.3; p=0.02) and axial (B=6.4; p=0.039) and circumferential (B=33.9; p&lt;0.001) WSS. Figure 1 Conclusions Dilation of the main pulmonary artery is prevalent in Marfan syndrome patients. Abnormal increase in systolic vortexes and reduction in axial WSS were present in dilated and non-dilated MPA in MFS patients. Axial and circumferential WSS were independently related to MPA diameter. The eventual predictive role of abnormal pulmonary flow pattern in pulmonary artery dilation in MFS patients remain to be established Acknowledgement/Funding Instituto de Salud Carlos III (PI14/0106), La Maratό de TV3 (20151330), CIBERCV and FP7/People (267128)

A novel transient thermohydraulic model of micro-channel heat sink

The purpose of this work is to develop an analytical model for prediction of the thermal fluid performance of a micro-channel heat sink by applying liquid thin-film theory. For this purpose, a one-dimensional transient model has been developed for a single channel of micro-channel heat sink and a series of numerical simulation was performed for various operating conditions. Mass, momentum and energy equations were applied separately for the vapor and liquid phases to predict more effective physical performance of the transient behavior. As a result, the axial distributions of mass flow, pressure, and temperature for the working fluid were obtained for vapor and liquid in the micro-channel. In particular, the phase change interface profile with the liquid thin-film was obtained using an augmented Young Laplace equation. Consequently, the interface areas of heat and mass transfer occupied by the liquid and vapor were predicted and incorporated into the governing equations of each phase. The analytical model was validated by comparison of its numerical solutions with experimental results. The discrepancy between the experimental and numerical results for the axial wall temperature was less than 4 °C, and that for the transient time to reach a steady-state wall temperature was within 1 sec. Through a series of performance simulations for a micro-channel model with pure water as the working fluid, transient response of the wall temperature, liquid film thickness, mass flow rate, liquid pressure, and vapor and liquid temperatures were investigated. The model developed in this study might be utilized for more refined performance prediction of a micro-channel heat sink.

Snap behaviour in the upheaval buckling of subsea pipelines under topographic step imperfection

Pipelines exposed to high temperature and high pressure with a topographic step imperfection are susceptible to the phenomenon of upheaval buckling potentially leading to a hazard for the structural integrity of the pipeline. To analyse this problem we derive analytical upheaval buckling solutions and obtain the locations of maximum displacement and maximum axial compressive stress. We also analyse the typical post-buckling behaviour and its dependence on step height, axial soil resistance and wall thickness. The difference in behaviour between a pipeline with step imperfection and one with a symmetric prop imperfection is discussed. Our results show that a pipeline with a step imperfection is more prone to upheaval buckling than a perfect pipeline. For sufficiently small step heights the pipeline may suffer a snap-back instability under decreasing thermal loading, raising the possibility of hysteretic snap behaviour under cyclic thermal loading (for instance caused by periodic start-ups and shut-downs). The snap-back buckling disappears for large enough step height and the minimum critical temperature difference decreases with increasing step height and wall thickness or with decreasing axial soil resistance. The maximum compressive stress decreases with increasing step height and axial soil resistance or with decreasing wall thickness. A pipeline with step imperfection is safer than one with a symmetric prop imperfection.

Axial wall angulation for rotational resistance in a theoretical-maxillary premolar model.

ObjectivesThe aim of this study was to determine the influence of short base lengths and supplemental grooves on surface area and rotational resistance in a simulated‐maxillary premolar.Materials and MethodsTrigonometric calculations were done to determine the total surface area with and without supplemental grooves. Additional computations were done to determine the maximum wall angle needed to resist rotation displacement in a premolar‐sized model. Wall heights of 3.0, 4.0, and 5.0 mm were used in the surface area and rotational axis computations. The rotational axis was located on the lingual restoration margin to produce a buccal‐to‐lingual rotational displacement.ResultsTotal surface area decreased with increasing four‐wall taper levels from 2° to 18° and decreasing preparation heights from 5 to 3 mm. Significant surface area improvements were found with the supplemental use of mesial and distal axial grooves compared with the same condition without grooves in all taper levels and preparation height categories. Resistance to rotational displacement was determined to occur at only at very low levels of opposing wall taper angles. The use of supplemental grooves on mesial and distal axial walls significantly improved both total surface area and rotational resistance.ConclusionsThe vertical wall taper angles, preparation heights, and supplemental grooves play a role in resistance form and restoration stability.