Edge Wall Research Articles

Chipping Resistance of Graded Zirconia Ceramics for Dental Crowns

A serious drawback of veneering porcelains is a pronounced susceptibility to chipping. Glass-infiltrated dense zirconia structures can now be produced with esthetic quality, making them an attractive alternative. In this study, we examined the hypothesis that such infiltrated structures are much more chip-resistant than conventional porcelains, and at least as chip-resistant as non-infiltrated zirconia. A sharp indenter was used to produce chips in flat and anatomically correct glass-infiltrated zirconia crown materials, and critical loads were measured as a function of distance from the specimen edge (flat) or side wall (crown). Control data were obtained on zirconia specimens without infiltration and on crowns veneered with porcelains. The results confirmed that the resistance to chipping in graded zirconia is more than 4 times higher than that of porcelain-veneered zirconia and is at least as high as that of non-veneered zirconia.

Mammography dosimetry using an in-house developed polymethyl methacrylate phantom

Phantom-based measurements in mammography are well-established for quality assurance (QA) and quality control (QC) procedures involving equipment performance and comparisons of X-ray machines. Polymethyl methacrylate (PMMA) is among the best suitable materials for simulation of the breast. For carrying out QA/QC exercises in India, a mammographic PMMA phantom with engraved slots for keeping thermoluminescence dosemeters (TLD) has been developed. The radiation transmission property of the developed phantom was compared with the commercially available phantoms for verifying its suitability for mammography dosimetry. The breast entrance exposure (BEE), mean glandular dose (MGD), percentage depth dose (PDD), percentage surface dose distribution (PSDD), calibration testing of automatic exposure control (AEC) and density control function of a mammography machine were measured using this phantom. MGD was derived from the measured BEE following two different methodologies and the results were compared. The PDD and PSDD measurements were carried out using LiF: Mg, Cu, P chips. The in-house phantom was found comparable with the commercially available phantoms. The difference in the MGD values derived using two different methods were found in the range of 17.5-32.6 %. Measured depth ranges in the phantom lie between 0.32 and 0.40 cm for 75 % depth dose, 0.73 and 0.92 cm for 50 % depth dose, and 1.54 and 1.78 cm for 25 % depth dose. Higher PSDD value was observed towards chest wall edge side of the phantom, which is due to the orientation of cathode-anode axis along the chest wall to the nipple direction. Results obtained for AEC configuration testing shows that the observed mean optical density (O.D) of the phantom image was 1.59 and O.D difference for every successive increase in thickness of the phantom was within±0.15 O.D. Under density control function testing, at -2 and -1 density settings, the variation in film image O.D was within±0.15 O.D of the normal density setting '0' and at +2 and +1 density setting, it was observed to be within±0.30 O.D. This study indicates that the locally made PMMA TLD slot phantom can be used to measure various mammography QC parameters which are essentially required for better outcomes in mammography.

TH-E-220-11: Proton Radiography in Scattered Proton Fields

Purpose: Proton imaging is very sensitive to changes in water equivalent pathlength (WEPL), and can therefore differentiate soft tissues from target volumes. Most systems under development today use pencil beam with detector grids for path and energy determination. We explored a novel method for proton imaging by taking advantage of the time-resolved dose rate of a scattered proton beam produced by passive scattering systems with a cyclical range-modulator. Methods: We show that for such system with the modulator spinning at a constant speed, the WEPL can be determined along any ray by measuring the time-resolved dose rate patterns at the ray endpoints on an imaging plane. If we use a beam with sufficient energy to pass through the patient and measure the dose rate function at points behind the patient, we can obtain a 2D image consisting of WEPLs. In order to simulate this effect, we implemented time-resolved dose calculations in our in-house proton dose-calculation framework and applied these to lung cancer cases. An AP beam was used with a proton range of 24 g/cm2 and the dose rate patterns in a plane right below the posterior skin of the patient were calculated. These patterns were used to determine the WEPL from the anterior to the posterior surfaces as an image of the tumor and the surrounding tissues. Results: The lung tumor volumes are easily identified in the resultant radiograph of WEPL. In addition, further processing of the patterns based on range mixing can enhance areas where WEPL changed rapidly, especially for the tumor edge and chest wall. The estimated dose for imaging is less than 0.5 cGy. Conclusions: Our method is rapid (∼100 ms) and simultaneous over the whole field, it can image mobile tumors without the problem of interplay effect inherently challenging for methods based on pencil beams.

Improving the design of a pickup head for particle removal using computational fluid dynamics

The purpose of this article is to optimize the design of a pickup head that removes particles from road surface. A validated computational fluid dynamics model was proposed to evaluate the particle removal performance of the designed pickup head with different inclination angles. The gas-particle flow through the pickup head was modelled using the EulerianLagrangian approach. The realizable k model and the discrete particle model were adopted to simulate gas flow field and solid particle trajectories, respectively. The results indicate that the inclination angle of the rear edge wall and the pressure drop across the pickup head have great impact on the particle removal performance. Both the particle overall removal efficiency and the grade efficiency increase with the increment of inclination angle, and higher pressure drop can pick up more particles from the road surface, but it would induce unnecessary energy consumption. Therefore, it is necessary to design a pickup head with high removal efficiency and low pressure drop. Through simulation, the optimal angle should be 135 for the range of the inclination angle in this study, and pressure drop is about 2400Pa. Furthermore, more information can be acquired for pickup head design.

Simulation of two regime sodium flows in a parallel plate channel during buoyancy-driven flow

Due to the remaining decay heat, the reactor core has yet to be cooled after shutdown. As the reactor power is low, the core can be sufficiently cooled by natural convection. The coolant flow is driven by buoyancy, as the heated fluid decreases its density. During buoyancy-driven flow, a reverse flow may take place when a heat sink exists close to the heat source, such as in a wall (edge) or corner subchannels. For simplicity in applying boundary condition, the reverse flow is simulated by two parallel plates, one as a heat source having positive heat flux and the other as heat sink with negative heat flux.

Dust technologies for magnetic fusion

Interaction of dust particles with magnetic fusion plasmas opens new opportunities in the field of fusion technology. This study considers using the dust jets for emergency tokamak discharge quench and SOL/wall control. For the emergency quench, a large amount of dust in a kilogram range can be produced and injected in one or sequential shots. For wall conditioning and edge plasma control in tokamaks and stellatators, the amount of injected particles is comparable with the fueling rate. The contemporary tokamaks are compatible with injection of tens or hundreds of milligrams per second, while a few grams per second are acceptable for reactors.

Studies of mobile dust in scrape-off layer plasmas using silica aerogel collectors

Dust capture with ultralow density silica aerogel collectors is a new method, which allows time resolved in situ capture of dust particles in the scrape-off layers of fusion devices, without substantially damaging the particles. Particle composition and morphology, particle flux densities and particle velocity distributions can be determined through appropriate analysis of the aerogel surfaces after exposure. The method has been applied in comparative studies of intrinsic dust in the TEXTOR tokamak and in the Extrap T2R reversed field pinch. The analysis methods have been mainly optical microscopy and SEM. The method is shown to be applicable in both devices and the results are tentatively compared between the two plasma devices, which are very different in terms of edge plasma conditions, time scale, geometry and wall materials.

The influence of three-dimensional stochastic magnetic boundaries on plasma edge transport and the resulting plasma wall interaction

The three-dimensional (3D) features of plasma edge profiles and wall interaction patterns induced by edge resonant magnetic perturbation fields (RMP) are discussed comparing TEXTOR and DIII-D. We show that the scrape-off layer (SOL) profiles and decay lengths depend the edge safety factor, the RMP base mode as well as on the plasma rotation during RMP application indicating modification of SOL transport by the 3D perturbation fields. This is compatible with channelling of particle and heat efflux along open perturbed field lines in the very edge of the plasma boundary into a completely re-arranged, helically striated 3D divertor footprint. The distribution of the measured divertor heat and particle fluxes at DIII-D match the vacuum modelled magnetic footprint topology in L-mode while in H-mode the striation width exceeds the modelled footprint width by 15–30%. This 3D structure of the measured heat and particle fluxes results in a new situation for the material erosion properties and initial quantification of the net-erosion within the 3D footprint shows in L-mode a 50% decrease of the chemical erosion yield and evidence for a comparably small 15-20% increase in physical sputtering. Extrapolation of these findings to ITER by vacuum modelling of the magnetic footprint for the actual ELM control coils shows a similar vacuum magnetic footprint topology as found at DIII-D during RMP ELM suppression. However, the open field lines escape the CFC covered ITER divertor area potentially transferring net-erosion characteristics from the CFC domain onto the Tungsten including so far unconsidered heat and particle loads on this sensitive material.

Mean out-of-plane dynamic plateau stresses of hexagonal honeycomb cores under impact loadings

Double-walled hexagonal honeycomb cores (DHHCs) are important cushioning materials and their out-of-plane impact properties depend upon their configuration parameters and impact velocities. In this paper, the reliable finite element (FE) model by using ANSYS/LS-DYNA was designed to investigate the relations between configuration parameters of DHHCs and their out-of-plane dynamic plateau stresses at the impact velocities from 3 to 350 m/s. FE simulations demonstrate, when all configuration parameters are kept constant, mean out-of-plane dynamic plateau stresses are related to impact velocities by conic curves. For a given impact velocity, mean out-of-plane dynamic plateau stresses are related to the ratios between cell wall thickness and edge length and to edge length ratios by power laws. There are complicated relations between mean out-of-plane dynamic plateau stresses and expanding angels, which are discussed in detail. Many empirical expressions on mean out-of-plane dynamic plateau stresses of DHHCs are suggested.

Evidence for a Greater Elevation in Vascular Shear Stress after Morning Exercise

The vascular endothelium plays an important role in the maintenance of vascular health and the modulation of vascular tone and blood pressure. Recently, it has been demonstrated that blood pressure reactivity to physical activity is greater in the morning, and possibly, diurnal variation in vascular function may also be evident. The aim of this study was to assess vascular responses after exercise at different times of day. After 45 min of supine rest, 12 male normotensives completed a 30-min bout of cycling at 70% peak oxygen uptake beginning on separate days at 0800 and 1600 h. Edge detection and wall tracking of high-resolution arterial B-mode ultrasound images combined with synchronized Doppler waveform analysis were used to measure brachial and femoral conduit artery diameter and to calculate blood flow and shear rate. Measurements were recorded before and 20 min after exercise. At 5 min after exercise, the mean +/- SE brachial shear rate was 72 +/- 21 arbitrary unit (AU) higher in the morning compared with the afternoon (P = 0.05), but this was not compensated for by enlargement of arterial diameter (P = 0.59). No diurnal variation was observed in the femoral artery measurements. Diurnal difference in conduit artery regulatory control manifests as an elevated intravascular shear stress after morning exercise. Potentially, higher postexercise shear rate in the morning in at-risk individuals could contribute to the elevated cardiovascular risk evident in the postwaking hours.

Brachial Artery Blood Flow Responses to Different Modalities of Lower Limb Exercise

Cycling is associated with a reproducible systolic anterograde and diastolic retrograde flow pattern in the brachial artery (BA) of the inactive upper limb, which results in endothelial nitric oxide (NO) release. The purpose of this study was to examine the impact of different types and intensities of lower limb exercise on the BA flow pattern. We examined BA blood flow and shear rate patterns during cycling, leg kicking, and walking exercise in 12 young subjects (24 +/- 3 yr). BA diameter, blood flow, and shear rate were assessed at baseline (1 min) and at three incremental intensity levels of cycling (60, 80, and 120 W), bilateral leg kicking (5, 7.5, and 10 kg), and walking (3, 4, and 5 km x h(-1)), performed for 3 min each. Edge detection and wall tracking of high-resolution B-mode arterial ultrasound images, combined with synchronized Doppler waveform envelope analysis, were used to calculate conduit artery diameter and anterograde/retrograde blood flow and shear rate continuously across the cardiac cycle. BA mean blood flow and shear rate increased significantly throughout each exercise protocol (P < 0.001), and BA anterograde blood flow and shear rate showed comparable increases throughout each protocol (P < 0.001). Retrograde blood flow and shear rate, however, demonstrated a significant increase during cycling and walking (P < 0.001) but not during leg kicking. Rhythmic lower limb exercise (cycling and walking) results in an increase in BA systolic anterograde blood flow and shear rate, directly followed by a large retrograde flow and shear rate. This typical pattern, previously linked with endothelial NO release, is not present during a different type of exercise such as leg kicking.

Strain and hardness distributions in the cup wall drawn with ironing of 3004-H19 aluminum alloy sheets

The strain and hardness distributions in the drawn cup walls of the cold rolled 3004 aluminum alloy sheet were measured and discussed on the anisotropy and the effect of simultaneous wall ironing during cup drawing. The thickness strain in the cup wall is large along the TD direction of the sheet and is small along the RD direction. This phenomenon is considered to be corresponding to the anisotropy of r value in the cold rolled 3004 aluminum alloy sheet. In RD direction, the ears grow up at the cup wall edge because of the large radial strain balanced with small thickness strain. The sizing work that means ironing a part of the thicker cup wall tends to unify the distributions of thickness strain, and then the ears at the edge of cup wall become to be small. The hardness of the cup wall decreases by drawing to less than the material, and the hardness drop seems to be remarkable especially in TD direction where the thickness strain is large and the sizing work is heavy. The cause of hardness drop is considered to be due to the change of work hardened metal structure that depends on the additive strain through the complex different strain passes during cup drawing.

Does arterial shear explain the magnitude of flow-mediated dilation?: a comparison between young and older humans

Flow-mediated dilatation (FMD) has become a commonly applied approach for the assessment of vascular function and health in humans. Recent studies emphasize the importance of normalizing the magnitude of FMD to its apparent eliciting stimulus, the postdeflation arterial shear. However, the relationship between shear stress and the magnitude of FMD may differ between groups. The aim of this study was to examine the relationship between the brachial FMD and four different indexes of postdeflation shear rate (SR) in healthy children (n = 51, 10 +/- 1 yr) and young (n = 57, 27 +/- 6 yr) and older (n = 27, 58 +/- 4 yr) adults. SR was calculated from deflation (time 0) until 9 s (peak), 30 s (0-30), 60 s (0-60), or until the time-to-peak diameter in each individual (0-ttp). Edge detection and wall tracking of high resolution B-mode arterial ultrasound images were used to calculate the conduit artery diameter. In young adults, the brachial artery FMD demonstrated a significant correlation with the area under the SR curve (SR(AUC)) 0-30 s (r(2) = 0.12, P = 0.009), 0-60 s (r(2) = 0.14, P = 0.005), and 0-ttp (r(2) = 0.14, P = 0.005) but not for the peak SR(AUC) 0-9 s (r(2) = 0.04, P = 0.12). In children and older adults, the magnitude of the brachial artery FMD did not correlate with any of the four SR(AUC) stimuli. These findings suggest that in young subjects, postdeflation SR(AUC) correlates moderately with the magnitude of the FMD response. However, the relationship between FMD and postdeflation shear appears to be age dependent, with less evidence for an association in younger and older subjects. Therefore, we support presenting SR(AUC) stimuli but not normalizing FMD responses for the SR(AUC) when using this technique.

Heterogeneity in conduit artery function in humans: impact of arterial size

To determine whether conduit artery size affects functional responses, we compared the magnitude, time course, and eliciting shear rate stimulus for flow-mediated dilation (FMD) in healthy men (n = 20; 31 +/- 7 yr). Upper limb (brachial and radial) and lower limb (common and superficial femoral) FMD responses were simultaneously assessed, whereas popliteal responses were measured in the same subjects during a separate visit. Glyceryl trinitrate (GTN)-mediated responses were similarly examined. Edge detection and wall tracking of high-resolution B-mode arterial ultrasound images, combined with synchronized Doppler waveform envelope analysis, were used to calculate conduit artery diameter, blood flow, and shear rate continuously across the cardiac cycle. Baseline artery size correlated inversely with the FMD response (r = -0.57, P < 0.001). Within-artery comparisons revealed a significant inverse correlation between artery size and FMD% for the radial (r = -0.66, P = 0.001), brachial (r = -0.55, P = 0.01), and popliteal artery (r = -0.48, P = 0.03), but not for the superficial and common femoral artery. Normalization of FMD responses for differences in eliciting shear rate did not abolish the between-artery relationship for artery function and size (r = -0.48, P < 0.001), suggesting that differences between artery function responses were not entirely due to size-related differences in shear rate. This was reinforced by a significant between-artery correlation for GTN responses and baseline artery size (r = -0.74, P < 0.001). In summary, systematic differences exist in vascular function responses of conduit arteries that differ in size. This raises the possibility that differences in artery size within or between individuals may influence functional responses.

The impact of baseline diameter on flow-mediated dilation differs in young and older humans

Flow-mediated dilation (FMD) has become a commonly applied approach for the assessment of vascular function and health, but methods used to calculate FMD differ between studies. For example, the baseline diameter used as a benchmark is sometimes assessed before cuff inflation, whereas others use the diameter during cuff inflation. Therefore, we compared the brachial artery diameter before and during cuff inflation and calculated the resulting FMD in healthy children (n=45; 10+/-1 yr), adults (n=31; 28+/-6 yr), and older subjects (n=22; 58+/-5 yr). Brachial artery FMD was examined after 5 min of distal ischemia. Diameter was determined from either 30 s before cuff inflation or from the last 30 s during cuff inflation. Edge detection and wall tracking of high resolution B-mode arterial ultrasound images was used to calculate conduit artery diameter. Brachial artery diameter during cuff inflation was significantly larger than before inflation in children (P=0.02) and adults (P<0.001) but not in older subjects (P=0.59). Accordingly, FMD values significantly differed in children (11.2+/-5.1% vs. 9.4+/-5.2%; P=0.02) and adults (7.3+/-3.2% vs. 4.6+/-3.3%; P<0.001) but not in older subjects (6.3+/-3.4% vs. 6.0+/-4.2%; P=0.77). When the diameter before cuff inflation was used, an age-dependent decline was evident in FMD, whereas FMD calculated using the diameter during inflation was associated with higher FMD values in older than younger adults. In summary, the inflation of the cuff significantly increases brachial artery diameter, which results in a lower FMD response. This effect was found to be age dependent, which emphasizes the importance of using appropriate methodology to calculate the FMD.

Tension, compression and shear fatigue of a closed cell polymer foam

A closed cell foam of polymetacrylimide (Rohacell) with three different densities is studied. The foam is tested quasistatically in tension, compression and shear. The tensile properties scale very well with the relative density of the foam, but the compression and shear properties do not scale the same way. It is believed to be due to cell edge and cell wall buckling being the dominated deformation mechanism in compression and shear for lower densities that does not occur for higher densities. Fatigue testing is then performed in tension, compression and shear. It is seen that for all load cases and densities, the fatigue life can be plotted using Basquin’s law. The results also show that the different failure mechanisms found in the static tests are the same in fatigue. This means that the fatigue life for different load types exhibit different failure mechanisms. This shows not only as a clear difference in the stress levels for fatigue failure, but also on the slope in the fatigue life relation.

Experimental study on fabricating Ni-Cr alloy coping with laser rapid forming

To probe the feasibility of fabricating Ni-Cr alloy coping with laser rapid forming (LRF). The digitalized model of coping was designed using the technology of reverse engineering and computer aided design (CAD) based on the abutment. The Ni-Cr alloy coping was fabricated with LRF. The gaps between the internal surface of coping and the external surface of abutment were measured respectively at the locations of occlusal surface edge, midpoint of axial wall and shoulder edge. The results were compared with the reference of 120 microm which was accepted generally to analyze the adaptation by statistical means. With statistical analysis of the t-test, the mean of gap width of each group, (82.60 +/- 13.58) microm for group A, (45.80 +/- 16.12) microm for group B, and (57.90 +/- 9.04) microm for group C, was less than 120 pm and the differences were statistically significant (t(A) = 8.71, t(B) = 14.56, t(C) =21.72, P <0.05). The Ni-Cr alloy coping with a thickness of 0.8 mm can be fabricated with LRF successfully and the adaptation can meet the reference of 120 microm.

Prenatal diagnosis of varix of the fetal intraabdominal umbilical vein: Case report

Varix of intraabdominal part of fetal umbilical vein is during a prenatal ultrasound scan seen as a hypoechogenic mass between anterior abdominal wall and lower edge of liver, and the diagnosis is confirmed when blood flow is seen during color Doppler examination. A case of prenatal diagnosis of this abnormality is presented, with review of contemporary literature regarding diagnosis and management as well as the outcome of such pregnancies.

A Monte Carlo Model for Energy Spectra Analysis in Dedicated Nuclear Breast Imaging

A Monte Carlo model for dedicated nuclear breast imaging was developed using the Monte Carlo N-particle (MCNP) code. The modeled gamma camera was the LumaGem 3200s system, which comprised a 96 times128 array of cadmium zinc telluride (CZT) elements with 1.6 times 1.6 mm2 and was equipped with a high sensitivity collimator. The patient model consisted of an 800-mL breast compressed to a thickness of 5.5 cm and an adjacent 8000-mL torso containing compartments modeling the liver and heart. Energy spectra from patients were acquired to determine an average patient energy spectrum. A phantom simulation was performed to determine the activity concentration in liver and heart regions versus the torso cavity and breast that produced an energy spectrum most closely matching the average patient spectrum. The Monte Carlo simulation was performed to simulate the energy spectra and breast images acquired from patient studies. The simulation allowed changes in intrinsic energy resolution of the detector and energy window. A correction to model the tailing effect in the CZT was also developed. The spectral components and their contribution to the energy windowed image were examined and the effect of changes in energy resolution on tumor contrast was determined. Results showed that 13-19% of counts in the breast image are scattered events (primarily first order Compton) and scatter from the torso region accounts for less than 4% of counts in the breast image for energy resolutions between 3.9-20%. Events from the torso are concentrated at the chest wall edge of the detector's field of view, consequentially decreasing tumor contrast in this area. Because of low overall scatter in the breast, changes in energy resolution were found to have minimal effect on tumor contrast.

회전하는 매끈한 정삼각 유로 내 열/물질전달 분포 측정

The present study investigated the heat/mass transfer characteristics in an equilateral triangular channel simulating the leading edge cooling passage in gas turbine blade. Using naphthalene sublimation method and pressure measurement experiments, local mass (heat) transfer and pressure coefficients were obtained. The experiments were conducted with three rotating numbers between 0.0 and 0.1; two channel orientations of 0°? (model A) and 30°? (model B); the fixed Reynolds number of 10,000. The results showed that the channel rotation caused the heat transfer discrepancy between suction and pressure sides. Due to the secondary flow induced by Coriolis force, the high heat transfer appeared on the pressure side. When the channel orientation was 30°? (model B), the secondary flow caused the more uniform heat transfer distribution among leading edge and inner wall on pressure side than that of the model A.