Mean Shear Research Articles

Comparison of the Adhesive Strength of Universal Systems with and without MDP on Dentin by Microblading

In dentistry today, evaluating adhesive strength is crucial for successful treatment with universal adhesive systems. This article evaluates the adhesive resistance to dentin micro bleaching of two universal adhesive systems with and without MDP. For this purpose, third molars (n=40), divided into two groups, were used without occlusal enamel using a low-speed bioactive diamond disc with cooling up to 4mm above the amelocemental line. The universal adhesive system with MDP was applied for group 1 (n=20), and the universal adhesive system without MDP for group 2 (n=20). A standardized resin cylinder of 2mm in diameter and 4mm in height was made for both groups using a silicone mold, placing it on the occlusal surface. Each group was divided into two subgroups, where (n=10) were subjected to thermocycling and (n=10) were not subjected to thermocycling, to subsequently perform the micro-shearing test using the Shimadzu AGS-X Universal Testing Machine. The data were analyzed by ANOVA test, stating that the groups with MDP showed significantly higher micro-shear values than those without MDP. This shows that the MDP group's mean shear load value of the resin cylinders is higher than that in the non-MDP group.

Evaluation of Ultrasound Based Point Shear Wave Elastography for Diagnosis of Inflammatory Pancreatic Diseases

Introduction: A variety of imaging techniques exists for the diagnosis of pancreatic disorders. None of the broadly accepted diagnostic methods, uses elasticity as an indicator of tissue damage. A well-known fact is that pathological changes influence tissue stiffness and elasticity. US elastography in its different modalities has been widely used for evaluation and characterization of multiple abdominal structures. Point Shear Wave Elastography (pSWE) particularly has been reported to be highly effective in various clinical diagnostic applications. However, data on the role of pSWE in a deep-seated organ like pancreas is scarce. Objective: To prospectively assess the diagnostic value of abdominal US elastography in the form of point shear wave elastography (pSWE) in characterizing and differentiating between normal pancreatic parenchyma and chronic pancreatitis. To establish a cut off value for the diagnosis of chronic pancreatitis. To investigate the influence of certain independent variables and the severity of pancreatitis on the acquired results. Patients Twenty five patients diagnosed with chronic pancreatitis who visited the Department of Gastroenterology in University Hospital Kaspela, between December 2020 and August 2021, for diagnosis and/or treatment and twenty eight individuals with no evidence of pancreatic disorder, admitted at the hospital during the same period of time, were included in the study. Based on the clinical symptomatic criteria, diagnostic imaging and histological findings, patients were divided into chronic pancreatitis (CP) and healthy pancreatic parenchyma group. Methods: The ultrasound based point Shear Wave Elastography (pSWE) imaging techniques were applied. A total of five measurements was obtained in each segment of the gland. The depth of region of interest (ROI) was also recorded. Design Prospective single-center study. Results: The mean shear wave speed (SWS) values of the entire pancreatic parenchyma were 1.71m/s, 1.15m/s for the chronic pancreatitis and the normal pancreatic parenchyma respectively. With a cut off value of 1.43m/s, sensitivity (Se), specificity (Sp), positive predictive value (PPV), negative predictive value (NPV) and accuracy (Ac) of 89.7%, 95.2%, 94.59%, 90.91% and 92.59% respectively were calculated for the diagnosis of chronic pancreatitis. Neither the independent variables researched, nor the severity of disease, defined according to the Cambridge score, proved to have statistically significant reflection on the SWS in patients with CP. Conclusion: pSWE established considerably higher SWS in patients with chronic pancreatitis, therefore it may be successfully adopted as a diagnostic modality in patients with chronic inflammatory pancreatic disorders. External factors have minor effect on the results obtained, suggesting that the technique is highly objective. High SWS were obtained both in patients with discrete structural abnormalities (Cambridge 2) and advanced forms of pancreatitis (Cambridge 4), which points that pSWE may be utilized as differential diagnostic method in cases in which other imaging techniques provide equivocal and inconclusive results.

Revised mixing coefficient scaling for sheared stably stratified turbulence

We revisit and extend the turbulent Froude number ( $Fr_k$ ) scaling for the mixing coefficient ( $\varGamma$ ) introduced by Garanaik & Venayagamoorthy (GV) (J. Fluid Mech., vol. 867, 2019, pp. 323–333) by directly incorporating the effects of mean shear through the non-dimensional shear parameter $S_{\ast } = S k/\epsilon _k$ . For flows where the effects of mean shear are stronger than the background vertical stratification, we find $\varGamma \sim Fr_k^{-2} S_\ast ^{-1}$ for weakly stratified sheared turbulence and $\varGamma \sim Fr_k^{-1}S_\ast ^{-1}$ for moderately stratified sheared turbulence. The scaling procedure is inconclusive for strongly stratified sheared turbulence, but using two independent datasets of homogeneous, sheared, stably stratified turbulence, we empirically observe $\varGamma \sim Fr_k^{-0.5} S_\ast ^{-1}$ . Our revised scaling better collapses both datasets compared with the original GV scaling, and we note that the moderately stratified sheared regime is extremely narrow (or maybe even non-existent). We also apply our scaling to the time-varying open channel simulations of Issaev et al. (J. Fluid Mech., vol. 935, 2022) and observe $\varGamma \sim Fr_k^{-2}S_\ast ^{-1}$ for weakly stratified sheared turbulence, but we observe deviations from our revised scaling for moderate and strong stratifications due to time-varying mean shear and vertical transport. Finally, we apply our revised scaling to field measurements of Conry, Kit & Fernando (Environ. Fluid Mech., vol. 20, 2020, pp. 1177–1197) and observe $\varGamma \sim Fr_k^{-2} S_\ast ^{-1}$ . We emphasize that our revised scaling is applicable only for stably stratified, vertically sheared turbulence with weak spatio-temporal variations of the mean shear and stratification, and we expect different scaling to apply when additional effects such as depth-varying radiative heating/cooling are present or when the orientation of the mean shear relative to the gravity vector is modified (e.g. horizontal shear).

Shear wave elastography for differentiating parathyroid neoplasms with malignant diagnosis or uncertain malignant potential from parathyroid adenomas: initial experience

ObjectiveParathyroid carcinoma (PC) and atypical parathyroid tumor (APT) are rare parathyroid disorders carrying the risk of recurrence of varying degrees. This study aims to explore the value of 2D-shear wave elastography (SWE) in the discrimination of PC/APT among suspicious parathyroid lesions.Methods and materialsIn this prospective study, patients with primary hyperparathyroidism and suspicious parathyroid lesions on ultrasonography (US) were recruited. All the lesions were assessed by SWE before surgery. The velocity (m/s), Young’s modulus (Kpa), and elastogram of SWE were compared between pathologically proven parathyroid carcinoma or atypical parathyroid tumor (Group1) and parathyroid adenoma (Group2). All the SWE parameters were displayed at the setting of 50 or 70 kPa. Correlations between SWE and the lesion size as well as biochemical parameters were analyzed.Results36 target lesions were enrolled for analysis. The mean shear wave velocity (SWV) between the two groups was 2.4 m/s vs 1.9 m/s, respectively, while the mean Young’s modulus was 11.1 kPa vs 18.2 kPa, respectively. The cut-off values are 2.35 m/s and 17.05 kPa correspondingly. The sensitivity and specificity of the selecting cut-off values were 0.56 vs 0.63 and 0.95 vs 1.0 (area under the curve [AUC]: 0.813 vs 0.852 [95% confidence interval (CI): 0.669–0.956 vs 0.720–0.983]; p < 0.001, p < 0.001; respectively). In contrast, the max SWV and Young’s modulus showed a better sensitivity of 0.75 and 0.81, respectively. The “colored lesion” and “stiff rim” patterns on the elastogram are more indicated in parathyroid carcinoma and atypical parathyroid tumor, whereas the negative elastogram prevails in parathyroid adenoma. The SWV and Young’s modulus of the parathyroid lesions were independent of the tumor size, but the max SWV and Young’s modulus slightly correlated with serum parathyroid hormone concentration (PTH) (r = 0.398, p = 0.016; r = 0.396, p = 0.017).Conclusions2D-shear wave elastography plays a useful role in the preoperative assessment of parathyroid lesions with suspicious malignancy. The mean SWV and Young’s modulus are advised as the favored diagnostic parameter with the best AUC and excellent specificities, while the max SWV and Young’s modulus are more sensitive to distinguish the PC and APT compared with other parameters.

Evaluation of shear bond strength of high molecular chitosan nanoparticle incorporated heat polymerized polymethyl methacrylate denture base resin with acrylic resin teeth: An in-vitro study

The present study is conducted to evaluate the shear bond strength of acrylic resin denture teeth to high molecular chitosan nanoparticle incorporated heat polymerized polymethylmethacrylate denture base resin. This comparative study is performed at the Department of Prosthodontics and Crown & Bridge, JSSDCH, Mysuru. 45 samples of acrylic resin blocks of size 8 × 10 × 20 mm were fabricated using mold such that the long axis of crosslinked acrylic resin maxillary central incisor teeth is aligned at 45° to the long side of the specimen to which the ridge lap surface is attached. Among these, 15 samples belong to the control group, 15 samples to the 0.5 % chitosan gel incorporated group, and the remaining 15 samples to the 1 % chitosan gel incorporated group. The test specimens were then subjected to a failure load test using the universal testing machine. The readings were tabulated and statistically analyzed using Mean, Standard deviation, Independent t-test, - way and two-way ANOVA, and Scheffes’ Post hoc test. The statistical analysis reveals that the mean bond strength of acrylic denture teeth to conventional heat cure PMMA denture base material increased from 4.6627 ± 0.54198 MPa to 7.5186 ± 0.57461 MPa and 8.9356 ± 0.63675 MPa upon addition of chitosan at 0.5 % and 1 % concentration, respectively. It can be concluded that The mean shear bond strength of acrylic denture teeth to conventional heat cure PMMA denture base material increased with the addition of chitosan at 0.5 and 1 % concentration. The best shear bond strength was observed with the addition of 1 % chitosan as per the evidence.

Comparison of fetal and maternal tissue elasticity between euploid and aneuploid pregnancies by shear wave elastography.

B-mode ultrasonography utilized for fetal screening of common trisomies is referred to as a genetic sonogram and includes determining major abnormalities and soft markers such as hypoplastic nasal bone and increased thickness of the nuchal fold. Elastography is a novel ultrasound technique giving information about tissue stiffness used for diagnosing cancer, transplant rejection, and organ fibrosis. This study aimed to determine via shear wave elastography (SWE) whether euploid and aneuploid fetal soft marker tissues vary in stiffness. The participants were all singleton pregnancies between 19 and 23 weeks of gestation; 35 euploid and 14 aneuploid fetus pregnancies were enrolled. Fetal bowel, kidney, liver, nasal bone, nuchal fold, placenta, and myometrium were investigated with SWE using acoustic radiation impulse force. Images were analyzed with a novel software calibrated and written by us using MATLAB. Statistical analysis was completed with the SPSS Program. Shapiro-Wilk normality distribution analysis, Student's t-test, and Mann-Whitney U methods were used. The mean shear wave speed of fetal nasal bone was significantly lower in aneuploid fetuses. There was no difference between other tissues in mean shear wave velocity. Euploid and aneuploid fetuses have different elastic properties of the nasal bone and this may have a role in differentiating aneuploid fetuses noninvasively.

EVALUATION OF THE USEFULNESS OF SHEAR WAVE ELASTOGRAPHY IN THE DIAGNOSTIC PROCESS FOR NONCANCEROUS SOFT TISSUE MASSES

Current study was carried out to assess efficacy of SWE as an adjunct to sonography in investigating superficial benign lesions. The retrospective study was conducted in Radiology department of Nishtar Medical Hospital from July 2021 to July 2022. The study included 45 patients with 49 lesions. Doppler and grayscale ultrasound and SWE was performed. Conventional ultrasonic features like depth (mm), size (mm), margin (ill defined or well defined), vascularity (present or absent) and echogenicity (isoechoic, anechoic, hyperechoic or hypoechoic) were investigated. Median shear modulus and ultrasonic features were documented. Mean shear modulus for epidermoid, ganglion and lipomatous cyst was 23.6kPa, 5.9kPa and 9.1kPa respectively. Difference between lipomatous tumors, ganglion cysts and epidermoid cysts were significant (P=0.018). Median shear modulus of epidermoid cyst was higher than ganglion cysts and lipomatous tumors. Shear wave elastography is valuable modality for diagnosis of superficial benign soft tissue masses through direct quantitative analysis.

DNS analysis of turbulence modulation by lean premixed prevaporized spray flames in a model combustor

Turbulence modulation by lean premixed prevaporized (LPP) spray flames, which involve droplet motion, evaporation and gaseous reaction, is complicated and essential to organizing clean and efficient combustion. Direct numerical simulations of LPP combustion in a model swirling combustor under high pressure of 20 bar are performed. The gaseous flow is solved in the low-Mach-number limit, and the droplets are tracked as two-way coupled Lagrangian particles. The corrected infinite thermal conductivity model is adopted to describe droplet evaporation, and a reduced two-step kerosene/air chemistry mechanism is used to present combustion. Four cases, i.e., a non-reacting gaseous flow, a non-reacting spray flow and two reacting spray flows with different droplet sizes, are conducted to cover key features of LPP flame on turbulence modulation. The results show that the spray combustion significantly depresses the mean axial velocity on the centerline in the upstream, indicating an enhancement of the inner recirculation zone. The influence of droplets on the mean and fluctuating velocities is generally negligible except on the azimuthal modulation, while combustion can increase the velocities, which is more evident in downstream due to the pressure effect. In reacting cases, the turbulent kinetic energy (TKE) spectra in the shear layers reduce at high wavenumbers, reflecting the combustion-induced dissipation at small scales (below the laminar flame thickness scale). Besides, droplet evaporation can introduce energy at small scales while this modulation is balanced by combustion. Moreover, TKE budget analysis indicates that spray combustion mainly depresses the TKE and redistributes mean shear along the radial direction. Heat release increases the local fluid viscosity, depresses local turbulent transport, and increases viscous dissipation. Finally, the vortex stretching analysis shows that LPP combustion enhances the alignment with the intermediate strain rate component.

Comparative evaluation of shear bond strength of two different GICs in pediatric dentistry

Background: New restorative materials and techniques continue to appear in the market, the knowledge of which is required, to make an informed decision on the most suitable successful and cost effective treatment strategy. Aim: To compare and evaluate the Shear bond strength of different glass ionomer cements used in Pediatric dentistry. Materials and Methods: 60 Premolars were taken which were extracted due to orthodontic reasons. The extracted teeth were cleaned with a disinfectant and stored in distilled water at room temperature until further use. The teeth were divided into five groups: Group A: Anhydrous GIC, Group B: Giomer. All the samples were then subjected to shear bond strength test using universal testing machine. The data collected was tabulated and statistically analyzed using Anova one way test followed by tukey post Hoc HSD test using SPSS 16.0 software. Results: The Mean Shear bond strength was found to be maximum for Group B (Giomer) i.e. 2.90±0.55. Conclusion: Research and technology has revolutionized dental procedures. This revolution has occurred at such a rapid pace that it has become almost over whelming to the clinician who must take decision based on combination of experience and current trends.

Suppression of the turbulent kinetic energy and enhancement of the flame-normal Reynolds stress in premixed jet flames at small Lewis numbers

We report the effects of the Lewis number on the turbulent kinetic energy, Reynolds stresses, and scalar fluxes in premixed jet flames with strong mean shear. The direct numerical simulation (DNS) of piloted turbulent premixed jet flames is performed under the same condition except for different Lewis numbers to isolate the Lewis number effects. The turbulence intensity within the mean flame brush is found to decay more rapidly along the axial distance with a smaller Lewis number. This Lewis number dependence results from the coupling of the mean shear and the combustion heat release, where the mean shear is the primary source of turbulence production. We show that, under the strain imposed by the mean shear and turbulence fluctuation, the heat release of premixed jet flames is significantly enhanced at the Lewis number smaller than unity, which is represented by the rising flamelet consumption speed and flame surface area. As a consequence, the mean shear within the flame brush is suppressed at small Lewis numbers via the dilatation effect, and the weakened mean shear production causes the fast turbulence suppression along the axial direction. The enhanced heat release at small Lewis numbers also increases the flame-normal Reynolds stress, and leads to the counter-Boussinesq behavior of the shear Reynolds stress and the counter-gradient transport of scalar fluxes. We model the Lewis number effects on local turbulence and scalar transport using the stretched laminar flame speed and thickness, and achieve overall good estimations of the flame-normal Reynolds stress and scalar transport at small Lewis numbers.

Clinical in-situ evaluation of the effect of rubber dam isolation on bond strength to enamel.

To evaluate the effect of rubber dam isolation on shear bond strength of two different adhesive systems to enamel. The mesial, distal, lingual, and vestibular enamel surfaces of thirty human third molars were prepared (total n= 120). A custom splint was made to fit a volunteer's maxilla, holding the specimens in place in the oral cavity. Four composite resin cylinders were bonded to each tooth with one of two bonding agents (OptiBond FL and Prime&Bond active) with or without rubber dam isolation. Shear bond strength was tested in a universal testing machine and failure modes were assessed. Significance level for statistical analyses was set at 5%. All pairwise comparisons revealed statistical differences (p< 0.05). The highest mean shear bond strength values were obtained in rubber dam experimental groups, regardless of the adhesive system. Group OptiBond FL with rubber dam presented the highest mean bond strength values. Fracture modes for specimens bonded without rubber dam isolation were adhesive and cohesive within enamel, while rubber dam experimental groups revealed only cohesive fractures. Absolute isolation with rubber dam increases bond strength to enamel, independent of the adhesive system. The three-step total-etch system OptiBond FL provided significantly higher bond strength values than Prime&Bond active under both experimental conditions. Rubber dam isolation has a significant effect on bond strengths to enamel, independent of the adhesive system. Its application is, therefore, advised whenever adhesive procedures are performed. A filled three-step etch-and-rinse adhesive performed superiorly, with or without rubber dam isolation, when bonding to enamel compared to an isopropanol-based universal adhesive.

The effect of smoking on quantification of aortic stiffness by ultrasound time-harmonic elastography

Smoking is a significant cardiovascular risk factor that causes stiffening of the central arteries, especially the aorta. While vessel stiffness can be determined indirectly by measuring pulse wave velocity, elastography allows image-based determination of vessel stiffness while at the same time providing information on vascular morphology. This study compares abdominal aortic wall stiffness as measured by ultrasound time-harmonic elastography (THE) in fifteen smokers and fifteen age-matched non-smoking controls without a history of cardiovascular disease. Smokers had a significantly higher abdominal aortic wall stiffness with a mean shear wave speed of 2.66 m/s (95% confidence interval (CI) 2.59–2.72 m/s) compared to 2.40 m/s (95% CI 2.34–2.47 m/s) (p < 0.01) in the group of non-smokers. All other baseline characteristics including aortic diameter showed no significant differences. Inter-rater variability was excellent with an intraclass correlation coefficient of 0.99 (95% CI 0.98–0.99). Our results show that THE is sensitive to subclinical stiffening of the aorta in young and middle-aged smokers even before morphological changes occur and may therefore has the potential to serve as a screening tool for early aortic abnormalities and longitudinal risk factors for cardiovascular health.

Evaluation of shear bond strength and adhesive remnant index of metal APC™ Flash-Free adhesive system: A comparative in vitro study with APC™ II and uncoated metal brackets

The aim of this in vitro study was to compare the shear bond strength (SBS) and the adhesive remnant index (ARI) of the metal APC™ Flash-Free adhesive system, the APC™ pre-coated adhesive system and a conventional uncoated system. One hundred eighty-six freshly extracted human premolars were randomly divided into 3 groups and bonded by a single operator. Group A/Control Group (60 teeth): the manual bonding group treated with Transbond™ XT Light Cure Adhesive Paste (3M™ Unitek). Group B (60 teeth): treated with APC™II metal maxillary premolar precoated brackets. Group C (66 teeth): treated with metal maxillary premolar APC Flash-Free brackets. The teeth were then stored in distilled water at 37̊C for 24hours, and five hundred cycles of thermocycling were performed. The Shear Bond Strength (SBS) test was performed using an Instron Universal Testing Machine, and the adhesive remnant index (ARI) was determined using a dental optical microscope at ×25 magnification. The mean shear bond strength values showed differences between the three types of brackets (P=0.016; Anova). It was significantly higher with APC™II and lower with APC Flash-Free brackets; however, no significant differences were found between conventional and APC Flash-Free brackets (P-value=0.574). The distribution of the dichotomized ARI score was significantly different between the three brackets (P-value=0.049). The ARI score for APC Flash-Free brackets was higher with no significant difference between the conventional system and APC brackets (P-value=0.361). The mean SBS values were not significantly different between APC Flash-Free metal brackets and uncoated metal brackets. The APC Flash-Free metal system's bond failure occurred at the bracket-adhesive interface, with the highest percentage of teeth having more than 50% of the residual composite on the enamel after debonding.

Thoracolumbar fascia mobility and chronic low back pain: Phase 2 of a pilot and feasibility study including multimodal chiropractic care

BackgroundThoracolumbar fascia mobility observed with ultrasound imaging and calculated as shear strain is lower in persons with chronic low back pain. This pilot and feasibility trial assessed thoracolumbar shear strain in persons with chronic low back pain following spinal manipulation and over an 8-week course of multimodal chiropractic care.MethodsAdults self-reporting chronic low back pain ≥ 1 year participated between September 2019 and April 2021 in a trial using ultrasound imaging to measure thoracolumbar shear strain. Ultrasound imaging occurred 2–3 cm lateral to L2-3 while participants relaxed prone on an automated table moving the lower extremities downward 15 degrees, for 5 cycles at 0.5 Hz. Pain intensity on an 11-point numerical rating scale, disability, pain interference, and global improvement were also collected. Participants received 8-weeks of twice-weekly chiropractic care including spinal manipulation, education, exercise, self-management advice and myofascial therapies. Shear strain was computed using 2 methods. The highest shear strain from movement cycles 2, 3, or 4 was averaged over right and left sides for each participant. Alternately, the highest shear strain from movement cycle 3 was used. All data were analyzed over time using mixed-effects models. Estimated mean changes are reported.ResultsOf 20 participants completing 8-weeks of chiropractic care (female n = 11), mean (SD) age was 41 years (12.6); mean BMI was 28.5 (6.2). All clinical outcomes improved at 8-weeks. Mean (95% confidence interval) pain intensity decreased 2.7 points (− 4.1 to − 1.4) for females and 2.1 points (− 3.7 to 0.4) for males. Mean Roland–Morris disability score decreased by 5 points (− 7.2 to − 2.8) for females, 2.3 points (− 4.9 to 0.2) for males. Mean PROMIS pain interference T-score decreased by 8.7 points (− 11.8 to − 5.5) for females, 5.6 points (− 9.5 to − 1.6) for males. Mean shear strain at 8-weeks increased in females 5.4% (− 9.9 to 20.8) or 15% (− 0.5 to 30.6), decreasing in males 6.0% (− 24.2 to 12.2) or 2% (− 21.0 to 16.8) depending on computational method.ConclusionSpinal manipulation does not likely disrupt adhesions or relax paraspinal muscles enough to immediately affect shear strain. Clinical outcomes improved in both groups, however, shear strain only increased in females following 8-weeks of multimodal chiropractic care.Trial registration ClinicalTrials.gov registration is NCT03916705.

Laser-Assisted Micro-Solder Bumping for Copper and Nickel-Gold Pad Finish.

Flip-chip bonding is a key packaging technology to achieve the smallest form factor possible. Using copper as a direct under-bump metal and performing bonding under little force and at a low temperature eliminates the processing step for the deposition of a suitable wetting metal and offers an economical solution for electronic chip packaging. In this paper, various samples with copper and nickel–gold surface finishes are used to apply an in-house solder bumping, flip-chip bonding and reflow process to exhibit the bump-bond feasibility. Native oxides are reduced using process gases, and copper surface protection and solder wetting are achieved using copper formate. Lead-free 40 µm solder balls were bumped on 80 µm copper pads and 120 µm copper pillars to demonstrate a full intermetallic Cu–Cu bond as a base study for stacking applications. Using a low-force bonding technique, various chips with different dimensions were bonded at 0.5–16 MPa, followed by a reflow step at a maximum temperature of 270 °C. Then, 30 µm solder balls are utilized to bump the samples with NiAu and Cu bond pads at 50 µm pitch. A mean shear strength of 44 MPa was obtained for the 30 µm Cu samples. To the best of our knowledge, 30 µm solder bumping directly on the copper pads by producing copper formate is a novel research contribution.

The effects of flame orientation and mean shear on flame stretch in highly turbulent premixed flames using DNS

In the present work, direct numerical simulation data of a laboratory-scale high Karlovitz number (Ka) jet flame with a strong mean shear and a high Ka freely propagating planar flame without a mean shear were analyzed to explore the influence of flame orientation and mean shear on flame stretch in highly turbulent flames. Three flame fronts, i.e. the leading, in-plane and trailing front, were identified for the jet flame. The leading and trailing front is defined as the flame normal being facing the downstream and upstream regions, respectively, while the flame normal of the in-plane front is near the cross-stream plane. It was found that the flame stretch is positive in the leading front, and is negative in the trailing front of the jet flame. As for the planar flame, the statistics of the flame stretch are similar in various flame fronts. The components of the flame stretch are analyzed. The normal vector of the leading front is aligned with the most compressive strain rate in the jet flame, resulting in a large tangential strain rate, while the tangential strain rate of the trailing front is significantly lower. In contrast, the alignment characteristics and the strain rates of the planar flame are not sensitive to the flame orientation. The value of the stretch due to curved propagating flame front is large and negative in the trailing front of the jet flame due to the negative correlation between the displacement velocity and curvature, which is weak in the leading and in-plane front. The correlation between the displacement velocity and curvature is, however, similar in various fronts of the planar flame. Overall, it is suggested that the effects of flame orientation and mean shear should be accounted for in understanding turbulence-flame interactions in practical combustion devices.

The shear bond strength difference of 8th generation bonding on nanocomposite resin and nanohybrid composite resin

Composite resins are increasingly being used in dentistry, particularly as restorative materials. There are currently nanoscale composite resins, such as nanocomposite resins and nanohybrid composite resins. Composite resins with smaller particle sizes can produce more aesthetically pleasing fillings. The disadvantage of composite resin as a restorative material is that it cannot bond directly to the tooth structure, so bonding as an intermediate material is required. Nano-sized particles are used in eighth-generation bonding, which is expected to increase bond strength. A total of 24 maxillary premolars were selected and randomly divided into 4 groups. Six maxillary premolars were in each group. Group I was treated with the application of nanocomposite resin without a bonding material, group II was treated with the application of a nanohybrid composite resin without a bonding material, group III was treated with the application of nanocomposite resin with an eighthgeneration bonding material, and group IV were treated with the application of nanohybrid composite resin with an eighthgeneration bonding material. The mean shear bond strength was 0.16 MPa, 0.51 MPa, 2.30 MPa, and 3.00 MPa, respectively. In conclusion, the eighth-generation bonding material has a higher shear bond strength on nanohybrid composite resin than it does on nanocomposite resin

AN IN VITRO COMPARISION OF BOND STRENGTH OF PRECOATED AND UNCOATED BRACKETS USING SELF ETCHING PRIMER

Aim: To test the hypothesis that there is no significant difference in the shear bond strength and the adhesive remnant on the tooth after debonding between precoated and uncoated brackets using a self etching primer.Materials and Methods: Adhesive Pre Coated Plus brackets, Uncoated brackets, Transbond XT adhesive and Transbond Plus self etching primer (TPSEP) were used in this study. The brackets were bonded to intact human premolar teeth. All the samples were divided into two groups --Group 1 (Uncoated brackets + Transbond Self Etching Primer + Transbond XT) &amp; Group 2 (Adhesive Precoated Brackets + Transbond Self Etching Primer). Universal Testing Machine was used for calculating the shear bond strength of all samples. Image analysis equipment was used to measure the adhesive remnant on each tooth after debonding. Scanning Electron Microscope was used for this purpose.Results: Group 1 (Uncoated brackets + Transbond Self Etching Primer + Transbond XT) &amp; Group 2 (Adhesive Precoated Brackets + Transbond Self Etching Primer) had nearly equal mean shear bond strength which is 8.86 +2.14 Mpa for precoated while 9.08 + 2.76 Mpa for the uncoated group. Statistically both the groups have almost same shear bond strength and significant difference was absent. In percentage of adhesive remnant also statistical difference between group 1 &amp; group 2 was absent.Conclusion: There was no significant difference in the shear bond strength and the adhesive remnant on the tooth after debonding between precoated and uncoated brackets using a self etching primer.

Dynamics of mixing flow with double-layer density stratification: Enstrophy and vortical structures

Previous studies on stratified shear layers involving two streams with different densities have been conducted under the Boussinesq approximation, while the combined effect of stratified instability and mean shear in relation to multi-layer density stratification induced by scalar fields remains an unresolved fundamental question. In this paper, the shear-driven mixing flow involving initial double-layer density interfaces due to the compositional differences are numerically investigated, in which the mean shear interacts with Rayleigh–Taylor instability (RTI). Since its critical role in dynamics of shear layers and scalar transport, we focus on the evolution of entrophy and vortical structures. We find that the dynamics of mixing layers are determined by the mean shear and the distance between the initial density stratification. The mean shear and the Kelvin–Helmholtz instability dominate the evolution of shear layers at the initial stage. The increase in mean shear, therefore, is favorable for turbulent mixing, irrespective of effect of RTI. However, once the transition of turbulence occurs, the mean shear becomes weaker and RTI becomes prominent. This promotes the destruction of hairpin vortex and generation of vortex tube. In addition, the interaction of mean shear with RTI becomes weaker with increasing distance between initial density stratification. Furthermore, the viscous dissipation of enstrophy is larger than enstrophy production in the turbulent region due to the effect of RTI. The baroclinic term has the larger contribution in the turbulent region than near the turbulent/non-turbulent interface, which is different from the results of stably stratified flow under the Boussinesq approximation.

Sensitivity analysis on supersonic-boundary-layer stability: Parametric influence, optimization, and inverse design

Perturbations of flow control parameters may yield a significant alteration in the boundary layer stability. Based on the previously established parameter-associated sensitivity, the present work derives the optimal minor parameter perturbation analytically under the constraint of base flow energy variation. Specifically, the steady blowing-suction factor and the generalized Hartree parameter are examined at Mach number 4.5 to stabilize the mode S. Good agreement between the linear stability theory calculation, sensitivity theory, and Lagrangian approach is achieved for the optimal parametric state. The optimal state occurs if the contribution of the base velocity distortion has the greatest advantage over the temperature counterpart. Contributions of various physical sources to the growth rate behave similarly and collapse onto one correlation if normalized by the maximum, particularly for the major four: advection, mean shear, base temperature gradient, and pressure gradient. When the parameter perturbation further becomes finite, the optimal state is found on the constraint border of control parameters. Although the favorable pressure gradient and wall suction stabilize the broadband mode S, an unusual opposite tendency may occur for a single-frequency disturbance. In this unusual parametric range, positive contributions of both the major and minor physical sources to the growth rate are promoted. The contributive increase in major and minor sources are attributed to the enhancement of mean shear and viscous effect, respectively. Whether the parametric influence is stabilization or destabilization is intrinsically determined by the sensitivities, and the intermediate process is analyzed. Finally, given the modification to the critical Reynolds number, the input control parameter perturbation is inversely obtained and verified.