Indentation of thin elastic films glued to rigid substrate: Asymptotic solutions and effects of adhesion

Indentation of a thin elastic film attached through an interlayer to a rigid support is studied. Because the common interpretations of depth-sensing indentation tests are not applicable to such structured coatings, usually various approximating functions are employed to take into account influence of the interlayer. Contrary to the common approaches, a strict mathematical approach is applied here to study the problems under consideration assuming that the thickness of the two-layer structure is much less than characteristic dimension of the region of contact between the indenter and the coating. A simple derivation of asymptotic relations for displacements and stresses is presented. It is shown that often the leading term approximation to the non-adhesive contact problems is equivalent to contact problem for a Winkler-Fuss elastic foundation with an effective elastic constant. Because the contact between the indenter and the film at nanoscale may be greatly affected by adhesion, the adhesive problem for these bilayer coatings is studied in the framework of the JKR (Johnson, Kendall, and Roberts) theory of adhesion. Assuming the indenter shape near the tip has some deviation from its nominal shape and using the leading term approximation of the layered coatings, the explicit expressions are derived for the values of the pull-off force and for the corresponding critical contact radius of adhesive contact region

Effect of a novel commercial potassium-oxalate containing tooth-desensitizing mouthrinse on the microhardness of resin composite restorative materials with different monomer compositions

The effects of mouthrinses on dental resin composites have been investigated extensively. However, there is little information available regarding the effects of ‘newly developed mouthrinse’ formulations on the microhardness of different monomer based composite systems. Therefore, the aim of this study was to investigate the effect of a novel potassium-oxalate containing desensitizing mouthrinse on the microhardness of different monomer based composite materials. A hundred and twenty specimens (6mm in diameter and 2mm in height) were prepared for composite resin groups (methacrylate based, DX-511 monomer based and silorane monomer based) and for storage solution groups (artificial saliva and potassium oxalate-containing tooth-desensitizing mouthrinse). After allowing post-polimerization the baseline Knoop microhardness measurements for all specimens were recorded. The specimens were stored in 20 mL mouthwash and artificial saliva for 12 hours at 37ºC. The post-immersion microhardness values of all specimens were also recorded. Data were subjected to ANOVA/Scheffe’s test at a significance level of 0.05. The intra group (pre and post immersion values) comparison of the mean microhardness values of the specimens was done using Wilcoxon signed rank test. The microhardness of the silorane based composite was not affected significantly (p>0.05). The hardness values of the DX-511 monomer based composite and the methacrylate based composite exhibited a slight but not significant microhardness change compared to the baseline values (p>0.05). Studies reported that the effect of mouthrinses on microhardness changes of composite resins may be material dependent, and the hardness change susceptibility of a restorative material may be attributed to its resin matrix or filler type. However, dental monomers as well as the oral care products have an ever-evolving technology and future studies should consider newer products. Potassium oxalate containing mouthrinses, especially alcohol-free ones, may be used safely with dental composites with newly developed low-shrink monomer compositions

Examining technological pedagogical content knowledge of teachers teaching Turkish to bilingual students in FranceFransa'da iki dilli öğrencilere Türkçe öğreten öğretmenlerin teknolojik pedagojik içerik bilgilerinin incelenmesi

The objective of this study is to examine the self-competency perceptions of the teachers teaching Turkish to bilingual children in France on technological pedagogical content knowledge. In accordance with this objective cross sectional survey method was used for this study. 65 Turkish teachers working in France were included in the study. An assessment instrument developed by Horzum, Akgün and Öztürk (2014) was used to determine the self-competency perceptions of the teachers on technological pedagogical content knowledge. The obtained results revealed that the self-competency perceptions of the teachers teaching Turkish (L1) to bilingual children in France on technological pedagogical content knowledge was over the average. Besides, it is observed that the self-competency perceptions of the teachers on content knowledge and technological pedagogical content knowledge were significantly lower than their self-competency perceptions on pedagogical content knowledge. ÖzetBu araştırmanın amacı Fransa'da iki dilli öğrencilere Türkçe öğreten öğretmenlerin teknolojik pedagojik içerik bilgilerine yönelik öz-yeterlik algılarını incelemektir. Bu amaç doğrultusunda araştırma kesitsel tarama modelinde yürütülmüştür. Araştırmaya Fransa'da görev yapan 65 Türkçe öğretmeni katılmıştır. Öğretmenlerin teknolojik pedagojik içerik bilgilerine yönelik öz-yeterlik algılarını ölçmek üzere Horzum, Akgün ve Öztürk (2014) tarafından geliştirilen ölçme aracı kullanılmıştır. Araştırma sonucunda Fransa'da iki dilli çocuklara Türkçe öğreten öğretmenlerin teknolojik pedagojik içerik bilgisine yönelik öz-yeterlik algılarının ortalamanın üzerinde olduğunu göstermektedir. Bunun yanında öğretmenlerin içerik bilgileri ve teknolojik pedagojik içerik bilgilerine yönelik öz-yeterlik algılarının pedagojik içerik bilgilerine yönelik öz-yeterlik algılarından anlamlı derecede düşük olduğu görülmüştür

Synthetic jets for electronics cooling applications

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.Compact, high functionality electronics resulted in high performance computing. These innovations lead to smaller electronic systems with higher heat fluxes than ever. However, thermal real estate has kept the same or even smaller for posing challenges to thermal scientists. Novel cooling techniques have been of interest to solve the demand. One of these technologies operates with microfludics principle creating vortex rings called synthetic jets. These jets are simply meso-scale devices operating at zero-net-mass-flux principle by ingesting and ejecting high velocity working fluid from a single opening. The ingestion/ejection produces periodic jet streams, which may have local velocities over 50 m/s. Based on the published literature, these jets can enhance the heat transfer in both natural and forced convection environments significantly. Recognizing the heat transfer physics over surfaces require a fundamental understanding of the flow physics caused by pulsating coolant flow. A computational study has been performed to understand the flow physics of a small scale synthetic jet. A second-order temporal implicit scheme was used for the unsteady terms to avoid stability issues. No secondary peaks are observed on the surface profiles, and the vortices created at the nozzle exit seem to have no effect on the surface profiles.dc201

MHD Stagnation Flow of a Newtonian Fluid towards a Uniformly Heated and Moving Vertical Plate

Stagnation flow of an electrically conducting incompressible viscous fluid towards a moving vertical plate in the presence of a constant magnetic field is investigated. By using the appropriate transformations for the velocity components and temperature, the partial differential equations governing flow and heat transfer are reduced to a set of nonlinear ordinary differential equations. These equations are solved approximately using a numerical technique for the following two problems: (i) two-dimensional stagnation-point flow on a moving vertical plate, (ii) axisymmetric stagnation-point flow on a moving vertical plate. The effects of non-dimensional parameters on the velocity components, wall shear stresses, temperature and heat transfer are examined carefully

Nanodomains due to Phason Defects at a Quasicrystal Surface

Among the three coexisting types of terraces found on the twofold surface of the d-Al-Cu-Co quasicrystal, nanodomains are essentially observed on the transition-metal rich ones, with a coherent interface boundary. Both clean surface and Ag growth analyses, demonstrate that nanodomain surfaces are structurally identical to one of the two other terraces, which contains 85 at. % Al. We provide evidence that the nanodomains are a manifestation of phason defects that extend downward toward the bulk, and state that nanodomains develop because the energetic cost of creating the phason is outweighed by the change in surface energy. Consequently, the formation of nanodomains involves more than just the surface layer, but is driven by surface energetics

How high is the inter-observer reproducibility in the LIRADS reporting system?

Purpose: To investigate the reproducibility of LIRADS v2014 and contribute to its widespread use in clinical practice. Material and methods: This retrospective, single-centre study was conducted between January 2010 and October 2015. A total of 132 patients who had dynamic magnetic resonance imaging (MRI)/computed tomography (CT) images in the Picture Archiving and Communication Systems (PACS) with liver nodule were included in the study, 37 of whom had histopathology results. Five radiologists who participated in the study, interpreted liver nodules independently on different PACS stations according to the LIRADS reporting system and its main parameters. Results: We determined that level of inter-observer agreement in the LR-1, LR-5, and LR-5V categories was higher than in the LR-2, LR-3, and LR-4 categories (κ = 0.522, 0.442, and 0.600 in the LR-1, LR-5, and LR-5V categories, respectively; κ = 0.082, 0.298, and 0.143 in the LR-2, LR-3, and LR-4 categories, respectively). The parameter that we observed to have the highest level of inter-observer agreement was venous thrombus (κ = 0.600). Conclusions: Our study showed that LIRADS achieves an acceptable inter-observer reproducibility in terms of clinical practice although it is insufficient at intermediate risk levels. We think that the prevalence of its use will be further increased with training related to the subject and the assignment of numerical values that express the probability of malignancy for each category and including the ancillary features in the algorithm according to clearer rules