Values Of Layer Thickness Research Articles

Effect of plasma actuator in boundary layer on flat plate model with turbulent promoter

This paper shows experimental results for velocity measurement in the boundary layer with the use of a flat plate model. The flat plate model is disrupted with a wire trip and the effect of the plasma actuator to alter the flow in the boundary layer is then observed. The purpose of this research is to characterize the performance of the plasma actuator in a no-flow condition and with the use of a 2 m/s flow and also to theoretically analyze the performance of actuator in the boundary layer namely, displacement thickness, momentum thickness, and energy thickness. This is all done to acquire a deeper understanding of the capabilities of plasma actuator as one of the alternative active flow control equipment and to increase the effect of aerodynamic drag reduction. One of the ways to decrease the aerodynamic drag is to manipulate the flow to have a low boundary layer thickness value in order to prevent an adverse pressure gradient from happening, which then may lead to the formation of a flow separation. From experimental results, it is known that plasma actuator could decrease the thickness of the boundary layer by 9 mm.

Two-phase convection in Ganymede’s high-pressure ice layer — Implications for its geological evolution

Ganymede, the largest moon in the solar system, has a fully differentiated interior with a layer of high-pressure (HP) ice between its deep ocean and silicate mantle. In this paper, we study the dynamics of this layer using a numerical model of two-phase ice–water mixture in two-dimensional Cartesian geometry. While focusing on the generation of water at the silicate/HP ice interface and its upward migration towards the ocean, we investigate the effect of bottom heat flux, the layer thickness, and the HP ice viscosity and permeability. Our results suggest that melt can be generated at the silicate/HP ice interface for small layer thickness ( ≲ 200 km) and high values of heat flux ( ≳ 20 mW m−2) and viscosity ( ≳ 1015 Pa s). Once generated, the water is transported through the layer by the upwelling plumes. Depending on the vigor of convection, it stays liquid or it may freeze before melting again as the plume reaches the temperate (partially molten) layer at the boundary with the ocean. The thickness of this layer as well as the amount of melt that is extracted from it is controlled by the permeability of the HP ice. This process constitutes a means of transporting volatiles and salts that might have dissolved into the melt present at the silicate/HP ice interface. As the moon cools down, the HP ice layer becomes less permeable because the heat flux from the silicates decreases and the HP ice layer thickens.

Predictive value of preoperative retinal nerve fiber layer thickness for postoperative visual recovery in patients with chiasmal compression.

The aim of this study was to evaluate the predictive role of preoperative retinal nerve fiber layer (RNFL) thickness for postoperative visual recovery in patients with chiasmal compression through performing a meta-analysis. PubMed, EMBASE, Cochrane Library and China National Knowledge Infrastructure were searched for relevant studies. The study and patient characteristics were extracted. Pooled odds ratio (OR) with 95% confidence interval (CI) was calculated to estimate the predictive value of RNFL thickness. Subgroup analyses were also performed. Four studies with 202 patients and 395 eyes were included. The pooled results showed that patients with normal RNFL thickness could achieve better visual recovery compared with those with thin RNFL with the OR of 15.61 (95% CI, 4.09-59.61). Significant heterogeneity was observed (I2 = 54.5%, P=0.086). Publication bias was not present. Normal preoperative RNFL thickness could predict better postoperative visual recovery than thin RNFL in patients with chiasmal compression.

Morphometric Variations in the Skin Layers of Frogs: An Exploration Into Their Relation With Ecological Parameters in Leptodactylus (Anura, Leptodactylidae), With an Emphasis on the Eberth-Kastschenko Layer.

Leptodactylus is a genus of frogs known to live in diverse habitats and to show both aquatic and terrestrial breeding habits. We studied 21 species of Leptodactylus to explore whether skin structure specialization relates to habitats and habit variation. Morphometric analyses of the skin thickness revealed that phylogeny has a strong influence on variations in the thickness of the epidermis, stratum spongiosum, Eberth-Kastschenko layer, and stratum compactum, while habitat and habits display no significant correlation. The optimization of the phylogenetic hypothesis suggested that a pattern of intermediate values for skin layer thickness are plesiomorphic for this group. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 300:1895-1909, 2017. © 2017 Wiley Periodicals, Inc.

Appropriate position of porous insert in a heat exchanger by thermohydraulic analysis

AbstractThis paper presents numerically an appropriate position of a porous insert to get a better thermohydraulic performance from a porous heat exchanger. The simulation is based on the Darcy‐Brinkman‐Forchheimer model in the porous field. Two‐dimensional continuity, momentum, and energy equations with incompressible, laminar, steady assumptions have been solved using a finite volume approach. The analysis is performed for different values of porous layer thickness, length, and porosity at a fixed value of Reynolds number (Re = 100) and thermal conductivity ratio (Rc = 5). The results showed that there is about a 48% and 13% reduction in pressure drop and Nusselt number, respectively, by decreasing horizontal porous substrate thickness from 1 to 1/2 for δv = 1/3 at ε = 0.7. As a result, the pressure drop reduces considerably with a reasonable reduction in heat transfer rate by decreasing horizontal porous substrate thickness from 1 to 1/2.

Study on performance of wave-plate mist eliminator with porous foam layer as enhanced structure. Part I: Numerical simulation

Wave-plate mist eliminator with porous foam layers as enhanced structures on vanes to improve separation efficiency for tiny droplets was proposed in this paper. Overall separation efficiency, grade separation efficiency and pressure drop of the mist eliminators were systematically studied by using Computational Fluid Dynamics (CFD) method. The Shear Stress Transport (SST) k-ω turbulence model and Discrete Phase Model (DPM) were adopted to describe the motion of gas phase and liquid phase, respectively. The computational field was simplified by introducing an assumption that the real 3D structure of porous foam can be equivalent to 2D layout with randomly arranged circles. The CFD results showed that the separation efficiency was enhanced by increasing the foam layer thickness. Moreover, a gradual increase in the foam porosity at fixed PPI (pores per inch) value made the separation efficiency increased to a maximum value, then fall to a lower level, while by decreasing the PPI value of the foam at fixed porosity, the separation efficiency increased. Pressure drop was increased both with the increase in the foam layer thickness and PPI value as well as the decrease of the porosity. Furthermore, the flow field and the droplet trajectories were also analyzed.

Study of the influence of the agarose hydrogel layer thickness on sensitivity of the coated silica microsphere resonator to humidity.

In this paper, we investigate both theoretically and experimentally the influence of the agarose hydrogel layer thickness on the sensitivity of a proposed relative humidity (RH) sensor based on a silica microsphere resonator coated with agarose hydrogel. The operating principle of the sensor relies on excitation of whispering gallery modes (WGMs) in the coated silica microsphere using the evanescent field of a tapered fiber. A change in the ambient relative humidity is detected by measuring the wavelength shift of the WGMs in the transmission spectrum of the tapered fiber. Using perturbation theory, we analyze the influence of the agarose coating thickness on the sensitivity of the proposed sensor and compare the results of this analysis with experimental findings for different coating layer thicknesses. We demonstrate that an increase in the coating layer thickness initially leads to an increase in the sensitivity to RH and reaches saturation at higher values of the agarose layer thickness. The results of the study are useful for the design and optimization of microsphere sensor parameters to meet a performance specification.

Interfacial characterization in ductile refractory metals reinforced MoSi2 based laminated composites

Efforts to develop MoSi2 for high temperature structural applications have been hampered by its extreme brittleness at temperatures below 1000°C. In the present work, toughening of MoSi2 at lower temperatures has been explored using the ductile refractory metals as reinforcements. Model tri-layer laminated composites were made using Mo, Ta and Nb sheets sandwiched in between two layers of MoSi2 based matrix. As these refractory metals are thermodynamically unstable with MoSi2, interfacial reaction layers were observed between MoSi2 and the refractory metal sheets. The main reaction product was identified to be as M5Si3 (M=Mo, Ta or Nb) consuming a part of the thickness of the ductile metal sheets. The Ta sheet reinforced laminated composite exhibited the minimum thickness of the reaction zone (~10μm) suggesting that the Ta has better chemical compatibility with MoSi2 as compared to Mo and Nb. Micro-hardness measurements made in the reaction zone revealed that the reaction products in all the three laminated composites were hard and brittle in nature. A quantitative idea of the thickness and micro-hardness values of the interfacial reaction layers is very useful to give some important guidelines to obtain the enhanced mechanical properties in MoSi2 based laminated composites.

Can Glaucomatous Visual Field Progression be Predicted by Structural and Functional Measures?

The aim of this study was to compare the predictive value of retinal nerve fiber layer thickness (RNFLT) measurements obtained by optical coherence tomography (OCT), morphometric parameters of confocal scanning laser ophthalmoscopy (CSLO), and frequency-doubling technique perimetry to predict visual field conversion of normal individuals, ocular hypertensive subjects, and early preperimetric glaucoma patients as determined by standard automated perimetry (SAP). This longitudinal single-center study included 107 eyes of 56 controls, 164 eyes of 98 patients with ocular hypertension, and 169 eyes of 110 patients with preperimetric glaucoma. At baseline, all patients and controls underwent OCT (Spectralis OCT), CSLO (Heidelberg Retina Tomograph) examination, optic disc photography, and frequency-doubling technique perimetry. At baseline SAP was normal in all participants. Univariate and multivariate hazard ratios (HRs) were measured to model the conversion-free survival including morphometric functional and clinical variables. The median follow-up period was 6.9 years. In total, 48 eyes (10.9%) demonstrated visual field conversion in the follow-up. RNFLT temporal-inferior outside normal limits demonstrated the highest HR with 1.2 (95% confidence interval, 1.1-1.4) per 10 μm loss for OCT, and Glaucoma probability score global outside normal limits demonstrated the highest HR with 1.3 (95 % confidence interval, 1.1-1.5) per 0.1 increase for CSLO in a multivariate model adjusted for photograph-based glaucoma staging, central corneal thickness, and SAP pattern SD. Both measurement of RNFLT by OCT and Glaucoma probability score by CSLO are highly predictive of future visual field conversion and provide independent predictive information beyond optic disc assessment, central corneal thickness, and SAP pattern SD.

Theoretical prediction of interfacial properties of PBT/CNT nanocomposites and its experimental evaluation

In present study, the interfacial properties of PBT/CNT nanocomposites with varying filler content from 0.1 to 0.5wt.% are theoretically predicted and correlated with the tensile properties evaluated experimentally. The interfacial adhesion parameter is quantitatively predicted using different micromechanics models. The interfacial shear strength (τ), interphase strength (σi) and interphase layer thickness (ti) are calculated using the combined Kelly-Tyson theory and Pukanszky model. The fit of this model with experimental data is also demonstrated. Apart, the combination of Leidner–Woodhams model and Pukanszky model, which has been previously developed for spherical nanoparticles, is modified for cylindrical nanofillers such as CNTs. The values of interphase strength (σi) and interphase layer thickness (ti) are calculated using this modified combination model and agrees well with the experimental data. Furthermore, all the calculations suggests that highest interfacial bonding is obtained for sample containing 0.3wt.% of CNTs, which is also indicated by experimental data.

Retinal nerve fibre layer thickness values and their associations with ocular and systemic parameters in Black South Africans.

To measure the retinal nerve fibre layer (RNFL) thickness values and investigate their associations with other parameters in healthy eyes of Black South Africans. 600 participants with healthy eyes, of whom 305 (50.83%) were males and 295 (49.17%) were females, with a mean age of 28.15 ± 13.09 years, underwent a detailed ophthalmic examination. RNFL thickness was measured by iVue SD-OCT. The mean global RNFL thickness was 110.01 ± 7.39 µm. The RNFL was thickest inferiorly (135.06 ± 9.66 µm) and superiorly (131.72 ± 10.46 µm), thinner nasally (87.24 ± 13.22 µm), and thinnest temporally (73.63 ± 15.66 µm). Multivariate analysis showed that thicker mean global RNFL thickness was significantly associated with younger age, shorter axial length (AL) and hyperopia (p < 0.001). Mean RNFL thickness decreased by approximately 0.11 µm per year of aging life, and by 1.02 µm for each 1-mm of axial elongation. There was a 0.62 µm RNFL thickness increase for every dioptre change in spherical power towards more hyperopia. Mean RNFL thickness values and their associations established in this population may be of clinical value when assessing factors that influence this parameter and diagnosing diseases affecting it.

Influence of plasma nitriding treatment on the adhesion of DLC films deposited on AISI 4140 steel by PVD magnetron sputtering

Duplex surface treatments composed of diamond like carbon (DLC) coating followed by plasma nitriding have drawn attention for a while. In this study, AISI 4140 steel substrates were plasma nitrided at different treatment temperatures and times. Then, DLC films were deposited on both untreated and plasma nitrided samples using PVD magnetron sputtering. The effect of different plasma nitriding temperatures and times on the structural, mechanical and adhesion properties of DLC coatings was investigated by XRD, SEM, microhardness tester and scratch tester, respectively. It was found that surface hardness, intrinsic stresses, layer thickness values and phase distribution in modified layers and DLC coating were the main factors on adhesion properties of duplex coating system. The surface hardness and residual stress values of AISI 4140 steel substrates significantly increased with both DLC coating and duplex surface treatment (plasma nitriding + DLC coating). Increasing plasma nitriding temperature and time also increased the diffusion depth and the thickness of modified layers. Hard surface layers led to a significant improvement on load bearing capacity of the substrate material. However, it was also determined that the process parameters, which provided lower intrinsic stresses, improved the adhesion properties of the duplex coating system.

Influence of Aligned Magneto Hydrodynamic of Jeffrey Fluid across a Stretching Sheet

Objectives: Effects of slip velocity and aligned Magneto hydro-dynamic on Jeffrey fluid which passing across a stretching sheet with Newtonian heating boundary condition are investigated. Methods/Statistical Analysis: Governing partial differential equations are first transformed into ordinary differential equation by applying the similarity transformations before undergo computation process using y bvp4c in MATLAB. Findings: For validation purposes, the present results are comparing with the outcome from previous publications for the case Constant Wall Temperature (CWT) and it shows a very strong agreement on the values of −θ′(0) . From the study, the increasing on the values of magnetic parameter, M drop the fluid velocity for the range value of boundary layer thickness 0 3.5 , the value of fluid velocity is increasing on the larger magnetic parameter. However, the distribution on temperature of fluid shows an opposite trend as compare with fluid velocity. On the range of 0 2.5 it evidently reduce the velocity of fluid. The fluid temperature is high at smaller values of Deborah number. The distribution on velocity and temperature of fluid presented in this article are strictly asymptotically fulfilling the boundary conditions which then contribute to the adequate of the present results. Application/Improvements: The results from this project will enhance the knowledge in non-Newtonian fluid problem via mathematical approach.

Unsteady Natural Convection Flow past an Infinite Cylinder with Thermal and Mass Stratification

This paper presents an analytical solution of unsteady one-dimensional free convection flow past an infinite vertical circular cylinder in a stratified fluid medium. The dimensionless coupled linear governing partial differential equations are solved by Laplace transform technique for unit Prandtl number and Schmidt number. Effects of various physical parameters are presented with graphs. Numerical values of boundary layer thickness for different parameters are presented in table. Due to the effects of thermal and mass stratifications, the velocity, temperature, and skin friction, Nusselt number shows oscillatory behaviour at smaller times and then reaches steady state at larger times.

Simulation design of P–I–N-type all-perovskite solar cells with high efficiency**Project supported by the Graduate Student Education Teaching Reform Project, China (Grant No. JG201512) and the Young Teachers Research Project of Yanshan University, China (Grant No. 13LGB028).

According to the good charge transporting property of perovskite, we design and simulate a p–i–n-type all-perovskite solar cell by using one-dimensional device simulator. The perovskite charge transporting layers and the perovskite absorber constitute the all-perovskite cell. By modulating the cell parameters, such as layer thickness values, doping concentrations and energy bands of n-, i-, and p-type perovskite layers, the all-perovskite solar cell obtains a high power conversion efficiency of 25.84%. The band matched cell shows appreciably improved performance with widen absorption spectrum and lowered recombination rate, so weobtain a high Jsc of 32.47 mA/cm2. The small series resistance of the all-perovskite solar cell also benefits the high Jsc. The simulation provides a novel thought of designing perovskite solar cells with simple producing process, low production cost and high efficient structure to solve the energy problem.

Analysis of the relation between spectral response and absorptivity of GaAs photocathode

In order to study the relation between spectral response and absorptivity of GaAs photocathode, two kinds of GaAs photocathodes are prepared by molecular beam epitaxy (MBE) and metal-organic chemical vapor deposition (MOCVD), respectively. The samples grown by the MBE include varying doping GaAs photocathodes with different values of emission layer thickness from A to E. The thickness of GaAs emission layer is 1.6 μm or 2 μm. The Al component is 0.5 or 0.63. The samples grown by the MOCVD include varying doping or various component GaAs photocathodes with different values of emission layer thickness and different window layer components from F to J. The thickness values of GaAs emission layer are 1.4 μm, 1.6 μm or 1.8 μm, respectively. The Al component is 0.7 or varies from 0.9 to 0. The doping concentration of the GaAs emission layer is divided into 8 sections between 1×1018 cm-3 and 1×1019 cm-3. The experimental spectral response curves for all samples are obtained by the optical spectrum analyzer. And the experimental reflectivity and transmittivity curves are measured by the ultraviolet visible near infrared spectrohootometer. Based on the law of energy conservation, the absorptivity curves are obtained according to the experimental reflectivity and transmittivity. In the same coordinate system, both the curves are obtained by unitary processing according to the max. A similar surface barrier can be given by dividing the normalized absorptivity by the normalized spectral response, and those are termed the similar I barrier and the similar Ⅱ barrier, respectively. The results indicate that for both the GaAs photocathodes, the experimental spectral response curves both tend to move to the infrared band compared with the experimental absorptivity curves. The average energy differences between absorptivity and spectral response are calculated to be 0.3101 eV for the MBE sample, and 0.3025 eV for the MOCVD sample, respectively. The red-shifts of the photocathodes grown by MBE are a bit bigger than those of the photocathodes grown by MOCVD. In the shortwave region, the absorptivity is very large, but the spectral response cuts off nearby 500 nm. In the visible wavelength region, the peak position of the spectral response curve shifts toward the infrared band for several hundred meV in comparison with the absorptivity curve. In the near infrared region, a red shift of several meV appears at the cut-off position of the spectral response curve in comparison with the absorptivity curve. The results have the guiding significance for improving the photoemission performance of wide-spectrum GaAs photocathode by optimizing the optical performance.

Structural and photoelectrical properties of AZO thin films improved by Ag buffer layers

In order to obtain more excellent photoelectric properties of transparent conductive film, a series of high-quality AZO thin films and AZO/Ag/AZO thin films with various thickness values of Ag buffer layers are prepared on glass substrates by the radio frequency magnetron sputtering method at room temperature. The phase and surface morphologies of films are characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM) respectively. The technology of Hall effect measurement and ultraviolet, visible spectrophotometer are employed to investigate the photoelectric properties of films. The electrical properties (including sheet resistance, sheet concentration and mobility) of films are also determined by using non isothermal technique to explore their thermal stability performances. The results indicate that the thickness values of Ag buffer layers have a large influence on the crystalline structures and photoelectric properties of AZO thin films. The XRD results show that with the increase of the thickness of Ag, the diffraction peak of Ag (111) is gradually enhanced, the ZnO (002) diffraction peak is gradually weakened, and the preferred orientation of ZnO (002) crystal plane is weakened. AFM test indicates that the change of Ag layer thickness has a great influence on the surface growth mode of the upper layer AZO thin film. When the Ag layer thickness is less than 5 nm, AZO thin film surface is rough and the grain size is smaller. When the Ag layer thickness is larger than 10 nm, the continuous surfaces of multilayer films begin to be shaped, directly affecte the photoelectric properties of the films. Hall effect measurement and transmittance test show that with the increase of Ag layer thickness, the transmission of AZO/Ag/AZO multilayer film gradually decreases, and also the resistance gradually decreases. When the thickness of Ag layer is 10 nm, AZO(30 nm)/Ag(10 nm)/AZO(30 nm) thin film gains a best figure of merit of 1.5910-1 -1 an average transmittance of 84.2% and a sheet resistance of 0.75 /sq. Hall effect measurement versus temperature indicates that AZO film without an Ag layer proves to be subjecte to the regular change of semiconductor resistance with temperature. When adding an Ag layer, the trend of the relationship of resistance with temperature presentes the characteristic of that metal resistance relating to temperature. Moreover, the sheet concentration of AZO with Ag layer is higher than that of AZO. The highest sheet concentration and the excellent thermal stability are obtained on AZO/Ag (10 nm)/AZO. The changes of the mobility of AZO under different temperatures turn out to be poorly stable. However, when adding an Ag layer, the better stability of AZO/Ag/AZO can be obtained. In conclusion, the photoelectric properties of films own excellent thermal stabilities with optimum thickness of Ag layer.

High performence visble-near infrared photovoltaic detector based on narrow bandgap polymer

Polymer-based visible-near infrared photodetectors have attracted considerable attention in the recent years due to their unique advantages of low cost of fabrication, compatibility with lightweight/flexible electronics, and wide material sources. Current researches mainly focus on high performence visble-near infrared photovoltaic detector based on narrow bandgap polymer. Device structure of the photodetector is ITO/PEDOT:PSS/photosensitive layer/Ca/Al. The weak light (0.4 mW/cm2, 800 nm) and reverse bias (-2 V) induce insignificant differences in photocurrent among the devices. Current values of 1.69×10-4 A/cm2, 7.96×10-5 A/cm2 and 6.98×10-5 A/cm2 are obtained with photosensitive layer thickness values of 100, 200 and 300 nm, respectively. However, the dark current density-voltage characteristics of the detectors with various thickness values of the photosensitive layer show that reverse bias (-2 V) induces significant differences in current among the devices. Current values of 1.35×10-6 A/cm2, 1.13×10-7 A/cm2 and 2.98×10-8 A/cm2 are obtained with photosensitive layer thickness values of 100 nm, 200 nm and 300 nm, respectively. Meanwhile, all detectors possess high rectification ratios over 105(±2 V), indicating good diode rectification characteristics. Photosensitivity measurements show that detection spectral regions of the detectors are extended from 380 nm to 960 nm. The values of detectivity (D*) of detectors with various thickness values of photosensitive layers are investigated, and the obtained values of D* of tested detectors are found to be very stable in a range from 400 nm to 860 nm, and the average D* value for the 300 nm thick device in this spectral range is as high as 6.89×1012 Jones. The latter compares well with values obtained with silicon detectors. In a range from 800 nm to 900 nm, the estimated detectivities of the 300 nm and 200 nm thick detectors are slightly higher than those obtained with InGaAs devices. Through analyzing energy band diagrams of the polymer photodetectors under reverse voltage bias it could be argued that the relatively weak electric field in the thicker device is the origin of the lower noise current density. The capacitance characteristics of polymer based detectors at high frequency (100 kHz) are examined through capacitance-voltage curves, and the resulting data show that capacitances of all devices at reverse and even small positive voltage are constant. This indicates that the device photosensitive layers are fully depleted and fast signal detections are theoretically possible. The time responses of detectors under near-infrared stimulation are also examined. The output signal appears to rise and fall periodically according to the input signal, suggesting a good repeatability. The rise and fall times for the devices are recorded to be ~5 μs and ~50 μs, indicating that the polymer photodetectors have quick response capabilities.

Ocular Image and Haemodynamic Features Associated with Different Gradings of Ipsilateral Internal Carotid Artery Stenosis.

Objectives To analyse the changes of ocular haemodynamics and morphology in Chinese patients with internal carotid artery (ICA) stenosis in the current study. Methods A retrospective case-control study was conducted with 219 patients. The haemodynamic characteristics, the calibre of retinal vessels, and the subfoveal choroidal thickness (SFChT) were compared. We analysed the correlations with the degree of ipsilateral ICA stenosis. Results There were no significant differences among the groups in the central retinal artery equivalent (CRAE), central retinal vein equivalent (CRVE), and AVR (p = 0.073, p = 0.188, and p = 0.738, resp.). The peak systolic velocity (PSV) and end diastolic velocity (EDV) in the central retinal artery (CRA) and the posterior ciliary artery (PCA) were significantly lower than normal eyes (p < 0.001). The outer retinal layer thickness and SFChT values of the ICA stenosis groups were significantly lower than normal eyes (p = 0.030 and p < 0.001, resp.). Conclusion The PSV and EDV in CRA and PCA and the SFChT and outer retinal layer thickness of ICA eyes were significantly lower than normal eyes. ICA stenosis may impact choroidal haemodynamics, and decreased choroidal circulation might affect the discordance of the SFChT and the outer retinal layer thickness.

Effect of smear layer thickness and pH of self-adhesive resin cements on the shear bond strength to dentin.

There are concerns in relation to the bonding efficacy of self-adhesive resin cements to dentin covered with the smear layer. This study aims to evaluate the effect of smear layer thickness and different pH values of self-adhesive resin cements on the shear bond strength to dentin. The dentin on the buccal and lingual surfaces of 48 sound human premolars were abraded with 60- and 600-grit silicon carbide papers to achieve thick and thin smear layers, respectively. The samples were divided into three groups (n = 16) based on the cement pH: Rely-X Unicem (RXU) (pH < 2); Clearfil SA Luting (CSL) (pH = 3); and Speed CEM (SPC) (pH = 4.5). In each group, composite resin blocks were bonded to the buccal and lingual surfaces. After 24 h, the shear bond strength values were measured in MPa, and the failure modes were evaluated under a stereomicroscope. Data were analyzed with two-way ANOVA and post hoc least significant difference tests (P < 0.05). Cement pH had a significant effect on the shear bond strength (P = 0.02); however, the smear layer thickness had no significant effect on the shear bond strength (P > 0.05). The cumulative effect of these variables was not significant, either (P = 0.11). The shear bond strengths of SPC and CSL self-adhesive resin cements were similar and significantly lower than that of RXU. The smear layer thickness was not a determining factor for the shear bond strength value of self-adhesive resin cements.