Relative Layer Thickness Research Articles

Degradation of Polymer Films on Surfaces: A Model Study with Poly(sebacic anhydride).

There is compelling evidence that the degradation kinetics of thin polymer films differ significantly from those of bulk materials, as interfacial effects become dominant. Therefore, it is crucial to investigate these kinetics separately. Qualitative analytics of thin film degradation exist, e.g. by scanning electron microscopy or atomic force microscopy (AFM), but a quantitative study is so far missing. In this work, poly(sebacic anhydride) (PSA), an aliphatic polyanhydride, is used as a model system for a quantitative degradation study. PSA was spin-coated onto silicon or gold substrates. The degradation of these PSA films was monitored by ellipsometry, surface-plasmon resonance spectroscopy (SPR), and Fourier transform infrared spectroscopy (FTIR). Two kinetic regimes were observed when plotting the relative layer thickness determined by FTIR and SPR against the degradation time. The data obtained by FTIR showed a single process for the rate of ester bond cleavage. Overall, the degradation rate constants of PSA determined by the different methods were consistent. The degradation rate constants of PSA film up to 378 nm thickness were constant. Several thicker free-standing samples studied gravimetrically had a degradation rate constant that was one order of magnitude slower, thus confirming thickness-dependent degradation rate constants.

Overcoming diffusion limitations in supercapacitors using layered electrodes

The impact of multi-layered electrode microstructures on the dynamic capacitance of electrochemical double layer supercapacitors is investigated. An electrochemical model that describes ion diffusion and double layer dynamics across the layered electrodes is first developed and then matched to experimental data. With TiO2 particulate and carbon nanotube layered electrodes, two knee frequencies were observed in the real and imaginary capacitance plots in both experiment and model simulations. These two knee frequencies resulted in an increase in real capacitance at high frequencies (ω≈100−102 rad s−1) but a reduction at lower frequencies (ω≈10−2 rad s−1), with the response being largely insensitive to the relative layer thicknesses. The increased capacity at high frequencies was due to increased ion mobility across the electrodes caused by the layering, allowing diffusion limitations of identical homogeneous electrodes to be overcome. These results imply the suitability of layered electrodes for applications with highly dynamic charge profiles and/or relatively thick electrodes.

Mathematical modeling and analysis of Cross nanofluid flow subjected to entropy generation

Here modeling and computations are performed to explore the aspects of entropy generation for magnetohydrodynamic (MHD) mixed convective flow of Cross nanoliquid. Heat transfer process comprises thermal radiation and Joule heating. Moreover, phenomenal aspect of current review is to consider the characteristics of activation energy. The idea of combined convective conditions and zero mass flux relation is introduced first time. The similarity transformation helps to simplify the complex model in the form of nonlinear PDEs into nonlinear ODEs. Numerical algorithm leads to solution computations. The numerical solutions of temperature, nanoparticle concentration fields, Nusselt number and coefficient of skin friction are exhibited via plots. It is noticed that radiation factor increases the thermal field and related layer thickness. Moreover, the obtained data reveal that profiles of Bejan number intensify for augmented values of radiation parameter. Intensifies

Buckling of a compliant hollow cylinder attached to a rotating rigid shaft

Bifurcations in the equilibrium shape of a thick elastic layer attached to a circular rigid cylinder rotating about its axis are investigated analytically and numerically. The centrifugal force breaks the symmetry of the system leading to deformations invariant along the axis as the result of an instability. The instability threshold depends at linear order on the relative thickness of the compliant layer, and on a dimensionless control parameter based on the elastic modulus, the angular velocity and the outer radius. A weakly non linear analysis, carried out for layers following the Mooney–Rivlin constitutive law, points out the discontinuous (sub-critical) features of the bifurcation, except for relative thickness laying in a very narrow range in which the bifurcation is super-critical. Numerical simulations in the fully post-buckled regime yield the absolute instability threshold, and the order in the rotational symmetry of the developed equilibrium shape.

Static Electromechanical Characteristics of Piezoelectric Converters with various Thickness and Length of Piezoelectric Layers

Abstract The paper presents the analysis of electromechanical characteristics of piezoelectric converters subjected to an electric field and mechanical load. The analyses were performed based on a method consisting implementation of special segments responsible for electrical boundary conditions to a homogeneous beam. Constitutive equations were developed, allowing one to obtain static electromechanical characteristics for piezoelectric actuators with freely defined boundary conditions and geometry. Moreover, based on constitutive equations obtained, a particular solution for cantilever transducer subjected to concentrated force has been developed. The resulting analytical solution was compared with the data available in the literature, and the developed FEM solution. Furthermore, the influence of factors such as relative length, thickness and location of particular piezoelectric layers on electromechanical characteristics of the transducer was defined.

Energy Dissipation during Vibrations of Heterogeneous Composite Structures: 3. Numerical Experiments

The influence of the relative thickness of a “stiff” viscoelastic polymer layer and the orientation of reinforcing layers of the bearing layer on the values of their natural frequencies and loss factors of damped vibrations of an unsupported two-layered composite plate has been investigated. It has been established that each natural vibration mode of a two-layered plate corresponds to a certain effective relative thickness of an isotropic viscoelastic polymer layer. A further increase in the relative thickness of plates with an orthotropic bearing layer depending on ambient temperature may result in both an increase and decrease in natural frequencies without any considerable change in their energy dissipation. For plates with a monoclinic bearing layer, the increase in relative thickness of the isotropic viscoelastic polymer layer is accompanied by both a decrease and increase of loss factor for different vibration modes. It is shown that a change in the stacking sequence of reinforcing layers in the bearing layer brings about mutual transformation domains of coupled vibration modes. It has been established that the mutual transformation of the natural shapes of coupled modes of an unsupported quasi-uniform rectangular plate vibrations appears if one of the natural shapes has an even number of quarter-wavelengths in at least one of the plate directions, whereas another natural shape has an odd number of those. It has been demonstrated that the temperature-frequency relationship of elastic-dissipative characteristics of the “stiff” viscoelastic polymer has a considerable effect upon natural frequencies and loss factors of all the investigated vibration modes for an unsupported rectangular two-layered plate.

Influences of Macropores on Infiltration into Seasonally Frozen Soil

Core Ideas Macropores allow water infiltration into a frozen soil close to 0°C and at high water saturation. Connected biopores channel water beneath the frozen layer. Frozen layer thickness in relation to connected macroporosity is a crucial factor. Infrared thermography can be used to measure frozen layer extent and variability. Water frozen in soil can reduce the soil infiltrability, depending on the water content. We hypothesize that air‐filled macropores control the infiltration of a seasonally frozen soil under high saturation degrees. Sprinkling experiments with different intensities on a seasonally frozen soil were conducted in two winters at high initial water contents. Brilliant Blue FCF (BB) was sprinkled on four plots equipped with soil moisture and temperature probes to mark flow paths. Frozen layer thickness was measured with infrared thermography of soil sections and overlaid with BB images. The frost depth of the experiments was 8 to 15 cm. Infiltration rates showed reduced infiltration compared with unfrozen conditions. By impeding refreezing of the infiltrating water with added NaCl, infiltration rates of 23 to 29 mm h−1 were measured. Without the addition of salt, the infiltration rates decreased to 5 to 10 mm h−1, attributed to pore blockage by refreezing water. Temperature measurements revealed that the frozen layer only thawed close to the soil surface during the experiments. Blue‐stained areas indicated that water was channeled through the frozen layer into the unfrozen soil. In addition, the soil moisture probes below the frozen layer measured an increase in unfrozen water content, whereas total water content in the frozen layer was constant. These observations were explained by a connected air‐filled porosity, such as biopores, which allowed water flow even under high initial water contents. These results illustrate the importance of macroporosity in relation to frost depth in controlling the infiltrability of seasonally frozen soils.

Correlation of Optical Coherence Tomographic Findings with Clinical Features in High Myopia

AbstractThis is a cross-sectional observational study to correlate relationship between macular and retinal nerve fiber layer (RNFL) thickness in relation to clinical features in high myopia. A total of 100 eyes of 50 consecutive patients underwent optical coherence tomography (OCT) of the macula and RNFL. It was observed that correlation of RNFL thickness to the axial length is better than that of RNFL thickness to the spherical equivalent. The macular thickness in the parafoveal region was observed to be thicker than the perifoveal region in all quadrants. This study therefore emphasizes the need to have macular thickness nomogram for high myopes to avoid misinterpretation of OCT results due to axial length and refractive error and, also, the need for a routine baseline OCT scan for all high myopia patients.

Macular Inner Retinal Layer Thickness in Relation to Photopic and Mesopic Contrast Sensitivity in Healthy Young and Older Subjects.

To examine relationships between the thicknesses of ganglion cell (GC)-related macular layers and central photopic or mesopic contrast sensitivity (CS) in healthy eyes. Measurements were made in 38 young and 38 older healthy individuals. Total, inner, and outer retinal layer (IRL) thicknesses were measured in the macula region through spectral-domain optical coherence tomography (SD-OCT) across three subfields, or rings, centered at the fovea: central foveal, pericentral, and peripheral. Ganglion cell complex and circumpapillary retinal nerve fiber layer thicknesses were also measured. Low-spatial-frequency CS for gratings presented at the central 10° visual field were measured through computerized psychophysical tests under photopic and mesopic conditions. Relationships were examined by uni- and multivariate regression analysis. Peripheral IRL thickness emerged as the only independent predictor of photopic CS (P = 0.001) in the young group and of photopic (P = 0.026) and mesopic CS (P = 0.001) in the older group. The slopes of regression lines used to predict CS from peripheral IRL thickness were significantly different for pair-wise comparisons of both photopic CS and age group (P = 0.0001) and mesopic CS (P = 0.0001) and age group. These models explained 37% of the variability in photopic CS and 36% of the variability in mesopic CS. Macular IRL thinning likely due to GC loss was related to reduced photopic and mesopic CS in older healthy eyes. In contrast, in the young eyes, a thicker macular IRL, possibly indicating transient gliosis, was associated with reduced CS.

The Effect of Soft Interlayers on the Behavior of a Four-Layer Titanium-Steel Composite at High Temperatures

The work presents the result of the finite element simulation of the titanium-steel composite with copper-niobium sublayer – VT6-VN2-M1-12Cr18Ni10Ti behavior under axial tension of a cylindrical sample by varying the relative thickness of the soft layer using a SIMULIA/Abaqus software package.

CONTACT PROBLEM FOR A TWO-LAYERED CYLINDER

Introduction. The investigation of the contact problems for cylindrical bodies is urgent due to the engineering contact strength analysis on shafts, cores and pipe-lines. In the present paper, a new contact problem of elastostatics on the interaction between a rigid band and an infinite two-layered cylinder, which consists of an internal continuous cylinder and an outer hollow one, with a frictionless contact between the cylinders, is studied. The outer cylindrical band of finite length is press fitted. By using a Fourier integral transformation, the problem is reduced to an integral equation with respect to the unknown contact pressure.Materials and Methods. Different combinations of linearly elastic materials of the composite cylinder are considered. Asymptotics of the symbol function of the integral equation kernel at zero and infinity is analyzed. This plays an important role for the application of the analytical solution methods. A key dimensionless geometric parameter is introduced, and a singular asymptotic technique is employed to solve the integral equation.Research Results. On the basis of the symbol function properties, a special easily factorable approximation being applicable in a wide variation range of the problem parameters is suggested. The Monte-Carlo method is used to determine the approximation parameters. The asymptotic formulas are derived both for the contact pressure, and for its integral characteristic. Calculations are made for different materials and for various relative thickness of the cylindrical layer including thin-walled layers.Discussion and Conclusions. The asymptotic solutions are effective for relatively wide bands when the contact zone length is bigger than the diameter of the composite cylinder. It is significant that the method is applicable also for those cases when the outer cylindrical layer is treated as a cylindrical shell. The asymptotic solutions can be recommended to engineers for the contact strength analysis of the elastic barrels with a flexible coating of another material.

3D MHD Free Convective Stretched Flow of a Radiative Nanofluid Inspired by Variable Magnetic Field

This paper carries on investigation to study the effects of variable magnetic field and thermal radiation on free convective flow of an electrically conducting incompressible nanofluid over an exponential stretching sheet. The model implemented in the present study significantly enriches the thermal conductivity and hence more heat transfer capability of nanofluids. The transformed governing equations have been solved numerically using fourth-order Runge–Kutta method along with shooting technique. The influence of variable magnetic field and thermal radiation associated with thermal buoyancy on the dimensionless velocity, temperature, skin friction and Nusselt number have been analyzed. The obtained numerical results in the present study are validated and found to be in excellent agreement with some previous results seen in the literature. The present study contributes to the result that augmented Hartmann number belittles the fluid flow and enhances the fluid temperature and the related thermal boundary layer thickness.

Numerical study of the bearing capacity of a strip footing on tow layered clay under inclined loading

The bearing capacity of a strip footing resting on a homogeneous and isotropic soil hasbeen the subject of numerous theoretical and experimental studies. However, in practice the soilis never homogeneous. It is therefore important to introduce the effect of stratification on thebearing capacity. This paper aims to indicate the modifications that must be made to the bearingcapacity of a rough strip footing resting on two layered clay subjected to inclined load. The finite-difference code Fast Lagrangian Analysis of Continua (FLAC) is used to estimate the bearingcapacity factor Nc* as well as the failure envelope and the inclination factors ic, in the case ofinclined loading. The study is carried out considering two layers clays of different shear strengths,where the thickness of the upper clay layer is comparable to the width of a rigid footing. Theresults obtained show clearly that the bearing capacity of a strip footing is generally depends onthe strength ratio of the soil layers (cu1/cu2) and the relative thickness of the top layer (D/B).

Optimization and Prediction of Durability and Utility Features of Three-Layer Piezoelectric Transducers

The paper presents the analysis of electromechanical characteristics of piezoelectric converters subjected to electric field and mechanical load. The analyses were performed based on a method consisting implementation of special segments, responsible for electrical boundary conditions, to a homogeneous beam. Constitutive equations were developed, allowing to obtain analytical solutions (bending of transducer) for piezoelectric actuators with freely defined boundary conditions and geometry. Moreover, based on obtained constitutive equations, for cantilever transducer, subjected to concentrated force, a special equation has been developed. The resulting analytical solution was compared with data available in the literature, and the developed FEM solution. Furthermore, influence of factors such as: relative length, thickness and location of particular piezoelectric layers on transducer's electromechanical characteristics, was defined DOI: http://dx.doi.org/10.5755/j01.mech.24.3.17953

Microstructure and magneto-optical surface plasmon resonance of Co/Au multilayers

Magneto-optical surface plasmon resonance (MOSPR) sensors benefit from a magneto-optic enhancement with respect to surface plasmon resonance (SPR) sensors, making these devices attractive for biosensing applications. Typical design compromises seek to balance magneto-optic effects and optical losses associated with surface plasmon waves extending to the ferromagnetic layer. Here, we demonstrate that Co/Au multilayers can yield sizeable MOSPR improvements in spite of the relative high total Co layer thickness. Co (tCo)/Au (2 nm) multilayers, with 1.2 ≤ tCo ≤ 1.8 nm are prepared and characterized. X-ray analysis shows that the microstructure maintains high layer periodicity and improves upon annealing. The multilayer structures were then modeled to study their SPR/MOSPR sensitivities, suggesting that the MOSPR sensitivity is enhanced by a factor of up to 3 and 4 with respect to the SPR sensitivity when the devices are operated in Air and Water media, respectively. We find that multilayers provide a particular advantage when operating the sensors in Water-based media.

Parametric computational analysis of indentation-induced shear band formation in metal-ceramic multilayer coatings

Shear band formation in multilayer thin-films subject to nanoindentation is studied numerically. The material system analyzed here is composed of alternating aluminum (Al) and silicon carbide (SiC) nanolayers, above a silicon (Si) substrate. Finite element models are developed to investigate system parameters that influence behavior of the shear band phenomenon. By introducing strain softening into the material model for the relatively hard ceramic layers, shear bands can be seen to emerge from the indentation site in the computational analyses. Effects of post-yield material parameter variations on the initiation of plastic instability are examined. Several geometric variations are also investigated, including the effect of relative layer thicknesses, homogeneity, layer order, and number of layers. The chain events that lead to shear band nucleation are postulated. Broad implications are noted, along with possible directions for future work.

Methylene Blue Attenuates Diabetic Retinopathy by Inhibiting NLRP3 Inflammasome Activation in STZ-Induced Diabetic Rats

ABSTRACTPurpose: This study aimed to investigate the regulatory effects of methylene blue (MB) on diabetic retinopathy (DR) and explored the molecular mechanisms of MB as a retina protection agent.Methods: The thicknesses of retinal layers and permeability of the blood–retinal barrier (BRB) were measured by histology analysis, and the expression levels of NLRP3, ASC, procaspase-1, caspase-1, IL-1β, and IL-18 were measured by western blotting. Lentivirus-based knockdown of NLRP3 gene was used to confirm the role of NLRP3 inflammasome.Results: MB treatment attenuates DR supported by the increase of relative thicknesses of retinal layers and the reduction of BRB permeability when compared with the untreated diabetic group. Further, MB significantly downregulated the levels of all detected inflammation mediators and showed inhibition on NLRP3 inflammasome activation similar to NLRP3 gene silencing.Conclusions: This study revealed a novel mechanism underlying the protection role of MB in the pathogenesis of DR.

Cooling of a Processor With the Use of a Heat Pump

In this paper the problem of cooling a component, in the interior of which heat is generated due to its work, was solved analytically. the problem of cooling of a processor with the use of a heat pump was solved based on a earlier theoretical analysis of authors of external surface cooling of the cooled component by using the phenomenon of liquid evaporation. Cases of stationary and non-stationary cooling were solved as well. The authors of the work created a simplified non-stationary analytical model describing the phenomenon, thanks to which heat distribution within the component, contact temperature between the component and liquid layer, and the evaporating substance layer thickness in relation to time, were determined. Numerical calculations were performed and appropriate charts were drawn. The resulting earlier analytical solutions allowed conclusions to be drawn, which might be of help to electronics engineers when designing similar cooling systems. Model calculations for a cooling system using a compressor heat pump as an effective method of cooling were performed.

The two sides of the C-factor

ObjectiveThe aim of this paper is to investigate the effects on shrinkage strain/stress development of the lateral constraints at the bonded surfaces of resin composite specimens used in laboratory measurement. MethodsUsing three-dimensional (3D) Hooke’s law, a recently developed shrinkage stress theory is extended to 3D to include the additional out-of-plane strain/stress induced by the lateral constraints at the bonded surfaces through the Poisson’s ratio effect. The model contains a parameter that defines the relative thickness of the boundary layers, adjacent to the bonded surfaces, that are under such multiaxial stresses. The resulting differential equation is solved for the shrinkage stress under different boundary conditions. The accuracy of the model is assessed by comparing the numerical solutions with a wide range of experimental data, which include those from both shrinkage strain and shrinkage stress measurements. ResultsThere is good agreement between theory and experiments. The model correctly predicts the different instrument-dependent effects that a specimen’s configuration factor (C-factor) has on shrinkage stress. That is, for noncompliant stress-measuring instruments, shrinkage stress increases with the C-factor of the cylindrical specimen; while the opposite is true for compliant instruments. The model also provides a correction factor, which is a function of the C-factor, Poisson’s ratio and boundary layer thickness of the specimen, for shrinkage strain measured using the bonded-disc method. For the resin composite examined, the boundary layers have a combined thickness that is ∼11.5% of the specimen’s diameter. SignificanceThe theory provides a physical and mechanical basis for the C-factor using principles of engineering mechanics. The correction factor it provides allows the linear shrinkage strain of a resin composite to be obtained more accurately from the bonded-disc method.

Vertical uplift resistance of rectangular plate anchors in two layered sand

Based on rigid block collapse mechanism and employing the upper bound theorem of limit analysis, the ultimate vertical uplift resistance of rectangular plate anchors embedded horizontally in two layered sand has been determined. Closed form analytical expressions were derived for computing the vertical uplift resistance in terms of dimensionless uplift factors Fγ and Fq, due to the components of soil unit weight (γ) and surcharge pressure (q) acting on the ground surface, respectively. For given embedment ratios of the anchor, the effect of relative position and thickness of sand layer with higher angle of internal friction (φh) and unit weight (γh), and sand layer with lower angle of internal friction (φl) and unit weight (γl), on the magnitude of Fγ and Fq was studied for different length to width ratio of anchor varying from unity to infinity (square to strip). The solutions obtained from the present theory compare reasonably well with the available data from literature.