Layered Structure Model Research Articles

Interactions of hyaluronan grafted on protein surfaces studied using a quartz crystal microbalance and a surface force balance.

Vocal folds are complex and multilayer-structured where the main layer is widely composed of hyaluronan (HA). The viscoelasticity of HA is key to voice production in the vocal fold as it affects the initiation and maintenance of phonation. In this study a simple layer-structured surface model was set up to mimic the structure of the vocal folds. The interactions between two opposing surfaces bearing HA were measured and characterised to analyse HA's response to the normal and shear compression at a stress level similar to that in the vocal fold. From the measurements of the quartz crystal microbalance, atomic force microscopy and the surface force balance, the osmotic pressure, normal interactions, elasticity change, volume fraction, refractive index and friction of both HA and the supporting protein layer were obtained. These findings may shed light on the physical mechanism of HA function in the vocal fold and the specific role of HA as an important component in the effective treatment of the vocal fold disease.

A comparison between the epoxy-bonded layer structure and shear-lag model in a thickness-shear mode circular cylindrical piezoelectric transformer

The thickness-shear modes in a circular cylindrical piezoelectric transformer considering the effect of an epoxy- bonded layer are analyzed, and an exact solution is obtained from the equations of the linear theory of piezoelectricity. Sys- tematic parametric studies are subsequently carried out to quantify the effects of the epoxy-bonded layer upon the transformer performance, including its thickness, elastic coefficient and mass density. It is demonstrated that whilst the thickness and elastic coefficient of the layer affect significantly the resonance frequencies, transforming ratio, power density, admittance and effi- ciency, and its mass density has negligible influence. On condition that the thickness of the epoxy layer is vanishingly small so that it degenerates into the solution by the classical shear-lag model. Upon comparing with the predictions obtained by employ- ing the traditional shear-lag model, it is found that the interface viscous damping is absolutely due to the elastic coefficient of the epoxy layer, and the present structure model is found to be more accurate especially when the thickness of the epoxy layer can not be neglected.

Hydration Layers on Clay Mineral Surfaces in Aqueous Solutions: a Review/Warstwy Uwodnione Na Powierzchni Minerałów Ilastych W Roztworach Wodnych: Przegląd

Abstract Hydration layer on clay mineral surfaces is originated from the adsorption of polar water molecules and hydrated cations on the surfaces through unsaturated ionic bonds, hydrogen bonds and van der Waals bonds. It has attracted great attentions because of their important influences on the dispersive stability of the particles in aqueous solutions. This review highlighted the molecular structure of clay minerals, the origin of hydration layers on clay mineral surfaces, the hydration layer structural model, hydration force and the main parameters of affecting the hydration layers on clay minerals (crystal structure, cationic type and strength, and solution pH). Also, the research methods for hydration layers were briefly described, especially the determination of hydration layer thickness by the Einstein viscosity method and AFM method. In addition, the applications of the stability of fine clay mineral particles in aqueous suspensions were summarized.

GPR determination of physical parameters of railway structural layers

Abstract The paper studies the possibility of quantitative processing of the GPR data for determining the refractive index and conductivity of motor road and railway constructional layers. The main objective of the work is to develop a method of obtaining quantitative information on chosen physical properties of soil layers from regular GPR surveys. Theoretical study of plane electromagnetic wave propagation is made for the model of layered soil structure. As a result of the study appropriate equation systems are derived for the calculations of refractive index and conductivity of structural layers. Based on these equations the method of quantitative processing of radargrams is proposed. The method includes the GPR data processing algorithm and theoretical techniques for determination of refractive index and conductivity of the structural layers. The applicability of the proposed method was initially validated by lab experiments using radargrams of the soil samples with specified values of moisture and conductivity and reliable results were achieved. The methods were also successfully used while monitoring the long term seasonal changes in structural layers of several Russian railways sections. The contamination of ballast material is also evaluated by this method in addition to the refractive index and conductivity.

In vitro measurement of the mechanical properties of skin by nano/microindentation methods

The elastic behaviors of stratum corneum, viable epidermis, dermis, and whole skin were investigated by nano/microindentation techniques. Insignificant differences in reduced elastic modulus of skin samples obtained from three different porcine breeds revealed breed type independent measurements. The reduced elastic modulus of stratum corneum is shown to be about three orders of magnitude higher than that of dermis. As a result, for relatively shallow and deep indentations, skin elasticity is controlled by that of stratum corneum and dermis, respectively. Skin deformation is interpreted in the context of a layered structure model consisting of a stiff and hard surface layer on a compliant and soft substrate, supported by microscopy observations and indentation measurements.

Stress Analysis about Flat Ratio and Surrounding Rock of Large Section Highway Tunnel

By utilizing finite element software MIDAS-GTS, layer structure model is established and the force situation of large section tunnel under the combination of three sets of surrounding rock and three sets of flat ratio is analyzed. Through comparing axial force of anchor, axial force and bending moment of shotcrete and displacement of the lining, the optimal flat ratio is selected. Results can provide reference for the design of the large section highway tunnel.

Simulation on Material Removal during Reciprocating Traveling WEDM of Insulating Ceramics

With the double layer structure model, the material removal of insulating ceramics ZrO2 during the machining process by reciprocating traveling wire electrical discharge machining (WEDM) was simulated and analyzed. The influence of conductive layer (C and ZrC) to material removal volume and crater dimension was compared. And the effect of peak current, pulse duration and the movement speed of wire electrode on discharge craters were researched. The simulation shows that the conductive layer exist has much influence to the material removal volume and crater length and width, but has less influence to crater depth during electrical discharge. The simulation for the effect of discharge parameter tells that, with the boiling removal form hypothesis, the material removal volume during single discharge is increasing with the increment of peak current and pulse duration but decreasing with the raising of wire electrode movement speed. For the variation of peak current, the removal volume of ZrO2 is exceeding the removal volume of conductive layer when Ip is bigger than 24A. Meanwhile, for the variation of movement speed of wire electrode, the removal volume of conductive layer is more than that of ZrO2 when v is over 5m/s.

A Solid Shell Finite Element Formulation for Dielectric Elastomers

This paper is concerned with a solid shell finite element formulation to simulate the behavior of thin dielectric elastomer structures. Dielectric elastomers belong to the group of electroactive polymers. Due to efficient electromechanical coupling and the huge actuation strain, they are very interesting for actuator applications. The coupling effect in the material is mainly caused by polarization. In the present work, a simple constitutive relation, which is based on an elastic model involving one additional material constant to describe the polarization state, is incorporated in a solid shell formulation. It is based on a mixed variational principle of Hu-Washizu type. Thus, for quasi-stationary fields, the balance of linear momentum and Gauss' law are fulfilled in a weak sense. As independent fields, the displacements, electric potential, strains, electric field, mechanical stresses, and dielectric displacements are employed. The element has eight nodes with four nodal degrees of freedom, three mechanical displacements, and the electric potential. The surface oriented shell element models the bottom and the top surfaces of a thin structure. This allows for a simple modeling of layered structures by stacking the elements through the thickness. Some examples are presented to demonstrate the ability of the proposed formulation.

Simulation of Temperature and Thermal Stress Filed during Reciprocating Traveling WEDM of Insulating Ceramics

With the double layer structure model, the effect of temperature field and thermal stress on material removal of insulating ceramics Si3N4 during the machining process by reciprocating traveling wire electrical discharge machining (WEDM) was simulated and analyzed. The distributions of temperature filed in C conductive layer and Si3N4 and double layer structure model during single electrical discharge were compared. And the influences of peak current, pulse duration and the movement speed of wire electrode to discharge craters were researched. The simulation shows that the conductive layer on insulating ceramics makes a larger effect on thermal transmission in the radius direction of discharge crater when discharge occurs. The simulation for temperature field tells that, with the boiling removal form hypothesis, the material removal volume during single discharge is increasing with the increment of peak current and pulse duration but decreasing with the raising of wire electrode movement speed. Meanwhile, in the simulation of thermal stress, the material removal form for Si3N4 is mainly to be boiling when peak current less than 20A (Ton V=8m/s). And when peak current is beyond 20A, the effect of thermal stress is becoming obvious gradually. With the variation of pulse duration, spalling material removal form is included in the material removed process when Ip=32A.

Cross-correlation Coefficients for the Study of Repeating Earthquakes: An Investigation of Two Empirical Assumptions/Conventions in Seismological Interpretation Practice

For the identification and analysis of ‘repeating earthquakes,’ there are two empirical concepts. The first is the assumption that the cross-correlation coefficient of the filtered seismograms of closely spaced ‘repeaters’ depends exponentially on the inter-event separation distance. The second is the convention that in processing regional seismograms, a 0.5–5.0-Hz band pass filter is used. In this article, using a simple layered structure model, we investigated the cross-correlation coefficient of the filtered synthetic seismograms of two closely located events, that is, a ‘doublet.’ We investigated the relation between the cross-correlation coefficient and the inter-event separation distance. Simulation shows that in the 0.5–5.0-Hz frequency band, even if for simple synthetic seismograms without considering lateral heterogeneity or scattering, the exponential dependence is only a first order approximation concept. To check the frequency dependence of the cross-correlation coefficient, we analyzed a group of seismograms of a ‘multiplet’ in Xiuyan, Liaoning, northeast China, recorded by the Regional Seismographic Network of Liaoning Province. The cross-correlation coefficients were observed to be relatively stable against frequency for the 0.5–5.0-Hz frequency band.

Corner Reflector as a Model of Layered Cylindrical Structures of Metallic Circular Rods

Electromagnetic radiation in a corner reflector consisting of metallic circular rods of perfect conductor is formulated using a model of layered cylindrical arrays. Radiation from Hertzian dipole coupled to the uniform and tapered corner reflectors is analyzed. The formulation is rigorous. It is shown that the directivity in forward direction is prominently enhanced in both H-plane and E-plane, when the corner reflector is composed of metallic circular rods with radii linearly increasing from the origin. Comparisons with radiation patterns of conventional two plate corner reflector are also presented.

Crystal structure, layer defects, and the origin of plastic deformability of Nb2Co7

The crystal structure of Nb2Co7 was identified on the basis of X-ray powder-diffraction data recorded by synchrotron radiation to be of the Zr2Ni7 type having monoclinic C2/m symmetry and Pearson symbol mC18 with lattice parameters a = 4.5874(2) Å, b = 8.1509(4) Å, c = 6.2223(3) Å and β = 107.181(3)°. Fractional coordinates were determined on the basis of Rietveld-refinement methods and geometrical considerations. The structure can be described by stacking of certain extended layer sandwiches parallel to (001). Each of these extended layer sandwiches consists of a central Kagomé layer composed of Co atoms only, which is sandwiched by two close-packed layers consisting of Co and Nb atoms. The occurrence of Warren peaks as well as of line broadening is attributed to a stacking disorder of adjacent layer extended sandwiches in the investigated specimen. The unexpected plastic deformability of the intermetallic compound Nb2Co7 can be related to specific features of the layered structure model, which provides a glide plane parallel to (001).

Core structure of aligned chitin fibers within the interlamellar framework extracted from Haliotis rufescens nacre. Part I: Implications for growth and mechanical response

By means of consecutive alkaline and proteolytic treatments of the organic framework?s interlamellar layers extracted from the nacre of H. rufescens, we have exposed a core of aligned parallel chitin fibers. Our findings both verify basic elements of the interlamellar layer structural model of Levi-Kalisman et al. (2001) and extend the more detailed model of Bezares et al. (2008, 2010). We observe via SEM imaging of square millimeter sized samples, which include numerous interlamellar layers and micron sized, yet nanocrystalline, CaCO3 tiles whose native orientation within the shell was first documented, that the chitin fibers in all layers are aligned normal to the growth direction of the shell. Similar alignment has been suggested in the literature for two other classes of mollusks, viz. N. rupertus and P. martensii (Weiner and Traub, 1983; Wada, 1958), suggesting that this may be a more general motif. We find that in order to expose the chitin core it is necessary to first remove protein by an alkaline treatment followed by enzymatic digestion with proteinase-K. We also observe what appear to be the points of traversal of the exposed chitin core by mineral bridges. The implications of these findings touch directly and most specifically upon the expected mechanical properties of organic framework layers such as stiffness and relaxation time constants, viz. they should be planeorthotropic. Single interlamellar layers extracted from nacre should, by implication, also exhibit an orthotropic stiffness. These novel findings provide the structural picture required for a complete anisotropic, time dependent, constitutive description of nacre long thought to be a paradigm of structural optimization. Such a model is briefly described herein and is developed, in full, in Part II of this series.

Studies on optical, structural and electrical properties of atomic layer deposited Al-doped ZnO thin films with various Al concentrations and deposition temperatures

We investigated transparent conducting aluminium-doped zinc oxide thin films fabricated by atomic layer deposition (ALD). For the thermal ALD, diethylzinc and trimethylaluminium were used as the Zn and Al precursors, respectively. The electrical, structural and optical properties were systematically investigated as functions of the Al doping contents and deposition temperature. The best resistivity and transmittance (4.2 mΩ cm and ∼85%) were observed at an Al doping concentration of about 2.5 at% at 250 °C. An increase in the carrier concentration was observed with increasing deposition temperature and doping concentration. This can be explained by the effective field model of layered structures. Also, the enhancement of the mobility with increasing doping concentration was studied by the grain-boundary scattering and percolative conduction mechanism. By correlating the electrical and structural properties, it was found that varying the carrier concentration was more effective in changing the mobility than the grain-boundary scattering, due to the hopping conduction.

Absorbing Properties of Fe-Based Amorphous Powder/S-Glass Fiber Reinforced Epoxy Composite Panels with Gradient Layer Structure

In this work, the Fe-based amorphous powder/S-glass fiber reinforced epoxy composite panels of different amorphous powder and gradient layer structure were prepared by mould pressing method. The waveguide method and arch form method can be used to measure the electromagnetic parameters and the reflectivity of the samples respectively in the frequency range from 2GHz to 18GHz. The results showed that the amorphous powders distributed evenly during the S-glass fiber reinforced epoxy layers and the main absorbing mechanism of composite panels is magnetic loss. The absorbing properties of samples improve with the increase of the Fe-based amorphous powder contents and the thickness of panels. The model of gradient layer structure has a significantly effect to improve the impedance matching between the samples and the air. Thus, the absorbing properties of the composite panels can be increased effectively. When the thickness of the gradient layer structure composite panels is designed at 4.8mm excepting the Al plate thickness with 0.6~1.3mm thickness of Fe-based amorphous powder/S-glass fiber reinforced epoxy, the absolute value of the reflection coefficient of the multi-composite panels is above 4dB in the frequency ranged from 2GHz to 8GHz and above 10dB during 8GHz ~18GHz.

Modeling nanostructured catalyst layer in PEMFC and catalyst utilization

A lattice model of the nanoscaled catalyst layer structure in proton exchange membrane fuel cells (PEMFC) was established by Monte Carlo method. The model takes into account all the four components in a typical PEMFC catalyst layer: platinum (Pt), carbon, ionomer and pore. The elemental voxels in the lattice were set fine enough so that each average sized Pt particulate in Pt/C catalyst can be represented. Catalyst utilization in the modeled catalyst layer was calculated by counting up the number of facets of Pt voxels where “three phase contact” are met. The effects of some factors, including porosity, ionomer content, Pt/C particle size and Pt weight percentage in the Pt/C catalyst, on catalyst utilization were investigated and discussed.

The computation of a finite-frequency travel time sensitive kernel for P-waves in the AK135 earth model

Finite-frequency travel time tomography is a newly developing method. The main procedure in this new method is to compute the traveltime sensitive kernel. The travel time of the same scatterer needs to be used for computing the traveltime sensitive kernel many times. It is a time-consuming task. It is easy and fast to get the travel time from analytic equations in a simple model such as a homogenous or linear velocity media. However, most of the earth models are layered. It is cumbersome to get the travel time from analytic equations. In order to enhance the computation efficiency, we used the table look-up method to compute the finite-frequency travel time sensitive kernel for P-waves in a layered structure model. We chose the AK135 earth model for the velocity model. The table look-up method saved about 50% of the computation time. We enhanced the computation speed by using the table lookup method in the same velocity model, which was very useful for enhancing the computation efficiency for the finite-frequency travel time tomography.

Preparation of nanostructured ultrathin silver layer

Silver is widely used for a fabrication of plasmonic devices due to its unique optical constants. Nanostructured Ag layer can exhibit strong localized surface plasmon resonance, which mainly affects its optical behavior in visible and near infrared spectra. The nanostructure of the Ag layer is mainly influenced during the initial stage of the silver nucleation. Therefore we focused our attention on the study of this stage of the silver growth. The nanostructured ultra-thin silver layers were prepared by means of the magnetron sputtering. The nucleation mode and the resulting nanostructure was controlled by the deposition conditions. The initial stage of the nucleation and the layer growth was studied by means of an optical monitoring, which is based on a principle of spectrophotometric measurement of sample reflectivity. The measured data were fitted to a model of layered structure. The non-continual (Volmer-Weber) mode of the layer nucleation was clearly distinguished in the monitored data. Thus we were able to estimate the point of the non-continual layer coalescence as well as the subsequent evolution of the surface roughness. The prepared nanostructured Ag layers were analyzed by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). Optical properties were studied by spectroscopic ellipsometry and spectrophotometry. The aim of this work was to study the formation of nanostructured Ag layer and its correlation to the optical behavior.

Co-adsorption of β-casein and calcium phosphate nanoclusters (CPN) at hydrophilic and hydrophobic solid–solution interfaces studied by neutron reflectometry

Neutron reflectometry was used to study the co-adsorption of calcium phosphate nanoclusters (CPN) and β-casein at hydrophobized and hydrophilic silica–water interfaces. The structural characteristics of the adsorbed layer were determined from neutron reflectivity curves analysed with multi-layer optical models. We used a highly specific proteolytic enzyme, endoproteinase Asp-N in conjunction with a single neutron contrast to verify the model of the protein layer structure. The results showed that the calcium phosphate nanoclusters profoundly affected the rate of adsorption and structure of the interface compared to the adsorption of β-casein alone and for the hydrophobic interface the effects depended on the point at which the nanoclusters were added. It is proposed that the nanoclusters become surface active because whole β-casein molecules can replace one or more of the hydrophilic peptides in the shell of the nanoclusters.

Electromechanical Behavior of Interface Deformable Piezoelectric Bilayer Beams

An interface deformable piezoelectric bilayer beam model is proposed to study the electromechanical responses and interface stress distributions in an intelligent layered structure. Like most of current approaches in the literature, the layerwise approximation of electric potential is employed. While in contrast to the linear approximation where the induced electric field is ignored, the present model takes a quadratic variation of the potentials across the thickness, thus warranting an efficient and accurate modeling of the electric field. Completely different from the widely used equivalent single layer model, in which the whole laminate is assumed to deform as a single layer and thus has a smooth variation of the displacement field over the thickness, the present model considers each sublayer as a single linearly elastic Timoshenko beam perfectly bonded together and therefore with individual deformations. To ensure the continuity of deformations of two adjacent sublayers along the interface, two interface compliance coefficients are introduced, by which both the longitudinal and vertical displacement components along the interface of two sublayers due to the interface shear and normal stresses are taken into account. To assess the performance of the present model, a number of benchmark tests are performed for a piezoelectric bimorph and a piezoelectric-elastic bilayer beam subjected to (1) a force density normal to the upper face and (2) an electric potential applied to the top and bottom faces. A remarkable agreement achieved between the present solution and the finite element computations illustrates the validity of the present study. The present model not only predicts well the global responses (displacement, electric charge, etc.), but also provides excellent estimates of the local responses (through-thickness variations of electromechanical state, interface stress distributions, etc.) of the piezoelectric layered structures. The novel mechanics model of electroelastic layered structures presented can be used to efficiently and effectively characterize hybrid smart devices and develop/optimize new multifunctional materials.