Inhomogeneous Interface Research Articles

Underneath the cerclage: an ex vivo study on the cerclage-bone interface mechanics

Cerclages regain interest due to a rising number of periprosthetic fractures. The contact distribution at the circumferential cerclage-bone interface is still unknown. Local interface pressure depends on the amount of contact area. Cortical damage at the interface would provoke cerclage loosening. Therefore, the contact area, the bone pressure along the interface and the cortical resistance underneath loaded cerclages were determined in an ex vivo model. Human diaphyseal femoral bone was used with differing cross-sectional geometry. Bone contact points of fixed 1.5 mm wire and 1.7 mm cable cerclages were identified from axial radiographs. Pressure distribution at the cerclage-bone interface was recorded with a pressure-measuring film using a distraction setup with two cortical half shells. Bone shells with installed cerclages were separated with up to 400 N force and were subsequently analyzed histologically to detect cortical damage. Both cerclage types exhibited a point contact fixation with non-loaded spanned zones in-between. Cables cover larger contact areas. Both cerclages exhibited an inhomogeneous interface pressure distribution depending on the bone surface geometry. Histology revealed intact cortical bone without cortical affection after loading of both cerclage types. Point contact fixation of the cerclages installs non-loaded, spanned zones where the periosteum is not compressed, rendering a strangulation of the blood supply unlikely. Cortical bone withstands static concentric pressure produced by the cerclage. Cortical groove formation is attributed to instability under functional load and not to weakness of the cortex itself.

SU‐E‐T‐373: The Comparative Research of Monte Carlo Simulation Based Inhomogeneous Tissue Correction Algorithm

Purpose: Two kinds of improved Batho method are proposed in this paper, the dose correction results for test example are compared also.Method and Materials:[Method1].The MC simulation model is : a 1cm3 cavity is placed in the central axis of 30cm3 water phantom. The center of the cavity is (0,0,0.5),'¦(0,0,29.5). The dose distribution of the cavity is simulated, the relative error with homogeneous water phantom is obtained and pre‐treated by the relative error databases. The corrected dose distribution is got in two steps, the cavity region and boundary point are corrected corresponding to the relative error databases firstly, then, the inhomogeneous tissue outside the cavity is corrected according to the Batho method.[Method2].The density of human tissue is divided into four corresponding intervals in terms of the value of CT. The simulation model is: a 1 cm3 typical inhomogeneous tissue is placed at the central axis of 30 cm3 homogeneous tissue phantom. Compared with the PDD of pure homogeneous tissue phantom, the relative error database can be obtained. The program judges the destiny change along the primary ray path. The Batho algorithm is used for dose correction when the destiny of tissue is relatively uniform. In the inhomogeneous interface between different tissues and inside cavity, the program will quickly find the relative error by index according to tissue density changes and depth, read the corresponding data to gain accurate correction results. Results: The method 1 obtain better correction result in the boundary point compared to MC simulation, but, in the cavity, the maximum error correction is 9.661%. Accordingly, the maximum correction error in the cavity region by method2 is 4.73%, in the boundary point is 2.47%, can satisfy the clinical precision requirement of 5%. Conclusions: The method 2 can obtain satisfactory correction Result in inhomogeneous tissue interface and the cavity area. The work is supported by the National Natural Science Foundation of China (60872112 and 10805012), the Natural Science Foundation of Anhui Province (11040606M132) and the Fundamental Research Funds for the Central Universities and the Science Research and Development Fund of Hefei University of Technology (2012HGXJ0062).

Collective Effects at Frictional Interfaces

We discussed the role of the long-range elastic interaction between the contacts inside an inhomogeneous frictional interface. The interaction produces a characteristic elastic correlation length λc = a 2 E/k c (where a is the distance between the contacts, k c is the elastic constant of a contact, and E is the Young modulus of the sliding body), below which the slider may be considered as a rigid body. The strong inter-contact interaction leads to a narrowing of the effective threshold distribution for contact breaking and enhances the chances for an elastic instability to appear. Above the correlation length, r > λc, the interaction leads to screening of local perturbations in the interface, or to appearance of collective modes—frictional cracks propagating as solitary waves.

The interaction between a screw dislocation and a rigid wedge inhomogeneity with an elastic circular inhomogeneity at the tip

The interaction between a screw dislocation and an elastic semi-cylindrical inhomogeneity abutting on a rigid half-plane is investigated. Utilizing the image dislocations method, the closed form solutions of the stress fields in the matrix and the inhomogeneity region are derived. The image force acting on the dislocation is also calculated. The results were used to study the interaction between a screw dislocation and a rigid wedge inhomogeneity with an elastic circular inhomogeneity at the tip by means of conformal mapping. The results show that an unstable equilibrium point of the dislocation near the semi-cylindrical inhomogeneity is found when the inhomogeneity is softer than the matrix. Moreover, the force on the dislocation is strongly affected by the position of the dislocation and the shear modulus of the semi-circular inhomogeneity. Positive screw dislocations can reduce the SIF of the rigid wedge inhomogeneity (shielding effect) only when it located in the lower half-plane. The shielding effect increases with the increase of the shear modulu of both the matrix and the inhomogeneity and increases with the increase of the wedge angle. The shielding effect (or anti-shielding effect) reaches the maximum when the dislocation tends to the wedge inhomogeneity interface.

Heat conduction in graphene flakes with inhomogeneous mass interface

Using nonequilibrium molecular dynamics simulations, we study the heat conduction ingraphene flakes composed by two regions. One region is mass-loaded and theother one is intact. It is found that the mass interface between the two regionsgreatly decreases the thermal conductivity, but it would not bring about a thermalrectification effect. The dependence of thermal conductivity upon the heat flux andthe mass difference ratio is studied to confirm the generality of the result. Theinterfacial scattering of solitons is studied to explain the absence of the rectificationeffect.

SU-E-T-577: Stereotactic Radiosurgery for AVMs: Impact of Embolization Media on Radiation Dose

Purpose: We investigate the dosimetric impact of surgical embolization of Arteriovascular‐malformations (AVM's) on further follow‐up Stereotactic Radiosurgery. Two embolization media are studied. By introducing a tissue inhomogeneity, the breakdown in electron equilibrium at the interface impacts actual tissue dose within a few mm. As this is the precise location of the target tissue the dose departure from standard prescription is to be quantified. Methods: Inhomogeneity phantoms were constructed to model regions of various thickness 2mm – 16mm. Each phantom was constructed of a tissue equivalent material while drilled embolization cavities were filled with 4 different admixtures of embolizing media: Onyx (TM) with contrast‐ to‐polymer ratio 18% and 34%; and Embucrilate (TM) (33% and 50%). Near tissue‐equivalent radiochromic film was placed in planes 0, 1, and 2mm up‐beam and down‐beam from the inhomogeneity. The simulated embolizations and films were then irradiated in a 6MV radiosurgery beam at tissue depth of 7cm. Results: In a narrow beam geometry, we observe an immediate depletion of dose at the interface downstream of the Onyx medium of up to 20% compared to 18% for the Embucrilate. The dose enhancement immediately upstream of the embolization medium interface is typically 25% for the Onxy and 15% for Embucrilate. Conclusions: While radiosurgery beams are typically directed from a large range of angles, the two connected dose interface effects tend to cancel only laterally. Typical beam arrangements have a superior‐to‐inferior directional bias and the inhomogeneity interface effects on dose will have an effect on the target tissue at those aspects of the embolized portions of the AVM lesion.

Nanometer-resolution measurement and modeling of lateral variations of the effective work function at the bilayerPt/Al/SiO2interface

A ballistic electron emission microscopy (BEEM) comparison of the dependence on gate voltage of the average energy barrier of a metal bilayer $\text{Pt}/\text{Al}/{\text{SiO}}_{2}/\text{Si}$ sample and a $\text{Pt}/{\text{SiO}}_{2}/\text{Si}$ sample suggests that the metal/oxide interface of the $\text{Pt}/\text{Al}/{\text{SiO}}_{2}/\text{Si}$ sample is laterally inhomogeneous at nm length scales. However, BEEM images of the bilayer sample do not show significantly larger lateral variations than observed on a (uniform) $\text{Pt}/{\text{SiO}}_{2}/\text{Si}$ sample, indicating that any inhomogeneous ``patches'' of lower-energy barrier height have size smaller than the lateral resolution of BEEM, estimated for these samples to be $\ensuremath{\sim}10\text{ }\text{nm}$. Finite element electrostatic simulations of an assumed inhomogeneous interface with nm size patches of different effective work function can fit the experimental data of the bilayer sample much better than an assumed homogenous interface, indicating that the bilayer film is laterally inhomogeneous at the nm scale.

Scattering of Thermal Waves and Unsteady Effective Thermal Conductivity of Particular Composites with Functionally Graded Interface

In this study, thermal wave method is applied to investigate the unsteady effective thermal conductivity of particular composites with a functionally graded interface, and the analytical solution of the problem is obtained. The Fourier heat conduction law is applied to analyze the propagation of thermal waves in the particular composite. The scattering and refraction of thermal waves by a spherical particle with an inhomogeneous interface layer in the matrix are analyzed, and the results of the single scattering problem are applied to the composite medium. The wave fields in different material layers are expressed by employing spherical wave function expansion method, and the expanded mode coefficients are determined by satisfying the boundary conditions of the layers. The theory of Waterman and Truell is applied to obtain the effective propagating wave number and the unsteady effective thermal conductivity of composites. Through the numerical examples, it is found that in different region of wave frequency, the effect of the thickness of the interface on the unsteady effective thermal conductivity of composites shows great difference. The effect of the thermal conductivity ratio of the particles and matrix on the unsteady effective thermal conductivity is closely related to the incident frequency of thermal waves. The variation of the interface properties between the particles and matrix also expresses great effect on the unsteady effective thermal conductivity of composites. Finally, comparison with the results obtained from other methods is made.

Interfacial tension of nonassociating pure substances and binary mixtures by density functional theory combined with Peng–Robinson equation of state

We develop a density functional theory and investigate the interfacial tension of several pure substances N(2), CO(2), H(2)S, normal alkanes from C(1) to nC(10), and binary mixtures C(1)/C(3), C(1)/nC(5), C(1)/nC(7), C(1)/nC(10), CO(2)/nC(4), N(2)/nC(5), N(2)/nC(6), N(2)/nC(8), N(2)/nC(10), nC(6)/nC(7), nC(6)/nC(8), and nC(6)/nC(10). The theory is combined with the semiempirical Peng-Robinson equation of state (PR-EOS). The weighted density approximation (WDA) is adopted to extend the bulk excess Helmholtz free energy to the inhomogeneous interface. Besides, a supplementary term, quadratic density expansion (QDE), is introduced to account for the long-range characteristic of intermolecular dispersion attractions, which cannot be accurately described by the WDA. In the bulk limit, the QDE vanishes and the theory is reduced to the PR-EOS. For pure substances, the potential expansion parameter is the only adjustable parameter in the QDE and determined by using a single measured interfacial tension at the lowest temperature examined. Then without any parameter adjustment, we faithfully predict the interfacial tensions of pure substances and mixtures over a wide range of conditions.

Inherent Buffer-layer Formation on Chalcopyrite Absorbers

AbstractWe report on epitaxial growth of ZnO on polycrystalline and (112) orientated CuInS2 and CuInSe2 thin films. Step-by-step growth and investigation by photoelectron spectroscopy (PES) and low energy electron diffraction (LEED) provided information on the growth mode and the electronic structure of the ZnO-CuInS2-interface. During the initial growth no ZnO is deposited. Instead a monolayer of ZnS is formed by depletion the CuInS2 surface of excess sulfur. Thereafter, the ZnO growth starts on the ZnS buffer layer. The band alignment derived from PES shows that the ZnS buffer layer is thin enough to provide a beneficial band alignment for photovoltaic applications. CuInSe2 (112) samples showed a similar behaviour, but at the chosen deposition temperature of 450°C only ZnSe growth is detected. At lower temperatures ZnO growth on top of ZnSe is observed. XPEEM experiments show an inhomogeneous interface.

Is surface crystallization in liquid eutectic AuSi surface-induced?

Recent x-ray measurements have revealed surface crystallization in the liquid eutecticAu0.82Si0.18 alloy accompanied by a pronounced surface-induced layering with a thickness of seven toeight well-defined atomic layers. For the crystalline surface monolayer a stoichiometry ofAuSi2 has been determined, implying a strong Si surface enrichment. In this study we haveanalysed the composition at the interface with vacuum of the solid and liquid eutectic alloyby means of x-ray photoelectron spectroscopy (XPS). Evaluation of the XPS spectra usinga homogeneous interface model and an inhomogeneous interface model clearly indicates astrong interfacial enrichment of Si in agreement with the x-ray measurements. In aninterfacial layer of 2 nm thickness the average Si concentration is nearly three times largerthan that in the bulk. However, the XPS spectra give evidence for a low concentration(∼3 at.%) of oxide impurities at the interface—in all probabilitySiO2—which raises the question of whether surface crystallization in this alloy is surface-induced or drivenby SiO2 nucleation centres.

Scattering of Thermal Waves and Non-steady Effective Thermal Conductivity of Unidirectional Fibrous Composites with Functionally Graded Interface

In this paper, a thermal wave method is applied to investigate the non-steady effective thermal conductivity of unidirectional fibrous composites with a functionally graded interface, and the analytical solution of the problem is obtained. The Fourier heat conduction law is applied to analyze the propagation of thermal waves in the fibrous composite. The scattering and refraction of thermal waves by a cylindrical fiber with an inhomogeneous interface layer in the matrix are analyzed, and the results of the single scattering problem are applied to the composite medium. The wave fields in different material layers are expressed by using the wave function expansion method, and the expanded mode coefficients are determined by satisfying the boundary conditions of the layers. The theory of Waterman and Truell is employed to obtain the effective propagating wave number and the non-steady effective thermal conductivity of composites. As an example, the effects of a graded interface on the effective thermal conductivity of composites are graphically illustrated and analyzed. Analysis shows that the non-steady effective thermal conductivity under higher frequencies is quite different from the steady thermal conductivity. In the region of intermediate and high frequencies, the effect of the properties of the interface on the effective thermal conductivity is greater. Comparisons with the steady thermal conductivity obtained from other methods are also presented.

Solving combined inverse problems for multicomponent parabolic distributed systems

The paper outlines a technique to construct computational algorithms for solving combined inverse problems for multicomponent parabolic systems with main and natural inhomogeneous interface conditions. Frechet derivatives are obtained in explicit form for quadratic residual functionals to construct gradient computational algorithms.

Scattering of antiplane shear wave by a piezoelectric circular cylinder with an imperfect interface

We present analytical solutions for the scattering of an antiplane shear wave by a piezoelectric circular cylinder with an imperfect interface. We first consider the simple case in which the imperfection is homogeneous along the interface. Two typical imperfect interfaces are addressed: 1) mechanically compliant and dielectrically weakly conducting interface, and 2) mechanically compliant and dielectrically highly conducting interface. The expressions for the directivity pattern and scattering cross-section of the scattered shear waves are derived. We then investigate the more difficult problem in which the imperfection is circumferentially inhomogeneous along the interface. A concise expression for an inhomogeneously compliant and weakly conducting interface is derived by means of matrix notation. Numerical examples are presented to demonstrate the effect of the imperfection and the circumferential inhomogeneity of the interface on the directivity patterns and scattering cross-sections of the scattered shear wave. The circumferentially inhomogeneous interface is also utilized to model the interface where an arbitrary number of cracks exist. Results show that when every part of the interface is rather compliant, large low-frequency peaks of the scattered cross-sections, which correspond to the resonance scattering, can be observed no matter if the interface is homogeneous or inhomogeneous. The appearance of large low-frequency peaks can be well explained by estimating the natural frequency of the corresponding reduced mass-spring system where the cylinder is assumed as a rigid body. Peaks of the scattered cross-sections spanning from low frequencies to high frequencies can be observed for a cylinder with a partially debonded interface.

High density dental materials and radiotherapy planning: Comparison of the dose predictions using superposition algorithm and fluence map Monte Carlo method with radiochromic film measurements

Background and purpose During radiotherapy planning high density dental materials create a major challenge in determining correct dose distribution inside patients with head-and-neck tumors. Patients and methods In this work we investigated the absorbed dose distribution inside a solid water ® slab phantom with embedded high density material irradiated by a 6 MV photon beam of field size 10 × 10 cm. We evaluated the absorbed dose distribution with three different techniques: superposition algorithm, radiochromic film, and the fluence map Monte Carlo (FMMC) method. Results The results obtained with radiochromic film and FMMC were in good agreement (within ±5% of the dose) with one another. The superposition algorithm, which is often considered superior to other commercially available dose calculation algorithms, produced appreciably less accurate results than FMMC. In particular, downstream from the high density cerrobend inhomogeneity the superposition algorithm predicts a higher dose than the measurement does by at least 10–16% depending upon the size of the inhomogeneity and the distance from it. Upstream of the high density inhomogeneities the superposition algorithm predicts a lower than measured dose due to its failure to predict the dose enhancement close to the inhomogeneity interface. Conclusions The delivered dose downstream from a high density inhomogeneity would be significantly less than the prescribed dose calculated by the superposition algorithm. The FMMC method which is based on a hybrid of the superposition algorithm input fluence data and Monte Carlo can be a useful tool in predicting dose in the presence of high density (e.g. dental) materials.

Interface Controlled Electronic Charge Inhomogeneities in Correlated Heterostructures

For heterostructures of ultrathin, strongly correlated copper-oxide films and dielectric perovskite layers, we predict inhomogeneous electronic interface states. Our study is based on an extended Hubbard model for the cuprate film. The interface is implemented by a coupling to the electron and phonon degrees of freedom of the dielectric oxide layer. We find that electronic ordering in the film is associated with a strongly inhomogeneous polaron effect. We propose to consider the interfacial tuning as a powerful mechanism to control the charge ordering in correlated electronic systems.

Size-dependent interaction between an edge dislocation and a nanoscale inhomogeneity with interface effects

The influence of the interface stress on the interaction between an edge dislocation and a circular nanoscale inhomogeneity is investigated. The explicit solutions are given for stress fields and the image force acting on the edge dislocation. The impact of interface properties and the size of the inhomogeneity on the glide/climb force are evaluated. The results show that the local hardening and softening effects at the interface of the nanoscale inhomogeneity due to the interface stress are remarkable and an additional repulsive/attractive force acting on the dislocation is produced. The normalized glide/climb force increases (decreases) with the decrease of the radius of the inhomogeneity, and the size dependence becomes significant when the radius of the inhomogeneity is reduced to the nanometer scale which differs from the size-independent classical solutions. For some cases, the glide/climb of the edge dislocation near the nanoinhomogeneity may be more difficult because more equilibrium locations are present.

An investigation of electrical and structural properties of Ni-germanosilicided Schottky diode

Ni-germanosilicided Schottky barrier diode has been fabricated by annealing the deposited Ni film on strained-Si and characterized electrically in the temperature range of 125 K–300 K. The chemical phases and morphology of the germanosilicided films were studied by using scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The Schottky barrier height ( ϕ b), ideality factor ( n) and interface state density ( D it) have been determined from the current–voltage ( I– V) and capacitance–voltage ( C– V) characteristics. The current–voltage characteristics have also been simulated using SEMICAD device simulator to model the Schottky junction. An interfacial layer and a series resistance were included in the diode model to achieve a better agreement with the experimental data. It has been found that the barrier height values extracted from the I– V and C– V characteristics are different, indicating the existence of an in-homogeneous Schottky interface. Results are also compared with bulk-Si Schottky diode processed in the same run. The variation of electrical properties between the strained- and bulk-Si Schottky diodes has been attributed to the presence of out-diffused Ge at the interface.

Growth and SIMS study of d.c.‐sputtered indium oxide films on silicon

AbstractIndium oxide thin films were grown onto Si and quartz substrates by d.c. reactive sputtering of elemental indium. X‐ray diffraction and transmission electron microscopy studies confirmed the single‐phase and polycrystalline nature of the films. Secondary ion mass spectrometry investigations of In2O3/Si structures showed the formation of an inhomogeneous interface region ∼20 nm thick between In2O3 and Si. The overall feature of the interface remained the same under annealing in an oxygen atmosphere, but annealing in an argon atmosphere drastically altered the nature of the interface. The observations indicate that interface formation and stability depend critically on the availability of oxygen. Copyright © 2005 John Wiley & Sons, Ltd.

Growth and ion beam study of DC sputtered indium oxide films

Transmission electron microscopy (TEM) and ion beam techniques were used to study the DC reactively sputtered In2O3 films on Si substrates. TEM studies showed that the films are single-phase and polycrystalline. Particle induced X-ray emission (PIXE) enabled trace analysis of the films. Rutherford backscattering spectrometry (RBS) investigations suggested the formation of 20nm thick inhomogeneous interface region between In2O3 film and Si. Secondary ion mass spectrometry (SIMS) depth profiling and current–voltage measurements confirmed the presence of the interface region.