Equivalent Interface Research Articles

Interfacial models in viscoplastic composites materials

The aim of the present work is to extend the concept of interphase and equivalent imperfect interface in the context of viscoplasticity. The interphase takes the form of a thin curved layer of constant thickness, made up of a rigid viscoplastic material located between two other surrounding materials. We aim at representing this interphase by an interface with appropriately devised interface conditions. To reach this objective, a Taylor expansion of the relevant physical fields in the thin region is used. It is shown that, depending of the degree of stiffness of the layer with respect to the neighboring media, this interphase can be replaced by an idealized imperfect interface involving the jump of the velocity field or the traction vector. The first kind of interface model, applicable to soft interphases, is the “spring-type” interface across which the traction are continuous but the velocity field exhibits a discontinuity which is given in term of the traction by a power-law type relation. Moreover, it is shown that the constant of the model can be expressed in terms of the material parameters of the interphase. When the interphase is stiffer than the two surrounding media, it can be replaced by an imperfect interface described by a generalization of the so-called Young Laplace model to viscoplastic solids.

On the relation between finite element and finite volume schemes for compressible flows with cylindrical and spherical symmetry

A complete set of equivalence conditions, connecting the node-centered finite volume and the mass-lumped finite element schemes, is derived for the first time for the one-dimensional compressible Euler equations with cylindrical and spherical symmetry. Analytical expressions for the evaluation of the equivalent cell volumes and interface normals in terms of the finite element integrals are presented. Numerical experiments for compressible unsteady flows, including expanding and converging shock problems, are carried out using the new approach and the differences with the results from a finite volume scheme violating the equivalence conditions are discussed.

A Simple Definition of Structural Regions in Proteins and Its Use in Analyzing Interface Evolution

Analysis of proteins commonly requires the partition of their structure into regions such as the surface, interior, or interface. Despite the frequent use of such categorization, no consensus definition seems to exist. This study thus aims at providing a definition that is general, is simple to implement, and yields new biological insights. This analysis relies on 397, 196, and 701 protein structures from Escherichia coli, Saccharomyces cerevisiae, and Homo sapiens, respectively, and the conclusions are consistent across all three species. A threshold of 25% relative accessible surface area best segregates amino acids at the interior and at the surface. This value is further used to extend the core–rim model of protein–protein interfaces and to introduce a third region called support. Interface core, rim, and support regions contain similar numbers of residues on average, but core residues contribute over two-thirds of the contact surface. The amino acid composition of each region remains similar across different organisms and interface types. The interface core composition is intermediate between the surface and the interior, but the compositions of the support and the rim are virtually identical with those of the interior and the surface, respectively. The support and rim could thus “preexist” in proteins, and evolving a new interaction could require mutations to form an interface core only. Using the interface regions defined, it is shown through simulations that only two substitutions are necessary to shift the average composition of a 1000-Å 2 surface patch involving ∼ 28 residues to that of an equivalent interface. This analysis and conclusions will help understand the notion of promiscuity in protein–protein interaction networks.

Stability of polar semiconductor heterostructures

AbstractIn the present paper we use an ab initio density functional theory approach to investigate the stability of differently terminated PbTe(rs)/CdTe(zb)(100) and ErAs(rs)/InGaAs2(zb)(100) heterostructures for different environmental conditions. While in PbTe/CdTesystems differently terminated interfaces are favored in ErAs/InGaAs2 heterostructure systems with two equivalent interface terminations are the most stable configuration. This behavior is the consequence of the less strong ionic character of InGaAs2 compared to CdTe (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Jump conditions for filtered quantities at an under-resolved discontinuous interface. Part 2: A priori tests

In order to study and validate the jump conditions established in part 1, we realize a priori tests thanks to the data of a 3D Direct Numerical Simulation (DNS) of a strongly deformable bubble in a spatially decaying turbulence. The complex interactions between interface and turbulence are fully resolved. An explicit filtering of the DNS has been employed to evaluate the filtered quantities and to check the potential of the models for two-phase flows in the Interface and Subgrid Scales (ISS) modeling case proposed in part 1. The ISS concept is our proposal of a two-phase equivalent for the one-phase Large Eddy Simulation (LES) modeling case with sharp-interfaces. In this concept, bubbles remain bigger than the mesh size. Due to the impossibility to define a filter equivalent to the matched asymptotic expansions, we only test the modeling of the equivalent interface transport (the momentum jump conditions are not tested in this article, but will deserve additional results in a posteriori tests). Because the closure of the transport equation of the under-resolved discontinuous interface requires more modeling assumptions than the closure of the momentum equation, we think that the most relevant test has been done. The a priori tests realized show excellent agreement between the ISS models and the real contributions.

Study on the thermal stability and electrical properties of the high-k dielectrics (ZrO2) x (SiO2)1−x

(ZrO2) x (SiO2)1−x (Zr-Si-O) films with different compositions were deposited on p-Si(100) substrates by using pulsed laser deposition technique. X-ray photoelectron spectra (XPS) showed that these films remained amorphous after annealing at 800°C with RTA process in N2 for 60 s. The XPS spectra indicated that Zr-Si-O films with x=0.5 suffered no obvious phase separation after annealing at 800°C, and no interface layer was formed between Zr-Si-O film and Si substrate. While Zr-Si-O films with x >0.5 suffered phase separation to precipitate ZrO2 after annealing under the same condition, and SiO2 was formed at the interface. To get a good interface between Zr-Si-O films and Si substrate, Zr-Si-O films with bi-layer structure (ZrO2)0.7(SiO2)0.3/(ZrO2)0.5(SiO2)0.5/Si was deposited. The electrical properties showed that the bi-layer Zr-Si-O film is of the lowest equivalent oxide thickness and good interface with Si substrate.

Chatter suppression in micro end milling with process damping

Micro milling utilizes miniature micro end mills to fabricate complexly sculpted shapes at high rotational speeds. One of the challenges in micro machining is regenerative chatter, which is an unstable vibration that can cause severe tool wear and breakage, especially in the micro scale. In order to predict chatter stability, the tool tip dynamics and cutting coefficients are required. However, in micro milling, the elasto-plastic nature of micro machining operations results in large process damping in the machining process, which affects the chatter. We have used the equivalent volume interface between the tool and the workpiece to determine the process damping parameter. Furthermore, the accurate measurement of the tool tip dynamics is not possible through direct impact hammer testing. The dynamics at the tool tip is indirectly obtained by employing the receptance coupling method, and the mechanistic cutting coefficients are obtained from experimental cutting tests. Chatter stability experiments have been performed to examine the proposed chatter stability model in micro milling.

Structure and Evolution of a Novel Dimeric Enzyme from a Clinically Important Bacterial Pathogen

Dihydrodipicolinate synthase (DHDPS) catalyzes the first committed step of the lysine biosynthetic pathway. The tetrameric structure of DHDPS is thought to be essential for enzymatic activity, as isolated dimeric mutants of Escherichia coli DHDPS possess less than 2.5% that of the activity of the wild-type tetramer. It has recently been proposed that the dimeric form lacks activity due to increased dynamics. Tetramerization, by buttressing two dimers together, reduces dynamics in the dimeric unit and explains why all active bacterial DHDPS enzymes to date have been shown to be homo-tetrameric. However, in this study we demonstrate for the first time that DHDPS from methicillin-resistant Staphylococcus aureus (MRSA) exists in a monomer-dimer equilibrium in solution. Fluorescence-detected analytical ultracentrifugation was employed to show that the dimerization dissociation constant of MRSA-DHDPS is 33 nm in the absence of substrates and 29 nm in the presence of (S)-aspartate semialdehyde (ASA), but is 20-fold tighter in the presence of the substrate pyruvate (1.6 nm). The MRSA-DHDPS dimer exhibits a ping-pong kinetic mechanism (k(cat)=70+/-2 s(-1), K(m)(Pyruvate)=0.11+/-0.01 mm, and K(m)(ASA)=0.22+/-0.02 mm) and shows ASA substrate inhibition with a K(si)(ASA) of 2.7+/-0.9 mm. We also demonstrate that unlike the E. coli tetramer, the MRSA-DHDPS dimer is insensitive to lysine inhibition. The near atomic resolution (1.45 A) crystal structure confirms the dimeric quaternary structure and reveals that the dimerization interface of the MRSA enzyme is more extensive in buried surface area and noncovalent contacts than the equivalent interface in tetrameric DHDPS enzymes from other bacterial species. These data provide a detailed mechanistic insight into DHDPS catalysis and the evolution of quaternary structure of this important bacterial enzyme.

MODELING AND SIMULATION OF COUPLING EFFECT ON LOW FREQUENCY NOISE IN ADVANCED SOI MOSFETS

Low frequency noise modeling and numerical simulation have been carried out to study the influence of the back interface quality and the silicon film thickness in Fully Depleted SOI MOSFETs, with special emphasis on the coupling effect. In devices with a standard film thickness, the noise level is higher than for an equivalent interface in bulk device, which could be a great concern for analog applications. On the other hand, it has been shown that in very thin SOI devices with a symmetrical structure (Double Gate architecture), the reduction of electric field in the silicon film, induces a conduction channel in the middle of the film, away from both interfaces which in turn reduces the scattering rate of carriers, decreasing the noise level.

Interface Forces in Laterally Impacted Steel Tubes

In engineering mechanisms, solid bodies frequently come to a contact with a variety of geometric and kinematic situations. There has been a trend to express the interaction of the contacted bodies in the form of equivalent interface forces. The interface force represents the level of load transferred from one body to another. In a static or quasi-static contact problem, the interface forces could be sensibly evaluated by integrating the normal and the shear stresses over the common interfaces. In a dynamic contact, the interface stresses and subsequently the interface forces happen to be more complicated. They are, furthermore, affected by other parameters such as inertia forces, stress waves propagation, the material strain rate dependency and damping. This paper reports interface forces recorded in a series of experimental impact tests on axially pre-compressed steel tubes along with those from the numerical simulations of the tests. To monitor the so called impact loads, two small steel rings as load cells have been built in the striker. Based on the experimental and numerical results, the concept of equivalent interface forces in the impacted tubes has been verified. It has been highlighted that the interface forces (or the impact loads) may vary on the striker or the specimen themselves, depending on the measuring locations. Effects of axial compressions on the interface forces picked up by the striker load cells, impact loads imparted to the specimen supports and on the impact duration have been discussed. It has been reported that the initial compression applied to the tubes does not remain constant during and after the impact event. The amount of variations also depends on the initial level of the tube compression.

Immersed-Interface Finite-Element Methods for Elliptic Interface Problems with Nonhomogeneous Jump Conditions

In this work, a class of new finite-element methods, called immersed-interface finite-element methods, is developed to solve elliptic interface problems with nonhomogeneous jump conditions. Simple non-body-fitted meshes are used. A single function that satisfies the same nonhomogeneous jump conditions is constructed using a level-set representation of the interface. With such a function, the discontinuities across the interface in the solution and flux are removed, and an equivalent elliptic interface problem with homogeneous jump conditions is formulated. Special finite-element basis functions are constructed for nodal points near the interface to satisfy the homogeneous jump conditions. Error analysis and numerical tests are presented to demonstrate that such methods have an optimal convergence rate. These methods are designed as an efficient component of the finite-element level-set methodology for fast simulation of interface dynamics that does not require remeshing.

Improved Monte Carlo algorithm of phonon transport in semiconductor nanodevices

In this work, we present the main features of an algorithm of phonon transport based on the particle Monte Carlo solution of the Boltzmann Transport Equation. In particular, we have developed an injection technique which consists in replacing a costly reservoir of phonons at thermodynamic equilibrium by an equivalent interface injecting in the device the appropriate phonon distribution. Additionally, we have derived a formulation of phonon–phonon scattering rates which includes realistic phonon dispersion of the material giving accurate frequency-dependence. An algorithm is proposed to improve the treatment of phonon interaction.

A New Dual-Primal Domain Decomposition Approach for Finite Element Simulation of 3-D Large-Scale Electromagnetic Problems

A novel dual-primal non-overlapping domain decomposition method (DDM) for the finite element solution of three-dimensional (3D) large-scale electromagnetic problems is proposed. This method reduces the computational complexity from solving the original 3D problem to an equivalent interface problem by utilizing the idea of the dual-primal finite element tearing and interconnecting (FETI-DPEM) method. The new method, which is referred to as the FETI-DPEM2, combines the dual-primal idea with two Lagrange multipliers and implements Robin-type transmission condition at the subdomain interfaces to significantly improve the convergence of the interface solution in the high-frequency region. Similar to the original version, a global coarse problem related to the degrees of freedom at the subdomain corner edges is designed to propagate the residual error to the whole computational domain at each iteration, which further increases the convergence. Numerical examples are presented to demonstrate the validity and the capability of this method. The results show that the proposed method produces fast solutions to large-scale problems in any frequency band.

Corrosion behaviour of Cu–10Sn bronze in aerated NaCl aqueous media – Electrochemical investigation

Investigation of the electrochemical behaviour of Cu–10Sn (wt.%) alloy has been conducted in aerated aqueous chloride solutions and compared to that of pure Cu and Sn. Cathodic and anodic bronze behaviours have been investigated in function of the chloride concentrations (0.1–0.001 M), the rotation speed of the electrode and the potential sweep rate after 1-h immersion time in open-circuit conditions. At the corrosion potential, the corrosion behaviour appears determined by the charge-transfer controlled reduction of oxygen and the mixed charge- and mass-transfer controlled electrodissolution. In 0.1 M NaCl solution, three anodic regions are evidenced corresponding to: (I) a dissolution part from Eoc value, (II) a maximum current region corresponding to peaks formation and (III) a large current plateau. A partial protective effect of the corrosion product layer is observed at high anodic potential. It has been interpreted as the result of a 3D growth mechanism involving the formation of stable tin species in the layer according to a “pore resistance model”. Results on synthetic alloy are compared with those obtained on an archaeological bronze with a similar composition immersed in the same medium. Equivalent interface behaviour is evidenced between the synthetic and the archaeological bronzes.

Force-balance interface circuit based on floating MOSFET capacitors for micro-machined capacitive accelerometers

The feasibility of a force-balance interface based on a second-order delta-sigma (/spl Delta//spl Sigma/) modulator for capacitive sensors has been analyzed in order to delimit the requirements to assure system stability for a given set of constraints related to the sensor-modulator system. A /spl Delta//spl Sigma/ modulator based on a switched-capacitor architecture with floating MOSFET capacitors has been implemented using a 0.7-/spl mu/m CMOS process. Nonlinear effects related to voltage dependence of the floating MOSFET capacitors have been avoided using a modulator architecture based on charge integrators. The behavior of the new proposed modulator has been measured experimentally and compared with an equivalent interface made with lineal capacitors. Similar results were obtained from both systems. In both circuits, the modulator resolution was better than 14 bits at a sample frequency of 250 kHz, and oversampling ratio of 256.

A study of HfO2 film interfaces with Si and SiO2

The interfaces studied were formed by the thermal oxidation of sputter-deposited Hf metal onto Si(100)- and SiO2-covered Si(100) wafers and were analyzed in situ and in real time using spectroscopic ellipsometry (SE) in the 1.5–4.5 photon energy range and with mass spectrometry of recoiled ions (MSRI). SE yielded optical properties and MSRI yielded film and interface composition. Reactivity between HfO2 and both substrates was found to be similar based upon the optical properties of the interface layer. Equivalent oxide thicknesses and interface trap levels were determined and significant reduction in interface traps was noticed for samples with a 2 nm SiO2 film on Si. In addition, hillock formation was seen to occur upon oxidation of Hf metal on the Si substrates and depended on the starting thickness of the metal layer and was not seen for the SiO2-covered substrates.

Large exchange bias and high stability of CoFe∕CrPt films with L10 CrPt as the pinning layer

We have studied an antiferromagnetic L10 CrPt film as a pinning layer. dc magnetron sputtered [Pt∕Cr] multilayers on a Co0.9Fe0.1 layer exhibit no exchange bias. After being annealed at 350 °C for 5 h in a vacuum, the equiatomic [Pt∕Cr] multilayer stack is transformed into a uniform CrPt alloy film with L10 phase, which pins the adjacent 120 Å CoFe layer with a pinning field of ∼70Oe and a coercivity of only 28 Oe. The hysteresis loop of this exchange biased system is almost square and the interdiffusion between the CrPt and the CoFe layers is rather small. The equivalent interface exchange energy ΔE, 0.12erg∕cm2, is comparable to the typical value of FeMn biasing system. However, the blocking temperature, at which the exchange bias disappears, is as high as 600 °C, 150 °C higher than the highest value ever reported. Since it possesses extremely good thermal stability, large exchange bias, little interdiffusion, and high corrosion resistance, the antiferromagnetic CrPt film is proposed to serve as a pinning layer for magnetoresistive devices.

Zr O 2 film interfaces with Si and SiO2

The interface formed by the thermal oxidation of sputter-deposited Zr metal onto Si(100)- and SiO2-coated Si(100) wafers was studied in situ and in real time using spectroscopic ellipsometry (SE) in the 1.5–4.5 photon energy range and mass spectrometry of recoiled ions (MSRI). SE yielded optical properties for the film and interface and MSRI yielded film and interface composition. An optical model was developed and verified using transmission electron microscopy. Interfacial reaction of the ZrO2 was observed for both substrates, with more interaction for Si substrates. Equivalent oxide thicknesses and interface trap levels were determined on capacitors with lower trap levels found on samples with a thicker SiO2 underlayer. In addition to the optical properties for the intermixed interface layer, the optical properties for Zr metal and unreacted ZrO2 are also reported.

Ge diffusion in Ge metal oxide semiconductor with chemical vapor deposition HfO2 dielectric

We report a study on Ge diffusion and its impact on the electrical properties of TaN∕HfO2∕Ge metal-oxide-semiconductor (MOS) device. It is found that Ge diffusion depends on the amount of GeO2 formed at the HfO2∕Ge interface and can be retarded by surface nitridation. It is speculated that Ge diffusion is in the form of GeO or Ge-riched HfGeO. Effective suppression of Ge diffusion by NH3 nitridation has resulted in improved electrical properties of TaN∕HfO2∕Ge MOS device, including equivalent oxide thickness (EOT), leakage current, hysteresis, and interface state density. The degradation of leakage current after high temperature post metallization anneal (PMA) is found to be due to Ge diffusion.

An anti-interpenetration model and connections between interphase and interface models in particle-reinforced composites

Linear spring interface model and interphase model are often used to simulate the interface behaviour of particle-reinforced composite materials. However, the former may give rise to nonphysical interpenetration at the interface between a particle and the surrounding material. In this paper, first, a model is presented to prevent the interpenetration phenomenon at the interface. This model can be used together with a given linear or nonlinear interface model to calculate the stress field in particle-reinforced composites with imperfect interface bonding condition, or with debonding damage. Second, the connections between the thin interphase model and interface models are studied for spherical particle-reinforced composites. It is found that while a relatively thin and compliant interphase can be well approximated by the equivalent linear spring interface model, a relatively thin and stiff interphase can be well approximated by the equivalent interface stress model. For the latter, the relations between the equivalent interface moduli and the interphase stiffness and thickness are presented.