Applicability Range of Stoneys Formula and Modified Formulas for a Film/Substrate Bilayer

In addition to the layer thickness and effective Young’s modulus, the impact of the kinematic assumptions, interfacial condition, in-plane force, boundary conditions, and structure dimensions on the curvature of a film/substrate bilayer is examined. Different models for the analysis of the bilayer curvature are compared. It is demonstrated in our model that the assumption of a uniform curvature is valid only if there is no in-plane force. The effects of boundary conditions and structure dimensions, which are not-fully-included in previous models are shown to be significant. Three different approaches for deriving the curvature of a film/substrate bilayer are presented, compared, and analyzed. A more comprehensive study of the conditions regarding the applicability of Stoney’s formula and modified formulas is presented.

Cell shape changes indicate a role for extrinsic tensile forces in Drosophila germ-band extension.

Drosophila germ-band extension (GBE) is an example of the convergence and extension movements that elongate and narrow embryonic tissues. To understand the collective cell behaviours underlying tissue morphogenesis, we have continuously quantified cell intercalation and cell shape change during GBE. We show that the fast, early phase of GBE depends on cell shape change in addition to cell intercalation. In antero-posterior patterning mutants such as those for the gap gene Krüppel, defective polarized cell intercalation is compensated for by an increase in antero-posterior cell elongation, such that the initial rate of extension remains the same. Spatio-temporal patterns of cell behaviours indicate that an antero-posterior tensile force deforms the germ band, causing the cells to change shape passively. The rate of antero-posterior cell elongation is reduced in twist mutant embryos, which lack mesoderm. We propose that cell shape change contributing to germ-band extension is a passive response to mechanical forces caused by the invaginating mesoderm.

Deformation twinning and its effect on crack extension

Deformation twinning near a crack tip is observed in b.c.c. metal Mo based on molecular dynamics simulation at temperature T = 50 K and loading rate (K) over dot(II) = 0.0706 MPa m(1/2)/ps. The defor mation twinning is closely controlled by both the crystal geometry orientation and the stress distribution. The width of the deformation twin band is affected by the distance between the upper and lower crack surfaces. The twin plane and twin direction are (<1(1)over bar>2) and [(1) over bar 11], respectively. The initial crack extension occurs in the deformation twin region near the crack tip. The simulation shows that the extension direction of the crack is changed as the crack propagates over the twinning boundary.

An Extension of 2D Janbu’s Generalized Procedure of Slices for 3D Slope Stability Analysis II—Numerical Method and Applications

This paper provides a numerical approach on achieving the limit equilibrium method for 3D slope stability analysis proposed in the theoretical part of the previous paper. Some programming techniques are presented to ensure the maneuverability of the method. Three examples are introduced to illustrate the use of this method. The results are given in detail such as the local factor of safety and local potential sliding direction for a slope. As the method is an extension of 2D Janbu's generalized procedure of slices (GPS), the results obtained by GPS for the longitudinal sections of a slope are also given for comparison with the 3D results. A practical landslide in Yunyang, the Three Gorges, of China, is also analyzed by the present method. Moreover, the proposed method has the advantages and disadvantages of GPS. The problem frequently encountered in calculation process is still about the convergency, especially in analyzing the stability of a cutting corner. Some advice on discretization is given to ensure convergence when the present method is used. However, the problem about convergency still needs to be further explored based on the rigorous theoretical background.

Long-Range Stress Redistribution Resulting From Damage in Heterogeneous Media

It has been shown in CA simulations and data analysis of earthquakes that declustered or characteristic large earthquakes may occur with long-range stress redistribution. In order to understand long-range stress redistribution, we propose a linear-elastic but heterogeneous-brittle model. The stress redistribution in the heterogeneous-brittle medium implies a longer-range interaction than that in an elastic medium. Therefore, it is surmised that the longer-range stress redistribution resulting from damage in heterogeneous media may be a plausible mechanism governing main shocks.

High tuning range AlSi RF MEMS capacitors fabricated with sacrificial amorphous silicon surface micromachining

This paper reports the fabrication and electrical characterization of high tuning range AlSi RF MEMS capacitors. We present experimental results obtained by a surface micromachining process that uses dry etching of sacrificial amorphous silicon to release Al-1%Si membranes and has a low thermal budget (<450 °C) being compatible with CMOS post-processing. The proposed silicon sacrificial layer dry etching (SSLDE) process is able to provide very high Si etch rates (3-15 μm/min, depending on process parameters) with high Si: SiO2 selectivity (>10,000:1). Single- and double-air-gap MEMS capacitors, as well as some dedicated test structures needed to calibrate the electro-mechanical parameters and explore the reliability of the proposed technology, have been fabricated with the new process. S-parameter measurements from 100 MHz up to 2 GHz have shown a capacitance tuning range higher than 100% with the double-air-gap architecture. The tuning range can be enlarged with a proper DC electrical bias of the capacitor electrodes. Finally, the reported results make the proposed MEMS tuneable capacitor a good candidate for above-IC integration in communications applications. © 2004 Elsevier B.V. All rights reserved.

Models for acoustic propagation through turbofan exhaust flows-lined ducts

Turbomachinery noise radiating into the rearward arc is an important problem. This noise is scattered by the trailing edges of the nacelle and the jet exhaust, and interacts with the shear layers between the external flow, bypass stream and jet, en route to the far field. In the past a range of relevant model problems involving semi-infinite cylinders have been solved. However, one limitation of these previous solutions is that they do not allow for the jet nozzle protruding a finite distance beyond the end of the nacelle (or in certain configurations being buried a finite distance upstream). With this in mind, we have used the matrix Wiener-Hopf technique to allow precisely this finite nacelle-jet nozzle separation to be included. We have previously reported results for the case of hard-walled ducts, which requires factorisation of a 2 × 2 matrix. In this paper we extend this work by allowing one of the duct walls, in this case the outer wall of the jet pipe, to be acoustically lined. This results in the need to factorise a 3 × 3 matrix, which is completed by use of a combination of pole-removal and Pad́e approximant techniques. Sample results are presented, investigating in particular the effects of exit plane stagger and liner impedance. Here we take the mean flow to be zero, but extension to nonzero Mach numbers in the core and bypass flow has also been completed. Copyright © 2009 by Nigel Peake & Ben Veitch.

Forced extension of P-selectin construct using steered molecular dynamics

P-selectin, a 70-nm-long cellular adhesive molecule, possesses elastic and extensible properties when neutrophils roll over the activated endotheliam of blood vessel in inflammatory reaction. Transient formation and dissociation of P-selectin/ligand bond on applied force of blood flow induces the extension of P-selectin and relevant ligands. Steered molecular dynamics simulations were performed to stretch a single P-selectin construct consisting of a lectin (Lec) domain and an epithelial growth factor (EGF)-like domain, where P-selectin construct was forced to extend in water with pulling velocities of 0.005-0.05 nm/ps and with constant forces of 1000-2500 pN respectively. Resulting force-extension profiles exhibited a dual-peak pattern on various velocities, while both plateaus and shoulders appeared in the extension-time profiles on various forces. The force or extension profiles along stretching pathways were correlated to the conformational changes, suggesting that the structural collapses of P-selectin Lec/EGF domains were mainly attributed to the burst of hydrogen bonds within the major beta sheet of EGF domain and the disruptions of two hydrophobic cores of Lee domain. This work furthers the understanding of forced dissociation of P-selectin/ligand bond.

Long-range automaton models of earthquakes: Power-law accelerations, correlation evolution, and mode-switching

We introduce a conceptual model for the in-plane physics of an earthquake fault. The model employs cellular automaton techniques to simulate tectonic loading, earthquake rupture, and strain redistribution. The impact of a hypothetical crustal elastodynamic Green's function is approximated by a long-range strain redistribution law with a r(-p) dependance. We investigate the influence of the effective elastodynamic interaction range upon the dynamical behaviour of the model by conducting experiments with different values of the exponent (p). The results indicate that this model has two distinct, stable modes of behaviour. The first mode produces a characteristic earthquake distribution with moderate to large events preceeded by an interval of time in which the rate of energy release accelerates. A correlation function analysis reveals that accelerating sequences are associated with a systematic, global evolution of strain energy correlations within the system. The second stable mode produces Gutenberg-Richter statistics, with near-linear energy release and no significant global correlation evolution. A model with effectively short-range interactions preferentially displays Gutenberg-Richter behaviour. However, models with long-range interactions appear to switch between the characteristic and GR modes. As the range of elastodynamic interactions is increased, characteristic behaviour begins to dominate GR behaviour. These models demonstrate that evolution of strain energy correlations may occur within systems with a fixed elastodynamic interaction range. Supposing that similar mode-switching dynamical behaviour occurs within earthquake faults then intermediate-term forecasting of large earthquakes may be feasible for some earthquakes but not for others, in alignment with certain empirical seismological observations. Further numerical investigation of dynamical models of this type may lead to advances in earthquake forecasting research and theoretical seismology.

Short-and resonant-range interactions between scales in turbulence and their applications

Interactions between different scales in turbulence were studied starting from the incompressible Navier-Stokes equations. The integral and differential formulae of the short-range viscous stresses, which express the short-range interactions between contiguous scales in turbulence, were given. A concept of the resonant-range interactions between extreme contiguous scales was introduced and the differential formula of the resonant-range viscous stresses was obtained. The short- and resonant-range viscous stresses were applied to deduce the large-eddy simulation (LES) equations as well as the multiscale equations, which are approximately closed and do not contain any empirical constants or relations. The properties and advantages of using the multiscale equations to compute turbulent flows were discussed. The short-range character of the interactions between the scales in turbulence means that the multiscale simulation is a very valuable technique for the calculation of turbulent flows. A few numerical examples were also given.

Effects of physical parameter range on dimensionless variable sensitivity in water flooding reservoirs

The similarity criterion for water flooding reservoir flows is concerned with in the present paper. When finding out all the dimensionless variables governing this kind of flow, their physical meanings are subsequently elucidated. Then, a numerical approach of sensitivity analysis is adopted to quantify their corresponding dominance degree among the similarity parameters. In this way, we may finally identify major scaling law in different parameter range and demonstrate the respective effects of viscosity, permeability and injection rate.

Effects of physical parameter range on dimensionless variable sensitivity in water flooding reservoirs

The similarity criterion for water flooding reservoir flows is concerned with in the present paper. When finding out all the dimensionless variables governing this kind of flow, their physical meanings are subsequently elucidated. Then, a numerical approach of sensitivity analysis is adopted to quantify their corresponding dominance degree among the similarity parameters. In this way, we may finally identify major scaling law in different parameter range and demonstrate the respective effects of viscosity, permeability and injection rate.

Validation of component assembly model and extension to plasticity

Material potential energy is well approximated by '' pair-functional '' potentials. During calculating potential energy, the orientational and volumetric components have been derived from pair potentials and embedding energy, respectively. Slip results in plastic deformation, and slip component has been proposed accordingly. Material is treated as a component assembly, and its elastic, plastic and damage properties are reflected by different components respectively. Material constitutive relations are formed by means of assembling these three kinds of components. Anisotropy has been incorporated intrinsically via the concept of component. Theoretical and numerical results indicate that this method has the capacity of reproducing some results satisfactorily, with the advantages of physical explicitness, etc. (c) 2007 Elsevier Ltd. All rights reserved.