In this paper, the lateral migration of a neutrally buoyant spherical particle in the pressure-driven rectangular channel flow of an Oldroyd-B fluid is numerically investigated with a fictitious domain method. The aspect ratio of the channel cross-section considered is 1 and 2, respectively. The particle lateral motion trajectories are shown for the bulk Reynolds number ranging from 1 to 100, the ratio of the solvent viscosity to the total viscosity being 0.5, and a Weissenberg number up to 1.5. Our results indicate that the lateral equilibrium positions located on the cross-section midline, diagonal line, corner and channel centreline occur successively as the fluid elasticity is increased, for particle migration in square channel flow with finite fluid inertia. The transition of the equilibrium position depends strongly on the elasticity number (the ratio of the Weissenberg number to the Reynolds number) and weakly on the Reynolds number. The diagonal-line equilibrium position occurs at an elasticity number ranging from roughly 0.001 to 0.02, and can coexist with the midline and corner equilibrium positions. When the fluid inertia is negligibly small, particles migrate towards the channel centreline, or the closest corner, depending on their initial positions and the Weissenberg number, and the corner attractive area first increases and then decreases as the Weissenberg number increases. For particle migration in a rectangular channel with an aspect ratio of 2, the transition of the equilibrium position from the midline, ‘diagonal line’ (the line where two lateral shear rates are equal to each other), off-centre long midline and channel centreline takes place as the Weissenberg number increases at moderate Reynolds numbers. An off-centre equilibrium position on the long midline is observed for a large blockage ratio of 0.3 (i.e. the ratio of the particle diameter to the channel height is 0.3) at a low Reynolds number. This off-centre migration is driven by shear forces, unlike the elasticity-induced rapid inward migration, which is driven by the normal force (pressure or first normal stress difference).

In June of 1991, a team of experts from the UN Special Commission (UNSCOM) inspected an Iraqi facility at Samarra, known as the “Muthanna State Enterprise for Pesticide Production.” Its inspection revealed a chemical weapons factory (United Nations, 1991). Inspectors found mustard gas and organophosphorus nerve agents, types GB and GF, as well as tabun—agent GA (CBW News, 1991). They estimated that the facility had the capacity to produce 2.5 tons of sarin and 5 tons of mustard gas per day. According to media reports, “dozens” of companies were implicated in the construction and production processes of the facility, including companies originating from Austria, France, Germany, India, Switzerland, the United States, and seven other countries (CBW News, 1991; Independent, July 17, 1991).

We investigate the dynamics and rheology of elastic particles in a viscous extensional flow under Stokes flow conditions by means of the large deformation method developed by Gao, Hu & Ponte Castañeda (J. Fluid Mech., vol. 687, 2011, pp. 209–237). The particles are assumed to be homogeneous, incompressible and neo-Hookean solids. When subjected to extensional flow, an initially ellipsoidal (elliptical) elastic particle stretches and rotates simultaneously, tending to deform into a stable ellipsoidal shape with the initial major axis aligned with the extension direction. However, the steady-state solutions may not exist when the particle stiffness is lower than a certain critical value. By using the solution of a single particle, the macroscopic rheological properties are evaluated for a dilute suspension of elastic particles under extension. Similar to some polymer blends, softer particles lead to a larger extensional viscosity for the suspension.

In this paper we consider a suspension of elastic solid particles in a viscous liquid. The particles are assumed to be neo-Hookean and can undergo finite elastic deformations. A polarization technique, originally developed for analogous problems in linear elasticity, is used to establish a theory for describing the finite-strain, time-dependent response of an ellipsoidal elastic particle in a viscous fluid flow under Stokes flow conditions. A set of coupled, nonlinear, first-order ODEs is obtained for the evolution of the uniform stress fields in the particle, as well as for the shape and orientation of the particle, which can in turn be used to characterize the rheology of a dilute suspension of elastic particles in a shear flow. When applied to a suspension of cylindrical particles with initially circular cross-section, the theory confirms the existence of steady-state solutions, which can be given simple analytical expressions. The two-dimensional, steady-state solutions for the particle shape and orientation, as well as for the effective viscosity and normal stress differences in the suspension, are in excellent agreement with direct numerical simulations of multiple-particle dispersions in a shear flow obtained by using an arbitrary Lagrangian–Eulerian (ALE) finite element method (FEM) solver. The corresponding solutions for the evolution of the microstructure and the rheological properties of suspensions of initially spherical (three-dimensional) particles in a simple shear flow are also obtained, and compared with the results of Roscoe (J. Fluid Mech., vol. 28, 1967, pp. 273–293) in the steady-state regime. Interestingly, the results show that sufficiently soft elastic particles can be used to reduce the effective viscosity of the suspension (relative to that of the pure fluid).

Molecular dynamic simulations of helium atoms escaping from a helium-filled nanobubble near the surface of crystalline palladium reveal unexpected behavior. Significant deformation and cracking near the helium bubble occur initially, and then a channel forms between the bubble and the surface, providing a pathway for helium atoms to propagate toward the surface. The helium atoms erupt from the bubble in an instantaneous and volcano-like process, which leads to surface deformation consisting of cavity formation on the surface, along with modification and atomic rearrangement at the periphery of the cavity. The present simulation results show that, near the palladium surface, there is a helium-bubble-free zone, or denuded zone, with a typical thickness of about 3.0 nm. Combined with experimental measurements and continuum-scale evolutionary model predictions, the present atomic simulations demonstrate that the thickness of the denuded zone, which contains a low concentration of helium atoms, is somewhat larger than the diameter of the helium bubbles in the metal tritide. Furthermore, a relationship between the tensile strength and thickness of metal film is also determined.

Small size at birth continues to be a problem worldwide and many factors, including reduced folate intake and Pb exposure, are associated with it. However, single factors rarely explain the variability in birth weight, suggesting a need for more complex explanatory models. We investigated environment–gene interactions to understand whether folate intake and maternal Pb exposure were associated with smaller newborn size in 474 women with uncomplicated pregnancies delivering term infants in Mexico City. We examined if folate intake modified the negative effects of maternal Pb burden on birth size. We also asked if maternal and infant methylenetetrahydrofolate reductase (MTHFR) genotypes (C677T, A1298C and G1793A) modified the effects of folate intake or Pb exposure on birth size. Women were aged 24·6 (sd 5·1) years; 43·5 % were primiparous. Maternal blood Pb at delivery was 86 (sd 42) μg/l, with 26·7 % having levels ≥ 100 μg/l. Tibia Pb level was 9·9 (sd 9·8) μg/g. Of the women, 35·3 % had folate intakes < 400 μg/d. Birth weight was 3170 (sd 422) g. In covariate-adjusted regressions, higher folate intake was associated with higher birth weight (β 0·04; P < 0·05). Higher bone Pb was associated with lower birth weight (β − 4·9; P < 0·05). Folate intake did not modify the effects of Pb on birth size, nor did MTHFR modify the association between Pb or folate intake on birth size. Although modest, the relationship between maternal nutrition, Pb burden and birth size does underscore the importance of environmental exposures to child health because patterns of fetal growth may affect health outcomes well into adulthood.

We have numerically investigated the interaction dynamics between two rigid spherical particles moving in a fluid-filled cylinder that is rotating at a constant speed. The cylinder rotation is about a horizontal axis. The particle densities are less than that of the fluid. The numerical procedure employed to solve the mathematical formulation is based on a three-dimensional arbitrary Larangian–Eulerian (ALE), moving mesh finite-element technique, described in a frame of reference rotating with the cylinder. Results are obtained in the ranges of particle Reynolds number, 1 <Rep≤60, and shear Reynolds number, 1≤Res<10. Two identical particles, depending on initial conditions at release, approach each other (‘drafting’ and ‘kissing’), tumble in the axial direction, and axially migrate towards opposing transverse planes on which they ‘settle’ (settling planes). Under some other initial conditions, the particles migrate directly onto their settling planes. For two identical particles, the settling planes are equidistant from the mid-transverse plane of the cylinder and the locations of the planes are determined by particle–particle and particle–wall force balances. Furthermore, for identical particles and given values of Rep and Res, the locations of such settling planes remain the same, independent of the initial conditions at release. While located on these settling planes, as viewed in an inertial frame, the particles may attain three possible distinct states depending on the values of the Reynolds numbers. In one state (low Rep, high Res), the particles attain and remain at fixed equilibrium points on their settling planes. In the second (all Rep, low Res), they execute spiralling motions about fixed points on their respective settling planes. These fixed points coincide with the locations of the equilibrium point which would occur on the mid-axial plane in the case of a single particle. In the third state (low Rep, moderate Res or high Rep, moderate to high Res), they execute near-circular orbital motion on their respective settling planes, again about fixed points. These fixed points also coincide with the locations of the equilibrium points corresponding to single-particle dynamics. Both the spiral and near-circular motions of the particles occur in an out-of-phase manner with regard to their radial positions about the fixed point; the near-circular out-of-phase motion resembles bicycle pedalling. Also, in the second and third states, the particles simultaneously experience very weak axial oscillations about their settling planes, the frequency of such oscillations coinciding with the frequency of rotation of the circular cylinder.

The behaviours of two non-identical particles (same density but different sizes, or same size but different densities) are different from those of identical particles. For example, non-identical particles may both end up settling on the mid-axial plane. This occurs when the locations of their corresponding single-particle equilibrium points are far apart. When such points are not far apart, particles may settle on planes that may not be symmetrical about the mid-axial plane. While located on their settling planes, their equilibrium states may not be similar. For example, for particles of the same density but of different sizes, the smaller of the two may execute a spiralling motion while the larger is in near-circular orbital motion. With particles of the same size but of different densities, while the lighter of the two approaches its equilibrium point on the mid-axial plane, the heavier one experiences a circular motion on the same plane about its equilibrium point. A major reason for the eventual attainment of these various states is noted to be the interplay between the particle–particle and particle–wall forces.

In this paper, we study the linearized stability of three symmetric arrangements of two liquids in core–annular Poiseuille flow in round pipes. Deferring to one important application, we say oil and water when we mean more viscous and less viscous liquids. The three arrangements are (i) oil is in the core and water on the wall, (ii) water is in the core and oil is outside and (iii) three layers, oil inside and outside with water in between. The arrangement in (iii) is our model for lubricated pipelining when the pipe walls are hydrophobic and it has not been studied before. The arrangement in (ii) was studied by Hickox (1971) who treated the problem as a perturbation of long waves, effectively suppressing surface tension and other essential effects which are necessary to explain the flows observed, say, in recent experiments of W. L. Olbricht and R. W. Aul. The arrangement in (i) was studied in Part 1 of this paper (Preziosi, Chen & Joseph 1987). We have confirmed and extended their pseudo-spectral calculation by introducing a more efficient finite-element code. We have calculated neutral curves, growth rates, maximum growth rate, wavenumbers for maximum growth and the various terms which enter into the analysis of the equation for the evolution of the energy of a small disturbance. The energy analysis allows us to identify the three competing mechanisms underway: interfacial tension, interfacial friction and Reynolds stress. Many results are presented.

Stability of core-annular flow of water and oil in a vertical circular pipe is studied with respect to non-axisymmetric disturbances. Results show that when the oil core is thin, the flow is most unstable to the asymmetric sinuous mode of disturbance, and the core moves in the form of corkscrew waves as observed in experiments. The asymmetric mode of disturbance is the most dangerous mode for quite a wide range of material and flow parameters. This asymmetric mode persists in vertical pipes with upward and downward flows and in horizontal pipes. The analysis also applies to the instability of freely rising axisymmetric cigarette smoke or a thermal plume. The study predicts a unique wavelength for the asymmetric meandering waves.

The motion of a heavy rigid ellipsoidal particle settling in an infinitely long circular tube filled with an incompressible Newtonian fluid has been studied numerically for three categories of problems, namely, when both fluid and particle inertia are negligible, when fluid inertia is negligible but particle inertia is present, and when both fluid and particle inertia are present. The governing equations for both the fluid and the solid particle have been solved using an arbitrary Lagrangian-Eulerian based finite-element method. Under Stokes flow conditions, an ellipsoid without inertia is observed to follow a perfectly periodic orbit in which the particle rotates and moves from side to side in the tube as it settles. The amplitude and the period of this oscillatory motion depend on the initial orientation and the aspect ratio of the ellipsoid. An ellipsoid with inertia is found to follow initially a similar oscillatory motion with increasing amplitude. Its orientation tends towards a flatter configuration, and the rate of change of its orientation is found to be a function of the particle Stokes number which characterizes the particle inertia. The ellipsoid eventually collides with the tube wall, and settles into a different periodic orbit. For cases with non-zero Reynolds numbers, an ellipsoid is seen to attain a steady-state configuration wherein it falls vertically. The location and configuration of this steady equilibrium varies with the Reynolds number.

Combinatorial approaches are successfully applied for the optimization of electric write-once, thin-film Si antifuse memory devices, as well as for studying the solid-phase epitaxy kinetics of amorphous silicon on c-Si. High forward, low reverse current thin film Si diode deposition recipes are selected using cross-strips of different combinations of amorphous and microcrystalline doped layers, as well as a thickness-wedged intrinsic a-Si:H buffer layer. By studying switching in thickness-wedged a-Si:H layers, it is found that switching requires both a critical field and a critical bias voltage across the metallic contacts. Solid-phase epitaxy speed has a non-linear dependence on the film thickness, which is easily observed by optical image monitoring and analysis in wedged a-Si:H films on c-Si wafers.

We investigate electrical stressing and switching in hydrogenated microcrystalline silicon (mc-Si:H) by thermal, and optical and electrical measurements of Cr/mc-Si:H/metal thin-film structures. Boron-doped microcrystalline Si films of 30-50 nm thick are deposited by hot-wire chemical vapor deposition (HWCVD) on Cr-coated glass at 160°C and contacted with Ag or Al. Switching in devices of size 5 to 30 mm is stimulated by a current-ramp from 10 nA to 50 mA. We find that the voltage across the mc-Si:H devices initially increases logarithmically with current, then saturates at 2∼3 V, and finally drops to a low value of 1 to 1.5 V. This drop indicates a permanent decrease of device resistance to below 1 kW. During current stressing, the surface temperature increases with the bias current, and the surface reflectivity changes. After switching, a small increase in crystalline fraction can be observed by micro-Raman scattering measurements. The observations suggest electrothermal processes which cause changes in microstructure of the mc-Si bulk during current stress.

Dispersed two-phase flows often involve interfacial activities such as chemical reaction and phase change, which couple the fluid dynamics with heat and mass transfer. As a step toward understanding such problems, we numerically simulate the sedimentation of solid bodies in a Newtonian fluid with convection heat transfer. The two-dimensional Navier–Stokes and energy equations are solved at moderate Reynolds numbers by a finite-element method, and the motion of solid particles is tracked using an arbitrary Lagrangian–Eulerian scheme. Results show that thermal convection may fundamentally change the way that particles move and interact. For a single particle settling in a channel, various Grashof-number regimes are identified, where the particle may settle straight down or migrate toward a wall or oscillate laterally. A pair of particles tend to separate if they are colder than the fluid and aggregate if they are hotter. These effects are analysed in terms of the competition between the thermal convection and the external flow relative to the particle. The mechanisms thus revealed have interesting implications for the formation of microstructures in interfacially active two-phase flows.

We report on the area dependence of switching in both Cr/p+a-Si:H/Ag(Al) and Cr/p+μc-Si/Ag(Al) filament switches. The doped amorphous (a-Si:H) or microcrystalline (μc-Si) thin Si layers are made by hot-wire chemical vapor deposition. The device active region area (A) is varied over 5 orders of magnitude, from 10-7 to 10-2 cm2, using photolithographically defined Ag and Al top contacts. Before switching, the resistance of 100-μm2 devices is normally about 100 kΩ for μc-Si and 10 GΩ for a-Si:H. After switching with applied current ramps, the resistance decreases to a few hundred ohms in all a-Si devices and to a few thousands ohms in μc-Si devices. In both μc-Si and a-Si:H devices, the switching voltage (Vsw) decreases with increasing device area according to Vsw ~ V0-αln(A/A0) with α=0.3V for a-Si:H and α=0.04V for μc-Si. For both materials, the switching current roughly obeys the power law Isw ∞ Aβ with β~1. A statistical model is proposed to explain the area scaling of the switching voltage and relate the parameters to the material properties.

We compare switching behaviour in Cr/a-Si:H(p)/Ag and c-Si(p)/a-Si:H(p)/Ag structures containing p-type hydrogenated amorphous silicon. The a-Si:H layer is made by hot wire chemical vapor deposition. We observed that the switching is polarity-dependent only in the sample on c-Si(p). Switching to a low-resistance state occurs at 0.4 mA/cm2 when any of the metal contacts are biased positive. When the c-Si(p) is biased positive holes are injected and no switching occurs even up to 4 A/cm2. We suggest that the switching requires a blocking metal/a-Si(p), possibly because local electrical breakdown initiates metal filament formation.

The relation of relaxation to surface morphology in linearly-graded InAlAs was examined as a function of growth temperature using x-ray diffraction and atomic force microscopy (AFM). Samples were grown at temperatures ranging from 370°C to 550°C. Weak diffraction features for samples grown at 370°C and 420°C limited determination of the extent of their relaxation . The fractional relaxation of samples grown between 470°C to 550°C was essentially identical (~77%) and symmetric in orthogonal [110] directions. The character of the surface morphology changed from random small scale roughness to a roughness more periodic in nature as the growth temperature increased. Although no asymmetry was observed in the relaxation, the roughness developed an asymmetry at higher growth temperatures with more prominent ridges along [110]-[110].