307 research outputs found
Constitutive Equations for Sands and Overconsolidated Clays under Dynamic Loads Based on Elasto-Plasticity
This paper is concerned with the constitutive equations of the sands and overconsolidated clays under cyclic loads. The constitutive equations are derived, based on the theory of plasticity and real stress-strain behavior of soils, The non-associated flow rule is applied to the derivation of the equations. The derived equations can explain the mechanical behavior of overconsolidated clays and sands under cyclic stresses and have nine soil parameters, and are applicable to liquefaction analysis
The dielectrophoresis of cylindrical and spherical particles submerged in shells and in semi-infinite media
Modeling the elastic deformation of polymer crusts formed by sessile droplet evaporation
Evaporating droplets of polymer or colloid solution may produce a glassy
crust at the liquid-vapour interface, which subsequently deforms as an elastic
shell. For sessile droplets, the known radial outward flow of solvent is
expected to generate crusts that are thicker near the pinned contact line than
the apex. Here we investigate, by non-linear quasi-static simulation and
scaling analysis, the deformation mode and stability properties of elastic caps
with a non-uniform thickness profile. By suitably scaling the mean thickness
and the contact angle between crust and substrate, we find data collapse onto a
master curve for both buckling pressure and deformation mode, thus allowing us
to predict when the deformed shape is a dimple, mexican hat, and so on. This
master curve is parameterised by a dimensionless measure of the non-uniformity
of the shell. We also speculate on how overlapping timescales for gelation and
deformation may alter our findings.Comment: 8 pages, 7 figs. Some extra clarification of a few points, and minor
corrections. To appear in Phys. Rev.
Angular sensitivity of blowfly photoreceptors: intracellular measurements and wave-optical predictions
The angular sensitivity of blowfly photoreceptors was measured in detail at wavelengths λ = 355, 494 and 588 nm.
The measured curves often showed numerous sidebands, indicating the importance of diffraction by the facet lens.
The shape of the angular sensitivity profile is dependent on wavelength. The main peak of the angular sensitivities at the shorter wavelengths was flattened. This phenomenon as well as the overall shape of the main peak can be quantitatively described by a wave-optical theory using realistic values for the optical parameters of the lens-photoreceptor system.
At a constant response level of 6 mV (almost dark adapted), the visual acuity of the peripheral cells R1-6 is at longer wavelengths mainly diffraction limited, while at shorter wavelengths the visual acuity is limited by the waveguide properties of the rhabdomere.
Closure of the pupil narrows the angular sensitivity profile at the shorter wavelengths. This effect can be fully described by assuming that the intracellular pupil progressively absorbs light from the higher order modes.
In light-adapted cells R1-6 the visual acuity is mainly diffraction limited at all wavelengths.
A hysteretic multiscale formulation for nonlinear dynamic analysis of composite materials
This article has been made available through the Brunel Open Access Publishing Fund.A new multiscale finite element formulation
is presented for nonlinear dynamic analysis of heterogeneous
structures. The proposed multiscale approach utilizes
the hysteretic finite element method to model the microstructure.
Using the proposed computational scheme, the micro-basis functions, that are used to map the microdisplacement components to the coarse mesh, are only evaluated once and remain constant throughout the analysis procedure. This is accomplished by treating inelasticity at the micro-elemental level through properly defined hysteretic evolution equations. Two types of imposed boundary conditions are considered for the derivation of the multiscale basis functions, namely the linear and periodic boundary conditions. The validity of the proposed formulation as well as its computational efficiency are verified through illustrative numerical experiments
A new multi-scale dispersive gradient elasticity modelwith micro-inertia: Formulation and C0-finiteelement implementation
Motivated by nano-scale experimental evidence on the dispersion characteristics of materials with a lattice structure, a new multi-scale gradient elasticity model is developed. In the framework of gradient elasticity, the simultaneous presence of acceleration and strain gradients has been denoted as dynamic consistency. This model represents an extension of an earlier dynamically consistent model with an additional micro-inertia contribution to improve the dispersion behaviour. The model can therefore be seen as an enhanced dynamic extension of the Aifantis' 1992 strain-gradient theory for statics obtained by including two acceleration gradients in addition to the strain gradient. Compared with the previous dynamically consistent model, the additional micro-inertia term is found to improve the prediction of wave dispersion significantly and, more importantly, requires no extra computational cost. The fourth-order equations are rewritten in two sets of symmetric second-order equations so that C0-continuity is sufficient in the finite element implementation. Two sets of unknowns are identified as the microstructural and macrostructural displacements, thus highlighting the multi-scale nature of the present formulation. The associated energy functionals and variationally consistent boundary conditions are presented, after which the finite element equations are derived. Considerable improvements over previous gradient models are observed as confirmed by two numerical examples
Structural, optical, and electrical properties of WOx(Ny) films deposited by reactive dual magnetron sputtering
The role of electrohydrodynamic forces in the dielectrophoretic manipulation and separation of particles
The Role of IL-15 Deficiency in the Pathogenesis of Virus-Induced Asthma Exacerbations
Rhinovirus infections are the major cause of asthma exacerbations. We hypothesised that IL-15, a cytokine implicated in innate and acquired antiviral immunity, may be deficient in asthma and important in the pathogenesis of asthma exacerbations. We investigated regulation of IL-15 induction by rhinovirus in human macrophages in vitro, IL-15 levels in bronchoalveolar lavage (BAL) fluid and IL-15 induction by rhinovirus in BAL macrophages from asthmatic and control subjects, and related these to outcomes of infection in vivo. Rhinovirus induced IL-15 in macrophages was replication-, NF-κB- and α/β interferon-dependent. BAL macrophage IL-15 induction by rhinovirus was impaired in asthmatics and inversely related to lower respiratory symptom severity during experimental rhinovirus infection. IL-15 levels in BAL fluid were also decreased in asthmatics and inversely related with airway hyperresponsiveness and with virus load during in vivo rhinovirus infection. Deficient IL-15 production in asthma may be important in the pathogenesis of asthma exacerbations
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