Constitutive modeling of void-growth-based tensile ductile failures with stress triaxiality effects

In most metals and alloys, the evolution of voids has been generally recognized as the basic failure mechanism. Furthermore, stress triaxiality has been found to influence void growth dramatically. Besides strain intensity, it is understood to be the most important factor that controls the initiation of ductile fracture. We include sensitivity of stress triaxiality in a variational porous plasticity model, which was originally derived from hydrostatic expansion. Under loading conditions rather than hydrostatic deformation, we allow the critical pressure for voids to be exceeded so that the growth due to plasticity becomes dependent on the stress triaxiality. The limitations of the spherical void growth assumption are investigated. Our improved constitutive model is validated through good agreements with experimental data. Its capacity for reproducing realistic failure patterns is also indicated by a numerical simulation of a compact tensile (CT) test.     

Distribution and environmental impact of radionuclides in marine sediments along the Venezuelan coast

The activity concentrations of ¹³⁷Cs, ⁴⁰K, ²²⁶Ra and ²³²Th in Bq/kg from 42 marine sediment samples collected at nine sampling sites were determined in order to establish a radiological baseline along the Venezuelan coast. The radioactivity levels were determined by means of a gamma-ray spectroscopy system using a hyper-pure germanium detector in a low-background configuration. Particle size distribution and total organic matter content were also determined. Activity concentrations of ¹³⁷Cs were lower than the detection limit of the analytical technique (0.9 Bq/kg) in all studied sites. The results suggest that the variation of grain-size distribution is one of the most important factors influencing the spatial variations of ⁴⁰K, ²²⁶Ra and ²³²Th in sediments along the Venezuelan coasts. In all sampling sites, average concentrations of ⁴⁰K, ²²⁶Ra and ²³²Th were lower than the world average values. Activity concentrations of ²²⁶Ra, ²³²Th and ⁴⁰K in coastal marine sediments along the Venezuelan coast could be considered to be low when compared with global average values, indicating that they are not apparently above of the range that might be considered normal or background. These results suggest that the studied sites do not pose any significant radiological threat to the population. The results attained in this study should be of considerable value as baseline data and background reference levels for Venezuelan coastlines.     

The time-dependent von K��rm��n plate equation as a limit of 3d nonlinear elasticity

The asymptotic behaviour of solutions of three-dimensional nonlinear elastodynamics in a thin plate is studied, as the thickness h of the plate tends to zero. Under appropriate scalings of the applied force and of the initial values in terms of h, it is shown that three-dimensional solutions of the nonlinear elastodynamic equation converge to solutions of the time-dependent von Kármán plate equation.     

Coupling a quantum dot, fermionic leads, and a microwave cavity on a chip

We demonstrate a hybrid architecture consisting of a quantum dot circuit coupled to a single mode of the electromagnetic field. We use single wall carbon nanotube based circuits inserted in superconducting microwave cavities. By probing the nanotube dot using a dispersive readout in the Coulomb blockade and the Kondo regime, we determine an electron-photon coupling strength which should enable circuit QED experiments with more complex quantum dot circuits.     

Giant charge relaxation resistance in the Anderson model

We investigate the dynamical charge response of the Anderson model viewed as a quantum RC circuit. Applying a low-energy effective Fermi liquid theory, a generalized Korringa-Shiba formula is derived at zero temperature, and the charge relaxation resistance is expressed solely in terms of static susceptibilities which are accessible by Bethe ansatz. We identify a giant charge relaxation resistance at intermediate magnetic fields related to the destruction of the Kondo singlet. The scaling properties of this peak are computed analytically in the Kondo regime. We also show that the resistance peak fades away at the particle-hole symmetric point.     

Electrospray Ionization Mechanisms for Large Polyethylene Glycol Chains Studied Through Tandem Ion Mobility Spectrometry

Ion mobility mass spectrometry (IMS-MS) is used to investigate the abundance pattern, n _z (m) of Poly-(ethyleneglycol) (PEG) electrosprayed from water/methanol as a function of mass and charge state. We examine n _z (m) patterns from a diversity of solution cations, primarily dimethylammonium and triethylammonium. The ability of PEG chains to initially attach to various cations in the spraying chamber, and to retain them (or not) on entering the MS, provide valuable clues on the ionization mechanism. Single chains form in highly charged and extended shapes in most buffers. But the high initial charge they hold under atmospheric pressure is lost on transit to the vacuum system for large cations. In contrast, aggregates of two or more chains carry in all buffers at most the Rayleigh charge of a water drop of the same volume. This shows either that they form via Dole’s charge residue mechanism, or that highly charged and extended aggregates are ripped apart by Coulombic repulsion. IMS-IMS experiments in He confirm these findings, and provide new mechanistic insights on the stability of aggregates. When collisionally activated, initially globular dimers are stable. However, slightly nonglobular dimers projecting out a linear appendix are segregated into two monomeric chains. The breakup of a charged dimer is therefore a multi-step process, similar to the Fenn-Consta polymer extrusion mechanism. The highest activation barrier is associated to the first step, where a short chain segment carrying a single charge escapes (ion-evaporates) from a charged drop, leading then to gradual field extrusion of the whole chain out of the drop.

Incorporating variable viscosity in vorticity-based formulations for Brinkman equations

In this brief note, we introduce a non-symmetric mixed finite element formulation for Brinkman equations written in terms of velocity, vorticity, and pressure with non-constant viscosity. The analysis is performed by the classical Babu?ka–Brezzi theory, and we state that any inf–sup stable finite element pair for Stokes approximating velocity and pressure can be coupled with a generic discrete space of arbitrary order for the vorticity. We establish optimal a priori error estimates, which are further confirmed through computational examples.     

Progress and prospect of anodic oxidation for the remediation of perfluoroalkyl and polyfluoroalkyl substances in water and wastewater using diamond electrodes

Although diamond electrodes are widely used in the field of electroanalysis and sensing, their application in the field of environmental engineering has yet to be fully realized. Many research studies have considered their potential application in water and wastewater treatment, where the in-situ electrochemical process can avoid the need for chemical additives by facilitating the oxidation of pollutants on the electrode surface or mediated by electrochemically synthesized oxidants in solution. Diamond-based electro-oxidation can effectively treat a number of organic micropollutants and is now being evaluated for the abatement of perfluoroalkyl and polyfluoroalkyl substances, which pose health concerns and are ubiquitous recalcitrant environmental contaminants. To move implementation of diamond-based electro-oxidation forward, the integration of modifications and codopants to yield more advanced electrode materials needs to be further developed and understood. The progress and current strategies associated with diamond electrode modifications for perfluoroalkyl and polyfluoroalkyl substances abatement as well as future considerations are discussed.     

A hydrodynamic injection approach for capillary electrophoresis using rotor–stator valves

Sample injection is a critical step in a capillary electrophoresis (CE) analysis. Electrokinetic injection is the simplest approach and is often selected for implementation in portable CE instruments. However, in order to minimize the effect of sample matrix upon the results of a CE analysis, hydrodynamic injection is preferred. Although portable CE instruments with hydrodynamic injection have been reported, injection has always been performed at the grounded end of the capillary. This simplifies fluidic handling but limits coupling with electrochemical detectors and electrospray ionization–mass spectrometry (ESI–MS). We demonstrated previously that injection at the high-voltage (HV) end of the capillary could be performed using an HV-compatible rotary injection valve (fixed-volume injection). However, the mismatch between the bore sizes of the channels on the rotor–stator valve and the separation capillary caused peak tailing and undesired mixing, impairing analytical performance. In this work, we present an HV-compatible hydrodynamic injection approach that overcomes the issues associated with the fixed-volume injection approach reported previously. The performance of the CE instrument was demonstrated by analyzing a mixture of 13 amino acids by CE coupled to laser-induced fluorescence, which showed relative standard deviations for peak area and migration time below 5% and 1%, respectively, for triplicate analysis. Additionally, replicate measurements of a mixture of amino acids, peptides, nucleobases, and nucleosides by CE coupled to electrospray ionization–mass spectrometry (CE–ESI–MS) were performed to evaluate peak tailing, and results were similar to those obtained with a commercial CE–ESI–MS setup.     

Endothelial cell adhesion on polyelectrolyte multilayer films functionalised with fibronectin and collagen

The seeding of endothelial cells on biomaterial surfaces has become a major challenge to achieve better haemocompatibility of these surfaces. Multilayers of polyelectrolytes formed by the layerby-layer method are promising in this respect. In this study, the interactions of endothelial cells with multilayered polyelectrolytes films were investigated. The build-ups were prepared by selfassembled alternatively adsorbed polyanions and polycations functionalised with fibronectin and collagen. Anionic poly(sodium 4-styrenesulfonate) and cationic poly(allylamine hydrochloride) polyelectrolytes were chosen as a model system. Elaborated surfaces were characterised by electrochemical impedance spectroscopy and cyclic voltammetry. The modified electrode showed good reversible electrochemical properties and high stability in an electrolyte solution. The film ohmic resistance was highest when the film was coated with fibronectin; the parameters so determined were correlated with atomic force microscopy images. Cell colorimetric assay (WST-1) and immunofluorescence were used to quantify the cell viability and evaluate the adhesion properties. When cultured on a surface where proteins were deposited, cells adhered and proliferated better with fibronectin than with collagen. In addition, a high surface free energy was favourable to adhesion and proliferation (48.8 mJ m⁻² for fibronectin and 39.7 mJ m⁻² for collagen, respectively). Endothelial cells seeded on functionalised-polyelectrolyte multilayer films showed a good morphology and adhesion necessary for the development of a new endothelium.