Plasma-treated poly(dimethylsiloxane) (PDMS) bonds irreversibly to Si-containing substrates. In electrochemical microfluidic cells, commonly used gold electrodes are inert to this bonding method, ...causing leaks in the PDMS
|
Au interface. In this work, the effect of the electrode connector width on the leak was studied. Leak pressure tests show that higher leak pressures can be obtained using narrower electrode connectors. A 4
μ
m connector width presents a leak pressure of 238±22 kPa, comparable to the typical failure pressures reported for PDMS
|
glass devices without electrodes. Finite element modeling suggests that the deformation of the PDMS under the pressure in the channel is the mechanism responsible for the sharp increase in leak resistance observed at narrow gold structures. To ensure that narrow connectors are suitable for faradaic electrochemical measurements, a model analyte was evaluated in cells with different electrode connector width. Voltammograms show that even when using the 4
μ
m structure, ohmic drop is negligible. We propose the use of narrow electrode connectors to reliably use the simple and widespread plasma bonding method while minimizing the solution leaking.
In this work, layerwise SAM-L model for thin to moderately thick laminated shells is introduced. Generalized equations are obtained from a stress approximation and from Hellinger–Reissner functional ...(Reissner, 1950). Stress approximation verifies the 3D equilibrium equations and boundary conditions on shell faces. Hellinger–Reissner functional allows identifying 5 generalized displacements per layer. The equations of the model are obtained using Reissner’s variational principle. The model takes into account in its constitutive equations the Poisson’s effect of out-of-plane normal stresses on in-plane strains. To prove the accuracy of the model, SAM-L is applied to the analysis of laminated cylinders and one catenoid. SAM-L results are compared to exact solutions, solid finite elements, and other models available in the literature. SAM-L shows high quality in predicting the stress and displacement fields, even for thick shells. Edge effects on interlaminar stresses are assessed with high precision. SAM-L model proves to be an alternative to solid finite elements and other higher computing cost theories for structural analysis of doubly curved laminated shells.
This article analyzes the contribution of certifiable environmental management standards—such as ISO 14001 and the Eco‐Management and Audit Scheme (EMAS)—to corporate environmental performance. Based ...on a content analysis of 414 third‐party‐verified environmental statements from EMAS‐registered Spanish organizations, which included information for around 6,700 detailed indicators, a weak improvement in environmental performance was found. Less than half of the analyzed indicators—namely, 48.27%—revealed a net improvement. Similarly, analysis of the justifications of the registered companies for the lack of improvement points to a rather symbolical adoption of the certification, intended to do only the bare minimum. These findings call into question the prevailing opinion about the positive impact of voluntary certifiable environmental management standards on environmental greening. Implications for managers and public policy makers, as well as for other stakeholders, are discussed.
Present-day heat flow model of Mars Parro, Laura M; Jiménez-Díaz, Alberto; Mansilla, Federico ...
Scientific reports,
04/2017, Volume:
7, Issue:
1
Journal Article
Peer reviewed
Open access
Until the acquisition of in-situ measurements, the study of the present-day heat flow of Mars must rely on indirect methods, mainly based on the relation between the thermal state of the lithosphere ...and its mechanical strength, or on theoretical models of internal evolution. Here, we present a first-order global model for the present-day surface heat flow for Mars, based on the radiogenic heat production of the crust and mantle, on scaling of heat flow variations arising from crustal thickness and topography variations, and on the heat flow derived from the effective elastic thickness of the lithosphere beneath the North Polar Region. Our preferred model finds heat flows varying between 14 and 25 mW m
, with an average value of 19 mW m
. Similar results (although about ten percent higher) are obtained if we use heat flow based on the lithospheric strength of the South Polar Region. Moreover, expressing our results in terms of the Urey ratio (the ratio between total internal heat production and total heat loss through the surface), we estimate values close to 0.7-0.75, which indicates a moderate contribution of secular cooling to the heat flow of Mars (consistent with the low heat flow values deduced from lithosphere strength), unless heat-producing elements abundances for Mars are subchondritic.
In this report the exact rotating charged black hole solution to the Einstein–nonlinear electrodynamics theory with a cosmological constant is presented. This black hole is equipped with mass, ...rotation parameter, electric and magnetic charges, cosmological constant Λ, and three parameters due to the nonlinear electrodynamics: β is associated to the potential vectors Aμ and ⋆Pμ, and two constants, F0 and G0, due to the presence of the invariants F and G in the Lagrangian L(F(xμ),G(xμ)). This solution is of Petrov type D, characterized by the Weyl tensor eigenvalue Ψ2, the traceless Ricci tensor eigenvalue S=2Φ(11), and the scalar curvature R; it allows for event horizons, exhibits a ring singularity and fulfils the energy conditions. Its Maxwell limit is the de Sitter-Anti–de Sitter–Kerr–Newman black hole solution.
We study the governance of public good provision in poor communities in Oaxaca, Mexico. We estimate the effect of usos y costumbres—a form of participatory democracy prevalent in indigenous ...communities—on the provision of local public goods. Because governance is endogenous, we address selection effects by matching on municipal characteristics and long-term settlement patterns. Using a first-differences design we show that these municipalities increase access to electricity, sewerage, and education faster than communities ruled by political parties. We also show they are places of vibrant political participation, not authoritarian enclaves protecting the political monopoly of local bosses.
This paper presents the development of a model of homogeneous, moderately thick shells for elastodynamic problems. The model is obtained by adapting and modifying SAM-H model (stress approach model ...of homogeneous shells) developed by Domínguez Alvarado and Díaz in (2018) for static problems. In the dynamic version of SAM-H presented herein, displacements and stresses are approximated by polynomials of the out-of-plane coordinate. The stress approximation coincides with the static version of SAM-H when dynamic effects are neglected. The generalized forces and displacements appearing in the approximations are the same as those involved in a classical, moderately thick shell model (CS model) but the stress approximation adopted herein is more complex: the 3D motion equations and the stress boundary conditions at the faces of the shell are verified. The generalized motion and constitutive equations of dynamic SAM-H model are obtained by applying a variant of Euler–Lagrange equation which includes pertinently Hellinger–Reissner functional. In the constitutive equations, Poisson’s effect of out-of-plane normal stresses on in-plane strains is not ignored; this is one important feature of SAM-H. To test the accuracy of dynamic SAM-H model, the following structures were considered: a hollow sphere and a catenoid. In each case, eigenfrequencies are first calculated and then a frequency analysis is performed applying a harmonic load. The results are compared to those of a CS model, MITC6 (mixed interpolation of tensorial components with 6 nodes per element) shell element calculations, and solid finite element computations. In the two problems, CS, MITC6, and dynamic SAM-H models yield accurate eigenfrequencies and eigenmodes. Nevertheless, the frequency analysis performed in each case showed that dynamic SAM-H provides much more accurate amplitudes of stresses and displacements than the CS model and the MITC6 shell finite element technique.
The Calzadilla Ophiolite is an ensemble of mafic and ultramafic rocks that represents the transition between lower crust and upper mantle of a Cadomian (peri‐Gondwanan) fore arc. Mapping and ...structural analysis of the ophiolite demonstrates that it was obducted in latest Ediacaran times, because the Ediacaran‐Early Cambrian sedimentary series (Malcocinado Formation) discordantly covers it. The ophiolite and emplacement‐related structures are affected by Variscan deformation (Devonian‐Carboniferous), which includes SW verging overturned folds (D1) and thrusts (D2), upright folds (D3), extensional faults (D4), and later faults (D5). These phases of deformation are explained in the context of Variscan tectonics as the result of the progressive collision between Gondwana and Laurussia. Qualitative unstraining of Variscan deformation reveals the primary geometry of Ediacaran‐Cambrian structures and uncovers the generation of east verging thrusts as responsible for the primary obduction of the Calzadilla Ophiolite. Restoration of planar and linear structures associated with this event indicates an Ediacaran, east directed obduction of the ophiolite, that is, emplacement of the Cadomian fore arc onto inner sections of the northern margin of Gondwana. According to regional data, the obduction separates two extension‐dominated stages in the tectonic evolution of the African margin of northern Gondwana preserved in southern Europe. Preobduction extension brought about the onset and widening of fore‐arc and back‐arc basins in the external part of the continent, while postobduction extension facilitated the formation of extensional migmatitic domes, an oceanward migration of back‐arc spreading centers across peri‐Gondwana, and the eventual opening of a major basin such as the Rheic Ocean.
Key Points
The Calzadilla Ophiolite is a fore‐arc ensemble obducted onto a section of a peri‐Gondwanan arc in latest Ediacaran times
Ophiolite obduction was directed to the ESE (present‐day coordinates), following a vector directed to mainland Gondwana
Obduction preceded back‐arc and fore‐arc spreading in peri‐Gondwana and was followed by the onset of extensional domes and rifting
This paper presents the development of a finite element model for functionally graded shells. The formulation solves the equations of the Stress Approach Model for Functionally Graded shells (SAM-FG) ...developed and validated by Rubio Rascón et al. (2020). SAM-FG involves only 5 generalized displacements and its equations differ from those of classical first order shear deformation theories mainly in the expressions of the generalized stiffnesses and the approximation of stresses. A 10-node isoparametric triangular element using cubic shape functions and 5 degrees of freedom per node is proposed. The equations of the numerical method were implemented in a program called FESAM-FG. The finite element code enables to calculate and visualize generalized fields on the middle surface of the shell and stress components at a given position across the thickness of the structure. To test the accuracy and convergence of FESAM-FG results, the numerical tool is applied to the structural analysis of four families of functionally graded shells with various distributions of material properties and thickness-to-radius ratios. Results are compared to those obtained by solid finite elements, a higher order shear deformation theory developed by Viola et al. (2014) and two shell models used for laminated composite structures: an equivalent single layer model and a layerwise model, both using 30 fictitious layers.
•FESAM-FG is a FEM-based tool for evaluating stresses in moderately thick FGM shells.•Accurate results are obtained even for FGMs with high gradients of their stiffnesses.•Great precision can be reached with significantly fewer DOFs than layerwise models.
Difference in terms of cost-of-living between rural and urban areas is a frequent theoretical analysis in Regional Economics. Lack of routine measures in rural areas does not usually allow to observe ...changes in rural costs. We adapt the Big Mac index, typically used to measure purchasing power parity between countries, as a potential quick and inexpensive indicator of short-term local price variations. With a national random sample of McDonald's stores repeated in time, we find prices grew slightly faster in rural areas than in urban areas. Spatial transmission of prices seems to be limited to very localized effects, meaning that rural price increases are not due to urban spillover effects.
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