Microelectrode study of pore size, ion size, and solvent effects on the charge/discharge behavior of microporous carbons for electrical double-layer capacitors

The capacitive behavior of TiC-derived carbon powders in two different electrolytes, NEt4BF4 in acetonitrile AN and NEt4BF4 in propylene carbonate PC, was studied using the cavity microelectrode CME technique. Comparisons of the cyclic voltammograms recorded at 10–1000 mV/s enabled correlation between adsorbed ion sizes and pore sizes, which is important for understanding the electrochemical capacitive behavior of carbon electrodes for electrical double-layer capacitor applications. The CME technique also allows a fast selection of carbon electrodes with matching pore sizes different sizes are needed for the negative and positive electrodes for the respective electrolyte system. Comparison of electrochemical capacitive behavior of the same salt, NEt4BF4, in different solvents, PC and AN, has shown that different pore sizes are required for different solvents, because only partial desolvation of ions occurs during the double-layer charging. Squeezing partially solvated ions into subnanometer pores, which are close to the desolvated ion size, may lead to distortion of the shape of cyclic voltammograms

Creep fatigue of low-cobalt superalloys: Waspalloy, PM U 700 and wrought U 700

The influence of cobalt content on the high temperature creep fatigue crack initiation resistance of three primary alloys was evaluated. These were Waspalloy, Powder U 700, and Cast U 700, with cobalt contents ranging from 0 up to 17 percent. Waspalloy was studied at 538 C whereas the U 700 was studied at 760 C. Constraints of the program required investigation at a single strain range using diametral strain control. The approach was phenomenological, using standard low cycle fatigue tests involving continuous cycling tension hold cycling, compression hold cycling, and symmetric hold cycling. Cycling in the absence of or between holds was done at 0.5 Hz, whereas holds when introduced lasted 1 minute. The plan was to allocate two specimens to the continuous cycling, and one specimen to each of the hold time conditions. Data was taken to document the nature of the cracking process, the deformation response, and the resistance to cyclic loading to the formation of small cracks and to specimen separation. The influence of cobalt content on creep fatigue resistance was not judged to be very significant based on the results generated. Specific conclusions were that the hold time history dependence of the resistance is as significant as the influence of cobalt content and increased cobalt content does not produce increased creep fatigue resistance on a one to one basis

Coarse Projective kMC Integration: Forward/Reverse Initial and Boundary Value Problems

In "equation-free" multiscale computation a dynamic model is given at a fine, microscopic level; yet we believe that its coarse-grained, macroscopic dynamics can be described by closed equations involving only coarse variables. These variables are typically various low-order moments of the distributions evolved through the microscopic model. We consider the problem of integrating these unavailable equations by acting directly on kinetic Monte Carlo microscopic simulators, thus circumventing their derivation in closed form. In particular, we use projective multi-step integration to solve the coarse initial value problem forward in time as well as backward in time (under certain conditions). Macroscopic trajectories are thus traced back to unstable, source-type, and even sometimes saddle-like stationary points, even though the microscopic simulator only evolves forward in time. We also demonstrate the use of such projective integrators in a shooting boundary value problem formulation for the computation of "coarse limit cycles" of the macroscopic behavior, and the approximation of their stability through estimates of the leading "coarse Floquet multipliers".Comment: Submitted to Journal of Computational Physic

Application of Anodic Stripping Voltammetry to assess sorption performance of an industrial waste entrapped in alginate beads to remove As(V)

AbstractA solid waste material containing Fe(III) and other metal (hydr)oxides produced in a metal surface treatment industry has been investigated for As(V) removal. In order to facilitate sorbent application, 2% of raw material has been entrapped in calcium alginate gel matrix (2% O-CA).An accurate characterization of the sorption on gel beads was undertaken, considering thermodynamic and kinetic aspects. All experiments were carried out at pH 8, since the maximum As(V) sorption was reached between pH 6 and 9. About isotherms, the best fit was obtained considering the Langmuir model and a capacity of 1.9mg/g was achieved. The kinetic profiles evidenced that a quantitative sorption was obtained within 10h. The 2% O-CA beads were also tested for continuous As(V) removal in a fixed bed column. Experiments were performed at constant flow rate, and varying the inlet As(V) concentration. With a view to design an automatic system for As(V) analysis in the outlet flow, the suitability of applying Anodic Stripping Voltammetry was evaluated: the method resulted appropriated to follow the As(V) content in the outlet solutions of columns with metal inlet concentration <1 mg/L.These results suggested that 2% O-CA beads could be a promising sorbent candidate for As(V) removal

La utilización de estudios prospectivos en la elaboración del plan estratégico en una institución científica tecnológica brasileña.

Projeto: 11.11.11.111

Stable Determination of the Electromagnetic Coefficients by Boundary Measurements

The goal of this paper is to prove a stable determination of the coefficients for the time-harmonic Maxwell equations, in a Lipschitz domain, by boundary measurements

Inverse problem for wave equation with sources and observations on disjoint sets

We consider an inverse problem for a hyperbolic partial differential equation on a compact Riemannian manifold. Assuming that $\Gamma_1$ and $\Gamma_2$ are two disjoint open subsets of the boundary of the manifold we define the restricted Dirichlet-to-Neumann operator $\Lambda_{\Gamma_1,\Gamma_2}$. This operator corresponds the boundary measurements when we have smooth sources supported on $\Gamma_1$ and the fields produced by these sources are observed on $\Gamma_2$. We show that when $\Gamma_1$ and $\Gamma_2$ are disjoint but their closures intersect at least at one point, then the restricted Dirichlet-to-Neumann operator $\Lambda_{\Gamma_1,\Gamma_2}$ determines the Riemannian manifold and the metric on it up to an isometry. In the Euclidian space, the result yields that an anisotropic wave speed inside a compact body is determined, up to a natural coordinate transformations, by measurements on the boundary of the body even when wave sources are kept away from receivers. Moreover, we show that if we have three arbitrary non-empty open subsets $\Gamma_1,\Gamma_2$, and $\Gamma_3$ of the boundary, then the restricted Dirichlet-to-Neumann operators $\Lambda_{\Gamma_j,\Gamma_k}$ for $1\leq j<k\leq 3$ determine the Riemannian manifold to an isometry. Similar result is proven also for the finite-time boundary measurements when the hyperbolic equation satisfies an exact controllability condition

Responsibility & Risk: Operationalizing comprehensive climate risk layering in Austria among multiple actors (RESPECT)

Damages caused by climate and weather extremes, such as floods and droughts, have increased over the last few decades and will likely broaden with the progression of climate change and socioeconomic development. Such climate-related risks are already being governed within the framework of natural disaster risk management, as well as climate change adaptation. However, to manage these climate risks more effectively it is necessary to link these two domains under the umbrella of Climate Risk Management (CRM)

On stability of discretizations of the Helmholtz equation (extended version)

We review the stability properties of several discretizations of the Helmholtz equation at large wavenumbers. For a model problem in a polygon, a complete $k$-explicit stability (including $k$-explicit stability of the continuous problem) and convergence theory for high order finite element methods is developed. In particular, quasi-optimality is shown for a fixed number of degrees of freedom per wavelength if the mesh size $h$ and the approximation order $p$ are selected such that $kh/p$ is sufficiently small and $p = O(\log k)$, and, additionally, appropriate mesh refinement is used near the vertices. We also review the stability properties of two classes of numerical schemes that use piecewise solutions of the homogeneous Helmholtz equation, namely, Least Squares methods and Discontinuous Galerkin (DG) methods. The latter includes the Ultra Weak Variational Formulation

A rigorous analysis of high order electromagnetic invisibility cloaks

There is currently a great deal of interest in the invisibility cloaks recently proposed by Pendry et al. that are based in the transformation approach. They obtained their results using first order transformations. In recent papers Hendi et al. and Cai et al. considered invisibility cloaks with high order transformations. In this paper we study high order electromagnetic invisibility cloaks in transformation media obtained by high order transformations from general anisotropic media. We consider the case where there is a finite number of spherical cloaks located in different points in space. We prove that for any incident plane wave, at any frequency, the scattered wave is identically zero. We also consider the scattering of finite energy wave packets. We prove that the scattering matrix is the identity, i.e., that for any incoming wave packet the outgoing wave packet is the same as the incoming one. This proves that the invisibility cloaks can not be detected in any scattering experiment with electromagnetic waves in high order transformation media, and in particular in the first order transformation media of Pendry et al. We also prove that the high order invisibility cloaks, as well as the first order ones, cloak passive and active devices. The cloaked objects completely decouple from the exterior. Actually, the cloaking outside is independent of what is inside the cloaked objects. The electromagnetic waves inside the cloaked objects can not leave the concealed regions and viceversa, the electromagnetic waves outside the cloaked objects can not go inside the concealed regions. As we prove our results for media that are obtained by transformation from general anisotropic materials, we prove that it is possible to cloak objects inside general crystals.Comment: The final version is now published in Journal of Physics A: Mathematical and Theoretical, vol 41 (2008) 065207 (21 pp). Included in IOP-Selec