Elastic interfaces on disordered substrates: From mean-field depinning to yielding

We consider a model of an elastic manifold driven on a disordered energy landscape, with generalized long range elasticity. Varying the form of the elastic kernel by progressively allowing for the existence of zero modes, the model interpolates smoothly between mean-field depinning and finite dimensional yielding. We find that the critical exponents of the model change smoothly in this process. Also, we show that in all cases the Herschel-Buckley exponent of the flow curve depends on the analytical form of the microscopic pinning potential. Within the present elastoplastic description, all this suggests that yielding in finite dimensions is a mean-field transition.Fil: Ferrero, Ezequiel E.. Comisión Nacional de Energía Atómica. Centro Atómico Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Jagla, Eduardo Alberto. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin

Criticality in elastoplastic models of amorphous solids with stress-dependent yielding rates

We analyze the behavior of different elastoplastic models approaching the yielding transition. We propose two kinds of rules for the local yielding events: Yielding occurs above the local threshold either at a constant rate or with a rate that increases as the square root of the stress excess. We establish a family of "static" universal critical exponents which do not depend on this dynamic detail of the model rules: In particular, the exponents for the avalanche size distribution P(S) ∼ S-τSf(S/Ldf) and the exponents describing the density of sites at the verge of yielding, which we find to be of the form P(x) ≃ P(0) + xθ with P(0) ∼ L-a controlling the extremal statistics. On the other hand, we discuss "dynamical" exponents that are sensitive to the local yielding rule. We find that, apart form the dynamical exponent z controlling the duration of avalanches, also the flowcurve's (inverse) Herschel-Bulkley exponent β ( ∼ (σ-σc)β) enters in this category, and is seen to differ in ½ between the two yielding rate cases. We give analytical support to this numerical observation by calculating the exponent variation in the Hébraud-Lequeux model and finding an identical shift. We further discuss an alternative mean-field approximation to yielding only based on the so-called Hurst exponent of the accumulated mechanical noise signal, which gives good predictions for the exponents extracted from simulations of fully spatial models.Fil: Ferrero, Ezequiel E.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; ArgentinaFil: Jagla, Eduardo Alberto. Comisión Nacional de Energía Atómica. Gerencia del Área de Energía Nuclear. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro | Universidad Nacional de Cuyo. Instituto Balseiro. Archivo Histórico del Centro Atómico Bariloche e Instituto Balseiro.; Argentin

Tuning the resistive switching properties of TiO2-x films

We study the electrical characteristics of TiO2-x-based resistive switching devices fabricated with different oxygen/argon flow ratio during the oxide thin film sputtering deposition. Upon minute changes in this fabrication parameter, three qualitatively different device characteristics were accessed in the same system, namely, standard bipolar resistive switching, electroforming-free devices, and devices with multi-step breakdown. We propose that small variations in the oxygen/ argon flow ratio result in relevant changes of the oxygen vacancy concentration, which is the key parameter determining the resistive switching behavior. The coexistence of percolative or non-percolative conductive filaments is also discussed. Finally, the hypothesis is verified by means of the temperature dependence of the devices in low resistance state.Fil: Ghenzi, Néstor. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Área Investigaciones y Aplicaciones no Nucleares; Argentina. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina. CIC nanoGUNE; EspañaFil: Rozenberg, M.J.. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Física; Argentina. Université Paris Sud; FranciaFil: Llopis, R.. CIC nanoGUNE; EspañaFil: Levy, Pablo Eduardo. Comisión Nacional de Energía Atómica. Gerencia del Área Investigaciones y Aplicaciones no Nucleares; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Hueso, Luis E.. Universidad del País Vasco; España. Fundación Vasca para la Ciencia; EspañaFil: Stoliar, Pablo Alberto. Universidad Nacional de San Martín. Escuela de Ciencia y Tecnología; Argentina. CIC nanoGUNE; Españ

Reactivity of a Pt(100) cluster modified by adsorption of a nickel tetramer

The aim of this paper is to report a study of the reactivity of Pt(100) cluster and the same system modified by a nickel tetramer towards the atomic hydrogen adsorption. This study was carried out in the framework of density functional theory which provides global and local indexes that can be used to characterize the reactivity. The analyzed reactivity descriptors were: chemical potential, chemical hardness, electrophilicity index and Fukui function. The results showed that the global reactivity descriptor predicts that the platinum cluster modified by nickel is more reactive than the pure platinum cluster and that the local Fukui function provides information about the most susceptible site to electrophilic attack in platinum cluster.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Reactivity of a Pt(100) cluster modified by adsorption of a nickel tetramer

The aim of this paper is to report a study of the reactivity of Pt(100) cluster and the same system modified by a nickel tetramer towards the atomic hydrogen adsorption. This study was carried out in the framework of density functional theory which provides global and local indexes that can be used to characterize the reactivity. The analyzed reactivity descriptors were: chemical potential, chemical hardness, electrophilicity index and Fukui function. The results showed that the global reactivity descriptor predicts that the platinum cluster modified by nickel is more reactive than the pure platinum cluster and that the local Fukui function provides information about the most susceptible site to electrophilic attack in platinum cluster.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Yielding of amorphous solids at finite temperatures

We analyze the effect of temperature on the yielding transition of amorphous solids using different coarse-grained model approaches. On one hand, we use an elastoplastic model, with temperature introduced in the form of an Arrhenius activation law over energy barriers. On the other hand, we implement a Hamiltonian model with a relaxational dynamics, where temperature is introduced in the form of a Langevin stochastic force. In both cases, temperature transforms the sharp transition of the athermal case in a smooth crossover. We show that this thermally smoothed transition follows a simple scaling form that can be fully explained using a one-particle system driven in a potential under the combined action of a mechanical and a thermal noise, namely, the stochastically driven Prandtl-Tomlinson model. Our work harmonizes the results of simple models for amorphous solids with the phenomenological ∼T2/3 law proposed by Johnson and Samwer [Phys. Rev. Lett. 95, 195501 (2005)PRLTAO0031-900710.1103/PhysRevLett.95.195501] in the framework of experimental metallic glasses yield observations, and extend it to a generic case. Conclusively, our results strengthen the interpretation of the yielding transition as an effective mean-field phenomenon.Fil: Ferrero, Ezequiel E.. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Bariloche; ArgentinaFil: Kolton, Alejandro Benedykt. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; ArgentinaFil: Jagla, Eduardo Alberto. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin

Aplicação da metodologia SMED na produção de rolhas capsuladas

Cada vez mais é exigido às empresas um elevado nível de qualidade e flexibilidade na produção. Para isto, e de forma a permanecer no mercado e se tornarem competitivas, os métodos de trabalho praticados devem ser fiáveis e eficientes. O presente projeto procurou a melhoria na mudança de referência de um equipamento da indústria da cortiça, através da aplicação de métodos Lean. O equipamento em estudo realiza a junção de uma rolha de cortiça a uma cápsula, sendo esta operação feita através da colagem com hot-melt. Como a variedade de produtos produzidos é enorme, isto leva a que os changeover sejam realizados com bastante frequência. O método seguido neste projeto foi o estudo e recolha de informação sobre a filosofia Lean de produção e a sua aplicação na indústria da cortiça. Também se analisou as condições de trabalho da máquina de capsular, e quais as oportunidades de melhoria possíveis. Para isto, foi elaborado o VSM (Value Stream Mapping), de forma a perceber quais são as operações que realmente acrescentam valor ao produto. Foram ainda implementados os 6S, com o objetivo de sensibilizar os operadores para os benefícios resultantes da organização e limpeza do local de trabalho e das ferramentas. A metodologia SMED (Single Minute of Exchange of Die), foi aplicada de forma a reduzir o tempo de paragem provocado por mudanças de ferramenta, sendo que foi obtida uma redução de 43% no tempo total de changeover. Para monitorizar todo o desenvolvimento do projeto SMED, foi ainda criado um modelo A3. Por fim, foi implementado o cálculo do OEE (Overall Equipment Effectiveness), como indicador da eficiência geral do equipamento, e de forma a melhorar a monitorização de possíveis desvios que possam ocorrer durante a produção. Os resultados obtidos comprovam ainda, que as ferramentas lean são um método poderoso para obter resultados sem a necessidade de grandes investimentos.Organizations are increasingly required to have a high level of quality and flexibility in production. In order to remain in the market and become competitive, the working methods practised must be reliable and efficient. The present project sought the improvement in the reference change of an equipment used in cork industry, through the application of Lean methods. The equipment under study performs the union of a cork stopper to a capsule, which is done by glueing it with hot-melt glue. Since the variety of products produced is huge, this almost makes the changeover activity a frequency. The method followed in this work was the study and collection of information on the Lean production philosophy and its application in the cork industry. The working conditions of the assembly machine were also analyzed, searching for improvement opportunities. Thus, it was elaborated the Value Stream Mapping (VSM) in order to perceive which are the operations that really add value to the product. The SMED (Single Minute of Exchange of Die) methodology was applied in a way to reduce the downtime caused by tool changes, and a reduction of 43% in total changeover time was obtained. To monitor the entire development of the SMED project, it was also created an A3 model. Finally, the OEE (Overall Equipment Efficiency) calculation was implemented as an indicator of overall equipment efficiency, in order to improve the monitoring of possible deviations during production. The results obtained also prove that lean tools are a powerful method to obtain results without the need for large investments

Conformation-Independent QSAR Study on Human Epidermal Growth Factor Receptor-2 (HER2) Inhibitors

Inhibition of HER2 (human epidermal growth factor receptor 2) expression and function is required in several cancer treatments. Numerous compounds with very different molecular structures have been suggested as HER2 inhibitors. Here we perform quantitative structure-activity relationship (QSAR) analysis on 444 of such compounds to investigate the molecular properties that may influence its efficiency. Models based on 1D and 2D flexible molecular descriptors are proposed to develop simple models based solely on constitutional and topological molecular features. A large number of nonconformational descriptors (17974) was used to thoroughly explore the structural characteristics that influence the HER2 inhibitory activity. Three different approaches were explored using: 1) Molecular Descriptors, 2) Flexible Molecular Descriptors, and 3) Hybrid Descriptors. A QSAR model for HER2 inhibitors was successfully developed. Some properties such as electronegativity, aromatic character, and the presence of amino groups appear as molecular characteristics that may have influence in the HER2 inhibitory activity.Facultad de Ciencias ExactasInstituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Eocene decapod crustacea (thalassinidea and brachyura) from Patagonia, Argentina

Rocks of the Rio Turbio Formation, exposed in southern Patagonia, Argentina, represent one of very few occurrences of Eocene rocks in the region. Decapod crustaceans collected from the unit include one species of thalassinidean mud shrimp; Turbiocheir minutospinata, new genus, new species; and three species of brachyurans; Raninoides rioturbiensis, new species; Megokkos patagoniensis, new species; and Nitotacarcinus antipodes, new species. The three brachyuran genera are also known from species in the Northeast Pacific, suggesting an amphitropical distributional pattern.Fil: Schweitzer, Carrie E.. Kent State University; Estados UnidosFil: Feldmann, Rodney M.. Kent State University; Estados UnidosFil: Casadio, Silvio Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; ArgentinaFil: Rodriguez Raising, Martin Eduardo. Universidad Nacional de La Pampa; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

About International Reserve Adequacy: The Case of Chile

Under a flexible exchange rate regime, international reserves contribute to reducing the risk of a financial crisis, and allow the monetary authority to intervene exceptionally in the exchange market. However, holding reserves is costly. In this paper, we analyze several issues concerning the adequate level of Chilean international reserves. First we compare the level of Chile's international reserves with those of different sets of countries, using various indicators. We then analyze empirically some of the benefits and costs of holding reserves. Our results show that Chile's international reserves are high when measured with respect to GDP or M2, but they are in line with those of countries of similar characteristics when measured as a fraction of short-term residual debt. On the other hand, given the low risk of the Chilean economy, marginal changes in reserves have a very low impact on both the probability of a financial crisis and the sovereign spread of the country. Finally, as the sovereign spread has decreased over the last years, so too has the cost of reserves. In fact, over the past few years Chile's cost of reserves as a fraction of GDP has been considerably lower than the cost of other emerging economies.