Structured Linearization of Discrete Mechanical Systems for Analysis and Optimal Control

Variational integrators are well-suited for simulation of mechanical systems because they preserve mechanical quantities about a system such as momentum, or its change if external forcing is involved, and holonomic constraints. While they are not energy-preserving they do exhibit long-time stable energy behavior. However, variational integrators often simulate mechanical system dynamics by solving an implicit difference equation at each time step, one that is moreover expressed purely in terms of configurations at different time steps. This paper formulates the first- and second-order linearizations of a variational integrator in a manner that is amenable to control analysis and synthesis, creating a bridge between existing analysis and optimal control tools for discrete dynamic systems and variational integrators for mechanical systems in generalized coordinates with forcing and holonomic constraints. The forced pendulum is used to illustrate the technique. A second example solves the discrete LQR problem to find a locally stabilizing controller for a 40 DOF system with 6 constraints.Comment: 13 page

Probing the catalytic activity of sulfate-derived Pristine and post-treated porous TiO2(101) anatase mesocrystals by the oxidative desulfurization of dibenzothiophenes

Mesocrystals (basically nanostructures showing alignment of nanocrystals well beyond crystal size) are attracting considerable attention for modeling and optimization of functionalities. However, for surface-driven applications (heterogeneous catalysis), only those mesocrystals with excellent textural properties are expected to fulfill their potential. This is especially true for oxidative desulfuration of dibenzothiophenes (hard to desulfurize organosulfur compounds found in fossil fuels). Here, we probe the catalytic activity of anatases for the oxidative desulfuration of dibenzothiophenes under atmospheric pressure and mild temperatures. Specifically, for this study, we have taken advantage of the high stability of the (101) anatase surface to obtain a variety of uniform colloidal mesocrystals (approximately 50 nm) with adequate orientational order and good textural properties (pores around 3-4 nm and surface areas around 200 m2/g). Ultimately, this stability has allowed us to compare the catalytic activity of anatases that expose a high number of aligned single crystal-like surfaces while differing in controllable surface characteristics. Thus, we have established that the type of tetrahedral coordination observed in these anatase mesocrystals is not essential for oxidative desulfuration and that both elimination of sulfates and good textural properties significantly improve the catalytic activity. Furthermore, the most active mesocrystals have been used to model the catalytic reaction in three-(oil-solvent-catalyst) and two-phase (solvent-catalyst) systems. Thus, we have been able to observe that the transfer of DBT from the oil to the solvent phase partially limits the oxidative process and to estimate an apparent activation energy for the oxidative desulfuration reaction of approximately 40 kJ/mol in the two-phase system to avoid mass transfer limitations. Our results clearly establish that (101) anatase mesocrystals with excellent textural properties show adequate stability to withstand several post-treatments without losing their initial mesocrystalline character and therefore could serve as models for catalytic processes different from the one studied here.Fil: Rivoira, Lorena Paola. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigación y Tecnología Química. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación y Tecnología Química; ArgentinaFil: Martinez, Maria Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación en Nanociencia y Nanotecnología; ArgentinaFil: Falcon, Horacio. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación en Nanociencia y Nanotecnología; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; ArgentinaFil: Beltramone, Andrea Raquel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba; Argentina. Universidad Tecnológica Nacional. Facultad Regional Córdoba. Centro de Investigación en Nanociencia y Nanotecnología; ArgentinaFil: Campos-Martin, Jose M.. Consejo Superior de Investigaciones Científicas; EspañaFil: García Fierro, José Luis. Instituto de Catalisis y Petroleoquimica-csic; EspañaFil: Tartaj, Pedro. Consejo Superior de Investigaciones Científicas. Instituto de Catálisis y Petroleoquímica; Españ

Iron oxide nanosized clusters embedded in porous nanorods: A new colloidal design to enhance capabilities of MRI contrast agents

“This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Nano, © 2010 American Chemical Society after peer review and technical editing by the publisher. To acces final work see “Iron oxide nanosized clusters embedded in porous nanorods: A new colloidal design to enhance capabilities of MRI contrast agents”, ACS Nano 4.4 (2010): 2095-2103, https://doi.org/10.1021/nn9013388"Development of nanosized materials to enhance the image contrast between the normal and diseased tissue and/or to indicate the status of organ functions or blood flow is essential in nuclear magnetic resonance imaging (MRI). Here we describe a contrast agent based on a new iron oxide design (superparamagnetic iron oxide clusters embedded in antiferromagnetic iron oxide porous nanorods). We show as a proof-of-concept that aqueous colloidal suspensions containing these particles show enhanced-proton relaxivities (i.e., enhanced MRI contrast capabilities). A remarkable feature of this new design is that large scale production is possible since aqueous-based routes are used, and porosity and iron oxide superparamagnetic clusters are directly developed from a single phase. We have also proved with the help of a simple model that the physical basis behind the increase in relaxivities lies on both the increase of dipolar field (interactions within iron oxide clusters) and the decrease of proton-cluster distance (porosity favors the close contact between protons and clusters). Finally, a list of possible steps to follow to enhance capabilities of this contrast agent is also included (partial coating with noble metals to add extra sensing capacity and chemical functionality, to increase the amount of doping while simultaneously carrying out cytotoxicity studies, or to find conditions to further decrease the size of the nanorods and to enhance their stability)We acknowledge financial support from the Spanish Ministerio de Ciencia e innovación trough MAT2008-03224/NAN and from the Comunidad Autónoma de Madrid under Project S-0505/MAT/019

Thermally driven self-assembly of nanomicelles: A facile route to functional monodisperse mesoporous colloidal nanocomposites of inorganic nature and mesoscale size

Thermally driven self-assembly of nanomicelles can be a feasible route to produce monodisperse porous colloidal nanocomposites of inorganic nature and sizes around the mesoscale (below 100 nm). Success relies on extending the lifetime of intermediate droplets (size below about 100 nm) that are obtained under particular conditions. Herein, the conditions for the long-term stabilization of these unique templates are studied and a model proposed to produce monodisperse porous colloidal nanocomposites. As an example of the potential applications of this methodology, functional colloidal nanocomposites with a high loading of the doping material (30 mol%) are obtained. In particular, superparamagnetic nanomagnets of metallic nature encapsulated in porous oxide colloidal matrixes of mesoscale size that easily respond to an external magnetic field are prepared and characterized in terms of structure and textural and magnetic properties. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA.This work was supported by the Spanish Ministerio de Ciencia e Innovacion under contract MAT2008-03224/NAN.Peer Reviewe

Pigmentos de alta temperatura preparados por reacciones químicas de aerosoles líquidos en el sistema sílice-circona

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química Inorgánica. Fecha de lectura: 08-03-199

Síntesis, sinterización y propiedades eléctricas de soluciones sólidas YNixMn1-xO3 preparadas a partir de Precursores Poliméricos

[ES] Las soluciones sólidas YNixMn1-xO3 (x=0.2…0.5), son materiales semiconductores con estructura perovsquita, simetría ortorrómbica y grupo espacial Pbnm. La obtención de estos compuestos a partir del método convencional de mezcla de óxidos está caracterizada por la alta temperatura de síntesis ( ≥ 1000 ºC ) y una vigorosa molienda. Mediante un método de polimerización (Pechini, con pequeñas modificaciones) se ha obtenido un material amorfo, poroso y muy blando, a partir del cual se sintetizan las manganitas de Itrio modificadas con Ni como fase única, con tamaño de partícula nanométrico, a una temperatura de síntesis comprendida entre 750−800ºC. Se ha estudiado, cualitativamente, la cinética de reacción de formación para el compuesto representativo YNi0,33Mn0,67O3 , empleando las técnicas de absorción de infrarrojo (FTIR) y difracción de rayos X (DRX) para su seguimiento. Además, se hace una comparación de la sinterización y del comportamiento eléctrico entre el compuesto representativo y el correspondiente preparado mediante la técnica convencional de mezcla de óxidos.[EN] The solid solutions YNixMn1-xO3 are semiconducting materials which show perovskite-like structure, ortorrombic symmetry, and spatial group Pbnm. Their electrical and magnetic properties are typical of materials with potential applications in sensor systems or as cathodes in solid oxide fuel cells (SOFC's). Usually, the conventional method of mixing oxides used to obtain these materials requires high-temperature synthesis and vigorous milling. By means of a polymerization method (the Pechini method, slightly modified) we have obtained an amorphous, porous, and soft material from which the Ni-modified yttrium manganite, as a single phase, can be synthesized. The powder was characterized by a nanometric particle size, a low temperature of synthesis within the interval 750–800 ºC, and it did not require much milling. The formation reaction has been studied for the compound YNi0,33Mn0,67O3 , using X-Ray diffraction (XRD) and the infrared absorption technique (FTIR). Also, a comparison of the electrical behaviour and the sinterization process is made between the sample prepared by the chemical and the mixing oxides method.Los autores agradecen al Ministerio de Ciencia de España, el apoyo recibido a través del proyecto CICYT–MAT–97–0679–C02–01.Peer reviewe

Porous inorganic nanostructures with colloidal dimensions: Synthesis and applications in electrochemical energy devices

Porous inorganic nanostructures with colloidal dimensions can be considered as ideal components of electrochemical devices that operate on renewable energy sources. They combine nanoscale properties with good accessibility, a high number of active sites, short diffusion distances and good processability. Herein, we review some of the liquid-phase routes that lead to the controlled synthesis of these nanostructures in the form of non-hollow, hollow or yolk-shell configurations. From solar and fuel cells to batteries and supercapacitors, we put special emphasis on showing how these sophisticated structures can enhance the efficiency of electrochemical energy devices. This journal is © The Royal Society of Chemistry.Financial support from projects MAT2011-23641 (to P.T.) MAT2011-25198 and MAT2011-22969 (to J.M.A.).Peer Reviewe

Multifunctional response of anatase nanostructures based on 25 nm mesocrystal-like porous assemblies

Mesocrystals are colloidal crystals whose elemental units are nanocrystals (size within the mesoscale) that all grow oriented in the same crystallographic direction. [1] Part of the interest in mesocrystals or, specifically, in mesocrystal-like porous nanostructures (MLPNs) is that their behavior is similar to single crystals while preserving nanoscale capabilities. We know that nanoscale capabilities are essential in many applications, including healthcare, catalysis, and energy storage, [2] but we also know that many properties depend on the number of crystalline defects and the type of exposed facets. [2c,3] The unique characteristics of MLPNs, such as good and uniform crystallinity, high surface area, and pore accessibility, could, thus, bring benefits to different fields. [4] Particularly, we are of the opinion that small anatase, a TiO2 polymorph, MLPNs could be of interest in photocatalysis, energy storage devices, and healthcare applications. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.Financial support from Spain Ministerio de Ciencia e Innovacion under projects MAT2008-03224 and MAT2008-03182 is acknowledged.Peer Reviewe

A Facile Route for the Preparation of Superparamagnetic Porous Carbons

5 pages, 6 figures.We present here a novel and simple synthetic strategy for fabricating superparamagnetic nanomagnets randomly dispersed in porous carbons. The method can be basically considered as a pyrolysis performed inside the restricted volume formed by the pores of an activated carbon. Such magnetic porous materials exhibit large surface areas (up to 1600 m2 g-1), high pore volumes (up to 1.0 cm3 g-1), and a porosity made up of accessible pores. An additional advantage of this method is its versatility, which allows composites with tunable magnetic properties to be obtained. In this way, it is possible to obtain superparamagnetic composites that can be easily manipulated by an external magnetic field.The financial support for this research provided by the MEC (MAT2005-00262, MAT2005-03179, and NANO2004-08805-C04-01) is gratefully acknowledged.Peer reviewe