Caracterización y puesta en valor del humedal inca de Wayllarqocha-Saqsaywaman: Cusco

El Programa de Patrimonio Natural del Parque Arqueológico de Saqsaywaman contempla línea de acción para recuperar, conservar y proteger ecosistemas estratégicos y frágiles que brindan servicio ambiental al lugar. Es por ello que ha identificado humedales altoandinos en el sector de Wayllarqocha, dentro del Parque Arqueológico de Saqsaywaman. Como parte de este programa, se ha puesto en evidencia antiguos humedales incas que forman parte de Wayllarcocha, y que hasta el 2008 estaban en vías de desaparición por el crecimiento urbano de la comunidad (Carlotto et al., 2008). Si bien en parte corresponden a humedales naturales, los estudios han puesto en evidencia obras de factura inca que incluyen captaciones, muros de represamiento, estructuras ovaladas, circulare y wakas que servían de culto religioso al agua. Los incas lograron captar y represar el agua, formando qochas con flora y fauna asociada como modelo de interacción entre lo natural y lo cultural. El objetivo de este trabajo es recuperar el sistema de humedales de Wayllarqocha, para lo cual se firmó un convenio entre el Instituto Nacional de Cultura del Cusco (Parque Arqueológico de Saqsaywaman) y la Comunidad de Wayllarqocha, que tiene el soporte técnico del INGEMMET, la UNSAAC y la ONG Guamán Poma para los estudios de geología, hidrogeología e intervención. Hasta enero del 2010 ya se ha recuperado parte del humedal y particularmente la Qocha 1, aunque si bien las qochas 2 y 3 ya reciben el agua a través del sistema hidráulico inca, aún falta la restauración de las mismas. Con la recuperación de los humedales se prevé mejorar la calidad de vida de los habitantes del sector, incrementando el flujo turístico, con más alternativas de actividades para los visitantes

Heterovalent BiIII/PbII ionic substitution in one-dimensional trimethylsulfoxonium halide pseudo-perovskites (X = I, Br)

We report on the synthesis and characterization of novel lead and bismuth hybrid (organic 12inorganic) iodide and bromide pseudo-perovskites (ABX3) containing the trimethylsulfoxonium cation (CH3)3SO+ (TMSO) in the A site, Pb/Bi in the Bsite, and Br or I as X anions. All of these compounds are isomorphic and crystallize in the orthorhombic Pnma space group. Lead-based pseudo-perovskites consist of one-dimensional (1D) chains of facesharing [PbX6] octahedra, while in the bismuth-based ones, the chains of [BiX6] are interrupted, with one vacancy every third site,leading to a zero-dimensional (0D) local structure based on separated [Bi2I9] 3 12 dimers. Five solid solutions for the iodide with different Pb2 +/Bi3 + ratios between (TMSO)PbI3 and (TMSO)3Bi2I9, and two for the bromide counterparts, were synthetized. Due to the charge compensation mechanism, these systems are best described by the (TMSO)3Pb3xBi2(1 12x)I9 (x = 0.98, 0.92, 0.89, 0.56, and 0.33) and (TMSO)3Pb3xBi2(1 12x)Br9 (x = 0.83 and 0.37) formulae. X-ray powder diffraction (XRPD) measurements were employed to determine the crystal structure of all studied species and further used to test the metal cation miscibility within monophasic samples not showing cation segregation. These systems can be described through an ionic defectivity on the pseudo-perovskite B site, where the Pb2+/Bi3+ replacement is compensated by one Pb2+ vacancy for every Bi3+ pair. This leads to a wide range of possible different (numerical and geometrical) chain configurations, leading to the unique features observed in XRPD patterns. The optical band gap of the iodide samples falls in the 2.11 122.74 eV range and decreases upon increasing the Bi3+ content. Interestingly, even a very low loading of Bi3+ (1%) is sufficient to reduce the band gap substantially from 2.74 to 2.25 eV. Periodic density functional theory (DFT) calculations were used to simulate the atomic and electronic structures of our samples, with predicted band gap trends in good agreement with the experimental ones. This work highlights the structural flexibility of such systems and accurately interprets the ionic defectivity of the different pseudo-perovskite structures

Amorphous WO3 as transparent conductive oxide in the near-IR

The demand for transparent conductive films (TCFs) is dramatically increasing. In this work tungsten oxide (WO3-x) is studied as a possible option additional to the existed TCFs. We introduce WO3-x thin films fabricated by a non-reactive magnetron RF-sputtering process at room temperature, followed by thermal annealing in dry air. Films are characterized morphologically, structurally, electrically, optically, and dielectrically. Amorphous WO3-x thin films are shown to be ntype conductive while the transparency extends to the near-IR. By evaluating a figure of merit for transparent-conductive performance and comparing to some most-widely used TCFs, WO3-x turns out to outperform in the near-IR optical range

Modeling of dynamic solvation effects

Reactivity of molecular and supramolecular systems is greatly modified by the surrounding environment, often a fluid medium, and an active area of research is nowadays the study of the influence of a solvent structure on the static and dynamic properties of photo-active and paramagnetic probes, varying solvent properties, sample geometry and external perturbations. Standard continuum solvent theories are based on crude representations of the probe. Solvation processes depend in a specific way upon the structure of the solute, and in particular on molecular features as shape, flexibility, distribution of charges and anisotropy of the polarizability. Augmented solvent continuum approaches have been developed to interpret chromophore dynamics to account for persistent solvent local structures. Description of collective solvent modes is also necessary to understand relaxation processes affecting dynamics at longer times, in complex fluid environments: phase transitions in supercooled liquids, rheological properties of emulsions and colloids, confinement effects and finally micro and nano-probes dynamics. The inclusion of solvent effects is of great importance, in order to understand the physical mechanisms responsible of the tuning of the optical properties and therefore to the ultimate possibility to design nanomaterials with specific optical response. Theoretical methodologies based on stochastic and hydrodynamic modeling have proven over the years to be a powerful approach, especially when coupled with advanced quantum mechanical treatments, to describe effectively the dynamical aspects of solvation. The relationship between spectroscopic measurements and molecular properties can be gathered only indirectly, that is, structural and dynamic molecular characteristics can be inferred by the systematic application of modelling and numerical simulations to interpret experimental observables. A straightforward way to achieve this goal is the employment of spectroscopic evidence as the "target" of a fitting procedure of molecular, mesoscopic and macroscopic parameters entering the model. A more refined methodology is based on the combination of quantum mechanical calculations of structural parameters possibly including environmental and fast vibrational and librational averaging, and direct feeding of calculated molecular parameters into dynamic models based on molecular dynamics, coarse grain dynamics, and above all stochastic modeling or a combination of the three. Our main objective in this PhD work has been to discuss the degree of progress of advanced theoretical models are explored, aimed at clarifying the influence of solvent-driven relaxation processes on optic, magnetic and rheological observables. In particular we have developed integrated computational approaches to the interpretation of fluorescence emission of organic molecules in solvated environments, CW-ESR spectroscopy and rheological properties of ordered systems via combination of advanced quantum mechanical approaches, stochastic modeling of relaxation processes, and, in the last case, macroscopic models. In the first period we have shown that the model proposed is able to reproduce the spectral position and shape of the emission spectra. In particular the model reproduces the red shift expected for TICT excited states when the dielectric constant of the solvent increases. We developed a stochastic approach to the interpretation of the emission fluorescence of 4-(N,N-dimethylamino) benzonitrile (DMABN). Than we proceed by extending the modeling approach, in which internal degrees of freedom are coupled with an effective solvent relaxation variable. The extension of the model is applied to the simulation of the emission spectra of DMABN-Crown5, a DMABN derivative. Evaluation of potential energy surfaces using advanced QM approach and estimates of dissipative parameters based on hydrodynamic arguments are discussed. Emission fluorescence is calculated by solving a diffusion/sink/source equation for the stationary population of excited state, and compared to experimentally measured emission fluorescence of DMABN and DMABN-Crown5. Next we developed the complete a priori simulation of the ESR spectra of complex systems in solution. The usefulness and reliability of the method are demonstrated on the very demanding playground represented by the tuning of the equilibrium between 310- and ?-helices of polypeptides by different solvents. The starting point is good agreement between computed and X-ray diffraction structures for the 310-helix adopted by the double spin-labelled heptapeptide Fmoc-(Aib-Aib-TOAC)2-Aib-OMe. Next, density functional computations, including dispersion interactions and bulk solvent effects, suggest another energy minimum corresponding to an ?-helix in polar solvents, which, eventually, becomes the most stable structure. Computation of magnetic and diffusion tensors provides the basic ingredients for the building of complete spectra by methods rooted in the Stochastic Liouville Equation (SLE). The remarkable agreement between computed and experimental spectra at different temperatures allowed us to identify helical structures in the various solvents. The generality of the computational strategy and its implementation in effective and user-friendly computer codes pave the route toward systematic applications in the field of biomolecules and other complex systems. Finally, the purpose of the last part of the PhD period has been to analyze the dynamical behavior of a low viscosity nematic liquid crystals in presence of micro-size probe. We present a study of the translational friction coefficients of spherical and ellipsoidal probes moving in nematic liquid crystalline fluids, by solving numerically the constitutive hydrodynamic equations of nematic. The evaluation of the translational friction coefficients is based on a numerical solution of Leslie-Ericksen constitutive equations for the case of incompressible nematic fluids. The nematic medium is described by a vector field which specifies the director orientation in each point and by the velocity vector field. Simulation of director dynamics surrounding the moving probe are presented, and the dependence of translational diffusion upon liquid crystal viscoelastic parameters is discussed. The time evolution of director field, described by Leslie-Ericksen equations, is studied in the presence of an orienting magnetic field in two characteristic situations: director of motion parallel and perpendicular to field

Al- and Mg-doped SrTiO3 perovskite steps: The catalytic performance for oxidative coupling of methane

One of the most important processes for converting methane into value-added chemical products is the reaction of the oxidative coupling of methane. The catalytic performance of a heterogenous catalyst can be evaluated using the first principles. The simultaneous presence of defects (oxygen vacancies, metal dopants and edges) on perovskites makes the simulations more realistic and closer to the experimental conditions. Results showed that CH3 adsorption and formation energy of the oxygen vacancy are sufficient to verify catalytic activity. The comparison of the steps and the surface simulations shows different properties and that the step is not always the preferred catalytic site

Theoretical Investigation of the Open Circuit Voltage: P3HT/9,9′-Bisfluorenylidene Derivative Devices

The calculation of the power conversion efficiency (PCE) value for a bulk heterojunction (BHJ) organic solar cell is complex due to the wide number of parameters involved in the processes. This study focuses the attention on the molecular parameters involved into the open circuit voltage and the PCE definitions and in particular on the electronic coupling and on the lowest unoccupied molecular orbital (LUMO) of the acceptor. A simplified model system composed by a polymer as donor and a novel class of molecules (9,9′-bisfluorenylidene derivatives) as acceptor has been proposed as prototype to simulate the BHJ organic solar cell interface. Several substituents on different positions are tested and the chemical nature/position of substituents have a relevant influence on the electronic coupling and energy level values. Geometrical and electronic properties are obtained using density functional theory (DFT) and time-dependent (TD)-DFT calculations, respectively. A new hypothesis suggests that the minimization of the electronic coupling between the LUMO of the acceptor and the highest occupied molecular orbital (HOMO) of the donor can enhance the PCE reducing the recombination interface processes and calculations showing the possibility to minimize this parameter and fine-tune acceptor energy level through the acceptor functionalization. An accurate balance between electronic coupling and on the LUMO of the acceptor allows to propose the more performing candidate as electron acceptor in a P3HT/99′BF derivative BHJ solar cell

Computational Study of Environmental Effects on Torsional Free Energy Surface ofN-Acetyl-N\u2032-methyl-l-alanylamide Dipeptide

We propose an articulated computational experiment in which both quantum mechanics (QM) and molecular mechanics (MM) methods are employed to investigate environment effects on the free energy surface for the backbone dihedral angles rotation of the small dipeptide N-acetyl-N\u2032-methyl-l-alanylamide. This computation exercise is appropriate for an upper-level physical chemistry course. The purposes are (i) to show the importance of solvent effects on the free energy surface of molecules in solution and (ii) to compare different computational chemistry tools in terms of computation complexity versus detail of information obtained from calculus. The QM section is divided in three parts: in vacuo, implicit solvent, and explicit solvent calculations. Similarly, also the MM section is divided in three parts: molecular mechanics, molecular dynamics, and adaptive biasing force molecular dynamics. QM and MM sections can be proposed by the instructor as different and complementary parts of the experiment or as independent QM or MM class lessons. Together, the two sections can be used to set up a computational chemistry laboratory exercise targeted to the study of solvent effects on molecular properties

Evaluation of translational friction coefficients of micro-sized spherical probes in nematic liquid crystals

We study the translational friction coefficients of a spherical micrometric probe moving in nematic liquid crystalline fluids, by solving numerically the constitutive hydrodynamic equations of uncompressible isothermal nematic fluids (Leslie–Ericksen equations). The nematic medium is described by a vector field, which specifies the director orientation at each point and by the velocity vector field. Simulations of director dynamics surrounding the moving probe are presented, and the dependence of translational diffusion upon liquid crystal viscoelastic parameters is discussed. The time evolution of director field is studied in the presence of an orienting magnetic field in two characteristic situations, i.e. direction of motion parallel and perpendicular to field. In particular, a detailed analysis is given for the case of a spherical probe in rectilinear motion in nematic MBBA (4-methoxibenzylidene-4′-n-butylaniline), together with a comparison with other nematogens

Evaluation of translational friction coefficients of macroscopic probes in nematic liquid crystals

We present a study of the translational friction coefficients of spherical and ellipsoidal probes in nematic liquid crystalline fluids, based on the numerical treatment of Leslie-Ericksen equations [ Q. J. Mech. Appl. Math. 19, 357 (1966) ; Adv. Liq. Cryst. 4, (1979) ; Trans. Soc. Rheol. 5, 23 (1961) ; Adv. Liq. Cryst. 2, 233 (1976) ] for incompressible nematic fluids. Simulations of director dynamics in a local environment surrounding the moving probe are presented, and the dependence of translational diffusion on liquid crystal viscoelastic parameters is discussed. The time evolution of the director field is studied in the presence of an orienting magnetic field in two characteristic situations: Directors of motion parallel and perpendicular with respect to the field. In the particular case under investigation, a detailed analysis is given for the case of spherical, prolate, and oblate ellipsoidal probes in rectilinear motion in nematic (4-methoxibenzylidene-4′-n-butylaniline), together with a comparison with other nematogens, namely, 4,4′-dimethoxuazoxy benzene and (4′-n-pentyl-4-cyanobiphenil). A discussion of the general methodology presented in this work is given for the case of colloidal dispersions in nematic liquid crystals, which are considered as model systems of dispersions of particles in host media with anisotropic physical properties