Theoretical model and experimental analysis of glulam beam reinforced with FRP

This work present a study of glulam beams reinforced with FRP. It was developed a theoretical model that calculates strength and stiffness of the beams. The model allows for the calculation of the bending moment, the hypothetical distribution of linear strains along the height of the beam, and considers the wood has a linear elastic fragile behavior in tension parallel to the fibers and bilinear in compression parallel to the fibers, initially elastic and subsequently inelastic, with a negative decline in the stress-strain diagram. The stiffness was calculated by the transformed section method. Twelve non-reinforced and fiberglass reinforced glulam beams were evaluated experimentally to validate the proposed theoretical model. The results obtained indicate good congruence between the experimental and theoretical values.

Towards an insight on photodamage in hair fibre by UV-light: An experimental and theoretical study

Synopsis: Objectives: In this research, an experimental and theoretical study was conducted to design a photodegradation mechanism of the amino acid tryptophan (Trp) in hair fibres. Methods: For the experimental research, Caucasian hair fibres were exposed to several different solar radiation simulation periods. Then, Trp and its photoproducts (N-formylkynurenine and kynurenine) were assayed by excitation and emission spectroscopic analysis. Results: For the theoretical study, reactions involved in the photodegradation of Trp were evaluated by high-level quantum mechanical calculations in a density functional theory (DFT) framework which indicate a probable Trp degradation mechanism with a minimum expended energy pathway. Conclusion: The biochemistry concerning these reactions is essentially important for a biological system where the degradation of Trp occurs. © 2013 John Wiley & Sons Ltd.

Experimental and theoretical approach of nanocrystalline TiO2 with antifungal activity

Using a solvothermal method for this research we synthesized nanocrystalline titanium dioxide (nc-TiO2) anatase particles with a mean diameter of 5.4 nm and evaluated their potential antifungal effect against planktonic cells of Candida albicans without UV radiation. To complement experimental data, we analyzed structural and electronic properties of both the bulk and the (1 0 1) surface of anatase by first-principles calculations. Based on experimental and theoretical results, a reactive O2H- and OH- species formation mechanism was proposed to explain the key factor which facilitates the antifungal activity. © 2013 Published by Elsevier B.V.

Synthesis, characterization, thermal behavior, and DFT calculation of solid 1,4-bis(3-carboxy-3-oxo-prop-1-enyl) benzene of some trivalent lanthanides

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A theoretical investigation of the structural and eletronic properties of orthorhombic CaZrO3

A CaZrO3 (CZO) powder was prepared by the soft chemical, polymeric precursor method (PPM). The CZO crystalline structure was investigated by powder X-ray diffraction (XDR), Retvield Refinament data, Raman spectra and ultraviolet–visible absorption spectroscopy. A theoretical study was performed using a periodic quantum mechanical calculation (CRYSTAL09 program). The periodic model built for the crystalline CZO structure was consistent with the experimental data obtained from structural and electronic properties. These results show that the material has an orthorhombic structure with experimental and theoretical gap values of 5.7 eV and 6.2 eV, respectively. In this article, we discuss the hybridization process of the oxygen p-orbitals and of the zirconium d-orbitals and analyze their band structures and density of states (partial and total).

A joint experimental and theoretical study on the electronic structure and photoluminescence properties of Al-2(WO4)(3) powders

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Interfacial concentrations of chloride and bromide in zwitterionic micelles with opposite dipoles: Experimental determination by chemical trapping and a theoretical description

Interfacial concentrations of chloride and bromide ions, with Li+, Na+, K+, Rb+, Cs+, trimethylammonium (TMA(+)), Ca2+, and Mg2+ as counterions, were determined by chemical trapping in micelles formed by two zwitterionic surfactants, namely N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and hexadecylphosphorylcholine (HDPC) micelles. Appropriate standard curves for the chemical trapping method were obtained by measuring the product yields of chloride and bromide salts with 2,4,6-trimethyl-benzenediazonium (BF4) in the presence of low molecular analogs (N,N,N-trimethyl-propane sulfonate and methyl-phosphorylcholine) of the employed surfactants. The experimentally determined values for the local Br- (Cl-) concentrations were modeled by fully integrated non-linear Poisson Boltzmann equations. The best fits to all experimental data were obtained by considering that ions at the interface are not fixed at an adsorption site but are free to move in the interfacial plane. In addition, the calculation of ion distribution allowed the estimation of the degree of ion coverage by using standard chemical potential differences accounting for ion specificity. (C) 2012 Elsevier Inc. All rights reserved.

X-ray diffraction and theoretical investigation of the Gedunin crystal structure

The Gedunin compound (C28H34O6) is a natural product extracted from Trichilia pallida that has shown a wide activity. The crystallographic structure shows two conformers in the asymmetric unit, which differ in a rotation of the furan group. To understand this molecular arrangement, the density functional calculations. Molecular Electrostatic Potential (MEP) and thermodynamic function calculation have been performed at the B3LYP/6-311++g(d,p) level. Both conformers were optimized and the agreement with the experimental structure was very good, making possible further theoretical analysis of the structure. The inter-conversion between two conformers depends on the energy barrier. This process is studied in the vacuum and shows two transition states with a low energetic barrier for a potential energy curve scanning rigid around furan group: 4.37 kcal/mol and 16.52 kcal/mol. As the first transition state has a notably lower energetic barrier, the preferred inter-conversion pathway between the conformers involves the first rather than the second transition state. Understanding this transition state in detail led us to perform its optimization, showing an energetic barrier around 3.66 kcal/mol. The negative free energy and low enthalpy confirm that the process is spontaneous and exothermic. The results show that this requirement makes the existence of the two conformers in the asymmetric unit possible. The structure of molecules in the asymmetric unit is better understood when the MEP is used on the interaction between molecules. For Gedunin, both molecules have shown MEP with well-defined regions, and this behavior contributes to the observed link between molecules and for the negative regions complementing positive regions of another molecule. (C) 2011 Elsevier B.V. All rights reserved.

Calculation of parameter ranges for robust gain tuning of power system controllers

This work proposes a computational tool to assist power system engineers in the field tuning of power system stabilizers (PSSs) and Automatic Voltage Regulators (AVRs). The outcome of this tool is a range of gain values for theses controllers within which there is a theoretical guarantee of stability for the closed-loop system. This range is given as a set of limit values for the static gains of the controllers of interest, in such a way that the engineer responsible for the field tuning of PSSs and/or AVRs can be confident with respect to system stability when adjusting the corresponding static gains within this range. This feature of the proposed tool is highly desirable from a practical viewpoint, since the PSS and AVR commissioning stage always involve some readjustment of the controller gains to account for the differences between the nominal model and the actual behavior of the system. By capturing these differences as uncertainties in the model, this computational tool is able to guarantee stability for the whole uncertain model using an approach based on linear matrix inequalities. It is also important to remark that the tool proposed in this paper can also be applied to other types of parameters of either PSSs or Power Oscillation Dampers, as well as other types of controllers (such as speed governors, for example). To show its effectiveness, applications of the proposed tool to two benchmarks for small signal stability studies are presented at the end of this paper.

Shear force and torsion in reinforced concrete beam elements: theoretical analysis based on Brazilian Standard Code ABNT NBR 6118:2007

Reinforced concrete beam elements are submitted to applicable loads along their life cycle that cause shear and torsion. These elements may be subject to only shear, pure torsion or both, torsion and shear combined. The Brazilian Standard Code ABNT NBR 6118:2007 [1] fixes conditions to calculate the transverse reinforcement area in beam reinforced concrete elements, using two design models, based on the strut and tie analogy model, first studied by Mörsch [2]. The strut angle θ (theta) can be considered constant and equal to 45º (Model I), or varying between 30º and 45º (Model II). In the case of transversal ties (stirrups), the variation of angle α (alpha) is between 45º and 90º. When the equilibrium torsion is required, a resistant model based on space truss with hollow section is considered. The space truss admits an inclination angle θ between 30º and 45º, in accordance with beam elements subjected to shear. This paper presents a theoretical study of models I and II for combined shear and torsion, in which ranges the geometry and intensity of action in reinforced concrete beams, aimed to verify the consumption of transverse reinforcement in accordance with the calculation model adopted As the strut angle on model II ranges from 30º to 45º, transverse reinforcement area (Asw) decreases, and total reinforcement area, which includes longitudinal torsion reinforcement (Asℓ), increases. It appears that, when considering model II with strut angle above 40º, under shear only, transverse reinforcement area increases 22% compared to values obtained using model I.

Theoretical Study of the Absorption Spectra of Photosynthetic Pigments

The first stage of the photosynthetic process is the extraordinary efficiency of sunlight absorption in the visible region [1]. This region corresponds to the maximum of the spectral radiance of the solar emission. The efficient absorption of visible light is one of the most important characteristics of photosynthetic pigments. In chlorophylls, for example, the absorptions are seen as a strong absorption in the region 400-450 nm in connection with other absorptions with small intensities in the region of 500-600 nm. This work aims at understanding the essential features of the absorption spectrum of photosynthetic pigments, in line with several theoretical studies in the literature [2, 3]. The absorption spectra were calculated for H2-Porphyrin, Mg-Porphyrin, and Zn-Porphyrin, and for H2-Phthalocyanine and Mg-Phthalocyanine with and without the four peripheral eugenol substituents. The geometries were optimized using the B3LYP/6-31+G(d) theoretical model. For the calculation of the absorption spectra different TD-DFT calculations were performed (B3LYP, CAM-B3LYP, O3LYP, M06-2X and BP86) along with CIS (D). For the spectra the basis set 6-311++G (d, p) was used for porphyrins and 6-31+G (d) was used for the other systems. At this stage the solvent effects were considered using the simplified continuum model (PCM). First a comparison between the results using the different methods was made. For the porphyrins the best results compared to experiment (both in position and intensities) are obtained with M06-2X and CIS (D). We also analyze the compatibility of the four-orbital model of Gouterman [4] that states that transitions could be well described by the HOMO-1, HOMO, LUMO, and LUMO+1 molecular orbitals. Our results for H2-Porphyrin shows an agreement with other theoretical results and experimental data [5]. For the phthalocyanines (including the four peripheral eugenol substituents) the results are also in good agreement compared with the experimental results given in ref [6]. Finally, the results show that the inclusion of solvent eÆects gives corrections for the spectral shift in the correct direction but numerically small. References [1] R.E. Blankenship; “Molecular Mechanisms of Photosynthesis", Blackwell Science (2002). [2] P. Jaramillo, K. Coutinho, B.J.C. Cabral and S. Canuto; Chem. Phys. Lett., 516, 250(2011). [3] L. Petit, A. Quartarolo, C. Adamo and N. Russo; J. Phys. Chem. B, 110, 2398(2006). [4] M. J. Gouterman; Mol. Spectr., 6, 138(1961). [5] M. Palummo, C. Hogan, F. Sottile, P. Bagal∂a and A. Rubio; J. Chem. Phys., 131, 084102(2009). [6] E. Agar, S. Sasmaz and A. Agar; Turk. J. Chem., 23, 131(1999).

Measurement and model calculation of the temperature dependence of ligand-to-metal energy transfer rates in lanthanide complexes

Temperature dependent transient curves of excited levels of a model Eu3+ complex have been measured for the first time. A coincidence between the temperature dependent rise time of the 5D0 emitting level and decay time of the 5D1 excited level in the [Eu(tta)3(H2O)2] complex has been found, which unambiguously proves the T1→5D1→5D0 sensitization pathway. A theoretical approach for the temperature dependent energy transfer rates has been successfully applied to the rationalization of the experimental data.

An experimental and theoretical approach to correct for the scattered radiation in an X-ray computer tomography system for industrial applications

The main problem connected to cone beam computed tomography (CT) systems for industrial applications employing 450 kV X-ray tubes is the high amount of scattered radiation which is added to the primary radiation (signal). This stray radiation leads to a significant degradation of the image quality. A better understanding of the scattering and methods to reduce its effects are therefore necessary to improve the image quality. Several studies have been carried out in the medical field at lower energies, whereas studies in industrial CT, especially for energies up to 450 kV, are lacking. Moreover, the studies reported in literature do not consider the scattered radiation generated by the CT system structure and the walls of the X-ray room (environmental scatter). In order to investigate the scattering on CT projections a GEANT4-based Monte Carlo (MC) model was developed. The model, which has been validated against experimental data, has enabled the calculation of the scattering including the environmental scatter, the optimization of an anti-scatter grid suitable for the CT system, and the optimization of the hardware components of the CT system. The investigation of multiple scattering in the CT projections showed that its contribution is 2.3 times the one of primary radiation for certain objects. The results of the environmental scatter showed that it is the major component of the scattering for aluminum box objects of front size 70 x 70 mm2 and that it strongly depends on the thickness of the object and therefore on the projection. For that reason, its correction is one of the key factors for achieving high quality images. The anti-scatter grid optimized by means of the developed MC model was found to reduce the scatter-toprimary ratio in the reconstructed images by 20 %. The object and environmental scatter calculated by means of the simulation were used to improve the scatter correction algorithm which could be patented by Empa. The results showed that the cupping effect in the corrected image is strongly reduced. The developed CT simulation is a powerful tool to optimize the design of the CT system and to evaluate the contribution of the scattered radiation to the image. Besides, it has offered a basis for a new scatter correction approach by which it has been possible to achieve images with the same spatial resolution as state-of-the-art well collimated fan-beam CT with a gain in the reconstruction time of a factor 10. This result has a high economic impact in non-destructive testing and evaluation, and reverse engineering.

Use of computer algebra in the calculation of Feynman diagrams

The increasing precision of current and future experiments in high-energy physics requires a likewise increase in the accuracy of the calculation of theoretical predictions, in order to find evidence for possible deviations of the generally accepted Standard Model of elementary particles and interactions. Calculating the experimentally measurable cross sections of scattering and decay processes to a higher accuracy directly translates into including higher order radiative corrections in the calculation. The large number of particles and interactions in the full Standard Model results in an exponentially growing number of Feynman diagrams contributing to any given process in higher orders. Additionally, the appearance of multiple independent mass scales makes even the calculation of single diagrams non-trivial. For over two decades now, the only way to cope with these issues has been to rely on the assistance of computers. The aim of the xloops project is to provide the necessary tools to automate the calculation procedures as far as possible, including the generation of the contributing diagrams and the evaluation of the resulting Feynman integrals. The latter is based on the techniques developed in Mainz for solving one- and two-loop diagrams in a general and systematic way using parallel/orthogonal space methods. These techniques involve a considerable amount of symbolic computations. During the development of xloops it was found that conventional computer algebra systems were not a suitable implementation environment. For this reason, a new system called GiNaC has been created, which allows the development of large-scale symbolic applications in an object-oriented fashion within the C++ programming language. This system, which is now also in use for other projects besides xloops, is the main focus of this thesis. The implementation of GiNaC as a C++ library sets it apart from other algebraic systems. Our results prove that a highly efficient symbolic manipulator can be designed in an object-oriented way, and that having a very fine granularity of objects is also feasible. The xloops-related parts of this work consist of a new implementation, based on GiNaC, of functions for calculating one-loop Feynman integrals that already existed in the original xloops program, as well as the addition of supplementary modules belonging to the interface between the library of integral functions and the diagram generator.

Theoretical study of correlated systems using hybrid functionals

Diese Arbeit unterstreicht das Potential von Hybridfunktionalen (B3LYP) für die Untersuchung einer großen Bandbreite von Systemen. Durch die Einbeziehung der exakten Hartree-Fock Austauschenergie kann B3LYP für molekulare und kristalline Systeme eingesetzt werden. Zum Beispiel können stark korrelierte Systeme mit B3LYP erfolgreich erforscht werden. Die elektronische Struktur von PAHs wurde mit B3LYP Hybriddichtefunktionalen untersucht. Mit der ∆SCF-Methode wurden Elektronenbindungsenergien bestimmt, welche die mit UPS gewonnenen experimentellen Resultate bestätigen und ergänzen. Symmetrieeigenschaften der molekularen Orbitale wurden analysiert, um eine Zuordnung und Einschätzung der zugehörigen Signalstärke zu ermöglichen. Während σ-artige Orbitale nur schwer durch UPS-Messungen an dünnen Filmen detektiert werden können, bieten Rechnungen eine detaillierte Einsicht in die verborgenen Teile der Spektren.rnWeiterhin wurden π−π-Komplexe untersucht, welche von verschiedenen Donor- und Akzeptor-Molekülen gebildet werden. Die Moleküle basieren auf polyzyklischen, aromatischen Kohlenwasserstoffen. Für Ladungstransferkomplexe finden DFT Rechnungen ein Minimum in der Oberfläche der potentiellen Energie. Diese attraktive Wechselwirkung wird durch Coulombanziehung verursacht. Allerdings ist die Coulombanziehung nicht die stärkste Wechselwirkung in Ladungstransferkomplexen. Die Einbeziehung von van der Waals-Korrekturen verbessert den intermolekularen Abstand und die Bindungsenergie.rnEine Verkleinerung der intermolekularen Abstände führt zu einer großen Verschiebung der HOMO- und LUMO-Energie.rnAus der Klasse der kristallinen korrelierten Systeme wurden Rb4O6 und FeSe untersucht. Im Falle von Rb4O6 führen Ladungsordnung und Korrelationen zu einem isolierenden Grundzustand. Das hypothetische druckabhängige Phasendiagramm wurde untersucht. Eine Erhöhung des Drucks führt zu einer vergrößerten Bandlücke. Bei etwa 75 GPa wird die Bandbreite W größer als der Bandabstand U und das System nimmt einen homogen gemischt valenten Zustand mit teilweise besetzten π−π-Orbitalen an. Für Drücke ab 160 GPa wird W sehr viel größer als U und das System wird metallisch.rnIm Fall von FeSe finden wir eine korrelierte und isolierende Phase bei hohen Drücken, während das System bei niedrigen Drücken supraleitendes Verhalten zeigt. Die Berechnungen der Elektronenstruktur mit dem Hybridfunktional B3LYP führt zum korrekten halbleitenden Grundzustand in der NiAs- und MnP-Struktur von FeSe. Die Rolle der Korrelationen, der Stöchiometrie und der Nähe zum Magnetismus wird besprochen. Im Speziellen wird gezeigt, dass die Phase mit NiAs-Struktur starke lokale Korrelationen aufweist, was zu einem halbleitenden Zustand in einem weiten Druckbereich führt.