Quantum chemical modeling of perovskite: An investigation of piezoelectricity in ferrite of yttrium

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Dielectric properties of soft chemical method derived CaCu3Ti4O12 thin films onto Pt/TiO2/Si(100) substrates

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Physico-chemical parameter correlations in the [RuCl2(CO)(L)(PPh3)2] complexes (L = N-heterocycles)

Fourteen complexes in the series [RuCl2(CO)(L)(PPh3)2] (where L = N-heterocycles) have been prepared and characterized by IR and NMR spectroscopies, and cyclic voltammetry. A good correlation is found between observed and calculated electrochemical potentials; E1/2 vs pKa or (Gp, σm for a series of similar ligands. It is now reported that the carbonyl stretching frequency, νCO, and the 13C and 31P NMR signals do not correlate well with any of the physico-chemical parameters used (E1/2, Taft's and Hammett's parameters). This behaviour is probably due to the characteristics of the Ru(II) species, which does not transmit the steric and electron donor/acceptor properties of the ligands to the carbonyl group, or because the measurements are not able to detect the effect induced by the changes in the ligand L. Indeed, good correlations are obtained when the measurements directly involve the metal centre, as is the case in the E1/2 measurements. Crystals of o[RuCl2(CO)(4-pic)(PPh3)2] are monoclinic, space group P21/n, a = 12.019(2), b = 13.825(3) and c = 22.253(3) . The structure was solved by the Patterson method and was refined by full-matrix least-squares procedure to R = 0.054 and Rw = 0.055, for 2114 reflections with I > 3σ(I). For L = 2-acetylpyridine and 2-methylimidazole, complexes with formulae [RuCl2(CO)(L)(PPh3)] · L and [RuCl2(CO)(L)2 (PPh3)], respectively, were obtained. © 1998 Elsevier Science Ltd. All rights reserved.

Study of a hybrid solid oxide fuel cell: Energetic analysis and sankey diagram

In this paper a hybrid solid oxide fuel cell (SOFC) system is analyzed. This system applies a combined cycle utilizing gas turbine associated to a SOFC for rational decentralized energy production. Initially the relative concepts about the fuel cell are presented, followed by some chemical and technical informations such as the change of Gibbs free energy in isothermal fuel oxidation (or combustion) directly into electricity. This represents a very high fraction of the lower heating value (LHV) of a hydrocarbon fuel. In the next step a methodology for the study of SOFC associated with a gas turbine system is developed, considering the electricity and steam production for a hospital, as regard to the Brazilian conditions. This methodology is applied to energetic analysis. Natural gas is considered as a fuel. In conclusion, it is shown by a Sankey Diagram that the hybrid SOFC system may be an excellent opportunity to strengthen the decentralized energy production in Brazil. It is necessary to consider that the cogeneration in this version also is a sensible alternative from the technical point of view, demanding special methods of design, equipment selection and mainly of the contractual deals associated to electricity and fuel supply.

Development of a thermoeconomic methodology for the optimization of biodiesel production - Part I: Biodiesel plant and thermoeconomic functional diagram

This work developed a methodology that uses the thermoeconomic functional diagram applied for allocating the cost of products produced by a biodiesel plant. The first part of this work discusses some definitions of exergy and thermoeconomy, with a detailed description of the biodiesel plant studied, identification of the system functions through Physical Diagram, calculation of the irreversibilities of the plant, construction of the Thermoeconomic Functional Diagram and determination of the expressions for the plant's exergetic functions. In order to calculate the exergetic increments and the physical exergy of certain flows in each step, the Chemical Engineering Simulation Software HYSYS 3.2 was used. The equipments that have the highest irreversibilities in the plant were identified after the exergy calculation. It was also found that the lowest irreversibility in the system refers to the process with a molar ratio of 6:1 and a reaction temperature of 60 °C in the transesterification process. In the second part of this work (Part II), it was calculated the thermoeconomic cost of producing biodiesel and related products, including the costs of carbon credits for the CO2 that is not released into the atmosphere, when a percentage of biodiesel is added to the petroleum diesel used by Brazil's internal diesel fleet (case study). © 2013 Elsevier Ltd. All rights reserved.

Study of the ℤ3 symmetry in QCD at finite temperature and chemical potential using a worm algorithm

Traditional Monte Carlo simulations of QCD in the presence of a baryon chemical potential are plagued by the complex phase problem and new numerical approaches are necessary for studying the phase diagram of the theory. In this work we consider a ℤ3 Polyakov loop model for the deconfining phase transition in QCD and discuss how a flux representation of the model in terms of dimer and monomer variable solves the complex action problem. We present results of numerical simulations using a worm algorithm for the specific heat and two-point correlation function of Polyakov loops. Evidences of a first order deconfinement phase transition are discussed. © 2013 American Institute of Physics.

Evidence of magnetoelectric coupling on calcium doped bismuth ferrite thin films grown by chemical solution deposition

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

CNO and F abundances in the globular cluster M22 (NGC 6656)

Context. Recent studies have confirmed the long standing suspicion that M 22 shares a metallicity spread and complex chemical enrichment history similar to that observed in omega Cen. M 22 is among the most massive Galactic globular clusters and its color-magnitude diagram and chemical abundances reveal the existence of sub-populations. Aims. To further constrain the chemical diversity of M 22, necessary to interpret its nucleosynthetic history, we seek to measure relative abundance ratios of key elements (carbon, nitrogen, oxygen, and fluorine) best studied, or only available, using high-resolution spectra at infrared wavelengths. Methods. High-resolution (R = 50 000) and high S/N infrared spectra were acquired of nine red giant stars with Phoenix at the Gemini-South telescope. Chemical abundances were calculated through a standard 1D local thermodynamic equilibrium analysis using Kurucz model atmospheres. Results. We derive [Fe/H] = -1.87 to -1.44, confirming at infrared wavelengths that M 22 does present a [Fe/H] spread. We also find large C and N abundance spreads, which confirm previous results in the literature but based on a smaller sample. Our results show a spread in A(C+N+O) of similar to 0.7 dex. Similar to mono-metallic globular clusters, M 22 presents a strong [Na/Fe]-[O/Fe] anticorrelation as derived from Na and CO lines in the K band. For the first time we recover F abundances in M 22 and find that it exhibits a 0.6 dex variation. We find tentative evidence for a flatter A(F)-A(O) relation compared to higher metallicity globular clusters. Conclusions. Our study confirms and expands upon the chemical diversity seen in this complex stellar system. All elements studied to date show large abundance spreads which require contributions from both massive and low mass stars.

Space-temporal dynamics of limnological variables in a floodplain wetland located at Ribeira do Iguape Valley (São Paulo, Brazil) at different hydrological periods

AIM: The main goal of this research was to investigate the influence of the hydrological pulses on the space-temporal dynamics of physical and chemical variables in a wetland adjacent to Jacupiranguinha River (São Paulo, Brazil); METHODS: Eleven sampling points were distributed among the wetland, a tributary by its left side and the adjacent river. Four samplings were carried out, covering the rainy and the dry periods. Measures of pH, dissolved oxygen, electrical conductivity and redox potential were taken in regular intervals of the water column using a multiparametric probe. Water samples were collected for the nitrogen and total phosphorus analysis, as well as their dissolved fractions (dissolved inorganic phosphorus, total dissolved phosphorus, ammoniacal nitrogen and nitrate). Total alkalinity and suspended solids were also quantified; RESULTS: The Multivariate Analysis of Variance showed the influence of the seasonality on the variability of the investigated variables, while the Principal Component Analysis gave rise in two statistical significant axes, which delimited two groups representative of the rainy and dry periods. Hydrological pulses from Jacupiranguinha River, besides contributing to the inputs of nutrients and sediments during the period of connectivity, accounted for the decrease in spatial gradients in the wetland. This "homogenization effect" was evidenced by the Cluster Analysis. The research also showed an industrial raw effluent as the main point source of phosphorus to the Jacupiranguinha River and, indirectly, to the wetland; CONCLUSIONS: Therefore, considering the scarcity of information about the wetlands in the study area, this research, besides contributing to the understanding of the influence of hydrological pulses on the investigated environmental variables, showed the need for adoption of conservation policies of these ecosystems face the increase anthropic pressures that they have been submitted, which may result in lack of their ecological, social and economic functions.

Bioremediation of PAHs - Limitations and soultions

Introduction 1.1 Occurrence of polycyclic aromatic hydrocarbons (PAH) in the environment Worldwide industrial and agricultural developments have released a large number of natural and synthetic hazardous compounds into the environment due to careless waste disposal, illegal waste dumping and accidental spills. As a result, there are numerous sites in the world that require cleanup of soils and groundwater. Polycyclic aromatic hydrocarbons (PAHs) are one of the major groups of these contaminants (Da Silva et al., 2003). PAHs constitute a diverse class of organic compounds consisting of two or more aromatic rings with various structural configurations (Prabhu and Phale, 2003). Being a derivative of benzene, PAHs are thermodynamically stable. In addition, these chemicals tend to adhere to particle surfaces, such as soils, because of their low water solubility and strong hydrophobicity, and this results in greater persistence under natural conditions. This persistence coupled with their potential carcinogenicity makes PAHs problematic environmental contaminants (Cerniglia, 1992; Sutherland, 1992). PAHs are widely found in high concentrations at many industrial sites, particularly those associated with petroleum, gas production and wood preserving industries (Wilson and Jones, 1993). 1.2 Remediation technologies Conventional techniques used for the remediation of soil polluted with organic contaminants include excavation of the contaminated soil and disposal to a landfill or capping - containment - of the contaminated areas of a site. These methods have some drawbacks. The first method simply moves the contamination elsewhere and may create significant risks in the excavation, handling and transport of hazardous material. Additionally, it is very difficult and increasingly expensive to find new landfill sites for the final disposal of the material. The cap and containment method is only an interim solution since the contamination remains on site, requiring monitoring and maintenance of the isolation barriers long into the future, with all the associated costs and potential liability. A better approach than these traditional methods is to completely destroy the pollutants, if possible, or transform them into harmless substances. Some technologies that have been used are high-temperature incineration and various types of chemical decomposition (for example, base-catalyzed dechlorination, UV oxidation). However, these methods have significant disadvantages, principally their technological complexity, high cost , and the lack of public acceptance. Bioremediation, on the contrast, is a promising option for the complete removal and destruction of contaminants. 1.3 Bioremediation of PAH contaminated soil & groundwater Bioremediation is the use of living organisms, primarily microorganisms, to degrade or detoxify hazardous wastes into harmless substances such as carbon dioxide, water and cell biomass Most PAHs are biodegradable unter natural conditions (Da Silva et al., 2003; Meysami and Baheri, 2003) and bioremediation for cleanup of PAH wastes has been extensively studied at both laboratory and commercial levels- It has been implemented at a number of contaminated sites, including the cleanup of the Exxon Valdez oil spill in Prince William Sound, Alaska in 1989, the Mega Borg spill off the Texas coast in 1990 and the Burgan Oil Field, Kuwait in 1994 (Purwaningsih, 2002). Different strategies for PAH bioremediation, such as in situ , ex situ or on site bioremediation were developed in recent years. In situ bioremediation is a technique that is applied to soil and groundwater at the site without removing the contaminated soil or groundwater, based on the provision of optimum conditions for microbiological contaminant breakdown.. Ex situ bioremediation of PAHs, on the other hand, is a technique applied to soil and groundwater which has been removed from the site via excavation (soil) or pumping (water). Hazardous contaminants are converted in controlled bioreactors into harmless compounds in an efficient manner. 1.4 Bioavailability of PAH in the subsurface Frequently, PAH contamination in the environment is occurs as contaminants that are sorbed onto soilparticles rather than in phase (NAPL, non aqueous phase liquids). It is known that the biodegradation rate of most PAHs sorbed onto soil is far lower than rates measured in solution cultures of microorganisms with pure solid pollutants (Alexander and Scow, 1989; Hamaker, 1972). It is generally believed that only that fraction of PAHs dissolved in the solution can be metabolized by microorganisms in soil. The amount of contaminant that can be readily taken up and degraded by microorganisms is defined as bioavailability (Bosma et al., 1997; Maier, 2000). Two phenomena have been suggested to cause the low bioavailability of PAHs in soil (Danielsson, 2000). The first one is strong adsorption of the contaminants to the soil constituents which then leads to very slow release rates of contaminants to the aqueous phase. Sorption is often well correlated with soil organic matter content (Means, 1980) and significantly reduces biodegradation (Manilal and Alexander, 1991). The second phenomenon is slow mass transfer of pollutants, such as pore diffusion in the soil aggregates or diffusion in the organic matter in the soil. The complex set of these physical, chemical and biological processes is schematically illustrated in Figure 1. As shown in Figure 1, biodegradation processes are taking place in the soil solution while diffusion processes occur in the narrow pores in and between soil aggregates (Danielsson, 2000). Seemingly contradictory studies can be found in the literature that indicate the rate and final extent of metabolism may be either lower or higher for sorbed PAHs by soil than those for pure PAHs (Van Loosdrecht et al., 1990). These contrasting results demonstrate that the bioavailability of organic contaminants sorbed onto soil is far from being well understood. Besides bioavailability, there are several other factors influencing the rate and extent of biodegradation of PAHs in soil including microbial population characteristics, physical and chemical properties of PAHs and environmental factors (temperature, moisture, pH, degree of contamination). Figure 1: Schematic diagram showing possible rate-limiting processes during bioremediation of hydrophobic organic contaminants in a contaminated soil-water system (not to scale) (Danielsson, 2000). 1.5 Increasing the bioavailability of PAH in soil Attempts to improve the biodegradation of PAHs in soil by increasing their bioavailability include the use of surfactants , solvents or solubility enhancers.. However, introduction of synthetic surfactant may result in the addition of one more pollutant. (Wang and Brusseau, 1993).A study conducted by Mulder et al. showed that the introduction of hydropropyl-ß-cyclodextrin (HPCD), a well-known PAH solubility enhancer, significantly increased the solubilization of PAHs although it did not improve the biodegradation rate of PAHs (Mulder et al., 1998), indicating that further research is required in order to develop a feasible and efficient remediation method. Enhancing the extent of PAHs mass transfer from the soil phase to the liquid might prove an efficient and environmentally low-risk alternative way of addressing the problem of slow PAH biodegradation in soil.

Retrieval simulations of the vertical profiles of water vapour and other chemical species in the Martian atmosphere using PACS

Water vapour, despite being a minor constituent in the Martian atmosphere with its precipitable amount of less than 70 pr. μm, attracts considerable attention in the scientific community because of its potential importance for past life on Mars. The partial pressure of water vapour is highly variable because of its seasonal condensation onto the polar caps and exchange with a subsurface reservoir. It is also known to drive photochemical processes: photolysis of water produces H, OH, HO2 and some other odd hydrogen compounds, which in turn destroy ozone. Consequently, the abundance of water vapour is anti-correlated with ozone abundance. The Herschel Space Observatory provides for the first time the possibility to retrieve vertical water profiles in the Martian atmosphere. Herschel will contribute to this topic with its guaranteed-time key project called "Water and related chemistry in the solar system". Observations of Mars by Heterodyne Instrument for the Far Infrared (HIFI) and Photodetector Array Camera and Spectrometer (PACS) onboard Herschel are planned in the frame of the programme. HIFI with its high spectral resolution enables accurate observations of vertically resolved H2O and temperature profiles in the Martian atmosphere. Unlike HIFI, PACS is not capable of resolving the line-shape of molecular lines. However, our present study of PACS observations for the Martian atmosphere shows that the vertical sensitivity of the PACS observations can be improved by using multiple-line observations with different line opacities. We have investigated the possibility of retrieving vertical profiles of temperature and molecular abundances of minor species including H2O in the Martian atmosphere using PACS. In this paper, we report that PACS is able to provide water vapour vertical profiles for the Martian atmosphere and we present the expected spectra for future PACS observations. We also show that the spectral resolution does not allow the retrieval of several studied minor species, such as H2O2, HCl, NO, SO2, etc.

Screening the Structural Space of Bicyclo-DNA: Synthesis and Properties of Bicyclo-DNA Functionalized at C(6’)

The synthesis of a novel bicyclo-thymidine nucleoside bearing an ester functionality at C(6') (bc(alpha-alk)-nucleosides) is reported. This nucleoside was incorporated into oligodeoxynucleotides via solid phase phosphoramidite chemistry, and the ester moiety was post-synthetically converted to an amide or a carboxy group, or was left unchanged. Thermal melting data (T-m) with complementary DNA and RNA were collected and compared to natural DNA and to bc- and bc(ox)-DNA. It was found that single incorporations of bc(alpha-alk)-nucleosides in DNA duplexes were destabilizing by 0.5 to 2.5 degrees C/mod, whereas two consecutive bc(alpha-alk)-residues were less destabilizing, and in some cases even stabilizing by 0.5 degrees C/mod. In duplexes with complementary RNA, isolated bc(alpha-alk)-residues destabilized the duplex by -1.0 to -4.0 degrees C/mod, depending on the chemical nature of the substituent, whereas two consecutive modifications were only destabilizing by 0.3-1.0 degrees C/mod. The pairing selectivity was similar to that of unmodified or bc-DNA.

A Simple Visual Demonstration of Phase Diagram Concepts for an Introductory Materials Science Course Using Colored Solvents

A simple and effective demonstration to help students comprehend phase diagrams and understand phase equilibria and transformations is created using common chemical solvents available in the laboratory. Common misconceptions surrounding phase diagram operations, such as components versus phases, reversibility of phase transformations, and the lever rule are addressed. Three different binary liquid mixtures of varying compatibility create contrastive phase equilibrium cases, where colorful dyes selectively dissolved in each of corresponding phases allow for quick and unambiguous perceptions of solubility limit and phase transformations. Direct feedback and test scores from a group of students show evidence of the effectiveness of the visual and active teaching tool.

RAPID SPACE TRAJECTORY GENERATION USING A FOURIER SERIES SHAPE-BASED APPROACH

With the insatiable curiosity of human beings to explore the universe and our solar system, it is essential to benefit from larger propulsion capabilities to execute efficient transfers and carry more scientific equipment. In the field of space trajectory optimization the fundamental advances in using low-thrust propulsion and exploiting the multi-body dynamics has played pivotal role in designing efficient space mission trajectories. The former provides larger cumulative momentum change in comparison with the conventional chemical propulsion whereas the latter results in almost ballistic trajectories with negligible amount of propellant. However, the problem of space trajectory design translates into an optimal control problem which is, in general, time-consuming and very difficult to solve. Therefore, the goal of the thesis is to address the above problem by developing a methodology to simplify and facilitate the process of finding initial low-thrust trajectories in both two-body and multi-body environments. This initial solution will not only provide mission designers with a better understanding of the problem and solution but also serves as a good initial guess for high-fidelity optimal control solvers and increases their convergence rate. Almost all of the high-fidelity solvers enjoy the existence of an initial guess that already satisfies the equations of motion and some of the most important constraints. Despite the nonlinear nature of the problem, it is sought to find a robust technique for a wide range of typical low-thrust transfers with reduced computational intensity. Another important aspect of our developed methodology is the representation of low-thrust trajectories by Fourier series with which the number of design variables reduces significantly. Emphasis is given on simplifying the equations of motion to the possible extent and avoid approximating the controls. These facts contribute to speeding up the solution finding procedure. Several example applications of two and three-dimensional two-body low-thrust transfers are considered. In addition, in the multi-body dynamic, and in particular the restricted-three-body dynamic, several Earth-to-Moon low-thrust transfers are investigated.