On apparent barrier-free reactions

Rate coefficients of bi-molecular chemical reactions are fundamental for kinetic models. The rate coefficient dependence on temperature is commonly extracted from the analyses of the reaction minimum energy path. However, a full dimension study of the same reaction may suggest a different asymptotic low-temperature limit in the rate constant than the obtained from the energetic profile.

The Dynamics of the S(1D)+H2/D2 Reactions at Low Temperature via Statistical Simulations

Two different statistical approaches, the statistical quantum model (SQM) and the mean potential phase space theory (MPPST), have been employed to calculate the integral cross sections for the reactive collisions between S(1D) and H2/ D2 in the low energy regime (below 0.3 eV collisional energy). The rate constant for the S(1D) + H2 → SH + H reaction has been also obtained and compared with previously reported experimental and theoretical results. The good agreement shows the capability of these two methods to study the dynamics of these complex-forming atom-diatom processes in the present energy regime.

An Impurity Effect for the Rates of the Interparticle Coulombic Decay

The interparticle Coulombic decay is a synchronized decay and ionization phenomenon occurring on two separated and only Coulomb interaction coupled electron binding sites. This publication explores how drastically small environmental changes in between the two sites, basically impurities, can alter the ionization properties and process rate, although the involved electronic transitions remain unaltered. A comparison among the present electron dynamics calculations for the example of different types of quantum dots, accommodating a one- or a two-dimensional continuum for the outgoing electron, and the well-investigated atomic and molecular cases with three-dimensional continuum, reveals that the impurity effect is most pronounced the stronger that electron is confined. This necessarily leads to challenges and opportunities in a quantum dot experiment to prove the interparticle Coulombic decay.

A A new matrix of MALDI-TOF MS derivative of 9-aminoacridine for lipid identification in positive ions mode

Matrix-assisted laser desorption/ionization (MALDI) has evolved to become a well- established technique during the last decades. Because of matrix peak interference in the low molecular-weight region, however, new matrices are often studied with the purpose of improving the spectral quality under m/z 500. Herein, we present the substance 2,4,5,7-tetranitro-9-aminoacridine (TNA) as a suitable alternative matrix for lipid detection in the positive-ion mode. TNA is obtained from 9-aminoacridine, a matrix commonly used to analyze lipids in negative-ion mode, with the addition of 4 nitro groups through a synthetic path. The procedure results in a highly conjugated system that presents a bigger electronic dispersion and therefore higher UV absorption. First, we demonstrated the high sensitivity of TNA for retinol. Second, TNA was applied to detect lipids in the liver of the water rat Nectomys squamipes. By using this natural model of hepatic steatosis (fat liver), a condition in which there is excessive accumulation of lipids, TNA provided a clearer identification of three species of polyunsaturated fatty acids (PUFAs) compared to other matrices. TNA presents better sensitivity and spectral resolution, little or no interference from matrix ions, high intensity of signal and low cost with high yield of matrix production.

Thyroxine: A Theoretical Study of the Vibrational and Electronic Properties

Through this work, we systematically studied the structural, vibrational and electronic properties of the fundamental state of the isolated thyroxine(3,5,3’,5-tetraiodothyronine). The minimum energy structures and properties were obtained using the Density Functional Theory (DFT). Our simulation results were compared with experimental results, including infra-red and Raman spectroscopy with an emphasis on the properties of iodine atoms. The UV-vis spectrum calculated in this work is the first result of this model for the thyroxine molecule.

Schwinger Model as Prototype for Confined Fermions

We will present the Schwinger Model by characteristics like Mechanism of Higgs-Schwinger, Fermionic Charge Shielding, and Chiral Anomaly. Confinement and Topological Vacuum are prototype of theories with Confined Fermions. We will present some aspects of Bosonization and, for example, we will make a representation of the Free Field of Dirac with null mass. We will do a review of Schwinger's model with Lowestein-Swieca, and we will discuss the theory. We also will present modified models of Rothe-Stamatescu, Schroer and Thirring, demonstrating its equivalence with Sine-Gordon's theory.

On the influence of low silica content on phosphates glasses doped with Erbium Ions

This work describes the spectroscopic characterization of a phosphate glass matrix doped with different Erbium concentrations. In order to increase the resistance of the glass, 3 mol %, of silicon oxide were added to the phosphate matrix. A study of the optical absorption, luminescence and lifetime was conducted in order to characterize the infrared emission of Er3+ ions at 1540 nm, due to the radiative transition 4I13/2 →4I15/2. Judd-Ofelt spectral analysis was carried out to determine the local structure and bonding in the vicinity of rare-earth ions. The experimental oscillator strengths calculated from the absorption spectra were used to evaluate the Judd-Ofelt intensity parameters Ωλ (λ = 2, 4 and 6). Changes in the glass density, refractive index and the values of Ω4 and Ω6 with different rare-earth concentrations are ascribed to changes in the glass network structure. Our results indicate that the present glass is a quite good matrix for Erbium ions, and the quantum efficiency of the 1540 nm emission was high. No quenching mechanisms were detected up to 2% of Erbium concentration.

Quantitative behavior study of velocity, radius and topological charge on skyrmion/edge interaction dynamics on Co/Pt nanotrack

Skyrmions are considered promising candidates to be the information carriers in the next generation of data storage and logic devices, due to its stability and easy control under the application of an electric current. For future technological applications in spintronic devices, it is important to study the properties behavior of these topological excitations during its movement on magnetic nanotracks, specially because in ferromagnetic materials they suffer a kind of magnus effect which tends to spell the skyrmion through the borders, preventing its transport throughout the nanotrack. We used micromagnetic simulations to study the dynamics of a skyrmion on a magnetic nanotrack induced by a spin polarized electric current. We considered thin magnetic nanotrack made of cobalt and platinum multilayers, whose magnetic state is perpendicular to the track plane and contain a single Néel-type Skyrmion. To describe this magnetic system, we used a Hamiltonian containing exchange, Dzyaloshinskii-Moriya, perpendicular magnetic anisotropy and dipole-dipole interactions. In our study we observed the well-known Skyrmion Hall effect and changes in the structure of the skyrmion when it approaches of the border. This alteration can be measured by determining the radius and the topological charge of the Skyrmion. Our simulation results show that both the radius and the topological charge decrease when it approaches of the border. Our study also demonstrates that the skyrmion-border interaction is repulsive, but there is a minimum distance from the border at which the interaction becomes attractive. If the skyrmion exceeds this critical position yc, it will be attracted and annihilated at the border of the nanotrack. We also performed simulations to obtain the limit value jc of the applied current density that the skyrmion can be transported along of the nanotrack without escaping from the side edge. From a technological point of view for possible applications in spintronic devices, the estimate of jc is of crucial importance.

Mathematical models for correlating electrical parameters and milk adulterants

This work presents mathematical models obtained from electrical measurements to control of milk quality and detection of adulterations, especially by ethanol, sodium chloride and sodium bicarbonate. These substances may cause changes in the electrical properties of raw milk. Electrical measurements are non-destructive and fast techniques. The proposed models correlate the addition of the mentioned substances with measurements of conductance and phase angle at a fixed frequency of 100 Hz. Linear models were proposed from the data and the independence, normality, lack of adjustment and homoscedasticity were verified. The detection limits obtained based on conductance were 0.01 %, 0.03 g/L and 2.1 g/L for samples adulterated with ethanol, sodium chloride and sodium bicarbonate, respectively. The limits for measurements based on the phase angle were 0.4%, 1.3 g/L and 16.4 g/L, respectively. The results demonstrated that the proposed models may be a powerful tool to improve milk analysis methodologies.

Theoretical Studies of Milk: Solvent Effects on the Molecular Properties of Retinoid Compounds

We discuss here the role of environment in the structural and spectroscopic properties of vitamin A in its retinoid forms: retinol and retinal. The analyzed compounds show three singlet excited states exhibiting wavelengths between 472 and 273 nm according to the medium. The transitions involve HOMO, LUMO, HOMO-1, LUMO and HOMO, LUMO+1 orbitals.