Ionic liquid: an efficient and reusable media for seleno- and thioester synthesis promoted by indium

A series of thio and selenoesters were efficiently obtained employing stable diorganyl chalcogenides, acyl chlorides, and In as reducing agent in BMIM·PF₆. Recycling of the ionic liquid was also performed, which was reused three times.     

Control of planar Bautin bifurcation

Nonlinear Dynamics - On a versal deformation of the Bautin bifurcation it is possible to find dynamical systems that undergo Hopf or non-hyperbolic limit cycle bifurcations. Our paper concerns a...     

A theoretical prediction of stability in hydrogen-bonded complexes formed between oxirane and oxetane rings with HX (X=F and Cl)

The optimised geometries of heterocyclic hydrogen-bonded complexes, C2H4O...HX and C3H6O...HX, where X=F or Cl, were determined at DFT/B3LYP/6-311++G(d,p) computational level. Structural, electronic and vibrational properties of these complexes are used in order to compare the strained ring, which confer the great reactivity of these heterocyclic rings with monoprotic acids, forming a primary hydrogen bond. A secondary hydrogen bond between the hydrogen atoms of the CH2 groups and the halide species also takes place, thus causing a nonlinearity (characterized by the theta angle), in the primary hydrogen bond.     

Elements in hair of an exposed group

Hair analysis presents a lot of advantages compared to the analysis of biological fluids or tissues. Hair of employers from the National (Brazilian) Nuclear Energy Commission (CNEN) was analyzed and compared with a control group. Samples were heated at 90°C with nitric acid, and diluted. Aliquot of these solutions was analyzed in ICP-MS. The concentration of U, Th, Pb and Zn were determined. Student t-test showed that there is no significant difference among the groups for all analyzed elements. The results demonstrated that men had more Pb than women. For Zn, the results showed that the levels are within the “normal” range, except for a woman that had her hair painted.     

Evaluation of laser induced breakdown spectroscopy for cadmium determination in soils

Cadmium is known to be a toxic agent that accumulates in the living organisms and present high toxicity potential over lifetime. Efforts towards the development of methods for microanalysis of environmental samples, including the determination of this element by graphite furnace atomic absorption spectrometry (GFAAS), inductively coupled plasma optical emission spectrometry (ICP OES), and inductively coupled plasma-mass spectrometry (ICP-MS) techniques, have been increasing. Laser induced breakdown spectroscopy (LIBS) is an emerging technique dedicated to microanalysis and there is a lack of information dealing with the determination of cadmium. The aim of this work is to demonstrate the feasibility of LIBS for cadmium detection in soils. The experimental setup was designed using a laser Q-switched (Nd:YAG, 10 Hz, λ = 1064 nm) and the emission signals were collimated by lenses into an optical fiber coupled to a high-resolution intensified charge-coupled device (ICCD)-echelle spectrometer. Samples were cryogenically ground and thereafter pelletized before LIBS analysis. Best results were achieved by exploring a test portion (i.e. sampling spots) with larger surface area, which contributes to diminish the uncertainty due to element specific microheterogeneity. Calibration curves for cadmium determination were achieved using certified reference materials. The metrological figures of merit indicate that LIBS can be recommended for screening of cadmium contamination in soils.     

On the stability of the equilibria of the Rikitake system

In this note we present an analytical study of the stability of the equilibria of the Rikitake system. We prove that the two non-hyperbolic equilibria of the Rikitake system are unstable for all positive values of the parameters.     

Time history speckle pattern under statistical view

The dynamic speckle analysis has been done because speckle interference began to be evaluated as an important source of information, especially those related to biological samples under laser beam. The time history speckle pattern, a THSP image, is an approach to analyze, which allows a summary to represent the activity monitored. THSP adoption has compelled the research to evaluate the information and the reliability of its inner pattern. This study presents a statistical approach to analyze the data using white noise tests and cross-spectrum analysis. The data analyzed was a set of THSP from animal sperm samples. The evaluation of white noise among lines was conducted using the Fischer test over eight THSP and the cross-spectral approach has been conducted by comparing the information in each THSP. The results presented that the THSP of the sperm did not behave as a white noise in a global evaluation, and specifically in the Gaussian white noise test over 4096 lines; only six lines presented the behavior of a white noise pattern. The strong rejection of white noise test confirms that the THSP pattern allows reliable information. The results obtained with the cross-spectral analysis presented differences between lines within the same THSP, showing that the information of an inner pattern varies in relation to space, which is against the findings in literature.     

Transport properties near the magneto/structural transition of Tb5Si2Ge2

We report high resolution measurements of the electrical resistivity (ρ, dρ/dT) and thermopower (S, dS/dT) measurements near the magnetic and structural transition of the layered Tb₅Si₂Ge₂ compound, which are fairly close but not fully coupled. The analysis of the transport properties confirms a split magneto/structural transition, with T_S ～ 97 K and T_S ～ 107 K for the structural transition (on cooling and heating respectively; 1st-order transition). The magnetic transition occurs only at T_C ～ 112 K and without hysteresis (2nd-order transition). The magnetic critical behavior of resistivity is analyzed, obtaining an almost classical mean field exponent (α ～ 0.59) for T > T_C. For the structural phase, and below T_S, we obtain a rather different exponent (α ～ 1.06).     

Complete Cl calculations on the ground state of HeH

Complete Cl calculations on the van der Waals molecule HeH with a large Gaussian basis set give the depth of the potential well as c = 0.50 meV and a minimum at R_m = 3.64 Å. An analytical function has been fitted to the ab initio points and to the best estimates of the dispersion energy coefficients. One further parameter in the potential has been chosen to reproduce the HeH scattering cross section.