Magnetic transitions in NiBr2 6NH3 and NiCl2 6NH3 up to 75 koe

The field dependence of the magnetic susceptibility of powdered NiBr₂ 6NH₃ and NiCl₂ 6NH₃ was measured up to 75 koe at temperatures above and below T_N. The anomalies found are discussed in terms of other magnetic data known for these salts.     

N- and P-channel transport behavior in thin film transistors based on tricyanovinyl-capped oligothiophenes

We report the structural and electrical characterization of thin films of organic semiconductor molecules consisting of an oligothiophene core capped with electron-withdrawing tricyanovinyl (TCV) groups. X-ray diffraction and atomic force microscopy of evaporated films of three different TCV-capped oligothiophenes showed that the films were highly crystalline. Electrical transport was measured in thin film transistors employing silver source and drain contacts and channel probes to correct for contact resistance. Three compounds exhibited n-channel (electron) conduction consistent with cyclic voltametry data that indicated they undergo facile reduction. Maximum electron mobilities were 0.02 cm2/V.s with an on/off current ratio of 10(6). A fourth end-capped molecule, TCV-6T-TCV, which had six thiophene rings, exhibited both p- and n-channel transport. Overall, these results confirm that substitution of oligothiophene cores with electron-withdrawing groups is a useful strategy to achieve electron-transporting materials.     

Structural Organization of syndiotactic polystyrene films crystallized in the β form

Syndiotactic polystyrene (sPS) films were obtained either by casting or by melt crystallization in the β form. Different thermal treatments of the melt led to mixed α and β forms. The structural organization was investigated by x-rays, transport properties, and Fourier transform infrared analysis. The β form is characterized by chains in zigzag planar conformation. For samples prevalently in β form, the fraction of impermeable phase, derived from sorption measurements, was found coincident with the fraction of crystalline phase derived from x-rays. In samples with mixed α and β forms, however, a fraction of mesophase is also present. The β form of sPS is stable to dichloromethane, whereas the α form is transformed into a crystalline form with the chains in helical conformation. Nevertheless, when the relative fraction of β form is lower than a critical value, it also dissolves in liquid dichloromethane, undergoing the conformational transition into the helical form.     

Sunset decay of the convective turbulence with Large-Eddy Simulation under realistic conditions

Large-Eddy Simulation is performed for a single day from the Cooperative Atmosphere-Surface Exchange Study (CASES-99) field program. This study investigates an observed case of evening transition boundary layer over land. Parameters of the ambient atmosphere in the LES-decay studies conducted so far were typically prescribed in an idealized form. To provide suitable data under the wide range of the PBL weather conditions, the LES should be able to adequately reproduce the PBL turbulence dynamics including–if possible–baroclinicity, radiation, large scale advection and not only be related to a decreasing surface heating. In addition LES-decay studies usually assume that the sensible heat flux decreases instantaneously or with a very short time scale. The main purpose of this investigation is to study the decay of boundary-layer average turbulent kinetic energy at sunset with Large-Eddy Simulation that is forced with realistic environment conditions. This allows investigating the Turbulent Kinetic Energy decay over the realistic time scale that is observed in the atmosphere. During the intermediate and last stage of decay of the boundary-layer average Turbulent Kinetic Energy the exponents of the decay power law t⁻ⁿ$t^{-n}$ go from 2 to 6, as evidenced by experimental results and recent analytical modeling in the surface layer.     

Evaluation of the concentration of chemical elements in suspended particulate matter inside a small bronze and iron foundry industry,using a streaker sampler and EDXRF

The aim of this study was to determine and evaluate the temporal profiles of the concentration of chemical elements in the suspended particulate matter present inside a small bronze and an iron foundry industry. To collect the samples, we used a streaker sampler that separates particles with aerodynamic diameters smaller than 10 µm (PM₁₀) in two fractions: fine (particles with aerodynamic diameters less than 2.5 µm; PM_2.5) and coarse (between 2.5 µm and less than 10 µm; PM_10–2.5). The collection of samples was taken every 20 min during a total time of 8 and 5 h of molding and casting of bronze and iron, respectively. The samples collected in the form of strips on a filter (fine fraction) and an impactor (coarse fraction) were analyzed by the energy dispersive X‐ray fluorescence technique. In the excitation, an X‐ray tube with Mo target and Zr filter was used, operated at 30 mA/30 kV. For detecting the characteristic of X‐rays, a semiconductor Si(Li) detector was used, coupled to a multi‐channel spectrometer, with a 300 s excitation/detection time. The results of the temporal profiles of chemical element concentrations in coarse and fine fractions were discussed and compared with the maximum levels set by the Brazilian and international environmental agencies. Copyright © 2013 John Wiley & Sons, Ltd.     

Luminescent Langmuir-Blodgett film of a new amphiphilic Eu β-diketonate

This work reports on the synthesis and characterization of the ligand 3-hexadecylpentane-2,4-dione (Hhdacac) and its Eu³⁺ complexes Eu(hdacac)₆·2H₂O, Eu(hdacac)₆·phen and Eu(hdacac)₆·tta, where phen and tta denote 1,10-phenanthroline and thenoyltrifluoroacetone, respectively. These new compounds present long carbon chains and their expected miscibility into non-polar ambients is confirmed by the emission spectra of Eu(hdacac)₆·tta in hexane. Moreover, the amphiphilic properties of Eu(hdacac)₆ complexes allow the obtainment of thin luminescent films by the Langmuir-Blodgett technique. In both cases (solids and films), the typical antenna effect of β-diketonates is observed. The alluring characteristics of these compounds raise great interest in many fields of Materials Science, like photo- and electro-luminescent materials (mainly thin “organic” films), metal catalysts or probes in non-polar solutions, and Langmuir-Blodgett films of several compositions. For the characterization of these products, nuclear magnetic resonance spectroscopy (¹H NMR), thermogravimetric analysis, elementary analyses (C, H), scanning electron microscopy (energy dispersive X-ray spectroscopy), absorption (UV-vis/FT-IR) and photoluminescence spectroscopies were used.