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1.
Dayana Borges Bittar Tiago Augusto Catelani Karina Nigoghossian Hernane da Silva Barud Sidney José Lima Ribeiro Leonardo Pezza 《Analytical letters》2017,50(5):829-841
A colorimetric method based on silver nanoparticles was developed for the determination of melamine in milk. Silver nanoparticles were synthesized without any stabilizer, using sodium borohydride as the reducing agent. Optimization of the variables for the formation of the nanoparticles was performed by factorial design, resulting in stable colloidal silver nanoparticles with a mean diameter of 14.0?±?2.7?nm. Spectrophotometric measurements performed at 475?nm showed a linear range from 0.033 to 1.50?mg?L?1 of melamine with limits of detection and quantification of 0.009 and 0.031?mg?L?1, respectively. The method provided highly sensitive determination of melamine in milk. 相似文献
2.
Gabriela Ionita Petre Ionita Victor EM. Sahini Constantin Luca 《Journal of inclusion phenomena and macrocyclic chemistry》2001,39(3-4):269-271
The kinetics of oxidation of amino acids (Arg, His, Lys, Phe, Thr and Tyr), a dipeptide (Gly-His), and BSA (bovine serum albumin) by two persistent water soluble free radicals of the hydrazyl type has been studied.The rate decreases in the order Arg>Lys>Tyr>Thr>HisBSAPheGly-His with bothfree radicals. Addition to the reaction mixture of - and -cyclodextrin decreases the oxidation rate, probably due to amino acidencapsulation in the cyclodextrin cavity. -Cyclodextrin protects more efficiently against oxidation than -cyclodextrin. 相似文献
3.
Jocelyn D Laughton Philippe Bittar Yves Charnay Luc Pellerin Enikö Kovari Pierre J Magistretti Constantin Bouras 《BMC neuroscience》2007,8(1):35
Background
For a long time now, glucose has been thought to be the main, if not the sole substrate for brain energy metabolism. Recent data nevertheless suggest that other molecules, such as monocarboxylates (lactate and pyruvate mainly) could be suitable substrates. Although monocarboxylates poorly cross the blood brain barrier (BBB), such substrates could replace glucose if produced locally. 相似文献4.
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We have used a variety of microscopic techniques to reveal the structure and motion of flux line arrangements, when the flux
lines in low T
c type II superconductors are caused to move by a transport current. Using small-angle neutron scattering by the flux line
lattice (FLL), we are able to demonstrate directly the alignment by motion of the nearest-neighbor FLL direction. This tends
to be parallel to the direction of flux line motion, as had been suspected from two-dimensional simulations. We also see the
destruction of the ordered FLL by plastic flow and the bending of flux lines. Another technique that our collaboration has
employed is the direct measurement of flux line motion, using the ultra-high-resolution spectroscopy of the neutron spin-echo
technique to observe the energy change of neutrons diffracted by moving flux lines. The muon spin rotation (μSR) technique gives the distribution of values of magnetic field within the FLL. We have recently succeeded in performing
μSR measurements while the FLL is moving. Such measurements give complementary information about the local speed and orientation
of the FLL motion. We conclude by discussing the possible application of this technique to thin film superconductors. 相似文献
7.
XDS: a flexible beamline for X‐ray diffraction and spectroscopy at the Brazilian synchrotron 下载免费PDF全文
F. A. Lima M. E. Saleta R. J. S. Pagliuca M. A. Eleotério R. D. Reis J. Fonseca Júnior B. Meyer E. M. Bittar N. M. Souza-Neto E. Granado 《Journal of synchrotron radiation》2016,23(6):1538-1549
The majority of the beamlines at the Brazilian Synchrotron Light Source Laboratory (LNLS) use radiation produced in the storage‐ring bending magnets and are therefore currently limited in the flux that can be used in the harder part of the X‐ray spectrum (above ~10 keV). A 4 T superconducting multipolar wiggler (SCW) was recently installed at LNLS in order to improve the photon flux above 10 keV and fulfill the demands set by the materials science community. A new multi‐purpose beamline was then installed at the LNLS using the SCW as a photon source. The XDS is a flexible beamline operating in the energy range between 5 and 30 keV, designed to perform experiments using absorption, diffraction and scattering techniques. Most of the work performed at the XDS beamline concentrates on X‐ray absorption spectroscopy at energies above 18 keV and high‐resolution diffraction experiments. More recently, new setups and photon‐hungry experiments such as total X‐ray scattering, X‐ray diffraction under high pressures, resonant X‐ray emission spectroscopy, among others, have started to become routine at XDS. Here, the XDS beamline characteristics, performance and a few new experimental possibilities are described. 相似文献
8.
D.C. Jiles P.W. Gilberd M.P. Staines A. Bittar 《Journal of Physics and Chemistry of Solids》1984,45(6):595-608
Piezoreflectance measurements have been made on a series of gold cobalt and gold vanadium alloys with impurity concentrations of up to 4% using a strain amplitude of 4 × 10?4 at a frequency of 68 kHz. The spectra show that the main interband transitions occur at 2.4, 3.5 and 4.5 eV. The deformation potentials with impurity concentration have been found for these transitions. An additional interband transition was found to occur at an energy of 1.8eV and this was enhanced significantly with impurity concentration. This may be due to the impurity causing a broadening of the d bands and hence a smearing of the interband threshold or alternatively it may be caused by a d band to Fermi level transition along the Δ direction close to the X point. 相似文献
9.
Solar thermal collectors have been prepared with thin TiOxNy films deposited using ion beam assisted deposition, on Si and Cu substrates. The films are amorphous and x and y were controlled
by altering the O2/N2 ratio in the gas source. After annealing at temperatures of 200 – 400 °C, films have been depth profiled using Secondary
Ion Mass Spectrometry. Profiles reveal the degradation of the film, particularly for films on Cu substrates, by migration
of the substrate atoms through the films, to the sample surface. In general, films with x<1 and y>1 show improved temperature
stability, ultimately at the expense of a reduced transmission window.
Contrary to previous suggestions in the literature, the degradation mechanism initially involves the formation of a nitrogen
rich phase, rather than an oxide at the film surface. On copper substrates, the nature of the films and of this phase, formed
by diffusion of the substrate atoms, have been investigated by X-ray photoelectron spectroscopy (XPS). These investigations
reveal complex behaviour in the early stages of film failure, with the suggestion that the initial films, at least near the
surface, are two phase, and the reaction layer mixes the TiOxNy with some Ti replacement by ions from the Cu substrate. 相似文献
10.
Bittar EM Adriano C Garitezi TM Rosa PF Mendonça-Ferreira L Garcia F Azevedo Gde M Pagliuso PG Granado E 《Physical review letters》2011,107(26):267402
The Fe K x-ray absorption near edge structure of BaFe(2-x)Co(x)As(2) superconductors was investigated. No appreciable alteration in shape or energy position of this edge was observed with Co substitution. This result provides experimental support to previous ab initio calculations in which the extra Co electron is concentrated at the substitute site and do not change the electronic occupation of the Fe ions. Superconductivity may emerge due to bonding modifications induced by the substitute atom that weakens the spin-density-wave ground state by reducing the Fe local moments and/or increasing the elastic energy penalty of the accompanying orthorhombic distortion. 相似文献