Cellulose nanofibers from curaua fibers

Curaua nanofibers extracted under different conditions were investigated. The raw fibers were mercerized with NaOH solutions; they were then submitted to acid hydrolysis using three different types of acids (H₂SO₄, a mixture of H₂SO₄/HCl and HCl). The fibers were analyzed by cellulose, lignin and hemicellulose contents; viscometry, X-ray diffraction (XRD) and thermal stability by thermogravimetric analysis (TG). The nanofibers were morphologically characterized by transmission electron microscopy (TEM) and their surface charges in suspensions were estimated by Zeta-potential. Their degree of polymerization (DP) was characterized by viscometry, crystallinity by XRD and thermal stability by TG. Increasing the NaOH solution concentration in the mercerization, there was a decrease of hemicellulose and lignin contents and consequently an increase of cellulose content. XRD patterns presented changes in the crystal structure from cellulose I to cellulose II when the fibers were mercerized with 17.5% NaOH solution. All curaua nanofibers presented a rod-like shape, an average diameter (D) of 6–10 nm and length (L) of 80–170 nm, with an aspect ratio (L/D) of around 13–17. The mercerization of fibers with NaOH solutions influenced the crystallinity index and thermal stability of the resulting nanofibers. The fibers mercerized with NaOH solution 17.5% resulted in more crystalline nanofibers, but thermally less stable and inferior DP. The aggregation state increases with the amount of HCl introduced into the extraction, due to the decrease of surface charges (as verified by Zeta Potential analysis). However, this release presented nanofibers with better thermal stability than those whose acid hydrolysis was carried out using only H₂SO₄.     

Lightly doped La2-xSrxCuO4 as a Lifshitz helimagnet

We study the static magnetic correlations in lightly doped La2-xSrxCuO4 within the framework of a dipolar frustration model for a canted antiferromagnet. We show that the stability of the canted Néel state for x < 2% is due to the Dzyaloshinskii-Moriya and XY anisotropies. For higher doping, the ground state is unstable towards a helicoidal magnetic phase, where the transverse components of the staggered magnetization rotate in a plane perpendicular to the orthorhombic b axis. Our theory reconciles, for the first time, the incommensurate peaks observed in elastic neutron scattering with Raman and magnetic susceptibility experiments in La2-xSrxCuO4 .     

DNA microarraying on compact disc surfaces. Application to the analysis of single nucleotide polymorphisms in Plum pox virus

The potential of using compact discs as high throughput screening platforms for DNA microarraying is discussed and applied to discriminate genetic variations of Plum pox virus.     

Development and validation of a novel method for the analysis of chlorinated pesticides in soils using microwave-assisted extraction–headspace solid phase microextraction and gas chromatography–tandem mass spectrometry

A new procedure for determining eleven organochlorine pesticides in soils using microwave-assisted extraction (MAE) and headspace solid phase microextraction (HS-SPME) is described. The studied pesticides consisted of mirex, α- and γ-chlordane, p,p′-DDT, heptachlor, heptachlor epoxide isomer A, γ-hexachlorocyclohexane, dieldrin, endrin, aldrine and hexachlorobenzene. The HS-SPME was optimized for the most important parameters such as extraction time, sample volume and temperature. The present analytical procedure requires a reduced volume of organic solvents and avoids the need for extract clean-up steps. For optimized conditions the limits of detection for the method ranged from 0.02 to 3.6 ng/g, intermediate precision ranged from 14 to 36% (as CV%), and the recovery from 8 up to 51%. The proposed methodology can be used in the rapid screening of soil for the presence of the selected pesticides, and was applied to landfill soil samples.     

Assembly of γ-Fe2O3/polyaniline nanofilms with tuned dipolar interaction

The internal morphology and magnetic properties of layer-by-layer assembled nanofilms of polyaniline (PANI) and maghemite (γ-Fe₂O₃—7.5-nm diameter) were probed with cross-sectional transmission electron microscopy (TEM) and magnetization measurements (magnetic hysteresis loops, magnetization using zero-field cooled/field-cooled protocols, and ac magnetic susceptibility). Additionally, simulations of the as-produced samples were performed to assess both the nanofilm’s morphology and the corresponding magnetic signatures using the cell dynamic system (CDS) approach and Monte Carlo (MC) through the standard Metropolis algorithm, respectively. Fine control of the film thickness and average maghemite particle–particle within this magnetic structure was accomplished by varying the number of bilayers (PANI/γ-Fe₂O₃) deposited onto silicon substrates or through changing the concentration of the maghemite particles suspended within the colloidal dispersion sample used for film fabrication. PANI/γ-Fe₂O₃ nanofilms comprising 5, 10, 25 and 50 deposited bilayers displayed, respectively, blocking temperatures (T _B) of 30, 35, 39 and 40 K and effective energy barriers (ΔE/k _B) of 1.0 × 10³, 2.3 × 10³, 2.8 × 10³ and 2.9 × 10³ K. Simulation of magnetic nanofilms using the CDS model provided the internal morphology to carry on MC simulation of the magnetic properties of the system taking into account the particle–particle dipolar interaction. The simulated (using CDS) surface–surface particle distance of 0.5, 2.5 and 4.5 nm was obtained for nanofilms with thicknesses of 36.0, 33.9 and 27.1 nm, respectively. The simulated (using MC) T _B values were 33.0, 30.2 and 29.5 K for nanofilms with thicknesses of 36.0, 33.9 and 27.1 nm, respectively. We found the experimental (TEM and magnetic measurements) and the simulated data (CDS and MC) in very good agreement, falling within the same range and displaying the same systematic trend. Our findings open up new perspectives for fabrication of magnetic nanofilms with pre-established (simulated) morphology and magnetic properties.     

Evidences of the evolution from solid solution to surface segregation in Ni‐doped SnO2 nanoparticles using Raman spectroscopy

Ni‐doped SnO₂ nanoparticles, promising for gas‐sensing applications, have been synthesized by a polymer precursor method. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) data analyses indicate the exclusive formation of nanosized particles with rutile‐type phase (tetragonal SnO₂) for Ni contents below 10 mol%. The mean crystallite size shows a progressive reduction with the Ni content. Room‐temperature Raman spectra of Ni‐doped SnO₂ nanoparticles show the presence of Raman active modes and modes activated by size effects. From the evolution of the A_1g mode with the Ni content, a solubility limit at ∼2 mol% was estimated. Below that content, Raman results are consistent with the occurrence of solid solution (ss) and surface segregation (seg.) of Ni ions. Above ∼2 mol% Ni, the redshift of A_1g mode suggests that the surface segregation of Ni ions takes place. Disorder‐activated bands were determined and their integrated intensity evolution with the Ni content suggest that the solid‐solution regime favors the increase of disorder; meanwhile, that disorder becomes weaker as the Ni content is increased. Copyright © 2010 John Wiley & Sons, Ltd.     

Study of ferrofluids by Mössbauer spectroscopy

The parameters of the log‐normal size distribution of a MnFe₂O₄ ferrofluid powder sample have been determined by X‐ray diffraction. The mean blocking temperature was determined from the maximum of _Xi . Mössbauer spectra at 4.2–300 K are interpreted by a new simple theory of superparamagnetism and taking a reduction of the internal magnetic field for small particles, a size dependence of the anisotropy constant, the size distribution and collective excitations into account.     

Generalized prolate spheroidal wave functions for offset linear canonical transform in Clifford analysis

Prolate spheroidal wave functions (PSWFs) possess many remarkable properties. They are orthogonal basis of both square integrable space of finite interval and the Paley–Wiener space of bandlimited functions on the real line. No other system of classical orthogonal functions is known to obey this unique property. This raises the question of whether they possess these properties in Clifford analysis. The aim of the article is to answer this question and extend the results to more flexible integral transforms, such as offset linear canonical transform. We also illustrate how to use the generalized Clifford PSWFs (for offset Clifford linear canonical transform) we derive to analyze the energy preservation problems. Clifford PSWFs is new in literature and has some consequences that are now under investigation. Copyright © 2012 John Wiley & Sons, Ltd.