Tetradecyltrimethylammonium bromide water-in-oil microemulsions: dependence of the minimum amount of alkanol required to produce a microemulsion with the alkanol and organic solvent topology

The amount of alcohol required to produce a microemulsion in a quaternary water-in-oil system was evaluated for a series of alcohols and hydrocarbon solvents of different size or topology. It was observed that the amount of n-hexanol and n-decanol required was similar in all the solvents considered. On the other hand, considerably higher concentrations of the branched alcohols (2,4-dimethyl-3-pentanol and 3-ethyl-3-pentanol) were required to produce the microemulsion, irrespective of the solvent topology (n-hexane or 2,2,4-trimethylpentane). From an analysis of the change in the analytical alcohol concentration with the surfactant concentration the amounts of alcohol present at the microaggregates' surface at the point of microemulsion formation were obtained. It is concluded that the high amounts of branched alcohols required are due to both less efficient incorporation at the interface and the larger number of alcohol molecules per surfactant required to stabilize the microemulsion.     

Genomic clustering of the Trypanosoma cruzi nonlong terminal L1Tc retrotransposon with defined interspersed repeated DNA elements

We have analyzed the genomic distribution and organization of the long interspersed nucleotide element (LINE) L1Tc, a nonlong terminal repeat (LTR) retrotransposon of Trypanosoma cruzi. The results indicate that the L1Tc element is dispersed along the parasite genome and that in some regions it is organized in tandem repeats. The data allowed us to define the existence of short direct-repeated sequences flanking the genomic L1Tc elements. Relevant is the finding that the LINE L1Tc is located in genomic regions rich in short interspersed nucleotide elements (SINE)-like sequences. In particular, the L1Tc element is found associated to E13-related sequences, redefined in this work and renamed RS13Tc, and to a newly described RS1Tc sequence. The RS1Tc sequence is present, per haploid genome, in about 3,200 copies. Northern blot analysis showed that the RS1Tc is being transcribed into RNAs of different sizes. The analysis of the chromosomal distribution of these elements in various strains of T. cruzi suggested that this type of clustering might be a common feature of the genome of these parasites.     

Consequences of weak Allee effect on prey in the May–Holling–Tanner predator–prey model

In this work, a modified Holling–Tanner predator–prey model is analyzed, considering important aspects describing the interaction such as the predator growth function is of a logistic type; a weak Allee effect acting in the prey growth function, and the functional response is of hyperbolic type. Making a change of variables and time rescaling, we obtain a polynomial differential equations system topologically equivalent to the original one in which the non‐hyperbolic equilibrium point (0,0) is an attractor for all parameter values. An important consequence of this property is the existence of a separatrix curve dividing the behavior of trajectories in the phase plane, and the system exhibits the bistability phenomenon, because the trajectories can have different ω ? limit sets; as example, the origin (0,0) or a stable limit cycle surrounding an unstable positive equilibrium point. We show that, under certain parameter conditions, a positive equilibrium may undergo saddle‐node, Hopf, and Bogdanov–Takens bifurcations; the existence of a homoclinic curve on the phase plane is also proved, which breaks in an unstable limit cycle. Some simulations to reinforce our results are also shown. Copyright © 2015 John Wiley & Sons, Ltd.     

Electrodes based on zeolites modified with cobalt and/or molybdenum for pesticide degradation: part II—2,4,6-trichlorophenol degradation

Journal of Solid State Electrochemistry - 2,4,6-trichlorophenol (TCP) is a persistent pollutant introduced in water by industrial processes and pesticides. We have studied the electrooxidation of...     

Theoretical study of the role of solvent Stark effect in electron transitions

The possible influence of the solvent Stark effect (SSE) on the solvatochromic shift in electron transitions has been analyzed by using the ASEP/MD (averaged solvent electrostatic potential from molecular dynamics) method. With this purpose, four molecules, two polar (acrolein and formaldehyde) and two non-polar (p-difluorobenzene and trans-difluoroethene) have been studied in solvents of diverse polarity. Independently of the nature of the system we found that the contribution of SSE on the average value of the solvent shift or on the multipole moment values is negligible. In the case of centro-symmetric molecules, our results permit to discard the SSE as cause of the solvent shift found, which must be assigned to the electrostatic interaction of the solute quadrupole and higher multipoles with the solvent. As the SSE values provide also a measure of the errors introduced by the mean field approximation (MFA), these results indicate that MFA permits a very accurate determination of the solvent shift at the same time that it reduces drastically the computational cost. Finally, a new procedure suited to the ASEP/MD method has been presented that permits to estimate the inhomogeneous broadening of spectral bands, complementing the information provided by mean field theories. This procedure does not need additional quantum calculations and its computational cost is minimal.     

Recrystallization of amorphous nanotracks and uniform layers generated by swift-ion-beam irradiation in lithium niobate

The thermal annealing of amorphous tracks of nanometer-size diameter generated in lithium niobate (LiNbO₃) by Bromine ions at 45 MeV, i.e., in the electronic stopping regime, has been investigated by RBS/C spectrometry in the temperature range from 250°C to 350°C. Relatively low fluences have been used (<10¹² cm⁻²) to produce isolated tracks. However, the possible effect of track overlapping has been investigated by varying the fluence between 3×10¹¹ cm⁻² and 10¹² cm⁻². The annealing process follows a two-step kinetics. In a first stage (I) the track radius decreases linearly with the annealing time. It obeys an Arrhenius-type dependence on annealing temperature with activation energy around 1.5 eV. The second stage (II) operates after the track radius has decreased down to around 2.5 nm and shows a much lower radial velocity. The data for stage I appear consistent with a solid-phase epitaxial process that yields a constant recrystallization rate at the amorphous-crystalline boundary. HRTEM has been used to monitor the existence and the size of the annealed isolated tracks in the second stage. On the other hand, the thermal annealing of homogeneous (buried) amorphous layers has been investigated within the same temperature range, on samples irradiated with Fluorine at 20 MeV and fluences of ∼10¹⁴ cm⁻². Optical techniques are very suitable for this case and have been used to monitor the recrystallization of the layers. The annealing process induces a displacement of the crystalline-amorphous boundary that is also linear with annealing time, and the recrystallization rates are consistent with those measured for tracks. The comparison of these data with those previously obtained for the heavily damaged (amorphous) layers produced by elastic nuclear collisions is summarily discussed.     

Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films

We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La_0.7Ca_0.3MnO₃ (LCMO) and YBa₂Cu₃O_7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO₃ (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on the LAO (control) and LCMO side of the substrate. Critical current, I _c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed that while the control side showed a J _c of ∼ 2 × 10⁶ A/cm², the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J _c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of J _c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length has been quantified. A control experiment carried out with LaNiO₃ deposited by PLD on YBCO did not show any evidence of self-injection.     

Micro-Raman spectroscopic identification of natural mineral phases and their weathering products inside an abandoned zinc/lead mine

Mining activities provide a good source of minerals of different nature. On the one hand, the primary minerals for whose formation a geological time-scale is required. On the other hand, secondary minerals, formed from removed products after the earlier weathering and alteration states. These are characteristic of the local geology and the environment context that commonly appears due to the low chemical stability of their original primary minerals. This work shows how quickly the reactions promoting secondary minerals may have taken place, due to the fact that these were found in newly formed solid materials called efflorescences. To achieve this purpose, the sampling is crucial. It was carried out in such a way that tried to guarantee that the samples collected consisted in the very top soil matter (first 2 cm depth). Thus, unlike the deeper soil, the material analysed may have been newly formed due to the interactions that they had with the place weathering agents (i.e. air oxygen, humidity, and microbial activities). Raman spectroscopy has emerged as a good and fast non-destructive technique that provides molecular information of the local mineralogy without the need of any pre-treatment of the samples. At the same time, the work looked for information on the variety of non-stable lead and-or zinc containing minerals due to the possible health and environmental risks they convey. Among the different minerals identified, 16 were of primary nature while 23 may be classified as secondary minerals, probably formed in the last decades as the result of the extractive activities.     

Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film

La_0.67Ba_0.33MnO₃ (LBMO) thin film is deposited on a 36.7°C SrTiO₃ bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance with the increase in temperature is due to enhanced spin-flip scattering process.