Kinetic determination of aromatic amines at millimolar level

A kinetic method for the determination of aromatic amines is reported. The method involves the formation of an azo dye between 1-(4-hydroxy-6-methylpyrimidin-2-yl)-3-methylpyrazolin-5-one and a diazonium salt formed from the amine in the presence of nitrite in weakly acidic media. The reaction is monitored via the initial rate of change of the absorbance of the azo dye at 420 nm, because this is proportional to the aniline concentration.The optimum acidity and concentration of reagents were established. The concentration ranges for which the calibration lines are linear are quite large. Detection limits were estimated. The effect of several metal ions usually present in real samples, e.g. waste water, was examined to assess interference.     

A topological characterization of complete distributive lattices

An ordered compact space is a compact topological space X, endowed with a partially ordered relation, whose graph is a closed set of X × X (cf. [4]). An important subclass of these spaces is that of Priestley spaces, characterized by the following property: for every x, y ? X with x ? y there is an increasing clopen set A (i.e. A is closed and open and such that a ? A, a ? z implies that z?A) which separates x from y, i.e., x ? A and y ? A. It is known (cf. [5, 6]) that there is a dual equivalence between the category Ld01 of distributive lattices with least and greatest element and the category P of Priestley spaces.In this paper we shall prove that a lattice L ? Ld01 is complete if and only if the associated Priestley space X verifies the condition: (E0) D ? X, D is increasing and open implies $\text{D}{}^1$ is increasing clopen (where A¹ denotes the least increasing set which includes A).This result generalizes a well-known characterization of complete Boolean algebras in terms of associated Stone spaces (see [2, Ch. III, Section 4, Lemma 1], for instance).We shall also prove that an ordered compact space that fulfils (E0) is necessarily a Priestley space.     

Single machine scheduling subject to precedence delays

A single-machine scheduling problem with precedence delays is analyzed. A set of n tasks is to be scheduled on the machine in such a way that the makespan is minimized. The executions of the tasks are constrained by precedence delays, i.e., a task can start its execution only after any of its predecessors has completed and the delay between the two tasks has elapsed. In the case of unit execution times and integer lengths of delays, the problem is shown to be NP-hard in the strong sense. In the case of integer execution times and unit length of delays, the problem is polynomial, and an O(n²) optimal algorithm is provided. Both preemptive and non-preemptive cases are considered.     

Anti‐Stokes Raman spectroscopy as a method to identify the metallic and semiconducting configurations of double‐walled carbon nanotubes

Although Raman spectra reveal, as a signature of double‐walled carbon nanotubes (DWCNTs), two radial breathing mode (RBM) lines associated with the inner and outer tubes, the specification of their nature as metallic or semiconducting remains a topic for debate. Investigating the spectral range of the RBM lines, we present a new procedure of the indexing of the semiconducting or metallic nature of the inner and outer shell that forms the DWCNT. The procedure exploits the difference between the intensities of recorded anti‐Stokes Raman spectrum and the anti‐Stokes spectrum calculated by applying the Boltzmann formulae to the recorded Stokes spectrum. The results indicate that the two spectra do not coincide with what should happen in a normal Raman process, namely, that there are RBM lines of the same intensity in both spectra, as well as RBM lines of higher intensity that are observed in the calculated spectrum. This discrepancy results from the surface‐enhanced Raman scattering mechanism that operates differently on metallic or semiconducting nanotubes. In this context, the analysis of the RBM spectrum can reveal pairs of lines associated with the inner/outer shell structure of DWCNT, and when the intensities between the recorded and calculated spectra coincide, the nanotube is metallic; otherwise, the nanotube is semiconducting. Copyright © 2014 John Wiley & Sons, Ltd.     

New features in the anti‐Stokes and Stokes Raman spectra of single‐walled carbon nanotubes that are highly separated into their semiconducting and metallic nanotube components

Surface‐enhanced Raman scattering studies were performed using nonresonant (514.5 nm) and resonant (676.4 nm) optical excitations on single‐walled carbon nanotubes thoroughly separated into semiconducting (pure 99%) and metallic (pure 98%) components. Regardless of the support (Au or Ag), the metallic nanotubes do not present an anomalous anti‐Stokes Raman emission. Regardless of whether an on‐resonant or off‐resonant optical excitation is used, only the semiconducting nanotubes produce an abnormal anti‐Stokes Raman emission that grows when increasing the excitation light intensity or temperature. The Raman studies under light polarized relative to the main nanotube axis demonstrate that only semiconducting nanotubes are sensitive toward changes in the polarization of the excitation light. Copyright © 2014 John Wiley & Sons, Ltd.     

Nanosized zinc and magnesium ferrites obtained from PVA–metal nitrates’ solutions

The paper presents a study regarding the possibility of obtaining zinc and magnesium ferrites starting from poly(vinyl alcohol)–metal nitrates solutions. By controlled heating of these solutions, a redox interaction takes place leading to the formation of some coordination compounds of the involved metal cations with the oxidation products of poly(vinyl alcohol) (PVA). FT-IR spectroscopy has evidenced the disappearance of the NO ₃ ^? anions at 140 °C due to the redox interaction with PVA. Thermal analysis evidenced the difference in the interaction of the individual metal nitrates and PVA and thus the particularity of the preparation of each ferrite. The thermal decomposition of the synthesized precursors was finished below 400 °C as resulting from both thermal analysis and FT-IR spectroscopy. The obtained ferrites powders consist of fine nanoparticle with diameters ranging from 10 to 30 nm for the powders annealed at 500 °C, as resulting from the SEM images. The specific surface area of the powders obtained at 500 °C was 32.2 m² g^?1 for ZnFe₂O₄ and 21.7 m² g^?1 for MgFe₂O₄, characteristic of nanoscaled powders. The increasing of the annealing temperature at 1,000 °C leads to sintering of both ferrites, more advanced in the case of zinc ferrite.     

Thermal decomposition of metal nitrates

The paper presents a study regarding the preparation of 40 %M^IIFe₂O₄/60 %SiO₂ nanocomposites (M = Ni, Zn, Cu) by thermal decomposition of metal nitrates—poly(vinyl alcohol)–tetraethyl orthosilicate gels. Thermal analysis and FT-IR spectroscopy have evidenced that a redox reaction takes place between PVA and NO ₃ ^? ions in the pores of the formed hybrid gels. The result of this redox reaction is the formation of carboxylate-type coordination compounds that have the role of a precursor of the ferrite nanoparticles. By thermal decomposition of these precursors inside the silica matrix, the corresponding MFe₂O₄/SiO₂ nanocomposites are obtained starting with 600 °C, as resulting from XRD analysis. Elemental maps of the corresponding involved elements M (Ni, Zn, Cu), Fe, and Si have confirmed the homogenous distribution of the ferrite nanoparticles within the silica matrix. TEM images have shown that the nanocomposites were obtained as fine nanoparticles, with diameter up to 20 nm. All nanocomposites 40 %M^IIFe₂O₄/60 %SiO₂ obtained at 1000 °C presented magnetic properties characteristic to this type of nanocomposite.     

Green Synthesis,Characterization, and Antibacterial Properties of Silver Nanoparticles Obtained by Using Diverse Varieties of Cannabis sativa Leaf Extracts

Cannabis sativa L. (hemp) is a plant used in the textile industry and green building material industry, as well as for the phytoremediation of soil, medical treatments, and supplementary food products. The synergistic effect of terpenes, flavonoids, and cannabinoids in hemp extracts may mediate the biogenic synthesis of metal nanoparticles. In this study, the chemical composition of aqueous leaf extracts of three varieties of Romanian hemp (two monoecious, and one dioecious) have been determined by Fourier-Transformed Infrared spectroscopy (FT-IR), high-performance liquid chromatography, and mass spectrometry (UHPLC-DAD-MS). Then, their capability to mediate the green synthesis of silver nanoparticles (AgNPs) and their pottential antibacterial applications were evaluated. The average antioxidant capacity of the extracts had 18.4 ± 3.9% inhibition determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH^•) and 78.2 ± 4.1% determined by 2,2′-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS™) assays. The total polyphenolic content of the extracts was 1642 ± 32 mg gallic acid equivalent (GAE) L⁻¹. After this, these extracts were reacted with an aqueous solution of AgNO₃ resulting in AgNPs, which were characterized by UV−VIS spectroscopy, FT-IR, scanning electron microscopy (SEM-EDX), and dynamic light scattering (DLS). The results demonstrated obtaining spherical, stable AgNPs with a diameter of less than 69 nm and an absorbance peak at 435 nm. The mixture of extracts and AgNPs showed a superior antioxidant capacity of 2.3 ± 0.4% inhibition determined by the DPPH^• assay, 88.5 ± 0.9% inhibition as determined by the ABTS^•+ assay, and a good antibacterial activity against several human pathogens: Escherichia coli, Klebsiella pneumoniae, Pseudomonas fluorescens, and Staphylococcus aureus.     

Correlations and cross-correlations in the Brazilian agrarian commodities and stocks

We investigate the auto-correlations and cross-correlations of the volatility time series in the Brazilian stock and commodity market, using the recently introduced Detrended Cross-Correlation Analysis. We find that the auto-correlations in stock volatilities are weaker than the auto-correlations in the commodity volatility series, contrary to earlier findings for the USA market where commodity volatility exponents were found to be lower than for stocks. We also find that the cross-correlations in the Brazilian stock and commodity market are stronger than what would be expected from simple combinations of auto-correlations of individual series, implying that there may be hidden factors that govern the behavior of the observed volatility series. This enhanced cross-correlation behavior is found in a considerable fraction of Brazilian stocks and agricultural commodities considered in the present work, suggesting that further studies should be directed into investigating these super-cross-correlations, and pinpointing the exogenous variables responsible for such behavior.