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- Author or Editor: A. Cruz x
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Abstract
It is increasingly important that chemistry reaches people who have not studied directly this field of science but that, daily, have practices where chemistry is involved in various extents. This is what happens, for instance, in the activities related with the study and the preservation of cultural heritage. In this sense, the present work is a short review of the particular case of techniques based on the thermal analysis and calorimetry applied within the context of the characterization of art and archeological objects, exemplified by various case studies, as the characterization of mortars, preparatory grounds, ancient painting materials and drying oils.
Canopy gaps modify the environmental conditions available for plant growth in forests. Small canopy gaps are frequent in Nothofagus betuloides forests of Tierra del Fuego. Our objective was to study whether the forest floor vascular and non-vascular plant species composition and diversity are influenced by the occurrence of small-scale disturbances due to changes in the below-canopy solar radiation transmittances and forest floor heterogeneity (cover of litter, bare soil and fallen woody debris classed in three decay stages) in a N. betuloides forest located in south western Tierra del Fuego (53° 59t’S, 69°58′W). The vegetation was sampled in and around 13 canopy gaps (47 m2 on average). Following a light gradient, 65 plots (2 × 2 m) were established. The cover of all plant species was recorded using Londo’s scale. Species richness and total cover were calculated for each of the following taxonomical groups: spermatophyta (monocotyledons, dicotyledons), pteridophyta, bryophyta, marchantiophyta, anthocerotophyta and lichens. There were 63 species found on the forest floor. Marchantiophyta was the most diverse group with the highest species richness (6.6 species per plot). The vegetation on the forest floor was very homogeneous in species composition, richness and species diversity. The ordination analysis (NMS) showed that the community composition was weakly influenced by the patterns of below-canopy solar radiation transmittances and substrate heterogeneity. MRPP analysis of the community composition did not reveal differences in plant species assemblages between positions along transects running from areas beneath closed canopy to the open centres of canopy gaps. The marchantiophyte Chiloscyphus magellanicus was the only species which can be considered to be an indicator species; it was more likely to occur in gap centres (more open conditions). We conclude that these small canopy gaps do not very much modify the forest floor communities and the communities can be considered relatively stable.
Abstract
Excitation functions for the production of198mAu,198Au,198(m+g)Au, by (
, 2pn) reactions on gold and isomeric ratios for198Au were determined experimentally. The method of activation of metallic foils was employed. The irradiations were performed in the isochronous cyclotron at Karlsruhe (Germany) with -particles at 90 MeV. Gamma-spectrometry by means of an intrinsic Ge detector was used to determine the nuclides produced. In addition, a comparison between the cross sections obtained and a calculation using the hybrid model of pre-equilibrium reactions, in combination with the statistical model development by ERNST is presented.
Abstract
The molybdate β-Bi2Mo2O9 synthesised by solid state reaction showed photocatalytic activity for the degradation of rhodamine B (rhB), indigo carmine (IC) and alizarin red S (ARS) through a photosensitization process of the organic dye. The activity of β-Bi2Mo2O9 to the degradation of organic dyes was compared with the corresponding γ-Bi2MoO6 phase. It was found that activities exhibited by β-Bi2Mo2O9 were four times higher than that obtained by γ-Bi2MoO6. The extent of mineralization was determined by means of total organic carbon (TOC) measurements, which showed a satisfactory TOC reduction (40%, within 50 h) for rhB.
Abstract
Primaquine (PQ) is the drug of choice for the radical cure of Plasmodium vivax malaria, and currently being administered in solid dosage form. In this study, the compatibility studies were carried out using differential scanning calorimetry (DSC), thermogravimetry (TG), and fourier transformed infrared (FT-IR). Non-isothermal and isothermal methods were employed to investigate kinetic parameters under nitrogen and air atmospheres using TG. The DSC investigations obtained by physical mixtures showed slight alterations in the melting temperatures of PQ with some excipients. The FT-IR confirmed the possible interactions obtained by DSC for the physical mixtures with PQ and lactose, magnesium stearate and mannitol. The results showed that the thermal decomposition followed a zero order kinetic in both atmospheres in non-isothermal method. The activation energy in both methods using nitrogen atmosphere was similar, and in air atmosphere the activation energy decreased.
In this work it was developed marker-free transgenic indica rice plants (cv J-104) by biolistic co-transformation and segregation approach. We attempted to express the NmDef02 antifungal defensin. Primary transformants were regenerated from embryogenic callus on culture medium with 50 mg/L hygromycin. Screening of hpt-marker-free transgenic lines was made by PCR in T1 progeny lines, germinated on semisolid medium without hygromycin. Relative expression of NmDef02 mRNA was examined by quantitative RT-PCR in marker-free T1 plants. In vitro antifungal test was performed by disk diffusion assay against Sarocladium oryzae. PCR assay verified that 15.12% of T1 plants were marker-free (NmDef02+/hpt−). RT-PCR analysis indicated that NmDef02 gene was successfully transcribed and the transgenic lines displayed different expression levels of the NmDef02 cDNA. Protein extracts of marker-free lines with high relative expression of NmDef02 inhibited fungus mycelial growth around disks. In contrast, it was confirmed fungus proliferation on disks impregnated with protein extracts of non-transgenic plants. The results of the present work demonstrated that the expression of the NmDef02 defensin in transgenic rice plants is effective against the phytopathogenic fungus Sarocladium oryzae under in vitro conditions. Thus, NmDef02 defensin could be a useful tool for J-104 rice improvement.
Thermal decomposition of lanthanide(III) complexes with 4,4,4-trifluoro-1-phenyl-1,3-butanedione
Photoluminescent properties and kinetic study
Abstract
The complexes of general formula Ln(btfa)3L, where Ln=Eu or Tb, btfa=4,4,4-trifluoro-1-phenyl-1,3-butanedione, L=1,10-phenanthroline (phen) or 2,2-bipyridine (bipy), were synthesized by reacting the corresponding metal chloride with the proper β-diketone and the other ligand. The complexes were obtained in the powder form and were characterized by photoluminescence and TG. Their thermal decomposition was studied by non-isothermal thermogravimetric techniques. The Eu(btfa)3bipy complex presented the highest thermal stability and it melts before being decomposed. The complex Eu(btfa)3phen presented the largest activation energy for a heating rate of 5C min–1.
Abstract
Terfenadine samples prepared by crystallization in different media and supersaturation conditions were used to investigate the polymorphism of the substance. The study was based on DSC melting curves. An empirical parametric equation was used for modelling the experimental data. The signal recorded was resolved into the corresponding overlapping peak components by fitting analysis. Four polymorphic phases were identified.
Abstract
PbMoO4 oxide with scheelite structure was obtained by hydrothermal synthesis in the absence of additives. The material was characterized by X-ray powder diffraction, scanning electron microscopy, diffuse reflectance spectroscopy, and adsorption–desorption N2 isotherms. The organic dyes rhodamine B (rhB), indigo carmine (IC), orange G (OG), and methyl orange (MO) were selected as molecules model to study its photocatalytic degradation over PbMoO4 oxide under UV irradiation. Total organic carbon analysis of samples irradiated revealed that mineralization of organic dyes by the action of PbMoO4 was feasible in 80 % (rhB), 69 % (IC), 71 % (MO), and 65 % (OG) after 96 h of UV irradiation.
In this paper, we used two methodological approaches to analyze the structure and function of a trophic web in the temperate coastal lagoon of Bahía Magdalena, Baja California Sur, Mexico, which represents the largest wetland ecosystem along the west coast of the Baja California peninsula. Ecosystem structure was studied using a topological approach, while ecosystem functioning was analyzed using a biomass balance model. Connectance values indicated a low number of functional group interactions, consistent with the range proposed for similar marine trophic webs. This pattern may reflect incorporation of a few functional groups clustered along the trophic web. Results would vary if the model included more functional groups or different levels of aggregation, since aggregation and diversity strongly influence the base of the food web. Topological results suggest that trophic web structure depends primarily on lower and intermediate trophic level organisms like macrobenthic invertebrates, penaeid shrimp and marine turtles. Balance biomass model results suggest that trophic groups positioned on the first level most strongly support Bahía Magdalena trophic web functioning. In particular, the pelagic red crab (Pleurocondes planipes) transfers energy between basal and upper levels of the food web (a wasp-waist energy control). When compared to ecosystems at different latitudes, the results indicate that the Bahía Magdalena ecosystem is still in a developmental phase, wherein trophic web functioning depends largely on the balance between energy flows originating from primary producers and those originating from detrital pathways. While these results are preliminary, they demonstrate the potential of combined topological and biomass approaches in analyzing highly organized ecosystems. The combined approach can make both theoretical and empirical predictions about the functional response of real systems to structural changes, thus enhancing evidence-based methods for ecosystem management.
