Entity

Time filter

Source Type

Manaus, Brazil

Archeological sites are frequent in the Brazilian Amazon. The physical, chemical and morphological properties, due to anthropic influence, are quite different from surrounding soils, mainly in the uplands. Although several studies have been carried out to understand the magnitude of these modifications and their influence on the genesis of such soils, aspects such as the mineralogical properties need to be better described. This study aimed at evaluating the chemical and mineralogical properties of anthropic horizons (Au) of soils of upland and floodplain sites located in the Sedimentary Basin of the Amazon, between the cities of Coari and Manaus. Soil samples were collected and analyzed for chemical properties (pH) and for the total contents of Fe, Al, Si and P. The mineralogical compositions of the clay and sand fractions were evaluated by X-ray diffraction (XRD). The results showed that anthropic modifications lowered the acidity and exchangeable Al soil contents and enhanced the contents of available Ca and P. The total P contents in the anthropic horizons ranged from 1630 to 8840 mg kg-1 of P2O5. Kaolinite was the main mineral found in the clay fraction of upland soils, followed by gibbsite, goethite and titanium oxides. The floodplain soils showed clay fractions composed of kaolinite, goethite and 2:1 silicates. The sand fractions of all studied soils consisted predominantly of quartz. The magnetic fractions consisted of hematite and maghemite. In conclusion, better chemical properties were observed in the anthropic horizons, as well as differences in their mineralogical composition as compared to the other studied sites. Source


Pereira R.R.C.,UFAM | Moraes J.C.,Federal University of Lavras | Prado E.,Epamig | Dacosta R.R.,Sao Paulo State University
Scientia Agricola | Year: 2010

The greenbug Schizaphis graminum (Rond.) (Hemiptera: Aphididae) is one of the main pest-insects of wheat (Triticum aestivum, L.). Resistance inducing agents as silicon (Si) and acibenzolar-s-methyl (ASM) can provide some protection against insects and diseases. The effect of Si and/or ASM on the development and probing behaviour of S. graminum in wheat plants was evaluated. Wheat plants (cultivar Embrapa 22) were treated with Si (silicic acid at the rate of 1%) and acibenzolar-S-methyl (ASM) at the rate of 0.5%. The effects of these treatments on greenbugs were analyzed by development parameters, honeydew excretion and probing behavior monitored by Electrical Penetration Graphs (EPG). The development and honeydew experiments consisted of ten replications each and EPG experiment was replicated 25 times. The application of both resistance inducing agents reduced fecundity, prolonged the duration of pre-reproductive period, and decreased honeydew production. Induced resistance was localized mainly at phloem level and caused a strong reduction of phloem sap ingestion, but some effect of ASM at parenchyma/mesophyll level could not be discounted as far fewer aphids reached the sieve elements. Source


Ghosh A.,UFAM | Pimentel B.M.,Sao Paulo State University
Physica C: Superconductivity and its Applications | Year: 2012

The q-deformed algebraic method based on the extension of the number concept as proposed by Gauss [1] is used to obtain a q-analog to the gap equation for the cuprates using a tight-binding model. The conventional s-wave symmetry along with the d x2-y2 wave order parameter are considered to understand the effect of q-fermionic theory which is a generalization or deformation of the usual Fermi theory. The dependence of the gap and/or the critical temperature on doping for various values of q is studied. Specific heat and the phase diagram are found to be explicitly dependent on the parameter and the well-known hump-like behavior is detected for q > 1. Moreover, the position of the maximum in T c in the phase diagram depends on the value of q and also on the value of the coupling. © 2011 Elsevier B.V. All rights reserved. Source


Ghosh A.,UFAM
Physica C: Superconductivity and its Applications | Year: 2012

The effect of non-magnetic impurity-scattering is considered on the asymmetric superconducting gap (SC) and the d-density wave (DDW) phase of the high Tc cuprates. The phase diagrams for the cuprates demonstrate that Tc decreases with scattering potential and is most affected in the coexisting phase of DDW and SC orders. Moreover, the SC gap to Tc ratio increases with doping and impurity scattering. The transition temperature of the DDW state, T* also decreases with scattering. The density of states in the mixed SC + DDW state for the underdoped (UD) phase, SC state in the overdoped phase and the DDW state in the UD phase, also suffers a modification. Its effect on specific heat results is also discussed. The increase in the gap to Tc ratio and the specific heat are also observed in the presence of the non-magnetic impurities. A suppression in the superfluid density is found with the increase in impurity. © 2012 Elsevier B.V. All rights reserved. Source


Ghosh A.,UFAM | Pimentel B.M.,Sao Paulo State University
Physica B: Condensed Matter | Year: 2012

Inspite of the direct evidence for Cooper pairing in the cuprates as in conventional superconductors, the pairing symmetry in the cuprate superconductors is still considered to be a controversial and a highly debatable topic. The microscopic equations appropriate for these new materials, essentially the yttrium based compounds, are discussed following Gorkovs formalism for the conventional superconductors. Various types of symmetry of the pairing parameter are considered. In this study we consider the anisotropic nature of the gap parameter to write the mean-field equations of the cuprates. We observe that the symmetry of the potential is fundamental in deciding the nature of the anisotropy in the gap parameter. © 2012 Elsevier B.V. All rights reserved. Source

Discover hidden collaborations