Heavy metals in soils and plants in mango orchards in Petrolina, Pernambuco, Brazil

The monitoring of heavy metal concentrations in areas under intensive agriculture is essential for the agricultural sustainability and food safety. This paper evaluates the total contents of heavy metals in soils and mango trees in orchards of different ages (6, 7, 8, 9, 10, 11, 14, 16, 17, 19, and 26 years) in Petrolina, Pernambuco, Brazil. Soil samples were taken from the layers 0-20 cm and 20-40 cm, and mango leaves were collected in the growth stage. Areas of native vegetation (Caatinga) adjacent to the cultivated areas were used for comparison. The total concentrations of heavy metals (Cu, Cr, Fe, Zn, Mn, Ni, and Pb) were determined in soils and leaves. In general, mango cultivation led to Cu and Zn accumulation in the soil surface and to a reduction in the contents of Ni, Pb, Mn, and Fe in surface and subsurface. Since contamination by Cu, Zn, and Cr was detected, these areas must be monitored to prevent negative environmental impacts. For instance, the presence of Cr in mango tree leaves indicates the need to investigate the source of the element in these orchards. The management strategies of the different companies led to deficiency or excess of some metals in the evaluated areas. However, the Fe and Mn levels were adequate for the mineral nutrition of mango in all areas.

[Lettre autographe signée de Giuseppe Verdi (sans lieu ni date)]

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[Lettre autographe signée de Giuseppe Verdi (sans lieu ni date)]

Destinataire non identifié. - Comprend aussi 2 lignes de la main de Joséphine Verdi

[Lettre autographe signée de Giuseppe Verdi (sans lieu ni date)]

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[Lettre autographe signée de Giuseppe Verdi (sans lieu ni date)]

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[Lettre autographe signée de Giuseppe Verdi (sans lieu ni date)]

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[Lettre autographe signée de Giuseppe Verdi (sans lieu ni date), (1847)]

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[Lettre autographe signée de Giuseppe Verdi (sans lieu ni date)]

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[Lettre autographe signée de Giuseppe Verdi (sans lieu ni date)]

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[Lettre autographe signée de Giuseppe Verdi (sans lieu ni date)]

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State equation for shape-memory alloys. Aplication to Cu-Zn-Al

We deal with the hysteretic behavior of partial cycles in the two¿phase region associated with the martensitic transformation of shape¿memory alloys. We consider the problem from a thermodynamic point of view and adopt a local equilibrium formalism, based on the idea of thermoelastic balance, from which a formal writing follows a state equation for the material in terms of its temperature T, external applied stress ¿, and transformed volume fraction x. To describe the striking memory properties exhibited by partial transformation cycles, state variables (x,¿,T) corresponding to the current state of the system have to be supplemented with variables (x,¿,T) corresponding to points where the transformation control parameter (¿¿ and/or T) had reached a maximum or a minimum in the previous thermodynamic history of the system. We restrict our study to simple partial cycles resulting from a single maximum or minimum of the control parameter. Several common features displayed by such partial cycles and repeatedly observed in experiments lead to a set of analytic restrictions, listed explicitly in the paper, to be verified by the dissipative term of the state equation, responsible for hysteresis. Finally, using calorimetric data of thermally induced partial cycles through the martensitic transformation in a Cu¿Zn¿Al alloy, we have fitted a given functional form of the dissipative term consistent with the analytic restrictions mentioned above.

Preisach modeling of hysteresis for a pseudoelastic Cu-Zn-Al single crystal

Stress-strain trajectories associated with pseudoelastic behavior of a Cu¿19.4 Zn¿13.1 Al (at.%) single crystal at room temperature have been determined experimentally. For a constant cross-head speed the trajectories and the associated hysteresis behavior are perfectly reproducible; the trajectories exhibit memory properties, dependent only on the values of return points, where transformation direction is reverted. An adapted version of the Preisach model for hysteresis has been implemented to predict the observed trajectories, using a set of experimental first¿order reversal curves as input data. Explicit formulas have been derived giving all trajectories in terms of this data set, with no adjustable parameters. Comparison between experimental and calculated trajectories shows a much better agreement for descending than for ascending paths, an indication of a dissymmetry between the dissipation mechanisms operative in forward and reverse directions of martensitic transformation.

Heat capacity measurements on the equiatomic compounds in Ni-X (X = Al, In, Si, Ge and Bi) and M-Sb (with M = Ni, Co and Fe) systems

Molar heat capacities of the binary compounds NiAl, NiIn, NiSi, NiGe, NiBi, NiSb, CoSb and FeSb were determined every 10 K by differential scanning calorimetry in the temperature range 310-1080 K. The experimental results have been fitted versus temperature according to C-p = a + b . T + c . T-2 + d . T-2. Results are given, discussed and compared to estimations found in the literature. Two compounds, NiBi and FeSb, are subject to transformations between 460 and 500 K. (C) 1999 Elsevier Science Ltd. All rights reserved.