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Abstract:The term calcium phosphate cement was introduced by Gruninger et al. (1). This type of cement can be prepared by reacting a calcium phosphate salt with an aqueous solution, which causes it to set by the crossing of the precipitated crystals. These cements offer a series of advantages that allow their use as grafts and substitutes of damaged parts of the bone system. However, these cements have low mechanical strength compared to human bones. This work studied the influence of the use of polyamide fibers in the mechanical properties of a calcium phosphate cement based on ␣-tricalcium phosphate as well as the mechanisms involved in the increase of mechanical strength. The results demonstrate the feasibility of the use of polymeric fibers to increase mechanical strength and the need for coupling agents for the effective performance of the fibers as reinforcement in these materials.

Aquatic humic substances (AHS) isolated from two characteristic seasons of the Negro river, winter and summer corresponding to floody and dry periods, were structurally characterized by 13C nuclear magnetic ressonance. Subsequently, AHS aqueous solutions were irradiated with a polychromatic lamp (290-475 nm) and monitored by its total organic carbon (TOC) content, ultraviolet-visible (UV-vis) absorbance, fluorescence, and Fourier transformed infrared spectroscopy (FTIR). As a result, a photobleaching up to 80% after irradiation of 48 h was observed. Conformational rearrangements and formation of low molecular complexity structures were formed during the irradiation, as deduced from the pH decrement and the fluorescence shifting to lower wavelengths. Additionally a significant mineralization with the formation of CO2, CO, and inorganic carbon compounds was registered, as assumed by TOC losses of up to 70%. The differences in photodegradation between samples expressed by photobleaching efficiency were enhanced in the summer sample and related to its elevated aromatic content. Aromatic structures are assumed to have high autosensitization capacity effects mediated by the free radical generation from quinone and phenolic moieties.

SUMMARYDespite the fact that aluminum toxicity to crops is eliminated near soil water pH of 5.5, lime recommendation in many regions aims to increase soil pH up to 6.0 or even higher. For highly buffered soils, high rates of limestone are required to raise the pH from 5.5 to 6.0, resulting in additional, sometimes unnecessary, costs. The objective of this study was to evaluate the effect of soil pH on corn yield in a very acid Hapludox. The experiment was carried out in Lages, Southern Brazil, from 1992 to 1996. The soil had water pH of 4.7, Al 3+ of 33 mmol c kg -1 , O.M. of 45 g kg -1 and lime requirement to pH 6.0 of 9.0 t ha -1 . Dolomitic limestone at rates of 0, 4.5, 9.0, 13.5 and 18.0 t ha -1 (equivalent to pure CaCO 3 ) was incorporated into the soil down to 17 cm depth, in 1992. Liming increased linearly the values of soil pH (from 4.7 to 6.6) and Ca and Mg, eliminated Al 3+ with rates of 9.0 t ha -1 or higher, decreased slightly Al-CuCl 2 , Fe and Cu, and did not affect Zn and Mn. Maximum average corn yield for grain (7.9 t ha -1 ) and for green matter for silage (GM) (59 t ha -1 ) was obtained, respectively, at soil pH of 6.0 (12 t ha -1 of limestone) and of 6.1 (14 t ha -1 of limestone); maximum economic efficiency for grain was obtained at pH 5.6 (7.5 t ha -1 of limestone). Maximum yield increments due to liming were 17% for grain and 20% for GM. profundidade, em 1992, nas doses de 0, 4,5, 9,0, 13,5 e 18,0 t ha -1 (PRNT 100%). A calagem aumentou linearmente os valores de pH (de 4,7 até 6,6)

Single-walled carbon nanotubes (SWCNTs) exhibit excellent nonlinear optical (NLO) properties due to the delocalized π electron states present along their tube axis. Using the open aperture Z-scan method in tandem with X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, we demonstrate the simultaneous tailoring of both electronic and NLO properties of SWCNTs, from ultrafast (femtosecond) to relatively slow (nanosecond) timescales, by doping with a single substituent, viz., boron. SWCNTs were doped via a wet chemical method using B2O3, and the boron content and bonding configurations were identified using XPS. While in the ns excitation regime, the nonlinear absorption was found to increase with increasing boron concentration in the SWCNTs (due to the increasing disorder and enhanced metallicity of the SWCNTs), the saturation intensity in the fs excitation regime decreased. We attribute this counter-intuitive behavior to excited state absorption on ns timescales, and saturable absorption combined with weak two-photon transitions on fs timescales between van Hove singularities.

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