Search Results

You are looking at 11 - 20 of 29 items for

  • Author or Editor: P. García x
  • Refine by Access: All Content x
Clear All Modify Search
Community Ecology
Authors:
A.F.S. Garcia
,
A.M. Garcia
,
S.R. Vollrath
,
F. Schneck
,
C.F.M. Silva
,
Í.J. Marchetti
, and
J.P. Vieira

Food partitioning among coexisting species in different habitats remains an important research topic in trophic ecology. In this work, we combined carbon and nitrogen stable isotope ratios and stomach content analyses to investigate differences in diet and niche overlap of two congeneric juvenile mullet species (Mugil curema and Mugil liza) coexisting in a marine surf-zone and an estuarine zone in southern Brazil (29oS). These habitats have contrasting levels of food availability, especially in terms of prey diversity, with higher microalgae diversity in the estuary than in the marine surf-zone. In these contrasting conditions, we predicted that both mullet species will have (a) higher niche overlap and smaller niche breadth at the marine surf-zone due to the common exploration of highly abundant surf-zone diatoms and (b) lower niche overlap and higher niche breadth inside the estuary due to selective feeding on more diverse food resources. Isotope niche areas (measured as standard ellipse areas) were higher in the estuary (6.10 and 6.18) than in the marine surf-zone (3.68 and 3.37) for both M. curema and M. liza, respectively. We observed an overlap of 52% in isotopic niches of both species in the marine surf-zone and none in the estuary. We also found contrasting patterns in the diet composition between species according to the habitat. At the marine surfzone, diatoms of the classes Bacillariophyceae and Coscinodiscophyceae dominated (> 99%) the food content of both mullet species. In contrast, green algae, cyanobacteria, dinoflagellates and flagellates comprised the diet of both species in the estuary. These results could be explained by spatial differences in food availability (especially regarding diversity of microalgae) between both habitats. At the marine site, both species explored the most abundant microalgae available (mostly the surf-zone diatom Asterionellopsis cf. guyunusae and fragments of Coscinodiscus), whereas in the estuary both species shifted their diets to explore the greater diversity of microalgae resources. Overall, our findings revealed that niche partitioning theory could not fully predict changes in breadth and overlap of food niches of estuarine dependent fish species with complex life cycles encompassing marine to estuarine systems with contrasting food availabilities.

Open access

Abstract  

A series of fluoropolymer films was synthesized by reacting 1,3-bis(1,1,1,3,3,3-hexafluoro-2-pentafluorophenylmethoxy-2-propyl)benzene (12F-FBE) with a series of bisphenol monomers via a polycondensation reaction. The biphenols used included a diphenol-substituted spirodilactam, biphenol, bisphenol A, bisphenol AF, bisphenol F and bisphenol O. Polymers films from these new fluoropolyaryl ethers were irradiated by a Gamma Beam 657-PT at a dose rate of 9 kGy/h; the absorbed dose was varied between 30 and 150 kGy. The effect on the chemical structure upon radiation was studied by DSC, TGA, FTIR-ATR, NMR, and GPC, both before and after irradiation. The data obtained allowed the determination of the degradation radiochemical yield (G s), between 0.24 and 7.43 crosslinking radiochemical yield (G x), from 0.03 to 1.47 and the ratio of G s/G x was between 2.89 and 8.28. There was no apparent physical change, from 30 to 150 kGy; the films continue to be flexible and transparent after irradiation.

Restricted access

Order-disorder transitions were investigated in native cassava starch at intermediate moisture contents (35 to 60% wt. water), using Differential Scanning Calorimetry (DSC) and dynamic Wide Angle X-ray Diffractometry (WAXS) with a synchrotron radiation source.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors:
M. Valenzuela
,
P. Bosch
,
B. Zapata
,
G. Aguilar-Ríos
,
V. Lara
,
E. García-Figueroa
, and
I. Schifter

Abstract  

ZnAl2O4 and Sn−ZnAl2O4 were synthesized by coprecipitation, sol-gel and impregnation methods. These materials were calcined and treated in H2 at 1073 K. Thermal analysis (DTA and TG), nitrogen physisorption (BET method), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used as characterization techniques. H2 treatment promoted AlxZny crystallization in the coprecipitated and impregnated samples. When tin was added to zinc aluminate, the tin acted as a protective shell against high-temperature reduction, independently of the preparation technique.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors:
S. Tejeda
,
G. Zarazúa-Ortega
,
P. Avila-Pérez
,
A. García-Mejía
,
L. Carapia-Morales
, and
C. Diaz-Delgado

Summary  

The Lerma is one of the most important rivers of Mexico, where it drains highly populated and industrialized regions. The concentration of six major and trace elements: titanium, manganese, iron, zinc, copper and lead in the surface sediments of the upper course of Lerma river was investigated, in order to identify its distribution along the river and to recognize the principal sites of pollution. The surface sediment samples were collected at 8 sites distributed following the stream flow direction of the river. Major and trace elements concentrations were determined by energy dispersive X-ray spectrometry. The results show that the metal concentrations in the sediments decrease in the sequence: Fe > Ti > Mn > Zn > Cu > Pb. Concentration of Fe, Mn and Ti were significantly higher than the other metals in site 8,200 meters downstream the Alzate Dam. The high concentrations and spatial variations of Zn, Cu and Pb in the middle sites of the upper course of the Lerma River indicate that the river pollution is probably associated with urban and industrial discharges.

Restricted access
Journal of Thermal Analysis and Calorimetry
Authors:
J. González-Irún Rodríguez
,
P. Carreira
,
A. García-Diez
,
D. Hui
,
R. Artiaga
, and
L. Liz-Marzán

Abstract  

The effect of silica nanofiller on the glass transition of a polyurethane was studied by DSC. The pristine polymer exhibits a single glass transition at about –10C. Uniform SiO2 spheres with different average sizes and narrow size distributions were synthesized in solution by the Stber method [1]. Both the effects of silica content within the polymer and particle size were investigated, as well as two different surface treatments. Scanning electron microscopy (SEM) clearly confirms the presence of the particles within the polymer matrix, showing uniform distribution and no agglomeration. While shifting of the glass transition has been reported by many authors, we have not seen any noticeable shift in this polymer. Surprisingly, we found no relevant effects when either increasing the filler content or changing the particle size. Different amounts of particles with average diameters of 175, 395 and 730 nm did not affect the glass transition temperature of the pristine polymer.

Restricted access

Phytoremediation could reduce heavy metal bioavailability in soils and obtain renewable energy from lands useless. Some fast-growing, high biomass crop species are known to display a significant heavy metal tolerance, particularly those from the genus Brassica. These species could be phytoremediator candidates for recuperate polluted soils with heavy metals. Brachypodium distachyon has also been recently proposed as a model species to develop bioenergy. However, there are no experiments about the tolerance of this plant to metals. The present work reports data concerning the ability of Brachypodium distachyon and Brassica napus seeds to germinate and grow in media containing different doses of Cd, Cr, As and Zn, in order to evaluate their use as energy crops in polluted sites. Biomass reduction and length decreasing were observed as consequence on increasing metal doses in both species, but the effect was different attending to metal and species. The maximum toxicity level was found in plants treated with Cr (VI). Exposures of 30 mg L−1 of Cd and As (V) reduced the shoot elongation by 50% in both species, while root was affected by lower doses than 30 mg L−1. Concentrations of Zn affected neither length, nor biomass of B. distachyon, but shoot and root elongation of B. napus were reduced from the lowest dose of Zn.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors:
T. Martinez
,
L. Cabrera
,
M. Navarrete
,
J. Garcia
,
P. Gonzalez
,
A. Ramirez
, and
U. Martinez

Abstract  

Gamma exposure rate and radon levels were measured in 75 single-family dwellings in Mexico City in order to correlate them with local environment. Radon monitoring was performed both indoors and outdoors using a continuous working level monitor for short-lived radon decay products; the gamma exposure rate was measured using CaSO4: Dy+PTFE. The results obtained show a log-normal distribution. The mean indoor radon concentration is lower than 45 Bq/m3 and the mean indoor gamma exposure rate was 11.29 R/h.

Restricted access
Journal of Radioanalytical and Nuclear Chemistry
Authors:
M. Solache-Ríos
,
I. García
,
V. Martínez-Miranda
,
P. Bosch
, and
S. Bulbulian

Abstract  

Co2+ ion exchange, at room temperature, from aqueous cobalt — sodium chloride solutions with NaY zeolite has been studied. The effect of contact time on the shape of the sorption curves of Co2+ using zeolite Y dehydrated at 600°C is similar to the one found in our previous work with a zeolite dehydrated at 150 °C. A fast sorption uptake is observed in which 1.8 meq of Na+ ions/g of zeolite are replaced by cobalt ions followed by a desorption process where the uptake decreases to 1.2 meq/g zeolite. The Co2+ sorption using zeolite Y dehydrated at 600 °C is increased when ethylenediamine solution is passed through the zeolite. The Co2+ sorption uptake, initially 2.0 meq/g, incrases to 2.8 meq/g of zeolite. This behavior is explained by the location and coordination of cobalt in zeolite Y sites. It is suggested that the highest uptake process is due to the blocking of zeolite sites by a Co complex compound.

Restricted access
Community Ecology
Authors:
J. Madrigal-González
,
J. García-Rodríguez
,
A. Puerto-Martín
,
B. Fernández-Santos
, and
P. Alonso-Rojo

In arid and semi-arid ecosystems, the presence of woody neighbours affects the existence of several herbaceous species by modifying critical aspects of the environment (e.g., soil humidity, nutrient content or light availability) beneath their canopies. Herbaceous species growing in the understory of Pinus pinaster may be distinct from those in open areas due to litter fall, light interception and changes in nutrient availability. We suggest that the overall effect of woody neighbours on herbaceous layer diversity may vary with the scale focus of analysis. To examine this hypothesis, we collected data on the abundance of herbaceous species in open pineland forests of the central Iberian Peninsula (Spain) using sample quadrats of 0.5 m × 0.5 m distributed beneath, at the edge, and outside the canopy of pines in a landscape composed of dunes and plains. The results of CCA ordination revealed significant spatial segregation of herbaceous species reflecting the occurrence of pines and dunes in the landscape. Nested ANOVA disclosed markedly lower species richness beneath the pines, particularly in the dune sites. Species richness partitioning showed higher pine-induced heterogeneity than expected from the sample-based randomized model, leading to significantly increased species richness at the patch level. Hence, the outcome of pine-induced effects on the herbaceous plant diversity is scale-dependent, negative if we focus on separate communities, but positive if the scale focus is extended to whole patches comprising the sum of communities beneath, at the edge, and outside pine tree canopies. These results emphasize the necessity of using various scale perspectives to clarify the different ways in which pines and other woody nurse species affect structure of herbaceous communities in semi-arid Mediterranean ecosystems.

Restricted access