Time filter

Source Type

Mexico City, Mexico

Klanian M.G.,Marista University
Journal of Experimental Marine Biology and Ecology | Year: 2013

Dormancy is a state of reduced metabolic activity adopted by organisms during periods of environmental stress, including physiological and biochemical adaptations. In this study, the physiological and immunological statuses of two populations of Isostichopus badionotus with different times of dormancy (B12. =. 12. months and B24. =. 24. months) are compared with a physiologically active population (BC. =. control). The coelomic liquid (CL) of 18 organisms from each batch (B24, B12, and BC) was used to perform the biochemical analysis. The body volume of dormant I. badionotus decreased exponentially as time passed under stable conditions. The total protein of B24 (9.26. mg/ml) was lower than that of B12 (15.64. mg/ml) and BC (13.21. mg/ml). Carbohydrate content was similar in both groups (B24 and B12) of dormant I. badionotus but lower than that of the control (6.93. mg/ml). The cholesterol content of B12 (0.40. mg/ml) was significantly higher than the similar cholesterol levels of B24 and the control. Activities of superoxide dismutase (T-SOD), catalase (CAT), and glutathione peroxidase (GPx) were higher in B12 than in B24 and BC. Phenoloxidase was lower in dormant sea cucumbers than the control (37.3. U/ml). Dormancy for the B12 organisms appears to be a fairly light state, involving no physiological changes that cannot be rapidly reversed. In contrast, the B24 organisms showed deterioration of their antioxidant complex and low lipid and protein reserves after 48. months, suggesting that the return to an active state would be impossible. © 2013 Elsevier B.V.

Gullian-Klania M.,Marista University
Journal of Aquatic Animal Health | Year: 2013

The effect of long-term freshwater acclimation on the blood and plasma ion composition of Red Drum Sciaenops ocellatus was investigated with the goal of elucidating the necessity of ion remediation. Four replicates (n = 50) of freshwater-acclimated (FW) fish (1.6 ± 0.2 g) were raised in 25-m3 tanks supported by 140,000 L of recirculating water. Four replicates (n = 50) of seawater (SW) fish groups were placed in 40-m3 offshore cages at 32-35 psu. Blood was collected from 100 fish (FW = 578 ± 50 g; SW = 686 ± 45 g) of each group (FW, SW) after 8 months of rearing. During the grow-out phase, the survival of FW and SW fish was 57.5% and 92.2%, respectively. The water ion composition (mainly the Ca2 + /K + [43%] and Ca2 + /Mg2 + ratios [1%]) explained 56.6% of the plasmatic ion variability in the fish groups. Freshwater exposure produced significant reductions in osmolality and in several plasma indicators (Na +, Cl-1, and Mg2 +); the K + levels from FW fish were the most compromised parameter. The water Ca2 + /Na + ratio had a greater influence (44%) on the plasma chemistry parameters, mainly glucose and creatinine. Freshwater-acclimated fish had a higher percentage of hematocrit, hemoglobin, and red blood cells than SW fish, but the water quality explained only 12.5% of the blood parameter variability between the FW and SW groups. The results support the conclusion that Red Drum tolerates salinity variations and can adopt a relatively stable condition for short periods; however, the data suggest that Red Drum have only a limited ability to withstand a hyposmotic environment for long periods due to their limited ability in maintaining K + concentrations without external supplementation. Freshwater environments with high Ca2 + /Na +, Ca2 + /K +, and Ca2 + /Mg2 + ratios appear to be a chronic stress factor that should be considered in future experiments.

Torres-Acosta A.A.,Marista University
Concrete under Severe Conditions: Environment and Loading - Proceedings of the 6th International Conference on Concrete under Severe Conditions, CONSEC'10 | Year: 2010

This paper presents the result obtained from an experimental study that evaluated the efficacy of a controlled current system for accelerating corrosion of reinforced concrete elements. In the study, twenty four reinforced concrete beams (10 × 15 × 150 cm) were subjected to a nominal constant current density between 80 and 200 μA/cm 2 and was achieved using special circuitry. On the other hand, twenty eight reinforced concrete slabs (15 × 30 × 60 cm) were used for natural corrosion tests. All the specimens were cast with 3% chloride by weight of cement in either a localized or generalized region. The beams were placed in two different environments: constantly wet or dry. The slabs were placed in a constant dry laboratory environment only. Predicted metal loss using Faraday's Law in the accelerated specimens were compared against actual losses obtained by the gravimetric method. The correspondence between concrete crack propagation and/or pit depth and metal loss was also determined for both methods. Good correlation was obtained between Faradaic and gravimetric losses for both methods. No apparent difference between corrosion parameters (mass loss, crack opening and extension, pit depth) in accelerated and natural corrosion tests were observed, which support the use of such constant current accelerated method for remaining life forecasting. © 2010 Taylor & Francis Group, London.

Espinosa-Faller F.J.,Marista University | Conradson D.R.,Los Alamos National Laboratory | Riha S.C.,Colorado State University | Martucci M.B.,Los Alamos National Laboratory | And 5 more authors.
Journal of Physical Chemistry C | Year: 2014

A thorough structure determination has been performed on Cu2ZnSnS4 nanoparticles, a popular photovoltaic material, using neutron diffraction-to characterize the long-range average crystal structure-and X-ray absorption fine structure (XAFS) spectroscopy at the Cu, Zn, and Sn K-edges to elucidate the element-specific local structure. This is the first combined multiscale approach on nanoparticles of this material. The results indicate the presence of aperiodic disorder on the cation sites that is diminished by annealing. This disorder involves local lattice distortions around the crystallographic sites rather than the presence of interstitial atoms. It is most consistent with the known antisite substitutions that are integral to CZTS (referring to the ordering of the Cu, Zn, and Sn between planes). However, instead of being confined within single unit cells so as to maintain the crystallographic symmetry, periodicity, and homogeneity, the substitutional disorder appears to extend over larger regions consisting of multiple unit cells but still smaller than the physical dimensions of the nanoparticles. These results therefore imply the presence of nanoscale domains characterized by local fluctuations in composition that cause the individual domains to be enriched in certain metal ions and depleted in others. These will be mirrored by domains with the opposite fluctuations at other locations in the crystal so that the overall composition remains close to the stoichiometric Cu2ZnSnS4. This disorder is likely pronounced in these samples due to the relatively low temperature reaction (300 °C) and annealing (350 °C) conditions and can be expected to have a significant effect on the resulting physical properties of the material and its photovoltaic performance. © 2014 American Chemical Society.

Seijo J.C.,Marista University | Villanueva-Poot R.,Marista University | Charles A.,Saint Marys University, Halifax
Fisheries Research | Year: 2016

The impact of ocean acidification on fisheries is a relatively new issue facing decision-makers, and one for which very little empirical data is available to draw upon. This paper demonstrates how, despite the lack of knowledge, well-established methods of bioeconomic modelling and decision analysis can be applied to address the challenge. A decision support framework is developed, incorporating a dynamic age-structured bioeconomic model together with a set of decision tables applicable in the absence of known probabilities of future change. With such a model it is possible to trace ocean acidification as an additional stressor, specifically on fisheries targeting calcifier species, such as many high value mollusks. We do so by shifting growth and natural mortality parameters into time varying functions of ocean acidity (pH), as forecasted by climate scenarios reported by the Intergovernmental Panel on Climate Change (IPCC). Possible effects of ocean acidification on calcifier species with various life cycles were modeled beginning with initial biological parameters of the growth and mortality dynamic functions reflecting differences in individual growth, natural mortality and species longevity. The analysis illustrates how fishery outcomes depend on the extent of ocean acidification and the life cycle of calcifier species. Results also indicate that under uncertainty, there is value in taking precautionary management measures, such as reducing fishing intensity. © 2015 Elsevier B.V.

Discover hidden collaborations