Finite element simulation of arcuates for astigmatism correction

In order to simulate the corneal incisions used to correct astigmatism, a three-dimensional finite element model was generated from a simplified geometry of the anterior half of the ocular globe. A hyperelastic constitutive behavior was assumed for cornea, limbus and sclera, which are collagenous materials with a fiber structure. Due to the preferred orientations of the collagen fibrils, corneal and limbal tissues were considered anisotropic, whereas the sclera was simplified to an isotropic one assuming that fibrils are randomly disposed. The reference configuration, which includes the initial strain distribution that balances the intraocular pressure, is obtained by an iterative process. Then the incisions are simulated. The final positions of the nodes belonging to the incised meridian and to the perpendicular one are fitted by both radii of curvature, which are used to calculate the optical power. The simulated incisions were those specified by Lindstrom's nomogram [Chu, Y., Hardten, D., Lindquist, T., Lindstrom, R., 2005. Astigmatic keratotomy. Duane's Ophthalmology. Lippincott Williams and Wilkins, Philadelphia] to achieve 1.5, 2.25, 3.0, 4.5 and 6.0D of astigmatic change, using the next values for the parameters: length of 45 degrees , 60 degrees and 90 degrees , an optical zone of 6mm, single or paired incisions. The model gives results similar to those in Lindstrom's nomogram [Chu et al., 2005] and can be considered a useful tool to plan and simulate refractive surgery by predicting the outcomes of different sorts of incisions and to optimize the values for the parameters involved: depth, length, position.     

Condensing and fluidizing effects of ganglioside GM1 on phospholipid films

Mixed monolayers of the ganglioside G_M1 and the lipid dipalmitoylphosphatidlycholine (DPPC) at air-water and solid-air interfaces were investigated using various biophysical techniques to ascertain the location and phase behavior of the ganglioside molecules in a mixed membrane. The effects induced by G_M1 on the mean molecular area of the binary mixtures and the phase behavior of DPPC were followed for G_M1 concentrations ranging from 5 to 70 mol %. Surface pressure isotherms and fluorescence microscopy imaging of domain formation indicate that at low concentrations of G_M1 (<25 mol %), the monolayer becomes continually more condensed than DPPC upon further addition of ganglioside. At higher G_M1 concentrations (>25 mol %), the mixed monolayer becomes more expanded or fluid-like. After deposition onto a solid substrate, atomic force microscopy imaging of these lipid monolayers showed that G_M1 and DPPC pack cooperatively in the condensed phase domain to form geometrically packed complexes that are more ordered than either individual component as evidenced by a more extended total height of the complex arising from a well-packed hydrocarbon tail region. Grazing incidence x-ray diffraction on the DPPC/G_M1 binary mixture provides evidence that ordering can emerge when two otherwise fluid components are mixed together. The addition of G_M1 to DPPC gives rise to a unit cell that differs from that of a pure DPPC monolayer. To determine the region of the G_M1 molecule that interacts with the DPPC molecule and causes condensation and subsequent expansion of the monolayer, surface pressure isotherms were obtained with molecules modeling the backbone or headgroup portions of the G_M1 molecule. The observed concentration-dependent condensing and fluidizing effects are specific to the rigid, sugar headgroup portion of the G_M1 molecule.     

Spectral sensitivities of photoreceptors and their role in colour discrimination in the green-backed firecrown hummingbird (<Emphasis Type="Italic">Sephanoides sephaniodes</Emphasis>)

We studied the photopic spectral sensitivity in the green-backed firecrown, Sephanoides sephaniodes, a South American hummingbird, and its possible ecological relationship with preferred flowers and body colouration. Avian colour vision is in general tetrachromatic with at least four types of cones, which vary in sensitivity from the near ultraviolet (UV) to the red wavelength range. Hummingbirds represent an important family of birds, yet little is known about their eye sensitivity, especially about the role of photoreceptors and their oil droplet complements. The photopic electroretinogram shows a main sensitivity peak at 560 nm and a secondary peak in the UV, and may be explained by the presence of four single cones (lambda (max) at ~370, 440, 508 and 560 nm), and a double cone (lambda (max) at 560 nm) screened by oil droplets. The flowers preferred by the firecrown are those in which the red-green wavelength region predominates and have higher contrast than other flowers. The crown plumage of males is highly iridescent in the red wavelength range (peak at 650 nm) and UV; when plotted in a high-dimensional tetrachromatic space, it falls in a "red + UV" purple hue line, suggesting a potential significant communication signal for sexual differentiation.     

Determinants of lepidopteran community composition and species diversity in eastern deciduous forests: roles of season, eco-region and patch size

Ecologists have long recognized that factors operating at both local and regional scales influence whether a given species occurs in an ecological community. The relative roles of variables manifested at local and regional scales on community structure, however, remain an unexplored issue for many faunas. To address this question, we compared the community composition and species diversity of forest Lepidoptera between (i) large forest tracts in historically glaciated and unglaciated regions of the eastern deciduous forest in North America, and (ii) large and small forest patches within a highly fragmented forest landscape. Specifically, we used seasonally stratified sampling to test whether regional and local differences in moth communities were related to variation in stand structure and floristic composition. At the local scale, we tested three alternative hypotheses describing the effects of patch size on moth species richness: species impoverishment, species replacement, or species supplementation. Cluster analysis revealed significant compositional differences in moth communities sampled between (i) early and late seasons, (ii) glaciated and unglaciated forest eco‐regions, and (iii) large and small forest patches. Canonical correspondence analysis suggested that floristic variation at regional scales had a greater role in determining moth community composition than local vegetation or patch‐size effects. Species richness was higher in the glaciated North Central Tillplain, and was attributable to a more diverse herbaceous feeding moth assemblage. Finally, we found evidence that both species impoverishment and species replacement processes structure the moth fauna of small woodlots; the richness of moths with larvae that feed on woody plants decreased with patch area, but herbaceous feeding species increased in diversity in smaller patches. Thus, our results suggest that local and regional differences in moth community structure are mediated by differences in host‐plant resources attributable to regional biogeographic history and local differences in patch size. Because community composition appeared to be more sensitive to environmental variation than species richness, we suggest that monitoring lepidopteran species diversity in forests will not detect significant changes in species composition due to environmental change.     

Adsorption of ethylenediaminetetraacetic dianhydride modified oxalate decarboxylase on calcium oxalate

We used ethylenediaminetetraacetic acid dianhydride (EDTAD) to modify oxalate decarboxylase (OXDC) to improve its adsorption on calcium oxalate stones. The modified sites were identified by Ultra performance liquid chromatography-mass spectrometry (UPLC-MS) and the adsorption mechanism of the EDTAD-modified OXDC on calcium oxalate (CaOx) was investigated. We investigated adsorption time, initial enzyme concentration, temperature and solution pH on the adsorption process. Data were analyzed using kinetics, thermodynamics and isotherm adsorption models. UPLC-MS showed that EDTAD was attached to OXDC covalently and suggested that the chemical modification occurred at both the free amino of the side chain and the α-NH₂ of the peptide. The adsorption capacity of the EDTAD-OXDC on calcium oxalate was 53.37% greater than that of OXDC at the initial enzyme concentration of 5 mg/ml, pH = 7.0, at 37° C. The modified enzyme (EDTAD-OXDC) demonstrated improved oxalate degradation activity at pH 4.5?6.0. Kinetic data fitting analysis suggested a pseudo second order kinetic model. Estimates of the thermodynamic parameters including ΔG⁰, ΔH⁰ and ΔS⁰ of the adsorption process showed it to be feasible, spontaneous and endothermic. Isotherm data fitting analysis indicated that the adsorption process is reduced to monolayer adsorption at a low enzyme concentration and to multilayer adsorption at a high enzyme concentration. It may be possible to apply OXDC to degradation of calcium oxalate stones.     

Novel application of magnetic nano-carbon composite as redox mediator in the reductive biodegradation of iopromide in anaerobic continuous systems

The redox-mediating capacity of magnetic reduced graphene oxide nanosacks (MNS) to promote the reductive biodegradation of the halogenated pollutant, iopromide (IOP), was tested. Experiments were performed using glucose as electron donor in an upflow anaerobic sludge blanket (UASB) reactor under methanogenic conditions. Higher removal efficiency of IOP in the UASB reactor supplied with MNS as redox mediator was observed as compared with the control reactor lacking MNS. Results showed 82% of IOP removal efficiency under steady state conditions in the UASB reactor enriched with MNS, while the reactor control showed IOP removal efficiency of 51%. The precise microbial transformation pathway of IOP was elucidated by high-performance liquid chromatography coupled to mass spectroscopy (HPLC-MS) analysis. Biotransformation by-products with lower molecular weight than IOP molecule were identified in the reactor supplied with MNS, which were not detected in the reactor control, indicating the contribution of these magnetic nano-carbon composites in the redox conversion of this halogenated pollutant. Reductive reactions of IOP favored by MNS led to complete dehalogenation of the benzene ring and partial rupture of side chains of this pollutant, which is the first step towards its complete biodegradation. Possible reductive mechanisms that took place in the biodegradation of IOP were stated. Finally, the novel and successful application of magnetic graphene composites in a continuous bioreactor to enhance the microbial transformation of IOP was demonstrated.

     

Effects of long-term ingestion of white tea on oxidation produced by aging and acute oxidative damage in rats

The infusion tea extracted from the leaves of the plant Camellia sinensis can be used in the prevention of cancer, cardiovascular and neurodegenerative diseases, and aging, while adriamycin (ADR) is an anticancer drug that increases oxidative stress in cells. The present study evaluated the protective effect of the long-term consumption of white tea used at two different doses against the oxidative stress produced by aging and acute oxidation caused ADR treatment. At wearing, rats received distilled water (control), or 0.15 (dose 1) or 0.45 mg (dose 2) of solid tea extract/kilogram body weight in their drink. At 12 months, about half of the rats of each group were injected with a bolus of ADR, and six rats of the control group with an injection of saline solution and sacrificed. The rest of the animals continued in their cages until 24 months of age, when they were sacrificed. Lipid and protein oxidation of liver and brain microsomes was analyzed by measuring hydroperoxide and carbonyl levels. White tea consumption for 12 months at a non-pharmacological dose was seen to reverse the oxidative damage caused by ADR in both liver and brain, while the consumption of white tea for 20 months at a non-pharmacological dose had no effect on carbonyl or hydroperoxides in these tissues. The long-term ingestion of white tea protected tissues from acute oxidative stress but did not affect chronic oxidative agents such aging.