Determining the influence of Itaipu Lake on thermal conditions for soybean development in adjacent lands.

Previous numerical simulations have suggested that the area adjacent to Itaipu Lake in Southern Brazil is significantly affecting the local thermal regime through development of a lake breeze. This has led to concerns that soybean growth and development, and consequently yield, has been affected by the creation of the artificial lake in this important agricultural region, but a systematic climatological study of the thermal effects of Itaipu Lake has not been conducted. The objectives of this study were to assess the spatial pattern of minimum and maximum air temperatures in a 10-km-wide area adjacent to Itaipu Lake as affected by distance from the water. Measurements were conducted over 3 years in seven transects along the shore of Itaipu Lake, with five weather stations placed in each transect. Phenological observations in soybean fields surrounding the weather stations were also conducted. Generalized additive models for location, scale, and shape (GAMLSS) analysis indicated no difference in the temperature time series as distance from water increased. Semivariograms showed that the random components in the air temperature were predominant and that there was no spatial structure to the signal. Wind direction measured over the three growing seasons demonstrated that, on average, the development of a lake breeze is limited to a few locations and a few hours of the day, supporting the temporal and spatial analysis. Phenological observations did not show differences in the timing of critical soybean stages. We suggest that the concerns that soybean development is potentially affected by the presence of Itaipu Lake are not supported by the thermal environment observed.

Superhydrophobic polyethylcyanoacrylate coatings. Contact area with water measured by Raman spectral images, contact angle and Cassie-Baxter model.

Apolar fibers wired into a mesh-like microstructure forming a coating with a contact angle larger than 160° and fabricated by polycyanoacrylate polymerization are described. Interconnected fibers with diameters measuring approximately 5 µm are formed by texturized linear or folded nanowires. The structure forming the deposited film occupies ~1.5% of the coating's top geometric area. This value agrees with the water/coating contact area given by the Cassie-Baxter contact-angle model (~1.5%). The spatial distribution of the surface in contact with water was determined by Raman spectral imaging (~1.5%) using the polycyanoacrylate lines and by scanning electron microscopy (~2.0%).

Nanotexturized polytetrafluoroethylene substrates formed by large crystalline nanofibrils in amorphous matrices.

Plastic deformation has proved to be an attractive tool for obtaining ultrafine grained and nanocrystalline metallic materials. A description of plastic deformation as a technique to create nanotexturized polytetrafluoroethylene substrates free of defects, such as pores or impurities, which has potential applications as templates for the oriented growth of organic and inorganic compounds, is presented here. The obtained morphology characterized by nanosized fibrils arrangements was revealed by atomic force microscopy. Nanofibrils with a width from 330 to 980 nm and lengths from 1.85 to 11 microm were observed on polytetrafluoroethylene substrates annealed at 330 degrees C and 390 degrees C, respectively. Wide angle X-ray scattering spectra for untreated and annealed samples show that there is a slight decrease in the amorphous component for samples annealed at 380 degrees C but not for samples annealed at 330 degrees C showing that the amorphous substrate matrix in little altered by the annealing. The pattern formation is associated with superficial polymeric domains that become large crystalline nanofibrils in an amorphous matrix.

Water molecule clusters measured at water/air interfaces using atomic force microscopy.

During the tip approach to hydrophobic surfaces like the water/air interface, the measured interaction force reveals a strong attraction with a range of approximately 250 nm at some points along the interface. The range of this force is approximately 100 times larger than the measured for gold (approximately 3 nm) and 10 times larger than the one for hydrophobic silicon surfaces (approximately 25 nm). At other points the interface exerts a medium range repulsive force growing stepwise as the tip approaches the interface plane, consequently the hydrophobic force is a strong function of position. To explain these results we propose a model where the force on the tip is associated with the exchange of a small volume of the interface with a dielectric permittivity epsilon(int) by the tip with a dielectric permittivity epsilon(tip). By assuming a oscillatory spatial dependence for the dielectric permittivity it is possible to fit the measured force profiles. This dielectric spatial variation was associated with the orientation of the water molecules arrangement in the interfacial region. Small nanosized hydrogen-bond connected cages of water molecules present in bulk water at the interface are oriented by the interfacial electric field generated by the water molecules broken bonds, one broken hydrogen bond out of every four. This interfacial field orients small clusters formed by approximately 100 water molecules into larger clusters (approximately 100 nm). In the limit of small (less than 5 nm thick) water molecule cages we have modeled the static dielectric permittivity (epsilon) as the average response of those cages. In these regions the dielectric permittivity for water/air interfaces decreases monotonically from the bulk value epsilon approximately 80 to approximately 2 at the interface. For regions filled with medium size cages, the tip senses the structure of each cage and the static dielectric permittivity is matched to the geometrical features of these cages sized approximately 25 to 40 nm. Interfacial electric energy density values were calculated using the electric field intensity and the dielectric permittivity obtained by the fitting of the experimental points. The integration of the electric energy density along the interfacial region gives a value of 0.072 J m(-2) for interfacial energy density for points where the hydrophobic force has a range of approximately 250 nm. Regions formed by various clusters result in lower values of the interfacial energy density.

Molecular arrangements of self-assembled surfactant films: characterization from atomic force microscopy data.

The adsorbed surfactant film molecular arrangement with thickness of approximately 5 nm is determined by measurements of the film dielectric permittivity. Before the advent of atomic force microscopy the dielectric permittivity was a macroscopic parameter, appropriate only for describing uniform environments since its profile was difficult to measure for local intermolecular interactions and its spatial distribution was frequently settled without experimental justification. Here, we show that atomic force microscopy made it possible to measure the dielectric permittivity profile in a scale below 5 nm for adsorbed layers of self-assembled surfactant films in water. The measured values of the film's dielectric permittivity and the film's thickness determine the compactness of the adsorbed film and consequently the presence of water molecules in the film and the conformal structure of the adsorbed molecules.

Interfacial water dielectric-permittivity-profile measurements using atomic force microscopy.

The arrangement of water molecules at charged aqueous interfaces is an important question in biology, electrochemistry, and geochemistry. Theoretical studies suggest that the molecules become arranged in several layers adjacent to a solid interface. Using atomic force microscopy we have measured the water dielectric-permittivity profile perpendicular to mica surfaces. The measured variable permittivity profile starting at epsilon approximately 4 at the interface and increasing to epsilon=80 about 10 nm from the surface suggests a reorientation of water molecule dipoles in the presence of the mica interfacial charge.

[Chronic active hepatitis and possible relationship with immunosuppressive therapy]. / Hepatite crônica ativa e possível relação com terapia imunossupressora.

A 54-year-old man with Chagas cardiomyopathy that was submitted to a heart transplantation and five months later presented a progressive increase in liver enzymes. Diagnosis of chronic active hepatitis was confirmed by histopathologic studies. A transitory interruption of treatment with azathioprine and the posterior re-introduction of small doses, as well as the use of lesser amounts of cyclosporin-A improved the clinical and laboratory pictures. Despite several investigations the pathogenesis of hepatitis remained undetermined, although some type of drug injury was presumed to be involved. The eventual role of viruses as the primary inciting event could not be completely ruled out.