Gap application results for adjacent electron beams treatment

Nowadays, electron beams from high-energy linear accelerators (LINAC) are widely used in a variety of radiotherapy treatments being suitable especially for superficial tumors. Since this sort of ionizing radiation has stopping power higher than photons, deeper and healthier tissues can be preserved. On the other hand, when applying adjacent electron beams, “hot” spots can be observed, due to penumbra and/or scattering, contributing to the increase of the absorbed dose in the target volume. In this sense, the objective of this work was to investigate the effects of parallel adjacent electron beams using the chemical dosimeter Fricke Xylenol Gel (FXG) and compare the experimental results with ones acquired using Monte Carlo simulation. Thus, 10 × 10, 15 × 15 and 20 × 20 cm² fields were irradiated with 5, 8 and 10 MeV electron beams applying different gap widths. The experimental results and the simulations indicated overdose values up to 40% from the prescribed one for the specific tumor. This demonstrates that specific gaps are necessary in the case of treatments with parallel adjacent electron beams in order to prevent overdoses in the depth of interest.     

Tridimensional quantitative porosity characterization of three set calcium silicate‐based repair cements for endodontic use

The aim of the this study was to quantitatively evaluate in three‐dimensional (3D), the porosity degree of three improved silicate‐based endodontic repair cements (iRoot BP Plus^®, Biodentine^®, and Ceramicrete) compared to a gold‐standard calcium silicate bioactive cement (Pro Root^® MTA). From each tested cement, four samples were prepared by a single operator following the manufacturer's instructions in terms of proportion, time, and mixing method, using cylindrical plastic split‐ring moulds. The moulds were lubricated and the mixed cements were inserted with the aid of a cement spatula. The samples were scanned using a compact micro‐CT device (Skyscan 1174, Bruker micro‐CT, Kontich, Belgium) and the projection images were reconstructed into cross‐sectional slices (NRecon v.1.6.9, Bruker micro‐CT). From the stack of images, 3D models were rendered and the porosity parameters of each tested material were obtained after threshold definition by comparison with standard porosity values of Biodentine^®. No statistically significant differences in the porosity parameters among the different materials were seen. Regarding total porosity, iRoot BP Plus^® showed a higher percentage of total porosity (9.58%), followed by Biodentine^® (7.09%), Pro Root^® MTA (6.63%), and Ceramicrete (5.91%). Regarding closed porosity, Biodentine^® presented a slight increase in these numbers compared to the other sealers. No significant difference in porosity between iRoot BP Plus^®, Biodentine^®, and Ceramicrete were seen. In addition, no significant difference in porosity between the new calcium silicate‐containing repair cements and the gold‐standard MTA were found. Microsc. Res. Tech., 76:1093–1098, 2013. © 2013 Wiley Periodicals, Inc.     

Soil phosphorus distribution in sequentially extracted fractions in tropical coffee-agroecosystems in the Atlantic Forest biome,Southeastern Brazil

Phosphorus (P) deficiency is one of the most important constraints to food production, particularly in tropical Oxisols. This study aimed to characterize the inorganic and organic P (Pi and Po) fractions in the soil in three smallholding coffee cultivation fields managed under either agroforestry (AGF) or full sun (FSC) agroecosystems. The work was carried out in areas situated at the municipalities of Divino and Araponga in the Zona da Mata in the state of Minas Gerais, southeastern Brazil. Soil P forms including H₂O–Pi; NaHCO₃–Pi,Po; NaOH–Pi,Po; diluted HCl–Pi; concentrate HCl–Pi,Po and Residual-P were sequentially extracted in samples from 0 to 5 and 5 to 10-cm soil layers. Together, H₂O–Pi and NaHCO₃–Pi accounted on average for only 4% of soil total P in the cultivated soils. HClconc.-Pi ranged from 142.8 to 372.4 mg kg⁻¹ being the predominant Pi fraction. AGF systems promoted an increment of 8% in the NaHCO₃–Po fraction in relation to the FSC systems in the upper soil layer. The AGF systems increased HClconc.-Po pool in relation to the FSC systems in Divino and Araponga(I) soils, indicating that agroforestry is an important management strategy to increase bioavailable P and for the maintenance of organic P pool. The distribution of inorganic and organic P pools varied among the different study sites, showing that P cycling depends on the inherent characteristic of each agroecosystem. The availability of P to plants in coffee-agroforestry fields is directly associated with the cycling of the organic P pool.     

Environmental impact of mining activities in the Lousal area (Portugal): chemical and diatom characterization of metal-contaminated stream sediments and surface water of Corona stream

Lousal mine is a typical “abandoned mine” with all sorts of problems as consequence of the cessation of the mining activity and lack of infrastructure maintenance. The mine is closed at present, but the heavy metal enriched tailings remain at the surface in oxidizing conditions. Surface water and stream sediments revealed much higher concentrations than the local geochemical background values, which the “Contaminated Sediment Standing Team” classifies as very toxic. High concentrations of Cu, Pb, Zn, As, Cd and Hg occurred within the stream sediments downstream of the tailings sites (up to: 817 mg kg⁻¹ As, 6.7 mg kg⁻¹ Cd, 1568 mg kg⁻¹ Cu, 1059 mg kg⁻¹ Pb, 82.4 mg kg⁻¹ Sb, 4373 mg kg⁻¹ Zn). The AMD waters showed values of pH ranging from 1.9 to 2.9 and concentrations of 9249 to 20,700 mg L⁻¹ SO₄⁻², 959 to 4830 mg L⁻¹ Fe and 136 to 624 mg L⁻¹ Al. Meanwhile, the acid effluents and mixed stream waters also carried high contents of SO₄^2−, Fe, Al, Cu, Pb, Zn, Cd, and As, generally exceeding the Fresh Water Aquatic Life Acute Criteria. Negative impacts in the diatom communities growing at different sites along a strong metal pollution gradient were shown through Canonical Correspondence Analysis: in the sites influenced by Acid Mine Drainage (AMD), the dominant taxon was Achnanthidium minutissimum. However, Pinnularia acoricola was the dominant species when the environmental conditions were extremely adverse: very low pH and high metal concentrations (sites 2 and 3). Teratological forms of Achnanthidium minutissimum (Kützing) Czarnecki, Brachysira vitrea (Grunow) Ross in Hartley, Fragilaria rumpens (Kützing) G. W. F. Carlson and Nitzschia hantzschiana Rabenhorst were found. A morphometric study of B. vitrea showed that a decrease in size was evident at the most contaminated sites. These results are evidence of metal and acidic pollution.     

TEM Characterization of HgCdTe/CdTe Grown on GaAs(211)B Substrates

A microstructural study of HgCdTe/CdTe/GaAs(211)B and CdTe/GaAs(211)B heterostructures grown using molecular beam epitaxy (MBE) was carried out using transmission electron microscopy and small-probe microanalysis. High-quality MBE-grown CdTe on GaAs(211)B substrates was demonstrated to be a viable composite substrate platform for HgCdTe growth. In addition, analysis of interfacial misfit dislocations and residual strain showed that the CdTe/GaAs interface was fully relaxed except in localized regions where GaAs surface polishing had caused small pits. In the case of HgCdTe/CdTe/GaAs(211)B, the use of thin HgTe buffer layers between HgCdTe and CdTe for improving the HgCdTe crystal quality was also investigated.     

Preparation and Study of Bismuth Rare-Earth Tungstate Composite Screen-Printed Thick Films

In this paper, we report the microstructural and dielectric properties of bismuth rare-earth tungstate composite screen-printed thick films (BiGd_1?X Nd _X WO₆, BiGd_1?X Y _X WO₆, and BiY_1?X Nd _X WO₆). The crystal structure of BiREWO₆ (RE = Gd, Nd, and Y) can be associated with the Bi₂WO₆ perovskite structure. It was observed that the crystalline structure was attributed to a monoclinic phase with space group A12/m1. BiYWO₆ and BiY_0.5Gd_0.5WO₆ films showed characteristics of the dielectric relaxation phenomenon. The thick films exhibited moderate dielectric permittivity (ε _r′) values from 10 to 42. The results showed that the obtained ε _r′ values for films can be useful for capacitor applications and certainly for microelectronics and microwave devices (mobile phones, for example), where miniaturization of devices is crucial.     

Analysis of Mesa Dislocation Gettering in HgCdTe/CdTe/Si(211) by Scanning Transmission Electron Microscopy

Due to its strong infrared absorption and variable band-gap, HgCdTe is the ideal detector material for high-performance infrared focal-plane arrays (IRFPAs). Next-generation IRFPAs will utilize dual-color high-definition formats on large-area substrates such as Si or GaAs. However, heteroepitaxial growth on these substrates is plagued by high densities of lattice-mismatch-induced threading dislocations (TDs) that ultimately reduce IRFPA operability. Previously we demonstrated a postgrowth technique with the potential to eliminate or move TDs such that they have less impact on detector operability. In this technique, highly reticulated mesa structures are produced in as-grown HgCdTe epilayers, and then subjected to thermal cycle annealing. To fully exploit this technique, better understanding of the inherent mechanism is required. In this work, we employ scanning transmission electron microscopy (STEM) analysis of HgCdTe/CdTe/Si(211) samples prepared by focused ion beam milling. A key factor is the use of defect-decorated samples, which allows for a correlation of etch pits observed on the surface with underlying dislocation segments viewed in cross-section STEM images. We perform an analysis of these dislocations in terms of the general distribution, density, and mobility at various locations within the mesa structures. Based on our observations, we suggest factors that contribute to the underlying mechanism for dislocation gettering.     

B-Fe-U Phase Diagram

The liquidus projection of the U-rich corner of the B-Fe-U phase diagram is proposed based on X-ray powder diffraction measurements, differential thermal analysis, and scanning electron microscopy observations complemented with energy- and wavelength-dispersive X-ray spectroscopies. Two ternary reactions in this U-rich region were observed and their approximate temperatures were established. In addition, an overview of the complete phase diagram is given, including the liquidus projection; isothermal sections at 1053 K, 1223 K, and 1373 K (780 °C, 950 °C, and 1100 °C); and a U:(Fe,B) = 1:5 isopleth.     

Hygrothermal and Stacking Sequence Effects on Carbon Epoxy Composites with Molded Edges

Moisture and high temperature may cause a variety of effects on the mechanical and thermophysical properties of polymeric composites. The diffusion of moisture in the laminate occurs primarily by capillarity until a state of equilibrium is reached. Moisture affects the matrix and the fiber/matrix interface. The stacking sequence and the free edge finishing may affect the laminate tensile strength causing a free edge delamination; they can also affect the moisture absorption process. Laminates produced with molded edges do not require machining operations for the trimming and finishing of the free edges causing a gain in productivity. However, the mechanical behavior of laminates with molded edges saturated with moisture has not been characterized. This work presents a comparative study of the tensile strength of cross ply laminates with molded and machined edges under dry condition and saturated with moisture.     

Post-treatment with high-power lasers to improve bond strength of adhesive systems to bleached dentin

To assess the effect of Er:YAG and diode lasers on the shear bond strength (SBS) of adhesive systems to bovine dentin submitted to bleaching with a high concentration agent. One hundred and twenty bovine dentin fragments were used. Fragments were distributed into 12 groups (n = 10) considering the bleaching (present or not), surface post-treatment (untreated, Er:YAG laser or diode laser) and adhesive system (total-etching or self-etching). Specimens received two applications of 38% hydrogen peroxide. Er:YAG laser (2940 nm, 200 mJ, 4 Hz) and diode laser (980 nm, 1.5 W) were applied for 15 s on bleached dentin surface. Restoration was performed with resin using split matrix. Specimens were submitted to SBS test and data (MPa) were analyzed by ANOVA and Tukey’s test (α = 0.05). SBS of bleached specimens decreased in comparison with non-bleached (p < 0.05). The highest values were obtained for the post-treatment with Er:YAG laser (p < 0.05). Total-etching adhesive was superior to self-etching system (p < 0.05). The irradiation of bleached dentin with Er:YAG laser followed by the application of the total-etching adhesive had similar SBS to unbleached dentin with no post-treatment (control) (p > 0.05). Er:YAG laser post-treatment followed by the total-etching adhesive system improve the bond strength of restorative material to bleached dentin.