Structural Effect of Potassium Sulfamate on Synthesis of Ammonium Dinitramide

Potassium sulfamate (PS) is an efficient starting material for the nitration reaction used in the synthesis of ammonium dinitramide (ADN), which is an environmentally friendly high-energy oxidizer for propellants that does not release chlorine-based compounds. PS is a core structure to form dinitramide, -N(NO₂)₂, by taking NO₂^? from nitric acid. In this work, five test batches of PS were prepared using a few solvents including ethanol, methanol, acetone, isopropanol, and their mixtures. The lab-made PSs matched well with the commercial PS in terms of the chemical structure. The use of acetone led to a high recovery of PS up to 97 w/w% and ultimately contributed to the formation of high-purity and (99.2%) and a high yield (57.3%) that are greater than those for commercial PS (87.3% purity and 31.3% yield). Therefore, we proved that the crystallinity and homogeneity of PS influenced the properties of ADN and the synthesis efficiency.     

Short‐term load forecasting based on support vector regression and load profiling

The article proposes a methodology to forecast the electric load for the 24 h of the following day based on support vector regression. The study considers 24 distinct models, one for each predicted hour, where each individual model is treated independently. Its objective is to find the optimal combination of support vector machine parameters that could generalize low forecasting errors, using simulated annealing as a metaheuristic. The adopted methodology is compared to concurrent methods based on neural networks when applied to a simulated load diagram (to illustrate a distribution feeder supplying a sample of 740 consumers). The results have proven its effectiveness with mean absolute percentage errors being less than 5% for testing samples. The study also focuses on evaluating the potential benefits of adopting load profiling information as input in support vector regression, giving a consistent proof of its importance. Copyright © 2013 John Wiley & Sons, Ltd.     

Structural Data on the Periplasmic Aldehyde Oxidoreductase PaoABC from Escherichia coli: SAXS and Preliminary X-ray Crystallography Analysis

The periplasmic aldehyde oxidoreductase PaoABC from Escherichia coli is a molybdenum enzyme involved in detoxification of aldehydes in the cell. It is an example of an αβγ heterotrimeric enzyme of the xanthine oxidase family of enzymes which does not dimerize via its molybdenum cofactor binding domain. In order to structurally characterize PaoABC, X-ray crystallography and small angle X-ray scattering (SAXS) have been carried out. The protein crystallizes in the presence of 20% (w/v) polyethylene glycol 3350 using the hanging-drop vapour diffusion method. Although crystals were initially twinned, several experiments were done to overcome twinning and lowering the crystallization temperature (293 K to 277 K) was the solution to the problem. The non-twinned crystals used to solve the structure diffract X-rays to beyond 1.80 Å and belong to the C2 space group, with cell parameters a = 109.42 Å, b = 78.08 Å, c = 151.77 Å, β = 99.77°, and one molecule in the asymmetric unit. A molecular replacement solution was found for each subunit separately, using several proteins as search models. SAXS data of PaoABC were also collected showing that, in solution, the protein is also an αβγ heterotrimer.     

Simultaneous Microwave Extraction and Separation of Volatile and Non-Volatile Organic Compounds of Boldo Leaves. From Lab to Industrial Scale

Microwave extraction and separation has been used to increase the concentration of the extract compared to the conventional method with the same solid/liquid ratio, reducing extraction time and separate at the same time Volatile Organic Compounds (VOC) from non-Volatile Organic Compounds (NVOC) of boldo leaves. As preliminary study, a response surface method has been used to optimize the extraction of soluble material and the separation of VOC from the plant in laboratory scale. The results from the statistical analysis revealed that the optimized conditions were: microwave power 200 W, extraction time 56 min and solid liquid ratio of 7.5% of plants in water. Lab scale optimized microwave method is compared to conventional distillation, and requires a power/mass ratio of 0.4 W/g of water engaged. This power/mass ratio is kept in order to upscale from lab to pilot plant.     

The relationship between the chemical structure and thermal conversion temperatures of thermally rearranged (TR) polymers

An attempt was made to elucidate the relationship between chemical structure, in terms of glass transition temperature (T_g), and conversion temperature (T_TR) of thermally rearranged polybenzoxazole membranes, by analyzing DSC and TGA data for a total of 15 sets of o-hydroxypolyimides and copolyimides, derived from two experimental and four commercial structurally different diamines, as well as four different dianhydride monomers. Our research revealed that T_TR was influenced by chain ridigity of o-hydroxypolyimides, and exhibited a linear relationship with T_g. Therefore, structure and thermal property of o-hydroxypolyimide should be considered when studying TR polymers to determine thermal conversion to polybenzoxazole.     

Generalized Hermitian Radial Basis Functions Implicits from polygonal mesh constraints

In this work we investigate a generalized interpolation approach using radial basis functions to reconstruct implicit surfaces from polygonal meshes. With this method, the user can define with great flexibility three sets of constraint interpolants: points, normals, and tangents; allowing to balance computational complexity, precision, and feature modeling. Furthermore, this flexibility makes possible to avoid untrustworthy information, such as normals estimated on triangles with bad aspect ratio. We present results of the method for applications related to the problem of modeling 2D curves from polygons and 3D surfaces from polygonal meshes. We also apply the method to problems involving subdivision surfaces and front-tracking of moving boundaries. Finally, as our technique generalizes the recently proposed HRBF Implicits technique, comparisons with this approach are also conducted.     

Oxygen-dependent enhancement of hydrogen production by engineering bacterial hemoglobin in Escherichia coli

H₂ production under aerobic conditions has been proposed as an alternative method to overcome the fundamentally low yield of H₂ production by fermentative bacteria by maximizing the number of electrons that are available for H₂. Here, we engineered Vitreoscilla hemoglobin (VHb) in Escherichia coli to study the effects of this versatile oxygen (O₂)-binding protein on oxic H₂ production in a closed batch system that was supplemented with glucose. The H₂ yields that were obtained with the VHb-expressing E. coli were greatly enhanced in comparison to the negative control cells in culture that started with high O₂ tensions. The formate hydrogen lyase (FHL) activity of oxically cultured, VHb-expressing cells was also much higher than that of the negative control cells. Through inhibitor studies and time-course experiments, VHb was shown to contribute to the improved H₂ yield primarily by increasing the efficiency of cellular metabolism during the aerobic phase before the onset of H₂ production and not by working as an O₂-scavenger during H₂ production. This new approach allowed more substrate to remain to be further utilized for the production of more H₂ from limited resources. We expect that VHb can be successfully engineered in potential aerobic H₂-producing microbial systems to enhance the overall H₂ production yield. In addition, the remarkably high FHL activity of oxically grown, VHb-expressing cells may make this engineered strain an attractive whole-cell biocatalyst for converting formate to H₂.     

Study on the reduction of flow-induced noise through the suppression of vortex shedding at rotating disk edge

We conducted a computational analysis to better understand the coherent flow structure that arises when the rotation of a disk drive generates flow-induced noise. We set the flow domain to be similar to the actual shape of the flow in Blu-ray disks and examined the phenomena of vortex generation and shedding at the disk edge, focusing on the source of the noise. Our results showed that disk edge vortex shedding was the primary cause of disk-drive-flow-induced noise; therefore, we investigated the technique of lowering the intensity of a disk edge vortex to reduce this noise. We attached concentric projections onto the cover of the disk to suppress the flow returning to the center of the disk through the gap between the disk and cover. Noise induced by disk rotation was reduced by 2.68 dB at the optimal setting: projections 0.002 m wide and 0.006 m width between the projections (and thus a ratio of 1: 3).     

Characterization of a water-based paint for corrosion protection

Corrosion of steel rebars in reinforced concrete is one of the major problems in the construction industry. Carbonation reactions of concrete with carbon dioxide and, mainly, the chloride salts action are the main causes responsible for concrete degradation. Protective coatings help to improve the durability of concrete structures by acting as a physical barrier against the corrosion agents. Waterborne paints are usually used for concrete protection rather than solvent-based paints since they are less pollutant. The aim of this work is to investigate the influence of the pore size and porosity on the permeability of the paints films toward sodium chloride. Three characterization methods from membrane science were implemented to characterize paint coatings. The time-lag method was used to determine the permeability toward the sodium chloride and toward helium and argon, these for approximately 100% relative humidity. From the seven waterborne paints formulated, only one was found to be suitable for surface protection of reinforced concrete, since its permeability toward NaCl was smaller than 10⁻¹⁴ m² s⁻¹, the threshold value required by National Laboratory of Civil Engineering (LNEC) in Portugal. For the formulated paints, it was observed that the average pore size correlates well with the permeability toward sodium chloride. This is an important result since obtaining the permeability toward sodium chloride of corrosion protective paints is very time consuming, while the average pore size can be obtained in a much shorter time.