Solution of sparse quasi-square rectangular systems by Gaussian elimination

We present a general method for the linear least-squares solutionof overdetermined and underdetermined systems. The method isparticularly efficient when the coefficient matrix is quasi-square,that is when the number of rows and number of columns is almostthe same. The numerical methods for linear least-squares problemsand minimum-norm solutions do not generally take account ofthis special characteristic. The proposed method is based onLU factorization of the original quasi-square matrix A, assumingthat A has full rank. In the overdetermined case, the LU factorsare used to compute a basis for the null space of A^T. The right-handside vector b is then projected onto this subspace and the least-squaressolution is obtained from the solution of this reduced problem.In the case of underdetermined systems, the desired solutionis again obtained through the solution of a reduced system.The use of this method may lead to important savings in computationaltime for both dense and sparse matrices. It is also shown inthe paper that, even in cases where the matrices are quite small,sparse solvers perform better than dense solvers. Some practicalexamples that illustrate the use of the method are included.     

3,17‐Dioxoandrost‐4‐en‐4‐yl acetate

The title compound, C₂₁H₂₈O₄, has a 4‐acetoxy substituent positioned on the steroid α face. The six‐membered ring A assumes a conformation intermediate between 1α,2β‐half chair and 1α‐sofa. A long Csp³—Csp³ bond is observed in ring B and reproduced in quantum‐mechanical ab initio calculations of the isolated molecule using a molecular‐orbital Hartree–Fock method. Cohesion of the crystal can be attributed to van der Waals interactions and weak C—H...O hydrogen bonds.     

Study of phenolic resin/EVA blends by thermal analysis

The properties of polymeric blends originate from the synergistic association of their components. In this investigation, phenolic resins obtained by the reaction of cashew-nut shell liquid (CNSL) and aldehyde are used in several applications. Mixtures of CNSL with industrial reject ethylene-co-vinyl acetate (EVA reject) were prepared with an EVA reject content up to 70%. The thermal compatibility and stability were evaluated by means of thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). For blends containing a high percentage of EVA reject, the TG curves clearly show two decomposition stages, one at 350C and the other at 450C (onset 467C). The DIG curves of the blend containing 70% CNSL exhibit decomposition at 240C. The DSC curves show that the samples containing a high percentage of EVA reject are incompatible, withT _g values around –30C.The authors would like to thank PETROBRAS/CENPES/DIQUIM for the NMR facilities and thermal measurements.     

Determination of uranium and impurities in Portuguese yellow-cakes

A method is described for separation of impurities in uranium yellow cakes from Urgeiriça (Portugal). The trace metals are separated and concentrated by solvent extraction from 6M nitric acid into 100% TBP. The raffinate is then analysed directly by flame spectrometry. Uranium is determined gravimetrically after stripping of the organic phase. The method is fast and economic, and the results are in good agreement with those obtained by specific methods for each element after prior separation of uranium by precipitation or solvent extraction with various solvents.     

Recent Strategies and Applications for l-Asparaginase Confinement

l-asparaginase (ASNase, EC 3.5.1.1) is an aminohydrolase enzyme with important uses in the therapeutic/pharmaceutical and food industries. Its main applications are as an anticancer drug, mostly for acute lymphoblastic leukaemia (ALL) treatment, and in acrylamide reduction when starch-rich foods are cooked at temperatures above 100 °C. Its use as a biosensor for asparagine in both industries has also been reported. However, there are certain challenges associated with ASNase applications. Depending on the ASNase source, the major challenges of its pharmaceutical application are the hypersensitivity reactions that it causes in ALL patients and its short half-life and fast plasma clearance in the blood system by native proteases. In addition, ASNase is generally unstable and it is a thermolabile enzyme, which also hinders its application in the food sector. These drawbacks have been overcome by the ASNase confinement in different (nano)materials through distinct techniques, such as physical adsorption, covalent attachment and entrapment. Overall, this review describes the most recent strategies reported for ASNase confinement in numerous (nano)materials, highlighting its improved properties, especially specificity, half-life enhancement and thermal and operational stability improvement, allowing its reuse, increased proteolysis resistance and immunogenicity elimination. The most recent applications of confined ASNase in nanomaterials are reviewed for the first time, simultaneously providing prospects in the described fields of application.     

Comparison between capillary electrophoresis and liquid chromatography for the determination of diclofenac sodium in a pharmaceutical tablet

Two novel analytical methodologies using capillary electrophoresis (CE) and liquid chromatography (LC) were developed and compared for the determination of diclofenac sodium in commercial and simulated tablet formulations. The CE analysis was performed in a bare fused-silica capillary with 75 microm id and total length of 50 cm (28 cm to the detector) with a buffer solution of 20 mM sodium tetraborate, pH 9.23. The applied voltage was 20 kV, and acetaminophen was used as the internal standard (IS). The LC analysis was performed with a LiChrospher 100 RP-18 (5 microm) column and a mobile phase of methanol-diluted glacial acetic acid (0.3 parts in 2500; 75 + 25) at a flow rate of 0.9 mL/min with propylparaben as the IS. In both analyses, detection was by ultraviolet absorption at 276 nm. Under optimized conditions, the CE migration times for the diclofenac sodium standard and acetaminophen (IS) were 2.07 and 1.59 min, respectively, and the LC retention times for the diclofenac sodium standard and propylparaben (IS) were 3.98 and 2.26 min, respectively. The resolution and efficiency for CE were 14.2 and 1.6 x 10(5) plates/m, respectively, and for LC, 5.0 and 8.6 x 10(3) plates/m, respectively. Calibration curves of peak area versus concentration gave correlation coefficients of 0.9992 for CE and 0.9994 for LC. The limits of detection and quantitation were 8.40 and 25.46 microg/mL, respectively, for CE and 4.60 and 13.93 microg/mL, respectively, for LC. Coefficients of variation were 1.68 and 0.37% for CE and LC, respectively. Average recoveries obtained with CE and LC were 103.12+/-0.90 and 99.59+/-0.21%, respectively. Although both methodologies were shown to be suitable for the determination of diclofenac sodium in tablets, performing in a similar manner with regard to several aspects (linearity, recovery, and specificity), CE provided faster analysis and better column efficiency, whereas LC provided superior repeatability and sensitivity.     

Determination of ametryn in soils via microwave-assisted solvent extraction coupled to anodic stripping voltammetry with a gold ultramicroelectrode

An extraction-anodic adsorptive stripping voltammetric procedure using microwave-assisted solvent extraction and a gold ultramicroelectrode was developed for determining the pesticide ametryn in soil samples. The method is based on the use of acetonitrile as extraction solvent and on controlled adsorptive accumulation of the herbicide at the potential of 0.50 V (vs. Ag/AgCl) in the presence of Britton-Robinson buffer (pH 3.3). Soil sample extracts were analysed directly after drying and redissolution with the supporting electrolyte but without other pre-treatment. The limit of detection obtained for a 10 s collection time was 0.021 g g^–1. Recovery experiments for the global procedure, at the 0.500 g g^–1 level, gave satisfactory mean and standard deviation results which were comparable to those obtained by HPLC with UV detection.     

Aluminium-doped catalysts for the high temperature shift reaction

The replacement of chromium by aluminium in high temperature shift catalysts was investigated. It was found that aluminium-doped hematite is a convenient candidate as an environmental friendly catalyst.