Surface remelting of 316 L + 434 L sintered steel: microstructure and corrosion resistance

This study presents arc surface remelting of three types of sintered stainless steels carried out in order to constitute a homogeneous microstructure in the surface layer which is free from open and interconnected porosity. The main aim of this treatment was to improve functional properties of the sinters analysed, especially their resistance to pitting corrosion. The sinters were obtained from powders of 316 L and 434 L steels. The PM austenitic-ferritic stainless steels are used mainly in the automotive industry, but their general application is still limited due to relatively poor corrosion properties when compared to casts or wrought components. This study used the gas tungsten arc welding (GTAW) process as a method of economical surface treatment. The effect of surface treatment was evaluated based on macro- and microstructural observations, energy-dispersive X-ray spectroscopy (EDX) analysis, X-ray phase analysis, measurements of surface roughness and electrochemical examinations. It was found that a cellular or mixed cellular and dendritic structure was formed in the remelted zone of the sinters after remelting. X-ray analysis demonstrated that application of remelting contributes to formation of the austenitic phase in the surface layer. The corrosion resistance of the remelted surface layers was evaluated using polarization tests in 0.5 M NaCl solution. It was found that arc surface remelted layers exhibit much better anticorrosive properties than sinters without surface treatment. Microstructural observations of the surface of specimens after electrochemical tests showed only a few single pits in the remelted layer, while the surface of initial sinters was much more corroded.     

LC Determination of the Skin Exposure to Oxamyl on Greenhouse Workers and Comparison Between DAD and MS–MS Detection

An LC–DAD method was developed to determine residues of oxamyl on greenhouse workers’ skin. The wipe test was used to obtain samples from hands, forearms, neck and gloves of workers taking cactus cuttings 48 h after pesticide treatment. It was validated in a concentration range 50–5,000 ng mL^?1. The results on six workers and ten office employees indicated significant differences particularly in the hand samples. To avoid the overestimation owing to an interfering substance we proceeded to confirm these findings with LC–MS–MS, which found the pesticide only on the surface of the workers’ gloves, proving that there was indeed some UV interference.     

Gold nanoclusters protected by conformationally constrained peptides

The preparation and properties of a series of gold nanoclusters protected by thiolated peptides based on the alpha-aminoisobutyric acid (Aib) unit are described. The peptides were devised to form 0-3 C=O...H-N intramolecular hydrogen bonds, as required by their 3(10)-helical structure. The monolayer-protected clusters (MPCs) were prepared, using a modified version of the two-phase Brust-Schiffrin preparation, and fully characterized with (1)H NMR spectrometry, IR and UV-vis absorption spectroscopies, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). The MPCs were obtained with core diameters in the range of 1.1-2.3 nm, depending on the reaction conditions. Structured peptides formed smaller clusters. The smallest MPC obtained is in agreement with the average formula Au(38)Pep(18). The results showed that the chemical integrity of the peptide is maintained upon monolayer formation and that the average number of peptide ligands per gold cluster is typically 75-85% the value calculated for alkanethiolate MPCs of similar sizes. The IR and NMR spectra indicated that in the monolayer the peptides are involved in both intra- and interligand C=O...H-N hydrogen bonds.     

Pesticides analysis by liquid chromatography and capillary electrophoresis

Nowadays, a wide range of pesticides are used in agricultural production, and their monitoring in samples of environmental and alimentary interest is of extreme importance to ensure, among others, the safety of consumption of foods. The aim of this work is to provide updated information about the major developments in CE and HPLC in pesticide analysis, covering relevant publications between 2004 and early 2006. The use of different sample pretreatment steps to provide a suitable extraction of these compounds from the different matrices as well as to increase the sensitivity of the determination is also discussed.     

Mathematics identity and achievement among Black students

Employing data from the National Center of Educational Statistics' High School Longitudinal Study and utilizing critical race theory and intersectionality as theoretical frameworks, this article interrogates the relationship between mathematics identity and math success for a nationwide sample of Black secondary school students. More specifically, hierarchical regression modeling is employed to examine the relative impact of math identity, demographic variables, and school/parent social capital variables on the math grade point averages of this sample. The article ends with a discussion of specific steps for teaching mathematics that put the identity of those from traditionally marginalized communities at the center of mathematics instruction. Thus making experiences, histories, culture, and abilities essential elements of students' learning, that are to be supported and built upon.     

The effect of polysialic acid on molecular dynamics of model membranes studied by 31P NMR spectroscopy

The paper reports the results of our study on the dynamics of model phospholipid membranes studied by 31P NMR spectroscopy. The 31P NMR spectra of multilamellar vesicles in temperatures below the main phase transition of PC are reported. The 31P NMR spectra revealed changes caused by an increase of the membrane fluidity when polysialic acid (polySia) was applied as a modifying agent. The presence of polySia in the external environment of the phospholipid vesicles changes the motional freedom in the region of phosphate group of lipids. Increase of polysialic acid concentration changes structural properties of a membrane by increasing its fluidity.     

TTF Triples in Functor Categories

We characterize the hereditary torsion pairs of finite type in the functor category of a ring R that are associated to tilting torsion pairs in the category of R-modules. Moreover, we determine a condition under which they give rise to TTF triples.     

Orthogonal polynomials in several variables for measures with mass points

Let dν be a measure in ? ^d obtained from adding a set of mass points to another measure dμ. Orthogonal polynomials in several variables associated with dν can be explicitly expressed in terms of orthogonal polynomials associated with dμ, so are the reproducing kernels associated with these polynomials. The explicit formulas that are obtained are further specialized in the case of Jacobi measure on the simplex, with mass points added on the vertices, which are then used to study the asymptotics kernel functions for dν.     

Finitely cotilting modules

Over an arbitrary ring, we consider cotilting modules endowed with some finiteness conditions. We show that they correspond to pairs of dualities between certain cat-egories consisting of finitely presented modules. This extends the Cotilting Theorem proved by Colby for the noetherian case. The relationship with the cotilting modules studied by Colpi, D'Este, Tonolo and Trlifaj is also discuss.d.