Spin-polarized electron tunneling in bcc FeCo/MgO/FeCo(001) magnetic tunnel junctions

In combining spin- and symmetry-resolved photoemission, magnetotransport measurements and ab initio calculations we detangled the electronic states involved in the electronic transport in Fe(1-x)Co(x)(001)/MgO/Fe(1-x)Co(x)(001) magnetic tunnel junctions. Contrary to previous theoretical predictions, we observe a large reduction in TMR (from 530 to 200% at 20 K) for Co content above 25 atomic% as well as anomalies in the conductance curves. We demonstrate that these unexpected behaviors originate from a minority spin state with Δ(1) symmetry that exists below the Fermi level for high Co concentration. Using angle-resolved photoemission, this state is shown to be a two-dimensional state that occurs at both Fe(1-x)Co(x)(001) free surface, and more importantly at the interface with MgO. The combination of this interface state with the peculiar density of empty states due to chemical disorder allows us to describe in details the complex conduction behavior in this system.     

An Enzyme Immunoassay for Determining Immunoreactive Trypsinogen (IRT) in Dried Blood Spots on Filter Paper Using an Ultra-Microanalytical System

Cystic fibrosis (CF) is a severe autosomal recessive disorder. It is caused by mutations in the CF transmembrane conductance regulator gene. Early diagnosis of CF can be carried out by determining high immunoreactive trypsinogen (IRT) blood values in newborns. A simple sandwich-type ultramicroELISA assay (UMELISA®) has been developed for the measurement of IRT in dried blood spots on filter paper. Strips coated with a high affinity monoclonal antibody directed against IRT are used as solid phase, to ensure the specificity of the assay. The assay is carried out within 20 h. The useful rank of the curve is 0–500 ng/mL, and the lowest detectable concentration is 4.8 ng/mL. Intra- and inter-assay coefficients of variation were lower than 10%. The recovery mean value was 100.3 ± 11.2%. Cross-reactivity with proteins structurally related to IRT (α2-macroglobulin, α1-antitrypsin, and human chymotrypsin) was lower than the detection limit of the assay. Four thousand four hundred six newborn samples from the Cuban Newborn Screening Program were analyzed, and the mean IRT concentration was 12.8 ng/mL. Higher IRT values were obtained when samples were eluted overnight. Regression analysis showed a good correlation with the commercially available AutoDELFIA® Neonatal IRT kit (n?=?3948, r =?0.885, ??=?0.976, p?<?0.01). The analytical performance characteristics of our UMELISA® TIR Neonatal suggest that it can be used for the neonatal screening of CF.     

An unprecedented hybrid scorpionate/cyclopentadienyl ligand

An efficient method for the preparation of the first hybrid scorpionate/cyclopentadienyllithium compound as a new class of tridentate ligand is described. This compound is an excellent reagent for the introduction of this ligand into transition metal complexes.     

EDXRF analysis of some samples of cigarette paper

The effects of tobacco on human health have been widely investigated and documented However, there are not too many specific reports on the potential risk associated to the presence of metals in the paper employed for cigarettes fabrication Even more, there is a lack of national and international norms in this respect. Otherwise, in the literature INAA appears as the unique method for wrapping paper analysis. Therefore, without a nuclear reactor available at the National University of Mexico (UNAM), EDXRF was selected with the aim to explore the possibility to apply this method, instead of INAA, to the analysis of wrapping paper assuming this task, at the beginning, as a supplement to a previous research which was recently presented (2005).¹ The analytical work was developed on the wrapping paper of eight of the most known marks of cigarettes in Mexico, in two non-destructive stages: a first survey, by the classical technique of energy dispersive X-ray fluorescence (EDXRF), used a 1 11 GB qradiation source of ²³⁸Pu and a SiLi detector. In the absence of standard reference materials for cigarette’s paper, the SRM-1832 and 1833 were required for calibration, a fiberglass air filter was used as a secondary standard. The second stage was performed in a spectrometer TX-2000, anode of Mo, quantification software EDXRF32 (fundamental parameters). This paper presents a comparison of the obtained values with those found in the literature. The results show that the EDXRF method, in the Mo tube version, has the adequate precision and detection limits for the analysis of wrapping paper.     

Neutron activation analysis and data mining techniques to discriminate between beef cattle diets

Journal of Radioanalytical and Nuclear Chemistry - Neutron activation analysis and data mining techniques were combined for assessing the mineral composition of diets commonly used to feed beef...     

Total reflection X-ray fluorescence analysis of trace-elements in candies marketed in Mexico

Trace metals concentrations in food are significant for nutrition, due either to their nature or toxicity. Sweets, including chewing gum and candies, are not exactly a food, but they usually are unwearied consumed by children, the most vulnerable age-group to any kind of metal contamination in the food chain. The presence of relatively high concentrations of heavy metals such as Lead elicits concern since children are highly susceptible to heavy metals poisoning. Trace-metals concentrations were determined for six different flavors of a Mexican candy by means of Total X-ray Fluorescence Spectrometry. Triplicate samples of the various candy's flavours (strawberry, pineapple, lemon, blackberry, orange and chilli) were digested in 8 mL of a mix of supra-pure HNO₃ and H₂O₂ (6 mL: 2 mL) in a microwave oven MARS-X. Results show the presence of essential and toxic elements such as Ti, Cr, Mn, Fe, Ni, Cu, Zn, Br, Rb, Sr, and Pb. All metal concentrations were higher and significantly different (α = 0.05) in chilli candy, compared to other candy flavours. Lead concentration fluctuated in the range of 0.102 to 0.342 μg g^− 1. A discussion about risk consumption and concentration allowed by Mexican and International Norms is made. As a part of the Quality Control Program, a NIST standard of “Citrus Leaves” and a blank were treated in the same way.     

Total reflection X-ray fluorescence spectrometric determination of elements in water hyacinth from the Lerma River

The Lerma River is one of the most polluted body water in Mexico. For this reason, only the highly resistant organisms such as water hyacinth are able to reproduce in this river. The aim of this work was to evaluate the concentration of K, S, Fe, Ca, Mn, Ti, Zn, Sr, Rb, Cu, Cr, Ni, Pb and Br in roots of water hyacinth (Eichhornia crassipes) from the Lerma River. The samples were collected from five sites in the river and analyzed in triplicate using a TXRF Spectrometer ‘TX-2000 Ital Structures’ with a Si(Li) detector and a resolution of 140 eV (FWHM) at Mn Kα. A Mo tube (40 kV, 30 mA) with 17.4 KeV excitation energy was used for a counting time of 500 s. Results show that the average metal concentration in the water hyacinth roots decrease in the following order: K (9698.2 µg/g) > S (7593.3 µg/g) > Fe (4406.6 µg/g) > Ca (2601.8 µg/g) > Mn (604.2 µg/g) > Ti (230.7 µg/g) > Zn (51.65 µg/g) > Sr (43.55 µg/g) > Rb (18.61 µg/g) > Cu (12.78 µg/g) > Cr (6.45 µg/g) > Ni (4.68 µg/g) > Pb (4.32 µg/g) > Br (4.31 µg/g) and the bioconcentration factors in the water hyacinth decrease in the sequence: Ti > Fe > Mn > Cu > Ni > Zn > S > Pb > Rb > K > Cr > Sr > Br > Ca. The concentrations in roots of water hyacinth reflect the high pollution level of the river.     

Determination of trace elements in blood samples by TXRF analysis

Trace elements were determined by TXRF in whole blood samples in a randomly non-occupational exposed population living in the Metropolitan Zone of the Mexico Valley (MZMV). Arithmetic and geometric means of S, Ca, Cu, Zn, Rb and Pb concentrations, were on the reported range values for non-occupational population in other countries, while those of K and Br were higher, possibly due to dietary habits and geographical or environmental factors. The noticeable decline in blood lead level (91%) should be positively perceived. As a part of the Quality Control Program, a certified IAEA-A13 was tested. This revised version was published online in August 2006 with corrections to the Cover Date.