Ultrafast Atomic Diffusion Inducing a Reversible (2sqrt[3]×2sqrt[3])R30°â†”(sqrt[3]×sqrt[3])R30° Transition on Sn/Si(111)∶B.

Dynamical phase transitions are a challenge to identify experimentally and describe theoretically. Here, we study a new reconstruction of Sn on silicon and observe a reversible transition where the surface unit cell divides its area by a factor of 4 at 250 °C. This phase transition is explained by the 24-fold degeneracy of the ground state and a novel diffusive mechanism, where four Sn atoms arranged in a snakelike cluster wiggle at the surface exploring collectively the different quantum mechanical ground states.

Self-assembly of iron oxide precursor micelles driven by magnetic stirring time in sol-gel coatings.

The purpose of this work is to fabricate self-assembled microstructures by the sol-gel method and study the morphological, structural and compositional dependence of ε-Fe2O3 nanoparticles embedded in silica when glycerol (GLY) and cetyl-trimethylammonium bromide (CTAB) are added as steric agents simultaneously. The combined action of a polyalcohol and a surfactant significantly modifies the morphology of the sample giving rise to a different microstructure in each of the studied cases (1, 3 and 7 days of magnetic stirring time). This is due to the fact that the addition of these two compounds leads to a considerable increase in gelation time as GLY can interact with the alkoxide group on the surface of the iron oxide precursor micelle and/or be incorporated into the hydrophilic chains of CTAB. This last effect causes the iron oxide precursor micelles to be interconnected forming aggregates whose size and structure depend on the magnetic stirring time of the sol-gel synthetic route. In this paper, crystalline structure, composition, purity and morphology of the sol-gel coatings densified at 960 °C are examined. Emphasis is placed on the nominal percentage of the different iron oxides found in the samples and on the morphological and structural differences. This work implies the possibility of patterning ε-Fe2O3 nanoparticles in coatings and controlling their purity by an easy one-pot sol-gel method.

Origin of the magnetic transition at 100 K in ε-Fe2O3 nanoparticles studied by x-ray absorption fine structure spectroscopy.

The current study unveils the structural origin of the magnetic transition of the ε-Fe2O3 polymorph from an incommensurate magnetic order to a collinear ferrimagnetic state at low temperature. The high crystallinity of the samples and the absence of other iron oxide polymorphs have allowed us to carry out temperature-dependent x-ray absorption fine structure spectroscopy experiments out. The deformation of the structure is followed by the Debye-Waller factor for each selected Fe-O and Fe-Fe sub-shell. For nanoparticle sizes between 7 and 15 nm, the structural distortions between the Fete and Fe-D1oc sites are localized in a temperature range before the magnetic transition starts. On the contrary, the inherent interaction between the other sub-shells (named Fe-O1,2 and Fe-Fe1) provokes cooperative magneto-structural changes in the same temperature range. This means that the Fete with Fe-D1oc polyhedron interaction seems to be uncoupled with temperature dealing with these nanoparticle sizes wherein the structural distortions are likely moderate due to surface effects.

Experimental design of a microwave-assisted extraction-derivatization method for the analysis of methylmercury.

A simultaneous microwave-assisted extraction-derivatization procedure was developed and optimized for methylmercury analysis from biological samples. The analyte was derivatized with sodium tetraphenylborate forming a more hydrophobic compound, methylphenylmercury, which was extractable in toluene. The microwave extraction-derivatization procedure was optimized using experimental design, 2(5-1) fractional factorial. This chemometrical approach considers main effects as well as interactions of the influential parameters, indicating that temperature and its interaction with NaBPh4 and acetic acid volumes were the variables that significantly affected methylmercury recoveries.

Methylmercury determination in biological samples by derivatization, solid-phase microextraction and gas chromatography with microwave-induced plasma atomic emission spectrometry.

A method for the extraction and gas chromatographic determination of methylmercury in biological matrices is presented. By combining the advantages of two extraction techniques-microwave-assisted extraction (MAE) and solid-phase microextraction (SPME)--the separation of methylmercury from biological samples is possible. Specifically, the procedure involves microwave extraction with 3 M hydrochloric acid, followed by aqueous-phase derivatization with sodium tetraphenylborate and headspace SPME with a silica fibre coated with polydimethylsiloxane (PDMS). For optimization of the derivatization-SPME procedure, a central composite experimental design with alpha = 1.682 and two central points was used to model gas-chromatographic peak areas as functions of pH, extraction temperature and sorption time. A desirability function was then used for the simultaneous optimization for methylmercury and Hg(II). The optimal derivatization-SPME conditions identified were close to pH 5, temperature 100 degrees C, and sorption time 15 min. The identification and quantification of the extracted methylmercury is carried out by gas chromatography with microwave-induced plasma atomic emission spectrometry detection. The validity of the new procedure is shown by the results of analyses of certified reference materials.

Cytogenetic characterization of the AS cell line derived from the Atlantic salmon (Salmo salar L.).

The chromosome complement of the fish cell line AS, derived from the Atlantic salmon (Salmo salar L., 2N = 58), was investigated by C-, Ag-NOR, restriction endonuclease, and BrdU-replication banding. The cell line has a modal chromosome number of 52 with a fixed number of chromosomal rearrangements. The variety of banding patterns obtained allowed us to identify three chromosome markers in the cell line. The identification of their possible origin and significance in karyotype evolution are discussed.

Restriction endonuclease/nick translation procedure on fixed chromosomes of the Atlantic salmon fish cell line.

We have used a restriction endonuclease/nick translation (RE/NT) procedure to study the ability of restriction enzymes to cleave DNA in fixed chromosomes of a fish cell line. This technique has proved to be very useful in revealing the chromatin heterogeneity underlying the chromosome structure that remains cryptic to other techniques also able to induce longitudinal differentiation on fish chromosomes. The differences observed in the banding patterns after nick translation procedure seem to be due, at least in part, to differences in activity among the enzymes assayed. The results obtained also reveal some evidence about the origin and evolution of the marker chromosomes of the Atlantic salmon cell line.

Localization of the repetitive telomeric sequence (TTAGGG)n in four salmonid species.

We have analyzed the localization of the highly conserved telomeric sequence (TTAGGG)n in four salmonid species, two of the genus Salmo (Salmo trutta and Salmo salar) and two of the genus Oncorhynchus (Onchorhynchus mykiss and Onchorhynchus kisutch), by fluorescent in situ hybridization. As expected, the hybridization signal was mostly localized at the telomeres of all chromosomes in the four species. Two species evidenced special hybridization sites with the telomeric probe: (i) interstitial heterochromatic blocks in particular long chromosomes in S. salar; this observation supports tandem fusions as the karyotypic evolutionary mechanism leading to the formation of the long acrocentric and submetacentric chromosomes in the karyotype of S. salar; (ii) the whole NOR region in O mykiss; this observation suggests that the (TTAGGG)n sequence is scattered all along this chromosome region.

A NOR-associated repetitive element present in the genome of two Salmo species (Salmo salar and Salmo trutta).

A repetitive element was isolated from the genome of Atlantic salmon. Nucleotide sequence analysis revealed the existence of variant monomers that range in length from approximately 200 to 230 bp. Repeat monomers contain regions of cryptic simplicity, internal repetition, and long direct repeats with deletions and insertions between individual units. The repetitive element was shown to have a tandem unit arrangement and was estimated to occupy between two and three percent of the Atlantic salmon genome. Southern blot analysis revealed the repetitive element to be unique to Atlantic salmon and brown trout species. In situ hybridization analysis showed this element to be localized at the main nucleolar organizer region bearing chromosomes of Atlantic salmon (Salmo salar), AS cell line (derived from S. salar), and brown trout (Salmo trutta).

El índice de reactividad al estrés de Rivera. 1. Relación con patología médica y psiquiátrica / The Rivera’s stress reactivity index: (1) Relation with medical and psychiatric patology

En este trabajo se presenta una revisión del concepto de reactividad al estrés de Gonzalez de Rivera en relación con la patología psicológica y psicosomática. Por una parte, la reactividad al estrés como factor predisponente al padecimiento de diversos cuadros psicopatológicos y somáticos; por otra, la reactividad al estrés como modulador del efecto de factores externos de estrés sobre la patología psicológica y somática; y, por último, las relaciones entre reactividad al estrés y dimensiones psicopatológicas en diferentes tipos de población. Los diferentes estudios muestran la importancia de la reactividad al estrés como factor de vulnerabilidad al padecimiento de múltiples cuadros psicopatológicos y trastornos psicosomáticos, su papel como modulador sobre el impacto de acontecimientos traumáticos en el individuo y la diferente organización factorial de variables de reactividad y la psicopatología dependiendo del tipo de muestra

In this paper, a review of the González de Rivera’s concept of stress reactivity in relation with psychological and psychosomatic pathology concept is presented. On the one hand, stress reactivity as an underlying factor to the suffering of different psychopathological and somatic illness; on the other hand, stress reactivity as a modulator of the effect of the external stress factors on the psychological and somatic pathology; and lastly, the relations between stress reactivity and psychopathological dimensions in different populations. These different studies point out the importance of stress reactivity as a vulnerability factor in the suffering of psychopathological and psychosomatic disorders, its role as modulator of the impact of traumatic events on the persons, and the different factorial organization of stress reactivity and psychopathology variables, depending of the sample

Cuestionario de estrategias de acoso psicológico:el LIPT-60 (Leymann Inventory of PsychologicalTerrorization) en versión española / LIPT-60: spanish version of the Leymann Inventory of Psychological Terrorization

El LIPT-60 es un cuestionario escalar autoadministrado que objetiva y valora 60 diferentes estrategias de acoso psicológico, derivado del LIPT original dicotómico de 45 items de Leymann. En una muestra de 125 sujetos de ambos sexos, participantes voluntarios en programas de información y/o atención sobre el acoso psicológico en el trabajo, la media de conductas de acoso experimentadas (NEAP) por los sujetos acosados fue de 29, con una intensidad media por cada conducta de acoso (IMAP) de 2,32. Los sujetos no acosados sufrieron una media de 4 conductas de acoso, con un IMAP de 1,23. El indice global de acoso psicológico (IGAP) fue de 1,23 para los acosados y 0,09 para los no acosados. Existe una importante correlación entre los indices de acoso y la edad del sujeto, pero no con su género. Las 17 estrategias más frecuentes e intensas pretenden incomunicar, intimidar, desprestigiar y entorpecer el progreso de la victima, y afectan al 70 por ciento de los acosados. Las estrategias de acoso menos frecuentes son conductas groseras, evidentes o que dejan huella, lo que confirma que, a diferencia de otras formas de violencia en el trabajo, el acoso psicológico consiste en estrategias sofisticadas y bien planeadas y no en meros arrebatos o exabruptos (AU)