Magneto-elastic waves in crystals of magnetic molecules

We study magneto-elastic effects in crystals of magnetic molecules. Coupled equations of motion for spins and sound are derived and the possibility of strong resonant magneto-acoustic coupling is demonstrated. Dispersion laws for interacting linear sound and spin excitations are obtained for bulk and surface acoustic waves. We show that ultrasound can generate inverse population of spin levels. Alternatively, the decay of the inverse population of spin levels can generate ultrasound. Possibility of solitary waves of the magnetization accompanied by the elastic twists is demonstrated.Comment: 8 PR pages, 3 figure

Quantum dynamics of a nanomagnet in a rotating field

Quantum dynamics of a two-state spin system in a rotating magnetic field has been studied. Analytical and numerical results for the transition probability have been obtained along the lines of the Landau-Zener-Stueckelberg theory. The effect of various kinds of noise on the evolution of the system has been analyzed.Comment: 7 pages, 7 figure

¿SON EFECTIVOS LOS CONSEJOS DE ADMINISTRACIÓN? LA EFICACIA DEL CONSEJO Y LOS RESULTADOS DE LA EMPRESA

Numerosos trabajos han estudiado la influencia del consejo de administración en las decisiones y resultados de sus empresas. No obstante, la enorme popularidad alcanzada en el campo del gobierno corporativo por estos estudios, no viene acompañada por sus resultados, que han sido ambiguos y, a veces, conflictivos En esta investigación proponemos que la efectividad de los consejos depende de las experiencias y conocimientos de los consejeros que lo conforman, así como de la estructura de estos consejos. Entendemos que ambas dimensiones (composición y estructura) no son “por si” suficientes para el logro de consejos plenamente efectivos, pero si se definen como elementos necesarios para ello. Desde nuestra perspectiva, constituyen el potencial que permitirá lograr una adecuada capacidad estratégica por parte del consejo. Nuestros resultados muestran la importancia de las variables que conforman la estructura y composición del consejo (tamaño del consejo, permanencia, experiencia de los consejeros) a la hora de explicar los resultados empresariales

Remittances, liquidity constraints and human capital investments in Ecuador.

Over the last decade Ecuador has experienced a strong increase in financial transfers from migrated workers. This paper investigates how remittances via trans-national networks affect human capital investments through relaxing resource constraints and facilitate households in consumption smoothing by reducing vulnerability to economic shocks. Our results show that remittances increase school enrolment and decrease incidence of child work, especially for girls and in rural areas. Furthermore, we find that aggregate shocks are associated with increased work activities, while remittances are used to finance education when households are faced with these shocks

Efecto inhibitorio de un extracto acuoso de las hojas de Allophylus cominia (L.) Sw sobre las proteínas tirosina fosfatasa 1B y dipeptidil peptidasa IV

Introduction: Allophylus cominia (L.) Sw is a Cuban medicinal plant used by traditional medicine for the treatment of diabetes with unknown mechanisms of action. Objective: to evaluate the effect of Allophylus cominia (L.) Sw leaves aqueous extract and its fractions on protein tyrosine phosphatase 1B (PTP1B) and dipeptidyl peptidase IV (DPPIV) enzymatic activity, as therapeutic targets of type 2 diabetes. Methods: the aqueous extract of A. cominia leaves was successively partitioned with organic solvents mixtures, thus increasing polarity in order to obtain ten fractions. The extract and its fractions were tested for their possible antidiabetic activity on therapeutic targets of type 2 diabetes: PTP1B and DPPIV. The enzymatic inhibition assays were performed and the inhibitory activity was calculated with the fluorescence values using an excitation wavelength of 360 nm and an emission wavelength of 460 nm. Results: the aqueous extract from A. cominia inhibited the enzymatic activity of PTP1B and DPPIV according to the concentration, being IC50 values equal to 0.69 μg/mL and 344.3 μg/mL, respectively. Several fractions were detected as potent PTP1B inhibitors. The most polar fractions AcF9 and AcF10 were more active, showing IC50 values of 4.4 µg/mL and 3.8 µg/mL respectively. The fractions showed a slight DPPIV inhibition, being fractions AcF6, AcF9 and AcF10 the most active, exhibiting inhibition percentages of 52.0 %, 39.0 % and 40.0 % respectively. Conclusions: A. cominia aqueous extract and its polar fractions (AcF9 and AcF10) have antidiabetic properties in vitro and are promissory candidates for development of new drugs with inhibitory activity of PTP1B and DPPIV for type 2 diabetes treatment

Impact of phosphate dosing on the microbial ecology of drinking water distribution systems: fieldwork studies in chlorinated networks

Phosphate is routinely dosed to ensure regulatory compliance for lead in drinking water distribution systems. Little is known about the impact of the phosphate dose on the microbial ecology in these systems and in particular the endemic biofilms. Disturbance of the biofilms and embedded material in distribution can cause regulatory failures for turbidity and metals. To investigate the impact of phosphate on developing biofilms, pipe wall material from four independent pipe sections was mobilised and collected using two twin-flushing operations a year apart in a chlorinated UK network pre- and post-phosphate dosing. Intensive monitoring was undertaken, including turbidity and water physico-chemistry, traditional microbial culture-based indicators, and microbial community structure via sequencing the 16S rRNA gene for bacteria and the ITS2 gene for fungi. Whole metagenome sequencing was used to study shifts in functional characteristics following the addition of phosphate. As an operational consequence, turbidity responses from the phosphate-enriched water were increased, particularly from cast iron pipes. Differences in the taxonomic composition of both bacteria and fungi were also observed, emphasising a community shift towards microorganisms able to use or metabolise phosphate. Phosphate increased the relative abundance of bacteria such as Pseudomonas, Paenibacillus, Massilia, Acinetobacter and the fungi Cadophora, Rhizophagus and Eupenicillium. Whole metagenome sequencing showed with phosphate a favouring of sequences related to Gram-negative bacterium type cell wall function, virions and thylakoids, but a reduction in the number of sequences associated to vitamin binding, methanogenesis and toxin biosynthesis. With current faecal indicator tests only providing risk detection in bulk water samples, this work improves understanding of how network changes effect microbial ecology and highlights the potential for new approaches to inform future monitoring or control strategies to protect drinking water quality

On numerical simulation of powder compaction process: powder transfer modelling and characterisation

A numerical model for the powder transfer stage in powder metallurgy cold compaction processes, and the corresponding material characterisation procedure, are proposed. They have been designed on the basis of the following requirements: robust and consistent computational mechanics ingredients, reliability of the obtained results for practical processes in powder metallurgy and industrial viability in the sense that characterisation of any mixture doesn't require either much effort or much time of the enduser. The starting point is a previously developed numerical model for powder compaction, formulated in terms of the large plastic deformation theory, which requires calibration of four parameters controlling the evolution of the yield surface. This calibration, which had been successfully carried out in the past in a range of moderate to high densities, is now extended to very low densities in order to make numerical simulations able to deal with compaction processes involving relevant powder transfer stages. To circumvent the difficulties inherent to direct measurements of very low powder densities, a simple apparatus, which allows studying the powder motion in the chamber, has been designed to provide an indirect way of calibration. On this basis, a set of calibration experiments is proposed. The proposed methodology appears to be simple and industrially viable. Although in the work it is applied to the specific constitutive model used by the authors, it also appears available for other families of constitutive models for powder compaction. As a relevant result, this would allow the same constitutive model to be used, via only the appropriated material characterisation, for simulation of densification in powder transfer stages as well as in pure compaction stage