Giant magnetic anisotropy at nanoscale: overcoming the superparamagnetic limit

It has been recently observed for palladium and gold nanoparticles, that the magnetic moment at constant applied field does not change with temperature over the range comprised between 5 and 300 K. These samples with size smaller than 2.5 nm exhibit remanence up to room temperature. The permanent magnetism for so small samples up to so high temperatures has been explained as due to blocking of local magnetic moment by giant magnetic anisotropies. In this report we show, by analysing the anisotropy of thiol capped gold films, that the orbital momentum induced at the surface conduction electrons is crucial to understand the observed giant anisotropy. The orbital motion is driven by localised charge and/or spin through spin orbit interaction, that reaches extremely high values at the surfaces. The induced orbital moment gives rise to an effective field of the order of 103 T that is responsible of the giant anisotropy.Comment: 15 pages, 2 figures, submitted to PR

La política de ciencia, tecnología e innovación y el retorno del Estado: 2007-2010, años de inestabilidad The policy of science, technology and innovation and the return of the state: 2007 2010, years of instability

This article analyzes the implementation process of the Ecuadorian science, technology and innovation policy (PCTI) within the framework of the beginning of the post-neoliberal period, which implied the strengthening of the State and the insertion of the paradigm of buen vivir. For this purpose, the novel elements in the definition of this policy under the framework of buen vivir are described as an introductory note. Then, the complex construction process of the explicit PCTI during these years is reviewed. Finally, the instruments implemented and their relationship with the definition of PCTI are analyzed. To this end, the concepts of explicit scientific policy and implicit scientific policy of Herrera [1] and the notion of scientific-technological paradigm of Velho [2] are used. The chosen approach is framed in the new institutionalism that understands the definition and implementation of the PCTI as the result of the strategic game of the actors involved in these processes. This case study uses investigation of historical archives, documentary analysis and in-depth interviews with relevant actors. It is found that the PCTI during these years was unstable, as there were several short-term policy documents, and that its implementation was far from the ambitious rhetoric and the major objectives, limited to two instruments: international postgraduate scholarships and financing of research and development projects

Two dimensional electron gas confined over a spherical surface: Magnetic moment

Magnetism of capped nanoparticles, NPs, of non- magnetic substances as Au and ZnO is briefly reviewed. The source of the magnetization is discussed on the light of recent X-ray magnetic circular dichroism experiments. As magnetic dichroism analysis has pointed out impurity atoms bonded to the surface act as donor or acceptor of electrons that occupy the surface states. It is proposed that mesoscopic collective orbital magnetic moments induced at the surface states can account for the experimental magnetism characteristic of these nanoparticles. The total magnetic moment of the surface originated at the unfilled Fermi level can reach values as large as 10(2) or 10(3) Bohr magnetons

Magnetic and superconducting phase diagrams in ErNi2B2C

We present measurements of the superconducting upper critical field Hc2(T) and the magnetic phase diagram of the superconductor ErNi2B2C made with a scanning tunneling microscope (STM). The magnetic field was applied in the basal plane of the tetragonal crystal structure. We have found large gapless regions in the superconducting phase diagram of ErNi2B2C, extending between different magnetic transitions. A close correlation between magnetic transitions and Hc2(T) is found, showing that superconductivity is strongly linked to magnetism.Comment: 5 pages, 4 figure

sp magnetism in clusters of gold-thiolates

Using calculations from first principles, we herein consider the bond made between thiolat e with a range of different Au clusters, with a particular focus on the spin moments inv olved in each case. For odd number of gold atoms, the clusters show a spin moment of 1.~ $\mu_B$. The variation of spin moment with particle size is particularly dramatic, with t he spin moment being zero for even numbers of gold atoms. This variation may be linked w ith changes in the odd-even oscillations that occur with the number of gold atoms, and is associated with the formation of a S-Au bond. This bond leads to the presence of an extra electron that is mainly sp in character in the gold part. Our results sugg est that any thiolate-induced magnetism that occurs in gold nanoparticles may be locali zed in a shell below the surface, and can be controlled by modifying the coverage of the thiolates

Obtención por vía SHS-AE de compuesto cerámico αSiC-αAl2O3-CaAl4O7

El presente trabajo muestra los resultados experimentales de la obtención del compuesto cerámico SiC-Al2O3-CaAl 4O7 mediante el proceso SHS-AE (síntesis auto-sostenida de alta temperatura combinada con arco eléctrico) a partir del sistema vidrio sódico-cálcico-Al-C. Se utilizó horno de arco eléctrico con atmósfera de argón para la reducción del contenido de sílice presente en el vidrio con aluminio.La combinación de la energía de la reacción de formación del Al2O3 con la del arco eléctrico provee suficiente energía térmica para superar las barreras cinéticas asociadas con la reacción de formación de los componentes cerámicos.A partir de las relaciones estequiométricas de las materias primas, (polvos que se compactan en forma de pastilla) se efectúa la síntesis alcanzando una temperatura superior a los 2500 K formándose el compuesto SiC-Al2O3-CaAl 4O7. Las muestras obtenidas se caracterizaron por DRX y MEB-EDX confirmando la obtención simultánea de αSiC-αAl2O3-CaAl4O7

Microneedle based electrochemical (bio)sensing: towards decentralized and continuous health status monitoring

Microneedle (MN) based electrochemical (bio)sensing has become a growing field within the discipline of analytical chemistry as a result of its unique capacity for continuous, decentralized health status monitoring. There are two significant advantages to this exclusive feature: i) the ability to directly analyze interstitial fluid (ISF), a body fluid with a similar enough composition to plasma (and blood) to be considered a plentiful source of information related to biologically relevant molecules and biomarkers; and ii) the capacity to overcome some of the major limitations of blood analysis including painful extraction, high interferant concentrations, and incompatibility with diagnosis of infants (and especially newborns). Recent publications have demonstrated important advancements in electrochemical MN sensor technology, among which are included new MN fabrication methods and various modification strategies, providing different architectures and allowing for the integration of electronics. This versatility highlights the undeniable need for interdisciplinary efforts towards tangible progress in the field. In a context evidently dominated by glucose sensing, which is slowly being expanded towards other analytes, the following crucial questions arise: to what extent are electrochemical MN (bio)sensors a reliable analytical tool for continuous ISF monitoring? Which is the best calibration protocol to be followed for in vivo assays? Which strategies can be employed to protect the sensing element during skin penetration? Is there an appropriate validation methodology to assess the accuracy of electrochemical MN (bio)sensors? How significant is the distinction between successful achievements in the laboratory and the real commercial feasibility of products? This paper aims to reflect on those previous questions while reviewing the progress of electrochemical MN (bio)sensors in the last decade with a focus on the analytical aspects. Overall, we describe the current state of electrochemical MN (bio)sensors, the benefits and challenges associated to ISF monitoring, as well as key features (and bottlenecks) regarding its implementation for in vivo assays

Toward in vivo transdermal pH sensing with a validated microneedle membrane electrode

We present herein the most complete characterization of microneedle (MN) potentiometric sensors for pH transdermal measurements for the time being. Initial in vitro assessment demonstrated suitable analytical performances (e.g., Nernstian slope, linear range of response from 8.5 to 5.0, and fast response time) in both buffer media and artificial interstitial fluid (ISF). Excellent repeatability and reproducibility together with adequate selectivity and resiliency facilitate the appropriateness of the new pH MN sensor for transdermal ISF analysis in healthcare. The ability to resist skin insertions was evaluated in several ex vivo setups using three different animal skins (i.e., chicken, pork, and rat). The developed pH MN sensor was able to withstand from 5 to 10 repetitive insertions in all the skins considered with a minimal change in the calibration graph (<3% variation in both slope and intercept after the insertions). Ex vivo pH measurements were validated by determining the pH with the MN sensor and a commercial pH electrode in chicken skin portions previously conditioned at several pH values, obtaining excellent results with an accuracy of <1% and a precision of <2% in all cases. Finally, pH MN sensors were applied for the very first time to transdermal measurements in rats together with two innovative validation procedures: (i) measuring subcutaneous pH directly with a commercial pH microelectrode and (ii) collecting ISF using hollow MNs and then the pH measurement of the sample with the pH microelectrode. The pH values obtained with pH MN sensors were statistically more similar to subcutaneous measurements, as inferred by a paired sample t-test at 95% of confidence level. Conveniently, the validation approaches could be translated to other analytes that are transdermally measured with MN sensors

Changes in the foraging strategy of female South American sea lions (Carnivora: Pinnipedia) after parturition.

This study tests the hypothesis that female South American sea lions shift from off-shore, pelagic prey to coastal, benthic prey after parturition in order to reduce the foraging trip duration and hence the time pups remain unattended on the beach during early lactation. The δ13C and δ15N values of the serum and blood cells of 26 South American sea lion suckling pups from northern Patagonia were used to track the dietary changes of their mothers from late pregnancy to early lactation, after correction for differential isotopic fractionation between tissues. Primary producers and potential prey species were also analysed to establish a baseline for interpreting the stable isotope concentration of serum and blood cells. Isotopic ratios revealed a generalized increase in the consumption of coastal-benthic prey after parturition. Such a generalized post-partum shift will allow females to spend more time on land and look after their pups. The effects of this foraging strategy on the nutritional quality of the female"s diet are discussed