Allele specific expression analysis identifies regulatory variation associated with stress-related genes in the Mexican highland maize landrace Palomero Toluqueño.

BackgroundGene regulatory variation has been proposed to play an important role in the adaptation of plants to environmental stress. In the central highlands of Mexico, farmer selection has generated a unique group of maize landraces adapted to the challenges of the highland niche. In this study, gene expression in Mexican highland maize and a reference maize breeding line were compared to identify evidence of regulatory variation in stress-related genes. It was hypothesised that local adaptation in Mexican highland maize would be associated with a transcriptional signature observable even under benign conditions.MethodsAllele specific expression analysis was performed using the seedling-leaf transcriptome of an F1 individual generated from the cross between the highland adapted Mexican landrace Palomero Toluqueño and the reference line B73, grown under benign conditions. Results were compared with a published dataset describing the transcriptional response of B73 seedlings to cold, heat, salt and UV treatments.ResultsA total of 2,386 genes were identified to show allele specific expression. Of these, 277 showed an expression difference between Palomero Toluqueño and B73 alleles under benign conditions that anticipated the response of B73 cold, heat, salt and/or UV treatments, and, as such, were considered to display a prior stress response. Prior stress response candidates included genes associated with plant hormone signaling and a number of transcription factors. Construction of a gene co-expression network revealed further signaling and stress-related genes to be among the potential targets of the transcription factors candidates.DiscussionPrior activation of responses may represent the best strategy when stresses are severe but predictable. Expression differences observed here between Palomero Toluqueño and B73 alleles indicate the presence of cis-acting regulatory variation linked to stress-related genes in Palomero Toluqueño. Considered alongside gene annotation and population data, allele specific expression analysis of plants grown under benign conditions provides an attractive strategy to identify functional variation potentially linked to local adaptation

Validity of the Néel-Arrhenius model for highly anisotropic CoxFe3−xO4 nanoparticles

We report a systematic study on the structural and magnetic properties of CoxFe3−xO4 magnetic nanoparticles with sizes between 5 and 25 nm, prepared by thermal decomposition of Fe(acac)3 and Co(acac)2. The large magneto-crystalline anisotropy of the synthesized particles resulted in high blocking temperatures (42 K < TB < 345 K for 5 < d < 13 nm) and large coercive fields (HC ≈ 1600 kA/m for T = 5 K). The smallest particles (⟨d⟩=5 nm) revealed the existence of a magnetically hard, spin-disordered surface. The thermal dependence of static and dynamic magnetic properties of the whole series of samples could be explained within the Neel–Arrhenius relaxation framework by including the thermal dependence of the magnetocrystalline anisotropy constant K1(T), without the need of ad-hoc corrections. This approach, using the empirical Brükhatov-Kirensky relation, provided K1(0) values very similar to the bulk material from either static or dynamic magnetic measurements, as well as realistic values for the response times (τ0 ≈ 10−10s). Deviations from the bulk anisotropy values found for the smallest particles could be qualitatively explained based on Zener's relation between K1(T) and M(T).This work was supported by the Spanish Ministerio de Economia y Competitividad (MINECO, Project Nos. MAT2010-19326 and MAT2013-42551).Peer Reviewe

Thermoelectric performance of spin Seebeck effect in Fe3O4/Pt-based thin film heterostructures

All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license.-- et al.We report a systematic study on the thermoelectric performance of spin Seebeck devices based on Fe3O4/Pt junction systems. We explore two types of device geometries: a spin Hall thermopile and spin Seebeck multilayer structures. The spin Hall thermopile increases the sensitivity of the spin Seebeck effect, while the increase in the sample internal resistance has a detrimental effect on the output power. We found that the spin Seebeck multilayers can overcome this limitation since the multilayers exhibit the enhancement of the thermoelectric voltage and the reduction of the internal resistance simultaneously, therefore resulting in significant power enhancement. This result demonstrates that the multilayer structures are useful for improving the thermoelectric performance of the spin Seebeck effect.This work was supported by the Spanish Ministry of Science (through Project Nos. PRI-PIBJP-2011-0794 and MAT2011-27553-C02, including FEDER funding), the Aragón Regional Government (Project No. E26), Thermo-spintronic Marie-Curie CIG (Grant Agreement No. 304043), JST-PRESTO “Phase Interfaces for Highly Ecient Energy Utilization” from JST, Japan, Grant in-Aid for Scientific Research on Innovative Areas “Nano-Spin Conversion Science” (Grant No. 26103005), Grant-in-Aid for Challenging Exploratory Research (Grant No. 26600067), Grant-inAid for Scientific Research (A) (Grant No. 15H02012) from MEXT, Japan, NEC Corporation, and The Noguchi Institute.Peer Reviewe

Long-term stability and reproducibility of magnetic colloids are key issues for steady values of specific power absorption over time

Virtually all clinical applications of magnetic nanoparticles (MNPs) require the formulation of biocompatible, water-based magnetic colloids. For magnetic hyperthermia, the requirements also include a high colloidal stability against precipitation and agglomeration of the constituent MNPs to maintain the heating efficiency of the ferrofluid in the long term. Agglomeration can change the heating efficiency by forming MNP clusters that modify the magnetic dipolar interactions between particles. Additionally, precipitation of the MNPs (i.e., the heating sources within the liquid) can change the measured heating rates of a colloid by altering the heat flow dynamics as the particles plunge to the precipitate. The specific power absorption (SPA) of single-domain MNPs depends critically on the average particle size and size distribution width and therefore first-rate reproducibility of different batches with respect to these parameters is also needed. We have studied the evolution of the SPA of highly reproducible and stable water-based colloids composed of polymer-coated Fe3O4 magnetic nanoparticles. By measuring the specific power absorption (SPA) values for 1 year as a function of field amplitude and frequency (H = 24 kA/m; 260 = f = 830 kHz), we have demonstrated that the SPA values of these samples can be reproduced in successive synthetic batches and stable for several months due to the in situ polymer coating that provides colloidal stability and keeps dipolar interactions negligible

Control de la dinámica de vórtices en nano-películas superconductoras con espesor modulado

Resumen del póster presentado a la 6ª Jornada de Jóvenes Investigadores en Física y Química de Aragón celebrada en Zaragoza el 20 de noviembre de 2014.Peer reviewe

Morphology and magnetic properties of W-capped Co nanoparticles

3 páginas, 3 figuras, 2 tablas.-- et al.Co–W nanoparticles formed by sequential sputtering of Co on amorphous alumina substrate and subsequent W capping are studied by high resolution and by scanning transmission electron microscopies, and by superconducting quantum interference device magnetometry. The analysis is focused on W nominal thickness dependence. Results suggest the formation of amorphous Co–W alloy nanoparticles, whose magnetic moment per Co atom is systematically reduced as the nominal thickness of W capping layer increases. The Co–W nanoparticles show superparamagnetic behavior. The activation energy for moment reversal and the effective anisotropy are obtained.The financial support of MAT08/1077 is acknowledged. A. I. Figueroa acknowledges a JAE-Predoc grant.Peer reviewe

Characteristic length scale of the magnon accumulation in Fe3O4/Pt bilayer structures by incoherent thermal excitation

The dependence of Spin Seebeck effect (SSE) with the thickness of the magnetic materials is studied by means of incoherent thermal excitation. The SSE voltage signal in Fe3O4/Pt bilayer structure increases with the magnetic material thickness up to 100 nm, approximately, showing signs of saturation for larger thickness. This dependence is well described in terms of a spin current pumped in the platinum film by the magnon accumulation in the magnetic material. The spin current is generated by a gradient of temperature in the system and detected by the Pt top contact by means of inverse spin Hall effect. Calculations in the frame of the linear response theory adjust with a high degree of accuracy the experimental data, giving a thermal length scale of the magnon accumulation (Λ) of 17 ± 3 nm at 300 K and Λ = 40 ± 10 nm at 70 K.This work was supported by the Spanish Ministry of Science (through Project No. MAT2014-51982-C2-R, including European social fund), the Aragon Regional government (Project No. E26), and Thermo-Spintronic Marie Curie CIG Project (Grant Agreement No. 304043).Peer Reviewe

Role of the surface states in the magnetotransport properties of ultrathin bismuth films

We have investigated the magnetotransport properties of ultrathin films of Bi grown on thermally oxidized Si(001) substrates with thickness ranging from 10 to 100 nm at temperatures down to 2 K and in magnetic fields up to 90 kOe. Remarkable differences both in temperature and field dependence of the Hall resistivity are found for the films with thickness above and below 20 nm. These observations can be explained due to the presence of surface states, which play an important role in determining the electronic transport properties of the thinnest films. The estimated surface carrier density 4 x 10^(13) cm^(-2) at room temperature correlates well with that recently reported from angle-resolved photoemission spectroscopy on ultrathin Bi(001) films

Enhancement of long-range correlations in a 2D vortex lattice by an incommensurate 1D disorder potential

arXiv:1410.7782v1Long-range correlations in two-dimensional (2D) systems are significantly altered by disorder potentials. Theory has predicted the existence of disorder-induced phenomena, such as Anderson localization or the emergence of a Bose glass. More recently, it has been shown that when disorder breaks 2D continuous symmetry, long-range correlations can be enhanced. Experimentally, developments in quantum gases have allowed the observation of the effects of competition between interaction and disorder. However, experiments exploring the effect of symmetry-breaking disorder are lacking. Here, we create a 2D vortex lattice at 0.1 K in a superconducting thin film with a well-defined 1D thickness modulation - the symmetry-breaking disorder - and track the field-induced modification using scanning tunnelling microscopy. We find that the 1D modulation becomes incommensurate with the vortex lattice and drives an order-disorder transition, behaving as a scale-invariant disorder potential. We show that the transition occurs in two steps and is mediated by the proliferation of topological defects. The resulting critical exponents determining the loss of positional and orientational order are far above theoretical expectations for scale-invariant disorder and follow instead the critical behaviour describing dislocation unbinding melting. Our data show that randomness disorders a 2D crystal, with enhanced long-range correlations due to the presence of a 1D modulation.This work was supported by the Spanish MINECO (FIS2011-23488, MAT2011-27553-C02, MAT 2012-38318-C03, Consolider Ingenio Molecular Nanoscience CSD2007-00010), the Comunidad de Madrid through program Nanobiomagnet (S2009/MAT-1726) and by the Marie Curie Actions under the project FP7-PEOPLE-2013-CIG-618321 and contract no. FP7-PEOPLE-2010-IEF-273105.Peer Reviewe