Identificación y estudio del agente causal de la mancha mantecosa del cafeto.

Se determinó el agente causal de la mancha mantecosa, sus relaciones con el hospedante y la susceptibilidad a este patógeno de 5 variedades de café.Café-CoffeaMaestría en CienciasMaestrí

PVA/ alginate/ tannic acid crosslinked aerogels with low flammability and high mechanical resistance

Aerogels are ultra-light, highly porous materials derived from gels in which the solvent has been replaced by gas. Aerogels based on renewable and biodegradable materials are gained attention as environmentally friendly alternatives to conventional foam [1]. This study focuses on the mechanical, thermal, and combustion behavior of a polyvinyl alcohol (PVA), sodium alginate (SA) and tannic acid (TA) aerogel obtained by freeze-drying and ion crosslinking (Ca2+ and B - ). Aerogels containing 5g of PVA, 3g of TA, and 2g of SA exhibit the highest compressive resistance, which was increased by 30% after crosslinking (87.4 MPa/gcm -3 ). In comparison to pure PVA, the addition of TA and SA to the blends decreased its thermal degradation rate. The crosslinking further contributed to an 81% of reduction of the degradation rate (0.16 %/ºC) making samples high thermally stable. Regarding flammability samples burnt after being exposed to radiation due to the presence of the highly combustible PVA. However, the heat release rate (HRR) and fire growth (FIGRA) parameters decreased by 67% and 50% respectively when TA and SA was added to pure PVA aerogel. After crosslinking, an additional decrement of 35% in HRR and 54% in FIGRA respectively was obtained (76 kW/m2 and 1.96 kW/m2 s), which corresponds to a very low flame intensity. These results are down below of previous values reported by Wu et al.[2], who worked on PVA/SA crosslinking aerogels filled with inorganic montmorillonite. Hence, the cross-linked aerogels presented here can be considered a very promising sustainable alternative to conventional fossil-derived foams

Temperature dependence of current self-oscillations and electric field domains in sequential tunneling doped superlattices

We examine how the current--voltage characteristics of a doped weakly coupled superlattice depends on temperature. The drift velocity of a discrete drift model of sequential tunneling in a doped GaAs/AlAs superlattice is calculated as a function of temperature. Numerical simulations and theoretical arguments show that increasing temperature favors the appearance of current self-oscillations at the expense of static electric field domain formation. Our findings agree with available experimental evidence.Comment: 7 pages, 5 figure

Spin-filtering and charge- and spin-switching effects in a quantum wire with periodically attached stubs

Spin-dependent electron transport in a periodically stubbed quantum wire in the presence of Rashba spin-orbit interaction (SOI) is studied via the nonequilibrium Green's function method combined with the Landauer-Buttiker formalism. The coexistence of spin filtering, charge and spin switching are found in the considered system. The mechanism of these transport properties is revealed by analyzing the total charge density and spin-polarized density distributions in the stubbed quantum wire. Furthermore, periodic spin-density islands with high polarization are also found inside the stubs, owing to the interaction between the charge density islands and the Rashba SOI-induced effective magnetic field. The proposed nanostructure may be utilized to devise an all-electrical multifunctional spintronic device.Comment: 4 pages, 4 figure

Anti-microbiota vaccines modulate the tick microbiome in a taxon-specific manner

The lack of tools for the precise manipulation of the tick microbiome is currently a major limitation to achieve mechanistic insights into the tick microbiome. Anti-tick microbiota vaccines targeting keystone bacteria of the tick microbiota alter tick feeding, but their impact on the taxonomic and functional profiles of the tick microbiome has not been tested. In this study, we immunized a vertebrate host model (Mus musculus) with live bacteria vaccines targeting keystone (i.e., Escherichia-Shigella) or non-keystone (i.e., Leuconostoc) taxa of tick microbiota and tested the impact of bacterial-specific antibodies (Abs) on the structure and function of tick microbiota. We also investigated the effect of these anti-microbiota vaccines on mice gut microbiota composition. Our results showed that the tick microbiota of ticks fed on Escherichia coli-immunized mice had reduced Escherichia-Shigella abundance and lower species diversity compared to ticks fed on control mice immunized with a mock vaccine. Immunization against keystone bacteria restructured the hierarchy of nodes in co-occurrence networks and reduced the resistance of the bacterial network to taxa removal. High levels of E. coli-specific IgM and IgG were negatively correlated with the abundance of Escherichia-Shigella in tick microbiota. These effects were not observed when Leuconostoc was targeted with vaccination against Leuconostoc mesenteroides. Prediction of functional pathways in the tick microbiome using PICRUSt2 revealed that E. coli vaccination reduced the abundance of lysine degradation pathway in tick microbiome, a result validated by qPCR. In contrast, the gut microbiome of immunized mice showed no significant alterations in the diversity, composition and abundance of bacterial taxa. Our results demonstrated that anti-tick microbiota vaccines are a safe, specific and an easy-to-use tool for manipulation of vector microbiome. These results guide interventions for the control of tick infestations and pathogen infection/transmission. © Copyright © 2021 Mateos-Hernández, Obregón, Wu-Chuang, Maye, Bornères, Versillé, de la Fuente, Díaz-Sánchez, Bermúdez-Humarán, Torres-Maravilla, Estrada-Peña, Hodžic, Šimo and Cabezas-Cruz

Four millennia of Iberian biomolecular prehistory illustrate the impact of prehistoric migrations at the far end of Eurasia

Population genomic studies of ancient human remains have shown how modern-day European population structure has been shaped by a number of prehistoric migrations. The Neolithization of Europe has been associated with large-scale migrations from Anatolia, which was followed by migrations of herders from the Pontic steppe at the onset of the Bronze Age. Southwestern Europe was one of the last parts of the continent reached by these migrations, and modern-day populations from this region show intriguing similarities to the initial Neolithic migrants. Partly due to climatic conditions that are unfavorable for DNA preservation, regional studies on the Mediterranean remain challenging. Here, we present genome-wide sequence data from 13 individuals combined with stable isotope analysis from the north and south of Iberia covering a four-millennial temporal transect (7, 500–3, 500 BP). Early Iberian farmers and Early Central European farmers exhibit significant genetic differences, suggesting two independent fronts of the Neolithic expansion. The first Neolithic migrants that arrived in Iberia had low levels of genetic diversity, potentially reflecting a small number of individuals; this diversity gradually increased over time from mixing with local hunter-gatherers and potential population expansion. The impact of post-Neolithic migrations on Iberia was much smaller than for the rest of the continent, showing little external influence from the Neolithic to the Bronze Age. Paleodietary reconstruction shows that these populations have a remarkable degree of dietary homogeneity across space and time, suggesting a strong reliance on terrestrial food resources despite changing culture and genetic make-up

Contextualisation and authenticity in TBLT: voices from Chinese classrooms

In view of ongoing debates about the future of TBLT in EFL contexts (Thomas & Reinders, 2015; Zheng & Borg, 2014), we present a detailed case study of teacher beliefs and practices regarding TBLT conducted in a secondary school in mainland China with a long history of communicative and task-based teaching approaches. We used a mixed-methods approach to gather a broad range of triangulated data, combining individual interviews, material analysis and observations coded using a novel task-focused version of the COLT scheme (Littlewood, 2011; Spada & Fröhlich, 1995). Quantitative and qualitative findings revealed positive beliefs about TBLT principles in general, reflecting strong institutional support for communicative teaching. However, there was marked variability between beliefs and practices in using tasks, especially with beginner-level learners. Most teachers demonstrated an intrinsic lack of confidence in using tasks as more than a communicative ‘add-on’ to standard form-focused teaching. We argue this demonstrates a need for building teacher autonomy (Aoki, 2002; Benson, 2007), in implementing TBLT, even in supportive settings, to support successful authentic contextualising TBLT principles in different EFL contexts

Kaon Production and Kaon to Pion Ratio in Au+Au Collisions at \snn=130 GeV

Mid-rapidity transverse mass spectra and multiplicity densities of charged and neutral kaons are reported for Au+Au collisions at \snn=130 GeV at RHIC. The spectra are exponential in transverse mass, with an inverse slope of about 280 MeV in central collisions. The multiplicity densities for these particles scale with the negative hadron pseudo-rapidity density. The charged kaon to pion ratios are $K^+/\pi^- = 0.161 \pm 0.002 {\rm (stat)} \pm 0.024 {\rm (syst)}$ and $K^-/\pi^- = 0.146 \pm 0.002 {\rm (stat)} \pm 0.022 {\rm (syst)}$ for the most central collisions. The $K^+/\pi^-$ ratio is lower than the same ratio observed at the SPS while the $K^-/\pi^-$ is higher than the SPS result. Both ratios are enhanced by about 50% relative to p+p and $\bar{\rm p}$+p collision data at similar energies.Comment: 6 pages, 3 figures, 1 tabl

Single Spin Asymmetry ANA_N in Polarized Proton-Proton Elastic Scattering at s=200\sqrt{s}=200 GeV

We report a high precision measurement of the transverse single spin asymmetry $A_N$ at the center of mass energy $\sqrt{s}=200$ GeV in elastic proton-proton scattering by the STAR experiment at RHIC. The $A_N$ was measured in the four-momentum transfer squared $t$ range $0.003 \leqslant |t| \leqslant 0.035$ \GeVcSq, the region of a significant interference between the electromagnetic and hadronic scattering amplitudes. The measured values of $A_N$ and its $t$-dependence are consistent with a vanishing hadronic spin-flip amplitude, thus providing strong constraints on the ratio of the single spin-flip to the non-flip amplitudes. Since the hadronic amplitude is dominated by the Pomeron amplitude at this $\sqrt{s}$, we conclude that this measurement addresses the question about the presence of a hadronic spin flip due to the Pomeron exchange in polarized proton-proton elastic scattering.Comment: 12 pages, 6 figure

Evolution of the differential transverse momentum correlation function with centrality in Au+Au collisions at sNN=200\sqrt{s_{NN}} = 200 GeV

We present first measurements of the evolution of the differential transverse momentum correlation function, {\it C}, with collision centrality in Au+Au interactions at $\sqrt{s_{NN}} = 200$ GeV. {\it C} exhibits a strong dependence on collision centrality that is qualitatively similar to that of number correlations previously reported. We use the observed longitudinal broadening of the near-side peak of {\it C} with increasing centrality to estimate the ratio of the shear viscosity to entropy density, $\eta/s$, of the matter formed in central Au+Au interactions. We obtain an upper limit estimate of $\eta/s$ that suggests that the produced medium has a small viscosity per unit entropy.Comment: 7 pages, 4 figures, STAR paper published in Phys. Lett.