508 research outputs found
Domain wall dynamics in expanding spaces
We study the effects on the dynamics of kinks due to expansions and
contractions of the space. We show that the propagation velocity of the kink
can be adiabatically tuned through slow expansions/contractions, while its
width is given as a function of the velocity. We also analyze the case of fast
expansions/contractions, where we are no longer on the adiabatic regime. In
this case the kink moves more slowly after an expansion-contraction cycle as a
consequence of loss of energy through radiation. All these effects are
numerically studied in the nonlinear Klein-Gordon equations (both for the
sine-Gordon and for the phi^4 potential), and they are also studied within the
framework of the collective coordinate evolution equations for the width and
the center of mass of the kink. These collective coordinate evolution equations
are obtained with a procedure that allows us to consider even the case of large
expansions/contractions.Comment: LaTeX, 18 pages, 2 figures, improved version to appear in Phys Rev
Magnetization structure of a Bloch point singularity
Switching of magnetic vortex cores involves a topological transition
characterized by the presence of a magnetization singularity, a point where the
magnetization vanishes (Bloch point). We analytically derive the shape of the
Bloch point that is an extremum of the free energy with exchange, dipole and
the Landau terms for the determination of the local value of the magnetization
modulus.Comment: 4 pages, 2 figure
Perturbaciones debidas a efluentes domésticos en poliquetos asociados a bancos de bivalvos de Brachidontes rodriguezii en Mar de Plata (Atlántico sudoccidental)
Continuous and short-term disturbances are produced on intertidal Brachidontes rodriguezii mussel beds by the sewage outfall of Mar del Plata, SW Atlantic. The effects on the associated polychaetes living on and between mussels were investigated, in both the spatial and short-term temporal scales. Multivariate methods show that the polychaete fauna was influenced by tidal level, total amount of sediment accumulated between mussels, distance from the sewage outfall, organic carbon of interstitial sediments, and sewage volume before and after the summer season. Environmental variables in the water column fitted with a spatial and temporal organic gradient. Capitella ‘capitata’ sp. showed typical opportunistic behaviour in relation to organic enrichment, as did Neanthes succinea, both being numerically dominant near the sewage discharge. Cirratulus sp., Caulleriella alata, and Boccardia polybranchia were common at intermediate distances from the outfall. Syllis prolixa, S. gracilis, and Protoariciella uncinata reached their highest abundance at intermediate stations and were characteristic of the control site. Close to the outfall mussel density and dominance is low, and opportunist polychaetes successfully colonize organically enriched interstitial sediments. At intermediate distances from the outfall sediments retained by mussels reach their maximum values, and density of polychaetes is also high. The control station is characterized by monolayered mussel beds and very low diversity of polychaetes. Opportunistic polychaetes increase in response to short-term increases of sewage discharge during the summer season (November-March).Perturbaciones contínuas y de corto período de tiempo debidas a efluentes domésticos afectan a los bancos de los bivalvos Brachidontes rodriguezii en Mar del Plata, Atlántico sudoccidental. Se investigaron sus efectos sobre los poliquetos que viven asociados dentro y sobre los bancos, tanto en la escala espacial como la temporal (corto plazo). Métodos multivariados mostraron que los poliquetos estuvieron relacionados al nivel de marea, al total de sedimentos acumulados entre los bivalvos, a la distancia al efluente, al carbono orgánico total de los sedimentos y al volumen de descarga antes y después del verano. Las variables ambientales de la columna de agua estuvieron en concordancia con un gradiente de enriquecimiento orgánico espacial y temporal. Capitella ‘capitata’ sp. mostró el típico comportamiento oportunista en relación al enriquecimiento orgánico, al igual que Neanthes succinea, siendo ambas especies numéricamente dominantes cerca del efluente. Cirratulus sp., Caulleriella alata y Boccardia polybranchia fueron comunes a distancias intermedias del efluente. Syllis prolixa, S. gracilis y Protoariciella uncinata alcanzaron sus más altas abundancias a distancias intermedias, pero fueron características del sitio control. Cerca de la descarga del efluente la densidad y dominancia de bivalvos es baja, y los poliquetos oportunistas colonizaron exitosamente los sedimentos intersticiales enriquecidos orgánicamente. A distancias intermedias del efluente los sedimentos retenidos por los bivalvos alcanzaron sus mayores valores, y la riqueza de los poliquetos fue también alta. Las áreas control estuvieron caracterizadas por una monocapa de bivalvos y muy baja riqueza de poliquetos. Los poliquetos oportunistas incrementaron sus abundancias en respuesta al incremento del volumen de descarga en el período antes-después del verano (noviembre-marzo).  
Sewage-induced disturbance on polychaetes inhabiting intertidal mussel beds of <i>Brachidontes rodriguezii</i> off Mar del Plata (SW Atlantic, Argentina).
Phosphomannosylation and the functional analysis of the extended Candida albicans MNN4-like gene family
We thank Luz A. López-Ramírez (Universidad de Guanajuato) for technical assistance. This work was supported by Consejo Nacional de Ciencia y Tecnología (ref. CB2011/166860; PDCPN2014-247109, and FC 2015-02-834), Universidad de Guanajuato (ref. 000025/11; 0087/13; ref. 1025/2016; Convocatoria Institucional para Fortalecer la Excelencia Académica 2015; CIFOREA 89/2016), Programa de Mejoramiento de Profesorado (ref. UGTO-PTC-261), and Red Temática Glicociencia en Salud (CONACYT-México). NG acknowledges the Wellcome Trust (086827, 075470, 101873, and 200208) and MRC Centre for Medical Mycology for funding (N006364/1). KJ was supported by a research visitor grant to Aberdeen from China Scholarship Council (CSC No. 201406055024). The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fmicb.2017.02156/full#supplementary-materialPeer reviewedPublisher PD
Fiber Laser Microcutting of AISI 316L Stainless Steel Tubes- influence of Pulse Energy and Spot Overlap on Back Wall Dross
AbstractThe design of coronary stents imposes high demands in terms of dimensional tolerance and surface finish. These devices are manufactured by laser microcutting of miniature tubes in materials such as stainless steel, cobalt chromium alloys and Nitinol. The work presented here is focused on fiber laser microcutting for coronary struts in AISI 316L stainless steel. This work studies the influence of gases such compressed air and argon passing through the tube in order to drag molten material while laser microcutting is performed. The experimental work studies the influence of beam spot overlap and pulse energy on back wall dross and average surface roughness, using response surface methodology. The results indicate that the introduction of compressed air or argon gas is a relevant method to reduce the amount of dross adhered in the back wall of the miniature tube
Advances in the study of nano-structured Co/MCM-41 materials : Surface and magnetic characterization
Co-modified mesoporous supports with MCM-41 structure and several metal loadings were successfully synthesized by a fast wet impregnation method. The nature and location of different Co species formed on the solids were inferred by TEM/SEM, XPS, XANES/EXAFS, adsorption of pyridine coupled to FT-IR spectroscopy and temperature dependence of magnetization. The presence of Co oxide species (clusters and Co3O4 nanoparticles) inside the channels of all the samples could be evidenced by TEM, XPS and XANES/EXAFS. In this sense, the surface Co/Si atomic ratios obtained by XPS were notably lower than the corresponding bulk Co/Si ratios obtained by ICP, indicating that the Co atoms are mostly incorporated inside the mesopores channels of the silica matrix. Nevertheless, by TEM, Co3O4 nanoparticles of small size segregated on the external surface of the silicate were also observed for the higher metal loadings. The temperature dependence of the magnetization performed for the Co/M(2.5) sample allowed to assign its superparamagnetic behavior to the presence of clusters and Co3O4 nanoparticles of very small size that grow inside the MCM-41 mesopores. Therefore, the analyses presented in this work indicate that a Co theoretical loading of 2.5 wt% leads to the formation of Co oxide nanospecies in the MCM-41 support with a particular superparamagnetic behavior. This sample with improved structural and magnetic properties result an attractive porous solid for drug hosting, to be applied in the field of the controlled release of medicaments.Instituto de Física La Plat
Vortex Polarity Switching in Magnets with Surface Anisotropy
Vortex core reversal in magnetic particle is essentially influenced by a
surface anisotropy. Under the action of a perpendicular static magnetic field
the vortex core undergoes a shape deformationof pillow- or barrel-shaped type,
depending on the type of the surface anisotropy. This deformation plays a key
point in the switching mechanism: We predict that the vortex polarity switching
is accompanied (i) by a linear singularity in case of Heisenberg magnet with
bulk anisotropy only and (ii) by a point singularities in case of surface
anisotropy or exchange anisotropy. We study in details the switching process
using spin-lattice simulations and propose a simple analytical description
using a wired core model, which provides an adequate description of the Bloch
point statics, its dynamics and the Bloch point mediated switching process. Our
analytical predictions are confirmed by spin-lattice simulations for Heisenberg
magnet and micromagnetic simulations for nanomagnet with account of a dipolar
interaction.Comment: 17 pages, 15 figure
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