3,617 research outputs found
Chemically tagging the Hyades Supercluster: A homogeneous sample of F6-K4 kinematically selected northern stars
Stellar kinematic groups are kinematical coherent groups of stars that might
have a common origin. These groups are dispersed throughout the Galaxy over
time by the tidal effects of both Galactic rotation and disc heating, although
their chemical content remains unchanged. The aim of chemical tagging is to
establish that the abundances of every element in the analysis are homogeneus
among the members. We study the case of the Hyades Supercluster to compile a
reliable list of members (FGK stars) based on our chemical tagging analysis.
For a total of 61 stars from the Hyades Supercluster, stellar atmospheric
parameters (Teff, logg, xi, and [Fe/H]) are determined using our code called
StePar, which is based on the sensitivity to the stellar atmospheric parameters
of the iron EWs measured in the spectra. We derive the chemical abundances of
20 elements and find that their [X/Fe] ratios are consistent with Galactic
abundance trends reported in previous studies. The chemical tagging method is
applied with a carefully developed differential abundance analysis of each
candidate member of the Hyades Supercluster, using a well-known member of the
Hyades cluster as a reference (vB 153). We find that only 28 stars (26 dwarfs
and 2 giants) are members, i.e. that 46% of our candidates are members based on
the differential abundance analysis. This result confirms that the Hyades
Supercluster cannot originate solely from the Hyades cluster.Comment: A&A, in pres
Vortices in U(1) Noncommutative Gauge Fields
Charged vortex solutions for noncommutative Maxwell-Higgs model in 3+1
dimensions are found. We show that the stability of these vortex solutions is
spoiled out for some, large enough, noncommutativity parameter. A non
topological charge, however, is induced by noncommutative effects.Comment: references added, slight modifications in the introduction and
conclusions. To be published in PR
Investigation of cell adhesion in chitosan membranes for peripheral nerve regeneration
Peripheral nerve injuries have produced major concerns in regenerative medicine for several years, as the recovery of normal nerve function continues to be a significant clinical challenge. Chitosan (CHT), because of its good biocompatibility, biodegradability and physicochemical properties, has been widely used as a biomaterial in tissue engineering scaffolding. In this study, CHT membranes were produced with three different Degrees of Acetylation (DA), envisioning its application in peripheral nerve regeneration. The three CHT membranes (DA I: 1%, DA II: 2%, DA III: 5%) were extensively characterized and were found to have a smooth and flat surface, with DA III membrane having slightly higher roughness and surface energy. All the membranes presented suitable mechanical properties and did not show any signs of calcification after SBF test. Biodegradability was similar for all samples, and adequate to physically support neurite outgrowth. The in vitro cell culture results indicate selective cell adhesion. The CHT membranes favoured Schwann cells invasion and proliferation, with a display of appropriate cytoskeletal morphology. At the same time they presented low fibroblast infiltration. This fact may be greatly beneficial for the prevention of fibrotic tissue formation, a common phenomenon impairing peripheral nerve regeneration. The great deal of results obtained during this work permitted to select the formulation with the greatest potential for further biological tests.This work has received funding from the European Community's Seventh Framework Programme (FP7-HEALTH-2011) under grant agreement no 278612 (BIOHYBRID). This study was also funded by European Union's FP7 Programme under grant agreement no REGPOT-CT2012-316331-POLARIS.The authors thank the chitosan raw material provided by Altakitin S.A., (Lisboa, Portugal). We are further thankful to Silke Fischer, Natascha Heidrich, Kerstin Kuhlemann, Jennifer Metzen, Hildegard Streich and Maike Wesemann (all from the Institute of Neuroanatomy, Hannover Medical School) for their technical support
Cellulose - Chitosan Nanocomposites - Evaluation of Physical, Mechanical and Biological Properties
This research describes the preparation of membranes with chitosan (CS) as the polymeric matrix and cellulose nanocrystals (CNC) as reinforcement. The aim was to evaluate their physical, mechanical and biological properties, and to determine their potential for biomedical use. Membranes were prepared via casting CNC suspensions in CS solution, at CNC concentrations of 0.5%, 1.0% and 2.0% (w/w) with pure chitosan as a reference. Analysis of membrane properties was performed using several techniques, such as ATR – FTIR, SEM, swelling test, maximum water absorption, dynamical mechanical analysis and in vivo (Winstar rats) biocompatibility and biodegradability assays for biological evaluation. Experimental results established that CNC reduced swelling rates and increased the maximum water absorption when CNC concentration was higher. Therefore, the presence of CNC in the matrix reduced Young’s modulus by approximately 50% in comparison with pure chitosan. All formulations demonstrated biocompatibility and biodegradability values ranged between 4% and 21% in the 30 days after implantation. Based on these results, these membranes may be of use for biomedical applications
La productividad del crédito en las pequeñas y medianas industrias (pymi) del sector manufacturero
The sustainability of productivity growth in an economy is not only generated by the utilization level of production factors - capital and labor - but also by the efficiency increase in the use and combination of these factors. In this sense, this research analyzes credit productivity in SMI in the manufacturing sector of the state of Yaracuy, in order to demonstrate the efficiency of credit use by industries’ owners or managers and its relationship with searching of productivity, through the factors profitability in final goods. This is a field design descriptive study, which addressed nine industries in the footwear, textiles, clothing and metallurgical sectors. Relevant conclusion shows that the desired productivity was not generated by the granted financing, according with the production indicators and employment generation, due to the country's economic environment and administrative barriers that significantly affected the industrial sector.La sostenibilidad del crecimiento de la productividad en una economía, no sólo se genera por el nivel de utilización de los factores de producción - capital y trabajo - sino también por el incremento en la eficiencia con la que se utilizan y combinan estos factores. En este sentido, la presente investigación analiza la productividad del crédito en las PYMI del sector Manufacturero del estado Yaracuy, con el propósito de demostrar la utilización eficiente de los créditos por parte de los dueños/gerentes de las industrias y su relación en la búsqueda de la productividad, por medio del aprovechamiento de los factores utilizados en la producción de bienes finales. El estudio es descriptivo bajo un diseño de campo, en el cual se abordó nueve industrias en áreas del calzado, textil, ropa y metalúrgico. Entre las conclusiones relevantes está que los indicadores de producción y generación de empleo con respecto al financiamiento otorgado, no generaron la productividad deseada, debido a coyunturas económicas propias del país y barreras administrativas que afectaron de manera significativa al sector industri
Human ISWI complexes are targeted by SMARCA5 ATPase and SLIDE domains to help resolve lesion-stalled transcription
Chromatin compaction of deoxyribonucleic acid (DNA) presents a major challenge to the detection and removal of DNA damage. Helix-distorting DNA lesions that block transcription are specifically repaired by transcription-coupled nucleotide excision repair, which is initiated by binding of the CSB protein to lesion-stalled RNA polymerase II. Using live cell imaging, we identify a novel
Vortices, Infrared effects and Lorentz Invariance Violation
The Yang-Mills theory with noncommutative fields is constructed following
Hamiltonian and lagrangean methods. This modification of the standard
Yang-Mills theory shed light on the confinement mechanism viewed as a Lorentz
invariance violation (LIV) effect. The modified Yang-Mills theory contain in
addition to the standard contribution, the term where
is a given space-like constant vector with canonical dimension of
energy. The field rescaling and the choice ,
one can show that the modified Yang-Mills theory in 3+1 dimensions can be made
equivalent to a Yang-Mills-Chern-Simons theory in 2+1 dimensions if one
consider only heavy fermionic excitations. Thus, the Yang-Mills-Chern-Simons
theory in 2+1 dimensions is a codified way of that include only heavy
quarks. The classical solutions of the modified Yang-Mills theory for the SU(2)
gauge group are confining ones.Comment: Title changed and comments added. To appear in PL
Self-similar and charged spheres in the diffusion approximation
We study spherical, charged and self--similar distributions of matter in the
diffusion approximation. We propose a simple, dynamic but physically meaningful
solution. For such a solution we obtain a model in which the distribution
becomes static and changes to dust. The collapse is halted with damped mass
oscillations about the absolute value of the total charge.Comment: 15 pages, 7 figure
Aharonov-Bohm interferometry with quantum dots: scattering approach versus tunneling picture
We address the question of how to model electron transport through closed
Aharonov-Bohm interferometers which contain quantum dots. By explicitly
studying interferometers with one and two quantum dots, we establish the
connection between a tunneling-Hamiltonian formulation on the one hand and a
scattering-matrix approach on the other hand. We prove that, under certain
circumstances, both approaches are equivalent, i.e., both types of models can
describe the same experimental setups. Furthermore, we analyze how the
interplay of the Aharonov-Bohm phase and the orbital phase associated with the
lengths of the interferometers' arms affect transport properties.Comment: 8 pages, 8 figures, published versio
Pair contact process with a particle source
We study the phase diagram and critical behavior of the one-dimensional pair
contact process (PCP) with a particle source using cluster approximations and
extensive simulations. The source creates isolated particles only, not pairs,
and so couples not to the order parameter (the pair density) but to a
non-ordering field, whose state influences the evolution of the order
parameter. While the critical point p_c shows a singular dependence on the
source intensity, the critical exponents appear to be unaffected by the
presence of the source, except possibly for a small change in beta. In the
course of our study we obtain high-precision values for the critical exponents
of the standard PCP, confirming directed-percolation-like scaling.Comment: 15 pages, 9 figure
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