The role of pressure on the magnetism of bilayer graphene

We study the effect of pressure on the localized magnetic moments induced by vacancies in bilayer graphene in the presence of topological defects breaking the bipartite nature of the lattice. By using a mean-field Hubbard model we address the two inequivalent types of vacancies that appear in the Bernal stacking bilayer graphene. We find that by applying pressure in the direction perpendicular to the layers the critical value of the Hubbard interaction needed to polarize the system decreases. The effect is particularly enhanced for one type of vacancies, and admits straightforward generalization to multilayer graphene in Bernal stacking and graphite. The present results clearly demonstrate that the magnetic behavior of multilayer graphene can be affected by mechanical transverse deformation

Harvesting Thermal Fluctuations: Activation Process Induced by a Nonlinear Chain in Thermal Equilibrium

We present a model in which the immediate environment of a bistable system is a molecular chain which in turn is connected to a thermal environment of the Langevin form. The molecular chain consists of masses connected by harmonic or by anharmonic springs. The distribution, intensity, and mobility of thermal fluctuations in these chains is strongly dependent on the nature of the springs and leads to different transition dynamics for the activated process. Thus, all else (temperature, damping, coupling parameters between the chain and the bistable system) being the same, the hard chain may provide an environment described as diffusion-limited and more effective in the activation process, while the soft chain may provide an environment described as energy-limited and less effective. The importance of a detailed understanding of the thermal environment toward the understanding of the activation process itself is thus highlighted

Dynamics of Holes and Universality Class of the Antiferromagnetic Transition in the Two Dimensional Hubbard Model

The dynamics of a single hole (or electron) in the two dimensional Hubbard model is investigated. The antiferromagnetic background is described by a N\`eel state, and the hopping of the carrier is analyzed within a configuration interaction approach. Results are in agreement with other methods and with experimental data when available. All data are compatible with the opening of a mean field gap in a Fermi liquid of spin polarons, the so called Slater type of transition. In particular, this hypothesis explains the unusual dispersion relation of the quasiparticle bands near the transition. Recent photoemission data for Ca$_2$CuO$_2$Cl$_2$ are analyzed within this context.Comment: New results and comparison with recent data adde

Force measurements with optical tweezers inside living cells

The force exerted by optical tweezers can be measured by tracking the momentum changes of the trapping beam, a method which is more general and powerful than traditional calibration techniques as it is based on first principles, but which has not been brought to its full potential yet, probably due to practical difficulties when combined with high-NA optical traps, such as the necessity to capture a large fraction of the scattered light. We show that it is possible to measure forces on arbitrary biological objects inside cells without an in situ calibration, using this approach. The instrument can be calibrated by measuring three scaling parameters that are exclusively determined by the design of the system, thus obtaining a conversion factor from volts to piconewtons that is theoretically independent of the physical properties of the sample and its environment. We prove that this factor keeps valid inside cells as it shows good agreement with other calibration methods developed in recent years for viscoelastic media. Finally, we apply the method to measuring the stall forces of kinesin and dynein in living A549 cells.Publisher PD

Compositeness effects, Pauli's principle and entanglement

We analyse some compositeness effects and their relation with entanglement. We show that the purity of a composite system increases, in the sense of the expectation values of the deviation operators, with large values of the entanglement between the components of the system. We also study the validity of Pauli's principle in composite systems. It is valid within the limits of application of the approach presented here. We also present an example of two identical fermions, one of them entangled with a distinguishable particle, where the exclusion principle cannot be applied. This result can be important in the description of open systems

Hiperpresión intraósea de la rótula como consecuencia de un traumatismo: Modelo experimental en oveja

El objetivo del presente estudio fue provocar un modelo experimental de hiperpresión intraósea que permita estudiar correlacionar esta alteración con los cambios degenerativos articulares en fases precoces y estudiar el efecto de distintas actuaciones terapéuticas. Se emplearon diez ovejas a las que se produjo un traumatismo controlado en la rótula derecha, la rótula izquierda se usó como control. A los cuatro meses posteriormente el traumatismo se observó un aumento significativo en la presión intraósea de las rótulas derechas (p<0.01). En conclusión, el estudio define un modelo experimental reproducible y fiable para su uso en el estudio de la hiperpresión intraósea de la rótula.The aim of the present study was to create a experimental modelo of intraosseous hiperpressure of the patella in sheep. Ten animals underwent a single blunt trauma over the pantalla. At tour-month follow-up period, there was a statistically significant increase of bone marrow pressure in traumatized patellae (p<0.01). In conclusión, the study provides an experimental model to study the pathophisiology and treatment of intraosseus hiperpressure of the patella

The Arabidopsis Synaptotagmin1 is enriched in endoplasmic reticulum-plasma membrane contact sites and confers cellular resistance to mechanical stresses

Eukaryotic endoplasmic reticulum (ER)-plasma membrane (PM) contact sites are evolutionarily conserved microdomains that have important roles in specialized metabolic functions such as ER-PM communication, lipid homeostasis, and Ca2+ influx. Despite recent advances in knowledge about ER-PM contact site components and functions in yeast (Saccharomyces cerevisiae) and mammals, relatively little is known about the functional significance of these structures in plants. In this report, we characterize the Arabidopsis (Arabidopsis thaliana) phospholipid binding Synaptotagmin1 (SYT1) as a plant ortholog of the mammal extended synaptotagmins and yeast tricalbins families of ER-PM anchors. We propose that SYT1 functions at ER-PM contact sites because it displays a dual ER-PM localization, it is enriched in microtubule-depleted regions at the cell cortex, and it colocalizes with Vesicle-Associated Protein27-1, a known ER-PM marker. Furthermore, biochemical and physiological analyses indicate that SYT1 might function as an electrostatic phospholipid anchor conferring mechanical stability in plant cells. Together, the subcellular localization and functional characterization of SYT1 highlights a putative role of plant ER-PM contact site components in the cellular adaptation to environmental stresses

Evolución en la enseñanza de la ciencia: una introducción para maestros

PDF de 41 páginas con gráficos y figuras a color. M.ª José Gómez Díaz es Coordinadora de El CSIC en la Escuela. VACC-CSIC José María López Sancho es Director de El CSIC en la Escuela. IFF-CSIC Esteban Moreno Gómez es director de los recursos WEB del programa El CSIC en la Escuela.Exponemos brevemente las últimas líneas de investigación centradas en cuestionarios de evaluación diagnóstica referentes a la NOS (Nature of Science). Utilizamos esta exposición para meditar acerca de las líneas fundamentales que definen la verdadera naturaleza de la ciencia que debemos aprender y transmitir a nuestros alumnos de acuerdo con sus características. El concepto de NOS se deriva de la forma en la que los científicos construyen el conocimiento científico y en sus características. Nosotros iremos un paso más allá en cuanto a abstracción: nos apoyamos en el modelo de conocimiento de Piaget que, como veremos, coincide exactamente con el esquema introducido por Kuhn para explicar la construcción del conocimiento de las comunidades científicas.Peer reviewe