Electrostatically induced undulations of lamellar DNA-lipid complexes

We consider DNA-cationic lipid complexes that form lamellar stacks of lipid bilayers with parallel DNA strands intercalated in between. We calculate the electrostatically induced elastic deformations of the lipid bilayers. It is found that the membranes undulate with a periodicity that is set by the DNA interaxial distance. As a consequence the lamellar repeat distance changes resulting in a swelling or compression of the lamellar stack. Such undulations may be responsible for the intermembrane coupling between DNA strands in different layers as it is observed experimentally.Comment: 7 pages, submitted to EPJ

Desarrollo de herramientas de búsqueda en los archivos históricos de la CompañÍa de Jesús

El trabajo de los historiadores es pesado y difícil ya que consiste, fundamentalmente, en la localización, análisis e interpretación de documentos antiguos. Estos documentos, cuando están disponibles para su consulta, deben ser leídos uno por uno y todas las posibles referencias cruzadas, revisadas una por una. La Compañía de Jesús llegó a la Nueva España en el siglo XV y trabajó en colegios, misiones, parroquias y hospitales a lo largo de todo el continente hasta la expulsión de la Orden en 1767. Durante este tiempo, la Compañía de Jesús puso en marcha un sistema de comunicación conocido como las Cartas Anuales o Cartas Annuas que el Provincial enviaba al General de la Compañía en Roma. Cada una de las Cartas Anuales relataba las actividades llevadas a cabo por miembros de la Compañía. Para ayudarse a redactar cada Carta y con el fin de circular la información en toda la Provincia de la Nueva España, cada uno de los encargados de las obras enviaba al Provincial una o varias cartas conocidas como Puntos de Annua. La Compañía de Jesús, junto con el Archivo General de la Nación y el Instituto Nacional de Antropología e Historia se dio a la tarea de recopilar todas las Cartas Anuales escritas desde que los jesuitas llegaron a la Nueva España hasta su expulsión en 1767. Esta búsqueda resultó en más de 13000 folios que debieron paleografiarse para ayudar a la investigación histórica sobre la Compañía de Jesús. Como resultado de este trabajo de recuperación y paleografía y para facilitar el acceso y manejo de los documentos, se decidió crear una herramienta informática que ofreciera a los investigadores un motor de búsqueda para hacer referencias cruzadas rápida y fácilmente, así como el acceso a los documentos a través de índices temáticos. El desarrollo de esta herramienta presentó varios problemas técnicos que se han ido solucionando. Por ejemplo, la necesidad de que los documentos en formato electrónico siguieran fielmente las reglas de la paleografía. Este requerimiento hizo necesaria la realización de un filtro para manipular los archivos en formato XML. Se desarrolló también la interfaz gráfica para acceder a los índices temáticos y el motor de búsqueda para realizar referencias cruzadas en una o varias palabras, continuas o discontinuas en el texto del documento. La herramienta ha sido bien recibida por los investigadores y se ha decido aumentarla con algoritmos de Text-Mining para aumentar las capacidades de la búsqueda así como la generación de referencias cruzadas entre los documentos.ITESO, A.C

Elongation and fluctuations of semi-flexible polymers in a nematic solvent

We directly visualize single polymers with persistence lengths ranging from $\ell_p=0.05$ to 16 $\mu$m, dissolved in the nematic phase of rod-like {\it fd} virus. Polymers with sufficiently large persistence length undergo a coil-rod transition at the isotropic-nematic transition of the background solvent. We quantitatively analyze the transverse fluctuations of semi-flexible polymers and show that at long wavelengths they are driven by the fluctuating nematic background. We extract both the Odijk deflection length and the elastic constant of the background nematic phase from the data.Comment: 4 pages, 4 figures, submitted to PR

Diffusive Charge Transport in Graphene on SiO2

We review our recent work on the physical mechanisms limiting the mobility of graphene on SiO2. We have used intentional addition of charged scattering impurities and systematic variation of the dielectric environment to differentiate the effects of charged impurities and short-range scatterers. The results show that charged impurities indeed lead to a conductivity linear in density in graphene, with a scattering magnitude that agrees quantitatively with theoretical estimates [1]; increased dielectric screening reduces scattering from charged impurities, but increases scattering from short-range scatterers [2]. We evaluate the effects of the corrugations (ripples) of graphene on SiO2 on transport by measuring the height-height correlation function. The results show that the corrugations cannot mimic long-range (charged impurity) scattering effects, and have too small an amplitude-to-wavelength ratio to significantly affect the observed mobility via short-range scattering [3, 4]. Temperature-dependent measurements show that longitudinal acoustic phonons in graphene produce a resistivity linear in temperature and independent of carrier density [5]; at higher temperatures, polar optical phonons of the SiO2 substrate give rise to an activated, carrier density-dependent resistivity [5]. Together the results paint a complete picture of charge carrier transport in graphene on SiO2 in the diffusive regime.Comment: 28 pages, 7 figures, submitted to Graphene Week proceeding

Advanced predictive quality control strategy involving different facilities

There are many industries that use highly technological solutions to improve quality in all of their products. The steel industry is one example. Several automatic surface-inspection systems are used in the steel industry to identify various types of defects and to help operators decide whether to accept, reroute, or downgrade the material, subject to the assessment process. This paper focuses on promoting a strategy that considers all defects in an integrated fashion. It does this by managing the uncertainty about the exact position of a defect due to different process conditions by means of Gaussian additive influence functions. The relevance of the approach is in making possible consistency and reliability between surface inspection systems. The results obtained are an increase in confidence in the automatic inspection system and an ability to introduce improved prediction and advanced routing models. The prediction is provided to technical operators to help them in their decision-making process. It shows the increase in improvement gained by reducing the 40 % of coils that are downgraded at the hot strip mill because of specific defects. In addition, this technology facilitates an increase of 50 % in the accuracy of the estimate of defect survival after the cleaning facility in comparison to the former approach. The proposed technology is implemented by means of software-based, multi-agent solutions. It makes possible the independent treatment of information, presentation, quality analysis, and other relevant functions

Membrane-mediated interactions

Interactions mediated by the cell membrane between inclusions, such as membrane proteins or antimicrobial peptides, play important roles in their biological activity. They also constitute a fascinating challenge for physicists, since they test the boundaries of our understanding of self-assembled lipid membranes, which are remarkable examples of two-dimensional complex fluids. Inclusions can couple to various degrees of freedom of the membrane, resulting in different types of interactions. In this chapter, we review the membrane-mediated interactions that arise from direct constraints imposed by inclusions on the shape of the membrane. These effects are generic and do not depend on specific chemical interactions. Hence, they can be studied using coarse-grained soft matter descriptions. We deal with long-range membrane-mediated interactions due to the constraints imposed by inclusions on membrane curvature and on its fluctuations. We also discuss the shorter-range interactions that arise from the constraints on membrane thickness imposed by inclusions presenting a hydrophobic mismatch with the membrane.Comment: 38 pages, 10 figures, pre-submission version. In: Bassereau P., Sens P. (eds) Physics of Biological Membranes. Springer, Cha