Detection of DNA and Poly-L-Lysine using CVD Graphene-channel FET Biosensors

A graphene channel field-effect biosensor is demonstrated for detecting the binding of double-stranded DNA and poly-l-lysine. Sensors consist of CVD graphene transferred using a clean, etchant-free transfer method. The presence of DNA and poly-l-lysine are detected by the conductance change of the graphene transistor. A readily measured shift in the Dirac Voltage (the voltage at which the graphenes resistance peaks) is observed after the graphene channel is exposed to solutions containing DNA or poly-l-lysine. The Dirac voltage shift is attributed to the binding/unbinding of charged molecules on the graphene surface. The polarity of the response changes to positive direction with poly-l-lysine and negative direction with DNA. This response results in detection limits of 8 pM for 48.5 kbp DNA and 11 pM for poly-l-lysine. The biosensors are easy to fabricate, reusable and are promising as sensors of a wide variety of charged biomolecule

Low-power photothermal self-oscillation of bimetallic nanowires

We investigate the nonlinear mechanics of a bimetallic, optically absorbing SiN-Nb nanowire in the presence of incident laser light and a reflecting Si mirror. Situated in a standing wave of optical intensity and subject to photothermal forces, the nanowire undergoes self-induced oscillations at low incident light thresholds of $<1\, \rm{\mu W}$ due to engineered strong temperature-position ($T$-$z$) coupling. Along with inducing self-oscillation, laser light causes large changes to the mechanical resonant frequency $\omega_0$ and equilibrium position $z_0$ that cannot be neglected. We present experimental results and a theoretical model for the motion under laser illumination. In the model, we solve the governing nonlinear differential equations by perturbative means to show that self-oscillation amplitude is set by the competing effects of direct $T$-$z$ coupling and $2\omega_0$ parametric excitation due to $T$-$\omega_0$ coupling. We then study the linearized equations of motion to show that the optimal thermal time constant $\tau$ for photothermal feedback is $\tau \to \infty$ rather than the widely reported $\omega_0 \tau = 1$. Lastly, we demonstrate photothermal quality factor ($Q$) enhancement of driven motion as a means to counteract air damping. Understanding photothermal effects on micromechanical devices, as well as nonlinear aspects of optics-based motion detection, can enable new device applications as oscillators or other electronic elements with smaller device footprints and less stringent ambient vacuum requirements.Comment: New references adde

The Chrono-geometrical Structure of Special and General Relativity: a Re-Visitation of Canonical Geometrodynamics

A modern re-visitation of the consequences of the lack of an intrinsic notion of instantaneous 3-space in relativistic theories leads to a reformulation of their kinematical basis emphasizing the role of non-inertial frames centered on an arbitrary accelerated observer. In special relativity the exigence of predictability implies the adoption of the 3+1 point of view, which leads to a well posed initial value problem for field equations in a framework where the change of the convention of synchronization of distant clocks is realized by means of a gauge transformation. This point of view is also at the heart of the canonical approach to metric and tetrad gravity in globally hyperbolic asymptotically flat space-times, where the use of Shanmugadhasan canonical transformations allows the separation of the physical degrees of freedom of the gravitational field (the tidal effects) from the arbitrary gauge variables. Since a global vision of the equivalence principle implies that only global non-inertial frames can exist in general relativity, the gauge variables are naturally interpreted as generalized relativistic inertial effects, which have to be fixed to get a deterministic evolution in a given non-inertial frame. As a consequence, in each Einstein's space-time in this class the whole chrono-geometrical structure, including also the clock synchronization convention, is dynamically determined and a new approach to the Hole Argument leads to the conclusion that "gravitational field" and "space-time" are two faces of the same entity. This view allows to get a classical scenario for the unification of the four interactions in a scheme suited to the description of the solar system or our galaxy with a deperametrization to special relativity and the subsequent possibility to take the non-relativistic limit.Comment: 33 pages, Lectures given at the 42nd Karpacz Winter School of Theoretical Physics, "Current Mathematical Topics in Gravitation and Cosmology", Ladek, Poland, 6-11 February 200

ESTUDIO DEL COMPORTAMIENTO ESTRUCTURAL DE LOSAS MACIZAS DE CONCRETO REFORZADO PARA VIVIENDA

A partir de resultados analíticos de ejemplos ilustrativos y del reporte de características observadas, quedó demostradoque las losas macizas de concreto reforzado para vivienda no son diseñadas ni construidas adecuadamente en el ámbitode la zona de estudio, lo que explica los altos porcentajes de fallas observadas en servicio. Fue calculado el índice deconfiabilidad en seis viviendas representativas al considerar tres posibles escenarios de la corrosión del acero de refuerzo,con lo que se mostró un alto riesgo de falla o cuantiosas inversiones en mantenimiento. Se concluyó que para el correctodiseño de las losas deberá no sólo revisarse la resistencia a flexión sino principalmente controlar las deformacionesverticales, el agrietamiento por contracción y la permeabilidad, lo cual implica especificar un concreto denso y durable.Se presentan recomendaciones específicas

Evanescent field optical readout of graphene mechanical motion at room temperature

Graphene mechanical resonators have recently attracted considerable attention for use in precision force and mass sensing applications. To date, readout of their oscillatory motion has typically required cryogenic conditions to achieve high sensitivity, restricting their range of applications. Here we report the first demonstration of evanescent optical readout of graphene motion, using a scheme which does not require cryogenic conditions and exhibits enhanced sensitivity and bandwidth at room temperature. We utilise a high $Q$ microsphere to enable evanescent readout of a 70 $\mu$m diameter graphene drum resonator with a signal-to-noise ratio of greater than 25 dB, corresponding to a transduction sensitivity of $S_{N}^{1/2} =$ 2.6 $\times 10^{-13}$ m $\mathrm{Hz}^{-1/2}$. The sensitivity of force measurements using this resonator is limited by the thermal noise driving the resonator, corresponding to a force sensitivity of $F_{min} = 1.5 \times 10^{-16}$ N ${\mathrm{Hz}}^{-1/2}$ with a bandwidth of 35 kHz at room temperature (T = 300 K). Measurements on a 30 $\mu$m graphene drum had sufficient sensitivity to resolve the lowest three thermally driven mechanical resonances.Comment: Fixed formatting errors in bibliograph

Structure of smectic defect cores: an X-ray study of 8CB liquid crystal ultra-thin films

We study the structure of very thin liquid crystal films frustrated by antagonistic anchorings in the smectic phase. In a cylindrical geometry, the structure is dominated by the defects for film thicknesses smaller than 150 nm and the detailed topology of the defects cores can be revealed by x-ray diffraction. They appear to be split in half tube-shaped Rotating Grain Boundaries (RGB). We determine the RGB spatial extension and evaluate its energy per unit line. Both are significantly larger than the ones usually proposed in the literatureComment: 4 page

A Pragmatic analysis of emotion-triggering strategies in TED talks

[EN] TED talks are a relatively new genre, in which experts in different fields share their knowledge, ideas and experiences to large audiences. The talks are broadcasted worldwide, thus reaching international and intercultural spectators. Although public spoken language has been extensively studied in literature, TED talks present a new field of study, and are considered as a hybrid genre. It has been argued that, although similar in some ways, they differ from other oral discourse types, such as university lectures, in many aspects, such as the epistemic stance, the presentation of ideas, or the macro-discourse markers used (Caliendo and Compagnone, 2014). The utilization of emotion for triggering audience response is the foundation of the present study, aimed at examining the way speakers use emotions to involve spectators in their monologues, and exploring other strategies exploited to spark feedback, so that the most successful ones can be identified. The paper discusses the analysis of 120 TED talks from two different topics, business and education, taking a basic list of emotion words as a starting point, to continue examining how these emotion words and audiences intermingle by looking into laughter and applause, as the two identified forms of feedback. Results indicate that no significant differences can be found in the two subcorpora analyzed in terms of emotion words, the use of multiple humor strategies, and the acknowledgment of multicultural audiences on the side of the speakers.Mestre-Mestre, EM.; Pérez-Cabello De Alba, MB. (2022). A Pragmatic analysis of emotion-triggering strategies in TED talks. Circulo de Linguistica Aplicada a la Comunicacion. (92):257-271. https://doi.org/10.5209/clac.7799625727192Abelin, Åsa and Allwood, Jens. 2000. Cross Linguistic Interpretation of Emotional Prosody. In Proceedings ISCA w/s Speech and Emotion. Newcastle, Northern Ireland, 110–113.Alba-Juez, Laura and J. Lachlan Mackenzie. 2019a. 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Corpus-Based and Corpus-driven Analyses of Language Variation and Use. In Heine, B. and H. Narrog. The Oxford Handbook of Linguistic Analysis. Oxford; New York: Oxford University Press. DOI: https://doi.org/10.1093/oxfordhb/9780199544004.013.0008Caliendo, Giuditta and Compagnone, Antonio. 2014. Expressing epistemic stance in University lectures and TED talks: a contrastive corpus–based analysis. Lingue Linguaggi. 11(11). 105–122. DOI: https://doi.org/10.1285/i22390359v11p105Compagnone, Antonio. 2015. The reconceptualization of academic discourse as a professional practice in the digital age: A critical genre analysis of TED Talks. Hermes (Denmark), (54). 49–69. DOI: https://doi.org/10.7146/hjlcb.v27i54.22947Compagnone, Antonio. 2017. The pragmatics of Spoken Academic discourse in the Framework of Ted Talks: A case Study. Utrecht studies in language and Communication. 29.Culpeper, Jonathan. 2011. Impoliteness: Using Language to Cause Offence. Cambridge: Cambridge University Press. 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Aprendizaje de imágenes histológicas utilizando un microscopio virtual: metodología y opinión de los alumnos

El concepto de tejido es un constructo teorético muy útil para aprender a conocer las estructuras microscópicas del organismo y para diagnosticar, de forma objetiva, la mayoría de las lesiones, a través de imágenes histológicas (IH). Tradicionalmente, aprender a interpretar IH se basa en su observación repetitiva y monótona. Esto y la consideración de la Histología como una disciplina meramente descriptiva, ha determinado su escasa relevancia y su alto nivel de olvido para los alumnos, como ha sido puesto de relieve en varias publicaciones. Los recursos digitales han facilitado, de forma sustancial, el aprendizaje de la Histología, aunque todavía sigue basándose en la observación iterativa y monótona de IH. Para facilitar y mejorar dicho aprendizaje hemos creando y publicado una clasificación y sistematización de las IH. En este trabajo presentamos la combinación de la sistematización de las IH con el uso de un microscopio virtual accesible a todos los alumnos en cualquier lugar y momento (tablets, smartphones, ordenadores de mesa, portátiles, etc.). La evaluación de esta metodología, mediante una encuesta, pone de manifiesto su alto grado de aceptación por los alumnos y sus enormes posibilidades para un aprendizaje, a la vez, autónomo y colaborativo

Ordered interfaces for dual easy axes in liquid crystals

International audienceUsing nCB films adsorbed on MoS 2 substrates studied by x-ray diffraction, optical microscopy and Scanning Tunneling Microscopy, we demonstrate that ordered interfaces with well-defined orientations of adsorbed dipoles induce planar anchoring locked along the adsorbed dipoles or the alkyl chains, which play the role of easy axes. For two alternating orientations of the adsorbed dipoles or dipoles and alkyl chains, bi-stability of anchoring can be obtained. The results are explained using the introduction of fourth order terms in the phenomenological anchoring potential, leading to the demonstration of first order anchoring transition in these systems. Using this phenomenological anchoring potential, we finally show how the nature of anchoring in presence of dual easy axes (inducing bi-stability or average orientation between the two easy axes) can be related to the microscopical nature of the interface. Introduction Understanding the interactions between liquid crystal (LC) and a solid substrate is of clear applied interest, the vast majority of LC displays relying on control of interfaces. However this concerns also fundamental problems like wetting phenomena and all phenomena of orientation of soft matter bulk induced by the presence of an interface. In LCs at interfaces, the so-called easy axes correspond to the favoured orientations of the LC director close to the interface. If one easy axis only is defined for one given interface, the bulk director orients along or close to this axis [1]. It is well known that, in anchoring phenomena, two major effects compete to impose the anchoring directions of a liquid crystal, first, the interactions between molecules and the interface, second, the substrate roughness whose role has been analyzed by Berreman [2]. The influence of adsorbed molecular functional groups at the interface is most often dominant with, for example in carbon substrates, a main influence of unsaturated carbon bonds orientation at the interface [3]. In common LC displays, there is one unique easy axis, but modifications of surfaces have allowed for the discovery of promising new anchoring-related properties. For instance, the first anchoring bi-stability has been established on rough surfaces, associated with electric ordo-polarization [4] and the competition between a stabilizing short-range term and a destabilizing long-range term induced by an external field, can induce a continuous variation of anchoring orientation [5]. More recently, surfaces with several easy axes have been studied extensively. It has been shown that control of a continuous variation of director pretilt, obtained in several systems [6, 7], is associated with the presence of two different easy axes, one perpendicular to the substrate (homeotropic) and one planar [7, 8]. Similar models can explain the continuous evolution of anchoring between two planar orientations observed on some crystalline substrates [9]. However, in the same time, two easy axes can also lead to anchoring bi-stability [10, 11] or discontinuous transitions of anchoring [9], which is not compatible with the model established to interpret observed control of pretilt. In order to be able to predict if bi-stability or continuous combination of the two easy axes occurs for one given system, it becomes necessary to understand the microscopic origin of the easy axes

Beyond the subject DP versus the subject pronoun divide in agreement switches

Producción CientíficaPrevious code-switching literature argues that no switch takes place between a pronoun and a verb, while Determiner Phrases (DPs) do code-switch. This paper uses code-switching acceptability judgment data elicited from three groups of English–Spanish bilinguals (2L1 children, L2 English children and L2 English adults) to test: (i) van Gelderen & MacSwan’s (2008) PF disjunction theorem intended to account for the DP/pronoun divide; and (ii) an agreement version of the analogical criterion (Liceras et al. 2008) which is based on Pesetsky & Torrego’s (2001) double-feature valuation mechanism intended to account for the different status of third person versus first and second person pronominal subjects. We show that the PF disjunction theorem is clearly rooted in the mind of the bilingual and that the Spanish dominant bilinguals can ‘relax’ its requirements to value person agreement features as predicted by the double-feature valuation mechanism.Ministerio de Ciencia e Innovación - FEDER (HUM2007-62213 and BFF2002-00442)Faculty of Arts of the University of Ottawa - Social Sciences and Humanities Research Council of Canada (410-2004-2034)International Council for Canadian Studies - Department of Foreign Affairs (10-CEA-A