Investigation of the Effects of Hydrodynamic and Parasitic Electrostatic Forces on the Dynamics of a High Aspect Ratio MEMS Accelerometer

AbstractWe present the results of an extensive characterization of physical and electrostatic effects influencing the dynamical behavior of a micro-electromechanical (MEMS) accelerometer based on commercial technology. A similar device has been utilized recently to demonstrate the effect of Casimir and other nano-scale interactions on the pull-in distance [Ardito et. al., Microelectron. Reliab., 52 (2012) 271]. In the present work, we focus on the influence of pressure, plate separation, and electric surface potentials on the spectral mechanical response. We finally find evidence for the presence of non-viscous damping due to compressibility of the ambient gas, and demonstrate a strong dependence of the sensitivity on the parameters of the operating point

Obstáculos en el aprendizaje de las matemáticas relacionados con deficiencias en la traducción del lenguaje cotidiano al lenguaje matemático y viceversa

El presente trabajo consiste en una serie de reflexiones en torno a los obstáculos en el aprendizaje de las matemáticas que se relacionan con la traducción, del lenguaje cotidiano en que se plantea un problema matemático escolar, al lenguaje matemático y la fase de modelado necesaria para la resolución. Es probable que la influencia del lenguaje no haya recibido mucha atención en la investigación de la matemática educativa, a pesar de los indicadores al respecto de su importancia como mediador de los procesos de aprendizaje complejo, por lo que su estudio podría arrojar información valiosa para determinar su influencia y elaborar estrategias y materiales que atiendan esa situación.Eje: Educación Universitaria ReflexionesRed de Universidades con Carreras en Informática (RedUNCI

Obstáculos en el aprendizaje de las matemáticas relacionados con deficiencias en la traducción del lenguaje cotidiano al lenguaje matemático y viceversa

El presente trabajo consiste en una serie de reflexiones en torno a los obstáculos en el aprendizaje de las matemáticas que se relacionan con la traducción, del lenguaje cotidiano en que se plantea un problema matemático escolar, al lenguaje matemático y la fase de modelado necesaria para la resolución. Es probable que la influencia del lenguaje no haya recibido mucha atención en la investigación de la matemática educativa, a pesar de los indicadores al respecto de su importancia como mediador de los procesos de aprendizaje complejo, por lo que su estudio podría arrojar información valiosa para determinar su influencia y elaborar estrategias y materiales que atiendan esa situación.Eje: Educación Universitaria ReflexionesRed de Universidades con Carreras en Informática (RedUNCI

La innovación curricular para la enseñanza en línea, bajo el enfoque basado en competencias

Se describen reflexiones al respecto de las habilidades y destrezas básicas docentes que es pertinente desarrollar ante el escenario para la modificación curricular hacia el enfoque de competencias profesionales, derivadas del desarrollo de un posgrado en ciencias en matemática educativa, ofrecido en modalidad a distancia, así como de la colaboración para la reforma curricular de dos universidades del occidente de México, una de las cuales ya adoptó el modelo y otra en donde apenas se inicia el proceso de transformación. Se plantea que una innovación curricular que no va acompañada de una capacitación docente paralela, está destinada a tener poco éxito, por lo que se señalan las áreas de actualización que han sido propuestas, a solicitud de las autoridades correspondientes. Aunque puede parecer trivial, se insiste en la necesidad de poner atención al empleo del lenguaje común a fin de superar la polisemia que presentan términos estratégicos, situación que se ha advertido como causante de angustia a los actores del proceso educativo, por no tener claro lo que implica el modelo. Además, se considera que es pertinente que los mismos profesores tengan claras cuáles competencias deben desarrollar para su función docente y que tomen conciencia de los obstáculos epistemológicos que implica la construcción de cualquier competencia. Como aspecto distintivo de las diferentes opciones de capacitación docente, se incluye la generación de productos para el propio trabajo docente, como requisito para acreditación. Además, se plantea incidir sobre los contenidos mínimos que debe dominar un profesor para la materia específica que imparta y como elemento para motivación, se propone proporcionar a los profesores -alumnos una certificación que acredite sus competencias como profesores de la materia particular. Además de las condiciones que impone el contexto, tanto de la disciplina como del entorno, se sugiere que es necesario tener en cuenta las competencias requeridas para el trabajo en línea, así como aspectos para su desarrollo, pues es claro que la tecnología debe estar presente, no sólo en el ambiente a distancia, sino cada vez más en la educación tradicional, por lo que se propone desarrollar la capacitación con el apoyo de una plataforma de aprendizaje basada en internet, con la intención de que los participantes puedan extrapolar el uso de los recursos tecnológicos involucrados en la capacitación, a su propia práctica docente.Eje: Educación universitaria: Experiencias uso NTICRed de Universidades con Carreras en Informática (RedUNCI

La innovación curricular para la enseñanza en línea, bajo el enfoque basado en competencias

Se describen reflexiones al respecto de las habilidades y destrezas básicas docentes que es pertinente desarrollar ante el escenario para la modificación curricular hacia el enfoque de competencias profesionales, derivadas del desarrollo de un posgrado en ciencias en matemática educativa, ofrecido en modalidad a distancia, así como de la colaboración para la reforma curricular de dos universidades del occidente de México, una de las cuales ya adoptó el modelo y otra en donde apenas se inicia el proceso de transformación. Se plantea que una innovación curricular que no va acompañada de una capacitación docente paralela, está destinada a tener poco éxito, por lo que se señalan las áreas de actualización que han sido propuestas, a solicitud de las autoridades correspondientes. Aunque puede parecer trivial, se insiste en la necesidad de poner atención al empleo del lenguaje común a fin de superar la polisemia que presentan términos estratégicos, situación que se ha advertido como causante de angustia a los actores del proceso educativo, por no tener claro lo que implica el modelo. Además, se considera que es pertinente que los mismos profesores tengan claras cuáles competencias deben desarrollar para su función docente y que tomen conciencia de los obstáculos epistemológicos que implica la construcción de cualquier competencia. Como aspecto distintivo de las diferentes opciones de capacitación docente, se incluye la generación de productos para el propio trabajo docente, como requisito para acreditación. Además, se plantea incidir sobre los contenidos mínimos que debe dominar un profesor para la materia específica que imparta y como elemento para motivación, se propone proporcionar a los profesores -alumnos una certificación que acredite sus competencias como profesores de la materia particular. Además de las condiciones que impone el contexto, tanto de la disciplina como del entorno, se sugiere que es necesario tener en cuenta las competencias requeridas para el trabajo en línea, así como aspectos para su desarrollo, pues es claro que la tecnología debe estar presente, no sólo en el ambiente a distancia, sino cada vez más en la educación tradicional, por lo que se propone desarrollar la capacitación con el apoyo de una plataforma de aprendizaje basada en internet, con la intención de que los participantes puedan extrapolar el uso de los recursos tecnológicos involucrados en la capacitación, a su propia práctica docente.Eje: Educación universitaria: Experiencias uso NTICRed de Universidades con Carreras en Informática (RedUNCI

Evolving Sensitivity Balances Boolean Networks

We investigate the sensitivity of Boolean Networks (BNs) to mutations. We are interested in Boolean Networks as a model of Gene Regulatory Networks (GRNs). We adopt Ribeiro and Kauffman’s Ergodic Set and use it to study the long term dynamics of a BN. We define the sensitivity of a BN to be the mean change in its Ergodic Set structure under all possible loss of interaction mutations. Insilico experiments were used to selectively evolve BNs for sensitivity to losing interactions. We find that maximum sensitivity was often achievable and resulted in the BNs becoming topologically balanced, i.e. they evolve towards network structures in which they have a similar number of inhibitory and excitatory interactions. In terms of the dynamics, the dominant sensitivity strategy that evolved was to build BNs with Ergodic Sets dominated by a single long limit cycle which is easily destabilised by mutations. We discuss the relevance of our findings in the context of Stem Cell Differentiation and propose a relationship between pluripotent stem cells and our evolved sensitive networks

Biocompatible Bacterial Cellulose-Poly(2-hydroxyethyl methacrylate) Nanocomposite Films

A series of bacterial cellulose-poly(2-hydroxyethyl methacrylate) nanocomposite films was prepared by in situ radical polymerization of 2-hydroxyethyl methacrylate (HEMA), using variable amounts of poly(ethylene glycol) diacrylate (PEGDA) as crosslinker. Thin films were obtained, and their physical, chemical, thermal, and mechanical properties were evaluated. The films showed improved translucency compared to BC and enhanced thermal stability and mechanical performance when compared to poly(2-hydroxyethyl methacrylate) (PHEMA). Finally, BC/PHEMA nanocomposites proved to be nontoxic to human adipose-derived mesenchymal stem cells (ADSCs) and thus are pointed as potential dry dressings for biomedical applications

Suicide attempts and related factors in patients admitted to a general hospital: a ten-year cross-sectional study (1997-2007)

[Abstract] Background: Suicide and suicide attempts represent a severe problem for public health services. The aim of this study is to determine the socio-demographic and psychopathological variables associated with suicide attempts in the population admitted to a General Hospital. Methods: An observational-descriptive study of patients admitted to the A Coruña University Hospital (Spain) during the period 1997-2007, assessed by the Consultation and Liaison Psychiatric Unit. We include n = 5,234 admissions from 4,509 patients. Among these admissions, n = 361 (6.9%) were subsequent to a suicide attempt. Admissions arising from a suicide attempt were compared with admissions occurring due to other reasons.Multivariate generalised estimating equation logistic regression models were used to examine factors associated with suicide attempts. Results: Adjusting by age, gender, educational level, cohabitation status, being employed or unemployed, the psychiatric diagnosis at the time of the interview and the information on previous suicide attempts, we found that the variables associated with the risk of a suicide attempt were: age, psychiatric diagnosis and previous suicide attempts. The risk of suicide attempts decreases with age (OR = 0.969). Psychiatric diagnosis was associated with a higher risk of suicide attempts, with the highest risk being found for Mood or Affective Disorders (OR = 7.49), followed by Personality Disorders (OR = 7.31), and Schizophrenia and Other Psychotic Disorders (OR = 5.03).The strongest single predictive factor for suicide attempts was a prior history of attempts (OR = 23.63). Conclusions: Age, psychopathological diagnosis and previous suicide attempts are determinants of suicide attempts

Production and processing of graphene and related materials

© 2020 The Author(s). We present an overview of the main techniques for production and processing of graphene and related materials (GRMs), as well as the key characterization procedures. We adopt a 'hands-on' approach, providing practical details and procedures as derived from literature as well as from the authors' experience, in order to enable the reader to reproduce the results. Section I is devoted to 'bottom up' approaches, whereby individual constituents are pieced together into more complex structures. We consider graphene nanoribbons (GNRs) produced either by solution processing or by on-surface synthesis in ultra high vacuum (UHV), as well carbon nanomembranes (CNM). Production of a variety of GNRs with tailored band gaps and edge shapes is now possible. CNMs can be tuned in terms of porosity, crystallinity and electronic behaviour. Section II covers 'top down' techniques. These rely on breaking down of a layered precursor, in the graphene case usually natural crystals like graphite or artificially synthesized materials, such as highly oriented pyrolythic graphite, monolayers or few layers (FL) flakes. The main focus of this section is on various exfoliation techniques in a liquid media, either intercalation or liquid phase exfoliation (LPE). The choice of precursor, exfoliation method, medium as well as the control of parameters such as time or temperature are crucial. A definite choice of parameters and conditions yields a particular material with specific properties that makes it more suitable for a targeted application. We cover protocols for the graphitic precursors to graphene oxide (GO). This is an important material for a range of applications in biomedicine, energy storage, nanocomposites, etc. Hummers' and modified Hummers' methods are used to make GO that subsequently can be reduced to obtain reduced graphene oxide (RGO) with a variety of strategies. GO flakes are also employed to prepare three-dimensional (3d) low density structures, such as sponges, foams, hydro- or aerogels. The assembly of flakes into 3d structures can provide improved mechanical properties. Aerogels with a highly open structure, with interconnected hierarchical pores, can enhance the accessibility to the whole surface area, as relevant for a number of applications, such as energy storage. The main recipes to yield graphite intercalation compounds (GICs) are also discussed. GICs are suitable precursors for covalent functionalization of graphene, but can also be used for the synthesis of uncharged graphene in solution. Degradation of the molecules intercalated in GICs can be triggered by high temperature treatment or microwave irradiation, creating a gas pressure surge in graphite and exfoliation. Electrochemical exfoliation by applying a voltage in an electrolyte to a graphite electrode can be tuned by varying precursors, electrolytes and potential. Graphite electrodes can be either negatively or positively intercalated to obtain GICs that are subsequently exfoliated. We also discuss the materials that can be amenable to exfoliation, by employing a theoretical data-mining approach. The exfoliation of LMs usually results in a heterogeneous dispersion of flakes with different lateral size and thickness. This is a critical bottleneck for applications, and hinders the full exploitation of GRMs produced by solution processing. The establishment of procedures to control the morphological properties of exfoliated GRMs, which also need to be industrially scalable, is one of the key needs. Section III deals with the processing of flakes. (Ultra)centrifugation techniques have thus far been the most investigated to sort GRMs following ultrasonication, shear mixing, ball milling, microfluidization, and wet-jet milling. It allows sorting by size and thickness. Inks formulated from GRM dispersions can be printed using a number of processes, from inkjet to screen printing. Each technique has specific rheological requirements, as well as geometrical constraints. The solvent choice is critical, not only for the GRM stability, but also in terms of optimizing printing on different substrates, such as glass, Si, plastic, paper, etc, all with different surface energies. Chemical modifications of such substrates is also a key step. Sections IV-VII are devoted to the growth of GRMs on various substrates and their processing after growth to place them on the surface of choice for specific applications. The substrate for graphene growth is a key determinant of the nature and quality of the resultant film. The lattice mismatch between graphene and substrate influences the resulting crystallinity. Growth on insulators, such as SiO2, typically results in films with small crystallites, whereas growth on the close-packed surfaces of metals yields highly crystalline films. Section IV outlines the growth of graphene on SiC substrates. This satisfies the requirements for electronic applications, with well-defined graphene-substrate interface, low trapped impurities and no need for transfer. It also allows graphene structures and devices to be measured directly on the growth substrate. The flatness of the substrate results in graphene with minimal strain and ripples on large areas, allowing spectroscopies and surface science to be performed. We also discuss the surface engineering by intercalation of the resulting graphene, its integration with Si-wafers and the production of nanostructures with the desired shape, with no need for patterning. Section V deals with chemical vapour deposition (CVD) onto various transition metals and on insulators. Growth on Ni results in graphitized polycrystalline films. While the thickness of these films can be optimized by controlling the deposition parameters, such as the type of hydrocarbon precursor and temperature, it is difficult to attain single layer graphene (SLG) across large areas, owing to the simultaneous nucleation/growth and solution/precipitation mechanisms. The differing characteristics of polycrystalline Ni films facilitate the growth of graphitic layers at different rates, resulting in regions with differing numbers of graphitic layers. High-quality films can be grown on Cu. Cu is available in a variety of shapes and forms, such as foils, bulks, foams, thin films on other materials and powders, making it attractive for industrial production of large area graphene films. The push to use CVD graphene in applications has also triggered a research line for the direct growth on insulators. The quality of the resulting films is lower than possible to date on metals, but enough, in terms of transmittance and resistivity, for many applications as described in section V. Transfer technologies are the focus of section VI. CVD synthesis of graphene on metals and bottom up molecular approaches require SLG to be transferred to the final target substrates. To have technological impact, the advances in production of high-quality large-area CVD graphene must be commensurate with those on transfer and placement on the final substrates. This is a prerequisite for most applications, such as touch panels, anticorrosion coatings, transparent electrodes and gas sensors etc. New strategies have improved the transferred graphene quality, making CVD graphene a feasible option for CMOS foundries. Methods based on complete etching of the metal substrate in suitable etchants, typically iron chloride, ammonium persulfate, or hydrogen chloride although reliable, are time- and resourceconsuming, with damage to graphene and production of metal and etchant residues. Electrochemical delamination in a low-concentration aqueous solution is an alternative. In this case metallic substrates can be reused. Dry transfer is less detrimental for the SLG quality, enabling a deterministic transfer. There is a large range of layered materials (LMs) beyond graphite. Only few of them have been already exfoliated and fully characterized. Section VII deals with the growth of some of these materials. Amongst them, h-BN, transition metal tri- and di-chalcogenides are of paramount importance. The growth of h-BN is at present considered essential for the development of graphene in (opto) electronic applications, as h-BN is ideal as capping layer or substrate. The interesting optical and electronic properties of TMDs also require the development of scalable methods for their production. Large scale growth using chemical/physical vapour deposition or thermal assisted conversion has been thus far limited to a small set, such as h-BN or some TMDs. Heterostructures could also be directly grown