Ideal isotropic auxetic networks from random networks

Auxetic materials are characterized by a negative Poisson's ratio, $\mathrm{\nu}$. As the Poisson's ratio becomes negative and approaches the lower isotropic mechanical limit of $\mathrm{\nu = -1}$, materials show enhanced resistance to impact and shear, making them suitable for applications ranging from robotics to impact mitigation. Past experimental efforts aimed at reaching the $\mathrm{\nu = -1}$ limit have resulted in highly anisotropic materials, which show a negative Poisson's ratio only when subjected to deformations along specific directions. Isotropic designs have only attained moderately auxetic behavior, or have led to structures that cannot be manufactured in 3D. Here, we present a design strategy to create isotropic structures from disordered networks that leads to Poisson's ratios as low as $\mathrm{\nu = -0.98}$. The materials conceived through this approach are successfully fabricated in the laboratory and behave as predicted. The Poisson's ratio $\mathrm{\nu}$ is found to depend on network structure and bond strengths; this sheds light on the structural motifs that lead to auxetic behavior. The ideas introduced here can be generalized to 3D, a wide range of materials, and a spectrum of length scales, thereby providing a general platform that could impact technology.Comment: 16 pages, 6 figure

Phase Transitions in Two-Dimensional Traffic Flow Models

We introduce two simple two-dimensional lattice models to study traffic flow in cities. We have found that a few basic elements give rise to the characteristic phase diagram of a first-order phase transition from a freely moving phase to a jammed state, with a critical point. The jammed phase presents new transitions corresponding to structural transformations of the jam. We discuss their relevance in the infinite size limit.Comment: RevTeX 3.0 file. Figures available upon request to e-address [email protected] (or 'dopico' or 'molera' or 'anxo', same node

Theoretical approach to two-dimensional traffic flow models

In this paper we present a theoretical analysis of a recently proposed two-dimensional Cellular Automata model for traffic flow in cities with the novel ingredient of turning capability. Numerical simulations of this model show that there is a transition between a freely moving phase with high velocity to a jammed state with low velocity. We study the dynamics of such a model starting with the microscopic evolution equation, which will serve as a basis for further analysis. It is shown that a kinetic approach, based on the Boltzmann assumption, is able to provide a reasonably good description of the jamming transition. We further introduce a space-time continuous phenomenological model leading to a couple of partial differential equations whose preliminary results agree rather well with the numerical simulations.Comment: 15 pages, REVTeX 3.0, 7 uuencoded figures upon request to [email protected]

Anisotropic effect on two-dimensional cellular automaton traffic flow with periodic and open boundaries

By the use of computer simulations we investigate, in the cellular automaton of two-dimensional traffic flow, the anisotropic effect of the probabilities of the change of the move directions of cars, from up to right ($p_{ur}$) and from right to up ($p_{ru}$), on the dynamical jamming transition and velocities under the periodic boundary conditions in one hand and the phase diagram under the open boundary conditions in the other hand. However, in the former case, the first order jamming transition disappears when the cars alter their directions of move ($p_{ur}\neq 0$ and/or $p_{ru}\neq 0$). In the open boundary conditions, it is found that the first order line transition between jamming and moving phases is curved. Hence, by increasing the anisotropy, the moving phase region expand as well as the contraction of the jamming phase one. Moreover, in the isotropic case, and when each car changes its direction of move every time steps ($p_{ru}=p_{ur}=1$), the transition from the jamming phase (or moving phase) to the maximal current one is of first order. Furthermore, the density profile decays, in the maximal current phase, with an exponent $\gamma \approx {1/4}$.}Comment: 13 pages, 22 figure

Arquitectura distribuida para un sistema soporte de decisiones globales

En este trabajo presentamos el diseño de una arquitectura distribuida para un Sistema Soporte de Decisiones global prototipo en desarrollo en el GIDSATD (Grupo de Investigación y desarrollo de Sistemas de Ayuda a la Toma de Decisiones). El prototipo del SSD consta de doce módulos diseñados para operar en forma “autónoma”. En este trabajo presentamos la arquitectura distribuida propuesta para el SSD, describiendo la partición del sistema, los requerimientos de cada módulo y un esquema de interacción. El modelo propuesto para la distribución del SSD global prototipo se ha basado en un mecanismo de comportamiento orientado a eventos, el cual ha permitido lograr una arquitectura en la que cada módulo se mantiene relativamente autónomo cooperando entre sí a través de un esquema de interacción que establece un bajo nivel de acoplamiento. De esta manera, logramos reflejar la forma natural de trabajo del sistema. Para esto, el diseño de la arquitectura de distribución del SSD no se ajustó a las características de un estilo arquitectónico definido, sino que se buscó el modelo más apropiado para el SSD. Por esta razón dicho modelo no satisface todas las características de un estilo. Además, el diseño se ha realizado de modo independiente de la tecnología de comunicación utilizada para implementarlo. Finalmente, para implementar la arquitectura distribuida propuesta para el SSD prototipo, se decidió utilizar la tecnología de Computación de Objetos Distribuidos, seleccionando al standard CORBA del OMG. Este tipo de middleware provee herramientas de alto nivel de abstracción para: Especificar interfaces orientadas a objetos que permiten definir los “contratos” entre los módulos del SSD y encapsularlos. Permite también establecer un esquema de comunicación asincrónico y desacoplado entre objetos de distintos módulos mediante un mecanismo denominado publicar/suscribir. De este modo, encontramos en esta tecnología el soporte a las características requeridas por el diseño propuesto.Sistemas Distribuidos - Redes Concurrencia - Sesión de póstersRed de Universidades con Carreras en Informática (RedUNCI

Arquitectura distribuida para un sistema soporte de decisiones globales

En este trabajo presentamos el diseño de una arquitectura distribuida para un Sistema Soporte de Decisiones global prototipo en desarrollo en el GIDSATD (Grupo de Investigación y desarrollo de Sistemas de Ayuda a la Toma de Decisiones). El prototipo del SSD consta de doce módulos diseñados para operar en forma “autónoma”. En este trabajo presentamos la arquitectura distribuida propuesta para el SSD, describiendo la partición del sistema, los requerimientos de cada módulo y un esquema de interacción. El modelo propuesto para la distribución del SSD global prototipo se ha basado en un mecanismo de comportamiento orientado a eventos, el cual ha permitido lograr una arquitectura en la que cada módulo se mantiene relativamente autónomo cooperando entre sí a través de un esquema de interacción que establece un bajo nivel de acoplamiento. De esta manera, logramos reflejar la forma natural de trabajo del sistema. Para esto, el diseño de la arquitectura de distribución del SSD no se ajustó a las características de un estilo arquitectónico definido, sino que se buscó el modelo más apropiado para el SSD. Por esta razón dicho modelo no satisface todas las características de un estilo. Además, el diseño se ha realizado de modo independiente de la tecnología de comunicación utilizada para implementarlo. Finalmente, para implementar la arquitectura distribuida propuesta para el SSD prototipo, se decidió utilizar la tecnología de Computación de Objetos Distribuidos, seleccionando al standard CORBA del OMG. Este tipo de middleware provee herramientas de alto nivel de abstracción para: Especificar interfaces orientadas a objetos que permiten definir los “contratos” entre los módulos del SSD y encapsularlos. Permite también establecer un esquema de comunicación asincrónico y desacoplado entre objetos de distintos módulos mediante un mecanismo denominado publicar/suscribir. De este modo, encontramos en esta tecnología el soporte a las características requeridas por el diseño propuesto.Sistemas Distribuidos - Redes Concurrencia - Sesión de póstersRed de Universidades con Carreras en Informática (RedUNCI

An ultra-sensitive aptasensor on optical fibre for the direct detection of Bisphenol A

We present a plasmonic biosensor capable of detecting the presence of bisphenol A in ultralow concentrations, yielding a wavelength shift of 0.15±0.01 nm in response to a solution of 1 fM concentration with limit of detection of 330±70 aM. The biosensing device consists of an array of gold nano-antennae with a total length of 2.3cm that generate coupled localised surface plasmons (cLSPs) and is covalently modified with an aptamer specific for bisphenol A recognition. The array of nanoantennae is fabricated on a lapped section of standard telecommunication optical fibre, allowing for potential multiplexing and its use in remote sensing applications. These results have been achieved without the use of enhancement techniques and therefore the approach allows the direct detection of bisphenol A, a low molecular weight (228 Da) target usually detectable only by indirect detection strategies. Its detection at such levels is a significant step forward in measuring small molecules at ultralow concentrations. Furthermore, this new sensing platform paves the way for the development of portable systems for in-situ agricultural measurements capable of retrieving data on a substance of very high concern at ultra-low concentrations

Extensive Plasmid Library to Prepare Tau Protein Variants and Study Their Functional Biochemistry

Tau neurofibrillary tangles are key pathological features of Alzheimer’s disease and other tauopathies. Recombinant protein technology is vital for studying the structure and function of tau in physiology and aggregation in pathophysiology. However, open-source and well-characterized plasmids for efficiently expressing and purifying different tau variants are lacking. We generated 44 sequence-verified plasmids including those encoding full length (FL) tau-441, its four-repeat microtubule-binding (K18) fragment, and their respective selected familial pathological variants (N279K, V337M, P301L, C291R, and S356T). Moreover, plasmids for expressing single (C291A), double (C291A/C322A), and triple (C291A/C322A/I260C) cysteine-modified variants were generated to study alterations in cysteine content and locations. Furthermore, protocols for producing representative tau forms were developed. We produced and characterized the aggregation behavior of the triple cysteine-modified tau-K18, often used in real-time cell internalization and aggregation studies because it can be fluorescently labeled on a cysteine outside the microtubule-binding core. Similar to the wild type (WT), triple cysteine-modified tau-K18 aggregated by progressive β-sheet enrichment, albeit at a slower rate. On prolonged incubation, cysteine-modified K18 formed paired helical filaments similar to those in Alzheimer’s disease, sharing morphological phenotypes with WT tau-K18 filaments. Nonetheless, cysteine-modified tau-K18 filaments were significantly shorter (p = 0.002) and mostly wider than WT filaments, explainable by their different principal filament elongation pathways: vertical (end-to-end) and lateral growth for WT and cysteine-modified, respectively. Cysteine rearrangement may therefore induce filament polymorphism. Together, the plasmid library, the protein production methods, and the new insights into cysteine-dependent aggregation should facilitate further studies and the design of antiaggregation agents

A comprehensive microarray-based DNA methylation study of 367 hematological neoplasms

Background: Alterations in the DNA methylation pattern are a hallmark of leukemias and lymphomas. However, most epigenetic studies in hematologic neoplasms (HNs) have focused either on the analysis of few candidate genes or many genes and few HN entities, and comprehensive studies are required. Methodology/Principal Findings: Here, we report for the first time a microarray-based DNA methylation study of 767 genes in 367 HNs diagnosed with 16 of the most representative B-cell (n = 203), T-cell (n = 30), and myeloid (n = 134) neoplasias, as well as 37 samples from different cell types of the hematopoietic system. Using appropriate controls of B-, T-, or myeloid cellular origin, we identified a total of 220 genes hypermethylated in at least one HN entity. In general, promoter hypermethylation was more frequent in lymphoid malignancies than in myeloid malignancies, being germinal center mature B-cell lymphomas as well as B and T precursor lymphoid neoplasias those entities with highest frequency of gene-associated DNA hypermethylation. We also observed a significant correlation between the number of hypermethylated and hypomethylated genes in several mature B-cell neoplasias, but not in precursor B- and T-cell leukemias. Most of the genes becoming hypermethylated contained promoters with high CpG content, and a significant fraction of them are targets of the polycomb repressor complex. Interestingly, T-cell prolymphocytic leukemias show low levels of DNA hypermethylation and a comparatively large number of hypomethylated genes, many of them showing an increased gene expression. Conclusions/Significance: We have characterized the DNA methylation profile of a wide range of different HNs entities. As well as identifying genes showing aberrant DNA methylation in certain HN subtypes, we also detected six genes—DBC1, DIO3, FZD9, HS3ST2, MOS, and MYOD1—that were significantly hypermethylated in B-cell, T-cell, and myeloid malignancies. These might therefore play an important role in the development of different HNs