Techniques to Understand Computer Simulations: Markov Chain Analysis

The aim of this paper is to assist researchers in understanding the dynamics of simulation models that have been implemented and can be run in a computer, i.e. computer models. To do that, we start by explaining (a) that computer models are just input-output functions, (b) that every computer model can be re-implemented in many different formalisms (in particular in most programming languages), leading to alternative representations of the same input-output relation, and (c) that many computer models in the social simulation literature can be usefully represented as time-homogeneous Markov chains. Then we argue that analysing a computer model as a Markov chain can make apparent many features of the model that were not so evident before conducting such analysis. To prove this point, we present the main concepts needed to conduct a formal analysis of any time-homogeneous Markov chain, and we illustrate the usefulness of these concepts by analysing 10 well-known models in the social simulation literature as Markov chains. These models are: • Schelling\'s (1971) model of spatial segregation • Epstein and Axtell\'s (1996) Sugarscape • Miller and Page\'s (2004) standing ovation model • Arthur\'s (1989) model of competing technologies • Axelrod\'s (1986) metanorms models • Takahashi\'s (2000) model of generalized exchange • Axelrod\'s (1997) model of dissemination of culture • Kinnaird\'s (1946) truels • Axelrod and Bennett\'s (1993) model of competing bimodal coalitions • Joyce et al.\'s (2006) model of conditional association In particular, we explain how to characterise the transient and the asymptotic dynamics of these computer models and, where appropriate, how to assess the stochastic stability of their absorbing states. In all cases, the analysis conducted using the theory of Markov chains has yielded useful insights about the dynamics of the computer model under study.Computer Modelling, Simulation, Markov, Stochastic Processes, Analysis, Re-Implementation

Errors and Artefacts in Agent-Based Modelling

The objectives of this paper are to define and classify different types of errors and artefacts that can appear in the process of developing an agent-based model, and to propose activities aimed at avoiding them during the model construction and testing phases. To do this in a structured way, we review the main concepts of the process of developing such a model – establishing a general framework that summarises the process of designing, implementing, and using agent-based models. Within this framework we identify the various stages where different types of errors and artefacts may appear. Finally we propose activities that could be used to detect (and hence eliminate) each type of error or artefact.Verification, Replication, Artefact, Error, Agent-Based Modelling, Modelling Roles

Thiol-based redox homeostasis and signaling

Plants imperatively have to cope with adverse conditions owing to their lack of mobility and to the high amounts of reactive oxygen species (ROS) generated from both respiration and photosynthetic metabolism. Although thiol redox homeostasis in plants is mainly preserved by the cellular glutathione pool, specific strategies have been adopted by the plant kingdom during evolution to manage these “extra” pro-oxidative conditions. Unlike human or yeast, plants generally possess a higher number of genes coding for antioxidant proteins, including protein families responsible of dithiol/disulfide exchange reactions. During the last decades, redox-dependent post-translational modifications of proteins proved to be pivotal to many cellular functions. In particular, this is critically important under some situations of environmental constraints taking into account the alterations and fine adjustment of the cellular redox status occurring during and after any biotic or abiotic stresses

The histology of ovarian cancer: worldwide distribution and implications for international survival comparisons (CONCORD-2)

Objective Ovarian cancers comprise several histologically distinct tumour groups with widely different prognosis. We aimed to describe the worldwide distribution of ovarian cancer histology and to understand what role this may play in international variation in survival. Methods The CONCORD programme is the largest population-based study of global trends in cancer survival. Data on 681,759 women diagnosed during 1995â\u80\u932009 with cancer of the ovary, fallopian tube, peritoneum and retroperitonum in 51 countries were included. We categorised ovarian tumours into six histological groups, and explored the worldwide distribution of histology. Results During 2005â\u80\u932009, type II epithelial tumours were the most common. The proportion was much higher in Oceania (73.1%), North America (73.0%) and Europe (72.6%) than in Central and South America (65.7%) and Asia (56.1%). By contrast, type I epithelial tumours were more common in Asia (32.5%), compared with only 19.4% in North America. From 1995 to 2009, the proportion of type II epithelial tumours increased from 68.6% to 71.1%, while the proportion of type I epithelial tumours fell from 23.8% to 21.2%. The proportions of germ cell tumours, sex cord-stromal tumours, other specific non-epithelial tumours and tumours of non-specific morphology all remained stable over time. Conclusions The distribution of ovarian cancer histology varies widely worldwide. Type I epithelial, germ cell and sex cord-stromal tumours are generally associated with higher survival than type II tumours, so the proportion of these tumours may influence survival estimates for all ovarian cancers combined. The distribution of histological groups should be considered when comparing survival between countries and regions

Análisis bibliográfico de la influencia de la poesía de J. Ch. F. Schiller en España a través de sus traducciones al castellano

Análisis crítico de la bibliografía completa en España sobre la poesía en castellano e Friedrich Schiller hasta 2000. Sohiller, junto con Goethe, es el máximo representante de la poesía alemana y uno de los más destacados miembros del romanticismo literario. Sin embargo, hasta la segunda mitad del s.XX apenas es conocida su poesía, y las traducciones que hay se muestran muy defectuosas. Después de un minucioso análisis, se muestra que todavía no hay ediciones de calidad, y, aunque se han traducido correctamente sus obras de teatro, no se ha hecho lo mismo con la poesía de la que apenas hay ediciones adecuadamente traducidas y ninguna edición de su poesía completa. | This paper presents a critical analysis of the complete bibliography in the spanisch language, up to 2000, of Friedrich Schillerâs poetry. Schiller was, with Goethe, the most representative of the German Romantic movement. Rut it was not until the 1950âs tbat bis poems, albeit in poor translations, began to be known. We have not quality publications; only his theatre itâs alí well transíated. Bis poetry is waiting a complete publication with a correctly transíation

Uso de robots txt. en la administración pública española

Se explica la importancia que tienen los ficheros robots.txt y los sitemaps para los sitios web. Se realiza un estudio sobre más de 4.000 webs de la administración pública española para analizar el uso de ficheros robots.txt y sitemaps como medio de optimización para los crawlers o arañas de los motores de búsqueda. | Robots.txt and sitemaps files are the main methods to regulate search engine crawler access to its content. This article explain the importance of such files and analyze robots.txt and sitemaps from more than 4,000 web sites belonging to spanish public administration to determine the use of these files as a medium of optimization for crawlers

CUHK electronic theses & dissertations collection

Wei Chunmei."September 2000."Thesis (Ph.D.)--Chinese University of Hong Kong, 2000.Includes bibliographical references (p. 137-140).Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web.Mode of access: World Wide Web.Abstracts in English and Chinese

On how correlations between excitatory and inhibitory synaptic inputs maximize the information rate of neuronal firing

Cortical neurons receive barrages of excitatory and inhibitory inputs which are not independent, as network structure and synaptic kinetics impose statistical correlations. Experiments in vitro and in vivo have demonstrated correlations between inhibitory and excitatory synaptic inputs in which inhibition lags behind excitation in cortical neurons. This delay arises in feed-forward inhibition circuits and ensures that coincident excitation and inhibition do not preclude neuronal firing. Conversely, inhibition that is too delayed broadens neuronal integration times, thereby diminishing spike-time precision and increasing the firing frequency. This led us to hypothesize that the correlation between excitatory and inhibitory synaptic inputs modulates the encoding of information of neural spike trains. We tested this hypothesis by investigating the effect of such correlations on the information rate (IR) of spike trains using the Hodgkin-Huxley model in which both synaptic and membrane conductances are stochastic. We investigated two different synaptic input regimes: balanced synaptic conductances and balanced currents. Our results show that correlations arising from the synaptic kinetics, tau, and millisecond lags, delta, of inhibition relative to excitation strongly affect the IR of spike trains. In the regime of balanced synaptic currents, for short time lags (delta ~ 1 ms) there is an optimal tau that maximizes the IR of the postsynaptic spike train. Given the short time scales for monosynaptic inhibitory lags and synaptic decay kinetics reported in cortical neurons under physiological contexts, we propose that feed-forward inhibition in cortical circuits is poised to maximize the rate of information transfer between cortical neurons. Our results also provide a possible explanation for how certain drugs and genetic mutations affecting the synaptic kinetics can deteriorate information processing in the brain

Adolescentes y maternidad en el cine: «Juno», «Precious» y «The Greatest» Teenagers and Motherhood in the Cinema: «Juno», «Precious» and «The Greatest»

En la actualidad son muchas las adolescentes en España que tienen embarazos no deseados. La ampliación de la Ley del aborto, así como la aprobación de la venta de la píldora del día después sin receta, han focalizado la atención en las jóvenes menores de 18 años. La maternidad, los embarazos no deseados y las alternativas ante estos son variables a las que las adolescentes se enfrentan en el mundo real, y sobre las cuales los filmes construyen sus propios discursos coincidentes o no con la realidad social. En las pantallas de cine películas como «Juno», «Precious» y «The Greatest» tratan bajo diferentes prismas el tema del embarazo adolescente. Estos textos audiovisuales inciden de manera directa en la reproducción y creación de modelos, actitudes y valores. Su influencia en la juventud es constatable y suponen una referencia junto con la familia y la escuela a la hora de adoptar determinados patrones de comportamiento e interiorizar arquetipos socialmente admitidos. Este trabajo examina estos filmes utilizando las herramientas tanto del lenguaje audiovisual como del análisis textual, atendiendo a una perspectiva de género. A través del análisis se constata qué visiones de la maternidad y el sexo en la adolescencia se construyen y cuáles son las estrategias de producción de sentido utilizadas. Los resultados muestran cómo los modelos y estereotipos tradicionales perviven bajo la apariencia de discursos audiovisuales renovados y alternativos.<br>Today in Spain there are many teenagers who suffer unwanted pregnancies. The extension of the abortion law and the approval of the sale of morning-after pill without a prescription have focused attention on girls under 18. The possibilities of motherhood, an unwanted pregnancy and the alternatives are variables that young women face in the real world, and upon which the discourses of films are constructed, some of which coincide with reality and some of which do not. On the big screen we can see movies like Juno, Precious and The Greatest which express different points of view about the topic of teenage pregnancy. These audiovisual texts have a direct impact on the creation and proliferation of models, attitudes and values. Their influence upon young people is evident and they form a reference alongside family and school for adopting certain patterns of behavior and assimilating socially accepted archetypes. This paper analyzes these films from a gender perspective, using the tools of both audiovisual language and textual analysis. Through this analysis, we establish that visions of motherhood and adolescent sex are constructed and identify the strategies used for the production of meaning in these films. The results show how the models and stereotypes survive under the appearance of renewed and alternative audiovisual discourse

Organization and coordinated assembly of the type III secretion export apparatus

Type III protein secretion systems are unique bacterial nanomachines with the capacity to deliver bacterial effector proteins into eukaryotic cells. These systems are critical to the biology of many pathogenic or symbiotic bacteria for insects, plants, animals, and humans. Essential components of these systems are multiprotein envelope-associated organelles known as the needle complex and a group of membrane proteins that compose the so-called export apparatus. Here, we show that components of the export apparatus associate intimately with the needle complex, forming a structure that can be visualized by cryo-electron microscopy. We also show that formation of the needle complex base is initiated at the export apparatus and that, in the absence of export apparatus components, there is a significant reduction in the levels of needle complex base assembly. Our results show a substantial coordination in the assembly of the two central elements of type III secretion machines