The Effect of Proximity, Explicitness, and Representation of Basic Science Information on Student Clinical Problem-Solving

Problem: Medical and veterinary students memorize facts but then have difficulty applying those facts in clinical problem solving. Cognitive engineering research suggests that the inability of medical and veterinary students to infer concepts from facts may be due in part to specific features of how information is represented and organized in educational materials. First, physical separation of pieces of information may increase the cognitive load on the student. Second, information that is necessary but not explicitly stated may also contribute to the student’s cognitive load. Finally, the types of representations – textual or graphical – may also support or hinder the student’s learning process. This may explain why students have difficulty applying biomedical facts in clinical problem solving. Purpose: To test the hypothesis that three specific aspects of expository text – the patial distance between the facts needed to infer a rule, the explicitness of information, and the format of representation – affected the ability of students to solve clinical problems. Setting: The study was conducted in the parasitology laboratory of a college of veterinary medicine in Texas. Sample: The study subjects were a convenience sample consisting of 132 second-year veterinary students who matriculated in 2007. The age of this class upon admission ranged from 20-52, and the gender makeup of this class consisted of approximately 75% females and 25% males. Results: No statistically significant difference in student ability to solve clinical problems was found when relevant facts were placed in proximity, nor when an explicit rule was stated. Further, no statistically significant difference in student ability to solve clinical problems was found when students were given different representations of material, including tables and concept maps. Findings: The findings from this study indicate that the three properties investigated – proximity, explicitness, and representation – had no statistically significant effect on student learning as it relates to clinical problem-solving ability. However, ad hoc observations as well as findings from other researchers suggest that the subjects were probably using rote learning techniques such as memorization, and therefore were not attempting to infer relationships from the factual material in the interventions, unless they were specifically prompted to look for patterns. A serendipitous finding unrelated to the study hypothesis was that those subjects who correctly answered questions regarding functional (non-morphologic) properties, such as mode of transmission and intermediate host, at the family taxonomic level were significantly more likely to correctly answer clinical case scenarios than were subjects who did not correctly answer questions regarding functional properties. These findings suggest a strong relationship (p < .001) between well-organized knowledge of taxonomic functional properties and clinical problem solving ability. Recommendations: Further study should be undertaken investigating the relationship between knowledge of functional taxonomic properties and clinical problem solving ability. In addition, the effect of prompting students to look for patterns in instructional material, followed by the effect of factors that affect cognitive load such as proximity, explicitness, and representation, should be explored.

Radiocarbon ages and 230Th data of five sediment cores from the Björn and Gardar Drift, North Atlantic

In locations of rapid sediment accumulation receiving substantial amounts of laterally transported material the timescales of transport and accurate quantification of the transported material are at the focus of intense research. Here we present radiocarbon data obtained on co-occurring planktic foraminifera, marine haptophyte biomarkers (alkenones) and total organic carbon (TOC) coupled with excess Thorium-230 (230Thxs) measurements on four sediment cores retrieved in 1649-2879 m water depth from two such high accumulation drift deposits in the Northeast Atlantic, Björn and Gardar Drifts. While 230Thxs inventories imply strong sediment focussing, no age offsets are observed between planktic foraminifera and alkenones, suggesting that redistribution of sediments is rapid and occurs soon after formation of marine organic matter, or that transported material contains negligible amounts of alkenones. An isotopic mass balance calculation based on radiocarbon concentrations of co-occurring sediment components leads us to estimate that transported sediment components contain up to 12% of fossil organic matter that is free of or very poor in alkenones, but nevertheless appears to consist of a mixture of fresh and eroded fossil material. Considering all available constraints to characterize transported material, our results show that although focussing factors calculated from bulk sediment 230Thxs inventories may allow useful approximations of bulk redeposition, they do not provide a unique estimate of the amount of each laterally transported sediment component. Furthermore, our findings provide evidence that the occurrence of lateral sediment redistribution alone does not always hinder the use of multiple proxies but that individual sediment fractions are affected to variable extents by sediment focussing.

Diversity of zooplankton assemblages at Station L4, Western English Channel, measured using next generation DNA sequencing

Background: Zooplankton play an important role in our oceans, in biogeochemical cycling and providing a food source for commercially important fish larvae. However, difficulties in correctly identifying zooplankton hinder our understanding of their roles in marine ecosystem functioning, and can prevent detection of long term changes in their community structure. The advent of massively parallel Next Generation Sequencing technology allows DNA sequence data to be recovered directly from whole community samples. Here we assess the ability of such sequencing to quantify the richness and diversity of a mixed zooplankton assemblage from a productive monitoring site in the Western English Channel. Methodology/Principle Findings: Plankton WP2 replicate net hauls (200 µm) were taken at the Western Channel Observatory long-term monitoring station L4 in September 2010 and January 2011. These samples were analysed by microscopy and metagenetic analysis of the 18S nuclear small subunit ribosomal RNA gene using the 454 pyrosequencing platform. Following quality control a total of 419,042 sequences were obtained for all samples. The sequences clustered in to 205 operational taxonomic units using a 97% similarity cut-off. Allocation of taxonomy by comparison with the National Centre for Biotechnology Information database identified 138 OTUs to species level, 11 to genus level and 1 to order, <2.5% of sequences were classified as unknowns. By comparison a skilled microscopic analyst was able to routinely enumerate only 75 taxonomic groups. Conclusions: The percentage of OTUs assigned to major eukaryotic taxonomic groups broadly aligns between the metagenetic and morphological analysis and are dominated by Copepoda. However, the metagenetics reveals a previously hidden taxonomic richness, especially for Copepoda and meroplankton such as Bivalvia, Gastropoda and Polychaeta. It also reveals rare species and parasites. We conclude that Next Generation Sequencing of 18S amplicons is a powerful tool for estimating diversity and species richness of zooplankton communities.

Políticas públicas para el fomento del asociacionismo intermunicipal : el caso de las provincias de Sevilla (España) y Mendoza (Argentina)

El presente artículo analiza las políticas públicas de fomento para la creación y fortalecimiento de organismos intermunicipales desarrolladas por niveles superiores de gobierno en Argentina y España. Dado el desarrollo incipiente de este tipo de experiencias en Iberoamérica, se propone un análisis comparado de las políticas públicas de fomento del asociativismo municipal en la Provincia de Mendaza (Argentina) y la Provincia de Sevilla (España), dos entidades gubernamentales intermedias que poseen características demográficas y económicas semejantes en el contexto de sus respectivos países y donde la creación de estas entidades locales se encuentra en plena actividad. En función de estos desarrollos, reflexionaremos en torno a las restricciones institucionales más relevantes que dificultan la ejecución de proyectos articulativos intermunicipales.

Environmental policy and knowledge. Copying with complexity through inclusive management

Scholars agree that governance of the public environment entails cooperation between science, policy and society. This requires the active role of public managers as catalysts of knowledge co-production, addressing participatory arenas in relation to knowledge integration and social learning. This paper deals with the question of whether public managers acknowledge and take on this task. A survey accessing Directors of Environmental Offices (EOs) of 64 municipalities was carried out in parallel for two regions - Tuscany (Italy) and Porto Alegre Metropolitan Region (Brazil). The survey data were analysed using the multiple correspondence method. Results showed that, regarding policy practices, EOs do not play the role of knowledge co-production catalysts, since when making environmental decisions they only use technical knowledge. We conclude that there is a gap between theory and practice, and identify some factors that may hinder local environmental managers in acting as catalyst of knowledge co-production, raising a further question for future research.

Vocation in the insertion of the university student and the graduate

The work plan aims at deepening the analysis of the theoretic assumptions which support the practice in Vocational Guidance: analyzing the incidence of endogenous and exogenous factors both in the election and studying of a particular course of study and in the occupational resolution of the graduate. This analysis enables the revision and the new theoretic conceptualization which is afterwards transferred to the course, and to different groups and provincial institutions where the practice of Vocational Guidance occurs, as well as to other schools in the Northwest provinces of Argentina. Semiotic analysis, statistical elaboration and the research-action approach which, while surveying data renders a service to the milieu, provide the base for the project. Said project focuses on the following individuals: 1) freshmen, who offer us the following aspects to be considered: a) factors which either favor or hinder the insertion of the students attending the first years of the course; b) the conditions making up the learning situation in each subject, from the teaching point of view; c) the influence of institutional dimension in the insertion process; 2) graduands: the characteristics of the situation following graduation from University, those of the labor field and the different ways of gaining access to it are investigated. This analysis is carried out in the courses of study of Psychology and English (education of Professionals in English and English for Professionals).

Vocation in the insertion of the university student and the graduate

The work plan aims at deepening the analysis of the theoretic assumptions which support the practice in Vocational Guidance: analyzing the incidence of endogenous and exogenous factors both in the election and studying of a particular course of study and in the occupational resolution of the graduate. This analysis enables the revision and the new theoretic conceptualization which is afterwards transferred to the course, and to different groups and provincial institutions where the practice of Vocational Guidance occurs, as well as to other schools in the Northwest provinces of Argentina. Semiotic analysis, statistical elaboration and the research-action approach which, while surveying data renders a service to the milieu, provide the base for the project. Said project focuses on the following individuals: 1) freshmen, who offer us the following aspects to be considered: a) factors which either favor or hinder the insertion of the students attending the first years of the course; b) the conditions making up the learning situation in each subject, from the teaching point of view; c) the influence of institutional dimension in the insertion process; 2) graduands: the characteristics of the situation following graduation from University, those of the labor field and the different ways of gaining access to it are investigated. This analysis is carried out in the courses of study of Psychology and English (education of Professionals in English and English for Professionals).

Vocation in the insertion of the university student and the graduate

The work plan aims at deepening the analysis of the theoretic assumptions which support the practice in Vocational Guidance: analyzing the incidence of endogenous and exogenous factors both in the election and studying of a particular course of study and in the occupational resolution of the graduate. This analysis enables the revision and the new theoretic conceptualization which is afterwards transferred to the course, and to different groups and provincial institutions where the practice of Vocational Guidance occurs, as well as to other schools in the Northwest provinces of Argentina. Semiotic analysis, statistical elaboration and the research-action approach which, while surveying data renders a service to the milieu, provide the base for the project. Said project focuses on the following individuals: 1) freshmen, who offer us the following aspects to be considered: a) factors which either favor or hinder the insertion of the students attending the first years of the course; b) the conditions making up the learning situation in each subject, from the teaching point of view; c) the influence of institutional dimension in the insertion process; 2) graduands: the characteristics of the situation following graduation from University, those of the labor field and the different ways of gaining access to it are investigated. This analysis is carried out in the courses of study of Psychology and English (education of Professionals in English and English for Professionals).

(Table 1) Uncompacted and compacted sedimentation rate values corrected for bedding attitudes at DSDP Leg 66 Holes

Sediment accumulation rates, computed using agesediment thickness curves obtained from DSDP cores, are rarely corrected for compaction or bedding attitude to better approximate true sediment accumulation rates (c.f. van Andel et al., 1975; Davies et al., 1977; and Whitman and Davies, 1979). Variations with depth in either of these factors can hinder interpreting relative rates of sedimentary processes associated with a particular depositional environment. This problem becomes particularly relevant for convergent margin sediments, which often display variable bedding attitudes and pronounced changes in porosity, bulk density, and other parameters related to the compaction process at shallow depth. These rapid shallow changes render correlation of sedimentation rates within a single transect of holes very difficult. Two techniques have been applied to data collected from a transect of holes along the southwestern Mexico continental margin, DSDP Leg 66 (Fig. 1), to correct sediment accumulation rates for variations in compaction and bedding attitude. These corrections should help resolve true fluctuations in accumulation rates and their implications regarding convergent margin processes.

Border Industry in Myanmar: Turning the Periphery into the Center of Growth

The Myanmar economy has not been deeply integrated into East Asia’s production and distribution networks, despite its location advantages and notably abundant, reasonably well-educated, cheap labor force. Underdeveloped infrastructure, logistics in particular, and an unfavorable business and investment environment hinder it from participating in such networks in East Asia. Service link costs, for connecting production sites in Myanmar and other remote fragmented production blocks or markets, have not fallen sufficiently low to enable firms, including multi-national corporations to reduce total costs, and so the Myanmar economy has failed to attract foreign direct investments. Border industry offers a solution. The Myanmar economy can be connected to the regional and global economy through its borders with neighboring countries, Thailand in particular, which already have logistic hubs such as deep-sea ports, airports and trunk roads. This paper examines the source of competitiveness of border industry by considering an example of the garment industry located in the Myanmar-Thai border area. Based on such analysis, we recognize the prospects of border industry and propose some policy measures to promote this on Myanmar soil.

Financing Small and Medium Enterprises in Myanmar

Small and medium enterprises (SMEs) share the biggest part in Myanmar economy in terms of number, contribution to employment, output, and investment. Myanmar economic growth is thus totally dependent on the development of SMEs in the private sector. Today, the role of SMEs has become more vital in strengthening national competitive advantage and the speedy economic integration into the ASEAN region. However, studies show that SMEs have to deal with a number of constraints that hinder their development potential, such as the shortage in power supply, unavailability of long-term credit from external sources and many others. Among them, the financing problem of SMEs is one of the biggest constraints. Such is deeply rooted in demand and supply issues, macroeconomic fundamentals, and lending infrastructure of the country. The government’s policy towards SMEs could also lead to insufficient support for the SMEs. Thus, focusing on SMEs and private sector development as a viable strategy for industrialization and economic development of the country is a fundamental requirement for SME development. This paper recommends policies for stabilizing macro economic fundamentals, improving lending infrastructures of the country and improving demand- and supply-side conditions from the SMEs financing perspective in order to provide a more accessible financing for SMEs and to contribute in the overall development of SMEs in Myanmar thereby to sharpen national competitive advantage in the age of speedy economic integration.

Innovative tools to address drought risk in grazing lands

Drought spells can impose severe impacts in most vulnerable farms. It is well known that uninsured exposure exacerbates income inequality in farming systems. However, high administrative costs of traditional insurance hinder small farmers? access to risk management tools. The existence of moral hazard and systemic risk prevents the implementation of traditional insurance programs to address drought risk in rural areas. Innovative technologies like satellite images are being used to derive vegetation index which are highly correlated with drought impacts. The implementation of this technology in agricultural insurance may help to overcome some of the limitations of traditional insurance. However, basis risk has been identified as one of the main problems that hinder the acceptance of index insurance. In this paper we focus on the analyses of basis risk under different contract options in the grazing lands of the Araucanía region. A vegetation index database is used to develop an actuarial insurance model and estimate risk premiums for moderate and severe drought coverage. Risk premium sharply increases with risk coverage. In contrast with previous findings in the literature, our results are not conclusive and show that lowering the coverage level does not necessarily imply a reduction in basis risk. Further analyses of the relation between contract design and basis risk is a promising area of research that may render an important social utility for most vulnerable farming systems.

PEPSI: Privacy-Enhanced Participatory Sensing Infrastructure.

Participatory Sensing combines the ubiquity of mobile phones with sensing capabilities of Wireless Sensor Networks. It targets pervasive collection of information, e.g., temperature, traffic conditions, or health-related data. As users produce measurements from their mobile devices, voluntary participation becomes essential. However, a number of privacy concerns -- due to the personal information conveyed by data reports -- hinder large-scale deployment of participatory sensing applications. Prior work on privacy protection, for participatory sensing, has often relayed on unrealistic assumptions and with no provably-secure guarantees. The goal of this project is to introduce PEPSI: a Privacy-Enhanced Participatory Sensing Infrastructure. We explore realistic architectural assumptions and a minimal set of (formal) privacy requirements, aiming at protecting privacy of both data producers and consumers. We design a solution that attains privacy guarantees with provable security at very low additional computational cost and almost no extra communication overhead.

Acceso de la mujer a puestos de dirección en organizaciones deportivas

Dos de los factores por los que se mide el progreso dentro de las sociedades avanzadas son la posición y estatus de las mujeres dentro de dicha sociedad. En el caso de España, la situación de la mujer ha cambiado mucho en de los últimos 40 años, y más concretamente a partir de su ingreso dentro del mercado laboral. De esta forma, sabemos que el avance hacia la igualdad en cualquier campo se ha estado produciendo, pero existen ámbitos en los que dicho avance tiene lugar de forma más lenta. Este es el caso de los puestos directivos donde la infrarrepresentación de la mujer en la toma de decisiones está observada en numerosos estudios anteriores. Pues bien, uno de los objetivos generales de la presente tesis doctoral es conocer las barreras actitudinales, lo que es conocido internacionalmente como el concepto “Techo de cristal”, en la consecución de este tipo de puestos por parte de las mujeres, dentro del sistema deportivo y en la Comunidad de Madrid. La metodología usada en esta investigación ha sido descriptiva, de corte transversal y estandarizada por medio de cuestionario, aplicado a una muestra final de 401 personas. Siendo la población objeto las personas que trabajan ocupando un puesto directivo dentro de entidades deportivas públicas y privadas ubicadas en la Comunidad de Madrid. Con una afijación proporcional según género y tipo de entidad. Los resultados obtenidos demuestran que a día de hoy todavía hay diferencias dentro de los puestos de responsabilidad, como por ejemplo, en el porcentaje de ocupación del puesto máximo, los salarios, etc, apareciendo diferentes actitudes que dificultan el acceso o promoción dentro de este tipo de puestos. Una de las principales conclusiones es que todavía no existe la equidad absoluta dentro de los puestos directivos de las organizaciones deportivas ubicadas en la Comunidad de Madrid, pero que el avance paulatino y constante se está produciendo para conseguir la plena igualdad. SUMMARY. Two of the factors that measured progress in advanced societies are the position and status of women within that society. In the case of Spain, the situation of women has changed a lot in the past 40 years, and more specifically from their entry into the labour market. In this way, we know that the progress towards equality in any field has been producing, but there are areas in which such progress takes place more slowly. This is the case of managerial posts where the under-representation of women in decision-making is observed in many previous studies. As well, one of the general objectives of this thesis it is know the attitudinal barriers, what is known internationally as the 'Glass ceiling' concept, in the pursuit of this type of posts by women within the sports system and in the community of Madrid. The methodology used in this research was descriptive, transversal and standardized cutting through questionnaire, applied to a final sample of 401 people. The target population to be people who work occupying a post steering within public and private sports organizations located in the community of Madrid. With a proportional affixation according to gender and type of entity. The results obtained show that today there are still differences in positions of responsibility, as for example, in the percentage of occupation since maximum, wages, etc., appearing different attitudes that hinder access to or promotion within this type of posts. One of the main conclusions is that there is still no absolute equity within the management positions of sport organisations located in the community of Madrid, but is occurring the gradual and steady progress to achieve full equality.

Modelización de los Procesos de Cristalización en Poliolefinas

“Por lo tanto, la cristalización de polímeros se supone, y en las teorías se describe a menudo, como un proceso de múltiples pasos con muchos aspectos físico-químicos y estructurales influyendo en él. Debido a la propia estructura de la cadena, es fácil entender que un proceso que es termodinámicamente forzado a aumentar su ordenamiento local, se vea obstaculizado geométricamente y, por tanto, no puede conducirse a un estado de equilibrio final. Como resultado, se forman habitualmente estructuras de no equilibrio con diferentes características dependiendo de la temperatura, presión, cizallamiento y otros parámetros físico-químicos del sistema”. Estas palabras, pronunciadas recientemente por el profesor Bernhard Wunderlich, uno de los mas relevantes fisico-quimicos que han abordado en las ultimas décadas el estudio del estado físico de las macromoléculas, adelantan lo que de alguna manera se explicita en esta memoria y constituyen el “leitmotiv” de este trabajo de tesis. El mecanismo de la cristalización de polímeros esta aun bajo debate en la comunidad de la física de polímeros y la mayoría de los abordajes experimentales se explican a través de la teoría LH. Esta teoría clásica debida a Lauritzen y Hoffman (LH), y que es una generalización de la teoría de cristalización de una molécula pequeña desde la fase de vapor, describe satisfactoriamente muchas observaciones experimentales aunque esta lejos de explicar el complejo fenómeno de la cristalización de polímeros. De hecho, la formulación original de esta teoría en el National Bureau of Standards, a comienzos de la década de los 70, sufrió varias reformulaciones importantes a lo largo de la década de los 80, buscando su adaptación a los hallazgos experimentales. Así nació el régimen III de cristalización que posibilita la creacion de nichos moleculares en la superficie y que dio pie al paradigma ofrecido por Sadler y col., para justificar los experimentos que se obtenian por “scattering” de neutrones y otras técnicas como la técnica de “droplets” o enfriamiento rapido. Por encima de todo, el gran éxito de la teoría radica en que explica la dependencia inversa entre el tamaño del plegado molecular y el subenfriamiento, definido este ultimo como el intervalo de temperatura que media entre la temperatura de equilibrio y la temperatura de cristalización. El problema concreto que aborda esta tesis es el estudio de los procesos de ordenamiento de poliolefinas con distinto grado de ramificacion mediante simulaciones numéricas. Los copolimeros estudiados en esta tesis se consideran materiales modelo de gran homogeneidad molecular desde el punto de vista de la distribución de tamaños y de ramificaciones en la cadena polimérica. Se eligieron estas poliolefinas debido al gran interes experimental en conocer el cambio en las propiedades fisicas de los materiales dependiendo del tipo y cantidad de comonomero utilizado. Además, son modelos sobre los que existen una ingente cantidad de información experimental, que es algo que preocupa siempre al crear una realidad virtual como es la simulación. La experiencia en el grupo Biophym es que los resultados de simulación deben de tener siempre un correlato mas o menos próximo experimental y ese argumento se maneja a lo largo de esta memoria. Empíricamente, se conoce muy bien que las propiedades físicas de las poliolefinas, en suma dependen del tipo y de la cantidad de ramificaciones que presenta el material polimérico. Sin embargo, tal como se ha explicado no existen modelos teóricos adecuados que expliquen los mecanismos subyacentes de los efectos de las ramas. La memoria de este trabajo es amplia por la complejidad del tema. Se inicia con una extensa introducción sobre los conceptos básicos de una macromolecula que son relevantes para entender el contenido del resto de la memoria. Se definen los conceptos de macromolecula flexible, distribuciones y momentos, y su comportamiento en disolución y fundido con los correspondientes parametros caracteristicos. Se pone especial énfasis en el concepto de “entanglement” o enmaranamiento por considerarse clave a la hora de tratar macromoléculas con una longitud superior a la longitud critica de enmaranamiento. Finaliza esta introducción con una reseña sobre el estado del arte en la simulación de los procesos de cristalización. En un segundo capitulo del trabajo se expone detalladamente la metodología usada en cada grupo de casos. En el primer capitulo de resultados, se discuten los estudios de simulación en disolución diluida para sistemas lineales y ramificados de cadena única. Este caso mas simple depende claramente del potencial de torsión elegido tal como se discute a lo largo del texto. La formación de los núcleos “babys” propuestos por Muthukumar parece que son consecuencia del potencial de torsión, ya que este facilita los estados de torsión mas estables. Así que se propone el análisis de otros potenciales que son igualmente utilizados y los resultados obtenidos sobre la cristalización, discutidos en consecuencia. Seguidamente, en un segundo capitulo de resultados se estudian moleculas de alcanos de cadena larga lineales y ramificados en un fundido por simulaciones atomisticas como un modelo de polietileno. Los resultados atomisticos pese a ser de gran detalle no logran captar en su totalidad los efectos experimentales que se observan en los fundidos subenfriados en su etapa previa al estado ordenado. Por esta razon se discuten en los capítulos 3 y 4 de resultados sistemas de cadenas cortas y largas utilizando dos modelos de grano grueso (CG-PVA y CG-PE). El modelo CG-PE se desarrollo durante la tesis. El uso de modelos de grano grueso garantiza una mayor eficiencia computacional con respecto a los modelos atomísticos y son suficientes para mostrar los fenómenos a la escala relevante para la cristalización. En todos estos estudios mencionados se sigue la evolución de los procesos de ordenamiento y de fusión en simulaciones de relajación isoterma y no isoterma. Como resultado de los modelos de simulación, se han evaluado distintas propiedades fisicas como la longitud de segmento ordenado, la cristalinidad, temperaturas de fusion/cristalizacion, etc., lo que permite una comparación con los resultados experimentales. Se demuestra claramente que los sistemas ramificados retrasan y dificultan el orden de la cadena polimérica y por tanto, las regiones cristalinas ordenadas decrecen al crecer las ramas. Como una conclusión general parece mostrarse una tendencia a la formación de estructuras localmente ordenadas que crecen como bloques para completar el espacio de cristalización que puede alcanzarse a una temperatura y a una escala de tiempo determinada. Finalmente hay que señalar que los efectos observados, estan en concordancia con otros resultados tanto teoricos/simulacion como experimentales discutidos a lo largo de esta memoria. Su resumen se muestra en un capitulo de conclusiones y líneas futuras de investigación que se abren como consecuencia de esta memoria. Hay que mencionar que el ritmo de investigación se ha acentuado notablemente en el ultimo ano de trabajo, en parte debido a las ventajas notables obtenidas por el uso de la metodología de grano grueso que pese a ser muy importante para esta memoria no repercute fácilmente en trabajos publicables. Todo ello justifica que gran parte de los resultados esten en fase de publicación. Abstract “Polymer crystallization is therefore assumed, and in theories often described, to be a multi step process with many influencing aspects. Because of the chain structure, it is easy to understand that a process which is thermodynamically forced to increase local ordering but is geometrically hindered cannot proceed into a final equilibrium state. As a result, nonequilibrium structures with different characteristics are usually formed, which depend on temperature, pressure, shearing and other parameters”. These words, recently written by Professor Bernhard Wunderlich, one of the most prominent researchers in polymer physics, put somehow in value the "leitmotiv "of this thesis. The crystallization mechanism of polymers is still under debate in the physics community and most of the experimental findings are still explained by invoking the LH theory. This classical theory, which was initially formulated by Lauritzen and Hoffman (LH), is indeed a generalization of the crystallization theory for small molecules from the vapor phase. Even though it describes satisfactorily many experimental observations, it is far from explaining the complex phenomenon of polymer crystallization. This theory was firstly devised in the early 70s at the National Bureau of Standards. It was successively reformulated along the 80s to fit the experimental findings. Thus, the crystallization regime III was introduced into the theory in order to explain the results found in neutron scattering, droplet or quenching experiments. This concept defines the roughness of the crystallization surface leading to the paradigm proposed by Sadler et al. The great success of this theory is the ability to explain the inverse dependence of the molecular folding size on the supercooling, the latter defined as the temperature interval between the equilibrium temperature and the crystallization temperature. The main scope of this thesis is the study of ordering processes in polyolefins with different degree of branching by using computer simulations. The copolymers studied along this work are considered materials of high molecular homogeneity, from the point of view of both size and branching distributions of the polymer chain. These polyolefins were selected due to the great interest to understand their structure– property relationships. It is important to note that there is a vast amount of experimental data concerning these materials, which is essential to create a virtual reality as is the simulation. The Biophym research group has a wide experience in the correlation between simulation data and experimental results, being this idea highly alive along this work. Empirically, it is well-known that the physical properties of the polyolefins depend on the type and amount of branches presented in the polymeric material. However, there are not suitable models to explain the underlying mechanisms associated to branching. This report is extensive due to the complexity of the topic under study. It begins with a general introduction to the basics concepts of macromolecular physics. This chapter is relevant to understand the content of the present document. Some concepts are defined along this section, among others the flexibility of macromolecules, size distributions and moments, and the behavior in solution and melt along with their corresponding characteristic parameters. Special emphasis is placed on the concept of "entanglement" which is a key item when dealing with macromolecules having a molecular size greater than the critical entanglement length. The introduction finishes with a review of the state of art on the simulation of crystallization processes. The second chapter of the thesis describes, in detail, the computational methodology used in each study. In the first results section, we discuss the simulation studies in dilute solution for linear and short chain branched single chain models. The simplest case is clearly dependent on the selected torsion potential as it is discussed throughout the text. For example, the formation of baby nuclei proposed by Mutukhumar seems to result from the effects of the torsion potential. Thus, we propose the analysis of other torsion potentials that are also used by other research groups. The results obtained on crystallization processes are accordingly discussed. Then, in a second results section, we study linear and branched long-chain alkane molecules in a melt by atomistic simulations as a polyethylene-like model. In spite of the great detail given by atomistic simulations, they are not able to fully capture the experimental facts observed in supercooled melts, in particular the pre-ordered states. For this reason, we discuss short and long chains systems using two coarse-grained models (CG-PVA and CG-PE) in section 3 and 4 of chapter 2. The CG-PE model was developed during the thesis. The use of coarse-grained models ensures greater computational efficiency with respect to atomistic models and is enough to show the relevant scale phenomena for crystallization. In all the analysis we follow the evolution of the ordering and melting processes by both isothermal and non isothermal simulations. During this thesis we have obtained different physical properties such as stem length, crystallinity, melting/crystallization temperatures, and so on. We show that branches in the chains cause a delay in the crystallization and hinder the ordering of the polymer chain. Therefore, crystalline regions decrease in size as branching increases. As a general conclusion, it seems that there is a tendency in the macromolecular systems to form ordered structures, which can grown locally as blocks, occupying the crystallization space at a given temperature and time scale. Finally it should be noted that the observed effects are consistent with both, other theoretical/simulation and experimental results. The summary is provided in the conclusions chapter along with future research lines that open as result of this report. It should be mentioned that the research work has speeded up markedly in the last year, in part because of the remarkable benefits obtained by the use of coarse-grained methodology that despite being very important for this thesis work, is not easily publishable by itself. All this justify that most of the results are still in the publication phase.