The Network Structure of Economic Output

Much of the analysis of economic growth has focused on the study of aggregate output. Here, we deviate from this tradition and look instead at the structure of output embodied in the network connecting countries to the products that they export. We characterize this network using four structural features: the negative relationship between the diversification of a country and the average ubiquity of its exports, and the non-normal distributions for product ubiquity, country diversification and product co-export. We model the structure of the network by assuming that products require a large number of non-tradable inputs, or capabilities, and that countries differ in the completeness of the set of capabilities they have. We solve the model assuming that the probability that a country has a capability and that a product requires a capability are constant and calibrate it to the data to find that it accounts well for all of the network features except for the heterogeneity in the distribution of country diversification. In the light of the model, this is evidence of a large heterogeneity in the distribution of capabilities across countries. Finally, we show that the model implies that the increase in diversification that is expected from the accumulation of a small number of capabilities is small for countries that have a few of them and large for those with many. This implies that the forces that help drive divergence in product diversity increase with the complexity of the global economy when capabilities travel poorly

The closed-edge structure of graphite and the effect of electrostatic charging

The properties of graphite, and of few-layer graphene, can be strongly influenced by the edge structure of the graphene planes, but there is still much that we do not understand about the geometry and stability of these edges. We present an experimental and theoretical study of the closed edges of graphite crystals, and of the effect of an electric field on their structure. High-resolution transmission electron microscopy is used to image the edge structure of fresh graphite and of graphite that has been exposed to an electric field, which experiences a separation of the graphene layers. Computer simulations based on density functional theory are used to rationalise and quantify the preference for the formation of multiple concentric loops at the edges. A model is also presented to explain how the application of an electric field leads to the separation of the folded edges

Modeling of Rolling-Piston Compressors with Special Attention to the Suction and Discharge Processes

The present paper describes a simulation model developed to predict the performance of rolling-piston compressors with special attention to the suction and discharge processes. The relevant input data required by the model, such as clearances between moving parts, valve stiffness and natural frequency and electric motor efficiency, were obtained experimentally. Correlations for effective flow and force areas associated with the suction and discharge processes were derived from flow simulations. It was found that the position of the rolling piston in relation to the suction and discharge ports must be included to fully characterize the effective flow and force areas. Numerical predictions of the thermodynamic inefficiencies associated with a R22 rolling-piston compressor were compared with measurements and good agreement was found at different operating conditions

Valoración de portafolios de bonos públicos en el mercado colombiano

Los inversionistas al entrar en el mercado de capitales y realizar inversiones en el mismo, encuentran que siempre existen riesgos asociados a las inversiones involucrados que son difíciles de controlar y que hacen que las inversiones tengan un grado de rentabilidad alto pero con un riesgo alto, para dar el primer paso a la disminución de este, generalmente se decanta por Títulos de Renta Fija que tiene un riesgo menor y con rentabilidades moderadas, que los hacen atractivos, pero realizar inversiones en uno solo título no hace que el riesgo del mismo siga latente, por ello se debe intentar una mezcla de títulos que permitan una disminución mayor del riesgo y que hagan atractivo realizar una inversión, para esto generalmente se realiza una composición de un portafolio de inversiones. Pero la realización de la composición del portafolio se realiza sin ningún soporte y se hace a criterio de la persona que realiza la composición. Este proyecto de investigación se centra en la definición de una metodología que permita la composición de portafolios de inversión de renta fija en Colombia, analizando variables como el riesgo y la rentabilidad para que basándose en ellas, nos permitan arrojar como resultado la composición del portafolio con los valores porcentuales de aporte de cada título dentro del portafolio

International Knowledge Diffusion and the Comparative Advantage of Nations

In this paper we document that the probability that a product is added to a country’s export basket is, on average, 65% larger if a neighboring country is a successful exporter of that same product. We interpret our result as evidence of international intra-industry knowledge diffusion. Our results are consistent with the overall consensus in the literature on technology spillovers: diffusion is stronger at shorter distances; is weaker for more knowledge-intensive products; and has become faster over time

Damage identification in structural health monitoring: a brief review from its implementation to the Use of data-driven applications

The damage identification process provides relevant information about the current state of a structure under inspection, and it can be approached from two different points of view. The first approach uses data-driven algorithms, which are usually associated with the collection of data using sensors. Data are subsequently processed and analyzed. The second approach uses models to analyze information about the structure. In the latter case, the overall performance of the approach is associated with the accuracy of the model and the information that is used to define it. Although both approaches are widely used, data-driven algorithms are preferred in most cases because they afford the ability to analyze data acquired from sensors and to provide a real-time solution for decision making; however, these approaches involve high-performance processors due to the high computational cost. As a contribution to the researchers working with data-driven algorithms and applications, this work presents a brief review of data-driven algorithms for damage identification in structural health-monitoring applications. This review covers damage detection, localization, classification, extension, and prognosis, as well as the development of smart structures. The literature is systematically reviewed according to the natural steps of a structural health-monitoring system. This review also includes information on the types of sensors used as well as on the development of data-driven algorithms for damage identification.Peer ReviewedPostprint (published version