Search, matching, and self-organization of a marketplace

In many developing countries, clusters of small shops are the typical market-place. We investigate an economic model in which, between buyers and sellers in a marketplace, a circular causality including the search process produces agglomeration forces, given the initial location of the marketplace location exogenously in a linear city. We conclude that initial number of buyers and sellers is important in forming a large marketplace.

Platforms and firm capabilities : a study of emerging global value chains

This paper discusses globalization’s impact on production and distribution systems in emerging economies. On one hand, globalization has resulted in an increasing number of multinational corporations to adopt a platform strategy for their customers in emerging markets. On the other hand, developing countries have witnessed the integration of an increasing number of traditional marketplaces into a powerful distribution system, characterized as a specialized market system. Consequently, an unique industrial organization has developed in emerging economies, regarded as emerging global value chains (EGVCs). They comprise a large number of small firms together with a small number of large platform providers and display the "market" type general governance patterns. Firms in EGVCs are more likely to realize functional upgrading and grow into strong lead firms.

Heterogeneous firms and cost sharing in China's marketplaces

This study extends Melitz's model with heterogeneous firms by introducing shared fixed costs in a marketplace. It aims to explain heterogeneous firms' choice between traditional marketplaces and modern distribution channels on the basis of their productivities. The results reveal that the co-existence of a traditional marketplace and modern distribution channels improves social welfare. In addition, a deregulation policy for firm entry outside a marketplace and accumulation of human capital are factors that contribute to improve the social welfare.

Propagation of Nuclear Data Uncertainties in Transmutation Calculations Using ACAB Code

The assessment of the accuracy of parameters related to the reactor core performance (e.g., ke) and f el cycle (e.g., isotopic evolution/transmutation) due to the uncertainties in the basic nuclear data (ND) is a critical issue. Different error propagation techniques (adjoint/forward sensitivity analysis procedures and/or Monte Carlo technique) can be used to address by computational simulation the systematic propagation of uncertainties on the final parameters. To perform this uncertainty assessment, the ENDF covariance les (variance/correlation in energy and cross- reactions-isotopes correlations) are required. In this paper, we assess the impact of ND uncertainties on the isotopic prediction for a conceptual design of a modular European Facility for Industrial Transmutation (EFIT) for a discharge burnup of 150 GWd/tHM. The complete set of uncertainty data for cross sections (EAF2007/UN, SCALE6.0/COVA-44G), radioactive decay and fission yield data (JEFF-3.1.1) are processed and used in ACAB code.

Modeling of the Division Point of Different Propagation Mechanisms in the Near-Region Within Arched Tunnels

An accurate characterization of the near-region propagation of radio waves inside tunnels is of practical importance for the design and planning of advanced communication systems. However, there has been no consensus yet on the propagation mechanism in this region. Some authors claim that the propagation mechanism follows the free space model, others intend to interpret it by the multi-mode waveguide model. This paper clarifies the situation in the near-region of arched tunnels by analytical modeling of the division point between the two propagation mechanisms. The procedure is based on the combination of the propagation theory and the three-dimensional solid geometry. Three groups of measurements are employed to verify the model in different tunnels at different frequencies. Furthermore, simplified models for the division point in five specific application situations are derived to facilitate the use of the model. The results in this paper could help to deepen the insight into the propagation mechanism within tunnel environments.

Propagation Mechanism Analysis Before the Break Point Inside Tunnels

There is no unanimous consensus yet on the propagation mechanism before the break point inside tunnels. Some deem that the propagation mechanism follows the free space model, others argue that it should be described by the multimode waveguide model. Firstly, this paper analyzes the propagation loss in two mechanisms. Then, by conjunctively using the propagation theory and the three-dimensional solid geometry, a generic analytical model for the boundary between the free space mechanism and the multi-mode waveguide mechanism inside tunnels has been presented. Three measurement campaigns validate the model in different tunnels at different frequencies. Furthermore, the condition of the validity of the free space model used in tunnel environment has been discussed in some specific situations. Finally, through mathematical derivation, the seemingly conflicting viewpoints on the free space mechanism and the multi-mode waveguide mechanism have been unified in some specific situations by the presented generic model. The results in this paper can be helpful to gain deeper insight and better understanding of the propagation mechanism inside tunnels

Propagation mechanism modelling in the near region of circular tunnels

Artículo sobre comunicaciones ferroviarias. Abstract: Along with the increase in operating frequencies in advanced radio communication systems utilised inside tunnels, the location of the break point is further and further away from the transmitter. This means that the near region lengthens considerably and even occupies the whole propagation cell or the entire length of some short tunnels. To begin with, this study analyses the propagation loss resulting from the free-space mechanism and the multi-mode waveguide mechanism in the near region of circular tunnels, respectively. Then, by conjunctive employing the propagation theory and the three-dimensional solid geometry, a general analytical model of the dividing point between two propagation mechanisms is presented for the first time. Moreover, the model is validated by a wide range of measurement campaigns in different tunnels at different frequencies. Finally, discussions on the simplified formulae of the dividing point in some application situations are made. The results in this study can be helpful to grasp the essence of the propagation mechanism inside tunnels.

Measurement of Distributed Antenna Systems at 2.4 GHz in a Realistic Subway Tunnel Environment.

Accurate characterization of the radio channel in tunnels is of great importance for new signaling and train control communications systems. To model this environment, measurements have been taken at 2.4 GHz in a real environment in Madrid subway. The measurements were carried out with four base station transmitters installed in a 2-km tunnel and using a mobile receiver installed on a standard train. First, with an optimum antenna configuration, all the propagation characteristics of a complex subway environment, including near shadowing, path loss,shadow fading, fast fading, level crossing rate (LCR), and average fade duration (AFD), have been measured and computed. Thereafter, comparisons of propagation characteristics in a double-track tunnel (9.8-m width) and a single-track tunnel (4.8-m width) have been made. Finally, all the measurement results have been shown in a complete table for accurate statistical modeling.

Propagation Mechanism modeling in the Near-Region of Arbitrary Cross-Sectional Tunnels.

Along with the increase of the use of working frequencies in advanced radio communication systems, the near-region inside tunnels lengthens considerably and even occupies the whole propagation cell or the entire length of some short tunnels. This paper analytically models the propagation mechanisms and their dividing point in the near-region of arbitrary cross-sectional tunnels for the first time. To begin with, the propagation losses owing to the free space mechanism and the multimode waveguide mechanism are modeled, respectively. Then, by conjunctively employing the propagation theory and the three-dimensional solid geometry, the paper presents a general model for the dividing point between two propagation mechanisms. It is worthy to mention that this model can be applied in arbitrary cross-sectional tunnels. Furthermore, the general dividing point model is specified in rectangular, circular, and arched tunnels, respectively. Five groups of measurements are used to justify the model in different tunnels at different frequencies. Finally, in order to facilitate the use of the model, simplified analytical solutions for the dividing point in five specific application situations are derived. The results in this paper could help deepen the insight into the propagation mechanisms in tunnels.

Combining data mining and ontology engineering to enrich ontologies and linked data

In this position paper, we claim that the need for time consuming data preparation and result interpretation tasks in knowledge discovery, as well as for costly expert consultation and consensus building activities required for ontology building can be reduced through exploiting the interplay of data mining and ontology engineering. The aim is to obtain in a semi-automatic way new knowledge from distributed data sources that can be used for inference and reasoning, as well as to guide the extraction of further knowledge from these data sources. The proposed approach is based on the creation of a novel knowledge discovery method relying on the combination, through an iterative ?feedbackloop?, of (a) data mining techniques to make emerge implicit models from data and (b) pattern-based ontology engineering to capture these models in reusable, conceptual and inferable artefacts.

Self-similar motion of laser half-space plasmas. I. Deflagration regime

The one-dimensional self-similar motion of an initially cold, half-space plasma of electron density 0,produced by the (anomalous) absorption of a laser pulse of irradiation = (j>0f/T(0< (< T) at the critical density nc(«c/«0=eoKe)213, where k, m, are Boltzmann's constant and the ion mass, and Ke X (electron temperature)5'2 = heat conductivity. If a >e- 4 ' 3 , a deflagration wave separates an isentropic compression with a shock bounding the undisturbed plasma, and an isentropic expansion flow to the vacuum. The structures of these three regions are completely determined; in particular, the Chapman-Jouguet condition is proved and the density behind the deflagration is found. The deflagration-compression thickness ratio is large (small) for a^e- 5 ' 3(a>e- 5 ' 3 ) . The compression to expansion ratio for both energy and thickness is 0(e"2). For Z,- large, a deflagration exists even if a~e~413. Condition a>e~4'3 may be applied to pulses that are not linear.

Modelo de diseño orientado a marcos para sistemas basados en el conocimiento

El objetivo de esta Tesis es crear un Modelo de Diseño Orientado a Marcos que, intermedio entre el Mundo Externo y el Modelo Interno del Mundo que supone el sistema ímplementado, disminuya la pérdida de conocimiento que se produce al formalizar la realidad en Bases de Conocimientos. El modelo disminuye la pérdida de conocimiento al formalizar Bases de Conocimiento, acercando el formalismo de Marcos al Mundo Externo, porque: 1. Crea una base teórica que uniformiza el concepto de Marco en el plano de la Formalización, estableciendo un conjunto de restricciones sintácticas y semánticas que impedirán, al Ingeniero del Conocimiento (IC) cuando formaliza, definir elementos no permitidos o el uso indebido de ellos. 2. Se incrementa la expresividad del formalismo al asociar a cada una de las propiedades de un marco clase un parámetro adicional que simboliza la representatividad de la propiedad en el concepto. Este parámetro, y las técnicas de inferencia que trabajan con él, permitirán al IC introducir en el Modelo Formalizado conocimiento que antes no introducía al construir la base de conocimientos y que, sin embargo, sí existía en la realidad. 3. Se propone una técnica de equiparación que trabaja con el conocimiento incierto presente en el dominio. Esta técnica de equiparación, utiliza la representatividad de las propiedades en los marcos clase y el grado de certeza de las propiedades de las entidades para calcular el valor de equiparación y, así, determinar en qué medida los marcos clase seleccionados son consistentes con la descripción de la situación actual dada por una entidad. 4. Proporciona nuevas técnicas de inferencia basadas en la transferencia de propiedades y modifica las ya existentes. Las transferencias de propiedades realizadas sobre relaciones "ad hoc" definidas por el IC al construir el sistema, es una nueva técnica de inferencia independiente y complementaria a la transferencia de propiedades llamada tradicionalmente Herencia (cesión de propiedades entre padres e hijos). A esta nueva técnica, se le ha llamado Donación, es decir, cesión de propiedades entre marcos sin parentesco. Como aportación práctica, se ha construido un entorno de construcción de Sistemas Basados en el Conocimiento formalizados en Marcos, donde se han introducido todos los nuevos conceptos del Modelo Teórico de la Tesis. Se trata de una cierta anidación. Es decir, son marcos que permiten formalizar cualquier SBC en marcos. El entorno permitirá al IC formalizar bases de conocimientos automáticamente y éste podrá validar el conocimiento del dominio en la fase de formalización en lugar de tener que esperar a que la BC esté implementada. Todo ello lleva a describir el Modelo de Diseño Orientado a Marcos como un puente que aproxima y comunica el Mundo Externo con el Modelo Interno asociado a la realidad e implementado en una computadora, disminuyendo así las diversas pérdidas de conocimiento que si bien no ocurren simultáneamente al construir Sistemas Basados en el Conocimiento, sí coexisten en él.---ABSTRACT---The goal of this thesis is to créate a Frame-Orlented Deslgn Model that, bridging the Outside World and the implemented system's Internal Model of the World, reduces the amount of knowledge lost when reality is formalized in Knowledge Bases (KB). The model diminishes the loss of knowledge when formalizing a KB and brings the Frame-formalized Model closer to the Outside World because: 1. It creates a theory that standardizes the concept of trame at the formalization level to establish a set of syntactic and semantic constraints that will prevent the Knowledge Engineer (KE) from defining forbidden elements or their undue use in the formalization process. 2. The formalism's expressiveness is increased by associating an additional parameter to each of the properties of a class frame to symbolize the representativeness of the concept property. This parameter and the related inference techniques will allow the KE to enter knowledge into the Formalized Model that actually existed but that was not used previously when building the KB. 3. The proposed technique involves matching and works with uncertain knowledge present in the domain. This matching technique takes the representativeness of the properties in the class frame and the degree of certainty of the properties of the entities to calcúlate the matching valué and thus determine to what extent the class frames selected are consistent with the description of the present situation given by an entity. 4. It offers new inference techniques based on property transfer and alters existing ones. Property transfer on ad hoc relations defined by the KE when building a system is a new inference technique independent of and complementary to property transfer traditionally termed Inheritance (transfer of properties between parents and children). This new technique has been callad Donation (transfer of properties between trames without relationships). 5. It improves control of the procedural knowledge defined in the trames by introducing OO concepta. A frame-formalized KBS building environment has been constructed, incorporating all the new concepts of the theoretical model set out in the thesis. There is some embedding, that is, they are trames that provide for any KBS to be formalizad in trames. The environment will enable the KE to formaliza KB automatically, and he will be able to valídate the domain knowledge in the formalization stage instead of havíng to wait until the KB has been implemented. This is a description of the Frame-oriented Design Model, a bridge that brings closer and communicates the Outside World with the Interna! Model associated to reality and implemented on a computar, thus reducing the different losses in knowledge that, though they do not occur simultaneosly when building a Knowledge-based System, coexist within it.

Acoustic overstimulation increases outer hair cell Ca2+ concentrations and causes dynamic contractions of the hearing organ

The dynamic responses of the hearing organ to acoustic overstimulation were investigated using the guinea pig isolated temporal bone preparation. The organ was loaded with the fluorescent Ca2+ indicator Fluo-3, and the cochlear electric responses to low-level tones were recorded through a microelectrode in the scala media. After overstimulation, the amplitude of the cochlear potentials decreased significantly. In some cases, rapid recovery was seen with the potentials returning to their initial amplitude. In 12 of 14 cases in which overstimulation gave a decrease in the cochlear responses, significant elevations of the cytoplasmic [Ca2+] in the outer hair cells were seen. [Ca2+] increases appeared immediately after terminating the overstimulation, with partial recovery taking place in the ensuing 30 min in some preparations. Such [Ca2+] changes were not seen in preparations that were stimulated at levels that did not cause an amplitude change in the cochlear potentials. The overstimulation also gave rise to a contraction, evident as a decrease of the width of the organ of Corti. The average contraction in 10 preparations was 9 μm (SE 2 μm). Partial or complete recovery was seen within 30–45 min after the overstimulation. The [Ca2+] changes and the contraction are likely to produce major functional alterations and consequently are suggested to be a factor contributing strongly to the loss of function seen after exposure to loud sounds.

Temperature dependence of amyloid β-protein fibrillization

Fibrillogenesis of the amyloid β-protein (Aβ) is believed to play a central role in the pathogenesis of Alzheimer’s disease. Previous studies of the kinetics of Aβ fibrillogenesis showed that the rate of fibril elongation is proportional to the concentration of monomers. We report here the study of the temperature dependence of the Aβ fibril elongation rate constant, ke, in 0.1 M HCl. The rate of fibril elongation was measured at Aβ monomer concentrations ranging from 50 to 400 μM and at temperatures from 4°C to 40°C. Over this temperature range, ke increases by two orders of magnitude. The temperature dependence of ke follows the Arrhenius law, ke = A exp (−EA/kT). The preexponential factor A and the activation energy EA are ≈6 × 1018 liter/(mol·sec) and 23 kcal/mol, respectively. Such a high value of EA suggests that significant conformational changes are associated with the binding of Aβ monomers to fibril ends.

Neural basis of an inherited speech and language disorder

Investigation of the three-generation KE family, half of whose members are affected by a pronounced verbal dyspraxia, has led to identification of their core deficit as one involving sequential articulation and orofacial praxis. A positron emission tomography activation study revealed functional abnormalities in both cortical and subcortical motor-related areas of the frontal lobe, while quantitative analyses of magnetic resonance imaging scans revealed structural abnormalities in several of these same areas, particularly the caudate nucleus, which was found to be abnormally small bilaterally. A recent linkage study [Fisher, S., Vargha-Khadem, F., Watkins, K. E., Monaco, A. P. & Pembry, M. E. (1998) Nat. Genet. 18, 168–170] localized the abnormal gene (SPCH1) to a 5.6-centiMorgan interval in the chromosomal band 7q31. The genetic mutation or deletion in this region has resulted in the abnormal development of several brain areas that appear to be critical for both orofacial movements and sequential articulation, leading to marked disruption of speech and expressive language.