867 resultados para Empirical studies


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Coral reefs are characterized by enormous carbonate production of the organisms. It is known that rapid calcification is linked to photosynthesis under control of the carbonate equilibrium in seawater. We have established a model simulating the coexisting states of photosynthesis and calcification in order to examine the effects of photosynthesis and calcification on the carbonate system in seawater. Supposing that the rates of photosynthesis and calcification are proportional to concentrations of their inorganic carbon source, the model calculations indicate that three kinds of unique interactions of the organic and inorganic carbon productions are expected. These are photosynthetic enhancement of calcification, calcification which benefits photosynthesis and carbonate dissolution induced by respiration. The first effect appears when the photosynthetic rate is more than approximately 1.2 larger than that of calcification. This effect is caused by the increase of CO3 content and carbonate saturation degree in seawater. If photosynthesis use molecular carbon dioxide, the second effect occurs when the calcification rate is more than approximately 1.6 times larger than that of photosynthesis. Time series model experiments indicate that photosynthesis and calcification potentially enhance each other and that organic and inorganic carbon is produced more efficiently in the coexisting system than in the isolated reactions. These coexisting effects on production enhancement of photosynthesis and calcification are expected to appear not only in the internal pool of organisms but also in a reef environment which is isolated from the outer ocean during low tide. According to the measurements on the fringing type Shiraho Reef in the Ryukyu Islands, the diurnal change of water properties (pH, total alkalinity, total carbon dioxide and carbonate saturation degree) were conspicuous. This environment offers an appropriate condition for the appearance of these coexisting effects. The photosynthetic enhancement of calcification and the respiratory inducement of decalcification were observed during day-time and night-time slack-water periods, respectively. These coexisting effects, especially the photosynthetic enhancement of calcification, appear to play important roles for fluorishing coral reef communities.

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This paper empirically analyzes the market efficiency of microfinance investment funds. For the empirical analysis, we use an index of the microfinance investment funds and apply two kinds of variance ratio tests to examine whether or not this index follows a random walk. We use the entire sample period from December 2003 to June 2010 as well as two sub-samples which divide the entire period before and after January 2007. The empirical evidence demonstrates that the index does not follow a random walk, suggesting that the market of the microfinance investment funds is not efficient. This result is not affected by changes in either empirical techniques or sample periods.

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Trade affects the internal location of industry in two ways: it induces firms to specialize and it expands the set of markets that firms serve. If there are industry-specific external economies, firms in related industries will spatially agglomerate (Hanson 1996a). In the context of economic integration, diminished barriers to trade affect industry location particularly in less developed countries. As described below, regional agreements in North America and Europe have caused frontier regions to expand. These regions, which include border regions and port cities, have advantages over internal regions in terms of access to foreign markets. Since trade liberalization induces many firms in developing countries to participate in production networks and to specialize in labor-intensive activities such as assembling and processing of foreign-made components, their inputs as well as final products need to be carried across borders. Therefore, the best industry location, one that minimizes transport costs, is likely to shift to frontier regions. In East Asia, China has developed rapidly since it opened up to international trade. Simultaneously, a large amount of foreign direct investment (FDI) has been attracted and industry agglomerations have been formed in coastal regions, that is, frontier regions linked to the global market by sea, leaving many internal regions behind. Similarly, Cambodia, Laos, Myanmar, and Vietnam (CLMV) have joined AFTA and/or the WTO and liberalized international trade since the 1990s. Moreover, transport infrastructures such as the East-West Economic Corridor, the Southern Economic Corridor, and the North-South Economic Corridor have been built and narrowed economic distances in the Greater Mekong Subregion (GMS). As a result, frontier regions are likely to increase their location advantages and lure labor-intensive operations from neighboring countries. It is expected that, as has happened in North America and Europe, economic integration in East Asia will significantly affect internal geography in CLMV. In this study, I first review theories relevant to economic integration and industry location within a country. In particular, emphasis is placed on the new economic geography (NEG). Secondly, empirical results for North America and Europe are surveyed since they have preceded East Asia in regional integration and a substantial number of studies have been conducted on these regions. The final section summarizes and discusses implications for internal geography in CLMV.

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Initially, service sector was defined as complementary to manufacturing sector. This situation has changed in recent times; services growth has resulted in a dominance of employment and economic activity in most developed nations and is becoming a key process for the competitiveness of their industrial sectors. New services related to commodities have become a strategy to differentiate their value proposition (Robinson et al., 2002). The service sector's importance is evident when evaluating its share in the gross domestic product. According to the World Bank (2011), in 2009, 74.8% of GDP in the euro area and 77.5% in United States were attributed to services. Globalization and use of information and communication technology has accelerated dissemination of knowledge and increasing customer expectations about services available worldwide. Innovation becomes essential to ensure that service organizations respond with appropriate products and services for each market segment. Customized and placed on time-tomarket new services require a more developed innovation process. Service innovation and new service development process are cited as one of the priorities for academic research in the following years (Karniouchina et al., 2005) This paper has the following objectives: -To present a model for the analysis of innovation process through the service value network, -To verify its applicability through an empirical research, and -To identify the path and mode of innovation for a group of studied organizations and to compare it with previous studies.

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Based on the empirical evidence that the ratio of email messages in public mailing lists to versioning system commits has remained relatively constant along the history of the Apache Software Foundation (ASF), this paper has as goal to study what can be inferred from such a metric for projects of the ASF. We have found that the metric seems to be an intensive metric as it is independent of the size of the project, its activity, or the number of developers, and remains relatively independent of the technology or functional area of the project. Our analysis provides evidence that the metric is related to the technical effervescence and popularity of project, and as such can be a good candidate to measure its healthy evolution. Other, similar metrics -like the ratio of developer messages to commits and the ratio of issue tracker messages to commits- are studied for several projects as well, in order to see if they have similar characteristics.

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The influence of climate on forest stand composition, development and growth is undeniable. Many studies have tried to quantify the effect of climatic variables on forest growth and yield. These works become especially important because there is a need to predict the effects of climate change on the development of forest ecosystems. One of the ways of facing this problem is the inclusion of climatic variables into the classic empirical growth models. The work has a double objective: (i) to identify the indicators which best describe the effect of climate on Pinus halepensis growth and (ii) to quantify such effect in several scenarios of rainfall decrease which are likely to occur in the Mediterranean area. A growth mixed model for P. halepensis including climatic variables is presented in this work. Growth estimates are based on data from the Spanish National Forest Inventory (SNFI). The best results are obtained for the indices including rainfall, or rainfall and temperature together, with annual precipitation, precipitation effectiveness, Emberger?s index or free bioclimatic intensity standing out among them. The final model includes Emberger?s index, free bioclimatic intensity and interactions between competition and climate indices. The results obtained show that a rainfall decrease about 5% leads to a decrease in volume growth of 5.5?7.5% depending on site quality.

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An increasing number of neuroimaging studies are concerned with the identification of interactions or statistical dependencies between brain areas. Dependencies between the activities of different brain regions can be quantified with functional connectivity measures such as the cross-correlation coefficient. An important factor limiting the accuracy of such measures is the amount of empirical data available. For event-related protocols, the amount of data also affects the temporal resolution of the analysis. We use analytical expressions to calculate the amount of empirical data needed to establish whether a certain level of dependency is significant when the time series are autocorrelated, as is the case for biological signals. These analytical results are then contrasted with estimates from simulations based on real data recorded with magnetoencephalography during a resting-state paradigm and during the presentation of visual stimuli. Results indicate that, for broadband signals, 50–100 s of data is required to detect a true underlying cross-correlations coefficient of 0.05. This corresponds to a resolution of a few hundred milliseconds for typical event-related recordings. The required time window increases for narrow band signals as frequency decreases. For instance, approximately 3 times as much data is necessary for signals in the alpha band. Important implications can be derived for the design and interpretation of experiments to characterize weak interactions, which are potentially important for brain processing.

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This paper reports extensive tests of empirical equations developed by different authors for harbour breakwater overtopping. First, the existing equations are compiled and evaluated as tools for estimating the overtopping rates on sloping and vertical breakwaters. These equations are then tested using the data obtained in a number of laboratory studies performed in the Centre for Harbours and Coastal Studies of the CEDEX, Spain. It was found that the recommended application ranges of the empirical equations typically deviate from those revealed in the experimental tests. In addition, a neural network model developed within the European CLASH Project is tested. The wind effects on overtopping are also assessed using a reduced scale physical model

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El presente trabajo de investigación se ocupa del estudio de las vibraciones verticales inducidas por vórtices (VIV) en aquellos puentes que, por sus características geométricas y propiedades dinámicas, muestran cierta sensibilidad este tipo de fenómeno aeroelástico. El objeto principal es el análisis del mecanismo de interacción viento-estructura sobre secciones no fuseladas de geometría simple, con objeto de realizar una adecuada caracterización del problema y poder abordar posteriormente el análisis de otras secciones de geometría más compleja, representativas de los principales elementos estructurales de los puentes, como arcos, tableros, torres y pilas. Este aspecto es fundamental durante la fase de diseño del puente, donde deberán tenerse en cuenta también una serie de detalles que pueden influir significativamente su sensibilidad ante problemas aerodinámicos, como la morfología y dimensiones principales de la sección transversal del tablero, la disposición de barreras de seguridad y barreras cortaviento, o las riostras que unen diferentes elementos estructurales. La configuración de dos elementos en tándem o la construcción de un puente en las inmediaciones de otro existente son otros aspectos a considerar respecto a la sensibilidad frente a efectos aeroelásticos. El estudio se ha llevado a cabo principalmente mediante la implementación de simulaciones numéricas que reproducen la interacción entre la corriente de aire y secciones representativas de modelos estructurales, a partir de un código CFD basado en el método de las partículas de vórtices (VPM), siguiendo por tanto un esquema Lagrangiano. Los resultados han sido validados con datos experimentales existentes, valores procedentes de ensayos en túnel de viento y registros reales a partir de diferentes casos de estudio: Alconétar (2006), Niterói (1980), Trans- Tokyo Bay (1995) y Volgogrado (2010). Finalmente, se propone un modelo semi-empírico para la estimación del rango de velocidades críticas y amplitudes de oscilación basado en la utilización de las derivadas de flameo de Scanlan, y la densidad espectral de las fuerzas aerodinámicas en el dominio de la frecuencia. The present research work concerns the study of vertical vortex-induced vibrations (VIV) in bridges which show certain sensitivity to this type of aeroelastic phenomenon. It focuses on the analysis of the wind-structure interaction mechanism on bluff sections, with the objective of making a good characterisation of the problem and subsequently addressing the analysis of sections with a complex geometry, which are representative of the bridge structural elements, such as arches, decks, towers and piers. This issue is of relative importance during the bridge design phase, since minor details of the aforementioned elements can significantly influence its sensitivity to aerodynamic problems. The shape and main dimensions of the deck cross section, the addition of safety barriers and windshields, the presence of braces to enhance the structure mechanical properties, the utilisation of cross sections in tandem arrangement, or the erection of a new bridge in the vicinity of another existing one are some of the aspects to be considered regarding the sensitivity to the aeroelastic effects. The study has been carried out mainly through the implementation of numerical simulations that reproduces the interaction between the airflow and the representative cross section of a structural bridge model, by the use of a CFD code based on the vortex particle method (VPM), thus following a Lagrangian scheme. The results have been validated with existing experimental data, values from wind tunnel tests and full scale observations from the different case studies: Alconétar (2006), Niterói (1980), Trans-Tokyo Bay (1995) and Volgograd (2010). Finally, a new semi-empirical model is proposed for the estimation of the critical wind velocity ranges and oscillation amplitudes based on the use of the Scanlan’s flutter derivatives and the power spectral density of aerodynamic force time history in the frequency domain.

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The main objective of this paper is twofold: on the one hand, to analyse the impact that the announcement of the opening of a new hotel has on the performance of its chain by carrying out an event study, and on the other hand, to compare the results of two different approaches to this method: a parametric specification based on the autoregressive conditional heteroskedasticity models to estimate the market model, and a nonparametric approach, which implies employing Theil’s nonparametric regression technique, which in turn, leads to the so-called complete nonparametric approach to event studies. The results that the empirical application arrives at are noteworthy as, on average, the reaction to such news releases is highly positive, both approaches reaching the same level of significance. However, a word of caution must be said when one is not only interested in detecting whether the market reacts, but also in obtaining an exhaustive calculation of the abnormal returns to further examine its determining factors.

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From the Introduction. In the aftermath of the EU’s enlargement towards Central and Eastern Europe, many scholars and observers of European integration were proclaiming that the French-German “engine” of Europe had come to an end. The political legitimacy of French-German initiatives was contested by coalitions of smaller member states and the ‘new Europe’ was calling for new leadership dynamics. However, the experience of the Eurozone debt crisis provided dramatic evidence that no alternative to the Franco-German partnership has yet to emerge in the enlarged EU. In a time of existential crisis, Franco-German initiatives appear to have remained the basic dynamic of integration. However, unlike in the past, agreements on steps forward have proven to be particularly difficult. This is largely due to these countries’ contrasting political economic policy ideas, cultures, and practices....the paper analyses the ideational ‘frames’ of the two leaders while tracing their discursive interactions against changing background conditions since the European debt crisis was triggered by Greece in October 2009 until the last measures taken in 2012 before the French Presidential elections. The empirical analysis is based on a systematic corpus of press conferences and media interviews by Nicolas Sarkozy and Angela Merkel after European summits. It is complemented by a number of press interviews including some given by their respective Finance Ministers) and important speeches in that same period of time.

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This paper provides a synthesis of the empirical literature on the key issues in agricultural and rural labour markets since 1960s, drawing mainly upon studies from the United States and the European Union, but also including relevant material from developing countries. The contribution of this meta-analysis lies in its unique structure as it covers the main research questions which have been addressed in the literature and includes the most cited papers from the American Journal of Agricultural Economics, Journal of Agricultural Economics, European Review of Agricultural Economics, Agricultural Economics as well as other reports and EU funded projects. Each research question is accompanied by tabular summaries which classify the individual studies according to the methodology and the variables employed. The heterogeneous conditions across countries, the different research questions and methodologies, and the type of data employed, have sometimes led to conflicting results. Nonetheless, by comparing the results it is possible to assess the significance and the direction of the determinants of rural labour allocation and its adjustments, and thus contribute to a better understanding on the functioning of rural labour markets. Lastly, by recognising the importance of the institutional framework, the paper provides useful policy insights.

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An increasing number of bilateral or plurilateral trade agreements (or regional trade agreements: RTAs) include "labor clauses" that require or urge the signatory countries to commit to maintaining a certain level of labor standards. This paper performs an empirical analysis of the impacts of such labor clauses provided in RTAs on working conditions that laborers in the RTA signatory countries actually face, using macro-level data for a wide variety of countries. The paper first examines the texts of labor provisions in more than 220 effective RTAs and (re-)classifies "RTAs with labor clauses" according to two criteria: (i) the agreement urges or expects the signatory countries to harmonize their domestic labor standards with internationally recognized standards, and (ii) the agreement stipulates the procedures for consultations and/or dispute settlement on labor-condition issues between the signatory countries. Based on this labor-clause RTA classification, the paper estimates the impacts of RTA labor clauses on working conditions in countries with two empirical specifications using the sample covering 136 countries or economies and years from 1995 through 2011. The estimation is extended to takes into account possible lags in the labor-condition effects of labor clauses as well as to consider potential difference in the impacts for countries in different income levels. The empirical results for the four measures of labor conditions (mean monthly real earnings, mean weekly work hours per employee, fatal occupational injury rate, and the number of the ILO's Core Conventions ratified) find no evidence for possible pro-labor-condition effects of RTA labor clauses overall, which should be consistent with the view of economics literature that questions the relevance of linking trade policy with issues in the domestic labor standards.