Thèses sur le sujet « Heterogeneous firm »

La tesi è formata da due capitoli su dinamica della distribuzione delle imprese e shock aggregati. Usando un modello ad imprese eterogenee, la tesi studia le fluttuazioni di ciclo economico dovute a shock alla tecnologia ed ai costi in entrata.
This dissertation collects two essays on firm size dynamics and aggregate shocks. By employing a model with heterogeneous firms, search frictions and endogenous entry/exit we investigate the business cycle dynamics of the firm size distribution by looking at entry cost and technology shocks. The thesis is divided into two chapters.\\ The first chapter explores how an increase in entry costs affects the size of new entrants and the concentration of employment according to firm size, along with its effects on macro-variables such as unemployment and the exit rate. To this aim we use a BVAR model to estimate the response of such variables to an entry cost shock, then we develop a heterogeneous-firm model with search frictions and endogenous entry/exit dynamics calibrated on data from Business Dynamics Statistics (BDS) database to address our empirical results.\\ We find that positive entry cost shocks increase the average size of entrants and move employment shares toward the largest firms. These results reveal the role of entry costs' fluctuations in explaining the dynamics at business cycle horizons of both firm and employment share distributions according to size.\\ The second chapter perturbed the model with a technology shock to replicate the long-run differential of job destruction due to exit between small and large firms and its empirical response to technology shocks (estimated by a BVAR). Contrary to frameworks with \textit{exogenous} exit, the model is able to account for the volatility of exit and the differential of job destruction due to exit between small and large firms conditional to the technology shock. Moreover we find that not only entry but also exit is a viable amplification channel for the response of unemployment to the shock.\\

This dissertation investigates how competition among heterogeneous firms affects R&D in quality enhancement in a quality-ladder type framework for a Cournot oligopolistic industry. The research also analyzes the welfare implications of various policies that promotes R&D. Some of the theoretical predictions are then tested empirically using firm-level data for Bangladesh from the World Bank's enterprise survey. Chapter 1 shows that a rise in the cost of production of the competitor will induce a firm to invest more in R&D if and only if the quality difference between the existing product and the product emerging from R&D activities is sufficiently large. Also, welfare-reducing effect of helping a `minor' firm is lower in the presence of possible quality differences. Empirical results supports the theoretical findings. Chapter 2 shows that protecting domestic industry of high quality goods encourages firms to invest more in R&D. The size of the optimal tariff depends on the degree of product differentiation and market share of the foreign firms and is not necessarily positive. Chapter 3 shows that a small tariff imposed by the trading partner on the high quality good will deter R&D. However, as the tariff gets bigger, the relationship changes sign. The size of an R&D subsidy depends on the market share of the firms. Empirical results provide support to the theoretical findings.

In this paper, we analyse the effects of a unilateral change in an emissions tax in a model of international trade with heterogeneous firms. We find a positive effect of tighter environmental policy on average productivity in the reforming country through reallocation of labour towards exporting firms. Domestic aggregate emissions fall, due to both a scale and a technique effect, but we show that the reduction in emissions following the tax increase is smaller than in autarky. Moreover, general equilibrium effects through changes in the foreign wage rate lead to a reduction in foreign emissions and, hence, to negative emissions leakage in case of transboundary pollution.

L'objectif principal de cette dissertation est d'examiner trois questions qui ont reçu peu d'attention dans les travaux théoriques existants sur le commerce international. Ainsi, cette thèse a trois objectifs. Le premier consiste à étudier les effets sur le bien-être de la libéralisation des normes entre des pays asymétriques. Le deuxième consiste à examiner théoriquement et empiriquement l'effet revenu sur les marges du commerce et leur degré de sensibilité aux coûts des échanges. Le troisième objectif est de se concentrer sur l'aspect firme-spécifique de l'élasticité prix de la demande au-delà de la CES et d'examiner le rôle qu'il joue dans la détermination de la magnitude et de la structure des gains à l'échange. En vue d'atteindre cet objectif, j'intègre des hypothèses alternatives dans le modèle canonique de Melitz-Chaney du commerce international avec des firmes hétérogènes (Melitz, 2003; Chaney, 2008). Ce faisant, la thèse actuelle contribue à la théorie du commerce avec des firmes hétérogènes sur trois axes. Dans le chapitre 1, je montre que la libéralisation des normes améliore le bien-être seulement lorsque la hiérarchie des normes est de type "verti-zontal" et que le partenaire commercial est plus large que le pays exclu. Dans le chapitre 2, je montre que la marge intensive n'augmente qu'avec le revenu par habitant en équilibre général, et que le revenu par habitant atténue la sensibilité des marges aux coûts des échanges. Dans le chapitre 3, je démontre que la structure et la magnitude des gains à l'échange dépendent principalement de la courbure de la demande et ne sont affectées que marginalement par le type des préférences
The main objective of this dissertation is to address three questions, which despite their theoretical appeal, received little attention in existing theoretical work in international trade, and are thus still open. The goal of this dissertation is thus threefold. The first consists in studying the welfare implications of standards liberalization under country-level asymmetry both in market size and stringency of local standards. The second is to examine both theoretically and empirically the income effect on trade margins and on the degree of their sensitivity to trade costs. The third objective is to concentrate on the firm-specific aspect of the demand elasticity beyond the CES, and to examine the role it plays in determining the magnitude and the structure of the gains from trade. Towards this goal, I embed alternative assumptions on both the demand and supply side in the canonical Melitz-Chaney model of international trade with heterogeneous firms (Melitz, 2003; Chaney, 2008). ln so doing, the current dissertation contributes to trade theory with heterogeneous firms along three lines. ln Chapter 1, I show that standards liberalization is welfare improving only when the cost hierarchy is "verti-zontal" and the trading partner is larger than the excluded country. ln Chapter 2, I show that the intensive margin of trade increases only with per-capita income in general equilibrium, and that per-capita income dampens the sensitivity of trade margins to trade costs. ln Chapter3, I demonstrate that demand curvature plays a crucial role in determining the structure and the magnitude of the gains from trade, whereas the type of preferences affects only marginally these results

This thesis consists of three independent papers, ordered chronologically with respect to when they were initiated. Empirical research has established that there are large and persistent productivity differences among firms in narrowly defined industries (Bartelsman and Doms, 2000). Other studies, in particular Bernard and Jensen (1999), have shown the existence of a causal link running from ex-ante firm productivity to export decisions. Furthermore, exposure to trade has been found to enhance growth opportunities only for some firms, reallocating market shares and resources toward the more productive ones and contributing thus to aggregate productivity growth (Clerides, Lach and Tybout, 1998; Bernard and Jensen, 2004). These findings have led to the development of new theoretical models emphasizing the interaction between firm heterogeneity and fixed market entry costs in generating international trade and inducing aggregate productivity growth. The first and third chapters of this thesis extend the framework developed by Melitz (2003) to analyze the implications of  firm heterogeneity for old and new issues in international trade. The first paper studies the effect of trade liberalization between countries that differ in their relative endowment of skilled workers when growth-promoting R&D activities are skill intensive with respect to goods production. In particular, the analysis focuses on the changes that falling trade costs induce on consumer welfare and on the number of firms active in the different markets. The third paper uses the heterogeneous firm framework to study the interaction between financial constraints and the market entry behavior of firms. It also analyzes whether the impact of trade liberalization on average firm productivity and on individual welfare is affected by the presence of credit frictions. The second chapter presents an empirical work that contributes to the recent but fast growing literature that studies how different institutions and their level of development affect countries comparative advantage. The analysis presented in this paper focuses on the role of legal and financial institution in driving the specialization in contract-intensive goods and on how the degree of institutional development interacts with the propensity of firms to vertical integrate with their suppliers.
Diss. Stockholm : Handelshögskolan i Stockholm, 2011

This thesis contributes to the literature on microeconomic linkage between globalization, economic growth and welfare. First, we study the impact of input trade liberalization on firm efficiency, aggregate productivity and welfare. We extend the Melitz (2003)'s framework to incorporate: a) trade in both intermediate inputs and final goods between similar countries, b) firm's decision to import intermediate inputs in addition to the decision to export the final output. This model shows different effects from reducing input tariffs, according to whether intermediates are assumed to be imported directly by final good firms or indirectly through an efficient wholesale system. Second, using data from Chinese manufacturing firms over the period 2002- 2006, we investigate empirically the effect of trade liberalization in intermediate inputs on firm's total factor productivity (TFP), considering the relevant role played by trade wholesalers. We document that direct-importers enjoy larger productivity gains from reducing input tariffs respect to other firms. But, the non-importers also benefit because they can access to foreign inputs through trade intermediaries. In sectors where input trade intermediation was relatively low, firms not directly involved in imports suffer efficiency losses. Finally, we also explore the effectiveness of different trade policy instruments on product-level Chinese imports over the period 2000-2006. More specifically, in addition to the declines in tariffs, we investigate the impact on imports of the gradual removal of non-tariff barriers (NTBs) as agreed within WTO's accession protocol in 2001 (such as import quotas, licenses and tendering). Overall, the results show that while manufacturing imports increased due to tariff cuts, agricultural imports grew thanks to the elimination of import licenses. We also find some complementarity between tariffs and NTBs.

Cette thèse se propose d’étudier le rôle de l’hétérogénéité des entreprises multinationales dans leurs stratégies d’investissements directs à l’étranger (IDE). Si de précédents travaux soulignent l’importance de la productivité individuelle des entreprises dans le fait de devenir une multinationale, peu évoquent l’hétérogénéité restante entre ces entreprises pour expliquer les différences de choix de mode d’entrée ou de motif d’implantation à l’étranger. A travers des approches théoriques et empiriques innovantes, basées sur l’utilisation de données confidentielles d’entreprises françaises, nous montrons que l’hétérogénéité des entreprises détermine chacun des trois aspects stratégiques détaillés dans cette thèse : Le taux de contrôle à l’étranger, le motif d’implantation et la structure du réseau de filiales. Plus précisément, la productivité et l'expérience de la firme favorisent un contrôle accru des filiales étrangères, leur importance relative dépendant du pays hôte. Ces caractéristiques sont également associées à une intégration plus profonde dans les chaînes de valeur mondiales, ainsi qu’à la constitution d'un réseau d’implantations plus original. Ces résultats permettent une meilleure compréhension des choix des multinationales, au-delà de l’apparente complexité des flux d’IDE
This thesis examines the role of firms´ heterogeneity in the Foreign Direct Investments (FDIs) strategies. We already know firms’ heterogeneity to sharply distinguish between domestic firms, exporters and multinationals (MNEs). Yet, to what extent it impacts their foreign direct investments (FDIs) strategies among MNEs is rarely evoked, while several entry mode choices and FDI motives coexist. Mixing both theoretical and empirical innovating approaches using French firm-level data, the four chapters of this PhD dissertation reveal that the firm heterogeneity influences all of the three dimensions of strategies we review: foreign ownership mode, FDI motive and structure of the overall network of affiliates. Specifically, firm-level productivity and international experience foster deeper integration with a changing relative importance according to the host country. They are also associated with production motives and vertical integration into the global value chains. The more productive firms also display original affiliates’ network structure. These findings allow a better understanding of multinationals’ choices underneath the ``complex’’ global picture of FDI flows

The common thread in this thesis is represented by general equilibrium models with heterogeneous firms. Initiated by Huggett (1993) and Aiyagari (1994), a strand of general equilibrium literature characterized by the distribution of heterogeneous individuals has been developed. In recent years, the introduction of heterogeneity in macroeconomics increased exponentially. The thesis is developed in this context. The first chapter provides a methodological analysis. It examines the importance of the modelization choice of the idiosyncratic productivity process of individuals. The second chapter proposes a theoretical model which can be able to reconcile four important facts shared by most of the advanced economies around the world: declining labor share of income, rising capital misallocation, low total factor productivity growth and the declining relative price of investment goods.

Submitted by Rafael Ornelas (rafael.amaral.ornelas@gmail.com) on 2014-10-13T14:42:40Z No. of bitstreams: 1 Comparative Advantage, Heterogeneous Firms and Variable Mark-ups.pdf: 719604 bytes, checksum: a740a6997be4cfdd2be9d1a7f48aad00 (MD5)
Approved for entry into archive by BRUNA BARROS (bruna.barros@fgv.br) on 2014-10-13T17:17:33Z (GMT) No. of bitstreams: 1 Comparative Advantage, Heterogeneous Firms and Variable Mark-ups.pdf: 719604 bytes, checksum: a740a6997be4cfdd2be9d1a7f48aad00 (MD5)
Approved for entry into archive by Marcia Bacha (marcia.bacha@fgv.br) on 2014-10-14T11:58:54Z (GMT) No. of bitstreams: 1 Comparative Advantage, Heterogeneous Firms and Variable Mark-ups.pdf: 719604 bytes, checksum: a740a6997be4cfdd2be9d1a7f48aad00 (MD5)
Made available in DSpace on 2014-10-14T11:59:35Z (GMT). No. of bitstreams: 1 Comparative Advantage, Heterogeneous Firms and Variable Mark-ups.pdf: 719604 bytes, checksum: a740a6997be4cfdd2be9d1a7f48aad00 (MD5) Previous issue date: 2014-06-27
We develop a model of comparative advantage with monopolistic competition, that incorporates heterogeneous firms and endogenous mark-ups. We analyse how these features vary across countries with different factor endowments, and across markets of different size. In this model we can obtain trade gains via two channels. First, when we open the economy, most productive firms start to export their product, then, they demand more producing factors and wages rises, thus, those firms that are less productive will be forced to stop to produce. Second channel is via endogenous mark-ups, when we open the economy, the competition gets ``tougher'', then, mark-ups falls, thus, those firms that are less productive will stop to produce. We also show that comparative advantage works as a ``third channel'' of trade gains, because, all trade gains results are magnified in comparative advantage industry of both countries. We also make a numerical exercise to see how endogenous variables of the model vary when trade costs fall.

Submitted by Érica Diniz (ericadiniz@gmail.com) on 2015-01-12T19:03:28Z No. of bitstreams: 1 versaodigital_tesedoutorado_EricaDiniz.pdf: 3599824 bytes, checksum: b9f58b1c27e6f83606dfd16d6c2e165d (MD5)
Approved for entry into archive by BRUNA BARROS (bruna.barros@fgv.br) on 2015-01-15T11:48:49Z (GMT) No. of bitstreams: 1 versaodigital_tesedoutorado_EricaDiniz.pdf: 3599824 bytes, checksum: b9f58b1c27e6f83606dfd16d6c2e165d (MD5)
Approved for entry into archive by Marcia Bacha (marcia.bacha@fgv.br) on 2015-02-05T12:01:45Z (GMT) No. of bitstreams: 1 versaodigital_tesedoutorado_EricaDiniz.pdf: 3599824 bytes, checksum: b9f58b1c27e6f83606dfd16d6c2e165d (MD5)
Made available in DSpace on 2015-02-05T12:02:06Z (GMT). No. of bitstreams: 1 versaodigital_tesedoutorado_EricaDiniz.pdf: 3599824 bytes, checksum: b9f58b1c27e6f83606dfd16d6c2e165d (MD5) Previous issue date: 2013-10-28
Essa tese é constituída por três artigos: 'Tax Filing Choices for the Household', 'Optimal Tax for the Household: Collective and Unitary Approaches' e 'Vertical Differentiation and Heterogeneous Firms'.

This thesis includes three independent empirical studies that examine the relationship between trade and wages for Chinese manufacturing industries for the period 2002-2006. Chapter 2 uses highly detailed firm-level industrial production data merged with product-level trade transaction data to make a direct test of Amiti and Davis (2011) model. The potential endogeneity issue of tariffs is addressed in several ways although our results support the premise that post-WTO period tariff reductions were exogenous. In Chapters 3 and 4 we pay close attention to processing trade. Chapter 3 reexamines the relationship between tariff reductions and firm wages taking into account the special tariff treatment given to processing firms. We find that processing firms pay higher wages following a fall in firm output tariffs. However, non-processing firms pay higher wages after a fall in firm input tariffs. Finally, Chapter 4 examines the impact of tariff reductions on the decision of firms to switch between different modes of exporting and explores how export switching affects firm wages through trade liberalization. The results highlight that input tariff reductions at the firm level determine a firm’s decision and direction of export switching. The future research ideas are also concluded.

Cette thèse met l'accent sur l'hétérogénéité des firmes du point de vue des facteurs financiers et leur impact sur la décision d'exportation et de délocalisation. Trois aspects sont traités : la relation entre l'effet de levier des firmes et la participation au marché exportateur ; l'impact différencie de l'incertitude sur la décision d'exportation des firmes selon leur attitude face au risque ; le lien entre les caractéristiques financières des firmes et le choix de délocalisation. Le premier chapitre introduit la dimension financière comme une source de l'hétérogénéité des firmes afin de comprendre la participation au marché exportateur et d'examiner comment l'impact de l'effet de levier sur la décision d'exportation varie selon les contraintes financières. A partir d'un panel d'entreprises manufacturières coréennes (1994-2001), il est montré que les firmes basent leur décision d'exportation sur différents critères par rapport à l'effet de levier. Le deuxième chapitre introduit l'attitude vis-à-vis du risque comme une source supplémentaire d'hétérogénéité des firmes influant sur la décision d'exportation des firmes. Deux aspects sont pris en compte : l'incertitude propre à la firme et l'incertitude macroéconomique. Le troisième chapitre s'intéresse aux mécanismes complexes par lesquels les IDE peuvent favoriser le commerce international dans un contexte de désintégration des processus de production et d'une intégration croissante des marchés mondiaux. A cette fin, la contrainte financière et la structure de propriété des entreprises sont prises en compte comme des sources additionnelles d'hétérogénéité agissant sur la décision de délocalisation des entreprises
This thesis emphasizes the role of firm heterogeneity in financial factors and their impact on exporting decisions or off-shoring decisions, and apply it to three different issues : the relationship between firms' leverage and export market participation ; the differential impact of uncertainty on exporting decision in risk-averse and risk-taking firms ; and financial characteristics of firms and relocation choice. The first chapter introduces a financial dimension as an additional source of firm heterogeneity to understand export market participation and examines how the impact of leverage on firms' exporting decisions varies depending on financial constraints, using a panel of korean manufacturing firms over the period of 1994-2011. It shows that the financially-constrained and financially-unconstrained firms base their exporting decision on a different set of rules regarding the leverage. Second, most of the existing literature which examines the links between firm heterogeneity and entry into exporting rests on the assumption that firms are risk-neutral. The second chapter relaxes a strict assumption that firms are risk-neutral and intends to introduce firms' different attitudes towards risk as an additional source of firm heterogeneity. In particular, it examines how risk attitude changes the effect of uncertainty on firms' decision to export, considering two aspect s: firm-specific uncertainty and macroeconomic uncertainty. The third chapter pays attention that fdi can fuel international trade in complicated ways. It intends to consider firms' financial constraints and ownership status as an additional source of firm heterogeneity that impact their offshoring decision

We set up a trade model with heterogeneous firms and a worker population that is heterogeneous in two dimensions: workers are either skilled or unskilled, and within each skill category there is a continuum of abilities. Workers with high abilities, both skilled and unskilled, are matched to firms with high productivities, and this leads to wage differentials within each skill category across firms. Self-selection of the most productive firms into exporting generates an exporter wage premium, and our framework with skilled and unskilled workers allows us to decompose this premium into its skill-specific components. We employ linked employer-employee data from Germany to structurally estimate the parameters of the model. Using these parameter estimates, we compute an average exporter wage premium of 5 percent. The decomposition by skill turns out to be quantitatively highly relevant, with exporting firms paying no wage premium at all to their unskilled workers, while the premium for skilled workers is 12 percent.

Considerable progress in the understanding of thin film flow over surfaces has been achieved thanks to lubrication theory which enables the governing Navier-Stokes equations to be reduced to a more tractable form, namely a coupled set of partial differential equations. These are solved numerically since the flows of interest involve substrates containing heterogeneities in the form of wetting patterns and/or topography. An efficient and accurate numerical method is described and used to solve two classes of problem: droplet spreading in the presence of wetting and topographic heterogeneities; gravity-driven flow of continuous thin liquid films down an inclined surface containing well defined topographic features. The method developed, employs a Full Approximation Storage (FAS) multigrid algorithm, is fully implicit and has embedded within it an adaptive time-stepping scheme that enables the same to be optimised in a controlled manner subject to a specific error tolerance. Contact lines are ubiquitous in the context of droplet spreading and the wellknown singularity which occurs there is alleviated by means of a disjoining pressure model. The latter allows prescription of a local equilibrium contact angle and three dimensional numerical simulations reveal how droplets can be forced to either wet or dewet a region containing topography depending on the surface wetting characteristics. The growth of numerical instabilities, in the contact line region, which can lead to the occurrence of non-physical, negative film thicknesses is avoided by using a Positivity Preserving Scheme. A range of two- and three-dimensional problems is explored featuring the gravity-driven flow of a continuous thin liquid film over a non-porous inclined flat surface containing topography. Important new results include: the quantification of the validity range of the lubrication approximation for step-up and step-down topographies; description of the "bow wave" triggered by localised topography and an explanation, in terms of the local flow rate, of the accompanying "downstream surge": an assessment of linear superposition as a means of examining free surface response to topographies. In addition, the potential of local mesh refinement as a means of reducing computational time is highlighted. Finally, more complex liquids composed of a non-volatile resin dissolved in a solvent and allowed to evaporate are considered. An evaporation model based on the wellmixed approximation is utilised. Results show that localised topographies produce defects in dried continuous films which persist far downstream of the topography, while with respect to droplet motion, solvent evaporation is found to be responsible for contact line pinning and thus a reduction in spreading.

This dissertation investigates the factors that firms take into consideration when they decide in which manner to expand internationally (i.e. foreign direct investment and international trade). Another component of the investigation focuses on what types of firms benefit the most and what are the associated benefits with expanding internationally. I investigate self-selection and learning-by-exporting hypothesis by applying matched sampling techniques and non-structural econometric models. Using a Chinese firm-level dataset, I find that firms that start exporting are more productive than non-exporting ones. Additionally, in most industries exporters become more productive in time. I then investigate how income inequality leads firms to make different choices on how they expand internationally. I develop a simple theoretical model by carefully choosing a mean-preserving income distribution. I find that changing the mean-preserving parameter of the income distribution affects market demand for firms' products and firms' choosing of strategies for international expansion. Some, but not all firms gain market shares due to larger market size caused by the more concentrated income distribution around the mean. Using Gini coefficient as the proxy for income distribution, I demonstrate empirically that some firms gain market shares and benefit from more consumers becoming part of the middle class due to the corresponding change in income distribution. I also study the aggregate implication of opening the economy in a two-country Dynamic Stochastic Equilibrium in which firms have heterogeneous productivity in the spirit of Melitz (2003). I show that benefits incurred by international engagement are not equally distributed among firms. I separate firms into four categories based on their productivity levels. The highest productivity firms gain the most by breaking into a new market as multinationals. The second highest productivity firms become exporters and obtain the second largest market share. The third highest productivity firms only serve the domestic market, while the lowest productivity firms exit the market.

The salient issues of integrated biosensors on a complementary metal-oxide semiconductor (CMOS) platform are the limited transducer design and the need for post-processing. To overcome these issues, a heterogeneously integrated system, which employs both CMOS and large-area processing, was proposed and developed. The system presented, could become a rapid, low-cost and disposable sensing platform for point-of-care applications. The heterogeneously integrated system, comprising a CMOS front-end circuit and disposable electrodes, was applied to measure the impedance of suspended DNA at different concentrations. The measurement showed a double sensitivity compared to the one carried out on the CMOS platform only. The noise analysis of CMOS transimpedance amplifiers was performed, and the impact of technology scaling on low-noise transimpedance amplifiers was studied using the Enz-Krummenacher-Vittoz (EKV) model. It was found that the noise performance improves slowly with device scaling down to 90 nm. Further device scaling may increase the gate leakage current noise due to the very thin gate oxide. Disposable electrodes fabricated using large-area processing are low cost and flexible in terms of design. In particular, inkjet-printed silver electrodes on glossy paper and gold electrodes on the glass substrate were characterised. Both electrodes with the same dimension agreed well in determining solution resistance. In addition, the paper-based electrodes presented an improved sensitivity of impedance measurement at low frequencies. The amorphous oxide thin-film transistor (TFT) is promising for implementing active circuits on disposable substrates. In particular, the low-frequency noise of amorphous indium-gallium-zinc-oxide (a-IGZO) TFTs was characterised, and a TFT-based regulated cascade transimpedance amplifier was designed and simulated with the extracted device parameters. The a-IGZO TFT showed a comparable noise performance to the PMOS device in deep submicron processes. The simulated circuit featured a transimpedance gain up to 120 dB, a bandwidth of 29.4 kHz, input-referred noise PSD of 2.91 pA/√Hz, and a power consumption of 18.55 μW, indicating that TFT-based front-end circuits are promising for implementing low-cost, low-noise and low-power biosensors.

Wildfire hazard and its destructive consequences have become a growing issue around the world especially in the context of global warming. An effective and efficient fire simulation model will make it possible to predict the fire spread and assist firefighters in the process of controlling the damage and containing the fire area. Simulating wildfire spread remains challenging due to the complexity of fire behaviors. The raster-based method and the vector-based method are two major approaches that allow one to perform computerized fire spread simulation. In this thesis, we present a scheme we have developed that utilizes a level set method to build a fire spread simulation model. The scheme applies the strengths and overcomes some of the shortcomings of the two major types of simulation method. We store fire data and local rules at cells. Instead of calculating which are the next ignition points cell by cell, we apply Huygens' principle and elliptical spread assumption to calculate the direction and distance of the expanding fire by the level set method. The advantage to storing data at cells is that it makes our simulation model more suitable for heterogeneous fuel and complex topographic environment. Using a level set method for our simulation model makes it possible to overcome the crossover problem. Another strength of the level set method is its continuous data processing. Applying the level set method in the simulation models, we need fewer vector points than raster cells to produce a more realistic fire shape. We demonstrate this fire simulation model through two implementations using narrow band level set method and fast marching method. The simulated results are compared to the real fire image data generated from Troy and Colina fires. The simulation data are then studied and compared. The ultimate goal is to apply this simulation model to the broader picture to better predict different types of fires such as crown fire, spotting fires, etc.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Economics, 2006.
Includes bibliographical references (p. 126-128).
This dissertation consists of three essays on the heterogeneous reactions of firms to shocks, with particular empirical applications to the Chilean economy. The first essay presents a model of heterogeneity in an economy with financial constraints. The main issue in the model is to characterize the entrepreneurs and firms that are affected by shocks or policy innovations. The model delivers a dual margin composed of a segment of relatively poorer but more productive entrepreneurs and a segment of richer but less productive entrepreneurs. The main result we present in this essay is that these two margins will react heterogeneously to shocks in economically meaningful ways. The second essay is devoted to the construction of the panel and the econometric use of the FUNDES-SII panel firm database. We use this database to study firm creation, destruction and performance on maps of firms. The main result of this essay is that there does seem to be some empirical evidence of a margin of high productivity, low capital entrepreneurs for the Chilean economy, as predicted in the first essay of the thesis. Finally, we find that among smaller firms leverage seems to be an indicator of financial constraint, while among larger firms it is an indicator of financial access.
(cont.) The third essay is devoted to the construction of the panel and econometric use of the INE-BFL panel worker database to study workplace creation and destruction in Chile. For local interest, the main feature of the chapter is that it is the first time that representative and consistent series of job creation and destruction that is made available for the Chilean economy. The main feature of the chapter, however, is the estimation and characterization of workplace fragility by firm size. We estimate separation, matching and bankruptcy probabilities, and inquire into their sensitivity to the economic cycle.
by Oscar Landerretche.
Ph.D.

This work is a collection of papers on innovation, a broad theme that covers several but interconnected issues. Innovation is one of the main determinants of firms’ performance in advanced economies and it is also an important driver of growth ((Romer 1990, Aghion and Howitt 1992, Acemoglu 2002, Jones 2002). Firms often invest huge amounts of resources in R&D to improve their production technology (process innovation, aiming to a cost reduction), create new products and increase the quality of the existing ones (product innovation); in this way, firms aim to increase their market shares and profits. Sometimes R&D investment is necessary to enter the market or simply not to exit. Firms’ innovative activities contribute to make the surrounding economic system more competitive and stimulate further investment and innovation. At the same time,consumers enjoy the benefits accrued by lower prices, better quality and more variety. Despite of the beneficial effects they bring to the society, innovative activities are often associated with a non competitive market structure (harmful for consumers) and with externalities, meaning that innovation is strictly related to situations that bring to market failures and to not socially desirable outcomes (in terms of prices, quantities produced and R&D effort). These considerations often justify the request of government intervention in terms of subsidies to R&D and patent protection. The level of innovation of an economic system is affected by the interaction of several agents and also influenced by external factors. Understanding how the different forces at work interact and which factors enhance or prevent innovation is of primary importance from the point of view of policy makers; aware of the possible incentives and obstacles to innovation, they can develop policies aimed to create an environment that favor investment and growth. In this work I investigate the role of agents’ heterogeneity in innovation processes, an issue that has received attention in the literature on innovation only quite recently, tough its importance has been recognized for a long time. I treat this topic from both a theoretical and empirical point of view, though applied to different subjects. In the theoretical part of the work (Chapter 2 and Chapter 3), I focus on a particular aspect of the issues related to innovation and market failure, namely the spillover externality problem and the use of R&D cooperation agreements (RJV) as a way to enhance innovation and lead the level of investment closer to its socially optimal level. The positive externality is caused by non-complete appropriability of the results of R&D activity and is responsible for R&D underinvestment. Since d’Aspremont and Jacquemin (1988) and Kamien et al. (1992), the positive effect of R&D cooperation agreements in presence of high spillovers has been widely analyzed. However, most of the previous works only consider symmetric firms, discarding the potential relevant impact of asymmetries on firms’ decisions. The empirical literature has emphasized the role of asymmetries in terms of gains from cooperation, that in turn affect decisions about RJV membership (Kogut 1991, Röller, Tombak and Siebert 1998), but these issues have been scarcely taken into account in the theoretical literature, with few exceptions (Baerenss 1999, Atallah 2005). So, in this part of the work I try to fill this gap in the literature taking into account firms’ heterogeneity. Firms can be heterogenous in many respects: efficiency level, type of technology, experience, market size etc. Here, firms’ heterogeneity regards the efficiency of R&D effort. In the empirical part, I study a quite different aspect of innovation, namely the link between immigration and innovation. Owing to the size that the phenomenon of immigration has assumed in the advanced countries in the last decades, immigration has been recently at the centre of the political and economic debate. Economists have studied extensively the potential impact of immigration on a variety of economic and social indicators of host countries, such as natives’ wages (Borjas 2003; 2005, Ottaviano and Peri 2012) and employment opportunities (Pischke and Velling 1997, Card 2001; 2005), firm productivity (Peri 2012), trade creation (Gould 1994, Rauch and Trinidade 2002, Peri and Requena-Silvente 2010) and crime (Bell et al. 2010, Bianchi et al. 2012), just to take a few examples. Until very recently the effect of immigration on innovation and technical change was instead much less studied. Although new evidence is progressively accumulating, it remains nonetheless mostly limited to the impact of skilled immigration in the U.S (Hunt and Gauthier-Loiselle 2010, Stuen et al. 2012, Lewis 2011, Peri 2012).Immigration can affect local innovation in several ways. First of all, immigration entails an inflow of foreign population into a region, and produces changes (i) in the size of the population; (ii) in the average skill level of the population; (iii) in the age structure of the population. All these variables have been recognized to be powerful predictor of innovation. Immigration has also a direct effect on innovation through cultural diversity (spillovers may arise from complementary abilities and different backgrounds, with a positive effect in the production of new ideas). At the same time, greater difficulties in communication and reduction of social capital can act as obstacles to innovation and growth (these negative effects are more likely to arise in presence of low skilled immigrants). Finally, immigrants flows affect firms’ choices concerning technology adoption and investment in physical capital, according to the change in the average skill level they cause in the population. So, in this part of the work, heterogeneity concerns the greater cultural ‘diversity’and the changes in the average skill level of the population induced by large immigration flows. The thesis has the following structure: Chapeter 1 provides an overview of the way in which the main issues related to innovative activity have been treated in the theoretical literature. Starting from earlier works on innovation, mainly focused on the value attached to innovation in monopolistic and competitive markets, it develops analising the two main fields in the literature on innovation: patent race and spillover externality. The part related to spillovers and R&D cooperation is treated in a more extensive way, since the theoretical models I present in Chapter 2 and Chapter 3 belong to this strand of the literature. This chapter contains also a review of the past literature on incomplete information in R&D models. In Chapter 2, I extend standard models on R&D competition vs R&D cooperation in a context of non-complete appropriability of the results of R&D activity. In a Cournot duopoly model with R&D investment stage and spillovers, I introduce asymmetries in R&D productivity between firms that may engage in R&D cooperation. Also, with the introduction of a further stage, I analyze the incentive to cooperate in R&D by forming a RJV. While the existent literature focuses on the comparison between two scenarios exogenously given, I endogenize the formation process and show that, when spillovers are high, due to firms’ asymmetries, RJV is not formed for most of the parameters’ values and does not fulfill the aim of stimulating innovation. This contributes to explain the relatively low diffusion of cooperative agreement in R&D and supports some empirical findings about and the determinants of RJVs formation. Also, in line with the theoretical literature, I find that, when spillovers are low, R&D cooperation reduces the total level of investment; in this case allowing this kind of agreements can be harmful, since in some regions of parameters both symmetric and asymmetric firms have incentive to cooperate in order to avoid investment. Chapter 3 presents a further extension of the model discussed in Chapter 2, namely the introduction of the incomplete information assumption. Here, I investigate the role of R&D cooperation agreements (RJVs) in a context of incomplete information with asymmetric firms, where firms, in addition to set the optimal R&D investment under two regimes (R&D competition and RJV), have also to take decisions about RJV membership. Some interesting results arise from this extended model. (i) When firms compete in R&D, incomplete information about rival’s R&D productivity leads to inefficient investment choices in some regions of parameters; in particular, when firms are actually symmetric, asymmetric information further reduces the investment, with respect to the complete information setting. (ii) A signaling role of cooperation agreements emerges, in addition to the already recognized role in reducing the inefficiencies arising from free riding problem. Revealing its willingness to participate, the efficient firm to signal its type, thus increasing the investment level (innovation enhancing effect) and improving total welfare. (iii) When firms are asymmetric, for most of the parameters’ values, RJV is not formed and does not fulfill the role of stimulating innovation. Chapter 4 (joint with Massimiliano Bratti1) investigates the causal effect of foreign immigration on innovation (patents’ applications) in Italian provinces. We provide evidence for a country which was exposed to a very fast and large wave of immigrations during the 2000s, using a very small geographical scale of analysis (NUTS-3 regions), which enables us to better control for differences in institutional and socio-economic factors which are difficult to observe but which may simultaneously contribute to both attracting new immigrants and increase the innovation potential of a region. Moreover, unlike most papers in the literature which only considered the effect of skilled immigration, (i) we first focus on the general impact of immigration, and then (ii) separately look at the effects of low-educated and high-educated immigrants on innovation. Using instrumental variables’ estimation (and instruments based on immigrant enclaves), we find that the overall stock of immigrants has a significant negative effect on innovation of Italian provinces: rising the share of immigrants by one percent point (p.p.) decreases patenting by 0.064 percent. However, distinguishing the effect between low and highskilled migrants shows that the aggregate negative effect is driven by the prevalence in Italy of low-educated immigrants. In fact, our estimates suggest that an increase of 1 p.p. in the share of low skilled foreign migrants on the population induces a reduction in patents’ applications per 1000 inhabitants in a range between 0.094 and 0.186 percent, according to the method used to classify immigrants by skill level. Instead, presumably due to the extremely low presence of high skilled immigrants in Italy and to the underutilization of their competencies, the impact of high skilled immigrants on innovation is positive, but cannot be precisely estimated.

Submitted by Rafael Santana (rafael.silvasantana@ufpe.br) on 2018-01-23T18:28:26Z No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) mestrado_FLORENTINO_vfinal.pdf: 34893603 bytes, checksum: 9f4e52bf21e32df95d14f3aa8c75cba0 (MD5)
Made available in DSpace on 2018-01-23T18:28:26Z (GMT). No. of bitstreams: 2 license_rdf: 811 bytes, checksum: e39d27027a6cc9cb039ad269a5db8e34 (MD5) mestrado_FLORENTINO_vfinal.pdf: 34893603 bytes, checksum: 9f4e52bf21e32df95d14f3aa8c75cba0 (MD5) Previous issue date: 2016-08-15
FACEPE
In the present work, the spread of forest fires in heterogeneous environments is studied through cellular automata (CA) models, that are commonly used to simulate contact processes, and display a critical self-organized dynamics. The concept of self-organized criticality (SOC) is related to the ability of a dynamical system to evolve towards a critical phase spontaneously. The signature of these processes is the scale invariance (power-law behavior) of its observables. The forest fire model proposed by Drossel and Schawbl (DSFFM) in 1992, regards an homogeneous population of trees and its fire-size and fire duration distributions suggest typical SOC behaviors. In the other hand, the literature reports wildland fires whose frequency-area histograms are either power-law distributions or ‘heavy-tailed’ distributions. In 2011, Camelo-Neto and Coutinho proposed a CA model in which two distinct populations of trees are considered: one comprising trees with low flammability (with a parameter R of resistance to ignite) and the other composed by high flammability (susceptible trees). Aiming to generalize this model, some ingredients have been added in order to amplify or constrain the effective reach of the fire spreading. By increasing the reach of the interactions, the system performs fires that spread more like a ‘field’ of heat than like a contact process as in the DSFFM. Another novel aspect of the model – related to the heterogeneity of the population – is the addition of a fraction s of forbidden sites (randomly placed), at which trees are not allowed to sprout. Moreover, theses forbidden sites do not interact with fire. Results have showed that the fire-size distributions can display either a ‘heavy-tailed’ behavior or a power-law behavior, depending on the resistance parameter R and on the fraction s of forbidden site.
Nesta dissertação, a propagação de incêndios em florestas heterogêneas é estudada através de modelos de autômatos celulares (AC) que descrevem processos de propagação por contato e apresentam características de uma dinâmica crítica auto-organizada. O conceito de criticalidade auto-organizada (CAO) está relacionado com a capacidade de um sistema dinâmico evoluir espontaneamente para um estado crítico. A assinatura desses processos é a invariância de escala (comportamento tipo lei de potência) das distribuições de certas grandezas observáveis. O modelo de incêndio florestal proposto por Drossel e Schawbl (DS), em 1992, considera apenas florestas homogêneas e as distribuições de tamanhos e duração das queimadas encontradas sugerem a existência de um estado crítico auto-organizado. A literatura, no entanto, reporta incêndios reais cujos histogramas de frequência de tamanho apresentam tanto distribuições tipo lei de potência, quanto casos de distribuições com “caudas pesadas”. Em 2011, Camelo-Neto e Coutinho propuseram um modelo de AC, onde são consideradas duas populações de árvores distintas, uma com baixa inflamabilidade, árvores com distintos graus R de resistência à ignição, e outra com alta inflamabilidade, ditas árvores susceptíveis. Com o intuito de generalizar o modelo, alguns ingredientes foram adicionados de modo a ampliar ou limitar o alcance efetivo da propagação do fogo na vizinhaça de uma árvore em chamas. O aumento do alcance das interações produz incêndios que se propagam como um “campo de calor”, desta forma difere dos processos de contato característicos do modelo DS. Outro novo aspecto do modelo para explorar a heterogeniedade da floresta foi a inclusão de um fração s de sítios proibidos (distribuídos aleatoriamente) nos quais árvores não podem brotar, além disso eles também não interagem com o fogo. Os resultados alcançados mostram que as distribuições de tamanho dos incêndios podem exibir tanto um comportamento de “cauda pesada”, como comportamento tipo lei de potência, dependendo do ajuste do parâmetro de resistência R e da concentração s de sítios proibidos.

We set up a general equilibrium model, in which offshoring to a low-wage country can lead to job polarisation in the high-wage country. Job polarisation is the result of a reallocation of labour across firms that differ in productivity and pay wages that are positively linked to their profits by a rent-sharing mechanism. Offshoring involves fixed and task-specific variable costs, and as a consequence it is chosen only by the most productive firms, and only for those tasks with the lowest variable offshoring costs. A reduction in those variable costs increases offshoring at the intensive and at the extensive margin, with domestic employment shifted from the newly offshoring firms in the middle of the productivity distribution to firms at the tails of this distribution, paying either very low or very high wages. We also study how the reallocation of labour across firms affects economy-wide unemployment. Offshoring reduces unemployment when it is confined to high-productivity firms, while this outcome is not guaranteed when offshoring is also chosen by low-productivity firms.

El gran impacto de la tecnología FBAR tanto en sistemas de radio frecuencia como más recientemente en sensores han motivado el desarrollo de aplicaciones integradas. Esto implica que los procesos de fabricación deberían lograr producir dispositivos resonadores con un alto factor de calidad, al tiempo que permitir la integración de los FBAR con tecnologías CMOS estándar. De tal manera, esta tesis doctoral aborda dichos requerimientos, contribuyendo con el diseño, fabricación y caracterización de resonadores FBAR; su integración con tecnologías CMOS estándar; y su aplicación a sistemas de sensores.
El desarrollo de la tecnología de fabricación de los FBAR ha involucrado la puesta a punto de las técnicas de depósito y micro-mecanización de la estructura en capas del resonador, la cual está comprendida por una película de material acústico hecha de nitruro de aluminio (AlN). Se realizaron diversas pruebas para analizar la calidad del AlN depositado. También se probaron y pusieron a punto diferentes tecnologías de micro¬mecanización para liberar la estructura del FBAR, destacando entre ellas la técnica de ataque en seco por la cara de componentes, dados los altos factores de calidad obtenidos (superiores a 2.000 a 2,4 GHz). Sobre los dispositivos fabricados se realizaron caracterizaciones estructurales, modelos utilizando análisis de elementos finitos y la extracción de parámetros de circuito equivalente. Una variación del proceso que involucraba el diseño, modelado y fabricación de un dispositivo FBAR con compensación de temperatura fue igualmente desarrollada. En este ámbito vale la pena resaltar la concepción y realización de una novedosa técnica post-fabricación para el ajuste fino de la frecuencia de resonancia de los FBAR por medio de un haz de iones focalizados (FIB).
Basado en la tecnología arriba mencionada, se desarrolló un método de integración heterogénea a nivel de oblea de los dispositivos FBAR en sustratos CMOS estándar. De acuerdo con este método, se logró fabricar por primera vez dispositivos FBAR flotando sobre sustratos CMOS estándar. Este método ha sido exitosamente demostrado por medio de la integración de los FBAR tanto con la tecnología comercial AMS035 como con la CNM25, desarrollada en el CNM-IMB (CSIC).
En el terreno de las aplicaciones, se diseñaron y realizaron diferentes aplicaciones de sensores basadas en FBAR, siendo el detector de masas localizadas la más relevante de entre ellas. Es de anotar que esta aplicación fue demostrada por primera vez utilizando FBARs de alta frecuencia como elemento sensor. De tal forma, se contrastaron los resultados experimentales y de modelado del sensor. Por otra parte, se presenta también el concepto de sensores mecánicos basados en FBAR. Para ello se han desarrollado dos ejemplos: el acelerómetro basado en FBAR y el sensor de fuerza para aplicaciones de puntas de AFM. Se reporta también en esta tesis la fabricación y caracterización de un nuevo tipo de resonadores acústicos de AlN sin contacto entre electrodos.
The high impact of FBAR on radio-frequency and, most recently, on sensing systems has motivated the development of integrated applications. This means that the fabrication process should succeed in producing high-quality-factor resonators and, at the same time, in integrating FBARs with standard CMOS technologies. Hence, this Ph.D. thesis addresses these requirements by contributing with the design, fabrication and characterization of thin-film bulk acoustic wave resonators (FBAR); their integration with standard complementary-metal-oxide-semiconductor (CMOS) technologies; and their application to sensing systems.
The development of the FBAR's fabrication technology has involved the set up of the deposition and micromachining techniques of the layered structure of the resonator, which comprises an acoustic layer made of aluminum nitride (AlN). Several tests on the deposition and characterization of the AlN quality were carried out. Also, different micro-machining technologies for FBAR releasing were tested, the front-side micro-machining technique having obtained the best quality-factor results (over 2,000 at 2.4 GHz). Structural and device experimental characterization; and equivalent-circuit parameter and finite-element modeling of the FBAR were carried out. A process variation involving the design, modeling and fabrication of a temperature-compensated (TC) FBAR device was also implemented. Another remarkable result is the implementation of a post-fabrication, focused-ion-beam assisted technique for tuning of the resonance frequency of the FBAR.
Based on the foregoing-mentioned FBAR technology, a method for performing wafer-level heterogeneous integration of the FBAR with a CMOS substrate was developed. According to this method, the fabrication of a floating FBAR above standard CMOS substrates has been achieved for the first time. The method was demonstrated by integrating FBARs on the commercial AMS035 and the in-house CNM25 CMOS technologies.
On the application side, different FBAR-based sensor applications were implemented, the localized-mass detector being the most relevant, which has been demonstrated for the first time for high-frequency bulk-acoustic resonators. Experimental and modeling results have been contrasted. Also, the concept of FBAR-based mechanical sensor has been introduced. Two examples are the embedded-FBAR accelerometer and the force sensor for AFM-cantilever applications. The fabrication and characterization results of an AlN-based contactless acoustic resonator are also reported in this thesis.

The objective of this study was firstly to investigate and understand sorption properties of earlywood, latewood, annual rings and gross wood. Secondly, to develop a heterogeneous sorption model for earlywood, latewood and annual rings by taking into consideration unified complex interactions of anatomy, chemical composition and thermodynamic parameters. Thirdly, to upscale the annual ring level model to gross wood by applying artificial neural networks (ANNs) modeling tools using dimensionally reduced inputs through dimensional analysis and genetic algorithms. Four novel physical models, namely, dynamical two-level systems (TLS) model of annual rings, sorption kinetics, sorption isotherms and TLS model of physical properties and chemical composition were derived and successfully validated using experimental data of Douglas-fir. The annual ring’s TLS model was capable to generate novel physical quantities, namely, golden ring volume (GRV) and golden ring cube (GRC) to which the sorption properties are very sensitive, according to the validation tests. A new heterogeneity test criterion (HTC) was also derived. Validations of the TLS sorption models revealed new evidence showing a transient nature of sorption hysteresis in which boundary sorption isotherms asymptotically converged to a single isotherm at large time limit. A novel method for the computation of internal surface area of wood was also validated using the TLS model of sorption isotherms. The fibre saturation point prediction of the model was also found to agree well with earlier reports. The TLS model of physical properties and chemical composition was able to reveal the self-organization in Douglas-fir that gives rise to allometric scaling. The TLS modeling revealed existence of self-organizing criticality (SOC) in Douglas-fir and demonstrated mechanisms by which it is generated. Ten categories of unified ANNs Douglas-fir sorption models that predict equilibrium moisture content, diffusion and surface emission coefficients were successfully developed and validated. The network models predict sorption properties of Douglas-fir using thermodynamic variables and parameters generated by the four TLS models from chemical composition and physical properties of annual rings. The findings of this study contribute to the creation of a decision support system that would allow predicting wood properties and processing characteristics based on chemical and structural attributes.

Developing high efficiency solar cells for lower manufacturing costs has been a key objective for photovoltaic researchers to drive down the levelized cost of energy for solar power. In this pursuit, III-V compound semiconductor based solar cells have steadily shown performance improvement at approximately 1% (absolute) increase per year, with a recent record efficiency of 46% under concentrator and 32% under AM0. However, the expensive cost has made it challenging for III-V solar cells to compete with the mainstream Silicon (Si) technology. Novel approaches to lower down the cost per watt for III-V solar cells will position them to be among the key contenders in the renewable energy sector. Integration of such high-efficiency III-V multijunction solar cells on significantly cheaper and large area Si substrate has the potential to address the future LCOE roadmaps by unifying the high-efficiency merits of III-V materials with low-cost and abundance of Si. However, the 4% lattice mismatch, thermal mismatch, polar on non-polar epitaxy makes the direct growth of GaAs on Si challenging, rendering the metamorphic cell sensitive to dislocations. The focus of this dissertation is to investigate heterogeneously integrated 1J GaAs solar cells on Si substrate using germanium (Ge) as an intermediate buffer layer that will address mitigation of defects and dislocations between GaAs active cell structure and Ge “virtual” substrate on Si. The all-epitaxial molecular beam epitaxy (MBE)-grown thin (<1 μm) hybrid GaAs/Ge “virtual” buffer approach provided 1J GaAs cell efficiency of ~10% on Si, as compared with cell structures with thick 3 μm GaAs buffers. Solar cell results were further corroborated with material analysis to provide a clear path for the reduction of performance limiting dislocations. The thin “Ge-on-Si” virtual buffer was then investigated comprehensively to understand the impact of the heterostructure on device performance. The growth, structural, morphological, and electrical transport properties of epitaxial thin-film Ge, grown by solid source MBE on Si using a two-step growth process, were investigated. High-resolution x-ray diffraction analysis demonstrated ~0.10% tensile strained Ge epilayer, owing to the thermal expansion coefficient mismatch between Ge and Si, and negligible epilayer lattice tilt due to misfit dislocations at the Ge/Si heterointerface. Micro-Raman spectroscopic analysis further corroborated the strain-state of the Ge thin-film on Si. Cross-sectional transmission electron microscopy revealed the formation of a 90° Lomer dislocation network at the Ge/Si heterointerface, suggesting the rapid and complete relaxation of the Ge epilayer during growth. Atomic force micrographs exhibited smooth surface morphologies with surface roughness < 2 nm. Hall mobility measurements, performed within a temperature range of 77 K to 315 K, and the modelling thereof indicated that ionized impurity scattering limited carrier mobility in the thin Ge epilayer. Additionally, capacitance- and conductance-voltage measurements were performed after fabricating the metal-oxide-semiconductor capacitors (MOS-Cs) in order to determine the effect of epilayer dislocation density on interfacial defect states (Dit), bulk trap density, and the energy distribution of Dit as a function of temperature for electronic device applications. Deep level transient spectroscopy was used to identify the location (within the Ge bandgap) of electrically active trap levels; however, no significant trap levels were detected. Finally, the extracted Dit values were benchmarked against previously reported Dit data for Ge MOS devices, as a function of threading dislocation density within the Ge layer. The results obtained in this work were found to be comparable with other Ge MOS devices integrated on Si via alternative buffer schemes. The understanding gained from this comprehensive study of Ge-on-Si will help optimize the 1J GaAs on Si via thin Ge buffer approach, to enable a future of high efficiency low cost solar cells for terrestrial applications.
Master of Science
The global energy landscape is projected to change remarkably in the coming decades with dwindling carbon based resource reserves and escalating energy demands, necessitating large-scale adoption of cleaner alternatives, such as solar energy. However, for widespread commercial and domestic adoption of photovoltaics, the cost of solar generated electricity must become competitive with non-renewable resources such as oil or coal. Thus, achieving high efficiency solar cells and driving down cell costs are key research objectives of the photovoltaic (PV) community in order to become more self-sufficient in the energy sector. In this pursuit, III-V compound semiconductor-based solar cells have steadily outperformed all other PV technologies, but cost-prohibitive for terrestrial deployment. Si is the undisputed standard in the PV industry; thus, to make a significant step forward in the pursuit of high efficiency solar cells, a promising approach will be to integrate the superior properties of compound semiconductors with the mature technology of Si. This research systematically investigates the integration of high efficiency III-V cells with low cost, abundant Si substrates via a germanium (Ge) layer to unify the performance merits of III-V cells with the cost benefits and superior mechanical and thermal properties of Si. Concurrently, Ge has also emerged as a strong candidate to boost transistor performance at low operating voltages, primarily owing to its superior carrier mobility and ease of integration into mainstream Si process flow. This research further delves into the structural and electrical properties of the Ge on Si structure. Overall, this research demonstrates the feasibility of the use of Ge directly integrated on Si for high efficiency solar cells and low-power electronic devices.

As pure oxides and mixed oxide systems play an ever-increasing role in a variety of research fields ranging from catalysis over electrochemical applications to microelectronics, the present contribution aims at introducing a straightforward concept for the easy and reproducible preparation of well-defined and well-structured thin film model systems both for pure and mixed oxide systems. Exploiting the special structural and surface properties of vacuum-cleaved NaCl (001) growth templates, the concept is exempli-fied for the formation of nano-spheres (Ga2O3), nano-pyramids (In2O3), plates and needles (V2O5) and den-dritic structures (Ga2O3-WO3). Careful tuning of the preparation conditions (substrate temperature, depo-sition rate, oxygen partial pressure or post-annealing temperature) allows the formation of special particle morphologies at much lower substrate temperatures (less than 400°C) than previously and usually applied. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/35049

The increasing demand for high performance and miniature high frequency electronics has motivated the development of Micro-electro Mechanical Systems (MEMS) resonators, some of which have already become a commercial success for the making of filters, duplexers and oscillators used in radio frequency (RF) front-end systems for portable electronic devices. These MEMS components not only enable size, power and cost reduction with respect to their existing counterparts, but also open exciting opportunities for implementing new functionalities when used in large arrays. Almost all MEMS resonators require interfacing with one or more Complementary Metal Oxide Semiconductor (CMOS) integrated circuit components or modules in processing raw signals from individual MEMS devices. Hence, these devices should be integrated with CMOS circuits in an efficient and robust way in order to facilitate their deployment in large arrays with minimal parasitics, delay and power losses due to signal routing and CMOS-MEMS interconnects. Among the MEMS resonators developed to date, Aluminum Nitride (AlN) MEMS Contour-Mode Resonators (CMRs) offer high electro-mechanical coupling coefficient (𝑘𝑡2) and quality factor (Q), and a center frequency (f0) that can be set lithographically by varying the device in-plane dimensions. Also, AlN MEMS CMRs can be fabricated using state-of-the-art CMOS processes and micromachining techniques. These properties allow the synthesis of multi-frequency band-pass filters (BPFs) on a single chip with a low insertion loss and the capability of direct matching to 50 Ω systems. All these advantages, along with a sufficiently mature fabrication process, make AlN CMRs one of the ideal candidates for pursuing their integration with CMOS technology and implement high performance filters with programming capability. In this work we develop for the first time a three-dimensional (3D) heterogeneously integrated AlN MEMS-CMOS platform that enables the realization of such systems as self- healing filters for RF front-ends and programmable filter arrays for cognitive radios. We collaborated with the A*STAR, Institute of Microelectronics (IME), Singapore in the development of AlN MEMS platform on an 8" silicon (Si) wafer; on the other hand, CMOS chips were fabricated in 65 nm International Business Machines Corporation (IBM) and 28 nm Samsung processes. Solder bumps were placed on CMOS chips by Tag and Label Manufacturers Institute (TLMI) under the supervision of Metal Oxide Semiconductor Implementation Service (MOSIS). We demonstrated 3D integrated chip stacks with primary RF signal routing on MEMS and on CMOS for self-healing filters, and showcased the other system via wire-bonding to off-the-shelf CMOS components on a printed circuit board (PCB) because of the inability to continue to have access to the CMOS wafers and bumping processes over the last two years of the project.

This thesis consists of three self-contained essays in International Trade, Exchange Rates and Prices. Although independent, these essays share some common themes. The first two papers can be related to the vast literature on exchange rate pass-through to prices. While the first paper uses firm-product level data from Sweden to study firms’ export price response to movements in exchange rate, the second paper employs aggregate level data from Ethiopia and looks at the issue from the importers’ perspective. The third paper, like the first paper, uses Swedish firm-level data and investigates firms’ exporting behavior. The third paper, however, specifically focuses on export margins of multi-product firms and studies their response when exporting to destinations of different size and distance from the home country.

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 2: Manuscript. Paper 3: Manuscript.

This dissertation consists of three essays in which I study the political economy of trade agreements. Using detailed information from lobbying reports filed under the Lobbying Disclosure Act, I systematically explore the role played by both the winners and the losers of globalization. The first chapter focuses on the winners, large multinational firms lobbying in favor of the ratification of free trade agreements. The second chapter looks at these winners when they lose, studying the impact of the non-ratification of a trade agreement on their profits. The last chapter focuses on labor interests and trade unions, the losers of globlalization.The first chapter (joint with Paola Conconi and Mathieu Parenti) is focused on firms. We show that the political economy of free trade agreements (FTAs) is dominated by large firms engaged in international trade that support the ratification of these agreements. We develop a model of endogenous lobbying on FTAs by heterogeneous firms, which can explain why only large pro-FTA firms select into lobbying. The model also delivers predictions on the intensive margin of lobbying. In line with these predictions, we find that larger firms spend more supporting a given FTA, and individual firms spend more supporting FTAs that generate larger gains – i.e. larger improvements in access to foreign consumers and suppliers and smaller increases in domestic competition – and that are more likely to be opposed by politicians.The second chapter (joint with Moritz Hennicke) is an event study on the 2016 U.S. presidential election, and the subsequent shock to U.S. trade policy – the non-ratification of the Trans-Pacific Partnership (TPP). We provide empirical evidence that corporate lobbying on trade agreements matters for corporate profits. We find that stock prices of companies that lobbied in favor of the TPP underperformed following Trump’s election. On the intensive margin, we find a strong and positive relationship between the amount spent in lobbying and the cumulative losses of lobbying firms. Finally, by comparing the original TPP agreement with its newer version (CPTPP), without U.S. participation, we provide evidence that firms’ lobbying activity was related to having some specific provisions included in the agreement. In the third chapter, I focus on the role played by trade unions, studying both their lobbying expenditures and their campaign contributions to politicians. I first show that unions are the main opposing force to the ratification of FTAs, and that larger unions, operating in tradable sectors, are more likely to lobby against FTAs. I then study union’s PAC contributions to political parties. During the last three decades, more than 90% of unions’ PAC contributions were directed to Democratic candidates. This has drastically changed when the Republican party took a more protectionist stance under Trump. I find that unions that lobbied against the ratification of FTAs started contributing more to Republican congressmen, particularly those who have taken an anti-trade stance.
Doctorat en Sciences économiques et de gestion
info:eu-repo/semantics/nonPublished

This dissertation explores the impact of international trade on the geographic location of manufacturing activities and on regional productivity growth patterns within countries. This study develops models of trade with monopolistic competition in the context of a two-region country. It also provides empirical estimates of the e ect of tari policy on the distribution of industrial activities and on productivity growth di erentials across Colombia's regions. The rst essay investigates the consequences of trade liberalization for the distribution of manufacturing activities between large and small cities. It presents an extension of the Melitz (2003) model of trade with monopolistic competition and heterogeneous rms where producers' location and export market participation decisions depend on their productivity. As a country's exposure to trade shifts, rms and output are reallocated between large and small urban areas. Data from Colombia's manufacturing sector lend support to theoretical predictions concerning tari reduction's impact on the repartition of industrial activities between metro- and nonmetropolitan areas in this country. The second essay extends the New Economic Geography, Footloose-Capital model to examine the e ect of commercial policy on the distribution of industrial activities between regions within a country. This study aims at distinguishing theoretical cases with regard to the nature of the trade policy change or to the source of asymmetry between regions. It shows that trade liberalization can have adverse consequences for the manufacturing sector of a small or isolated region under bilateral liberalization, but a positive impact under unilateral trade liberalization. The third essay adapts the Melitz and Ottaviano (2008) model of trade with monopolistic competition, heterogeneous rms, and variable mark-ups to analyze the relationship between trade openness, regional market size, and regional aggregate industry performance. It demonstrates that the impact of trade liberalization on aggregate industry productivity growth varies across regions as a function of regional market size and proximity to foreign markets. A larger region experiences a greater increase in aggregate productivity through intra-industry reallocation of market shares. Similarly, a region with better access to international markets enjoys a higher productivity growth from tari reduction. Empirical evidence is obtained from the Colombian manufacturing sector.

The availability of firm level data in international trade started a very quickly developing theoretical literature that focused on the micro evidence and understanding its implications for aggregate productivity and welfare. The new models were dealing with individual firm characteristics determining entry and exit from foreign markets and the different ways in which firms chose to enter. Two of the main features of this literature are that firms have heterogeneous productivities and need to pay a fixed costs in order to enter both their home and foreign markets. As a result, some do not find it optimal to export and it is those with higher productivity that do. This thesis is comprised of three theoretical papers (chapters) in which the models are with firms with heterogeneous productivities and there is steady state economic growth. The purpose in all three papers has been to generate results that are already established empirical facts but that have not been incorporated in the theoretical trade and growth literature.
Diss. Stockholm : Handelshögskolan i Stockholm, 2011

This paper examines the distributional effects of international trade in a general equilibrium model with heterogeneous agents and a welfare state redistributing income. The redistribution scheme is financed by a progressive income tax and gives the same absolute transfer to all individuals. Ceteris paribus, international trade leads to an increase in income per capita but also to higher income inequality on two fronts. Inter-group inequality between managers and workers increases, and intra-group inequality within the group of managers goes up as well. We show that for constant tax rates, there is an endogenous increase in the size of the welfare state that works against the increase in inequality, yet cannot offset it. The paper also sheds light on the conditions under which trade can actually lead to a Pareto improvement.

This paper investigates the effects of international trade in a general equilibrium model with heterogeneous firms where a welfare state redistributes income. We look at a very stylised progressive non-distortionary redistribution scheme. We show that for a given tax rate international trade increases income per capita, but also leads to higher income inequality. Two aspects of income inequality are examined. First, inter-group inequality between managers and workers is considered. Second, intra-group inequality within the group of managers is investigated. For a given tax rate the size of the welfare state and therefore the transfer per capita increases when going from autarky to trade. This second-round effect counteracts the primary increase in inequality, yet cannot outweigh it. Since the redistribution scheme is non-distortionary, it is possible to decrease trade-induced inequality by increasing the tax rate without jeopardising the gains from trade.

This thesis presents a research project in the field of oxygen system fire safety relating to the heterogeneous burning of iron in normal gravity and reduced gravity. Fires involving metallic components in oxygen systems often occur, with devastating and costly results, motivating continued research to improve the safety of these devices through a better understanding of the burning phenomena. Metallic materials typically burn in the liquid phase, referred to as heterogeneous burning. A review of the literature indicates that there is a need to improve the overall understanding of heterogeneous burning and better understand the factors that influence metal flammability in normal gravity and reduced gravity. Melting rates for metals burning in reduced gravity have been shown to be higher than those observed under similar conditions in normal gravity, indicating that there is a need for further insight into heterogeneous burning, especially in regard to the rate-limiting mechanism. The objective of the current research is to determine the cause of the higher melting rates observed for metals burning in reduced gravity to (a) identify the rate-limiting mechanism during heterogeneous burning and thus contribute to an improved fundamental understanding of the system, and (b) contribute to improved oxygen system fire safety for both ground-based and space-based applications. In support of the work, a 2-s duration ground-based drop tower reduced-gravity facility was commissioned and a reduced-gravity metals combustion test system was designed, constructed, commissioned and utilised. These experimental systems were used to conduct tests involving burning 3.2-mm diameter cylindrical iron rods in high-pressure oxygen in normal gravity and reduced gravity. Experimental results demonstrate that at the onset of reduced gravity, the burning liquid droplet rapidly attains a spherical shape and engulfs the solid rod, and that this is associated with a rapid increase in the observed melting rate. This link between the geometry of the solid/liquid interface and melting rate during heterogeneous burning is of particular interest in the current research. Heat transfer analysis was performed and shows that a proportional relationship exists between the surface area of the solid/liquid interface and the observed melting rate. This is confirmed through detailed microanalysis of quenched samples that shows excellent agreement between the proportional change in interfacial surface area and the observed melting rate. Thus, it is concluded that the increased melting rates observed for metals burning in reduced gravity are due to altered interfacial geometry, which increases the contact area for heat transfer between the liquid and solid phases. This leads to the conclusion that heat transfer across the solid/liquid interface is the rate-limiting mechanism for melting and burning, limited by the interfacial surface area. This is a fundamental result that applies in normal gravity and reduced gravity and clarifies that oxygen availability, as postulated in the literature, is not rate limiting. It is also established that, except for geometric changes at the solid/liquid interface, the heterogeneous burning phenomenon is the same at each gravity level. A conceptual framework for understanding and discussing the many factors that influence heterogeneous burning is proposed, which is relevant to the study of burning metals and to oxygen system fire safety in both normal-gravity and reduced-gravity applications.

This thesis presents a research project in the field of oxygen system fire safety relating to the heterogeneous burning of iron in normal gravity and reduced gravity. Fires involving metallic components in oxygen systems often occur, with devastating and costly results, motivating continued research to improve the safety of these devices through a better understanding of the burning phenomena. Metallic materials typically burn in the liquid phase, referred to as heterogeneous burning. A review of the literature indicates that there is a need to improve the overall understanding of heterogeneous burning and better understand the factors that influence metal flammability in normal gravity and reduced gravity. Melting rates for metals burning in reduced gravity have been shown to be higher than those observed under similar conditions in normal gravity, indicating that there is a need for further insight into heterogeneous burning, especially in regard to the rate-limiting mechanism. The objective of the current research is to determine the cause of the higher melting rates observed for metals burning in reduced gravity to (a) identify the rate-limiting mechanism during heterogeneous burning and thus contribute to an improved fundamental understanding of the system, and (b) contribute to improved oxygen system fire safety for both ground-based and space-based applications. In support of the work, a 2-s duration ground-based drop tower reduced-gravity facility was commissioned and a reduced-gravity metals combustion test system was designed, constructed, commissioned and utilised. These experimental systems were used to conduct tests involving burning 3.2-mm diameter cylindrical iron rods in high-pressure oxygen in normal gravity and reduced gravity. Experimental results demonstrate that at the onset of reduced gravity, the burning liquid droplet rapidly attains a spherical shape and engulfs the solid rod, and that this is associated with a rapid increase in the observed melting rate. This link between the geometry of the solid/liquid interface and melting rate during heterogeneous burning is of particular interest in the current research. Heat transfer analysis was performed and shows that a proportional relationship exists between the surface area of the solid/liquid interface and the observed melting rate. This is confirmed through detailed microanalysis of quenched samples that shows excellent agreement between the proportional change in interfacial surface area and the observed melting rate. Thus, it is concluded that the increased melting rates observed for metals burning in reduced gravity are due to altered interfacial geometry, which increases the contact area for heat transfer between the liquid and solid phases. This leads to the conclusion that heat transfer across the solid/liquid interface is the rate-limiting mechanism for melting and burning, limited by the interfacial surface area. This is a fundamental result that applies in normal gravity and reduced gravity and clarifies that oxygen availability, as postulated in the literature, is not rate limiting. It is also established that, except for geometric changes at the solid/liquid interface, the heterogeneous burning phenomenon is the same at each gravity level. A conceptual framework for understanding and discussing the many factors that influence heterogeneous burning is proposed, which is relevant to the study of burning metals and to oxygen system fire safety in both normal-gravity and reduced-gravity applications.

This paper examines the effects of a unilateral reform of the redistribution policy in an economy open to international trade. We set up a general equilibrium trade model with heterogeneous agents allowing for country asymmetries. We show that under international trade compared to autarky, a unilateral tax increase leads to a less pronounced decline in aggregate real income in the reforming country, while income inequality is reduced to a larger extent for sufficiently small initial tax rates. We highlight as a key mechanism a tax-induced reduction in the market size of the reforming country relative to its trading partner, resulting in a firm selection effect towards exporting. From the perspective of a non-reforming trading partner, the unilateral redistribution policy reform resembles a unilateral increase in trade costs leading to a deterioration of terms-of-trade and a decline in both aggregate real income and inequality.

To meet the new challenges of the chemical indutries, the developpement of new heterogeneous catalytic reactors and their understanding are mandatory. From these perspectives, new reactor designs based on structuring at micro or millimeter scales have emerged. They have sparked interest for their ability to decrease physical limitations for heat and mass transfers. Thus, two advanced reactor technologies for gas-liquid-solid catalysed reactions are studied. The first reactor is a micro-structured falling film (FFMR) in which vertical sub millimetric grooves are etched and coated with a catalyst. This structuration allows stabilizing the gas-liquid interface of a down flow liquid phase. A thin liquid film is generated leading to high specific surface areas. Commercially available, it represents a very good potential for performing demanding reactions (i.e.fast, exothermic) for small scale productions such as pharmaceuticals. In a second part, a new reactor concept is proposed. Open cell foams are used as catalyst support and inserted in a milli-square channel. The reactor is then submitted to a preformed gas-liquid Taylor flow. In both cases, hydrodynamics features are studied by using microscopy based methods. Their potential in terms of mass transfers are also studied by performing catalyzed α-methylstyren hydrogenation. For both reactors, it comes out that the particular flow induced by micro or milli structures leads to at least one order of magnitude higher mass transfers performances than mutliphase reactors currently used in the industry albeit it remains to be demonstrated at such scale. From all these studies, correlations, models and methods for chemical engineers (hydrodynamics, pressure drops, mass transfer) are proposed for the two reactors

Thesis advisor: Fabio Ghironi
In Chapter 1, I analyze the cross-country transmission of business cycles when firms relocate production abroad, at locations with lower labor costs. In the model, I distinguish between fluctuations in the number of offshoring firms (the extensive margin) and the value added per offshoring firm (the intensive margin) as separate transmission mechanisms. Firms are heterogeneous in labor productivity. They face a sunk entry cost at home and an additional fixed cost to produce offshore. The model replicates the extensive and intensive margin dynamics that I document for Mexico's maquiladora sector. Offshoring enhances the co-movement of output between the countries involved. Offshoring also reduces price dispersion across countries, because it dampens the real exchange rate appreciation that follows improvements in domestic productivity. In Chapter 2, I estimate the conditional correlations and impulse responses of three indicators of offshoring to Mexico (total value added, value added per plant, and the number of plants) for U.S. permanent technology shocks. Using data from U.S. manufacturing and Mexico's maquiladora sector, I identify U.S. permanent technology shocks in a structural VAR model with long-run restrictions. Following a positive shock, offshore production in Mexico exhibits an immediate increase along its intensive margin, but returns to its initial level over time. The extensive margin does not adjust on impact, but increases gradually towards a permanently higher level. The model of offshoring in Chapter 1 matches qualitatively the business cycle dynamics of offshoring to Mexico. In Chapter 3 (co-authored with Federico Mandelman), we analyze the dynamics of labor migration and the insurance role of remittances in a two-country, real business cycle framework. Emigration increases with the expected stream of future wage gains, and is dampened by the sunk cost reflecting border enforcement. During booms in the destination economy, the scarcity of established immigrants enhances the volatility of the immigrant wage and remittances. The welfare gain from the inflow of unskilled labor increases with the complementarity between skilled and unskilled labor, and with the share of the skilled among native labor. The model matches the cyclical dynamics of the unskilled immigration into the U.S. and remittances sent back to Mexico
Thesis (PhD) — Boston College, 2009
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Economics

Submitted by Daniella Santos (daniella.santos@fgv.br) on 2010-03-23T12:06:11Z No. of bitstreams: 1 Dissertação_Erica_Diniz.pdf: 328909 bytes, checksum: 1fb57ef9f720ee93e22f116f1b459033 (MD5)
Approved for entry into archive by Andrea Virginio Machado(andrea.machado@fgv.br) on 2010-03-23T12:37:36Z (GMT) No. of bitstreams: 1 Dissertação_Erica_Diniz.pdf: 328909 bytes, checksum: 1fb57ef9f720ee93e22f116f1b459033 (MD5)
Made available in DSpace on 2010-03-24T13:37:57Z (GMT). No. of bitstreams: 1 Dissertação_Erica_Diniz.pdf: 328909 bytes, checksum: 1fb57ef9f720ee93e22f116f1b459033 (MD5) Previous issue date: 2009-11-21
This paper presents a duopolist model with heterogeneous firms (different marginal costs) and assimetric information about the vertical preferences of the consumers. We find that the asymmetry of information on the vertical dimension and the difference in costs greatly influences the pricing and the structures for market equilibrium. An important result arising from these two aspects is the existence of a mass of consumers that can buy from both firms. It is also observed that the greater the heterogeneity of costs, the greater the market power of the most efficient firm.
O trabalho apresenta um modelo de competição duopolista, com firmas heterogêneas (custos marginais diferentes), produtos espacialmente diferenciados quanto a dimensão vertical e horizontal, e informação privada sobre as preferências por qualidade dos consumidores. Identifica-se que a assimetria de informação sobre a dimensão vertical e a diferença de custos exercem grande relevância sobre a decisão de apreçamento das firmas e sobre as estruturas de mercado de equilíbrio. Um resultado relevante decorrente desses dois aspectos é a existência de uma massa de consumidores que, em equilíbrio, pode demandar de qualquer uma das firmas, sendo essa decisão pautada sobre o real parâmetro de preferência por qualidade de cada consumidor. Observa-se também que quanto maior a heterogeneidade dos custos, maior é o poder de mercado da firma de menor custo.