Mexico's integration into NAFTA markets: a view from sectoral real exchange rates

Using a self-exciting threshold autoregressive model, we confirm the presence of nonlinearities in sectoral real exchange rate (SRER) dynamics across Mexico, Canada and the US in the pre-NAFTA and post-NAFTA periods. Measuring transaction costs using the estimated threshold bands, we find evidence that Mexico still faces higher transaction costs than their developed counterparts. Trade liberalization is associated with reduced transaction costs and lower relative price differentials among countries. Other determinants of transaction costs are distance and nominal exchange rate volatility. Our results show that the half-lives of SRERs shocks, calculated by Monte Carlo integration, imply much faster adjustment in the post-NAFTA period.Foreign exchange rates ; North American Free Trade Agreement ; Mexico

Mexico's integration into NAFTA markets: a view from sectoral real exchange rates

The authors use a threshold autoregressive model to confirm the presence of nonlinearities in sectoral real exchange rate dynamics across Mexico, Canada, and the United States for the periods before and after the North American Free Trade Agreement (NAFTA). Although trade liberalization is associated with reduced transaction costs and lower relative price differentials among countries, the authors find, by using estimated threshold bands, that Mexico still faces higher transaction costs than its developed counterparts. Other determinants of transaction costs are distance and nominal exchange rate volatility. The authors' results show that the half-lives of sectoral real exchange rate shocks, calculated by Monte Carlo integration, imply much faster adjustment in the post-NAFTA period.Foreign exchange rates ; North American Free Trade Agreement ; Mexico

Review: to be or not to be an identifiable model. Is this a relevant question in animal science modelling?

International audienceWhat is a good (useful) mathematical model in animal science? For models constructed for prediction purposes, the question of model adequacy (usefulness) has been traditionally tackled by statistical analysis applied to observed experimental data relative to model-predicted variables. However, little attention has been paid to analytic tools that exploit the mathematical properties of the model equations. For example, in the context of model calibration, before attempting a numerical estimation of the model parameters, we might want to know if we have any chance of success in estimating a unique best value of the model parameters from available measurements. This question of uniqueness is referred to as structural identifiability; a mathematical property that is defined on the sole basis of the model structure within a hypothetical ideal experiment determined by a setting of model inputs (stimuli) and observable variables (measurements). Structural identifiability analysis applied to dynamic models described by ordinary differential equations (ODE) is a common practice in control engineering and system identification. This analysis demands mathematical technicalities that are beyond the academic background of animal science, which might explain the lack of pervasiveness of identifiability analysis in animal science modelling. To fill this gap, in this paper we address the analysis of structural identifiability from a practitioner perspective by capitalizing on the use of dedicated software tools. Our objectives are (i) to provide a comprehensive explanation of the structural identifiability notion for the community of animal science modelling, (ii) to assess the relevance of identifiability analysis in animal science modelling and (iii) to motivate the community to use identifiability analysis in the modelling practice (when the identifiability question is relevant). We focus our study on ODE models. By using illustrative examples that include published mathematical models describing lactation in cattle, we show how structural identifiability analysis can contribute to advancing mathematical modelling in animal science towards the production of useful models and highly informative experiments. Rather than attempting to impose a systematic identifiability analysis to the modelling community during model developments, we wish to open a window towards the discovery of a powerful tool for model construction and experiment design

Transcriptome profiling of the feeding-to-fasting transition in chicken liver

<p>Abstract</p> <p>Background</p> <p>Starvation triggers a complex array of adaptative metabolic responses including energy-metabolic responses, a process which must imply tissue specific alterations in gene expression and in which the liver plays a central role. The present study aimed to describe the evolution of global gene expression profiles in liver of 4-week-old male chickens during a 48 h fasting period using a chicken 20 K oligoarray.</p> <p>Results</p> <p>A large number of genes were modulated by fasting (3532 genes with a pvalue corrected by Benjamini-Hochberg < 0.01); 2062 showed an amplitude of variation higher than +/- 40% among those, 1162 presented an human ortholog, allowing to collect functional information. Notably more genes were down-regulated than up-regulated, whatever the duration of fasting (16 h or 48 h). The number of genes differentially expressed after 48 h of fasting was 3.5-fold higher than after 16 h of fasting. Four clusters of co-expressed genes were identified by a hierarchical cluster analysis. Gene Ontology, KEGG and Ingenuity databases were then used to identify the metabolic processes associated to each cluster. After 16 h of fasting, genes involved in ketogenesis, gluconeogenesis and mitochondrial or peroxisomal fatty acid beta-oxidation, were up-regulated (cluster-1) whereas genes involved in fatty acid and cholesterol synthesis were down-regulated (cluster-2). For all genes tested, the microarray data was confirmed by quantitative RT-PCR. Most genes were altered by fasting as already reported in mammals. A notable exception was the <it>HMG-CoA synthase 1 </it>gene, which was up-regulated following 16 and 48 h of fasting while the other genes involved in cholesterol metabolism were down-regulated as reported in mammalian studies. We further focused on genes not represented on the microarray and candidates for the regulation of the target genes belonging to cluster-1 and -2 and involved in lipid metabolism. Data are provided concerning PPARa, SREBP1, SREBP2, NR1H3 transcription factors and two desaturases (FADS1, FADS2).</p> <p>Conclusion</p> <p>This study evidences numerous genes altered by starvation in chickens and suggests a global repression of cellular activity in response to this stressor. The central role of lipid and acetyl-CoA metabolisms and its regulation at transcriptional level are confirmed in chicken liver in response to short-term fasting. Interesting expression modulations were observed for <it>NR1H3, FADS1 </it>and <it>FADS2 </it>genes. Further studies are needed to precise their role in the complex regulatory network controlling lipid metabolism.</p

A Systematic Review of Immunological Studies of Erythema Nodosum Leprosum.

Erythema nodosum leprosum (ENL) is a painful inflammatory complication of leprosy occurring in 50% of lepromatous leprosy patients and 5-10% of borderline lepromatous patients. It is a significant cause of economic hardship, morbidity and mortality in leprosy patients. Our understanding of the causes of ENL is limited. We performed a systematic review of the published literature and critically evaluated the evidence for the role of neutrophils, immune complexes (ICs), T-cells, cytokines, and other immunological factors that could contribute to the development of ENL. Searches of the literature were performed in PubMed. Studies, independent of published date, using samples from patients with ENL were included. The search revealed more than 20,000 articles of which 146 eligible studies were included in this systematic review. The studies demonstrate that ENL may be associated with a neutrophilic infiltrate, but it is not clear whether it is an IC-mediated process or that the presence of ICs is an epiphenomenon. Increased levels of tumor necrosis factor-α and other pro-inflammatory cytokines support the role of this cytokine in the inflammatory phase of ENL but not necessarily the initiation. T-cell subsets appear to be important in ENL since multiple studies report an increased CD4+/CD8+ ratio in both skin and peripheral blood of patients with ENL. Microarray data have identified new molecules and whole pathophysiological pathways associated with ENL and provides new insights into the pathogenesis of ENL. Studies of ENL are often difficult to compare due to a lack of case definitions, treatment status, and timing of sampling as well as the use of different laboratory techniques. A standardized approach to some of these issues would be useful. ENL appears to be a complex interaction of various aspects of the immune system. Rigorous clinical descriptions of well-defined cohorts of patients and a systems biology approach using available technologies such as genomics, epigenomics, transcriptomics, and proteomics could yield greater understanding of the condition

Inflation and Monetary Pass-Through in Guinea

The paper analyzes the dynamics of inflation in Guinea during 1992-2003 applying cointegration and error-correction modeling to a bivariate model that includes consumer price and monetary variables. The empirical results, based on quarterly data, confirm the existence of a long-run relationship between money supply and consumer prices. This paper argues further that the pass-through has increased in recent years. Short-term dynamics are shown to accentuate the long-run impact. Impulse response analysis shows that a shock in the money stock will have an increasing impact over two years and will then stabilize at a higher level.Consumer prices;Economic models;inflation, money supply, monetary policy, price level, money growth, money demand, money stock, monetary fund, rate of inflation, high inflation, price inflation, monetary financing, monetary aggregates, inflationary pressures, real money, inflation equation, money balances, monetary growth, money market, liquidity management, inflation money, resurgence of inflation, reduction in inflation, central bank, rates of inflation, inflation dynamics, actual rate of inflation, nominal interest rates, inflation growth, loose monetary policy, monetary expansion, inflationary expectations, average rate of inflation, monetary shock

Identification des éléments clefs du métabolisme des lipides et de leurs régulateurs

Diplôme : Dr. Ing.Lipid quantity and their fatty-acid composition are partly responsible for meat quality traits and play a major role in many pathologies. A better control of the lipid metabolism is then important in terms of public health and food production. Numerous experimental and biblio- graphical data now available on lipid metabolism ; however both the hierarchy of importance of metabolic pathways and the key regulators remain unhnown under various conditions. Mod- elling tools may be helpful to a better understanding of lipid metabolism in various organisms. Two complementary models were developed: a simple dynamic model based on a minimum set of biological functions and regulations necessary to explain experimental data observed on lipid metabolism, and a large-scale model including a maximum of information extracted from knowledge databases. The first model is composed of a set of ordinary differential equations describing the main biochemical pathways involved in lipid metabolism, independently of the species, the organ and experimental conditions. This model was confronted with biological data describing the variation of fatty-acid content in the liver and adipose tissue of two types of mice during a 72 hours fasting : wild-type mice and knockout for PPARα (i.e., a transcription factor that mediates fatty acid oxidation during fasting). Liver fatty acid influx from blood, fatty acid oxidation and unexpected elongation and desaturation of fatty acid were identified as important during fasting in mice liver. Morever the existence of an unknown activator of elongation and desaturation different from PPARα was suggested. The second model consists on a regulatory network which aims at gathering literature knowl- edge, and to compare it to high throughput transcriptomic data. Three literature databases focusing on biological interactions were compared(Gardon, i.e., a small database handmade by experts of lipid metabolism, and TRANSPATH and Ingenuity, i.e., two commercial databases of biological interactions). A strong complementarity between these three databases regarding their sources and the exploitable contents in terms of extractable influences was shown. A regulatory network was then built by merging their automatically-extracted contents and the most connected elements related to energy metabolism were found by topological analysis. Models are then useful to identify know and unknown regulators and pathways, and suggest new biological experiments.La quantité totale de lipides et la composition en acides gras participent au déterminisme de la qualité des produits carnés et jouent un rôle dans de nombreuses pathologies. Par conséquent la maitrise du métabolisme des lipides constitue un important enjeu industriel et de santé publique. De nombreuses données expérimentales et bibliographiques sont actuellement disponibles sur le métabolisme des lipides dans différentes espèces. Néamoins, la hiérarchie d'importance des voies métaboliques et les régulateurs clefs de ce métabolisme dans différentes conditions expérimentales restent mal connus. Cette these propose d'utiliser les outils de la modélisation pour intégrer les données disponibles sur le métabolisme des lipides et des acides gras. Pour cela, deux modèles complémentaires ont été développés : un modèle dynamique simple comprenant le minimum de fonctions biologiques et de régulations nécessaire pour expliquer des données expérimentales métaboliques, et un modèle à large échelle comprenant un maximum d'informations issues des bases de données de connaissances. Le premier est un ensemble d'équations différentielles ordinaires décrivant les principales voies biochimiques du métabolisme des lipides indépendamment de l'espèce, de l'organe et des conditions expérimentales. Ce modèle a été confronté aux données biologiques décrivant les variations des acides gras dans le foie et le tissu adipeux lors de 72 heures de mise à jeun chez des souris de génotype sauvages et knockout pour PPARα (un facteur de transcription responsable notamment de l'activation de l'oxydation des acides gras). Nous mettons ainsi en évidence l'importance de la captation des acides gras sanguins par le foie, de l'oxydation hépatique des acides gras mais aussi et de maniere plus surprenante, des voies de désaturation et élongation des acides gras actives meme chez l'animal a jeun. L'existence d'un régulateur inconnu de l'élongation-désaturation des acides gras autre que PPARα est également suggérée. Le second modèle est un graphe d'influence qui réunit un maximum d'informations bibliogra- phiques pour les croiser avec des données transcriptomiques obtenues à haut débit. L'analyse de trois bases de connaissances bibliographiques (Gardon, une base interne experte ; TRANSPATH et Ingenuity, deux bases commerciales) a permis de mettre en évidence une forte complémenta- rité de la bibliographie extraite et des influences exploitables qu'elles référencent. Suite à cette analyse un graphe d'influence a été construit et l'analyse de sa topologie a permis de mettre en évidence les éléments les plus connectés possédant un lien avec le métabolisme énergétique. Ces deux démarches ont souligné l'intéret de la modélisation pour mettre en exergue des voies connues mais aussi inconnues, et suggérer ainsi de nouvelles expérimentations