Forward Vertical Integration: The Fixed-Proportion Case Revisited

Assuming a fixed-proportion downstream production technology, partial forward integration by an upstream monopolist may be observed whether the monopolist is advantaged or disadvantaged cost-wise relative to fringe firms in the downstream market. Integration need not induce cost-predation and the profits of the fringe may increase. The output price falls and welfare unambiguously rises.

Forward Vertical Integration: The Fixed-Proportion Case Revisited

Assuming a fixed-proportion downstream production technology, partial forward integration by an upstream monopolist may be observed whether the monopolist is advantaged or disadvantaged cost-wise relative to fringe firms in the downstream market. Integration need not induce cost predation and the fringe firms’ margin may even increase. The output price falls and welfare unambiguously rises.Vertical integration; cost predation; cost asymmetries

On convergence of the auxiliary-vector beamformer with rank-deficient covariance matrices

The auxiliary-vector beamformer is an algorithm that generates iteratively a sequence of beamformers which, under the assumption of a positive definite covariance matrix R, converges to the minimum variance distortionless response beamformer, without resorting to any matrix inversion. In the case where R is rank-deficient, e.g., when R is substituted for the sample covariance matrix and the number of snapshots is less than the number of array elements, the behavior of the AV beamformer is not known theoretically. In this letter, we derive a new convergence result and show that the AV beamformer weights converge when R is rank-deficient, and that the limit belongs to the class of reduced-rank beamformers

Robust approaches to remote calibration of a transmitting array

We consider the problem of estimating the gains and phases of the RF channels of a M-element transmitting array, based on a calibration procedure where M orthogonal signals are sent through M orthogonal beams and received on a single antenna. The received data vector obeys a linear model of the type y ¼ AFg þ n where A is an unknown complex scalar accounting for propagation loss and g is the vector of unknown complex gains. In order to improve the performance of the least-squares (LS) estimator at low signal to noise ratio (SNR), we propose to exploit knowledge of the nominal value of g, viz g. Towards this end, two approaches are presented. First, a Bayesian approach is advocated where A and g are considered as random variables, with a non-informative prior distribution for A and a Gaussian prior distribution for g. The posterior distributions of the unknown random variables are derived and a Gibbs sampling strategy is presented that enables one to generate samples distributed according to these posterior distributions, leading to the minimum mean-square error (MMSE) estimator. A second approach consists in solving a constrained least-squares problem in which h ¼ Ag is constrained to be close to a scaled version of g. This second approach yields a closed-form solution, which amounts to a linear combination of g and the LS estimator. Numerical simulations show that the two new estimators significantly outperform the conventional LS estimator, especially at low SNR

Adaptive beamforming for large arrays in satellite communications systems with dispersed coverage

Conventional multibeam satellite communications systems ensure coverage of wide areas through multiple fixed beams where all users inside a beam share the same bandwidth. We consider a new and more flexible system where each user is assigned his own beam, and the users can be very geographically dispersed. This is achieved through the use of a large direct radiating array (DRA) coupled with adaptive beamforming so as to reject interferences and to provide a maximal gain to the user of interest. New fast-converging adaptive beamforming algorithms are presented, which allow to obtain good signal to interference and noise ratio (SINR) with a number of snapshots much lower than the number of antennas in the array. These beamformers are evaluated on reference scenarios

Investigating Non-Linearities in the Relationship Between Real Exchange Rate Volatility and Agricultural Trade

The article analyzes production and marketing lags in agri-food supply chains that force competitive producers and processors to commit to output targets before prices and exchange rates are realized. We show that export markets act as put options for exporters and an increase in the volatility of the real exchange rate will generally increase exports. Relaxing the assumptions about the real exchange rate distribution and risk preferences of producers and/or processors can introduce non-linearities in the relationship between exports and real exchange rate volatility. This relationship is investigated using the flexible non-linear inference framework of Hamilton (2001). Bilateral export equations for Canadian pork exports to the U.S. and Japan are specified. The empirical model shows that real exchange rate volatility has statistically significant non-linear effects on aggregate pork exports. Moreover, bilateral pork exports are less sensitive to country- specific variables than aggregate volatility in the real exchange rate.Real exchange rate volatility, non-linear flexible inference, production lags, pork exports

Investigating Non-Linearities in the Relationship Between Real Exchange Rate Volatility and Trade

Production and marketing lags in agri-food supply chains force competitive primary producers and food processors to commit to output targets before prices and exchange rates are realized. A theoretical model with one processor and many price-taking primary producers is developed to show that an increase in the volatility of the export price generally increases exports under risk neutrality. Furthermore, relaxing the assumption that the processing firm is risk neutral introduces non- linearities in the relationship between exports and export price volatility. This relationship is empirically investigated using the flexible non-linear inference framework developed by Hamilton (2001). The theoretical model provides the foundation for empirical bilateral export equations for Canadian pork exports to the U.S. and Japan. The empirical investigation supports the hypothesis that export price volatility has statistically significant non-linear effects on Canadian pork exports.Exchange rate volatility, non-linear flexible inference, production lags, pork exports

Forward Vertical Integration: The Fixed-Proportion Case Revisited

Assuming a fixed-proportion downstream production technology, partial forward integration by an upstream monopolist may be observed whether the monopolist is advantaged or disadvantaged cost-wise relative to fringe firms in the downstream market. Integration need not induce cost predation and the fringe firms’ margin may even increase. The output price falls and welfare unambiguously rises

Large mammals on small islands : short term effects of forest fragmentation on the large mammal fauna in french Guiana

In this study, we present data on species richness of large marnrnals (mostly with body mass > 1 kg) in two contiguous areas at Saint-Eugène, French Guiana, before and after forest fragmentation by flooding. Assessment realized in 1993-94, i.e. before and during flooding, showed similar species richness and composition in the two studied areas. Before fragmentation, the large mammal community at Saint-Eugène was comparable to that recorded from a site of pristine forest in French Guiana. After forest fragmentation, one of these zones became isolated (medium-sized island) while the second one remained as a continuous forest. As a consequence, the number of species present on that newly isolated patch decreased of 30 % while it seemed non-affected in the continuous forest. This Joss in species richness on the fragmented area was confirmed by a survey conducted in 1995-99 at three additional medium-sized islands (> 20 ha), 22 small-sized islands (1-10 ha) and 11 islets (< 1 ha). Occurrence status of the 32 large mammal species observed at Saint-Eugène is drawn up for ail studied sites, and preliminary results on their overall abundance are presented for nine sites. The number of species present in a site was positively correlated to its area, but seemed not to be correlated to its isolation distance from the nearest larger landmass. Islands of less than 10 hectares had a mammal community that was rapidly impoverished and imbalanced in comparison to the one observed on medium-sized islands. The latter presented a marnrnal community that was richer and more complex, including all trophic guilds, despite it appeared affected in comparison to the continuous forest. Large mammal community on small and medium islands typically included species with small home ranges, and mostly generalist or herbivorous 1 granivorous feeding habits: armadillos (Dasypus spp.), acouchi (Myoprocta acouchy), agouti (Dasyprocta leporina), kinkajou (Potos flavus), sloths (Choelopus didactylus and Bradypus tridactylus), and squirrels (Sciurus aestuans and Sciurillus pusillus). However, species with larger home range, as felids, tapir (Tapirus terrestris), peccaries (Pecari tajacu and Tayassu pecari) and brocket deers (Mazama spp.) still frequented islands, at least temporarily. We thus discuss the role that fragments may potentially have in connecting larger landmassesLa richesse spécifique en gros mammifères (pour la plupart, de masse corporelle > 1 kg) a été étudiée à Saint-Eugène, Guyane française, dans deux zones adjacentes d'une forêt humide avant et après isolement de l'une d'elles par la mise en eau d'un barrage hydroélectrique. L'état des lieux en 1993-94, avant et pendant la montée des eaux, montre une richesse et une composition spécifiques de gros mammifères similaires entre les deux zones. Avant fragmentation, le peuplement de gros mammifères de Saint-Eugène était relativement complet et comparable à celui d'un site de forêt peu perturbée en Guyane française. Après fragmentation et isolement de l' une des deux zones, devenue une île de taille moyenne, le nombre d' espèces y a diminué d'un tiers tandis qu' il semble inchangé sur la terre ferme. Le suivi après fragmentation (1995-99) de trois îles moyennes supplémentaires (> 20 ha), 22 petites îles (1-10 ha), et 11 îlots ( < 1 ha) confirme la perte de richesse spécifique en situation insulaire. Un bilan de l'occurrence des 32 espèces de gros mammifères détectés à Saint-Eugène est dressé pour chaque site, et des résultats préliminaires sur leur abondance globale présentés pour neuf d'entre eux. Le nombre d'espèces présentes sur les îles augmente avec la surface, mais ne semble pas corrélé à la distance d'isolement par rapport à une terre émergée de superficie supérieure. Les îles de moins de 10 ha montrent un peuplement de gros mammifères rapidement appauvri et déséquilibré par rapport à celui des îles de taille moyenne, qui possèdent un peuplement plus riche et plus complexe, comprenant l'ensemble des guildes trophiques, bien que nettement altéré par rapport à la forêt continue. Le peuplement de gros mammifères présents sur les petites et moyennes îles est typiquement composé d'espèces ayant un petit domaine vital et pour la plupart un régime alimentaire généraliste ou herbivore 1 granivore : les tatous (Dasypus spp.), l'Acouchi (Myoprocta acouchy), l' Agouti (Dasyprocta leporina), le Kinkajou (Potos jlavus), ainsi que les paresseux (Choelopus didactylus et Bradypus tridactylus) et les écureuils (Sciurus aestuans et Sciurillus pusillus) . Cependant, les espèces à grand domaine vital, telles que les félins, le Tapir (Tapirus terrestris), les pécaris (Pecari tajacu et Tayassu pecari) et les mazamas (Mazama ame ricana et M. gouazoubira), exploitent encore les îles, au moins de façon transitoire. Ceci nous amène à discuter du rôle potentiel que pourraient jouer les fragments dans la connectivité entre de plus grands blocs forestier

REGULATION DE LA TRANSITION EPITHELIUM-MESENCHYME PAR LES INTERACTIONS ENTRE LE FACTEUR DE CROISSANCE IGF-II, SON RECEPTEUR IGF1R ET LA MOLECULE D'ADHERENCE E-CADHERINE

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