Spatial competition and price formation

We look at price formation in a retail setting, that is, companies set prices, and consumers either accept prices or go someplace else. In contrast to most other models in this context, we use a two-dimensional spatial structure for information transmission, that is, consumers can only learn from nearest neighbors. Many aspects of this can be understood in terms of generalized evolutionary dynamics. In consequence, we first look at spatial competition and cluster formation without price. This leads to establishement size distributions, which we compare to reality. After some theoretical considerations, which at least heuristically explain our simulation results, we finally return to price formation, where we demonstrate that our simple model with nearly no organized planning or rationality on the part of any of the agents indeed leads to an economically plausible price.Comment: Minor change

Apport diagnostique et pronostique additionnel des examens non-invasifs à la prédiction du risque de premier événement coronarien

L'objectif général du travail était d'étudier l'apport respectif de trois tests non-invasifs courants - l'examen clinique, l'épreuve d'effort et l'écho-doppler artériel - à la prédiction du risque d'événement coronaire en prévention primaire. Nous avons utilisé le jeu de données constitué par la cohorte prospective EVADEC (EVAluation du DEpistage de la Coronaropathie). Cette cohorte a suivi pendant une médiane de 6 ans 3034 sujets asymptomatiques et sans antécédent cardiovasculaire entre 1995 et 2004. Les analyses ont donné lieu à quatre travaux originaux. 1) Une épreuve d'effort électriquement positive était associée à la survenue d'événements coronaires chez les sujets à plus haut risque, y compris après ajustement sur les facteurs de risque. 2) Dans une approche diagnostique transversale, la présence d'un souffle fémoral apportait une information significative, au-delà des facteurs de risque traditionnels, à la fois sur la présence d'AOMI asymptomatique, définie par un IPS<0,9 et sur la présence de plaque fémorale. 3) Alors que 40% des sujets étaient porteurs de plaques, de sténoses ou d'AOMI asymptomatiques, une épaisseur intima-média (EIM) modérément augmentée ou la présence de plaques carotidiennes ou fémorales était associées au pronostic, après ajustement sur le risque de Framingham. 4) L'introduction successive dans le modèle des facteurs de risque, de l'épreuve d'effort, l'EIM, puis des plaques fémorales permettait une augmentation incrémentale de l'aire sous la courbe ROC et d'une augmentation de 50% de la valeur prédictive positive sans effet délétère sur la valeur prédictive négativeThe aim of this work was to assess the information provided by three widely used non-invasive tests (physical examination, exercise testing and arterial ultrasound) for the prediction of coronary events in primary prevention. To do so, we used the data from the EVADEC prospective cohort study. Participants were 3034 adults free of any past history of coronary disease. The mean follow-up time was 6 years. 1) An electrically positive exercise test was associated with the onset of coronary events among subjects at higher pre-test risk, after adjustment for major risk factors. 2) In a diagnostic cross-sectional approach, a femoral bruit provided a significant information on both the presence of asymptomatic peripheral arterial disease (PAD, defined by an ABI>0.9) and on the presence of a femoral plaque. 3) With 40% of ours sample having plaques, stenosis or asymptomatic PAD, a moderate increase in intima-media thickness (IMT) or the presence of carotid or femoral plaque were associated with the prognosis, after adjustment on Framingham risk. 4) The consecutive introduction in the model of traditional risk factors, exercise testing, IMT then femoral plaques resulted in an incremental increase in the area under ROC curves and an increase of 50% in the positive predictive value without negative effect on the negative predictive value. Patients with at least three clinical or paraclinical abnormalities had an observed risk equivalent to coronary patient

Unit versus ad valorem taxes: monopoly in general equilibrium

We show that if a monopoly sector is imbedded in a general equilibrium framework and profits are taxed at one hundred percent, then unit (specific) taxation and ad valorem taxation are welfare-wise equivalent. This is contrary to all known claims

Continuous-Variable Quantum Games

We investigate the quantization of games in which the players can access to a continuous set of classical strategies, making use of continuous-variable quantum systems. For the particular case of the Cournot's Duopoly, we find that, even though the two players both act as "selfishly" in the quantum game as they do in the classical game, they are found to virtually cooperate due to the quantum entanglement between them. We also find that the original Einstein-Podolksy-Rosen state contributes to the best profits that the two firms could ever attain. Moreover, we propose a practical experimental setup for the implementation of such quantum games.Comment: 3 figure

Aluminum action on mouse bone cell metabolism and response to PTH and 1,25(OH)2D3

Aluminum action on mouse bone cell metabolism and response to PTH and 1,25(OH)2D3. Aluminum (Al) accumulation in bone is associated with low bone formation and mineralization rates; resorption may also be reduced. The mechanism of these Al-induced changes was investigated using cultured mouse osteoblast–like (OB) and osteoclast–like (OC) cells. The Al effect on bone resorption was measured by the in vitro release of 45Ca and β-glucuronidase from mouse fetal limb–bones. Al had a biphasic effect. High concentrations (>1.5 × 10-6 M) of Al inhibited collagen and DNA synthesis, ornithine decarboxylase and alkaline phosphatase activity in OB, and depressed tartrate-resistant acid phosphatase activity in OC. Lower Al concentrations stimulated these cellular activities and 45Ca and β-glucuronidase release from fetal bones. Al had no effect on basal cAMP levels in OB but inhibited the stimulating effect of bPTH on cAMP content. Al also altered the 1,25(OH)2D3 effects on the ornithine decarboxylase activity of OB cells. These data suggest that: (i) the low bone formation observed in vivo during Al intoxication may be due to the inhibition of collagen synthesis and to depressed cell proliferation; and (ii) Al may indirectly influence bone remodeling by interfering with the actions of bPTH and 1,25(OH)2D3 on bone cells