A nonparametric analysis of the Cournot model

An observer makes a number of observations of an industry producing a homogeneous good. Each observation consists of the market price, the output of individual firms and perhaps information on each firm's production cost. We provide various tests (typically, linear programs) with which the observer can determine if the data set is consistent with the hypothesis that firms in this industry are playing a Cournot game at each observation. When cost information is wholly or partially unavailable, these tests could potentially be used to derive cost information on the firms. This paper is a contribution to the literature that aims to characterize (in various contexts) the restrictions that a data set must satisfy for it to be consistent with Nash outcomes in a game. It is also inspired by the seminal result of Afriat (and the subsequent literature) which addresses similar issues in the context of consumer demand, though one important technical difference from most of these results is that the objective functions of firms in a Cournot game are not necessarily quasiconcave

Temperature dependence of the microscopic structure and density anomaly of the SPC/E and TIP4P-Ew water models. Molecular dynamics simulation results

We have investigated temperature trends of the microscopic structure of the SPC/E and TIP4P-Ew water models in terms of the pair distribution functions, coordination numbers, the average number of hydrogen bonds, the distribution of bonding states of a single molecule as well as the angular distribution of molecules by using the constant pressure molecular dynamics simulations. The evolution of the structure is put in correspondence with the dependence of water density on high temperatures down to the region of temperatures where the system becomes supercooled. It is shown that the fraction of molecules with three and four bonds determine the maximum density for both models. Moreover, the temperature dependence of the dielectric constant is obtained and analyzed.Comment: 11 pages, 5 figure

Large isotope effect on TcT_c in cuprates despite of a small electron-phonon coupling

We calculate the isotope coefficients $\alpha$ and $\alpha^\ast$ for the superconducting critical temperature $T_c$ and the pseudogap temperature $T^\ast$ in a mean-field treatment of the t-J model including phonons. The pseudogap phase is identified with the $d$-charge-density wave ($d$-CDW) phase in this model. Using the small electron-phonon coupling constant $\lambda_d \sim 0.02$ obtained previously in LDA calculations in YBa$_2$Cu$_3$O$_7$, $\alpha^{\ast}$ is negative but negligible small whereas $\alpha$ increases from about 0.03 at optimal doping to values around 1 at small dopings in agreement with the general trend observed in many cuprates. Using a simple phase fluctuation model where the $d$-CDW has only short-range correlations it is shown that the large increase of $\alpha$ at low dopings is rather universal and does not depend on the existence of sharp peaks in the density of states in the pseudogap state or on specific values of the phonon cutoff. It rather is caused by the large depletion of spectral weight at low frequencies by the $d$-CDW and thus should also occur in other realizations of the pseudogap.Comment: 8 pages, 5 figures, to be publ. in PR

Hydrophobically modified polyelectrolytes as potential drugs reservoirs of n-alkyl-nitroimidazoles

Indexación: ScieloThe solubilization of three commercial drugs (ornindazole, metronidazole and tinidazole) and model compounds (N-alkyl-2-methyl-4-nitroimidazoles) on aggregates formed by anionic polyelectrolytes, carrying alkyl side chains of different length, have been investigated in aqueous solution at pH 3.0, 7.0 and 11.0. Potassium salts of poly(maleic acid-co-1-olefins), PA-nK2 with n ranging from 8 to 18, were used as micelle-forming polymers. The partition of these drugs between water and the hydrophobic microdomains provided by PA-nK2 was studied by the pseudo-phase model to determinate the distribution coefficient KS, and the standard free energy of transfer Δμºt. The results indicate that solubility of alkyl-nitroimidazoles on these polymer micelles depends moderately on the length of the alkyl chain, and therefore is mainly determined by the heterocyclic group. On the other hand, the solubilization of 1-hexyl-2-methyl-4-nitroimidazole increase with decreasing length of the side alkyl chain; i.e. KS follows the order PA-8K2 > PA-10K2 > PA-12K2 > PA-14K2 > PA-16K2 >PA-18K2.http://www.scielo.cl/scielo.php?script=sci_arttext&pid=S0717-97072007000100014&nrm=is

Do European Stock Markets Affect Latin American Stock Markets?

In this study, we examine the response of Latin American stock markets to movements in European stock markets using VAR models. Our results vary depending on the openness of the country in terms of international trade. We find evidence that Latin American stock markets are responsive to changes in the stock market from Spain. Additionally, during the second and third subperiods, Spain has much stronger ties with Brazil, and this might explain why Brazil responds more to the shocks originating from Spain than from France. In conclusion, this study uncovers two important findings. First, Spain influences Latin American markets but these responses are not homogeneous across markets. Second, the influence of Spain has different magnitude in the three subperiods.Emerging Markets, Latin America, Stock Markets Interdependence, VAR

Spin exchange and superconductivity in a t−J′−Vt-J'-V model for two-dimensional quarter-filled systems

The effect of antiferromagnetic spin fluctuations on two-dimensional quarter-filled systems is studied theoretically. An effective $t-J'-V$ model on a square lattice which accounts for checkerboard charge fluctuations and next-nearest-neighbors antiferromagnetic spin fluctuations is considered. From calculations based on large-N theory on this model it is found that the exchange interaction, $J'$, increases the attraction between electrons in the d$_{xy}$ channel only, so that both charge and spin fluctuations work cooperatively to produce d$_{xy}$ pairing.Comment: 9 pages, 6 figure

On the excitation of inertial modes in an experimental spherical Couette flow

Spherical Couette flow (flow between concentric rotating spheres) is one of flows under consideration for the laboratory magnetic dynamos. Recent experiments have shown that such flows may excite Coriolis restored inertial modes. The present work aims to better understand the properties of the observed modes and the nature of their excitation. Using numerical solutions describing forced inertial modes of a uniformly rotating fluid inside a spherical shell, we first identify the observed oscillations of the Couette flow with non-axisymmetric, retrograde, equatorially anti-symmetric inertial modes, confirming first attempts using a full sphere model. Although the model has no differential rotation, identification is possible because a large fraction of the fluid in a spherical Couette flow rotates rigidly. From the observed sequence of the excited modes appearing when the inner sphere is slowed down by step, we identify a critical Rossby number associated with a given mode and below which it is excited. The matching between this critical number and the one derived from the phase velocity of the numerically computed modes shows that these modes are excited by an instability likely driven by the critical layer that develops in the shear layer staying along the tangent cylinder of the inner sphere.Comment: 11 pages, 17 figure

Self-energy renormalization around the flux phase in the t−Jt-J model: Possible implications in underdoped cuprates

The flux phase predicted by the $t-J$ model in the large-N limit exhibits features that make it a candidate for describing the pseudogap regime of cuprates. However certain properties, as for instance the prediction of well defined quasiparticle peaks, speak against this scenario. We have addressed these issues by computing self-energy renormalizations in the vicinity to flux phase. The calculated spectral functions show features similar to those observed in experiments. At low doping, near the flux phase, the spectral functions are anisotropic on the Fermi surface and very incoherent near the hot spots. The temperature and doping evolution of self-energy and spectral functions are discussed and compared with the experiment.Comment: 4.3 pages, 4 figures, accepted for publication in Phys. Rev.