From vortex molecules to the Abrikosov lattice in thin mesoscopic superconducting disks

Stable vortex states are studied in large superconducting thin disks (for numerical purposes we considered with radius R = 50 \xi). Configurations containing more than 700 vortices were obtained using two different approaches: the nonlinear Ginzburg-Landau (GL) theory and the London approximation. To obtain better agreement with results from the GL theory we generalized the London theory by including the spatial variation of the order parameter following Clem's ansatz. We find that configurations calculated in the London limit are also stable within the Ginzburg-Landau theory for up to ~ 230 vortices. For large values of the vorticity (typically, L > 100), the vortices are arranged in an Abrikosov lattice in the center of the disk, which is surrounded by at least two circular shells of vortices. A Voronoi construction is used to identify the defects present in the ground state vortex configurations. Such defects cluster near the edge of the disk, but for large L also grain boundaries are found which extend up to the center of the disk.Comment: 15 pages, 10 figures, RevTex4, submitted to Phys. Rev.

An Equilibrium Approach to International Merger Policy

treat international merger policy as a repeated veto game. I show that there exists a unique efficient equilibrium within a particular class of trigger strategy equilibria. I then consider a series of comparative statics and extensions: (a) if for some exogenous reason one of the countries becomes more lenient towards mergers, than the other country becomes more lenient as well; (b) merger remedies increase the probability that a merger is approved and increase total welfare; (c) the effects of a merger wave are magnified by the equilibrium approval policy

First detection of CF+ towards a high-mass protostar

We report the first detection of the J = 1 - 0 (102.6 GHz) rotational lines of CF+ (fluoromethylidynium ion) towards CygX-N63, a young and massive protostar of the Cygnus X region. This detection occurred as part of an unbiased spectral survey of this object in the 0.8-3 mm range, performed with the IRAM 30m telescope. The data were analyzed using a local thermodynamical equilibrium model (LTE model) and a population diagram in order to derive the column density. The line velocity (-4 km s-1) and line width (1.6 km s-1) indicate an origin from the collapsing envelope of the protostar. We obtain a CF+ column density of 4.10e11 cm-2. The CF+ ion is thought to be a good tracer for C+ and assuming a ratio of 10e-6 for CF+/C+, we derive a total number of C+ of 1.2x10e53 within the beam. There is no evidence of carbon ionization caused by an exterior source of UV photons suggesting that the protostar itself is the source of ionization. Ionization from the protostellar photosphere is not efficient enough. In contrast, X-ray ionization from the accretion shock(s) and UV ionization from outflow shocks could provide a large enough ionizing power to explain our CF+ detection. Surprisingly, CF+ has been detected towards a cold, massive protostar with no sign of an external photon dissociation region (PDR), which means that the only possibility is the existence of a significant inner source of C+. This is an important result that opens interesting perspectives to study the early development of ionized regions and to approach the issue of the evolution of the inner regions of collapsing envelopes of massive protostars. The existence of high energy radiations early in the evolution of massive protostars also has important implications for chemical evolution of dense collapsing gas and could trigger peculiar chemistry and early formation of a hot core.Comment: 6 page

Dynamic Competition with No Efficiency Effect

I uncover a new force towards increasing dominance (the property whereby, in dynamic games, the leader tends to increase her lead in expected terms). The new effect results from the strategic choice of covariance in races. I assume that players must choose not the amount of resources to spend but how to allocate those resources. I show that the laggard has an incentive to chose a different path from the leader. In equilibrium, this results in the laggard choosing a less promising path, in effect trading off lower expected value for lower correlation with respect to the leader. This in turn leads to increasing dominance. In order to make the point as clear as possible and differentiate it from the forces previously characterized, I assume that no joint payoff (or efficiency) effect is present.

Detection survey for grapevine rust at the irrigated areas of the São Francisco Valley, Brazil.

1 CD-ROM

Are Sunk Costs A Barrier To Entry?

The received wisdom is that sunk costs create a barrier to entry if entry fails, then the entrant, unable to recover sunk costs, incurs greater losses. In a strategic context where an incumbent may prey on the entrant, sunk entry costs have a countervailing effect: they may effectively commit the entrant to stay in the market. By providing the entrant with commitment power, sunk investments may soften the reactions of incumbents. The net effect may imply that entry is more profitable when sunk costs are greater