Synchronization of networks with variable local properties

We study the synchronization transition of Kuramoto oscillators in scale-free networks that are characterized by tunable local properties. Specifically, we perform a detailed finite size scaling analysis and inspect how the critical properties of the dynamics change when the clustering coefficient and the average shortest path length are varied. The results show that the onset of synchronization does depend on these properties, though the dependence is smooth. On the contrary, the appearance of complete synchronization is radically affected by the structure of the networks. Our study highlights the need of exploring the whole phase diagram and not only the stability of the fully synchronized state, where most studies have been done up to now.Comment: 5 pages and 3 figures. APS style. Paper to be published in IJBC (special issue on Complex Networks' Structure and Dynamics

A monopole solution from noncommutative multi-instantons

We extend the relation between instanton and monopole solutions of the selfduality equations in SU(2) gauge theory to noncommutative space-times. Using this approach and starting from a noncommutative multi-instanton solution we construct a U(2) monopole configuration which lives in 3 dimensional ordinary space. This configuration resembles the Wu-Yang monopole and satisfies the selfduality (Bogomol'nyi) equations for a U(2) Yang-Mills-Higgs system.Comment: 19 pages; title and abstract changed, brane interpretation corrected. Version to appear in JHE

Kerr-Schild type initial data for black holes with angular momenta

Generalizing previous work we propose how to superpose spinning black holes in a Kerr-Schild initial slice. This superposition satisfies several physically meaningful limits, including the close and the far ones. Further we consider the close limit of two black holes with opposite angular momenta and explicitly solve the constraint equations in this case. Evolving the resulting initial data with a linear code, we compute the radiated energy as a function of the masses and the angular momenta of the black holes.Comment: 13 pages, 3 figures. Revised version. To appear in Classical and Quantum Gravit

Exponential improvement in photon storage fidelities using subradiance and "selective radiance" in atomic arrays

A central goal within quantum optics is to realize efficient interactions between photons and atoms. A fundamental limit in nearly all applications based on such systems arises from spontaneous emission, in which photons are absorbed by atoms and then re-scattered into undesired channels. In typical treatments of atomic ensembles, it is assumed that this re-scattering occurs independently, and at a rate given by a single isolated atom, which in turn gives rise to standard limits of fidelity in applications such as quantum memories or quantum gates. However, this assumption can be violated. In particular, spontaneous emission of a collective atomic excitation can be significantly suppressed through strong interference in emission. Thus far the physics underlying the phenomenon of subradiance and techniques to exploit it have not been well-understood. In this work, we provide a comprehensive treatment of this problem. First, we show that in ordered atomic arrays in free space, subradiant states acquire an interpretation in terms of optical modes that are guided by the array, which only emit due to scattering from the ends of the finite chain. We also elucidate the properties of subradiant states in the many-excitation limit. Finally, we introduce the new concept of selective radiance. Whereas subradiant states experience a reduced coupling to all optical modes, selectively radiant states are tailored to simultaneously radiate efficiently into a desired channel while scattering into undesired channels is suppressed, thus enabling an enhanced atom-light interface. We show that these states naturally appear in chains of atoms coupled to nanophotonic structures, and we analyze the performance of photon storage exploiting such states. We find that selectively radiant states allow for a photon storage error that scales exponentially better with number of atoms than previously known bounds.Comment: Fixed minor typos, is now analogous to published versio

A case study of spin-11 Heisenberg model in a triangular lattice

We study the spin-$1$ model in a triangular lattice in presence of a uniaxial anisotropy field using a Cluster Mean-Field approach (CMF). The interplay between antiferromagnetic exchange, lattice geometry and anisotropy forces Gutzwiller mean-field approaches to fail in a certain region of the phase diagram. There, the CMF yields two supersolid (SS) phases compatible with those present in the spin-$1/2$ XXZ model onto which the spin-$1$ system maps. Between these two SS phases, the three-sublattice order is broken and the results of the CMF depend heavily on the geometry and size of the cluster. We discuss the possible presence of a spin liquid in this region.Comment: 7 pages, 4 figures, RevTeX 4. The abstract and conclusions have been modified and the manuscript has been extende

Spectrophotometry of early type stars

A photoelectric spectrum scanner attached to the 16-inch telescope of the Cerro Tololo Inter-American Observatory was used to determine the relative spectral intensity distribution for early type stars. Observations on a minimun of three nights per star have been obtained for about two hundred stars. The tracings extend from 3100 Å to 6000 Å. They were obtained with a slit width from 50 Å to 80 Å , and thus can be used also for a determination of the equivalent widths of H-beta, H-gamma, and H-delta, As a byproduct precise information on the monochromatic atmospheric extinction at Cerro Tololo is obtained. In this investigation special, emphasis was given to Be stars.Asociación Argentina de Astronomí

Spectrophotometry of early type stars

A photoelectric spectrum scanner attached to the 16-inch telescope of the Cerro Tololo Inter-American Observatory was used to determine the relative spectral intensity distribution for early type stars. Observations on a minimun of three nights per star have been obtained for about two hundred stars. The tracings extend from 3100 Å to 6000 Å. They were obtained with a slit width from 50 Å to 80 Å , and thus can be used also for a determination of the equivalent widths of H-beta, H-gamma, and H-delta, As a byproduct precise information on the monochromatic atmospheric extinction at Cerro Tololo is obtained. In this investigation special, emphasis was given to Be stars.Asociación Argentina de Astronomí

Spectrophotometry of early type stars

A photoelectric spectrum scanner attached to the 16-inch telescope of the Cerro Tololo Inter-American Observatory was used to determine the relative spectral intensity distribution for early type stars. Observations on a minimun of three nights per star have been obtained for about two hundred stars. The tracings extend from 3100 Å to 6000 Å. They were obtained with a slit width from 50 Å to 80 Å , and thus can be used also for a determination of the equivalent widths of H-beta, H-gamma, and H-delta, As a byproduct precise information on the monochromatic atmospheric extinction at Cerro Tololo is obtained. In this investigation special, emphasis was given to Be stars.Asociación Argentina de Astronomí