53053895
Cluster Transformations from Bipartite Field Theories
Bipartite field theories (BFTs) are a new class of 4D N=1 quantum field theories defined by bipartite graphs on bordered Riemann surfaces. In this paper we derive, purely in terms of the gauge theory, the cluster transformations of face weights under square moves in the graph. In this context, we obtain them by connecting regular parametrizations of the master space of the associated BFTs. For BFTs on a disk, these transformations follow from the properties of coordinates in the Grassmannian. This represents a new addition to the list of combinatorial objects for the Grassmannian, such as matching and matroid polytopes, that have been shown to emerge from BFT dynamics.
119211259
Interstellar reddening towards six small areas in Puppis-Vela ,
Context. The line-of-sight towards Puppis-Vela contains some of the most interesting and elusive objects in the solar neighbourhood, including the Gum nebula, the IRAS Vela shell, the Vela SNR, and dozens of cometary globules. Aims. We investigate the distribution of the interstellar dust towards six small volumes of the sky in the region of the Gum nebula. Methods. New high-quality four-colour uvby and H! Stromgren photometry obtained for 352 stars in six selected areas of Kapteyn and complemented with data obtained in a previous investigation for two of these areas, were used to estimate the colour excess and distance to these objects. The obtained colour excess versus distance diagrams, complemented with other information, when available, were analysed in order to infer the properties of the interstellar medium permeating the observed volumes. Results. On the basis of the overall standard deviation in the photometric measurements, we estimate that colour excesses and distances are determined with an accuracy of 0. 010 and better than 30%, respectively, for a sample of 520 stars. A comparison with 37 stars in common with the new Hipparcos catalogue attests to the high quality of the photometric distance determination. The obtained colour excess versus distance diagrams testify to the low density volume towards the observed lines-of-sight. Very few stars out to distances of 1kpc from the Sun have colour excesses larger than E(b " y) = 0. m 1. Conclusions. In spite of the low density character of the interstellarmedium towards the Puppis-Vela direction, the obtained reddening as a function of the distance indicates that two or more interstellar structures are crossed towards the observed lines-of-sight. One of these structures may be associated with the very low density “wall” of the Local Cavity, which has a distance of 100" 150 pc from the Sun. Another structure might be related to the Gum nebula, and if so, its front face would be located at # 350pc from the Sun.
15710229
LNLS CONTROL SYSTEM
The control system of the LNLS Synchrotron Light Source facility is presented. The system is composed of a number of local controllers based on the Zilog Z80 CPU, which are connected through a 2 Mbps serial line (running an in-house developed communication protocol) to concentrators which provide the interface to microcomputers, which are responsible for the high level user interface. The high level software is developed using object-oriented techniques and visual design tools, whereas the low level software is mostly assembly language.
119213994
DETAILED INTERSTELLAR POLARIMETRIC PROPERTIES OF THE PIPE NEBULA AT CORE SCALES
We use R-band CCD linear polarimetry collected for about 12,000 background field stars in 46 fields of view toward the Pipe nebula to investigate the properties of the polarization across this dark cloud. Based on archival Two Micron All Sky Survey data, we estimate that the surveyed areas present total visual extinctions in the range 0.6 mag ? AV ? 4.6 mag. While the observed polarizations show a well-ordered large-scale pattern, with polarization vectors almost perpendicularly aligned to the cloud's long axis, at core scales one sees details that are characteristics of each core. Although many observed stars present degrees of polarization that are unusual for the common interstellar medium (ISM), our analysis suggests that the dust grains constituting the diffuse parts of the Pipe nebula seem to have the same properties as the normal Galactic ISM. Estimates of the second-order structure function of the polarization angles suggest that most of the Pipe nebula is magnetically dominated and that turbulence is sub-Alv?nic. The Pipe nebula is certainly an interesting region to investigate the processes that prevailed during the initial phases of low-mass stellar formation.
122778951
Commissioning and operation of the Brazilian Synchrotron Light Source
The Brazilian National Synchrotron Light Laboratory, LNLS, operates a 1.37 GeV electron storage ring with a 120 MeV injector linac. Commissioning of the storage ring at low energy started on May 1996 and now, an year later, we can store 120 mA at 120 MeV and ramp more than 75 mA to 1.37 GeV. A summary of the latest commissioning results and a description of the present operational performance of the LNLS Synchrotron Light Source facility is presented.
118676748
Particle acceleration and magnetic field structure in PKS 2155−304: optical polarimetric observations
In this paper, we present multiband optical polarimetric observations of the very-high energy blazar PKS 2155-304 made simultaneously with a HESS/Fermi high-energy campaign in 2008, when the source was found to be in a low state. The intense daily coverage of the data set allowed us to study in detail the temporal evolution of the emission, and we found that the particle acceleration time-scales are decoupled from the changes in the polarimetric properties of the source. We present a model in which the optical polarimetric emission originates at the polarized mm-wave core and propose an explanation for the lack of correlation between the photometric and polarimetric fluxes. The optical emission is consistent with an inhomogeneous synchrotron source in which the large-scale field is locally organized by a shock in which particle acceleration takes place. Finally, we use these optical polarimetric observations of PKS 2155-304 at a low state to propose an origin for the quiescent gamma-ray flux of the object, in an attempt to provide clues for the source of its recently established persistent TeV emission.
14023047
Metastable vacua and D-branes at the conifold
We consider quiver gauge theories arising on D-branes at simple Calabi-Yau singularities (quotients of the conifold). These theories have metastable supersymmetry breaking vacua. The field theoretic mechanism is basically the one exhibited by the examples of Intriligator, Seiberg and Shih in SUSY QCD. In a dual description, the SUSY breaking is captured by the presence of anti-branes. In comparison to our earlier related work, the main improvements of the present construction are that we can reach the free magnetic range of the SUSY QCD theory where the existence of the metastable vacua is on firm footing, and we can see explicitly how the small masses for the quark flavors (necessary to the existence of the SUSY breaking vacua) are dynamically stabilized. One crucial mass term is generated by a stringy instanton. Finally, our models naturally incorporate R-symmetry breaking in the non-supersymmetric vacuum, in a way similar to the examples of Kitano, Ooguri and Ookouchi.