University of Los Andes

About: University of Los Andes is a education organization based out in Bogotá, Colombia. It is known for research contribution in the topics: Population & Large Hadron Collider. The organization has 17616 authors who have published 25555 publications receiving 413463 citations.

Herbig Ae/Be Stars in nearby OB Associations

Abstract: We have carried out a study of the early-type stars in nearby OB associations spanning an age range of ~3–16 Myr, with the aim of determining the fraction of stars that belong to the Herbig Ae/Be class. We studied the B, A, and F stars in the nearby (≤500 pc) OB associations Upper Scorpius, Perseus OB2, Lacerta OB1, and Orion OB1, with membership determined from Hipparcos data. We also included in our study the early-type stars in the Trumpler 37 cluster, part of the Cep OB2 association. We obtained spectra for 440 Hipparcos stars in these associations, from which we determined accurate spectral types, visual extinctions, effective temperatures, luminosities and masses, using Hipparcos photometry. Using colors corrected for reddening, we find that the Herbig Ae/Be stars and the classical Be (CBe) stars occupy clearly different regions in the JHK diagram. Thus, we use the location on the JHK diagram, as well as the presence of emission lines and of strong 12 μm flux relative to the visual, to identify the Herbig Ae/Be stars in the associations. We find that the Herbig Ae/Be stars constitute a small fraction of the early-type stellar population even in the younger associations. Comparing the data from associations with different ages and assuming that the near-infrared excess in the Herbig Ae/Be stars arises from optically thick dusty inner disks, we determined the evolution of the inner disk frequency with age. We find that the inner disk frequency in the age range 3–10 Myr in intermediate-mass stars is lower than that in the low-mass stars (<1 M⊙); in particular, it is a factor of ~10 lower at ~3 Myr. This indicates that the timescales for disk evolution are much shorter in the intermediate-mass stars, which could be a consequence of more efficient mechanisms of inner disk dispersal (viscous evolution, dust growth, and settling toward the midplane).

International relations scholarship around the world

Abstract: 1. Introduction: Geocultural Epistemologies Arlene B. Tickner and Ole Waever 2. Latin America: Still Policy Dependant after all these Years? Arlene B. Tickner 3. South Africa: Between History and a Hard Place Maxi Schoeman 4. Africa: Teaching IR Where its Not Supposed to Be Cirino Hiteng Ofuho 5. Japan, Korea and Taiwan: Are One Hundred Flowers about to Bloom? Takashi Inoguchi 6. China: Between Copying and Constructing Yiwei Wang 7. Southeast Asia: Theory and Praxis in International Relations See Seng Tan 8. South Asia: A "Realist" Past and Alternative Futures Navnita Chadha Behera 9. Iran: Accomplishments and Limitations in IR Mahmood Sariolghalam 10. Arab World Baghat Korany and Karim Makidisi 11. Israel: The Development of a Discipline in a Unique Setting Arie M. Kacowicz 12. Turkey: Towards Homebrown Theorizing and Building a Disciplinary Community Ersel Aydinli and Julie Mathews 13. Russia: IR at a Cross-Road Alexander Sergounin 14. Central and Eastern Europe: Between Continuity and Change Petr Drulak, Jans Karlas and Lucie Konigova 15. Western Europe: Structure and Strategy at the National and Regional Levels Jorg Freidrichs and Ole Waever 16. The "Crimson World": The Anglo Core, the Post-Imperial Non-Core, and the Hegemony of American IR Wayne S. Cox and Kim Richard Nossal 17. The Parochialism of Hegemony: Challenges for "American" International Relations Tom J. Biersteker 18. Conclusion: Worlding Where the West Once Was Arlene B. Tickner and Ole Waever

Suppression of non-prompt J/ψ, prompt J/ψ, and Y(1S) in PbPb collisions at √s NN = 2.76 TeV

Abstract: Yields of prompt and non-prompt J/psi, as well as Y(1S) mesons, are measured by the CMS experiment via their dimuon decays in PbPb and pp collisions at sqrt(sNN) = 2.76 TeV for quarkonium rapidity |y|<2.4. Differential cross sections and nuclear modification factors are reported as functions of y and transverse momentum pt, as well as collision centrality. For prompt J/psi with relatively high pt (6.5

The QUEST RR Lyrae Survey: Confirmation of the Clump at 50 Kiloparsecs and Other Overdensities in the Outer Halo

Abstract: We have measured the periods and light curves of 148 RR Lyrae variables from V = 13.5 to 19.7 from the first 100 deg2 of the Quasar Equatorial Survey Team RR Lyrae survey. Approximately 55% of these stars belong to the clump of stars detected earlier by the Sloan Digital Sky Survey. According to our measurements, this feature has ~10 times the background density of halo stars, spans at least 375 by 35 in α and δ (≥30 by ≥3 kpc), lies ~50 kpc from the Sun, and has a depth along the line of sight of ~5 kpc (1 σ). These properties are consistent with the recent models that suggest that it is a tidal stream from the Sagittarius dwarf spheroidal galaxy. The mean period of the type ab variables, 0.58 days, is also consistent. In addition, we have found two smaller overdensities in the halo, one of which may be related to the globular cluster Pal 5.

Search for invisible decays of Higgs bosons in the vector boson fusion and associated ZH production modes

Abstract: A search for invisible decays of Higgs bosons is performed using the vector boson fusion and associated ZH production modes. In the ZH mode, the Z boson is required to decay to a pair of charged leptons or a $b\bar{b}$ quark pair. The searches use the 8 TeV pp collision dataset collected by the CMS detector at the LHC, corresponding to an integrated luminosity of up to 19.7 inverse femtobarns. Certain channels include data from 7 TeV collisions corresponding to an integrated luminosity of 4.9 inverse femtobarns. The searches are sensitive to non-standard-model invisible decays of the recently observed Higgs boson, as well as additional Higgs bosons with similar production modes and large invisible branching fractions. In all channels, the observed data are consistent with the expected standard model backgrounds. Limits are set on the production cross section times invisible branching fraction, as a function of the Higgs boson mass, for the vector boson fusion and ZH production modes. By combining all channels, and assuming standard model Higgs boson cross sections and acceptances, the observed (expected) upper limit on the invisible branching fraction at $m_H$=125 GeV is found to be 0.58 (0.44) at 95% confidence level. We interpret this limit in terms of a Higgs-portal model of dark matter interactions.