New records of biting midges of the genus Culicoides Latreille from Mexico (Diptera: Ceratopogonidae)

We provide the first records of six species of biting midges (Diptera: Ceratopogonidae) in the genus Culicoides Latreille from Mexico: C. baueri Hoffman, C. castillae Fox, C. debilipalpis Lutz, C. iriartei Fox, C. leoni Barbosa and C. pusilloides Wirth and Blanton. In addition, C. leopoldoi Ortiz is confirmed from Mexico, and new records are included for 25 other species previously recorded in Mexico: C. arubae Fox and Hoffman, C. blantoni Vargas and Wirth, C. crepuscularis Malloch, C. daedalus Macfie, C. diabolicus Hoffman, C. foxi Ortiz, C. furens (Poey), C. gabaldoni Ortiz, C. haematopotus Malloch, C. hylas Macfie, C. insignis Lutz, C. jamaicensis Edwards, C. luteovenus Root and Hoffman, C. neopulicaris Wirth, C. nigrigenus Wirth and Blanton, C. pampoikilus Macfie, C. panamensis Barbosa, C. paraensis (Goeldi), C. phlebotomus (Williston), C. poikilonotus Macfie, C. pusillus Lutz, C. stigmalis Wirth, and all three species in the C. (Monoculicoides) variipennis complex, C. variipennis (Coquillett), C. occidentalis Wirth and Jones, and C. sonorensis Wirth and Jones

X-ray photoelectron spectroscopy studies of non-stoichiometric superconducting NbB2+x

Polycrystalline samples of NbB2+x with nominal composition (B/Nb) = 2.0, 2.1, 2.2, 2.3, 2.4 and 2.5 were studied by X-ray photoelectron spectroscopy (XPS). The spectra revealed Nb and B oxides on the surface of the samples, mainly B2O3 and Nb2O5. After Ar ion etching the intensity of Nb and B oxides decreased. The Nb 3d5/2 and B 1s core levels associated with the chemical states (B/Nb) were identified and they do not change with etching time. The Binding Energy of the Nb 3d5/2 and B 1s core levels increase as boron content increases, suggesting a positive chemical shift in the core levels. On the other hand, analysis of Valence Band spectra showed that the contribution of the Nb 4d states slightly decreased while the contribution of the B 2p(pi) states increased as the boron content increased. As a consequence, the electronic and superconducting properties were substantially modified, in good agreement with band-structure calculations.Comment: 10 pages, 7 figures, 1 tabl

A Young Planet Search in Visible and IR Light: DN Tau, V836 Tau, and V827 Tau

In searches for low-mass companions to late-type stars, correlation between radial velocity variations and line bisector slope changes indicates contamination by large starspots. Two young stars demonstrate that this test is not sufficient to rule out starspots as a cause of radial velocity variations. As part of our survey for substellar companions to T Tauri stars, we identified the ~2 Myr old planet host candidates DN Tau and V836 Tau. In both cases, visible light radial velocity modulation appears periodic and is uncorrelated with line bisector span variations, suggesting close companions of several M_Jup in these systems. However, high-resolution, infrared spectroscopy shows that starspots cause the radial velocity variations. We also report unambiguous results for V827 Tau, identified as a spotted star on the basis of both visible light and infrared spectroscopy. Our results suggest that infrared follow up observations are critical for determining the source of radial velocity modulation in young, spotted stars.Comment: Accepted for publication in the Astrophysical Journal Letter

Influencia del contexto en el uso e interpretación de medidas de centralización afectadas por valores atípicos

En esta investigación estamos interesados en analizar hasta qué punto el uso e interpretación de las medidas de centralización están influidas por el contexto en el que se formulan los datos y si la presencia de valores atípicos entre ellos influye en la elección del mejor representante del conjunto de datos proporcionados. Se analizan las respuestas de los estudiantes a un cuestionario de problemas desde el punto de vista de su dificultad y de la influencia que tienen el contexto y los valores atípicos sobre su resolución

A priori mixing of mesons and the |Delta I|=1/2 rule in K\to\pi\pi

We consider the hypothesis of a priori mixings in the mass eigenstates of mesons to obtain the |Delta I|=1/2 rule in K\to\pi\pi. The Hamiltonian responsible for the transition is the strong interacting one. The experimental data are described using the isospin symmetry relations between the strong coupling constants

Condensation in an Economic Model with Brand Competition

We present a linear agent based model on brand competition. Each agent belongs to one of the two brands and interacts with its nearest neighbors. In the process the agent can decide to change to the other brand if the move is beneficial. The numerical simulations show that the systems always condenses into a state when all agents belong to a single brand. We study the condensation times for different parameters of the model and the influence of different mechanisms to avoid condensation, like anti monopoly rules and brand fidelity.Comment: Accepted in: International Journal of Modern Physics

Wilson Cycles, Tectonic Inheritance, and Rifting of the North American Gulf of Mexico Continental Margin

The tectonic evolution of the North American Gulf of Mexico continental margin is characterized by two Wilson cycles, i.e., repeated episodes of opening and closing of ocean basins along the same structural trend. This evolution includes (1) the Precambrian Grenville orogeny; (2) formation of a rift-transform margin during late Precambrian opening of the Iapetus Ocean; (3) the late Paleozoic Ouachita orogeny during assembly of Pangea; and (4) Mesozoic rifting during opening of the Gulf of Mexico. Unlike the Atlantic margins, where Wilson cycles were first recognized, breakup in the Gulf of Mexico did not initially focus within the orogen, but was instead accommodated within a diffuse region adjacent to the orogen. This variation in location of rifting is a consequence of variations in the prerift architecture of the orogens. The Appalachian-Caledonian orogeny involved substantial crustal shortening and formation of a thick crustal root. In contrast, the Ouachita orogeny resulted in minimal crustal shortening and thickening. In addition, rather than a crustal root, the Ouachita orogen was underlain by the lower plate of a relatively pristine Paleozoic subduction system that is characterized by a shallow mantle. A finite element model simulating extension on the margin demonstrates that this preexisting structure exerted fundamental controls on the style of Mesozoic rifting. The shallow mantle created a strong lithosphere beneath the orogen, causing extension to initiate adjacent to, rather than within, the orogen. On the Atlantic margins, the thick crustal root resulted in a weak lithosphere and initiation of extension within the interior of the orogen. Major features of the modern Gulf of Mexico margin, including the Interior Salt Basin, outboard unextended Wiggins arch, and an unusually broad region of extension beneath the coastal plain and continental shelf, are direct consequences of the prerift structure of the margin