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A study was conducted to analyze the factorial structure and measurement invariance of the Curriculum-Based Measurement (CBM) Indicadores de Progreso de Aprendizaje en Matemáticas (IPAM [Indicators of Basic Early Math Skills]), in 2.sup.nd grade Spanish students. The model proposed is a one-factor model in which the five IPAM tasks (i.e., number comparison, missing number, single-digit computation, multi-digit computation, and place value) serve as observable indicators for a single underlying factor (i.e., number sense). The IPAM, composed of three parallel forms (i.e., A, B, and C), was administered to 252 Spanish second graders, three times throughout the school year (i.e., fall, winter, and spring). Consequently, the goodness of fit of the proposed model was analyzed for each measurement time. Furthermore, longitudinal measurement invariance was explored to analyze whether the measurement model would remain stable throughout the three-time points of measurement. Discriminant, predictive, and concurrent validity were also tested. The results support that the number sense latent factor explains the common variance of the observable indicators throughout the school year. Each latent factor was found highly related to the next. Moreover, the IPAM showed adequate indices for discriminant, concurrent and predictive validity. We conclude that the IPAM is an appropriate measure to assess number sense competence in second grade., Author(s): Sara C. de León [sup.1] , Juan E. Jiménez [sup.1] , Juan A. Hernández-Cabrera [sup.1] Author Affiliations: (1) grid.10041.34, 0000000121060879, Faculty of Psychology, Universidad de La Laguna, , Campus [...]

SS 433 is a binary system containing a supergiant star that is overflowing its Roche lobe with matter accreting onto a compact object (either a black hole or neutron star).sup.1-3. Two jets of ionized matter with a bulk velocity of approximately 0.26c (where c is the speed of light in vacuum) extend from the binary, perpendicular to the line of sight, and terminate inside W50, a supernova remnant that is being distorted by the jets.sup.2,4-8. SS 433 differs from other microquasars (small-scale versions of quasars that are present within our own Galaxy) in that the accretion is believed to be super-Eddington.sup.9-11, and the luminosity of the system is about 10.sup.40 ergs per second.sup.2,9,12,13. The lobes of W50 in which the jets terminate, about 40 parsecs from the central source, are expected to accelerate charged particles, and indeed radio and X-ray emission consistent with electron synchrotron emission in a magnetic field have been observed.sup.14-16. At higher energies (greater than 100 gigaelectronvolts), the particle fluxes of [gamma]-rays from X-ray hotspots around SS 433 have been reported as flux upper limits.sup.6,17-20. In this energy regime, it has been unclear whether the emission is dominated by electrons that are interacting with photons from the cosmic microwave background through inverse-Compton scattering or by protons that are interacting with the ambient gas. Here we report teraelectronvolt [gamma]-ray observations of the SS 433/W50 system that spatially resolve the lobes. The teraelectronvolt emission is localized to structures in the lobes, far from the centre of the system where the jets are formed. We have measured photon energies of at least 25 teraelectronvolts, and these are certainly not Doppler-boosted, because of the viewing geometry. We conclude that the emission--from radio to teraelectronvolt energies--is consistent with a single population of electrons with energies extending to at least hundreds of teraelectronvolts in a magnetic field of about 16 microgauss. Observations of teraelectronvolt [gamma]-rays accelerated by the jets of the miniature quasar SS 433 are reported., Author(s): A. U. Abeysekara [sup.1] , A. Albert [sup.2] , R. Alfaro [sup.3] , C. Alvarez [sup.4] , J. D. Álvarez [sup.5] , R. Arceo [sup.4] , J. C. Arteaga-Velázquez [...]

In this Letter, owing to a production error, the penultimate version of the PDF was published. The HTML version was always correct. The PDF has been corrected online., Author(s): A. U. Abeysekara [sup.1] , A. Albert [sup.2] , R. Alfaro [sup.3] , C. Alvarez [sup.4] , J. D. Álvarez [sup.5] , R. Arceo [sup.4] , J. C. Arteaga-Velázquez [...]