1,841 research outputs found
Notes on Oscillator-Like Interactions of Various Spin Relativistic Particles
The equations for various spin particles with oscillator-like interactions
are discussed in this talk. Contents: 1. Comment on "The Klein-Gordon
Oscillator"; 2. The Dirac oscillator in quaternion form; 3. The Dirac-Dowker
oscillator; 4. The Weinberg oscillator; 5. Note on the two-body Dirac
oscillator.Comment: LaTeX file, 12 pp. Talk given at the Second Workshop "Osciladores
Arm\'onicos". Cocoyoc, M\'exico, March 23-25, 1994. To be published in NASA
Conference Proceedings. Preprint IFUNAM FT-94-44, EFUAZ-94-0
Interactions of Galaxies: Systems with Tidal Bridges
In this work we present a sample of elliptical interacting galaxy pairs connected by a bridge, obtained from a visual classification of a pair catalogue dereived from the data of the 7th Sloan Digital Sky Survey (SDSS-DR7). We present preliminary results of the general characteristics of galaxies in these systems, such as star formation rate, age of the stellar populations, concentration indices, colours and environment local density.www.iafe.uba.ar/AstroNum/html/workshop2014publishedVersionAstronomía (incluye Astrofísica y Ciencias del Espacio
Cálculo de constantes ópticas de películas delgadas de Cu3BiS3 a través del método de Wolfe
Se calculó la obtención de las constantes ópticas usando el método de Wolfe. Dichas contantes: coeficiente de absorción (α), índice de refracción (n) y espesor de una película delgada (d ), son de importancia en el proceso de caracterización óptica del material. Se realizó una comparación del método del Wolfe con el método empleado por R. Swanepoel. Se desarrolló un modelo de programación no lineal con restricciones, de manera que fue posible estimar las constantes ópticas de películas delgadas semiconductoras, a partir únicamente, de datos de transmisión conocidos. Se presentó una solución al modelo de programación no lineal para programación cuadrática. Se demostró la confiabilidad del método propuesto, obteniendo valores de α = 10378.34 cm−1, n = 2.4595, d =989.71 nm y Eg = 1.39 Ev, a través de experimentos numéricos con datos de medidas de transmitancia espectral en películas delgadas de Cu3BiS3.Using the Wolfe method, we calculated the procurement of optical constants. These constants, absorption coefficient (α), refraction index of (n) and thin film thickness (d ), are significant in the optical characterization of the material. We compared the Wolfe method with the method employed by R. Swanepoel. To estimate theoptical constants of semiconductor thin films, we developed a constrained nonlinear programming model, based solely, on known transmission data. Ultimately, we presented a solution to this nonlinear programming model for quadratic programming. Through numerical experiments and transmittance spectral data of Cu3BiS3 thin films, we obtained values of a= 10378.34 cm−1, n = 2.4595, d =989.71 nm and Eg= 1.39 Ev, demonstrating the reliability of the proposed method
Momentum distribution in heavy deformed nuclei: role of effective mass
The impact of nuclear deformation on the momentum distributions (MD) of
occupied proton states in U is studied with a phenomenological
Woods-Saxon (WS) shell model and the self-consistent Skyrme-Hartree-Fock (SHF)
scheme. Four Skyrme parameterizations (SkT6, SkM*, SLy6, SkI3) with different
effective masses are used. The calculations reveal significant deformation
effects in the low-momentum domain of states, mainly of
those lying near the Fermi surface. For other states, the deformation effect on
MD is rather small and may be neglected. The most remarkable result is that the
very different Skyrme parameterizations and the WS potential give about
identical MD. This means that the value of effective mass, being crucial for
the description of the spectra, is not important for the spatial shape of the
wave functions and thus for the MD. In general, it seems that, for the
description of MD at MeV/c, one may use any single-particle
scheme (phenomenological or self-consistent) fitted properly to the global
ground state properties.Comment: 14 pages, 6 figure
Rubidium and zirconium abundances in massive Galactic asymptotic giant branch stars revisited
Luminous Galactic OH/IR stars have been identified as massive (>4-5 M_s) AGB
stars experiencing HBB and Li production. Their Rb abundances and [Rb/Zr]
ratios derived from hydrostatic model atmospheres, are significantly higher
than predictions from AGB nucleosynthesis models, posing a problem to our
understanding of AGB evolution and nucleosynthesis. We report new Rb and Zr
abundances in the full sample of massive Galactic AGB stars, previously studied
with hydrostatic models, by using more realistic extended model atmospheres. We
use a modified version of the spectral synthesis code Turbospectrum and
consider the presence of a circumstellar envelope and radial wind. The Rb and
Zr abundances are determined from the 7800 A Rb I resonant line and the 6474 A
ZrO bandhead, respectively, and we explore the sensitivity of the derived
abundances to variations of the stellar (Teff) and wind (M_loss, beta and vexp)
parameters in the extended models. The Rb and Zr abundances derived from the
best spectral fits are compared with the most recent AGB nucleosynthesis
theoretical models. The new Rb abundances are much lower (even 1-2 dex) than
those derived with the hydrostatic models, while the Zr abundances are similar.
The Rb I line profile and Rb abundance are very sensitive to the M_loss rate
but much less sensitive to variations of the wind velocity-law and the
vexp(OH). We confirm the earlier preliminary results based on a smaller sample
of massive O-rich AGB stars, that the use of extended atmosphere models can
solve the discrepancy between the AGB nucleosynthesis theoretical models and
the observations of Galactic massive AGB stars. The Rb abundances, however, are
still strongly dependent of the M_loss, which is unknown in these AGB stars.
Accurate M_loss rates in these massive Galactic AGB stars are needed in order
to break the models degeneracy and get reliable Rb abundances in these stars.Comment: Accepted for publication in A&A, 14 pages, 12 figures, 4 table
Teacher Questioning in Problem Solving in Community College Algebra Classrooms
In this chapter, we focus on the ways two community college instructors worked with students to demonstrate the solution of contextualized algebra problems in their college algebra lessons. We use two classroom episodes to illustrate how they sought to elicit students' mathematical ideas of algebraic topics, attending primarily to teachers' questioning approaches. We found that the instructors mostly asked questions of lower cognitive demand and used a variety of approaches to elicit the mathematical ideas of the problems, such as using examples relevant to the students and dividing the problems into smaller tasks, that together help identify a solution. We conclude by offering considerations for instruction at community colleges and potential areas for professional development
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