28,904 research outputs found
Effects of a mixed vector-scalar kink-like potential for spinless particles in two-dimensional spacetime
The intrinsically relativistic problem of spinless particles subject to a
general mixing of vector and scalar kink-like potentials () is investigated. The problem is mapped into the exactly solvable
Surm-Liouville problem with the Rosen-Morse potential and exact bounded
solutions for particles and antiparticles are found. The behaviour of the
spectrum is discussed in some detail. An apparent paradox concerning the
uncertainty principle is solved by recurring to the concept of effective
Compton wavelength.Comment: 13 pages, 4 figure
Assessing the Impact of Computer Programming in Understanding Limits and Derivatives in a Secondary Mathematics Classroom
This study explored the development of student’s conceptual understanding of limit and derivative when specific computational tools were utilized. Fourteen students from a secondary Advanced Placement Calculus AB course explored the limit and derivative concepts from calculus using computational tools in the Maple computer algebra system. Students worked in pairs utilizing the pair-programming collaborative model. Four groups of student pairs constructed computational tools and used them to explore the limit and derivative concepts. The remaining four student pairs were provided similar tools and asked to perform identical explorations.
A multiple embedded case design was utilized to explore ways students in two classes, a programming class P and a non-programming class N, constructed understandings focusing upon their interactions with each other and with the computational tools. The Action-Process-Object-Schema (APOS) conceptual model and Constructionist framework guided design and construction of the tools, outlined developmental goals and milestones, and provided interpretive context for analysis.
Results provided insights into the effective design and use of computational tools in fostering conceptual understanding. The study found the additional burden of programming redirected students’ attention away from the intended conceptual understandings. The study additionally found, however, that pre-constructed tools effectively promote conceptual understanding of the limit concept when coupled with a mature conceptual model of development. Four themes influencing development of these understandings emerged: An instructional focus on skills over concepts, the instructional sequence, the willingness and ability of students to adopt and utilize computational tools, and the ways cognitive conflict was mediated
Spin and Pseudospin symmetries in the Dirac equation with central Coulomb potentials
We analyze in detail the analytical solutions of the Dirac equation with
scalar S and vector V Coulomb radial potentials near the limit of spin and
pseudospin symmetries, i.e., when those potentials have the same magnitude and
either the same sign or opposite signs, respectively. By performing an
expansion of the relevant coefficients we also assess the perturbative nature
of both symmetries and their relations the (pseudo)spin-orbit coupling. The
former analysis is made for both positive and negative energy solutions and we
reproduce the relations between spin and pseudospin symmetries found before for
nuclear mean-field potentials. We discuss the node structure of the radial
functions and the quantum numbers of the solutions when there is spin or
pseudospin symmetry, which we find to be similar to the well-known solutions of
hydrogenic atoms.Comment: 9 pages, 2 figures, uses revte
The influence of statistical properties of Fourier coefficients on random surfaces
Many examples of natural systems can be described by random Gaussian
surfaces. Much can be learned by analyzing the Fourier expansion of the
surfaces, from which it is possible to determine the corresponding Hurst
exponent and consequently establish the presence of scale invariance. We show
that this symmetry is not affected by the distribution of the modulus of the
Fourier coefficients. Furthermore, we investigate the role of the Fourier
phases of random surfaces. In particular, we show how the surface is affected
by a non-uniform distribution of phases
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