15,783 research outputs found
A Quantum Quasi-Harmonic Nonlinear Oscillator with an Isotonic Term
The properties of a nonlinear oscillator with an additional term ,
characterizing the isotonic oscillator, are studied. The nonlinearity affects
to both the kinetic term and the potential and combines two nonlinearities
associated to two parameters, and , in such a way that for
all the characteristics of of the standard isotonic system are
recovered. The first part is devoted to the classical system and the second
part to the quantum system. This is a problem of quantization of a system with
position-dependent mass of the form , with a
-dependent non-polynomial rational potential and with an additional
isotonic term. The Schr\"odinger equation is exactly solved and the
-dependent wave functions and bound state energies are explicitly
obtained for both .Comment: two figure
Constraining the Accretion Geometry of the Intermediate Polar EX Hya Using NuSTAR, Swift, and Chandra Observations
In magnetically accreting white dwarfs, the height above the white dwarf surface where the standing shock is formed is intimately related with the accretion rate and the white dwarf mass. However, it is difficult to measure. We obtained new data with NuSTAR and Swift that, together with archival Chandra data, allow us to constrain the height of the shock in the intermediate polar EX Hya. We conclude that the shock has to form at least at a distance of about one white dwarf radius from the surface in order to explain the weak Fe Kα 6.4 keV line, the absence of a reflection hump in the high-energy continuum, and the energy dependence of the white dwarf spin pulsed fraction. Additionally, the NuSTAR data allowed us to measure the true, uncontaminated hard X-ray (12-40 keV) flux, whose measurement was contaminated by the nearby galaxy cluster Abell 3528 in non-imaging X-ray instruments.Fil: Luna, Gerardo Juan Manuel. Consejo Nacional de Investigaciónes CientÃficas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de AstronomÃa y FÃsica del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de AstronomÃa y FÃsica del Espacio; ArgentinaFil: Mukai, K.. National Aeronautics and Space Administration; Estados UnidosFil: Orio, M.. Università di Padova; ItaliaFil: Zemko, P.. Università di Padova; Itali
Nonlinear Stochastic Resonance with subthreshold rectangular pulses
We analyze the phenomenon of nonlinear stochastic resonance (SR) in noisy
bistable systems driven by pulsed time periodic forces. The driving force
contains, within each period, two pulses of equal constant amplitude and
duration but opposite signs. Each pulse starts every half-period and its
duration is varied. For subthreshold amplitudes, we study the dependence of the
output signal-to-noise ratio (SNR) and the SR gain on the noise strength and
the relative duration of the pulses. We find that the SR gains can reach values
larger than unity, with maximum values showing a nonmonotonic dependence on the
duration of the pulses.Comment: 7 pages, 2 figure
Shear viscosity of a superfluid Fermi gas in the unitarity limit
We compute the shear viscosity of a superfluid atomic Fermi gas in the
unitarity limit. The unitarity limit is characterized by a divergent scattering
length between the atoms, and it has been argued that this will result in a
very small viscosity. We show that in the low temperature T limit the shear
viscosity scales as xi^5/T^5, where the universal parameter 'xi' relates the
chemical potential and the Fermi energy, mu=xi E_F. Combined with the high
temperature expansions of the viscosity our results suggest that the viscosity
has a minimum near the critical temperature T_c. A naive extrapolation
indicates that the minimum value of the ratio of viscosity over entropy density
is within a factor of ~ 5 of the proposed lower bound hbar/(4\pi k_B).Comment: 9 pages, 7 figures, LaTeX2
DICHOTOMY OF INTRINSIC MOTIVATION IN OMANI ESL CLASSROOM
Getting something done is always about motivation. Generally, teaching English language to non native speakers takes so much of effort considering the diverse factors that shape the educative process. In a pedagogical vantage point though, success in ESL teaching may be possible through learners' own initiative or motivation. Motivation is viewed as the main factor affecting directly or indirectly English language learning and teaching (Gardner, 1985). This study ventured on the types of motivation of the foundation students of the Ministry of Health Nursing Institute in Oman. A modified and enhanced survey instrument from Gardner's Motivation and Attitude Test Battery instrumented the research flow which was augmented by triangulation method for reliable analysis. Findings reveal that students have closely inter-related reasons for learning English which fall in two major categories: such as “instrumental" and "integrative". Findings also show that students are generally "highly" motivated and slightly "instrumentally" motivated to study English in the institute. Hence, legitimate improvement strategies and co curricular tasks are recommended to be reinforced either to sustain or redirect the existing motivations. Article visualizations
Colourings of lattices and coincidence site lattices
The relationship between the coincidence indices of a lattice and
a sublattice of is examined via the colouring of
that is obtained by assigning a unique colour to each coset of
. In addition, the idea of colour symmetry, originally defined for
symmetries of lattices, is extended to coincidence isometries of lattices. An
example involving the Ammann-Beenker tiling is provided to illustrate the
results in the quasicrystal setting.Comment: 9 pages, 6 figure
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