264 research outputs found
Analytical Treatment of the Oscillating Yukawa Potential
Using a suitable Laguerre basis set that ensures a tridiagonal matrix
representation of the reference Hamiltonian, we were able to evaluate in closed
form the matrix elements of the generalized Yukawa potential with complex
screening parameter. This enabled us to treat analytically both the cosine and
sine-like Yukawa potentials on equal footing and compute their bound states
spectrum as the eigenvalues of the associated analytical matrix representing
their Hamiltonians. Finally we used a carefully designed complex scaling method
to evaluate the resonance energies and compared our results satisfactorily with
those obtained in the literature.Comment: 8 pages 2 table
Singular Short Range Potentials in the J-Matrix Approach
We use the tools of the J-matrix method to evaluate the S-matrix and then
deduce the bound and resonance states energies for singular screened Coulomb
potentials, both analytic and piecewise differentiable. The J-matrix approach
allows us to absorb the 1/r singularity of the potential in the reference
Hamiltonian, which is then handled analytically. The calculation is performed
using an infinite square integrable basis that supports a tridiagonal matrix
representation for the reference Hamiltonian. The remaining part of the
potential, which is bound and regular everywhere, is treated by an efficient
numerical scheme in a suitable basis using Gauss quadrature approximation. To
exhibit the power of our approach we have considered the most delicate region
close to the bound-unbound transition and compared our results favorably with
available numerical data.Comment: 14 pages, 5 tables, 2 figure
Reaction mechanisms in the 6Li+59Co system
The reactions induced by the weakly bound 6Li projectile interacting with the
intermediate mass target 59Co were investigated. Light charged particles
singles and - coincidence measurements were performed at the near
barrier energies E_lab = 17.4, 21.5, 25.5 and 29.6 MeV. The main contributions
of the different competing mechanisms are discussed. A statistical model
analysis, Continuum-Discretized Coupled-Channels calculations and two-body
kinematics were used as tools to provide information to disentangle the main
components of these mechanisms. A significant contribution of the direct
breakup was observed through the difference between the experimental sequential
breakup cross section and the CDCC prediction for the non-capture breakup cross
section.Comment: 30 pages, 8 figure
Inferring learning from big data:The importance of a transdisciplinary and multidimensional approach
The use of big data in higher education has evolved rapidly with a focus on the practical application of new tools and methods for supporting learning. In this paper, we depart from the core emphasis on application and delve into a mostly neglected aspect of the big data conversation in higher education. Drawing on developments in cognate disciplines, we analyse the inherent difficulties in inferring the complex phenomenon that is learning from big datasets. This forms the basis of a discussion about the possibilities for systematic collaboration across different paradigms and disciplinary backgrounds in interpreting big data for enhancing learning. The aim of this paper is to provide the foundation for a research agenda, where differing conceptualisations of learning become a strength in interpreting patterns in big datasets, rather than a point of contention
The Green Bank North Celestial Cap Pulsar Survey. IV: Four New Timing Solutions
We present timing solutions for four pulsars discovered in the Green Bank
Northern Celestial Cap (GBNCC) survey. All four pulsars are isolated with spin
periods between 0.26s and 1.84s. PSR J00382501 has a 0.26s
period and a period derivative of ,
which is unusually low for isolated pulsars with similar periods. This low
period derivative may be simply an extreme value for an isolated pulsar or it
could indicate an unusual evolution path for PSR J00382501, such as a
disrupted recycled pulsar (DRP) from a binary system or an orphaned central
compact object (CCO). Correcting the observed spin-down rate for the Shklovskii
effect suggests that this pulsar may have an unusually low space velocity,
which is consistent with expectations for DRPs. There is no X-ray emission
detected from PSR J00382501 in an archival swift observation, which suggests
that it is not a young orphaned CCO. The high dispersion measure of PSR
J1949+3426 suggests a distance of 12.3kpc. This distance indicates that PSR
J1949+3426 is among the most distant 7% of Galactic field pulsars, and is one
of the most luminous pulsars.Comment: 7 pages, 5 figure
Investigating the purpose of an online discussion group for health professionals: a case example from forensic occupational therapy
Background: Thousands of health-related online discussion groups are active world-wide however, very little is known about the purpose and usefulness of such groups. In 2003 an online discussion group called ‘forensic occupational therapy' was established in the United Kingdom. This group was examined to gain an understanding of the purpose and use of online discussion groups for health professionals who may be practically and geographically isolated from others in similar areas of practice. Methods: Following a case study design, descriptive characteristics on members' locations and number of posts were collected from the forensic occupational therapy online discussion group. Eight years of posts (2003-2011) were examined using a theoretical thematic analysis process to identify and describe the purposes for which members were using the group. Results: Members from 20 countries contributed to the discussion group; the vast majority of posts being from members in the United Kingdom. Activity within the group was consistently high for the first five years however, activity within the group declined in the final three years. Six purposes for which members use the online discussion group were identified: seeking and giving advice, networking, requesting and sharing material resources, service development, defining the role of occupational therapists, and student learning. Conclusions: Findings suggest that health professionals in specialized and often isolated areas of practice are keen to connect with colleagues and learn from each other's experiences. The main purposes for which the online discussion group was used could be summarized as communication, information sharing and networking; though activity within the group declined significantly during the last three years of the data collection period. This raises questions about the sustainability of online discussion groups within the rapidly developing social media environment
Liquid-gas phase transition in nuclear multifragmentation
The equation of state of nuclear matter suggests that at suitable beam
energies the disassembling hot system formed in heavy ion collisions will pass
through a liquid-gas coexistence region. Searching for the signatures of the
phase transition has been a very important focal point of experimental
endeavours in heavy ion collisions, in the last fifteen years. Simultaneously
theoretical models have been developed to provide information about the
equation of state and reaction mechanisms consistent with the experimental
observables. This article is a review of this endeavour.Comment: 63 pages, 27 figures, submitted to Adv. Nucl. Phys. Some typos
corrected, minor text change
First Discovery of a Fast Radio Burst at 350 MHz by the GBNCC Survey
We report the first discovery of a fast radio burst (FRB), FRB 20200125A, by
the Green Bank Northern Celestial Cap (GBNCC) Pulsar Survey conducted with the
Green Bank Telescope at 350 MHz. FRB 20200125A was detected at a Galactic
latitude of 58.43 degrees with a dispersion measure of 179 pc cm, while
electron density models predict a maximum Galactic contribution of 25 pc
cm along this line of sight. Moreover, no apparent Galactic foreground
sources of ionized gas that could account for the excess DM are visible in
multi-wavelength surveys of this region. This argues that the source is
extragalactic. The maximum redshift for the host galaxy is ,
corresponding to a maximum comoving distance of approximately 750 Mpc. The
measured peak flux density for FRB 20200125A is 0.37 Jy, and we measure a pulse
width of 3.7 ms, consistent with the distribution of FRB widths observed at
higher frequencies. Based on this detection and assuming an Euclidean flux
density distribution of FRBs, we calculate an all-sky rate at 350 MHz of
FRBs sky day above a peak flux
density of 0.42 Jy for an unscattered pulse having an intrinsic width of 5 ms,
consistent with rates reported at higher frequencies. Given the recent
improvements in our single-pulse search pipeline, we also revisit the GBNCC
survey sensitivity to various burst properties. Finally, we find no evidence of
interstellar scattering in FRB 20200125A, adding to the growing evidence that
some FRBs have circumburst environments where free-free absorption and
scattering are not significant.Comment: 15 pages, 6 figures, Submitted to Ap
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