12,421 research outputs found
Comment on: Diffusion through a slab
Mahan [J. Math. Phys. 36, 6758 (1995)] has calculated the transmission
coefficient and angular distribution of particles which enter a thick slab at
normal incidence and which diffuse in the slab with linear anisotropic,
non-absorbing, scattering. Using orthogonality relations derived by McCormick &
Kuscer [J. Math. Phys. 6, 1939 (1965); 7, 2036 (1966)] for the eigenfunctions
of the problem, this calculation is generalised to a boundary condition with
particle input at arbitrary angles. It is also shown how to use the
orthogonality relations to relax in a simple way the restriction to a thick
slab.Comment: 3 pages, LaTeX, uses RevTe
Web assisted teaching: an undergraduate experience
The emergence of the Internet has created a number of claims as to the future of education and the possibility of dramatically changing the way in which education is delivered. Much of the attention has focussed on the adoption of teaching methods that are solely web-based. We set out to incorporate web-based teaching as support for more traditional teaching methods to improve the learning outcomes for students. This first step into web-based teaching was developed to harness the benefits of web-based teaching tools without supplanting traditional teaching methods.
The aim of this paper is to report our experience with web-assisted teaching in two undergraduate courses, Accounting Information Systems and Management Accounting Services, during 2000. The paper evaluates the approach taken and proposes a tentative framework for developing future web-assisted teaching applications.
We believe that web-assisted and web-based teaching are inevitable outcomes of the telecommunications and computer revolution and that academics cannot afford to become isolated from the on-line world. A considered approach is needed to ensure the integration of web-based features into the overall structure of a course. The components of the course material and the learning experiences students are exposed to need to be structured and delivered in a way that ensures they support student learning rather than replacing one form of learning with another. Therefore a careful consideration of the structure, content, level of detail and time of delivery needs to be integrated to create a course structure that provides a range of student learning experiences that are complimentary rather than competing.
The feedback was positive from both extramural (distance) and internal students, demonstrating to us that web sites can be used as an effective teaching tool in support of more traditional teaching methods as well as a tool for distance education. The ability to harness the positives of the web in conjunction with more traditional teaching modes is one that should not be overlooked in the move to adopt web based instruction methods. Web-based teaching need not be seen as an all or nothing divide but can be used as a useful way of improving the range and type of learning experiences open to students.
The Web challenges traditional methods and thinking but it also provides tools to develop innovative solutions to both distance and on campus learning. Further research is needed to determine how we can best meet the needs of our students while maintaining high quality learning outcomes
A multi-zone model for simulating the high energy variability of TeV blazars
We present a time-dependent multi-zone code for simulating the variability of
Synchrotron-Self Compton (SSC) sources. The code adopts a multi-zone pipe
geometry for the emission region, appropriate for simulating emission from a
standing or propagating shock in a collimated jet. Variations in the injection
of relativistic electrons in the inlet propagate along the length of the pipe
cooling radiatively. Our code for the first time takes into account the
non-local, time-retarded nature of synchrotron self-Compton (SSC) losses that
are thought to be dominant in TeV blazars. The observed synchrotron and SSC
emission is followed self-consistently taking into account light travel time
delays. At any given time, the emitting portion of the pipe depends on the
frequency and the nature of the variation followed. Our simulation employs only
one additional physical parameter relative to one-zone models, that of the pipe
length and is computationally very efficient, using simplified expressions for
the SSC processes. The code will be useful for observers modeling GLAST, TeV,
and X-ray observations of SSC blazars.Comment: ApJ, accepte
Physical Conditions in Quasar Outflows: VLT Observations of QSO 2359-1241
We analyze the physical conditions of the outflow seen in QSO 2359-1241 (NVSS
J235953-124148), based on high resolution spectroscopic VLT observations. This
object was previously studied using Keck/HIRES data. The main improvement over
the HIRES results is our ability to accurately determine the number density of
the outflow. For the major absorption component, level population from five
different Fe II excited level yields n_H=10^4.4 cm^-3 with less than 20%
scatter. We find that the Fe ii absorption arises from a region with roughly
constant conditions and temperature greater than 9000 K, before the ionization
front where temperature and electron density drop. Further, we model the
observed spectra and investigate the effects of varying gas metalicities and
the spectral energy distribution of the incident ionizing radiation field. The
accurately measured column densities allow us to determine the ionization
parameter log(U) = -2.4 and total column density of the outflow (log(N_H) =
20.6 cm^-2). Combined with the number density finding, these are stepping
stones towards determining the mass flux and kinetic luminosity of the outflow,
and therefore its importance to AGN feedback processes.Comment: 21 pages, 3 figures (accepted for publication in the ApJ
Passion, music, and psychological well-being
Passionate music engagement is a defining feature of music fans worldwide. Although benefits to psychosocial well-being are often experienced by fans of music, some fans experience maladaptive outcomes from their music engagement. The Dualistic Model of Passion proposes that two types of passion—harmonious and obsessive—are associated with positive and negative outcomes of passionate engagement, respectively. This model has been employed in research on passion for a wide range of pursuits including music performers, but not for passionate listeners. The present study employed this model to investigate whether (1) harmonious passion for music is associated with positive music listening experiences and/or psychological well-being and (2) obsessive passion for music is associated with negative music listening experiences and/or psychological ill-being. Passionate fans (n = 197) of 40 different musical genres were surveyed about their experiences when listening to their favorite music. Measures included the passion scale, affective experiences with music, and psychological well-being and ill-being. Results supported the Dualistic Model of Passion. Structural equation modeling revealed that harmonious passion for music predicted positive affective experiences which, in turn, predicted psychological well-being. Conversely, obsessive passion for music predicted negative affective experiences which, in turn, predicted psychological ill-being. The findings suggest that the nature of passionate engagement with music has an integral role in the psychological impact of music engagement and implications for the well-being of music fans.</p
A variational problem on Stiefel manifolds
In their paper on discrete analogues of some classical systems such as the
rigid body and the geodesic flow on an ellipsoid, Moser and Veselov introduced
their analysis in the general context of flows on Stiefel manifolds. We
consider here a general class of continuous time, quadratic cost, optimal
control problems on Stiefel manifolds, which in the extreme dimensions again
yield these classical physical geodesic flows. We have already shown that this
optimal control setting gives a new symmetric representation of the rigid body
flow and in this paper we extend this representation to the geodesic flow on
the ellipsoid and the more general Stiefel manifold case. The metric we choose
on the Stiefel manifolds is the same as that used in the symmetric
representation of the rigid body flow and that used by Moser and Veselov. In
the extreme cases of the ellipsoid and the rigid body, the geodesic flows are
known to be integrable. We obtain the extremal flows using both variational and
optimal control approaches and elucidate the structure of the flows on general
Stiefel manifolds.Comment: 30 page
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