11,361 research outputs found
Student user preferences for features of next-generation OPACs: a case study of University of Sheffield international students
Purpose. The purpose of this study is to identity the features that international student users prefer for next generation OPACs.
Design/ methodology/ approach. 16 international students of the University of Sheffield were interviewed in July 2008 to explore their preferences among potential features in next generation OPACs. A semi-structured interview schedule with images of mock-up screens was used.
Findings. The results of the interviews were broadly consistent with previous studies. In general, students expect features in next generation OPACs should be save their time, easy to use and relevant to their search. This study found that recommender features and features that can provide better navigation of search results are desired by users. However, Web 2.0 features, such as RSS feeds and those features which involved user participation were among the most popular.
Practical implications. This paper produces findings of relevance to any academic library seeking to implement a next-generation OPAC.
Originality/value. There have been no previous published research studies of users’ preferences among possible features of next-generation OPACs
Coronal heating in multiple magnetic threads
Context. Heating the solar corona to several million degrees requires the
conversion of magnetic energy into thermal energy. In this paper, we
investigate whether an unstable magnetic thread within a coronal loop can
destabilise a neighbouring magnetic thread. Aims. By running a series of
simulations, we aim to understand under what conditions the destabilisation of
a single magnetic thread can also trigger a release of energy in a nearby
thread. Methods. The 3D magnetohydrodynamics code, Lare3d, is used to simulate
the temporal evolution of coronal magnetic fields during a kink instability and
the subsequent relaxation process. We assume that a coronal magnetic loop
consists of non-potential magnetic threads that are initially in an equilibrium
state. Results. The non-linear kink instability in one magnetic thread forms a
helical current sheet and initiates magnetic reconnection. The current sheet
fragments, and magnetic energy is released throughout that thread. We find
that, under certain conditions, this event can destabilise a nearby thread,
which is a necessary requirement for starting an avalanche of energy release in
magnetic threads. Conclusions. It is possible to initiate an energy release in
a nearby, non-potential magnetic thread, because the energy released from one
unstable magnetic thread can trigger energy release in nearby threads, provided
that the nearby structures are close to marginal stability
Noise characteristics of upper surface blown configurations: Analytical Studies
Noise and flow results of upper surface blown configurations were analyzed. The dominant noise source mechanisms were identified from experimental data. From far-field noise data for various geometric and operational parameters, an empirical noise prediction program was developed and evaluated by comparing predicted results with experimental data from other tests. USB aircraft compatibility studies were conducted using the described noise prediction and a cruise performance data base. A final design aircraft was selected and theory was developed for the noise from the trailing edge wake assuming it as a highly sheared layer
On the Validity of the Tomonaga Luttinger Liquid Relations for the One-dimensional Holstein Model
For the one-dimensional Holstein model, we show that the relations among the
scaling exponents of various correlation functions of the Tomonaga Luttinger
liquid (LL), while valid in the thermodynamic limit, are significantly modified
by finite size corrections. We obtain analytical expressions for these
corrections and find that they decrease very slowly with increasing system
size. The interpretation of numerical data on finite size lattices in terms of
LL theory must therefore take these corrections into account. As an important
example, we re-examine the proposed metallic phase of the zero-temperature,
half-filled one-dimensional Holstein model without employing the LL relations.
In particular, using quantum Monte Carlo calculations, we study the competition
between the singlet pairing and charge ordering. Our results do not support the
existence of a dominant singlet pairing state.Comment: 7 page
Phase Diagram of the Holstein-Hubbard Two-Leg Ladder
Using a functional renormalization group method, we obtain the phase diagram
of the two-leg ladder system within the Holstein-Hubbard model, which includes
both electron-electron and electron-phonon interactions. Our renormalization
group technique allows us to analyze the problem for both weak and strong
electron-phonon coupling. We show that, in contrast results from conventional
weak coupling studies, electron-phonon interactions can dominate
electron-electron interactions because of retardation effects.Comment: 4 page
A Hubble Space Telescope Imaging Survey of Nearby Active Glactic Nuclei
We obtained 500-second F606W WFPC2 images of 256 of the nearest (z<0.035)
Seyfert 1,Seyfert 2, and starburst galaxies. Less than 10% show tidal features
or multiple nuclei. The incidence of inner starburst rings is about 10% in both
classes of Sy galaxies. In contrast, galaxies with H II region emission line
spectra appear substantially more irregular because of their much higher
specific rates of star formation. An unresolved central continuum source in our
HST images is a virtually perfect indicator of a Sy1 spectrum. 52% of these Sy1
point sources are saturated in our images; we use their wings to estimate their
magnitudes. The converse is not however true, as over a third of Sy's with
direct spectroscopic evidence for broad Balmer wings show no nuclear point
source. Like the Sy2's, they have central surface brightnesses consistent with
those expected for the bulges of normal galaxies. The frequency of bars in
Sy1's and 2's and non-Sys are the same. The Sy2 galaxies are significantly more
likely to show nuclear dust absorption, especially in lanes and patches which
are irregular or reach close to the nucleus. The difference cannot be explained
by different average redshifts or selection techniques. This is confirmed by
our morphology classifications, which show that Sy1 nuclei reside in earlier
type galaxies than Sy2 nuclei. This intrinsic difference in host galaxy
properties may undermine the strong unification hypothesis for Sy galaxies that
they appear different due to the orientation of their central engine. The
excess galactic dust we see in Sy2's may cause substantial absorption which
obscures their hypothesized broad emission-line regions and central nonstellar
continua. This galactic dust could produce much of the absorption in Sy2 nuclei
which had instead been attributed to a thick dusty accretion torus.Comment: The text of the paper is 23 pages (ms.tex), there are 8 tables, and 9
figures. Figures 1, 2, and 3 are the image gallery (45 pages) and are NOT
included here. They can be ftp'ed from ftp.astro.ucla.edu. Log in as
anonymous and give your e-mail address as the password. The images are in the
/pub/submit/vg/AGNgallery . Figures 4-9 are in eps format and are included
here and can be printed using the lpr command in unix system
Physics of Acoustic Radiation from Jet Engine Inlets
Numerical simulations of acoustic radiation from a jet engine inlet are performed using advanced computational aeroacoustics (CAA) algorithms and high-quality numerical boundary treatments. As a model of modern commercial jet engine inlets, the inlet geometry of the NASA Source Diagnostic Test (SDT) is used. Fan noise consists of tones and broadband sound. This investigation considers the radiation of tones associated with upstream propagating duct modes. The primary objective is to identify the dominant physical processes that determine the directivity of the radiated sound. Two such processes have been identified. They are acoustic diffraction and refraction. Diffraction is the natural tendency for an acoustic wave to follow a curved solid surface as it propagates. Refraction is the turning of the direction of propagation of sound waves by mean flow gradients. Parametric studies on the changes in the directivity of radiated sound due to variations in forward flight Mach number and duct mode frequency, azimuthal mode number, and radial mode number are carried out. It is found there is a significant difference in directivity for the radiation of the same duct mode from an engine inlet when operating in static condition and in forward flight. It will be shown that the large change in directivity is the result of the combined effects of diffraction and refraction
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