3,841 research outputs found
An Anniversary Opportunity: Digitization of Student Yearbooks
Anniversary celebrations provide archivists and librarians with many unique opportunities to build public support for their programs. Archivists, in particular, are expected to be a resource for such events. Handled adroitly, anniversary programming can offset the âdusty shelfâ stereotype that frustrates many professionals. Moreover, resource allocators planning an anniversary are likely to look to their archives for ideas and special projects, initiatives that may result in additional financial and staffing resources. Describing the positive public relations value of anniversaries, archivist Tim Ericson has gone so far as to suggest âThe Archivist\u27s First Law of Outreachâ:
Human beings are unable to resist celebrating any anniversary divisible by twenty-five
The magnetar model for Type I superluminous supernovae I: Bayesian analysis of the full multicolour light curve sample with MOSFiT
We use the new Modular Open Source Fitter for Transients (MOSFiT) to model 38
hydrogen-poor superluminous supernovae (SLSNe). We fit their multicolour light
curves with a magnetar spin-down model and present the posterior distributions
of magnetar and ejecta parameters. The colour evolution can be well matched
with a simple absorbed blackbody. We find the following medians (1
ranges): spin period 2.4 ms (1.2-4 ms); magnetic field G
(0.2-1.8 G); ejecta mass 4.8 Msun (2.2-12.9 Msun); kinetic
energy erg (1.9-9.8 erg). This
significantly narrows the parameter space compared to our priors, showing that
although the model is flexible, the parameter space relevant to SLSNe is well
constrained by existing data. The requirement that the instantaneous engine
power is erg at the light curve peak necessitates either a large
rotational energy (P<2 ms), or more commonly that the spin-down and diffusion
timescales be well-matched. We find no evidence for separate populations of
fast- and slow-declining SLSNe, which instead form a continuum both in light
curve widths and inferred parameters. Variations in the spectra are well
explained through differences in spin-down power and photospheric radii at
maximum-light. We find no correlations between any model parameters and the
properties of SLSN host galaxies. Comparing our posteriors to stellar evolution
models, we show that SLSNe require rapidly rotating (fastest 10%) massive stars
(> 20 Msun), and that this is consistent with the observed SLSN rate. High
mass, low metallicity, and likely binary interaction all serve to maintain
rapid rotation essential for magnetar formation. By reproducing the full set of
SLSN light curves, our posteriors can be used to inform photometric searches
for SLSNe in future survey data
Systematic investigation of the fallback accretion powered model for hydrogen-poor superluminous supernovae
The energy liberated by fallback accretion has been suggested as a possible
engine to power hydrogen-poor superluminous supernovae. We systematically
investigate this model using the Bayesian light-curve fitting code MOSFiT
(Modular Open Source Fitter for Transients), fitting the light curves of 37
hydrogen-poor superluminous supernovae assuming a fallback accretion central
engine. We find that this model can yield good fits to their light curves, with
a fit quality that rivals the popular magnetar engine models. Examining our
derived parameters for the fallback model, we find the total energy
requirements from the accretion disk are estimated to be 0.002 - 0.7 Msun c^2.
If we adopt a typical conversion efficiency ~ 1e-3, the required mass to
accrete is thus 2 - 700 Msun. Many superluminous supernovae, therefore, require
an unrealistic accretion mass, and so only a fraction of these events could be
powered by fallback accretion unless the true efficiency is much greater than
our fiducial value. The superluminous supernovae that require the smallest
amounts of fallback mass still remain to be the fallback accretion powered
supernova candidates, but they are difficult to be distinguished solely by
their light curve properties.Comment: 12 pages, 8 figures, 3 tables, accepted by The Astrophysical Journa
Beyond Power over Ethernet : the development of Digital Energy Networks for buildings
Alternating current power distribution using analogue control and safety devices has been the dominant process of power distribution within our buildings since the electricity industry began in the late 19th century. However, with advances in digital technology, the seeds of change have been growing over the last decade. Now, with the simultaneous dramatic fall in power requirements of digital devices and corresponding rise in capability of Power over Ethernet, an entire desktop environment can be powered by a single direct current (dc) Ethernet cable. Going beyond this, it will soon be possible to power entire office buildings using dc networks. This means the logic of âone-size fits allâ from the existing ac system is no longer relevant and instead there is an opportunity to redesign the power topology to be appropriate for different applications, devices and end-users throughout the building. This paper proposes a 3-tier classification system for the topology of direct current microgrids in commercial buildings â called a Digital Energy Network or DEN. The first tier is power distribution at a full building level (otherwise known as the microgrid); the second tier is power distribution at a room level (the nanogrid); and the third tier is power distribution at a desktop or appliance level (the picogrid). An important aspect of this classification system is how the design focus changes for each grid. For example; a key driver of the picogrid is the usability of the network â high data rates, and low power requirements; however, in the microgrid, the main driver is high power and efficiency at low cost
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