7,377 research outputs found
Coherence properties of the microcavity polariton condensate
A theoretical model is presented which explains the dominant decoherence
process in a microcavity polariton condensate. The mechanism which is invoked
is the effect of self-phase modulation, whereby interactions transform
polariton number fluctuations into random energy variations. The model shows
that the phase coherence decay, g1(t), has a Kubo form, which can be Gaussian
or exponential, depending on whether the number fluctuations are slow or fast.
This fluctuation rate also determines the decay time of the intensity
correlation function, g2(t), so it can be directly determined experimentally.
The model explains recent experimental measurements of a relatively fast
Gaussian decay for g1(t), but also predicts a regime, further above threshold,
where the decay is much slower.Comment: 5 pages, 1 figur
The Behaviour of Finely Ground Bottom Ash in Portland Cement
The aim of this project was to assess the effects of finely ground MSWI bottom ash in Portland cement. Mortar mixes were prepared with 10% and 40% replacement of cement by ground IBA and then tested with regards to their material composition and engineering behaviour. IBA was found not to be inert, but showed some degree of reactivity. Replacement of cement with IBA was found to have no detrimental effects at low concentrations. This was not the case for 40% replacement, where cement replacement greatly affected strength, creep and drying shrinkage
Saddle Points and Stark Ladders: Exact Calculations of Exciton Spectra in Superlattices
A new, exact method for calculating excitonic absorption in superlattices is
described. It is used to obtain high resolution spectra showing the saddle
point exciton feature near the top of the miniband. The evolution of this
feature is followed through a series of structures with increasing miniband
width. The Stark ladder of peaks produced by an axial electric field is
investigated, and it is shown that for weak fields the line shapes are strongly
modified by coupling to continuum states, taking the form of Fano resonances.
The calculated spectra, when suitably broadened, are found to be in good
agreement with experimental results.Comment: 9 pages Revtex v3.0, followed by 4 uuencoded postscript figures,
SISSA-CM-94-00
Family memories in the home: contrasting physical and digital mementos
We carried out fieldwork to characterise and compare physical and digital mementos in the home. Physical mementos are highly valued, heterogeneous and support different types of recollection. Contrary to expectations, we found physical mementos are not purely representational, and can involve appropriating common objects and more idiosyncratic forms. In contrast, digital mementos were initially perceived as less valuable, although participants later reconsidered this. Digital mementos were somewhat limited in function and expression, largely involving representational photos and videos, and infrequently accessed. We explain these digital limitations and conclude with design guidelines for digital mementos, including better techniques for accessing and integrating these into everyday life, allowing them to acquire the symbolic associations and lasting value that characterise their physical counterparts
Area Studies and Special Collections: Shared Challenges, Shared Strength
Copyright © 2015 by Johns Hopkins University Press, This article first appeared in portal, Volume 15, Issue 2,
April, 2015, pages 353-373.Special collections and area studies librarians face similar challenges in the changing academic library environment, including the need to articulate the value of these specialized collections and to mainstream processes and practices into larger discovery, teaching, learning, and research efforts. For some institutions, these similarities have led to combining these areas of librarianship into a shared administrative structure. This article articulates the concept of “distinctive collections,” identifies the shared challenges of these programs, and enumerates some essential differences, as well as outlines some observations from institutions that have taken this step. It further suggests opportunities for these areas to build strength and significantly impact teaching, learning, and research together. Future research agendas that might propel further investigation of “distinctive collections” are proposed
Relative entropy as a measure of inhomogeneity in general relativity
We introduce the notion of relative volume entropy for two spacetimes with
preferred compact spacelike foliations. This is accomplished by applying the
notion of Kullback-Leibler divergence to the volume elements induced on
spacelike slices. The resulting quantity gives a lower bound on the number of
bits which are necessary to describe one metric given the other. For
illustration, we study some examples, in particular gravitational waves, and
conclude that the relative volume entropy is a suitable device for quantitative
comparison of the inhomogeneity of two spacetimes.Comment: 15 pages, 7 figure
The Wahlquist metric cannot describe an isolated rotating body
It is proven that the Wahlquist perfect fluid space-time cannot be smoothly
joined to an exterior asymptotically flat vacuum region. The proof uses a power
series expansion in the angular velocity, to a precision of the second order.
In this approximation, the Wahlquist metric is a special case of the rotating
Whittaker space-time. The exterior vacuum domain is treated in a like manner.
We compute the conditions of matching at the possible boundary surface in both
the interior and the vacuum domain. The conditions for matching the induced
metrics and the extrinsic curvatures are mutually contradictory.Comment: 13 pages, 0 figure
Easy on that trigger dad: a study of long term family photo retrieval
We examine the effects of new technologies for digital photography on people's longer term storage and access to collections of personal photos. We report an empirical study of parents' ability to retrieve photos related to salient family events from more than a year ago. Performance was relatively poor with people failing to find almost 40% of pictures. We analyze participants' organizational and access strategies to identify reasons for this poor performance. Possible reasons for retrieval failure include: storing too many pictures, rudimentary organization, use of multiple storage systems, failure to maintain collections and participants' false beliefs about their ability to access photos. We conclude by exploring the technical and theoretical implications of these findings
The eVALuate study: two parallel randomised trials, one comparing laparoscopic with abdominal hysterectomy, the other comparing laparoscopic with vaginal hysterectomy
OBJECTIVE: To compare the effects of laparoscopic hysterectomy
and abdominal hysterectomy in the abdominal trial, and
laparoscopic hysterectomy and vaginal hysterectomy in the
vaginal trial.
DESIGN: Two parallel, multicentre, randomised trials.
Setting 28 UK centres and two South African centres.
Participants 1380 women were recruited; 1346 had surgery;
937 were followed up at one year.
PRIMARY OUTCOME: outcome Rate of major complications.
RESULTS: In the abdominal trial laparoscopic hysterectomy was
associated with a higher rate of major complications than
abdominal hysterectomy (11.1% v 6.2%, P = 0.02; difference
4.9%, 95% confidence interval 0.9% to 9.1%) and the number
needed to treat to harm was 20. Laparoscopic hysterectomy
also took longer to perform (84 minutes v 50 minutes) but was
less painful (visual analogue scale 3.51 v 3.88, P = 0.01) and
resulted in a shorter stay in hospital after the operation (3 days
v 4 days). Six weeks after the operation, laparoscopic
hysterectomy was associated with less pain and better quality of
life than abdominal hysterectomy (SF-12, body image scale, and
sexual activity questionnaires).
In the vaginal trial we found no evidence of a difference in
major complication rates between laparoscopic hysterectomy
and vaginal hysterectomy (9.8% v 9.5%, P = 0.92; difference
0.3%, − 5.2% to 5.8%), and the number needed to treat to harm
was 333.We found no evidence of other differences between
laparoscopic hysterectomy and vaginal hysterectomy except
that laparoscopic hysterectomy took longer to perform (72
minutes v 39 minutes) and was associated with a higher rate of
detecting unexpected pathology (16.4% v 4.8%, P = < 0.01).
However, this trial was underpowered.
CONCLUSIONS: Laparoscopic hysterectomy was associated with a
significantly higher rate of major complications than abdominal
hysterectomy. It also took longer to perform but was associated
with less pain, quicker recovery, and better short term quality of
life. The trial comparing vaginal hysterectomy with laparoscopic
hysterectomy was underpowered and is inconclusive on the rate
of major complications; however, vaginal hysterectomy took less
time
Anomalous relaxation kinetics of biological lattice-ligand binding models
We discuss theoretical models for the cooperative binding dynamics of ligands
to substrates, such as dimeric motor proteins to microtubules or more extended
macromolecules like tropomyosin to actin filaments. We study the effects of
steric constraints, size of ligands, binding rates and interaction between
neighboring proteins on the binding dynamics and binding stoichiometry.
Starting from an empty lattice the binding dynamics goes, quite generally,
through several stages. The first stage represents fast initial binding closely
resembling the physics of random sequential adsorption processes. Typically
this initial process leaves the system in a metastable locked state with many
small gaps between blocks of bound molecules. In a second stage the gaps
annihilate slowly as the ligands detach and reattach. This results in an
algebraic decay of the gap concentration and interesting scaling behavior. Upon
identifying the gaps with particles we show that the dynamics in this regime
can be explained by mapping it onto various reaction-diffusion models. The
final approach to equilibrium shows some interesting dynamic scaling
properties. We also discuss the effect of cooperativity on the equilibrium
stoichiometry, and their consequences for the interpretation of biochemical and
image reconstruction results.Comment: REVTeX, 20 pages, 17 figures; review, to appear in Chemical Physics;
v2: minor correction
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