22,374 research outputs found
Efficient Management of Short-Lived Data
Motivated by the increasing prominence of loosely-coupled systems, such as
mobile and sensor networks, which are characterised by intermittent
connectivity and volatile data, we study the tagging of data with so-called
expiration times. More specifically, when data are inserted into a database,
they may be tagged with time values indicating when they expire, i.e., when
they are regarded as stale or invalid and thus are no longer considered part of
the database. In a number of applications, expiration times are known and can
be assigned at insertion time. We present data structures and algorithms for
online management of data tagged with expiration times. The algorithms are
based on fully functional, persistent treaps, which are a combination of binary
search trees with respect to a primary attribute and heaps with respect to a
secondary attribute. The primary attribute implements primary keys, and the
secondary attribute stores expiration times in a minimum heap, thus keeping a
priority queue of tuples to expire. A detailed and comprehensive experimental
study demonstrates the well-behavedness and scalability of the approach as well
as its efficiency with respect to a number of competitors.Comment: switched to TimeCenter latex styl
Small scale lateral superlattices in two-dimensional electron gases prepared by diblock copolymer masks
A poly(styrene-block-methylmethacrylate) diblock copolymer in the hexagonal
cylindrical phase has been used as a mask for preparing a periodic gate on top
of a Ga[Al]As-heterostructure. A superlattice period of 43 nm could be imposed
onto the two-dimensional electron gas. Transport measurements show a
characteristic positive magnetoresistance around zero magnetic field which we
interpret as a signature of electron motion guided by the superlattice
potential.Comment: 3 pages, 3 figure
D-branes in the diagonal SU(2) coset
The symmetry preserving D-branes in coset theories have previously been
described as being centered around projections of products of conjugacy classes
in the underlying Lie groups. Here, we investigate the coset where a diagonal
action of SU(2) is divided out from SU(2)\times SU(2). The corresponding target
space is described as a (3-dimensional) pillow with four distinguished corners.
It is shown that the (fractional) brane which corresponds to the fixed point
that arises in the CFT description, is spacefilling. Moreover, the spacefilling
brane is the only one that reaches all of the corners. The other branes are 3,
1 and 0 - dimensional.Comment: v2: reference added, 9 page
Performance of the LHCb High Level Trigger in 2012
The trigger system of the LHCb experiment is discussed in this paper and its
performance is evaluated on a dataset recorded during the 2012 run of the LHC.
The main purpose of the LHCb trigger system is to separate heavy flavour
signals from the light quark background. The trigger reduces the roughly 11MHz
of bunch-bunch crossings with inelastic collisions to a rate of 5kHz, which is
written to storage.Comment: Proceedings for the 20th International Conference on Computing in
High Energy and Nuclear Physics (CHEP
Using the chromatic Rossiter-McLaughlin effect to probe the broadband signature in the optical transmission spectrum of HD 189733b
Transmission spectroscopy is a powerful technique for probing exoplanetary
atmospheres. A successful ground-based observational method uses a differential
technique based on high-dispersion spectroscopy, but that only preserves narrow
features in transmission spectra. Here we use the chromatic Rossiter-McLaughlin
(RM) effect to measure the Rayleigh-scattering slope in the transmission
spectrum of HD 189733b with the aim to show that it can be effectively used to
measure broadband transmission features. The amplitude of the RM effects
depends on the effective size of the planet, and in the case of an atmospheric
contribution therefore depends on the observed wavelength. We analysed archival
HARPS data of three transits of HD 189733b, covering a wavelength range of 400
to 700 nm. We measured the slope in the transmission spectrum of HD 189733b at
a significance. Assuming it is due to Rayleigh scattering and not
caused by stellar activity, it would correspond to an atmospheric temperature,
as set by the scale height, of , well in line with
previously obtained results. This shows that ground-based high-dispersion
spectral observations can be used to probe broad-band features in the
transmission spectra of extrasolar planets, by using the chromatic RM effect.
This method will be particularly interesting in conjunction with the new
echelle spectrograph ESPRESSO, which currently is under construction for ESOs
Very Large Telescope and will provide a gain in signal-to-noise ratio of about
a factor 4 compared to HARPS. This will be of great value because of the
limited and uncertain future of the Hubble Space Telescope and because the
future James Webb Space Telescope will not cover this wavelength regime.Comment: 8 pages, 7 figures, accepted for publication on Astronomy and
Astrophysic
Long-lived non-classical correlations for scalable quantum repeaters at room temperature
Heralded single-photon sources with on-demand readout are promising
candidates for quantum repeaters enabling long-distance quantum communication.
The need for scalability of such systems requires simple experimental
solutions, thus favouring room-temperature systems. For quantum repeater
applications, long delays between heralding and single-photon readout are
crucial. Until now, this has been prevented in room-temperature atomic systems
by fast decoherence due to thermal motion. Here we demonstrate efficient
heralding and readout of single collective excitations created in warm caesium
vapour. Using the principle of motional averaging we achieve a collective
excitation lifetime of ms, two orders of magnitude larger than
previously achieved for single excitations in room-temperature sources. We
experimentally verify non-classicality of the light-matter correlations by
observing a violation of the Cauchy-Schwarz inequality with .
Through spectral and temporal analysis we identify intrinsic four-wave mixing
noise as the main contribution compromising single-photon operation of the
source.Comment: 21 pages total, the first 17 pages are the main article and the
remaining pages are supplemental materia
Empirical studies in labour and migration economics
This thesis consists of three empirical studies investigating topics in the fields of labour and migration economics, using a combination of administrative and survey data. The first study in labour economics seeks to answer the question whether international differences in earnings inequality between skilled and (relatively) unskilled workers can be explained by differences in the relative supply of and demand for skilled and unskilled workers across countries. Both the second and third studies are placed in the field of migration economics, dealing with the topical issue of refugee migration. Specifically, they investigate the social and attitudinal effects of the reception of refugees on host communities. The second study employs a case study of a town in rural Australia to examine how a large influx of refugees to the township has impacted social capital among the native residents. The third study broadens the context by using refugee centre data from all of the Netherlands over a number of years to link exposure to refugees to changes in natives’ attitudes to immigration. While the three studies differ (in parts) in the subfield, context and methodology of empirical microeconomics, a uniting factor is that they are motivated by important real-world problems, and that any conclusions drawn are based on the thorough analysis of a suitable dataset
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