4,453 research outputs found
Purification of large bicolorable graph states
We describe novel purification protocols for bicolorable graph states. The
protocols scale efficiently for large graph states. We introduce a method of
analysis that allows us to derive simple recursion relations characterizing
their behavior as well as analytical expressions for their thresholds and fixed
point behavior. We introduce two purification protocols with high threshold.
They can, for graph degree four, tolerate 1% (3%) gate error or 20% (30%) local
error.Comment: 12 pages, 5 figures, revtex; typos and clarifications adde
Enhanced flux pinning in YBa2Cu3O7-d films by nano-scaled substrate surface roughness
Nano-scaled substrate surface roughness is shown to strongly influence the
critical current density Jc in YBCO films made by pulse-laser-deposition on the
crystalline LaAlO3 substrates consisting of two separate twin-free and
twin-rich regions. The nano-scaled corrugated surface was created in the
twin-rich region during the deposition process. Using magneto-optical imaging
techniques coupled with optical and atomic force microscopy, we observed an
enhanced flux pinning in the YBCO films in the twin-rich region, resulted in
\~30% increase in Jc, which was unambiguously confirmed by the direct transport
measurement.Comment: 16 pages, 3 figures, accepted by Applied Physics Letter
A balanced iterative random forest for gene selection from microarray data
Background: The wealth of gene expression values being generated by high throughput microarray technologies leads to complex high dimensional datasets. Moreover, many cohorts have the problem of imbalanced classes where the number of patients belonging
Entanglement between more than two hundred macroscopic atomic ensembles in a solid
We create a multi-partite entangled state by storing a single photon in a
crystal that contains many large atomic ensembles with distinct resonance
frequencies. The photon is re-emitted at a well-defined time due to an
interference effect analogous to multi-slit diffraction. We derive a lower
bound for the number of entangled ensembles based on the contrast of the
interference and the single-photon character of the input, and we
experimentally demonstrate entanglement between over two hundred ensembles,
each containing a billion atoms. In addition, we illustrate the fact that each
individual ensemble contains further entanglement. Our results are the first
demonstration of entanglement between many macroscopic systems in a solid and
open the door to creating even more complex entangled states.Comment: 10 pages, 8 figures; see also parallel submission by Frowis et a
Word Embeddings for Entity-annotated Texts
Learned vector representations of words are useful tools for many information
retrieval and natural language processing tasks due to their ability to capture
lexical semantics. However, while many such tasks involve or even rely on named
entities as central components, popular word embedding models have so far
failed to include entities as first-class citizens. While it seems intuitive
that annotating named entities in the training corpus should result in more
intelligent word features for downstream tasks, performance issues arise when
popular embedding approaches are naively applied to entity annotated corpora.
Not only are the resulting entity embeddings less useful than expected, but one
also finds that the performance of the non-entity word embeddings degrades in
comparison to those trained on the raw, unannotated corpus. In this paper, we
investigate approaches to jointly train word and entity embeddings on a large
corpus with automatically annotated and linked entities. We discuss two
distinct approaches to the generation of such embeddings, namely the training
of state-of-the-art embeddings on raw-text and annotated versions of the
corpus, as well as node embeddings of a co-occurrence graph representation of
the annotated corpus. We compare the performance of annotated embeddings and
classical word embeddings on a variety of word similarity, analogy, and
clustering evaluation tasks, and investigate their performance in
entity-specific tasks. Our findings show that it takes more than training
popular word embedding models on an annotated corpus to create entity
embeddings with acceptable performance on common test cases. Based on these
results, we discuss how and when node embeddings of the co-occurrence graph
representation of the text can restore the performance.Comment: This paper is accepted in 41st European Conference on Information
Retrieva
Understanding BL Lac objects Structural & kinematic mode changes in the BL Lac object PKS 0735+178
Context. We present evidence that parsec-scale jets in BL Lac objects may be
significantly distinct in kinematics from their counterparts in quasars. We
argued this previously for the BL lac sources 1803+784 and 0716+714, report
here a similar pattern for another well-known BL Lac object, PKS 0735+178,
whose nuclear jet is found to exhibit kinematics atypical of quasars. Aims. A
detailed study of the jet components' motion reveals that the standard AGN
paradigm of apparent superluminal motion does not always describe the
kinematics in BL Lac objects. We study 0735+178 here to augment and improve the
understanding of the peculiar motions in the jets of BL Lac objects as a class.
Methods. We analyzed 15 GHz VLBA (Very Long Baseline Array) observations
(2cm/MOJAVE survey) performed at 23 epochs between 1995.27 and 2008.91.
Results. We found a drastic structural mode change in the VLBI jet of 0735+178,
between 2000.4 and 2001.8 when its twice sharply bent trajectory turned into a
linear shape.We further found that this jet had undergone a similar transition
sometime between December 1981 and June 1983. A mode change, occurring in the
reverse direction (between mid-1992 and mid-1995) has already been reported in
the literature. These structural mode changes are found to be reflected in
changed kinematical behavior of the nuclear jet, manifested as an apparent
superluminal motion and stationarity of the radio knots. In addition, we found
the individual mode changes to correlate in time with the maxima in the optical
light curve. The last two transitions occurred before a (modest) radio flare.
The behavior of this pc-scale jet appears to favor a scenario involving
non-ballistic motions of the radio knots, produced by the precession of a
continuous jet within the ambient medium.Comment: Accepted for publication in A&A (Abstract reduced for astro-ph
Symmetry structure and phase transitions
We study chiral symmetry structure at finite density and temperature in the
presence of external magnetic field and gravity, a situation relevant in the
early Universe and in the core of compact stars.
We then investigate the dynamical evolution of phase transition in the
expanding early Universe and possible formation of quark nuggets and their
survival.Comment: Plenary talk given at the 4th. ICPAQGP held at Jaipur, India from Nov
26-30, 2001.laTex 2e file with 8 ps figures and 12 page
The effect of metallicity on the atmospheres of exoplanets with fully coupled 3D hydrodynamics, equilibrium chemistry, and radiative transfer (article)
This is the author accepted manuscript. The final version is available from EDP Sciences for European Southern Observatory (ESO) via the DOI in this record.The dataset associated with this article is located in ORE at: http://hdl.handle.net/10871/32593In this work we have performed a series of simulations of the atmosphere of GJ 1214b assuming different metallicities
using the Met Office Unified Model (UM). The UM is a general circulation model (GCM) that solves the deep, nonhydrostatic
equations of motion and uses a flexible and accurate radiative transfer scheme, based on the two-stream
and correlated-k approximations, to calculate the heating rates. In this work we consistently couple a well-tested
Gibbs energy minimisation scheme to solve for the chemical equilibrium abundances locally in each grid cell for a
general set of elemental abundances, further improving the flexibility and accuracy of the model. As the metallicity
of the atmosphere is increased we find significant changes in the dynamical and thermal structure, with subsequent
implications for the simulated phase curve. The trends that we find are qualitatively consistent with previous works,
though with quantitative differences. We investigate in detail the effect of increasing the metallicity by splitting the
mechanism into constituents, involving the mean molecular weight, the heat capacity and the opacities. We find the
opacity effect to be the dominant mechanism in altering the circulation and thermal structure. This result highlights
the importance of accurately computing the opacities and radiative transfer in 3D GCMs.This work is partly supported by the European
Research Council under the European Community’s Seventh
Framework Programme (FP7/2007-2013 Grant Agreement No.
247060-PEPS and grant No. 320478-TOFU). BD acknowledges funding
from the European Research Council (ERC) under the European
Unions Seventh Framework Programme (FP7/2007-2013) / ERC
grant agreement no. 336792 and thanks the University of Exeter for
support through a PhD studentship. DSA acknowledges support from
the NASA Astrobiology Program through the Nexus for Exoplanet
System Science. NJM and JG’s contributions were in part funded by
a Leverhulme Trust Research Project Grant, and in part by a University
of Exeter College of Engineering, Mathematics and Physical
Sciences studentship. This work used the DiRAC Complexity system,
operated by the University of Leicester IT Services, which forms
part of the STFC DiRAC HPC Facility. This equipment is funded
by BIS National E-Infrastructure capital grant ST/K000373/1 and
STFC DiRAC Operations grant ST/K0003259/1. DiRAC is part of
the National E-Infrastructure. This work also used the University of
Exeter Supercomputer, a DiRAC Facility jointly funded by STFC,
the Large Facilities Capital Fund of BIS and the University of Exeter.
Material produced using Met Office Software
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