7,931 research outputs found
Adaptive Computation of the Swap-Insert Correction Distance
The Swap-Insert Correction distance from a string of length to
another string of length on the alphabet is the minimum
number of insertions, and swaps of pairs of adjacent symbols, converting
into . Contrarily to other correction distances, computing it is NP-Hard in
the size of the alphabet. We describe an algorithm computing this distance
in time within , where there are occurrences of
in , occurrences of in , and where
measures the
difficulty of the instance. The difficulty is bounded by above by various
terms, such as the length of the shortest string , and by the maximum number
of occurrences of a single character in . Those results illustrate how, in
many cases, the correction distance between two strings can be easier to
compute than in the worst case scenario.Comment: 16 pages, no figures, long version of the extended abstract accepted
to SPIRE 201
Formation of Galaxy Clusters
In this review, we describe our current understanding of cluster formation:
from the general picture of collapse from initial density fluctuations in an
expanding Universe to detailed simulations of cluster formation including the
effects of galaxy formation. We outline both the areas in which highly accurate
predictions of theoretical models can be obtained and areas where predictions
are uncertain due to uncertain physics of galaxy formation and feedback. The
former includes the description of the structural properties of the dark matter
halos hosting cluster, their mass function and clustering properties. Their
study provides a foundation for cosmological applications of clusters and for
testing the fundamental assumptions of the standard model of structure
formation. The latter includes the description of the total gas and stellar
fractions, the thermodynamical and non-thermal processes in the intracluster
plasma. Their study serves as a testing ground for galaxy formation models and
plasma physics. In this context, we identify a suitable radial range where the
observed thermal properties of the intra-cluster plasma exhibit the most
regular behavior and thus can be used to define robust observational proxies
for the total cluster mass. We put particular emphasis on examining assumptions
and limitations of the widely used self-similar model of clusters. Finally, we
discuss the formation of clusters in non-standard cosmological models, such as
non-Gaussian models for the initial density field and models with modified
gravity, along with prospects for testing these alternative scenarios with
large cluster surveys in the near future.Comment: 66 pages, 17 figures, review to be published in 2012 Annual Reviews
of Astronomy & Astrophysic
Visual Text Correction
Videos, images, and sentences are mediums that can express the same
semantics. One can imagine a picture by reading a sentence or can describe a
scene with some words. However, even small changes in a sentence can cause a
significant semantic inconsistency with the corresponding video/image. For
example, by changing the verb of a sentence, the meaning may drastically
change. There have been many efforts to encode a video/sentence and decode it
as a sentence/video. In this research, we study a new scenario in which both
the sentence and the video are given, but the sentence is inaccurate. A
semantic inconsistency between the sentence and the video or between the words
of a sentence can result in an inaccurate description. This paper introduces a
new problem, called Visual Text Correction (VTC), i.e., finding and replacing
an inaccurate word in the textual description of a video. We propose a deep
network that can simultaneously detect an inaccuracy in a sentence, and fix it
by replacing the inaccurate word(s). Our method leverages the semantic
interdependence of videos and words, as well as the short-term and long-term
relations of the words in a sentence. In our formulation, part of a visual
feature vector for every single word is dynamically selected through a gating
process. Furthermore, to train and evaluate our model, we propose an approach
to automatically construct a large dataset for VTC problem. Our experiments and
performance analysis demonstrates that the proposed method provides very good
results and also highlights the general challenges in solving the VTC problem.
To the best of our knowledge, this work is the first of its kind for the Visual
Text Correction task
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Captain Buzz
This is the author accepted manuscript. The final version is available from ACM at https://dl.acm.org/citation.cfm?id=2750682.Fully autonomous hobbyist drones are typically controlled
using bespoke microcontrollers, or general purpose low-level
controllers such as the Arduino. However, these devices
only have limited compute power and sensing capabilities,
and do not easily provide cellular connectivity options. We
present Captain Buzz, an Android smartphone app capable
of piloting a delta-wing glider autonomously. Captain Buzz
can control servos directly via pulse width modulation sig-
nals transmitted over the smartphone audio port. Compared
with traditional approaches to building an autopilot, Cap-
tain Buzz allows users to leverage existing Android libraries
for flight attitude determination, provides innovative use-
cases, allows users to reprogram their autopilot mid-flight for
rapid prototyping, and reduces the cost of building drones.This work was supported by Google Inc., the Engineering
and Physical Sciences Research Council; and CSR, Cambridge
Transcriptional and functional profilling of human embryonic stem cell-derived cardiomyocytes
Human embryonic stemcells (hESCs) can serve as a potentially limitless source of cells that may enable regeneration of diseased tissue and organs. Here we investigate the use of human embryonic stemcell-derived cardiomyocytes (hESC-CMs) in promoting recovery from cardiac ischemia reperfusion injury in a mouse model. Using microarrays, we have described the hESC-CM transcriptome within the spectrum of changes that occur between undifferentiated hESCs and fetal heart cells. The hESC-CMs expressed cardiomyocyte genes at levels similar to those found in 20-week fetal heart cells, making this population a good source of potential replacement cells in vivo. Echocardiographic studies showed significant improvement in heart function by 8 weeks after transplantation. Finally, we demonstrate long-term engraftment of hESC-CMs by using molecular imaging to track cellular localization, survival, and proliferation in vivo. Taken together, global gene expression profiling of hESC differentiation enables a systems-based analysis of the biological processes, networks, and genes that drive hESC fate decisions, and studies such as this will serve as the foundation for future clinical applications of stem cell therapies. © 2008 Cao et al.published_or_final_versio
A theory for the impact of a wave breaking onto a permeable barrier with jet generation
We model a water wave impact onto a porous breakwater. The breakwater surface is modelled as a thin barrier composed of solid matter pierced by channels through which water can flow freely. The water in the wave is modelled as a finite-length volume of inviscid, incompressible fluid in quasi-one-dimensional flow during its impact and flow through a typical hole in the barrier. The fluid volume moves at normal incidence to the barrier. After the initial impact the wave water starts to slow down as it passes through holes in the barrier. Each hole is the source of a free jet along whose length the fluid velocity and width vary in such a way as to conserve volume and momentum at zero pressure. We find there are two types of flow, depending on the porosity, ß , of the barrier. If ß : 0 = ß < 0.5774 then the barrier is a strong impediment to the flow, in that the fluid velocity tends to zero as time tends to infinity. But if ß : 0.5774 = ß = 1 then the barrier only temporarily holds up the flow, and the decelerating wave water passes through in a finite time. We report results for the velocity and impact pressure due to the incident wave water, and for the evolving shape of the jet, with examples from both types of impact. We account for the impulse on the barrier and the conserved kinetic energy of the flow. Consideration of small ß gives insight into the sudden changes in flow and the high pressures that occur when a wave impacts a nearly impermeable seawall
High Energy Cosmic Rays From Supernovae
Cosmic rays are charged relativistic particles that reach the Earth with
extremely high energies, providing striking evidence of the existence of
effective accelerators in the Universe. Below an energy around
eV cosmic rays are believed to be produced in the Milky Way while above that
energy their origin is probably extragalactic. In the early '30s supernovae
were already identified as possible sources for the Galactic component of
cosmic rays. After the '70s this idea has gained more and more credibility
thanks to the the development of the diffusive shock acceleration theory, which
provides a robust theoretical framework for particle energization in
astrophysical environments. Afterwards, mostly in recent years, much
observational evidence has been gathered in support of this framework,
converting a speculative idea in a real paradigm. In this Chapter the basic
pillars of this paradigm will be illustrated. This includes the acceleration
mechanism, the non linear effects produced by accelerated particles onto the
shock dynamics needed to reach the highest energies, the escape process from
the sources and the transportation of cosmic rays through the Galaxy. The
theoretical picture will be corroborated by discussing several observations
which support the idea that supernova remnants are effective cosmic ray
factories.Comment: Final draft of a chapter in "Handbook of Supernovae" edited by Athem
W. Alsabti and Paul Murdi
Fast and flexible selection with a single switch
Selection methods that require only a single-switch input, such as a button
click or blink, are potentially useful for individuals with motor impairments,
mobile technology users, and individuals wishing to transmit information
securely. We present a single-switch selection method, "Nomon," that is general
and efficient. Existing single-switch selection methods require selectable
options to be arranged in ways that limit potential applications. By contrast,
traditional operating systems, web browsers, and free-form applications (such
as drawing) place options at arbitrary points on the screen. Nomon, however,
has the flexibility to select any point on a screen. Nomon adapts automatically
to an individual's clicking ability; it allows a person who clicks precisely to
make a selection quickly and allows a person who clicks imprecisely more time
to make a selection without error. Nomon reaps gains in information rate by
allowing the specification of beliefs (priors) about option selection
probabilities and by avoiding tree-based selection schemes in favor of direct
(posterior) inference. We have developed both a Nomon-based writing application
and a drawing application. To evaluate Nomon's performance, we compared the
writing application with a popular existing method for single-switch writing
(row-column scanning). Novice users wrote 35% faster with the Nomon interface
than with the scanning interface. An experienced user (author TB, with > 10
hours practice) wrote at speeds of 9.3 words per minute with Nomon, using 1.2
clicks per character and making no errors in the final text.Comment: 14 pages, 5 figures, 1 table, presented at NIPS 2009 Mini-symposi
Evolutionary connectionism: algorithmic principles underlying the evolution of biological organisation in evo-devo, evo-eco and evolutionary transitions
The mechanisms of variation, selection and inheritance, on which evolution by natural selection depends, are not fixed over evolutionary time. Current evolutionary biology is increasingly focussed on understanding how the evolution of developmental organisations modifies the distribution of phenotypic variation, the evolution of ecological relationships modifies the selective environment, and the evolution of reproductive relationships modifies the heritability of the evolutionary unit. The major transitions in evolution, in particular, involve radical changes in developmental, ecological and reproductive organisations that instantiate variation, selection and inheritance at a higher level of biological organisation. However, current evolutionary theory is poorly equipped to describe how these organisations change over evolutionary time and especially how that results in adaptive complexes at successive scales of organisation (the key problem is that evolution is self-referential, i.e. the products of evolution change the parameters of the evolutionary process). Here we first reinterpret the central open questions in these domains from a perspective that emphasises the common underlying themes. We then synthesise the findings from a developing body of work that is building a new theoretical approach to these questions by converting well-understood theory and results from models of cognitive learning. Specifically, connectionist models of memory and learning demonstrate how simple incremental mechanisms, adjusting the relationships between individually-simple components, can produce organisations that exhibit complex system-level behaviours and improve the adaptive capabilities of the system. We use the term “evolutionary connectionism” to recognise that, by functionally equivalent processes, natural selection acting on the relationships within and between evolutionary entities can result in organisations that produce complex system-level behaviours in evolutionary systems and modify the adaptive capabilities of natural selection over time. We review the evidence supporting the functional equivalences between the domains of learning and of evolution, and discuss the potential for this to resolve conceptual problems in our understanding of the evolution of developmental, ecological and reproductive organisations and, in particular, the major evolutionary transitions
Identification of a protein encoded in the EB-viral open reading frame BMRF2
Using monospecific rabbit sera against a peptide derived from a potential antigenic region of the Epstein-Barr viral amino acid sequence encoded in the open reading frame BMRF2 we could identify a protein-complex of 53/55 kDa in chemically induced B95-8, P3HR1 and Raji cell lines. This protein could be shown to be membrane-associated, as predicted by previous computer analysis of the secondary structure and hydrophilicity pattern, and may be a member of EBV-induced membrane proteins in lytically infected cells
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