8,784 research outputs found
Body image distortions following spinal cord injury
Background: Following spinal cord injury (SCI) or anaesthesia, people may continue to experience feelings of the size, shape, and posture of their body, suggesting that the conscious body image is not fully determined by immediate sensory signals. How this body image is affected by changes in sensory inputs from, and motor outputs to the body remains unclear.
Methods: We tested paraplegic and tetraplegic SCI patients on a task that yields quantitative measures of body image. Participants were presented with an anchoring stimulus on a computer screen and told to imagine that the displayed body part was part of a standing mirror image of themselves. They then identified the position on the screen, relative to the anchor, where each of several parts of their body would be located. Veridical body dimensions were identified based on measurements and photographs of participants.
Results: Compared to age-matched controls, paraplegic and tetraplegic patients alike perceived their torso and limbs as elongated relative to their body width. No effects of lesion level were found.
Conclusions: The common distortions in body image across patient groups, despite differing SCI levels, imply that a body image may be maintained despite chronic sensory and motor loss. Systematic alterations in body image follow SCI, though our results suggest these may reflect prolonged changes in body posture and wheelchair use, rather than loss of specific sensorimotor pathways. These findings provide new insight into how the body image is maintained, and may prove useful in treatments that intervene to manipulate the body image
Sampled Weighted Min-Hashing for Large-Scale Topic Mining
We present Sampled Weighted Min-Hashing (SWMH), a randomized approach to
automatically mine topics from large-scale corpora. SWMH generates multiple
random partitions of the corpus vocabulary based on term co-occurrence and
agglomerates highly overlapping inter-partition cells to produce the mined
topics. While other approaches define a topic as a probabilistic distribution
over a vocabulary, SWMH topics are ordered subsets of such vocabulary.
Interestingly, the topics mined by SWMH underlie themes from the corpus at
different levels of granularity. We extensively evaluate the meaningfulness of
the mined topics both qualitatively and quantitatively on the NIPS (1.7 K
documents), 20 Newsgroups (20 K), Reuters (800 K) and Wikipedia (4 M) corpora.
Additionally, we compare the quality of SWMH with Online LDA topics for
document representation in classification.Comment: 10 pages, Proceedings of the Mexican Conference on Pattern
Recognition 201
Entanglement generation in relativistic quantum fields
We present a general, analytic recipe to compute the entanglement that is
generated between arbitrary, discrete modes of bosonic quantum fields by
Bogoliubov transformations. Our setup allows the complete characterization of
the quantum correlations in all Gaussian field states. Additionally, it holds
for all Bogoliubov transformations. These are commonly applied in quantum
optics for the description of squeezing operations, relate the mode
decompositions of observers in different regions of curved spacetimes, and
describe observers moving along non-stationary trajectories. We focus on a
quantum optical example in a cavity quantum electrodynamics setting: an
uncharged scalar field within a cavity provides a model for an optical
resonator, in which entanglement is created by non-uniform acceleration. We
show that the amount of generated entanglement can be magnified by initial
single-mode squeezing, for which we provide an explicit formula. Applications
to quantum fields in curved spacetimes, such as an expanding universe, are
discussed.Comment: 8 pages, 2 figures, Ivette Fuentes previously published as Ivette
Fuentes-Guridi and Ivette Fuentes-Schuller; v2: published version (online),
to appear in the J. Mod. Opt. Special Issue on the Physics of Quantum
Electronic
Entanglement of Dirac fields in an expanding spacetime
We study the entanglement generated between Dirac modes in a 2-dimensional
conformally flat Robertson-Walker universe. We find radical qualitative
differences between the bosonic and fermionic entanglement generated by the
expansion. The particular way in which fermionic fields get entangled encodes
more information about the underlying space-time than the bosonic case, thereby
allowing us to reconstruct the parameters of the history of the expansion. This
highlights the importance of bosonic/fermionic statistics to account for
relativistic effects on the entanglement of quantum fields.Comment: revtex4, 7 figures, I.F. previously published as Fuentes-Guridi and
Fuentes-Schuller. Journal reference update
Stationary distributions of sums of marginally chaotic variables as renormalization group fixed points
We determine the limit distributions of sums of deterministic chaotic
variables in unimodal maps assisted by a novel renormalization group (RG)
framework associated to the operation of increment of summands and rescaling.
In this framework the difference in control parameter from its value at the
transition to chaos is the only relevant variable, the trivial fixed point is
the Gaussian distribution and a nontrivial fixed point is a multifractal
distribution with features similar to those of the Feigenbaum attractor. The
crossover between the two fixed points is discussed and the flow toward the
trivial fixed point is seen to consist of a sequence of chaotic band mergers.Comment: 7 pages, 2 figures, to appear in Journal of Physics: Conf.Series
(IOP, 2010
Early warning signals in plant disease outbreaks
Infectious disease outbreaks in plants threaten ecosystems, agricultural crops and food trade. Currently, several fungal diseases are affecting forests worldwide, posing a major risk to tree species, habitats and consequently ecosystem decay. Prediction and control of disease spread are difficult, mainly due to the complexity of the interaction between individual components involved. In this work, we introduce a lattice-based epidemic model coupled with a stochastic process that mimics, in a very simplified way, the interaction between the hosts and pathogen. We studied the disease spread by measuring the propagation velocity of the pathogen on the susceptible hosts. Our quantitative results indicate the occurrence of a critical transition between two stable phases: local confinement and an extended epiphytotic outbreak that depends on the density of the susceptible individuals. Quantitative predictions of epiphytotics are performed using the framework early-warning indicators for impending regime shifts, widely applied on dynamical systems. These signals forecast successfully the outcome of the critical shift between the two stable phases before the system enters the epiphytotic regime. Our study demonstrates that early-warning indicators could be useful for the prediction of forest disease epidemics through mathematical and computational models suited to more specific pathogen–host-environmental interactions. Our results may also be useful to identify a suitable planting density to slow down disease spread and in the future, design highly resilient forests
Water calcium concentration modifies whole-body calcium uptake in sea bream larvae during short-term adaptation to altered salinities
Whole-body calcium uptake was studied in gilthead sea bream larvae (9–83·mg) in response to changing environmental salinity and [Ca2+]. Calcium uptake increased with increased fish size and salinity. Fish
exposed to calcium-enriched, diluted seawater showed increased calcium uptake compared with fish in diluted seawater alone. Calcium uptake was unchanged in Na+-
enriched, diluted seawater. Overall, [Ca2+], and not salinity/osmolarity per se, appears to be the main factor contributing to calcium uptake. By contrast, drinking was
reduced by a decrease in salinity/osmolarity but was little affected by external [Ca2+]. Calculations of the maximum contribution from drinking-associated calcium uptake
showed that it became almost insignificant (less than 10%) through a strong decrease in drinking rate at low salinities (0–8‰). Diluted seawater enriched in calcium to the
concentration present in full-strength seawater (i.e. constant calcium, decreasing salinity) restored intestinal calcium uptake to normal. Extra-intestinal calcium uptake
also benefited from calcium addition but to a lesser extent
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