252 research outputs found
N-complexes as functors, amplitude cohomology and fusion rules
We consider N-complexes as functors over an appropriate linear category in
order to show first that the Krull-Schmidt Theorem holds, then to prove that
amplitude cohomology only vanishes on injective functors providing a well
defined functor on the stable category. For left truncated N-complexes, we show
that amplitude cohomology discriminates the isomorphism class up to a
projective functor summand. Moreover amplitude cohomology of positive
N-complexes is proved to be isomorphic to an Ext functor of an indecomposable
N-complex inside the abelian functor category. Finally we show that for the
monoidal structure of N-complexes a Clebsch-Gordan formula holds, in other
words the fusion rules for N-complexes can be determined.Comment: Final versio
Active Video/Arcade Games (Exergaming) and Energy Expenditure in College Students.
Video games have become increasingly popular among young adults. The purpose of this pilot study was to determine if interactive video/arcade games, requiring physical activity to play, increase the energy expenditure (EE) and heart rate (HR) of young adults enough to elicit a training response. Thirteen male and female participants 26.6 ± 5.7 years of age were in the study. Participants were familiarized with equipment and allowed to practice with three games: (1) moving and striking lighted pads, (2) riding a bike to increase the pace of a race car, and (3) boxing against a video simulated opponent. A portable metabolic cart and HR monitor were attached to participants to measure baseline and exercise values. Participants could play any of the three games for 30 minutes while metabolic and HR data were collected. Exercise data were compared to baseline measures, and the 3 games were compared for EE. Paired sample t-tests showed baseline and exercise values differed for HR (t(12) = -18.91, p \u3c 0.01), and EE (t(12) = -15.62, p \u3c 0.01). The boxing game provided the highest VO2 (17.47 ± 4.79 ml·kg·-1min-1). Participants achieved 60% or better of their HR reserve (162.82 ± 10.78 beats·min-1), well within the ACSM guidelines for a training HR. Caloric expenditure during the 30-minute exercise session (226. 07 ± 48.68) is also within the ACSM recommendations for daily physical activity. Thus, interactive video/arcade games that require physical activity to play can be utilized as part of an overall aerobic exercise program
Instability of one-step replica-symmetry-broken phase in satisfiability problems
We reconsider the one-step replica-symmetry-breaking (1RSB) solutions of two
random combinatorial problems: k-XORSAT and k-SAT. We present a general method
for establishing the stability of these solutions with respect to further steps
of replica-symmetry breaking. Our approach extends the ideas of [A.Montanari
and F. Ricci-Tersenghi, Eur.Phys.J. B 33, 339 (2003)] to more general
combinatorial problems.
It turns out that 1RSB is always unstable at sufficiently small clauses
density alpha or high energy. In particular, the recent 1RSB solution to 3-SAT
is unstable at zero energy for alpha< alpha_m, with alpha_m\approx 4.153. On
the other hand, the SAT-UNSAT phase transition seems to be correctly described
within 1RSB.Comment: 26 pages, 7 eps figure
Diversity of the gut microbiota and eczema in early life
<p>Abstract</p> <p>Background</p> <p>A modest number of prospective studies of the composition of the intestinal microbiota and eczema in early life have yielded conflicting results.</p> <p>Objective</p> <p>To examine the relationship between the bacterial diversity of the gut and the development of eczema in early life by methods other than stool culture.</p> <p>Methods</p> <p>Fecal samples were collected from 21 infants at 1 and 4 months of life. Nine infants were diagnosed with eczema by the age of 6 months (cases) and 12 infants were not (controls). After conducting denaturating gradient gel electrophoresis (DGGE) of stool samples, we compared the microbial diversity of cases and controls using the number of electrophoretic bands and the Shannon index of diversity (<it>H'</it>) as indicators.</p> <p>Results</p> <p>Control subjects had significantly greater fecal microbial diversity than children with eczema at ages 1 (mean <it>H' </it>for controls = 0.75 vs. 0.53 for cases, P = 0.01) and 4 months (mean <it>H' </it>for controls = 0.92 vs. 0.59 for cases, P = 0.02). The increase in diversity from 1 to 4 months of age was significant in controls (P = 0.04) but not in children who developed eczema by 6 months of age (P = 0.32).</p> <p>Conclusion</p> <p>Our findings suggest that reduced microbial diversity is associated with the development of eczema in early life.</p
A population of gamma-ray emitting globular clusters seen with the Fermi Large Area Telescope
Globular clusters with their large populations of millisecond pulsars (MSPs)
are believed to be potential emitters of high-energy gamma-ray emission. Our
goal is to constrain the millisecond pulsar populations in globular clusters
from analysis of gamma-ray observations. We use 546 days of continuous
sky-survey observations obtained with the Large Area Telescope aboard the Fermi
Gamma-ray Space Telescope to study the gamma-ray emission towards 13 globular
clusters. Steady point-like high-energy gamma-ray emission has been
significantly detected towards 8 globular clusters. Five of them (47 Tucanae,
Omega Cen, NGC 6388, Terzan 5, and M 28) show hard spectral power indices and clear evidence for an exponential cut-off in the range
1.0-2.6 GeV, which is the characteristic signature of magnetospheric emission
from MSPs. Three of them (M 62, NGC 6440 and NGC 6652) also show hard spectral
indices , however the presence of an exponential cut-off
can not be unambiguously established. Three of them (Omega Cen, NGC 6388, NGC
6652) have no known radio or X-ray MSPs yet still exhibit MSP spectral
properties. From the observed gamma-ray luminosities, we estimate the total
number of MSPs that is expected to be present in these globular clusters. We
show that our estimates of the MSP population correlate with the stellar
encounter rate and we estimate 2600-4700 MSPs in Galactic globular clusters,
commensurate with previous estimates. The observation of high-energy gamma-ray
emission from a globular cluster thus provides a reliable independent method to
assess their millisecond pulsar populations that can be used to make
constraints on the original neutron star X-ray binary population, essential for
understanding the importance of binary systems in slowing the inevitable core
collapse of globular clusters.Comment: Accepted for publication in A&A. Corresponding authors: J.
Kn\"odlseder, N. Webb, B. Pancraz
Automated hippocampal segmentation in 3D MRI using random undersampling with boosting algorithm
The automated identification of brain structure in Magnetic Resonance Imaging is very important both in neuroscience research and as a possible clinical diagnostic tool. In this study, a novel strategy for fully automated hippocampal segmentation in MRI is presented. It is based on a supervised algorithm, called RUSBoost, which combines data random undersampling with a boosting algorithm. RUSBoost is an algorithm specifically designed for imbalanced classification, suitable for large data sets because it uses random undersampling of the majority class. The RUSBoost performances were compared with those of ADABoost, Random Forest and the publicly available brain segmentation package, FreeSurfer. This study was conducted on a data set of 50 T1-weighted structural brain images. The RUSBoost-based segmentation tool achieved the best results with a Dice’s index of (Formula presented.) (Formula presented.) for the left (right) brain hemisphere. An independent data set of 50 T1-weighted structural brain scans was used for an independent validation of the fully trained strategies. Again the RUSBoost segmentations compared favorably with manual segmentations with the highest performances among the four tools. Moreover, the Pearson correlation coefficient between hippocampal volumes computed by manual and RUSBoost segmentations was 0.83 (0.82) for left (right) side, statistically significant, and higher than those computed by Adaboost, Random Forest and FreeSurfer. The proposed method may be suitable for accurate, robust and statistically significant segmentations of hippocampi
Brain Health Services: organization, structure, and challenges for implementation. A user manual for Brain Health Services—part 1 of 6
Dementia has a devastating impact on the quality of life of patients and families and comes with a huge cost to society. Dementia prevention is considered a public health priority by the World Health Organization. Delaying the onset of dementia by treating associated risk factors will bring huge individual and societal benefit. Empirical evidence suggests that, in higher-income countries, dementia incidence is decreasing as a result of healthier lifestyles. This observation supports the notion that preventing dementia is possible and that a certain degree of prevention is already in action. Further reduction of dementia incidence through deliberate prevention plans is needed to counteract its growing prevalence due to increasing life expectancy. An increasing number of individuals with normal cognitive performance seek help in the current memory clinics asking an evaluation of their dementia risk, preventive interventions, or interventions to ameliorate their cognitive performance. Consistent evidence suggests that some of these individuals are indeed at increased risk of dementia. This new health demand asks for a shift of target population, from patients with cognitive impairment to worried but cognitively unimpaired individuals. However, current memory clinics do not have the programs and protocols in place to deal with this new population. We envision the development of new services, henceforth called Brain Health Services, devoted to respond to demands from cognitively unimpaired individuals concerned about their risk of dementia. The missions of Brain Health Services will be (i) dementia risk profiling, (ii) dementia risk communication, (iii) dementia risk reduction, and (iv) cognitive enhancement. In this paper, we present the organizational and structural challenges associated with the set-up of Brain Health Services
Fermi Large Area Telescope Constraints on the Gamma-ray Opacity of the Universe
The Extragalactic Background Light (EBL) includes photons with wavelengths
from ultraviolet to infrared, which are effective at attenuating gamma rays
with energy above ~10 GeV during propagation from sources at cosmological
distances. This results in a redshift- and energy-dependent attenuation of the
gamma-ray flux of extragalactic sources such as blazars and Gamma-Ray Bursts
(GRBs). The Large Area Telescope onboard Fermi detects a sample of gamma-ray
blazars with redshift up to z~3, and GRBs with redshift up to z~4.3. Using
photons above 10 GeV collected by Fermi over more than one year of observations
for these sources, we investigate the effect of gamma-ray flux attenuation by
the EBL. We place upper limits on the gamma-ray opacity of the Universe at
various energies and redshifts, and compare this with predictions from
well-known EBL models. We find that an EBL intensity in the optical-ultraviolet
wavelengths as great as predicted by the "baseline" model of Stecker et al.
(2006) can be ruled out with high confidence.Comment: 42 pages, 12 figures, accepted version (24 Aug.2010) for publication
in ApJ; Contact authors: A. Bouvier, A. Chen, S. Raino, S. Razzaque, A.
Reimer, L.C. Reye
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
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