1,523 research outputs found
Analysis and Assembling of Network Structure in Mutualistic Systems
It has been observed that mutualistic bipartite networks have a nested
structure of interactions. In addition, the degree distributions associated
with the two guilds involved in such networks (e.g. plants & pollinators or
plants & seed dispersers) approximately follow a truncated power law. We show
that nestedness and truncated power law distributions are intimately linked,
and that any biological reasons for such truncation are superimposed to finite
size effects . We further explore the internal organization of bipartite
networks by developing a self-organizing network model (SNM) that reproduces
empirical observations of pollination systems of widely different sizes. Since
the only inputs to the SNM are numbers of plant and animal species, and their
interactions (i.e., no data on local abundance of the interacting species are
needed), we suggest that the well-known association between species frequency
of interaction and species degree is a consequence rather than a cause, of the
observed network structure.Comment: J. of. Theor. Biology, in pres
High energy photon-neutrino elastic scattering
The one-loop helicity amplitudes for the elastic scattering process
in the Standard Model are computed at high center of
mass energies. A general decomposition of the amplitudes is utilized to
investigate the validity of some of the key features of our results. In the
center of mass, where , the cross section grows roughly as
to near the threshold for -boson production, .
Although suppressed at low energies, we find that the elastic cross section
exceeds the cross section for when
GeV. We demonstrate that the scattered photons are circularly polarized and the
net value of the polarization is non-zero. Astrophysical implications of high
energy photon-neutrino scattering are discussed.Comment: 9 pages, 7 figures, RevTeX
Real-time evaluation of the on-board comfort of standing passenger in bus transit services
Bus on-board comfort may be intended as a multidimensional concept declined according to several attributes (e.g., vibrations, the load factor, the driving style, etc.) and represents a key factor of service quality. Thus, its measurement is crucial for public transport companies as it can support for the monitoring, evaluation and implementation of specific actions to improve their services.
The objective of this paper is to build a numerical scale for real-time measurement of bus on-board comfort. This is pursued integrating subjective measurements of the driving style provided by the passengers with objective ones of longitudinal and transversal accelerations data collected by Intelligent Transportation System tools.
The results are very useful because they represent a contribution to establish a comfort scale in a real operational environment, as a tool to regulate the driver's behavior: each driver is in the position of real-time monitoring the quality of a bus ride regarding on-board comfort level
Measurement of the inclusive-isolated prompt-photon cross section in p(p)over-bar collisions using the full CDF data set
A measurement of the inclusive production cross section of isolated prompt photons in proton-antiproton collisions at center-of-mass energy root s = 1.96 TeV is presented. The results are obtained using the full Run II data sample collected with the Collider Detector at the Fermilab Tevatron, which corresponds to an integrated luminosity of 9.5 fb(-1). The cross section is measured as a function of photon transverse energy, E-T(gamma), in the range 30 <E-T(gamma) <500 GeV and in the pseudorapidity region |eta(gamma)| <1.0. The results are compared with predictions from parton-shower Monte Carlo models at leading order in QCD and from next-to-leading-order perturbative QCD calculations. The latter show good agreement with the measured cross section.Peer reviewe
A genome-wide association study identifies a susceptibility locus for biliary atresia on 2p16.1 within the gene EFEMP1
Biliary atresia (BA) is a rare pediatric cholangiopathy characterized by fibrosclerosing obliteration of the extrahepatic bile ducts, leading to cholestasis, fibrosis, cirrhosis, and eventual liver failure. The etiology of BA remains unknown, although environmental, inflammatory, infectious, and genetic risk factors have been proposed. We performed a genome-wide association study (GWAS) in a European-American cohort of 343 isolated BA patients and 1716 controls to identify genetic loci associated with BA. A second GWAS was performed in an independent European-American cohort of 156 patients with BA and other extrahepatic anomalies and 212 controls to confirm the identified candidate BA-associated SNPs. Meta-analysis revealed three genome-wide significant BA-associated SNPs on 2p16.1 (rs10865291, rs6761893, and rs727878; P < 5 Ă—10-8), located within the fifth intron of the EFEMP1 gene, which encodes a secreted extracellular protein implicated in extracellular matrix remodeling, cell proliferation, and organogenesis. RNA expression analysis showed an increase in EFEMP1 transcripts from human liver specimens isolated from patients with either BA or other cholestatic diseases when compared to normal control liver samples. Immunohistochemistry demonstrated that EFEMP1 is expressed in cholangiocytes and vascular smooth muscle cells in liver specimens from patients with BA and other cholestatic diseases, but it is absent from cholangiocytes in normal control liver samples. Efemp1 transcripts had higher expression in cholangiocytes and portal fibroblasts as compared with other cell types in normal rat liver. The identification of a novel BA-associated locus, and implication of EFEMP1 as a new BA candidate susceptibility gene, could provide new insights to understanding the mechanisms underlying this severe pediatric disorder
The light-cone gauge and the calculation of the two-loop splitting functions
We present calculations of next-to-leading order QCD splitting functions,
employing the light-cone gauge method of Curci, Furmanski, and Petronzio (CFP).
In contrast to the `principal-value' prescription used in the original CFP
paper for dealing with the poles of the light-cone gauge gluon propagator, we
adopt the Mandelstam-Leibbrandt prescription which is known to have a solid
field-theoretical foundation. We find that indeed the calculation using this
prescription is conceptionally clear and avoids the somewhat dubious
manipulations of the spurious poles required when the principal-value method is
applied. We reproduce the well-known results for the flavour non-singlet
splitting function and the N_C^2 part of the gluon-to-gluon singlet splitting
function, which are the most complicated ones, and which provide an exhaustive
test of the ML prescription. We also discuss in some detail the x=1 endpoint
contributions to the splitting functions.Comment: 41 Pages, LaTeX, 8 figures and tables as eps file
Hungry brains: A meta-analytical review of brain activation imaging studies on food perception and appetite in obese individuals
The dysregulation of food intake in chronic obesity has been explained by different theories. To assess their explanatory power, we meta-analyzed 22 brain-activation imaging studies. We found that obese individuals exhibit hyper-responsivity of the brain regions involved in taste and reward for food-related stimuli. Consistent with a Reward Surfeit Hypothesis, obese individuals exhibit a ventral striatum hyper-responsivity in response to pure tastes, particularly when fasting. Furthermore, we found that obese subjects display more frequent ventral striatal activation for visual food cues when satiated: this continued processing within the reward system, together with the aforementioned evidence, is compatible with the Incentive Sensitization Theory. On the other hand, we did not find univocal evidence in favor of a Reward Deficit Hypothesis nor for a systematic deficit of inhibitory cognitive control. We conclude that the available brain activation data on the dysregulated food intake and food-related behavior in chronic obesity can be best framed within an Incentive Sensitization Theory. Implications of these findings for a brain-based therapy of obesity are briefly discussed
Next-to-Leading Order QCD Corrections to Jet Cross Sections and Jet Rates in Deeply Inelastic Electron Proton Scattering
Jet cross sections in deeply inelastic scattering in the case of transverse
photon exchange for the production of (1+1) and (2+1) jets are calculated in
next-to-leading order QCD (here the `+1' stands for the target remnant jet,
which is included in the jet definition for reasons that will become clear in
the main text). The jet definition scheme is based on a modified JADE cluster
algorithm. The calculation of the (2+1) jet cross section is described in
detail. Results for the virtual corrections as well as for the real initial-
and final state corrections are given explicitly. Numerical results are stated
for jet cross sections as well as for the ratio \sigma_{\mbox{\small (2+1)
jet}}/\sigma_{\mbox{\small tot}} that can be expected at E665 and HERA.
Furthermore the scale ambiguity of the calculated jet cross sections is studied
and different parton density parametrizations are compared.Comment: 40 pages, LBL-34147 (Latex file). (figures available by mail on
request (send e-mail to [email protected]), please include your address
such that it can be used as an address label
Perturbative Calculation of the Adiabatic Geometric Phase and Particle in a Well with Moving Walls
We use the Rayleigh-Schr\"odinger perturbation theory to calculate the
corrections to the adiabatic geometric phase due to a perturbation of the
Hamiltonian. We show that these corrections are at least of second order in the
perturbation parameter. As an application of our general results we address the
problem of the adiabatic geometric phase for a one-dimensional particle which
is confined to an infinite square well with moving walls.Comment: Plain Latex, accepted for publication in J. Phys. A: Math. Ge
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