8,156 research outputs found
Environmental Epidemiology of Intestinal Schistosomiasis in Uganda: Population Dynamics of Biomphalaria (Gastropoda: Planorbidae) in Lake Albert and Lake Victoria with Observations on Natural Infections with Digenetic Trematodes
This study documented the population dynamics of Biomphalaria and associated natural infections with digenetic trematodes, along the shores of Lake Albert and Lake Victoria, recording local physicochemical factors. Over a two-and-a-half-year study period with monthly sampling, physicochemical factors were measured at 12 survey sites and all freshwater snails were collected. Retained Biomphalaria were subsequently monitored in laboratory aquaria for shedding trematode cercariae, which were classified as either human infective (Schistosoma mansoni) or nonhuman infective. The population dynamics of Biomphalaria differed by location and by lake and had positive relationship with pH (P < 0.001) in both lakes and negative relationship with conductivity (P = 0.04) in Lake Albert. Of the Biomphalaria collected in Lake Albert (N = 6,183), 8.9% were infected with digenetic trematodes of which 15.8% were shedding S. mansoni cercariae and 84.2% with nonhuman infective cercariae. In Lake Victoria, 2.1% of collected Biomphalaria (N = 13,172) were infected with digenetic trematodes with 13.9% shedding S. mansoni cercariae, 85.7% shedding nonhuman infective cercariae, and 0.4% of infected snails shedding both types of cercariae. Upon morphological identification, species of Biomphalaria infected included B. sudanica, B. pfeifferi, and B. stanleyi in Lake Albert and B. sudanica, B. pfeifferi, and B. choanomphala in Lake Victoria. The study found the physicochemical factors that influenced Biomphalaria population and infections. The number and extent of snails shedding S. mansoni cercariae illustrate the high risk of transmission within these lake settings. For better control of this disease, greater effort should be placed on reducing environmental contamination by improvement of local water sanitation and hygiene
Spillover and diffraction sidelobe contamination in a double-shielded experiment for mapping Galactic synchrotron emission
We have analyzed observations from a radioastronomical experiment to survey
the sky at decimetric wavelengths along with feed pattern measurements in order
to account for the level of ground contamination entering the sidelobes. A
major asset of the experiment is the use of a wire mesh fence around the
rim-halo shielded antenna with the purpose of levelling out and reducing this
source of stray radiation for zenith-centered 1-rpm circular scans. We
investigate the shielding performance of the experiment by means of a geometric
diffraction model in order to predict the level of the spillover and
diffraction sidelobes in the direction of the ground. Using 408 MHz and 1465
MHz feed measurements, the model shows how a weakly-diffracting and unshielded
antenna configuration becomes strongly-diffracting and double-shielded as
far-field diffraction effects give way to near-field ones. Due to the
asymmetric response of the feeds, the orientation of their radiation fields
with respect to the secondary must be known a priori before comparing model
predictions with observational data. By adjusting the attenuation coefficient
of the wire mesh the model is able to reproduce the amount of differential
ground pick-up observed during test measurements at 1465 MHz.Comment: 14 pages, 17 eps + 1 gif figures and 4 Tables. Accepted for
publication in A&AS. Fig.7 available at full resolution from
http://www.das.inpe.br/~tello/publications.ht
Optimizing Connectivity through Network Gradients for the Restricted Boltzmann Machine
Leveraging sparse networks to connect successive layers in deep neural
networks has recently been shown to provide benefits to large scale
state-of-the-art models. However, network connectivity also plays a significant
role on the learning performance of shallow networks, such as the classic
Restricted Boltzmann Machines (RBM). Efficiently finding sparse connectivity
patterns that improve the learning performance of shallow networks is a
fundamental problem. While recent principled approaches explicitly include
network connections as model parameters that must be optimized, they often rely
on explicit penalization or have network sparsity as a hyperparameter. This
work presents a method to find optimal connectivity patterns for RBMs based on
the idea of network gradients (NCG): computing the gradient of every possible
connection, given a specific connection pattern, and using the gradient to
drive a continuous connection strength parameter that in turn is used to
determine the connection pattern. Thus, learning RBM parameters and learning
network connections is truly jointly performed, albeit with different learning
rates, and without changes to the objective function. The method is applied to
the MNIST and other datasets showing that better RBM models are found for the
benchmark tasks of sample generation and input classification. Results also
show that NCG is robust to network initialization, both adding and removing
network connections while learning
Nonperturbative Ball-Chiu construction of the three-gluon vertex
We present the detailed derivation of the longitudinal part of the
three-gluon vertex from the Slavnov-Taylor identities that it satisfies, by
means of a nonperturbative implementation of the Ball-Chiu construction; the
latter, in its original form, involves the inverse gluon propagator, the ghost
dressing function, and certain form factors of the ghost-gluon kernel. The main
conceptual subtlety that renders this endeavor nontrivial is the infrared
finiteness of the gluon propagator, and the resulting need to separate the
vertex into two pieces, one that is intimately connected with the emergence of
a gluonic mass scale, and one that satisfies the original set of Slavnov-Taylor
identities, but with the inverse gluon propagator replaced by its "kinetic"
term. The longitudinal form factors obtained by this construction are presented
for arbitrary Euclidean momenta, as well as special kinematic configurations,
parametrized by a single momentum. A particularly preeminent feature of the
components comprising the tree-level vertex is their considerable suppression
for momenta below 1 GeV, and the appearance of the characteristic
"zero-crossing" in the vicinity of 100-200 MeV. Special combinations of the
form factors derived with this method are compared with the results of recent
large-volume lattice simulations as well as Schwinger-Dyson equations, and good
overall agreement is found. A variety of issues related to the distribution of
the pole terms responsible for the gluon mass generation are discussed in
detail, and their impact on the structure of the transverse parts is
elucidated. In addition, a brief account of several theoretical and
phenomenological possibilities involving these newly acquired results is
presented.Comment: 55 pages, 18 figure
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