175 research outputs found
Probing Yukawian gravitational potential by numerical simulations. I. Changing N-body codes
In the weak field limit general relativity reduces, as is well known, to the
Newtonian gravitation. Alternative theories of gravity, however, do not
necessarily reduce to Newtonian gravitation; some of them, for example, reduce
to Yukawa-like potentials instead of the Newtonian potential. Since the
Newtonian gravitation is largely used to model with success the structures of
the universe, such as for example galaxies and clusters of galaxies, a way to
probe and constrain alternative theories, in the weak field limit, is to apply
them to model the structures of the universe. In the present study, we consider
how to probe Yukawa-like potentials using N-body numerical simulations.Comment: 17 pages, 11 figures. To appear in General Relativity and Gravitatio
Analysis of Neighbourhoods in Multi-layered Dynamic Social Networks
Social networks existing among employees, customers or users of various IT
systems have become one of the research areas of growing importance. A social
network consists of nodes - social entities and edges linking pairs of nodes.
In regular, one-layered social networks, two nodes - i.e. people are connected
with a single edge whereas in the multi-layered social networks, there may be
many links of different types for a pair of nodes. Nowadays data about people
and their interactions, which exists in all social media, provides information
about many different types of relationships within one network. Analysing this
data one can obtain knowledge not only about the structure and characteristics
of the network but also gain understanding about semantic of human relations.
Are they direct or not? Do people tend to sustain single or multiple relations
with a given person? What types of communication is the most important for
them? Answers to these and more questions enable us to draw conclusions about
semantic of human interactions. Unfortunately, most of the methods used for
social network analysis (SNA) may be applied only to one-layered social
networks. Thus, some new structural measures for multi-layered social networks
are proposed in the paper, in particular: cross-layer clustering coefficient,
cross-layer degree centrality and various versions of multi-layered degree
centralities. Authors also investigated the dynamics of multi-layered
neighbourhood for five different layers within the social network. The
evaluation of the presented concepts on the real-world dataset is presented.
The measures proposed in the paper may directly be used to various methods for
collective classification, in which nodes are assigned to labels according to
their structural input features.Comment: 16 pages, International Journal of Computational Intelligence System
Baseline pathological data of the wedge clam Donax trunculus from the Tyrrhenian Sea (Mediterranean Basin)
In recent years, a collapse in Donax trunculus fishing yields has occurred in the Tyrrhenian Sea (Mediterranean Basin). There is little information available on the impact disease may have had on D. trunculus populations. For the first time, a pathological survey was performed on the natural beds of the bivalve on the Campania and Lazio coasts, western Italy. Detected pathogens and related diseases were analysed, and their prevalence and mean intensity values were calculated. Viral particles, Chlamydia-like organisms, ciliates, coccidians, microcells and trematodes were observed. An unknown ciliate was linked to severe inflammatory and necrotic lesions in the digestive gland. Metacercariae of the trematode Postmonorchis sp. were also strongly represented in almost all samples, reaching high levels of infection; however, none of the pathogens described required the World Organisation for Animal Health to be notified. Initial results indicated that further surveys related to environmental data are necessary in order to assess the relevance of these early observations in managing the declining D. trunculus population in the Tyrrhenian Sea.postprin
A solution for galactic disks with Yukawian gravitational potential
We present a new solution for the rotation curves of galactic disks with
gravitational potential of the Yukawa type. We follow the technique employed by
Toomre in 1963 in the study of galactic disks in the Newtonian theory. This new
solution allows an easy comparison between the Newtonian solution and the
Yukawian one. Therefore, constraints on the parameters of theories of
gravitation can be imposed, which in the weak field limit reduce to Yukawian
potentials. We then apply our formulae to the study of rotation curves for a
zero-thickness exponential disk and compare it with the Newtonian case studied
by Freeman in 1970. As an application of the mathematical tool developed here,
we show that in any theory of gravity with a massive graviton (this means a
gravitational potential of the Yukawa type), a strong limit can be imposed on
the mass (m_g) of this particle. For example, in order to obtain a galactic
disk with a scale length of b ~ 10 kpc, we should have a massive graviton of
m_g << 10^{-59} g. This result is much more restrictive than those inferred
from solar system observations.Comment: 7 pages; 1 eps figure; to appear in General Relativity and
Gravitatio
Potential-density pairs for axisymmetric galaxies: the influence of scalar fields
We present a formulation for potential-density pairs to describe axisymmetric
galaxies in the Newtonian limit of scalar-tensor theories of gravity. The
scalar field is described by a modified Helmholtz equation with a source that
is coupled to the standard Poisson equation of Newtonian gravity. The net
gravitational force is given by two contributions: the standard Newtonian
potential plus a term stemming from massive scalar fields. General solutions
have been found for axisymmetric systems and the multipole expansion of the
Yukawa potential is given. In particular, we have computed potential-density
pairs of galactic disks for an exponential profile and their rotation curves.Comment: 8 pages, no figures, corrected version to the one that will appear in
Gen. Relativ. Gravit., where a small typo in eq. (13) is presen
Probing Yukawian Gravitational Potential by Numerical Simulations. II. Elliptical Galaxies
Since the Newtonian gravitation is largely used to model with success the
structures of the universe, such as galaxies and clusters of galaxies, for
example, a way to probe and constrain alternative theories, in the weak field
limit, is to apply them to model the structures of the universe. We then
modified the well known Gadget-2 code to probe alternative theories of
gravitation through galactic dynamics. In particular, we modified the Gadget-2
code to probe alternatives theories whose weak field limits have a Yukawa-like
gravitational potential. As a first application of this modified Gadget-2 code
we simulate the evolution of elliptical galaxies. These simulations show that
galactic dynamics can be used to constrain the parameters associated with
alternative theories of gravitation.Comment: 6 pages, 5 figures - To appear in General Relativity and Gravitatio
A machine learning approach to support deep brain stimulation programming
Adjusting the stimulation parameters is a challenge in deep brain stimulation (DBS) therapy due to the vast number of different configurations available. As a result, systems based on the visualization of the volume of tissue activated (VTA) produced by a particular stimulation setting have been developed. However, the medical specialist still has to search, by trial and error, for a DBS set-up that generates the desired VTA. Therefore, our goal is developing a DBS parameter tuning strategy for current clinical devices that allows defining a target VTA under biophysically viable constraints. We propose a machine learning approach that allows estimating the DBS parameter values for a given VTA, which comprises two main stages: i) A K-nearest neighbors-based deformation to define a target VTA preserving biophysically viable constraints. ii) A parameter estimation stage that consists of a data projection using metric learning to highlight relevant VTA properties, and a regression/classification algorithm to estimate the DBS parameters that generate the target VTA. Our methodology allows setting a biophysically compliant target VTA and accurately predicts the required configuration of stimulation parameters. Also, the performance of our approach is stable for both isotropic and anisotropic tissue conductivities. Furthermore, the computational time of the trained system is acceptable for real-world implementations
A complete genome screen for genes predisposing to severe bipolar disorder in two Costa Rican pedigrees
Evidence for a mixed mass composition at the `ankle' in the cosmic-ray spectrum
We report a first measurement for ultra-high energy cosmic rays of the
correlation between the depth of shower maximum and the signal in the water
Cherenkov stations of air-showers registered simultaneously by the fluorescence
and the surface detectors of the Pierre Auger Observatory. Such a correlation
measurement is a unique feature of a hybrid air-shower observatory with
sensitivity to both the electromagnetic and muonic components. It allows an
accurate determination of the spread of primary masses in the cosmic-ray flux.
Up till now, constraints on the spread of primary masses have been dominated by
systematic uncertainties. The present correlation measurement is not affected
by systematics in the measurement of the depth of shower maximum or the signal
in the water Cherenkov stations. The analysis relies on general characteristics
of air showers and is thus robust also with respect to uncertainties in
hadronic event generators. The observed correlation in the energy range around
the `ankle' at differs significantly from
expectations for pure primary cosmic-ray compositions. A light composition made
up of proton and helium only is equally inconsistent with observations. The
data are explained well by a mixed composition including nuclei with mass . Scenarios such as the proton dip model, with almost pure compositions, are
thus disfavoured as the sole explanation of the ultrahigh-energy cosmic-ray
flux at Earth.Comment: Published version. Added journal reference and DOI. Added Report
Numbe
Guillain-Barré Syndrome Outbreak in Peru 2019 Associated With Campylobacter jejuni Infection
OBJECTIVE: To identify the clinical phenotypes and infectious triggers in the 2019 Peruvian Guillain-Barré syndrome (GBS) outbreak. METHODS: We prospectively collected clinical and neurophysiologic data of patients with GBS admitted to a tertiary hospital in Lima, Peru, between May and August 2019. Molecular, immunologic, and microbiological methods were used to identify causative infectious agents. Sera from 41 controls were compared with cases for antibodies to Campylobacter jejuni and gangliosides. Genomic analysis was performed on 4 C jejuni isolates. RESULTS: The 49 included patients had a median age of 44 years (interquartile range [IQR] 30-54 years), and 28 (57%) were male. Thirty-two (65%) had symptoms of a preceding infection: 24 (49%) diarrhea and 13 (27%) upper respiratory tract infection. The median time between infectious to neurologic symptoms was 3 days (IQR 2-9 days). Eighty percent had a pure motor form of GBS, 21 (43%) had the axonal electrophysiologic subtype, and 18% the demyelinating subtype. Evidence of recent C jejuni infection was found in 28/43 (65%). No evidence of recent arbovirus infection was found. Twenty-three cases vs 11 controls (OR 3.3, confidence interval [CI] 95% 1.2-9.2, p < 0.01) had IgM and/or IgA antibodies against C jejuni. Anti-GM1:phosphatidylserine and/or anti-GT1a:GM1 heteromeric complex antibodies were strongly positive in cases (92.9% sensitivity and 68.3% specificity). Genomic analysis showed that the C jejuni strains were closely related and had the Asn51 polymorphism at cstII gene. CONCLUSIONS: Our study indicates that the 2019 Peruvian GBS outbreak was associated with C jejuni infection and that the C jejuni strains linked to GBS circulate widely in different parts of the world
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