328 research outputs found
High frequency wave packets for the Schrödinger equation and its numerical approximations [Paquets d'ondes à haute fréquence pour l'équation de Schrödinger et ses approximations numériques]
We build Gaussian wave packets for the linear Schrödinger equation and its finite difference space semi-discretization and illustrate the lack of uniform dispersive properties of the numerical solutions as established in Ignat and Zuazua (2009) [6]. It is by now well known that bigrid algorithms provide filtering mechanisms allowing to recover the uniformity of the dispersive properties as the mesh size goes to zero. We analyze and illustrate numerically how these high frequency wave packets split and propagate under these bigrid filtering mechanisms, depending on how the fine grid/coarse grid filtering is implemented
Propagation of 1D Waves in Regular Discrete Heterogeneous Media: A Wigner Measure Approach
In this article, we describe the propagation properties of the one-dimensional wave and transport equations with variable coefficients semi-discretized in space by finite difference schemes on non-uniform meshes obtained as diffeomorphic transformations of uniform ones. In particular, we introduce and give a rigorous meaning to notions like the principal symbol of the discrete wave operator and the corresponding bi-characteristic rays. The main mathematical tool we employ is the discrete Wigner transform, which, in the limit as the mesh size parameter tends to zero, yields the so-called Wigner (semiclassical) measure. This measure provides the dynamics of the bi-characteristic rays, i.e., the solutions of the Hamiltonian system describing the propagation, in both physical and Fourier spaces, of the energy of the solution to the wave equation. We show that, due to dispersion phenomena, the high-frequency numerical dynamics does not coincide with the continuous one. Our analysis holds for the class (Formula presented.) of globally Lipschitz coefficients and non-uniform grids obtained by means of (Formula presented.)-diffeomorphic transformations of a uniform one. We also present several numerical simulations that confirm the predicted paths of the space–time projections of the bi-characteristic rays. Based on the theoretical analysis and simulations, we describe some of the pathological phenomena that these rays might exhibit as, for example, their reflection before touching the boundary of the space domain. This leads, in particular, to the failure of the classical properties of boundary observability of continuous waves, arising in control and inverse problems theory
CUSTOMIZED WEBGIS SOLUTIONS FOR EXPOSOMICS
Abstract. Exposomics is a science aiming at quantifying the effects on human health of all the factors influencing it, but genetic ones. They include environment, food, mobility habits and cultural factors. The percentage of the world's population living in the urban areas is projected to increase in the next decades. Rising industrialization, urbanization and heterogeneity are leading to new challenges for public health and quality of life in the population. The prevalence of conditions such as asthma and cardiovascular diseases is increasing due to a change in lifestyle and air quality. This enlightens the necessity of targeted interventions to increase citizens' quality of life and decrease their health risks. Within the EU H2020 PULSE project, a multi-technological system to assist the population in the prevention and treatment of asthma and type 2 diabetes has been developed. The system created in PULSE features several parts, such as a personal App for the citizens, a set of air quality sensors, a WebGIS and dashboards for the public health operators. Citizens are directly involved in an exchange paradigm in which they send their own data and receive feedbacks and suggestions about their health in return. The WebGIS is a very distinguishing element of the PULSE technology and the paper illustrates its main functionalities focusing on the distinguishing and innovative features developed
Thermal signal propagation in soils in Romania: conductive and non-conductive processes
Temperature data recorded in 2002 and 2003 at 10 stations out of the 70 available in the Romanian automatic weather stations network are presented and analyzed in terms of the heat transfer from air to underground. The air temperature at 2 m, the soil temperatures at 0, 5, 10, 20, 50 and 100 cm below the surface as well as rain fall and snow cover thickness have been monitored. The selected locations sample various climate environments in Romania. Preliminary analytical modelling shows that soil temperatures track air temperature variations at certain locations and, consequently, the heat transfer is by conduction, while at other stations processes such as soil freezing and/or solar radiation heating play an important part in the heat flux balance at the air/soil interface. However, the propagation of the annual thermal signal in the uppermost one meter of soil is mainly by conduction; the inferred thermal diffusivity for 8 stations with continuous time series at all depth levels ranges from 3 to 10&times;10<sup>&minus;7</sup> m<sup>2</sup> s<sup>&minus;1</sup>
Perceiving the crust in 3D: a model integrating geological, geochemical, and geophysical data
Regional characterization of the continental crust has classically been
performed through either geologic mapping, geochemical sampling, or geophysical
surveys. Rarely are these techniques fully integrated, due to limits of data
coverage, quality, and/or incompatible datasets. We combine geologic
observations, geochemical sampling, and geophysical surveys to create a
coherent 3-D geologic model of a 50 x 50 km upper crustal region surrounding
the SNOLAB underground physics laboratory in Canada, which includes the
Southern Province, the Superior Province, the Sudbury Structure and the
Grenville Front Tectonic Zone. Nine representative aggregate units of exposed
lithologies are geologically characterized, geophysically constrained, and
probed with 109 rock samples supported by compiled geochemical databases. A
detailed study of the lognormal distributions of U and Th abundances and of
their correlation permits a bivariate analysis for a robust treatment of the
uncertainties. A downloadable 3D numerical model of U and Th distribution
defines an average heat production of 1.5W/m, and
predicts a contribution of 7.7TNU (a Terrestrial Neutrino Unit
is one geoneutrino event per 10 target protons per year) out of a
crustal geoneutrino signal of 31.1TNU. The relatively high
local crust geoneutrino signal together with its large variability strongly
restrict the SNO+ capability of experimentally discriminating among BSE
compositional models of the mantle. Future work to constrain the crustal heat
production and the geoneutrino signal at SNO+ will be inefficient without more
detailed geophysical characterization of the 3D structure of the heterogeneous
Huronian Supergroup, which contributes the largest uncertainty to the
calculation.Comment: 25 pages, 9 figures, 6 table
First archaeological evidence for ginger consumption as a potential medicinal ingredient in a late medieval leprosarium at St Leonard, Peterborough, England
Leprosy was one of the most outwardly visible diseases in the European Middle Ages, a period during which leprosaria were founded to provide space for the sick. The extant documentary evidence for leprosy hospitals, especially in relation to diet, therapeutic, and medical care, is limited. However, human dental calculus stands to be an important source of information as it provides insight into the substances people were exposed to and accumulated in their bodies during their lives. In the present study, microremains and DNA were analysed from the calculus of individuals buried in the late medieval cemetery of St Leonard, a leprosarium located in Peterborough, England. The results show the presence of ginger (Zingiber officinale), a culinary and medicinal ingredient, as well as evidence of consumption of cereals and legumes. This research suggests that affected individuals consumed ingredients mentioned in medieval medical textbooks that were used to treat regions of the body typically impacted by leprosy. To the authors' knowledge, this is the first study which has identified Zingiber officinale in human dental calculus in England or on the wider European continent
Electromagnetic follow-up of gravitational wave transient signal candidates
Pioneering efforts aiming at the development of multi-messenger gravitational
wave and electromagnetic astronomy have been made. An electromagnetic
observation follow-up program of candidate gravitational wave events has been
performed (Dec 17 2009 to Jan 8 2010 and Sep 4 to Oct 20 2010) during the
recent runs of the LIGO and Virgo gravitational wave detectors. It involved
ground-based and space electromagnetic facilities observing the sky at optical,
X-ray and radio wavelengths. The joint gravitational wave and electromagnetic
observation study requires the development of specific image analysis
procedures able to discriminate the possible electromagnetic counterpart of
gravitational wave triggers from contaminant/background events. The paper
presents an overview of the electromagnetic follow-up program and the image
analysis procedures.Comment: Proceedings of the 12th International Conference on "Topics in
Astroparticle and Underground Physics" (TAUP 2011), Munich, September 2011
(to appear in IoP Journal of Physics: Conference Series
Anodal-tDCS over the human right occipital cortex enhances the perception and memory of both faces and objects
Accurate face processing skills are pivotal for typical social cognition, and impairments in
this ability characterise various clinical conditions (e.g., prosopagnosia). No study to date has
investigated whether transcranial direct current stimulation (tDCS) can causally enhance face
processing. In addition, the category- and the process- specificity of tDCS effects, as well as
the role of the timing of neuromodulation with respect to the execution of cognitive tasks are
still unknown. In this single-blind, sham-controlled study, we examined whether the
administration of anodal-tDCS (a-tDCS) over the right occipital cortex of healthy volunteers
(N = 64) enhances performance on perceptual and memory tasks involving both face and
object stimuli. Neuromodulation was delivered in two conditions: online (a-tDCS during task
execution) and offline (a-tDCS before task execution). The results demonstrate that offline atDCS
enhances the perception and memory performance of both faces and objects. There was
no effect of online a-tDCS on behaviour. Furthermore, the offline effect was site-specific
since a-tDCS over the sensory-motor cortex did not lead to behavioural changes. Our results
add relevant information about the breadth of cognitive processes and visual stimuli that can
be modulated by tDCS, and about the design of effective neuromodulation protocols, which
have implications for advancing theories in cognitive neuroscience and clinical applications
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