4,244 research outputs found
Geometrical statistics of the vorticity vector and the strain rate tensor in rotating turbulence
We report results on the geometrical statistics of the vorticity vector
obtained from experiments in electromagnetically forced rotating turbulence. A
range of rotation rates is considered, from non-rotating to rapidly
rotating turbulence with a maximum background rotation rate of rad/s
(with Rossby number much smaller than unity). Typically, in our experiments
. The measurement volume is located in the
centre of the fluid container above the bottom boundary layer, where the
turbulent flow can be considered locally statistically isotropic and
horizontally homogeneous for the non-rotating case, see van Bokhoven et al.,
Phys. Fluids 21, 096601 (2009). Based on the full set of velocity derivatives,
measured in a Lagrangian way by 3D Particle Tracking Velocimetry, we have been
able to quantify statistically the effect of system rotation on several flow
properties. The experimental results show how the turbulence evolves from
almost isotropic 3D turbulence ( rad/s) to quasi-2D
turbulence ( rad/s) and how this is reflected by several
statistical quantities. In particular, we have studied the orientation of the
vorticity vector with respect to the three eigenvectors of the local strain
rate tensor and with respect to the vortex stretching vector. Additionally, we
have quantified the role of system rotation on the self-amplification terms of
the enstrophy and strain rate equations and the direct contribution of the
background rotation on these evolution equations. The main effect is the strong
reduction of extreme events and related (strong) reduction of the skewness of
PDFs of several quantities such as, for example, the intermediate eigenvalue of
the strain rate tensor and the enstrophy self-amplification term.Comment: 17 pages, 6 figures, 3 table
Task 3- Deliverable 5
Il data-base dei dati accelerometrici italiani (Italian Strong Motion Data Base) copre un periodo di tempo di oltre 20 anni durante i quali non solo le reti sismiche italiane hanno subito una evoluzione notevolissima, ma lâintera sismologia mondiale e la tecnologia ad essa applicata Ăš stata completamente rivoluzionata. La rete Sismica Nazionale gestita dallâINGV (ING fino al 1999), Ăš cresciuta da 12 strumenti riportati nei bollettini del 1972 a oltre 180 nel 2004. Il Bollettino Sismico Italiano dellâanno 1972 include le fasi di 6 sismometri per un terremoto di magnitudo 5 avvenuto al largo di Ancona il 14 giugno 1972. Un terremoto di magnitudo analoga avvenuto il 25 novembre 2004 nellâAdriatico centrale, ben piĂč lontano del precedente dalle coste italiane, Ăš stato registrato da oltre 70 stazioni della Rete Sismica Nazionale. Occorre tenere presente questi dati nellâutilizzo del data-base accelerometrico perchĂ© la precisione con cui sono stati valutati i parametri ipocentrali dei terremoti Ăš variata nellâarco di tempo coperto dal data-base di un ordine di grandezza
Finite-size scaling as a way to probe near-criticality in natural swarms
Collective behaviour in biological systems is often accompanied by strong
correlations. The question has therefore arisen of whether correlation is
amplified by the vicinity to some critical point in the parameters space.
Biological systems, though, are typically quite far from the thermodynamic
limit, so that the value of the control parameter at which correlation and
susceptibility peak depend on size. Hence, a system would need to readjust its
control parameter according to its size in order to be maximally correlated.
This readjustment, though, has never been observed experimentally. By gathering
three-dimensional data on swarms of midges in the field we find that swarms
tune their control parameter and size so as to maintain a scaling behaviour of
the correlation function. As a consequence, correlation length and
susceptibility scale with the system's size and swarms exhibit a near-maximal
degree of correlation at all sizes.Comment: Selected for Viewpoint in Physics; PRL Editor's Suggestio
Collective behaviour without collective order in wild swarms of midges
Collective behaviour is a widespread phenomenon in biology, cutting through a
huge span of scales, from cell colonies up to bird flocks and fish schools. The
most prominent trait of collective behaviour is the emergence of global order:
individuals synchronize their states, giving the stunning impression that the
group behaves as one. In many biological systems, though, it is unclear whether
global order is present. A paradigmatic case is that of insect swarms, whose
erratic movements seem to suggest that group formation is a mere epiphenomenon
of the independent interaction of each individual with an external landmark. In
these cases, whether or not the group behaves truly collectively is debated.
Here, we experimentally study swarms of midges in the field and measure how
much the change of direction of one midge affects that of other individuals. We
discover that, despite the lack of collective order, swarms display very strong
correlations, totally incompatible with models of noninteracting particles. We
find that correlation increases sharply with the swarm's density, indicating
that the interaction between midges is based on a metric perception mechanism.
By means of numerical simulations we demonstrate that such growing correlation
is typical of a system close to an ordering transition. Our findings suggest
that correlation, rather than order, is the true hallmark of collective
behaviour in biological systems.Comment: The original version has been split into two parts. This first part
focuses on order vs. correlation. The second part, about finite-size scaling,
will be included in a separate paper. 15 pages, 6 figures, 1 table, 5 video
A Bridge between CP violation at Low Energies and Leptogenesis
We discuss the possibility of relating the size and sign of the observed baryon asymmetry of the universe to CP violation observable at low energies, in a framework where the observed baryon asymmetry is produced by leptogenesis through the out of the equilibrium decay of heavy Majorana neutrinos. We identify the CP violating phases entering in leptogenesis as well as those relevant for CP violation at low energies in the minimal seesaw model. We show that although in general there is no relation between these two sets of phases, there are specific frameworks in which such a connection may be established and we give a specific grand unification inspired example where such a connection does exist. We construct weak-basis invariants related to CP violation responsible for leptogenesis, as well as those relevant for CP violation at low energies
Edge Selection in Bilinear Dynamical Networks
In large-scale networks, agents (e.g., sensors and actuators) and links
(e.g., couplings and communication links) can fail or be (cyber-)attacked. In
this paper, we focus on continuous-time bilinear networks, where additive
disturbances model attack/uncertainty on agents/states (a.k.a. node
disturbances) and multiplicative disturbances model attack/uncertainty on
couplings between agents/states (a.k.a. link disturbances). We then investigate
a network robustness notion in terms of the underlying digraph of the network,
and structure of exogenous uncertainties/attacks. Specifically, we define the
robustness measure using the H2-norm of the network and calculate it in terms
of the reachability Gramian of the bilinear system. The main result shows that
under certain conditions, the measure is supermodular over the set of all
possible attacked links. The supermodular property facilitates the efficient
solution finding of the optimization problem. We conclude the paper with a few
examples illustrating how different structures can make the system more or less
vulnerable to malicious attacks on links and present our concluding remarks.Comment: 6 pages, 2 figure
Desarrollo y validación de un modelo numérico para el anålisis de uniones abulonadas en materiales compuestos
La combinaciĂłn de bajo peso y alta resistencia que brindan los materiales compuestos, los posiciona conveniente en aplicaciones estructurales exigentes, sin embargo es conocido que la vinculaciĂłn o uniĂłn entre elementos estructurales fabricados en compuestos es un punto crĂtico. En este trabajo se desarrolla un modelo numĂ©rico para estudiar una uniĂłn abulonada de solape simple de dos placas de material compuesto. El anĂĄlisis del problema se hace empleando un cĂłdigo de elementos finitos, y el modelo desarrollado contempla el mĂșltiple contacto entre las placas de compuesto, el cuerpo del bulĂłn y las arandelas. Las placas se consideran fabricadas en fibra de carbono unidireccional en una matriz de epoxi, las arandelas son de acero, mientras que el bulĂłn y la tuerca se consideran construidas en titanio. Los resultados de este anĂĄlisis computacional concuerdan muy bien con los obtenidos a nivel experimental por otros autores, no solo en cuanto a nivel tensional sino tambiĂ©n en las deformaciones y distorsiones mostradas por las placas. A partir de los resultados satisfactorios obtenidos en este trabajo, es posible proseguir con el estudio del comportamiento de otras configuraciones de abulonado.Fil: Rodriguez, Cristhian. Universidad de las Fuerzas Armadas. Departamento de Seguridad y Defensa. Ărea de Ciencias AeronĂĄuticas; Argentina.Fil: Castello, Walter B. Universidad Nacional de CĂłrdoba. Facultad de Ciencias Exactas, FĂsicas y Naturales. Departamento de Estructuras; Argentina.IngenierĂa Aeroespacia
Modulation of Hydrogen Peroxide Production in Cellular Systems by Low Level Magnetic Fields
Increased generation of reactive oxygen species (ROS) and an altered redox status have long been observed in cancer cells, suggesting that ROS might be involved in the development of these cells. However, recent studies suggest that inducing an excess of ROS in cancer cells can be exploited for therapeutic benefits. Cancer cells in advanced stage tumors frequently exhibit multiple genetic alterations and high oxidative stress, suggesting that it might be possible to preferentially modulate the development of these cells by controlling their ROS production. Low levels of ROS are also important for the development and survival of normal cells. In this manuscript, we present data on the influence of the suppression of the Earth's magnetic field (low level magnetic fields or LLF) which magnitudes range from 0.2 ”T to 2 ”T on the modulation of hydrogen peroxide (H2O2) in human fibrosarcoma cancer cell line HT1080, pancreatic AsPC-1 cancer cell line, and bovine pulmonary artery endothelial cells (PAEC) exposed to geomagnetic field (control; 45 ”Tâ60 ”T). Reduction of the Earth's magnetic field suppressed H2O2 production in cancer cells and PAEC. The addition of catalase and superoxide dismutase (SOD) mimetic MnTBAP inhibited the magnetic field effect. Modulating ROS production by magnetic fields may open new venues of biomedical research and therapeutic strategies
Modulation of humoral immune response to oral BCG vaccination by Mycobacterium bovis BCG Moreau Rio de Janeiro (RDJ) in healthy adults
BACKGROUND: Oral administration of BCG was the route initially used by Calmette and Guérin, but was replaced by intradermal administration in virtually all countries after the Lubeck accident. However, Brazil continued to administer oral BCG Moreau RDJ, which was maintained until the mid-1970s when it was substituted by the intradermal route. Although BCG vaccination has been used in humans since 1921, little is known of the induced immune response. The aim of this study was to analyse immunological responses after oral vaccination with M. bovis BCG Moreau RDJ. METHODS: This study in healthy volunteers has measured cellular and humoral aspects of the immunological response to oral M. bovis BCG Moreau RDJ in Rio de Janeiro, Brazil. T-cell trafficking and Th(1 )and Th(2 )cytokine responses are described, as well as isotype-specific antibody production using novel techniques. RESULTS: Oral immunisation has no adverse effects. We have shown that there are cellular and humoral immunological responses after oral immunisation. Oral revaccination does not induce a positive skin test in responsive individuals and multiple booster orally was able to induce modulation in humoral immunological responses (switch from IgG to IgA) in previously immunised subjects and incapable of inducing tolerance. In contrast, the cellular immune response does not differ between vaccinated individuals with positive and negative skin test reactions. CONCLUSION: All subjects, including those who did not respond to the skin test at study commencement, were capable of mounting humoral and cellular immune response to the antigens tested
Geodiversity assessment in the Beigua UNESCO Global Geopark (Liguria, Italy): valuing geoheritage for education, tourism, and community engagement
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