783 research outputs found
An observational and numerical case study of a flash sea storm over the Gulf of Genoa
International audienceDuring the night between the 8 and 9 December 2006 the seawall of the Savona harbour (Liguria Region in north west of Italy) was overtopped by waves. In this work the "Savona flash sea storm" has been studied by analyzing the data recorded by meteo-marine observing stations and the data produced by high resolution meteo-marine numerical models. The data show that, due to the presence of a fast moving low pressure system, the event was characterized by a rapid transition and interaction between two different regimes of winds and related sea states. The results of the study suggest that the most damaging dynamics of the event could be correlated to a bi-modal structure of the wave spectrum. Based on this the authors suggest that a deeper study of the spectral structure of sea storms could lead to define new operational forecasting tools for the preventive evaluation of sea storms damaging potential
Spin Hall Effect and Spin Orbit coupling in Ballistic Nanojunctions
We propose a new scheme of spin filtering based on nanometric crossjunctions
in the presence of Spin Orbit interaction, employing ballistic nanojunctions
patterned in a two-dimensional electron gas. We demonstrate that the flow of a
longitudinal unpolarized current through a ballistic X junction patterned in a
two-dimensional electron gas with Spin Orbit coupling (SOC) induces a spin
accumulation which has opposite signs for the two lateral probes. This spin
accumulation, corresponding to a transverse pure spin current flowing in the
junction, is the main observable signature of the spin Hall effect in such
nanostructures.
We benchmark the effects of two different kinds of Spin Orbit interactions.
The first one (-SOC) is due to the interface electric field that
confines electrons to a two-dimensional layer, whereas the second one
(-SOC) corresponds to the interaction generated by a lateral confining
potential.Comment: 6 pages, 3 figure
Vortex knots in a Bose-Einstein condensate
We present a method for numerically building a vortex knot state in the
superfluid wave-function of a Bose-Einstein condensate. We integrate in time
the governing Gross-Pitaevskii equation to determine evolution and stability of
the two (topologically) simplest vortex knots which can be wrapped over a
torus. We find that the velocity of a vortex knot depends on the ratio of
poloidal and toroidal radius: for smaller ratio, the knot travels faster.
Finally, we show how unstable vortex knots break up into vortex rings.Comment: 18 pages, 15 figures, 1 tabl
Experimental assessment of a new form of scaling law for near-wall turbulence
Scaling laws and intermittency in the wall region of a turbulent flow are
addressed by analyzing moderate Reynolds number data obtained by single
component hot wire anemometry in the boundary layer of a flat plate. The paper
aims in particular at the experimental validation of a new form of refined
similarity recently proposed for the shear dominated range of turbulence, where
the classical Kolmogorov-Oboukhov inertial range theory is inappropriate. An
approach inspired to the extended self-similarity allows for the extraction of
the different power laws for the longitudinal structure functions at several
wall normal distances. A double scaling regime is found in the logarithmic
region, confirming previous experimental results. Approaching the wall, the
scaling range corresponding to the classical cascade-dominated range tends to
disappear and, in the buffer layer, a single power law is found to describe the
available range of scales. The double scaling is shown to be associated with
two different forms of refined similarity. The classical form holds below the
shear scale L s . The other, originally introduced on the basis of DNS data for
a turbulent channel, is experimentally confirmed to set up above L s . Given
the experimental diffulties in the evaluation of the instantaneous dissipation
rate, some care is devoted to check that its one-dimensional surrogate does not
bias the results. The increased intermittency as the wall is approached is
experimentally found entirely consistent with the failure of the refined
Kolmogorov-Oboukhov similarity and the establishment of its new form near the
wall.Comment: 27 pages, 9 figure
The impact of the sarsâcov2 pandemic on a persuasive educational antimicrobial stewardship program in a university hospital in southern italy: A preâpost study
Objectives: We evaluated the effect of the pandemic on the disruption of a persuasive educational antimicrobial stewardship program (ASP) conducted in a university hospital in southern Italy. Methods: In March 2020, the ASP, which began in January 2017 and was carried out at different times in 10 wards, was stopped due to the COVIDâ19 pandemic. We conducted an observational study with interrupted time series analysis to compare the antibiotic consumption and costs, average length of hospital stay and inâhospital mortality between 12 months before and 9 months after the interruption. Results: Four medical, four surgical wards and two ICUs were included in the study, for a total of 35,921 patient days. Among the medical wards we observed after the interruption a significant increase in fluoroquinolone use, with a change in trend (CT) of 0.996, p = 0.027. In the surgical wards, we observed a significant increase in the overall consumption, with a change in level (CL) of 24.4, p = 0.005, and in the use of third and fourth generation cephalosporins (CL 4.7, p = 0.003). In two ICUs, we observed a significant increase in piperacillin/tazobactam and fluoroquinolone consumption (CT 9.28, p = 0.019, and 2.4, p = 0.047). In the wards with a duration of ASP less than 30 months, we observed a significant increase in antibiotic consumption in the use of piperacillin/tazobactam and fluoroquinolones (CT 12.9, p = 0.022: 4.12, p = 0.029; 1.004, p = 0.011). Conclusions: The interruption of ASP during COVIDâ19 led to an increase in the consumption of broadâspectrum antibiotics, particularly in surgical wards and in those with a duration of ASP less than 30 months
Correlation between acoustic divergence and phylogenetic distance in soniferous European gobiids (Gobiidae; Gobius lineage)
In fish, species identity can be encoded by sounds, which have been thoroughly investigated
in European gobiids (Gobiidae, Gobius lineage). Recent evolutionary studies suggest
that deterministic and/or stochastic forces could generate acoustic differences among
related animal species, though this has not been investigated in any teleost group to date. In
the present comparative study, we analysed the sounds from nine soniferous gobiids and
quantitatively assessed their acoustic variability. Our interspecific acoustic study, incorporating
for the first time the representative acoustic signals from the majority of soniferous
gobiids, suggested that their sounds are truly species-specific (92% of sounds correctly
classified into exact species) and each taxon possesses a unique set of spectro-temporal
variables. In addition, we reconstructed phylogenetic relationships from a concatenated
molecular dataset consisting of multiple molecular markers to track the evolution of acoustic
signals in soniferous gobiids. The results of this study indicated that the genus Padogobius
is polyphyletic, since P. nigricans was nested within the Ponto-Caspian clade, while the congeneric
P. bonelli turned out to be a sister taxon to the remaining investigated soniferous
species. Lastly, by extracting the acoustic and genetic distance matrices, sound variability
and genetic distance were correlated for the first time to assess whether sound evolution follows
a similar phylogenetic pattern. The positive correlation between the sound variability
and genetic distance obtained here emphasizes that certain acoustic features from representative
sounds could carry the phylogenetic signal in soniferous gobiids. Our study was
the first attempt to evaluate the mutual relationship between acoustic variation and genetic
divergence in any teleost fish
Freely decaying weak turbulence for sea surface gravity waves
We study numerically the generation of power laws in the framework of weak
turbulence theory for surface gravity waves in deep water. Starting from a
random wave field, we let the system evolve numerically according to the
nonlinear Euler equations for gravity waves in infinitely deep water. In
agreement with the theory of Zakharov and Filonenko, we find the formation of a
power spectrum characterized by a power law of the form of .Comment: 4 pages, 3 figure
Intermittency and structure functions in channel flow turbulence
We present a study of intermittency in a turbulent channel flow. Scaling
exponents of longitudinal streamwise structure functions, ,
are used as quantitative indicators of intermittency.
We find that, near the center of the channel the values of
up to are consistent with the assumption of homogeneous/isotropic
turbulence. Moving towards the boundaries, we observe a growth of intermittency
which appears to be related to an intensified presence of ordered vortical
structures. In fact, the behaviour along the normal-to-wall direction of
suitably normalized scaling exponents shows a remarkable correlation with the
local strength of the Reynolds stress and with the \rms value of helicity
density fluctuations. We argue that the clear transition in the nature of
intermittency appearing in the region close to the wall, is related to a new
length scale which becomes the relevant one for scaling in high shear flows.Comment: 4 pages, 6 eps figure
Three-dimensional imaging of waves and floes in the marginal ice zone during a cyclone
The marginal ice zone is the dynamic interface between the open ocean and consolidated inner pack ice. Surface gravity waves regulate marginal ice zone extent and properties, and, hence, atmosphere-ocean fluxes and ice advance/retreat. Over the past decade, seminal experimental campaigns have generated much needed measurements of wave evolution in the marginal ice zone, which, notwithstanding the prominent knowledge gaps that remain, are underpinning major advances in understanding the regionâs role in the climate system. Here, we report three-dimensional imaging of waves from a moving vessel and simultaneous imaging of floe sizes, with the potential to enhance the marginal ice zone database substantially. The images give the directionâfrequency wave spectrum, which we combine with concurrent measurements of wind speeds and reanalysis products to reveal the complex multi-component wind-plus-swell nature of a cyclone-driven wave field, and quantify evolution of large-amplitude waves in sea ice
Wave modelling - the state of the art
This paper is the product of the wave modelling community and it tries to make a picture of the present situation in this branch of science, exploring the previous and the most recent results and looking ahead towards the solution of the problems we presently face. Both theory and applications are considered.
The many faces of the subject imply separate discussions. This is reflected into the single sections, seven of them, each dealing with a specific topic, the whole providing a broad and solid overview of the present state of the art. After an introduction framing the problem and the approach we followed, we deal in sequence with the following subjects: (Section) 2, generation by wind; 3, nonlinear interactions in deep water; 4, white-capping dissipation; 5, nonlinear interactions in shallow water; 6, dissipation at the sea bottom; 7, wave propagation; 8, numerics. The two final sections, 9 and 10, summarize the present situation from a general point of view and try to look at the future developments
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