437 research outputs found
Axion–sterile neutrino dark matter
Extending the standard model with three right-handed neutrinos and a simple QCD axion sector can account for neutrino oscillations, dark matter and baryon asymmetry; at the same time, it solves the strong CP problem, stabilizes the electroweak vacuum and can implement critical Higgs inflation (satisfying all current observational bounds). We perform here a general analysis of dark matter (DM) in such a model, which we call the a nu MSM. Although critical Higgs inflation features a (quasi) inflection point of the inflaton potential, we show that DM cannot receive a contribution from primordial black holes in the a nu MSM. This leads to a multicomponent axion-sterile neutrino DM and allows us to relate the axion parameters, such as the axion decay constant, to the neutrino parameters. We include several DM production mechanisms: the axion production via misalignment and decay of topological defects as well as the sterile neutrino production through the resonant and non-resonant mechanisms and in the recently proposed CPT-symmetric universe
Detection of Volcanic Plumes by GPS: the 23 November 2013 Episode on Mt. Etna
The detection of volcanic plumes produced during explosive eruptions is important to improve our under-
standing on dispersal processes and reduce risks to aviation operations. The ability of Global Position-ing
System (GPS) to retrieve volcanic plumes is one of the new challenges of the last years in volcanic plume de -
tection. In this work, we analyze the Signal to Noise Ratio (SNR) data from 21 permanent stations of the GPS
network of the Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio Etneo, that are located on the Mt.
Etna (Italy) flanks. Being one of the most explosive events since 2011, the eruption of November 23, 2013 was
chosen as a test-case. Results show some variations in the SNR data that can be correlated with the presence of
an ash-laden plume in the atmosphere. Benefits and limitations of the method are highlighted
Low efficacy of the combination artesunate plus amodiaquine for uncomplicated falciparum malaria among children under 5 years in Kailahun, Sierra Leone.
OBJECTIVE: In 2004, Sierra Leone adopted artesunate plus amodiaquine as first-line antimalarial treatment. We evaluated the efficacy of this combination in Kailahun, where a previous study had shown 70.2% efficacy of amodiaquine in monotherapy. METHODS: Method and outcome classification of the study complied with WHO guidelines. Children 6-59 months with uncomplicated malaria were followed-up for 28 days. PCR genotyping was used to distinguish recrudescence from reinfection. Reinfections were reclassified as cured. RESULTS: Of 172 children who were referred to the study clinic, 126 satisfied inclusion criteria and were enrolled. No early treatment failures were reported. The day 14, efficacy was 98.2% (95% CI: 93.8-99.8). Of 65 recurrent parasitaemias analysed by PCR, 17 were recrudescences. The PCR-adjusted day 28 efficacy was 84.5% (95% CI: 76.4-90.7). All true failures occurred in the last 8 days of follow-up. Of 110 children who completed the 28-day follow-up, 54 (49.1%) experienced a novel infection. CONCLUSION: The efficacy of this combination was disappointing. The high reinfection rate suggested little prophylactic effect. In Kailahun a more efficacious combination might be necessary in the future. The efficacy of AS + AQ needs to be monitored in Kailahun and in the other regions of Sierra Leone
A lab-scale experiment to measure terminal velocity of volcanic ash
In this paper, a novel methodology to measure trajectory and terminal velocity of volcanic ash in laboratory is presented. The methodology consists of: i) planning a lab-scale experiment in order to reproduce the sedimentation processes of fine volcanic ash based on the principle of dynamic similarity; ii) realizing the experimental set-up using a glass tank filled with glycerine, a web-cam based vision system and a dedicated image post processing tool able to estimate the position and
the terminal velocity of any particle falling in the tank; iii) performing a calibration procedure to accurately estimate the uncertainty on particle velocity; iv) comparing the experimental results with estimations obtained by some particle fallout models available in literature. Our results shows that there is a good agreement between experimental terminal velocities and those obtained applying a model which includes information on particle shape. The proposed methodology allows us to investigate how the particle shape affects the sedimentation processes. Since the latter is strategic to improve the accuracy on modeling ash fallout, this work will contribute to reduce risks to aviations during explosive eruptions
Maximum-likelihood retrieval of volcanic ash concentration and particle size from ground-based scanning lidar
An inversion methodology, named maximum-likelihood (ML) volcanic ash light detection and ranging (Lidar) retrieval (VALR-ML), has been developed and applied to estimate volcanic ash particle size and ash mass concentration within volcanic plumes. Both estimations are based on the ML approach, trained by a polarimetric backscattering forward model coupled with a Monte Carlo ash microphysical model. The VALR-ML approach is applied to Lidar backscattering and depolarization profiles, measured at visible wavelength during two eruptions of Mt. Etna, Catania, Italy, in 2010 and 2011. The results are compared with those of ash products derived from other parametric retrieval algorithms. A detailed comparison among these different retrieval techniques highlights the potential of VALR-ML to determine, on the basis of a physically consistent approach, the ash cloud area that must be interdicted to flight operations. Moreover, the results confirm the usefulness of operating scanning Lidars near active volcanic vents
Tephra hazard assessment at Mt. Etna (Italy)
In this paper we present a probabilistic hazard assessment
for tephra fallout at Mt. Etna (Italy) associated with
both short- and long-lived eruptions. Eruptive scenarios and
eruption source parameters were defined based on the geological
record, while an advection–diffusion–sedimentation
model was used to capture the variation in wind speed and
direction with time after calibration with the field data. Two
different types of eruptions were considered in our analysis:
eruptions associated with strong short-lived plumes and eruptions
associated with weak long-lived plumes. Our probabilistic
approach was based on one eruption scenario for both
types and on an eruption range scenario for eruptions producing
weak long-lived plumes. Due to the prevailing wind direction,
the eastern flanks are the most affected by tephra deposition, with the 122 BC Plinian and 2002–2003 eruptions showing the highest impact both on infrastructures and agriculture
Monitoring and forecasting Etna volcanic plumes
In this paper we describe the results of a project
ongoing at the Istituto Nazionale di Geofisica e Vulcanologia
(INGV). The objective is to develop and implement a
system for monitoring and forecasting volcanic plumes of
Etna. Monitoring is based at present by multispectral infrared
measurements from the Spin Enhanced Visible and
Infrared Imager on board the Meteosat Second Generation
geosynchronous satellite, visual and thermal cameras, and
three radar disdrometers able to detect ash dispersal and fallout.
Forecasting is performed by using automatic procedures
for: i) downloading weather forecast data from meteorological
mesoscale models; ii) running models of tephra dispersal,
iii) plotting hazard maps of volcanic ash dispersal and deposition
for certain scenarios and, iv) publishing the results on
a web-site dedicated to the Italian Civil Protection. Simulations
are based on eruptive scenarios obtained by analysing
field data collected after the end of recent Etna eruptions.
Forecasting is, hence, supported by plume observations carried
out by the monitoring system. The system was tested on
some explosive events occurred during 2006 and 2007 successfully.
The potentiality use of monitoring and forecasting
Etna volcanic plumes, in a way to prevent threats to aviation
from volcanic ash, is finally discussed
Eruption column height estimation of the 2011-2013 Etna lava fountains
In this paper, we use calibrated images collected by the video-surveillance
system of the Istituto Nazionale di Geofisica e Vulcanologia, Osservatorio
Etneo, to retrieve the height of the eruption column during the recent
Etna explosive activity. The analysis is carried out on nineteen lava fountains
from the New South East Crater dataset. The novel procedure described
in this work is achieved in three main steps: at first we calibrated
the camera, then we selected the images which recorded the maximum
phase of the eruptive activity, and finally we applied an appropriate correction
to account for the plume projection on the camera line of sight due
to the wind. The results show that the column altitudes range between 6
and 9 km (upper limit of the camera system). The comparison with the
plume height values estimated from the analysis of several SEVIRI and
MODIS satellite images, show a good agreement. Finally, for nine events
we also evaluated the thickness of the volcanic plumes in the umbrella region
which ranges between 2 and 3 km
A Statistical Approach to Evaluate the Tephra Deposit and Ash Concentration from Puff Model Forecasts
In this paper we present a new statistical approach able to provide tephra deposit load and ash concentration
using PUFF, a lagrangian model widely used to forecast volcanic ash dispersal during volcanic crisis. We
perform a parametric study in order to analyze the influence of each input parameter on model outputs. For
this test, we simulate two eruptive scenarios like to the 2001 (Scenario 1) and 1998 (Scenario 2) Etna
eruptions using high resolution weather data and a domain of 170 x 170 km. Results show that for both
scenarios, we are able to calculate the tephra deposit load and ash concentration but the use of millions of
particles is required. Specifically, up to 33 and 220 millions of particles were necessary to accurately
predict the tephra deposit and ash concentration in air, respectively. This is approximately two orders of
magnitude larger than values typically considered running PUFF. The parametric study shows that the
horizontal diffusion coefficient, the time step of the simulations, the topography and the standard deviation
of the particle distribution greatly affect the model outputs. We also validate the model by best fit
procedures. Results show a good comparison between field data of the 2001 Etna eruption and PUFF
simulations, being inside 5 and 1/5 times the observed data, comparable with results of Eulerian models.
This work will allow to reliably outlining the areas of contaminated airspace using PUFF or any other
lagrangian model in order to define the No Fly Zone and ensure the safety to aviation operations as required
after the Eyjafjallajökull eruption
- …