4,819 research outputs found
Characterization of Carbon-Contaminated B4C-Coated Optics after Chemically Selective Cleaning with Low-Pressure RF Plasma
Boron carbide (B4C) is one of the few materials that is expected to be mostly
resilient with respect to the extremely high brilliance of the photon beam
generated by free electron lasers (FELs) and is thus of considerable interest
for optical applications in this field. However, as in the case of many other
optics operated at modern light source facilities, B4C-coated optics are
subject to ubiquitous carbon contaminations. These contaminations represent a
serious issue for the operation of high performance FEL beamlines due to severe
reduction of photon flux, beam coherence, creation of destructive interference,
and scattering losses. A variety of B4C cleaning technologies were developed at
different laboratories with varying success. We present a study regarding the
low-pressure RF plasma cleaning of carbon contaminated B4C test samples via
inductively coupled O2/Ar, H2/Ar, and pure O2 RF plasma produced following
previous studies using the same IBSS GV10x downstream plasma source. Results
regarding the chemistry, morphology as well as other aspects of the B4C optical
coating before and after the plasma cleaning are reported. We conclude from
these comparative plasma processes that pure O2 feedstock plasma only exhibits
the required chemical selectivity for maintaining the integrity of the B4C
optical coating.Comment: 27 pages, 15 figure
Progressive approach to eruption at Campi Flegrei caldera in southern Italy
Unrest at large calderas rarely ends in eruption, encouraging vulnerable communities to perceive emergency warnings of volcanic activity as false alarms. A classic example is the Campi Flegrei caldera in southern Italy, where three episodes of major uplift since 1950 have raised its central district by about 3 m without an eruption. Individual episodes have conventionally been treated as independent events, so that only data from an ongoing episode are considered pertinent to evaluating eruptive potential. An implicit assumption is that the crust relaxes accumulated stress after each episode. Here we apply a new model of elastic-brittle failure to test the alternative view that successive episodes promote a long-term accumulation of stress in the crust. The results provide the first quantitative evidence that Campi Flegrei is evolving towards conditions more favourable to eruption and identify field tests for predictions on how the caldera will behave during future unrest
On the mechanics of caldera resurgence of Ischia Island (southern Italy)
A model of caldera resurgence was applied to the Island of Ischia to explain uplift,
volcanic activity and tectonics on Mount Epomeo, as well as historical seismicity and slow
ground movements recorded for the past 2000 years. A two-dimensional mechanical model
was utilized for the crust, which was considered to be an elastic plate overlying a laccolith.
Geometric dimensions and mechanical parameters were constrained using geological,
geophysical and geochemical data.
We propose that a laccolith, with a diameter L of c. 10 km, and a depth of up to 1 km in the
centre of the island, triggered the caldera resurgence after the Mount Epomeo Green Tuff
eruption forming the caldera (55 000 a BP). A bending phase and a punched laccolith phase are
thought to have caused the observed deformations in the caldera. These processes control the
tectonics at the boundary of the Mount Epomeo resurgent structure, volcanic activity and
dynamics of the island
Studying the relationships between hourly precipitation extremes and dewpoint temperature in Sicily.
According to the well-known Clausius-Clapeyron relation, the maximum moisture content of the atmosphere increases
with approximately 7% per degree temperature raise (CC-scaling rate). Under the hypothesis that relative
humidity does not change, an increase in the water vapor should occur at the same rate. For this reason we could
expect for the coming years an increase in the intensity of extreme precipitation as a consequence of the global
climate warming.
Trend on precipitation extremes and possible links to changes in atmospheric temperature and moisture are investigated
in different parts of the world, and a number of observational studies has exhibited scaling rates that
are either higher (super-CC) or lower (sub-CC) than CC scaling rate depending on the climatic areas under analysis.
One of the most common approaches consists in a regression analysis to interpret the relationships between
extreme percentiles of rainfall and surface temperature, and this is often due to the lack of availability of consistent
historical data series for other variables of interest, such as the relative air humidity. In some applications,
combined temperature-humidity measures, such as the dew point temperature, have been used as proxy measures.
In this study we investigate, at the regional scale (Sicily, Italy), the scaling rate between hourly precipitation
extremes and dew point temperature. This last is then used as a measure of near surface absolute humidity and is
computed for each rainfall event at the same time (T0) and, 2 (T2) and 4 (T4) hours before the event occurrence.
The scaling rate is studied at both the level of entire hydrological year and the seasonal level, dividing the calendar
year in a wet, colder and more rainy, season and a dry warmer season.
The high-resolution dataset from the regional agency SIAS (Agro-meteorological Information Service of Sicily)
has been used and it is constituted by data of 10-min rainfall, hourly temperature and maximum hourly relative air
humidity, collected by 107 gauges from 2003 to 2015. The hourly temperature and maximum hourly relative air
humidity data are combined to provide hourly time-series of dew-point temperature at each gauge. The samples
from the different gauges are pooled together forming six different samples relative to six different sub-regions
defined within the Sicilian island and at the level of entire region (unique regional sample). At the level of single
sub-region a binning procedure is used, investigating the suitability of exponential regression models for interpreting
the relationships between dew point temperature (median for bin) and extreme rainfall intensity (95th percentile
for bin). A LOESS (LOcally-wEighted Scatter-plot Smoothing) regression analysis is considered for the study of
the regional sample.
Similar results are obtained from the analysis at the annual level and for the wet season, with high coefficients of
determination (R2 >0.94) for all the sub-regions, demonstrating the appropriateness of the used regression models,
and with sub-CC scaling rate (4-5%°C1). For the dry season, both the R2 and the rates (especially for T2 and T4)
are lower; moreover, the LOESS analysis highlights a decreasing scaling rate at higher dew point temperatures
Influence of temperature on extreme rainfall intensity in Sicily (Italy)
Some climate model experiments suggest an intensification of short-duration extreme precipitation in many parts of the world associated with a warming climate. This behavior could have a physical motivation due to the fact that warmer air has the potential to hold more atmospheric moisture and, then, to provide more water to rainfall events. The theoretical basis of the relationship that links air temperature and atmospheric humidity is provided by the Clausius-Clapeyron relation, according to which, if the relative humidity remains constant, then atmospheric humidity will increase with temperature at a rate (often referred to as CC-rate) in the order of 6-7% C-1, following the saturation vapour pressure curve as a function of temperature. The study of the relationship between extreme rainfall events and surface temperature could be of capital importance for evaluating the effects of global warming on future precipitation, since it may have important impacts on society with relevant fallouts on several aspects (e.g. flooding, risk protection, etc.). Different approaches have been proposed for the study at different locations of the scaling relationship between extreme rainfall intensity and surface temperature. In some cases, it has been observed a rate consistent with the thermodynamic Clausius-Clapeyron relation (CC-rate). Nevertheless, in many cases, the existence of scaling rate between temperature and extreme precipitation has been demonstrated with significantly different values with respect to the theoretical CC-rate, being in some cases sensibly higher (super-CC) and in other relevantly lower (sub-CC). In this work, an analysis of the scaling relationship between sub-daily extreme rainfall and surface temperature in a semi-arid region (Sicily, Italy) is carried out, also investigating the role of different factors, such as the duration of maximum rainfall depths for fixed duration (i.e. 10, 30 and 60 minutes), the type of adopted regression models (exponential regression, two-segments piecewise regression and LOESS - Locally-weighted scatterplot smoothing - regression), and the climate seasonality (unique season for the entire hydrological year; dry season from April to September and wet season for the remaining part of the year). The original dataset is constituted by hourly temperature and 10-minutes rainfall data collected from 2003 to 2015 by the regional agency SIAS (Servizio Informativo Agrometeorologico Siciliano) through 107 weather stations spread over the region. The results demonstrate that in Sicily the scaling rates are generally lower than the CC-rate; however, the observed tendency towards sub-CC rates is smoothed by the consideration of shorter duration for rainfall maximum depths (higher rates for 10-minutes durations) and under wetter periods (higher rates considering only wet season values), demonstrating how such factors play a fundamental role
Resurgence and flank failure of Mt. Epomeo, Ischia Island (Southern Italy)
Risorgenza e collasso laterale del Monte Epomeo, Isola
d’Ischia
Il Monte Epomeo (787 m a.s.l.), ubicato nel settore centrale dell’isola
d’Ischia, mostra lo smantellamento del settore meridionale, depositi
di debris e franamenti diffusi che testimoniano la natura instabile
del monte. A seguito dell’eruzione ignimbritica del Tufo Verde
dell’Epomeo (55.000 anni), che genera una struttura calderica (10x7
km2), inizia la risorgenza della caldera fino alla formazione del Monte
Epomeo. Il sollevamento, generato dall’intrusione di un laccolite fino
a circa 1 km di profonditĂ , avrebbe determinato una forte instabilitĂ
gravitativa del blocco risorgente e prodotto uno o piĂą collassi laterali.
Questi hanno lasciato una struttura a ferro di cavallo, tipica di
processi da “avalancing”, aperta verso sud, e depositi con topografia
“hummocky” estesi a sud dell’Epomeo e rilevati recentemente da esplorazioni
sul fondo marino. Il processo che ha generato il collasso
e la formazione di un avalanche caldera è stato esaminato attraverso
l’analisi della dinamica e dei caratteri geologici, geomorfologici e
strutturali dell’area. Attualmente l’isola è caratterizzata da una fase di
stasi della risorgenza testimoniata da una condizione di moderata stabilitĂ
dei versanti dell’Epomeo. Quanto osservato indicherebbe una
bassa dinamica endogena nell’isola
Singular points in N=2 SQCD
We revisit the study of singular points in N=2 SQCD with classical gauge
groups. Using a technique proposed recently by Gaiotto, Seiberg and Tachikawa
we find that the low-energy physics at the maximally singular point involves
two superconformal sectors coupled to an infrared free SU(2) gauge group. When
one softly breaks extended supersymmetry to N=1 adding a mass term for the
chiral multiplet in the adjoint representation, a finite number of vacua remain
and the theory becomes confining. Our analysis allows to identify the
low-energy physics at these distinguished points in the moduli space. In some
cases, which we will describe in detail, two sectors coupled to an infrared
free SU(2) gauge group emerge as before. For USp and SO gauge groups one of
these sectors is always free, contrary to the SU case.Comment: 22 pages, 2 figure
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