4,310 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
Historical eartquakes at Ischia island and seismic hazard assessment
Hystorical data of seismicity at Ischia island (Southern Italy) cover a period of almost
800 years. Since 1228 numerous events exceeded VII MCS degree. The epicentral
areas of the earthquakes are located in the northern sector of the island; only one
earthquake (1302, VIII MCS degree) was correlated with the latter eruption occurred
during 1301-02 AD along the eastern sector of the island. In few cases the earthquakes
(1228, 1863, 1881, 1883 AD) were followed by landslides which have produces serious
damage while, in average, ground effects (i.e. fractures, capacity and temperature
variation of hot springs) were often observed before and after each event. The historical
seismicity of Ischia shows the peculiar characteristics of volcanic earthquakes
as shallow ipocentral depth ( 1 km), high intensity, strong directional attenuation
of effects and local amplification of damages. At Ischia, the 1883 AD earthquake of
“Casamicciola” represents the unique example of modern age earthquake in Mediterranean
volcanic area which produced more than 2300 fatalities. The catastrophic effects
of this earthquake (Imax=XI MCS degree) covered an area of about 3 km2 in
the northern sector of the island, while strong attenuation effects were observed, especially
along the south and east directions. From 1883 AD until today a seismic silence
in the island has been observed. Some events have been felt from the beginning of the
20th century while, in the last 10 years just few events (M < 2), have been recorded
by the INGV-OV surveillance seismic network, localized prevalently in the northern
sector of the island. The lack of significant seismicity allow the study of macroseimic
data of 1883 earthquake as the fundament issue for hazard assessment, also if considering
the increasing of housing density and the high exposed value in the island. Data
of earthquake damages and ground effects, obtained by archives sources and literature,
have been utilized (also using GIS cross-correlation with geological data) in order to
evaluate the tendency of the attenuation for different zones of the island, to detach the contribution of the source from the medium, and define the zones of maximum expected damage
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
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
Sensitivity of food webs to nitrogen pollution: a study of three transitional water ecosystems embedded in agricultural landscapes
1 - Transitional water ecosystems constitute extremely complex and productive environments, a preferred route of migrating birds and optimal nursery locations for many fish species. In these interesting environments, descriptors of trophic relationships between species in a web have been suggested as potential integrative and sensitive endpoints for anthropogenic pressure.2 - To better understand the effects of environmental disturbance on the resident macroinvertebrate assemblage structure, we analysed food webs in three neighbouring transitional water ecosystems located along the Thyrrenian coastal area of Central Italy (Lake Caprolace, Lake Fogliano and Lake Sabaudia), which are affected by different inputs of nitrates from agricultural, farming and urban activities.3 - Macrozoobenthos, aquatic macrophytes and attached macroalgae, leaf detritus from sediments and suspended organic matter in the water column were sampled at four sites in each ecosystem and stable isotope analysis (C and N) was carried out in order to describe trophic pathways and the food web structure.4 - ä15N values of macroinvertebrates increased from Caprolace to Sabaudia according to increasing nitrate concentration derived from organic sources. Macrozoobenthic assemblages varied in species composition with the lowest biodiversity found in Sabaudia, the most polluted ecosystem. Also proportion of primary consumers, predators and omnivorous species varied, with cascade effects on food web topology and nutrient flow pathways.5 - In particular, omnivorous and generalist predators were more numerous in Sabaudia, where food chains were longer and webs less compartmentalised than in Caprolace and Fogliano. In Sabaudia a lower level of web robustness to species loss was also observed.6 - These results suggest that nitrogen pollution can be responsible of evident changes in the architecture of biodiversity between ecosystems, determining less robust trophic structures with strong implication for biodiversity management and conservation
Non-Abelian vortex dynamics: Effective world-sheet action
The low-energy vortex effective action is constructed in a wide class of
systems in a color-flavor locked vacuum, which generalizes the results found
earlier in the context of U(N) models. It describes the weak fluctuations of
the non-Abelian orientational moduli on the vortex worldsheet. For instance,
for the minimum vortex in SO(2N) x U(1) or USp(2N) x U(1) gauge theories, the
effective action found is a two-dimensional sigma model living on the Hermitian
symmetric spaces SO(2N)/U(N) or USp(2N)/U(N), respectively. The fluctuating
moduli have the structure of that of a quantum particle state in spinor
representations of the GNO dual of the color-flavor SO(2N) or USp(2N) symmetry,
i.e. of SO(2N) or of SO(2N+1). Applied to the benchmark U(N) model our
procedure reproduces the known CP(N-1) worldsheet action; our recipe allows us
to obtain also the effective vortex action for some higher-winding vortices in
U(N) and SO(2N) theories.Comment: LaTeX, 25 pages, 0 figure
- …