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

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

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

Modulating Thermal Properties of Polymers through Crystal Engineering

Crystal engineering has exclusively focused on the development of advanced materials based on small organic molecules. We now demonstrate how the cocrystallization of a polymer yields a material with significantly enhanced thermal stability but equivalent mechanical flexibility. Isomorphous replacement of one of the cocrystal components enables the formation of solid solutions with melting points that can be readily fine-tuned over a usefully wide temperature range. The results of this study credibly extend the scope of crystal engineering and cocrystallization from small molecules to polymers

Hidden local symmetry and color confinement

The hidden local symmetry is a successful model to describe the properties of the vector mesons in QCD. We point out that if we identify this hidden gauge theory as the magnetic picture of QCD, a linearized version of the model simultaneously describes color confinement and chiral symmetry breaking. We demonstrate that such a structure can be seen in the Seiberg dual picture of a softly broken supersymmetric QCD. The model possesses exact chiral symmetry and reduces to QCD when mass parameters are taken to be large. Working in the regime of the small mass parameters, we show that there is a vacuum where chiral symmetry is spontaneously broken and simultaneously the magnetic gauge group is Higgsed. If the vacuum we find persists in the limit of large mass parameters, one can identify the rho meson as the massive magnetic gauge boson, that is an essential ingredient for color confinement.Comment: 20 pages, 3 figure