XANES Study of Structural Disorder in Amorphous Silicon

An investigation of the structure of several amorphous silicon (a-Si) films is presented. Samples were prepared by using the ion beam sputtering technique at different substrate deposition temperatures. X-ray absorption spectroscopy and multiple scattering formalism have been used to detect structural variations of the a-Si films. The analysis of the XANES (X-ray absorption near-edge structure) spectra shows that increasing the substrate deposition temperature leads to a structural change toward a higher-level short-range order.

The KLOE-2 experiment at DAΦNE

KLOE-2 is the main experiment of the INFN Frascati National Laboratories and represents the continuation of KLOE. The previous apparatus, consisting in a huge Drift Chamber and an Electromagnetic Calorimeter, both immersed in a 0.5 T magnetic field, has been upgraded with new detectors to perform high-precision CPT symmetry and quantum coherence tests using neutral kaons, γγ-physics studies and searches of particles of hidden dark matter sectors. KLOE-2 started its data taking in November 2014 and is presently collecting data, achieving record performance in terms of peak luminosity and maximum daily integrated luminosity, which will allow to integrate more than 5fb−1 of data in the next 2 years

X-ray-absorption fine-structure study of ZnSexTe1−x alloys

X-ray-absorption fine-structure experiments at different temperatures in ZnSexTe1−x (x=0, 0.1, 0.2, 0.55, 0.81, 0.93, 0.99, and 1.0) have been performed in order to obtain information about the structural relaxation and disorder effects occurring in the alloys. First and second neighbor distance distributions have been characterized at the Se and Zn K edges, using multiple-edge and multiple-scattering data analysis. The first neighbor distance distribution was found to be bimodal. The static disorder associated with the Zn–Te distance variance did not depend appreciably on composition. On the other hand, the static disorder associated with the Zn–Se distance increased as the Se content diminished. Using the bonding angle information provided by our experiments the point of view of the anion has been related to that of the cation. The resulting structural model indicates that Zn tetrahedra surrounding the anions remain essentially undistorted, but forced to tilt from their ideal zincblende orientation to accommodate the minority element. The main origin of structural disorder is [email protected] ; [email protected]

Spatio-temporal variability of micro-, nano- and pico-phytoplankton in the Mediterranean Sea from satellite ocean colour data of SeaWiFS

Abstract. The seasonal and year-to-year variability of the phytoplankton size class (PSC) spatial distribution has been examined in the Mediterranean Sea by using the entire time series of Sea-viewing Wide Field-of-view Sensor (SeaWiFS) space observations (1998–2010). Daily maps of PSCs have been determined using an empirical model based on a synoptic relationship between surface chlorophyll a and diagnostic pigments referred to different taxonomic groups. The analysis of micro-, nano- and pico-phytoplankton satellite time series (1998–2010) describes, quantitatively, the algal assemblage structure over the basin and reveals that the main contribution to chlorophyll a in most of the Mediterranean Sea comes from the pico-phytoplankton component, especially in nutrient-poor environments. Regions with different and peculiar features are the Northwestern Mediterranean Sea, the Alborán Sea and several coastal areas, such as the North Adriatic Sea. In these areas, local interactions between physical and biological components modulate the composition of the three phytoplankton size classes. It results that, during the spring bloom season, micro-phytoplankton dominates in areas of intense vertical winter mixing and deep/intermediate water formation, while in coastal areas micro-phytoplankton dominates in all seasons because of the nutrient supply from the terrestrial inputs. In the Alborán Sea, where the Atlantic inflow modulates the nutrient availability, any predominance of one class over the other two has been observed. The nano-phytoplankton component instead remains widespread over the entire basin along the year, and its contribution to chlorophyll a is of the order of 30–40 %. The largest inter-annual signal occurs in the Northwestern Mediterranean Sea, driven by the year-to-year variation in intensity and extension of the spring bloom, followed by the Alborán Sea, in which the inter-annual variability is strongly modulated by the Atlantic inflow. In absence of sufficient in situ data of community composition, the satellite-based analysis demonstrated that pico-, nano- and micro-phytoplankton classes often coexist. The predominance of one group over the other ones is strongly dependent on the physical and biological processes occurring at the mesoscale. These processes directly influence the nutrient and light availability, which are the principal forcing for the algae growth

Experimental testing of an adsorption thermal energy storage system

The objective of this work is to test and characterize a lab-scale silica gel/water test bench realized at POLIMI labs and operating as Thermal Energy Storage (TES) system for domestic applications. Several charging and discharging cycles were performed setting 20-35, 30-50, and 80-90 °C as heat transfer fluid temperatures for the evaporation, condensation/adsorption and desorption processes. The system performance is evaluated in terms of energy efficiency, charge and discharge rate, and operating cost

Testing of an adsorption chiller prototype for data center cooling.

The main objective of this study is to present a novel adsorption chiller prototype (designed and realized by the company Sorption Technologies GmbH) that is suitable for cooling of data center servers. This prototype has been designed to fit into commercially-available data center racks. This adsorption prototype has been designed to cool down the rack servers by means of liquid cooling. Furthermore, an air-cooler heat exchanger is also integrated into the adsorption machine to cool down the rest of the rack components (i.e., patch panels, HDD). This way, the adsorption system is able to cool down all rack components. Phase-change chambers are integrated into the adsorption modules for direct evaporation/condensation, removing the need of large vacuum valves and allowing to have a more simpler and compact vacuum system. This also means that the refrigerant distribution is completely done in liquid phase. The prototype is installed at the Department of Energy at the Politecnico di Milano and testing will be carried out using cooling water temperatures in the range 25 – 30 °C and hot water temperatures in the range 55 – 65 °C

Robots for Exploration, Digital Preservation and Visualization of Archeological Sites

Monitoring and conservation of archaeological sites are important activities necessary to prevent damage or to perform restoration on cultural heritage. Standard techniques, like mapping and digitizing, are typically used to document the status of such sites. While these task are normally accomplished manually by humans, this is not possible when dealing with hard-to-access areas. For example, due to the possibility of structural collapses, underground tunnels like catacombs are considered highly unstable environments. Moreover, they are full of radioactive gas radon that limits the presence of people only for few minutes. The progress recently made in the artificial intelligence and robotics field opened new possibilities for mobile robots to be used in locations where humans are not allowed to enter. The ROVINA project aims at developing autonomous mobile robots to make faster, cheaper and safer the monitoring of archaeological sites. ROVINA will be evaluated on the catacombs of Priscilla (in Rome) and S. Gennaro (in Naples)

Modelling of a falling-film evaporator for adsorption chillers.

The objective of the present study was to develop a dynamic model to simulate a prototype falling-film evap-orator that is part of a single-bed adsorption chiller test bench located at the Department of Energy of the Politecnico di Milano. The model is based on the evaporator energy and mass balances and was calibrated and validated using experimental data coming from realistic operating conditions in a range of inlet chilled water temperatures (Tin,chw) from 15 to 25 °C. From the experimental data, it was obtained that the average overall heat transfer conductance (UA) was approximately 530 W/K for all temperatures during the quasi steady-state section of the process. A correlation to calculate the wetted surface through a variable called wettability factor (fwet) was developed from experimental data. The fwet factors were identified using the model and were in the range of 0.80 - 0.20 (Tin,chw= 15 °C) and 0.60 - 0.20 (Tin,chw= 25 °C). It was seen that, the higher the Tin,chw, the lower the fwet values. The UA and saturation temperature (Tref,sat) values from the model were in good accordance with experimental data during the quasi steady-state section of the process. Nevertheless, the final transition stage (i. e., a situation in which the evaporator's refrigerant pool is empty) required an additional hypothesis due to the uncertain process' dynamics. The mass and energy balances that are part of the hydrodynamics and heat transfer sections of the model use Nusselt's classic theory for falling-film

Structural change of carbon supported Pt nanocatalyst subjected to a step-like potential cycling in PEM-FC

Abstract In this paper we present detailed X-ray absorption fine structure (XAFS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) investigations of the changes in the local geometric and electronic structure of Pt nanoparticles used as a cathode catalyst in proton exchange membrane fuel cell (PEMFC), working under controlled potential cycling conditions. The body of the results obtained suggests that in the first stage of \{PEMFC\} operation, small particle dissolution was a dominant process. Subsequent 100 h of work led to the progressive agglomeration of nanoparticles followed by a pronounced growth of the mean nanoparticle size. At the same time, high-quality \{XAFS\} spectra analysis demonstrated that negligible changes in structural local ordering and a slight increase in Pt 5d-electron density occurred during the whole \{FC\} operation period under consideration