338 research outputs found
Fisica dello sci alpino
No full textCapitolo sulla interpretazione fisica della tecnica dello sci alpino elaborata dalla scuola italiana di sc
Field study of mass balance, and hydrology of the West Khangri Nup glacier (Khumbu, Everest)
No full textThe depiction of glaciers' dynamics in the high altitudes of Himalaya and the hydrological fluxes therein is often limited. Although sparse seasonal (snow/ice) melt data may be available, dense precipitation networks are not available everywhere, and especially in the highest area, and the assessment of accumulation processes and mass balance may be difficult. Hydrological fluxes are little measured in the high altitudes, and few studies are available covering flow modeling and flow partitioning. Here, we investigate the snow accumulation, ice melt, and mass balance ofWest Khangri Nup (WKN) glacier (0.23 km2, mean altitude 5494 m asl), which is a part of the Khumbu glacier in the Everest region, where information of precipitation and hydro-glaciological dynamics in the highest altitudes was made available recently in fulfillment of several research projects. Weather, glaciological, snow pits, hydrologic, and isotopic data gathered during field campaigns (2010-2014) on the glacier and at the EVK2CNR Pyramid site were used to (i) set up the Poli-Hydro glacio-hydrological model to describe ice and snow melt and hydrological flows from the glacier, and (ii) investigate seasonal snow dynamics on this high region of the glacier. Coupling ice ablation data and Poli-Hydro simulation for ca. 5 years (January 2010-June 2014), we estimate that the WKN depleted ca.-10.46 m of ice water equivalent per year m IWE year-1 (i.e., annually ca.-2.32 meter of water equivalent per year m WE year-1). Then, using snowpack density and isotopic (δ18O) profiles on the WKN, we demonstrate that the local snowpack is recent (Fall-Winter 2013-2014) and that significant snow accumulation did not occur recently, so this area has not been a significant one of accumulation recently. Analysis of recent snow cover from LANDSAT images also confirms snow dynamics as depicted. Our study presents original data and results, and it complements present studies covering glaciers' mass balance as well as an investigation of accumulation zones in the Everest region and the Himalayas, which is also potentially helpful in the assessment of future dynamics under ongoing climate change
Propagation in outdoor environments of aerosol droplets produced by breath and light cough
No full textDuring respiration-based activities, possibly ejected microorganisms such as viruses pass from an infected subject to a target person through aerosol droplets. Research focused mostly on the mechanisms of aerosol generation, the droplet size, initial velocity, velocity and size distribution, the indoor aerosol propagation. We here consider the saliva aerosol associated with breath and light cough chosen since they are the standard and much common, gentle respiratory activities. We study the propagation in stagnant air of such aerosols from a point placed ahead of the mouth at a distance from it such that we can approximate the ejecta as a non-turbulent flux. We focus on different outdoor environments for selected weather conditions. We analyze the free fall of droplets (diameter, 5 μm to 200 μm), verifying whether they evaporate, or they impact on the ground, for different environment temperature, pressure, and relative humidity values. We provide a two-dimensional description of the evaporation path and of the dynamics of droplets (diameter, 5 μm to 100 μm) either moving within the air flux associated with the aerosol, or settling out of it and experiencing free fall through air. Calculated droplet propagation distances with the boundary conditions for the considered environments can be useful when discussing prevention measures to limit airborne transmission of pathogens
Synthesis of natural-like snow by ultrasonic nebulization of water: Morphology and raman characterization
No full textThe current devices used to produce massive amounts of snow (i.e., snow machines) can be improved with concern to both the energy efficiency and the quality of snow. Here we investigate an alternative snow production method based on the ultrasonic nebulization of water and its subsequent condensation on the cold surfaces of a refrigerator. Inspection of the snow samples with a stereo optical microscope shows both dendritic and granular snow morphologies. The characterization of the samples by Raman spectroscopy shows a behavior consistent with that of a natural, low-density snow. Our results indicate that ultrasonic nebulization of water is an effective strategy for producing natural-like snow at the laboratory scale
Raman spectroscopy-based assessment of the liquid water content in snow
No full textIn snow, water coexists in solid, liquid and vapor states. The relative abundance of the
three phases drives snow grain metamorphism and affects the physical properties of the snowpack.
Knowledge of the content of the liquid phase in snow is critical to estimate the snowmelt runoff and
to forecast the release of wet avalanches. Liquid water does not spread homogeneously through a
snowpack because different snow layers have different permeabilities; therefore, it is important to
track sudden changes in the amount of liquid water within a specific layer. We reproduced water
percolation in the laboratory, and used Raman spectroscopy to detect the presence of the liquid phase
in controlled snow samples. We performed experiments on both fine- and coarse-grained snow. The
obtained snow spectra are well fitted by a linear combination of the spectra typical of liquid water
and ice. We progressively charged snow with liquid water from dry snow up to soaked snow. As a
result, we exploited continuous, qualitative monitoring of the evolution of the liquid water content as
reflected by the fitting coefficient c
METHOD FOR TREATING A SLIDING SURFACE OF A SLIDING DEVICE AND THE SLIDING DEVICE COMPRISING THAT SLIDING SURFACE
No full textMethod for treating a base (11) able to be used in a sliding apparatus (10) and provided with at least a sliding surface (21); the method comprises at least a first step of cutting the base (11) by means of which a plurality of craters (22) with a controlled depth (P) and diameter (D) are made on the sliding surface (21), and at least a second step of structuring and finishing the sliding surface (21) in zones of said sliding surface (21) defined inside the craters (22) and/or in zones of the sliding surface (21) defined between one crater (22) and the other, so as to obtain a plurality of ridges (24) distributed on the sliding surface (21) of the base (11) in the craters (22) and/or between one crater (22) and the other
Pre-resonance effects in deep UV Raman spectra of normal and deuterated water
No full textWe have investigated the shape of the OH/OD stretching Raman band of water as a function of the excitation wavelength in the deep UV region (200-266 nm). By analyzing the spectral profiles, we highlighted selective pre-resonance effects in the high wavenumber component of the OH/OD stretching band, associated to distorted H-bonded water configurations. A van’t Hoff treatment of the temperature-dependent Raman spectra provides an estimate of the thermal energy associated to the change from ordered (ice-like) to disordered configurations that agrees with values obtained by related methods based on a two-state model of water. These results open the possibility of exploiting the observed pre-resonance deep-UV signal enhancement to investigate H-bonding properties in aqueous media
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