Search results for "efficient"
showing 10 items of 1603 documents
Special Issue “Smart Urban Lighting Systems”
2020
The design and operation of multifunctional infrastructures for public lighting as well as their impact on the urban environment and citizens’ life is today of great interest. The cost of energy for public lighting is often an issue for the budget of municipalities. Furthermore, researchers’ and designers’ attention is increasingly focused on aspects of public lighting not directly valuable through economic factors. Starting from the “quality” of the light environment, looking at citizens’ visual comfort, the light has to be considered as an instrument to improve the urban context and objects therein (including buildings). Indeed, urban degradation (lack of infrastructures, maintenance, ser…
Diffusion of oxygen in nickel: A variable charge molecular dynamics study
2010
Abstract Variable charge molecular dynamics have been performed to study the diffusion mechanisms of oxygen atoms (O) in nickel (Ni) in the temperature range 950 K–1600 K. It is observed that oxygen does not diffuse via jumps of oxygen through interstitial sites but via a vacancy diffusion mechanism. The oxygen diffusivity can be well described by an Arrhenius law over the temperature range considered. The oxygen diffusion coefficient has been analysed and indicates a value of E a = 1.99 eV for the activation energy and D 0 = 39.2 cm 2 s − 1 for the pre-exponential factor. Our numerical results were compared with a compilation of experimental and theoretical studies, and exhibit a good agre…
Dependence of O2 diffusion dynamics on pressure and temperature in silica nanoparticles
2013
An experimental study of the molecular O2 diffusion process in high purity non-porous silica nanoparticles having 50 m2/g BET specific surface and 20 nm average radius was carried out in the temperature range from 127 to 177 °C at O2 pressure in the range from 0.2 to 66 bar. The study was performed by measuring the volume average interstitial O2 concentration by a Raman and photoluminescence technique using a 1,064 nm excitation laser to detect the singlet to triplet emission at 1,272 nm of the molecular oxygen in silica. A dependence of the diffusion kinetics on the O2 absolute pressure, in addition to temperature dependence, was found. The kinetics can be fit by the solution of Fick’s dif…
O2 Diffusion in Amorphous SiO2 Nanoparticles Probed by Outgassing
2012
An experimental study of the O2 diffusion process in nanoparticles of amorphous SiO2 in the temperature range from 98 to 157 °C was carried out by Raman and photoluminescence techniques. We studied O2 diffusion in high purity silica nanoparticles with a mean diameter of 14, 20, and 40 nm detecting the outgassing of molecules trapped during the manufacturing. The kinetics of diffusion is well described for all the investigated nanoparticles by the Fick’s equation proving its applicability to nanoscale systems. The diffusion coefficient features an Arrhenius law temperature dependence in the explored temperature range, and the diffusion coefficient values are in good agreement with extrapolat…
Memory effects and coverage dependence of surface diffusion in a model adsorption system
1999
We study the coverage dependence of surface diffusion coefficients for a strongly interacting adsorption system O/W(110) via Monte Carlo simulations of a lattice-gas model. In particular, we consider the nature and emergence of memory effects as contained in the corresponding correlation factors in tracer and collective diffusion. We show that memory effects can be very pronounced deep inside the ordered phases and in regions close to first and second order phase transition boundaries. Particular attention is paid to the details of the time dependence of memory effects. The memory effect in tracer diffusion is found to decay following a power law after an initial transient period. This beha…
Development of Eco-Friendly and Self-Cleaning Lime-Pozzolan Plasters for Bio-Construction and Cultural Heritage
2020
Summarization: Nowadays, the design and use of multi-functional mortars has increased significantly, with interesting applications in the green building and cultural heritage conservation sectors. A key point for a correct adoption of these innovative materials is their behavior along time and their resistance to the weathering. The objective of this project was to define the performance and durability of innovative mortars, in order to use them correctly and to avoid irreparable damage over time. For the development of this project, lime–metakaolin and hydraulic lime–metakaolin based mortars (hereinafter called A, B), as well as A and B with the addition of nano-TiO2 and perlite (hereinaft…
Multiple criteria assessment of methods for forecasting building thermal energy demand
2020
Abstract Nowadays worldwide directives have focused the attention on improving energy efficiency in the building sector. The research of models able to predict the energy consumption from the first design and energy planning phase is conducted to improve building sustainability. Use of traditional forecasting tools for building thermal energy demand tends to encounter difficulties relevant to the amount of data required, implementation of the models, computational costs and inability to generalize the output. Therefore, many studies focused on the research and development of alternative resolution methods, but the choice of the most convenient is not clear and simple. Single comparison of s…
Search for Tensor, Vector, and Scalar Polarizations in the Stochastic Gravitational-Wave Background
2018
The detection of gravitational waves with Advanced LIGO and Advanced Virgo has enabled novel tests of general relativity, including direct study of the polarization of gravitational waves. While general relativity allows for only two tensor gravitational-wave polarizations, general metric theories can additionally predict two vector and two scalar polarizations. The polarization of gravitational waves is encoded in the spectral shape of the stochastic gravitational-wave background, formed by the superposition of cosmological and individually-unresolved astrophysical sources. Using data recorded by Advanced LIGO during its first observing run, we search for a stochastic background of generic…
Multiyear in-situ measurements of atmospheric aerosol absorption properties at an urban coastal site in western Mediterranean
2016
Abstract In-situ aerosol absorption properties measured in Valencia (Spain) for four years, from February 2011 to February 2015, have been analysed. Spectral absorption properties have been obtained using a seven-wavelength Aethalometer AE-31 which covers the range from UV (370 nm) to IR (950 nm). In order to obtain the absorption coefficients, compensation parameters have been calculated for the Aethalometer considering seasonal and spectral differences. For this multiyear measurement period, seasonal site-specific calibration parameters have been obtained. Furthermore, estimations of the absorption Angstrom Exponent (α abs ) have been calculated using the seven Aethalometer wavelengths. T…
Single particle characterization of black carbon aerosols at a tropospheric alpine site in Switzerland
2010
The refractory black carbon (rBC) mass, size distribution (190–720 nm) and mixing state in sub-micron aerosols were characterized from late February to March 2007 using a single particle incandescence method at the high alpine research station Jungfraujoch (JFJ), Switzerland (46.33° N, 7.59° E, 3580 m a.s.l.). JFJ is a ground based location, which is at times exposed to continental free tropospheric air. A median mass absorption coefficient (MAC) of 10.2&plusmn;3.2 m<sup>2</sup> g<sup>−1</sup> at &lambda;=630 nm was derived by comparing single particle incandescence measurements of black carbon mass with continuous measurements of absorption coefficient. This…