Search results for "efficien"
showing 10 items of 3014 documents
Multivariate Nonparametric Tests
2004
Multivariate nonparametric statistical tests of hypotheses are described for the one-sample location problem, the several-sample location problem and the problem of testing independence between pairs of vectors. These methods are based on affine-invariant spatial sign and spatial rank vectors. They provide affine-invariant multivariate generalizations of the univariate sign test, signed-rank test, Wilcoxon rank sum test, Kruskal–Wallis test, and the Kendall and Spearman correlation tests. While the emphasis is on tests of hypotheses, certain references to associated affine-equivariant estimators are included. Pitman asymptotic efficiencies demonstrate the excellent performance of these meth…
New complex polycyclic compounds: Synthesis, antiproliferative activity and mechanism of action
2020
Abstract Polycyclic or O-glycoconiugate polycyclic compounds 1a-g were previously tested for their in vitro antiproliferative activity. In this series of compounds, activity increases as log P decreases. Specifically, compounds 1d and 1g showed lower log P values together with the best antiproliferative profiles. With the aim of extending our understanding of the structure–activity relationship (SAR) of this class of compounds, we prepared new polycyclic derivatives 2a-c, which bear on each of the two phenyl rings hydrophilic substituents (OH, SO2NH2 or NHCOCH3). These substituents are able to form hydrogen bonds and to decrease the partition coefficient value as compared with compound 1d. …
Macromolecules in ordered media: 4. Poly(2-vinyl pyridine)-liposome association induced by electrostatic interactions
1997
Abstract We have investigated the interaction between vesicles based on dimyristoyl phosphatidic acid (DMPA) and a polymer, such as poly(2-vinyl pyridine) (P2VPy), on the basis of both partition and binding models. The resulting association curves are non monotonous being three regions clearly evidenced. The electrostatic and steric origin of the attractive or repulsive interactions are analyzed as a function of pH, ionic strength and temperature using the fluorescence spectroscopy technique. We emphasize the importance of differentiating the ideal definition of the binding constant from the theoretically evaluated including the activity coefficient, γ, to take into account shifts from the …
A spatially resolved investigation of oxygen adsorption on polycrystalline copper and titanium by means of photoemission electron microscopy
2004
Abstract The interaction of oxygen with polycrystalline copper and titanium surfaces was studied by means of photoemission electron microscopy. Variations in the image brightness were used to determine the work function of different Cu crystallites. The change of the work function was monitored during oxygen adsorption on both, Cu and Ti. Those changes are smooth for Cu whereas different Ti crystallites exhibit a rather complicated behavior during oxygen adsorption. The transformation of brightness versus exposure curves into work function versus coverage curves allows to determine the initial dipole moment of the adsorbed oxygen atoms. A value of about 20 mD was found for O on Cu(1 1 0). V…
Sticking Probability on Zeolites
2006
The sticking coefficient, i.e., the probability that, on hitting the surface of a nanoporous particle (zeolite), a molecule shall be able to enter the intracrystalline space, is a key quantity for the application of such materials in heterogeneous catalysis and molecular sieving. On the basis of pulsed field gradient NMR diffusion measurements and molecular dynamics simulations, typical values of this probability are found to be close to one. They exceed previous estimates on the basis of IR uptake measurements by many orders of magnitude.
The influence of the “hot”-dimer adsorption mechanism on the kinetics of a monomer-dimer surface reaction
1993
“Hot” dimers are molecules which after adsorption dissociate and each of the remaining “hot” monomers fly apart up to a maximum distance R from the original adsorption site. The influence of the “hot”-dimer adsorption mechanism on relevant aspects of the bimolecular catalyzed reaction of the type A − (1/2)B2(“hot”) → AB is studied by means of the Monte-Carlo simulation technique. The temporal evolution of both the reactant's coverages as well as the rate of AB-production is evaluated and discussed. Due to the enhanced probability of “hot” species for encounters with other adsorbed particles, the rate of AB-production becomes faster when increasing R. This behavior may be relevant in the dyn…
A dish-stirling solar concentrator coupled to a seasonal thermal energy storage system in the southern mediterranean basin: A cogenerative layout hyp…
2020
Abstract In the future, renewable energy sources will increasingly represent an efficient energy source capable of meeting the demands of residential and industrial buildings avoiding the emissions of greenhouse gases into the atmosphere. In this paper, a heat and electric power cogeneration plant implementing a field of dish-Stirling collectors, a seasonal geothermal storage and a system of water-to-water heat pumps is proposed for the first time. The cogeneration plant has been designed both to supply thermal energy to the heating system of Building 9 of the Department of Engineering in Palermo and to produce electricity. The operation of the plant has been tested by means of hourly-based…
A validated energy model of a solar dish-Stirling system considering the cleanliness of mirrors
2020
Solar systems based on the coupling of parabolic concentrating collectors and thermal engines (i.e. dish-Stirling systems) are among the most efficient generators of solar power currently available. This study focuses on the modelling of functioning data from a 32 kWe dish-Stirling solar plant installed at a facility test site on the University of Palermo campus, in Southern Italy. The proposed model, based on real monitored data, the energy balance of the collector and the partial load efficiency of the Stirling engine, can be used easily to simulate the annual energy production of such systems, making use of the solar radiation database, with the aim of encouraging a greater commercialisa…
A methodology for optimisation of solar dish-Stirling systems size, based on the local frequency distribution of direct normal irradiance
2021
Abstract In geographical areas where direct solar irradiation levels are relatively high, concentrated solar energy systems are one of the most promising green energy technologies. Dish-Stirling systems are those that achieve the highest levels of solar-to-electric conversion efficiency, and yet they are still among the least common commercially available technologies. This paper focuses on a strategy aimed at promoting greater diffusion of dish-Stirling systems, which involves optimizing the size of the collector aperture area based on the hourly frequency distributions of beam irradiance and defining a new incentive scheme with a feed-in tariff that is variable with the installed costs of…
How Does the Public Spending Affect Technical Efficiency? Some Evidence from 15 European Countries
2019
The relationship between government size and economic growth has been widely debated. Departing from this issue, we provide an empirical analysis of the impact of government size on technical efficiency. The aim of this paper is to estimate by using a True Random Effect model the impact of public sector’s size and of public expenditure components on 15 European countries’ technical efficiency from 1996 to 2011. Using the total public expenditure as a proxy for the government size we estimate simultaneously national optimal production function and technical efficiency model by controlling for income distribution and institutional quality. Our main findings show that the effect of public sect…