1,352 research outputs found
Drug user dynamics: a compartmental model of drug users for scenario analyses
A six-typology compartment model of trends in the
use of illicit drugs in Italy is developed to evaluate
policies and interventions through scenario analyses.
Inside the big compartments of just-cannabis users
and multiple drug users, three subpopulations are
taken into account: the occasional, regular and
intensive user. Moreover, compartments for health
care, assisted persons together with a constant
source (susceptible) are added; removed people
(i.e. those who leave drugs for any reason) are put in
a compartment which does not participate in the
dynamics. Flows from the susceptible reservoir
among the drug-user compartments and to the
removed or the health care compartments are
studied in a deterministic linear ODE framework,
where parameters are estimated using Italian data.
This system shows an evolution towards a steady
state, the speed of convergence being dependent on
parameters in a fairly visible way. This model
represents a theoretical development in drug policy
analysis, as it shows the relevance of flux parameters,
which are in principle subject to modifications
due to institutional efforts, together with a quantitative
evaluation of their role in the evolution of the
whole system
SVEP and local spectral radius formula for unbounded operators
In this paper we study the localized single valued extension property for an unbounded operator
T. Moreover, we provide sufficient conditions for which the formula of the local spectral radius holds for
these operators
Maximal extensions of a linear functional
Extensions of a positive hermitian linear functional ω, defined on a dense *-subalgebra A0 of a topological *-algebra A[τ] are analyzed. It turns out that their maximal extensions as linear functionals or hermitian linear functionals are everywhere defined. The situation however changes deeply if one looks for positive extensions. The case of fully positive and widely positive extensions considered in [2] is revisited from this point of view. Examples mostly taken from the theory of integration are discussed
Fingerprinting white marbles of archaeometric interest by means of combined SANS and USANS
We have performed a series of USANS and SANS measurements on
a selected group of marble samples characterized by similar chemical composition but wide range of known metamorphic conditions. With these samples we start the building up of a data base in an attempt to correlate metamorphism and mesoscopic structure of white marbles. Experimental data have been analysed in terms of a hierarchical model. The present data highlight the importance of the structure at
meso scale in identifying the provenance of the marble samples. A remarkable simple relation between the model parameters and the metamorphic degree has been found. This curve might represent a master curve to allow fingerprinting of white marbles. Also, two coloured marbles from Villa Adriana (Tivoli, Italy) have been investigated
by means of the same techniques. Results obtained follow the general trend found for the white marbles
New Insight on Medieval Painting in Sicily: The Virgin Hodegetria Panel in Monreale Cathedral (Palermo, Italy)
: The Virgin Hodegetria, located in the Cathedral of Santa Maria Nuova in Monreale, near
Palermo (Italy), probably dating the first half of the 13th century, is one of the earliest examples
of medieval panel painting in Sicily. A diagnostic campaign was carried out on the panel aiming
to identify the constituting materials and the executive technique, as well as to assess the state of
conservation for supporting the methodological choice of the restoration intervention. Both non invasive (X-ray radiography, digital microscope, multispectral imaging, ED-X-ray fluorescence) and
micro-invasive (polarised light microscopy, ESEM-EDX, ATR-FTIR spectroscopy and micro-Raman
spectroscopy) analyses were performed. According to the results, the executive technique followed
the 13th–14th-century Italian painting tradition. A complex structure was applied on the wooden
support, consisting of a double layer of canvas and several ground layers of gypsum and glue based binder. The underdrawing was made by a brush using carbonaceous black pigment. The
original palette includes red ochre, red lead, azurite, carbon black and bone black. During the several
restorations, mercury-based red, indigo, smalt blue, orpiment and synthetic mars were used. The
original silver leaf of the frame was covered with red tin-based lake and subsequently regilded with
gold leaf. Proteinaceous and oil binders were also detecte
Evaluation of electrospun spinel-type high-entropy (Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)3O4, (Cr0.2Mn0.2Fe0.2Co0.2Zn0.2)3O4 and (Cr0.2Mn0.2Fe0.2Ni0.2Zn0.2)3O4 oxide nanofibers as electrocatalysts for oxygen evolution in alkaline medium
Electrochemical water splitting is a promising sustainable-energy technology, but the slow kinetics of the oxygen evolution reaction represents a limitation for its broad market penetration. Spinel-structured transition metal (TM) oxides have shown great potential as a sustainable alternative to precious metal-based electrocatalysts. High-entropy oxides (HEOs) with multiple TM-cation sites lend themselves to engineering of the octahedral redox-active centres to enhance the catalyst reactivity. This work focuses on the preparation of electrospun spinel-type HEO nanofibers (NFs), based on equimolar (Cr,Mn,Fe,Co,Ni), (Cr,Mn,Fe,Co,Zn) and (Cr,Mn,Fe,Ni,Zn) combinations, and their evaluation as electrocatalysts in alkaline medium together with (Cr,Mn,Fe,Co,Ni) HEO nanoparticles (NPs) prepared via the sol-gel method. (Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)3O4 NFs and NPs (Tafel slopes: 49.1 and 51.3 mV dec−1, respectively) outperform both (Cr0.2Mn0.2Fe0.2Co0.2Zn0.2)3O4 and (Cr0.2Mn0.2Fe0.2Ni0.2Zn0.2)3O4 NFs (62.5 and 59.6 mV dec−1, respectively) and IrO2 reference electrocatalyst (52.9 mV dec−1). The higher concentration of oxygen vacancies on their surface and the higher occupation of octahedral sites by redox-active Co2+ and Ni2+ centres are responsible for their behaviour. The present electrospun HEO NFs have great potential as ink-jet printable electrocatalysts
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