10,149 research outputs found
Mechanical behaviour with temperatures of aluminum matrix composites with CNTs
Aluminum is a very useful structural metal employed in different industrial sectors, in particular it is used in
large quantities in automotive, aeronautic and nautical industries. The main reasons of its wide use are: a very
good oxidation resistance, excellent ductility, low melting temperature (660 °C) and low density (2.71 g/cm3).
However, in order to reduce the emissions and fuel consumption is necessary to reduce the overall weight of
vehicles by increasing mechanical properties of the structural material. The improvement of mechanical
properties is normally achieved through use of reinforcement in materials, used like matrix, in order to improve
some specific characteristics.
In this work composites of carbon nanotubes (CNTs) dispersed in aluminum were made. The most difficulties
in the preparation of this type of composite are represented by the low wettability between metallic matrix and
fillers and the possibility of the oxidation of metal during melting with consequent decreasing of mechanical
proprieties. The composite was obtained by three consecutive step: the first one is the functionalization of
fillers surface to improve the fillers dispersion, the second one is the dispersion of fillers in the matrix by
powder mixing and the third one is the melting and casting of the mix prepared.
In particular, fillers used are multi walled carbon nanotubes (MWCNTs) with functionalized surface by
treatment with a solfonitric solution. Melting and casting are carried out with the aid of an induction furnace
with a controlled atmosphere system and centrifugal casting. Argon is the inert gas used to prevent the
oxidation of aluminium during fusion. Young’s modulus was evaluated at different temperature and correlated
with the different CNTs percentage. The dispersion rate of fillers and the microstructure of the sample were
evaluated by FESEM micrograph
Electrokinetic Lattice Boltzmann solver coupled to Molecular Dynamics: application to polymer translocation
We develop a theoretical and computational approach to deal with systems that
involve a disparate range of spatio-temporal scales, such as those comprised of
colloidal particles or polymers moving in a fluidic molecular environment. Our
approach is based on a multiscale modeling that combines the slow dynamics of
the large particles with the fast dynamics of the solvent into a unique
framework. The former is numerically solved via Molecular Dynamics and the
latter via a multi-component Lattice Boltzmann. The two techniques are coupled
together to allow for a seamless exchange of information between the
descriptions. Being based on a kinetic multi-component description of the fluid
species, the scheme is flexible in modeling charge flow within complex
geometries and ranging from large to vanishing salt concentration. The details
of the scheme are presented and the method is applied to the problem of
translocation of a charged polymer through a nanopores. In the end, we discuss
the advantages and complexities of the approach
The effect of being awardees for academic careers. ERC and FIRB recipients' outcomes compared to ordinary academics – performances and promotions
Some individual funding schemes aim at recognize excellence of early and/or mid-career researchers in order to allow them boost their potential. Some schemes are munificent endowments, assuring autonomy and security. This is the case of one of the European flagship schemes – the European Research Council (ERC). In Italy, a very similar scheme called FIRB has a similar rationale. Both schemes are supposed to make excellence “fly higher”. The paper checks whether such ERC and FIRB recipients are thereafter more productive in terms of quality and influence testing against a control group of Italian academics of similar age, rank and discipline who did not win such individual grants. Results show that ERC recipients ameliorate research performance more than FIRB recipients did, although differences with control group don’t show always a particular additional effect in research outputs when comparing with pre-awarding performances (difference-in-difference tests). On the other hand, we find a strong Matthew effect in promotions, being the credential of having recipient of an ERC or a FIRB per se the strongest predictor of promotion, other achievements being equal. Policy recommendations speculate whether an egalitarian non-stratified higher education system like the Italian one is ideal home for these schemes, and whether the Italian system can afford a national scheme overlapping international ones, considering long-lasting shortage of financial resources and the egalitarian structure of its system
The gender promotion gap in Italy
The topic of gender differences and career progression is high not only on the scholarly agenda, it is often discussed in the media as well – sometimes in quite controversial terms. We investigate this theme in Italy, a country that in recent years introduced a level of institutional autonomy in determining the career paths of academics. We provide analysis of census data about promotion to full professorship, looking at indicators of productivity, rank, age and prestige of an individual’s department of affiliation. Our analysis also takes into account institutional performative indicators, which affect promotion probabilities. Our study (Marini & Meschitti 2018) found that when promotion decisions lacked transparency a strong discrimination existed against women, despite their productivity matching that of their male counterparts. However, gender discrimination was almost absent when fully transparent procedures were adopted. The seminar will also look at whether this discrimination can be explained by similarities in professors’ communities (those in charge of bestowing promotions), considering specifically the combination of discipline and institution
Amplification of surface plasmon polaritons in the presence of nonlinearity and spectral signatures of threshold crossover
We describe effects of nonlinearity on propagation of surface plasmon
polaritons (SPPs) at an interface between a metal and an amplifying medium of
the externally pumped two-level atoms. Using Maxwell equations we derive the
nonlinear dispersion law and demonstrate that, the nonlinear saturation of the
linear gain leads to formation of stationary SPP modes with the intensities
independent from the propagation distance. Transition to the regime of
stationary propagation is similar to the threshold crossover in lasers and
leads to narrowing of the SPP spectrum.Comment: http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-34-18-286
Ginzburg-Landau equation bound to the metal-dielectric interface and transverse nonlinear optics with amplified plasmon polaritons
Using a multiple-scale asymptotic approach, we have derived the complex cubic
Ginzburg-Landau equation for amplified and nonlinearly saturated surface
plasmon polaritons propagating and diffracting along a metal-dielectric
interface. An important feature of our method is that it explicitly accounts
for nonlinear terms in the boundary conditions, which are critical for a
correct description of nonlinear surface waves. Using our model we have
analyzed filamentation and discussed bright and dark spatially localized
structures of plasmons.Comment: http://link.aps.org/doi/10.1103/PhysRevA.81.03385
From endorsement of ambivalent sexism to psychological IPV victimization: The role of attitudes supportive of IPV, legitimating myths of IPV, and acceptance of psychological aggression.
Research on intimate partner violence (IPV) has recognized psychological abuse as a precursor of physical and sexual violence in intimate relationships. However, risk factors in predicting women’s psychological abuse victimization in such a context are still unclear. The goal of the present work was to investigate the role of ambivalent sexism on psychological IPV victimization, by taking into account in the same study the effect of three additional social-psychological factors: women’s i) attitudes supportive of IPV, ii) endorsement of legitimating myths of IPV, and iii) acceptance of psychological aggression in intimate relationships. A total of 408 Italian young women (Mage = 23.87; SD = 2.39) involved in non-marital heterosexual romantic relationships completed measures aimed at assessing i) hostile and benevolent sexism, ii) attitudes supportive of IPV, iii) legitimating myths of IPV, iv) prevalence of psychological abuse experienced within the last 12 months, and performed a task developed ad hoc to measure v) acceptance of psychological aggression in intimate relationships. Results showed that the effect of ambivalent sexism on participants’ prevalence of psychological abuse was mediated by the endorsement of attitudes supportive of IPV and legitimating myths of IPV, as well as by acceptance of psychological aggression. Findings are discussed based on literature about ambivalent sexism, and attitudes and beliefs about IP
What a thousand children tell us about grammatical complexity and working memory: A cross-sectional analysis on the comprehension of clitics and passives in Italian
Data from 996 Italian-speaking children were collected and analyzed to assess whether a movement-based notion of grammatical complexity is adequate to capture the developmental trend of clitics and passives in Italian. A second goal of the study was to address the relationship between working memory and syntactic development, exploring the hypothesis that higher digit span values predict better comprehension of complex matrix sentences. The results confirm the validity of a ranking of grammatical structures based on constituent movement, with both clitics and passives developing in parallel and later than canonical SVO sentences. Working memory also shows an effect on sentence comprehension in general, but standard measures (digit span forward/backward) do not show a selective advantage in handling complex constructions such as clitics and passives
Which is the temperature of granular systems? A mean field model of free cooling inelastic mixtures
We consider a mean field model describing the free cooling process of a two
component granular mixture, a generalization of so called Maxwell model. The
cooling is viewed as an ordering process and the scaling behavior is attributed
to the presence of an attractive fixed point at for the dynamics. By
means of asymptotic analysis of the Boltzmann equation and of numerical
simulations we get the following results: 1)we establish the existence of two
different partial granular temperatures, one for each component, which violates
the Zeroth Law of Thermodynamics; 2) we obtain the scaling form of the two
distribution functions; 3) we prove the existence of a continuous spectrum of
exponents characterizing the inverse-power law decay of the tails of the
velocity, which generalizes the previously reported value 4 for the pure model;
4) we find that the exponents depend on the composition, masses and restitution
coefficients of the mixture; 5) we also remark that the reported distributions
represent a dynamical realization of those predicted by the Non Extensive
Statistical Mechanics, in spite of the fact that ours stem from a purely
dynamical approach.Comment: 23 pages, 9 figures. submitted for publicatio
Steady state properties of a mean field model of driven inelastic mixtures
We investigate a Maxwell model of inelastic granular mixture under the
influence of a stochastic driving and obtain its steady state properties in the
context of classical kinetic theory. The model is studied analytically by
computing the moments up to the eighth order and approximating the
distributions by means of a Sonine polynomial expansion method. The main
findings concern the existence of two different granular temperatures, one for
each species, and the characterization of the distribution functions, whose
tails are in general more populated than those of an elastic system. These
analytical results are tested against Monte Carlo numerical simulations of the
model and are in general in good agreement. The simulations, however, reveal
the presence of pronounced non-gaussian tails in the case of an infinite
temperature bath, which are not well reproduced by the Sonine method.Comment: 23 pages, 10 figures, submitted for publicatio
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