1359 research outputs found
Sort by
Statistical physics of network communities in economic systems
Get PDFIn the last decade, the study of big networked systems has received a great deal of attention
thanks to the increased availability of large datasets and the technology to analyze them. To unravel
regularities and behaviours from his enormous quantity of data and supply suitable models, we need
appropriate tools, one of them being community detection. Finding meaningful communities in a
networks is still a diffcult task but essential to unveil functional relations between the parts.
The research presented here has been carried out focusing on community detection; in particular
were considered cases where the spatial component was relevant or intrinsic. It is indeed true that,
nowadays, many systems, represented as complex networks, are affected, more or less naturally,
by the geographical distance, location and organization. This holds true even for economic events:
it has been proved that trade and exchanges between countries are necessarily suffocated by the
geographical proximity or impeded by natural obstacles.
Still, community detection alone is not sufficient to describe the whole picture, since it gives
no information about the internal structure of a community. Therefore we developed the novel
core detection method, natural counterpart of the community detection algorithm and meant to be
performed alongside it, which is, at the same time, simple and powerful.
We aim to apply community detection and core detection methodologies to the analysis of the
global market and its functioning, in order to understand the origin of economic turmoils and critical
events.
In this work we analyze different economic systems from a complex network perspective and
find some interesting results: we study patent data in order to measure internationalization of
European countries and assess the effectiveness of EU policies; we examine the dynamics of network
effects on the performances of individual countries and trade relationships in the International Trade
Network; we represent World Input-Output data as an interdependent complex network and study
its properties, showing evidence of the crisis .
Thanks to both community and core detection, we are able to have a deeper insight on the
inner workings of community formation, we can identify the leading members in a group and reveal
in
uence basins, unknown otherwise
Characterization and application of Pb-based organometal halide perovskite
Get PDFIn the foreseeable future, the global energy consumption is expected to increase
significantly. Solar energy, as an alternative form of energy, has gained popularity as a
way to solve the greenhouse gas emission and sustainability problem of fossil fuels.
This thesis mainly concerns a novel materials system, namely organometal trihalide
perovskite, that is currently receiving considerable attention as light absorber in
solar cells, due to the promise to obtain significant improvements in the efficiency
of solar cells fabricated with very low cost, scalable techniques. The main idea of this
thesis is to study the photophysical properties and the mechanisms affecting the
performance of solar cells.
In chapter 1, the history of solar cell materials will be reviewed briefly.
The synthesis and basic characterization are described in chapter 2. In this
chapter, it is explained how the methylammonium iodide was synthesized and
purified. Perovskite films were fabricated by three different methods, resulting in very
different film morphologies. Perovskite structure was confirmed by X-ray diffraction,
and CH3NH3PbI3 shows a tetragonal phase with lattice parameters a=b=8.872 Å and c
=12.637 Å. The morphology investigation shows that solution spin-casting method
produces needle-shaped crystals, leading to a partial surface coverage and limited
conductivity. The two-step from solution method was based on spin-casting PbI2 and
CH3NH3I solution gradually, creating the perovskite upon reaction of the two
compounds. The result is a film with smaller grains and more uniform coverage.
Finally, the vapour assisted method, where a PbI2 film is first obtained by spin-casting
from solution, then evaporation of CH3NH3I occurs for several hours in N2
atmosphere. A uniform film was achieved by this method with RMS roughness
around 38 nm.
The optical properties of the CH3NH3PbI3 are investigated in chapter 3. The
optical bandgap of it is 1.64 eV, as extracted from the absorption edge, which is
higher than the theoretical 1.55 eV. The absorption coefficient exceeds ~105 cm-1 for
incident light wavelength shorter than 500 nm. The transient photoluminescence
spectroscopy analysis shows that the lifetime of the excitons could be as high as τ =
80 ns under low excitation conditions. As long as the film is processed in such a way
that the mean PL lifetime exceeds several nanoseconds at sun illumination, carrier
mobility is sufficiently high to guarantee efficient charge collection in the
photovoltaic device.
In chapter 4, simple planar solar cells are described, which have been fabricated
with compact TiO2 as electron transport layer, covered with perovskite as light
harvester; poly (3-hexylthiophene- 2,5-diyl) (P3HT) was spin-casted as hole transport
layer; at last, transition metal oxide MoO3 or LiF was evaporated onto P3HT as
interfacial modifying material, final electrode was a thin layer of Ag. The relationship
between TiO2 morphology and the solar cell performance is discussed. The
morphology of compact TiO2 appears to be an important factor to influence the
photovoltaic, which still needs further understanding in order to obtain better
performing devices.
The investigation on perovskite morphology indicates that the vapour assisted
two-step deposition technique is useful for preparing perovskite films. We rationalize
the crystal growth process with the conjecture that the organic and inorganic
components have an efficient reaction by vapour intercalation into the PbI2 film. The
resulting film has full surface coverage, microscale grain size and uniform grain
structure.
The investigation on interfacial modification shows that the solar cell with MoO3
as modification material has excellent performance with a PCE of 7.95%. And the
solar cell with LiF as modification material has good performance with a Jsc of 21.73
mA/cm2. Both of the two materials have positive affection to the solar cell. The MoO3
is a proper material for modifying the interface between the electrode and hole
transporting layer, which could replace the ITO in a heterojunction solar cell. And the
LiF could decrease the work function of the metal contact, which may increase the
transporting ability and increase the compatibility of the metal electrode. The
investigation implies that the interface engineering is very important to the device
science
Tuning the magnetic anisotropy in nanostructured magnetic oxides
Get PDFAmong nanostructured magnetic materials, nanoparticles (NPs) are unique complex physical objects: in these systems a multidomain organization is energetically unfavorable and single-magnetic-domain particles are formed, each one with a huge magnetic moment with comparison to that of single atoms, thus they are often named “supermoment”. The attractive performance of magnetic NPs based materials are appealing for several technological fields ranging from nanomedicine to high-density magneto recording. Thus, understanding the physics of magnetic nanoparticles and controlling their magnetic properties represent hot topics not only for fundamental studies but also for technological applications. The magnetic behavior of such entities is related to the reversal of their magnetization; this can be a thermal or a field activated transition, which is characterized by an energy barrier defined as a magnetic anisotropy energy (MAE), which is influenced by several parameters. Thus, the tuning of the magnetic properties of nanoparticles means control of the MAE.
In this work it will be discussed how to tune the MAE at the nanoscale showing the main parameters that can influence the anisotropy itself. It will be investigated the role of particle volume in the effective anisotropy, and its correlation with the surface contribution, exploring its strong effect with particle size below 10 nm. In this framework it will be investigated the role of organic coating, underlining its ability to reduce the magnetic disorder arising from the broken symmetry at particles surface. In addition, in nanoparticle ensemble, the MAE may differ from one particle to another due to particles size and shape distributions. Thus it will be defined a detailed statistical analysis of particles’ morphology, leading to the development of a new instrument to analyze particles morphology, called “aspect maps”.
The relation between the physical chemical structures of nanoparticles will be investigated on nickel doped cobalt ferrite samples, demonstrating how to tune the MAE by chemical composition, i.e., controlling magnetocrystalline anisotropy. Furthermore it will be analyzed the evolution of interparticles interactions with respect single particle magnetic anisotropy by means of a modified random anisotropy model.
The last part of this work will deal with the design of novel nanostructured composites. La0.67Ca0.33MnO3 and CoFe2O4 will be combined using two different structures, which can be easily extent to other materials, to improve their magnetic interactions in order to obtain tunable magnetotrasport proprieties of the final composites
Paesaggio e trasformazione. Metodologie di lettura e valutazione per nuovi modelli organizzativi
Get PDFThe thesis explores the link between project and landscape from the point of view of the evaluation
methodologies of the landscape quality and on the grounds of the contemporary debate and the
different cultural and legislative attitudes to the topic. Beginning from the definition of the word,
which has its origin in the studies of geographical disciplines of the XIX century, the landscape is no
longer a simple object of the aesthetical perception, but a complex category founded on a variety of
different factors which all contribute to its definition: strictly “scientific” factors, pertaining to a vast
range of established disciplines, and so-called “cultural” factors combining the historical, social,
economic aspects which are the result of the indissoluble relation between man and environment.
The landscape represents the complexity of reality, an interpretative cultural category that units and
adds a variety of aspects, traces, material and immaterial elements determined by the processes and
the actions that over the centuries changed the territory.
Against the remark, on the one end, of the processes of transformation to which are continuously
submitted the contemporary landscapes which, by creating a crisis of the model that historically
accompanies their development and the transformations, nowadays reveal a situation deeply
compromised of the Italian context and, on the other end, of the weakness of the traditional
instruments of planning which are no longer adequate to the interpretation and the management
of the complexity of the transformation processes caused by the present phase of globalization,
the research analyzes the potentiality of the landscape role as an instrument of transformation and
main motor of the territorial policies trough the identification of instruments and methods aimed at
the construction of parameters and criteria for the implementation of new organizational models
of the territory.
While we register a rising sensitization towards the implementation of a sustainable development of the
territory, the promotion of the cultural heritage and the recognition of the local identities, only today
has a need emerged of methodologies and innovative models able to interpret at different scales and
in different contexts the principles inherent in the international convention and to give appropriate
policies for the regeneration and the rehabilitation of landscapes that are often damaged.
Definition of a rigorous methodology for the study of landscape, supported by the experimental
application in some processes especially significant and exemplary in the Italian context, offers
objective criteria and elements for assessment of the main factors and policies contributing to the
development of sustainable models of organisation of the territory and is therefore an innovative
tool to the application of the European Convention and thereby can become a valid support to
indicate a direction for the action and evolution of the dynamics of the transformation processes
of the landscape
Enabling data-intensive biomedical studies
Get PDFThe constantly increasing size and complexity of datasets involved in biomedical
projects is deeply transforming approaches to their solution. Large scale
studies require specifically designed computational frameworks that are capable
of fulfilling many diverse requirements, the most important of which can
be summarized in the fundamental properties of scalability, reproducibility
and traceability. Although in recent years several new technologies have
emerged that help deal with the issues raised by data-intensive research
projects, applying them to the construction of a computational solution for
the specific problem at hand is far from trivial, as no one-size-fits-all recipe
exists for such a task. This work describes a methodology for approaching
this new class of studies through several examples of solutions applied to
concrete research problems
La città creativa.Politiche culturali e riqualificazione urbana tra conservazione e sviluppo
Get PDFIn the last two decades territorial competitiveness has profoundly changed the objectives of government intervention in the field of culture. No longer seen as a tool of social integration, Culture is now considered a tool for the economic revitalization of the city, especially in relation to chronic deficit of public finances. This depends mainly on the fact that the cultural heritage, as a scarce and irreproducible resource, is now the only economic good capable of competing on the global market, conquering niches in the "new new economy" and, at the same time, ensuring new forms of development, sustainable and able to unleashing positive processes at the micro-scale.
Scientific literature on protection, conservation, enhancement and management of Cultural and Environmental Heritage, gives reason for these large-scale dynamics, exhorting to a general renovation of the sector. Researches carried out in order to respond to this instance often aim to the identification of physical, economic and human resources already present in a given region in the attempt to create a 'local cultural chain' functional and working.
In Italy, the reference model for networking is Third Italy's industrial district, whose success is due to the close correlation between production, territory and local knowledge. The application of industrial district's organizational principles to cultural and environmental heritage has given rise to the 'advanced cultural district', now also applied to the more technical aspects of conservation, as demonstrated by the Regional Technology Districts for Cultural Heritage and Activities of Lazio and Tuscany.
The identification of physical, economic and human resources already present in a region and necessary for the cultural district operation is, as in the industrial field, based on the analysis of cultural and creative clusters, i.e. the measure of the geographic concentration of businesses, suppliers, and institutions networks which operate in the fields of culture and creativity.
The analyses developed in Anglo-Saxon countries in relation to the theme of the creative city, have had a wide spread, especially thanks to the works of Charles Landry and Richard Florida where creativity and culture are read as the principal agents of the economic transformation processes and, in some cases, as the ideal solution to all the contradictions and issues of urban. This, however, leads to a reductive and distorted view of the two concepts which, in their original meaning, have instead strong implications from ethical and civic point of view, so much important as to suggest possible links with the theme of the common goods and the historic urban landscape (as palimpsest of human-nature interactions in a given geographical area).
The PhD thesis, entitled “The creative city. Cultural policies and urban regeneration between conservation and development”, focused on these relationships between creative city principles and landscape approach outlined by the European Landscape Convention in order to identify best practices for the development of innovative cultural policies and new urban regeneration tools.
The research is characterized by a cross-cutting approach to cultural heritage which involves conservation technologies, cultural planning, urban studies and creative economy. In particular, the thesis faces and deepens many questions related to creative city and cultural districts in Italy leading to a theoretical model for the design of advanced cultural districts, consisting of:
a
benchmark methodology which explains, step by step, how to built an advanced cultural district, i.e. a district focused on cultural heritage, based on urban policies inspired to “creative city” theories and included in landscape planning framework;
a
"toolbox" of spatial, economic and social analysis and indicators that can be used to build the necessary knowledge on the future district’s territory as to draw a feasibility study.
Finally, having Sardinia region as reference, the thesis offers a picture of programs and plans to which the methodology and toolbox can be applied, outlining potential impacts of the proposed theoretical model within regional programming and landscape planning
Light conversion processes in lanthanide-based molecular materials
Get PDFThis work is mainly focused on the investigation and processing of luminescent molecular complexes of lanthanide ions (Ln), for the development of efficient near infrared (NIR)-emitting materials. In the light of a detailed understanding of the chemical/photophysical properties of the special class of lanthanide quinolinolato complexes, as prototype molecular materials for NIR applications, two main aspects have been taken into consideration for a progress in this field: i) (multi-) functional NIR-emissive heterolanthanide complexes and ii) lanthanide-doped sol-gel glasses as NIR-emissive optical materials.
Heterometallic assemblies, containing two or more different lanthanide cations as carriers of distinctive functionalities, represent promising materials where different physical properties can coexist or be in interplay thanks to intermetallic communication. A thorough discussion on heterolanthanide assemblies, pointing out the general strategies to achieve the desired (multi-) functionalities in these systems, is provided herein.
In this framework, heterolanthanide Er/Yb systems have attracted significant interest for Er3+ sensitization through resonance energy transfer (RET) from Yb3+ leading to enhancement of Er3+ NIR emission at 1.5 μm in glass host Yb-Er co-doped optical fiber amplifiers. A strategy to achieve composition control and homogeneity in such materials resorts to the encapsulation of Er and Yb in the same molecule to afford intermetallic communication between lanthanide ions sitting at short distance in a discrete polynuclear architecture. Fully efficient Yb-to-.Er RET at molecular level is firstly demonstrated in the mixed-lanthanide Yb2ErQ9 complex (Q = quinolinol ligand), and, as an extension of these studies, the investigation of the full photocycle leading to narrow-band NIR emission in a series of heterolanthanide ErxYb3-x quinolinolato compounds, on variation of metal composition and molecular stoichiometry, has been performed. Moreover, the first example of a tri-lanthanide discrete polynuclear molecule containing three NIR-emissive lanthanide ions: Nd3+, Yb3+ and Er3+, is presented. The NdYbErQ9 complex was investigated as a potential broad-band NIR emitter where the intensities of the three different main emissions from each lanthanide ion can be finely tuned on varying metal composition.
The investigation of the processing potential of luminescent lanthanide complexes through doping into inorganic or polymeric host matrixes is of crucial interest for the development of optical devices (amplifiers, optical waveguides, OLEDs, etc.). To this purpose, studies on the incorporation of an Yb quinolinolate complex into a silica sol-gel glass, with a thorough account of the photophysical properties of this hybrid material, have been performed. Promising results on silica thin films doped with heterolanthanide Er/Yb quinolinolates are also presented as a molecular approach to achieve controlled light conversion in NIR-emissive optical materials
Wearable sensors networks for safety applications in industrial scenarios
Get PDFIndustrial contexts, and in particular the port areas, are very complex systems to be monitored
and controlled due to the combined presence of vehicles and people. The port areas are the gateway
between navigation and terrestrial transportation and are of great importance in transport logistics.
Unfortunately, the management of port areas is quite complex because the safety of the workers
must be always assured. Therefore, in such a context, a centralized control system for the
monitoring and the prevention of risks is of particular importance. In this thesis, a real-time control
system for the monitoring of people and vehicles in industrial areas is proposed. The proposed
system is based on the Internet of Things paradigm, i.e. a network of “things” (such as sensors, tag
RFID, actuators etc.) which can communicate and interact with each other within a shared IP
addressing range, in order to share data and contribute to the management and development of
advanced applications. Specifically, the thesis is focused on the design of a wearable sensors
network based on RFID technology, and specifically on WISP sensors, for assuring the safety of the
workers. In this network, wearable devices that can be inserted directly on the textile have been
selected. Differently from conventional sensors, wearable sensors ensure a higher level of comfort,
and provide higher electromagnetic performance. Furthermore, textile materials are easily available.
Microstrips are good candidates for these applications because they mainly radiate perpendicularly
to the planar structure, and their ground plane allows a good shielding on the body tissues.
Therefore, I have designed specific antennas for RFID, that unlike the classical microstrip antennas
have the radiating surface composed of several "side by side" conductive "threads of textile". Since
the microwave model does not allow the design of an antenna with these characteristics with a good
approximation, a specific microwave model for coupled lines has been designed. With this model,
the specific antenna for RFID has been designed, with Jeans as substrate. The particular antenna’s
substrate allows direct integration into garments, but since the wearable antennas are placed very
close to the human body, biological issues which may arise on the human body from the use of
these sensors have been analysed. The Specific Absorption Rate (SAR) has been considered and
simulations have been conducted for evaluating the effects on the human body, and especially on
the head, when irradiated with the electromagnetic waves generated by the wearable antenna
realized with different materials. Dosimetric effects have been evaluated in function of the distance
from the body, in order to define a safe distance for placing the antenna on the human body. The
SAR has been evaluated also for full patches with different textile substrates, whose surface is
larger than that of the proposed model of coupled lines. Therefore, if the SAR values evaluated for the full patch are satisfying, the SAR values for the model of coupled lines will surely be
acceptable
L’isolamento sociale riduce marcatamente la risposta dei neuroni dopaminergici mesocorticali agli stimoli piacevoli.
Get PDFThe mesolimbic dopaminergic pathway plays an important role in the genesis of emotional arousal and behavioral activation in response to stimuli that provide a reward. This neural circuitry is also active in the early stages of learning and stabilization of addictive behavior due to substances abuse. Isolated animals have a different sensitivity to natural or artificial reinforcers. Accordingly, experimental evidences suggest that exposure to stress can deeply modify eating behavior. In light of these evidences the aim of this study was to investigate the influence of a chronic stress, like social isolation at weaning, on the sensitivity of mesocorticolimbic dopaminergic neurons to anticipation and consumption of food. Rats have been food restricted using a protocol that consists in training the animals to consume their meal for only two hours for day. Using vertical microdialysis, extracellular concentrations of dopamine in response to anticipation and consumption of food were measured both in the mPFC and the NAC.
In PFC of GH rats extracellular DA increased (+180%) 80 minutes before food presentation showing the maximal increase (+350%) during food intake. On the contrary, in the NAc of GH rats no significant changes were observed. In SI animals trained to food restriction the increase in mPFC DA output observed in GH animals was completely blunted, while, in the NAc, 40 min before the presentation of the food, a significant increase in extracellular concentrations of DA was observed.
Our results show that exposure to chronic stress modified the response of mesocortico-limbic dopaminergic neurons to an enjoyable stimulus and suggest that these changes might be important to explain the greater sensitivity to abuse that is observed in individuals subjected to stressful stimuli. This underlying alteration in brain function might be a crucial mechanism that predisposes individuals to impulsive behavior and increases the risk of developing addiction
La non-distopia di Jeremy Bentham. Il Panopticon tra utilitarismo e riformismo
Get PDFBetween 1786 and 1791 Jeremy Bentham conceived and complete the drafting of the
Panopticon. It is a proposal of prison's reform to which he will work for twenty years, both
introducing changes and clarifications to the original text, and trying to give it concrete
implementation. Despite the intellectual and economic efforts made by the philosopher for the
construction of the prison, and although it is one of the few texts he published, the Panopticon
was mostly overlooked by critics and, among those who have dealt with it, there were who
have considered it as a theoretical exercise, and many were those who have reduced it to a
utopian model and, most often, as an inhuman tool, and tracked in it an example of dystopia.
A crucial role in this regard has played the reading proposed by Foucault in Surveiller et punir
(1975) in which the Panopticon is presented as the paradigm of society conceived by
Bentham, a society dominated by a disciplinary power. These interpretations are the result of
a misunderstanding of the Bentham's work produced by its contextualization both as
compared to the historical period and the particular socio-economic conditions in which it
was conceived, and as to a greater and more decisive consequences with respect to the
philosophical system of which it flows. The Panopticon is proof positive of the reformatory
spirit of its author and it is conceived by him as a powerful tool for the realization of the
"artificial harmony" between individual interest and collective interest that is the basic
problem of the English philosopher's whole political-legal project. Starting from the centrality
that the criminal dimension occupies within the Bentham's philosophical and reformatory
system and from the priority that security takes on among the purposes of government, my
research aims to offer a new reading of the text, that without consider it like a paradigm of
each proposal promoted by Jeremy Bentham, both ethical and more specifically political,
recognize it as a key moment in the development of utilitarian philosopher's thought: the
practical outcome of a comprehensive theoretical work, much stranger both utopian horizon,
and despite the dominant control, the dystopian prospect