Progetto di radome selettivi in frequenza mediante algoritmi genetici

L'attività di tesi consiste nella realizzazione di un radome per mezzo di una struttura multistrato composta da superfici selettive in frequenza e dielettrici. Il comportamento frequenziale è imposto nelle specifiche di progetto da una maschera del coefficiente di trasmissione da 1Ghz fino a 18Ghz

Gamma Ray Burst origin and their afterglow: story of a discovery and more

In this paper we review the story of the BeppoSAX discovery of the Gamma Ray Burst afterglow and their cosmological distance, starting from their first detection with Vela satellites and from the efforts done before BeppoSAX. We also discuss the consequences of the BeppoSAX discovery, the issues left open by BeppoSAX, the progress done up to now and its perspectives.Comment: 31 pages, 14 figures, published in 2011 in the international refereed journal "La Rivista del Nuovo Cimento" of the Italian Physical Society, vol. 34. The occasion of this review paper was the award of the Fermi Prize 2010 to their authors "For the discovery of the X-ray afterglow of Gamma-Ray Burst with the BeppoSAX satellite" (http://www.sif.it/SIF/en/portal/activities/fermi_award

On the Bandwidth of High-Impedance Frequency Selective Surfaces

In this letter, the bandwidth of high-impedance surfaces (HISs) is discussed by an equivalent circuit approach. Even if these surfaces have been employed for almost 10 years, it is sometimes unclear how to choose the shape of the frequency selective surface (FSS) on the top of the grounded slab in order to achieve the largest possible bandwidth. Here, we will show that the conventional approach describing the HIS as a parallel connection between the inductance given by the grounded dielectric substrate and the capacitance of the FSS may induce inaccurate results in the determination of the operating bandwidth of the structure. Indeed, in order to derive a more complete model and to provide a more accurate estimate of the operating bandwidth, it is also necessary to introduce the series inductance of the FSS.We will present the explicit expression for defining the bandwidth of a HIS, and we will show that the reduction of the FSS inductance results in the best choice for achieving wide operating bandwidth in correspondence with a given frequency.Comment: 4 pages, 6 figure

A Circuit-based Model for the Interpretation of Perfect Metamaterial Absorbers

A popular absorbing structure, often referred to as Perfect Metamaterial Absorber, comprising metallic periodic pattern over a thin low-loss grounded substrate is studied by resorting to an efficient transmission line model. This approach allows the derivation of simple and reliable closed formulas describing the absorption mechanism of the subwavelength structure. The analytic form of the real part of the input impedance is explicitly derived in order to explain why moderate losses of the substrate is sufficient to achieve matching with free space, that is, perfect absorption. The effect of the constituent parameters for tuning the working frequency and tailoring the absorption bandwidth is addressed. It is also shown that the choice of highly capacitive coupled elements allows obtaining the largest possible bandwidth whereas a highly frequency selective design is achieved with low capacitive elements like a cross array. Finally, the angular stability of the absorbing structure is investigated.Comment: Accepted for publication on IEEE Transactions on Antennas and Propagatio

World society as a shared ethnos and the limits of world society in Central Asia

After the demise of the Soviet Union, the five Central Asian republics have struggled to maintain a degree of regional identity within the wider region of Eurasia by combining historical, religious and value-related discourses of commonality. In particular, ‘the Central Asian people’ has always been hailed as the ‘glue’ of this region, despite the fact that states in this area are following different political and economic orientations. Although ‘Kazakhs, Kyrgyz, Tajiks, Turkmens and Uzbeks have lived for centuries together as brothers’, as it is often heard in regional official statements, this ‘regional world society’ is being fractured by what I call the hyper-institutionalisation of pluralist institutions of international society. Using an English School approach, this paper explores the detachment of the Central Asian international society from the Central Asian world society, and investigates into the role played by the institutions of the former in weakening the substance of the latter.PostprintPeer reviewe

Analysis and Modeling of High-Impedance Surfaces for the Design of Electromagnetic Absorbers and Antennas

High-impedance surfaces (HIS) are resonant cavities synthesized by printing a periodic frequency selective surface (FSS) on the top of a grounded dielectric slab. The use of such metasurfaces allows to achieve remarkable improvements in the performance of several microwave devices. The first part of the thesis is dedicated to the modeling of high-impedance surfaces and frequency selective surfaces which constitute the key element of the HIS structures. A model for analyzing frequency selective surfaces is first introduced and then employed also in the analysis of high-impedance surfaces. The circuital approach is also employed to derive a new definition of the bandwidth of the metasurfaces. High-impedance surfaces are employed in the design of low-profile antennas and ultra-thin electromagnetic absorbers. In the latter case thin high-impedance surfaces are used to replace the typical quarter-wavelength grounded dielectric slab making the absorbing structure much thinner. Most part of this thesis is dedicated to this issue and in particular the physical mechanisms leading to the absorption of electromagnetic waves are studied by the aforementioned transmission line model. Different designs based on resistive frequency selective surfaces for synthesize thin, wideband and lightweight absorbers with enhanced performances with respect to the available solution are proposed and analyzed. Other techniques as the use of vias as instrument to enlarge the operating bandwidth for oblique incidence and the use of the HIS boundary in place of the electrical one in classical commercial absorbers are proposed. High-impedance surfaces are also employed as ground plane for make an horizontal dipole to radiate efficiently. In this configuration, the interaction between the wire antenna and the high-impedance surface excites complex waves and generates different resonant phenomena that require a rigorous analysis. The problem is thoroughly analyzed by breaking up the problem in two different contributions depending on the surface waves that are allowed to propagate in the HIS structure and important design rules are derived. The validity of the homogeneization models for approximating the finite antenna structure is also addressed. The last part of the thesis deals with the so-called Fabry-Perot antenna in which high-impedance surfaces are used to strongly reduce the height of this antenna which typically is equal to a half wavelength. In particular the thesis describes an active structure which is able to work as a tunable high-gain antenna over a wide band. The presented theoretical work is supported by several experimental demonstrations

Turkestan and the rise of Eurasian empires: a study of politics and invented traditions. By Ali Anooshahr

PostprintNon peer reviewe

Beyond the pendulum : situating Adam Watson in International Relations and the English School

Among the founding figures of the English School of International Relations (ES) and the British Committee (BC), Adam Watson is perhaps the least studied and researched. How, for example, did his past as diplomat informed his Weltanschauung and his understanding of combining theory and practice? How did his academic relationship and friendship with other members of the BC and colleagues shaped his outlook on international politics? What was his political theory and philosophy? And what have his contributions been, not simply to the ES, but to IR writ large? This paper offers an intellectual portrait of Adam Watson and his persona, making use not only of his published written production, but also of so far unexplored archives and materials. Specifically, the paper situates Adam Watson within the ES and the broader IR panorama, taking into account the professional, academic, and human material that the extensive research for this paper has uncovered.Publisher PDFPeer reviewe

Of nomads and khanates : heteronomy and interpolity order in 19th-century Central Asia

Scholars of International Relations (IR) and Global Historical Sociology alike have recently become more and more interested in Eurasian order(s). Yet, most recent works on Eurasian historical international relations approach the subject from a long durée perspective, mostly focusing on “big polities” from a “high altitude.” Central Asia, or “Turkestan,” and its constitutive polities such as the khanates of Bukhara, Khiva, and Khoqand and the vast array of nomadic groups surrounding them are yet terra incognita in IR, specifically with respect to the pre-Tsarist period. By relying on both primary and secondary sources, this inductive research reveals how precolonial Central Asia was an interpolity order on its own, premised on heteronomy and based on the institutions of sovereignty between the khanates and suzerainty between khanates and nomads; territoriality; Sunni Islam; trade and slavery; diplomacy; and war and aq oyluk. This paper contributes to filling this gap, and to the broader literature on Eurasian historical orders, in three respects. First, it adds granularity, detail, and specificity to current IR knowledge on Eurasia by looking at smaller polities as opposed to empires, which as noted have been the main analytical focus so far. Second, the paper adopts an emic approach to uncover local practices, institutions, and norms of precolonial Central Asia, thus adding to the recent “Global IR” debate. Third, by focusing on a case where heteronomy was the rule, this paper adds a new case to the literature on the entrenchment and durability of heteronomy in historical IR and contributes to its theory-building.Publisher PDFPeer reviewe

The institutionalisation of environmentalism in Central Asia

In 2021, in a largely ignored yet significant step towards regional coordination and convergence, the Central Asian republics took part in the 26th Conference of the Parties in Glasgow as a single entity, speaking with one voice and advocating a joint approach to climate change. Yet, to what extent is Central Asia complying with the norms and rules of environmental governance? Are environmental protection, climate-change mitigation and the push for an energy transition merely a set of shallow practices and rhetoric to signal performative compliance, or are they based on a logic of appropriateness and embedded in a normative understanding of green politics? Drawing on recent scholarship on international society and based on the assumption that environmentalism is now an established institution of the contemporary international order, this chapter considers whether, and in what way, Central Asia has embraced the institution of environmentalism, exploring discourses and practices at the global, regional and local levels. Far from being an exercise in pure theorisation, this can help shape policy engagement from and with the region, allowing us to assess the depth of commitment of these republics and societies in fighting climate change by distinguishing challenges deriving from structural, instrumental or ideological factors.Publisher PD