1,088 research outputs found
SETTE NOTE PER CREMONACremona City Hub. Riqualificazione urbanistica dell'ambito di trasformazione delle aree ex-Annonaria, concorso internazionale di idee in una fase con preselezione bandito dal Comune di Cremona.(primo classificato).
No full textLa proposta progettuale di riqualificazione urbanistica dell’area ex Annonaria “7 note per Cremona”, persegue l’idea di una città compatta, fondata sulla durevolezza degli interventi, densa di significati: passati, presenti, futuri, in grado di rafforzare il continuum spazio-temporale con il centro storico di Cremona costituendo, di fatto, un proseguimento naturale della città fondata, delle sue geometrie e delle sue logiche endogene. Ciò si concretizza in una strategia per la valorizzazione delle risorse tra storia e città contemporanea così articolata: riconoscibilità del tessuto urbano esistente; armonia ed equilibrio dei rapporti spaziali, dimensionali e volumetrici; densità abitativa correlata ad un corretto dimensionamento degli spazi aperti; accessibilità ai trasporti pubblici e riduzione degli spostamenti veicolari con conseguente riduzione dell’inquinamento; incentivazione di una mobilità dolce; presenza di spazi pubblici integrati e attrezzati i quali, mediante arredo urbano e specie arboree, siano in grado di valorizzare il paesaggio anche da un punto di vista sensoriale; corretta e mirata distribuzione dei servizi all’interno del comparto urbano; sviluppo di una comunità autocentrata fondata sull’equità, sull’attenzione alla persona, al suo valore e alle sue esigenze
ON THE LINEAR INSTABILITY OF HIGHER DIMENSIONAL WORMHOLES SUPPORTED BY SELF-INTERACTING PHANTOM SCALAR FIELDS
No full textQuesta tesi si occupa della questione della stabilità lineare di wormholes (tunnel spaziotemporali) statici e a simmetria sferica, supportati da campi scalari di tipo fantasma autointeragenti, nel contesto della Relatività Generale per spazitempi di dimensione arbitraria. In letteratura, attraverso un'analisi gauge-invariante delle configurazioni di tipo wormhole, spesso si riesce a disaccoppiare le equazioni di campo linearizzate, ottenendo un'equazione delle onde (master equation) che, tuttavia, tipicamente è singolare dove il coefficiente radiale della metrica ha un punto critico, cioè nella gola del tunnel. Per risolvere questo problema, nei lavori passati è stato proposto un metodo
di regolarizzazione che trasforma l'equazione delle onde singolare in una regolare; questo metodo è solitamente denominato "S-deformazione" (e spesso richiede parzialmente un'implementazione numerica, specialmente nel caso di campi scalari con un'autointerazione non banale). Il primo risultato del mio lavoro è la riduzione delle equazioni di campo linearizzate ad un sistema delle onde vincolato e completamente regolare, per due funzioni gauge-invarianti delle perturbazioni dei coefficienti della metrica e del campo scalare, opportunamente definite; il secondo risultato è una strategia per disaccoppiare questo sistema, ottenendo una sola master equation delle onde per un'altra quantità gauge-invariante. Nessun passaggio di questa costruzione determina l'apparizione di singolarità nella gola del tunnel o in altri punti (sempre che il campo scalare imperturbato non abbia punti critici, cosa che accade in moti esempi); quindi non è necessario regolarizzare a posteriori la master equation utilizzando il metodo di S-deformazione. Questo formalismo gauge-invariante e libero da singolarità, che generalizza a dimensione arbitraria l'approccio del mio articolo [1], è applicato ad alcune soluzioni di tipo wormhole statiche note (la maggior parte, ma non tutte, considerate in [1]). La più importante applicazione è ad un wormhole Anti-de Sitter (AdS), la cui stabilità lineare non pare sia mai stata analizzata da altri autori finora; utilizzando il presente metodo è possibile derivare una master equation completamente regolare che descrive le perturbazioni del wormhole AdS e quindi dimostrare che quest'ultimo è linearmente instabile, dopo aver dettagliatamente analizzato le proprietà spettrali di un operatore di tipo Schrödinger che compare
nella master equation. Sulla stessa linea, è ottenuto un risultato parziale per l'analogo wormhole di tipo de Sitter (dS), caso tecnicamente più sottile a causa della presenza di orizzonti. Come ulteriore applicazione, ho riottenuto in maniera libera da singolarità le master equations per le perturbazioni di dei wormholes di Ellis-Bronnikov e di Torii-Shinkai. Ad integrazione, l'instabilità lineare dei wormholes AdS e di Torii-Shinkai sono riottenute utilizzando un metodo alternativo, privo di singolarità ma gauge-dipendente: in questo caso, si ottiene una master equation per la perturbazione della coordinata radiale, e l'indipendenza dal gauge del risultato di instabilità è testata a posteriori. Questo approccio alternativo e gauge-dipendente generalizza quello introdotto
in [2] per il wormhole di Ellis-Bronnikov a simmetria riflessiva. Vorrei citare infine [3], dal quale ho riportato alcuni fatti sui wormholes appena menzionati in assenza di perturbazione.
BIBLIOGRAFIA:
[1] F. Cremona, L. Pizzocchero, and O. Sarbach. Gauge-invariant spherical linear perturbations of wormholes in einstein gravity minimally coupled to a self-interacting phantom scalar field. Physical Review D, 101, 05 2020.
[2] F. Cremona, F. Pirotta, and L. Pizzocchero. On the linear instability of the Ellis-Bronnikov-Morris-Thorne wormhole. Gen. Relativ. Gravitat., 51:19, 2019.
[3] F. Cremona. Geodesic structure and linear instability of some wormholes. Proceeding for the conference: Domoschool 2019 (submitted).In this thesis I deal with the linear stability analysis of static, spherically symmetric wormholes supported by phantom self-interacting scalar fields, in the framework of General Relativity with arbitrary spacetime dimension. In the previous literature, a gauge-invariant stability analysis of wormhole configurations often succeeds in decoupling the linearized field equations, yielding a wave-type master equation which, however, is typically singular where the radial coefficient of the metric has a critical point, that is, at the wormhole throat. In order to overcome this problem a regularization method has been proposed in previous works, which transforms the singular wave equation to a regular one; this method is usually referred to as “S-deformation” (and sometimes requires a partly numerical implementation, especially, in the case of scalar fields with nontrivial self-interaction). The first result of my work is the reduction of the linearized field equations to a completely regular, constrained wave system for two suitably defined gauge-invariant functions of the perturbations in the metric coefficients and in the scalar field; the second result is a strategy for decoupling this system, obtaining a single wave-type master equation for another gauge-invariant quantity. No step of this construction causes the appearing of singularities at the wormhole throat or elsewhere (provided that the unperturbed scalar field has no critical points, which occurs in many examples); therefore, it is not necessary to regularize a posteriori the master equation via the S-deformation method. This gauge-invariant and singularity-free formalism, which generalizes to arbitrary spacetime dimensions the approach of my paper [1], is then applied to some known static wormhole solutions (most, but not all of them considered in [1]). The most relevant application is a certain Anti-de Sitter (AdS) wormhole, whose linear stability analysis does not seem to have been performed previously by other authors; by using the present method, it is possible to derive a completely regular master equation describing the perturbations of the AdS wormhole and prove that the latter is actually linearly unstable, after providing a detailed analysis of the spectral properties of the Schrödinger type operator appearing in the master equation. A partial instability result is derived along the same lines for the analogous de Sitter (dS) wormhole, a technically more subtle case due to the presence of horizons. As a further application, I rederive in a singularity-free fashion the master equations for the perturbed Ellis-Bronnikov and Torii-Shinkai wormholes. As a supplement, the linear instability results for the AdS and for the Torii-Shinkai wormholes are also recovered using an alternative, singularity free but gauge-dependent method: in this case a regular master equation is derived for the perturbed radial coordinate, and the gauge-independence of the instability result is tested a posteriori. This alternative, gauge-dependent approach generalizes that introduced in my paper [2] for the reflection symmetric Ellis-Bronnikov wormhole. Let me also cite [3], from which I report some facts about the previously mentioned wormholes in absence of perturbations.
BIBLIOGRAPHY:
[1] F. Cremona, L. Pizzocchero, and O. Sarbach. Gauge-invariant spherical linear perturbations of wormholes in einstein gravity minimally coupled to a self-interacting phantom scalar field. Physical Review D, 101, 05 2020.
[2] F. Cremona, F. Pirotta, and L. Pizzocchero. On the linear instability of the Ellis-Bronnikov-Morris-Thorne wormhole. Gen. Relativ. Gravitat., 51:19, 2019.
[3] F. Cremona. Geodesic structure and linear instability of some wormholes. Proceeding for the conference: Domoschool 2019 (submitted)
Elemente der projectivischen Geometrie
No full textL. Cremona ; unter Mitwirkung des Verfassers übertragen von F. R. Trautvette
Cremona e Bedriacum in età romana: scultura, decorazione architettonica, arredo di lusso
No full textThe realization of the volume of the Corpus Signorum Imperii Romani dedicated to Cremona allows consideration of the sculpture and architectural decoration of the Cisalpine colony, founded in 218 BC The findings are scant, but interesting architectural elements are related to public buildings, and some sculptural fragments refer to divine or ideal statues. The funerary stelae with portraits or decorative elements were found in different city cemeteries. The vicus of Calverley-Bedriacum returned some sculptures, like the famous bronze statue of Victory, and home decor items made of marble and stone
I pavimenti delle domus di piazza Marconi a Cremona
No full textStudio dei pavimenti cementizi e musivi rinvenuti nell'indagine archeologica delle domus di età romana in piazza Marconi a Cremona. Considerazioni sulla tecnica e la cronologi
Contributions to automorphisms of affine spaces
No full textWe study aspects of the group G_n of polynomial automorphisms of the affine space A^n, the so-called affine Cremona group. Shafarevich introduced on G_n the structure of an ind-variety, an infinite-dimensional analogon to a (classical) variety. The aim of this thesis is to study G_n within the framework of ind-varieties. The thesis consists of five articles. In the following we summarize them.
1. On the Topologies on ind-Varieties and related Irreducibility Questions.
In the literature there are two ways of endowing an affine ind-variety with a topology. One possibility is due to Shafarevich and the other due to Kambayashi. We specify a large class of affine ind-varieties where these two topologies differ. We give an example of an affine ind-variety that is reducible with respect to Shafarevich’s topology, but irreducible with respect to Kambayashi’s topology. Moreover, we give a counter-example of a supposed irreducibility criterion given by Shafarevich which is different from a counter-example given by Homma. We finish the article with an irreducibility criterion similar to the one given by Shafarevich.
2. On Automorphisms of the Affine Cremona Group (joint with Hanspeter Kraft)
We show that every automorphism of the group G_n is inner up to field automorphisms when restricted to the subgroup TG_n of tame automorphisms. This generalizes a result of Julie Déserti who proved this in dimension n = 2 where all automorphisms are tame, i.e. TG_2 = G_2. The methods are different, based on arguments from algebraic group actions.
3. A Note on Automorphisms of the Affine Cremona Group
Let G be an ind-group and let U be a unipotent ind-subgroup. We prove that an abstract automorphism f: G -> G maps U isomorphically onto a unipotent ind-subgroup of G, provided that f fixes a closed torus T in G that normalizes U and the action of T on U by conjugation fixes only the neutral element. As an application we generalize the main result of the article "On Automorphisms of the Affine Cremona Group" as follows: If an abstract automorphism of G_3 fixes the subgroup of tame automorphisms TG_3, then it also fixes a whole family of non-tame automorphisms (including the Nagata automorphism).
4. Automorphisms of the Plane Preserving a Curve (joint with Jérémy Blanc)
We study the group of automorphisms of the affine plane preserving some given curve, over any field. The group is proven to be algebraic, except in the case where the curve is a bunch of parallel lines. Moreover, a classification of the groups of positive dimension occuring is also given in the case where the curve is geometrically irreducible and the field is perfect.
5. Centralizer of a Unipotent Automorphism in the Affine Cremona Group
Let g be a unipotent element of G_3. We describe the centralizer Cent(g) inside G_3. First, we treat the case when g is a modified translation. In the other case, we describe the subset Cent(g)_u of unipotent elements of Cent(g) and prove that it is a closed normal subgroup of Cent(g). Moreover, we show that Cent(g) is the semi-direct product of Cent(g)_u with a closed algebraic subgroup R of Cent(g). Finally, we prove that the subgroup of Cent(g) consisting of those elements that induce the identity on the algebraic quotient Spec O(A^3)^g form a characteristic subgroup of Cent(g)
Sustainable Landscape Planning for Cremona, Italy
No full textSustainable landscape planning at the provincial level is explained through the example of the province of Cremona, Italy.
Six topics are addressed. First, the topic of why planning in Italy, in general, and Cremona, more speciÆcally, is important will
be addressed. Cremona province is located in northern Italy, where traditionally rural regions are facing expanding
urbanization. Second, a background of Italian planning is provided. A 1990 law, in particular, emphasizes provincial-level
planning. Third, the history and landscape of Cremona will be described. For most of its history, Cremona has been dominated
by agriculture, which is reØected in the landscape. Fourth, the province of Cremona planning process will be summarized. The
planning activity began in 1994 and continues to the present. Fifth, the design of a sustainability index is explained. The
sustainability index is used to assess how land-use modiÆcations might affect the environment. Finally, the key lessons from
the process will be noted. The Cremona provincial plan applies concepts of sustainability to a changing landscap
Modular symbols over number fields
No full textLet K be a number field, R its ring of integers. For some classes of fields, spaces of cusp forms of weight 2 for GL(2;K) have been computed using methods based on modular symbols. J.E. Cremona [9] began the programme of extending the classical methods over Q to the case of imaginary quadratic fields. This work was continued by some of his Ph.D. students [35, 6, 22], and results have been obtained for some imaginary quadratic fields with small class number. More recently, P. Gunnells and D. Yasaki [18] have developed related algorithms for real quadratic fields.
The aim of this thesis is to contribute to the extension of the modular symbols method, when possible developing algorithms and implementations for effective computations. Some parts of the theory are purely algebraic and can be extended to all number fields. We generalise the theory for cusps and Manin symbols; we also describe a generalisation of Atkin-Lehner involutions and study other normaliser elements. On the other hand, all previous explicit computations for the imaginary quadratic field case were done only for specific fields. In the last part of this thesis we begin work towards a general implementation of the techniques used in this case. In particular, we are able to compute a fundamental domain of the hyperbolic 3-space for any imaginary quadratic field.
Implementations of the algorithms described in this thesis have been written by the author in the open-source mathematics software Sage [31]
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