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1
Brighi, Massimo <1954>. « Implicazioni teoriche e sperimentali della sincronizzazione assoluta nella teoria della relatività speciale ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6232/1/Brighi_Massimo_tesi.pdf.
Texte intégralRésumé :
Sono indagate le implicazioni teoriche e sperimentali derivanti dall'assunzione, nella teoria della relatività speciale, di un criterio di sincronizzazione (detta assoluta) diverso da quello standard.
La scelta della sincronizzazione assoluta è giustificata da alcune considerazioni di carattere epistemologico sullo status di fenomeni quali la contrazione delle lunghezze e la dilatazione del tempo. Oltre che a fornire una diversa interpretazione, la sincronizzazione assoluta rappresenta una estensione del campo di applicazione della relatività speciale in quanto può essere attuata anche in sistemi di riferimento accelerati. Questa estensione consente di trattare in maniera unitaria i fenomeni sia in sistemi di riferimento inerziali che accelerati.
L'introduzione della sincronizzazione assoluta implica una modifica delle trasformazioni di Lorentz. Una caratteristica di queste nuove trasformazioni (dette inerziali) è che la trasformazione del tempo è indipendente dalle coordinate spaziali.
Le trasformazioni inerziali sono ottenute nel caso generale tra due sistemi di riferimento aventi velocità (assolute) u1 e u2 comunque orientate. Viene mostrato che le trasformazioni inerziali possono formare un gruppo pur di prendere in considerazione anche riferimenti non fisicamente realizzabili perché superluminali.
È analizzato il moto rigido secondo Born di un corpo esteso considerando la sincronizzazione assoluta.
Sulla base delle trasformazioni inerziali si derivano le trasformazioni per i campi elettromagnetici e le equazioni di questi campi (che sostituiscono le equazioni di Maxwell). Si mostra che queste equazioni contengono soluzioni in assenza di cariche che si propagano nello spazio come onde generalmente anisotrope in accordo con quanto previsto dalle trasformazioni inerziali. L'applicazione di questa teoria elettromagnetica a sistemi accelerati mostra l'esistenza di fenomeni mai osservati che, pur non essendo in contraddizione con la relatività standard, ne forzano l'interpretazione. Viene proposto e descritto un esperimento in cui uno di questi fenomeni è misurabile.Theoretical and experimental implications in the theory of special relativity resulting from the assumption of synchronization criterion (called absolute) other than the standard, are investigated. The choice of the absolute synchronization is justified by considerations of epistemological status of phenomena such as length contraction and time dilation. The absolute synchronization provides a different interpretation of the theory and is an extension of the scope of special relativity as it can be implemented even in accelerated frames of reference. Therefore it is possible to treat in a unified way the phenomena in both inertial and accelerated frame. The introduction of the absolute synchronization implies a modification of the Lorentz transformations. A characteristic of these new transformations (called inertial) is that the transformation of time is independent of the spatial coordinates . The inertial transformations are obtained in the general case between two systems having (absolute) velocity u1 and u2 in any orientation . It is shown that the inertial transformations can have a group structure if unphysical superluminal frames are considered too. The Born rigid motion of an extended body is analyzed by applying the absolute synchronization. Transformations for electromagnetic fields and the equations of these fields (substituting Maxwell's equations) are derived on the basis of inertial transformations. It is shown that these equations contain solutions in the absence of charges that propagate through space as waves generally anisotropic as provided by the inertial transformations in the propagation of light. The application of electromagnetic theory to accelerated systems show the existence of phenomena never observed before. These phenomena, although not in contradiction with standard relativity, force the interpretation of the theory. An experiment in which one of these phenomena is measurable is proposed and described in this thesis.
2
Brighi, Massimo <1954>. « Implicazioni teoriche e sperimentali della sincronizzazione assoluta nella teoria della relatività speciale ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2014. http://amsdottorato.unibo.it/6232/.
Texte intégralRésumé :
Sono indagate le implicazioni teoriche e sperimentali derivanti dall'assunzione, nella teoria della relatività speciale, di un criterio di sincronizzazione (detta assoluta) diverso da quello standard.
La scelta della sincronizzazione assoluta è giustificata da alcune considerazioni di carattere epistemologico sullo status di fenomeni quali la contrazione delle lunghezze e la dilatazione del tempo. Oltre che a fornire una diversa interpretazione, la sincronizzazione assoluta rappresenta una estensione del campo di applicazione della relatività speciale in quanto può essere attuata anche in sistemi di riferimento accelerati. Questa estensione consente di trattare in maniera unitaria i fenomeni sia in sistemi di riferimento inerziali che accelerati.
L'introduzione della sincronizzazione assoluta implica una modifica delle trasformazioni di Lorentz. Una caratteristica di queste nuove trasformazioni (dette inerziali) è che la trasformazione del tempo è indipendente dalle coordinate spaziali.
Le trasformazioni inerziali sono ottenute nel caso generale tra due sistemi di riferimento aventi velocità (assolute) u1 e u2 comunque orientate. Viene mostrato che le trasformazioni inerziali possono formare un gruppo pur di prendere in considerazione anche riferimenti non fisicamente realizzabili perché superluminali.
È analizzato il moto rigido secondo Born di un corpo esteso considerando la sincronizzazione assoluta.
Sulla base delle trasformazioni inerziali si derivano le trasformazioni per i campi elettromagnetici e le equazioni di questi campi (che sostituiscono le equazioni di Maxwell). Si mostra che queste equazioni contengono soluzioni in assenza di cariche che si propagano nello spazio come onde generalmente anisotrope in accordo con quanto previsto dalle trasformazioni inerziali. L'applicazione di questa teoria elettromagnetica a sistemi accelerati mostra l'esistenza di fenomeni mai osservati che, pur non essendo in contraddizione con la relatività standard, ne forzano l'interpretazione. Viene proposto e descritto un esperimento in cui uno di questi fenomeni è misurabile.Theoretical and experimental implications in the theory of special relativity resulting from the assumption of synchronization criterion (called absolute) other than the standard, are investigated. The choice of the absolute synchronization is justified by considerations of epistemological status of phenomena such as length contraction and time dilation. The absolute synchronization provides a different interpretation of the theory and is an extension of the scope of special relativity as it can be implemented even in accelerated frames of reference. Therefore it is possible to treat in a unified way the phenomena in both inertial and accelerated frame. The introduction of the absolute synchronization implies a modification of the Lorentz transformations. A characteristic of these new transformations (called inertial) is that the transformation of time is independent of the spatial coordinates . The inertial transformations are obtained in the general case between two systems having (absolute) velocity u1 and u2 in any orientation . It is shown that the inertial transformations can have a group structure if unphysical superluminal frames are considered too. The Born rigid motion of an extended body is analyzed by applying the absolute synchronization. Transformations for electromagnetic fields and the equations of these fields (substituting Maxwell's equations) are derived on the basis of inertial transformations. It is shown that these equations contain solutions in the absence of charges that propagate through space as waves generally anisotropic as provided by the inertial transformations in the propagation of light. The application of electromagnetic theory to accelerated systems show the existence of phenomena never observed before. These phenomena, although not in contradiction with standard relativity, force the interpretation of the theory. An experiment in which one of these phenomena is measurable is proposed and described in this thesis.
3
Deleidi, Laura. « Studio degli aspetti teorici e fenomenologici della fisica di particelle ». Doctoral thesis, Università degli studi di Bergamo, 2019. http://hdl.handle.net/10446/128587.
Texte intégralRésumé :
In questa tesi sono state indagate le condizioni cinematiche e dinamiche in cui potrebbero essere rilevati possibili
neutrini superluminali ossia con massa quadrata negativa emessi nel decadimento binario di pioni. Si è ricavato che
sopra un'energia di soglia pionica il comportamento dell'energia dei neutrini tachionici rispetto all'angolo di emissione
cambia drasticamente rispetto al caso bradionico ordinario; in particolare, sopra l'energia di soglia, che dipende dalla massa del neutrino, si potrebbe osservare anche un'emissione trasversale (angoli maggiori di 90o), proibita per
neutrini ordinari. Questo potrebbe costituire una chiara evidenza per i neutrini superluminali.
4
Busato, Giulio. « Analisi teorica e sperimentale sulle pompe di calore ». Doctoral thesis, Università degli studi di Padova, 2013. http://hdl.handle.net/11577/3423621.
Texte intégralRésumé :
This doctoral thesis is concerning the theoretical and experimental analysis of heat pumps. In the first section of this study a design tool for predicting steady-state cooling and heating performance of vapor compression refrigerating machines is developed. In order to achieve correct results, accurate thermodynamic models are implemented to predict heat transfer coefficients, pressure drops and refrigerant mass charge. The software has been firstly developed for charge inventory purpose, and, as a consequence, it also has the capability to predict performance in off-design conditions given a fixed refrigerant charge. Moreover it can be useful for the liquid receiver dimensioning in reversible heat pumps, or for subcooling degree optimization at the condensers. In the present work the methodologies used for the calculation of the performance of each component are presented. The second part of the work is concerning gas absorption heat pumps, working with the refrigerant mixture water-ammonia. A theoretical design procedure is carried out and again verified by means of experimental measurement on a prototype. The last part of the study is concerning the estimation of the possible advantages of combined heating plants including solar collectors, air source heat pump and a condensing boiler. The investigation is carried out in collaboration with the manufacturers of the machines, allowing to have precise information about all the components. Investigations are carried out to compare the proposed systems with a standard solution with a condensing boiler only. Three different locations are considered in the present study. Comparisons are made regarding primary energy consumption, equivalent CO2 emission, percentage of renewable energy used and possible economical saving. For this purpose TRNSYS-based approach is adopted. The whole heating plant and the building are modeled together. Each component performance was previously measured in order to tune the mathematical model to be used in TRNSYS. In particular, experimental measurements were performed on a test-plant, allowing to tune a model for the stratification of the real storage tank, and for its dynamic response. The estimation of the dynamic behavior, and thus the heating load of the considered building, is carried out by means of TRNSYS. Domestic Hot Water consumption is calculated as well.Questa tesi di dottorato è incentrata sull’analisi teorica e sperimentale di macchine frigorifere e in particolare di pompe di calore. Nella prima parte si affronta il calcolo di progetto e di verifica di macchine frigorifere e dei loro componenti. Attraverso un’accurata modellizzazione dei dispositivi coinvolti e dello scambio termico si è giunti a sviluppare un software di calcolo completo, che permette di valutare il comportamento di questo tipo di macchine anche in punti di lavoro off-design. Una parte consistente del lavoro è stata dedicata al calcolo della carica di refrigerante ottimale e agli effetti di accumulo di carica nel ricevitore di liquido con diverse condizioni al contorno. I risultati che si sono ottenuti sono stati verificati confrontando i risultati teorici con prove sperimentali effettuate ad hoc su un prototipo appositamente predisposto e su varie altre produzioni di serie presso la sala prove di Hiref S.p.A. La seconda sezione affronta lo studio delle pompe di calore ad assorbimento ad acqua-ammoniaca. Anche in questo caso l’approccio è dapprima quello del calcolo di progetto termodinamico, seguito da una verifica delle stime effettuate attraverso prove sperimentali su di un prototipo. Nella terza sezione del lavoro viene effettuata un’analisi energetica su un impianto di nuova concezione confrontando i possibili vantaggi rispetto a sistemi tradizionali di generazione. Lo studio si articola attraverso varie simulazioni dinamiche svolte in ambiente TRNSYS. A tal fine è stato possibile ottimizzare i modelli di simulazione dei singoli componenti, avendo accesso ai dati sperimentali sulle prestazioni delle singole macchine. Inoltre è stato possibile condurre delle prove su un impianto pilota installato presso i laboratori di SIME S.p.A. Ciò ha permesso di ricavare informazioni utili per modellizzare il comportamento dinamico di un serbatoio di accumulo combinato con stratificazione. Dopo aver calibrato i modelli dei singoli componenti di impianto è stato possibile ricostruire un modello completo dell’impianto e di una villetta bifamiliare in ambiente TRNSYS; il modello considera il riscaldamento sia a bassa che ad alta temperatura e la produzione di acqua calda sanitaria. Il sistema ibrido composto da caldaia modulante a condensazione, pompa di calore reversibile e solare termico viene messo a confronto con una soluzione convenzionale, ovvero un impianto con sola caldaia, e con diverse combinazioni di fonti energetiche.
5
Dandrea, Lucia. « Quantum Monte Carlo Methods applied to strongly correlated and highly inhomogeneous many-Fermion systems ». Doctoral thesis, Università degli studi di Trento, 2009. https://hdl.handle.net/11572/369209.
Texte intégral
6
Bausmerth, Ingrid. « Fermi Mixtures : Effects of Engineered Confinements ». Doctoral thesis, Università degli studi di Trento, 2009. https://hdl.handle.net/11572/368660.
Texte intégralRésumé :
In this thesis we first review the theory of the normal state of the unitary Fermi gas at T = 0 and the main properties of the normal-to-superfluid transition. Then we study the trapped gas under adiabatic rotation, i.e., avoiding the formation of vortices. We show that for polarized systems the rotation enhances the Chandrasekhar-Clogston limit due to pair breaking at the border between the superfluid and the normal phase, while it leaves the global critical polarization Pc of the trapped system unaffected. In the case of an unpolarized unitary superfluid the rotation causes a phase separation between a superfluid core and an unpolarized normal shell, in which the densities of the spin-up and spin-down atom numbers is equal. For both the polarized and the unpolarized systems we calculate experimental observables such as the density profiles and the angular momenta. From the study of Bose-Einstein condensates it is well known that an adiabatic
rotation induces a quadrupole deformation of the trapped atomic cloud when the rotation exceeds a certain angular velocity. In Fermi gases the situation is different due to the phase separation discussed above, and the quadrupole
instabilities are found to set on at smaller angular velocity than in the BEC case. This phenomenon together with a more general discussion concerning not only the energetic but also the dynamic instabilities of the phase separated system is presented. We use the present knowledge of the equation of state of Fermi mixtures with unequal masses to give quantitative predictions for the phase separation between the normal and superfluid components. The analysis is based on the study of the zero temperature μ-h phase diagram of the uniform two component gas. The phase diagram at unitarity is determined thanks to the knowledge of the equation of state available from diagrammatic techniques applied to highly polarized configurations and from Monte Carlo simulations. The phase diagram is then used, in the local density approximation,
to calculate the density profiles of the two Fermi components in the presence of harmonic trapping. Eventually we investigate the polarization produced by the relative displacement of the potentials trapping two spin species of a unitary Fermi gas with population imbalance. We investigate the dipole polarizability of a polarized system both in the two-fluid and the three-fluid model at zero temperature and point out the major differences between the two treatments.
7
Marin, Diego. « From the Hamiltonian formalism to the Spin-Foams : The final step in LQG ? » Doctoral thesis, Università degli studi di Trento, 2010. https://hdl.handle.net/11572/368076.
Texte intégralRésumé :
Already in ancient Greece, the pre-Socratic philosophers thought that natural phenomena, although different, were homogeneous, of the same fundamental nature. In their theories can be found the search for a common reference point (arché) that puts order in the chaotic multiplicity of phenomena. After Albert Einstein’s theory of gravitation (General Relativity -GR-) was published in 1915, the search for a unified field theory that combines gravity with electromagnetism began to become serious. It seemed plausible that there were no other fundamental forces. The main contributors were Gunnar Nordstrom, Hermann Weyl, Arthur Eddington, Theodor Kaluza, Oskar Klein (See Theory of Kaluza-Klein, 1921) and most notably the many attempts by Einstein
and his collaborators. No attempt went through. In the first half of the twentieth century quantum mechanics was consolidated, an instrument capable of overcoming the inadequacy of classical mechanics to explain phenomena and properties such as blackbody radiation, the photoelectric effect, the specific heat of solids, the atomic spectra, the stability of atoms, the Compton effect, .... When in the thirties Fermi and Yukawa ’s studies led to the discovery of nuclear forces, the quantum formalism proved to be appropriate for the description of the new phenomena and, in 1967-68, Sheldon Glashow, Steven Weinberg and Abdus Salam showed how the weak nuclear
force and the electromagnetism were simply different manifestations of the same force (electroweak). Since then, proposals have been done to include in a single grand unification theory also the strong nuclear force, and some of them (GTU SU(5) and SO(10)) have provided testable predictions as the quantization of electric charge. At classical level there is an extension of the Kaluza-Klein theory on a 11-dimensional space M4 × S1 × S2 × CP2. It corresponds to Einstein’s General Relativity with 7 extra dimensions, and considers all four forces as different expressions of a “mega†gravitational field. The forces are unified at the classical level but, once quantized,
the theory turns out to be inconsistent and therefore unusable. This is because the nuclear forces have range of 10−15 m for strong force and of 10−18 m for weak force, distances at which classical physics loses its meaning. Ultimately, it seems that quantum mechanics is compatible with electroweak and strong interactions only if we limit ourselves to spaces of dimensionality less than or equal to 4. In addition, it is inconsistent with General Relativity for spaces with more of 3 dimensions. For these reasons, the theory of Kaluza-Klein fails doubly. Really, the incompatibility is not between general relativity and quantum mechanics in its entirety, but rather between General
Relativity and the method of calculation used in quantum mechanics: perturbative expansion whose terms, in the cases indicted above, become . To get around this problem two different approaches have been taken: String Theory and Loop Quantum Gravity. The first has completely changed the wording of quantum theory, from considering local interactions, where the phenomena occur at specific points (of Feynman graphs), to interactions “extended†, where the phenomena are distributed along one limited dimension (string), open or closed. This system has eliminated the divergences in the terms of perturbative expansion, but has developed other anomalies, eliminated only by building up the theory on a space of 11 dimensions. Unfortunately, the extra dimensions introduce a huge number of arbitrariness, such as the theory can predict
everything and nothing. The scientific community hopes to identify some potential whose minimum make a selection between these arbitrariness, but we are still far from such a result. The alternative discussed in this thesis is the Loop Quantum Gravity.
This is simply the union of GR and quantum mechanics, without modifying the basic axioms of both. It can be made only in spaces of dimensionality equal to 4 and it surrenders completely the perturbative expansion. This produces fascinating predictions, such as the inflation of early universe, and the lack of singularities in the black holes and in the big bang. It also provides the picture of a “combinatorial†universe, described by nodes connected by paths, whose only necessary variables are integer numbers associated with nodes and paths. This last point in particular escapes the string theory which, whilst losing the locality, is however concentrated within the “very small†. The Loop Quantum Gravity, by contrast, is able to describe the universe as a whole, and to deal with transitions between universes of different topology. The downside is that the calculations are so complex that they are impracticable. Strategies have been developed
to introduce a different perturbative expansion that makes the calculations feasible, but this introduces important changes to the initial structure of the theory, in a way that eliminate the beautiful cosmological predictions. Nevertheless, we tried to calculate the graviton propagator in this new “modified framework†, and the result is compatible with linearized quantum GR . For this reason, this framework has not been abandoned. It also seems that this formalism can easily be extended to include extra-dimensions and adapted to the unified theory of Kaluza Klein.
This thesis has been developed in an attempt to contribute to the desire for simplification and connection to the essence that has always been in the natural sciences. In particular, it was given a demonstration of how the †modified framework†of Loop Quantum Gravity is derivable from a classical formulation of the GR of Palatini type.
Finally, we give suggestions for extending the model to 11 dimensions, because 11 is the number suggested by String theory, by the classical theory of Kaluza Klein, and by the GTU SO(10). Probably the truth lies somewhere in between, maybe an action of a 4-dimensional brane immersed in a 11-dimensional universe would be the right compromise between String Theory and Loop Quantum Gravity. A 4-dimensional brane represents our universe, and any contact with other branes of a much smaller scale put small pieces of it in vibration. Depending on the number of dimensions in which contact is, the part could be a vibrating string or a two- or three-brane (with probability decreasing rapidly moving from string to the three-brane). So, we even lose the distinction between the notions of particles and universes, making the first totally unnecessary. The action of a 4-brane is equivalent to the action of Loop Quantum Gravity, with the coordinate-fields which assume the role of gauge fields, and the indexes in the 11-dimensional space that would become similar to the indexes of internal gauge. This thesis focuses on two specific problems: the calculation of the graviton propagator in Loop Quantum Gravity and the derivation of the “modified framework†from the Palatini formulation of GR (Chapter 8). While the first it was
simply supported with a minimum contribution, the second is a problem undertaken by the student in a completely independent way that, while waiting for more in-depth audits, has not yet shown any inconsistency and for now can be hailed a success. A small space is reserved for some inedited consideration undertaken by the student on the “physical†projector. This operator is intended to project the Hilbert space of kinematic states in the subspace of physical states. The conclusion of the argument is simple and somewhat disturbing: the Loop Quantum Gravity is not an unitary theory!
8
Di, Criscienzo Roberto. « Semi-classical aspect of black hole physics ». Doctoral thesis, Università degli studi di Trento, 2011. https://hdl.handle.net/11572/367865.
Texte intégral
9
Autieri, Emmanuel. « Development of Free Energy Calculation Methods for the Study of Monosaccharides Conformation in Computer Simulations ». Doctoral thesis, Università degli studi di Trento, 2011. https://hdl.handle.net/11572/368084.
Texte intégralRésumé :
This thesis is devoted to the study of the conformation of monosacchrides in six-membered ring form. The main goal is to develop and apply new computational tools to investigate conformational properties and to improve the description of carbohydrates in the framework of molecular dynamics simulations.
In the field of monosaccharides, modeling the system within the molecular dynamics framework presents troublesome aspects. The most important issue is that some force fields (e.g., the chosen gromos 45a4 parameter set) fail in reproducing the conformational preferences of the sugar constituents, with the appearance of unphysical conformations. This lack stems from the fact that the conformational behavior, dominated by few structures, generates a severe bottleneck: the non-ergodicity of the system by any practical means. This aspect explains the interest in free energy calculations, and methods exist, such as umbrella sampling or metadynamics, that allow to accelerate the sampling of different conformations by adding bias forces. In general, accelerated sampling methods are based on the choice of collective variables (CVs), which is of particular importance for the proper reconstruction of free energy landscapes. In the field of conformational analysis, suitable CVs have to be considered to describe non-planar, puckered conformations of cyclic structures.
One of the main goals of this work is the enhancement of the gromos 45a4 force field for carbohydrates, with respect to the ability to describe ring conformation (that is, puckering) of six-membered rings. To this end, the development of efficient computational tools for the investigation of the general puckering problem are presented. In particular, we indicate how to exploit the capabilities of the metadynamics algorithm applied to the investigation of puckered ring conformers, exploring also different parametrizations of puckered structures to assess their respective advantages as collective variables for metadynamics.
10
Sebastiani, Lorenzo. « General Aspects of Modified Theories of Gravity ». Doctoral thesis, Università degli studi di Trento, 2011. https://hdl.handle.net/11572/367870.
Texte intégralRésumé :
The aim of this work is to investigate the both, some mathematical and physical general aspect of modified gravity, and, more specifically, the proprieties of viable, realistic models of modified gravity which can be used to reproduce the inflation and the dark energy epoch of universe today.
11
Acquaviva, Giovanni. « Tunnelling and Unruh-DeWitt methods in curved spacetimes ». Doctoral thesis, Università degli studi di Trento, 2013. https://hdl.handle.net/11572/368925.
Texte intégralRésumé :
The analysis and the results contained in this work are rooted in a first contact between the quantum theory and the general theory of relativity. By first contact it is meant that we are not considering candidates for “unified theories", but rather we focus on aspects of the full quantum theory in changing geometric backgrounds: the analysis of such an interaction already had important applications in cosmology, e.g. in the description of the evolution of fields in inflationary scenarios. Another compelling – and still growing – area of application is the study of thermodynamical properties of gravitional systems, which covers the main bulk of this thesis.
12
Forini, Valentina. « Non trivial string backgrounds : Tachyons in String Field Theory and Plane-waves in DLCQ Strings ». Doctoral thesis, Università degli studi di Trento, 2006. https://hdl.handle.net/11572/368486.
Texte intégralRésumé :
One of the most interesting problems in string theory is to understand how the background space-time on which the string propagates arises in a self-consistent way. For open strings, there are two main approaches to this problem, boundary string field theory (BSFT) and cubic string field theory (CSFT). In the first part of this Thesis we deal with the construction of the spacetime tachyon effective action in BSFT. Renormalization fixed points are solutions of classical equations of motion and should be viewed as solutions of classical string field theory. We have constructed the Witten-Shatashvili (WS) space-time action S and shown that some solitonic solutions are lower dimensional D-branes for which the finite value of S provides a quite accurate prediction of the D-brane tension. We have derived the explicit relation between the CSFT and WS action as a field redefinition which is nonsingular on-shell only when the normalization factor in the WS action coincides with the tension of the D25-brane, in agreement with the conjectures involving tachyon condensation. We have also found a time-dependent solution of CSFT whose evolution is driven by a diffusion equation that makes the equations of motion local with respect to the time variable. The analysis here proposed has attracted a good deal of attention for its potential cosmological applications. The profile can be expressed in terms of a series in powers of exponentials of the time coordinate, and gives evidence of a well-defined but wildly oscillatory behavior. The tachyon rolls well past the minimum of the potential, then turns around and begins to oscillate with ever increasing amplitude. Furthermore, we have derived an analytic series solution of the elliptic equations providing the 4-tachyon off-shell amplitude. From such a solution we computed the exact coefficient of the quartic effective action relevant for time-dependent solutions and we derived the exact coefficient of the quartic tachyon coupling. We studied the rolling tachyon solution expressed as a series of exponentials of the time coordinate both using level-truncation computations and the exact 4-tachyon amplitude. The results for the level-truncated coefficients converge to those derived using the exact string amplitude and confirm the wild oscillatory behavior.
In the second part of the Thesis we consider the extension of the gauge/gravity correspondence to systems with reduced and hence more realistic supersymmetry, which is one of the main steps towards a non-perturbative description of confining, QCD-like, gauge theories in terms of gravitational backgrounds. If string theory on AdS5xS5 is integrable, the theory on simple orbifolds of that space would also be expected to be integrable. We have computed the planar finite size corrections to the spectrum of the dilatation operator acting on states of a certain limit of conformal N = 2 quiver gauge field theory which is a ZM-orbifold of N = 4 SYM theory. We matched the result to the string dual, IIB superstrings on a pp-wave background with a periodically identified null coordinate. Up to two loops, we have shown that the computations done by using an effective Hamiltonian technique and a twisted Bethe Ansatz agree with each other and also agree with a computation of the analogous quantity in string theory. Our results are consistent with integrability of the N = 2 theory.
13
Zou, Peng. « Mean-field theory for the dynamics of superfluid fermions in the BCS-BEC crossover ». Doctoral thesis, Università degli studi di Trento, 2014. https://hdl.handle.net/11572/368592.
Texte intégralRésumé :
We use mean-field theory to investigate the dynamics of superfluid fermions. This thesis includes our two works.
The first one is to study Josephson oscillations and self-trapping of superfluid fermions in a double-well potential with time-dependent Bogoliubov-de Gennes equations. We investigate the behaviour of a two-component Fermi superfluid. We numerically solve the time-dependent Bogoliubov-de Gennes equations and characterize the regimes of Josephson oscillations and self-trapping for different potential barriers and initial conditions. In the weak link limit the results agree with a two-mode model where the relative population and the phase difference between the two wells obey coupled nonlinear Josephson equations. A more complex dynamics is predicted for large amplitude oscillations and large tunneling. The second one is to calculate the dynamic structure factor of unitary fermions. We have studied the dynamic structure factor of unitary fermions both at zero and finite temperature using the Bogoliubov-de Gennes theory and also Superfluid Local Density Approximation. We have derived the expression of the linear response function and the dynamic structure factor in the random phase approximation. At zero temperature, the SLDA+RPA formalism indeed provides a better accuracy at low momentum transfer and also its static structure factor is closer to quantum Monte Carlo value than that in BdG+RPA; however SLDA seems to give worse results for the molecular excitations at large momentum transfer. We have discussed the role of temperature and the comparison between SLDA and BdG, as well as with experimental data. The analysis is still at a preliminary level, but it suggests that mean-field theories can indeed be used to extract quantitative
information about the order parameter and the excitations of the system by two-photon Bragg scattering experiments.
14
Sartori, Alberto. « Dynamical properties of Bose-Bose Mixtures ». Doctoral thesis, Università degli studi di Trento, 2016. https://hdl.handle.net/11572/369114.
Texte intégralRésumé :
In this Thesis is presented a study on dynamical properties of mixtures of ultraold Bose gases. The behaviour of this system in different regimes is analysed: with and without coherent coupling between the two components, in homogeneous and harmonic shaped trapping potentials and in different dimensions and geometries. Most of the results presented here have been obtained by means of numerical solutions of coupled Gross-Pitaevskii equations and have been compared with theoretical predictions (and sometimes experiments), describing the same phenomena. In particualr the stability of persistent currents in a two-component Bose-Einstein condensate in a toroidal trap is studied in both the miscible and the immiscible regime. In the miscible regime we show that superflow decay is related to linear instabilities of the spin-density Bogoliubov mode. We find a region of partial stability, where the flow is stable in the majority component while it decays in the minority component. We also characterize the dynamical instability appearing for a large relative velocity between the two components. In the immiscible regime the stability criterion is modified and depends on the specific density distribution of the two components. The effect of a coherent coupling between the two components is also discussed. A study on the collective modes of the minority component of a highly unbalanced Bose-Bose mixture is also presented. In the immiscible case we find that the ground state can be a two-domain walls soliton. Although the mode frequencies are continuous at the transition, their behaviour is very different with respect to the miscible case. The dynamical behaviour of the solitonic structure and the frequency dependence on the inter- and intra-species interaction is numerically studied using coupled Gross-Pitaevskii equations. The results of the study on the static and the dynamic response of coherently coupled two component Bose-Einstein condensates due to a spin-dipole perturbation is also sown. The static dipole susceptibility is determined and is shown to be a key quantity to identify the second order ferromagnetic transition occurring at large inter-species interactions. The dynamics, which is obtained by quenching the spin-dipole perturbation, is very much affected by the system being paramagnetic or ferromagnetic and by the correlation between the motional and the internal degrees of freedom. In the paramagnetic phase the gas exhibits well defined out-of-phase dipole oscillations, whose frequency can be related to the susceptibility of the system using a sum rule approach. In particular in the interaction SU (2) symmetric case, when all the two-body interactions are the same, the external dipole oscillation coincides with the internal Rabi flipping frequency. In the ferromagnetic case, where linear response theory is not applicable, the system shows highly non-linear dynamics. In particular we observe phenomena related to ground state selection: the gas, initially trapped in a domain wall configuration, reaches a final state corresponding to the magnetic ground state plus small density ripples. Interestingly, the time during which the gas is unable to escape from its initial configuration is found to be proportional to the square root of the wall surface
tension.
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De, Rosi Giulia. « Collective oscillations of a trapped atomic gas in low dimensions and thermodynamics of one-dimensional Bose gas ». Doctoral thesis, Università degli studi di Trento, 2017. https://hdl.handle.net/11572/368019.
Texte intégralRésumé :
Ultracold atoms are exceptional tools to explore the physics of quantum matter. In fact, the high degree of tunability of ultracold Bose and Fermi gases makes them ideal systems for quantum simulation and for investigating macroscopic manifestations of quantum effects, such as superfluidity.
In ultracold gas research, a central role is played by collective oscillations. They can be used to study different dynamical regimes, such as superfluid, collisional, or collisionless limits or to test the equation of state of the system. In this thesis, we present a unified description of collective oscillations in low dimensions covering both Bose and Fermi statistics, different trap geometries and zero as well as finite temperature, based on the formalism of hydrodynamics and sum rules. We discuss the different behaviour exhibited by the second excited breathing mode in
the collisional regime at low temperature and in the collisionless limit at high temperature in a 1D trapped Bose gas with repulsive contact interaction. We show how this mode exhibits a single-valued excitation spectrum in the collisional regime and two different frequencies in the collisionless limit. Our predictions could be important for future research related to the thermalization and damping phenomena in this low-dimensional system. We show that 1D uniform Bose gases exhibit a non-monotonic temperature dependence of the chemical potential characterized by an increasing-with-temperature behaviour at low temperature. This is due to the thermal excitation of phonons and reveals an interesting analogy with the behaviour of superfluids.
Finally, we investigate a gas with a finite number N
of atoms in a ring geometry at T = 0. We discuss explicitly the deviations of the thermodynamic behaviour in the ring
from the one in the large N limit.
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Chinaglia, Stefano. « The Singularity Problem in Gravitational Theory. The Spherically Symmetric Case ». Doctoral thesis, Università degli studi di Trento, 2018. https://hdl.handle.net/11572/368528.
Texte intégralRésumé :
In this work we discuss some specific features related to the concept of singularity in the gravitational theory. We give a brief review of some various definitions for singularity, then we explore some "negative" results, in the sense they are not able to reproduce, in general, a regular solution. We present some of these approaches, namely the non-commutative geometry; the Non-Linear Electrodynamics; and the conformal approach. We later generalize these results into a no-go theorem, which is actually a fully original result. In the second part of this work, we discuss some working examples of regular solutions: we present three of them already present in literature (non-minimal Yang-Mills coupling, mimetic field approach and non-polynomial gravity), then we use such results to build up a model of a regular cosmological solution. Its generating mechanism and its main features are described, replacing the Big Bang with a bounce; the inflationary behavior at large time is also recovered. In the following two chapters, we present some different schemes to build regular solutions from the coupling between gravity and a scalar field. In particular, in chapter 7, we use a minimal coupling, while in chapter 8 we find some sufficient (though not necessary) conditions to build a regular solution, within the framework of the Horndeski theory. In both cases we are not able to find explicit results. In the ninth chapter we discuss a model of a regular black hole, coupling gravity with some fluid: in this case, an exact solution is found. We prove it is regular and we show some of its general features; we also discuss the time-dependent case, although we are only able to discuss its asymptotic behavior. We also discuss some of its problems, mainly due to instability. In the appendices we try to extend the no-go theorem to $F(R)$ theories and try to solve the instabilities of the fluid approach respectively.
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GARLASCHI, STEFANO. « Approccio fisico-statistico a tematiche ecologiche e biologiche ». Doctoral thesis, Università degli studi di Padova, 2021. http://hdl.handle.net/11577/3447313.
Texte intégralRésumé :
Gli scienziati sono sempre stati attratti dallo studio del fenomeno della vita, poiché essa mostra una pletora di comportamenti curiosi ed enigmatici. In particolare, negli ultimi decenni si è registrato un crescente interesse da parte della comunità composta dai fisici nei confronti dei sistemi ecologici e biologici. Questo deriva dal fatto che la disciplina della Meccanica Statistica offre molti strumenti, framework e idee che si sono rivelati naturalmente adatti, oltre che molto efficienti, per trattare sistemi affetti da un enorme grado di complessità, come sono i sistemi viventi.
In questa tesi abbracciamo tale prospettiva e quindi affrontiamo tematiche bio-ecologiche utilizzando una mentalità meccanico-statistica.
Innanzitutto proponiamo un modello che descrive comunità ecologiche in cui diverse specie competono per il consumo di un pool condiviso di risorse, con l'obiettivo di capire come possa avere origine l'enorme biodiversità che si incontra empiricamente in molti ecosistemi. Per fare ciò, abbiamo esteso il celebre modello di MacArthur per tendere conto in modo efficace di contributi spaziali, originati da una varietà di meccanismi ecologici. Grazie a ciò, dimostriamo analiticamente che la dinamica prevede la coesistenza di diverse specie in competizione per un numero limitato di risorse, in completo accordo con le evidenze provenienti dalle osservazioni empiriche. Questo è dovuto esclusivamente alla modifica che introduciamo, basata su argomenti sia fisici che ecologici, poiché un tale risultato non può essere ottenuto nella formulazione classica del modello.
In seguito, spostiamo la nostra attenzione sullo studio delle caratteristiche universali delle strutture spaziali regolari auto-organizzate, che possono essere trovate in indagini ecologiche sia empiriche che teoriche. Data la loro ampia diffusione anche in altri campi scientifici, ricerchiamo l’esistenza di un comportamento universale nella loro evoluzione spazio-temporale, indipendentemente dalle peculiarità microscopiche che caratterizzano un certo sistema. Forniamo quindi un framework matematico in grado di stabilire se tali pattern emergano o meno. Inoltre, nella fase di pattern-formation del modello, siamo in grado di mostrare che esiste un regime in cui l'evoluzione dell'involucro di tali strutture spaziali su lunghe scale temporali e grandi scale spaziali è indipendente dal modello, cioè che tale evoluzione è governata da un'equazione, la cui forma non dipende dai dettagli della dinamica.
Infine, motivati da scenari biologici reali, costruiamo un quadro teorico che acquisisce la forma di una dinamica di Langevin generalizzata, tenendo conto dei contributi stocastici demografici e degli effetti dei ritardi temporali. Quindi modelliamo sistemi la cui evoluzione, soggetta a effetti stocastici, è determinata anche dagli stati visitati in passato dal sistema. Dimostriamo come un tale framework predica abbastanza naturalmente l'emergere di comportamenti oscillatori quasi regolari, sotto forma di cicli indotti dal rumore, nell'evoluzione temporale del sistema. Applichiamo poi questi risultati teorici per comprendere le evidenze provenienti da esperimenti che studiano reti di regolazione dell'espressione genica all’interno delle cellule, in cui i contributi del rumore e del ritardo sono effettivamente in gioco.Natural scientists have been always attracted by the study of the phenomenon of Life, since it displays a plethora of curious and yet puzzling behaviors. In the last decades it has been registered an increasing interest in the investigations of ecological and biological systems by the Physics community. This stems from the fact that the physical discipline of Statistical Mechanics offers many tools, frameworks and ideas that have turned out to be naturally adapted, as well as very efficient, to deal with systems affected by an huge degree of complexity, like living systems are. In this Thesis we embrace such a perspective and so we tackle ecological and biological topics employing a Statistical Mechanics mindset.% and we focus on three different remarkable features, which are hallmarks of the complex nature of living systems. We firstly model ecological communities in which several different species compete for the consumption of a shared pool of resources with the aim of understanding how the huge biodiversity empirically encountered can originate. To do so, we extended the celebrated MacArthur's consumer-resource model to account for spatial contributions, originating from a variety of ecological mechanisms, in an effective way. Thanks to this, we show analytically the model predicts several species coexisting while competing for a limited number of resources, in complete agreement with evidences coming from empirical observations. This is solely due to the modification we introduce, based on both physical and ecological arguments, since such a result can not be obtained within the classical formulation of the model. Then, we move our attention to study the universal features of self-organized regular spatial structures, which can be found in both empirical and theoretical ecological investigations. Due to their wide diffusion also in other scientific fields, we search for any universal behavior in their spatio-temporal evolution, regardless the microscopic peculiarities characterizing a certain system. We provide a mathematical framework able to state whether such patterns emerge or not. More interestingly, in the pattern formation phase of the model, we are able to show that it exists a regime in which the evolution of the envelope of such spatial structures on long timescales and large spatial scales is model independent, i.e., it is governed by an equation, whose shape does not dependent on the dynamics details. Finally, motivated by real-world biological scenarios, we build a theoretical framework, which acquires the form of a generalized Langevin dynamics, accounting for demographic stochastic contributions and temporal delays effects. Hence we model systems whose evolution, subjected to noisy effects, is determined also by the past states visited by the system. We demonstrate how such a framework predicts quite naturally the emergence of almost regular oscillating behaviors, in the form of noise-induced cycles, in the temporal evolution of the system. We then apply these theoretical findings to understand the experimental results studying gene expression regulatory networks, in which noise and delay contributions indeed are at stake.
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Testi, Matteo. « Novel methods and models to validate H2 storage in solid state materials ». Doctoral thesis, Università degli studi di Trento, 2017. https://hdl.handle.net/11572/368801.
Texte intégralRésumé :
In this work an improved methodology for the study of hydrogen storage material (HSM) is presented, for the characterization of smaller samples of HSM at increased
accuracy. It includes: the realization of innovative differential instrument; a novel approach to the detailed micro kinetic modelling; increase the comprehension of
absorption and desorption mechanisms; support research efforts in this topic. As side results, a macro and lumped model for the design of generic hydrogen storage tank
are developed and validated. The study of a novel IDA (Isochoric Differential apparatus) is presented, describing all the steps from the initial theoretical approach, to the detailed design and the definition of an experimental proceeding. It includes the necessary technical improvements
to increase the measure uncertainty compared to the classical SIevert. Novel microkinetic modelling for HSM is explained as variation of classic nucleation and growth
model (JMAK model). The nuclei’s growth is assumed to be limited by surface or even by radius of powder’s particles. Micro modelling is applied on Mg-based material,
introducing high accurate kinetic measures obtained by IDA. This leads to extrapolate information about kinetic parameters and kinetic mechanisms of hydrogen sorption.
The obtained micro modelling is used as core for the development of a model at a higher scale (macro) which keeps in consideration also heat and hydrogen diffusion in porous materials typical in hydrogen storage tank. Experimental data collected by a prototipal realization of hydrogen storage tank are used to validate macro modelling.
Moreover, a lumped model is developed with the scope to built a numerical tool able to give preliminary indications on proper design/layout of hydrogen storage tank, based on hydrogen flow, temperature or pressure requirements. Lumped modelling is finally compared with results by the numerical simulation of validated macro model. Finally, micro kinetic model is applied on high accuracy sorption data (by IDA) on innovative catalysed Mg-material. Material is produced by a novel approach, where catalyst, Nb2O5, is deposited by PVD techniques at extremely low concentration on the surface of powder to exploit its higher catalyst proprieties.
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Melati, Alberto. « Renormalization of Wick polynomials for Boson fields in locally covariant AQFT ». Doctoral thesis, Università degli studi di Trento, 2018. https://hdl.handle.net/11572/367938.
Texte intégralRésumé :
The aim of this thesis is to study renormalization of Wick polynomials of quantum Boson fields in locally covariant algebraic quantum field theory in curved spacetime. Vector fields are described as sections of natural vector bundles over globally hyperbolic spacetimes and quantized in a locally covariant framework through the known functorial machinery in terms of local *-algebras. These quantized fields may be defined on spacetimes with given classical background fields, also sections of natural vector bundles: The most obvious one is the metric of the spacetime itself, but we encompass also the case of generic spacetime tensors as background fields. In our framework also physical quantities like the mass of the field or the coupling to the curvature are viewed as background fields. Wick powers of the quantized vector field are then axiomatically defined imposing in particular local covariance, scaling properties and smooth dependence on smooth perturbation of the background fields. A general classification theorem is established for finite renormalization terms (or counterterms) arising when comparing different solutions satisfying the defining axioms of Wick powers. The result is then specialized to the case of spacetime tensor fields. In particular, the case of a vector Klein-Gordon field and the case of a scalar field renormalized together with its derivatives are discussed as examples. In each case, a more precise statement about the structure of the counterterms is proved. The finite renormalization terms turn out to be finite-order polynomials tensorially and locally constructed with the backgrounds fields and their covariant derivatives whose coefficients are locally smooth functions of polynomial scalar invariants constructed from the so-called marginal subset of the background fields.
Our main technical tools are based on the Peetre-Slov\'ak theorem characterizing differential operators and on the classification of smooth invariants on representations of reductive Lie groups.
20
Ghio, Simone. « Design and microfabrication of multifunctional bio-inspired surfaces ». Doctoral thesis, Università degli studi di Trento, 2018. https://hdl.handle.net/11572/367604.
Texte intégralRésumé :
In this thesis, we used CMOS-like technologies to produce improved, hierarchical multifunctional bioinspired surfaces. Different natural surfaces have been surveyed including well-known lotus leaf, sharkskin, back of the Namib Desert beetle, butterfly wings, and legs of water-walking insects. The lotus leaf features superhydrophobicity, which leads to low adhesion and self-cleaning. Sharkskin is composed of ripples that manage to reduce skin-friction and thus drag resistance. The Namib Desert beetle, harvests water from the heterogeneous pattern having hydrophilic/hydrophobic bumps on his back. Butterfly wings have re-entrant structures that manage to reach superhydrophobicity from a hydrophilic substrate. Hairy legs of water-walking insects are superhydrophobic with low adhesion that allows them to fight and jump on water.
In chapter 1, we have undertaken a review of bioinspired surfaces that emulate the abilities of such natural surfaces.
Then, in chapter 2 we have described the innovative CMOS-like techniques used for generating several hierarchical and re-entrant microstructures.
Chapter 3 depicts the analysis of surfaces with hierarchical structures generated with a fast and easy process; this latter forms a second hierarchical level composed of random pyramidal elements using wet etching. Surfaces realized with this process manage to reach remarkably high contact angle and low contact angle hysteresis. Additionally, in this chapter we have introduced an analytical model to study the stability of Cassie-Baxter state over Wenzel state for these hierarchical surfaces.
In chapter 4 the fabrication and analysis of surfaces composed of controlled hierarchical levels, which combine sharkskin with single-level lotus leaf-inspired pillared structures are reported. These particular hierarchical surfaces are demonstrated to hold high superhydrophobic properties along with low skin-friction. The superhydrophobicity of these surfaces has been characterized in a series of tests on an inclined plane. The data extrapolated from this measurement was used to evaluate the total dissipated energy of the sliding drop. Combining the data collected during this experiment with contact angle and contact angle hysteresis measurements we propose a global parameter that evaluates the superhydrophobic “level†of a surface.
Furthermore, in chapter 5 similar hierarchical surfaces have also been tested for water harvesting together with single-level pillared surfaces that feature heterogeneous chemistry with hydrophilic/hydrophobic spot on every single pillar.
In chapter 6 a series of tests have also been performed on butterfly-inspired surfaces. Although the substrate of such surfaces is hydrophilic, thanks to the re-entrant structures the surfaces reach high level of hydrophobicity. An implemented mathematical model and experimental test confirm the stability of this hydrophobic state.
In chapter 7, we describe two sets of surfaces inspired by the hairy legs of water walking insect the first is composed of stretchable pyramidal-pillars and the second of truncated-conical silicon pillars. The ability of sharp structures to easily detach from water surfaces is exploited to change the contact angle value of a water drop deposed on this fast type of stretchable micropatterned surface. A mathematical model has been implemented and experimental tests have been carried out to evaluate the stability of the water-air composite interface on both types of microstructured surfaces. In particular, in the polymeric surfaces elasto-capillarity seams to influence the metastability of the Cassie-Baxter state.
21
Arenzon, Jeferson Jacob. « O modelo RS para redes de neurônios ». reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 1991. http://hdl.handle.net/10183/149206.
Texte intégralRésumé :
Um modelo para redes de neurônios é estudado onde a função energia E é dada pelo produto do quadrado das distâncias no espaço de fase entre o estado S da rede e os P padrões armazenados.Os tempos de convergência e as correspondentes dispersões também foram estudados numericamente e estão relacionados ao número de estados espúrios ao redor de cada configuração armazenada. Ambas quantidades sâo pequenas na fase de recuperaçâo , indicando a homogeneidade e suavidade do espaço de fase.A model for neural networks is studied through a multineuron interaction energy function E given by the product of the squared distances in phase space between the state S of the net and the P stored patterns. Convergence times and the corresponding dispersions have also been studied numerically a.s para.meters to measure the efficiency of this model. These quantities are related to the number of spurious sLates for ea.ch configuration of stored pa.tterns. Both the average convergence time and the dispersions are small in the retrieval phase, indicating the homogeneity and smoothness of the phase space.
22
Simoes, Acirete Souza da Rosa. « Solução diagramática de um hamiltoniano de valência intermediária e da rede Kondo ». reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 1986. http://hdl.handle.net/10183/150167.
Texte intégralRésumé :
Neste trabalho, é feito um estudo de sistemas de valência intermediária e sistemas Kondo, utilizando um método diagramático para calcular as funções de Green, necessárias ao cálculo das densidades de estado, para estes sistemas.We studied intermediate valence and Kondo systems using a diagrammatic technique to calculate the Green functions.
23
Gradenigo, Giacomo. « The study of surface tension within the random first-order theory of glass transition ». Doctoral thesis, Università degli studi di Trento, 2009. https://hdl.handle.net/11572/369214.
Texte intégralRésumé :
The behavior of surface tension within the random first-order theory (RFOT) of glass transition is studied in a glass-forming liquid model by means of ad-hoc numerical methods. The spinodal point for RFOT excitations turns out to be well defined as a function of the energy of inherent structures (IS), i.e. the minima of potential energy which underlie the equilibrium configurations. The corresponding spinodal temperature, although not sharply defined, lies definitely above the mode coupling one. The role played by surface tension within the context of dynamical heterogeneities is also studied by means of a dynamic algorithm in which the overlap with the initial configuration is constrained along equilibrium dynamics. Indications are found that, in the proximity of the mode coupling temperature, a phase-separation between high and low overlap regions occurs, driven by surface tension. The existence of a positive surface tension between amorphous excitations, in the proximity of the mode-coupling temperature, is therefore observed for both static and dynamic excitations.
24
Matveeva, Natalia. « Study of dynamic and ground-state properties of dipolar Fermi gases using mean-field and quantum Monte Carlo methods ». Doctoral thesis, Università degli studi di Trento, 2013. https://hdl.handle.net/11572/368391.
Texte intégralRésumé :
In this thesis I theoretically study the dynamic and ground state properties of ultracold dipolar Fermi gases. The mean-field approach based on the Thomas-Fermi energy functional is applied to consider the dynamic properties of bilayer harmonically trapped dipolar Fermi gases. The fixed-node Diffusion Monte Carlo method (FNDMC) is used instead to investigate the ground-state properties
of two dimensional dipolar Fermi gases. This technique is also applied to the problem of one impurity in a bilayer configuration with dipolar fermions.
25
Martone, Giovanni Italo. « Static and dynamic properties of spin-orbit-coupled Bose-Einstein condensates ». Doctoral thesis, Università degli studi di Trento, 2014. https://hdl.handle.net/11572/367751.
Texte intégralRésumé :
The recent realization of synthetic spin-orbit coupling represents an outstanding achievement in the physics of ultracold quantum gases. In this thesis we explore the properties of spin-orbit-coupled Bose-Einstein condensates with equal Rashba and Dresselhaus strengths. These systems present a rich phase diagram, which exhibits a tricritical point separating a single-minimum phase, a spin-polarized plane-wave phase, and a stripe phase. In the stripe phase translational invariance is spontaneously broken, in analogy with supersolids. Spin-orbit coupling also strongly affects the dynamics of the system. In particular, the excitation spectrum exhibits intriguing features, including the suppression of the sound velocity, the emergence of a roton minimum in the plane-wave phase, and the appearance of a double gapless band structure in the stripe phase. Finally, we discuss a combined procedure to make the stripes visible and stable, thus allowing for a direct experimental detection.
26
Schneider, Elia. « Quantum Transport of Electronic Excitations through Macromolecules ». Doctoral thesis, Università degli studi di Trento, 2015. https://hdl.handle.net/11572/367965.
Texte intégralRésumé :
The investigation of real-time dynamics of charged and neutral quantum excitation propagating
through macromolecular systems is receiving growing attention due to its potentially countless
applications in nano-scale (opto-)electronics and in biophysics.
Several key issues have not been fully clarified yet, including the role played by molecular thermal fluctuations and the possible correlations between the degree of quantum coherence and the efficiency of the transport process. In order to gain some insight, we developed a rigorous and systematic framework describing quantum transport, based on a field-theoretic formalism.
27
Peña, Ardila Luis A. « Impurities in a Bose-Einstein condensate using quantum Monte-Carlo methods : ground-state properties ». Doctoral thesis, Università degli studi di Trento, 2015. https://hdl.handle.net/11572/369010.
Texte intégralRésumé :
In this thesis we investigate the properties of impurities immersed in a dilute Bose gas at zero temperature using quantum Monte-Carlo methods. The interactions between bosons are modeled by a hard sphere potential with scattering length a, whereas the interactions between the impurity and the bosons are modeled by a short-range, square-well potential where both the sign and the strength of the scattering length b can be varied by adjusting the well depth. We calculate the binding energy, the effective mass and the pair correlation functions of a impurity along the attractive and the repulsive polaron branch. In particular, at the unitary limit of the impurity-bosons interaction, we find that the binding energy is much larger than the chemical potential of the bath signaling that many bosons dress the impurity thereby lowering its energy and increasing its effective mass. We characterize this state by calculating the bosons-boson pair correlation function and by investigating the dependence of the binding energy on the gas parameter of the bosonic bath. We also investigate the ground-state properties of M impurities in a Bose gas at T=0. In particular, the energy and the phase diagram by using both quantum Monte-Carlo and mean field methods.
28
Salerno, Grazia. « Artificial gauge fields in photonics and mechanical systems ». Doctoral thesis, Università degli studi di Trento, 2016. https://hdl.handle.net/11572/368464.
Texte intégralRésumé :
Recent technological advances in quantum simulators have proven that synthetic materials are very well suited to study and realise many condensed matter models.
However, many of these synthetic systems are characterized by neutral particles that do not couple to real gauge fields. In order to simulate interesting electromagnetic phenomena, such as the topological insulators, or the Landau levels, there is the need for the implementation of artificial gauge fields. In particular, the topological insulators are very interesting both from the point of view of fundamental physics and concrete applications. They are bulk insulating materials that carry a certain number of edge states which are topologically protected against small perturbations of the system. An example of a topological insulator is the integer quantum Hall effect.
While there have been many works studying topological physics with quantum artificial systems, little attention was dedicated to the interplay of topology and the purely classical world. Only in the last couple of years, pioneering efforts to encode a non-trivial topology in the dynamical matrix or into the Hamiltonian of a system have proven that the hallmarks of a topological insulator are not the prerogative of quantum mechanics, but can be also observed with a classical system governed by Newton’s equations. The first part of this thesis is therefore based on our studies dedicated to the implementation of a classical analogue of the integer quantum Hall system, by realizing the Harper-Hofstadter model for classical frequency-modulated coupled harmonic oscillators.
The achievement of an artificial gauge field allows also for the deeper study of magnetic effects such as Landau levels.
In graphene, an inhomogeneous strain of the lattice is equivalent to an artificial pseudo-magnetic field, and the low-energy spectrum shows the formation of relativistic pseudo-Landau levels. The second part of the thesis is therefore focussed on the photonics honeycomb lattice geometry and our theoretical proposal for a configuration based on an intrinsically driven-dissipative system in which to probe the physics of the Landau levels, and especially the spatial structure of their wavefunctions.
Finally, we have also studied spin-orbit coupling in a mechanical system of masses and springs induced by pre-tensioned springs that split the longitudinal and transverse couplings in the honeycomb geometry. We have presented the experimental results of a simple mechanical benzene composed of six pendula connected with pre-tensioned springs, to verify that the eigenmodes of this system are well described by our theory in the presence of spin-orbit coupling.
29
Larcher, Fabrizio. « Dynamical excitations in low-dimensional condensates : sound, vortices and quenched dynamics ». Doctoral thesis, Università degli studi di Trento, 2018. https://hdl.handle.net/11572/368598.
Texte intégralRésumé :
The dynamics of systems out of equilibrium, such as the phase transition process, are very rich, and related to largely scalable problems, from very small ultracold gases to large expanding galaxies. Quantum low-dimensional systems show interesting features, notably different from the canonical three-dimensional case. Bose-Einstein condensates are very good platforms to study macroscopic quantum phenomena. These three points describe well the motivation behind the study presented in this work.
In this thesis, some dynamical problems of trapped and uniform condensates are studied, both at zero and finite temperature. In particular, we focus on the analysis of the propagation of linear and nonlinear excitations in a quasi-1D and in quasi-2D systems. In the first case, we are able to correctly describe the dynamics of a solitonic vortex in an elongated condensate, as measured by Serafini et al. [Phys. Rev. Lett. 115, 170402 (2015)]. In the second case, we reproduce the decay rate of a phase-imprinted soliton (collaboration with Birmingham), and assess its dependence on the temperature. We also replicate the propagation speed of sound waves over a wide range of temperatures as in Ville et al. [arXiv:1804.04037] (collaboration with Collège de France). The result of this analysis is included in Ota et al. [arXiv:1804.04032], which is currently under revision.
In uniform low-dimensional systems Bose-Einstein condensation is technically not possible, and in two dimensions it is replaced by the Berezinskii-Kosterlitz-Thouless superfluid phase transition. We study its critical properties by analysing the spontaneous generation of vortices during a quench, produced via the Kibble-Zurek mechanism. This procedure predicts, for any dimension, the scaling for the density of defects formed during a fast transition, when the system is not adiabatically following the control parameter, and regions of phase inhomogeneity are formed. We address the role of reduced dimensionality on this process. All finite temperature simulations are performed by means of the stochastic (projected) Gross-Pitaevskii equation, a model fully incorporating density and phase fluctuations for weakly interacting Bose gases.
30
Parisi, Luca. « Mixtures of ultracold Bose gases in one dimension : A Quantum Monte Carlo study ». Doctoral thesis, Università degli studi di Trento, 2019. https://hdl.handle.net/11572/368311.
Texte intégralRésumé :
In this thesis we investigate the properties of mixtures of Bose gases in one dimensions at zero temperature using quantum Monte-Carlo methods. First we investigate the limiting case of an impurity interacting with an atomic bath. We characterize the impurity, by calculating its effective mass, binding energy as well as the contact parameter between the impurity and the bath. In particular, we find that the effective mass rapidly increases to very large values when the impurity gets strongly coupled to an otherwise weakly repulsive bath. Then we describe uniform balanced mixtures with repulsive interactions. We investigate the miscibility phase diagram of the two components and find that correlations do not alter the phase diagram predicted by mean-field theories. We investigate the Andreev-Bashkin effect , a non-dissipative drag between the the two components of the gas and find that the drag becomes very large in the strongly interacting regime. In non-homogeneous systems we also investigate the frequency of the spin-dipole mode. Finally we describe mixtures with attractive inter-species interactions, where one can obtain a liquid ground state because of the competition between the inter-species attraction and intra-species repulsion. We characterize the the liquid and we find that the liquid state can be formed if the ratio of coupling strengths between inter-species attractive and intra-species repulsive interactions exceeds a critical value.
31
Bazzani, Mattia. « Formulazione della meccanica quantistica tramite integrali di cammino con applicazione al moto Browniano ». Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2021. http://amslaurea.unibo.it/24623/.
Texte intégralRésumé :
In questa tesi si espone il formalismo degli integrali di percorso proposto da
Feynman per lo studio della meccanica quantistica. Dopo un breve ripasso dei
concetti fondamentali della teoria ondulatoria di Schrödinger si procede con
l’introduzione concettuale e formale del nuovo formalismo basato sull’integra-
zione sui cammini. In particolare si procederà a ricavare una nuova forma per
il propagatore quantistico utilizzando gli integrali sui percorsi. Si dimostra
poi l’equivalenza tra il formalismo proposto da Feynman ed il formalismo di
Schrödinger. Infine si presenta la stretta connessione esistente tra l’integrazio-
ne sui cammini ed il moto Browniano e quindi in particolare tra l’integrazione
sui cammini e l’integrazione di Wiener.
32
Endler, Antônio. « Aspectos algébricos de sistemas dinâmicos ». reponame:Biblioteca Digital de Teses e Dissertações da UFRGS, 2002. http://hdl.handle.net/10183/5310.
Texte intégralRésumé :
Este trabalho trata o problema genérico da obtenção analítica exata das variedades algébricas que definem domínios de estabilidade e multiestabilidade para sistemas dinâmicos dissipativos com equações de movimento definidas por funções racionais. Apresentamos um método genérico, válido para qualquer sistema dinâmico, que permite reduzir a análise de sistemas multidimensionais arbitrários à análise de um sistema unidimensional equivalente. Este método é aplicado ao mapa de Hénon, o exemplo paradigmático de sistema multidimensional, para estudar a estrutura aritmética imposta pela dinâmica das órbitas de períodos 4, 5, e 6, bem como seus domínios de estabilidade no espaço de parâmetros. Graças à obtençao de resultados analíticos exatos, podemos explorar pela primeira vez as peculariedades de cada um dos períodos mencionados. Algumas das novidades mais marcantes encontradas são as seguintes: Para período 4, encontramos um domínio de multiestabilidade caracterizado pela coexistência de duas órbitas definidas em corpos algébricos distintos. Observamos a existência de discontinuidades na dinâmica simbólica quando os parâmetros são mudados adiabáticamente ao longo de circulações fechadas no espaço de parâmetros e explicamos sua origem algébrica. Publicamos tais resultados em dois artigos: Physica A, 295, 285-290(2001) e Physical Review E, 65, 036231 (2002). Para período 5, obtivemos a variedade algébrica que define o "camarão" (shrimp) característico, obtemos uma expressão analítica para todas as órbitas de período 5, classificamos todas as singulariedades presentes no espaço de parâmetros e analisamos todas as mudanças que ocorrem ao circular-se em torno de tais singulariedades. Para período 6, da expressão analítica que fornece todas as órbitas, encontramos um resultado muito surpreendente, o mais notável desta dissertação: a possibilidade de coexistência de órbitas reais e complexas estáveis, para valores reais dos parâmetros físicos. Resultados preliminares parecem indicar serem tais órbitas complexas uma espécie de órbitas fantasmas, com semelhanças as órbitas encontradas por Gutzwiller para sistemas Hamiltonianos (não- dissipativos).
33
Zanlungo, Francesco <1976>. « Microscopic dynamics of artificial life systems ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/355/1/tesi_zanlungo.pdf.
Texte intégral
34
Zanlungo, Francesco <1976>. « Microscopic dynamics of artificial life systems ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/355/.
Texte intégral
35
Mura, Antonio <1978>. « Non-Markovian stochastic processes and their applications : from anomalous diffusion to time series analysis ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/846/1/Tesi_Mura_Antonio.pdf.
Texte intégralRésumé :
This work provides a forward step in the study and comprehension of the relationships between
stochastic processes and a certain class of integral-partial differential equation, which can be used in
order to model anomalous diffusion and transport in statistical physics. In the first part, we brought
the reader through the fundamental notions of probability and stochastic processes, stochastic
integration and stochastic differential equations as well. In particular, within the study of H-sssi
processes, we focused on fractional Brownian motion (fBm) and its discrete-time increment process,
the fractional Gaussian noise (fGn), which provide examples of non-Markovian Gaussian processes.
The fGn, together with stationary FARIMA processes, is widely used in the modeling and
estimation of long-memory, or long-range dependence (LRD). Time series manifesting long-range
dependence, are often observed in nature especially in physics, meteorology, climatology, but also
in hydrology, geophysics, economy and many others. We deepely studied LRD, giving many real
data examples, providing statistical analysis and introducing parametric methods of estimation.
Then, we introduced the theory of fractional integrals and derivatives, which indeed turns out to be
very appropriate for studying and modeling systems with long-memory properties. After having
introduced the basics concepts, we provided many examples and applications. For instance, we
investigated the relaxation equation with distributed order time-fractional derivatives, which
describes models characterized by a strong memory component and can be used to model relaxation
in complex systems, which deviates from the classical exponential Debye pattern. Then, we focused
in the study of generalizations of the standard diffusion equation, by passing through the
preliminary study of the fractional forward drift equation. Such generalizations have been obtained
by using fractional integrals and derivatives of distributed orders. In order to find a connection
between the anomalous diffusion described by these equations and the long-range dependence, we
introduced and studied the generalized grey Brownian motion (ggBm), which is actually a
parametric class of H-sssi processes, which have indeed marginal probability density function
evolving in time according to a partial integro-differential equation of fractional type. The ggBm is
of course Non-Markovian. All around the work, we have remarked many times that, starting from a
master equation of a probability density function f(x,t), it is always possible to define an
equivalence class of stochastic processes with the same marginal density function f(x,t). All these
processes provide suitable stochastic models for the starting equation. Studying the ggBm, we just
focused on a subclass made up of processes with stationary increments. The ggBm has been
defined canonically in the so called grey noise space. However, we have been able to provide a
characterization notwithstanding the underline probability space. We also pointed out that that the
generalized grey Brownian motion is a direct generalization of a Gaussian process and in particular
it generalizes Brownain motion and fractional Brownain motion as well. Finally, we introduced and
analyzed a more general class of diffusion type equations related to certain non-Markovian
stochastic processes. We started from the forward drift equation, which have been made non-local
in time by the introduction of a suitable chosen memory kernel K(t). The resulting non-Markovian
equation has been interpreted in a natural way as the evolution equation of the marginal density
function of a random time process l(t). We then consider the subordinated process Y(t)=X(l(t))
where X(t) is a Markovian diffusion. The corresponding time-evolution of the marginal density
function of Y(t) is governed by a non-Markovian Fokker-Planck equation which involves the same
memory kernel K(t). We developed several applications and derived the exact solutions. Moreover,
we considered different stochastic models for the given equations, providing path simulations.
36
Mura, Antonio <1978>. « Non-Markovian stochastic processes and their applications : from anomalous diffusion to time series analysis ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/846/.
Texte intégralRésumé :
This work provides a forward step in the study and comprehension of the relationships between
stochastic processes and a certain class of integral-partial differential equation, which can be used in
order to model anomalous diffusion and transport in statistical physics. In the first part, we brought
the reader through the fundamental notions of probability and stochastic processes, stochastic
integration and stochastic differential equations as well. In particular, within the study of H-sssi
processes, we focused on fractional Brownian motion (fBm) and its discrete-time increment process,
the fractional Gaussian noise (fGn), which provide examples of non-Markovian Gaussian processes.
The fGn, together with stationary FARIMA processes, is widely used in the modeling and
estimation of long-memory, or long-range dependence (LRD). Time series manifesting long-range
dependence, are often observed in nature especially in physics, meteorology, climatology, but also
in hydrology, geophysics, economy and many others. We deepely studied LRD, giving many real
data examples, providing statistical analysis and introducing parametric methods of estimation.
Then, we introduced the theory of fractional integrals and derivatives, which indeed turns out to be
very appropriate for studying and modeling systems with long-memory properties. After having
introduced the basics concepts, we provided many examples and applications. For instance, we
investigated the relaxation equation with distributed order time-fractional derivatives, which
describes models characterized by a strong memory component and can be used to model relaxation
in complex systems, which deviates from the classical exponential Debye pattern. Then, we focused
in the study of generalizations of the standard diffusion equation, by passing through the
preliminary study of the fractional forward drift equation. Such generalizations have been obtained
by using fractional integrals and derivatives of distributed orders. In order to find a connection
between the anomalous diffusion described by these equations and the long-range dependence, we
introduced and studied the generalized grey Brownian motion (ggBm), which is actually a
parametric class of H-sssi processes, which have indeed marginal probability density function
evolving in time according to a partial integro-differential equation of fractional type. The ggBm is
of course Non-Markovian. All around the work, we have remarked many times that, starting from a
master equation of a probability density function f(x,t), it is always possible to define an
equivalence class of stochastic processes with the same marginal density function f(x,t). All these
processes provide suitable stochastic models for the starting equation. Studying the ggBm, we just
focused on a subclass made up of processes with stationary increments. The ggBm has been
defined canonically in the so called grey noise space. However, we have been able to provide a
characterization notwithstanding the underline probability space. We also pointed out that that the
generalized grey Brownian motion is a direct generalization of a Gaussian process and in particular
it generalizes Brownain motion and fractional Brownain motion as well. Finally, we introduced and
analyzed a more general class of diffusion type equations related to certain non-Markovian
stochastic processes. We started from the forward drift equation, which have been made non-local
in time by the introduction of a suitable chosen memory kernel K(t). The resulting non-Markovian
equation has been interpreted in a natural way as the evolution equation of the marginal density
function of a random time process l(t). We then consider the subordinated process Y(t)=X(l(t))
where X(t) is a Markovian diffusion. The corresponding time-evolution of the marginal density
function of Y(t) is governed by a non-Markovian Fokker-Planck equation which involves the same
memory kernel K(t). We developed several applications and derived the exact solutions. Moreover,
we considered different stochastic models for the given equations, providing path simulations.
37
Testi, Matteo. « Novel methods and models to validate H2 storage in solid state materials ». Doctoral thesis, University of Trento, 2017. http://eprints-phd.biblio.unitn.it/1949/1/thesis.pdf.
Texte intégralRésumé :
In this work an improved methodology for the study of hydrogen storage material (HSM) is presented, for the characterization of smaller samples of HSM at increased
accuracy. It includes: the realization of innovative differential instrument; a novel approach to the detailed micro kinetic modelling; increase the comprehension of
absorption and desorption mechanisms; support research efforts in this topic. As side results, a macro and lumped model for the design of generic hydrogen storage tank
are developed and validated. The study of a novel IDA (Isochoric Differential apparatus) is presented, describing all the steps from the initial theoretical approach, to the detailed design and the definition of an experimental proceeding. It includes the necessary technical improvements
to increase the measure uncertainty compared to the classical SIevert. Novel microkinetic modelling for HSM is explained as variation of classic nucleation and growth
model (JMAK model). The nuclei’s growth is assumed to be limited by surface or even by radius of powder’s particles. Micro modelling is applied on Mg-based material,
introducing high accurate kinetic measures obtained by IDA. This leads to extrapolate information about kinetic parameters and kinetic mechanisms of hydrogen sorption.
The obtained micro modelling is used as core for the development of a model at a higher scale (macro) which keeps in consideration also heat and hydrogen diffusion in porous materials typical in hydrogen storage tank. Experimental data collected by a prototipal realization of hydrogen storage tank are used to validate macro modelling.
Moreover, a lumped model is developed with the scope to built a numerical tool able to give preliminary indications on proper design/layout of hydrogen storage tank, based on hydrogen flow, temperature or pressure requirements. Lumped modelling is finally compared with results by the numerical simulation of validated macro model. Finally, micro kinetic model is applied on high accuracy sorption data (by IDA) on innovative catalysed Mg-material. Material is produced by a novel approach, where catalyst, Nb2O5, is deposited by PVD techniques at extremely low concentration on the surface of powder to exploit its higher catalyst proprieties.
38
Melati, Alberto. « Renormalization of Wick polynomials for Boson fields in locally covariant AQFT ». Doctoral thesis, University of Trento, 2018. http://eprints-phd.biblio.unitn.it/2836/1/PhD_Melati.pdf.
Texte intégralRésumé :
The aim of this thesis is to study renormalization of Wick polynomials of quantum Boson fields in locally covariant algebraic quantum field theory in curved spacetime. Vector fields are described as sections of natural vector bundles over globally hyperbolic spacetimes and quantized in a locally covariant framework through the known functorial machinery in terms of local *-algebras. These quantized fields may be defined on spacetimes with given classical background fields, also sections of natural vector bundles: The most obvious one is the metric of the spacetime itself, but we encompass also the case of generic spacetime tensors as background fields. In our framework also physical quantities like the mass of the field or the coupling to the curvature are viewed as background fields. Wick powers of the quantized vector field are then axiomatically defined imposing in particular local covariance, scaling properties and smooth dependence on smooth perturbation of the background fields. A general classification theorem is established for finite renormalization terms (or counterterms) arising when comparing different solutions satisfying the defining axioms of Wick powers. The result is then specialized to the case of spacetime tensor fields. In particular, the case of a vector Klein-Gordon field and the case of a scalar field renormalized together with its derivatives are discussed as examples. In each case, a more precise statement about the structure of the counterterms is proved. The finite renormalization terms turn out to be finite-order polynomials tensorially and locally constructed with the backgrounds fields and their covariant derivatives whose coefficients are locally smooth functions of polynomial scalar invariants constructed from the so-called marginal subset of the background fields.
Our main technical tools are based on the Peetre-Slov\'ak theorem characterizing differential operators and on the classification of smooth invariants on representations of reductive Lie groups.
39
Ghio, Simone. « Design and microfabrication of multifunctional bio-inspired surfaces ». Doctoral thesis, University of Trento, 2018. http://eprints-phd.biblio.unitn.it/2854/1/Thesis_GHIO_S..pdf.
Texte intégralRésumé :
In this thesis, we used CMOS-like technologies to produce improved, hierarchical multifunctional bioinspired surfaces. Different natural surfaces have been surveyed including well-known lotus leaf, sharkskin, back of the Namib Desert beetle, butterfly wings, and legs of water-walking insects. The lotus leaf features superhydrophobicity, which leads to low adhesion and self-cleaning. Sharkskin is composed of ripples that manage to reduce skin-friction and thus drag resistance. The Namib Desert beetle, harvests water from the heterogeneous pattern having hydrophilic/hydrophobic bumps on his back. Butterfly wings have re-entrant structures that manage to reach superhydrophobicity from a hydrophilic substrate. Hairy legs of water-walking insects are superhydrophobic with low adhesion that allows them to fight and jump on water.
In chapter 1, we have undertaken a review of bioinspired surfaces that emulate the abilities of such natural surfaces.
Then, in chapter 2 we have described the innovative CMOS-like techniques used for generating several hierarchical and re-entrant microstructures.
Chapter 3 depicts the analysis of surfaces with hierarchical structures generated with a fast and easy process; this latter forms a second hierarchical level composed of random pyramidal elements using wet etching. Surfaces realized with this process manage to reach remarkably high contact angle and low contact angle hysteresis. Additionally, in this chapter we have introduced an analytical model to study the stability of Cassie-Baxter state over Wenzel state for these hierarchical surfaces.
In chapter 4 the fabrication and analysis of surfaces composed of controlled hierarchical levels, which combine sharkskin with single-level lotus leaf-inspired pillared structures are reported. These particular hierarchical surfaces are demonstrated to hold high superhydrophobic properties along with low skin-friction. The superhydrophobicity of these surfaces has been characterized in a series of tests on an inclined plane. The data extrapolated from this measurement was used to evaluate the total dissipated energy of the sliding drop. Combining the data collected during this experiment with contact angle and contact angle hysteresis measurements we propose a global parameter that evaluates the superhydrophobic “level” of a surface.
Furthermore, in chapter 5 similar hierarchical surfaces have also been tested for water harvesting together with single-level pillared surfaces that feature heterogeneous chemistry with hydrophilic/hydrophobic spot on every single pillar.
In chapter 6 a series of tests have also been performed on butterfly-inspired surfaces. Although the substrate of such surfaces is hydrophilic, thanks to the re-entrant structures the surfaces reach high level of hydrophobicity. An implemented mathematical model and experimental test confirm the stability of this hydrophobic state.
In chapter 7, we describe two sets of surfaces inspired by the hairy legs of water walking insect the first is composed of stretchable pyramidal-pillars and the second of truncated-conical silicon pillars. The ability of sharp structures to easily detach from water surfaces is exploited to change the contact angle value of a water drop deposed on this fast type of stretchable micropatterned surface. A mathematical model has been implemented and experimental tests have been carried out to evaluate the stability of the water-air composite interface on both types of microstructured surfaces. In particular, in the polymeric surfaces elasto-capillarity seams to influence the metastability of the Cassie-Baxter state.
40
Benini, Riccardo <1979>. « Classical and quantum features of the inhomogeneous mixmaster model ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/327/1/PhD_Thesis.pdf.
Texte intégral
41
Benini, Riccardo <1979>. « Classical and quantum features of the inhomogeneous mixmaster model ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/327/.
Texte intégral
42
Casarini, Luciano <1978>. « The nature of dark energy : theoretical assumptions and experimental tests ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/330/1/casarini.phd.pdf.
Texte intégral
43
Casarini, Luciano <1978>. « The nature of dark energy : theoretical assumptions and experimental tests ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/330/.
Texte intégral
44
Fabbri, Luca <1978>. « Higher-order theories of gravitation ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/333/1/libro.pdf.
Texte intégral
45
Fabbri, Luca <1978>. « Higher-order theories of gravitation ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/333/.
Texte intégral
46
Luzzi, Mattia <1979>. « Semiclassical approximations to cosmological perturbations ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/347/1/Tesi_Dottorato_Mattia_Luzzi.pdf.
Texte intégral
47
Luzzi, Mattia <1979>. « Semiclassical approximations to cosmological perturbations ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2007. http://amsdottorato.unibo.it/347/.
Texte intégral
48
Latini, Emanuele <1978>. « Wordline approach to higher spin fields ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/843/1/Tesi_Latini_Emanuele.pdf.
Texte intégralRésumé :
The main object of this thesis is the analysis and the quantization of spinning particle
models which employ extended ”one dimensional supergravity” on the worldline, and their
relation to the theory of higher spin fields (HS).
In the first part of this work we have described the classical theory of massless spinning
particles with an SO(N) extended supergravity multiplet on the worldline, in flat and more
generally in maximally symmetric backgrounds. These (non)linear sigma models describe,
upon quantization, the dynamics of particles with spin N/2.
Then we have analyzed carefully the quantization of spinning particles with SO(N)
extended supergravity on the worldline, for every N and in every dimension D. The physical
sector of the Hilbert space reveals an interesting geometrical structure: the generalized higher
spin curvature (HSC). We have shown, in particular, that these models of spinning particles
describe a subclass of HS fields whose equations of motions are conformally invariant at the
free level; in D = 4 this subclass describes all massless representations of the Poincar´e group.
In the third part of this work we have considered the one-loop quantization of SO(N)
spinning particle models by studying the corresponding partition function on the circle.
After the gauge fixing of the supergravity multiplet, the partition function reduces to an
integral over the corresponding moduli space which have been computed by using orthogonal
polynomial techniques.
Finally we have extend our canonical analysis, described previously for flat space, to
maximally symmetric target spaces (i.e. (A)dS background). The quantization of these
models produce (A)dS HSC as the physical states of the Hilbert space; we have used an
iterative procedure and Pochhammer functions to solve the differential Bianchi identity in
maximally symmetric spaces.
Motivated by the correspondence between SO(N) spinning particle models and HS gauge
theory, and by the notorious difficulty one finds in constructing an interacting theory for fields
with spin greater than two, we have used these one dimensional supergravity models to study
and extract informations on HS.
In the last part of this work we have constructed spinning particle models with sp(2) R
symmetry, coupled to Hyper K¨ahler and Quaternionic-K¨ahler (QK) backgrounds.
49
Latini, Emanuele <1978>. « Wordline approach to higher spin fields ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/843/.
Texte intégralRésumé :
The main object of this thesis is the analysis and the quantization of spinning particle
models which employ extended ”one dimensional supergravity” on the worldline, and their
relation to the theory of higher spin fields (HS).
In the first part of this work we have described the classical theory of massless spinning
particles with an SO(N) extended supergravity multiplet on the worldline, in flat and more
generally in maximally symmetric backgrounds. These (non)linear sigma models describe,
upon quantization, the dynamics of particles with spin N/2.
Then we have analyzed carefully the quantization of spinning particles with SO(N)
extended supergravity on the worldline, for every N and in every dimension D. The physical
sector of the Hilbert space reveals an interesting geometrical structure: the generalized higher
spin curvature (HSC). We have shown, in particular, that these models of spinning particles
describe a subclass of HS fields whose equations of motions are conformally invariant at the
free level; in D = 4 this subclass describes all massless representations of the Poincar´e group.
In the third part of this work we have considered the one-loop quantization of SO(N)
spinning particle models by studying the corresponding partition function on the circle.
After the gauge fixing of the supergravity multiplet, the partition function reduces to an
integral over the corresponding moduli space which have been computed by using orthogonal
polynomial techniques.
Finally we have extend our canonical analysis, described previously for flat space, to
maximally symmetric target spaces (i.e. (A)dS background). The quantization of these
models produce (A)dS HSC as the physical states of the Hilbert space; we have used an
iterative procedure and Pochhammer functions to solve the differential Bianchi identity in
maximally symmetric spaces.
Motivated by the correspondence between SO(N) spinning particle models and HS gauge
theory, and by the notorious difficulty one finds in constructing an interacting theory for fields
with spin greater than two, we have used these one dimensional supergravity models to study
and extract informations on HS.
In the last part of this work we have constructed spinning particle models with sp(2) R
symmetry, coupled to Hyper K¨ahler and Quaternionic-K¨ahler (QK) backgrounds.
50
Iafelice, Pasquale Luca <1980>. « Perturbative and non perturbative effects in the Standard Model and orbifolded ADS/CFT based theories ». Doctoral thesis, Alma Mater Studiorum - Università di Bologna, 2008. http://amsdottorato.unibo.it/844/1/Tesi_Iafelice_Pasquale_Luca.pdf.
Texte intégralRésumé :
We study some perturbative and nonperturbative effects in the framework of the
Standard Model of particle physics. In particular we consider the time dependence
of the Higgs vacuum expectation value given by the dynamics of the StandardModel
and study the non-adiabatic production of both bosons and fermions,
which is intrinsically non-perturbative. In theHartree approximation, we analyze
the general expressions that describe the dissipative dynamics due to the backreaction
of the produced particles. Then, we solve numerically some relevant
cases for the Standard Model phenomenology in the regime of relatively small
oscillations of the Higgs vacuum expectation value (vev). As perturbative effects,
we consider the leading logarithmic resummation in small Bjorken x QCD, concentrating
ourselves on the Nc dependence of the Green functions associated to
reggeized gluons. Here the eigenvalues of the BKP kernel for states of more than
three reggeized gluons are unknown in general, contrary to the large Nc limit
(planar limit) case where the problem becomes integrable. In this contest we consider
a 4-gluon kernel for a finite number of colors and define some simple toy
models for the configuration space dynamics, which are directly solvable with
group theoretical methods. In particular we study the depencence of the spectrum
of thesemodelswith respect to the number of colors andmake comparisons
with the planar limit case. In the final part we move on the study of theories
beyond the Standard Model, considering models built on AdS5 S5/Γ orbifold
compactifications of the type IIB superstring, where Γ is the abelian group Zn.
We present an appealing three family N = 0 SUSY model with n = 7 for the order
of the orbifolding group. This result in a modified Pati–Salam Model which
reduced to the StandardModel after symmetry breaking and has interesting phenomenological
consequences for LHC.