365 research outputs found
O Araguaia pelos Militares: Imaginários e Barbáries
No full textReview text “Araguaia by the Military: Imaginary and Barbaries” (2008), by the author Flávia M. Franchini Ribeiro.Review text “Araguaia by the Military: Imaginary and Barbaries” (2008), by the author Flávia M. Franchini Ribeiro.Texto da resenha "O Araguaia pelos Militares: Imaginários e Barbáries " da autora Flávia M. Franchini Ribeiro
Modular invariance in the gapped XYZ spin-1/2 chain
No full textWe show that the elliptic parametrization of the coupling constants of the quantum XYZ spin chain can be analytically extended outside of their natural domain, to cover the whole phase diagram of the model, which is composed of 12 adjacent regions, related to one another by a spin rotation. This extension is based on the modular properties of the elliptic functions and we show how rotations in parameter space correspond to the double covering PGL(2,Z) of the modular group, implying that the partition function of the XYZ chain is invariant under this group in parameter space, in the same way as a conformal field theory partition function is invariant under the modular group acting in real space. The encoding of the symmetries of the model into the modular properties of the partition function could shed light on the general structure of integrable models
Hydrodynamics of local excitations after an interaction quench in 1D cold atomic gases
No full textWe discuss the hydrodynamic approach to the study of the time evolution -induced by a quench- of local excitations in one dimension. We focus on interaction quenches: the considered protocol consists in creating a stable localized excitation propagating through the system, and then operating a sudden change of the interaction between the particles. To highlight the effect of the quench, we take the initial excitation to be a soliton. The quench splits the excitation into two packets moving in opposite directions, whose characteristics can be expressed in a universal way. Our treatment allows to describe the internal dynamics of these two packets in terms of the different velocities of their components. We confirm our analytical predictions through numerical simulations performed with the Gross-Pitaevskii equation and with the Calogero model (as an example of long range interactions and solvable with a parabolic confinement). Through the Calogero model we also discuss the effect of an external trapping on the protocol. The hydrodynamic approach shows that there is a difference between the bulk velocities of the propagating packets and the velocities of their peaks: it is possible to discriminate the two quantities, as we show through the comparison between numerical simulations and analytical estimates. In the realizations of the discussed quench protocol in a cold atom experiment, these different velocities are accessible through different measurement procedures. ArXI
Mutual information for fermionic systems
No full textWe study the behavior of the mutual information (MI) in various quadratic
fermionic chains, with and without pairing terms and both with short- and
long-range hoppings. The models considered include the short-range limit and
long-range versions of the Kitaev model as well, and also cases in which the
area law for the entanglement entropy is - logarithmically or
non-logarithmically - violated. In all cases surveyed, when the area law is
violated at most logarithmically, the MI is a monotonically increasing function
of the conformal four-point ratio x. Where non-logarithmic violations of the
area law are present, non-monotonic features can be observed in the MI and the
four-point ratio, as well as other natural combinations of the parameters, is
found not to be sufficient to capture the whole structure of the MI with a
collapse onto a single curve. We interpret this behavior as a sign that the
structure of peaks is related to a non-universal spatial configuration of Bell
pairs. For the model exhibiting a perfect volume law, the MI vanishes
identically. For the Kitaev model the MI is vanishing for x -> 0 and it remains
zero up to a finite x in the gapped case. In general, a larger range of the
pairing corresponds to a reduction of the MI at small x. A discussion of the
comparison with the results obtained by the AdS/CFT correspondence in the
strong coupling limit is presented
Correlation length and unusual corrections to entanglement entropy
No full textWe study analytically the corrections to the leading terms in the Rényi entropy of a massive lattice theory, showing significant deviations from naive expectations. In particular, we show that finite size and finite mass effects give rise to different contributions (with different exponents) and thus violate a simple scaling argument. In the specific, we look at the entanglement entropy of a bipartite XYZ spin-1/2 chain in its ground state. When the system is divided into two semi-infinite half-chains, we have an analytical expression of the Rényi entropy as a function of a single mass parameter. In the scaling limit, we show that the entropy as a function of the correlation length formally coincides with that of a bulk Ising model. This should be compared with the fact that, at criticality, the model is described by a c=1 conformal field theory and the corrections to the entropy due to finite size effects show exponents depending on the compactification radius of the theory. We will argue that there is no contradiction between these statements. If the lattice spacing is retained finite, the relation between the mass parameter and the correlation length generates new subleading terms in the entropy, whose form is path dependent in phase space and whose interpretation within a field theory is not available yet. These contributions arise as a consequence of the existence of stable bound states and are thus a distinctive feature of truly interacting theories, such as the XYZ chain.Marie Curie International (Outgoing Fellowship Grant PIOF-PHY-276093)United States. Dept. of Energy. (Contract DE-FG02- 05ER41360)Istituto nazionale di fisica nucleare (INFN) COM4 (Grant FI11)Istituto nazionale di fisica nucleare (INFN) COM4 (Grant NA41
Universal dynamics of a soliton after an interaction quench
No full textWe propose a new type of experimentally feasible quantum quench protocol in which a quantum system is prepared in a coherent, localized excited state of a Hamiltonian. During the evolution of this solitonic excitation, the microscopic interaction is suddenly changed. We study the dynamics of solitons after this interaction quench for a wide class of systems using a hydrodynamic approach. We find that the post-quench dynamics is universal at short times, i.e. it does not depend on the microscopic details of the physical system. Numerical support for these results is presented using generalized nonlinear Schrödinger equation, relevant for the implementation of the proposed protocol with ultracold bosons, as well as for the integrable Calogero model in harmonic potential. Finally, it is shown that the effects of integrability breaking by a parabolic potential and by a power-law nonlinearity do not change the universality of the short-time dynamics
Studio delle relazioni tra acidità, concentrazione zuccherina, concentrazione di composti di natura furanica ed invecchiamento in batterie per la produzione di Aceto Balsamico Tradizionale di Reggio Emilia mediante metodologie chemiometriche
No full textL’Aceto Balsamico Tradizionale (ABT) di Reggio Emilia deriva da mosto concentrato, che subisce un invecchiamento di almeno 12 anni in batterie costituite generalmente da 5 botti, diverse per capacità ed essenza legnosa. In questo lavoro di ricerca sono stati elaborati modelli matematici allo scopo di indagare le relazioni esistenti tra l’acidità, la concentrazione zuccherina, la concentrazione di composti di natura furanica e l’invecchiamento dell’ABT. I derivati furanici si originano durante la concentrazione del mosto, e il loro contenuto tende ad aumentare nel corso dell’invecchiamento, a causa della graduale perdita d’acqua che caratterizza il processo. Tuttavia le cinetiche d’accumulo sono diverse poiché i composti furanici, molecole piuttosto reattive, subiscono verosimilmente una rapida evoluzione in questa matrice. Ne risulta una cinetica di accumulo non sempre regolare, che richiede il ricorso a metodi d’indagine basati su tecniche chemiometriche multivariate, quale l’analisi delle componenti principali (PCA) per poter essere interpretata. Il derivato del furano più importante dal punto di vista quantitativo è l’idrossimetilfurfurale (HMF), dosato, mediante tecnica HPLC, insieme ad acido furoico (AF), furfurale (Fal) e 5-acetossimetilfurfurale (AMFA)
- …
