Frustration-driven QPT in the 1D extended anisotropic Heisenberg model

By using Density Matrix Renormalization Group (DMRG) technique we study the 1D extended anisotropic Heisenberg model. We find that starting from the ferromagnetic phase, the system undergoes two quantum phase transitions (QPTs) induced by frustration. By increasing the next-nearest-neighbor (NNN) interaction, the ground state of the system changes smoothly from a completely polarized state to a NNN correlated one. On the contrary, letting the in-plane interaction to be greater than the out-of-plane one, the ground state changes abruptly.Comment: 4 pages, 4 figures, to be presented at CSMAG-07 Kosice, Slovakia, July 200

Bosonic sector of the two-dimensional Hubbard model studied within a two-pole approximation

The charge and spin dynamics of the two-dimensional Hubbard model in the paramagnetic phase is first studied by means of the two-pole approximation within the framework of the Composite Operator Method. The fully self-consistent scheme requires: no decoupling, the fulfillment of both Pauli principle and hydrodynamics constraints, the simultaneous solution of fermionic and bosonic sectors and a very rich momentum dependence of the response functions. The temperature and momentum dependencies, as well as the dependency on the Coulomb repulsion strength and the filling, of the calculated charge and spin susceptibilities and correlation functions are in very good agreement with the numerical calculations present in the literature

Enriching Hate-Tuned Transformer-Based Embeddings with Emotions for the Categorization of Sexism

We present the results of the participation of our team Unibo in the shared task sEXism Identification in Social neTworks (EXIST). We target all three tasks: a) binary sexism identification, b) discerning the author’s intention, and c) categorizing instances into fine-grained categories. For all the tasks, both English and Spanish data are to be considered. We compare two approaches to address this multilingual aspect: we employ machine translation to convert the Spanish data into English, allowing us to utilize a specially fine-tuned version of RoBERTa to detect hateful content, and we experiment with a multilingual version of RoBERTa to perform classification while preserving data in their original language. Furthermore, we predict emotions associated with each post and leverage them as additional features by concatenating them with the original text. This augmentation improves the performance of our models in Task 2 and 3. Our official submissions obtain F1=0.77 in Task 1 (13th position out of 69), macro-averaged F1=0.53 in Task 2 (4th position out of 35) and macro-averaged F1=0.59 in Task 3 (4th position out of 32)

A Study of the Antiferromagnetic Phase in the Hubbard Model by means of the Composite Operator Method

We have investigated the antiferromagnetic phase of the 2D, the 3D and the extended Hubbard models on a bipartite cubic lattice by means of the Composite Operator Method within a two-pole approximation. This approach yields a fully self-consistent treatment of the antiferromagnetic state that respects the symmetry properties of both the model and the algebra. The complete phase diagram, as regards the antiferromagnetic and the paramagnetic phases, has been drawn. We firstly reported, within a pole approximation, three kinds of transitions at half-filling: Mott-Hubbard, Mott-Heisenberg and Heisenberg. We have also found a metal-insulator transition, driven by doping, within the antiferromagnetic phase. This latter is restricted to a very small region near half filling and has, in contrast to what has been found by similar approaches, a finite critical Coulomb interaction as lower bound at half filling. Finally, it is worth noting that our antiferromagnetic gap has two independent components: one due to the antiferromagnetic correlations and another coming from the Mott-Hubbard mechanism.Comment: 20 pages, 37 figures, RevTeX, submitted to Phys. Rev.

Underdoped cuprates phenomenology in the 2D Hubbard model within COM(SCBA)

The two-dimensional Hubbard model is studied within the Composite Operator Method (COM) with the residual self-energy computed in the Self-Consistent Born Approximation (SCBA). COM describes interacting electrons in terms of the new elementary excitations appearing in the system owing to strong correlations; residual interactions among these excitations are treated within the SCBA. The anomalous features appearing in the spectral function A(k,\omega), the momentum distribution function n(k) and the Fermi surface are analyzed for various values of the filling (from overdoped to underdoped region) in the intermediate coupling regime at low temperatures. For low doping, in contrast with the ordinary Fermi-liquid behavior of a weakly-correlated metal found at high doping, we report the opening of a pseudogap and some non-Fermi-liquid features as measured for cuprates superconductors. In addition, we show the presence of kinks in the calculated electronic dispersion in agreement with ARPES data.Comment: 5 pages, 5 figure

Ponderomotive entangling of atomic motions

We propose the use of ponderomotive forces to entangle the motions of different atoms. Two situations are analyzed: one where the atoms belong to the same optical cavity and interact with the same radiation field mode; the other where each atom is placed in own optical cavity and the output field of one cavity enters the other.Comment: Revtex file, five pages, two eps figure

Molecular detection of parasites (Trematoda, Digenea: Bucephalidae and Monorchiidae) in the European flat oyster Ostrea edulis (Mollusca: Bivalvia)

Members of the globally distributed bivalve family Ostreidae (oysters) have a significant role in marine ecosystems and include species of high economic importance. In this work, we report the occurrence of digenean parasites of the families Bucephalidae (Prosorhynchoides sp.) and Monorchiidae (Postmonorchis sp.) in Mediterranean native populations of Ostrea edulis (but not in the introduced Magallana gigas). Molecular detection was based on DNA sequencing of the ribosomal intergenic spacer 2 (ITS2) marker. The importance of detecting the presence of overlooked digenean parasites in Mediterranean oysters is discussed. © 2018 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group

Synthesis and characterization of entangled mesoscopic superpositions for a trapped electron

We propose a scheme for the generation and reconstruction of entangled states between the internal and external (motional) degrees of freedom of a trapped electron. Such states also exhibit quantum coherence at a mesoscopic level.Comment: 4 pages, 1 figure, RevTeX (twocolumn

Overcoming the false-minima problem in direct methods: Structure determination of the packaging enzyme P4 from bacteriophage φ13

The problems encountered during the phasing and structure determination of the packaging enzyme P4 from bacteriophage φ13 using the anomalous signal from selenium in a single-wavelength anomalous dispersion experiment (SAD) are described. The oligomeric state of P4 in the virus is a hexamer (with sixfold rotational symmetry) and it crystallizes in space group C2, with four hexamers in the crystallographic asymmetric unit. Current state-of-the-art ab initio phasing software yielded solutions consisting of 96 atoms arranged as sixfold symmetric clusters of Se atoms. However, although these solutions showed high correlation coefficients indicative that the substructure had been solved, the resulting phases produced uninterpretable electron-density maps. Only after further analysis were correct solutions found (also of 96 atoms), leading to the eventual identification of the positions of 120 Se atoms. Here, it is demonstrated how the difficulties in finding a correct phase solution arise from an intricate false-minima problem. © 2005 International Union of Crystallography - all rights reserved

Characterizing the entanglement of bipartite quantum systems

We derive a separability criterion for bipartite quantum systems which generalizes the already known criteria. It is based on observables having generic commutation relations. We then discuss in detail the relation among these criteria.Comment: 5 pages, 2 figures. Revised versio