Local properties in the two-dimensional t-t'-U model

We have studied the t-t'-U model by means of the composite operator method. The effect of the bare diagonal hopping term t' that appears to be material dependent for high-Tc cuprate superconductors is analyzed in detail. In particular, some local quantities are computed and a comprehensive comparison with the data by numerical simulations on finite size lattices is presented. The result show a good agreement with those obtained by Monte Carlo methods.Comment: 3 pages, 3 figures in one Postscript file, RevTeX, to be published in Physica

The two-dimensional t-t'-U model as a minimal model for cuprate materials

The addition to the Hubbard Hamiltonian of a t' diagonal hopping term, which is considered to be material dependent for high-Tc cuprate superconductors, is generally suggested to obtain a model capable to describe the physics of high-Tc cuprate materials. In this line of thinking, the two-dimensional t-t'-U model has been studied by means of the Composite Operator Method, which allows to determine the dynamics in a fully self-consistent way by use of symmetry requirements, as the ones coming from the Pauli principle. At first, some local quantities have been calculated to be compared with quantum Monte Carlo data. Then, the structure of the energy bands, the shape of the Fermi surface and the position of the van Hove singularity have been computed as functions of the model parameters and studied by the light of the available experimental data. The results of our study show that there exists two sets of parameters that allows the model to describe the relevant features of 1-layer compounds NCCO and LSCO. On the other hand, for the 2-layer compound YBCO is not possible to find a reasonable set of parameters which could reproduce the position of the van Hove singularity as predicted by ARPES experiments. Hence, it results questionable the existence of an unique model that could properly describe the variety of cuprate superconductors, as the t-t'-U model was thought to be.Comment: 8 pages, RevTex, 10 Postscript figures, submitted to Phys. Rev. B. This paper, as many others from the same authors, can be downloaded by anonymous FTP at ftp://pcalea.csied.unisa.i

Incommensurate spin fluctuations in the two-dimensional t-t'-U model

Magnetic properties of the two-dimensional t-t'-U model are investigated by studying the static spin magnetic susceptibility as a function of momentum for various temperatures. The calculations are performed by means of the Composite Operator Method in the static approximation. By increasing the value of the t' parameter the magnetic scattering in the reciprocal space evolves to an isotropic structure. It is shown that the results are in qualitative agreement with the experimental situation observed in LSCO and YBCO compounds.Comment: 3 pages, 6 Postscript figures, RevTeX, submitted to Phys. Lett.

Integration of the VIMOS Control System

The VIRMOS consortium of French and Italian Institutes (PI: O. Le Fevre, co-PI: G. Vettolani) is manufacturing two wide field imaging multi-object spectrographs for the European Southern Observatory Very Large Telescope (VLT), with emphasis on the ability to carry over spectroscopic surveys of large numbers of sources: the VIsible Multi-Object Spectrograph, VIMOS, and the Near InfraRed Multi-Object Spectrograph, NIRMOS. There are 52 motors to be controlled in parallel in the spectrograph, making VIMOS a complex machine to be handled. This paper will focus on the description of the control system, designed in the ESO VLT standard control concepts, and on some integration issues and problem solving strategies...

Boosting Deep Open World Recognition by Clustering

While convolutional neural networks have brought significant advances in robot vision, their ability is often limited to closed world scenarios, where the number of semantic concepts to be recognized is determined by the available training set. Since it is practically impossible to capture all possible semantic concepts present in the real world in a single training set, we need to break the closed world assumption, equipping our robot with the capability to act in an open world. To provide such ability, a robot vision system should be able to (i) identify whether an instance does not belong to the set of known categories (i.e. open set recognition), and (ii) extend its knowledge to learn new classes over time (i.e. incremental learning). In this work, we show how we can boost the performance of deep open world recognition algorithms by means of a new loss formulation enforcing a global to local clustering of class-specific features. In particular, a first loss term, i.e. global clustering, forces the network to map samples closer to the class centroid they belong to while the second one, local clustering, shapes the representation space in such a way that samples of the same class get closer in the representation space while pushing away neighbours belonging to other classes. Moreover, we propose a strategy to learn class-specific rejection thresholds, instead of heuristically estimating a single global threshold, as in previous works. Experiments on RGB-D Object and Core50 datasets show the effectiveness of our approach.Comment: IROS/RAL 202

Effect of concrete tensile strength in non linear analyses of 2D structures - a comparison between three commercial finite element softwares

Non-linear finite element method (FEM) allows to take into account material and geometrical non-linearities in the simulation of the behaviour of reinforced concrete structures. However, the accuracy of the numerical solution with respect to experimental tests is often questionable, especially in the case of 2D and 3D structures. Several competitions showed in the past significant scatter of the predicted results with respect to the correct ones. Even though internationally well-known computer softwares can be used to predict the structural response, the uncertainty of the numerical simulation cannot be neglected. Therefore, the application of finite element models to the assessment of concrete structures requires a proper investigation of the uncertainty related to the results of the simulations. This paper presents a comparison of numerical simulations of sixteen case studies taken from past experimental tests and modelled with three commercial non-linear softwares. The purpose of the investigation is to show how significant could be the difference between the experimental and numerically evaluated failure load and displacement in function of the code used and the variation of only one material parameter

On the Challenges of Open World Recognitionunder Shifting Visual Domains

Robotic visual systems operating in the wild must act in unconstrained scenarios, under different environmental conditions while facing a variety of semantic concepts, including unknown ones. To this end, recent works tried to empower visual object recognition methods with the capability to i) detect unseen concepts and ii) extended their knowledge over time, as images of new semantic classes arrive. This setting, called Open World Recognition (OWR), has the goal to produce systems capable of breaking the semantic limits present in the initial training set. However, this training set imposes to the system not only its own semantic limits, but also environmental ones, due to its bias toward certain acquisition conditions that do not necessarily reflect the high variability of the real-world. This discrepancy between training and test distribution is called domain-shift. This work investigates whether OWR algorithms are effective under domain-shift, presenting the first benchmark setup for assessing fairly the performances of OWR algorithms, with and without domain-shift. We then use this benchmark to conduct analyses in various scenarios, showing how existing OWR algorithms indeed suffer a severe performance degradation when train and test distributions differ. Our analysis shows that this degradation is only slightly mitigated by coupling OWR with domain generalization techniques, indicating that the mere plug-and-play of existing algorithms is not enough to recognize new and unknown categories in unseen domains. Our results clearly point toward open issues and future research directions, that need to be investigated for building robot visual systems able to function reliably under these challenging yet very real conditions. Code available at https://github.com/DarioFontanel/OWR-VisualDomainsComment: RAL/ICRA 202

Comparison between non-linear numerical models for R.C. shear walls under cyclic loading

The non-linear behaviour of concrete structures is the result of a series of phenomena, as material non-linear constitutive law and cracking process. As a consequence, in order to understand the behaviour of reinforced concrete members from elastic field to ul-timate condition, is necessary to use instruments able to simulate the material damaging evolution under growing loads. Commer-cial non-linear finite elements codes are generally able to simulate concrete behaviour with good approximation when a progressive incremental load is applied. However, the same result could not be reached under a cyclic loading. In this work two commercial non-linear finite element codes have been considered in order to assess the skill of these codes to simulate non-linear concrete be-haviour under cyclic loading. The results of six laboratory tests on shear walls have been compared with the ones obtained by means of numerical models and some conclusions on the numerical predictions are presented. / Il comportamento non lineare delle strutture realizzate in calcestruzzo è il risultato di una serie di fenomeni, come la non linearità della legge costitutiva del materiale ed il processo di fessurazione. Al fine di comprendere il comportamento degli elementi struttura-li in calcestruzzo armato è necessario disporre di strumenti in grado di simulare il progressivo danneggiamento del materiale in pre-senza di carichi crescenti. In generale, i codici di calcolo presenti in commercio sono in grado di cogliere abbastanza bene il compor-tamento delle strutture in cemento armato soggette a carichi monotoni crescenti. Risulta invece più complesso seguire il compor-tamento strutturale in presenza di un carico ciclico. In questo lavoro sono stati considerati due diversi codici di calcolo non lineare agli elementi finiti al fine di verificare la loro capacità nel simulare il comportamento di pareti a taglio soggette a un carico ciclico. Sono stati considerati i risultati di sei prove di laboratorio disponibili in letteratura; tali risultati sono stati confrontati con quelli otte-nuti numericamente per trarre delle conclusioni sull’affidabilità dei modelli numerici

The VST Telescope Control Software in the ESO VLT Environment

The VST (VLT Survey Telescope) is a 2.6 m Alt-Az telescope to be installed at Mount Paranal in Chile, in the European Southern Observatory (ESO) site. The VST is a wide-field imaging facility planned to supply databases for the ESO Very Large Telescope (VLT) science and carry out stand-alone observations in the UV to I spectral range. This paper will focus mainly on control software aspects, describing the VST software architecture in the context of the whole ESO VLT control concept. The general architecture and the main components of the control software will be described...