Search results for "Online"

Ac-locking of thermally-induced sine-Gordon breathers

2023

A complete framework for exciting and detecting thermally-induced, stabilized sine-Gordon breathers in ac-driven long Josephson junctions is developed. The formation of long-time stable breathers locked to the ac source occurs for a sufficiently high temperature. The latter emerges as a powerful control parameter, allowing for the remarkably stable localized modes to appear. Nonmonotonic behaviors of both the breather generation probability and the energy spatial correlations versus the thermal noise strength are found. The junction's resistive switching characteristics provides a clear experimental signature of the breather.

Nonlinear Response of RC Structures: Statistical Effects of Artificial Ground Motions

2020

The selection of seismic inputs for nonlinear dynamic analysis is widely debated, mainly focusing on the advantages and disadvantages provided by the choice of natural, simulated or artificial records. However, most of the available technical codes do not provide always the same suggestions and well-defined procedures for the generation of artificial ground motions. Considering that the strategy of the generation of accelerograms makes some doubts raise about the possible effect on the structural response, the work aims to investigate on the differences of the structural behavior by using accelerograms nominally equivalent but different in terms of stationarity. This paper presents a compar…

Influence of wall-to-floor connections and pounding on pre- and post-diction simulations of a masonry building aggregate tested on a shaking table

2023

AbstractThis paper presents numerical simulations within the frame of the project SERA—AIMS (Seismic Testing of Adjacent Interacting Masonry Structures). The study includes blind pre-diction and post-diction stages. The former was developed before performing the shaking table tests at the laboratory facilities of LNEC (Lisbon), while the latter was carried out once the test results were known. For both, three-dimensional finite element models were prepared following a macro-modelling approach. The structure consisted of a half-scaled masonry aggregate composed by two units with different floor levels. Material properties used for the pre-diction model were based on preliminary tests previou…

Numerical seismic performance of a rammed earth dwelling considering the use of a textile reinforced mortar system

Rammed earth buildings represent a considerable portion of the existing vernacular building stock of several countries and they are very common in the southern region of Portugal. The historical and architectural values of these constructions, along with their recognized high seismic vulnerability, have made the structural rehabilitation of earthen buildings a priority among the scientific community. Despite some recent studies, the prediction of the seismic response of these buildings is still a challenging task. This paper presents the results of a numerical investigation on the seismic behaviour of a representative rammed earth building located in Alentejo (South of Portugal). Numerical …

Variable Friction Dampers (VFD) for a modulated mitigation of the seismic response of framed structures: Characteristics and design criteria

2022

In this paper a new approach for the energy dissipation is discussed based on the use of Variable Friction Dampers (VFDs). The VFD device is borrowed from braking systems mechanical engineering, able to modulate its capability of dissipation, providing a constant pure friction force coupled with an additional (variable) damping force with the increasing of the displacement. Resorting to a previous study, the characteristics and the efficiency of the “braking” system in terms of reduction of the displacements and the restoring forces is described for SDOF systems under seismic excitations and compared with the performances achievable by classic constant friction dampers (CFDs). Then, a desig…

Analysis of Users Behaviour from a Movie Preferences Perspective

2018

Despite their tremendous popularity, Online Social Networks (OSNs) have several issues related to the privacy of social users. These issues have motivated researchers to develop OSN services that take advantage of the decentralized platforms (such as P2P systems or opportunistic networks). Decentralized Online Social Networks (DOSNs) need specific approaches to manage the decentralization of social data. In particular, data availability is one of the main issues and current proposals exploit properties of the social relationships to manage it. At the best of our knowledge, there are no proposals which exploit similarity between users, expressed with the term homophily. Homophily has been we…

Exploiting community detection to recommend privacy policies in decentralized online social networks

2018

The usage of Online Social Networks (OSNs) has become a daily activity for billions of people that share their contents and personal information with the other users. Regardless of the platform exploited to provide the OSNs’ services, these contents’ sharing could expose the OSNs’ users to a number of privacy risks if proper privacy-preserving mechanisms are not provided. Indeed, users must be able to define its own privacy policies that are exploited by the OSN to regulate access to the shared contents. To reduce such users’ privacy risks, we propose a Privacy Policies Recommended System (PPRS) that assists the users in defining their own privacy policies. Besides suggesting the most appro…

Adaptive type-2 fuzzy logic control of a bioreactor

2010

Two adaptive type-2 fuzzy logic controllers with minimum number of rules are developed and compared by simulation for control of a bioreactor in which aerobic alcoholic fermentation for the growth of Saccharomyces cerevisiae takes place. The bioreactor model is characterized by nonlinearity and parameter uncertainty. The first adaptive fuzzy controller is a type-2 fuzzy-neuro-predictive controller (T2FNPC) that combines the capability of type-2 fuzzy logic to handle uncertainties, with the ability of predictive control to predict future plant performance making use of a neural network model of the nonlinear system. The second adaptive fuzzy controller is instead a self-tuning type-2 PI cont…

Nonlinear fuzzy control of a fed-batch reactor for penicillin production

2012

Abstract The process of penicillin production is characterized by nonlinearities and parameter uncertainties that make it difficult to control. In the paper the development and testing of a multivariable fuzzy control system that makes use of type-2 fuzzy sets for the control of pH and temperature are described. The performance of the type-2 fuzzy logic control system (T2FLCS) is compared by simulation with that of a type-1 fuzzy logic control system (T1FLCS) and that of a control system with traditional proportional-integral-derivative (PID) controllers proposed in the literature. The fuzzy controllers are optimized using an ANFIS algorithm. The best results are obtained with the T2FLCS pa…

Control of a nonlinear continuous bioreactor with bifurcation by a type-2 fuzzy logic controller

2008

The object of this paper is the application of a type-2 fuzzy logic controller to a nonlinear system that presents bifurcations. A bifurcation can cause instability in the system or can create new working conditions which, although stable, are unacceptable. The only practical solution for an efficient control is the use of high performance controllers that take into account the uncertainties of the process. A type-2 fuzzy logic controller is tested by simulation on a nonlinear bioreactor system that is characterized by a transcritical bifurcation. Simulation results show the validity of the proposed controllers in preventing the system from reaching bifurcation and instable or undesirable s…