Search results for "Stability"

Speeding up the Consensus Clustering methodology for microarray data analysis

2010

Abstract Background The inference of the number of clusters in a dataset, a fundamental problem in Statistics, Data Analysis and Classification, is usually addressed via internal validation measures. The stated problem is quite difficult, in particular for microarrays, since the inferred prediction must be sensible enough to capture the inherent biological structure in a dataset, e.g., functionally related genes. Despite the rich literature present in that area, the identification of an internal validation measure that is both fast and precise has proved to be elusive. In order to partially fill this gap, we propose a speed-up of Consensus (Consensus Clustering), a methodology whose purpose…

ANALISI DELLE RISORSE FINANZIARIE NAZIONALI PER LA RIDUZIONE DEI CONSUMI ENERGETICI NELLE PUBBLICHE AMMINISTRAZIONI

2015

The compliance with the Italian Internal Stability Pact represents a relevant constraint for Public Administrations in their aims of improving the efficiency with which they use energy, despite several interesting financial tools have been released for helping these institutions in the imple mentation of effective actions. The available domestic financial tools are here shortly revised, particularly about their compatibility with the Stability Pact. The role of the socalled rotative founds is moreover described as a tool for supporting Public Administrations in improving their energy efficiency, even in the observance of the limits established by the Stability Pact.

Gli strumenti finanziari nazionali di supporto alla riduzione dei consumi energetici negli edifici delle pubbliche amministrazioni

2015

Public Administrations are currently constrained, in their aims of carrying out actions and projects for the limitation of the energy consumption of buildings, by the scarcity of adequate budgets and by the need of observing the Growth and Stability Pact. On the contrary, the availability of (and the access to) suitable financial sources would represent significant opportunities for an economic development characterized by energy and environmental sustainability. This paper, after a short review of the domestic financial tools actually available for the reduction of their energy consumption of municipalities, analyses the technical and economic barriers that limit their effective utilizatio…

Hysteretic whirl stabilization in rotor-shaft-bearing systems on dry friction suspension

2009

SUMMARY. The undesired whirl of rotating machines can be reduced by elastic journal box suspension systems equipped with dry friction dampers. The critical speeds can be cut off by the adhesion of the friction surfaces and the whirl amplitude can be restrained throughout the remaining sliding range by a proper choice of the suspension-to-shaft stiffness ratio and of the support-to-rotor mass ratio. The dry friction forces counteract also efficiently the well known destabilising effect of the shaft hysteresis in the supercritical range. This lecture deals firstly with the natural precession speeds, investigates the steady response to unbalance and defines the ranges of adhesive or sliding co…

ON THE WEIGHT DISPLACEMENT IN CURVE AND THE ROADABILITY OF A 4WS VEHICLE

2013

A simplified theory on the vehicle stability in curve is explained in this paper; it allows the calculation of the force on the wheels during the motion in curve, supposing unchanging the position of the rolling centre; moreover it does not take in account the turn of the wheels and the behaviour of the tires, so that the theory can be applied to 2WS and 4WS vehicles for vertical loads calculation. The virtual simulations of 2WS and 4WS vehicles are executed, extracting all the data interesting the vehicle stability; it needs the distinction between manoeuvrability and handling. The simulations of two different tests are executed: the elk test like manoeuvrability test and a similar one at …

Lemongrass Plant as Potential Sources of Reinforcement for Biocomposites: A Preliminary Experimental Comparison Between Leaf and Culm Fibers

2022

AbstractNowadays, the world requires more sustainable and eco-friendly materials to replace or limit the usage of synthetic materials. Moreover, several researchers focused their attention on the use of agricultural sources as reinforcement for biocomposites since they are abundant, cost-effective and environmentally favorable sources. In such a context, purpose of the present paper is the evaluation of lemongrass plant (Cymbopogon flexuosus) as possible source of natural reinforcement for biocomposites. To this aim, natural fibers were obtained from the leaf and the stem of lemongrass and their main properties were compared for the first time. To this scope, mechanical and thermal characte…

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…

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…

Control of a non-isothermal continuous stirred tank reactor by a feedback–feedforward structure using type-2 fuzzy logic controllers

2011

A control system that uses type-2 fuzzy logic controllers (FLC) is proposed for the control of a non-isothermal continuous stirred tank reactor (CSTR), where a first order irreversible reaction occurs and that is characterized by the presence of bifurcations. Bifurcations due to parameter variations can bring the reactor to instability or create new working conditions which although stable are unacceptable. An extensive analysis of the uncontrolled CSTR dynamics was carried out and used for the choice of the control configuration and the development of controllers. In addition to a feedback controller, the introduction of a feedforward control loop was required to maintain effective control…

Numerical simulation of electroconvection phenomena in electrodialysis

In water desalination by electrodialysis, the current density i cannot exceed specific constraints, notably the diffusion limit. Working at higher i (overlimiting current regime) would make higher desalination rates possible. The main phenomenon allowing overlimiting current densities is the electrokinetic instability that arises when a sufficiently intense electric potential gradient is imposed, and leads to electroconvective mixing in the near-wall layer. In this study, these phenomena were investigated by CFD. The governing equations were the Nernst-Planck transport equations for anions and cations, the Poisson equation for the electrical potential and the Navier-Stokes and continuity eq…