Search results for "Nonlinear"

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…

CFD Predictions of Sufficient Suspension Conditions in Solid-Liquid Agitated Tanks

2012

Abstract Most research efforts on mechanically agitated solid-liquid contactors have been devoted to the assessment of the minimum impeller speed for complete off-bottom suspension, N js . Actually, many industrial vessels are operated at impeller speeds slightly lower than N js (Oldshue, 1983; Rieger et al., 1988). This suggests that the sufficient suspension condition, which is quantitatively specified in this paper by introducing a suitably defined quantity N ss , may represent a valid alternative to that of complete suspension. In the present work time-dependent RANS simulations were carried out with the aim of predicting the achievement of sufficient suspension conditions. The Eulerian…

INVERTER-BASED DISTRIBUTED GENERATORS, MODELING AND CONTROL

In the last few years, electrical power generation is moving from a centralized generation towards distributed generation including on-site Renewable Energy Sources (RESs). In order to overcome RES related issues, as intermittent and fluctuating power, storage elements are included in the on-site generation system. The interaction between distributed generator (DG) units including RES, storage and front-end power converters should be carefully modeled in order to analyze the power system stability. An accurate modeling of DGs is required. In this thesis, a new modeling approach has been proposed for the inverter-based DGs based on the concept of electrostatic synchronous machines. Detailed …

Backward second-harmonic generation of near infrared picosecond pulses

2014

We report on backward second-harmonic generation using picosecond laser pulses in congruent lithium niobate with 3.2 µm periodic poling. By tuning both the pump wavelength and the sample temperature, we observed three resonant peaks in the range 1530-1730 nm, corresponding to 16th, 17th and 18th quasi-phase-matching orders, respectively. A maximum conversion efficiency of 0.475% was achieved at the 16th order with a 10 kW peak pump power. The latter is the highest conversion reported in bulk to date, for the backward configuration, with an improvement greater than 50% with respect to those previously achieved with nanosecond pulses for the same order of resonance.

Wideband THz time domain spectroscopy set-up based on ultrafast pulsed laser: model and experiments

2014

We present an analytical model describing the full electromagnetic propagation in a THz Time Domain Spectroscopy (THz-TDS) laser based system. We pay particular attention to the modelling of the time-frequency behavior of all the stages, which compose our experimental set-up. In particular, our model takes into account the following features: pump beam focusing into the generation crystal; phase-matching between pump and THz pulses inside both the generation and detection crystals; chromatic dispersion and absorption inside the materials; Fabry-Perot effect in both the crystals; diffraction along the propagation, focalization and overlapping between THz and probe beams; Electro-Optic Sampli…

Backward Frequency Doubling in Periodically Poled Lithium Niobate in the Pulsed Regime

2011

Normalised compression distance and evolutionary distance of genomic sequences: comparison of clustering results

2009

Genomic sequences are usually compared using evolutionary distance, a procedure that implies the alignment of the sequences. Alignment of long sequences is a time consuming procedure and the obtained dissimilarity results is not a metric. Recently, the normalised compression distance was introduced as a method to calculate the distance between two generic digital objects and it seems a suitable way to compare genomic strings. In this paper, the clustering and the non-linear mapping obtained using the evolutionary distance and the compression distance are compared, in order to understand if the two distances sets are similar.

Assessment of Cardiorespiratory Interactions During Spontaneous and Controlled Breathing: Non-linear Model-free Analysis

2022

In this work, nonlinear model-free methods for bivariate time series analysis have been applied to study cardiorespiratory interactions. Specifically, entropy-based (i.e. Transfer Entropy and Cross Entropy) and Convergent Cross Mapping asymmetric coupling measures have been computed on heart rate and breathing time series extracted from electrocardiographic (ECG) and respiratory signals acquired on 19 young healthy subjects during an experimental protocol including spontaneous and controlled breathing conditions. Results evidence a bidirectional nature of cardiorespiratory interactions, and highlight clear similarities and differences among the three considered measures.

First and second critical exponents for an inhomogeneous Schrödinger equation with combined nonlinearities

2022

AbstractWe study the large-time behavior of solutions for the inhomogeneous nonlinear Schrödinger equation $$\begin{aligned} iu_t+\Delta u=\lambda |u|^p+\mu |\nabla u|^q+w(x),\quad t>0,\, x\in {\mathbb {R}}^N, \end{aligned}$$ i u t + Δ u = λ | u | p + μ | ∇ u | q + w ( x ) , t > 0 , x ∈ R N , where $$N\ge 1$$ N ≥ 1 , $$p,q>1$$ p , q > 1 , $$\lambda ,\mu \in {\mathbb {C}}$$ λ , μ ∈ C , $$\lambda \ne 0$$ λ ≠ 0 , and $$u(0,\cdot ), w\in L^1_{\mathrm{loc}}({\mathbb {R}}^N,{\mathbb {C}})$$ u ( 0 , · ) , w ∈ L loc 1 ( R N , C ) . We consider both the cases where $$\mu =0$$ μ = 0 and $$\mu \ne 0$$ μ ≠ 0 , respectively. We establish existence/nonexistence of global weak solutions. In ea…

Multiple solutions with sign information for a (p,2)-equation with combined nonlinearities

2020

We consider a parametric nonlinear Dirichlet problem driven by the sum of a p-Laplacian and of a Laplacian (a (p,2)-equation) and with a reaction which has the competing effects of two distinct nonlinearities. A parametric term which is (p−1)-superlinear (convex term) and a perturbation which is (p−1)-sublinear (concave term). First we show that for all small values of the parameter the problem has at least five nontrivial smooth solutions, all with sign information. Then by strengthening the regularity of the two nonlinearities we produce two more nodal solutions, for a total of seven nontrivial smooth solutions all with sign informations. Our proofs use critical point theory, critical gro…