Model-driven engineering for mobile robotic systems: a systematic mapping study

Software and Systems Modeling - Mobile robots operate in various environments (e.g. aquatic, aerial, or terrestrial), they come in many diverse shapes and they are increasingly becoming parts of...     

Global adaptive output feedback controllers with application to non‐linear friction compensation

In this paper, we consider a class of non‐linear systems in which a set of constant parameters is unknown and some state variables are not available for measurement. For such systems we provide a constructive procedure for the solution of the global adaptive tracking problem with dynamic partial state feedback. We illustrate an application of the control strategy to the adaptive non‐linear friction compensation of a DC motor servomechanism. We improve previous results in tow directions: we allow for a subset of the unmeasurable states to enter in a system non‐linearly; we consider systems which are linearly parametrized with respect to a set of unknown constant parameters. Copyright © 2002 John Wiley & Sons, Ltd.     

Comparison between TRH-stimulated TSH and basal TSH measurement by a commercial immunoradiometric assay in the management of thyroid disease

In order to assess the current diagnostic role of the TRH test following the introduction of more sensitive "second generation" TSH assays, we studied a series of 259 outpatients, 237 women and 22 men, mean age 44.7 years (range 12-82), 91 of whom (35%) with untreated simple goiter, 133 (51%) with simple nodular goiter on steady state I-thyroxine treatment, 18 (7%) with overt or subclinical hyperthyroidism and 17 (7%) with overt or subclinical hypothyroidism, compared to a control group of 26 euthyroid healthy subjects. Serum TSH was measured by a commercial immunoradiometric assay (clinical sensitivity 0.1 microU/ml). TSH response to TRH was evaluated 30 minutes after giving 200 micrograms TRH i.v. bolus, the results being analyzed both as absolute increase (delta-TSH=stimulated TSH minus basal TSH) and as relative increase (R-TSH stimulated TSH/basal TSH). Using cut-off values of 0.3-3.2 microU/ml, basal TSH measurement was able to detect hypothyroidism (specificity = 100%) and to exclude hyperthyroidism (sensivity = 96.9%), but failed to accurately prove hyperthyroidism (specificity = 93.4%) and, above all, to exclude hypothyroidism (sensitivity = 35.3%) in our ambulatory patients. The delta-TSH values showed a basal TSH dependent linear increase (r = + 0.87, p < 0.001) both including only patients (n = 139) with basal TSH level in the euthyroidism range and including all patients (n = 223) having TSH responsive to TRH. All the patients with detectable basal TSH level displayed detectable TSH response to TRH, as did 19 (= 23.5%) of 81 patients with undetectable (< 0.1 microU/ml) basal value. In particular: a) for subnormal but detectable basal TSH ranging between 0.1 and 0.2 microU/ml, TSH was always hyporesponsive (delta-TSH < or = 2.5 microU/ml), while between 0.2 and 0.3 microU/ml TSH was hyporesponsive in 72.2% and normoresponsive (delta-TSH > 2.5 and < or = 11.9 microU/ml) in the remaining 27.8%; b) for basal TSH values within the normal range (0.3-3.2 microU/ml). TSH was hyporesponsive in 13.7%, normoresponsive in 74.8% and hyperresponsive in 11.5%; c) for high basal TSH values TSH was always hyperresponsive. The analysis of R TSH showed relatively constant values in the range of euthyroidism and hypothyroidism (m +/- SD: 7.4 +/- 2.3 and 7.7 +/- 3.1, respectively), and a marked differentiation of hyperthyroid patients whose R-TSH values were significantly lower (4.2 +/- 3.4) but had a wide individual variability. Linear regression analysis of basal or stimulated TSH and circulating thyroid hormones showed a close negative relationship, being highly significant between delta-TSH and T4 (r = 0.57, p < 0.001) and delta-TSH and FT4 (r = 0.46, p < 0.001). In conclusion, after the introduction of current second generation TSH immunoradiometric assay, the diagnostic role of the TRH test is greatly limited but not to be excluded: it can provide additional information to that obtained with simple basal TSH measurement in the diagnosis of subclinical hypothyroidism and in the precise evaluation of the degree of TSH suppression in patients with a subnormal basal TSH, either for endogenous thyrotoxicosis or I.-thyroxine treatment.     

Markov Jump Linear Systems with switching transition rates: Mean square stability with dwell-time

The stability of a class of Markov Jump Linear Systems characterized by piecewise-constant transition rates and system dynamics is investigated. For these Switching Markov Jump Linear Systems, mean square stability is analyzed through the time evolution of the second-order moment of the state. The main result is a sufficient condition that guarantees mean square stability under constraints on the dwell-time between switching instants. An alternative condition based on Kronecker calculus is worked out. It is shown that both the stability criteria admit an LMI implementation.     

EEG signal preprocessing for biometric recognition

Electroencephalography (EEG) has been recently investigated as a biometric modality for automatic people recognition purposes. Several studies have shown that brain signals possess subject-specific traits that allow distinguishing people. Nonetheless, extracting discriminative characteristics from EEG recordings may be a challenging task, due to the significant presence of artifacts in the acquired data. In order to cope with such issue, in this paper we evaluate the effectiveness of some preprocessing techniques in automatically removing undesired EEG contributions, with the aim of improving the achievable recognition rates. Specifically, methods based on blind source separation and sample entropy estimation are here investigated. An extensive set of experimental tests, performed over a large database comprising recordings taken from 50 healthy subjects during three distinct sessions spanning a period of about one month, in both eyes-closed and eyes-open conditions, is carried out to analyze the performance of the proposed approaches.     

An adaptive learning regulator for uncertain minimum phase systems with undermodeled unknown exosystems

The design of an adaptive learning regulator is addressed for uncertain minimum phase linear systems (with known bounds, known upper bound on system order, known relative degree, known high frequency gain sign) and for unknown exosystems (with unknown order, uncertain frequencies). On the basis of a known bound on system uncertainties and a known bound on the modeled exosystem frequencies, a new adaptive output error feedback control algorithm is proposed which guarantees exponential convergence of both the output and the control input errors into residual bounds which decrease as the exosystem modeling error decreases. Exponential convergence of both errors to zero is obtained when the regulator exactly models all exosystem excited frequencies, while asymptotic convergence of both errors to zero is achieved when the actual exosystem is overmodeled by the regulator. The new algorithm generalizes existing learning controllers since, in the case of periodic references and/or disturbances, the knowledge of the period is not required.     

Algebraic Riccati equation and J-spectral factorization for estimation

In this paper we investigate on the existence of the stabilizing solution of the algebraic Riccati equation (ARE) related to the filtering problem with a prescribed attenuation level γ. It is well known that such a solution exists and is positive definite for γ larger than a certain γ_F and it does not exist for γ smaller than a certain γ₀. We consider the intermediate case γ(γ₀,γ_F] and show that in this interval the stabilizing solution does exist, except for a finite number of values of γ. We show how the solution of the ARE may be employed to obtain a minimum-phase J-spectral factor of the J-spectrum associated with the filtering problem.     

The most dangerous flaw orientation in brittle materials and structures

In the present paper a sheet of material is considered. It is loaded by uniaxial tensile stress and contains a random distribution of flaw orientations, with the flaws thought of as flat pre-cracks of comparable length, and with all crack planes being oriented perpendicular to the faces of the sheet. Intuition suggests that the most likely flaw to initiate fracture, which will be termed the “most dangerous defect”, lies orthogonally to the major load axis. The purpose of the present paper is to show that such an assumption is incorrect. Neither the most dangerous defect nor the first increments of crack growth will be oriented perpendicularly to the stress direction (nor will they be co-planar with the orientation of the most critical flaw).     

A Structure-Properties Relationship Study of Self-Healing Materials Based on Styrene and Furfuryl Methacrylate Cross-Linked via Diels–Alder Chemistry

A series of copolymers of styrene and furfuryl methacrylate characterized by various molecular structures (linear and star, block and random) is synthesized via atom transfer radical polymerization, and cross-linked with a bismaleimide by means of thermally reversible Diels–Alder (DA) reaction, to obtain self-healing materials. The prepared materials are studied in terms of gelation, swelling, thermal, and dynamic-mechanical analysis, with the aim of correlating relevant properties to their chemical structure. It is found that the furan/styrene ratio, as well as the molecular architecture, have a major influence on the properties. It is also found that the reversibility of the DA reaction is not complete in the solid state for materials with high cross-linking density. This study provides some important tools for the design of materials characterized by thermally reversible behavior, which find usually application as self-healing thermosets, coatings, or adhesives.     

Expanding the application field of post‐consumer poly(ethylene terephthalate) through structural modification by reactive blending

With the aim of up‐grading the material properties of post‐consumer PET, making them suitable for extrusion of thermoformable thick sheets, a series of polyepoxy chain extenders have been comparatively evaluated as melt viscosity modifiers for a toughened compatibilized blend containing up to 80 wt % of bottle‐grade post‐consumer recycled poly(ethylene terephtalate) (r‐PET). Combinations of a commercial modifier with pentaerythritol were also successfully employed to cause simultaneous hyperbranching and controlled chain scission, thereby modifying the melt rheology of the material without excessively increasing the molecular weight, as highlighted by common technological melt viscosity measurements such as online torque and off‐line melt flow rate (MFR). Since the high melt fluidity of PET plays a critical role on its flame resistance, the combined effect of chain extenders and halogen‐free phosphorated additives on the fire resistance of the modified toughened blends was also investigated. Preliminary results indicate that the chemical reactions among polymer and additives must be taken into careful account to prevent unfavorable effects on the ultimate melt rheology and mechanical properties. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40881.