Linear parameter varying control design for rotating systems supported by journal bearings

Linear parameter varying (LPV) control is a model-based control technique that takes into account time-varying parameters of the plant. In the case of rotating systems supported by lubricated bearings, the dynamic characteristics of the bearings change in time as a function of the rotating speed. Hence, LPV control can tackle the problem of run-up and run-down operational conditions when dynamic characteristics of the rotating system change significantly in time due to the bearings and high vibration levels occur. In this work, the LPV control design for a flexible shaft supported by plain journal bearings is presented. The model used in the LPV control design is updated from unbalance response experimental results and dynamic coefficients for the entire range of rotating speeds are obtained by numerical optimization. Experimental implementation of the designed LPV control resulted in strong reduction of vibration amplitudes when crossing the critical speed, without affecting system behavior in sub- or super-critical speeds.     

Evidences of macromolecular chains confinement of ethylene–propylene copolymer in organophilic montmorillonite nanocomposites

A random ethylene–propylene copolymer (EPM) functionalized with grafted diethylsuccinate groups was melt blended with increasing amount (to 20 wt%) of organophilic montmorillonite (OMMT) to prepare nanocomposites with different morphologies as evidenced by XRD and TEM analysis. All the nanocomposites were treated with boiling toluene that did not extract a significant amount of EPM. The increase of not-extracted EPM with the increasing quantity of OMMT suggested strong interactions of the polymer chains with the inorganic substrate. The DSC measurements of nanocomposites and the corresponding insoluble residues revealed a higher T_g values with larger amount of inorganic particles. The dielectric relaxation analysis confirmed the evidence of strong interactions among montmorillonite and the polar diethylsuccinate groups for the macromolecules trapped due to the presence of the inorganic layers. The results were discussed with reference to their relevance as an evidence of nanoconfinement at polymer clay interface and correlated with the clay basal distance variation due to the intercalation process.     

Identification,Cloning and Biochemical Characterization of Pseudomonas putida A (ATCC 12633) Monooxygenase Enzyme necessary for the Metabolism of Tetradecyltrimethylammonium Bromide

This study presents the first report of the purification and characterization of a monooxygenase enzyme from Pseudomonas putida A (ATCC 12633) that is responsible for the oxidation of physiologically relevant quaternary ammonium compounds, the tetradecyltrimethylammonium bromide. The degradation of tetradecyltrimethylammonium bromide by P. putida A (ATCC 12633) is initiated by N-dealkylation and catalysed by tetradecyltrimethylammonium monooxygenase (TTABMO), resulting in the formation of tetradecylalkanal and trimethylamine. Based on sequence analysis, the gene for TTABMO (ttbmo) corresponded to an ORF named PP2033 in the genome of P. putida KT2440. Mutation in ttabmo blocked the utilization of tetradecyltrimethylammonium bromide by Pseudomonas putida A (ATCC 12633) as carbon and nitrogen sources. The enzyme can be highly overexpressed in P. putida Δttabmo-T7 in active form and purified as a hexahistidine fusion protein. Like the native enzyme, the his-TTABMO was found to be a monomer with molecular mass of 40 kDa, the isoelectric point 7.3, that catalyses the breakdown of tetradecyltrimethylammonium bromide and utilized NADPH and FAD as cofactor. The biochemical properties and the analysis of the respective protein sequence revealed that TTABMO represents a typical flavoprotein monooxygenase, which is member of a flavoprotein family that is distinct from Baeyer–Villiger monooxygenases.     

Interdependence of primary and Johari-Goldstein secondary relaxations in glass-forming systems

We report evidence from broadband dielectric spectroscopy that the dynamics of the primary alpha- and secondary Johari-Goldstein (JG) beta-processes are strongly correlated in different glass-forming systems over a wide temperature T and pressure P range, in contrast with the widespread opinion of statistical independence of these processes. The alpha-beta mutual dependence is quantitatively confirmed by (a) the overall superposition of spectra measured at different T-P combinations but with an invariant alpha-relaxation time; (b) the contemporary scaling of the isothermal-pressure and isobaric-temperature dependences of the alpha-and beta-relaxation times as plotted versus the reduced variable Tg(P)/T where Tg is the glass transition temperature. These novel and model-independent evidences indicate the relevance of the JG relaxation phenomenon in glass transition, often overlooked by most current theories.     

The pressure broadening and shift for the J=1−0 line of CH3C14N: Resolved and overlapped hyperfine components

Summary Pressure broadening and shift parameters are measured for theJ=1−0 line of CH₃C¹⁴N at 18.4 GHz, both for the three hyperfine components and for the single line which envelopes the hyperfine components, observed at higher pressures (p≥40 mTorr). In agreement with theoretical predictions, these parameters are the same for all the observed lines: Γ _p = (50 ± 5) MHz/Torr,s=(7±2) MHz/Torr. These values are compared with previous measurements, showing a large variance expecially for the shift parameter. The measured broadening parameter is 40% lower than prediction of the Anderson theory.

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Riassunto Sono stati misurati i parametri di allargamento e spostamento per pressione della rigaJ=1−0 del CH₃C¹⁴N a 18.4 GHz. Tali misure sono state eseguite, sulle tre componenti iperfini e sul loro inviluppo osservato a pressionip≥40 mTorr. In accordo con le previsioni teoriche, questi parametri risultano gli stessi per tutte le righe osservate: Γ _p = (50 ± 5) MHz/Torr,s=(7±2) MHz/Torr. Questi valori sono confrontati con quelli delle precedenti misure che mostrano una considerevole dispersione, specialmente per quanto riguarda il parametro di spostamento. L'allargamento per pressione è risultato piú basso di quello previsto dalla teoria di Anderson di circa il 40%.

     

EPR Studies of Tl0.5Pb0.5Sr1.6Ba0.4CaCu2?xRuxO7?δ Superconductor

Bulk superconducting samples of type Tl_0.5Pb_0.5Sr_1.6Ba_0.4CaCu_2−x Ru _x O_7−δ, (Tl, Pb)/Sr-1212, with 0.0 ≤ x ≤ 0.525 were prepared by the conventional one-step solid-state reaction technique. The prepared samples were investigated using X-ray powder diffraction, electrical resistivity and electron paramagnetic resonance (EPR) measurements. Enhancement of the phase formation, superconducting transition temperature T _c and hole carriers concentration P was observed up to x = 0.075. For x > 0.075, a reverse trend was observed. EPR spectra were measured at different temperatures (120–290 K) for all prepared samples. The number of spins N participating in the resonance and the paramagnetic susceptibility χ were calculated as a function of both Ru-content and temperature. N and χ increased as the Ru-content increased. A linear relationship between logN and 1/T was established, from which the activation energy E _a was calculated as a function of the Ru-content. The temperature dependence of χ was fitted according to Curie–Weiss type of magnetic behavior. Curie constant C, Curie temperature θ, the effective magnetic moment μ and the electronic specific heat γ were estimated as a function of the Ru-content.     

Longitudinally detected electron spin resonance: Recent developments

Multiple-quantum spectroscopies are reviewed in the frame of electron paramagnetic resonance. Some properties of different nonlinear techniques are discussed for both transverse and longitudinal detection. The connections of effects recently presented with the procedure of longitudinal detection of electron paramagnetic resonance (LODESR) in presence of double transverse irradiation are stressed. Peculiarities of LODESR spectroscopy and its capabilities in facing problems related to relaxations in presence of very slow dynamic processes are evidentiated. Recent results show the vitality of the LODESR technique, that in the future could be applied to new fields, owing to experimental updating.     

Equivalent dissipation postulates in classical plasticity

Summary In classical plasticity dissipation postulates on cycles, such as those proposed by Drucker, Martin e Il'yushin, rule the evolution of elastic-plastic deformation processes. In this paper, within the framework of the infinitesimal theory of isotropic materials with elastic range of [7], each one of those three postulates is given an equivalent local formulation; moreover, they are shown to be all equivalent.

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Sommario In plasticitá classica l'evoluzione dei processi elasto-plastici é regolata da postulati di dissipazione su cicli quali quelli proposti da Drucker, Martin e Il'yushin. In questo lavoro, nell'ambito della teoria infinitesima dei materiali isotropi con dominio elastico proposta in [7], si fornisce una formulazione locale equivalent per ciascuno di quei tre postulati e si mostra che essi sono tutti tra loro equivalenti.