Output feedback stabilizability and passivity in nonstationary and nonlinear systems

Passivity properties and passivity conditions have been shown to be very important for the stability of various methodologies of control with uncertainty in linear‐time‐invariant (LTI) systems. Many publications have defined the conditions that allow LTI systems to become strictly passive (and their transfer function strictly positive real) via constant or dynamic output feedback. As beyond the usual uncertainty, real‐world systems are not necessarily invariant, this paper expands the applicability of previous results to nonstationary and nonlinear systems. The paper first reviews a few pole–zero dynamics definitions in nonstationary systems and relates them to stability and passivity of the systems. The paper then finds the sufficient conditions that allow nonstationary systems to become stable and strictly passive via static or dynamic output feedback. Applications in robotics and adaptive control are also presented. Copyright © 2009 John Wiley & Sons, Ltd.     

Prolonging Shelf-Life of Carp by Combined Ionising Radiation and Refrigeration

Experiments were performed using ionisating radiation in order to prolong the shelf-life of two groups of refrigerated fish ( Cyprinus carpio ). After irradiation fish were kept at 0–2°C. Non-irradiated fish reached the non-acceptability point in 16 days and irradiated fish reached that point in 31 days. No difference was found between shelf-life of whole or eviscerated fish. If fish were immediately cooled to 0°C after death, their shelf-life was prolonged considerably. From this study it is clear that chemical tests of freshness such as TVB-N and K value determination are not appropriate for the study of irradiated fish. Organoleptic estimations and a new determination using an odour concentration meter seem to fit best the objective determination of freshness.     

Aroused versus calm positive affects as predictors of lipids.

Objective: The authors hypothesized that high-pleasure low-arousal (HPLA) would predict a subsequent decrease of low-density lipoprotein cholesterol (LDL-C) and triglycerides (TRI), as well as a subsequent increase of high-density lipoprotein cholesterol (HDL-C). The authors also hypothesized that high-pleasure high-arousal (HPHA) would have the opposite effects on these blood lipids, predicting a subsequent increase of LDL-C and TRI, and a decrease of HDL-C. Design: Participants were 990 male and 595 female apparently healthy employees who underwent a routine periodic health examination at two points in time, Time 1 (T1) and Time 2 (T2), about 24 months apart. Data were analyzed separately for the men and women, and the authors controlled for possible confounders shown in past research to be implicated with hyperlipidemia. Main Outcome Measures: HPHA and HPLA were assessed based on the Job-Related Affective Well-Being Scale, while LDL-C, TRI, and HDL-C were assessed based on fasting blood samples. Results: For the men, support for our hypotheses was found relative to HDL-C and TRI. The authors did not find support for our hypotheses for thee women. Conclusion: Our findings suggest that for men, the two types of positive affects may have opposite physiological consequences with respect to subsequent changes in blood lipid levels. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Characterization of titanium coatings obtained by the cold plasma technique

Titanium coatings obtained by the RF cold plasma technique at a temperature of 550°C were characterized in order to create a model mechanism for the formation process. Scanning Electron Microscopy (SEM), X-ray diffraction, Transmission Electron Microscopy (TEM), Energy Dispersive Analysis of X-ray (EDAX) and Auger Electron Spectroscopy (AES) were employed to identify and to characterize the sputtered films. The coatings obtained were composed of titanium-copper intermetallic compounds. It is suggested that the intermetallic compounds are formed in a solid state reaction due to local energetic processes taking place in the plasma, in spite of the relatively low temperature of the substrate. According to the suggested model copper migrates outwards from the substrate, in an enhanced synergistic process, along the surfaces of the titanium deposited particles.     

Nitriding of AISI M2 tool steel in an inductive r.f. plasma

The nitriding of AISI M2 tool steel in an inductive r.f. plasma was investigated. The plasma was sustained with a 27.12 MHz generator in gas mixtures of N₂ and H₂ at a pressure of 10 mbar. The ion nitriding was performed at a net r.f. power of 400 W at substrate temperatures of 450–500 °C. X-ray diffraction studies of the treated samples revealed that the most efficient formation of nitride phases was observed in samples nitrided in a pure N₂ plasma. As a result of the ion nitriding the surface hardness was substantially increased from a Vickers hardness VHN of 290 kgf mm^-2 for untreated samples to a maximum VHN of 1200 kgf mm^-2 for samples treated in a plasma sustained in a gas mixture with N₂:H₂ = 1:1.     

Fourier transform infrared-attenuated total reflection nitrate determination of soil pastes using principal component regression, partial least squares, and cross-correlation

This paper investigates the use of Fourier transform infrared (FTIR) attenuated total reflectance (ATR) spectroscopy as a fast and simple way for direct determination of nitrate concentration in soil pastes, which would assist precision fertilizer placement and reduce nitrate pollution. Eight types of soils are investigated, with nitrate concentrations ranging from 0 to 1000 ppm-N. The spectral region around the nitrate band (1300-1550 cm(-1)) is analyzed by (1) principal component regression (PCR), (2) partial least squares (PLS), and (3) cross-correlation with reference libraries that include spectra of pure ions and/or soils. The main obstacle to accurate nitrate measurement appears to be an interfering band present in calcareous soils. This band, which may be due to carbonate, is located around 1450 cm(-1) and overlaps with the nitrate band centered around 1370 cm(-1). For non-calcareous soils, and in particular for light sandy agricultural soils, PLS and cross-correlation with a reference library containing only spectra of ions in water give similar results (about 8 ppm-N on dry soil basis), while PCR leads to slightly poorer results. When calcareous soils are included in the analysis, the prediction errors are about twice as large. In this case, the best results are obtained using PLS, followed by PCR, while cross-correlation with reference libraries leads to poorer results.     

Care and cleanliness of the environment in public places: a survey of Kibbutzim in Israel

It is argued that the problems of environmental pollution, and those of the inadequacy of formal social control mechanisms in contemporary societies are the unintended dysfunctional consequences of two separate but interrelated clusters of change processes. Consequently, solutions to the former require a thorough study of the latter in their relation to behaviour of individuals vis a vis the physical environment in public places.

A survey of all 332 kibbutzim in Israel, conducted in 1973, assessed the level of “active care” (i.e. landscaping, lawns, trees, etc.) and “cleanliness” (i.e. absence of litter, refuse, etc.) found in eleven different locations in each kibbutz. Although kibbutzim are generally considered rural settlements, the data showed a typically urban reliance on “the authorities” to take care of the appearance of public places. Further analysis indicated that at least three variables are systematically related to this normative pattern: residential instability, age of settlement, and population size. Other background variables considered and analyzed were not found to be statistically related to active care and cleanliness.     

Responses of freshwater prawn,Macrobrachium rosenbergii,to chemical attractants

Chemoreception in the adults of the freshwater prawnMacrobrachium rosenbergii was investigated under controlled laboratory conditions, using behavioral assays. Tests were carried out on groups, as well as on individuals, all at their intermolt stages of the molt cycle, and prestarved for three to four days. Of 28 different substances tested, the amino acids taurine, glycine, arginine, and betaine, as well as trimethylamine, elicited a positive behavioral response in at least 50% of the test animals when applied at a threshold concentration of 10^–5-10^–8 M. A positive response comprises enhanced antennular flicking and food search motion. Of the various nucleotides tested for chemoattraction, only adenosine monophosphate elicited a response similar to that of the above amino acids, although at a concentration of 10^–4 M, whereas adenosine diphosphate required a dosage of 10^–1 M.     

On the kinematics and kinetics of mechanical seals, rotors, and wobbling bodies

Mechanical seals, rotors, and wobbling bodies whirl about a point and are characterized by a kinematical constraint that prevents them from having integral motion with respect to the axis of whirl. A valid kinematical model is a prerequisite to subsequent dynamic analyses. Three previous works have suggested distinctly different kinematical models for the same problem. The analysis herein presents yet another kinematical model that preserves (actually enforces) the proper kinematical constraint. Interestingly, it is found that although no integral rotation is allowed about the axis of whirl, the wobbling body possesses a sustained nonzero angular velocity about that axis. The derivation is done for any finite nutation angle and only final results are being degenerated to small tilt angles. The outcome reaffirms the results of a previous work. For this time-invariant problem the notion of virtual velocity and virtual power emerges, and the equations of motion are derived using Lagrange’s equations to complement results obtained previously by Newton–Euler mechanics.     

Study of the Tribological Behavior of a Thrust Washer Bearing

This study addresses the mechanisms that distress a flat-faced thrust washer bearing system. This washer bearing system separates a helical gear and its carrier within a gearset. It was found that the bearing can experience distress by the combination of rotational speed, axial load, and the sequence and rate of their application. Distress is defined as a sudden rise in the real-time frictional torque and temperature.

The various tests suggest the presence of hydrodynamic effects at certain rotational speeds and axial load combinations marked by decreases in the calculated effective coefficient of friction with decreases in velocity. In the tested cases, a distinct increase in the coefficient of friction occurs at the instant of distress.