A globally stable discrete-time controller for current-fed induction motors

In this short paper we present a discrete-time field oriented controller (FOC) for current-fed induction motors which insures global asymptotic speed regulation as well as rotor flux norm tracking. To the best of our knowledge, this is the first time such a result is rigorously established for a controller implemented in discrete-time. To insure global stability a condition on the reference for the rotor flux norm, which is time-varying, is imposed. This condition disappears as the sampling period goes to zero, hence allowing for independent speed regulation and rotor flux norm tracking. One important feature of our scheme is that, compared with the first-difference approximation of the classical indirect FOC, the additional computational burden is negligible. It is also shown that the result can easily be extended to the case of tracking time-varying references in speed or position.     

Rheology of foamed cement

Foams are being used in a number of petroleum industry applications that exploit their high viscosity and low density. Foamed cement slurries can have superior displacement properties relative to non-foamed cement slurries. This article presents results of an experimental study of foamed cement rheology. Viscosity curves of foamed cements were obtained using a flow-through rotational viscometer. Foamed cements with different foam qualities were generated under different pressures using a foam generator/viscometer apparatus. The foam qualities during the tests ranged from 0% to 30%, and the shear rate varied between 5 s^− 1 and 600 s^− 1. Experimental results indicate that: i) unlike conventional aqueous foams, low-quality cement foams have a lower viscosity than the base fluid; ii) as the cement foam quality (gas volumetric fraction) increases from 10% to 30%, the viscosity also increases; and iii) the viscosity of low-quality cement foam slightly increases after depressurization or expansion.     

Cytotoxic activity and mechanism of action of 5-Aza-2'-deoxycytidine in human CML cells

We investigated the cytotoxic activity and some aspects of the mode of action of 5-aza-2'-deoxycytidine (Aza-dC) in 21 primary cultures of leukemic cells freshly obtained from patients with chronic myeloid leukemia (CML) in blast crisis. The cytotoxic potency of Aza-dC was comparable or even greater than that of 1-beta-D-arabinofuranosylcytosine (Ara-C) in most cases, suggesting that this drug has potential in the therapy of blast crisis of CML. Drug incorporation into DNA was evaluated by exposing leukemic cells simultaneously to 3H-Aza-dC at the concentration of 0.1 micrograms/ml and 14C-thymidine (TdR) used as internal standard. Incorporation of Aza-dC into DNA was detectable in all cases. In 17 samples we evaluated the DNA integrity of leukemic cells exposed to Aza-dC using alkaline elution techniques. The drug caused a detectable amount of DNA alkali labile sites (ALS). DNA-ALS increased in cells exposed to Aza-dC concentrations from 0.1 to 1 microgram/ml but did not further increase at 10 micrograms/ml. A plateau in the levels of DNA-ALS was also seen in human K562 cells exposed to increasing concentrations of Aza-dC from 5 to 10 micrograms/ml, whereas in these cells Aza-dC incorporation into DNA increased with increasing Aza-dC concentrations. Therefore, DNA-ALS caused by Aza-dC are not simply the result of the chemical decomposition of azacytosine molecules incorporated into DNA, but are presumably the result of a saturable DNA repair mechanism (e.g., glycosylases) leading to formation of the apyrimidinic sites.     

Short-term treatment with a low dose of inhaled fluticasone propionate decreases the number of CD1a+ dendritic cells in asthmatic airways

The activation of T-lymphocytes through the recognition of specific allergens is a crucial event in the development of allergic inflammation. Dendritic cells (DC) are potent accessory cells that play an important role in initiating bronchial immune responses by activation of T-lymphocytes. We investigated the distribution of CD1a+ DC in the bronchial biopsies from asthmatic patients, and evaluated the effects of a short course of low dose inhaled fluticasone propionate treatment. Twenty-three mild to moderate stable asthmatic patients and eight normal subjects were included in the study. Bronchoscopy with bronchial biopsies were performed in each subject. Eighteen of the 23 asthmatics underwent a second bronchoscopy after 6 weeks of low dose inhaled fluticasone propionate treatment (250 mcg bd) in a placebo-controlled double-blind study. Biopsies were embedded into glycolmethacrylate resin and analysed by immunohistochemistry methods using specific monoclonal antibodies against CD1a, which is a widely recognized marker for DC. In asthmatics, CD1a+ DC number was significantly higher in bronchial epithelium (P < 0.001) and in lamina propria (P < 0.001) when compared with normal controls. In addition, we observed that a short course of low dose inhaled fluticasone propionate treatment decreased the number of CD1a+ DC in both the bronchial epithelium (P < 0.05) and lamina propria (P < 0.01). The increased number of CD1a+ DC support the hypothesis that DC play an important role in the modulation of the immune response in chronic asthma. Short-term low dose fluticasone propionate treatment induces down-regulation of the CD1a+ DC number.     

In vitro and in vivo evaluation of silicated hydroxyapatite and impact of insulin adsorption

This study evaluates the biological behaviour, in vitro and in vivo, of silicated hydroxyapatite with and without insulin adsorbed on the material surface. Insulin was successfully adsorbed on hydroxyapatite and silicated hydroxyapatite bioceramics. The modification of the protein secondary structure after the adsorption was investigated by means of infrared and circular dichroism spectroscopic methods. Both results were in agreement and indicated that the adsorption process was likely to change the secondary structure of the insulin from a majority of α-helix to a β-sheet form. The biocompatibility of both materials, with and without adsorbed insulin on their surface, was demonstrated in vitro by indirect and direct assays. A good viability of the cells was found and no proliferation effect was observed regardless of the material composition and of the presence or absence of insulin. Dense granules of each material were implanted subcutaneously in mice for 1, 3 and 9 weeks. At 9 weeks of implantation, a higher inflammatory response was observed for silicated hydroxyapatite than for pure hydroxyapatite but no significant effect of adsorbed insulin was detected. Though the presence of silicon in hydroxyapatite did not improve the biological behaviour, the silicon substituted hydroxyapatite remained highly viable.     

Processing, physico-chemical characterisation and in vitro evaluation of silicon containing β-tricalcium phosphate ceramics

For bone grafting applications, the elaboration of silicon containing beta-tricalcium phosphate (β-TCP) was studied. The synthesis was performed using a wet precipitation method according to the hypothetical theoretical formula Ca_3 − x(PO₄)_2 − 2x(SiO₄)_x. Two silicon loaded materials (0.46 wt.% and 0.95 wt.%) were investigated and compared to a pure β-TCP. The maturation time of the synthesis required in order to obtain β-TCP decreased with the amount of silicon. Only restrictive synthesis conditions allow preparing silicon containing β-TCP with controlled composition. To obtain dense ceramics, the sintering behaviour of the powders was evaluated. The addition of silicon slowed the densification process and decreased the grain size of the dense ceramics. Rietveld refinement may indicate a partial incorporation of silicon in the β-TCP lattice. X-ray photoelectron spectroscopy and transmission electron microscopy analyses revealed that the remaining silicon formed amorphous clusters of silicon rich phase. The in vitro biological behaviour was investigated with MC3T3-E1 osteoblast-like cells. After the addition of silicon, the ceramics remained cytocompatible, highlighting the high potential of silicon containing β-TCP as optimised bone graft material.     

Application of powder coatings: Viscosity and density measurements in a conventional fluidized bed

The values of dynamic viscosity characteristic of the different stages in a fluidized bed were determined using a torsional viscometer (Dragge Eppretch Rheometer type STVK) with a specially designed cup. Experiments were made with three kinds of rotor: a full paddle, a cylinder and a split paddle. Apparent densities have been determined by measuring differential pressures across known heights in an experimental fluidized bed. A modified Matheson equation has been developed to determine the values of maximum bed density and minimum bed porosity, associated with the inset of fluidization. The experimental determinations were made with a white powder coating in which the granulometric distribution and composition were previously established.     

Occurrence and fate of emerging wastewater contaminants in Western Balkan Region

This paper reports on a comprehensive reconnaissance of over seventy individual wastewater contaminants in the region of Western Balkan (WB; Bosnia and Herzegovina, Croatia and Serbia), including some prominent classes of emerging contaminants such as pharmaceuticals and personal care products, surfactants and their degradation products, plasticizers, pesticides, insect repellents, and flame retardants. All determinations were carried out using a multiresidue analytical approach, based on the application of gas chromatographic and liquid chromatographic techniques coupled to mass spectrometric detection. The results confirmed a widespread occurrence of the emerging contaminants in municipal wastewaters of the region. The most prominent contaminant classes, determined in municipal wastewaters, were those derived from aromatic surfactants, including linear alkylbenzene sulphonates (LAS) and alkylphenol polyethoxylates (APEO), with the concentrations in raw wastewater reaching into the mg/l range. All other contaminants were present in much lower concentrations, rarely exceeding few microg/l. The most abundant individual compounds belonged to several classes of pharmaceuticals (antimicrobials, analgesics and antiinflammatories, beta-blockers and lipid regulators) and personal care products (fragrances). Due to the rather poor wastewater management practices in WB countries, with less than 5% of all wastewaters being biologically treated, most of the contaminants present in wastewaters reach ambient waters and may represent a significant environmental concern.