Improving the functional properties of (K0.5Na0.5)NbO3 piezoceramics by acceptor doping

ZrO2 and TiO2 modified lead-free (K0.5Na0.5)NbO3 (KNN) piezoelectric ceramics are prepared by a conventional solid-state reaction. The effect of acceptor doping on structural and functional properties is investigated. A decrease in the Curie temperature and an increase in the dielectric constant values are observed when doping. More interestingly, an increase in the coercive field E-c and remanent polarization P-r is observed. The piezoelectric properties are greatly increased when doping with small concentrations dopants. ZrO2 doped ceramic exhibits good piezoelectric properties with piezoelectric coefficient d(33) = 134 pC/N and electromechanical coupling factor k(p) = 35%. It is verified that nonlinearity is significantly reduced. Thus, the creation of complex defects capable of pinning the domain wall motion is enhanced with doping, probably due to the formation of oxygen vacancies. These results strongly suggest that compositional engineering using low concentrations of acceptor doping is a good means of improving the functional properties of KNN lead-free piezoceramic system. (C) 2014 Elsevier Ltd. All rights reserved.Postprint (published version

Natuurlijke immobilisatie van zware metalen in de bodem

In Nederland zijn grote hoeveelheden licht met zware metalen verontreinigde grond en baggerspecie aanwezig. Een eenvoudige methode om hiermee om te gaan is immobilisatie van de zware metalen in de vorm van sulfiden. Hiervoor is het noodzakelijk dat degrond of baggerspecie anaëroob onder aanwezigheid of toevoer van sulfaat wordt opgeslagen. Risico van dit concept van natuurlijke immobilisatie is dat, als gedurende een periode niet kan worden voldaan aan de randvoorwaarden, er hermobilisatie kan optreden. Dit risico is onderzocht. Het grootste risico is een onverwachte verlaging van het grondwaterpeil of het optreden van een extreem droge periode. Dit is gesimuleerd in het Rhizotron van Wageningen UR. Er is gebruik gemaakt van een baggerspecie met verhoogde concentraties zink en cadmium. In de uitgangssituatie bevatte het poriewater verhoogde hoeveelheden zware metalen. Opnieuw vastleggen van de zware metalen in sulfiden vereiste circa vijftig dagen. Hierna zijn grondwaterpeilen verlaagd en is een extreem droog jaar gesimuleerd. Dit zorgde boven in de specie voor sulfaatvorming, wat werd gevolgd door mobilisatie van zware metalen. Dit proces duurde vier maanden of langer, waarbij de aanwezigheid van gewas het proces versnelde. Op de plaatsen in de specie waar geen aërobie werd aangetroffen, is waargenomen dat de zware metalen op den duur sterker worden gebonden, wat resulteert in lagere concentraties. Deze waarden lagen onder de streefwaarde voor water. Resultaten van het onderzoek zijn vertaald naar adviezen voor de inrichting van locaties voor natuurlijke immobilisatie. Aangegeven is waarmee rekening moet worden gehouden bij het herstel van de situatie na een verstoring

Rational Ways to Use Fiber Concrete

During the analysis, the most rational areas of application of fiber-reinforced concrete and the influence of various fibers on the physico-mechanical characteristics of concrete were identified. The positive effect of dispersed concrete reinforcement on their performance is described

Practice of Contemporary Dance Promotes Stochastic Postural Control in Aging

As society ages and the frequency of falls increases, counteracting gait and posture decline is a challenging issue for countries of the developed world. Previous studies have shown that exercise and hazard management help to improve balance and/or decrease the risks for falling in normal aging. Motor activity based on motor-skill learning, particularly dance, can also benefit balance and decreases falls with age. Recent studies have suggested that older dancers have better balance, posture, or gait than non-dancers. Additionally, clinical or laboratory measures have shown improvements in some aspects of balance after dance interventions in elderly trainees. This study examined the impact of contemporary dance (CD) and of fall prevention (FP) programs on postural control of older adults. Posturography of quiet upright stance was performed in 41 participants aged 59–86 years before and after 4.4-month training in either CD or FP once a week. Though classical statistic scores failed to show any effect, dynamic analyses of the center-of-pressure displacements revealed significant changes after training. Specifically, practice of CD enhanced the critical time interval in diffusion analysis, and reduced recurrence and mathematical stability in recurrence quantification analysis, whereas practice of FP induced or tended to induce the reverse patterns. Such effects were obtained only in the eyes open condition. We suggest that CD training based on motor improvisation favored stochastic posture inducing plasticity in motor control, while FP training based on more stereotyped behaviors did not

Primary prevention of the main dental diseases in children at different stages of orthodontic treatment with bracket systems

Aim. Evaluation of the effective preventive methods of dental caries in children with dentoalveolar anomalies. Methods. Orthodontic treatment was received by 50 children aged 12-14 years with dentoalveolar anomalies who were treated by an orthodontist using ligature bracket and who had a compensated form of dental caries before the beginning of the hardware treatment. In the first group of children (control, 25 subjects) professional oral hygiene twice a year was followed by the coating of all teeth with fluoride. Children of the second group (25 subjects) after professional oral hygiene twice a year had their teeth covered with tooth enamel around brackets with Clinpro XT Varnish (3M ESPE) material containing fluorine, calcium and phosphate compounds. Dental examination every three months included assessment of oral hygiene and the state of the gums, the presence of carious defects, fillings and removed teeth, followed by the calculation of the main dental indices. Results. On the basis of studies of the dental status in children undergoing orthodontic treatment using brackets, the main dental indices such as DCF (decay/missing/filled), complex periodontal index, papillary-marginal-alveolar index were characterized at the stages of treatment. The analysis of the recorded values was performed in the comparison groups for each research method and the main statistically significant differences were identified. The study revealed that children from group 2 had positive dynamics of the state of periodontium within 18 months: the value of papillary-marginal-alveolar index among children from group 2 decreased by 5.4 times, the value of complex periodontal index decreased by 3.5 times. Children from group 2 had a significantly lower incidence of caries compared to the control group after 18 months of remineralizing therapy: the increase of complex periodontal index among children receiving orthodontic treatment with Clinpro XT Varnish coverage twice a year was only 1.42±0.16, incidence of caries of teeth surface reduced by 55%. Conclusion. On the basis of these studies, a comparative characteristics of the dental indices was performed at the stages of treatment using the brackets, depending on the used primary preventive measures; dental status of children at the stages of orthodontic treatment have their features: special oral hygiene tools should be guided by hygiene indices and complemented by remineralizing drugs

Critical loads and excess loads of cadmium, copper and lead for European forest soils

Recently, concern has arisen about the impact of the dispersion of heavy metals in Europe. Therefore, a study (ESQUAD) was initiated to assess critical loads and steady-state concentrations of cadmium, copper and lead for European forest soils. The calculation methods used strongly resemble those used to compute critical loads for acidifying compounds. Results show that the computed critical loads and associated excess loads for forest soils strongly depend on the threshold values chosen and on the soil phase (adsorbed/dissolved) considered. Further research is needed to improve input data and the modelling of heavy metal adsorption

Application of Alkali-Resistant Glass Nets Waste in Fibro Concrete

The article describes the modern building material – fibro concrete. A list of basic materials used for dispersed reinforcement for concrete is presented. The basic mechanical and physical properties of these materials are described. Also, the possibility of using alkali-resistant fiberglass waste as a fiber is considered