The Solubilization of Rock Phosphate by Organic Acids

Bases of the production of phosphoric fertilizers are classical methods involving acid dissolution of rock phosphates. The development of new methods applicable both to high-quality and low-quality phosphates is important for solving technological and ecological problems and to increase the economical effectiveness of phosphorus fertilizer technologies. In this respect, the bioconversion of rock phosphates in order to obtain phosphorus fertilizers is very promising. The basic principle of the biotechnological processing of natural phosphates is the production of organic acids, mainly citric, oxalic, and gluconic acid, that attack and dissolve the phosphates, converting the phosphorus to a form utilizable for the plants. The aim of this research is to optimize the process of Tunisian phosphorite solubilization with citric, oxalic, and gluconic acids in relation to the following main factors: the acid concentration, reaction time, solid/liquid phases ratio, and natural phosphate fraction. Two objective functions have been investigated: the quantity of the available acid in the system and the extent of phosphate dissolution. The research data has been processed according to the standard statistical tests. A mathematical model describing the phosphate decomposition process by organic acids has been obtained. A multicriteria optimization has been performed to determine the optimum levels of the examined factors. It was established that the different factors have a different effect on the goal parameters. A maximum degree of 91.89% of phosphorus extraction has been reached at phosphate solubilization by citric acid.     

Effect of the Loading of Metal Salts on the Formation of Fe–Co Solid Solution Nanoparticles in the IR-Pyrolyzed Chitosan Matrix

Russian Journal of General Chemistry - In this study, metal-carbon nanocomposites have been synthesized via the method of simultaneous formation of bimetallic Fe–Co nanoparticles and carbon...     

Removal of cadmium and copper ions by <Emphasis Type="Italic">Trichosporon cutaneum</Emphasis> R57 cells immobilized onto polyvinyl alcohol/tetraethoxysilane hybrid matrices

Polyvinyl alcohol (PVA) and tetraethoxysilane (TEOS) hybrid materials were prepared by sol-gel methods and tested as matrices for immobilization of Trichosporon cutaneum R57, capable of removing cadmium and copper ions from aqueous solutions. A kinetic model was applied and the effects of matrix TEOS content on the copper and cadmium uptake equilibria and rate constants were investigated.      

Endoscope Motion Compensation for Laryngeal High-Speed Videoendoscopy

The purpose of this study was to develop and evaluate a method for automatic endoscopic motion compensation (MC) specialized for laryngeal high-speed videoendoscopy (HSV) of sustained phonation. Specifically, the left-right and posterior-anterior endoscopic shifts were addressed. The method is based on the hypothesis that the difference between endoscopic and vocal fold dynamics is sufficient for accurate estimation of the endoscopic motion relative to the vocal folds. The research questions of particular interest were as follows: is MC of laryngeal HSV possible at the subpixel level, and what are the validity, reliability, and accuracy of the proposed MC method? First, the MC accuracy was assessed on simulated HSV data with exactly known motion trajectories. Then, the accuracy and reliability of MC were evaluated on real HSV data. Finally, the validity of MC was established by correlating objective to perceptual ratings. The method demonstrated subpixel accuracy and reliable performance when tested on both simulated and real data. Perceptual ratings of the endoscopic motion demonstrated high intrarater and interrater reliabilities. Perceptual and quantitative assessments of endoscopic motion were in agreement. The reported result is encouraging for resolving a persistent problem toward building better methods for visual and quantitative voice assessment.     

Investigating acoustic correlates of human vocal fold vibratory phase asymmetry through modeling and laryngeal high-speed videoendoscopy

Vocal fold vibratory asymmetry is often associated with inefficient sound production through its impact on source spectral tilt. This association is investigated in both a computational voice production model and a group of 47 human subjects. The model provides indirect control over the degree of left-right phase asymmetry within a nonlinear source-filter framework, and high-speed videoendoscopy provides in vivo measures of vocal fold vibratory asymmetry. Source spectral tilt measures are estimated from the inverse-filtered spectrum of the simulated and recorded radiated acoustic pressure. As expected, model simulations indicate that increasing left-right phase asymmetry induces steeper spectral tilt. Subject data, however, reveal that none of the vibratory asymmetry measures correlates with spectral tilt measures. Probing further into physiological correlates of spectral tilt that might be affected by asymmetry, the glottal area waveform is parameterized to obtain measures of the open phase (open/plateau quotient) and closing phase (speed/closing quotient). Subjects' left-right phase asymmetry exhibits low, but statistically significant, correlations with speed quotient (r=0.45) and closing quotient (r=-0.39). Results call for future studies into the effect of asymmetric vocal fold vibration on glottal airflow and the associated impact on voice source spectral properties and vocal efficiency.     

On the geometry of connections with totally skew-symmetric torsion on manifolds with additional tensor structures and indefinite metrics

This paper is a survey of results obtained by the authors on the geometry of connections with totally skew-symmetric torsion on the following manifolds: almost complex manifolds with Norden metric, almost contact manifolds with B-metric and almost hypercomplex manifolds with Hermitian and anti-Hermitian metric.