Effect of calcination temperature on structural,vibrational, optical,and rheological properties of zirconia nanoparticles

ZrO₂ nanoparticles (NPs) were prepared by a simple, versatile, and an efficient methodology based on microwave. The synthesized NPs were calcined at temperatures ranging from 100 °C to 600 °C. The samples were characterized by X-ray powder diffraction (XRD), transmission electron microscope (TEM), FT-IR spectroscopy, Far-IR spectroscopy, Raman spectroscopy, and UV-vis absorption spectroscopy. The results clearly showed the presence of purely monoclinic phase of zirconia when the calcination temperature exceeds 400 °C. The experimental results showed that the viscosity of zirconia NPs in ethylene glycol (EG) increases with increasing the particle volume fraction and decreases with increasing temperature.     

Carbon nanotube-modified glassy carbon electrode for anodic stripping voltammetric detection of Uranyle

A multi-wall carbon nanotube (MWNT) modified glassy carbon electrode (GCE) is described for the measurement of trace levels of uranium by anodic stripping voltammetry. In a pH 4.4 NaAc-Hac buffer containing 0.010 mol L⁻¹ Mg(NO₃)₂, UO₂ ²⁺ was adsorbed onto the surface of a MWNT film coated glassy carbon electrode and then reduced at −0.40 V vs. Ag/AgCl. During the positive potential sweep the reduced uranium was oxidized and a well-defined stripping peak appeared at +0.20 V vs. Ag/AgCl. Low concentrations of Mg²⁺ significantly enhanced the stripping peak currents since they induced UO₂ ²⁺ to adsorb at the electrode surface. The response was linear up to 1.2 × 10⁻⁷ mol L⁻¹ and the relative standard deviation at 2.0 × 10⁻⁸ mol L⁻¹ uranium was 5.2%. Potential interferences were examined. The attractive behavior of the new “mercury-free” uranium sensor holds promise for on-site environmental and industrial monitoring of uranium.     

Automatic Detection of Words Associations in Texts Based on Joint Distribution of Words Occurrences

In this article, we propose a novel approach for measuring word association based on the joint occurrences distribution in a text. Our approach relies on computing a sum of distances between neighboring occurrences of a given word pair and comparing it with a vector of randomly generated occurrences. The idea behind this assumption is that if the distribution of co‐occurrences is close to random or if they tend to appear together less frequently than by chance, such words are not semantically related. We devise a distance function S that evaluates the words association rate. Using S, we build a concept tree, which provides a visual and comprehensive representation of keywords association in a text. In order to illustrate the effectiveness of our algorithm, we apply it to three different texts, showing the consistency and significance of the obtained results with respect to the semantics of documents. Finally, we compare the results obtained by applying our proposed algorithm with the ones achieved by both human experts and the co‐occurrence correlation method. We show that our method is consistent with the experts' evaluation and outperforms with respect to the co‐occurrence correlation method.     

Synthesis of Organosoluble and Optically Active Poly(ester-imide)s by Direct Polycondensation with Tosyl Chloride in Pyridine and Dimethylformamide

Summary 4,4′-Oxydiphthalic anhydride (1) was reacted with L-methionine (2) in acetic acid and the resulting N,N′-(4,4′-oxydiphthaloyl)-bis-L-methionine diacid (4) was obtained in high yield. The direct polycondensation reaction of this diacid with several aromatic diols such as bisphenol A (5a), phenolphthalein (5b), 1,4-dihydroxyanthraquinone (5c), 4,4′-dihydroxydiphenyl sulfide (5d), 2,6-dihydroxytoluene (5e), 4,4′-dihydroxydiphenyl sulfone (5f) and 2,4′-dihydroxyacetophenone (5g) was carried out in a system of tosyl chloride (TsCl), pyridine (Py) and N,N-dimethylformamide (DMF). The reactions with TsCl were significantly promoted by controlling alcoholysis with diols in the presence of the catalytic amounts of DMF to give a series of optically active poly(ester-imide)s (PEI)s with good yield and moderate inherent viscosity ranging 0.21–0.71 dL/g. The polycondensation reactions were significantly affected by the amounts of DMF, molar concentration of monomers, TsCl and pyridine, aging time, addition time of diols, temperature and the reaction time. All of the above polymers were fully characterized by ¹H-NMR, FT-IR, elemental analysis and specific rotation. Some structural characterization and physical properties of these new optically active PEIs are reported.     

Synthesis and Properties of Novel Soluble and Thermally Stable Optically Active Poly(amide-imide)s from N,N’-(4,4’-Oxydiphthaloyl)-bis-L-phenylalanine Diacid Chloride and Aromatic Diamines

Summary In this research work, 4,4-oxydiphthalic anhydride (1) was reacted with L-phenylalanine (2) in acetic acid and the resulting imide-acid 3 was obtained in high yield. This imide-acid 3 was converted to diacid chloride 4 by reaction with thionyl chloride. The polycondensation reaction of diacid chloride 4 with several aromatic diamines such as 4,4-sulfonyldianiline (5a), 4,4-diaminodiphenyl methane (5b), 4,4-diaminodiphenylether (5c), p-phenylenediamine (5d), m-phenylenediamine (5e), and 4,4-diaminobiphenyl (5f) was performed by two conventional methods: low temperature solution polycondensation and short period reflux conditions. Several new thermally stable optically active poly(amide-imide)s with inherent viscosity ranging from 0.34–0.62 dL/g were obtained with high yield. All of the above polymers were fully characterized by ¹H-NMR, FT-IR, elemental analyses and specific rotation techniques. Some structural characterizations and physical properties of this new optically active poly (amide-imide)s are reported.     

A robust adaptive observer for a class of singular nonlinear uncertain systems

This paper proposes a robust adaptive observer for a class of singular nonlinear non-autonomous uncertain systems with unstructured unknown system and derivative matrices, and unknown bounded nonlinearities. Unlike many existing observers, no strong assumption such as Lipschitz condition is imposed on the recommended system. An augmented system is constructed, and the unknown bounds are calculated online using adaptive bounding technique. Considering the continuous nonlinear gain removes the chattering which may appear in practical applications such as analysis of electrical circuits and estimation of interaction force in beating heart robotic-assisted surgery. Moreover, a simple yet precise structure is attained which is easy to implement in many systems with significant uncertainties. The existence conditions of the standard form observer are obtained in terms of linear matrix inequality and the constrained generalised Sylvester's equations, and global stability is ensured. Finally, simulation results are obtained to evaluate the performance of the proposed estimator and demonstrate the effectiveness of the developed scheme.     

Effects of sintering temperature on morphology and mechanical characteristics of 3D printed porous titanium used as dental implant

Porous titanium samples were manufactured using the 3D printing and sintering method in order to determine the effects of final sintering temperature on morphology and mechanical properties. Cylindrical samples were printed and split into groups according to a final sintering temperature (FST). Irregular geometry samples were also printed and split into groups according to their FST. The cylindrical samples were used to determine part shrinkage, in compressive tests to provide stress-strain data, in microCT scans to provide internal morphology data and for optical microscopy to determine surface morphology. All of the samples were used in microhardness testing to establish the hardness. Below 1100 °C FST, shrinkage was in the region of 20% but increased to approximately 30% by a FST of 1300 °C. Porosity varied from a maximum of approximately 65% at the surface to the region of 30% internally. Between 97 and 99% of the internal porosity is interconnected. Average pore size varied between 24 μm at the surface and 19 μm internally. Sample hardness increased to in excess of 300 HV0.05 with increasing FST while samples with an FST of below 1250 °C produced an elastic–brittle stress/strain curve and samples above this displayed elastic–plastic behaviour. Yield strength increased significantly through the range of sintering temperatures while the Young's modulus remained fairly consistent.     

Electrocatalytic oxygen reduction on single-walled carbon nanotubes supported Pt alloys nanoparticles in acidic and alkaline conditions

The objective of this study is to improve the catalytic activity of platinum by alloying with transition metal (Pd) in gas diffusion electrodes (GDEs) by oxygen reduction reaction (ORR) at cathode site and comparison of the acidic and alkaline electrolytes. The high porosity of single-walled carbon nanotubes (SWCNTs) facilitates diffusion of the reactant and facilitates interaction with the Pt surface. It is also evident that SWCNTs enhance the stability of the electrocatalyst. Functionalized SWCNTs are used as a means to facilitate the uniform deposition of Pt on the SWCNT surface. The structure of SWCNTs is nearly perfect, even after functionalization, while other types of CNTs contain a significant concentration of structural defects in their walls. So catalysts supported on SWCNTs are studied in this research. The electrocatalytic properties of ORR were evaluated by cyclic voltammetry, polarization experiments, and chronoamperometry. The morphology and elemental composition of Pt alloys were characterized by X-ray diffraction (XRD) analysis and inductively coupled plasma atomic emission spectroscopy (ICP-AES) system. The catalytic activities of the bimetallic catalysts in GDEs have been shown to be not only dependent on the composition, but also on the nature of the electrolytes. The GDEs have shown a transition from the slow ORR kinetics in alkaline electrolyte to the fast ORR kinetics in the acidic electrolyte. The results also show that introduction of Pd as transition metal in the Pt alloys provides fast ORR kinetics in both acidic and alkaline electrolytes. The performance of GDEs with Pt–Pd alloy surfaces towards the ORR as a function of the alloy’s overall composition and their behavior in acidic electrolyte was also studied. These results show that the alloy’s overall composition and also the nature of the electrolytes have a large effect on the performance of GDEs for ORR.     

Spectrophotometric determination of Sb(III) and Sb(V) in biological samples after micelle-mediated extraction

This work presents a micelle-mediated extraction method for simultaneous preconcentration and determination of Sb(III) and Sb(V) species in biological samples as a prior preconcentration step to their spectrophotometric determination. The analytical system is based on the selective reaction between Sb(III) and bromopyrogallol red (BPR) in the presence of cetyltrimethylammonium bromide (CTAB) and potassium iodide at pH 6.4. Total Sb concentration was determined after reduction of Sb(V) to Sb(III) in the presence of potassium iodide and ascorbic acid. The optimal extraction and reaction conditions were studied and the analytical characteristics of the method (e.g., limit of detection, linear range, preconcentration factor, and improvement factors) were obtained. Linearity for Sb(III) and Sb(V) were obeyed in the range of 0.2–20.0 ng mL⁻¹ and 0.4–25.0 ng mL⁻¹, respectively. The detection limit for the determination of Sb(III) and Sb(V) were 0.05 ng mL⁻¹ and 0.08 ng mL⁻¹, respectively. The interference effect of some anions and cations was also studied. The method was applied to the determination of Sb(III) in the presence of Sb(V) and total antimony in blood plasma and urine samples.     

Prediction of the volumetric and thermodynamic properties of some refrigerants using GMA equation of state

The density of 11 refrigerants (hydrochlorofluorocarbon (HCFCs) and hydrofluorocarbon (HFCs)) in the extended ranges of temperature and pressure has been calculated using Goharshadi–Morsali–Abbaspour equation of state (GMA EoS) and the results have been shown as the three-dimensional surfaces of density–temperature–pressure. A wide comparison with experimental data was made. The accuracy of the equation of state in the prediction of density was determined by statistical parameters. The results show that the GMA EoS can reproduce the experimental PVT data of HCFCs and HFCs within experimental errors throughout the liquid phase. The thermodynamic properties such as isobaric expansion coefficient, isothermal compressibility, and vapor–liquid equilibrium (VLE) prediction for these HCFC and HFC refrigerants have been performed using GMA EoS. GMA EoS can predict the characteristic feature of pressure behavior of isobaric expansion and isothermal compressibility coefficients.