Compositional changes during guava fruit ripening

Compositional changes of fruit pulp and peel during ripening of white- and pink-fleshed guava fruits were studied. The white and pink guava fruits exhibited a typical climacteric pattern of respiration. Fruit tissue firmness decreased progressively, in a similar manner, in both guava fruit types. Total soluble solids (TSS) and total sugars increased in pulp and peel of both guava types with decrease in flesh firmness. More increase in total sugars was observed after the climacteric peak of respiration. Reducing sugars and titratable acidity increased up to the full-ripe stage and then decreased. Ascorbic acid and phenolic compounds decreased continuously during ripening of the two types. The peel showed higher values of ascorbic acid, total protein and phenolic compounds than the plup. The white-fleshed guavas had higher levels of TSS, total sugars, reducing sugars. titratable acidity, phenolic compounds and ascorbic acid content then the pink-fleshed fruits.     

Structure, mechanical metallurgy and electrical transport properties of rapidly solidified Pb50Sn50-xBix alloys

Electrical transport properties, structure and mechanical properties of Pb₅₀Sn_50-xBi_x(0≤x≤50) alloys have been studied and analyzed. The addition of bismuth in the amounts of 30 wt % and 50 wt % results in the appearance of the crystalline metastable χ(Pb-Bi) phase. Y phase is also identified and it is found at 50 wt % bismuth. Electrical transport is sensitive to the alloys composition, decreasing as the bismuth content increases. The Vickers hardness number is sensitive to the structure of the quenched ribbons. The lowest value of H_v is 55 MPa for the Pb₅₀Sn₂₀Bi₃₀ alloy, which is attributed to the formation of the metastable χ(Pb-Bi) after a rapid quench from the melt. Values of the equivalent Fermi temperature, T_F Fermi velocity, V_F and the Fermi wave vector, K_F , are also computed. © 2000 Kluwer Academic Publishers     

Spectrophotometric study of the complexation equilibria of iron(III) with 3-hydroxypicolinic acid and determination of iron in pharmaceutical preparations

The complexation equilibria of iron(III) with 3-hydroxypicolinic acid (hypa) have been studied spectrophotometrically in 40% (v/v) ethanol—water medium at 25°C and an ionic strength of 0.1 M NaClO₄. The equilibria occurring in solution were established and the basic characteristics of the complexes formed were determined. The spectral study of the reaction solutions containing equimolar concentrations or an excess of one component in the pH range 1.5 to 10.5 gave the evidence for the formation of [FeLH]²⁺, [FeL]⁺ and [FeL₂]^? complex species, depending upon the pH of the medium (LH₂ symbolising the molecular form of hypa). The possible complex transitions that occur in solution were demonstrated using graphical and logarithmic analysis of the absorbance—pH graphs. A simple, rapid, sensitive and selective method for spectrophotometric determination of trace levels of iron(III) was proposed based on the formation of Fe(hypa)₂ complex at pH 5.5 (λ = 440 nm, ? = 1.5 × 10⁴ dm³ mol^?1 cm^?1). The interference of a large number of foreign ions was investigated. The method has been applied successfully to the analysis of multivitamin and mineral preparations containing iron.     

Ultrasonic studies of aqueous solutions of polyvinylalcohol

Ultrasonic absorption and velocity measurements are reported on aqueous solutions of polyvinylalcohol of different molecular weights, degrees of hydrolysis and concentration. The absorption measurements cover a frequency range from 2–1000 MHz and the velocity data a frequency range from 2–200 MHz, the data were obtained over a temperature range from 273 to 333 K. Comparison of the data obtained as a function of the degree of hydrolysis indicate the magnitude of the contributions due to relaxation of the backbone and of the side chain acetyl groups. In the case of the 100% hydrolysed material, the relaxation spectrum is simplified and corresponds to that of motion of the pendant hydroxyl groups. Deviations of the variation of the attenuation with concentration from the ‘ideal’ dilute solution behaviour are ascribed to the effects of polymer-polymer interactions. The magnitude of the volume change associated with polymer-solvent interactions is estimated and discussed.     

Novel polyhydrazides and polyoxadiazoles based on 1,3,4-thiadiazole moiety in the main chain with high thermal stability,good solubility,and notable antimicrobial activity

Polyoxadiazoles (PODs) and polyhydrazides (PHs) have wide potential applications; however, PODs are normally insoluble in organic solvents, do not melt, and do not express glass-transition temperature (T_g), and also PHs do not have high-temperature resistance. In this work, novel PHs based on 1,3,4-thiadiazole in the polymer main chain were synthesized by low-temperature polycondensation. New PODs were then obtained by cyclodehydration of the PHs. The thermal behavior, surface morphology, and crystalline structure were studied using differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, and X-ray diffraction. In addition, the viscosity, solubility, UV–visible absorption, and antimicrobial activity were examined. The new polymers showed melting, T_g, high thermal stability, good solubility in polar aprotic solvents, and significant antimicrobial activities. The enhanced solubility may be attributed to the ability of thiadiazole moiety to form hydrogen bonding with the solvent molecules. Also, it can be concluded that introducing 1,3,4-thiadiazole and other bulky moieties like the oxadiazole ring into the polymer main chain encouraged more free volumes and weakened the chains packing; hence, the solubility was enhanced and T_g decreased without affecting the thermal stability. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47770.     

Vibration isolation of a symmetric rigid plate using struts under static and dynamic axial excitation

This paper presents vibration isolators in the form of post-buckled elastic clamped–clamped struts to relief the vibrating machines from the harmful effects of vibration. These vibrations are in most cases uncontrollable and lead to sudden failure. Therefore, mechanical engineers should control, isolate, and minimize such unwanted vibrations. A mathematical model is introduced consisting of pre-bent post-buckled struts acting as vibration isolators supporting a symmetric rigid plate. The model is subject to axial harmonic excitation at the base, and allowed to displace laterally with respect to axial center line of the isolated plate. The displacement transmissibility is the governing parameter of the isolator’s effectiveness at the mitigating vibrations transmitted from the base to the plate. The transmissibility is calculated over a wide range of frequencies and plotted in form of design charts. The transmissibility plots showed the ranges of frequencies, at which isolation can be maintained. The system resonance frequencies can be easily depicted from the design graphs. The present study reveals that at resonance frequencies the most effective transmissibility is well below unity. Vibration characteristics are determined under specific frequencies such that the physical behavior of the system can be thoroughly analyzed. All variables used are normalized, such that the results aren’t dependent on any material or geometric property, such as the modulus of elasticity of the material, section modulus of the used profile, or the length of the strut. In this way, the obtained results can be applied over a wide range of elastic materials, regardless of the material type or section properties.     

The effect of rapid solidification on the structure, decomposition behavior, electrical and mechanical properties of the Sn–Cd binary alloys

A group of rapidly solidified Sn–Cd alloys has been prepared by a melt-spinning technique. X-ray diffraction, microstructure, and differential thermal analysis have been carried out. Youngs modulus and internal friction have been measured, and the temperature dependence of resistivity has been evaluated. The results show a modification in both the microstructure and decomposition behavior. Also, an interesting connection between Youngs modulus and the axial ratio (c/a) of the unit cell of the -Sn was found in which Youngs modulus increases by increasing the axial ratio (c/a). It was found also that the internal friction increases on increasing the Cd concentration.