Stability analysis of internally damped rotating composite shafts using a finite element formulation

This paper deals with the stability analysis of internally damped rotating composite shafts. An Euler–Bernoulli shaft finite element formulation based on Equivalent Single Layer Theory (ESLT), including the hysteretic internal damping of composite material and transverse shear effects, is introduced and then used to evaluate the influence of various parameters: stacking sequences, fiber orientations and bearing properties on natural frequencies, critical speeds, and instability thresholds. The obtained results are compared with those available in the literature using different theories. The agreement in the obtained results show that the developed Euler–Bernoulli finite element based on ESLT including hysteretic internal damping and shear transverse effects can be effectively used for the stability analysis of internally damped rotating composite shafts. Furthermore, the results revealed that rotor stability is sensitive to the laminate parameters and to the properties of the bearings.     

Energy harvesting in a Mathieu–van der Pol–Duffing MEMS device using time delay

This paper investigates quasi-periodic vibration-based energy harvesting in a delayed nonlinear MEMS device consisting of a delayed Mathieu–van der Pol–Duffing type oscillator coupled to a delayed piezoelectric coupling mechanism. We use the multiple scales method to approximate the quasi-periodic response and the related power output near the principal parametric resonance. The effect of time delay on the energy harvesting performance is studied. It is shown that for appropriate combination of time delay parameters, there exists an optimum range of excitation frequency beyond the resonance where quasi-periodic vibration-based energy harvesting is maximum. Numerical simulations are performed to confirm the analytical predictions.     

Antimicrobial and antitumor activities of 1,2,4‐triazoles/polypyrrole chitosan core shell nanoparticles

Combination of natural biodegradable polymer with a synthetic polymer offers excellent properties for the support in drug delivery system. For this purpose, biodegradable conductive nanoparticle polypyrrole based on chitosan (PPC) has been prepared via oxidative polymerization of pyrrole in presence of chitosan using FeCl₃ as oxidant in acidic medium and used as a carrier for 1,2,4‐triazoles. The resultant nanoparticles were characterized by X‐ray diffraction, Fourier transform infrared analysis, transmission electron microscopy, scanning electron microscopy, and thermal gravimetric analysis. The results indicate that spherical nanoparticle of average diameter 52 ± 8 nm was successfully prepared. The spherical particles were composed of dark sphere surrounded by grey shell. A circumferential dark ring is observed in the shell after loading 1,2,4‐triazoles into PPC nanoparticles. The loaded triazoles were released almost linearly against time in a sustained fashion into different pH media. The mechanism of triazoles release was determined using different kinetics equations. The antibacterial activities against the gram‐negative and gram‐positive bacteria were examined. Furthermore, the antitumor activity of PPC nanoparticles loaded 1,2,4‐triazoles was also examined against Ehrlich ascites carcinoma cells and breast cancer cell line (MCF7). Polypyrrole chitosan loaded nanoparticles exhibited higher antitumor activity than 1,2,4‐triazoles.     

Functionalization of Macroporous Organic Polymer Monolith Based on Succinimide Ester Reactivity for Chiral Capillary Chromatography: A Cyclodextrin Click Approach

Macroporous cross‐linked organic polymer based on N‐acryloxysuccinimide (NAS) and ethylene dimethacrylate (EDMA) was prepared inside 75 µm id fused silica capillary as a functionalizable monolithic stationary phase for chromatographic applications. Succinimide groups on the monolith surface provide reactive sites able to react readily through standard electrophile–nucleophile chemistry. Propargylamine was used to prepare alkyne functionalized poly(NAS‐co‐EDMA). Onto this azido‐reactive polymer surface was grafted β‐cyclodextrin (CD) via a triazole ring utilizing the copper(I)‐catalyzed 1,3‐dipolar cyclo‐addition reaction. Chemical characterization was performed in situ after each synthetic step by means of Raman spectroscopy. Good enantioseparations of flavanone enantiomers, chosen as test chiral compound, were achieved under reversed phase conditions by both capillary electrochromatography and nano‐liquid chromatography (nano‐LC) techniques. These results demonstrate the potentiality and usefulness of click chemistry in the preparation of β‐CD containing chiral organic polymer monolith.

     

Magnetocaloric properties in the Cr-doped La0.7Sr0.3MnO3 manganites

Single-phase polycrystalline samples of La_0.7Sr_0.3Mn_1-xCr_xO₃ with nominal composition of x=0.00, 0.20, 0.40 and 0.50 were prepared by a conventional solid-state reaction method in air. Investigations of magnetization were carried out in the temperature range 5-400 K and magnetic field range 0-8 T. It was found that the Curie temperature T_C decreases with increasing x and the maximum magnetic entropy change (−ΔS_M) for x=0.20 is ∼1.203 and ∼2.653 J/kg K, respectively for 2 and 6 T magnetic field near the temperature of 280 K.     

The Nephroprotective Effect of Zizyphus lotus L. (Desf.) Fruits in a Gentamicin-Induced Acute Kidney Injury Model in Rats: A Biochemical and Histopathological Investigation

Zizyphus lotus L. (Desf.) (Z. lotus) is a medicinal plant largely distributed all over the Mediterranean basin and is traditionally used by Moroccan people to treat many illnesses, including kidney failure. The nephrotoxicity of gentamicin (GM) has been well documented in humans and animals, although the preventive strategies against it remain to be studied. In this investigation, we explore whether the extract of Zizyphus lotus L. (Desf.) Fruit (ZLF) exhibits a protective effect against renal damage produced by GM. Indeed, twenty-four Wistar rats were separated into four equal groups of six each (♂/♀ = 1). The control group was treated orally with distilled water (10 mL/kg); the GM treated group received distilled water (10 mL/kg) and an intraperitoneal injection of GM (80 mg/kg) 3 h after; and the treated groups received ZLF extract orally at the doses 200 or 400 mg/kg and injected intraperitoneally with the GM. All treatments were given daily for 14 days. At the end of the experiment, the biochemical parameters and the histological observation related the kidney function was explored. ZLF treatment has significantly attenuated the nephrotoxicity induced by the GM. This effect was indicated by its capacity to decrease significantly the serum creatinine, uric acid, urea, alkaline phosphatase, gamma-glutamyl-transpeptidase, albumin, calcium, sodium amounts, water intake, urinary volume, and relative kidney weight. In addition, this effect was also shown by the increase in the creatinine clearance, urinary creatinine, uric acid, and urea levels, weight gain, compared to the rats treated only with the GM. The hemostasis of oxidants/antioxidants has been significantly improved with the treatment of ZLF extract, which was shown by a significant reduction in malondialdehydes levels. Histopathological analysis of renal tissue was correlated with biochemical observation. Chemical analysis by HPLC-DAD showed that the aqueous extract of ZLF is rich in phenolic compounds such as 3-hydroxycinnamic acid, catechin, ferulic acid, gallic acid, hydroxytyrosol, naringenin, p- coumaric Acid, quercetin, rutin, and vanillic acid. In conclusion, ZLF extract improved the nephrotoxicity induced by GM, through the improvement of the biochemical and histological parameters and thus validates its ethnomedicinal use.     

Efficient coupling and relaxed alignment tolerances in pigtailing of a laser diode using dual ball lenses

In this paper, we report an efficient coupling scheme with relaxed misalignment tolerances. The proposed coupling scheme consists of two ball lenses of same diameter (1 mm) and different refractive indices. The second ball lens which is facing the fiber tip has a higher refractive index (1.833), whereas the first one which faces the laser diode has a refractive index of 1.5. Employing Gaussian and ABCD ray tracing optics, the theoretically obtained coupling efficiency can reach a unity with relaxed working distance (separation of the coupling system from the fiber tip) in the range between 1 and 4 mm at some optimum positions of the coupling lenses with regard to each other and to the facet of the laser diode. It has been found that if the distance between the first ball lens and the laser diode (d₁) is fixed at 1.1 mm, which is twice its focal length, the coupling efficiency and the working distance as well as the misalignment tolerances are greatly affected by variation of the separation between the two ball lenses (s), and for this proposed coupling scheme the highest coupling efficiency and largest working distance are obtained when s is in the range of 0.3-0.35 mm. Above and below this range there is a significant reduction in the values of the above-mentioned parameters. Experimentally, the Nd:YAG laser welding system has been used for the alignment and welding of the coupling components in a butterfly configuration; the experimentally obtained coupling efficiency of the proposed coupling system was around 75% with relaxed working distance. From the effect of lateral and angular offsets on coupling efficiency, it is clearly noticed that the mode field of laser diode is transformed from elliptical into circular and hence effectively matched with that of the single-mode fiber.     

Tandem diazonium salt electroreduction and click chemistry as a novel, efficient route for grafting macromolecules to gold surface

Bis-alkynylated oligoethyleneglycol (OEG) and a monopropargyl-functionalized perfluorinated ethylene glycol (FEG) were clicked to azide-functionalized gold surface (Au–N₃) at room temperature via the well known 1,3 cycloaddition click chemical reaction. The Au–N₃ substrate was obtained by nucleophilic attack of NaN₃ on gold substrates modified by the electrochemical reduction of the , ⁺N₂–C₆H₄–CH₂Br diazonium salt. This electrochemical process yields aryl layer-modified gold of the type Au–C₆H₄–CH₂Br (hereafter Au–Br). The untreated and modified gold plates were examined by XPS, PMIRRAS and contact angle measurements. XPS brought evidence for electrografting aryl layers by the detection of Br3d; azide functionalization by the increase of the N/Br atomic ratio; and click reaction of OEG with Au–N₃ by the increase of O/N ratio. In addition, the perfluorinated plate (Au-FEG) exhibited F1s and characteristic C1s peaks from -(CF₂)₇- chain and terminal CF₃. Infra red spectroscopy (PMIRRAS) evidenced (i) grafting N₃ to Au–Br; (ii) characteristic stretching bands, from ethylene glycol units, C–O–C (1100–1300 cm⁻¹); CF₂ (1000–1100 cm⁻¹) and CF₃ (1100–1350 cm⁻¹) from FEG grafts; and (iii) suppression of alkynyl bands from OEG and FEG after surface click chemistry. More importantly, PMIRRAS results support an important bridging of the bispropargyl oligoethylene glycol at the gold surface. Water drop contact angles were found to be 48.7° and 83.0° for Au-OEG and Au-FEG, respectively, therefore highlighting the control over the hydrophilic/hydrophobic character of the clicked substrate.This work shows that clicking macromolecules to grafted, diazonium salt-derived aryl layers is a novel, simple and valuable approach for designing robust, functional surface organic coatings.     

Enhancing the Decolorization of Methylene Blue Using a Low-Cost Super-Absorbent Aided by Response Surface Methodology

The presence of organic dyes from industrial wastewater can cause pollution and exacerbate environmental problems; therefore, in the present work, activated carbon was synthesized from locally available oil palm trunk (OPT) biomass as a low-cost adsorbent to remove synthetic dye from aqueous media. The physical properties of the synthesized oil palm trunk activated carbon (OPTAC) were analyzed by SEM, FTIR-ATR, and XRD. The concurrent effects of the process variables (adsorbent dosage (g), methylene blue (MB) concentration (mg/L), and contact time (h)) on the MB removal percentage from aqueous solution were studied using a three-factor three-level Box–Behnken design (BBD) of response surface methodology (RSM), followed by the optimization of MB adsorption using OPTAC as the adsorbent. Based on the results of the analysis of variance (ANOVA) for the three parameters considered, adsorbent dosage (X₁) is the most crucial parameter, with an F-value of 1857.43, followed by MB concentration (X₂) and contact time (X₃) with the F-values of 95.60 and 29.48, respectively. Furthermore, the highest MB removal efficiency of 97.9% was achieved at the optimum X₁, X₂, and X₃ of 1.5 g, 200 mg/L, and 2 h, respectively.     

Determination of quinocide as impurity in primaquine tablets by capillary zone electrophoresis

A capillary zone electrophoretic method has been developed and validated for the determination of the impurity quinocide (QC) in the antimalarial drug primaquine (PQ). Different buffer additives such as native cyclodextrins and crown ethers were evaluated. Promising results were obtained when either β‐cyclodextrin (β‐CD) or 18‐crown‐6 ether (18C6) were used. Their separation conditions such as type of buffer and its pH, buffer additive concentration, applied voltage capillary temperature and injection time were optimized. The use of 18C6 offers slight advantages over β‐CD such as faster elution times and improved resolution. Nevertheless, migration times of less than 5 min and resolution factors (R_s) in the range of 2–4 were obtained when both additives were used. The method was validated with respect to selectivity, linearity, limits of detection and quantitation, analytical precision (intra‐ and inter‐day variability) and repeatability. Concentrations of 2.12 and 2.71% (w/w) of QC were found in pharmaceutical preparations of PQ from two different manufacturers. A possible mechanism for the successful separation of the isomers is also discussed. Copyright © 2008 John Wiley & Sons, Ltd.