Nanopositioning control of an electrostatic MEMS actuator: adaptive terminal sliding mode control approach

Nonlinear Dynamics - This research proposes an adaptive terminal sliding mode control strategy dedicated to motion tracking control of an electrostatic-actuated nanopositioning system. The...     

Exploring the interaction between “site-markers,aspirin and esterase-like activity” ternary systems on the human serum albumin: direct evidence for modulation of catalytic activity of the protein in different inhibition modes

Albumin which is the most abundant drug carrier protein in plasma controls the distribution aspect of drug pharmacokinetics. The aim of this study has been to elucidate the concurrent binding behavior of indomethacin/ibuprofen/heme to HSA under the effect of aspirin-mediated protein acetylation and also to explore the esterase-like catalytic property of the unmodified/modified proteins, as binary or ternary systems, by using various spectroscopic and molecular docking techniques. We found that aspirin-based modification of HSA affects the protein conformation as well as ligand binding at sites I–III. Decrease in pNPA-mediated esterase activity of HSA in different reversible inhibition modes, upon the protein–ligand interactions, was also documented, an issue that may receive considerable attention for computational prodrug design in near future.     

Potentiality of independent component regression in assessment of the peaks responsible for antimicrobial activity of <Emphasis Type="Italic">Satureja hortensis</Emphasis> L. and <Emphasis Type="Italic">Oliveria decumbens</Emphasis> Vent. using GC–MS

Satureja hortensis L. and Oliveria decumbens Vent. are used in traditional medicine in the world due to its antifungal, antibacterial and antioxidant properties. In this study, the antimicrobial activities in Satureja hortensis L. and Oliveria decumbens Vent. essential oils against three microbial strains were evaluated by two different methods, including: disk diffusion method and micro-broth dilution assay [with minimal inhibitory concentration (MIC) between 0.025 and 0.500 µL/mL, and minimal lethal concentration (MLC) between 0.050 and 1.000 µL/mL] and qualitative analysis was performed by gas chromatography–mass spectrometry technique (GC–MS). The peaks potentially responsible for the antimicrobial activity in essential oils samples were indicated by some linear multivariate calibration techniques with different preprocessing methods. From the studied techniques, independent component regression (ICR) was preferred to exhibit the potential antimicrobial active compounds in Satureja hortensis L. and Oliveria decumbens Vent. essential oils because of its high repeatability, simplicity, and interpretability of the regression coefficients. Independent components (ICs) can give more chemical explanation than principal components (PCs), because independence is a high-order statistic that is a much stronger condition than orthogonality.     

Comparative assessment of the ability of a microwave absorber nanocatalyst in the microwave-assisted biodiesel production process

In this study, a carbon-supported KOH/Ca₁₂Al₁₄O₃₃ nanocomposite was fabricated via the microwave combustion method, in which dextrose was used as a carbon source, and its activity in the microwave-assisted transesterification reaction as a microwave absorption material was assessed. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry, Brunauer–Emmett–Teller (BET), field-emission scanning electron microscopy, and energy dispersive X-ray analyses. The results showed that the carbonate and noncarbonate samples had a calcium aluminate (Ca₁₂Al₁₄O₃₃) structure as a support. Different carbon groups were formed during preparation of the carbon-supported KOH/Ca₁₂Al₁₄O₃₃ nanocomposite, which improved its surface area and porosity. Although the samples presented similar basicity, the carbonated nanocomposite exhibited twice as much activity as the KOH/Ca₁₂Al₁₄O₃₃ nanocatalyst for conversion of canola oil to biodiesel in the microwave-assisted transesterification reaction at 270 W microwave power. The nanocomposite with a larger pore size made active sites easily accessible and exhibited higher catalytic ability where the conversion of 98.8% was obtained under the optimized conditions of 270 W microwave power, methanol/oil molar ratio of 15, 4 wt% of the nanocomposite, and 30 min of reaction time. The carbon-supported nanocatalyst can be reused for at least four times with less reduction in activity. Furthermore, the obtained biodiesel showed that it met the standard values (EN 14214 and ASTM D-6751) with respect to the density, kinematic viscosity at 40 °C, acid number, and flash point.     

An off-line NMPC strategy for continuous-time nonlinear systems using an extended modal series method

This paper presents a new off-line nonlinear model predictive control (NMPC) approach for continuous-time affine-input nonlinear systems. In this approach, the NMPC-related nonlinear two-point boundary value problem derived from the Pontryagin’s maximum principle is solved by the extended modal series method. The resulting suboptimal control law explicitly depends on the initial conditions and is updated by replacing the initial conditions with the new state measurements in future sampling instants. Therefore, there is no need to repeat the recursive online optimization process in each sampling instant. Since the applicability of NMPC is generally restricted by computational burden of the online optimization, we propose an NMPC scheme, which not only reduces the online computational burden significantly, but also can be applied to fast dynamic systems with short prediction horizons. An efficient algorithm is presented which approximates the order of the modal series such that feasibility of the optimization problem is guaranteed. Closed-loop stability of the proposed NMPC approach is shown using the off-line terminal region calculations suggested in quasi-infinite horizon NMPC scheme. The applicability and effectiveness of the proposed approach are illustrated by two numerical examples.     

Water Expandable Polystyrene-Organoclay Nanocomposites: Role of Clay and Its Dispersion State

A published process for preparing expandable polystyrene containing water as a blowing agent was applied to synthesize water expandable polystyrene-organoclay nanocomposites (WEPS-OCN). Organoclay was uniformly dispersed in styrene monomer. During suspension polymerization, water was trapped in the polystyrene (PS) matrix through the use of starch, ending up with spherical PS-organoclay beads. By selecting organoclays with various surfactants and modifier concentrations, different distribution states of nanoclay in the PS matrix, from cluster (poor dispersion) to either intercalated (limited dispersion) or exfoliated (full dispersion) were obtained. The incorporation of organoclay led to higher water content in the expandable beads. However, as expected, the flammability of the expanded product was increased with organoclay content. Furthermore, the results showed that the average unexpanded bead size, density of preexpanded beads, foam cell morphology, and flammability were directly influenced by the dispersion status of the organoclay. The best results were obtained when full dispersion (exfoliation) of nanoclay in PS matrix occurred.     

Single-electron tunneling in silicon-on-insulator nano-wire transistors

The gate bias dependent evolution of the Coulomb oscillations in a silicon-on-insulator nano-wire transistor is reported. Transport data obtained for a wide range of front- and back-gate bias strongly suggest that multiple quantum dots (QDs) with different potential depths are formed in the nano-wire channel. Our data can be clearly interpreted as arising from the turning on or off of one of these QDs as the back-gate bias is varied. Quantitative calculation based on the model of single-electron tunneling through two parallel QDs is in reasonable agreement with the measured data in the back-gate bias range where the third dot is not activated.     

Fluorimetric Determination of Gentamicin in Dosage Forms and Biological Fluids Through Derivatization with 4-Chloro-7-Nitrobenzo-2-Oxa-1,3-Diazole (NBD-Cl)

 A highly sensitive fluorimetric method has been developed for the determination of gentamicin. The method is based on its coupling with 4-chloro-7-nitrobenzo-2-oxa-1,3-diazole (NBD-Cl) in 50% (v/v) methanolic phosphate buffer (pH 7.2) to give an intensely fluorescent product having excitation and emission wavelengths at 465 nm and 530 nm, respectively. The experimental parameters were carefully studied and incorporated into the procedure. The fluorescence-concentration plot is rectilinear over the range 0.56–2.8 μg/mL (r = 0.999) with minimum detectability (S/N = 2) of 0.11 μg/mL (1.6 × 10⁻⁷ mol/L). The method was applied successfully to the determination of the drug in pharmaceutical dosage forms and the percentage recoveries were satisfactorily accurate and precise. The method was further applied to spiked human plasma samples, the percentage recovery was 97.9 ± 3.4. The interference encountered from endogenous amino acids could be eliminated through selective complexation with freshly prepared copper (II) hydroxide. A proposal of the reaction pathway is presented. The method can measure the intact drug, and can be used in presence of possible interference. Received April 18, 2001; accepted April 10, 2002     

Electrochemical approach for monitoring the effect of anti tubulin drugs on breast cancer cells based on silicon nanograss electrodes

One of the most interested molecular research in the field of cancer detection is the mechanism of drug effect on cancer cells. Translating molecular evidence into electrochemical profiles would open new opportunities in cancer research. In this manner, applying nanostructures with anomalous physical and chemical properties as well as biocompatibility would be a suitable choice for the cell based electrochemical sensing. Silicon based nanostructure are the most interested nanomaterials used in electrochemical biosensors because of their compatibility with electronic fabrication process and well engineering in size and electrical properties. Here we apply silicon nanograss (SiNG) probing electrodes produced by reactive ion etching (RIE) on silicon wafer to electrochemically diagnose the effect of anticancer drugs on breast tumor cells. Paclitaxel (PTX) and mebendazole (MBZ) drugs have been used as polymerizing and depolymerizing agents of microtubules. PTX would perturb the anodic/cathodic responses of the cell-covered biosensor by binding phosphate groups to deformed proteins due to extracellular signal-regulated kinase (ERK^1/2) pathway. MBZ induces accumulation of Cytochrome C in cytoplasm. Reduction of the mentioned agents in cytosol would change the ionic state of the cells monitored by silicon nanograss working electrodes (SiNGWEs). By extending the contacts with cancer cells, SiNGWEs can detect minor signal transduction and bio recognition events, resulting in precise biosensing. Effects of MBZ and PTX drugs, (with the concentrations of 2 nM and 0.1 nM, respectively) on electrochemical activity of MCF-7 cells are successfully recorded which are corroborated by confocal and flow cytometry assays.