Dielectric characteristics and nonlinear properties of ZnO–polypyrrole composites

The nonlinear properties and frequency characteristics of ZnO–polypyrrole composites were investigated at 200 Hz–5 MHz frequency interval with different zinc oxide contents. Samples were prepared using hot press method at 130 °C. Results show an optimum point for breakdown voltage at ZnO content of 70%. Breakdown voltage decreases from 590 to 380 V and after that tends to increase from 450 to 740 V due to the absence of polypyrrole at grain boundaries. No matter how breakdown voltage behaves, nonlinear coefficient increases from 4.2 to 9 by increasing ZnO content because of the increase in acceptor-like states at grain boundaries by increasing ZnO content. The electrical parameters such as dielectric constant, dielectric loss and series resistance of samples show a strong dependence on frequency especially below 1 kHz. These parameters fall off by increasing frequency up to 1 kHz, which is related to charge transportation through the Schottky barrier at grain boundaries. The high dielectric constant of samples below 1kHz is related to the Maxwell–Wagner polarization at grain boundaries. The presence of different anomalies at different frequency intervals is related to interfacial polarization because of different structures of grains and intergranular layer with a huge difference in conductivity.     

Sorption of phenols onto sandy aquifer material: the effect of dissolved organic matter (DOM)

The influence of dissolved organic matter (DOM) on the sorption of four phenols, 2,4,6-trichlorophenol (2,4,6-TCP), pentachlorophenol (PCP), 2,4-dinitrophenol (2,4-DNP) and 2-methyl-4,6-dinitrophenol (2-M-4,6-DNP), onto sandy aquifer material at different pH values was investigated using flow through column experiments. The pH-dependent sorption of the chlorinated phenols 2,4,6-TCP and PCP was not significantly affected by DOM (measured as dissolved organic carbon, DOC), whereas in the case of nitrophenols a significant lower retardation was found, depending on the DOC concentration and pH value of the aqueous solution. Sorption decreases with increasing DOC concentration, which indicates a binding of these compounds by DOM. The degree of sorption reduction depends on the pH value and increases with increasing fraction of neutral species. The different behaviour of nitrophenols in comparison to the chlorophenols is assumed to be a result of specific charge-transfer interactions. A combined sorption and complex formation model was used to describe the effect of pH and DOC concentration on the sorption of nitrophenols onto aquifer material and to estimate binding coefficients of neutral nitrophenols on DOM.     

Controlled release of drugs from gradient hydrogels for high-throughput analysis of cell-drug interactions

In this paper, we report a method to fabricate microengineered hydrogels that contain a concentration gradient of a drug for high-throughput analysis of cell-drug interactions. A microfluidic gradient generator was used to create a concentration gradient of okadaic acid (OA) as a model drug within poly(ethylene glycol) diacrylate hydrogels. These hydrogels were then incubated with MC3T3-E1 cell seeded glass slides to investigate the cell viability through the spatially controlled release of OA. The drug was released from the hydrogel in a gradient manner and induced a gradient of the cell viability. The drug concentration gradient containing hydrogels developed in this study have the potential to be used for drug discovery and diagnostics applications due to their ability to simultaneously test the effects of different concentrations of various chemicals.     

Magnetic nanocomposite of multi-walled carbon nanotube as effective adsorbent for methyl violet removal from aqueous solutions: Response surface modeling and kinetic study

Magnetic nanocomposite of multi-walled carbon nanotube (m-MWCNT) was synthesized for adsorptive removal of methyl violet (MV) from aqueous solutions. The experiments were conducted using a central composite design (CCD) with the variables of adsorbent dosage (0.4-1.2 g/L), solution pH (3-9), contact time (10-42 min) and ionic strength (0.02-0.1mol L^?1). Regression analysis showed good fit of the experimental data to a quadratic response surface model whose statistical significance was verified by analysis of variance. By applying the desirability functions, optimum conditions of the process were predicted as adsorbent dosage of 0.99g/L, pH=4.92, contact time of 40.98 minutes and ionic strength of 0.04 mol L^?1 to achieve MV removal percentage of 101.19. Experimental removal efficiency of 99.51% indicated that CCD along with the desirability functions can be effectively applied for optimizing MV removal by m-MWCNT. Based on the study, the adsorption process followed Langmuir isotherm model and pseudo-second-order kinetic model could realistically describe the dye adsorption onto m-MWCNT.     

Effects of formulation properties on sol–gel behavior of chitosan/glycerolphosphate hydrogel

Chitosan solution containing glycerolphosphate disodium salt (Gp) is an injectable thermosensitive in situ gel-forming system which undergoes sol–gel transition under certain physiological pH and temperature conditions. When a drug-incorporated chitosan/Gp solution is injected into the body, it forms a three-dimensional gel at 37 °C, which allows the drug to be released in a sustained manner. This hydrogel can be used as a drug delivery system for prolonged release of peptides and glycopeptides. The objective of this work was to investigate the effect of different excipients on the sol–gel behavior of this thermosensitive hydrogel. Chitosan polymeric solutions (2 % w/v) containing Gp and different excipients, such as hydroxypropyl methyl cellulose (HPMC), polyethylene glycol (PEG) with two different molecular weights (PEG200 and PEG1000), and poloxamer (F127) in various concentrations, were prepared, and the pH, sol–gel transition time, and syringeability of the final solutions were evaluated. The obtained results point to HPMC as the best additive for chitosan/Gp solutions in developing an in situ gel-forming drug delivery system with optimum gelling time. A significant decrease was noted in the sol-to-gel transition time (from 90 to 60 s) when HPMC was added to the system. This may have been due to the HPMC structure which acted as a viscosity-enhancing and gel-promoting agent. The in vitro release of vancomycin hydrochloride from chitosan/Gp/HPMC hydrogel was also studied. Vancomycin release studies showed a sustained release profile for over 20 days. It can be concluded that combining chitosan/Gp and HPMC is a promising strategy for preparing a thermally reversible in situ gel-forming delivery system with an optimized gelation time.     

Color-based skin segmentation in videos using a multi-step spatial method

Recently, skin detection has been employed in multifarious applications of computer vision including face detection, gesture recognition, etc. This is mainly due to the appealing characteristics of skin color and its potency to segment objects. However, there are certain challenges involved in utilizing human complexion as a feature to detect faces, and they have led to the inefficiency of many methods. In order to counteract these factors, in this paper, a skin segmentation method which exploits a multi step diffusion algorithm to detect skin regions is presented. The method starts with conservative extraction of skin seeds in each frame which is accomplished by using fusion of ternary-based human motion detection, modified Bayesian classifier, and a feedback mechanism. Subsequently, these candidate skin pixels are utilized in a 2-stage diffusion scheme to detect other skin pixels. Both quantitative and qualitative results demonstrate the effectiveness of the proposed system in comparison with other works.