Density Based Problem Space Search for the Capacitated Clustering p-Median Problem

In the Capacitated Clustering Problem (CCP), a given set of n weighted points is to be partitioned into p clusters such that, the total weight of the points in each cluster does not exceed a given cluster capacity. The objective is to find a set of p centers that minimises total scatter of points allocated to them. In this paper a new constructive method, a general framework to improve the performance of greedy constructive heuristics, and a problem space search procedure for the CCP are proposed. The constructive heuristic finds patterns of natural subgrouping in the input data using concept of density of points. Elements of adaptive computation and periodic construction–deconstruction concepts are implemented within the constructive heuristic to develop a general framework for building efficient heuristics. The problem-space search procedure is based on perturbations of input data for which a controlled perturbation strategy, intensification and diversification strategies are developed. The implemented algorithms are compared with existing methods on a standard set of bench-marks and on new sets of large-sized instances. The results illustrate the strengths of our algorithms in terms of solution quality and computational efficiency.     

Stability of Cosserat fluid motions

We obtain criteria of stability of the unsteady motion of an incompressible Cosserat fluid in an arbitrary time-dependent domain, employing a general energy method due to J. Serrin. It is shown that the original motion is stable if R _e ² 80 + 12800 C ₀ or if R _e80 + 6400 C ₀. The quantities R _e and C ₀ are the Reynolds number and Cosserat number, respectively, and - is the lower bound for the eigenvalues of the strain rate tensor D _ij.The theorems established for the stability criteria are universal in the sense that they do not depend either on the shape of the domain or on the distribution of the basic field variables. Finally an experimental scheme is proposed to determine the upper bound of the Cosserat number and consequently the characteristic length of a Cosserat fluid.     

Tautomerization of pyrido[2′,1′:2,3]imidazo[4,5-B]quinoline-12-ylcyanide: A DFT study

The titled imidazo compound can exist as three tautomers: OH, CH, and NH forms. Firstly, the OH tautomer is produced, which can be tautomerized to the CH and NH tautomers via the intramolecularproton transfer. Herein, employing density functional theory and handling the solvent effects with the PCM model, the structural parameters, energy behavior, and also tautomerization mechanism of the tautomers are investigated. Based on the DFT results and the obtained-AIM parameters, the CH tautomer is considered to be the most stable one. Also, the CH tautomer is a kinetically and thermodynamically controlled product in tautomerization of the OH tautomer in a methanol solution.     

Electrochemically controlled in-tube solid phase microextraction

We report a new in-tube solid phase microextraction approach named electrochemically controlled in-tube solid phase microextraction (EC in-tube SPME). This approach, which combined electrochemistry and in-tube SPME, led to decrease in total analysis time and increase in sensitivity. At first, pyrrole was elctropolymerized on the inner surface of a stainless steel tube. Then, the polypyrrole (PPy)-coated in-tube SPME was coupled on-line to liquid chromatography (HPLC) to achieve automated in-tube SPME–HPLC analysis. After the completion of EC-in-tube SPME–HPLC setup, the PPy-coated tube was used as working electrode for uptake of diclofenac as target analyte. Extraction ability of the tube in presence and in absence of applied electrical field was investigated. It was found that, under the same extraction conditions, the extraction efficiency could be greatly enhanced by using the constant potential. Important factors are also optimized. The detection limit (S/N = 3) and precision were 0.1 μg L⁻¹ and 4.4%, respectively.     

In-tube magnetic solid phase microextraction of some fluoroquinolones based on the use of sodium dodecyl sulfate coated Fe3O4 nanoparticles packed tube

In-tube magnetic solid phase microextraction (in-tube MSPME) of fluoroquinolones from water and urine samples based on the use of sodium dodecyl sulfate (SDS) coated Fe₃O₄ nanoparticles packed tube has been reported. After the preparation of Fe₃O₄ nanoparticles (NPs) by a batch synthesis, these NPs were introduced into a stainless steel tube by a syringe and then a strong magnet was placed around the tube, so that the Fe₃O₄ NPs were remained in the tube and the tube was used in the in-tube SPME-HPLC/UV for the analysis of fluoroquinolones in water and urine samples. Plackett–Burman design was employed for screening the variables significantly affecting the extraction efficiency. Then, the significant factors were more investigated by Box–Behnken design. Calibration curves were linear (R² > 0.990) in the range of 0.1–1000 μg L⁻¹ for ciprofloxacin (CIP) and 0.5–500 μg L⁻¹ for enrofloxacin (ENR) and ofloxacin (OFL), respectively. LODs for all studied fluoroquinolones ranged from 0.01 to 0.05 μg L⁻¹. The main advantages of this method were rapid and easy automation and analysis, short extraction time, high sensitivity, possibility of fully sorbent collection after analysis, wide linear range and no need to organic solvents in extraction.     

Synthesis of Ag nanoparticles for the electrochemical detection of anticancer drug flutamide

Ag nanoparticles were synthesized on the surface of a glassy carbon electrode modified with p‐tert‐butylcalix[4]arene and p‐tert‐butylcalix[6]arene by the deposition of Ag+at an open circuit potential ...     

Sensing behavior of BN nanosheet toward nitrous oxide: A DFT study

In order to develop a sensor for the detection of toxic N₂O molecules, the interaction of pristine and Aldoped BN nanosheets with an N₂O molecule was investigated using density functional theory calculations. It was found that unlike the pristine sheet, the Al-doped sheet can effectively interact with the N₂O molecule so that its electronic properties and conductivity are dramatically changed. Webelieve that replacing a B atom of the BN sheet with an Al atom may be a good strategy for improving the sensitivity of these nanosheets toward N₂O, which cannot be trapped and detected by the pristine sheet.     

Effect of different blend compositions on properties of low-density polyethylene/ethylene vinyl alcohol/clay toward high oxygen barrier nanocomposite films

In this study, high oxygen barrier nanocomposite films were prepared by melt blending of low-density polyethylene/ethylene vinyl alcohol/nanoclay/polyethylene-grafted-maleic anhydride (LDPE/EVOH/nanoclay/LDPE-g-MA). Effect of each component presence was determined by using Box-Behnken experiment design methodology. For all the responses obtained, R ² was between 0.956 and 0.981 indicating a very good fitting of the experimental data with the response surface method (RSM) in the models. Oxygen transfer rate (OTR) results shown that the addition of EVOH, compatibilizer, and nanoclay in formulations significantly decreases oxygen permeability. The experimental results showed that addition of 30 wt % EVOH, 4 wt % nanoclay, and 5 wt % LDPE-g-MA to the LDPE matrix gave the best oxygen barrier properties. The crystallization behaviors of the samples and thermal analysis have been characterized by using differential scanning calorimetry (DSC). The addition of nanoclay to the blends has resulted in increased crystallinity of LDPE phase. The state of nanoclay dispersion in the samples was examined by the X-ray diffraction (XRD) tests. The reduction of EVOH and nanoclay content, as well as the increase of LDPE-g-MA, has resulted in the better dispersion of nanoclay in the polymer matrix. The morphology of specimens was observed by using energy-dispersive X-ray spectroscopy (EDX) and scanning electron microscopy (SEM).     

Reactively compatibilized and dynamically vulcanized thermoplastic elastomers based on high-density polyethylene and reclaimed rubber

Melt blending was employed to prepare thermoplastic elastomer (TPE) of reclaimed rubber (RR) and high density polyethylene (HDPE). Mechanical properties of TPE samples were improved in different methods including dynamic vulcanization and reactive blending (reactive compatibilization) during melt mixing in an internal Haake mixer. The physical and mechanical properties of the TPE blends were investigated by the dynamic mechanical analysis (DMA) and tensile tests. The thermal behavior was characterized by differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA). The phase morphology of the blends was studied by scanning electron microscopy (SEM). Experimental results showed that, both static and dynamic mechanical properties of reactively-compatibilized and dynamically-vulcanized samples improved significantly compared with the virgin samples. The effect of dynamic-vulcanization and reactivecompatibilization on the mechanical properties revealed that the Young’s modulus and storage modulus increased with both improvement methods. SEM results showed that, dynamic-vulcanization and reactivecompatibilization methods improved the distribution of RR particles in HDPE matrix. Although both methods improved the thermal and mechanical properties of the HDPE/RR blends, dynamic-vulcanization was more effective and promising approach due to the higher properties of HDPE/RR blends prepared by this method.