Two- and three-dimensional comparative study of heat transfer and pressure drop characteristics of nanofluids flow through a ventilated cubic cavity (part I: Newtonian nanofluids)

Journal of Thermal Analysis and Calorimetry - Through this paper, three-dimensional fluid flow and heat transfer of Al2O3 nanofluid within ventilated enclosures was taken into consideration....     

Effect of carbon nanotubes on the thermal conductivity enhancement of synthesized hydroxyapatite filled with water for dental applications: experimental characterization and numerical study

Journal of Thermal Analysis and Calorimetry - The hydroxyapatite is one of the biocompatible and insulating bioceramics, while the carbon nanotube has a high thermal conductivity potential. This...     

Constructing a new optical sensor for monitoring ammonia in water samples using bis(acetylacetoneethylendiamine)-tributylphosphin cobalt(III) tetraphenylborate complex-coated triacetylcellulose.

A new ammonia optical sensor was designed using bis(acetylacetoneethylendiamine)tributylphosphin cobalt(III) tetraphenylborate complex, coated on transparent triacetylcellulose film as membrane. The change in the absorbance of the optode at the maximum wavelength of 408 nm was related to ammonia concentration in aqueous samples. A buffer solution with a pH of 9 (sodium borate-HCl) was used. The optode was fully regenerated in pH 2. The linear dynamic range for determination of ammonia was 3.3 x 10(-4) to 6.9 x 10(-3) mol l(-1) with a detection limit of 5.0 x 10(-5) mol l(-1) and a response time range of 4 - 6 min. This membrane was successfully applied for determination of ammonia in drinking water.     

A rate-dependent algebraic stress model for turbulence

Based on the stress transport model, a rate-dependent algebraic expression for the Reynolds stress tensor is developed. It is shown that the new model includes the normal stress effects and exhibits viscoelastic behavior. Furthermore, it is compatible with recently developed improved models of turbulence. The model is also consistent with the limiting behavior of turbulence in the inertial sublayer and is capable of predicting secondary flows in noncircular ducts. The TEACH code is modified according to the requirements of the rate-dependent model and is used to predict turbulent flow fields in a channel and behind a backward-facing step. The predicted results are compared with the available experimental data and those obtained from the standard k-ε and algebraic stress models. It is shown that the predictions of the new model are in better agreements with the experimental data.     

Hydroxyl radical is the active species in photochemical DNA strand scission by bis(peroxo)vanadium(V) phenanthroline

Bis(peroxo)vanadium(V) complexes are widely investigated as anticancer agents. They exert their antitumor and cyctotoxic effects through inhibition of tyrosine phosphatases and DNA cleavage, respectively. The latter process remains poorly understood. The mechanism of DNA cleavage by NH(4)[(phen)V(O)(eta(2)-O(2))(2)] (phen = 1,10-phenanthroline) was investigated. Kinetic studies on DNA cleavage revealed that the complex is a single-strand nicking agent with no specificity. EPR experiments using 2,2,6,6-tetramethyl-4-piperidone (TMP) and 5,5'-dimethyl-1-pyrroline-N-oxide (DMPO) as spin-traps for singlet oxygen and hydroxyl radical, respectively, implicated hydroxyl radical production upon photodecomposition of bis(peroxo)vanadium(V). This was corroborated by benzoate inhibition of DNA strand scission and stoichiometric oxidation of 2-propanol to acetone upon irradiation of bis(peroxo)vanadium(V) phenanthroline. High-resolution polyacrylamide gel analysis of the vanadium cleavage reaction and [Fe(II)EDTA](2)(-)/H(2)O(2) resulted in comigration of "ladder" pattern bands, which superimposed when both reactions were run on the same lane. These findings identify hydroxyl radical produced from the photooxidation of the peroxo ligand on vanadium as the active species in DNA cleavage.     

Excited-state distortions determined from structured luminescence of nitridorhenium(V) complexes

The nitridorhenium(V) complexes ReNCl(2)(PCy3)(2) (1), ReNBr(2)(PCy3)(2) (2), ReNCl(2)(PPh3)(2) (3), and ReNBr(2)(PPh3)(2) (4) produce structured emission spectra upon excitation at low temperature. The origin, E(00), occurs at 15 775, 16 375, 15 875, and 16 300 cm(-1), respectively. The vibronic peaks are regularly spaced with an average energy separation corresponding to the Re triple bond N stretching frequency. The nitridorhenium stretching frequency ranges from 1095 to 1101 cm(-1), as determined by Raman and IR spectroscopy. The excited-state distortions are calculated by fitting the emission spectra. The excited state arises primarily from a d(xy) (ReN nonbonding) to d(yz) (ReN pi antibonding) transition. The rhenium-nitrogen bond length in the excited state is 0.08 A longer than in the ground electronic state, which is consistent with the difference in bond lengths of ReN bonds of bond order 3 and bond order 2.5 as determined from molecular structures.     

Supercritical carbon dioxide extraction of Mentha pulegium L. essential oil

The dependence of Mentha pulegium L. (pennyroyal) essential oil composition, obtained by supercritical carbon dioxide (SC-CO₂), with the following parameters: pressure, temperature, extraction time (dynamic), and modifier (methanol) was studied. The results were also compared with those obtained by conventional hydrodistillation method in laboratory conditions. Regarding the percentages of menthone (30.3%) and pulegone (52.0%), the optimum SFE results were obtained at the following experimental conditions: pressure=100 atm, T=35 °C, dynamic time=10 min, and V_modifier=0 μl. The results of hydrodistillation showed that the major components of M. pulegium L. were pulegone (37.8%), menthone (20.3%), and piperitenone (6.8%). The evaluation of the composition of each extract was performed by gas chromatography-mass spectrometry.     

Clustering files of chemical structures using the fuzzy k-means clustering method

This paper evaluates the use of the fuzzy k-means clustering method for the clustering of files of 2D chemical structures. Simulated property prediction experiments with the Starlist file of logP values demonstrate that use of the fuzzy k-means method can, in some cases, yield results that are superior to those obtained with the conventional k-means method and with Ward's clustering method. Clustering of several small sets of agrochemical compounds demonstrate the ability of the fuzzy k-means method to highlight multicluster membership and to identify outlier compounds, although the former can be difficult to interpret in some cases.