Time resolved optical Kerr effect analysis of urea–water system

The nuclear dynamics of urea aqueous solution was analyzed by time resolved optical Kerr effect (OKE). The data analysis was achieved in time and in frequency domains. Three relaxation times characterize the time decay of the OKE signal at high mole fractions of urea, while only two relaxation times characterize this decay for the low mole fractions. The observed slowest relaxation time increases with increasing the mole fraction of urea. The comparison between this relaxation time and the ones determined by Raman and nuclear magnetic resonance spectroscopies suggests that the slow relaxation time is related to the reorientation of an axis lying in the plane of the urea molecule. At high mole fractions, the power spectra derived from the Fourier transform of the OKE signal are characterized by one broad peak at around 70 cm−1 and by a shoulder at around 160 cm−1 in the high frequency part of the former peak. This shoulder is related to the hydrogen bond interactions which involve urea molecules. Molecular dynamics simulation results on urea/water system suggest that the power spectra derived from OKE data could be interpreted in terms of translational motions (caging effect) and in terms of rotational motion (libration) of urea molecules

Preparation and characterization of a composite material based on a geopolymer binder and quartzite aggregates

We have developed a geopolymer material by alkaline reaction on thermally activated kaolin. Initially we characterized the geopolymer by different methods (rheology, DTA-TGA, etc.) and we mixed it with different amounts of natural sand to obtain a granular composite. The structural characterization of this material was undertaken by several techniques (XRF, XRD and microscopic observations). A rheological study was implemented to determine the influence of the aggregate rate on the setting kinetic. Three-point bending and compression tests were conducted for mechanical characterization. We also conducted microindentation tests to study the influence of quartzite rate on the hardness of the material. The results indicate that the integration of quartzite (up to 15 wt. %) did not alter the setting kinetic. We noted a small degradation of the mechanical behavior when the quartzite rate is increased; this effect is due to a higher density of microcracks. However, adding the aggregate has a beneficial effect on the hardness of the material. These attractive features make this material a plausible matrix whose reinforcement with plant fibers will provide a ternary composite suitable for multiple applications

Development of an apatitic calcium phosphate cements: effect of liquid/powder ratio on the setting time

Calcium phosphate cement (CPC) sets in situ to form resorbable hydroxyapatite with chemical and crystallographic similarity to the apatite in human bones, hence it is highly promising for clinical applications. Among the clinical requirements for calcium phosphate bone cements are initial setting time and final setting time. α-tricalcium phosphate (α-TCP) and hydroxyapatite (HA) were mixed with dicalcium phosphate dehydrate (DCPD) to form the cement powder which is mixed with aqueous solutions of 3% Na2HPO4.2H2O in weight at four different liquid-to‐powder ratios (0.35, 0.40, 0.45 and 0.50 mL/g). The cement powder, on wetting with the medium, formed a workable putty. X-ray diffraction (XRD), Energy dispersive X-ray spectroscopic (EDS), transmission electron microscope (TEM) and scanning electron microscopy (SEM) techniques were employed to evaluate the phase composition and surface morphology of the cements. The results revealed similar phase composition for all samples before and after soaking in distilled water at 37°C. According to the results, it is shown that almost complete transformation of cements in calcium-deficient hydroxyapatite (CDHA) occur after soaking 7 days in destilled water with nanosized rod-like hydroxyapatite crystals. Also by reducing the L/P ratio from 0.50 to 0.35, initial and final setting times of the CPCs decreased 11 and 10 minutes respectively

Temporal behavior of two-wave-mixing in photorefractive InP:Fe versus temperature

The temporal response of two-wave-mixing in photorefractive InP:Fe under a dc electric field at different temperatures has been studied. In particular, the temperature dependence of the characteristic time constant has been studied both theoretically and experimentally, showing a strongly decreasing time constant with increasing temperature

Study of volatile compounds of Pyrus mamorensis Trab. a characteristic plant of Mamora forest (north-western Morocco)

Pyrus mamorensis Trab. commonly called “wild pear” was considered for long time as an endemic of the Mamora forest of Morocco (north-west). Although lack of protection and it is threatened with extinction in its range, this tree is of great interest due to its ecological and medicinal properties. This study focused on evaluation of volatiles in Pyrus mamorensis for its valorisation as a natural resource. So, the volatile compounds from different parts (leaves, stems, fruits, and flowers) were investigated after extraction by cold maceration in ethyl ether and analyzed by gas chromatography coupled to the mass spectrometry (GC - MS). Thirty one (31) compounds were identified and quantified including fifteen (15) terpenes, seven (7) alcans, two (2) aldehydes, four (4) esters and three (3) allyl alkoxybenzen derivatives. Estragol was the dominant component of the plant and that was only detected in leaves (83,09 %), while hexadecane (36,92 %) and allyl hexanoate (29,39 %) were mainly detected in the stems. The fruits showed relatively high levels (20,59 %) of benzyl butanoate, whereas in the flowers, limonene is the most abundant constituent (30,12 %). The analysis of the relative rates of different classes of volatile compounds, revealed the diversity of these compounds in P. mamorensis compared to two cultivars of edible species : P. communis L. et P. pyrifolia. The significant difference in composition in this case could be due to the wild character of P. mamorensis

Structure-toxicity relationships for phenols and anilines towards Chlorella vulgaris using quantum chemical descriptors and statistical methods.

Quantitative structure–toxicity relationship (QSTR) models are useful to understand how chemical structure relates to the toxicity of natural and synthetic chemicals. The chemical structures of 67 phenols and anilines have been characterized by electronic and physic-chemical descriptors. Density functional theory (DFT) with Beck’s three parameter hybrid functional using the LYP correlation functional (B3LYP/6-31G(d)) calculations have been carried out in order to get insights into the structure chemical and property information for the study compounds. The statistical quality of the MLR and MNLR models was found to be efficient for the predicting of the toxicity, but when compared to the obtained results by ANN model, we realized that the predictions achieved by this latter one were more effective. The results indicated that the developed models could produce satisfactory predictive results for the four different toxicity endpoints with high squared correlation coefficients (R2 ). Leave-one-out cross validation, external validation, Y-randomized validation and application domain analysis demonstrated the accuracy, robustness and reliability of these models. Accordingly.the obtained results suggested that the proposed descriptors could be useful to predict the toxicity of phenols and anilines towards Chlorella vulgaris.