Ochratoxin A in rice on the Moroccan retail market

One hundred (100) samples of rice purchased from retail markets in five different cities (Rabat, Témara, Salé, Casablanca and Méknès) in Morocco from January to October 2006 were surveyed for the presence of ochratoxin A (OTA) using Accelerated Solvent Extraction (ASE) coupled to liquid chromatography with fluorescence detection. The identification of OTA in positive rice samples was confirmed by methyl ester derivatization. Analytical results showed a frequency of contamination of 26% of total analyzed rice samples. The percentage of contamination of samples was 24, 26.6, 16.6, 27.7 and 30% in Rabat, Témara, Méknès, Salé and Casablanca respectively. Levels of OTA in positive samples ranged between 0.08 and 47 ng/g. The average contamination of all analyzed samples was 3.5 ng/g. The highest frequency of positive samples (30%) and the most contaminated sample (47 ng/g) was found in a sample from Casablanca city. 14 out of 100 total samples exceeded the maximum level of 5 ng/g set by European regulations for OTA in cereals. Based in the results presented in this study, the estimated daily intake of OTA in rice was 0.32 ng/kg bw/day for Moroccan consumers.     

On the mechanism of twin formation in Fe–Mn–C TWIP steels

Although it is well known that Fe–Mn–C TWIP steels exhibit high work-hardening rates, the elementary twinning mechanisms controlling the plastic deformation of these steels have still not been characterized. The aim of the present study is to analyse the extended defects related to the twinning occurrence using transmission electron microscopy. Based on these observations, the very early stage of twin nucleation can be attributed to the pole mechanism with deviation proposed by Cohen and Weertman or to the model of Miura, Takamura and Narita, while the twin growth is controlled by the pole mechanism proposed by Venables. High densities of sessile Frank dislocations are observed within the twins at the early stage of deformation, which can affect the growth and the stability of the twins, but also the strength of these twins and their interactions with the gliding dislocations present in the matrix. This experimental evidence is discussed and compared to recent results in order to relate the defects analysis to the macroscopic behaviour of this category of material.     

Influence of alkali,silicate, and sulfate content of carbonated concrete pore solution on mild steel corrosion behavior

The increase in the rebar corrosion rate due to the concrete carbonation is the major cause of reinforced concrete degradation. The aim of this study was to investigate the corrosion behavior of mild steel rebars in simulated carbonated concrete solution. For this purpose, thermodynamic calculations, electrochemical techniques, gravimetric measurements, and surface analyses were used. Thermodynamic investigations of the nature of the interstitial solution provides an estimation of the influence of sulfate ( ) and alkali (Na⁺, K⁺) content on carbonate alkalinity of the CO₂/H₂O open system (pCO₂ = 0.3 mbar). In this system, calcium‐silicate hydrates (C–S–H) remain thermodynamically unstable and amorphous silica controls silicate aqueous content at 100 ppm. Electrochemical results highlight a decrease in the corrosion rate with increasing carbonate alkalinity and the introduction of silicate. The introduction of sulfate at fixed carbonate alkalinity shows a dual effect: at high carbonate alkalinity, the corrosion rate is increased whereas at low carbonate alkalinity, corrosion rate is decreased. Those results are supported by surface analysis. Authors conclude that silicate and sulfate release from cement hydrates and fixation of alkali on carbonated hydrates are key parameters to estimate mild steel corrosion in carbonated concrete.     

Okadaic acid and its interaction with sodium, potassium, magnesium and calcium ions: complex formation and transport across a liquid membrane

Okadaic acid, a macrocyclic polyether compound, was shown to mediate the transfer of Na+, K+, Mg2+ and Ca2+ ions from aqueous solution to an organic phase, with a preference for Na+ ions. A kinetic study of the transport of these ions across a liquid membrane showed that the Na+ ion was more rapidly transported than the other ions and that the Na+ ion flux was dependent on the okadaic acid concentration.     

Calorimetric investigation on the Pb---Sm and Sn---Sm alloys

The integral enthalpy of formation of the Sm---Pb and Sm---Sn melts at 1203 K, h^f, was determined by direct reaction calorimetry (drop method) in the Pb and Sn rich sides with the help of a high-temperature Tian-Calvet calorimeter. The results can be fitted respectively with reference to the mole fraction of samarium, x, as follows:

h^f/kJ mol⁻¹=x(1−x)(−109.8−372.0.7x) with0> X_Sm >0.27

and

h^f/kJ mol⁻¹=x(1−x)(−277.0−105.4.x) with0> X_Sm >0.27

for the Sm---Pb and Sm---Sn melts respectively. They yield the following partial enthalpies of samarium at infinite dilution: −109.8 and −277.0 kJ mol⁻¹ respectively.

Such negative values suggest the existence of a strong short-range order in the liquid state. The stoichiometry and the thermal stability of these associations needs additional thermodynamic determinations concerning mainly the free enthalpy of formation. It will be determined by Knudsen-effusion combined with mass spetrometry in a further work.     

Enhanced performance of dye-sensitized solar cells by utilization of an external, bifunctional layer consisting of uniform β-NaYF₄:Er³⁺/Yb³⁺ nanoplatelets

Uniform β-NaYF(4):Er(3+)/Yb(3+) hexagonal nanoplatelets were synthesized via a modified hydrothermal route, and the nanoplatelets were applied as an external, bifunctional layer in a novel DSC configuration consisting of only one internal TiO(2) transparent layer. Approximately 10% enhancements of photocurrent and overall DSC efficiency are demonstrated by the addition of the external layer, which exhibits two functions of light reflecting and near-infrared (NIR) light harvesting. The novel DSC configuration not only simplifies the DSC fabrication process but also eliminates charge recombination induced by the conducting up-converting nanocrystals when used internally thus opening the path for other more efficient up-converting nanocrystals to be designed and applied.     

Limited survey for the occurrence of aflatoxins in cereals and poultry feeds from Rabat, Morocco

Fifty eight (58) samples of cereals for human consumption (20 corn flour, 17 wheat flour) and poultry feeds (n=21) purchased from popular markets of Rabat in Morocco were analyzed for aflatoxins (AF) by HPLC with immunoaffinity column (IAC) clean-up and fluorimetric detection. The incidence of AF in corn, wheat flour and poultry feeds was about 80, 17.6 and 66.6% respectively. High contamination levels were found in corn and poultry feeds samples. Levels of contamination of analyzed samples with AFB1 ranged from 0.23 to 11.2, 0.03 to 0.15 and 0.05 to 5.38 ng/g for corn, wheat and poultry feeds respectively. Results showed also that the contamination of 10% of samples of corn was higher than the limit set by EU regulations for AFB1 and total AF. This is the first report on the determination of AF in corn, wheat and poultry feeds from Morocco by HPLC and IAC.     

Influence of Pd addition on the electrochemical performance of Mg–Ni–Ti–Al-based metal hydride for Ni–MH batteries

Amorphous Mg_0.9Ti_0.1NiAl_0.05 and Mg_0.9Ti_0.1NiAl_0.05Pd_0.1 alloys were prepared by high energy ball milling and evaluated as metal hydride electrodes for Ni–MH batteries. The Mg_0.9Ti_0.1NiAl_0.05Pd_0.1 alloy showed a much higher cycle life with a capacity retention of 72% after 100 cycles (C_100th = 288 mAh g⁻¹) compared to 26% for the Pd-free alloy (C_100th = 117 mAh g⁻¹). This was mainly attributed to the improvement of the alloy oxidation resistance in KOH electrolyte with Pd addition, as confirmed by cyclic voltammetry experiments and X-ray diffraction analyses on cycled electrodes. In addition, in situ acoustic emission (AE) measurements revealed that the energy of the AE signals related to the particle cracking is lower for the Mg_0.9Ti_0.1NiAl_0.05Pd_0.1 electrode, suggesting that the cracks are smaller in size than with the Pd-free alloy. The Mg_0.9Ti_0.1NiAl_0.05Pd_0.1 electrode also displayed a higher discharge rate capability than the Mg_0.9Ti_0.1NiAl_0.05 electrode. On the basis of their respective electrochemical pressure–composition isotherm, it was shown that the presence of Pd in the alloy decreases the thermodynamic stability of the metal hydride. Through a comparative analysis of discharge polarization curves, it was also shown that Pd addition decreases substantially the H-diffusion resistance in the alloy whereas its positive effect on the charge-transfer resistance is limited.     

Experimental and numerical validation of hygrothermal transfer in brick wall

In this paper, a mathematical model dealing with a coupled heat, air, and moisture transfer in a building envelope was developed. Based on the three-following driving potential: vapor pressure, dry air pressure, and temperature, an application on a hygrothermal behavior of a real wall was carried out for different climatic conditions. For this purpose, a characterization of the heat and moisture properties of the materials constituting the wall made with red brick and cement mortar was carried out in the laboratory. This was used to evaluate experimentally the input parameters of the model as a function of relative humidity. To validate the numerical model, an experimental platform was improved. The wall was set up in a double-climatic chamber with different boundary conditions, and then the temperature and humidity evolutions were recorded using several sensors within the wall thickness. The results have highlighted a good agreement between numerical simulation results and experimental ones.