Plasma diagnostics by optical emission spectroscopy on manganese ore in conjunction with XRD,XRF and SEM-EDS

Manganese (Mn) is an important industrial mineral. Information about the chemical and phase constitution along with the concentration of impurities presented in Mn ore is compulsory in assessing its suitability for different applications. We performed the qualitative and quantitative analysis of low-grade Mn ore (LGMO) using laser-induced breakdown spectroscopy (LIBS) in conjunction with x-ray diffraction (XRD), x-ray fluorescence (XRF) and scanning electron microscopy (SEM) coupled with energy dispersive x-ray electron spectroscopy (EDS). The optical emission spectra of the LGMO sample displayed the presence of Mn, Si, Ca, Fe, Al, Mg, V, Ti, Sr, Ni, Na, Ba and Li. The plasma parameters, electron temperature and number density were estimated using the Boltzmann plot and Stark broadening line profile methods and were found to be 7500 K±750 K and 8.18±0.8×10¹⁷ cm⁻³, respectively. Quantitative analysis was performed using the calibration-free LIBS (CF-LIBS) method and its outcome along with XRD, XRF and SEM-EDS data showed almost analogous elemental composition, while the LIBS method gave acceptably precise elemental analysis by detecting the low atomic number element Li besides V and Sr. The results obtained using LIBS for the LGMO exhibited its ability as a powerful analytical tool and XRF, XRD and SEM-EDS as complementary methods for the compositional analysis of complex low-grade mineral ore.     

BOUNDARY ELEMENT–FINITE ELEMENT COUPLED EIGENANALYSIS OF FLUID–STRUCTURE SYSTEMS

The eigenanalysis of acoustical cavities with flexible structure boundaries, such as a fluid-filled container or an automobile cabin enclosure, is considered. An algebraic eigenvalue problem formulation for the fluid–structure problem is presented by combining the acoustic fluid boundary element eigenvalue analysis method and the structural finite elements. For many practical eigenproblems, use of finite elements to discretize the fluid domain leads to large stiffness and mass matrices. Since the acoustic boundary element discretization requires putting nodes only on the wetted surface of the structure, the size of the eigenproblem is reduced considerably, thus reducing the eigenvalue extraction effort. Futhermore, unlike in ordinary cases, the finite element discretization of pressure–displacement based fluid–structure problem gives rise to unsymmetric matrices. Therefore, the fact that the boundary element formulation produces unsymmetric matrices does not introduce additional difficulties here compared to the finite element case in the choice of an eigenvalue extraction procedure. Examples are included to demonstrate the fluid–structure eigenanalysis using boundary elements for the fluid domain and finite elements for the structure.     

建筑结构缝的设置要求及施工质量控制

根据国家现行规范和标准的要求，结合工程应用实际，就沉降缝、伸缩缝和抗震缝的作用及设置规定进行了论述，提出了减少建筑物裂缝的技术措施。     

Fatigue crack growth of filled rubber under constant and variable amplitude loading conditions

Service conditions experienced by rubber components often involve cyclic loads which are more complex than a constant amplitude loading history. Consequently, a model is needed for relating the results of constant amplitude characterization of fatigue behaviour to the effects of variable amplitude loading signals. The issue is explored here via fatigue crack growth experiments on pure shear specimens conducted in order to evaluate the applicability of a linear crack growth model equivalent to Miner's linear damage rule. This model equates the crack growth rate for a variable amplitude signal to the sum of the constant amplitude crack growth rates associated with each individual cycle. The variable amplitude signals were selected to show the effects of R-ratio (ratio of minimum to maximum energy release rate), load level, load sequence, and dwell periods on crack growth rates. In order to distinguish the effects of strain crystallization on crack growth behaviour, two filled rubber compounds were included: one that strain crystallizes, natural rubber, and one that does not, styrene-butadiene rubber. The linear crack growth model was found to be applicable in most cases, but a dwell effect was observed that is not accounted for by the model.     

MECHANICAL DAMAGE INDUCED BY CONTROLLED FREEZING IN APPLE AND POTATO

Freezing was used to induce controlled damage to apple and potato parenchyma. As the tissue freezes ice crystals form extra- or intracellularly, pushing the cells apart or rupturing cell walls producing large voids within the tissue. Mechanical tests (wedge penetration, tensile and compression) on specimens frozen to a certain temperature at a controlled rate and thawed show that the changes in the mechanical behaviour of the material are directly related to the degree of cell damage. As the tissue freezes, the fastest rate of tissue damage occurs between -3C and -10C. In this range there is a marked decrease in stiffness and an increase in the deformation required to cause failure. In apples, slow freezing leads to the intercellular spaces expanding, increasing their aspect ratio and hence, the anisotropy of the tissue. The increasing number of voids increases crack-stopping and ductility; more energy is dissipated in flow elevating the fracture toughness. Toughness then decreases with further damage. This effect can be mimicked with brittle paper: fracture toughness of tracing paper initially increases with increasing number of holes punched randomly in it.     

EVALUATION OF ANTIOXIDANT ACTIVITY, PHENOLICS, SUGAR AND MINERAL CONTENTS IN DATE PALM FRUITS

Sugar and mineral compositions of 10 Tunisian date varieties were investigated. Hydrophilic (aqueous extract) and hydrophobic extracts (ethanol extract) were used to determine the phenol contents and the total antioxidant activities of these dates. Results showed that date fruit varieties were rich in soluble sugars, which varied from 35.57 (Smiti variety) to 77.88 g/100 g fresh weight (FW) (Korkobbi variety). Several minerals were also present in the following order; K, Ca, P, Mg, Na, Fe, Cu, Zn and Mn. The potassium content reached 0.74 g/100 g dry weight in Smiti variety. For all date varieties, the phenol content did not exceed 9.70 (milligram of gallic acid equivalent/100 g FW). The original antioxidant activity reached 31.86 mg of ascorbic acid equivalent antioxidant capacity/100 g (FW) for Garn ghzal variety. However, it was only 17.77 for the Nefzaoui. Therefore, it can be deduced from these results that all these fruit varieties can be considered as high-energy food and only Garn ghzal seems to be interesting for technological purposes as food antioxidants.

PRACTICAL APPLICATIONS

The date palm ( Phoenix dactylifera L.) has a very important economic, social and ecological role for the people of the arid and semiarid regions. The date world production tripled while passing from 2,289,511 tons in 1974 to 6,772,068 tons in 2004. In Tunisia, dates witnessed a remarkable development during the last years and the production reached an average of 110,000 tons per year. Unfortunately, this progress in production is accompanied by an increasing loss of secondary varieties. Among these abandoned varieties are those of Gabès oasis. In this context, our work focuses on valorizing these secondary varieties by determining their nutritional and medicinal properties.