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  • Author or Editor: M. Popa x
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Abstract  

The present research describes the synthesis of the citrate of Pr by the amorphous citrate method and the study of the thermal decomposition of the complex in air, nitrogen and oxygen, in order to identify the final compounds and the intermediates obtained during the decomposition. A special study was dedicated to the thermal decomposition of the Pr-carbonate octahydrate used in the synthesis as starting material. The thermal decomposition of the lanthanide citrate was investigated mainly by thermogravimetry, differential thermal analysis, X-ray diffraction and infrared spectroscopy. The results showed that the complex decomposes to PrO1.83 with formation of an intermediate oxycarbonate compound in air or directly to the oxide in oxygen; in nitrogen atmosphere, amorphous products were obtained after thermal decomposition.

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Abstract  

This paper reports a comparative study of the non-isothermal decompositions of the heteropolyacids HPM and HPVM, with structures consisting of Keggin units (KUs). Non-isothermal analysis at low heating rates demonstrated the existence of 4 crystal hydrate species, depending on the temperature. The stability domains of the anhydrous forms of HPM and HPVM were found to be 150–380°C, respectively. Processing of the TG curves obtained at different heating rates by the Ozawa method revealed that the decomposition of anhydrous HPM takes place according to a unitary mechanism, whilst for anhydrous HPVM two mechanisms are observed. Thus, the first part of the constitution water is lost simultaneously with the departure of vanadium from the KU as VO2+, while the second part is lost at higher temperatures as in the case HPM.

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Abstract  

The aim of this study is to investigate the influence of some monovalent counter-ions (NH4 +, K+ and Cs+) on thermal behavior of polyoxometalates derived from H3PMo12O40 (HPM) and H4PVMo11O40 (HPVM) by replacing the protons. The IR and UV-VIS-DRS spectra of some acid and neutral NH4 +, K+, Cs+ salts, which derived from HPM and HPVM, confirmed the preservation of Keggin units (KU) structure. The X-ray diffraction spectra clearly showed the presence of a cubic structure. The non-isothermal decomposition of studied polyoxometalates proceeds by a series of processes: the loss of crystallization water; the loss of O2 accompanying with a reduction of V5+→V4+ and Mo6+→Mo5+; the loss of constitution water started at 360C for HPVM salts and 420C for HPM salts; the decomposition of ammonium ion over 420C with NH3, N2 and H2O elimination and simultaneous processes of reduction (V5+→ V4+ and Mo6+→ Mo5+ or Mo4+) associating with endothermic effects; reoxidation of Mo5+, Mo4+ and V4+with a strong exothermic effect; destruction of KU to the oxides: P2O5, MoO3 and V2O5 and the crystallization of MoO3.

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Nowadays, vegetarian nutrition is getting more widespread. The risk of choosing vegetarian diet in young people remains a controversial subject. The aim of this paper is to assess the dietary intake and nutritional status of a vegetarian group aged 16–20 years and to compare the results with those of a non-vegetarian group. On the basis of 10 days of dietary records, the intake of vegetarian group tended to be lower in proteins (P<0.05), fat (P<0.05), cholesterol (P<0.001) and higher in carbohydrates (P<0.05) and dietary fiber (P<0.001). Vegetarians have a lower intake of calcium (P<0.001), and vitamin B12 (P<0.001) and higher intake of phosphorus, magnesium (P<0.001), iron, vitamin E (especially in males), folate and vitamin C (especially in females) than omnivores. In addition, none of the vegetarian subject was overweight and their anthropometric indicators were lower than those found in the nonvegetarian group. Triacylglycerol (P<0.05), total cholesterol (P<0.05), ionised calcium (P<0.05), seric iron (P<0.001) and vitamin B 12 (P<0.001) are lower in vegetarians than in omnivores, but all are still in the normal range.

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The Vrancea seismic region represents a unique case of well-defined and intense intermediate-depth earthquake activity as a consequence of specific geodynamic processes at the continental contact between East-European, Moesian and Intra-Alpine plates. Apart the subcrustal earthquakes generated in the Vrancea slab, the analysis of seismicity puts into evidence two other clusters of subcrustal earthquakes ( h > 50 km) toward the back-arc side of the SE Carpathians bend, one to the west (Sinaia), the other to the north-west (Braşov Depression) relative to the Vrancea seismic source. The hypocenters lay down between 50 to 105 km in Sinaia and between 50 and 136 km in Braşov Depression. The rate of seismic energy release is much lower ( M w ≤ 3.7 in Sinaia and M w ≤ 3.1 in Braşov Depression) than for Vrancea activity. The seismicity pattern in the SE Carpathians back-arc region upper mantle correlates well with the high-velocity structures depicted by seismic tomography investigations suggesting possible remnant deep lithospheric roots apart from the narrow well-defined slab generating Vrancea major earthquakes. The results outline significant lateral heterogeneities in the mantle and provide new data for incorporating seismological, geotectonic and volcanological data in a unified modeling of the complex processes taking place in the study region.

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Notable clustering effects in seismic activity are observed at the sharp bend of the South-Eastern Carpathians both at subcrustal and crustal domains. The seismic energy release is strongly increasing with depth, where apparently the principal source controlling the geodynamics of the entire system is located. New developments of instrumental monitoring and relatively extended historical data spanning several seismic cycles in Vrancea allow refined analyses of earthquake patterns, outlining high-resolution images of specific alignments of seismicity in the Vrancea region. Refined joint locations are carried out for the most recent earthquakes, produced after 1995. In parallel, a new approach has been implemented to produce numerical simulations of the Vrancea seismic cycle and to reproduce its main characteristics: return period, main shock magnitude, depth location, non-linear frequency-magnitude distribution, aftershock activity and their variability from one cycle to other.

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Abstract  

This work introduces results obtained during the preparation of a Bi-based material with superconducting properties by oxalate coprecipitation. The influence of Fe presence on the precursors thermal stability and on the superconducting phases formation mechanism are presented. The thermal decomposition and the stability in air of FeC2O42H2O and also of the components mixture were studied by DTA/TG. It was evidenced that iron oxalate decomposes at the lowest temperature compared to the decomposition temperatures of the individual oxalates. XRD, IR and TEM/ED studies were approached to investigate the individual oxalates and the mixture coprecipitates for the high-T c superconducting material synthesis.

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The Vrancea region, in the South-Eastern Carpathians (Romania), represents a unique case among the seismic areas in the world taking into account the extreme concentration and persistence of seismicity and tectonic stress field. Our goal is to show that the particular shape of attenuation and shear wave splitting properties can be interpreted in the light of the decoupling and slab retreat processes, which hypothetically induce a specific configuration of the upper mantle flow. Delamination and break-off processes combined with retrograde motion of the slab imply lateral asymmetry in flow geometry and geotectonic properties. Particularly relevant is the strike-parallel flow localized in front of the downgoing slab, in contrast with the steeply dip flow along the slab in the back side. The local upper mantle flows around the descending seismic active body explains the contrast of the seismic wave attenuation in the back-arc region against fore-arc region and the strong anisotropy anomaly observed in the South-East Carpathians (time delays of 1.5–2 s). Outside the epicentral area, the coherent pattern of the shear wave splitting follows the trends of the deformation field as outlined by the GPS measurements, in favour of a strong coupling between the surface and mantle processes.

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Abstract  

TG, DTG and DTA methods were used for the investigation of some waste agricultural products, such as grape seeds, walnut shells, plum and peach stones, which can serve as raw materials for the production of active carbons. It was demonstrated that thermo analytical methods are appropriate to study the thermal characteristics of the above wastes and the data obtained can be applied to the technological processes of active carbon preparation.

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Abstract  

Dehydration of irradiated and non-irradiated asparagine monohydrate was investigated by means of a computer interfaced PerkinElmer 1B DSC in isothermal conditions and static atmosphere. Isothermal runs were performed at 358, 363, 368 and 373 K. Samples were γ-irradiated at room temperature, using a 137Cs source with an activity of 3·1013 Bq and a dose rate of 4·102 Gy h−1, with irradiation times between 8–116 h. Isothermal kinetics were analyzed via the common factorized rate equation. Šesták-Berggren conversion function was found to best fit the experimental data. Of the three fitting parameters, only the one associated with the activation energy was found to follow a coherent variation with the exposure time. Even within this simple model, that makes the activation energy a useful stability criterion within a set of similar samples.

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