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- Author or Editor: F. Popescu x
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We present a short review of the most recent results coming from the numerical modeling of seismic hazard and interpretation of the new observations provided by the recently installed seismic stations in Romania. There are still controversial questions related to the asymmetric distribution of the ground motion radiated by the Vrancea intermediate-depth earthquakes and which is the main factor responsible for this particular distribution: seismic source, structural model, site effects or vulnerability. Our main goal is to provide a solution to this key problem, with direct implications upon the seismic hazard assessment. NE-SW elongation of the isoseismals and the maximum values in the Romanian Plain are well explained by the source radiation pattern and the average structural model. The attenuation toward NW is shown to be a frequency-dependent effect, much more important in the high frequency range (≯1 Hz). We conclude that the present seismic hazard of Romania, computed by the deterministic approach, fits well, as a first approximation, the ground motion distribution for the low-frequency band, and the apparent contradiction with the historically-based intensity maps arises mainly from a systematic difference in the vulnerability of the buildings in the intra- and extra-Carpathians regions.
Abstract
In order to determine uranium from raw phosphoric acid solutions, resulted by the sulphuric acid attack of phosphate rocks and the strip solutions of the solvent extraction process for uranium recovery, two classes of analytical methods were established: one for low uranium content in phosphoric acid, and the other for higher uranium concentration in the same medium. The study was based on specific methods, therefore interference probability with other impurities in phosphoric acid medium is low. In the first class, X-ray fluorescence and spectrophotocolorimetric methods were used. X-ray fluorescence was applied on direct raw phosphoric acid solution and raffinate. The last one was associated with solvent extraction [di-(2-ethylhexyl) phosphate + triocylphosphine oxide] on the U(IV)-Arsenazo III complex in strip. The methods of the second class, were used for strip uranium concentrated solutions: X-ray fluorescence isotopic dilution and mass spectrometry, spectrophotocolorimetry and activation analysis associated with gamma-spectrometry. Here spectrophotocolorimetry involves two methods. The first one is based on the U(IV)-Arsenazo III complex and the other on direct U(IV)—phosphoric acid solutions measurements. A good agreement was obtained in each case for all comparative measurements involving various methods.
Abstract
The isoconversional methods (Friedman and Flynn-Wall-Ozawa) as well as the invariant kinetic parameters method (IKP) were used in order to work the TG data corresponding to the thermal dissociation of smithsonite. As a result we mention a mechanism change at T≈671 K. For T>671 K, which corresponds to heating rates in the range 0.57– 8.06 K min–1, a reaction order model with 1<n≤1.4 describes the experimental data.
Abstract
The TG, DTG, DTA methods were used for investigation of the thermal degradation in static air atmosphere of some collagen-based materials (some sorts of collagen, recent manufactured parchments and tanned leathers, patrimonial (historical) leathers). At the progressive heating, all investigated materials exhibit two main successive processes, associated with the dehydration and thermo-oxidative degradation. The patrimonial leathers were divided in two groups, namely: a group containing the majority of the analyzed materials, for which the rates of the thermo-oxidation process are substantially lower than those corresponding to the recent manufactured leathers, and a group for which the rates of thermo-oxidation process are closed to those corresponding to the recent manufactured leathers. Consequently, if by the thermal analysis in air atmosphere of a leather sample, a value of the rate of the thermo-oxidation process smaller than that corresponding to the recent manufactured leathers is obtained, then the analyzed leather is a patrimonial one. The reciprocal statement of this qualitative criterion for distinction between recent manufactured leather and patrimonial leather is not valid. The DSC analyses of collagen-based materials were performed in air (DSC(air)) and in water (DSC(water)). The denaturation process takes place at lower temperatures in water than in air. Unlike recent manufactured leathers and parchments, each patrimonial leather exhibits on DSC(water) plot 2-4 peaks. Consequently, the number of peaks from DSC(water) curve could be another qualitative criterion for distinction between a recently manufactured leather and a patrimonial leather.
Abstract
The thermal analysis methods (TG, DTG and DTA) were used for the investigation of the thermal degradation of some recent manufactured tanned leathers, leathers that are supports of cultural or historical objects (leather from book covers (XVII-XIX centuries); leather from an Austrian belt (Franz Joseph period), Cordoba leather (XVII century), lining leathers), recent and patrimonial parchments and recent extracted collagen (sorts of collagen obtained from bovine leather at different pH-values, bovine collagen with different hydration degree). At progressive heating, all investigated materials exhibit two main successive processes, associated with the dehydration and thermo-oxidative degradation. Each analyzed material has a characteristic thermal analysis curve (TG, DTG and DTA) that can be considered a material 'fingerprint'. This result suggests the use of the thermal analysis methods to identify of leathers from which the patrimonial objects are manufactured. The rate of thermo-oxidation of recent manufactured tanned leathers is substantially higher than the rate of the same process corresponding to naturally aged leathers that exhibit values of the thermo-oxidation rate appropriate to those obtained for parchments and collagens. The rate of thermo-oxidation of leather can thus be used as a criterion to distinguish between recent manufactured leather and patrimonial one.
