"Free" Constituent Quarks and Dilepton Production in Heavy Ion Collisions

An approach is suggested, invoking vitally the notion of constituent massive quarks (valons) which can survive and propagate rather than hadrons (except of pions) within the hot and dense matter formed below the chiral transition temperature in course of the heavy ion collisions at high energies. This approach is shown to be quite good for description of the experimentally observed excess in dilepton yield at masses 250 MeV < M < 700 MeV over the prompt resonance decay mechanism (CERES cocktail) predictions. In certain aspects, it looks to be even more successful, than the conventional approaches: it seems to match the data somewhat better at dilepton masses before the two-pion threshold and before the rho-meson peak as well as at higher dilepton masses (beyond the phi-meson one). The approach implies no specific assumptions on the equation of state (EOS) or peculiarities of phase transitions in the expanding nuclear matter.Comment: 13 pages, 3 PNG figures. submitted to Sov. Nucl. Phy

Crystal structure of mixed fluorites Ca(1-x)Sr(x)F(2) and Sr(1-x)Ba(x)F(2) and luminescence of Eu(2+) in the crystals

Within the framework of the virtual crystal method implemented in the shell model and pair potential approximation the crystal structure of mixed fluorites Ca(1-x)Sr(x)F(2) and Sr(1-x)Ba(x)F(2) has been calculated. The impurity center Eu(2+) and the distance Eu(2+)-F in this crystals have been also calculated. The low level position of excited 4f65d configuration of the Eu(2+) ion has been expressed using phenomenological dependence on distance E(2+)-F. The dependences of Stokes shift and Huang-Rhys factor on concentration x have been received for yellow luminescence in Sr(1-x)Ba(x)F(2):Eu(2+). The value x, for which the eg -level of Eu(2+) ion will be in conduction band in Sr(1-x)Ba(x)F(2):Eu(2+) has been calculated.Comment: 8 pages, 3 figures. The manuscript is sent to journal 'Physics of the solid state'. The results will be submitted on inernational conference SCINTMAT'2002 in oral session (june,20-22,2002,Ekaterinburg,Russia). Corresponding author e-mail: [email protected]

Дистанционный лазерный метод контроля нефтяных загрязнений на земной поверхности

Most of all oil and oil products spill on a terrestrial surface when running through the pipelines. Presently existing systems of monitoring spillages in the pipelines record large spillages and have a sensitivity limit, which makes about 1% of the pipeline capacity. However, such systems do not record spillages with intensity of less than 1%.One of the options of a leakage detection system of oil products with intensity less than 1% can be a remote monitoring system of oil pollution of a terrestrial surface from the aircraft flying over the route of the pipeline.The paper studies the possibilities of using a remote laser fluorescent method to detect and classify oil pollution on a terrestrial surface. This method allows to detect oil products pollution of a terrestrial surface and classify them into four groups: terrestrial surface (free of oil product contaminations); spill of the light cleared oil products on a terrestrial surface; spill of crude oil; spill of heavy oil products.To study the fluorescence spectra features of natural formations and oil pollution a laboratory installation was created for the 266 nm wavelength of fluorescence excitation. The laboratory installation allows measurement of fluorescence spectra in range from 295 to 740 nm.Over 850 fluorescence spectra of various oil products of the pure and polluted terrestrial surfaces received during laboratory researches were further used as the basic data to develop a detection and classification method of oil pollution on a terrestrial surface.Results of pilot studies and mathematical modelling show that the laser remote method of oil pollution detection on a terrestrial surface, which uses the excitement wavelength of 266 nm, records the fluorescent radiation in three narrow spectral ranges with central wavelengths of 313,5; 334,5; 400,0 nm and scattered radiation at the wavelength of 266 nm allows reliable detection of oil pollution with a probability of the correct detection more than 98%. Addition of one more narrow spectral ranges with the central wavelengths of 358.5 nm allows to provide classification of oil products into three types: light oil products, heavy oil products, crude oil with probability of the correct classification more than 0,99. This allows us to consider the described laser method as one of their perspective options of remote system for detection and classification of oil pollution on a terrestrial surface.Рассматривается лазерный метод обнаружения и классификации нефтяных загрязнений на земной поверхности. Приводятся экспериментальные спектры флуоресценции нефтепродуктов и различных земных поверхностей. Показано, что метод, использующий длину волны возбуждения 266 нм, регистрацию флуоресцентного излучения в трех спектральных диапазонах с центральными длинами волн 313,5; 334,5; 400,0 нм и рассеянного излучения на длине волны 266 нм, позволяет обнаруживать нефтяные загрязнения с вероятностью правильного обнаружения 0,98. Использование еще одного спектрального диапазона с центральной длиной волны 358,5 нм позволяет проводить классификацию по трем типам - легкие и тяжелые нефтепродукты, сырая нефть с вероятностью правильной классификации больше 0,99. DOI: 10.7463/rdopt.0315.078207