Long-term changes in solar activity,based on the data for <Superscript>10</Superscript>Be and <Superscript>14</Superscript>C cosmogenic isotopes over the last 10000 years

The results from a spectral analysis of production rate of ¹⁰Be cosmogenic isotope over the last 10000 years are considered. It is shown that the ¹⁰Be production rate is cyclic. Duration of the most powerful cycle is about 2300 years. In addition to this cycle, thousand-year variations in the ¹⁰Be production rate are observed. The thousand-year cycle could be due to the modulation of the cosmic ray flux by solar activity.     

Catalytic properties,surface composition,and acidity of Ga-ZSM-5 catalysts for aromatization of lower paraffins

A study has been made of the catalytic and acidic properties together with the surface composition of the zeolite HZSM-5 modified by gallium by hydrothermal treatment with a sodium gallate solution and also by impregnation with gallium nitrate solution. It has been established that the first method of introducing gallium produces a more selective catalyst for aromatization of n-butane. It has been shown that under the conditions of the catalytic reaction several types of active centers incorporating Ga are formed: Ga₂O₃ on the zeolite surface, gallium ions inside the zeolite canals, and gallium atoms at the surface of and in the lattice that are bonded to OH groups.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2726–2732, December, 1991.     

Transformations of isobutylene in the presence of various types of zeolites

Conclusions In contrast to zeolites with ultrahigh silica content, type A, X, Y, and M zeolites in the Na form and also those modified by decationization, cation exchange, and addition of-Al₂O₃, Al₂O₃-SiO₂, Pt, and Rh show a low activity in the aromatization reaction of C₃-C₄ olefins at 450–550°C at times of contact of 2–14.4 sec. The zeolites studied become rapidly deactivated as the result of intense coke formation.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 6, pp. 1300–1304, June, 1981.     

Approximately 2400-Year Cycle in the Concentration of Cosmogenic Radionuclides: Sources of Variations

Cosmogenic isotopes, including ¹⁴C, ¹⁰Be, and ⁷Be, are produced in the Earth’s atmosphere under the effect of cosmic rays. The rate of their production is determined by several factors, such as the intensity of primary galactic cosmic rays, the level of solar activity, and the strength of the Earth’s magnetic field. Changes in the isotope concentrations and distributions receive contributions from mixing processes proceeding in the surrounding medium: the atmosphere, biosphere, and oceans. The isotopes ¹⁴C and ¹⁰Be are the most important for studying solar activity and climate. Investigation of isotope concentrations reveal that there are both long-term trends and cyclic components. As for ¹⁴C, the long-term component caused by the change in the magnetic dipole moment of the Earth with a characteristic time of about 10⁴ years is the most commonly known. It is well known that the concentrations of cosmogenic isotopes change cyclically with time. The ~2400-year cycle (Hallstatt cycle) and the ~210-year cycle (de Vries cycle) are the most famous. In the present article, we discuss the possible origin of the ~2400-year cycle.     

Generation of picosecond pulses with a large axial interval in the IR and visible spectral regions

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 52, No. 1, pp. 20–24, January, 1990.