An approach for describing the hindrance of the nuclear 2νββ -decay amplitude is proposed. The approach is based on a new formula obtained by a model-independent transformation of the initial expression for the amplitude. This formula takes explicitly into account the hindrance of the decay-amplitude due to the presence of the collective Gamow-Teller state. Calculations are performed within the simplest version of the approach. Calculated and experimental 2νββ halve-lives are compared for a wide range of nuclei.

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A thermodynamic study of a many-particle two-level system with the $SU(2) \otimes SU(2)$--symmetry interaction in the particle-particle and particle-hole channels is carried out. Using the symmetry of the system, its free energy and phase diagram are calculated. It is demonstrated that the superconducting (particle-particle) and excitonic (particle-hole) condensates are both formed in the considered system which undergoes two phase transitions. The calculated phase diagram represents qualitatively the phase diagram typical for materials with the high-temperature superconducting properties, including the existence of two phase transitions, the first and second order phase transitions, triple and tricritical points.

'ev, L M. Mityushtna, O. A. Rumyantsev, UDC 624.138.22:625.084.001.5 and R. S. Gordeeva RESULTS OF INVESTIGATIONSThe many years of experience of constructing dams by hydraulic filling In the Soviet Union convlnclngly showed that hydrau1ically filled coheslonless soils according to Terzaghl's classlflcatlon can be assigned to soils of average density, to which corresponds a value of the coeffclent of relative density D =0.3-0.5. For an example we give in Table 1 Investigations [i] establlshed that some increase of the unlt weight of the hydraulic flll can be achieved by increasing the specific flow rate of the soll--water mixture mud at the hydraulic flll slte as a consequence of an increase of the shearing forces of the flow on the soll particles being deposited on the bottom, and also as a result of a decrease in ~he actual rate of hydraulic fllllng, whlchmakes It posslble to disperse the simultaneous deposition of soll over a large area and thereby provide selective placement of the particles on the bottom in depressions between other particles or in the "shadow" zone of earlier settled particles. Consequently, the optimal technology should provide q~---,.max and R=~T--~ where qw Is the speclflc flow rate of the slurry on the slope being hydraulically fllled; R is the rate of hydraulic filling; Ah Is the thickness of the layer of hydraulic fill; Ar Is the tlme of hydraullc filling of the layer.The optimal technology is achieved In the case of an end trestle-less trough method of hydraulic fl11ing wlth the use of large dredges for construction of dams with a flattened proflle. It was established that, other conditions being equal, by using the optimal technology of hydraulic f111Ing it is posslble to increase the unlt weight of hydraulically filled sand In comparison with narrow-proflle dams on the average by more than 0.02-0.03 g/ cm s [i]. However, in a number of cases, for example, in seismic regions, a substantial increase in the density of the hydraulic flll with the coefficient being brought to 0.8-0.9 is required to meet the conditions of structural reliabillty. The most expedient means of increasing the density of hydraulic flll is the use of compacting mechanisms, for example, vibrating rollers or caterpillar tractors.