Dynamics of a phase change at the base of the mantle consistent with seismological observations

The phase change model for the origin of the D″ seismic discontinuity is tested by comparing the results of convection modeling with seismic observations. We compute a number of global dynamic models that incorporate a phase change at the base of the mantle with different characteristics and transform the resulting temperature field and the distribution of phases to seismic velocities. Over 900 two-dimensional synthetic waveforms are computed for each of the models from which S, ScS, and Scd phases are picked. The distribution of the relative amplitudes and differential travel time residuals for these phases are statistically compared with the distribution of data from four well studied regions (northern Siberia, Alaska, India, and Central America) in a search for the characteristics of a phase transition that best match these seismic observations. We find that the best fit among the models considered is obtained for phase transitions characterized by a Clapeyron slope of ∼6 MPa K−1 and an elevation above the core-mantle boundary of ∼150 km under adiabatic temperature or 127 GPa and 2650 K on a (P,T) diagram. Dynamic models demonstrate that the value of Clapeyron slope and the density difference between the phases can have significant influence on the dynamics of plumes but probably only a minor influence on the dynamics of subducted slabs. We find that the thermal structure of subducted slabs can be important in giving rise to the seismic triplication; the strongest Scd arrivals in our models are observed in the area of subduction. The folding of the slab at the base of the mantle leads to patterns in differential travel time distributions consistent with seismic observations and suggests that the largest heterogeneity occurs at the top of the D″ layer or just above it. Analysis of the spatial autocorrelation functions of the differential travel time residuals suggests that their characteristic peaks reflect the patterns of slab folding and may provide constraints on the rheology of slabs at the base of the mantle

Flicker-noise spectroscopy in earthquake prediction research

International audienceThe problem of earthquake prediction and the methods of identification of geophysical precursory signals are discussed. To get information on the dynamics of earthquake preparation processes, fluctuations in geophysical time series are analyzed with the method of flicker-noise spectroscopy. Integral indices ? power spectra and various moments ("structural functions") ? are used as information relations. We demonstrate that the method allows us to reveal earthquake precursors

Characteristics of the secondary electrons calibration beam of the accelerator S-25R "Pakhra"

The characteristics of the secondary electrons` calibration quasi-monochromatic beam of the accelerator S-25R "Pakhra" of the Lebedev Physical Institute of the Russian Academy of Sciences (LPI) on the basis of magnet SP-57 are presented. With an electron energy in the range of 45-280 MeV, a collimator diameter in front of the trigger counters of 3 mm and copper Converter thicknesses of 1-3 mm, the energy resolution and beam intensity were 4.4-2.2% and around 16 e/sec, respectively

Organ-sparing treatment for primarily disseminated breast cancer with metachronous bilateral involvement

Systemic drug therapy remains first-line treatment for primarily disseminated breast cancer (BC). The problem in the use of local methods to treat BC patients with distant metastases has not been fully solved. The most of investigations presented in the modern literature suggest that patients show significantly better survivals after adjuvant systemic therapy with local exposure of a primary tumor, the main goal of which is its local monitoring. At the same time, the choice of optimal treatments and their sequence and combination remain to be explored. The paper describes a case of successful organ-sparing chemoradiation therapy for primarily disseminated BC with metachronous bilateral involvement

Creation and decay of eta-mesic nuclei

First experimental results on photoproduction of eta-mesic nuclei are analyzed. In an experiment performed at the 1 GeV electron synchrotron of the Lebedev Physical Institute, correlated pi+n pairs arising from the reaction gamma + 12C -> N + eta(A-1) -> N + pi+ + n + (A-2) and flying transversely to the photon beam have been observed. When the photon energy exceeds the eta-meson production threshold, a distribution of the pi+n pairs over their total energy is found to have a peak in the subthreshold region of the internal-conversion process eta p -> pi+ n which signals about formation of eta-mesic nuclei.Comment: 6 pages, 6 figures. Talk at CIPANP, May 2000, Quebe