Paleointensity of the geomagnetic field in the last half-million years in regions of the Red Sea and south of the Mid-Atlantic Ridge

The paleointensity of a geomagnetic field is determined on the basis of the standard Thellier’s method using the remanent magnetization (H _a ) of basalts of the rift zone of the Red Sea (with an age of 0.5 million years) and south of the Mid-Atlantic Ridge (with an age of 0.1–0.3 million years). Samples were selected whose natural remanent magnetization (NRM) was mainly one-component and the measured Curie temperatures of the titanium-magnetite fraction (T _C = 205–250°C) were close to the calculated values. Samples with T _C = 580°C were also used. It was shown that NRM of basalts with both high and low T _C values have a thermoremanent nature. The studies have revealed that the law of independence and additivity of partial thermoremanent magnetizations (PTRMs) is satisfied for the collected samples with an error of no more than 6% and the error of determination of the field of TRM creation using the Arai-Nagata diagram is no more than 10%. The value H _a = 32 A/m determined from NRM of basalts south of the Mid-Atlantic Ridge appears to be approximately equal to the contemporary intensity of the geomagnetic field (H _c ) in this region. In the Red Sea region, H _a = 77.5 A/m, which is 2.5 times higher than the current value. It is suggested that during formation of the basalts of the Red Sea rift zone the geomagnetic pole was located in that region and the virtual dipole moment was 35% higher than its contemporary value.     

Synthesis and Structure of 1-Bromo-1-nitro-2-piperidino(cyclohexylamino)-2-phenylethenes

A preparation method was developed for new representatives of halonitroenamines, 1-bromo-1-nitro-2-piperidino(cyclohexylamino)-2-phenylethenes. Both molecules possess E configuration and are of high polarity.     

Radiation induced defects in SiO 2

The main luminescent centers in SiO 2 films are the red luminescence R (650 v nm; 1.85 v eV) of the non-bridging oxygen hole center (NBOHC) and the twofold-coordinated (divalent) silicon with a blue B (460 v nm; 2.7 v eV) and a UV band (285 v nm; 4.4 v eV). Especially the latter ones are produced under irradiation, but from existing precursors assumed as silicon related oxygen deficient centers (SiODC). Therefore, in order to prove these models we compare a direct oxygen implantation with a direct silicon implantation into SiO 2 layers. The main result is: implanting oxygen increases the red band R but does not affect the blue band B. Silicon surplus increases the amplitude of the blue (B) luminescence, but reduces the amplitude of the red (R) one. Studying the cathodoluminescence dose dependence of these blue and red bands we have established defect transformation kinetics in SiO 2 including six main defects and precursors as well as the mobile oxygen as the main transmitter between precursors and the radiation induced defects. The kinetics is described by eight rate equations which predict the dose dependence of the red (R) and blue (B) luminescence intensities and their temperature dependences very well.     

Structure of 4-nitro-3-benzoyloxy-1,1-dimethyl-1-silacyclopentane in liquid and solid phases

Conclusions By means of¹³C and¹H NMR using a lanthanide shift reagent, along with x-ray structure analysis, a structural study has been made of 4-nitro-3-benzoyloxy-1,1-dimethyl-1-silacyclopentane; and it has been shown that the five-membered organosilicon heterocycle in the liquid and solid phases has the half-chair conformation with predominantly diequatorial orientation of the substituents.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1773–1777, August, 1987.The authors wish to thank A. G. Kozlovskii for participating in this work.     

Effect of hydrostatic pressure on isothermal remanent magnetization of rocks

The effect of hydrostatic pressure (up to 1.3 GPa) on the isothermal remanent magnetization of rocks is studied experimentally using a new-type nonmagnetic high-pressure cell produced at the Institute of High-Pressure Physics (Troitsk, Moscow oblast). The experiments were carried out at the European Center for Research and Education in Environmental Geoscience (CEREGE), France.     

Luminescence of GeO2 glass, rutile-like and α-quartz-like crystals

The luminescence of GeO₂ rutile-like crystals was studied. Crystals were grown from a melt of germanium dioxide and sodium bicarbonate mixture. Luminescence of the crystal was compared with that of sodium germanate glasses produced in reduced and oxidized conditions. A luminescence band at 2.3 eV was observed under N₂ laser (337 nm). At higher excitation photon energies and X-ray excitation an additional band at 3 eV appears in luminescence. The band at 2.3 eV possesses intra-center decay time constant about 100 μs at 290 K and about 200 μs at low temperature. Analogous luminescence was obtained in reduced sodium germanate glasses. No luminescence was observed in oxidized glasses under nitrogen laser, therefore the luminescence of rutile-like crystal and reduced sodium germanate glass was ascribed to oxygen-deficient luminescence center modified by sodium. The band at 2.3 eV could be ascribed to triplet-singlet transition of this center, whereas the band at 3 eV, possessing decay about 0.2 μs, could be ascribed to singlet-singlet transitions. Both bands could be excited in recombination process with decay kinetics determined by traps, when excitation realized by ArF laser or ionizing irradiation with X-ray or electron beam. Another luminescence band at 3.9 eV in GeO₂ rutile-like crystal was obtained under ArF laser in the range 100-15 K. Damaging e-beam irradiation of GeO₂ crystal with α-quartz structure induces similar luminescence band.     

Experimental evidence of time-delay-induced death in coupled limit-cycle oscillators

Experimental observations of time-delay-induced amplitude death in two coupled nonlinear electronic circuits that are individually capable of exhibiting limit-cycle oscillations are described. The existence of multiply connected death islands in the parameter space of coupling strength and time delay for coupled identical oscillators is established. The existence of such regions was predicted earlier on theoretical grounds [Phys. Rev. Lett. 80, 5109 (1998); Physica (Amsterdam) 129D, 15 (1999)]. The experiments also reveal the occurrence of multiple frequency states, frequency suppression of oscillations with increased time delay, and the onset of both in-phase and antiphase collective oscillations.     

Triplet Fullerenes as Prospective Spin Labels for Nanoscale Distance Measurements by Pulsed Dipolar EPR Spectroscopy

Precise nanoscale distance measurements by pulsed electron paramagnetic resonance (EPR) spectroscopy play a crucial role in structural studies of biomolecules. The properties of the spin labels used in this approach determine the sensitivity limits, attainable distances, and proximity to biological conditions. Herein, we propose and validate the use of photoexcited fullerenes as spin labels for pulsed dipolar (PD) EPR distance measurements. Hyperpolarization and the narrower spectrum of fullerenes compared to other triplets (e.g., porphyrins) boost the sensitivity, and superior relaxation properties allow PD EPR measurements up to a near‐room temperature. This approach is demonstrated using fullerene–nitroxide and fullerene–triarylmethyl pairs, as well as a supramolecular complex of fullerene with nitroxide‐labeled protein. Photoexcited triplet fullerenes can be considered as new spin labels with outstanding spectroscopic properties for future structural studies of biomolecules.     

Autosoliton model of the spinning fronts of reaction

Experiments with reaction fronts (detonation waves and solidflames) reveal that, near the combustion limit, the fronts movein a spinning regime when localized zones of intensive reactiontravel along spiral trajectories. In the paper, the spinningwave is interpreted as an autosoliton and described phenomenologicallyby a nonlinear partial differential equation. The equation isstudied numerically, and the presence of the stable spinningand autosoliton solutions is shown.