Stars outside the Hipparcos list closely encountering the Solar system

Based on currently available kinematic data, we have searched for stars outside the Hipparcos list that either closely encountered in the past or will encounter in the future the Solar system within several parsecs. For the first time, we have identified two single stars, GJ 3379 (G 099-049) and GJ 3323 (LHS 1723), as candidate for a close encounter with the solar orbit. The star GJ 3379 could encounter the Sunmore closely to aminimumdistance d _min = 1.32±0.03 pc at time t _min = −163 ± 3 thousand years. We have found two potential candidates for a close encounter that have only photometrical distances: the white dwarf SSSPM J1549-3544 without any data on its radial velocity and the L-dwarf SDSS J1416+1348. The probabilities of their penetration into the Oort cloud region are 0.09 (at a model radial velocity <V _r < = 50 km s⁻¹) and 0.05, respectively.     

First record of petrified Permian pecopterids from the Paraná Basin,Brazil (Corumbataí Formation,Passa Dois Group,northeastern State of São Paulo): Morphology,anatomy and paleoecological implications

Petrified pecopterids are described for the first time in the Paraná Basin. They were collected at an outcrop of the Corumbataí Formation (Passa Dois Group, Middle Permian) in the Municipality of Piracicaba (State of São Paulo, Brazil). The assemblage is composed of Pecopteris taguaiensis Rohn and Rösler, 1986, Pecopteris sp. 1, Pecopteris sp. 2 and Pecopteris sp. 3. An emendation to the diagnosis of P. taguaiensis is proposed on the basis of the characteristics shown by the preserved three-dimensional external leaf morphology and partially by the epidermis (not available in the previously described impressions). The small size of the pinnules, the thick, downward-rolled leaf lamina, the thick veins, the straight walls of the epidermal cells, and the trichomes of the four pecopterid taxa may be interpreted as xeromorphic features developed in response to relatively dry climatic conditions and/or direct incidence of the sunlight. The leaves were impregnated with silica before the final burial, considering that they are fragmented, not deformed and associated with angular breccia clasts.     

Diffuse cosmic gamma-ray background in the 28 ke V-4.1 MeV range from Kosmos 461 observations

Diffuse cosmic background and atmospheric gamma-radiation in the range 28 keV-4.1 MeV were studied with a scintillation spectrometer on board of the Kosmos 461 satellite. Separation of the cosmic and atmospheric components was made possible through a reliable determination of the geomagnetic dependences of albedo gamma-radiation: The spectrum of diffuse background in the energy range covered cannot be fitted with a common law. At energies below 400 keV the spectrum follows a power-law $$I = (5.6 \pm 0.5) \times 10^{ - 3} E^{ - (2.80 \pm 0.05)} cm^{ - 2} s^{ - 1} sr^{ - 1} MeV^{ - 1} .$$ Starting from 400 keV, this power-law breaks down; the spectrum revealing a clearly pronounced shoulder. Extrapolation of the power-law spectrum to higher energies shows that the gamma-ray component responsible for the change in the shape of the spectrum is quite strong, becoming predominant in the diffuse background in the range 1–100 MeV. The intensity of excess radiation is maximum in the region of 700–800 keV reaching ～1.8×10^?2 cm^?2s^?1sr^?1 MeV^?1. The shape of the high energy component spectrum of the diffuse background constructed using the data of Kosmos 461 and SAS-2 is in agreement with the hypotheses of the cosmological origin of the radiation.     

RADIO MAPS OF THE SOLAR WIND TRANSITION REGION

Occultation studies of near-Sun plasmas using several natural sources simultaneously result in large-scale patterns, radio maps of the solar wind flow. Large radio telescopes of the P.N. Lebedev Physical Institute, Pushino, were used. Previously it had been shown that the plasma acceleration and traverse of the sound barrier proceed in an extended region, the transition region of the solar wind, located at radial distances of about 10–40 solar radii from the Sun. The 1989–1994 experiments showed that the evolution of the transition region geometry is very close to that of the optical corona. On the other hand, the plasma flow structures characteristic of the transition region persist in the course of the 11-year cycle, which demonstrates the existence of some specific mechanism of the solar wind acceleration, independent of wide variations of the general solar activity state. These experimental facts are discussed in connection with the existing theoretical approaches.     

Underwater Acoustic Signaling of Bearded Seals (Erignatus barbatus) in the White Sea

Oceanology - The bearded seal occurs in virtually all Arctic seas. During the spring (pupping and mating season), this species is characterized by high underwater acoustic activity; studies...     

New Models for Long Range Forecasts of Summer Monsoon Rainfall over North West and Peninsular India

Summary New models based on (a) Multivariate Principal Component Regression (PCR) (b) Neural Network (NN) and (c) Linear Discriminant Analysis (LDA) techniques were developed for long-range forecasts of summer monsoon (June–September) rainfall over two homogeneous regions of India, viz., North West India and Peninsular India. The PCR and NN models were developed with two different data sets. One set consisted 42 years (1958–1999) of data with 8 predictors and the other, 49 years (1951–1999) of data with 6 predictors. The predictors were subjected to the Principal Component Analysis (PCA) before model development. Two different neural networks were designed with 2 and 3 hidden neurons. To avoid the nonlinear instability, 20 ensemble runs were made while training the network and the ensemble mean results are discussed. The LDA model was developed with 42 years of data (1958–1999) for classifying three rainfall intervals with equal prior probability of 0.33. Both the PCR and NN models showed useful forecast skill for NW India and Peninsular India. Models with 8 predictors performed better than the models with only 6 predictors. The NN model with 3 hidden neurons performed better than model with 2 hidden neurons. For NW India, the NN model performed better than the PCR model. The RMSE of the NN model and PCR model with 8 predictors for NW India (Peninsular India) during the independent period 1984–99 was 12.5% (12.2%) and 12.6% (11.5%), respectively. Corresponding figures for the models with 6 predictors are 15.0% (13.0%) and 13.9% (11.4%) respectively. During the independent period, model errors were large in 1991, 1994, 1997 and 1999. However all the models showed deteriorating predictive skill after 1988, both for NW India and Peninsular India. The LDA model correctly classified 62% of grouped cases for NW India and Peninsular India. The LDA model showed better skill in classifying deficient rainfall (< − 8%) over NW India and excess rainfall (> 3%) over Peninsular India. Received October 2, 1999 Revised December 28, 1999     

The Role of Forests in the Implementation of Russia’s Low-Carbon Development Strategy

Doklady Earth Sciences - The potential role of forests in achieving carbon neutrality in the Russian Federation by 2060 is analyzed. It is shown that the key rate in the Strategy for the...     

Kinetics of collisional-collisional pumping of cosmic H2O masers

Astronomical Council, USSR Academy of Sciences; Urals State University. Translated from Astrofizika, Vol. 28, No. 2, pp. 405–417, March–April, 1988.     

On the entropy of self-gravitating systems

Leningrad State University; Kursk Institute for Improvement of Teachers. Translated from Astrofizika, Vol. 29, No. 3, pp. 595–601, November–December, 1988.     

Active Galactic Nuclei among Polar-Ring Galaxies

Astronomy Letters - Based on SDSS data, we consider the fraction of active galactic nuclei among polar-ring galaxies. We have found evidence for an excess of Seyfert galaxies and LINERS among...