The chemical composition of stars in the globular clusters M 10, M 12, and M 71     

T. V. Mishenina  V. E. Panchuk  N. N. Samus’ 《Astronomy Reports》2003,47(3):248-253

The abundances of 19 chemical elements in the atmospheres of five stars belonging to three globular clusters have been determined by applying the model-atmospheremethod to 430.0–790.0 nm spectra obtained with the échelle spectrometer of the 6-m telescope of the Special Astrophysical Observatory. The abundances of silicon, calcium, iron-peak elements, copper, zinc, and neutron-capture elements follow the abundance patterns for halo stars. The abundance of sodium in M 10 giants provides evidence that different mixing mechanisms operate in halo and cluster stars or that light elements are enriched in different ways in the pre-stellar matter from which some globular clusters and halo stars were formed.  相似文献   

The empirical Melchior laws and parametric excitation of the Chandler wobble     

G. S. Kurbasova  L. V. Rykhlova  G. N. Shlikar’ 《Astronomy Reports》2003,47(6):525-530

Models of the motion of the terrestrial reference frame with respect to an inertial frame can describe the motions of the Earth-Moon system, which are traditionally separated into precession, nutation, the polar motion, and rotation about the Earth’s axis. Existing theoretical models do not describe variations in the Earth-orientation parameters with the required accuracy, so that the current polar coordinates and duration of the day must be determined from observations. To improve theoretical models for the time dependence of the coordinates of the Earth’s pole, we examine the possible excitation of the Chandler wobble due to internal properties of the Earth-Moon system. A differential equation describing the parametric resonance in the Earth-Moon system is obtained for the first region of the parametric excitation. The solution of this equation analytically describes the finite amplitudes of the nonlinear conservative system. The theoretical results are compared with the empirical laws of Melchior deduced from observational data on the coordinates of the Earth’s pole.  相似文献   

The chemically distinct nucleus and structure of the S0 galaxy NGC 80     

O. K. Sil’chenko  S. E. Koposov  V. V. Vlasyuk  O. I. Spiridonova 《Astronomy Reports》2003,47(2):88-98

The giant lenticular galaxy NGC 80, which is the brightest member of a rich group, possesses a central evolutionarily-distinct region: the stars in the nucleus and in a circumnuclear ring of radius 5″t–7″ have a mean age of only 7 Gyr, whereas the stellar population of the bulge is older than 10 Gyr. The nucleus of NGC 80 is also chemically distinct: it is a factor of 2–2.5 richer in metals than its immediate neighborhood and is characterized by a high magnesium-to-iron abundance ratio [Mg/Fe]≈+0.3. The global stellar disk of NGC 80 has a two-tiered structure: its outer part has an exponential scale length of 11 kpc and normal surface density, while the inner disk, which is also exponential and axisymmetric, is more compact and brighter. Although the two-tiered structure and the chemically distinct nucleus obviously have a common origin and owe their existence to some catastrophic restructuring of the protogalactic gaseous disk, the origin of this remains unclear, since the galaxy lacks any manifestations of perturbed morphology or triaxiality.  相似文献   

Estuary-specific variation in the air-water gas exchange coefficient for oxygen     

James N. Kremer  Alyssa Reischauer  Charlene D’Avanzo 《Estuaries and Coasts》2003,26(4):829-836

Oxygen air-water gas exchange was measured using floating chambers in two shallow tidal estuaries of differing bathymetry and local terrain, near Waquoit Bay, Massachusetts (United States). The specific chamber design permitted measurements of gas flux in 15 min, allowing analysis of the relationship with wind speed and tidal stage. Exchange coefficients ranged from 0.5 to 2.5 g O₂·m^?2 h^?1 atm^?1 (equivalent to piston velocities of 1.5 to 7 cm h^?1) for wind speeds of 0.3 to 9 m s^?1 at 10 m elevation. While the relationships for each estuary appear linear (significant linear regressions with wind speed were shown for each estuary, and the slopes were different at the 99.5% confidence level), the range of speeds differed at the two sites and an exponential function of wind speed was consistent with the combined data from both estuaries. A power function of wind speed was not an acceptable model. The exchange coefficients for our estuaries are from 57% to as low as 9% of that predicted by previously published generic equations. Because the atmospheric correction can be significant in shallow, metabolically active coastal waters, we suggest that empirically determined relationships for gas exchange versus wind for a specific estuary are preferable to the predictions of the general equations. While the floating chamber method should be used cautiously, at low winds speeds (below 8 m s^?1) and in slowly flowing waters, it provides a convenient approach for quantifying these site-specific differences. The differences, especially those between shallow sheltered systems and the open waters best fit by some published relationships, are ecologically important and do not appear yet to be measurable by other methods.  相似文献   

The eclogites in the Monotonous Series of the Moldanubian zone and the theory of thermal pulses: a reply     

P. J. O’Brien  S. Vrána 《International Journal of Earth Sciences》1997,86(3):716-719

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Calculations of horizontal mixing rates using222Rn and the controls on hypoxia in western Long Island Sound, 1991     

Thomas Torgersen  Edward DeAngelo  James O’Donnell 《Estuaries and Coasts》1997,20(2):328-345

Late summer hypoxia (<3 ppm oxygen) in western Long Island Sound (WLIS) is a persistent environmental and management issue whose controlling processes are poorly understood. Measured rates of sediment and water-column oxygen consumption in the bottom water suggest that a condition of no oxygen should be attained on the time scale of 13–30 d. Observations, however, indicate the onset of hypoxia is of the order 150 d. Therefore, horizontal and/or vertical transport of oxygen into the area of hypoxia must play an important role. Hypoxia decreases benthic activity and the sediment flux of²²²Rn. The resulting horizontal gradient in bottom water²²²Rn was measured and used to estimate the effective horizontal transport rate (>5–50 m² s^?1), which is considerably slower than previous estimates. Scale analysis of the hypoxia process indicates that horizontal transport rates alone can explain the slow progression of hypoxia in XLIS but that vertical processes may also be capable of delaying the onset of hypoxia especially under conditions of weak stratification or weak intermediate layer oxygen consumption. This scale analysis indicates a delicately balanced process that is sensitive to both climatologically-driven variability in the rates of horizontal and vertical transport as well as the biologically-driven rates of oxygen consumption. An improved ability to predict and/or control hypoxia must be based on a better understanding of temporal and spacial variations in circulation, mixing, and stratification as well as the biological processes in the water column and the sediments.  相似文献   

ASPI experiment: measurements of fields and waves on board the INTERBALL-1 spacecraft     

S. Klimov  S. Romanov  E. Amata  J. Blecki  J. Büchner  J. Juchniewicz  J. Rustenbach  P. Triska  L. J. C. Woolliscroft  S. Savin  Yu. Afanas’yev  U. de Angelis  U. Auster  G. Bellucci  A. Best  F. Farnik  V. Formisano  P. Gough  R. Grard  V. Grushin  G. Haerendel  V. Ivchenko  V. Korepanov  H. Lehmann  B. Nikutowski  M. Nozdrachev  S. Orsini  M. Parrot  A. Petrukovich  J. L. Rauch  K. Sauer  A. Skalsky  J. Slominski  J. G. Trotignon  J. Vojta  R. Wronowski 《Annales Geophysicae》1997,15(5):514-527

The plasma-wave experiment ASPI (analysis of spectra of plasma waves and instabilities) on board the INTERBALL spacecraft is a combined wave diagnostics experiment. It performs measurements of the DC and AC magnetic field vector by flux-gate and searchcoil sensors, the DC and AC electric field vector by Langmuir double probes and the plasma current by Langmuir split probe. Preliminary data analysis shows the low noise levels of the sensors and the compatibility of new data with the results of previous missions. During several months of in-orbit operation a rich collection of data was acquired, examples of which at the magnetopause and plasma sheet are presented in second part of the paper.  相似文献   

盐田港3000吨级钢板码头原体观测试验研究     

徐亘  祝小丰 《华东地质学院学报》1997,(3)

本文介绍了对钢板桩码头岸壁进行的原体观测试验，通过观测钢板桩的挠度、作用在钢板桩上的土压力以及拉杆轴向拉力，可以了解板桩岸壁在回填土的作用下，其结构各主要部分的受力及变形情况，为今后同类型结构的合理分析和设计以及港口工程技术规范有关条文的编制，提供了实测资料。  相似文献   

A statistical analysis of methanol maser groups     

I. E. Val’tts  S. Yu. Lyubchenko 《Astronomy Reports》2004,48(10):834-839

An analysis of the flux densities of the 5₁-6₀ A ⁺ (6.7 GHz) and 2₀-3_?1 E (12.2 GHz) class II methanol maser lines in a large and homogeneous sample of maser sources has been carried out. For convenience, the maser lines were divided into three groups: group I contains spectral features for the lines most prominent in the 5₁-6₀ A ⁺ (6.7 GHz) transition, group II contains spectral features for the lines strongest in the 2₀-3_?1 E (12.2 GHz) transition, group III contains spectral features for which the velocities of the emission maxima of the two lines coincide. The same dependence was found for group II and group III: log S _6.7=(0.79±0.05)×log S _12.2+(0.79±0.05). The spectral features in group I do not obey this relation, and deviations from a linear dependence are considerably greater. It is suggested that methanol class II masers be divided into a subclass IIa, which has special conditions favoring 6.7 GHz masers, and a subclass IIb, which is comprised of the 12.2 GHz masers and those 6.7 GHz masers that necessarily accompany them under the same conditions.  相似文献   

Relative variations of the physical parameters of variable extragalactic radio sources     

S. A. Tyul’bashev  P. A. Chernikov 《Astronomy Reports》2004,48(9):716-723

A method for studying the physical conditions in compact components of extragalactic radio sources displaying variability on time scales of hundreds of days is proposed. The method can be used to estimate the relative variations of the magnetic-field strength and number density of relativistic electrons in superluminal jets from the cores of quasars and radio galaxies. Results are presented for the jets of the quasars 3C 120, 3C 273, 3C 279, and 3C 345. The energies of the magnetic field and relativistic particles in these objects are not in equipartition. As a rule, the magnetic-field strength decreases appreciably during the evolution of an expanding jet, while the number of relativistic electrons grows.  相似文献