Analysis of density fluctuations in models of open clusters

The frequencies for homologous and non-homologous density flucutations in unisolated, ellipsoidal models of open clusters are determined. These fluctuations are stable. In the cases considered, the frequencies of non-homologous fluctuations are higher than those for homologous fluctuations of the ellipsoidal models. The instability of the proper fluctuations of the phase density at the center of a homogeneous ellipsoid whose central characteristics correspond to the core parameters of a dynamical, numericalmodel cluster is demonstrated. The development of instability of the phase-density flucutations at the center of such an ellipsoid leads to the domination of fluctuations with the frequency γ ₁, corresponding to the growth increment γ ₂ for this instability. Estimates of γ ₁ and γ ₂ agree with estimates obtained for the core of the corresponding dynamical, numerical model cluster. Astrophysical applications of the results are discussed.     

Timescales for mechanisms for the dynamical evolution of open star clusters

We have obtained the stellar velocity dispersion in three mutually perpendicular directions in the halos and cores of clusters as a function of time for several non-stationary open-cluster models. During the dynamical evolution of the open-cluster models, the velocity dispersions undergo oscillations that do not decay during 5–10 violent-relaxation timescales, τ _vr . We estimated the time for synchronization of the rotation of the open-cluster models and their motion around the center of the Galaxy, t _s , which, depending on the model parameters, is t _s ? (5–27)τ _vr . Synchronization mechanisms for the models are discussed. The disruption of the systems in the force field of the Galaxy is strongly affected by tidal friction. We have also estimated the time for the formation of a spherical stellar-velocity distribution in the cluster models, t _σ ? (6 ? 25)τ _vr . The impact of instability in the stellar motions in a cluster on the formation of a spherical velocity distribution in the open-cluster models is discussed. We have noted a tendency for a weakening of the dependence of the coarse phase density of the cluster on small initial perturbations of the stellar phase coordinates in the model cluster cores for times about five times longer than the violent-relaxation time.     

Equilibrium after violent relaxation in numerical dynamical models of open clusters

Models of open clusters in a state of equilibrium in the space of the three parameters of the stellar motion and simultaneously far from virial equilibrium are analyzed. A formula for the phase-space stellar number density in such cluster models is derived, as well as formulas for the integrated and differential energy distributions of the phase-space volume occupied by cluster stars per unit stellar mass. These three quantities are computed for several times exceeding the time for violent relaxation of the cluster model. The phase-space density function obtained is used to compute the distribution of the absolute values of stellar velocities for the cluster model considered.     

Relation between daytime and nighttime values of the critical frequency foF2

The relation between the daytime in the nighttime values of the critical frequencies (foF2) of the ionospheric F ₂ layer is considered. The correlation coefficient of foF2 measured at 1400 and 0200 LT of the same day is considered in various seasons of years with different solar activity (during the complete cycle of solar activity in 1979–1989). Special accent is made on the dependencies of the above mentioned correlation on a choice of magnetically quiet days with various limitations on maximal values of geomagnetic index Ap. It has been obtained that a statistically significant negative correlation between the foF2(1400) and foF2(0200) is more pronounced in the periods of high solar activity. The effect increases with increasing limitation of the considered days on value of Ap: the largest values of the correlation coefficient are observed if only very quiet days are considered (Ap < 6). There are preliminary indications that the considered relation between daytime and nighttime foF2 values depends on latitude.     

Corrosion Resistance of the Nd–Ti Matrix for Actinides

Doklady Earth Sciences - Leaching of Np and Pu in water from samples composed of two titanate phases Nd2Ti3O9 (75 wt %) and Nd2Ti2O7 (25 wt %) is investigated. The rates of leaching actinides...     

Geomagnetic activity as a reflection of processes in the magnetospheric tail: 1. The source of diurnal and semiannual variations in geomagnetic activity

Diurnal and semiannual variations in geomagnetic activity are considered. We prove that there exists an inner magnetospheric source of magnetic activity, which depends on the angle φ between the planes of the magnetotail plasma sheet and the geomagnetic equator. It is shown that diurnal and semiannual variations in magnetic activity result from changes in the value of this angle.     

Behavior of parameters of the ionospheric F2 layer at the edge of the centuries: 2. Height of the layer

The trends in the height of the ionospheric F2 layer, hmF2, for the period from the end of the 1990s to the beginning of the 2010s are considered. It is shown that for a majority of the considered situations (time of the day plus season) negative trends are obtained for all stations for which series of initial data satisfying the requirements were found. They vary from ?1.2 to ?3.1 km per year. The trends in the daytime are slightly higher than in the postsunset period which apparently manifests the influence of the contraction of the upper atmosphere on changes in the hmF2 value.     

FESOM under coordinated ocean-ice reference experiment forcing

Characteristics of the ocean state simulated with the Finite-Element Sea-Ice Ocean Model (FESOM) under the normalized year forcing of Coordinated Ocean-ice Reference Experiments (COREs; Griffies et al., Ocean Model 26:1–46, 2009) are compared with those of other models participating in COREs. In contrast to these models, FESOM is run on an unstructured mesh (with resolution varying between 20 and 150 km). It is shown that the ocean state simulated by FESOM is in most cases within the spread of other models, demonstrating that the unstructured mesh technology has reached the stage when it becomes a reliable tool for studying the large-scale ocean general circulation.