We consider general radially moving frames realized in the background of nonextremal black holes having causal structure similar to that Schwarzschild metric. In doing so, we generalize Lema\^{\i}tre approach, constructing free-falling which are built from reference particles with an arbitrary specific energy $e_{0}$ including $e_{0}<0$ and a special case $e_{0}=0$. The formula 3-velocity freel...

In this methodological paper we consider geodesic motion of particles in a spherically symmetric black hole space-times. We develop an approach based on splitting the velocity freely falling particle to flow velocity, which depends only metric, and deviation from it (a peculiar velocity). It applies wide class metrics is exploited under horizon Schwarzschild hole. The present work generalizes p...

To improve our understanding of the pulsational instabilities found in some of the PG1159-type pre-white dwarfs we performed detailed nonradial stability analyses on heliumstar evolutionary models. Adopting canonical chemical compositions as derived from spectroscopic observations, we found pulsational instabilities for all stellar masses considered (0.57, 0.63, 0.7 M ). The blue boundary of th...

We summarize a longer campaign of spectroscopic observations of the suspected Maia variable star γ CrB . Previously published data are complemented by two-longitudinal observations. We investigate 1262 CCD spectra for short-term radial velocity variations. Results show that A0 stars can pulsate with periods quite similar to those of the well-known δ Scu stars. From a frequency analysis of the d...

This paper studies the inverse data envelopment analysis using the nonradial enhanced Russell model. Necessary and sufficient conditions for inputs/outputs determination are introduced based on Pareto solutions of multiple-objective linear programming. In addition, an approach is investigated to identify extra input/lack output in each of input/output components (maximum/minimum reduction/incre...

The gravitational clustering of collisionless particles in an expanding universe is modelled using some simple physical ideas. I show that it is possible to understand the nonlinear clustering in terms of three well defined regimes: (1) linear regime; (2) quasilinear regime which is dominated by scale-invariant radial infall and (3) nonlinear regime dominated by nonradial motions and mergers. M...

We review the current state of Cepheid modeling and discuss its dominant deficiency, namely the use of time dependent mixing length. Notwithstanding, Cepheid modeling has achieved some excellent successes, and we mention some of the most recent ones. Discrepancies between observations and modeling appear not so much in the gross properties of single mode Cepheids, but rather when more subtle no...