Abstract Upon specifying an equation of state, spherically symmetric steady states the Einstein-Euler system are embedded in 1-parameter families solutions, characterized by value their central redshift. In 1960’s Zel’dovich (Voprosy Kosmogonii 9:157–170, 1963) and Harrison et al. (Gravitation Theory Gravitational Collapse. The University Chicago press, Chicago, 1965) formulated a turning point...

the focus of studies in the field of passive walking has often been on straight walking, while less attention has been paid to the field of turning motions. in this paper, the passive motions of a finite width rimless wheel as the simplest 3d model of passive biped walkers was investigated with a focus on turning motions. for this purpose, the hybrid model of the system consisting of continuous...

the time-optimal trajectory for an airplane from some starting point to some final point is studied by many authors. here, we consider the extension of robot planer motion of dubins model in three dimensional spaces. in this model, the system has independent bounded control over both the altitude velocity and the turning rate of airplane movement in a non-obstacle space. here, in this paper a g...

Even in state-of-the-art virtual reality (VR) setups, participants often feel lost when navigating through virtual environments. In VR applications and psychological experiments, such disorientation is often compensated for by extensive training. Here, two experimental series investigated participants’ sense of direction by means of a rapid point-to-origin paradigm without any performance feedb...

We investigate cosmological evolution in models where the effective potential V (φ) may become negative for some values of the field φ. Phase portraits of such theories in space of variables (φ, φ̇,H) have several qualitatively new features as compared with phase portraits in the theories with V (φ) > 0. Cosmological evolution in models with potentials with a “stable” minimum at V (φ) < 0 is sim...