arXiv subjects

N. Tsitverblit

Publications and source records attributed to N. Tsitverblit.

4 recordsLinked to original sources

arXiv2013

Initial Friedmann universe, its spatial flatness, matter creation, and the cosmological term

In the Friedmann equations, an infinite initial density is avoided only when the universe is spatially flat. With such equations being then valid when the scale factor $a=0$, the universe must also be in the state of vacuum when $a$ is infinitesimal. Matter creation thus largely comes from nonlinearity of the Friedmann equations at a finite $a$. For the correspondence between such an initial vacuum and the Friedmann universe, therefore, a vacuum density is suggested to be gravitationally significant only when it could also have a matter phase. The effective cosmological term is then due to such a vacuum density.

gr-qc↗

arXiv2011

Double-component convection due to different boundary conditions with broken reflection symmetry for a component

Onset of double-component convection due to different boundary conditions is studied in a diversely oriented infinite slot with broken reflection symmetry between the slot conditions for a component. Among other outcomes, the broken symmetry results in small-amplitude viscous convection remaining of an oscillatory nature for any slot orientation other than a horizontal one. Such a universality also involves various abrupt changes in the marginal-stability curves. In inviscid fluid, such changes emerge with zero instability thresholds. Some of these abrupt changes give rise to new mechanisms for three-dimensionality of the instability. One such a mechanism comes with multiplicity and isolated existence of as well as hysteresis between solutions of the linear stability equations. Both the hysteresis region and the other abrupt 3D changes are described in terms of an analogy between the effect of a ratio of the 2D and 3D wave numbers and that of a 2D ratio between two gravity components. The mechanism of finite-amplitude steady convection in a horizontal slot is also analyzed and its relevance to abrupt climate change is discussed. (This is a substantially shortened Abstract. The full version of Abstract is on the manuscript itself.)

physics.flu-dyn↗

arXiv2007

Double-component convection due to different boundary conditions in an infinite slot diversely oriented to the gravity

Onset of small-amplitude oscillatory and both small- and finite-amplitude steady double-component convection arising due to component different boundary conditions in an infinite slot is studied for various slot orientations to the gravity. The main focus is on two compensating background gradients of the components. The physical mechanisms underlying steady and oscillatory convection are analyzed from the perspective of a universally consistent understanding of the effects of different boundary conditions.

physics.flu-dyn↗

arXiv2004

Mechanism of finite-amplitude double-component convection due to different boundary conditions

A new mechanism of double-component convection is discovered. It emerges in a horizontal layer of Boussinesq fluid as a stable stratification due to flux boundary conditions is added to an unstable gradient specified by fixed boundary values. A large enough perturbation substantially decreases the stable flux gradient but fails to mix the unstable fixed-value gradient. Steady finite-amplitude flows reminiscent of Rayleigh--Benard convection then arise even as the net background stratification is stable, emphasizing the importance of the identified mechanism for double-component fluid systems. V2 Abstract: A new mechanism of double-component convection is discovered. It emerges in a horizontal layer of Boussinesq fluid as a stable stratification due to flux boundary conditions is added to an unstable gradient specified by fixed boundary values. Driven by this mechanism, steady finite-amplitude flows reminiscent of Rayleigh--Benard convection arise even when the background density stratification is stable.

physics.flu-dyn↗