46,166 research outputs found
Shock Wave Development in the Collapse of a Cloud of Bubbles
A numerical simulation of the collapse of a cloud of bubbles has been used to demonstrate the development of an inwardly propagating shock wave which grows rapidly in magnitude. The fully non-linear nonbarotropic homogeneous flow equations are coupled with single bubble dynamics and solved by a stable numerical scheme. The computational results demonstrate the structure of the shock wave as well as its strengthening effect due to the coupling of the single bubble dynamics with the global dynamics of the flow through the pressure and velocity fields. This appears to confirm the speculation of Morch and his co-workers that such shock formation is an important part of cloud collapse
Zeros of Ramanujan polynomials
Abstract. In this paper, we investigate the properties of Ramanujan polynomials, a family of reciprocal polynomials with real coefficients originating from Ramanujan’s work. We begin by finding their number of real zeros, establishing a bound on their sizes, and determining their limiting values. Next, we prove that all nonreal zeros of Ramanujan polynomials lie on the unit circle, and are asymptotically uniformly distributed there. Finally, for each Ramunujan polynomial, we find all its zeros that are roots of unity. 1
Incremental Knowledge Base Construction Using DeepDive
Populating a database with unstructured information is a long-standing
problem in industry and research that encompasses problems of extraction,
cleaning, and integration. Recent names used for this problem include dealing
with dark data and knowledge base construction (KBC). In this work, we describe
DeepDive, a system that combines database and machine learning ideas to help
develop KBC systems, and we present techniques to make the KBC process more
efficient. We observe that the KBC process is iterative, and we develop
techniques to incrementally produce inference results for KBC systems. We
propose two methods for incremental inference, based respectively on sampling
and variational techniques. We also study the tradeoff space of these methods
and develop a simple rule-based optimizer. DeepDive includes all of these
contributions, and we evaluate DeepDive on five KBC systems, showing that it
can speed up KBC inference tasks by up to two orders of magnitude with
negligible impact on quality
Spectral and dynamical analysis of a single vortex ring in anisotropic harmonically trapped three-dimensional Bose-Einstein condensates
In the present work, motivated by numerous recent experimental developments
we revisit the dynamics of a single vortex ring in anisotropic harmonic traps.
At the theoretical level, we start from a general Lagrangian dynamically
capturing the evolution of a vortex ring and not only consider its spectrum of
linearized excitations, but also explore the full nonlinear dynamical evolution
of the ring as a vortical filament. The theory predicts that the ring is stable
for , where is the ratio of
the trapping frequencies along the and axes, i.e., for spherical to
slightly oblate condensates. We compare this prediction with direct numerical
simulations of the full 3D Gross-Pitaevskii equation (GPE) capturing the
linearization spectrum of the ring for different values of the chemical
potential and as a function of the anisotropy parameter . We identify
this result as being only asymptotically valid as the chemical potential , revealing how the stability interval narrows and, in
particular, its upper bound decreases for finite . Finally, we compare at
the dynamical level the results of the GPE with the ones effectively capturing
the ring dynamics, revealing the unstable evolution for different values of
, as well as the good agreement between the two.Comment: Corrected citation, 10 pages and many fun figure
- …
