62,513 research outputs found
Levitation of non-magnetizable droplet inside ferrofluid
The central theme of this work is that a stable levitation of a denser
non-magnetizable liquid droplet, against gravity, inside a relatively lighter
ferrofluid -- a system barely considered in ferrohydrodynamics -- is possible,
and exhibits unique interfacial features; the stability of the levitation
trajectory, however, is subject to an appropriate magnetic field modulation. We
explore the shapes and the temporal dynamics of a plane non-magnetizable
droplet levitating inside ferrofluid against gravity due to a spatially
complex, but systematically generated, magnetic field in two dimensions. The
effect of the viscosity ratio, the stability of the levitation path and the
possibility of existence of multiple-stable equilibrium states is investigated.
We find, for certain conditions on the viscosity ratio, that there can be
developments of cusps and singularities at the droplet surface; this phenomenon
we also observe experimentally and compared with the simulations. Our
simulations closely replicate the singular projection on the surface of the
levitating droplet. Finally, we present an dynamical model for the vertical
trajectory of the droplet. This model reveals a condition for the onset of
levitation and the relation for the equilibrium levitation height. The
linearization of the model around the steady state captures that the nature of
the equilibrium point goes under a transition from being a spiral to a node
depending upon the control parameters, which essentially means that the
temporal route to the equilibrium can be either monotonic or undulating. The
analytical model for the droplet trajectory is in close agreement with the
detailed simulations. (See draft for full abstract).Comment: This article has been published in a revised form in Journal of Fluid
Mechanics http://dx.doi.org/10.1017/jfm.2018.733. Copyright: copyright holde
Adiabatic quantum pumping in an Aharonov-Bohm loop and in a Si-like nanowire: Role of interference in real space and in momentum space
We study the consequences of interference effects on the current generated by
adiabatic quantum pumping in two distinct one-dimensional (1D) lattice model.
The first model contains an Aharonov-Bohm (AB) loop within a tight-binding
chain of lattice sites. The static AB phase is shown to strongly affect
interference between the two arms of the loop, serving as an on-off switch and
regulator for the pumped current. The second model simulates pumping in
semiconductors with indirect band-gaps, by utilizing a tight-binding chain with
next-nearest-neighbor coupling. The model exhibits signatures of interference
between degenerate conduction band states with different Fermi wavevectors.Comment: 7 pages, 7 figure
Globalization, oh that versitile villian!
The contemporary phase of economic globalization is regarded by some social scientists as a serious source of problems. There are others who, logically or illogically, consider it a negative, harmful, destructive, marginalizing and malevolent influence over economies and societies. No doubt, globalization can create opportunities for accelerating growth for the participating economies, but it can also pose myriad of challenges to and impose constraints on policymakers. In addition, it is justly blamed for uneven distribution of benefits from globalization. They are badly skewed within countries and between countries. Present policy environment is far from globalization-friendly. This paper focuses on the limitations of globalization in an objective and unbiased manner
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