67,325 research outputs found
Sound separation probe
Probe separates sound waves from turbulent flow pressure fluctuations in ducted airstreams by using principle that sound waves and turbulent flow pressure perturbations travel at different velocities
Atom-Atom Scattering Under Cylindrical Harmonic Confinement: Numerical and Analytical Studies of the Confinement Induced Resonance
In a recent article [M. Olshanii, Phys. Rev. Lett. {\bf 81}, 938 (1998)], an
analytic solution of atom-atom scattering with a delta-function pseudopotential
interaction in the presence of transverse harmonic confinement yielded an
effective coupling constant that diverged at a `confinement induced resonance.'
In the present work, we report numerical results that corroborate this
resonance for more realistic model potentials. In addition, we extend the
previous theoretical discussion to include two-atom bound states in the
presence of transverse confinement, for which we also report numerical results
hereComment: New version with major revisions. We now provide a detailed physical
interpretation of the confinement-induced resonance in tight atomic
waveguide
Machiavelli’s Walls: The Legacy of Realism in International Relations Theory
In this paper we argue that Niccolò Machiavelli has little to do with Realism in International Relations theory. By concentrating, as Machaivelli did, on the walls that define political relations—both inside and outside the polity—we find his insights deeply rooted in the specific political contexts of Sixteenth century Italy. Others may wish to generalize from them, but Machiavelli did not. In fact, as we show, Machiavelli was mindful of the difficulties of generalizing about walls and acknowledged the dangers political actors faced in navigating between the internal and external walls of the polity. We examine the geopolitical contours of Machiavelli’s walls and seek to demonstrate how morality is present in these historical spaces. In contrast to Realists, Machiavelli was ready and willing to make ethical judgments. We argue that theorists of international politics should exercise care in reaching for Machiavelli as the iconic thinker for making sense of anarchy in world politics. This article concludes by suggesting that the ideology of Machiavellianism has obscured deeper understanding of the particular contexts of Machiavelli’s own world
Parallel Metric Tree Embedding based on an Algebraic View on Moore-Bellman-Ford
A \emph{metric tree embedding} of expected \emph{stretch~}
maps a weighted -node graph to a weighted tree with such that, for all ,
and
. Such embeddings are highly useful for designing
fast approximation algorithms, as many hard problems are easy to solve on tree
instances. However, to date the best parallel -depth algorithm that achieves an asymptotically optimal expected stretch of
requires
work and a metric as input.
In this paper, we show how to achieve the same guarantees using
depth and
work, where and is an arbitrarily small constant.
Moreover, one may further reduce the work to at the expense of increasing the expected stretch to
.
Our main tool in deriving these parallel algorithms is an algebraic
characterization of a generalization of the classic Moore-Bellman-Ford
algorithm. We consider this framework, which subsumes a variety of previous
"Moore-Bellman-Ford-like" algorithms, to be of independent interest and discuss
it in depth. In our tree embedding algorithm, we leverage it for providing
efficient query access to an approximate metric that allows sampling the tree
using depth and work.
We illustrate the generality and versatility of our techniques by various
examples and a number of additional results
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