10,601 research outputs found
Optimal design of pipes in series: An explicit approximation
This paper introduces a new methodology for the optimum design of pipes in series, named Optimum Hydraulic Grade Line (OHGL). This methodology is explicit and is based on the knowledge of the series topology and the geometrical distribution of water demands on nodes, i.e. the way in which the pipe in series delivers water mass as function of the distance from the entrance. OHGL consists in the pre-determination of that hydraulic grade line which gives the minimum construction cost, in an explicit way. Once this line has been established, calculation of the pipe’s continuous diameters is direct; after a round up to commercial diameters is developed. To validate the proposed methodology, several pipes in series were designed both using GA and OHGL. Four hundred series were used in total, each with different topological characteristics and demands. Keywords: Pipe in series, optimum design, genetic algorithms, optimum hydraulic grade line
Precovery of near-Earth asteroids by a citizen-science project of the Spanish Virtual Observatory
This article describes a citizen-science project conducted by the Spanish
Virtual Observatory (SVO) to improve the orbits of near-Earth asteroids (NEAs)
using data from astronomical archives. The list of NEAs maintained at the Minor
Planet Center (MPC) is checked daily to identify new objects or changes in the
orbital parameters of already catalogued objects. Using NEODyS we compute the
position and magnitude of these objects at the observing epochs of the 938 046
images comprising the Eigth Data Release of the Sloan Digitised Sky Survey
(SDSS). If the object lies within the image boundaries and the magnitude is
brighter than the limiting magnitude, then the associated image is visually
inspected by the project's collaborators (the citizens) to confirm or discard
the presence of the NEA. If confirmed, accurate coordinates and, sometimes,
magnitudes are submitted to the MPC. Using this methodology, 3,226 registered
users have made during the first fifteen months of the project more than
167,000 measurements which have improved the orbital elements of 551 NEAs (6%
of the total number of this type of asteroids). Even more remarkable is the
fact that these results have been obtained at zero cost to telescope time as
NEAs were serendipitously observed while the survey was being carried out. This
demonstrates the enormous scientific potential hidden in astronomical archives.
The great reception of the project as well as the results obtained makes it a
valuable and reliable tool for improving the orbital parameters of near-Earth
asteroids.Comment: 9 pages, 5 figures. Accepted in Astron. Nach
Selective Control of the Symmetric Dicke Subspace in Trapped Ions
We propose a method of manipulating selectively the symmetric Dicke subspace
in the internal degrees of freedom of N trapped ions. We show that the direct
access to ionic-motional subspaces, based on a suitable tuning of
motion-dependent AC Stark shifts, induces a two-level dynamics involving
previously selected ionic Dicke states. In this manner, it is possible to
produce, sequentially and unitarily, ionic Dicke states with increasing
excitation number. Moreover, we propose a probabilistic technique to produce
directly any ionic Dicke state assuming suitable initial conditions.Comment: 5 pages and 1 figure. New version with minor changes and added
references. Accepted in Physical Review
Field squeeze operators in optical cavities with atomic ensembles
We propose a method of generating unitarily single and two-mode field
squeezing in an optical cavity with an atomic cloud. Through a suitable laser
system, we are able to engineer a squeeze field operator decoupled from the
atomic degrees of freedom, yielding a large squeeze parameter that is scaled up
by the number of atoms, and realizing degenerate and non-degenerate parametric
amplification. By means of the input-output theory we show that ideal squeezed
states and perfect squeezing could be approached at the output. The scheme is
robust to decoherence processes.Comment: Four pages and one figure. Accepted in Physical Review Letter
Fluctons
From the perspective of topological field theory we explore the physics
beyond instantons. We propose the fluctons as nonperturbative topological
fluctuations of vacuum, from which the self-dual domain of instantons is
attained as a particular case. Invoking the Atiyah-Singer index theorem, we
determine the dimension of the corresponding flucton moduli space, which gives
the number of degrees of freedom of the fluctons. An important consequence of
these results is that the topological phases of vacuum in non-Abelian gauge
theories are not necessarily associated with self-dual fields, but only with
smooth fields. Fluctons in different scenarios are considered, the basic
aspects of the quantum mechanical amplitude for fluctons are discussed, and the
case of gravity is discussed briefly
Heralded Entanglement of Arbitrary Degree in Remote Qubits
Incoherent scattering of photons off two remote atoms with a Lambda-level
structure is used as a basic Young-type interferometer to herald long-lived
entanglement of an arbitrary degree. The degree of entanglement, as measured by
the concurrence, is found to be tunable by two easily accessible experimental
parameters. Fixing one of them to certain values unveils an analog to the
Malus' law. An estimate of the variation in the degree of entanglement due to
uncertainties in an experimental realization is given.Comment: published version, 4 pages and 2 figure
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