17,547 research outputs found
Vortex interactions and decay in aircraft wakes
The dynamic interaction of aircraft wake vortices was investigated using both inviscid and viscous models. For the viscous model, a computer code was developed using a second-order closure model of turbulent transport. The phenomenon of vortex merging which results in the rapid aging of a vortex wake was examined in detail. It was shown that the redistribution of vorticity during merging results from both convective and diffusive mechanisms
Double Compact Objects III: Gravitational Wave Detection Rates
The unprecedented range of second-generation gravitational-wave (GW)
observatories calls for refining the predictions of potential sources and
detection rates. The coalescence of double compact objects (DCOs)---i.e.,
neutron star-neutron star (NS-NS), black hole-neutron star (BH-NS), and black
hole-black hole (BH-BH) binary systems---is the most promising source of GWs
for these detectors. We compute detection rates of coalescing DCOs in
second-generation GW detectors using the latest models for their cosmological
evolution, and implementing inspiral-merger-ringdown (IMR) gravitational
waveform models in our signal-to-noise ratio calculations. We find that: (1)
the inclusion of the merger/ringdown portion of the signal does not
significantly affect rates for NS-NS and BH-NS systems, but it boosts rates by
a factor for BH-BH systems; (2) in almost all of our models BH-BH
systems yield by far the largest rates, followed by NS-NS and BH-NS systems,
respectively, and (3) a majority of the detectable BH-BH systems were formed in
the early Universe in low-metallicity environments. We make predictions for the
distributions of detected binaries and discuss what the first GW detections
will teach us about the astrophysics underlying binary formation and evolution.Comment: published in ApJ, 19 pages, 11 figure
Double Compact Objects II: Cosmological Merger Rates
The development of advanced gravitational wave (GW) observatories, such as
Advanced LIGO and Advanced Virgo, provides impetus to refine theoretical
predictions for what these instruments might detect. In particular, with the
range increasing by an order of magnitude, the search for GW sources is
extending beyond the "local" Universe and out to cosmological distances. Double
compact objects (neutron star-neutron star (NS-NS), black hole-neutron star
(BH-NS) and black hole-black hole (BH-BH) systems) are considered to be the
most promising gravitational wave sources. In addition, NS-NS and/or BH-NS
systems are thought to be the progenitors of gamma ray bursts (GRBs), and may
also be associated with kilonovae. In this paper we present the merger event
rates of these objects as a function of cosmological redshift. We provide the
results for four cases, each one investigating a different important evolution
parameter of binary stars. Each case is also presented for two metallicity
evolution scenarios. We find that (i) in most cases NS-NS systems dominate the
merger rates in the local Universe, while BH-BH mergers dominate at high
redshift; (ii) BH-NS mergers are less frequent than other sources per unit
volume, for all time; and (iii) natal kicks may alter the observable properties
of populations in a significant way, allowing the underlying models of binary
evolution and compact object formation to be easily distinguished. This is the
second paper in a series of three. The third paper will focus on calculating
the detection rates of mergers by gravitational wave telescopes.Comment: 8 pages, 10 figures, second in series, accepted for Ap
Porqpine: a peer-to-peer search engine
In this paper, we present a fully distributed and collaborative search
engine for web pages: Porqpine. This system uses a novel query-based model
and collaborative filtering techniques in order to obtain user-customized
results. All knowledge about users and profiles is stored in each user
node?s application. Overall the system is a multi-agent system that runs on
the computers of the user community. The nodes interact in a peer-to-peer
fashion in order to create a real distributed search engine where
information is completely distributed among all the nodes in the network.
Moreover, the system preserves the privacy of user queries and results by
maintaining the anonymity of the queries? consumers and results? producers.
The knowledge required by the system to work is implicitly caught through
the monitoring of users actions, not only within the system?s interface but
also within one of the most popular web browsers. Thus, users are not
required to explicitly feed knowledge about their interests into the system
since this process is done automatically. In this manner, users obtain the
benefits of a personalized search engine just by installing the application
on their computer. Porqpine does not intend to shun completely conventional
centralized search engines but to complement them by issuing more accurate
and personalized results.Postprint (published version
Faith in the Algorithm, Part 1: Beyond the Turing Test
Since the Turing test was first proposed by Alan Turing in 1950, the primary
goal of artificial intelligence has been predicated on the ability for
computers to imitate human behavior. However, the majority of uses for the
computer can be said to fall outside the domain of human abilities and it is
exactly outside of this domain where computers have demonstrated their greatest
contribution to intelligence. Another goal for artificial intelligence is one
that is not predicated on human mimicry, but instead, on human amplification.
This article surveys various systems that contribute to the advancement of
human and social intelligence
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