31,014,066 research outputs found
Adaptive performance optimization for large-scale traffic control systems
In this paper, we study the problem of optimizing (fine-tuning) the design parameters of large-scale traffic control systems that are composed of distinct and mutually interacting modules. This problem usually requires a considerable amount of human effort and time to devote to the successful deployment and operation of traffic control systems due to the lack of an automated well-established systematic approach. We investigate the adaptive fine-tuning algorithm for determining the set of design parameters of two distinct mutually interacting modules of the traffic-responsive urban control (TUC) strategy, i.e., split and cycle, for the large-scale urban road network of the city of Chania, Greece. Simulation results are presented, demonstrating that the network performance in terms of the daily mean speed, which is attained by the proposed adaptive optimization methodology, is significantly better than the original TUC system in the case in which the aforementioned design parameters are manually fine-tuned to virtual perfection by the system operators
HTTP Mailbox - Asynchronous RESTful Communication
We describe HTTP Mailbox, a mechanism to enable RESTful HTTP communication in
an asynchronous mode with a full range of HTTP methods otherwise unavailable to
standard clients and servers. HTTP Mailbox allows for broadcast and multicast
semantics via HTTP. We evaluate a reference implementation using ApacheBench (a
server stress testing tool) demonstrating high throughput (on 1,000 concurrent
requests) and a systemic error rate of 0.01%. Finally, we demonstrate our HTTP
Mailbox implementation in a human assisted web preservation application called
"Preserve Me".Comment: 13 pages, 6 figures, 8 code blocks, 3 equations, and 3 table
Fractional Quantum Hall State in Coupled Cavities
We propose a scheme to realize the fractional quantum Hall system with atoms
confined in a two-dimensional array of coupled cavities. Our scheme is based on
simple optical manipulation of atomic internal states and inter-cavity hopping
of virtually excited photons. It is shown that as well as the fractional
quantum Hall system, any system of hard-core bosons on a lattice in the
presence of an arbitrary Abelian vector potential can be simulated solely by
controlling the phases of constantly applied lasers. The scheme, for the first
time, exploits the core advantage of coupled cavity simulations, namely the
individual addressability of the components and also brings the gauge potential
into such simulations as well as the simple optical creation of particles.Comment: 4 pages, 3 figure
Anyonic Quantum Walks
The one dimensional quantum walk of anyonic systems is presented. The anyonic
walker performs braiding operations with stationary anyons of the same type
ordered canonically on the line of the walk. Abelian as well as non-Abelian
anyons are studied and it is shown that they have very different properties.
Abelian anyonic walks demonstrate the expected quadratic quantum speedup.
Non-Abelian anyonic walks are much more subtle. The exponential increase of the
system's Hilbert space and the particular statistical evolution of non-Abelian
anyons give a variety of new behaviors. The position distribution of the walker
is related to Jones polynomials, topological invariants of the links created by
the anyonic world-lines during the walk. Several examples such as the SU(2)
level k and the quantum double models are considered that provide insight to
the rich diffusion properties of anyons.Comment: 17 pages, 10 figure
Probing the effects of interaction in Anderson localization using linear photonic lattices
We show how two-dimensional waveguide arrays can be used to probe the effect
of on-site interaction on Anderson localization of two interacting bosons in
one dimension. It is shown that classical light and linear elements are
sufficient to experimentally probe the interplay between interaction and
disorder in this setting. For experimental relevance, we evaluate the
participation ratio and the intensity correlation function as measures of
localization for two types of disorder (diagonal and off-diagonal), for two
types of interaction (repulsive and attractive), and for a variety of initial
input states. Employing a commonly used set of initial states, we show that the
effect of interaction on Anderson localization is strongly dependent on the
type of disorder and initial conditions, but is independent of whether the
interaction is repulsive or attractive. We then analyze a certain type of
entangled input state where the type of interaction is relevant and discuss how
it can be naturally implemented in waveguide arrays. We conclude by laying out
the details of the two-dimensional photonic lattice implementation including
the required parameter regime.Comment: 5 pages, 5 figure
Streaming Video over HTTP with Consistent Quality
In conventional HTTP-based adaptive streaming (HAS), a video source is
encoded at multiple levels of constant bitrate representations, and a client
makes its representation selections according to the measured network
bandwidth. While greatly simplifying adaptation to the varying network
conditions, this strategy is not the best for optimizing the video quality
experienced by end users. Quality fluctuation can be reduced if the natural
variability of video content is taken into consideration. In this work, we
study the design of a client rate adaptation algorithm to yield consistent
video quality. We assume that clients have visibility into incoming video
within a finite horizon. We also take advantage of the client-side video
buffer, by using it as a breathing room for not only network bandwidth
variability, but also video bitrate variability. The challenge, however, lies
in how to balance these two variabilities to yield consistent video quality
without risking a buffer underrun. We propose an optimization solution that
uses an online algorithm to adapt the video bitrate step-by-step, while
applying dynamic programming at each step. We incorporate our solution into
PANDA -- a practical rate adaptation algorithm designed for HAS deployment at
scale.Comment: Refined version submitted to ACM Multimedia Systems Conference
(MMSys), 201
HTTP adaptive streaming with media fragment URIs
HTTP adaptive streaming was introduced with the general idea that user agents interpret a manifest file (describing different representations and segments of the media); where-after they retrieve the media content using sequential HTTP progressive download operations. MPEG started with the standardization of an HTTP streaming protocol, defining the structure and semantics of a manifest file and additional restrictions and extensions for container formats. At the same time, W3C is working on a specification for addressing media fragments on the Web using Uniform Resource Identifiers. The latter not only defines the URI syntax for media fragment identifiers but also the protocol for retrieving media fragments over HTTP. In this paper, we elaborate on the role of Media Fragment URIs within HTTP adaptive streaming scenarios. First, we elaborate on how different media representations can be addressed by means of Media Fragment URIs, by using track fragments. Additionally, we illustrate how HTTP adaptive streaming is realized relying on the Media Fragments URI retrieval protocol. To validate the presented ideas, we implemented Apple's HTTP Live streaming technique using Media Fragment URI
A Simple Cooperative Diversity Method Based on Network Path Selection
Cooperative diversity has been recently proposed as a way to form virtual
antenna arrays that provide dramatic gains in slow fading wireless
environments. However most of the proposed solutions require distributed
space-time coding algorithms, the careful design of which is left for future
investigation if there is more than one cooperative relay. We propose a novel
scheme, that alleviates these problems and provides diversity gains on the
order of the number of relays in the network. Our scheme first selects the best
relay from a set of M available relays and then uses this best relay for
cooperation between the source and the destination. We develop and analyze a
distributed method to select the best relay that requires no topology
information and is based on local measurements of the instantaneous channel
conditions. This method also requires no explicit communication among the
relays. The success (or failure) to select the best available path depends on
the statistics of the wireless channel, and a methodology to evaluate
performance for any kind of wireless channel statistics, is provided.
Information theoretic analysis of outage probability shows that our scheme
achieves the same diversity-multiplexing tradeoff as achieved by more complex
protocols, where coordination and distributed space-time coding for M nodes is
required, such as those proposed in [7]. The simplicity of the technique,
allows for immediate implementation in existing radio hardware and its adoption
could provide for improved flexibility, reliability and efficiency in future 4G
wireless systems.Comment: To appear, IEEE JSAC, special issue on 4
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