54,005 research outputs found
Radiation transport equations in non-Riemannian space-times
The transport equations for polarized radiation transfer in non-Riemannian,
Weyl-Cartan type space-times are derived, with the effects of both torsion and
non-metricity included. To obtain the basic propagation equations we use the
tangent bundle approach. The equations describing the time evolution of the
Stokes parameters, of the photon distribution function and of the total
polarization degree can be formulated as a system of coupled first order
partial differential equations. As an application of our results we consider
the propagation of the cosmological gamma ray bursts in spatially homogeneous
and isotropic spaces with torsion and non-metricity. For this case the exact
general solution of the equation for the polarization degree is obtained, with
the effects of the torsion and non-metricity included. The presence of a
non-Riemannian geometrical background in which the electromagnetic fields
couple to torsion and/or non-metricity affect the polarization of photon beams.
Consequently, we suggest that the observed polarization of prompt cosmological
gamma ray bursts and of their optical afterglows may have a propagation effect
component, due to a torsion/non-metricity induced birefringence of the vacuum.
A cosmological redshift and frequency dependence of the polarization degree of
gamma ray bursts also follows from the model, thus providing a clear
observational signature of the torsional/non-metric effects. On the other hand,
observations of the polarization of the gamma ray bursts can impose strong
constraints on the torsion and non-metricity and discriminate between different
theoretical models.Comment: 12 pages, 3 figures, accepted for publication in PR
A review of personal communications services
This article can be accessed from the link below - Copyright @ 2009 Nova Science Publishers, LtdPCS is an acronym for Personal Communications Service. PCS has two layers of
meaning. At the low layer, from the technical perspective, PCS is a 2G mobile
communication technology operating at the 1900 MHz frequency range. At the upper
layer, PCS is often used as an umbrella term that includes various wireless access and
personal mobility services with the ultimate goal of enabling users to freely communicate
with anyone at anytime and anywhere according to their demand. Ubiquitous PCS can be implemented by integrating the wireless and wireline systems on the basis of intelligent network (IN), which provides network functions of terminal and personal mobility. In this chapter, we focus on various aspects of PCS except location management. First we describe the motivation and technological evolution for personal communications. Then we introduce three key issues related to PCS: spectrum allocation, mobility, and standardization efforts. Since PCS involves several different communication
technologies, we introduce its heterogeneous and distributed system architecture. IN is
also described in detail because it plays a critical role in the development of PCS. Finally, we introduce the application of PCS and its deployment status since the mid-term of 1990’s.This work was supported in part by the National Natural Science Foundation of China
under Grant No. 60673159 and 70671020; the National High-Tech Research and Development Plan of China under Grant No. 2006AA01Z214, and the Engineering and Physical Sciences Research Council (EPSRC) of UK under Grant EP/E060722/1
Braiding statistics approach to symmetry-protected topological phases
We construct a 2D quantum spin model that realizes an Ising paramagnet with
gapless edge modes protected by Ising symmetry. This model provides an example
of a "symmetry-protected topological phase." We describe a simple physical
construction that distinguishes this system from a conventional paramagnet: we
couple the system to a Z_2 gauge field and then show that the \pi-flux
excitations have different braiding statistics from that of a usual paramagnet.
In addition, we show that these braiding statistics directly imply the
existence of protected edge modes. Finally, we analyze a particular microscopic
model for the edge and derive a field theoretic description of the low energy
excitations. We believe that the braiding statistics approach outlined in this
paper can be generalized to a large class of symmetry-protected topological
phases.Comment: 17 pages, 12 figures, reorganized section V, added a referenc
Soft computing for intelligent data analysis
Intelligent data analysis (IDA) is an interdisciplinary study concerned with the effective analysis of data. The paper briefly looks at some of the key issues in intelligent data analysis, discusses the opportunities for soft computing in this context, and presents several IDA case studies in which soft computing has played key roles. These studies are all concerned with complex real-world problem solving, including consistency checking between mass spectral data with proposed chemical structures, screening for glaucoma and other eye diseases, forecasting of visual field deterioration, and diagnosis in an oil refinery involving multivariate time series. Bayesian networks, evolutionary computation, neural networks, and machine learning in general are some of those soft computing techniques effectively used in these studies
Micro-distortion detection of lidar scanning signals based on geometric analysis
When detecting micro-distortion of lidar scanning signals, current hardwires and algorithms have low compatibility, resulting in slow detection speed, high energy consumption, and poor performance against interference. A geometric statistics-based micro-distortion detection technology for lidar scanning signals was proposed. The proposed method built the overall framework of the technology, used TCD1209DG (made by TOSHIBA, Tokyo, Japan) to implement a linear array CCD (charge-coupled device) module for photoelectric conversion, signal charge storage, and transfer. Chip FPGA was used as the core component of the signal processing module for signal preprocessing of TCD1209DG output. Signal transmission units were designed with chip C8051, FT232, and RS-485 to perform lossless signal transmission between the host and any slave. The signal distortion feature matching algorithm based on geometric statistics was adopted. Micro-distortion detection of lidar scanning signals was achieved by extracting, counting, and matching the distorted signals. The correction of distorted signals was implemented with the proposed method. Experimental results showed that the proposed method had faster detection speed, lower detection energy consumption, and stronger anti-interference ability, which effectively improved micro-distortion correction
A novel fast fractal image compression method based on distance clustering in high dimensional sphere surface
Fractal encoding method becomes an effective image compression method because of its high compression ratio and short decompressing time. But one problem of known fractal compression method is its high computational complexity and consequent long compressing time. To address this issue, in this paper, distance clustering in high dimensional sphere surface is applied to speed up the fractal compression method. Firstly, as a preprocessing strategy, an image is divided into blocks, which are mapped on high dimensional sphere surface. Secondly, a novel image matching method is presented based on distance clustering on high dimensional sphere surface. Then, the correctness and effectiveness properties of the mentioned method are analyzed. Finally, experimental results validate the positive performance gain of the method
Reliability analysis of an air traffic network: from network structure to transport function
To scientifically evaluate the reliability of air traffic networks, a definition of air traffic network reliability is proposed in this paper. Calculation models of the connectivity reliability, travel-time reliability, and capacity reliability of the air traffic network are constructed based on collected historical data, considering the current status and the predicted future evolution trends. Considering the randomness and fuzziness of factors affecting reliability, a comprehensive evaluation model of air traffic networks based on the uncertainty transformation model is established. Finally, the reliability of the US air traffic network is analyzed based on data published by the Transportation Statistics Bureau of the US Department of Transportation. The results show that the connectivity reliability is 0.4073, the capacity reliability is 0.8300, the travel-time reliability is 0.9180, and the overall reliability evaluated is “relatively reliable”. This indicates that although the US structural reliability is relatively low, the US air traffic management is very efficient, and the overall reliability is strong. The reliability in nonpeak hours is much higher than that in peak hours. The method can identify air traffic network reliability efficiently. The main factors affecting reliability can be found in the calculation process, and are beneficial for air traffic planning and management. The empirical analysis also reflects that the evaluation model based on the uncertainty transformation model can transform the quantitative data of network structure and traffic function into the qualitative language of reliability
Near-Optimal Distributed Approximation of Minimum-Weight Connected Dominating Set
This paper presents a near-optimal distributed approximation algorithm for
the minimum-weight connected dominating set (MCDS) problem. The presented
algorithm finds an approximation in rounds,
where is the network diameter and is the number of nodes.
MCDS is a classical NP-hard problem and the achieved approximation factor
is known to be optimal up to a constant factor, unless P=NP.
Furthermore, the round complexity is known to be
optimal modulo logarithmic factors (for any approximation), following [Das
Sarma et al.---STOC'11].Comment: An extended abstract version of this result appears in the
proceedings of 41st International Colloquium on Automata, Languages, and
Programming (ICALP 2014
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