72,777 research outputs found
Passivity-preserving splitting methods for rigid body systems
A rigid body model for the dynamics of a marine vessel, used in simulations
of offshore pipe-lay operations, gives rise to a set of ordinary differential
equations with controls. The system is input-output passive. We propose
passivity-preserving splitting methods for the numerical solution of a class of
problems which includes this system as a special case. We prove the
passivity-preservation property for the splitting methods, and we investigate
stability and energy behaviour in numerical experiments. Implementation is
discussed in detail for a special case where the splitting gives rise to the
subsequent integration of two completely integrable flows. The equations for
the attitude are reformulated on using rotation matrices rather than
local parametrizations with Euler angles.Comment: 27 pages, 4 figures. To be published in 'Multibody System Dynamics
Development of a stratospheric and mesospheric microwave temperature sounder experiment
A passive microwave spectrometer system for measuring global atmospheric temperature profiles from 0-75 km altitude was developed and analyzed. The system utilizes 12 channels near the 5 mm wavelength oxygen absorption band and is designed to provide global coverage by scanning perpendicular to the orbital track of a polar orbiting satellite. A significant improvement in the accuracy of theoretical atmospheric microwave transmittance functions was achieved through the development of a first-order approximation to overlapping line theory for the oxygen molecule. This approximation is particularly important in the troposphere and lower stratosphere where pressure-broadening blends nearby lines. Ground-based and aircraft observations of several resonances of stratospheric oxygen generally support the theory. The 23, 25, 29, and 31 atmospheric oxygen lines were measured and the frequencies of several such oxygen lines were measured with improved precision. The polarization and Zeeman splitting of the atmospheric 27 line was also observed
Security Analysis of an Untrusted Source for Quantum Key Distribution: Passive Approach
We present a passive approach to the security analysis of quantum key
distribution (QKD) with an untrusted source. A complete proof of its
unconditional security is also presented. This scheme has significant
advantages in real-life implementations as it does not require fast optical
switching or a quantum random number generator. The essential idea is to use a
beam splitter to split each input pulse. We show that we can characterize the
source using a cross-estimate technique without active routing of each pulse.
We have derived analytical expressions for the passive estimation scheme.
Moreover, using simulations, we have considered four real-life imperfections:
Additional loss introduced by the "plug & play" structure, inefficiency of the
intensity monitor, noise of the intensity monitor, and statistical fluctuation
introduced by finite data size. Our simulation results show that the passive
estimate of an untrusted source remains useful in practice, despite these four
imperfections. Also, we have performed preliminary experiments, confirming the
utility of our proposal in real-life applications. Our proposal makes it
possible to implement the "plug & play" QKD with the security guaranteed, while
keeping the implementation practical.Comment: 35 pages, 19 figures. Published Versio
Perfect tag identification protocol in RFID networks
Radio Frequency IDentification (RFID) systems are becoming more and more
popular in the field of ubiquitous computing, in particular for objects
identification. An RFID system is composed by one or more readers and a number
of tags. One of the main issues in an RFID network is the fast and reliable
identification of all tags in the reader range. The reader issues some queries,
and tags properly answer. Then, the reader must identify the tags from such
answers. This is crucial for most applications. Since the transmission medium
is shared, the typical problem to be faced is a MAC-like one, i.e. to avoid or
limit the number of tags transmission collisions. We propose a protocol which,
under some assumptions about transmission techniques, always achieves a 100%
perfomance. It is based on a proper recursive splitting of the concurrent tags
sets, until all tags have been identified. The other approaches present in
literature have performances of about 42% in the average at most. The
counterpart is a more sophisticated hardware to be deployed in the manufacture
of low cost tags.Comment: 12 pages, 1 figur
Application of Fiber Ring for Protection of Passive Optical Infrastructure
Today, passive optical networks (PONs) are mostly used as modern high-speed access networks for various applications. However, there are also several specific applications, such as in business, office, army or science sector, which require a complex protection and backup system against failures and malfunctions. Typically, tree or star topologies are used for passive optical networks PONs. These topologies are vulnerable mainly against the failures of central optical line termination (OLT) unit. This paper presents an innovative method for protecting PONs by using ring topologies, especially the OLT unit. The method is described in the article, and an elementary mathematical model for calculations of asymmetric passive optical splitters together with an example is included as well
Retrodirective optical system
Fabry-Perot interferometer retrodirective reflector modulator for optical communicatio
- …