338 research outputs found
Entropic fluctuations in XY chains and reflectionless Jacobi matrices
We study the entropic fluctuations of a general XY spin chain where initially
the left(x0) part of the chain is in thermal equilibrium at inverse
temperature Tl/Tr. The temperature differential results in a non-trivial
energy/entropy flux across the chain. The Evans-Searles (ES) entropic
functional describes fluctuations of the flux observable with respect to the
initial state while the Gallavotti-Cohen (GC) functional describes these
fluctuations with respect to the steady state (NESS) the chain reaches in the
large time limit. We also consider the full counting statistics (FCS) of the
energy/entropy flux associated to a repeated measurement protocol, the
variational entropic functional (VAR) that arises as the quantization of the
variational characterization of the classical Evans-Searles functional and a
natural class of entropic functionals that interpolate between FCS and VAR. We
compute these functionals in closed form in terms of the scattering data of the
Jacobi matrix h canonically associated to the XY chain. We show that all these
functionals are identical if and only if h is reflectionless (we call this
phenomenon entropic identity). If h is not reflectionless, then the ES and GC
functionals remain equal but differ from the FCS, VAR and interpolating
functionals. Furthermore, in the non-reflectionless case, the ES/GC functional
does not vanish at 1 (i.e., the Kawasaki identity fails) and does not have the
celebrated ES/GC symmetry. The FCS, VAR and interpolating functionals always
have this symmetry. In the cases where h is a Schr\"odinger operator, the
entropic identity leads to some unexpected open problems in the spectral theory
of one-dimensional discrete Schr\"odinger operators
Level Crossing Rate of Macrodiversity System in the Presence of Multipath Fading and Shadowing
Macrodiversity system including macrodiversity SC receiver and two microdiversity SC receivers is considered in this paper. Received signal experiences, simultaneously, both, long term fading and short term fading. Microdiversity SC receivers reduces Rayleigh fading effects on system performance and macrodiversity SC receiver mitigate Gamma shadowing effects on system performance. Closed form expressions for level crossing rate of microdiversity SC receivers output signals envelopes are calculated. This expression is used for evaluation of level crossing rate of macrodiversity SC receiver output signal envelope. Numerical expressions are illustrated to show the influence of Gamma shadowing severity on level crossing rate
Implementation of Video Compression Standards in Digital Television
In this paper, a video compression standard used in digital television systems is discussed. Basic concepts of video compression and principles of lossy and lossless compression are given. Techniques of video compression (intraframe and interframe compression), the type of frames and principles of the bit rate compression are discussed. Characteristics of standard-definition television (SDTV), high-definition television (HDTV) and ultra-high-definition television (UHDTV) are given. The principles of the MPEG-2, MPEG-4 and High Efficiency Video Coding (HEVC) compression standards are analyzed. Overview of basic standards of video compression and the impact of compression on the quality of TV images and the number of TV channels in the multiplexes of terrestrial and satellite digital TV transmission are shown. This work is divided into six sections
Properties of latent interface-trap buildup in irradiated metal-oxide-semiconductor transistors determined by switched bias isothermal annealing experiments
Isothermal annealing experiments with switched gate bias have been performed to determine the properties of the latent interface-trap buildup during postirradiation annealing of metal-oxide-semiconductor transistors. It has been found that a bias-independent process occurs until the start of the latent interface-trap buildup. During the buildup itself, oxide-trap charge is not permanently neutralized, but is temporarily compensated. (C) 2000 American Institute of Physics. (DOI: 10.1063/1.1336159
Nanostructuring Graphene by Dense Electronic Excitation
The ability to manufacture tailored graphene nanostructures is a key factor
to fully exploit its enormous technological potential. We have investigated
nanostructures created in graphene by swift heavy ion induced folding. For our
experiments, single layers of graphene exfoliated on various substrates and
freestanding graphene have been irradiated and analyzed by atomic force and
high resolution transmission electron microscopy as well as Raman spectroscopy.
We show that the dense electronic excitation in the wake of the traversing ion
yields characteristic nanostructures each of which may be fabricated by
choosing the proper irradiation conditions. These nanostructures include unique
morphologies such as closed bilayer edges with a given chirality or nanopores
within supported as well as freestanding graphene. The length and orientation
of the nanopore, and thus of the associated closed bilayer edge, may be simply
controlled by the direction of the incoming ion beam. In freestanding graphene,
swift heavy ion irradiation induces extremely small openings, offering the
possibility to perforate graphene membranes in a controlled way.Comment: 16 pages, 5 figures, submitted to Nanotechnolog
Hamiltonian structure for dispersive and dissipative dynamical systems
We develop a Hamiltonian theory of a time dispersive and dissipative
inhomogeneous medium, as described by a linear response equation respecting
causality and power dissipation. The proposed Hamiltonian couples the given
system to auxiliary fields, in the universal form of a so-called canonical heat
bath. After integrating out the heat bath the original dissipative evolution is
exactly reproduced. Furthermore, we show that the dynamics associated to a
minimal Hamiltonian are essentially unique, up to a natural class of
isomorphisms. Using this formalism, we obtain closed form expressions for the
energy density, energy flux, momentum density, and stress tensor involving the
auxiliary fields, from which we derive an approximate, ``Brillouin-type,''
formula for the time averaged energy density and stress tensor associated to an
almost mono-chromatic wave.Comment: 68 pages, 1 figure; introduction revised, typos correcte
A comprehensive study of the delay vector variance method for quantification of nonlinearity in dynamical systems
Although vibration monitoring is a popular method to monitor and assess dynamic structures, quantification of linearity or nonlinearity of the dynamic responses remains a challenging problem. We investigate the delay vector variance (DVV) method in this regard in a comprehensive manner to establish the degree to which a change in signal nonlinearity can be related to system nonlinearity and how a change in system parameters affects the nonlinearity in the dynamic response of the system. A wide range of theoretical situations are considered in this regard using a single degree of freedom (SDOF) system to obtain numerical benchmarks. A number of experiments are then carried out using a physical SDOF model in the laboratory. Finally, a composite wind turbine blade is tested for different excitations and the dynamic responses are measured at a number of points to extend the investigation to continuum structures. The dynamic responses were measured using accelerometers, strain gauges and a Laser Doppler vibrometer. This comprehensive study creates a numerical and experimental benchmark for structurally dynamical systems where output-only information is typically available, especially in the context of DVV. The study also allows for comparative analysis between different systems driven by the similar input
Inventory management with advance capacity information
One of the important aspects of supply chain management is dealing with demand and supply uncertainty. The uncertainty of future supply can be reduced, if a company is able to obtain advance capacity information (ACI) on future supply/production capacity availability from its supplier. We address a periodic-review inventory system under stochastic demand and stochastic limited supply, for which ACI is available. We show that the optimal ordering policy is a state-dependent base stock policy characterized by a base stock level that is a function of ACI. We establish a link to inventory models using advance demand information (ADI) by developing a capacitated inventory system with ADI, and showing that the model is closely related to the proposed ACI model. Our numerical results reveal several managerial insights. In particular, we show that ACI is most beneficial when there exists sufficient flexibility to react to anticipated demand and supply capacity mismatches. Further, most of the benefits can be reached with only limited future visibility. We also show that the system parameters affecting the value of ACI interact in a complex way, and therefore need to be considered in an integrated manner
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