56 research outputs found
Electronic transport in a randomly amplifying and absorbing chain
We study localization properties of a one-dimensional disordered system
characterized by a random non-hermitean hamiltonian where both the randomness
and the non-hermiticity arises in the local site-potential; its real part being
ordered (fixed), and a random imaginary part implying the presence of either a
random absorption or amplification at each site. The transmittance (forward
scattering) decays exponentially in either case. In contrast to the disorder in
the real part of the potential (Anderson localization), the transmittance with
the disordered imaginary part may decay slower than that in the case of ordered
imaginary part.Comment: 7 LaTex pages plus 2 PS figures; e-mail: [email protected]
Phase Distribution in a Disordered Chain and the Emergence of a Two-parameter Scaling in the Quasi-ballistic to the Mildly Localized Regime
We study the phase distribution of the complex reflection coefficient in
different configurations as a disordered 1D system evolves in length, and its
effect on the distribution of the 4-probe resistance . The stationary () phase distribution is almost always strongly non-uniform and is in
general double-peaked with their separation decaying algebraically with growing
disorder strength to finally give rise to a single narrow peak at infinitely
strong disorder. Further in the length regime where the phase distribution
still evolves with length (i.e., in the quasi-ballistic to the mildly localized
regime), the phase distribution affects the distribution of the resistance in
such a way as to make the mean and the variance of diverge
independently with length with different exponents. As , these
two exponents become identical (unity). Obviously, these facts imply two
relevant parameters for scaling in the quasi-ballistic to the mildly localized
regime finally crossing over to one-parameter scaling in the strongly localized
regime.Comment: 12 LaTeX pages plus 3 EPS figure
Wavelet analysis of low-frequency variability in oak tree-ring chronologies from east Central Europe
This study investigates the low-frequency (interannual and longer period) variability in three hydroclimatic records from east Central Europe. Two of these records consist of climate proxies derived from oak-tree rings in Bakta forest, and Balaton Highlands in Hungary, for the time interval 1783-2003. The third record consists of homogenized instrumental precipitation data from Budapest, Hungary, from 1842 to 2003. Using wavelet analysis, the three time series are analyzed and compared with one another. It is found that all three time series exhibit strong interannual variability at the 2-4 years timescales, and these variations occur intermittently throughout the length of each record. Significant variability is also observed in all the records at decadal timescales, but these variations persist for only two to three cycles. Wavelet coherence among the various time series is used to explore their time-varying correlation. The results reveal significant coherence at the 2-4 years band. At these timescales, the climatic variations are correlated to the tree-ring signal over different time intervals with changing phase. Increased (decreased) contribution of large-scale stratiform precipitation offers a potential explanation for enhanced (faded) coherence at the interannual timescale. Strong coherence was also observed occasionally at decadal timescales, however these coherences did not appear uniformly. These results reinforce the earlier assertion that neither the strength nor the rank of the similarity of the local hydroclimate signals is stable throughout the past two centuries
Multiresolution Wavelet Analysis of the Dynamics of a Cracked Rotor
We examine the dynamics of a healthy rotor and a rotor with a transverse crack, which opens and closes due to its self weight. Using discrete wavelet transform, we perform a multiresolution analysis of the measured vibration signal from each of these rotors. In particular, the measured vibration signal is decomposed into eight frequency bands, and the rms amplitude values of the healthy and cracked rotors are compared in the three lowest-frequency bands. The results indicate that the rms vibration amplitudes for the cracked rotor are larger than those of the healthy rotor in each of these three frequency bands. In the case of externally applied harmonic force excitation to the rotor, the rms values of the vibration amplitude of the cracked rotor are also found to be larger than those of a healthy rotor in the three lowest-frequency bands. Furthermore, the difference in the rms values between the healthy and cracked rotors in each of the three lowest-frequency bands is more pronounced in the presence of external excitation than that with no excitation. The obtained results suggest that the present multiresolution approach can be used effectively to detect the presence of a crack in a rotor
Recurrence Plots for Diesel Engine Variability Tests
Cycle-to-cycle variations of maximum pressure in a diesel engine are studied by using the methods of recurrence plots and recurrence quantification analysis. The pressure variations are found to exhibit strong periodicities in low frequency bands and intermittent oscillations at higher frequencies. The results are confirmed by wavelet analysis
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