Entropy and Poincar\'e recurrence from a geometrical viewpoint

We study Poincar\'e recurrence from a purely geometrical viewpoint. We prove that the metric entropy is given by the exponential growth rate of return times to dynamical balls. This is the geometrical counterpart of Ornstein-Weiss theorem. Moreover, we show that minimal return times to dynamical balls grow linearly with respect to its length. Finally, some interesting relations between recurrence, dimension, entropy and Lyapunov exponents of ergodic measures are given.Comment: 11 pages, revised versio

Influence of the SSBI mitigation on the in-band crosstalk tolerance of virtual carrier-assisted DD multi-band OFDM metro networks

In this work, the tolerance to in-band crosstalk of virtual carrier (VC)-assisted direct detection (DD) multi-band orthogonal frequency division multiplexing (MB-OFDM) metro networks, with and without signal-to-signal beat interference (SSBI) mitigation, is compared numerically for 4-ary, 16-ary and 64-ary quadrature amplitude modulation (QAM) formats in the OFDM subcarriers. Our results show that the tolerance to in-band crosstalk is improved for lower modulation format orders. The tolerance to in-band crosstalk of DD OFDM receivers considering 4-QAM modulation format at the DD OFDM subcarriers is above 14 dB higher than the one obtained for the 64-QAM modulation format, regardless the receiver configuration. We have also shown that, the tolerance to in-band crosstalk for a given modulation format order depends on the difference between the virtual carrier-to-band power ratio (VBPR) of the selected and interfering signals, as interferers with same VBPR as the selected signal leads to equal tolerance to in-band crosstalk, independently from the DD OFDM receiver configuration and the subcarrier modulation format order considered.info:eu-repo/semantics/acceptedVersio

Tolerance to in-band crosstalk of virtual carrier-assisted direct detection multi-band OFDM system

The tolerance to in-band crosstalk of virtual carrier (VC)-assisted direct detection (DD) multi-band orthogonal frequency division multiplexing (MB-OFDM) system is assessed numerically through Monte-Carlo simulation and considering a single interferer. The influence of the virtual carrier-to-band power ratio (VBPR) and the virtual carrier-to-band gap (VBG) of the interferer on the in-band tolerance is also studied. We show that, for interferers with the same VBG as the selected signal, the increase of the VBPR of the interferer leads to lower optical signal-to-noise ratio (OSNR) penalties. The increase of the VBG of the interferer with central frequency different from the selected signal also leads to lower OSNR penalties. When the central frequencies of the interferer and selected bands are the same, the variation VBG of the interferer can lead to 11 dB less tolerance to in-band crosstalk of the VC-assisted DD OFDM system.info:eu-repo/semantics/acceptedVersio

Reação de cultivares de cenoura a meloidogyne incognita raça 1 e Meloidogyne mayaguensis.

bitstream/item/139651/1/bpd-69.pd

Impact of inter-core crosstalk on the performance of multi-core fibers-based SDM systems with coherent detection

Inter-core crosstalk (ICXT) can limit the multi-core fiber (MCF) systems performance and transmission reach. Over the last years, the impact of the ICXT on the performance of MCF optical communication systems with coherent detection has been investigated in several works. However, the influence of the MCF parameters and transmitted signal characteristics on the ICXT mechanism and the degradation induced by it on the performance of coherent detection MCF systems are still to be completely assessed. In this work, the impact of the ICXT on the performance of coherent detection MCF-based transmission systems is assessed through numerical simulation considering fiber linear propagation. The metrics used to assess the MCF system performance are the bit error rate (BER) and the optical signal-to-noise ratio (OSNR) penalty due to the ICXT. Our results show that the BER and the OSNR penalty due to the detected ICXT, in MCF-based systems with coherent detection, are influenced by the s kew, time misalignment between the transmitted signals and the roll-off factor of the transmitted signals. In the range of skew and roll-off factors analyzed, the maximum reduction of maximum ICXT level for a 1 dB OSNR penalty by appropriate choice of skew and roll-off factor does not exceed 1.7 dB.info:eu-repo/semantics/acceptedVersio

Inter-core crosstalk dependence on design parameters in coherent detection weakly-coupled multicore fiber systems

We assess, through numerical simulation, the dependence of the variance of the inter-core crosstalk (ICXT) and the maximum allowable ICXT level on the design parameters of coherent detection MCF systems. The analysed design parameters are the order of the quadrature amplitude modulation (QAM) signals, roll-off factor, time misalignment between the signal in different cores and skew between cores. The results show that, when the roll-off factor is 0, the maximum allowable ICXT level is independent of the skew and decreases for higher QAM orders. For a roll-off factor of 1, the maximum allowable ICXT level depends on the skew and time misalignment of core signals. In this case, the maximum allowable ICXT level increases by 3.6 dB relative to the case of roll-off factor of 0 with null skew, and by 2 dB, when the skew is much higher than the symbol period.info:eu-repo/semantics/acceptedVersio

Analysis of inter-core crosstalk in weakly-coupled multi-core fiber coherent systems

The influence of the inter-core crosstalk (ICXT) on the performance of weakly-coupled multi-core fiber (WC-MCF) systems with coherent detection and arbitrary inter-core skew is studied numerically and analytically. We analyze the evolution of the instantaneous ICXT power, induced by polarization division multiplexed quadrature amplitude modulation signals, short term average crosstalk (STAXT), and detected ICXT components along the time to get insight on how the ICXT affects the coherent system performance. Numerical results show that, with low skew-symbol rate product ($\ll$1), the STAXT can have large fluctuations along the time and the variance of the detected ICXT can also have large fluctuations along the time, causing large variations of the bit error rate (BER) along time. With large skew-symbol rate product ($\gg$1), the STAXT is almost constant along the time and, although the detected ICXT varies along time, the detected ICXT variance is almost constant along time leading to very small fluctuations of BER along time. Analytical expressions for the variance of the coherently detected ICXT, average BER and optical signal-to-noise ratio (OSNR) penalty are proposed and shown to agree with Monte-Carlo simulation results for arbitrary skew, modulation format order, and roll-off factor of the transmitted signals. Numerical results show that the maximum allowable ICXT level for 1 dB OSNR penalty increases when the skew augments and can reach 1.3 dB for a roll-off factor of 1. For most cases of interest of low roll-off factor, the increase of the maximum allowable ICXT level is very small. It is shown that the OSNR penalty estimates agree quite well with other authors' experimental results (with nearly zero roll-off factor).info:eu-repo/semantics/acceptedVersio

Reação de genótipos de cebola a mancha-púrpura (Alternaria porri).

O objetivo deste trabalho foi avaliar a resistência de genótipos de cebola a mancha-púrpura no campo. Foram avaliados 64 genótipos (cultivares, populações e linhagens do programa de melhoramento de cebola da Embrapa) em sistema convencional de cultivo. Como testemunha resistente foi utilizada a população CNPH 6342 e como testemunha suscetível a linha macho-fértil 420B.bitstream/item/84970/1/bpd-98.pd

Resistência de progênies de cenoura à queima-das-folhas.

O objetivo deste trabalho foi avaliar a resistência de progênies experimentais de cenoura à queima-das-folhas