Determination of Tap Positions for Sparse Equalizers

Sparse equalizers, in which only a small subset of the filter taps is selected to be nonzero, were recently proposed as a low-complexity solution for receivers operating in wireless frequency-selective channels with sparse power profiles. The performance of the sparse equalizer heavily depends on its tap-positioning algorithm. This paper presents efficient low-complexity algorithms for determination of sparse equalizer tap positions based on a forward sequential search. We develop low-complexity metrics for the evaluation of the candidate tap positions in the search space as well as methods to effectively reduce the search space size. The proposed algorithms are shown to be superior over previously proposed algorithms in a wide range of channel conditions. Actually, the proposed algorithms yield, in most of the tested cases, performance identical to the optimal, prohibitively complex, tap-positioning algorithm. The main emphasis is on linear equalization suitable for wideband code-division multiple-access systems but the algorithm can be extended to a variety of equalization schemes and channels.     

Theory and simulation of the dynamics and stability of actively modelocked lasers

A new model is proposed for the active modulation component of a mode-locked laser cavity. By using Jacobi elliptic functions to capture the periodic forcing to the cavity, we are able to construct exact solutions representing a mode-locked pulse train. Two families of pulse-train solutions are generated: one in which neighboring pulses are in-phase and a second in which neighboring pulses are out-of-phase. We show that only out-of-phase solutions allow for stable mode-locked pulse trains. Further, pulse-to-pulse interactions can generate instabilities that destroy the pulse train altogether or lead to Q-switching.     

Observation of the breakup of a prechirped N-soliton in an optical fiber

We present what is believed to be the first experimental evidence showing the breakup of a chirped N-soliton pulse into an ordered train of fundamental solitons, as predicted by theory. We also present numerical experiments that confirm this phenomenon. Implications for optical communications systems that use chirped pulses are discussed.     

Dispersion-managed breathers with average normal dispersion

Analytic and numerical evidence is presented that demonstrates that a dispersion-managed breather can be supported in an optical fiber even when the average dispersion is in the normal regime. This nonlinear behavior, which is contrary to guiding-center theory, is shown to originate from the reversible dynamics associated with the strong quadratic chirp that is generated in both the anomalous and the normal dispersion regimes.     

Aromatic substitution by N-arylhydroxylamines—II : Generation of nitrenes from arylhydroxylamines and N-benzenesulfonylhydroxylamines and phosphorous pentoxide

Substitution of benzene by N-benzene- and N-(4-methylbenzenesulfonyl)hydroxylamines occurs in the presence of phosphorous pentoxide whereas N-methyl-N-benzenesulfonylhydroxylamine gave no substitution product under the same conditions. When N-(4-methylbenzenesulfonyl)hydroxylamine was treated with phosphorous pentoxide in pyridine, N-(4-methylbenzenesulfonimido)pyridinium ylide was formed. Nitrene intermediates are postulated to account for these products. Similarly carbazole was formed from 2-hydroxylamino[1,1′-biphenyl] and phosphorous pentoxide but with phosphorous pentachloride, 3- and 3-chloro-2-amino[1,1′-biphenyls] were formed, most likely via a nitrenium ion intermediate.     

Target-normal single spin asymmetries measured with positrons

The European Physical Journal A - The dipole response of the proton-magic nucleus $${}^{124}\hbox {Sn}$$ was previously investigated with electromagnetic and hadronic probes. Different responses...     

Parsimony as the ultimate regularizer for physics-informed machine learning

Nonlinear Dynamics - Data-driven modeling continues to be enabled by modern machine learning algorithms and deep learning architectures. The goals of such efforts revolve around the generation of...     

Discrete Curves in and the Toda Lattice

In this paper, we investigate flows on discrete curves in     , and     . A novel interpretation of the one-dimensional Toda lattice hierarchy and reductions thereof as flows on discrete curves are given.     

Spectral filtering for ultra-fast mode-locking in the normal dispersive regime

A theoretical model is developed which characterizes the physical process responsible for generating ultra-short, high-energy, mode-locked pulses in a normal GVD laser cavity with spectral filtering. Two physical parameters are critical to achieving optimal performance: the ratio of the filter bandwidth to the gain bandwidth and the placement of the output coupler in the laser cavity. The spectral filtering allows for the high-energy of typical normal GVD laser cavities to be maintained while the pulse intensity doubles and the FWHM reduces by an order of magnitude. This phenomenon is generic and ubiquitous to normal GVD mode-locking. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)