Intrachannel Interactions Research Articles

Resonant nonlinear intrachannel interactions in strongly dispersion-managed transmission systems

Nonlinear intrachannel interactions in a transmission system with strong periodic dispersion management are studied. The ghost pulse at the zero bit is shown to grow resonantly as a result of periodic forcing and temporal phase matching with the signal pulses. The growth rate depends on the degree of overlap between the signals. The analysis agrees with direct numerical simulation of the full system. Growth rates for various bit patterns as a function of map strength are obtained.

Pulse interactions and collisions in asymmetric higher-order dispersion managed fiber link

Intra-channel pulse interactions and inter-channel collisions may substantially limit the transmission performance in dispersion managed fiber optics links. We discuss how the theory of dispersion-managed solitons may be applied to optimize the dispersion map, as to reduce both pulse interactions and cross-phase modulation induced timing jitter at the system output.

Guest–guest interactions in urea inclusion compounds †

Different types of urea inclusion compounds have been studied to test the importance of the molecular interactions between the guests. Experimental evidence has been obtained from the EPR spectra of radicals derived from guests by room temperature γ-ray irradiation of the inclusion compounds. The guest–guest intra-channel interactions are very important in the case of tridecanedioic and tetradecanedioic dicarboxylic acid guests which give rise to strong intermolecular hydrogen bonding between the carboxylic groups. It is found that the molecular conformation of the tetradecanedioic acid is strongly distorted to fit in the host channel dimensions. The interactions between guest molecules included in adjacent host channels have been modulated by varying the relative guest composition in a mixed nonadecan-10-one–nonadecane inclusion compound. It is shown that the molecular reorientation of the nonadecan-10-one guest becomes faster by increasing the nonadecane percentage as a consequence of the reduced inter-channel interactions.

Stress-induced domain reorientation in urea inclusion compounds

FOR over 50 years urea inclusion compounds (UICs)-in which molecules are entrapped within the cavities of a hydrogen-bonded urea network—have intrigued chemists, crystallographers and spectroscopists1. Most previous work on these and other inclusion compounds has focused on intrachannel interactions and dynamics. We have now found that UICs can serve as useful models to probe long-range interactions and cooperative phenomena in crystals. Here we report the structure of 2,10-undecanedione/urea (1:9) (1/ urea), in which an extended hydrogen-bonded array connecting hosts and guests serves to distort the urea channel away from the hexagonal symmetry normally observed for UIC crystals. The distortion is large enough, and exhibits enough cooperativity, to generate macroscopic domains, but is small enough to allow facile domain reorientation under small compressive stresses. By incorporating a specific impurity (2-undecanone) into 1/urea, we can modify the domain size and optical properties, and make the domain reorientation spontaneously reversible when the uniaxial stress is released. All of these phenomena can be understood in terms of cooperative interactions between different channels of the hydrogen-bonded network formed by urea and its guest.

Target recovery in visual backward masking: no clear explanation in sight.

Theories of visual backward masking have generally ignored demonstrations of the perceptual recovery of a masked target when the masking stimulus (M1) is followed by a second masking stimulus (M2). This failure to address recovery may reflect a belief that recovery effects are relatively small and inconsistent. The present article reports a series of experiments, using single-letter targets, a patterned M1 and a light-flash M2, which indicate that recovery can be a robust and substantial phenomenon. It is observable under a variety of conditions, and the magnitude of recovery matches the masking effect itself. A two-choice discrimination task was employed to test an explanation for recovery that attributes the effect to inhibition from the transient response to the light flash on the sustained response to the patterned mask. That explanation calls for the shape of the function relating the discriminability of the patterned mask to the onset asynchrony of M1 and M2 to be U-shaped in form. The data, however, reveal a monotonic masking function, suggesting that only sustained, intrachannel interactions are involved in the recovery of the target percept. Two conflicting explanations for recovery are discussed, one based upon inhibition of M1 responses, the other upon enhancement of target features. Thus, while recovery is demonstrated to be very real, its explanation remains elusive.

Photoionisation of Hg in the soft X-ray energy range

The photoionisation cross sections relative to the 5d, 5p and 4f subshells of Hg have been calculated with two models: the Hartree-Slater and Hartree-Fock models. The influence of intrachannel interactions on the cross sections and the photoelectron angular distribution parameter for the 4f subshell is discussed.