Periodic amplification of dark solitons using stimulated Raman scattering

The possibility of periodically amplifying dark solitons in a normally dispersive optical fiber is studied. It is found that, as with bright solitons, an all-optical, repeaterless, and stable system for dark-soliton transmission at a rate of 20 GHz over thousands of kilometers in a lossy fiber is achievable, if periodic amplification using stimulated Raman scattering is incorporated.

Propagation properties of dark solitons

We numerically study the initial-value problem of the nonlinear Schrödinger equation in the normal-dispersion regime of an optical fiber. A nonchirped hyperbolic tangent input pulse having arbitrary amplitude is found to evolve into a primary dark soliton having a constant amplitude and speed. The effect of the input amplitude is to alter the pulse width of the primary dark soliton. In addition, a set of secondary dark solitons of smaller amplitude moving away from the primary pulse is also generated. It is also shown that nonlinear dark pulses in optical fibers are more stable than bright pulses with respect to loss and noise.

The relationship between Hb Bart's levels in cord blood and the deletions of alpha-globin genes

A relationship between Hb Bart's levels in cord blood and the number of alpha-globin genes has been established by screening cord blood samples from 1,075 newborn babies. Diagnosis was made by gene mapping of DNA samples with restriction endonuclease digestion. The presence of Hb Bart's was determined with a discontinuous microelectrophoresis on cellulose acetate at pH 8.34. The establishment of this relationship allows an early diagnosis of alpha-thalassemia by this simple microelectrophoretic procedure.

Evolution of femtosecond pulses in single-mode fibers having higher-order nonlinearity and dispersion

Using computer simulations, we examine the effects of higher-order dispersive and nonlinear propagation processes on the spectral and time development of ultrashort, high-intensity pulses propagating in single-mode optical fibers having normal dispersion. Our results indicate that both the cubic-dispersion term and the shock term of the nonlinear Schrödinger equation contribute to asymmetry in the pulse power spectrum and cause highly nonlinear chirp.

Two cDNA clones coding for the legumin protein of Pisum sativum L. contain sequence repeats

The sequence of two cDNA clones coding for the whole of the β-subunit and most of the α-subunit of legumin are presented together with a considerable amount of protein sequence data to confirm the predicted amino acid sequence. A unique feature shown by these cDNAs is the presence of three 56 base pair tandem repeats in the region encoding the C terminal of the α polypeptide. The tandem repeats are also exhibited in the predicted polypeptide sequence as three 18 amino acid repeats which contain extremely high proportions of polar, mainly acidic, residues. The new sequences are compared to the previously published sequence of some shorter legumin cDNAs (Nature 295: 76-79). In the region where the sequences overlap, the previous cDNAs differ from the new ones by only a few base substitutions but most of the repeated region is not present though the sequences on either side are. The possibility that the absence of the repeats may reflect the difference between two types of legumin gene, rather than an artefact of the cloning of the cDNAs, is discussed.