Dual-mode Switching Research Articles

Stochastic blind equalization based on PDF fitting using Parzen estimator

This work presents a new blind equalization approach that aims to force the probability density function (pdf) at the equalizer output to match the known constellation pdf. Quadratic distance between pdf's is used as the cost function to be minimized. The proposed method relies on the Parzen window method to estimate the data pdf and is implemented by a stochastic gradient descent algorithm. The kernel size of the Parzen estimator allows a dual mode switch or a soft switch between blind and decision-directed equalization. The proposed method converges faster than the constant modulus algorithm (CMA) working at the symbol rate, with a similar computational burden, and reduces the residual error of the CMA in multilevel modulations at the same time. A comparison with the most common blind techniques is presented.

Redox and ionic-binding switched fluorescence of phenosafranine and thionine included in Nafion® films

This report describes electrochemical and optical properties of azine-loaded Nafion® film electrodes that generate redox-activated optical signal. The apparent charge diffusion coefficient in the film decreased abruptly as the solution pH increased from 0.4 to 3, probably because deprotonation of the dyes lowered the rate of intermolecular electron hopping. Reversible switching of the fluorescence of phenosafranine was performed by electrochemical oxidation/reduction cycles. Both of the redox couple were isolable and stable; the reduced form was non-fluorescent, whereas the oxidized form was strongly fluorescent. Since the photonic output depended on chemical binding, the electrode system could operate as a dual-mode switching device. The second protonation of the dye molecule changed the fluorescence intensity sufficiently for chemical signaling of the photonic output, because the fully protonated oxidized-form was non-fluorescent; however, a p K a1 of 0.8 was too low to change the pH rapidly. 1,1′-ferrocenedimethanol quenched the fluorescence of the oxidized form efficiently to cause the ‘switching off’ of fluorescence. In the presence of the guest, however, the dye-loaded film did not recover the fluorescent state at any potential, because the cationic dye formed a nonfluorescent complex with the guest incorporated into the film.

Long-wavelength (/spl lambda/=10 /spl mu/m) quadrupolar-shaped GaAs-AlGaAs microlasers

In this paper, we present experimental results of our investigations on deformed GaAs-AlGaAs microlasers emitting around /spl lambda/=10 /spl mu/m. These quantum cascade lasers exhibit interesting features regarding the threshold current densities, optical output, and far-field pattern. A slight aberration from a circular cross section decreases the threshold current density for microlasers (which have a radius of 50 /spl mu/m). For larger deformations /spl epsiv/, the threshold starts to increase because of the increasing mirror losses. For smaller microlasers (radii between 22 and 34 /spl mu/m), the threshold current density increases already for slight deformations due to the increase of the mirror losses. The experimental results can be fitted very well with the mirror losses as a fitting parameter using a well-known and simple model. Threshold currents as low as 170 mA are measured for a cylindrical microlaser with a radius of 22 /spl mu/m. The peak optical output is increasing quasi-exponentially with rising deformation. Lasing emission from slightly concave resonator shapes is detected. The bow-tie mode and other modes-different from Whispering-gallery modes-are responsible for highly directed emission along the diagonal axis and along the short axis, respectively, of the microlasers. Single-mode emission with a side-mode suppression ratio larger than 25 dB is shown over the entire drive current range for a highly deformed microlaser. The laser line can be temperature tuned with /spl Delta//spl nu//T=-0.027 cm/sup -1//K. A dual mode switching depending on the drive current with a mode spacing of /spl Delta//spl nu/=8.1 cm/sup -1/ between 999 and 1007.1 cm/sup -1/ is observed for a less deformed microlaser.

Single- or Dual-Mode Switching of Semisynthetic Ribonuclease S′ with an Iminodiacetic Acid Moiety in Response to the Copper(II) Concentration

Single- or Dual-Mode Switching of Semisynthetic Ribonuclease S′ with an Iminodiacetic Acid Moiety in Response to the Copper(II) Concentration

Single- or Dual-Mode Switching of Semisynthetic Ribonuclease S′ with an Iminodiacetic Acid Moiety in Response to the Copper(II) Concentration

Ribonuclease S′ bearing iminodiacetic acid as a metal-bindingsite was designed and semisynthesized by self-assembly of native S-protein with chemically modified S-peptide. Rationally designed incorporation of unnatural iminodiacetic acid groups as transition metal receptors can confer the dual mode of response to a metal cation (stabilization/destabilization, and thus activation/deactivation) with regard to the structure and activity of an enzyme (see diagram).