Refracted Near-Field Measurements of Refractive Index and Geometry of Silica-on-Silicon Integrated Optical Waveguides.

The standard refracted near-field technique for measuring the refractive-index profile of optical fibers cannot be directly used for silica-on-silicon integrated optical waveguides because of the opacity of silicon. A modified method is thus presented to characterize this kind of waveguide. The resolution it gives, both spatially and in the refracted index, is practically as good as that obtained with the standard technique for measuring optical fibers.

Polarization-induced pulse spreading in birefringent optical fibers with zero differential group delay.

The polarization properties of concatenations of trunks of birefringent fibers and elements with polarization-dependent losses are analyzed. We show both theoretically and experimentally that the concatenation can have zero differential group delay over a whole range of wavelengths but that a pulse propagating down the concatenation can still experience significant pulse spreading. In this example the two main methods used for characterizing polarization mode dispersion in optical fiber systems, i.

Existence of solitons in infinite lattice.

We consider necessary conditions for existence of optical solitons in one-dimensional nonlinear periodic layered array. We show analytically that in the array with the cubic-quintic nonlinearity bistable solitons are possible whereas for the Kerr nonlinearity they never exist. We investigate asymptotic behavior of the soliton amplitude at infinity.

Finite-band solitons in the Kronig-Penney model with the cubic-quintic nonlinearity.

We present a model combining a periodic array of rectangular potential wells [the Kronig-Penney (KP) potential] and the cubic-quintic (CQ) nonlinearity. A plethora of soliton states is found in the system: fundamental single-humped solitons, symmetric and antisymmetric double-humped ones, three-peak solitons with and without the phase shift pi between the peaks, etc. If the potential profile is shallow, the solitons belong to the semi-infinite gap beneath the band structure of the linear KP model, while finite gaps between the Bloch bands remain empty.

Spontaneous symmetry breaking and switching in planar nonlinear optical antiwaveguides.

We consider guided light beams in a nonlinear planar structure described by the nonlinear Schrodinger equation with a symmetric potential hill. Such an "antiwaveguide" (AWG) structure induces a transition from symmetric to asymmetric modes via a transcritical pitchfork bifurcation, provided that the beam's power exceeds a certain critical value. It is shown analytically that the asymmetric modes always satisfy the Vakhitov-Kolokolov (necessary) stability criterion; nevertheless, the application of a general Jones' theorem shows that the AWG modes are always unstable.

Follow-up study of seasonal affective disorder in Switzerland.

Of 39 diagnosed Seasonal Affective Disorder (SAD) patients who were interviewed 2-5 years after participation in a light therapy trial, 10 continued to have recurrent major depressive episodes in winter, and 17 manifested sub-syndromal SAD (2 patients also had recurrent brief depression, seasonal type). 8 patients had recovered, and 4 had shifted in symptomatology. Thus, over a number of years, the clinical diagnosis changed for the better in 64% of the patients, suggesting that SAD is not a prodromal form of a more chronic major affective disorder, and that light therapy (and perhaps also light-oriented behaviour) reduced the incidence and depth of subsequent depressive episodes.

Transmission gratings for chromatic dispersion compensation.

It is theoretically demonstrated that a succession of four unchirped gratings, ~20 mm long, induces a negative chromatic dispersion in transmission of -100 ps/nm over a 0.2-nm bandwidth, with a power loss below 1 dB. The stability of the proposed arrangement is also considered and found to be within today's technology.

Light therapy in seasonal affective disorder is independent of time of day or circadian phase.

Objective: We tested the hypothesis that phase-delayed circadian rhythms underlie seasonal affective disorder (SAD) by measuring phase position of 6-sulfatoxymelatonin excretion and comparing antidepressant response to morning or evening light given as a first treatment.

Design: Randomized controlled trial.

Setting: Ambulatory.

Morning or night-time melatonin is ineffective in seasonal affective disorder.

Melatonin, at the same doses used to treat circadian-rhythm related sleep disturbances, had no effect on the depressive symptoms in seasonal affective disorder (SAD) patients, whether given early (7 a.m.) or late (11 p.

Ion transport mediated by the valinomycin analogue cyclo(L-Lac-L-Val-D-Pro-D-Val)3 in lipid bilayer membranes.

Cyclo(L-Lac-L-Val-D-Pro-D-Val)3 (PV-Lac) a structural analogue of the ion-carrier valinomycin, increases the cation permeability of lipid bilayer membranes by forming a 1:1 ion-carrier complex. The selectively sequence for PV-Lac is identical to that of valinomycin; i.e.

Kinetics of ion transport in lipid membranes induced by lysine-valinomycin and derivatives.

Lysine-valinomycine and two N epsilon-acyl derivatives are compared with respect to their potency to transport Rb+ ions across thin lipid membranes. Lysine-valinomycin acts as a neutral ion carrier only above a pH of about 7 of the aqueous solutions, while at lower pH the molecules seem to be positively charged due to a protonation of the epsilon-NH2 group of the lysine residue. A kinetic analysis based on voltage jump relaxation experiments and on the nonlinearity of the current-voltage characteristics showed that the conductance increment delta per carrier molecule for uncharged lysine-valinomycin is similar to that of natural valinomycin.

Synthesis of lysine-valinomycin by solid-phase segment condensation.

In order to obtain a readily derivatized analog of the ionophore antibiotic valinomycin, [1-lysine] valinomycin (Lys-VAL) was synthesized. The compound was built up on a polystyrene support by stepwise segment condensation and was cyclized in solution. The segments used were didepsipeptides protected by the t-butyloxycarbonyl and p-nitrobenzyloxycarbonyl groups.

Selective ion binding and membrane activity of synthetic cyclopeptides.

Four cyclic peptides related to the membrane-active complexones PV, cyclo-(L-Pro-Lval-D-Pro-D-Val)3, and valinomycin were synthesized: (1) cyclo-(L-Pro-L-Ala-D-Val)3 or PVPA, (2) cyclo-(L-Ala-L-Val-D-Pro-D-Val)3 or PVAV, (3) cyclo-(L-Pro-L-Val-D-Pro-D-Val)2-L-Pro-D-Val or PV-10, (4) cyclo-(L-Pro-L-Val-D-Pro-D-Val)2 or PV-8. In a two-phase extraction assay the affinity of PV and PVPA for alkali picrates was about three orders or magnitude greater than that of valinomycin. It was about equal to valinomycin for PVAV and much lower for PV-10 and PV-8.

Synthesis of a 19-residue peptide with alamethicin-like activity.

This paper describes the chemical synthesis of a compound with voltage-gating characteristics similar to those observed in nerve membranes. For alamethicin (ALA), a natural antibiotic that induces such properties in lipid bilayer membranes, there are two proposed structures, one a cyclic and the other an open chain peptide. The open chain sequence (ALA-o) proposed by Martin and Williams [(1976) Biochem.

Mechanism of ion transport through lipid bilayer-membranes mediated by peptide cyclo-(D-Val-L-Pro-L-Val-D-Pro).

The cyclic dodecapeptide PV, cyclo-(D-Val-L-Pro-L-Val-D-Pro)3, a structural analogue of the ion-carrier valinomycin, increases the cation permeability of lipid bilayer membranes. This paper reports the results of two types of relaxation experiments, namely relaxation of the membrane current after a voltage jump and decay of the membrane voltage after a charge pulse in lipid bilayer membranes exposed to PV. From the relaxation data, the rate constant for the translocation of the ion carrier complex across the membrane, as well as the partition coefficient of the complex between water and membrane solution interface were computed and found to be about one order of magnitude less than the comparable values for valinomycin (Val).

Optical and electrical studies on dansyllysine-valinomycin in thin lipid membranes.

Dansyllysine-valinomycin, a fluorescent analogue of the ionophore valinomycin was synthesized and incorporated into black lipid membranes. Its concentration inside the membrane was measured fluorometrically and was also determined from electrical relaxation experiments, which were analyzed on the basis of a previously proposed carrier model. The results of both methods agreed within less than one order of magnitude.

Conformational studies of peptide cyclo-(D-Val-L-Pro-L-Val-D-Pro]3, a cation-binding analogue of valinomycin.

The solution conformation of cyclo-[D-Val-L-Pro-L-Val-D-Pro]3 (PV) and its alkali-metal ion complexes was investigated by proton nuclear magnetic resonance spectroscopy. It is concluded that the cation complexes of PV have S6 symmetry and are essentially isostructural with the K complex of valinomycin. In contrast to valinomycin, the Li- and Na-PV complexes are stable in methanol and have dissociation rate constants that are several orders of magnitude slower than the corresponding valinomycin complexes.

Effect of peptide PV on the ionic permeability of lipid bilayer membranes.

THIS PAPER REPORTS THE EFFECTS OF PEPTIDE PV (PRIMARY STRUCTURE: cyclo-(D-val-L-pro-L-val-D-pro)(delta)) on the electrical properties of sheep red cell lipid bilayers. The membrane conductance (G(m)) induced by PV in either Na(+) or K(+) medium is proportional to the concentration of PV in the aqueous phase. The PV concentration required to produce a comparable increase in G(m) in K(+) medium is about 10(4) times greater than for its analogue, valinomycin (val).