Formation of topological defects in nematic shells with a dumbbell-like shape.

The present study investigates dumbbell-shaped nematic liquid crystal shells. Using molecular dynamics (MD) simulations, we consider the effects of an external electric field on nematic ordering by computing the average molecular alignment's time evolution and equilibrium configuration. We show that the number and location of topological defects are strongly affected by the external field, with the orientational ordering's equilibrium configuration depending on field direction about the shell's long axis. For a transverse external field, it is verified that the defect rearrangement presents a non-linear dynamics, with a field independent characteristic time scale delimiting the short and long time regimes. Effects associated with varying the shell's Gaussian curvature are also analyzed.

Photonics bridges between turbulence and spin glass phenomena in the 2021 Nobel Prize in Physics.

A photonic connection between turbulence and spin glasses has been recently established both theoretically and experimentally using a random fiber laser as a photonic platform. Besides unveiling this interplay, it links the works of two 2021 Nobel laureates in Physics.

Hepatitis C in Brazil: lessons learned with boceprevir and telaprevir.

In 2012, the first-generation protease inhibitors telaprevir (TVR) and boceprevir (BOC) were introduced in the Brazilian health system for treatment of chronic hepatitis C, after their approval by the National Committee for Health Technology Incorporation (CONITEC). However, these medicines were discontinued in 2015. The short period of use in therapy and their high cost require a discussion about the consequences for patients and for the health system of the early incorporation of new therapies. The article presents a qualitative analysis of the incorporation process of both medications in Brazil and the results of a multicenter study that included patients treated with BOC or TVR between January 2011 and December 2015 in five Brazilian cities. The study included 855 patients (BOC: n=247) and (TVR: n=608). The document analysis showed that CONITEC's decision to incorporate BOC and TVR was based on results of phase III clinical trials that compared sustained virologic response (SVR) rates of patients treated with BOC and TVR with rates of those that received placebo. However, these studies included a low percentage of cirrhotic patients. The SVR rates observed in this multicenter study were worse than clinical trials pointed out (BOC: 45.6%; TVR: 51.8%), but similar to those achieved with previously adopted therapies. The discontinuation rate due to adverse events was (BOC: 15.4%; TVR: 12.7%). Based on these unsatisfactory results, the study brings a discussion that goes beyond the therapy outcomes, exploring the incorporation of these high-cost medicines and the related decision-making process, contributing to future decisions in medicine policies and in the treatment of chronic hepatitis C.

All-optical power-controlled switching in wave mixing: application to semiconductor-doped glasses.

An all-optical power-controlled switch is described. It is based on the modulation of self-diffracted beams by a control beam that modifies the third-order grating excited in a nonlinear medium. The experimental results obtained by using Cd(S, Se)-doped glasses are in agreement with the theoretical predictions. For an application, we also report the generation of dark pulses with subnanosecond width based on the studied process.

Raman-assisted polarization beats in time-delayed four-wave mixing.

We demonstrate a method for determining the phase of the third-order susceptibility, chi ((3)), in the proximity of a Raman resonance. The measurements were based on the phenomenon of polarization beats, which was exploited in a time-delayed four-wave-mixing experiment with bichromatic beams. The phase dispersion of chi((3)) was studied close to resonance with the 655.7-cm(-1) vibrational mode of carbon disulfide.

Method to determine the phase dispersion of the third-order susceptibility.

A new method for measuring the phase of the third-order susceptibility chi((3)) that is based on the phenomenon of polarization beats is proposed and demonstrated. As a first application, the method was employed to study the phase dispersion of chi((3)) in Cd(S, Se)-doped glasses.

Exploitation of the Z-scan technique as a method to optically probe pK(a) in organic materials: application to porphyrin derivatives.

We demonstrate the use of the Z-scan technique as a method to measure a chemical parameter, the pK(a) value, that characterizes the equilibrium constant in acid-base reactions. The measurements were performed with picosecond pulses at 532 nm in Fe(III)-meso-tetrakis(4-N-methyl-pyridyl) porphyrin. The results were compared with linear absorption measurements and electron paramagnetic resonance, the usual techniques employed to determine pK(a) values in aqueous solutions, and showed excellent agreement.

Changes in porphyrin nonlinear absorption owing to interaction with bovine serum albumin.

The changes in the nonlinear absorption of meso-tetrakis (p-sulfonatophenyl) porphyrin (TPPS(4)) caused by its binding to bovine serum albumin (BSA) were investigated in aqueous solutions. The nonlinear absorption depended on the excitation wavelength and pH. It is noteworthy that, for excitation at 640 nm, saturated absorption was observed in a TPPS(4) solution (pH 4.0), whereas reverse saturated absorption occurred for all pH values from 4.0 to 7.0 when BSA was added to TPPS(4). The presence of BSA also initiates an increase in the saturation intensity and a reduction of the nonlinear absorption coefficient. The interpretation of the results based on the binding of TPPS(4) to BSA is corroborated by linear absorption, fluorescence, light scattering, and flash-photolysis data.

Stimulated effects in one-photon resonant interferometric four-wave mixing with incoherent light.

The interferometric four-wave mixing technique with broadband light is extended to measurements of population relaxation. For what is believed to be the first time, the population relaxation rate in the presence of a pump field is measured. It is shown that stimulated emission can significantly affect the results when one is dealing with resonant transient wave mixing, and, consequently, in most cases stimulated processes should be taken into account.

Potassium source for ion-exchange glass waveguide fabrication.

We propose and demonstrate the use of a new potassium-ion source for glass waveguide fabrication based on a KI -ZnCl2 mixture. Planar waveguide were made using glasses such as BK7, Pyrex, soda lime, and commercial semiconductor doped glasses. The optical quality of the waveguides prepared compare favorably with the quality obtained using other fabrication techniques and the processing time is considerably reduced.

Reverse saturable absorption and anti-Stokes fluorescence in mesoionic compounds pumped at 532 nm.

Reverse saturable absorption and fluorescence in liquid solutions of mesoionic compounds are reported. Intensity-dependent transmittance and anti-Stokes fluorescence were observed when the samples were excited with radiation at 532 nm. The results are attributed to excited-state absorption, and the process is understood based on quantum-chemistry calculations that allow the energy levels that correspond to the relevant transitions to be located. A phenomenological description of the nonlinear beam propagation inside the samples is presented, and the nonlinear absorption coefficient as well as the saturation intensity is determined.

Nonlinear-optical properties of a poly(vinyl alcohol)-polyaniline interpenetrating polymer network.

The nonlinear-optical properties of a semi-interpenetrating polymer network of poly(vinyl alcohol) glutaralde-hyde-polyaniline were studied. Large (>/=10(-12) cm(2)/W) and fast (<50 ps) refractive optical nonlinearites were observed. The potential of this novel material for photonic applications is evaluated.