Electro-optic effect of laser photobleaching on viscoelastic properties of chiral liquid crystals

Viscoelastic properties are one of the most fundamental properties of chiral liquid crystals. In general, their determination is not a straightforward task. The main problem is the multitude of physical parameters needed to determine the value of the elasticity and viscosity constants. It is also necessary to consider the character of a respective phase. This problem is particularly important in the case of chiral phases such as ferroelectric and antiferroelectric phases or in the blue phases. There are several experimental methods to measure viscosity and elasticity constants in chiral phases. These methods use various phenomena to detect deformation, e.g., light transmission, polarization current, light modulation, dielectric constant and helix deformation or helix unwinding. Commonly, an external electric field is used to induce deformation, the homogeneity of which inside the cell is essential. This study is focused on the analysis of the effect of laser photobleaching on the electro-optic properties of the antiferroelectric liquid crystal and on the homogeneity of the electric field. The results obtained by confocal microscopy as a function of the cell depth are presented. The influence of the stabilization procedure of the isolated region performed by controlled laser photobleaching on the electro-optic properties has been studied. The observation was conducted using a polarizing microscope, and numerical analysis of two-dimensional colored textures was performed. The obtained results suggest that laser photobleaching can produce an anchoring effect, which has a positive effect on the electro-optic properties of antiferroelectric liquid crystal

Electro-Optic Effect of Laser Photobleaching on Viscoelastic Properties of Chiral Liquid Crystals

Viscoelastic properties are one of the most fundamental properties of chiral liquid crystals. In general, their determination is not a straightforward task. The main problem is the multitude of physical parameters needed to determine the value of the elasticity and viscosity constants. It is also necessary to consider the character of a respective phase. This problem is particularly important in the case of chiral phases such as ferroelectric and antiferroelectric phases or in the blue phases. There are several experimental methods to measure viscosity and elasticity constants in chiral phases. These methods use various phenomena to detect deformation, e.g., light transmission, polarization current, light modulation, dielectric constant and helix deformation or helix unwinding. Commonly, an external electric field is used to induce deformation, the homogeneity of which inside the cell is essential. This study is focused on the analysis of the effect of laser photobleaching on the electro-optic properties of the antiferroelectric liquid crystal and on the homogeneity of the electric field. The results obtained by confocal microscopy as a function of the cell depth are presented. The influence of the stabilization procedure of the isolated region performed by controlled laser photobleaching on the electro-optic properties has been studied. The observation was conducted using a polarizing microscope, and numerical analysis of two-dimensional colored textures was performed. The obtained results suggest that laser photobleaching can produce an anchoring effect, which has a positive effect on the electro-optic properties of antiferroelectric liquid crystal

Healthcare workers highly affected during the COVID-19 epidemic wave in Poland prior to vaccination availability: seroprevalence study

The aim of the study was to assess seroprevalence of anti-SARS-CoV-2 antibodies among healthcare workers (HCW) before introduction of vaccination, in selected areas in Poland as well as to identify potential risk factors and estimate the cumulative incidence of COVID-19 infections in this population.Material and MethodsThe authors conducted a sero-epidemiological, cross-sectional study among HCW of 5 non-COVID-19 hospitals in Poland. The recruitment took place in December 1–23, 2020, all HCW at selected hospitals could volunteer into the study. All persons were screened with rapid SARS-CoV-2 IgM/IgG tests in capillary blood. In case of positive result, 5 ml of venous blood was drawn for confirmatory testing with ELISA assay. The authors estimated prevalence of laboratory confirmed anti-SARS-CoV-2 antibody presence and examined factors associated with positive result. Cumulative incidence was estimated applying 2-source capture-recapture method to serology results and self-report of past infection.ResultsOut of 1040 HCW included in the analysis, one-fourth (25.2%) received a positive result for anti-SARS-CoV-2 antibodies by ELISA test, the prevalence among women was 25.3% (95% CI: 22.5–28.4) and 24.6% (95% CI: 19–31.2) among men. The prevalence of anti-SARS-CoV-2 antibodies was the highest among respondents who declared home contact with a confirmed COVID-19 case, 43.9% (95% CI: 32.4–56.1). It was also elevated among those who indicated contact with patients with COVID-19, 32.5% (95% CI: 26.7–38.8) and business contacts, including at the workplace, 28.9% (95% CI: 22.5–36.3). The estimated cumulative incidence of COVID-19 infections in the population, using the capture-recapture method was 41.2% (95% CI: 38.1–44.2).ConclusionsHealthcare workers remained at increased risk of infection largely due to work-related contacts with infected patients, although home exposure was also common. Estimated cumulative incidence is higher than the antibody prevalence, which indicates the need to monitor HCW for possible immunity waning, also post-immunization immunity. Med Pr. 2022;73(2):109–2