Tunable Surface Patterning of Azopolymer by Vectorial Holography: The Role of Photoanisotropies in the Driving Force.

The capability to pattern polymer surfaces at different length scales is an important goal in different research fields, including display technologies, microelectronics, optics, as well as biorelated and medical science. However, the ability to optically and dynamically manipulate topography is a key feature enabling remote control of associated effects/processes mediated by the surface. Azopolymers are largely investigated to this aim based on their sensitivity to optical fields and reconfigurability capabilities. In this work, surface relief formation induced by polarization patterns on an amorphous azopolymer structurally engineered to have large photoinduced birefringence has been investigated both experimentally and theoretically. Based on the different light polarization patterns, depth and shape of the relief grating can be controlled. An optically induced gradient force model that includes both the spatial distribution and the anisotropy of the material permittivity has been theoretically analyzed. The proposed approach is able to explain the experimental results and to overcome the limitation of existing models.

Surface-induced photorefractivity in twistable nematics: toward the all-optical control of gain.

We report the first two-beam coupling investigation of the surface-induced photorefractive effect (SIPRE) in optically twistable nematic liquid crystal cell. The unique space-charge field of SIPRE is exploited to achieve optical tuning of the photorefractive gain. A reconfigurable photoaligning substrate is used to adjust the twist angle, which is proved to be a control parameter for the photorefractive gain. The amplitude of the optical modulation increases gradually with the twist. Its phase shift changes from 0 degrees to 90 degrees with the polarization state of the two interfering beams. These results pave the way to the all-optical control of the photorefractive gain.

Liquid crystal as laser medium with tunable gain spectra.

Amplified spontaneous emission intensity and gain spectra in polarized light have been measured in a dye doped nematic liquid crystal for different orientation of its optical axis and pump intensity. A possibility for switching the gain of the liquid crystal by an external electric field is shown experimentally. The liquid crystal materials with field controlled gain can be used in microlasers and light micro-amplifiers in both planar and waveguiding geometry.

Electrically tunable two-dimensional liquid crystals gratings induced by polarization holography.

Two-dimensional (2D) gratings made up of an array of differently twisted nematic structures are obtained by crossed assembling of 1D polarization holograms recorded at the photoaligning substrates. The rotating linear polarization pattern, produced by the interference of two opposite circularly polarized beams, is recorded on the azo-dye doped polyimide aligning layers. The 2D gratings diffract light in different directions with different polarization states, that can be optically controlled. Orthogonal circularly and linearly polarized diffraction orders are simultaneously obtained irradiating the grating with a linearly polarized beam. An external ac voltage allows to completely control the diffracted energy distribution.

Light manipulation of nanoparticles in arrays of topological defects.

We report a strategy to assemble and manipulate nanoparticles arrays. The approach is based on the use of topological defects, namely disclination lines, created in chiral liquid crystals. The control of nanoparticle-loaded topological defects by low power light is demonstrated. Large-scale rotation, translation and deformation of quantum dots light-emitting chains is achieved by homogeneous LED illumination. Full reconfigurability and time stability make this approach attractive for future developments and applications.

Light-induced rotations of chiral birefringent microparticles in optical tweezers.

We study the rotational dynamics of solid chiral and birefringent microparticles induced by elliptically polarized laser light in optical tweezers. We find that both reflection of left circularly polarized light and residual linear retardance affect the particle dynamics. The degree of ellipticity of laser light needed to induce rotations is found. The experimental results are compared with analytical calculations of the transfer of angular moment from elliptically polarized light to chiral birefringent particles.

Chiral resolution of spin angular momentum in linearly polarized and unpolarized light.

Linearly polarized (LP) and unpolarized (UP) light are racemic entities since they can be described as superposition of opposite circularly polarized (CP) components of equal amplitude. As a consequence they do not carry spin angular momentum. Chiral resolution of a racemate, i.e. separation of their chiral components, is usually performed via asymmetric interaction with a chiral entity. In this paper we provide an experimental evidence of the chiral resolution of linearly polarized and unpolarized Gaussian beams through the transfer of spin angular momentum to chiral microparticles. Due to the interplay between linear and angular momentum exchange, basic manipulation tasks, as trapping, spinning or orbiting of micro-objects, can be performed by light with zero helicity. The results might broaden the perspectives for development of miniaturized and cost-effective devices.

Colposcopic survey of Papanicolaou test-negative cases with hyperkeratosis or parakeratosis.

A colposcopic survey was performed in 269 consecutive women with negative cytology showing hyperkeratosis or parakeratosis. A colposcopy-guided biopsy specimen of cervical abnormalities was taken in 88 cases, and human papillomavirus infection (HPV) was detected histologically in 25 cases. No cervical intraepithelial neoplasia (CIN) was detected. The detection rate of HPV was not significantly different from that observed in a consecutive series of 1073 Papanicolaou test-negative subjects self-referred for colposcopy. Colposcopic screening of subjects showing hyperkeratosis or parakeratosis with otherwise negative smears is not recommended because it does not allow detection of cytologically false-negative CIN.

Photorefractive effect due to a photoinduced surface-charge modulation in undoped liquid crystals.

We demonstrate that some peculiarities of the surface-induced photorefractive effect (SIPRE) in undoped nematic planar cells can be simply explained considering the electric field induced by a modulated surface-charge distribution. Polarization-dependent forced light scattering and two-beam coupling experiments indicate that the observed anisotropy of the diffraction efficiency and the energy transfer between the pump beams strongly depend on the experimental geometry. The investigation suggests that the unusual dichotomy between local and nonlocal behavior can be ascribed to a modulated longitudinal electric field component, in phase with the interference pattern, which is not accountable by the conventional photorefractivity. In a simple and general approach we demonstrate that the conceived charge distribution model for the SIPRE produces a space-charge field having two orthogonal modulated components, in-phase and pi/2 out of phase, respectively. The electric field configuration within the nematic sample gives reason for the main experimental features.

Homoclinic gluing bifurcations during the light induced reorientation in nematic-liquid-crystal films.

An s-polarized laser beam that impinges at small incidence angle on a homeotropically aligned nematic liquid crystal produces very interesting nonlinear phenomena. In this paper, we show that, due to the symmetry of the system, a cascade of successive homoclinic gluing bifurcations is responsible for the transition towards a stochastic regime in the experiment. We compare the experimental results with a model describing a sequence of gluing bifurcations.

Influence of the ions on the dynamical response of a nematic cell submitted to a dc voltage.

The influence of the ions present in a liquid crystal on the dynamical response of a nematic slab submitted to a dc voltage is studied. The evolution of the system toward the equilibrium state is investigated by solving the continuity equation for the electric charge, taking into account the current of drift and of diffusion. Our analysis shows that the formation of the double layers close to the electrodes strongly modifies the distribution of the electric field across the sample. We evaluate the surface polarization due to the ions movements and the contribution to the anisotropic part of the surface energy having a dielectric origin. We show also that, even if the optical response of the liquid crystal is a slow phenomenon, the distribution of the ionic charge is rather fast. Consequently, the presence of the ions cannot be neglected in the determination of the flexoelectric coefficients when the nematic sample is submitted to a square wave having a period of the order of 1 s.

Famotidine in the short-term treatment of duodenal ulcer and of concomitant peptic lesions: comparison with cimetidine.

Twenty patients affected with endoscopically demonstrated duodenal ulcer were studied. They were randomly divided into two groups of ten individuals each. The first group was treated with famotidine 40 mg/die/os, the second one with cimetidine 800 mg/die/os; both drugs were administered in one medication at bedtime. In each group, eight patients completed the treatment: six out of eight famotidine treated and five out of eight cimetidine treated patients showed ulcer healing on upper digestive endoscopy after four weeks of treatment; after eight weeks of therapy, all patients of both groups displayed ulcer healing. Nevertheless, an overall quantitative evaluation of all peptic lesions (performed according to an endoscopic arbitrary score) indicated a higher effectiveness of famotidine. Famotidine did not affect humoral parameters of renal, hepatic and myelopoietic function and did not significantly change fasting serum gastrin levels.

Contribution of cytology, colposcopy, target biopsy and conization to the early diagnosis of precancerous and cancerous lesions of the cervix uteri.

The study is based on 334 cytologic suspect or positive women observed in the area of Florence. Cytologic diagnoses of dysplasia, carcinoma in situ (CIS), and invasive carcinoma are related to the histologic reports. To the same histologic reports are related the colposcopic aspects. Lastly, diagnoses made by target biopsy are compared with the final diagnoses made by cone biopsy. The 3 diagnostic methods and their diagnostic accuracy are then compared. As regards dysplasia, the diagnostic precision of cytology is 40.2% and for target biopsy in 76.9%. In the diagnosis of CIS, cytology shows a diagnostic accuracy (77.7%) that is a little lower than that of target biopsy (81.7%). In invasive carcinoma, cytology has a good diagnostic precision (88.2%), which becomes 100% if the diagnosis is made by target biopsy. The correlation between colposcopic aspects and histologic reports is not very reliable. We conclude that cytology is a valid test in an extensive mass screening, that colposcopy is essential to execute target biopsy, and that the latter is useful in defining dysplasia and invasive carcinoma diagnoses. On the contrary, in the case of CIS, target biopsy does not greatly increase cytology diagnostic precision.

Analysis of false-negative and underreported smears in the Florence district screening program for cervical carcinoma.

AIMS AND BACKGROUND: To review false-negative or underreported (reactive changes, squamous or glandular atypia) smears performed in women developing histologically proven CIN2 or more severe lesions within 24 months and evaluate error causes. The study setting was the Florence District cervical cancer population-based screening: about 60,000 women age 25-60 years screened per year. METHODS: 118 false-negative or underreported cases were identified at screening files-cancer Registry matching, and the original smears were reviewed by six independent readers to judge smear adequacy and error type. RESULTS: Sampling errors (reported as inadequate, negative or less severe than CIN1 at review) accounted for 74% and screening/interpretation errors (reported as CIN1 or more severe at review) accounted for 26% of studied cases. Screening/interpretation errors were more likely ascribed to misinterpretation and underreporting than to misperception of cellular abnormalities. CONCLUSIONS: Quality control should above all address the problem of sampling adequacy. Due to the rarity of misperceived abnormalities (true screening errors), manual or automated rescreening of negative smears would not be an effective procedure for quality control.

"Nonclassic" cytologic signs of cervical condyloma. A case-control study.

The association between "nonclassic" cytologic signs of condyloma and human papillomavirus (HPV) infection in women with negative Papanicolaou smears was analyzed via a case-control study. The cytologic signs considered were mild koilocytosis, mild dyskeratosis, binucleation or multinucleation, cleared cytoplasm and nuclear hyperchromatism. The Papanicolaou smears of 166 cases that showed colposcopic and histologic evidence of HPV infection (but whose smears lacked the classic cytologic signs of condyloma) and 166 controls that were negative colposcopically were randomly admixed and blindly reviewed by a panel of cytologists. A significant association to HPV infection was observed for all of the nonclassic signs studied, but multivariate analysis showed a weakly independent association only for mild koilocytosis. The sensitivity (0.46) and the specificity (0.87) of these nonclassic signs were not satisfactory. The utility of selecting women with negative Papanicolaou smears for colposcopy on the basis of these signs is discussed.

Routine colposcopic survey of patients with squamous atypia. A method for identifying cases with false-negative smears.

Routine colposcopy was performed on 376 women with cervical squamous atypia (originally reported as "inflammatory atypia"). Colposcopy showed no abnormalities in 240 cases and a lesion in 136 cases; the latter were sampled by colposcopy-guided biopsy. The biopsy samples showed evidence of human papillomavirus (HPV) infection and/or grade I cervical intraepithelial neoplasia (CIN I) in 42 cases (11.1%), CIN II in 4 cases (1.1%) and CIN III in 5 cases (1.3%); the other 85 biopsied cases were histologically negative. Most cases of HPV/CIN I (35 of 42) and all of the cases of CIN II-III occurred in women under the age of 40. The detection rates were 4.4% for CIN II-III in women under the age of 40, 4.0% for HPV/CIN I in women 40 and older and 17.2% for HPV/CIN I in women under the age of 40 (P less than .001). It thus appears that women under the age of 40 who show cytologic evidence of squamous atypia would benefit from colposcopic examination.

[Evaluation of the efficacy of bicarbonate-alkaline water action on gallbladder motility]. / Valutazione dell'efficacia di un'acqua bicarbonato-alcalina sulla motilità colecistica.

Physiological gallbladder contraction, delivering bile salts during meals, plays a key role in digestive mechanisms. A bicarbonate-alkaline water (Uliveto) shows a positive effect on gallbladder kinetics: so it may be useful in order to improve dyspepsia due to delayed gallbladder emptying.

Polarization-dependent optomechanics mediated by chiral microresonators.

Chirality is one of the most prominent and intriguing aspects of nature, from spiral galaxies down to aminoacids. Despite the wide range of living and non-living, natural and artificial chiral systems at different scales, the origin of chirality-induced phenomena is often puzzling. Here we assess the onset of chiral optomechanics, exploiting the control of the interaction between chiral entities. We perform an experimental and theoretical investigation of the simultaneous optical trapping and rotation of spherulite-like chiral microparticles. Due to their shell structure (Bragg dielectric resonator), the microparticles function as omnidirectional chiral mirrors yielding highly polarization-dependent optomechanical effects. The coupling of linear and angular momentum, mediated by the optical polarization and the microparticles chiral reflectance, allows for fine tuning of chirality-induced optical forces and torques. This offers tools for optomechanics, optical sorting and sensing and optofluidics.

Orientational gratings in dye-doped polymer-dispersed liquid crystals induced by the photorefractive effect.

We report the observation of orientational gratings induced by the photorefractive effect in dye-doped polymer-dispersed liquid crystals. The photorefractive origin of the grating-induction effect is supported by the results of two-beam coupling experiments and by the possibility of erasing the grating by uniform illumination. For all the samples a stable memory effect was observed.