Optical control of light polarization in heliconical cholesteric liquid crystals.

We show here that light polarization of a beam propagating through a heliconical cholesteric cell can be controlled by tuning the Bragg resonance of the structure. We demonstrate that this control is achieved by varying either the low-frequency electric field or the intensity of a pump beam impinging on the sample. The study confirms the recently reported phenomenon of optical tuning of the heliconical cholesterics and opens the door for the development of simple and efficient polarization modulators controlled electrically or optically.

Nonlinear optical propagation near the Bragg resonance in heliconical cholesteric liquid crystals.

We show here that the light-induced tuning of the Bragg reflection recently demonstrated in heliconical cholesterics opens new perspectives to nonlinear optical propagation in liquid crystals. We highlight that, by properly adjusting the static electric field that stabilizes the heliconical structure, a dramatic change of the refractive index of the circularly polarized resonant mode can be achieved. Additionally, a stop band for a definite range of light intensity is obtained that can be tuned in order to get the conditions of self-induced transparency.

Low threshold Fabry-Perot optofluidic resonator fabricated by femtosecond laser micromachining.

We report the realization and characterization of an optofluidic microlaser based on a Fabry-Perot resonator fabricated by exploiting two direct writing fabrication techniques: the femtosecond laser micromachining and the inkjet printing technology. In this way a standard Fabry-Perot cavity has been integrated into an optofluidic chip. When using rhodamine 6G dissolved in ethanol at concentration of 5∙10-3 mol/l, laser emission was detected at a threshold energy density of 1.8 µJ/mm2 at least one order of magnitude lower than state-of-the-art optofluidic lasers. Linewidth below ~0.6 nm was measured under these conditions with a quality factor Q~103. These performances and robustness of the device makes it an excellent candidate for biosensing, security and environment monitoring applications.

Structured beam diffraction.

We report on the observation of a modulated pattern induced by a single laser beam in a polymeric film. In spite of the simple geometrical configuration, the analysis of the far field diffraction pattern allows a sensitive retrieving of the wavelength of the recording beam and of its incidence angle, pointing out the high information content of the recorded spot. A theoretical model is presented which satisfactorily explains the observed behavior. It takes into account the interaction of structured light with structured matter with the same symmetries and spatial modulation frequencies close to each other. This result shows a feature of the interaction between structured light and structured matter which has not been explored yet.

Light controlled phase shifter for optofluidics.

We report the light-induced control of optical phase shift by a liquid crystal cell made with LiNbO3:Fe crystals as substrates. We show that a phase shift of a few πs can be easily reached for two orthogonal polarizations due to liquid crystal reorientation driven by the photovoltaic electric field originated in the substrates. This effect is exploited to get all-optical switching with a contrast of about 80%, by 2 s pump pulse.

Optical nonlinearity in the nematic phase of bent-core mesogens.

Nonlinear optical response of the cybotactic nematic phase of a bent-core mesogen has been investigated for the first time through self-phase modulation induced by a Gaussian beam. The material exhibits a high nonlinear response achieving a nonlinear index n(2)≈5×10(-5) cm(2)/W and an unconventional behavior characterized by two different regimes. While the high-intensity regime can be easily explained in terms of a thermal indexing effect, the low-intensity regime is metastable and characterized by an unusual dependence on the irradiation energy. It is suggested that a change of the director configuration, possibly due to a light-induced modification of surface anchoring, is responsible for the observed behavior.

Role of space charges on light-induced effects in nematic liquid crystals doped by methyl red.

We show that both the extraordinarily large nonlinear response and the light-induced permanent reorientation in liquid crystals doped by the azo dye methyl red originates from the same phenomenon of modification of the charge density on the irradiated surface. The demonstration is done by applying ac voltage to the samples, showing that in this case no permanent anchoring is possible. The measurements confirm the role of photoisomerization that gives a transient contribution to the actual reorientation process only in the high dose regime. This result allows us to draw a picture for light-induced effects that might be applied to a large class of compounds.

First-order optical Freedericksz transition in a dye-doped nematic liquid crystal.

A first-order optical Freedericksz transition in a nematic liquid crystal doped by a small quantity of a dichroic dye with negative dichroism is observed. The initial homeotropic state corresponds to maximum absorption for the linearly polarized incident beam, while reorientation reduces absorption increasing the optical torque: this process produces the positive feedback leading to the observed bistable behavior.

Optical trapping induced by reorientational nonlocal effects in nematic liquid crystals.

We report a detailed analysis of optical trapping of low index particles in liquid crystals under experimental conditions that prevent the effect of conventional trapping originated by optical gradient forces. The observation of stable, long-range trapping shows that this phenomenon in liquid crystals is regulated by a completely different mechanism than in isotropic media. In particular, the role of the nonlocality of optical reorientation is highlighted by showing the dependence of the trapping force on the size of the reoriented area. A model based on the actual form of the Gaussian focused beam impinging on the liquid-crystalline medium in the trapping experiment is also reported, with good agreement with experimental data.

Thoracic ultrasonography: A new method for the work-up of patients with dyspnea().

OBJECTIVE: Differential diagnosis of dyspnea is vital for the management of respiratory failure, where routine parameters can now be integrated with thoracic ultrasound data. The objective of this study was to evaluate the validity and accuracy of this approach in a department of internal medicine. MATERIALS AND METHODS: We enrolled 152 patients consecutively hospitalized with a diagnosis of dyspnea. After clinical evaluation, chest radiography, biochemical assays (NT-proBNP), and emergency treatment, patients underwent ultrasound examination of the lungs. Results were considered positive if the total number of lines B was higher than 8. The ultrasound examination and NT-proBNP assay were repeated after 48 h. The gold standard was the clinical diagnosis of heart failure made by medical experts in accordance with AHA guidelines. RESULTS: The group of patients with positive ultrasound findings had a higher frequency of heart failure diagnoses (X(2) 92.5, p < 0.005) and significantly higher values of NT-proBNP (10,384 ng/l vs 3889 ng/l, p < 0.05). Moreover, the decrease in the number of B lines at 48 h was significantly greater (p < 0.005) among patients treated for heart failure. There were no significant changes in the values of NT-proBNP (p = 0.37). DISCUSSION: In conclusion we have shown that even in a department of internal medicine, lung ultrasonography is a useful tool for diagnosing respiratory insufficiency and monitoring its response to therapy.

US in the evaluation of abdominal pain in a department of internal medicine.

INTRODUCTION: US (US) examination of the abdomen has acquired a growing role in the investigation of abdominal pain; however its role in the diagnosis of some important causes of abdominal pain is still under investigation. The aim of this study was to evaluate the role of US of the abdomen in the diagnosis of abdominal pain in patients referred to a department of internal medicine. MATERIALS AND METHODS: A retrospective analysis was carried out on 248 US examinations performed in our department due to abdominal pain. For each examination the data written on the request form were registered as well as US findings which could be correlated with abdominal pain. RESULTS: In 105 patients (42%), US examination of the abdomen resulted in a relevant clinical finding and was thus considered positive. A high percentage of patients were elderly (>65 years; 52%) and very elderly (>80 years; 24%); these patients showed a significantly higher percentage of positive US scans. The proportion of positive scans was not significantly different between localized and non-localized pain. Specific pain location was associated with US findings such as hepatic masses, ovarian masses and renal stones, whereas non-localized pain was associated with abdominal free fluid and fluid-distended bowel loops. DISCUSSION: A high percentage of US examinations identified conditions that could possibly cause abdominal pain. Diagnostic yield of abdominal US was higher in elderly and very elderly patients. When a US examination is requested, it should always be evaluated within the clinical context. The physician should be aware of the great value of abdominal US in the diagnosis of the various causes of abdominal pain, but also of its possible limitations.

Surface-induced nonlinearities of liquid crystals driven by an electric field.

We report the study of the effect of a static electric field on the huge optical nonlinearity of methyl-red doped nematic liquid crystals. Experimental data are well fitted using a theoretical model that takes into account the modulation of the surface charge density due to the impinging light beam. It is demonstrated that the optical nonlinearity can be varied by orders of magnitude with application of a low voltage below the threshold of the Fredericks transition. These results confirm the previously proposed model of surface induced nonlinear effects.

Optical and mechanical shrinkage effects in dye-doped photonic bandgap structures based on organic materials.

In this work we study the effects of the optical shrinkage in polymer and liquid crystal (LC) mixtures optimized for their use as active media in compact plastic laser devices. These mixtures are characterized by the presence of the rhodamine 6G as an active dye. Modifications in the reflection properties of the gratings as a function of the active dye concentration have been determined experimentally and a detailed theoretical simulation of the optical transmittance properties of these devices is provided. Moreover, the comparison between two different experimental approaches clarifies the contribution to the optical shrinkage due to the presence of the active dye. In principle this approach allows determining the linear mechanical shrinkage by separating the contribution to optical shrinkage due to photochemical transformations from that due to mechanical effects.

Colossal optical nonlinearity induced by a low frequency external electric field in dye-doped liquid crystals.

We report on the effects of a low-frequency electric field on the optical nonlinear response of thin dye-doped liquid crystal cells. Experimental data show that the external field allows reaching extremely high values of the optical nonlinearity without any critical control of the cell interfaces. A qualitative interpretation of the collected data, based on the light-induced modulation of the bulk voltage through surface modifications, is proposed.

Light-induced molecular adsorption and reorientation at polyvinylcinnamate-fluorinated/liquid-crystal interface.

We have carried out a detailed experimental study, by means of x-ray reflectometry (XRR) and half-leaky guided mode (HLGM) optical characterization, of the light-induced molecular adsorption and reorientation at the polyvinylcinnamate-fluorinated (PVCN-F)/liquid-crystal (LC) interface of a LC cell doped with the azo-dye methyl red (MR). The XRR data allowed characterizing the microscopic structure of the adsorbed dye layer both before irradiation (dark adsorption) and after irradiation (light-induced adsorption). The HLGM optical characterization has made possible the experimental determination of the nematic director profile in the LC cell and evaluation of the effects of light-induced adsorption on the LC anchoring conditions. The experimental findings have confirmed the formation of a dark-adsorbed layer and are in agreement with the absorption model previously proposed to account for the complex phenomenology related to light-induced anchoring and reorientation in dye-doped liquid crystals.

Coinheritance of BRCA1 and BRCA2 mutations with Fanconi anemia and Bloom syndrome mutations in Ashkenazi Jewish population: possible role in risk modification for cancer development.

Fanconi anemia (FA) and Bloom syndrome (BS) are rare autosomal recessive genetic disorders manifesting in childhood, with a predisposition to cancer development in adolescence and adulthood. Both syndromes are relatively prevalent among the Ashkenazi Jewish population, and, in both syndromes, mutations specific to this population have been identified. Similarly, unique Ashkenazi mutations were found in the genes BRCA1 and BRCA2. These two genes, when mutated, play important roles in familial breast and ovarian carcinogenesis. The genes involved in the pathogenesis of the FA and BS belong to the general class of instability genes. Heterozygosity for the FA gene has no known promalignant potential, while the BS mutation carrier state was associated with an increased frequency of colorectal cancer. The especially frequent carrier state among the Ashkenazi Jewish population coupled with the high prevalence of BRCA1 and BRCA2 in the same population has led us to search for coinheritance affecting the potential for cancer development. One hundred Ashkenazi women with known BRCA1 and BRCA2 mutations were screened for the FA mutation IVS4+4 A-->T and the BS mutation blm(Ash). Our results indicate that there is an increased prevalence of both FA and BS mutation carriers among the population studied compared with the general Ashkenazi population (prevalence of FA mutation 4/100 women [4%] as compared to 35/3104 previously published controls [1.1%], P=0.031, and for BS mutation 3/100 [3.2%] as compared to 36/4001 [0.9%], P=0.058). There was no statistically significant effect of the coinheritance on cancer prevalence, type of cancer, or age of cancer onset. Coinheritance of FA and/or BS mutations seems to be more prevalent among BRCA mutation carriers, but a larger study encompassing more women may help in clarifying this issue.

Surface reorientation induced by short light pulses in doped liquid crystals.

Fast surface reorientation induced by a single 4-ns low-energy laser pulse in dye-doped liquid crystals is reported. The reorientation is due to light-induced modification of the surface anisotropy, which affects the liquid crystal's director through the appearance of a preferred direction on the irradiated surface. The detected signals can be interpreted as being the result of light-induced desorption and adsorption of dye molecules.

Determination of small anisotropy of holographic phase gratings.

We show the possibility of detecting small anisotropies in holographic polymer dispersed liquid-crystal samples, using a simple experimental setup that allows us to determine the behavior of the diffraction efficiency versus incident angle for two reading polarizations. This analysis is extremely sensitive to small changes in the parameters that define the grating anisotropy, giving us a way to determine with great accuracy the components of the modulated part of the dielectric tensor.

Chimerism testing and detection of minimal residual disease after allogeneic hematopoietic transplantation using the bioView (Duet) combined morphological and cytogenetical analysis.

Recurrent disease remains a major obstacle to cure after allogeneic transplantation. Various methods have been developed to detect minimal residual disease (MRD) after transplantation to identify patients at risk for relapse. Chimerism tests differentiate recipient and donor cells and are used to identify MRD when there are no other disease-specific markers. The detection of MRD does not always correlate with relapse risk. Chimerism testing may also identify normal hematopoietic cells or other cells not contributing to relapse. In this study we report our initial experience with a novel system that provides combined morphological and cytogenetical analysis on the same cells. This system allows rapid automatic scanning of a large number of cells, thus increasing the sensitivity of detection of small recipient population. The clinical significance of MRD detection is improved by identifying the morphology of recipient cells. Identification of recipient characteristics within blasts predicts overt relapse in leukemia patients and precedes it by a few weeks to months. Identification within mature hematopoietic cells may not be closely associated with relapse. The system also allows chimerism testing after sex-mismatched transplants, within cellular subsets, with no need for sorting of cells. The system merits further study in larger scale trials.