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F Simoni

Publications and source records attributed to F Simoni.

At least 19 recordsLinked to original sources
PubMed2006

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.

Journal Article↗
PubMed2005

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.

Journal Article↗
PubMed2003

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.

Journal Article↗
PubMed2003

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.

Journal Article↗
PubMed2001

Photo-orientation of liquid crystals due to light-induced desorption and adsorption of dye molecules on an aligning surface.

We show that adsorption of dye molecules control the light-induced alignment of dye-doped nematic liquid crystal (LC) on a nonphotosensitive polymer surface. The dependencies of light-induced twist structures on exposure, thermal baking, thickness, and aging before irradiation of the LC cells allowed us to propose the following mechanism for the alignment. Before irradiation, the "dark"-adsorbed layer on the tested surface is formed from dye molecules predominantly aligned along the initial direction of the director. Irradiation of the cell with linearly polarized light produces an additional layer with different orientational ordering of dye molecules. The final easy axis is determined by the competition of "dark" and light-induced contributions to anchoring and is aligned between the "dark" easy axes and polarization of the light. For quantitative interpretation, we apply the tensor model of anchoring and assume that the photoalignment in the mesophase is a cumulative effect of the light-induced anchoring on the background of the already existing anisotropic "dark" dye layer.

Journal Article↗
PubMed2001

Hidden photoalignment of liquid crystals in the isotropic phase.

We found the effect of a hidden photoalignment of a dye-doped nematic liquid crystal (LC) on a nonphotosensitive polymer surface after polarized irradiation of the cell in the isotropic phase. We observed that irradiation resulted in a uniform planar orientation of the LC after cooling to the mesophase. The direction of a light-induced easy axis on the polymer can be either parallel or perpendicular to the polarization of the incident light, depending on the light intensity. We attribute this behavior to two mechanisms of photoalignment: light-induced adsorption of dye molecules on the substrate, and anisotropic desorption in a previously adsorbed dye layer. The experimental results on photoalignment of a LC on a thin dye film confirm our model.

Journal Article↗
PubMed2000

Megaureter: classification, pathophysiology, and management.

The term megaureter does not define a specific pathological condition, because it can be due to different underlying abnormalities. The most used classification includes three groups: refluxing megaureter, associated with vesicoureteral reflux (VUR); obstructive megaureter, associated with urine flow impairment at the vesicoureteral junction; non-refluxing non-obstructive megaureter, if neither obstruction nor reflux can be identified. Each group can be divided into two subgroups: primary megaureter; secondary megaureter. With the advent of antenatal ultrasound an increased number of cases are identified prior to the onset of symptoms. The common used investigation are: urinary tract ultrasound, voiding cystourethrography, urography, serial diuretic renography and pressure-perfusion studies (Whitaker test). The advent of prenatal and neonatal echography has modified the natural history of megaureter. Nowadays non operative management is preferred. Operative intervention is indicated only in these cases: significant impairment to urine flow; worsening renal function during the observation time; recurrent UTI in spite of adequate antibiotic prophylaxis.

Child↗
PubMed1987

Undifferentiated leukemia of infancy with t(11:17) chromosomal rearrangement. Coexpressing myeloid and B cell restricted antigens.

It has been suggested that the malignant transformation, in some of the acute leukemias, may involve totipotent stem cells resulting in a biphenotypic leukemia expressing both myeloid, and lymphoid characteristics. We describe here a hybrid cell acute leukemia, in a 16-day-old infant, in whom leukemic cells coexpressed myeloid and lymphoid B cell antigens. Blast cells in the bone marrow showed L2 morphology according to the French American British (FAB) classification, with positive periodic-acid Schiff, and nonspecific esterase staining. Sudan black, and specific esterase were negative. Terminal deoxynucleotidyl transferase, was strongly positive in 5% of blasts, and faintly reactive with the rest. Karyotypic analysis demonstrated a translocation of t(11:17);(q23;p13). Immunoglobulin gene analysis revealed rearrangement of the heavy chain genes. The blasts' phenotype was HLA/DR+ B4+ My7+ My9+ common acute lymphoblastic leukemia antigen (CALLA) B1- T11-. Dual immunofluorescence staining using anti My7, and My9 fluorescein isothiocyanate, and anti B4 pycoerythrin conjugated monoclonal antibodies, and flow cytofluorometry, revealed a labeling pattern of 25% B4+; 10% to 15% My7+; 17% My9+; and 50% of cells coexpressing B4 My7, and My9 antigens. These results provide evidence for a hybrid leukemia with lymphomyeloblasts being part of a single clone, which may indicate the origin of this leukemic clone from a pluripotent (lymphoid/myeloid) stem cell.

Antibodies, Monoclonal↗
PubMed1985

"Retroposon" insertion into the cellular oncogene c-myc in canine transmissible venereal tumor.

We examined by Southern blotting the state of the cellular oncogene c-myc in the dog transmissible venereal tumor. The tumor DNA contains a 16.8-kilobase pair (kbp) rearranged c-myc fragment in addition to the normal 15-kbp and 7.5-kbp fragments. We compared the structure of the cloned rearranged c-myc (re-myc) with that of a cloned normal c-myc and found that the rearrangement was due to the insertion of a 1.8-kbp DNA upstream to the first exon of c-myc. The inserted DNA is flanked by 10-base-pair direct repeats and contains a dA-rich tail, suggesting its origin from mRNA. Partial sequence of the inserted element showed 62% homology with the primate interdispersed Kpn I repetitive element. These results provide an example for the behavior of repetitive DNA sequences like the Kpn I family, as movable elements that can transpose nearby to oncogenes or other structural genes and perhaps affect their activity.

Animals↗
PubMed1984

Properties of retrovirus-like particles produced by a human breast carcinoma cell line: immunological relationship with mouse mammary tumor virus proteins.

Clonal derivatives 8 and 11 of the T47D human breast carcinoma cell line release particles that have the biochemical characteristics of a retrovirus. Particles recovered from cultures of [3H]uridine-labeled clone 11 had a density of 1.18 g/ml and contained 60-70S and 35S RNAs associated with reverse transcriptase activity. The production of these particles was steroid-dependent. Clone 8 particles had a higher density, 1.195 g/ml, and their production was independent of steroid hormone. By RIA, antigens crossreactive with the 52,000-dalton envelope glycoprotein gp52, the major external protein of mouse mammary tumor virus, were found associated with these particles and in the media. Most of the gp52-related antigen was in soluble form, but it was enriched in the particle preparation. A lesser amount of antigen was distributed within the cultured cells. Absorption of rabbit antibody to gp52 with clone 11 particle preparations eliminated the ability of this antibody to detect immunocytochemically a crossreactive antigen previously localized in tissue sections of human breast carcinoma. These results indicate that the particle isolates from T47D contain the same gp52-related antigen found in human breast carcinomas and constitute an excellent source for the purification and characterization of this antigen.

Breast Neoplasms↗
PubMed1979

Adenosine deaminase activity of normal lymphocytes and leukemic cells.

Adenosine deaminase (ADA) activity was determined in peripheral blood T cells, thymocytes and blasts of 42 acute leukemia patients. Thymocytes had higher ADA activity than mature peripheral blood T cells. B ALL (acute lymphoblastic leukemia) cells had significantly lower activity compared with T ALL and non-B, non-T cells. The latter had a wide range of enzymatic activities but mostly in the T cell range. Based on these results, as well as on assays of B and T cell lines, it seems that thymus-derived cells--and especially prethymic and immature T cells--have high ADA activity. This finding could be useful in subtyping the heterogeneous group of non-B, non-T ALL.

Adenosine Deaminase↗
PubMedDate not supplied

[Fukuyama-type congenital muscular dystrophy with the presence of ocular anomalies].

The authors report a case with Fukuyama type congenital muscular dystrophy (FCMD) and severe ocular abnormalities. Muscular dystrophy was confirmed by EMG, high muscle enzyme value and muscular biopsy. Computed tomography (CT) of the brain at 15 months of life showed mild central and cortical atrophy. Repeated CT scans at 22 and 32 months showed progressive character of the atrophy, with preservation of the cerebellar areas and the central grey matter only. Ophthalmologist examination revealed nystagmus, severe visual deficit, optic nerve atrophy and irregular color of the retina, especially in the peripheric areas. Electroretinography (ERG) was normal, cortically evoked visual responses (PEV) were absent. The association of congenital muscular dystrophy with brain changes and ocular abnormalities were found in FCMD, muscle-eye-brain disease (MEB) and Walker-Walburg syndrome (WWS). Our report, according to the recent literature, suggests that ocular lesions are caused by the same mechanism that provokes the central nervous system anomalies. It is probably of genetic origin: FCMD, MEB and WWS could be development abnormalities with a continual spectrum of disease severity.

Brain↗
PubMedDate not supplied

[Localized scleroderma in childhood].

Scleroderma is a rare disease in children: the clinical presentation in childhood is even more varied than in adult life. It is characterized by 'hard skin' with cutaneous features including hypo- and hyperpigmentation, thickening or thinning and loss of elasticity. It ranges from circumscribed and self-limiting pigmentary disorders to disabling and disfiguring involvement of an extremity and a rapidly fatal outcome. Scleroderma must be differentiated from many scleroderma-like conditions. Therapeutic problems are also discussed.

Adrenal Cortex Hormones↗