1,721,040 research outputs found
An integrated 2x2 SSFLC optical switch with channel ion-exchanged glass waveguides
No full textA novel compact structure suitable for the realization of a 2 × 2 bistable integrated optical, switch using ferroelectric liquid crystal is reported. The switch consists of a vertical coupler formed by two Ag +-Na+ ion-exchanged single-mode channel waveguides diffused in two BK7 glass substrates of a surface stabilized liquid crystal cell. The coupling properties, and thus the switching state (bar or cross), of this structure can be controlled by electrically reorienting the director of the aligned liquid crystal layer. The device was simulated and optimized at λ = 1550 nm by using a beam propagation method algorithm. The simulation of the TE00 mode propagating along the designed device showed crosstalk attenuation and losses of 42.5 dB and 0.49 dB respectively with a coupling length of 141 μm
Gastrointestinal and Hepatobiliary Manifestations Associated with Untreated Celiac Disease in Adults and Children: A Narrative Overview
No full textCeliac disease (CeD) is a chronic inflammatory disease of the small intestine, produced by ingesting dietary gluten products in susceptible people. Gluten causes an impairment of the mucosal surface and, consequently, an abnormal absorption of nutrients. Although malabsorption of essential nutrients is a major risk factor for various CeD-associated morbidities, genetic, immunological, and environmental factors also play an important role. The clinical presentation of CeD widely varies and can range from asymptomatic to full-blown symptoms due to the multi-system nature of CeD. The typical gastrointestinal (GI) manifestations of CeD include abdominal pain, diarrhea, bloating, and weight loss, but several hepatobiliary manifestations and a poor nutritional status have also been described. Currently, a gluten-free diet (GFD) is the only current evidence-based treatment that leads to the complete recovery of mucosal damage and the reversibility of its progression. Conversely, undiagnosed CeD might have severe consequences in children as well as in adult patients. This narrative overview aims to characterize the GI and hepatobiliary manifestations, nutritional deficiencies, and delayed pediatric development associated with unrecognized CeD in order to identify it promptly. Moreover, the role of GFD and how it could prevent long-term complications of CeD are described
A polarization independent liquid crystal assisted vertical coupler switch
No full textA novel compact cascaded structure suitable for the realization of a 2 × 2 polarization independent integrated optical switch using liquid crystal is reported. The switch consists of a vertical coupler formed by two Ag +-Na + ion-exchanged single-mode channel waveguides diffused in two BK7 glass substrates of a liquid crystal cell, The coupling properties, and thus the switching state (bar or cross), of this structure can be controlled by electrically reorienting the director of the aligned liquid crystal layer. The device was simulated and optimized at λ = 1550 nm by using a beam propagation method algorithm. Calculated crosstalk attenuation and losses of an optimized TE switch with the TE 00 mode propagating in the input waveguide are 42.5 dB and 0.49 dB respectively with a coupling length of 141 μm. A TM switch, with the TM 00 propagating mode, exhibits a crosstalk attenuation of 37.7 dB and losses of 1.42 dB with a coupling length of 127 μm. Estimated average crosstalk attenuation and losses of a polarization insensitive cascaded switch are 39.7 dB and 0.93 dB respectively. The evaluated driving voltage magnitude required for the switching operation results below 20 V
La ventilazione assistita proporzionale: una nuova tecnica per il trattamento dell’insufficienza respiratoria del neonato.
No full textAssociations between Celiac Disease, Extra-Gastrointestinal Manifestations, and Gluten-Free Diet: A Narrative Overview
No full textMillions of children and adults worldwide suffer from undiagnosed and untreated celiac disease (CeD). The clinical picture of CeD is highly heterogeneous and comprises manifestations that can affect almost the whole body. This narrative overview is aimed at characterizing diseases and complaints that are associated with unrecognized CeD and that frequently involve sites other than the gastrointestinal (G.I.) tract, i.e., dental, otorhinolaryngological, and ocular complications; skin and hair abnormalities; afflictions of the bones, joints, and muscles; cardiovascular affectations; kidney diseases; neuro-psychiatric disorders; and gynecological-obstetrical manifestations. The association between CeD and extra-GI manifestations is frequently overlooked, which leads to a delay in diagnosis. Most CeD-mediated disorders can be treated with a strict gluten-free diet (GFD), but some of them are irreversible unless CeD is diagnosed in time. Some manifestations can be classified as risk factors for CeD, and CeD screening tests for affected patients should be selectively considered. Apart from gastroenterologists, specialists in other medical disciplines can play an important role in identifying people with unrecognized CeD and may help prevent its progress and long-term complications. Further comprehensive investigations are necessary to clarify the pathogenesis of extra-GI manifestations and the effect of a GFD
Guided wave optical switches using liquid crystals for high capacity communication systems
No full textWavelength division multiplexing (WDM) optical networks, able to operate at Tb/s data speed, to satisfy the continuous growth of the world wide web, require signal format transparent all-optical switches, routers, filters, add and drop multi/demultiplexers. A successful technology to make such devices must allow to get high performance and large integration scale at low fabrication costs.
A new class of materials to make photonic devices are liquid crystals (LC), mostly developed so far for flat panel display applications. The novel interest for LC photonic devices is mainly due to their high birefringence (0.1-0.2) and high electro-optic effect, which allows low driving voltages with relatively short switching times in the range of microseconds, as in the case of ferroelectric LC (FLC). Furthermore LC are characterized by refractive indices close to that of glass and silica used to make optical fibers and optical waveguides, therefore low LC-waveguide coupling losses can be expected. By presenting a couple of device examples we intend to demonstrate that liquid crystals can be effectively used to create a novel generation of low cost and high performing integrated optical devices.
Glass waveguides and LC can be combined to make integrated optic circuits to be employed both in sensor and telecommunication applications. The fabrication of integrated optic devices using LC and optical glass waveguides is not too much different from the well-established flat panel display fabrication process. Furthermore optical transparency of glass substrates allows to observe liquid crystal orientation.
We experimentally demonstrated an optical bistable switch using FLC and ion-exchanged glass optical waveguides. The switch, based on a vertical directional coupler made of an FLC layer embedded between two optical waveguides, showed losses less than 5 dB, short switching time of 270 μm and required low driving voltages of about 20 V to obtain extinction ratios over 15 dB, with a coupling length shorter than 4mm at wavelength of 632.8 nm [1]. A novel design by using diffused channel waveguides obtained by ion exchange operating at the wavelength of 1550 nm will be presented in which coplanar electrodes are used to switch liquid crystals to reduce losses due to light absorption. The optimized device configuration is characterized by a coupling length as short as 140 μm, losses below 0.5 dB and crosstalk, defined as ratio between optical power at the output ports, above 40 dB.
Low power and ultrashort optical switches can be obtained also by using a simple nematic liquid crystal layer as a voltage assisted optical waveguide switch. An applied voltage lower than just 1.5 V can provide lateral confinement of the signal, whereas its increase of about 119 mV can switch the light output between two different positions in a device length of just 230 μm. The investigated geometry allows the realization of a versatile and fully electro-optic Y-junction switch, which can be optimized for operation at any wavelength of interest by acting on the bias [2].
References
[1] A. d’Alessandro, R. Asquini, F. Menichella, C. Ciminelli, “Realisation and characterisation of a ferroelectric liquid crystal bistable optical switch”, Mol. Cryst. Liq. Cryst., vol 372, pp. 353-363, (2001).
[2] R. Asquini, A. d’Alessandro, G. Assanto, “Electro-optic guided-wave router using nematic liquid crystals”, Europ. Conf. on Integrated Optics ECIO 2003, vol. 1, pp. 249-52 (2003)
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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