171,123 research outputs found
Optical properties of ionic liquid passivated CdSe/ZnS quantum dots dispersed in POC copolymer
No full textA new blue emitter oxadiazole/carbazole copolymer has been synthesized and combined with CdSe/ZnS quantum dots (QDs). Surface passivation of the QDs by ionic liquids was crucial to improve their compatibility with the polymer allowing the deposition of homogeneous nanocomposites films. The nanocomposites have been characterized by thermogravimetric analysis, infrared, UV–visible absorption, and photoluminescence spectroscopy. The emission spectra of nanocomposites show a wide spectrum from blue to orange wavelengths due to the combination of colors emitted by the polymer and QDs, respectively. POLYM. COMPOS., 34:1471–1476, 2013. © 2013 Society of Plastics Engineer
What we would like to know about extreme horizontal branch stars in globular clusters
No full textIn this contribution, we explore some open questions about Extreme Horizontal Branch (EHB) stars in globular clusters. In particular, we present the current status of the search for rapid pulsators, He-depleted stars, and close binaries, three kind of objects very common among field EHB stars, but which first surveys failed to detect in clusters. We also analyze how the lack of cluster EHB binaries can reconcile with theoretical expectations. We give special attention to the first close EHB binary discovered in a globular cluster, whose characteristics point to a very rare or even unique object. Finally, we analyze some recent puzzling results about spectroscopically derived masses, that could point to the presence of two distinct families of EHB’s in clusters. For all these topics, we present the recent advancement in knowledge, the results requiring more investigation, and what has still to be done to fix the unsolved problems, showing the main points of our studies, the aims of our works, and what we expect to obtain from them
Superhydrophobic Coatings and Artificial Neural Networks: Design, Development and Optimization
No full textRecently, considerable attention has been devoted to the development of superhydrophobic surfaces due to their advantageous antifouling and antimicrobial capacity. While significant effort has been devoted to fabricating such surfaces, very few polymeric superhydrophobic surfaces can be considered durable against various externally imposed stresses. Pyrogenic hydrophobic silica nanoparticles were used to confer superhydrophobic properties to the coatings. 450 samples were prepared using a layer-by-layer approach, deposing an epoxy resin or PDMS layer as adhesive on a substrate (PC/ABS), followed by one or more layers of silica nanoparticles, or silica-resin mixed layers. The best coating obtained shows a contact angle of 157° and a tape peeling grade resistance. The applied method involves the spray deposition of a multilayer coating composed of: silica layer/epoxy resin layer/silica layer, followed by partial curing of the coating (15 min, 70 °C); another silica layer is then sprayed on the surface and is cured for 10 min. Given the high number of parameters involved, process optimization is quite tricky. Artificial Neural Networks are the best tool to deal with multivariate analysis problems and for this reason, data from all the prepared samples were collected into a matrix and was used to train a neural network capable of predicting the degree of hydrophobicity of a silica nanoparticles-based coating
Area optimization of very low-frequency Gm-C filters
No full textFully integrated low frequency filters are critical cells that should be carefully designed in order to avoid excessive area occupation. In this work we propose an automatic procedure capable of optimizing the design of Gm-C integrators, constituting the basis of a wide class of Gm-C filters. The optimization target is minimizing the cell area with constraints on input range and low frequency noise. The procedure is exploited to show the effect of various design constraints on important filter parameters. Verification with the result of electrical simulations is included
Synthesis and characterization of new photoluminescent oxadiazole/carbazole-containing polymers
No full textWe report on the synthesis and the characterization of a new class of segmented polyethers POC containing the oxadiazole and
carbazole units. The polymers exhibit a high thermal stability, high glass transition temperatures, and good solubility in common
organic solvents, despite the extended aromatic portion in the main polymer chain. The synthetic procedures are simple, and
no acid side-products are obtained. According to previous reports on oxadiazole/carbazole-containing materials, POCs show
high photoluminescence activity in the blue region of the visible spectra. The good solubility in chlorinate solvents allows the
preparation of films with homogeneous thickness by spin coating. Glass transition temperature in the range 115–125◦C ensures
good stability of film morphology at room temperature. The only exception is POC(6), which shows a poor solubility and higher
Tg (170◦C), due to its shorter aliphatic chain portion. For these features, polymers POC are potential candidate materials for
fabricating blue light-emitting devices
Electrochemical etching in HF solution for silicon micromachining
No full textElectrochemical etching of silicon in hydrofluoric acid (HF) solution is employed as a micromachining technique. It is demonstrated that the commonly accepted geometric constraints on the shape of electrochemically etched silicon structures can be significantly relaxed. Several new structures etched on the same n-doped silicon wafer are reported. The fabricated structures include wall arrays, hole arrays, meander-shaped structures, spiral-like walls, microtubes, micropillars, microtips and more. A simple model for the electrochemical etch process, which describes the effect of the dimension of the initial seed, the current density, and also the KOH etching time of the initial pattern on the final geometries, is detailed. (C) 2002 Elsevier Science B.V. All rights reserved
Electrochemical fabrication of buried folded microchannels into silicon substrates
No full textIn this work an original process for buried folded silicon microchannel fabrication is reported. Electrochemical micromachining is exploited to etch high aspect ratio meander-shaped trenches into a silicon substrate. Thermal oxidation is then employed to seat the top of etched trenches and obtain buried microchannels at the bottom. The process is straightforward and allows the integration of buried folded channels into silicon substrates with a high density. Experimental results are reported and advantages and drawbacks of the proposed process are discussed. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
An automated area optimization routine for the design of very low frequency Gm-C integrators
No full textVery low frequency Gm-C filters are critical cells that should be carefully designed in order to avoid an excessive occupation of silicon area, especially when a high dynamic range is required. In this work we propose a routine, which exploits the MATLAB Optimization Toolbox in order to perform an optimum sizing of low frequency Gm-C integrators. The target is minimizing the integrator area, while satisfying design specifications such as unity gain frequency and dynamic range. Upper and lower bounds have been assigned to several design parameters to obtain solutions compatible with real processes. The interaction between noise and low frequency specifications has been investigated and their impact on the area occupation has been shown. The accuracy of the routine, configured with the parameters of a commercial process, has been shown using electrical simulations
Temperature stabilised tunable Gm-C filter for very low frequencies
No full textIn this work, a continuous time low pass filter, with sub-Hz upper band limit, is presented. The circuit is based on a Gm-C approach, where the transconductance is stabilised against temperature variations over a wide temperature range (0-80°C) using a DC feedback loop applied to a dummy transconductor (master). The very low transconductance values required to obtain low frequency singularities are achieved by means of multistage current division. A first order low pass prototype filter has been fabricated by means of the 1-μm BCD3S process of STMicroelectronics
Synthesis and Characterization of New Photoluminescent Oxadiazole/Carbazole-Containing Polymers
No full textWe report on the synthesis and the characterization of a new class of segmented polyethers POC containing the oxadiazole and carbazole units. The polymers exhibit a high thermal stability, high glass transition temperatures, and good solubility in common organic solvents, despite the extended aromatic portion in the main polymer chain. The synthetic procedures are simple, and no acid side-products are obtained. According to previous reports on oxadiazole/carbazole-containing materials, POCs show high photoluminescence activity in the blue region of the visible spectra. The good solubility in chlorinate solvents allows the preparation of films with homogeneous thickness by spin coating. Glass transition temperature in the range 115–125∘C ensures good stability of film morphology at room temperature. The only exception is POC(6), which shows a poor solubility and higher
(170∘C), due to its shorter aliphatic chain portion. For these features, polymers POC are potential candidate materials for fabricating blue light-emitting devices
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