1,720,988 research outputs found
Towards Perfect Absorption of Single Layer CVD Graphene in an Optical Resonant Cavity: Challenges and Experimental Achievements
Full text linkGraphene is emerging as a promising material for the integration in the most common Si platform, capable to convey some of its unique properties to fabricate novel photonic and optoelectronic devices. For many real functions and devices however, graphene absorption is too low and must be enhanced. Among strategies, the use of an optical resonant cavity was recently proposed, and graphene absorption enhancement was demonstrated, both, by theoretical and experimental studies. This paper summarizes our recent progress in graphene absorption enhancement by means of Si/SiO2-based Fabry–Perot filters fabricated by radiofrequency sputtering. Simulations and experimental achievements carried out during more than two years of investigations are reported here, detailing the technical expedients that were necessary to increase the single layer CVD graphene absorption first to 39% and then up to 84%. Graphene absorption increased when an asymmetric Fabry–Perot filter was applied rather than a symmetric one, and a further absorption increase was obtained when graphene was embedded in a reflective rather than a transmissive Fabry–Perot filter. Moreover, the effect of the incident angle of the electromagnetic radiation and of the polarization of the light was investigated in the case of the optimized reflective Fabry–Perot filter. Experimental challenges and precautions to avoid evaporation or sputtering induced damage on the graphene layers are described as well, disclosing some experimental procedures that may help other researchers to embed graphene inside PVD grown materials with minimal alterations
Photo-Thermal Dry Reforming of Methane with PGM-Free and PGM-Based Catalysts: A Review
Full text link: Dry reforming of methane (DRM) is considered one of the most promising technologies for efficient greenhouse gas management thanks to the fact that through this reaction, it is possible to reduce CO2 and CH4 to obtain syngas, a mixture of H2 and CO, with a suitable ratio for the Fischer-Tropsch production of long-chain hydrocarbons. Two other main processes can yield H2 from CH4, i.e., Steam Reforming of Methane (SRM) and Partial Oxidation of Methane (POM), even though, not having CO2 as a reagent, they are considered less green. Recently, scientists' challenge is to overcome the many drawbacks of DRM reactions, i.e., the use of precious metal-based catalysts, the high temperatures of the process, metal particle sintering and carbon deposition on the catalysts' surfaces. To overcome these issues, one proposed solution is to implement photo-thermal dry reforming of methane in which irradiation with light is used in combination with heating to improve the efficiency of the process. In this paper, we review the work of several groups aiming to investigate the pivotal promoting role of light radiation in DRM. Focus is also placed on the catalysts' design and the progress needed for bringing DRM to an industrial scale
Intraneural Device for Electrostimulation of Vagus Nerve in Rats: A Feasibility Study for Modulating Glucose Tolerance
No full textObjectives: This study introduces EMPATIC (Electro-Modulation of PAncreaTic Islet Cells), a miniaturized intraneural device designed for transversal insertion into small nerves with a mean diameter of 400 μm. EMPATIC aims to modulate glucose tolerance through intraneural vagus nerve stimulation (VNS) in rats. Materials and Methods: EMPATIC design was optimized to fit into the cervical vagus nerve of rats and was developd through thin film microtechnologies. We evaluated the efficacy of the stimulation protocol (200 μA for 10 μs at 1 Hz) on glucose tolerance after intraperitoneal injection of glucose in three rat groups: control (no implant), sham (EMPATIC implant, no stimulation), and VNS (EMPATIC implant with stimulation). Results: EMPATIC treatment in the VNS group significantly affected glucose tolerance tests compared with control and sham groups. The glucose tolerance test's area under the curve was 17,652 ± 913 mg∗min/dL in the control group, 16,929 ± 765 mg∗min/dL in the sham group, and reduced to 12,749 ± 1,075 mg∗min/dL in the stimulated group with statistical significance (p < 0.05 stimulated vs sham group, p < 0.05 stimulated vs control group). Blood glucose and insulin levels were measured, also under fasting conditions, for control and VNS groups, producing no statistically significant difference. Conclusions: EMPATIC treatment is effective in hyperglycemic conditions after glucose intake. No significant effects were observed when VNS was applied under fasting conditions. This study indicated the suitability of applying thin-film intrafascicular electrodes for transversal insertion into small nerves (mean diameter of 400 μm), which, to the best of our knowledge, represents an advancement over the state of the art. It also establishes the feasibility of investigating neural pathways related to glucose homeostasis using invasive intraneural electrodes in the right cervical vagus nerve of rats
Optical transmission filters for observation of lightning phenomena in the Earth atmosphere
No full textVery narrowband transmission filters, as parts of an instrument for the study of lightning phenomena, are described. Their performance must be maintained at an incidence angle of ±5:5° and this condition poses some limitations on the minimum bandwidth of the order of a few nanometers. The fabrication of such coatings on large area substrates is quite challenging because of the required thickness accuracy. Moreover, their performance should be not influenced by the environmental conditions in space
Optical and photoacoustic investigation of AZO/Ag/AZO transparent conductive coating for solar cells
No full textGreat attention has been recently paid to transparent conductive oxides (TCOs) due to their application in optoelectronic devices, flat panel displays, solar cells, and anti-static coatings. Concerning photovoltaic applications, the reduction of the material and processing costs are the key factors in the production process. Due to In scarcity and cost, alternative solutions to indium tin oxide (ITO) are needed. Al-doped ZnO (AZO) meets the requirements for application in thin film solar cells, thanks to its good optoelectrical properties, low cost and higher resistance to Hydrogen-reach plasmas. Recently many papers analyze innovative AZO based TCO structures where a thin layer of Silver is introduced in the TCO so to increase the electrical conductivity without loosing transparency. In this work we study the transparency and the electrical sheet resistance of a multilayer AZO/Ag/AZO as a function of the silver thin layer, and discuss the problem of optimizing the thicknesses of the multilayers to get the best performances. We have realized an AZO/Ag/AZO multilayer coating by radio frequency (RF) sputtering with an optimal thickness of the silver layer. Optical and photoacoustic spectroscopy (PAS) have been applied to perform the characterization of the sample. In particular PAS seems the most efficient technique to test directly the absorbance of the structure which should be reduced to avoid overheating and loss of the solar cell efficiency
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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Possible alternatives to critical elements in coatings for extreme applications
Full text linkE-MRS Fall Symposium I: Solutions for Critical Raw Materials Under Extreme Conditions
18–21 September 2017, Warsaw, PolandSurface functionalisation and protection have been used since a long time for improving specific properties of materials such as lubrication, water repellence, brightness, and for increasing durability of objects and tools. Among the different kinds of surface treatments used to achieve the required properties, the use of coatings is fundamental to guarantee substrate durability in harsh environments. Extreme working conditions of temperature, pressure, irradiation, wear and corrosion occur in several applications, thus very often requiring bulk material protection by means of coatings. In this study, three main classes of coatings used in extreme conditions are considered: i) hard and superhard coatings for application in machining tools, ii) coatings for high temperatures (thermal barrier coatings), and iii) coatings against corrosion. The presence of critical elements in such coatings (Cr, Y, W, Co, etc.) is analysed and the possibility to use CRMs-free substitutes is reviewed. The role of multilayers and nanocomposites in tailoring coating performances is also discussed for thermal barrier and superhard coatings.COST Action “Solutions for Critical Raw Materials under Extreme Conditions”, supported by COST
(European Cooperation in Science and Technology) and H2020 Grant Agreement TWINNING
692216 "The virtual Center for sustainable development of Advanced Materials operating under
extreme conditions"- Acronym SUPERMA
- …
