86,534 research outputs found
Fabricating superhydrophobic aluminum: An optimized one-step wet synthesis using fluoroalkyl silane
No full textIn this paper we present a simple but effective procedure to impart superhydrophobicity to aluminum through a one-step wet chemistry synthesis. The synthesis is performed in one step, thanks to simultaneous etching with NaOH and grafting with fluoroalkyl silane (FAS) molecules, which allow aluminum surface functionalization. By optimizing the proper amount of reagents, controlling the reaction batch temperature and particularly by allowing pre-activation of the solution, we showed that the process can be used turn into water repellant superhydrophobic surfaces four aluminum samples in sequence, using the same reaction batch. Also, if FAS is further added to the solution the procedure can impart superhydrophobicity to further aluminum samples. The synthesis with the optimized parameters is green and cost effective, since it was developed to minimize the use of both base and fluorinated molecules. In addition, it is easy to scale up to large area treatments and to industrial application, because the procedure is one-step, is reproducible, and allows multiple use of the same reaction batch, for the treatment of multiple samples. Finally, we show that not only the surfaces show excellent non-wetting properties in quasi-static conditions, with contact angles ∼150̊ and with very low contact angle hysteresis, ∼4̊, but also in dynamic conditions, as proved by means of drop impact analysis up to Weber number of 690
Drop rebound after impact: The role of the receding contact angle
No full textData from the literature suggest that the rebound of a drop from a surface can be achieved when the wettability is low, i.e., when contact angles, measured at the triple line (solid-liquid-air), are high. However, no clear criterion exists to predict when a drop will rebound from a surface and which is the key wetting parameter to govern drop rebound (e.g., the "equilibrium" contact angle, θeq, the advancing and the receding contact angles, θA and θR, respectively, the contact angle hysteresis, Δθ, or any combination of these parameters). To clarify the conditions for drop rebound, we conducted experimental tests on different dry solid surfaces with variable wettability, from hydrophobic to superhydrophobic surfaces, with advancing contact angles 108 < θA < 169 and receding contact angles 89 < θR < 161. It was found that the receding contact angle is the key wetting parameter that influences drop rebound, along with surface hydrophobicity: for the investigated impact conditions (drop diameter 2.4 < D0 < 2.6 mm, impact speed 0.8 < V < 4.1 m/s, Weber number 25 < We < 585), rebound was observed only on surfaces with receding contact angles higher than 100. Also, the drop rebound time decreased by increasing the receding contact angle. It was also shown that in general care must be taken when using statically defined wetting parameters (such as advancing and receding contact angles) to predict the dynamic behavior of a liquid on a solid surface because the dynamics of the phenomenon may affect surface wetting close to the impact point (e.g., as a result of the transition from the Cassie-Baxter to Wenzel state in the case of the so-called superhydrophobic surfaces) and thus affect the drop rebound. © 2013 American Chemical Society
Designing a 3D printable polypropylene-based material from after use recycled disposable masks
No full textDifferent percentages of talc were added to polypropylene deriving from pristine surgical masks in a small scale extrusion equipment to confer specific rheological and thermal properties to the resulting materials. This is not a fully satisfactory solution, thus the quantity of masks has been partially replaced by a first-use polypropylene copolymer. Two selected formulations with 35 and 50 wt.% of material deriving from pristine masks and 30 wt.% of talc have been identified as suitable for the 3D printing process.
Finally, the formulations were scaled up with a lab twin-screw extruder and by recycling sanitized after use masks to be as close as possible to field recycling conditions. The extruded pellets were processed to produce printing filament and finally validated as extrusion material for 3D printing. 3D printed tensile specimens were characterized for the mechanical properties and observed for their microstructure even comparing them with a commercial 3D printable material. For the first time is verified that a 3D printable extrusion material recycled from the disposable face masks can be obtained and shows comparable stiffness and strength to a commercial one
Optical code reader
No full textIn an optical code reader of the imager type, comprising at least one not collimated light source having an illumination optics associated therewith, and a photodetector device having a receiving optics associated therewith, at least one lens of the illumination optics and at least one lens of the receiving optics are displaceable together to change their distance from said at least one light source and from said photodetector device, respectively
Application of modal flexibility-based deflections for damage diagnosis of a steel frame structure
No full textIn this paper a modal flexibility-based approach for damage diagnosis is presented and discussed. Modal flexibility matrices of structural systems can be derived from vibration tests and changes in these matrices can be associated to structural damage. One of the main challenges is to apply modal flexibility-based methods on real-life civil structures, to detect damage on structures using ambient vibration data. A recent method has been formulated for damage detection, localization, and quantification of building structures; it is based on the modal flexibility-based deflections of such structures under uniform loads. The method was originally formulated for frame buildings that can be modeled as plane shear-type structures. The objective of the paper is to test this methodology on generic buildings that, in principle, cannot be easily modeled as plane shear-type structures. The method was applied to the ambient vibration data of a steel frame structure that has a monitoring system with acceleration sensors. Various damage configurations were induced to the structure by removing diagonal braces on the external surface of the frame. The results showed that the method is able to identify the stories and the directions of the frame that have been affected by the damage
Evaluation and reduction of the truncation effects on modal flexibility-based damage-sensitive features in frame buildings with mass irregularities
No full textRecent approaches for vibration-based damage detection in building structures are based on the calculation of modal flexibility (MF) based deflections. These deflections are estimated by applying uniform loads (UL) to experimentally derived modal flexibility matrices of the structures, and the interstory drifts are considered as damage-sensitive features (DSFs). However, in practical applications only a limited number of modes is usually identified from vibration data, and thus modal truncation effects are introduced on the deflections. To address this problem a mass proportional load (MPL) has been proposed, in a previous study by the authors, as an alternative to the uniform load with the aim of reducing the truncation effects on the displacement components of MF-based deflections of structures with mass irregularities. The objective of this work is to investigate further the mentioned problem by evaluating the truncation errors that affect the MF-based interstory drifts of frame buildings (i.e. the DSFs that can be conveniently used for damage detection). For structures with mass irregularities the truncation errors related to the application of the proposed MPL are thus compared with those related to the UL. Parametric studies were carried out on numerical models of shear-type frame buildings by considering structures with a different number of stories and various distributions of the story mass ratios, and by considering different subsets of modes included in the calculations
Damage Detection Through Modal Flexibility-Based Deflections: Application to a Full-Scale RC Shear Wall Building
No full textIn civil engineering structures it is highly desirable to detect the presence of damage and changes in the global structural behavior at the earliest possible stage, and, among the many existing strategies for vibration-based damage detection, modal flexibility (MF)-based approaches are promising tools. However, in most of the existing studies, the experimental validation of such approaches has been performed on small-scale laboratory structures, where damage has been artificially imposed as stiffness reductions, for example by substituting some structural elements. It is thus important to continue to test the effectiveness of such MF-based approaches on full-scale structures characterized by more realistic damaged conditions. This paper focuses on the methods for output-only damage detection and localization that are based on the estimation of structural deflections from modal flexibility, and the objective of this paper is to test the applicability of such methods for locating damage in a full-scale reinforced concrete (RC) structure that has experienced earthquake-induced damage. The considered structure is a shear wall building that can be modeled as a bending moment-deflecting cantilever structure, and was tested on the large-scale University of California, San Diego—Network for Earthquake Engineering Simulation (UCSD-NEES) shaking table. Two approaches, which are based, respectively, on the estimation of the curvature and the damage-induced rotation from the deflections, have been applied and compared on the data of the considered case study. These approaches have been applied in different scenarios characterized by different data sets and by a different number of degrees-of-freedom measured on the considered structure
Variations on the Author
No full text“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
Recycled PP for 3D Printing: Material and Processing Optimization through Design of Experiment
No full textIn this work, blends that were based on first use PP added with talc (PPt) and recycled polypropylene (r-PP) were designed and formulated, aiming at producing filaments that are suitable for 3D printing fused filament fabrication (FFF) processes. A preliminary characterization of PPt/r-PP blends at different weight ratios allowed selecting two systems showing adequate rheological behavior for FFF. The selected blends were melt compounded in a twin-screw extruder, optimizing the processing conditions through a design of experiments approach, involving the use of Taguchi’s method. The materials that were prepared with the optimized processing conditions, hence showing the best performance in terms of rheological behavior and thermal characteristics, were then selected for the production of the filament and for the subsequent FFF processing. Finally, the morphology of the filament and the mechanical properties of 3D-printed samples were assessed, demonstrating the achievement of satisfactory results in terms of performances. In general, the obtained results clearly demonstrated that a proper optimization of both material and processing conditions offers the possibility of using recycled PP-based formulations for additive manufacturing processes, hence allowing a remarkable valorization of a low added-value material through its utilization for an innovative and sustainable manufacturing approach
A 3D numerical model for the evaluation of the tunneling water inflow: The fortezza – ponte gardena case study
No full textThe Brenner Base Tunnel (BBT) is being built to connect Italy with Austria. The southern access connects Ponte Gardena with Fortezza by two railway tunnels named Gardena and Scaleres. A 3D groundwater flow model, extended through an area of about 200 km2, has been built using MODFLOW code to evaluate the water inflow. The model thickness is 1200 m, divided into 8 layers varying from 100 m to 400 m. The model has been solved in transient conditions, allowing the water inflow both during 6 excavation stages reproducing the design excavation time schedule and during the subsequent equilibrium phase to be evaluated. Based on the geological and geotechnical model, the excavation methods have been defined; the results of the evaluation of water inflow and of the possible impact on the hydrogeological resources have been taken into account by defining risk mitigation measures to ensure hydraulic ante-operam conditions
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