1,721,006 research outputs found
Stiffness effect of using polywave or monowave LED units for photo-curing different bulk fill composites
No full textWe investigated three bulk fill composites (Mat1, Mat2, Mat3) cured by two polywave (Poly1, Poly2) and one monowave (Mono) lamps. We used infrared spectroscopy, nanoindentation and atomic force microscopy to assess degree of conversion (DC), stiffness, and roughness after polishing, respectively. Mat2 exhibited the highest DC with Poly1 and second highest with Mono, however was the less stiff. Both Mat1 and Mat3 showed highest DC with Poly2, while Poly1 scored better than Mono. Mat3 scored better than Mat1 and was the third highest when cured with Poly2. For each composite cured by different lamps the stiffness ranked same as the DC. However, roughness did not correlate with hardness. Absolute stiffness value depends on composite formulation. Polywave lamps work better than monowave but not in all cases, as Mat2 showed higher DC with Mono than with Poly2. However, all lamps guarantee a DC≥50% but Mono for Mat1
The electrolyte layer composition: A key element for improving the performance of carbon nanotube actuator
No full textBucky gel actuators are typically fabricated by having an electrolyte layer sandwiched by two carbon nanotubes electrodes. They possess outstanding electrical and mechanical properties thanks to their composition, which make them very attractive for robotics applications. Even though carbon nanotube electrodes have been extensively studied in the recent years, the electrolyte layer has not been investigated in depth yet. In this study, we demonstrate that the performances (strain and blocking force) of carbon nanotubes actuators can be improved by tuning the electrolyte layer composition. The viscosity and the ionic conductivity of various binary solvent–ionic liquid mixtures (ethylene glycol, polyethylene glycol, acetonitrile, propylene carbonate, 4-methyl-2-pentanone as solvents and 1-butyl-3-methylimidazolium tetrafluoroborate as the ionic liquid) were first examined and used as key parameters to select the optimal electrolyte layer composition. We observed a remarkable increase of strain and blocking force when the ionic conductivity and the viscosity of the electrolyte were maximum and minimum respectively
Four-order stiffness variation of laser-fabricated photopolymer biodegradable scaffolds by laser parameters modulation
No full textThe effects of various fabrication parameters of our Mask Projection Excimer Laser StereoLithography (MPExSL) system were investigated. We demonstrate that laser parameters directly change the physical properties (stiffness, thermal degradation, and height/thickness) of the poly(propylene fumarate) (PFF) scaffold structures. The tested parameters were the number of pulses, fluence per pulse and laser repetition rate. We present a four-order tuning capability of MPExSL-fabricated structures' stiffness without altering the resin composition or using cumbersome post-treatment procedures. Thermogravimetric analysis and differential scanning calorimetry confirmed this tuning capability. Prototype-segmented scaffold designs are presented and analyzed to further expand the concept and exploit this in situ stiffness tuning capability of the scaffolds for tissue engineering and regenerative medicine applications
Significant strain and force improvements of single-walled carbon nanotube actuator: A metal chalcogenides approach
No full textCarbon nanotube actuators possess the requirements to be used in soft robotic applications as they are lightweight, simple to assemble and can operate at low voltage. However, there is still a need to further enhance their performances - in particular strain and blocking force - in order to render their implementation in devices more viable. In this study, we report the electrochemical and electromechanical properties of carbon nanotube-polymer actuators containing metal chalcogenides (BN, WS2 and MoS2). We demonstrate that the incorporation of such particles in the carbon-based electrodes results in a remarkable increase of the actuators' performances. Indeed, by tuning the amount of metal chalcogenides, we improve both the strain and blocking force responses of the actuators by 60%
Towards nanopatterning by femtosecond laser ablation of pre-stretched elastomers
No full textDiffraction limits the focusing capabilities of an optical system seriously constraining the use of lasers for nanopatterning. In this work, we present a novel and simple approach to reduce the minimum feature size of a laser-direct write system by ablating a pre-stretched material. In particular, by focusing and scanning a femtosecond laser beam on the surface of a uniaxially pre-stretched elastomeric membrane we are able to obtain microstructures according to a desired pattern. After removing the stress applied to the elastomer, the membrane relaxes to its original size and the ablated patterns shrink while preserving their shape. In this way, the minimum feature size that is typically determined by the optical properties of the focusing system can be now controlled by the strain applied to the elastomer during the ablation process. We demonstrate this approach by ablating lines on a stretchable polymeric membrane at different strain conditions. Experimental results are in good agreement with theoretical predictions. The proposed method opens up new interesting possibilities for the rapid prototyping of micro- and nano-structures suitable for a wide range of applications such as soft-lithography, micro-/nano-fluidics and lab-on-chip
Poly(ionic liquid)-carbon nanotubes self-supported, highly electroconductive composites and their application in electroactive devices
No full textA series of novel poly(ionic liquid)s/carbon nanotubes composites were prepared and studied. The effect of the anion on the thermal, mechanical and electrical properties of the composites was investigated. We obtained electrical conductivities ranged from 20 to 40 S cm−1 which are amongst the highest reported for a material involving poly(ionic liquid)s and carbon nanotubes only. Dry electrochemical actuators were successfully prepared using poly(ionic liquid)s composites as electrodes, without the use of a polymer support such as polyvinylidene difluoride. It was found that the anion size influences the displacement response of the actuator. A maximum bending displacement of up to 0.5 mm was recorded under a low applied voltage of ±1 V
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
Bio/non-bio interfaces: a straightforward method for obtaining long term PDMS/muscle cell biohybrid constructs
No full textStable surface modifications of polydimethylsiloxane (PDMS) are of crucial importance for the exploitation of the versatile physical properties of silicone in many biological applications. Surface hydrophobic recovery in fact poses severe time limitations to the observation of biological events and, in particular, to cell culturing. A novel method of stable modification of PDMS surface chemistry was therefore elaborated, relying on the use of genipin as a natural low-toxicity cross-linker, and involving free amine moieties. Its effectiveness to long-term cultures was studied by preparation of thin PDMS films with different stiffness. After assessment of surface chemistry and substrate stiffness, H9c2 muscle cells were cultured on the modified films, and differentiating myoblasts were observed for a period of four weeks since differentiation induction. A lower PDMS stiffness increased myotube width and supported a higher actin and myosin colocalization within myotubes, suggesting the achievement of myotube functional maturity. These results provide evidence of the effectiveness of the proposed procedures to PDMS surface chemistry modification. Furthermore, modified PDMS membranes prove to be suitable to several long-term studies of cell behaviour in vitro, including muscle cell contractility investigations
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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