1,720,968 research outputs found
Conducting Polymer-Based Multifunctional Materials
No full textConducting polymers are employable as low-voltage actuators, sensors, energy storage and delivery components, structural elements, computational circuitry, memory, and electronic components, making them a versatile choice for creating integrated, multifunctional materials and devices. Here we show one such conducting polymer-based, multifunctional system, derived from the versatility of the conducting polymer polypyrrole. Three functions of polypyrrole (actuation, length sensation, and energy storage) have been individually evaluated and cooperatively combined in the synthesis of a multifunctional, polymeric system that actuates, senses strain deformation, and stores energy. The system operates whereby the strain of a polypyrrole actuator is measured by a polypyrrole length sensor, whilst being powered by an array of polypyrrole supercapacitors. Independently, polypyrrole actuators were evaluated at 250 discrete frequencies ranging from 0.01 to 10 Hz using fixed, ±1 V sinusoidal excitation. Polypyrrole length sensors were evaluated using a thin-film dynamic mechanical analyzer for the same range of frequencies with a 2% sinusoidal input strain. Polypyrrole supercapacitors were evaluated using cyclic voltammetry (-1.0 V to +1.0 V; 12.5 to 100 mV/sec) and galvanostatic charge-discharge cycling (0.5 to 2 mA/mg). As an actuator, polypyrrole samples showed measureable actuation strain between 0.001% and 1.6% for the frequency range tested, with amplitude versus frequency decay behavior similar to a first-order low-pass filter. As a length sensor, polypyrrole samples showed linear-elastic behavior up to 3% strain and gauge factors near 4. As a symmetric supercapacitor, polypyrrole had capacitance values higher than 20 kF/kg, energy densities near 20 kJ/kg, and power densities near 2 kW/kg. The evaluation of each component, independently, justified creating a cooperative system composed of these three components operating simultaneously. Polypyrrole supercapacitors provided ample power to excite polypyrrole actuators. Polypyrrole length sensors attached in series to polypyrrole actuators were capable of measuring strain from coupled polypyrrole actuators. Performance metrics and future possibilities regarding conducting polymer-based multifunctional materials are discussed. Topics: Polymers , Multifunctional materialsUnited States. Intelligence Advanced Research Projects Activity (Grant NBCHC080001
Closed loop performance of polypyrrole linear contractile actuators
No full textConducting polymer actuators such as polypyrrole can generate stresses over 10 times larger than skeletal muscle and have typical repeatable strains between 1% and 12%, making them potential candidates for lightweight, low-cost, robotic applications. Polypyrrole linear actuators under closed loop control have not been previously reported. Here we report the open and closed loop performance of polypyrrole linear contractile actuators evaluated at pre-loaded stresses of 1 MPa to 3 MPa. A standard PI control scheme driving a potentiostat was implemented in conjunction with positioning feedback from a DC/DC linear variable differential transformer (LVDT). A dynamic positioning range of 3400 is reported, with a positioning resolution of 125 nm (0.001% strain) and a maximum repeatable displacement of 427 microns (3.6% strain). The open loop frequency response of actuator strain shows characteristics of a first-order low pass filter with a log gain versus log frequency slope near -1 for frequencies tested between 0.05 Hz to 2 Hz. The closed loop frequency response of actuator strain when tracking a sinusoidal set-point signal of 0.5% strain shows characteristics of a first order system with one zero, with a corner frequency near 0.08 Hz and an operating bandwidth up to 1 Hz. Step responses at various controller output maximum voltages show a reduction in contractile response times by a factor of four, where higher voltages yield faster contractile responses.United States. Intelligence Advanced Research Projects Activity (Grant NBCHC080001
Linear Synchronous Motors for Needle-free Jet Injection
No full textNeedle-free jet injection allows delivery of liquid drugs through the skin in the
form of a narrow fluid jet traveling at high speed, minimizing the risk of accidents.
The use of a controllable actuator to drive this process has many advantages, but
the voice coil actuators previously used for this purpose are too large and heavy for
practical use with common injection volumes (1 mL). Linear synchronous motors, on
the other hand, promise significant mass reduction for future portable jet injection
systems.
In this thesis, the requirements on linear synchronous motors were examined
and tailored to selecting a linear synchronous motor design capable of delivering
1 mL jet injections in the form of a clinically appropriate injectors. The types of
linear synchronous motors included Permanent Magnet Linear Synchronous Motor
(PMLSM), Linear Flux Switching Motor (LFSM), and Linear Transverse Flux Motor
(LTFM).
Two modelling approaches for linear synchronous motors were developed: A
semi-analytical solution for Harmonic Modeling for PMLSM; and a Response Surface
Modelling method, powered by Artificial Neural Networks for PMLSM, LFSM,
and LTFM. Both Harmonic Modeling and Response Surface Modelling were found
to have very similar modeling results. All three types of motors were optimized to
the same set of requirements previously engineered with minor adaptations. PMLSM
was found to be the best performing type of motor in this case study.
A final prototype motor design was determined using an optimization scheme
for finding the lowest motor mass at a fixed power dissipation, and an automated
routine for estimating the cogging force using finite-element analysis. A prototype
motor was constructed, with a nominal mass of 322 g, a stroke of 80 mm, and a
target operating power of 1.2 kW; experimental data show that the motor constant
is within 10% of the target, and that the cogging force is in close agreement with the
model. Test ejection of water into a force sensor and porcine tissue verified that the
motor is fit for delivering 1 mL needle-free injections.
The design methodology explained here shows the benefits to integrated design
optimization of both the actuator and the load, particularly in systems that drive
fluid pressure loads, and also opens the door to controllable injector designs for
larger volumes
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Multi-component single-substrate conducting polymer actuation systems and fabrication techniques
No full textConducting polymer materials can be employed as actuation elements, length sensors, force sensors, energy storage devices, and electrical components. Combining the various functionalities of conducting polymers to create singlesubstrate, integrated systems remains a challenge, as chemical and electrical insulation barriers, adhesion techniques, and the possibility of scaling need to be taken into consideration. Here fabrication techniques for combining multiple conducting polymer components by means of electrically insulated, mechanical attachments are developed. Electrochemically synthesized polypyrrole substrates were coated with thin films of polystyrene, Parylene, and polyimide. The isotonic actuation performance of each coated film was evaluated in comparison to non-coated films, with an observed decrease in peak-to-peak maximum strain output near 95% (polystyrene and Parylene), 20% (vacuum, 0.8 Pa), 50% (curing at 110°C) and 20% (localized polyimide deposition). The chemical barrier properties of each manufacturing technique were evaluated by exposing the coated polypyrrole substrates to an oxidative chemical vapor deposition of Poly(3,4-ethylenedioxythiophene) (PEDOT). Vapor-deposited PEDOT made the insulation layers of polystyrene and Parylene conductive at thicknesses up to four microns. Spin-coated films of polyimide, greater than ten microns thick, maintained electrical insulation properties after PEDOT depositions. Conducting polymer film-to-film attachments using each manufacturing technique were attempted, with polyimide working successfully when employed under a specific deposition, drying, and curing protocol, as discussed. Three dimensional conducting polymer actuation systems composed of actuators, length sensors, and energy storage devices were constructed on flexible, single substrates. These results build a foundation upon which scalable, self-powered, polymer actuation systems can be developed.United States. Intelligence Advanced Research Projects Activity (Grant NBCHC080001
Variations on the Author
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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