1,720,983 research outputs found
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
Optimization of the Morphology of Solid-Chitosan based Electrolyte for Zn-MnO2 Alkaline Rechargeable Batteries by Freeze Casting Method
No full textThe ever-increasing demand for electrochemical energy storage systems across the globe has paved the way for researchers worldwide to focus on environmentally friendly batteries, with a prime focus on rechargeable Zn-MnO2 alkaline batteries. This study sheds light on the potential of the Chitosan-PVA membrane to be used as a solid, and flexible electrolyte for Zn-MnO2 batteries. It incorporates a distinct synthesis approach for the Chitosan-PVA electrolyte films, i.e., room temperature synthesis in a planetary ball mill, followed by freeze drying method at -80C to form an electrolyte film with a lamellar structure that allows it to have increased mechanical strength without compromising the flexible nature of the electrolyte. Three distinct compositions of Chitosan (600mg, 800mg, & 1000mg) were mixed with (20% & 10%) PVA to form a range of electrolyte films with different thicknesses (230 µm, 250µm, and 270µm). The obtained electrolyte films displayed varying Ionic conductivities (ICs), and Ion transference numbers (ITN) of the different swelling ratios (SR) based on the soaking time in 5M KOH. The electrolyte with 800mg of Chitosan-10%PVA, and a thickness of ~270um showed promising results in comparison with the rest of the variations in terms of the ICs and ITN, which provides a way forward for the researchers to explore the potential of this electrolyte in Zn-MnO2 rechargeable batteries
OPTIMIZATION OF ELECTROLYTE AND CATHODE LAYER FOR ZN/MNO2 ALKALINE BATTERIES
No full textRechargeable zinc-manganese dioxide (Zn-MnO2) alkaline chemistry has intrigued the research community due to its low cost, inherent safety, and high theoretical capacity for its application in medium voltage devices like wearable electronics. However, this chemistry is still pre-mature for commercialization due to the formation of irreversible compounds and requires more effort to enhance its performance by optimizing anode, cathode and electrolyte. Therefore, several experiments were performed on electrolytes and cathode substrates to gain insight into their behavior. Two electrolyte samples with different thicknesses (170 ?m and 270 ?m) were tested for swelling ratio, ionic conductivity, and ion transference number. Moreover, the surface properties of stainless steel mesh and graphene sheet were studied to determine their compatibility with the active material. The analysis of these results led to the conclusion that electrolytes with a thickness of 170 ?m and graphene sheets are optimal choices for electrolyte and cathode substrates for Zn-MnO2 batteries. Moreover, with the intercalation of bismuth (Bi) and copper (Cu) in MnO2, the reversibility of the battery was verified through electrochemical tests
High Performance Flexible and Scalable Thermoelectric Device and its Application as a Self-Sufficient Power Supply for Wearable Electronic Devices
No full textThe rise of wearable electronics has emphasized the need for alternative power sources, as traditional batteries have limitations in terms of portability and cost. One promising solution is thermoelectric power generation, which can harvest waste heat or body heat to power these devices using thermoelectric (TE) materials. To address the global demand for low-cost, flexible thermoelectric generators (TEGs), this work describes a novel, energy-efficient TEG fabrication method of controlling the composite microstructure using 4 synergetic factors. The combination of (1) a small amount of chitosan binder (0.05 wt%), (2) heterogeneous (mixed nanoscale and microscale) TE particles, (3) applied mechanical pressure of 20 MPa combined with curing at a low temperature of 120°C for 30 mins and (4) thickness variation (170, 240, 300 ?m), results in an enhanced TE property of TEGs. The combination of these four factors controls the micro and nanostructure of the films to decouple their electrical and thermal conductivity effectively by achieving a improved electrical conductivity and a reduced thermal conductivity. This resulted in figures of merit (ZTs) of 0.89 and 0.5 for p-BST and n-BTS thinner (170 µm) films, respectively, comparable to other additive manufacturing methods despite eliminating the high-temperature, long-duration curing process. The process was also used to fabricate a 6-couple TEG device, which could generate 357.6 µW with a power density of 5.0 mW/cm2 at a ?T of 40 K. The device demonstrated air stability and flexibility for 1000 cycles of bending. Finally, the device was integrated with a voltage step-up converter to power an LED and charge and discharge capacitor at a ?T of 17 K, demonstrating its applicability as a self-sufficient power source.
This work also further explored possibilities and approaches to integrate the TEGs to real world applications. Although the TE results are promising, there are still 2 factors to concern, (1) chalcogenides materials like p-BST and n-BTS are toxic and earth-rare, (2) The temperature difference will not be ideal as it in the research labs. Therefore, it is important to find new materials and methods to address these concerns. Tetrahedrites are promising thermoelectric materials in high-temperature applications because they are non-toxic and earth-abundant. MXene (Ti3C2) is a novel 2D material which has ultra-high electrical conductivity. Herein, this work demonstrates the fabrication of scalable and sustainable Cu12Sb4S13 (CAS) based composite films and flexible TEG devices (f-TEGs) with 2D MXene nanosheets using the previously developed energy efficient method for room temperature applications. 2D MXene nanosheets introduced energy-barrier scattering and nanoscale features to effectively increase the room-temperature ZT to 0.22, 10% higher than bulk CAS, by decoupling electrical conductivity, Seebeck coefficient, and thermal conductivity. CAS and 2D MXenes were found to be environmentally safe through a bacterial viability study. The process is used to create a 5-leg f-TEG device producing a power of 5.3 µW and a power density of 140 at a ?T of 25 K. Therefore, this work demonstrates that combining scalable and sustainable materials and methods is an effective strategy for high-performance room-temperature f-TEGs that could potentially harvest the low waste heat energy of the human body
The Effects of a Premixed Electrolyte in Zn-MnO2 Alkaline Rechargeable Batteries
No full textZinc-Manganese Dioxide (Zn-MnO2) batteries have been at the forefront of rechargeable battery research due to their low cost, increased safety, and high capacity for use in small electronic devices and wearable technology. Zn-MnO2 batteries however form inactive compounds during charge and discharge that hinder their ability to be utilized in rechargeable settings. Due to this, optimization of the layers of the battery (Anode, Cathode, and Electrolyte) must be performed to improve the performance of the battery. This research was centered on the improvement of the electrolyte layer in the battery. Many electrolytes fabricated utilize two different solutions that are mixed. Due to this, both solutions are never fully incorporated into one another, causing discrepancies in the consistency of the electrolyte. Here, the electrolyte utilized was a 5:1 ratio of Chitosan and Polyvinyl Alcohol respectively, that was premixed before drying. This new process of electrolyte formation was compared between 150?m and 250?m, and the best electrolyte was then compared tothe old process of electrolyte formation of mixing solutions separately, and to a premixed electrolyte thinner than 150?m to see at what point the preferred thickness is reached. These electrolytes were compared on their Ionic Conductivity, Ionic Conductance, and Ion Transference Number. These electrolytes were then used in the fabrication of Zn-MnO2 batteries to see their performance within a full battery as compared to previously used electrolytes
Flexible, safe, cost-effective, and highly reversible Zinc-Manganese dioxide alkaline battery
No full textWearable electronics are one of the most rapidly growing industries, due to their extended use in everyday applications resulting in an increased demand for portable energy storage devices. Amongst all types, Lithium-ion batteries (LIBs) have been occupying the majority of the market as energy storage devices for decades now. Despite immense success in commercialization, conventional LIBs suffer from issues of cost and safety. The expanding need for cheaper, and safer energy storage devices led explorations towards alternatives. After careful considerations, Zinc (Zn)-Manganese dioxide (MnO2) based alkaline system was chosen to be investigated in this work due to its low cost, inherent safety, and high theoretical energy density. However, challenges associated with making the aforementioned system rechargeable and highly performing still remains. The work in this study is directed towards enhancing the overall performance of the Zn-MnO2 alkaline battery in addition to making it suitable for flexible and wearable applications. A highly ionically conducting polymer electrolyte with excellent physical and electrochemical stability primarily comprising biopolymer chitosan is prepared by using a time and energy-efficient technique. Incorporation of this polymer electrolyte with Zn anode and MnO2 cathode enabled the successful preparation of a physically flexible cell. To obtain high cyclability and performance of the system; issues of inactive phase formations, low active material availability, pronounced shape changes at the anode surface, and zincate ion transfer towards cathode were overcome by enhancing the electrochemically active layers in the system. The assembled cell comprising the enhanced fabricated layers; (i.e. a Zinc/Stainless steel mesh composite anode, a hierarchical binder-free bismuth and copper additives based MnO2 cathode, and a chitosan-based polymer electrolyte with calcium hydroxide additive) indicated excellent rate capabilities (278.9 mAh/g @ 2 A/g & 172.8 mAh/g @ 5 A/g), high capacity utilization (78% of the theoretical 2-electron capacity on MnO2) and long cycling stabilities (70% retention over 1000 cycles). Moreover, initial bending tests conducted on the fabricated cell also showed not much performance deterioration when bent to different radii indicating good performance stability. The successful working of the fabricated cell was validated by lighting up an LED. The successful findings presented in this thesis can chart new pathways to the development of safe, flexible, cost-effective, and more environmentally responsible alternative energy storage sources for wearables
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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