1,721,077 research outputs found
Optimising lithium-ion cell design for plug-in hybrid and battery electric vehicles
Full text linkIncreased driving range and enhanced fast charging capabilities are two immediate goals of transport electrification. However, these are of competing nature, leading to increased energy and power demand respectively from the on-board battery pack. By fine-tuning the number of layers versus active electrode material of a lithium ion pouch cell, tailored designs targeting either of these goals can be obtained. Achieving this trade-off through iterative empirical testing of layer choices is expensive and often produces sub-optimal designs. This paper presents a model-based methodology for determining the optimal number of layers, maximising usable energy whilst satisfying specific acceleration and fast charging targets. The proposed methodology accounts for the critical need to avoid lithium plating during fast charging and searches for the optimal layer configuration considering a range of thermal conditions. A numerical implementation of a cell model using a hybrid finite volume-spectral scheme is presented, wherein the model equations are suitably reformulated to directly accept power inputs, facilitating rapid and accurate searching of the layer design space. Electrode materials exhibiting high solid phase diffusion rates are highlighted as being equally as important for extended range as the development of new materials with higher inherent capacity. The proposed methodology is demonstrated for the common module design of a battery pack in a plug-in hybrid vehicle, thereby illustrating how the cost of derivative vehicle models can be reduced. To facilitate model based layer optimisation, the open-source toolbox, BOLD (Battery Optimal Layer Design) is provided
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
The effect of micro and nano scale phenomena on system level design and engineering of hybrid pemfc systems
No full textHybrid PEMFC vehicles are an important technological solution in the electrification of transport and the viability of sustainable systems. The degradation of Lithium Ion batteries used in this application is heavily dependent on the thermal management of the system, as well as the ratio between total storage capacity and peak power required. These are also inherently linked in implementation due to the non-isotropic thermal conductivity of the devices, and so de-coupling their impact on long term performance is impossible in situ. To better understand the separate contributions, as well as the interaction between these two parameters with respect to degradation, custom cells composed of a single layer of active material were commissioned. These were then mounted in a custom rig for the purpose of ensuring uniform temperature across all of the active material, and cycled at a variety of temperatures and discharge rates. The results show that above a threshold discharge rate the degradation is significantly accelerated, as well as the shift between degradation modes across a range of temperatures. In addition, the specific power of a PEMFC can be increased by use of current perturbation, a well known technique. However, the mechanism through which this acts is poorly understood, as well as the implementation being rudimentary. A custom PEMFC system was built to demonstrate that modern automotive style PEMFC designs do still benefit from this technique, and that the parameters of the perturbation can be optimised in operando to yield greater benefit. Finally,the voltage response during and after a perturbation was measured at significantly higher sample rate than any present in the literature, giving greater insight into both the mechanism through which the technique acts, as well as informing more elegant future implementations to minimise drawbacks, such as accelerated catalyst and GDL degradation due to frequent voltage cycling.Open Acces
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
ImperialCollegeESE/BOLD_Toolbox: Initial Release
No full text<p>Updated the specific heat capacity of electrolyte to a more appropriate value (2055.1 J/ KgK)</p>
Effects of temperature inhomogeneity in lithium-ion batteries connected in series: experiments and modelling
Full text linkIn serial battery packs a mismatch in cell capacity, resistance and state of charge prevents
the full utilization of the capacity of each of the cells. Cell utilization is also constrained
by temperature effects as these affect the internal resistance of the cells and determine
the onset of degradation. All these effects directly affect the capacity and the energy of
serial battery packs and voltage imbalance is a symptom of discrepancies within the pack.
The aim of this work is to understand the effect of temperature on voltage imbalance and
propose mitigation solutions to the problem.
To give the necessary background to the study, the electrochemical processes within a
single lithium-ion battery and their temperature dependency are explained. The analysis
is then expanded to describe the effects of temperature distribution on serial and parallel
battery packs. To justify the topic of the present study, the causes of temperature distribution within battery packs are explained and existing mitigation methods, involving pack
design and pack management, are discussed.
The emerging voltage imbalance is experimentally studied in a pack of four cells in series. The effects of imbalance are experimentally quantified by comparing the performance
of a battery pack under thermal equilibrium with that of a battery pack under temperature
distribution. It is found that, when a battery pack is subject to a temperature distribution,
cell operating voltage is a misleading indicator of State of Charge.
The effects of balancing strategies on the thermally imbalanced pack are studied via a
validated, thermally-coupled physics-based model created in Comsol. The instantaneous
imbalance caused by temperature-dependent cell overpotentials is quantified and provides
the basis for recommendations of effective balancing strategies for improved pack performance.Open Acces
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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