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Regenerative hydrogen/vanadium flow cells (RHVFCs) require electrode architectures combining electrochemical, catalytic, and mechanical properties across nano-, micro-, and milliscales. The use of current carbon-based electrodes can lead to poor electrolyte utilization, slow kinetics, and rapid electrode deterioration, resulting in suboptimal electrochemical performance and hindering RHVFC's commercial viability. To address this, we here demonstrate the application of trichome-like carbon-metal fabrics (CMFs) made of carbon microfibers, carbon nanotubes, and iron-based nanoparticles as both a catalytic layer and electrode in RHVFCs by evaluating their key figures of merit. CMFs in combination with commercial carbon cloth not only offer a high power density ∼645 mW cm-2 (∼0.82 V) but also excellent cycling performance at 150 mA cm-2, yielding nearly 100% energy efficiency and a high average discharge capacity of ∼23 Ah L-1 (∼90% electrolyte utilization). These electrochemical results together with electrode microstructural features assessed by X-ray tomography and projected cost analysis represent a step change in the design and development of tailored electrodes capable of withstanding RHVFC cycling conditions without compromising electrochemical performance.

The present work deals with the effect of iron intermetallics on the microstructure and mechanical properties of Al-7% Si alloys. Two different iron additions were made, 0.6% Fe and 2% Fe, to study the effect of iron intermetallics on Al-Si alloys. Microstructure property correlations were carried out using SEM-EDS and tensile testing of alloys. Microstructure results show that the rise in iron content significantly increased the average size, thickness and number of intermetallic particles in the alloys. Nano-indentation study shows that the iron intermetallics are too brittle compared with the primary aluminium. Moreover, the hardness and Young’s modulus of iron intermetallics are higher than those of primary aluminium. Tensile test results show that there is no significant difference in strength levels between Al-7%Si and Al-7Si-0.6Fe alloys. However, an increase in iron from 0.6% to 2% resulted in a significant decrease in tensile strength and elongation of the alloys. Two-dimensional SEM studies suggest that the increased number of needle-shaped β-phase intermetallic particles formed because of increased amounts of Fe could be the reason for early failure of the alloy. To further understand the early failure of iron-containing alloys, the fractured tensile specimens were studied using the 3D x-ray tomography technique. XCT results show that the failure in tensile testing of 2% Fe alloy was not mainly due to breaking of brittle β-phase intermetallic particles, but due to the morphology and particle-matrix interface debonding. XCT shows that the needle-shaped particles are long, sharp-edged platelets in 3D, which act as stress raisers for crack initiation and propagation along the interphase.\ud \ud

Evaluation of cartridge cases is essential within forensic ballistic analysis and is used in an attempt to establish a connection to the weapon used to fire it. This study consists of two experiments. The aims of Experiment 1 were to establish whether micro-CT is appropriate and repeatable for ballistic cartridge case analysis and if measurements can be extracted repeatably and reliably. Experiment 2 aimed to compare cartridge cases from two weapons to establish the magnitude of variation within and between weapons. A total of 48 cartridge cases fired by two distinct weapons were collected and micro-CT scanned to a high resolution. One randomly selected cartridge was scanned ten times under the same conditions to ensure repeatability of the scanning conditions in Experiment 1. Three novel measurements to quantitatively assess the firing pin impressions were proposed in Experiment 1 and comparatively analysed from two weapons in Experiment 2. Experiment 1 showed that micro-CT is an effective and highly repeatable and reliable method for 3-dimensional imaging and measurement of ballistic cartridge cases. Furthermore, high agreement for inter-rater reliability was found between five raters. Quantitative micro-CT analysis of the firing pin impression measurements in Experiment 2 showed a significant difference between the two studied weapons using Welch’s t-test (p < 0.01). This study shows the advantage and reliability of utilising micro-CT for firing pin impression analysis. Quantitation of the firing pin impression allows distinction between the weapons studied. With expansion to further weapons, application of this methodology could complement current analysis techniques through classification models.\ud \ud

Performance assessments on miniature cylindrical cells used in Fitbit Flex 2 fitness trackers have been performed to understand the dominant ageing modes and small format implications. We utilise electrochemical testing, x-ray photoelectron Spectroscopy (XPS), x-ray computed tomography (XCT) and scanning electron microscopy (SEM), to reveal device and component structural features and changes. The cell maintains 82% cell capacity retention after 500 continuous charging and discharging cycles at 3.0–4.35 V, 0.75C rate at 20 °C. The anode shows severe delamination due to high bending stress exerted on the cell components, however this seemingly has minimum impact on the electrochemical performance if the coating is sufficiently compressed in the jelly roll with a good electrical contact. After ageing, the surface layers continue to grow, with more LiF found on the cathode and anode. The formation of LiF is discussed and we suggest the main ageing mechanism of the Fitbit cell is related to increasing charge transfer resistance due to the transportation of Li+ ions being inhibited by the thicker surface layer, which contains LiF. That preferential delamination on the inner sides of the electrode coatings was observed consistently opens up an interesting avenues for advances in cylindrical cell manufacturing at large.

We consider a sub-critical Gaussian multiplicative chaos (GMC) measure defined on the unit interval [0,1] and prove an exact formula for the fractional moments of the total mass of this measure. Our formula includes the case where log-singularities (also called insertion points) are added in 0 and 1, the most general case predicted by the Selberg integral. The idea to perform this computation is to introduce certain auxiliary functions resembling holomorphic observables of conformal field theory that will be solutions of hypergeometric equations. Solving these equations then provides non-trivial relations that completely determine the moments we wish to compute. We also include a detailed discussion of the so-called reflection coefficients appearing in tail expansions of GMC measures and in Liouville theory. Our theorem provides an exact value for one of these coefficients. Lastly we mention some additional applications to small deviations for GMC measures, to the behavior of the maximum of the log-correlated field on the interval and to random hermitian matrices., Comment: 54 pages, 1 figure

Liouville conformal field theory (LCFT) is considered on a simply connected domain with boundary, specializing to the case where the Liouville potential is integrated only over the boundary of the domain. We work in the probabilistic framework of boundary LCFT introduced by Huang-Rhodes-Vargas (2015). Building upon the known proof of the bulk one-point function by the first author, exact formulas are rigorously derived for the remaining basic correlation functions of the theory, i.e., the bulk-boundary correlator, the boundary two-point and the boundary three-point functions. These four correlations should be seen as the fundamental building blocks of boundary Liouville theory, playing the analogue role of the DOZZ formula in the case of the Riemann sphere. Our study of boundary LCFT also provides the general framework to understand the integrability of one-dimensional Gaussian multiplicative chaos measures as well as their tail expansions. Finally these results have applications to studying the conformal blocks of CFT and set the stage for the more general case of boundary LCFT with both bulk and boundary Liouville potentials., 71 pages, 2 figures

In a remarkable paper in 2008, Fyodorov and Bouchaud conjectured an exact formula for the density of the total mass of (sub-critical) Gaussian multiplicative chaos (GMC) associated to the Gaussian free field (GFF) on the unit circle. In this paper we will give a proof of this formula. In the mathematical literature this is the first occurrence of an explicit probability density for the total mass of a GMC measure. The key observation of our proof is that the negative moments of the total mass of GMC determine its law and are equal to one-point correlation functions of Liouville conformal field theory in the disk defined by Huang, Rhodes and Vargas. The rest of the proof then consists in implementing rigorously the framework of conformal field theory (BPZ equations for degenerate field insertions) in a probabilistic setting to compute the negative moments. Finally we will discuss applications to random matrix theory, asymptotics of the maximum of the GFF and tail expansions of GMC., 27 pages

There is a substantial literature concerning Liouville quantum gravity (LQG) in two dimensions with conformal matter field of central charge ${\mathbf{c}}_{\mathrm M}\in(-\infty,1]$. Via the DDK ansatz, LQG can equivalently be described as the random geometry obtained by exponentiating $\gamma$ times a variant of the planar Gaussian free field (GFF), where $\gamma\in(0,2]$ satisfies $\mathbf c_{\mathrm M}=25-6(2/\gamma+\gamma/2)^2$. Physics considerations suggest that LQG should also make sense in the regime when $\mathbf c_{\mathrm M}>1$. However, the behavior in this regime is rather mysterious in part because the corresponding value of $\gamma$ is complex, so analytic continuations of various formulas give complex answers which are difficult to interpret in a probabilistic setting. We introduce and study a discretization of LQG which makes sense for all values of $\mathbf c_{\mathrm M}\in(-\infty,25)$. Our discretization consists of a random planar map, defined as the adjacency graph of a tiling of the plane by dyadic squares which all have approximately the same "LQG size" with respect to the GFF. We prove that several formulas for dimension-related quantities are still valid for $\mathbf c_{\mathrm M}\in(1,25)$, with the caveat that the dimension is infinite when the formulas give a complex answer. In particular, we prove an extension of the (geometric) KPZ formula for $\mathbf c_{\mathrm M}\in(1,25)$, which gives a finite quantum dimension iff the Euclidean dimension is at most $(25-\mathbf c_{\mathrm M})/12$. We also show that the graph distance between typical points with respect to our discrete model grows polynomially whereas the cardinality of a graph distance ball of radius $r$ grows faster than any power of $r$ (which suggests that the Hausdorff dimension of LQG is infinite for $\mathbf c_{\mathrm M}\in(1,25)$). We include a substantial list of open problems., Comment: 53 pages, 6 figures

In this work we construct Liouville quantum gravity on an annulus in the complex plane. This construction is aimed at providing a rigorous mathematical framework to the work of theoretical physicists initiated by Polyakov in 1981. It is also a very important example of a conformal field theory (CFT). Results have already been obtained on the Riemann sphere and on the unit disk so this paper will follow the same approach. The case of the annulus contains two difficulties: it is a surface with two boundaries and it has a non-trivial moduli space. We recover the Weyl anomaly - a formula verified by all CFT - and deduce from it the KPZ formula. We also show that the full partition function of Liouville quantum gravity integrated over the moduli space is finite. This allows us to give the joint law of the Liouville measures and of the random modulus and to write the conjectured link with random planar maps., 31 pages

Lithium ion battery (LIB) is gaining popularity in energy storage device due to its high energy density per unit mass and has found application in mobile phone, laptops, power tools and electric vehicle. More recently, LIB has also been utilised to power smart wearable devices such as fitness tracker, smart watches and smart glasses. Wearable device is gaining popularity and the market will continue to grow1. With devices shrinking so drastically, the need for smaller but higher energy density battery and good cycle life is more demanding than ever. Understanding battery performance and its degradation process are therefore crucial to give insights on how to extend battery life and reduce capacity-fading. Here, we performed cell assessment on miniature cylindrical cell extracted from Fitbit Flex 2 fitness tracker and with an attempt to understand capacity-fading process of Fitbit cell utilising electrochemical, teardown and materials analysis. This miniature cylindrical cell is 3.65 x 20 mm in size with energy density of 503Wh/L and nominal capacity of 15mAh. Teardown analysis on several numbers of non-cycled Fitbit cells have shown severe anode coating delamination from the copper current collector when the jelly roll were unravelled and with anode materials transferred to the separator. Nevertheless, Fitbit cell shows 82 % cell capacity retention after 500 continuous charging and discharging cycles at 3.0-4.35 V, 0.75C rate at 20 °C. Electrochemical Impedance Spectroscopy (EIS) shows increase in internal cell resistance, in which Li+ ion charge-transfer resistance (Rct) is the main contributor. Scanning electron microscope (SEM) with energy dispersive spectroscopy (EDS) shows no visible morphological and compositional changes between fresh and aged cathode, anode and separator. X-ray photoelectron spectroscopy (XPS) reveals surface film contains organic compounds as well as lithium fluoride (LiF) and phosphates other than LiPF6 forming on both cathode and anode surface. XPS also shows increasing LiF and phosphates in cathode and anode surface film. The cause of increasing Rct and the possible source of LiF will be discussed. 1. https://www.statista.com/statistics/610447/wearable-device-revenue-worldwide/ [assessed on 17 January 2019] Figure 1

The ongoing demand for smaller and lighter devices, with batteries having longer usage times, has put increasing operational pressure on the batteries. The use of higher capacity cathodes, increasing areal capacity and thinner separators are some of the approaches used to achieve higher energy densities. Here we report two case studies on batteries from the Samsung Galaxy Note 7 phone and fitness tracker wristband, Fitbit Flex 2, highlighting where the device manufacturers were pushing the boundaries to achieve this higher energy density. In September 2016, several reports were published of the Samsung Galaxy Note 7 phone batteries overheating, exploding or catching fire, which led to a total product recall of the Samsung Galaxy Note 7 phone. “The launch of what was supposed to be its flagship model has turned into a fiasco for the world's largest smartphone maker”, the BBC reported1. We carried out a more in-depth investigation, “Looking Deeper into the Galaxy (Note 7)2”, inspecting each of the battery components. The study incorporated X-ray computed tomography, thermal imaging and scanning electron microscopy (with energy dispersive spectroscopy), to identify the most likely root causes of the battery failure. The findings reveal that thermal properties of the battery is not thought to be a contributing factor to battery failure but are from battery design/cell manufacturing defects: (1) Unintended folding of the anode coating at the corner near to the anode tab resulted from insufficient space to safely accommodate the electrodes; (2) No Insulating tape on the cathode tab, and (3) un-bonded welding sections with protrusion features observed at the cathode tab which may penetrate the separator. Such flaws can lead to internal short circuit between the cathode and anode; (4) A much thinner separator (≤ 5 µm, with 2O3 coating on both sides) used in Galaxy Note 7 also increased the likelihood of separator damage which can lead to short circuit. The ceramic coating layer detached itself quite easily when the cell was unravelled, indicating a lack of interfacial integrity. We also report another forensic investigation on a miniature lithium ion rechargeable cylindrical cell with a diameter of 3.65 mm and length in 20 mm, and nominal capacity of 15 mAh, which is fitted in Fitbit Flex 2 fitness tracker. This miniature cylindrical cell shows an impressive volumetric energy density of 503 Wh/L despite having a limited space. The unravelling of the jelly roll shows severe anode coating delamination from the copper current collector, transferring unto the separator. The high bending stress exert on the cell components when rolled up to a 3 mm diameter jelly roll has resulted severe delamination of the anode coating. 1. http://www.bbc.co.uk/news/technology-37615496 2. Melanie J. Loveridge, Guillaume Remy, Nadia Kourra, Ronny Genieser, Anup Barai, Mike J. Lain, Yue Guo, Mark Amor-Segan, Mark A. Williams, Tazdin Amietszajew, Mark Ellis, Rohit Bhagat and David Greenwood, Looking Deeper into the Galaxy (Note 7). Batteries 2018, 4 (1), 3. Figure 1

Li-ion cell designs, component integrity, and manufacturing processes all have critical influence on the safety of Li-ion batteries. Any internal defective features that induce a short circuit, can trigger a thermal runaway: a cascade of reactions, leading to a device fire. As consumer device manufacturers push aggressively for increased battery energy, instances of field failure are increasingly reported. Notably, Samsung made a press release in 2017 following a total product recall of their Galaxy Note 7 mobile phone, confirming speculation that the events were attributable to the battery and its mode of manufacture. Recent incidences of battery swelling on the new iPhone 8 have been reported in the media, and the techniques and lessons reported herein may have future relevance. Here we look deeper into the key components of one of these cells and confirm evidence of cracking of electrode material in tightly folded areas, combined with a delamination of surface coating on the separator, which itself is an unusually thin monolayer. We report microstructural information about the electrodes, battery welding attributes, and thermal mapping of the battery whilst operational. The findings present a deeper insight into the battery’s component microstructures than previously disseminated. This points to the most probable combination of events and highlights the impact of design features, whilst providing structural considerations most likely to have led to the reported incidences relating to this phone.\ud

International audience; In the latest few years, lot of efforts have been done to pave the way to sustainable mobility, in order to solve pollution problems and fuel shortage. The use of electric vehicles (EV) is considered as one of the best ecologic and economic solution. However, autonomy barriers and limitations slow the progress and the deployment of this technology. In this paper, we propose an advanced electric vehicles' fleet management architecture. This architecture considers the most important factors that can affect the traveling mode of electric vehicles, in order to offer different services to fleet management companies for an efficient monitoring and management of their fleets. One of the most important service, considered in this paper, consists on providing economic itineraries planning for electric vehicles. Best routes, in term of electric power consumption, are computed based on the collected information about road topology (elevation variations, source, destination, etc.), weather conditions, vehicle characteristics, driver profile, traffic conditions and electric charging stations positions. In case of battery drop, new routes passing through the nearest available charging stations are recalculated and provided to the driver. To prove the concept, we implemented a lightweight traffic management server that provides this itinerary planning service to an EV fleet company. The server provides a web application to book an EV and plan the trip. All possible itineraries are displayed on a map with electric power consumption, traveled distance and duration details. Then, the server uploads the chosen itinerary into the vehicle's GPS or into the driver's smartphone.

International audience; Over the last decade, great efforts are invested in reducing emissions of greenhouse gases at a world scale. We should therefore elaborate new global solutions to this type of pollution, in which fleets of vehicles are heavily contributing. In this paper, we propose a novel green architecture for global fleet management that considers the most important actors. The proposed architecture allows to collect useful information from several fleets of vehicles and their environment, and provides real-time services to companies that own one of these fleets. One important service is the calculation of economic itinerary. We propose a new "green" calculation method that is based on an efficient and high precision fuel consumption estimation. Our method uses: (i) topological information such as the elevation variations, source and destination of the trip, (ii) weather conditions, (iii) vehicle's characteristics, and (iv) driver's behavior. We implemented a lightweight traffic management server that provides a real-time service allowing to find the most economic itinerary for vehicles belonging to the fleet. The utilization of such architecture and mechanisms associated with itinerary planning results in a highly green fleet management system.

International audience; The difficulties associated with network connectivity, unreliable channels, and city environment characteristics make data dissemination task in vehicular urban networks a real challenge. Recently, some interesting solutions have been proposed to perform data dissemination in this environment. Starting from the analysis of these solutions, we present a new dissemination protocol named DHVN (Dissemination protocol for Heterogeneous Cooperative Vehicular Networks) that considers: (i) roads topology, (ii) network connectivity and possible partitioning in case of low traffic density, and (iii) heterogeneous communication capabilities of the vehicles. We compare our protocol to other dissemination protocols and analyze its performances using NS-3 simulator [1]. Performance studies show interesting DHVN compared to existing solutions. Indeed, DHVN is able to provide a low end-to-end delay, a high delivery ratio and a minimum bandwidth usage since only a limited number of vehicles are involved in the broadcast scheme.

In a recent work [1], we proposed LTE4V2X, a novel framework for a centralized vehicular network organization based on 4G LTE network. We demonstrated the efficiency of our framework for an FCD (Floating Car Data) application. Such applications are based on data collected from vehicles (localization, speed, direction, etc.) in order to feed a traffic management server. In the continuity of this work, this new paper presents two extensions of LTE4V2X. The first one is the multi-hop extension, which uses multi-hop communications to deal with areas where there is no LTE coverage (e.g. tunnels). The second extension deals with the adaptation of LTE4V2X framework for a dissemination application that aims to disseminate a specific message in a given geographical area. We analyze the performances of LTE4V2X using NS-3 simulation environment and a realistic highway mobility model. The results show that the multi-hop extension leads to an improvement of LTE4V2X performances, for applications based on both data collection and data dissemination.

International audience; In the near future, most new vehicles will be equipped with short-range radios capable to communicate with other vehicles or with roadside infrastructure. These new networks known as vehicular networks are seen to be one of the most valuable concept for improving road safety and transport efficiency, and as a key technology enabling the provisioning of value-added services to passengers and drivers. Vehicular net works raise a number of unique challenges due to the extremely dynamic network topology and the highly variable number of mobile nodes. To overcome these problems, an effective solution is to organize the network in a way which will facilitate the management tasks and permit to deploy a wide panoply of applications such as urban sensing applications. In a recent work [1], we proposed LTE4V2X, a novel framework for a centralized vehicular network organization using LTE. In the continuity to this work, this paper presents new performances evaluation of LTE4V2X in highway scenarios in order to evaluate the impact of high mobility. We studied its performances against a decentralized organization protocol and AII-LTE protocol for a well known urban sensing application, Floating Car Data (FCD) application. We analyze the performances of LTE4V2X using NS-3 simulation environment and a realistic highway mobility model. We also analyze analytically the impact of the handover on the performances. The results show that LTE4V2X can handle efficiently high vehicles' velocities and leads to performance improvement by lowering the overhead induced by control messages, reducing the FCD packet losses, as well as enhancing LTE bandwidth usage.