2,019 research outputs found
A new consideration for validating battery performance at low ambient temperatures
Existing validation methods for equivalent circuit models (ECMs) do not capture the effects of operating lithium-ion cells over legislative drive cycles at low ambient temperatures. Unrealistic validation of an ECM may often lead to reduced accuracy in electric vehicle range estimation. In this study, current and power are used to illustrate the different approaches for validating ECMs when operating at low ambient temperatures (−15 °C to 25 °C). It was found that employing a current-based approach leads to under-testing of the performance of lithium-ion cells for various legislative drive cycles (NEDC; FTP75; US06; WLTP-3) compared to the actual vehicle. In terms of energy demands, this can be as much as ~21% for more aggressive drive cycles but even ~15% for more conservative drive cycles. In terms of peak power demands, this can range from ~27% for more conservative drive cycles to ~35% for more aggressive drive cycles. The research findings reported in this paper suggest that it is better to use a power-based approach (with dynamic voltage) rather than a current-based approach (with fixed voltage) to characterise and model the performance of lithium-ion cells for automotive applications, especially at low ambient temperatures. This evidence should help rationalize the approaches in a model-based design process leading to potential improvements in real-world applications for lithium-ion cell
Low temperature performance of Lithium-ion batteries for different drive cycles
Lithium-ion batteries, suitable for Battery-electric vehicles (BEVs) due to their high energy and power densities, and lifetime demonstrate deterioration in energy and power available at lower temperatures. It is attributed to reduction in capacity and increase in internal resistance. Investigations are carried out to determine energy, and power decline for four drive-cycles: FTP, NEDC, UDDS and US06. The minimum temperatures where the battery meets the drive-cycles’ energy and power requirements are determined. The impact of regenerativebraking and self-heating on battery performance is discussed. The minimum temperature where any drive-cycle is met by the battery is directly proportional to its aggressiveness
Practical aspects of electrophoretic deposition to produce commercially viable supercapacitor energy storage electrodes
Electrophoretic deposition (EPD) is a highly convenient and demonstrated industrial operation for the manufacture of surface coatings. Recent years are seeing increasing evidence in using this technique to produce energy storage electrodes (notably for lithium-ion batteries, solid-state devices, supercapacitors, and flow batteries), but their advancement for industrialisation remains unclear. Using activated carbon (AC) as an exemplary supercapacitor material, this study reports the practical aspects of porous energy storage electrodes produced by the EPD technique. Practical electrodes with commercially viable parameters are shown, specifically high density active material (in excess of 9.8 mg cm−2) and very thick coating layer (about 168 μm). Research investigations including colloidal electrolyte formulations, electrode deposition parameters and cell performance testing are reported. Materials and electrode properties were studied by various charactersisation tools. Prototype A7 sized pouch cells were assembled and tested to show evidence of practical EPD electrodes in a commercial cell format. Electrochemical performance of EPD over slurry casting is presented. In short, this research shows the successful production of practical EPD electrodes for electrochemical energy storage, which is directly relevant for scale-up industrial adoption and can be applied as a platform electrode manufacturing technology for any battery and supercapacitor materials
Heteroatom-doped core/shell carbonaceous framework materials : synthesis, characterization and electrochemical properties
Organic-inorganic hybrid core@shell nanospherical particles with 200 nm to 600 nm in diameter were formed between cyclomatrix poly(organophosphazenes) (POP) and zeolitic imidazolate framework-8 (ZIF-8) in a methanol solution at room temperature. This facile synthesis route produced core@shell spheres with controlled structure and properties, such as mono-dispersed particles, 50 nm to 100 nm shell thickness, surface area of 1557 m2 g-1 and homogenously doped Zn and heteroatoms (N, S, P, O, Cl). The POP/ZIF-8 core@shell structures were subsequently converted into porous carbonaceous materials, and investigated as anode materials in a lithium-ion coin cell battery. It showed a stable discharge capacity of 538 mA h g-1 over 250 cycles, high rate capability (0.1 C to 1 C) and excellent capacity retention, which are promising for rapid charge-discharge applications. Higher ZIF-8 loading ratio in the core@shell structure increased the capacity of the electrode material and stablised the lithiated active materials. The facile synthesis method and the carbonaceous framework materials are applicable for high performance energy storage materials in electrochemical power devices
Variations of Little Higgs Models and their Electroweak Constraints
We calculate the tree-level electroweak precision constraints on a wide class
of little Higgs models including: variations of the Littlest Higgs SU(5)/SO(5),
SU(6)/Sp(6), and SU(4)^4/SU(3)^4. By performing a global fit to the precision
data we find that for generic regions of the parameter space the bound on the
symmetry breaking scale f is several TeV, where we have kept the normalization
of f constant in the different models. For example, the ``minimal''
implementation of SU(6)/Sp(6) is bounded by f>3.0 TeV throughout most of the
parameter space, and SU(4)^4/SU(3)^4 is bounded by f^2 = f_1^2+f_2^2 > (4.2
TeV)^2. In certain models, such as SU(4)^4/SU(3)^4, a large f does not directly
imply a large amount of fine tuning since the heavy fermion masses that
contribute to the Higgs mass can be lowered below f for a carefully chosen set
of parameters. We also find that for certain models (or variations) there exist
regions of parameter space in which the bound on f can be lowered into the
range 1-2 TeV. These regions are typically characterized by a small mixing
between heavy and standard model gauge bosons, and a small (or vanishing)
coupling between heavy U(1) gauge bosons and the light fermions. Whether such a
region of parameter space is natural or not is ultimately contingent on the UV
completion.Comment: 32 pages, 13 figures; revised discussion of SU(4)^4/SU(3)^4 model,
bound on f is slightly highe
Seiberg-Witten Description of the Deconstructed 6D (0,2) Theory
It has recently been suggested that, in a large N limit, a particular four
dimensional gauge theory is indistinguishable from the six dimensional CFT with
(0,2) supersymmetry compactified on a torus. We give further evidence for this
correspondence by studying the Seiberg-Witten curve for the "deconstructed"
theory and demonstrating that along the reduced Coulomb branch of moduli space
(on the intersection of the Higgs and Coulomb branches) it describes the low
energy physics on a stack of M5-branes on a torus, which is the (0,2) theory on
a torus as claimed. The M-theory construction helps to clarify the enhancement
of supersymmetry in the deconstructed theory at low energies, and demonstrates
its stability to radiative and instanton corrections. We demonstrate the role
of the theta vacuum in the deconstructed theory. We point out that by varying
the theta parameters and gauge couplings in the deconstructed theory, the
complex structure of the torus can be chosen arbitrarily, and the torus is not
metrically S^1 x S^1 in general.Comment: 13 pages, 2 figure
PCA-based lung motion model
Organ motion induced by respiration may cause clinically significant
targeting errors and greatly degrade the effectiveness of conformal
radiotherapy. It is therefore crucial to be able to model respiratory motion
accurately. A recently proposed lung motion model based on principal component
analysis (PCA) has been shown to be promising on a few patients. However, there
is still a need to understand the underlying reason why it works. In this
paper, we present a much deeper and detailed analysis of the PCA-based lung
motion model. We provide the theoretical justification of the effectiveness of
PCA in modeling lung motion. We also prove that under certain conditions, the
PCA motion model is equivalent to 5D motion model, which is based on physiology
and anatomy of the lung. The modeling power of PCA model was tested on clinical
data and the average 3D error was found to be below 1 mm.Comment: 4 pages, 1 figure. submitted to International Conference on the use
of Computers in Radiation Therapy 201
Theoretical and Experimental Studies of Schottky Diodes That Use Aligned Arrays of Single Walled Carbon Nanotubes
We present theoretical and experimental studies of Schottky diodes that use
aligned arrays of single walled carbon nanotubes. A simple physical model,
taking into account the basic physics of current rectification, can adequately
describe the single-tube and array devices. We show that for as grown array
diodes, the rectification ratio, defined by the
maximum-to-minimum-current-ratio, is low due to the presence of m-SWNT shunts.
These tubes can be eliminated in a single voltage sweep resulting in a high
rectification array device. Further analysis also shows that the channel
resistance, and not the intrinsic nanotube diode properties, limits the
rectification in devices with channel length up to ten micrometer.Comment: Nano Research, 2010, accepte
High power and stable P-doped yolk-shell structured Si@C anode simultaneously enhancing conductivity and Li+ diffusion kinetics
Silicon is a low price and high capacity anode material for lithium-ion batteries. The yolk-shell structure can effectively accommodate Si expansion to improve stability. However, the limited rate performance of Si anodes can’t meet people’s growing demand for high power density. Herein, the phosphorus-doped yolk-shell Si@C materials (P-doped Si@C) were prepared through carbon coating on P-doped Si/SiOx matrix to obtain high power and stable devices. Therefore, the as-prepared P-doped Si@C electrodes delivered a rapid increase in Coulombic efficiency from 74.4% to 99.6% after only 6 cycles, high capacity retention of ∼ 95% over 800 cycles at 4 A·g−1, and great rate capability (510 mAh·g−1 at 35 A·g−1). As a result, P-doped Si@C anodes paired with commercial activated carbon and LiFePO4 cathode to assemble lithium-ion capacitor (high power density of ∼ 61,080 W·kg−1 at 20 A·g−1) and lithium-ion full cell (good rate performance with 68.3 mAh·g−1 at 5 C), respectively. This work can provide an effective way to further improve power density and stability for energy storage devices
<i>Pseudomonas aeruginosa</i> AlgF is a protein-protein interaction mediator required for acetylation of the alginate exopolysaccharide
Enzymatic modifications of bacterial exopolysaccharides enhance immune evasion and persistence during infection. In the Gram-negative opportunistic pathogen Pseudomonas aeruginosa, acetylation of alginate reduces opsonic killing by phagocytes and improves reactive oxygen species scavenging. Although it is well-known that alginate acetylation in P. aeruginosa requires AlgI, AlgJ, AlgF, and AlgX, how these proteins coordinate polymer modification at a molecular level remains unclear. Here, we describe the structural characterization of AlgF and its protein interaction network. We characterize direct interactions between AlgF and both AlgJ and AlgX in vitro, and demonstrate an association between AlgF and AlgX, as well as AlgJ and AlgI, in P. aeruginosa. We determine that AlgF does not exhibit acetylesterase activity and is unable to bind to polymannuronate in vitro. Therefore, we propose that AlgF functions to mediate protein-protein interactions between alginate acetylation enzymes, forming the periplasmic AlgJFXK (AlgJ-AlgF-AlgX-AlgK) acetylation and export complex required for robust biofilm formation.</p
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