77,801 research outputs found
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Cathode chemistries and electrode parameters affecting the fast charging performance of li-ion batteries
Li-ion battery fast-charging technology plays an important role in popularizing electric vehicles (EV), which critically need a charging process that is as simple and quick as pumping fuel for conventional internal combustion engine vehicles. To ensure stable and safe fast charging of Li-ion battery, understanding the electrochemical and thermal behaviors of battery electrodes under high rate charges is crucial, since it provides insight into the limiting factors that restrict the battery from acquiring energy at high rates. In this work, charging simulations are performed on Li-ion batteries that use the LiCoO2 (LCO), LiMn2O4 (LMO), and LiFePO4 (LFP) as the cathodes. An electrochemical-thermal coupling model is first developed and experimentally validated on a 2.6Ah LCO based Li-ion battery and is then adjusted to study the LMO and LFP based batteries. LCO, LMO, and LFP based Li-ion batteries exhibited different thermal responses during charges due to their different entropy profiles, and results show that the entropy change of the LCO battery plays a positive role in alleviating its temperature rise during charges. Among the batteries, the LFP battery is difficult to be charged at high rates due to the charge transfer limitation caused by the low electrical conductivity of the LFP cathode, which, however, can be improved through doping or adding conductive additives. A parametric study is also performed by considering different electrode thicknesses and secondary particle sizes. It reveals that the concentration polarization at the electrode and particle levels can be weaken by using thin electrodes and small solid particles, respectively. These changes are helpful to mitigate the diffusion limitation and improve the performance of Li-ion batteries during high rate charges, but careful consideration should be taken when applying these changes since they can reduce the energy density of the batteries
How Well Do We Know the Beta-Decay of 16N and Oxygen Formation in Helium Burning
We review the status of the 12C(a,g)16O reaction rate, of importance for
stellar processes in a progenitor star prior to a super-nova collapse. Several
attempts to constrain the p-wave S-factor of the 12C(a,g)16O reaction at Helium
burning temperatures (200 MK) using the beta-delayed alpha-particle emission of
16N have been made, and it is claimed that this S-factor is known, as quoted by
the TRIUMF collaboration. In contrast reanalyses (by G.M. hale) of all thus far
available data (including the 16N data) does not rule out a small S-factor
solution. Furthermore, we improved our previous Yale-UConn study of the beta-
delayed alpha-particle emission of \n16 by improving our statistical sample (by
more than a factor of 5), improving the energy resolution of the experiment (by
20%), and in understanding our line shape, deduced from measured quantities.
Our newly measured spectrum of the beta-delayed alpha-particle emission of 16N
is not consistent with the TRIUMF('94) data, but is consistent with the
Seattle('95) data, as well as the earlier (unaltered !) data of Mainz('71). The
implication of this discrepancies for the extracted astrophysical p-wave
s-factor is briefly discussed.Comment: 6 pages, 4 figures, Invited Talk, Physics With Radioactive Beams,
Puri, India, Jan. 12-17, 1998, Work Supported by USDOE Grant No.
DE-FG02-94ER4087
Dynamics of self-organized driven particles with competing range interaction
Non-equilibrium self-organized patterns formed by particles interacting
through competing range interaction are driven over a substrate by an external
force. We show that, with increasing driving force, the pre-existed static
patterns evolve into dynamic patterns either via disordered phase or depinned
patterns, or via the formation of non-equilibrium stripes. Strikingly, the
stripes are formed either in the direction of the driving force or in the
transverse direction, depending on the pinning strength. The revealed dynamical
patterns are summarized in a dynamical phase diagram.Comment: 8 pages, 11 figure
Warped embeddings between Einstein manifolds
Warped embeddings from a lower dimensional Einstein manifold into a higher
dimensional one are analyzed. Explicit solutions for the embedding metrics are
obtained for all cases of codimension 1 embeddings and some of the codimension
n>1 cases. Some of the interesting features of the embedding metrics are
pointed out and potential applications of the embeddings are discussed.Comment: 12 pages, to appear in Mod. Phys. Lett.
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Current practice and challenges towards handling uncertainty for effective outcomes in maintenance
The combination of viable heuristic attributes with statistical measurements presents significant challenges in industrial maintenance for complex assets under through-life service contracts. Techniques to obtain and process heuristic attributes raise numerous uncertainties which often go undefined and unmitigated. A holistic view of these uncertainties may improve decision-making capabilities and reduce maintenance costs and turnaround time. It is therefore necessary to identify and rank factors that influence uncertainties originating from challenges in the above context. This, along with an identification of who contributes to such challenges and current practice to handle them, sets the focus for this study.
The influence of 32 categorised factors on uncertainty is assessed through a questionnaire completed by nine experienced maintenance managers from a leading defence company. The pedigree approach is applied to score validity of respondents’ answers according to their experience and job role to normalise scores. Results are discussed in interviews with respondents along with current practice in and ways to improve uncertainty assessment. Scores are weighted through the Analytical Hierarchy Process (AHP) in order to identify the most influential factors on uncertainty in maintenance. The analysis revealed that these include: intellectual property rights (IPR), maintainer performance, quality of information, resistance to change, stakeholder communication and technology integration. These are verified with 40 practitioners from various industrial backgrounds. From the interviews, it is deemed that a holistic view of heuristic and statistical attributes ultimately allows for more accomplished decision-making but requires trade-offs between quality and cost over the asset’s life cycle
Fast moving of a population of robots through a complex scenario
Swarm robotics consists in using a large number of coordinated autonomous robots, or agents, to accomplish one or more tasks, using local and/or global rules. Individual and collective objectives can be designed for each robot of the swarm. Generally, the agents' interactions exhibit a high degree of complexity that makes it impossible to skip nonlinearities in the model. In this paper, is implemented both a collective interaction using a modified Vicsek model where each agent follows a local group velocity and the individual interaction concerning internal and external obstacle avoidance. The proposed strategies are tested for the migration of a unicycle robot swarm in an unknown environment, where the effectiveness and the migration time are analyzed. To this aim, a new optimal control method for nonlinear dynamical systems and cost functions, named Feedback Local Optimality Principle - FLOP, is applied
Power dependence of pure spin current injection by quantum interference
We investigate the power dependence of pure spin current injection in GaAs
bulk and quantum-well samples by a quantum interference and control technique.
Spin separation is measured as a function of the relative strength of the two
transition pathways driven by two laser pulses. By keeping the relaxation time
of the current unchanged, we are able to relate the spin separation to the
injected average velocity. We find that the average velocity is determined by
the relative strength of the two transitions in the same way as in classical
interference. Based on this, we conclude that the density of injected pure spin
current increases monotonically with the excitation laser intensities. The
experimental results are consistent with theoretical calculations based on
Fermi's golden rule.Comment: 6 pages, 4 figure
Normal heat conduction in one dimensional momentum conserving lattices with asymmetric interactions
The heat conduction behavior of one dimensional momentum conserving lattice
systems with asymmetric interparticle interactions is numerically investigated.
It is found that with certain degree of interaction asymmetry, the heat
conductivity measured in nonequilibrium stationary states converges in the
thermodynamical limit, in clear contrast to the well accepted viewpoint that
Fourier's law is generally violated in low dimensional momentum conserving
systems. It suggests in nonequilibrium stationary states the mass gradient
resulted from the asymmetric interactions may provide an additional phonon
scattering mechanism other than that due to the nonlinear interactions.Comment: 4 pages, 4 figure
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