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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
A New Parameter In Accretion Disk Model
Taking optically thin accretion flows as an example, we investigate the
dynamics and the emergent spectra of accretion flows with different outer
boundary conditions (OBCs) and find that OBC plays an important role in
accretion disk model. This is because the accretion equations describing the
behavior of accretion flows are a set of {\em differential} equations,
therefore, accretion is intrinsically an initial-value problem. We argue that
optically thick accretion flow should also show OBC-dependent behavior. The
result means that we should seriously consider the initial physical state of
the accretion flow such as its angular momentum and its temperature. An
application example to Sgr A is presented.Comment: 6 pages, 4 figures, to appear in the Proceeding of "Pacific Rim
Conference on Stellar Astrophysics", Aug. 1999, HongKong, Chin
Visualising and quantifying 'excess deaths' in Scotland compared with the rest of the UK and the rest of Western Europe
BACKGROUND: Scotland has higher mortality rates than the rest of Western Europe (rWE), with more cardiovascular disease and cancer among older adults; and alcohol-related and drug-related deaths, suicide and violence among younger adults. METHODS: We obtained sex, age-specific and year-specific all-cause mortality rates for Scotland and other populations, and explored differences in mortality both visually and numerically. RESULTS: Scotland's age-specific mortality was higher than the rest of the UK (rUK) since 1950, and has increased. Between the 1950s and 2000s, 'excess deaths' by age 80 per 100 000 population associated with living in Scotland grew from 4341 to 7203 compared with rUK, and from 4132 to 8828 compared with rWE. UK-wide mortality risk compared with rWE also increased, from 240 'excess deaths' in the 1950s to 2320 in the 2000s. Cohorts born in the 1940s and 1950s throughout the UK including Scotland had lower mortality risk than comparable rWE populations, especially for males. Mortality rates were higher in Scotland than rUK and rWE among younger adults from the 1990s onwards suggesting an age-period interaction. CONCLUSIONS: Worsening mortality among young adults in the past 30 years reversed a relative advantage evident for those born between 1950 and 1960. Compared with rWE, Scotland and rUK have followed similar trends but Scotland has started from a worse position and had worse working age-period effects in the 1990s and 2000s
Melosh rotation: source of the proton's missing spin
It is shown that the observed small value of the integrated spin structure
function for protons could be naturally understood within the naive quark model
by considering the effect from Melosh rotation. The key to this problem lies in
the fact that the deep inelastic process probes the light-cone quarks rather
than the instant-form quarks, and that the spin of the proton is the sum of the
Melosh rotated light-cone spin of the individual quarks rather than simply the
sum of the light-cone spin of the quarks directly.Comment: 5 latex page
A refined invariant subspace method and applications to evolution equations
The invariant subspace method is refined to present more unity and more
diversity of exact solutions to evolution equations. The key idea is to take
subspaces of solutions to linear ordinary differential equations as invariant
subspaces that evolution equations admit. A two-component nonlinear system of
dissipative equations was analyzed to shed light on the resulting theory, and
two concrete examples are given to find invariant subspaces associated with
2nd-order and 3rd-order linear ordinary differential equations and their
corresponding exact solutions with generalized separated variables.Comment: 16 page
Quantum initial condition sampling for linearized density matrix dynamics: Vibrational pure dephasing of iodine in krypton matrices
This paper reviews the linearized path integral approach for computing time
dependent properties of systems that can be approximated using a mixed
quantum-classical description. This approach is applied to studying vibrational
pure dephasing of ground state molecular iodine in a rare gas matrix. The
Feynman-Kleinert optimized harmonic approximation for the full system density
operator is used to sample initial conditions for the bath degrees of freedom.
This extremely efficient approach is compared with alternative initial
condition sampling techniques at low temperatures where classical initial
condition sampling yields dephasing rates that are nearly an order of magnitude
too slow compared with quantum initial condition sampling and experimental
results.Comment: 20 pages and 8 figure
A New Solution of the Yang-Baxter Equation Related to the Adjoint Representation of
A new solution of the Yang-Baxter equation, that is related to the adjoint
representation of the quantum enveloping algebra , is obtained by
fusion formulas from a non-standard solution.Comment: 16 pages (Latex), Preprint BIHEP-TH-93-3
Brueckner-Hartree-Fock and its renormalized calculations for finite nuclei
We have performed self-consistent Brueckner-Hartree-Fock (BHF) and its
renormalized theory to the structure calculations of finite nuclei. The
-matrix is calculated within the BHF basis, and the exact Pauli exclusion
operator is determined by the BHF spectrum. Self-consistent occupation
probabilities are included in the renormalized Brueckner-Hartree-Fock (RBHF).
Various systematics and convergences are studies. Good results are obtained for
the ground-state energy and radius. RBHF can give a more reasonable
single-particle spectrum and radius. We present a first benchmark calculation
with other {\it ab initio} methods using the same effective Hamiltonian. We
find that the BHF and RBHF results are in good agreement with other
methods
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