15,963 research outputs found
Rate-dependent morphology of Li2O2 growth in Li-O2 batteries
Compact solid discharge products enable energy storage devices with high
gravimetric and volumetric energy densities, but solid deposits on active
surfaces can disturb charge transport and induce mechanical stress. In this
Letter we develop a nanoscale continuum model for the growth of Li2O2 crystals
in lithium-oxygen batteries with organic electrolytes, based on a theory of
electrochemical non-equilibrium thermodynamics originally applied to Li-ion
batteries. As in the case of lithium insertion in phase-separating LiFePO4
nanoparticles, the theory predicts a transition from complex to uniform
morphologies of Li2O2 with increasing current. Discrete particle growth at low
discharge rates becomes suppressed at high rates, resulting in a film of
electronically insulating Li2O2 that limits cell performance. We predict that
the transition between these surface growth modes occurs at current densities
close to the exchange current density of the cathode reaction, consistent with
experimental observations.Comment: 8 pages, 6 fig
Neutrino mixing with broken symmetry
We explore the consequences of assuming that the neutrino mass matrix is a
linear combination of the matrices of a three dimensional representation of the
group and that it has one zero mass eigenvalue. When implemented, these
two assumptions allow us to express the transformation matrix relating the mass
eigenstates to the flavor eigenstates in terms of a single parameter which we
fit to the available data.Comment: Final version. Published in Phys. Rev. D 82, 033005 (2010
Influence of vector interactions on the hadron-quark/gluon phase transition
The hadron-quark/gluon phase transition is studied in the two-phase model. As
a further study of our previous work, both the isoscalar and isovector vector
interactions are included in the Polyakov loop modified Nambu--Jona-Lasinio
model (PNJL) for the quark phase. The relevance of the exchange (Fock) terms is
stressed and suitably accounted for. The calculation shows that the isovector
vector interaction delays the phase transition to higher densities and the
range of the mixed phase correspondingly shrinks. Meanwhile the asymmetry
parameter of quark matter in the mixed phase decreases with the strengthening
of this interaction channel. This leads to some possible observation signals
being weakened, although still present. We show that these can be rather
general effects of a repulsion in the quark phase due to the symmetry energy.
This is also confirmed by a simpler calculation with the MIT--Bag model.
However, the asymmetry parameter of quark matter is slightly enhanced with the
inclusion of the isoscalar vector interaction, but the phase transition will be
moved to higher densities. The largest uncertainty on the phase transition lies
in the undetermined coupling constants of the vector interactions. In this
respect new data on the mixed phase obtained from Heavy Ion Collisions at
Intermediate Energies appear very important.Comment: submitted to Phys. Rev.
Hadron-quark phase transition in asymmetric matter with dynamical quark masses
The two-Equation of State (EoS) model is used to describe the hadron-quark
phase transition in asymmetric matter formed at high density in heavy-ion
collisions. For the quark phase, the three-flavor Nambu--Jona-Lasinio (NJL)
effective theory is used to investigate the influence of dynamical quark mass
effects on the phase transition. At variance to the MIT-Bag results, with fixed
current quark masses, the main important effect of the chiral dynamics is the
appearance of an End-Point for the coexistence zone. We show that a first order
hadron-quark phase transition may take place in the region T=(50-80)MeV and
\rho_B=(2-4)\rho_0, which is possible to be probed in the new planned
facilities, such as FAIR at GSI-Darmstadt and NICA at JINR-Dubna. From isospin
properties of the mixed phase somepossible signals are suggested. The
importance of chiral symmetry and dynamical quark mass on the hadron-quark
phase transition is stressed. The difficulty of an exact location of
Critical-End-Point comes from its appearance in a region of competition between
chiral symmetry breaking and confinement, where our knowledge of effective QCD
theories is still rather uncertain.Comment: 13 pages, 16 figures (revtex
A nonpolynomial Schroedinger equation for resonantly absorbing gratings
We derive a nonlinear Schroedinger equation with a radical term, in the form
of the square root of (1-|V|^2), as an asymptotic model of the optical medium
built as a periodic set of thin layers of two-level atoms, resonantly
interacting with the electromagnetic field and inducing the Bragg reflection. A
family of bright solitons is found, which splits into stable and unstable
parts, exactly obeying the Vakhitov-Kolokolov criterion. The soliton with the
largest amplitude, which is |V| = 1, is found in an explicit analytical form.
It is a "quasi-peakon", with a discontinuity of the third derivative at the
center. Families of exact cnoidal waves, built as periodic chains of
quasi-peakons, are found too. The ultimate solution belonging to the family of
dark solitons, with the background level |V| = 1, is a dark compacton, also
obtained in an explicit analytical form. Those bright solitons which are
unstable destroy themselves (if perturbed) attaining the critical amplitude,
|V| = 1. The dynamics of the wave field around this critical point is studied
analytically, revealing a switch of the system into an unstable phase.
Collisions between bright solitons are investigated too. The collisions between
fast solitons are quasi-elastic, while slowly moving ones merge into breathers,
which may persist or perish (in the latter case, also by attaining |V| = 1).Comment: Physical Review A, in pres
Possible approach to improve sensitivity of a Michelson interferometer
We propose a possible approach to achieve an 1/N sensitivity of Michelson
interferometer by using a properly designed random phase modulation. Different
from other approaches, the sensitivity improvement does not depend on
increasing optical powers or utilizing the quantum properties of light.
Moreover the requirements for optical losses and the quantum efficiencies of
photodetection systems might be lower than the quantum approaches and the
sensitivity improvement is frequency independent in all detection band.Comment: 8 pages, 3 figures, new versio
Note on a new fundamental length scale instead of the Newtonian constant
The newly proposed entropic gravity suggests gravity as an emergent force
rather than a fundamental one. In this approach, the Newtonian constant
does not play a fundamental role any more, and a new fundamental constant is
required to replace its position. This request also arises from some
philosophical considerations to contemplate the physical foundations for the
unification of theories. We here consider the suggestion to derive from
more fundamental quantities in the presence of a new fundamental length scale
, which is suspected to originate from the structure of quantum space-time,
and can be measured directly from Lorentz-violating observations. Our results
are relevant to the fundamental understanding of physics, and more practically,
of natural units, as well as explanations of experimental constraints in
searching for Lorentz violation.Comment: 10 latex pages, final version for journal publicatio
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