6,334 research outputs found
Phase field modeling of electrochemistry II: Kinetics
The kinetic behavior of a phase field model of electrochemistry is explored
for advancing (electrodeposition) and receding (electrodissolution) conditions
in one dimension. We described the equilibrium behavior of this model in [J. E.
Guyer, W. J. Boettinger, J.A. Warren, and G. B. McFadden, ``Phase field
modeling of electrochemistry I: Equilibrium'', cond-mat/0308173]. We examine
the relationship between the parameters of the phase field method and the more
typical parameters of electrochemistry. We demonstrate ohmic conduction in the
electrode and ionic conduction in the electrolyte. We find that, despite making
simple, linear dynamic postulates, we obtain the nonlinear relationship between
current and overpotential predicted by the classical ``Butler-Volmer'' equation
and observed in electrochemical experiments. The charge distribution in the
interfacial double layer changes with the passage of current and, at
sufficiently high currents, we find that the diffusion limited deposition of a
more noble cation leads to alloy deposition with less noble species.Comment: v3: To be published in Phys. Rev. E v2: Attempt to work around
turnpage bug. Replaced color Fig. 4a with grayscale 13 pages, 7 figures in 10
files, REVTeX 4, SIunits.sty, follows cond-mat/030817
Non-analytical power law correction to the Einstein-Hilbert action: gravitational wave propagation
We analyze the features of the Minkowskian limit of a particular
non-analytical f(R) model, whose Taylor expansion in the weak field limit does
not hold, as far as gravitational waves (GWs) are concerned. We solve the
corresponding Einstein equations and we find an explicit expression of the
modified GWs as the sum of two terms, i.e. the standard one and a modified
part. As a result, GWs in this model are not transverse, and their polarization
is different from that of General Relativity. The velocity of the GW modified
part depends crucially on the parameters characterizing the model, and it
mostly results much smaller than the speed of light. Moreover, this
investigation allows one to further test the viability of this particular f(R)
gravity theory as far as interferometric observations of GWs are concerned.Comment: 18 pages, 3 figure
Partial domain wall partition functions
We consider six-vertex model configurations on an n-by-N lattice, n =< N,
that satisfy a variation on domain wall boundary conditions that we define and
call "partial domain wall boundary conditions". We obtain two expressions for
the corresponding "partial domain wall partition function", as an
(N-by-N)-determinant and as an (n-by-n)-determinant. The latter was first
obtained by I Kostov. We show that the two determinants are equal, as expected
from the fact that they are partition functions of the same object, that each
is a discrete KP tau-function, and, recalling that these determinants represent
tree-level structure constants in N=4 SYM, we show that introducing 1-loop
corrections, as proposed by N Gromov and P Vieira, preserves the determinant
structure.Comment: 30 pages, LaTeX. This version, which appeared in JHEP, has an
abbreviated abstract and some minor stylistic change
Threshold Resonant Structure of the 232Th Neutron-Induced Fission Cross Section
The structures observed in the sub-threshold neutron-induced fission of
^{232}Th were investigated employing a recent developed model. Theoretical
single-particle excitations of a phenomenological two-humped barrier are
determined by solving a system of coupled differential equations for the motion
along the optimal fission path. A rather good agreement with experimental data
was obtained using a small number of independent parameters. It is predicted
that the structure at 1.4 and 1.6 MeV is mainly dominated by spin 3/2 partial
cross-section with small admixture of spin 1/2, while the structure at 1.7 MeV
is given by a large partial cross section of spin 5/2.Comment: 17 pages 11 figure
Disseminated bacillus Calmette-Guérin (BCG): a cause of delirium in an older adult
Intra-vesical Bacillus Calmette-Guérin (BCG) immunotherapy is an effective treatment for high-risk bladder cancer. Less well known is that fewer than 1% of patients receiving BCG treatment can develop disseminated BCG. The reaction can range from a mild flu-like illness to a systemic disorder with a fulminant course which in the most severe cases can lead to death. The diagnostic yield is low and diagnosis is often made after a comprehensive exclusion of more common causes of pyrexia of unknown origin. A high level of suspicion is therefore required in those who may be at risk. We report a case of disseminated BCG in an older patient for whom early involvement of his family was pertinent to determining the precipitant for delirium
Understanding light quanta: First quantization of the free electromagnetic field
The quantization of the electromagnetic field in vacuum is presented without
reference to lagrangean quantum field theory. The equal time commutators of the
fields are calculated from basic principles. A physical discussion of the
commutators suggest that the electromagnetic fields are macroscopic emergent
properties of more fundamental physical system: the photons
Consequences of critical interchain couplings and anisotropy on a Haldane chain
Effects of interchain couplings and anisotropy on a Haldane chain have been
investigated by single crystal inelastic neutron scattering and density
functional theory (DFT) calculations on the model compound SrNiVO.
Significant effects on low energy excitation spectra are found where the
Haldane gap (; where is the intrachain exchange
interaction) is replaced by three energy minima at different antiferromagnetic
zone centers due to the complex interchain couplings. Further, the triplet
states are split into two branches by single-ion anisotropy. Quantitative
information on the intrachain and interchain interactions as well as on the
single-ion anisotropy are obtained from the analyses of the neutron scattering
spectra by the random phase approximation (RPA) method. The presence of
multiple competing interchain interactions is found from the analysis of the
experimental spectra and is also confirmed by the DFT calculations. The
interchain interactions are two orders of magnitude weaker than the
nearest-neighbour intrachain interaction = 8.7~meV. The DFT calculations
reveal that the dominant intrachain nearest-neighbor interaction occurs via
nontrivial extended superexchange pathways Ni--O--V--O--Ni involving the empty
orbital of V ions. The present single crystal study also allows us to
correctly position SrNiVO in the theoretical - phase
diagram [T. Sakai and M. Takahashi, Phys. Rev. B 42, 4537 (1990)] showing where
it lies within the spin-liquid phase.Comment: 12 pages, 12 figures, 3 tables PRB (accepted). in Phys. Rev. B (2015
The Statistics of the Points Where Nodal Lines Intersect a Reference Curve
We study the intersection points of a fixed planar curve with the
nodal set of a translationally invariant and isotropic Gaussian random field
\Psi(\bi{r}) and the zeros of its normal derivative across the curve. The
intersection points form a discrete random process which is the object of this
study. The field probability distribution function is completely specified by
the correlation G(|\bi{r}-\bi{r}'|) = .
Given an arbitrary G(|\bi{r}-\bi{r}'|), we compute the two point
correlation function of the point process on the line, and derive other
statistical measures (repulsion, rigidity) which characterize the short and
long range correlations of the intersection points. We use these statistical
measures to quantitatively characterize the complex patterns displayed by
various kinds of nodal networks. We apply these statistics in particular to
nodal patterns of random waves and of eigenfunctions of chaotic billiards. Of
special interest is the observation that for monochromatic random waves, the
number variance of the intersections with long straight segments grows like , as opposed to the linear growth predicted by the percolation model,
which was successfully used to predict other long range nodal properties of
that field.Comment: 33 pages, 13 figures, 1 tabl
A Liquid Model Analogue for Black Hole Thermodynamics
We are able to characterize a 2--dimensional classical fluid sharing some of
the same thermodynamic state functions as the Schwarzschild black hole. This
phenomenological correspondence between black holes and fluids is established
by means of the model liquid's pair-correlation function and the two-body
atomic interaction potential. These latter two functions are calculated exactly
in terms of the black hole internal (quasilocal) energy and the isothermal
compressibility. We find the existence of a ``screening" like effect for the
components of the liquid.Comment: 20 pages and 6 Encapsulated PostScript figure
A radiation-like era before inflation
We show that the semiclassical approximation to the Wheeler-DeWitt equation
for the minisuperspace of a minimally coupled scalar field in the spatially
flat de Sitter Universe prompts the existence of an initial power-law evolution
driven by non-adiabatic terms from the gravitational wavefunction which act
like radiation. This simple model hence describes the onset of inflation from a
previous radiation-like expansion during which the cosmological constant is
already present but subleading.Comment: LaTeX, 8 pages, no figures; final version to be published in JCA
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