16 research outputs found
Nonlinear waves in coherently coupled Bose-Einstein condensates
We consider a quasi-one-dimensional two-component Bose-Einstein condensate
subject to a coherent coupling between its components, such as realized in
spin-orbit coupled condensates. We study how nonlinearity modifies the dynamics
of the elementary excitations. The spectrum has two branches which are affected
in different ways. The upper branch experiences a modulational instability
which is stabilized by a long wave-short wave resonance with the lower branch.
The lower branch is stable. In the limit of weak nonlinearity and small
dispersion it is described by a Korteweg-de Vries equation or by the Gardner
equation, depending on the value of the parameters of the system
Solution of the Riemann problem for polarization waves in a two-component Bose-Einstein condensate
We provide a classification of the possible flow of two-component
Bose-Einstein condensates evolving from initially discontinuous profiles. We
consider the situation where the dynamics can be reduced to the consideration
of a single polarization mode (also denoted as "magnetic excitation") obeying a
system of equations equivalent to the Landau-Lifshitz equation for an
easy-plane ferro-magnet. We present the full set of one-phase periodic
solutions. The corresponding Whitham modulation equations are obtained together
with formulas connecting their solutions with the Riemann invariants of the
modulation equations. The problem is not genuinely nonlinear, and this results
in a non-single-valued mapping of the solutions of the Whitham equations with
physical wave patterns as well as to the appearance of new elements --- contact
dispersive shock waves --- that are absent in more standard, genuinely
nonlinear situations. Our analytic results are confirmed by numerical
simulations
Statistics of extreme events in integrable turbulence
We use the spectral kinetic theory of soliton gas to investigate the
likelihood of extreme events in integrable turbulence described by the
one-dimensional focusing nonlinear Schr\"odinger equation (fNLSE). This is done
by invoking a stochastic interpretation of the inverse scattering transform for
fNLSE and analytically evaluating the kurtosis of the emerging random nonlinear
wave field in terms of the spectral density of states of the corresponding
soliton gas. We then apply the general result to two fundamental scenarios of
the generation of integrable turbulence: (i) the asymptotic development of the
spontaneous (noise induced) modulational instability of a plane wave, and (ii)
the long-time evolution of strongly nonlinear, partially coherent waves. In
both cases, involving the bound state soliton gas dynamics, the analytically
obtained values of the kurtosis are in perfect agreement with those inferred
from direct numerical simulations of the the fNLSE, providing the long-awaited
theoretical explanation of the respective rogue wave statistics. Additionally,
the evolution of a particular non-bound state gas is considered providing
important insights related to the validity of the so-called virial theorem.Comment: 11 pages, 5 figure
Evolution of initial discontinuities in the Riemann problem for the Kaup-Boussinesq equation with positive dispersion
We consider the space-time evolution of initial discontinuities of depth and
flow velocity for an integrable version of the shallow water Boussinesq system
introduced by Kaup. We focus on a specific version of this "Kaup-Boussinesq
model" for which a flat water surface is modulationally stable, we speak below
of "positive dispersion" model. This model also appears as an approximation to
the equations governing the dynamics of polarisation waves in two-component
Bose-Einstein condensates. We describe its periodic solutions and the
corresponding Whitham modulation equations. The self-similar, one-phase wave
structures are composed of different building blocks which are studied in
detail. This makes it possible to establish a classification of all the
possible wave configurations evolving from initial discontinuities. The
analytic results are confirmed by numerical simulations
A single amino acid distorts the Fc γ receptor IIIb/CD16b structure upon binding immunoglobulin G1 and reduces affinity relative to CD16a
Therapeutic mAbs engage Fc γ receptor III (CD16) to elicit a protective cell-mediated response and destroy the target tissue. Newer drugs designed to bind CD16a with increased affinity surprisingly also elicit protective CD16b-mediated responses. However, it is unclear why IgG binds CD16a with more than 10-fold higher affinity than CD16b even though these receptors share more than 97% identity. Here we identified one residue, Gly-129, that contributes to the greater IgG binding affinity of CD16a. The CD16b variant D129G bound IgG1 Fc with 2-fold higher affinity than CD16a and with 90-fold higher affinity than the WT. Conversely, the binding affinity of CD16a-G129D was decreased 128-fold relative to WT CD16a and comparably to that of WT CD16b. The interaction of IgG1 Fc with CD16a, but not with CD16b, is known to be sensitive to the composition of the asparagine-linked carbohydrates (N-glycans) attached to the receptor. CD16a and CD16b-D129G displaying minimally processed oligomannose N-glycans bound to IgG1 Fc with about 5.2-fold increased affinity compared with variants with highly processed complex-type N-glycans. CD16b and the CD16a-G129D variant exhibited a smaller 1.9-fold affinity increase with oligomannose N-glycans. A model of glycosylated CD16b bound to IgG1 Fc determined to 2.2 Å resolution combined with a 250-ns all-atom molecular dynamics simulation showed that the larger Asp-129 residue deformed the Fc-binding surface. These results reveal how Asp-129 in CD16b affects its binding affinity for IgG1 Fc and suggest that antibodies engineered to engage CD16b with high affinity must accommodate the Asp-129 side chain
Dispersive hydrodynamics of nonlinear polarization waves in two-component Bose-Einstein condensates
We study one dimensional mixtures of two-component Bose-Einstein condensates
in the limit where the intra-species and inter-species interaction constants
are very close. Near the mixing-demixing transition the polarization and the
density dynamics decouple. We study the nonlinear polarization waves, show that
they obey a universal (i.e., parameter free) dynamical description, identify a
new type of algebraic soliton, explicitly write simple wave solutions, and
study the Gurevich-Pitaevskii problem in this context