4,446 research outputs found
Quadratic invariants for discrete clusters of weakly interacting waves
We consider discrete clusters of quasi-resonant triads arising from a Hamiltonian three-wave equation. A cluster consists of N modes forming a total of M connected triads. We investigate the problem of constructing a functionally independent set of quadratic constants of motion. We show that this problem is equivalent to an underlying basic linear problem, consisting of finding the null space of a rectangular M × N matrix with entries 1, −1 and 0. In particular, we prove that the number of independent quadratic invariants is equal to J ≡ N − M* ≥ N − M, where M* is the number of linearly independent rows in Thus, the problem of finding all independent quadratic invariants is reduced to a linear algebra problem in the Hamiltonian case. We establish that the properties of the quadratic invariants (e.g., locality) are related to the topological properties of the clusters (e.g., types of linkage). To do so, we formulate an algorithm for decomposing large clusters into smaller ones and show how various invariants are related to certain parts of a cluster, including the basic structures leading to M* < M. We illustrate our findings by presenting examples from the Charney–Hasegawa–Mima wave model, and by showing a classification of small (up to three-triad) clusters
A family of Nikishin systems with periodic recurrence coefficients
Suppose we have a Nikishin system of measures with the th generating
measure of the Nikishin system supported on an interval \Delta_k\subset\er
with for all . It is well known that
the corresponding staircase sequence of multiple orthogonal polynomials
satisfies a -term recurrence relation whose recurrence coefficients,
under appropriate assumptions on the generating measures, have periodic limits
of period . (The limit values depend only on the positions of the intervals
.) Taking these periodic limit values as the coefficients of a new
-term recurrence relation, we construct a canonical sequence of monic
polynomials , the so-called \emph{Chebyshev-Nikishin
polynomials}. We show that the polynomials themselves form a sequence
of multiple orthogonal polynomials with respect to some Nikishin system of
measures, with the th generating measure being absolutely continuous on
. In this way we generalize a result of the third author and Rocha
\cite{LopRoc} for the case . The proof uses the connection with block
Toeplitz matrices, and with a certain Riemann surface of genus zero. We also
obtain strong asymptotics and an exact Widom-type formula for the second kind
functions of the Nikishin system for .Comment: 30 pages, minor change
Cilia and Mucociliary Clearance
Mucociliary clearance (MCC) is the primary innate defense mechanism of the lung. The functional components are the protective mucous layer, the airway surface liquid layer, and the cilia on the surface of ciliated cells. The cilia are specialized organelles that beat in metachronal waves to propel pathogens and inhaled particles trapped in the mucous layer out of the airways. In health this clearance mechanism is effective, but in patients with primary cilia dyskinesia (PCD) the cilia are abnormal, resulting in deficient MCC and chronic lung disease. This demonstrates the critical importance of the cilia for human health. In this review, we summarize the current knowledge of the components of the MCC apparatus, focusing on the role of cilia in MCC
Force dependent fragility in RNA hairpins
We apply Kramers theory to investigate the dissociation of multiple bonds
under mechanical force and interpret experimental results for the
unfolding/refolding force distributions of an RNA hairpin pulled at different
loading rates using laser tweezers. We identify two different kinetic regimes
depending on the range of forces explored during the unfolding and refolding
process. The present approach extends the range of validity of the two-states
approximation by providing a theoretical framework to reconstruct free-energy
landscapes and identify force-induced structural changes in molecular
transition states using single molecule pulling experiments. The method should
be applicable to RNA hairpins with multiple kinetic barriers.Comment: Latex file, 4 pages+3 figure
Dynamic force spectroscopy of DNA hairpins. II. Irreversibility and dissipation
We investigate irreversibility and dissipation in single molecules that
cooperatively fold/unfold in a two state manner under the action of mechanical
force. We apply path thermodynamics to derive analytical expressions for the
average dissipated work and the average hopping number in two state systems. It
is shown how these quantities only depend on two parameters that characterize
the folding/unfolding kinetics of the molecule: the fragility and the
coexistence hopping rate. The latter has to be rescaled to take into account
the appropriate experimental setup. Finally we carry out pulling experiments
with optical tweezers in a specifically designed DNA hairpin that shows
two-state cooperative folding. We then use these experimental results to
validate our theoretical predictions.Comment: 28 pages, 12 figure
Effect of the dynamical phases on the nonlinear amplitudes' evolution
In this Letter we show how the nonlinear evolution of a resonant triad
depends on the special combination of the modes' phases chosen according to the
resonance conditions. This phase combination is called dynamical phase. Its
evolution is studied for two integrable cases: a triad and a cluster formed by
two connected triads, using a numerical method which is fully validated by
monitoring the conserved quantities known analytically. We show that dynamical
phases, usually regarded as equal to zero or constants, play a substantial role
in the dynamics of the clusters. Indeed, some effects are (i) to diminish the
period of energy exchange within a cluster by 20 and more; (ii) to
diminish, at time scale , the variability of wave energies by 25 and
more; (iii) to generate a new time scale, , in which we observe
considerable energy exchange within a cluster, as well as a periodic behaviour
(with period ) in the variability of modes' energies. These findings can be
applied, for example, to the control of energy input, exchange and output in
Tokamaks; for explanation of some experimental results; to guide and improve
the performance of experiments; to interpret the results of numerical
simulations, etc.Comment: 5 pages, 15 figures, submitted to EP
A non-symmetric Yang-Baxter Algebra for the Quantum Nonlinear Schr\"odinger Model
We study certain non-symmetric wavefunctions associated to the quantum
nonlinear Schr\"odinger model, introduced by Komori and Hikami using Gutkin's
propagation operator, which involves representations of the degenerate affine
Hecke algebra. We highlight how these functions can be generated using a
vertex-type operator formalism similar to the recursion defining the symmetric
(Bethe) wavefunction in the quantum inverse scattering method. Furthermore,
some of the commutation relations encoded in the Yang-Baxter equation for the
relevant monodromy matrix are generalized to the non-symmetric case.Comment: 31 pages; added some references; minor corrections throughou
A charged particle in a magnetic field - Jarzynski Equality
We describe some solvable models which illustrate the Jarzynski theorem and
related fluctuation theorems. We consider a charged particle in the presence of
magnetic field in a two dimensional harmonic well. In the first case the centre
of the harmonic potential is translated with a uniform velocity, while in the
other case the particle is subjected to an ac force. We show that Jarzynski
identity complements Bohr-van Leeuwen theorem on the absence of diamagnetism in
equilibrium classical system.Comment: 5 pages, minor corrections made and journal reference adde
A novel sequencing-based vaginal health assay combining self-sampling, HPV detection and genotyping, STI detection, and vaginal microbiome analysis
The composition of the vaginal microbiome, including both the presence of pathogens involved in sexually transmitted infections (STI) as well as commensal microbiota, has been shown to have important associations for a woman´s reproductive and general health. Currently, healthcare providers cannot offer comprehensive vaginal microbiome screening, but are limited to the detection of individual pathogens, such as high-risk human papillomavirus (hrHPV), the predominant cause of cervical cancer. There is no single test on the market that combines HPV, STI, and microbiome screening. Here, we describe a novel inclusive vaginal health assay that combines self-sampling with sequencing-based HPV detection and genotyping, vaginal microbiome analysis, and STI-associated pathogen detection. The assay includes genotyping and detection of 14 hrHPV types, 5 low-risk HPV types (lrHPV), as well as the relative abundance of 31 bacterial taxa of clinical importance, including Lactobacillus, Sneathia, Gardnerella, and 3 pathogens involved in STI, with high sensitivity, specificity, and reproducibility. For each of these taxa, reference ranges were determined in a group of 50 self-reported healthy women. The HPV sequencing portion of the test was evaluated against the digene High-Risk HPV HC2 DNA test. For hrHPV genotyping, agreement was 95.3% with a kappa of 0.804 (601 samples); after removal of samples in which the digene hrHPV probe showed cross-reactivity with lrHPV types, the sensitivity and specificity of the hrHPV genotyping assay were 94.5% and 96.6%, respectively, with a kappa of 0.841. For lrHPV genotyping, agreement was 93.9% with a kappa of 0.788 (148 samples), while sensitivity and specificity were 100% and 92.9%, respectively. This novel assay could be used to complement conventional cervical cancer screening, because its self-sampling format can expand access among women who would otherwise not participate, and because of its additional information about the composition of the vaginal microbiome and the presence of pathogens.Fil: Bik, Elisabeth M.. Ubiome;Fil: Bird, Sara W.. Ubiome;Fil: Bustamante, Juan Pablo. Universidad Nacional de Entre Ríos. Instituto de Investigación y Desarrollo en Bioingeniería y Bioinformática - Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto de Investigación y Desarrollo en Bioingeniería y Bioinformática; ArgentinaFil: Leon, Luis E.. Ubiome
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