832 research outputs found
Covariant hydrodynamic Lyapunov modes and strong stochasticity threshold in Hamiltonian lattices
We scrutinize the reliability of covariant and Gram-Schmidt Lyapunov vectors
for capturing hydrodynamic Lyapunov modes (HLMs) in one-dimensional Hamiltonian
lattices. We show that,in contrast with previous claims, HLMs do exist for any
energy density, so that strong chaos is not essential for the appearance of
genuine (covariant) HLMs. In contrast, Gram-Schmidt Lyapunov vectors lead to
misleading results concerning the existence of HLMs in the case of weak chaos.Comment: 4 pages, 4 figures. Accepted for publication in Physical Review
On the origin of subvisible cirrus clouds in the tropical upper troposphere
Spaceborne lidar observations have recently revealed a previously undetected significant population of Subvisible Cirrus (SVC). We show them to be colder than −74 °, with an optical depth below 0.0015 on average. The formation and persistence over time of this new cloud population could be related to several atmospheric phenomena. In this paper, we investigate if these clouds follow the same formation mechanisms as the general tropical cirrus population (including convection and in-situ ice nucleation), or if specific nucleation sites and trace species play a role in their formation. The importance of three scenarios in the formation of the global SVC population is investigated through different approaches that include comparisons with data imaging from several spaceborne instruments and back-trajectories that document the history and behavior of air masses leading to the point in time and space where subvisible cirrus were detected. In order to simplify the study of their formation, we singled out SVC with coherent temperature histories (mean variance lower than 4 K) according to back-trajectories along 5, 10 or 15 days (respectively 58, 25 and 11% of SVC). Our results suggest that external processes, including local increases in liquid and hygroscopic aerosol concentration (either through biomass burning or volcanic injection forming sulfate-based aerosols in the troposphere or the stratosphere) have very limited short-term or mid-term impact on the SVC population. On the other hand, we find that ~20% of air masses leading to SVC formation interacted with convective activity 5 days before they led to cloud formation and detection, a number that climbs to 60% over 15 days. SVC formation appears especially linked to convection over Africa and Central America, more so during JJA than DJF. These results support the view that the SVC population observed by CALIOP is an extension of the general upper tropospheric ice clouds population with its extreme thinness as its only differentiating factor
Nonlinear dynamics of the viscoelastic Kolmogorov flow
The weakly nonlinear regime of a viscoelastic Navier--Stokes fluid is
investigated. For the purely hydrodynamic case, it is known that large-scale
perturbations tend to the minima of a Ginzburg-Landau free-energy functional
with a double-well (fourth-order) potential. The dynamics of the relaxation
process is ruled by a one-dimensional Cahn--Hilliard equation that dictates the
hyperbolic tangent profiles of kink-antikink structures and their mutual
interactions. For the viscoelastic case, we found that the dynamics still
admits a formulation in terms of a Ginzburg--Landau free-energy functional. For
sufficiently small elasticities, the phenomenology is very similar to the
purely hydrodynamic case: the free-energy functional is still a fourth-order
potential and slightly perturbed kink-antikink structures hold. For
sufficiently large elasticities, a critical point sets in: the fourth-order
term changes sign and the next-order nonlinearity must be taken into account.
Despite the double-well structure of the potential, the one-dimensional nature
of the problem makes the dynamics sensitive to the details of the potential. We
analysed the interactions among these generalized kink-antikink structures,
demonstrating their role in a new, elastic instability. Finally, consequences
for the problem of polymer drag reduction are presented.Comment: 26 pages, 17 figures, submitted to The Journal of Fluid Mechanic
Pharmacokinetic and pharmacodynamic study of Paclitaxel-loaded lipid nanocapsules after intravenous and oral administration in rats, on Paclitaxel resistant tumor
Characteristic Lyapunov vectors in chaotic time-delayed systems
We compute Lyapunov vectors (LVs) corresponding to the largest Lyapunov
exponents in delay-differential equations with large time delay. We find that
characteristic LVs, and backward (Gram-Schmidt) LVs, exhibit long-range
correlations, identical to those already observed in dissipative extended
systems. In addition we give numerical and theoretical support to the
hypothesis that the main LV belongs, under a suitable transformation, to the
universality class of the Kardar-Parisi-Zhang equation. These facts indicate
that in the large delay limit (an important class of) delayed equations behave
exactly as dissipative systems with spatiotemporal chaos.Comment: 7 page
The IS_MIRRI21 H2020 Project: Implementing the MIRRI-ERIC
The IS_MIRRI21 project running from 2020-2023 aims to implement the Microbial Resource Research Infrastructure (MIRRI) and secure its long-term sustainability. The mission of MIRRI is to serve Bioscience and Bioindustry by providing (a) a broad range of high-quality biological resources and associated data, (b) long-term sustainability of microbial biodiversity, and (c) knowledge and professional development. This mission will be achieved by offering users from academia, governmental laboratories and the private sector access to a portfolio of microbial Biological Resource Centres´ (mBRCs), services, expertise, education and training build-up and synergistically on the top of mBRCs proficiencies. To accelerate innovative research processes in life sciences and biotechnology using microorganisms, or their derivatives, IS_MIRRI21 has set up MIRRIs single-entry point portal to promote its services, resources, expertise and knowledge transfer activities, as well as to provide access to partners´ resource associated data made interoperable for data searching and data mining. The continuously increasing knowledge will be transferred to users via expert clusters (e.g., for legal framework, for biosecurity, to support training and education programs, information and cut edge technology, etc.). It will promote cross-disciplinary and innovative solutions (industry and academic) research collaboration through the transnational access offer in different microbial topics defined in pipeline services. With this project, MIRRI has become an ERIC in June 2022, and is a Landmark in the Health & Food domain of the European Strategy Forum on Research Infrastructures (ESFRI) Roadmap. It is still working to consolidate its operation and enlarge the membership and European coverage and beyond.info:eu-repo/semantics/publishedVersio
Structure of characteristic Lyapunov vectors in spatiotemporal chaos
We study Lyapunov vectors (LVs) corresponding to the largest Lyapunov
exponents in systems with spatiotemporal chaos. We focus on characteristic LVs
and compare the results with backward LVs obtained via successive Gram-Schmidt
orthonormalizations. Systems of a very different nature such as coupled-map
lattices and the (continuous-time) Lorenz `96 model exhibit the same features
in quantitative and qualitative terms. Additionally we propose a minimal
stochastic model that reproduces the results for chaotic systems. Our work
supports the claims about universality of our earlier results [I. G. Szendro et
al., Phys. Rev. E 76, 025202(R) (2007)] for a specific coupled-map lattice.Comment: 9 page
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Determination of eddy-diffusivity in the lowermost stratosphere
We present a 2D-advection-diffusion model that simulates the main transport pathways influencing tracer distributions in the lowermost stratosphere (LMS). The model describes slow diabatic descent of aged stratospheric air, vertical (cross-isentropic) and horizontal (along isentropes) diffusion within the LMS and across the tropopause using equivalent latitude and potential temperature coordinates. Eddy diffusion coefficients parameterize the integral effect of dynamical processes leading to small scale turbulence and mixing. They were specified by matching model simulations to observed CO distributions. Interestingly, the model suggests mixing across isentropes to be more important than horizontal mixing across surfaces of constant equivalent latitude, shining new light on the interplay between various transport mechanisms in the LMS. The model achieves a good description of the small scale tracer features at the tropopause with squared correlation coefficients R2 = 0.72…0.94
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