Stability of synchronization in simplicial complexes.

Various systems in physics, biology, social sciences and engineering have been successfully modeled as networks of coupled dynamical systems, where the links describe pairwise interactions. This is, however, too strong a limitation, as recent studies have revealed that higher-order many-body interactions are present in social groups, ecosystems and in the human brain, and they actually affect the emergent dynamics of all these systems. Here, we introduce a general framework to study coupled dynamical systems accounting for the precise microscopic structure of their interactions at any possible order. We show that complete synchronization exists as an invariant solution, and give the necessary condition for it to be observed as a stable state. Moreover, in some relevant instances, such a necessary condition takes the form of a Master Stability Function. This generalizes the existing results valid for pairwise interactions to the case of complex systems with the most general possible architecture.

Apoptotic and cell cycle response to homoharringtonine and harringtonine in wild and mutant p53 hepatocarcinoma cells.

This study aimed to evaluate the modes of action of harringtonine (HT) and homoharringtonine (HHT) alkaloids in cell with wild (HepG2/C3A) and mutant p53 (HuH-7.5). We performed assays for cytotoxicity, genotoxicity, induction of apoptosis, cell cycle phase, and membrane integrity. Obtained data were compared with the relative expression of mRNA of genes related to proliferation, apoptosis, cell cycle control, metabolism of xenobiotics, and reticulum endoplasmic stress. The relative expression of the genes showed an increase in apoptosis-inducing mRNAs, such as TNF and BBC3, as well as a reduction in BCL2 and BAK. The mRNAs of CYP2E1 and CYP2C19 xenobiotic metabolism genes increased in both lineages, while CYP3A4 increased only in the HuH-7.5 lineage. The mRNA expression of endoplasmic reticulum (ER) stress genes (ERN1 and EIF2AK3) was shown to increase in HHT and HT treatments. A similar increase was recorded in the mRNA expression of the TRAF2 gene. The changes observed in this study support the hypothesis that ER stress was more strongly associated with TNF induction, causing cell death by apoptosis in p53 mutant cells. This result with wild and mutant p53 cells may have clinical implications in the use of these compounds.

The origin of the local 1/4-keV X-ray flux in both charge exchange and a hot bubble.

The solar neighbourhood is the closest and most easily studied sample of the Galactic interstellar medium, an understanding of which is essential for models of star formation and galaxy evolution. Observations of an unexpectedly intense diffuse flux of easily absorbed 1/4-kiloelectronvolt X-rays, coupled with the discovery that interstellar space within about a hundred parsecs of the Sun is almost completely devoid of cool absorbing gas, led to a picture of a 'local cavity' filled with X-ray-emitting hot gas, dubbed the local hot bubble. This model was recently challenged by suggestions that the emission could instead be readily produced within the Solar System by heavy solar-wind ions exchanging electrons with neutral H and He in interplanetary space, potentially removing the major piece of evidence for the local existence of million-degree gas within the Galactic disk. Here we report observations showing that the total solar-wind charge-exchange contribution is approximately 40 per cent of the 1/4-keV flux in the Galactic plane. The fact that the measured flux is not dominated by charge exchange supports the notion of a million-degree hot bubble extending about a hundred parsecs from the Sun.

(S)-Goniothalamin induces DNA damage, apoptosis, and decrease in BIRC5 messenger RNA levels in NCI-H460 cells.

(R)-Goniothalamin (R-GNT) is a secondary metabolite isolated from the plants of the genus Goniothalamus. This molecule has attracted the attention of researchers because of its selective cytotoxicity against tumor cells and its ability to induce apoptosis. (S)-Goniothalamin (S-GNT) is a synthetic enantiomer of R-GNT, and its mechanism of action is largely unknown. In this study, we investigated the activity of S-GNT in a human non-small cell lung cancer NCI-H460 cells. We observed that the cells exposed to this compound exhibited cytotoxicity in a concentration-dependent manner. Based on the data obtained through the assessment of apoptosis induction in situ and the comet assay, we suggest that this cytotoxicity occurs due to the potential ability of this molecule to induce DNA damage with the consequent induction of cell death via apoptosis. A significant reduction in the messenger RNA levels of baculoviral inhibitor of apoptosis repeat-containing 5 (BIRC5) gene that encodes the survivin protein was found. This novel finding may explain the inhibition of cell proliferation and induction of apoptosis in tumor cells caused by this compound.

Eigenstates and instabilities of chains with embedded defects.

We consider the eigenvalue problem for one-dimensional linear Schrödinger lattices (tight-binding) with an embedded few-sites linear or nonlinear, Hamiltonian or non-conservative defect (an oligomer). Such a problem arises when considering scattering states in the presence of (generally complex) impurities as well as in the stability analysis of nonlinear waves. We describe a general approach based on a matching of solutions of the linear portions of the lattice at the location of the oligomer defect. As specific examples, we discuss both linear and nonlinear, Hamiltonian and PT-symmetric dimers and trimers. In the linear case, this approach provides us a handle for semi-analytically computing the spectrum [this amounts to the solution of a polynomial equation]. In the nonlinear case, it enables the computation of the linearization spectrum around the stationary solutions. The calculations showcase the oscillatory instabilities that strongly nonlinear states typically manifest.

Particle model for nonlocal heat transport in fusion plasmas.

We present a simple stochastic, one-dimensional model for heat transfer in weakly collisional media as fusion plasmas. Energies of plasma particles are treated as lattice random variables interacting with a rate inversely proportional to their energy schematizing a screened Coulomb interaction. We consider both the equilibrium (microcanonical) and nonequilibrium case in which the system is in contact with heat baths at different temperatures. The model exhibits a characteristic length of thermalization that can be associated with an interaction mean free path and one observes a transition from ballistic to diffusive regime depending on the average energy of the system. A mean-field expression for heat flux is deduced from system heat transport properties. Finally, it is shown that the nonequilibrium steady state is characterized by long-range correlations.

Asymptotic energy profile of a wave packet in disordered chains.

We investigate the long-time behavior of a wave packet initially localized at a single site n0 in translationally invariant harmonic and anharmonic chains with random interactions. In the harmonic case, the energy profile averaged on time and disorder decays for large |n-n0| as a power law ≈ C|n-n0|(⁻η), where η=5/2 and ³/2 for initial displacement and momentum excitations, respectively. The prefactor C depends on the probability distribution of the harmonic coupling constants and diverges in the limit of weak disorder. As a consequence, the moments of the energy distribution averaged with respect to disorder diverge in time as t(ß(ν)) for ν ≥ 2, where ß=ν+1-η for ν>η-1 . Molecular-dynamics simulations yield good agreement with these theoretical predictions. Therefore, in this system, the second moment of the wave packet diverges as a function of time despite the wave packet is not spreading. Thus, this only criterion, often considered earlier as proving the spreading of a wave packet, cannot be considered as sufficient in any model. The anharmonic case is investigated numerically. It is found for intermediate disorder that the tail of the energy profile becomes very close to those of the harmonic case. For weak and strong disorders, our results suggest that the crossover to the harmonic behavior occurs at much larger |n-n0| and larger time.

Pattern formation and localization in the forced-damped Fermi-Pasta-Ulam lattice.

We study spatial pattern formation and energy localization in the dynamics of an anharmonic chain with quadratic and quartic intersite potential, subject to an optical, sinusoidally oscillating field and a weak damping. The zone-boundary mode is stable and locked to the driving field below a critical forcing that we determine analytically using an approximate model, which describes mode interactions. Above such a forcing, a standing modulated wave forms for driving frequencies below the band edge, while a "multibreather" state develops at higher frequencies. Of the former, we give an explicit approximate analytical expression, which compares well with numerical data. At higher forcing, space-time chaotic patterns are observed.