In living systems, DNA is continuously reorganized through condensation, looping, and disentanglement to regulate gene expression, chromosome segregation, and morphogenesis. We present a minimal physical system that reproduces key aspects of this dynamic remodeling through purely mechanical interactions between activity and polymers. By embedding long DNA polymers within an active microtubule-kinesin fluid, we create a self-morphing material in which mechanical flows stretch and entangle DNA into a self-organized viscoelastic network. This emergent network feeds back onto the flow, progressively amplifying correlations and driving a sharp transition from active turbulence to synchronized millimeter-scale oscillations. The onset of large-scale coherence is controlled by a single parameter DNA polymer contour length and emerges through a feedback loop between active stresses, orientational dynamics, and self-generated viscoelasticity. These results reveal a new and minimal route to autonomous oscillations in active matter, and suggest broader design principles for programmable materials that coordinate, reshape, and mechanically organize themselves through dynamically generated elasticity pre-assembled networks, or geometric confinement.
Sub-Saturns, with radii between approximately 4 and 8.5 R⊕, occupy a critical transitional regime between the ice giants and the gas giants. In this talk, I will present two complementary studies that use the interior structure and system architecture of sub-Saturns to constrain their formation and migration histories.
In the first part, I will present a population-level analysis of the envelope mass fractions of warm sub-Saturns. Using the GASTLI interior structure code (Acuña et al. 2024) on a sample of 28 sub-Saturns, we identify a bimodal distribution in the envelope mass fraction f_env, with a gap whose location depends on the assumed atmospheric metallicity. For high metallicities, the gap falls between f_env = 0.5 and 0.7, consistent with the prediction that runaway accretion is triggered when the envelope mass approaches the core mass. I will discuss how this potential "runaway accretion gap" may represent an observational imprint of the transition from slow to rapid gas accretion, effectively marking the physical boundary between the Neptune and Jupiter populations.
In the second part, I will turn to the system architecture of sub-Saturns across the Neptunian landscape. Using injection-recovery tests on the available RV and transit data, we model the detection completeness of each system to correct for observational biases in companion occurrence rates. We find that sub-Saturns in the Neptune savanna (periods longer than ~6 days) frequently reside in multi-planet systems, while those in the Neptune desert and ridge are predominantly solitary. This period-dependent trend parallels observations for hot and warm Jupiter systems, suggesting that sub-Saturns may undergo analogous migration processes, with close-in sub-Saturns having arrived through dynamically violent channels that disrupt nearby companions.
Photo-active (bio-)materials are usually characterised by molecular photochemical processes originating from elementary steps, such as intra- and intermolecular electron- and proton-transfer processes in photocatalysis, or in photochromic reactions involving cis-trans isomerization, hemolytic bond cleavage or cyclization reaction with the formation or break of a bond. These reactions happen first in the excited state at the sub-picosecond to nanosecond timescale followed by the formation of different photo-products in the ground state that relax and also evolve in the micro-millisecond timescale to the final photo-active functional product. Revealing crucial species that control the photo-activity requires the ability to probe dynamics over multiple timescales, ranging from hundreds of femtoseconds to seconds. Historically, short and long timescales have been addressed using different experimental techniques, detrimental to a unified description of the entire multiple timescale dynamics, as it often leads to different excitation conditions in terms of lights characteristics and sample environment. Fortunately, this situation has evolved significantly over the last two decades due to the advent of new high frequency femtosecond Yb laser and development of multiple timescale spectroscopy. I will discuss here the potential of this new method to decipher the photomechanism of photo-active bio-molecules.
