Baryogenesis from ultra-slow-roll inflation

The ultra-slow-roll (USR) inflation represents a class of single-field models with sharp deceleration of the rolling dynamics on small scales, leading to a significantly enhanced power spectrum of the curvature perturbations and primordial black hole (PBH) formation. Such a sharp transition of the inflationary background can trigger the coherent motion of scalar condensates with effective potentials governed by the rolling rate of the inflaton field. We show that a scalar condensate carrying (a combination of) baryon or lepton number can achieve successful baryogenesis through the Affleck-Dine mechanism from unconventional initial conditions excited by the USR transition. Viable parameter space for creating the correct baryon asymmetry of the Universe naturally incorporates the specific limit for PBHs to contribute significantly to dark matter, shedding light on the cosmic coincidence problem between the baryon and dark matter densities today.

Spatial organization of chromosomes leads to heterogeneous chromatin motion and drives the liquid- or gel-like dynamical behavior of chromatin

Chromosome organization and dynamics are involved in regulating many fundamental processes such as gene transcription and DNA repair. Experiments unveiled that chromatin motion is highly heterogeneous inside cell nuclei, ranging from a liquid-like, mobile state to a gel-like, rigid regime. Using polymer modeling, we investigate how these different physical states and dynamical heterogeneities may emerge from the same structural mechanisms. We found that the formation of topologically associating domains (TADs) is a key driver of chromatin motion heterogeneity. In particular, we showed that the local degree of compaction of the TAD regulates the transition from a weakly compact, fluid state of chromatin to a more compact, gel state exhibiting anomalous diffusion and coherent motion. Our work provides a comprehensive study of chromosome dynamics and a unified view of chromatin motion enabling interpretation of the wide variety of dynamical behaviors observed experimentally across different biological conditions, suggesting that the “liquid” or “solid” state of chromatin are in fact two sides of the same coin.

Collective behavior in the North Rhine-Westphalia motorway network

To understand the dynamics on complex networks, measurement of correlations is indispensable. In a motorway network, it is not sufficient to collect information on fluxes and velocities on all individual links, i.e. parts of the freeways between ramps and highway crosses. The interdependencies and mutual connections are also of considerable interest. We analyze correlations in the complete motorway network in North Rhine-Westphalia, the most populous state in Germany. We view the motorway network as a complex system consisting of road sections which interact via the motion of vehicles, implying structures in the corresponding correlation matrices. In particular, we focus on collective behavior, i.e. coherent motion in the whole network or in large parts of it. To this end, we study the eigenvalue and eigenvector statistics and identify significant sections in the motorway network. We find collective behavior in these significant sections and further explore its causes. We show that collectivity throughout the network cannot directly be related to the traffic states (free, synchronous and congested) in Kerner’s three-phase theory. Hence, the degree of collectivity provides a new, complementary observable to characterize the motorway network.

Propagating wave in a fluid by coherent motion of 2D colloids

Just like in living organisms, if precise coherent operation of tiny movable components is possible, one may generate a macroscopic mechanical motion. Here we report that ~1010 pieces of colloidally dispersed nanosheets in aqueous media can be made to operate coherently to generate a propagating macroscopic wave under a non-equilibrium state. The nanosheets are initially forced to adopt a monodomain cofacial geometry with a large and uniform plane-to-plane distance of ~420 nm, where they are strongly correlated by competitive electrostatic repulsion and van der Waals attraction. When the electrostatic repulsion is progressively attenuated by the addition of ionic species, the nanosheets sequentially undergo coherent motions, generating a propagating wave. This elaborate wave in time and space can transport microparticles over a long distance in uniform direction and velocity. The present discovery may provide a general principle for the design of macroscopically movable devices from huge numbers of tiny components.

Spontaneous rotations in epithelia as an interplay between cell polarity and RhoA activity at boundaries.

Directed flows of cells in vivo are essential in morphogenesis. They shape living matter in phenomena involving cell mechanics and regulations of the acto-myosin cytoskeleton. However the onset of coherent motion during collective cell migration is still poorly understood. Here we show that coherence is set by spontaneous alignments of cell polarity by designing cellular rings of controlled dimensions. A tug-of-war between opposite polarities dictates the onset of coherence, as assessed by tracking live cellular shapes and motions in various experimental conditions. In addition, we identify an internally driven constraint by cellular acto-myosin cables at boundaries as essential to ensure coherence and active force is generated as evaluated by the high RhoA activity. Its contribution is required to trigger coherence as shown by our numerical simulations based on a novel Vicsek-type model including free active boundaries. Altogether, spontaneous coherent motion results from basic interplay between cell orientations and active cables at boundaries.

Efficient tuning of attention to narrow and broad ranges of task-relevant feature values

Feature-based attention is the ability to select relevant information on the basis of visual features, such as a particular color or motion direction. In contrast to spatial attention, where the attentional focus has been shown to be flexibly adjustable to select small or large regions, it is unclear whether feature-based attention can be efficiently tuned to different feature ranges. Here, we establish that the focus of feature-based attention can be adjusted more broadly or narrowly to select currently relevant features. Participants attended to a set of target-colored dots among distractor dots to detect brief decreases in luminance (Experiments 1a and 1b) or bursts of coherent motion (Experiments 2). To vary the size of the attentional focus, we manipulated the range of colors that the target dots spanned and found that while participants’ performance decreased with larger feature ranges to select, it remained at a relatively high level even at the largest color range, suggesting that broadening the focus of feature-based attention comes only at a small cost and that large feature ranges can be selected relatively efficiently at once. We further show that this broad selection occurs uniformly in color space (Experiment 3). Overall, our findings argue against the idea that feature-based attention is limited to a single feature value at a time and demonstrate that selecting large swaths of feature space is surprisingly efficient. Broadly, these results are consistent with accounts that propose a flexible and generalized set of attentional mechanisms that act across both spatial and feature-based domains.

A network-based perspective on coherent structure detection from very-sparse Lagrangian data

Coherent structure detection (CSD) is a long-lasting issue in fluid mechanics research as the presence of spatio-temporal coherent motion enables simpler ways to characterize the flow dynamics. Such reducedorder representation, in fact, has significant implications for the understanding of the dynamics of flows, as well as their modeling and control (Hussain, 1986). While the Eulerian framework has been extensively adopted for CSD, Lagrangian coherent structures have recently received increasing attention, mainly driven by advancements in Lagrangian flow measurement techniques (Haller, 2015; Hadjighasem et al., 2017). Lagrangian particle tracking (LPT), in particular, is widely used nowadays due to its ability to quantity fluid-parcel trajectories in three-dimensional volumes (Schanz et al., 2016).

Unlocking coherent control of ultrafast plasmonic interaction

Striking a metallic nanostructure with a short and intense pulse of light excites a complex out-of-equilibrium distribution of electrons that rapidly interact and lose their mutual coherent motion. Due to the highly nonlinear dynamics, the photo-excited nanostructures may further emit energetic photons beyond the spectrum of the incident beam, where the shortest pulse duration is traditionally expected to induce the greatest nonlinear emission. Here, we coherently control these photo-induced extreme ultrafast dynamics by spectrally shaping a sub-10 fs pulse within the timescale of coherent plasmon excitations. Contrary to the common perception, we show that stretching the pulse to match its internal phase with the plasmon-resonance increases the second-order nonlinear emission by > 25%. The enhancement is observed only when shaping extreme-ultrashort pulses (< 20 fs), thus signifying the coherent electronic nature as a crucial source of the effect. We provide a detailed theoretical framework that reveals the optimal pulse shapes for enhanced nonlinear emission regarding the nanostructures’ plasmonic-resonances. The demonstrated truly-coherent plasma control paves the way to engineer rapid out-of-equilibrium response in solids state systems and light-harvesting applications.

Ultrafast coherent motion and helix rearrangement of homodimeric hemoglobin visualized with femtosecond X-ray solution scattering

Ultrafast motion of molecules, particularly the coherent motion, has been intensively investigated as a key factor guiding the reaction pathways. Recently, X-ray free-electron lasers (XFELs) have been utilized to elucidate the ultrafast motion of molecules. However, the studies on proteins using XFELs have been typically limited to the crystalline phase, and proteins in solution have rarely been investigated. Here we applied femtosecond time-resolved X-ray solution scattering (fs-TRXSS) and a structure refinement method to visualize the ultrafast motion of a protein. We succeeded in revealing detailed ultrafast structural changes of homodimeric hemoglobin involving the coherent motion. In addition to the motion of the protein itself, the time-dependent change of electron density of the hydration shell was tracked. Besides, the analysis on the fs-TRXSS data of myoglobin allows for observing the effect of the oligomeric state on the ultrafast coherent motion.