Our eyes are never still. Even when fixating, they exhibit small, jittery motions. While it has long been argued that these fixational eye movements (FEMs) aid the acquisition of visual information, a complete theoretical description of their impact on the information available in the early visual system has been lacking. Here, we consider the drift component of FEMs. We describe these FEMs as a diffusive process and build a minimal theoretical model of the early visual response, including the critical process of adaptation (a fading response to a fixed image). We establish the effect of FEMs on the mutual information between a visual stimulus and this response. Our approach identifies the key dimensionless parameters that characterize the effect of fixational eye movements and reveals the regimes in which this effect can be beneficial, detrimental, or negligible. Taking parameter values appropriate for human vision, we show that the spatiotemporal couplings induced by fixational eye movements can explain the qualitative features of the human contrast sensitivity function as well as classic experiments on temporal integration. To our knowledge, the consideration of fixational eye movements in this latter context is unique, and our results suggest the need for future experiments to determine the mechanisms by which spatial and temporal responses are coupled in the human visual system.

In this work, we demonstrate that key aspects of the dynamical behavior of coral reefs at the macro scale, which evolve over time scales of centuries, can be accurately described using a model that integrates a few fundamental ecological and physical mechanisms. The model displays excitable behavior, generating various dynamical regimes, including traveling pulses and waves, which lead to the formation of spatial structures similar to those observed in real reefs. Notably, this occurs without relying on a classical pattern formation mechanism, such as the Turing scenario. We conduct a thorough analysis of the model's bifurcations in response to two ecologically significant parameters, laying the foundation for using this model to explain coral reef formation.

Earth rotates through the axisymmetric part of its own magnetic field, but a simple proof shows that it is impossible to use this to generate electricity in a conductor rotating with Earth. However, we previously identified implicit assumptions underlying this proof and showed theoretically that these could be violated and the proof circumvented. This requires using a soft magnetic material with a topology satisfying a particular mathematical condition and a composition and scale favoring magnetic diffusion, i.e., having a low magnetic Reynolds number ${\mathrm{R}}_{\mathrm{m}}$ [Chyba and Hand, Phys. Rev. Appl. 6, 014017 (2016)]. Here we realize these requirements with a cylindrical shell of manganese-zinc ferrite. Controlling for thermoelectric and other potentially confounding effects (including 60 Hz and RF background), we show that this small demonstration system generates a continuous DC voltage and current of the (low) predicted magnitude. We test and verify other predictions of the theory: voltage and current peak when the cylindrical shell's long axis is orthogonal to both Earth's rotational velocity $\mathbf{v}$ and magnetic field; voltage and current go to zero when the entire apparatus (cylindrical shell together with current leads and multimeters) is rotated ${90}^{\circ }$ to orient the shell parallel to $\mathbf{v}$; voltage and current again reach a maximum but of opposite sign when the apparatus is rotated a further ${90}^{\circ }$; an otherwise-identical solid MnZn ferrite cylinder generates zero voltage at all orientations; and a high-${\mathrm{R}}_{\mathrm{m}}$ cylindrical shell produces zero voltage. We also reproduce the effect at a second experimental location. The purpose of these experiments was to test the existence of the predicted effect. Ways in which this effect might be scaled to generate higher voltage and current may now be investigated.

Music has a complex structure that expresses emotion and conveys information. Humans process that information through imperfect cognitive instruments that produce a gestalt, smeared version of reality. How can we quantify the information contained in a piece of music? Further, what is the information inferred by a human, and how does that relate to (and differ from) the true structure of a piece? To tackle these questions quantitatively, we present a framework to study the information conveyed in a musical piece by constructing and analyzing networks formed by notes (nodes) and their transitions (edges). Using this framework, we analyze music composed by J. S. Bach through the lens of network science, information theory, and statistical physics. Regarded as one of the greatest composers in the Western music tradition, Bach's work is highly mathematically structured and spans a wide range of compositional forms, such as fugues and choral pieces. Conceptualizing each composition as a network of note transitions, we quantify the information contained in each piece and find that different kinds of compositions can be grouped together according to their information content and network structure. Moreover, using a model for how humans infer networks of information, we find that the music networks communicate large amounts of information while maintaining small deviations of the inferred network from the true network, suggesting that they are structured for efficient communication of information. We probe the network structures that enable this rapid and efficient communication of information—namely, high heterogeneity and strong clustering. Taken together, our findings shed light on the information and network properties of Bach's compositions. More generally, our simple framework serves as a stepping stone for exploring further musical complexities, creativity, and questions therein.

Econophysics aims to understand the macroscopic behavior of financial markets from the underlying microscopic decision-making dynamics. In particular, the order splitting of large metaorders is one of the most important trading strategies in this literature: while traders have large potential metaorders, they split the large orders into small pieces (called child orders) to minimize market impact. This strategic behavior is believed to be important because it is a promising candidate for the microscopic origin of the long-range correlation (LRC) in the persistent order flow. Indeed, Lillo, Mike, and Farmer (LMF) [Phys. Rev. E 71, 066122 (2005)] introduced a simple microscopic model of the order-splitting traders to predict the asymptotic behavior of the LRC from the microscopic dynamics, even quantitatively. The plausibility of this scenario has been investigated by Tóth et al. [J. Econ. Dyn. Control 51, 218 (2015)] at a qualitative level. However, no solid support has been presented yet on the quantitative prediction by the LMF model in the lack of large microscopic data sets. In this paper, we have provided a quantitative statistical analysis of the order-splitting behavior at the level of each trading account. We analyze a large data set of the Tokyo stock exchange (TSE) market over nine years, including the account data of traders (called virtual servers). The virtual server is a unit of trading accounts in the TSE market, and we can effectively define the trader IDs by an appropriate preprocessing. We apply a strategy clustering to individual traders in terms of market orders to identify the order-splitting traders and the random traders. The length distribution of metaorders is empirically estimated for each stock every year. For most of the stocks, we find that the metaorder length distribution obeys power laws with exponent $\alpha$, such that $P\left(L\right)\propto L^{-\alpha -1}$ with the metaorder length $L$, as theoretically assumed in the LMF model. By analyzing the sign correlation of order flow $C\left(\tau \right)\propto {\tau }^{-\gamma }$, we draw the scatterplot between $\alpha$ and $\gamma$, directly confirming the LMF prediction $\gamma \approx \alpha -1$. Furthermore, we discuss how to estimate the total number of splitting traders only from public data via the autocorrelation function prefactor formula in the LMF model. Our work provides quantitative evidence of the LMF model, strongly supporting the order-splitting hypothesis as the origin of LRC.

Pattern-forming systems can exhibit a diverse array of complex behaviors as external parameters are varied, enabling a variety of useful functions in biological and engineered systems. First-principles derivations of the underlying transitions can be characterized using bifurcation theory on model systems whose governing equations are known. In contrast, data-driven methods for more complicated and realistic systems whose governing evolution dynamics are unknown have only recently been developed. Here, we develop a data-driven approach, the sparse identification for nonlinear dynamics with control parameters (SINDyCP), to discover dynamics for systems with adjustable control parameters, such as an external driving strength. We demonstrate the method on systems of varying complexity, ranging from discrete maps to systems of partial differential equations. To mitigate the impact of measurement noise, we also develop a weak formulation of SINDyCP and assess its performance on noisy data. We demonstrate applications including the discovery of universal pattern-formation equations, and their bifurcation dependencies, directly from data accessible from experiments and the extrapolation of predictions beyond the weakly nonlinear regime near the onset of an instability.

Complex plasmas, i.e., low-temperature plasmas containing suspensions of solid microparticles, exhibit electrorheological properties which are manifested by the formation of stringlike clusters (SLCs) in microgravity experiments. It is thought that SLCs form due to a long-range effective attraction between the particles under the influence of a directed ion flow. We performed molecular dynamics (MD) simulations of negatively charged microparticles with positive model wakes to mimic the effect of ion flow in experiments, and achieved SLC formation without long-range attraction between the microparticles. We show that long-range-reduced repulsion was enough to obtain the SLCs similar to the experiments and found that the simulations with the long-range attraction became unstable due to particle accelerations. Destruction and recrystallization of the stringlike structure was also studied experimentally using the Plasmakristall-4 facility on board the International Space Station, and the experimental findings were compared to those from three–dimensional MD simulations. We found excellent qualitative agreement between simulation and experiment when recrystallization was simulated using an interparticle potential without effective long-range attraction.

In the lower atmosphere of Earth, oxygen contains a higher fraction of the heavy ${}^{18}\mathrm{O}$ isotope than ocean water does (Dole effect). This isotopic enrichment is a signature of biological activity, set by the equilibrium between oxygenic photosynthesis and respiratory metabolisms in terrestrial and oceanic ecosystems. While the mixing between stratospheric and tropospheric oxygen leads to a slow isotopic homogenization, little is known about the isotopic oxygen enrichment in the mesosphere and thermosphere of Earth. In situ measurements from rocket-borne air samplers are limited to altitudes below the mesopause, while higher layers have only been accessible through the analysis of the oxidation of ancient cosmic spherules. Here we report the detection of the far-infrared fine-structure lines (${}^3{\mathrm{P}}_1\leftarrow {}^3{\mathrm{P}}_2$ and ${}^3{\mathrm{P}}_0\leftarrow {}^3{\mathrm{P}}_1$) of ${}^{18}\mathrm{O}$ in absorption against the Moon, and determine the ${}^{16}\mathrm{O}/{}^{18}\mathrm{O}$ ratio in atomic oxygen from the mesosphere and lower thermosphere in absorption. After correcting for isotopic exchange between atomic and molecular oxygen, our values for the bulk ${}^{16}\mathrm{O}/{}^{18}\mathrm{O}$ ratio of 468 and 382 in February and November 2021, respectively, fall significantly below that found in solar wind samples ($530\pm 2$), and encompass, within uncertainties, the corresponding ratios pertaining to the Dole effect in the troposphere (487), and those found in stratospheric ozone (429 to 466). We show that with existing technology, future, more sensitive measurements will allow us to monitor deviations from isotopic homogeneity in the mesosphere and lower thermosphere of Earth by remote sensing. We demonstrate that the collisional excitation of the fine-structure levels of the ${}^3\mathrm{P}$ ground-state triplet of ${}^{18}\mathrm{O}$ may compete with isotopic exchange reactions, implying a deviation from the Boltzmann distribution that would be established under local thermodynamic equilibrium.

The determination of the spin state of iron-bearing compounds at high pressure and temperature is crucial for our understanding of chemical and physical properties of the deep Earth. Studies on the relationship between the coordination of iron and its electronic spin structure in iron-bearing oxides, silicates, carbonates, iron alloys, and other minerals found in the Earth's mantle and core are scarce because of the technical challenges to simultaneously probe the sample at high pressures and temperatures. We used the unique properties of a pulsed and highly brilliant x-ray free electron laser (XFEL) beam at the High Energy Density (HED) instrument of the European XFEL to x-ray heat and probe samples contained in a diamond anvil cell. We heated and probed with the same x-ray pulse train and simultaneously measured x-ray emission and x-ray diffraction of an ${\mathrm{FeCO}}_3$ sample at a pressure of 51 GPa with up to melting temperatures. We collected spin state sensitive Fe $K{\beta }_{1,3}$ fluorescence spectra and detected the sample's structural changes via diffraction, observing the inverse volume collapse across the spin transition. During x-ray heating, the carbonate transforms into orthorhombic ${\mathrm{Fe}}_4{\mathrm{C}}_3{\mathrm{O}}_{12}$ and iron oxides. Incipient melting was also observed. This approach to collect information about the electronic state and structural changes from samples contained in a diamond anvil cell at melting temperatures and above will considerably improve our understanding of the structure and dynamics of planetary and exoplanetary interiors.

We demonstrate theoretically and numerically that a warm fluid model of a plasma supports space-time quasicrystalline structures. These structures are highly nonlinear, two-phase, ion acoustic waves that are excited autoresonantly when the plasma is driven by two small amplitude chirped-frequency ponderomotive drives. The waves exhibit density excursions that substantially exceed the equilibrium plasma density. Remarkably, these extremely nonlinear waves persist even when the small amplitude drives are turned off. We derive the weakly nonlinear analytical theory by applying Whitham's averaged variational principle to the Lagrangian formulation of the fluid equations. The resulting system of coupled weakly nonlinear equations is shown to be in good agreement with fully nonlinear simulations of the warm fluid model. The analytical conditions and thresholds required for autoresonant excitation to occur are derived and compared to simulations. The weakly nonlinear theory guides and informs numerical study of how the two-phase quasicrystalline structure “melts” into a single phase traveling wave when one drive is below a threshold. These nonlinear structures may have applications to plasma photonics for extremely intense laser pulses, which are limited by the smallness of density perturbations of linear waves.

We demonstrate the use of dual-comb spectroscopy for isotope ratio measurements. We show that the analysis spectral range of a free-running near-infrared dual-comb spectrometer can be extended to the midinfrared by difference frequency generation to target specific spectral regions suitable for such measurements and especially the relative isotopic ratio $\delta {}^{13}\mathrm{C}$. The measurements performed present very good repeatability over several days with a standard deviation below 2‰ for a recording time of a few tens of seconds, and the results are compatible with measurements obtained using an isotope ratio mass spectrometer. Our setup also shows the possibility to target several chemical species without any major modification, which can be used to measure other isotopic ratios. Further improvements could decrease the uncertainties of the measurements, and the spectrometer could thus compete with isotope ratio spectrometers currently available on the market.

Cavity control of quantum matter may offer new ways to study and manipulate many-body systems. A particularly appealing idea is to use cavities to enhance superconductivity, especially in unconventional or high-$T_c$ systems. Motivated by this, we propose a scheme for coupling terahertz resonators to the antiferromagnetic fluctuations in a cuprate parent compound, which are believed to provide the glue for Cooper pairs in the superconducting phase. First, we derive the interaction between magnon excitations of the Neél order and polar phonons associated with the planar oxygens. This mode also couples to the cavity electric field, and in the presence of spin-orbit interactions mediates a linear coupling between the cavity and magnons, forming hybridized magnon-polaritons. This hybridization vanishes linearly with photon momentum, implying the need for near-field optical methods, which we analyze within a simple model. We then derive a higher-order coupling between the cavity and magnons, which is only present in bilayer systems, but does not rely on spin-orbit coupling. This interaction is found to be large, but only couples to the bimagnon operator. As a result, we find a strong, but heavily damped, bimagnon-cavity interaction which produces highly asymmetric cavity line shapes in the strong-coupling regime. To conclude, we outline several interesting extensions of our theory, including applications to carrier-doped cuprates and other strongly correlated systems with terahertz-scale magnetic excitations.

We discuss the stochastic trajectories of single molecules in a phase-separated liquid, when a dense and a dilute phase coexist. Starting from a continuum theory of macroscopic phase separation we derive a stochastic Langevin equation for molecular trajectories that takes into account thermal fluctuations. We find that molecular trajectories can be described as diffusion with drift in an effective potential, which has a steep gradient at phase boundaries. We discuss how the physics of phase coexistence affects the statistics of molecular trajectories and in particular the statistics of displacements of molecules crossing a phase boundary. At thermodynamic equilibrium detailed balance imposes that the distributions of displacements crossing the phase boundary from the dense or from the dilute phase are the same. Our theory can be used to infer key phase separation parameters from the statistics of single-molecule trajectories. For simple Brownian motion, there is no drift in the presence of a concentration gradient. We show that interactions in the fluid give rise to an average drift velocity in concentration gradients. Interestingly, under non-equilibrium conditions, single molecules tend to drift uphill the concentration gradient. Thus, our work bridges between single-molecule dynamics and collective dynamics at macroscopic scales and provides a framework to study single-molecule dynamics in phase-separating systems.

The Edelstein effect produces a homogeneous magnetization in nonmagnetic materials with broken inversion symmetry which is generated and tuned exclusively electrically. Often the spin Edelstein effect—that is, a spin density in response to an applied electric field—is considered. In this paper we report on the electrically induced magnetization that comprises contributions from the spin and the orbital moments. Our theory for these spin and orbital Edelstein effects is applied to the topologically nontrivial two-dimensional electron gas at ${\mathrm{SrTiO}}_3$ interfaces. In this particular system the orbital Edelstein effect exceeds the spin Edelstein effect by more than one order of magnitude. This finding is explained mainly by orbital moments of different magnitude in the Rashba-like split band pairs, while the spin moments are of almost equal magnitude.

The growing number of patients who require organ transplants, combined with the low number of organ donors, has resulted in organ shortages; therefore, the fabrication of human tissues and organs is an urgent need. However, the time required to fabricate an organ may result in risky delays for end-stage patients who urgently require transplants. During bioprinting, the maturation of the engineered tissue that is required before it is ready for implantation is lengthy. Here we use a previously introduced microscopic and mathematical model, the “zipper CAMs” (for ell dhesion olecules), to investigate the effective parameters involved in tissue dynamics. In our current study, we validated the ability of our model to accelerate the tissue maturation process. Our model shows that exploiting cellular mechanotransduction can accelerate post-printing tissue maturation. To verify this prediction experimentally, we devised a mechanotransduction-based bioprinter that accelerates the production of tissues by speeding up the fusion bioink particles. The mathematical microscopic model and the bioprinter described herein are expected to be highly useful in cell biology, tissue engineering, and biofabrication.

We establish the feasibility of measuring the neutron lifetime via an alternative, space-based class of methods, which use neutrons generated by galactic cosmic ray spallation of planets surfaces and atmospheres. Free neutrons decay via the weak interaction with a mean lifetime of around 880 s. This lifetime constrains the unitarity of the CKM matrix and is a key parameter for studies of Big-Bang nucleosynthesis. However, current laboratory measurements, using two independent approaches, differ by over $4\sigma$. Using data acquired in 2007 and 2008 during flybys of Venus and Mercury by NASA's MESSENGER spacecraft, which was not designed to make this measurement, we estimate the neutron lifetime to be $780\pm {60}_{\text{stat}}\pm {70}_{\text{syst}}$ s, thereby demonstrating the viability of this new approach.

The charge density wave (CDW) in solids is a collective ground state combining lattice distortions and charge ordering. It is defined by a complex order parameter with an amplitude and a phase. The amplitude and wavelength of the charge modulation are readily accessible to experiment. However, accurate measurements of the corresponding phase are significantly more challenging. Here we combine reciprocal and real space information to map the full complex order parameter based on topographic scanning tunneling microscopy (STM) images. Our technique overcomes limitations of Fourier space based techniques to achieve distinct amplitude and phase images with high spatial resolution. Applying this analysis to transition metal dichalcogenides provides striking evidence that their CDWs consist of three individual unidirectional charge modulations whose ordering vectors are connected by the fundamental rotational symmetry of the crystalline lattice. Spatial variations in the relative phases of these three modulations account for the different CDW contrasts often observed in STM topographic images. Phase images further reveal topological defects and discommensurations, a singularity predicted by theory for a nearly commensurate CDW. Such precise real space mapping of the complex order parameter provides a powerful tool for a deeper understanding of the CDW ground state whose formation mechanisms remain largely unclear.

We theoretically study the effect of a magnetic field on quasicrystalline superconductors, by modeling them as an attractive Hubbard model on a Penrose-tiling structure. We find that at low temperatures and under a high magnetic field there appears an exotic superconducting state with the order parameter changing its sign in real space. We discuss the state in comparison with the Fulde-Ferrell-Larkin-Ovchinnikov state proposed many years ago for periodic systems, clarifying commonalities and differences. It is remarkable that, even in the absence of periodicity, the electronic system finds a way to keep a coherent superconducting state with a spatially sign-changing order parameter compatible with the underlying quasiperiodic structure.