Mitochondria are dynamic cell organelles that constantly undergo fission and fusion events. These dynamical processes, which tightly regulate mitochondrial morphology, are essential for cell physiology. Here we propose an elastocapillary mechanical instability as a mechanism for mitochondrial fission. We experimentally induce mitochondrial fission by rupturing the cell’s plasma membrane. We present a stability analysis that successfully explains the observed fission wavelength and the role of mitochondrial morphology in the occurrence of fission events. Our results show that the laws of fluid mechanics can describe mitochondrial morphology and dynamics.

The rapid collapse of a polymer, due to external forces or changes in solvent, yields a long-lived “crumpled globule.” The conjectured fractal structure shaped by hierarchical collapse dynamics has proved difficult to establish, even with large simulations. To unravel this puzzle, we study a coarse-grained model of in-falling spherical blobs that coalesce upon contact. Distances between pairs of monomers are assigned upon their initial coalescence, and do not “equilibrate” subsequently. Surprisingly, the model reproduces quantitatively the dependence of distance on segment length, suggesting that the slow approach to scaling is related to the wide distribution of blob sizes.

The rheology of suspensions of Brownian, or colloidal, particles (diameter $d\lesssim 1\mu \mathrm{m}$) differs markedly from that of larger grains ($d\gtrsim 50\mu \mathrm{m}$). Each of these two regimes has been separately studied, but the flow of suspensions with intermediate particle sizes ($1\mu \mathrm{m}\lesssim d\lesssim 50\mu \mathrm{m}$), which occur ubiquitously in applications, remains poorly understood. By measuring the rheology of suspensions of hard spheres with a wide range of sizes, we show experimentally that shear thickening drives the transition from colloidal to granular flow across the intermediate size regime. This insight makes possible a unified description of the (noninertial) rheology of hard spheres over the full size spectrum. Moreover, we are able to test a new theory of friction-induced shear thickening, showing that our data can be well fitted using expressions derived from it.

A substantial volume of research is devoted to studies of community structure in networks, but communities are not the only possible form of large-scale network structure. Here, we describe a broad extension of community structure that encompasses traditional communities but includes a wide range of generalized structural patterns as well. We describe a principled method for detecting this generalized structure in empirical network data and demonstrate with real-world examples how it can be used to learn new things about the shape and meaning of networks.

We show that within the left-right symmetric model, lepton number violating decays of the Higgs boson can be discovered at the LHC. The process is due to the mixing of the Higgs boson with the triplet that breaks parity. As a result, the Higgs boson can act as a gateway to the origin of the heavy Majorana neutrino mass. To assess the LHC reach, a detailed collider study of the same-sign dileptons plus jets channel is provided. This process is complementary to the existing nuclear and collider searches for lepton number violation and can probe the scale of parity restoration even beyond other direct searches.

Supramolecular self-assembly is a multiple length-scale and time-dependent process involving many coexisting components. Such complexity requires suitable strategies to extract quantitative dynamical and structural information on all involved species. Here, we detail an original light scattering method to study the kinetics of tailored triarylamine molecules capable of self-assembling in supramolecular highly conductive nanowires upon light exposure. These micrometric assemblies cause the emergence of intermittences in the scattered intensity and the construction of a predominant slow mode in the correlation function making separation between small-and large-size species impossible using conventional treatments. Our strategy is based on the time monitoring of intermittences and allows us to determine the fraction of nanowires as well as those of small critical nuclei and triarylamine building blocks as a function of time and light exposure, in good agreement with recent theoretical predictions.

The Wiener-Khinchin theorem shows how the power spectrum of a stationary random signal $I(t)$ is related to its correlation function $⟨I(t)I(t+\tau )⟩$. We consider nonstationary processes with the widely observed aging correlation function $⟨I(t)I(t+\tau )⟩\sim t^{\gamma }{\varphi }_{\mathrm{EA}}(\tau /t)$ and relate it to the sample spectrum. We formulate two aging Wiener-Khinchin theorems relating the power spectrum to the time- and ensemble-averaged correlation functions, discussing briefly the advantages of each. When the scaling function ${\varphi }_{\mathrm{EA}}(x)$ exhibits a nonanalytical behavior in the vicinity of its small argument we obtain the aging $1/f$-type of spectrum. We demonstrate our results with three examples: blinking quantum dots, single-file diffusion, and Brownian motion in a logarithmic potential, showing that our approach is valid for a wide range of physical mechanisms.

We derive a generalization of the Wiener-Khinchin theorem for nonstationary processes by introducing a time-dependent spectral density that is related to the time-averaged power. We use the nonstationary theorem to investigate aging processes with asymptotically scale-invariant correlation functions. As an application, we analyze the power spectrum of three paradigmatic models of anomalous diffusion: scaled Brownian motion, fractional Brownian motion, and diffusion in a logarithmic potential. We moreover elucidate how the nonstationarity of generic subdiffusive processes is related to the infrared catastrophe of $1/f$ noise.

We computationally study the behavior of the diffusion coefficient $D$ in granular flows of monodisperse and bidisperse particles spanning regions of relatively high and low shear rate in open and closed laterally confined heaps. Measurements of $D$ at various flow rates, streamwise positions, and depths collapse onto a single curve when plotted as a function of $\dot{\gamma }{\overline{d}}^2$, where $\overline{d}$ is the local mean particle diameter and $\dot{\gamma }$ is the local shear rate. When $\dot{\gamma }$ is large, $D$ is proportional to $\dot{\gamma }{\overline{d}}^2$, as in previous studies. However, for $\dot{\gamma }{\overline{d}}^2$ below a critical value, $D$ is independent of $\dot{\gamma }{\overline{d}}^2$. The acceleration due to gravity $g$ and particle stiffness (or, equivalently, the binary collision time $t_c$) together determine the transition in $D$ between regimes. This suggests that while shear rate and particle size determine diffusion at relatively high shear rates in surface-driven flows, diffusion at low shear rates is an elastic phenomenon with time and length scales dependent on gravity ($\sqrt{\overline{d}/g}$) and particle stiffness ($t_c\sqrt{\overline{d}g}$), respectively.

The mechanism responsible for domain registration in two membrane leaflets has thus far remained enigmatic. Using continuum elasticity theory, we show that minimum line tension is achieved along the rim between thicker (ordered) and thinner (disordered) domains by shifting the rims in opposing leaflets by a few nanometers relative to each other. Increasing surface tension yields an increase in line tension, resulting in larger domains. Because domain registration is driven by lipid deformation energy, it does not require special lipid components or interactions at the membrane midplane.

Adsorption-desorption processes are ubiquitous in physics, chemistry, and biology. Models usually assume hard particles, but within the realm of soft matter physics the adsorbing particles are compressible. A minimal 1D model reveals that softness fundamentally changes the kinetics: Below the desorption time scale, a logarithmic increase of the particle density replaces the usual Rényi jamming plateau, and the subsequent relaxation to equilibrium can be nonmonotonic and much faster than for hard particles. These effects will impact the kinetics of self-assembly and reaction-diffusion processes.

We formulate a convergent sequence for the energy gap estimation in the worldline quantum Monte Carlo method. The ambiguity left in the conventional gap calculation for quantum systems is eliminated. Our estimation will be unbiased in the low-temperature limit, and also the error bar is reliably estimated. The level spectroscopy from quantum Monte Carlo data is developed as an application of the unbiased gap estimation. From the spectral analysis, we precisely determine the Kosterlitz-Thouless quantum phase-transition point of the spin-Peierls model. It is established that the quantum phonon with a finite frequency is essential to the critical theory governed by the antiadiabatic limit, i.e., the $k=1$ SU(2) Wess-Zumino-Witten model.

New constraints on exotic dipole-dipole interactions between electrons at the micrometer scale are established, based on a recent measurement of the magnetic interaction between two trapped ${}^{88}{\mathrm{Sr}}^{+}$ ions. For light bosons ($\text{mass}\le 0.1\mathrm{eV}$) we obtain a 90% confidence interval for an axial-vector-mediated interaction strength of $|g_A^e{g}_A^e/4\pi \hslash c|\le 1.2\times {10}^{-17}$. Assuming $CPT$ invariance, this constraint is compared to that on anomalous electron-positron interactions, derived from positronium hyperfine spectroscopy. We find that the electron-electron constraint is 6 orders of magnitude more stringent than the electron-positron counterpart. Bounds on pseudoscalar-mediated interaction as well as on torsion gravity are also derived and compared with previous work performed at different length scales. Our constraints benefit from the high controllability of the experimental system which contained only two trapped particles. It therefore suggests a useful new platform for exotic particle searches, complementing other experimental efforts.

A method for calculating the Kohn-Sham exchange-correlation potential $v_{\mathrm{XC}}(\mathbf{r})$ from a given electronic wave function is devised and implemented. It requires on input one- and two-electron reduced density matrices and involves construction of the generalized Fock matrix. The method is free from numerical limitations and basis-set artifacts of conventional schemes for constructing $v_{\mathrm{XC}}(\mathbf{r})$ in which the potential is recovered from a given electron density, and is simpler than various many-body techniques. The chief significance of this development is that it allows one to directly probe the functional derivative of the true exchange-correlation energy functional and to rigorously test and improve various density-functional approximations.