Negative tension controls stability and structure of intermediate filament networks

Networks, whose junctions are free to move along the edges, such as two-dimensional soap froths and membrane tubular networks of endoplasmic reticulum are intrinsically unstable. This instability is a result of a positive tension applied to the network elements. A paradigm of networks exhibiting stable polygonal configurations in spite of the junction mobility, are networks formed by bundles of Keratin Intermediate Filaments (KIFs) in live cells. A unique feature of KIF networks is a, hypothetically, negative tension generated in the network bundles due to an exchange of material between the network and an effective reservoir of unbundled filaments. Here we analyze the structure and stability of two-dimensional networks with mobile three-way junctions subject to negative tension. First, we analytically examine a simplified case of hexagonal networks with symmetric junctions and demonstrate that, indeed, a negative tension is mandatory for the network stability. Another factor contributing to the network stability is the junction elastic resistance to deviations from the symmetric state. We derive an equation for the optimal density of such networks resulting from an interplay between the tension and the junction energy. We describe a configurational degeneration of the optimal energy state of the network. Further, we analyze by numerical simulations the energy of randomly generated networks with, generally, asymmetric junctions, and demonstrate that the global minimum of the network energy corresponds to the irregular configurations.

On state instability of the bi-stable flow past a notchback bluff body

The wake of a notchback Ahmed body presenting a bi-stable nature is investigated by performing wind tunnel experiments and large-eddy simulations. Attention is confined to the Reynolds number ( $Re$ ) influence on the wake state instability within $5\times 10^{4}\leq Re \leq 25\times 10^{4}$ . Experimental observations suggest a wake bi-stability with low-frequency switches under low $Re$ . The wake becomes ‘tri-stable’ with the increase of $Re$ with the introduction of a new symmetric state. The higher presence of the symmetric state can be considered as a symmetrization of the wake bi-stability with an increasing $Re$ . The wake symmetry under high $Re$ attributed to the highly frequent switches of the wake is extremely sensitive to small yaw angles, showing the feature of bi-stable flows. The wake asymmetry is confirmed in numerical simulations with both low and high $Re$ . The wake asymmetries are indicated by the wake separation, the reattachment and the wake dynamics identified by the proper orthogonal decomposition. However, the turbulence level is found to be significantly higher with a higher $Re$ . This leads to a higher possibility to break the asymmetric state, resulting in highly frequent switches showing symmetry.

Hidden conformations differentiate day and night in a circadian pacemaker

The AAA+ protein KaiC is the central pacemaker for cyanobacterial circadian rhythms. Composed of two hexameric rings with tightly coupled activities, KaiC undergoes changes in autophosphorylation on its C-terminal (CII) domain that restrict binding of of clock proteins on its N-terminal (CI) domain to the evening. Here, we use cryo-electron microscopy to investigate how daytime and nighttime states of CII regulate KaiB binding to CI. We find that the CII hexamer is destabilized during the day but takes on a rigidified C2-symmetric state at night, concomitant with ring-ring compression. Residues at the CI-CII interface are required for phospho-dependent KaiB association, coupling ATPase activity on CI to cooperative KaiB recruitment. Together these studies reveal how daily changes in KaiC phosphorylation regulate cyanobacterial circadian rhythms.

The efficacy of event isotropy as an event shape observable

Event isotropy $$ {\mathcal{I}}^{\mathrm{sph}} $$ I sph , an event shape observable that measures the distance of a final state from a spherically symmetric state, is designed for new physics signals that are far from QCD-like. Using a new technique [1] for producing a wide variety of signals that can range from near-spherical to jetty, we compare event isotropy to other observables. We show that thrust T and the C parameter (and λmax, the largest eigenvalue of the sphericity matrix) are strongly correlated and thus redundant, to a good approximation. By contrast, event isotropy adds considerable information, often serving to break degeneracies between signals that would have almost identical T and C distributions. Signals with broad distributions in T (or λmax) and in $$ {\mathcal{I}}^{\mathrm{sph}} $$ I sph separately often have much narrower distributions, and are more easily distinguished, in the ($$ {\mathcal{I}}^{\mathrm{sph}} $$ I sph , λmax) plane. An intuitive, semi-analytic estimation technique clarifies why this is the case and assists with the interpretation of the distributions.

Asymmetry underlies stability in power grids

Behavioral homogeneity is often critical for the functioning of network systems of interacting entities. In power grids, whose stable operation requires generator frequencies to be synchronized—and thus homogeneous—across the network, previous work suggests that the stability of synchronous states can be improved by making the generators homogeneous. Here, we show that a substantial additional improvement is possible by instead making the generators suitably heterogeneous. We develop a general method for attributing this counterintuitive effect to converse symmetry breaking, a recently established phenomenon in which the system must be asymmetric to maintain a stable symmetric state. These findings constitute the first demonstration of converse symmetry breaking in real-world systems, and our method promises to enable identification of this phenomenon in other networks whose functions rely on behavioral homogeneity.

The minimal interaction induced by the translation subgroup has a gap and possible relates to the strong fundamental interaction.

The paper investigates the low-symmetric state of the compensating field of the distortion tensor and proves that there is a gap in this state. It is shown that the distortion tensor is the compensating field of the minimal interaction induced by the translation subgroup. On the example of electron pairing in a Cooper pair it was proved that the distortion tensor is responsible for the electron-phonon interaction. In this paper, for the first time, an exact wave solution for sound pressure in a continuous medium is obtained from the equations of state for the distortion tensor. It is shown that the sound is described as "massive" wave of the distortion tensor, the spectrum of which has the minimal frequency, which corresponds to a gap. The presence of a gap in the low-symmetric state gives grounds to believe that the distortion tensor, as a compensating interaction field, describes a strong fundamental interaction. As it is known, the description of the gap in the strong fundamental interaction is declared a Millennium problem by the Clay Mathematical Institute (CMI).

Образование полуполярных III-нитридных слоев на поверхности Si(100), структурированной с помощью самоформирующейся наномаски

The epitaxial growth of AlN and GaN layers was studied by Metalorganic Vapor Phase Epitaxy, on a Si(100) substrate, on the surface of which a V-shaped nanostructure with sub-100 nm element size (NP-Si(100)) was formed. It is shown that a corrugated surface is formed from semipolar AlN(10-11) planes with opposite "c"axes during the formation of a semipolar AlN layer at the initial stage of epitaxy. Then, during the growth of the GaN layer, the transition from the symmetric state of two semipolar AlN planes to an asymmetric state with a single orientation of the "c"-axis of the semipolar GaN(10-11) layer occurs, and the "c" direction in the growing semipolar layer coincides with the direction of the flow of N2+ ions to the silicon surface during the formation of a nanomask.

Study of tunneling and oscillation in a GaAs/〖Al〗_(0.3) 〖Ga〗_(0.7) As superlattice: using transfer matrix method

The study of superlattice (SL) system in lower dimensions, which shows tunneling and oscillation of particles, is very interesting from the point of view of fundamental physics and is important for devices. Here, we present results of our calculations related to tunneling/oscillations in a general SL system using a Symmetrical Quadruple Well (SQW) potential. This class of problems is handled using a transfer matrix (T-matrix), which is obtained by taking the solution of Schroedinger equation with appropriate boundary conditions on either side of SQW and then repeatedly applying it for the SL system. The electron wave functions in the system are found to be either in a symmetric or an anti-symmetric state with a very small energy difference between the two, leading to oscillations between these states. In this study, probability density and period of oscillation of the particle in SQW is calculated. The result is useful for high frequency operations in devices using SL. BIBECHANA 18 (2021) 91-99

Ultimate Unification: Gravity-led Democracy vs. Uber-Symmetries

In this paper, we start from conventional GUTs and ToEs and discuss their challenges due not only to the lack of observations of proton decays and magnetic monopoles, but also to the fact that when gravity is considered, especially with mechanisms à la multi-folds, where gravity emerges from entanglement, both these phenomena are expected to not exist. With only a few exception, ToEs are badly hurt, including many superstrings, and most GUTs are knocked out. Because of the massive gravity at small scale contributed by entanglement in a multi-fold universe, we encounter new lifecycles for charged black holes and discover that, at small scales, gravity is no more the weakest interaction. In fact, sources and carriers of all interactions democratically carry gravity along with their interaction the same way and all interactions have similar strength. It becomes a new symmetric state with an Ultimate Unification of all the forces, but without the hierarchies of symmetry groups typically involved in GUTs, and without intermediate GUTs not involving gravity from the get-go. These results are obtained in a multi-fold universe, but with discussions of what can be said about our real universe.