Discrete Breathers in a Nonlinear Polarizability Model of Ferroelectrics

We present a family of discrete breathers, which exists in a nonlinear polarizability model of ferroelectric materials. The core-shell model is set up in its non-dimensionalized Hamiltonian form and its linear spectrum is examined. Subsequently, seeking localized solutions in the gap of the linear spectrum, we establish that numerically exact and potentially stable discrete breathers exist for a wide range of frequencies therein. In addition, we present nonlinear normal mode, extended spatial profile solutions from which the breathers bifurcate, as well as other associated phenomena such as the formation of phantom breathers within the model. The full bifurcation picture of the emergence and disappearance of the breathers is complemented by direct numerical simulations of their dynamical instability, when the latter arises.Comment: 9 pages, 7 figures, 1 tabl

Non-local spin Seebeck effect in the bulk easy-plane antiferromagnet NiO

We report the observation of magnon spin currents generated by the Spin Seebeck effect (SSE) in a bulk single crystal of the easy-plane antiferromagnet NiO. A magnetic field induces a non-degeneracy and thereby an imbalance in the population of magnon modes with opposite spin. A temperature gradient then gives rise to a non-zero magnon spin current. This SSE is measured both in a local and a non-local geometry at 5$\,$K in bulk NiO. The magnetic field dependence of the obtained signal is modelled by magnetic field splitting of the low energy magnon modes, affecting the spin Seebeck coefficient. The relevant magnon modes at this temperature are linked to cubic anisotropy and magnetic dipole-dipole interactions. The non-local signal deviates from the expected quadratic Joule heating by saturating at a current from around 75$\,\mu A$ in the injector. The magnon chemical potential does not decay exponentially with distance and inhomogeneities may be the result of local magnon accumulations

The Fibers and Range of Reduction Graphs in Ciliates

The biological process of gene assembly has been modeled based on three types of string rewriting rules, called string pointer rules, defined on so-called legal strings. It has been shown that reduction graphs, graphs that are based on the notion of breakpoint graph in the theory of sorting by reversal, for legal strings provide valuable insights into the gene assembly process. We characterize which legal strings obtain the same reduction graph (up to isomorphism), and moreover we characterize which graphs are (isomorphic to) reduction graphs.Comment: 24 pages, 13 figure

Myosin II synergizes with F-actin to promote DNGR-1-dependent cross-presentation of dead cell-associated antigens

Conventional type 1 DCs (cDC1s) excel at cross-presentation of dead cell-associated antigens partly because they express DNGR-1, a receptor that recognizes exposed actin filaments on dead cells. In vitro polymerized F-actin can be used as a synthetic ligand for DNGR-1. However, cellular F-actin is decorated with actin-binding proteins, which could affect DNGR-1 recognition. Here, we demonstrate that myosin II, an F-actin-associated motor protein, greatly potentiates the binding of DNGR-1 to F-actin. Latex beads coated with F-actin and myosin II are taken up by DNGR-1+ cDC1s, and antigen associated with those beads is efficiently cross-presented to CD8+ T cells. Myosin II-deficient necrotic cells are impaired in their ability to stimulate DNGR-1 or to serve as substrates for cDC1 cross-presentation to CD8+ T cells. These results provide insights into the nature of the DNGR-1 ligand and have implications for understanding immune responses to cell-associated antigens and for vaccine design

Antiferromagnetic Ordering and Uncoupled Spins in CaFe₂O₄ Thin Films Probed by Spin Hall Magnetoresistance

CaFe2O4 is a uniaxial antiferromagnet displaying two coexisting magnetic orderings, A and B, characterized by ↑↑↓↓ and ↑↓↑↓ spin modulation, respectively, and the emergence of a net magnetization in a limited temperature range, which is not yet understood. The spin Hall magnetoresistance (SMR) is probed at the interface between Pt and CaFe2O4 and the crystallographic domain structure of thin film samples is exploited to perform single- and multi-domain scale measurements. The SMR response, upon rotating the magnetic field along three orthogonal planes, shows little effect of the strong magnetocrystalline and shape anisotropies. Together with the response to a varying magnetic field strength, the modulations in the SMR signal allow to extract two contributions: one corresponds to the long-range antiferromagnetic ordering, supporting a single ground state scenario; while the second contribution originates from uncompensated, non-interacting spins. These are expected to exist at the antiphase boundaries between antiferromagnetic domains. Here, it is shown that these are also uncoupled from the antiferromagnetic ordering. Nonetheless, the long range correlations that emerge in the proximity of the critical antiferromagnetic transition can give rise to ordering of the uncompensated spins and be responsible for the net magnetization observed in this antiferromagnet

Magnetic order of Dy3+ and Fe3+ moments in antiferromagnetic DyFeO3 probed by spin Hall magnetoresistance and spin Seebeck effect

We report on spin Hall magnetoresistance (SMR) and spin Seebeck effect (SSE) in single crystal of the rare-earth antiferromagnet DyFeO$_{3}$ with a thin Pt film contact. The angular shape and symmetry of the SMR at elevated temperatures reflect the antiferromagnetic order of the Fe$^{3+}$ moments as governed by the Zeeman energy, the magnetocrystalline anisotropy and the Dzyaloshinskii-Moriya interaction. We interpret the observed linear dependence of the signal on the magnetic field strength as evidence for field-induced order of the Dy$^{3+}$ moments up to room temperature. At and below the Morin temperature of 50$\,$K, the SMR monitors the spin-reorientation phase transition of Fe$^{3+}$ spins. Below 23$\,$K, additional features emerge that persist below 4$\,$K, the ordering temperature of the Dy$^{3+}$ magnetic sublattice. We conclude that the combination of SMR and SSE is a simple and efficient tool to study spin reorientation phase transitions and sublattice magnetizations

VE-cadherin and claudin-5: it takes two to tango

Endothelial barrier function requires the adhesive activity of VE-cadherin and claudin-5, which are key components of adherens and tight endothelial junctions, respectively. Emerging evidence suggests that VE-cadherin controls claudin-5 expression by preventing the nuclear accumulation of FoxO1 and -catenin, which repress the claudin-5 promoter. This indicates that a crosstalk mechanism operates between these junctional structures