Motion Of Core Research Articles

Motion detection: cells, circuits and algorithms

Abstract Many animals use visual motion cues to inform different behaviors. The basis for motion detection is the comparison of light signals over space and time. How a nervous system performs such spatiotemporal correlations has long been considered a paradigmatic neural computation. Here, we will first describe classical models of motion detection and introduce core motion detecting circuits in Drosophila. Direct measurements of the response properties of the first direction-selective cells in the Drosophila visual system have revealed new insights about the implementation of motion detection algorithms. Recent data suggest a combination of two mechanisms, a nonlinear enhancement of signals moving into the preferred direction, as well as a suppression of signals moving into the opposite direction. These findings as well as a functional analysis of the circuit components have shown that the microcircuits that process elementary motion are more complex than anticipated. Building on this, we have the opportunity to understand detailed properties of elementary, yet intricate microcircuits.

Quantitative imaging of carbon dimer precursor for nanomaterial synthesis in the carbon arc

Delineating the dominant processes responsible for nanomaterial synthesis in a plasma environment requires measurements of the precursor species contributing to the growth of nanostructures. We performed comprehensive measurements of spatial and temporal profiles of carbon dimers (C2) in sub-atmospheric-pressure carbon arc by laser-induced fluorescence. Measured spatial profiles of C2 coincide with the growth region of carbon nanotubes (Fang et al 2016 Carbon 107 273–80) and vary depending on the arc operation mode, which is determined by the discharge current and the ablation rate of the graphite anode. The C2 density profile exhibits large spatial and time variations due to motion of the arc core. A comparison of the experimental data with the 2D simulation results of self-consistent arc modeling shows good agreement. The model predicts well the main processes determining spatial profiles of carbon dimers (C2).

Size dependence of vortex-type spin torque oscillation in a Co2Fe0.4Mn0.6Si Heusler alloy disk

This paper reports the systematic investigation of vortex-type spin torque oscillation in circular disks of highly spin-polarized Co2Fe0.4Mn0.6Si (CFMS) Heusler alloys. We fabricated the current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) devices with various disk diameters (D) using the layer stack of CFMS/Ag3Mg/CFMS. The gyrotropic motion of the vortex core was successfully excited for the CFMS circular disks with 0.2 µm ⩽ D ⩽ 0.3 µm. The CPP-GMR device with D = 0.2 µm exhibited the Q factor of more than 5000 and the large output power of 0.4 nW owing to the high coherency of vortex dynamics and the high spin-polarization of CFMS. However, the Q factor was remarkably decreased as D was reduced from 0.2 µm to 0.14 µm. The comparison with the calculated resonance frequencies suggested that this degradation of the Q factor was due to the transition of the oscillation mode from the vortex mode to other modes such as the low-coherent out-of-plane precession mode. The present experimental results also suggest that there exists an adequate disk size for the enhanced Q factor of the vortex-type spin torque oscillation.

Aldehyde group driven aggregation-induced enhanced emission in naphthalimides and its application for ultradetection of hydrazine on multiple platforms.

Restriction of intramolecular motion (RIM) of rigid aromatic cores is the most universal mechanism so far that can successfully explain almost all AIE/AIEEgenic systems. By designing two novel naphthalimide derivatives (NIB and NIBD), we experimentally demonstrated the effect of a single formyl group that can efficiently transform an aggregation caused quenching (ACQ) system (NIB) into an AIEEgenic system (NIBD) by strengthening the RIM process. Besides, the newly designed naphthalimide AIEEgen (NIBD) accomplished ultrasensitive detection of hydrazine at the parts per trillion level (LOD/81 ppt) in aqueous media with high selectivity and enormous improvement over the existing state of the art. An exceptional sensitivity is also achieved in the vapor phase (LOD/0.003%) using a Whatman paper strip based portable device for simple and cost-effective on-site detection. The detection mechanism involved a reaction-based spontaneous formation of a non-fluorescent hydrazone Schiff base derivative (NIBDH). The in vitro potentiality of the AIEEgenic probe was also demonstrated in two mammalian cell lines i.e. HeLa (human cervical cancer cell line) and HEK293T (Human embryonic kidney cell line that expresses a mutant version of the SV40 large T antigen). Owing to the highly selective formation of the hydrazone Schiff base complex with hydrazine, NIBD responds to the existence of hydrazine in both these cell lines without any interference from other biologically rich metal ions and amino acids. These outcomes could initiate a much wider use of formyl group induced condensed state emission and a key hypothesis that could generate newer avenues for ACQ to AIEE transformations for several practical applications including hydrazone Schiff base complexation for probing and manipulating hydrazine biology associated with several metabolic activities.

Nutation-like-mode excitation of coupled vortex cores in magnetic spherical shells

We performed micromagnetic numerical calculations to explore the novel dynamics of two vortex cores magnetically coupled via long-range dipolar interactions and short-range exchange interactions in a single element of spherical nano-shells. One vortex core is located in the upper half-shell and the other in the lower half-shell. Under a given static magnetic field, they show unique coupled dynamic motions that have yet to be reported so far. For the parallel core orientations, they show slow and large-amplitude orbital motions around the static field direction, and both cores' positions on the surface are out-of-phase with each other. This motion resembles the precession motion of a single vortex core around the static magnetic field direction in a nanosphere. In addition to such a precession-like motion, each core simultaneously shows relatively fast and small-amplitude gyration-like motions that move along with the precession-like motion. The superposition of the two distinct dynamic modes results in an overall nutation-like motion as observed in other non-linear systems such as gyroscopes and geodynamics. For the anti-parallel configuration of both cores, further complex fast decaying, irregular motions are shown, because their opposite core orientations show an almost null surface-normal component of the average magnetization of both cores as well as the opposite rotational senses of their gyration motions. This work provides not only a further understanding of dynamic-coupled motions of magnetic vortices in 3D nano-structures but also an efficient way to utilize nano-spherical shells in other possible applications related to novel dynamic-modes excitation.

Spiral wave chimera states in large populations of coupled chemical oscillators

The coexistence of coherent and incoherent dynamics in a population of identically coupled oscillators is known as a chimera state 1,2 . Discovered in 2002 3 , this counterintuitive dynamical behaviour has inspired extensive theoretical and experimental activity 4–15 . The spiral wave chimera is a particularly remarkable chimera state, in which an ordered spiral wave rotates around a core consisting of asynchronous oscillators. Spiral wave chimeras were theoretically predicted in 2004 16 and numerically studied in a variety of systems 17–23 . Here, we report their experimental verification using large populations of nonlocally coupled Belousov–Zhabotinsky chemical oscillators 10,18 in a two-dimensional array. We characterize previously unreported spatiotemporal dynamics, including erratic motion of the asynchronous spiral core, growth and splitting of the cores, as well as the transition from the chimera state to disordered behaviour. Spiral wave chimeras are likely to occur in other systems with long-range interactions, such as cortical tissues 24 , cilia carpets 25 , SQUID metamaterials 26 and arrays of optomechanical oscillators 9 . A spiral chimera state, composed by an ordered spiral surrounding a core of asynchronous oscillators, is revealed in a large grid of chemical oscillators.

Dynamically controlled energy dissipation for fast magnetic vortex switching

Manipulation of vortex states in magnetic media provides new routes towards information storage and processing technology. The typical slow relaxation times (∼100 ns) of magnetic vortex dynamics may present an obstacle to the realization of these applications. Here, we investigate how a vortex state in a ferromagnetic microdisk can be manipulated in a way that translates the vortex core while enhancing energy dissipation to rapidly damp the vortex dynamics. We use time-resolved differential magneto-optical Kerr effect microscopy to measure the motion of the vortex core in response to applied magnetic fields. We first map out how the vortex core becomes sequentially trapped by pinning sites as it translates across the disk. After applying a fast magnetic field step to translate the vortex from one pinning site to another, we observe long-lived dynamics of the vortex as it settles to the new equilibrium. We then demonstrate how the addition of a short (<10 ns) magnetic field pulse can induce additional energy dissipation, strongly damping the long-lived dynamics. A model of the vortex dynamics using the Thiele equation of motion explains the mechanism behind this effect.

Dynamics of the inner core wobble under mantle‐inner core gravitational interactions

AbstractWe investigate the dynamics of the inner core wobble (ICW), the Euler‐Liouville wobbling motion of the Earth's solid inner core, under the mantle‐inner core gravitational (MICG) torques within the Earth. Chao (2016) derived the full 3‐D equation of motion for the MICG dynamics in terms of the spherical‐harmonic multipoles of mass density and focused on the axial component for inner core's torsional libration. Here aiming for the ICW, we deduce the 2‐D equatorial component of the MICG torque owing to the oblateness of the mantle and the inner core. The period of the free Eulerian wobble of a hypothetical isolated rigid inner core would be a prograde +414 days. The action of the added MICG equatorial torque is found to be (negatively) strong enough to render the wobbling motion to become retrograde (with a negative frequency), which is further but slightly modified by the elastic yielding feedback of the inner core. Imposing yet further the passive effect of the hydrostatic pressure due to the fluid outer core greatly lengthens the natural period to become decadal. The final estimate of the ICW natural period in accordance with the (seismological) PREM Earth model is a retrograde PICW ≈ −15.6 years, in contrast to a prograde +6.6 years supposed in the literature. The corresponding spring constant (per radian of wobble) is 5.5 × 1022 N m. Our results instigate likely identification of the ICW with decadal wobbles observed in the Earth's polar motion.

Zero-Bias-Field Spin Torque Induced Oscillation of a Vortex Core in a Magnetic Junction Nano-Pillar with High Magnetoresistance Ratio

Spin torque induced dynamics of a vortex core in a magnetic junction nano-pillar is studied by paying special attention to the effect of the in-plane current due to the spatial variation of magnetization. We calculated the motion of the vortex core and the current distribution simultaneously. The current has a considerable in-plane component within the magnetic junction nano-pillar with a high magnetoresistance ratio, and the stable rotational motion of the vortex core is caused by a spin transfer torque from the in-plane current without a bias field when the magnetoresistance ratio is over 180%. It is shown that the zero-bias-field oscillation of the vortex core can be maintained if the magnetoresistance ratio and strength of the in-plane current exceed a certain critical value.

Reduced Transition Probabilities for the Gamma Decay of the 7.8eV Isomer in ^{229}Th.

The reduced magnetic dipole and electric quadrupole transition probabilities for the radiative decay of the ^{229}Th 7.8 eV isomer to the ground state are predicted within a detailed nuclear-structure model approach. We show that the presence and decay of this isomer can only be accounted for by the Coriolis mixing emerging from a remarkably fine interplay between the coherent quadrupole-octupole motion of the nuclear core and the single-nucleon motion within a reflection-asymmetric deformed potential. We find that the magnetic dipole transition probability which determines the radiative lifetime of the isomer is considerably smaller than presently estimated. The so-far disregarded electric quadrupole component may have non-negligible contributions to the internal conversion channel. These findings support new directions in the experimental search of the ^{229}Th transition frequency for the development of a future nuclear frequency standard.

Motion and Switching of Dual-Vortex Cores in Elliptical Permalloy Nanodisk Stimulated by a Gaussian Magnetic Field Pulse

Magnetic nanostructures have potential applications in ultrahigh-density magnetic storage. In this paper, the dynamics of the dual magnetic vortices in elliptical Permalloy nanodisk are investigated using micromagnetic modeling. Under the stimulation of the short-axis ( $y$ -axis) Gaussian field pulse and long-axis ( $x$ -axis) constant field, the equilibrium positions of dual-vortex cores can be driven away from the initial positions. The displacement in the $y$ -direction is proportional to the magnitude of the $x$ -axis constant field. The displacement in the $x$ -direction exhibit periodic reliance on the pulsewidth of the $y$ -axis Gaussian field pulse. The threshold value of pulse strength for dual-vortex motion increases with the magnitude of the $x$ -axis constant field. The mechanism of polarity and chirality switching in dual-vortex cores are studied through analyzing the trajectories of vortex cores in the annihilation and nucleation processes. The switching of polarity exhibits an oscillatory dependence on the pulsewidth and strength. The minimum pulse strength required for chirality switching is 120 mT, while the corresponding pulsewidth is influenced by the $x$ -axis constant field. This paper provides insights on the magnetization dynamics of nanostructures containing dual vortices subject to external excitations.

Topoisomerase Poison Disturbs Relaxation of Mechanical Stresses During Gating Motion of DNA-Binding Core

Topoisomerase Poison Disturbs Relaxation of Mechanical Stresses During Gating Motion of DNA-Binding Core

Promiscuous Contacts and Heightened Dynamics Increase Thermostability in an Engineered Variant of the Engrailed Homeodomain

The Engrailed Homeodomain (EnHD) is a three-helix-bundle transcription factor that is popular within the protein folding community due to its ultra-fast un/folding kinetics. In 2007, the Mayo group used EnHD as a backbone template for their repacking algorithm and designed UVF as a proof of principle. UVF not only folded as designed but was extremely stable; its Tm is >99°C whereas the Tm of EnHD is 52°C. Here, we present a structural and dynamical explanation for UVF's increased thermostability based on 1 μs of all-atom, explicit-solvent molecular dynamics simulations of the two proteins at room temperature (25°C) and high temperature (100°C). UVF had heightened dynamics at room temperature, relative to EnHD, as measured by Cα motion and interchangeability of side-chain contacts. UVF maintained these dynamics at 100°C whereas EnHD began to unfold. UVF's binary distribution of amino acids, with only hydrophobic residues at buried positions and only hydrophilic residues on the surface, allowed buried residues to move independently from the surface, effectively acting as an entropy sink. Hydrogen bonds and salt bridges between buried and surface residues of EnHD coupled core motion to surface motion, resulting in EnHD denaturing at 100°C. Based on our simulation data, we hypothesize that UVF benefits from more favorable entropy of folding in addition to its rationally designed, more-favorable enthalpy of folding. Future work will investigate this hypothesis experimentally and determine how the heightened dynamics effect native DNA-binding function.

Screw-Dislocation-Induced Strengthening-Toughening Mechanisms in Complex Layered Materials: The Case Study of Tobermorite.

Nanoscale defects such as dislocations have a profound impact on the physics of crystalline materials. Understanding and characterizing the motion of screw dislocation and its corresponding effects on the mechanical properties of complex low-symmetry materials has long been a challenge. Herein, we focus on triclinic tobermorite, as a model system and a crystalline analogue of layered hydrated cement, and report for the first time how the motion of screw dislocation can influence the strengthening-toughening relationship, imparting brittle-to-ductile transitions. By applying shear loading in tobermorite systems with single and dipole screw dislocations, we observe dislocation jogs around the dislocation core, which increases the yield shear stress and the work-of-fracture when the dislocation lines are along the [100] and [010] directions. Our results demonstrate that the dislocation core acts as a bottleneck for the initial straight gliding to induce intralaminar gliding, which consequently leads to a significant improvement in the mechanical properties. Together, the fundamental knowledge gained in this work on the role of the motion of the dislocation core on the mechanical properties provides an improved understanding of deformation mechanisms in cementitious materials and other complex layered systems, providing new hypotheses and design guidelines for the development of strong, ductile, and tough materials.

Vortex motion in amorphous ferrimagnetic thin film elements

Amorphous Fe64Gd36 thin film square elements are investigated by imaging in the Fresnel mode of a transmission electron microscope (TEM). The equilibrium state without an applied field shows the well-known four-domain flux closure pattern with in-plane magnetization. However, the vortex is displaced from the center of the square element and the domain walls are curved. In a reference measurement of a thin Ni81Fe19 element, the vortex core is perfectly centered and the domain walls straight. When an increasing external field is applied in-plane, the vortex core can be moved. While this motion of the vortex core is linear in NiFe elements, in the ferrimagnetic FeGd squares the vortex core moves by sudden jumps. Micromagnetic simulations show that the asymmetry of the domain patterns as well as the vortex core pinning and depinning can be attributed to random anisotropy and a patchy microstructure in amorphous films.

Yolk/Shell Colloidal Crystals Incorporating Movable Cores with Their Motion Controlled by an External Electric Field.

Yolk/shell particles composed of a submicrometer-sized movable core and a silica shell are promising building blocks for novel optical colloidal crystals, because the locations of cores in the shell compartment can be reversibly changed by using external stimuli. Two dimensional arrays of yolk/shell particles incorporating movable cores were prepared by a self-assembly method. The movable cores of colloidal crystals in water could be observed with an optical microscope under application of external electric field. The motions of inner silica cores depended on the electric field strength and frequency and were categorized into three cases: (1) Random Brownian motion, (2) anisotropic motion of cores moving in a direction orthogonal to a field, and (3) suppressed motion fixed in the center of shell compartment. Random Brownian motion of cores was scarcely affected by field strength when a high frequency (in the MHz range) electric field was applied. On the other hand, an increase in field strength at low-frequency fields (kHz) transiently changed the core motion from (1) to (2) and a further increase in field strength changed it from (2) to (3). When the silica core was incorporated in a large void a stronger electric field was needed to suppress its motion than when it was in a small void. The high responsivity to electric fields in a low-frequency range indicated the importance of electric double layer (EDL) interaction between core and inner shell in controlling the core location in yolk/shell colloidal crystals. It was also shown that movable titania cores in yolk/shell particles required a low-frequency field with a high strength to change from the random to anisotropic motion. The result suggested that the electrostatic interaction between EDLs of the silica core and the inner silica wall could be stronger than that between EDLs of the titania core and the silica shell.

Skyrmion dynamics in a chiral magnet driven by periodically varying spin currents*

In this work, we investigated the spin dynamics in a slab of chiral magnets induced by an alternating (ac) spin current. Periodic trajectories of the skyrmion in real space are discovered under the ac current as a result of the Magnus and viscous forces, which originate from the Gilbert damping, the spin transfer torque, and the β-nonadiabatic torque effects. The results are obtained by numerically solving the Landau-Lifshitz-Gilbert equation and can be explained by the Thiele equation characterizing the skyrmion core motion.

Time-resolved imaging of magnetic vortex dynamics using holography with extended reference autocorrelation by linear differential operator.

The magnetisation dynamics of the vortex core and Landau pattern of magnetic thin-film elements has been studied using holography with extended reference autocorrelation by linear differential operator (HERALDO). Here we present the first time-resolved x-ray measurements using this technique and investigate the structure and dynamics of the domain walls after excitation with nanosecond pulsed magnetic fields. It is shown that the average magnetisation of the domain walls has a perpendicular component that can change dynamically depending on the parameters of the pulsed excitation. In particular, we demonstrate the formation of wave bullet-like excitations, which are generated in the domain walls and can propagate inside them during the cyclic motion of the vortex core. Based on numerical simulations we also show that, besides the core, there are four singularities formed at the corners of the pattern. The polarisation of these singularities has a direct relation to the vortex core, and can be switched dynamically by the wave bullets excited with a magnetic pulse of specific parameters. The subsequent dynamics of the Landau pattern is dependent on the particular configuration of the polarisations of the core and the singularities.

Decoherence and radiation-free relaxation in Meissner transmon qubit coupled to Abrikosov vortices

We present a new type of transmon split-junction qubit which can be tuned by Meissner screening currents in the adjacent superconducting film electrodes. The best detected relaxation time ($T_1$) was of the order of 50 $\mu$s and the dephasing time ($T_2$) about 40 $\mu$s. The achieved period of oscillation with magnetic field was much smaller than in usual SQUID-based transmon qubits, thus a strong effective field amplification has been realized. This Meissner qubit allows an efficient coupling to superconducting vortices. We present a quantitative analysis of the radiation-free energy relaxation in qubits coupled to Abrikosov vortices. The observation of coherent quantum oscillations provides strong evidence that vortices can exist in coherent quantum superpositions of different position states. According to our suggested model, the wave function collapse is defined by Caldeira-Leggett dissipation associated with viscous motion of the vortex cores.

Vortex spin-torque oscillator usingCo2FexMn1−xSiHeusler alloys

We show spin-transfer-torque-driven vortex oscillations in current-perpendicular-to-plane giant magnetoresistance junctions using epitaxially grown ${\mathrm{Co}}_{2}{\mathrm{Fe}}_{x}{\mathrm{Mn}}_{1\ensuremath{-}x}\mathrm{Si}$ (CFMS) Heusler alloy thin films. The soft magnetic property and high spin polarization of CFMS enable us to realize vortex oscillation emitting large microwave power with a low threshold current. The output power is maximized for a certain Fe-Mn composition ratio associated with a reduction of the threshold current for the oscillation, which is in agreement with a general model for spin-torque oscillation. Through comparison with an analytical theory that describes the translational motion of a vortex core, we show that the vortex core motion excited in the present device is inhomogeneous along the thickness direction. In spite of the inhomogeneity, the gyration radius at the CFMS/spacer interface region was estimated to be $\ensuremath{\sim}75%$ of the actual ferromagnetic layer radius, which indicates that the CFMS-based all-metallic junction is useful for achieving large-amplitude vortex core motion. This comprehensive investigation would also be useful for designing high-performance all-metallic nano-oscillators based on magnetic vortex dynamics.