Antiparallel Directions Research Articles

Stress Engineering of Magnetization Fluctuation and Noise Spectra in Low-Barrier Nanomagnets Used as Analog and Binary Stochastic Neurons.

A single-domain nanomagnet, shaped like a thin elliptical disk with small eccentricity, has a double-well potential profile with two degenerate energy minima separated by a small barrier of a few kT (k = Boltzmann constant and T = absolute temperature). The two minima correspond to the magnetization pointing along the two mutually anti-parallel directions along the major axis of the ellipse. At room temperature, the magnetization fluctuates randomly between the two minima, mimicking telegraph noise. This makes the nanomagnet act as a "binary" stochastic neuron (BSN) with the neuronal state encoded in the magnetization orientation. If the nanomagnet is magnetostrictive, then the barrier can be depressed further by applying (electrically generated) uniaxial stress along the ellipse's major axis, thereby gradually eroding the double-well shape. When the barrier almost vanishes, the magnetization begins to randomly assume any arbitrary orientation (not just along the major axis), making the nanomagnet act as an "analog" stochastic neuron (ASN). The magnetization fluctuation then begins to increasingly resemble white noise. The full width at half maximum (FWHM) of the noise auto-correlation function decreases with increasing stress, as the fluctuation gradually transforms from telegraph noise to white noise. Consistent with this trend, the noise spectral density exhibits a 1/fβ spectrum (at high frequencies) with β decreasing from 2.00 to 1.88 with increasing stress. Stress can thus not only reconfigure a BSN to an ASN, which has its own applications, but it can also perform "noise engineering", i.e., tune the auto-correlation function and power spectral density, having applications in signal processing.

Enhancing the magnetic field gradient between two superconductors with rotational motion under a background DC field

The ability of bulk high-temperature superconductors to trap magnetic flux densities up to one order of magnitude larger than the saturation magnetization of conventional ferromagnetic materials offers the prospect of generating large magnetic flux density gradients. Combining multiple superconductors, akin to assembling a Halbach array of permanent magnets, may increase the generated gradient even further. The associated challenge is that superconductors are prone to demagnetization when exposed to field components perpendicular to their main magnetization direction. In the present work, we investigate the magnetic flux density gradient achieved with a pair of cubic, bulk, large-grain melt-textured superconductors in the presence of a background DC magnetic field at 77 K. We investigate the increase of the performance when decreasing the temperature down to 59 K. The studied configuration consists in two facing cubic YBa2Cu3O 7−x superconductors of 6 mm side with anti-parallel magnetization directions. It is obtained after the simultaneous magnetization of the samples followed by a rotation of 180∘ of the top superconductor. Although the background field reduces the trapped field ability of individual samples, it is shown that this phenomenon is significantly mitigated at 65 K and at 59 K compared to 77 K. The results reveal that a sample-to-sample distance ( ∼16 mm) of the order of their size is sufficient to avoid any mutual demagnetization effect during the rotational motion. Furthermore, it is shown that decreasing the temperature is not only beneficial in increasing the field and field gradient achieved but also in extending the range of background fields in which the superconductor can be rotated without demagnetization. This superconducting assembly yields a magnetic flux density gradient exceeding that of an isolated superconductor and has the potential to surpass the capabilities of permanent magnets.

Fully logical NOT operation of self-aligned liquid crystal optical control devices with two-slit Young’s interference experiment

ABSTRACT Liquid crystal devices have been in practical use for more than half a century and are now widely used as low-voltage, low-power-consumption displays and optical elements. We have confirmed the partial NOT logic operation of some optical interference peaks in two-slit Young’s interference experiments using a liquid crystal device with a self-aligned structure. In this report, we report that we were able to obtain a fully NOT logic operation of the entire optical interference pattern by investigating the liquid crystal alignment of antiparallel direction.

Unraveling the Mechanical Property Decrease of Electrospun Spider Silk: A Molecular Dynamics Simulation Study.

This study investigated the impact of electric fields on Nephila clavipes spider silk using molecular dynamics modeling. Electric fields with varying amplitudes and directions were observed to disrupt the β sheet structure of spider silk and reduce its mechanical properties. However, a notable exception was observed when a 0.1 V/nm electric field was applied in the antiparallel direction, resulting in improvements in Young's modulus and ultimate tensile strength. The antiparallel direction was observed to be particularly sensitive to electric fields, causing disruptions in beta sheets and hydrogen bonds, which significantly influence the mechanical properties. This study demonstrates that spider silk maintains its structural integrity at 0.1 V/nm. Possibly, lowering the power levels of typical electrospinning machines can prevent secondary structural disruption. These findings provide valuable insights for enhancing silk fiber production and applications using natural silk proteins while shedding light on the impact of electric fields on other silk proteins. Finally, this study opens up possibilities for optimizing electrospinning processes to enhance performance in various silk electrospinning applications.

Quantifying collective motion patterns in mesenchymal cell populations using topological data analysis and agent-based modeling

Fibroblasts in a confluent monolayer are known to adopt elongated morphologies in which cells are oriented parallel to their neighbors. We collected and analyzed new microscopy movies to show that confluent fibroblasts are motile and that neighboring cells often move in anti-parallel directions in a collective motion phenomenon we refer to as “fluidization” of the cell population. We used machine learning to perform cell tracking for each movie and then leveraged topological data analysis (TDA) to show that time-varying point-clouds generated by the tracks contain significant topological information content that is driven by fluidization, i.e., the anti-parallel movement of individual neighboring cells and neighboring groups of cells over long distances. We then utilized the TDA summaries extracted from each movie to perform Bayesian parameter estimation for the D’Orsgona model, an agent-based model (ABM) known to produce a wide array of different patterns, including patterns that are qualitatively similar to fluidization. Although the D’Orsgona ABM is a phenomenological model that only describes inter-cellular attraction and repulsion, the estimated region of D’Orsogna model parameter space was consistent across all movies, suggesting that a specific level of inter-cellular repulsion force at close range may be a mechanism that helps drive fluidization patterns in confluent mesenchymal cell populations.

Anomalous Laser-Fluence Dependence of Electron Spin Excitation in CdS Colloidal Quantum Dots: Surface Effects.

Electron spin dynamics in CdS quantum dots (QDs) with hole acceptor 1-octanethiol organic molecules are investigated by time-resolved ellipticity spectroscopy. An anomalous dependence of laser fluences on electron spin excitation for the first time is reported. Increasing the laser fluence, the electron spin is switched from one direction to an antiparallel direction (spin direction switching, SDS) when adding enough 1-octanethiol hole acceptors in an air atmosphere. The analysis shows that the electron spin direction changes from heavy hole excitation defined to spin-orbit split hole excitation defined. In as-grown CdS QDs with native ligands, laser-fluence-dependent SDS phenomena are absent. Electron wave function spread into 1-octanethiol molecules is demonstrated to be important for the presence of SDS phenomena. The finding here thus reveals the importance of surface conditions on electron spin excitation processes in semiconductor QDs and that the surface can be used as an important factor to manipulate the spin.

Suprathermal Ions Observed Inside a Magnetic Flux Rope in the Earth's Magnetotail

AbstractSuprathermal ions have not been observed inside magnetic flux ropes, although energetic electrons have been extensively detected and were thought to be accelerated inside magnetic flux ropes. In this paper, we present the first observation of the suprathermal ions inside a magnetic flux rope in the Earth's magnetotail with a spatial‐scale of tens of ion inertial length. This flux rope was propagating earthward, and its leading part was substantially compressed while its trailing part was significantly stretched. The suprathermal ions can be detected inside the whole flux rope and displayed distinct pitch angle distributions between its leading and trailing parts. In the leading part, the ion fluxes were enhanced primarily in the direction perpendicular to the magnetic field in the all measured energy range, while the ion fluxes increased in the parallel and antiparallel directions in the trailing parts. A large flow vortex was observed immediately behind the flux rope, consistent with Kármán vortex street. The observation suggested that a flux rope even with a large scale can still be highly dynamic, and the charged particles can be significantly accelerated during the flux rope evolution in magnetic reconnection.

Control of high-harmonic generation from periodic asymmetric lattices

Periodic asymmetric lattices, viewed from one side to the other, have different spatial potential energies. This difference affects the electronic structure of valence electrons. Our work shows that pronounced even harmonic signals are observed from periodic asymmetric lattices driven by a multi-cycle pulse field. The phases of the odd and even harmonics driven by parallel and anti-parallel laser polarization directions are compared and show different dependences on laser polarization direction. Moreover, it is found that each burst in the synthesized attosecond pulse trains in a periodic asymmetric lattice shows the same carrier-envelope phase. We also show that the even-order harmonic efficiency in periodic asymmetric lattices can be enhanced (reduced) by using a multi-cycle driving laser in the presence of a weak terahertz pulse field.

Energy computation and multiplier-less implementation of the two-dimensional FitzHugh-Nagumo (FHN) neural circuit.

In this work, with the aim of reducing the cost of the implementation of the traditional 2D FHN neuron circuit, a pair of diodes connected in an anti-parallel direction is used to replace the usual cubic nonlinearity (implemented with two multipliers). Based on the stability of the model, the generation of self-excited firing patterns is justified. Making use of the famous Helmholtz theorem, a Hamilton function is provided for the estimation of the energy released during each electrical activity of the model. From the investigation of the 1D evolution of the maxima of the membrane potential of the model, it was recorded that the considered model is able to experience a period of doubling bifurcation followed by a crisis that enables the increasing of the volume of the attractor. This contribution ends with the realization of a neural circuit without analog multipliers for the validation of the obtained results.

The values of the Dedekind–Rademacher cocycle at real multiplication points

The values of the Dedekind–Rademacher cocycle at certain real quadratic arguments are shown to be global p-units in the narrow Hilbert class field of the associated real quadratic field, as predicted by the conjectures of Darmon–Dasgupta (2006) and Darmon–Vonk (2021). The strategy for proving this result combines the approach of prior work of the authors (2021) with one crucial extra ingredient: the study of infinitesimal deformations of irregular Hilbert Eisenstein series of weight 1 in the anti-parallel direction.

MAVEN Observations of Whistler-mode Waves Within the Magnetic Dips in the Martian Ionopause/Ionosphere

Whistler-mode waves are natural and common electromagnetic emissions observed both surrounding planets and their moons with and without intrinsic magnetic field. Numerous observations have shown that the magnetic dip is a favorable region for the whistler-mode wave generation in the Earth’s magnetosphere. However, up to now, seldom observations of these waves have been reported in such regions at Mars. Based on the measurements from Mars Atmosphere and Volatile EvolutioN mission, quasi-parallel propagating whistler-mode waves are observed within magnetic dip structures in the Martian ionopause and ionosphere. Correspondingly, significant electron beams in the antiparallel direction are observed, and a linear instability analysis shows that f pe/f ce becomes extremely large (∼1500) inside the magnetic dip. Thus, the electron minimum resonant energy of whistler-mode waves decreases to several eV, which increases the number density of resonant beam electrons. Such beam electron distribution results in the necessary free energy for the whistler-mode wave growth. Our study indicates magnetic dips may be favorable regions for the whistler-mode wave excitation even in the Martian ionosphere, which has an extremely high f pe/f ce but does not have a global intrinsic magnetic field.

In situ investigation of the mechanism of propagation of Portevin-Le Chatelier deformation bands

Based on the analysis of high-speed video data of propagating deformation bands in an aluminum-magnesium alloy, it was found that the movable deformation band contains an excess of dislocations of one mechanical sign, and the main mechanism for the propagation of the localized plastic deformation front along the sample axis is a relay transmission of sliding in the antiparallel direction to relax the bending moment created by the primary deformation band. It is shown that the "instantaneous" rate of plastic deformation during ~1 ms in the growing band reaches a value of ~103 s-1, comparable to the rate of deformation during shock tests. Keywords: intermittent deformation, vocalization, dislocations, mechanical charge, aluminum-magnesium alloy.

Vortex lattices in binary Bose–Einstein condensates: collective modes, quantum fluctuations, and intercomponent entanglement

We study binary Bose–Einstein condensates subject to synthetic magnetic fields in mutually parallel or antiparallel directions. Within the mean-field theory, the two types of fields have been shown to give the same vortex-lattice phase diagram. We develop an improved effective field theory to study properties of collective modes and ground-state intercomponent entanglement. Here, we point out the need to introduce renormalized coupling constants for coarse-grained densities. We show that the low-energy excitation spectra for the two types of fields are related to each other by suitable rescaling with the renormalized coupling constants. By calculating the entanglement entropy, we find that for an intercomponent repulsion (attraction), the two components are more strongly entangled in the case of parallel (antiparallel) fields, in qualitative agreement with recent studies for a quantum (spin) Hall regime. We also find that the entanglement spectrum exhibits an anomalous square-root dispersion relation, which leads to a subleading logarithmic term in the entanglement entropy. All of these are confirmed by numerical calculations based on the Bogoliubov theory with the lowest-Landau-level approximation. Finally, we investigate the effects of quantum fluctuations on the phase diagrams by calculating the correction to the ground-state energy due to zero-point fluctuations in the Bogoliubov theory. We find that the boundaries between rhombic-, square-, and rectangular-lattice phases shift appreciably with a decrease in the filling factor.

Synthesis and characterization of hard magnetic soft hydrogels

A unique approach to synthesize novel hard magnetic soft hydrogels with higher water content is proposed. The hard magnetic soft hydrogel contains cross-linked macromolecules of gelatin and water with embedded strontium hexaferrite (SFO) particles. First, SFO nanoparticles are synthesized using the auto-combustion method. Subsequently, the particles prepared are added to the hydrogels with three different weight fractions. The hydrogels are subjected to mechanical and magnetic loadings to investigate the mechanical, and actuation behavior, respectively. In addition, the hydrogels are also subjected to cyclic magnetic loading in transverse and antiparallel directions. Based on the experiments, it is observed that the deflections of the hydrogels can be controlled remotely by varying magnetic fields. Moreover, this study can be utilized to design a hydrogel beam with variable particle concentrations that can form complex shapes.

H+ Pitch Angle Distributions in the Outer Magnetosphere Observed by MMS HPCA

AbstractWe analyze 3 years of 1 eV–40 keV H+ pitch angle distributions (PADs) near the magnetic equatorial plane, observed by the Magnetospheric Multiscale (MMS) Hot Plasma Composition Analyzer (HPCA). Our analysis includes an energy correction to shift ion energy upward by an amount equal to the spacecraft potential. We find asymmetric distributions for cold (<10 eV) and warm (10–100 eV) H+ ions coming preferentially from the northern hemisphere (NH) over those from the southern hemisphere (SH). Specifically, the average phase space density (PSD) in the antiparallel direction (pitch angle above 135°) is about 1.7 times higher than in the parallel direction (below 45°) for H+ with energy <100 eV on the dawn side (MLT: 3–9 hr) for all L shells. To understand the cause of this NH‐SH asymmetry, we sort the distributions by Interplanetary Magnetic Field (IMF) direction and dipole tilt angle. Sorting by IMF direction shows that PSDs in the antiparallel direction are higher than in the parallel direction when IMF By is dawnward (By < 0). The outflow of cold H+ from the NH is higher when the dipole tilt angle is positive (μ > 10°). In contrast, when the dipole tilt is negative (μ < −10°), the outflow of cold H+ from the SH is not significantly higher and PADs can have either symmetric or asymmetric favoring from NH. These results suggest there may be general interhemispheric asymmetry of ion outflow that favors the NH.

Tuning Ferroelectric Response of Electroactive Materials by Controlling Multilayered Structures to Achieve Excellent Energy Storage Performance

Flexible ferroelectric polymers are key candidates for flexible capacitive electronic devices. However, there is a lack of functional and accessible methods to control the ferroelectric response of polymers. Herein, a novel and effective approach is adopted to tune the ferroelectric response of polymers, over the conventional methods (graft or block copolymerization). Specifically, a central ferroelectric poly(vinylidene fluoride‐co‐trifluoroethylene) (P(VDF‐TrFE)) layer is sandwiched between shielding layers (polymethacrylate (PMMA)). The differently distributed electric fields were generated in inner and outer layers owing to a larger polarization gradient between PMMA and P(VDF‐TrFE), building a competition in the local ferroelectric layer. Controlling the polarization and thickness of the shielding layer may result in the electric field in it being lesser than the electric field in the ferroelectric layer during reverse poling, leading to a part of the dipoles reverting to the initial direction in the ferroelectric layer. Then dipoles along antiparallel directions coexist in P(VDF‐TrFE), leading to antiferroelectric‐like behavior. With the low remnant polarization, antiferroelectric‐like films possess an excellent discharge energy density (11.72 J cm−3 at 3300 kV cm−1). Given the practicability and simplicity of tuning the ferroelectric response, it is firmly believed that this method will cut a conspicuous figure in a supercapacitor with ultrahigh energy density and discharged efficiency.

Flux Enhancements of Field‐Aligned Low‐Energy O+ Ion (FALEO) in the Inner Magnetosphere: A Possible Source of Warm Plasma Cloak and Oxygen Torus

AbstractFlux enhancements of field‐aligned low‐energy O+ ion (FALEO) are simultaneously observed by Arase, Van Allen Probes A and B in the nightside inner magnetosphere during 05–07 UT on September 22, 2018. FALEOs appear after a magnetic dipolarization signature with approximately 6–20 min delay. It has the energy‐dispersion signature from a few keV to ∼100 eV only in the direction parallel to the magnetic field at Arase, while it decreases its energy from a few keV down to 10 eV in both the parallel and antiparallel directions at Probes A and B. We perform a numerical simulation to trace trajectories of test O+ ions in a model magnetosphere, which are launched from above the ionosphere 3–15 min after a substorm. Flying virtual satellites that have the same orbits as the real satellites, we create virtual energy‐time spectrograms of O+ ions to compare with the observed ones. Results show a very good correspondence between them, indicating that FALEOs originate from ionospheric O+ ions that are extracted from the upper ionosphere at substorm onset and flow along the magnetic field toward the geomagnetic equator. It is also revealed that 3–9 hr after their launch, test O+ ions less than 400 eV have a spatial distribution in the inner magnetosphere which is similar to those of the warm plasma cloak and the oxygen torus. We therefore conclude that FALEO is a source of those cold ion populations.

A Case Study of the Induced Magnetosphere Boundary at the Martian Subsolar Region

Abstract One Martian induced magnetosphere boundary (IMB) crossing at the subsolar region is analyzed here with multiple instruments on board MAVEN. Properties of the magnetic field and particles around the IMB are evaluated. We find different trends of variation in magnetic field components at the two sides of an interface coincident with the previously defined ion composition boundary. This case shows the IMB at the Martian dayside could be divided into three parts: two regions (denoted as R1 and R2), with different field and plasma properties, and an interface between them. Currents found in R1 and R2 are flowing in antiparallel, and the current density in R2 (at lower altitude) is significantly larger than that in R1 (at higher altitude). Results indicate the interaction between Mars and the solar wind could induce strong currents in the IMB, which are with antiparallel current directions and separated by an interface where the ion composition changes. This could be a typical feature that occurred during the interaction between the solar wind and the nonmagnetized planets.

Observations of kinetic Alfvén waves and associated electron acceleration in the plasma sheet boundary layer

Kinetic Alfvén waves (KAWs), with a strong parallel disturbed electric field, play an important role in the energy transport and particle acceleration in the magnetotail. Based on the high-resolution observations of the Magnetospheric Multiscale (MMS) mission, we present the detailed acceleration process of electrons by KAWs in the plasma sheet boundary layer (PSBL). MMS observed strong electromagnetic disturbances carrying parallel disturbed electric field with an amplitude up to 8 mV/m. The measured ratio of the electric to magnetic field perturbations is larger than the local Alfvén speed and enhances as the frequency increases, in consistent with the theoretical predictions for KAWs. These evidences indicate that the electromagnetic disturbances should be identified as KAWs. During the KAWs, the energy flux of electrons at energies above 1 keV in the parallel and anti-parallel direction significantly enhance, implying occurrences of electron beams at higher energies. Meanwhile, the KAWs become more electrostatic-like and filled with high frequency ion acoustic waves. The energy enhancement of electron beams accords to the derived work done by the observed parallel disturbed electric field of KAWs, indicating electron acceleration caused by KAWs. Therefore, the paper provides a direct evidence of electron acceleration by KAWs embodying electrostatic ion acoustic waves in the PSBL.

Friction and wear behaviour of additively manufactured continuous carbon fibre reinforced PA6 composites

In the present work, continuous carbon fibre (CCF) reinforced polyamide 6 (PA6) composites were fabricated using the Fused Filament Fabrication (FFF) 3D printing technique. The sliding friction and wear behaviour of the printed CCF/PA6 composites was investigated as a function of varying fibre orientations (i.e. normal, parallel, and anti-parallel) and layer deposition directions (i.e. parallel and perpendicular) with respect to the sliding direction. It emerged that fibre orientation played a key role in determining the wear resistance of 3D printed composites. Severe fibre breakage was observed when the orientation of fibre was in normal direction against the sliding direction, associated with a higher wear rate than that obtained in parallel or anti-parallel direction. To better understand the effects of voids on wear mechanism, tribo-tests were further carried out with the specimens that underwent compression moulding (CM) post-treatment process. The results confirmed that the internal defects could cause adverse impacts on wear performance, depending on the fibre orientations. In particular, it was found that fibre distribution, as well as the fibre/matrix interface within the filament, was the crucial parameter affecting the overall tribological performance of the printed structures. The findings add to our understanding of designing and fabricating wear-resistant polymer composites using 3D printing technologies.