Uniform Mode Research Articles

Ion therapy guideline (Version 2020)

Ion therapy guideline (Version 2020)

Wideband and Low-Loss Mode Scrambler for Few-Mode Fibers Based on Distributed Multiple Point-Loads

We propose a new type of all-fiber mode scrambler for mode division multiplexed data transmission based on few mode fibers. By randomly placing multiple point-loads along the fiber length, low loss and wideband mode coupling is obtained amongst all the guided modes. The effect of mode coupling is simulated from a single point-load to multiple point-loads with a specific focus on the insertion loss and wavelength dependence. In an exemplar experimental demonstration we present a mode scrambler for step-index two mode fibers incorporating 150 randomly located point-loads. Uniform mode coupling is achieved over the C band with an insertion loss of less than 1 dB.

Spin waves and high-frequency response in layered superconductors with helical magnetic structure

We evaluate the spin-wave spectrum and dynamic susceptibility in a layered superconductors with helical interlayer magnetic structure. We especially focus on the structure in which the moments rotate 90$^{\circ}$ from layer to layer realized in the iron pnictide RbEuFe$_{4}$As$_{4}$. The spin-wave spectrum in superconductors is strongly renormalized due to the long-range electromagnetic interactions between the oscillating magnetic moments. This leads to strong enhancement of the frequency of the mode coupled with uniform field and this enhancement exists only within a narrow range of the c-axis wave vectors of the order of the inverse London penetration depth. The key feature of materials like RbEuFe$_{4}$As$_{4}$ is that this uniform mode corresponds to the maximum frequency of the spin-wave spectrum with respect to c-axis wave vector. As a consequence, the high-frequency surface resistance acquires a very distinct asymmetric feature spreading between the bare and renormalized frequencies. We also consider excitation of spin waves with Josephson effect in a tunneling contact between helical-magnetic and conventional superconductors and study the interplay between the spin-wave features and geometrical cavity resonances in the current-voltage characteristics.

Phase-resolved electrical detection of hybrid magnonic devices.

We demonstrate the electrical detection of magnon-magnon hybrid dynamics in yttrium iron garnet/permalloy (YIG/Py) thin film bilayer devices. Direct microwave current injection through the conductive Py layer excites the hybrid dynamics consisting of the uniform mode of Py and the first standing spin wave (n = 1) mode of YIG, which are coupled via interfacial exchange. Both the two hybrid modes, with Py or YIG dominated excitations, can be detected via the spin rectification signals from the conductive Py layer, providing phase resolution of the coupled dynamics. The phase characterization is also applied to a nonlocally excited Py device, revealing the additional phase shift due to the perpendicular Oersted field. Our results provide a device platform for exploring hybrid magnonic dynamics and probing their phases, which are crucial for implementing coherent information processing with magnon excitations.

Fundamental limit of single-mode integral-field spectroscopy

There are several high-performance adaptive optics systems that deliver diffraction-limited imaging on ground-based telescopes, which has renewed interest in single-mode fiber (SMF) spectroscopy for exoplanet characterization. However, the fundamental mode of a telescope is not well matched to those of conventional SMFs. With the recent progress in asphere manufacturing techniques, it may be possible to reshape the fundamental mode of a SMF into any arbitrary distribution. An optimization problem is set up to investigate what the optimal mode field distribution is and what the fundamental throughput limit is for SMF spectroscopy. Both single-object spectrographs and integral-field spectrographs are investigated. The optimal mode for single-object spectrographs is found to be the aperture function of the exit pupil; for integral-field spectrographs, the optimal mode depends on the spatial sampling of the focal plane. For dense sampling, a uniform mode is optimal; for sparse sampling, the mode of a conventional SMF is near optimal. With the optimal fiber mode, a high throughput ( > 80 % ) can be achieved when the focal plane is (super) Nyquist sampled. For Nyquist sampled cases, the optimal mode has almost 20% more throughput than a conventional SMF.

Hyperspectral imaging classification based on LBP feature extraction and multimodel ensemble learning

When aiming at hyperspectral classification, spectral characteristics are often considered, while spatial characteristics and information redundancy between spectra are neglected. We propose a method of feature extraction using a uniform local binary pattern and ensemble multiple models to classify features. This model uses a uniform local binary mode to extract the spatial features of hyperspectral images. The spatial features and the spectral features are fused to obtain high-dimensional fusion data, which are input into the sparse representation model for learning, and the residual of the test sample is obtained. At the same time, hyperspectral images have serious information redundancy, so we use the product moment correlation coefficient to reduce the interference between classes of sample information. Finally, through ensemble learning of different classification models, the hyperspectral classification can be accurately predicted. The experimental results on hyperspectral data show that this method can effectively improve the effect of hyperspectral image classification.

Improved uniform phase empirical mode decomposition and its application in machinery fault diagnosis

As an adaptive non-stationary signal decomposition method, empirical mode decomposition (EMD) has a serious mode mixing problem. The uniform phase empirical mode decomposition (UPEMD) was proposed by adding a sinusoidal wave of uniform phase as a masking signal to overcome the shortcomings of EMD. However, the amplitude of added sinusoidal wave lacks adaptability, the mean curve cannot be completely separated from the signal in the iterative sifting process and thus the residual noise will affect the decomposition accuracy. To enhance the performance of UPEMD, in this paper, the improved uniform phase empirical mode decomposition (IUPEMD) method is developed to adaptively select the amplitude of added sinusoidal wave and then choose the optimal result from the iterative sifting of mean curves with different weights according to the index of orthogonality. The simulation signal analysis results show that IUPEMD has better decomposition ability and accuracy than the original UPEMD and ensemble empirical mode decomposition (EEMD). Finally, IUPEMD is applied to the rolling bearing and rotor rubbing fault diagnosis by comparing it with UPEMD, empirical wavelet transform (EWT) and variational mode decomposition (VMD) methods. The results show that IUPEMD can effectively identify the rolling bearing and rotor faults, and have better recognition effect than the comparison methods.

Control of Hybrid Energy Storage System for Hybrid Electric Vehicles using Uniform Continuous Higher Order Sliding Mode Control

The goal of this paper is to control a fully active hybrid energy storage System (HESS) with a battery and super capacitor (SC) by introducing an uniform higher order sliding mode control. The system parameters to be tracked are the battery and SC current. To track the reference values of battery and SC currents, an uniform continuous higher order sliding mode controller (UCHOSMC) is applied which is a combination of two controllers one is an uniform super twisting control for disturbance rejection and other is uniform time convergence for a disturbance free system. Current references to be trackedare generated by a rule-based energy management system, the stability of the system is validated using Lyapunov stability analysis. The simulation results show the robustness of the controller with an effective tracking of the reference values under different load conditions.

Learning of classification tasks with an array of uniform-mode spin Hall nano-oscillators

Recently, a system of spintronic vortex oscillators has been experimentally trained to classify vowel sounds. In this paper, we have carried out a combination of device-level and system-level simulations to train a system of spin Hall nano oscillators (SHNOs) of smaller size (25X lower in area compared to those vortex oscillators) for such data classification tasks. Magnetic moments precess in an uniform mode as opposed to the vortex mode in our oscillators. We have trained our system to classify inputs in various popular machine learning data sets like Fisher’s Iris data set of flowers, Wisconsin Breast Cancer (WBC) data set, and MNIST data set of handwritten digits. We have employed a new technique for input dimensionality reduction here so that the clustering/target synchronization pattern changes based on the nature of the data in the different data sets. Our demonstration of learning in a system of such small SHNOs for a wide range of data sets is promising for scaling up the oscillator-based neuromorphic system for complex data classification tasks.

Puckering and wrinkling in a growing composite ring

Pattern formation driven by differential strain in constrained elastic systems is a common motif in many technological and biological systems. Here we introduce a biologically motivated case of elastic patterning that allows us to explore the conditions for the existence of local puckering and global wrinkling patterns: a soft growing composite ring adhered elastically to a constraining rigid ring. We explore how differential growth of the soft ring and the elastic resistance to shear and stretching deformations induced by soft adherence lead to a range of phenomena that include uniform aperture-like modes, localized puckers that are Nambu–Goldstone-like modes and global wrinkles in the system. Our analysis combines computer simulations of a discrete rod model with a nonlinear stability analysis of the differential equations in the continuum limit. We provide phase diagrams and scaling relations that reveal the nature and extent of the deformation patterns. Overall, our study reveals how geometry and mechanics conspire to yield a rich phenomenology that could serve as a guide to the design of programmable localized elastic deformations while being relevant for the mechanical basis of biological morphogenesis.

Strong magnon–magnon coupling in synthetic antiferromagnets

A synthetic antiferromagnet, composed of two ferromagnetic layers separated by a non-magnetic layer, possesses two uniform precession resonance modes: in-phase acoustic mode and out-of-phase optic mode. In this work, we theoretically and numerically demonstrated the strong coupling between acoustic and optic magnon modes. The strong coupling is attributed to the symmetry breaking of the system, which can be realized by tilting the bias field or constructing an asymmetrical synthetic antiferromagnet. It is found that the coupling strength can be highly adjusted by tuning the tilting angle of bias field, the magnitude of antiferromagnetic interlayer exchange coupling, and the thicknesses of ferromagnetic layers. Furthermore, the coupling between acoustic and optic magnon modes can even reach the ultrastrong coupling regime. Our findings show high promise for investigating the quantum phenomenon with a magnonic platform.

The discharge selectivity in an atmospheric pressure helium–argon dielectric barrier discharge

In this paper, an atmospheric pressure polyethylene terephthalate dielectric barrier discharge is produced in a helium–argon mixture. The influences of the electrode voltage on the discharge mode are experimentally investigated. The results show that, at a fixed argon content of 50%, the discharge transits from local uniform, through the isolated pattern, to whole uniform with the increase in the electrode voltage. Both the peak value of current pulse and argon spectra (696.54, 763.13, 772.09, 811.17, and 911.81 nm) intensities are captured to clarify the characteristics of the discharge mode transition. The different discharge characteristic regions are obtained by varying the argon content. In addition, the influence of the argon content on the above-mentioned argon spectra intensities is also researched. The spectra intensities enhance at 696.54, 763.13, and 772.09 nm but weaken at 811.17 and 911.81 nm with the increase in the argon content when the discharge operates in the whole uniform mode. The physical reasons for these results are discussed.

Improved elastocaloric cooling performance in gradient-structured NiTi alloy processed by localized laser surface annealing

The coefficient of performance of material (COPmat, the ratio of caloric effect to energy dissipation), a key figure-of-merit for solid-state refrigerants, is significantly degenerated by the inherent hysteresis of materials. In this work, a low-hysteresis NiTi refrigerant with gradient structures (grain sizes varying from ~ 10 nm to ~ 3500 nm) is fabricated for elastocaloric cooling by localized laser surface annealing on a severely-deformed substrate (50% thickness reduction). The obtained gradient-structured (GS) NiTi exhibits more than 83% improvement in COPmat with a comparable adiabatic temperature change ΔTad compared to the homogeneous coarse-grained NiTi and extends the lower limit of operational temperature from above 283 K to 243 K. Furthermore, the large specific cooling capacity (~ 4.5 K/1%), narrow stress hysteresis (~ 60 MPa) and robust mechanical properties (high strength, high ductility and high stability) make the GS NiTi superior to most elastocaloric materials in refrigeration capability and efficiency. Such significantly enhanced cooling and mechanical performances of the GS NiTi originate from the unique gradient structure, which possesses a sound synergetic strengthening effect and an overall uniform phase transformation mode. The work proposes a promising strategy for optimization of thermomechanical performances of elastocaloric materials and demonstrates a great industrial potential of the GS NiTi in solid-state cooling.

Gauge fixing for strongly correlated electrons coupled to quantum light

We discuss the problem of gauge fixing for strongly correlated electrons coupled to quantum light, described by projected low-energy models such as those obtained within tight-binding methods. Drawing from recent results in the field of quantum optics, we present a general approach to write down quantum light-matter Hamiltonian in either dipole or Coulomb gauge which are explicitly connected by a unitary transformation, thus ensuring gauge equivalence even after projection. The projected dipole gauge Hamiltonian features a linear light-matter coupling and an instantaneous self-interaction for the electrons, similar to the structure in the full continuum theory. On the other hand, in the Coulomb gauge the photon field enters in a highly non-linear way, through phase factors that dress the electronic degrees of freedom. We show that our approach generalises the well-known Peierls approximation, to which it reduces when only local, on-site orbital contributions to light-matter coupling are taken into account. As an application, we study a two-orbital model of interacting electrons coupled to a uniform cavity mode, recently studied in the context of excitonic superradiance and associated no-go theorems. Using both gauges we recover the absence of superradiant phase in the ground state and show that excitations on top of it, described by polariton modes, contain instead non-trivial light-matter entanglement. Our results highlight the importance of treating the non-linear light-matter interaction of the Coulomb gauge non-perturbatively, to obtain a well-defined ultrastrong coupling limit and to not spoil gauge equivalence.

Estimation of ultimate strength of ring-stiffened cylindrical shells under external pressure with local shell buckling or torsional buckling of stiffeners

This study discusses the ultimate strength and collapse behavior of ring-stiffened cylindrical shells under external pressure with local shell buckling or torsional buckling of stiffeners. In past studies, the effect of initial deflection shape on the ultimate strength has not been completely elucidated. Additionally, a clarification of the collapse behavior and theoretical formulation based on it has not yet been reached. Therefore, in this study, the influence of the initial deflection shape is investigated using eigenmodes obtained from the elastic buckling eigenvalue analysis and the hungry-horse mode described by a simple equation. Then, the ultimate strength analyses of 432 models of ring-stiffened cylindrical shells with various dimensions are carried out using the nonlinear finite element method. From the analysis, the collapse modes are classified into five categories, namely, the shell buckling (SB) collapse (localized mode SB-1 and uniform deformation mode SB-2), the torsional buckling (TB) collapse (localized mode TB-1 and uniform deformation mode TB-2), and the combined shell-torsional buckling collapse. A new slenderness ratio is proposed using the formula for strength when the circumferential stress reaches yield stress, and the formula for the elastic buckling strength developed previously by the authors. Then, theoretical formulas for the ultimate strength are developed using the slenderness ratio, which can rationally estimate the strength.

Atmospheric dielectric barrier discharge containing helium–air mixtures: the effect of dry air impurities on the spatial discharge behavior

Air is a typical and arguably unavoidable impurity in atmospheric pressure dielectric barrier discharges (DBDs). The introduction of air may bring rich plasma chemical effects on DBDs and lead to a significant change of discharge characteristics. Here we implement a two-dimensional fluid model to study the spatial discharge behavior in a helium–dry-air DBD under the air impurity level (N air) of 10–200 ppm. The simulation results reveal that under low impurity content (less than 30 ppm), the gas gap cannot be ignited due to the feeble Penning ionization during the breakdown. However, with an elevation in the impurity level, the progressively enhanced Penning ionization makes the DBD experience three different spatial modes, namely uniform, columnar, and complementary quasi-uniform modes. Of particular note is that the improvement of discharge uniformity observed after the second mode transition is not directly controlled by seed electron level—a previously reported qualitative indicator of the discharge uniformity concluded by helium DBDs with only nitrogen traces. And the main contributor to this phenomenon is the complementary spatial structure appearing in successive two discharges induced by the further reinforced Penning ionization with extra oxygen doped. The result suggests the necessity of considering oxygen in helium–air DBDs when the impurity effect of air is concerned.

Effects of service condition on the performance of conductive polymer composites for flexible strain sensors

Flexible strain sensors based on conductive polymer composites (CPCs) are widely used in wearable electronics and electronic skin due to their simple preparation and outstanding performance. However, the performance like sensitivity and dynamical stability of flexible strain sensors is coupled with complex operational conditions, which prevents the sensors from large-scale practical applications. In this work, the effects of different loading rates and loading modes on the performance of the flexible strain sensor were systematically investigated. It was found that high loading rate can increase the sensitivity and the degree of hysteresis phenomenon (shoulder peak, spoon valley and drift), which is attributed to the viscoelasticity of polymer. Meanwhile, non-uniform loading mode has insignificant influence on the sensitivity and hysteresis of strain sensors in comparison to uniform loading mode. Moreover, the force-electric equivalent model was proposed to explain the causes of various hysteresis phenomena as well as the sensitivity mechanism affected by loading rate. Furthermore, a theoretical formula of the resistance of flexible strain sensor was presented and optimized to describe the relationship of variation of resistance against different loading rates. These presented results bring useful insights on the exploration of CPCs based strain sensors for wide applications under complex service conditions.

Observation of Standing Spin Waves in a van der Waals Magnetic Material.

Spin waves are studied for data storage, communication, and logic circuits in the field of spintronics based on their potential to substitute electrons. The recent discovery of magnetism in 2D systems such as monolayer CrI3 and Cr2 Ge2 Te6 has led to a renewed interest in such applications of magnetism in the 2D limit. Here, direct evidence of standing spin waves is presented along with the uniform precessional resonance modes in the van der Waals magnetic material, CrCl3 . This is the first direct observation of standing spin-wave modes, set up along a thickness of 20mm, in a van der Waals material. Standing spin waves are detected in the vicinity of both branches, optical and acoustic, of the antiferromagnetic resonance. Magnon-magnon coupling and softening of resonance modes with temperature enable extraction of interlayer exchange field as a function of temperature.

Probing edge condition of nanoscale CoFeB/MgO magnetic tunnel junctions by spin-wave resonance

We investigate spin-wave resonance in nanoscale CoFeB/MgO magnetic tunnel junctions (MTJs) with a perpendicular easy axis and various free-layer sizes. Two types of MTJs are fabricated by different process conditions, and the spin-wave resonance is measured with homodyne-detected ferromagnetic resonance. We focus on the distance between resonance frequencies of the uniform and spin-wave modes as a function of the free-layer size in order to examine the effect of the edge state of MTJs. A marked difference is observed between the two types of MTJs, and the result is consistently reproduced by a model assuming free- or fixed-edge boundary conditions with or without reduced magnetic properties near the pattern edge for each MTJ. The obtained results indicate that the edge state of nanoscale MTJs is crucially affected by the process condition, and spin-wave resonance can serve as a sensitive probe for the edge condition.

Magnetically mediated thermoacoustic imaging with single coil based on non-uniform magnetic field excitation

In order to eliminate the limitation caused by the use of a uniform magnetic field mode in magnetically mediated thermoacoustic imaging (MM-TAI), non-uniform magnetic field excitation with a single coil for MM-TAI is proposed in this paper. The theoretical model of the electromagnetic field based on time–space separation and acoustic field problems for MM-TAI is solved. For the inverse problem, the heat absorption distribution is reconstructed by the time reversal technique. The reconstructed results are in good accord with the original structure model, and the image can be clearly identified and agree well with the electric conductivity model. The experimental system is optimized to test the method, then the phantoms with conductivities of 8 S/m and 7 S/m are used for thermoacoustic signal detection and imaging. The signal detecting ability of the low conductivity target has improved significantly. These results provide the basis of MM-TAI for further application in biomedical imaging.