Nonreciprocal Transport in a Bilayer of MnBi2Te4 and Pt.

MnBi2Te4 (MBT) is the first intrinsic magnetic topological insulator with the interaction of spin-momentum locked surface electrons and intrinsic magnetism, and it exhibits novel magnetic and topological phenomena. Recent studies suggested that the interaction of electrons and magnetism can be affected by the Mn-doped Bi2Te3 phase at the surface due to inevitable structural defects. Here, we report an observation of nonreciprocal transport, that is, current-direction-dependent resistance, in a bilayer composed of antiferromagnetic MBT and nonmagnetic Pt. The emergence of the nonreciprocal response below the Néel temperature confirms a correlation between nonreciprocity and intrinsic magnetism in the surface state of MBT. The angular dependence of the nonreciprocal transport indicates that nonreciprocal response originates from the asymmetry scattering of electrons at the surface of MBT mediated by magnon. Our work provides an insight into nonreciprocity arising from the correlation between magnetism and Dirac surface electrons in intrinsic magnetic topological insulators.

Novel Magnetic Field Modulation Concept Using Multiferroic Heterostructure for Magnetoresistive Sensors.

The low frequency magnetic field detection ability of magnetoresistive (MR)sensor is seriously affected by 1/f noise. At present, the method to suppress the influence of low frequency noise is mainly to modulate the measured magnetic field by mechanical resonance. In this paper, a novel modulation concept employing a magnetoelectric coupling effect is proposed. A design method of modulation structure based on an equivalent magnetic circuit model (EMCM) and a single domain model of in-plane moment was established. An EMCM was established to examine the relationship between the permeability of flux modulation film (FMF) and modulation efficiency, which was further verified through a finite element simulation model (FESM). Then, the permeability modulated by the voltage of a ferroelectric/ferromagnetic (FE/FM) multiferroic heterostructure was theoretically studied. Combining these studies, the modulation structure and the material were further optimized, and a FeSiBPC/PMN-PT sample was prepared. Experimental results show that the actual magnetic susceptibility modulation ability of FeSiBPC/PMN-PT reached 150 times, and is in good agreement with the theoretical prediction. A theoretical modulation efficiency higher than 73% driven by a voltage of 10 V in FeSiBPC/PMN-PT can be obtained. These studies show a new concept for magnetoelectric coupling application, and establish a new method for magnetic field modulation with a multiferroic heterostructure.

Double-Gap Magnetic Flux Concentrator Design for High-Sensitivity Magnetic Tunnel Junction Sensors.

To improve the sensitivity of the magnetic tunnel junction(MTJ)sensor, a novel architecture for a double-gap magnetic flux concentrator (MFC) was studied theoretically and experimentally in this paper. The three-dimensional finite element model of magnetic flux was established to optimize the magnetic field amplification factor, with different gaps. The simulation results indicate that the sensitivity of an MTJ sensor with a double-gap MFC can be significantly better than that of a sensor with a traditional single-gap MFC, due to the fact that the magnetic magnification sharply increases with the decrease in effective gap width. Besides this, the half-bridge MTJ sensors with the double-gap MFC were fabricated using photolithography, ion milling, evaporation, and electroplating processes. Experimental results show that the sensitivity of the MTJ sensor increased by ten times compared to the sensor without the double-gap MFC, which underlines the theoretical predictions. Furthermore, there is no significant increase in the sensor noise. The work in this paper contributes to the development of high-performance MTJ sensors.

Spatially Resolved Electric-Field Manipulation of Magnetism for CoFeB Mesoscopic Discs on Ferroelectrics.

Electric-field control of magnetism in ferromagnetic/ferroelectric multiferroic heterostructures is a promising way to realize fast and nonvolatile random-access memory with high density and low-power consumption. An important issue that has not been solved is the magnetic responses to different types of ferroelectric-domain switching. Here, for the first time three types of magnetic responses are reported induced by different types of ferroelectric domain switching with in situ electric fields in the CoFeB mesoscopic discs grown on PMN-PT(001), including type I and type II attributed to 109°, 71°/180° ferroelectric domain switching, respectively, and type III attributed to a combined behavior of multiferroelectric domain switching. Rotation of the magnetic easy axis by 90° induced by 109° ferroelectric domain switching is also found. In addition, the unique variations of effective magnetic anisotropy field with electric field are explained by the different ferroelectric domain switching paths. The spatially resolved study of electric-field control of magnetism on the mesoscale not only enhances the understanding of the distinct magnetic responses to different ferroelectric domain switching and sheds light on the path of ferroelectric domain switching, but is also important for the realization of low-power consumption and high-speed magnetic random-access memory utilizing these materials.

Novel cross-linkable fluorescent probe with oriented antibody to enhance lateral immunoassay strip for the detection of acetamiprid.

Time-resolved fluorescent lateral immunoassay strip (TRFLIS) is a reliable and rapid method for detecting acetamiprid. However, its sensitivity is often affected by the structural patterns and stability of the fluorescent probe. Researchers have shown significant interests in using goat anti-mouse IgG (GaMIgG) which is indirectly bound to time-resolved fluorescent microsphere (TRFM) and antibody. This allowed for oriented modification of the antibody. However, the stability of fluorescent probe in this binding mode remained unexplored. Herein, 1-ethyl-(3-dimethylaminopropyl) carbodiimide hydrochloride was innovatively used as a cross-linking agent to enhance the binding of antibody to GaMIgG, which improved the stability of the fluorescent probe. Under optimal working conditions, this strategy exhibited a wide linear response range of 5-700 ng/mL. Its limit of detection (LOD) was 0.62 ng/mL, the visual LOD was 5 ng/mL, and the limit of quantification (LOQ) of 2.06 ng/mL. Additionally, under tomato matrix, leek matrix and Chinese cabbage matrix, the linear response ranges were 5-400, 5-300, and 5-700 ng/mL, with LODs of 0.16, 0.60, and 0.41 ng/mL, with LOQs of 0.53, 2.01 and 1.37 ng/mL, respectively. In conclusion, this strategy effectively reduced the dosage of acetamiprid antibody compared with TRFM directly linking acetamiprid antibody, and greatly increased the sensitivity of TRFLIS. Meanwhile, it demonstrated outstanding specificity and accuracy in acetamiprid detection and had been successfully applied to vegetable samples. This method enables rapid and accurate detection of large-volume samples by combining qualitative and quantitative methods. As such, it has great potential in the development of low-cost and high-performance immunochromatographic platforms.

Multifunctional nanoenzyme lateral flow immunoassay strip for rapid and ultrasensitive detection of carbofuran in vegetables.

A lateral flow immunoassay strip (LFIAS) is one of the most frequently rapid test technologies for carbofuran (CAR). Nevertheless, the LFIAS has a poor quantitative capability and low sensitivity. And, it also requires often complex sample handling steps, making testing time longer. In this study, Fe3O4 nanoparticles were successively modified with MIL-100(Fe)-based metal-organic framework (MOF) and chloroplatinic acid hexahydrate to obtain a core-shell complex of Fe3O4-MOF-Pt. The complex had a peroxidase-mimicking activity catalytic function that enabled signal amplification and sensitivity enhancement. Upon coupling with carbofuran monoclonal antibody (CAR-mAb), the magnetic separation properties of the probe enabled target-specific enrichment. The LFIAS based on Fe3O4-MOF-Pt nanocomposites could detect CAR in the range of 0.25-50 ng mL-1 with a limit of detection (LOD) of 0.15 ng mL-1, enabling colorimetric and catalytic analysis. In addition, the method showed high specificity and stability for detecting CAR in various vegetables, and recovery rates of the spiked samples were 91.40%-102.40%. In conclusion, this study provided one-stop detection of "target enrichment-visual inspection". While lowering the LOD, it reduced the detection time and improved the detection efficiency. The multifunctional Fe3O4-MOF-Pt nanocomposite provides an idea for the construction of novel multifunctional probes to improve the detection performance of conventional LFIAS.

An underwater vest containing an antioxidant MXene hydrogel for sensitive recognition of fish locomotion.

The perception of fish locomotion is important for understanding their adaptive behaviors and ethological characteristics. However, the main strategy used for extracting fish attitudes involves the use of a vision-based monitoring system, which is limited in its range of observation and cannot perform tracking for long times. Here, we report the use of a wearable tagging electronic device, referred to as an underwater vest, to capture the surrounding flow field disturbances triggered by swimming or momentary postural changes. All of these goals were achieved by integrating a pair of pseudocapacitive pressure-sensing units and a flexible circuit board. Notably, additional conditions, such as variable hydraulic pressures and minimal changes in fish posture, require high stability and sensitivity of the sensing units. Thus, hybrid hydrogel electrodes were developed through cross-linking MXene with holey-reduced graphene oxide nanosheets and further modification with 1-ethyl-3-methylimidazolium dicyanamide ionic liquids, which increased the interfacial capacitance and long-term interfacial activity of the MXene. Consequently, the sensing unit exhibited ultrahigh sensitivity (Smax~136,207 kPa-1) in an aquatic environment for 60 days and superior high-pressure resolution (10 Pa) within a wide working range of 1 MPa. Ultimately, an underwater vest integrated with such sensing units clearly distinguished and recorded fish locomotion. We believe that the designed device may open avenues in flow field monitoring and ocean current detection and provide new insights into the development of sensitive underwater tagging.

Novel electrochemiluminescence aptasensor based on AuNPs-ABEI encapsulated TiO2 nanorod for the detection of acetamiprid residues in vegetables.

Gold nanoparticles (AuNPs)@N-(4-aminobutyl)-N-ethylisoluminol (ABEI)@Titanium dioxide nanorods (TiO2NRs) were used as sensing materials to produce a unique encapsulated nanostructure aptasensor for the detection of acetamiprid residues in this work. ABEI, an analog of luminol, was extensively used as an electrochemiluminescence (ECL) reagent. The ECL mechanism of ABEI- hydrogen peroxide (H2O2) system had connections to a number of oxygen-centered free radicals. TiO2NRs improved ECL response with high electron transfer and a specific surface area. AuNPs were easy to biolabel and could catalyze H2O2 to enhance ECL signal. AuNPs were wrapped around TiO2NRs by utilizing the reduction property of ABEI to form wrapped modified nanomaterials. The sulfhydryl-modified aptamer bound to the nanomaterial by forming gold-sulfur (Au-S) bonds. The aptamer selectively bound to its target with the addition of acetamiprid, which caused a considerable decrease in ECL intensity and enabled quantitative detection of acetamiprid. The aptasensor showed good stability, repeatability and specificity with a broad detection range (1×10-2-1×103 nM) and a lower limit of detection (3 pM) for acetamiprid residues in vegetables. Overall, this aptasensor presents a simple and highly sensitive method for ECL detecting acetamiprid, with potential applications in vegetable safety monitoring.

Metal-organic framework-based aptasensor utilizing a novel electrochemiluminescence system for detecting acetamiprid residues in vegetables.

The work was based on N-(4-Aminobutyl)-N-ethylisoluminol (ABEI)-functionalized Fe-MIL-101 and gold nanoparticles (AuNPs) as sensing materials, and an electrochemiluminescence (ECL) aptasensor was constructed for detecting acetamiprid. As a metal-organic framework (MOF) material, Fe-MIL-101, was renowned for its unique three-dimensional network structure and efficient catalytic capability. ABEI, a common ECL reagent, was widely applied. ABEI was introduced into the Fe-MIL-101 structure as a luminescence functionalization reagent to form Fe-MIL-101@ABEI. This approach avoided limitations on the loading capacity of luminescent reagents imposed by modification and encapsulation methods. With character of excellent catalytic activity and ease of bioconjugation, AuNPs offered significant advantages in biosensing. Leveraging the reductive properties of ABEI, AuNPs were reduced around Fe-MIL-101@ABEI, resulting in the modified luminescent functionalized material denoted as Fe-MIL-101@ABEI@AuNPs. An aptamer was employed as a recognition element and was modified accordingly. The aptamer was immobilized on Fe-MIL-101@ABEI@AuNPs through gold-sulfur (Au-S) bonds. After capturing acetamiprid, the aptamer induced a decrease in the ECL signal intensity within the ABEI-hydrogen peroxide (H2O2) system, enabling the quantitative detection of acetamiprid. The aptasensor displayed remarkable stability and repeatability, featured a detection range of 1×10-3-1×102 nM, and had a limit of detection (LOD) of 0.3 pM (S/N=3), which underscored its substantial practical application potential.

Novel electrochemiluminescence sensing platform for ultrasensitive detection of malathion residue in tea based on SiO2NSs doped Luminol/AgNPs as a signal amplification strategy.

To address the potential hazards of organophosphorus pesticides (OPs) residues in tea, an electrochemiluminescence (ECL) aptasensor based on functionalized nanomaterials was constructed in this work. Firstly, gold nanoparticles (AuNPs) were attached on the surface of multi-walled carbon nanotubes (MWCNTs) by the constant potential electrodeposition to form a compound, and it was utilized to provide excellent immobilization sites for complementary DNA (cDNA). Subsequently, composite nanomaterials were synthesized by a one-pot method with aminated Luminol/silver nanoparticles@silica nanospheres (NH2-Luminol/Ag@SiO2NSs). Finally, NH2-Luminol/Ag@SiO2NSs was combined with a malathion aptamer (Apt) to obtain signal probes (SPs) for the construction of an aptasensor. The aptasensor had a wide linear range (1×10-3-1×103 ng/mL) and a low limit of detection (LOD) (0.3×10-3 ng/mL). It had the virtues of high sensitivity, wonderful stability and excellent specificity, which could be used for the detection of malathion residue in tea. The work provides a proven way for the construction of a rapid and ultrasensitive aptasensor with low-cost.

Electrochemiluminescence detection of diazinon in vegetables based on the synergistic interaction of WO3-x dots with Au@SiO2 nanocapsules.

In this work, a simple synthesis of low-toxicity transition metal material of WO3-x dots was used as a co-reactant with Au@SiO2 as a core-shell material and a signal amplification factor to collaboratively promote Ru(bpy)32+ electrochemiluminescence (ECL) for the construction of a highly sensitive aptasensor for the detection of diazinon (DZN) in vegetables. Electrodes modified with multi-walled carbon nanotubes-chitosan composite membranes (MWCNTs-CS) were used to load and immobilize more Ru(bpy)32+.can load more Ru(bpy)32+. WO3-x dots synthesized by a simple method showed excellent ECL efficiency as a novel co-reactant for Ru(bpy)32+. Under optimized conditions, this aptasensor for DZN has a wide detection range (10 pg mL-1 - 1 µg mL-1.) and a low detection limit (0.0197 ng L-1). The aptasensor has shown good results in the analysis of real samples in the experiment. This work provides a new approach to the construction of a novel electrochemiluminescence sensor for the detection of pesticides.

An Ultrahighly Pressure Sensitive Electronic Fish Skin for Underwater Wave Sensing.

Underwater flexible sensors have a future for wide application, which is promising for attaching them to underwater creatures to monitor vital signals and biomechanical analysis of their motion and perceive tiny environmental disturbances. However, the pressure waves induced by biological swimming are extremely weak and susceptible to undercurrents, making them difficult to sense. Here, we report an ultrahighly sensitive biomimetic electronic fish skin designed by embedding an artificial pseudocapacitive-based hair cell into a simulated canal neuromast encapsulation structure, in which the artificial hair cell, as the key sensitive unit, is assembled from hybrid film electrodes and polyurethane-acidic electrolyte foam. Such a film is prepared by inter-cross-linking MXene and holey reduced graphene oxide with the assistance of l-cysteine, effectively increasing the interfacial capacitance and alleviating the oxidation issues of MXene. Meanwhile, the acidic foam with high porosity shows great compressibility to adapt to a high-pressure underwater environment. Consequently, the device exhibits ultrahighly sensitivity (maximum sensitivity ∼173688 kPa-1) over a wide range of depths (0-100 m) and remains stable after 10000 repeated tests. As an example case, the device is integrated as a motion monitoring system to identify the minor disturbances triggered by instantaneous postural changes of fish. The electronic fish skin is expected to demonstrate enormous potentials in flow field monitoring, ocean current detecting, and even seismic waves warning.

Normal-Direction Graded Hemispheres for Ionic Flexible Sensors with a Record-High Linearity in a Wide Working Range.

Flexible pressure sensors developed rapidly with increased sensitivity, a fast response time, high stability, and excellent deformability. These progresses have expanded the application of wearable electronics under high-pressure backgrounds while also bringing new challenges. In particular, the nonlinearity and narrow working range lead to a gradually insensitive response, principally because the microstructure deforms inconsistently on the device interfaces in the whole working range. Herein, we report an ionic flexible sensor with a record-high linearity (R2 = 0.99994) in a wide working range (up to 600 kPa). The linearity response comes from the normal-direction graded hemisphere (GH) microstructure. It is prepared from poly(dimethylsiloxane) (PDMS)/carbon nanotubes (CNTs)/Au into flexible and deformable electrodes, and its geometry is precisely designed from the linear elastic theory and optimized through finite element simulation. The sensor can achieve a high sensitivity of S = 165.5 kPa-1, a response-relaxation time of <30 ms, and superb consistency, allowing the device to detect vibration signals. Our sensor has been assembled with circuits and capsulation in order to monitor the function state of players in underwater sports in the frequency domain. This work deepens the theory of linearized design of microstructures and provides a strategy to make flexible pressure sensors that have combined the performances of ultrahigh linearity, high sensitivity, and a wide working range.

Year-round observations of stable carbon isotopic composition of carboxylic acids, oxoacids and α-Dicarbonyls in fine aerosols at Tianjin, North China: Implications for origins and aging.

To better understand the origins and photochemical processing (aging) of organic aerosols (OA), we studied fine aerosols (PM2.5) collected at urban (Nankai District (ND)) and suburban (Haihe Education Park (HEP)) Tianjin, North China over a one-year period (2018-2019) for stable carbon isotopic composition (δ13C) of water-soluble diacids, oxoacids, α-dicarbonyls and fatty acids. Maleic (M, -18.3 ± 10.9‰ at ND and -23.5 ± 10.2‰ at HEP) and fumaric (F, -22.0 ± 12.1‰ at ND and -22.5 ± 10.5‰ at HEP) acids were found to be most enriched with 13C followed by oxalic acid (C2, -24.7 ± 3.9‰ at ND and -25.9 ± 4.7‰ at HEP) during the campaign. Based on seasonal changes in δ13C of selected marker species: C6 and C9 diacids, phthalic, glyoxylic and pyruvic acids and glyoxal, and their comparison with the source signatures, we found that water-soluble OA in Tianjin were mainly originated from fossil fuel combustion and biomass burning emissions and were subjected for significant aging. The contribution from fossil fuel combustion including coal combustion was high in autumn and winter, especially at ND. Considering the enrichment of 13C in specific species together with linear relations of δ13C of selected species with their concentrations, with mass ratios and with the relative abundance of C2 diacid, we inferred that the photochemical transformations of longer-chain diacids, oxidation of α-dicarbonyls (Gly and mGly), preferably in gas phase, were important in warm period (March-September), whereas the oxidation of Gly, mGly and other precursors in aqueous phase were major in cold period (October-February).

Apelin/APJ system in inflammation.

Apelin, an endogenous ligand for the G protein-coupled receptor (APJ), is widely distributed within the central nervous system and diverse organs in human and animals. Recent studies indicate that the apelin/APJ system plays an important role in physiological and pathophysiological situations. Apelin/APJ could inhibit inflammatory response by down-regulation of the nuclear factor-κB (NF-κB) pathway and by up-regulation of the extracellular signal-regulated kinase 1 and 2 (ERK1/2) pathway etc. Basic and preliminary research demonstrated that apelin/APJ system was involved in multiple diseases such as cardiovascular system diseases, liver and kidney diseases, neurological diseases, inflammatory intestinal diseases, pancreatitis, lung injury, aging, and obesity. Further, deficiency or overabundance of apelin can aggravate disease states in that inflammation is not only an important physiologic defense mechanism but also a potential mediator of organ damage. In this review, we summarize recent apelin/APJ system research progress with emphasis on the influence of the system on inflammation. Further, the mechanistic basis by which apelin regulates various inflammation-related diseases is analyzed. Finally, apelin and APJ might be presented as potential therapeutic targets for treatment of diseases mediated or exacerbated by inflammation.

Wide-Range Linear Iontronic Pressure Sensor with Two-Scale Random Microstructured Film for Underwater Detection.

A broad linear range of ionic flexible sensors (IFSs) with high sensitivity is vital to guarantee accurate pressure acquisition and simplify back-end circuits. However, the issue that sensitivity gradually decreases as the applied pressure increases hinders the linearity over the whole working range and limits its wide-ranging application. Herein, we design a two-scale random microstructure ionic gel film with rich porosity and a rough surface. It increases the buffer space during compression, enabling the stress deformation to be more uniform, which makes sure that the sensitivity maintains steady as the pressure loading. In addition, we develop electrodes with multilayer graphene produced by a roll-to-roll process, utilizing its large interlayer spacing and ion-accessible surface area. It benefits the migration and diffusion of ions inside the electrolyte, which increases the unit area capacitance and sensitivity, respectively. The IFS shows ultra-high linearity and a linear range (correlation coefficient ∼ 0.9931) over 0-1 MPa, an excellent sensitivity (∼12.8 kPa-1), a fast response and relaxation time (∼20 and ∼30 ms, respectively), a low detection limit (∼2.5 Pa), and outstanding mechanical stability. This work offers an available path to achieve wide-range linear response, which has potential applications for attaching to soft robots, followed with sensing slight disturbances induced by ships or submersibles.

Magnetoelectric Memory Based on Ferromagnetic/Ferroelectric Multiferroic Heterostructure.

Electric-field control of magnetism is significant for the next generation of large-capacity and low-power data storage technology. In this regard, the renaissance of a multiferroic compound provides an elegant platform owing to the coexistence and coupling of ferroelectric (FE) and magnetic orders. However, the scarcity of single-phase multiferroics at room temperature spurs zealous research in pursuit of composite systems combining a ferromagnet with FE or piezoelectric materials. So far, electric-field control of magnetism has been achieved in the exchange-mediated, charge-mediated, and strain-mediated ferromagnetic (FM)/FE multiferroic heterostructures. Concerning the giant, nonvolatile, and reversible electric-field control of magnetism at room temperature, we first review the theoretical and representative experiments on the electric-field control of magnetism via strain coupling in the FM/FE multiferroic heterostructures, especially the CoFeB/PMN-PT [where PMN-PT denotes the (PbMn1/3Nb2/3O3)1-x-(PbTiO3)x] heterostructure. Then, the application in the prototype spintronic devices, i.e., spin valves and magnetic tunnel junctions, is introduced. The nonvolatile and reversible electric-field control of tunneling magnetoresistance without assistant magnetic field in the magnetic tunnel junction (MTJ)/FE architecture shows great promise for the future of data storage technology. We close by providing the main challenges of this and the different perspectives for straintronics and spintronics.

Using Dipole Interaction to Achieve Nonvolatile Voltage Control of Magnetism in Multiferroic Heterostructures.

Nonvolatile electrical control of magnetism is crucial for developing energy-efficient magnetic memory. Based on strain-mediated magnetoelectric coupling, a multiferroic heterostructure containing an isolated magnet requires nonvolatile strain to achieve this control. However, the magnetization response of an interacting magnet to strain remains elusive. Herein, Co/MgO/CoFeB magnetic tunnel junctions (MTJs) exhibiting dipole interaction on ferroelectric substrates are fabricated. Remarkably, nonvolatile voltage control of the resistance in the MTJs is demonstrated, which originates from the nonvolatile magnetization rotation of an interacting CoFeB magnet driven by volatile voltage-generated strain. Conversely, for an isolated CoFeB magnet, this volatile strain induces volatile control of magnetism. These results reveal that the magnetization response to volatile strain among interacting magnets is different from that among isolated magnets. The findings highlight the role of dipole interaction in multiferroic heterostructures and can stimulate future research on nonvolatile electrical control of magnetism with additional interactions.

Nano-magnetic tunnel junctions controlled by electric field for straintronics.

The magnetic tunneling junction (MTJ) controlled by electric field as an alternate approach for energy efficiency is the highlight for nonvolatile RAM, while there is still a lack of research on resistance manipulation with the electric field in nanoscale MTJs. In this study, we integrated nanoscale MTJs on the (011) orientated Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) ferroelectric substrates and systematically investigated the magnetoresistance as a function of the magnetic field and electric field. A single domain state of the nanoscale MTJ was demonstrated by the experimental result and theoretical simulation. Afterward, the obvious electric field control of R-H curves was obtained and explained by the competition between magnetoelastic energy and shape anisotropy. More importantly, simulation results also predicted that the switching pathway of magnetic moments under the magnetic field is strongly dependent on the applied electric field, displaying the electric field control of chiral switching in the nano-MTJ. Our work is a milestone in the realization of the emerging dubbed straintronics field.