Field Cycling Research Articles

MATHEMATICAL MODEL OF DIESEL ENGINE CHARACTERISTICS FOR DETERMINING THE PERFORMANCE OF TRACTION DYNAMICS OF WHEEL-TYPE TRACTOR

Wheel-type tractors carry out a range of processing operations, with the exception of early spring work, when caterpillar tractors are used to reduce the compaction effect on the soil. Therefore, to plan the costs and reserves associated with fuel consumption, it is necessary to have an estimate of the fuel economy of the tractor in basic agricultural operations. An objective assessment of fuel consumption requires a mathematical model that describes the fuel characteristics of the engine, taking into account the speed and load torque in a wide range of variation. Verification of the model is possible only with experimental data. Since the efficiency and fuel economy of a tractor depends not only on engine performance, but also on the perfection of the transmission, the running system and the rational choice of speed, it is necessary to take into account the time-varying nature of the tractor’s traction load. The complex of agricultural operations can be divided into characteristic cycles of load change over time. This principle is the basis of PowerMix test cycles, which are conducted on a concrete track to ensure repeatability of the experiment. The use of the variable load on the tractor in the PowerMix tests is positive, but in actual field tests the results may differ due to the instability of the soil properties. On the other hand, PowerMix field cycles can be taken as standard test loads in the simulation of tractor traction tests on the ground

High quality epitaxial thin films and exchange bias of antiferromagnetic Dirac semimetal FeSn

FeSn is a topological semimetal (TSM) and kagome antiferromagnet (AFM) composed of alternating Fe3Sn kagome planes and honeycomb Sn planes. This unique structure gives rise to exotic features in the band structures such as the coexistence of Dirac cones and flatbands near the Fermi level, fully spin-polarized 2D surface Dirac fermions, and the ability to open a large gap in the Dirac cone by reorienting the Néel vector. In this work, we report the synthesis of high-quality epitaxial (0001) FeSn films by magnetron sputtering. Using FeSn/Py heterostructures, we show a large exchange bias effect that reaches an exchange field of 220 Oe at 5 K, providing unambiguous evidence of antiferromagnetism and strong interlayer exchange coupling in our films. Field cycling studies show steep initial training effects, highlighting the complex magnetic interactions and anisotropy. Importantly, our work provides a simple, alternative means to fabricate FeSn films and heterostructures, making it easier to explore the topological physics of AFM TSMs and develop FeSn-based spintronics.

Suppression of Metamagnetic Transitions of Martensitic Type by Particle Size Reduction in Charge-Ordered La0.5Ca0.5MnO3

In this paper, we have studied the effect of size reduction on charge ordering (CO) and magnetic phase separation in La0.5Ca0.5MnO3. The magnetic ground state at low temperature shifts from ferromagnetic (nanoparticles) to CO-antiferromagnetic (bulk) with increasing annealing temperature. The studied samples exhibit relevant phenomena such as Griffiths phase and training effect. Magnetic field cycling can stabilize ferromagnetic or antiferromagnetic domains, depending on the temperature value as well as the sample’s nature. For the compound sintered at 1200 °C, step-like metamagnetic transitions of martensitic type were observed at 4 K, indicating the presence of weak spin-phonon coupling. The disappearance of magnetic phase separation at 4 K (the sample is purely antiferromagnetic) can be a possible origin for the occurrence of such transitions. Lowering the sintering temperature leads to the disappearance of martensitic transitions. The obtained results indicate that the occurrence of step-like metamagnetic transition of martensitic type necessarily requires the onset of a long-range CO-antiferromagnetic state.

Involvement of Unsaturated Switching in the Endurance Cycling of Si‐doped HfO2 Ferroelectric Thin Films

AbstractIn the past decade, extensive studies on HfO2‐based ferroelectric thin films have been carried out in order to realize their application in high‐density, low‐power, and high‐speed nonvolatile memories. However, understanding the field cycling endurance, which is extremely important for device performance, is still a serious issue. In this work, the frequency and field dependent subcycling behavior is carefully examined. The differences in split‐up effects induced at different subcycling conditions are analyzed by comparing the evolution of polarization‐electric field and transient current hysteresis loops monitored by two subsequent triangular voltage waveforms with different amplitudes. Using the first‐order reversal curves, the evolution of the switching and backswitching field distribution before and after numerous subcycles is characterized. An intuitive model based on the migration of oxygen vacancies from switchable regions to non‐switchable regions and subsequent movement toward top/bottom electrode interface driven by the transient depolarization field is proposed to explain the generation and enhancement of local bias fields.

Cascaded pyroelectric conversion: Optimizing the ferroelectric phase transition and electrical losses

The dramatic increase in the pyroelectric coefficient around the ferroelectric–paraelectric phase transition suggests high potential energy conversion efficiencies, but the reality is more complicated when thermal and electrical losses are considered. The performance of prototype mono-domain lead titanate thin films is simulated around phase transition using a phenomenological modeling approach. Thermodynamic properties are calculated using a modified Landau–Devonshire potential that is a function of temperature, applied electric field, and uniaxial tensile stress for bulk films. Significant performance enhancement near the ferroelectric–paraelectric phase transition is observed. However, increases in both the specific heat and the dielectric constant reduced the anticipated improvement. Critically, electrical losses during charging and discharging processes within the energy conversion cycle are included and calculated using the dielectric dissipation factor. Cascaded pyroelectric conversion cycles are considered where heat for each subsequent stage is provided by the previous stage, allowing for the segmentation of large temperature changes into multiple cycles. The implementation of a multi-stage or cascade approach could greatly increase the cycle efficiency over a large temperature range while utilizing lower, more realistic, electric field strengths. We show how each stage could be optimized through a secondary multi-caloric effect where the ferroelectric–paraelectric transition temperature is shifted using an applied biaxial stress. Loss tangents as low as 5% are shown to negate the benefits of cascading for high number of stages (n > 10). Using a stress-tuned optimum phase transition temperature for cascade stages provides roughly a 100% increase in thermal efficiency vs the unoptimized material for low electric field cycles.

Crystal orientation and crystal structure of paramagnetic \u03b1-Al under a pulsed electromagnetic field

The intermittent electromagnetic fields with a large partial mathrm{B}/partial mathrm{t} can enhance the properties of ferromagnetic materials and significantly affect paramagnetic materials. In this study, the effect of a pulsed electromagnetic field on the crystal orientation of the primary phase and microstructure evolution of an Al–Zn–Mg–Cu alloy was investigated. A mathematical model was developed to describe crystal rotation under a pulsed electromagnetic field. The model predictions show that the magnetic energy difference generated by the magnetic anisotropy of the primary crystal produces primary phases with sizes of 225–100 μm to rotate into a <111> preferred orientation. The lattice constant, the interplanar spacing, and the microstrain increase with the duty cycle of the pulsed magnetic field, especially for the (111) and (200) crystal planes. This study provides preliminary theoretical support for using pulsed electromagnetic fields to control the orientation and microscopic properties of materials.

High-energy storage performance of (1 − x)[0.935(Bi0.5Na0.5)TiO3–0.065BaTiO3]–xBa(Zr0.3Ti0.7)O3 ceramics with wide temperature range

The (1 − x)[0.935(Bi0.5Na0.5)TiO3–0.065BaTiO3]–xBa(Zr0.3Ti0.7)O3 (BNT–BT–xBZT) ceramics with high-energy storage properties were designed and characterized. All the BNT–BT–xBZT ceramics exhibit a pure perovskite structure. The grain size of ceramics becomes larger as the BZT content increases. Enhanced energy density performances (Wrec = 1.9 J/cm3, η = 86%) are achieved for the BNT–BT–0.4BZT ceramics at 210 kV/cm. Specifically, the energy stored in the material can be rapidly released within 0.27 µs. Excellent temperature stability with the variation of Wrec less than 7% is realized in a wide temperature range from 20 to 140 °C. Moreover, the energy storage performances have good reliability after 105 electric field cycles. The high-energy storage performances indicate that the BNT–BT–0.4BZT ceramics are promising candidates in pulsed-power applications.

Enzyme-Substrate-Cofactor Dynamical Networks Revealed by High-Resolution Field Cycling Relaxometry.

The remarkable power and specificity of enzyme catalysis rely on the dynamic alignment of the enzyme, substrates, and cofactors, yet the role of dynamics has usually been approached from the perspective of the protein. We have been using an underappreciated NMR technique, subtesla high-resolution field cycling 31P NMR relaxometry, to investigate the dynamics of the enzyme-bound substrates and cofactor on guanosine-5'-monophosphate reductase (GMPR). GMPR forms two dead end, yet catalytically competent, complexes that mimic distinct steps in the catalytic cycle: E·IMP·NADP+ undergoes a partial hydride transfer reaction, while E·GMP·NADP+ undergoes a partial deamination reaction. A different cofactor conformation is required for each partial reaction. Here we report the effects of mutations designed to perturb cofactor conformation and ammonia binding with the goal of identifying the structural features that contribute to the distinct dynamic signatures of the hydride transfer and deamination complexes. These experiments suggest that Asp129 is a central cog in a dynamic network required for both hydride transfer and deamination. In contrast, Lys77 modulates the conformation and mobility of substrates and cofactors in a reaction-specific manner. Thr105 and Tyr318 are part of a deamination-specific dynamic network that includes the 2'-OH of GMP. These residues have comparatively little effect on the dynamic properties of the hydride transfer complex. These results further illustrate the potential of high-resolution field cycling NMR relaxometry for the investigation of ligand dynamics. In addition, exchange experiments indicate that NH3/NH4+ has a high affinity for the deamination complex but a low affinity for the hydride transfer complex, suggesting that the movement of ammonia may gate the cofactor conformational change. Collectively, these experiments reinforce the view that the enzyme, substrates, and cofactor are linked in intricate, reaction-specific, dynamic networks and demonstrate that distal portions of the substrates and cofactors are critical features in these networks.

Hoop Stress Modification, Stress Hysteresis and Degradation of a REBCO Coil Due to the Screening Current Under External Magnetic Field Cycling

Degradation of a REBCO coil under external magnetic fields is one of the major technical problems in the field of HTS magnet technology. A possible cause of such degradation is an inhomogeneous hoop stress distribution, or hoop stress modification (both increase and decrease), induced by the screening current. In this work, we investigate such a hoop stress modification by a small coil experiment with a strain measurement and a numerical simulation. An experimental result shows a very high stress increase factor of >4.1, defined by the maximum circumferential stress over BzJR stress, and the simulated result is in qualitative agreements. The strain (stress) shows a hysteresis effect corresponding to the screening current behavior. A large hoop stress modification causes not only a hoop stress increase, but also buckling of the conductor, which induces delamination and micro-clacks of the superconducting layer. We also show the stress modification can be reduced by bonding turns with epoxy.

Effect of the Optical Pumping and Magnetic Field on the States of Phase Separation Domains in Eu0.8Ce0.2Mn2O5

The effect of optical pumping and applied magnetic field on the characteristics of ferromagnetic layers in one-dimensional superlattices is studied. At low enough temperatures, these layers correspond to phase separation domains in RMn_2O_5 and R_{0.8}Ce_{0.2}Mn_2O_5 multiferroics. The formation of such domains occurs owing to the charge ordering of Mn^{3+} and Mn^{4+} ions and to the finite probability for e_g electrons to tunnel between these pairs of ions. The volume occupied by such superlattices is rather small, and they can be treated as isolated ferromagnetic semiconductor heterostructures, spontaneously formed in the host crystal. The sequences of ferromagnetic resonances related to the superlattice layers in Eu_{0.8}Ce_{0.2}Mn_2O_5 are studied. The characteristics of these resonances give information on the properties of such layers. For the first time, it is demonstrated that the optical pumping gives rise to a new metastable state of superlattices, which can be recovered by the magnetic field cycling to the state existing before the optical pumping. It is found that the superlattices recovered by the magnetic field exist up to temperatures higher than those in as-grown crystals.

Predicting the dominating factors during heat transfer in magnetocaloric composite wires

Magnetocaloric composite wires have been studied by pulsed-field measurements up to μ0ΔH = 10 T with a typical rise time of 13 ms in order to evaluate the evolution of the adiabatic temperature change of the core, ΔTad, and to determine the effective temperature change at the surrounding steel jacket, ΔTeff, during the field pulse. An inverse thermal hysteresis is observed for ΔTad due to the delayed thermal transfer. By numerical simulations of application-relevant sinusoidal magnetic field profiles, it can be stated that for field-frequencies of up to two field cycles per second heat can be efficiently transferred from the core to the outside of the jacket. In addition, intense numerical simulations of the temperature change of the core and jacket were performed by varying different parameters, such as frequency, heat capacity, thermal conductivity and interface resistance in order to shed light on their impact on ΔTeff at the outside of the jacket in comparison to ΔTad provided by the core.

Limits imposed by liquid/surface interactions in the determination of tortuosity in mesopores

Abstract The restricted mobility of different liquids, polar and non-polar, were studied by means of 1H NMR diffusion and Larmor frequency dependent relaxation measurements, upon confinement in mesoporous silica with mean pore sizes ranging from 3–30 nm. The use of alkanes as a reference in the determination of the true tortuosity value was observed to be accurate for pores larger than 6 nm, while for smaller pore sizes geometrical restrictions affect the diffusion even for short chain linear alkanes. 1H NMR fast field cycling relaxometry was used to measure the relaxation times as a function of the Larmor frequency. We observed that the total observable dispersion (TOD), which is a measure of the surface/liquid interaction, is mainly driven by the liquid polarity for pores larger than 10 nm, while less dependence on polarity is observed for smaller pore sizes. Our results indicate that as confinement increases, liquid/surface interactions become more relevant than the structural properties of the porous network, imposing a limit to the use of alkanes to probe the geometrical tortuosity.

Phase-Exchange-Driven Wake-Up and Fatigue in Ferroelectric Hafnium Zirconium Oxide Films.

Ferroelectric hafnium zirconium oxide holds great promise for a broad spectrum of complementary metal-oxide-semiconductor (CMOS) compatible and scaled microelectronic applications, including memory, low-voltage transistors, and infrared sensors, among others. An outstanding challenge hindering the implementation of this material is polarization instability during field cycling. In this study, the nanoscale phenomena contributing to both polarization fatigue and wake-up are reported. Using synchrotron X-ray diffraction, the conversion of non-polar tetragonal and polar orthorhombic phases to a non-polar monoclinic phase while field cycling devices comprising noble metal contacts is observed. This phase exchange accompanies a diminishing ferroelectric remanent polarization and provides device-scale crystallographic evidence of phase exchange leading to ferroelectric fatigue in these structures. A reduction in the full width at half-maximum of the superimposed tetragonal (101) and orthorhombic (111) diffraction reflections is observed to accompany wake-up in structures comprising tantalum nitride and tungsten electrodes. Combined with polarization and relative permittivity measurements, the observed peak narrowing and a shift in position to lower angles is attributed, in part, to a phase exchange of the non-polar tetragonal to the polar orthorhombic phase during wake-up. These results provide insight into the role of electrodes in the performance of hafnium oxide-based ferroelectrics and mechanisms driving wake-up and fatigue, and demonstrate a non-destructive means to characterize the phase changes accompanying polarization instabilities.

The complex structural mechanisms behind strain curves in bismuth sodium titanate–barium titanate

In this work, the lead-free composition (1-x)Bi0.5Na0.5TiO3–xBaTiO3 (BNT–BT) with x = 0.12 was investigated using in situ Synchrotron x-ray powder diffraction. With the applied electric field, the pseudo-cubic relaxor phase reversibly transforms to a ferroelectric state. The reversibility is still preserved after 104 bipolar electric field cycles. A Rietveld refinement with a structure, strain, and texture analysis using a model based on the atomic scale was applied for four frequencies from 10−4 to 101 Hz. The analysis allowed us to separately determine the two coexisting phases, their electric field dependent evolution, and the underlying strain mechanisms. For all the applied frequencies, we showed that domain switching is the only strain mechanism appearing in the tetragonal phase and the lattice strain is the only mechanism in the rhombohedral phase. The coercive field of the tetragonal phase (4 kV/mm) is found to be higher than that of the rhombohedral phase (3 kV/mm). This divergence has not been observed in previously investigated lead-containing materials and cannot be detected solely using macroscopic strain and polarization experiments. Moreover, the domain strain abruptly starts to occur only after a threshold field value and exhibits high hysteresis. The lattice strain, on the other hand, starts nearly from the beginning and increases more linearly during the bipolar field cycle. It could, therefore, be demonstrated that complex structural mechanisms underlie the apparent clear and continuous macroscopic strain curve. These findings are crucial for all actuator materials undergoing a relaxor to ferroelectric phase transformation and provide approaches and strategies to optimize lead-free materials for tailored applications.

Role of magnetic and temperature cycling on martensite formation in Ni2.19Mn0.81Ga single crystals of a Heusler alloy

The results of in situ studies of the magnetostructural transition occurring in single crystals of an Ni2.19Mn0.81Ga Heusler alloy are presented in this paper. The formation of martensitic twins on exposure to high magnetic fields up to 10 T in the magnetostructural transition regime was observed using an indigenously developed optical microscope. Experiments on magnetization were performed on single crystals of Ni2.19Mn0.81Ga in high magnetic fields, a phase diagram between magnetic field and temperature was constructed, and the isothermal entropy change was estimated. Based on the experimental data and the results from optical microscopic examination, the influence of magnetic field and thermal cycling on martensitic twins and, in turn, on the magnetocaloric effect, is discussed.

The Hidden Cycle of the Solar Tesseral-Quadrupole Magnetic Field

Based on the Stanford harmonic coefficients of the solar magnetic fields and on the results of Shannon entropy transfer technique applied to magnetic mode intensities (Mikhaylutsa in J. Astrophys. Astron.40, 22, 2019), we have found that most of the medium and small-scale solar magnetic modes (order $l > 3$; degree $m > 0$) must be interdependent. The features and physical sense of these dependencies are analyzed and suggest that an unknown process in the Sun may control clusters of dependent magnetic modes according to some underlying physical scenario. The scenario may be revealed by studying the spatial distribution of the global surface magnetic field. We find that the tesseral-quadrupole ($l = 2$; $m = 1$) polarity distribution reappears periodically over four solar cycles. The periodicity (${T}\approx 72$ solar rotations) is synchronized with the phases of modulation of the Shannon entropy transfer from the tesseral-quadrupole mode. An unknown process (twice per sunspot cycle) organizes a recurring cluster of interconnected magnetic modes that restore the global structure of the tesseral-quadrupole polarity, as a kind of “template.” This cycle is hidden in traditional methods of analysis, but its spatial-phase origin is made clear by the Shannon entropy transfer technique. Investigation of the “template” rotation rate suggests a probable coincidence with the 27-day Bartels rotation period.

Interfacial dielectric layer as an origin of polarization fatigue in ferroelectric capacitors

Origins of polarization fatigue in ferroelectric capacitors under electric field cycling still remain unclear. Here, we experimentally identify origins of polarization fatigue in ferroelectric PbZr0.52Ti0.48O3 (PZT) thin-film capacitors by investigating their fatigue behaviours and interface structures. The PZT layers are epitaxially grown on SrRuO3-buffered SrTiO3 substrates by a pulsed laser deposition (PLD), and the capacitor top-electrodes are various, including SrRuO3 (SRO) made by in-situ PLD, Pt by in-situ PLD (Pt-inPLD) and ex-situ sputtering (Pt-sputtered). We found that fatigue behaviour of the capacitor is directly related to the top-electrode/PZT interface structure. The Pt-sputtered/PZT/SRO capacitor has a thin defective layer at the top interface and shows early fatigue while the Pt-inPLD/PZT/SRO and SRO/PZT/SRO capacitor have clean top-interfaces and show much more fatigue resistance. The defective dielectric layer at the Pt-sputtered/PZT interface mainly contains carbon contaminants, which form during the capacitor ex-situ fabrication. Removal of this dielectric layer significantly delays the fatigue onset. Our results clearly indicate that dielectric layer at ferroelectric capacitor interfaces is the main origin of polarization fatigue, as previously proposed in the charge injection model.

Off-design performance of a supercritical CO2 Brayton cycle integrated with a solar power tower system

This work focuses on the off-design performance of the system integrated a simple recuperative supercritical CO2 Brayton cycle, solar power tower, and thermal energy storage (TES). The system design parameters are obtained first; then, the off-design performance of power cycle and solar receiver are analyzed from the perspective of influencing factors; finally, the daily performance simulations of overall system are conducted. This work is aimed at analyzing the system performance under more realistic conditions, and clarifying the influence mechanism between parameters of solar field, TES and power cycle under off-design conditions. Results show that the increase in ambient temperature and input energy to the receiver, and the decrease in molten salt temperature from the cold tank are beneficial to improve the solar receiver efficiency. As the power demand deviates farther from design value, the temperature of molten salt at the heater outlet is higher, which leads to lower solar receiver efficiency. On the summer solstice, the system operates continuously for 24 h with 100% electricity powered by solar energy and 17.8% daily averaged solar-to-electricity efficiency. On the winter solstice, the system operates continuously for 17 h with 72.6% electricity powered by solar energy and 17.1% daily averaged solar-to-electricity efficiency.

Laser-driven tunneling photocurrent as a source of midinfrared to microwave multidecade supercontinua yoked to high-order harmonics

Electron tunneling induced by a strong-field laser driver can lead to an ultrafast stepwise buildup of the photoelectron density \ensuremath{\rho}. When the laser field is strong enough, each such step in the temporal profile of \ensuremath{\rho} is confined well within the field cycle, providing an ultrabroadband, multidecade force that drives the photoelectron current $j$. However, whether or not the photocurrent can emit electromagnetic radiation with such an extraordinarily broad spectrum depends on the damping, which defines the low-frequency cutoff in the spectrum of this radiation. We show that, with a suitable choice of the gas pressure and parameters of the laser driver, the laser-induced tunneling photocurrent can serve as a source of a remarkably broadband electromagnetic radiation with a multidecade spectrum stretching from the vacuum ultraviolet all the way down to the microwave range. We demonstrate that the supercontinuum fields emitted by individual photocurrent steps, induced by different field half cycles, can coherently combine, giving rise to well-resolved high-order harmonics on the high-frequency end of the spectrum yoked to a bright midinfrared to microwave supercontinuum, dominating the long-wavelength part of the multidecade radiation output.

Enhanced catalytic performance of Ag2O/BaTiO3 heterostructure microspheres by the piezo/pyro-phototronic synergistic effect

Abstract The introduction of a built-in electric field by using ferroelectric materials is an efficient way to modulate the carrier generation and transportation behavior of photocatalysts. Here, we propose a hydrothermal-synthesized Ag2O/BaTiO3 heterostructure composite, whose photocatalytic performance can be largely enhanced by a four-way coupling effect among piezoelectricity, pyroelectricity, semiconductor and photoexcitation, referred as the piezo/pyro-phototronic synergistic effect. The photoelectrochemical (PEC) test of Ag2O/BaTiO3 shows a high photocurrent density of 3.48 mA/cm2 at 1.5 VSCE, which is 1.5 and 1.3 times as high as that of pristine BaTiO3 and Ag2O, respectively, and the transient photocurrent density of the composite at 0.5 VSCE is 20 times higher than that of the pure BaTiO3. Under varying temperature field and ultrasonic excitation condition, the photocatalytic degradation efficiency of the Ag2O/BaTiO3 composite is enhanced greatly when compared to that under only light illumination condition. This enhancement can be attributed to the attraction and release process of photogenerated carriers during the varying temperature field and ultrasonic excitation cycling. These results indicate that the ferroelectric heterostructure composites can act as a promising photocatalyst in wastewater treatment field under different environmental conditions.