LCL resonance complicates the design of a current control loop and can even threaten its stability. Extensive approaches have been proposed to deal with this resonance, among which active damping ...(AD) schemes based on the feedback of a single filter variable have been shown to be effective and cost-efficient. This paper presents a study of such AD techniques, where a generalized approach to developing an AD controller by relating a control diagram to an equivalent circuit is proposed. Based on this approach, AD controller forms with any one of four commonly used filter variables to realize virtual resistors (VRs) in six different connections to the LCL filter are derived. Comparisons are then made between these 24 AD controller alternatives by considering the implementation complexity of the AD controller, the number of measuring sensors, and the effect of the AD controller on the power stage. Consequently, grid-side current feedback AD to realize a VR in parallel with the filter capacitor is selected as a considered alternative. Next, two issues associated with the practical implementation of the selected grid-side current feedback AD, caused by the second-order differential expression and the digital time delay, are discussed and solved. Finally, the selected AD method is analyzed in the discrete z-domain, and its effectiveness is experimentally verified.
Abstract
Spin wave has attracted significant attention in various fields because of its rich physics and potential applications in the development of spintronics devices in the post-Moore era. ...However, the analog of a subluminal-like propagation in the field of spin waves has not been well discussed. Here, we theoretically demonstrate the ultra-slow spin waves propagation in a nanoscale two-dimensional ferromagnetic film in the presence of magnon-skyrmion interaction. The minimum spin waves propagation velocity was estimated to be as low as 1.8 m s
−1
by adjusting the system parameters properly, and the spin waves group delay and advance are dynamically tunable via the intensity or detuning of the control field, which allows the possibility of observing superluminal- and subluminal-like spin waves propagation in a single experimental setup. These results deepen our understanding of the spin wave–skyrmion interactions, open a novel and efficient pathway to realize ultra-slow spin waves propagation, and are expected to be applied to magnetic information storage and quantum operations of magnons.
We quantify the bulk topographic characteristics of the Tibet‐Qinghai plateau with specific focus on three representative regions: northern, central, and southeastern Tibet. Quantitative landscape ...information is extracted from Shuttle Radar Topography Mission digital elevation models. We find that the morphology of the Tibetan plateau is nonuniform with systematic regional differences. The northern and central parts of the plateau are characterized by what we suggest to call “positive topography,” i.e., a topography in which elevation is positively correlated with relief and mean slope. A major change from the internally drained central part of Tibet to the externally drained part of eastern Tibet is accompanied by a transition from low to high relief and from positive to “negative topography,” i.e., a topography where there is an inverse or negative correlation between elevation and relief and between elevation and mean slope. Relief in eastern Tibet is largest along rivers as they cross an ancient, eroded plateau margin at high angle to the major strike‐slip faults, the Yalong‐Yulong thrust belt, implying strong structural control of regional topography. We propose that the evolution of river systems and drainage efficiency, the ability of rivers to transport sediments out of the orogen, coupled with tectonic uplift, is the simplest mechanism to explain systematic regional differences in Tibetan landscapes. Basin filling due to inefficient drainage played a major role in smoothing out the tectonically generated structural relief. This mode of smoothing started concurrently with tectonic construction of the relief, as most clearly illustrated today in the Qilian Shan‐Qaidam region of the northeastern plateau. In the interior of Tibet, further “passive” filling, due to internal drainage only, continued to smooth the local relief millions of years after the cessation of major phases of surface uplift due to crustal shortening. Thus, diachronous beveling at high elevation produced the low‐relief surface of the high plateau. In southeast Tibet, headward retreat of external drainages brought back “in” the global ocean base level, first disrupting then interrupting the relief‐reduction process. It produced a transitional topography by dissecting the “old” remnant plateau surface, which introduced younger and steeper incision of this hitherto preserved high base level. This provides a unifying mechanism for the formation of the low‐relief plateau interior, and for the origin of the high‐elevation, low‐relief relict surface in southeastern Tibet. Our analysis brings forth the importance of surface processes, in particular drainage efficiency, in shaping plateau morphology and landscape relief. Such key processes appear to have been mostly ignored in numerical models of plateau deformation. Our results also cast doubt on and provide a more realistic alternative to the fashionable contention that a continuous preuplift, low‐relief surface first formed at low elevation, extending all the way to the South China Sea shore, before being warped upward in the late Miocene‐Pliocene by lower crustal channel flow.
Fault geometric complexity plays a critical role in earthquake rupture dimension. Fault bifurcations are commonly observed in earthquake geology, yet, robust kinematic rupture processes on bifurcated ...fault branches are largely missing, limiting our understanding of rupture dynamics and seismic hazard. Here, we holistically study the fault geometry and bilateral rupture of the 2021 Mw7.4 Maduo, China earthquake, that shows clear fault bifurcation near its eastern terminal. We integrate space geodesy imaging, back‐projection of high‐frequency teleseismic array waveforms, multiple point source and finite fault inversions, and constrain in detail the rupture process, in particular, through its fault bifurcation. Our models reveal a stable rupture speed of ∼2.5 km/s throughout the entire rupture and a simultaneous rupture through fault branches bifurcated at 20°. The rupture on bifurcated faults radiated more high‐frequency waves, especially from the stopping phases. The stopping phase on the southern branch likely stopped the rupture on the northern branch.
Plain Language Summary
Earthquake is produced by sudden shear dislocation across the fault. The geometric complexity of fault structure, such as bend, step‐over, branching and bifurcation, play important roles in determining the final rupture dimension (hence the magnitude) of the earthquake, as they can easily produce stress heterogeneity on the faults. Although geological and recent space geodetic observations have well‐recorded the fault geometry complexity, detailed spatial and temporal evolution of rupture through such fault segments, especially fault bifurcations, are rarely well‐imaged. In this study, we integrate broadband seismic waveform and geodetic observations for the 2021 Mw7.4 Maduo earthquake in China, and process and model them with a set of tools, to produce a high resolution rupture model for the earthquake. The preferred model reveals a near constant rupture speed of 2.5 km/s throughout the entire rupture, and resolves the detailed rupture process through the bifurcated fault segments at its eastern terminal, where the termination of the rupture on the southern branch stopped the rupture on the northern branch.
Key Points
Geodetic imaging, back‐projection, multiple point source and finite fault inversions are conducted for the Maduo earthquake
We show a stable rupture speed (∼2.5 km/s) of the entire rupture and a simultaneous rupture through bifurcated fault branches
The stopping phase on the southern branch likely stopped the rupture on the northern branch
The degree to which deformation and seismicity is focused on major mapped structures remains a key unknown in assessing seismic hazards and testing continental deformation models. Here we combine 208 ...Global Positioning System (GPS) velocities with 12‐track Interferometric Synthetic Aperture Radar (InSAR) rate maps to form high‐resolution velocity and strain rate fields for south‐central Tibet. Our results show that deformation is not evenly distributed across the region. We find a few zones with high strain rates, most notably the Yutian‐Zhongba strain rate zone. However, the average of the strain rates is similar within and outside the mapped fault zones. In addition, the slip rates are low on all the conjugate strike‐slip faults widespread in central Tibet. The observations are difficult to reconcile with time‐invariant block models or with continuum models that lack mechanisms for strain localization. Our results support arguments that the most robust estimates of seismic hazard should integrate seismicity catalogues, active fault maps, and geodetic strain rate models.
Key Points
Geodetic velocity field shows spatially variable strain within south‐central Tibet
Strain rates are similar outside and inside the mapped fault zones
Conjugate strike‐slip faults in south‐central Tibet have low slip rates (≤4 mm/year)
The magnetostrictive effect provides an opportunity for exploring fundamental phenomena related to the phonon-magnon interaction. Here we show a tunable slow light in a cavity magnetomechanical ...system consisting of photon, magnon and phonon modes with a nonlinear phonon-magnon interaction, which originates from magnetostrictive forces. For a strong photon-magnon coupling strength, we can observe a transparency (absorption) window for the probe by placing a strong control field on the red (blue) detuned sideband of the hybridized modes, which are comprised of photons and magnons. In this work, we mainly show the characteristic changes in dispersion in the range of the transparency window. The value of group delay can be continuously adjusted by using different frequencies of magnon, which are determined by the external bias magnetic field and therefore can be conveniently tuned in a broad range. Both the intensity and the frequency of the control field have an influence on the transformation from subluminal to superluminal propagation and vice versa. Furthermore, one may achieve long-lived slow light (group delay of millisecond order) by enlarging the pump power. These results may find applications in information interconversion based on coherent coupling among photons, phonons and magnons.
Glycidyl fatty acid esters (GEs), one of the main contaminants in processed oils, are mainly formed during the deodorization step in the refining process of edible oils and therefore occur in almost ...all refined edible oils. GEs are potential carcinogens, due to the fact that they readily hydrolyze into the free form glycidol in the gastrointestinal tract, which has been found to induce tumors in various rat tissues. Furthermore, glycidol has already been identified as a “possible human carcinogen’’ (group 2A) by the Intl. Agency for Research on Cancer (IARC). Therefore, significant effort has been devoted to inhibit and eliminate the formation of GEs. The aim of this review is to provide a comprehensive summary on the following topics: (i) GE occurrence data for different edible oils and oil‐based food products, (ii) precursors of GEs, (iii) factors influencing the formation of GEs, (iv) potential reaction mechanisms involving the leaving group and reaction intermediates, and (v) analytical methods, including the indirect and direct methods. More importantly, the various elimination methods for GEs in refined edible oils are being reviewed with focus on 3 aspects: (i) inhibition and removal of reactants, (ii) modification of reactive conditions, and (iii) elimination of GE products.
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