Search

The quantum spin Hall effect lays the foundation for the topologically protected manipulation of waves, but is restricted to one-dimensional-lower boundaries of systems and hence limits the diversity and integration of topological photonic devices. Recently, the conventional bulk-boundary correspondence of band topology has been extended to higher-order cases that enable explorations of topological states with codimensions larger than one such as hinge and corner states. Here, we demonstrate a higher-order quantum spin Hall effect in a two-dimensional photonic crystal. Owing to the non-trivial higher-order topology and the pseudospin-pseudospin coupling, we observe a directional localization of photons at corners with opposite pseudospin polarizations through pseudospin-momentum-locked edge waves, resembling the quantum spin Hall effect in a higher-order manner. Our work inspires an unprecedented route to transport and trap spinful waves, supporting potential applications in topological photonic devices such as spinful topological lasers and chiral quantum emitters., The quantum spin Hall effect is limited to one-dimensional lower boundary states which limits the possibilities for its exploitation in photonic devices. Here, the authors demonstrate a higher-order quantum spin Hall effect in a photonic crystal and observe opposite pseudospin corner states.

The authors demonstrate a feasible design of a one-dimensional non-Hermitian Su-Schrieffer-Heeger model based on photonic coupled resonant optical waveguides. The phase transition points are different from those of the periodic boundary, thus revealing a non-Bloch bulk-boundary correspondence. Moreover, the field distribution is found to be exponentially localized at the ends of an open-boundary chain, which demonstrates a non-Hermitian skin effect.

BackgroundMicrotubule organization is essential for bipolar spindle assembly and chromosome segregation, which contribute to genome stability. Kinesin-5 Eg5 is known to be a crucial regulator in centrosome separation and spindle assembly in mammalian somatic cells, however, the functions and mechanisms of Eg5 in male meiotic cell division remain largely unknown.ResultsIn this study, we have found that Eg5 proteins are expressed in mouse spermatogonia, spermatocytes and spermatids. After Eg5 inhibition by specific inhibitors Monastrol, STLC and Dimethylenastron, the meiotic spindles of dividing spermatocytes show spindle collapse and the defects in bipolar spindle formation. We demonstrate that Eg5 regulates spindle bipolarity and the maintenance of meiotic spindles in meiosis. Eg5 inhibition leads to monopolar spindles, spindle abnormalities and chromosome misalignment in cultured GC-2 spd cells. Furthermore, Eg5 inhibition results in the decrease of the spermatids and the abnormalities in mature sperms.ConclusionsOur results have revealed an important role of kinesin-5 Eg5 in male meiosis and the maintenance of male fertility. We demonstrate that Eg5 is crucial for bipolar spindle assembly and chromosome alignment in dividing spermatocytes. Our data provide insights into the functions of Eg5 in meiotic spindle assembly of dividing spermatocytes.

Magnetic insulating and exchange bias (EB) are two basic magnetic states with actual and potential applications in spintronic and magnonic devices. However, ferromagnetic insulators (FMIs) are rare, and it is even more challenging to obtain a FMI with large EB. In this paper, high performance of FMIs and EB in $\mathrm{LaMn}{\mathrm{O}}_{3}$:NiO nanocomposite epitaxial thin films is reported. The antiferromagnetic NiO nanoparticles, randomly embedded in a ferromagnetic $\mathrm{LaMn}{\mathrm{O}}_{3}$ matrix, enhance the robustness of the insulating state and result in an EB field as large as 1100 Oe. The simultaneously enhanced resistivity and EB are attributed to localized oxygen vacancy, preserved strain state, and increased ferromagnetic-antiferromagnetic interface ratio. This paper provides not only a material candidate for spintronics but also a referential strategy to design artificial materials with multifunctionality.

Monolayer antimony (antimonene) has been reported for its excellent properties, such as tuneable band gap, stability in the air, and high mobility. However, growing high quality, especially large-area antimonene, remains challenging. In this study, we report the direct growth of antimonene on c-plane sapphire substrate while using molecular beam epitaxy (MBE). We explore the effect of growth temperature on antimonene formation and present a growth phase diagram of antimony. The effect of antimony sources (Sb2 or Sb4) and a competing mechanism between the two-dimensional (2D) and three-dimensional (3D) growth processes and the effects of adsorption and cracking of the source molecules are also discussed. This work offers a new method for growing antimonene and it provides ideas for promoting van der Waals epitaxy.

With the development of 3D printing technique, additive manufactured (AM) components are becoming more and more important in the fields of manufacturing industry. However, in the process of manufacturing and utilizing, it is necessary to inspect the appearance of internal defects to ensure safety and to reduce economic losses. In this paper, a pulsed laser is used to generate the ultrasonic waves inside Nickel (Ni) and Titanium (Ti) based alloy samples with internal defects of different diameters, and the propagating ultrasonic waves are detected by an optical interferometer. By analyzing the experimental results, defects with diameters greater than 300 μm in the Ni based alloy sample and that in the Ti based alloy sample can be detected, and this can be validated by X-ray computed tomography. In addition, the effects of ultrasonic waves propagating inside the samples and interacting with the defects are studied theoretically. The experimental results are consistent with the numerical simulation results. These results present that laser ultrasonic technology can evaluate the reliability of AM components, and has the potential to inspect AM components during their production as a non-contact method.

The quality inspection of micro solder joints in laser spot welding (LSW) is a problem of great concern in industrial application. In this paper, a laser ultrasonic technology (LUT) was proposed to inspect the quality of micro solder joints in LSW. Firstly, based on the thermoelastic model of acoustic wave propagation in solid, a theoretical model was built and used to analyze the propagation properties of the Lamb wave in the whole field by finite element method (FEM), the transmitting properties of the excited Lamb wave via solder joint were affected by the effective contacted area of solder joint. Secondly, LUT was used to inspect the 1.2 mm/0.4 mm welding spot of standard/false 304 stainless steel welded components. By comparing the propagating properties of excited ultrasonic wave in different samples with different weld quality, the standard and false welding can be visually distinguished. Finally, a industrial CT was used to check the quality of the samples used in our experiment. Inclusions and pores have been found in the false solder joints, which will reduce the effective contacted area of solder joint, and then affected the propagation of ultrasonic wave. By combining the CT results and the experimental analysis, the experimental results detected by LUT are in good agreement with the simulation results. So, the LUT is a potential method in field of the quality inspection of micro solder joints in LSW.

This paper comprehensively analyzes the stability of a grid-interfacing inverter with the LCL -filter in the discrete domain, where the LCL -filter, along with the controller, is modeled in a polar coordinate. System open-loop and closed-loop poles are analytically studied and expressed in the z -domain. Through the poles movement and distribution analysis, the relationship between system stability and the ratio of resonance frequency over sampling frequency is mathematically revealed and calculated as well as the system control gain limit. Moreover, this paper demonstrates that a grid-voltage feedforward regulator would significantly alter the inverter stability in a weak power system. By means of Jury stability criterion, the stability status under different filter resonance frequency is given. The selection of resonance frequency and filter parameters makes a considerable difference on system behavior. Finally, to improve the robustness against grid inductance variation, a conservative design recommendation of filter parameters and control gain is given. Through the tests on a laboratory-scale prototype, the theoretical analysis is validated by experimental results.

Thermoelectric multilayer thin films used in nanoscale energy conversion have been receiving increasing attention in both academic research and industrial applications. Thermal transport across multilayer interface plays a key role in improving thermoelectric conversion efficiency. In this study, the cross-plane thermal conductivities of nano-constructed Sb2Te3/(Cu, Ag, Au, Pt) thermoelectric multilayer thin films have been measured using time-domain thermoreflectance method. The interface morphology features of multilayer thin film samples were characterized by using scanning and transmission electron microscopes. The effects of interface microstructure on the cross-plane thermal conductivities of the multilayer thin films have been extensively examined and the thermal transfer mechanism has been explored. The results indicated that electron–phonon coupling occurred at the semiconductor/metal interface that strongly affected the cross-plane thermal conductivity. By appropriately optimizing the period thickness of the metal layer, the cross-plane thermal conductivity can be effectively reduced, thereby improving the thermoelectric conversion efficiency. This work presents both experimental and theoretical understanding of the thermal transport properties of Sb2Te3/metal multilayer thin film junctions with important implications for exploring a novel approach to improving the thermoelectric conversion efficiency.

PdS is theoretically proposed to novel topological material with eight-band fermions. Here, PdS 1−δ crystals were successfully grown from KI as solvent by modified flux method. The single crystalline quality and compositional homogeneity of grown PdS 1−δ are characterized by X-ray diffraction and energy dispersion spectroscopy. Temperature dependent electrical transport property of PdS 1−δ demonstrates a semiconductor-like behavior. Analysis of temperature-dependent resistance indicates that there is variable-range-hopping behavior at low temperature. The clear negative MR of PdS 1−δ single crystals is measured at the low temperature (

Further improving electromechanical properties and overcoming relatively low Curie temperature (Tc) of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-100xPT) are still two scientific issues. Here, we demonstrate a stable coexistence of monoclinic-tetragonal (MC-T) phases in ZnO-modified PMN-32PT (PMN-32PT:xZnO) due to the diffusion-induced substitution of Zn2+ for Mg2+. The Curie temperature, saturated polarization, remnant polarization, piezoelectric coefficient (Tc, Ps, Pr, d33) are increased from (160 °C, 22.0 μC/cm2, 13.3 μC/cm2, 350 pC/N) for x = 0 to (180 °C, 30.3 μC/cm2, 22.4 μC/cm2, 470 pC/N) for x = 0.06. Moreover, the thermal stability is improved. After annealing at 150 °C, the x = 0.06 sample shows retrained d33 value of 209 pC/N, about 4 times larger than that of x = 0 counterpart. The improved properties are attributed to the substituting increased polar nanoregions and easy domain switching in MC phase.

Interfacial thermal transport plays a prominent role in the thermal management of nanoscale objects and is of fundamental importance for basic research and nanodevices. At metal/insulator interfaces, a configuration commonly found in electronic devices, heat transport strongly depends upon the effective energy transfer from thermalized electrons in the metal to the phonons in the insulator. However, the mechanism of interfacial electron-phonon coupling and thermal transport at metal/insulator interfaces is not well understood. Here, the observation of a substantial enhancement of the interfacial thermal resistance and the important role of surface charges at the metal/ferroelectric interface in an Al/BiFeO3 membrane are reported. By applying uniaxial strain, the interfacial thermal resistance can be varied substantially (up to an order of magnitude), which is attributed to the renormalized interfacial electron-phonon coupling caused by the charge redistribution at the interface due to the polarization rotation. These results imply that surface charges at a metal/insulator interface can substantially enhance the interfacial electron-phonon-mediated thermal coupling, providing a new route to optimize the thermal transport performance in next-generation nanodevices, power electronics, and thermal logic devices., Y.Z., C.D., and Z.G. contributed equally to this work. This work was supported by the National Natural Science Foundation of China (nos. 11774153, 51772143, 11474158, 11890700, 11904162, 1861161004, 11625418, 11974163, 51732006, 52027803, 61704074, and 91963211), the National Basic Research (Key R&D) Program of China (2017YFA0303702 and 2018YFA0306200), the introduced innovative R&D team of Guangdong (2017ZT07C062), the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (51720001), and the Fundamental Research Funds for the Central Universities (nos. 0213-14380198 and 0213-14380167). Y.N. was supported by High-Level Entrepreneurial and Innovative Talents Introduction, Jiangsu Province. Theoretical work was funded by the Luxembourg National Research Fund through project FNR/C18/MS/12705883/REFOX. (H.A. and J.Í.). C.C. acknowledges support from the Spanish Ministry of Science, Innovation, and Universities under the “Ramón y Cajal” fellowship RYC2018-024947-I. R.R. acknowledges financial support by the Ministerio de Ciencia e Innovación (MICINN) under grant FEDER-MAT2017-90024-P and the Severo Ochoa Centres of Excellence Program under Grant CEX2019-000917-S and by the Generalitat de Catalunya under grants no. 2017 SGR 1506. The authors thank the Centro de Supercomputación de Galicia (CESGA) for the use of their computational resources. The authors thank Yaya Zhou for the support of SEM and EDS measurement., With funding from the Spanish government through the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000917-S).

Acoustics is a classical field of study that has witnessed tremendous developments over the past 25 years. Driven by the novel acoustic effects underpinned by phononic crystals with periodic modulation of elastic building blocks in wavelength scale and acoustic metamaterials with localized resonant units in subwavelength scale, researchers in diverse disciplines of physics, mathematics, and engineering have pushed the boundary of possibilities beyond those long held as unbreakable limits. More recently, structure designs guided by the physics of graphene and topological electronic states of matter have further broadened the whole field of acoustic metamaterials by phenomena that reproduce the quantum effects classically. Use of active energy-gain components, directed by the parity–time reversal symmetry principle, has led to some previously unexpected wave characteristics. It is the intention of this review to trace historically these exciting developments, substantiated by brief accounts of the salient milestones. The latter can include, but are not limited to, zero/negative refraction, subwavelength imaging, sound cloaking, total sound absorption, metasurface and phase engineering, Dirac physics and topology-inspired acoustic engineering, non-Hermitian parity–time synthetic active metamaterials, and one-way propagation of sound waves. These developments may underpin the next generation of acoustic materials and devices, and offer new methods for sound manipulation, leading to exciting applications in noise reduction, imaging, sensing and navigation, as well as communications.

The notion of non-Hermitian optics and photonics rooted in quantum mechanics and photonic systems has recently attracted considerable attention ushering in tremendous progress on theoretical foundations and photonic applications, benefiting from the flexibility of photonic platforms. In this review, we first introduce the non-Hermitian topological physics from the symmetry of matrices and complex energy spectra to the characteristics of Jordan normal forms, exceptional points, biorthogonal eigenvectors, Bloch/non-Bloch band theories, topological invariants and topological classifications. We further review diverse non-Hermitian system branches ranging from classical optics, quantum photonics to disordered systems, nonlinear dynamics and optomechanics according to various physical equivalences and experimental implementations. In particular, we include cold atoms in optical lattices in quantum photonics due to their operability at quantum regimes. Finally, we summarize recent progress and limitations in this emerging field, giving an outlook on possible future research directions in theoretical frameworks and engineering aspects.

Background This study investigates the relationships and mechanism between perceived social support, loneliness, and life satisfaction among Chinese parents of children with autism spectrum disorder (ASD). Method Cross-sectional data were collected from 306 parents of children with ASD, including fathers and mothers, in Guangzhou, Guangdong province, mainland China. A survey comprising the parent-rated Strength and Difficulties Questionnaire, the Multidimensional Scale of Perceived Social Support, the UCLA Loneliness Scale, and the Satisfaction with Life Scale was administered. Results Perceived social support was significantly associated with loneliness and life satisfaction. Loneliness both mediated and moderated the relationship between perceived social support and life satisfaction. Conclusions Theoretically, the findings highlight the role of loneliness in explaining the mechanism through which perceived social support is linked to life satisfaction. Practically, this study suggests that high levels of perceived social support and low levels of loneliness are socio-psychological resources that can be targeted to enhance the life satisfaction of Chinese parents of children with ASD.

Light beams with helical wave fronts, also called optical vortices, have attracted great interest in the community of optics and photonics. They provide an additional degree of freedom for light manipulation, leading to wide-ranging potential applications in micro-particle trapping, optical microscopy, and even quantum information processing. Recently, metallic microstructures are introduced to confine the plasmonic vortices into deep subwavelength dimension, which benefits photonic integration on chip. In this Letter, exploiting the excitation of spoof surface plasmon, we experimentally demonstrate the near-field optical vortices with tunable topological charges supported by a single metaparticle in the microwave regime. These microwave plasmonic-like vortices are excited by surface waves with a spatial asymmetric distribution of electromagnetic field, which are launched by a metallic comb-shaped waveguide. Experimental characterization of highly localized and controllable near-field vortices with the nature of deep subwavelength confirms the numerical simulation. In addition, an equivalent physical model based on the coupled mode theory is proposed to understand the generation mechanism of these spoof plasmonic vortices. Our approach offers an efficient way to generate deterministic subwavelength optical vortices, which provides the potential for critical vortex elements on photonic integrated chip.

Autophagy is well-known as a conserved survival mechanism that protects cells from adverse environments, and autophagy-related protein 8 (ATG8) plays a key role in autophagy process as an essential component. However, the contribution of ATG8 to plant tolerance to environmental stresses is ambiguous. To gain insight into whether and how ATG8 gene functions in plant adaptation to adverse environment conditions, we characterized an ATG8 gene CaATG8c from pepper (Capsicum annuum L.), and found that the deduced amino acid sequence of CaATG8c gene contained the conserved necessary domains and residue for ATG8 functions. Under normal condition, the expression of CaATG8c was detected in all pepper tissues/organs, and its subcellular expression was located to the cytoplasm in onion epidermal cells. The silencing-expression of CaATG8c rendered pepper seedlings more sensitive to heat and salt stress by aggravating the chlorophyll degradation, MDA accumulation and SOD activity decrease. Unexpectedly, the over-expression of CaATG8c gene also reduced Arabidopsis tolerance to heat and salt stress by inhibiting the growth of primary roots and the generation of secondary roots, and disturbing the expression of stress response genes. Our results suggested that both silencing- and over-expression of CaATG8c gene conferred plants more sensitivity to heat and salt stress. Furthermore, the possible mechanism for CaATG8c silencing is speculated to the reduced ability to remove accumulated ROS, whereas for gene over-expression, it is supposed to the disturbance of ROS signal. We propose that the stable and timely expression of CaATG8c may be important for plant adaption to adverse environments.

The topological phase of matter, originally proposed and first demonstrated in fermionic electronic systems, has drawn considerable research attention in the past decades due to its robust transport of edge states and its potential with respect to future quantum information, communication, and computation. Recently, searching for such a unique material phase in bosonic systems has become a hot research topic worldwide. So far, many bosonic topological models and methods for realizing them have been discovered in photonic systems, acoustic systems, mechanical systems, etc. These discoveries have certainly yielded vast opportunities in designing material phases and related properties in the topological domain. In this review, we first focus on some of the representative photonic topological models and employ the underlying Dirac model to analyze the edge states and geometric phase. On the basis of these models, three common types of two-dimensional topological photonic systems are discussed: 1) photonic quantum Hall effect with broken time-reversal symmetry; 2) photonic topological insulator and the associated pseudo-time-reversal symmetry-protected mechanism; 3) time/space periodically modulated photonic Floquet topological insulator. Finally, we provide a summary and extension of this emerging field, including a brief introduction to the Weyl point in three-dimensional systems.

Recently, transition metal pentatellurides MTe5 (M = Zr, Hf) have inspired intensive research effort. Being predicted to be quantum spin Hall insulators (QSHI) with the bulk gap up to hundreds of meVs, it could lead to promising applications at unprecedented high temperature compared with previously discovered QSHI (e.g. HgTe/CdTe or InAs/GaSb quantum wells). However, the experimental works soon followed illustrated considerable discrepancies regarding to whether MTe5 compounds possess a full bulk gap, making their topological nature (topological insulators or Dirac semimetals) illusive. In this work, combining investigations of angle-resolved photoemission spectroscopy (ARPES) and scanning tunneling microscopy (STM), we systematically studied the electronic properties of ZrTe5. In intrinsic samples, we observed little evidence for the existence of topological surface states or large bulk gap. With bulk and surface doping to adjust the position of the Fermi-level, ARPES spectra indicate gapless and highly linear dispersions at the valance band top, in consistence with the STM measurements that show a V-shaped total density of states near the Fermi-level (i.e. suggesting a gapless nature of the electronic structure of ZrTe5). Moreover, near the terrace edge on the surface, we observed non-zero DOS, indicating the existence of edge states.

Transition metal compounds with quasi-two-dimensional structure demonstrate a series of un-precedent quantum phases, such as topological insulator, topological phase transition under thermal/pressure stimuli, which is attributed to delicate interplay among interlayer coupling, spin-orbit coupling and stoichiometry. Here, Cu2TlSe2 and Cu2TlTe2 crystals were successfully synthesized by Bridgeman method. Highly crystalline quality of these samples is verified by X-ray diffraction and microstructural characterization. Temperature-dependent-Hall-resistivity shows that Cu2TlSe2 is hole-like and Hall resistivity is in-sensitive to temperature; while Hall resistivity of Cu2TlTe2 is positive at room temperature and change to negative at 30 K. Combined experimental results and electronic band structures calculated by first-principles method, it is revealed that Cu2TlSe2 is a metal, but Cu2TlTe2 is a semi-metal. This work demonstrates the rich physical phases of layered transition metal compounds under the interplay among interlayer coupling, spin-orbit coupling and stoichiometry.

Bulk silicon possesses no second-order susceptibility (χ(2)), inhibiting second-order nonlinear processes in the emerging silicon photonic platform. Here, we propose a method to overcome this limitation by enabling a third-order (χ(3)) nonlinear mixing scheme between optical waves and an externally applied static electric field inside a silicon waveguide. We show in theory that facilitated by a modal phase-matching scheme efficient second-harmonic generation can be realized under an applied voltage of 65 V, giving rise to an equivalent χ(2) = 4.7 pm/V. We also show that unlike the classical second-harmonic generation, the wavelengths of phase-matched pump and second-harmonic waves are pump-power dependent due to the χ (3) nature of this process.

A long-term goal of phononic communication is controlled transport of elastic wave signals with improved robustness and enhanced information capacity, but existing approaches suffer from unwanted backscattering by defects and disorder that may substantially reduce the transmission rate, or even disable a data channel. This study uses the robust edge states along the interfaces between distinct topological classes to make progress. These fault-tolerant edge channels are protected jointly by both pseudospin and valley degrees of freedom, naturally providing doubled information carriers within every channel, and may serve as a building block for large-scale phononic circuits and networks.

We establish the bilayer non-Hermitian theory with interlayer coupling between two graphenelike lattices described by non-Hermitian Hamiltonians. Two exceptional rings (ERs) and an exceptional concentric ring (ECR) in this system are discovered. A topological classification has been identified for such non-Hermitian Hamiltonians via their global topological invariants. We find that two ERs and the ECR correspond to the global ${\mathbb{Z}}_{3}$ topological invariant $V=+1$ and $V=\ensuremath{-}1$, respectively, whose topological properties are determined by the four-level bands and go beyond the topological properties of a single ER. It is shown that in contrast to the Hermitian case, the topological surface arcs with gain and loss are both present and redistributed in the two ERs and the ECR systems. We further propose an experimental design with bilayer photonic crystals (PCs) to realize the ECR. Our work can potentially pave the way for unveiling the unusual topological properties in such stacked two-dimensional materials and trigger further theoretical and experimental investigations.

Misfit-layered compounds constitute a significant component in the development of thermoelectric materials. Prominent thermoelectric properties arise from their low lattice thermal conductivity, which was supposed to be a consequence of intense phonon scattering at the misfit interfaces. Nevertheless, in most misfit compounds, the coexistence of van der Waals interfaces makes it hard to reveal the effect of misfit interfaces individually. Here, we investigate the impact of misfit interfaces and Bi–O/Bi–O interfaces on the thermal transport of a series of single crystals, including layered KxCoO2 (KCO, reference), misfit-layered compounds Ca3Co4O9 (CCO, with misfit interfaces) and Bi2Ca2Co2Oy (BCCO, with misfit interfaces and Bi–O/Bi–O interfaces) and layered compound Bi2Sr2CaCu2Oy (BSCCO, with Bi–O/Bi–O interfaces). Ultralow thermal conductivity approaching the theoretically predicted thermal conductivity minimum (∼0.28 W m−1 K−1 at 300 K) is achieved only with the existence of Bi–O/Bi–O interfaces with van der Waals interactions. Further analyses of the phonon scattering mechanisms verify that the strength of phonon Umklapp scattering and phonon–boundary (interface) scattering is comparable in KCO and CCO, while in BCCO and BSCCO phonon–boundary scattering dominates. Furthermore, the characteristic lengths for phonon–boundary scattering in BCCO and BSCCO are one magnitude lower than those of KCO and CCO, which proves the remarkable effect of the Bi–O/Bi–O interfaces in reducing thermal conductivity. Our work demonstrates the vital impact of interfaces with strong van der Waals interactions on the thermal conductivity reduction, and provides inspiration for the design of advanced thermoelectric materials.

In this paper, we present a virtual oscillator control (VOC) strategy for power inverters to operate in either grid-connected or islanded settings. The proposed controller is based on the dynamics of the nonlinear Andronov-Hopf oscillator and it provides voltage regulation, frequency support in islanded mode. It also features the potential to respond to real- and reactive-power setpoints for dispatchability in grid-connected mode. In contrast to early VOC incarnations which exhibit undesirable harmonics, the proposed controller offers a sinusoidal ac limit cycle as well as improved dynamic performance. Moreover, the proposed controller intrinsically generates orthogonal signals which facilitate implementation in three-phase systems. We study the controller dynamical model and outline a systematic design procedure such that the inverter satisfies standard ac performance specifications. Numerical simulations validate the analytical developments.

International audience; Poor wettability and acoustic mismatch between diamond and copper cause low interface thermal conductance and thus low thermal conductivity in their composites. In this work, beyond widely used strategies such as surface metallization and matrix alloying, in-situ grown graphene is introduced as a highly effective interlayer. The positive role of graphene on improving wetting between diamond and copper was supported by the increase of relative density, fractured surface morphology and interface microstructure. Thanks to the improved wetting and mitigated acoustic mismatch between diamond and copper, the interfacial thermal conductance is increased by ~3.7 times in the diamond/graphene/copper composite as indicated by differential effective medium calculation. Such a positive role of graphene 2 interlayer also agrees with the results from the time-domain thermoreflectance measurements. As a result, the thermal conductivity of the diamond/graphene/copper composite is 61% higher than that of the counterpart without graphene interlayer. This study provides a new approach for interface modification by 2D materials for a high TC of diamond/copper composite beyond surface metallization and matrix alloying.

Kinesin-6 KIF20A is essential for microtubule organization and central spindle assembly during cytokinesis. However, the functions of KIF20A in meiotic division and spermatogenesis remain elusive. Here, we report that kinesin-6 KIF20A locates at the microtubules in mouse spermatogenic cells and co-localizes with the spindle midzone and midbody. We demonstrate that central spindle organization and chromosomal stability are regulated by KIF20A in male meiotic division. KIF20A inhibition leads to the defects in central spindle assembly and cytokinetic abscission, and finally results in the increase of aneuploid cells and the alteration of cell populations in the spermatogenic cells. Furthermore, we have revealed that kinesin-6 KIF20A is associated with the formation and maturation of the acrosomes during spermatogenesis. Our findings have identified the specific roles of KIF20A in central spindle organization in meiotic division.

In modern power systems, the increasing penetration of renewables and power electronics, particularly inverter-based wind and solar power generation, is altering power system dynamics and bringing new stability concerns. One challenging issue that is attracting considerable attention is the wide range of power oscillations associated with multiple parallel grid-connected inverters. In such systems, the characteristics in terms of resonance and oscillation are significantly different from single-inverter systems. This paper investigates the mutual interaction and stability issues of multiple grid-interfacing inverters with LCL -filters in power-electronics-based power systems under various grid conditions. The investigation reveals that such interactions between power inverters and the grid may excite multiple resonances at various frequencies under certain grid conditions. The nodal admittance matrix concept, which was originally from power systems engineering, is adopted here. Moreover, this paper further develops an Interaction-Admittance model that can effectively describe these mutual interactions in terms of a physical network admittance. We apply our model to various scenarios such as stiff grid conditions and inductive grids with/without power factor correction capacitors. The results with the proposed framework demonstrate an intuitive interpretation of multi-inverter system resonance and instabilities. Finally, simulations and experiments on a lab-scale system are provided to verify the theoretical analysis.

Bound states in the continuum (BICs) in photonic crystals represent the unique solutions of wave equations possessing an infinite quality-factor. We design a type of bilayer photonic crystal and study the influence of symmetry and coupling between TE and TM polarizations on BICs. The BIC modes possess $C_{3v}$ symmetry in the x-y plane while the mirror-flip symmetry in the z-direction is broken, and they provide selective coupling into different layers by varying frequency. The enhanced TE-TM coupling due to broken mirror-flip symmetry in the z-direction gives rise to high-Q factor BIC states with unique spatial characteristics. We show the emergence of such BIC states even in the presence of coupling between the TE- and TM-like modes, which is different from the existing single polarization BIC models. We propose to study BICs in multilayer systems, and the results may be helpful in designing photonic settings to observe and manipulate BICs with various symmetries and polarizations for practical applications., 15 pages, 6 figures

In this paper, we introduce a method to analyze three-phase inverters with current control as equivalent circuits. In contrast to existing methods, both the averaged power stage model and its closed-loop controller are represented as a single unified circuit. Since the complete system can be examined as one equivalent circuit, we can glean several insights on design and operation; particularly relating to the time scales at which the controller tracks reference signals and the ability to reject disturbances. We leverage the insights afforded by this general approach to outline design strategies for controllers in both synchronous and stationary reference frames.

Exploring new topological materials with large topological nontrivial bandgaps and simple composition is attractive for both theoretical investigation and experimental realization. Recently alpha tin ({\alpha}-Sn) has been predicted to be such a candidate and it can be tuned to be either a topological insulator or a Dirac semimetal by applying appropriate strain. However, free-standing {\alpha}-Sn is only stable below 13.2 {\deg}C. In this study, a series of high-quality {\alpha}-Sn films with different thicknesses have been successfully grown on InSb substrates by molecular beam epitaxy (MBE). Confirmed by both X-ray diffraction (XRD) and reciprocal space mapping (RSM), all the films remained fully strained up to 4000 {\AA}, proving the strain effect from the substrate. Remarkably, the single-crystalline {\alpha} phase can persist up to 170 {\deg}C for the 200 {\AA} thick sample. The critical temperature where the {\alpha} phase disappears decreases as the film thickness increases, showing the thermal stabilization can be engineered by varying the {\alpha}-Sn thickness. A plastic flow model taking the work hardening into account is introduced to explain this dependence, assuming the strain relaxation and the phase transition occur successively. This enhanced thermal stability is prerequisite for above room-temperature characterization and application of this material system., Comment: 21 pages, 4 figures, 1 table

Recently, the oxide semiconductor $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ nanoplates with an ultrahigh mobility demonstrated superior ultrafast photoelectronic properties of which physical origins are hotly studied theoretically and experimentally. Here we grew the $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ crystals via the chemical vapor transport method. The $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ crystal exhibits an ultrahigh Hall mobility $(\ensuremath{\sim}2.24\ifmmode\times\else\texttimes\fi{}{10}^{5}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{2}{\mathrm{V}}^{\ensuremath{-}1}{\mathrm{s}}^{\ensuremath{-}1}\mathrm{at}\phantom{\rule{0.16em}{0ex}}2\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ and a giant magnetoresistance $(\mathrm{MR}\ensuremath{\sim}0.9\ifmmode\times\else\texttimes\fi{}{10}^{4}%\phantom{\rule{4pt}{0ex}}\mathrm{at}\phantom{\rule{4pt}{0ex}}9\phantom{\rule{0.16em}{0ex}}\mathrm{T}\phantom{\rule{4pt}{0ex}}\mathrm{and}\phantom{\rule{4pt}{0ex}}2\phantom{\rule{0.16em}{0ex}}\mathrm{K})$ that are comparable with those in $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ nanoplates. MR data clearly shows Shubnikov--de Haas (SdH) oscillations. Systematic analysis of SdH oscillation verifies that the electrical carrier in $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ is a conventional Schr\"odinger fermion and that the Fermi surface of $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ is quasi-two-dimensional-like. Remarkably, the resistivity of $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ is quadratically dependent on temperature from 2 to 300 K, inferring the electron-electron scattering in $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$. Kohler's rule analysis of temperature-dependent MR verifies only electron-electron scattering dominated by the electrical and magnetotransport properties of $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$. Combining first-principle calculations and empirical Landau Fermi liquid theory, we substantiate that the Fermi surface of the electron in $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ is an elongated ellipsoid, as well as that the electron-electron interaction and screening length of $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$ are estimated as 7.49 eV and 5.53 \AA{}, respectively. These values are quite large among the conventional doped semiconductors. Our study may shed more light on the physical origin of the ultrafast photoelectric response of $\mathrm{B}{\mathrm{i}}_{2}{\mathrm{O}}_{2}\mathrm{Se}$.

Heat stress has become a major threat to crop production due to global warming; however, the mechanisms underlying plant high-temperature sensing are not well known. In plants, the membrane-anchored receptor-like kinases (RLKs) relay environmental signals into the cytoplasm. In a previous study, we isolated a wall-associated RLK-like (WAKL) gene CaWAKL20 from pepper (Capsicum annuum L.). Here, the amino acid sequence of CaWAKL20 was characterized and found to consist of conserved domains of WAK/WAKL family, including an extracellular region containing a GUB-WAK binding domain and a degenerated EGF2-like domain; a transmembrane region; and an intercellular region with an STKc catalytic domain. Moreover, CaWAKL20 transcription was inhibited by heat stress, whereas it was induced by both ABA and H2O2 treatments. Silencing of CaWAKL20 enhanced pepper thermotolerance, while overexpression decreased Arabidopsis thermotolerance. Additionally, Arabidopsis lines overexpressing CaWAKL20 showed less sensitivity to ABA during seed germination and root growth. Finally, the survival rate of Arabidopsis seedlings under heat stress treatment was enhanced by ABA pre-treatment, while it was compromised by the overexpression of CaWAKL20. Furthermore, the heat-induced expression of several ABA-responsive genes and some key regulator genes for thermotolerance was decreased in Arabidopsis CaWAKL20-overexpression lines. These results suggest that CaWAKL20 negatively modulates plant thermotolerance by reducing the expression of ABA-responsive genes, laying a foundation for further investigation into the functional mechanisms of WAKs/WAKLs in plants undergoing environmental stresses.

Wave trapping and manipulation are at the heart of modern integrated photonics and acoustics. Grand challenges emerge on increasing the integration density and reducing the wave leakage/noises due to fabrication imperfections, especially for waveguides and cavities at subwavelength scales. The rising of robust wave dynamics based on topological mechanisms offers possible solutions. Ideally, in a three-dimensional (3D) topological integrated chip, there are coexisting robust two-dimensional (2D) interfaces, one-dimensional (1D) waveguides and zero-dimensional (0D) cavities. Here, we report the experimental discovery of such a dimensional hierarchy of the topologically-protected 2D surface states, 1D hinge states and 0D corner states in a single 3D system. Such an unprecedented phenomenon is triggered by the higher-order topology in simple-cubic sonic crystals and protected by the space group \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${P}_{m\bar{3}m}$$\end{document}Pm3 ¯m. Our study opens up a new regime for multidimensional wave trapping and manipulation at subwavelength scales, which may inspire future technology for integrated acoustics and photonics., Here, the authors report the experimental discovery of such a dimensional hierarchy of the topologically-protected 2D surface states, 1D hinge states and 0D corner states in a single 3D acoustic system by using higher-order topological sonic crystals.

Topological insulators (TIs), featured by a symmetry-protected gapless surface Dirac cone(s) in their complete energy band gaps, have been extended from condensed-matter physics to classical bosonic systems in the last decade. However, acoustic TIs in three dimensions remain elusive because of a lack of a spin or polarization degree of freedom for longitudinal airborne sound. Here, we experimentally demonstrate a feasible way to hybridize an acoustic TI in three dimensions based on band inversion through a three-dimensional (3D) hybrid Dirac point (HDP). Such a 3D HDP, with linear dispersion in the layer plane while quadratic out of the layer, is distinct from a general point with linear dispersion in all directions. Interestingly, a single nearly gapless conical-like dispersion for acoustic surface states can be achieved at both zigzag and armchair interfaces, supporting robust sound transport. Our findings can serve as a tabletop platform for exploring unique acoustic applications based on the two-dimensional topological interfaces.

Virtual oscillator control (VOC) is a decentralized time-domain control technique for ac microgrids where inverters are regulated to emulate the dynamics of weakly nonlinear oscillators. VOC enables the design of modular and scalable systems where inverters can synchronize and share power without communication and in near real-time. In this paper, we show how off-the-shelf commercial inverters with current control can be reprogrammed to behave as voltage sources with virtual oscillator dynamics for deployment in islanded settings. We focus on commercial grid-tied inverters that have an inner current-control loop and show how the outer-loop controls can be straightforwardly modified to enable voltage-control-mode operation. To illustrate the practicality and ease of our approach, the proposed strategy was implemented on a 3.2 kVA experimental test bed composed of 10 SunPower-brand micro-inverters with special firmware for VOC implementation. Results from the experiments not only demonstrate feasibility of the proposed dual-loop VOC architecture on a hardware setup but also show improved voltage regulation due to the additional voltage control loop.

Time-reversal symmetry (TRS) of electrons is associated with an anti-unitary operator with T 2 = &minus, 1 , which induces Kramers degeneracy and plays an important role in realizing the quantum spin Hall effect (QSHE). By contrast, TRS of photons is described by T b 2 = 1 . We point out that due to this difference, TRS is not the necessary condition for the construction of the photonic analogue of the QSHE. Instead, by constructing an artificial pseudo TRS T p with T p 2 = &minus, 1 in a photonic system, one can realize the photonic Kramers degeneracy and a pair of topological protected edge states, a photonic analogue of the QSHE. Specifically, by retrieving the optical parameters of materials with the pseudo TRS, we propose a photonic topological insulator (PTI) utilizing a pair of double-degenerate transverse electric (TE) and transverse magnetic (TM) polarizations to mimic the spin up and down states of the electron. We demonstrate that the unidirectional polarization-dependent transportation of TE and TM edge states can be realized in this system based on computer simulations. For all possible symmetry types, we check the robustness of these topological states by using a complete set of impurities, including three Pauli matrices and one complex conjugate operator. The results show that the PTI is protected by the pseudo TRS T p . In general, an arbitrary pair of optical polarizations on the Bloch sphere can be utilized to construct photonic pseudospin states and the PTI. Our findings confirm the physical meaning of the pseudo TRS and may provide guidance for future PTI designs.

Precise control of solid-state elastic waves’ mode content and coherence is of great use nowadays in reinforcing mechanical energy harvesting/storage, nondestructive material testing, wave-matter interaction, high sensitivity sensing, and information processing, etc. Its efficacy is highly dependent on having elastic transmission channels with lower loss and higher degree of freedom. Here, we demonstrate experimentally an elastic analog of the quantum spin Hall effects in a monolithically scalable configuration, which opens up a route in manipulating elastic waves represented by elastic pseudospins with spin-momentum locking. Their unique features including robustness and negligible propagation loss may enhance elastic planar-integrated circuit-level and system-level performance. Our approach promotes topological materials that can interact with solid-state phonons in both static and time-dependent regimes. It thus can be immediately applied to multifarious chip-scale topological phononic devices, such as path-arbitrary elastic wave-guiding, elastic splitters and elastic resonators with high-quality factors., Precise control of elastic waves is of great use in current technologies. Here, Yu et al. realize the analogue of quantum spin Hall effects for the elastic waves in a plain plate consisting of identical perforated holes in wavelength scales.

Effective heat dissipation in highly integrated electronic (nano-)devices is being a technical bottleneck in the microelectronic industry, where diamond/copper matrix (Dia/Cu) composite is considered as a promising heat sink material for thermal management applications. However, poor wettability and acoustic mismatch between diamond and Cu lead to low interfacial thermal conductance (ITC), producing much lower thermal conductivity (TC) of such a composite than that of pure Cu. Surface metallization and matrix alloying have widely been utilized for interface engineering by introducing carbide interlayer, while an uniform and nano-sized (< 100 nm) interlayer cannot be obtained and alloying decreases overall TC of matrix. Here, a novel and highly thermal conductive Dia/Cu composite component, using in-situ grown graphene as the highly effective interlayer, was prepared by vacuum hot pressing. The graphene interlayer improves interfacial wetting and mitigates acoustic mismatch between diamond and Cu, thereby improving ITC of composite. As results, the TC of diamond/graphene/copper (Dia/Gr/Cu) composite is 61% higher than that of the Dia/Cu counterpart. Differential effective medium (DEM) calculation further indicates that the Dia/Gr/Cu interface exhibits an ITC ~3.7 times higher than the Dia/Cu counterpart. This study provides a new approach for interface modification by 2D materials for high TC Dia/Cu composite beyond surface metallization and matrix alloying.

Acoustic analogue computation and signal processing are of great significance, however, it's challenging to realize the acoustic computing devices because of their limitations of single function and complex structure. In this paper, an acoustic multifunctional device, which can gate or amplify acoustic waves without resorting to altering the frequency and structure using a passive acoustic parity-time (PT)-symmetric metamaterial, is realized theoretically and experimentally. The metamaterial is constructed by five lossless-loss periodically distributed media which are modulated to achieve the passive PT symmetry. At the coherent perfect absorber (CPA)-emitter point in the broken PT-symmetric phase, the logic gates (AND, OR, XOR and NOT) and small signal amplifier are realized in a single system by adjusting the phase and amplitude differences between two incoming beams, respectively. This work provides a new route for the connection between the PT symmetry and the acoustic metamaterial, which has great potential applications in acoustic modulation and acoustic multifunctional device.

The epitaxial growth of tin in an alpha phase (α-Sn) is desired for its topological properties. In this study, we have successfully grown a series of α-Sn films on CdTe (001) substrates by molecular beam epitaxy with different thicknesses. A (2 × 1) surface reconstruction of CdTe is obtained due to efficient cleaning by atomic hydrogen, which favors the α-Sn growth. The high quality of the α-Sn films has been confirmed by x-ray diffraction, atomic force microscopy, etc. Thickness and temperature-dependent electrical transport properties have been studied. All the samples show a p-type transport at room temperature, but transitions in transport type are observed at lower temperatures. These transport behaviors can be well explained by a three-band model, and a phase diagram illustrating the transport behaviors in α-Sn is presented.

Frontier investigations on a contemporary family of materials comprise a new class of topological materials that have been discovered in three dimensional (3D) semimetallic crystals. Beyond already unconventional topological quasiparticles in Dirac and Weyl semimetals, nodal-line semimetals provide an even richer platform encompassing robust band-touching manifolds and exotic transport properties. Classical configurations including artificial crystals have emerged as popular systems not only to replicate these new properties in wave-based scenarios, but particularly also to ease experimental complexities of electronic systems and to permit topological tuning via variable geometrical designs. Sonic crystals are one of such example, in which dissimilar fluid or rigid inclusions or channels are combined to tailor the acoustic material response at will. Here, we design a cubic lattice of guiding channels allowing us to map topological characteristics of quasi-particles excitations to audible sound properties. Simply by varying the cross section of these channels, we bring forward multiple phase transitions among four different interlaced nodal features, which resemble the knitting of 3D Bloch-bulk bands in momentum space. One nodal attribute appears to feature an acoustic version of directional massless Dirac fermions, which is experimentally characterized and displays linear crossing in one direction and flat bands in the perpendicular one, enabling strongly focused and collimated sound beams, thanks to this peculiar dispersion. J.C. acknowledges the support from the European Research Council (ERC) through the Starting Grant No. 714577 PHONOMETA and from the MINECO through a Ramón y Cajal grant (Grant No. RYC-2015-17156). X.J.Z. M.H.L. and Y.F.C. acknowledge the support from the National Key R & D Program of China (2017YFA0303702, 2018YFA0306200), the National Natural Science Foundation of China (Grant No. 51902151, 11625418, 11890700, 51732006 and 51902151), the Natural Science Foundation of Jiangsu Province (Grant No. BK20190284) and the Fundamental Research Funds for the Central Universities (14380165). Publicado