Tunable topological charge vortex microlaser Zhang, Zhifeng; Qiao, Xingdu; Midya, Bikashkali ...
Science (American Association for the Advancement of Science),
05/2020, Volume:
368, Issue:
6492
Journal Article
Peer reviewed
Open access
The orbital angular momentum (OAM) intrinsically carried by vortex light beams holds a promise for multidimensional high-capacity data multiplexing, meeting the ever-increasing demands for ...information. Development of a dynamically tunable OAM light source is a critical step in the realization of OAM modulation and multiplexing. By harnessing the properties of total momentum conservation, spin-orbit interaction, and optical non-Hermitian symmetry breaking, we demonstrate an OAM-tunable vortex microlaser, providing chiral light states of variable topological charges at a single telecommunication wavelength. The scheme of the non-Hermitian-controlled chiral light emission at room temperature can be further scaled up for simultaneous multivortex emissions in a flexible manner. Our work provides a route for the development of the next generation of multidimensional OAM-spin-wavelength division multiplexing technology.
Modular multilevel converters (MMC) are an effective option for the continuously growing demands of voltage-sourced converter-based high-voltage direct-current (VSC-HVDC) transmission. However, ...accurate modeling of MMC with a high level in PSCAD/EMTDC is extremely time-consuming and requires hardware. Based on the Kirchhoff's Law, an equivalent accelerated model for MMC is proposed. The essence of the new model is the partition of one large-scale admittance matrix into substantial small-scale matrices, which is mathematically demonstrated with the nodal analysis method. Finally, the detailed electromagnetic transient simulations are implemented for the comparisons of steady state and transient performances, and the results validate the proposed model.
Applications that use the orbital angular momentum (OAM) of light show promise for increasing the bandwidth of optical communication networks. However, direct photocurrent detection of different OAM ...modes has not yet been demonstrated. Most studies of current responses to electromagnetic fields have focused on optical intensity-related effects, but phase information has been lost. In this study, we designed a photodetector based on tungsten ditelluride (WTe
) with carefully fabricated electrode geometries to facilitate direct characterization of the topological charge of OAM of light. This orbital photogalvanic effect, driven by the helical phase gradient, is distinguished by a current winding around the optical beam axis with a magnitude proportional to its quantized OAM mode number. Our study provides a route to develop on-chip detection of optical OAM modes, which can enable the development of next-generation photonic circuits.
Topological photonics in strongly coupled light-matter systems offer the possibility for fabricating tunable optical devices that are robust against disorder and defects. Topological polaritons, ...i.e., hybrid exciton-photon quasiparticles, have been proposed to demonstrate scatter-free chiral propagation, but their experimental realization to date has been at deep cryogenic temperatures and under strong magnetic fields. We demonstrate helical topological polaritons up to 200 kelvin without external magnetic field in monolayer WS
excitons coupled to a nontrivial photonic crystal protected by pseudo time-reversal symmetry. The helical nature of the topological polaritons, where polaritons with opposite helicities are transported to opposite directions, is verified. Topological helical polaritons provide a platform for developing robust and tunable polaritonic spintronic devices for classical and quantum information-processing applications.
Mg isotopic composition of river water is dominantly controlled by the dissolution of both silicate and carbonate sources and a series of biogeochemical processes. However, the relative importance of ...source and isotopic fractionation control at basin/global scale is poorly constrained. This study presents the Mg isotopic composition of river water and suspended load in river draining silicate rocks in the southeastern coastal region of China. The fractionation effect of silicate weathering on Mg isotopes is documented in both dissolved and solid phases. Mg isotopic composition of rivers draining silicate rocks exhibit ∼0.3‰ δ26Mg difference, the release of Mg from Mg‐rich minerals and formation of clays are the dominant processes controlling Mg isotopic composition of river water. The variation of Mg isotopic compositions of suspended load is closely related to the species of secondary clays (illite and chlorite); the fractionation direction during illite and chlorite formation contrasts, isotopically heavy Mg preferentially incorporates into illite while light Mg incorporates into chlorite. Furthermore, the negative correlation between 1/Mg and Mg isotopic compositions of river water indicates the Mg re‐distribution and isotope fractionation between weathering solutions and secondary clays during silicate weathering. Such isotope fractionation‐induced Mg isotope variations could be employed to estimate the contribution of Mg from silicate weathering at basin/continental scale.
Key Points
The δ26Mg values of Southeast Coastal Rivers draining silicate rocks exhibit ∼0.3% difference due to isotope fractionation
There is a clay control on δ26Mg values of suspended load
The Mg isotope fractionation is coupled with Mg re‐distribution during silicate weathering
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
•The isotopic composition of stream water is controlled by the different sources.•The lapse rate of δ18O was −0.19 ‰/100 m across the YZR Basin.•Potential sources of YZR were identified and ...quantified.
Investigations of the hydrological processes of the Yarlung Zangbo River (YZR), a sizeable highland river on the southern margin of the Tibetan Plateau (TP), face challenging constraints owing to the complexities in the water sources and cycle pathway. A total of 156 stream water samples from the YZR Basin were collected and analyzed to elucidate our understanding of regional hydroclimate. The isotopic values were more negative in the uppermost reaches of the YZR and progressively increased along the river, with mean δ18O and δD values at − 15.16 ‰ and − 111.58 ‰, respectively. A clear negative gradient of − 0.19 ‰/100 m was obtained from the datasets, which is consistent with that of the southeastern TP. The linear regression for all samples was δD = 8.64 × δ18O + 19.80 (R2 = 0.93, n = 192), and the slope and intercept were highly similar to those of the meteoric water line in the TP, suggesting that precipitation plays a dominant role in stream recharge sources. Combining the results from the air mass trajectory model and the d-excess values, we found that moisture in the YZR originates mainly from the Bay of Bengal, with westerly mixing in the upper reaches. In addition to precipitation, glacial meltwater and geothermal waters were considered significant water sources for the YZR based on geographic and geological conditions. The proportion of glacial meltwater in the uppermost reaches was calculated to range from 68.2 % to 70.4 % using the end-member mixing analysis method. The contribution ratios of precipitation, glacial meltwater, and geothermal water were almost equal in the middle of the basin, while glacial meltwater contribution dominated in the downstream regions. These findings will significantly impact understanding of the hydrological cycle in the study area and provide vital baseline knowledge about the contribution proportion of different recharge sources in the YZR basin.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Microtubules play an important role in the process of cell mitosis and can form a spindle in the mitotic prophase of the cell, which can pull chromosomes to the ends of the cell and then divide into ...two daughter cells to complete the process of mitosis. Tubulin inhibitors suppress cell proliferation by inhibiting microtubule dynamics and disrupting microtubule homeostasis. Thereby inducing a cell cycle arrest at the G2/M phase and interfering with the mitotic process. It has been found that a variety of chalcone derivatives can bind to microtubule proteins and disrupt the dynamic balance of microtubules, inhibit the proliferation of tumour cells, and exert anti-tumour effects. Consequently, a great number of studies have been conducted on chalcone derivatives targeting microtubule proteins. In this review, synthetic or natural chalcone microtubule inhibitors in recent years are described, along with their structure-activity relationship (SAR) for anticancer activity.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The performance of LiNi0.8Co0.15Al0.05O2 is shown to be improved by fluorine doping via a modified low-temperature method. Scanning electron microscopy shows that fluorine doping catalyzes the growth ...of the primary particles. X-ray diffraction (XRD) results reveal that all the synthesized materials have typical hexagonal structure without impurities. The lattice parameters calculated from the XRD data by Rietveld refinement methods indicate that the interslab spacing distance is enlarged by fluorine doping. Inductively coupled plasma atomic emission spectroscopy and energy-dispersive X-ray spectroscopy show that fluorine atoms are preferentially enriched on the surface of the particle. X-ray photoelectron spectroscopy indicates that the valence state of nickel ions at the surface is lowered. The cycling performance of modified samples at room temperature, at high temperature (55°C), and at high upper cut-off potentials is improved. Electrochemical impedance spectroscopy measurements reveal that fluorine doping could lower the impedance rise during cycling and suppress the degradation of the cathode material.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Topological photonics provides an ideal platform for demonstrating novel band topology concepts, which are also promising for robust waveguiding, communication, and computation applications. However, ...many challenges such as extremely large device footprint and functionality at short wavelengths remain to be solved which are required to make practical and useful devices that can also couple to electronic excitations in many important organic and inorganic semiconductors. In this letter, we report an experimental realization of Z2 photonic topological insulators with their topological edge state energies spanning across the visible wavelength range including in the sub-500 nm regime, which requires highly optimized nanofabrication. The photonic structures are based on deformed hexagonal lattices with preserved 6-fold rotational symmetry patterned on suspended SiN x membranes. The experimentally measured energy-momentum dispersion of the topological lattices directly shows topological band inversion by the swapping of the brightness of the bulk energy bands, and also the helical edge states when the measurement is taken near the topological interface. The robust topological transport of the helical edge modes in real space is demonstrated by successfully guiding circularly polarized light beams unidirectionally through sharp kinks without significant signal loss. This work paves the way for small footprint photonic topological devices working in the short wavelength range that can also be utilized to couple to excitons for unconventional light–matter interactions at the nanoscale.
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IJS, KILJ, NUK, PNG, UL, UM
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