Abstract
MnBi
2
Te
4
and its derivative compounds have received focused research interests recently for their inherent magnetic order and the rich, robust and tunable topological phases hosted in ...them. Here, I briefly introduce MnBi
2
Te
4
-family intrinsic magnetic topological materials—the electronic and magnetic properties, the topological phase diagrams and the research progress made on them in the past years. I try to present a simple picture to understand their rich electronic, magnetic and topological properties, and a concise guide to engineer them for intended topological phases and the quantum anomalous Hall effect at higher temperature.
Herein, the first acceptorless dehydrogenation of tetrahydroquinolines (THQs), indolines, and other related N‐heterocycles, by merging visible‐light photoredox catalysis and cobalt catalysis at ...ambient temperature, is described. The potential applications to organic transformations and hydrogen‐storage materials are demonstrated. Primary mechanistic investigations indicate that the catalytic cycle occurs predominantly by an oxidative quenching pathway.
Cobalt and blue: The titled method is utilized for the reversible dehydrogenation‐hydrogenation protocol at ambient temperature under mild reaction conditions. Primary mechanistic investigations indicate that the catalytic cycle relies predominantly on an oxidative quenching pathway.
Exciting advancements have been made in the field of flexible electronic devices in the last two decades and will certainly lead to a revolution in peoples’ lives in the future. However, because of ...the poor sustainability of the active materials in complex stress environments, new requirements have been adopted for the construction of flexible devices. Thus, hierarchical architectures in natural materials, which have developed various environment-adapted structures and materials through natural selection, can serve as guides to solve the limitations of materials and engineering techniques. This review covers the smart designs of structural materials inspired by natural materials and their utility in the construction of flexible devices. First, we summarize structural materials that accommodate mechanical deformations, which is the fundamental requirement for flexible devices to work properly in complex environments. Second, we discuss the functionalities of flexible devices induced by nature-inspired structural materials, including mechanical sensing, energy harvesting, physically interacting, and so on. Finally, we provide a perspective on newly developed structural materials and their potential applications in future flexible devices, as well as frontier strategies for biomimetic functions. These analyses and summaries are valuable for a systematic understanding of structural materials in electronic devices and will serve as inspirations for smart designs in flexible electronics.
The accretion around the black hole plays a pivotal role in the theoretical analysis of black hole shadow, and of the black hole observation in particular. We mainly study the shadow and observation ...characteristics of noncommutative Schwarzschild black holes wrapped by three accretion models, and then explore the influence of noncommutative parameters on the observation appearance and spacetime geometry of black holes. When the black hole is surrounded by an optically and geometrically thin accretion disk, it shows that the direct emissions always dominate the total observed intensity, while the lensing ring superimposed upon the direct emission produces a thin ring, which improves the observation intensity of the black hole image. However, the photon rings makes negligible contributions to the total observed brightness due to its exponential narrowness, although the photon ring intersects the thin plane more than three times to pick up larger intensity. More importantly, when the noncommutative parameters changed, the corresponding regions and observation intensities of photon ring, lensing ring and direct emission all change correspondingly. For optical thin spherically symmetric accretion, we consider the static and infalling matters, respectively. We find that the observation intensity of the two spherical accretion models increase with the increase of noncommutative parameters. In addition, due to the Doppler effect of the infalling movement, the shadow image of infalling accretion is darker than that of static accretion. In a word, the different accretion models and noncommutative parameters will lead to different shadow images and optical appearances of noncommutative Schwarzschild black holes.
In this paper, we explore three simple models of accretions on a global monopole black hole in
f
(
R
) theory, and numerically study the corresponding observational appearances as seen by an observer ...located at the asymptotic infinity and the certain region out of black hole. For the thin-disk accretion, the results here show that the brighter lensing ring and the darker photon ring that around black hole shadow, always make a small contribution and a negligible contribution to total observed intensity respectively. While, the direct emission of disk contributes a dominant part, and the size of shadow always depends on the disk’s location. For the static and infalling spherical accretions, it turns out that the radiuses of the shadows and photon spheres are always same for both accretions, which implies that the boundary of shadow represents the signature of the spacetime geometry in this case. However, we also find that the brightness of shadow in infalling accretion is darker than that in static case since the Doppler effect is taken into account. In addition, the effect of the global monopole parameter
η
and
f
(
R
) parameter
ψ
0
on observational appearances of black hole are clearly emphasized throughout of this paper. Finally, we conclude that black hole shadows and the related rings with some different observable features can be used for us to distinguish black holes from different gravity theories and set the upper limits to the
f
(
R
) parameter
ψ
0
.
Recently, PM2.5 (atmospheric fine particulate matter with aerodynamic diameter ≤2.5μm) have received so much attention that the observations, source appointment and countermeasures of it have been ...widely studied due to its harmful impacts on visibility, mood (mental health), physical health, traffic safety, construction, economy and nature, as well as its complex interaction with climate. A review on the PM2.5 related research is necessary. We start with summary of chemical composition and characteristics of PM2.5 that contains both macro and micro observation results and analysis, wherein the temporal variability of concentrations of PM2.5 and major components in many recent reports is embraced. This is closely followed by an overview of source appointment, including the composition and sources of PM2.5 in different countries in the six inhabitable continents based on the best available results. Besides summarizing PM2.5 pollution countermeasures by policy, planning, technology and ideology, the World Air Day is proposed to be established to inspire and promote the crucial social action in energy-saving and emission-reduction. Some updated knowledge of the important topics (such as formation and evolution mechanisms of hazes, secondary aerosols, aerosol mass spectrometer, organic tracers, radiocarbon, emissions, solutions for air pollution problems, etc.) is also included in the present review by logically synthesizing the studies. In addition, the key research challenges and future directions are put forward. Despite our efforts, our understanding of the recent reported observations, source identifications and countermeasures of PM2.5 is limited, and subsequent efforts both of the authors and readers are needed.
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•Newly reported characteristics, sources and control of PM2.5 pollution are reviewed.•The characteristics of PM2.5 involve all the world's six inhabitable continents.•This review, based on over 300 new reports, could serve as an updated PM2.5 database.•Hot topics, challenges and future directions of PM2.5 research are pointed out.•Education can improve ideology, and the World Air Day is proposed to be established.
•WCX is better suited than HLB for solid-phase extraction of fluoroquinolones.•Real wastewater matrix had minimal impact on recovery and fluorescence response.•HPLC-FLD method fully resolves 11 ...fluoroquinolones.•SPE with HPLC-FLD method demonstrates sensitivity equivalent to LC–MS/MS.•FQs detected in raw wastewater, wastewater effluent, and surface water.
This paper describes a selective and ultra-sensitive analytical method for simultaneous determination of 11 fluoroquinolone (FQ) antibiotics in environmental and wastewater samples. The method employs offline solid-phase extraction (SPE) and reversed-phase high performance liquid chromatography with fluorescence detection (HPLC-FLD). A weak cation exchange SPE protocol was developed with a novel loading volume optimization algorithm and a methanol cleanup step to remove background organic matter. Various parameters were optimized to recover FQs from water/wastewater and analyte recovery was generally greater than 80%. Chromatographic separation of the 11 FQs was achieved on a 150mm pentafluorophenyl column using a gradient elution scheme with methanol, acetonitrile, and 20mM phosphate buffer (pH=2.4). Excitation and emission wavelengths were individually optimized for each FQ using fluorescence spectroscopy; the excitation and emission wavelengths were 276–296nm and 444–506nm, respectively. Instrumental quantitation limits were 20–100pg of mass injected. Of the 11 FQs investigated, seven (i.e., ciprofloxacin, difloxacin, enrofloxacin, fleroxacin, norfloxacin, moxifloxacin, and ofloxacin) were detected during a four-month sampling campaign of wastewater and wastewater-impacted surface water. Concentrations of FQs in raw wastewater, wastewater effluent, and wastewater-impacted surface water were 5–1292, 2–504, and 4–187ng/L, respectively.
In this paper, we carefully study the shadow and observational signature of the black hole with torsion charge for a distant observer, and further compare the results with that gotten in ...Schwarzschild spacetime. For thin disk accretion cases, the result shows that there are not only dark areas in the observed image of black hole, but also photon rings and lensing rings, which are closely associated with the torsion charge. The change of torsion charge will directly affect the range of photon ring and lens ring, and the contribution proportion of these rings to the observed intensity. In addition, the total flux of observed intensity is mainly provided by direct emission, and the lensing ring and photon ring contribute only a small part. By further considering the static and infalling cases of spherically symmetric accretion, one can find that the observed image is much darker for the falling accretion matters, but the shadow radius does not change. However, both the observed intensity and shadow size are significantly different when the torsion charge changes. That is, the size of the observed shadow is related to the spacetime geometry. In addition, based on the shadow of M87, we also constraint the torsion charge of black hole by using the diameter of shadow approximately. Finally, by comparing our results and that in Schwarzschild spacetime, it shows that black hole shadow can provide a feasible method for distinguishing those two spacetime.
Indoor positioning using Bluetooth Low Energy (BLE) beacons has attracted considerable attention after the release of the BLE protocol. A number of efforts have been exerted to improve the ...performance of BLE-based indoor positioning. However, few studies pay attention to the BLE-based indoor positioning in a dense Bluetooth environment, where the propagation of BLE signals become more complex and more fluctuant. In this paper, we draw attention to the problems resulting from the dense Bluetooth environment, and it turns out that the dense Bluetooth environment would result in a high received signal strength indication (RSSI) variation and a longtime interval collection of BLE. Hence, to mitigate the effects of the dense Bluetooth environment, we propose a hybrid method fusing sliding-window filtering, trilateration, dead reckoning and the Kalman filtering method to improve the performance of the BLE indoor positioning. The Kalman filter is exploited to merge the trilateration and dead reckoning. Extensive experiments in a real implementation are conducted to examine the performance of three approaches: trilateration, dead reckoning and the fusion method. The implementation results proved that the fusion method was the most effective method to improve the positioning accuracy and timeliness in a dense Bluetooth environment. The positioning root-mean-square error (RMSE) calculation results have showed that the hybrid method can achieve a real-time positioning and reduce error of indoor positioning.
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