Spatiotemporal lasing dynamics in a Limaçon-shaped microcavity.

Limaçon-shaped microdisk lasers are promising on-chip light sources with low lasing threshold and unidirectional output. We conduct an experimental study on the lasing dynamics of Limaçon-shaped semiconductor microcavities. The edge emission exhibits intensity fluctuations over a wide range of spatial and temporal scales. They result from multiple dynamic processes with different origins and occur on different spatiotemporal scales. The dominant process is an alternate oscillation between two output beams with a period as short as a few nanoseconds.

A Path Planning Method with a Bidirectional Potential Field Probabilistic Step Size RRT for a Dual Manipulator.

The search efficiency of a rapidly exploring random tree (RRT) can be improved by introducing a high-probability goal bias strategy. In the case of multiple complex obstacles, the high-probability goal bias strategy with a fixed step size will fall into a local optimum, which reduces search efficiency. Herein, a bidirectional potential field probabilistic step size rapidly exploring random tree (BPFPS-RRT) was proposed for the path planning of a dual manipulator by introducing a search strategy of a step size with a target angle and random value. The artificial potential field method was introduced, combining the search features with the bidirectional goal bias and the concept of greedy path optimization. According to simulations, taking the main manipulator as an example, compared with goal bias RRT, variable step size RRT, and goal bias bidirectional RRT, the proposed algorithm reduces the search time by 23.53%, 15.45%, and 43.78% and decreases the path length by 19.35%, 18.83%, and 21.38%, respectively. Moreover, taking the slave manipulator as another example, the proposed algorithm reduces the search time by 6.71%, 1.49%, and 46.88% and decreases the path length by 19.88%, 19.39%, and 20.83%, respectively. The proposed algorithm can be adopted to effectively achieve path planning for the dual manipulator.

The Extraction of Ocean Tidal Loading from ASAR Differential Interferograms.

The spatiotemporal crustal non-tectonic deformation caused by ocean tidal loading (OTL) can reach the centimeters scale in coastal land areas. The temporal variation of the site OTL displacements can be estimated by the global positioning system (GPS) technique, but its spatial variation needs to be further determined. In this paper, in order to analyze the spatial characteristics of the OTL displacements, we propose a multi-scale decomposition method based on signal spatial characteristics to derive the OTL displacements from differential interferometric synthetic aperture radar (D-InSAR) measurements. The method was tested using long-term advanced synthetic aperture radar (ASAR) data and GPS reference site data from the Los Angeles Basin in the United States, and we compared the results with the FES2014b tide model. The experimental results showed that the spatial function of the OTL displacements in an ASAR image can be represented as a higher-order polynomial function, and the spatial trends of the OTL displacements determined by the InSAR and the GPS techniques are basically consistent with the FES2014b tide model. The root-mean-square errors of the differences between the spatial OTL displacements of these two methods and the FES2014b tide model are less than 0.8 mm. The results indicate that the OTL displacement extracted from InSAR data can accurately reflect the spatial characteristics of the OTL effect, which will help to improve the spatial resolution and accuracy of the OTL displacement in coastal areas.

Accurate Evaluation of Vertical Tidal Displacement Determined by GPS Kinematic Precise Point Positioning: A Case Study of Hong Kong.

Global Positioning System (GPS) kinematic precise point positioning (KPPP) is an effective approach for estimating the Earth's tidal deformation. The accuracy of KPPP is usually evaluated by comparing results with tidal models. However, because of the uncertainties of the tidal models, the accuracy of KPPP-estimated tidal displacement is difficult to accurately determine. In this paper, systematic vector differences between GPS estimates and tidal models were estimated by least squares methods in complex domain to analyze the uncertainties of tidal models and determine the accuracy of KPPP-estimated tidal displacements. Through the use of GPS data for 12 GPS reference stations in Hong Kong from 2008 to 2017, vertical ocean tide loading displacements (after removing the body tide effect) for eight semidiurnal and diurnal tidal constituents were obtained by GPS KPPP. By an in-depth analysis of the systematic and residual differences between the GPS estimates and nine tidal models, we demonstrate that the uncertainty of the tidal displacement determined by GPS KPPP for the M2, N2, O1, and Q1 tidal constituents is 0.2 mm, and for the S2 constituent it is 0.5 mm, while the accuracy of the GPS-estimated K1, P1, and K2 tidal constituents is weak because these three tidal constituents are affected by significant common-mode errors. These results suggest that GPS KPPP can be used to precisely constrain the Earth's vertical tidal displacement in the M2, N2, O1, and Q1 tidal frequencies.

Assessing the Use of GACOS Products for SBAS-InSAR Deformation Monitoring: A Case in Southern California.

The Generic Atmospheric Correction Online Service (GACOS) products for interferometric synthetic aperture radar (InSAR) are widely used near-real-time and global-coverage atmospheric delay products which provide a new approach for the atmospheric correction of repeat-pass InSAR. However, it has not been determined whether these products can improve the accuracy of InSAR deformation monitoring. In this paper, GACOS products were used to correct atmospheric errors in short baseline subset (SBAS)-InSAR. Southern California in the U.S. was selected as the research area, and the effect of GACOS-based SBAS-InSAR was analyzed by comparing with classical SBAS-InSAR results and external global positioning system (GPS) data. The results showed that the accuracy of deformation monitoring was improved in the whole study area after GACOS correction, and the mean square error decreased from 0.34 cm/a to 0.31 cm/a. The improvement of the mid-altitude (15-140 m) point was the most obvious after GACOS correction, and the accuracy was increased by about 23%. The accuracy for low- and high-altitude areas was roughly equal and there was no significant improvement. Additionally, GACOS correction may increase the error for some points, which may be related to the low accuracy of GACOS turbulence data.

Quantitative Analysis of Gas Phase IR Spectra Based on Extreme Learning Machine Regression Model.

Advanced chemometric analysis is required for rapid and reliable determination of physical and/or chemical components in complex gas mixtures. Based on infrared (IR) spectroscopic/sensing techniques, we propose an advanced regression model based on the extreme learning machine (ELM) algorithm for quantitative chemometric analysis. The proposed model makes two contributions to the field of advanced chemometrics. First, an ELM-based autoencoder (AE) was developed for reducing the dimensionality of spectral signals and learning important features for regression. Second, the fast regression ability of ELM architecture was directly used for constructing the regression model. In this contribution, nitrogen oxide mixtures (i.e., N2O/NO2/NO) found in vehicle exhaust were selected as a relevant example of a real-world gas mixture. Both simulated data and experimental data acquired using Fourier transform infrared spectroscopy (FTIR) were analyzed by the proposed chemometrics model. By comparing the numerical results with those obtained using conventional principle components regression (PCR) and partial least square regression (PLSR) models, the proposed model was verified to offer superior robustness and performance in quantitative IR spectral analysis.

High-efficiency ultrafast Tm-doped fiber amplifier based on resonant pumping.

We demonstrated a high-efficiency ultrafast Tm-doped fiber amplifier based on a resonant pumping technique. A continuous-wave fiber laser at 1940 nm was employed as the pump laser. The slope efficiency of the resonantly pumped pulsed Tm-doped fiber amplifier reached 87% with respect to the launched pump power. The maximum average output power reached 40 W when the launched pump power was 53 W. The repetition rate and the pulse duration of the output pulses from a fiber amplifier were 248 MHz and 129 ps, respectively. The corresponding peak power was 1.25 kW, and the pulse energy was 161.3 nJ. To the best of our knowledge, this is the first demonstration of a resonant pumping enabled high-power high-efficiency ultrafast fiber laser operating at a 2 µm band.

Flexible single-mode delivery of a high-power 2 µm pulsed laser using an antiresonant hollow-core fiber.

We demonstrate flexible single-mode transmission of a high average power 2 µm nanosecond pulse using antiresonant hollow-core fibers (AR-HCFs). 39.1 W average power is delivered using a coiled 1.7 m AR-HCF, which is designed for single-mode guidance and good higher-order mode suppression. The effect of bending on the fiber output power and beam profile is also investigated. The Gaussian-like output beam profile is maintained up to a 7.5 cm bending radius. This is the highest average power delivered by a flexible long HCF in this wavelength without the need for an enclosed controlled environment, to the best of our knowledge.

Gibbs-Thomson Effect in Planar Nanowires: Orientation and Doping Modulated Growth.

Epitaxy-enabled bottom-up synthesis of self-assembled planar nanowires via the vapor-liquid-solid mechanism is an emerging and promising approach toward large-scale direct integration of nanowire-based devices without postgrowth alignment. Here, by examining large assemblies of indium tin oxide nanowires on yttria-stabilized zirconia substrate, we demonstrate for the first time that the growth dynamics of planar nanowires follows a modified version of the Gibbs-Thomson mechanism, which has been known for the past decades to govern the correlations between thermodynamic supersaturation, growth speed, and nanowire morphology. Furthermore, the substrate orientation strongly influences the growth characteristics of epitaxial planar nanowires as opposed to impact at only the initial nucleation stage in the growth of vertical nanowires. The rich nanowire morphology can be described by a surface-energy-dependent growth model within the Gibbs-Thomson framework, which is further modulated by the tin doping concentration. Our experiments also reveal that the cutoff nanowire diameter depends on the substrate orientation and decreases with increasing tin doping concentration. These results enable a deeper understanding and control over the growth of planar nanowires, and the insights will help advance the fabrication of self-assembled nanowire devices.

Mid-IR supercontinuum pumped by femtosecond pulses from thulium doped all-fiber amplifier.

We present a mid-infrared (mid-IR) supercontinuum (SC) light source pumped by femtosecond pulses from a thulium doped fiber amplifier (TDFA) at 2 µm. An octave-spanning spectrum from 1.1 to 3.7 µm with an average power of 253 mW has been obtained from a single mode ZBLAN fiber. Spectral flatness of 10 dB over a 1390 nm range has been obtained in the mid-IR region from 1940 - 3330 nm. It is resulted from the enhanced self phase modulation process in femtosecond regime. The all-fiber configuration makes such broadband coherent source a compact candidate for various applications.

Hybrid III-V/silicon laser with laterally coupled Bragg grating.

In this paper, we demonstrate a compact electrically pumped distributed-feedback hybrid III-V/silicon laser with laterally coupled Bragg grating for the first time to the best of our knowledge. The hybrid laser structure consists of AlGaInAs/InP multi-quantum-well gain layers on top of a laterally corrugated silicon waveguide patterned on a silicon on insulator (SOI) substrate. A pair of surface couplers is integrated at the two ends of the silicon waveguide for the optical coupling and characterization of the ouput light. Single wavelength emission of ~1.55µm with a side-mode-suppression- ratio larger than 20dB and low threshold current density of 1.54kA/cm(2) were achieved for the device under pulsed operation at 20 °C.

Broad cross neutralizing antibodies against sarbecoviruses generated by SARS-CoV-2 infection and vaccination in humans.

The outbreaks of severe acute respiratory syndrome coronavirus (SARS-CoV-1), Middle East respiratory syndrome coronavirus (MERS-CoV), and SARS-CoV-2 highlight the need for countermeasures to prevent future coronavirus pandemics. Given the unpredictable nature of spillover events, preparing antibodies with broad coronavirus-neutralizing activity is an ideal proactive strategy. Here, we investigated whether SARS-CoV-2 infection and vaccination could provide cross-neutralizing antibodies (nAbs) against zoonotic sarbecoviruses. We evaluated the cross-neutralizing profiles of plasma and monoclonal antibodies constructed from B cells from coronavirus disease 2019 (COVID-19) convalescents and vaccine recipients; against sarbecoviruses originating from bats, civets, and pangolins; and against SARS-CoV-1 and SARS-CoV-2. We found that the majority of individuals with natural infection and vaccination elicited broad nAb responses to most tested sarbecoviruses, particularly to clade 1b viruses, but exhibited very low cross-neutralization to SARS-CoV-1 in both natural infection and vaccination, and vaccination boosters significantly augmented the magnitude and breadth of nAbs to sarbecoviruses. Of the nAbs, several exhibited neutralization activity against multiple sarbecoviruses by targeting the spike receptor-binding domain (RBD) and competing with angiotensin-converting enzyme 2 (ACE2) binding. SCM12-61 demonstrated exceptional potency, with half-maximal inhibitory concentration (IC50) values of 0.001-0.091 µg/mL against tested sarbecoviruses; while VSM9-12 exhibited remarkable cross-neutralizing breadth against sarbecoviruses and SARS-CoV-2 Omicron subvariants, highlighting the potential of these two nAbs in combating sarbecoviruses and SARS-CoV-2 Omicron subvariants. Collectively, our findings suggest that vaccination with an ancestral SARS-CoV-2 vaccine, in combination with broad nAbs against sarbecoviruses, may provide a countermeasure for preventing further sarbecovirus outbreaks in humans.

SARS-CoV-2 spike-specific TFH cells exhibit unique responses in infected and vaccinated individuals.

Long-term humoral immunity to SARS-CoV-2 is essential for preventing reinfection. The production of neutralizing antibody (nAb) and B cell differentiation are tightly regulated by T follicular help (TFH) cells. However, the longevity and functional role of TFH cell subsets in COVID-19 convalescents and vaccine recipients remain poorly defined. Here, we show that SARS-CoV-2 infection and inactivated vaccine elicited both spike-specific CXCR3+ TFH cell and CXCR3- TFH cell responses, which showed distinct response patterns. Spike-specific CXCR3+ TFH cells exhibit a dominant and more durable response than CXCR3- TFH cells that positively correlated with antibody responses. A third booster dose preferentially expands the spike-specific CXCR3+ TFH cell subset induced by two doses of inactivated vaccine, contributing to antibody maturation and potency. Functionally, spike-specific CXCR3+ TFH cells have a greater ability to induce spike-specific antibody secreting cells (ASCs) differentiation compared to spike-specific CXCR3- TFH cells. In conclusion, the persistent and functional role of spike-specific CXCR3+ TFH cells following SARS-CoV-2 infection and vaccination may play an important role in antibody maintenance and recall response, thereby conferring long-term protection. The findings from this study will inform the development of SARS-CoV-2 vaccines aiming to induce long-term protective immune memory.

Berry Curvature Dipole Induced Giant Mid-Infrared Second-Harmonic Generation in 2D Weyl Semiconductor.

Due to its inversion-broken triple helix structure and the nature of Weyl semiconductor, 2D Tellurene (2D Te) is promising to possess a strong nonlinear optical response in the infrared region, which is rarely reported in 2D materials. Here, a giant nonlinear infrared response induced by large Berry curvature dipole (BCD) is demonstrated in the Weyl semiconductor 2D Te. Ultrahigh second-harmonic generation response is acquired from 2D Te with a large second-order nonlinear optical susceptibility (χ(2) ), which is up to 23.3 times higher than that of monolayer MoS2 in the range of 700-1500 nm. Notably, distinct from other 2D nonlinear semiconductors, χ(2) of 2D Te increases extraordinarily with increasing wavelength and reaches up to 5.58 nm V-1 at ≈2300 nm, which is the best infrared performance among the reported 2D nonlinear materials. Large χ(2) of 2D Te also enables the high-intensity sum-frequency generation with an ultralow continuous-wave (CW) pump power. Theoretical calculations reveal that the exceptional performance is attributed to the presence of large BCD located at the Weyl points of 2D Te. These results unravel a new linkage between Weyl semiconductor and strong optical nonlinear responses, rendering 2D Te a competitive candidate for highly efficient nonlinear 2D semiconductors in the infrared region.

Application of UAV Remote Sensing in Monitoring Water Use Efficiency and Biomass of Cotton Plants Adjacent to Shelterbelt.

Tree shelterbelts are crucial for maintaining the ecological environment of oasis, but they may also compete for soil water with adjacent crops, affecting crop yields. To evaluate the impacts of the shelterbelt on water use efficiency (WUE) and normalized water productivity (WP) of adjacent cotton plants, the biomass (B) and WUE of cotton with different distances from the shelterbelt (0.1H, 0.5H, 1H, 2H, and 3H; average tree height = 15 m [H]) were estimated based on unmanned aerial vehicle (UAV) remote sensing data combined with the FAO crop water response model AquaCrop. Besides, the accuracy and universality of the estimation method were also evaluated. The results showed that the method based on UAV remote sensing data and AquaCrop can accurately estimate the impact range and intensity of shelterbelt on WUE, water consumption, and B of adjacent cotton plants. Fierce water competition between shelterbelt and cotton was detected within 0.1H-1H, and the competitiveness of the shelterbelt was weaker in the plots >1H than in the 0.1H-1H. The B, actual evapotranspiration (Tc), and WUE of cotton at 0.1H decreased by 59.3, 48.8, and 23.6%, respectively, compared with those at 3H, but the cotton plants at 2H and 3H were completely unaffected by the shelterbelt. Besides, the B estimated based on WP (root mean square error [RMSE] = 108 g/m2, d = 0.89) was more accurate than that estimated based on WUE (RMSE = 118 g/m2, d = 0.85). This study clarifies the inter-species competition for soil water between crops and shelterbelts under drip irrigation in oases in China.

Spike-specific circulating T follicular helper cell and cross-neutralizing antibody responses in COVID-19-convalescent individuals.

Coronavirus disease 2019 (COVID-19) is caused by infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)1-3 and individuals with COVID-19 have symptoms that can be asymptomatic, mild, moderate or severe4,5. In the early phase of infection, T- and B-cell counts are substantially decreased6,7; however, IgM8-11 and IgG12-14 are detectable within 14 d after symptom onset. In COVID-19-convalescent individuals, spike-specific neutralizing antibodies are variable3,15,16. No specific drug or vaccine is available for COVID-19 at the time of writing; however, patients benefit from treatment with serum from COVID-19-convalescent individuals17,18. Nevertheless, antibody responses and cross-reactivity with other coronaviruses in COVID-19-convalescent individuals are largely unknown. Here, we show that the majority of COVID-19-convalescent individuals maintained SARS-CoV-2 spike S1- and S2-specific antibodies with neutralizing activity against the SARS-CoV-2 pseudotyped virus, and that some of the antibodies cross-neutralized SARS-CoV, Middle East respiratory syndrome coronavirus or both pseudotyped viruses. Convalescent individuals who experienced severe COVID-19 showed higher neutralizing antibody titres, a faster increase in lymphocyte counts and a higher frequency of CXCR3+ T follicular help (TFH) cells compared with COVID-19-convalescent individuals who experienced non-severe disease. Circulating TFH cells were spike specific and functional, and the frequencies of CXCR3+ TFH cells were positively associated with neutralizing antibody titres in COVID-19-convalescent individuals. No individuals had detectable autoantibodies. These findings provide insights into neutralizing antibody responses in COVID-19-convalescent individuals and facilitate the treatment and vaccine development for SARS-CoV-2 infection.

Radiation Enhancement by Graphene Oxide on Microelectromechanical System Emitters for Highly Selective Gas Sensing.

Infrared gas sensors have been proven promising for broad applications in Internet of Things and Industrial Internet of Things. However, the lack of miniaturized light sources with good compatibility and tunable spectral features hinders their widespread utilization. Herein, a strategy is proposed to increase the radiated power from microelectromechanical-based thermal emitters by coating with graphene oxide (GO). The radiation can be substantially enhanced, which partially stems from the high emissivity of GO coating demonstrated by spectroscopic methods. Moreover, the sp2 structure within GO may induce plasmons and thus couple with photons to produce blackbody radiation and/or new thermal emission sources. As a proof-of-concept demonstration, the GO-coated emitter is integrated into a multifunctional monitoring platform and evaluated for gas detection. The platform exhibits sensitive and highly selective detection toward CO2 at room temperature with a detection limit of 50 ppm and short response/recovery time, outperforming the state-of-the-art gas sensors. This study demonstrates the emission tailorability of thermal emitters and the feasibility of improving the associated gas sensing property, offering perspectives for designing and fabricating high-end optical sensors with cost-effectiveness and superior performance.

InSAR analysis of surface deformation over permafrost to estimate active layer thickness based on one-dimensional heat transfer model of soils.

This paper presents a novel method to estimate active layer thickness (ALT) over permafrost based on InSAR (Interferometric Synthetic Aperture Radar) observation and the heat transfer model of soils. The time lags between the periodic feature of InSAR-observed surface deformation over permafrost and the meteorologically recorded temperatures are assumed to be the time intervals that the temperature maximum to diffuse from the ground surface downward to the bottom of the active layer. By exploiting the time lags and the one-dimensional heat transfer model of soils, we estimate the ALTs. Using the frozen soil region in southern Qinghai-Tibet Plateau (QTP) as examples, we provided a conceptual demonstration of the estimation of the InSAR pixel-wise ALTs. In the case study, the ALTs are ranging from 1.02 to 3.14 m and with an average of 1.95 m. The results are compatible with those sparse ALT observations/estimations by traditional methods, while with extraordinary high spatial resolution at pixel level (~40 meter). The presented method is simple, and can potentially be used for deriving high-resolution ALTs in other remote areas similar to QTP, where only sparse observations are available now.

Photonic microwave phase shifter/modulator based on a nonlinear optical loop mirror incorporating a Mach-Zehnder interferometer.

We realize a novel photonic microwave phase shifter/modulator based on a nonlinear optical loop mirror incorporating a Mach-Zehnder interferometer. A near-linear phase shifter exceeding 180 degrees and a phase modulation with 2.5 Gbit/s baseband signal are obtained for a 10 GHz microwave signal by this proposed device.