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According to the capability difference among the clustered space robot members, the coordinated localization strategies were proposed in this paper. Firstly, the cluster dynamics was established by state functions, then based on linear Kalman filter theorem, the centralized localization filter was designed. In order to reduce the computation load of the centralized localization filter, the distributed navigation filter was also proposed. Finally the performance of the localization filters was evaluated, the stabilities and accuracies of the coordinated localization strategies were verified by numerical simulations. [ABSTRACT FROM AUTHOR]

A linear monocular vision determination method is proposed based on feature point extraction for orbit target capture. With a consideration of the interference from the highlight facula, the feature point extraction method based on geometry index threshold is designed, and the influence from highlight facula posed on the extraction is obviously suppressed. After that, the relative pose and position determination algorithm is developed based on nonlinear terms transformation. Compared with the nonlinear propagation method, the proposed method can work stably with low computation load. Finally the ground-based monocular vision system is established, and he vision determination experiments are carried out when target is floating slowly. The accuracy and real time performance of the vision determination method are illustrated by simulation results. [ABSTRACT FROM AUTHOR]

In order to probe CO2-coal interactions, differential scanning calorimetry(DSC) experiment was carried out in the atmosphere of He, N2 and CO2 with coals from Huozhou and Jincheng area in Shanxi Province. The results show that, in a He atmosphere, the curves are straightforward, the curves in the N2 atmosphere are smooth and upward compared with curves in the He atmosphere, however, in a CO2 atmosphere, all the three curves show exothermic peaks and endothermic peaks are irreversible. It is proposed that, as an inert gas, He can't be adsorbed on coal surface, hence no enthalpy released. For N2, physical adsorption occurs, charactered with lower enthalpy releasing. The larger enthalpy variation in a CO2 atmosphere indicates that, except for physical reactions, chemical reactions may also occur. Based on the analysis of coal interactions, CO2 interactions and molecular-scale interactions of CO2 with substances other than coal, the CO2-coal interactions were explained as follows: the C atom of CO2 accepted electrons from coal molecular, and formed an "electron donor-acceptor complex" ( i. e. , an "EDA complex" ), in other words, chemical reactions occurred, hence exothermic peaks occurred. The interconnections of the active sites to other groups in coal molecular are weakened due to the formation of EDA complex, so to be easily broken during heating, hence endothermic peaks occurred. The irreversibility of the curves indicates that coal structure is changed. [ABSTRACT FROM AUTHOR]

Aimed at the problems of ensuring the approaching safety of net-based space robotic system and reducing fuel consumption by trajectories plannings during proximity maneuver to the target, according to the passive safety concept, the multi-pulses flying-by approaching trajectory is designed for thruster with the consideration of collision avoidance under relative measurement failures, and the trajectory enables the robotic system to perform the capture operation when passing by the target. Based on the relative dynamics of the spacecrafts, the flying-by approaching trajectory planning model is established with safety inequality constraints, and the solution is achieved by applying linear programming method with velocity increment optimization. Finally, the rationality and trajectory safety are verified by a series of simulations. [ABSTRACT FROM AUTHOR]

Abstract: A new concept using flexible tether–net system to perform on-orbit capture is presented in this paper. As a promising on-orbit capture strategy, the tether–net system has many exciting advantages by contrast with the existing orbital capture system. However, under the disturbance of orbital dynamics an attitude libration, which leads to a capture error, will be presented when the capture net is ejected towards the target aiming at investigating the relationship between the capture error and initial capture conditions, the governing equations of the tether–net system in orbital frame is developed by applying Lagrange equations. In order to optimize capture operation, the in-plane capture constraints are studied by numerical simulations with an effort to damp the in-plane libration and compensate the capture error, the control scheme based on tether tension is investigated firstly, after that an integrated control scheme is proposed by introduced the thrusters into the system, the nonlinear closed-loop dynamics is linearized by feedforward strategy, the simulation results show that feedforward controller is effective for in-plane libration damping and enable the capture net to track an expected trajectory. [Copyright &y& Elsevier]

A single-photon detector based on an InGaAs avalanche photodiode has been developed for use at telecom wavelengths. A suitable delay and sampling gate modulation circuit are used to prevent positive and negative transient pulses from influencing the detection of true photon induced avalanches. A monostable trigger circuit eliminates the influence of avalanche peak jitter, and a dead time modulation feedback control circuit decreases the afterpulsing. From performance tests we find that at the optimum operation point, the quantum efficiency is 12% and the dark count rate 1.5×10?6ns?1, with a detection rate of 500 kHz. [ABSTRACT FROM AUTHOR]

Production of ammonia is currently realized by the Haber–Bosch process, while electrochemical N2 fixation under ambient conditions is recognized as a promising green substitution in the near future. A lack of efficient electrocatalysts remains the primary hurdle for the initiation of potential electrocatalytic synthesis of ammonia. For cheaper metals, such as copper, limited progress has been made to date. In this work, we boost the N2 reduction reaction catalytic activity of Cu nanoparticles, which originally exhibited negligible N2 reduction reaction activity, via a local electron depletion effect. The electron-deficient Cu nanoparticles are brought in a Schottky rectifying contact with a polyimide support which retards the hydrogen evolution reaction process in basic electrolytes and facilitates the electrochemical N2 reduction reaction process under ambient aqueous conditions. This strategy of inducing electron deficiency provides new insight into the rational design of inexpensive N2 reduction reaction catalysts with high selectivity and activity. Electrocatalytic nitrogen reduction is promising for ammonia production, but electrocatalysts are limited by low efficiency and high cost. Here, the authors report electron-deficient copper nanoparticles, induced by rectifying contact with polyimide, for selective reduction of nitrogen to ammonia. [ABSTRACT FROM AUTHOR]

In this article, the synergetic effect between the B‐ and Al‐based acidic sites in B–Al co‐doped mesoporous MFI nanocrystals (denoted as m‐B‐Al‐S1) is rationally applied to modify the alcoholysis process of furfuryl alcohol. The porosity and dopant concentration of the m‐B‐Al‐S1 materials are optimized via a modified Kirkendall growth method to boost the ultra‐high selectivity to ethyl levulinate reactions (94%). The m‐B‐Al‐S1 catalyst also shows good stability for further reuses. [ABSTRACT FROM AUTHOR]

The detailed mechanism of induced seismicity associated with salt mining remains elusive. Herein we compile the geological, industrial data, and seismic records within the Changning salt mining zone, China, and simulate the changes in crustal stresses and seismicity rate based on the physics-based poroelastic model and rate-and-state earthquake nucleation model. Our models reveal that the regional induced seismicity, including the 2019 Ms. 6.0 Changning earthquake, which might be one of the largest induced events by industrial exploitation ever recorded, is mainly driven by the pore-pressure diffusion, but suppressed by pumping operations. Motivated by the injection-extraction scenario, we further investigate the effect of wells' locations on stress changes, which could be potentially used for well site optimization to minimize the poroelastic response. A simple mode of setting extraction wells around the injection well could reduce the seismicity rate by a factor of two. These results collectively advance the understanding of physics and hazards associated with injection-extraction-induced earthquakes, and help design or guide industrial well deployment. • The state of stress and seismicity rate in Changning salt mining zone, China, are modulated by injection and extraction. • The induced seismicity in Changning salt mining zone, including the Ms 6.0 earthquake, is driven by pore-pressure diffusion. • Seismicity rate is sensitive to the rate of Coulomb stress change and wells' position. • The induced seismic hazard could be potentially reduced by adjusting the extraction wells' position. [ABSTRACT FROM AUTHOR]

Wastewater injection over the past decade has increased seismicity in the central USA, in some cases accompanied by detectable surface uplift. Here, we use this uplift to constrain subsurface properties and pore pressure evolution. We apply an advanced multitemporal interferometric algorithm to 35 synthetic aperture radar images acquired by ALOS satellite over four years before the 2012 earthquake sequence in east Texas, where large volumes of wastewater are disposed at depths of ∼800 m and ∼1800 m. To solve for the hydraulic diffusivity of the injection layers, we jointly inverted the injected volume and uplift data, considering a poroelastic layered half space. We find diffusivity values of 0.3 ± 0.1 m2/s and 0.7 ± 0.15 m2/s for shallow and deep injection layers, respectively, which combined with seismically-derived bulk moduli yields permeability values of 5.5 ± 2.6 × 10 − 14 m2 and 1.9 ± 0.25 × 10 − 13 m2 for these layers, consistent with permeability range reported for Rodessa formation and well test values. Hydraulic conductivity determines the evolution of pore pressure and thus the origin and location of induced seismicity. This study highlights the value of geodetic observations to constrain key hydrogeological properties of injection layers and to monitor the evolution of the subsurface pressure change. • Fluid injection near Timpson, East Texas caused an uplift detectable by InSAR. • Surface deformation data are inverted to solve for hydraulic diffusivity of injection layer. • Pore pressure increase due to injection has triggered the 2012 M w 4.8 earthquake. [ABSTRACT FROM AUTHOR]

The aim of this study was to estimate the performance of active learning algorithm for detecting blueberry damage using hyperspectral transmittance data with the very low labeling cost. A hyperspectral transmittance imaging system was first applied to collect the hyperspectral transmittance data of blueberries. Subsequently, the mean hyperspectral transmittance data was extracted. With only 9 labeled berries, the estimated error reduction could achieve the accuracy, precision and recall of 0.87, 0.93 and 0.78 respectively, and it consistently improved or maintained the performance of classifier for the remainder of the queries. In contrast to the SOM and SVM models, the classifier based on estimated error reduction also provided higher accuracy, precision and recall with the much fewer labeled samples. The active learning algorithms can be extended to the large scale applications in which the labeled samples are very limited or expensive and the models are required to be frequently transferred. In our case, due to the significant biological variations existing among blueberry samples, the classifier required frequent updates in practical applications, and the active learning algorithms could remarkably reduce label effort during the model updating processes. [ABSTRACT FROM AUTHOR]

A simple hydride system is fabricated to measure the superconducting transition temperature Tc under high pressure using a diamond anvil cell (DAC). The system is designed with centrosymetric coils around the diamond that makes it easy to keep balance between the pick-up coil and the inductance coil, while the superconducting states can be modulated with a low-frequency small external magnetic field. Using the device we successfully obtain the Tc evolution as a function of applied pressure up to 10 GPa for YBa2Cu3O6+d superconductor single crystal. [ABSTRACT FROM AUTHOR]

Groundwater withdrawal can cause localized and rapid poroelastic subsidence, spatially broad elastic uplift of low amplitude, and changes in the gravity field. Constraining groundwater loss in Mexico City, we analyze data from the Gravity Recovery and Climate Experiment and its follow‐on mission (GRACE/FO) and Synthetic Aperture Radar (SAR) Sentinel‐1A/B images between 2014 and 2021. GRACE/FO observations yield a groundwater loss of 0.85–3.87 km3/yr for a region of ∼300 × 600 km surrounding Mexico City. Using the high‐resolution interferometric SAR data set, we measure >35 cm/yr subsidence within the city and up to 2 cm/yr of uplift in nearby areas. Attributing the long‐term subsidence to poroelastic aquifer compaction and the long‐term uplift to elastic unloading, we apply respective models informed by local geology, yielding groundwater loss of 0.86–12.57 km3/yr. Our results suggest Mexico City aquifers have been depleting at faster rates since 2015, exacerbating the socioeconomic and health impacts of long‐term groundwater overdrafts. Plain Language Summary: Groundwater overdraft in Mexico City results from excessive freshwater demand and unsustainable water resource management in a subtropical environment with warm summers and dry winters. Groundwater depletion can result in ground surface deformation and changes in the gravity field, observable by Sentinel‐1 and GRACE satellites. Here, we examine data from both satellite missions between November 2014 and October 2021 to determine groundwater volume loss. Using GRACE, which has a footprint of ∼350 km, we quantify groundwater volume loss to a rate of 0.85–3.87 km3 per year in the broader area surrounding Mexico City. Analysis of high‐resolution Sentinel‐1 synthetic aperture radar images shows land sinks at a rate of 35 cm/yr within the city and surrounding areas uplifts at a rate of ∼2 cm/yr. While the subsidence is a consequence of aquifer compaction, the uplift represents an elastic unloading response of the Earth's crust to water mass loss. Using geophysical models informed by local geology, we show that the region loses groundwater at rates of 0.86–12.57 km3/yr. Our results emphasize the need for groundwater monitoring in Mexico City to assist with managing freshwater resources. Key Points: A subsidence rate of >35 cm/yr within Mexico City, surrounded by ∼2 cm/yr of uplift, is observed using space‐borne synthetic aperture radarGroundwater loss of 0.86–12.57 km3/yr in Mexico City causes poroelastic subsidence, a broad‐scale elastic uplift, and gravity field changeMexico City aquifers have been depleting at least since 2015, exacerbating groundwater overdrafts' socioeconomic and health impacts [ABSTRACT FROM AUTHOR]

Background: The need for intraoperative endoscopic nasobiliary drainage during laparoscopic cholecystectomy and laparoscopic common bile duct exploration with primary closure is controversial in the treatment of cholecystolithiasis combined with choledocholithiasis. The aim of this study was to evaluate the safety and efficacy of laparoscopic cholecystectomy + laparoscopic common bile duct exploration + intraoperative endoscopic nasobiliary drainage + primary closure (LC + LCBDE + IO-ENBD + PC). The safety of different intubation methods in IO-ENBD was also evaluated. Method: From January 2018 to January 2022, 168 consecutive patients with cholecystolithiasis combined with choledocholithiasis underwent surgical treatment in our institution. Patients were divided into two groups: group A (n = 96) underwent LC + LCBDE + IO-ENBD + PC and group B (n = 72) underwent LC + LCBDE + PC. Patient characteristics, perioperative indicators, complications, stone residual, and recurrence rates were analyzed. Group A was divided into two subgroups. In group A1, the nasobiliary drainage tube was placed in an anterograde way, and in group A2, nasobiliary drainage tube was placed in an anterograde–retrograde way. Perioperative indicators and complications were analyzed between subgroups. Results: No mortality in the two groups. The operation success rates in groups A and B were 97.9% (94/96) and 100% (72/72), respectively. In group A, two patients were converted to T-tube drainage. The stone clearance rates of group A and group B were 100% (96/96) and 98.6% (71/72), respectively. Common bile duct diameter was smaller in group A [10 vs. 12 mm, P < 0.001] in baseline data. In perioperative indicators, group A had a longer operation time [165 vs.135 min, P < 0.001], but group A had a shorter hospitalization time [10 vs.13 days, P = 0.002]. The overall complications were 7.3% (7/96) in group A and 12.5% (9/72) in group B. Postoperative bile leakage was less in group A [0% (0/96) vs. 5.6% (4/72), P = 0.032)]. There were no residual and recurrent stones in group A. And there were one residual stone and one recurrent stone in group B (all 1.4%). The median follow-up time was 12 months in group A and 6 months in group B. During the follow-up period, 2 (2.8%) patients in group B had a mild biliary stricture. At subgroup analysis, group A1 had shorter operation time [150 vs. 182.5 min, P < 0.001], shorter hospitalization time [9 vs. 10 days, P = 0.002], and fewer patients with postoperative elevated pancreatic enzymes [32.6% (15/46) vs. 68% (34/50), P = 0.001]. Conclusion: LC + LCBDE + IO-ENBD + PC is safer and more effective than LC + LCBDE + PC because it reduces hospitalization time and avoids postoperative bile leakage. In the IO-ENBD procedure, the antegrade placement of the nasobiliary drainage tube is more feasible and effective because it reduces the operation time and hospitalization time, and also reduces injury to the duodenal papilla. [ABSTRACT FROM AUTHOR]

Production of more than 20 million tons of epoxides per year from olefins suffers from low atom economy due to the use of oxidants and complex catalysts with unsatisfactory selectivity, leading to huge environmental and economic costs. We present a proof‐of‐concept application of electron‐rich RuO2 nanocrystals to boost the highly selective epoxidation of cyclooctene via direct oxygen transfer from water as the sole oxygen source under mild conditions. The enhanced electron enrichment of RuO2 nanocrystals via the Schottky effect with nitrogen‐doped carbons largely promotes the capture and activation of cyclooctene to give a high turnover frequency (260 h−1) of cyclooctene oxide, far surpassing the reported values (<20 h−1) of benchmarked catalysts at room temperature with oxidants. Our electron‐rich RuO2 electrocatalysts enable efficient and durable hydrogen production (Faradaic efficiency >90 %) on the cathode without impacting on the selectivity to epoxide (>99 %) on the anode. [ABSTRACT FROM AUTHOR]

Platinum (Pt) is the most effective bench‐marked catalyst for producing renewable and clean hydrogen energy by electrochemical water splitting. There is demand for high HER catalytic activity to achieve efficient utilization and minimize the loading of Pt in catalysts. In this work, we significantly boost the HER mass activity of Pt nanoparticles in Ptx/Co to 8.3 times higher than that of commercial Pt/C by using Co/NC heterojunctions as a heterogeneous version of electron donors. The highly coupled interfaces between Co/NC and Pt metal enrich the electron density of Pt nanoparticles to facilitate the adsorption of H+, the dissociation of Pt−H bonds and H2 release, giving the lowest HER overpotential of 6.9 mV vs. RHE at 10 mA cm−2 in acid among reported HER electrocatalysts. Given the easy scale‐up synthesis due to the stabilization of ultrafine Pt nanoparticles by Co/NC solid ligands, Ptx/Co can even be a promising substitute for commercial Pt/C for practical applications. [ABSTRACT FROM AUTHOR]

NOx− reduction acts a pivotal part in sustaining globally balanced nitrogen cycle and restoring ecological environment, ammonia (NH3) is an excellent energy carrier and the most valuable product among all the products of NOx− reduction reaction, the selectivity of which is far from satisfaction due to the intrinsic complexity of multiple‐electron NOx−‐to‐NH3 process. Here, we utilize the Schottky barrier‐induced surface electric field, by the construction of high density of electron‐deficient Ni nanoparticles inside nitrogen‐rich carbons, to facilitate the enrichment and fixation of all NOx− anions on the electrode surface, including NO3− and NO2−, and thus ensure the final selectivity to NH3. Both theoretical and experimental results demonstrate that NOx− anions were continuously captured by the electrode with largely enhanced surface electric field, providing excellent Faradaic efficiency of 99 % from both electrocatalytic NO3− and NO2− reduction. Remarkably, the NH3 yield rate could reach the maximum of 25.1 mg h−1 cm−2 in electrocatalytic NO2− reduction reaction, outperforming the maximum in the literature by a factor of 6.3 in neutral solution. With the universality of our electrocatalyst, all sorts of available electrolytes containing NOx− pollutants, including seawater or wastewater, could be directly used for ammonia production in potential through sustainable electrochemical technology. [ABSTRACT FROM AUTHOR]

Imaging quality is a critical component of compressive imaging in real applications. In this study, we propose a compressive imaging method based on multi-scale modulation and reconstruction in the spatial frequency domain. Theoretical analysis and simulation show the relation between the measurement matrix resolution and compressive sensing (CS) imaging quality. The matrix design is improved to provide multi-scale modulations, followed by individual reconstruction of images of different spatial frequencies. Compared with traditional single-scale CS imaging, the multi-scale method provides high quality imaging in both high and low frequencies, and effectively decreases the overall reconstruction error. Experimental results confirm the feasibility of this technique, especially at low sampling rate. The method may thus be helpful in promoting the implementation of compressive imaging in real applications. [ABSTRACT FROM AUTHOR]

A traditional single-pixel camera needs a large number of measurements to reconstruct the object with compressive sensing computation. Compared with the 1/0 matrices in classical measurement, the 1/−1 matrices in the complementary measurement has better property for reconstruction computation and returns better reconstruction results. However, each row of the 1/−1 matrices needs two measurements with the traditional single-pixel camera which results into double measurements compared with the 1/0 matrices. In this paper, we consider the pseudo complementary measurement which only takes the same amount of measurements with the row number of some properly designed 1/0 matrix to compute the total luminous flux of the objective and derives the measurement data of the corresponding 1/−1 matrix in a mathematical way. The numerical simulation and experimental result show that the pseudo complementary measurement is an efficient tool for the traditional single-pixel camera imaging under low measurement rate, which can combine the advantages of the classical and complementary measurements and significantly improve the peak signal-to-noise ratio. [ABSTRACT FROM AUTHOR]

Ghost imaging, which is an indirect imaging technique that uses correlations between two beams to retrieve the information of an object, is applicable to any wavelength. It has been performed with a growing range of light sources, including x-rays, the visible, and the infrared, and has also been extended to atoms and electrons recently. In this Letter, we demonstrate acoustical ghost imaging using the correlation between random acoustic patterns, which are generated by the phase and delaying manipulation of a transducer array and the total transmitted intensity signals. Furthermore, the reconstruction quality and resolution can be further improved by compressed sensing. This study shows a demonstration of ghost imaging using mechanical waves. Moreover, this approach requires fewer computational resources and offers great promise for high-speed and high-resolution acoustical imaging. [ABSTRACT FROM AUTHOR]

Computed-tomography imaging spectrometry (CTIS) can achieve non-scanning and high speed imaging recording of spatial and spectral data of a rapidly changing target scene. However, it has the problem of missing cone, which means the projection data cannot be fully sampled. This limits its practicality due to the ill-posed spectral reconstruction from limited angles of projection tomography. This paper proposes a compressed sensing (CS) sampling model for the CTIS, or CSCTIS in short, with the under sampling advantage of CS to improve the problem. The simulation results validates that the CS model is more effective than the traditional computed-tomography (CT) one, and further experimental results prove that the CSCTIS performs more accurate spectral reconstruction than the traditional CTIS. • Introduced the compressed sensing (CS) sampling in improving the computed-tomography imaging spectrometry (CTIS) to establish the CSCTIS. • The proposed CSCTIS enables instantaneous or snapshotting acquisition of spatial and spectral information of a moving scene with accurate and high-throughput measurement. • It provides promising application prospects in medical diagnosis, remote sensing, material detection. [ABSTRACT FROM AUTHOR]

This paper presents a trajectory-optimization method for a chaser spacecraft operating in ultra-close proximity to a failed satellite. Based on the combination of active and passive trajectory protection, the constraints in the optimization framework are formulated for collision avoidance and successful docking in the presence of any thruster failure. The constraints are then handled by an adaptive Gauss pseudospectral method, in which the dynamic residuals are used as the metric to determine the distribution of collocation points. A finite-time feedback control is further employed in tracking the optimized trajectory. In particular, the stability and convergence of the controller are proved. Numerical results are given to demonstrate the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

Thermal imaging is an essential tool in a wide variety of research areas. In this work we demonstrate high-throughput double-wavelength temperature distribution imaging using a modified single-pixel camera without the requirement of a beam splitter (BS). A digital micro-mirror device (DMD) is utilized to display binary masks and split the incident radiation, which eliminates the necessity of a BS. Because the spatial resolution is dictated by the DMD, this thermal imaging system has the advantage of perfect spatial registration between the two images, which limits the need for the pixel registration and fine adjustments. Two bucket detectors, which measures the total light intensity reflected from the DMD, are employed in this system and yield an improvement in the detection efficiency of the narrow-band radiation. A compressive imaging algorithm is utilized to achieve under-sampling recovery. A proof-of-principle experiment was presented to demonstrate the feasibility of this structure. [ABSTRACT FROM AUTHOR]

This paper discusses the noisy phase retrieval problem: recovering a complex image signal with independent noise from quadratic measurements. Inspired by the dark fringes shown in the measured images of the array detector, a novel phase retrieval approach is proposed and demonstrated both theoretically and experimentally to apply the information of extracted dark fringes and its relationship with designed phase patterns. Here the dark fringes are extracted from the image plane, rather than the Fourier/focal plane, and the invalid extracted fringes can be tactfully bypassed to improve the anti-noise capability. A more accurate relative phase ratio between arbitrary two pixels is achieved by calculating the multiplicative ratios (or the sum of phase difference) on the path between them. Then the object phase image can be reconstructed precisely. Our approach is a good choice for retrieving high-quality phase images from noisy signals and has broad prospects in practical applications such as X-ray crystallography, diffractive imaging, and so on. [ABSTRACT FROM AUTHOR]

We present a new technique to denoise a single-pixel camera, in which complementary compressive imaging and a threshold strategy have been combined to improve image quality. The number of measurements recorded by the detector is reduced by setting a threshold. With an appropriate choice of threshold value, the quality of the reconstructed image is enhanced with a small number of measurements. This denoising method thus offers a very effective approach to promote the implementation of single-pixel camera in real applications. [ABSTRACT FROM AUTHOR]