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Two pairs of regio-isomeric V- and T-shaped red thermally activated delayed fluorescent molecules involving a new acceptor pyridobenzoquinoxaline are developed, which enable high external quantum efficiencies up to 12.9%.

In this work, a wear prediction model considering the dynamic load is proposed for spur gears in mixed elastohydrodynamic lubrication (EHL). The dynamic load is calculated by gear dynamic model. Combining gear wear model and dynamic model, the wear depth under the dynamic load is determined and compared with that under quasi-static load. The comparative results show that the maximum wear depth under dynamic load is significantly larger than that under quasi-static load near engaging-in point. The effects of fractional film defect coefficient on wear depth are considerable under dynamic load, which is closely related to gear contact temperature. Furthermore, the effects of surface roughness and gear geometrical parameters on wear depth are studied. The investigation reveals that the wear depth decreases with the increased tooth width, module and pressure angle, but increases with the surface roughness. It illustrates that gear wear depth under the dynamic load can be reduced by optimizing gear geometrical parameters.

SUMMARY With the emergence of massive seismic data sets, surface wave methods using deep learning (DL) can effectively obtain shear wave velocity (Vs) structure for non-invasive near-surface investigations. Previous studies on DL inversion for deep geophysical investigation have a reference model to generate the training data set, while near-surface investigations have no model. Therefore, we systematically give a set of training data set generation processes. In the process, we use both prior information and the observed data to constrain the data set so that the DL inversion model can learn the local geological characteristics of the survey area. Because the space of inverted Vs models is constrained and thus narrowed, the inversion non-uniqueness can be reduced. Furthermore, the mean squared error, which is commonly used as loss function, may cause a poor fitting accuracy of phase velocities at high frequencies in near-surface applications. To make the fitting accuracy evenly in all frequency bands, we modify the loss function into a weighted mean squared relative error. We designed a convolutional neural network (CNN) to directly invert fundamental-mode Rayleigh-wave phase velocity for 1-D Vs models. To verify the feasibility and reliability of the proposed algorithm, we tested and compared it with the Levenberg–Marquardt (L-M) inversion and neighbourhood algorithm (NA) using field data from the Lawrence experiment (USA) and the Wuwei experiment (China). In both experiments, the inverted Vs models by CNN are consistent with the borehole information and are similar to that from existing methods after fine tuning of model parameters. The average root mean squares errors (RMSEs) of the CNN, NA and L-M methods are also similar, except in the Lawrence experiment, the RMSE of CNN is 17.33 m s−1 lower than previous studies using the L-M method. Moreover, the comparison of different loss functions for the Wuwei experiment indicates that the modified loss function can achieve higher accuracy than the traditional one. The proposed CNN is therefore ideally suited for rapid, repeated near-surface subsurface imaging and monitoring under similar geological settings.

As a critical element of time-varying mesh stiffness (TVMS), contact stiffness of a gear drive has been defined based on simplified Hertzian contact stiffness or semi-empirical nonlinear Hertzian contact stiffness in previous works. This study proposes a general contact stiffness model for elastic bodies through piecewise linear interpolation of contact pressure. The TVMS of a spur gear drive is determined through potential energy method and proposed contact stiffness model verified by Hertzian contact theory and finite-element method. Then, the influence of applied load on contact stiffness is studied, and the differences among proposed contact stiffness, simplified Hertzian contact stiffness, and nonlinear Hertzian contact stiffness are analyzed. Results show that contact stiffness increases with the applied load, and the TVMS based on the proposed contact stiffness model is the smallest among the three contact stiffness models. Effects of tooth width and input torque on the TVMS are further discussed. The TVMS becomes bigger with increased tooth width and input torque, but the increase rate decreases as tooth width or input torque increases. These findings indicate that reasonable matching of design parameters is beneficial for increasing load capacity and optimizing the dynamic performance of gear systems.

Accurate understanding of near-surface structures of the solid earth is challenging, especially in urban areas where active source seismic surveys are constrained and difficult to perform. The analysis of anthropogenic seismic noise provides an alternative way to image the shallow subsurface in urban environments. We have developed an application of using traffic noise with seismic interferometry to investigate near-surface structures in Hangzhou City, Eastern China. Noise data were recorded by dense linear arrays with approximately 5 m spacing deployed along two crossing roads. We analyze the characteristics of traffic-induced noise using 36 h continuous recordings. Coherent Rayleigh surface waves between 2 and 20 Hz are retrieved based on crosscorrelations within 1 h time windows. Robust phase-velocity dispersion curves are extracted from virtual shot gathers using multichannel analysis of surface waves and coincide with the results from active seismic data, noise beamforming analysis, and measurements with the spatial autocorrelation method. S-wave velocity profiles are derived for the top 100 m of the subsurface at the array locations. The estimated S-wave velocities from traffic noise correspond to the velocities estimated from logging data. The 2D S-wave velocity maps reveal different soil deposits and bedrock structures in the estuarine sedimentary area. The results demonstrate the accuracy and efficiency of delineating near-surface structures from traffic-induced noise, which has great potential for monitoring subsurface changes in urban areas.

A reversible dual-responsive luminescent material was introduced by our group to show the simultaneous color and lifetime switching in response to external stimuli. Pristine crystalline powder of (...

The gear wear is closely relative to the rough tooth surface morphology and the load distribution; however, their interactions have been rarely given focus. In this work, an adhesive wear model of rough gear surface is proposed considering modified load distribution factor. The mesh stiffness and load distribution factor are modified by the tooth surface morphology and wear depth. Then, the mean pressure is obtained by Hertzian theory, and the wear depths of the pinion and gear are calculated using Archard model. The wear model is verified by comparing with the pervious works. The effects of surface morphologies, geometric and operating parameters on the wear depth, mesh stiffness, and load distribution factor are investigated. Results indicate that (1) the wear depth is determined by profile error rather than roughness, and the wear depth and the load distribution factor increase with the profile error. (2) The roughness decreases, remains unchanged and then increases with the increment of the mesh cycle. (3) As the module and tooth width decrease or the input torque and mesh cycle increase, the tooth wear depth increases. These findings are significant in reducing tooth wear and improving the service life of gear drive.

Precisely regulating the key parameters associated with the thermally activated delayed fluorescence process is accomplished with optimized π-bridges or end-groups, affording improved maximum external quantum efficiencies of 18.9% (@630 nm).

This work not only gives a new functional group for the construction of deep-red pure organic efficient excimer materials, but also further verifies that the “hot exciton” theory can also be effective in excimer-based OLEDs.

Three TADF emitters based on a parallelly aligned bi-spiro-acridine donor are developed featuring enhanced radiative decay which achieve a high external quantum efficiency of maximum 26.1%.

Today, well durations are relatively longer due to several factors. Some of these include but not limited to intermediate section down hole losses. Therefore, there is an opportunity to explore possible ways to reduce well duration and cost while meeting all business objectives with 100% HSE. Dammam, U.E.R, and Simsima are karsts-prone carbonate aquifers widely developed across UAE. As formation pressures are depleted, severe to total losses is increasingly occurred during drilling through these shallow aquifers. Conventional loss curing agents are often failed, especially in Simsima, because of their inability to set in such complex and large fractures and caverns. ZND gel is a water-soluble high molecular polymer, which will automatically set and seal the space after being pumped into loss channels. As hardly be diluted by any formation fluid, a gel slug is formed to isolate drilling fluids and consolidate agent from being washed away into loss zones. In this study, we present a composite solution of ZND gel and Cement applied in onshore Abu Dhabi, which effectively mitigated the total losses encountered in Simsima.

Developing organic thermally activated delayed fluorescence (TADF) emitters with high efficiency and narrowband emissions is crucial and challenging for high-quality organic light-emitting diodes (OLEDs). Here, three multiresonance TADF emitters DPACzBN1, DPACzBN2, and DPACzBN3 are designed via a peripheral decoration strategy and synthesized through a lithium intermediate cascade borylation reaction (15% yield for DPACzBN1) or a more efficient lithium-free direct borylation reaction (45% yield for DPACzBN2 and 75% yield for DPACzBN3). All the emitters exhibit a similar blue emission with small full-width at half maximum (fwhm) values as low as 20 nm in toluene solutions. The introduction of the diphenylamino moiety into the parent molecule DPACzBN1 can not only maintain the high photoluminescence quantum yields over 90% but also narrow the bandwidth and enhance the rate constant of the reverse intersystem crossing process, as well as suppress the spectral broadening in devices. Benefiting from the excellent TADF properties and good inhibition of spectral broadening, TADF OLEDs based on DPACzBN3 achieve the highest maximum external quantum efficiency of 27.7% and the smallest fwhm of 24 nm among the three emitters.

Exploration of geothermal resources has become one of the major drivers for urbanization and economic transformation in southeast China, and it calls for temporal and spatial resolution improvements on conventional geophysical techniques under complex near-surface conditions. A dense seismic network including 192 sensors, with its aperture around 4.8 km, was deployed to record ambient noise for local-scale geothermal reservoir imaging in central Zhejiang Province, southeast China. With the ultrashort (less than 5 days) observation, a subset of the total station pairs was extracted to conduct seismic interferometry and dispersion measurements. This customized subnet was qualified to be an overdetermined system to achieve similar performance of entire network for the eikonal tomography with higher efficiency. The recorded high-frequency noise sources turned out to be rather homogeneous distributions, except for the dominant direction of northern Jinhua urban area. Azimuthal effects and wavelength restriction of dispersion measurements were quantified by simulating source–receiver responses under non-equipartitions of energy. The azimuth–velocity variations of field dataset verified that phase velocity measurements using the tested wavelength restriction were robust under different source–receiver orientations. The obtained phase velocity maps were comparable with the geological map. Furthermore, the inverted body wave velocities coincide well with the borehole data. Shear wave velocity profiles revealed corresponding fracture and depression structures of the reservoir. Finally, multiple geophysical properties delineate the shallow geothermy to be karst fissure water heated at certain earth temperature gradient.

Author(s): Cheng, Feng; Xia, Jianghai; Zhang, Kai; Zhou, Changjiang; Ajo-Franklin, Jonathan B | Abstract: SUMMARY Surface wave retrieval from ambient noise records using seismic interferometry techniques has been widely used for multiscale shear wave velocity (Vs) imaging. One key step during Vs imaging is the generation of dispersion spectra and the extraction of a reliable dispersion curve from the retrieved surface waves. However, the sparse array geometry usually affects the ability for high-frequency (g1 Hz) seismic signals’ acquisition. Dispersion measurements are degraded by array response due to sparse sampling and often present smeared dispersion spectra with sidelobe artefacts. Previous studies usually focus on interferograms’ domain (e.g. cross-correlation function) and attempt to enhance coherent signals before dispersion measurement. We propose an alternative technique to explicitly deblur dispersion spectra through use of a phase-weighted slant-stacking algorithm. Numerical examples demonstrate the strength of the proposed technique to attenuate array responses as well as incoherent noise. Three different field examples prove the flexibility and superiority of the proposed technique: the first data set consists of ambient noise records acquired using a nodal seismometer array; the second data set utilizes distributed acoustic sensing (DAS) and a marine fibre-optic cable to acquire a similar ambient noise data set; the last data set is a vibrator-based active-source surface wave data. The enhanced dispersion measurements provide cleaner and higher-resolution spectra without distortions which will assist both human interpreters as well as ML algorithms in efficiently picking curves for subsequent Vs inversion.

Three-dimensional asperity model of rough surfaces is proposed using valley–peak ratio (VPR) of the maximum peak. Asperities of rough surfaces are reconstructed according to paraboloid asperity function, which is derived using least square method and asperity projection plane determined via VPR. The minimum profile deviation between reconstructed asperities and rough surface is calculated using simulated annealing method to optimize VPR. Effects of simulated mutation surfaces, measured surfaces, and different sampling intervals (SIs) on profile deviation are investigated. Compared with nine–point method, the proposed model demonstrates a smaller deviation of mutational rough surface, the absence of interference among asperities, and more stable surface parameters and contact mechanics performance at different SIs.

Novel smart materials that can achieve a diverse range of practical applications with simple molecular structures and green synthesis routes are still in great demand. Herein, by a green photo-oxidation reaction, two simple aggregation-induced emission luminogens (AIEgens) CZ-PYZ and p-CZ-BYZ were developed, with the difference of linking type between the donor group (carbazole) and the acceptor group (a benzoylimino derivative). These two analogues exhibited different luminescence behaviors in the aggregation state. The molecule p-CZ-BYZ showed mechanochromic luminescence and room-temperature phosphorescence simultaneously, while none of the similar phenomena was observed in the case of CZ-PYZ. According to photophysical property tests, single crystal structural analyses and theoretical calculations, we found that this difference was induced by their different stacking manners. It was believed that the present results may provide us with a better understanding of structure–property relationship and offer an important guideline for multifunctional molecular design.

High performance solution processable thermally activated delayed fluorescence (TADF) emitters are of huge importance in the development of organic light-emitting diodes (OLEDs). In this article, two solution processable D3–A star-shaped TADF emitters, namely TATC-TRZ and TATP-TRZ, with different flexible alkyl and rigid phenyl side chains are developed. Both emitters show similar photophysical properties and obvious TADF characteristics with a sub-micro second delayed lifetime of 0.6 μs for TATC-TRZ and 0.4 μs for TATP-TRZ while the flexible alkyl chain ensures TATC-TRZ with superior film forming ability and morphological stability compared to TATP-TRZ. Owing to such advantages, solution processed non-doped OLEDs based on TATC-TRZ secure a high maximum external quantum efficiency (EQEmax) of 7.5% and current efficiency (CEmax) of 19.9 cd A−1, respectively, which is much higher than that of TATP-TRZ with EQEmax of 2.8% and CEmax of 7.4 cd A−1. This work demonstrates the effectiveness of a flexible alkyl tail on the performance of solution-processed devices.

Developing highly efficient red thermally activated delayed fluorescence (TADF) emitters remains a formidable challenge due to strict molecular design principles. In this contribution, two red emitters PXZ-AQPy and PXZ-AQPhPy with high structural rigidity and linear configurations are designed and synthesized based on phenoxazine (PXZ) as a donor and acenaphtho[1,2-b]quinoxaline (AQ) as an acceptor. Both molecules with horizontal orientation are endowed with TADF and aggregation-induced emission (AIE) properties. By elongating the acceptor segment via phenyl decoration, PXZ-AQPhPy exhibits higher horizontal ratios of the emitting dipole orientation (Θ‖ = 85%), while the emission characteristics are almost unaltered. Consequently, the PXZ-AQPhPy based device achieves a high external quantum efficiency of 19.6% with an emission peak at 610 nm. This work provides a simple and effective design strategy to selectively promote the horizontal orientation of red TADF emitters.

Efficient blue thermally activated delayed fluorescent emitters based on organic boron-acceptor are developed with high external quantum efficiencies and finely tuned CIE coordinates.

Multi-resonance TADF (MR-TADF) emitters are promising for high-resolution OLEDs, but the concurrent optimization of excited-state dynamics and color purity remains a tough challenge. Herein, three deep-blue MR-TADF compounds (BN1-BN3) featuring gradually enlarged ring-fused structures and increased rigidity are accessed by lithium-free borylation in high yields from the same precursor, with all the emitters possessing CIE

Thermally activated delayed fluorescent (TADF) emitters have been extensively investigated in the past decade. Compared to the prosperous development of the donor unit, the development of an effici...

A tri-armed arylsulfone-based acceptor (SF) linked by triphenylbenzene (TPB) has been developed to construct solution-processable thermally activated delayed fluorescence (TADF) materials with large band gaps. The acceptor suffered limited conjugation due to the tetrahedral geometry of sulfonyl groups, as well as a meta-linkage at the central TPB moiety. By simple conjugation of the SF with appropriate donor units, luminophores SF–DMAC and SF–PXZ capable of producing efficient blue/green emissions were obtained, with peak efficiencies of 11.3% (19.0 cd A−1 and 10.0 lm W−1) and 12.4% (35.6 cd A−1 and 17.8 lm W−1) in the corresponding wet-processed OLEDs. Decent resistance to roll-off at high brightness was noticed in the device based on SF–PXZ, ascribing to reduced intermolecular interactions due to its star-shaped architecture and an efficient reverse intersystem crossing (RISC) process.

Photoluminescence quantum yield (PLQY) and the reverse intersystem crossing (RISC) process are critical for next-generation highly efficient organic light-emitting diodes (OLEDs). However, it is not easy to simultaneously obtain high PLQY and fast RISC, especially in TADF emitters with twisted donor–acceptor structures due to their conflicting requirements for wave function overlapping. Herein, based on a rigid planar dibenzo[a,c]phenazine (DPPZ) unit as an acceptor, four emitters (isomers of DMAC-11-DPPZ and DMAC-10-DPPZ, and isomers of PXZ-11-DPPZ and PXZ-10-DPPZ) with 9,9-dimethylacridine (DMAC) and 10H-phenoxazine (PXZ) as donors substituted via 11- and 10-positions were designed and synthesized to balance the wave function overlapping and explore the relationship between their structures and luminescence properties. Photophysical characterization and theoretical calculations suggest small energy gaps (ΔEST) featuring fast RISC rates in all these compounds. Meanwhile, DMAC-11-DPPZ and PXZ-11-DPPZ achieve higher PLQYs due to the largely suppressed non-radiative transition as revealed by the decreased Huang–Rhys factors. As a result, high external quantum efficiencies (EQEmax) of 23.8% for DMAC-11-DPPZ and 13.7% for PXZ-11-DPPZ are obtained. This work provides a promising strategy to improve the PLQY of TADF materials by adjusting the substituted site, and also shows the potential of phenazine derivatives for OLED applications.

Three donor–acceptor–donor type emitters of 2TPA-BT, 2MeTPA-BT and 2DMeTPA-BT were synthesized. Crystal structures for all compounds were determined by single-crystal X-ray diffraction analysis, showing that by introducing one or two methyl groups between the donors and acceptor, the spatial configuration changes greatly for 2MeTPA-BT and 2DMeTPA-BT compared to their parent compound 2TPA-BT. Density functional theory analysis reveals that the emission of 2MeTPA-BT has a more obvious hybridized local and charge-transfer (HLCT) feature based on the influence of steric hindrance of methyl substituents. Attributed to their different spatial configurations and luminescence mechanisms, different emission wavelengths with high photoluminescence quantum yields (ΦPLs) of 75.43%, 93.43% and 89.63% in toluene solvent, as well as 44.76%, 52.19 and 33.87% in neat film, were observed for 2TPA-BT, 2MeTPA-BT and 2DMeTPA-BT, respectively. Furthermore, strong electroluminescence was observed with the emission peaks at 602, 560 and 544 nm, maximum current efficiencies of 11.05 cd A−1, 30.40 cd A−1 and 25.02 cd A−1, maximum power efficiencies of 6.01 lm W−1, 23.67 lm W−1 and 20.37 lm W−1, and maximum external quantum efficiencies of 4.43%, 8.47% and 7.29% for 2TPA-BT, 2MeTPA-BT and 2DMeTPA-BT doped organic light-emitting devices (OLEDs), respectively. This work clearly illustrates the effect of spatial configuration changes on the luminescence properties of organic emitters.

Herein, we report a new pyrene (PY)-based derivative, 1-(4-(phenylsulfonyl)phenyl)pyrene (1-DPS-PY), whose two crystals (crystal-B and crystal-G) exhibit sky-blue and green excimer fluorescence, respectively. Crystal-B and crystal-G have a similar dimeric π–π PY stacking in the crystals, but with a different single-molecule conformation. The experimental and theoretical investigations demonstrate that the substituent orientation of 4-(phenylsulfonyl)phenyl (DPS) plays a crucial role in modulating the excited-state properties of the PY excimer. The small twist angle (Φ) between DPS and PY facilitates the larger overlap between two PY planes in the excited state, resulting in more red-shifted excimer emission, and vice versa. Moreover, crystal-B shows a photoluminescence (PL) efficiency (ηPL) as high as 77% due to the better discreteness of PY dimer stacking, in contrast to ηPL = 60% of crystal-G with the non-discrete PY dimer stacking. Organic light-emitting diodes (OLEDs) were fabricated with doped and non-doped device structures. The devices showed a gradual emission change from deep blue to sky blue with increasing doping concentration, corresponding to the emission species transformation from a monomer to an excimer. A non-doped device exhibited the best performance with an external quantum efficiency (EQE) of nearly 4.5% and a maximum luminance of 13 733 cd m−2. These results provide us with a new understanding of the mechanism of the PY excimer, and a new strategy to design the polymorphic PY dimers for high-efficiency excimer fluorescence with tunable emission color.

The development of hydrogen sensors is of paramount importance for timely leak detection and remains a crucial unmet need. Palladium-based materials, well known as hydrogen sensors, still suffer from poisoning and deactivation. Here, a hybrid hydrogen sensor consisting of a Pd nanocluster (NC) film, a metal-organic framework (MOF), and a polymer, are proposed. The polymer coating, as a protection layer, endows the sensor with excellent H

Named entity recognition is a traditional task in natural language processing. In particular, nested entity recognition receives extensive attention for the widespread existence of the nesting scenario. The latest research migrates the well-established paradigm of set prediction in object detection to cope with entity nesting. However, the manual creation of query vectors, which fail to adapt to the rich semantic information in the context, limits these approaches. An end-to-end entity detection approach with proposer and regressor is presented in this paper to tackle the issues. First, the proposer utilizes the feature pyramid network to generate high-quality entity proposals. Then, the regressor refines the proposals for generating the final prediction. The model adopts encoder-only architecture and thus obtains the advantages of the richness of query semantics, high precision of entity localization, and easiness of model training. Moreover, we introduce the novel spatially modulated attention and progressive refinement for further improvement. Extensive experiments demonstrate that our model achieves advanced performance in flat and nested NER, achieving a new state-of-the-art F1 score of 80.74 on the GENIA dataset and 72.38 on the WeiboNER dataset., Comment: Accepted to the Neural Processing Letters (2023)

In the context of high-quality development of education, vigorously promoting the construction of new agricultural science is the need to serve the national strategy and rural revitalization, and is an inevitable choice for the development of agriculture-related colleges and universities. Exploring a new path of agricultural science construction that is in line with both national policies and local socio-economic development, and cultivating high-quality agricultural talents is a realistic problem that needs to be solved at present. This paper adopts inductive method through interviews with experts from agriculture-related colleges and universities, research institutes, industry enterprises and government authorities, and expert discussion sessions, and proposes that the construction of new agricultural science in Xinjiang needs to adopt such paths as innovative talent cultivation system, innovative talent practice platform, innovative curriculum system, innovative teacher team construction, innovative research platform for rural revitalization, and support for the construction of Xinjiang New Agricultural Science Education Union to achieve high-quality talent cultivation and enhance the ability to serve rural revitalization. This study tries to propose a new construction path for the construction of Xinjiang agricultural science, explore a new track for agriculture-related colleges and universities to serve the needs of rural strategy and shape a new development momentum.

Revealing the photoluminescence (PL) origin and mechanism is a most vital but challenging topic of carbon dots. Herein, confined-domain crosslink-enhanced emission (CEE) effect was first studied by a well-designed model system of carbonized polymer dots (CPDs), serving as an important supplement to CEE in the aspect of spatial interactions. The “addition-condensation polymerization” strategy was adopted to construct CPDs with substituents exerting different degrees of steric hindrance. The effect of confined-domain CEE on the structure and luminescence properties of CPDs have been systematically investigated by combining characterizations and theoretical calculations. Such tunable spatial interactions dominated the coupling strength of the luminophores in one particle, and eventually resulted in the modulated PL properties of CPDs. These findings provide insights into the structural advantages and the PL mechanism of CPDs, which are of general significance to the further development of CPDs with tailored properties.

Endoscopic image has complex backgrounds and spatially different noise, bringing mainstream denoising methods to the problem of incomplete noise removal and the loss of image detail. Thus, an endoscopic image denoising algorithm based on spatial attention UNet network is proposed in this paper. UNet based on residual learning is utilized as the backbone network. Spatial attention modules based on noise intensity estimation and edge feature extraction modules are used to remove noise better while preserving the image details and improving generalization ability. We take endoscopic images of real scenes using gastroscopy and compare our method with mainstream methods. Experimental results show that our approach improves PSNR by 3.51 or 2.93 and SSIM by 0.03 or 0.015 compared with CBDNet or EDCNN, respectively. Our method can effectively improve the impact of noise on the image quality of endoscopic images, thus better assisting doctors in diagnosis and treatment.