Automatic velocity picking with restricted weighted k-means clustering using prior information

Automatic picking of seismic velocity can be performed using k-means clustering. In simple k-means clustering, the number of clusters needs to be predetermined, while the picking result is affected by the initial value of each cluster center. In this study, we present an unsupervised weighted k-means clustering velocity-picking method that picks the centers of the energy clusters instead of the geometric centers of the clusters. This method works on the semblance velocity spectrum and requires an initial velocity function and three user-defined thresholds to limit the search area. The number of cluster centers and their initial times are obtained according to a rectangular signal resulting from the three thresholds, while the initial velocities of the cluster centers can be subsequently obtained using their initial times and the initial velocity function. Inaccurate selection of thresholds may merge two clusters wrongly, in which case only a stronger event is selected. In the weighted k-means clustering algorithm, weights are calculated by using the amplitudes of the velocity points. Meanwhile, points far from the center are gradually removed to ensure that each cluster center coincides with the respective energy cluster center. We also propose a method for ignoring non-primary velocities, such as multiples, by removing points that create sudden changes in the slope of the reference velocity beyond a user-defined limit. The processing of the model and real data show that the proposed seismic velocity-picking method has high efficiency and picking accuracy

Chemisorption Induced Formation of Biphenylene Dimer on Surfaces

We report an example that demonstrates the clear interdependence between surface-supported reactions and molecular adsorption configurations. Two biphenyl-based molecules with two and four bromine substituents, i.e. 2,2-dibromo-biphenyl (DBBP) and 2,2,6,6-tetrabromo-1,1-biphenyl (TBBP), show completely different reaction pathways on a Ag(111) surface, leading to the selective formation of dibenzo[e,l]pyrene and biphenylene dimer, respectively. By combining low-temperature scanning tunneling microscopy, synchrotron radiation photoemission spectroscopy, and density functional theory calculations, we unravel the underlying reaction mechanism. After debromination, a bi-radical biphenyl can be stabilized by surface Ag adatoms, while a four-radical biphenyl undergoes spontaneous intramolecular annulation due to its extreme instability on Ag(111). Such different chemisorption-induced precursor states between DBBP and TBBP consequently lead to different reaction pathways after further annealing. In addition, using bond-resolving scanning tunneling microscopy and scanning tunneling spectroscopy, we determine the bond length alternation of biphenylene dimer product with atomic precision, which contains four-, six-, and eight-membered rings. The four-membered ring units turn out to be radialene structures

Chemisorption-induced formation of biphenylene dimer on Ag(111)

We report an example that demonstrates the clear interdependence between surface-supported reactions and molecular-adsorption configurations. Two biphenyl-based molecules with two and four bromine substituents, i.e., 2,2′-dibromobiphenyl (DBBP) and 2,2′,6,6′-tetrabromo-1,1′-biphenyl (TBBP), show completely different reaction pathways on a Ag(111) surface, leading to the selective formation of dibenzo[e,l]pyrene and biphenylene dimer, respectively. By combining low-temperature scanning tunneling microscopy, synchrotron radiation photoemission spectroscopy, and density functional theory calculations, we unravel the underlying reaction mechanism. After debromination, a biradical biphenyl can be stabilized by surface Ag adatoms, while a four-radical biphenyl undergoes spontaneous intramolecular annulation due to its extreme instability on Ag(111). Such different chemisorption-induced precursor states between DBBP and TBBP consequently lead to different reaction pathways after further annealing. In addition, using bond-resolving scanning tunneling microscopy and scanning tunneling spectroscopy, we determine with atomic precision the bond-length alternation of the biphenylene dimer product, which contains 4-, 6-, and 8-membered rings. The 4-membered ring units turn out to be radialene structures.This work was financially supported by the National Natural Science Foundation of China (21773222, 51772285, 21872131, U1732272, and U1932214), the National Key R&D Program of China (2017YFA0403402, 2017YFA0403403, and 2019YFA0405601), and Users with Excellence Program of Hefei Science Center CAS (2020HSC-UE004). The work at Washington State University was primarily funded through the National Science Foundation CAREER program under Contract no. CBET-1653561. This work was also partially funded by the Joint Center for Deployment and Research in Earth Abundant Materials (JCDREAM) in Washington State. Most of the computational resources were provided by the Kamiak HPC under the Center for Institutional Research Computing at Washington State University. This research also used resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility operated under Contract no. DE-AC02-05CH11231. The work at Donostia International Physics Center was primarily funded through the Juan de la Cierva Grant (no. FJC2019-041202-I) from Spanish Ministry of Economy and Competitiveness, the European Union’s Horizon 2020 Research and Innovation program (Marie Skłodowska-Curie Actions Individual Fellowship (no. 101022150), and the MCIN/AEI/ 10.13039/501100011033 (Grant no. PID2019-107338RB-C63).Peer reviewe

Herkinorin pretreatment alleviates cerebral injury in rat models with ischemic stroke

Objective To investigate the regulation and mechanism of Herkinorin preconditioning on NOD-like receptor protein 3 (NLRP3) in brain tissue of transient middle cerebral artery occlusion (tMCAO) rats. Methods Rats were randomly divided into sham operation group (sham), model group (tMCAO) and Herkinorin group (Herkinorin). Before modeling, rats in Herkinorin group were intraperitoneally given Herkinorin (10 mg/kg) once a day for a week. The rats were evaluated by neurologic score, TTC staining, TUNEL staining 24 h after reperfusion. The expression levels of IκBα, p65, p-p65, pro-IL-1β, IL-1β, pro-caspase1, caspase1 p20 and NLRP3 were detected by Western blot. The binding level of IκBα to β-arrestin2 was detected by co-immunoprecipitation (Co-IP). Results Compared with sham group, rats in tMCAO group had higher behavioral score (P＜0.01), increased cerebral infarction percentage and increased cerebral edema rate (P＜0.01). The level of cell apoptosis was increased in ischemic penumbra (P＜0.01). The expression levels of IκBα and p65 were decreased (P＜0.01) and the expression levels of p-p65, IL-1β, caspase1 p20 and NLRP3 were increased in ischemic penumbra (P＜0.01). The binding level of IκBα to β-arrestin2 was decreased in ischemic penumbra (P＜0.01). Compared with tMCAO group, rats in Herkinorin group had lower behavioral score (P＜0.01), lower cerebral infarction percentage and lower cerebral edema rate (P＜0.01). The level of cell apoptosis was decreased in ischemic penumbra(P＜0.01). The expression of IκBα and p65 was increased (P＜0.01) and the expression of p-p65, IL-1β, caspase1 p20 and NLRP3 was decreased in ischemic penumbra (P＜0.01). The binding of IκBα to β-arrestin2 was increased in ischemic penumbra (P＜0.01). Conclusions Herkinorin may negatively regulate NF-κB/NLRP3 pathway to alleviate cerebral ischemia-reperfusion injury of tMCAO rats

A Thermovisco-Hyperelastic Constitutive Model of NEPE Propellant Over a Large Range of Strain Rates

The uniaxial compressive mechanical curves of nitrate ester plasticized polyether (NEPE) propellant under different temperatures and strain rates have been obtained with a universal testing machine and modified split Hopkinson pressure bar (SHPB). The experimental results show that the mechanical properties of NEPE propellant are both rate dependent and temperature dependent. With decreasing temperature or increasing strain rate, the modulus and rigidity obviously increase. Based on the previous models proposed by Yang and Pouriayevali, we propose a modified viscohyperelastic constitutive model which can describe the mechanical response over a large range of strain rates. Then we add a rate-dependent temperature item into the modified model to make a thermovisco-hyperelastic constitutive model. By comparing the experimental results with the model, we find that the thermovisco-hyperelastic constitutive model can correctly describe the uniaxial compressive mechanical properties of NEPE propellant at different temperatures and over a large range of strain rates from the static state to 4500 s À1

Improved Numerical Calculation of the Single-Mode-No-Core-Single-Mode Fiber Structure Using the Fields Far from Cutoff Approximation

Multimode interferometers based on the single-mode-no-core-single-mode fiber (SNCS) structure have been widely investigated as functional devices and sensors. However, the theoretical support for the sensing mechanism is still imperfect, especially for the cladding refractive index response. In this paper, a modified model of no-core fiber (NCF) based on far from cut-off approximation is proposed to investigate the spectrum characteristic and sensing mechanism of the SNCS structure. Guided-mode propagation analysis (MPA) is used to analyze the self-image effect and spectrum response to the cladding refractive index and temperature. Verified by experiments, the performance of the SNCS structure can be estimated specifically and easily by the proposed method

Effect of Different Combustion Modes on the Performance of Hydrogen Internal Combustion Engines under Low Load

Detailed hydrogen–air chemical reaction mechanisms were coupled with the three-dimensional grids of an experimental hydrogen internal combustion engine (HICE) to establish a computational fluid dynamics (CFD) combustion model based on the CONVERGE software. The effects of different combustion modes on the combustion and emission characteristics of HICE under low load were studied. The simulation results showed that, with the increase in excess hydrogen, the equivalent combustion and excessive hydrogen combustion modes with medium-cooled exhaust gas recirculation (EGR) dilution could improve the intensity of the in-cylinder combustion of HICE, increase the peak values of pressure and temperature in the cylinder, and then improve the indicated thermal efficiency of HICE under low load. However, larger excessive hydrogen combustion could weaken the improvement in performance; therefore, the performance of HICE could be comprehensively improved by the adoption of excessive hydrogen combustion with a fuel–air ratio below 1.2 under low load. The obtained conclusions indicate the research disadvantages in the power and emission performances of HICE under low load, and they are of great significance for the performance optimization of HICE. Furthermore, a control strategy was proposed to improve the stability of HICE under low load