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This work investigates a Bayesian network model (BNM) to implement the autonomous decision-making process of welding positions during gas metal arc multipass welding with T-joints for automated manufacturing. The laser vision sensor is used to profile the weld seam, and the weld seam profile (WSP) is extracted with a novel scheme based on scale-invariant feature transform and orientation feature detection. The feature points of the extracted WSP are effectively identified through slope mutation detection. A BNM is built with these points and the determined welding state online, and the priori probabilities of the model variables are acquired in a computational manner integrated with welding experience. The feature point with the maximum posteriori probability is selected as the current welding position using the evidence pre-propagation importance sampling inference algorithm. The analytic hierarchy process and the C4.5 decision tree algorithm are used to compare with the proposed BNM regarding decision effectiveness. Experimental results show that the proposed BNM can give the effective decision-making results of welding positions with T-joints of different thicknesses and show great potential for higher manufacturing efficiency and automatic levels.

Biosensors based on terahertz (THz) metasurfaces have recently attracted widespread attention. However, few have been reported so far because it is a challenge to achieve ultrasensitive multidimensional detection in the THz spectrum. Here, we propose a novel THz biosensor that consists of a metasurfaces and a metal oxide semiconductor-like structure (MOSLS), which is based on patterned graphene–polyimide–perovskite. We varied the photoconductivity of the MOSLS via the electrostatic doping effect. The biosensor could detect whey protein down to a concentration limit of 6.25 ng/mL. Significant responses in frequency, phase, and transmission amplitude were all detected for different protein concentrations. The transmission value difference, frequency shift, and phase difference increased with the concentration of whey protein, clearly demonstrating multidimensional biosensing. Moreover, by applying lasers with different wavelengths, we have realized reversible biosensing in THz region for the first time. These results are very promising for applications of THz metasurfaces in the field of biosensing.

The intrinsic link between surface plasmon modes (eigenmodes) and lattice modes in subwavelength periodic structures is investigated based on the split-ring metamaterial structure. The paper shows that the strong coupling between the eigenmodes and the lattice modes can be achieved by appropriately adjusting the period of the metamaterial structure, and the emergence of new, to the best of our knowledge, modes at low frequencies is observed, resulting in a lower spectral loss of a single hybrid resonance and an increase in its Q factor up to 110. In addition, an asymmetric double-split-ring structure is proposed, and the Fano resonance is excited, giving rise to a spectral line with three resonance valleys. The coupled harmonic-oscillator model is used to interpret the underlying coupling mechanism in lattice-induced transparent systems, which agrees well with our simulation results. This strong-coupling scheme between the lattice and the mixed modes of the metamaterial unit provides a new avenue to modulate lattice-induced transparency, high- Q resonance, and strong-field confinement, which may find applications in the design of ultrasensitive sensors, slow-light devices, as well as multiple frequency absorbers and other fields.

The Dirac fermion, a high-mobility electron in the Dirac cone of monolayer graphene, has significant potential for use in the terahertz probing technique. For undoped graphene, ultrafast terahertz ...

Analogous to black phosphorus, SnS processes folded structure that shows a strongly anisotropic optical absorption. Herein, by using ultrafast two-color pump and probe spectroscopy, the azimuthal angle dependence of nonlinear optical anisotropy in SnS is investigated. After 390 nm photoexcitation, the reflectivity of the 780 nm probe beam is first reduced significantly, followed by a complex alternation with the rotation of the sample along the

Ultrasonic-assisted metal inert gas (U-MIG) welding experiments were performed to analyze the effect of Cu addition on the microstructure and mechanical properties of galvanized steel sheet welds, and first-principles calculations were undertaken to predict the effect of Cu on the mechanical properties of α-Fe based structures. As shown by scanning electron microscopy analysis, Cu is conducive to the refinement and uniformity of the microstructure in the weld zone. Energy-dispersive spectrometry data indicated the presence of Cu in the welds after welding with Cu powder. The elastic moduli of the welds without and with Cu powder, obtained from nanoindentation tests, were (217.66 ± 5.11) GPa and (223.13 ± 9.12) GPa, respectively, which were close to the calculated results. The mechanical properties of the crystal structures of α-Fe and α-Fe1.9Cu0.1 were calculated using Materials Studio software. Both the experimental and calculated results showed that Cu doping reduced the bulk modulus of the weld but increased its shear modulus.

Zn vapour is easily generated on the surface by fusion welding galvanized steel sheet, resulting in the formation of defects. The present study develops a novel method for automatically detect typical undercuts, pores and burn-through defects from CCD using concepts of Convolutional Neural Network(CNN) and active vision. Four deep learning methods of training a defects classifier using 1) an AlexNet built from scratch, 2) a Visual Geometry Group 16 (VGG16) built from scratch, 3) the output features of the VGG16 network architecture previously trained on the general ImageNet dataset, 4) the convolutional block attention module adaptively refining the intermediate feature map of VGG16 are investigated. To detect the weld defects, laser streak images of different weld defects are collected and two types of data augmentation are used to reduce overfitting caused by the limited training dataset. In the method 1 and 2, the improvement of accuracy by data augmentation is gradually slow. VGG16 model in combination with data augmentation 2 achieve the state-of-the-art performance for defects detection in the galvanized steel sheets lap joint. Transfer learning methods using the output features of VGG16 and attention mechanism methods introducing the convolutional block attention module achieve improved accuracy in the case of a small number of training dataset. And all classifiers have a 100 % recognition rate for good welds. This shows that the method of combining CNN and laser vision is feasible, and this method can be used to record the number and location of typical defects in continuous welds.

Due to the existence of high-temperature and high-pressure zinc vapor in the gas metal arc welding (GMAW) process of galvanized steel, it is difficult to achieve accurate and real-time detection of...

In this paper, a chiral metamaterial (MM) structure composed of bilayer twisted split-ring resonator (SRR) arrays is proposed and demonstrated to realize polarization-controlled, dual-directional, and multifunctional polarization conversion for terahertz (THz) waves. Simulated results show that the converter can selectively achieve linear-to-linear, or linear to left-handed circular, or linear to right-handed circular’s polarization conversion according to the polarization state and propagating direction of the incident THz wave. Stokes parameters, ellipticity, and polarized rotation angle are introduced to determine the polarization states of the output waves. The circular polarization transmission coefficients and surface current distributions at the resonance frequency points are simulated to explain and demonstrate the physical origin of polarization conversion. The proposed multifunctional converter can find potential applications in THz sensing, imaging and communication areas.

The intrinsic link between surface plasmon modes (eigenmodes) and lattice mode in subwavelength periodic structures is investigated based on the split-ring metamaterial structure. The study shows that the strong coupling between the eigenmodes and the lattice modes can be achieved by appropriately adjusting the period of the metamaterial structure, and the emergence of new modes at low frequencies is observed, resulting in a lower spectral loss of a single hybrid resonance and an increase in its Q-factor up to 110. In addition, an asymmetric double split-ring structure is proposed, and the Fano resonance is excited, giving rise to a spectral line with three resonance valleys. The coupled harmonic oscillator model is used to interpret the underlying coupling mechanism in lattice-induced transparent systems, which agrees well with our simulation results. This strong coupling scheme between the lattice and the mixed modes of the metamaterial unit provides a new avenue to modulate lattice-induced transparency, high-Q resonance, and strong-field confinement, which may find applications in the design of ultrasensitive sensors, slow-light devices, as well as multiple frequency absorbers and other fields.

We present a novel method to monitor the weld geometry for metal inert gas (MIG) welding process with galvanized steel plates using Bayesian network (BN), and propose an effective method of extracting the weld reinforcement and width online. The laser vision sensor is mounted after the welding torch and used to profile the weld. With the extracted weld geometry and the adopted process parameters, a back propagation neural network (BPNN) is constructed offline and used to predict the weld reinforcement and width corresponding to the current parameter settings. A BN from welding experience and tests is presented to implement the decision making of welding current/voltage when the error between the predictive geometry and the actual one occurs. This study can deal with the negative welding tendency to adapt to welding randomness and indicates a valuable application prospect in the welding field.

In present study, Graphene nanoparticles (GNPs) are incorporated into the steel plate by dip coating technology, and the steel plate is welded by a composite welding process combined with an ultrasonic generator and a MIG welding machine (U-MIG). Joint samples of different contents of GNPs were obtained. After welding, the microstructure of the welded joint is characterized by OM, SEM, XRD, and RAMAN and compared with the bare sample. The results show that a certain amount of graphene nanoparticles can be evenly distributed in the center of the weld area, and the grains in the center of the weld are significantly refined. Using the nanoindentation technique to study the microhardness of the weld cross section, the hardness of the weld center has increased due to the addition of graphene; compared with the bare sample, the maximum enhancement rate of the GNPs coating sample is ∼ 125.6%. The enhancement of the strength of the composite material is achieved by a variety of strengthening mechanisms, such as non-uniform nucleation, pinning effect, and hindering dislocation movement. This improvement in mechanical properties is attributed to the uniform dispersion of the hybrid particles and the refinement of the matrix grains and the good interface combination between the hybrid particles and the matrix.

To solve the problem of zinc to the weld quality of galvanised sheet, alloy elements (Cu, Nb, Y) have been added to combine with zinc to form stable compounds during welding. The structure and prop...

The atomically thin layered transition metal dichalcogenide (TMDCs) PtSe2 is a new emerging two-dimension (2D) material, which has a transition from indirect-gap semiconductor to semimetal with increasing thickness. Defects in 2D TMDCs are very ubiquitous and play a crucial role in understanding many electronics and optoelectronics in TMDCs. In this article, PtSe2 films with different thickness are obtained by selenizing the variously thick Pt films. Extrapolation of the onset absorption from the visible-infrared spectrum demonstrates that the selenization of 1 and 3 nm Pt films shows semiconductor-like character, while those of thick Pt films (with thickness of 10 and 15 nm) show metallic behavior. The transient absorption (TA) spectroscopy reveals that all films show immediately photobleaching signals after photoexcitation at 800 nm, and the subsequent relaxation process shows strongly thickness dependence. The thinnest film shows biexponential relaxation with typical time constants of 1.28 and 101.2 ps. In contrast, the photobleaching signals are developed into photoinduced absorption signals in thicker films, and the absorption magnitude increases with the thickness of the films. The optical pump and terahertz (THz) probe spectroscopy reveals that all samples show positive photoconductivity after photoexcitation of 800 nm, the subsequent recovery is completed within 2.0 ps, and the recovery time constant decreases with the increase of the films' thickness. Our TA and THz spectroscopy results reveal that the defect states of the films play dominated role in the relaxation of photocarrier after photoexcitation, and edgesite states are inferred to make dominated contributions to the defect states in the selenization of platinum films.

Magnesium and its alloys, as the metal materials with the lowest density among structural materials, have attracted much attention due to their excellent properties such as high specific stiffness,...

The common but unexpectedly neglected natural particle suspensions (NPSs) have significant effects on the characteristics of molten salts. In the present work, NPSs were generated via the corrosion of Cr or Fe cubes in molten ZnCl2 at 370, 420 or 470 °C in air and then investigated using in situ ultraviolet-visible spectroscopy, infrared spectroscopy and inductively coupled plasma optical emission spectrometry. The behaviors of Cr and Fe in these systems were quite different. In the case of Cr, particle (mainly contained Cr2O3) sizes grew over time and temperature. The elemental concentrations of Cr also increased over time; in addition, its values at 420 °C were slightly larger than that at 370 °C but much lower than that at 470 °C. For Fe, particle (mainly contained Fe2O3) sizes and elemental concentrations of Fe decreased with temperature, whereas they first increased (the time required for the increase reduced with temperature) and then decreased slowly over time. These results can be ascribed to the chemical reactions of these metals with the molten salts and/or various impurities.

Efficient interfacial light-electric interconversion in van der Waals heterostructures is critical for their optoelectronic applications. Using time-resolved terahertz spectroscopy and transient absorption spectroscopy, the charge transfer and the dynamical interlayer excitons were investigated in the heterostructures comprising monolayer WSe2 and monolayer graphene with varying stacking order on a sapphire substrate. Herein, a more comprehensive understanding of ultrafast charge transfer and exciton dynamics in two-dimensional heterostructures is shown. Owing to the effective electric field induced by the sapphire substrate, the WSe2/graphene heterostructure exhibits positive terahertz photoconductivity after photoexcitation, while negative terahertz photoconductivity is observed in the graphene/WSe2 heterostructure. The transient absorption spectra indicate that the exciton lifetimes also exhibit a considerable difference, where WSe2/graphene exhibits the longest exciton lifetime, followed by monolayer WSe2, while graphene/WSe2 exhibits the shortest lifetime. These observations provide a new idea for using van der Waals heterostructures in electronic and photonic devices.

By using optical pump and terahertz probe spectroscopy, we have investigated the photocarrier dynamics in PdSe

BACKGROUND Neoadjuvant chemotherapy is an important treatment for advanced gastric cancer, but it has been unclear whether neoadjuvant chemotherapy is closely related to lymph node metastasis. Therefore, based on the disease characteristics of the cT2-cT4N0M0 gastric cancer population, this study established a nomogram prediction model of lymph node metastasis risk in this gastric cancer population to help clinicians optimize clinical decision-making. MATERIAL AND METHODS We analyzed the data of 336 patients with advanced gastric cancer with CT imaging stage of cT2-cT4N0M0 admitted to the Third Department of the Fourth Hospital of Hebei Medical University from 2015 to 2021. Combined with the results of univariate and multivariate logistic regression analysis, 7 indicators were selected to establish a nomogram prediction model. The calibration curves, ROC curves, and decision curves were drawn against the nomogram model using R language. RESULTS The results showed that the AUC value of the model and the external validation data set were 0.925 and 0.911, respectively. The P value of the Hosmer-Lemeshow test for the internal validation dataset was 0.082, and the P value of Hosmer-Lemeshow test for the external validation dataset was 0.076.The decision curve results showed that when the threshold probability was 0.1-0.9, this model could benefit patients by predicting the risk of lymph node metastasis in patients with advanced gastric cancer, and formulating appropriate treatment schemes accordingly. CONCLUSIONS This nomogram has shown good discrimination and fit, and can also be combined with imaging examination to screen the populations suitable for neoadjuvant chemotherapy, avoid the risk of misdiagnosis of N staging to the greatest extent, and to assist clinicians to optimize clinical decision-making.

Understanding of ultrafast spin dynamics is crucial for future ultrafast and energy efficient magnetic memory and storage applications. We study the ultrafast laser-induced magneto-optical response of a CoFeB/MgO/CoFeB magnetic tunneling junction (MTJ), when exciting with a short laser pulse, as a function of magnetic configuration and pump fluence. The ultrafast magnetization of the MTJ drops rapidly in the timescale of 0.33–0.37 ps, which is driven by both electron-spin scattering and spin transport mutually. Subsequently, the energy from the electron and spin reservoirs transfers into the lattice with the timescale of 1.5–2.0 and 5.0–15.0 ps through the electron–phonon and spin–phonon interactions, respectively. Our results suggest that the interfacial spin-orientation of CoFeB/MgO/CoFeB could modulate the interaction constant between spins and phonons. These findings provide insight into the role of MTJ interface in spin dynamics, which will be helpful for opto-spintronic tunnel junction stack designs and applications.

The ultrafast photocurrents in a typical 3D topological insulator (TI) Sb2Te3 were probed with THz emission spectroscopy by tuning the polarization of excitation pulses and the sample’s azimuthal angle. The different ultrafast photocurrents driven by the linear photogalvanic effect, circular photogalvanic effect, and thermoelectric effect were distinguished from THz emission signal. Results potentially provide insights into the ultrafast all optical modulation of THz emission with non-external bias field, which could play a vital role in future TI-based high-speed THz optoelectronic and optospintronic devices.

By using optical pump THz probe spectroscopy, the transient photoconductivity (Δσ) of semimetallic MoTe2 thin film was investigated in the temperature range from 5K to 290 K. For 1T’-MoTe2, at room temperature, photoexcitation induces positive THz Δσ that decays within a few picoseconds. In contrast, the negative THz Δσ of MoTe2 appears at low temperature following the initial positive Δσ. The negative Δσ relaxes to the equilibrium within time scale of nanoseconds. The negative Δσ in MoTe2 at low temperature is ascribed to the formation of small polaron in Weyl semimetal phase.

The ultrafast photoexcited carrier and coherent phonon dynamics of 20 nm PtTe2 film on fused silica substrate were investigated systematically at room temperature using degenerate and non-degenerate femtosecond (fs) pump-probe spectroscopy. After 780 nm optical pump, photo-induced bleaching (PB) signal was observed, which originated from the band filling effect. The incoherent relaxation processes can be reproduced well with a double-exponential decay function, which have been assigned as the cooling of the thermal carriers and the recombination of electron-hole pairs mediated by phonon, respectively. Two distinct oscillation modes were identified, the low-frequency mode corresponds to the excitation of coherent acoustic phonon by photolaunched stress wave, and the high frequency mode is due to the coherent optical phonon stemming from out-of-plane (A1g) lattice motion. Our study provides an in-depth understanding to the relaxation mechanisms and phonons behavior of PtTe2 film in nonequilibrium states, and might pave the way for the design of electronic and optoelectronic devices.

We demonstrate that the tunneling magneto-resistance (TMR) can be used to modulate terahertz (THz) wave propagation through a magnetic tunnel junctions (MTJ). Operating at the THz frequency range, a maximal modulation depth of 60% is reached for the parallel state of the MTJ with the thickness of 77.45 nm, by using a small magnetic field of 30 mT. The THz conductivity spectrum of the MTJ is governed by the spin-dependent electron tunneling. This findings open that the MTJ device will have potential applications in THz magnetic modulators, filtering and sensing.

By employing ultrafast time-resolved optical pump terahertz (THz) probe spectroscopy, we report a comparative THz response on CVD grown topological insulator (TI) Sb 2 Te 3 under different temperatures. Both photo induced carrier dynamics attributed to the surface and bulk electrons are observed. The electron system undergoes an ultrafast excitation and relaxation and releases through intra-band and inter-band scattering.