Triplet Mechanism Research Articles

PCB defect detection algorithm based on deep learning

Deep learning gained great popularity in the task of object detection. This paper proposes a printed circuit board (PCB) defect detection algorithm based on deep learning, which can improve product quality and avoid potential failures and accidents in the electronics manufacturing industry. In this paper, the YOLOv7 model is selected as the original model for PCB defect detection. Firstly, the K-means++ clustering algorithm is used to calculate the target anchor parameters which can enhance the dataset. Secondly, the receptive field enhancement (RFE) module is added to the head layer of the network to take full advantage of the receptive field in the feature map. Thirdly, the loss function CIoU of the YOLOv7 model is changed to WIoUv2. Fourthly, add the Triplet attention mechanism to the CBS and SPPCSPC modules. Finally, the detection accuracy of the improved YOLOv7 model is compared with that of Faster R-CNN, SSD, YOLOv3-tiny, YOLOv5s, and YOLOv7 models. The experimental results show that the detection accuracy and detection speed of the improved YOLOv7 model are enhanced compared with the original YOLOv7 model.

Comprehensive Understanding of the Heavy Oil Combustion Process: Reaction Behavior, Kinetic Triplet, and Mechanism Implication.

In this work, thermo-oxidative behavior, kinetic triplet, and free radical mechanism of ultraheavy oil during an in situ combustion (ISC) process were systematically surveyed via multiple thermal analysis techniques (TG/DTG/DSC/PDSC), model-free methods, and related mathematical simulation. First, specific mass loss, exothermic intensity, and corresponding temperature intervals were respectively determined in low-/high-temperature oxidation (LTO/HTO) regions. In addition, the comparison of atmospheric/pressurized differential scanning calorimetry (DSC/PDSC) experiments indicated that the pressurized conditions could obviously strengthen the oxidation progress with more heat emission. Then two model-free methods were contrastively employed for PDSC data to calculate LTO and HTO activation energy variations with the conversion rate. Moreover, the acceleratory rate model for LTO and the Sestak-Berggren model for HTO were accordingly picked as the most probable mechanism functions, which were later used to determine the simulated curves. Then, the simulations of α-T and dα/dT-T curves were respectively attained using Friedman equation in MATLAB software and contrasted with experimental data to validate the accuracy of the yielded kinetic triplet and forecast the combustion behavior. Further, the evolution pathways of the underlying oxidation mechanism was illustrated. This study updates the understanding of the nonisothermal combustion process, contributing to the subsequent numerical simulation and feasible investigation for in situ combustion implementation to enhance heavy oil recovery.

Double Strain-Release [2π+2σ]-Photocycloaddition.

In pursuit of potent pharmaceutical candidates and to further improve their chemical traits, small ring systems can serve as a potential starting point. Small ring units have the additional merit of loaded strain at their core, making them suitable reactants as they can capitalize on this intrinsic driving force. With the introduction of cyclobutenone as a strained precursor to ketene, the photocycloaddition with another strained unit, bicyclo[1.1.0]butane (BCB), enables the reactivity of both π-units in the transient ketene. This double strain-release driven [2π+2σ]-photocycloaddition promotes the synthesis of diverse heterobicyclo[2.1.1]hexane units, a pharmaceutically relevant bioisostere. The effective reactivity under catalyst-free conditions with a high functional group tolerance defines its synthetic utility. Experimental mechanistic studies and density functional theory (DFT) calculations suggest that the [2π+2σ]-photocycloaddition takes place via a triplet mechanism.

Estimation of Heisenberg exchange interaction in rigid photoexcited chromophore-radical compound by transient EPR.

The magnetic field dependence of the spin polarization in a photoexcited rigid chromophore-radical conjugate is theoretically investigated. The excitation of the chromophore-radical conjugate often populates the metastable doublet and quartet states formed by the interactions of the unpaired electrons of the triplet chromophore and the radical. The intensities of the +1/2 ↔ - 1/2 transitions of the doublet and quartet manifolds are sensitive to the ratio jω = 3J/ω0 between the triplet-doublet exchange interaction J and the Zeeman energy ω0. It is shown that the analytical expressions of these intensities previously found for the triplet mechanism of the initial spin polarization can be expanded and applied to a broader class of compounds that may have other intersystem crossing pathways of the depopulation of the excited singlet state of the chromophore. It is also shown that the exchange interaction can be evaluated not only by comparing the electron paramagnetic resonance spectra obtained in different microwave frequency bands but also by comparing the data obtained in the same microwave band but with a shift of the frequency of the resonator. The results obtained broaden the potential applications of the previously proposed approach for analyzing the correlation between the exchange coupling and the distance separating the radical and the chromophore spins, as well as the structure of the bridge connecting their fragments.

Chemical Nuclear Polarization during the Photoreduction of Anthraquinones

The mechanism and products of the photoreaction of 2-isopropyl-9,10-anthraquinone (1) with ethanol have been established. An analysis of the signals of chemical nuclear polarization (CNP) showed that during the formation of CNP, only the mechanism of singlet-triplet transitions in radical pairs takes place without the participation of a triplet mechanism. In the study of the phase of multiplet and integral effects, the elementary acts of photoreaction were determined, and the structure of the anthrasemiquinone radical participating in the reaction was established.

Investigation of Pyrolysis Kinetic Triplet, Thermodynamics, Product Characteristics and Reaction Mechanism of Waste Cooking Oil Biodiesel under the Influence of Copper Slag

WCO-Biodiesel can be used as a fuel instead of fossil energy for the copper smelting industry will not only save resources but also protect the environment. The pyrolysis of WCO-Biodiesel in the melting pool is influenced to some extent by the copper slag (CS) generated during the copper smelting process. In this study, the effects of CS on the kinetic triplet, thermodynamics, product characteristics and reaction mechanism of WCO-Biodiesel are comprehensively investigated via a thermogravimetric analyzer and pyrolysis experimental system. Firstly, the apparent activation energy (Eα) is calculated using STR, and Eα decreased at different α under the influence of CS. Then, the trend of the WCO-Biodiesel pyrolysis mechanism with α is determined by the master plots method based on 18 commonly used models similar to the Pn and D1 models. The analysis of WCO-Biodiesel pyrolysis gas products shows that more flammable gases containing H are formed under the influence of CS. The analysis of the liquid products shows that more PAHs and more small molecule products are generated under the influence of CS. Two coke products are produced at high temperatures, which differ significantly in microscopic morphology, spherical carbon particle size and chemical structure. Finally, the mechanism of pyrolysis of the main components in WCO-Biodiesel in the high-temperature environment of melt pool melting is explored.

Triplet Mechanism of the Chemical Polarization of Nuclei in the Photoreduction of Qinones

Triplet Mechanism of the Chemical Polarization of Nuclei in the Photoreduction of Qinones

Excited state modulation of C70 dimerization in a carbon nanotube under a variable electron acceleration voltage

Cinematographic recording of chemical reactions with transmission electron microscopy provides information unavailable by any other analytical methods. Studies have thus far remained mostly phenomenological, lacking information on the reactive species involved. To gain insight into the nature of the reactive species, we need to obtain kinetic information under various temperatures and variable acceleration voltages, i.e., electronic energy supply. We studied the mechanism of [2 + 2] dimerization of [70] fullerene in a carbon nanotube as an example. We describe herein a statistical analysis of individual reaction events of the dimerization that revealed dose-dependent first-order kinetics and voltage-dependent crossover from a singlet to a triplet mechanism, as highlighted by the pre-exponential factor (the frequency of excitation) that is a million times larger for the singlet reaction than for the triplet one. Comparison with the results of a recent study of [60] fullerene dimerization lets us propose that electron-impact excitation of the carbon nanotube is the first step, followed by energy transfer to fullerene molecules and their dimerization via an excited state. The results show that a variable-voltage kinetic study is indispensable for discussing the mechanism of chemical transformations under electron microscopic observation.

Toward deconstructing the simplest seesaw mechanism

The triplet or type-II seesaw mechanism is the simplest way to endow neutrinos with mass in the Standard Model (SM). Here we review its associated theory and phenomenology, including restrictions from $S$, $T$, $U$ parameters, neutrino experiments, charged lepton flavour violations as well as collider searches. We also examine restrictions coming from requiring consistency of electroweak symmetry breaking, i.e. perturbative unitarity and stability of the vacuum. Finally, we discuss novel effects associated to the scalar mediator of neutrino mass generation namely, (i) rare processes, e.g. $l_\alpha \to l_\beta \gamma$ decays, at the intensity frontier, and also (ii) four-lepton signatures in colliders at the high-energy frontier. These can be used to probe neutrino properties in an important way, providing a test of the absolute neutrino mass and mass-ordering, as well as of the atmospheric octant. They may also provide the first evidence for charged lepton flavour violation in nature. In contrast, neutrino non-standard interaction strengths are found to lie below current detectability.

High Triplet Energy Level Molecule Enables Highly Efficient Sky-Blue Perovskite Light-Emitting Diodes.

The role of triplet states in the interfacial energy transfer in perovskite light-emitting diodes (PeLEDs) has so far not been clarified because of the complex exciton recombination and decay dynamics. This work aims to study this issue and accordingly proposes a novel interfacial-engineering strategy for efficient sky-blue PeLEDs. To this end, bis[2-(diphenylphosphino)phenyl]ether oxide with a high triplet energy level is introduced into sky-blue PeLEDs. It effectively reduces undesirable exciton transfer from the perovskite emission layer to the electron-transport layer, largely suppresses exciton quenching at the interface, and simultaneously passivates defects at the perovskite surfaces. As a result of the multichannel energy-loss reduction, sky-blue PeLED that emits at 488 nm is achieved with a peak external quantum efficiency of 10.17% and a maximum brightness of 6728.41 cd m-2. This work thus provides indirect evidence for the triplet mechanism of blue emission of mixed-halide perovskites and sheds new light on a promising way of boosting the performance of blue PeLEDs.

Generation of N,N-Di(4-bromophenyl)nitrenium Ion under Acidic Conditions: Search for a Nitrenium Dication.

The behavior of the N,N-di(4-bromophenyl)nitrenium ion under acidic aqueous conditions was examined via laser flash photolysis experiments. A long-lived species forms and can be assigned as the cation radical or the dication. This species is unreactive toward nucleophiles and reactive toward strong electron donors, consistent with a cation radical. Mechanistic analysis indicates that its formation is through a separate pathway compared to that of the nitrenium ion, suggestive of a triplet mechanism.

Magnetic ordering and specific features of its coexistence with superconductivity in Dy0.6Y0.4Rh3.85Ru0.15B4

The temperature dependences of dynamic magnetic susceptibility of a magnetic superconductor Dy0.6Y0.4Rh3.85Ru0.15B4 in a temperature range of 2–50 К and the field dependence of magnetization up to 6 T at fixed temperatures 2, 11, 18, and 50 K were studied for the first time. It is found that at ТFM = (21 ± 1) К there is a transition to the ferromagnetic state, and at Тc = (6.7 ± 0.1) К a transition to superconducting state is observed, which coexists with the ferromagnetic state in a broad range of temperatures of 2–6.7 K. It is suggested that there exists a triplet mechanism of superconducting coupling in Dy0.6Y0.4Rh3.85Ru0.15B4.

The triplet mechanism of electron spin polarization in moderately coupled triplet-doublet rigid complexes as a source of the enhanced +1/2 ↔ -1/2 transitions.

The light-induced electron spin polarization generated in the excited quartet and doublet states of a system consisting of a chromophore with an attached radical is investigated theoretically. Excitation of the chromophore and subsequent relaxation leads to a coupled triplet-doublet spin system. In many such systems, the electronic coupling between the triplet and doublet spins is expected to be strong enough to split the spin system into so-called trip-doublet and trip-quartet states but sufficiently weak that it does not promote significant mixing between the sing-doublet and trip-doublet states. In such moderately coupled systems, the sing-doublet can relax to the trip-doublet and trip-quartet states by spin-orbit coupling mediated intersystem crossing within the chromophore. An analytical expression is derived for the intensity of the polarization generated by this mechanism for the ms = +1/2 ↔ -1/2 electron paramagnetic resonance transitions of the trip-doublet and trip-quartet states. The expression shows that the intensity and sign of the polarization depend strongly on ratio jω = 3J/ω0 between the triplet-doublet exchange interaction J and the Zeeman energy ω0. The polarization becomes undefined when jω = 1 and when jω = 2 because level-anticrossings between the trip-doublet and trip-quartet sublevels occur. The sign of the polarization is also found to change above and below these values. Thus, for such moderately coupled systems, the sign of the polarization and its Zeeman energy dependence can be used to estimate the magnitude of the exchange coupling.

The effect of DNA backbone on the triplet mechanism of UV-induced thymine-thymine (6-4) dimer formation.

Density functional theory calculations were carried out to investigate the formation mechanism of the thymine-thymine (6-4) dimer ((6-4)TT), which is one of the main DNA lesions induced by ultraviolet radiation and is closely related to skin cancers. The DNA backbone was found to have nonnegligible effects on the triplet reaction pathway, particularly the reaction steps involving substantial base rotations. The mechanism for the isomerization from (6-4)TT to its Dewar valence isomer (DewarTT) was also explored, confirming the necessity of absorbing a second photon. In addition, the solvation effects were examined and showed considerable influence on the potential energy surface. Graphical Abstract DFT calculations on the influence of DNA backbone on the mechanism of UV-induced thymine-thymine (6-4) dimer formation.

Development of Chemical Polarization of Nuclei During Photolysis of Benzoquinones with Aromatic Amines

Formation of nuclei polarization via triplet mechanism has been observed and described, allowing reliable identification of ion-radicals stages of the reaction, estimation of the triplets and ion-radical pairs lifetime from the effects of chemical polarization of the nuclei. The data on relative values of isotropic and anisotropic interactions of unpaired electrons and nuclei have been obtained.

Photochemical Reaction Cascade from O-Pent-4-enyl-Substituted Salicylates to Complex Multifunctional Scaffolds.

The arene ring of the title compounds is cleaved by a reaction cascade which is initiated by an intramolecular ortho photocycloaddition reaction. Tricyclic products were obtained in a highly regio- and diastereoselective fashion via a cyclooctatriene intermediate. The facial diastereoselectivity exerted by a stereogenic center in the tether is moderate to good (dr = 65/35 to 82/18). Yields were acceptable (44-87%) except for a single substrate which had a geminal dimethyl substitution in the tether and which gave the respective product in only 14% yield. The reaction is stereoconvergent with regard to the olefin configuration ( E or Z) in agreement with a triplet mechanism of the ortho photocycloaddition step.

Triplet photosensitization mechanism of thymine by an oxidized nucleobase: from a dimeric model to DNA environment.

Nucleic acids are constantly exposed to external agents that can induce chemical and photochemical damage. In spite of the great advances achieved in the last years, some molecular mechanisms of DNA damage are not completely understood yet. A recent experimental report (I. Aparici-Espert et al., ACS Chem. Biol. 2018, 13, 542) proved the ability of 5-formyluracil (ForU), a common oxidatively generated product of thymine, to act as an intrinsic sensitizer of nucleic acids, causing single strand breaks and cyclobutane pyrimidine dimers in plasmid DNA. In the present contribution, we use theoretical methodologies to study the triplet photosensitization mechanism of thymine exerted by ForU in a model dimer and in DNA environment. The photochemical pathways in the former system are described combining the CASPT2 and TD-DFT methods, whereas molecular dynamics simulations and QM/MM calculations are employed for the DNA duplex. It is unambiguously shown that the 1n,π* state localised in ForU mediates the population of the triplet manifold, most likely the 3π,π* state centred in ForU, whereas the 3π,π* state localized in thymine can be populated via triplet-triplet energy transfer given the small energy barrier of <0.23 eV determined for this pathway.

Hydrated electron (eaq−) generation from p-benzoquinone/UV: Combined experimental and theoretical study

A p-benzoquinone (p-BQ)/UV process to induce hydrated electron (eaq−) generation was predicted by quantum chemical calculations and validated by experiment in this work. Theoretically, the photolysis of p-BQ under UV irradiation at 253.7nm could induce water to generate eaq− with a molar ratio of 1:2 via the direct triplet mechanism, in which 1,4-addition reaction of the first triplet state of p-BQ with water was the key step. Experimentally, monochloroacetic acid (MCAA) (the probe of eaq−) was used to detect eaq− generated in the p-BQ/UV process. The generation efficiency showed a positive linear dependence on the p-BQ concentration, which illustrated the crucial role of p-BQ on the generation of eaq−. During the photolysis, p-hydroquinone was the primary intermediate for the generation of eaq−. Kinetically, the energy barriers of the eaq− generation from p-HOC6H4OH, p-HOC6H4O− and p-−OC6H4O− were 100.8kcalmol−1, 46.5kcalmol−1 and 5.6kcalmol−1, respectively. Both the experimental and theoretical results show that the generation of eaq− was much more efficient from the anions than that from p-HOC6H4OH. The findings in the present study may help to understand the mechanism of eaq− generation from natural organic matters (NOM), since quinone-like groups are usually contained in NOM.

Characteristic features of the singlet–triplet mechanism of the electron spin polarization

Characteristic features of net chemically induced dynamic electron spin polarization (CIDEP) P n in triplet–radical (TR) quenching are analyzed in detail within the framework of a general model that enables one to analyze CIDEP both numerically and analytically. This model also makes it possible to accurately describe the nonadiabatic transitions between the terms of the TR-pair spin Hamiltonian that lead to CIDEP generation. The proposed theory yields a simple analytical dependence of P n on the parameters of the model. In particular, it is shown that, within a wide region of parameters, the dependence of P n on the coefficient of relative TR diffusion D r is described by a simple linear relation: $$P_n^{ - 1}\left( {{D_r}} \right) = {Q_0} + \overline {{q_n}} {D_r}$$ (with Q 0 and $${{q_n}}$$ independent of D r ). It is also demonstrated that the numerical and analytical results obtained are very useful in analysis of experimental data, as demonstrated by analyzing the experimental dependence of P n on D r .

Synthesis and Photo-Alignment Properties of Novel Polyimides with Cyclobutane-1, 2, 3, 4-Tetracarboxylic Dianhydride (CBDA)

To improve effectiveness of photo-alignment, new polyimides containing cyclobutane-1, 2, 3, 4-tetracarboxylic dianhydride (CBDA) were designed including 4, 4′-diaminobenzophenone (DABP) and carbohydrazide by amide bond. For evaluating polyimides, a mole ratio of 4, 4′-diaminobenzophenone(DABP) and carbohydrazide was controlled to 0:100, 30:70, 50:50, 70:30, 100:0. The mixed solid contains 15wt% of solvent which is n-methyl-2-pyrrolidone (NMP). The synthesized polyimide was analyzed using the Fourier transform infrared (FT-IR). We obtained polar dichroic ratios and evaluate alignment of liquid crystal. For more aggressive photo-decomposition of polyimide, the photoreactions employing triplet mechanism and the double fragmentation reactions were carried out.