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The mechanism and charge effect of cycloisomerization of ω-alkynylfuran (Hashmi phenol synthesis) catalyzed by single-walled helical gold nanotubes (Au SWNTs) have been systematically investigated via density functional theory. Cycloisomerization of ω-alkynylfuran occurs by the 5-exo Friedel–Crafts-type (FCT) mechanism, namely 5-exo cyclization, furan ring opening, and ring closing of the dienone carbene–gold intermediate. The reactions with Au(6,0), Au(6,1), Au(6,2) and Au(6,3) SWNTs show low energy barriers along the 5-exo FCT path in acetonitrile solvent, but have different the rate-determining steps. From an energy perspective, the reaction rate-determining step catalyzed by Au(6,0) and Au(6,3) is the ring-closing of dienone carbine-gold intermediate, but that of Au(6,1) and Au(6,2) is the IM5 dissociation from the Au SWNTs, which can be attributed to the diversity of the d-band centers of the Au(6,m) SWNTs. The effect of the charge of the Au SWNTs on the catalytic activity was also investigated. Theoretical analysis shows a prominent charge effect, where the cationic Au(6,0), Au(6,3) SWNTs and anionic Au(6,1), Au(6,2) SWNTs are more favorable for the Hashmi phenol synthesis reaction. This results can be attributed to the Au(6,0) and Au(6,3) SWNTs with positive charge can reduce the adsorption energy of the substrate on the catalyst surface and decrease the energy barrier of the cyclization process and ring-closing step. Besides, the Au(6,1) and Au(6,2) with an anion could obviously decrease the dissociation energy of IM5 which is help for the Hashmi phenol reaction. Theoretical analysis shows that the structure and charge effects could influence the catalytic activity of Au(6,m) SWNTs toward Hashmi phenol synthesis. This work will provide insight into cycloisomerization of ω-alkynylfuran and valuable information for application of Au SWNTs in catalysis.

Understanding the mechanism of the catalytic reaction is an effective way to design new high-performance catalysts. The mechanisms of alkyne/olefin hydrogenations catalyzed by a nonclassical Co–N2 ...

Understanding the mechanism of a catalytic reaction is of fundamental importance not only scientifically but also technologically to the design of high-performance catalysts. In this work, the mechanisms of 1-phenyl-1-propyne and cis-β-methylstyrene hydrogenations catalyzed by Cu55 and ligand-coated Cu55 are explored in detail by means of density functional theory (DFT). The calculated results indicate that the semihydrogenation selectivity of the catalyst can be effectively controlled by employing a suitable ligand. That is, the PCy3 and PPh3 ligands used to coat Cu55 can largely raise the energy barrier of the rate-determining step for cis-β-methylstyrene hydrogenation. By the study of energy decomposition analysis (EDA) and charge density difference, it can be found that the deformation energies of the substrate fragments play a crucial role in the energy barriers of the rate-determining steps. The large hindrance effect of the ligands is beneficial for improving the semihydrogenation selectivity of the catalysts. This study provides significant information for future catalyst design and on the physical origin of the phosphine ligand-coated nanoparticle catalysis for semihydrogenation.

Based on the movement model of overburden in longwall mining, a 12-parameter model of stope overburden pressure considering the physical and mechanical parameters of the strata and structural parameters of the stope is established, which can be used to calculate the abutment pressure of each roof to the working face. The maximum pressure-causing stratum is proposed, and the determination of the maximum pressure-causing stratum and the quantitative analysis on the factors influencing the maximum pressure-causing stratum are given. Finally, maximum pressure-causing stratum analysis was carried out under the geological conditions of the Tongxin coal mine. It is found that the stratum horizon has a great influence on the determination of the maximum pressure-causing stratum. The lower the stratum horizon and the greater the bulk density and thickness, the more likely a stratum is to be the maximum pressure-causing stratum. Other parameters need to be combined under certain conditions to determine the maximum pressure-causing stratum. In addition, the structure of the stope overburden also has a great influence on the abutment pressure of the working face. The roof near the working face and the key strata plays significant pressurisation roles in the structure of the stope overburden, even far exceeding the pressure of their self-weight on the working face. The research results can be used to calculate the abutment pressure of the working face, to determine the maximum pressure-causing stratum, to select the measurement stratum and to prevent and control mine disasters.

Unveiling the reaction mechanism is significant for developing high-performance catalysts. In this paper, a series of precisely controlled PdxM147-x (M = Cu, Pt, Au, Rh, Ru) dendrimer encapsulated nanoparticles (DENs) has been successfully synthesized. The mechanisms of PdxM147-x as catalysts for Suzuki cross-coupling reactions were investigated by combining experimental and theoretical methods. The experimental results indicate that Pd74Cu73 DEN shows similar activity to Pd147 DEN and excellent substrate adaptability under mild reaction conditions. Moreover, the Cu component can play an important role in tuning the catalytic activity of PdxCu147-x DEN. Density functional theory (DFT) calculations illustrate that the similar activities of the Pd147 and Pd74Cu73 DENs originate from the comparable energy barriers of the rate-determining steps. The partial density of states (PDOS) and electron density differences demonstrate that Cu decreases the intensities of the valence orbitals of the top and edge Pd atoms and weakens orbital interactions between the intermediates and Pd74Cu73 DEN, leading to low desorption energies of the products. This work can provide a promising strategy to reduce the cost of Pd catalysts in Suzuki cross-coupling reactions.

An Ugi, novel pseudo-Knoevenagel, ring expansion cascade reaction was discovered and utilized for the synthesis of aziridinyl succinimides in one-pot. Subsequently, densely functionalized aziridines and maleimides have been designed and synthesized through similar cascade reactions. The target compounds were prepared by means of a mild reaction and a simple operation procedure, which could be applicable to a broad scope of starting materials. This series of novel cascade reactions generates opportunities for the tailored synthesis of a wide range of biologically active scaffolds through tuneable Ugi inputs. Discovery of compound 8i with comparable potency to sorafenib in liver cancer cell lines could provide a new avenue for liver cancer drug discovery.

Herein, the radiative and non-radiative decay processes of six carborane-based Pt(II) complexes were explored with the help of the density functional theory and time-dependent density functional theory. In order to interpret the influence of non-metal heavy atoms on the phosphorescent quantum yields, the determined factors, i.e., the ZFS (zero-point filed splitting) parameters, radiative decay rate constants and photodeactivation mechanisms, were unveiled. The results indicate that the spin-orbital coupling effects can be slightly regulated via introducing the non-metal heavy atoms into the carborane. Also, the non-metal heavy atoms substituents could cause slightly decrease of the energy barriers between the 3ES and 3MC excited states, and thus, for Pt-6, a fast non-radiative decay process may occur. Moreover, compared with the Pt-1, the rotation of methyl in Pt-2 ∼ 5, can be effectively restricted with the aid of hydrogen bonding and halogen bonding, which is beneficial for obtaining small non-radiative decay rate constants. Accordingly, it provides a strategy for realizing the restriction of small group rotation to achieve the high-efficient phosphorescent emitters.

Controlling the photostability of the organometallic complex is vital for obtaining the long-lasting phosphorescent organic light-emitting diode. In this article, the density functional theory was employed to investigate the photostabilities of a series of tridentate Pt(II) complexes in the triplet–triplet annihilation (TTA) processes. The calculated results indicate that the existence of the Pt–C*(NHC) bond can increase the Gibbs free main ligand dissociation energy to avoid the main ligand dissociation during the TTA process. According to the Wiberg bond order and electron localization function, the positive effect of the Pt–C*(NHC) bond originates from the strong d and p orbital interactions and more electron localization between C*(NHC) and Pt atoms. In addition, the study in this article also manifests that the auxiliary ligands with strong electron-withdrawing/-donating properties can facilitate the electron localization, leading to the increase of photostabilities for the tridentate Pt(II) complexe...

In this article, the photo-deactivation mechanism of dual emission of a neutral iridium (III) complex is explored by using density function theory (DFT) and time-dependent density function theory (TD-DFT) calculations. To explore the phosphorescence quantum yield of the iridium (III) complex, the radiative decay constant of each emission excited state was computed by TD-DFT calculations, including spin-orbit coupling (SOC). In these calculations, factors such as the transition dipole moments, energy gaps, and SOC elements between the emission states and singlet excited states are taken into account in the evaluation of the radiative decay constants. Additionally, the non-radiative decay is revealed by considering the temperature-independent and the temperature-dependent non-radiative processes. The computational results indicate that the order of the two emission excited states can exert a significant effect on the phosphorescence quantum yield, which is beneficial for understanding the properties of photo-deactivation of phosphorescent emitters.

Effectively adjusting the phosphorescent quantum efficiency of transition metal complexes is of great significance for the development of new energy-saving organic light-emitting diodes devices. In this article, density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods are employed to investigate the effects of electronegativity caused by introduction of azole moieties on the phosphorescence properties, radiative and nonradiative decay rate constants and photodeactivation mechanism of cyclometalated (CˆC*) platinum(II) NHC complexes. According to calculated results, by decreasing the electronegativity of NHC ligand, the maximum wavelength of the complex appears blue shift; the electron transition density of the lowest triplet state is concentrated to the Pt(II) atom, the singlet-triplet splitting energy and the spin-orbital coupling (SOC) matrix elements are obviously increased, leading to a significant increase of radiative decay rate constant. However, the decrease of ligand electronegativity results in a slight decrease in molecular rigidity and the SOC matrix elements between the ground state and the lowest triplet excited state increase, the energy barriers in photodeactivation pathway decrease, which eventually leads to the increase of nonradiative decay rate constant. Considering its prominent effect on the enhancement of the radiative decay rate constant, this method may still effectively improve the phosphorescence quantum yield of the complexes. This work has a certain theoretical reference value for the design of highly efficient phosphorescent complexes.

Unveiling the acetylene adsorption is crucial for designing novel and highly active catalyst for the semihydrogenation of alkyne. In order to achieve this goal, we have studied C 2 H 2 adsorption on the various nanoporous gold models in detail, including the Au(100), Au(111) and Au(321) slab models. The calculated results indicate that the C atoms of C 2 H 2 experience rehybridization from sp toward sp 2 /sp 3 when the adsorption occurs on bridge and hollow sites, which can be illustrated via the projected density of state (PDOS) and crystal orbital Hamilton population (COHP). Meanwhile, the formation of σ(Au C) bond is beneficial for facilitating acetylene adsorption and the kink Au atom plays an important role for the C 2 H 2 adsorption. In addition, for C 2 H 2 adsorption on the Ag doped nanoporous gold, the configurations strongly depend on the position of superficial unsubstituted Au atoms. Further, the inversely relationship has been found between the adsorption energies and number of the Ag substituents, demonstrating that the superficial Ag substituents are harmful for C 2 H 2 adsorption and activation.

Coal is a dual-porosity medium with an internal pore-fracture structure that serves as a channel for the migration of coalbed methane. Understanding the relationship between permeability and pore-fracture structure characteristics is therefore of great significance to accurately predict coalbed methane productivity. In this work, we analyze the pore-fracture structure characteristics of real coal samples and establish a new fractal permeability model of dual-porosity media embedded with natural tortuous fractures. Compared with the traditional dual-porosity medium model with embedded parallel plane fractures, this model not only considers the characteristics of pore tortuosity but also those of fracture tortuosity. The results show that the predicted permeability values obtained from the proposed model are 1–2 orders of magnitude lower than those of the traditional model, which implies that the latter overestimates coal seam permeability. The coal matrix permeability is approximately 13 orders of magnitude lower than the fracture permeability, and the latter mainly controls the overall coal seam permeability. Gas flow analysis of the coal seam is conducted in COMSOL Multiphysics, in which a fracture structure image is transformed to the computational domain. We use the results to discuss the relationships between coal permeability and fracture geometric characteristic parameters. The results show that the porosity ϕf and fractal dimension Dl of the fracture substantially affect coal seam permeability and follow a strong power-law relationship. The numerical simulation results are in good agreement with the theoretical predicted values (the average error is about 11.97%), which verifies the accuracy of the proposed model.

Rough surfaces exist widely in nature, and the measurement of these surfaces’ fractal dimension is beneficial for understanding their formation mechanism and effect. The basic principles of previous cubic covering methods are described, and then the stable cubic covering method (SCCM) and stable differential cubic covering method (SDCCM) are proposed based on the box-counting method. Afterward, a real sandstone fracture surface and Takagi surfaces are adopted to compare these methods’ differences. The results show that different measurement methods are needed to measure surfaces with different theoretical fractal dimensions. Meanwhile, the SCCM and SDCCM can obtain more stable measurement results than previous methods. Then, the recommended methods and their corresponding scale factors are summarized. Finally, the potential of these cubic covering methods to measure a thick film is described. The research is of great significance to the fractal dimension measurement of a rough surface or a thick film.

In the present article, the mechanism of 1,6-enyne cycloisomerization catalyzed by the planar Au 8 cluster was investigated in details by means of density functional theory. The effects of the size and shape of the gold nanoclusters (Au 7-20 ) on their catalysis of 1,6-enyne cycloisomerization were also studied. The computational results indicate that the main reaction channels of the 1,6-enyne cycloisomerization on the Au 8 cluster are the 5–exo–anti–cycloisomerization, and the single cleavage pathway is slightly more feasible than the double cleavage pathway. The selectivity of 1,6-enyne cycloisomerization catalyzed by the gold clusters is controlled by the orbital interaction between the gold atoms and the carbene fragment in the migration of CH 2 group. In addition, the influence of coordinate environment of the gold atoms on adsorption energy, catalytic activity, and regio-selectivity were amply interpreted as well.

Understanding the role of CeO2(111) supports is meaningful for designing high-performance metal oxide-supported gold nanoparticle catalysts. Here, density functional theory calculations were employed to study ω-alkynylfuran cycloisomerisation on CeO2(111)-supported Au clusters. The various reactive sites, including the atop, interface and edge sites, and the role of oxygen vacancies on the defective CeO2(111) surface were taken into account. On the basis of the computed results and energetic analysis, it was found that the atop and interface sites show high catalytic activity toward ω-alkynylfuran cycloisomerisation, and the edge site of Au10/CeO2(111)-s (stoichiometric) exhibits similar catalytic activity. Meanwhile, the surface oxygen vacancies of CeO2(111) can cause some negative and positive effects on the adsorption energy and the catalytic activity. Furthermore, to shed light on the role of the CeO2(111) support, an analysis of ω-alkynylfuran cycloisomerisation catalyzed by Au3–4/CeO2(111) and free Au3–4 clusters was performed as well. Our results indicate that the presence of the CeO2(111) support can not only change the orbital levels of the gold clusters, but also cause charge recombination and decrease the positive charge on the Au (top) atom. These virtues can effectively lead to a decrease in the adsorption energy, facilitating electrophilic attack of the C atom on the furan ring.

With the emergence of drug-resistant Plasmodium falciparum, the treatment of malaria has become a significant challenge; therefore, the development of antimalarial drugs acting on new targets is extremely urgent. In Plasmodium falciparum, type II nicotinamide adenine dinucleotide (NADH) dehydrogenase (NDH-2) is responsible for catalyzing the transfer of two electrons from NADH to flavin adenine dinucleotide (FAD), which in turn transfers the electrons to coenzyme Q (CoQ). As an entry enzyme for oxidative phosphorylation, NDH-2 has become one of the popular targets for the development of new antimalarial drugs. In this study, reliable motion trajectories of the NDH-2 complex with its co-factors (NADH and FAD) and inhibitor, RYL-552, were obtained by comparative molecular dynamics simulations. The influence of cofactor binding on the global motion of NDH-2 was explored through conformational clustering, principal component analysis and free energy landscape. The molecular interactions of NDH-2 before and after its binding with the inhibitor RYL-552 were analyzed, and the key residues and important hydrogen bonds were also determined. The results show that the association of RYL-552 results in the weakening of intramolecular hydrogen bonds and large allosterism of NDH-2. There was a significant positive correlation between the angular change of the key pocket residues in the NADH-FAD-pockets that represents the global functional motion and the change in distance between NADH-C4 and FAD-N5 that represents the electron transfer efficiency. Finally, the possible non-competitive inhibitory mechanism of RYL-552 was proposed. Specifically, the association of inhibitors with NDH-2 significantly affects the global motion mode of NDH-2, leading to widening of the distance between NADH and FAD through cooperative motion induction; this reduces the electron transfer efficiency of the mitochondrial respiratory chain. The simulation results provide useful theoretical guidance for subsequent antimalarial drug design based on the NDH-2 structure and the respiratory chain electron transfer mechanism.

In this work, we propose a pixel crack reconstruction method based on digital image processing and mathematical morphology theory. To ensure that the obtained crack data are suitable for fracture evolution simulation, a coarsening coefficient is introduced. Different crack geological models are then established to characterize the heterogeneous characteristics of different specimens. The completed simulation models are carried out in combination with the cohesive element method. The comparison of the numerical simulation results with the corresponding experimental results demonstrates the feasibility of the pixel crack reconstruction method. The influence of the coarsening coefficient on the crack visualization and fracture evolution simulation is then discussed, and the application prospects, limitations, and solutions of the pixel crack reconstruction method are described. The results indicate that the selection of the coarsening coefficient must comprehensively consider its influence on the reconstruction accuracy and numerical simulation efficiency. The reconstruction accuracy could be improved by increasing the resolution of the obtained fracture image. In addition, the fracture evolution is readily affected by possible heterogeneous characteristics. The method proposed herein is of great significance for fracture evolution simulation in heterogeneous materials.

The Hashmi phenol synthesis reaction (the ω-alkynylfuran cycloisomerization) catalyzed by the M6@Au32 (M=Ag, Cu, Pd, Pt, Ru, and Rh) core–shell nanoclusters was investigated systematically. The 5-exo Friedel–Crafts-type mechanism of the ω-alkynylfuran cycloisomerization on the six core–shell nanoclusters was analyzed in details. The adsorption property and catalytic activity of the Au38 nanocluster could be effectively tuned by the substitution of the core Au atoms. The adsorption properties of alkynes on core–shell and Au38 clusters depended on four factors, including the numbers of unoccupied and occupied d orbitals, orientation of d orbital and d-bonding down-shift. Compared with the Au38 cluster, the core–shell nanoclusters could cause larger changes in the interaction energies between the substrate and cluster fragments, which are beneficial for facilitating the cyclization step and the ring closing of the dienone carbene–gold intermediate. In addition, according to the calculated results, the catalytic activity of Au38 can be tuned by substitution of the core gold atoms.

In this article, the radiative and nonradiative decay processes of four cyclometalated (C∧C*) platinum(II) N-heterocyclic carbene (NHC) complexes were unveiled via density functional theory and time-dependent density functional theory. In order to explore the influence of π-conjugation on quantum yields of (NHC)Pt(acac) (NHC═N-heterocyclic carbene, acac = acetylacetonate) complexes, the factors that determine the radiative process, including singlet–triplet splitting energies, transition dipole moments, and spin–orbit coupling (SOC) matrix elements between the lowest triplet states and singlet excited states were calculated. In addition, the SOC matrix elements between the lowest triplet state and the ground state as well as Huang–Rhys factors were also computed to describe the temperature-independent nonradiative decay processes. Also, the triplet potential energy surfaces were investigated to elucidate the temperature-dependent nonradiative decay processes. The results indicate that complex Pt-1 has hig...

Unveiling the photodeactivation mechanisms of transition metal complexes is crucial for designing high-efficiency phosphorescent materials. Herein, the photodeactivation mechanisms of cyclometalated (C^C*) platinum(II) N-heterocyclic carbene (NHC) complexes modified by carboranes were systematic study with the help of the density functional theory (DFT) and time-dependent density functional theory (TD-DFT). In order to illustrate the photodeactivation mechanisms, three vital photodeactivation processes, namely radiative decay process, temperature-independent nonradiative decay process and thermally activated nonradiative photodeactivation process, were taken into account. On the basis of calculated results, the emission wavelengths of the cyclometalated (C^C*) platinum(II) N-heterocyclic carbene (NHC) complex can be effectively tuned via the carborane-functionalized ligand structures. Meanwhile, compared with the original (NHC)Pt(II)(acac) complex, the radiative decay processes can be facilitated and the nonradiative decay processes can be managed via attaching distinct carboranes to the main ligand of the (NHC)Pt(II)(acac) complex, indicating that this is a feasible strategy for obtaining high-performance phosphorescence emitters.

Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were employed to explore the electronic structures and phosphorescence properties of synthesized terdentate Pt(II) complexes bearing highly-rigid 3,6-bis(p-anizolyl)-2-carboranyl-pyridine as a cyclometalated ligand and triphenylphosphine (1) or t-butylisonitrile (2) as ancillary ligand. To understand the marked difference in phosphorescence quantum efficiency between 1 and 2, the relaxation dynamics of excited states were elucidated in detail. Aiming to formulate the radiative relaxation, the zero-field splitting (ZFS) and the radiative decay rate constant (kr) were calculated by SOC-perturbed TDDFT (pSOC-TDDFT). Meanwhile, the temperature-independent non-radiative relaxation was analyzed by calculating the Huang–Rhys factor (S), the SOC interaction between the emitting state and the ground state. While the temperature-dependent non-radiative decay mechanism was studied by depicting the thermal deactivation process via a metal-centered excited 3MC state. Based on the results, 1 and 2 show a few differences in their temperature-independent non-radiative rates. However, the activation barrier for the population of non-emissive 3MC is greatly raised for complex 2. Therefore, the temperature-dependent non-radiative decay behavior of 2 is considerably suppressed, which ultimately leads to a substantially enhanced phosphorescence quantum efficiency for 2. To further tune the emission wavelength towards blue, four new complexes 3–6 were theoretically designed by modifying the terdentate ligand with azole groups based on the parent complex 2. As a result, pyrazole modified complex 4 stands out with enhanced deep-blue phosphorescence located at 434 nm.

A detailed reaction mechanism of the triatomic gold cluster-catalyzed cycloisomerization of ω-alkynylfuran was systemically investigated via density functional theory at the TPSSh/def2-TZVP level. The computational results indicated that the 5-exo Friedel–Crafts-type mechanism is the most favorable mechanism to form the phenol derivatives. The strong interaction between the gold and vinyl fragments in the Friedel–Crafts adduct is essential for the priority of the 5-exo Friedel–Crafts-type mechanism. Then, the 5-exo Friedel–Crafts-type mechanism on the various planar gold clusters (Au4–10) was studied to clarify the size-effects of the planar gold clusters catalyzed ω-alkynylfuran cycloisomerization. The appropriate interactions between the alkyne group in the substrate and gold clusters play a key role for the 5-exo cyclization step. The energy barriers of the ring-closure of the dienone carbene–gold intermediate step show an interesting “odd–even” behavior respective to the number of gold atoms. The Au3 and Au4 clusters are the most active catalysts for the ω-alkynylfuran cycloisomerization to the phenol derivative. We also found that the active catalyst of the ω-alkynylfuran cycloisomerization catalyzed by the gold(I) complexes should be the gold(0) complexes of the in situ generation. The catalytic activity of the gold(0) complex is comparable with that of the planar gold clusters. These findings may guide the rational design of highly active gold catalysts for the ω-alkynylfuran cycloisomerization to phenol derivatives.

Effective control of high-position hard roofs (HHRs) is important to meet the requirements of safe and efficient mining. Vertical-well hydraulic fracturing (VWHF) is an innovative control method developed for releasing strong ground pressure behavior induced by HHRs. Understanding the hydraulic fracture extension law and its spatial form is critical for VWHF applications on HHRs. To address this problem, we have developed a large-scale three-dimensional fracturing simulation apparatus. The effective sample size is 2,060 by 1,200 by 1,200 mm. The primary loading subsystem maintains full closed-loop control of stress and displacement and can perform one-way, two-way, three-way, and step-wise independent loading and unloading with a maximum three-dimensional loading capacity of 10 MPa. The apparatus can achieve gas sealing of 3 MPa. The time-space distribution law of multiple parameters in the apparatus can be monitored using 240 simultaneous test channels, and experimental phenomena can be observed in real time using the visual monitoring system. The fracturing subsystem can achieve flow infinite transformation between 0 to 107 mL/min and water pressure up to 51.7 MPa. The apparatus simulates hydraulic (supercritical carbon dioxide or liquid nitrogen) fracturing of coal-rock mass under complex stress and a gas-containing environment. To the best of our knowledge, these are the first large-scale three-dimensional fracturing simulation experiments performed on hard roof sandstone samples. We analyze the distribution and change of acoustic emission signal and stress before and after fracturing and determine the hydraulic fracture propagation law, which reflects characteristics of hydraulic fracturing hard roof processes in a large-scale fracture network. These experiments validate the capability and reliability of the newly developed apparatus. The results provide strong technical support for VWHF to weaken HHRs.

Thermal stress is one of the major failure factors of power devices. High junction temperature and high temperature gradient during operation induce mechanical stress, especially where surfaces of material with different thermal expansion coefficients are in contact, which may lead to the deterioration or the complete failure. In order to avoid the failure, it is very important to understand the failure mode of the power IGBT in different application conditions of the thermal stress [1]. The failure of the die attach which is the contact layer of the chip and the substrate is one of the main influences by the heat dissipation of the junction. For the analysis, the change in the thermal resistance [2-3] value due to the deterioration of the device was analyzed by using the structural function from the result of thermal transient test which performed every 1000 cycles during the power cycling test under different ΔT J (the temperature change of the junction), V CE (Collector-Emitter Voltage) and cycling current conditions of the power IGBT module. According to the test results, the increase in the thermal resistance inside the device was due mainly to the deterioration of the die attach part. And degree of failure of die attach, basically directly related to the value of ΔT J , but not affected by the value of V CE and applied current.

In this study, five cyclometalated Pt(II) complexes were chosen as research subjects to investigate the effects of main-group moieties on the electronic structure, photophysical properties and radiative deactivation processes of the phosphorescent metal complexes. Density functional theory (DFT)/time-dependent DFT investigation was conducted to gain a better understanding of the properties of these Pt(II) complexes, including the ground and triplet state geometries, absorption spectra and emission wavelength. Moreover, the self-consistent spin–orbit coupling TDDFT (SOC-TDDFT) was used to calculate zero-field splitting (ZFS), radiative rate and radiative lifetime to unveil the radiative deactivation processes for these complexes. The results reveal that the different main-group moieties added on the 4′-position of the phenyl ring in [Pt(ppy)(acac)] could not only dramatically affect molecular and electronic structure, absorption and luminescence properties, but also radiative deactivation processes. And the emission wavelengths of five complexes are in the range from 434 to 562 nm. Furthermore, among the studied complexes, the designed complex 4 shows great potential to serve as an efficient deep-blue-light emitter in OLED.

The electronic structures and photophysical properties of eleven PtII complexes divided into three series by their degree of π conjugation were studied through density functional theory (DFT) and time-dependent density functional theory (TDDFT) calculations. To investigate the effect of triarylboron substituents and the changes caused by the extension of the π conjugation, the nonradiative and radiative decay efficiencies, the geometric relaxations, d orbital splitting, and spin–orbit couplings at the optimized S0 and T1 geometries were computed. The results show that complexes with triarylboron substituents may have higher phosphorescence efficiencies than those with cyano groups. Furthermore, complexes with larger π conjugation (anthracene groups) may weaken the effects caused by the introduction of triarylboron substituents and are less likely to possess enhanced phosphorescence efficiency. Predictions of the absorption spectra and emission colors indicated that complexes with triarylboron substituents would emit blue colors, whereas the emission colors of the complexes with larger π conjugation would be located in the near-infrared region. This work highlights that the introduction of the triarylboron substituents and appropriate π conjugation (naphthalene groups) can result in highly efficient phosphorescence in complexes containing donor N-heterocyclic carbene (NHC) ligands.

Carboranes have attracted increasing interest in the scientific community due to their remarkable structures and strong electron-withdrawing abilities. In this article, four platinum complexes [(C^N^N)PtC[triple bond, length as m-dash]CPh](1), [(C^N^N)PtC[triple bond, length as m-dash]C-TPA](2), [(C^N^N)PtC[triple bond, length as m-dash]C-TAB](3), [(C^N^N)PtC[triple bond, length as m-dash]C-CB](4) (where TPA = triphenylamine, TAB = triarylboryl, CB = o-carborane) have been calculated via density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods to mainly explore the influence of carborane substituents on electronic structures, photophysical properties and radiative decay processes. The calculated results reveal that 2 with electron-donating triphenylamine has a low radiative decay rate constant and a red-shifted emission band, but 3 and 4 containing electron-withdrawing triarylboryl and o-carborane exhibit the opposite properties, especially 4 is supposed to have the highest phosphorescence quantum yield with the smallest nonradiative decay rate constant. These findings successfully illustrated the structure-property relationship and the designed complex 4 with carborane can serve as a highly efficient phosphorescent material in the future.

Virtual learning community is an important organizational form for collaborative learning. And the learning emotion, interaction degree, knowledge test are important characteristics of learning. However, the existing constructing strategy is unable to accurately determine the matching degree between the learner and the community. The lower matching degree will weaken the learning performance of learners. This paper comprehensively considers and uses the learning characteristics to evaluate the matching degree between learners and commmunities, and presents a new dynamic constructing strategy, then give its corresponding adjusting algorithm for virtual learning community. It is easy and more accurate to identify whether a certain community suits the learner, and it can help a learner to find a suitable community to further improve his learning performance and experience. Case study and analysis shows the feasibility and practicability of our proposed constructing strategy.

Fault-free production is a basic characteristic of intelligent workshop. The existing model-based fault prediction methods depend much more on the precise models of the equipment, while the data-driven ones can only use some basic state data with very limited volume. These features make them not only impractical, but also not able to meet the real-time requirement of analyzing industrial big data under the environment of Industrial Internet of Things. This paper presents a fault prediction method based on industrial big data, which directly excavates the relationship between the data such as the sound and status data, and the equipment faults by machine learning methods. What is more, the equipment state can be monitored in real time leading to the failure would be checked out timely. The simulation result shows that our method has high accuracy and real-time features compared with the existing ones.

We present an effective strategy to modulate the electron-rich capability in donor–acceptor (D-A) polymers for improving the performances of organic solar cell (OSC) devices. In order to confirm this strategy, based on a series of the reported D–A polymers ((PCPDTBT(Pa1), PCPDTFBT (Pa2), and PCPDTDFBT (Pa3)) which contain the electron-donating cyclopentadithiophene (CPDT) and differently electron-withdrawing units of benzo[c][1,2,5,]thiadiazole (BT), 5-fluorobenzo[c][1,2,5]thiadiazole (FBT), and 5,6-difluorobenzo[c] [1,2,5]thiadiazole (DFBT), we replace CPDT with electron-donating dithienogermolodithiophene (DTTG) in polymers Pa1–Pa3, respectively, and design a series of new D–A polymers Pb1–Pb3. Compared with the polymers Pa1–Pa3, the new designed polymers Pb1–Pb3 not only yield a greater red-shift of the absorption spectrum of the donor polymer and result in a larger absorption region within the solar emission spectrum and an improved light-absorbing efficiency but also exhibit much better electron tran...

The electrothermal characteristics and degradation mechanism of 4H-SiC JBS under high temperature power cycling (HTPC) stress were investigated based on thermal structure function, failure analysis and electrothermal simulation. Results show that, the HTPC stress at different temperature conditions (maximum junction temperature Tjmax = 150 °C and Tjmax = 200 °C) have different effects on the reverse breakdown voltage (Vbr), reverse leakage current and the on-resistance (Ron-sp). It was that the increased reverse leakage currents with HTPC stress are due to the Schottky barrier lowering at the beginning. However, as the heat concentration effect increased at the metal/4H-SiC interface, the contribution of tunneling to leakage current is the major components. So the heat flux path and thermal distribution are very crucial to the reliability of chip and package. It can be concluded that the degradations of die-attach, die surface and metal/SiC interface are the main reliability limiting factors of SiC JBS diodes under high temperature applications.

This study focuses on an improved synthesis of a branched poly (ethylene imine) (PEI)-modified cellulose-based adsorbent (Cell-g-PGMA-PEI). We aim to improve the adsorbent capacity by reducing side reaction of epoxide ring opening during graft copolymerization of glycidyl methacrylate (GMA) onto cellulose which increases the content of epoxy groups, anchors to immobilize branched PEI moieties. FTIR spectra provided the evidence of successful graft copolymerization of GMA onto cellulose initiated by benzoyl peroxide (BPO) and modification with PEI. The amount of epoxy groups of Cell-g-PGMA was 4.35 mmol g−1 by epoxy titration. Subsequently, the adsorption behavior of Cu(II) on cell-g-PGMA-PEI in aqueous solution has been investigated. The data from the adsorption kinetic experiments agreed well with pseudo-second-order model. The adsorption isotherms can be interpreted by the Langmuir model with the maximum adsorption capacity of 102 mg g−1 which was largely improved compared with the similar adsorbent reported. The dynamic adsorption capacity obtained from the column tests was 119 mg g−1 and the adsorbent could be regenerated by HCl of 0.1 mol L−1. Results indicate that the novel pathway for the synthesis of Cell-g-PGMA-PEI exhibits significant potential to improve the performance of adsorbents in removal and recovery of Cu(II) from aqueous solution. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Aromatic sulfonyl groups have attracted increasing interest due to their unique electronic features. In this article, a series of IrIII complexes bearing fluorinated phenylsulfonyl groups were evaluated by density functional theory and time-dependent density functional theory methods. To explore their phosphorescence efficiencies, factors that determine the radiative decay rate constant, kr , and the nonradiative decay rate constant, knr , were computed. As demonstrated by the results, complex 4, which has fluorinated phenylsulfonyl groups at the 5-positions of the phenyl rings for all three C^N ligands, was found to have the highest phosphorescence efficiencies with the largest kr and smallest knr values among these complexes. Moreover, it was found to exhibit significantly blueshifted behavior relative to complex 1 and emits in the blue region, and thus, it can serve as a highly efficient blue emitter for application in organic light-emitting diodes. These findings successfully illustrated the structure-properties relationship and provided valuable information for the development of future highly efficient blue-emitting phosphors.

In this study, density functional theory (DFT) and time-dependent DFT were employed to elucidate the photo-deactivation mechanisms of (C^N)Pt(O^O) complexes 1-4 (where C^N = 2-phenylpyridine derivatives, O^O = dipivolylmethanoate). To make thorough understanding of the radiative decay, the singlet-triplet splitting energies ΔE(Sn-T1) (n = 1, 2, 3, 4, ...), transition dipole moment μ(Sn) for S0-Sn transitions and the spin-orbit coupling (SOC) matrix elements ⟨T1|HSOC|Sn⟩ were all calculated. Moreover, the spin-orbit coupling between T1 and S0 ⟨T1|HSOC|S0⟩ and Huang-Rhys factors were calculated to estimate the temperature-independent nonradiative decay processes. Meanwhile, the thermal deactivation via metal-centered (3)MC was described to analyze the temperature-dependent nonradiative decay processes. As a result, the effective SOC interaction between the lowest triplet and singlet excited states successfully rationalize why complexes 1 and 3 have higher radiative decay rate constant than that of complex 2, while the larger ⟨T1|HSOC|S0⟩ and lower energy barrier for thermal deactivation in 3 reasonably explains why 3 has larger nonradiative rate than that of 1 and 2. Consequently, it can be concluded that it is the ⟨T1|HSOC|S0⟩ and thermal population of (3)MC that account for the nonemissive behavior of (C^N)Pt(O^O) complexes, and controlling π-conjugation is an efficient method for tuning phosphorescence properties of transition-metal complexes.

In this work, six Pt(II) complexes have been studied via density functional theory (DFT)/time-dependent DFT caculations to explore the influence of different ancillary ligand on electron structures, photophysical properties and radiative decay processes. Moreover, the self-consistent spin–orbit coupling TDDFT was used to calculate zero-field splitting, radiative rate and radiative lifetime to unveil the radiative deactivation processes for these complexes. The results indicated that [Pt(ppy)(ppz)] (ppy = 2-phenylpyridine and ppz = 5-(2-pyridyl)-pyrazole) has a higher radiative decay rate constant and a smaller nonradiative decayrate constant than that of [Pt(ppy)(acac)] (acac = acetylacetonate). Furthermore, complex 5, with dimesityboron added on the 3′-position of the pyrazole ring in [Pt(ppy)(ppz)], shows great potential to serve as an efficient blue-green light emitter in OLED. Better phosphorescent properties can be obtained from proper alteration or modification of the ancillary ligand in cyclometalated platinum complexes.

SnO2 nanoparticles (NPs)@carbon nanofibers as anode materials for lithium-ion battery are synthesized by a novel facile route using the commercial filter paper and tin dichloride dehydrate (SnCl2·2H2O). The weight ratio between carbon nanofibers and SnO2 NPs, which seriously affects the battery performance, has been demonstrated to be easily tuned by adjusting the sintering temperature. The electrochemical investigations show that the SnO2 NPs@carbon nanofibers with 9 wt% carbon have the best performance with the highest capacity of 383 mAh g−1 after 30 cycles at a current density of 100 mA g−1. The method introduced in this study provides an easy strategy for the controlled introduction of carbon to optimize the performance of lithium-ion battery using SnO2 NPs@carbon nanofibers as anode materials.

A simple and cost-effective chemical method was introduced to assemble gold (Au) nanoparticles on smooth silver (Ag) spheres for realizing surface-enhanced Raman scattering (SERS) enhancement by the replacement reaction between chloroauric acid and Ag spheres. In addition, the Ag-Au core-shell spheres were fabricated when a certain amount of chloroauric acid was used in the reaction solution. We found that the Ag particles decorated with small Au nanoparticles demonstrated the strongest SERS enhancement, while Ag-Au core-shell spheres showed the weakest enhancement.

Thermal structure function is a proven methodology to do experiment based structural analysis of heat path inside electronics package or cooling devices. However, how to understand the 3D heat flux structure from a 1D structural function is always the most difficult job for thermal engineers. In this article, 3D CFD software is used to describe the transaction image from 1D structure function to 3D heat flux distribution.

In this article, the influence of the tert-butyl unit on the photodeactivation pathways of Pt[O^N^C^N] (O^N^C^N=2-(4-(3,5-di-tert-butylphenyl)-6-(3-(pyridin-2-l)phenyl) pyridin-2-yl)phenolate) is investigated by DFT/TDDFT calculations. To further explore the factors that determine the radiative processes, the transition dipole moments of the singlet excited states, spin-orbit coupling (SOC) matrix elements, and energy gaps between the lowest triplet excited states and singlet excited states are calculated. As demonstrated by the results, compared with Pt-3, Pt-1 and Pt-2 have larger SOC matrix elements between the lowest triplet excited states and singlet excited states, an indicator that they have faster radiative decay processes. In addition, the SOC matrix elements between the lowest triplet excited states and ground states are also computed to elucidate the temperature-independent non-radiative decay processes. Moreover, the temperature-dependent non-radiative decay mechanisms are also explored via the potential energy profiles.

Temperature sensitivity is used to measure the junction temperature of semiconductor devices without using external temperature sensors. Temperature sensitivity may vary more than 10% due to the measurement environments, which affects the accuracy of the junction temperature. However, this fact hasn't been well recognized. It is presumed that temperature sensitivity measurement is not reliable when a single sided cold plate is used. It is due to the temperature gradient between the cold plate and the ambient, through the junction of the semiconductor. Unless the device is put inside the temperature controlled chamber, it is hard to eliminate the temperature gradient between the junction of the semiconductor and the ambient. This paper presents the results of several temperature sensitivity measurements using 2 types of temperature controlled environments: a single sided cold plate and a temperature controlled chamber. Also, we have tested with several packages such as TO-220, TO-264, SOT-227, and D3 package, to see how it varies. We have come to the conclusion that it is better to use a temperature controlled chamber to measure temperature sensitivity, while some devices allow us to use a single sided cold plate as well. The differences due to the devices and environments are discussed by using CFD simulation, visualizing the temperature gradient inside the packages.

The heat flow distribution in IGBT package is significantly affected by its interfacing materials and dimension of metal frame. In order to increase heat-sink capability which is critical for kW IGBT device, lateral heat spreading technology is introduced. To design in such 3D heat flux structure in real power device package, accurate thermal distribution analysis is required. Using three dimensional thermal CFD simulators is proven to be valid for thermal structural analysis, however in most of practical cases material properties like thermal conductivity or contact thermal resistance are always unknown. In this paper we are going show the possibility of utilizing thermal transient test and thermal structure function[1][2] based approach to analyze thermal characteristic and heat flux in a real IGBT package.

Traditional thermal conductivity measurement such as laser-flash method for thermal-conductivity measurement is limited to homogenous materials or limited geometry, therefore, such method is not suitable for characterizing real semiconductor packages which have complex heat flow structure. In this paper, we are going to introduce structure function based evaluation of the thermal transient measurements, which is most appropriate for the characterization of heat flow path in complex semiconductor packages. The structure functions are “graphical” representations of the RC-model of thermal systems. With the help of structure function one can determine partial thermal resistances and partial thermal capacitances in a heat flow path not only inside the device package like die attach, but also outside electronic components like PCB board, surface-air boundary layer, contact thermal resistance etc., with high accuracy.

The paper calculates the grey incidence degree of the Research and Development investment and Economic Development in some countries on the basis of the grey incidence theory in the main three performance sectors. The results demonstrate that the investment of science and technology talents is more important than R&D expenditure in promoting the development of economy. R&D expenditure gets higher degree of grey incidence in government performance sector than the researchers in China. The researcher input in business enterprise sector should be improved. To be supported by more R&D funds is necessary for the high education sector.