Search

Photoexcitation polarons in semiconductor materials play a crucial role in various fields, such as enhancing electrical conductivity, influencing chemical selectivity, and improving reaction efficiency in semiconductor photocatalysis. To comprehensively understand the properties of polarons, time-resolved mid-infrared, near-infrared, and visible transient absorption spectroscopies were employed to investigate the photogenerated carriers in cadmium sulfide (CdS) single crystals. We have determined the midgap energy levels of defect states by transient infrared absorption-excitation energy scanning spectra. Furthermore, we observed the formation of both the electron and hole polarons, where the electron polarons are coupled to the longitudinal acoustic phonons, while the hole polarons are coupled to both optical and longitudinal acoustic phonons. The photogenerated free electrons were trapped by the S-vacancies at 0.14 eV below the minimum of the conduction band, leading to the formation of electron polarons with a trapping time constant of 4.5 ps, while hole polarons are formed at Cd vacancies located at 0.04 eV above the maximum of the valence band with a time constant of 2.9 ps. Our determined midgap energy levels of the trapped states together with dynamical properties of electron and hole polarons provide insights into optimizing the photocatalytic property of CdS.

The major light-harvesting complex of photosystem II (LHCII) has a dual regulatory function in a process called non-photochemical quenching to avoid the formation of reactive oxygen. LHCII undergoes reversible conformation transitions to switch between a light-harvesting state for excited-state energy transfer and an energy-quenching state for dissipating excess energy under full sunshine. Here we report cryo-electron microscopy structures of LHCII in membrane nanodiscs, which mimic in vivo LHCII, and in detergent solution at pH 7.8 and 5.4, respectively. We found that, under low pH conditions, the salt bridges at the lumenal side of LHCII are broken, accompanied by the formation of two local α-helices on the lumen side. The formation of α-helices in turn triggers allosterically global protein conformational change, resulting in a smaller crossing angle between transmembrane helices. The fluorescence decay rates corresponding to different conformational states follow the Dexter energy transfer mechanism with a characteristic transition distance of 5.6 Å between Lut1 and Chl612. The experimental observations are consistent with the computed electronic coupling strengths using multistate density function theory.

Objective: MicroRNA (miRNA/miR)-633 is dysregulated in several types of cancers and is involved in tumorigenesis. However, the function and role of this miRNA in gastric cancer (GC) are not fully understood. The aim of the present study was to evaluate miR-633 expression in GC cell lines and in GC tissue vs. adjacent normal tissue, and to determine its association with clinicopathological data. This work was extended to investigate the effects of miR-633 overexpression on tumor cells in vitro. Methods: Reverse transcription-quantitative PCR (RT-qPCR) was used to detect and compare the expression level of miR-633 in GC cells, as well as in GC and normal adjacent tissue samples. The clinical significance of miR-633 was also analyzed. MiR-633 lentivirus (LV-miR-633) and negative control lentivirus (LV-NC) were generated and used to transduce SGC-7901 and HGC-27 GC cells in order to analyze the effect of miR-633 on their phenotype. The effects of miR-633 overexpression on GC cell proliferation, apoptosis, migration and invasion were investigated. The target gene of miR-633 was predicted, then confirmed using a dual luciferase reporter gene assay, RT-qPCR and Western blotting. Results: MiR-633 was significantly downregulated in GC cell lines, as well as in GC tissue compared with adjacent normal tissue. Moreover, miR-633 expression was associated with the tumor/node/metastasis (TNM) stage, invasion depth, Borrmann classification and lymph node metastasis (P<0.05). Compared with the LV-NC group, transduction with LV-miR-633 reduced the proliferation, the number of clones, the wound healing rate, the number of invading cells and the number of cells in the G1phase of the cell cycle (P<0.01). LV-miR-633 also increased the apoptosis rate (P<0.01). The expression level of mitogen-activated protein kinase (MAPK) 1, high-mobility group box 3 (HMGB3), claudin 1 (CLDN1) and MAPK13 were downregulated in LV-miR-633-transduced cells (P<0.01). The dual luciferase reporter assay confirmed that the 3′-untranslated region of MAPK1 was the target site of miR-633 (P<0.01). Conclusion: MiR-633 acts as a tumor suppressor in GC, and its expression level is associated with TNM stage, invasion depth, Borrmann type and lymph node metastasis. Overexpression of miR-633 inhibits the proliferation and migration of GC cells and induces apoptosis and cell cycle arrest at the in G1phase. In addition, miR-633 negatively regulates the expression of MAPK1, HMGB3, CLDN1 and MAPK13 and directly targets MAPK1.

The shell thickness dependence of the ultrafast plasmon-induced hot-electron injection process in Au@CdS core–shell nanocrystals has been studied with mid-infrared and visible femtosecond transient absorption spectroscopies. As the thickness of the CdS shell increases, we observe that the hot-electron injection efficiency initially increases but then decreases after a critical point (at around 8–10 nm), which is consistent with the trend for the shell thickness-dependent photocatalytic hydrogen evolution. Combined with the theoretical calculation, we find that the electron injection efficiency is mainly determined by two decisive factors, which are the initial hot-electron energy distribution in the Au core after Landau damping and the Schottky potential in the interface of the Au core and the CdS shell. This finding offers a practical and effective approach to optimize the photocatalytic efficiency of a metal–semiconductor heterostructure by tuning its structure.

Insufficient active sites and fast charge carrier recombination are detrimental to photocatalytic activity of graphitic carbon nitride (g-C3N4). In this work, a combination of pore creating with thermal exfoliation was employed to prepare porous g-C3N4nanosheets for photocatalytic water splitting into hydrogen. Hexadecyl trimethyl ammonium chloride (CTAC) as the soft template promoted the formation of porous g-C3N4during the thermal condensation of melamine. On further post-synthesis calcination, the porous g-C3N4aggregates were exfoliated into discrete nanosheets, accompanied by an increase in specific surface area and defects. Optimal porous g-C3N4nanosheets achieved 3.6 times the photocatalytic hydrogen evolution rate for bulk counterpart. The enhanced photocatalytic activity may be ascribed to TCN-1%CTAC has larger specific surface area, stronger optical absorption intensity and higher photogenerated electron–hole separation efficiency. The external quantum efficiency of TCN-1%CTAC was measured to be 3.4% at 420 nm. This work provides a simple combinatorial strategy for the preparation of porous g-C3N4nanosheets with low cost, environmental friendliness and enhanced photocatalytic activity.

Elucidating the property of the polaronic state at ultrafast temporal resolution is of great significance, especially for photocatalytic and solar-energy materials. In this work, femtosecond transient absorption (TA) spectroscopy with state selectivity is utilized to monitor the dynamics of the polaron generated by exciting the mid-gap states from the oxygen vacancy into the polaronic state in a single-crystal ZnO. The photoexcited polaronic state is verified by the observed coherent acoustic phonon with an oscillation on the kinetics at the initial several picoseconds at a frequency of about 50 GHz. We found that the excited state of polaron is located inside the conduction band (CB), which injects an electron into the CB within about 1 ps observed via a broad-band TA spectrum ranging from 400 to 4000 nm. Compared with that of free carriers generated by direct band gap excitation, the lifetime of the carriers resulted from the electron injection from the polaronic states is significantly prolonged, an important feature beneficial to photocatalysts.

Defect states and polarons of photocatalytic semiconductors play important roles by notably influencing carrier mobility and reactivity. Extensive studies have focused on identifying defect states and the physical properties of polarons, as well as their consequential impact on catalytic efficiency. This Featured Article summarizes recent investigations of defects and polarons using time-resolved spectroscopies in photocatalytic semiconductors. These include transient infrared absorption–excitation energy scanning spectroscopy to identify defect states within the bandgap of photocatalytic materials such as anatase and rutile TiO2, ZnO, and CdS and time-resolved spectroscopic studies on the temporal evolution of photogenerated electron and hole polarons within these semiconductors. Finally, we address the current challenges in the study of defects and polarons.

Metal halide perovskites with direct band gap and strong light absorption are promising materials for harvesting solar energy; however, their relatively narrow band gap limits their redox ability when used as a photocatalyst. Adding a second semiconductor component with the appropriate band structure offsets can generate a Z-scheme photocatalytic system, taking full advantage of the perovskite’s intrinsic properties. In this work, we develop a direct Z-scheme photocatalyst based on formamidinium lead bromide and bismuth tungstate (FAPbBr3/Bi2WO6) with strong redox ability for artificial solar-to-chemical energy conversion. With desirable band offsets and strong joint redox potential, the dual photocatalyst is shown to form a semicoherent heterointerface. Ultrafast transient infrared absorption studies employing selective excitation reveal synergetic photocarrier dynamics and demonstrate Z-scheme charge transfer mechanisms. Under simulated solar irradiation, a large driving force photoredox reaction (∼2.57 eV) of CO2reduction coupled with benzyl alcohol oxidation to benzaldehyde is achieved on the Z-scheme FAPbBr3/Bi2WO6photocatalyst, harnessing the full synergetic potential of the combined system.

Novel fullerene-based donor–acceptor (DA) dyads, Sc3N@C80-PTZ and C60-PTZ, have been synthesized and investigated in which the photoinduced electron transfer direction is proved to be switchable by regulating the redox state. In detailed photophysical experiments, reductive electron transfer from the PTZ moiety to Sc3N@C80is confirmed with transient absorption (TA) spectroscopy in the neutral Sc3N@C80-PTZ dyad. After oxidizing the PTZ moiety to PTZ•+in a reversible manner, oxidative electron transfer from the Sc3N@C80moiety to the PTZ•+radical cation is corroborated experimentally and theoretically, leading to formation of a metastable charge transfer (CT) state (Sc3N@C80)•+-PTZ, which is not observed in the C60-PTZ•+dyad. To the best of our knowledge, this is the first time in situ tunable molecular photodiode-like behavior is fulfilled utilizing a fullerene dyad. These findings will contribute to the future application of fullerene-based DA conjugates in molecular electronic devices.

The difference between the excited- and ground-state vibrational wavepackets remains to be fully explored when multiple vibrational modes are coherently excited simultaneously by femtosecond pulses. In this work, we present a series of one- and two-dimensional electronic spectroscopy for studying multimode wavepackets of oxazine 720 in solution. Fourier transform (FT) maps combined with time–frequency transform (TFT) are employed to unambiguously distinguish the origin of low-frequency vibrational wavepackets, that is, an excited-state vibrational wavepacket of 586 cm–1with a dephasing time of 0.7 ps and a ground-state vibrational wavepacket of 595 cm–1with a dephasing time of 1.3–1.7 ps. We also found the additional low-frequency vibrational wavepackets resulting from the coupling of the 595 cm–1mode to a series of high-frequency modes centered at 1150 cm–1via electronic transitions. The combined use of FT maps and TFT analysis allows us to reveal the potential vibrational coupling of wavepackets and offers the possibility of disentangling the coupling between the electronic and vibrational degrees of freedom in condensed-phase systems.

Plasmons in conducting nanostructures offer the means to efficiently manipulate light at the nanoscale with subpicosecond speed in an all-optical operation fashion, thus allowing for construction of high performance all-optical signal-processing devices. Here, by exploiting the ultrafast nonlinear optical properties of broadly tunable mid-infrared (MIR) plasmons in solution-processed, degenerately doped oxide nanoparticles, we demonstrate ultrafast all-optical switching in the MIR region, which features subpicosecond response speed (with recovery time constant of <400 fs) as well as an ultrabroadband response spectral range (covering 3.0–5.0 μm). Furthermore, with the degenerately doped nanoparticles as Q-switch, pulsed fiber lasers covering 2.0–3.5 μm were constructed, of which a watt-level fiber laser at 3.0 μm band shows superior overall performance among previously reported passively Q-switched fiber lasers at the same band. Notably, the degenerately doped nanoparticles show great potential to work in the spectral range over 3.0 μm, which is beyond the accessibility of commercially available but expensive semiconducting saturable absorber mirror (SESAM). Our work demonstrates a versatile while cost-effective material solution to ultrafast photonics in the technologically important MIR region.

The two-tailed comet assay (2T-comet assay) is a method for simultaneously evaluating DNA single-strand breaks (SSBs) and double-strand breaks (DSBs). In the present study, the endonuclease DNase I and hydrogen peroxide were used to induce DSBs and SSBs in bone marrow mononuclear cells (BMMNCs) from mice, and the damaged DNAs were assessed with a 2T-comet assay. The results demonstrated that this method can detect and discriminate between BMMNC DNA SSBs and DSBs simultaneously. Using this method, we studied DNA damage in BMMNCs from female BALB/c mice after total body irradiation with X-rays and carbon ions. The results indicated that these two types of radiation induced serious DNA damage in BMMNCs in a dose-dependent manner. The DNA damage induced by carbon ions was more severe than that induced by X-rays at the same dose, and a high dose of carbon ion radiation was more likely to cause death in mice. The DSBs and SSBs induced by X-rays were the highest on the 3rd day post-IR. For carbon ion radiation, DSBs were the most serious on the 3rd day, while SSBs were more obvious on the 3rd day and 13th day post-IR. The ratio of DSBs/SSBs was clearly related to the different types of radiation.

Several dumbbell conjugates featuring M3N@Ih-C80(M = Sc, Y) and C60were prepared to systematically investigate interfullerene electronic interactions and excited state dynamics. From electrochemical investigations, we concluded that the redox potentials of our M3N@Ih-C80(M = Sc, Y) dumbbells depend largely on the interfullerene electronic interactions. Assisted by DFT calculation, the unique role of metal atoms was highlighted. Most importantly, ultrafast spectroscopy experiments revealed symmetry-breaking charge separation in Sc3N@C80-dumbbell to yield an unprecedented (Sc3N@C80)•+-(Sc3N@C80)•–charge separated state. This is, to the best of our knowledge, the first time that symmetry-breaking charge separation following photoexcitation is corroborated in a fullerene system. As such, our work shed light on the significance of interfullerene electronic interactions and their uniqueness for modulating excited state properties.

A series of novel surface Ru–H bipyridine complexes-grafted TiO2nanohybrids were for the first time prepared by a combined procedure of surface organometallic chemistry with post-synthetic ligand exchange for photocatalytic conversion of CO2to CH4with H2as electron and proton donors under visible light irradiation. The selectivity toward CH4increased to 93.4% by the ligand exchange of 4,4′-dimethyl-2,2′-bipyridine (4,4′-bpy) with the surface cyclopentadienyl (Cp)–RuH complex and the CO2methanation activity was enhanced by 4.4-fold. An impressive rate of 241.2 μL·g–1·h–1for CH4production was achieved over the optimal photocatalyst. The femtosecond transient IR absorption results demonstrated that the hot electrons were fast injected in 0.9 ps from the photoexcited surface 4,4′-bpy–RuH complex into the conduction band of TiO2nanoparticles to form a charge-separated state with an average lifetime of ca. 50.0 ns responsible for the CO2methanation. The spectral characterizations indicated clearly that the formation of CO2•–radicals by single electron reduction of CO2molecules adsorbed on surface oxygen vacancies of TiO2nanoparticles was the most critical step for the methanation. Such radical intermediates were inserted into the explored Ru–H bond to generate Ru–OOCH species and finally CH4and H2O in the presence of H2.

As requirements for the acquisition of workshop production information tends to be more instant and reliable, this paper proposed a workshop production information acquisition system based on RFID and ZigBee technology. After analyzing the system information demand, this paper designs the system physical structures, communication protocol, tag encoding and software hierarchy. Finally, designs and implements the server-side and terminal-side system which can make information acquisition more real-time and make the production more efficient.

In the energy crisis environment, V2G and G2V energy exchange is an important issue for attention. We studied the V2G and G2V energy exchange process and electric energy transaction mode. The design of an energy transaction management system for V2G and G2V is given, and the management system is developed. This system is an information system for V2G and G2V two-way mode trading platform, which include two parts: the first is the system management and basic information management module, the second is V2G and G2V transaction module. Based on transactions between electric vehicles and the grid, the system realizes the plan and arrangement for the electric automobile to charge and discharge orderly.

In this paper, we addressed the problems faced by flexible manufacturing system, which make the manufacturing process complex and difficult to scheduling, by the introduction of a Multi-Agent System (MAS) model. The internal structure of each agent was based on the Belief-Desire-Intention (BDI) architecture to represent autonomic and coordinated scheduling mechanism and the ability to acquire information provided by exogenous sources. We built an evaluation system based on products’ preference about time and cost values to explore new assigning weights for the ranking of the candidate designs. In conclusion we provide ways to assemble manufacturing units into MAS while guaranteeing the internal real-time requirements of each agent.

The hydrophilic and mechanical strength of the cellulose acetate microporous membrane (CAMM) were improved by dealt with TiO2 nanoparticles, which were obtained by adding a super dispersant into TiO2-aqueous dispersion. The influence of such factors as temperature, processing time and TiO2 concentration on adsorption amount of CAMM were investigated. The experiment data indicated that water flux of the modified CAMM increased with the increase of the TiO2 adsorption amount. It suggested that hydrophilic of the CAMM was improved than that of blank. Experiments data also showed that the modified CAMM was better in mechanical strength but was weaker in elastic deformation than those of the blank. Water flux stability of the modified CAMM has improved significantly. Better modified conditions are as follows:TiO2 concentration 0.1mol·L-1,temperature 35°C, processing time 6h, and adsorption amount 9.708mg/g.

4-(β-sulfatoethylsulfone)-N-ethyl-aniline was synthesized from 4-(β-hydroxyethyl-sulfonyl)-N-ethyl-aniline in the presence of sulfuric acid using toluene and N,N-dimethyl-dodecylamine as mix solvent. The product was efficiently precipitated from the reaction mixture by addition of a sufficient amount of acetone. Several influencing factors on the esterification were investigated, and the results show that, the optimal conditions were: the molar ratio of 4-(β-hydroxyethylsulfonyl)- N-ethyl-aniline, N,N-dimethyl-dodecylamine and sulfuric acid was 1:1:1.5, the dosage of toluene 800 mL per molar 4-(β-hydroxyethylsulfonyl)- N-ethyl-aniline, and the esterification was taken for 9 hours under reflux. Under the optimal conditions, total yield of the product was 85% with the purity of 97%. It was also found that the yield of product can be promoted up to 90 % by using the recycled solvent. The structure of product was characterized by MS.

A kind of calculating model was proposed according to the structure and load characteristics of push-back rack. On the basis of study on modeling and analysis technology using ANSYS, the finite element analysis of push-back rack was realized, which can provide reference to the design and calculation of push-back rack.

According to the problems of the footwear packaging boxes presented in Chinese manufacturing enterprises, this research proposes an optimization strategy to design a series of standard footwear packaging boxes. This strategy consists of two main parts, the optimization design of plane size and the optimization design of height size. The first part is targeted to maximize the comprehensive weighted plane utilization rate and meanwhile meet the total amount limitation of plane size. During this process, the plane size of each inner shoebox, the K-medoids algorithm and bin packing patterns are used. The second part is targeted to maximize the comprehensive weighted space utilization rate within the limited boxes amount and in this part, multiple lengths of inner shoeboxes and linear 0-1 programming is used for the optimization design. Finally, with the data obtained from enterprise production practices, the empirical study shows the optimization strategy's effectiveness and adaptability to solve practical problem.

There are two main aspects of problems in home appliance product lifecycle information management. One is the loss of information and unable to share information in time. The other is the existing bar code and other information recording methods are easy to wear or deface, resulting in low efficiency in information collection and high error rate, even cannot be read. This paper established a home appliance product lifecycle information management system based on RFID. RFID is used to collect and store data. Under such information sharing circumstance, not only integrity and instantaneity of product information are improved, but also the information management of home appliance product lifecycle is strengthened.

In order to help vehicle users to save fuel cost, combining the refueling with transportation task, this paper provided a scientific solution of gas station selection during transportation task. Considering users’ personalized requirements, gasoline price, etc, this paper established a multi-objective decision-making model based on the aims of the shortest distance and minimum cost of given refueling volume. The model can be resolved by the algorithm designed. In order to improve its practical applicability, a visual decision support system which can show the gas station selected and route had been developed based on GIS. This system can provide selection of gas station which meets user’s personalized requirements and make the objective function optimal

A new expert system was built for safety assessment of soft soil roadbed, in which the characteristics was taken into account by using Analytic Hierarchy Process (AHP) for identifying weight matrix of evaluating index, Fuzzy Synthetically Judgment for modeling safety evaluation of soft soil roadbed. The authors had attempted to develop the expert system to be comprehensive, concise, scientific, independent and flexible. Also, the system had been used to assess the safety of the Binhai highway of Tangshan, China. The results showed that the system is objective, feasible and practical, and can be used to assess the safety of soft soil roadbed.

Surface modification of poly(vinylidene fluoride) (PVDF) membrane was accomplished by the adsorption of ferric hydroxide sol to impove its hydrophilicity. The adsorption curves of the membranes were analyzed by weight measurements, and the typical results showed a two-platform character in low concentration. The effects of the adsorption time, the ferric hydroxide sol concentration, the test temperature, as well as the water cleaning time on the adsorption amount were observed. Attenuated total reflection-Fourier transform infrared spectroscopy (ATR/ FTIR) analysis showed that the adsorption of ferric hydroxide sol on poly(vinylidene fluoride) microporous membranes (PVDFMM) is effective. The membranes hydrophilic performance was represented by water contact angle measurements. The water contact angles changes from the virgin 128°to the lowest value 81.90° in the range of 0~0.10 mol/L ferric hydroxide aqueous solution. The results indicated that ferric hydroxide sol can be immobilized on the PVDF films by adsorption, and the membrane hydrophilic performence increases with the increase of the adsorption amount of the ferric hydroxide sol onto the PVDF membrane surface.

We have developed an experimental system for real-time vibrational spectroscopy of molecules in a specific electronic excited state. A synchronized UV light source and a few-cycle visible laser pulse were utilized to prepare and investigate the ultrafast dynamics of molecules in the electronic excited states. A multichannel lock-in amplifier detection system operating in a tandem double lock-in detection mode was used to extract the signal correlated only to the UV and visible pump pulses. Real-time vibrational spectroscopy of chrysene in the triplet state and 1^′, 3^′-dihydro-1^′, 3^′, 3^′-trimethyl-6-nitrospiro [2H-1-benzopyran-2, 2^′-(2H)-indole] in a photochromic state was demonstrated.

In view of the task assignment problem of the picking station in the online Parts-to-Picker Picking System, a mathematical model was established that targeting the minimum number of total rounds of the bins and the equalization of the picking of each station, constrained by the uniqueness of the order attribution and the maximum amount of orders processed by the workstation. Then, the solution flow and method of multi-objective function problem based on Genetic Algorithm are designed. The algorithm constrains the secondary objective function and defines the rules of the objective function constraint. Finally, an empirical study on the actual Parts-to-Picker System of an e-commerce enterprise is carried out. The results show that the algorithm can effectively reduce the two objective function values and verify the effectiveness of the algorithm.

Ablation experiments with femtosecond (fs) laser pulse (pulse duration 37 fs, wavelength 800 nm) on organic polymers have been performed in air. The ablation threshold is found to be only several nanojoules. The diameters of the dots ablated in the organic polymers are influenced by the laser fluence and the number of laser pulses. It is observed that heat is diffused in a threadlike manner in all directions around the central focus region.Explanations of the observed phenomena are resented. A one-dimensional waveguide is also ablated in the organic polymers.

The Ti:sapphire oscillator is used to realize structural change in an organic glass (polymethyl -methacrylate (PMMA)). Single pulse fluence threshold of PMMA and the relation of the breakdown threshold with different numerical aperture objectives are determined using a formula deduced from an existent equation. Three-dimensional dots in the organic glass is performed at the same time.

A passive mode-locked diode-pumped self-frequency-doubling Yb:YAB laser with a low modulation depth semiconductor saturable absorber mirror operating at 374 MHz is demonstrated. The measured pulse duration is 1.98 ps at the wavelength of 1044 nm. The maximum average power reaches 45 mW.