From Porphyrin-Like Rings to High-Density Single-Atom Catalytic Sites: Unveiling the Superiority of p-C2N for Bifunctional Oxygen Electrocatalysis.

With effective utilization of the catalytic site, single-atom catalysts (SACs) supported by nitrogen atoms surrounding built-in pores of two-dimensional (2D) materials, such as porphyrin/phthalocyanine-based covalent organic frameworks, have been highly promising electrocatalysts in the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) processes for the air electrode of the metal-air battery. However, the number of stable single-atom anchoring sites, i.e., accessible single-atom metal sites, has been concerning as a result of the appearance of heterogeneous or large and even supersized pores in substrate materials. 2D porous graphitic carbon nitride (PGCN) with a stronger stability and smaller component is regarded as a more potential alternative owing to similar controllability and designability. In this work, inspired by the robust coordinated TM-N4 environment of porphyrin/phthalocyanine molecules, novel p-C2N with a high density of porphyrin-like organic units is rationally designed. In well-designed p-C2N, a higher homogeneity and uniformity of coordination sites can enhance the electrocatalytic activity in the whole catalytic material and better prevent SACs from sintering and agglomerating into thermodynamically stable nanoclusters. Utilizing density functional theory (DFT), the stability of the p-C2N monolayer, TM@p-C2N, and OER/ORR catalytic activities of TM@p-C2N (TM including Mn, Fe, Co, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, and Au) are systematically evaluated. Among them, Ir@p-C2N (0.31 V of the OER and 0.36 V of the ORR), Co@p-C2N (0.47 and 0.22 V), and Rh@p-C2N (0.55 and 0.27 V) are screened as promising SACs for the bifunctional ORR and OER. The proposal of p-C2N guides a new direction for the development of TM-N-C-based SAC bifunctional electrocatalysts.

Four undescribed triterpenes from the aerial parts of Verbena officinalis.

Verbena officinalis is used as a Chinese folk medicine for the treatment of rheumatism and bronchitis. Herein, four undescribed triterpenes, officinalisoids A-D (1-4), together with thirty-three known compounds (5-37) were isolated from the aerial parts of V. officinalis. The chemical structures of the new compounds were determined by spectrometric data interpretation using NMR, HRESIMS, IR and UV spectroscopy. Biological evaluation results revealed that compound 30 exhibited potential anti-inflammatory activity with IC50 value of 6.07 µM (CC50 > 50 µM) and compound 12 showed moderate anti-dengue virus activity with the IC50 value of 24.55 µM (CC50 > 50 µM).

Trapping and diffusion of hydrogen in iron-doped Y2O3.

Y2O3 is a promising material for use as a tritium permeation barrier (TPB) coating and as dispersed particles in oxide dispersion strengthened steels for experimental fusion reactors. By using first-principles approaches, we found that substituting Fe for Y in Y2O3 is the most energetically favourable under O-deficient and H-rich conditions, leading to easier formation of the nearby O vacancies. These O vacancies serve as effective trapping sites for H atoms with a formation energy of -2.36 eV. The presence of Fe defects also makes it more difficult for H atoms to migrate in Y2O3 from three possible H-related defects. These findings suggest that incorporating Fe into Y2O3 could yield a better TPB and provide insight into the improved H trapping ability of Y2O3 with Fe dopants.

Visualization Experimental Study on Silicon-Based Ultra-Thin Loop Heat Pipe Using Deionized Water as Working Fluid.

As a type of micro flat loop heat pipe, s-UTLHP (silicon-based ultra-thin loop heat pipe) is of great significance in the field of micro-scale heat dissipation. To prove the feasibility of s-UTLHP with high heat flux in a narrow space, it is necessary to study its heat transfer mechanism visually. In this paper, a structural design of s-UTLHP was proposed, and then, to realize the working fluid charging and visual experiment, an experimental system including a holding module, heating module, cooling module, data acquisition module, and vacuum chamber was proposed. Deionized water was selected as a working fluid in the experiment. The overall and micro phenomena of s-UTLHP during startup, as well as the evaporation and condensation phenomena of s-UTLHP during stable operation, were observed and analyzed. Finally, the failure phenomenon of s-UTLHP was analyzed, and several solutions were proposed. The observed phenomena and experimental conclusions can provide references for further related experimental research.

Study on Flow Characteristics of Working Medium in Microchannel Simulated by Porous Media Model.

As a phase change evaporator, a microchannel array heat exchanger is of great significance in the field of microscale heat dissipation. The performance of which strongly depends on the flow resistance, capillary force, and other factors. In order to improve the heat dissipation efficiency, it is necessary to perform an in-depth study of the characteristics of microchannel flow using numerical simulation. However, the current simulation model requires high computational cost and long simulation time. To solve this problem, this paper simplifies the numerical simulation of the rectangular parallel array microchannels by building the basic flow model based on the concept of porous media. In addition, we explore the effect of aspect-ratio (AR), hydraulic diameter, inlet velocity, and other parameters of fluid flow behavior inside the microchannels. Meanwhile, a user-defined function (UDF) is formulated to add the capillary force into the model to introduce capillary force into the porous media model. Through the above research, the paper establishes the porous media model for single-phase and gas-liquid two-phase flow, which acts as a simplification of microchannel array simulation without grossly affecting the results obtained. In addition, we designed and manufactured experiments using silicon-based microchannel heat exchangers with different-ratios, and combined with the visualization method to measure the performance of the device and compared them with simulation results. The theoretical model is verified through the suction experiment of array microchannel evaporator capillary core. The simplified model of microchannel array significantly saves the computational cost and time, and provides guidance for the related experimental researches.

Enhanced Electrical Conductivity of Sb2S3 Thin Film via C60 Modification and Improvement in Solar Cell Efficiency.

Sb2S3 has attracted great research interest very recently as a promising absorber material for photoelectric and photovoltaic devices because of its unique optical and electrical properties and single, stable phase. However, the intrinsic high resistivity property of Sb2S3 material is one of the major factors restricting the further improvement of its application. In this work, the C60 modification of Sb2S3 thin films is investigated. The conductivity of Sb2S3 thin films increases from 4.71 × 10-9 S cm-1 for unmodified condition to 2.86 × 10-8 S cm-1 for modified thin films. Thin-film solar cells in the configuration of glass/(SnO2:F) FTO/TiO2/Sb2S3(C60)/Spiro-OMeTAD/Au are fabricated, and the conversion efficiency is increased from 1.10% to 1.74%.

Analysis on Machining Performance of Nickel-Base Superalloy by Electrochemical Micro-milling with High-Speed Spiral Electrode.

As one of the most promising micro-machining methods, electrochemical micro-machining is widely used in the field of metal micro-structures. The electrochemical micro-milling on Nickel-base superalloy by using high-speed spiral electrode was studied in detail. Firstly, the electric field and flow field models of micro-electrochemical milling are established and analyzed by the finite element method. Then, the milling profile was predicted and the effect of high-speed rotation of electrodes on electrolyte promotion and secondary electrolysis prevention were analyzed. Secondly, the influence of the main machining parameters, such as rotating speed, electrical parameters, and feed rate on machining precision and efficiency was analyzed experimentally. Finally, by optimizing the machining parameters, a series of micro-graphic structures with a width of about 150 µm were obtained on Nickel-base superalloy 718 by using the spiral electrode with a diameter of 100 µm. The experimental and simulation results show that the high-speed rotation of electrodes can greatly improve the machining efficiency and stability. It was proved that micro-electrochemical milling with the high-speed rotating electrode technique is an effective method for machining micro-metal parts.

Characterization of ginsenoside extracts by delayed luminescence, high-performance liquid chromatography, and bioactivity tests.

Ginsenoside extracts are often used as raw materials for various pharmaceutical, cosmetic and food supplement products. Development of a direct, rapid, cheap, and comprehensive measurement tool for the quality assessment of ginsenoside extracts, and indeed all herbal extracts, is urgently needed. In addition, a bioactivity-based assessment should be linked with quality control. In this report, we try to develop a novel quality control tool using ginsenoside extracts as an example. High-performance liquid chromatography (HPLC) was used to detect nine principal ginsenosides in 11 batches of ginsenoside extracts. Delayed luminescence (DL) was used to analyze the same ginsenoside extract samples. DL measurements showed the same results in terms of differentiating 11 ginsenoside extract samples compared with chemical analysis, and DL properties could be closely linked to index ginsenosides in the quality control of ginsenoside extracts. Next, a zebrafish tail-fin amputation model was used to study differences in anti-inflammatory effect between the ginsenoside extract batches. The results indicate that both chemical analysis and DL measurements could partially reflect biological activity. Thus, DL may serve as a rapid, direct, sensitive, and systemic tool for studying the overall properties of ginsenoside extracts. Our proposal for linking bioactivities as a tool for evaluation of the quality of ginsenoside extracts opens a new direction for quality control.

Improvement in Sb2Se3 Solar Cell Efficiency through Band Alignment Engineering at the Buffer/Absorber Interface.

Energy band alignment plays an important role in heterojunction thin-film solar cells. In this work, we report the application of ternary Cd xZn1- xS buffer layers in antimony selenide (Sb2Se3) thin-film solar cells. The results of our study revealed that the Cd/Zn element ratios not only affected the optical band gap of Cd xZn1- xS buffers but also modified the band alignment at the junction interface. A Sb2Se3 solar cell with an optimal conduction-band offset value (0.34 eV) exhibited an efficiency of 6.71%, which represents a relative 32.1% enhancement as compared to the reference CdS/Sb2Se3 solar cell. The results further indicated that a "spike"-like band structure suppressed the recombination rate at the interface and hence increased the device open-circuit voltage and fill factor. Electrochemical impedance spectroscopy analysis exhibited that the Cd xZn1- xS/Sb2Se3 solar cell had higher recombination resistance and longer carrier lifetime than the CdS/Sb2Se3 device.

Experimental Research on Machining Localization and Surface Quality in Micro Electrochemical Milling of Nickel-Based Superalloy.

Micro electrochemical machining is becoming increasingly important in the microfabrication of metal parts. In this paper, the machining characteristics of micro electrochemical milling with nanosecond pulse were studied. Firstly, a mathematical model for the localization control of micro electrochemical milling with nanosecond pulse was established. Secondly, groups of experiments were conducted on nickel-based superalloy and the effects of parameters such as applied voltage, pulse on time, pulse period, electrolyte concentration and electrode diameter on machining localization and surface roughness were analyzed. Finally, by using the optimized machining parameters, some 2D complex shapes and 3D square cavity structures with good shape precision and good surface quality were successfully obtained. It was proved that the micro electrochemical milling with nanosecond pulse technique is an effective machining method to fabricate metal microstructures.

The Difference between White and Red Ginseng: Variations in Ginsenosides and Immunomodulation.

Ginseng Radix (Panax ginseng) is one of the most commonly used herbs worldwide for the treatment of inflammation-related diseases among others, supported by ancient historical records. Throughout this long history, the large-scale cultivation of ginseng created an increasing demand for long-term storage of the harvested plant material, accelerating the development of post-harvesting procedures. Dried white ginseng and processed (steamed) red ginseng are the products of the two most common traditional post-harvest processes. Although there are a significant number of reports on practice-based therapeutic applications of ginseng, science-based evidence is needed to support these uses. Using a reverse pharmacology approach in conjunction with high-throughput techniques and animal models may offer clear, simple paths for the elucidation of the mechanisms of activity of herbal medicines. Moreover, it could provide a new and more efficient method for the discovery of potential drug candidates. From this perspective, the different chemical compositions of white ginseng and red ginseng could very likely result in different interactions with signaling pathways of diverse biological responses. This paper provides an overview of white ginseng and red ginseng, mainly focusing on their chemical profile and immunomodulation activities. Synergistic effects of ginseng herbal drugs with combinations of other traditional herbal drugs or with synthetic drugs were reviewed. The use of the zebrafish model for bioactivity testing greatly improves the prospects for future ginseng research.

Energy Level-Based Abnormal Crowd Behavior Detection.

The change of crowd energy is a fundamental measurement for describing a crowd behavior. In this paper, we present a crowd abnormal detection method based on the change of energy-level distribution. The method can not only reduce the camera perspective effect, but also detect crowd abnormal behavior in time. Pixels in the image are treated as particles, and the optical flow method is adopted to extract the velocities of particles. The qualities of different particles are distributed as different value according to the distance between the particle and the camera to reduce the camera perspective effect. Then a crowd motion segmentation method based on flow field texture representation is utilized to extract the motion foreground, and a linear interpolation calculation is applied to pedestrian's foreground area to determine their distance to the camera. This contributes to the calculation of the particle qualities in different locations. Finally, the crowd behavior is analyzed according to the change of the consistency, entropy and contrast of the three descriptors for co-occurrence matrix. By calculating a threshold, the timestamp when the crowd abnormal happens is determined. In this paper, multiple sets of videos from three different scenes in UMN dataset are employed in the experiment. The results show that the proposed method is effective in characterizing anomalies in videos.

Atomistic Insights into FeF3 Nanosheet: An Ultrahigh-Rate and Long-Life Cathode Material for Li-Ion Batteries.

Iron fluoride with high operating voltage and theoretical energy density has been proposed as a high-performance cathode material for Li-ion batteries. However, the inertness of pristine bulk FeF3 results in poor Li kinetics and cycling life. Developing nanosheet-based electrode materials is a feasible strategy to solve these problems. Herein, on the basis of first-principles calculations, first the stability of FeF3 (012) nanosheet with different atomic terminations under different environmental conditions was systematically studied, then the Li-ion adsorption and diffusion kinetics were thoroughly probed, and finally the voltages for different Li concentrations were given. We found that F-terminated nanosheet is energetically favorable in a wide range of chemical potential, which provide a vehicle for lithium ion diffusion. Our Li-ion adsorption and diffusion kinetics study revealed that (1) the formation of Li dimer is the most preferred, (2) the Li diffusion energy barrier of Li dimer is lower than isolated Li atom (0.17 eV for Li dimer vs 0.22 eV for Li atom), and (3) the diffusion coefficient of Li is 1.06 × 10-6 cm2·s-1, which is orders of magnitude greater than that of Li diffusion in bulk FeF3 (10-13-10-11 cm2·s-1). Thus, FeF3 nanosheet can act as an ultrahigh-rate cathode material for Li-ion batteries. More importantly, the calculated voltage and specific capacity of Li on the FeF3 (012) nanosheet demonstrate that it has a much more stable voltage profile than bulk FeF3 for a wide range of Li concentration. So, few layers FeF3 nanosheet provides the desired long-life energy density in Li-ion batteries. These above findings in the current study shed new light on the design of ultrahigh-rate and long-life FeF3 cathode material for Li-ion batteries.

Robust half-metallic ferromagnetism and curvature dependent magnetic coupling in fluorinated boron nitride nanotubes.

The fluorinated boron nitride (F-BN) nanostructures are found to be fully spin polarized and half-metallic by means of first-principles calculations based on the Heyd-Scuseria-Ernzerhof hybrid functional. It is found that the full spin polarization and 1 µB local moment in F-BN nanotubes are independent of tube radius and it is also robust in planar ribbons and sheets. The long-ranged ferromagnetic coupling between local moments decreases with decreasing tube radius. This suggests that F-BN systems with small local curvatures could be more easily experimentally observed and have greater potential applications in spin devices.

Strain tuning of the charge density wave in monolayer and bilayer 1T-TaS2.

Using first-principles calculations, we investigate the strain effects on the charge density wave states of monolayer and bilayer 1T-TaS2. The modified stability of the charge density wave in the monolayer is understood in terms of the strain dependent electron localization, which determines the distortion amplitude. On the other hand, in the bilayer, the effect of strain on the interlayer interaction is also crucial. The rich phase diagram under strain opens new venues for applications of 1T-TaS2. We interpret the experimentally observed insulating state of bulk 1T-TaS2 as inherited from the monolayer by effective interlayer decoupling.

Exploring Molecules beyond CO as Tip Functionalizations in High-Resolution Noncontact Atomic Force Microscopy: A First Principles Approach.

Atomic resolution of molecules has been achieved using noncontact atomic force microscopy (AFM) with the key step to functionalize the tip apex by attaching suitable molecules so as to achieve high spatial resolution through a sharper tip. A few molecular terminations have been explored theoretically and experimentally, and they exhibit various imaging behaviors. Here, we explore the influence of the structures and chemical compositions of various molecular candidates as tips on the contrast of AFM images by a first principles approach. Our results reveal that the two end atoms of a linear molecule terminating nearest the sample dominate the imaging behaviors, for example, atomic resolution, sharpness, distortion, and so forth, whereas the symmetry of the termination plays an important role in the distortion of AFM images. These findings suggest that new tip terminations can be engineered by decoupling the three end atoms responsible for imaging behaviors from the tip structure behind them, which is attached to the macro tip apex.

RB Particle Filter Time Synchronization Algorithm Based on the DPM Model.

Time synchronization is essential for node localization, target tracking, data fusion, and various other Wireless Sensor Network (WSN) applications. To improve the estimation accuracy of continuous clock offset and skew of mobile nodes in WSNs, we propose a novel time synchronization algorithm, the Rao-Blackwellised (RB) particle filter time synchronization algorithm based on the Dirichlet process mixture (DPM) model. In a state-space equation with a linear substructure, state variables are divided into linear and non-linear variables by the RB particle filter algorithm. These two variables can be estimated using Kalman filter and particle filter, respectively, which improves the computational efficiency more so than if only the particle filter was used. In addition, the DPM model is used to describe the distribution of non-deterministic delays and to automatically adjust the number of Gaussian mixture model components based on the observational data. This improves the estimation accuracy of clock offset and skew, which allows achieving the time synchronization. The time synchronization performance of this algorithm is also validated by computer simulations and experimental measurements. The results show that the proposed algorithm has a higher time synchronization precision than traditional time synchronization algorithms.

How strain affects the reactivity of surface metal oxide catalysts.

Highly dispersed molybdenum oxide supported on mesoporous silica SBA-15 has been prepared by anion exchange resulting in a series of catalysts with changing Mo densities (0.2-2.5 Mo atoms nm(-2) ). X-ray absorption, UV/Vis, Raman, and IR spectroscopy indicate that doubly anchored tetrahedral dioxo MoO4 units are the major surface species at all loadings. Higher reducibility at loadings close to the monolayer measured by temperature-programmed reduction and a steep increase in the catalytic activity observed in metathesis of propene and oxidative dehydrogenation of propane at 8 % of Mo loading are attributed to frustration of Mo oxide surface species and lateral interactions. Based on DFT calculations, NEXAFS spectra at the O-K-edge at high Mo loadings are explained by distorted MoO4 complexes. Limited availability of anchor silanol groups at high loadings forces the MoO4 groups to form more strained configurations. The occurrence of strain is linked to the increase in reactivity.

[Analysis on the degradation of optical properties of high power white LED].

One watt white light emitting diodes (LEDs) were made by GaN-based blue light chips. The chips were coated by YAG phosphor and transparent silica gel. Current of 900 mA as electrical stress was carried on the LED samples and the optical properties of the samples were observed by measuring the main optical parameters during the aging test. After 4 200 hours of aging, the luminous flux rate of LEDs declined by a factor between 15% and 18%. Changes in I-V curves indicated the increase in leakage current, which were caused by the increase in defect density. Radiant flux of the blue light drawn from the spectrogram didn't decrease while the yellow light decreased obviously, which implies the degradation of conversion efficiency of YAG phosphor. Reasons for the increase in color temperature and keeping constant in color rendering index (CRI) were theoretically analyzed. The results of the experiment will provide a reference to the illumination applications of the high power white LED.

Prospects for resolving chemical structure by atomic force microscopy: a first-principles study.

In a recent paper, the chemical structure of a molecule was resolved by means of atomic force microscopy (AFM): using a metal tip terminated in a CO molecule, the authors could image the internal bonding arrangement of a pentacene molecule with remarkable spatial resolution (notably better than with other tip terminations), as verified by their first-principles calculations. Here we further explore with first-principles calculations the mechanisms, applicability, and capabilities of this approach for a wider range of situations, by varying the imaged molecule and the tip beyond the experimental cases. In our simulations, a high atomic resolution is found to be dominated by the electronic structure of the last two atoms on the tip apex which are set perpendicularly to the sample molecule. For example, tips terminated in CH(4) or pentacene itself (both having a C-H apex) yield similar images, while tips terminated in O(2) or CO give quite different images. While using a CO-terminated tip successfully resolves the chemical structure of pentacene and of other extended planar networks based on C(6) rings, this tip fails to resolve the structures of benzene (with its single C(6) ring) or nonplanar C(6) networks, such as C(60) or small-diameter carbon nanotubes. Defects (such as N substitution for a C-H group) were also found to significantly influence the image resolution. Our findings indicate that further application of this approach requires, for each sample, careful selection of a suitable "imaging" molecule as tip termination.