High photo-excited carrier multiplication by charged InAs dots in AlAs/GaAs/AlAs resonant tunneling diode

We present an approach for the highly sensitive photon detection based on the quantum dots (QDs) operating at temperature of 77K. The detection structure is based on an AlAs/GaAs/AlAs double barrier resonant tunneling diode combined with a layer of self-assembled InAs QDs (QD-RTD). A photon rate of 115 photons per second had induced 10nA photocurrent in this structure, corresponding to the photo-excited carrier multiplication factor of 10^7. This high multiplication factor is achieved by the quantum dot induced memory effect and the resonant tunneling tuning effect of QD-RTD structure.Comment: 10 pages,5 figures. Submitted to Applied Physics Letter

An Integrated Electromechanical Model of the Fixed-Speed Induction Generator for Turbine-Grid Interactions Analysis

When wind turbine is connected to the power grid, the turbine-grid interactions restrict its lifespan and produce adverse effects to the grid. Electrical or mechanical oscillations caused by turbine-grid interactions could gradually be weakened or amplified seriously at a certain frequency. This article discusses all types of interactions between a wind turbine and the grid and the influence of the initial operating point, the parallel capacitor, and the series capacitor on the stability of system. Firstly, an integrated dynamic electromechanical model of a single fixed-speed induction generator (FSIG) wind generation system is derived based on the small signal model of each element. Then, a method of stability analysis based on Kharitonov theorem is introduced. Then, the model details the frequency and damping ratio of oscillation mode and classifies those modes' interactions according to participation factors, followed by time domain simulations by the single FSIG generation system to testify the results. Finally, the article studies all the oscillation modes when the initial operating point, the parallel capacitor, or the series capacitor change in the integrated model, which can be verified by Kharitonov polynomials. The indicative findings help to design the damping control to mitigate turbine-grid interactions.</p

Model transfer from 2D to 3D study for boxing pose estimation

IntroductionBoxing as a sport is growing on Chinese campuses, resulting in a coaching shortage. The human pose estimation technology can be employed to estimate boxing poses and teach interns to relieve the shortage. Currently, 3D cameras can provide more depth information than 2D cameras. It can potentially improve the estimation. However, the input channels are inconsistent between 2D and 3D images, and there is a lack of detailed analysis about the key point location, which indicates the network design for improving the human pose estimation technology.MethodTherefore, a model transfer with channel patching was implemented to solve the problems of channel inconsistency. The differences between the key points were analyzed. Three popular and highly structured 2D models of OpenPose (OP), stacked Hourglass (HG), and High Resolution (HR) networks were employed. Ways of reusing RGB channels were investigated to fill up the depth channel. Then, their performances were investigated to find out the limitations of each network structure.Results and discussionThe results show that model transfer learning by the mean way of RGB channels patching the lacking channel can improve the average accuracies of pose key points from 1 to 20% than without transfer. 3D accuracies are 0.3 to 0.5% higher than 2D baselines. The stacked structure of the network shows better on hip and knee points than the parallel structure, although the parallel design shows much better on the residue points. As a result, the model transfer can practically fulfill boxing pose estimation from 2D to 3D

TMSB4 Overexpression Enhances the Potency of Marrow Mesenchymal Stromal Cells for Myocardial Repair

ObjectiveThe actin-sequestering proteins, thymosin beta-4 (Tβ4) and hypoxia-inducible factor (HIF)-1α, are known to be associated with angiogenesis after myocardial infarction (MI). Herein, we aimed to identify the mechanism of HIF-1α induction by Tβ4 and investigate the effects of bone marrow mesenchymal stromal cells (BMMSCs) transfected with the Tβ4 gene (TMSB4) in a rat model of MI.MethodsRat BMMSCs were isolated, cultured, and transfected with the TMSB4 gene by using the lentivirus-mediated method. Rats with surgically induced MI were randomly divided into three groups (n = 9/group); after 1 week, the rats were injected at the heart infarcted border zone with TMSB4-overexpressed BMMSCs (BMMSC-TMSB4OE), wild-type BMMSCs that expressed normal levels of TMSB4 (BMMSC-TMSB4WT), or medium (MI). The fourth group of animals (n = 9) underwent all surgical procedures necessary for MI induction except for the ligation step (Sham). Four weeks after the injection, heart function was measured using transthoracic echocardiography. Infarct size was calculated by TTC staining, and collagen volume was measured by Masson staining. Angiogenesis in the infarcted heart area was evaluated by CD31 immunofluorescence histochemistry. In vitro experiments were carried out to observe the effect of exogenous Tβ4 on HIF-1α and explore the various possible mechanism(s).ResultsIn vivo experiments showed that vascular density 4 weeks after treatment was about twofold higher in BMMSC-TMSB4OE-treated animals than in BMMSC-TMSB4WT-treated animals (p &lt; 0.05). The cardiac function and infarct size significantly improved in both cell-treatment groups compared to controls. Notably, the cardiac function and infarct size were most prominent in BMMSC-TMSB4OE-treated animals (both p &lt; 0.05). HIF-1α and phosphorylated HIF-1α (p-HIF-1α) in vitro were significantly enhanced by exogenous Tβ4, which was nonetheless blocked by the factor-inhibiting HIF (FIH) promoter (YC-1). The expression of prolyl hydroxylase domain proteins (PHD) was decreased upon treatment with Tβ4 and further decreased with the combined treatment of Tβ4 and FG-4497 (a specific PHD inhibitor).ConclusionTMSB4-transfected BMMSCs might significantly improve recovery from myocardial ischemia and promote the generation of HIF-1α and p-HIF-1α via the AKT pathway, and inhibit the degradation of HIF-1α via the PHD and FIH pathways

Special Metal-Alloy Coating and Catalysis

Special metal alloy coating is an important material technology that has a wide range of applications in many fields [...

An Integrated Electromechanical Model of the Fixed-Speed Induction Generator for Turbine-Grid Interactions Analysis

When wind turbine is connected to the power grid, the turbine-grid interactions restrict its lifespan and produce adverse effects to the grid. Electrical or mechanical oscillations caused by turbine-grid interactions could gradually be weakened or amplified seriously at a certain frequency. This article discusses all types of interactions between a wind turbine and the grid and the influence of the initial operating point, the parallel capacitor, and the series capacitor on the stability of system. Firstly, an integrated dynamic electromechanical model of a single fixed-speed induction generator (FSIG) wind generation system is derived based on the small signal model of each element. Then, a method of stability analysis based on Kharitonov theorem is introduced. Then, the model details the frequency and damping ratio of oscillation mode and classifies those modes' interactions according to participation factors, followed by time domain simulations by the single FSIG generation system to testify the results. Finally, the article studies all the oscillation modes when the initial operating point, the parallel capacitor, or the series capacitor change in the integrated model, which can be verified by Kharitonov polynomials. The indicative findings help to design the damping control to mitigate turbine-grid interactions.</p

Influences of Bath Chemistry and Plating Variables on Characteristics of Electroless Ni–P Films on Si Wafers from Alkaline Citrate Solutions

Electroless nickel–phosphorus (Ni–P) films were produced on the surface of p-type monocrystalline silicon in the alkaline citrate solutions. The influences of bath chemistry and plating variables on the chemical composition, deposition rate, morphology, and thermal stability of electroless Ni–P films on silicon wafers were studied. The as-deposited Ni–P films were almost all medium- and high-P deposits. The concentrations of Ni2+ and citric ions influenced the deposition rate of the films but did not affect P content in the deposits. With increasing H2PO2− content, the P content and deposition rate were steadily increased. The pH and plating temperature had a significant effect on the chemical composition and the deposition rate of the films. The thermal stability of the medium-P film was better than that of the high-P deposit. At the same time, the proposed mechanism of Ni–P films on monocrystalline silicon substrates in the alkaline bath solution was discussed and addressed

Microstructure and Corrosion Resistance of Fusion Welding Zone for Duplextubes Welded with Q345R Tube Sheet under Different Welding Currents

Duplextubes are widely used in oil and gas storage and transportation, the nuclear industry, and other fields, but the welding quality of metals is an important factor affecting the use of equipment. In order to study the welding quality of S10C steel/Incoloy 825 duplextubes and Q345R tube sheet based on gas tungsten arc welding technology with a filler of ER50-6 carbon steel welding wire, the microstructure and grain size of fusion welding zone of duplextubes and tube sheet under welding currents of 150 A, 160 A, and 170 A were studied by optical microscopy and scanning electron microscopy. At the same time, the corrosion behavior of fusion welding zone after the welding was investigated in 3.5 wt.% NaCl solution by potentiodynamic polarization and electrochemical impedance spectroscopy. The results show that the metallurgical structure of the fusion welding zone was mainly composed of δ-ferrite and retained austenite. The grain size in the fusion welding zone increased with the increase of the welding current. The corrosion resistance of the fusion welding zone welded with a high welding current of 170 A was better than that with low welding currents. However, the pitting corrosion resistance of fusion welding zone with the lowest welding current of 150 A was better than that with high welding currents. This study can provide a preliminary exploration for the manufacture and applicability of duplextubes air coolers