Atomic-scale visualisation of fermion-pair condensates in strongly correlated quantum materials

Since its discovery in 1986, high-temperature superconductivity in copper oxides has puzzled researchers. Its intricate phase diagram, which unveils unusual physical properties, is particularly challenging to understand because of its strongly correlated nature. Despite numerous efforts, a consensus on the mechanism that forms electron-pair condensate underpinning the high-temperature superconductivity remains elusive. The research presented in this thesis endeavours to shed new light on the electron-pairing mechanism. In this thesis, I use advanced scanning tunnelling microscopy (STM) techniques to study the mechanisms behind the high-temperature superconductor Bi₂Sr₂CaCu₂O₈₊ₓ (Bi-2212). Chapter 1 presents an introduction to conventional superconductivity which leads to a review of the cuprate superconductivity from both theory and experiment. Chapter 2 is devoted to introducing two novel STM techniques that are instrumental to the scientific findings presented in this thesis. In Chapter 3, I present the development of a next-generation STM, Gemini, that I built and operated during my DPhil. This home-built STM is designed to function at milli-kelvin temperatures with a 14 Tesla superconducting magnet. An in-depth examination of the design details and various testing results are presented. In Chapter 4, using the innovative STM techniques, an experimental discovery of an exotic quantum state in optimally doped Bi-2212 called the nematic pair-density wave (PDW) state is presented. Towards identifying the electron-pairing mechanism in Bi-2212, Chapter 5 first introduces a modern numerical technique called the dynamical mean-field theory (DMFT) that predicts the paring mechanism as the charge-transfer superexchange interaction. Then, this chapter presents an analogue isotope effect experiment that identifies the distance between the Cu atom and its apical O atom as the tuning parameter that alters the pairing strength. The anti-correlation relationship between the charge-transfer energy and the pairing amplitude is established whose slope conforms to the predictions of DMFT, which indicates that the charge-transfer superexchange interaction is key to the electron-pairing mechanism in optimally doped Bi-2212. Lastly, in Chapter 6, I present my recent STM experiments on candidate excitonic insulator 1T-TiSe₂. The results reveal directly the charge-transfer process between the Ti and Se atoms which is responsible for exciton formation. Furthermore, visualisation of the excitonic energy gap reveals a highly heterogeneous spatial pattern inconsistent with a conventional CDW but which indicates strong electron-electron interactions

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

Optimal Dose of Epidural Dexmedetomidine Added to Ropivacaine for Epidural Labor Analgesia: A Pilot Study

Background. Dexmedetomidine combined with local anesthetics can decrease the concentration of epidural ropivacaine. However, the optimal dose of epidural dexmedetomidine combined with ropivacaine for labor analgesia is still uncertain. This study investigated the effect of adding different dose of epidural dexmedetomidine to ropivacaine during epidural labor analgesia. Methods. One hundred women were randomly assigned to one of the four groups (Groups A, B, C, and D received 0.25, 0.5, 0.75, and 1 μg/ml of dexmedetomidine plus 0.1% ropivacaine, resp.). The onset of epidural anesthesia and stages of labor were studied, and pain was assessed using a visual analogue scale (VAS). Hemodynamic parameters and fetal heart rate were monitored. Apgar scores and umbilical artery pH were recorded. The side effects, if any, were recorded also. Results. The addition of 0.25, 0.5, and 0.75 μg/ml of dexmedetomidine to 0.1% ropivacaine provided safe and effective analgesia, but 1 μg/ml of dexmedetomidine resulted in increasing incidence of motor block. The hemodynamic parameters were similar between groups (P>0.05). Side effects in Group D were significantly higher than those in the other three groups (P<0.05). Conclusions. When dexmedetomidine is combined with 0.1% ropivacaine, the optimal concentration of dexmedetomidine is 0.5 μg/ml for epidural labor analgesia (this trial is registered with ChiCTR-OPC-16008548)

Intravenous ondansetron for the prevention of supine hypotensive syndrome during spinal anesthesia for cesarean section: a randomized controlled trial

Background: Supine hypotensive syndrome is a common complication in late pregnancy. This study aims to explore the effects of ondansetron on the prevention of supine hypotensive syndrome during spinal anesthesia for cesarean section.Methods: A total of 80 women undergoing elective cesarean delivery were randomly assigned to two groups (the ondansetron group and the control group), with 40 cases in each group. The ondansetron group received 0.075 mg/kg of ondansetron intravenously 5 min before the induction of spinal anesthesia; the control group was given the same volume of saline solution. The blood pressure and heart rate were measured. Umbilical artery pH was analyzed, and the incidence of nausea and vomiting and vasoconstrictor drug usage were noted.Results: The incidence of supine hypotensive syndrome, nausea and vomiting, and vasoconstrictor drug use were significantly lower in the ondansetron group than the control group (2.5% vs. 20%, p = 0.029; 2.5% vs. 22.5%, p = 0.007; and 5% vs. 22.5%, p = 0.012, respectively). Umbilical artery pH was higher in the ondansetron group than the control group, and statistical significance was observed (7.31 ± 0.03 vs. 7.28 ± 0.04, p = 0.002). The maternal hemodynamic parameters and the neonatal Apgar score were similar between the two groups.Conclusion: Ondansetron can effectively prevent supine hypotensive syndrome, reduce the incidence of nausea, vomiting, and vasoconstrictor drug use, and improve neonatal umbilical arterial pH during spinal anesthesia for cesarean section.Clinical Trial Registration:https://www.chictr.org.cn/, identifier ChiCTR180018756

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

Dose-effect relationship analysis of TCM based on deep Boltzmann machine and partial least squares

A dose-effect relationship analysis of traditional Chinese Medicine (TCM) is crucial to the modernization of TCM. However, due to the complex and nonlinear nature of TCM data, such as multicollinearity, it can be challenging to conduct a dose-effect relationship analysis. Partial least squares can be applied to multicollinearity data, but its internally extracted principal components cannot adequately express the nonlinear characteristics of TCM data. To address this issue, this paper proposes an analytical model based on a deep Boltzmann machine (DBM) and partial least squares. The model uses the DBM to extract nonlinear features from the feature space, replaces the components in partial least squares, and performs a multiple linear regression. Ultimately, this model is suitable for analyzing the dose-effect relationship of TCM. The model was evaluated using experimental data from Ma Xing Shi Gan Decoction and datasets from the UCI Machine Learning Repository. The experimental results demonstrate that the prediction accuracy of the model based on the DBM and partial least squares method is on average 10% higher than that of existing methods

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