Using SiGe HBTs for quantum science at deep cryogenic temperatures

The objective of this research is to investigate the feasibility of using BiCMOS technology for these quantum science applications and clear some major roadblocks. The requirement for these applications is detailed, and the research is conducted in a systematic way targeting four important aspects of SiGe HBTs, namely, cryogenic characterizations, device physics, compact modeling, and circuit designs.Ph.D

Magnetic-coupled electronic landscape in bilayer-distorted titanium-based kagome metals

Quantum materials whose atoms are arranged on a lattice of corner-sharing triangles, $\textit{i.e.}$, the kagome lattice, have recently emerged as a captivating platform for investigating exotic correlated and topological electronic phenomena. Here, we combine ultra-low temperature angle-resolved photoemission spectroscopy (ARPES) with scanning tunneling microscopy and density functional theory calculations to reveal the fascinating electronic structure of the bilayer-distorted kagome material $\textit{Ln}$Ti${_3}$Bi${_4}$, where $\textit{Ln}$ stands for Nd and Yb. Distinct from other kagome materials, $\textit{Ln}$Ti${_3}$Bi${_4}$ exhibits two-fold, rather than six-fold, symmetries, stemming from the distorted kagome lattice, which leads to a unique electronic structure. Combining experiment and theory we map out the electronic structure and discover double flat bands as well as multiple van Hove singularities (VHSs), with one VHS exhibiting higher-order characteristics near the Fermi level. Notably, in the magnetic version NdTi${_3}$Bi${_4}$, the ultra-low base temperature ARPES measurements unveil an unconventional band splitting in the band dispersions which is induced by the ferromagnetic ordering. These findings reveal the potential of bilayer-distorted kagome metals $\textit{Ln}$Ti${_3}$Bi${_4}$ as a promising platform for exploring novel emergent phases of matter at the intersection of strong correlation and magnetism

Collector current transport mechanisms in SiGE HBTs operating at cryogenic temperatures

Silicon germanium heterojunction bipolar transistors (SiGe HBTs) have recently gained attention due to their potential for use in quantum computing readout circuits. To serve such applications, which requires low noise, low to medium speed, and low power, it is crucial to understand the transport physics of SiGe HBTs at cryogenic temperatures. This thesis aims to extend the existing transport theories for collector current through theoretical analysis, experimental data, and TCAD simulation. A novel transport mechanism, namely the direct tunneling mechanism, is found to account for a portion of collector current at cryogenic temperatures. A method is proposed to differentiate between direct tunneling and quasi-ballistic transport. With the understanding of collector current and its physics, the impact of technology scaling on future SiGe HBTs are evaluated.M.S

Increased selenium and decreased iron levels in relation to risk of coronary artery disease in patients with diabetes

BackgroundObservational studies have reported inconsistent associations between micronutrient levels and the risk of coronary artery disease (CAD) in diabetic patients. We aim to explore the causal association between genetically predicted concentrations of micronutrients (phosphorus, magnesium, selenium, iron, zinc, and copper) and CAD in patients with diabetes.MethodsSingle nucleotide polymorphisms (SNPs) connected to serum micronutrient levels were extracted from the corresponding published genome-wide association studies (GWASs). Summary-level statistics for CAD in diabetic patients were obtained from a GWAS of 15,666 patients with diabetes. The primary analysis was carried out with the inverse variance weighted approach, and sensitivity analyses using other statistical methods were further employed to assess the robustness of the results.ResultsGenetically predicted selenium level was causally associated with a higher risk of CAD in diabetic patients (odds ratio [OR]: 1.25; 95% confidence interval [CI]: 1.10–1.42; p = 5.01 × 10−4). While, genetically predicted iron concentrations in patients with diabetes were inversely associated with the risk of CAD (OR: 0.82; 95% CI: 0.75–0.90; p = 2.16 × 10−5). The association pattern kept robust in most sensitivity analyses. Nominally significant associations were observed for magnesium and copper with the risk of CAD in patients with diabetes. No consistent evidence was found for the causal associations between phosphorus and zinc levels, and the risk of CAD in patients with diabetes.ConclusionWe provide consistent evidence for the causal effect of increased selenium and decreased iron levels on CAD in patients with diabetes, highlighting the necessity of micronutrient monitoring and application in these patients

Study on the Influence Law of Temperature Profile of Water Injection Well

Due to the lack of knowledge on the influence law of the temperature profile of layered water injection wells, it is still highly challenging to quantitatively diagnose the water injection profile of layered water injection wells using distributed optical fiber temperature sensing (DTS). In this paper, a temperature profile prediction model for layered water injection wells has been developed by considering the micro-thermal effect and non-isothermal reservoir seepage. The influence of various single-factor changes on the temperature profile of layered water injection wells is simulated and analyzed. Orthogonal experiment analysis results demonstrate that the sensitivity of different factors on wellbore temperature from strong to weak is the injection temperature of the water, injection time, water injection rate, wellbore diameter, formation thermal conductivity, wellbore trajectory, and the permeability of injection formations (Tinj＞t＞Qinj＞D＞Kt＞θ＞k). The injection temperature of water, injection time, and water injection rate are the dominant factors affecting the temperature profile of water injection wells. The results of this paper provide a theoretical foundation for the accurate evaluation of the water injection profile and water injection scheme optimization for the layered water injection wells

Inhibition of the PI3K-Akt-mTOR signaling pathway in T lymphocytes in patients with active tuberculosis

Objectives: To investigate PI3K-Akt-mTOR signaling pathway changes and the proliferation of FoxP3+Treg cells in patients with active tuberculosis. Methods: We isolated PBMCs and CD4+CD25+FoxP3+Treg cells from peripheral blood collected from patients with active tuberculosis and healthy controls. We compared the proportion and MFI of PI3K-Akt-mTOR pathway components and PTEN by flow cytometry using specific cell-surface and intracellular markers. Moreover, we detected the specific secretory proteins ESAT-6 and Ag85B, cytokines IL-10, TGF-β1 and IL-35 in serum by ELISA. Results: Compared with healthy controls, the proportions of CD3+Akt+, CD3+p-Akt+, CD3+mTOR+, CD3+p-mTOR+ and CD3+PTEN+ cells, in the T lymphocyte population of patients with active tuberculosis, were decreased (p < 0.05), while CD3+FoxP3+ cells were increased (p = 0.013). Similarly, for CD4+CD25+FoxP3+Treg cells, the proportions of Akt+ cells, p-Akt+ cells, mTOR+ cells, p-mTOR+ cells and PTEN+ cells were decreased (p < 0.05) in patients with active tuberculosis. Compared with healthy controls, the levels of ESAT-6 and Ag85B were higher in patients with active tuberculosis (p < 0.001). Levels of IL-10 and TGF-β1 were higher (p < 0.001), whereas the level of IL-35 was lower (p < 0.001). Conclusion: The PI3K-Akt-mTOR signaling pathway in T lymphocytes and CD4+CD25+FoxP3+Treg cells was inhibited, which could explain why M.tuberculosis can induce FoxP3+Treg cell to expand