GaN Electronics for High-Temperature Applications

Gallium nitride is a promising candidate for harsh environment electronics, thanks to its excellent material properties, which have given rise to high-performance (room temperature) transistors for RF, power, MEMS, and mixed-signal applications. Previous works on high-temperature (HT) electronics have been typically limited to two aspects, namely, the high-temperature robustness of discrete transistors and basic circuit building blocks, which are mainly combinational logic. While these studies offer a strong indication of the potential of GaN transistor technology for HT applications, the development of HT (500 °C) GaN-ICs is still at its early stage due to the low degree of complexity and integration demonstrated so far. Major challenges in the realization of GaN HT-robust sequential logic circuits or more complex systems is the lack of a scalable technology. This thesis aims to advance the integration technology of GaN HT electronics by demonstrating a comprehensive HT (500°C) enhancement-mode (E-mode) GaN-on-Si technology from device to circuit perspectives: (1) a scalable device technology based on p-GaN-gate AlGaN/GaN HEMTs with high uniformity, which is optimized for HT operation and demonstrated to offer robust performance at least up to 500 °C with the help of in-house developed packaging technology and characterization platform, (2) compact modeling of monolithically integrated enhancement/depletion-mode HEMTs up to 500 °C HEMTs, (3) robustness-driven circuit design based on GaN technology, (4) demonstration of GaN-based combinational and sequential building blocks including inverter, NAND, NOR, ring oscillators, ROM, SRAM, D Latch, D Flip-Flop operational up to 500 °C.Ph.D

A New Multi-Objective Comprehensive Optimization Model for Homogeneous Slope Reinforced by Anti-Slide Piles: Insights from Numerical Simulation

AbstractLandslides have posed a huge threat to the ecological environment and human society all over the world. As the most conventional reinforcement method, anti-slide piles are widely used in the reinforcement of slopes. Currently, more and more attention has been paid to the low-cost and high-efficiency optimal design of anti-slide piles. However, limitations in the method of the optimization design for slopes reinforced with piles still exist. In this paper, a new multi-objective comprehensive optimization method was proposed for the optimization of the slope reinforced with anti-slide piles. The factor of safety, internal force, and deflection of piles were selected as the optimization indexes, and the optimization index weight was determined by integrating the subjective and objective weights. The influence of pile locations, pile lengths, and pile spacings on the reinforcement effect of a homogeneous slope was analyzed via the numerical simulation. Through the simulation case analysis, the proposed model had achieved good effects on the optimization design of anti-slide piles, which could effectively reduce the engineering costs. The optimization results showed that the best reinforcement effect for the homogeneous slope could be obtained when the anti-slide piles with the critical pile length and small pile spacing were located in the middle of the slope. This provides a new solution for the optimization design of other types of complex slopes and has broad application prospects

MPHM: Model poisoning attacks on federal learning using historical information momentum

Federated learning(FL) development has grown increasingly strong with the increased emphasis on data for individuals and industry. Federated learning allows individual participants to jointly train a global model without sharing local data, which significantly enhances data privacy. However, federated learning is vulnerable to poisoning attacks by malicious participants. Since federated learning does not have access to the participants’ training process, i.e., attackers can compromise the global model by uploading elaborate malicious local updates to the server under the guise of normal participants. Current model poisoning attacks usually add small perturbations to the local model after it is trained to craft harmful local updates and the attacker finds the appropriate perturbation size to bypass robust detection methods and corrupt the global model as much as possible. In contrast, we propose a novel model poisoning attack based on the momentum of history information (MPHM), that is, the attacker makes new malicious updates by dynamically crafting perturbations using the historical information in the local training, which will make the new malicious updates more effective and stealthy. Our attack aims to indiscriminately reduce the testing accuracy of the global model with minimal information. Experiments show that in the classical defense case, our attack can significantly corrupt the accuracy of the global model compared to other advanced poisoning attacks

3D super-resolution deep-tissue imaging in living mice.

Stimulated emission depletion (STED) microscopy enables the three-dimensional (3D) visualization of dynamic nanoscale structures in living cells, offering unique insights into their organization. However, 3D-STED imaging deep inside biological tissue is obstructed by optical aberrations and light scattering. We present a STED system that overcomes these challenges. Through the combination of two-photon excitation, adaptive optics, red-emitting organic dyes, and a long-working-distance water-immersion objective lens, our system achieves aberration-corrected 3D super-resolution imaging, which we demonstrate 164 µm deep in fixed mouse brain tissue and 76 µm deep in the brain of a living mouse

Spatial distribution of tuberculosis and its association with meteorological factors in mainland China

BACKGROUND: The incidence of tuberculosis (TB) remains high worldwide. Current strategies will not eradicate TB by 2035; instead, by 2182 is more likely. Therefore, it is urgent that new risk factors be identified. METHODS: An ecological study was conducted in 340 prefectures in China from 2005 to 2015. The spatial distribution of TB incidence was shown by clustering and hotspot analysis. The relationship between the distribution patterns and six meteorological factors was evaluated by the geographically weighted regression (GWR) model. RESULTS: During the 11 years of the study period, TB incidence was persistently low in the east and high in the west. Local coefficients from the GWR model showed a positive correlation between TB incidence and yearly average rainfall (AR) but a negative correlation with other meteorological factors. Average relative humidity (ARH) was negatively correlated with the incidence of TB in all prefectures (p \u3c 0.05). CONCLUSION: Meteorological factors may play an important role in the prevention and control of TB

UHRF1 is required for basal stem cell proliferation in response to airway injury

Cellular senescence is a cell fate characterized by an irreversible cell cycle arrest, but the molecular mechanism underlying this senescence hallmark remains poorly understood. Through an unbiased search for novel senescence regulators in airway basal cells, we discovered that the epigenetic regulator ubiquitin-like with PHD and ring finger domain-containing protein 1 (UHRF1) is critical for regulating cell cycle progression. Upon injury, basal cells in the mouse airway rapidly induce the expression of UHRF1 in order to stimulate stem cell proliferation and tissue repair. Targeted depletion of Uhrf1 specifically in airway basal cells causes a profound defect in cell cycle progression. Consistently, cultured primary human basal cells lacking UHRF1 do not exhibit cell death or differentiation phenotypes but undergo a spontaneous program of senescence. Mechanistically, UHRF1 loss induces G1 cell cycle arrest by abrogating DNA replication factory formation as evidenced by loss of proliferating cell nuclear antigen (PCNA) puncta and an inability to enter the first cell cycle. This proliferation defect is partially mediated by the p15 pathway. Overall, our study provides the first evidence of an indispensable role of UHRF1 in somatic stem cells proliferation during the process of airway regeneration

Intra-tumoural heterogeneity characterization through texture and colour analysis for differentiation of non-small cell lung carcinoma subtypes

Radiomics has shown potential in disease diagnosis, but its feasibility for non-small cell lung carcinoma (NSCLC) subtype classification is unclear. This study aims to explore the diagnosis value of texture and colour features from positron emission tomography computed tomography (PET-CT) images in differentiation of NSCLC subtypes: adenocarcinoma (ADC) and squamous cell carcinoma (SqCC). Two patient cohorts were retrospectively collected into a dataset of 341 18F-labeled 2-deoxy-2fluoro-d-glucose ([18F] FDG) PET-CT images of NSCLC tumours (125 ADC, 174 SqCC, and 42 cases with unknown subtype). Quantification of texture and colour features was performed using freehand regions of interest. The relation between extracted features and commonly used parameters such as age, gender, tumour size, and standard uptake value (SUVmax) was explored. To classify NSCLC subtypes, support vector machine algorithm was applied on these features and the classification performance was evaluated by receiver operating characteristic curve analysis. There was a significant difference between ADC and SqCC subtypes in texture and colour features (P  <  0.05); this showed that imaging features were significantly correlated to both SUVmax and tumour diameter (P  <  0.05). When evaluating classification performance, features combining texture and colour showed an AUC of 0.89 (95% CI, 0.78–1.00), colour features showed an AUC of 0.85 (95% CI, 0.71–0.99), and texture features showed an AUC of 0.68 (95% CI, 0.48–0.88). DeLong's test showed that AUC was higher for features combining texture and colour than that for texture features only (P  =  0.010), but not significantly different from that for colour features only (P  =  0.328). HSV colour features showed a similar performance to RGB colour features (P  =  0.473). The colour features are promising in the refinement of NSCLC subtype differentiation, and features combining texture and colour of PET-CT images could result in better classification performance

Safety, tolerability, pharmacokinetics, and pharmacodynamics of single and multiple doses of aficamten in healthy Chinese participants: a randomized, double-blind, placebo-controlled, phase 1 study

Objectives: Aficamten is a selective, small-molecule allosteric inhibitor of cardiac sarcomere being developed as a chronic oral treatment for patients with symptomatic obstructive hypertrophic cardiomyopathy. This was the first-in-Chinese study aiming to investigate the safety, tolerability, pharmacokinetics, and pharmacodynamics of aficamten in healthy adults.Methods: This double-blind, randomized, placebo-controlled, phase 1 study was conducted in 28 healthy male and female Chinese participants after single ascending dose (SAD) and multi-dose (MD) administrations of aficamten. In the SAD cohort, 16 participants were randomized to receive a single oral dose of aficamten: 10 mg, 20 mg, or placebo. In the MD cohort, 12 participants were randomized to receive multiple doses of aficamten: 5 mg or placebo once daily for 14 days. Safety was monitored throughout the study with electrocardiograms, echocardiograms, clinical laboratory tests, and reporting of adverse events (AEs). Pharmacokinetic profiles of aficamten and metabolites, as well as CYP2D6 genetic impact, were evaluated.Results: A total of 35 treatment-emergent AEs were reported by 14 (50%) participants with mild severity. There were no serious AEs or adverse decreases in left ventricular ejection fraction below 50% during the study. Aficamten was dose-proportional over the dose range of 5–20 mg and accumulated in the MD cohort.Conclusion: Aficamten was safe and well-tolerated in the healthy Chinese adult participants. The pharmacokinetics of aficamten in the Chinese population was comparable to those previously found in Western participants. These phase 1 data support the progression of aficamten into future clinical studies in Chinese patients.Clinical Trial registration:https://clinicaltrials.gov, identifier: NCT04783766

Gallium nitride electronics for high-temperature applications

Thesis: S.M., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, February, 2020Cataloged from PDF version of thesis.Includes bibliographical references (pages 95-100).Gallium nitride is a promising candidate for high-temperature applications. However, despite the excellent performance shown by early high-temperature prototypes, several issues in traditional lateral AlGaN/GaN HEMTs could cause early degradation and failure under high-temperature operation (over 300°C). These include ohmic degradation, gate leakage, buffer leakage, and poor passivation. Besides, enhancement-mode HEMTs are preferred from the application point of view by reducing the circuit complexity and cost. At the same time, the two-dimensional electron gas induced by AlGaN/GaN heterostructures makes HEMTs be naturally depletion-mode devices. This thesis aims to demonstrate devices capable of high-temperature operation without extra cooling systems by combing gate injections transistors (GITs) with ion-implanted refractory metal contacts. The Si ion implantation in AlGaN/GaN heterostructures was comprehensively studied here regarding implantation conditions, activation annealing conditions, metallization schemes. A self-aligned gate-first process, together with etch-stop process, was developed and optimized to improve fabrication efficiency and device uniformity for large-scale integration. Basic logic building blocks, including inverters, NAND gate, NOR gate, SRAM, and ring oscillator, have been demonstrated and characterized at both room temperature and high temperature.by Mengyang Yuan.S.M.S.M. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Scienc