Optical Negative Index Metamaterials.

Research of metamaterials focuses on unprecedented optical properties that may be obtained from composite media, and has attracted great attention since the seminal paper “Negative Refraction Makes a Perfect Lens”. The theory underpinning this field treats electromagnetic composites using homogenization and effective medium theory (EMT). This thesis discusses negative index metamaterials (NIMs) that exhibit negative refraction. The results can be summarized as follows: 1. The refractive index and maximum unit cell size of an arbitrary NIM can be determined from its photonic band structure in the zero-loss limit. 2. A unified, quantitative explanation can be given to negative refraction observed in both lossy NIMs and lossless photonic crystals. 3. A near-infrared subwavelength NIM is demonstrated. 4. There is no theoretical basis for constructing a superlens. We first derive a general relationship between the bulk index of an arbitrary NIM and its photonic band structure and a maximum unit cell size in the zero-loss limit. Based on discrete translational symmetry, we generalize Bloch’s theorem to a phase matching condition with a complex transverse wavevector, which provides a unified explanation of negative refraction observed in lossless photonic crystals and lossy NIMs. A near-infrared NIM using paired metallic strips is also designed and fabricated using electron beam lithography. It operates at a wavelength of 1μm, and has a ratio of wavelength to periodicity of 7, to our knowledge the highest yet achieved among experimental optical NIMs. The NIM is characterized by scanning electron and atomic force microscopies. Optical transmission and interferometric measurements are also consistent with a bulk negative index derived from band structure. Finally, a model NIM is designed based on Mie resonances, resulting in an effective medium with ε=µ=-1 after homogenization. EMT predicts that such a material is capable of perfect lensing, but is found to substantially overestimate the range of recoverable evanescent waves due to neglect of the microstructure. This result explains the fact that the perfect lens has not been demonstrated after a decade of experimental effort. This dissertation emphasizes the physical behavior of composites, as well as the importance of microscopic models and experiment in metamaterials research.Ph.D.PhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/89644/1/zhangxh_1.pd

Tracking progress towards universal health coverage for essential health services in China, 2008-2018.

INTRODUCTION: We comprehensively evaluate whether the Chinese Government's goal of ensuring Universal Health Coverage for essential health services has been achieved. METHODS: We used data from the 2008, 2013 and 2018 National Health Services Survey to report on the coverage of a range of Sustainable Development Goals (SDG) indicator 3.8.1. We created per capita household income deciles for urban and rural samples separately. We report time trends in coverage and the slope index (SII) and relative index (RII). RESULTS: Despite much lower levels of income and education, rural populations made as much progress as their urban counterparts for most interventions. Coverage of maternal and child health interventions increased substantially in urban and rural areas, with decreasing rich-poor inequalities except for antenatal care. In rural China, one-fifth women could not access 5 or more antenatal visits. Coverage of 8 or more visits were 34% and 68%, respectively in decile D1 (the poorest) and decile D10 (the richest) (SII 35% (95% CI 22% to 48%)). More than 90% households had access to clean water, but basic sanitation was poor for rural households and the urban poorest, presenting bottom inequality. Effective coverage for non-communicable diseases was low. Medication for hypertension and diabetes were relatively high (>70%). But adequate management, counting in preventive interventions, were much lower and decreased overtime, although inequalities were small in size. Screening of cervical and breast cancer was low in both urban and rural areas, seeing no progress overtime. Cervical cancer screening was only 29% (urban) and 24% (rural) in 2018, presenting persisted top inequalities (SII 25% urban, 14% rural). CONCLUSION: China has made commendable progress in protecting the poorest for basic care. However, the 'leaving no one behind' agenda needs a strategy targeting the entire population rather than only the poorest. Blunt investing in primary healthcare facilities seems neither effective nor efficient

Analysis of Pressure Fluctuation Characteristics of Central Swirl Combustors Based on Empirical Mode Decomposition

In order to study the characteristics of pressure fluctuation during unstable combustion, experimental studies had been conducted on the mechanism model of the swirl combustor and the industrial swirl combustor. The signal of dynamic pressure, heat release rate, and the high-speed flame image in the two combustors were synchronously collected by using dynamic pressure sensors, a photoelectric sensor, and a high-speed camera under normal temperature and pressure. After empirical mode decomposition of the dynamic pressure signal, several intrinsic mode functions were obtained. It was found that the pressure pulsation energy is concentrated in the first three order intrinsic mode function. Through fast Fourier transform spectrum calculation, it was found that the first three order intrinsic mode function pulsation can characterize the changes of heat release rate and air flow pulsation under cold state and flame instability. It showed that the decomposition of the dynamic pressure in the combustor by this method can obtain the main physical processes in its connotation, and provide data processing methods for the induction mechanism of oscillating combustion and combustion diagnosis in an industrial combustor test

Numerical Simulation of Combustion and Emission Characteristics during Gas Turbine Startup Procedure

The annual operation data of an F-class gas turbine generator set revealed that the duration of the startup process accounts for about 8.5% of the whole operation process. The three combustion models of a DLN2.0+ combustor demonstrated higher NOx emissions than the premixed mode under normal load during the startup process. In order to evaluate the scale of NOx emissions at this stage, numerical simulation was carried out for the startup process to discern the NOx emission pattern. Typical simulation conditions for each season were established to calculate the total annual NOx emissions at the initial stage based on operating data. On this basis, the characteristics of NOx emissions influenced by changes in the atmospheric environment were studied in depth. The results of this study provide referential data for evaluating the pollution characteristics and combustion adjustment of a ground gas turbine during startup

Study on Unstable Combustion Characteristics of Model Combustor with Different Swirler Schemes

In this paper, the effect of the swirler scheme on combustion instability is studied. Through the proper orthogonal decomposition (POD) of flame images, Abel inverse transform and other methods, the influence of swirl intensity on the characteristic frequency of combustion instability was emphatically studied. Based on the low order thermoacoustic network (LOTAN) of the combustor, the flame transfer function (FTF) under different swirl schemes was obtained by the optimization method. The experimental results show that the stable combustion equivalence ratio boundary of the system decreases monotonously with the decrease in swirl intensity, while the characteristic frequency of unstable combustion is not monotonous with the swirl intensity (the oscillating frequency of swirler A with the largest swirl intensity is approximately 319 Hz, swirler B is approximately 280 Hz, swirler C with the smallest swirl intensity is approximately 290 Hz). The optimization results of FTF can easily introduce this non monotonic phenomenon. The swirl intensity mainly affects the hysteresis time of the system (the lag time of swirlers A, B and C are 5.98 ms, 6.82 ms and 6.20 ms, respectively), which is mainly caused by affecting the flame structure and convection velocity. At the same time, the FTF obtained by optimization reflects the same trend with the experimental results, and there is no significant difference in value, which proves the rationality of the optimization method. This work emphasizes the importance of FTF for combustion instability analysis

HLA-DQB1*05 subtypes and not DRB1*10:01 mediates risk in anti-IgLON5 disease

Anti-IgLON5 disease is a rare and likely underdiagnosed subtype of autoimmune encephalitis. The disease displays a heterogeneous phenotype that includes sleep, movement, and bulbar-associated dysfunction. Presence of IgLON5-antibodies in CSF/serum, together with a strong association with HLA-DRB1*10:01∼DQB1*05:01, support an autoimmune basis. In this study, a multicentric HLA study of 87 anti-IgLON5 patients revealed a stronger association with HLA-DQ than HLA-DR. Specifically, we identified a predisposing rank-wise association with HLA-DQA1*01:05∼DQB1*05:01, HLA-DQA1*01:01∼DQB1*05:01 and HLA-DQA1*01:04∼DQB1*05:03 in 85% of patients. HLA sequences and binding cores for these three DQ heterodimers were similar, unlike those of linked DRB1 alleles, supporting a causal link to HLA-DQ. This association was further reflected in an increasingly later age of onset across each genotype group, with a delay of up to 11 years, while HLA-DQ-dosage dependent effects were also suggested by reduced risk in the presence of non-predisposing DQ1 alleles. The functional relevance of the observed HLA-DQ molecules was studied with competition binding assays. These proof-of-concept experiments revealed preferential binding of IgLON5 in a post-translationally modified, but not native, state to all three risk-associated HLA-DQ receptors. Further, a deamidated peptide from the Ig2-domain of IgLON5 activated T cells in two patients, compared to one control carrying HLA-DQA1*01:05∼DQB1*05:01. Taken together, these data support a HLA-DQ-mediated T cell response to IgLON5 as a potentially key step in the initiation of autoimmunity in this disease

Early non-neutralizing, afucosylated antibody responses are associated with COVID-19 severity

A damaging inflammatory response is implicated in the pathogenesis of severe coronavirus disease 2019 (COVID-19), but mechanisms contributing to this response are unclear. In two prospective cohorts, early non-neutralizing, afucosylated immunoglobulin G (IgG) antibodies specific to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) were associated with progression from mild to more severe COVID-19. To study the biology of afucosylated IgG immune complexes, we developed an in vivo model that revealed that human IgG-Fc-gamma receptor (FcγR) interactions could regulate inflammation in the lung. Afucosylated IgG immune complexes isolated from patients with COVID-19 induced inflammatory cytokine production and robust infiltration of the lung by immune cells. In contrast to the antibody structures that were associated with disease progression, antibodies that were elicited by messenger RNA SARS-CoV-2 vaccines were highly fucosylated and enriched in sialylation, both modifications that reduce the inflammatory potential of IgG. Vaccine-elicited IgG did not promote an inflammatory lung response. These results show that human IgG-FcγR interactions regulate inflammation in the lung and define distinct lung activities mediated by the IgG that are associated with protection against, or progression to, severe COVID-19