Doctor of Philosophy

dissertationThe atmospheric boundary layer (ABL) has been widely investigated due to the complexity of its physical processes and its impact on human life. One of the most challenging yet critical topics in this layer is scalar transport. Many efforts have been dedicated to investigating heat and moisture transport in the ABL using experimental and numerical approaches over the last several decades. However, there are still many knowledge gaps that limit the performance of numerical weather prediction models, in particular over complex terrain. For example, insufficient understanding of near-surface processes has resulted difficulties in parameterizing meteorological variables in numerical models. Hence, the main objective of this work is to gain a better fundamental understanding of flow processes and scalar transport in the surface boundary layer over different types of terrain with the ultimate goal of improving numerical weather forecasting models by developing more accurate surface parameterizations. Three different topics are discussed in this dissertation. The first topic is a study of land-atmosphere interactions over a desert playa to better understand the impacts of spatial and temporal heterogeneity in water availability as part of the short-term hydrologic cycle. High evaporation rates and the exponential decay of these rates are observed following occasional rainfall events. Three main factors explained the fast evaporation observed following rain- fall. The first factor is the existence of a powerful positive feedback mechanisms initialized by rainfall events that leads to increasing volumetric water content, decreasing surface albedo and Bowen ratio, followed by increases in net radiation, and eventually the enhancement of evaporation rates. The second factor is the clay soil texture, which has low permeability and high capacity. The soil property makes more water available near the surface for evaporation. The third factor is the non-negligible nocturnal evaporation rates that are correlated with increasing soil moisture content. Moreover, a higher spatial variability of surface soil moisture and evaporation is observed when the surface is dry. The second topic is articulated around a case study of the mechanisms that modulates the evolution of valley fog. A typical shallow, early-morning, short- lived valley fog is observed in a sheltered alpine valley. This work shows that mountain circulations play a critical role in the formation and development of shallow valley fog by modulating temperature and moisture fields through katabatic flow interactions and gravity waves. In particular, internal gravity waves are shown to modulate fog processes by varying the near-surface temperature within a time period of ≈ 20 min. The purpose of the last topic is to better understand the potential temperature variance budget over three different surfaces, a desert playa (dry lakebed), characterized by a flat surface devoid of vegetation; a vegetated site, characterized by a flat valley floor covered with greasewood vegetation, and a mountain terrain site with a slope angle of 2 -4° and covered by high-elevation vegetation. The analysis reveals the presence of a 5-m layer where the production and dissipation terms of potential temperature variance drop rapidly below this level. Within the 5-m layer, turbulent transport of potential temperature variance acts as a sink term at all sites of interest. The ratio of turbulent transport to production of potential temperature variance remains constant as stability decreases. The imbalance ratio between production and dissipation shows no correlation with the stability conditions

The Relationship between Type 2 Diabetes Mellitus and Related Thyroid Diseases

Type 2 diabetes mellitus (T2DM) has an intersecting underlying pathology with thyroid dysfunction. The literature is punctuated with evidence indicating a contribution of abnormalities of thyroid hormones to type 2 DM. The most probable mechanism leading to T2DM in thyroid dysfunction could be attributed to perturbed genetic expression of a constellation of genes along with physiological aberrations leading to impaired glucose utilization and disposal in muscles, overproduction of hepatic glucose output, and enhanced absorption of splanchnic glucose. These factors contribute to insulin resistance. Insulin resistance is also associated with thyroid dysfunction. Hyper- and hypothyroidism have been associated with insulin resistance which has been reported to be the major cause of impaired glucose metabolism in T2DM. The state-of-art evidence suggests a pivotal role of insulin resistance in underlining the relation between T2DM and thyroid dysfunction. A plethora of preclinical, molecular, and clinical studies have evidenced an undeniable role of thyroid malfunctioning as a comorbid disorder of T2DM. It has been investigated that specifically designed thyroid hormone analogues can be looked upon as the potential therapeutic strategies to alleviate diabetes, obesity, and atherosclerosis. These molecules are in final stages of preclinical and clinical evaluation and may pave the way to unveil a distinct class of drugs to treat metabolic disorders

Performance of electronic dispersion compensator for 10Gb/s multimode fiber links

In high-speed optical links, electronic compensation circuits can be utilized to greatly improve the data transmission performance limited by fiber dispersion. In this paper, we develop a full link model, including multimode fibers, optical/electronics/optical components, clock-and-data recovery and electronic compensation circuits. The performance of various electronic compensation techniques, such as feed-forward equalizer and decision feedback equalizer for optical multimode fiber is investigated and numerically evaluated. Finally, a comparison of the performance of each compensation techniques and a proposal of optimal equalizer circuit implementation, achieving a 10-Gb/s transmission over 1-km standard multimode fiber are presented

Arctic Observations and Numerical Simulations of Surface Wind Effects on Multi-Angle Snowflake Camera Measurements

Ground-based measurements of frozen precipitation are heavily influenced by interactions of surface winds with gauge-shield geometry. The Multi-Angle Snowflake Camera (MASC), which photographs hydrometeors in free-fall from three different angles while simultaneously measuring their fall speed, has been used in the field at multiple midlatitude and polar locations both with and without wind shielding. Here, we present an analysis of Arctic field observations – with and without a Belfort double Alter shield – and compare the results to computational fluid dynamics (CFD) simulations of the airflow and corresponding particle trajectories around the unshielded MASC. MASC-measured fall speeds compare well with Ka-band Atmospheric Radiation Measurement (ARM) Zenith Radar (KAZR) mean Doppler velocities only when winds are light (≤5ms−1) and the MASC is shielded. MASC-measured fall speeds that do not match KAZR-measured velocities tend to fall below a threshold value that increases approximately linearly with wind speed but is generally \u3c0.5ms−1. For those events with wind speeds ≤1.5ms−1, hydrometeors fall with an orientation angle mode of 12° from the horizontal plane, and large, low-density aggregates are as much as 5 times more likely to be observed. Simulations in the absence of a wind shield show a separation of flow at the upstream side of the instrument, with an upward velocity component just above the aperture, which decreases the mean particle fall speed by 55 % (74 %) for a wind speed of 5 m s−1 (10 m s−1). We conclude that accurate MASC observations of the microphysical, orientation, and fall speed characteristics of snow particles require shielding by a double wind fence and restriction of analysis to events where winds are light (≤5ms−1). Hydrometeors do not generally fall in still air, so adjustments to these properties\u27 distributions within natural turbulence remain to be determined

Role of Vitamin D in Cardiometabolic Diseases

Vitamin D deficiency is a highly prevalent condition. Low vitamin D levels have long been associated with bone diseases, such as rickets in children and osteomalacia and osteoporosis in adults. However, it has become apparent in recent years that adequate vitamin D levels are also important for optimal functioning of many organs and tissues throughout the body, including the cardiovascular system. Evolving data indicate that vitamin D deficiency is associated with an increased risk of cardiovascular disease (CVD). Studies have shown that low vitamin D levels are associated with hypertension, diabetes, metabolic syndrome, left ventricular hypertrophy, and chronic vascular inflammation, all of which are risk factors for CVD. This paper reviews the definition and pathophysiology of vitamin D deficiency, clinical evidence linking vitamin D and CVD risk, diabetes and its complications, and metabolic syndrome

The Measurement and Influencing Factors of Total Factor Productivity in the Chinese Rural Distribution Industry

Total factor productivity (TFP) is critical to the sustainable development of the rural distribution industry. Improvements in productivity of the rural distribution industry can promote the high-quality development of the Chinese distribution industry. Studying the characteristics and influencing factors of total factor productivity in regard to the rural distribution industry in China is significant for promoting the transformation and development of the rural distribution industry. This paper uses the DEA–Malmquist Index to measure the total factor productivity (TFP) of the Chinese rural distribution industry and its decomposition index, and uses a panel data model to empirically study its influencing factors. The results show that, from 2008 to 2018, the TFP of the Chinese rural distribution industry showed a trend of rising first and then fluctuating and declining, with an average annual growth rate of 2.93%; the fluctuation direction of the TFP of the rural distribution industry in the eastern and western regions of China is basically the same, which has had a reverse change relationship with the central and northeast regions for many years. The industrial structure, urbanization rate, rural informatization rate, and conditions of the transportation facilities have significant impacts on the TFP of the rural distribution industry, among which the informatization rate has the greatest positive impact

The Impact of Cognitive Heterogeneity on the Behavioral Integration of the R&D Team: The Perspective of Conflict Management

The impact of team heterogeneity on team effectiveness has received extensive attention. The paper aims to explore the mechanism of the effect of cognitive heterogeneity on behavioral integration in R&D teams. Based on the IPO theory, this study proposed six hypotheses about how cognitive heterogeneity directly and indirectly (via team conflict and conflict management) affect behavioral integration in R&D teams. Using data collected from 383 R&D teams in 326 high-tech enterprises in China, we investigated whether the dimensions of team conflict mediate the relationship between cognitive heterogeneity and behavioral integration and whether the dimensions of conflict management regulate the impact of cognitive heterogeneity on behavioral integration. The results show the following: (1) cognitive heterogeneity has a significant negative impact on the behavioral integration of R&D teams. Task conflict and relationship conflict fully mediate the relationship between cognitive heterogeneity and behavioral integration. (2) Cooperative conflict management positively moderates the impact of cognitive heterogeneity on task conflict and the impact of task conflict on team behavioral integration. (3) Avoidance conflict management reversely adjusts the positive impact of cognitive heterogeneity on task conflict and relationship conflict and the negative impact of relationship conflict on team behavioral integration. The research results can provide theoretical guidance to improve the process management of cognitive heterogeneity R&D teams