In-situ x-ray scattering studies of Ag nano-structures

When metals are synthesized on the nanoscale, new physics can arise in the growth process as quantum confinement of the conduction electrons, known as quantum size effects, can lead to preferred heights of metallic nanoscale islands. Despite a significant amount of prior research, there has been a poor understanding of the growth behavior of the simple noble metal, Ag, on the Si(111)7x7 substrate and researchers have been unable to connect its growth morphology to quantum size effects. This dissertation investigated the growth of Ag on Si(111)7x7, in situ and in ultra-high vacuum, using synchrotron x-ray scattering. Because of the unique ability of this technique to explore the structure of a buried interface on the atomic scale, these studies led to a clear understanding of the role of quantum size effects in the growth behavior of this system. The studies address the epitaxial relationship between Ag and the substrate as well as the transition from the wetting layer to the growth of nanoscale islands. It is found that islands have a minimum thickness of three Ag atomic layers, which is in contrast to the bilayer on top of a wetting layer that has been reported in previous scanning tunneling microscopy studies. Ag islands are found to form after the completion of the Ag/Si(111)7x7 wetting layer and they convert the underlying wetting layer into the FCC structure of the island. The observed preference of the Ag islands is explained by the energy per area of the island, which derives from quantum confinement effects, and its two phase coexistence with the wetting layer. For thicker island heights, it is found that the distribution of island heights refl ect the minimum thickness of three layers. The height fluctuations are observed to exhibit a Poisson-like distribution where only the low heights in the fl uctuation spectrum deviate from a Poisson distribution. A model of the height distribution is presented. Techniques for exploring buried nanoscale vacancy defects in metals using diffuse x-ray scattering were also explored in this dissertation. Strain fields due to nanoscale vacancy clusters located below a surface were explored through analytical modeling of elastic displacements as well from results of accelerated molecular dynamics simulations. A method for numerically calculating diffuse scattering from nanoscale vacancy clusters was also explored. As new technologies continue to exploit thin-film metals on nanoscale dimensions, this investigation provides important new understanding about how metals grow on the nanoscale

Ammonia Nitrogen Pollution Characteristics of Natural Rainfall in Urban Business District in Southern China: A Case Study of Chengdu City

Chengdu city was chosen as the representative of southern cities in China in this work, characteristics of ammonia nitrogen (NH3-N) pollution in natural rainfall were analyzed by measuring the concentration in 15 natural rainfalls from April to September in 2017. The influence of ammonia emission from toilet vent of building on NH3-N pollution in rainfall was investigated, and the variation of total NH3-N pollutants and its influencing factors were expounded. The results showed that the average concentration of NH3-N in first rainfall was the highest, reaching 18.2mg/L, the average concentration of NH3-N in the subsequent 14 rainfalls was between 2.0 and 5.0mg/L, which is higher than Grade V (?2mg/L) of Environmental Quality Standards of Surface Water (GB 3838-2002), and was an important source of NH3-N pollution in water. The concentration of NH3-N in natural rainfalls decreased with the increase of the distance between the sampling point and the toilet vent, indicating that the ammonia discharged from toilet exhaust is a major source of NH3-N pollution in urban atmosphere. The main factors affecting total NH3-N pollutants in natural precipitation include rainfall intensity, rainfall duration and drought days. The total amount of NH3-N pollutants in surface runoff is less than that in natural rainfall

Quantum magnetic properties and metal-to-insulator transition in chemically doped calcium ruthenate perovskite

Ruthenates provide comprehensive platform to study a plethora of novel properties, such as quantum magnetism, superconductivity and magnetic fluctuation mediated metal-insulator transition. In this article, we provide an overview of quantum mechanical phenomenology in calcium ruthenium oxide with varying compositions. While the stochiometric composition of CaRuO$_{3}$ exhibits non-Fermi liquid behavior with quasi-criticality, chemically doped compounds depict prominent signatures of quantum magnetic fluctuations at low temperature that in some cases are argued to mediate in metal-insulator transition. In the case of cobalt doped- CaRuO$_{3}$, an unusual continuum fluctuation is found to persist deep inside the glassy phase of the material. These observations reflect the richness of ruthenate research platform in the study of quantum magnetic phenomena of fundamental importance.Comment: 7 pages, 8 figure

Fast Terahertz 3D Super-Resolution Surface Reconstruction by Variational Model from Limited Low-Resolution Sampling

Integrating with the signal processing, inverse Radon transform, and the variational model, the framework at least saving 83% data acquisition time for fast, smooth three-dimensional (3D) reconstruction from the limited dataset is elucidated in the field of terahertz imaging applications. In hot pursuit, under the viewpoint of discrete geometry, the quantifiable comparison for 3D surfaces by computing the standard deviation of mean curvatures is also proposed to show the reconstructed effectiveness from less input with gaps

Northport 100% Renewable Energy Feasibility Study

Situated in northern Michigan, Northport and Leelanau Township comprise a small community with a significant tourist industry, agricultural presence and natural beauty. A local non-profit, Northport Energy Action Taskforce (NEAT) has articulated a goal to transition their community to 100% locally-generated renewable energy. This feasibility study focused on electricity and included research on the disposition of the community as well as technical analyses of renewable energy systems that would be suitable for attaining the goal. The team created a household survey, followed by resource assessments for wind and solar power, as well as site identification for renewable energy systems. The survey results showed that the community is open to the possibility of increasing the share of renewable energy in the Township, with 71% of respondents expressing support to the initiative. Based on the resource assessment results, we concluded that the resource availability in the location is enough to provide the required electricity to meet the 100% goal. Land availability makes feasible the deployment of large-scale systems needed for the plan. Additional analyses of energy-efficiency potential and energy policies were conducted to inform the development of three scenarios for achieving 100% local renewable energy.Master of ScienceNatural Resources and EnvironmentUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/111054/1/Northport Report_2015.pd

Heavy Metal Emission Characteristics of Urban Road Runoff

Pavement runoff sampling points were set up on the main roads of Chengdu city. Six rainfall-runoff events from July to September in 2017 were sampled by synchronous observation of rainfall, runoff and pollution. The concentration changes of copper, lead, zinc, chromium and cadmium in the runoff process were monitored, and the pollution emission regularity and initial scouring effect were studied. The results show that the emission regularity of pavement runoff pollution is closely related to rainfall characteristics and pollutant occurrence, and the concentration of dissolved heavy metals reaches its peak at the initial stage of runoff. The peak time of particulate heavy metal concentration lagged slightly behind that of rainfall intensity. There is a big difference between the strength of initial scouring degree and dissolved heavy metals the stronger the initial scouring degree of total heavy metals, the weaker the dissolved heavy metals. Reducing pavement runoff in the early stage of rainfall is an effective means to control heavy metal pollution

Super-resolution surface reconstruction from few low-resolution slices

In many imaging applications where segmented features (e.g. blood vessels) are further used for other numerical simulations (e.g. finite element analysis), the obtained surfaces do not have fine resolutions suitable for the task. Increasing the resolution of such surfaces becomes crucial. This paper proposes a new variational model for solving this problem, based on an Euler-Elastica-based regulariser. Further, we propose and implement two numerical algorithms for solving the model, a projected gradient descent method and the alternating direction method of multipliers. Numerical experiments using real-life examples (including two from outputs of another variational model) have been illustrated for effectiveness. The advantages of the new model are shown through quantitative comparisons by the standard deviation of Gaussian curvatures and mean curvatures from the viewpoint of discrete geometry