Bayesian updating for ground surface settlements of shield tunneling

Accurate prediction of ground surface settlements induced by shield construction is of great significance for ensuring the safety of shield construction. This paper proposes a ground surface settlement prediction method for shield tunneling based on Bayesian updating. The sequential observation data during the advance of excavation is utilized to update the key soil parameters, leading to a more accurate settlement prediction for the subsequent excavation stages. Response surfaces are constructed to replace the finite element model as the forward models for higher computational efficiency. A tunnel excavation project in Hangzhou, China, is selected to illustrate the effectiveness of the proposed method. The shield excavation face passes through four soil layers, and two soil parameters (i.e., Young’s modulus and friction angle) of these soil layers are selected as random variables to be updated. The results show that the soil parameters can be effectively updated based on the observation data at multiple points and various excavation stages. The predictions of ground surface settlements are improved by using the updated soil parameters. The prediction accuracy of the proposed method increases as more stages of observation data are sequentially obtained and incorporated

Triplet-sensitization by lead halide perovskite thin films for near-infrared-to-visible upconversion

Lead halide-based perovskite thin films have attracted great attention due to the explosive increase in perovskite solar cell efficiencies. The same optoelectronic properties that make perovskites ideal absorber materials in solar cells are also beneficial in other light-harvesting applications and make them prime candidates as triplet sensitizers in upconversion via triplet-triplet annihilation in rubrene. In this contribution, we take advantage of long carrier lifetimes and carrier diffusion lengths in perovskite thin films, their high absorption cross sections throughout the visible spectrum, as well as the strong spin-orbit coupling owing to the abundance of heavy atoms to sensitize the upconverter rubrene. Employing bulk perovskite thin films as the absorber layer and spin-mixer in inorganic/organic heterojunction upconversion devices allows us to forego the additional tunneling barrier owing from the passivating ligands required for colloidal sensitizers. Our bilayer device exhibits an upconversion efficiency in excess of 3% under 785 nm illumination

Finite element analysis of different fixation methods of screws on absorbable plate for rib fractures

Multiple rib fractures caused by trauma are common injuries and the internal fixation methods of these injuries have been paid more and more attention by surgeons. Absorbable plates and screws are the effective way to treat rib fractures, but there are no reports on which type of screw fixation method is most effective. In this study, finite element analysis was used to study the effects of five different types of screw fixation methods on anterior rib, lateral rib and posterior rib. The finite element model of the ribs was reconstructed from CT images, and the internal pressure (40 kPa) and intercostal force (30 N) on the surfaces of the ribs were simulated accordingly. An intercostal force of 30 N was applied to the upper and lower surfaces of the ribs to simulate the effect of intercostal muscle force. The pressure of 40 kPa was applied to the inner surface of the ribs, and the normal direction was applied to the inner surface of the ribs. The positive direction was considered inspiratory pressure, and the negative direction was considered expiratory pressure. The results indicate the optimal type of screw fixation on the absorbable plate for rib fractures, and provide a basis and reference for clinical application

MODELING AND SIMULATION FOR INTEREST RATE DERIVATIVES UNDER HJM FRAMEWORK

Bachelor'sBACHELOR OF SCIENCE (HONOURS

A study of restructuring in the Chinese petroleum sector

Thesis (M.B.A.)--Massachusetts Institute of Technology, Sloan School of Management, 2002.Includes bibliographical references (leaf 90).China's oil industry has experienced fundamental changes since 1988. China's oil market will be open to foreign companies just a few years after its entry into the WTO in the end of 2001. The three national petroleum companies had been privatized and listed in overseas capital market exchanges during 2000~2001. This thesis reviews the restructuring process at both industry level and company levels. At the industry level, it summarizes what has been done since 1988 by the Chinese government, and how entry into WTO will influence the industry. At the company level, it reviews how the national oil companies were reorganized, restructured, and privatized. The thesis also paints a picture of the current competitive situation in the China oil industry, and explores how the three Chinese oil companies initiated a series of internal re-structurings after their listing in order to achieve a better positioning in the new competition context. The thesis also studies how the companies perform in a changed industry environment. It discusses the learning process that happened on both sides - the companies and the capital markets. It also analysis what impacts the capital markets have had on the three previously state-owned companies.by Mengfei Wu.M.B.A

Infrared-to-visible upconversion in hybrid thin films of colloidal nanocrystals and organic molecules

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Science, 2018Cataloged from PDF version of thesis.Includes bibliographical references (pages 152-163).Photon upconversion is a process where two or more low-energy photons are converted into a single higher-energy photon. Upconversion that turns infrared photons into visible ones is particularly useful, having potential applications in photovoltaics, infrared sensing, and biological imaging. In this thesis, I present a solid-state thin-film device that converts infrared photons with wavelength up to 1.1 [mu]m into visible wavelengths around [lambda] = 610 nm. The device consists of a monolayer of lead sulfide colloidal nanocrystals (NCs) and a thin film of rubrene mixed with emissive DBP molecules. Upconversion is realized via triplet-triplet annihilation (TTA) in rubrene sensitized by the NCs. We demonstrate that compared to the previous all-molecular upconverting systems, the use of inorganic NCs helps extend the excitation wavelength into the infrared and offers simple wavelength tunability.However, a monolayer of NCs has low infrared absorption, severely limiting the upconversion efficiency and necessitating a high excitation intensity. Here, by adding a silver back reflector with an optical spacer to the device structure, we achieve a five-fold increase in the NC absorption due to optical interference effects and an eleven-fold enhancement in the up-converted output. To extend the idea, we further introduce a distributed Bragg reflector at the front of the device. A resonant microcavity is formed with the NCs placed at the peak of a drastically enhanced optical field. The upconversion efficiency is improved by another order of magnitude, with threshold excitation intensity falling to 13 mW/cm² , which is below the available solar flux. At resonance, the device converts (0.06±0.01)% of incident photons at [lambda] = 980 nm into emitted higher-energy photons. In addition, we improve the upconversion efficiency by shortening the surface ligands on NCs.With faster triplet transfer, the upconverting device attains higher intrinsic efficiency, converting (7±l)% of the absorbed photons at [lambda] = 808 nm into higher-energy emissive excitons in rubrene. This thesis demonstrates the feasibility of NC-sensitized infrared-to-visible upconversion in solid thin films under low excitation intensities comparable to the solar flux, and paves the way toward the practical utilization of TTA-based upconversion in photovoltaics, imaging, and sensing technologies.by Mengfei Wu.Ph. D.Ph.D. Massachusetts Institute of Technology, Department of Electrical Engineering and Computer Scienc

On four new species of the orb-weaver spider genus Araneus Clerck, 1757 (Araneae, Araneidae) from southern China

Four new species of Araneus Clerck, 1757 from southern China are described: A. mayanghe Mi & Wang, sp. nov. (♂♀) from Guizhou, A. shiwandashan Mi & Wang, sp. nov. (♂♀) from Guangxi, and A. zhoui Mi & Wang, sp. nov. (♂♀) from Hainan are assigned to the A. sturmi group, and A. fenzhi Mi & Wang, sp. nov. (♂♀) from Hunan, Guizhou and Jiangxi is not assigned to any species group. A new combination is also proposed: Aoaraneus octumaculalus (Han & Zhu, 2010) comb. nov