Time domain inverse source problem and fluid-saturated porous media scattering problem

This dissertation applied Corones and Krueger\u27s invariant imbedding and wave splitting techniques to two time domain direct and inverse scattering problems. In the first problem, invariant imbedding and wave splitting are extended to the case of a transient electric source J(t) inside a dispersive or inhomogeneous dielectric slab. Representations of composite transmission operators are obtained. These operators are used to establish a delay Volterra type integral equation, which is used to infer the transient source J(t) from the transmitted field. One analytical frequency-domain example and two numerical time-domain examples are presented. Also, Green\u27s operators that map the source J(t) to the field at an arbitrary observation point are defined and used to determine the internal E field. For the Green\u27s operator kernels, we obtain linear integrodifferential equations with various initial, boundary and jump conditions. In the second problem, representations of reflection and transmission matrix operators are found, and integrodifferential equations for the operator kernels are derived from the Biot system of compressional wave equations for a finite slab of dispersive, dissipative, fluid-saturated porous medium. Some properties of these operator kernels, such as reciprocity relations and the multiple modes of propagation of discontinuities, are discussed. A numerical scheme for solving the inverse problem is described, and specific numerical computations for a half-space direct and inverse scattering problem are presented

Magnetostratigraphy of the Lower Triassic beds from Chaohu(China) and its implications for the Induan–Olenekian stage boundary.

A magnetostratigraphic study was performed on the lower 44 m of the West Pingdingshan section near Chaohu city, (Anhui province, China) in order to provide a magnetic polarity scale for the early Triassic. Data from 295 paleomagnetic samples is integrated with a detailed biostratigraphy and lithostratigraphy. The tilt-corrected mean direction from the West Pingdingshan section, passes the reversal and fold tests. The overall mean direction after tilt correction is D=299.9º, I=18.3º (κ=305.2, α95=1.9, N=19). The inferred paleolatitude of the sampling sites (31.6ºN, 117.8ºE) is about 9.4º, consistent with the stable South China block (SCB), though the declinations indicate some 101o counter-clockwise rotations with respect to the stable SCB since the Early Triassic. Low-field anisotropy of magnetic susceptibility indicates evidence of weak strain. The lower part of the Yinkeng Formation is dominated by reversed polarity, with four normal polarity magnetozones (WP2n to WP5n), with evidence of some thinner (<0.5 m thick) normal magnetozones. The continuous magnetostratigraphy from the Yinkeng Formation, provides additional high-resolution details of the polarity pattern through the later parts of the Induan into the lowest Olenekian. The magnetostratigraphic and biostratigraphic data shows the conodont marker for the base of the Olenekian (first presence of Neospathodus waageni) is shortly prior to the base of normal magnetozone WP5n. This provides a secondary marker for mapping the base of the Olenekian into successions without conodonts. This section provides the only well-integrated study from a Tethyan section across this boundary, but problems remain in definitively relating this boundary into Boreal sections with magnetostratigraphy

Reversible Transition Between Thermodynamically Stable Phases with Low Density of Oxygen Vacancies on SrTiO3_3(110) Surface

The surface reconstruction of SrTiO$_3$(110) is studied with scanning tunneling microscopy and density functional theory (DFT) calculations. The reversible phase transition between (4$\times$1) and (5$\times$1) is controlled by adjusting the surface metal concentration [Sr] or [Ti]. Resolving the atomic structures of the surface, DFT calculations verify that the phase stability changes upon the chemical potential of Sr or Ti. Particularly, the density of oxygen vacancies is low on the thermodynamically stabilized SrTiO$_3$(110) surface.Comment: Accepted by Physical Review Letter

Synthesis of natural porous minerals supported TiO2 nanoparticles and their photocatalytic performance towards Rhodamine B degradation

Natural porous mineral supported (TiO/diatomite) photocatalyst was prepared via a modified sol-gel method using titanium (IV) butoxide (TBOT) and diatomite. The effect of TBOT dosage on adsorption capacity and photocatalytic activity for Rhodamine B (RhB) solution was investigated. The morphology and elemental distribution were determined by scanning electron microscopy with attached energy-dispersive X-ray detector. The porous and crystalline structures were characterized using nitrogen adsorption-desorption and X-ray diffraction techniques, respectively. The prepared TiO/diatomite hybrid catalyst has shown relatively even porous structure and dispersion of TiO over the surface. This suggests that the diatomite matrix prevented the agglomeration of TiO particles. Initially, the surface area and pore volume of the hybrid catalyst were increased by adding TBOT then decreased for dosages higher than 1.0ml. The crystalline size of TiO immobilized on diatomite matrix by sol-gel method was around 20nm. When the experiments were carried out in the absence of diatomite, this value was increased to 33.73nm. The use of diatomite also promoted an increase of the transformation temperature of the crystalline phase anatase to rutile for the TiO. The as-prepared TiO/diatomite composite exhibited high photocatalytic activity (96.0% for 0.5h UV-light irradiation) for the degradation of RhB from wastewater as a result of its unique porous structure and optimum TiO loading. In addition, it can be easily separated from suspension and possess a good durability. This hybrid material holds great promise in the engineering field for the environmental remediation

Advanced Modeling and Design Methodology for Pavements using Plasticity-Based Shakedown Theory

Pavement design is a process intended to find the most economical combination of layer thickness and material type for the pavement, taking into account the properties of the subgrade soil and the traffic to be carried during the service life of the road. The currently prevalent methods of pavement analysis and design, however, are more or less empirical in U.S., which possess the shortcoming that the important type of pavement distress of rutting related to the accumulation of plastic or permanent deformations cannot be effectively considered. This project proposes an exploratory study on the application of the plasticity theory-based shakedown concept to the analysis and design of pavements under repeated loading, with a more realistic incorporation of the roughness impact of the top pavement layer on the dynamic amplification of vehicle loading as well as on the elastic stress responses in the underlying subsoils. Numerical results from the newly developed vehicle-road coupling model show that the total vehicle load amplification factor ranges from 0.88 to 1.16 under different roughness levels and traveling speeds. This indicates the necessity and importance of incorporating the factors of roughness/vehicle speed in the pavement response analysis. Extensive parametric analyses for the shakedown limit show that increases in the pavement cohesion strength and internal friction angle and in the pavement thickness have a positive influence on the calculated shakedown limit value. The analysis results also indicate that there generally exists an optimal Young’s modulus ratio between the pavement and subsoil, for which a maximum shakedown load of the pavement system will be reached. The outcomes of this project on one hand add contributions to the development of a more rational theoretical framework for the pavement design/analysis. On the other hand, the shakedown design approach can prevent the flexible pavement from excessive rutting failure, and hence is of great practical value for prediction/design of the vehicle load, traveling speed, and layer thickness that is required to warrant shakedown state of the pavements (i.e., no excessive rutting) in the long run

Global research characteristics and trends of infection after spinal implant surgery: a bibliometric analysis

Background: With the growing awareness of postoperative infection, increasing focus has been placed on infection after spinal implant surgery (IASIS). This study aimed to explore the development and trends of research regarding IASIS using bibliometric analysis. Methods: Scientific articles on IASIS research published between February 1, 2000, and December 31, 2020 were retrieved from the Web of Science database. Results: A total of 820 publications were included in the bibliometric analysis, with studies originating from 46 countries and 6 languages. Researchers from the United States published the highest number of articles and collaborated closely with researchers in Canada, Germany, and Japan. The author with the most publications was Alexander R. Vaccaro. The journal with the most articles and citations was Spine. Most of the research was performed on risk factors and the incidence of IASIS. Co-occurrence analysis revealed that the most recent research trend was likely related to the management of IASIS and the international consensus meeting. Three clusters of research were identified through a thematic map: diagnosis and treatment of IASIS, scoliosis-related infection, and risk factors and prevention of IASIS. Conclusions: Research on IASIS increasingly grew between 2000 and 2020. Spinal surgeons and institutes from the United States had the highest number of publications and academic impact in this field. Diagnosisrelated problems and multidisciplinary work on IASIS require further attention in the future. Current trends in IASIS are likely associated with IASIS management and the international consensus meeting

Burden of falls attributable to low bone mineral density among people aged 60 years and over in China from 1990 to 2019

ObjectiveFalls in older people have become a major public health, economic and societal problem. Osteoporosis predisposes older adults to high risk of falls, which were the most common outcome attributable to low bone mineral density (LBMD). In this study, we analyze the long-term trends in falls burden attributable to LBMD among people aged 60 years and over from 1990 to 2019, using data from the Global Burden of Diseases, Injuries, and Risk Factors Study 2019 (GBD 2019).MethodsData from GBD 2019 were used to assess the long-term trends in mortality and disability-adjusted life-year (DALY) rates by Joinpoint regression. The age-period-cohort (APC) model was used to evaluate the effects of age, period and cohort on mortality rate of falls attributable to LBMD.ResultsThe mortality and DALYs rates of falls attributable to LBMD among people aged 60 years and over increased from 1990 to 2019, with average annual percentage changes (AAPCs) of 1.74% (95% CI: −1.47 to 2.01%) and 0.99% (95% CI: 0.80–1.19%), respectively. APC analysis revealed that the mortality rate due to LBMD significantly increased among the older people over the age of 75 years. The risk of falls mortality due to LBMD during the period of 1990–2019 initially declined but later elevated. An overall increasing risk for falls death attributable to LBMD was presented across birth cohorts, but in cohorts born after 1930, the upward trend has slowed down. The overall net drift per year attributable to LBMD was above 0. The corresponding results showed that the negative impact of period and cohort effects among males was more pronounced than those among females.ConclusionsFalls attributable to LBMD remain an ongoing health burden in the older people in China, and the mortality has been on the rise from 1990 to 2019, especially among the older people aged 80+ years group. The prevention and treatment of LBMD should be emphasized, especially among males and oldest-old people. Furthermore, there is an urgent need to strengthen the implementation of system-wide, integrated and effective public health policies and other health interventions in China

3-Fluoro-12H-benzimidazo[2,1-b][1,3]benzothia­zin-12-one

In the title compound, C14H7FN2OS, prepared by the reaction of 2-bromo-4-fluoro­benzoyl choride with 2-mercaptobenzimidazole, the four-membered fused-ring system is essentially planar [maximum deviation from the mean plane = 0.035 (2) Å]. The crystal packing is stabilized by weak inter­molecular π–π [minimum ring centroid–centroid separation = 3.509 (7) Å], weak C—F⋯π [F⋯centroid = 3.4464 (17) Å, C—F⋯centroid = 97.72 (11)°] and C—O⋯π [O⋯centroid = 3.5230 (16) and 3.7296 (17) Å, C—O⋯centroid = 86.40 (10) and 86.25 (10)°] inter­actions and weak inter­molecular C—H⋯N hydrogen bonds