Short Term Observations of In Vitro Biocorrosion of Two Commonly Used Implant Alloys

Orthopedic metal implant materials may mediate a variety of adverse tissue reactions by releasing ions through corrosion. Adverse tissue reactions include inflammation, fibrosis and hypersensitivity. All of these reactions eventually lead to implant failure. The goal of this study was to provide a better understanding of the cellular-material interaction at the metal surface. The hypotheses were that 1. the attachment of cells and their released reactive inflammatory compounds (e.g. hydrogen peroxide H2O2, superoxide O2. and nitric oxide NO.) on the surfaces alter the alloys? corrosion and surface properties and 2. the changes in corrosion and chemical properties of the surfaces affect cell behavior. To evaluate the hypotheses, a custom-made electrochemical corrosion cell was used to evaluate how cell culture medium, macrophage cells and macrophage cells activated to simulate inflammation affected the corrosion and surface properties of Co-Cr-Mo and Ti-6Al-4V alloys and how released alloy corrosion products affected cell behaviors. The macrophage cell line used was known to produce reactive species H2O2, O2. and NO. when activated by antigen and interferon. The alloy corrosion properties were enhanced by observing the open circuit potential (OCP), charge transfer, metal ion release, and changes in surface oxides. Proliferation, viability and metabolism were used to evaluate effects of corrosion on the cells. The OCP of Co-Cr-Mo remained unchanged whereas that of Ti-6Al-4V increased over three days for all three test conditions. Both alloys cultured with medium had the lowest OCP among all conditions. With activated macrophage cells, both alloys had the lowest total charge transfer and concentrations of metal ion released. This improved corrosion resistance was mostly due to an enhancement of the surface oxide due to the reactive species released from activated cells, as indicated from the surface analyses. Both alloys were found to have increased percentage (in peak intensity) of O and Ti or Cr peaks, which indicated an increase of Ti and Cr oxides on Ti-6Al-4V and Co-Cr-Mo alloys respectively. The improved corrosion properties resulted in less metal ion release than those without enhanced surface oxides, thus alloys did not further activate cell immune responses in the three day period. The non-activated or activated cells with released metal ions did not exhibit any degradation in their viability, intracellular ATP, NO and IL-1b release as compared to controls. This is consistent with the generally accepted good biocompatibility of these alloys

Polarization-independent Liquid Crystal Devices

Liquid crystal (LC) devices can be operated as amplitude modulators and phase modulators. LC amplitude modulation is commonly used in liquid crystal display (LCD) while phase-only modulation is useful for laser beam steering, tunable grating, prism, lens, and other photonic devices. Most LC devices are polarization dependent and require at least one polarizer. As a result, the optical efficiency is low. To enhance display brightness, a power hungry backlight has to be used leading to a high power consumption and short battery life. In a LC phase modulator, the polarization dependent property complicates the laser beam steering system. It is highly desirable to develop new operating mechanisms that are independent of the incident light polarization. In this dissertation, we have developed eight polarization-independent liquid crystal operation principles: three of them are aimed for displays and the other five are for phase modulators. For amplitude modulations, a new polymer-dispersed liquid crystal (PDLC) and two new dye-doped LC gels are polarizer-free by combining light scattering with dye-absorption effects. In phase modulation, we explore five device concepts: PDLC and Polymer-Stabilized Cholesteric Texture (PSCT), homeotropic LC gels, thin polymer film separated double-layered structure, and double-layered LC gels. In the low voltage regime, both PDLC and PSCT have a strong light scattering. However, as the voltage exceeds a certain level, the phase modulation is scattering-free and is independent of polarization. The homeotropic LC gels do not require any biased voltage and the response time is still fast. Although the remaining phase in these devices is small, they are still useful for micro-photonic device applications. To increase the phase change, thin polymer film separated double-layered structure is a solution. The orthogonal arrangement of top and bottom LC directors results in polarization independence. However, the response time is slow. Similarly, double-layered LC gels are not only polarization independent but also fast response due to the established polymer network

A Revisit of the Relation between Central Bank Independence and Inflation

Conventional wisdom argues that the relation between central bank independence (CBI) and inflation is negative. However, empirical studies based upon regressing inflation rates on CBI tend to reject this hypothesis and show that there is no negative relationship. This article investigates the effect of CBI on inflation by quantile regression. The empirical result shows that the relation could be negative or positive for different quantiles of inflation. Quantile regression provides a method for investigating the relation completely between CBI and inflation.Central Bank Independence; Inflation; Quantile Regression.

Causality in Quantiles and Dynamic Stock Return-Volume Relations

This paper investigates the causal relations between stock return and volume based on quantile regressions. We first define Granger non-causality in all quantiles and propose testing non-causality by a sup-Wald test. Such a test is consistent against any deviation from non-causality in distribution, as opposed to the existing tests that check only noncausality in certain moment. This test is readily extended to test non-causality in different quantile ranges, and the testing results enable us to identify the quantile range for which causality is relevant. In the empirical studies of 3 major stock market indices, we find that, while the conventional test suggests no causality in mean, there are strong evidences that lagged volume Granger causes return in all but some middle quantiles. In particular, the causal effects have opposite signs at lower and upper quantiles and are stronger at more extreme quantiles. These relations form (symmetric) V shapes across quantiles. They also show that the dispersion of the return distribution increases with volume so that volume has a positive effect on return volatility. It is also shown that the quantile causal effects of lagged return on volume are mainly negative.Granger non-causality in quantiles, quantile causal effect, quantile regression, return-volume relation, sup-Wald test

A Study on the Growth and Formation of Single Person Households and Their Housing Decisions in Taiwan

The number of single person households has dramatically increased in Taiwan in the past several decades as it has elsewhere in the world, but this phenomenon has been largely neglected in the literature. This research explores the factors that affect the formation of single person households and their housing decisions. Taiwan¡¦s population census data for 1980, 1990 and 2000 are used. Some interesting trends can be found. First of all, people who are married or cohabiting have exhibited an increasing tendency to live alone census by census. This shows the increasing need in a modern society for the husband and wife to live separately due to employment or other reasons. Secondly, unmarried and widowed elderly persons have had an increasing probability of living alone over the decades. Thirdly, the number of female single person households has been increasing rapidly, and there is a higher probability that they are homeowners and also occupying a larger living space than their male counterparts. To sum up, the results of this study show that the demand for housing among single person households will continue to increase as their numbers increase. Their demand for homeownership and living space are also increasing.Single person household formation; Tenure choice; Living space; Binary probit model; Sample selection model

Dealing with Childbirth in Medieval Chinese Buddhism: Discourses and Practices

In Buddhism birth is regarded as the origin of suffering and impurity, whereas it also forms the physical basis indispensible for seeking and attaining awakening. Birth is both the starting points of incuring defilement and achieving sanctity. Pointing out this paradox on birth in Buddhism and situating the issue within the context of Chinese religion and history, this dissertation extensively investigates Buddhist discourses and practices of reproduction in medieval China. It anwsers how Buddhist discourses and practices of childbirth were transmitted, transformed, and applied in medieval China, and how they interacted with indigenous healing resources and practices in both Chinese religious and medical realms. Through examining the primary sources such as the excavated Day Books (Chapter One), Buddhist hagiographies (Chapter Two), Buddhist obstetric and embryological discourses (Chapter Three and Four) and healing resources preserved in Tripiṭaka and Dunhuang manuscripts, Dunhuang transformation texts and tableaux, and miracle tales and anecdote literature (Chapter Four and Five), I argue that not only was there a paradoxical dualism at the heart of Buddhism's relationship with reproduction, but also Buddhism provides abundant healing resources for dealing with childbirth on the practical level. Overall I contend that Buddhist healing resources for childbirth served as an effective channel through which Buddhist teaching, worldview and concepts of gender and body were conveyed to its supplicants. Through this investigation, this dissertation contributes to the understanding of the association of Buddhism with medicine, the influence of Buddhist discourses and practices of reproduction on China, and the transmission of Buddhist views of gender, the body, and life to China through its healing activities related to childbirth

Dispersion Properties of Transport Equations and Applications

The concept of transport is fundamental and has great influence in a wide range of fields across science. This dissertation provides three topics possessing the character of transport phenomena from the perspective of partial differential equations. The three parts include: (1) Commutator method for averaging lemma: A new commutator method is introduced to prove a new type of averaging lemmas, the regularizing effect for the velocity average of solutions for kinetic equations. This novel approach shows a new range of assumptions that are sufficient for the velocity average to be in $L^2([0,T],H^{1/2}_x)$ and improves the regularity result for the measure-valued solutions of scalar conservation laws in space one-dimensional case. (2) Unmixing property of incompressible flows on 2d tori: The local Hamiltonian structure of a 2d torus is utilized to show that the unmixing property of incompressible flows can be preserved under a sup-norm perturbation on stream functions. With this perturbation result, a quantitative statement was provided by considering vector fields in the form of a random Fourier series. This statement offers an interesting observation for the unmixing property from the perspective of Fourier analysis. (3) Memory effect on animal migration: The goal of this work is to obtain a better understanding of the memory effect on the animals' migration patterns under periodic environments. A memory model and a corresponding memory-driven dynamic were constructed. Through simulations, it is discovered that in order to have periodic movement, the individual must be able to gather and carry sufficient information from both short-term memory and long-term memory, and possess the ability to discriminate which information is more important with appropriate time scales. Furthermore, our mathematical model is general and can be used to test the memory effect under different circumstances. Several interesting examples are demonstrated