Yttria stabilised zirconia (YSZ) membranes and their applications

1 Abstract The development of ceramic hollow-fibre membranes has gradually grown in the past decade. This specific geometry which has a high surface area per unit volume can dramatically increase the efficiency of separation processes and can be adapted to a variety of industrial applications. In addition, ceramic membranes are well known for their superior chemical and thermal stability which allows them to operate at high temperatures and/or in chemically harsh environments. Nevertheless, the main challenge for their industrial application is their insufficient mechanical strength. Yttria-stabilized zirconia (YSZ) is selected as a membrane material in this study. This is because the material has superior mechanical strength and it is relatively cheaper than other ceramic materials. The ionic conducting property of YSZ material is also a benefit when it is used in electrochemical applications. Porous and dense YSZ hollow-fibre membranes have been developed in the study using a combined phase inversion and sintering process. Different membrane morphologies, surface properties, mechanical strength and porosity could be achieved by controlling the YSZ content and sintering temperature. The developed YSZ hollow-fibre membranes with porous or dense structures show great potential for a variety of applications. Porous YSZ hollow-fibre membranes can be used as membrane contactors in aqueous media or for fluid separations in harsh environments, which most polymeric membranes cannot withstand. For the application of membrane contactors in aqueous media, the nature of the YSZ membranes must be modified from hydrophilic to hydrophobic in order to keep them non-wetted during the aqueous contacting processes. A robust and hydrophobic YSZ hollow-fibre membrane was developed by introducing a pretreatment technique, followed by a grafting procedure. The hydrophobic YSZ membrane was found to be thermally stable up to 270 °C and chemically stable in hexane for 100 h. This membrane was then applied to the absorption of carbon dioxide from a high concentration aqueous ethanolamine solution. The results demonstrated the high efficiency of the ceramic hollow-fibre membrane contactor compared to traditional devices. Dense YSZ hollow-fibre membranes with outer diameters of 1.28 mm have been used as an electrolyte support in a solid oxide fuel cell. The YSZ electrolyte-supported SOFC was prepared at relatively lower sintering temperatures and shorter sintering durations. The YSZ-based hollow fibre SOFC demonstrated its ionic stability in a redox environment and mechanical stability at temperatures up to 800 °C. The results also demonstrated its electrochemical performance at high temperature. In summary, this thesis focuses on the development of YSZ hollow-fibre membranes from the initial step of fabricating the membrane to the final step of their potential application. Different structures of YSZ hollow-fibre membranes were studied, discussed and their potential performance was compared to the achievements of others in order to gain more understanding and information on the use of the membranes for practical applications

Dynamically generated flat-band phases in optical kagome lattices

Motivated by recent advances in the realization of complex two-dimensional optical lattices, we investigate theoretically the quantum transport of ultracold fermions in an optical kagome lattice. In particular, we focus on its extensively degenerate localized states (flat band). By loading fermions in a partial region of the lattice and depleting the mobile atoms at the far boundary of the initially unoccupied region, we find a dynamically generated flat-band insulator, which is also a population-inverted state. We further show that inclusion of weak repulsion leads to a dynamical stripe phase for two-component fermions in a similar setup. Finally, by preparing a topological insulating state in a partially occupied kagome lattice, we find that the topological chiral current decays but exhibits an interesting oscillating dynamics during the nonequilibrium transport. Given the broad variety of lattice geometries supporting localized or topological states, our work suggests new possibilities to use geometrical effects and their dynamics in atomtronic devices.Comment: 5 pages, 5 figure

Effect of rollover risk on default risk: evidence from bank financing

We study the effect of rollover risk on the risk of default using a comprehensive database of U.S. industrial firms during 1986–2013. Dependence on bank financing is the key driver of the impact of rollover risk on default risk. Default risk and rollover risk present a significant positive relation in firms dependent on bank financing. In contrast, rollover risk is uncorrelated with default probability in the case of firms that do not rely on bank financing. Our measure of rollover risk is the amount of long-term debt maturing in one year, weighted by total assets. In the case of a firm that depends on bank financing, an increase of one standard deviation in this measure leads to a significant increase of 3.2% in its default probability within one year. Other drivers affecting the interaction between rollover risk and default risk are whether a firm suffers from declining profitability and has poor credit. Additionally, rollover risk's impact on default probability is stronger during periods when credit market conditions are tighter

The Emergent Landscape of Detecting EGFR Mutations Using Circulating Tumor DNA in Lung Cancer.

The advances in targeted therapies for lung cancer are based on the evaluation of specific gene mutations especially the epidermal growth factor receptor (EGFR). The assays largely depend on the acquisition of tumor tissue via biopsy before the initiation of therapy or after the onset of acquired resistance. However, the limitations of tissue biopsy including tumor heterogeneity and insufficient tissues for molecular testing are impotent clinical obstacles for mutation analysis and lung cancer treatment. Due to the invasive procedure of tissue biopsy and the progressive development of drug-resistant EGFR mutations, the effective initial detection and continuous monitoring of EGFR mutations are still unmet requirements. Circulating tumor DNA (ctDNA) detection is a promising biomarker for noninvasive assessment of cancer burden. Recent advancement of sensitive techniques in detecting EGFR mutations using ctDNA enables a broad range of clinical applications, including early detection of disease, prediction of treatment responses, and disease progression. This review not only introduces the biology and clinical implementations of ctDNA but also includes the updating information of recent advancement of techniques for detecting EGFR mutation using ctDNA in lung cancer

Inverse Problem of an Embedded Metallic Cylinder

[[abstract]]In this paper we address an inverse scattering problem whose aim is to discuss the CPU time for recovering a perfectly conducting cylindrical object buried in a slab medium. First, we use Fourier-series or cubic- spline methods to describe the shape and reformulate the inverse problem into an optimization one. Then we solved it by the improved steady state genetic algorithm (SSGA) with different crossover rate and simple genetic algorithm (SGA) respectively and compare the cost time in finding out the global extreme solution of the objective function. It is found the searching ability of SSGA is much powerful than that of the SGA. Numerical results are given to show that the imaging problem by using SSGA is much better than SGA in time costing.[[conferencetype]]國際[[conferencedate]]20070625~20070630[[conferencelocation]]Kharkov, Ukrain

Cubic-spline expansion for a two-dimensional periodic conductor in free space

[[abstract]]This paper presents a computational approach to the imaging of a two-dimensional periodic conductor. Both cubic-spline method and trigonometric series for shape description are used and compared. A periodic conducting cylinder with unknown shape in free space and the scattered field is recorded outside. Based on the boundary condition and the recorded scattered field, a set of nonlinear integral equations is derived and the imaging problem is reformulated into an optimization problem. The genetic algorithm is employed to find out the global extreme solution of the object function. It is found that the shape described by cubic-spline can be reconstructed. In such a case, Fourier series expansion will fail. Even when the initial guess is far away from the exact one, the cubic-spline expansion and genetic algorithm can avoid the local extreme and converge to a global extreme solution. Numerical results are given to show that the shape description by using cubic-spline method is much better than that by the Fourier series. In addition, the effect of Gaussian noise on the reconstruction is investigated.[[notice]]補正完畢[[journaltype]]國外[[incitationindex]]SCI[[incitationindex]]EI[[booktype]]紙本[[countrycodes]]NL

Inverse scattering for shape and conductivity

[[abstract]]We consider the inverse problem of determining both the shape and the conductivity of a two-dimensional conducting scatterer from a knowledge of the far-field pattern of TM waves by solving the ill posed nonlinear equation. Based on the boundary condition and the measured scattered field, a set of nonlinear integral equations is derived and the imaging problem is reformulated into an optimization problem. Satisfactory reconstructions have been achieved by the genetic algorithm. Numerical results demonstrated that, even when the initial guess is far away from the exact one, good reconstruction has been obtained. Numerical results show that multiple incident directions permit good reconstruction of shape and conductivity.[[conferencetype]]國際[[conferencedate]]20031028~20031101[[conferencelocation]]Beijing, Chin