Optical Tweezers as a Micromechanical Tool for Studying Defects in 2D Colloidal Crystals

This paper reports on some new results from the analyses of the video microscopy data obtained in a prior experiment on two-dimensional (2D) colloidal crystals. It was reported previously that optical tweezers can be used to create mono- and di-vacancies in a 2D colloidal crystal. Here we report the results on the creation of a vacancy-interstitial pair, as well as tri-vacancies. It is found that the vacancy-interstitial pair can be long-lived, but they do annihilate each other. The behavior of tri-vacancies is most intriguing, as it fluctuates between a configuration of bound pairs of dislocations and that of a locally amorphous state. The relevance of this observation to the issue of the nature of 2D melting is discussed.Comment: 6 pages, 4 figure

Three Essays on Capital Inflows to Emerging Markets

Thesis (Ph.D.)--University of Washington, 2019This dissertation examines the determinants of portfolio inflows to emerging market economies with a special focus on Korea. Chapter 1, "The Determinants of Disaggregated Capital Inflows to Korea", studies the key factors in determining portfolio investment flows to Korea from four separate investment groups: global banks, mutual funds, securities companies, and pension companies. I sort the total portfolio investment flows by each investment group such as global banks, mutual funds, securities companies, and pension companies. The US industrial production index, TED spread, and VIX are included as push factors and the Korean industrial production index, Korean bond rate, Korean stock index, and exchange rate are considered as pull factors. From the structural VAR model with dummy variables, this paper finds that portfolio investment flows to Korea are more affected by push factors during the crisis while they are more dependent on pull factors after the crisis. Portfolio investment flows to the stock market are affected mainly by the domestic stock market and global risk appetite while portfolio investment flows to the bond market react more strongly to US output growth and the domestic interest rate. Finally, this paper finds that the properties of capital inflows from each institution are quite different. For example, securities and mutual funds are more responsive to the stock market index, while insurance and pension companies are more sensitive to domestic output growth. Chapter 2, "The Determinants of Capital Inflows from Each Country", analyzes the determinants of portfolio flows to Korea using portfolio flows from each economy to Korea as the dependent variable. For the empirical model, the investor country factor was added to the existing push-pull approach, and a panel VAR model was used as the estimation method. The results suggest that investor country factors such as shocks on the interest rate and stock market in the investor country are the most important determinants to portfolio flows from advanced economies (AEs) while pull factors of recipient countries mainly drive the portfolio flows from emerging market economies (EMEs). The impact on the stock market is the dominant factor during the Fed's expansionary monetary policy, while the effects of the interest rate are the most important factor after the end of the QE. The results also show that portfolio flows from AEs respond positively to the impact of the investor country's stock market, while those from EMEs respond negatively. This study supports recent findings that the impact of the drivers on the capital flows is dependent on economic conditions and is time-varying. Chapter 3, "The International Spillovers of US Monetary Policy on Capital Flows to Emerging Market Economies", studies the impact of the US Fed's monetary policy on portfolio flows to the emerging economies, differentiating across the investor economies and type of flows. This paper also compares the effects of US monetary policy before and after the end of Quantitative Easing (QE). The results show that equity flows were retrenched to the US and AEs in response to the announcement of QE1 while the total impact of the Quantitative Easing increased the capital inflows to the emerging markets from the advanced economies. This chapter also finds that the response of portfolio flows in response to US monetary policy is conditional on the stance of US monetary policy. The findings build a bridge on the recent controversy over determinants of capital inflows by showing that QE has a significant impact on the capital inflows to EMEs, and its effects are related to the business cycle

Study on Roasting for Selective Lithium Leaching of Cathode Active Materials from Spent Lithium-Ion Batteries

Recently, many studies have been conducted on the materialization of spent batteries. In conventional cases, lithium is recovered from an acidic solution through the leaching and separation of valuable metals; however, it is difficult to remove impurities because lithium is recovered in the last step. Cathode active materials of lithium-ion batteries comprise oxides with lithium, such as LiNixCoyMnzO2 and LiCoO2. Thus, lithium should be converted into a compound that can be leached in deionized water for selective lithium leaching. Recent studies on the leaching and recovery of Li2CO3 through a carbon reduction reaction show low economic efficiency, due to the solubility of Li2CO3 at room temperature being as low as 13 g/L. This paper proposes a method of roasting after nitric acid deposition for selective lithium leaching and recovery to LiNO3. Based on experiments involving the varying of the amount of nitric acid, roasting temperature, and solid–liquid ratio, optimal values were found to be dipping in 10 M HNO3 2 mL/g, roasting at 275 °C, and deionized water with a solid–liquid ratio of 10 mL/g, respectively. Over 80% Li leaching was possible under these conditions. IC analysis confirmed that the purity was 97% lithium nitrate

Multimodal Sensing Capabilities for the Detection of Shunt Failure

Hydrocephalus is a medical condition characterized by the abnormal accumulation of cerebrospinal fluid (CSF) within the cavities of the brain called ventricles. It frequently follows pediatric and adult congenital malformations, stroke, meningitis, aneurysmal rupture, brain tumors, and traumatic brain injury. CSF diversion devices, or shunts, have become the primary therapy for hydrocephalus treatment for nearly 60 years. However, routine treatment complications associated with a shunt device are infection, obstruction, and over drainage. Although some (regrettably, the minority) patients with shunts can go for years without complications, even those lucky few may potentially experience one shunt malfunction; a shunt complication can require emergency intervention. Here, we present a soft, wireless device that monitors distal terminal fluid flow and transmits measurements to a smartphone via a low-power Bluetooth communication when requested. The proposed multimodal sensing device enabled by flow sensors, for measurements of flow rate and electrodes for measurements of resistance in a fluidic chamber, allows precision measurement of CSF flow rate over a long time and under any circumstances caused by unexpected or abnormal events. A universal design compatible with any modern commercial spinal fluid shunt system would enable the widespread use of this technology

Multimodal Sensing Capabilities for the Detection of Shunt Failure

Hydrocephalus is a medical condition characterized by the abnormal accumulation of cerebrospinal fluid (CSF) within the cavities of the brain called ventricles. It frequently follows pediatric and adult congenital malformations, stroke, meningitis, aneurysmal rupture, brain tumors, and traumatic brain injury. CSF diversion devices, or shunts, have become the primary therapy for hydrocephalus treatment for nearly 60 years. However, routine treatment complications associated with a shunt device are infection, obstruction, and over drainage. Although some (regrettably, the minority) patients with shunts can go for years without complications, even those lucky few may potentially experience one shunt malfunction; a shunt complication can require emergency intervention. Here, we present a soft, wireless device that monitors distal terminal fluid flow and transmits measurements to a smartphone via a low-power Bluetooth communication when requested. The proposed multimodal sensing device enabled by flow sensors, for measurements of flow rate and electrodes for measurements of resistance in a fluidic chamber, allows precision measurement of CSF flow rate over a long time and under any circumstances caused by unexpected or abnormal events. A universal design compatible with any modern commercial spinal fluid shunt system would enable the widespread use of this technology

A Soft, Biocompatible Magnetic Field Enabled Wireless Surgical Lighting Patty for Neurosurgery

General surgical procedures are subject to low-light conditions or a narrow angle of view, and such limitations in light limit visibility and complicate the given surgical procedure. Conventional lighted surgical tools rely on an external light source, which may be oriented into a cavity or mounted on a surgical instrument such as retractor, endoscopes, or suction tubes. However, such conventional lighted instruments do not provide adequate lighting during various surgical procedures. Here, we present a soft, miniaturized magnetic-enabled wireless surgical lighting patty. Specifically, the proposed surgical lighting patty that can be temporarily implanted into a cavity or surgical corridor provides lighting to the surgical subject and manages fluids in a surgical field. The surgical lighting patty is a multilayer patty, two outer layers of the lighted surgical patty and the center lighted layer. A reed switch in the central layer can activate the power supply in response to a magnet to emit the light from the light source. The result allows a dramatically simplified wireless operation. Moreover, it can provide various wavelengths of light to a surgical field for purposes such as illuminating the surgeon’s field of vision, exciting dyes, and sterilizing surgical fields

Organ-specific, multimodal, wireless optoelectronics for high-throughput phenotyping of peripheral neural pathways

Advances in wireless technologies have enabled internalisation of light sources, but organ specific illumination is challenging. Here, the authors present a durable, multimodal, wireless system enabling optogenetic stimulation of peripheral neurons within organs