Observation of Liquid Metal Actuation in Microfluidic Channels and Implementation to Tunable RF Inductors

The overreaching goal of this thesis research is to analyze liquid metal plug actuation in microfluidic channels and to exemplify this actuation in a tunable inductor design using liquid metal as a switching material, and to demonstrate the feasibility of liquid metal in other devices. A gallium and indium based alloy, EGaIn, which is liquid at room temperature is the liquid metal type chosen for this research. Although it owns some advantages such as high vapor pressure, non-toxicity and good conductivity, there are some crucial factors that we should pay attention to move the liquid metal in microchannels as a result of oxidation with contact to air and stickiness of oxidized skin to any surface. One of them is to determine the right coating material for coating the channel and the best surfactant to carry the liquid metal plug without leaving residues with sufficient amount of pressure. So far, liquid metals have been used in some RF applications, but EGaIn could not be implemented properly in a microfluidic channel as a separate liquid metal plug because of the oxidation issue. Our aim is here to verify that there are ways to handle the actuation of based liquid metals in microchannels. In this thesis, we have used EGaIn in the experiments conducted, but the acquired results are also applicable to galinstan, which is another gallium based alloy. Right after the liquid metal actuation is exhibited in microfluidic channels, this actuation is exemplified in tunable loop and spiral inductors on both PCB and glass slides using lithography technique. A closed loop channel with peristaltic pumping valves has been designed with the help of LabVIEWTM and proper channel designing technique. Therefore, moving the liquid metal in a desired way with an expected speed is achieved. At the end of the study, tunability in an RF inductor using liquid metal as a switching part is provided, once a solution to the nagging oxidation problem of liquid metals is offered, and thus the feasibility of liquid metals to the electrical device applications is demonstrated

The Influence of Dividend Payments on Company Performance: The Case of Istanbul Stock Exchange (BIST)

The aim of this study is to analyze the relation between dividend policies and financial performances of the companies operating in Istanbul Stock Exchange (BIST). The study uses data of 172 companies outside of financial sector for the period of 2008-2011.  In the study firms are divided into two groups: the ones regularly paying dividends and the ones that don’t make regular dividend payments.  The tests were conducted in order to understand whether there is a difference between accounting and market based financial performances of these two groups or not.  Empirical analyses used multiple regression, T test methods as well as descriptive statistics.  The results of analysis showed that dividend payments had influence on companies’ performances. Furthermore, there was a positive and statistically meaningful relation between the dividend per share rate (DPS) within groups and market based performance indicator Tobin’s q while there was a statistically meaningless relation between accounting based performance indicators ROA and ROE and dividend per share rate. These results are of supporting quality for the dividend relation developed by Myron Gordon and John Lintner (GL). Keywords: Dividend Payments, Firm Performance, Dividend Per Share, BIS

Mm Scale 3d Silica Waveguide Fabrication Technique for Solar Energy Concentration Systems

The overreaching goal of this dissertation research is to achieve fabrication of mm scale waveguide structure for solar energy concentration systems. In the proposed design, a high concentrator photovoltaics (HCPV) with 1000x concentration and >90 % optical efficiency is targeted. The concept consists of three components: lens array, coupler and waveguiding section. Fused silica is assigned as the waveguide material, since it has a high optical transmission and low absorption and it provides the scalability and low manufacturing cost sought in the fabrication technique. To acquire the desired shape in waveguide, femtosecond laser irradiation followed by chemical etching (FLICE) process is used for fused silica light pipes fabrication. Among two widely used etchants potassium hydroxide (KOH) is preferred over hydrogen fluoride (HF) regarding its higher selectivity. FLICE process parameters have been optimized to achieve higher selectivity, higher manufacturing speed and better surface quality. The minimum number of overlapped pulses is reduced to 3.2 which corresponds to 1.25 m/s writing speed at given 2 MHz laser pulse repetition rate at given 2 μm spot size and an acceptable filtered surface roughness of 400 nm for 1 mm^2 area is achieved. The achieved minimum filtered surface roughness is scaled down to 21.8 nm for given 1 mm^2 area. Up to 1X5 staggered and tapered light pipes with up to 12.75x geometric concentration factor with a 45° angled input facet is successfully fabricated. The achieved accuracy of the angled surfaces is smaller than ±0.5° and ±0.01° for 45° and side wall tapered surfaces, respectively. Having evaluated the polishing techniques, CO2 laser polishing is decided to be employed in this study to obtain a smooth surface finish. Surface profiles are measured by atomic force microscopy (AFM) for generally high spatial frequency analysis and white light interferometry (WLI) for low spatial frequency analysis. Measurements demonstrate that the surface root mean square (RMS) roughness is decreased almost two order of magnitude. 95% transmission efficiency is measured for waveguide samples up to 50 mm in length and 1 mm^2 cross sectional area when the Fresnel losses are ignored and incident angles (in air) are averaged according to F/1.5 lens. Complex shapes in waveguides such as angled facets, tapering of the cross-section along the length, and combiners are proven to be possible to fabricate with high precision

On isophote curve and its characterizations

Isophote comprises a locus of the surface points whose normal vectors make a constant angle with a fixed vector. Main objective of this paper is to find the axis of an isophote curve via its Darboux frame and afterwards to give some characterizations about isophote and its axis. Particularly, for isophotes lying on a canal surface will be obtained other characterizations again.Comment: 15 page

The effect of crest shape on discharge coefficient at linear weirs

U radu se daje detaljan prikaz eksperimentalne laboratorijske analize utjecaja oblika krune na koeficijent prelijevanja oštrobridnih preljeva. Eksperimenti su provedeni za četiri različita oblika krune. Obavljeni eksperimenti i analize pokazuju da visina krune preljeva vrlo značajno utječe na brzinu otjecanja, a naročito na koeficijent prelijevanja. U zaključku se navodi da se najveća brzina protoka ostvaruje pri jednočetvrtinskom zaobljenju krune. U praksi se prednost daje izvođenju oštrobridnih preljeva zbog jednostavnosti izvođenja, iako je njihov koeficijent prelijevanja niži u usporedbi s preljevima s jednočetvrtinskim zaobljenjem krune.A detailed experimental laboratory analysis of the effect of crest shape on the discharge coefficient of sharp-crested weirs is presented in the paper. The experiments were conducted for four different crest shapes. The experiments and analyses show that discharge capacity, and discharge coefficient in particular, are significantly affected by weir crest height. It is stated in conclusion that rounded crest shape has the highest discharge capacity. In practice, sharp crested weirs are generally preferred to other crest shapes due to construction facility, although the discharge coefficient values of sharp crested weirs are lower compared to rounded crest shape