73 research outputs found
Fourier series of higher-order Daehee and Changhee functions and their applications
No full textAbstract In the paper, the author considers the Fourier series related to higher-order Daehee and Changhee functions and establishes some new identities for higher-order Daehee and Changhee functions
Shape memory polymer adhesive gripper for pick-and-place applications
No full textOver the past few years, shape memory polymers (SMPs) have been extensively studied in term of their remarkable reversible dry adhesive properties and related smart adhesive applications. However, these exceptional properties of SMPs have not been exploited for pick-and-place applications, which would otherwise advance the robotic manipulation. This work explores the use of SMPs to design an adhesive gripper which pick and place target solid objects relying on reversible dry adhesion of SMP. Compared with common finger or soft grippers, the SMP adhesive gripper interacts with a single surface of a target object for pick-and-place. Furthermore, it is easy and inexpensive to manufacture and applicable to various surfaces since it involves reversible dry adhesion. In this paper, associated physical mechanisms and temperature analyses are studied and conducted. Also, the study includes manufacturing of a dual SMP and a release tip which substantially enhances the adhesion strength and considerably minimizes the releasing force. Finally, the versatility and utility of the SMP adhesive gripper are demonstrated through pick-and-place experiments.Submission published under a 24 month embargo labeled 'Closed Access', the embargo will last until 2021-08-01The student, ChangHee Son, accepted the attached license on 2019-07-12 at 16:53.The student, ChangHee Son, submitted this Thesis for approval on 2019-07-12 at 16:58.This Thesis was approved for publication on 2019-07-17 at 09:31.DSpace SAF Submission Ingestion Package generated from Vireo submission #14272 on 2019-11-26 at 14:03:59Made available in DSpace on 2019-11-26T20:59:46Z (GMT). No. of bitstreams: 3
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Synthesis and utilization of the perovskite as energy materials
No full textSchool of Energy and Chemical Engineering (Energy Engineering)clos
Enhanced light out-coupling in OLED employing thermal-assisted, self-aggregated silver nano particles
No full textMetallic nano-structures in micro-cavity organic light emitting diode (OLED) can significantly enhance light out-coupling efficiency. Nevertheless, they are not widely accepted in conventional devices due to its complicated process and increased manufacturing cost. In this study, we demonstrate a production-ready alternative for increasing the efficiency of OLEDs by implementing thermal-assisted self-aggregated metallic nanoparticles (NPs). Silver NPs are fabricated by thermal annealing of vacuum deposited thin silver layer without any complicated process, which is easily scalable in large area with low cost. Theoretical calculation and dark field microscopy image indicate that these stochastic Ag NPs provide light scattering in broad range. By incorporating Ag NPs to OLED with micro-cavity structure, 11% improvement in the external quantum efficiency was obtained without deteriorating viewing angle.OAIID:RECH_ACHV_DSTSH_NO:T201806816RECH_ACHV_FG:RR00200001ADJUST_YN:EMP_ID:0000029430CITE_RATE:3.68DEPT_NM:전기·정보공학부EMAIL:[email protected]_YN:YN
Templated epitaxy of TiO2(B) on a perovskite
No full text© 2020 Author(s). The bronze-phase TiO2(B) has an open atomic framework that makes it a good candidate for applications in photochemical and electrochemical conversion of energy. However, the synthesis of bronze-phase TiO2(B) thin films on perovskite substrates, such as SrTiO3 (STO), which is one of the most conventional versatile substrates for oxide epitaxy, has been extremely challenging owing to the preferential formation of the anatase TiO2 over TiO2(B). The main reason is that the anatase TiO2 has not only a smaller lattice mismatch than TiO2(B), but also a better structural symmetry match when grown on STO. Here, we demonstrate a way to circumventing this problem by using a VO2(B) buffer layer, yielding the growth of a high-quality single crystalline TiO2(B) film on a (001)-oriented STO substrate. From the resulting TiO2(B) film, we found that this film has a large optical bandgap of similar to 3.6eV, which is close to the known theoretical value, the largest among TiO2 polymorphs, and useful for developing high-power energy devices11sciescopu
Distributed CSMA Algorithms for Link Scheduling in Multihop MIMO Networks Under SINR Model
No full textabstract: In this paper, we study distributed scheduling in multihop multiple-input-multiple-output (MIMO) networks. We first develop a "MIMO-pipe" model that provides the upper layers a set of rates and signal-to-interference-plus-noise ratio (SINR) requirements that capture the rate-reliability tradeoff in MIMO communications. The main thrust of this paper is then dedicated to developing distributed carrier sense multiple access (CSMA) algorithms for MIMO-pipe scheduling under the SINR interference model. We choose the SINR model over the extensively studied protocol-based interference models because it more naturally captures the impact of interference in wireless networks. The coupling among the links caused by the interference under the SINR model makes the problem of devising distributed scheduling algorithms very challenging. To that end, we explore the CSMA algorithms for MIMO-pipe scheduling from two perspectives. We start with an idealized continuous-time CSMA network, where control messages can be exchanged in a collision-freemanner, and devise a CSMA-based link scheduling algorithm that can achieve throughput optimality under the SINR model. Next, we consider a discrete-time CSMA network, where the message exchanges suffer from collisions. For this more challenging case, we develop a "conservative" scheduling algorithm by imposing a more stringent SINR constraint on the MIMO-pipe model. We show that the proposed conservative scheduling achieves an efficiency ratio bounded from below.This is the authors' final accepted manuscript. The published version can be accessed at http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=6256765.
“© © 2013 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.
Charge transport in amorphous low bandgap conjugated polymer/fullerene films
No full textCopyright (2012) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.The structural and charge transport properties of a low bandgap copolymer poly(3-hexylthiophene-alt-6,7-dimethyl-4,9-bis-(4-hexylthien-2yl)-[1,2,5]thiadiazolo[3,4-g]quinoxaline) (P(3HT-MeTDQ)) and its blend with [6,6]-phenyl-C-61-butyric acid methyl ester (PCBM) are investigated. Thermal analysis, X-ray scattering diffraction (XRD), atomic force microscopy and transmission electron microscopy (TEM) of P(3HT-MeTDQ) reveal that the polymer is amorphous in solid state. As the hole mobility of P(3HT-MeTDQ) was measured by the time-of-flight photoconductivity method, the mobility was 3.35 x 10(-4) cm(2)/Vs, which is very comparable to that of semicrystalline poly(3-hexylthiophene). When the mobility of amorphous P(3HT-MeTDQ) was analyzed according to the Gaussian disorder model, the polymer has the energetic and positional disorders with the values of sigma = 62 meV and Sigma = 1.7, respectively, indicating that the polymer has a relatively narrow Gaussian distribution of transport states. Interestingly, when P(3HT-MeTDQ) is blended with PCBM, the amorphous P(3HT-MeTDQ) becomes partially ordered, as evidenced by observation of two discernible XRD peaks at 20 = 5 degrees (d = 17.7 angstrom) and 25.5 degrees (d = 3.5 angstrom) corresponding to the interchain distance and pi-stacking distance, respectively. The bicontinuous network morphology was identified at the blend with 60 wt.% PCBM by TEM, at which the charge carrier transport changes from hole-only to ambipolar. (C) 2012 American Institute of Physics. [doi:10.1063/1.3686633]OAIID:oai:osos.snu.ac.kr:snu2012-01/102/0000001236/2SEQ:2PERF_CD:SNU2012-01EVAL_ITEM_CD:102USER_ID:0000001236ADJUST_YN:YEMP_ID:A004558DEPT_CD:445CITE_RATE:2.168FILENAME:2. Charge Transport in Amorphous.pdfDEPT_NM:재료공학부EMAIL:[email protected]_YN:YCONFIRM:
A close look on the impact and performance of financial analysts
No full textThis dissertation consists of two essays on financial analysts’ stock recommendations. The first essay examines the relationship between corporate social responsibility (CSR) report and the value of financial analysts’ stock recommendation revisions. We find that the value of stock recommendations for socially responsible companies is lower than non-socially responsible companies. Also, we show that there is an inverse relation between the level of information on CSR strengths and concerns and the value of financial analysts’ stock recommendations. Furthermore, when we focus on the sensitivity of change of CSR ratings, our result indicates that the value of stock recommendations is negatively associated with a firm’s improvement on CSR score. As a firm experiences more change in social responsibility strengths and concerns, the value of analysts’ stock recommendations decreases. Our results imply that the value of recommendation is a function of firms’ CSR ratings and the amount of information on CSR strengths and concerns. In the second essay, we hypothesize that a perception of higher ability is implicit when an analyst makes a bold recommendation, and that this self-assessment is more likely to be correct when there are few analysts covering the firm. Consistent with our hypothesis, we find that it is highly profitable to trade based on bold recommendations for firms with low analyst coverage (risk-adjusted return of 30% per year), but not bold recommendations for high coverage firms. Herding recommendations, whether for firms with low or high coverage, are not profitable. The profit from this trading strategy is related to the news released during earnings announcements.Ph.D.Includes bibliographical referencesIncludes vitaby Changhee Le
Coherent extreme-ultraviolet emission generated through frustrated tunnelling ionization
No full textCoherent extreme-ultraviolet emission can be obtained through high-harmonic generation and multiphoton excitation from atoms exposed to a strong laser field. We report the generation of a new kind of coherent extreme-ultraviolet emission from He atoms excited by intense few-cycle laser pulses. An atom can be excited after tunnelling in a strong laser field, in the process known as frustrated tunnelling ionization (FTI). We find that excitation through FTI leads to coherent extreme-ultraviolet emission, and its intensity strongly depends on the ellipticity and carrier-envelope phase of the laser pulses. Additionally, the propagation direction of the emission can be coherently controlled by employing the attosecond lighthouse technique. This coherent control of tunnelling and recombination dynamics, which has provided the fundamental basis of attosecond physics, promises the utilization of FTI emission as a coherent light source and offers new opportunities in ultrafast spectroscopy. © 2018, The Author(s), under exclusive licence to Springer Nature Limite
Electronic structure and insulating gap in epitaxial VO2 polymorphs
No full textDetermining the origin of the insulating gap in the monoclinic V O2(M1) is
a long-standing issue. The difficulty of this study arises from the simultaneous
occurrence of structural and electronic transitions upon thermal cycling. Here, we
compare the electronic structure of the M1 phase with that of single crystalline
insulating V O2(A) and V O2(B) thin films to better understand
the insulating phase of VO2. As these A and B phases do not undergo a
structural transition upon thermal cycling, we comparatively study the origin of the
gap opening in the insulating VO2 phases. By x-ray absorption and
optical spectroscopy, we find that the shift of unoccupied
t2g orbitals away from the Fermi level is a common
feature, which plays an important role for the insulating behavior in VO2
polymorphs.
The distinct splitting of the half-filled t2g orbital is
observed only in the M1 phase, widening the bandgap up to ∼0.6
eV. Our approach of comparing all three insulating VO2 phases provides
insight into a better understanding of the electronic structure and the origin of the
insulating gap in VO2
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