Real-space imaging of acoustic plasmons in large-area CVD graphene

An acoustic plasmonic mode in a graphene-dielectric-metal heterostructure has recently been spotlighted as a superior platform for strong light-matter interaction. It originates from the coupling of graphene plasmon with its mirror image and exhibits the largest field confinement in the limit of a nm-thick dielectric. Although recently detected in the far-field regime, optical near-fields of this mode are yet to be observed and characterized. Direct optical probing of the plasmonic fields reflected by the edges of graphene via near-field scattering microscope reveals a relatively small damping rate of the mid-IR acoustic plasmons in our devices, which allows for their real-space mapping even with unprotected, chemically grown, large-area graphene at ambient conditions. We show an acoustic mode that is twice as confined - yet 1.4 times less damped - compared to the graphene surface plasmon under similar conditions. We also image the resonant acoustic Bloch state in a 1D array of gold nanoribbons responsible for the high efficiency of the far-field coupling. Our results highlight the importance of acoustic plasmons as an exceptionally promising platform for large-area graphene-based optoelectronic devices operating in mid-IR

Ultrastrong plasmon–phonon coupling via epsilon-near-zero nanocavities

Vibrational ultrastrong coupling, where the light–matter coupling strength is comparable to the vibrational frequency of molecules, presents new opportunities to probe the interactions between molecules and zero-point fluctuations, harness cavity-modified chemical reactions and develop novel devices in the mid-infrared spectral range. Here we use epsilon-near-zero nanocavities filled with a model polar medium (SiO2) to demonstrate ultrastrong coupling between phonons and gap plasmons. We present classical and quantum-mechanical models to quantitatively describe the observed plasmon–phonon ultrastrong coupling phenomena and demonstrate a modal splitting of up to 50% of the resonant frequency (normalized coupling strength η > 0.25). Our wafer-scale nanocavity platform will enable a broad range of vibrational transitions to be harnessed for ultrastrong coupling application

닉테이션 행동의 다양성과 가소성에 대한 유전학적 연구

학위논문 (박사)-- 서울대학교 대학원 : 생명과학부, 2017. 2. 이준호.Animal behavior is the most complex phenotypes arising from the interaction of genes and environment through biological systems and exhibits significantly higher phenotypic diversity and plasticity than other traits. For the successful execution of behavior, the entire biological system must develop properly and function accurately. This overall process involves some regulatory mechanisms programmed in the genome, and some of these regulatory mechanisms work robustly without being greatly affected by the environment, while some regulatory mechanisms are sensitive to the given condition and contribute to behavioral plasticity. Also, the genetic variation among different individuals produces heritable behavior variation. In this study, I performed genetic analysis on nictation behavior, a hitchhiking behavior of C. elegans, to reduce the genetic diversity and environmental plasticity of behavior to gene level. Specifically, I analyzed the heritable variation of nictation behavior among wild isolates of C. elegans sampled from all over the world. Using quantitative genetic techniques, I identified a single genetic locus which underlies behavioral variation between N2 strain from Bristol and CB4856 strain from Hawaii. Genetic analysis of the locus revealed that small RNAs might serve as potential regulators of the nictation behavior variation. Additional genetic analysis between two strains showed that the neuropeptide receptor gene which had been artificially selected in the laboratory is involved in regulation of nictation behavior. I also investigated the plasticity of nictation behavior according to environmental cues and related regulatory signaling pathways. Feeding pathogenic bacteria and nematode pheromone treatment can lead to quantitative differences in nictation behavior, which is mediated by TGF-β signaling pathway and cGMP signaling pathway. In summary, genetic approach on nictation behavior successfully analyzed the genetic basis of behavioral variation and plasticity at the gene level. These findings suggest a molecular mechanism of behavior adaptation and evolution in nature.Introduction 1 1. Life cycle of C. elegans in natural habitat 2 2. Phoretic strategy for dispersal and survival of C. elegans 4 3. Previous studies on nictation behavior 6 4. From genes to behavior 7 5. Behavior diversity and plasticity at the gene-environment interface 9 Materials and Methods 11 Results and Discussions 24 Part I. Genetic basis of heritable variation in nictation behavior of C. elegans 25 1. Natural variation of nictation behavior and phoretic dispersal 26 2. Domestication effect on nictation behavior in laboratory N2 strain 41 Part II. Genetic basis of environmental plasticity in nictation behavior 78 1. Regulation of nictation behavior by TGF-β signaling 79 2. Rescue of nictation defect of TGF-β mutant by pheromone treatment and downregulation of cGMP signaling 87 Reference 105 Abstract in Korean 112Docto

Effect of Tungsten Carbide Morphology, Quantity, and Microstructure on Wear of a Hardfacing Layer Manufactured by Plasma Transferred Arc Welding

Hardfacing layers on mild steel substrates were successfully manufactured using a plasma transferred arc welding (PTAW) process to combine tungsten carbide powder and binder metal. Three morphological types of tungsten carbide powder were employed: spherical, fused angular, and mixed powder. The effects of both the morphology and the quantity of tungsten carbide powder on the wear property of the products were determined using a dry sand wheel abrasion test. The results revealed that two conditions effectively increased the wear resistance of the hardfacing layers: the use of spherical tungsten carbide and the use of an increased quantity of tungsten carbide. Moreover, the formation of an interfacial layer of intermetallic compounds (IMCs) between the tungsten carbide and binder metal, and the relationship between the microstructure of the IMC layer and its wear property were also investigated. It was confirmed that, in general, preferential wear occurs in the binder metal region. It was also unveiled that the wear property improves when interfacial IMC bands are formed and grown to appropriate width. To obtain a sound layer more resistant to wear, the PTAW conditions should be adequately controlled. In particular, these include the process peak temperature and the cooling rate, which affect the formation of the microstructure

Harmonisation of Coolant Flow Pattern with Wake of Stator Vane to Improve Sealing Effectiveness Using a Wave-Shaped Rim Seal

The rim seal of the gas turbine is intended to protect the material of the turbine disk from hot combustion gases. The study of the rim seal structure is important to minimise the coolant flow and maximise the sealing effect. In this paper, a wave-shaped rim seal for stator disks is proposed and its effect is confirmed by numerical analysis. To characterise the flow phenomena near the wave-shaped rim seal, a simplified model of the wave-shaped rim seal (Type 1 model), which excludes the rotor blade and stator vane, is analysed and compared with the conventional rim seal. Then, through analysis of the wave-shaped rim seal geometry (Type 2 model), which includes the rotor blade and stator vane, a reduction in egress and ingress flow was observed owing to the wave-shaped rim seal, and the sealing effectiveness on the stator disk of turbine was increased by up to 3.8%. Implementation of the wave-shape geometry in the radial seal is a novel choice for turbine designers to consider in future for better-performing and more-efficient turbines

Atomistic Simulations on Dynamics of a Magnetic Skyrmion: Role of Atomic Defects in the Breathing Mode

Owing to the fascinating properties of the magnetic skyrmion such as topological robustness, high density, and high energy efficiency [1], it has been considered as one of the prominent candidates for future spintronic devices. It has been known that the magnetic skyrmions are topologically protected, however, it has intrinsically atomistic nature: this topological spin structure formed physically on the atomic sites in monolayer-scaled-thickness thin films. Consequently, it is inevitably influenced by the interfacial roughness and the thermal fluctuation. To study such atomistic effects on the skyrmion, a numerical method based on the atomic scale micromagnetic model is necessary. In this work, we observe effects of atomic defects on dynamics of the skyrmion, the breathing modes, by atomistic micromagnetic simulations [2]. As a model system, monolayers Co nanodisk with 60 nm diameter was used. We assumed that the Co film has simple cubic (SC) structure with the lattice constant of 2.5 ??? and the interfacial Dzyaloshinskii-Moriya interaction (DMI) appears only at the bottom surface [3][4]. The DMI is considered as the tensor form of magnetic interaction between neighbor spins. The randomly formed vacancies on the surface showed the roughness of the interface as shown in Fig. 1(a). As shown in Fig. 1 (b), the breathing modes varies dramatically with the roughness. Furthermore, we found that the stable size of the skyrmion affected sensitively by the roughness