Showing papers in "Journal of the Korean Physical Society in 2018"

Mesoscopic Transport Events and the Breakdown of Fick’s Law for Turbulent Fluxes

Abstract: This paper presents a pedagogical review of the physics of mesoscopic transport events and their role in the breakdown of Fick’s Law for turbulent transport in magnetically confined plasma It is now clear that the conventional picture of localized turbulence and quasi-linear calculation of fluxes fails to address and account for the phenomenology of tokamak transport One key issue is the observed departure from the expected gyro-Bohm transport scaling The causes of this breakdown of Fickian thinking include turbulent avalanching and pulse propagation (turbulence spreading) Both are mesoscopic transport events, and both tend to de-localize the flux–gradient relation Turbulence spreading is the process of self-scattering and expansion of a slug or other local exciton of turbulence Spreading is described by theoretically-motivated, phenomenological reaction–diffusion models for the turbulence activity (intensity) field, much in the spirit of Ginzburg–Landau theory Such models imply that spreading will occur by propagation of intensity fronts After discussing the basic theory, this paper presents several critical tests of turbulence spreading models using gyrokinetic simulation Applications include rho-star scaling, penetration of transport barriers and core-edge coupling Relevant experiment–theory comparisons are addressed, as well Avalanching refers to a process whereby correlated topplings of nearby localized cells overturn sequentially and drive a burst of transport Avalanching is a process intrinsic to systems that support a broad range of scales l between a cell size Δ and system size L, ie Δ < l < L Avalanching is also a natural way to produce transport events on scales that exceed the cell size or correlation length Therefore, the PDF (probability distribution function) of avalanches as a function of l is a crucial quantity, necessary for predicting confinement in a system like ITER, with a very large-scale separation between L and Δ Avalanching emerged from the theory of selforganized criticality but is a more general phenomenon The paper traces the intellectual prehistory of avalanching through the advent of self-organized criticality Special focus is devoted to reduced continuum models of avalanching The physics of avalanching in confined plasma is discussed in detail, via several multi-faceted comparisons to flux-driven fluid and gyrokinetic simulations The dominance of bursty, large transport events in the flux is identified Evidence for avalanching in basic and confinement experiments is summarized The paper concludes with sections on selected special topics, a discussion of the relation between turbulence spreading and avalanching, and a list of possible future directions Throughout the paper, an effort is made to set fusion theory and phenomenology in the context of ideas discussed in the broader scientific community

Recent advances of percolation theory in complex networks

Abstract: During the past two decades, percolation has long served as a basic paradigm for network resilience, community formation and so on in complex systems. While the percolation transition is known as one of the most robust continuous transitions, the percolation transitions occurring in complex systems are often of different types such as discontinuous, hybrid, and infinite-order phase transitions. Thus, percolation has received considerable attention in network science community. Here we present a very brief review of percolation theory recently developed, which includes those types of phase transitions, critical phenomena, and finite-size scaling theory. Moreover, we discuss potential applications of theoretical results and several open questions including universal behaviors.

Thermodynamic Properties of the Modified Yukawa Potential

Abstract: Within the framework of the modified factorization method, we solve the Schrodinger equation with the modified Yukawa potential. The energy spectrum is obtained using the Pekeris approximation scheme for the centrifugal term. The thermodynamic properties, including the vibrational partition function, vibrational mean energy, vibrational mean free energy, vibrational specific heat capacity and vibrational entropy, are calculated. As a special case, we compare our result with that work of Dong [Int. J. Quant. Chem. 107, 366 (2007)] and find good agreement.

A Review of SnSe: Growth and Thermoelectric Properties

Abstract: SnSe is a 2D semiconductor with an indirect energy gap of 0.86 - 1 eV; it is widely used in solar cell, optoelectronics, and electronic device applications. Recently, SnSe has been considered as a robust candidate for energy conversion applications due to its high thermoelectric performance (ZT = 2.6 in p-type and 2.2 in n-type), which is assigned mainly to its anhamornic bonding leading to an ultralow thermal conductivity. In this review, we first discuss the crystalline and electronic structures of SnSe and the source of its p-type characteristic. Then, some typical single crystal and polycrystal growth techniques, as well as an epitaxial thin film growth technique, are outlined. The reported thermoelectric properties of SnSe grown by using each technique are also reviewed. Finally, we will describe some remaining issues concerning the use of SnSe for thermoelectric applications.

Optical and electrical properties of GeSe and SnSe single crystals

Abstract: GeSe and SnSe single crystals were fabricated by using Bridgman technique. The properties of the two crystals were investigated by temperature-dependent Hall effects, optical absorption, and pressure-dependent Raman scattering measurements. The hole carrier concentrations of the GeSe and SnSe samples were 5.31×1016 cm−3 and 1.19×1019 cm −3, respectively, at room temperature. The activation energy of acceptor levels in GeSe and SnSe were measured to be 37.8 meV and 2.21 meV, respectively. These compounds had indirect band gap, which were measured to be 1.10 eV for GeSe and 0.88 eV for SnSe, respectively. The Raman spectra of GeSe and SnSe were obtained under high pressure up to 5.62 GPa. GeSe showed four major peaks at 89 cm-1 (A g ), 154 cm-1 (B3g), 180 cm-1 (A g ), and 191 cm-1 (A g ), and SnSe had three peaks at 84 cm-1 (A g ), 118 cm-1 (B3g), and 137 cm-1 (A g ). The effects of applying high pressure on these modes were also discussed.

On the Conformable Fractional Quantum Mechanics

Abstract: In this paper, a conformable fractional quantum mechanic has been introduced using three postulates. Then in such a formalism, Schr¨odinger equation, probability density, probability flux and continuity equation have been derived. As an application of considered formalism, a fractional-radial harmonic oscillator has been considered. After obtaining its wave function and energy spectrum, effects of the conformable fractional parameter on some quantities have been investigated and plotted for different excited states.

Water-Through Triboelectric Nanogenerator Based on Ti-Mesh for Harvesting Liquid Flow

Abstract: Water flow has mechanical energy as well as triboelectric energy generated by the friction between the solid surface and the water. We describe a water-through triboelectric nanogenerator (WTTENG) based on Ti-mesh that harvests electrical energy from contact electrification between the water flow and polytetrafluoroethylene (PTFE) nanowires. The electrical output from the fabricated WT-TENG is due to deionized water flowing through the polypropylene (PP) channel. The WTTENG generated a peak voltage and current of up to −9.4 V and −5.1 μA, respectively. In particular, the WT-TENG, which harvests the electrical energy from flowing deionized water, tap water and even a 0.6 M NaCl solution, can be used in applications of any existing kinds of fluids for not only harvesting mechanical energy but also sensing metal ions in the liquid.

A Bending-Type Piezoelectric Energy Harvester with a Displacement-Amplifying Mechanism for Smart Highways

Abstract: Piezoelectric energy harvesting has gained attention owing to its effectiveness at harvesting electrical energy from various energy sources. Especially, with the increasing demand for smart highways, piezoelectric energy harvesting from road traffic has been increasingly studied. However, existing piezoelectric road-energy harvesters have limitations of low electrical output and low durability. A novel piezoelectric energy harvester was designed and fabricated to overcome these limitations. The proposed harvester had a maximum output power of 3.93 mW at a load resistance of 130 kΩ under an input displacement of 2.5 mm. The proposed harvester had 4.2 times more output power than the existing vibration-type road energy harvesters and was much less susceptible to destruction-in contrast to existing impact-type road-energy harvesters. The proposed road-energy harvester can be used as a power source for wireless sensor networks in smart highways.

Recent Progress in Potassium Sodium Niobate Lead-free Thin Films

Abstract: Lead-free potassium sodium niobate (KNN)-based thin films have attracted much interest in replacing current lead zirconate titanate (PZT)-based piezoelectric thin films in micro electromechanical (MEMS) devices due to the increasing awareness and legislation concerning lead oxide toxicity. Recently, promising piezoelectric performance has been achieved in KNN-based thin films by compositional modification. Over the last decade, our group has concentrated on the fabrication of KNN-based thin films using sol-gel and RF sputtering techniques and has obtained encouraging results. However, controlling the complex stoichiometric compositions in KNN-based thin films is still challenging due to volatilization of alkaline elements and the high leakage current density. In the current review, the available synthetic approaches, chemical modification strategies, and stabilizing agents used to try and overcome these challenges and improve the piezoelectric properties of KNN-based thin films are reviewed. Herein, we systematically describe the recent advancements of the ferroelectric and piezoelectric properties of KNN-based thin films and summarize the properties of KNN-based thin films fabricated by various techniques, such as sol-gel and RF magnetron sputtering.

Improved 3D Printing Plastic Scintillator Fabrication

Abstract: 3D printing techniques can be widely used for various applications owing to their fast speed, convenience, and customized shape output. The 3D printing technique is applicable to plastic scintillator fabrication which typically uses polymerization. Currently, research on application of the 3D printing technique based on photopolymerization to plastic scintillator fabrication is being pursued. However, performance of the photopolymerized scintillators reported till now is lower than that of commercial plastic scintillators (~ 30%). We have carried out research on performance improvement of the scintillator fabricated by the photopolymerization, for radiation dose measurement. Photopolymer resin with novel recipe based on acrylic monomer and naphthalene was used to fabricate the scintillator instead of the photopolymer resin based on styrene, which is typically used as the monomer for commercial scintillator. 3D printer with digital light processing was used for the photopolymerization of the photopolymer resin. As a result, light output performance of the fabricated plastic scintillator was about 67% compared with that of the commercial plastic scintillator, BC-408. The performance of the scintillator fabricated by the photopolymerization was thus improved to more than two times that obtained by previous researchers. This is sufficient to be applied to the radiation dose measurement with high dose rates such as radiation therapy. It also demonstrated the applicability of the 3D printing technique in scintillator fabrication.

A Brief Overview of RAON Physics

Abstract: The Rare Isotope Science Project (RISP) of the Institute for Basic Science (IBS) has been initiated to construct a rare isotope accelerator complex, named RAON, in Daejeon, Korea. In this short article, we briefly introduce the RAON accelerator and experimental systems and summarize essential and important physics issues that RAON could address, focusing on nuclear physics.

Submonolayer Quantum Dots for Optoelectronic Devices

Abstract: Semiconductor quantum dots (QD) have been extensively applied in optical and optoelectronic devices because of their strong quantum confinement and bandgap tunability. Most research has focused on the design, material growth, and characterization of self-assembled QDs grown by Stranski- Krastanov (S-K) growth mode. As an alternative to S-K QDs, sub-monolayer (SML) QDs have recently attracted much attention due to their ultrahigh dot density, excellent size uniformity, and high crystal quality. These better material properties of SML QDs promise great application potential in optoelectronic devices such as infrared photodetectors and solar cells. In this review, we present and discuss the material and device characteristics of the infrared photodetectors and solar cells with InAs QDs grown by S-K and SML growth modes.

Investigation of the Dirac Equation by Using the Conformable Fractional Derivative

Abstract: In this paper,the Dirac equation is constructed using the conformable fractional derivative so that in its limit for the fractional parameter, the normal version is recovered. Then, the Cornell potential is considered as the interaction of the system. In this case, the wave function and the energy eigenvalue equation are derived with the aim of the bi-confluent Heun functions. use of the conformable fractional derivative is proven to lead to a branching treatment for the energy of the system. Such a treatment is obvious for small values of the fractional parameter, and a united value as the fractional parameter approaches unity.

Progress of the KSTAR Research Program Exploring the Advanced High Performance and Steady-State Plasma Operations

Abstract: Korea Superconducting Tokamak Advanced Research (KSTAR) program is strongly focused on solving the scientific and technological issues in steady-state high performance plasma operation in preparation for ITER operation as well as the design basis for DEMO In this regards, KSTAR has made significant advances in developing long pulse and high performance plasma scenarios utilizing the advantage of the fully superconducting tokamak Ten-year of KSTAR operation showed the outstanding progress in the plasma control extending the operation window of the plasma discharges achieving the H-mode up to 1 MA in plasma current, up to 72 s in flat top duration, and up to 216 in elongation In addition to the long pulse discharge, high performance discharges with high betas (βN ~ 3) could be achieved in the broad range of edge safety factor (q95) without external error field correction The unique features of the KSTAR device (magnetic accuracy with extremely low error fields, steady-state capable heating systems, in-vessel control coils, and advanced imaging and profile diagnostics) has been fully exploited to explore the unveiled physics as well as to exploring the systematic solution for suppression of edge localized mode (ELM) crash Achieved examples are the record long pulse of H-mode operation without an ELM crash (~ 30 s up to date), and progress in the fundamental transport physics through systematic study using these unique capabilities Based on the previous research results, intensive research will be followed to explore the advanced high beta operation (βN ~ 4) with fully suppressed harmful MHD instabilities aiming the integrated solution for DEMO In this regards, an additional current drive systems and in-vessel structures will be upgraded

A High Efficient Piezoelectric Windmill using Magnetic Force for Low Wind Speed in Wireless Sensor Networks

Abstract: An innovative small-scale piezoelectric energy harvester has been proposed to gather wind energy. A conventional horizontal-axis wind power generation has a low generating efficiency at low wind speed. To overcome this weakness, we designed a piezoelectric windmill optimized at low-speed wind. A piezoelectric device having high energy conversion efficiency is used in a small windmill. The maximum output power of the windmill was about 3.14 mW when wind speed was 1.94 m/s. Finally, the output power and the efficiency of the system were compared with a conventional wind power system. This work will be beneficial for the piezoelectric energy harvesting technology to be applied to the real world such as wireless sensor networks (WSN).

Use of Graphene for Solar Cells

Abstract: In the last decade, graphene has been spotlighted as one of the novel materials for transparent conductive electrodes (TCEs) of solar cells. This paper provides an overview of recent progress for the application of graphene TCEs in solar cells employing representative active materials. This review focuses especially on the structure and characteristics of solar cells employing three majorgroup materials: Si-based materials (crystalline Si, porous Si, Si nanowire, and Si quantum dots), compound (CdTe and GaAs) thin films; organic and perovskite materials. The graphene TCEs are very promising for producing high-efficiency solar cells, but their stabilities are a key issue to overcome for the practical applications. The significance and outlook of the graphene-TCE-based solar cells are finally summarized.

Heavy Baryons in a Pion Mean-Field Approach: A Brief Review

Abstract: We review in this paper a series of recent works on properties of singly heavy baryons, based on a pion mean-field approach. In the limit of an infinitely heavy-quark mass, the heavy quark inside a heavy baryon can be regarded as a static color source. In this limit, a heavy baryon can be viewed as Nc − 1 valence quarks bound by the pion mean fields which are created self-consistently by the presence of the Nc valence quarks. We show that this mean-field approach can successfully describe the masses and the magnetic moments of the lowest-lying singly heavy baryons, using all the parameters fixed in the light-baryon sector except for the hyperfine spin-spin interactions. We also review a recent work on identifying the newly found excited Ωc baryons reported by the LHCb Collaboration. We discuss possible scenarios to identify them. Finally, we give a future perspective on this pion mean-field approach.

Microstructure of As-cast Co-Cr-Mo Alloy Prepared by Investment Casting

Abstract: The microstructure of a cobalt-base alloy (Co-Cr-Mo) obtained by an investment casting process was studied. This alloy complies with the ASTM F75 standard and is widely used in the manufacturing of orthopedic implants owing to its high strength, good corrosion resistance, and excellent biocompatibility. This work focuses on the resulting microstructures arising from normal industrial environmental conditions. The characterization of the samples was carried out using optical microscopy, field emission scanning electron microscopy and energy-dispersive spectroscopy. In this study, the as-cast microstructure is an γ-Co (face-centered cubic) dendritic matrix with the presence of a secondary phase, such as M23C6 carbides precipitated at grain boundaries and interdendritic zones. These precipitates are the main strengthening mechanism in this type of alloy. Other minority phases, such as the σ phase, were also detected, and their presence could be linked to the manufacturing process and environment.

Mg 2 B IV : Narrow Bandgap Thermoelectric Semiconductors

Abstract: Thermoelectric materials can convert thermal energy directly into electric energy and vice versa. The electricity generation from waste heat via thermoelectric devices can be considered as a new energy source. For instance, automotive exhaust gas and all industrial processes generate an enormous amount of waste heat that can be converted to electricity by using thermoelectric devices. Magnesium compound Mg2BIV (BIV = Si, Ge or Sn) has a favorable combination of physical and chemical properties and can be a good base for the development of new efficient thermoelectrics. Because they possess similar properties to those of group BIV elemental semiconductors, they have been recognized as good candidates for thermoelectric applications. Mg2Si, Mg2Ge and Mg2Sn with an antifluorite structure are narrow bandgap semiconductors with indirect band gaps of 0.77 eV, 0.74 eV, and 0.35 eV, respectively. Mg2BIV has been recognized as a promising material for thermoelectric energy conversion at temperatures ranging from 500 K to 800 K. Compared to other thermoelectric materials operating in the similar temperature range, such as PbTe and filled skutterudites, the important aspects of Mg2BIV are non-toxic and earth-abundant elements. Based on classical thermoelectric theory, the material factor β ~ (m*~ /me)3/2μκ L −1 can be utilized as the criterion for thermoelectric material selection, where m* is the density-of-states effective mass, me is the mass of an electron, μ is the carrier mobility, and κL is the lattice thermal conductivity. The β for magnesium silicides is 14, which is very high compared to 0.8 for iron silicides, 1.4 for manganese silicides, and 2.6 for silicon-germanium alloys. In this paper, basic phenomena of thermoelectricity and transport parameters for thermoelectric materials were briefly introduced, and thermoelectric properties of Mg2BIV synthesized by using a solid-state reaction were reviewed. In addition, various Mg2BIV compounds were discussed: intrinsic Mg2Si, doped Mg2Si:Dm (D = Al, In, Bi, Sb, Te or Se), and solid solutions of intrinsic/doped Mg2Si1 − xSn x :D m and Mg2Si1 − xGe x :D m .

Design for Hybrid Circular Bragg Gratings for a Highly Efficient Quantum-Dot Single-Photon Source

Abstract: We present a design for hybrid circular Bragg gratings (hCBGs) for efficiently extracting single-photons emitted by InAs quantum dots (QDs) embedded in GaAs. Finite-difference time-domain simulations show that a very high photon collection efficiency (PCE) up to 96% over a 50 nm bandwidth and pronounced Purcell factors up to 19 at cavity resonance are obtained. We also systematically investigate the geometry parameters, including the SiO2 thickness, grating period, gap width and the central disk radius, to improve the device performances. Finally, the PCEs and the Purcell factors of QDs located at different positions of the hCBG are studied, and the results show great robustness against uncertainties in the location of the QD.

Entropy Generation Minimization in MHD Boundary Layer Flow over a Slendering Stretching Sheet in the Presence of Frictional and Joule Heating

Abstract: In the present paper, we study the entropy analysis of boundary layer flow over a slender stretching sheet under the action of a non uniform magnetic field that is acting perpendicular to the flow direction. The effects of viscous dissipation and Joule heating are included in the energy equation. Using similarity transformation technique the momentum and thermal boundary layer equations to a system of nonlinear differential equations. Numerical solutions are obtained using the shooting and fourth-order Runge-Kutta method. The expressions for the entropy generation number and Bejan number are also obtained using a suggested similarity transformation. The main objective of this article is to investigate the effects of different governing parameters such as the magnetic parameter (M2), Prandtl number (Pr), Eckert number (Ec), velocity index parameter (m), wall thickness parameter (α), temperature difference parameter (Ω), entropy generation number (Ns) and Bejan number (Be). All these effects are portrayed graphically and discussed in detail. The analysis reveals that entropy generation reduces with decreasing wall thickness parameter and increasing temperature difference between the stretching sheet and the fluid outside the boundary layer. The viscous and magnetic irreversibilities are dominant in the vicinity of the stretching surface.

In-situ XPS Study of Core-levels of ZnO Thin Films at the Interface with Graphene/Cu

Abstract: We have investigated core-levels of ZnO thin films at the interface with the graphene on Cu foil using in-situ X-ray Photoelectron Spectroscopy (XPS). Spectral evolution of C 1s, Zn 2p, and O 1s are observed in real time during RF sputtering deposition. We found binding energy (BE) shifts of Zn 2p and ‘Zn−O’ state of O 1s depending on ZnO film thickness. Core-levels BE shifts of ZnO will be discussed on the basis of electron transfer at the interface and it may have an important role in the electronic transport property of the ZnO/graphene-based electronic device.

How Can We Erase States Inside a Black Hole

Abstract: We investigate an entangled system, which is analogous to a composite system of a black hole and Hawking radiation. If Hawking radiation is well approximated by an outgoing particle generated from pair creation around the black hole, such a pair creation increases the total number of states. There should be a unitary mechanism to reduce the number of states inside the horizon for black hole evaporation. Because the infalling antiparticle has negative energy, as long as the infalling antiparticle finds its partner such that the two particles form a separable state, one can trace out such a zero energy system by maintaining unitarity. In this paper, based on some toy model calculations, we show that such a unitary tracing-out process is only possible before the Page time while it is impossible after the Page time. Hence, after the Page time, if we assume that the process is unitary and the Hawking pair forms a separable state, the internal number of states will monotonically increase, which is supported by the Almheiri-Marolf-Polchinski-Sully (AMPS) argument. In addition, the Hawking particles cannot generate randomness of the entire system; hence, the entanglement entropy cannot reach its maximum. Based on these results, we modify the correct form of the Page curve for the remnant picture. The most important conclusion is this: if we assume unitarity, semi-classical quantum field theory, and general relativity, then the black hole should violate the Bekenstein-Hawking entropy bound around the Page time at the latest; hence, the infinite production arguments for remnants might be applied for semi-classical black holes, which seems very problematic.

Numerical Analysis of Nanogap Effects in Metallic Nano-disk and Nano-sphere Dimers: High Near-field Enhancement with Large Gap Sizes

Abstract: Various gap sizes are investigated numerically to extract the local electric field enhancement from a gold sphere and disk dimer systems. Our simulations predict that a metallic disk dimer system(s) exhibit large local electric field enhancements at larger gap sizes (20 nm, 40 nm) as compared to that of sphere dimer designs (gap size = 8 nm, 14 nm). These gap size differences ~ 2.5 -3.3 times larger as compared to that of sphere dimer systems, facilitates the device fabrication. These numbers are obtained by the influence of uniform gap size distribution as a function of total volume “±Z direction”. Such geometry, by achieving good local electric field enhancement from larger gap size, will enhance the variety of potential applications in the field of plasmonics, sensors, single molecule detection, surface enhanced spectroscopy, and so on.

Low Cost Alcoholic Breath Sensor Based on SnO 2 Modified with CNTs and Graphene

Abstract: In this work, SnO2 modified with reduced graphene oxide (rGO) and carbon nanotubes (CNTs) separately and combined sensitized by using the co-precipitation method and their sensing behavior toward ethanol vapor at room temperature were investigated. An interdigitated electrode (IDE) gold substrate is very expensive compared to a fluorine doped tin oxide (FTO) substrate; hence, we used the latter to reduce the fabrication cost. The structure and the morphology of the studied materials were characterized by using differential thermal analyses (DTA) and thermogravimetric analysis (TGA), transmission electron microscope (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller surface area and Barrett-Joyner-Halenda (BJH) pore size measurements. The studied composites were subjected to ethanol in its gas phase at concentrations from 10 to 200 ppm. The present composites showed high-performance sensitivity for many reasons: the incorporation of SnO2 and CNTs which prevents the agglomeration of rGO sheets, the formation of a 3D mesopourus structure and an increase in the surface area. The decoration with rGO and CNTs led to more active sites, such as vacancies, which increased the adsorption of ethanol gas. In addition, the mesopore structure and the nano size of the SnO2 particles allowed an efficient diffusion of gases to the active sites. Based on these results, the present composites should be considered as efficient and low-cost sensors for alcohol.

Electrodeposition of CdS Thin Films at Various pH Values

Abstract: The effects of pH value on CdS thin films fabricated by using electrodeposition were investigated in detail. The pH values of the final solutions were adjusted between 1 and 5. Aqueous solutions of HCl and NaOH were used to adjust the pH. The reaction rates were changed by the pH due to the fact that the pH affected the rate of release of sulphide from sodium thiosulfate. The structural, optical and morphological properties of the films were analyzed by using X-ray diffraction, Ultraviolet-visible spectroscopy and scanning electron microscopy, respectively. Compact films with good crystallinity were obtained at pH value of 4 and 5.

Electron Transport in a Multiple Quantum Dot: Recent Progress

Abstract: A multiple quantum dot provides an experimental tool for manipulating and detecting many-body quantum states of electrons in a level of controlling parameters of the corresponding Hamiltonians. We review recent experimental and theoretical studies on many-body states of electrons with orbital or charge degrees of freedom in multiple quantum dot systems and the resulting electron transport, focusing on triple quantum dots. This review article covers experimental backgrounds of quantum dots, orbital states and the resulting Kondo e ects in a double quantum dot, charge frustration in a triple quantum dot, charge Kondo e ects in a triple quantum dot, and quantum entanglement in electron states of quantum dots.

Synthesis and Characterization of Some Alkaline-Earth-Oxide Nanoparticles

Abstract: The present work reports the synthesis of MgO and CaO nanoparticles by using the sol-gel autocombustion method. The annealing of the precursor at 1200 °C was observed to lead the formation of MgO nanoparticles having average crystallite size of ~ 31 nm. Annealing the precursor at same temperature produced materials having a CaO phase with a minor impure phase of calcium carbonate (~ 3%). The crystallite size corresponding to the CaO phase was 38 nm. A change of thermal history in the precursor was observed not to result in an improvement of the CaO phase. The change of thermal history in the precursor gave rise to mixed phases of CaCO3 and Ca(OH)2 rather than the phase of CaO. Further, annealing at 1200 °C for 12 h resulted in the formation of the CaO phase along with almost 1 - 5% of calcium hydroxide as an impurity phase. X-ray absorption spectroscopic measurements carried out on these materials revealed that the local electronic/atomic structure of these oxides was not only affected by the impurity phases but also influenced by the carbaneous impurities attached to the crystallites.

Magnetocaloric Properties of AlFe2B2 Including Paramagnetic Impurities of Al13Fe4

Abstract: AlFe2B2 produced by using a conventional arc melter has a ferromagnetic material with a Curie temperature (TC) of around 300 K, but the arc-melt generates paramagnetic Al13Fe4 impurities during the synthesis of AlFe2B2. Impurities are brought to cause a decrease in magnetocaloric effects (MCEs). To investigate the effects of Al13Fe4 impurities on MCEs, we prepared and compared ascast and acid-treated samples, where the acid treatment was performed to remove the Al13Fe4 impurities. For the structural analysis, powder X-ray diffraction was carried out, and the measured data were subjected to a Rietveld refinement. The presence of Al13Fe4 impurities in the as-cast sample was observed in the phase analysis measurements. Magnetic properties were investigated by using Superconducting Quantum Interference Device (SQUID) measurements for the as-cast and the acid-treated AlFe2B2 samples. From isothermal magnetization measurements, Arrott plots were obtained showing that the transition of AlFe2B2 has a second-order magnetic phase transition (SOMT). The TC and the saturation magnetization increased for the acid-treated sample due to removal of the paramagnetic impurities. As a consequence, the magnetic entropy change (−ΔS) increased in the pure AlFe2B2 samples, but the full width at half maximum in the plot of −ΔS vs. T decreased due to the absence of impurities.

Sensing and Vetoing Loud Transient Noises for the Gravitational-wave Detection

Abstract: Since the first detection of gravitational-wave (GW), GW150914, September 14th 2015, the multimessenger astronomy added a new way of observing the Universe together with electromagnetic (EM) waves and neutrinos. After two years, GW together with its EM counterpart from binary neutron stars, GW170817 and GRB170817A, has been observed. The detection of GWs opened a new window of astronomy/astrophysics and will be an important messenger to understand the Universe. In this article, we briefly review the gravitational-wave and the astrophysical sources and introduce the basic principle of the laser interferometer as a gravitational-wave detector and its noise sources to understand how the gravitational-waves are detected in the laser interferometer. Finally, we summarize the search algorithms currently used in the gravitational-wave observatories and the detector characterization algorithms used to suppress noises and to monitor data quality in order to improve the reach of the astrophysical searches.