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[IEEE 2018 20th International Symposium on High-Current Electronics (ISHCE) - Tomsk, Russia (2018.9.16-2018.9.22)] 2018 20th International Symposium on High-Current Electronics (ISHCE) - Generation of Terahertz Radiation by Electron Beam-Plasma Interaction
摘要： At present, the search for new methods of generation electromagnetic radiation in the terahertz frequency range (THz) has emerged as one of the most promising rapidly in science and engineering, developing areas of research including security and medical diagnostics. One of the modern solutions of the problem is the generation of electromagnetic (EM) waves due to the interaction of high-current relativistic electron beams with plasma. Since in this case the radiation frequency is comparable with the plasma frequency, it can be easily adjusted by simply changing the plasma density. The efficient terahertz electromagnetic emission was produced during the injection of relativistic electron beams into plasma in laboratory experiments at the GOL-3 facility INP SB RAS. In this paper the mechanisms of the high efficiency of energy transfer from the relativistic electron beam to the EM radiation in turbulent regime of collisionless plasma are investigated on the base of computer simulation. The kinetic approach for ion and electron plasma components, as well as for electron beam, was used in 2D numerical model with the real mass ratio of charged particles. A parallel electromagnetic particle-in-cell (PIC) code UMKA2D3V was applied to simulate beam-plasma system for parameters close to the parameters of laboratory experiments at GOL-3 facility. Regimes of injection of one electron beam into the plasma and the counter injection of electron beams were considered. Computational experiments were performed using modern computer systems with massively parallel architecture.
关键词： terahertz radiation,electron beam-plasma interaction,PIC-method,plasma physics
更新于2025-09-09 09:28:46
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Reference Module in Materials Science and Materials Engineering || Piezoelectric Ultrasonic Motors
摘要： In general, piezoelectric ultrasonic motors (USMs) contain two basic components that are the stator and the rotor. Piezoelectric and elastic materials in a stator are combined in various ways forming a composite structure. Exciting at least two orthogonal mechanical vibration modes of the composite stator using single or orthogonal multiple high-frequency a.c. signals generates mechanical elliptical motion on the stator surface. The rotor is pressed against the stator's surface and a rotation is produced by frictional interaction between the touching stator and rotor surfaces.
关键词： Stator,Piezoelectric,Rotor,Frictional Interaction,Ultrasonic Motors
更新于2025-09-09 09:28:46
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Spontaneous and stimulated radiative emission of modulated free-electron quantum wavepackets—semiclassical analysis
摘要： Here we present a semiclassical analysis of spontaneous and stimulated radiative emission from unmodulated and optically-modulated free-electron quantum wavepackets. We show that the radiative emission/absorption and corresponding deceleration/acceleration of the wavepackets depend on the controllable ‘history-dependent’ wavepacket size. The characteristics of the radiative interaction when the wavepacket size (duration) is short relative to the radiation wavelength, are close to the predictions of the classical point-particle modelling. On the other hand, in the long-sized wavepacket limit, the interaction is quantum-mechanical, and it diminishes exponentially at high frequency. We exemplify these effects through the scheme of Smith-Purcell radiation, and demonstrate that if the wavepacket is optically-modulated and periodically-bunched, it exhibits ?nite radiative emission at harmonics of the modulation frequency beyond the limit of high-frequency cutoff. Besides, the radiation analysis is further extended to the cases of superradiant emission from a beam of phase-correlated modulated electron wavepackets. The features of the wavepacket-dependent radiative emission explain the classical-to-quantum transition, and indicate a way for measuring the quantum electron wavepacket size. This suggests a new direction for exploring light–matter interaction.
关键词： radiative emission,light–matter interaction,wavepacket-dependent radiative emission
更新于2025-09-09 09:28:46
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A Dynamic Tetracationic Macrocycle Exhibiting Photoswitchable Molecular Encapsulation
摘要： Designing macrocycles with appropriate molecular recognition features that allow for the integration of suitable external stimuli to control host?guest processes is a challenging endeavor which enables molecular containers to solubilize, stabilize and separate chemical entities in an externally controlled manner. Herein, we introduce photo- and thermal-responsive elements into a semi-rigid tetracationic cyclophane, OPVEx2Box4+, that is composed of oligo(p-phenylenevinylene) pyridinium units and the biphenylene-bridged 4,4-bipyridinium extended viologens, and adopts a rectangle-like geometry. It transpires that the reversibility of the photoactive oligo(p-phenylenevinylene) pyridinium unit is dramatically improved when incorporated in a macrocyclic scaffold, and the configurations of the cyclophane can go back and forth between (EE)- and (EZ)-isomers upon alternating blue light irradiation and heat. When the macrocycle is found in its (EE)-configuration, it is capable of binding various π-electron-rich guests?e.g., anthracene and perylene?as well as π-electron-deficient guests?e.g., 9,10-anthraquinone and 5,12-tetracenequinone?through charge transfer and van der Waals interactions. When irradiated with blue light, the (EE)-isomer of the cyclophane can be transformed successfully to the (EZ)-isomer, resulting in the switching off of the binding affinity for guest molecules, which are bound once again upon heating. The use of light and heat as external stimuli to control host?guest interaction involving a multi-responsive host and various guests provides us with a new opportunity to design and construct more advanced molecular switches and machines.
关键词： photoswitchable,tetracationic cyclophane,host-guest interaction,molecular encapsulation,macrocycle
更新于2025-09-09 09:28:46
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Near-threshold bound states of the dipole-dipole interaction
摘要： We study the two-body bound states of a model Hamiltonian that describes the interaction between two field-oriented dipole moments. This model has been used extensively in the many-body physics of ultracold polar molecules and magnetic atoms, but its few-body physics has been explored less fully. With a hard-wall short-range boundary condition, the dipole-dipole bound states are universal and exhibit a complicated pattern of avoided crossings between states of different character. For more realistic Lennard–Jones short-range interactions, we consider parameters representative of magnetic atoms and polar molecules. For magnetic atoms, the bound states are dominated by the Lennard–Jones potential, and the perturbative dipole-dipole interaction is suppressed by the special structure of van der Waals bound states. For polar molecules, we find a dense manifold of dipole-dipole bound states with many avoided crossings as a function of induced dipole or applied field, similar to those for hard-wall boundary conditions. This universal pattern of states may be observable spectroscopically for pairs of ultracold polar molecules.
关键词： Lennard–Jones potential,bound states,ultracold polar molecules,dipole-dipole interaction,magnetic atoms
更新于2025-09-09 09:28:46
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Single-beam resonant spin amplification of electrons interacting with nuclei in a GaAs/(Al,Ga)As quantum well
摘要： The dynamic polarization of nuclear spins interacting with resident electrons under resonant excitation of trions is studied in a nominally undoped GaAs/(Al,Ga)As quantum well. Unlike in common time-resolved pump-probe techniques, we used a single-beam approach in which the excitation light is modulated between the circular and linear polarization states. The time-integrated intensity of the excitation laser re?ected from the sample surface, proportional to the optical generation rate and changing due to the pumping of the resident electrons, is detected. Polarized electrons, on the other hand, transfer their spin to the lattice nuclei via the hyper?ne interaction. Exciting the sample with a train of pulses in an external magnetic ?eld leads to resonant spin ampli?cation observed when the Larmor precession frequency is synchronized with the laser pulse repetition rate. A buildup of the nuclear spin polarization causes a shifting of the resonant spin ampli?cation peaks since the resulting nuclear ?eld alters the strength of the external magnetic ?eld experienced by the electrons. It was established that the nuclear spin polarization time T1 is temperature dependent and, owing to the electron localization at lower temperatures, becomes shorter. “Locking” of the nuclear (Overhauser) ?eld in the oblique external magnetic ?eld, related to the anisotropy of the electron g factor, was observed. The g factor ratio between the in-plane (g(cid:2)) and out-of-plane (g⊥) components was estimated to be g⊥/g(cid:2) = 1.3.
关键词： hyper?ne interaction,resonant spin ampli?cation,resonant excitation,electron g factor,quantum well,dynamic polarization,single-beam approach,nuclear spins
更新于2025-09-09 09:28:46
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Study of interaction between citrate-coated silver nanoparticles and gamma globulin using spectroscopic method
摘要： Studies on the biomedical applications of silver nanoparticles (AgNPs) have attracted great attention during the past decades. In this paper, the citrate-coated AgNPs with uniform size and good monodispersity are synthesized. The diameter of the synthesized AgNPs is about 25.4 nm. Its interaction with γ-globulin was thoroughly studied using UV-vis absorption spectroscopy, fluorescence spectroscopy, fluorescence lifetime measurement, synchronous fluorescence spectroscopy, 3D fluorescence spectroscopy as well as CD spectroscopy. From the above experiments, we can obtain that citrate-coated AgNPs can bind to γ-globulin with high affinity. The fluorescence quenching of γ-globulin by AgNPs is in a static mechanism. Van der Waals interactions and hydrogen bonds play great role in the binding interaction. The interaction can induce slight conformational change of γ-globulin.
关键词： citrate-coated,γ-globulin,interaction,silver nanoparticles,spectroscopic method
更新于2025-09-09 09:28:46
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[IEEE 2018 International Conference on Information and Communication Technology Robotics (ICT-ROBOT) - Busan, Korea (South) (2018.9.6-2018.9.8)] 2018 International Conference on Information and Communication Technology Robotics (ICT-ROBOT) - Real-time Face Tracking for Human-Robot Interaction
摘要： This paper proposes a real-time human face tracking to be used for human robot interaction (HRI). The system consists of human face like region detection, its tracking and camera motion control according to the displacement between the time interval. The former task is performed via utilizing Viola-Jones algorithm as the face tracking uses the Kanade-Lucas-Tomasi (KLT) algorithm with various poses conditions. The camera is controlled by the displacement according to its displacement between image frames as a tracking result from the previous stage. The experimental results show that human faces were successfully tracked even while the users are wearing glasses, hat, or lateral face postures in real-time. The experiments were done in the 28.32 frames per second as maximum speed.
关键词： Real-time System,Human Robot Interaction,Face Tracking,KLT Algorithm
更新于2025-09-09 09:28:46
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Precise Nanoparticle – Reactant Interaction Outplays Ligand Poisoning in Visible-Light Photocatalysis
摘要： Metal nanoparticles (NPs) and ligands are two inseparable entities. However, ligands present on the surface of NPs can ‘poison’ a photocatalyst by hindering the NP accessibility to reactants and the movement of charge carriers. Here we present an elegant strategy to accomplish efficient photocatalysis by taking advantage of ligands on the NP surface. Our approach of introducing favorable interactions between NP catalyst and reactant is tested in the model photocatalytic reduction of ferricyanide by gold nanoparticles (AuNP). The favorable interaction arising from the precise tuning of electrostatic potential results in the localization of reactants around the AuNP catalyst. The close proximity between AuNP and ferricyanide improves the NP accessibility and electron transfer rate, thereby suppressing the ligand poisoning effect. Such interaction driven enhancement in photocatalytic performances can be prominent in the emerging area of ‘ligand directed product formation’ in NP catalysis.
关键词： Nanoparticles,Gold Nanoparticles,Ligand Poisoning,Electrostatic Interaction,Photocatalysis
更新于2025-09-09 09:28:46
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Nitrogen Trapping Ability of Hydrogen-Induced Vacancy and the Effect on the Formation of AlN in Aluminum
摘要： This paper presents the ternary interaction of N, H, and vacancy point defects and the nitrogen trapping ability of aluminum vacancies induced by hydrogen by means of DFT methods employed in VASP (Vienna Ab initio Simulation Package) and Abinit packages. The obtained vacancy formation energy of 0.65 eV is close to experimental values. Although the N–vacancy complex is unstable with the negative binding energy of ?0.51 eV, the stability of H–vacancy–N is proved by the positive binding energy of 0.59 eV and the appearance of the orbital hybridization in the density of state (DOS) of atoms connecting to this complex. Moreover, Al vacancies can trap more than 4 N atoms, which prevents the formation of aluminum nitride and subsequently affects not only the hardness of the Al surface but also many practical applications of AlN coating.
关键词： ternary point-defect interaction,first-principles calculations,alpha aluminum,superabundant vacancy
更新于2025-09-09 09:28:46