We have successfully created a Direct Simulation Monte Carlo (DSMC) model on a commercial FEM software COMSOL Multiphysics (COMSOL). As far as we know, this is the first DSMC model developed on COMSOL. Since two particles as a colliding pair cannot be sampled simultaneously from the same population in the Particle-tracing module of COMSOL, a new inter-molecular collision scheme named “quasi-Nanbu scheme” has been introduced to the model. The results obtained for benchmark problems using the present DSMC model agree well with those from a theory and other DSMC codes.
SuperKEKB is an electron–positron collider with asymmetric energies at KEK aiming at a high luminosity of 8.0×1035 cm－2 s－1. During the Phase-1 commissioning from February to June 2016 and the Phase-2 commissioning from March to July 2018, the vacuum system worked well as a whole, and the increase in pressure per unit beam current decreased steadily. The photodesorption coefficients at arc sections reached approximately 1×10－6 molecules photon－1 and 7×10－8 molecules photon－1 finally for the positron and electron rings, respectively. The beam lifetime was mainly limited by the Touschek effect in both rings, rather than the beam-gas scattering. The electron cloud effect was observed in the positron ring during Phase-1, but it was suppressed by additional countermeasures applied before Phase-2.
Crystalline vanadium dioxide (VO2) shows a sharp insulator-metal transition (IMT) at relatively low temperature of around 68℃. Even in the polycrystalline VO2 film, IMT with resistance change over several orders of magnitude is realized. Voltage addition on the VO2 film leads to current jump at certain voltage with negative resistance (NR). In such I-V characteristics with NR, voltage across VO2 shows automatic transition between high and low resistance positions, which is called “self-oscillation phenomenon”. In this study, we fabricated VO2 thin films on conductive TiN layers, in which IMT with resistance change more than two orders of magnitude for out-of-plane direction was realized. Utilizing the VO2/TiN layered structure, we observed I-V characteristics with NR and self-oscillation with frequency higher than 1 MHz. Dependence of oscillation frequency on some parameters, such as source voltage, load resistance, and VO2 films thickness was examined. Furthermore, coupled-oscillation phenomenon achieved by capacitively-coupled two VO2 oscillators was investigated. Characteristic coupling with synchronized oscillation frequency and phase was observed. Coupled-oscillator is expected to be used for integrate and fire neuron element in neuro-morphic computing.
Surface analysis of the negative electrode materials for Li-based secondary batteries are essential. Here we focused on the oxide-based material (Li4Ti5O12) and Li-metal for promising negative electrode, and introduced the current studies of scanning probe microscopy based analysis. Atomistic structure of Li4Ti5O12(111) surface was investigated by scanning tunneling microscopy and medium energy ion scattering spectrometry, revealed Li-terminated structure was most suitable one. The revealed surface structure should be essential for discuss the surface reactivity and surface chemistry of Li-ion battery reaction for Li4Ti5O12 based electrode. Electrochemical Li-metal deposition process was investigated by operand atomic force microscopy (AFM) and surface adhesion mapping. Specific Li-metal deposition was revealed and explained by inhomogeneous surface film formation. The surface mechanism should contribute to develop the novel electrolyte and suitable modification of Li-metal surface.
We investigated the adsorption states and diffusion behavior of Pt and Fe atoms on pristine and various light-element-doped graphene using first-principle calculations based on density functional theory to reveal the support that can keep particle size of metal clusters for a long time. We show a weak interaction between Pt, Fe atoms and pristine graphene. The corresponding diffusion barrier for a Pt atom on pristine graphene is only 0.14 eV, which causes rapid agglomeration of Pt clusters. However, light-element-doped graphene shows large diffusion barrier for metal atoms. Notably, O, Si and P doped graphene show large diffusion barrier for both Pt and Fe atoms. Therefore, these light-element-doped graphene is a promising support for Pt and Fe clusters.
Thermal oxidation of Si substrate is an indispensable process for the Si device fabrication. However, as the required SiO2 film thickness becomes thinner, the influence of oxidation induced strain cannot be ignored. We adopted real-time photoelectron spectroscopy using synchrotron radiation as a method to measure simultaneously the oxidation induced strain and oxidation rate at the same place. Strain causes a photoelectron spectral shift of the inner shell, so we qualitatively estimated the strain from the shift amount. Using the spectral shifts, we found that there is a correlation between the strain and the SiO2/Si interface oxidation reaction rate. It also revealed that the interfacial oxidation accelerating effect is also obtained by thermal strain due to rapid temperature rise. These results can be explained by our proposed model in which point defects caused by strain become reaction sites at the SiO2/Si interface.
Bio-inspired and neuromorphic system now attracts great attention due to its high capacity for optimization and energy frugality in problem-solving. Use of physical noise fluctuations and spontaneous spiking signal are considered to be significant advantages in signal sensing and informational processing. We investigated a noise generation from single molecule adsorbed on a carbon nanotube (CNT), where a unique state fluctuation of molecule is origin of the noise. By using the molecule as a noise generator in CNT based nano-electronic device, we demonstrated a stochastic resonance device that detects small subthreshold signals. Furthermore, generation of spontaneous spikes similar to nerve impulses from a random CNT/molecule network were found. We propose an abstract molecular network model that yields results in good agreement with the experimental spike generation. These results indicate the possibility that complex functional networks can be constructed using molecular devices, and contribute to the development of neuromorphic devices.
High-voltage and plasma applications for agriculture, fishery and food processing are described in this paper. Repetitive operated compact pulsed power generators with a moderate peak power were developed for the applications in several stages of agriculture and food processing. Pulsed high-voltage produces intense high-electric field which can cause some biological effects such as stress response (stimulation) and electroporation. Types of pulsed power that also have biological effects are caused with gas and water discharges which include reactive species such as ROS and RNS. The repetitive pulse discharge was used for promoting growth of the vegetables and fruits. The growth rate of the vegetables and sugar content in the strawberry harvested after the cultivation increased by the plasma irradiation to the hydroponic solution. The leaf size of the plants increased with plasma treatment time. Number of colony forming units (CFU) of R. solanacearum in the liquid fertilizer decreased from 107 to 102 CFU/mL by the plasma treatment. Seedlings with the plasma treatment were relatively healthy ; in contrast, all seedlings in the positive control wilted and died from infection of R. solanacearum. The yielding rate of Shiitake mushroom (L. edodes) was improved with the high-voltage stimulation in fruit-body formation phase. The AC high-voltage keeping freshness for a relatively longer period of agricultural. The electrostatic effects can contribute to remove airborne bacteria and fungi spore from the storage house and container. This removal contributed to reduce the infection risk with fungi and bacteria. These applications can contribute a food supply chain in the world.
This review follows the previous one and covers the remaining issues and the operational parameters to be considered. The issues are thermal desorption mainly from an RGA ion source, sputtering of both an ion extraction plate of the source and some surface of an electron multiplier and consequent sputter deposition of contaminant on the source and the multiplier. Parameters such as an electron impact energy, an ion path energy and a dwell time of ion detection for appropriate RGA operation depending on measurement conditions will be discussed as well. A couple of tips for better RGA operation will be also given like consideration of gas molecule cracking pattern and how to use a differential pumping for a RGA.