γ-radiation effects on metal oxide particles and their wetted surfaces

ABSTRACT

Typical metal oxide corrosion products of structural materials have been irradiated with γ-rays in ultra-pure water to investigate the effect of radiation on the surface oxide and the nature of adsorbed water. Analysis techniques including thermal gravimetric analysis, differential thermal analysis, diffuse reflectance infrared Fourier transform spectroscopy, and X-ray photoelectron spectroscopy before and after γ-irradiation were employed to investigate surface structural effects and adsorbed water behaviour. The production of H₂ in the oxide nanoparticle mixtures was investigated by gas chromatography to probe the mechanism of radiolysis in the water/oxide mixtures and the relationship with surface water. The nature of water at the surface of the oxides was affected by γ-radiation and the relationship was dependent on the particle composition. The rate of H₂ production was shown to be oxide dependent, and higher rates of H₂ formation were attributed to the decomposition of surface adsorbed water. Changes to the surface chemistry and H₂ production rates were found to be highly dependent on the surface chemistry of the metal oxide nanoparticle and no bulk structural changes were observed.     

Direct Observation of Worm‐Like Nanochannels and Emergent Magnon Motifs in Artificial Ferromagnetic Quasicrystals

Quasicrystalline structures and aperiodic metamaterials find applications ranging from established consumer gadgets to potential high‐tech photonic components owing to both complex arrangements of constituents and exotic rotational symmetries. Magnonics is an evolving branch of magnetism research where information is transported via magnetization oscillations (magnons). Their control and manipulation are so far best accomplished in periodic metamaterials which exhibit properties artificially modulated on the nanoscale. They give rise to functional components, such as band stop filters, magnonic transistors and nanograting couplers. Here, spin‐wave excitations in artificial ferromagnetic quasicrystals created via aperiodic arrangement of nanoholes are studied experimentally. Their ten‐fold rotational symmetry results in multiplexed magnonic nanochannels, suggesting a width down to 50 nm inside a so‐called Conway worm. Key elements of design are emergent magnon motifs and the worm‐like features which are scale‐invariant and not present in the periodic metamaterials. By imaging wavefronts in quasicrystals, insight is gained into how the discovered features materialize as a dense wavelength division multiplexer.     

Cross-layer selective routing for cost and delay minimization in IEEE 802.11ac wireless mesh network

Wireless Networks - A Wireless Internet-access Mesh NETwork (WIMNET) provides scalable and reliable internet access through the deployment of multiple access points (APs) and gateways (GWs). In...     

Combining remote sensing with physical flow laws to estimate river channel geometry

A reliable representation of river terrains is essential to river research. Field surveys of river channel geometry are time‐consuming, costly, and logistically constrained and thus would encounter difficulties to achieve sufficient spatial coverage, resolution, and frequency of resurvey. This paper aims to demonstrate an efficient approach to building a river terrain model (RTM), the emphasis being on how to combine bathymetry and topography derived from satellite images captured at different flow stages. A method for calculating the difference between high and low stages (DHLS) based on the uniform‐flow theory is proposed. Calculations are carried out for a 13‐km long meandering section of the gravel‐bed Goulais River in Canada, which features pools and riffles, alternating point bars, and midchannel bars. A RTM for this complex section has been successfully produced. It consists of three data components: bathymetry at low stage, topography at high stage, and DHLS. The results capture realistic characteristics, including thalweg shift, steep outer banks, and gradual inner banks. They also show realistic longitudinal and lateral locations of pools and riffles. To illustrate potential applications of RTM, this paper has computed extreme bed shear stresses at bankfull discharge through hydrodynamics simulations of depth‐averaged flow in the river section and further estimated bed‐sediment grain‐size distributions. The estimates compare well with field measurements. The DHLS can vary significantly along a river channel. The proposed method for determining it is not site‐specific, and hence applicable to other rivers. The novelty of the methodology discussed lies in combining remote sensing techniques with physical flow laws.     

Robust bin-picking system using tactile sensor

ABSTRACT

This paper presents a robust bin-picking system utilizing tactile sensors and a vision sensor. The object position and orientation are estimated using a fast template-matching method through the vision sensor. When a robot picks up an object, the tactile sensors detect the success or failure of the grasping, and a force sensor detects the contact with the environment. A weight sensor is also used to judge whether the lifting of the object has been successful. The robust and efficient bin-picking system presented herein is implemented through the integration of different sensors. In particular, the tactile sensors realize rope-shaped object picking that has yet to be made possible with conventional picking systems. The effectiveness of the proposed method was confirmed through grasping experiments and in a competitive event at the World Robot Challenge 2018.     

Analytical formula for the pseudoinverse and its application for singular path tracking with a class of redundant robotic limbs

This work introduces a novel formula for calculating the right pseudoinverse, proposed for a class of kinematically redundant robotic limbs with one degree of redundancy. The formula is derived from the Singularity-Consistent method and is expressed as a sum of scalable vector fields parameterized by the desired end link twist. Pseudoinverse properties are ensured by assigning proper vector field intensities. The formula is applied to the IK problem, whereby the end link tracks a degenerate singular path, i.e. a nontangential path that penetrates the workspace boundary, and thus resulting in an unavoidable kinematic singularity. Through this method, the instability of the conventional pseudoinverse solution and the stationary point problem obtained when the solution is stripped from the ill-conditioned denominator is avoided. In addition, the appearance of the ‘inner obstacle’ algorithmic singularity problem known from a previous work can be circumvented. The performance of the method is verified via numerical simulations with an S-R-S-type structure and the Barrett WAM.     

A New Approach to Suppress the Effect of Machining Error for Waveguide Septum Circular Polarizer at 230 GHz Band in Radio Astronomy

A new stepped septum-type waveguide circular polarizer (SST-CP) was developed to operate in the 230 GHz band for radio astronomy, especially submillimeter-band VLBI observations. For previously reported SST-CP models, the 230 GHz band is too high to achieve the design characteristics in manufactured devices because of unexpected machining errors. To realize a functional SST-CP that can operate in the submillimeter band, a new method was developed, in which the division surface is shifted from the top step of the septum to the second step from the top, and we simulated the expected machining error. The SST-CP using this method can compensate for specified machining errors and suppress serious deterioration. To verify the proposed method, several test pieces were manufactured, and their characteristics were measured using a VNA. These results indicated that the insertion losses were approximately 0.75 dB, and the input return losses and the crosstalk of the left- and right-hand circular polarization were greater than 20 dB at 220–245 GHz on 300 K. Moreover, a 230 GHz SST-CP was developed by the proposed method and installed in a 1.85-m radio telescope receiver systems, and then had used for scientific observations during one observation season without any problems. These achievements demonstrate the successful development of a 230 GHz SST-CP for radio astronomical observations. Furthermore, the proposed method can be applicable for observations in higher frequency bands, such as 345 GHz.     

Proposal for selective isotope transmutation of long-lived fission products using quasi-monochromatic γ-ray beams

We have proposed a new selective isotope transmutation method using photonuclear reactions with quasi-monochromatic γ-ray beams. This method is based on the fact that the particle threshold of a long-lived fission product (LLFP) such as ⁹³Zr, ¹⁰⁷Pd, or ⁷⁹Se is lower than those of stable isotopes of the same chemical element. Therefore, this method has the excellent advantage that LLFPs cannot, in principle, be produced newly even if the target materials include stable isotopes in addition to LLFPs. Furthermore, this method is effective for ¹²⁶Sn, ^{135, 137}Cs, ⁹⁰Sr, and ³H. The nuclear data involved and suitable γ-ray sources are discussed. Laser Compton scattering γ-ray sources and neutron capture γ-rays in nuclear reactors are candidates for this method.     

Effect of nitrate on corrosion of austenitic stainless steel in boiling nitric acid solution containing chromium ions

The oxidation behavior of chromium and the corrosion behavior of austenitic stainless steel in boiling nitric acid solution containing highly concentrated nitrates were investigated using UV-visible spectroscopic measurements, Raman spectral measurements, immersion tests, and potentiodynamic polarization measurements. The oxidation rate measurement of chromium from Cr(III) to Cr(VI) was performed by 1 M boiling nitric acid solution containing each highly concentrated nitrates: Al(NO₃)₃, Nd(NO₃)₃, Ca(NO₃)₂, Mg(NO₃)₂, and NaNO₃ as a simulant of uranium nitrate in uranium concentrator in reprocessing plants. As a result, the rate of chromium oxidation was different depending on the added nitrates even at the same nitric acid concentration. In addition, the oxidation rate of chromium was increased with increasing the calculated partial pressure of nitric acid in consideration of the hydration of cation of nitrates. Furthermore, the corrosion rate of type 310 stainless steel was accelerated by the solution having a high chromium oxidation rate containing nitrates. These results indicated that the acceleration of the corrosion rate in the solutions depending on the oxidation rate of chromium, and the rate is affected by the salt-effect of nitrates.     

Design of carrier tRNAs and selection of four-base codons for efficient incorporation of various nonnatural amino acids into proteins in Spodoptera frugiperda 21 (Sf21) insect cell-free translation system

Spodoptera frugiperda 21 (Sf21) insect cell-free protein synthesizing system was expanded to include nonnatural amino acids. Orthogonal tRNAs that work as carriers of nonnatural amino acids in the insect system were explored. Four-base codons for assigning the positions of nonnatural amino acids were also selected. Mutated streptavidin mRNAs that contained different four-base codons were prepared and added to the insect cell-free system in the presence of various tRNAs possessing the corresponding four-base anticodons. The tRNAs were chemically aminoacylated with various types of nonnatural amino acids to examine their incorporation efficiencies. Using p-nitrophenylalanine as the nonnatural amino acid and streptavidin as the target protein, tRNA sequences and the types of four-base codons were optimized to maximize the yield of the nonnatural mutant and to minimize production of full-length proteins that do not contain the nonnatural amino acid. Among the tRNA sequences taken from a variety of tRNAs of nonstandard structures, the tRNA derived from Methanosarcina acetivorans tRNA(Pyl) was the most efficient and orthogonal tRNA. Of the CGGN-type four-base codons, CGGA and CGGG were the most efficient ones for assigning the positions of nonnatural amino acids. p-Nitrophenylalanine and 2-naphthylalanine were efficiently incorporated as in the case of Escherichia coli and rabbit reticulocyte cell-free systems. Much less efficient incorporation was observed, however, for other nonnatural amino acids, indicating that the insect system is less tolerant to the structural diversity of amino acids than the E. coli cell-free system.