Finite element analyses and verifying tests for a shock-absorbing effect of a pad in a spent fuel storage cask

A spent fuel storage cask is required to prove the safety of its canister under a hypothetical accidental drop condition which means that the canister is assumed to be free dropped on to a pad of the storage cask during the loading of the canister into a storage cask. In this paper, finite element analyses and verifying tests for a shock-absorbing effect of a pad in a spent fuel dry storage cask were carried out to improve the structural integrity of the canister under a hypothetical accidental drop condition. The pad of the storage cask was originally designed as cylindrical steel structure filled with concrete. The pad was modified by using the structure composed of steel and polyurethane-foam instead of the quarter of the upper concrete as an impact limiter. The effects of the shape and the thickness of the steel structure and the density of the polyurethane-foam which was used in between steel structures were studied. As the optimized pad of a spent fuel dry storage cask, the quarter of the upper concrete was replaced with 12 mm thick circular steel structure and polyurethane-foam whose density was 85 kg/m³. The drop tests of a 1/3 scale model for the canister on to the original pad and the optimized pad were conducted. The effect of the pad structure was evaluated from the drop tests. The optimized pad has a greater shock-absorbing effect than the original pad. In order to verify the analysis results, strains and accelerations in the time domain by the analytical methods were compared with those by a test. The numerical method of simulating the free drop test for a dry storage cask was verified and the numerical results were found to be reliable.     

One‐Step Transfer and Integration of Multifunctionality in CVD Graphene by TiO2/Graphene Oxide Hybrid Layer

We present a straightforward method for simultaneously enhancing the electrical conductivity, environmental stability, and photocatalytic properties of graphene films through one‐step transfer of CVD graphene and integration by introducing TiO₂/graphene oxide layer. A highly durable and flexible TiO₂ layer is successfully used as a supporting layer for graphene transfer instead of the commonly used PMMA. Transferred graphene/TiO₂ film is directly used for measuring the carrier transport and optoelectronic properties without an extra TiO₂ removal and following deposition steps for multifunctional integration into devices because the thin TiO₂ layer is optically transparent and electrically semiconducting. Moreover, the TiO₂ layer induces charge screening by electrostatically interacting with the residual oxygen moieties on graphene, which are charge scattering centers, resulting in a reduced current hysteresis. Adsorption of water and other chemical molecules onto the graphene surface is also prevented by the passivating TiO₂ layer, resulting in the long term environmental stability of the graphene under high temperature and humidity. In addition, the graphene/TiO₂ film shows effectively enhanced photocatalytic properties because of the increase in the transport efficiency of the photogenerated electrons due to the decrease in the injection barrier formed at the interface between the F‐doped tin oxide and TiO₂ layers.     

Fullerene polymer film as a highly efficient photocatalyst for selective solar fuel production from CO2

C₆₀-based polymeric systems have been constantly anticipated for sustainable solar energy conversion. Reported, herein is a C₆₀ polymer film as visible light active photocatalyst for efficient and selective reduction of CO₂ for the first time. The C₆₀ polymer photocatalyst is synthesized via covalent coupling of C₆₀ monomer units consisting of tetra substituted C₆₀-pyrene conjugates through spacer groups. The synthesized C₆₀ polymer photocatalyst possesses an extended network of well-defined repeating monomer units with good stability and visible light-induced photocatalytic activity. The enhanced visible light harvesting ability of C₆₀ polymer photocatalyst reasonably yields it with higher catalytic ability than its monomer unit. The C₆₀ polymer film photocatalyst upon coupling with the biocatalyst carries out highly selective visible light driven reduction of CO₂ to HCOOH (239.46 μmol). The tandem way of incorporating C₆₀ into visible light active polymeric films for continuous use may be highly rewarding for their extended photocatalytic activity for solar fuel production from CO₂. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48536.     

Systematic Study of Widely Applicable N‐Doping Strategy for High‐Performance Solution‐Processed Field‐Effect Transistors

A specific design for solution‐processed doping of active semiconducting materials would be a powerful strategy in order to improve device performance in flexible and/or printed electronics. Tetrabutylammonium fluoride and tetrabutylammonium hydroxide contain Lewis base anions, F^? and OH^?, respectively, which are considered as organic dopants for efficient and cost‐effective n‐doping processes both in n‐type organic and nanocarbon‐based semiconductors, such as poly[[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)] (P(NDI2OD‐T2)) and selectively dispersed semiconducting single‐walled carbon nanotubes by π‐conjugated polymers. The dramatic enhancement of electron transport properties in field‐effect transistors is confirmed by the effective electron transfer from the dopants to the semiconductors as well as controllable onset and threshold voltages, convertible charge‐transport polarity, and simultaneously showing excellent device stabilities under ambient air and bias stress conditions. This simple solution‐processed chemical doping approach could facilitate the understanding of both intrinsic and extrinsic charge transport characteristics in organic semiconductors and nanocarbon‐based materials, and is thus widely applicable for developing high‐performance organic and printed electronics and optoelectronics devices.     

Monolithic Graphene Trees as Anode Material for Lithium Ion Batteries with High C‐Rates

Monolithically structured reduced graphene oxide (rGO), prepared from a highly concentrated and conductive rGO paste, is introduced as an anode material for lithium ion batteries with high rate capacities. This is achieved by a mixture of rGO paste and the water‐soluble polymer sodium carboxymethylcellulose (SCMC) with freeze drying. Unlike previous 3D graphene porous structures, the monolithic graphene resembles densely branched pine trees and has high mechanical stability with strong adhesion to the metal electrodes. The structures contain numerous large surface area open pores that facilitate lithium ion diffusion, while the strong hydrogen bonding between the graphene layers and SCMC provides high conductivity and reduces the volume changes that occur during cycling. Ultrafast charge/discharge rates are obtained with outstanding cycling stability and the capacities are higher than those reported for other anode materials. The fabrication process is simple and straightforward to adjust and is therefore suitable for mass production of anode electrodes for commercial applications.     

Polymer Dielectrics and Orthogonal Solvent Effects for High‐Performance Inkjet‐Printed Top‐Gated P‐Channel Polymer Field‐Effect Transistors

We investigated the effects of a gate dielectric and its solvent on the characteristics of top‐gated organic field‐effect transistors (OFETs). Despite the rough top surface of the inkjet‐printed active features, the charge transport in an OFET is still favorable, with no significant degradation in performance. Moreover, the characteristics of the OFETs showed a strong dependency on the gate dielectrics used and its orthogonal solvents. Poly(3‐hexylthiophene) OFETs with a poly(methyl methacrylate) dielectric showed typical p‐type OFET characteristics. The selection of gate dielectric and solvent is very important to achieve high‐performance organic electronic circuits.     

Charge injection engineering of ambipolar field-effect transistors for high-performance organic complementary circuits

Ambipolar π-conjugated polymers may provide inexpensive large-area manufacturing of complementary integrated circuits (CICs) without requiring micro-patterning of the individual p- and n-channel semiconductors. However, current-generation ambipolar semiconductor-based CICs suffer from higher static power consumption, low operation frequencies, and degraded noise margins compared to complementary logics based on unipolar p- and n-channel organic field-effect transistors (OFETs). Here, we demonstrate a simple methodology to control charge injection and transport in ambipolar OFETs via engineering of the electrical contacts. Solution-processed caesium (Cs) salts, as electron-injection and hole-blocking layers at the interface between semiconductors and charge injection electrodes, significantly decrease the gold (Au) work function (～4.1 eV) compared to that of a pristine Au electrode (～4.7 eV). By controlling the electrode surface chemistry, excellent p-channel (hole mobility ～0.1-0.6 cm(2)/(Vs)) and n-channel (electron mobility ～0.1-0.3 cm(2)/(Vs)) OFET characteristics with the same semiconductor are demonstrated. Most importantly, in these OFETs the counterpart charge carrier currents are highly suppressed for depletion mode operation (I(off) < 70 nA when I(on) > 0.1-0.2 mA). Thus, high-performance, truly complementary inverters (high gain >50 and high noise margin >75% of ideal value) and ring oscillators (oscillation frequency ～12 kHz) based on a solution-processed ambipolar polymer are demonstrated.     

Control of Ambipolar and Unipolar Transport in Organic Transistors by Selective Inkjet‐Printed Chemical Doping for High Performance Complementary Circuits

The selective tuning of the operational mode from ambipolar to unipolar transport in organic field‐effect transistors (OFETs) by printing molecular dopants is reported. The field‐effect mobility (μ_FET) and onset voltage (V_on) of both for electrons and holes in initially ambipolar methanofullerene [6,6]‐phenyl‐C61‐butyric acid methyl ester (PCBM) OFETs are precisely modulated by incorporating a small amount of cesium fluoride (CsF) n‐type dopant or tetrafluoro‐tetracyanoquinodimethane (F4‐TCNQ) p‐type dopant for n‐channel or p‐channel OFETs either by blending or inkjet printing of the dopant on the pre‐deposited semiconductor. Excess carriers introduced by the chemical doping compensate traps by shifting the Fermi level (E_F) toward respective transport energy levels and therefore increase the number of mobile charges electrostatically accumulated in channel at the same gate bias voltage. In particular, n‐doped OFETs with CsF show gate‐voltage independent Ohmic injection. Interestingly, n‐ or p‐doped OFETs show a lower sensitivity to gate‐bias stress and an improved ambient stability with respect to pristine devices. Finally, complementary inverters composed of n‐ and p‐type PCBM OFETs are demonstrated by selective doping of the pre‐deposited semiconductor via inkjet printing of the dopants.     

MCC, a cytoplasmic protein that blocks cell cycle progression from the G0/G1 to S phase

The MCC gene was isolated from the human chromosome 5q21 by positional cloning and was found to be mutated in several colorectal tumors. In this study, we prepared specific antibodies and detected the MCC gene product as a cytoplasmic 100-kDa phosphoprotein in mouse NIH3T3 cells. Immunoelectron microscopic analysis showed that the MCC protein is associated with the plasma membrane and membrane organelles in mouse intestinal epithelial cells and neuronal cells. The amount of the MCC protein remained constant during the cell cycle progression of NIH3T3 cells, while its phosphorylation state changed markedly in a cell cycle-dependent manner, being weakly phosphorylated in the G0/G1 and highly phosphorylated during the G1 to S transition. Overexpression of the MCC protein blocked the serum-induced cell cycle transition from the G1 to S phase, whereas a mutant MCC, initially identified in a colorectal tumor, did not exhibit this activity. These results suggest that the MCC protein may play a role in the signaling pathway negatively regulating cell cycle progression.