Field-induced CDW in HMTSF-TCNQ

Field-induced successive transitions were observed in magnetoresistance in the quasi-one-dimensional organic conductor, HMTSF-TCNQ, hexamethylene-tetraselena-fulvalene-tetracyanoquinodimethane. The magnetoresistance exhibits kink transitions accompanying hysteresis at pressures around 1 GPa, but neither at p=0 nor at 2 GPa. At p=0 and below 30 K, this material undergoes charge density wave (CDW) state, which is suppressed around 1 GPa, where successive transitions are observed. Since these behavior is only observed at the boundary in pressure between insulator and metal, and the nature of the insulating state is CDW at p=0, it is strongly suggested that the successive transitions observed in magnetoresistance might be associated with CDW, accordingly a field-induced CDW by the one-dimensionalization by strong magnetic field ranging from 10 to 30 T. The behaviors are compared with previously claimed FICDW and the established FISDW (field-induced-spin-density-wave).     

基于熵的离子导体电导率公式推导

电导率是表示导体导电能力强弱的度量,离子导体的电导率可以通过平均漂移速度求得.文中通过对离子导体的分析,给出一种基于熵的新的推导方法.首先分析系统熵和环境熵的竞争关系,其次运用熵最大原理求出最概然电流,进而导出电导率公式.最后将基于熵的推导方法与漂移速度方法加以区别和对比,并推广到一般导体电导率公式的推导.     

Fractal analysis and atomic force microscopy measurements of surface roughness for Hastelloy C276 substrates and amorphous alumina buffer layers in coated conductors

In coated conductors, surface roughness of metallic substrates and buffer layers could significantly affect the texture of subsequently deposited buffer layers and the critical current density of superconductor layer. Atomic force microscopy (AFM) is usually utilized to measure surface roughness. However, the roughness values are actually relevant to scan scale. Fractal geometry could be exerted to analyze the scaling performance of surface roughness. In this study, four samples were prepared, which were electro polished Hastelloy C276 substrate, mechanically polished Hastelloy C276 substrate and the amorphous alumina buffer layers deposited on both the substrates by ion beam deposition. The surface roughness, described by root mean squared (RMS) and arithmetic average (R_a) values, was analyzed considering the scan scale of AFM measurements. The surfaces of amorphous alumina layers were found to be fractal in nature because of the scaling performance of roughness, while the surfaces of Hastelloy substrates were not. The flatten modification of AFM images was discussed. And the calculation of surface roughness in smaller parts divided from the whole AFM images was studied, compared with the results of actual AFM measurements of the same scan scales.     

Influence of proton irradiation on the photoluminescence spectra of zinc oxide modified by ZrO2 and ZrO2·Y2O3 nanopowders

ZnO powder photoluminescence spectra at 360-660 nm modified and unmodified by ZrO₂, ZrO₂Y₂O₃ nanopowders before and after 100 keV proton irradiation were investigated. It was found that introduction of nanoparticles led to ultraviolet band intensity decrease and to visual spectrum band intensity increase. Extinction of intensity occurs under the effect of protons in both bands of luminescence. Decomposition of spectra into elementary defects and analysis of their area change during modification and irradiation were carried out.     

Time-dependent density functional theory study on excited state intramolecular proton transfer of 3-hydroxy-2-(pyridin-2-yl)-4H-chromen-4-one

The time-dependent density functional theory (TDDFT) method was carried out to investigate the excited state intramolecular proton transfer (ESIPT) process of 3-hydroxy-2-(pyridin-2-yl)-4H-chromen-4-one (1a). 1a has two tautomeric forms: one is 1a(O), which is induced by intramolecular hydrogen bond O-H?O=C, and the other one is 1a(N), which is caused by intramolecular hydrogen bond O-H?N. From excited state to tautomer excited state coming from ESIPT, the hydroxyl hydrogen breaks away and the dissociated hydrogen adsorbed on pyridinic nitrogen or carbonyl oxygen formed new intramolecular HB and the corresponding bond length and bond angle varied greatly. In comparison, a similar process of proton transfer for 1a(N)H⁺ protonated 1a(N) from ground state to excited state was obtained. This detailed proton transfer mechanism was provided by molecular orbitals analysis and it may be applied to molecular switch and organic Lewis acid/base. We investigated the excited state proton transfer mechanism of the four molecules through the theoretical method for the first time and gave unambiguous geometry of excited state.     

Optical and electrical properties of In-doped CdO thin films fabricated by pulse laser deposition

Transparent indium-doped cadmium oxide (In-CdO) thin films were deposited on quartz glass substrates by pulse laser deposition (PLD) from ablating Cd-In metallic target at a fixed pressure 10 Pa and a fixed substrate temperature 300 °C. The influences of indium concentrations in target on the microstructure, optical and electrical performances were studied. When the indium concentration reaches to 3.9 wt%, the as-deposited In-CdO film shows high optical transmission in visible light region, obviously enhanced direct band gap energy (2.97 eV), higher carrier concentration and lower electric resistivity compared with the undoped CdO film, while a further increase of indium concentration to 5.6 wt% induces the formation of In₂O₃, which reverse the variation of these parameters and performance.     

Synthesis and characterization of fluorinated ionomer p-perfluoro-[1-(2-sulfonic)ethoxy]ethylated polyacrylonitrile-styrene

Fluorinated ionomer p-perfluoro[1-(2-sulfonic)ethoxy]ethylated polyacrylonitrile-styrene (SFAS) (5) was synthesized via electron transfer reaction between polyacrylonitrile-styrene (AS) (1) and perfluoro-di[2-(2-fluorosulfonyl)ethoxy]propionyl peroxide (FAP) (2) and followed by alkali hydrolysis and acidification of p-perfluoro[1-(2-fluorosulfonyl)ethoxy]ethylated polyacrylonitrile-styrene (3). The microstructure of ionomer 5 was well characterized by FTIR and ¹⁹F NMR. Its desulfonation occurred above 197 °C was found by TGA, the degree of substitution (DS) and ion exchange capacity (IEC) determined by titration were well controlled through changing the molar ratio of 2:1. The proton exchange membranes made of ionomer 5 have water uptake from 13.4 to 135.3% and conductivity up to 10⁻² S cm⁻¹ at 25 °C.     

Radiation grafted poly(vinylidene fluoride)-graft-polystyrene sulfonic acid membranes for fuel cells: Structure-property relationships

<正>Structure-property relationships for poly(vinylidene fluoride)-graft-polystyrene sulfonic acid(PVDF-g-PSSA) fuel cell membranes prepared by a single step method involving radiation-induced grafting of sodium styrene sulfonate(SSS) onto electron beam(EB) irradiated poly(vinylidene fluoride)(PVDF) films were established.The physico-chemical properties of the membranes such as ion exchange capacity,water swelling and proton conductivity were correlated with the degree of grafting(G,%) and the structural changes taking place in the membrane matrix during the preparation procedure. The variation in the crystallinity and the thermal stability of membranes was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis(TGA),respectively.The membranes were found to undergo substantial structural changes in forms of ionic sites increase,hydrophilicity enhancement,hydrophobicity reduction and crystallinity decrease with the variation in G(%) and the preparation method.The structural and thermal properties of the obtained membranes were also compared with their counterparts prepared by a conventional two-steps method i.e.radiation induced grafting of styrene onto EB irradiated PVDF films followed by sulfonation.The PVDF-g-PSSA membranes obtained by a single-step method were found to have superior properties compared to those obtained by the conventional two-steps method.     

Considerations in applying 3D PRESS H-1 brain MRSI with an eight-channel phased-array coil at 3 T

The purpose of this study was to assess the benefits of a 3 T scanner and an eight-channel phased-array head coil for acquiring three-dimensional PRESS (Point REsolved Spectral Selection) proton (H-1) magnetic resonance spectroscopic imaging (MRSI) data from the brains of volunteers and patients with brain tumors relative to previous studies that used a 1.5 T scanner and a quadrature head coil. Issues that were of concern included differences in chemical shift artifacts, line broadening due to increased susceptibility at higher field strengths, changes in relaxation times and the increased complexity of the postprocessing software due to the need for combining signals from the multichannel data. Simulated and phantom spectra showed that very selective suppression pulses with a thickness of 40 mm and an overpress factor of at least 1.2 are needed to reduce chemical shift artifact and lipid contamination at higher field strengths. Spectral data from a phantom and those from six volunteers demonstrated that the signal-to-noise ratio (SNR) in the eight-channel coil was more than 50% higher than that in the quadrature head coil. For healthy volunteers and eight patients with brain tumors, the SNR at 3 T with the eight-channel coil was on average 1.5 times higher relative to the eight-channel coil at 1.5 T in voxels from normal-appearing brains. In combination with the effect of a higher field strength, the use of the eight-channel coil was able to provide an increase in the SNR of more than 2.33 times the corresponding acquisition at 1.5 T with a quadrature head coil. This is expected to be critical for clinical applications of MRSI in patients with brain tumors because it can be used to either decrease acquisition time or improve spatial resolution.