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Vestgården JI Shantsev DV Olsen AA Galperin YM Yurchenko VV Goa PE Johansen TH 《Physical review letters》2007,98(11):117002
A theoretical model for how Bloch walls occurring in in-plane magnetized ferrite garnet films can serve as efficient magnetic micromanipulators is presented. As an example, the walls' interaction with Abrikosov vortices in a superconductor in close contact with a garnet film is analyzed within the London approximation. The model explains how vortices are attracted to such walls, and excellent quantitative agreement is obtained for the resulting peaked flux profile determined experimentally in NbSe(2) using high-resolution magneto-optical imaging of vortices. In particular, this model, when generalized to include charged magnetic walls, explains the counterintuitive attraction observed between vortices and a Bloch wall of opposite polarity. 相似文献
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Bhanudas Naik Vilas Desai Meenal Kowshik Vadakkethonippurathu Sivankutty Prasad Gerard Franklyn Fernando Narendra Nath Ghosh 《中国颗粒学报》2011,(3)
Simple aqueous solution-based chemical methods have been developed for the synthesis of Ag/AgCl nanoparticle-mesoporous silica nanocomposites. Ag loading in the mesoporous silica was accomplished using a wet-impregnation method. The AgCl-mesoporous silica nanocomposite material(AgCl-mSi) was synthesized by using a 'one pot' method. Synthesized materials were characterized using X-ray diffraction,N2 adsorption-desorption analysis and high-resolution transmission electron microscopy. Antibacterial activity of... 相似文献
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Effect of low-energy ion bombardment on the crystal structure and superconductivity of niobium films
V. V. Naumov V. F. Bochkarev A. A. Goryachev A. S. Kunitsyn E. I. Il’yashenko P. E. Goa T. H. Johansen 《Technical Physics》2004,49(4):426-430
The effect of ion bombardment on the growth of Nb films and their crystal structure is investigated. Epitaxial niobium films with the (001) orientation are grown on (01i2) Al2O3 substrates heated to 600°C and biased at ?20 V. Niobium films with pronounced axial texture in the [110] direction are grown on water-cooled Sitall (devitrified glass such as Pyroceram) substrates. In Nb films biased at ?50 V, which are in the superconducting state, the motion of individual magnetic vortices is observed with a magnetooptic indicator. 相似文献
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The physiological noise in 3D image acquisition is shown to depend strongly on the sampling scheme. Five sampling schemes are considered: Linear, Centric, Segmented, Random and Tuned. Tuned acquisition means that data acquisition at k-space positions k and -k are separated with a specific time interval. We model physiological noise as a periodic temporal oscillation with arbitrary spatial amplitude in the physical object and develop a general framework to describe how this is rendered in the reconstructed image. Reconstructed noise can be decomposed in one component that is in phase with the signal (parallel) and one that is 90° out of phase (orthogonal). Only the former has a significant influence on the magnitude of the signal. The study focuses on fMRI using 3D EPI. Each k-space plane is acquired in a single shot in a time much shorter than the period of the physiological noise. The above mentioned sampling schemes are applied in the slow k-space direction and noise propagates almost exclusively in this direction. The problem then, is effectively one-dimensional. Numerical simulations and analytical expressions are presented. 3D noise measurements and 2D measurements with high temporal resolution are conducted. The measurements are performed under breath-hold to isolate the effect of cardiac-induced pulsatile motion. We compare the time-course stability of the sampling schemes and the extent to which noise propagates from a localized source into other parts of the imaging volume. Tuned and Linear acquisitions perform better than Centric, Segmented and Random. 相似文献
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A dedicated small‐angle X‐ray scattering beamline with a superconducting wiggler source at the NSRRC
Din‐Goa Liu Chien‐Hung Chang Chin‐Yen Liu Shih‐Hung Chang Jwei‐Ming Juang Yen‐Fang Song Kuan‐Li Yu Kuei‐Fen Liao Ching‐Shiang Hwang Hok‐Sum Fung Ping‐Chung Tseng Chi‐Yi Huang Liang‐Jen Huang Shih‐Chun Chung Mau‐Tsu Tang King‐Long Tsang Yu‐Shan Huang Chien‐Kuang Kuan Yi‐Chih Liu Keng S. Liang U‐Ser Jeng 《Journal of synchrotron radiation》2009,16(1):97-104
At the National Synchrotron Radiation Research Center (NSRRC), which operates a 1.5 GeV storage ring, a dedicated small‐angle X‐ray scattering (SAXS) beamline has been installed with an in‐achromat superconducting wiggler insertion device of peak magnetic field 3.1 T. The vertical beam divergence from the X‐ray source is reduced significantly by a collimating mirror. Subsequently the beam is selectively monochromated by a double Si(111) crystal monochromator with high energy resolution (ΔE/E? 2 × 10?4) in the energy range 5–23 keV, or by a double Mo/B4C multilayer monochromator for 10–30 times higher flux (~1011 photons s?1) in the 6–15 keV range. These two monochromators are incorporated into one rotating cradle for fast exchange. The monochromated beam is focused by a toroidal mirror with 1:1 focusing for a small beam divergence and a beam size of ~0.9 mm × 0.3 mm (horizontal × vertical) at the focus point located 26.5 m from the radiation source. A plane mirror installed after the toroidal mirror is selectively used to deflect the beam downwards for grazing‐incidence SAXS (GISAXS) from liquid surfaces. Two online beam‐position monitors separated by 8 m provide an efficient feedback control for an overall beam‐position stability in the 10 µm range. The beam features measured, including the flux density, energy resolution, size and divergence, are consistent with those calculated using the ray‐tracing program SHADOW. With the deflectable beam of relatively high energy resolution and high flux, the new beamline meets the requirements for a wide range of SAXS applications, including anomalous SAXS for multiphase nanoparticles (e.g. semiconductor core‐shell quantum dots) and GISAXS from liquid surfaces. 相似文献
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Dr. Shih‐Hong Chang Dr. Wei‐Nien Su Dr. Min‐Hsin Yeh Dr. Chun‐Jern Pan Dr. Kuan‐Li Yu Din‐Goa Liu Dr. Jyh‐Fu Lee Prof. Bing‐Joe Hwang 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(36):11064-11071
We report a systematic investigation on the structural and electronic effects of carbon‐supported PtxPd1?x bimetallic nanoparticles on the oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) in acid electrolyte. PtxPd1?x/C nanocatalysts with various Pt/Pd atomic ratios (x=0.25, 0.5, and 0.75) were synthesized by using a borohydride‐reduction method. Rotating‐disk electrode measurements revealed that the Pt3Pd1/C nanocatalyst has a synergistic effect on the ORR, showing 50 % enhancement, and an antagonistic effect on the MOR, showing 90 % reduction, relative to JM 20 Pt/C on a mass basis. The extent of alloying and Pt d‐band vacancies of the PtxPd1?x/C nanocatalysts were explored by extended X‐ray absorption fine‐structure spectroscopy (EXAFS) and X‐ray absorption near‐edge structure spectroscopy (XANES). The structure–activity relationship indicates that ORR activity and methanol tolerance of the nanocatalysts strongly depend on their extent of alloying and d‐band vacancies. The optimal composition for enhanced ORR activity is Pt3Pd1/C, with high extent of alloying and low Pt d‐band vacancies, owing to favorable O? O scission and inhibited formation of oxygenated intermediates. MOR activity also shows structure dependence. For example, Pt1Pd3/C with Ptrich?corePdrich?shell structure possesses lower MOR activity than the Pt3Pd1/C nanocatalyst with random alloy structure. Herein, extent of alloying and d‐band vacancies reveal new insights into the synergistic and antagonistic effects of the PtxPd1?x/C nanocatalysts on surface reactivity. 相似文献
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Ion-exchange of [Ti,Al]-beta with quaternary ammonium acetates greatly enhances the epoxide selectivity in the oxidation of alkenes with hydrogen peroxide; this is due to the selective poisoning of the acid sites without suppressing the oxidation activity of Ti sites. 相似文献
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Feng‐Ju Lai Wei‐Nien Su Loka Subramanyam Sarma Dr. Din‐Goa Liu Cheng‐An Hsieh Jyh‐Fu Lee Dr. Bing‐Joe Hwang Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(15):4602-4611
The chemical dealloying mechanism of bimetallic Pt–Co nanoparticles (NPs) and enhancement of their electrocatalytic activity towards the oxygen reduction reaction (ORR) have been investigated on a fundamental level by the combination of X‐ray absorption spectroscopy (XAS) and aberration‐corrected scanning transmission electron microscopy (STEM). Structural parameters, such as coordination numbers, alloy extent, and the unfilled d states of Pt atoms, are derived from the XAS spectra, together with the compositional variation analyzed by line‐scanning energy‐dispersive X‐ray spectroscopy (EDX) on an atomic scale, to gain new insights into the dealloying process of bimetallic Pt–Co NPs. The XAS results on acid‐treated Pt–Co/C NPs reveal that the Co–Co bonding in the bimetallic NPs dissolves first and the remaining morphology gradually transforms to a Pt‐skin structure. From cyclic voltammetry and mass activity measurements, Pt–Co alloy NPs with a Pt‐skin structure significantly enhance the catalytic performance towards the ORR. Further, it is observed that such an imperfect Pt‐skin surface feature will collapse due to the penetration of electrolyte into layers underneath and cause further dissolution of Co and the loss of Pt. The electrocatalytic activity decreases accordingly, if the dealloying process lasts for 4 h. The findings not only demonstrate the importance of appropriate treatment of bimetallic catalysts, but also can be referred to other Pt bimetallic alloys with transition metals. 相似文献