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[en] We investigate the steady state photon transport in a nonequilibrium collective-qubit model. By adopting the noninteracting blip approximation, which is applicable in the strong photon–qubit coupling regime, we describe the essential contribution of indirect qubit–qubit interaction to the population distribution, mediated by the photonic baths. The linear relations of both the optimal flux and noise power with the qubits system size are obtained. Moreover, the inversed power-law style for the finite-size scaling of the optimal photon–qubit coupling strength is exhibited, which is proposed to be universal.
[en] The Scanning tunneling microscope (STM) has been used to study the effects of Fe doping on the charge-density wave (CDW) structure in NbSe3 and 1T-TaS2. In NbSe3 small amounts of Fe reduce both CDW gaps by 25--30% and change the relative CDW amplitudes of the high and low temperature CDWs. The CDW amplitudes remain strong on all three chains of the surface unit cell with no evident disorder. In 1T-Fe0.05Ta0.95S2 the Fe introduces substantial disorder in the CDW pattern, but the local CDW amplitude remains strong. The CDW energy gap is reduced by approximately 50% and the resistive anomaly at the commensurate-incommensurate transition is removed. The STM in both the image and spectroscopy modes can detect subtle changes in CDW structure due to impurities
[en] Adherent Cu films were electrodeposited onto polycrystalline W foils from purged solutions of 0.05 M CuSO4 in H2SO4 supporting electrolyte and 0.025 M CuCO3Cu(OH)2 in 0.32 M H3BO3 and corresponding HBF4 supporting electrolyte, both at pH 1. Films were deposited under constant potential conditions at voltages between -0.6 V and -0.2 V vs. Ag/AgCl. All films produced by pulses of 10 s duration were visible to the eye; copper colored, and survived the Scotch tape test. Characterization by scanning electron microscopy (SEM)/energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of metallic Cu, with apparent dendritic growth. No sulfur impurity was observable by XPS or EDX. Kinetics measurements indicate that the Cu nucleation process in the sulfuric bath is slower than in the borate bath. In both baths, nucleation kinetics does not correspond to either instantaneous or progressive nucleation. Films deposited from 0.05 M CuSO4/H2SO4 solution at pH>1 at -0.2 V exhibited poor adhesion and decreased Cu reduction current. In both borate and sulfate baths, small Cu nuclei are observable by SEM upon deposition at higher negative overpotentials, while only large nuclei (approx. 1 μm or larger) are observed upon deposition at less negative potentials
[en] Atomic force microscopy (AFM) and scanning tunneling microscopy (STM) have been employed in situ and ex situ to directly study the aggregation of β-amyloid(1-42) (Aβ42) peptide on hydrophobic graphite. From in situ AFM images, Aβ42 peptides were seen to aggregate into the sheets that preferred to three orientations with characteristic 3-fold symmetry (Proc. Natl. Acad. Sci. USA 96 (1999) 3688). The sheets were formed by parallel narrow lines with a height of 0.8-1.0 nm and a width of 12-14 nm. The narrow lines looked like beaded chains and have a right-handed axial periodicity. The high-resolution ex situ AFM and STM images showed that some fibrils of β-amyloid had a characteristic domain texture, indicating they were formed through the association of protofibrils and monomers. The fibril containing lateral associated filaments that exhibited right-handed twist was clearly observed in the STM image. These results provide important clues to study the detailed structure of β-amyloid aggregates and the mechanism of the Aβ fibrils formation on hydrophobic surface
[en] Highlights: • Mesoporous NiCo_2O_4 fibers were synthesized by a simple template-free method. • The NiCo_2O_4 fibers displayed fibrous morphology with well-distributed mesopores. • The mesoporous NiCo_2O_4 fibers were used as anodes for direct ethanol fuel cells (DEFCs). • The NiCo_2O_4 fibers exhibited excellent electrocatalytic activity for ethanol oxidation. • A notable reduction was found in the onset potential on NiCo_2O_4 electrodes. - Abstract: Well-dispersed mesoporous NiCo_2O_4 fibers as anode catalysts for the electrooxidation of ethanol were synthesized by an easy-controlled template-free method. Their structure and morphology were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and N_2 adsorption/desorption analysis. The electrochemical oxidation of ethanol on mesoporous NiCo_2O_4 fibers modified glassy carbon electrode (NiCo_2O_4/GCE) in alkaline solutions was systematically evaluated by cyclic voltammetry (CV), double-step chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS). The NiCo_2O_4 materials showed typical intertwined porous nanofibrous structures with specific surface area of 54.469 m"2 g"−"1 and average pore size of 13.5 nm. The NiCo_2O_4/GCE exhibited significantly high electrocatalytic activity with higher current density and lower onset potential compared to those of Co_3O_4 and NiO in CV measurement. The linear relationship between the ethanol concentration and the square root of scan rate indicated that diffusion of ethanol is a rate-determining step in its oxidation on mesoporous NiCO_2O_4 fibers. The electrochemical mechanism of ethanol oxidation on NiCo_2O_4/GCE was also proposed
[en] Highlights: • SEM, XRD, EDS and MMW attenuation performances of alloys coated CFs were studied. • Resistivity and P content in alloys were main factors on MMW attenuation property. • The weight gain of coated CFs has effects on the MMW attenuation performance. - Abstract: Carbon fibers (CFs) coated with Ni–X–P (X = W, Co–W or none) alloys were prepared by electroless plating. The morphology, crystal structure, and element composition of alloy-coated CFs were characterized by scanning electron microscopy, X-ray diffractometry, energy-dispersive spectrometry and microwave attenuation. The results showed that CFs were coated with a layer of alloy particles. P content in Ni–Co–W–P or Ni–W–P alloys was lower than that in Ni–P alloy, and coating alloy Ni–P was amorphous. After W or Co introduction, coating alloys exhibited crystal characteristics. MMW-attenuation performance analysis showed that the 3 mm wave attenuation performance of CFs/Ni–Co–W–P, CFs/Ni–W–P and CFs/Ni–P increased by 7.27 dBm, 4.88 dBm and 3.55 dBm, and the 8 mm wave attenuation effects increased by 11.61 dBm, 6.11 dBm, and 4.06 dBm respectively, compared with those of CFs. MMW-attenuation performance is attributable to the sample bulk resistivity and P content in the alloy. Moreover, an optimal weight gain value existed for the MMW-attenuation performance of alloy-coated CFs.
[en] Metallic uranium and uranium dioxide material were ablated by laser beam in order to simulate the process of forming the uranium particles in pyrochemical process. The morphology characteristic of uranium particles and the surface of uranium material were represented by SEM and TEM. Those two kinds of materials are melted, the surface of metal uranium presents a series wavelike segments and the surface of dioxide uranium presents pellets aggregation under the bombardment of laser beam. The irregular micron-sized particles and about 1 μm spherical particles occurred in ambient environment. Silver aerosol particles produced by explosion also were characterized as spherical particles. The results show that the regular uranium oxide spheres with high density characteristic pyrochemical process are quite different from particles with low temperature denudation. They are characteristic of pyrochemical process based on particle morphology. These results will provide references for uranium particles research related to high temperature and high pressure process. (authors)
[en] SiC fiber was fabricated by chemical vapor deposition on tungsten filament heated by direct current in a CH3SiCl3-H2 gas system. Microstructure of W/SiC interfacial reaction zone in the fiber was identified by means of scanning electron microscope and transmission electron microscope. Results showed that the thickness of the interfacial reaction zone is between 350 and 390 nm, and two reaction products of W5Si3 and WC were formed during fabricating SiC fiber. Electron diffraction analysis and composition detection indicated that W5Si3 is adjacent to tungsten core and WC is adjacent to SiC sheath, and the W/SiC interface can be described as W/W5Si3/WC/SiC. Furthermore, the formation mechanism of the interfacial reaction zone is discussed.
[en] Elbow is a type of components widely used in a piping system, and is particularly important from the point of view of structural behaviour. In practice, the existence of cracks in excess of the defect limits can not be excluded. So it is very important to know the effect of cracks on the collapse loads of elbows for integrity assessment of the piping system. The existing closed-form limit loads for elbows with meridional defects are either too conservative or inadequate, therefore, the present studies focus on plastic limit loads of elbows with both part-through and fully through axial cracks with the crack configurations are assumed to be constant-depth rectangle, subjected to internal pressure and in-plane opening/closing bending moments respectively. The crack-like defects are postulated to be in extrados, crown or intrados of elbows with different crack sizes. Based on the von-Mises yield crierion, the simplified estimation formulas for plastic limit loads of cracked elbows without effects of tangent straight pipes, are derived by using of theoretical analysis. The limit collapse loads and weakening influences of defects on the plastic load carrying capacity of cracked elbows with the connecting tangent pipes are investigated in detail, by use of three-dimensional (3D) non-linear finite element (FE) analyses, assuming elastic-perfectly-plastic material behavior and taking geometric nonlinearity into account. The results from comprehensive parametric studies indicate that the limit load capacity of cracked elbows may reduce with the increasing of crack length and crack depth, these trends are more serious for long radius elbows. Generally speaking, the thickness-radius ratio t/rm of elbow have insignificant effects on crack weakening factor (PL/PL0 or ML/ML0 ).Base on extensive collapse load numeric data and comprehensive parametric studies, the revised closed form equations for cracked elbows involving effects of tangent pipes, under pressure or in-plane close/open moments, are established respectively. The formula's suitability and feasibility applied in engineering practice are also validated with experimental results available in the open literature in the paper. (authors)
[en] Highlights: • The spatial–temporal instability of a liquid sheet with thermal effects was studied. • The flow can transit to absolutely unstable with certain flow parameters. • The effects of non-dimensional parameters on the transition were studied. -- Abstract: The spatial–temporal instability behavior of a viscous liquid sheet with temperature difference between the two surfaces was investigated theoretically. The practical situation motivating this investigation is liquid sheet heated by ambient gas, usually encountered in industrial heat transfer and liquid propellant rocket engines. The existing dispersion relation was used, to explore the spatial–temporal instability of viscous liquid sheets with a nonuniform temperature profile, by setting both the wave number and frequency complex. A parametric study was performed in both sinuous and varicose modes to test the influence of dimensionless numbers on the transition between absolute and convective instability of the flow. For a small value of liquid Weber number, or a great value of gas-to-liquid density ratio, the flow was found to be absolutely unstable. The absolute instability was enhanced by increasing the liquid viscosity. It was found that variation of the Marangoni number hardly influenced the absolute instability of the sinuous mode of oscillations; however it slightly affected the absolute instability in the varicose mode