Inter-particle interaction induced by broadband radiation

The recent fabrication of optical traps using super-continuum light impresses the need for a theory of inter-particle interactions under such conditions. Development of the theory provides a basis for calculation of the observations expected under experimental conditions. An expression for the inter-particle potential energy induced by continuum states of light is first derived using quantum electrodynamics. This energy expression is cast as a function of the spectral irradiance of the light, and the electric susceptibility of the interacting particles. Specific results are derived for light with a Lorentzian spectrum. It is shown that by filtering part of the spectrum, it is possible to exert control over the length of linear particle chains organized along the Poynting vector. The results exhibit scope for the optical fabrication of moldable structures using broadband light.     

Comment on the paper: H.-E. Hwang, P. Han, Theoretical analysis for surface tilt and translation detection based on speckle photography in the Fresnel domain, Opt. Commun. 282 (2009) 351-354

In a recent paper [H.-E. Hwang, P. Han, Opt. Commun. 282 (2009) 351] a speckle based metrology system is proposed which it is claimed provides significant advantages over existing systems. In this paper, we show that the discussion presented in [H.-E. Hwang, P. Han, Opt. Commun. 282 (2009) 351] is deficient, and that several of the statements made are incorrect and/or misleading.     

湿工况下平直翅片对流传热传质数值研究

建立了湿空气流经平直翅片通道并伴有凝结现象发生的三维对流传热传质的数值模型,在空气进口雷诺数Re为190～3770,进口相对湿度φ_(in)为50%～90%的范围内,对干湿两种工况,平直翅片通道内的换热流动进行了对比研究。结果表明:湿工况换热系数为干工况换热系数的2.8～3.1倍,干工况翅片效率比湿工况翅片效率高35.8%～41.9%。当翅片为部分湿工况时,翅片效率随进口相对湿度的增大而增大,换热系数随进口相对湿度的增大而减小;当翅片为全湿工况后,进口相对湿度对翅片效率和换热系数的影响微弱。     

Electronic energy gaps and optical properties of LaMnO3

We investigate electronic structure and optical properties of LaMnO₃ through density-functional-theory calculations with a recent improved exchange potential. Calculated gaps are consistent with recent experimental values, and calculated optical conductivities and dielectric constants as functions of photon energy are in excellent agreement with low-temperature experimental results. These lead to a satisfactory theoretical understanding of the electronic gaps and optical properties of LaMnO₃ without tuning atomic parameters and can help elucidate electronic structures and magnetic properties of other manganite materials.     

Numerical study of induction heating in melt growth systems—Frequency selection

A set of 2D finite element numerical simulation of induction heating process for an oxide Czochralski crystal growth system has been made for a range of f=1–100 kHz applied frequency of driving current. It was shown that the frequency selection has a marked effect in all basic induction phenomena, including electromagnetic field distribution, skin depth, coil efficiency, and intensity and structure of heating in the growth setup.     

Synthesis of praseodymium oxide nanofiber by electrospinning

Well-defined and uniform Pr₆O₁₁ nanofibers were synthesized by electrospinning of an aqueous sol-gel consisting of praseodymium nitrate hexa-hydrate and polyvinyl acetate. The synthesized Pr₆O₁₁ nanofibers mat was dried at 80 °C for 24 h under vacuum and finally annealed at 600 °C for 2 h in static air furnace. From crystalline properties, the synthesized Pr₆O₁₁ nanofibers XRD analysis revealed the typical cubic structure. The morphological observation showed that the synthesized Pr₆O₁₁ nanofibers composed of fibers length in several 100 nm and diameter of ∼20 nm. Similarly, transmission electron microscope (TEM) measurement revealed the good crystalline nature of the synthesized Pr₆O₁₁ nanofibers with the average diameter of ∼20 nm. Photoluminescence (PL) demonstrated a strong green-blue emission peak at 521 nm, suggesting that the Pr₆O₁₁ nanofiber exhibited good crystal quality with very less structural defects.     

Optical modes in nanoscale one-dimensional spin chains

The spin chain systems with one-dimensional magnetic ordering are promising candidates for quantum optical devices. This paper shows how the optical excitation can induce various phonon modes in an ideal Cu-O chain at various lengths. The calculation was carried out at different level theories including configuration interaction singles for excited states, density functional theory and second-order Möller-Plesset perturbation. In general, the number of modes increases with chain length due to growing asymmetry of atomic positions when chain exceeds 5 nm. There were, however, only two basic modes: one is associated with the symmetric oscillation of oxygen and another with the asymmetric motion of the same along the chain. At the length below 4.3 nm, the Raman activity of the symmetric mode (440 cm⁻¹) dominates. From analysis of density of states, this mode may be associated with the excitation across the lowest LUMO bands with changing in spin state.     

A two-phase, two-component model for vertical upward gas-liquid annular flow

In this paper, a new two-fluid two-component computational fluid dynamics (CFD) model is developed to simulate vertical upward two-phase annular flow. The two-phase VOF scheme is utilized to model the roll wave flow, and the gas core is described by a two-component phase consisting of liquid droplets and gas phase. The entrainment and deposition processes are taken into account by source terms of the governing equations. Unlike the previous models, the newly developed model includes the effect of liquid roll waves directly determined from the CFD code, which is able to provide more detailed and, the most important, more self-standing information for both the gas core flow and the film flow as well as their interactions. Predicted results are compared with experimental data, and a good agreement is achieved.     

The Semiquantitative Determination of Impurities in High-Purity Molybdenum Metal by Optical Emission Spectrography

Abstract

A method is reported for the determination of Ni, Co, Bi, Al, V, Ti, Cu, Si, Pb, Cr, Mg, Sn, and Fe in molybdenum metal by optical emission spectrography. The procedure consists of dissolving the metal in HNO₃ and HCl, evaporating to dryness, and igniting at 500–550°C to MoO₃. The MoO₃ is mixed with an equal weight of GeO₂, which acts as an inert collector, and ignited at 700–750°C to volatilize the MoO₃. This double ignition method concentrates the impurities on the GeO₂ thereby placing the trace elements within the range of the spectrograph. The residue is excited in a d c are at 10 amps and the spectra are recorded on a photographic emulsion.