Comparative analysis on gas–solid drag models in MFIX-DEM simulations of bubbling fluidized bed

In this study,the open-source software MFIX-DEM simulations of a bubbling fluidized bed(BFB)are applied to assess nine drag models according to experimental and direct numerical simulation(DNS)results.The influence of superficial gas velocity on gas–solid flow is also examined.The results show that according to the distribution of time-averaged particle axial velocity in y direction,except for Wen–Yu and Tenneti–Garg–Subramaniam(TGS),other drag models are consistent with the experimental and DNS results.For the TGS drag model,the layer-by-layer movement of particles is observed,which indicates the particle velocity is not correctly predicted.The time domain and frequency domain analysis results of pressure drop of each drag model are similar.It is recommended to use the drag model derived from DNS or fine grid computational fluid dynamics–discrete element method(CFD-DEM)data first for CFD-DEM simulations.For the investigated BFB,the superficial gas velocity less than 0.9 m·s^(-1) should be adopted to obtain normal hydrodynamics.

Optical properties of titanium oxide films obtained by cathodic arc plasma deposition

Structural and optical properties of nanometric titanium oxide（TixOy） films obtained by cathodic arc plasma deposition were investigated. Phase analysis by x-ray diffraction and Fouriertransform infrared spectroscopy showed the presence of anatase, rutile, Ti_2O_3, Ti_4O_7 and amorphous phases. Scanning electron microscopy images showed well-developed surface morphology with nano-patterns. Spectroscopic ellipsometry revealed film thicknesses of 53 and50 nm, variable refractive indices dependent on the light wavelength and close to zero extinction coefficients for wavelengths higher than 500 nm. On the basis of ultraviolet–visible spectroscopy data and using the Tauc equation, band gap values for direct and indirect electron transitions were determined.

Channeling of fast ions through the bent carbon nanotubes： The extended two-fluid hydrodynamic model

We investigate the interactions of charged particles with straight and bent single-walled carbon nanotubes （SWNTs） under channeling conditions in the presence of dynamic polarization of the valence electrons in carbon, This polarization is described by a cylindrical, two-fluid hydrodynamic model with the parameters taken from the recent modelling of several independent experiments on electron energy loss spectroscopy of carbon nano-structures. We use the hydrodynamic model to calculate the image potential for protons moving through four types of SWNTs at a speed of 3 atomic units. The image potential is then combined with the Doyle-Turner atomic potential to obtain the total potential in the bent carbon nanotubes. Using that potential, we also compute the spatial and angular distributions of protons channeled through the bent carbon nanotubes, and compare the results with the distributions obtained without taking into account the image potential.

Three-Dimensional Simulations with Fields and Particles in Software and Inflector Designs

Particles and fields represent two major modeling paradigms in pure and applied science at all. In this paper a methodology and some of the results for three-dimensional (3D) simulations that include both field and particle abstractions are presented. Electromagnetic field calculations used here are based on the discrete differential form representation of the finite elements method, while the Monte Carlo method makes foundation of the particle part of the simulations. The first example is the simulation of the feature profile evolution during SiO2 etching enhanced by Ar + /CF4 non-equilibrium plasma based on the sparse field method for solving level set equations. Second example is devoted to the design of a spiral inflector which is one of the key devices of the axial injection system of the VINCY Cyclotron.

纳秒、皮秒和飞秒激光脉冲对材料表面的改性(英文)

对基体材料镉镍铁合金600和多层TiAlN/TiN涂层的激光表面改性在基础研究和实际应用中有着很好的前景。本文观察了由超短脉冲(fs和ns)和短脉冲(ns)激光器引起的镉镍铁合金600和TiAlN/TiN镀层的表面变化。结果显示,3种激光都能使靶面发生形态改变,超短脉冲的破坏轮廓更为清晰。与ps激光脉冲相比,fs激光脉冲能产生更严重的破坏。与产生半球体形状的ps激光束相反,fs激光脉冲产生的破坏斑是圆锥形的。另外,ns脉冲辐照时热效应占支配地位,且所有的辐照都伴随着等离子体。

恒电位电沉积银纳米枝晶晶体结构与形貌的关系（英文）

采用恒电位电解法用不同电解质、在不同过电位下获得银枝晶纳米结构,并用扫描电镜(SEM)技术和X射线衍射分析对所得粉末进行表征。采用硝酸盐电解质在极限扩散电流密度的平台范围内外,分别形成了银针状和蕨状枝晶。采用氨盐电解质时,在极限扩散电流密度的平台范围内外均形成了由近球形晶粒构成的银三维松树状枝晶。在半量子化水平上,银枝晶的形貌与其晶体结构相关。在极限扩散电流密度平台范围外的过电位条件下形成的松树状枝晶,其晶体取向从针状枝晶的强(111)面择优取向转变为球形晶粒的几乎随机取向,同时,所得粉末的比表面积显著增加。形成的银颗粒的平均晶粒尺寸在38~50 nm之间,证明了其纳米结构特征。

不同电解条件下制备铜粉的形貌及结晶学比较分析（英文）

研究不同析氢条件下恒电位电解法制备铜粉的过程。采用扫描电镜(SEM)、X射线衍射(XRD)、粒度分布(PSD)和比表面积测定(SSA)对铜粉进行表征。根据电解过程析氢量的大小,形成树枝状和菜花状两种类型的颗粒。当析氢量大到足以对近电极层中的流体动力学条件产生强烈影响时,形成菜花状颗粒,否则形成树枝状颗粒。虽然颗粒的宏观结构差异很大,但他们的微观结构却相似,也就是说,这两种颗粒在微观层面上都是由近似球形的Cu颗粒小团聚体组成;球状形貌的存在是造成两种颗粒中Cu晶粒随机取向的原因。菜花样颗粒的比表面积是树枝状颗粒的3倍以上,其粒径则比树枝状颗粒的小很多。由此可见,强析氢条件对于铜粉制备是有益的。

触变成形和热处理ZA27合金在NaCl溶液中的腐蚀行为(英文)

研究触变成形和热处理ZA27合金在NaCl溶液中腐蚀后的显微组织的变化。结果表明,热处理会影响触变成形ZA27合金的组织。对经热处理和未经热处理的触变成形ZA27合金,电化学腐蚀均发生在η相区。浸泡试验和电化学测试结果表明,未经热处理的触变成形ZA27合金的腐蚀速率比经过热处理的触变成形ZA27合金的低50%,表明T4热处理会降低触变成形ZA27合金的耐腐蚀性能。

氯化钠溶液中腐蚀对复合铸造ZA27/SiC_p复合材料表观和显微组织的影响（英文）

ZA27/SiC_p复合材料在氯化钠溶液中浸泡30 d,通入氧气,研究腐蚀对其表观和显微组织的影响。通过复合铸造制备不同SiC粒子含量的复合材料。采用光学显微镜和扫描电子显微镜研究材料的显微组织,结果表明复合材料基体发生了腐蚀,且优先发生在富锌η相。腐蚀过程不影响嵌入基体合金中的SiC粒子。电化学极化测试表明,复合材料中SiC粒子含量的增加,导致复合材料的耐腐蚀性降低。

Dynamical time versus system time in quantum mechanics

Properties of an operator representing the dynamical time in the extended parameterization invariant formulation of quantum mechanics are studied. It is shown that this time operator is given by a positive operator measure analogously to the quantities that are known to represent various measurable time operators. The relation between the dynamical time of the extended formulation and the best known example of the system time operator, i.e., for the free one- dimensional particle, is obtained.

利用浮质方法将硝酸盐和PDDA-Pt(IV)复合溶液合成纯净及Pt掺杂的ZnO颗粒(英文)

Pure and Pt-doped ZnO nanophase particles were synthesized using the ultrasonic spray pyrolysis. Particles were obtained through decomposition of zinc nitrate and new developed Pt（IV） complex with 1,3-propylenediamine-N,N-diacetate ligand （pdda） belonging to the tetradentate class. The complex is characterized by elemental analysis, electronic absorption and infrared spectra. The crystal structure of trans-[Pt（pdda）Br2]·H2O complex has been determined implying that Pt（IV） ion has a distorted octahedral coordination due to intramolecular N-H ...Br interaction. Ultrasonically derived pure and Pt-doped ZnO particles were characterized by XRD, SEM, EDS and TEM analysis. It was shown that zincite phase exhibits different growing morphologies influenced by precursor chemistry and processing parameters. The composite inner structure, primary particle size and mechanism of Pt 4+ ion introducing into ZnO cell is discussed based on structural refinement and selected area electron diffraction analysis.

Nuclear DNA damages generated by reactive oxygen molecules (ROS) under oxidative stress and their relevance to human cancers, including ionizing radiation-induced neoplasia part II: Relation between ROS-induced DNA damages and human cancer

Oxidative stress(OS)occurs when the production of reactive oxygen species(ROS)overrides the body’s natural defence.When the cell nucleus represents the target,macromolecular damage may result in mutations.Cancer is a disease of mutations,and DNA damages that are not repaired or mis-repaired during cell proliferation are necessary but not sufficient for cancer development.A role of ROS for cancer initiation depends on the likelihood of interaction between reactive electrophilic molecules and nuclear DNA.As described in part one of this presentation,the physico-chemical properties of the ROS involved in OS and of the ensuing DNA lesions are of major importance.Current knowledge dictates that emphasis should be shifted from oxidative DNA damages of low genotoxicity towards pro-mutagenic lesions induced by reaction products of nitrogen monoxide and complex highly reactive carbonyls,e.g.from the peroxidation of lipids.Based on the determination of pro-mutagenic DNA adducts in human tissues there is compelling evidence for a causal relation between OS and cancers of the liver,colon/rectum,cervix,pancreas and stomach.However,modulation by the simultaneous presence of an ubiquitous high background of potent pro-carcinogenic DNA adducts,which are not generated by ROS should be taken into account.Ionizing radiation is established human carcinogenic agent,and generate some of the same oxidative ROS as those involved in OS.However,the cancer spectrum from whole body radiation exposure differs in some important respects from that associated with OS.The scientific support for a causal link between exposure to non-ionizing electromagnetic radiation and human cancer is judged to be insufficient.As exemplified by diabetes,a common shortcoming when assessing the role of OS in disease is the failure to distinguish between cause and effect-i.e.could the indicators of harmful oxidative stress be the result of the pathological condition in question,rather than its cause.

Nuclear DNA damages generated by reactive oxygen molecules (ROS) under oxidative stress and their relevance to human cancers, including ionizing radiation-induced neoplasia part I: Physical, chemical and molecular biology aspects

Oxidative stress(OS)occurs when the production of reactive oxygen species(ROS)overpowers the body’s natural defence,causing macromolecular damage.The role of OS in cancer initiation will depend on the likelihood of interaction between short lived ROS and nuclear DNA.For this reason,a description of the physico-chemical properties of the various ROS that have been suggested to be involved is included.DNA damages that are not repaired or mis-repaired during cell proliferation are necessary but not sufficient for cancer initiation.The characteristics of DNA pro-mutagenic lesions and their potential role in cancer induction will be assessed,while stressing quantitative aspects as well as the importance of DNA repair.A low level of a specific DNA adduct can be compensated for by its persistence and high pro-mutagenic potency.Because ionizing radiations generate some of the same oxidative ROS as those involved in OS,the cancer spectrum from whole body radiation exposure should be compared with that associated with OS.A causal link between electromagnetic radiations and human cancer lacks adequate scientific support.Current knowledge dictates that emphasis should be shifted from oxidative damages of low genotoxicity towards pro-mutagenic lesions induced by reaction products of nitrogen monoxide and complex highly reactive carbonyls,e.g.from the peroxidation of lipids.A common shortcoming when assessing the role of OS in disease is the failure to distinguish between cause and effect-i.e.could the indicators of harmful OS be the result of the pathological condition in question,rather than its cause?Further,little attention has been paid to exposure in food to some of the same ROS(e.g.reactive carbonyl compounds),as are generated endogenously by OS.Nor have the simultaneous presence of an ubiquitous high background of potent pro-carcinogenic DNA adducts which are not generated by ROS been taken into account.

Pesticide-induced photoluminescence quenching of ultra-small Eu3+-activated phosphate and vanadate nanoparticles

The aim of this research was to investigate the luminescent behavior of ultra-small Eu3+-activated phosphate and vanadate nanoparticles in the presence of pesticides.Nanoparticles have an average diameter of approximately 2 nm with a narrow size distribution.The monazite crystal structure of phosphate-based particles(space group P121/n1)and single tetragonal zircon-type structure of vanadate-based particles(space group of I41/amd)have been confirmed using X-ray diffraction measurements.All synthesized Eu3+-activated colloidal nanoparticles show sharp emission peaks in the red spectral region.Photoluminescence measurements revealed emission quenching upon addition of millimolar concentrations of following pesticides:4-Chloro-2-methyl-phenoxyacetic acid(MCPA),2,4-Dichlorophenoxyacetic acid(2,4-D)and N-(phosphonomethyl)glycine(Glyphosate).In both phosphate and vanadate-based colloidal nanoparticles luminescence quenching is more evident in the presence of 2,4-D pesticide with the lowest limit of detection(0.7μM)obtained for phosphate-based nanoparticles.

On Improving Accuracy of Finite-Element Solutions of the Effective-Mass Schr¨odinger Equation for Interdiffused Quantum Wells and Quantum Wires

We use the Galerkin approach and the finite-element method to numerically solve the effective-mass Schr¨odinger equation.The accuracy of the solution is explored as it varies with the range of the numerical domain.The model potentials are those of interdiffused semiconductor quantum wells and axially symmetric quantum wires.Also,the model of a linear harmonic oscillator is considered for comparison reasons.It is demonstrated that the absolute error of the electron ground state energy level exhibits a minimum at a certain domain range,which is thus considered to be optimal.This range is found to depend on the number of mesh nodes N approximately as α_0 log_e^(α1)(α_2N),where the values of the constants α_0,α_1,and α_2are determined by fitting the numerical data.And the optimal range is found to be a weak function of the diffusion length.Moreover,it was demonstrated that a domain range adaptation to the optimal value leads to substantial improvement of accuracy of the solution of the Schr¨odinger equation.

Rectification and phase locking of graphite

Rectification phenomena and the phase locking in a two-dimensional overdamped Frenkel-Kontorova model with a graphite periodic substrate were studied. The presence of dc and ac forces in the longitudinal direction causes the appearance of dynamicalmode locking and the steps in the response function of the system. On the other hand, the presence of an ac force in the transverse direction causes the appearance of rectification,even though there is no net dc force in the transverse direction. It is found that whereas the longitudinal velocity increases in a series of steps, rectification in the transverse direction can occur only between two neighbor steps. The amplitude and phase of the external ac driving force affect the depinning force,rectification of the system and particles trajectories.

Opinion on reconsideration of lung cancer risk from domestic radon exposure

Two extensive collaborative meta studies including 13 residential case-control studies from Europe and 7 from North America have demonstrated that domestic radon clearly poses a risk for lung cancer at exposure levels approaching those for underground miners.An excess risk for lung cancer of 0.08–0.16 per 100 Bq/m3 increase in radon concentration was obtained,with a positive trend of increased relative risk at above 200 Bq/m3.However,estimation of the cancer risk associated with domestic radon obtained by the pooling of multiple casecontrol studies has led to inaccuracies of the derived risk estimates in the low dose range,mainly due to smoking misclassification bias,uncertainties with respect to radon dosimetry,the histopathological characterization of lung cancers,as well as confounding by co-exposures with tobacco smoke and other indoor air pollutants.Together with a lack of biological plausibility,these deficiencies have a negative impact on the reliability of reported statistical relations between radon exposure and lung cancer at concentrations below 200 Bq/m3.It is vital that costly remedial actions to reduce domestic radon exposure are based on a scientifically robust risk assessment,and in view of aforementioned flaws,the hitherto proposed risk estimates need to be reconsidered.

Stable optical vortices in nonlinear multicore fibers

The multicore fiber(MCF)is a physical system of high practical importance.In addition to standard exploitation,MCFs may support discrete vortices that carry orbital angular momentum suitable for spatial-division multiplexing in high-capacity fiber-optic communication systems.These discrete vortices may also be attractive for high-power laser applications.We present the conditions of existence,stability,and coherent propagation of such optical vortices for two practical MCF designs.Through optimization,we found stable discrete vortices that were capable of transferring high coherent power through the MCF.

Sub-leading flow modes in PbPb collisions at (~sNN)^(1/2) = 2.76 TeV from the HYDJET++ model

Recent LHC results on the appearance of sub-leading flow modes in Pb Pb collisions at 2.76 TeV, related to initial-state fluctuations, are analyzed and interpreted within the HYDJET＋＋ model. Using the newly introduced Principal Component Analysis（PCA） method applied to two-particle azimuthal correlations extracted from the model calculations, the leading and sub-leading flow modes are studied as a function of the transverse momentum（p T） over a wide centrality range. The leading modes of the elliptic（v2^（1）） and triangular（v3^（1）） flow calculated with the HYDJET＋＋ model reproduce rather well the v2 {2} and v3 {2} coefficients measured experimentally using the two-particle correlations. Within the p T 3 Ge V/c range, where hydrodynamics dominates, the sub-leading flow effects are greatest at the highest p T of around 3 Ge V/c. The sub-leading elliptic flow mode（v2^（2））, which corresponds to the n = 2 harmonic, has a small non-zero value and slowly increases from central to peripheral collisions, while the sub-leading triangular flow mode（v3^（2））, which corresponds to the n = 3 harmonic, is even smaller and does not depend on centrality. For n= 2, the relative magnitude of the effect measured with respect to the leading flow mode shows a shallow minimum for semi-central collisions and increases for very central and for peripheral collisions. For the n= 3 case, there is no centrality dependence. The sub-leading flow mode results obtained from the HYDJET＋＋model are in rather good agreement with the experimental measurements of the CMS Collaboration.