The effect of anisotropic surface tension on the morphological stability of planar interface during directional solidification

This paper considers the effect of the anisotropic surface tension on the morphological stability of the planar interface during directional solidification. When the expression exhibiting the four-fold symmetry is included, the modified absolute stability criterion is obtained by employing the multi-variable expansion method. The linear stability analysis reveals that for the given temperature gradient, as the anisotropic surface tension parameter increases, the stability zone tends to decrease.     

关于Birkhoff逆问题中Santilli方法的研究

研究构造Birkhoff动力学函数的Santilli方法.首先,基于Cauchy-Kovalevskaya型方程解的存在性定理,采用反证法证明自治系统总有自治Birkhoff表示;其次,给出更简洁的方法证明Santilli第二方法可以被简化;找到Santilli第三方法中所隐含的一种等量关系,提出改进的Santilli第三方法,并研究该方法的MATLAB程序化计算;最后,总结全文并对结果进行讨论.     

Extrusions and intrusions in fatigued metals. Part 2. AFM and EBSD study of the early growth of extrusions and intrusions in 316L steel fatigued at room temperature

Early stages of surface relief evolution of persistent slip markings (PSMs), formed in areas where persistent slip bands (PSBs) intersect the free surface, in polycrystalline 316L stainless steel cycled with constant plastic strain amplitude were studied using atomic force microscopy (AFM) and electron backscattering diffraction (EBSD). Focused ion beam (FIB) technique was employed to obtain additional, more detailed information on the shape of PSMs. To reveal true qualitative and quantitative information on the simultaneous growth of intrusions and extrusions within individual PSMs, identical areas both on the specimen surface and on its inverse copy obtained via plastic replica were studied using AFM. Intrusions are preceded by extrusions regardless of orientation of individual grains of the polycrystal. The first intrusions appear largely around 1% of fatigue life at the moment when ‘static’ extrusions are developed. They appear predominantly but not exclusively at the side of extrusions where the emerging active slip plane is inclined to the surface at an acute angle. They grow faster than the stage of stable extrusion growth. Typical morphology of mature PSMs developed at 15% of fatigue life consists of ribbon-like extrusions accompanied by two thin parallel intrusions along both PSB–matrix interfaces. Experimental data on the morphology and growth of extrusions and intrusions are discussed in relation to the theoretical models and computer simulations of surface relief evolution leading to fatigue crack initiation.     

Performance of La-doped strontium titanate (LST) anode on LaGaO3-based SOFC

Ni-containing anode is currently used with many electrolytes of solid oxide fuel cells (SOFCs). However, Ni is easily oxidized and deteriorates the LaGaO₃-based electrolyte. A La-doped SrTiO₃ (LST, La_0.2Sr_0.8TiO₃) is a candidate as an anode material to solve the Ni poisoning problem in LaGaO₃-based SOFC. In this study, a single-phase LST and an LST-Gd_0.2Ce_0.8O_2 ? δ (GDC) composite were tested as the possible anodes on La_0.9Sr_0.1Ga_0.8Mg_0.2O_3 ? δ (LSGM) electrolyte. In order to further improve the anodic performance, Ni was impregnated into the LST-GDC composite anode. The performance was examined from 600 °C to 800 °C by measuring impedance of the electrolyte-supported, symmetric (anode/electrolyte/anode) cells. A polarization resistance (R_p) of LST-GDC anode was much reduced from that of LST anode. When Ni was impregnated into LST-GDC composite, the R_p value was further reduced to ~ 10% of the single-phase LST anode, and it was 1 Ωcm² at 800 °C in 97% H₂ + 3% H₂O atmosphere. A single cell with Ni-impregnated LST-GDC as an anode, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 ? δ (BSCF) as a cathode and LSGM as an electrolyte exhibited the maximum power density of 275 mW/cm² at 800 °C, increased from ~ 60 mW/cm² for the cell using the LST-GDC as an anode. Thus, LST-GDC composite is promising as a component of anode.     

Band-selection filters with concatenated long-period gratings in few-mode fibers

We demonstrate a novel device that comprises a pair of broadband and narrowband long-period gratings written in specially designed few-mode fibers to achieve in-fiber bandpass filtering. This device configuration opens the possibility of using long-period gratings for complex spectral shaping in a band-selection as opposed to the conventional band-rejection configuration. The devices are low loss (<0.5dB) as well as tunable over large spectral ranges (26 nm). We demonstrate, for the first time to our knowledge, that the unique dispersive properties of long-period gratings allow for constructing dispersion-free bandpass filters with arbitrarily sharp spectral profiles.     

Effect of annealing time on the structural and ferromagnetic properties of the GaMnN thin films

GaMnN thin films were deposited on a sapphire (0001) substrate by using laser assisted molecular beam epitaxy. Subsequently, the samples were annealed in the ammonia ambience at 1000 °C for different time lengths. The crystalline quality was improved gradually, and the room temperature ferromagnetism of our samples becomes stronger with the increase of the annealing time within 25 min. The X-ray photoelectron spectra analysis confirmed that the Mn³⁺ concentration in the GaMnN films increased after annealing. The stronger ferromagnetism was observed in the sample with the higher Mn³⁺ concentration. However, too long annealing time, such as 35 min, will lead to the degradation of the crystalline quality and the decrease of Mn³⁺ concentration, which results in the weakened ferromagnetism. The optimal annealing time is 25 min at 1000 °C in our experiments. Finally, the origin of the room temperature ferromagnetism in our samples was discussed preliminarily.     

Microstructural and domain effects in epitaxial CoFe2O4 films on MgO with perpendicular magnetic anisotropy

CoFe₂O₄ (CFO) epitaxial thin films of various thicknesses were grown on MgO substrates using the pulsed electron-beam deposition technique. The films have excellent in-plane coherence with the substrate, exhibit layer-by-layer growth and have well-defined thickness fringes in x-ray diffraction measurements. Atomic force microscopy (AFM) measurements indicate that misfit dislocations form in thicker films and the critical thickness for the dislocation formation is estimated. Perpendicular magnetic anisotropy in CFO due to epitaxial in-plane tensile strain from the substrate was found. A stripe-like domain structure in the demagnetized state is demonstrated using magnetic force microscopy (MFM), in agreement with previous predictions. Coercivity increased in thicker films, which is explained by domain wall pinning due to misfit dislocations at the CFO/MgO interface.     

Phase-locked, erbium-fiber-laser-based frequency comb in the near infrared

A phase-locked frequency comb in the near infrared is demonstrated with a mode-locked, erbium-doped, fiber laser whose output is amplified and spectrally broadened in dispersion-flattened, highly nonlinear optical fiber to span from 1100 to >2200 nm. The supercontinuum output comprises a frequency comb with a spacing set by the laser repetition rate and an offset by the carrier-envelope offset frequency, which is detected with the standard f-to-2f heterodyne technique. The comb spacing and offset frequency are phase locked to a stable rf signal with a fiber stretcher in the laser cavity and by control of the pump laser power, respectively. This infrared comb permits frequency metrology experiments in the near infrared in a compact, fiber-laser-based system.     

MEVVA金属离子源的研制与调试

本文介绍的ＭＥＶＶＡ源采用电动推进式可更换单阴极弧放电机构和加减速三栅引出系统，耐压水平在于５０ｋＶ，平均束流大于５ｍＡ，束班约Ф１５０，束的不均匀度小于±２０％。束的分布测量表明，在中心区有约Ф４０的平顶区。我们已获得了Ａｌ，Ｔｉ，Ｃｒ，Ｆｅ，Ｎｉ，Ｃｕ，Ｙ，Ｚｒ，Ｍｏ，Ｔａ，Ｗ，Ｃ，ＬａＢ６等的离子束流及其最佳的运行条件。     

Slowly rotating Bose Einstein condensate galactic dark matter halos,and their rotation curves

If dark matter is composed of massive bosons, a Bose–Einstein condensation process must have occurred during the cosmological evolution. Therefore galactic dark matter may be in a form of a condensate, characterized by a strong self-interaction. We consider the effects of rotation on the Bose–Einstein condensate dark matter halos, and we investigate how rotation might influence their astrophysical properties. In order to describe the condensate we use the Gross–Pitaevskii equation, and the Thomas–Fermi approximation, which predicts a polytropic equation of state with polytropic index \(n=1\). By assuming a rigid body rotation for the halo, with the use of the hydrodynamic representation of the Gross–Pitaevskii equation we obtain the basic equation describing the density distribution of the rotating condensate. We obtain the general solutions for the condensed dark matter density, and we derive the general representations for the mass distribution, boundary (radius), potential energy, velocity dispersion, tangential velocity and for the logarithmic density and velocity slopes, respectively. Explicit expressions for the radius, mass, and tangential velocity are obtained in the first order of approximation, under the assumption of slow rotation. In order to compare our results with the observations we fit the theoretical expressions of the tangential velocity of massive test particles moving in rotating Bose–Einstein condensate dark halos with the data of 12 dwarf galaxies and the Milky Way, respectively.