Modeling of Shear-Induced Diapycnal Mixing in Frontal Systems

Three shear-induced mixing models are examined and applied to oceanic frontal systems. These are a simple diagnostic model, a one-dimensional kinematical model and a two-dimensional geostrophic model. All of these are process-oriented models in isopycnic coordinates, with diapycnal mixing depending on the gradient Richardson number and mixing rapidly developing in subcritical flows. In the first model an initial subcritical condition is specified and mixing is allowed to redistribute the vertical density flux. In the second model the dynamics is specified ad hoc to simulate a frontal system which leads to subcritical conditions and we are left to solve the mass conservation equation. In the final model a two-dimensional density-depth field is forced through an externally imposed deformation velocity field and we solve both the mass and momentum conservation equations. In this last model diapycnal mixing controls the mass conservation equation while the momentum equations consist in cross-stream geostrophic balance. All three models produce mixed regions which probably correspond to some of the fine structure density-depth steps that are observed in geophysical flows. The very simple diagnostic and kinematical models have the merit of providing a clear picture of the physical mechanism that produces the density-depth steps, but the potential complexity of the solution is only appreciated when incorporating the dynamics, such as in the geostrophic model.     

Magnetic‐Structure‐Stabilized Polarization in an Above‐Room‐Temperature Ferrimagnet

Above‐room‐temperature polar magnets are of interest due to their practical applications in spintronics. Here we present a strategy to design high‐temperature polar magnetic oxides in the corundum‐derived A₂BB′O₆ family, exemplified by the non‐centrosymmetric (R3) Ni₃TeO₆‐type Mn²⁺₂Fe³⁺Mo⁵⁺O₆, which shows strong ferrimagnetic ordering with T_C=337 K and demonstrates structural polarization without any ions with (n?1)d¹⁰ns⁰, d⁰, or stereoactive lone‐pair electrons. Density functional theory calculations confirm the experimental results and suggest that the energy of the magnetically ordered structure, based on the Ni₃TeO₆ prototype, is significantly lower than that of any related structure, and accounts for the spontaneous polarization (68 μC cm^?2) and non‐centrosymmetry confirmed directly by second harmonic generation. These results motivate new directions in the search for practical magnetoelectric/multiferroic materials.     

Synthesis and crystal structures of RE7Zn21+xSi2–x [RE = Ce,Pr, and Nd; 0.09 (1) < x < 0.95 (1)]

The focus of this paper is on the synthesis and crystal structures of three Zn‐rich compounds with the general formula RE₇Zn_21+xSi_2−x, where RE = Ce [x = 0.95 (1); heptacerium docosazinc silicon], Pr [x = 0.09 (1); heptapraseodymium henicosazinc disilicon], and Nd [x = 0.53 (1); heptaneodymium docosazinc silicon]. The compounds were obtained by high‐temperature reactions, using the respective elements as starting materials. The structures were determined by single‐crystal X‐ray diffraction. The title compounds crystalize in the orthorhombic space group Pbam (No. 55, Pearson symbol oP60) and are isostructural with about a dozen RE₇Zn_21+xTt_2−x (RE = La–Nd; Tt = Ge, Sn, and Pb) compounds previously reported by our group. The results from the present refinements confirm the previously published data on RE₇Zn_21+xSi_2−x (RE = La and Ce; x≃ 1.45) [Malik et al. (2013). Intermetallics, 36 , 118–126]. Additionally, magnetic susceptibility measurements on the corresponding bulk samples show Curie–Weiss paramagnetic behavior from 5 to 300 K, consistent with RE³⁺ ground states and local‐moment magnetism due to the core 4f electrons.     

Supercritical fluid chromatography as a tool for enantioselective separation; A review

Supercritical fluid chromatography (SFC) has become popular in the field of enantioselective separations. Many works have been reported during the last years. This review covers the period from 2000 till August 2013. The article is divided into three main chapters. The first one comprises a basic introduction to SFC. The authors provide a brief explanation of general principles and possibilities of this method. The advantages and drawbacks are also listed. Next part deals with chiral separation systems available in SFC, namely with the commonly used chiral stationary phases. Properties and interaction possibilities of the chiral separation systems are described. Recent theoretical papers are emphasized in this chapter. The last part of the paper gives an overview of applications of enantioselective SFC in analytical chemistry, in both analytical and preparative scales. Separation systems and conditions are summed up in tables so that they provide a helpful tool for analysts who search for a particular method of analysis.     

Estimates for the low‐frequency electromagnetic fields scattered by two adjacent metal spheres in a lossless medium

Inductive electromagnetic means, currently employed in real physical applications and dealing with voluminous bodies embedded in lossless media, often call for analytically demanding tools of field calculation at modeling stage and later on at numerical stage. Here, one is considering two closely adjacent perfect conductors, possibly almost touching one another, for which the 3D bispherical geometry provides a good approximation. The particular scattering problem is modeled with respect to the two solid impenetrable metallic spheres, which are excited by a time‐harmonic magnetic dipole, arbitrarily orientated in the 3D space. The incident, the scattered, and the total non‐axisymmetric electromagnetic fields yield rigorous low‐frequency expansions in terms of positive integral powers of the real‐valued wave number in the exterior medium. We keep the most significant terms of the low‐frequency regime, that is, the static Rayleigh approximation and the first three dynamic terms, while the additional terms are small contributors and they are neglected. The typical Maxwell‐type problem is transformed into intertwined either Laplace's or Poisson's potential‐type boundary value problem with impenetrable boundary conditions. In particular, the fields are represented via 3D infinite series expansions in terms of bispherical eigenfunctions, obtaining analytical closed‐form solutions in a compact fashion. This procedure leads to infinite linear systems, which can be solved approximately within any order of accuracy through a cutoff technique.     

Integral inequalities for coordinated Harmonically convex functions

In this paper, we introduce the notion of coordinated harmonically convex functions. We derive some new integral inequalities of Hermite–Hadamard type for coordinated Harmonically convex functions. The interested readers are encouraged to find the applications of harmonically convex functions in pure and applied sciences.     

LaTiO3(110)薄膜分子束外延生长的精确控制和表面截止层的研究

LaTiO₃ 是一种典型的强关联电子材料, 其(110) 薄膜为通过晶格对称性、应变等的设计调控外延结构的物理性质提供了新的机会. 本文研究了SrTiO₃(110) 衬底表面金属La 和Ti 沉积所引起的微观结构变化, 进而利用电子衍射信号对分子束外延薄膜生长表面阳离子浓度的灵敏响应, 发展了原位、实时、精确控制金属蒸发源沉积速率的方法, 实现了高质量LaTiO₃(110) 薄膜的生长和对阳离子化学配比的精确控制. 由于LaTiO₃中Ti³⁺ 3d 电子的库仑排斥作用, 氧原子层截止的(110) 表面更容易实现极性补偿, 因此生长得到的薄膜表面暴露出单一类型的氧截止面.     

Hyperkähler metric and GMN ansatz on focus–focus fibrations

In this paper, we study the hyperkähler metric and practise GMN’s construction of hyperkähler metric on focus–focus fibrations. We explicitly compute the action–angle coordinates on the local model of focus–focus fibrations, and show its semi-global invariant should be harmonic to admit a compatible holomorphic 2-form. Then we study the canonical semi-flat metric on it. After the instanton correction, finally we are able to get a reconstruction of the generalized Ooguri–Vafa metric.     

Copolymerizations of ethylene and polar comonomers with bis(phenoxyketimine) group IV complexes: Effects of the central metal properties

With triisobutylaluminum as a protection reagent, copolymerizations of ethylene with 10‐undecen‐1‐ol, 10‐undecenoic acid, and 5‐hexen‐1‐ol have been performed with bis[(3,5‐di‐^tBu? C₆H₂? 2‐O)? PhC?N(2‐F? C₆H₄)]ZrCl₂ ( a )/methylaluminoxane or bis[(3,5‐di‐^tBu? C₆H₂? 2‐O)? PhC?N(2‐F? C₆H₄)]TiCl₂ ( b )/methylaluminoxane as the catalyst. Both catalysts exhibit high activities of copolymerization in the presence of polar groups. The properties of the copolymers are strongly affected by the central metal properties of the catalysts. In comparison with complex a , titanium complex b appears to be less sensitive to polar monomers and more favorable for the preparation of higher molecular weight functionalized polyethylenes containing higher contents of polar groups. Studies on the polymerization temperature indicate that the catalytic activities decrease greatly with both complex a and complex b . The comonomer contents incorporated into the copolymers are slightly dependent on the polymerization temperature in the case of complex a , whereas in the case of complex b , the effect of the polymerization temperature is more distinct: an increase in the polymerization temperature can efficiently facilitate the incorporation of polar comonomers. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 59–68, 2007