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We develop a monotone finite volume element scheme for the diffusion problem on arbitrary polygonal grids inspired by the scheme in the literature ([35]). The main contributions of this paper include three aspects. Firstly, some auxiliary lines or points are introduced for any polygonal element so that it can be partitioned into two or more triangles, and one novel type of its control volume is concomitantly designed. In this paper, we mainly discuss quadrilateral grids. Secondly, some piecewise linear finite element spaces are imported for the trial spaces. Fictitious elements, continuous extensions and the nonlinear two-point flux idea can all be inherited from the triangular case. Therefore, the monotonicity of the scheme is easily proved only by the assembling of some triangles' element stiff matrices. Thirdly, the agreeable adaptability for distorted grids is completely borned. The strict convexity restriction on the grids can also be removed, the concave or severely distorted polygonal (such as quadrilateral) grids are transformed as the convex and general regular triangles. Finally, numerical results confirm its monotonicity, accuracy and stability. [ABSTRACT FROM AUTHOR]

Missing data are common in medical and social science studies and often face a serious challenge in ultrahigh-dimensional data analysis. In this paper, a nonparametric feature screening approach based on the imputation technique is proposed for ultrahigh-dimensional data with responses missing at random, where the imputation technique is used to replacing each missing value with a set of plausible values. Our approach has many advantages. On one hand, the suggested method relies only on imputation, and its impact is considerably less than that of the feature screening procedure based on the inverse probability weighting approach in missing probabilities. On the other hand, our method does not rely on any model assumption and works generally for all kinds of situations. Simulation studies are conducted to examine the performance of our approach, and a real data example is also presented for illustration. [ABSTRACT FROM AUTHOR]

The additive-multiplicative hazards (AMH) regression model specifies an additive and multiplicative form on the hazard function for the counting process associated with a multidimensional covariate process, which contains the Cox proportional hazards model and the additive hazards model as its special cases. In this paper, we study the AMH model with current status data, where the cumulative hazard hazard function is assumed to be nonparametric and is estimated using B-splines with monotonicity constraint on the functional, while a simultaneous sieve maximum likelihood estimation is proposed to estimate regression parameters. The proposed estimator for the parameter vector is shown to be asymptotically normal and semiparametric efficient. The B-splines estimator of the functional of the cumulative hazard function is shown to achieve the optimal nonparametric rate of convergence. A simulation study is conducted to examine the finite sample performance of the proposed estimators and algorithm, and a real data example is presented for illustration. [ABSTRACT FROM AUTHOR]

In this paper, we propose a new approach to the empirical likelihood inference for the parameters in heteroscedastic partially linear single-index models. In the growing dimensional setting, it is proved that estimators based on semiparametric efficient score have the asymptotic consistency, and the limit distribution of the empirical log-likelihood ratio statistic for parameters (β⊤,θ⊤)⊤ is a normal distribution. Furthermore, we show that the empirical log-likelihood ratio based on the subvector of β is an asymptotic chi-square random variable, which can be used to construct the confidence interval or region for the subvector of β. The proposed method can naturally be applied to deal with pure single-index models and partially linear models with high-dimensional data. The performance of the proposed method is illustrated via a real data application and numerical simulations. [ABSTRACT FROM AUTHOR]

Estimation and variable selection in partially linear models for massive data has been discussed by several authors. However, there does not seem to exist an established procedure for other semiparametric models, such as the semiparametric varying-coefficient linear model, the single index regression model, the partially linear errors-in-variables model, etc. In this paper, we propose a general procedure for variable selection in high-dimensional general semiparametric models by penalized semiparametric estimating equations. Under some regularity conditions, the oracle property is established, which the number of parameters is allowed to diverge. Furthermore, we also propose a split-and-conquer variable selection procedure for high-dimensional general semiparametric models with massive data. Under some weak regularity conditions, we establish the oracle property of the proposed procedure when the number of subsets does not grow too fast. What is more, the split-and-conquer procedure enjoys the oracle property as the penalized estimator by using all the dataset, and can substantially reduce computing time and computer memory requirements. The performance of the proposed method is illustrated via a real data application and numerical simulations. [ABSTRACT FROM AUTHOR]

In this paper, we apply empirical likelihood for two-sample problems with growing high dimensionality. Our results are demonstrated for constructing confidence regions for the difference of the means of twop-dimensional samples and the difference in value between coefficients of twop-dimensional sample linear model. We show that empirical likelihood based estimator has the efficient property. That is, asp→ ∞ for high-dimensional data, the limit distribution of the EL ratio statistic for the difference of the means of two samples and the difference in value between coefficients of two-sample linear model is asymptotic normal distribution. Furthermore, empirical likelihood (EL) gives efficient estimator for regression coefficients in linear models, and can be as efficient as a parametric approach. The performance of the proposed method is illustrated via numerical simulations. [ABSTRACT FROM AUTHOR]

We apply empirical likelihood (EL) for high-dimensional semiparametric models and propose penalized empirical likelihood (PEL) method for parameter estimation and variable selection. It is shown that the estimator based on EL has the asymptotic consistent property, and that the limit distribution of the EL ratio statistic for the parameters θ is asymptotic normal distribution. Furthermore, in a high-dimensional setting, we prove that PEL in semiparametric models has the oracle property, that is, with probability tending to 1 , the estimator based on PEL for the nonzero coefficients is efficient. Moreover, the PEL ratio statistic for the parameters θ is a χ q 2 distribution under the true null hypothesis. The performance of the proposed method is illustrated via a real data application and numerical simulations. [ABSTRACT FROM AUTHOR]

In this article, we apply the empirical likelihood (EL) method to the additive hazards model with high-dimensional data and propose the penalised empirical likelihood (PEL) method for parameter estimation and variable selection. It is shown that the estimator based on the EL method has the efficient property, and the limit distribution of the EL ratio statistic for the parameters is a asymptotic normal distribution under the true null hypothesis. In a high-dimensional setting, we prove that the PEL method in the additive hazards model has the oracle property, that is, with probability tending to 1, and the estimator based on the PEL method for the nonzero parameters is estimation and selection consistent if the hypothesised model is true. Moreover, the PEL ratio statistic for the parameters is adistribution under the true null hypothesis. The performance of the proposed methods is illustrated via a real data application and numerical simulations. [ABSTRACT FROM PUBLISHER]

Nanoparticles of Bi4Ti3O12 have been prepared by chemical coprecipitation. The phase structure was investigated by X-ray diffraction (XRD) and refined using the Rietveld method. Orthorhombic Bi4Ti3O12 particles were obtained after heating at 700 and 800 °C; however, for the particles calcined at 500–650 °C, the results suggested the presence of a high-temperature tetragonal phase at room temperature. This structural anomaly was further confirmed by differential thermal analysis (DTA). [Copyright &y& Elsevier]

Organic and polymer fluorescent nanomaterials are a frontier research focus. Here in this work, a series of fluorinated zwitterionic random copolymers end‐attached with a quasi‐chromophoric group of pyrene or tetraphenylethylene (TPE) are well synthesized via atom transfer radical polymerization with activators regenerated by electron transfer (ARGET ATRP). Those random copolymers with total degree of polymerization 100 or 200 are able to produce fluorescent single‐chain nanoparticles (SCNPs) through intra‐chain self‐folding assembly with quite uniform diameters in the range of 10–20 nm as characterized by dynamic light scattering and transmission electron microscopy. By virtue of the segregation or confinement effect, both SCNPs functionalized with pyrene or TPE group are capable of emitting fluorescence, with pyrene tethered SCNPs exhibiting stronger fluorescence emission reaching the highest quantum yield ≈20%. Moreover, such kind of fluorescent SCNPs manifest low cytotoxicity and good cell imaging performance for Hela cells. The creation of fluorescent SCNPs through covalently attached one quasi‐chromophore to the end of one fluorinated zwitterionic random copolymer provides an alternative strategy for preparing polymeric luminescence nanomaterials, promisingly serving as a new type of fluorescent nanoprobes for biological imaging applications. [ABSTRACT FROM AUTHOR]

The local Walsh-average regression has been shown to be a comparable method to the others in nonparametric regression. In this paper, we develop a new estimation procedure based on local Walsh-average regression for single index varying coefficient models. Under some general assumptions, we establish the asymptotic properties of the proposed estimators for both the parametric and nonparametric parts. We further demonstrate that the proposed estimates have great efficiency gains across a wide spectrum of non-normal error distributions and almost not lose any efficiency for the normal error compared with that of local polynomial regression estimates under the least squares loss. Even in the worst case scenarios, the asymptotic relative efficiency owns a lower bound equaling to 0.864 for estimating the single-index parameter and a lower bound being 0.8896 for estimating the nonparametric link functions respectively, versus the least squares estimators. A simulation study is conducted to assess the finite sample properties of the proposed procedure, and a real data analysis is followed to further illustrate the application of the proposed methodology. [ABSTRACT FROM AUTHOR]

Liquid crystal (LC) dimers with well‐defined composition and structure arouse broad attentions for their exhibiting LC properties beyond conventional low molar mass mesogens and serving as fascinating model compounds for LC polymers. Here in this work, a series of LC dimers bridged with a phosphonic group have been synthesized through a facile free radical mediated addition reaction between hypophosphorous acid and vinyl terminated cyanobiphenyl mesogens with variant length alkyl spacers. In addition, two esterified derivatives and a group of mono‐addition homologues with a terminal phosphonic acid group have also been prepared for comparison study. All the newly synthesized compounds exhibit monotropic nematic (N) phase with typical schlieren textures except for the LC dimer with the longest eleven‐methylene spacer, which surprisingly shows twist‐bend nematic (NTB) phase directly from the isotropic state upon cooling. Moreover, the thermal transition properties such as the nematic‐isotropic transition temperatures and associated entropy changes of the series LC dimers display a modest odd‐even effect. Furthermore, both the LC dimers and the mono‐addition homologues in N phase are quite easy to achieve homeotropic alignment upon annealing thanks to the supramolecular interactions between the introduced phosphonic acid group and the hydroxylated glass surface. This work thus provides a novel synthesis strategy for a class of LC materials bridged with a phosphonic acid group prone to further functionalization, which may serve as promising vertical alignment agents and pave the way for developing a new kind of functionalized LC materials of NTB phase. [ABSTRACT FROM AUTHOR]

Abstract: NdFeB films with Nd compositions varied from 13.34 to 24.30at% were deposited by DC gradient sputtering using targets Nd12.5Fe71.5B16 and Nd. The hard magnetic properties, grain growth direction and magnetic domain structures were dramatically influenced by Nd composition. The samples with intermediate Nd concentrations exhibited optimal magnetic properties and microstructures, such as large squareness ratio over 0.9, large energy product up to 174kJ/m3, and vertical domain structure. However, the samples with higher and lower Nd compositions showed almost isotropic loops. (00 l) as main X-ray diffraction peaks in the optimal Nd composition region indicated most of Nd2Fe14B grains with c-axis perpendicular to the film plane, while NdFeB grains in other region are almost random growth. The good magnetic properties can be attributed to the vertical growth of Nd2Fe14B grains. [Copyright &y& Elsevier]

Abstract: CrSb film was deposited on KCl (100) substrates by magnetron sputtering. Strong ferromagnetism was observed in the CrSb film, which can be attributed to the CrSb phase with ferromagnetic zinc-blended structure. The investigated ZB-CrSb film about 5 nm in thickness is sufficiently thicker to be investigated the half-metallic nature of ZB-CrSb and to be practically applied in spintronics devices. [Copyright &y& Elsevier]

Liquid crystalline elastomers (LCEs) combine the ordering character of a liquid crystal and the elasticity of a polymer network. The development of fully light-driven LCE-based soft actuators with good reshapeability and recyclability is in high demand. In this work, we prepared SWCNT/LCE composite films through the introduction of allyl sulfide-based dynamic covalent crosslinks in the LCE matrix and the well-dispersed filler single-walled carbon nanotubes (SWCNTs) with a strong photothermal effect. The SWCNT/LCE composite films were facilely fabricated with reorientation and remouldable capabilities regulated by 405 nm visible light. The monodomain composite films demonstrated multimode actuations of contraction, bending, curling, stretching recovery, and even shape memory driven by 808 nm near-infrared (NIR) light. Moreover, the monodomain spiral ribbon or stretching flat strip and the original polydomain composite film can be readily transformed into each other, and reshaped through easily achievable fabrication conditions. Therefore, the well-prepared SWCNT/LCE composite films with exchangeable covalent crosslinks showed promise as candidates for the development of multimode NIR photomechanical soft actuators with fully light-driven controllability and good remouldability. [ABSTRACT FROM AUTHOR]

Nanostructured materials of various shape and dimension have aroused intensive interests, among which copper(i) sulfide (Cu2S) nanomaterials are of particular prominence. In this work, various nanostructured Cu2S have been facilely prepared via solventless thermolysis, with well-controlled shape and dimension determined by and inherited from the layered structures of the azobenzene-containing single-source copper thiolate mesogenic precursors. The precursors with longer alkyl tails exhibit highly ordered layered liquid crystalline mesophases and retain persistent order up to temperatures beyond the clearing points. Under non-vacuum inert atmosphere or with further elevated temperature, large undulations of the constrained lamellar space result in significantly enhanced diffusion, migration and mass transfer, thus leading to the morphologies changing from one-dimensional (1D) ultrathin nanowires into thickened nanorods then to discrete 2D nanodisks. Based on a variety of modern techniques, especially in situ variable-temperature small angle X-ray scattering (SAXS), an extended universal “layered-precursor to lamellar-nanomaterial” (LPLM) mechanism has been proposed to account for the structural evolution of Cu2S nanomaterials. Our findings provide a novel pathway with clearer mechanism for well-controlled preparation of metal chalcogenides of various dimension and shape. In particular, the ultrathin Cu2S nanowires are anticipated to serve as fascinating semiconducting materials for various promising device applications. [ABSTRACT FROM AUTHOR]

ABSTRACT Liquid crystalline block copolymers (LCBCPs) are fascinating for their combining molecular level liquid crystalline orders and microphase separated multidomain morphologies. Here in this article, a series of PEG-containing side-chain discotic LCBCPs of PEG- b- Pm- n with variant spacer length m = 6, 10 and degree of polymerization (DP) of discotic LC block from n = 10 to 45, have been well-synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization. The RAFT process mediated by macromolecular chain transfer agent (macroCTA) shows remarkable monomer concentration dependence. The influence of the introduced PEG block on the nano-scale microphase-segregation and mesophase organization is closely related to the side-chain triphenylene (TP) discogens stacking mode dependent on the spacer length. Wherein, the PEG- b- P6- n series with a six-methylene spacer exhibit consistent microphase separation with slightly disturbed yet ordered columnar structures. While for PEG- b- P10- n series with a longer ten-methylene spacer, the columnar organization in the copolymers is even improved in contrast with the low order of randomly TP stacking in their corresponding homopolymers. This work offers a viable and inspiring pathway for controlled synthesis of block copolymers with bulky side groups, as well as enhances in-depth understanding of the hierarchical superstructure organization in discotic units involved complex block copolymers. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2544-2553 [ABSTRACT FROM AUTHOR]

Abstract: Partial substitution of Al by Mg was studied to reveal the influence of the neighboring element for glass forming ability (GFA) of La62Al14Cu24 alloy. A series of quaternary La62Al14−x Mg x Cu24 (x =2.8, 3.2, 3.5, 4.2, 5.0) alloys were cast by copper mold casting. As a result, the La–Al–Mg–Cu alloys with full glassy rods of 10mm in diameter were achieved, suggesting that partial substitution of Al by Mg dramatically enhances the GFA. The enhancement of GFA can be mainly attributed to the large atomic size ratios among these constituent elements. [ABSTRACT FROM AUTHOR]

Abstract: The preparation and application of overbased nanodetergents with excess alkaline calcium carbonate is a good example of nanotechnology in practice. The phase transformation of calcium carbonate is of extensive concern since CaCO3 serves both as an important industrial filling material and as the most abundant biomineral in nature. Industrially valuable overbased nanodetergents have been prepared based on calcium salts of heavy alkylbenzene sulfonate by a one-step process under ambient pressure, the carbonation reaction has been monitored by the instantaneous temperature changes and total base number (TBN). A number of analytical techniques such as TGA, DLS, SLS, TEM, FTIR, and XRD have been utilized to explore the carbonation reaction process and phase transformation mechanism of calcium carbonate. An enhanced understanding on the phase transformation of calcium carbonate involved in calcium sulfonate nanodetergents has been achieved and it has been unambiguously demonstrated that amorphous calcium carbonate (ACC) transforms into the vaterite polymorph rather than calcite, which would be of crucial importance for the preparation and quality control of lubricant additives and greases. Our results also show that a certain amount of residual Ca(OH)2 prevents the phase transformation from ACC to crystalline polymorphs. Moreover, a vaterite nanodetergent has been prepared for the first time with low viscosity, high base number, and uniform particle size, nevertheless a notable improvement on its thermal stability is required for potential applications. [Copyright &y& Elsevier]

An unprecedented tetranuclear complex bridged by 3,5-pyridinedicarboxylate (abbreviated as 3,5-PDC) with an empirical formula [Cu2(2,2′-bpy)3(3,5-PDC)]2(ClO4)4 · 2(H2O), has been synthesized and spectrally characterized. X-ray structural analysis reveals that there are two types of copper(II) centers, one is penta-coordinate with a distorted pyramidal geometry, while the other is tetra-coordinate with a distorted square planar geometry. 3,5-PDC serves as a tridentate ligand linking three adjacent metals with its one nitrogen and two monodentate carboxylic donors. [Copyright &y& Elsevier]