方阱链状分子临界性质的Monte Carlo模拟

在巨正则系综下对阱宽为λ=1.5,链长分别为4、8、16的方阱链状流体实施Monte Carlo模拟,采用建立在完整标度基础上的无偏的Q-参数方法,通过histogram reweighting技术以及有限尺寸标度理论得到了热力学极限下该系列流体的临界温度和临界密度.模拟结果表明,方阱链流体的临界温度随着链长的增加而升高.并且不同链长方阱流体的临界温度均低于已报道的结果.由于本文所采用的完整标度的无偏性,我们估计的临界点更加准确.并且流体的临界温度与链长之间的关系与Flory-Huggins理论相一致.我们还预测了无限链长方阱流体的临界温度,比已有结果略高.     

模拟吸附在狭缝微孔中的丙烷的微观结构

用巨正则系综MonteCarlo（GCEMC）方法模拟了活性碳孔吸附丙烷时的微观结构．在GCEMC模拟中,非极性丙烷分子采用单点LJ球状分子模型,狭缝活性碳孔墙采用10－4-3势能模型．在温度T＝134．3K下,模拟并观察到了丙烷分子在狭缝活性碳孔中的吸附、脱附以及毛细凝聚现象,得到了吸附等温线和孔中流体的局部密度轮廓图．从分子水平出发,详细分析了吸附、毛细冷凝时孔中流体的微观结构,为认识、理解吸附的微观机理提供了工具与借鉴．     

层柱状微孔材料吸附存储天然气的Monte Carlo模拟

采用巨正则系综MonteCarlo方法模拟了天然气中主要成分甲烷在层柱状微孔材料中T=300K下的吸附存储,在模拟中层柱状微孔采用Yi等人建立的柱子均匀分布在两炭孔墙之间的模型来表征。甲烷分子采用Lennard-Jones球型分子模型,炭孔墙采用Steele的10-4-3模型,对孔宽为1.36nm的层柱微孔,模拟了四个不同孔率的层柱材料吸附甲烷的情形。得到了孔中流体的局部密度分布以及吸附等温线,对比不同孔率下甲烷的吸附量,得到了此情形吸附甲烷的较佳孔率为0.94。     

A facile method for preparation of graphene film electrodes with tailor-made dimensions with Vaseline as the insulating binder

This communication describes a facile but effective method to prepare graphene film electrodes with tunable dimensions with Vaseline as the insulating binder. Cyclic voltammetry (CV) studies reveal that the as-prepared graphene film electrodes have tunable dimensions ranging from a conventional electrode to a nanoelectrode ensemble, depending on the amount of graphene dispersed into the insulting Vaseline matrix. A large amount of graphene (typically, 10.0 μg/mL) leads to the formation of the film electrodes with a conventional dimension, while a small amount of graphene (typically, 1.0 μg/mL) essentially yields the graphene film electrodes like a nanoelectrode ensemble. As one new kind of carbon-based film electrodes with tailor-made dimensions and a good electrochemical activity as well as a high stability, the graphene film electrodes are believed to be potentially useful for fundamental electrochemical studies and for practical applications.     

受限狭缝中CO_2-CH_4体系的汽液相平衡性质

受限条件下CO2-CH4体系的相平衡性质对化工工艺过程的设计具有非常重要的意义.采用Gibbs系综Monte Carlo模拟,对220K下CO2-CH4体系在主体相和受限狭缝中的相平衡性质进行了系统地研究.通过主体相模拟与实验结果比较,验证了流体分子势能参数的合理性;通过改变狭缝壁面原子的能量参数,研究了受限环境对CO2-CH4体系汽液相平衡性质的影响.与主体相相比,在硬壁狭缝中,CO2-CH4体系的露点压力增加,泡点压力降低,压力-组成相图变窄,且体系更容易达到超临界状态;在吸引狭缝中,随壁面原子能量参数的增大,CO2-CH4体系的压力-组成相图上移,临界点处CH4的摩尔分数减小,相图变窄.在体系汽液相总组成相同情况下,硬壁狭缝内体系的汽液相密度均比主体相中小;随壁面原子能量参数增大,气相密度变大、液相密度在CH4的摩尔分数较小时变大而当CH4的摩尔分数达到一定值后反而减小.在体系汽液相总组成相同时,受限环境下的汽化热比主体相的汽化热小且随壁面吸引势的增强越来越小;在主体相和硬壁狭缝中体系的汽化热随CH4含量的增加单调减小,而当壁面势能参数较大时汽化热随CH4含量增加先增大后减小.     

Carbon clusters

Some of the most significant discoveries and achievements concerning the mass spectra and gas phase ion chemistry of carbon clusters are reviewed. These include (1) nanosecond and femtosecond laser ionizations; (2) ion structures through ion/molecule reactions, ion chromatography, and computational methods; (3) carbon cluster cooling through radiative decay, dissociative decay, and thermionic emission; (4) mechanisms and energetics of fragmentation reactions; (5) endohedral fullerenes including recent data on ion beam implantation, and (6) ion chemistry as a function of the fullerene charge state.     

Near-Infrared Spectroscopy Analytical Model Using Ensemble Partial Least Squares Regression

A novel ensemble-based feature selection method was developed which is designated as ensemble partial least squares regression coeffientents (EPRC). It was composed of two steps: generating a series of different single feature selectors and aggregating them to reach a consensus. Specifically, the bootstrap resampling approach was used to generate a diversity of single feature selectors, and the absolute values of the regression coefficients of the partial least squares (PLS) model were used to rank the features. Next, these feature rankings out of single feature selectors were aggregated by the weighted-sum approach. Finally, coupled with the regression model, the features selected by EPRC were evaluated through cross validation and an independent test set. By experiments of constructing the spectroscopy analysis model on three near infrared spectroscopy (NIRS) datasets, it was shown that the EPRC located key wavelengths, gave a promotion to regression performance, and was more stable and interpretable to the domain experts.     

Limit theorems for critical first-passage percolation on the triangular lattice

Consider (independent) first-passage percolation on the sites of the triangular lattice $\mathbb{T}$ embedded in $\mathbb{C}$. Denote the passage time of the site $v$ in $\mathbb{T}$ by $t\left(v\right)$, and assume that $P(t\left(v\right)=0)=P(t\left(v\right)=1)=1∕2$. Denote by $b_{0,n}$ the passage time from 0 to the halfplane $\{v\in \mathbb{T}:\text{Re}\left(v\right)\ge n\}$, and by $T(0,nu)$ the passage time from 0 to the nearest site to $nu$, where $\left|u\right|=1$. We prove that as $n\to \infty$, $b_{0,n}∕logn\to 1∕\left(2\sqrt{3}\pi \right)$ a.s., $E\left[b_{0,n}\right]∕logn\to 1∕\left(2\sqrt{3}\pi \right)$ and Var$\left[b_{0,n}\right]∕logn\to 2∕\left(3\sqrt{3}\pi \right)?1∕\left(2{\pi }^2\right)$; $T(0,nu)∕logn\to 1∕\left(\sqrt{3}\pi \right)$ in probability but not a.s., $E\left[T(0,nu)\right]∕logn\to 1∕\left(\sqrt{3}\pi \right)$ and Var$\left[T(0,nu)\right]∕logn\to 4∕\left(3\sqrt{3}\pi \right)?1∕{\pi }^2$. This answers a question of Kesten and Zhang (1997) and improves our previous work (2014). From this result, we derive an explicit form of the central limit theorem for $b_{0,n}$ and $T(0,nu)$. A key ingredient for the proof is the moment generating function of the conformal radii for conformal loop ensemble ${\mathrm{CLE}}_6$, given by Schramm et al. (2009).     

Numerical analysis of two ensemble eddy viscosity numerical regularizations of fluid motion

This report analyzes an efficient ensemble regularization algorithm for under‐resolved and convection dominated flows (including ones at higher Reynolds numbers). Computing an ensemble simultaneously allows each realization to access ensemble data. This allows use of means and fluctuations in regularizations used for each realization. The combined approach of ensemble time stepping and ensemble regularizations allows direct calculation of the turbulent viscosity coefficient and gives an unconditionally stable algorithm. It also suggests reconsidering an old but not as well‐developed definition of the mixing length. This mixing length vanishes at solid walls without van Driest damping, increases stability, and improves flow predictions in our preliminary tests. © 2014 Wiley Periodicals, Inc. Numer Methods Partial Differential Eq 31: 630–651, 2015     

THE ENSEMBLE KALMAN FILTER FOR MULTIDIMENSIONAL BIOECONOMIC MODELS

To integrate economic considerations into management decisions in ecosystem frameworks, we need to build models that capture observed system dynamics and incorporate existing knowledge of ecosystems, while at the same time accommodating economic analysis. The main constraint for models to serve in economic analysis is dimensionality. In addition, to apply in long‐term management analysis, models should be stable in terms of adjustments to new observations. We use the ensemble Kalman filter to fit relatively simple models to ecosystem or foodweb data and estimate parameters that are stable over the observed variability in the data. The filter also provides a lower bound on the noise terms that a stochastic analysis requires. In this paper, we apply the filter to model the main interactions in the Barents Sea ecosystem. In a comparison, our method outperforms a regression‐based approach.