Evolution on neutral networks accelerates the ticking rate of the molecular clock

Large sets of genotypes give rise to the same phenotype, because phenotypic expression is highly redundant. Accordingly, a population can accept mutations without altering its phenotype, as long as the genotype mutates into another one on the same set. By linking every pair of genotypes that are mutually accessible through mutation, genotypes organize themselves into neutral networks (NNs). These networks are known to be heterogeneous and assortative, and these properties affect the evolutionary dynamics of the population. By studying the dynamics of populations on NNs with arbitrary topology, we analyse the effect of assortativity, of NN (phenotype) fitness and of network size. We find that the probability that the population leaves the network is smaller the longer the time spent on it. This progressive ‘phenotypic entrapment’ entails a systematic increase in the overdispersion of the process with time and an acceleration in the fixation rate of neutral mutations. We also quantify the variation of these effects with the size of the phenotype and with its fitness relative to that of neighbouring alternatives.     

Asymptotic stability of general linear methods for systems of linear neutral delay differential-algebraic equations

This paper is concerned with numerical stability of general linear methods (GLMs) for a system of linear neutral delay differential-algebraic equations. A sufficient and necessary condition for asymptotic stability of GLMs solving such system is derived. Based on this main result, we further investigate the asymptotic stability of linear multistep methods, Runge–Kutta methods, and block θ-methods, respectively. Numerical experiments confirm our theoretical result.     

削减桩基负摩阻力的室内模拟试验

为探明桩基混凝土不同涂料对桩基负摩阻力的削减效果,通过大型剪切试验,以塑限18%的黏性土为试验土,着重研究了试验土含水率变化以及桩基混凝土侧面不同涂料对桩基负摩阻力的影响。结果表明,当黏性土含水率略大于塑限时,桩基负摩阻力的削减效果较好,此时在混凝土表面涂石蜡机油混合物、聚合物纳米材料或者油漆产生的削减效果基本一致;当黏性土含水率与塑限含水率相差较大时,采用石蜡机油混合物作为桩侧混凝土涂料对于桩基负摩阻力的削减效果最佳;可通过不同方式对中性点位置进行确定并采用不同适用条件下涂料对桩基负摩阻力进行削减。     

Bimetallic CuCo2S4 Nanozymes with Enhanced Peroxidase Activity at Neutral pH for Combating Burn Infections

Peroxidase-mimicking nanozymes that can generate toxic hydroxyl radicals (^.OH) hold great promise as antibacterial alternatives. However, most of them display optimal performance under strongly acidic conditions (pH 3–4), and are thus not feasible for many medical uses, including burn infections with a wound pH close to neutral. Herein, we report a copper-based nanozyme (CuCo₂S₄) that exhibits intrinsic peroxidase-like activity and can convert H₂O₂ into ^.OH at neutral pH. In particular, bimetallic CuCo₂S₄ nanoparticles (NPs) exhibited enhanced peroxidase-like activity and antibacterial capacity, superior to that of the corresponding monometallic CuS and CoS NPs. The CuCo₂S₄ nanozymes possessed excellent ability to kill various bacteria, including methicillin-resistant Staphylococcus aureus (MRSA). Furthermore, this CuCo₂S₄ nanozymes could effectively disrupt MRSA biofilms in vitro and accelerate MRSA-infected burn healing in vivo. This work provides a new peroxidase mimic to combat bacteria in neutral pH milieu and this CuCo₂S₄ nanozyme could be a promising antibacterial agent for the treatment of burn infections.     

300M超高强钢在中性盐雾环境中的腐蚀行为及机制

摘要：为了研究300M超高强钢在中性盐雾环境中的腐蚀行为及腐蚀机制，采用失重法，宏观、微观腐蚀形貌分析，三维表面轮廓分析及电化学分析的研究方法，来表征腐蚀实验现象并进行分析。结果表明：300M超高强钢在中性盐雾环境中的腐蚀产物为FeOOH、Fe2O3、Fe(OH)3和Fe3O4；腐蚀速率随着腐蚀时间逐渐降低，腐蚀后期（72h）腐蚀速率降低50%；腐蚀初期以点蚀为主，点蚀坑通过横向扩展，逐渐发展为后期的均匀腐蚀，腐蚀表面形貌呈沟壑状；外腐蚀层对基体的保护能力很弱，Cr元素在锈层靠近基体的一侧偏聚使内腐蚀层具有一定的抗腐蚀性。     

热镀锌渣中浸渣硫酸浸出锌的工艺研究

以锌含量为17.22%的热镀锌渣中浸渣为原料,在水热反应釜中以硫酸为浸出剂浸出其中锌。结果表明,最佳浸出条件为: 硫酸体积浓度15%、浸出温度180 ℃、液固比6∶1、浸出时间8 h,此条件下锌浸出率可达到99.71%; 浸渣主要成分为硫酸铝盐和硫酸钙。     

Technical note: Evaluation of a novel enzymatic method to predict in situ undigested neutral detergent fiber of forages and nonforage fibrous feeds

The purpose of this study was to optimize the conditions of a previously proposed enzymatic method used to estimate in situ undigested neutral detergent fiber (uNDF). We used a multi-step enzymatic approach, in which samples were first solubilized in NaOH solutions as a preincubation (PreInc) phase. After rinsing, samples were incubated (24 h at 39°C) in a buffered solution (pH 6) containing hemicellulase, cellulase, and Viscozyme L enzymes (Sigma-Aldrich s.r.l., Milan, Italy), followed by incubation (24 h at 39°C) in a buffered solution (pH 5) containing xylanase. Two sets of experiments were performed: a calibration trial (that tested different PreInc conditions on 9 selected forages) and a validation trial (that verified the results by testing multiple samples of 6 different forage types and a group of fibrous by-products). In the calibration trial, samples (300 mg in Ankom F57 filter bags; Ankom Technology Corp., Fairport, NY) were preincubated at 39°C in a 0.1 M NaOH solution for 90, 180, or 240 min, or in 0.2, 0.5, 1.0, or 2.0 M NaOH solution for 90 min. The results indicated that the best PreInc method, in terms of intra-laboratory repeatability and estimation of reference in situ values, was 90 min in a 0.2 M NaOH solution. Thus, we used this PreInc condition to determine enzymatic uNDF of 257 samples in the validation trial. Although the selected method generally had good accuracy in predicting in situ uNDF, inconsistencies were noted for certain forage types. Overall, when enzymatic uNDF was used to predict the in situ uNDF of all samples, the regression was satisfactory (intercept = 7.098, slope = 0.920, R² = 0.73). The regression models developed for alfalfa hays, corn silages, and small grain silages had also acceptable regression performances and mean square error of prediction (MSEP) values, and the main sources of MSEP variation were error due to incomplete (co)variation and random error. Even when R² values were >0.70, the MSEP value of the regression model for grass hays was 149.55, and that for nonforage fibrous feeds was 155.16. Although enzymatic uNDF partially overestimated the in situ uNDF, particularly in grass silages, the proposed procedure seems to be promising for accurately predicting in situ uNDF, because it generally had good repeatability and provided satisfactory estimates of in situ uNDF.     

汉江上游干支流沉积物细菌群落多样性和影响因素

为了解汉江上游干支流沉积物细菌多样性以及确定性过程和随机性过程在沉积物细菌群落构建过程中的相对重要性,基于Illumina高通量测序技术,分析了环境因子对细菌群落组成的影响,采用非度量多维尺度(NMDS)排序探究了季节之间沉积物细菌群落的差异,并结合中性群落模型和标准化随机率量化了确定性过程和随机过程对群落构建的影响。结果表明:汉江上游及其支流细菌群落主要由变形菌门(Proteobacteria)、拟杆菌门(Bacteroidetes)、蓝藻门(Cyanophyta)、浮霉菌门(Planctomycetes)和酸杆菌门(Acidobacteria)等组成；细菌群落在不同季节有显著差异；地理距离和环境因子对细菌群落结构影响较小,确定性过程并未在细菌群落组成中起到主导作用；随机过程很大程度上影响了群落在秋季和春季的组成,是沉积物细菌群落构建的主导因素。     

聚中性红修饰玻碳电极的制备及应用

通过循环伏安法(CV)对聚中性红修饰玻碳电极的制备方法进行了研究,同时研究了谷氨酸在聚中性红修饰玻碳电极上的电化学行为。结果表明,聚中性红修饰玻碳电极对谷氨酸有明显的伏安响应,在电位范围为-0.8~0V、扫描速率为100mV·s-1的条件下,谷氨酸在该修饰电极上产生一对氧化还原峰,谷氨酸在5.0×10-6~2.0×10-4mol·L-1浓度范围内与峰电流呈良好的线性关系,检出限(S/N=3)为2.0×10-6 mol·L-1。据此,建立了谷氨酸的电化学分析方法。