浅评《化学元素综论》

在众多专业性化学类科技书中,《化学元素综论》作为化学元素知识手册型书籍,其通俗易懂的编写形式和准确可靠、丰富而又齐全的科学数据,为广大读者提供一本难得的学习和工作参考书。     

A Nonlocal Total Variation Model for Image Decomposition: Illumination and Reflectance

In this paper, we study to use nonlocal bounded variation (NLBV) techniques to decompose an image intensity into the illumination and reflectance components. By considering spatial smoothness of the illumination component and nonlocal total variation (NLTV) of the reflectance component in the decomposition framework, an energy functional is constructed. We establish the theoretical results of the space of NLBV functions such as lower semicontinuity, approximation and compactness. These essential properties of NLBV functions are important tools to show the existence of solution of the proposed energy functional. Experimental results on both grey-level and color images are shown to illustrate the usefulness of the nonlocal total variation image decomposition model, and demonstrate the performance of the proposed method is better than the other testing methods.     

一类新的位置不变矩估计及其渐近正态性

The moment estimator has been widely used in extreme value theory in order to estimate the extreme value index, however it is not location invariant. In this paper, based on the moment-type estimator, we propose a new location invariant moment-type estimator,and discuss its asymptotic normality under the second order regular variation. Finally, a simulation is presented to compare this new estimator with another location invariant momenttype estimator γ_n~M(k_0, k) proposed by Ling, which indicates that the new estimator has good performances.     

椭圆孔口端点和裂纹端点处的变动态应力分析

分析了椭圆孔口端点和裂纹端点处的变动态应力．在分析中,设带椭圆孔口的无限平板受远处应力作用,变动态应力分析指的是,令动点趋近于椭圆孔端点和椭圆孔变成裂纹这二个过程在各种相对关系下进行．在不同相对关系下,求出椭圆孔口或裂纹端点应力的极限值．分析表明,随着不同的变动状态,对于端点处的某些应力会得到不同的极限值．     

点接触方式纳米锌润滑添加剂自修复规律的研究

本文采用四球试验法,以含纳米锌自修复剂的基础油为润滑介质,运用均匀设计试验方法对磨损的钢球进行在线自修复试验,建立并验证回归模型,对影响自修复效果的因素量化排序.选择不同修复效果的试验条件,分别加入抗氧抗腐剂T202和空白试验研究点接触方式下自修复过程特点.用带能谱仪的扫描电镜对修复后钢球磨斑表面进行表征.结果表明:试验验证结果与预测值符合较好,说明回归模型可行、可信.纳米锌自修复剂能对磨损的钢球表面进行修复,向表层基体元素扩散并牢固结合,使磨斑直径减小,具有自修复特点.     

广义有界变差函数的复合

研究了ΛBV（P）（I）和ΛBMV函数的复合,给出一个函数与ΛBV^（p）（I）或ΛBMV的函数复合后仍为ΛBV（P）（I）或ΛBMV的充要条件;同时根据MV[v]的定义,给出了MV[v]函数复合的充要条件．     

Improved simultaneous multislice magnetic resonance imaging using total variation regularization

Controlled aliasing in parallel imaging results in higher acceleration(CAIPIRINHA) for simultaneous multislice imaging has been proposed recently, which combines multiband excitation and phase cycling techniques to reduce scan time and improve subsequent imaging reconstruction. In this work, the total variation(TV) regularization method is used to further improve CAIPIRINHA. The TV regularization uses an edge-preserving prior, which establishes a relationship between neighboring pixels for image reconstruction. It reduces artifacts and suppresses noise amplification simultaneously.The results are presented with a standard eight-channel head coil with an acceleration factor of 4, where the TV-regularized CAIPIRINHA generates an improved reconstruction as compared with a typical nonregularized CAIPIRINHA.     

Volatolomics of Sardinian and Spanish Bituminaria: Characterization of Different Accessions Using Chemometrics

The present study aims to determine the volatile compositions of 15 different accessions of native Sardinian populations of Bituminaria morisiana (Pignatti & Metlesics) Greuter, Bituminaria bituminosa (L.) C. H. Stirt. (B. b.), and Spanish native accessions of B. bituminosa. Furthermore, we particularly focused on the essential oil characterization of these accessions and discriminated within populations with low furocoumarin content useful for fodder production in Mediterranean environments or furocoumarin extraction for pharmaceutical utilization. The plant extracts were analyzed by GC/MS, showing great variability in the content and composition. No differences were found in Bituminaria bituminosa (L.) C.H. Stirt. var. bituminosa essential oils, while the varieties Bituminaria bituminosa (L.) C.H. Stirt. var. crassiuscula P. Méndez, Fern. Galván & A. Santos and Bituminaria bituminosa (L.) C.H. Stirt. var. albomarginata P. Méndez, Fern. Galván & A. Santos are characterized by the presence of a high concentration of long-chain alcohols and of salicylic acid benzylic ester. In B. bituminosa var. albomarginata, we observed a different profile with predominance of a large concentration of alcohols as dodecanol and tetradecanol. The endemic B. morisiana can be identified for the predominant presence of farnesene. In methanolic fractions, we detected the presence of maltol, methyl citrate, methyl cumarate, santonin, and methyl linoleate. B. morisiana showed a low content of psoralens, and the accession of B. morisiana, from Siliqua indicated the presence of apocynin.     

Effects of ultraviolet radiation, temperature and moisture on aging of coatings and sealants - A chemical and rheological study

Photodegradation of polymeric materials leads to significant modifications in both chemical properties and mechanical-rheological behaviors over time. Thus, it is important to characterize both properties to gain a better understanding of the durability of the materials. In this contribution, the chemorheological tools based upon Fourier transform infrared (FTIR) spectroscopy and dynamic mechanical thermal analysis (DMTA) were used to study the effects of temperature and moisture on photodegradation of a model sealant/coating system based upon a styrene-butadiene-styrene triblock copolymer. Specimens were exposed coincidentally to ultraviolet-visible radiation between 295 nm and 600 nm, and one of four different combinations of temperature and relative humidity (RH), i.e., (a) 30 °C and <1% RH, (b) 30 °C and 80% RH, (c) 55 °C and <1% RH, and (d) 55 °C and 80% RH. The rate of photodegradation was examined in terms of formation of oxidation species and evolution of mechanical-rheological data, including glass transition temperatures, moduli, and the number of effective crosslinked butadiene chains per unit volume per exposure time. Environmental exposure resulted in similar degradation modes for all four environments but the rate of photodegradation was found to depend strongly on temperature. Conversely, the role of moisture on photodegradation was not significant. The study shows that chemical modification can be directly related to the corresponding rheological modifications. In addition, the relative stability of styrene and butadiene against photodegradation as a function of temperature and moisture was compared.     

On the robustness of Bayesian networks to learning from non-conjugate sampling

Recent results concerning the instability of Bayes Factor search over Bayesian Networks (BN’s) lead us to ask whether learning the parameters of a selected BN might also depend heavily on the often rather arbitrary choice of prior density. Robustness of inferences to misspecification of the prior density would at least ensure that a selected candidate model would give similar predictions of future data points given somewhat different priors and a given large training data set. In this paper we derive new explicit total variation bounds on the calculated posterior density as the function of the closeness of the genuine prior to the approximating one used and certain summary statistics of the calculated posterior density. We show that the approximating posterior density often converges to the genuine one as the number of sample point increases and our bounds allow us to identify when the posterior approximation might not. To prove our general results we needed to develop a new family of distance measures called local DeRobertis distances. These provide coarse non-parametric neighbourhoods and allowed us to derive elegant explicit posterior bounds in total variation. The bounds can be routinely calculated for BNs even when the sample has systematically missing observations and no conjugate analyses are possible.