Transition state and formation process of Stone—Wales defects in graphene

Stone—Wales (SW) defects are possibly formed in graphene and other two-dimensional materials, and have multiple influence on their physical and chemical properties. In this study, the transition state of SW defects in graphene is determined with the fully discrete Peierls theory. Furthermore, the atomic formation process is investigated by means of ab-initio simulations. The atomic structure change and energetics of the SW transformation are revealed. It is found that the transition state is at the SW bond rotation of 34.5° and the activation energy barrier is about 12 eV. This work provides a new method to investigate SW transformations in graphene-like materials and to explore unknown SW-type defects in other 2D materials.     

寿山水坑石的透明度影响因素

采用红外光谱(IR)、X射线粉晶衍射(XRD)、扫描电子显微镜(SEM)和差热分析(DTA)等测试,分别从地开石的有序度。矿物微形貌特征以及地开石中水的存在形式对水坑石透明度的影响因素进行了深入研究。红外光谱和XRD测试结果显示样品主要矿物组成为地开石。红外光谱中高频区3 704和3 621 cm-1两吸收峰的分裂程度和XRD图谱中2θ为19°~24°之间的衍射峰的分裂程度可表示地开石有序度,分别计算样品红外光谱中3 704和3 621 cm-1两吸收峰的强度比值(OI)及XRD图谱中(111)晶面衍射峰和(111)晶面衍射峰的分裂程度指数(DHI);计算结果表明这两个表征有序度的参数与透明度并无密切关系。扫描电镜测试结果显示地开石矿物晶体颗粒整体发育越均匀,晶体颗粒形态越相近、粒径大小越均一时,样品透明度越高,但晶体颗粒自身的结晶度、自形程度和粒径的绝对大小与透明度并无关系。差热分析测试结果表明水坑石的透明度与地开石晶体结构中结构水和吸附水的含量有关,结构水含量越接近理论值,样品晶体结构越完整,透明度越高;结构水的含量降低时,部分羟基缺失导致晶体结构完整性下降,结构单元层内部的电荷平衡被破坏,层间域中吸附更多水分子,吸附水在层间域中作为杂质分子存在,使样品的透明度下降。     

漫反射光谱在“老挝石”颜色成因上的应用

近来,一种产自老挝的新型印章石(俗称“老挝石”)涌进国内市场,对我国印章石市场造成一定影响,“老挝石”的研究尚处于起步阶段,对其颜色成因的研究更为缺乏。采用漫反射光谱(DRS)结合X射线粉晶衍射(XRD)、红外光谱(FTIR)、X射线荧光光谱(EDXRF)等测试对红色“老挝石”的矿物成分和致色机理进行深入研究。结果显示,“老挝石”的主要矿物成分为地开石,并含有少量高岭石,化学成分中的Fe含量和“老挝石”红色色调呈正相关关系,即颜色越深Fe的含量越高。铁质矿物呈微晶集合体浸染分布于地开石的颗粒间,由于其含量低、粒度细小,常规的微区测试方法无法确认其种属。相比之下,漫反射光谱对微晶铁矿物的鉴定十分有效,对可见光波段漫反射光谱处理得到导数等,在土壤沉积物中已经被用来定量测定针铁矿和赤铁矿。该研究中“老挝石”基体与土壤沉积物均为粘土矿物,可以用漫反射光谱来判定“老挝石”中铁矿物种属。漫反射光谱一阶导数法显示,其谱峰位于565～570 nm,由此确认铁矿物的种属为赤铁矿。微晶赤铁矿分布于“老挝石”矿物颗粒间,使样品产生红色,赤铁矿含量越高,红色调越深。     

The Priestley Separation Axiom for Scattered Spaces

Let R be a quasi-order on a compact Hausdorff topological space X. We prove that if X is scattered, then R satisfies the Priestley separation axiom if and only if R is closed in the product space X×X. Furthermore, if X is not scattered, then we show that there is a quasi-order on X that is closed in X×X but does not satisfy the Priestley separation axiom. As a result, we obtain a new characterization of scattered compact Hausdorff spaces.     

Evaluation of polymers for conservation treatments of outdoor exposed stone monuments. Part II: Photo-oxidative and salt-induced weathering of acrylic-silicone mixtures

The behaviour of the acrylic-silicone mixture commonly known as Bologna Cocktail, composed of commercial acrylic polymer Paraloid B72 and the silicon-based product, Dri Film 104, extensively employed as stone preservative for monuments in the last thirty years, has been tested on specimens appropriately prepared and submitted to ageing simulating reliable outdoor environment. After chemical characterization, the acrylic-silicone mixture was applied as thin film on slides, as thick film on Petri dishes and on marble by brush or by absorption; the resulting samples were artificially aged by light and saline solution. The chemical modifications were evaluated by FT-IR, NMR and SEC determinations, while preservative properties were tested by removability tests, ultrasonic and colorimetric measurements. The mixture consists of two immiscible phases and the two components have distinctive chemical behaviours, leading - after ageing - to irreversible molecular modifications and loss of conservative properties. The deterioration processes identified through laboratory simulation have been also verified on treated marble surfaces of two Venetian case studies.     

Fuzzy Topological Representation Theory For D_(01)

In this paper, we shall introduce the concepts of fuzzy prime ideal, fuzzy Stone space, fuzzy fundamental set, etc. And the representations of a distributive lattice with 0, 1 (D_(01) denotes the equational class of such lattices) by fuzzy sets will be investigated and many useful results are obtained.     

Characterization of monumental carbonate stones by thermal analysis (TG, DTG and DSC)

Thermogravimetry (TG), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC), were found to be suitable instrumental techniques for the study of monumental rocks because they need small amounts of sample and provide extensive qualitative and quantitative information. From DTG curves, the calcite/dolomite ratio in the samples as well as the differences between limestones and dolomites can be quantitatively determined. DSC curves are adequate for the identification of the degradation products in the monumental stones since they are usually salts (sometimes hydrates) which present first-order processes under 600°C. This technique makes it possible to carry out quantitative and semiquantitative analysis of the degradation of monumental rocks since it provides data about its mineralogic composition.     

A reasonable criterion of reactivities at the defective region of single‐walled carbon nanotubes

Defect directional curvature K_D‐def was proposed as a reasonable criterion for the reactivities and adduct structures at the defective region of single‐walled carbon nanotubes (SWCNTs). B3LYP/6‐31G* calculations for the [2 + 1] and [1 + 1] additions of a series of 11‐layer (n, n) (n = 4–8) and six‐layer (10,0) SWCNTs with Stone‐Wales defects showed that the K_D‐def or its mean K_M‐def was a good index to judge the adduct structures and the reactivities. Adducts of the [2 + 1] additions were divided into two types: one was the adduct with the C‐X‐C configuration and corresponding to the large K_D‐def and the large binding energy, and another was the adduct with the closed ?3MR structure and corresponding to the small K_D‐def and the small binding energy. It must be pointed out that, besides mainly relying on the K_D‐def, the adduct structures and the reactivities of the [2 + 1] additions had been weakly affected by topologic structures. The calculated results for the [1 + 1] additions of the 11‐layer (5,5) SWCNT with defect A revealed that the binding energies monotonously increased with the K_M‐def. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009     

New bio-cleaning strategies on porous building materials affected by biodeterioration event

In this paper, a new bio-cleaning procedure based on the glucose oxidase (GOx) has been applied on the travertine and peperino substrata to remove the biological patina (i.e., biofilm). Glucose oxidase, used as a model enzyme system, is able to produce in situ H₂O₂ (the cleaning agent having oxidizing properties) by the enzymatic reaction at room temperature. The travertine and peperino samples came from the Villa Torlonia in Rome (Italy), and an analytical diagnosis on them was performed applying several analytical techniques, such as the differential interference contrast microscopy (DIC), the optical microscope (OM), the Fourier transform infrared spectroscopy (FT-IR) and the X-ray fluorescence (XRF) that evidence the presence of biofilms on the substrata. Better results were obtained on the travertine samples in terms of the cleaning efficiency and the absence of the etching effect on the surface, eventually induced by the peroxide molecule. These results could be explained in terms of the different porosities of the two kinds of stone materials, according to the BET data. A comparative study was also performed to validate the new bio-cleaning procedure, using both traditional approaches based on saturated (NH₄)₂CO₃ solution and EDTA in buffer solution and the enzyme lipase treatments. Among all, the cleaning procedure via GOx shows the best result, probably because the enzyme controls the concentration of the H₂O₂ in situ and also retains the H₂O₂ preferentially on the surface (where the biological patina is present) depending on the porosity of the substrata. A synergistic effect, with other enzymes such as lipase and protease, combined with the biocompatibility of the enzymatic treatments, could represent a new way for a higher cleaning efficiency to apply on different stone substrata.