The energy of step defects on the TiO2 rutile (110) surface: An ab initio DFT methodology

We present a novel methodology for dealing with quantum size effects (QSE) when calculating the energy per unit length and step–step interaction energy of atomic step defects on crystalline solid surfaces using atomistic slab models. We apply it to the TiO2 rutile (110) surface using density functional theory (DFT) for which it is well-known that surface energies converge in a slow and oscillatory manner with increasing slab size. This makes it difficult to reliably calculate step energies because they are very sensitive to supercell surface energies, and yet the surface energies depend sensitively on the choice of slab chemical formula due to the dominance of QSE at computationally practical slab sizes. The commonly used method of calculating surface energies by taking the intercept of a best fit line of total supercell energies against slab size breaks down and becomes highly unreliable for such systems. Our systematic approach, which can be applied to any crystalline surface, bypasses such statistical estimation techniques and cross checks and makes robust what is otherwise a very unreliable process of extracting the energies of steps. We use the calculated step energies to predict island shapes on rutile (110) which compare favorably with published scanning tunneling microscopy (STM) images

Principais aspectos da polimerização do 1,3-butadieno Principles aspects of butadiene 1,3 polymerization

Atualmente, há uma grande demanda pelo polibutadieno com alto teor de unidades 1,4-cis, devido às suas excelentes propriedades físicas, tais como alta resistência à abrasão, baixo desenvolvimento de calor, baixa resistência ao rolamento, maior resistência à tensão, alta resistência à fadiga, baixa histerese e alta resistência à fratura. Tais características fazem com que esse elastômero seja cada vez mais utilizado na indústria pneumática. Assim, este trabalho apresenta uma breve revisão sobre a polimerização do 1,3-butadieno com diferentes sistemas catalíticos, sendo os sistemas à base de lantanídeos o principal foco desta revisão, pois esses sistemas são os mais estereoespecíficos para a polimerização 1,4-cis do butadieno.<br>Nowadays, there is a great demand for polybutadiene with high contents of cis groups owing to its excellent physical properties, such as high abrasion resistance and low heat build up. These characteristics make this elastomer one of the most used in pneumatic industry. Thus, this paper presents a brief review about the 1,3-butadiene polymerization by different catalysts systems, with the systems based on lanthanides being the main focus, as they are the most stereospecific for cis-1,4 polymerization of butadiene

Histopathological, molecular, and genetic profile of hereditary diffuse gastric cancer: Current knowledge and challenges for the future

Familial clustering is seen in 10 % of gastric cancer cases and approximately 1–3 % of gastric cancer arises in the setting of hereditary diffuse gastric cancer (HDGC). In families with HDGC, gastric cancer presents at young age. HDGC is predominantly caused by germline mutations in CDH1 and in a minority by mutations in other genes, including CTNNA1. Early stage HDGC is characterized by a few, up to dozens of intramucosal foci of signet ring cell carcinoma and its precursor lesions. These include in situ signet ring cell carcinoma and pagetoid spread of signet ring cells. Advanced HDGC presents as poorly cohesive/diffuse type carcinoma, normally with very few typical signet ring cells, and has a poor prognosis. Currently, it is unknown which factors drive the progression towards aggressive disease, but it is clear that most intramucosal lesions will not have such progression. Immunohistochemical profile of early and advanced HDGC is often characterized by abnormal E-cadherin immunoexpression, including absent or reduced membranous expression, as well as “dotted” or cytoplasmic expression. However, membranous expression of E-cadherin does not exclude HDGC. Intramucosal HDGC (pT1a) presents with an “indolent” phenotype, characterized by typical signet ring cells without immunoexpression of Ki-67 and p53, while advanced carcinomas (pT > 1) display an “aggressive” phenotype with pleomorphic cells, that are immunoreactive for Ki-67 and p53. These features show that the IHC profile is different between intramucosal and more advanced HDGC, providing evidence of phenotypic heterogeneity, and may help to define predictive biomarkers of progression from indolent to aggressive, widely invasive carcinomas