Stress corrosion cracking: Characteristics, Mechanisms and Experimental study

Stress corrosion cracking (SCC) is a phenomenon in which the cracking of a metal alloy usually results from the combined action of a corrodent and tensile stress. Stresses that cause cracking can be residual or may be applied during service. A degree of mechanistic understanding of SCC will enable most metallic engineering materials to operate safely though stress corrosion cracking failures still continue to occur unexpectedly in industry. In this paper, the characteristics, mechanisms and methods of SCC prevention are reviewed. The results of experimental studies on alpha brass are also reported of which the failure mode conformed with the film-rupture and anodic dissolution mechanism

Analysis and characterization of heparin impurities

This review discusses recent developments in analytical methods available for the sensitive separation, detection and structural characterization of heparin contaminants. The adulteration of raw heparin with oversulfated chondroitin sulfate (OSCS) in 2007–2008 spawned a global crisis resulting in extensive revisions to the pharmacopeia monographs on heparin and prompting the FDA to recommend the development of additional physicochemical methods for the analysis of heparin purity. The analytical chemistry community quickly responded to this challenge, developing a wide variety of innovative approaches, several of which are reported in this special issue. This review provides an overview of methods of heparin isolation and digestion, discusses known heparin contaminants, including OSCS, and summarizes recent publications on heparin impurity analysis using sensors, near-IR, Raman, and NMR spectroscopy, as well as electrophoretic and chromatographic separations

Estudo da incidência de coledocolitíase em pacientes com colecistite calculosa aguda e crônica submetidos à colecistectomia vídeolaparoscópica

OBJETIVO: Avaliar a incidência da coledocolitiase em pacientes submetidos à colecistectomia laparoscópica, portadores de colecistopatia calculosa aguda e crônica. O presente estudo, também, analisa se a era laparoscópica modificou a incidência e a história natural da litíase da via biliar quando compara os dados da literatura com os índices do Grupo estudado. MÉTODO: O estudo foi realizado em um Grupo de 946 pacientes, distribuídos em Grupo A de 214 pacientes de 1991-1995 e Grupo B de 732 pacientes de 1999-2007 colecistectomizados pelo método laparoscópico. O critério diagnóstico de coledocolitíase foi estabelecido por colangiofluoroscopia de rotina em todas as operações. RESULTADOS: A incidência total de coledocolitiase no Grupo A de 9,8% e no B de 5,8% não mostram diferença estatística significativa entre si e com a literatura mundial (p=0,08).Nos pacientes operados por colecistite aguda também não se observou diferença estatística entre o grupo A e B na incidência de litíase da via biliar( p=0,8). A análise dos dados nos pacientes operados por colecistite crônica revela uma taxa de coledocolitíase menor no Grupo B de 3,7% com significância estatística do que no A de 8,4% p=0,03. CONCLUSÃO: O presente estudo revela uma diminuição expressiva na incidência de coledocolitiase no Grupo B em relação ao A e a literatura mundial quando a indicação cirúrgica ocorre na fase não complicada da doença litiásica biliar. O estudo também demonstra um aumento significativo na indicação da colecistectomia laparoscópica eletiva mais precoce no Grupo B como já observado em diversas publicações da literatura médica

Detailed study of polystyrene solubility using pyrolysis–gas chromatography–mass spectrometry and combination with size-exclusion chromatography

Measuring polymer solubility accurately and precisely is challenging. This is especially true at unfavourable solvent compositions, when only very small amounts of polymer dissolve. In this paper, pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) is demonstrated to be much more informative and sensitive than conventional methods, such as ultraviolet spectroscopy. By using a programmed-temperature-vapourisation injector as the pyrolysis chamber, we demonstrate that Py-GC-MS can cover up to five orders of magnitude in dissolved polymer concentrations. For polystyrene, a detection limit of 1 ng mL(-1) is attained. Dissolution in poor solvents is demonstrated to be discriminating in terms of the analyte molecular weight. Py-GC-MS additionally can yield information on polymer composition (e. g. in case of copolymers). In combination with size-exclusion chromatography, Py-GC-MS allows us to estimate the molecular weight distributions of minute amounts of a dissolved polymer and variations therein as a function of time