Value of MR cholangiopancreatography in evaluating choledochal cysts

OBJECTIVE: The aim of this retrospective study was to clarify whether MR cholangiopancreatography (MRCP) is a suitable replacement for ERCP in evaluation of the choledochal cyst. MATERIALS AND METHODS: Sixteen patients (six adult and 10 pediatric) with choledochal cysts underwent MRCP using a half-Fourier acquisition single-shot turbo spin-echo sequence. Extent of the cyst, defects within the biliary tree, and presence or absence of the anomalous junction of the pancreaticobiliary duct were evaluated. Findings were compared with those of ERCP. RESULTS: MRCP better defined the proximal biliary tree than did ERCP in two patients. Defects within the biliary tree were diagnosed correctly on MRCP in eight patients; however, two defects within the distal common bile duct were missed in pediatric patients. The presence of the anomalous junction of the pancreaticobiliary duct was revealed accurately by MRCP in all adult patients but was revealed accurately in only four of the 10 pediatric patients. CONCLUSION: MRCP appears to offer diagnostic information that is equivalent to that of ERCP for assessment of choledochal cysts in adults. In pediatric patients, MRCP should not replace ERCP; however, MRCP can play an important role as a noninvasive examination and should be considered a first-choice imaging technique for evaluation of choledochal cysts.     

Synthesis and degradation behavior of poly(propylene carbonate) derived from carbon dioxide and propylene oxide

High molecular weight and regular molecular structure poly(propylene carbonate) (PPC) was successfully synthesized from carbon dioxide and propylene oxide. The PPC copolymer structure was an exact alternating copolymer as evidenced by the ¹³C‐NMR technique. Degradative behavior of the PPC was conducted by soil burial and buffer solution immersion (pH = 6) tests, respectively. The results showed that the weight loss of soil buried in PPC films increased more slowly than that immersed in the buffer solution after 6‐month exposure. However, the weight loss of sample immersed in the buffer solution increased rapidly during the first 2 months and reached a value of 4.59%. Water sorption measurement also revealed that the PPC membranes immersed in buffer solution were more hydrophilic than those in soil burial tests. The degradation mechanism of PPC membranes was correlated with the sample morphologies, FTIR, and ¹H‐NMR spectra. The SEM morphologies were consistent with the weight loss and water sorption measurements. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1840–1846, 2004     

Properties of electron-beam-welded and laser-welded austenitic Fe-28Mn-5Al-1C alloy

Austenitic Fe-28Mn-5Al-1C alloy was welded by electron-beam and CW CO₂ laser techniques. Tensile tests, impact tests, potentiodynamic and cyclic polarization measurements were used to evaluate the mechanical properties and corrosion behaviour of the weld materials, Metallographic examination showed that the microstructure of the electron-beam-welded and laser-welded metals consisted mainly of the columnar and equiaxed austenitic structures. Grain growth in the heat-affected zone (HAZ) was minimal for welding with these two techniques. The tensile and impact tests indicated that the weld materials exhibited lower tensile strength, percentage elongation, percentage reduction in area and impact energy than those of the base alloy. The polarization measurements revealed that the anodic polarization behaviour of the HAZs of the electron-beam-welded and laser-welded materials was identical to that of the base alloy when exposed in 1M Na₂SO₄ solution. However, the electron-beam-welded and laser-welded metals exhibited a higher current density in the passive region than that of the base alloy when exposed to 1N H₂SO₄ acid solution.     

Recent progress in the development and properties of novel metal matrix nanocomposites reinforced with carbon nanotubes and graphene nanosheets

One-dimensional carbon nanotubes and two-dimensional graphene nanosheets with unique electrical, mechanical and thermal properties are attractive reinforcements for fabricating light weight, high strength and high performance metal-matrix composites. Rapid advances of nanotechnology in recent years enable the development of advanced metal matrix nanocomposites for structural engineering and functional device applications. This review focuses on the recent development in the synthesis, property characterization and application of aluminum, magnesium, and transition metal-based composites reinforced with carbon nanotubes and graphene nanosheets. These include processing strategies of carbonaceous nanomaterials and their composites, mechanical and tribological responses, corrosion, electrical and thermal properties as well as hydrogen storage and electrocatalytic behaviors. The effects of nanomaterial dispersion in the metal matrix and the formation of interfacial precipitates on these properties are also addressed. Particular attention is paid to the fundamentals and the structure–property relationships of such novel nanocomposites.     

X-ray photoelectron spectroscopy and electrochemical characterization of a FeCrMoNiRu alloy in 0.5 M HCl solution

The spontaneous passivation behaviour of a Fe-22Cr-3Mo-5Ni alloy system containing small amounts of ruthenium in 0.5 M HCl solution has been investigated by means of immersion tests, electrochemical measurements and the XPS technique. The weight loss and electrochemical measurements show that increasing amounts of ruthenium (up to 0.3 wt%) in Fe-22Cr-3Mo-5Ni substantially improve resistance to attack by hydrochloric acid. The XPS results show that the spontaneously formed passive film on this alloy with ruthenium mainly consists of Cr and Mo oxyhydrox-ides. Molybdenum is incorporated as Mo⁴⁺ and Mo⁶⁺, while neither ruthenium nor nickel are found in the passive film. The effects of ruthenium additions on the spontaneous passivation of FeCrMoNi alloys are discussed.     

Some aspects of electron beam welded and laser welded ferritic Fe-22Cr-3Mo-5Ni-0.3Ru alloy

Ferritic Fe-22Cr-3Mo-5Ni-0.3Ru alloy was welded by electron beam (EB) and laser techniques. Tensile tests, impact tests, oxalic acid etch, electrochemical potentiokinetic reactivation (EPR) and potential-time measurements were employed to investigate the mechanical properties, microstructural features and corrosion behaviour of the EB and laser welded metals. The oxalic acid etch tests revealed that the microstructure of the EB and laser welded metals consisted of columnar grains and cells, respectively. These structures were formed directly from the substrate by epitaxial solidification. Furthermore, the oxalic acid tests also showed that the EB and laser welded metals were immune to intergranular corrosion. Similar results were obtained by double loop EPR tests.