Weitere Beiträge zur Differenzirung des Shiga-Kruse'schen und des Flexner'schen Bacillus

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Validation of the Powder Metallurgical Processing of Duplex Stainless Steels through Hot Isostatic Pressing with Integrated Heat Treatment

Duplex stainless steels exhibit an excellent combination of corrosion resistance and strength and are increasingly being manufactured through powder metallurgy (PM) to produce large, near-net-shaped components, such as those used for offshore applications. Hot isostatic pressing (HIP) is often used for PM production, in which pre-alloyed powders are compacted under high pressures and temperatures. Recent developments in HIP technology enable fast cooling as part of the process cycle, reaching cooling rates comparable to oil quenching or even faster. This enables the integrated solution annealing of duplex stainless steels directly after compaction. In contrast to the conventional HIP route, which requires another separate solution annealing step after compaction, the integrated heat treatment within the HIP process saves both energy and time. Due to this potential gain, HIP compaction at a high pressure of 170 MPa and 1150 °C with integrated solution annealing for the production of duplex stainless steels was investigated in this work. Firstly, the focus was to investigate the influence of pressure on the phase stability during the integrated solution annealing of the steel X2CrNiMoN22-5-3. Secondly, the steel X2CrNiMoCuWN25-7-4, which is highly susceptible to sigma phase embrittlement, was used to investigate whether the cooling rates used in the HIP are sufficient for preventing the formation of this brittle microstructural constituent. This work shows that the high pressure used during the solution heat treatment stabilizes the austenite. In addition, it was verified that the cooling rates during quenching stage in HIP are sufficient for preventing the formation of the sigma phase in the X2CrNiMoCuWN25-7-4 duplex stainless steel.     

Processing of a Martensitic Tool Steel by Wire-Arc Additive Manufacturing

This work investigates the processability of hot-work tool steels by wire-arc additive manufacturing (DED-Arc) from metal-cored wires. The investigations were carried out with the hot-work tool steel X36CrMoWVTi10-3-2. It is shown that a crack-free processing from metal-cored wire is possible, resulting from a low martensite start (M_s) temperature, high amounts of retained austenite (RA) in combination with increased interpass temperatures during deposition. Overall mechanical properties are similar over the built-up height of 110 mm. High alloying leads to pronounced segregation during processing by DED-Arc, achieving a shift of the secondary hardness maximum towards higher temperatures and higher hardness in as-built + tempered condition in contrast to hardened + tempered condition, which appears to be beneficial for applications of DED-Arc processed material at elevated temperatures.     

Testing surgical skills of obstetric and gynecologic residents in a bench laboratory setting: Validity and reliability

OBJECTIVE: Resident surgical skills are acquired mainly through observing and later performing procedures in the operating room. Evaluation of surgical skills has traditionally been done through subjective faculty evaluation, a technique that has poor reliability and unknown validity. Our goal was to develop specific surgical tasks, both laparoscopic and open abdominal, that could be objectively and reliably evaluated in a bench laboratory setting. STUDY DESIGN: The prospective development of a reliable and valid resident surgical skills test in a bench laboratory setting was our goal. A written test of surgical knowledge and 12 skills tests were administered to 36 residents. Laparoscopic bench tasks were simulated with the use of a box and camera with a video display. Six laparoscopic tasks were assessed, including placing pegs on a board, running the bowel simulation, and other tasks that involve hand-eye coordination and manual dexterity. Open abdominal skills simulated incision closure, suturing a vaginal cuff, knot tying, and using a tie on a passer. Residents were timed at each given station and were given a rating score by 2 examiners. RESULTS: Knowledge scores showed a significant improvement by residency level. Assessment of construct validity (the ability to discriminate among residency levels) demonstrated significant differences on the rating of overall performance and individual tasks by level (determined by 1-way analysis of variance). Interrater reliability (agreement between 2 raters) with the use of intraclass correlation was 0.79 for the total score. The cost to administer the bench laboratory test was less than $50 and required 30 hours of faculty time. CONCLUSION: The results of this study suggest that surgical bench laboratory tasks can assess residents' surgical skills with good reliability and validity on most tasks. Our previous study, which used an animal laboratory, was expensive, and the bench laboratory model may provide an alternative means to assess surgical skills.