16 research outputs found
Analysis of a Preloaded Bolted Joint in a Ceramic Composite Combustor
This paper presents the detailed analysis of a preloaded bolted joint incorporating ceramic materials. The objective of this analysis is to determine the suitability of a joint design for a ceramic combustor. The analysis addresses critical factors in bolted joint design including preload, preload uncertainty, and load factor. The relationship between key joint variables is also investigated. The analysis is based on four key design criteria, each addressing an anticipated failure mode. The criteria are defined in terms of margin of safety, which must be greater than zero for the design criteria to be satisfied. Since the proposed joint has positive margins of safety, the design criteria are satisfied. Therefore, the joint design is acceptable
Development of an Improved Standard Reference Material for Vitamin D Metabolites in Human Serum
The
National Institute of Standards and Technology (NIST) has developed
Standard Reference Material (SRM) 972a Vitamin D Metabolites in Frozen
Human Serum as a replacement for SRM 972, which is no longer available.
SRM 972a was developed in collaboration with the National Institutes
of Health’s Office of Dietary Supplements. In contrast to the
previous reference material, three of the four levels of SRM 972a
are composed of unmodified human serum. This SRM has certified and
reference values for the following 25-hydroxyvitamin D [25(OH)D] species:
25(OH)D<sub>2</sub>, 25(OH)D<sub>3</sub>, and 3-<i>epi</i>-25(OH)D<sub>3</sub>. The value assignment and certification process
included three isotope-dilution mass spectrometry approaches, with
measurements performed at NIST and at the Centers for Disease Control
and Prevention (CDC). The value assignment methods employed have been
modified from those utilized for the previous SRM, and all three approaches
now incorporate chromatographic resolution of the stereoisomers, 25(OH)D<sub>3</sub> and 3-<i>epi</i>-25(OH)D<sub>3</sub>