Failure sequences

A uniform definition of a failure and a method of classifying failures is essential if data from different sources are to be compared. The anatomy of a failure includes the initiating or root cause of a failure that is propagated by contributory causes and results in a failure mode—the effect by which a failure occurs or is observed. Modes include failure to operate, no output, failure to alarm on demand. The end result of a failure sequence is the failure effect, such as no fluid is pumped to the absorber, or a tank overflows. As discussed in Appendix A of IEEE Std. 500-1984, only the equipment failure mode is relevant for data that are needed in a CPQRA. The failure model used in this book is based upon those in the IEEE publication and IPRDS. ... 

Failure sequence modeling techniques such as fault tree analysis or event tree analysis are used to estimate tlie likelihood of incidents in facilities where historical data is unai ailable, or is inadequate to accurately estimate tlie likelihood of the liazardous incidents of concern. Otlier modeling tecluiiques may be required to consider tlie impact of external events (eartliquakes, floods, etc.), common cause failures, and human factors and hmnan reliability. 

Cause-consequence analysis serx es to characterize tlie physical effects resulting from a specific incident and the impact of these physical effects on people, the environment, and property. Some consequence models or equations used to estimate tlie potential for damage or injury are as follows Source Models, Dispersion Models, Fire Explosion Models, and Effect Models. Likelihood estimation (frequency estimation), cliaractcrizcs the probability of occurrence for each potential incident considered in tlie analysis. The major tools used for likelihood estimation are as follows Historical Data, Failure sequence modeling techniques, and Expert Judgment. 

This group, used for 5 -phosphate protection, has hydrophobicity similar to that of the dimethoxytrityl group and thus was expected to assist in reverse-phase HPLC purification of product from failure sequences in oligonucleotide synthesis. The group is cleaved with Bu4N F in DMSO at 70°. ... 

Instrument Failure assume instrument control valves freeze or fail in open position (or closed, which ever is worse), determine capacity for relief based on flows, temperatures, or pressures possible under these circumstances. The judicious selection of instrument failure sequence may eliminate or greatly reduce relief valve requirements. 

Purification of biopharmaceuticals often involves the removal of materials with physical characteristics very similar to the desired product, such as failure sequences from DNA synthesis or misfolded proteins from bacterial fermentations. The contaminants, however, may have biological characteristics very different from the desired product, including different antigenicities, bioactivities, and specificities. There are even systems in which the... 

The HIC column was equilibrated in ammonium acetate, pH 8.5 to 11.0, and elution was achieved by washing in a solution of lowered salt concentration. Preliminary experiments indicated that the salt concentration of the crude ammoniacal solutions had to be increased by addition of ammonium acetate to ensure binding of DMT-on product to the column. While elution with low concentrations of ammonium acetate was tried, the most successful procedures involved use of plain water (in this case, water for injection). Flow-through and wash fractions contain the DMT-off failure sequences. The water wash contains the DMT-on sequences. Table 2 contains a summary of some of the key experiments used to develop the final HIC protocol. 

Scheme 9.3 Polymer-supported synthesis of oligosaccharides employing a hydrophobic handle attached to the growing chain in the last step of the synthetic sequence. The handle permits separation of the majority of failure sequences accumulated during the synthesis.

A recently developed technique that has found extensive use in the characterization of dendrimers, specifically in determining the purity and monodispersity of these novel materials, has been matrix-assisted laser desorption/ionization (MALDI) mass spectrometry [16,17]. For dendrimers grown by the divergent strategy, incomplete functionalization of the periphery can lead to subsequent failure sequences and loss of strict dendritic growth. Observation and quantification of these defects is extremely difficult by other techniques, however MALDI mass spectrometry has been successfully employed by a variety of authors to... 

You can pull some tricks when you understand the failure sequence Ordinarily - when a diode does a reverse voltage break-over - the current rises catastrophically, persists as a near-short till the Junction heats self destructs, usually shorts then burns open - and then the dead silicon freezes. 

Figures 12 and 13 illustrate the CE separation of s P-labeled 29- and 30-base heterooligomers, respectively. In the two electropherograms, the major component is nicely resolved from several failure sequences that were also phosphorylated in the labeling procedure of the 5 end. Figure 14 illustrates the capillary gel separation of a mixture containing these two heteropolymers. These two polymers differ only by the absence or presence of a 3 terminal thymidine residue.

Bayer et al. used mass spectrometry to detect the formation of failure sequences in the solid phase method 16). Mass spectrometric dilution assay coupled with Edman... 

The typical failure sequence observed in the experiments of Xu and Rosakis [1] is sketched in Fig. 7. One of the major conclusions of Xu and Rosakis is that shear-dominated inter-layer (or interfacial) cracks are the ones that initiate first and that such cracks grow very dynamically, their speeds and shear nature being enhanced by the large wave mismatch between the core and the face-sheets (the ratio of shear wave speeds of steel to Homalite is 2.6, Table 2). It is the kinking of these cracks into the sandwich core that triggers the complex mechanisms of intralayer failure. 

Fig. 7 Typical failure sequence observed in the experiments of Xu and Rosakis, where the arrows indicate the direction of the crack propagation, while the central line in (c) and (d) depicts the Rayleigh wave propagation after the interface separation.

After the serious hazards have been identified with a HAZOP study or some other type of qualitative approach, a quantitative examination should be performed. Hazard quantification or hazard analysis (HAZAN) involves the estimation of the expected frequencies or probabilities of events with adverse or potentially adverse consequences. It logically ties together historical occurrences, experience, and imagination. To analyze the sequence of events that lead to an accident or failure, event and fault trees are used to represent the possible failure sequences. 

A fundamental aspect of the divergent-growth approach is the rapid increase in the number of chain-end functional groups. Associated with this is the increase in the number of reactions required to functionalize the chain ends fully. Incomplete reaction of these rapidly increasing terminal groups leads to failure sequences or imperfections in the next generation. These potential difficulties and the lack of control over the number and placement of functionalities at die chain ends led us to reevaluate the synthetic approach to dendritic macromolecules. 

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