Stepladders

PPQs possess a stepladder stmcture that combines good thermal stabiUty, electrical insulation, and chemical resistance with good processing characteristics (81). These properties allow unique appHcations in the aerospace and electronics industries (82,83). PPQ can be made conductive by the use of an electrochemical oxidation method (84). The conductivities of these films vary from 10 to 10 S/cm depending on the dopant anions, thus finding appHcations in electronics industry. Similarly, some thermally stable PQs with low dielectric constants have been produced for microelectronic appHcations (85). Thin films of PQs have been used in nonlinear optical appHcations (86,87). 

The GEMS model is based on a more detailed model of human performance known as the stepladder model developed by Rasmussen (see Rasmussen 1986) and illustrated in Figure 2.7. In this model, Rasmussen depicted the various stages that a worker could go through when handling a process disturbance. 

The dotted lines in the diagram indicate the various feedback paths that exist to enable the individual to identify if a particular stage of the processing chain was executed correctly. Thus, if the operating team had planned a strategy to handle a complex plant problem, they would eventually obtain feedback with regard to whether or not the plan was successful. Similar feedback loops exist at the rule and skill-based levels, and indicate opportunities for error correction. The application of the stepladder model to a process industry example is given in Appendix 2A at the end of this chapter. 

The applications of the SRK, GEMS, stepladder and sequential block diagram models to human error in process safety can be summarized as follows ... 

APPENDIX 2A PROCESS PLANT EXAMPLE OF THE STEPLADDER MODEL... 

In order to explain each box in the stepladder model shown in Figure 2.7 (reprinted on the facing page), we shall use the same batch processing example as in Section 2.6.3. 

It can be seen that the various boxes in the flowchart can be associated with different stages of the stepladder model. For example, the first box on the left corresponds to skill-based behavior and its associated internal failure mechanisms. The second box illustrates the situation (Stereotype Fixation) where the worker erroneously does not change to a rule-based mode when encountering an unusual situation in the skill-based mode (see also the discussion of the GEMS model in Section 2.6.3). 

This is the actual mental function required by the task that failed (see Figure 2.17). In the case study imder consideration the failure was at the Execute Action stage of the stepladder model, since the worker intended to operate the valve for reactor A, so there was no question of failure in the selection of actions. The connection with the task characteristics box indicates the fact that action is a fimction required by the task. 

This method is based on the Rasmussen stepladder model described in Chapter 2. It was first described in Embrey (1986). The basic units of CADET are the critical actions or decisions (CADs) that need to be made by the operator usually in response to some developing abnormal state of the plant. A CAD is defined in terms of its consequences. If a CAD fails, it will have a significant effect on safety, produchon or availability. 

An extension of the tree of causes, called variation diagrams (Leplat and Rasmussen, 1984) was developed to answer some of these criticisms. In this method, the Rasmussen stepladder model of human error (see Chapter 2) is applied to analyze causal factors at each node of the tree. A detailed example of the use of this technique is provided in Chapter 7 (Case Study 1). 

Tritt, m. tread, step footprint, track, -ge-blase, n. foot bellows, foot blower, -leiter, m. stepladder. 

It was logical to combine this principle for the preparation of stepladder structures possessing a minimized twist between consecutive phenylene units... 

As described for the corresponding polymers, a powerful strategy for arriving at soluble oligomers with maximum conjugative interaction is incorporation of the PPP backbone into a stepladder - or ladder (see Sect. 2.2.) - framework, in... 

The logical continuation of the stepladder strategy outlined above for minimizing the mutual distorsion of adjacent main chain phenylene units was the incorporation of the complete PPP-parent chromophore into the network of a completely planar ladder polymer. The complete flattening of the conjugated 7T-system by bridging of all the subunits should then lead to maximum conjuga-tive interaction. As with the PTHP 11 systems, alkyl or alkoxy side chains should lead to solubilization of the polymers. 

G. Grem, C. Paar, J. Stampfl, G. Leising, J. Huber, and U. Scherf, Soluble segmented stepladder poly(p-phenylencs) for blue-light-emitting diodes, Chem. Mater., 7 2-4, 1995. 

After lunch, he asked to take a picture of Dr. Silver, the head of CRDL, COL Blair, his medical deputy, COL Lnirig, the head of the Med Labs and me. He got up on a stepladder and shot a picture of the four of us looking up into the sun. 

Different conformations of base-paired DNA (a) the untwisted straight ladder, (b) the normal spiral ladder. The stepladder structure is unstable it can be converted into a spiral ladder by a right-handed twist, a change that permits the planes of the base pairs to come into close contact. 

A between adjacent nucleotides in the direction of the long axis. This 6.8-A distance between adjacent base pairs produces a gap that would presumably be filled by water. Such a conformation is unstable because the planes of the bases prefer close contacts with one another as does water. The stepladder structure is related to the helix structure by a simple right-handed (clockwise) twist (see fig. 25.1a). Following this operation the distance between base pairs decreases until they are in close contact, with a spacing of 3.4 A. 

A structural compromise between the fully bridged ladder system and the parent polyphenylene are stepladder polyphenylenes in which repeat units, such as fluorene, indenofluorene, or tetrahydropy-... 

Ask Asia for a cup of sour cream, then your cakes will be light without much soda, which I don t like," was the first order. Demi tore downstairs, and returned with the cream, also a puckered-up face, for he had tasted it on his way, and found it so sour that he predicted the cakes would be uneatable. Mrs. Jo took this occasion to deliver a short lecture from the stepladder on the chemical properties of soda, to which Daisy did not listen, but Demi did, and understood it, as he proved by the brief but comprehensive reply "Yes, 1 see, soda turns sour things sweet, and the fizzling up makes them light. Let s see you do it, Daisy."... 

Polyfluorenes (PFs), the simplest regular stepladder-type polyphenylenes, in which only every second ring is bridged, have been much studied in recent years due to their large PL quantum efficiencies and excellent chemical and... 

Polyfluorenes are sometimes referred to as stepladder poly(przra-phenylene) (PPP) polymers as they have a backbone with a planar, ladder-like structure. The first poly-fluorene LED was made by Yoshino and coworkers using poly(9,9-dihexylfluorene) 16 [50]. 

We have utilized the stepladder transition probability model, which assumes that only constant energy increments [] are transferred during the deactivating collisions. The nascent CH3CF2 F species have been assumed to be in translational equilibrium with the host reservoir and to decompose only by HF-elimination Reactions 99 and 100. These... 

Several other stepladder simulations yielded reasonable consistency with the measured data. Parametric increases in shift the calculated results to progressively reduced (D/S) ratios with increasing (P/Z), This effect can be compensated by increasing Eo though not without introducing ciurvature changes in the falloff plots. 

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