General event symbol

TTiree event symbols are used in preparing analytical trees (Fig. 10-4). The general event symbol is a rectangle. The rectangle is the main building block for analytical trees. It is used throughout analytical trees as the event symbol, except in two cases. 

Logically, any general event symbol (rectangle) has one gate attached to it and two or more events as input to that gate. Circles (base events) and diamonds (undeveloped terminal events) are bottom-tier or terminal events that have nothing below them. 

Rectangles are used as general event symbols, circles are used to show base events, and diamonds are used to show undeveloped terminal events. And gates are used to indicate that, in order to get an output, all inputs below that gate are required, and or gates are used to indicate that, in order to get an output, any one or any combination of the inputs is required. 

The symbols used on the MORT chart are basically those used for other analytical trees (Chapter 10) and fault tree analysis (Chapter 15). They include the rectangle as the general event symbol, the circle as the base event symbol, the diamond as an undeveloped terminal event, the and gate, the or gate, and the ellipse as a constraint symbol (Rgs. 18-1 and 18-2). 

General event symbol Basic event symbol... 

Figure 18-1 Event Symbols. The General Event symbol, Basic Event symbol, and Undeveloped Terminal event symbol are the same as commonly used for other fault trees. The use of the stretched circle for a Satisfactory Event and the scroll for a Normally Expected Event are unique to the MORT chart.

The other event symbol is the diamond, which represents an undeveloped terminal event. The diamond is used in place of a rectangle for a general event that is not going to be further developed (as part of this particular tree at this time). An event may not be developed because the information or the time needed is not available. Sometimes an event is not developed because it is not... 

Another symbol is the oval, which is used as a constraint symbol. Ovals are the footnotes or caveats in the system. They can be used to modify or to show additional information and can be attached to either a general event, a base event, or an undeveloped terminal event. They can be used in conjunction with logic gates. They generally show a specific condition or constraint or modify the meaning of either the event symbol or the gate. 

In spatial OSDs the flow of events and symbols is overlaid on a map of all items of equipment with which the operator interacts during the task. The map itself does not have to be very accurate, provided that the general geographical relationships among items of equipment are shown. The spatial OSD thus provides a graphical description of the perceptual-motor load a particular task imposes on the performance of the worker. For multiperson tasks, the operational sequences for several workers can be coded in different colors and superimposed onto the same equipment map. This can generate useful information for the distribution of tasks to different members of the operating team. 

Figure 19-4. Open and solid symbols are the measured quantum yields (events per incident electron) for the induction of single strand breaks (SSB) (a) and double strand breaks (DSB) (b) in DNA films by 4-100 eV electron impact. The solid curves through the data are guides to the eye. The dotted curves symbolize general electron energy dependence of the cross sections for various nonresonant damage mechanisms, such as ionization cross sections, normalized here to the measured strand break yields at lOOeV...

For the most part, doses quoted in this review are given in electron volts absorbed per gram of material, ev/gm. The electron volt is a suitable unit if one wishes to fix his attention on individual atomic or molecular events, and it has become generally used in radiation chemistry. The yields of radiation-chemical processes are conventionally given in molecules affected per 100 ev (symbolized by G). Thus 6r —H2O) = 4.6 means that 4.6 molecules of water are decomposed by the absorption of 100 ev of the specified radiation under the other given conditions. 

---