Model Information Section
Applicability: Cranium, Synapse (core versions 0315+)

Cranium’s and Synapse's physical property estimation process consists of three major steps:

  1. The application collects all estimation techniques that match the current property and state variables being estimated. The applicability model of each of these techniques is executed.
  2. Those techniques whose applicability models execute successfully, e.g., the code returns TRUE, are collected and sorted by accuracy.
  3. The estimation models of each of these sorted techniques is then tried starting with the most accurate. An estimate is assigned as soon as one technique is successful. The remaining techniques are skipped.

The Model Information Section contains two property fields:

  • Accuracy and Applicability Field: code which determines the applicability of the technique and its estimation error.
  • Estimation Model Field: code which generates this technique's physical property estimate.
Accuracy and Applicability Field

This field contains a large data entry control displaying the technique’s applicability code. This code must accomplish two tasks:

  1. The code must return either TRUE or FALSE denoting the technique’s applicability for the current chemical or mixture and state variables.
  2. The code must assign an estimation error as its resulting value. This error is used to sort applicable estimation techniques.

If a technique does not have applicability code, it is still executed. It is simply appended to the end of the sorted techniques list.

Very often a technique's applicability code consider a chemical’s chemical family or a mixture’s individual components when generating an error of estimation. For example, a particular estimation technique may work very well except for associating chemicals like acids. The applicability code would search for the occurrence of a -COOH group within the current chemical. The standard error of estimation would be returned if the acid group was not found or a larger error if the acid group was present.

The accuracy/applicability code for several estimation techniques are shown here:

Cranium and Synapse do not interpret or convert the returned estimation error. The value could represent an error, absolute error, percent error, or some other measure of accuracy. Since errors and absolute errors may be dependent upon the units of measure, it is important that all techniques estimating a particular property are consistent so that selection can occur properly. To ensure this consistency, it is very important that technique implementers document their applicability models adequately. You should also read through applicability code comments or accompanying notes when copying a new estimation technique into your own knowledge bases.

Estimation Model Field

The Estimation Model field contains a large data entry control displaying the technique’s estimation code. This code must accomplish two tasks:

  1. The model must return either TRUE or FALSE denoting the success of execution.
  2. The model must assign a numerical estimate as its resulting value.

Estimation models typically access a techniques parameters or group contributions, estimate additional properties, analyze molecular structures and perform various mathematical operations to generate an estimate. A good source of documentation for writing estimation technique models is to read through the estimation techniques contained in the knowledge bases we provide with Cranium and Synapse or those that are available on our website.

Editing Code

Both the Applicability Model and the Estimation Model are edited using the Code Edit dialog. This dialog is also used to enter design and selection functions. See documentation for the Code Edit Dialog for details.

Clicking the right mouse button within either field's edit control activates the field's commands menu. The menu's commands enable you to copy, cut and paste code to and from the control. See Common Menu Commands for documentation on the menu's commands.

Example: Enter a new model for the critical temperature

In the documentation for the Text Export Dialog, a new model for the critical temperature was developed using the regression tools of Microsoft Excel.

Tc = 95.3 + 1.22 * Tb

The following steps detail how to create a new estimation technique based upon this new equation.

  1. Open a knowledge base document. (Open a "working" document or create a copy of a document (see here) if you are just experimenting with this functionality.)
  2. Change to the document's Techniques chapter.
  3. Create a new Technique entity by pressing the "+" button in the menubar or executing the "Add New Page" command found on the Edit menu. A new, blank Technique page will be added to the current document.
  4. Click the left mouse button in the new technique's identifier pane and enter a new name for the technique.
  5. Click the left mouse button on the Descriptive information Section's Property field's edit control. Select "Critical Temperature" from the displayed dialog and press the Save button. The selected property will be displayed in the field.
  6. Scroll to the Model Information Section and click the left mouse button on the Estimation Model field's large edit control. The application will activate the Estimation Model Edit dialog.
  7. Copy the following code and paste it into the Edit dialog.
  8. Press the dialog's Save button. The entered code will be store in the current knowledge base.
  9. Select the Evaluate Technique from the chapter's Commands menu. The application will execute the newly entered estimation technique on every chemical in the current knowledge base and display an analysis of the results. (See the documentation Technique Evalutation Dialog for details on estimation technique evaluation.)
Related Documentation
Topic Description
Estimating Chemical Properties a short video demonstrating how to estimate physical properties using either Synapse or Cranium.
Estimating Mixture Properties a short video demonstrating how to estimate physical properties using either Synapse or Cranium.
Getting Started using Cranium provides a quick tour of Cranium's capabilities including a discussion of structure editing.
Techniques Chapter the techniques chapter contains numerous sections for entering and displaying the code and parameter values needed to generate physical property estimates.