The Constraints Dialog box allows the user to specify a multistep reaction path and impose constraints on the system as it evolves along this path.  The user constructs a reaction path by choosing independent variables for the system thermodynamic potential, then specifies maximal and minimal values of those variables.  Optionally the user turns on or off phase fractionation and may specify that the system evolves under fixed oxygen fugacity constraints.

Specifying a Reaction Path: Overview

As long as the constraints dialog box has the input focus, the current text entry boxes display a number corresponding to the current value of the system T, H, S, P, or V, depending on what option is selected in the popup menus.   Input focus means the dialog box is capable of responding to user input.  The dialog will have input focus when it is first launched or when the user clicks somewhere in the dialog box window using the mouse.  If the user leaves the constraints dialog box open and clicks the mouse somewhere on the main APPLET display, she will notice that the text displayed in the current text entry boxes changes to invalid. Clicking back onto the constraints dialog box returns focus to the dialog and reinitializes the current text entry values.  The user may not type a number into the current text entry box.  The only way to set the values of the current text entry boxes is to initialize them from the main APPLET display.   For T and P this means filling in the appropriate text fields on that display.  For H, S, and V, this requires first specifying a T and P, and pressing the Equilibrate button to initialize the equilibrium state of the system.  This action computes an initial H, S and V for the assemblage.  That current equilibrium value for H, S or V is assigned to the box when it receives input focus or is selected by the THS or PV popup menus.

If the APPLET is performing a multistep calculation, launching the constraints dialog box or shifting input focus back to the box will automatically terminate the calculation sequence after the current call to the server returns.  This is a very convenient way to interrupt a calculation sequence that the user wishes to terminate before completion. The Click here to stop iterations button is provided on the dialog to remind the user of this feature - clicking on the button does nothing but give the constraints dialog box input focus.

The following table summaries the permitted combinations of independent variables and reaction path constraints:
 

Popup Selection Specified Current & Target Text Values	P isobaric	P polybaric	V isochoric	V polychoric
T isothermal	yes ± fixed fO2	yes ± fixed fO2	yes	yes
T polythermal	yes ± fixed fO2	yes ± fixed fO2	yes	yes
H isenthalpic	yes	yes	no	no
H polyenthalpic	yes	yes	no	no
S isentropic	yes	yes	no	no
S polyentropic	yes	yes	no	no

Note that is is only possible to constrain the evolution of the oxidation state of the system if the user chooses temperature and pressure as the independent variables and that the user cannot specify as independent variables both H and V or S and V.  This is a design limitation in the server code and may be corrected in some future revision of the server.

Specifying T as an independent variable of the thermodynamic potential

• Select the Temperature entry from the THS popup menu.
• The Current T value will be taken from the T (C) text entry box on the main APPLET display.
• Fill in the value in the Target T text entry box.  For an isothermal path this value will be the same as that in the Current T text entry box. For a polythermal path this value may be larger or smaller than that in the Current T text entry.
• Fill in the value in the Increment T text entry box.  This value is always positive; the correct sign will be computed from the current and target values.  If the user leaves the value set to 0, it will be changed to | target - current | when input focus is transferred away from the constraints dialog box.

Specifying S as an independent variable of the thermodynamic potential

• Select the Entropy entry from the THS popup menu.  NOTE that when Entropy is selected from this popup Pressure must be selected from the PV popup menu.  A reaction path with both S and V as independent variables is not allowed in the server code. This is design limitation and may be corrected in some future revision of the server.  If the user has not yet initialized the equilibrium state of the assemblage (see Overview) an error message will be displayed and the popup menu will reset itself to Temperature.
• The Current S value will be taken from the system entropy of the current equilibrium assemblage.
• Fill in the value in the Target S text entry box.  For an isentropic path this value will be the same as that in the Current S text entry box. For a polyentropic path this value may be larger or smaller than that in the Current S text entry. Note that an adiabatic reaction path is an isentropic one.
• Fill in the value in the Increment S text entry box.  This value is always positive; the correct sign will be computed from the current and target values.  If the user leaves the value set to 0, it will be changed to | target - current | when input focus is transferred away from the constraints dialog box.

Specifying H as an independent variable of the thermodynamic potential

• Select the Enthalpy entry from the THS popup menu. NOTE that when Enthalpy is selected from this popup Pressure must be selected from the PV popup menu.  A reaction path with both H and V as independent variables is not allowed in the server code. This is design limitation and may be corrected in some future revision of the server.  If the user has not yet initialized the equilibrium state of the assemblage (see Overview) an error message will be displayed and the popup menu will reset itself to Temperature.
• The Current H value will be taken from the system enthalpy of the current equilibrium assemblage.
• Fill in the value in the Target H text entry box.  For an isenthalpic path this value will be the same as that in the Current H text entry box. For a polyenthalpic path this value may be larger or smaller than that in the Current H text entry. Note that an adiabatic reaction path is an isentropic one NOT an isenthalpic one.
• Fill in the value in the Increment H text entry box.  This value is always positive; the correct sign will be computed from the current and target values.  If the user leaves the value set to 0, it will be changed to | target - current | when input focus is transferred away from the constraints dialog box.

Specifying P as an independent variable of the thermodynamic potential

• Select the Pressure entry from the PV popup menu.
• The Current P value will be taken from the P (bars) text entry box on the main APPLET display.
• Fill in the value in the Target P text entry box.  For an isobaric path this value will be the same as that in the Current P text entry box. For a polybaric path this value may be larger or smaller than that in the Current P text entry.
• Fill in the value in the Increment P text entry box.  This value is always positive; the correct sign will be computed from the current and target values.  If the user leaves the value set to 0, it will be changed to | target - current | when input focus is transferred away from the constraints dialog box.

Specifying V as an independent variable of the thermodynamic potential

• Select the Volume entry from the PV popup menu.  NOTE that when Volume is selected from this popup Temperature must be selected from the THS popup menu.  A reaction path with both S and V or H and V as independent variables is not allowed in the server code. This is design limitation and may be corrected in some future revision of the server.  If the user has not yet initialized the equilibrium state of the assemblage (see Overview) an error message will be displayed and the popup menu will reset itself to Pressure.
• The Current V value will be taken from the system volume of the current equilibrium assemblage.
• Fill in the value in the Target V text entry box.  For an isochoric path this value will be the same as that in the Current V text entry box. For a polychoric path this value may be larger or smaller than that in the Current V text entry.
• Fill in the value in the Increment V text entry box.  This value is always positive; the correct sign will be computed from the current and target values.  If the user leaves the value set to 0, it will be changed to | target - current | when input focus is transferred away from the constraints dialog box.

Specifying Fractionation of Phases

Specifying an f_O2 Evolution Path

• Click the on radio button located to the right of the Fix f O2 label on the constraints dialog box display.
• Shift input focus to the main APPLET display.

• Select one of HM, NNO, QFM or IW from the log fO2 popup menu.

• OPTIONALLY: Change the value in the log fO2 text entry box to reflect the f_O2 constraint path to impose on system.  For example, in the above, the user has chosen QFM from the log fO2 popup menu and specified that the system be constrained to follow an f_O2 path 1.5 log₁₀ units below QFM.

Last modified: Fri, Jan 3, 2003