Tau1 to axial induction bugfix

[dzalkind]

Purpose

Small fix to avoid nans in tau1_const. An axial induction of 1 gives a tau1_const of 66, which might be too high, so we may want to limit it to something lower, but I'll leave that final decision to @ptrbortolotti.

Type of change

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (non-backwards-compatible fix or feature)
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no API changes)
• Documentation update
• Maintenance update
• Other (please describe)

Testing

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Checklist

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• I have run existing tests which pass locally with my changes
• I have added new tests or examples that prove my fix is effective or that my feature works
• I have added necessary documentation