| 21. | Although signs for these values vary, sign convention usually dictates positive curvature when convex and negative when concave.
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| 22. | Throughout this article we work with a metric signature that is mostly positive ( ); see sign convention.
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| 23. | Engineering descriptions of the computation of bending moments can be confusing because of unexplained sign conventions and implicit assumptions.
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| 24. | In an important sign convention, work that adds to the internal energy of the system is counted as positive.
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| 25. | With this now often used sign convention for work, the first law for a closed system may be written:
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| 26. | In particular, many undergraduate physics textbooks use an alternate sign convention in which convex surfaces of lenses are always positive.
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| 27. | An alternate sign convention is to consider the work performed " on " the system by its surroundings as positive.
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| 28. | It is common to take a different sign convention for this equation than one typically does when defining fundamental solutions.
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| 29. | This latter convention has the convenient advantage that the s and p sign conventions are the same at normal incidence.
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| 30. | The choice of sign for time-dependence, exp (-" i?t " ), dictates the sign convention for the imaginary part of permittivity.
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