Re: [boost] [Review][PQS] Physical Quantities System review

From: fred bertsch (fred.bertsch_at_[hidden])
Date: 2006-06-08 13:10:19

White noise of all sorts is frequently expressed in terms of the
square root of the dimension of interest. V/sqrt(Hz) is probably the
most frequently used unit for electrical noise, for example.

-Fred Bertsch

On 6/8/06, Deane Yang <deane_yang_at_[hidden]> wrote:
> Leland Brown wrote:
> > I suspect (though someone may well correct me!) that fractional dimensions
> > are never strictly necessary, in the sense that the formulas can probably
> > be rewritten to avoid them.
> >
>
> In earlier discussions, there were a few examples of fractional
> dimensions provided. The one I am familiar with is called "volatility"
> in finance but probably has a name like "heat conductance" or "diffusion
> coefficient" in physics. It is the coefficient c in the heat equation:
>
> u_t = c^2 u_xx
>
> You can see that c has units of length/sqrt(time). You can argue that
> people should use c^2 directly instead of c (this is analogous to using
> the variance of a Gaussian in place of the standard deviation), but it
> *is* very useful to be able to work with c itself.
>
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-- 
F