- Timestamp:
- Oct 28, 2017 9:28:22 PM (7 years ago)
- Branches:
- master, core_shell_microgels, magnetic_model, ticket-1257-vesicle-product, ticket_1156, ticket_1265_superball, ticket_822_more_unit_tests
- Children:
- 0db85af
- Parents:
- e964ab1
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doc/guide/orientation/orientation.rst (modified) (4 diffs)
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doc/guide/orientation/orientation.rst
re964ab1 r3d40839 8 8 or orientation in a magnetic field. 9 9 10 In general we first need to define the mean, or areference orientation10 In general we first need to define the reference orientation 11 11 of the particles with respect to the incoming neutron or X-ray beam. This 12 12 is done using three angles: $\theta$ and $\phi$ define the orientation of … … 29 29 30 30 Definition of angles for oriented elliptical cylinder, where axis_ratio 31 b/a is shown >1, Note that rotation $\theta$, initially in the $x z$32 plane, is carried out first, then rotation $\phi$ about the $z$ 31 b/a is shown >1, Note that rotation $\theta$, initially in the $x$-$z$ 32 plane, is carried out first, then rotation $\phi$ about the $z$-axis, 33 33 finally rotation $\Psi$ is around the axis of the cylinder. The neutron 34 34 or X-ray beam is along the $z$ axis. … … 42 42 Having established the mean direction of the particle we can then apply 43 43 angular orientation distributions. This is done by a numerical integration 44 over a range of angles in a similar way to p olydispersity for particle size.44 over a range of angles in a similar way to particle size dispersity. 45 45 In the current version of sasview the orientational dispersity is defined 46 46 with respect to the axes of the particle. 47 47 48 The $\theta$ and $\phi$ parameters to orient the cylinder only appear in the49 modelwhen fitting 2d data. On introducing "Orientational Distribution" in48 The $\theta$ and $\phi$ orientation parameters for the cylinder only appear 49 when fitting 2d data. On introducing "Orientational Distribution" in 50 50 the angles, "distribution of theta" and "distribution of phi" parameters will 51 51 appear. These are actually rotations about the axes $\delta_1$ and $\delta_2$ 52 52 of the cylinder, the $b$ and $a$ axes of the cylinder cross section. (When 53 53 $\theta = \phi = 0$ these are parallel to the $Y$ and $X$ axes of the 54 instrument.) The third orientation distribution, in $\ psi$, is about the $c$54 instrument.) The third orientation distribution, in $\Psi$, is about the $c$ 55 55 axis of the particle. Some experimentation may be required to understand the 56 56 2d patterns fully. A number of different shapes of distribution are … … 65 65 numerical integrations over one or more variables, so care should be taken, 66 66 especially with very large particles or more extreme aspect ratios. Users can 67 experiment with the values of Npts and Nsigs, the number of steps used in the67 experiment with the values of *Npts* and *Nsigs*, the number of steps used in the 68 68 integration and the range spanned in number of standard deviations. The 69 69 standard deviation is entered in units of degrees. For a rectangular 70 (uniform) distribution the full width should be $\pm \sqrt(3)$ ~ 1.73 standard70 (uniform) distribution the full width should be $\pm \sqrt(3)$ ~ 1.73 standard 71 71 deviations (this may be changed soon). 72 72
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