Regularised SAS data for use with ATSAS applications. Usually created by either DATGNOM or GNOM.

.out files contain a copy of the experimental data used as input to GNOM, as well as the calculated smeared and desmeared experimental curves. In addition, the file also contains the distance distribution function \(p(r)\), as well as the maximum real-space distance \(d_{\max}\). The application GNOMPLOT may be used to plot all data side-by-side.

The .out file format is ATSAS internal and not intended as a general-purpose data exchange format. Users are not expected to create or modify .out files manually.

Some ATSAS applications accept .out files as input (listed below), with the express assumption that they were produced by other ATSAS applications beforehand.

Angular units and conventions

There is no universally enforced standard for how the scattering vector is encoded in experimental SAXS data files. In practice, at least four commonly used conventions exist, differing both in the mathematical definition and in the physical units. For regularised data, only the two listed below two are relevant.

Many ATSAS applications require knowledge of the angular units in order to interpret the data correctly. Depending on the program, the units may be:

  • specified explicitly by the user via the --unit option,
  • requested interactively,
  • or inferred heuristically from the data.

Both the --unit option and interactive configuration require the user to specify an alpha-numeric identifier:

Identifier Description
1 \(s = 4 \pi \cdot sin(\theta)/\lambda\) in \(\AA^{-1}\).
2 \(s = 4 \pi \cdot sin(\theta)/\lambda\) in \(\text{nm}^{-1}\).
u, unknown The application may use a heuristic to determine the angular units.

If no explicit unit is provided, or u is entered, the application may attempt to determine the units automatically using a simple heuristic.

Heuristic unit detection

If unit guessing is enabled and no explicit unit is given, the following heuristic may be applied:

  • if the maximum diameter \(d_{max}\) of the particle is larger than a threshold (\(d_{\max} > 30.0\)), the data are assumed to be given in inverse ångströms (unit 1);
  • otherwise, the data are assumed to be given in inverse nanometers (unit 2).

Note:

  • for very large particles this heuristic fails, and the unit has to be specified explicitly

Applications that read .out:

  • ambimeter - Ambiguity assessment of small-angle scattering curves from monodisperse systems.
  • dammif - Rapid ab-initio bead modelling
  • dammin - Ab-initio bead modelling
  • datclass - Classification of experimental data into geometric shape classes.
  • datmow - Molecular weight from Apparent Volume
  • datmw - Molecular weight estimation by multiple methods
  • datporod - Determine Porod Volume and Exponent
  • datvc - Molecular weight from Volume of Correlation
  • ffmaker - Assembles form-factor files for eom and oligomer.
  • gasbori/gasborp - Ab-initio dummy residue modelling
  • gasbormx - Ab-initio dummy residue modelling for oligomeric equilibria
  • gnomplot - SAS Data Plotting
  • launcher - ATSAS launcher
  • oligomer - Determine volume fractions of a multi-component mixture.
  • shanum - Quantitative assessment of the useful angular data range

Applications that write .out:

  • datgnom - Calculate the p(r) from experimental data files.