In this algorithm, the pixels in the residual image are binned by a multiple of the major axis of the synthesized beam (in pixels). More detailed descriptions of each algorithm are given below. The "auto-multithresh" uses multiple thresholds based on the noise and sidelobe levels in the residual image to determine what emission to mask. All of the above algorithms have functionality to remove ("prune") small mask regions that are unlikely to be real astronomical emission. The "auto-thresh2" algorithm is the same as the "auto-thresh" algorithm, except it does not bin the image. The "auto-thresh" algorithm bins the input residual image by a multiple of the synthesized beam size prior to thresholding to reduce the influence of small spurious regions and avoid masking emission too tightly. For all algorithms, the mask will be updated at the beginning of a minor cycle based on the current residual image. The desired algorithm can be selected via the usemask parameter. The tclean task has an option to generate clean masks automatically during the deconvolution process by applying flux density thresholds to the residual image. There are currently three different automasking algorithms available in tclean: "auto-thresh", "auto-thresh2", or "auto-multithresh". The 'mask' used in imaging normally refers to a 1/0 image, which is directly used to define deconvolution region(s) (or set a 'clean mask') in the tclean or clean tasks. One is used for CASA images/image analysis is a T/F mask (pixel mask), which can be embedded in the parent CASA image. In CASA, the term, 'mask' for an image is used in two different contexts. Mixed types of masks can be specified in the clean and tclean tasks. When mask files are read in and have undefined values, these values are treated as 1s by CASA. However they are created, the masks are all converted (as necessary) and stored as CASA images consisting of the pixel values of 1 and 0. You can combine this method with the options above to create an initial clean mask and modify it interactively. A mask created by tclean/ clean while interactively cleaning using the viewer.These algorithms will replace the older autoclean option in the clean task. See the automasking section below for more details. There are several experimental algorithms available in tclean for automatically masking emission during the deconvolution cycle. An automatically generated mask ( tclean only).Such images can be generated or modified using tasks such as boxit or makemask.
An image consisting of only 1 (valid) and 0 (invalid) pixel values.To do this, an image must already exist to serve as a reference or template to create the mask image or the region. You can use the viewer to save a region formatted according to the CRTF specification. The CASA region text format can be used to define clean regions either by specifying the region directly in the tclean/ clean command or by using an ASCII text file containing the specifications. There are several different ways to specify a clean mask, including: This mask is generally referred to as a clean mask.
NEXUS has a site licence for the CasaXPS software package, and makes it available to NEXUS users via the Remote Application Service (RAS).For the most careful imaging, you will want to restrict the region over which you allow CLEAN components to be found by using a mask. Software for XPS spectrum analysis and quantification
NEXUS intends to produce training videos in the future, but in the meantime a selection of those videos produced by give a helpful introduction to the technique and how to use the equipment.
We are particularly keen to promote the use of XPS by academic communities that have traditionally not been intensive users of the technique, but for whom modern instruments and methods can be great sources of information on surfaces of critical interest. Training and seminars are delivered by scientists with an international reputation.