The complexity of the list homomorphism problem for signed graphs appears difficult to classify. Existing results focus on special classes of signed graphs, such as trees [4] and reflexive signed graphs [25]. Irreflexive signed graphs are in a certain sense the heart of the problem, as noted by a recent paper of Kim and Siggers. We focus on a special class of irreflexive signed graphs, namely those in which the unicoloured edges form a spanning path or cycle, which we call separable signed graphs. We classify the complexity of list homomorphisms to these separable signed graphs; we believe that these signed graphs will play an important role for the general resolution of the irreflexive case. We also relate our results to a conjecture of Kim and Siggers concerning the special case of weakly balanced irreflexive signed graphs; we have proved the conjecture in another paper, and the present results add structural information to that topic.
Computer automation of cathodoluminescence (CL) experiments using equipment developed in our laboratory is described. The equipment provides various experiments for CL efficiency, CL spectra, and CL time response studies. The automation was realized utilizing the graphical programming environment LabVIEW. The developed application software with procedures for equipment control and data acquisition during various CL experiments is presented. As the measured CL data are distorted by technical limitations of the equipment, such as equipment spectral sensitivity and time response, data correction algorithms were incorporated into the procedures. Some examples of measured data corrections are presented.
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