Preface: MENU-2019, the 15th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon
In the first part I briefly survey recent issues in constituent quark models raised by the observation of unusual hadronic states. In particular I discuss the role of higher Fock components in the wave function of baryons and the possible interpretation of open charm and of new charmonium-type resonances as tetraquarks. In the second part I show support for the quark model dynamics obtained in a model independent way from the 1/Nc expansion approach of QCD which proved to be successful in describing baryon properties.
On the existence of heavy tetraquarks
Previous work done in collaboration with David Brink is reviewed in the light of the recent observation of new charmonium-like resonances which can be interpreted as tetraquarks. In the framework of a schematic quark model the spectrum of ccqq tetraquarks is presented. 1 e-mail: fstancu@ulg.ac.be
Transformation from availability expression to failure frequency expression
The problem of computing the system's Failure Frequency is reduced to the problem of computing its Availability. This is performed by a transformation operator. However, the existing transformation operator is not practical because its transformation time increases exponentially with system size. To overcome this difficulty, this paper proposes a new method of transforming the Availability expression of a system into the corresponding Failure Frequency expression of the system. This method is based on a matrix approach using a 2 /spl times/ 2 matrix consisting of 0, Availability, and Failure Frequency in an appropriate manner. This transformation also enables algorithms for computing the Availability of a system to be transformed into algorithms for computing its Failure Frequency by replacing parameters and operations with matrix parameters and operations. The computation time after transformation is linear with respect to the original Availability algorithm. This implies that the problems of computing other well-known reliability measures including, Availability, Unavailability, MTBF, MTTR, MCT, Failure Rate, Failure Rate, and Failure Frequency, are reduced to only the Availability computation problem.