Fast Algorithms for General Spin Systems on Bipartite Expanders

A spin system is a framework in which the vertices of a graph are assigned spins from a finite set. The interactions between neighbouring spins give rise to weights, so a spin assignment can also be viewed as a weighted graph homomorphism. The problem of approximating the partition function (the aggregate weight of spin assignments) or of sampling from the resulting probability distribution is typically intractable for general graphs. In this work, we consider arbitrary spin systems on bipartite expander Δ-regular graphs, including the canonical class of bipartite random Δ-regular graphs. We develop fast approximate sampling and counting algorithms for general spin systems whenever the degree and the spectral gap of the graph are sufficiently large. Roughly, this guarantees that the spin system is in the so-called low-temperature regime. Our approach generalises the techniques of Jenssen et al. and Chen et al. by showing that typical configurations on bipartite expanders correspond to “bicliques” of the spin system; then, using suitable polymer models, we show how to sample such configurations and approximate the partition function in Õ( n 2 ) time, where n is the size of the graph.

Band head spin for triaxial super-deformed bands in 165,167Lu

We use VMI model for the prediction of band head spin of Triaxial Super- Deformed (TSD) rotational bands. The calculated and observed transition energies are agreed well when an accurate band head spin (I0) is predicted. The results are in good agreement with the experimentally known values of spin and transition energies. In the present paper, we have reported the band head spin of TSD bands for Lu isotope. This method brings comprehensive interpretation for spin assignment of TSD bands which could help in designing future experiments for these bands. Thus, we have reported the band head spin value of 5 TSD rotational band of Lu isotope.

Band head spin assignment of superdeformed bands in A ∼60−80 mass region through nuclear softness formula

The nuclear softness formula has been applied to obtain the band head spin ([Formula: see text]) of 7 superdeformed rotational bands ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text]) in A[Formula: see text]60−80 mass region. To obtain the band head spin ([Formula: see text]) of 7 superdeformed rotational bands in A[Formula: see text]60−80 mass region least square fitting method is used. The parameters are extracted by fitting the intraband transition energies in the nuclear softness formula from where the root mean deviation (RMD) between the calculated and the observed transition energies are obtained. The calculated transition energies are in good agreement with the experimental transition energies whenever exact band head spin ([Formula: see text]) is assigned. The calculated values of dynamic moment of inertia and its variation with rotational frequency for seven superdeformed rotational bands in A[Formula: see text]60−80 mass region are also studied. Hence, it is suggested that the nuclear softness formula works very well in A[Formula: see text]60−80 mass region.

Band head spin assignment of Tl isotopes of superdeformed rotational bands

The Variable Moment of Inertia (VMI) model is proposed for the assignment of band head spin of super deformed (SD) rotational bands, which in turn is helpful in the spin prediction of SD bands. The moment of inertia and stiffness parameter (C), were calculated by fitting the proposed transition energies. The calculated transition energies are highly dependent on the prescribed spins. The calculated and observed transition energies agree well when an accurate band head spin (I 0) is assigned. The results are in good agreement with other theoretical results reported in literature. In this paper, we have reported the band head spin value 16 rotational band of super deformed Tl isotopes.