The virial expansion of a classical interacting system

We consider N particles interacting pair-wise by an inverse square potential in one dimension (Calogero-Sutherland-Moser model). When trapped harmonically, its classical canonical partition function for the repulsive regime is known in the literature. We start by presenting a concise re-derivation of this result. The equation of state is then calculated both for the trapped and the homogeneous gas. Finally, the classical limit of Wu's distribution function for fractional exclusion statistics is obtained and we re-derive the classical virial expansion of the homogeneous gas using this distribution function.Comment: 9 pages; added references to some earlier work on this problem; this has led to a significant shortening of the paper and a changed titl

Characterization of pyridine nucleotide binding site of UDP-glucose 4-epimerase from Saccharomyces fragilis

UDP-glucose 4-epimerase from Saccharomyces fragilis has 1 mol of NAD firmly bound per mol of the dimeric apoenzyme. This prevents a direct study of the coenzyme binding site of the protein. Dissociation of the dimer with p-chloromercuribenzoate and its reconstitution with exogenous NAD or one of its analogues and 2-mercaptoethanol provides an indirect method of study of the site. Depending on the reconstitution properties, the analogues can be classified in the following groups: (i) analogues that have no affinity for the site; (ii) analogues that have affinity but are not incorporated into the apoenzyme; (iii) analogues that produce catalytically inactive holoenzymes; and (iv) analogues that produce catalytically active holoenzymes. Minimum structural requirements that lead to affinity for the coenzyme site and to binding to the apoenzyme can also be discerned from these studies. Reconstitution with etheno-NAD, a fluorescent analogue of NAD, indicates the presence of a hydrophobic pocket for the adenosine subsite

Chiral symmetry breaking and stability of quark droplets

We discuss the stability of strangelets -- quark droplets with strangeness -- in the Nambu--Jona-Lasinio model supplemented by a boundary condition for quark confinement. Effects of dynamical chiral symmetry breaking are considered properly inside quark droplets of arbitrary baryon number. We obtain the energy per baryon number of quark droplets with baryon number from one to thousands. It is shown that strangelets are not the ground states as compared with nuclei, though they can be locally stable

Some exactly solvable three-body problems in one dimension

The three-body problem in one dimension with a repulsive inverse-square potential between every pair was solved by Calogero. After mapping the three-body problem to that of a particle on a plane, the known results of supersymmetric quantum mechanics are used to solve this problem, as well as a number of new ones, algebraically. This general technique is applicable when the potential is separable in the radial and angular variables on the plane, and its supersymmetric partner is shape invariant. After discussing one example in detail, an exhaustive list of such exactly solvable potentials is given

Fermionic ground state at unitarity and Haldane Exclusion Statistics

We consider a few-particle system of trapped neutral fermionic atoms at ultra-low temperatures, with the attractive interaction tuned to Feshbach resonance. We calculate the energies and the spatial densities of the few-body systems using a generalisation of the extended Thomas-Fermi (ETF) method, and assuming the particles obey the Haldane-Wu fractional exclusion statistics (FES) at unitarity. This method is different from the scaled ETF version given by Chang and Bertsch (Phys. Rev. A76,021603(R) (2007)). Our semiclassical FES results are consistent with the Monte-Carlo calculations of the above authors, but can hardly be distinguished from their over all scaling of the ETF result at unitarity.Comment: 4 pages, 3 figure

Are there compact heavy four-quark bound states?

We present an exact method to study four-quark systems based on the hyperspherical harmonics formalism. We apply it to several physical systems of interest containing two heavy and two light quarks using different quark-quark potentials. Our conclusions mark the boundaries for the possible existence of compact, non-molecular, four-quark bound states. While $QQ\bar n \bar n$ states may be stable in nature, the stability of $Q\bar Qn \bar n$ states would imply the existence of quark correlations not taken into account by simple quark dynamical modelsComment: 10 pages, 1 figure. Accepted for publication in Phys. Rev.