Phase transitions in simple clusters

Formation of the liquid state of clusters with pairwise interactions between atoms is examined within the framework of the void model, in which configurational excitation of atoms results from formation of voids. Void parameters are found from computer simulation by molecular dynamics methods for Lennard-Jones clusters. From that standpoint, phase transitions are analyzed in terms of two aggregate states. This information allows us to divide the entropy jump during a solid-liquid phase transition into two parts: one corresponds to configurational excitation at zero temperature and the other arises from thermal vibrations of atoms. The latter part contributes approximately 40% for Lennard-Jones clusters consisting of 13 and 55 atoms, increasing to 56% for bulk inert gases. These magnitudes explain the validity of melting criteria based on thermal motion of atoms, even though the distinctive mechanism of this phase transition results from configurational excitations. It is shown that the void concept allows analyzing various aspects of the liquid state of clusters including the existence of a limiting freezing temperature below which no metastable liquid state exists, as well as the existence and properties of glassy states that may exist below the freezing limit.     

Dilute solution studies of pyrrone prepolymers

Data on dilute solutions of a pyrrone “prepolymer” are presented and the tendency of this polymer to aggregate in certain solvents commonly used in dilute solution studies is discussed. It is concluded that reliable molecular weights can be determined if solvents that interact with the prepolymer through hydrogen bonding are used.     

Unequal freezing and melting temperatures for clusters

Using a previously introduced quantum statistical model, analyze necessary and sufficient conditions on the density of states for coexistence of liquid and solid clusters. We conclude that clusters of N particles have sharp freezing and melting temperatures limiting the ranges of phase stability and that these temperatures are unequal.     

High power,single frequency operation of a Q-switched TEM00 Mode NdYAG laser

An actively Q-switched NdYAG laser, using a telescopic resonator configuration has produced single longitudinal mode, TEM₀₀ outputs of 100 mJ with output pulses free from any observable mode-beating.     

Cryoscopy on sulfuric acid solutions of a heterocyclic polymer (BBB) and related compounds

Cryoscopic measurements have been carried out on solutions in sulfuric acid of a heterocyclic polymer, its monomers, and certain of its oligomers. The polymer, BBB, is prepared by the polycondensation of 1,4,5,8-naphthalenetetracarboxylic acid (NTC) with 3,3′-diaminobenzidine (DAB). The results show that the polymer, its oligomers and one of its monomers, DAB, are all extensively protonated in sulfuric acid, whereas its other monomer is not. The degree of protonation appears to be greater for the polymer than for its low molecular weight oligomers.     

Correlation diagram for rigid and nonrigid three-body systems

We consider the relation between energy level patterns of rigid structures and those of systems in which the particle motions are uncorrelated. Defining an ideal model system of the non-rigid limit for N identical particles, we exhibit the correlation diagram connecting this limit to an ideal rigid system for N = 3. States of the two limits are related in a simple manner. Vibration-rotation levels for three identical spin-0 and spin-1/2 particles are classified explicitly, according to their quantum numbers in both limits.     

Stokes’ phenomenon; smoothing a victorian discontinuity

Summary Small exponentials in asymptotic representations of functionsy(k; X) (k → ∞) can appear and disappear across sets of codimension 1 in the space of variables X. These changes are not discontinuous but happen smoothly and according to a universal law. Dedicated to René Thom.