Dynamics Of Cluster Formation Research Articles

Cluster formation in a Fermi system with long-range attraction

Based on a statistical approach we describe the possible formation of a spatiallyinhomogeneous distribution in the system of interacting Fermi particles by long-rangeforces, and we demonstrate the nonperturbative calculation of the partitionfunction in this case. It is shown that particles interacting with an attractive1/r potential form clusters when the pressure due to the interactions balances the effectiverepulsion due to the Fermi statistics. A cluster is the equilibrium structure if we supposethat the average energy of interaction of two particles is much less than their averagekinetic energy. The dynamics of cluster formation is considered in this approach and thetime of relaxation to the equilibrium state is found. It is shown that phase transition froma spatially inhomogeneous state to a homogeneous state only occurs in a finite system. Thetemperature of such a phase transition is determined by the size of the finite system andthe average density.

Effects of early dark energy on strong cluster lensing

We use the semi-analytic method developed earlier for computing strong-lensing optical depths to study the statistics of gravitational arcs in four dark-energy cosmologies. Specifically, we focus on models with early dark energy and compare them to more conventional models. Merger trees are constructed for the cluster population because strong cluster lensing is amplified by factors of two to three during mergers. We find that the optical depth for gravitational arcs in the early dark-energy models is increased by up to a factor of ~3 compared to the other models because of the modified dynamics of cluster formation. In particular, the probability of gravitational arcs in high-redshift clusters is considerably increased, which may offer an explanation for the unexpectedly high lensing efficiency of distant clusters.

Cluster formation in the system of interacting Bose particles

Based on statistical approach we described possible formation of spatially inhomogeneous distribution in the system of interacting Bose particles. The condition of cluster formation in both gas and condensed phases was obtained in this system. We studied the dynamics of cluster formation in the limit case of high temperatures. We compared the cluster-formation processes in the attractive system (with short-range interaction) and in the gravitational system at the low temperatures of Bose-Einstein condensate regime.

Dynamics of cluster formation in liquid–gas phase transitions

Dynamics of cluster formation in liquid–gas phase transitions

Star Formation in Large N Clusters

We focus here on the gas dynamics of cluster formation and the early stellar dynamical evolution of young clusters. We point out that the condition that a cloud can fragment into a large number of pieces places rather particular constraints on its initial state; we also review the processes that shape the stellar IMF in cluster formation simulations. We show how N-body calculations and observations can be combined to discover the properties of clusters at the point at which they first become stellar dynamical (as opposed to gas dynamical systems). Finally, we touch on the question of how proto-cluster clouds are assembled and reopen the issue of whether dark matter may play a role in globular cluster formation.

Structures and dynamical properties ofCn,Sin,Gen,andSnnclusters withnup to 13

Car-Parrinello molecular dynamics simulated annealings were carried out for clusters ${\mathrm{Si}}_{n},$ ${\mathrm{Ge}}_{n},$ and ${\mathrm{Sn}}_{n}$ $(nl~13).$ We investigate the temperature regions in which these clusters transform from a ``liquidlike'' phase to a ``solidlike'' phase, and then from the ``solidlike'' phase to the ground-state structures. Additional simulated annealing was also performed for the cluster ${\mathrm{C}}_{13}$ which is selected as a prototype of small carbon clusters. In addition to the discovery of structures for Sn and Ge clusters, our simulation results also provide insights into the dynamics of cluster formation.

Cluster formation dynamics in a locally-confined gas layer mixed with the plume ablated by pulsed laser irradiation

The dynamical process of pulsed laser ablation is investigated by means of Monte Carlo simulations in order to develop a new cluster source. The interaction between the ablated Cu vapor plume and the He ambient gas induces strong shock compression of the gas by which the gas density is one order of magnitude increased and forms a stable gas layer mixed with the plume at the contact front. It is found that even with the target-wall distance as short as about 80 μm, a mixed layer more than 10 μm in thickness can be formed at about 15 μm away from the source wall. This layer can be locally-confined for a considerable long time of hundreds of ns. Frequent collisions occur among the atoms of vapor and gas within the confined layer which induce effective cluster aggregation. The thermodynamic state of this region is well defined, so that the mono-dispersed growth condition might form cluster beam with well-defined internal freedom.

Statistical theory of the diffusion of a passive tracer in a random velocity field

A passive tracer on the surface of an incompressible liquid behaves like a tracer in two-dimensional compressible flows, whose characteristic feature is the formation of cluster structures, i.e., compact regions of increased density surrounded by vast low-density regions. The cluster formation dynamics are studied, and statistical spatiotemporal characteristics of the density fields, which faithfully reflect the properties of the cluster structures, are calculated.

Cluster formation in a stepping-stone model with continuous, hierarchically structured sites

A stepping-stone model with site space a continuous, hierarchical group is constructed via duality with a system of (delayed) coalescing "stable" Lévy processes. This model can be understood as a continuum limit of discrete state-space, two-allele, genetics models with hierarchically structured resampling and migration. The existence of a process rescaling limit on suitably related large space and time scales is established and interpreted in terms of the dynamics of cluster formation. This paper was inspired by recent work of Klenke.

Cluster dynamics on vicinal surfaces.

We have carried out a study of the dynamics of cluster formation during epitaxial growth and recovery on vicinal surfaces. By considering all of the possible configurations for up to four-atom clusters, we have been able to elucidate the role of different island types and shapes during the various stages of growth. Inclusion of species with slow decay pathways is crucial for describing the recovery of the surface morphology, since the breakup of stable configurations is the rate-determining step for the relaxation of the surface once the incoming flux has been turned off. We find that the recovery of the surface can be divided into two stages: an initial rapid decay due to activity of atoms with one nearest neighbor, and a subsequent slower stage is coupled up to third order to the breakup of the most stable species.

Ablation of the fetal mouse spinal cord: The effect on soleus muscle cytoarchitecture

A technique is described whereby it is possible to surgically ablate the lumbosacral spinal cord of a developing mouse fetus without interfering with fetal viability. The lumbosacral spinal cords of 14-day in utero, 129ReJ mice were ablated with a Cooper Nd-YAG laser, and the fetuses, enclosed in their membranes and attached to the uterus by their placentae, were allowed to develop in the abdominal cavity of the dam. The cytoarchitecture and the temporal pattern of organogenesis of aneural soleus muscles were studied in spaced, serial, transverse, ultrathin sections of muscles of 16- and 18-day gestation and newborn (20-day gestation) mice. At the time of surgery, the soleus muscle was a discrete mass consisting of primary myotubes and a pleomorphic population of mononucleated cells. Axon bundles and blood vessels were found at the muscle's periphery, but had not penetrated throughout the muscle mass. The organogenesis of the aneural muscle was remarkably similar to that of the innervated soleus muscle (Ontell et al., Am J Anat 181:267-278, 1988). In the aneural muscle, as in the innervated muscle, significant numbers of secondary myotubes formed all along the lengths of primary myotubes. Moreover, the time course of myotube formation, the dynamics of cluster formation and cluster dispersal, and the ultrastructural appearance of the myotubes mimicked that observed in innervated muscle. The frequency of necrotic myotubes was no greater in the aneural muscle than in the innervated soleus muscle. Myotube maturation was similar in aneural and innervated soleus muscles until 18 days gestation. However, at birth, aneural myotubes appeared to be slightly less mature than innervated myotubes. Thus, the major morphogenic phenomena that characterize the development of the soleus muscle appear to be independent of innervation.

The formation of cluster vibrations in imperfectly structured materials

Abstract The dynamics of cluster formation in imperfectly structured materials is discussed in terms of their evolution from a prepared state fluctuation. It is shown that this is accompanied by the generation of group oscillations of displacements in the centres/axes of motion of the cluster components. A fractional index defining the partitioning of the vibrational/librational energy between the group oscillations and the centre of motion vibrations is shown to be related to the structural regularity of the cluster. The generation of group oscillation has also been related to the change in configurational entropy attendant upon the irreversible formation of imperfectly structured clusters, expressed as the same fraction of the change arising from complete dissociation of the ideal state.