Hierarchical Model for the Evolution of Cloud Complexes

The structure of cloud complexes appears to be well described by a "tree structure" representation when the image is partitioned into "clouds". In this representation, the parent-child relationships are assigned according to containment. Based on this picture, a hierarchical model for the evolution of Cloud Complexes, including star formation, is constructed, that follows the mass evolution of each sub-structure by computing its mass exchange (evaporation or condensation) with its parent and children, which depends on the radiation density at the interphase. For the set of parameters used as a reference model, the system produces IMFs with a maximum at too high mass (~2 M_sun) and the characteristic times for evolution seem too long. We show that these properties can be improved by adjusting model parameters. However, the emphasis here is to illustrate some general properties of this nonlinear model for the star formation process. Notwithstanding the simplifications involved, the model reveals an essential feature that will likely remain if additional physical processes are included. That is: the detailed behavior of the system is very sensitive to variations on the initial and external conditions, suggesting that a "universal" IMF is very unlikely. When an ensemble of IMFs corresponding to a variety of initial or external conditions is examined, the slope of the IMF at high masses shows variations comparable to the range derived from observational data. (Abridged)Comment: Latex, 29 pages, 13 figures, accepted for publication in Ap

Dynamics of Coupling Functions in Globally Coupled Maps: Size, Periodicity and Stability of Clusters

It is shown how different globally coupled map systems can be analyzed under a common framework by focusing on the dynamics of their respective global coupling functions. We investigate how the functional form of the coupling determines the formation of clusters in a globally coupled map system and the resulting periodicity of the global interaction. The allowed distributions of elements among periodic clusters is also found to depend on the functional form of the coupling. Through the analogy between globally coupled maps and a single driven map, the clustering behavior of the former systems can be characterized. By using this analogy, the dynamics of periodic clusters in systems displaying a constant global coupling are predicted; and for a particular family of coupling functions, it is shown that the stability condition of these clustered states can straightforwardly be derived.Comment: 12 pp, 5 figs, to appear in PR

On the Thermal Instability in a Contracting Gas Cloud and Formation of a Bound Cluster

We perform linear analysis of thermal instability in a contracting large cloud filled with warm HI gas and investigate the effect of metallicity and radiation flux. When the cloud reaches critical density n_f, the cloud fragments into cool, dense condensations because of thermal instability. For a lower metallicity gas cloud, the value of n_f is high. Collision between condensations will produce self-gravitating clumps and stars thereafter. From the result of calculation, we suggest that high star formation efficiency and bound cluster formation are realized in low-metallicity and/or strong-radiation environments.Comment: 7 pages, including 7 figures, LaTeX2e(emulateapj5.sty) To appear in ApJ, Jun 10, 200

Emergence of patterns in driven and in autonomous spatiotemporal systems

The relationship between a driven extended system and an autonomous spatiotemporal system is investigated in the context of coupled map lattice models. Specifically, a locally coupled map lattice subjected to an external drive is compared to a coupled map system with similar local couplings plus a global interaction. It is shown that, under some conditions, the emergent patterns in both systems are analogous. Based on the knowledge of the dynamical responses of the driven lattice, we present a method that allows the prediction of parameter values for the emergence of ordered spatiotemporal patterns in a class of coupled map systems having local coupling and general forms of global interactions.Comment: 7 pages, 3 figs, submitted to PRE (2002

Interleukin-1beta tear concentration in glaucomatous and ocular hypertensive patients treated with preservative-free nonselective beta-blockers

PURPOSE: To evaluate the ocular surface inflammatory response to the presence of preservatives in nonselective beta-blocker eyedrops. DESIGN: Prospective, crossover, single-masked, randomized clinical study. METHODS: STUDY POPULATION: Twenty primary open angle glaucoma or ocular hypertensive patients were divided in two groups, one treated with preservative-free timolol 0.5% (group 1) and the other with preserved timolol 0.5% (group 2) eyedrops. After 60 days of therapy and 3 more weeks of washout, the two groups switched to the other therapy. PROCEDURE: At each visit,basal tear samples were collected from the inferior conjunctival fornix for the determination of interleukin (IL)-1 tear concentrations by an enzyme-linked immunosorbent assay. Intraocular pressure measurement, conjunctival hyperemia, superficial punctate keratitis, and tear film breakup time were evaluated. MAIN OUTCOME MEASURE: IL-1 concentration in tears following the use of preserved eyedrops. RESULTS: IL-1 tear concentrations increased significantly in both groups, compared with baseline values,during preserved timolol therapy. There were no statistically significant changes in hyperemia and superficial punctate keratitis throughout the study in either group.A statistically significant breakup time reduction was observed in both groups after 30 days and after 60 days of preserved therapy. CONCLUSION: The use of preservatives in timolol 0.5% eyedrops leads to tear film instability and ocular surface inflammatory changes documented by a reduction of breakup time and an increase of IL-1 tear concentrations.Preservative-free beta-blockers are preferable for long-term hypotensive therapy to prevent ocular surface inflammation

Interleukin-1beta tear concentration in glaucomatous and ocular hypertensive patients treated with preservative-free nonselective beta-blockers

PURPOSE: To evaluate the ocular surface inflammatory response to the presence of preservatives in nonselective beta-blocker eyedrops. DESIGN: Prospective, crossover, single-masked, randomized clinical study. METHODS: STUDY POPULATION: Twenty primary open angle glaucoma or ocular hypertensive patients were divided in two groups, one treated with preservative-free timolol 0.5% (group 1) and the other with preserved timolol 0.5% (group 2) eyedrops. After 60 days of therapy and 3 more weeks of washout, the two groups switched to the other therapy. PROCEDURE: At each visit,basal tear samples were collected from the inferior conjunctival fornix for the determination of interleukin (IL)-1 tear concentrations by an enzyme-linked immunosorbent assay. Intraocular pressure measurement, conjunctival hyperemia, superficial punctate keratitis, and tear film breakup time were evaluated. MAIN OUTCOME MEASURE: IL-1 concentration in tears following the use of preserved eyedrops. RESULTS: IL-1 tear concentrations increased significantly in both groups, compared with baseline values,during preserved timolol therapy. There were no statistically significant changes in hyperemia and superficial punctate keratitis throughout the study in either group.A statistically significant breakup time reduction was observed in both groups after 30 days and after 60 days of preserved therapy. CONCLUSION: The use of preservatives in timolol 0.5% eyedrops leads to tear film instability and ocular surface inflammatory changes documented by a reduction of breakup time and an increase of IL-1 tear concentrations.Preservative-free beta-blockers are preferable for long-term hypotensive therapy to prevent ocular surface inflammation

Catalytic oxygen transfer between ethylene and ethylene oxide

The transfer of oxygen between ethylene and ethylene oxide has been studied at surfaces of Ag, Au, (VO2)x, and bismuth molybdate. The study was carried out by following the rate of redistribution of isotopic carbon between ethylene and ethylene oxide. The conditions employed in the experiments were: temperature 22-305 [deg]C, partial pressure ratios of ethylene oxide to ethylene 0.1-50, contact time 1-10 sec. Silver was supported on high- and low-area Al2O3 zeolite and complexed with poly(4-vinyl-pyridine). Au was supported on Al2O3 and MgO. The dependence of the rate of isotopic redistribution upon the ratio of ethylene oxide to ethylene was taken as an indication of the process of reactive and competitive chemisorptions of ethylene and ethylene oxide. Information on the nature of the adsorption, in terms of number of surface centers per adsorbate molecule, was derived. From this point of view, the catalysts tested may be divided into two groups. In one group, single-center adsorption of ethylene predominated, while in the second the adsorption of ethylene included two surface centers per molecule. Thus, on the first group, ethylene fragmentation should not be favored. These catalysts, therefore, should prove more selective to ethylene oxide in the net reaction of ethylene oxidation with molecular O2. These predictions are fully confirmed by direct experimentation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/33511/1/0000009.pd