Globular fields

The field of synthetic enzyme models encompasses attempts to prepare enzymelike functional macromolecules by chemical synthesis [30]. One particularly relevant approach to such enzyme mimics concerns dendrimers, which are treelike synthetic macromolecules with a globular shape similar to a folded protein, and useful in a range of applications including catalysis [31]. Peptide dendrimers, which, like proteins, are composed of amino acids, are particularly well suited as mimics for proteins and enzymes [32]. These dendrimers can be prepared using combinatorial chemistry methods on solid support [33], similar to those used in the context of catalyst and ligand discovery programs in chemistry [34]. Peptide dendrimers used multivalency effects at the dendrimer surface to trigger cooperativity between amino acids, as has been observed in various esterase enzyme models [35]. 

There is considerable experimental evidence indicating loss of biological activity of macromolecules such as globular proteins and enzymes at gas-Hquid [57], liquid-solid (Fig. 26) [107] and liquid-liquid [108] interfaces. The extent of inactivation has been shown to be strongly influenced by the prevailing flow field and by, many other factors including the presence and/or absence of additives and contaminants and the type of solid surfaces (Figs. 27 and 28) [107]. 

A stress that is describable by a single scalar can be identified with a hydrostatic pressure, and this can perhaps be envisioned as the isotropic effect of the (frozen) medium on the globular-like contour of an entrapped protein. Of course, transduction of the strain at the protein surface via the complex network of chemical bonds of the protein 3-D structure will result in a local strain at the metal site that is not isotropic at all. In terms of the spin Hamiltonian the local strain is just another field (or operator) to be added to our small collection of main players, B, S, and I (section 5.1). We assign it the symbol T, and we note that in three-dimensional space, contrast to B, S, and I, which are each three-component vectors. T is a symmetrical tensor with six independent elements ... 

Abstract. A review is presented on abundance determinations in stars of the Galactic bulge, both in the field and in globular clusters. Previous low-resolution spectroscopy results are revised. Recent high resolution and high S/N spectroscopy results based on Keck-Hires, Gemini-Phoenix and VLT-UVES data are presented. Finally, recent analyses of FLAMES data are discussed. 

The metallicity distribution of globular clusters in the Galaxy has a metal-rich peak at [Fe/H] -0.5 and a metal-poor peak at [Fe/H] -1.6 (e.g. Cote 1999), where most of the metal-rich ones are bulge clusters. Metallicities for samples of field stars were derived by McWilliam Rich (1994, hereafter MR94), Sadler et al. (1996), Ramirez et al. (2000). Zoccali et al. (2003) presented the... 

In addition to results from this study, Table 1 includes two of the relatively more metal-rich globular clusters associated with the Sgr dSph. There appears to be little in common between the two metallicity groups in their < a>-abundances relative to iron. Abundances reported so far for in situ Sgr dSph field stars of comparable metallicities [4] are in accord with those of its metal-rich clusters. 

C. Sneden, I. I. Ivans, J. P. Fulbright Globular Clusters and Halo Field Stars . In Origin and Evolution of the Elements Volume 4, Carnegie Observatories Astrophysics Series, ed. by A. McWilliam, M. Rauch (Cambridge, 2004)... 

Fig. 1. The range of [C/Fe] (left panel) and [N/Fe] (right panel) is shown as a function of metallicity ([Fe/H]) for the globular clusters from our work on M71, M5, M13, and M15 as well as for 47 Tuc (from Briley et al 2004a). Large samples of stars, mostly subgiants, were used in each case. Each GC is represented by a horizontal line. The characteristic field star ratio, from Carretta, Gratton Sneden (2000) for C and from Henry, Edmunds Koppen (2000) for N, are indicated by vertical arrows in each panel.

Spectroscopic observations of globular clusters (GCs) have revealed star-to-star inhomogeneities in the light metals that are not observed in field stars. These light metal anomalies could be interpreted with a self-pollution scenario. But what about heavier (Z > 30) elements Do they also show abundance anomalies Up to now, no model has been developed for the synthesis of n-capture elements in GCs, and the self-pollution models do not explain the origin of their metallicity. In 1988, Truran suggested a test for the self-enrichment scenario [4], which could possibly explain the metallicity and the heavy metal abundances in GCs if self-enrichment occurred in GCs, even the most metal-rich clusters would show both high [a/Fe] ratios and r-process dominated heavy elements patterns, which characterize massive star ejecta as it is seen in the most metal-poor stars. 

Globular clusters are quite distant and their turnoff (TO) stars are intrinsically relatively faint. Following the advent of state-of-the-art instrumentation in 4m class telescopes, the first Li observations were carried on in GC stars, while with the advent of 8m class telescopes a quality jump occurred high quality spectra can now be obtained for the TO stars of the closest clusters, comparable to that available for field stars. In spite of this advancement, only a handful of published refereed papers have been devoted to the study of Li in globular cluster stars, and only one to beryllium. Based upon the wealth of information made available as a result of this data, I will present new findings concerning stellar mixing, primordial Li production and GC formation. 

Abstract. We present a new calibration of the Call triplet as metallicity indicator based in 4 globular and 11 open clusters which cover a range of metallicity -2<[Fe/H]<+0.1 and age 13<(Age/Gyr)<0.25. We use it to derive the metallicity distribution in two fields situated at 5 and 8 degrees from the center of the LMC. We show that the mean [Fe/H] of the LMC field decreases as we move away from the bar. 

Fig. 1. a) Linear correlation between metallicity, in the Carreta Gratton (1997) scale versus W . Triangles are the open clusters, open circles are the globular clusters and open stars are the data by [2]. b) Metallicity distribution for the field situated at 5° (dashed line) and 8° (solid line) from the bar. The amount of stars with metallicity bellow [Fe/H]=-1 increases at larger distances from the bar. 

In addition to the CN-anomalies, similar (anti-)correlations for Na and O, and Mg and A1 have been known for some time to occur in globular cluster giants, though not in field stars (see [21] for a compilation). Initially thought to be... 

Red giant stars, both in the field and in globular clusters, present abundance anomalies that can not be explained by standard stellar evolution models. Some of these peculiarities, such as the decline of 12C/13C, and that of Li and 12C surface abundances for stars more luminous than the bump, clearly point towards the existence of extra-mixing processes at play inside the stars, the nature of which remains unclear. Rotation has often been invoked as a possible source for mixing inside Red Giant Branch (RGB) stars ([8], [1], [2]). In this framework, we present the first fully consistent computations of rotating low mass and low metallicity stars from the Zero Age Main Sequence (ZAMS) to the upper RGB. 

The most metal-deficient stars comprise field stars in the solar neighbourhood (where in some cases distances and luminosities can be found from parallaxes) and stars in globular clusters where the morphology of the HR diagram can be studied (Fig. 4.8). Such stars are of particular interest because their content of heavy elements (synthesized in still earlier generations of stars) is so low that they can... 

Fig. 8.20. Metallicity distribution function of globular clusters (crosses indicating error bars and bin widths) and halo field stars (boxes), after Pagel (1991). Copyright by Springer-Verlag.

The distribution function for field stars in the halo is reasonably well fitted by the Simple model equation (8.20) with a small remaining gas fraction, but with a very low effective yield p 10-11Z for oxygen (see earlier comments on dwarf galaxies). This was first noted (actually for globular clusters) by Hartwick (1976), who pointed out that it could be readily explained by continuous loss of gas from the halo in the form of a homogeneous wind with a mass loss rate from the system proportional to the rate of star formation. In this case,... 

This equation with D positive represents the tendency of stars to spread under the effect of collisions. Such a tendency surely exists in the case of globular clusters. Each star in the mean field of the others remains on an orbit that is bounded and even integrable if the cluster is spherically symmetric. Collisions bring the star to another orbit and thus yield some diffusion in the position space. This process is... 

Schaink, H.M., Smit, J.A.M. (1997). Mean field calculation of polymer segment depletion and depletion-induced demixing in ternary systems of globular proteins and flexible polymers in a common solvent. Journal of Physical Chemistry, 107, 1004-1015. 

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